Anti-Inflammatory Potential of the Anti-Diabetic Drug Metformin in the Prevention of Inflammatory Complications and Infectious Diseases Including COVID-19: A Narrative Review.

Metformin, a widely used first-line anti-diabetic therapy for the treatment of type-2 diabetes, has been shown to lower hyperglycemia levels in the blood by enhancing insulin actions. For several decades this drug has been used globally to successfully control hyperglycemia. Lactic acidosis has been shown to be a major adverse effect of metformin in some type-2 diabetic patients, but several studies suggest that it is a typically well-tolerated and safe drug in most patients. Further, recent studies also indicate its potential to reduce the symptoms associated with various inflammatory complications and infectious diseases including coronavirus disease 2019 (COVID-19). These studies suggest that besides diabetes, metformin could be used as an adjuvant drug to control inflammatory and infectious diseases. In this article, we discuss the current understanding of the role of the anti-diabetic drug metformin in the prevention of various inflammatory complications and infectious diseases in both diabetics and non-diabetics.

Significance of Vitamin Supplementation in Reducing the Severity of COVID-19.

Coronavirus disease-19 (COVID-19), a serious pandemic due to the SARS-CoV-2 virus infection, caused significant lockdowns, healthcare shortages, and deaths worldwide. The infection leads to an uncontrolled systemic inflammatory response causing severe respiratory distress and multiple-organ failure. Quick development of several vaccines efficiently controlled the spread of COVID-19. However, the rise of various new subvariants of COVID-19 demonstrated some concerns over the efficacy of existing vaccines. Currently, better vaccines to control these variants are still under development as several new subvariants of COVID-19, such as omicron BA-4, BA-5, and BF-7 are still impacting the world. Few antiviral treatments have been shown to control COVID-19 symptoms. Further, control of COVID-19 symptoms has been explored with many natural and synthetic adjuvant compounds in hopes of treating the deadly and contagious disease. Vitamins have been shown to modulate the immune system, function as antioxidants, and reduce the inflammatory response. Recent studies have investigated the potential role of vitamins, specifically vitamins A, B, C, D, and E, in reducing the immune and inflammatory responses and severity of the complication. In this brief article, we discussed our current understanding of the role of vitamins in controlling COVID-19 symptoms and their potential use as adjuvant therapy.

Role of Innate Immune and Inflammatory Responses in the Development of Secondary Diabetic Complications.

Increased hyperglycemia due to uncontrolled diabetes is the major cause of secondary diabetic complications such as retinopathy, neuropathy, nephropathy, and cardiovascular diseases. Although it is well known that increased oxidative stress, activation of the polyol pathway, protein kinase C and increased generation of advanced glycation end products could contribute to the development of diabetic complications, recent studies implicated the role of innate immunity and its related inflammatory responses in the pathophysiology of secondary diabetic complications. Increased activation of oxidative stress signaling could regulate NLRP3 inflammasome-mediated innate immune responses as well as NF-κB signalosome-mediated pro-inflammatory responses. This review article focused on the pathogenic role of innate immune and inflammatory responses in the progression of hyperglycemia-induced secondary diabetic complications. Specifically, we discussed in depth how deregulated innate immune and inflammatory responses could lead to an aggravated release of cytokines, chemokines, and growth factors resulting in the development of various secondary complications of diabetes.

Therapeutic potential of vitamin B1 derivative benfotiamine from diabetes to COVID-19.

Benfotiamine (S-benzoylthiamine-O-monophosphate), a unique, lipid-soluble derivative of thiamine, is the most potent allithiamine found in roasted garlic, as well as in other herbs of the genus Allium. In addition to potent antioxidative properties, benfotiamine has also been shown to be a strong anti-inflammatory agent with therapeutic significance to several pathological complications. Specifically, over the past decade or so, benfotiamine has been shown to prevent not only various secondary diabetic complications but also several inflammatory complications such as uveitis and endotoxemia. Recent studies also demonstrate that this compound could be used to prevent the symptoms associated with various infectious diseases such as HIV and COVID-19. In this review article, the authors discuss the significance of benfotiamine in the prevention of various pathological complications.

Aldose reductase regulates doxorubicin-induced immune and inflammatory responses by activating mitochondrial biogenesis.

