Into the light? Diabetic nephropathy and vitamin D

1α,25(OH)2 D3 alleviates high glucose-induced lipid accumulation in rat renal tubular epithelial cells by inhibiting SREBPs

Lipid accumulation is a vital event in the progression of diabetic nephropathy. 1,25-Dihydroxyvitamin D3 (1α,25(OH)₂ D₃ ) is considered to have a protective effect on diabetic nephropathy. However, it remains unclear whether 1α,25(OH)₂ D₃ can inhibit lipid accumulation, and the potential mechanisms responsible for lipid metabolism are incompletely understood. In this study, we evaluated the effects of 1α,25(OH)₂ D₃ on lipid metabolism in high glucose-exposed rat renal tubular epithelial NRK-52E cells. Results indicated that high glucose-enhanced lipid accumulation in NRK-52E cells and 1α,25(OH)₂ D₃ can remarkably decrease high glucose-induced lipid accumulation. Western blot showed that 1α,25(OH)₂ D₃ alleviated high glucose-induced upregulation of sterol regulatory element-binding protein-1c (SREBP-1c) and SREBP2, along with their established target genes fatty acid synthase (FASN) and hydroxymethylglutaryl CoA reductases (HMGCR). Overall, these findings suggest that 1α,25(OH)₂ D₃ downregulated the expressions of SREBPs to inhibit high glucose-induced lipid accumulation, which provides new sights into the protective effects of 1α,25(OH)₂ D₃ on diabetic nephropathy.

Active vitamin D regulates macrophage M1/M2 phenotypes via the STAT-1-TREM-1 pathway in diabetic nephropathy

AIM

Imbalance of M1/M2 macrophages phenotype activation is a key point in diabetic nephropathy (DN). This study aimed to investigate whether active vitamin D (VD) suppresses macrophage transition to the M1 phenotype via inhibiting the high glucose-induced STAT-1 phosphorylation to reduce TREM-1 expression.

METHODS

In vivo, pathological changes in kidney tissue were detected and the expression of CD68 TREM-1, STAT-1, M1 makers, and M2 makers were acquired in renal tissue of patients with DN and 18w DN rats. In vitro, RAW 264.7 cells were incubated in the presence of high glucose with or without VD_. Silencing and overexpression of TREM-1 and silencing and activate of STAT-1 were explored to elucidate the underlying mechanism. The expression of TREM-1 and STAT-1 and the changes of macrophage phenotype were examined separately by western blot and immunofluorescence staining.

RESULTS

(a) Expression of TREM-1, p-STAT-1, and M1 markers (iNOS and TNF-α) were increased and positively correlated in kidneys from patients with DN. (b) In DN rats, the enlargement of glomerular surface area, expansion of glomerular mesangial matrix, the expression of CD68, TREM-1, p-STAT-1, and M1 marker (iNOS) were significantly increased in comparison with the normal control group, whereas above changes were markedly decreased in the diabetic group treated with the VD group. (c) In vitro, VD significantly decreased high glucose-induced CD68, TREM-1, p-STAT-1, and M1 marker (iNOS) expression. However, above-mentioned effects of VD are abolished when TREM-1 is overexpressed or STAT-1 is activated. Reductions in STAT-1 expression decreased the TREM-1 expression.

CONCLUSION

VD can inhibit macrophage transition to the M1 phenotype through the STAT-1/TREM-1 pathway.

Vitamin D suppresses macrophage infiltration by down-regulation of TREM-1 in diabetic nephropathy rats

This study intends to investigate the effect of active vitamin D (VD) on the expression of triggering receptor expressed on myeloid cells-1 (TREM-1) in the renal tissues of diabetic nephropathy (DN) rats and to explore the impact of TREM-1 on macrophage adhesion and migration. We find that the expressions of TREM-1 and CD68 protein are higher in DN rats compared with rats in the normal control group and that these changes are decreased in the DN + VD group. In vitro, the capacity for macrophage adhesion and migration and the expression of TREM-1 are increased under high-glucose conditions, but VD inhibits this progress. TREM-1 siRNA decreases high-glucose-induced macrophage adhesion and migration, whereas over-expression of TREM-1 inhibits its action. However, VD cannot suppress high glucose-induced TREM-1 expression and macrophage adhesion and migration when TREM-1 is over-expressed. These results demonstrate that VD can suppress macrophage adhesion and migration by reducing the expression of TREM-1.

The Envy of Scholars: Applying the Lessons of the Framingham Heart Study to the Prevention of Chronic Kidney Disease

During the past 50 years, a dramatic reduction in the mortality rate associated with cardiovascular disease has occurred in the US and other countries. Statistical modeling has revealed that approximately half of this reduction is the result of risk factor mitigation. The successful identification of such risk factors was pioneered and has continued with the Framingham Heart Study, which began in 1949 as a project of the US National Heart Institute (now part of the National Heart, Lung, and Blood Institute). Decreases in total cholesterol, blood pressure, smoking, and physical inactivity account for 24%, 20%, 12%, and 5% reductions in the mortality rate, respectively. Nephrology was designated as a recognized medical professional specialty a few years later. Hemodialysis was first performed in 1943. The US Medicare End-Stage Renal Disease (ESRD) Program was established in 1972. The number of patients in the program increased from 5,000 in the first year to more than 500,000 in recent years. Only recently have efforts for risk factor identification, early diagnosis, and prevention of chronic kidney disease (CKD) been undertaken. By applying the approach of the Framingham Heart Study to address CKD risk factors, we hope to mirror the success of cardiology; we aim to prevent progression to ESRD and to avoid the cardiovascular complications associated with CKD. In this paper, we present conceptual examples of risk factor modification for CKD, in the setting of this historical framework.

