Metformin Protects against Podocyte Injury in Diabetic Kidney Disease

Synthesis and biological evaluation of 2'-hydroxychalcone derivatives as AMPK activators

A series of 2'-hydroxychalcone derivatives with various substituents on B-ring were synthesized and evaluated for AMP-activated protein kinase (AMPK) activation activity in podocyte cells. The results displayed that hydroxy, methoxy and methylenedioxy groups on B-ring could enhance the activitiy better than O-saturated alkyl, O-unsaturated alkyl or other alkoxy groups. Compounds 27 and 29 possess the highest fold change of 2.48 and 2.73, respectively, which were higher than those of reference compound (8) (1.28) and metformin (1.88). Compounds 27 and 29 were then subjected to a concentration-response study to obtain the EC50 values of 2.0 and 4.8 µM, respectively and MTT assays also showed that cell viability was not influenced by the exposure of podocytes to compounds 27 and 29 at concentrations up to 50 μM. In addition, compound 27 was proved to activate AMPK via calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ)-dependent pathway without affecting intracellular calcium levels. The computational study showed that the potent compounds exhibited stronger ligand-binding strength to CaMKKβ, particularly compounds 27 (-8.4 kcal/mol) and 29 (-8.0 kcal/mol), compared to compound 8 (-7.5 kcal/mol). Fragment molecular orbital (FMO) calculation demonstrated that compound 27 was superior to compound 29 due to the presence of methyl group, which amplified the binding by hydrophobic interactions. Therefore, compound 27 would represent a promising AMPK activator for further investigation of the treatment of diabetes and diabetic nephropathy.

Metformin inhibits high glucose-induced apoptosis of renal podocyte through regulating miR-34a/SIRT1 axis

BACKGROUND

Previous studies have reported SIRT1 was inversely modulated by miR-34a, However, mechanism of metformin (MFN)'s renal podocyte protection under high glucose (HG) conditions and the connection between miR-34a and SIRT1 expression in diabetic nephropathy (DN) remain unclear.

METHOD

We aimed to further elucidate the role of miR-34a in HG-treated podocytes in DN. A conditionally immortalized human podocyte cell line was cultivated in d-glucose (30 mM).

RESULTS

Microarray and RT-qPCR revealed that miR-34a was downregulated in HG-treated podocytes. Additionally, miR-34a levels increased in MFN-treated HG-induced podocytes. CCK-8 assay, colony formation assay, flow cytometry, and Western blot detection showed that HG treatment reduced cell viability and promoted via HG treatment, and MFN treatment reversed this phenotypic change. MiR-34a upregulation caused restored cell viability and suppressed cell apoptosis in HG-treated podocytes, and miR-34a downregulation led to damaged cell survival and induced apoptosis in MFN-administered and HG-treated podocytes. The dual luciferase reporter assay showed that SIRT1 3'-UTR was a direct miR-34a target. Further studies demonstrated an elevation in SIRT1 levels in HG-exposed podocytes, whereas MFN treatment decreased SIRT1 levels. In addition, miR-34a upregulation led to reduced SIRT1 expression, whereas miR-34a inhibition increased SIRT1 levels in cells. MFN-induced miR-34a suppresses podocyte apoptosis under HG conditions by acting on SIRT1.

CONCLUSION

This study proposes a promising approach to interpret the mechanisms of action of the MFN-miR-34a axis involved in DN.

A sulfonamide chalcone AMPK activator ameliorates hyperglycemia and diabetic nephropathy in db/db mice