We have recently demonstrated that aldose reductase (AR) inhibitor; fidarestat prevents doxorubicin (Dox)-induced cardiotoxic side effects and inflammation in vitro and in vivo. However, the effect of fidarestat and its combination with Dox on immune cell activation and the immunomodulatory effects are not known. In this study, we examined the immunomodulatory effects of fidarestat in combination with Dox in vivo and in vitro. We observed that fidarestat decreased Dox-induced upregulation of CD11b in THP-1 monocytes. Fidarestat further attenuated Dox-induced upregulation of IL-6, IL-1ß, and Nos2 in murine BMDM. Fidarestat also attenuated Dox-induced activation and infiltration of multiple subsets of inflammatory immune cells identified by expression of markers CD11b+, CD11b+F4/80+, Ly6C+CCR2high, and Ly6C+CD11b+ in the mouse spleen and liver. Furthermore, significant upregulation of markers of mitochondrial biogenesis PGC-1α, COX IV, TFAM, and phosphorylation of AMPKα1 (Ser485) was observed in THP-1 cells and livers of mice treated with Dox in combination with fidarestat. Our results suggest that fidarestat by up-regulating mitochondrial biogenesis exerts protection against Dox-induced immune and inflammatory responses in vitro and in vivo, providing further evidence for developing fidarestat as a combination agent with anthracycline drugs to prevent chemotherapy-induced inflammation and toxicity.

Development of Aldose Reductase Inhibitors for the Treatment of Inflammatory Disorders and Cancer: Current Drug Design Strategies and Future Directions.

Aldose Reductase (AR) is an enzyme that converts glucose to sorbitol during the polyol pathway of glucose metabolism. AR has been shown to be involved in the development of secondary diabetic complications due to its involvement in causing osmotic as well as oxidative stress. Various AR inhibitors have been tested for their use to treat secondary diabetic complications, such as retinopathy, neuropathy, and nephropathy in clinical studies. Recent studies also suggest the potential role of AR in mediating various inflammatory complications. Therefore, the studies on the development and potential use of AR inhibitors to treat inflammatory complications and cancer besides diabetes are currently on the rise. Further, genetic mutagenesis studies, computer modeling, and molecular dynamics studies have helped design novel and potent AR inhibitors. This review discussed the potential new therapeutic use of AR inhibitors in targeting inflammatory disorders and cancer besides diabetic complications. Further, we summarized studies on how AR inhibitors have been designed and developed for therapeutic purposes in the last few decades.

2'-Hydroxyflavanone prevents LPS-induced inflammatory response and cytotoxicity in murine macrophages.

2'-Hydroxyflavanone (2-HF) is a natural flavonoid isolated from citrus fruits. Multiple studies have demonstrated that 2-HF with its anti-proliferative and pro-apoptotic effects prevent the growth of various cancers. Although 2-HF is a well known anti-oxidative and chemopreventive agent, its role as an anti-inflammatory agent is not well established. In this study, we examined the effect of 2-HF on LPS-induced cytotoxicity and inflammatory response in murine RAW 264.7 macrophages. Flow cytometry analysis showed that pre-treatment of RAW 264.7 macrophages with 2-HF significantly prevented LPS-induced macrophage apoptosis. 2-HF also prevented LPS-induced reactive oxygen species (ROS) and nitric oxide (NO) production, lipid peroxidation, and loss of mitochondrial membrane potential in murine macrophages. Most importantly, the release of multiple inflammatory cytokines and chemokines such as eotaxin, IL-2, IL-10, IL-12p40, LIX, IL-15, IL-17, MCP-1, and TNF-α induced by LPS in the macrophages was inhibited by 2-HF. 2-HF also prevented LPS-induced activation of protein kinases p38MAPK and SAPK/JNK. Apart from this, LPS-induced phosphorylation, nuclear translocation, and DNA-binding of the redox transcription factor, NF-κB, was prevented by 2-HF. Our results demonstrate that 2-HF by regulating ROS/MAPK/NF-κB prevents LPS-induced inflammatory response and cytotoxicity in murine macrophages suggesting that the need of potential development of 2-HF as an anti-inflammatory agent to ameliorate various inflammatory complications.

4-Hydroxy-Trans-2-Nonenal in the Regulation of Anti-Oxidative and Pro-Inflammatory Signaling Pathways.

