Comparison of the effects of insulin and SGLT2 inhibitor on the Renal Renin-Angiotensin system in type 1 diabetes mice

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.

Hedgehog interacting protein activates sodium-glucose cotransporter 2 expression and promotes renal tubular epithelial cell senescence in a mouse model of type 1 diabetes

AIMS/HYPOTHESIS

Senescent renal tubular cells may be linked to diabetic kidney disease (DKD)-related tubulopathy. We studied mice with or without diabetes in which hedgehog interacting protein (HHIP) was present or specifically knocked out in renal tubules (Hhip^RT-KO), hypothesising that local deficiency of HHIP in the renal tubules would attenuate tubular cell senescence, thereby preventing DKD tubulopathy.

METHODS

Low-dose streptozotocin was employed to induce diabetes in both Hhip^RT-KO and control (Hhip^fl/fl) mice. Transgenic mice overexpressing Hhip in renal proximal tubular cells (RPTC) (Hhip^RPTC-Tg) were used for validation, and primary RPTCs and human RPTCs (HK2) were used for in vitro studies. Kidney morphology/function, tubular senescence and the relevant molecular measurements were assessed.

RESULTS

Compared with Hhip^fl/fl mice with diabetes, Hhip^RT-KO mice with diabetes displayed lower blood glucose levels, normalised GFR, ameliorated urinary albumin/creatinine ratio and less severe DKD, including tubulopathy. Sodium-glucose cotransporter 2 (SGLT2) expression was attenuated in RPTCs of Hhip^RT-KO mice with diabetes compared with Hhip^fl/fl mice with diabetes. In parallel, an increased tubular senescence-associated secretory phenotype involving release of inflammatory cytokines (IL-1β, IL-6 and monocyte chemoattractant protein-1) and activation of senescence markers (p16, p21, p53) in Hhip^fl/fl mice with diabetes was attenuated in Hhip^RT-KO mice with diabetes. In contrast, Hhip^RPTC-Tg mice had increased tubular senescence, which was inhibited by canagliflozin in primary RPTCs. In HK2 cells, HHIP overexpression or recombinant HHIP increased SGLT2 protein expression and promoted cellular senescence by targeting both ataxia-telangiectasia mutated and ataxia-telangiectasia and Rad3-related-mediated cell arrest.

CONCLUSIONS/INTERPRETATION

Tubular HHIP deficiency prevented DKD-related tubulopathy, possibly via the inhibition of SGLT2 expression and cellular senescence.

Enhanced Cardiorenal Protective Effects of Combining SGLT2 Inhibition, Endothelin Receptor Antagonism and RAS Blockade in Type 2 Diabetic Mice

Treatments with sodium-glucose 2 cotransporter inhibitors (SGLT2i) or endothelin receptor antagonists (ERA) have shown cardiorenal protective effects. The present study aimed to evaluate the cardiorenal beneficial effects of the combination of SGLT2i and ERA on top of renin-angiotensin system (RAS) blockade. Type 2 diabetic mice (db/db) were treated with different combinations of an SGLT2i (empagliflozin), an ERA (atrasentan), and an angiotensin-converting enzyme inhibitor (ramipril) for 8 weeks. Vehicle-treated diabetic mice and non-diabetic mice were included as controls. Weight, blood glucose, blood pressure, and kidney and heart function were monitored during the study. Kidneys and heart were collected for histological examination and to study the intrarenal RAS. Treatment with empagliflozin alone or combined significantly decreased blood glucose compared to vehicle-treated db/db. The dual and triple therapies achieved significantly greater reductions in diastolic blood pressure than ramipril alone. Compared to vehicle-treated db/db, empagliflozin combined with ramipril or in triple therapy significantly prevented GFR increase, but only the triple combination exerted greater protection against podocyte loss. In the heart, empagliflozin alone or combined reduced cardiac isovolumetric relaxation time (IVRT) and left atrium (LA) diameter as compared to vehicle-treated db/db. However, only the triple therapy was able to reduce cardiomyocyte area. Importantly, the add-on triple therapy further enhanced the intrarenal ACE2/Ang(1-7)/Mas protective arm of the RAS. These data suggest that triple therapy with empagliflozin, atrasentan and ramipril show synergistic cardiorenal protective effects in a type 2 diabetic mouse model.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

