Pancreatic kallikrein protects against diabetic retinopathy in KK Cg-Ay/J and high-fat diet/streptozotocin-induced mouse models of type 2 diabetes.

AIMS/HYPOTHESIS: Many studies have shown that tissue kallikrein has effects on diabetic vascular complications such as nephropathy, cardiomyopathy and neuropathy, but its effects on diabetic retinopathy are not fully understood. Here, we investigated the retinoprotective role of exogenous pancreatic kallikrein and studied potential mechanisms of action. METHODS: We used KK Cg-Ay/J (KKAy) mice (a mouse model of spontaneous type 2 diabetes) and mice with high-fat diet/streptozotocin (STZ)-induced type 2 diabetes as our models. After the onset of diabetes, both types of mice were injected intraperitoneally with either pancreatic kallikrein (KKAy + pancreatic kallikrein and STZ + pancreatic kallikrein groups) or saline (KKAy + saline and STZ + saline groups) for 12 weeks. C57BL/6J mice were used as non-diabetic controls for both models. We analysed pathological changes in the retina; evaluated the effects of pancreatic kallikrein on retinal oxidative stress, inflammation and apoptosis; and measured the levels of bradykinin and B1 and B2 receptors in both models. RESULTS: In both models, pancreatic kallikrein improved pathological structural features of the retina, increasing the thickness of retinal layers, and attenuated retinal acellular capillary formation and vascular leakage (p < 0.05). Furthermore, pancreatic kallikrein ameliorated retinal oxidative stress, inflammation and apoptosis in both models (p < 0.05). We also found that the levels of bradykinin and B1 and B2 receptors were increased after pancreatic kallikrein in both models (p < 0.05). CONCLUSIONS/INTERPRETATION: Pancreatic kallikrein can protect against diabetic retinopathy by activating B1 and B2 receptors and inhibiting oxidative stress, inflammation and apoptosis. Thus, pancreatic kallikrein may represent a new therapeutic agent for diabetic retinopathy.

Empagliflozin prevents cardiomyopathy via sGC-cGMP-PKG pathway in type 2 diabetes mice.

Cardiovascular complications contribute to the major mortality and morbidity in type 2 diabetes. Diabetic cardiomyopathy (DCM) is increasingly recognized as an important cause of heart failure. EMPA-REG OUTCOME trial has reported that empagliflozin, the sodium-glucose cotransporter 2 inhibitor, exerts cardiovascular benefits on diabetic population. However, the mechanism by which empagliflozin alleviates DCM still remains unclear. In the current study, we investigated the cardiac protective effects of empagliflozin on spontaneous type 2 diabetic db/db mice and its potential mechanism. Eight weeks of empagliflozin treatment (10 mg/kg/day) decreased body weight and blood glucose level, and increased urinary glucose excretion (UGE) in diabetic mice. Echocardiography revealed that both systolic and diastolic functions of db/db mice were also obviously improved by empagliflozin. Furthermore, empagliflozin-treated diabetic mice presented with amelioration of cardiac hypertrophy and fibrosis. In addition, diabetic hearts exhibited the deterioration of oxidative stress, apoptosis and pyroptosis, while these effects were significantly counteracted after empagliflozin treatment. Moreover, empagliflozin rescued diabetes-induced suppression of sGC (soluble guanylate cyclase enzyme)-cGMP (cyclic guanosine monophosphate)-PKG (cGMP-dependent protein kinase) pathway. However, when sGC-ß expression of hearts was inhibited by transvascular delivery of small interfering RNA, cardiac dysfunction was aggravated and the advantages of empagliflozin were reversed through inhibiting sGC-cGMP-PKG pathway. Collectively, these findings indicate that empagliflozin improves cardiac function involving the inhibition of oxidative stress-induced injury via sGC-cGMP-PKG pathway and may be a promising therapeutic option for DCM.

Triptolide prevents extracellular matrix accumulation in experimental diabetic kidney disease by targeting microRNA-137/Notch1 pathway.

