Metformin ameliorates podocyte damage by restoring renal tissue nephrin expression in type 2 diabetic rats

Delaying Renal Aging: Metformin Holds Promise as a Potential Treatment

Given the rapid aging of the population, age-related diseases have become an excessive burden on global health care. The kidney, a crucial metabolic organ, ages relatively quickly. While the aging process itself does not directly cause kidney damage, the physiological changes that accompany it can impair the kidney's capacity for self-repair. This makes aging kidneys more susceptible to diseases, including increased risks of chronic kidney disease and end-stage renal disease. Therefore, delaying the progression of renal aging and preserving the youthful vitality of the kidney are crucial for preventing kidney diseases. However, effective strategies against renal aging are still lacking due to the underlying mechanisms of renal aging, which have not been fully elucidated. Accumulating evidence suggests that metformin has beneficial effects in mitigating renal aging. Metformin has shown promising anti-aging results in animal models but has not been tested for this purpose yet in clinical trials. These findings indicate the potential of metformin as an anti-renal aging drug. In this review, we primarily discuss the characteristics and mechanisms of kidney aging and the potential effects of metformin against renal aging.

Autophagy and podocytopathy

Autophagy is a complex process of lysosomal-dependent degradation of unwanted cellular material. In response to endogenous or exogenous stimuli, autophagy is induced and regulated by two kinases: the AMP activated kinase and the mammalian target of rapamycin (mTOR). Cells activated by Unc-51-like kinase 1 form a double membrane complex that sequesters the cargo (phagophore) and elongates producing spherical vesicles (autophagosomes). These reach and fuse with lysosomes, which degrade the cargo (autolysosomes). The resulting macromolecules are released back and recycled in the cytosol for reuse. In the podocyte, autophagy is a homeostatic mechanism that contributes to the formation and preservation of the morphological and functional integrity of actin cytoskeleton. Podocytes, fenestrated endothelial cells and glomerular basement membrane compose the glomerular filtration barrier. Podocyte damage may cause dysfunction of the glomerular barrier, proteinuria and glomerulosclerosis in different glomerular diseases and particularly in so-called podocytopathies, namely minimal change disease and focal segmental glomerulosclerosis. Several drugs and molecules may activate autophagic function in murine models. Among them, aldosterone inhibitors, mineralocorticoid inhibitors and vitamin D3 were proven to protect podocyte from injury and reduce proteinuria in clinical studies. However, no clinical trial with autophagy regulators in podocytopathies has been conducted. Caution is needed with other autophagy activators, such as mTOR inhibitors and metformin, because of potential adverse events.

Insight into the Molecular Mechanism of Diabetic Kidney Disease and the Role of Metformin in Its Pathogenesis

Diabetic kidney disease (DKD) is one of the leading causes of death among patients diagnosed with diabetes mellitus. Despite the growing knowledge about the pathogenesis of DKD, we still do not have effective direct pharmacotherapy. Accurate blood sugar control is essential in slowing down DKD. It seems that metformin has a positive impact on kidneys and this effect is not only mediated by its hypoglycemic action, but also by direct molecular regulation of pathways involved in DKD. The molecular mechanism of DKD is complex and we can distinguish polyol, hexosamine, PKC, and AGE pathways which play key roles in the development and progression of this disease. Each of these pathways is overactivated in a hyperglycemic environment and it seems that most of them may be regulated by metformin. In this article, we summarize the knowledge about DKD pathogenesis and the potential mechanism of the nephroprotective effect of metformin. Additionally, we describe the impact of metformin on glomerular endothelial cells and podocytes, which are harmed in DKD.

Versatile Solid Modifications of Multicomponent Pharmaceutical Salts: Novel Metformin-Rhein Salts Based on Advantage Complementary Strategy Design

This study aimed to develop an effective treatment for diabetes and diabetic complications, based on the advantage complementary strategy of drug-drug salt, by designing and synthesizing the multicomponent molecular salts containing metformin (MET) and rhein (RHE). Finally, the salts of MET-RHE (1:1), MET-RHE-H₂O (1:1:1), MET-RHE-ethanol-H₂O (1:1:1:1), and MET-RHE-acetonitrile (2:2:1) were obtained, indicating the polymorphism of salts formed by MET and RHE. The structures were analyzed by the combination of characterization experiments and theoretical calculation, and the formation mechanism of polymorphism was discussed. The obtained results of in vitro evaluation showed that MET-RHE had a similar hygroscopicity with metformin hydrochloride (MET·HCl), and the solubility of the component of RHE increased by approximately 93 times, which laid a foundation for improving the bioavailability of MET and RHE in vivo. The evaluation of hypoglycemic activity in mice (C57BL/6N) indicated that MET-RHE exhibited better hypoglycemic activity than the parent drugs and the physical mixtures of MET and RHE. The above findings demonstrate that this study achieved the complementary advantages of MET and RHE through the multicomponent pharmaceutical salification technique, and provides new possibilities for the treatment of diabetic complications.

