Potential influence of gut microbiota on the process of hypertriglyceridemia-aggravated acute pancreatitis

Abstract

Acute pancreatitis (AP) is sudden inflammation of the pancreas, which can lead to multiple organ dysfunction in severe cases. Hypertriglyceridemia (HTG) is the third most common cause. In recent years, HTG-induced AP (HTG-AP) has garnered increasing attention. Compared to AP caused by other causes, HTG-AP often has a more subtle onset but is more likely to progress to a severe, critical illness that poses a serious threat to a patient’s life and health. Research suggests a potential connection between the gut microbiota and AP, which could be mediated by bacterial metabolites, immune cells, and inflammatory factors. This is supported by observations of microbial imbalance and higher intestinal permeability in patients with AP. In addition, studies have shown that HTG-induced changes in gut microbiota can worsen AP by negatively impacting the host metabolism, immune response, and function of the intestinal barrier. In this review, we summarize recent clinical and animal studies on the role and mechanism of gut microbiota in the severity of AP aggravated by HTG. The application prospects of the newly proposed microbial-host-isozyme concept are summarized, focusing on its potential for the precision diagnosis and treatment of HTG-AP through gut microbiota regulation.

Key Words: Gut microbiota; Hypertriglyceridemia; Gut-pancreas axis; Acute pancreatitis; Microbial-host-isozyme

Core Tip: Current academic consensus is that hypertriglyceridemia (HTG) primarily exacerbates acute pancreatitis (AP) through lipotoxicity. This traditional view emphasizes that in HTG, pancreatic lipase in acinar cells hydrolyzes triglycerides, generating excessive free fatty acids, which exacerbates AP severity. However, recent evidence has increasingly demonstrated the critical role of the gut microbiota in this pathological process. This review explores how gut microbiota dysbiosis mediates the aggravation of AP caused by HTG, focusing on mechanisms such as microbial translocation, immune dysregulation, and metabolites. The novel “microbial-host-isozyme” concept is proposed for precise diagnosis and therapy in HTG-AP.

INTRODUCTION

Acute pancreatitis (AP) is the “self-digestion” of the pancreas caused by overactivation of pancreatic enzymes. It is a common digestive system disease in clinical practice, and its incidence has been on the rise in recent years. Currently, its incidence reaches more than 34 cases per 100000 people per year[1]. The majority of patients with AP have a mild form of the disease that resolves on its own; however, a smaller percentage, approximately 20%-30%, develop severe AP, with fatality rates ranging from 30% to 50%[2,3].

The degree of damage to the pancreas and distal organs determines the severity of AP[2]. Patients with mild AP do not develop local or systemic complications, while patients with severe AP develop pancreatic necrosis, systemic inflammatory damage, and even multiple organ failure[4,5]. In patients with severe AP, the related organs of the respiratory system, kidney system, and cardiovascular system are most prone to organ failure, which is also an important factor contributing to the increased risk of death in patients with AP[5]. Therefore, it is very important to explore the pathogenesis and risk factors of AP for the triage and targeted therapy of patients with early AP.

To date, it is generally believed that genetics, age, obesity, and alcoholism are important factors affecting the severity of AP[6]. However, in recent years, the incidence of hypertriglyceridemia (HTG) has grown due to changes in people’s diet and lifestyle[7]. The incidence of HTG in the United States has exceeded 30%, becoming a major public health problem[8]. HTG is mainly classified into primary and secondary categories, with primary HTG characterized by familial heritability and secondary HTG mainly related to Western diet, alcoholism, obesity, and other factors[9]. HTG is a recognized and important cause of AP and the third most common cause of AP after cholelithiasis and alcohol[10,11]. Moreover, HTG has been identified as an independent risk factor for persistent organ failure and local complications in patients with AP[12,13]. Some studies indicate that AP caused by HTG is more severe and carries a higher risk of respiratory and renal failure than AP with other etiologies[14-16]. Animal studies have also shown that higher serum triglyceride (TG) levels worsen the course of AP[17-20]. This is believed to occur because the hydrolysis of TG produces large amounts of free fatty acids (FFAs), which promote inflammation by upregulating the pro-inflammatory cytokines, thereby increasing the risk of systemic inflammatory response and local complications[21-23]. However, because the mechanism linking HTG to the aggravation AP is unclear, there are no therapeutic guidelines for the treatment of HTG-AP[20].

Recent advancements in our knowledge of the gut microbiota have resulted in remarkable progress in managing related diseases. The gut contains a vast microbial community that interacts with the human body through genes and metabolites, thereby regulating individual health. Over the past decade, there has been ongoing concern about how changes in the gut microbiota affect distant organs, notably the pancreas and their intricate interactions. The pancreas is physically linked to the gastrointestinal tract through the pancreatic duct, allowing its exocrine function to significantly impact the gut microbiota by delivering digestive enzymes that influence the composition of microbes in the gastrointestinal tract[24]. Gut microbiota use short-chain fatty acids (SCFAs) to regulate the synthesis of cathelicidin-related antimicrobial peptide (CRAMP) within pancreatic β cells[25]. In addition, recent studies have found that gut microbiota can migrate to the pancreas and change the pancreatic microenvironment[26]. The imbalance of gut microbiota is closely related to the occurrence and development of AP, which can lead to the increased abundance of pathogenic bacteria such as Staphylococcus, Enterococcus, Escherichia coli (E. coli), and Klebsiella and the impairment of gut barrier function. The impaired intestinal barrier may then permit the translocation of pathogenic bacteria through the gut wall to distant organs[27,28]. In addition, a recent study demonstrated that the gut microbiota of patients with HTG-AP significantly differs from that of patients with non-HTG-AP, and these differences correlate with a poorer prognosis. However, the precise pathogenic pathway connecting the altered microbiome to mucosal barrier integrity and inflammatory modulation in HTG-AP remains unclear[29]. Growing evidence suggests that the gut microbiota mediates the link between HTG and worsening AP, particularly through changes in microbial composition, immune regulation, and metabolic pathways[29,30]. These studies provide novel insights into the mechanism by which HTG exacerbates the progression of AP, which has important guiding significance for the early triage and targeted treatment of HTG-AP.

This review focuses on the potential mechanisms by which gut microbiota mediates the exacerbation of AP by HTG. This analysis will contextualize the findings by identifying deficiencies in our current knowledge and proposing future avenues of inquiry.

