Metformin prevents renal interstitial fibrosis in mice with unilateral ureteral obstruction

Renal fibrosis progression following partial unilateral ureteral obstruction: mechanisms and therapeutic insights

Ureteral obstruction, a common clinical condition, is associated with various renal disorders affecting all age groups and can lead to permanent renal damage. In Partial unilateral ureteral obstruction (PUUO), increased ureteral pressure, and decreased glomerular filtration rate (GFR) in the affected kidney cause cellular and molecular abnormalities, which ultimately lead to renal fibrosis if untreated. While removing the obstruction (RUUO) is essential to prevent long-term damage, additional therapeutic approaches may be necessary to fully restore kidney function. The PUUO model is used to induce renal fibrosis, primarily characterized by tubular injury resulting from obstructed urine flow. PUUO in rodents can simulate human chronic obstructive nephropathy at an accelerated rate. Although alleviating the obstruction can reduce immediate symptoms, it is often insufficient to reverse established fibrosis, emphasizing the need for adjunctive therapies. The renal response to RUUO depends on factors like the obstruction's duration and severity, as well as the contralateral kidney's functional state.

Simvastatin attenuates silica-induced pulmonary inflammation and fibrosis in rats via the AMPK-NOX pathway

BACKGROUND

Simvastatin (Sim), a hydroxy-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, has been widely used in prevention and treatment of cardiovascular diseases. Studies have suggested that Sim exerts anti-fibrotic effects by interfering fibroblast proliferation and collagen synthesis. This study was to determine whether Sim could alleviate silica-induced pulmonary fibrosis and explore the underlying mechanisms.

METHODS

The rat model of silicosis was established by the tracheal perfusion method and treated with Sim (5 or 10 mg/kg), AICAR (an AMPK agonist), and apocynin (a NOX inhibitor) for 28 days. Lung tissues were collected for further analyses including pathological histology, inflammatory response, oxidative stress, epithelial mesenchymal transformation (EMT), and the AMPK-NOX pathway.

RESULTS

Sim significantly reduced silica-induced pulmonary inflammation and fibrosis at 28 days after administration. Sim could reduce the levels of interleukin (IL)-1β, IL-6, tumor necrosis factor-α and transforming growth factor-β1 in lung tissues. The expressions of hydroxyproline, α-SMA and vimentin were down-regulated, while E-cad was increased in Sim-treated rats. In addition, NOX4, p22pox, p40phox, p-p47phox/p47phox expressions and ROS levels were all increased, whereas p-AMPK/AMPK was decreased in silica-induced rats. Sim or AICAR treatment could notably reverse the decrease of AMPK activity and increase of NOX activity induced by silica. Apocynin treatment exhibited similar protective effects to Sim, including down-regulating of oxidative stress and inhibition of the EMT process and inflammatory reactions.

CONCLUSIONS

Sim attenuates silica-induced pulmonary inflammation and fibrosis by downregulating EMT and oxidative stress through the AMPK-NOX pathway.

Fine Tuning Mesenchymal Stromal Cells - Code For Mitigating Kidney Diseases

Kidney Disease (KD), has a high global prevalence and accounts for one of the most prominent causes of morbidity and mortality in the twenty-first century. Despite the advances in our understanding of its pathophysiology, the only available therapy options are dialysis and kidney transplantation. Mesenchymal stem cells (MSCs) have proven to be a viable choice for KD therapy due to their antiapoptotic, immunomodulatory, antioxidative, and pro-angiogenic activities. However, the low engraftment, low survival rate, diminished paracrine ability, and delayed delivery of MSCs are the major causes of the low clinical efficacy. A number of preconditioning regimens are being tested to increase the therapeutic capabilities of MSCs. In this review, we highlight the various strategies to prime MSCs and their protective effects in kidney diseases.

Emerging therapeutic targets in systemic sclerosis

Systemic sclerosis is an autoimmune connective tissue disease which is characterised by vascular perturbations, inflammation, and fibrosis. Although huge progress recently into the underlying molecular pathways that are perturbed in the disease, currently no therapy exists that targets the fibrosis element of the disease and consequently there is a huge unmet medical need. Emerging studies reveal new dimensions of complexity, and multiple aberrant pathways have been uncovered that have shed light on disturbed signalling in the disease, primarily in inflammatory pathways that can be targeted with repurposed drugs. Pre-clinical animal models using these inhibitors have yielded proof of concept for targeting these signalling systems and progressing to clinical trials. This review will examine the recent evidence of new perturbed pathways in SSc and how these can be targeted with new or repurposed drugs to target a currently intractable disease.

Reno-protective effect of protocatechuic acid is independent of sex-related differences in murine model of UUO-induced kidney injury

BACKGROUND

Obstructive nephropathy is a condition often caused by urinary tract obstruction either anatomical (e.g., tumors), mechanical (e.g., urolithiasis), or compression (e.g., pregnancy) and can progress to chronic kidney disease (CKD). Studies have shown sexual dimorphism in CKD, where males were found to have a more rapid decline in kidney function following kidney injury compared to age-matched females. Protocatechuic acid (PCA), an anti-oxidant and anti-inflammatory polyphenolic compound, has demonstrated promising effects in mitigating drug-induced kidney injuries. The current study aims to explore sexual dimorphism in kidney injury after unilateral ureteral obstruction (UUO) and assess whether PCA treatment can mitigate kidney injury in both sexes.

METHODS

UUO was induced in 10-12 weeks old male and female C57BL/6J mice. Mice were categorized into four groups (n = 6-8/group); Sham, Sham plus PCA (100 mg/kg, I.P daily), UUO, and UUO plus PCA.

RESULTS

After 2 weeks of induction of UUO, markers of kidney oxidative stress (TBARs), inflammation (IL-1α and IL-6), tubular injury (neutrophil gelatinase-associated lipocalin, NGAL and urinary kidney injury molecule-1, KIM-1), fibrosis (Masson's trichrome staining, collagen IV expression, MMP-2 and MMP-9) and apoptosis (TUNEL+ cells, active caspase-1 and caspase-3) were significantly elevated in both males and females relative to their sham counterparts. Males exhibited significantly greater kidney oxidative stress, inflammation, fibrosis, and apoptosis after induction of UUO when compared to females. PCA treatment significantly attenuated UUO-induced kidney injury, inflammation, fibrosis, and apoptosis in both sexes.

CONCLUSION

Our findings suggest a differential gender response to UUO-induced kidney injury with males being more sensitive to UUO-induced kidney inflammation, fibrosis, and apoptosis than age-matched females. Importantly, PCA treatment reduced UUO-induced kidney injury in a sex-independent manner which might be attributed to its anti-oxidant, anti-inflammatory, anti-fibrotic, and anti-apoptotic properties.

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.

Metformin suppressed tendon injury-induced adhesion via hydrogel-nanoparticle sustained-release system

Tendon adhesion is one of the sequelae of tendon injury and can lead to disability in severe cases. Metformin is a commonly used antidiabetic drug. Some studies had shown that metformin could reduce tendon adhesion as well. Considering the characteristic of low absorption rate and short half-life, we established a sustained-release system, i.e., hydrogel-nanoparticle system to deliver metformin. In vitro, metformin could effectively suppress TGF-β1-induced cell proliferation and accelerate cell apoptosis, according to cell counting kit-8, flow cytometry, and 5-ethynyl-2'-deoxyuridine (EdU) staining studies. In vivo, hydrogel-nanoparticle/metformin system could significantly lower adhesion scores and improve the gliding function of repaired flexor tendons, as well as decrease the expression of fibrotic proteins Col1a1, Col3a1, and α-smooth muscle actin (α-SMA). Histological staining revealed that the inflammation had subsided and that the gap between the tendon and the surrounding tissue was wider in the hydrogel-nanoparticle/metformin treatment group. Finally, we speculated that effect of metformin on reducing tendon adhesion might be achieved by regulating both Smad and MAPK-TGF-β1 signaling pathways. In conclusion, metformin delivered through hydrogel-nanoparticle sustained-release system may be a promising strategy for coping with tendon adhesion.

