SGLT2 inhibitor empagliflozin and DPP4 inhibitor linagliptin reactivate glomerular autophagy in db/db mice, a model of type 2 diabetes. Int J Mol Sci. 2020;21. [PMID: 32340263 PMCID: PMC7215949 DOI: 10.3390/ijms21082987]

Podocyte programmed cell death in diabetic kidney disease: Molecular mechanisms and therapeutic prospects

Diabetic kidney disease (DKD) is the primary cause of chronic kidney and end-stage renal disease. Glomerular podocyte loss and death are pathological hallmarks of DKD, and programmed cell death (PCD) in podocytes is crucial in DKD progression. PCD involves apoptosis, autophagy, ferroptosis, pyroptosis, and necroptosis. During DKD, PCD in podocytes is severely impacted and primarily characterized by accelerated podocyte apoptosis and suppressed autophagy. These changes lead to a gradual decrease in podocyte numbers, impairing the glomerular filtration barrier function and accelerating DKD progression. However, research on the interactions between the different types of PCD in podocytes is lacking. This review focuses on the novel roles and mechanisms of PCD in the podocytes of patients with DKD. Additionally, we summarize clinical drugs capable of regulating podocyte PCD, present challenges and prospects faced in developing drugs related to podocyte PCD and suggest that future research should further explore the detailed mechanisms of podocyte PCD and interactions among different types of PCD.

Targeting senescence to prevent diabetic kidney disease: Exploring molecular mechanisms and potential therapeutic targets for disease management

BACKGROUND/AIMS

As a microvascular complication, diabetic kidney disease is the leading cause of chronic kidney disease and end-stage renal disease worldwide. While the underlying pathophysiology driving transition of diabetic kidney disease to renal failure is yet to be fully understood, recent studies suggest that cellular senescence is central in disease development and progression. Consequently, understanding the molecular mechanisms which initiate and drive senescence in response to the diabetic milieu is crucial in developing targeted therapies that halt progression of renal disease.

METHODS

To understand the mechanistic pathways underpinning cellular senescence in the context of diabetic kidney disease, we reviewed the literature using PubMed for English language articles that contained key words related to senescence, inflammation, fibrosis, senescence-associated secretory phenotype (SASP), autophagy, and diabetes.

RESULTS

Aberrant accumulation of metabolically active senescent cells is a notable event in the progression of diabetic kidney disease. Through autocrine- and paracrine-mediated mechanisms, resident senescent cells potentiate inflammation and fibrosis through increased expression and secretion of pro-inflammatory cytokines, chemoattractants, recruitment of immune cells, myofibroblast activation, and extracellular matrix remodelling. Compounds that eliminate senescent cells and/or target the SASP - including senolytic and senomorphics drugs - demonstrate promising results in reducing the senescent cell burden and associated pro-inflammatory effect.

CONCLUSIONS

Here we evidence the link between senescence and diabetic kidney disease and highlight underlying molecular mechanisms and potential therapeutic targets that could be exploited to delay disease progression and improve outcomes for individuals with the disease. Trials are now required to translate their therapeutic potential to a clinical setting.

The Renoprotective Mechanisms of Sodium-Glucose Cotransporter-2 Inhibitors (SGLT2i)-A Narrative Review

Chronic kidney disease (CKD) is a noncommunicable condition that has become a major healthcare burden across the globe, often underdiagnosed and associated with low awareness. The main cause that leads to the development of renal impairment is diabetes mellitus and, in contrast to other chronic complications such as retinopathy or neuropathy, it has been suggested that intensive glycemic control is not sufficient in preventing the development of diabetic kidney disease. Nevertheless, a novel class of antidiabetic agents, the sodium-glucose cotransporter-2 inhibitors (SGLT2i), have shown multiple renoprotective properties that range from metabolic and hemodynamic to direct renal effects, with a major impact on reducing the risk of occurrence and progression of CKD. Thus, this review aims to summarize current knowledge regarding the renoprotective mechanisms of SGLT2i and to offer a new perspective on this innovative class of antihyperglycemic drugs with proven pleiotropic beneficial effects that, after decades of no significant progress in the prevention and in delaying the decline of renal function, start a new era in the management of patients with CKD.

Empagliflozin, a sodium-glucose cotransporter inhibitor enhancing mitochondrial action and cardioprotection in metabolic syndrome

Metabolic syndrome (MetS) has a large clinical population nowadays, usually due to excessive energy intake and lack of exercise. During MetS, excess nutrients stress the mitochondria, resulting in relative hypoxia in tissues and organs, even when blood supply is not interrupted or reduced, making mitochondrial dysfunction a central pathogenesis of cardiovascular disease in the MetS. Sodium-glucose cotransporter 2 inhibitors were designed as a hyperglycemic drug that acts on the renal tubules to block sugar reabsorption in primary urine. Recently they have been shown to have anti-inflammatory and other protective effects on cardiomyocytes in MetS, and have also been recommended in the latest heart failure guidelines as a routine therapy. Among these inhibitors, empagliflozin shows better clinical promise due to less influence from glomerular filtration rate. This review focuses on the mitochondrial mechanisms of empagliflozin, which underlie the anti-inflammatory and recover cellular functions in MetS cardiomyocytes, including stabilizing calcium concentration, mediating metabolic reprogramming, maintaining homeostasis of mitochondrial quantity and quality, stable mitochondrial DNA copy number, and repairing damaged mitochondrial DNA.

Narrative Review of Immunomodulatory and Anti-inflammatory Effects of Sodium-Glucose Cotransporter 2 Inhibitors: Unveiling Novel Therapeutic Frontiers

Sodium-glucose cotransporter 2 inhibitors (SGLT2 inhibitors) have evolved from their initial role as antidiabetic drugs to garner recognition for their remarkable cardio-protective and reno-protective attributes. They have become a crucial component of therapeutic guidelines for congestive heart failure and proteinuric chronic kidney disease (CKD). These benefits extend beyond glycemic control, because improvements in cardiovascular and renal outcomes occur swiftly. Recent studies have unveiled the immunomodulatory properties of SGLT2 inhibitors; thus, shedding light on their potential to influence the immune system and inflammation. This comprehensive review explores the current state of knowledge regarding the impact of SGLT2 inhibitors on the immune system and inflammation, focusing on preclinical and clinical evidence. The review delves into their antiinflammatory and immunomodulating effects, offering insights into clinical implications, and exploring emerging research areas related to their prospective immunomodulatory impact.

Role of β-cell autophagy in β-cell physiology and the development of diabetes

Elucidating the molecular mechanism of autophagy was a landmark in understanding not only the physiology of cells and tissues, but also the pathogenesis of diverse diseases, including diabetes and metabolic disorders. Autophagy of pancreatic β-cells plays a pivotal role in the maintenance of the mass, structure and function of β-cells, whose dysregulation can lead to abnormal metabolic profiles or diabetes. Modulators of autophagy are being developed to improve metabolic profile and β-cell function through the removal of harmful materials and rejuvenation of organelles, such as mitochondria and endoplasmic reticulum. Among the known antidiabetic drugs, glucagon-like peptide-1 receptor agonists enhance the autophagic activity of β-cells, which might contribute to the profound effects of glucagon-like peptide-1 receptor agonists on systemic metabolism. In this review, the results from studies on the role of autophagy in β-cells and their implication in the development of diabetes are discussed. In addition to non-selective (macro)autophagy, the role and mechanisms of selective autophagy and other minor forms of autophagy that might occur in β-cells are discussed. As β-cell failure is the ultimate cause of diabetes and unresponsiveness to conventional therapy, modulation of β-cell autophagy might represent a future antidiabetic treatment approach, particularly in patients who are not well managed with current antidiabetic therapy.

Linagliptin ameliorates tacrolimus-induced renal injury: role of Nrf2/HO-1 and HIF-1α/CTGF/PAI-1

BACKGROUND

Tacrolimus (TAC) is a frequently used immunosuppressive medication in organ transplantation. However, its nephrotoxic impact limits its long-term usage. This study aims to investigate the effect of linagliptin (Lina) on TAC-induced renal injury and its underlying mechanisms.