Diabetic nephropathy: diagnosis and treatment

Nephropathy remains a major cause of morbidity and a key determinant of mortality in patients with type 1 or type 2 diabetes mellitus. Research is ongoing to identify biomarkers that in addition to albuminuria and glomerular filtration rate assist in the prediction and monitoring of renal disease in diabetes mellitus. Current strategies to treat this condition focus on intensification of glycaemic control and excellent control of blood pressure using regimens based on blockade of the renin-angiotensin system. Other approaches to control blood pressure and afford renoprotection are under active clinical investigation, including renal denervation and endothelin receptor antagonism. With increasing understanding of the underlying pathophysiological processes implicated in diabetic nephropathy, new specific renoprotective treatment strategies are anticipated to become available over the next few years.

Renal anaemia and EPO hyporesponsiveness associated with vitamin D deficiency: the potential role of inflammation

Resistance to erythropoiesis-stimulating agents (ESAs) has been observed in a considerable proportion of patients with chronic kidney disease (CKD) and it is reportedly associated with adverse outcomes, such as increased cardiovascular morbidity, faster progression to end-stage renal disease (ESRD) and all-cause mortality. The major causes of ESA resistance include chronic inflammation producing suppressive cytokines of early erythroid progenitor proliferation. In addition, pro-inflammatory cytokines stimulate hepcidin synthesis thus reducing iron availability for late erythropoiesis. Recent studies showing an association in deficiencies of the vitamin D axis with low haemoglobin (Hb) levels and ESA resistance suggest a new pathophysiological co-factor of renal anaemia. The administration of either native or active vitamin D has been associated with an improvement of anaemia and reduction in ESA requirements. Notably, these effects are not related to parathyroid hormone (PTH) values and seem to be independent on PTH suppression. Another possible explanation may be that calcitriol directly stimulates erythroid progenitors; however, this proliferative effect by extra-renal activation of 1α-hydroxylase enzyme is only a hypothesis. The majority of studies concerning vitamin D deficiency or supplementation, and degree of renal anaemia, point out the prevalent role of inflammation in the mechanism underlying these associations. Immune cells express the vitamin D receptor (VDR) which in turn is involved in the modulation of innate and adaptive immunity. VDR activation inhibits the expression of inflammatory cytokines in stromal and accessory cells and up-regulates the lymphocytic release of interleukin-10 (IL-10) exerting both anti-inflammatory activity and proliferative effects on erythroid progenitors. In CKD patients, vitamin D deficiency may stimulate immune cells within the bone marrow micro-environment to produce cytokines, inducing impaired erythropoiesis. Immune activation involves the reticuloendothelial system, increasing hepcidin synthesis and functional iron deficiency. Consequences of this inflammatory cascade are erythropoietin (EPO) resistance and anaemia. Given the key role of inflammation in the response to EPO, the therapeutic use of agents with anti-cytokines properties, such as vitamin D and paricalcitol, may provide benefit in the prevention/treatment of ESA hyporesponsiveness.

[Vitamin D hormone system and diabetes mellitus: lessons from selective activators of vitamin D receptor and diabetes mellitus]

The vitamin D hormone system has significant skeletal and extra-skeletal effects. Vitamin D receptor occurs in different tissues, and several cells other than renal cells are able to locally produce active vitamin D, which is responsible for transcriptional control of hundreds of genes related to its pleiotropic effects. There is increasing evidence relating vitamin D to development and course of type 1 and 2 diabetes mellitus. Specifically, influence of vitamin D on the renin-angiotensin-aldosterone system, inflammatory response, and urinary albumin excretion could explain the relevant impact of vitamin D status on diabetic nephropathy. Selective vitamin D receptor activators are molecules able to reproduce agonistic or antagonistic effects of active vitamin D depending on the tissue or even on the cell type. Specifically, paricalcitol has a beneficial profile because of its potency to reduce parathyroid hormone, with lower effects on serum calcium or phosphate levels. Moreover, in patients with diabetes and renal disease, paricalcitol decreases microalbuminuria, hospitalization rates, and cardiovascular mortality. Therefore, these molecules represent an attractive new option to improve prognosis of renal disease in patients with diabetes.

Novel roles of vitamin D in disease: what is new in 2011?

Vitamin D is a steroid molecule, mainly produced in the skin that regulates the expression of a large number of genes. Until recently its main known role was to control bone metabolism and calcium and phosphorus homeostasis. During the last 2 decades it has been realized that vitamin D deficiency, which is really common worldwide, could be a new risk factor for many chronic diseases, such as the metabolic syndrome and its components, the whole spectrum of cardiovascular diseases, several auto-immune conditions, and many types of cancer as well as all-cause mortality. Except for the great number of epidemiological studies that support the above presumptions, vitamin D receptors (VDRs) have been identified in many tissues and cells. The effect of vitamin D supplementation remains controversial and the need for more persuasive study outcomes is intense.