Mini-review: diabetic renal complications, a potential stinky remedy

Diabetic Nephropathy and Gaseous Modulators

Diabetic nephropathy (DN) remains the leading cause of vascular morbidity and mortality in diabetes patients. Despite the progress in understanding the diabetic disease process and advanced management of nephropathy, a number of patients still progress to end-stage renal disease (ESRD). The underlying mechanism still needs to be clarified. Gaseous signaling molecules, so-called gasotransmitters, such as nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), have been shown to play an essential role in the development, progression, and ramification of DN depending on their availability and physiological actions. Although the studies on gasotransmitter regulations of DN are still emerging, the evidence revealed an aberrant level of gasotransmitters in patients with diabetes. In studies, different gasotransmitter donors have been implicated in ameliorating diabetic renal dysfunction. In this perspective, we summarized an overview of the recent advances in the physiological relevance of the gaseous molecules and their multifaceted interaction with other potential factors, such as extracellular matrix (ECM), in the severity modulation of DN. Moreover, the perspective of the present review highlights the possible therapeutic interventions of gasotransmitters in ameliorating this dreaded disease.

Effects of Sodium Thiosulfate During Resuscitation From Trauma-and-Hemorrhage in Cystathionine-γ-Lyase Knockout Mice With Diabetes Type 1

Background

Sodium thiosulfate (STS) is a recognized drug with antioxidant and H2S releasing properties. We recently showed that STS attenuated organ dysfunction and injury during resuscitation from trauma-and-hemorrhage in CSE-ko mice, confirming its previously described organ-protective and anti-inflammatory properties. The role of H2S in diabetes mellitus type 1 (DMT1) is controversial: genetic DMT1 impairs H2S biosynthesis, which has been referred to contribute to endothelial dysfunction and cardiomyopathy. In contrast, development and severity of hyperglycemia in streptozotocin(STZ)-induced DMT1 was attenuated in CSE-ko mice. Therefore, we tested the hypothesis whether STS would also exert organ-protective effects in CSE-ko mice with STZ-induced DMT1, similar to our findings in animals without underlying co-morbidity.

Methods

Under short-term anesthesia with sevoflurane and analgesia with buprenorphine CSE-ko mice underwent DMT1-induction by single STZ injection (100 μg⋅g-1). Seven days later, animals underwent blast wave-induced blunt chest trauma and surgical instrumentation followed by 1 h of hemorrhagic shock (MAP 35 ± 5 mmHg). Resuscitation comprised re-transfusion of shed blood, lung-protective mechanical ventilation, fluid resuscitation and continuous i.v. norepinephrine together with either i.v. STS (0.45 mg⋅g-1) or vehicle (n = 9 in each group). Lung mechanics, hemodynamics, gas exchange, acid-base status, stable isotope-based metabolism, and visceral organ function were assessed. Blood and organs were collected for analysis of cytokines, chemokines, and immunoblotting.

Results

Diabetes mellitus type 1 was associated with more severe circulatory shock when compared to our previous study using the same experimental design in CSE-ko mice without co-morbidity. STS did not exert any beneficial therapeutic effect. Most of the parameters measured of the inflammatory response nor the tissue expression of marker proteins of the stress response were affected either.

Conclusion

In contrast to our previous findings in CSE-ko mice without underlying co-morbidity, STS did not exert any beneficial therapeutic effect in mice with STZ-induced DMT1, possibly due to DMT1-related more severe circulatory shock. This result highlights the translational importance of both integrating standard ICU procedures and investigating underlying co-morbidity in animal models of shock research.

GYY4137 Regulates Extracellular Matrix Turnover in the Diabetic Kidney by Modulating Retinoid X Receptor Signaling

Diabetic kidney is associated with an accumulation of extracellular matrix (ECM) leading to renal fibrosis. Dysregulation of retinoic acid metabolism involving retinoic acid receptors (RARs) and retinoid X receptors (RXRs) has been shown to play a crucial role in diabetic nephropathy (DN). Furthermore, RARs and peroxisome proliferator-activated receptor γ (PPARγ) are known to control the RXR-mediated transcriptional regulation of several target genes involved in DN. Recently, RAR and RXR have been shown to upregulate plasminogen activator inhibitor-1 (PAI-1), a major player involved in ECM accumulation and renal fibrosis during DN. Interestingly, hydrogen sulfide (H₂S) has been shown to ameliorate adverse renal remodeling in DN. We investigated the role of RXR signaling in the ECM turnover in diabetic kidney, and whether H₂S can mitigate ECM accumulation by modulating PPAR/RAR-mediated RXR signaling. We used wild-type (C57BL/6J), diabetic (C57BL/6-Ins2^Akita/J) mice and mouse mesangial cells (MCs) as experimental models. GYY4137 was used as a H₂S donor. Results showed that in diabetic kidney, the expression of PPARγ was decreased, whereas upregulations of RXRα, RXRβ, and RARγ1 expression were observed. The changes were associated with elevated PAI-1, MMP-9 and MMP-13. In addition, the expressions of collagen IV, fibronectin and laminin were increased, whereas elastin expression was decreased in the diabetic kidney. Excessive collagen deposition was observed predominantly in the peri-glomerular and glomerular regions of the diabetic kidney. Immunohistochemical localization revealed elevated expression of fibronectin and laminin in the glomeruli of the diabetic kidney. GYY4137 reversed the pathological changes. Similar results were observed in in vitro experiments. In conclusion, our data suggest that RXR signaling plays a significant role in ECM turnover, and GYY4137 modulates PPAR/RAR-mediated RXR signaling to ameliorate PAI-1-dependent adverse ECM turnover in DN.