GUT-PANCREAS AXIS

Recent advancements in our understanding of the gut has led to increasing attention on the gut-organ axis. The interactions between the gut and remote organs are mediated by environmental factors, gut microbiota-driven metabolites, neurotransmitters, microbial components, and immune regulation[31-34]. Compared with studies on the interaction between the gut and other organs, such as the gut-brain axis, gut-liver axis, and gut-lung axis, the gut-pancreas axis has been less studied. However, recent studies have confirmed that the gut-pancreas axis plays an important role in the occurrence and development of pancreatic diseases[35-39]. For example, in C57BL/6 mice, treatment with low-dose sodium glucan sulfate can induce the translocation of gut pathogens to the pancreas, leading to local inflammation of the pancreas, β-cell damage, and insulin-dependent diabetes[36]. Clinical research on AP has shown that patients have an increased abundance of certain pathogens, and these enriched pathogens increased the severity of AP mice[40]. Similarly, another study revealed that Western diet can increase the risk of transmission of gut bacteria, especially E. coli, by aggravating AP-induced gut barrier dysfunction[41]. These studies conclusively show a clear interaction between the gut and pancreas in the host, which is mediated by the crosstalk of gut microbiota, immune response, microbial components and metabolites driven by gut microbiota (Figure 1).

Figure 1 Bidirectional communication between the gut and pancreas. Gut microbiota may enter the pancreas through: Portal circulation; Mesenteric lymph nodes; Pancreatic duct reflux. Gut microbiota metabolites mediate bidirectional communication between the gut and pancreas. Gut microbiota can cause bacterial translocation by regulating the regulatory T cell/T helper 17 cell ratio. The reduction of Bacteroides abundance can regulate neutrophils to form neutrophil extracellular traps, leading to impairment of intestinal barrier function. The inflammatory response of the pancreas leads to a decrease in antimicrobial peptide synthesis, which results in a disturbance of the gut microbiota. Gut microbiota disorders lead to lipopolysaccharide elevation, leading to pancreatic acinar cell damage. IL: Interleukin; Treg: Regulatory T; Th: T helper; CD: Cluster of differentiation; SCFAs: Short-chain fatty acids; TMAO: Trimethylamine N-oxide; LPS: Lipopolysaccharide.

Crosstalk between the gut microbiota and pancreas

Although located separately, the gut and pancreas are in constant communication and work together. The pancreas is anatomically linked to the gastrointestinal tract via the pancreatic duct, through which it secretes pancreatic enzymes into the small intestine, aiding in food digestion. This connection between the pancreas and gastrointestinal tract, which is mediated by the pancreatic duct, also allows for communication between these organs, with gut microbiota playing a key role[27]. So, given that the gut microbiota and pancreas communicate with each other, does this mean the pancreas has its own microbiota, similar to that of the gut? For a long time, the pancreas was believed to be a sterile organ, but recent advances in sequencing technology have challenged this conclusion[42]. Despite ongoing debate regarding the specific composition, the concept of an intrinsic pancreas microbiota is widely recognized[43-45].

Gut microbiota is known to contribute to formation of the pancreas microbiota[27]. Research in the 1980s established a strong link between the gut microbiota and most infections involving the pancreas and surrounding tissues[28,46]. Then the researchers conducted numerous animal experiments to explore and verify the mechanism behind this phenomenon. In 1993, Tarpila et al[47] found that systemic bacterial colonization in AP rats might be the result of gut microbiota translocation but did not clarify how bacteria entered the pancreas from the gut. Subsequently, Kazantsev et al[48] used plasmid labeling to confirm the presence of gut bacteria in the pancreas of dogs with AP. Widdison et al[49] demonstrated in cats with AP that E. coli can migrate from the colon to the pancreas via the bloodstream. Samel et al[50] used intravital microscopy of fluorescent bacteria to show that green fluorescent protein-expressing E. coli can transfer from the small intestine to the pancreas in rats by crossing the mucosal and muscularis propria layers of the gut, providing conclusive evidence supporting the hypothesis of gut origin for pancreatic bacteria. These studies have shown that gut bacteria can cross the intestinal wall and travel to the pancreas through the portal vein. In addition, it has been reported that bacteria can be transferred from the gut to the mesenteric lymph nodes[51,52]. This transfer process may be mediated by immune cells; one study in particular showed that activation of dendritic cells can promote the translocation of selective gut bacteria to extraintestinal tissues[51]. In addition, mononuclear phagocytes with high levels of C-X3-C motif chemokine receptor 1 are responsible for transporting gut bacteria in a C-C chemokine receptor (CCR) type 7 (CCR7)-dependent manner. This process only occurs when the gut microbiota is disrupted by antibiotics or when myeloid differentiation primary response 88 (MyD88) is deleted[53]. Another theory is that microbes travel upstream from the upper digestive tract, including the esophagus, stomach, duodenum, and biliary tract, into the pancreas via the pancreatic duct. In mouse models of pancreatic ductal adenocarcinoma (PDAC), oral administration of Bifidobacterium pseudolongum led to its presence in the pancreas within 2 weeks, indicating that the bacteria had likely refluxed into the pancreatic duct; however, this reflux was not found in normal control mice[44]. A 2019 sequencing report identified oral microbiota (e.g., Fusobacterium, Prevotella, Dialister, Veillonella, and Haemophilus) in the pancreas of both patients with PDAC and cadaveric healthy controls[54]. However, there is no definitive link between oral bacteria and pancreatic bacteria, as both factors are independently associated with smoking[27]. Therefore, more basic research is needed to support the hypothesis that the oral microbiota is involved in formation of the pancreas microbiota.

Immune response

Necrotizing pancreatic infection occurs in about 20% of patients with AP, which is thought to be caused by bacterial translocation[55]. Bacterial translocation from the gut in AP depends on microbes overcoming the physical intestinal barrier and evading the host immune system. As such, maintaining homeostasis of the gut immune system is crucial for patient outcomes. The results of an animal study showed that the regulatory T cell (Treg)/T helper (Th) 17 cell (commonly known as Th17) balance has important effects on gut barrier function in AP mice. Treg activation can impair gut barrier function in the duodenum and increase the risk of bacteria translocation to the pancreas, leading to pancreatic necrosis[56]. AP mice show reduced microbial diversity and abundance in the duodenum and cecum, which correspond with increased forkhead box P3-positive/cluster of differentiation (CD) 25-positive Treg-mediated immunosuppression[57]. Under normal physiological conditions, gut microbiota can inhibit the translocation of bacteria to the mesenteric lymph nodes; however, MyD88 deletion or antibiotic-induced dysregulation of gut microbiota can induce non-invasive bacteria to translocate to mesenteric lymph nodes in a CCR7-dependent manner[53], which allows bacteria to gain access to the pancreas simply by anatomic lymphatic drainage routes[27]. In addition, a large number of CD4 (+) T cells are recruited to pancreatic tissue during AP, and depletion of CD4 (+) T cells can reduce the severity of AP[58]. A recent study found that reduced Bacteroides abundance in the gut recruits neutrophils and promotes the formation of neutrophil extracellular traps (NETs) and the release of interleukin 17 (IL-17) in the colon[30]. Parabacteroides in the gut can reduce the severity of AP by reducing the infiltration of neutrophils to produce acetate[59]. Studies on AP rats have revealed a significant reduction in macrophage killing ability[60], while clinical research has found that patients with fewer natural killer cells have a higher risk of secondary infection[61].