METHODS AND RESULTS

Thirty-two Sprague Dawley rats were treated with TAC (1.5 mg/kg/day, subcutaneously) and/or Lina (5 mg/kg/day, orally) for 4 weeks. Histological examination was conducted, and serum and urinary biomarkers were measured to assess kidney function and integrity. Furthermore, ELISA, Western blot analysis and immunohistochemical assay were employed to determine signaling molecules of oxidative stress, profibrogenic, hypoxic, and apoptotic proteins. Tacrolimus caused renal dysfunction and histological deterioration evidenced by increased serum creatinine, blood urea nitrogen (BUN), urinary cystatin C, and decreased serum albumin as well as elevated tubular injury and interstitial fibrosis scores. Additionally, TAC significantly increased the expression of collagen type-1, alpha-smooth muscle actin (α-SMA), plasminogen activator inhibitor-1 (PAI-1), and transforming growth factor-beta1 (TGF-β1) renal content. Moreover, TAC decreased the expression of nuclear factor erythroid-2-related factor2 (Nrf2), heme oxygenase 1 (HO-1), and mitochondrial superoxide dismutase (SOD2). In addition, TAC increased protein expression of hypoxia-inducible factor1-alpha (HIF-1α), connective tissue growth factor (CTGF), inducible nitric oxide synthase (iNOS), 8-hydroxy-2-deoxyguanosine (8-OHdG), as well as nitric oxide (NO), 4-hydroxynonenal, caspase-3 and Bax renal contents. Furthermore, TAC decreased Bcl-2 renal contents. The Lina administration markedly attenuated these alterations.

CONCLUSION

Lina ameliorated TAC-induced kidney injury through modulation of oxidative stress, hypoxia, and apoptosis related proteins.

Tangshen formula protects against podocyte apoptosis via enhancing the TFEB-mediated autophagy-lysosome pathway in diabetic nephropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic nephropathy (DN) is the leading cause of end-stage kidney disease and currently there are no specific and effective drugs for its treatment. Podocyte injury is a detrimental feature and the major cause of albuminuria in DN. We previously reported Tangshen Formula (TSF), a Chinese herbal medicine, has shown therapeutic effects on DN. However, the underlying mechanisms remain obscure.

AIM OF THE STUDY

This study aimed to explore the protective effect of TSF on podocyte apoptosis in DN and elucidate the potential mechanism.

MATERIALS AND METHODS

The effects of TSF were assessed in a murine model using male KKAy diabetic mice, as well as in advanced glycation end products-stimulated primary mice podocytes. Transcription factor EB (TFEB) knockdown primary podocytes were employed for mechanistic studies. In vivo and in vitro studies were performed and results assessed using transmission electron microscopy, immunofluorescence staining, and western blotting.

RESULTS

TSF treatment alleviated podocyte apoptosis and structural impairment, decreased albuminuria, and mitigated renal dysfunction in KKAy mice. Notably, TSF extracted twice showed a more significant reduction in proteinuria than TSF extracted three times. Accumulation of autophagic biomarkers p62 and LC3, and aberrant autophagic flux in podocytes of DN mice were significantly altered by TSF therapy. Consistent with the in vivo results, TSF prevented the apoptosis of primary podocytes exposed to AGEs and activated autophagy. However, the anti-apoptosis capacity of TSF was countered by the autophagy-lysosome inhibitor chloroquine. We found that TSF increased the nuclear translocation of TFEB in diabetic podocytes, and thus upregulated transcription of its several autophagic target genes. Pharmacological activation of TFEB by TSF accelerated the conversion of autophagosome to autolysosome and lysosomal biogenesis, further augmented autophagic flux. Conversely, TFEB knockdown negated the favorable effects of TSF on autophagy in AGEs-stimulated primary podocytes.

CONCLUSIONS

These findings indicate TSF appears to attenuate podocyte apoptosis and promote autophagy in DN via the TFEB-mediated autophagy-lysosome system. Thus, TSF may be a therapeutic candidate for DN.

FoxG1 as a Potential Therapeutic Target for Alzheimer's Disease: Modulating NLRP3 Inflammasome via AMPK/mTOR Autophagy Pathway

An increasing body of research suggests that promoting microglial autophagy hinders the neuroinflammation initiated though the NLRP3 inflammasome activation in Alzheimer's disease (AD). The function of FoxG1, a crucial transcription factor involved in cell survival by regulating mitochondrial function, remains unknown during the AD process and neuroinflammation occurs. In the present study, we firstly found that Aβ peptides induced AD-like neuroinflammation upregulation and downregulated the level of autophagy. Following low-dose Aβ25-35 stimulation, FoxG1 expression and autophagy exhibited a gradual increase. Nevertheless, with high-concentration Aβ25-35 treatment, progressive decrease in FoxG1 expression and autophagy levels as the concentration of Aβ25-35 escalated. In addition, FoxG1 has a positive effect on cell viability and autophagy in the nervous system. In parallel with the Aβ25-35 stimulation, we employed siRNA to decrease the expression of FoxG1 in N2A cells. A substantial reduction in autophagy level (Beclin1, LC3II, SQSTM1/P62) and a notable growth in inflammatory response (NLRP3, TNF-α, and IL-6) were observed. In addition, we found FoxG1 overexpression owned the effect on the activation of AMPK/mTOR autophagy pathway and siRNA-FoxG1 successfully abolished this effect. Lastly, FoxG1 suppressed the NLRP3 inflammasome and enhanced the cognitive function in AD-like mouse model induced by Aβ25-35. Confirmed by cellular and animal experiments, FoxG1 suppressed NLRP3-mediated neuroinflammation, which was strongly linked to autophagy regulated by AMPK/mTOR. Taken together, FoxG1 may be a critical node in the pathologic progression of AD and has the potential to serve as therapeutic target.

Canagliflozin improves fatty acid oxidation and ferroptosis of renal tubular epithelial cells via FOXA1-CPT1A axis in diabetic kidney disease

Impaired fatty acid oxidation (FAO) is a metabolic hallmark of renal tubular epithelial cells (RTECs) under diabetic conditions. Disturbed FAO may promote cellular oxidative stress and insufficient energy production, leading to ferroptosis subsequently. Canagliflozin, an effective anti-hyperglycemic drug, may exert potential reno-protective effects by upregulating FAO and inhibiting ferroptosis in RTECs. However, the mechanisms involved remain unclear. The present study is aimed to characterize the detailed mechanisms underlying the impact of canagliflozin on FAO and ferroptosis. Type 2 diabetic db/db mice were administrated daily by gavage with canagliflozin (20 mg/kg/day, 40 mg/kg/day) or positive control drug pioglitazone (10 mg/kg/day) for 12 weeks. The results showed canagliflozin effectively improved renal function and structure, reduced lipid droplet accumulation, enhanced FAO with increased ATP contents and CPT1A expression, a rate-limiting enzyme of FAO, and relieved ferroptosis in diabetic mice. Moreover, overexpression of FOXA1, a transcription factor related with lipid metabolism, was observed to upregulate the level of CPT1A, and further alleviated ferroptosis in high glucose cultured HK-2 cells. Whereas FOXA1 knockdown had the opposite effect. Mechanistically, chromatin immunoprecipitation assay and dual-luciferase reporter gene assay results demonstrated that FOXA1 transcriptionally promoted the expression of CPT1A through a sis-inducible element located in the promoter region of the protein. In conclusion, these data suggest that canagliflozin improves FAO and attenuates ferroptosis of RTECs via FOXA1-CPT1A axis in diabetic kidney disease.

Linagliptin, a DPP-4 inhibitor, activates AMPK/FOXO3a and suppresses NFκB to mitigate the debilitating effects of diethylnitrosamine exposure in rat liver: Novel mechanistic insights

Accumulating evidence suggests that dysregulation of FOXO3a plays a significant role in the progression of various malignancies, including hepatocellular carcinoma (HCC). FOXO3a inactivation, driven by oncogenic stimuli, can lead to abnormal cell growth, suppression of apoptosis, and resistance to anticancer drugs. Therefore, FOXO3a emerges as a potential molecular target for the development of innovative treatments in the era of oncology. Linagliptin (LNGTN), a DPP-4 inhibitor known for its safe profile, has exhibited noteworthy anti-inflammatory and anti-oxidative properties in previous in vivo studies. Several potential molecular mechanisms have been proposed to explain these effects. However, the capacity of LNGTN to activate FOXO3a through AMPK activation has not been investigated. In our investigation, we examined the potential repurposing of LNGTN as a hepatoprotective agent against diethylnitrosamine (DENA) intoxication. Additionally, we assessed LNGTN's impact on apoptosis and autophagy. Following a 10-week administration of DENA, the liver underwent damage marked by inflammation and early neoplastic alterations. Our study presents the first experimental evidence demonstrating that LNGTN can reinstate the aberrantly regulated FOXO3a activity by elevating the nuclear fraction of FOXO3a in comparison to the cytosolic fraction, subsequent to AMPK activation. Moreover, noteworthy inactivation of NFκB induced by LNGTN was observed. These effects culminated in the initiation of apoptosis, the activation of autophagy, and the manifestation of anti-inflammatory, antiproliferative, and antiangiogenic outcomes. These effects were concomitant with improved liver function and microstructure. In conclusion, our findings open new avenues for the development of novel therapeutic strategies targeting the AMPK/FOXO3a signaling pathway in the management of chronic liver damage.