Recent studies indicate that 4-hydroxy-trans-2-nonenal (HNE), a major oxidative stress triggered lipid peroxidation-derived aldehyde, plays a critical role in the pathophysiology of various human pathologies including metabolic syndrome, diabetes, cardiovascular, neurological, immunological, and age-related diseases and various types of cancer. HNE is the most abundant and toxic α, ß-unsaturated aldehyde formed during the peroxidation of polyunsaturated fatty acids in a series of free radical-mediated reactions. The presence of an aldehyde group at C1, a double bond between C2 and C3 and a hydroxyl group at C4 makes HNE a highly reactive molecule. These strong reactive electrophilic groups favor the formation of HNE adducts with cellular macromolecules such as proteins and nucleic acids leading to the regulation of various cell signaling pathways and processes involved in cell proliferation, differentiation, and apoptosis. Many studies suggest that the cell-specific intracellular concentrations of HNE dictate the anti-oxidative and pro-inflammatory activities of this important molecule. In this review, we focused on how HNE could alter multiple anti-oxidative defense pathways and pro-inflammatory cytotoxic pathways by interacting with various cell-signaling intermediates.

Aldose reductase regulates hyperglycemia-induced HUVEC death via SIRT1/AMPK-α1/mTOR pathway.

Although hyperglycemia-mediated death and dysfunction of endothelial cells have been reported to be a major cause of diabetes associated vascular complications, the mechanisms through which hyperglycemia cause endothelial dysfunction is not well understood. We have recently demonstrated that aldose reductase (AR, AKR1B1) is an obligatory mediator of oxidative and inflammatory signals induced by growth factors, cytokines and hyperglycemia. However, the molecular mechanisms by which AR regulates hyperglycemia-induced endothelial dysfunction is not well known. In this study, we have investigated the mechanism(s) by which AR regulates hyperglycemia-induced endothelial dysfunction. Incubation of human umbilical vein endothelial cells (HUVECs) with high glucose (HG) decreased the cell viability and inhibition of AR prevented it. Further, AR inhibition prevented the HG-induced ROS generation and expression of BCL-2, BAX and activation of Caspase-3 in HUVECs. AR inhibition also prevented the adhesion of THP-1 monocytes on HUVECs, expression of iNOS and eNOS and adhesion molecules ICAM-1 and VCAM-1 in HG-treated HUVECs. Further, AR inhibition restored the HG-induced depletion of SIRT1 in HUVECs and increased the phosphorylation of AMPKα1 along-with a decrease in phosphorylation of mTOR in HG-treated HUVECs. Fidarestat decreased SIRT1 expression in HUVECs pre-treated with specific SIRT1 inhibitor but not with the AMPKα1 inhibitor. Similarly, knockdown of AR in HUVECs by siRNA prevented the HG-induced HUVECs cell death, THP-1 monocyte adhesion and SIRT1 depletion. Furthermore, fidarestat regulated the phosphorylation of AMPKα1 and mTOR, and expression of SIRT1 in STZ-induced diabetic mice heart and aorta tissues. Collectively, our data suggest that AR regulates hyperglycemia-induced endothelial death and dysfunction by altering the ROS/SIRT1/AMPKα1/mTOR pathway.

Endotoxin-Induced Uveitis in Rodents.

Uveitis can affect individuals of all ages, genders, and races and accounts for 10-15% of all cases of blindness. Uveitis represents a diverse array of intraocular inflammatory conditions that can be associated with complications from autoimmune diseases, bacterial infections, viral infections, chemical injuries, and metabolic issues. In rodents, endotoxin-induced uveitis (EIU) is an efficient experimental model to study pathological mechanisms associated with the disease and evaluate the pharmacological efficacy of potential new drug agents. In the EIU model, uveitis is characterized by clinically relevant inflammation, including inflammatory exudates and cells infiltrated into the anterior and vitreous eye chambers. EIU in small animal models, including rats, mice, and rabbits, is characterized by a short-lived uveal inflammation. This inflammation can be facilitated using bacterial endotoxins, such as lipopolysaccharide (LPS). In this chapter, we present a reliable, reproducible, and simplified protocol to induce EIU in mice. This method is flexible and can be applied for EIU induction in other small animals and rodents.

Didymin by suppressing NF-κB activation prevents VEGF-induced angiogenesis in vitro and in vivo.