Antimicrobial peptides (AMPs) are primarily secreted by the innate immune system in the gastrointestinal tract but are also secreted by the pancreas[62]. Acinar cells and islet cells of the pancreas can produce AMPs, such as defensin α1, defensin β3, and CRAMP[25,63,64]. CRAMP has been shown to exert therapeutic effects on type 1 diabetes by its regulation of the gut microbiota, gut barrier function, and immune response[35]. CRAMP may also protect the integrity of gut barrier function and immune homeostasis of the gut-pancreas axis by regulating gut immune homeostasis, gut microbiota, and gut-primed interferon gamma-positive T cell transfer to the pancreas[35]. In one study, transplanting the gut microbiota of elderly individuals into C57BL/6 mice made their AP more severe and caused a decrease in AMPs messenger RNA levels in the ileum and pancreas[39]. Low levels of AMPs can cause an overgrowth of pathogenic bacteria in the gut, which can lead to impaired gut barrier function and gut leakage. Following damage to the gut barrier, gut bacteria and endotoxins can migrate to the pancreas, where they activate macrophages and trigger apoptosis in pancreatic acinar cells[65].

Metabolites driven by gut microbiota

The metabolites of gut microbiota play an important role in the gut-pancreas axis and can mediate bidirectional communication between the gut and the pancreas through the circulatory system. SCFAs, the most studied gut microbiota metabolites, are essential for maintaining the gut barrier. SCFAs are produced primarily by the fermentation of undigested fiber by bacteria in the cecum and proximal colon[66], which are the main sources of energy for colon epithelial cells and can protect gut barrier function[67]. The decrease in abundance of SCFAs-producing bacteria was observed in both mice and patients with pancreatitis, accompanied by a decrease in SCFA content. Exogenous supplementation of SCFAs can alleviate pancreatic fibrosis caused by pancreatitis[68]. SCFAs promoted the production of regenerating family member 3 gamma (RegIIIγ) and β-defensins in wild-type mice, but not in G-protein coupled receptor 43 knockout [GPR43 (-/-)] mice, suggesting that SCFAs promote AMP production in a GPR43-dependent manner, thereby regulating gut homeostasis[69]. One study in AP mice showed that a Western-type diet led to higher mortality rates, increased systemic inflammation, and a greater risk of bacterial transmission compared to mice on a dietary fiber diet, which led to butyrate depletion. However, oral butyrate reduced mortality, decreased bacterial transmission, and enhanced gut barrier function[44]. Butyrate, as a representative SCFA, provides 70% of the energy for colon epithelial cells. It is metabolized by colon epithelial cells via the β-oxidation pathway in their mitochondria, a process that consumes large amounts of oxygen and helps maintain the gut’s anaerobic environment[70]. The anaerobic microenvironment of the gut supports the proliferation of anaerobic bacteria. Studies have found that in young mice, the colonization of anaerobic bacteria maintains the integrity of gut barrier function[71], which is essential to reduce the risk of pancreatic tissue necrosis and multiple organ failure in patients with AP[72].

Trimethylamine-N-oxide (TMAO) is produced when trimethylamine (TMA) enters the liver through the vein and is oxidized by flavin-containing monooxygenase. In the gut, choline from red meat and fish is converted into TMA by gut bacteria using the enzyme choline-TMA lyase[73,74]. At present, the role and mechanism of TMAO in cardiovascular disease have been gradually confirmed, but few studies have explored its role in pancreatic disease[75,76]. In vitro studies have shown that TMAO stimulates the growth of Enterobacteriaceae[77], which can, in turn increase the inflammatory response in inflammatory bowel disease, especially for adherent-invasive E. coli[78]. In addition, the most common species in the pancreas of patients infected with necrotic pancreatitis is Enterobacteriaceae[79]. Studies have demonstrated that TMAO reduces the viability of MPC-83 cells through activation of the inositol-requiring enzyme 1 alpha/X-box binding protein 1 pathway, ultimately leading to apoptosis[80]. In addition, in a mouse model of hyperlipidemia AP, TMAO was found to promote the inflammatory response and pancreatic tissue injury through the Toll-like receptor (TLR)/p65 signaling pathway[81]. Metabolomic analysis revealed a significant increase in serum TMAO levels in AP rats, suggesting its potential as an early biomarker[82]. While the negative effects of TMAO on pancreatic diseases are generally recognized, a clearer understanding of its mechanism is needed to improve early diagnosis and targeted treatment.

Microbial components of gut microbiota

Microbial components are soluble substances that can mediate interactions between the gut and pancreas through the circulatory system. Microbial components, such as microbial-associated molecular patterns (MAMPs), are detected by host pattern recognition receptors such as TLR4, which then trigger an immune response upon activation[83,84]. MAMPs include peptidoglycan and lipopolysaccharide (LPS), of which LPS is an important component of the outer membrane of gram-negative bacteria. LPS binds to TLR4, which triggers the immune system. Activation of TLR4 initiates intracellular signaling, engaging the nuclear factor kappa B and mitogen-activated protein kinase pathways and eventually resulting in an inflammatory response[85]. Dysbiosis of the gut microbiota promotes LPS generation, while a damaged gut barrier accelerates the leakage of LPS into the bloodstream[86,87]. A long-term, high-fat diet is a significant risk factor for worsening pancreatic injury in AP[88]. A high-fat diet can cause imbalances in gut microbiota and increase plasma LPS levels[89], which may serve as a contributing mechanism for the worsening of pancreatic injury in AP. In addition, the inflammatory response to caerulein-induced AP was reduced in TLR4 knockout mice compared to wild-type mice, indicating a crucial role for TLR4 activation[90]. Therefore, regulating the gut microbiota and inhibiting excessive TLR activation caused by LPS are important for the prevention and treatment of AP.

