1,25(OH)2D3-Mediated Amelioration of Aortic Injury in Streptozotocin-Induced Diabetic Rats

Vitamin D deficiency may predispose patients to increased risk of kidney transplant rejection

BACKGROUND

Vitamin D deficiency occurs in more than 80% of kidney transplant recipients. Its immunomodulatory effects can predispose transplant recipients to rejection and chronic allograft nephropathy (CAN). This study determined the association between serum 25 (OH) vitamin D, biopsy-proven allograft rejection, and CAN rates.

AIM

To determine the relationship between serum 25 (OH) vitamin D level and biopsy-proven allograft rejection and CAN rate in renal transplant recipients.

METHODS

Adult renal transplant recipients followed at the clinic between January 2013 and 2018 were included. Recipients requiring graft biopsy due to declined function, hematuria, and proteinuria were reviewed. The two groups were compared regarding collected data, including the biopsy results, immunologic parameters, vitamin D, parathyroid hormone (PTH), phosphorus, albumin levels, and graft function tests.

RESULTS

Fifty-two recipients who underwent graft biopsy met the inclusion criteria. In all, 14 recipients had a vitamin D level > 15 ng/mL (group 1) vs ≤ 15 ng/mL (group 2) in 38. In total, 27 patients had biopsy-proven rejection, and 19 had CAN. There was only 1 recipient with biopsy-proven rejection in group 1, whereas there were 24 patients with rejection in group 2. The rejection rate was significantly higher in group 2 than in group 1 (P < 0.001). Four patients were diagnosed with CAN in group 1 vs fifteen in group 2. There was no significant difference in the CAN rate between the two groups. PTH was higher at the time of graft biopsy (P = 0.009, P = 0.022) in group 1 with a mean of 268 pg/mL. Donor-specific antibodies were detected in 14 (56.0%) of the recipients with rejection. Vitamin D level was 9.7 ± 3.4 ng/mL in the rejection group vs 14.7 ± 7.2 in the non-rejection group; this difference was statistically significant (P = 0.003). The albumin levels were significantly lower in patients with rejection than in those without rejection (P = 0.001). In univariate regression analysis of risk factors affecting rejection, sex, serum vitamin D, phosphorus and albumin were found to have an impact (P = 0.027, P = 0.007, P = 0.023, P = 0.008). In multivariate regression analysis, the same factors did not affect rejection.

CONCLUSION

The serum 25 (OH) vitamin D level in kidney transplant recipients remained low. Although low serum vitamin D level emerged as a risk factor for rejection in univariate analysis, this finding was not confirmed by multivariate analysis. Prospective studies are required to determine the effect of serum vitamin D levels on allograft rejection.

Blockade of the TLR4-MD2 complex lowers blood pressure and improves vascular function in a murine model of type 1 diabetes

While the pathogenesis of diabetes-induced high blood pressure (BP) is not entirely clear, current evidence suggests that Toll-like receptor 4 (TLR4) is a key player in the mechanisms associated with hypertension. However, it is unknown whether this receptor affects BP under type 1 diabetes. Likewise, there is insufficient knowledge about the role of TLR4 in diabetes-associated vascular dysfunction of large arteries. To narrow these gaps, in this study, we investigated if blockade of the TLR4-MD2 complex impacts BP and vascular function in diabetic rats. We injected streptozotocin in male Sprague Dawley rats and treated them with a neutralizing anti-TLR4 antibody for 14 days. BP was directly measured in conscious animals at the end of the treatment. In another set of experiments, we excised the aorta from control and diabetic animals, and measured TLR4 and MD2—a co-receptor that confers functionality to TLR4—levels by Western blotting. We also performed functional studies and evaluated ROS levels with and without a pharmacological inhibitor for TLR4 as well as for MD2. Additionally, we scrutinized a large human RNA-Seq dataset of aortic tissue to assess the co-expression of TLR4, MD2, and subunits of the vascular NADPH oxidases under diabetes and hypertension. We report that (a) chronic blockade of the TLR4–MD2 complex lowers BP in diabetic animals; that (b) type 1 diabetes modulates the levels of MD2 expression in the aorta, but not TLR4, at least in the conditions evaluated in this study; and, that (c) acute inhibition of TLR4 or MD2 diminishes vascular contractility and reduces oxidative stress in the aorta of these animals. In summary, we show evidence that the TLR4–MD2 complex is involved in the mechanisms linking type 1 diabetes and hypertension.