Intestinal microbiome diversity of diabetic and non-diabetic kidney disease: Current status and future perspective

A significant portion of the health burden of diabetic kidney disease (DKD) is caused by both type 1 and type 2 diabetes which leads to morbidity and mortality globally. It is one of the most common diabetic complications characterized by loss of renal function with high prevalence, often leading to acute kidney disease (AKD). Inflammation triggered by gut microbiota is commonly associated with the development of DKD. Interactions between the gut microbiota and the host are correlated in maintaining metabolic and inflammatory homeostasis. However, the fundamental processes through which the gut microbiota affects the onset and progression of DKD are mainly unknown. In this narrative review, we summarised the potential role of the gut microbiome, their pathogenicity between diabetic and non-diabetic kidney disease (NDKD), and their impact on host immunity. A well-established association has already been seen between gut microbiota, diabetes and kidney disease. The gut-kidney interrelationship is confirmed by mounting evidence linking gut dysbiosis to DKD, however, it is still unclear what is the real cause of gut dysbiosis, the development of DKD, and its progression. In addition, we also try to distinguish novel biomarkers for early detection of DKD and the possible therapies that can be used to regulate the gut microbiota and improve the host immune response. This early detection and new therapies will help clinicians for better management of the disease and help improve patient outcomes.

Metformin: new applications for an old drug

Metformin is a biguanide, evolved as one of the most widely used medicines. The applications of this component include but are not limited to reducing blood glucose, weight loss, and polycystic ovary syndrome. Studies about other probable indications have emerged, indicating that this agent can also be utilized for other purposes. In this review, applications of metformin are noticed based on the current evidence. Metformin commonly is used as an off-label drug in non-alcoholic fatty liver disease (NAFLD), but it worsens inflammation and should not be used for this purpose, according to the latest research. Metformin decreased the risk of death in patients with liver cirrhosis. It is an effective agent in the prevention and improvement of survival in patients suffering hepatocellular carcinoma. There is evidence of the beneficial effects of metformin in colorectal cancer, early-stage prostate cancer, breast cancer, urothelial cancer, blood cancer, melanoma, and bone cancer, suggesting metformin as a potent anti-tumor agent. Metformin shows neuroprotective effects and provides a potential therapeutic benefit for mild cognitive impairment and Alzheimer's disease (AD). It also has been shown to improve mental function and reduce the incidence of dementia. Another condition that metformin has been shown to slow the progression of is Duchenne muscular dystrophy. Regarding infectious diseases, tuberculosis (TB) and coronavirus disease (COVID-19) are among the conditions suggested to be affected by metformin. The beneficial effects of metformin in cardiovascular diseases were also reported in the literature. Concerning renal function, studies showed that daily oral administration of metformin could ameliorate kidney fibrosis and normalize kidney structure and function. This study reviewed the clinical and preclinical evidence about the possible benefits of metformin based on recent studies. Numerous questions like whether these probable indications of metformin can be observed in non-diabetics, need to be described by future basic experiments and clinical studies.

Protective Effects of Rifampicin and Its Analog Rifampicin Quinone in a Mouse Model of Obesity-Induced Type 2 Diabetes

Advanced glycation end-products (AGEs) form when glucose reacts non-enzymatically with proteins, leading to abnormal protein function, oxidative stress, and inflammation. AGEs are associated with aging and age-related diseases; their formation is aggravated during diabetes. Therefore, drugs preventing AGE formation can potentially treat diabetic complications, positively affecting health. Earlier, we demonstrated that rifampicin and its analogs have potent anti-glycating activities and increase the life span of Caenorhabditis elegans. This study aimed to investigate the effects of rifampicin during hyperglycemia in C. elegans and in a mouse model of obesity-induced type 2 diabetes. The effects of rifampicin were assessed by determining the life span of C. elegans cultured in the presence of glucose and by measuring HbA1c, AGE levels, and glucose excursions in the diabetic mouse model. Our results show that rifampicin protects C. elegans from glucose-induced toxicity and increases life span. In mice, rifampicin reduces HbA1c and AGEs, improves insulin sensitivity, and reduces indications of diabetic nephropathy without inducing hepatotoxicity. Rifampicin quinone, an analog with lower anti-microbial activity, also reduces HbA1c levels, improves glucose homeostasis and insulin sensitivity, and lowers indications of diabetic nephropathy, without adversely affecting the liver of the diabetic mice. Altogether, our results indicate that rifampicin and its analog have protective roles during diabetes without inflicting hepatic damage and may potentially be considered for repositioning to treat hyperglycemia-related complications in patients.

SGLT2 inhibitors attenuate nephrin loss and enhance TGF-β1 secretion in type 2 diabetes patients with albuminuria: a randomized clinical trial

To evaluate the effect of SGLT2 inhibitor (SGLT2i) on albuminuria, nephrin (NPH) and transforming-growth-factor-beta₁ (TGF-β1) levels in urine and low-grade inflammation in type 2 diabetes (T2D) patients. A randomized, blank-controlled clinical trial included 68 T2D patients and 10 controls. Based on the urinary albumin-to-creatinine ratio (UACR), 68 diabetic patients were stratified into three levels, UACR < 30 mg/g, UACR ≧ 30 mg/g to ≦ 300 mg/g and UACR ˃ 300 mg/g, who were randomized (1:1:1) to receive SGLT2i treatment for 12 weeks. The concentrations of NPH and TGF-β1 in urine were measured as indications of podocyte injury and renal fibrosis. Low-grade inflammation was assessed by the levels of IL-6, TNFα and hsCRP. After 12 weeks of SGLT2i treatment, the levels of UACR and NPH decreased, UTGF-β1 increased in the T2D with microalbuminuria and macroalbuminuria groups, NPH (1.12 [0.59, 1.29] vs. 0.71 [0.41, 1.07] µg/ml, P = 0.022) and (1.29 [0.99, 1.96] vs. 0.93 [0.57, 1.31] µg/ml, P = 0.002), UTGF-β1 (4.88 ± 1.31 vs. 7.27 ± 1.21 pg/ml, P  < 0.001) and (4.30 ± 1.34 vs. 6.78 ± 2.59 pg/ml, P  < 0.001), respectively. The changes in NPH were positively correlated with the UACR and negatively correlated with UTGF-β1 in T2D with albuminuria. SGLT2i alleviate nephrin loss and enhance TGF-β1 excretion in urine in T2DM with albuminuria. The anti-albuminuric effect of SGLT2i could be attributed to mitigating podocyte apoptosis and attenuating renal fibrosis.