DIFFERENCE IN GUT MICROBIOTA BETWEEN HTG-AP AND AP

The gastrointestinal tract is the largest organ in the human body and home to a large number of bacteria, fungi, archaea, and viruses, forming a vast ecosystem known as the gut microbiota. These contain about 10¹⁴ microbes, which equates to 4 × 10⁶ genes that constitutes the natural gene pool of each host[91]. The genes of gut microbiota directly or indirectly participate in various physiological functions of the host, including heredity, metabolism and immunity, and have an important impact on the health of the host. While the role and mechanism of gut microbiota in AP are known, there is less research on how they contribute to the worsening of AP caused by HTG (Figure 2). In this section, we summarized the difference in gut microbiota between HTG-AP and AP (Table 1), which lays the foundation for further understanding the role and mechanism of gut microbiota in HTG-aggravated AP severity.

Figure 2 Changes in gut microbiota composition in hypertriglyceridemia-induced acute pancreatitis and acute pancreatitis. Clinically, it has been observed that acute pancreatitis (AP) can lead to changes in the composition and function of gut microbiota, and the gut microbiota of patients with hypertriglyceridemia-induced AP shows different dominant bacteria from that of AP. AP: Acute pancreatitis; HTG: Hypertriglyceridemia; ANP: Acute necrotizing pancreatitis.

Table 1 Changes in gut microbiota[29,30,40,92,101,164-166].

Ref.	Sample (sample size)	Differential taxa feature	Sequencing method
Hu et al[29]	Patients with HTG-AP (n = 30). Patients with non-HTG-AP (n = 20)	Increase: Firmicutes, Enterococcaceae, Clostridiales Incertae Sedis XI, Finegoldia, Enterococcus. Decrease: Alpha diversity, Lachnospiraceae, Bacteroidaceae, Bacteroides	16S rRNA sequencing
Li et al[30]	Patients with HTG-AP (n = 25). Patients with non-HTG-AP (n = 30)	Increase: Escherichia-Shigella, Klebsiella. Decrease: Alpha diversity, Bacteroides, Bacteroides uniformis	16S rRNA sequencing
Yun et al[101]	Patients with HTG (n = 259). Healthy controls (n = 882)	Increase: Prevotella, Fusobacterium, Megamonas, Megasphaera, Acidaminococcus. Decrease: Oscillospira, Anaerostipes	16S rRNA sequencing
Zhu et al[92]	Patients with AP (n = 130). Healthy controls (n = 35)	Increase: Proteobacteria, Escherichia-Shigella, Enterococcus, Enterobacteriaceae. Decrease: Bacteroidetes, Prevotella_9, Faecalibacterium, Blautia, Lachnospiraceae, Bifidobacterium	16S rRNA sequencing
Yazici et al[164]	Patients with AP (n = 54). Healthy controls (n = 46)	Increase: Veillonella, Klebsiella, Enterococcus, Actinomyces, Haemophilus. Decrease: Alpha diversity, Faecalibacterium, Blautia	16S rRNA sequencing
Liu et al[40]	Patients with AP (n = 82). Healthy controls (n = 115)	Increase: Escherichia coli, Parabacteroides, Veillonella, Enterococcus. Decrease: Faecalibacterium prausnitzii, Ruminococcus, Eubacterium, Roseburia and Bifidobacterium	Metagenome shotgun sequencing
Zhu et al[92]	AP mice (n = 10). Control mice (n = 5)	Increase: Escherichia-Shigella, Enterococcus, Enterococcaceae. Decrease: Blautia	16S rRNA sequencing
Chen et al[165]	ANP mice (n = 10). SO mice (n = 10)	Increase: Escherichia-Shigella and Phascolarctobacterium. Decrease: Candidatus_Saccharimonas, Prevotellaceae_UCG-001, Lachnospiraceae_UCG-001, Ruminiclostridium_5, and Ruminococcaceae_UCG-008	16S rRNA sequencing
Xiong et al[166]	AP mice (n = 5). SO mice (n = 5)	Increase: No rank of Muribaculaceae, Lachnospiraceae. Decrease: Bifidobacterium, Akkermansia	16S rRNA sequencing

ANP: Acute necrotizing pancreatitis; AP: Acute pancreatitis; HTG: Hypertriglyceridemia; SO: Sham-operated.

Patient study

Patients with HTG-AP and AP: A recent cohort study revealed an association between gut microbiota and HTG-AP. Patients with HTG-AP had reduced alpha diversity compared with patients with AP with other etiologies. Different taxonomic features of gut microbiota were observed in patients with HTG-AP and non-HTG-AP. At the phylum level, patients with HTG-AP had a higher abundance of Firmicutes. At the family level, Enterococcaceae and Clostridiales Incertae Sedis XI were enriched in patients with HTG-AP, whereas Lachnospiraceae and Bacteroidaceae were reduced in abundance. At the genus level, patients with HTG-AP had a higher abundance of Finegoldia and Enterococcus and lower abundance of Bacteroides than patients with non-HTG-AP[29]. In addition, Escherichia-Shigella, Enterococcus, and Enterococcaceae were positively correlated with adverse outcomes, such as shock, intensive care unit (ICU) admission, and ICU stay[29]. Unfortunately, the relationship between the taxonomic features of gut microbiota and the pathogenesis of HTG-AP has not been elucidated. Studies suggest that increased gut abundance of Escherichia-Shigella is linked to disease deterioration in patients with AP, with a further increase observed in severe cases. This is accompanied by greater ability of the bacteria to invade epithelial cells[92]. Clinically, the detection rate of Escherichia-Shigella in patients with acute necrotizing pancreatitis is also significantly higher than that in AP[93]. Therefore, the increased abundance of potential pathogenic bacteria (e.g., Escherichia-Shigella) in the gut could contribute to worse outcomes in patients with HTG-AP. However, more in-depth studies are needed to understand how HTG-AP exacerbates potential pathogens, which would be highly significant for developing better prevention and treatment strategies. In line with previous research, the alpha diversity of gut microbiota was observed to be reduced in patients with hypertriglyceridemic pancreatitis (HTGP) vs those with non-HTGP[30]. Patients with HTGP had a higher abundance of Escherichia-Shigella and Klebsiella and lower abundance of Bacteroides and Bacteroides uniformis (B. uniformis) in the gut[30]. In addition, B. uniformis from the patient was transplanted into the HTGP mouse model, and the results showed that B. uniformis could alleviate pancreatic injury in HTGP mice[30]. Meanwhile, serum and fecal taurine levels were positively correlated in B. uniformis and HTGP mice. Exogenous administration of taurine can reduce pancreatic injury in HTGP mice by reducing neutrophil infiltration and the formation of NETs[30], which suggest that B. uniformis could alleviate pancreatic injury in HTGP mice by promoting host taurine synthesis to reduce neutrophil infiltration and NET formation.