Regulation of autophagy by perilysosomal calcium: a new player in β-cell lipotoxicity

Autophagy is an essential quality control mechanism for maintaining organellar functions in eukaryotic cells. Defective autophagy in pancreatic beta cells has been shown to be involved in the progression of diabetes through impaired insulin secretion under glucolipotoxic stress. The underlying mechanism reveals the pathologic role of the hyperactivation of mechanistic target of rapamycin (mTOR), which inhibits lysosomal biogenesis and autophagic processes. Moreover, accumulating evidence suggests that oxidative stress induces Ca2+ depletion in the endoplasmic reticulum (ER) and cytosolic Ca2+ overload, which may contribute to mTOR activation in perilysosomal microdomains, leading to autophagic defects and β-cell failure due to lipotoxicity. This review delineates the antagonistic regulation of autophagic flux by mTOR and AMP-dependent protein kinase (AMPK) at the lysosomal membrane, and both of these molecules could be activated by perilysosomal calcium signaling. However, aberrant and persistent Ca2+ elevation upon lipotoxic stress increases mTOR activity and suppresses autophagy. Therefore, normalization of autophagy is an attractive therapeutic strategy for patients with β-cell failure and diabetes.

Interference in the nutrient-sensing and inflammatory signaling pathways by renal autophagy activation in mice with late stage diabetic nephropathy

PURPOSE

Disturbance in metabolism and inflammation are the main causes of kidney injury in patients with late stage diabetic nephropathy (DN). Here, we explored whether autophagy was activated in mice with late stage DN and whether it was associated with disturbance in metabolism and inflammation.

METHODS

In total, mice were divided into the control group (db/m) and DN group (db/db). Mice were raised for 7 months, and their biochemical indices were measured. Subsequently, their kidneys were collected to detect autophagy and the related nutrient-sensing and inflammatory signaling pathways in late stage DN.

RESULTS

The expression levels of autophagy markers LC3-I and LC3-II were significantly increased in mice with late stage DN, whereas that of autophagy flux marker P62 was significantly decreased, indicating activation of autophagy. Concurrently, mechanistic target of rapamycin was highly expressed as a cellular nutrient-sensing and energy regulator in mice with late stage DN. Additionally, the expression levels of markers of nutrient-sensing signaling pathways adenosine monophosphate-activated protein kinase (AMPK) were increased markedly in mice with late stage DN. Additionally, the expression levels of the marker of nutrient-sensing signaling pathways silent information regulator T1 (SIRT1), the marker of inflammatory signaling pathways high mobility group box protein 1 (HMGB1), and interferon regulatory factor 3 (IRF3) were significantly increased in mice with late stage DN.

CONCLUSIONS

The findings of our study indicate that autophagy activation in late stage DN may interfere with nutrient-sensing and inflammatory signaling pathways involving AMPK, SIRT1, HMGB1, and IRF3.

The Role of Autophagy in Type 2 Diabetic Kidney Disease Management

Diabetic kidney disease (DKD), or diabetic nephropathy (DN), is one of the most prevalent complications of type 2 diabetes mellitus (T2DM) and causes severe burden on the general welfare of T2DM patients around the world. While several new agents have shown promise in treating this condition and potentially halting the progression of the disease, more work is needed to understand the complex regulatory network involved in the disorder. Recent studies have provided new insights into the connection between autophagy, a physiological metabolic process known to maintain cellular homeostasis, and the pathophysiological pathways of DKD. Typically, autophagic activity plays a role in DKD progression mainly by promoting an inflammatory response to tissue damage, while both overactivated and downregulated autophagy worsen disease outcomes in different stages of DKD. This correlation demonstrates the potential of autophagy as a novel therapeutic target for the disease, and also highlights new possibilities for utilizing already available DN-related medications. In this review, we summarize findings on the relationship between autophagy and DKD, and the impact of these results on clinical management strategies.

Single and Combined Effects of Short-Term Selenium Deficiency and T-2 Toxin-Induced Kidney Pathological Injury Through the MMPs/TIMPs System

The single and combined effects of short-term selenium (Se) deficiency and T-2 toxin-induced kidney pathological injury through the MMPs/TIMPs system were investigated. Forty-eight rats were randomly divided into control, 10 ng/g T-2 toxin, 100 ng/g T-2 toxin, Se-deficient, 10 ng/g T-2 toxin and Se deficiency combined, and 100 ng/g T-2 toxin and Se deficiency combined groups for a 4-week intervention. The kidney Se concentration was measured to evaluate the construction of animal models of Se deficiency. Kidney tissues were analyzed by hematoxylin-eosin staining, Masson staining, and transmission electron microscope to observe the pathological changes, the severity of kidney fibrosis, and ultrastructural changes, respectively. Meanwhile, quantitative polymerase chain reaction and immunohistochemical staining were used to analyze the gene and protein expression levels of matrix metallopeptidase 2/3 (MMP2/3) and tissue inhibitor of metalloproteinase 1 (TIMP1). The results showed that short-term Se deficiency and T-2 toxin exposure can cause kidney injury through tubular degeneration and even lead to kidney fibrosis. And the combination of T-2 toxin and Se deficiency had a synergistic effect on the kidney. A dose-response effect of the T-2 toxin was also observed. At the gene and protein levels, the expression of MMP2/3 in the intervention group increased, while the expression of TIMP1 decreased compared with the control group. In conclusion, short-term Se deficiency and T-2 toxin exposure might lead to injury and even the development of fibrosis in the kidneys, and combined intervention can increase the severity with a dose-dependent trend. MMP2/3 and TIMP1 likely play a significant role in the development of kidney fibrosis.

Sinensetin ameliorates high glucose-induced diabetic nephropathy via enhancing autophagy in vitro and in vivo

Diabetic nephropathy (DN) affects around 40% of people with diabetes, the final outcome of which is end-stage renal disease. The deficiency of autophagy and excessive oxidative stress have been found to participate in the pathogenesis of DN. Sinensetin (SIN) has been proven to have strong antioxidant capability. However, the effect of SIN on DN has not been studied. We examined the effect of SIN on cell viability and autophagy in the podocyte cell line, MPC5 cells, treated with high glucose (HG). For in vivo studies, DN mice models were established by intraperitoneal injected with streptozotocin (40 mg/kg) for 5 consecutive days and fed with a 60% high-fat diet, and SIN was given (10, 20, and 40 mg/kg) for 8 weeks via intraperitoneal injection. The results showed that SIN could protect MPC5 cells against HG-induced damage and significantly improve the renal function of DN mice. Moreover, SIN remarkably restored the autophagy activity of MPC5 cells which was inhibited under HG conditions. Consistent with this, SIN efficiently improved autophagy in the kidney tissue of DN mice. In brief, our findings demonstrated the protective effect of SIN on DN via restoring the autophagic function, which might provide a basis for drug development.

The role of autophagy in the treatment of type II diabetes and its complications: a review

Type II diabetes mellitus (T2DM) is a chronic metabolic disease characterized by prolonged hyperglycemia and insulin resistance (IR). Its incidence is increasing annually, posing a significant threat to human life and health. Consequently, there is an urgent requirement to discover effective drugs and investigate the pathogenesis of T2DM. Autophagy plays a crucial role in maintaining normal islet structure. However, in a state of high glucose, autophagy is inhibited, resulting in impaired islet function, insulin resistance, and complications. Studies have shown that modulating autophagy through activation or inhibition can have a positive impact on the treatment of T2DM and its complications. However, it is important to note that the specific regulatory mechanisms vary depending on the target organ. This review explores the role of autophagy in the pathogenesis of T2DM, taking into account both genetic and external factors. It also provides a summary of reported chemical drugs and traditional Chinese medicine that target the autophagic pathway for the treatment of T2DM and its complications.

A Role for Sodium-Glucose Cotransporter 2 Inhibitors in the Treatment of Chronic Kidney Disease: A Mini Review

BACKGROUND

Sodium-glucose cotransport protein 2 (SGLT2) inhibitors, a new type of glucose-lowering drug, have been well proved in several clinical studies for their glucose-lowering and nephroprotective effects, and the nephroprotective effects include both indirect effects of metabolic improvement and direct effects, independent of glucose-lowering effects.