Trial registration This clinical trial was registered on 15/10/2019, in ClinicalTrials.gov, and the registry number is NCT04127084.

Metformin activates Wnt/β-catenin for the treatment of diabetic osteoporosis

BACKGROUND

With the deepening of social aging, the incidence rate of osteoporosis and diabetes continues to rise. More and more clinical studies show that diabetes is highly correlated with osteoporosis. Diabetes osteoporosis is considered as a metabolic bone disease of diabetes patients. This study aims to explore the role and mechanism of metformin (Met) in diabetic osteoporosis.

METHODS

Mouse MC3T3-E1 cells were treated with Met (0.5 mM) and exposed to high glucose (HG, 35 mM). The cells were cultured in an osteogenic medium for osteogenic differentiation, and the cell proliferation ability was determined using Cell Counting Kit-8; Alkaline phosphatase (ALP) activity detection and alizarin red staining were utilized to evaluate the effect of Met on MC3T3-E1 osteogenic differentiation. Western blot was used to detect the expressions of osteogenesis-related proteins (Runx2 and OCN) as well as Wnt/β-catenin signaling pathway-related proteins in MC3T3-E1 cells.

RESULTS

HG inhibited proliferation and calcification of MC3T3-E1 cells, down-regulated ALP activity, and the expression of Runx2 and OCN in MC3T3-E1 cells. Meanwhile, the activity of the Wnt/β-catenin signaling pathway was inhibited. Met treatment was found to significantly stimulate the proliferation and calcification of MC3T3-E1 cells under HG conditions, as well as increase the ALP activity and the protein expression level of Runx2 and OCN in the cells. As a result, osteogenic differentiation was promoted and osteoporosis was alleviated. Apart from this, Met also increased the protein expression level of Wnt1, β-catenin, and C-myc to activate the Wnt/β-catenin signaling pathway.

CONCLUSION

Met can stimulate the proliferation and osteogenic differentiation of MC3T3-E1 cells under HG conditions. Met may also treat diabetic osteoporosis through Wnt/β-catenin activation.

Effects of curcumin and metformin on oxidative stress and apoptosis in heart tissue of type 1 diabetic rats

Introduction: Hyperglycemia enhances oxidative stress and apoptosis and induces damages in heart tissue. Based on antioxidant properties of curcumin and metformin, we hypothesized that these agents may exhibit cardioprotective effects by attenuating oxidative stress and modulating expression of the genes involved in apoptosis in type-1 diabetes.

Methods: Thirty-six male rats were randomly divided into six groups; (N): control; (D): streptozotocin-induced diabetic rats; (D+Cur50) and (D+Cur150): diabetic rats treated with 50 and 150 milligram of curcumin per kilogram of body weight (mg/kg.bw), respectively; (D+Met300) and (D+Met500): diabetic rats received 300 and 500 mg/kg.bw of metformin, respectively. Heart tissues were dissected and gene expression levels of Bax, Bcl-2, and caspase-3 were analyzed. Total anti-oxidant capacity (TAC), total oxidant status (TOS), and malondialdehyde (MDA) level, and activities of catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) were measured.

Results: Enhancement in TOS, OSI, and MDA levels as well as increased in the activity of CAT and reduction in SOD and GPx activities were observed in diabetic group (D) compared with control rats. Treatment of diabetic animals with either curcumin or metformin normalized TOS, OSI, and MDA levels and restored CAT, SOD, and GPx activities. Diabetes caused extensive damages in heart tissue of rats (group D) and increased expression of caspase-3 and Bax genes and enhanced ratio of Bax/Bcl-2 expression compared with controls. Treatment with curcumin or metformin mitigated histopathological changes and dampened apoptosis by normalizing Bax and caspase-3 expression.

Conclusion: Curcumin and metformin modulated diabetes-induced cardiac damage probably by reducing oxidative stress.

Adiponectin promotes repair of renal tubular epithelial cells by regulating mitochondrial biogenesis and function

BACKGROUND

Mitochondrial biogenesis and dysfunction are associated with renal tubular epithelial cell injury and the pathophysiological development of diabetic nephropathy (DN). Adiponectin (APN) is a plasma hormone protein specifically secreted by adipocytes. In the present study, we studied the effects of APN on mitochondrial biogenesis and function in renal tubular epithelial cells and examined the mechanisms underlying its actions.

MATERIALS

A rat model of type 2 diabetes mellitus (T2DM) was established using streptozotocin (STZ), and an NRK-52E culture model exposed to high glucose was also used. We found that APN treatment alleviated kidney histopathological injury in T2DM rats, reduced fasting blood glucose (FBG) and postprandial blood glucose (PBG) levels, maintained stable animal weight, promoted cell viability, inhibited apoptosis and the formation of autophagosomes, and also increased mitochondrial mass, mitochondrial DNA (mtDNA) content and mitochondrial membrane potential (MMP) in vivo and in vitro.

