L-arginine: A promising metabolite in enhancing the protective effects of adipose-derived stem cells against ischemic pathologies

Abstract

Bone marrow-derived mesenchymal stem cells (BMSCs) and adipose tissue-derived mesenchymal stem cells (ADSCs), two principal subtypes of mesenchymal stem cells with multilineage regenerative potential, have emerged as promising therapeutic strategies for various diseases. While BMSCs and ADSCs exhibit distinct functional profiles tailored to different therapeutic applications, emerging evidence suggests that ADSCs may be a more promising approach for treating ischemic pathologies, including myocardial infarction, ischemic stroke, and peripheral artery disease, in comparison with BMSCs. However, the precise molecular mechanisms by which ADSCs enhance the therapeutic outcomes in these diseases remain poorly understood. In this editorial, we comment on the article by Li et al, which systematically compares the therapeutic efficacy of ADSCs and BMSCs derived from the same elderly patients with coronary heart disease and explores the underlying mechanism from a metabolic perspective. This study proposes that the metabolite L-arginine in ADSCs isolated from elderly patients promotes angiogenesis and protects against apoptosis in a hypoxic and ischemic microenvironment, thereby enhancing myocardial repair following infarction. These findings not only highlight the metabolic plasticity of ADSCs but also position L-arginine as a pivotal therapeutic effector in coronary heart disease. Given the novel and crucial role of L-arginine in ischemic heart diseases, further exploration of L-arginine in ADSCs (particularly those derived from elderly individuals) is essential, including its roles in angiogenesis, cell death, and the potential therapeutic implications in other ischemic pathologies. Additionally, further investigation into additional metabolites in ADSCs is warranted to enhance the therapeutic potential of ADSCs in ischemic pathologies.

Key Words: L-arginine; Metabolite; Bone marrow-derived mesenchymal stem cells; Adipose tissue-derived mesenchymal stem cells; Ischemic pathologies

Core Tip: Ischemic pathologies impose global health challenges and economic burden due to limited therapeutic efficacy. Li et al revealed that the metabolite L-arginine, enriched in adipose tissue-derived mesenchymal stem cells (ADSCs) obtained from elderly patients, could enhance the therapeutic efficacy of ADSCs by promoting angiogenesis and inhibiting cell apoptosis in ischemic conditions. This research underscores the significance of L-arginine for ADSCs-based therapy from a metabolic perspective, highlighting the potential of combining metabolic modulation with ADSCs therapy to improve clinical outcomes in ischemic diseases, particularly in aging populations. However, additional clinical studies are essential to validate the clinical application of these findings.

INTRODUCTION

Ischemia, defined as the restriction or blockage of blood supply to specific organs, leads to a deficiency in oxygen and nutrients essential for cellular metabolism, ultimately contributing to a wide range of pathologies, including ischemic heart disease, cerebral ischemia, ischemic acute kidney injury, and peripheral artery disease[1-4]. The underlying mechanisms of ischemic injury are multifactorial, such as oxygen and nutrient deprivation, inflammatory responses, oxidative stress and endothelial dysfunction[5-7]. Ischemic pathologies have emerged as a significant public health challenge and economic burden worldwide, given their rising prevalence, high morbidity rates, and multiple severe complications[8-10]. Currently, available treatments for ischemia primarily involve pharmacological interventions and physical procedures aimed at restoring blood supply to ischemic tissues and minimizing subsequent tissue injury[11,12]. Despite significant advances in the development of ischemic therapy, current treatments remain invasive and ineffective, particularly in cases of severe ischemia or delayed hospital admission. Elucidating the pathophysiological mechanisms, as well as identifying new therapeutic strategies to improve ischemic control and mitigate complications, continues to be an ongoing effort with significant implications for global social and economic development.