Mutation of regulatory phosphorylation sites in PFKFB2 does not affect the anti-fibrotic effect of metformin in the kidney

The anti-fibrotic effect of metformin has been widely demonstrated. Fibrosis in the kidney after injury is associated with reduced expression of genes involved in both fatty acid and glycolytic energy metabolism. We have previously reported that the anti-fibrotic effect of metformin requires phosphoregulation of fatty acid oxidation by AMP-activated protein kinase (AMPK). To determine whether metformin also acts via regulation of glycolysis, we mutated regulatory phosphosites in the PFKFB2 isoform of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB2), a key regulator of glycolysis in the kidney. Mice with inactivating knockin (KI) mutations of the phosphorylation sites in PFKFB2 (PFKFB2 KI mice), which reduces the ability to increase the rate of glycolysis following stimulation, were used. Metformin was administered via drinking water to mice with a unilateral ureteric obstruction (UUO) model of renal fibrosis. In the PFKFB2 KI mice treated with metformin, there was decreased fibrosis and macrophage infiltration following UUO as assessed by Western blot for fibronectin and RT-PCR for α-smooth muscle actin, collagen 3, and F4.80, and confirmed by histology. Expression of the inducible PFKFB3 isoform was increased with metformin in UUO in both WT and PFKFB2 KI mice. There was no significant difference between WT and PFKFB2 KI mice treated with metformin in the degree of fibrosis following UUO in any of the Western blot or RT-PCR parameters that were measured. These data show that inhibition of the regulation of glycolysis by PFKFB2 does not diminish the anti-fibrotic effect of metformin in a model of renal fibrosis.

Kidney-Targeted Drug Delivery System Based on Metformin-Grafted Chitosan for Renal Fibrosis Therapy

Our previous study demonstrated that metformin plays an anti-fibrotic role in addition to its hypoglycemic effect. Worryingly, it often requires more than 5 times the hypoglycemic dose to achieve a satisfactory anti-fibrotic effect, which greatly increases the risk of systemic acidosis caused by metformin overdose. Low-molecular-weight chitosan (LMWC) has natural kidney-targeting properties and good biocompatibility and degradability. Thus, we synthesized a novel carrier metformin-grafted chitosan (CS-MET) based on an imine reaction between oxidized chitosan and metformin. Then, GFP was recruited to form GFP-loaded CS-MET nanoparticles (CS-MET/GFP NPs) with controllable particle size. We hypothesized that CS-MET/GFP NPs would enrich in the kidney and be absorbed by HK-2 cells via megalin-mediated endocytosis by intravenous injection, which may avoid systemic acidosis caused by metformin overdose. Subsequently, the nanoparticle ruptures and releases metformin to exert its anti-apoptotic, anti-inflammatory, and anti-fibrotic effects. Our results showed that CS-MET/GFP NPs have great transfection efficiency and could enter HK-2 cells mainly through megalin-mediated endocytosis. Compared to the free metformin, CS-MET/GFP NPs showed similar anti-apoptotic ability but better therapeutic effects on cellular inflammation and fibrosis in vitro. On the other hand, CS-MET/GFP NPs showed great kidney-targeting ability and superior anti-apoptotic, anti-inflammatory, and anti-fibrotic effects in vivo.

AMPK agonist alleviate renal tubulointerstitial fibrosis via activating mitophagy in high fat and streptozotocin induced diabetic mice

Renal tubulointerstitial fibrosis was a crucial pathological feature of diabetic nephropathy (DN), and renal tubular injury might associate with abnormal mitophagy. In this study, we investigated the effects and molecular mechanisms of AMPK agonist metformin on mitophagy and cellular injury in renal tubular cell under diabetic condition. The high fat diet (HFD) and streptozotocin (STZ)-induced type 2 diabetic mice model and HK-2 cells were used in this study. Metformin was administered in the drinking water (200 mg/kg/d) for 24 weeks. Renal tubulointerstitial lesions, oxidative stress and some indicators of mitophagy (e.g., LC3II, Pink1, and Parkin) were examined both in renal tissue and HK-2 cells. Additionally, compound C (an AMPK inhibitor) and Pink1 siRNA were applied to explore the molecular regulation mechanism of metformin on mitophagy. We found that the expression of p-AMPK, Pink1, Parkin, LC3II, and Atg5 in renal tissue of diabetic mice was decreased obviously. Metformin reduced the levels of serum creatinine, urine protein, and attenuated renal oxidative injury and fibrosis in HFD/STZ induced diabetic mice. In addition, Metformin reversed mitophagy dysfunction and the over-expression of NLRP3. In vitro pretreatment of HK-2 cells with AMPK inhibitor compound C or Pink1 siRNA negated the beneficial effects of metformin. Furthermore, we noted that metformin activated p-AMPK and promoted the translocation of Pink1 from the cytoplasm to mitochondria, then promoted the occurrence of mitophagy in HK-2 cells under HG/HFA ambience. Our results suggested for the first time that AMPK agonist metformin ameliorated renal oxidative stress and tubulointerstitial fibrosis in HFD/STZ-induced diabetic mice via activating mitophagy through a p-AMPK-Pink1-Parkin pathway.

Metformin Attenuates Silica-Induced Pulmonary Fibrosis by Activating Autophagy via the AMPK-mTOR Signaling Pathway

Long-term exposure to crystalline silica particles leads to silicosis characterized by persistent inflammation and progressive fibrosis in the lung. So far, there is no specific treatment to cure the disease other than supportive care. In this study, we examined the effects of metformin, a prescribed drug for type || diabetes on silicosis and explored the possible mechanisms in an established rat silicosis model in vivo, and an in vitro co-cultured model containing human macrophages cells (THP-1) and human bronchial epithelial cells (HBEC). Our results showed that metformin significantly alleviated the inflammation and fibrosis of lung tissues of rats exposed to silica particles. Metformin significantly reduced silica particle-induced inflammatory cytokines including transforming growth factor-β1 (TGF-β1), tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in rat lung tissue and HBEC culture supernatant. The protein levels of Vimentin and α-smooth muscle actin (α-SMA) were significantly decreased by metfomin while expression level of E-cadherin (E-Cad) increased. Besides, metformin increased the expression levels of phosphorylated adenosine 5′-monophosphate (AMP)-activated protein kinase (p-AMPK), microtubule-associated protein (MAP) light chain 3B (LC3B) and Beclin1 proteins, and reduced levels of phosphorylated mammalian target of rapamycin (p-mTOR) and p62 proteins in vivo and in vitro. These results suggest that metformin could inhibit silica-induced pulmonary fibrosis by activating autophagy through the AMPK-mTOR pathway.

Metformin and Glaucoma-Review of Anti-Fibrotic Processes and Bioenergetics

Glaucoma is the leading cause of irreversible blindness globally. With an aging population, disease incidence will rise with an enormous societal and economic burden. The treatment strategy revolves around targeting intraocular pressure, the principle modifiable risk factor, to slow progression of disease. However, there is a clear unmet clinical need to find a novel therapeutic approach that targets and halts the retinal ganglion cell (RGC) degeneration that occurs with fibrosis. RGCs are highly sensitive to metabolic fluctuations as a result of multiple stressors and thus their viability depends on healthy mitochondrial functioning. Metformin, known for its use in type 2 diabetes, has come to the forefront of medical research in multiple organ systems. Its use was recently associated with a 25% reduced risk of glaucoma in a large population study. Here, we discuss its application to glaucoma therapy, highlighting its effect on fibrotic signalling pathways, mitochondrial bioenergetics and NAD oxidation.

miRNA-130b-5p promotes hepatic stellate cell activation and the development of liver fibrosis by suppressing SIRT4 expression

Liver fibrosis is a progressive disease accompanied by the deposition of extracellular matrix (ECM). Numerous reports have demonstrated that alterations in the expression of microRNAs (miRNAs) are related to liver disease. However, the effect of individual miRNAs on liver fibrosis has not been studied. Hepatic stellate cells (HSCs), being responsible for producing ECM, exert an important influence on liver fibrosis. Then, microarray analysis of non-activated and activated HSCs induced by transforming growth factor β1 (TGF-β1) showed that miR-130b-5p expression was strongly up-regulated during HSC activation. Moreover, the progression of liver fibrosis had a close connection with the expression of miR-130b-5p in different liver fibrosis mouse models. Then, we identified that there were specific binding sites between miR-130b-5p and the 3' UTR of Sirtuin 4 (SIRT4) via a luciferase reporter assay. Knockdown of miR-130b-5p increased SIRT4 expression and ameliorated liver fibrosis in mice transfected with antagomiR-130b-5p oligos. In general, our results suggested that miR-130b-5p promoted HSC activation by targeting SIRT4, which participates in the AMPK/TGF-β/Smad2/3 signalling pathway. Hence, regulating miR-130b-5p maybe serve as a crucial therapeutic treatment for hepatic fibrosis.