Although didymin, a dietary flavonoid glycoside from citrus fruits, known to be a potent antioxidant with anti-cancer activities, its role in angiogenesis is not known. In this study, we examined the effect of didymin on VEGF-induced angiogenesis in vitro and in vivo models. Our results suggest that treatment of human umbilical vein endothelial cell (HUVECs) with didymin significantly prevented the VEGF-induced cell proliferation, migration, and invasion. Further, didymin significantly prevented the VEGF-induced endothelial tube formation in culture. Didymin also attenuated the VEGF-induced generation of ROS, activation of NF-κB and the expression of adhesion molecules such as VCAM-1, ICAM-1, and E-selectin in HUVECs. Further, didymin also prevented the VEGF-induced microvessel sprouting in ex vivo mouse aortic rings. Most importantly, didymin significantly prevented the invasion of endothelial cells and formation of blood capillary-like structures in Matrigel plug model of angiogenesis in mice. Thus, our results suggest a novel antiangiogenic efficacy of didymin in addition to its reported anti-cancer properties, which warrant further development of this agent for cancer therapy.

Vialinin A, an Edible Mushroom-Derived p-Terphenyl Antioxidant, Prevents VEGF-Induced Neovascularization In Vitro and In Vivo.

Increased side toxicities and development of drug resistance are the major concern for the cancer chemotherapy using synthetic drugs. Therefore, identification of novel natural antioxidants with potential therapeutic efficacies is important. In the present study, we have examined how the antioxidant and anti-inflammatory activities of vialinin A, a p-terphenyl compound derived from Chinese edible mushroom T. terrestris and T. vialis, prevents human umbilical vascular endothelial cell (HUVEC) neovascularization in vitro and in vivo models. Pretreatment of HUVECs with vialinin A prevents vascular endothelial growth factor- (VEGF) induced HUVEC cell growth in a dose-dependent manner. Further, vialinin A also inhibits VEGF-induced migration as well as tube formation of HUVECs. Treatment of HUVECs prevents VEGF-induced generation of reactive oxygen species (ROS) and malondialdehyde (MDA) and also inhibits VEGF-induced NF-κB nuclear translocation as well as DNA-binding activity. The VEGF-induced release of various angiogenic cytokines and chemokines in HUVECs was also significantly blunted by vialinin A. Most importantly, in a mouse model of Matrigel plug assay, vialinin A prevents the formation of new blood vessels and the expression of CD31 and vWF. Thus, our results indicate a novel role of vialinin A in the prevention of neovascularization and suggest that anticancer effects of vialinin A could be mediated through its potent antioxidant and antiangiogenic properties.

Didymin prevents hyperglycemia-induced human umbilical endothelial cells dysfunction and death.

Although didymin, a flavonoid-O-glycosides compound naturally found in the citrus fruits, has been reported to be a potent anticancer agent in the prevention of various cancers, its role in the prevention of cardiovascular complications is unclear. Most importantly, its effect in the prevention of endothelial dysfunction, a pathological process involved in the atherogenesis, is unknown. We have examined the efficacy of didymin in preventing the high glucose (HG; 25 mM)-induced human umbilical vein endothelial cells (HUVECs) dysfunction. Our results indicate that incubation of HUVECs with HG resulted in the loss of cell viability, and pre-incubation of didymin prevented it. Further, didymin prevented the HG-induced generation of reactive oxygen species (ROS) as well as lipid peroxidation product, malondialdehyde. Pretreatment of HUVECs with didymin also prevented the HG-induced decrease in eNOS and increase in iNOS expressions. Further, didymin prevented the HG-induced monocytes cell adhesion to endothelial cells, expressions of ICAM-1 and VCAM-1 and activation of NF-κB. Didymin also prevented the release of various inflammatory cytokines and chemokines in HG-treated HUVECs. In conclusion, our results demonstrate that didymin with its anti-oxidative and anti-inflammatory actions prevents hyperglycemia-induced endothelial dysfunction and death. Thus, it could be developed as a potential natural therapeutic agent for the prevention of cardiovascular complications in diabetes.

Aldose reductase inhibitor, fidarestat prevents doxorubicin-induced endothelial cell death and dysfunction.