TG itself is not toxic to pancreatic acinar cells; rather, its breakdown into FFAs by lipase is what causes lipotoxicity. Pancreatic acinar cells synthesize and secrete lipase, which hydrolyzes TG into FFAs. Under normal physiological conditions, these cells release lipase into the pancreatic duct via the apical membrane, thereby preventing the enzyme from prematurely contacting and hydrolyzing TG in the serum or surrounding tissues. Under pathological stimuli, the actin cytoskeleton within the acinar cell is reorganized. This leads to the exocytosis of enzyme precursor granules at the basal side and the leakage of lipase into the interstitium. The leaked lipase then hydrolyzes interstitial TG, resulting in the excessive production of FFAs[94]. Apart from TG, peripancreatic fat necrosis can also contribute to pancreatic lipotoxicity. It is recognized that the large amounts of unsaturated fatty acids released from necrotic peripancreatic fat can trigger a more intense inflammatory response and lead to multiple organ failure, thereby exacerbating the condition from mild to severe AP[22].

The generation of FFAs is not only derived from the host but also has a close relationship with gut microbiota[95,96]. In patients with obesity, Fusimonas intestini is highly colonized and can produce FFAs. Excessive production of FFAs can lead to gut barrier damage, promoting metabolic endotoxemia[97], which is one of the mechanisms by which a high-fat diet aggravates AP[41]. There is no doubt that the gut microbiota has an important influence on host lipid metabolism and that microbial genes related to lipid metabolism are involved in this process; for example, the fatty acid metabolism regulator can increase the production of saturated fatty acids[97]. In addition, gut microbiota-derived conjugated linoleic acid hydratase, a key linoleic acid metabolic enzyme, is involved in linoleic acid metabolism to form 10-hydroxy-cis-12-octadecenoic acid[98]. However, the role of gut microbiota in regulating fatty acid metabolism during the pathogenesis of HTG-AP has not been confirmed. Metagenomics and metabolomics represent an effective strategy for solving this problem in future research.

Patients with HTG: Long-term patients with HTG have a gradual increase in the risk of AP. A study of 129 patients with severe HTG found that 20.2% had a history of AP, and the mean TG level was significantly higher in patients with than without AP[99]. In another study of 300 patients with TG levels above 1000 mg/mL, 8% had a history of AP. Of these patients with AP, more than two-thirds were in the highest TG quartile group[100]. In a study of 1141 people, the abundance of Oscillospira and Anaerostipes was significantly lower in patients with HTG, with levels strongly and negatively correlated with TG content. Prevotella, Fusobacterium, Megamonas, Megasphaera, and Acidaminococcus were significantly increased in patients with HTG[101]. A South China population study involving 4781 individuals found an inverse association of Christensenellaceae with HTG and body mass index. In addition, decreased levels of lipid biosynthesis and energy metabolism pathways were found in populations with a higher abundance of Christensenellaceae, which may explain the negative association between HTG and Christensenellaceae. In addition, as the abundance of Christensenellaceae increased, the abundance of Veillonella, Fusobacterium, and Klebsiella was significantly decreased[102]. These studies confirm that HTG can increase the abundance of pathogenic bacteria in the gut of patients, and some of them such as Prevotella, Fusobacterium, and Klebsiella are associated with increased gut permeability[103-105]. However, whether the HTG-modulated gut microbiota is involved in the process of HTG-aggravated AP is unclear. Furthermore, in different studies, the observed advantageous species are not always the same, which may reflect influence by such wide ranging confounding factors as regions included in the studies, sequencing methods, use of antibiotics and/or proton pump inhibitors, sex, age, body mass index, and diet. Therefore, when conducting clinical research, the study design should control for as many of these confounding factors as possible in order to minimize the related bias.

Animal study

HTG-AP mouse models are primarily developed by first causing HTG through a high-fat diet and intraperitoneal injection of poloxamer-407 and then inducing AP with caerulein administration[106,107]. In addition, genetically modified mice such as lipoprotein lipase (LPL)-deficient mice and human-apolipoprotein CIII transgenic mice are frequently used in HTG-AP studies[23,108-111]. One study compared the effects of standard and high-fat diets on the severity of taurocholate-induced AP in mice. The results showed that a high-fat diet can lead to more severe pancreatic injury and higher mortality by impairing gut barrier function and increasing gut bacterial translocation[41]. Compared with standard diets in AP mice, Escherichia-Shigella proliferated in the gut of AP mice fed a high-fat diet, which were also the dominating pathogens of pancreatic infection[41]. Enrichment of Escherichia-Shigella in the pancreas is an important factor for the severity of AP aggravated by a high-fat diet; however, the underlying mechanism has not been elucidated. The PldA gene, encoding an outer membrane PldA, is widely distributed in Enterobacteriaceae[112], which can regulate the transition of glycerophospholipid metabolism to lysophosphatidylcholine (LysoPC) formation[113]. LysoPC is a pro-inflammatory mediator, and elevated LysoPC is associated with a variety of diseases such as AP, colorectal cancer, and ulcerative colitis[114-116]. However, it is unclear whether Enterobacteriaceae-derived PldA or gut microbiota-derived microbial genes are involved in the pathogenesis of HTG-AP. This ambiguity is due to a lack of extensive, in-depth studies on the gut microbiota in HTG-AP. Another study found that the abundance of B. uniformis in the gut of HTG-AP mice was reduced, leading to insufficient taurine production and increased IL-17 release in the colon, which triggered the formation of NETs and ultimately aggravated pancreatic injury and systemic inflammation[30].

In addition, both animal studies and clinical studies have revealed that gut microbiota is involved in the occurrence and development of HTG-AP, but it is important to recognize that most of these studies relied on stool or gut content analysis. The gut is not uniformly mixed, and its various regions have different microenvironments (e.g., potential of hydrogen, oxygen concentration, peristalsis rate, AMPs)[117-119]. Given the small intestine’s anatomical link to the pancreas, exploring the relationship between the composition of the small intestine microbiota and pancreatic diseases (e.g., AP) is a valuable area of research. A recent study also supported this view. Using 16S ribosomal RNA sequencing and principal coordinate analysis, significant microbiota dysbiosis was confirmed in the duodenal, colonic, and cecal samples of AP mice compared to normal controls, with the duodenal microbiota exhibiting the most substantial alterations[56]. However, there is a notable research gap regarding the effects and mechanisms of gut microbiota in the small intestine on the pathogenesis of AP.

MECHANISM OF HTG AGGRAVATING AP: PERSPECTIVE OF GUT MICROBIOTA-DERIVED METABOLITES

Gut microbiota-derived metabolites are important mediators of the gut regulation of distal organs. Here, we summarize the molecular mechanism of HTG-aggravated AP from the perspective of gut microbiota-driven metabolites (Figure 3), which provides an innovative paradigm for the management and early diagnosis of HTG-AP.