THERAPEUTIC POTENTIAL OF MESENCHYMAL STEM CELLS IN ISCHEMIC PATHOLOGIES

Mesenchymal stem cells (MSCs), defined as multipotent progenitor cells with the capacity for self-renewal and differentiation, can be routinely harvested from various tissues, including dental pulp, adipose tissue, bone marrow, and umbilical cord blood[13]. MSCs have been demonstrated to play significant roles in tissue repair due to their pleiotropic functions, such as antiapoptotic, antifibrotic, proangiogenic, and neuroprotective effects[14-16]. This unique set of characteristics positions MSCs as promising candidates for therapeutic potential in the field of regenerative medicine[17-19]. Recent advances in cell therapy have established MSC-based treatments as safe and effective interventions that can be used to alleviate ischemic conditions[20,21]. For example, MSCs transplantation following acute myocardial infarction (MI) can inhibit ischemia-induced autophagy by the miR-125b-5p/p53/Bnip3 signaling pathway, ultimately exerting myocardial protective effects in the context of MI and ischemia/reperfusion injury[22]; MSC-derived exosomes alleviate cell cycle arrest and apoptosis in renal tubular epithelial cells through the miR-125b-5p/p53 signaling pathway, thereby mitigating ischemic acute kidney injury and promoting tubular repair[23]; gingival MSCs-derived exosomes confer neuroprotective effects in retinal ischemic injury via modulating the maternally expressed gene 3/miR-21a-5p/programmed cell death 4 pathway, ultimately suppressing retinal ganglion cell apoptosis and attenuating microglia-mediated neuroinflammation[24]. Additionally, both clinical trials and preclinical studies involving MSCs transplantation have shown significant improvement in patients with different types of ischemia[25,26]. The first-in-human PASSIoN trial (NCT03356821) demonstrated that intranasally administered bone marrow-derived MSCs (BMSCs) are feasible and safe in term neonates with perinatal arterial ischemic stroke[27]. A long-term follow-up of intravenously administrated MSCs in ischemic stroke patients revealed a favorable safety profile, along with enhanced functional outcomes and improved survival rates[28]. Collectively, these data support the feasibility and safety of MSCs for treating ischemic conditions in clinical trials, suggesting that MSCs transplantation may serve as a promising cell-based therapy in the future. However, additional investigation is required to comprehensively understand the underlying mechanisms of MSCs action in ischemic pathologies and to translate these insights into clinical treatments.

ADIPOSE DERIVED MSCS: A MORE EFFECTIVE CANDIDATE FOR THE TREATMENT OF ISCHEMIC PATHOLOGIES THAN BMSCS

BMSCs and adiposederived MSCs (ADSCs) are considered to be primary sources of MSCs, offering significant potential in cell-based therapy for multiple diseases, including ischemic pathologies[29-31]. Currently, accumulating evidence suggests that ADSCs may offer superior therapeutic benefits over BMSCs in ischemic conditions due to their unique advantages (Table 1)[32]. For instance, ADSCs are widely distributed and can be relatively easily harvested in larger quantities via a minimally invasive procedure from diverse adipose tissue types in the body, including the abdomen, thigh, and arm, without being constrained by patient-specific conditions. Whereas BMSCs are typically isolated from the iliac crest and their extraction can be hindered by challenges related to the patient’s bone marrow quality, which may degrade with age or underlying conditions such as osteoporosis[33-35]; ADSCs have been shown to undergo senescence later than BMSCs and possess a higher proliferation capacity, making them a superior candidate for regenerative applications that require large numbers of cells[36-38]; compared with BMSCs, ADSCs also exhibit enhanced autocrine and paracrine production of proangiogenic factors, such as vascular endothelial growth factor-D (VEGF-D) and insulin-like growth factor 1, positioning them as optimal candidates for rescuing microvascular perfusion defects in ischemic tissues[39-43]; both ADSCs and BMSCs harbor immunomodulatory properties critical for controlling inflammation and facilitating tissue repair in ischemic conditions. Notably, ADSCs demonstrate a greater ability to suppress immune responses by regulating the secretion of anti-inflammatory cytokines and macrophage function, thereby providing more efficient control of ischemia-induced inflammation[44]. As previously reported, ADSCs are more suitable than BMSCs for cell transplantation-based therapy of atherosclerosis, as ADSCs exhibit superior anti-inflammatory properties, enhanced phagocytic activity, stronger anti-apoptotic capacity and higher cell viability compared with BMSCs[45]. Overall, ADSCs demonstrate superior translational potential for the therapy of ischemic pathologies due to their ease of acquisition, higher yields, superior immunomodulatory effects, greater proliferative capacity, enhanced phagocytic activity, increased anti-apoptotic capability, robust angiogenic potential, and improved engraftment efficiency[46-48].