RESULTS

We found that the expression of AdipoR1/CREB/PGC-1α/TFAM pathway proteins and respiratory chain complex subunits CO1, CO2, CO3, ATP6 and ATP8 were significantly increased after APN treatment. We also found that inhibition of cAMP response element binding protein (CREB) weakened the effects of APN in NRK-52E cells treated with high glucose. Coimmunoprecipitation experiments showed that AdipoR1 interacted with CREB.

CONCLUSION

APN promoted mitochondrial biogenesis and function in renal tubular epithelial cells by regulating the AdipoR1/CREB/PGC-1α/TFAM pathway. APN has the potential to serve as an effective drug for the treatment of DN.

Moringa oleifera Lam. seed extract protects kidney function in rats with diabetic nephropathy by increasing GSK-3β activity and activating the Nrf2/HO-1 pathway

BACKGROUND

Moringa oleifera Lam. (M. oleifera) seeds are widely used in traditional folk medicine and as nutritional supplements in the Middle East, Africa, and other regions. Published research showed that M. oleifera seeds (MOS) have pharmacological activities such as blood glucose-lowering, anti-inflammatory, and antitumor effects. However, experimental evidence on the use of MOS to treat diabetic nephropathy and its underlying mechanisms were rarely reported.

PURPOSE

To evaluate the therapeutic effects of MOS extract on the kidneys of high-fat diet (HFD)-fed rats with streptozotocin-induced diabetic nephropathy and reveal its underlying mechanisms.

STUDY DESIGN

HFD-fed rats with streptozotocin-induced diabetic nephropathy and high-glucose induced Human Renal Mesangial Cells (HRMC) were used to explore the protective effect of MOS on diabetic nephropathy in vivo and in vitro.

METHODS

HRMC were used to preliminarily evaluate the effect of MOS extract under high glucose conditions. For the in vivo study, rats were divided into the following 6 groups (n = 5): normal control group (NC), diabetic nephropathy model group (DN), high dose of MOS-treatment group (DN + MOS-H, 200 mg/kg/d); medium dose of MOS-treatment group (DN + MOS-M, 100 mg/kg/d); low dose of MOS-treatment group (DN + MOS-l, 50 mg/kg/d), and metformin-treatment group (DN + MET, 200 mg/kg/d). After 4 weeks of treatment, the damage caused by DN was assessed based on the related parameters of urine and blood. Periodic acid-Schiff (PAS) staining and hematoxylin and eosin (HE) staining were used to assess pathological tissue damage. Immunohistochemistry was used to detect nuclear factor erythroid-derived 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and phosphorylated-glycogen synthase kinase-3beta (P-GSK-3β) levels, whereas western blotting was used to detect Nrf2, HO-1, nephrin, GSK-3β, and p-GSK-3β levels.

RESULTS

MOS extract could inhibit the proliferation of HRMCs induced by high glucose levels. Compared with the rats in the DN group, MOS not only significantly reduced blood glucose levels and oxidative stress in the experimental rats but also improved their kidney function and reduced kidney tissue damage. Additionally, MOS extract increased GSK-3β activity and the expression of Nrf2 and HO-1.

CONCLUSIONS

This study showed that MOS could activate GSK-3β and Nrf2/HO-1 pathways to exert antioxidant and anti-renal fibrosis activities, and delay the progression of diabetic nephropathy.

Insulin resistance in glomerular podocytes: Potential mechanisms of induction

Glomerular podocytes are a target for the actions of insulin. Accumulating evidence indicates that exposure to nutrient overload induces insulin resistance in these cells, manifested by abolition of the stimulatory effect of insulin on glucose uptake. Numerous recent studies have investigated potential mechanisms of the induction of insulin resistance in podocytes. High glucose concentrations stimulated reactive oxygen species production through NADPH oxidase activation, decreased adenosine monophosphate-activated protein kinase (AMPK) phosphorylation, and reduced deacetylase sirtuin 1 (SIRT1) protein levels and activity. Calcium signaling involving transient receptor potential cation channel C, member 6 (TRPC6) also was demonstrated to play an essential role in the regulation of insulin-dependent signaling and glucose uptake in podocytes. Furthermore, podocytes exposed to diabetic environment, with elevated insulin levels become insulin resistant as a result of degradation of insulin receptor (IR), resulting in attenuation of insulin signaling responsiveness. Also elevated levels of palmitic acid appear to be an important factor and contributor to podocytes insulin resistance. This review summarizes cellular and molecular alterations that contribute to the development of insulin resistance in glomerular podocytes.

Beneficial effects of metformin on glomerular podocytes in diabetes

Podocytes and their foot processes form an important cellular layer of the glomerular barrier involved in regulating glomerular permeability. Disturbances in podocyte function play a central role in the development of proteinuria in diabetic nephropathy. The retraction of podocyte foot processes forming a slit diaphragm is a common feature of proteinuria. Metformin is an oral antidiabetic agent of the biguanide class that is widely recommended for the treatment of high blood glucose in patients with type 2 diabetes mellitus. In addition to lowering glucose, several recent studies have reported potential beneficial effects of metformin on diabetic kidney function. Furthermore, a key molecule of the antidiabetic mechanism of action of metformin is adenosine 5'-monophospate-activated protein kinase (AMPK), as the metformin-induced activation of AMPK is well documented. The present review summarizes current knowledge on the protective effects of metformin against pathological changes in podocytes that are induced by hyperglycemia.

