Vitamin D increases plasma renin activity independently of plasma Ca2+ via hypovolemia and β-adrenergic activity

High blood pressure induced by vitamin D deficiency is associated with renal overexpression and hyperphosphorylation of Na+-K+-2Cl- cotransporter type 2

OBJECTIVES

Clinical and epidemiological studies have suggested a correlation between vitamin D deficiency (VDD) and high blood pressure (BP). This study aimed to test the hypothesis that high BP induced by VDD is associated with altered expression and covalent modification of apical sodium transporters along the nephron. The contributions of the intrarenal renin-angiotensin system (RAS) and oxidative stress were also investigated.

METHODS

Male Wistar rats were fed a vitamin D-free (n = 26) or standard diet (n = 25) for 30 days. BP was recorded using noninvasive and invasive procedures. The expression levels of total and phosphorylated apical sodium transporters in rat renal cortex and medulla were evaluated by immunoblotting. Intrarenal RAS components were assessed by immunoblotting and ELISA. Renal oxidative stress was analyzed by measuring the concentrations of thiobarbituric acid reactive substances and reduced glutathione.

RESULTS

Higher BP levels in VDD rats than controls were accompanied by overexpression and hyperphosphorylation of renal cortical and medullary Na+-K+-2Cl- cotransporter type 2, enhanced levels of phosphorylated Na+/H+ exchanger type 3, and reduced expression levels of total and phosphorylated Na+/Cl- cotransporter. Changes in intrarenal RAS induced by VDD vs. controls included the marked elevation of medullary renin expression, higher expression of cortical angiotensinogen, higher urinary angiotensinogen excretion, and higher cortical and medullary angiotensin II content. VDD rats displayed higher thiobarbituric acid reactive substances/glutathione ratios in the renal cortex and medulla than controls.

CONCLUSION

These results suggest that the molecular mechanisms underlying the effects of VDD on BP may include the upregulation of Na+-K+-2Cl- cotransporter type 2 and activation of intrarenal RAS and oxidative stress.

Vitamin D, vitamin D binding protein, vitamin D receptor levels and cardiac dysautonomia in patients with multiple sclerosis: a cross-sectional study

OBJECTIVES

Vitamin D is a pleiotropic steroid hormone that modulates the autonomic balance. Its deficiency has been described as an environmental risk factor for multiple sclerosis (MS). The aim of this study was to investigate the serum levels of vitamin D, vitamin D binding protein (VDBP) and vitamin D receptors (VDR) and to evaluate cardiac dysautonomia in MS patients due to bidirectional interaction between vitamin D and the autonomic nervous system.

METHODS

The current cross-sectional study was conducted on 26 patients with relapsing-remitting MS and on 24 healthy controls. Twenty-four-hour ambulatory blood pressure variability (BPV) was calculated and the participants were evaluated for orthostatic hypotension and supine hypertension. Serum levels of vitamin D, VDBP and VDR were measured.

RESULTS

The mean serum vitamin D level was significantly lower in MS patients than in controls (p = 0.044); however there was no significant difference in terms of VDR and VDBP levels between the groups. Supine hypertension and orthostatic hypotension were significant and the 24-hour systolic BPV was significantly decreased in patients with MS (p < 0.05) compared to controls. No correlation was found between vitamin D, VDBP and VDR with supine hypertension, orthostatic hypotension and systolic BPV values (p > 0.05). Also, there was a negative correlation between VDBP and the EDSS (p = 0.039, r = -0.406).

CONCLUSION

There was no correlation between orthostatic hypotension, supine hypertension and systolic BPV values and serum vitamin D, VDBP and VDR in MS patients. Future prospective studies with large number of patients may help us to better understand the relationship between vitamin D and the autonomic nervous system.

Hypertension induces glomerulosclerosis in phospholipase C-ε1 deficiency

Loss-of-function mutations in phospholipase C-ε1 (PLCE1) have been detected in patients with nephrotic syndrome, but other family members with the same mutation were asymptomatic, suggesting additional stressor are required to cause the full phenotype. Consistent with these observations, we determined that global Plce1-deficient mice have histologically normal glomeruli and no albuminuria at baseline. Angiotensin II (ANG II) is known to induce glomerular damage in genetically susceptible individuals. Therefore, we tested whether ANG II enhances glomerular damage in Plce1-deficient mice. ANG II increased blood pressure equally in Plce1-deficient and wild-type littermates. Additionally, it led to 20-fold increased albuminuria and significantly more sclerotic glomeruli in Plce1-deficient mice compared with wild-type littermates. Furthermore, Plce1-deficient mice demonstrated diffuse mesangial expansion, podocyte loss, and focal podocyte foot process effacement. To determine whether these effects are mediated by hypertension and hyperfiltration, rather than directly through ANG II, we raised blood pressure to a similar level using DOCA + salt + uninephrectomy and norepinephrine. This caused a fivefold increase in albuminuria in Plce1-deficient mice and a significant increase in the number of sclerotic glomeruli. Consistent with previous findings in mice, we detected strong PLCE1 transcript expression in podocytes using single cell sequencing of human kidney tissue. In hemagglutinin-tagged Plce1 transgenic mice, Plce1 was detected in podocytes and also in glomerular arterioles using immunohistochemistry. Our data demonstrate that Plce1 deficiency in mice predisposes to glomerular damage secondary to hypertensive insults.