Figure 3 Gut microbiota-driven metabolites regulate the inflammatory response of the pancreas. Short-chain fatty acids (SCFAs) can regulate the regulatory T cell/T helper 17 cell ratio and the production of antimicrobial peptides in the pancreas, and inhibit the infiltration of macrophages into the pancreas. In addition, SCFAs can activate peroxisomes, promote colonic epithelial cells toward β-oxidation, and deplete gut oxygen to maintain an anaerobic environment and inhibit the overgrowth of pathogenic bacteria. Trimethylamine N-oxide (TMAO) impairs mitochondrial function in colonic epithelial cells, resulting in an increase in gut oxygen concentration and promoting the growth of Escherichia-Shigella. In addition, TMAO also leads to decreased insulin secretion and aggravates pancreatic inflammation through Toll-like receptor/p65. Bacteroides ovatus in the gut can synthesize lysophosphatidylcholine to promote inflammation of the pancreas. SCFAs: Short-chain fatty acids; TMAO: Trimethylamine N-oxide; AMP: Antimicrobial peptides; Treg: Regulatory T; Th: T helper; TLR: Toll-like receptor; LysoPC: Lysophosphatidylcholine.

SCFAs

SCFAs are produced by fermentation of non-digestible carbohydrates. In the gut environment, complex interactions between gut microbiota and diet lead to the production of SCFAs, which are distributed throughout the body tissues and organs via the bloodstream. FFA receptors 2 and 3, as natural receptors of SCFAs, are expressed in various cells, including enteroendocrine cells and immune cells, suggesting that gut microbiota-derived SCFAs play an important regulatory role in various organs[120,121], with the pancreas being a key target[65,122,123]. The reduced content of SCFAs is often observed in patients with AP and animal models[41,65,124], which are involved in gut barrier dysfunction, gut microbiota translocation, pancreatic tissue necrosis, and infection during AP[41,123]. The decreased SCFAs were associated with a reduction in SCFA-producing strains. In patients with AP, Enterobacteriaceae, Enterococcus, and Escherichia-Shigella had increased abundance and Bifidobacterium had decreased abundance[92,125]. Bifidobacterium mainly secretes acetate and lactate, which can reduce gut potential of hydrogen and inhibit the growth of harmful bacteria[92]. Butyrate can activate peroxisomes, promote colonic epithelial cells toward β-oxidation, consume oxygen in the gut, maintain the anaerobic microenvironment of the gut, and inhibit the growth of aerobic bacteria such as Escherichia-Shigella[126]. SCFAs can serve as a major energy source for colonic epithelial cells, thereby enhancing epithelial barrier function[67], which can reduce the risk of gut microbiota translocation to distant organs in AP.

In addition, SCFAs can activate signaling cascades that control immune function by binding to G protein-coupled receptors on the cell surface. Studies have found that exogenous SCFAs supplementation or SCFAs-producing strains can reduce the migration of peripheral CCR2-positive monocytes to the pancreas, inhibit macrophage infiltration and M2 phenotype switching, and reduce the activation of pancreatic stellate cells, ultimately alleviating the degree of fibrosis in AP[68]. While few studies exist on the local function of SCFAs in pancreatic tissue during AP, there is evidence that SCFAs can modulate the immune microenvironment of the pancreas by regulating the production of AMPs by pancreatic β cells[123]. Several studies have observed a consistent reduction in the content of SCFAs and the expression of pancreatic AMPs in AP; however, the mechanism by which SCFAs regulate the production of pancreatic AMPs is not fully clear[127,128]. In one study, the expression of RegIIIγ and β-defensins 1, 3, and 4 in the intestinal epithelial cells of wild-type but not GPR43 (-/-) mice was increased by exogenous SCFA supplementation[69]. These results suggest that SCFAs may regulate the expression of AMPs in intestinal epithelial cells through GPR43, but this mechanism has not been tested in the pancreas. SCFAs can also promote the differentiation of T cells into effector T cells and Tregs, which is mainly dependent on histone deacetylase inhibitor activity[129]. SCFAs can also regulate the Th17/Treg ratio[130]. Studies in mice have shown that the overgrowth of facultative pathogenic taxa like Escherichia-Shigella typically associated with severe disease and necrosis is suppressed in the duodenum of Treg-deficient AP mice, and disruption in the balance of Th17 and Tregs can compromise the immune barrier of the duodenum and allow translocation of commensal bacteria into the pancreas[56].

In general, SCFAs play an important role in the occurrence and development of AP. A large number of studies have shown that patients with HTG or a long-term high-fat diet can lead to a decrease in SCFAs-producing bacteria and an increase in pathogenic bacteria in the gut[101-103]. This change in the gut microbiota can damage the gut barrier, cause microbial translocation, and trigger an immune response in HTG-AP, which intensifies the severity of AP. However, to date, no relevant studies have investigated the role and mechanism of SCFAs in the pathogenesis of HTG-AP. Future studies should use metagenomics, metabolomics, and transcriptomics to investigate how SCFAs are synthesized in HTG-AP and how this process affects the severity of AP. This research will help identify novel therapeutic targets for HTG-AP and provide an important theoretical basis for clinical diagnosis and treatment.

TMAO

TMAO is mainly derived from choline in dietary red meat, and is broken down by choline-TMA lyase in gut microbiota to form TMA, which is then transported to the liver to form TMAO. Excessive intake of red meat not only leads to an increase of plasma TMAO but also increases the risk of HTG[131]. Recent studies have shown that high levels of TMAO increase the risk of HTG[132,133]; however, the underlying mechanisms remain unclear. Although there is no clear evidence that long-term HTG causes an increase in circulating TMAO levels, a long-term high-fat diet can damage mitochondrial function in colonic epithelial cells, lead to an increase in intestinal oxygen concentration, and promote the proliferation of aerobic bacteria such as Escherichia-Shigella and the breakdown of choline, ultimately leading to an increase in circulating TMAO levels and intestinal permeability[134].