Rutaecarpine enhances the anti-diabetic activity and hepatic distribution of metformin via up-regulation of Oct1 in diabetic rats

Diabetes mellitus is a chronic metabolic disorder with multiple complications, patients who receive metformin may have a simultaneous intake of herbal medicine containing rutaecarpine due to cardiovascular protection and hypolipidemic effects of rutaecarpine. There might be drug interactions between metformin and rutaecarpine. This study aimed to investigate the effects of rutaecarpine on the pharmacodynamics and pharmacokinetics of metformin in diabetic rats.The diabetic rat model was induced with high-fat diet and low dose streptozotocin. Metformin with or without rutaecarpine was administered by oral gavage for 42 days. Pharmacodynamics and pharmacokinetics parameters were evaluated.The pharmacodynamics results revealed that co-administration of rutaecarpine with metformin resulted in a remarkable reduction of serum glucose and lipid profiles in diabetic rats compared to metformin treated alone. The pharmacokinetics results showed that co-treatments of rutaecarpine with metformin did not affect the systemic exposure and renal distribution of metformin, but increased metformin concentration in liver. Furthermore, rutaecarpine increased Oct1-mediated metformin uptake into hepatocytes by upregulation of Oct1 expression in the liver.The above data indicate that rutaecarpine enhanced the anti-diabetic effect of metformin, which may be associated with the increased hepatic distribution of metformin through up-regulation of Oct1 in response to rutaecarpine.

Mechanism and application of metformin in kidney diseases: An update

Metformin is an oral antihyperglycemic drug widely used to treat type 2 diabetes mellitus (T2DM), acting via indirect activation of 5' Adenosine monophosphate-activated Protein Kinase (AMPK). Beyond the anti-diabetic effect, accumulative pieces of evidence have revealed that metformin also everts a beneficial effect in diverse kidney diseases. In various acute kidney diseases (AKI) animal models, metformin protects renal tubular cells from inflammation, apoptosis, reactive oxygen stress (ROS), endoplasmic reticulum (ER) stress, epithelial-mesenchymal transition (EMT) via AMPK activation. In diabetic kidney disease (DKD), metformin also alleviates podocyte loss, mesangial cells apoptosis, and tubular cells senescence through AMPK-mediated signaling pathways. Besides, metformin inhibits cystic fibrosis transmembrane conductance regulator (CFTR)-mediated fluids secretion and the mammalian target of rapamycin (mTOR)-involved cyst formation negatively regulated by AMPK in autosomal dominant polycystic kidney disease (APDKD). Furthermore, metformin also contributes to the alleviation of urolithiasis and renal cell carcinoma (RCC). As the common pathway for chronic kidney disease (CKD) progressing towards end-stage renal disease (ESRD), renal fibrosis is ameliorated by metformin, to a great extent dependent on AMPK activation. However, clinical data are not always consistent with preclinical data, some clinical investigations showed the unmeaningful even detrimental effect of metformin on T2DM patients with kidney diseases. Most importantly, metformin-associated lactic acidosis (MALA) is a vital issue restricting the application of metformin. Thus, we conclude the application of metformin in kidney diseases and uncover the underlying molecular mechanisms in this review.

Metformin Benefits: Another Example for Alternative Energy Substrate Mechanism?

Since the UK Prospective Diabetes Study (UKPDS), metformin has been considered the first-line medication for patients with newly diagnosed type 2 diabetes. Though direct evidence from specific trials is still lacking, several studies have suggested that metformin may protect from diabetes- and nondiabetes-related comorbidities, including cardiovascular, renal, neurological, and neoplastic diseases. In the past few decades, several mechanisms of action have been proposed to explain metformin's protective effects, none being final. It is certain, however, that metformin increases lactate production, concentration, and, possibly, oxidation. Once considered a mere waste product of exercising skeletal muscle or anaerobiosis, lactate is now known to act as a major energy shuttle, redistributed from production sites to where it is needed. Through the direct uptake and oxidation of lactate produced elsewhere, all end organs can be rapidly supplied with fundamental energy, skipping glycolysis and its possible byproducts. Increased lactate production (and consequent oxidation) could therefore be considered a positive mechanism of action of metformin, except when, under specific circumstances, metformin and lactate become excessive, increasing the risk of lactic acidosis. We are proposing that, rather than considering metformin-induced lactate production as dangerous, it could be considered a mechanism through which metformin exerts its possible protective effect on the heart, kidneys, and brain and, to some extent, its antineoplastic action.

Metformin Protects against Podocyte Injury in Diabetic Kidney Disease

Metformin is the most commonly prescribed drug for treating type 2 diabetes mellitus (T2D). Its mechanisms of action have been under extensive investigation, revealing that it has multiple cellular targets, either direct or indirect ones, via which it regulates numerous cellular pathways. Diabetic kidney disease (DKD), the serious complication of T2D, develops in up to 50% of the individuals with T2D. Various mechanisms contribute to the development of DKD, including hyperglycaemia, dyslipidemia, oxidative stress, chronic low-grade inflammation, altered autophagic activity and insulin resistance, among others. Metformin has been shown to affect these pathways, and thus, it could slow down or prevent the progression of DKD. Despite several animal studies demonstrating the renoprotective effects of metformin, there is no concrete evidence in clinical settings. This review summarizes the renoprotective effects of metformin in experimental settings. Special emphasis is on the effects of metformin on podocytes, the glomerular epithelial cells that are central in maintaining the glomerular ultrafiltration function.