Table 1 Characteristics of adipose tissue-derived mesenchymal stem cells vs bone marrow-derived mesenchymal stem cells in the therapy of ischemic conditions.

Characteristics	Mechanism of action	Ref.
Higher availability and abundance	Widely distributed and richer adipose tissue harvest	[33-35]
Higher proliferation capacity and enhanced survival under hypoxic stress	Upregulated expression of a variety of cellular signaling molecules (such as IGF-3, FGF-2, HIF-1α), and activation anti-apoptotic signaling pathway, etc.	[36-38]
Superior angiogenic potential	Higher secretion of pro-angiogenic factors (e.g., L-arginine, VEGF, FGF-2), enhanced MMP-2/9-mediated extracellular matrix remodeling	[40,46]
Enhanced paracrine activity	Release a broader spectrum of functional molecules (such as growth factors, chemokines and cytokines) through paracrine manner	[39,42,43]
Stronger immunosuppressive and anti-inflammatory effects	Higher production of immunosuppressive factors (such as IL-10, TGF-β, and PGE2), and promoting M2 macrophage polarization	[30,44,45]
Improved homing and engraftment	Highly expression of chemokine receptors (e.g., CXCR4 and CXCL12), enhancing cells migration and engraftment to ischemic tissues	[47,48]

IGF-3: Insulin-like growth factor-3; FGF-2: Fibroblast growth factor-2; HIF-1α: Hypoxia-inducible factor-1alpha; VEGF: Vascular endothelial growth factor; MMP: Matrix metalloproteinase; IL: Interleukin; TGF-β: Transforming growth factor beta; PGE2: Prostaglandin E2; CXCR4: C-X-C chemokine receptor type 4; CXCL12: C-X-C motif chemokine ligand 12.

CHALLENGES AND ADVANCES IN CLINICAL APPLICATIONS OF ADSCS IN ISCHEMIC PATHOLOGIES

Although numerous preclinical studies and clinical trials have been conducted to investigate the efficacy of ADSCs in ischemic conditions, phase III clinical studies have been impeded by some challenges. For instance, one study reported that in vitro-cultured unmodified MSCs derived from mice possess chromosomal abnormalities in early passages, and their local transplantation could induce malignant tumor formation in mouse models[49]; similarly, autologous adult human MSCs have been shown to acquire tumorigenic potential and contribute to the development of epithelial cancers[50,51]; studies have shown that ADSCs from obese subjects promote breast cancer proliferation and tumorigenicity both in vitro and in vivo via an estrogen-leptin pathway, potentially elevating the risk of tumor development[52]. Moreover, MSC immunogenicity is heightened during amplification processes as most MSC products are manufactured by amplifying a small number of cells obtained from donors. Accumulating evidence has also demonstrated that inflammatory cytokines (e.g., interferon-γ, tumor necrosis factor-α), interleukin 2-activated natural killer cells, and CD3/CD28-stimulated T cells could induce BMSCs apoptosis through the Fas-mediated pathway, thereby impairing the viability and differentiation capacity of MSCs[53,54]. It has also been reported that implanted human MSCs can activate the complement system of innate immunity upon contact with serum, leading to subsequent injury via complement-mediated attack[55]. In addition, intravenous infusion of ADSCs has been shown to induce pulmonary embolism in mice due to the procoagulant properties triggered by tissue factor[56]. These thrombotic complications mediated by the instant blood-mediated inflammatory reaction have raised significant safety concerns, with incidences of death in both animal models and patients[57]. Altogether, MSC transplantation and therapy are plagued by adverse events and poor survival in vivo, such as tumorigenicity, immunogenicity, pulmonary embolism, and poor engraftment, which pose a substantial barrier to the translation of ADSCs from preclinical research to clinical application. Further studies are warranted to elucidate the precise mechanisms of their action and to assess the potential for translating experimental findings into clinical practice.