MicroRNAs (miRNAs) are involved in multiple biological functions via suppressing target genes. Triptolide is a monomeric compound isolated from a traditional Chinese herb, which exerts protective roles in many kinds of glomerular diseases. However, our understanding of the triptolide effect on miRNAome is still limited. In this study, we found that triptolide significantly decreased albuminuria and improved glomerulosclerosis in rats with diabetic kidney disease (DKD). And triptolide also inhibited extracellular matrix (ECM) protein accumulation and the notch1 pathway activation under diabetic conditions. MiR-137 was significantly decreased in the HG (high glucose)-treated HRMCs and in the kidney tissues of the diabetic rats, but was upregulated by triptolide. In addition, overexpression of miR-137 exerted similar effects to those of triptolide, while miR-137 inhibition aggravated ECM protein accumulation. Luciferase reporter assay results demonstrated that miR-137 directly targets Notch1. Furthermore, the miR-137-dependent effects were due to Notch1 suppression that in turn inhibited ECM protein expression, key mediators of glomerulosclerosis. Finally, downregulation of miR-137 reversed the ECM inhibition role of triptolide in HG cultured HRMCs. Taken together, these findings indicate that triptolide is a potential therapeutic option for DKD and that miR-137/Notch1 pathway play roles in the anti-glomerulosclerosis mechanism of triptolide.

Saxagliptin regulates M1/M2 macrophage polarization via CaMKKß/AMPK pathway to attenuate NAFLD.

Non-alcoholic fatty liver disease (NAFLD), a hepatic manifestation of metabolic disease, is an important complication of diabetes mellitus (DM). Inflammation plays a crucial role in the development and progression of NAFLD. Moreover, the pathological formation of NAFLD is closely related to accumulation and polarization of hepatic macrophages. Saxagliptin, a newly antidiabetic agent, can suppress hepatic inflammation reportedly. However, underlying mechanisms remain poorly explored. In this study, we showed saxagliptin alleviated lipid accumulation and attenuated liver inflammation with downregulation of inflammation factors in diabetic rats. Moreover, saxagliptin could reduce the phenotype of M1 macrophage iNOS and increase the phenotype of M2 macrophage CD206. We also found saxagliptin increased CaMKKß/AMPK activation. In vitro, human THP-1 monocytes were differentiated into M1/M2 macrophages by LPS/IL-4. We clarified saxagliptin's anti-inflammatory effect by reducing NF-κB, TNF-α expression and promoting M2 macrophage polarization. Furthermore, we demonstrated CaMKKß-dependent AMPK activation was involved in macrophage polarization. In conclude, our results detected saxagliptin could attenuated inflammation through regulation of M1/M2 macrophage polarization and might be via CaMKKß/AMPK pathway.

Erratum: Triptolide Suppresses Glomerular Mesangial Cell Proliferation in Diabetic Nephropathy Is Associated with Inhibition of PDK1/Akt/mTOR Pathway: Erratum.

[This corrects the article DOI: 10.7150/ijbs.20485.].

Erratum: Triptolide Suppresses Glomerular Mesangial Cell Proliferation in Diabetic Nephropathy Is Associated with Inhibition of PDK1/Akt/mTOR Pathway: Erratum.

[This corrects the article DOI: 10.7150/ijbs.20485.].

Empagliflozin Attenuates Hyperuricemia by Upregulation of ABCG2 via AMPK/AKT/CREB Signaling Pathway in Type 2 Diabetic Mice.

Hyperuricemia (HUA) is a metabolic disease characterized by elevated serum uric acid (SUA). Empagliflozin, a kind of sodium-glucose cotransporter 2 inhibitors, has recently emerged as a new antidiabetic agent by facilitating glucose excretion in urine. Moreover, there was evidence of SUA reduction following treatment with empagliflozin in addition to glycaemic control, while the molecular mechanisms remain unknown. To investigate the potential mechanisms, the model of type 2 diabetes (T2DM) with HUA was established by combination of peritoneal injection of potassium oxonate and intragastric administration of hypoxanthine in KK-Ay mice. A series of method such as RT-PCR, western blot, immunochemistry, immunofluorescence were conducted to explore the mechanism. Our results showed that empagliflozin significantly ameliorated the levels of SUA and blood glucose in T2DM mice with HUA. Furthermore, in both kidney and ileum, empagliflozin obviously promoted protein expression of uric acid (UA) transporter ABCG2, p-AMPK, p-AKT and p-CREB. The same trend was observed in human tubular epithelial (HK-2) cells. Additionally, through application of an AMPK inhibitor (Compound C), it was further confirmed empagliflozin exerted its anti-hyperuricemic effects in an AMPK dependent manner. Meanwhile, with the help of ChIP assay and luciferase reporter gene assay, we found that CREB further activated ABCG2 via binding to the promoter of ABCG2 to induce transcription. Taken together, our study demonstrated that empagliflozin treatment played an essential role in attenuating HUA by upregulation of ABCG2 via AMPK/AKT/CREB signaling pathway.

