Preclinical pharmacology studies of zingerone with special reference to potential therapeutic applications

Abstract

Zingiber officinale Roscoe (ginger) is traditionally used as a culinary spice worldwide. In folklore medicine, raw and fresh ginger has been used for treating nausea and vomiting, to improve liver function and digestion, antidiarrheal, to treat menstrual cramps, and as an aphrodisiac. Zingerone [4-(4-hydroxy-3-methoxyphenyl)-2-butanone] is the major bioactive ingredient present in ginger. Zingerone has shown a wide-range of pharmacological activities in vitro and in vivo studies. While zingerone is present in small amount in fresh ginger, but its level is increased during drying or heating during cooking. The amount of zingerone increases significantly due to the conversion of gingerol into zingerone through retro-aldol reaction. Owing to its strong antioxidant and anti-inflammatory properties, zingerone has the ability to scavenge reactive oxygen species and to assist in curing a wide array of non-communicable diseases associated with oxidative stress such as diabetes mellitus, obesity, cardiometabolic and cardiovascular disorders, neurological abnormalities, osteoarthritic, and certain cancer types. For this review, extensive literature searches were performed using PubMed, Google Scholar, Science Direct, and other search engines. The major aims of our review are to describe the chemical characteristics of zingerone as well as the various in vitro and in vivo studies reported regarding the pharmacological effects of zingerone and the mechanism of action observed at the cellular and molecular levels. The results of published preclinical and few clinical studies suggest that zingerone has several promising therapeutic applications due to its strong antioxidant, anti-inflammatory and anti-proliferative activities without any serious side effects. However, well-designed, randomized, placebo-controlled, and multi-center clinical studies are needed to determine the optimal therapeutic doses, and long-term safety of zingerone.

Key Words: Zingerone; Anti-inflammation; Antioxidant; Anti-proliferative; Antidiabetic

Core Tip: Zingerone is one of the potent natural bioactive molecules isolated from the ginger, a natural spice distributes all over the world. In this review, we have identified that zingerone possesses several pharmacological properties such as potent anti-oxidant, anti-inflammatory, anti-apoptotic, antiproliferative effects in pre-clinical studies. These properties suggest that the zingerone is more beneficial in curing several disorders. However, exploration of structure activity relationship could be useful to enhance its stability, safety and effectiveness. Thus, there is a need of future exploration for the therapeutic potential of zingerone in clinical studies. On the basis of literature reviews, it is concluded that zingerone possesses a great potential against various diseases.

INTRODUCTION

Traditional folklore medicines have been used for curing and preventing several diseases all over the world since antiquity[1]. According to World Health Organization[2], more than half of the world population uses the traditional and alternative medicines for their health care because of their cost-effective and safe properties. Zingiber officinale Roscoe, Family: Zingiberaceae, is a traditional herbal remedy that firstly originated in South-East Asia, then became popular all over the world and at present is most commonly used as a culinary spice. It’s pungent and aromatic smell provides a special flavor and taste to our foods. Apart from this property, it is known to prevent different non-communicable diseases worldwide. A large number of bioactive compounds are present in ginger, whose composition fluctuates significantly due to different varieties of ginger and geographical regions. More than 60 bioactive constituents are documented to be present in ginger[3,4].

Among the bioactive ingredients of ginger, zingerone [4-(4-hydroxy-3-methoxyphenyl)-2-butanone] is the major and stable bioactive compound found in ginger[5]. Zingerone is an alkaloid belonging to the methoxyphenol family and its associated derivatives[6]. It was first isolated from the ginger root in 1917 by Nomura[7]. It is primarily present in dry ginger (approximately 9.25%), but cooking increases its concentration via conversion of other constituents of ginger including 6-gingerol, 8-gingerol and 10-gingerol into zingerone through retro-aldol reaction[8]. Zingerone is chemically related to eugenol present in cloves and vanillin from vanilla. It is a crystalline solid with very low solubility in water, but is soluble in ether and it decomposes under light[9]. Zingerone possess low oral bioavailability because of its poor water solubility, which is a great challenge for its clinical applications. Thus, nanotechnology-based self-microemulsifying drug delivery systems of zingerone have been developed to improve its oral bioavailability[10]. Human and rat studies have shown that after oral dosing, zingerone is rapidly metabolized in the gastrointestinal tract and only small amount reaches the systemic circulation, and is eliminated within 6 hours from the body[11,12]. Following oral or intraperitoneal administration, zingerone is metabolized by the side chain oxidation, and the glucuronide and sulphate conjugates are excreted in the urine[3]. Cotton[13] was the first chemist to patent the synthesizing process of zingerone in the year 1945. Chemically synthesized zingerone is vanillyl acetone, which is a phenolic alkanone with different pharmacological activities[3]. Figure 1 shows the structure of zingerone.

Figure 1  Chemical structure of zingerone.