Deletion of heterogeneous nuclear ribonucleoprotein F in renal tubules downregulates SGLT2 expression and attenuates hyperfiltration and kidney injury in a mouse model of diabetes

AIMS/HYPOTHESIS

We previously reported that renal tubule-specific deletion of heterogeneous nuclear ribonucleoprotein F (Hnrnpf) results in upregulation of renal angiotensinogen (Agt) and downregulation of sodium-glucose co-transporter 2 (Sglt2) in Hnrnpf^RT knockout (KO) mice. Non-diabetic Hnrnpf^RT KO mice develop hypertension, renal interstitial fibrosis and glycosuria with no renoprotective effect from downregulated Sglt2 expression. Here, we investigated the effect of renal tubular Hnrnpf deletion on hyperfiltration and kidney injury in Akita mice, a model of type 1 diabetes.

METHODS

Akita Hnrnpf^RT KO mice were generated through crossbreeding tubule-specific (Pax8)-Cre mice with Akita floxed-Hnrnpf mice on a C57BL/6 background. Male non-diabetic control (Ctrl), Akita, and Akita Hnrnpf^RT KO mice were studied up to the age of 24 weeks (n = 8/group).

RESULTS

Akita mice exhibited elevated systolic blood pressure as compared with Ctrl mice, which was significantly higher in Akita Hnrnpf^RT KO mice than Akita mice. Compared with Akita mice, Akita Hnrnpf^RT KO mice had lower blood glucose levels with increased urinary glucose excretion. Akita mice developed kidney hypertrophy, glomerular hyperfiltration (increased glomerular filtration rate), glomerulomegaly, mesangial expansion, podocyte foot process effacement, thickened glomerular basement membranes, renal interstitial fibrosis and increased albuminuria. These abnormalities were attenuated in Akita Hnrnpf^RT KO mice. Treatment of Akita Hnrnpf^RT KO mice with a selective A1 adenosine receptor inhibitor resulted in an increase in glomerular filtration rate. Renal Agt expression was elevated in Akita mice and further increased in Akita Hnrnpf^RT KO mice. In contrast, Sglt2 expression was increased in Akita and decreased in Akita Hnrnpf^RT KO mice.

CONCLUSIONS/INTERPRETATION

The renoprotective effect of Sglt2 downregulation overcomes the renal injurious effect of Agt when these opposing factors coexist under diabetic conditions, at least partly via the activation of tubuloglomerular feedback.

The Na/K-ATPase Signaling and SGLT2 Inhibitor-Mediated Cardiorenal Protection: A Crossed Road?

In different large-scale clinic outcome trials, sodium (Na⁺)/glucose co-transporter 2 (SGLT2) inhibitors showed profound cardiac- and renal-protective effects, making them revolutionary treatments for heart failure and kidney disease. Different theories are proposed according to the emerging protective effects other than the original purpose of glucose-lowering in diabetic patients. As the ATP-dependent primary ion transporter providing the Na⁺ gradient to drive other Na⁺-dependent transporters, the possible role of the sodium–potassium adenosine triphosphatase (Na/K-ATPase) as the primary ion transporter and its signaling function is not explored.

Sodium-Glucose Cotransporter-2 Inhibitors in Vascular Biology: Cellular and Molecular Mechanisms

Sodium-glucose cotransporter-2 (SGLT2) inhibitors are new antidiabetic drugs that reduce hyperglycemia by inhibiting the glucose reabsorption in renal proximal tubules. Clinical studies have shown that SGLT2 inhibitors not only improve glycemic control but also reduce major adverse cardiovascular events (MACE, cardiovascular and total mortality, fatal or nonfatal myocardial infarction or stroke) and hospitalization for heart failure (HF), and improve outcome in chronic kidney disease. These cardiovascular and renal benefits have now been confirmed in both diabetes and non-diabetes patients. The precise mechanism(s) responsible for the protective effects are under intensive investigation. This review examines current evidence on the cardiovascular benefits of SGLT2 inhibitors, with a special emphasis on the vascular actions and their potential mechanisms.