Regulation of podocytes function by AMP-activated protein kinase

Podocytes are unique, highly specialized, terminally differentiated cells that form an essential, integral part of the glomerular filter. These cells limit the outside border of the glomerular basement membrane, forming a tight barrier that prevents significant protein loss from the capillary space. The slit diaphragm formed by podocytes is crucial for maintaining glomerular integrity and function. They are the target of injury in many glomerular diseases, including hypertension and diabetes mellitus. Accumulating studies have revealed that AMP-activated protein kinase (AMPK), an essential cellular energy sensor, might play a fundamental role in regulating podocyte metabolism and function. AMPK participates in insulin signaling, therefore controls glucose uptake and podocytes insulin sensitivity. It is also involved in insulin-dependent cytoskeleton reorganization in podocytes, mediating glomerular albumin permeability. AMPK plays an important role in the regulation of autophagy/apoptosis processes, which influence podocytes viability. The present review aimed to highlight the molecular mechanisms associated with AMPK that are involved in the regulation of podocyte function in health and disease states.

Accelerated Kidney Aging in Diabetes Mellitus

With aging, the kidney undergoes inexorable and progressive changes in structural and functional performance. These aging-related alterations are more obvious and serious in diabetes mellitus (DM). Renal accelerated aging under DM conditions is associated with multiple stresses such as accumulation of advanced glycation end products (AGEs), hypertension, oxidative stress, and inflammation. The main hallmarks of cellular senescence in diabetic kidneys include cyclin-dependent kinase inhibitors, telomere shortening, and diabetic nephropathy-associated secretory phenotype. Lysosome-dependent autophagy and antiaging proteins Klotho and Sirt1 play a fundamental role in the accelerated aging of kidneys in DM, among which the autophagy-lysosome system is the convergent mechanism of the multiple antiaging pathways involved in renal aging under DM conditions. Metformin and the inhibitor of sodium-glucose cotransporter 2 are recommended due to their antiaging effects independent of antihyperglycemia, besides angiotensin-converting enzyme inhibitors/angiotensin receptor blockers. Additionally, diet intervention including low protein and low AGEs with antioxidants are suggested for patients with diabetic nephropathy (DN). However, their long-term benefits still need further study. Exploring the interactive relationships among antiaging protein Klotho, Sirt1, and autophagy-lysosome system may provide insight into better satisfying the urgent medical needs of elderly patients with aging-related DN.

Significance of Metformin Use in Diabetic Kidney Disease

Metformin is a glucose-lowering agent that is used as a first-line therapy for type 2 diabetes (T2D). Based on its various pharmacologic actions, the renoprotective effects of metformin have been extensively studied. A series of experimental studies demonstrated that metformin attenuates diabetic kidney disease (DKD) by suppressing renal inflammation, oxidative stress and fibrosis. In clinical studies, metformin use has been shown to be associated with reduced rates of mortality, cardiovascular disease and progression to end-stage renal disease (ESRD) in T2D patients with chronic kidney disease (CKD). However, metformin should be administered with caution to patients with CKD because it may increase the risk of lactic acidosis. In this review article, we summarize our current understanding of the safety and efficacy of metformin for DKD.

SHIPping out diabetes-Metformin, an old friend among new SHIP2 inhibitors

SHIP2 (Src homology 2 domain‐containing inositol 5′‐phosphatase 2) belongs to the family of 5′‐phosphatases. It regulates the phosphoinositide 3‐kinase (PI3K)‐mediated insulin signalling cascade by dephosphorylating the 5′‐position of PtdIns(3,4,5)P3 to generate PtdIns(3,4)P2, suppressing the activity of the pathway. SHIP2 mouse models and genetic studies in human propose that increased expression or activity of SHIP2 contributes to the pathogenesis of the metabolic syndrome, hypertension and type 2 diabetes. This has raised great interest to identify SHIP2 inhibitors that could be used to design new treatments for metabolic diseases. This review summarizes the central mechanisms associated with the development of diabetic kidney disease, including the role of insulin resistance, and then moves on to describe the function of SHIP2 as a regulator of metabolism in mouse models. Finally, the identification of SHIP2 inhibitors and their effects on metabolic processes in vitro and in vivo are outlined. One of the newly identified SHIP2 inhibitors is metformin, the first‐line medication prescribed to patients with type 2 diabetes, further boosting the attraction of SHIP2 as a treatment target to ameliorate metabolic disorders.

Association of Metformin Use With End-Stage Renal Disease in Patients With Type 2 Diabetes Mellitus: A Nationwide Cohort Study Under the Pay-for-Performance Program

Animal studies have demonstrated that metformin exerts a renoprotective effect. Human studies of patients with diabetes mellitus (DM) regarding the association of metformin use with end-stage renal disease (ESRD) are lacking. Patients with type 2 DM and without a history of kidney disease who were enrolled under the pay-for-performance program of the National Health Insurance in Taiwan were identified. Those who received ≥90 cumulative defined daily doses of metformin within 1 year were selected (metformin users) and compared with a 1:1 propensity score-matched metformin nonuser cohort. Primary and secondary outcomes were development of ESRD and chronic kidney disease (CKD), respectively. Independent predictors were investigated using Cox regression analysis. A total of 24 158 pairs of metformin users and nonusers were enrolled, with an incidence of ESRD of 1908 and 1723 and CKD of 1095 and 1056 cases per 100 000 person-years, respectively. Metformin use was independently associated with increased risks of ESRD (adjusted hazard ratio, 1.22; 95% confidence interval, 1.12-1.32) and CKD (adjusted hazard ratio, 1.25; 95% confidence interval, 1.12-1.40) in a dose-response relationship. Patients with hypertension plus nonuse of angiotensin-converting enzyme inhibitors or angiotensin II receptor blockers potentiated kidney damage by metformin. In patients with DM, use of metformin may increase the risk of ESRD and CKD. Health care professionals should be alert and closely monitor renal function when prescribing metformin.