HISTORICAL PERSPECTIVES ABOUT THE ISOLATION, CHARACTERIZATION, AND SYNTHESIS OF ZINGERONE

Isolation of zingerone was first carried out by a Japanese chemist Nomura[7] from ginger root in 1917 using ether and sodium hydroxide extraction method. Later on, Kuo et al[14] extracted zingerone from the dried powdered rhizomes of Zingiber officinale Rosc. by using extraction process with hot methanol. The concentrated methanol extract was mixed with water and then partitioned with chloroform. After few hours, the aqueous layer with draws and the residue of the chloroform was chromatographed on a silica gel. Different gradients of chloroform: Methanol was employed as the mobile phase for fractionation. After wards the fractions were directly applied to silica gel column chromatography using n-hexane and ethyl acetate (3:1) as eluent, to acquire subfractions. Furthermore, re-crystallization of sub fraction with acetone caused the formation of zingerone which was confirmed through ultraviolet-visible spectra, IR spectra and H- and 13C nuclear magnetic resonance spectra[14].

In 1917, Nomura[7] developed a method for the synthesis of zingerone by the hydrogenation of dihydrozingerone through the condensation of vanillin and acetone under the influence of alkalosis (Figure 2). This method consists of two stages: (1) Production of dihydrozingerone by the condensation of acetone with vanillin in the presence of effective heterogeneous catalysts; and (2) Hydrogenation of dihydrozingerone to form zingerone in the catalytic activity of hydrotalcite (Figure 3). This two-stage method is not only costly and time-consuming, but also produces large amount of industrial waste. To overcome these problems, Chistyakova et al[15] proposed a single-stage process that can be used to synthesize zingerone from isopropanol and vanillin. In this method, nickel-copper catalyst is used without using any alkalis and solvents, thus making it possible to exclude the hydrogenation step of synthesis[15].

Figure 2 Chemical synthesis of zingerone involves condensation of vanillin and acetone and hydrogenation of dihydrozingerone. This method consists of two stages: (1) Production of dihydrozingerone by the condensation of acetone with vanillin in the presence of effective heterogeneous catalysts; and (2) Hydrogenation of dihydrozingerone to form zingerone in the catalytic activity of hydrotalcite (Figure 3).

Figure 3  Chemical synthesis of zingerone by the combination of isopropanol and vanillin.

PHARMACOLOGICAL ACTIVITIES OF ZINGERONE IN RATS AND MICE

Pharmacological activities of zingerone in rats and mice (Figure 4). The pharmacological activities of zingerone in rats and mice treated acutely or chronically with different doses of zingerone are summarized in Table 1.

Figure 4 Graphical abstract: Several pharmacological activities of zingerone with mechanism of actions. EPSC: Excitatory post-synaptic current; TG: Triglycerides; LDL: Low density lipoprotein; VLDL: Very low density lipoprotein; HDL: High density lipoproteins; NF-κB: Nuclear factor kappa B; IL: Interleukin; TNF-α: Tumor necrosis factor alpha; COX-2: Cyclooxygenase-2; iNOS: Inducible nitric oxide synthase; SOD: Superoxide dismutase; GPx: Glutathione peroxidase; GSH: Glutathione; CAT: Catalase; TBARS: Thiobarbituric acid reactive substances; TGF-β1: Transforming growth factor-beta 1; Bcl-2: B cell lymphoma-2; MPO: Myeloperoxidase; CRP: C-reactive protein; AST: Aspartate transaminase; ALT: Alanine transaminase; ALP: Alkaline phosphatase; TRL-4: Toll-like receptor-4.

Table 1 Zingerone possessing various pharmacological activities.

No.	Activities	Doses	Route	Animals	Treatment duration	Ref.
1	Antioxidant	20 mg/kg	Oral	Rats	30 days	[20]
2	Anti-inflammatory	100 mg/kg	Oral	Mice	4 hours	[24]
3	Anti-cancer	10 mg/kg	Intraperitoneal	Mice	14 days	[8]
4	Radioprotective	20 mg/kg	Oral	Mice	5 days	[37]
5	Nephroprotective	50 mg/kg	Ora	Rats	7 days	[44]
6	Hepatoprotective	20 mg/kg	Oral	Rats	30 days	[52]
7	Cardioprotective	6 mg/kg	Oral	Rats	14 days	[60]
8	Neuroprotective	100 mg/kg	Oral	Rats	24 hours	[67]
9	Anti-diarrheal	10 mg/kg	Intraluminal	Rats	-	[71]
10	Anti-microbial	1 mg/mL	In-vitro			[76]
11	Anti-diabetic	100 mg/kg	Oral	Rats	21 days	[80]
12	Gonad-protective	40 mg/kg and 50 mg/kg	Oral	Male mice and female rats	35 days and 7 days	[84]
13	Ant-arthritic activity	25 mg/kg	Oral	Rats	21 days	[87]

Antioxidant activity of zingerone

Exposure to the environmental toxicants, intake of large amounts of oxidative dietary products and some xenobiotics as well as oxidative stress cause mitochondrial-damaging biochemical reactions in our body, resulting in the excessive production of highly reactive oxygen species (ROS) and reactive nitrogen species. The unabated excessive production of ROS and reactive nitrogen species cause different pathophysiological conditions such as cardiovascular disorders, neurological abnormalities, osteoarthritis, and certain cancers[16]. Ginger shown potent antioxidant activity because it contains various antioxidant constituents[17] and zingerone is one of them which donates the electron to prevent the generation of peroxynitrite and avoid nitration of tyrosine residues in tissues as illustrated in Figure 5[18]. Zingerone has also shown protection of DNA against ROS by Fenton’s reaction and ultraviolet/H₂O₂ as evidenced by inhibition of DNA strand broken in plasmid and genomic DNA (Figure 5)[19]. In addition, zingerone treatment reduces the thiobarbituric acid reactive substances, conjugated dienes and lipid hydroperoxides in the plasma and lipid peroxidation in the tissues of alcohol treated rats. Further, zingerone helps to enhance the activities of enzymatic and non-enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and reduced glutathione (GSH), respectively[20].