Calcium Dobesilate Restores Autophagy by Inhibiting the VEGF/PI3K/AKT/mTOR Signaling Pathway.

Objective: Calcium dobesilate (CaD), an effective drug for the treatment of diabetic microvascular complications, especially diabetic retinopathy, is widely used in the clinic. Interestingly, several studies have indicated that CaD is therapeutic for diabetic kidney disease (DKD). Recently, evidence has indicated that altered vascular endothelial growth factor (VEGF) expression and decreased autophagy are the main pathological mechanisms of proteinuria. Thus, this study was conducted to explore the effect of CaD on restoring autophagy in DKD and the possible signaling pathway between VEGF and autophagy. Methods: Obese mice with spontaneous diabetes (KK-Ay) and high-fat diet- and streptozotocin-induced diabetic mice (HFD/STZ) were used in this study. Biochemical staining, western blotting, and immunohistochemistry were conducted to determine the angioprotective effect of CaD and the underlying mechanism between autophagy and VEGF/VEGFR. Results: Our results showed that CaD was capable of reducing albuminuria and restoring renal histological changes in KK-Ay and HFD/STZ-induced diabetic mice. CaD restored autophagy by decreasing the protein expression of LC3 II, Atg5, and beclin 1 and increasing the expression of P62. Moreover, CaD reduced the activation of the autophagy-related PI3K/AKT/mTOR pathway possibly via decreasing VEGF and downregulating VEGF receptor 2. Conclusion: Overall, CaD, as a novel potential therapeutic drug for DKD, plays a key role in protecting renal function and restoring autophagy by blocking VEGF/VEGFR2 and inhibiting the PI3K/AKT/mTOR signaling pathway.

Triptolide Attenuates Renal Tubular Epithelial-mesenchymal Transition Via the MiR-188-5p-mediated PI3K/AKT Pathway in Diabetic Kidney Disease.

Triptolide possesses the trait of renal protection. Epithelial-mesenchymal transition (EMT) is closely linked to the pathogenesis of diabetic kidney disease (DKD). MicroRNAs have recently emerged as critical regulators of DKD. However, it is poorly understood whether triptolide alleviates renal EMT by regulating microRNAs in DKD. In this study, we found that triptolide decreased albuminuria, improved the renal structure and reduced renal EMT in rats with DKD. Furthermore, activation of the PI3K/AKT signaling pathway was increased in diabetic rats, which was partly reversed by triptolide. Triptolide also alleviated glucose-induced EMT in HK-2 cells in vitro. PI3K/AKT signaling pathway activation was reduced after triptolide treatment. Moreover, triptolide decreased the increase in miR-188-5p expression stimulated by high glucose levels in HK-2 cells. miR-188-5p inhibited PTEN expression by directly interacting with the PTEN 3'-untranslated region. Additionally, downregulation of miR-188-5p, which imitates the effects of triptolide, attenuated the activation of the PI3K/AKT pathway and HG-induced EMT, whereas miR-188-5p overexpression reversed the effects of triptolide on the PI3K/AKT pathway and EMT. In conclusion, we demonstrated that triptolide ameliorates renal EMT via the PI3K/AKT signaling pathway through the interaction between miR-188-5p and PTEN, indicating that miR-188-5p may be a therapeutic target of triptolide in DKD.

Triptolide Suppresses Glomerular Mesangial Cell Proliferation in Diabetic Nephropathy Is Associated with Inhibition of PDK1/Akt/mTOR Pathway.