Vitamin D3 improves lipophagy-associated renal lipid metabolism and tissue damage in diabetic mice

Oxidative stress and abnormal lipid metabolism in diabetes can trigger renal lipotoxicity, extending to diabetic nephropathy. Vitamin D₃ has been known to be involved in lipid metabolism as well as insulin secretion or inflammation. Therefore, we hypothesized that vitamin D₃ supplementation attenuated hyperglycemia-induced renal damage in diabetic mice. Diabetes was induced by a 40% kJ high-fat diet with 30 mg/kg body weight of streptozotocin by intraperitoneal injection twice in male C57BL/6J mice. Among diabetic mice (fasting blood glucose > 140 mg/dL), mice were supplemented with 300 ng/kg body weight of vitamin D₃ dissolved in olive oil for 12 weeks. Normal control and diabetic control mice were orally administrated with olive oil as a vehicle. Normal control mice were fed with an AIN-93G diet during the experiment. Vitamin D₃ supplementation in diabetic mice improved glucose intolerance and kidney function, demonstrated by diminishing glomerular areas. Vitamin D₃ supplementation in diabetic mice significantly reduced triglycerides and low-density lipoprotein cholesterol in plasma as well as triglycerides and total cholesterol in the kidney. Furthermore, vitamin D₃ supplementation attenuated lipid synthesis, oxidative stress, and apoptosis, accompanied by activation of β-oxidation, antioxidant defense enzymes, and autophagy in diabetic mice. In conclusion, vitamin D₃ supplementation ameliorates hyperglycemia-induced renal damage through the regulation of lipid metabolisms, oxidative stress, apoptosis, and autophagy in diabetes. Vitamin D₃ could be a promising nutrient to weaken diabetic nephropathy.

Anti-inflammatory effects of 1,25-dihydroxyvitamin D3 in monocytes cultured in serum from patients with type 2 diabetes mellitus and diabetic nephropathy with uremia via Toll-like receptor 4 and nuclear factor-κB p65

Type 2 diabetes mellitus (T2DM) and diabetic nephropathy (DN) seriously affect the quality of human life. 1,25-dihydroxyvitamin D3 (VD3) is known to exert anti‑inflammatory and immunomodulatory effects. The present study investigated the effects of VD3 on Toll‑like receptor 4 (TLR4) and nuclear factor (NF)‑κB p65 expression in monocytes from patients with T2DM and investigated the underlying mechanisms. Serum from subjects of the control, T2DM and DN with uremia groups was isolated, and THP‑1 monocytes were cultured in these sera with or without VD3. After treatment with lipopolysaccharide (LPS) and interleukin (IL)‑15, monocytes and culture supernatants were collected. The expression of TLR4, TLR9 and IL‑15 mRNA was detected using reverse‑transcription polymerase chain reaction analysis. Furthermore, the protein expression of TLR4, NF‑κB p65 and inhibitor of NF‑κB (IκB) was determined using western blot analysis. The levels of IL‑6 and monocyte chemotactic protein in culture supernatants were detected using ELISAs. The impact of LPS, IL‑15 and VD3 on the TLR/NF‑κB signaling pathway in the T2DM and DN uremia groups was also investigated. In the T2DM and DN uremia groups, LPS and IL‑15 downregulated the expression of IκB and upregulated levels of proteins, including TLR4, NF‑κB p65, IL‑6 and monocyte chemoattractant protein 1, as well as TLR4 and IL‑15 mRNA. There was no significant difference in TLR9 mRNA protein expression among the three groups. VD3 partially blocked the above effects; However, pre‑treatment with VD3 had no significant effect on TLR4 mRNA expression, protein expression of NF-κB p65 and IκB, or the levels of associated inflammatory cytokines. In conclusion, the present study indicated that anti‑inflammatory effects of VD3 in inflammatory immune responses in T2DM and DN uremia are associated with the TLR4/NF-κB p65 signaling pathway.

Expression and cellular distribution of TLR4, MyD88, and NF-κB in diabetic renal tubulointerstitial fibrosis, in vitro and in vivo

AIM

Inflammation and extracellular matrix hyperplasia are crucial in the pathogenesis of tubulointerstitial fibrosis (TIF) involved in diabetic nephropathy (DN). Macrophage accumulation plays a major role, but whether immune factors contribute to DN pathogenesis is not well understood. This study aimed to investigate TLR4-MyD88-NF-κB-dependent pathway's involvement in TIF pathogenesis.

METHODS

STZ-induced diabetic rats and rat renal tubular epithelial NRK-52E cells cultured under high glucose conditions were used as in vivo and in vitro models, respectively. Real-time RT-PCR, western blot, immunohistochemistry and immunofluorescence were performed to examine the mRNA and protein levels of TLR4, MyD88, NF-κB, MCP-1, and α-SMA.

RESULTS

Compared with 5.5 mmol/L glucose, treatment of NRK-52E cells with 25 and 50 mmol/L d-glucose resulted in significantly increased TLR4 and MyD88 mRNA and protein levels (P<0.05). TLR4 and MyD88 were detected in the cytoplasm of most NRK-52E cells cultured under high glucose. Pronounced damage in the renal tubulointerstitium was observed in diabetic rats (scores: 3.82 ± 0.65 vs. 0.38 ± 0.08, P<0.01). Compared with the normal controls, a sharp upregulation of TLR4, MyD88, NF-κB p65, MCP-1, and α-SMA mRNA and protein levels was observed in diabetic rat kidneys (P<0.05). In diabetic animals, TLR4 and MyD88 were strongly expressed in the cytoplasm, while NF-κB p65 was widely expressed in cytoplasm and nuclei of renal tubular epithelial cells.

CONCLUSION

The inflammatory reaction and epithelial-mesenchymal transformation observed in renal tubulointerstitium may be the result of overactivation of the TLR4-MyD88-NF-κB-dependent innate immunity under high glucose, and may be involved in DN occurrence and progression.