Figure 5 Diagrammatic representation of the antioxidant effects of zingerone against oxidative stress-induced lipid peroxidation and deoxyribose nucleic acid damage in cells. SOD: Superoxide dismutase; NO: Nitric oxide.

Anti-inflammatory activity of zingerone

Inflammation is among the several biological processes of the body’s response to microbial infection, cellular irritation or injury characterized by an increased production of inflammatory biomarkers, swelling, redness, and pain[21]. Clinically, it is reported that purified and standardized ginger extract has exhibited a statistically significant effect in decreasing the chronic inflammation and pain with a good safety profile[22]. There are various cytokines such as inducible nitric oxide synthase (iNOS), nuclear factor kB (NF-κB), interleukins (ILs), mitogen-activated protein kinase (MAPK), tumour necrosis factor (TNF)-α and interferon activation observed in acute and chronic inflammatory conditions in different ways and regulating the gene expression related to pro-inflammatory markers[23].

Zingerone has been reported to decrease the inflammation in kidney, liver, heart, intestine, spleen, lungs and brain by suppressing the stimulation of NF-κB, induction of IL-1β and infiltration of inflammatory cells. Zingerone has depicted maximum anti-inflammatory activity in the intestine, lungs and spleen[24]. Furthermore, zingerone treatment restrains the gene expression of pro-inflammatory markers, cyclooxygenase-2 (COX-2) and iNOS stimulated by NF-κB and IKK/MAPK signaling pathway involved in many age-associated inflammatory disorders as represented in Figure 6[25]. Moreover, pre-treatment of zingerone to the rats which were subjected to induction of inflammation by carrageenan injection in paws produces anti-inflammatory effect via attenuating TNF-α, IL-1β, COX-2, and PGE2 levels[26].

Figure 6 Zingerone showed anti-inflammatory effect by suppressing nuclear factor kappa B, tumor necrosis factor alpha, cyclooxygenase-2 and inducible nitric oxide synthase cytokines. NF-κB: Nuclear factor kappa B; TNF-α: Tumor necrosis factor alpha; COX-2: Cyclooxygenase-2; iNOS: Inducible nitric oxide synthase; IL: Interleukins; IkB: Inhibitor of kappa B.

Anti-cancer activity of zingerone

It is considered that initiation of cancer involves the regulation of some important cell markers and processes such as P-glycoprotein, breast cancer resistance protein, multi drug-resistance-related proteins, human tumour suppressor protein p53, epidermal growth factor receptor, mitochondria, caspases, angiogenesis and components of MAPK signalling pathways. A number of dietary supplements, plant extracts, and isolated bioactive compounds exert cytotoxic and anti-proliferative effects through different modes of action, including activation of caspases, change in mitochondrial membrane potential, and production of ROS in tumour cells[27]. The ginger extract contains phenolic compounds that inhibits the growth of cancer cells[28].

Many studies have indicated that zingerone exerts anti-tumor activity through the inhibition of matrix metalloproteinases during tumour growth and tumour angiogenesis in endothelial cells involving JNK pathway[8]. Combination of zingerone with its derivatives shows the synergistic effect to decrease the transforming growth factor-beta 1 (TGF-β1) induced epithelial-mesenchymal transition which plays an important role in tumour metastasis. Moreover, zingerone inhibits the activation of Smad, nuclear translocation of NF-κB and activation of MAPK signalling pathway involved in carcinoma metastasis (Figure 7)[29]. In addition, zingerone has the efficiency to protect the colon epithelium against oxidative stress and the development of aberrant crypt foci in dimethylhydrazine-induced colon cancer in rats[30]. Treatment with zingerone helps in the inhibition of enzyme carcinoembryonic antigen, reduction in number of aberrant crypt foci, down-regulation of NF-κB-p65 and Nrf-2 up-regulation[31]. Zingerone has expressed an anti-mitotic effect in human neuroblastoma by inhibiting cell viability and survival in cell line studies[32]. Moreover, nanosized zingerone showed anticancer and anti-angiogenesis activities by attenuating the levels of CD31 and VEGF-mediated PI3K/Akt/mTOR axis signaling in human hepatocellular carcinoma[33].

Figure 7 Diagrammatic illustration showing the anti-tumor activity of zingerone by reducing the expression of transforming growth factor-beta. TGF-β: Transforming growth factor-beta; MAPK: Mitogen-activated protein kinases; TAK-1: Transforming growth factor-beta-activated kinase 1; JAK: Janus kinase.

Radioprotective effects of zingerone

Nowadays, radiation therapy plays a very important role in the treatment and management of all type of cancer patient[34]. General population suffering from the health disorders such as of heart, liver, bone, colon, pancreas, lungs and other body parts are being exposed to radiation during diagnosis[35]. Radiations build the oxidative stress in exposing area via generation of ROS, causes the complication in the body that may lead to mortality[36,37]. Workers who operate the diagnostic medical radiation system also suffering from health problem due to exposure of radiation during diagnosis but workers have less risk of mortality than the general population in a few countries[36].