Narrative review of the effects of antidiabetic drugs on albuminuria

Diabetes mellitus is the most prevalent metabolic disorder worldwide. Glycemic control is the main focus of antidiabetic therapy. However, there are data suggesting that some antidiabetic drugs may have intrinsic beneficial renal effects and protect against the development and progression of albuminuria, thus minimizing the risk of diabetic nephropathy. These pharmacological agents can suppress upstream molecular pathways involved in the pathophysiology of diabetes-induced renal dysfunction such as oxidative stress, inflammatory responses, and apoptosis. In this narrative review, the pathophysiology of albuminuria in patients with diabetic nephropathy is discussed. Furthermore, the renoprotective effects of antidiabetic drugs, focusing on albuminuria, are reviewed.

Tiaolipiwei Acupuncture Reduces Albuminuria by Alleviating Podocyte Lesions in a Rat Model of Diabetic Nephropathy

Background

Diabetic nephropathy is a common and serious complication of diabetes and a major cause of end-stage renal disease. Tiaolipiwei acupuncture is a safe treatment approach that may be effective for lowering albuminuria in diabetic nephropathy. Yet, the exact mechanisms of this therapeutic effect are unclear.

Methods

A rodent model of type 2 diabetic nephropathy (T2DN) was induced by a high-fat diet combined with low-dose streptozotocin. T2DN rats were treated with Tiaolipiwei acupuncture (ACU) for 4, 8, or 12 weeks. At the end of treatment, urinary and blood samples were collected for analysis. Transmission electron microscopy was used to observe morphological changes, and protein expression levels of nephrin, CD2AP, podocalyxin, and desmin were quantified in renal tissue.

Results

Compared to the T2DN groups, the T2DN + ACU groups showed significant improvements in 24-hour urinary protein, serum urea, cholesterol, and triglycerides at all time points. ACU treatment also improved the density of slit diaphragms. Simultaneously, ACU promoted the renal expression of nephrin, CD2AP, and podocalyxin and decreased the expression of desmin.

Conclusion

Our study suggests that Tiaolipiwei acupuncture ameliorates podocyte lesions to reduce albuminuria and prevent the progression of T2DN in a rat model.

Metformin Improves Epithelial-to-Mesenchymal Transition Induced by TGF-β1 in Renal Tubular Epithelial NRK-52E Cells via Inhibiting Egr-1

The early growth response- (Egr-) 1 has been found to play a key role in organ fibrosis. Metformin has been shown to be effective in attenuating renal tubular epithelial-to-mesenchymal transition (EMT), which is involved in renal fibrosis. However, it is unknown whether metformin improves EMT via inhibiting Egr-1. In this study, rat renal tubular epithelial (NRK-52 E) cells, treated by transforming growth factor- (TGF-) β1 of 10 ng/ml with or without metformin of 1 mmol/l, were transfected by siEgr-1 or M61-Egr-1 plasmids to knock down or overexpress Egr-1, respectively. The gene and protein expressions of E-cadherin, α-SMA, fibronectin (FN), and Egr-1 were determined by real-time quantitative PCR and Western blotting, respectively. We observed that TGF-β1 significantly reduced E-cadherin expression and upregulated the expressions of FN, α-SMA, and Egr-1, which can be reversed by metformin. M61-Egr-1 transfection could exacerbate EMT, which can be reversed by metformin. Taken together, our data show that Egr-1 plays an important role in TGF-β1-induced EMT of renal tubular epithelial cells and metformin improves EMT while inhibiting Egr-1, which provides a potential novel target to combat renal fibrosis.

Effects of type 2 diabetes mellitus on the pharmacokinetics of berberine in rats

CONTEXT

Berberine is an active alkaloid isolated from Rhizoma coptidis [Coptis chinensis Franch. (Ranunculaceae)] that is widely used for the treatment of diabetes, hyperlipidemia and hypertension. However, the pharmacokinetics of berberine in normal rats and type 2 diabetes mellitus (T2DM) model rats are not clear.

OBJECTIVE

This study compares the pharmacokinetics of berberine between normal and T2DM model rats.

MATERIALS AND METHODS

The T2DM model rats were fed with high fat diet for 4 weeks, induced by low-dose (30 mg/kg) streptozotocin for 72 h and validated by determining the peripheral blood glucose level. Rats were orally treated with berberine at a dose of 20 mg/kg and then berberine concentration in rat plasma was determined by employing a sensitive and rapid LC-MS/MS method.

RESULTS

The significantly different pharmacokinetic behaviour of berberine was observed between normal and T2DM model rats. When compared with the normal group, C_max, t_1/2 and AUC_(0-t) of berberine were significantly increased in the model group (17.35 ± 3.24 vs 34.41 ± 4.25 μg/L; 3.95 ± 1.27 vs 9.29 ± 2.75 h; 151.21 ± 23.96 vs 283.81 ± 53.92 μg/h/L, respectively). In addition, oral clearance of berberine was significantly decreased in the model group (134.73 ± 32.15 vs 62.55 ± 16.34 L/h/kg).