Pharmacological activation of SIRT1 by metformin prevented trauma-induced heterotopic ossification through inhibiting macrophage mediated inflammation

Trauma-induced heterotopic ossification (HO) is the aberrant extra-skeletal bone formation that severely incapacitates patient's daily life. Inflammation is the first stage of this progression, becoming an appealing target of early therapeutic intervention. Metformin, a widely used antidiabetic drug, also poses the therapeutic potential to modulate various inflammatory-related diseases. Therefore, this study aimed to investigate the preventive effect of metformin on trauma-induced HO progression, and unveil the underlying molecular mechanisms. A murine burn/tenotomy model was established to mimic trauma-induced HO in vivo. The anti-inflammation and anti-ossification effects of metformin were evaluated by histological staining and micro-CT. The inhibitory effects of metformin on macrophages activation in vitro were examined by ELISA and qRT-PCR. The underlying molecular mechanisms were further explored by immunofluorescence staining and western-blotting in vivo. Increased macrophages infiltration and inflammatory responses were found at early stage during HO progression. However, metformin dose-dependently attenuated the macrophage-mediated inflammatory responses both in vivo and vitro, which might account for the inhibitory effect of metformin on chondrogenesis and HO formation after trauma. Furthermore, elevated SIRT1 expression and decreased NF-κB p65 acetylation were found in the beneficial effects of metformin. Moreover, similar preventive effects were also found in SRT1720 HCI, a specific SIRT1 activator, while were remarkably reversed after the administration of EX527 (a specific SIRT1 inhibitor) with metformin. Taken together, our results provide a novel evidence that metformin can effectively attenuate trauma-induced HO by mitigating macrophage inflammatory responses through inhibiting NF-κB signaling via SIRT1-dependent mechanisms, which favors future therapeutic investigations for trauma-related disease.

Sustained In Vitro and In Vivo Delivery of Metformin from Plant Pollen-Derived Composite Microcapsules

We developed a dual microencapsulation platform for the type 2 diabetes drug metformin (MTF), which is aimed to increase its bioavailability. We report the use of Lycopodium clavatum sporopollenin (LCS), derived from their natural spores, and raw Phoenix dactylifera L. (date palm) pollens (DPP) for MTF microencapsulation. MTF was loaded into LCS and DPP via a vacuum and a novel method of hydration-induced swelling. The loading capacity (LC) and encapsulation efficiency (EE) percentages for MTF-loaded LCS and MTF-loaded DPP microcapsules were 14.9% ± 0.7, 29.8 ± 0.8, and 15.2% ± 0.7, 30.3 ± 1.0, respectively. The release of MTF from MTF-loaded LCS microcapsules was additionally controlled by re-encapsulating the loaded microcapsules into calcium alginate (ALG) microbeads via ionotropic gelation, where the release of MTF was found to be significantly slower and pH-dependent. The pharmacokinetic parameters, obtained from the in vivo study, revealed that the relative bioavailability of the MTF-loaded LCS-ALG beads was 1.215 times higher compared to pure MTF, following oral administration of a single dose equivalent to 25 mg/kg body weight MTF to streptozotocin (STZ)-induced diabetic male Sprague-Dawley rats. Significant hypoglycemic effect was obtained for STZ-induced diabetic rats orally treated with MTF-loaded LCS-ALG beads compared to control diabetic rats. Over a period of 29 days, the STZ-induced diabetic rats treated with MTF-loaded LCS-ALG beads showed a decrease in the aspartate aminotransferase (AST), alanine aminotransferase (ALT), triglycerides, cholesterol, and low-density lipoprotein-cholesterol (LDL-C) levels, as well as an increase in glutathione peroxidase (GPx) and a recovery in the oxidative stress biomarker, lipid peroxidation (LPx). In addition, histopathological studies of liver, pancreas, kidney, and testes suggested that MTF-loaded LCS-ALG beads improved the degenerative changes in organs of diabetic rats. The LCS-ALG platform for dual encapsulation of MTF achieved sustained MTF delivery and enhancement of bioavailability, as well as the improved biochemical and histopathological characteristics in in vivo studies, opening many other intriguing applications in sustained drug delivery.

Chloride channel accessory 1 integrates chloride channel activity and mTORC1 in aging-related kidney injury

The mechanism of kidney injury in aging are not well understood. In order to identify hitherto unknown pathways of aging‐related kidney injury, we performed RNA‐Seq on kidney extracts of young and aged mice. Expression of chloride (Cl) channel accessory 1 (CLCA1) mRNA and protein was increased in the kidneys of aged mice. Immunostaining showed a marked increase in CLCLA1 expression in the proximal tubules of the kidney from aged mice. Increased kidney CLCA1 gene expression also correlated with aging in marmosets and in a human cohort. In aging mice, increased renal cortical CLCA1 content was associated with hydrogen sulfide (H₂S) deficiency, which was ameliorated by administering sodium hydrosulfide (NaHS), a source of H₂S. In order to study whether increased CLCA1 expression leads to injury phenotype and the mechanisms involved, stable transfection of proximal tubule epithelial cells overexpressing human CLCA1 (hCLCA1) was performed. Overexpression of hCLCA1 augmented Cl⁻ current via the Ca⁺⁺‐dependent Cl⁻ channel TMEM16A (anoctamin‐1) by patch‐clamp studies. hCLCA1 overexpression also increased the expression of fibronectin, a matrix protein, and induced the senescence‐associated secretory phenotype (SASP). Mechanistic studies underlying these changes showed that hCLCA1 overexpression leads to inhibition of AMPK activity and stimulation of mTORC1 as cellular signaling determinants of injury. Both TMEM16A inhibitor and NaHS reversed these signaling events and prevented changes in fibronectin and SASP. We conclude that CLCA1‐TMEM16A‐Cl⁻ current pathway is a novel mediator of kidney injury in aging that is regulated by endogenous H₂S.

The Effect of Metformin in Diabetic and Non-Diabetic Rats with Experimentally-Induced Chronic Kidney Disease

This work aimed to investigate whether treatment with the antidiabetic drug metformin would affect adenine-induced chronic kidney disease (CKD) in non-diabetic rats and rats with streptozotocin (STZ)-induced diabetes. Rats were randomly divided into eight groups, and given either normal feed, or feed mixed with adenine (0.25% w/w, for five weeks) to induce CKD. Some of these groups were also simultaneously treated orally with metformin (200 mg/kg/day). Rats given adenine showed the typical signs of CKD that included detrimental changes in several physiological and traditional and novel biochemical biomarkers in plasma urine and kidney homogenates such as albumin/creatinine ratio, N-acetyl-beta-D-glucosaminidase, neutrophil gelatinase-associated lipocalin, 8-isoprostane, adiponectin, cystatin C, as well as plasma urea, creatinine, uric acid, indoxyl sulfate, calcium, and phosphorus. Several indices of inflammation and oxidative stress, and renal nuclear factor-κB and nuclear factor erythroid 2-related factor 2 levels were also measured. Histopathologically, adenine caused renal tubular necrosis and fibrosis. The activation of the intracellular mitogen-activated protein kinase signaling pathway was inhibited in the groups that received metformin and STZ together, with or without adenine induced-CKD. Induction of diabetes worsened most of the actions induced by adenine. Metformin significantly ameliorated the renal actions induced by adenine and STZ when these were given singly, and more so when given together. The results suggest that metformin can be a useful drug in attenuating the progression of CKD in both diabetic and non-diabetic rats.

1,25-(OH)2D3 ameliorates renal interstitial fibrosis in UUO rats through the AMPKα/mTOR pathway

Objective

To investigate the effects of 1,25(OH)₂D₃ on renal fibrosis associated with the AMP-activated protein kinase (AMPK)α/mechanistic target of rapamycin (mTOR) signalling pathway in a rat model of unilateral ureteral obstruction (UUO).

Methods

A total of 54 male Sprague Dawley rats were randomly divided into three groups: sham-operation group, UUO group, and UUO plus calcitriol (3 ng/100 g) group. Renal tissue was excised for histological examination by immunohistochemistry and Western blot, and for gene expression analysis using real-time polymerase chain reaction.

Results

1,25(OH)₂D₃ enhanced AMPKα levels, inhibited mTOR levels and slowed the development of interstitial fibrosis in kidney tissue. Compared with the UUO plus calcitriol group, UUO rats demonstrated more severe renal damage characterized by marked tubular atrophy, interstitial fibrosis and significant induction of fibrogenic transforming growth factor-β1 and increased extra-cellular matrix proteins (α-smooth muscle actin and collagen type III), and decreased E-cadherin.

