Vitamin D and diabetic nephropathy

Role of Bile Acid Receptors in the Development and Function of Diabetic Nephropathy

Diabetic nephropathy (DN) is a prevalent microvascular complication that occurs often in individuals with diabetes. It significantly raises the mortality rate of affected patients. Therefore, there is an urgent need to identify therapeutic targets for controlling and preventing the occurrence and development of DN. Bile acids (BAs) are now recognized as intricate metabolic integrators and signaling molecules. The activation of BAs has great promise as a therapeutic approach for preventing DN, renal damage caused by obesity, and nephrosclerosis. The nuclear receptors (NRs), farnesoid X receptor (FXR), pregnane X receptor (PXR), vitamin D receptor (VDR); and the G protein-coupled BA receptor, Takeda G-protein-coupled receptor 5 (TGR5) have important functions in controlling lipid, glucose, and energy metabolism, inflammation, as well as drug metabolism and detoxification. Over the past 10 years, there has been advancement in comprehending the biology and processes of BA receptors in the kidney, as well as in the creation of targeted BA receptor agonists. In this review, we discuss the role of BA receptors, FXR, PXR, VDR, and TGR5 in DN and their role in renal physiology, as well as the development and application of agonists that activate BA receptors for the treatment of kidney diseases.

Vitamin D Supplementation: Shedding Light on the Role of the Sunshine Vitamin in the Prevention and Management of Type 2 Diabetes and Its Complications

As the incidence of type 2 diabetes mellitus (T2DM) continues to increase globally, researchers are keen to investigate various interventions to mitigate its impact. Among these, vitamin D supplementation has attracted significant attention due to its influence on insulin secretion from the pancreas and insulin receptors in body cells. A substantial body of evidence indicates that vitamin D supplementation can reduce low-grade inflammation, a critical factor in developing insulin resistance. In addition, vitamin D aids in sustaining low resting concentrations of reactive oxygen species and free radicals, normalizes Ca2+ signaling, diminishes the expression of cytokines that are pro-inflammatory, and enhances the production of cytokines that are anti-inflammatory. This review discusses the effects of vitamin D on the glycemic control of individuals with T2DM and evaluates the impact of vitamin D supplementation on glycemic markers in this population. The investigation employs a comprehensive analysis of the existing literature with a special focus on recent studies published in the past decade. Based on the findings in the literature, it can be concluded that vitamin D supplementation alongside anti-diabetic medications may enhance glycemic control and potentially reduce the risk of diabetic complications. The evidence supports the notion that vitamin D supplementation can be a valuable addition to pharmacological agents for the management of T2DM, potentially enhancing glycemic control and overall health outcomes in affected individuals.

The Role of Vitamin D in Diabetic Nephropathy: A Translational Approach

According to several animal and human studies, vitamin D appears to play a significant role in the development of diabetic nephropathy. However, the possible renoprotective effect of vitamin D and its influence on the reversal of already existing renal damage remains doubtful. At this moment, there are a few hypotheses concerning the underlying molecular and genetic mechanisms including the link between vitamin D and inflammation, oxidative stress, and extracellular matrix accumulation. The present review aims to investigate the potential role of vitamin D in the development of diabetic kidney disease from a translational approach.

Association of urinary calcium and phosphorus excretion with renal disease progression in type 2 diabetes

OBJECTIVES

Diabetes is associated with a high incidence of microvascular disease, including nephropathy. The current study aimed to investigate the association of urinary calcium and phosphorus excretion with chronic kidney disease (CKD) progression in type 2 diabetes mellitus.

METHODS

A total of 159 T2DM patients with chronic kidney disease (CKD stage G1-G4) were retrospectively included. Patients were categorized into three groups according to the tertiles of 24-h urinary calcium and phosphorus excretion, respectively. Clinical parameters and laboratory findings were compared among the three groups. Cox proportional hazards models were used to estimate the associations of urinary calcium and phosphorus excretion with CKD progression and adjusted for baseline eGFR, urinary protein excretion, mean arterial pressure, and use of RAAS inhibitor. A cubic spline curve was used to explore the association between urinary calcium excretion and CKD progression, as well as urinary phosphorus excretion and CKD progression. Moreover, the subgroup effects of urinary calcium and phosphorus excretion on CKD progression were estimated using Cox regression. CKD progression was defined as double of baseline serum creatinine or occurrence of ESRD.