DISCUSSION AND CONCLUSION

In T2DM model rats, the pharmacokinetic behaviour of berberine was significantly altered, which indicated that berberine dosage should be modified in T2DM patients.

Pancreatic mitochondrial complex I exhibits aberrant hyperactivity in diabetes

It is well established that NADH/NAD+ redox balance is heavily perturbed in diabetes, and the NADH/NAD+ redox imbalance is a major source of oxidative stress in diabetic tissues. In mitochondria, complex I is the only site for NADH oxidation and NAD+ regeneration and is also a major site for production of mitochondrial reactive oxygen species (ROS). Yet how complex I responds to the NADH/NAD+ redox imbalance and any potential consequences of such response in diabetic pancreas have not been investigated. We report here that pancreatic mitochondrial complex I showed aberrant hyperactivity in either type 1 or type 2 diabetes. Further studies focusing on streptozotocin (STZ)-induced diabetes indicate that complex I hyperactivity could be attenuated by metformin. Moreover, complex I hyperactivity was accompanied by increased activities of complexes II to IV, but not complex V, suggesting that overflow of NADH via complex I in diabetes could be diverted to ROS production. Indeed in diabetic pancreas, ROS production and oxidative stress increased and mitochondrial ATP production decreased, which can be attributed to impaired pancreatic mitochondrial membrane potential that is responsible for increased cell death. Additionally, cellular defense systems such as glucose 6-phosphate dehydrogenase, sirtuin 3, and NQO1 were found to be compromised in diabetic pancreas. Our findings point to the direction that complex I aberrant hyperactivity in pancreas could be a major source of oxidative stress and β cell failure in diabetes. Therefore, inhibiting pancreatic complex I hyperactivity and attenuating its ROS production by various means in diabetes might serve as a promising approach for anti-diabetic therapies.

Function of NLRP3 in the Pathogenesis and Development of Diabetic Nephropathy

Background

The aim of this research was to study the function of NLRP3 in the pathogenesis and development of diabetic nephropathy (DN).

Material/Methods

We compared the expression of NLRP3-related protein in human glomerular mesangial cells under high glucose conditions at different times and in rats with DN of different ages. We also compared changes in IL-18 and IL-1β expression levels at different stages of DN.

Results

After six hours, 12 hours, and 24 hours of high glucose stimulation, the secretion of IL-1β in human glomerular mesangial cells, compared to unstimulated cells, was 1.85-fold, 3.04-fold, and 4.14-fold; the expression of NLRP3 increased by 2.20-fold, 4.62-fold, and 8.32-fold; and the expression of caspase-1 was increased by 1.60-fold, 2.72-fold, and 3.67-fold. The expression levels of nephrin in eight-week-old and 12-week-old DN rats compared to 4-week rats were 49.60% and 21.20%, respectively. The IL-1β levels compared to four-week DN rats were 2.57-fold and 4.17-fold, respectively; NLRP3 levels were 1.29-fold and 2.17-fold respectively, and caspase-1 levels were 3.37-fold and 4.16-fold, respectively. The serum levels of IL-18 and IL-1β in the DN group were the highest at 218.53±30.69 pg/mL and 62.47±9.36 pg/mL, respectively; followed by the mild DN group at 177.07±32.88 pg/mL and 28.13±5.37 pg/mL, respectively, with the diabetic mellitus (DM) group having the lowest levels at 141.47±9.49 pg/mL and 15.53±3.26 pg/mL, respectively. The healthy control group levels were 99.40±22.72 pg/mL and 12.40±5.08 pg/mL, respectively.

Conclusions

NLRP3 and high glucose activation may participate in the occurrence and development of DN by mediating the inflammatory response.

Differential expression profile analysis of PSTK-regulated mRNAs in podocytes

This study aimed to elucidate the precise mechanisms underlying the protective effects of phosphoseryl-tRNA kinase (PSTK) against cisplatin-induced podocyte injury. PSTK overexpression and knockdown vectors were generated and transfected into murine podocyte cells-5. PSTK levels were measured, and transcriptome sequencing was conducted. Differential expression analysis was performed to identify messenger RNAs (mRNAs) that were positively and negatively correlated with PSTK. We selected 10 candidate genes identified via real-time quantitative polymerase chain reaction and Western blot analysis for further analysis. As expected, PSTK levels were significantly higher in PSTK-overexpressing podocytes and significantly lower in PSTK-knockdown podocytes. PSTK overexpression resulted in the upregulation of 122 genes and downregulation of 372 genes in podocytes. On the other hand, PSTK knockdown resulted in the upregulation of 231 genes and downregulation of 445 genes. Furthermore, the analysis revealed that 11 genes were positively correlated with PSTK, whereas 20 genes were negatively correlated with PSTK. The obtained PSTK-regulated genes were primarily involved in molecular function, biological process, and cellular component, as well as the angiogenesis pathway. The Wnt family member 10A levels were significantly higher after PSTK overexpression, but were significantly lower after PSTK knockdown. In addition, Na+/K+ ATPase subunit α-2 and matrix metalloproteinase 9 levels were significantly downregulated after PSTK overexpression, but significantly upregulated upon PSTK knockdown. Cell proliferation was significantly increased upon PSTK overexpression, but significantly decreased upon PSTK suppression. The results of this study not only identified several significant PSTK-regulated genes for further validation, but also provided insights into the mechanisms underlying the protective effects of PSTK on podocytes.