SUMMARY

In patients with diabetic kidney disease (DKD), several studies have demonstrated the potential nephroprotective mechanisms of SGLT2 inhibitors, and evidence of nephroprotective mechanisms in the non-DKD population is accumulating. Although the nephroprotective mechanism of SGLT2 inhibitors has not been fully elucidated, several laboratory studies have illustrated the mechanism underlying the effects of SGLT2 inhibitors at various aspects.

KEY MESSAGES

The purpose of this article is to review the mechanism of nephroprotective effect of SGLT2 inhibitors and to look forward to promising research in the future.

Renal intrinsic cells remodeling in diabetic kidney disease and the regulatory effects of SGLT2 Inhibitors

Diabetic kidney disease (DKD) is a prevalent complication of diabetes and a major secondary factor leading to end-stage renal disease. The kidney, a vital organ, is composed of a heterogeneous group of intrinsic cells, including glomerular endothelial cells, podocytes, mesangial cells, tubular epithelial cells, and interstitial fibroblasts. In the context of DKD, hyperglycemia elicits direct or indirect injury to these intrinsic cells, leading to their structural and functional changes, such as cell proliferation, apoptosis, and transdifferentiation. The dynamic remodeling of intrinsic cells represents an adaptive response to stimulus during the pathogenesis of diabetic kidney disease. However, the persistent stimulus may trigger an irreversible remodeling, leading to fibrosis and functional deterioration of the kidney. Sodium-glucose cotransporter 2 (SGLT2) inhibitors, a new class of hypoglycemic drugs, exhibit efficacy in reducing blood glucose levels by curtailing renal tubular glucose reabsorption. Furthermore, SGLT2 inhibitors have been shown to modulate intrinsic cell remodeling in the kidney, ameliorate kidney structure and function, and decelerate DKD progression. This review will elaborate on the intrinsic cell remodeling in DKD and the underlying mechanism of SGLT2 inhibitors in modulating it from the perspective of the renal intrinsic cell, providing insights into the pathogenesis of DKD and the renal protective action of SGLT2 inhibitors.

A systematic review on renal effects of SGLT2 inhibitors in rodent models of diabetic nephropathy

We have performed a systematic review of studies reporting on the renal effects of SGLT2 inhibitors in rodent models of diabetes. In 105 studies, SGLT2 inhibitors improved not only the glycemic control but also various aspects of renal function in most cases. These nephroprotective effects were similarly reported whether treatment with the SGLT2 inhibitor started concomitant with the onset of diabetes (within 1 week), early after onset (1-4 weeks) or after nephropathy had developed (>4 weeks after onset) with the latter probably having the greatest translational value. They were observed across various animal models of type 1 and type 2 diabetes/obesity (4 and 23 models, respectively), although studies in the type 2 diabetes model of db/db mice more often had negative data than in other models. Among possibly underlying pathophysiological mechanisms of nephroprotection, treatment with SGLT2 inhibitors had beneficial effects on lipid metabolism, blood pressure, glomerulosclerosis as well as renal tubular fibrosis, apoptosis, oxidative stress, and inflammation. These pathomechanisms highly influence atherosclerosis and renal health, which are two major factors that lead to an enhanced mortality in patients with diabetes and/or chronic kidney disease. Interestingly, renal SGLT2 inhibitor effects did not always correlate with those on glucose homeostasis, particularly in a limited number of direct comparative studies with other anti-diabetic treatments, indicating that nephroprotection may at least partly occur by mechanisms other than improving glycemic control. Our analyses did not provide evidence for different nephroprotective efficacy between SGLT2 inhibitors. Importantly, only four of 105 studies reported on female animals, and none provided direct comparative data between sexes. We conclude that more data on female animals and more direct comparative studies with other anti-diabetic compounds and combinations of treatments are needed.

Autophagy and diabetes

The current literature findings on autophagy’s beneficial and detrimental roles in diabetes mellitus (DM) and diabetes-related comorbidities were reviewed. The effects of oral hypoglycaemic medicines and autophagy in DM. Autophagy plays an important function in cellular homeostasis by promoting cell survival or initiating cell death in physiological settings was also assessed. Although autophagy protects insulin-target tissues, organelle failure caused by autophagy malfunction influences DM and other metabolic diseases. Endoplasmic reticulum and oxidative stress enhance autophagy levels, making it easier to regulate stress-induced intracellular changes. Evidence suggests that autophagy-caused cell death can occur when autophagy is overstimulated and constitutively activated, which might prevent or develop DM. Even though the precise role of autophagy in DM complications is uncertain, deregulation of the autophagic machinery is strongly linked to beta cell destruction and the aetiology of DM. Thus, improving autophagy dysfunction is a possible therapeutic objective in treating DM and other metabolic disorders.

Tubular injury in diabetic kidney disease: molecular mechanisms and potential therapeutic perspectives

Diabetic kidney disease (DKD) is a chronic complication of diabetes and the leading cause of end-stage renal disease (ESRD) worldwide. Currently, there are limited therapeutic drugs available for DKD. While previous research has primarily focused on glomerular injury, recent studies have increasingly emphasized the role of renal tubular injury in the pathogenesis of DKD. Various factors, including hyperglycemia, lipid accumulation, oxidative stress, hypoxia, RAAS, ER stress, inflammation, EMT and programmed cell death, have been shown to induce renal tubular injury and contribute to the progression of DKD. Additionally, traditional hypoglycemic drugs, anti-inflammation therapies, anti-senescence therapies, mineralocorticoid receptor antagonists, and stem cell therapies have demonstrated their potential to alleviate renal tubular injury in DKD. This review will provide insights into the latest research on the mechanisms and treatments of renal tubular injury in DKD.

Neuroprotective Impact of Linagliptin against Cadmium-Induced Cognitive Impairment and Neuropathological Aberrations: Targeting SIRT1/Nrf2 Axis, Apoptosis, and Autophagy

Cadmium is an environmental contaminant associated with marked neurotoxicity and cognitive impairment. Linagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor, has demonstrated promising neuroprotection against cerebral ischemia and diabetic dementia. However, there has been no study of its effect on cadmium-induced cognitive deficits. In the present work, linagliptin's prospective neuroprotective effects against cadmium-evoked cognitive decline were examined in vivo in rats. The molecular pathways related to oxidative stress, apoptosis, and autophagy were investigated. Histology, immunohistochemistry, ELISA, and biochemical assays were performed on brain hippocampi after receiving linagliptin (5 mg/kg/day). The current findings revealed that cadmium-induced learning and memory impairment were improved by linagliptin as seen in the Morris water maze, Y-maze, and novel object recognition test. Moreover, linagliptin lowered hippocampal neurodegeneration as seen in histopathology. At the molecular level, linagliptin curtailed hippocampal DPP-4 and augmented GLP-1 levels, triggering dampening of the hippocampal neurotoxic signals Aβ42 and p-tau in rats. Meanwhile, it enhanced hippocampal acetylcholine and GABA and diminished the glutamate spike. The behavioral recovery was associated with dampening of the hippocampal pro-oxidant response alongside SIRT1/Nrf2/HO-1 axis stimulation. Meanwhile, linagliptin counteracted hippocampal apoptosis markers and inhibited the pro-apoptotic kinase GSK-3β. In tandem, linagliptin activated hippocampal autophagy by lowering SQSTM-1/p62 accumulation, upregulating Beclin 1, and stimulating AMPK/mTOR pathway. In conclusion, linagliptin's antioxidant, antiapoptotic, and pro-autophagic properties advocated its promising neuroprotective impact. Thus, linagliptin may serve as a management approach against cadmium-induced cognitive deficits.

Is it time to repurpose geroprotective diabetes medications for prevention of dementia?

See related Editorial by Tang et al. in this issue.

Nutritional Treatment as a Synergic Intervention to Pharmacological Therapy in CKD Patients

Nutritional and pharmacological therapies represent the basis for non-dialysis management of CKD patients. Both kinds of treatments have specific and unchangeable features and, in certain cases, they also have a synergic action. For instance, dietary sodium restriction enhances the anti-proteinuric and anti-hypertensive effects of RAAS inhibitors, low protein intake reduces insulin resistance and enhances responsiveness to epoetin therapy, and phosphate restriction cooperates with phosphate binders to reduce the net phosphate intake and its consequences on mineral metabolism. It can also be speculated that a reduction in either protein or salt intake can potentially amplify the anti-proteinuric and reno-protective effects of SGLT2 inhibitors. Therefore, the synergic use of nutritional therapy and medications optimizes CKD treatment. Quality of care management is improved and becomes more effective when compared to either treatment alone, with lower costs and fewer risks of unwanted side effects. This narrative review summarizes the established evidence of the synergistic action carried out by the combination of nutritional and pharmacological treatments, underlying how they are not alternative but complementary in CKD patient care.