Conclusion

Treatment with 1,25(OH)₂D₃ altered the AMPKα/mTOR signalling pathway to suppress excessive fibroblast activation observed in UUO rats. This may serve as a novel mechanism to ameliorate renal dysfunction and fibrotic lesions.

Cellular senescence and the senescence-associated secretory phenotype: Potential therapeutic targets for renal fibrosis

Renal fibrosis plays a crucial role in the progression of chronic kidney disease and end-stage renal disease. However, because the aetiology of this pathological process is complex and remains unclear, there is still no effective treatment. Cellular senescence and the senescence-associated secretory phenotype (SASP) have been reported to lead to renal fibrosis. This review first discusses the relationships among cellular senescence, the SASP and renal fibrosis. Then, the key role of the SASP in irreversible renal fibrosis, including fibroblast activation and abnormal extracellular matrix accumulation, is discussed, with the results of studies having indicated that inhibiting cellular senescence and the SASP might be a potential preventive and therapeutic strategy for renal fibrosis. Finally, we summarize promising therapeutic strategies revealed by existing research on senescent cells and the SASP, including emerging interventions targeting the SASP, caloric restriction and mimetics, and novel regeneration therapies with stem cells.

Use of Anti-Diabetic Agents in Non-Diabetic Kidney Disease: From Bench to Bedside

New drugs were recently developed to treat hyperglycemia in patients with type 2 diabetes mellitus (T2D). However, metformin remains the first-line anti-diabetic agent because of its cost-effectiveness. It has pleiotropic action that produces cardiovascular benefits, and it can be useful in diabetic nephropathy, although metformin-associated lactic acidosis is a hindrance to its use in patients with kidney failure. New anti-diabetic agents, including glucagon-like peptide-1 receptor (GLP-1R) agonists, dipeptidyl peptidase-4 (DPP-4) inhibitors, and sodium-glucose transporter-2 (SGLT-2) inhibitors, also produce cardiovascular or renal benefits in T2D patients. Their glucose-independent beneficial actions can lead to cardiorenal protection via hemodynamic stabilization and inflammatory modulation. Systemic hypertension is relieved by natriuresis and improved vascular dysfunction. Enhanced tubuloglomerular feedback can be restored by SGLT-2 inhibition, reducing glomerular hypertension. Patients with non-diabetic kidney disease might also benefit from those drugs because hypertension, proteinuria, oxidative stress, and inflammation are common factors in the progression of kidney disease, irrespective of the presence of diabetes. In various animal models of non-diabetic kidney disease, metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors were favorable to kidney morphology and function. They strikingly attenuated biomarkers of oxidative stress and inflammatory responses in diseased kidneys. However, whether those animal results translate to patients with non-diabetic kidney disease has yet to be evaluated. Considering the paucity of new agents to treat kidney disease and the minimal adverse effects of metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors, these anti-diabetic agents could be used in patients with non-diabetic kidney disease. This paper provides a rationale for clinical trials that apply metformin, GLP-1R agonists, DPP-4 inhibitors, and SGLT-2 inhibitors to non-diabetic kidney disease.

Towards Better Drug Repositioning: Targeted Immunoinflammatory Therapy for Diabetic Nephropathy

Diabetic nephropathy (DN) is one of the most common and important microvascular complications of diabetes mellitus (DM). The main clinical features of DN are proteinuria and a progressive decline in renal function, which are associated with structural and functional changes in the kidney. The pathogenesis of DN is multifactorial, including genetic, metabolic, and haemodynamic factors, which can trigger a sequence of events. Controlling metabolic risks such as hyperglycaemia, hypertension, and dyslipidaemia is not enough to slow the progression of DN. Recent studies emphasized immunoinflammation as a critical pathogenic factor in the progression of DN. Therefore, targeting inflammation is considered a potential and novel treatment strategy for DN. In this review, we will briefly introduce the inflammatory process of DN and discuss the anti-inflammatory effects of antidiabetic drugs when treating DN.

Targeting immune cell metabolism in kidney diseases

Insights into the relationship between immunometabolism and inflammation have enabled the targeting of several immunity-mediated inflammatory processes that underlie infectious diseases and cancer or drive transplant rejection, but this field remains largely unexplored in kidney diseases. The kidneys comprise heterogeneous cell populations, contain distinct microenvironments such as areas of hypoxia and hypersalinity, and are responsible for a functional triad of filtration, reabsorption and secretion. These distinctive features create myriad potential metabolic therapeutic targets in the kidney. Immune cells have crucial roles in the maintenance of kidney homeostasis and in the response to kidney injury, and their function is intricately connected to their metabolic properties. Changes in nutrient availability and biomolecules, such as cytokines, growth factors and hormones, initiate cellular signalling events that involve energy-sensing molecules and other metabolism-related proteins to coordinate immune cell differentiation, activation and function. Disruption of homeostasis promptly triggers the metabolic reorganization of kidney immune and non-immune cells, which can promote inflammation and tissue damage. The metabolic differences between kidney and immune cells offer an opportunity to specifically target immunometabolism in the kidney.

Metformin ameliorates the severity of experimental Alport syndrome

Metformin is widely used for the treatment of type 2 diabetes, and increasing numbers of studies have shown that metformin also ameliorates tumor progression, inflammatory disease, and fibrosis. However, the ability of metformin to improve non-diabetic glomerular disease and chronic kidney disease (CKD) has not been explored. To investigate the effect of metformin on non-diabetic glomerular disease, we used a mouse model of Alport syndrome (Col4a5 G5X) which were treated with metformin or losartan, used as a control treatment. We also investigated the effect of metformin on adriamycin-induced glomerulosclerosis model. Pathological and biochemical analysis showed that metformin or losartan suppressed proteinuria, renal inflammation, fibrosis, and glomerular injury and extended the lifespan in Alport syndrome mice. Transcriptome analysis showed that metformin and losartan influenced molecular pathways-related to metabolism and inflammation. Metformin altered multiple genes including metabolic genes not affected by losartan. Metformin also suppressed proteinuria and glomerular injury in the adriamycin-induced glomerulosclerosis mouse model. Our results showed that metformin ameliorates the glomerular sclerosis and CKD phenotype in non-diabetic chronic glomerular diseases. Metformin may have therapeutic potential for not only diabetic nephropathy but also non-diabetic glomerular disease including Alport syndrome.

The Current and Potential Therapeutic Use of Metformin-The Good Old Drug

Metformin, one of the oldest oral antidiabetic agents and still recommended by almost all current guidelines as the first-line treatment for type 2 diabetes mellitus (T2DM), has become the medication with steadily increasing potential therapeutic indications. A broad spectrum of experimental and clinical studies showed that metformin has a pleiotropic activity and favorable effect in different pathological conditions, including prediabetes, type 1 diabetes mellitus (T1DM) and gestational diabetes mellitus (GDM). Moreover, there are numerous studies, meta-analyses and population studies indicating that metformin is safe and well tolerated and may be associated with cardioprotective and nephroprotective effect. Recently, it has also been reported in some studies, but not all, that metformin, besides improvement of glucose homeostasis, may possibly reduce the risk of cancer development, inhibit the incidence of neurodegenerative disease and prolong the lifespan. This paper presents some arguments supporting the initiation of metformin in patients with newly diagnosed T2DM, especially those without cardiovascular risk factors or without established cardiovascular disease or advanced kidney insufficiency at the time of new guidelines favoring new drugs with pleotropic effects complimentary to glucose control. Moreover, it focuses on the potential beneficial effects of metformin in patients with T2DM and coexisting chronic diseases.