RESULTS

During a median of 18.23 months of follow-up, the composite renal outcomes were noted in 27%. Cumulative renal outcomes were significantly lower in the highest tertile of urinary calcium excretion and phosphorus excretion in Kaplan-Meier analyses. The multivariate Cox proportional hazards regression analyses indicated that both the highest tertile of urinary calcium and phosphorus excretion was associated with a lower risk for CKD progression compared with the lowest tertile. Restricted cubic spline analyses of the association between urinary calcium excretion and CKD progression indicated a linear association. Additionally, there was also a linear association between urinary phosphorus excretion and CKD progression. Subgroup analyses showed that higher urinary phosphorus excretion was particularly associated with a lower risk of CKD progression in non-diabetic kidney disease (NDKD) patients.

CONCLUSION

Higher urinary calcium and phosphorus excretion were associated with decreased risk of CKD progression in T2DM patients.

Type 2 Diabetes Mellitus, Insulin Resistance, and Vitamin D

PURPOSE OF REVIEW

There is a growing, largely inconsistent, literature on the role of vitamin D in association with type 2 diabetes, insulin resistance/insulin secretion, glycemic indices, and complications of type 2 diabetes. Pathophysiologic, bystander, preventive, and treatment roles of vitamin D have all been proposed. In this focused review, we attempt to organize and clarify our current information in this area.

RECENT FINDINGS

Clinical study interpretation is difficult because of variability in dosage, dosage form, study duration, and populations studied, as well as recently reported normal human polymorphisms in vitamin D synthesis and catabolism, vitamin D-binding protein, and vitamin D receptors in addition to a host of potential epigenetic confounders. Low vitamin D status appears to be associated with type 2 diabetes and most other insulin resistance disorders reported to date. The extraskeletal benefits of supplementation/repletion in these disorders in our species, with a few highlighted exceptions, remain to be established. This focused review attempts to summarize our current knowledge in this burgeoning area through a review of key meta-analyses, observational studies, randomized control trials, and Mendelian randomization studies and will hopefully serve as a guide to indicate future research directions and current best practice.

Serum 25-hydroxyvitamin D level and diabetic nephropathy in patients with type 2 diabetes mellitus

OBJECTIVE

Patients with chronic kidney disease have a very high prevalence of deficiency of 25-hydroxyvitamin D [25(OH)D]. We evaluate the association between 25(OH)D and diabetic nephropathy (DN) in a Chinese sample with type 2 diabetes mellitus.

METHOD

The subjects were patients with diabetes mellitus who were hospitalized at our hospital during the period from June 2012 to July 2014. Serum levels of 25(OH)D were tested at admission. DN was defined as a urinary albumin-to-creatinine ratio ≥30 mg/g in a random spot urine sample. Multivariate analyses were performed using logistic regression models.

RESULTS

We found that serum 25(OH)D levels were significantly lower in diabetes with DN as compared to without DN [8.5 (IQR 6.8-11.3) vs. 13.9 (IQR 11.2-18.2) ng/ml, P < 0.0001]. Based on the ROC curve, the optimal cutoff value of serum 25(OH)D levels as an indicator for diagnosis of DN was projected to be 10.5 ng/ml, which yielded a sensitivity of 82.6 % and a specificity of 72.7 %, with the area under the curve at 0.807 [95 % confidence interval (CI) 0.764-0.849]. Multivariate logistic regression analysis adjusted for common risk factors showed that with serum 25(OH)D level ≤10.5 ng/ml was an independent indicator of DN [odds ratio (OR) = 6.559; 95 % CI 2.864-11.368].

CONCLUSIONS

Our findings suggested that diabetes with DN had lower serum 25(OH)D levels and that determination of 25(OH)D statuses might be used to identify patients at increased risk of developing nephropathy complications.

25-Hydroxyvitamin D [25(OH)D] levels and diabetic foot ulcer: is there any relationship?