Novel Drugs for the Management of Diabetes Kidney Transplant Patients: A Literature Review

The management of diabetes and renal failure is changing thanks to the appearance of new drugs such as glucagon-like peptide 1 receptor agonists (GLP1-RA) and sodium-glucose cotransporter type 2 inhibitors (SGLT2i) that have benefits in terms of survival and cardiorenal protection. Based on the potential mechanisms of GLP1-RA, kidney transplant recipients (KTRs) could benefit from their effects. However, high-quality studies are needed to demonstrate these benefits, in the transplant population, especially those related to cardiovascular benefits and renal protection. Studies with SGLT2i performed in KTRs are much less potent than in the general population and therefore no benefits in terms of patient or graft survival have been clearly demonstrated in this population to date. Additionally, the most frequently observed side effects could be potentially harmful to this population profile, including severe or recurrent urinary tract infections and impaired kidney function. However, benefits demonstrated in KTRs are in line with a known potential effects in cardiovascular and renal protection, which may be essential for the outcome of transplant recipients. Better studies are still needed to confirm the benefits of these new oral antidiabetics in the renal transplant population. Understanding the characteristics of these drugs may be critical for KTRs to be able to benefit from their effects without being damaged. This review discusses the results of the most important published studies on KTRs with GLP1-RA and SGLT2i as well as the potential beneficial effects of these drugs. Based on these results, approximate suggestions for the management of diabetes in KTRs were developed.

Empagliflozin inhibits autophagy and mitigates airway inflammation and remodelling in mice with ovalbumin-induced allergic asthma

Empagliflozin, a selective inhibitor of Na⁺-glucose cotransporter-2, has been reported to exert anti-inflammatory and anti-fibrotic effects in addition to autophagy modulation. Addressing the role of autophagy in allergic asthma revealed controversial results. The potential effect of empagliflozin treatment on airway inflammation and remodelling as well as autophagy modulation in a murine model of allergic asthma was investigated. Over a 7-week period, male BALB/c mice were sensitized and challenged by intraperitoneal injection and inhalation of ovalbumin, respectively. Animals were treated with empagliflozin (10 mg/kg; orally) and/or rapamycin (an autophagy inducer; 4 mg/kg; intraperitoneally) before every challenge. Methacholine-induced airway hyperresponsiveness was evaluated one day after the last challenge. After euthanasia, serum, bronchoalveolar lavage fluid, and lung tissues were collected for biochemical, histopathological, and immunohistochemical assessment. Results revealed that empagliflozin decreased airway hyperresponsiveness, serum ovalbumin-specific immunoglobulin E, and bronchoalveolar lavage total and differential leukocytic counts. Levels of inflammatory and profibrotic cytokines (IL-4, IL-5, IL-13, IL-17, and transforming growth factor-β1) were all inhibited. Moreover, empagliflozin preserved pulmonary microscopic architecture and alleviated bronchiolar epithelial thickening, goblet cell hyperplasia, fibrosis and smooth muscle hypertrophy. These effects were associated with inhibition of ovalbumin-activated autophagic flux, as demonstrated by decreased LC3B expression and LC3BII/I ratio, as well as increased P62 expression. However, the therapeutic potential of empagliflozin was inhibited when rapamycin was co-administered. In conclusion, this study demonstrates that empagliflozin has immunomodulatory, anti-inflammatory, and anti-remodelling properties in ovalbumin-induced allergic asthma and suggests that autophagic flux inhibition may play a role in empagliflozin's anti-asthmatic effects.

Dysregulated autophagy: A key player in the pathophysiology of type 2 diabetes and its complications

Autophagy is essential in regulating the turnover of macromolecules via removing damaged organelles, misfolded proteins in various tissues, including liver, skeletal muscles, and adipose tissue to maintain the cellular homeostasis. In these tissues, a specific type of autophagy maintains the accumulation of lipid droplets which is directly related to obesity and the development of insulin resistance. It appears to play a protective role in a normal physiological environment by eliminating the invading pathogens, protein aggregates, and damaged organelles and generating energy and new building blocks by recycling the cellular components. Ageing is also a crucial modulator of autophagy process. During stress conditions involving nutrient deficiency, lipids excess, hypoxia etc., autophagy serves as a pro-survival mechanism by recycling the free amino acids to maintain the synthesis of proteins. The dysregulated autophagy has been found in several ageing associated diseases including type 2 diabetes (T2DM), cancer, and neurodegenerative disorders. So, targeting autophagy can be a promising therapeutic strategy against the progression to diabetes related complications. Our article provides a comprehensive outline of understanding of the autophagy process, including its types, mechanisms, regulation, and role in the pathophysiology of T2DM and related complications. We also explored the significance of autophagy in the homeostasis of β-cells, insulin resistance (IR), clearance of protein aggregates such as islet amyloid polypeptide, and various insulin-sensitive tissues. This will further pave the way for developing novel therapeutic strategies for diabetes-related complications.

Endothelial Autophagy Dysregulation in Diabetes

Diabetes mellitus is a major public health issue that affected 537 million people worldwide in 2021, a number that is only expected to increase in the upcoming decade. Diabetes is a systemic metabolic disease with devastating macro- and microvascular complications. Endothelial dysfunction is a key determinant in the pathogenesis of diabetes. Dysfunctional endothelium leads to vasoconstriction by decreased nitric oxide bioavailability and increased expression of vasoconstrictor factors, vascular inflammation through the production of pro-inflammatory cytokines, a loss of microvascular density leading to low organ perfusion, procoagulopathy, and/or arterial stiffening. Autophagy, a lysosomal recycling process, appears to play an important role in endothelial cells, ensuring endothelial homeostasis and functions. Previous reports have provided evidence of autophagic flux impairment in patients with type I or type II diabetes. In this review, we report evidence of endothelial autophagy dysfunction during diabetes. We discuss the mechanisms driving endothelial autophagic flux impairment and summarize therapeutic strategies targeting autophagy in diabetes.

Inhibition of SGLT2 co-transporter by dapagliflozin ameliorates tubular proteinuria and tubule-interstitial injury at the early stage of diabetic kidney disease

Diabetic kidney disease (DKD) is characterized by progressive impairment of kidney function. It has been postulated that tubule-interstitial injury, associated with tubular albuminuria, precedes glomerular damage in the early stage of DKD. Here, we wanted to determine if the development of tubule-interstitial injury at the early stage of DKD implies modulation of megalin-mediated protein reabsorption in proximal tubule epithelial cells (PTECs) by SGLT2-dependent high glucose influx. Rats with streptozotocin (STZ)-induced diabetes were treated or not with dapagliflozin (DAPA) for 8 weeks. Four experimental groups were generated: (1) CONT, control; (2) DAPA, rats treated with DAPA; (3) STZ, diabetic rats; (4) STZ + DAPA, diabetic rats treated with DAPA. No changes in glomerular structure and function were observed. The STZ group presented proteinuria and albuminuria associated with an increase in the fractional excretion of proteins. A positive correlation between glycemia and proteinuria was found. These phenomena were linked to a decrease in luminal and total megalin expression and, consequently, in albumin reabsorption in PTECs. We also observed tubule-interstitial injury characterized by an increase in urinary tubular injury biomarkers and changes in tubular histomorphometry parameters. In addition, inverse correlations were found between cortical albumin uptake and tubule-interstitial injury or glycemia. All these modifications were attenuated in the STZ + DAPA group. These results suggest that SGLT2-dependent high glucose influx into PTECs promotes a harmful effect on the PTECs, leading to the development of tubular albuminuria and tubule-interstitial injury preceding glomerular damage. These results expand current knowledge on the renoprotective effects of gliflozins.

Autophagy and its therapeutic potential in diabetic nephropathy

Diabetic nephropathy (DN), the leading cause of end-stage renal disease, is the most significant microvascular complication of diabetes and poses a severe public health concern due to a lack of effective clinical treatments. Autophagy is a lysosomal process that degrades damaged proteins and organelles to preserve cellular homeostasis. Emerging studies have shown that disorder in autophagy results in the accumulation of damaged proteins and organelles in diabetic renal cells and promotes the development of DN. Autophagy is regulated by nutrient-sensing pathways including AMPK, mTOR, and Sirt1, and several intracellular stress signaling pathways such as oxidative stress and endoplasmic reticulum stress. An abnormal nutritional status and excess cellular stresses caused by diabetes-related metabolic disorders disturb the autophagic flux, leading to cellular dysfunction and DN. Here, we summarized the role of autophagy in DN focusing on signaling pathways to modulate autophagy and therapeutic interferences of autophagy in DN.