L-ARGININE: A PROMISING METABOLITE IN ENHANCING THE PROTECTIVE EFFECTS OF ADSCS AGAINST ISCHEMIC PATHOLOGIES

Emerging studies have highlighted that specific metabolites may enhance the therapeutic efficacy of MSCs-based therapies across multiple pathologies by improving cell survival, promoting angiogenesis, and modulating inflammation[58-60]. For example, lactate, as a critical intermediate and energy source, has been reported to enhance osteogenic differentiation of BMSCs through histone lactylation as well as the Olfr1440/Ca²⁺ signaling pathway, thereby ameliorating osteoporosis and improving bone defect repair[61,62]; similarly, lactate could enhance MSCs immunosuppressive activity through inhibiting the proinflammatory response of M1-like macrophages[58]. Pyruvate, the end-product of glycolysis and a primary source of the tricarboxylic acid cycle intermediates oxaloacetate and acetyl-CoA, has emerged as a critical regulator of MSCs functionality, potentially serving as a promising biomarker for optimizing large-scale MSC manufacturing processes in clinical trials[63]. L-arginine, a semi-essential amino acid derived from dietary intake, intracellular synthesis, and net proteolysis[64], plays crucial roles in various metabolic and physiological processes, including glycolysis, protein synthesis, vasodilation, mitochondrial homeostasis, immune modulation, and the production of ornithine, urea as well as nitric oxide (NO, a key intercellular messenger molecule)[65-67]. As a primary precursor of NO, L-arginine exhibits the capacities to regulate angiogenesis and hemodynamics[68]; improve endothelium-dependent blood flow and vasodilatation in hypercholesterolemic individuals[69]; inhibit platelet aggregation and thrombosis[70]; suppress macrophage infiltration and edema formation[71]; and promote the recovery of damaged tissues. Additionally, L-arginine supplementation has been extensively investigated in the treatment of numerous diseases[72]. Both acute and chronic administration of L-arginine has emerged as a promising therapeutic strategy for a range of diseases, such as cognitive impairment, endothelial dysfunction, atherosclerosis, and ischemic acute renal failure[73-75]. Nevertheless, its protective role in ADSCs, particularly in the context of ischemic injury, is still poorly understood.

Recently, metabolomic analyses revealed that ADSCs and BMSCs isolated from elderly patients with coronary heart disease exhibit significant discrepancies in certain metabolites (e.g., α-ketoisovaleric acid, pyruvate) and their corresponding metabolic pathways, which may serve as the underlying mechanisms contributing to the varying efficacies of MSCs-based therapies in atherosclerosis-associated diseases[60]. However, the specific metabolite differences and underlying mechanisms responsible for superior therapeutic potential of ADSCs over BMSCs across multiple pathologies, especially in ischemic pathologies, remain poorly elucidated. The study entitled “L-arginine from elder human mesenchymal stem cells induces angiogenesis and enhances therapeutic effects on ischemic heart diseases” proposes that ADSCs isolated from elderly patients exhibit a twofold increase in L-arginine levels compared to BMSCs[44]. This elevated L-arginine promotes ADSCs-mediated angiogenesis and protects against ADSCs apoptosis in hypoxic and ischemic microenvironments, consequently enhancing myocardial repair following infarction. The authors further reveal that arginine succinate lyase, a key regulatory enzyme in L-arginine production, could increase the secretion of VEGF and basic fibroblast growth factor, which promote endothelial cell migration and capillary-like structure formation via the L-arginine/VEGF receptor 2/mitogen-activated protein kinase signaling pathway; simultaneously, arginine succinate lyase enhances the resistance of ADSCs to post-transplantation hypoxia and ischemia, ultimately improving therapeutic effects through the improvement of angiogenetic induction, ventricular chamber maintenance, and cardioprotection[44]. This study proposes an ADSCs-based therapeutic strategy for ischemic diseases to address the challenges associated with aging-related conditions by focusing on elderly patients, positioning L-arginine as a promising metabolite in enhancing the protective effects of ADSCs against ischemic pathologies (Figure 1).