AIMS

In recent years, there has been an effort to understand possible roles of 25(OH)D, including its role in the immune system particularly on T cell medicated immunity, pancreatic insulin secretion and insulin action. 25(OH)D stimulates the cell differentiation and reduces cell proliferation, which is essential for cell growth and wound healing. However, data on the association between low level of plasma 25(OH)D and diabetic foot syndrome are scarce.

MATERIALS AND METHODS

Circulating plasma levels of 25(OH)D were measured in diabetic patients with ulcer (n=162) and without ulcer (n=162) in a prospective cohort hospital based study.

RESULTS

Of these patients, 85.1% had type 2 diabetes. Subjects with diabetic foot ulcer showed lower median plasma level of 25(OH)D [6.3(4.2-11.1) vs 28.0(21.4-37.0)] ng/ml after adjusting the age and BMI. Regardless of the low levels of 25(OH)D in cases and controls, it was associated with neuropathy, sex (female), duration of ulcer healing, and smoking status and independent of confounding factors, including BMI (kg/m²), A1c (%), hypertension, nephropathy, foot ulcer, retinopathy, CAD, PAD, HDL-C (mg/dl) and LDL-C (mg/dl). The factors which predict the risk of developing ulcer independent of 25(OH)D status were A1c (>6.9%) [OR 4.37; RR 1.77], HDL-C (<40mg/dl) [OR 1.16; RR 1.07], LDL-C (>100mg/dl) [OR 1.07; RR 1.03], triglycerides (>200mg/dl) [OR 1.40; RR 1.19], neuropathy [OR 6.88; RR 3.12], retinopathy [OR 3.34; RR 1.91], hypertension [OR 1.64; RR 1.28], nephropathy [OR 3.12; RR 1.87] and smoking [OR 4.53; RR 2.99] using odds and risk ratios.

CONCLUSION

It is not clear whether the suppression of delayed wound healing seen during 25(OH)D deficiency is due to the secondary effect or is a direct action of vitamin D on certain components of the immune system. Long-term randomized trials are needed to see the impact of vitamin D supplementation on the outcome of diabetic foot patients.

Role of vitamin D in the development of insulin resistance and type 2 diabetes

Vitamin D deficiency is mainly a consequence of insufficient sunlight induced vitamin D production in the skin and has been associated with various chronic diseases including type 2 diabetes. Experimental data have shown that vitamin D is important for glucose induced insulin secretion, improves insulin resistance, and exerts anti-inflammatory actions. Epidemiological studies have largely documented that a poor vitamin D status is associated with higher risk of insulin resistance and type 2 diabetes. The majority of randomized controlled trials (RCTs) in healthy or prediabetic individuals have, however, failed to demonstrate relevant vitamin D effects on insulin resistance or diabetes incidence. In patients with type 2 diabetes, a few RCTs reported some moderate effects of vitamin D on glycemic control and insulin resistance. While these findings warrant further in-depth studies, the current evidence is insufficient to recommend vitamin D supplementation for the prevention or treatment of type 2 diabetes.

CYP24A1 exacerbated activity during diabetes contributes to kidney tubular apoptosis via caspase-3 increased expression and activation

Decreases in circulating 25,hydroxyl-vitamin D3 (25 OH D3) and 1,25,dihydroxyl-vitamin D3 (1,25 (OH)2 D3) have been extensively documented in patients with type 2 diabetes. Nevertheless, the molecular reasons behind this drop, and whether it is a cause or an effect of disease progression is still poorly understood. With the skin and the liver, the kidney is one of the most important sites for vitamin D metabolism. Previous studies have also shown that CYP24A1 (an enzyme implicated in vitamin D metabolism), might play an important role in furthering the progression of kidney lesions during diabetic nephropathy. In this study we show a link between CYP24A1 increase and senescence followed by apoptosis induction in the renal proximal tubules of diabetic kidneys. We show that CYP24A1 expression was increased during diabetic nephropathy progression. This increase derived from protein kinase C activation and increased H₂O₂ cellular production. CYP24A1 increase had a major impact on cellular phenotype, by pushing cells into senescence, and later into apoptosis. Our data suggest that control of CYP24A1 increase during diabetes has a beneficial effect on senescence induction and caspase-3 increased expression. We concluded that diabetes induces an increase in CYP24A1 expression, destabilizing vitamin D metabolism in the renal proximal tubules, leading to cellular instability and apoptosis, and thereby accelerating tubular injury progression during diabetic nephropathy.