Critical Reanalysis of the Mechanisms Underlying the Cardiorenal Benefits of SGLT2 Inhibitors and Reaffirmation of the Nutrient Deprivation Signaling/Autophagy Hypothesis

SGLT2 (sodium-glucose cotransporter 2) inhibitors produce a distinctive pattern of benefits on the evolution and progression of cardiomyopathy and nephropathy, which is characterized by a reduction in oxidative and endoplasmic reticulum stress, restoration of mitochondrial health and enhanced mitochondrial biogenesis, a decrease in proinflammatory and profibrotic pathways, and preservation of cellular and organ integrity and viability. A substantial body of evidence indicates that this characteristic pattern of responses can be explained by the action of SGLT2 inhibitors to promote cellular housekeeping by enhancing autophagic flux, an effect that may be related to the action of these drugs to produce simultaneous upregulation of nutrient deprivation signaling and downregulation of nutrient surplus signaling, as manifested by an increase in the expression and activity of AMPK (adenosine monophosphate-activated protein kinase), SIRT1 (sirtuin 1), SIRT3 (sirtuin 3), SIRT6 (sirtuin 6), and PGC1-α (peroxisome proliferator-activated receptor γ coactivator 1-α) and decreased activation of mTOR (mammalian target of rapamycin). The distinctive pattern of cardioprotective and renoprotective effects of SGLT2 inhibitors is abolished by specific inhibition or knockdown of autophagy, AMPK, and sirtuins. In the clinical setting, the pattern of differentially increased proteins identified in proteomics analyses of blood collected in randomized trials is consistent with these findings. Clinical studies have also shown that SGLT2 inhibitors promote gluconeogenesis, ketogenesis, and erythrocytosis and reduce uricemia, the hallmarks of nutrient deprivation signaling and the principal statistical mediators of the ability of SGLT2 inhibitors to reduce the risk of heart failure and serious renal events. The action of SGLT2 inhibitors to augment autophagic flux is seen in isolated cells and tissues that do not express SGLT2 and are not exposed to changes in environmental glucose or ketones and may be related to an ability of these drugs to bind directly to sirtuins or mTOR. Changes in renal or cardiovascular physiology or metabolism cannot explain the benefits of SGLT2 inhibitors either experimentally or clinically. The direct molecular effects of SGLT2 inhibitors in isolated cells are consistent with the concept that SGLT2 acts as a nutrient surplus sensor, and thus, its inhibition causes enhanced nutrient deprivation signaling and its attendant cytoprotective effects, which can be abolished by specific inhibition or knockdown of AMPK, sirtuins, and autophagic flux.

SGLT2 inhibitors protect cardiomyocytes from myocardial infarction: a direct mechanism?

SGLT2 inhibitors have been developed as a novel class of glucose-lowering drugs affecting reabsorption of glucose and metabolic processes. They have been recently identified to be remarkably favorable in treating cardiovascular diseases, especially heart failure. Preclinical experiments have shown that SGLT2 inhibitors could hinder the progression of myocardial infarction and alleviate cardiac remodeling by mechanisms of metabolism influence, autophagy induction, inflammation attenuation and fibrosis reduction. Here we summarize the direct mechanism of SGLT2 inhibitors on myocardial infarction and investigate whether it could be applied to the clinic in improving cardiac function and healing after myocardial infarction.

SGLT2 inhibitors suppress epithelial-mesenchymal transition in podocytes under diabetic conditions via downregulating the IGF1R/PI3K pathway

Loss of podocyte is a characteristic pathological change of diabetic nephropathy (DN) which is associated with increased proteinuria. Many studies have shown that novel inhibitors of sodium-glucose cotransporter 2 (SGLT2-is), such as dapagliflozin, exert nephroprotective effect on delaying DN progression. However, the mechanisms underlying SGLT2-associated podocyte injury are still not fully elucidated. Here, we generated streptozotocin-induced DN models and treated them with dapagliflozin to explore the possible mechanisms underlying SGLT2 regulation. Compared to mice with DN, dapagliflozin-treated mice exhibited remission of pathological lesions, including glomerular sclerosis, thickening of the glomerular basement membrane (GBM), podocyte injury in the glomeruli, and decreased nephrotoxin levels accompanied by decreased SGLT2 expression. The mRNA expression profiles of these treated mice revealed the significance of the insulin-like growth factor-1 receptor (IGF1R)/PI3K regulatory axis in glomerular injury. KEGG analysis confirmed that the phosphatidylinositol signaling system and insulin signaling pathway were enriched. Western blotting showed that SGLT2-is inhibited the increase of mesenchymal markers (α-SMA, SNAI-1, and ZEB2) and the loss of podocyte markers (nephrin and E-cad). Additionally, SGLT2, IGF1R, phosphorylated PI3K, α-SMA, SNAI-1, and ZEB2 protein levels were increased in high glucose-stimulated human podocytes (HPC) and significantly decreased in dapagliflozin-treated (50 nM and 100 nM) or OSI-906-treated (inhibitor of IGF1R, 60 nM) groups. However, the use of both inhibitors did not enhance this protective effect. Next, we analyzed urine and plasma samples from a cohort consisting of 13 healthy people and 19 DN patients who were administered with (n = 9) or without (n = 10) SGLT2 inhibitors. ELISA results showed decreased circulating levels of IGF1 and IGF2 in SGLT2-is-treated DN patients compared with DN patients. Taken together, our study reported the key role of SGLT2/IGF1R/PI3K signaling in regulating podocyte epithelial-mesenchymal transition (EMT). Modulating IGF1R expression may be a novel approach for DN therapy.

Empagliflozin ameliorates type 2 diabetes mellitus-related diabetic nephropathy via altering the gut microbiota

BACKGROUND

The dysregulation of gut microbiota can be found in patients with type 2 diabetes mellitus (T2DM)-related diabetic nephropathy (DN). Inhibitors of sodium-glucose co-transporter 2 (SGLT2) were reported to affect gut microbiota. This study aimed to identify whether empagliflozin (EMPA) attenuated DN via regulating gut microbiota.

MATERIALS AND METHODS

The high-fat diet (HFD) combining streptozocin (STZ) injection was performed to induce DN in mice. The therapeutic effects of EMPA were observed by staining of renal tissues and urine albumin/creatinine ratio (UACR). Mouse feces were collected for 16S rRNA sequencing. Fecal short-chain fatty acids (SCFAs) and fecal and serum lipopolysaccharide (LPS) were determined. An antibiotic-ablated model was established to confirm the role of the gut microbiota in the actions of EMPA.

RESULTS

EMPA reduced the elevation of blood glucose and UACR caused by HFD/STZ. It inhibited the thickening of the colonic crypt and restored goblet cells and the expressions of ZO-1 and Occludin. The 16S rRNA sequencing showed that the diversity of gut microbiota was reduced after HFD/STZ treatment, while it was restored after EMPA treatment. The LPS-producing bacteria, Oscillibacter, and the SCFA-producing bacteria, Bateroid and Odoribacter, were changed after EMPA administration. The therapeutic effects of EMPA on ABX-treated mice were reduced. Meanwhile, the level of fecal SCFAs was decreased, while the levels of fecal and serum LPS were elevated, in T2DM mice, and they were negated by the administration of EMPA.

CONCLUSION

EMPA ameliorates T2DM-related DN via altering the gut microbiota, especially reducing LPS-producing bacteria and increasing SCFA-producing bacteria.