Angiotensin II up-regulates sodium-glucose co-transporter 2 expression and SGLT2 inhibitor attenuates Ang II-induced hypertensive renal injury in mice

Clinical trials indicate that sodium/glucose co-transporter 2 (SGLT2) inhibitors (SGLT2i) improve kidney function, yet, the molecular regulation of SGLT2 expression is incompletely understood. Here, we investigated the role of the intrarenal renin-angiotensin system (RAS) on SGLT2 expression. In adult non-diabetic participants in the Nephrotic Syndrome Study Network (NEPTUNE, n=163), multivariable linear regression analysis showed SGLT2 mRNA was significantly associated with angiotensinogen (AGT), renin, and angiotensin-converting enzyme (ACE) mRNA levels (P<0.001). In vitro, angiotensin II (Ang II) dose-dependently stimulated SGLT2 expression in HK-2, human immortalized renal proximal tubular cells (RPTCs); losartan and antioxidants inhibited it. Sglt2 expression was increased in transgenic (Tg) mice specifically overexpressing Agt in their RPTCs, as well as in WT mice with a single subcutaneous injection of Ang II (1.44 mg/kg). Moreover, Ang II (1000 ng/kg/min) infusion via osmotic mini-pump in WT mice for 4 weeks increased systolic blood pressure (SBP), glomerulosclerosis, tubulointerstitial fibrosis, and albuminuria; canaglifozin (Cana, 15 mg/kg/day) reversed these changes, with the exception of SBP. Fractional glucose excretion (FeGlu) was higher in Ang II+Cana than WT+Cana, whereas Sglt2 expression was similar. Our data demonstrate a link between intrarenal RAS and SGLT2 expression and that SGLT2i ameliorates Ang II-induced renal injury independent of SBP.

The Rationale and Evidence for SGLT2 Inhibitors as a Treatment for Nondiabetic Glomerular Disease

Background

Recent studies show that sodium-glucose cotransporter 2 inhibitors (SGLT2i), originally approved for glycemic control in patients with type 2 diabetes, also exert renoprotective effects independently from effects on dysglycemia. Moreover, recent work indicates that SGLT2i treatment may be effective in patients with nondiabetic chronic kidney disease, including primary and secondary glomerular diseases.

Summary

SGLT2i lower blood glucose by blocking glucose resorption in the early renal proximal tubule through the glucose transporter, SGLT2, leading to enhanced urinary glucose excretion. Recent studies indicate that SGLT2i may have pleiotropic effects on cells other than proximal tubular cells. SGLT2i reduce the glomerular workload by decreasing the intraglomerular pressure, thus ameliorating hyperfiltration, if present, and may also decrease systemic blood pressure. SGLT2i may also act directly on endothelial cells, possibly via modulating the effects of adhesion molecules and reducing inflammatory cytokines and reactive oxygen species. SGLT2i may have direct anti-inflammatory and antifibrotic effects on renal tubules. Some reports suggest direct protective effects on podocytes and mesangial cells as well. Here, we provide a review of the potential mechanisms of renoprotection, therapeutic utility, and potential side effects of SGLT2i in patients with nondiabetic glomerular diseases, based on data from studies carried out in cells, experimental animals, and humans.

Key Messages

SGLT2i may be a promising addition to the glomerular disease treatment armamentarium. However, it is unclear at what point of the natural history of specific glomerular diseases (whether this is immune or nonimmune mediated) SGLT2i can be beneficial. Additionally, further studies are needed to assess the long-term efficacy and safety of SGLT2i in patients with nondiabetic glomerular diseases.