Despite doxorubicin (Dox) being one of the most widely used chemotherapy agents for breast, blood and lung cancers, its use in colon cancer is limited due to increased drug resistance and severe cardiotoxic side effects that increase mortality associated with its use at high doses. Therefore, better adjuvant therapies are warranted to improve the chemotherapeutic efficacy and to decrease cardiotoxicity. We have recently shown that aldose reductase inhibitor, fidarestat, increases the Dox-induced colon cancer cell death and reduces cardiomyopathy. However, the efficacy of fidarestat in the prevention of Dox-induced endothelial dysfunction, a pathological event critical to cardiovascular complications, is not known. Here, we have examined the effect of fidarestat on Dox-induced endothelial cell toxicity and dysfunction in vitro and in vivo. Incubation of human umbilical vein endothelial cells (HUVECs) with Dox significantly increased the endothelial cell death, and pre-treatment of fidarestat prevented it. Further, fidarestat prevented the Dox-induced oxidative stress, formation of reactive oxygen species (ROS) and activation of Caspase-3 in HUVECs. Fidarestat also prevented Dox-induced monocyte adhesion to HUVECs and expression of ICAM-1 and VCAM-1. Fidarestat pre-treatment to HUVECs restored the Dox-induced decrease in the Nitric Oxide (NO)-levels and eNOS expression. Treatment of HUVECs with Dox caused a significant increase in the activation of NF-κB and expression of various inflammatory cytokines and chemokines which were prevented by fidarestat pre-treatment. Most importantly, fidarestat prevented the Dox-induced mouse cardiac cell hypertrophy and expression of eNOS, iNOS, and 3-Nitrotyrosine in the aorta tissues. Further, fidarestat blunted the Dox-induced expression of various inflammatory cytokines and chemokines in vivo. Thus, our results suggest that by preventing Dox-induced endothelial cytotoxicity and dysfunction, AR inhibitors could avert cardiotoxicity associated with anthracycline chemotherapy.

Aldose Reductase Inhibitor, Fidarestat Prevents High-fat Diet-induced Intestinal Polyps in ApcMin/+ Mice.

BACKGROUND: Recent epidemiological and experimental studies have shown that obesity is a major risk factor for Colorectal Cancer (CRC). Regular intake of high fat-containing diet can promote obesity and metabolic syndrome by increasing the insulin resistance and inflammatory response which contribute to carcinogenesis. Previously, we have shown that inhibition of polyol pathway enzyme aldose reductase (AR) prevents carcinogens- and inflammatory growth factorsinduced CRC. However, the effect of AR inhibition on a high-fat diet (HFD)-induced formation of intestinal polyps in Apc-deficient Min (multiple intestinal neoplasia; ApcMin/+) mice is not known. METHODS: We examined the effect of AR inhibitor, fidarestat on the HFD-induced formation of preneoplastic intestinal polyps in ApcMin/+ mice which is an excellent model of colon cancer. RESULTS: APCMin/+ mice fed for 12 weeks of HFD caused a significant increase in the formation of polyps in the small and large intestines and fidarestat given along with the HFD prevented the number of intestinal polyps. Fidarestat also decreased the size of the polyps in the intestines of HFDtreated APC Min mice. Further, the expression levels of beta-catenin, PCNA, PKC-ß2, P-AKT, Pp65, COX-2, and iNOS in the small and large intestines of HFD-treated mice significantly increased, and AR inhibitor prevented it. CONCLUSION: Our results thus suggest that fidarestat could be used as a potential chemopreventive drug for intestinal cancers due to APC gene mutations.

Aldose reductase inhibitor, fidarestat regulates mitochondrial biogenesis via Nrf2/HO-1/AMPK pathway in colon cancer cells.

Although we have shown earlier that aldose reductase (AR) inhibitors prevent colorectal cancer cell (CRC) growth in culture as well as in nude mice xenografts, the mechanism(s) is not well understood. In this study, we have investigated how AR inhibition prevents CRC growth by regulating the mitochondrial biogenesis via Nrf2/HO-1 pathway. Incubation of CRC cells such as SW-480, HT29, and HCT116 with AR inhibitor, fidarestat that non-covalently binds to the enzyme, increases the expression of Nrf2. Further, fidarestat augmented the EGF-induced expression of Nrf2 in CRC cells. Fidarestat also increased the Nrf2 -DNA binding activity as well as expression of HO-1 and NQO1 and activation of SOD and catalase in SW480 cells. Similarly, in nude mice xenograft tumor tissues, Nrf2 and HO-1 levels were significantly higher in fidarestat-treated mice compared to controls. Further, stimulation of CRC cells with EGF in the presence of fidarestat increased the mRNA levels of PGC-1α, Nrf1 and TFAM and protein levels of PGC-1α, TFAM and COX-IV and decreased the mitochondrial DNA damage as measured by 8-hydroxy-2'-deoxyguanosine levels. AR inhibitor also modulated the phosphorylations of AMPK and mTOR and expression of p53 in EGF-treated cells. Collectively, our results indicate that AR inhibitor prevents CRC growth by increasing mitochondrial biogenesis via increasing the expression of Nrf2/HO-1/AMPK/p53 and decreasing the mitochondrial DNA damage.