Schisandrin B alleviates diabetic nephropathy through suppressing excessive inflammation and oxidative stress

Diabetic nephropathy (DN) is a progressive kidney disease due to glomerular capillary damage in diabetic patients, with inflammation and oxidative stress implicated as crucial pathogenic factors. There is an urgent need to develop effective therapeutic drug. Natural medicines are rich resources for active lead compounds. They would provide new opportunities for the treatment of DN. The present study was designed to investigate the protective effects of Schisandrin B (SchB) on DN and to delineate the underlying mechanism. Oral administration of SchB in the diabetic mouse model significantly alleviated hyperglycemia-induced renal injury, which was accompanied by maintenance of urine creatinine and albumin levels at similar to those of control non-diabetic mice. Histological examination of renal tissue indicated that both development of fibrosis and renal cell apoptosis were dramatically inhibited by SchB. The protective effect of SchB on DN associated with suppression of inflammatory response and oxidative stress. These results strongly suggested that SchB could be a potential therapeutic agent for treatment of DN. Moreover, our findings provided a fuller understanding of the regulatory role of NF-κB and Nrf2 in DN, indicating that they could be important therapeutic targets.

Hydrogen sulfide ameliorates aging-associated changes in the kidney

Aging is associated with replacement of normal kidney parenchyma by fibrosis. Because hydrogen sulfide (H₂S) ameliorates kidney fibrosis in disease models, we examined its status in the aging kidney. In the first study, we examined kidney cortical H₂S metabolism and signaling pathways related to synthesis of proteins including matrix proteins in young and old male C57BL/6 mice. In old mice, increase in renal cortical content of matrix protein involved in fibrosis was associated with decreased H₂S generation and AMPK activity, and activation of insulin receptor (IR)/IRS-2-Akt-mTORC1-mRNA translation signaling axis that can lead to increase in protein synthesis. In the second study, we randomized 18-19 month-old male C57BL/6 mice to receive 30 μmol/L sodium hydrosulfide (NaHS) in drinking water vs. water alone (control) for 5 months. Administration of NaHS increased plasma free sulfide levels. NaHS inhibited the increase in kidney cortical content of matrix proteins involved in fibrosis and ameliorated glomerulosclerosis. NaHS restored AMPK activity and inhibited activation of IR/IRS-2-Akt-mTORC1-mRNA translation axis. NaHS inhibited age-related increase in kidney cortical content of p21, IL-1β, and IL-6, components of the senescence-associated secretory phenotype. NaHS abolished increase in urinary albumin excretion seen in control mice and reduced serum cystatin C levels suggesting improved glomerular clearance function. We conclude that aging-induced changes in the kidney are associated with H₂S deficiency. Administration of H₂S ameliorates aging-induced kidney changes probably by inhibiting signaling pathways leading to matrix protein synthesis.

EGFR inhibition attenuates diabetic nephropathy through decreasing ROS and endoplasmic reticulum stress

Diabetic nephropathy (DN) is a progressive kidney disease due to glomerular capillary damage in diabetic patients. Endoplasmic reticulum (ER) stress caused by reactive oxygen species (ROS) is associated with DN progression. Epidermal growth factor receptor (EGFR) mediates oxidative stress and damage of cardiomyocytes in diabetic mice. Here we demonstrated that AG1478, a specific inhibitor of EGFR, blocked EGFR and AKT phosphorylation in diabetic mice. Oxidative stress and ER stress markers were eliminated after AG1478 administration. AG1478 decreased pro-fibrotic genes TGF-β and collagen IV. Furthermore, we found that high glucose (HG) induced oxidative stress and ER stress, and subsequently increased ATF4 and CHOP. These changes were eliminated by either AG1478 or ROS scavenger N-acetyl-L-cysteine (NAC) administration. These results were confirmed by knock-down approaches in renal mesangial SV40 cells. However, AG1478, not NAC, reversed HG induced EGFR and AKT phosphorylation. These results suggest that EGFR/AKT/ROS/ER stress signaling plays an essential role in DN development and inhibiting EGFR may serve as a potential therapeutic strategy in diabetic kidney diseases.

High Glucose Induces Mouse Mesangial Cell Overproliferation via Inhibition of Hydrogen Sulfide Synthesis in a TLR-4-Dependent Manner

Background/Aims: Overproliferation of mesangial cells was believed to play an important role in the progress of diabetic nephropathy, one of the primary complications of diabetes. Hydrogen sulfide (H2S), a well-known and pungent gas with the distinctive smell of rotten eggs, was discovered to play a protective role in diabetic nephropathy. Methods: MTT assay was used to examine the viability of mesangial cells. Small interfering RNA was used to knock down the expression of TLR4 while specific inhibitor LY294002 to suppress the function of PI3K. H2S generation rate was determined by a H2S micro-respiration sensor. Results: Glucose of 25mM induced significant mesangial cells proliferation, which was accomplished by significantly inhibited endogenous H2S synthesis. And exogenous H2S treatment by NaHS markedly mitigated the overproliferation of mouse mesangial cells. Furthermore, it was found that H2S deficiency could result in TLR4 activation. And H2S supplementation remarkably inhibited TLR4 expression and curbed the mesangial cell overproliferation. Besides, PI3K/Akt pathway inhibition also significantly ameliorated the cell overproliferation. Conclusion: High glucose (HG) induces mouse mesangial cell overproliferation via inhibition of hydrogen sulfide synthesis in a TLR-4-dependent manner. And PI3K/Akt pathway might also play a vital part in the HG-induced mesangial cell overproliferation.