TMAO is closely related to the occurrence and development of a variety of diseases, including pancreatic diseases. For example, elevated TMAO impairs insulin secretion, β-cell ratio, and glucose tolerance in male C57BL/6 mice. In addition, long-term TMAO exposure causes endoplasmic reticulum stress, dedifferentiation, and apoptosis in β cells, and inhibits the transcriptional properties of β cells[135]. In addition, TMAO can also promote the occurrence of hyperlipidemic AP by promoting inflammatory response through the TLR/p65 signaling pathway[81]. A study found that serum TMAO levels were significantly increased in a rat model of AP induced by retrograde catheter infusion of taurine, which may be a potential biomarker for early AP[82]; however, further studies are needed to reveal the underlying mechanisms of this association. Escherichia-Shigella and Desulfovibrio are enriched in individuals with HTG or on a long-term high-fat diet[29,136], and these bacteria are associated with an increase of serum TMAO[134,137], which may be one mechanism by which HTG or a long-term high-fat diet aggravates AP. However, to date, there is no clear evidence that HTG can aggravate AP by regulating gut microbiota to increase TMAO. Future studies should use metagenomics and metabolomics to further explore the role and molecular mechanisms of the gut microbiota-host metabolism axis in the aggravation of HTP-induced AP.

Other metabolites

LysoPC is a metabolite that is co-metabolized by both the gut microbiota and the host. In the host, LysoPC is produced by the phospholipase A2 (PLA2) family of enzymes, including cytosolic PLA2s, calcium-independent PLA2s, secreted PLA2s, lysosomal PLA2s, platelet-activating factor acetylhydrolases, and adipose-specific PLA2s. The first three PLA2 families play important roles in inflammation-related diseases[138]. In AP, PLA2 has been proposed as a potential therapeutic target and biomarker[139]. In addition, gut microbiota affects the development of various diseases by mediating the production of LysoPC[116]. Bacteroides ovatus has been found to mediate the synthesis of LysoPC, but its role and mechanism in AP and HTG-AP are still unclear[140]. Although the effects of LysoPC on AP are still largely unknown, LysoPC has been shown to play negative roles in a variety of diseases such as colitis, colorectal cancer, and non-alcoholic steatohepatitis[116,141]. In addition, it is not clear whether HTG-modulated gut microbiota can aggravate AP by affecting LysoPC metabolism. However, LysoPC has been shown to improve cognitive function and promote myelination and repair by reducing amyloid beta load in 5 × FAD mice[140]. These conflicting results indicate that our understanding of gut microbiota-derived LysoPC is very limited, and more studies are needed in the future.

There is also an important connection between bile acid metabolism and AP. A cohort study showed that chenodeoxycholic acid significantly increased during the acute phase of AP and decreased during the recovery phase. Moreover, in vitro experiments and mouse model systems have revealed that chenodeoxycholic acid may exert protective effects against pancreatic necrosis in mice through the oxidative phosphorylation pathway[142]. The gut microbiota is an important source of secondary bile acids, and recent studies have discovered novel modifications of bile acids attributed to it. For instance, B. uniformis can mediate the 3-acetylation modification of bile acids through the 3-succinyl-CoA synthetase, promoting the generation of 3-succinyl-CoA and thereby alleviating progression of metabolic dysfunction-associated steatohepatitis[143]. The gut microbiota can regulate breakdown of tryptophan through the indole, kynurenine and serotonin pathways. Ecological imbalance of the gut microbiota can thus damage the tryptophan breakdown metabolic pathway, leading to pathologic conditions and diseases such as inflammation, neuro-psychiatric disorders, metabolic syndrome and cancer[144]. A study showed that the norharman tryptophan metabolite derived from Lactobacillus exhibited the most potent inhibitory effect on M1 macrophages, resulting in suppressed release of inflammatory factors both in vivo and in vitro. Furthermore, through its ability to preserve the integrity of lipid rafts and restore lipid metabolic dysfunction, norharman blocks multiple inflammatory responses during the exacerbation of AP[145]. Up to now, however, the research on interactions between tryptophan and bile acid metabolism and the gut microbiota in HTG-AP remains insufficient.

MICROBIAL-HOST-ISOZYME: A NOVEL INTERACTION MODE BETWEEN GUT MICROBIOTA AND THE HOST

Although numerous studies have demonstrated that the gut microbiota plays a significant role in both occurrence and development of various human metabolic diseases, most current research on the gut microbiota focuses on the effects of the small molecule metabolites it produces on the body, leaving a lacuna of studies on other functional molecules such as proteins. Various enzymes of gut symbiotic bacteria play important roles in the generation and metabolism of metabolites. Moreover, the bacterial-derived enzymes also have multiple functions independent of metabolites, but their roles in host metabolic diseases remain unclear. A recent study has proposed a new concept of “microbial-host-isozyme (MHI)”, which can effectively simulate the functions of host enzymes and participate in the occurrence and development of diseases (Figure 4). Among them, the bacterial dipeptidyl peptidase 4 (DPP4) can enter the host body through bacterial secretion, where it then degrades the host glucagon-like peptide-1 and consequently induces abnormal glucose tolerance. The host DPP4 inhibitor sitagliptin is unable to effectively inhibit the activity of bacterial DPP4. Importantly, patients with enhanced bacterial DPP4 present low responsiveness to sitagliptin provided as clinical treatment[146].

Figure 4 Future prospects of microbial-host-isozyme in the diagnosis and treatment of hypertriglyceridemia-induced acute pancreatitis. Bacteroides spp. in the gut can secrete dipeptidyl peptidase 4 (DPP4). Sitagliptin can only inhibit host DPP4 activity but not microbial-derived DPP4 activity, leading to a low response to sitagliptin in patients. Escherichia coli (E. coli) is frequently enriched in patients with hypertriglyceridemia. PldA of E. coli can synthesize products with phospholipase A2 activity to promote the production of lysophosphatidylcholine and thus aggravate the inflammatory response of acute pancreatitis. DPP4: Dipeptidyl peptidase 4; AP: Acute pancreatitis; HTG: Hypertriglyceridemia; PLA2: Phospholipase A2; LysoPC: Lysophosphatidylcholine.

MHI is a new tool for studying and regulating gut microbiota, but its role in disease is not well understood. It is widely recognized that the gut microbiota interacts with its host through metabolites, and such interactions are most likely mediated by MHI. For example, the pro-inflammatory metabolite LysoPC can worsen a variety of inflammatory diseases including AP[114,115], which could be formed by metabolism of the host PLA2 and also by metabolism of the gut microbiota[116]. However, it is unclear which gene of which strain plays a role in this process. The gene PldA, which encodes the active enzyme PLA2 in E. coli[147,148], may provide a mechanism for HTG and long-term high-fat diets to worsen AP[29,41]. While HTG and high-fat diets increase the population of E. coli in the gut, this proposed link to AP aggravation needs further investigation.