SGLT2 inhibitors improve kidney function and morphology by regulating renal metabolic reprogramming in mice with diabetic kidney disease

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD) worldwide. SGLT2 inhibitors are clinically effective in halting DKD progression. However, the underlying mechanisms remain unclear. The serum and kidneys of mice with DKD were analyzed using liquid chromatography with tandem mass spectrometry (LC–MS/MS)-based metabolomic and proteomic analyses. Three groups were established: placebo-treated littermate db/m mice, placebo-treated db/db mice and EMPA-treated db/db mice. Empagliflozin (EMPA) and placebo (10 mg/kg/d) were administered for 12 weeks. EMPA treatment decreased Cys-C and urinary albumin excretion compared with placebo by 78.60% and 57.12%, respectively (p < 0.001 in all cases). Renal glomerular area, interstitial fibrosis and glomerulosclerosis were decreased by 16.47%, 68.50% and 62.82%, respectively (p < 0.05 in all cases). Multi-omic analysis revealed that EMPA treatment altered the protein and metabolic profiles in the db/db group, including 32 renal proteins, 51 serum proteins, 94 renal metabolites and 37 serum metabolites. Five EMPA-related metabolic pathways were identified by integrating proteomic and metabolomic analyses, which are involved in renal purine metabolism; pyrimidine metabolism; tryptophan metabolism; nicotinate and nicotinamide metabolism, and glycine, serine and threonine metabolism in serum. In conclusion, this study demonstrated metabolic reprogramming in mice with DKD. EMPA treatment improved kidney function and morphology by regulating metabolic reprogramming, including regulation of renal reductive stress, alleviation of mitochondrial dysfunction and reduction in renal oxidative stress reaction.

Research progress on the relationship between autophagy and chronic complications of diabetes

Diabetes is a common metabolic disease whose hyperglycemic state can induce diverse complications and even threaten human health and life security. Currently, the treatment of diabetes is restricted to drugs that regulate blood glucose and have certain accompanying side effects. Autophagy, a research hotspot, has been proven to be involved in the occurrence and progression of the chronic complications of diabetes. Autophagy, as an essential organismal defense mechanism, refers to the wrapping of cytoplasmic proteins, broken organelles or pathogens by vesicles, which are then degraded by lysosomes to maintain the stability of the intracellular environment. Here, we review the relevant aspects of autophagy and the molecular mechanisms of autophagy in diabetic chronic complications, and further analyze the impact of improving autophagy on diabetic chronic complications, which will contribute to a new direction for further prevention and treatment of diabetic chronic complications.

Repositioning Linagliptin for the Mitigation of Cadmium-Induced Testicular Dysfunction in Rats: Targeting HMGB1/TLR4/NLRP3 Axis and Autophagy

Cadmium, a ubiquitous environmental toxicant, disrupts testicular function and fertility. The dipeptidyl peptidase-4 inhibitor linagliptin has shown pronounced anti-inflammatory and anti-apoptotic features; however, its effects against cadmium-evoked testicular impairment have not been examined. Herein, the present study investigated targeting inflammation, apoptosis, and autophagy by linagliptin for potential modulation of cadmium-induced testicular dysfunction in rats. After 60 days of cadmium chloride administration (5 mg/kg/day, by gavage), testes, epididymis, and blood were collected for analysis. The present findings revealed that linagliptin improved the histopathological lesions, including spermatogenesis impairment and germ cell loss. Moreover, it improved sperm count/motility and serum testosterone. The favorable effects of linagliptin were mediated by curbing testicular inflammation seen by dampening of HMGB1/TLR4 pathway and associated lowering of nuclear NF-κBp65. In tandem, linagliptin suppressed the activation of NLRP3 inflammasome/caspase 1 axis with consequent lowering of the pro-inflammatory IL-1β and IL-18. Jointly, linagliptin attenuated testicular apoptotic responses seen by Bax downregulation, Bcl-2 upregulation, and suppressed caspase 3 activity. With respect to autophagy, linagliptin enhanced the testicular autophagy flux seen by lowered accumulation of p62 SQSTM1 alongside upregulation of Beclin 1. The observed autophagy stimulation was associated with elevated AMPK (Ser487) phosphorylation and lowered mTOR (Ser2448) phosphorylation, indicating AMPK/mTOR pathway activation. In conclusion, inhibition of testicular HMGB1/TLR4/NLRP3 pro-inflammatory axis and apoptosis alongside stimulation of autophagy were implicated in the favorable actions of linagliptin against cadmium-triggered testicular impairment.

Anti-Arrhythmic Effects of Sodium-Glucose Co-Transporter 2 Inhibitors

Arrhythmias are clinically prevalent with a high mortality rate. They impose a huge economic burden, thereby substantially affecting the quality of life. Sodium-glucose co-transporter 2 inhibitor (SGLT2i) is a new type of hypoglycemic drug, which can regulate blood glucose level safely and effectively. Additionally, it reduces the occurrence and progression of heart failure and cardiovascular events significantly. Recently, studies have found that SGLT2i can alleviate the occurrence and progression of cardiac arrhythmias; however, the exact mechanism remains unclear. In this review, we aimed to discuss and summarize new literature on different modes in which SGLT2i ameliorates the occurrence and development of cardiac arrhythmias.

Sodium-glucose Cotransporter Type 2 Inhibitors: A New Insight into the Molecular Mechanisms of Diabetic Nephropathy

Diabetic nephropathy is one of the chronic microvascular complications of diabetes and is a leading cause of end-stage renal disease. Fortunately, clinical trials have demonstrated that sodium-glucose cotransporter type 2 inhibitors could decrease proteinuria and improve renal endpoints and are promising agents for the treatment of diabetic nephropathy. The renoprotective effects of sodium-glucose cotransporter type 2 inhibitors cannot be simply attributed to their advantages in aspects of metabolic benefits, such as glycemic control, lowering blood pressure, and control of serum uric acid, or improving hemodynamics associated with decreased glomerular filtration pressure. Some preclinical evidence suggests that sodium-glucose cotransporter type 2 inhibitors exert their renoprotective effects by multiple mechanisms, including attenuation of oxidative and endoplasmic reticulum stresses, anti-fibrosis and anti-inflammation, protection of podocytes, suppression of megalin function, improvement of renal hypoxia, restored mitochondrial dysfunction and autophagy, as well as inhibition of sodium-hydrogen exchanger 3. In the present study, the detailed molecular mechanisms of sodium-glucose cotransporter type 2 inhibitors with the actions of diabetic nephropathy were reviewed, with the purpose of providing the basis for drug selection for the treatment of diabetic nephropathy.

Role of Dipeptidyl Peptidase 4 Inhibitors in Antidiabetic Treatment

In recent years, important changes have occurred in the field of diabetes treatment. The focus of the treatment of diabetic patients has shifted from the control of blood glucose itself to the overall management of risk factors, while adjusting blood glucose goals according to individualization. In addition, regulators need to approve new antidiabetic drugs which have been tested for cardiovascular safety. Thus, the newest class of drugs has been shown to reduce major adverse cardiovascular events, including sodium-glucose transporter 2 (SGLT2) and some glucagon like peptide 1 receptor (GLP1) analog. As such, they have a prominent place in the hyperglycemia treatment algorithms. In recent years, the role of DPP4 inhibitors (DPP4i) has been modified. DPP4i have a favorable safety profile and anti-inflammatory profile, do not cause hypoglycemia or weight gain, and do not require dose escalation. In addition, it can also be applied to some types of chronic kidney disease patients and elderly patients with diabetes. Overall, DPP4i, as a class of safe oral hypoglycemic agents, have a role in the management of diabetic patients, and there is extensive experience in their use.

circSTRN3 aggravates sepsis-induced acute kidney injury by regulating miR-578/ toll like receptor 4 axis

Sepsis is a systemic inflammatory response caused by infection, and severe sepsis is commonly associated with the development of acute kidney injury (AKI). Accumulating evidence has revealed the implication of circular RNAs in AKI. In this study, we explored the potential engagement and the underlying mechanism of hsa_circ_010157 (circSTRN3) in sepsis-induced AKI. CircSTRN3 levels in HK2 cells and serum samples of patients were determined by RT-PCR. The protein levels of TLR4 (Toll Like Receptor 4), bax (Bcl-2-associated X protein), cleaved caspase 3 and bcl-2 (B-cell lymphoma-2) were detected by Western blotting (WB), and the levels of proinflammatory cytokines were detected by ELISA. The molecular interactions between mir-578/TLR4 and circSTRN3/miR-578 were analyzed by dual luciferase reporter assay as well as RNA pull-down experiment. Lipopolysaccharide (LPS) treated HK2 cells were used as an in vitro model to investigate the functional interaction of circSTRN3/miR-578/TLR4 axis. We found that the expression level of circSTRN3 in patients with sepsis-induced AKI and LPS-induced HK2 cells was higher. Silencing cicrSTRN3 alleviated LPS-induced cell proliferation, and suppressed the inflammatory response and apoptosis in LPS-treated HK2 cells. In contrast, the overexpression of circSTRN3 aggravated the cellular damages induced by LPS treatment. CircSTRN3 targeted miR-578/TLR4 axis to influence the damage effect induced by LPS. miR-578 inhibitor or TLR4 overexpression impaired the rescue effect of circSTRN3 knockdown. These results indicate that circSTRN3 upregulation in sepsis-induced AKI modulates miR-578/TLR4 axis to promote the pathogenesis of AKI, which could serve as future therapeutic targets for AKI treatment.