Zingerone has potential to mitigate and neutralize the oxidative stress as well as complications induced by radiations. Zingerone attributes to scavenge radiation-induced free radicals by up-regulation of antioxidant enzymes such as GSH-S-transferase, CAT, SOD, GSH. Pre-treatment with zingerone attenuate the radiation-induced inhibition of cell proliferation, erythroblast death, damaged cells elimination and forming new cells at affected areas of the mice[37]. Furthermore, zingerone has the potential to decrease the depolarization of the mitochondria, production of malonaldehyde and DNA damage in radiation-exposed cells. It increases the cell survival rate and decreases the cytotoxicity and genotoxicity. Zingerone diminished the radiation-induced apoptosis via inhibiting the stimulation of cysteine aspartate-specific protease-3 (caspase-3), Bax proteins and increasing the expression of B cell lymphoma-2 (Bcl-2) protein that play a major role in maintaining the release of cytochrome C, mitochondrial membrane integrity and permeability[38] (Figure 8).

Figure 8 Protective effects of zingerone against ultraviolet radiation. Bcl-2: B cell lymphoma 2; UV: Ultraviolet.

Nephroprotective effects of zingerone

Nephrotoxicity is characterized by alteration in renal perfusion, glomerular filtration rate, and tubular dysfunction that leads to electrolyte imbalance, and accumulation in the levels of creatinine and nitrogenous waste products in the blood[39]. Exposure to xenobiotics, including some antibiotics and anti-cancer drugs, environmental pollutants, industrial chemicals, and heavy metals (As, Pb, Hg, Cd) are considered as the causes of nephrotoxicity[40]. Clinically, medicinal plants have been used to restore kidney functions as well as reduce the risk of nephrotoxicity induced by drugs and xenobiotics[41]. Ginger itself and zingerone have potent antioxidant activity and can be used to reduce renal impairment[42].

Several investigators have reported that zingerone can prevent kidney injury due to oxidative stress, and prevention of inflammation and apoptosis. According to Safhi[43], administration of zingerone to mice increases the level of antioxidant enzymes and reduces the level of ILs, TNF-α and caspases in carbon tetrachloride-induced nephrotoxicity. Alibakhshi et al[44] demonstrated that co-administration of zingerone with cisplatin mitigates the pathological changes such as glomerulus expansion, fibrosis and loss of brush border of tubules in renal tissue produced by cisplatin (Figure 9). Apart from these findings, zingerone also improved the renal functioning in the diabetic nephropathy[45]. Pro-inflammatory cytokines like NF-κB, IL-1β, IL-6, Fas and TNF-α play an important role in the development of diabetic nephropathy. Zingerone treatment ameliorates the renal impairment by significantly decreasing kidney injury molecule-1, blood urea nitrogen, creatinine, lactate dehydrogenase, and suppressing TGF-β (Figure 9)[45]. Moreover, zingerone help to reduce the levels of serum insulin, C-peptide, glycosylated hemoglobin A1c and albumin content in urine of db/db mice. The pathological changes in the kidney, including reduction of surface area, space of Bowman’s capsule and glomerular tufting the nephron were also observed in zingerone treated db/db mice. The expression of collagen IV, nicotinamide adenine-dinucleotide phosphate oxidase 4 and fibronectin were also reduced in kidneys of diabetic mice during treatment with zingerone (50 mg/kg/day) for 10 weeks[5]. Lee et al[46] have explored the renal protective potential of zingerone by inhibition of NF-κB activation and nitric oxide synthase induction in cecal ligation and puncture surgery-induced renal damage in the mice.

Figure 9 Diagrammatic representation of the protective effects of zingerone against hyperglycaemia and cisplatin-induced nephrotoxicity. AGEs: Advanced glycation end products; NF-κB: Nuclear factor kappa B; TNF-α: Tumor necrosis factor alpha; COX-2: Cyclooxygenase-2; iNOS: Inducible nitric oxide synthase; IL: Interleukins; PKC: Protein kinase C; NADPH: Nicotinamide adenine dinucleotide phosphate; TGF-β: Transforming growth factor-beta.

In rats, zingerone at doses of 25 mg/kg and 50 mg/kg ameliorated the histopathological alterations, oxidative stress, inflammation, apoptosis, oxidative DNA damage and kidney aquaporin 1 in vancomycin-induced nephrotoxicity[47,48]. Anti-cancer agent like cisplatin causes nephrotoxicity via induction of kidney lipid peroxidation, decreased antioxidant enzymes (SOD, CAT, GPx and GSH), and increases the activities of IL-33, iNOS, COX-2, 8-hydroxy-2’-deoxyguanosine, p53, caspase-3, Bcl-2-associated X protein, while decreasing Bcl-2. However, oral administration of zingerone at the dose 25 mg/kg/day and 50 mg/kg/day to female rats showed significant reduction in these altered parameters in cisplatin-induced kidney dysfunctions[47]. Oral treatment with zingerone at different doses (50 mg/kg, 100 mg/kg and 150 mg/kg for 28 days) exhibit renoprotective activity under the influence of lead-induced kidney toxicity in rats[49]. Moreover, zingerone (50 mg/kg, orally) treatment down-regulated the overexpression of iNOS, MAPK14, MAKP15 and JNK in the renal tissue of sodium arsenite-induced nephrotoxic rats[50].