Diabetic nephropathy (DN) is a serious complication of diabetes mellitus (DM), which currently lacks effective treatments. AMP-activated protein kinase (AMPK) stimulation by chalcones, a class of polyphenols abundantly found in plants, is proposed as a promising therapeutic approach for DM. This study aimed to identify novel chalcone derivatives with improved AMPK-stimulating activity in human podocytes and evaluate their mechanisms of action as well as in vivo efficacy in a mouse model of DN. Among 133 chalcone derivatives tested, the sulfonamide chalcone derivative IP-004 was identified as the most potent AMPK activator in human podocytes. Western blot analyses, intracellular calcium measurements and molecular docking simulation indicated that IP-004 activated AMPK by mechanisms involving direct binding at allosteric site of calcium-dependent protein kinase kinase β (CaMKKβ) without affecting intracellular calcium levels. Interestingly, eight weeks of intraperitoneal administration of IP-004 (20 mg/kg/day) significantly decreased fasting blood glucose level, activated AMPK in the livers, muscles and glomeruli, and ameliorated albuminuria in db/db type II diabetic mice. Collectively, this study identifies a novel chalcone derivative capable of activating AMPK in vitro and in vivo and exhibiting efficacy against hyperglycemia and DN in mice. Further development of AMPK activators based on chalcone derivatives may provide an effective treatment of DN.

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.

Laminaria japonica polysaccharide attenuates podocyte epithelial-mesenchymal transformation via TGF-β1-mediated Smad3 and p38MAPK pathways

In the present work, we explored the interventional effect and potential mechanism of a purified Laminaria japonica polysaccharide (LJP61A) on podocyte epithelial-mesenchymal transition (EMT) in TGF-β1-induced podocytes and adriamycin-treated mice. Results showed that compared to the model groups, LJP61A significantly up-regulated the levels of epithelial markers (Nephrin, WT-1, podocin) and down-regulated the levels of mesenchymal markers (α-SMA, FN1) in vitro and in vivo, thus preventing EMT-like morphological changes of podocytes, proteinuria and kidney injury. Smad3 and p38MAPK are two central pathways mediating podocyte EMT activated by TGF-β1. We found that LJP61A suppressed TGF-β1-induced activation of Smad3, Smad4 and p38MAPK in vitro and in vivo. Moreover, the inhibitory actions of LJP61A on podocyte EMT were synergistically strengthened by Smad3 inhibitor SIS3 and p38MAPK inhibitor SB203580. Taken together, these findings revealed that LJP61A could prevent podocyte EMT, which might be related to the inhibition of TGF-β1-mediated Smad3 and p38MAPK pathways.

Cellular mechanism of action of forsythiaside for the treatment of diabetic kidney disease

Background: Diabetic kidney disease (DKD) becomes the leading cause of death for end-stage renal disease, whereas the potential mechanism is unclear and effective therapy is still rare. Our study was designed to investigate the cellular mechanism of Forsythiaside against DKD. Materials and Methods: The targets of Forsythiaside and the DKD-related targets were obtained from databases. The overlapping targets in these two sets were regarded as potential targets for alleviation of DKD by Forsythiaside. The targets of diabetic podocytopathy and tubulopathy were also detected to clarify the mechanism of Forsythiaside ameliorating DKD from the cellular level. Results: Our results explored that PRKCA and RHOA were regarded as key therapeutic targets of Forsythiaside with excellent binding affinity for treating DKD podocytopathy. Enrichment analysis suggested the underlying mechanism was mainly focused on the oxidative stress and mTOR signaling pathway. The alleviated effects of Forsythiaside on the reactive oxidative species accumulation and PRKCA and RHOA proteins upregulation in podocytes were also confirmed. Conclusion: The present study elucidates that Forsythiaside exerts potential treatment against DKD which may act directly RHOA and PRKCA target by suppressing the oxidative stress pathway in podocytes. And Forsythiaside could be regarded as one of the candidate drugs dealing with DKD in future experimental or clinical researches.