Metformin Attenuates Renal Fibrosis in a Mouse Model of Adenine-Induced Renal Injury Through Inhibiting TGF-β1 Signaling Pathways

It is well-known that all progressive chronic kidney disease (CKD) is pathologically characterized by tubulointerstitial fibrosis process. Multiple studies have shown the critical role of inflammation and fibrosis in the development of CKD. Hence strategies that target inflammatory and fibrotic signaling pathways may provide promising opportunities to protect against renal fibrosis. Metformin has been used as the first-line glucose-lowering agent to treat patients with type 2 diabetes mellitus (T2DM) for over 50 years. Accumulating evidence suggests the potential for additional therapeutic applications of metformin, including mitigation of renal fibrosis. In this study, the anti-fibrotic effects of metformin independent of its glucose-lowering mechanism were examined in an adenine -induced mouse model of CKD. Expressions of inflammatory markers MCP-1, F4/80 and ICAM, fibrotic markers type IV collagen and fibronectin, and the cytokine TGF-β1 were increased in adenine-induced CKD when compared to control groups and significantly attenuated by metformin treatment. Moreover, treatment with metformin inhibited the phosphorylation of Smad3, ERK1/2, and P38 and was associated with activation of the AMP-activated protein kinase (AMPK) in the kidneys of adenine-treated mice. These results indicate that metformin attenuates adenine-induced renal fibrosis through inhibition of TGF-β1 signaling pathways and activation of AMPK, independent of its glucose-lowering action.

Metformin inhibits chronic kidney disease-induced DNA damage and senescence of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are promising source of cell‐based regenerative therapy. In consideration of the risk of allosensitization, autologous MSC‐based therapy is preferred over allogenic transplantation in patients with chronic kidney disease (CKD). However, it remains uncertain whether adequate cell functionality is maintained under uremic conditions. As chronic inflammation and oxidative stress in CKD may lead to the accumulation of senescent cells, we investigated cellular senescence of CKD MSCs and determined the effects of metformin on CKD‐associated cellular senescence in bone marrow MSCs from sham‐operated and subtotal nephrectomized mice and further explored in adipose tissue‐derived MSCs from healthy kidney donors and patients with CKD. CKD MSCs showed reduced proliferation, accelerated senescence, and increased DNA damage as compared to control MSCs. These changes were significantly attenuated following metformin treatment. Lipopolysaccharide and transforming growth factor β1‐treated HK2 cells showed lower tubular expression of proinflammatory and fibrogenesis markers upon co‐culture with metformin‐treated CKD MSCs than with untreated CKD MSCs, suggestive of enhanced paracrine action of CKD MSCs mediated by metformin. In unilateral ureteral obstruction kidneys, metformin‐treated CKD MSCs more effectively attenuated inflammation and fibrosis as compared to untreated CKD MSCs. Thus, metformin preconditioning may exhibit a therapeutic benefit by targeting accelerated senescence of CKD MSCs.

Metformin: A Novel Weapon Against Inflammation

It has become widely accepted that inflammation is a driving force behind a variety of chronic diseases, such as cardiovascular disease, diabetes, kidney disease, cancer, neurodegenerative disorders, etc. However, the existing nonsteroidal anti-inflammatory drugs show a limited utility in clinical patients. Therefore, the novel agents with different inflammation-inhibitory mechanisms are worth pursuing. Metformin, a synthetic derivative of guanidine, has a history of more than 50 years of clinical experience in treating patients with type 2 diabetes. Intense research efforts have been dedicated to proving metformin’s inflammation-inhibitory effects in cells, animal models, patient records, and randomized clinical trials. The emerging evidence also indicates its therapeutic potential in clinical domains other than type 2 diabetes. Herein, this article appraises current pre-clinical and clinical findings, emphasizing metformin’s anti-inflammatory properties under individual pathophysiological scenarios. In summary, the anti-inflammatory effects of metformin are evident in pre-clinical models. By comparison, there are still clinical perplexities to be addressed in repurposing metformin to inflammation-driven chronic diseases. Future randomized controlled trials, incorporating better stratification/targeting, would establish metformin’s utility in this clinical setting.

Targeting energy pathways in kidney disease: the roles of sirtuins, AMPK, and PGC1α

The kidney has extraordinary metabolic demands to sustain the active transport of solutes that is critical to renal filtration and clearance. Mitochondrial health is vital to meet those demands and maintain renal fitness. Decades of studies have linked poor mitochondrial health to kidney disease. Key regulators of mitochondrial health-adenosine monophosphate kinase, sirtuins, and peroxisome proliferator-activated receptor γ coactivator-1α-have all been shown to play significant roles in renal resilience against disease. This review will summarize the latest research into the activities of those regulators and evaluate the roles and therapeutic potential of targeting those regulators in acute kidney injury, glomerular kidney disease, and renal fibrosis.

Role of the CTRP6/AMPK pathway in kidney fibrosis through the promotion of fatty acid oxidation

CTRP6, a newly identified adiponectin analogue, has been shown to be involved in inflammation, diabetes and cardiovascular diseases. Recently, increasing evidence has shown that CTRP6 plays a critical role in fibrotic diseases, such as myocardial fibrosis and skin fibrosis. FAO, an important energy source for kidney proximal tubular cells, also participates in the process of fibrosis. Therefore, our study aimed to investigate the effect of CTRP6 on mediating FAO in kidney fibrosis and the underlying associated mechanism. Firstly, the activity of CTRP6 and the key enzymes of FAO (CPT1A, ACOX1) were tested in vivo and vitro. Next, the regulatory effect of CTRP6/AMPK on FAO was accessed in animal models and in cell lines. Additionally, we explored the effect of exogenous recombinant CTRP6 on renal tubular epithelial cell differentiation. Decreased CTRP6 and p-AMPK were detected in UUO-induced kidney fibrosis and in TGF-β1-treated HK-2 cells. We also observed that defective FAO occurred during kidney fibrosis. Moreover, the human CTRP6 peptide could inhibit the ECM deposition and promote the phosphorylation of AMPK by promoting FAO. However, the inhibitory effects of CTRP6 on TGF-β1-induced ECM deposition and the protective effects of CTRP6 on FAO could be abolished by compound C, a selective inhibitor of AMPK. Compound C also reversed the CTRP6-mediated upregulation of p-AMPK. The mediation of FAO by CTRP6 plays a key role in kidney fibrosis by regulating TGF-β1-induced renal tubular epithelial cell differentiation by promoting FAO, which is mediated via AMPK activation.

Design, fabrication, and optimization of a dual function three-layer scaffold for controlled release of metformin hydrochloride to alleviate fibrosis and accelerate wound healing

Abnormal wound healing caused by the over-expression of collagen and fibronectin leads to fibrosis, the major complication of all treatment modalities. A three-layer nanofiber scaffold was designed, optimized, and fabricated. This scaffold comprised two supportive polycaprolactone (PCL)-chitosan layers on the sides and a polyvinyl alcohol (PVA)-metformin hydrochloride (metformin-HCl) in the middle. The physico-chemical properties of scaffold, such as mechanical characteristics, degradation, swelling, and in-vitro drug release, were evaluated. The biological tests, including cell viability in response to metformin-HCl and Tween 80, scaffold biocompatibility, cell attachment, and antibacterial activity, were further conducted. The wound healing effect of scaffold loaded with metformin-HCl (MSc+Met) was assessed in donut-shaped silicone splints in rats. Histopathological and immunohistochemical evaluation as well as mRNA expression levels of fibrosis markers were also studied. SEM images indicated a uniform, bead-less morphology and high porosity. Surface modification of scaffold by Tween 80 improved the surface hydrophilicity and enhanced the adhesion and proliferation of fibroblasts. The scar area on day 15 in MSc+Met was significantly lower than that of other groups. Histopathological and immunohistochemical evaluation revealed that group MSc+Met was the best, having significantly lower inflammation, higher angiogenesis, the smallest scar width and depth, maximum epitheliogenesis score, and the most optimal modulation of collagen density. Local administration of metformin-HCl substantially down-regulated the expression of fibrosis-involved genes: transforming growth factor (TGF-β1), collagen type 1 (Col-I), fibronectin, collagen type 3 (Col-III), and alpha-smooth muscle actin (α-SMA). Inhibiting these genes alleviates scar formation but delays wound healing; thus, an engineered scaffold was used to prevent delay in wound healing. These results provided evidence for the first time to introduce an anti-fibrogenic slow-releasing scaffold, which acts in a dual role, both alleviating fibrosis and accelerating wound healing.