Hepatoprotective effects of zingerone

Liver malfunctions or hepatotoxicity is one of the major public health problems that causes morbidity and mortality in many countries. It is characterized by the leakage of liver enzymes [alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), lactate dehydrogenase], jaundice, loss of appetite, reduced lipid absorption from the gastrointestinal tract. Several drugs such as non-steroidal anti-inflammatory drugs (acetaminophen), antifungal (ketoconazole), antituberculosis (isoniazid), loop diuretic (tienilic acid), and anti-hypertensives are known to cause acute and chronic hepatotoxicity[51]. Although, several currently available drugs are used to treat liver disorders, but lately herbal remedies obtained from plants have attracted the attention of hepatologists due to their high efficacy, safety and better therapeutic response[36].

It is reported that zingerone exerts hepatoprotective actions by ameliorating the oxidative stress and by increasing the activity of enzymatic and non-enzymatic antioxidants: Namely SOD, CAT, GPx, GR, GSH, vitamins C and E in plasma and liver tissue. According to Mani et al[52], zingerone alters the inflammatory biomarkers and decreases the expression of NF-κB, COX-2, TNF-α, and IL-6 along with increased expression of Nrf2 in alcoholi cacute hepatotoxicity (Figure 10). Zingerone normalizes the secretion of liver enzymes such as AST, ALT and ALP in serum. The mRNA expression of inflammatory biomarkers, including macrophage inflammatory protein-2, toll-like receptor-4 (TLR4), RelA, NF-κB2, TNF-α,iNOS, COX-2 are reduced during zingerone treatment against antibiotic released endotoxin-induced hepatotoxicity[53]. Apart from this, zingerone exhibits anti-hyperlipidaemic, anti-fibrotic and anti-apoptotic effects which are evidenced by the improvement in lipid profile and restoration of plasma lipoproteins. It decreases the activity of β-hydroxyβ-methylglutaryl-CoA reductase, collagen deposition in liver tissue, DNA fragmentation, and apoptosis in alcoholic liver disease[54]. Furthermore, zingerone at a dose of 0.78 mg/kg reduced the mortality, enzymes secretion, portal inflammation, parenchymal necrosis, and haemorrhagic necrosis in the lipopolysaccharide-induced liver dysfunction in mice. Zingerone suppressed the lipopolysaccharide mediated MyD88 protein expression and the activation of MAPKs. This action led to a decrease in the expression of NF-κB and p-c-Jun proteins via inhibition of the phosphorylation of p38, ERK, and JNK[37]. In addition, zingerone exhibited anti-fibrotic activity at 100 μM in TGF-β1 activated hepatic stellate cells-T6 in vitro and an oral dose of 10 mg/kg, 20 mg/kg ameliorated dimethylnitrosamine-induced liver fibrosis in vivo. Zingerone has the capability to suppress the stimulation of hepatic stellate cells by preventing lipid peroxidation and hepatic inflammation in the early stages of hepatic fibrosis. Zingerone was also found to increase cell viability against a cytotoxic agent t-butoxy-t-butylperoxyl, and 100 μM seems to be its EC₅₀ value[54]. Change in body weight, abdominal circumference, lipid profile, blood glucose, and hepatic tissue was reversed by zingerone at a 100 mg/kg dose in a preclinical model of hepatotoxicity induced by fructose-enriched diet[55].

Figure 10  Diagrammatic representation of the ameliorative effects of zingerone against alcohol-induced liver damage. ROS: Reactive oxygen species; TGF-β: Transforming growth factor-beta; IL: Interleukins; TNF-α: Tumor necrosis factor alpha.

Administration of zingerone along with antibiotic vancomycin prevents the liver enzyme activities, liver function biomarkers (AST, ALP and ALT) and histopathological integrity of hepatocytes[48,56]. Oral administration of zingerone at dose 50 mg/kg, 100 mg/kg and 150 mg/kg for 28 days showed hepatoprotective activity against lead-induced liver toxicity in rats[49].

Cardiovascular protective effects

Cardiovascular disorders are the leading causes of morbidity and mortality all over the world. Cardiovascular disorders include acute coronary disease, myocardial infarction, tachycardia, bradycardia, angina, atherosclerosis, arterial revascularization, stroke, ischemic heart attack and congestive heart failure etc. Some factors such as high blood glucose level, smoking, hyperlipidaemia, and high alcohol consumption are considered to be involved in the etiology of cardiovascular disorders, which are escalating annually worldwide[57].