Figure 1 L-arginine: A promising metabolite in enhancing the protective effects of adipose tissue-derived mesenchymal stem cells against ischemic pathologies. The metabolite L-arginine, enriched in adipose tissue-derived mesenchymal stem cells obtained from elderly patients, may enhance the therapeutic efficacy of adipose tissue-derived mesenchymal stem cells in ischemic conditions through multiple mechanisms, including promoting angiogenesis and inhibiting cell apoptosis. The schematic model was plotted with BioRender (https://www.biorender.com).

Although the data presented in this study are persuasive, several important issues must be resolved before L-arginine could be regarded as a viable therapeutic target for clinical application. As the sole substrate for endothelial NO synthase and a primary precursor of NO, L-arginine’s pro-angiogenesis has been well established. Specifically, NO and endothelial NO synthase have been demonstrated to enhance endothelial cell proliferation and migration, modulate cytoskeletal organization, as well as promote capillary tube formation via multiple signaling pathways, including the soluble guanylate cyclase/cyclic guanosine monophosphate/protein kinase G, protein kinase B/extracellular signal-regulated kinase 1/2, and activator protein-1/nuclear factor kappa B/matrix metalloproteinase 2 pathways[76,77]. It remains to be elucidated whether L-arginine potentiates ADSCs-mediated angiogenesis via these pathways. Furthermore, does L-arginine augment tissue repair in ischemic diseases through other mechanisms, like immune modulation? Given the pivotal roles of metabolites in modulating MSCs functionality, could other metabolites also enhance ADSCs functionality through distinct pathways? And the combination of L-arginine with other key metabolites (e.g., α-ketoglutarate, succinate) may exert synergistic effects in boosting the therapeutic efficacy of ADSCs for ischemic diseases, which warrants further investigation. Besides, could the therapeutic effects of L-arginine observed in elderly patients be generalized to younger populations? Importantly, sustained and comprehensive assessment of L-arginine’s specificity, safety, and potential adverse effects in ADSCs-based therapy for ischemic diseases is warranted. Therefore, further in depth and comprehensive studies are needed to fully elucidate the role and underlying mechanisms of L-arginine in ADSCs, as well as to facilitate its application as a key metabolite in enhancing MSCs-based therapies for ischemic pathologies.

CONCLUSION

Ischemic pathologies, including MI, ischemic stroke, and peripheral artery disease, continue to pose a substantial health burden worldwide. While stem cell therapy, particularly ADSCs, holds great promise in treating these conditions, enhancing their therapeutic efficacy is necessary for clinical translation. L-arginine, a key metabolite, plays critical roles in multiple physiological and pathological processes. Through systematically comparing the therapeutic efficacy of ADSCs and BMSCs derived from the same elderly patients, and exploring the underlying mechanism from a metabolic perspective, L-arginine was demonstrated to augment the protective effects of ADSCs against MI through inhibiting cell apoptosis and promoting angiogenesis. These findings imply that L-arginine is a key therapeutic metabolite in improving the efficacy of ADSCs for treating ischemic diseases. Moreover, considering the low cost of L-arginine compared to the significant therapeutic benefits it may offer, the combination of ADSCs and L-arginine presents a promising therapeutic strategy for ischemic diseases, potentially offering a new approach to enhance tissue repair and recovery, especially in elderly patients, within clinical settings. However, the potential risks associated with excessive L-arginine and NO should also be taken into consideration, such as vascular or inflammatory issues caused by imbalanced NO levels. Further exploration is essential to fully clarify their pharmacological effects, determine the optimal dosing range, and thoroughly assess their clinical applications.