Metformin attenuates renal interstitial fibrosis through upregulation of Deptor in unilateral ureteral obstruction in rats

Renal interstitial fibrosis (RIF) is a common pathological process that accompanies chronic kidney disease (CKD) and that progresses to end-stage renal failure (ESRD). Accumulating evidence has revealed that persistent mammalian target of rapamycin (mTOR) activation in kidneys is closely associated with the occurrence and progression of CKD. The DEP domain-containing mTOR interacting protein (Deptor) is an endogenous negative regulator of mTOR. Metformin can attenuate renal fibrosis in an animal model of diabetic nephropathy. Previous studies demonstrated that metformin can attenuate renal fibrosis in several models of CKD. However, the precise mechanisms of this effect are not well understood. The present study aimed to examine the mechanism of action of metformin on unilateral ureteral obstruction (UUO)-induced RIF in rats in vivo. Sprague-Dawley rats were randomly divided into a sham-operated group, three UUO groups examined at different time points (3, 7 and 14 days after UUO surgery), and three metformin-treated groups, treated with three different concentrations of metformin. The metformin-treated groups were administered metformin orally every day for 14 consecutive days following surgery. The protein expression levels of Deptor, α-smooth muscle actin (α-SMA), phosphorylated (p-)mTOR, p-ribosomal protein S6 kinase (p-p70S6K) and CD68 were assessed. The present results suggested that, following UUO, there was a significant reduction of Deptor expression, and an increase in collagen deposition in the extracellular matrix over time, accompanied by an increased expression of several proteins including CD68, α-SMA, p-mTOR and p-p70S6K. Notably, metformin treatment reversed these effects. In conclusion, the present results suggested that metformin attenuated RIF of UUO rats, and the mechanism of action was found to be associated with the increase in Deptor expression and inhibition of the mTOR/p70S6K pathway in the kidneys of UUO rats.

Endothelin converting enzyme-1 (ECE-1) deletion in association with Endothelin-1 downregulation ameliorates kidney fibrosis in mice

Kidney fibrosis is a common final pathway of chronic kidney diseases, which are characterized by renal architecture damage, inflammation, fibroblast expansion and myofibroblast formation. Endothelin converting enzyme-1 (ECE-1) contributes to activation of Endothelin-1 (ET-1), a potent vasoconstrictor and pro-fibrotic substance. This study elucidated the effect of ECE-1 knockout in kidney fibrosis model in mice in association of ET-1 downregulation. Kidney fibrosis was performed in ECE-1 knockout (ECE-1 KO) and vascular endothelial derived ET-1 KO (VEETKO) mice (2 months, 20-30 g, n = 30) and their wild type (WT) littermates using unilateral ureteral obstruction (UUO) procedure. Mice were euthanized on day-7 and day-14 after UUO. Histopathological analysis was conducted for fibrosis and tubular injury. Immunostainings were done to quantify macrophages (F4/80), fibroblasts (FSP-1) and myofibroblasts (α-SMA). Monocyte Chemoattractant Protein-1 (MCP-1), ECE-1 and preproET-1 (ppET-1) mRNA expression were quantified with qRT-PCR, while Transforming Growth Factor-β1 (TGF-β1) and α-SMA protein level were quantified with Western blot. ECE-1 KO mice demonstrated reduction of ECE-1 and ppET-1 mRNA expression, attenuation of kidney fibrosis, tubular injury, MCP-1 mRNA expression and macrophage number compared to WT. Double immunostaining revealed fibroblast to myofibroblast formation after UUO, while ECE-1 KO mice had significantly lower fibroblast number and myofibroblast formation compared to WT, which were associated with significantly lower TGF-β1 and α-SMA protein levels in day-14 of UUO. VEETKO mice also demonstrated attenuation of ET-1 protein level, fibrosis and myofibroblast formation. In conclusion, ECE-1 knockout and ET-1 downregulation attenuated kidney fibrosis.

Metformin effectively treats Tsc1 deletion-caused kidney pathology by upregulating AMPK phosphorylation

Tuberous sclerosis complex (TSC) is characterized by hamartomatous lesions in multiple organs, with most patients developing polycystic kidney disease and leading to a decline of renal function. TSC is caused by loss-of-function mutations in either Tsc1 or Tsc2 gene, but currently, there is no effective treatment for aberrant kidney growth in TSC patients. By generating a renal proximal tubule-specific Tsc1 gene-knockout (Tsc1 ptKO) mouse model, we observed that Tsc1 ptKO mice developed aberrantly enlarged kidneys primarily due to hypertrophy and proliferation of proximal tubule cells, along with some cystogenesis, interstitial inflammation, and fibrosis. Mechanistic studies revealed inhibition of AMP-activated protein kinase (AMPK) phosphorylation at Thr-172 and activation of Akt phosphorylation at Ser-473 and Thr-308. We therefore treated Tsc1 ptKO mice with the AMPK activator, metformin, by daily intraperitoneal injection. Our results indicated that metformin increased the AMPK phosphorylation, but decreased the Akt phosphorylation. These signaling modulations resulted in inhibition of proliferation and induction of apoptosis in the renal proximal tubule cells of Tsc1 ptKO mice. Importantly, metformin treatment effectively prevented aberrant kidney enlargement and cyst growth, inhibited inflammatory response, attenuated interstitial fibrosis, and protected renal function. The effects of metformin were further confirmed by in vitro experiments. In conclusion, this study indicates a potential therapeutic effect of metformin on Tsc1 deletion-induced kidney pathology, although currently metformin is primarily prescribed to treat patients with type 2 diabetes.

Metformin arrests the progression of established kidney disease in the subtotal nephrectomy model of chronic kidney disease

Metformin, an AMP-activated protein kinase (AMPK) activator, has been shown in previous studies to reduce kidney fibrosis in different models of experimental chronic kidney disease (CKD). However, in all of these studies, the administration of metformin was initiated before the establishment of renal disease, which is a condition that does not typically occur in clinical settings. The aim of the present study was to investigate whether the administration of metformin could arrest the progression of established renal disease in a well-recognized model of CKD, the subtotal kidney nephrectomy (Nx) model. Adult male Munich-Wistar rats underwent either Nx or sham operations. After the surgery (30 days), Nx rats that had systolic blood pressures of >170 mmHg and albuminuria levels of >40 mg/24 h were randomized to a no-treatment condition or to a treatment condition with metformin (300 mg·kg−1·day−1) for a period of either 60 or 120 days. After 60 days of treatment, we did not observe any differences in kidney disease parameters between Nx metformin-treated and untreated rats. However, after 120 days, Nx rats that had been treated with metformin displayed significant reductions in albuminuria levels and in markers of renal fibrosis. These effects were independent of any other effects on blood pressure or glycemia. In addition, treatment with metformin was also able to activate kidney AMPK and therefore improve mitochondrial biogenesis. It was concluded that metformin can arrest the progression of established kidney disease in the Nx model, likely via the activation of AMPK.

Metformin alleviates oxidative stress and enhances autophagy in diabetic kidney disease via AMPK/SIRT1-FoxO1 pathway

Metformin, as the basic pharmacological therapy and the first preventive drug in type 2 diabetes mellitus (T2DM), is proved to have potential protection in diabetic kidney disease (DKD). Here, we established a diabetic rat model induced by high-fat diet and low dose streptozotocin, and high glucose cultured rat mesangial cells (RMCs) pre-treated with metformin or transfected with AMPK, SIRT1 and FoxO1 small interfering RNA, and detected oxidative stress and autophagy related factors to explore the molecular mechanisms of metformin on DKD via adenosine monophosphate-activated protein kinase (AMPK)/silent mating type information regulation 2 homolog-1 (sirtuin-1, SIRT1)-Forkhead box protein O1 (FoxO1) pathway. We found that metformin effectively alleviated the disorders of glycolipid metabolism, renal function injury in diabetic rats, and relieved oxidative stress, enhanced autophagy and slowed down abnormal cell proliferation in high glucose cultured RMCs through AMPK/SIRT1-FoxO1 pathway, indicating the protective role of metformin against the pathological process of DKD.

Upregulation of Cortical Renin and Downregulation of Medullary (Pro)Renin Receptor in Unilateral Ureteral Obstruction

Chronic kidney disease (CKD) is characterized by renal dysfunction, which is a common feature of other major diseases, such as hypertension and diabetes. Unilateral ureteral obstruction (UUO) has been used as a model of CKD in experimental animals and consists of total obstruction of one kidney ureter. The UUO decreases renal blood flow, which promotes the synthesis of renin in the juxtaglomerular apparatus, the first step in renin–angiotensin system (RAS) cascade. RAS induces inflammation and remodeling, along with reduced renal function. However, it remains unknown whether intrarenal RAS (iRAS) is activated in early stages of CKD. Our objective was to characterize different iRAS components in the renal cortex and in the medulla in an early phase of UUO. Male C57BL/6 mice (8–12 weeks old) were subjected to UUO in the left kidney, or to sham surgery, and were euthanized after 7 days (n = 5/group). Renal function, renal inflammatory/remodeling processes, and iRAS expression were evaluated. UUO increased plasma creatinine, right renal hypertrophy (9.08 ± 0.31, P < 0.05 vs. Sham), and tubular dilatation in the left kidney cortex (42.42 ± 8.19µm, P < 0.05 vs. Sham). This correlated with the increased mRNA of IL-1β (1.73 ± 0.14, P < 0.01 vs. Sham, a pro-inflammatory cytokine) and TGF-β1 (1.76 ± 0.10, P < 0.001 vs. Sham, a pro-fibrotic marker). In the renal cortex of the left kidney, UUO increased the mRNA and protein levels of renin (in 35% and 28%, respectively, P < 0.05 vs. Sham). UUO decreased mRNA and protein levels for the (pro)renin receptor in the renal medulla (0.67 ± 0.036 and 0.88 ± 0.028, respectively, P < 0.05 vs. Sham). Our results suggest that modulation of iRAS components depends on renal localization and occurs in parallel with remodeling and pro-inflammatory/pro-fibrotic mechanisms.