Oral administration of zingerone (20 mg/kg) reduces the prolonged cardiac repolarization by substantial suppression of QT and QTc duration in rats. It was the decreased PR interval that resulted in the improvement of atrioventricular delay, without affecting the P-wave interval in diabetic rats. Zingerone ameliorates the blood lipid profile, oxidative stress and inflammatory cytokines with the reduction in collagen deposition and muscle degeneration in the heart[58]. Pre-treatment with zingerone mitigates the deleterious effects of chemotherapy and radiotherapy in the cardiac muscles. It regulated the level of antioxidant enzymes, lipid peroxidation in the cardiac tissue and inflammatory biomarkers such as TNF-α, cardiac myeloperoxidase and COX-2 expression. Furthermore, zingerone attenuated the elevated gene expression of caspase-3, fragmentation of prominent DNA and mitochondrial complexes’ activities[59]. The anti-apoptotic effect of zingerone was demonstrated by its pre-treatment at 6 mg/kg dose in isoproterenol-induced myocardial infarction model in rats. The expression of the cell-protecting gene, including Bcl-2 and Bcl-xL increased, whereas the expression of cell death-promoting genes such as Bax and Bad simultaneously decreased. Stanely Mainzen Prince and Hemalatha[60] reported that zingerone down-regulated the expression of Fas-receptor, caspase-3 caspase-8 and caspase-9 (Figure 11). Moreover, pre-treatment with zingerone has the potential to decrease the levels of serum cTnI, high-sensitivity C-reactive protein, the concentration of heart lysosomal lipid peroxidation, β-glucuronidase, β-galactosidase, cathepsin-B, cathepsin-D, and accomplished the removal of coronary thrombosis in myocardial infarcted rats[61]. Pretreatment with zingerone at a dose 100 mg/kg showed significant reduction in AST, creatine kinase-myocardial band, lactate dehydrogenase and oxidative stress in the trastuzumab-induced cardiotoxicity in rats[62].

Figure 11  Diagrammatic representation of the protective role of zingerone in diabetes and isoproterenol induced cardiac dysfunctions. PKC: Protein kinase C; cAMP: Cyclic adenosine monophosphate; AGE: Advanced glycation end product; β1AR: Beta-1 adrenergic receptor.

Neuroprotective effects

Neurodegenerative diseases such as Alzheimer’s disease, multiple sclerosis, Huntington’s disease, Parkinson’s disease, Schizophrenia, and amyotrophic lateral sclerosis pose a major problem in the aging population. They are characterized by neurotransmitter alterations and loss of neuronal activity and structure damage in the central nervous system that exert a negative effect on the psychological and physical functioning of the body. Generally, dementia and decision-making dysfunction are observed in elderly persons that increased psychological problems, pro-inflammatory markers, oxidative stress, viral infections and change in brain metabolism are considered to be the main causative pathways. Several factors like glial cell-derived neurotrophic factor, brain-derived neurotrophic factors, insulin-like growth factor-1 have been shown to be beneficial in maintaining neuronal activities[63,64].

Some studies have shown that zingerone crosses the blood-brain barrier and enters to striatum of the brain where it prevents neurotoxicity through its antioxidant activity[65-67]. SOD plays a very important role to protect dopaminergic neuron against neuronal toxicity and zingerone protect striatal dopaminergic neurons through activation of SOD which might have further stimulated adrenal catecholamines secretion[68]. Nociceptive transmission is regulated by transient receptor potential channels in spinal substantia gelatinosa (SG) neurons and zingerone has the ability to increase excitatory post-synaptic current retaining SG neurons. Additionally, zingerone decreases mono-synaptical induced excitatory post-synaptic current amplitudes and improves GABAergic spontaneous excitatory transmission through the activation of TRPA1 without affecting transient receptor potential vanilloid 1 channels in the SG[69]. Recently, it was suggested that pre-treatment with zingerone at a dose of 100 mg/kg in Swiss albino mice protected neuronal cell failure. Zingerone caused up up-regulation of antioxidant enzyme and decreasing lipid peroxidation in the brain mitochondrial toxicity induced by carbon tetrachloride. In addition, Vaibhav et al[67] showed that zingerone significantly reduced the volume of infarcted area and mitochondrial injury of the brain in experimental induced middle cerebral artery occlusion in rats. However, zingerone treatment extensively recover behavioural response and histological changes via ameliorating oxidative stress and recover Na⁺/K⁺ ATPase in middle cerebral artery occlusion injury. Zingerone effectively protected the ischemic penumbral zone of neurons from intrinsic programmed cell death by lowering the expression of pro-apoptotic proteins Apaf-1 and Bax caspase-3 and caspase-9 (Figure 12)[67].

Figure 12  Diagrammatic representation of the neuronal protective effects of zingerone. NMDA: N-methyl-D-aspartate; ATP: Adenosine triphosphate.

Antidiarrheal effects

Diarrhoea is a one of the serious health problems affecting near about 3-5 billion people per year worldwide, particularly children having less than 5 years. About 70% population of the world prefer herbal and indigenous remedies for the treatment of their health problems. According to the Ayurvedic system, there are various potent plants used in the treatment of diarrhoea[70]. Zingerone possesses the therapeutic potential to regulate the colonic motility which was demonstrated in vitro on separate segments of the colon from the rats. However, administration of zingerone reduced the colonic motility in vivo evidenced by a decrease in expelled fluid volume and intraluminal pressure. It was acting directly on the smooth muscles without disturbing heart rate and blood pressure[71]. Interstitial cells of cajal (ICC) of Gi are the pacemaker cells which increase motility of gastrointestinal tract. Zingerone has been reducing the activity of ICCs by inhibiting the transient receptor potential vanilloid 1 channel but activate ATP-sensitive K⁺ channel. However, zingerone inhibits the activity of pacemaker cells through activation of guanylate cyclase, protein kinase G, nitric oxide synthase and cyclic guanosine monophosphate production in ICCs. It suggests that zingerone acts via NO/cyclic guanosine monophosphate-dependent ATP-sensitive K⁺ channels through MAPK-dependent pathways (Figure 13)[72]. Due to the capability of zingerone to decrease fluid secretion, it is considered that zingerone will be useful for preventing diarrhoea and other gastrointestinal diseases at concentrations above 10 mmol/L.