Role of miR-379 in high-fat diet-induced kidney injury and dysfunction

Obesity is associated with increased risk for diabetes and damage to the kidneys. Evidence suggests that miR-379 plays a role in the pathogenesis of diabetic kidney disease. However, its involvement in obesity-induced kidney injury is not known and was therefore investigated in this study by comparing renal phenotypes of high-fat diet (HFD)-fed wild-type (WT) and miR-379 knockout (KO) mice. Male and female WT mice on the HFD for 10 or 24 wk developed obesity, hyperinsulinemia, and kidney dysfunction manifested by albuminuria and glomerular injuries. However, these adverse alterations in HFD-fed WT mice were significantly ameliorated in HFD-fed miR-379 KO mice. HFD feeding increased glomerular expression of miR-379 and decreased its target gene, endoplasmic reticulum (ER) degradation enhancing α-mannosidase-like protein 3 (Edem3), a negative regulator of ER stress. Relative to the standard chow diet-fed controls, expression of profibrotic transforming growth factor-β1 (Tgf-β1) was significantly increased, whereas Zeb2, which encodes ZEB2, a negative regulator of Tgf-β1, was decreased in the glomeruli in HFD-fed WT mice. Notably, these changes as well as HFD-induced increased expression of other profibrotic genes, glomerular hypertrophy, and interstitial fibrosis in HFD-fed WT mice were attenuated in HFD-fed miR-379 KO mice. In cultured primary glomerular mouse mesangial cells (MMCs) isolated from WT mice, treatment with high insulin (mimicking hyperinsulinemia) increased miR-379 expression and decreased its target, Edem3. Moreover, insulin also upregulated Tgf-β1 and downregulated Zeb2 in WT MMCs, but these changes were significantly attenuated in MMCs from miR-379 KO mice. Together, these experiments revealed that miR-379 deletion protects mice from HFD- and hyperinsulinemia-induced kidney injury at least in part through reduced ER stress.NEW & NOTEWORTHY miR-379 knockout mice are protected from high-fat diet (HFD)-induced kidney damage through key miR-379 targets associated with ER stress (Edem3). Mechanistically, treatment of mesangial cells with insulin (mimicking hyperinsulinemia) increased expression of miR-379, Tgf-β1, miR-200, and Chop and decreases Edem3. Furthermore, TGF-β1-induced fibrotic genes are attenuated by a GapmeR targeting miR-379. The results implicate a miR-379/EDEM3/ER stress/miR-200c/Zeb2 signaling pathway in HFD/obesity/insulin resistance-induced renal dysfunction. Targeting miR-379 with GapmeRs can aid in the treatment of obesity-induced kidney disease.

Effect of metformin as an add-on therapy on neuregulin-4 levels and vascular-related complications in adolescents with type 1 diabetes: A randomized controlled trial

BACKGROUND

Inflammation is closely associated with atherosclerosis and plays a crucial role in the development of cardiovascular disease. Metformin sensitizes body cells to insulin, which may cause a reduction of atherogenic lipid fractions. Low neuregulin-4 (Nrg-4) levels, an adipokine, are linked to obesity, insulin resistance, impaired glucose tolerance and type 2 diabetes.

OBJECTIVES

We assessed the effect of oral supplementation with metformin on glycemic control, neuregulin-4 levels and carotid intima media thickness (CIMT) as a marker for subclinical atherosclerosis in adolescents with type 1 diabetes mellitus (T1DM) and microvascular complications.

METHODS

This randomized placebo-controlled trial included 80 type 1 diabetic patients with microvascular complications who were randomly divided to receive either 24 weeks of metformin 500 mg/day or matching placebo. Fasting blood glucose (FBG), HbA1c, C-reactive protein (CRP), urinary albumin creatinine ratio (UACR), lipid profile, Nrg-4 and CIMT were assessed at baseline and study end.

RESULTS

Both groups were well-matched as regards baseline clinical and laboratory data (p greater than 0.05). After 24-weeks, metformin therapy for the intervention group resulted in a significant decrease of HbA1c, CRP, UACR, total cholesterol and CIMT while Nrg-4 levels were increased compared with baseline levels (p < 0.001) and with placebo group(p < 0.001). Baseline Nrg-4 levels were negatively correlated to FBG, HbA1c, total cholesterol, CRP and CIMT. Metformin was well-tolerated.

CONCLUSIONS

Oral metformin supplementation once daily for 24 weeks as an adjuvant therapy to intensive insulin in pediatric T1DM was safe and effective in improving glycemic control, dyslipidemia and Nrg-4 levels; hence, it decreased inflammation, microvascular complications and subclinical atherosclerosis.

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.