Mesangial cell proliferation has been identified as a mainly contributing factor to glomerulosclerosis, which is typical of diabetic nephropathy. However, the specific mechanisms and therapies remain unclear. PDK1 is a critical regulator of cell proliferation, but the specific role of PDK1 in diabetic nephropathy has not been fully illuminated. In the current study, we demonstrated that triptolide (TP) ameliorated albuminuria in the high fat diet/STZ-induced diabetic rats. TP also suppressed the increased proliferating cell markers Ki-67 and PCNA in the kidney tissues. Our results of MTT and cell cycle analysis further confirmed that TP significantly inhibited mesangial cell proliferation, and the inhibition of PDK1/Akt/mTOR pathway might be the underlying mechanisms. In addition, we also found that the PDK1 activator (PS48) could reverse the cell proliferation inhibition role of TP. These data suggest that TP may be useful in prevention of diabetic glomerulosclerosis and that PDK1/Akt/mTOR pathway might be the underlying mechanism.

Saxagliptin Attenuates Albuminuria by Inhibiting Podocyte Epithelial- to-Mesenchymal Transition via SDF-1α in Diabetic Nephropathy.

The dipeptidyl peptidase-4 (DPP-4) inhibitor saxagliptin has been found to reduce progressive albuminuria, but the exact mechanism of inhibition is unclear. Podocyte epithelial-to-mesenchymal transition (EMT) has emerged as a potential pathway leading to proteinuria in diabetic nephropathy (DN). Stromal cell-derived factor-1α (SDF-1α), one of the substrates of DPP-4, can activate the protein kinase A pathway and subsequently inhibit its downstream effector, transforming growth factor-ß1 (TGF-ß1), which induces podocyte EMT. Thus, this study was designed to test the hypothesis that saxagliptin reduces progressive albuminuria by preventing podocyte EMT through inhibition of SDF-1α cleavage in DN. The results of a series of assays, including ELISA, western blotting, and immunochemistry/immunofluorescence, showed that saxagliptin treatment obviously ameliorated urinary microalbumin excretion and renal histological changes in high-fat diet/streptozotocin-induced diabetic rats. Furthermore, saxagliptin-treated diabetic rats presented with suppression of DPP-4 activity/protein expression accompanied by restoration of SDF-1α levels, which subsequently hindered NOX2 expression and podocyte EMT. In vitro, we consistently observed that saxagliptin significantly inhibited increased DPP-4 activity/expression, oxidative stress and podocyte EMT. Application of an SDF-1α receptor inhibitor (AMD3100) to cultured podocytes further confirmed the essential role of SDF-1α in podocyte EMT inhibition. In sum, we demonstrated for the first time that saxagliptin treatment plays an essential role in ameliorating progressive DN by preventing podocyte EMT through a SDF-1α-related pathway, suggesting that saxagliptin could offer renoprotection and that SDF-1α might be a potential therapeutic target for DN.

Triptolide Restores Autophagy to Alleviate Diabetic Renal Fibrosis through the miR-141-3p/PTEN/Akt/mTOR Pathway.

Fibrosis is the major pathological feature of diabetic kidney disease (DKD). Autophagy, a process to maintain metabolic homeostasis, is obviously inhibited in DKD. Triptolide (TP) is a traditional Chinese medicine extract known for immune suppression and anti-inflammatory and anti-cancer activities. In this study, we investigated the effects of TP on autophagy and fibrosis in DKD. TP restored autophagy and alleviated fibrosis in DKD rats and high-glucose-incubated human mesangial cells. After we applied 3-methyladenine (an autophagy inhibitor) and autophagy-related gene 5-small interfering RNA (siRNA), we found that the improvement of fibrosis on TP was related to the restoration of autophagy. In addition, miR-141-3p levels were increased under high glucose but reduced after TP treatment. miR-141-3p overexpression aggravated the fibrosis and restrained the autophagy further, while miR-141-3p inhibition imitated the effects of TP. As an action target, phosphatase and tensin homolog (PTEN) showed corresponding opposite changes. After PTEN-siRNA transfection, the effects of TP on autophagy and fibrosis were inhibited. PTEN levels were downregulated, with downstream phosphorylated protein kinase B (Akt) and the mammalian target of rapamycin (mTOR) upregulated in high glucose, which were reversed by TP treatment. These findings indicate that TP alleviates fibrosis by restoring autophagy through the miR-141-3p/PTEN/Akt/mTOR pathway and is a novel therapeutic option for DKD.