Figure 13  Zingerone possessed protective effect against diarrhoea. TRPV1: Transient receptor potential vanilloid 1; NO: Nitric oxide; GTP: Guanosine triphosphate; cGMP: Cyclic guanosine monophosphate; PKG: Protein kinase G.

Anti-microbial effects

Micro-organisms are tiny living organisms spread around the universe, becoming a very important part of the animal life and having the role in the establishment of pathological and physiological functions of human life. Microbes have a major role in the metabolism and stimulation of the immune system via generating anti-bodies in the human. Beside this, there are also abundant harmful microbes which secrete toxic substances or inhibit bimolecular functions may cause life-threatening diseases after exposing direct by or indirectly. Traditional plants and their derived products have been used against various microbes as antimicrobial agents with bacteriostatic and bactericidal activity possessing a different mechanism of action[73].

Zingerone acts as immune stimulant and appetizer by increasing the body weight, feed efficacy, phenoloxidase levels, respiratory bursts, lysozyme, phagocytic activities and survival rate. The disease resistance towards pathogen Vibrio alginolyticus in Pacific white shrimp (Litopenaeusvannamei) juvenile is prevented during dietary supplementation of zingerone[74]. Anti-biotics resistance provide opportunities to the pathogens to make communities of macro-organism called biofilms which have the capability to construct a complex barrier. It resists the permeability of immune cells and antibiotics for the protection of pathogens that lead to persistent and chronic infectivity of the pathogens. Combination therapy of zingerone and antibiotic has been reported to reduce drug resistance with higher significant inhibition and eradication of the biofilm of Pseudomonas aeruginosa than zingerone alone (Figure 14)[75]. However, quorum sensing accelerates the formation of biofilm and anti-microbial resistance through the cell to the cellular communication network to regulate the gene expression. Beside the anti-film activity, zingerone was found to be a potent blocker of quorum sensing cascade via inhibition of ligand-receptor interaction with quorum sensing receptor pathways and diminished the virulence of Pseudomonas aeruginosa (Figure 14)[76]. Not only micro-organisms are responsible to cause disease, sometimes use of a potent antibiotic for the prevention or treatment of microbial infections produced endotoxins. These endotoxins have the capability to cause other complications, e.g., amikacin and cefotaxime induced endotoxin associated liver inflammation. During antibiotic therapy, endotoxin binding protein binds to antibiotic-induced endotoxin and activates TLR 4, CD14 and MD2 surface receptor of hepatocytes, macrophages and monocytes cells of the liver following in potent inflammatory response. Simultaneously administration of zingerone at the dose of 100 mg/kg and antibiotics reduced the risk of antibiotic-induced endotoxin-related inflammation without affecting the bacterial count. Zingerone decreases inflammatory markers like malondialdehyde, reactive nitrogen intermediates and inflammatory cytokines (MIP-2, IL-6, and TNF-α). It also suppressed the expression of mRNA of TLR4, RelA, NF-κB2, TNF-α, iNOS, and COX-2 which attribute in cell signalling of inflammatory pathways[53]. Along with antioxidant and anti-inflammatory properties, zingerone possesses anti-microbial activity which may further attribute in various microbial infections.

Figure 14  Zingerone showing anti-microbial activity.

Anti-diabetic activity

Diabetes is one of the major metabolic disorders characterised by chronic hyperglycemic condition. It is a metabolic disorder resulting from the malfunctioning of various tissue to reduce the utilization of insulin hormone or its inadequate secretion from pancreas in the body[77]. It is considered as fifth leading cause of death in the world. About 4.2 million diabetic patients (aged 20-79 years) are estimated to die in 2019 in which more deaths were associated with diabetes in women (2.3 million) than in men (1.9 million)[78].

Recently, modulatory effect of zingerone has been seen in streptozotocin-nicotinamide induced type-2 diabetes mellitus in the experimental rats. Zingerone not only reduced only the glucose and insulin levels but it also normalized the lipid profile significantly in diabetic rats which was demonstrated by substantial reduction in cholesterol, triglycerides and increase high-density cholesterol level. Zingerone administration exhibited reduction in the level of lipid peroxidation along with restoration of GSH contents and improvement in antioxidant enzymes[79]. However, zingerone possess its protective effect via downregulation of the expression of NF-κB proteins in alloxan-induced diabetes in rats. Administration of zingerone at a dose 50 mg/kg and 100 mg/kg daily for 21 days causes the downstream of various inflammatory cytokines such as ILs (IL1-β, IL-2, IL-6) and TNF-α in the diabetic rats (Figure 15)[80,81]. Moreover, chronic use of zingerone has been reported to prevent diabetic complications via ameliorating oxidative stress and inflammation. It shows nephroprotective activity through the inhibition of nicotinamide adenine dinucleotide phosphate oxidase 4 and ameliorates enhanced vascular contraction in diabetic aortae through nitric acid and guanylate cyclase stimulation[5,81].