THE CURRENT MAIN CLINICAL TREATMENT METHODS FOR HTG-AP

Lipid-lowering drugs

The key measure of HTG-AP treatment efficacy is lowered blood lipid levels. Currently, the main drugs for lowering blood lipid levels include statins, fibrates, and niacin, and fibrates are usually selected when the goal is to reduce TG. Recent studies have shown that the combination of fenofibrate and octreotide acetate yields superior outcomes in the treatment of patients with HTG-AP; specifically, the combination therapy demonstrated greater efficacy in controlling inflammation, protecting liver function, and improving patient prognosis[149]. However, a case study was published that documented an instance of AP induced by pravastatin; after excluding other causes and assessment using the Naranjo scale, the event was attributed to drug-induced pancreatitis[150]. Therefore, with the increasing use of statins, clinicians should exercise heightened vigilance regarding the indications, dosage, and administration of lipid-lowering agents. For patients presenting with AP and a recent history of statin use, prompt discontinuation of the medication is crucial to mitigate potential exacerbation of pancreatic injury.

Treatment with insulin and heparin

Insulin can activate LPL and stimulate its synthesis. The latter, in turn, promotes the degradation of chylomicrons, thereby reducing TG levels. On the other hand, exogenous supplementation of insulin is also beneficial for the pancreas, allowing it to “rest”, and it can improve immune paralysis by up-regulating the expression of human leukocyte antigen on neutrophils, thereby reducing cell apoptosis[151]. Currently, no randomized controlled trials have compared the use of insulin with conventional conservative therapy in the treatment of HTG-AP. It is recommended to administer insulin at a dose of 0.1-0.3 U/kg per hour to reduce TG levels, regardless of the presence of hyperglycemia. Blood glucose should be monitored frequently to prevent hypoglycemia, and glucose solution should be added to the infusion when necessary[151]. Patients with HTG-AP receiving continuous insulin infusion are advised to be admitted to the ICU, where a higher level of monitoring can be provided to avoid complications such as hypoglycemia[152].

LPL is typically anchored to the capillary endothelium via heparan sulfate proteoglycan chains. Continuously infused heparin exhibits a stronger binding affinity for the LPL binding site than heparan sulfate, leading to dissociation of the heparan sulfate LPL complex from the endothelium and its release into the plasma. This substantial release of LPL accelerates lipoprotein metabolism and reduces serum TG levels. Low molecular weight heparin has been demonstrated to function similarly to heparin in this process of LPL-mediated TG reduction[153]. Some studies have suggested that long-term use of heparin may lead to the depletion of LPL, thereby reducing the hydrolysis of chylomicrons and resulting in a rebound increase in TG levels, which signifies the recurrence of HTG. Since heparin is known to increase the risk of bleeding[154], however, some researchers recommend avoiding it as a lipid-lowering treatment to avoid the potential adverse effects[155]. Conflicting findings have been reported, with cases of HTG patients receiving sustained heparin administration maintaining TG levels at low concentrations without HTG recurrence[156]. The therapeutic value of heparin in the management of HTG-AP remains to be conclusively determined.

Plasma exchange

Plasma exchange can rapidly reduce the concentrations of TG and pancreatic enzymes in patients; at the same time, it can filter out inflammatory mediators in the blood, effectively and quickly improving the symptoms of patients with HTG-AP. Studies have shown that plasma exchange combined with hemoperfusion can enhance lipid reduction at an early stage, thereby reducing the inflammatory markers in patients with HTG-AP, shortening the lengths of both stay in the ICU and total hospital stay, but it has no significant impact on the mortality rate[157]. It was also shown that a single plasma exchange led to a 70.4% decrease of TG level on average; the lipid-lowering effect was best after the first exchange, reaching 89.3% decrease[158].

Plasma exchange is not free of risk and adverse effects include allergies, infections, disease transmission, and consumption of coagulation factors. It also requires a large volume of plasma and has high treatment costs. In recent years, the double-membrane plasma separation (DFPP) technology has been gradually introduced into clinical practice with the aims of addressing the issue of dependence on plasma in plasma exchange and eliminating the inherent risks of adverse reactions caused by the infusion of blood products. DFPP relies on a primary plasma separator to first separate the plasma and blood cells, which is followed by processing through a plasma component separator (with smaller membrane pores) to remove pathological plasma components; this allows for re-infusion of the patient’s healthy components such as albumin, water, electrolytes, and blood cells back into their body while reducing waste of useful components. Proof of benefit exists in the first treatment with DFPP reducing TG levels by up to 87.4%[159]. It remains important to consider that DFPP is unable to remove FFAs that have already been produced within the cycle, and its operation is complex and requires guidance from experienced clinical doctors. Therefore, the application of DFPP remains limited in clinical settings. As a result, plasma exchange is suitable for patients with HTG-AP who have extremely high initial lipid levels but also sufficient plasma and non-allergic status. DFPP is still considered appropriate for situations where there is a shortage of plasma resources, the patients are allergic, and the clinical physicians have rich experience.

CONCLUSION

The timely identification of HTG in AP is critical for effective initial and long-term treatment. Accordingly, the focus of research has shifted to understanding the potential biomarkers and molecular targets of HTG-AP with the goal of improving prognosis and individualizing treatment strategies. The symbiotic relationship between the human gut microbiota and its host influences immunity, metabolism, and inflammation; the gut microbiota itself influences the adaptive immune system through bacterial components and metabolites, which is critical for maintaining immune homeostasis[160]. Therefore, it is crucial to understand and explore the potential biomarkers and molecular targets of HTG-AP. From this perspective, exploring the role and mechanism of gut microbiota and its metabolites in HTG-aggravated AP may open a new window for the early diagnosis and long-term prevention and treatment of HTG-AP. Fecal microbiota transplantation (FMT) is a promising new treatment for patients with Clostridium difficile infection and children with autism spectrum disorder, showing good results[161,162]. However, FMT techniques are donor-derived washed mixtures, which contain both beneficial and harmful bacteria, posing potential risks for clinical treatment. For example, in a study involving 103 children with autism spectrum disorder, a total of 28 adverse events occurred[163]. To date, FMT has not been used clinically for AP. Experiments in AP mice showed that receiving gut microbiota from healthy mice worsened pancreatic injury, intestinal permeability, and mortality[41]. This finding suggests that FMT may not be suitable for treatment for AP and that its effectiveness can vary for different diseases. Future research should use metagenomics and metabolomics to identify strains with important regulatory effects on the occurrence and development of diseases, laying the groundwork for precision medicine initiatives and personalized treatment plans. In recent years, targeting gut microbiota has shown great potential in the treatment of metabolic diseases, but it is undeniable that there are still many challenges in translating these research results into clinical practice. Further evaluation of the adaptability and safety of FMT technology in different diseases and precise disease management based on an individual’s unique microbiome composition may be important issues in future research. The proposal of MHI provides novel ideas and methods for the targeted control of gut microbiota and precise diagnosis and treatment of metabolic diseases.