Metformin inhibits high glucose-induced mesangial cell proliferation, inflammation and ECM expression through the SIRT1-FOXO1-autophagy axis

The aim of this study was to investigate the role of metformin in high glucose-induced mesangial cell proliferation, inflammation and extracellular matrix (ECM) accumulation and to elucidate the underlying mechanism of metformin function. An MTT assay was used to examine rat mesangial cell (RMC) proliferation. The levels of TNF-α, IL-6 and TGF-β in RMCs were determined by ELISA. The protein expression of fibronectin, collagen IV and autophagy-related proteins (Beclin-1, LC3-I and LC3-II) in RMCs was detected using western blot. Fluorescence microscopy analysis was carried out to evaluate RMC autophagy. Our results showed that high glucose-induced RMC proliferation, inflammation and ECM expression, but these effects were markedly reduced by metformin. We confirmed that metformin suppressed high glucose-induced RMC proliferation, inflammation and ECM expression via induction of autophagy. Mechanistic investigation demonstrated an axis of SIRT1-FOXO1 in RMC autophagy. Our data indicated that metformin inhibits high glucose-induced mesangial cell proliferation, inflammation and ECM expression through a SIRT1-FOXO1-autophagy axis.

Absence of the β1 subunit of AMP-activated protein kinase reduces myofibroblast infiltration of the kidneys in early diabetes

Activation of the heterotrimeric energy-sensing kinase AMP-activated protein kinase (AMPK) has been reported to improve experimental diabetic kidney disease. We examined the effect of type 1 diabetes in wild-type (WT) mice and mice lacking the β1 subunit of AMPK (AMPK β1^-/- mice), which have reduced AMPK activity in kidneys and other organs. Diabetes was induced using streptozotocin (STZ) and the animals followed up for 4 weeks. Hyperglycaemia was more severe in diabetic AMPK β1^-/- mice, despite the absence of any difference in serum levels of insulin, adiponectin and leptin. There was no change in AMPK activity in the kidneys of diabetic WT mice by AMPK activity assay, or phosphorylation of either the αT172 activation site on the α catalytic subunit of AMPK or the AMPK-specific phosphosite S79 on acetyl CoA carboxylase 1 (ACC1). Phosphorylation of the inhibitory αS485 site on the α subunit of AMPK was significantly increased in the WT diabetic mice compared to non-diabetic controls. Despite increased plasma glucose levels in the diabetic AMPK β1^-/- mice, there were fewer myofibroblasts in the kidneys compared to diabetic WT mice, as evidenced by reduced α-smooth muscle actin (α-SMA) protein by Western blot, mRNA by qRT-PCR and fewer α-SMA-positive cells by immunohistochemical staining. Albuminuria was also reduced in the AMPK β1^-/- mice. In contrast to previous studies, therefore, myofibroblasts were reduced in the kidneys of AMPK β1^-/- diabetic mice compared to diabetic WT mice, despite increased circulating glucose, suggesting that AMPK can worsen renal fibrosis in type 1 diabetes.

Unilateral Ureteral Obstruction as a Model to Investigate Fibrosis-Attenuating Treatments

Renal fibrosis is the common pathway for most forms of progressive renal disease. The Unilateral Ureteral Obstruction (UUO) model is used to cause renal fibrosis, where the primary feature of UUO is tubular injury as a result of obstructed urine flow. Furthermore, experimental UUO in rodents is believed to mimic human chronic obstructive nephropathy in an accelerated manner. Renal fibrosis is the common pathway for most forms of progressive renal disease. Removing the obstruction may not be sufficient to reverse fibrosis, so an accompanying treatment may be of benefit. In this review, we have done a revision on treatments shown to ameliorate fibrosis in the context of the UUO experimental model. The treatments inhibit the production of fibrotic and inflammatory proteins such as Transforming Growth Factor β1 (TGF-β₁), Tumor Necrosis Factor α (TNF-α), collagen and fibronectin, Heat Shock Protein 47 (HSP47), suppress the proliferation of fibroblasts, prevent epithelial-to-mesenchymal transition, reduce oxidative stress, inhibit the action of the Nuclear Factor κB (NF-κB), reduce the phosphorylation of mothers against decapentaplegic homolog (SMAD) family members 2 and 3 (Smad2/3) or Mitogen-Activated Protein Kinases (MAPKs), inhibit the activation of the renin-angiotensin system. Summaries of the UUO experimental methods and alterations observed in the UUO experiments are included.

Inhibition of class I HDACs attenuates renal interstitial fibrosis in a murine model

Renal interstitial fibrosis is the most common of all the forms of chronic kidney disease (CKD). Research has shown that histone deacetylases (HDACs) participate in the process leading to renal fibrosis. However, the effects of class I HDAC inhibitors on the mechanisms of onset and progression of renal interstitial fibrosis are still unclear. Here, we present the effects and mechanisms of action of FK228 (a selective inhibitor of class I HDACs) in the murine model of unilateral ureteral obstruction (UUO) and in vitro models. We investigated the antifibrotic role of FK228 in a murine model of UUO. We used two key effector cell populations, rat renal interstitial fibroblasts and renal tubular epithelial cells exposed to recombinant transforming growth factor-beta 1 (TGF-β1), to explore the mechanistic pathways among in vitro models. The results indicated that FK228 significantly suppressed the production of extracellular matrix (ECM) in both in vivo and in vitro models. FK228 inhibited renal fibroblast activation and proliferation and increased the acetylation of histone H3. We found that FK228 also inhibited the small mothers against decapentaplegic (Smad) and non-Smad signaling pathways. So FK228 could significantly suppress renal interstitial fibrosis via Smad and non-Smad pathways. FK228 may be the basis for a new and effective medicine for alleviating renal fibrosis in the future.

Metformin prevents nephrolithiasis formation by inhibiting the expression of OPN and MCP-1 in vitro and in vivo

Treatment targeting osteopontin (OPN) and monocyte chemoattractant protein 1 (MCP-1) has been recognized as a novel approach in renal crystal formation. The present study was designed to investigate the suppressive effects of metformin on nephrolithiasis formation and its potential mechanism. The cytotoxicity of metformin on MDCK and HK-2 cells was determined using a Cell Counting Kit-8 assay in vitro. Subsequently, the mRNA transcription and protein expression levels of MCP-1 and OPN were detected by reverse transcription-quantitative-polymerase chain reaction analysis, western blot analysis and ELISA. Male Sprague-Dawley rats were divided into a control group, ethylene glycol (EG) group and EG + metformin group. The expression levels of MCP-1 and OPN and crystal formations were evaluated in renal tissues following an 8-week treatment period. In vitro, metformin significantly inhibited the production of MCP-1 and OPN induced by oxalate at the mRNA and protein expression levels. In vivo, increased expression levels of MCP-1 and OPN were detected in the EG group compared with the controls, and this upregulation was reversed in the EG + metformin group. Renal crystal deposition in the EG + metformin group was markedly decreased compared with that in the EG group. Therefore, the results of the study suggest that metformin suppressed urinary crystal deposit formation, possibly by mediating the expression of inflammatory mediators OPN and MCP-1.