Figure 15  Diagrammatic representation of zingerone-mediated protection against diabetes mellitus induced harms to kidneys, heart, liver, and eyes. TG: Triglycerides; LDL: Low density lipoprotein; VLDL: Very low density lipoprotein; HDL: High density lipoproteins; NF-κB: Nuclear factor kappa B; IL: Interleukin; TNF-α: Tumor necrosis factor alpha; iNOS: Inducible nitric oxide synthase.

Ovarian and testes protective activity of zingerone

Nowadays, fertility issues are becoming a chief global health concern. Infertility which is the inability to achieve clinical pregnancy after 12 months or more of unprotected and regular sexual intercourse. Infertility a chief health challenge in many developing countries[82]. Male-related issues contribute about 30% of fertility problems which may be due to drug treatment, environmental toxins, air pollution, stress and idiopathic causes[83]. Fertility protection in females has become well established over the last two decades. However, patients with benign diseases, patients with endometriosis before surgery and genetic predispositions patients having risk to a premature ovarian failure and demand for fertility preservation procedures which will be increase in coming years[84].

Zingerone has shown protective effect on spermatogenesis in mice. Pre-treatment of zingerone at a dose 20 mg/kg and 40 mg/kg to the mice with zinc oxide nanoparticle-induced testicular damage showed significant reduction in the histological criteria, increased morphometric parameters, enhancement in serum testosterone levels, improvement in sperm quality, attenuation in apoptotic index and amelioration in oxidative stress by reducing lipid peroxidation and increasing the activity of antioxidant enzymes. Zingerone has property to enhance the viability of leydig (TM3) and mouse Sertoli (TM4) cells in dose dependent manner (Figure 16)[84,85]. In vitro study of zingerone against prostate cancer cells revealed that it possesses strong apoptotic, anti-invasive, and supressing migration of cancer cells properties towards PC-3 cells[86].

Figure 16  Reproductive toxicological evaluation of zingerone in male and female rats. NF-κB: Nuclear factor kappa B; TNF-α: Tumor necrosis factor alpha; COX-2: Cyclooxygenase-2; iNOS: Inducible nitric oxide synthase; IL: Interleukins; 8OHdG: 8-hydroxy-2’-deoxyguanosine.

In female rats, zingerone caused reduction in serum level of follicle-stimulating hormone, whereas it increased the serum estradiol (E2) hormone level without causing any histopathological changes in the uteri and ovaries. Zingerone also enhanced the activities of antioxidant enzymes, and decreased the levels of inflammatory biomarkers such as NF-κB, TNF-α, IL-1β, IL-6, COX-2, iNOS as well as caused downregulation of caspase-3 and 8-hydroxy-2’-deoxyguanosine expression coupled with an upregulated Bcl-2 level in the ovarian and uterine tissues of cisplatin-treated female rats[85]. All these effects of zingerone are depicted in Figure 16.

Ant-arthritic activity

Oral administration of zingerone 25 mg/kg for three weeks to the Freund’s complete adjuvant-induced arthritic experimental rats reduced lipid peroxidation, increasing the activity of antioxidant enzymes such as SOD, CAT and GPx and regulating the levels of inflammatory cytokines such as NF-κB, TGF-β, TNF-α, IL-1β and IL-6. These biochemical alterations exhibit strong antioxidant and anti-inflammatory properties of zingerone against Freund’s complete adjuvant-induced rheumatoid arthritis, suggesting that the protective effect of zingerone may be possible by reducing oxidative stress and inflammation (Figure 17). Bashir et al[87] suggested that the combined antioxidant and anti-inflammatory properties of zingerone may be a mechanism to facilitate the prevention and treatment of joint arthritic diseases.

Figure 17  Zingerone showing protective effect at Freund’s complete adjuvant-induced arthritis in rats. NF-κB: Nuclear factor kappa B; TNF-α: Tumor necrosis factor alpha; TGF-β: Transforming growth factor-beta; IL: Interleukins.

Acute toxicity study of zingerone

Acute toxicity of zingerone was studied at different doses in male Swiss albino mice. Zingerone did not show any animal mortality at the dose 500 mg/kg orally during the period of two weeks. However, an increase in the dose of drug leads to reduction in the animal survival rate and 50% reduction in survival was observed at a dose of 1000 mg/kg. Oral administration of zingerone at a dose 1200 mg/kg caused 80% mortality and at the dose of 1500 mg/kg, there were no any survived animals observed during the experimental period. It was found that the lethal dose of zingerone is 912 mg/kg which was calculated by using probit analysis[37].

CONCLUSION

Worldwide, there is a great interest for cost-effective and affordable natural remedies for the prevention or treatment of major and minor health problems. Zingerone is one of the potent natural bioactive molecules isolated from the ginger (Zingiber officinale Roscoe), a natural spice distributes all over the world. In this review, we have identified that zingerone possesses several pharmacological properties such as potent anti-oxidant, anti-inflammatory, anti-apoptotic, anti-proliferative effects observed in pre-clinical studies. These properties suggest the zingerone more effective and beneficial in curing several disorders. However, exploration of structure activity relationship could be useful to enhance its stability, safety and effectiveness. Thus, there is a need for future research to explore the therapeutic potential of zingerone in clinical studies. On the basis of literature searches done, it may be concluded that zingerone possess great potential for treating non-communicable diseases. Overall, the information presented in this review will act as vital segment to produce zingerone-related drugs.