Serum 25-hydroxyvitamin D concentration and arterial stiffness among type 2 diabetes

AIM

To evaluate the association between serum 25-hydroxyvitamin D [25(OH)D] and arterial stiffness in patients with type 2 diabetes.

METHODS

Serum 25(OH)D was measured in a cross-sectional sample of 131 men and 174 women aged 30 years and over in Korea. Arterial stiffness was assessed by pulse wave velocity (PWV) obtained with a VP-2000 pulse wave unit. Fasting plasma glucose, insulin, lipid profile, HbA1c, calcium, phosphorous, and HS-CRP were measured.

RESULTS

The prevalence of vitamin D deficiency was high (85.9%). Those with lower vitamin D levels had increased PWV. Using multivariate regression analysis, low 25(OH)D concentrations independently predicted PWV (p<0.001) in people with type 2 diabetes after adjustment for other risk factors such as age, smoking, hypertension, HS-CRP, diabetes duration, hypertension duration, HbA1c, and BMI.

CONCLUSIONS

Vitamin D deficiency is common in type 2 diabetes, and a low 25(OH)D level is significantly associated with increased arterial stiffness in these patients. Vitamin D may influence the development of cardiovascular disease. Clinical intervention studies are needed to clarify whether treatment with vitamin D decreases the risk of cardiovascular disease in patients with type 2 diabetes.

The prevalence of vitamin D abnormalities in South Asians with type 2 diabetes mellitus in the UK

BACKGROUND

The high prevalence of both hypovitaminosis D and type 2 diabetes (T2DM) in the Asian community is well recognised, but the impact of diabetes on vitamin D status and vice versa, has not been well reported.

AIMS

To determine the prevalence of hypovitaminosis D in Asian patients with T2DM and its impact on glycaemic control.

METHODS

A cross-sectional study was conducted in a tertiary referral centre in the UK. Two hundred and ten Asian patients aged more than 40 years were included (170 with and 40 without T2DM). Each had a standard bone profile (serum calcium, phosphate and alkaline phosphatase), serum parathyroid hormone and 25-hydroxycholecalciferol.

RESULTS

The prevalence of low serum 25-hydroxyvitamin D (< 50 nmol/l) was high in the group as a whole (> 80%) and more common in diabetics compared with controls (83% vs. 70%; p = 0.07). This was particularly so in men (82.5% vs. 57.9%; p = 0.02). HbA1c was higher in women with vitamin D deficiency (< 12.5 nmol/l) (8.11 +/- 1.11% vs. 7.33 +/- 1.32%, p = 0.046). In logistic regression analysis, T2DM was an independent predictor of hypovitaminosis D. In linear regression analysis, vitamin D deficiency was independently related to HbA1c in women with T2DM.

CONCLUSIONS

Hypovitaminosis D remains a major public health issue in the Asian population and is exaggerated in patients with T2DM. The fact that vitamin D deficient women had higher HbA1c levels raises the possibility that vitamin D replacement may improve glycaemic control.

The use of vitamin D analogues in chronic kidney diseases: possible mechanisms beyond bone and mineral metabolism

Chronic kidney disease (CKD) is a common and costly medical condition, and currently available therapeutic options remain unsatisfactory. Vitamin D analogues are widely used for the bone and mineral disorder associated with CKD. However, accumulating evidence suggests that vitamin D analogues may have actions other than their effects on bone and mineral metabolism. In this article, we review the following aspects on the use of vitamin D analogues for the treatment of CKD: (1) epidemiological studies showing that patients with late-stage CKD have better survival than untreated patients; (2) animal studies showing that vitamin D analogues may retard the progression of CKD; (3) human studies on the anti-proteinuric and possibly renal protecting effects of vitamin D analogues in CKD and (4) the potential mechanisms of its therapeutic benefit. Nonetheless, definitive proof of the clinical benefits by randomized control trial would be necessary before one could advocate the routine use of vitamin D analogues for the treatment of CKD patients.