Metformin: A Candidate Drug for Renal Diseases

Over the past decades metformin has been the optimal first-line treatment for type 2 diabetes mellitus (T2DM). Only in the last few years, it has become increasingly clear that metformin exerts benign pleiotropic actions beyond its prescribed use and ongoing investigations focus on a putative beneficial impact of metformin on the kidney. Both acute kidney injury (AKI) and chronic kidney disease (CKD), two major renal health issues, often result in the need for renal replacement therapy (dialysis or transplantation) with a high socio-economic impact for the patients. Unfortunately, to date, effective treatment directly targeting the kidney is lacking. Metformin has been shown to exert beneficial effects on the kidney in various clinical trials and experimental studies performed in divergent rodent models representing different types of renal diseases going from AKI to CKD. Despite growing evidence on metformin as a candidate drug for renal diseases, in-depth research is imperative to unravel the molecular signaling pathways responsible for metformin's renoprotective actions. This review will discuss the current state-of-the-art literature on clinical and preclinical data, and put forward potential cellular mechanisms and molecular pathways by which metformin ameliorates AKI/CKD.

Metformin use in the first year after kidney transplant, correlates, and associated outcomes in diabetic transplant recipients: A retrospective analysis of integrated registry and pharmacy claims data

While guidelines support metformin as a therapeutic option for diabetic patients with mild-to-moderate renal insufficiency, the frequency and outcomes of metformin use in kidney transplant recipients are not well described. We integrated national U.S. transplant registry data with records from a large pharmaceutical claims clearinghouse (2008-2015). Associations (adjusted hazard ratio, 95% LCL aHR95% UCL ) of diabetes regimens (with and excluding metformin) in the first year post-transplant with patient and graft survival over the subsequent year were quantified by multivariate Cox regression, adjusted for recipient, donor, and transplant factors and propensity for metformin use. Among 14 144 recipients with pretransplant type 2 diabetes mellitus, 4.7% filled metformin in the first year post-transplant; most also received diabetes comedications. Compared to those who received insulin-based regimens without metformin, patients who received metformin were more likely to be female, have higher estimated glomerular filtration rates, and have undergone transplant more recently. Metformin-based regimens were associated with significantly lower adjusted all-cause (aHR 0.18 0.410.91 ), malignancy-related (aHR 0.45 0.450.99 ), and infection-related (aHR 0.12 0.320.85 ) mortality, and nonsignificant trends toward lower cardiovascular mortality, graft failure, and acute rejection. No evidence of increased adverse graft or patient outcomes was noted. Use of metformin-based diabetes treatment regimens may be safe in carefully selected kidney transplant recipients.

Phosphorylation of Acetyl-CoA Carboxylase by AMPK Reduces Renal Fibrosis and Is Essential for the Anti-Fibrotic Effect of Metformin

BACKGROUND

Expression of genes regulating fatty acid metabolism is reduced in tubular epithelial cells from kidneys with tubulointerstitial fibrosis (TIF), thus decreasing the energy produced by fatty acid oxidation (FAO). Acetyl-CoA carboxylase (ACC), a target for the energy-sensing AMP-activating protein kinase (AMPK), is the major controller of the rate of FAO within cells. Metformin has a well described antifibrotic effect, and increases phosphorylation of ACC by AMPK, thereby increasing FAO.

METHODS

We evaluated phosphorylation of ACC in cell and mouse nephropathy models, as well as the effects of metformin administration in mice with and without mutations that reduce ACC phosphorylation.

RESULTS

Reduced phosphorylation of ACC on the AMPK site Ser79 occurred in both tubular epithelial cells treated with folate to mimic cellular injury and in wild-type (WT) mice after induction of the folic acid nephropathy model. When this effect was exaggerated in mice with knock-in (KI) Ser to Ala mutations of the phosphorylation sites in ACC, lipid accumulation and fibrosis increased significantly compared with WT. The effect of ACC phosphorylation on fibrosis was confirmed in the unilateral ureteric obstruction model, which showed significantly increased lipid accumulation and fibrosis in the KI mice. Metformin use was associated with significantly reduced fibrosis and lipid accumulation in WT mice. In contrast, in the KI mice, the drug was associated with worsened fibrosis.

CONCLUSIONS

These data indicate that reduced phosphorylation of ACC after renal injury contributes to the development of TIF, and that phosphorylation of ACC is required for metformin's antifibrotic action in the kidney.

Metformin attenuates folic-acid induced renal fibrosis in mice

Progressive tubulointerstitial fibrosis has been recognized as a common pathological process that leads to the progression of all chronic kidney disease (CKD). Innovative strategies are needed to both prevent and treat CKD. Inflammatory and fibrotic signaling pathways play central roles in the progression of CKD regardless of aetiology. Hence, targeting inflammatory and fibrotic responses holds promise to limit renal fibrosis. Metformin has been the most prescribed glucose-lowering medicine worldwide, and its potential for many other therapeutic applications is also being explored intensively. Increasing evidence indicates metformin may limit renal fibrosis. However, the exact mechanisms whereby metformin limits renal injury are not fully understood. The anti-fibrotic effects of metformin, independent of improved glycaemic control was examined in a folic acid-induced mouse model of nephropathy for 14 days. Human proximal tubular cells (HK2 cells) exposed to TGF-β1 were used in in vitro models to examine mechanistic pathways. Folic acid induced nephropathy was associated with the overexpression of inflammatory markers MCP-1, F4/80, type IV collagen, fibronectin and TGF-β1 compared to control groups, which were partially attenuated by metformin treatment. In vitro studies confirmed that metformin inhibited TGF-β1 induced inflammatory and fibrotic responses through Smad3, ERK1/2, and P38 pathways in human renal proximal tubular cells. These results suggest that metoformin attenuates folic acid-induced renal interstitial fibrogenesis through TGF-β1 signaling pathways.

Metformin Regulating miR-34a Pathway to Inhibit Egr1 in Rat Mesangial Cells Cultured with High Glucose

BACKGROUND

Activating AMPKα negatively regulates Egr1 to inhibit inflammatory cytokines in high glucose. miR-34a inhibition increases phosphorylated AMPKα through mediating SIRT1 to suppress the development of fatty liver.

AIM OF THE STUDY

To clarify the function of Egr1 on the inflammation and fibrosis in high glucose-cultured MCs, as well as to explore the effects of metformin on miR-34a pathway and Egr1 expression.

METHODS

We transfected MCs with miR-34a inhibitor. And MCs were transfected with small interfering RNA for silencing Egr1 and SIRT1. Quantitative real-time PCR was used to assay the transcription levels of Egr1 mRNA and miR-34a. Western blot was used to test the protein. And ELISA was used to measure inflammatory factors.

RESULTS

High glucose upregulates Egr1 to aggravate the inflammation and fibrosis in MCs. miR-34a suppresses the activation of SIRT1/AMPKα and results in promoting Egr1 in high glucose-cultured MCs. Metformin attenuates high glucose-stimulated inflammation and fibrosis in MCs by regulating miR-34a-mediated SIRT1/AMPKα activity and the downstream Egr1 protein.

CONCLUSION

We enriched the effects of miR-34a pathway regulating Egr1 in high glucose-cultured MCs. It provides a foundation for future researches considering Egr1 as a therapeutic target and a new direction for the clinical application of metformin in early DKD.

Metformin prevents peritendinous fibrosis by inhibiting transforming growth factor-β signaling

Injury-induced peritendinous adhesion is a critical clinical problem that leads to tendon function impairment. Therefore, it is very urgent to explore potential approaches to attenuate peritendinous adhesion formation. Recently, several studies have demonstrated the biological effect of metformin in inhibiting multiple tissue fibrosis. In this study, we performed in vitro and in vivo experiments to examine whether metformin prevents injury-induced peritendinous fibrosis. We found that tendon injury induced severe fibrosis formation in rats. However, orally administered metformin significantly alleviated the fibrosis based on macroscopic and histological evaluation. Peritendinous tissue from metformin-treated rats also showed decreased expression of fibrotic genes including col1a1, col3a1, and α-smooth muscle actin (α-SMA), and inhibition of transforming growth factor (TGF)-β1 signaling. The cell counting kit (CCK)-8, flow cytometry, and 5-ethynyl-2′-deoxyuridine (EdU) staining analyses showed that treatment of NIH/3T3 fibroblasts with metformin significantly inhibited excessive cell proliferation and promoted cell apoptosis. Metformin treatment also inhibited the expression of fibrotic genes and decreased the phosphorylation of smad2/3 and extracellular signal-regulated kinase (ERK) 1/2. Furthermore, blocking AMP-activated protein kinase (AMPK) signaling abolished the inhibitory effect of metformin on fibrosis. Our findings indicate that metformin has a protective role against peritendinous tissue fibrosis and suggest its clinical use could be a promising therapeutic approach.