Geroscience-guided repurposing of FDA-approved drugs to target aging: A proposed process and prioritization

Common chronic diseases represent the greatest driver of rising healthcare costs, as well as declining function, independence, and quality of life. Geroscience-guided approaches seek to delay the onset and progression of multiple chronic conditions by targeting fundamental biological pathways of aging. This approach is more likely to improve overall health and function in old age than treating individual diseases, by addressing aging the largest and mostly ignored risk factor for the leading causes of morbidity in older adults. Nevertheless, challenges in repurposing existing and moving newly discovered interventions from the bench to clinical care have impeded the progress of this potentially transformational paradigm shift. In this article, we propose the creation of a standardized process for evaluating FDA-approved medications for their geroscience potential. Criteria for systematically evaluating the existing literature that spans from animal models to human studies will permit the prioritization of efforts and financial investments for translating geroscience and allow immediate progress on the design of the next Targeting Aging with MEtformin (TAME)-like study involving such candidate gerotherapeutics.

An Overview of the Cardiorenal Protective Mechanisms of SGLT2 Inhibitors

Sodium-glucose co-transporter 2 (SGLT2) inhibitors block glucose reabsorption in the renal proximal tubule, an insulin-independent mechanism that plays a critical role in glycemic regulation in diabetes. In addition to their glucose-lowering effects, SGLT2 inhibitors prevent both renal damage and the onset of chronic kidney disease and cardiovascular events, in particular heart failure with both reduced and preserved ejection fraction. These unexpected benefits prompted changes in treatment guidelines and scientific interest in the underlying mechanisms. Aside from the target effects of SGLT2 inhibition, a wide spectrum of beneficial actions is described for the kidney and the heart, even though the cardiac tissue does not express SGLT2 channels. Correction of cardiorenal risk factors, metabolic adjustments ameliorating myocardial substrate utilization, and optimization of ventricular loading conditions through effects on diuresis, natriuresis, and vascular function appear to be the main underlying mechanisms for the observed cardiorenal protection. Additional clinical advantages associated with using SGLT2 inhibitors are antifibrotic effects due to correction of inflammation and oxidative stress, modulation of mitochondrial function, and autophagy. Much research is required to understand the numerous and complex pathways involved in SGLT2 inhibition. This review summarizes the current known mechanisms of SGLT2-mediated cardiorenal protection.

Sodium Glucose Cotransporter-2 Inhibitors: Spotlight on Favorable Effects on Clinical Outcomes beyond Diabetes

Sodium glucose transporter type 2 (SGLT2) molecules are found in proximal tubules of the kidney, and perhaps in the brain or intestine, but rarely in any other tissue. However, their inhibitors, intended to improve diabetes compensation, have many more beneficial effects. They improve kidney and cardiovascular outcomes and decrease mortality. These benefits are not limited to diabetics but were also found in non-diabetic individuals. The pathophysiological pathways underlying the treatment success have been investigated in both clinical and experimental studies. There have been numerous excellent reviews, but these were mostly restricted to limited aspects of the knowledge. The aim of this review is to summarize the known experimental and clinical evidence of SGLT2 inhibitors' effects on individual organs (kidney, heart, liver, etc.), as well as the systemic changes that lead to an improvement in clinical outcomes.

Empagliflozin Enhances Autophagy, Mitochondrial Biogenesis, and Antioxidant Defense and Ameliorates Renal Ischemia/Reperfusion in Nondiabetic Rats

Background. Recent meta-analyses have shown that sodium-glucose cotransporter 2 (SGLT-2) inhibitors alleviate chronic kidney disease and acute kidney injury in diabetic patients. In this study, we aimed to investigate the effect of empagliflozin on renal ischemia/reperfusion (I/R) in nondiabetic rats and find the possible mechanisms. Experimental Approach. Eighteen male Wistar rats were randomly divided into three groups, including healthy control, ischemic control, and empagliflozin-treated group. Thirty minutes of bilateral renal ischemia was induced by clamping the renal hilum. Forty-eight hours after reopening the clamps, rats’ blood samples and tissue specimens were collected. Empagliflozin 10 mg/kg was administered by gavage, 2 hours before ischemia and 24 hours after the first dose. Results. I/R injury led to a significant rise in serum creatinine and blood urea nitrogen which was significantly decreased after treatment with empagliflozin. Empagliflozin also alleviated tubulointerstitial and glomerular damage and significantly decreased tissue histology scores. Empagliflozin decreased the increased levels of malondialdehyde, interleukin 1β, and tumor necrosis factor α. SGLT2 inhibition increased the decreased expression of nuclear factor erythroid 2-related factor 2 and PPARG coactivator 1 alpha that conduct antioxidant defense and mitochondrial biogenesis, respectively. Furthermore, empagliflozin markedly increased LC3-II/LC3-I and bcl2/bax ratios, showing its beneficial effect on activation of autophagy and inhibition of apoptosis. Despite its effects on diabetic nephropathy, empagliflozin did not activate the Sestrin2/AMP-activated protein kinase pathway in this study. Conclusion. Empagliflozin improved renal I/R injury in nondiabetic rats in this study by promoting autophagy and mitochondrial biogenesis and attenuation of oxidative stress, inflammation, and apoptosis.

Canagliflozin protects against cisplatin-induced acute kidney injury by AMPK-mediated autophagy in renal proximal tubular cells

Sodium-glucose cotransporter 2 inhibitors, which are recently introduced as glucose-lowering agents, improve cardiovascular and renal outcomes in patients with diabetes mellitus. These drugs also have beneficial effects in various kidney disease models. However, the effect of SGLT2 inhibitors on cisplatin-induced acute kidney injury (AKI) and their mechanism of action need to be elucidated. In this study, we investigated whether canagliflozin protects against cisplatin-induced AKI, depending on adenosine monophosphate-activated protein kinase (AMPK) activation and following induction of autophagy. In the experiments using the HK-2 cell line, cell viability assay and molecular analysis revealed that canagliflozin protected renal proximal tubular cells from cisplatin, whereas addition of chloroquine or compound C abolished the protective effect of canagliflozin. In the mouse model of cisplatin-induced AKI, canagliflozin protected mice from cisplatin-induced AKI. However, treatment with chloroquine or compound C in addition to administration of cisplatin and canagliflozin eliminated the protective effect of canagliflozin. Collectively, these findings indicate that canagliflozin protects against cisplatin-induced AKI by activating AMPK and autophagy in renal proximal tubular cells.

Sodium-Glucose Cotransporter 2 Inhibitors Mechanisms of Action: A Review

Sodium-Glucose Cotransporter 2 inhibitors (SGLT2i), or gliflozins, are a group of antidiabetic drugs that have shown improvement in renal and cardiovascular outcomes in patients with kidney disease, with and without diabetes. In this review, we will describe the different proposed mechanisms of action of SGLT2i. Gliflozins inhibit renal glucose reabsorption by blocking the SGLT2 cotransporters in the proximal tubules and causing glucosuria. This reduces glycemia and lowers HbA_1c by ~1.0%. The accompanying sodium excretion reverts the tubuloglomerular feedback and reduces intraglomerular pressure, which is central to the nephroprotective effects of SGLT2i. The caloric loss reduces weight, increases insulin sensitivity, lipid metabolism, and likely reduces lipotoxicity. Metabolism shifts toward gluconeogenesis and ketogenesis, thought to be protective for the heart and kidneys. Additionally, there is evidence of a reduction in tubular cell glucotoxicity through reduced mitochondrial dysfunction and inflammation. SGLT2i likely reduce kidney hypoxia by reducing tubular energy and oxygen demand. SGLT2i improve blood pressure through a negative sodium and water balance and possibly by inhibiting the sympathetic nervous system. These changes contribute to the improvement of cardiovascular function and are thought to be central in the cardiovascular benefits of SGLT2i. Gliflozins also reduce hepcidin levels, improving erythropoiesis and anemia. Finally, other possible mechanisms include a reduction in inflammatory markers, fibrosis, podocyte injury, and other related mechanisms. SGLT2i have shown significant and highly consistent benefits in renal and cardiovascular protection. The complexity and interconnectedness of the primary and secondary mechanisms of action make them a most interesting and exciting pharmacologic group.