Total, Bioavailable, and Free Vitamin D Levels and Their Prognostic Value in Pulmonary Arterial Hypertension

Introduction: Epidemiological studies suggest a relationship between vitamin D deficiency and cardiovascular and respiratory diseases. However, whether total, bioavailable, and/or free vitamin D levels have a prognostic role in pulmonary arterial hypertension (PAH) is unknown. We aimed to determine total, bioavailable, and free 25-hydroxy-vitamin D (25(OH)vitD) plasma levels and their prognostic value in PAH patients. Methods: In total, 67 samples of plasma from Spanish patients with idiopathic, heritable, or drug-induced PAH were obtained from the Spanish PH Biobank and compared to a cohort of 100 healthy subjects. Clinical parameters were obtained from the Spanish Registry of PAH (REHAP). Results: Seventy percent of PAH patients had severe vitamin D deficiency (total 25(OH)vitD < 10 ng/mL) and secondary hyperparathyroidism. PAH patients with total 25(OH)vitD plasma above the median of this cohort (7.17 ng/mL) had better functional class and higher 6-min walking distance and TAPSE (tricuspid annular plane systolic excursion). The main outcome measure of survival was significantly increased in these patients (age-adjusted hazard ratio: 5.40 (95% confidence interval: 2.88 to 10.12)). Vitamin D-binding protein (DBP) and albumin plasma levels were downregulated in PAH. Bioavailable 25(OH)vitD was decreased in PAH patients compared to the control cohort. Lower levels of bioavailable 25(OH)vitD (<0.91 ng/mL) were associated with more advanced functional class, lower exercise capacity, and higher risk of mortality. Free 25(OH)vitD did not change in PAH; however, lower free 25(OH)vitD (<1.53 pg/mL) values were also associated with high risk of mortality. Conclusions: Vitamin D deficiency is highly prevalent in PAH, and low levels of total 25(OH)vitD were associated with poor prognosis.

New Insights on Low Vitamin D Plasma Concentration as a Potential Cardiovascular Risk Factor

The role of Vitamin D hormone in human health and disease is still debated. Recently, growing attention has been paid to its putative role in cardiovascular system homeostasis with several studies that suggested a correlation between low vitamin D levels and increased cardiovascular risk. Several mechanisms are involved in the development of cardiovascular diseases: systemic inflammation, endothelial dysfunction, arterial hypertension and insulin resistance. In the present paper, we have revised the current literature supporting a role for vitamin D in the development of these pathogenetic processes. Finally, we have evaluated the current evidence linking vitamin D to atherosclerosis and its natural consequence, cardiovascular diseases.

Adrenal disorders: Is there Any role for vitamin D?

An emerging branch of research is examining the linkage between Vitamin D and nonskeletal disorders, including endocrine diseases. In this regard, a still little studied aspect concerns the involvement of vitamin D in adrenal gland disorders. Adrenal gland disorders, which might be theoretically affected by vitamin D unbalance, include adrenal insufficiency, Cushing's syndrome, adrenocortical tumors and hyperaldosteronism. In this review, we provide an updated document, which tries to collect and discuss the limited evidence to be found in the literature about the relationship between vitamin D and adrenal disorders. We conclude that there is insufficient evidence proving a causal relationship between vitamin D levels and adrenal disorders. Evidence coming from cross-sectional clinical studies can hardly clarify what comes first between vitamin D unbalance and adrenal disease. On the other hand, longitudinal studies monitoring the levels of vitamin D in patients with adrenal disorders or, conversely, the possible development of adrenal pathologies in subjects affected by impaired vitamin D levels would be able to elucidate this still unclear issue.

Beneficial effects of calcitriol on hypertension, glucose intolerance, impairment of endothelium-dependent vascular relaxation, and visceral adiposity in fructose-fed hypertensive rats

Besides regulating calcium homeostasis, the effects of vitamin D on vascular tone and metabolic disturbances remain scarce in the literature despite an increase intake with high-fructose corn syrup worldwide. We investigated the effects of calcitriol, an active form of vitamin D, on vascular relaxation, glucose tolerance, and visceral fat pads in fructose-fed rats. Male Wistar-Kyoto rats were divided into 4 groups (n = 6 per group). Group Con: standard chow diet for 8 weeks; Group Fru: high-fructose diet (60% fructose) for 8 weeks; Group Fru-HVD: high-fructose diet as Group Fru, high-dose calcitriol treatment (20 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding; and Group Fru-LVD: high-fructose diet as Group Fru, low-dose calcitriol treatment (10 ng / 100 g body weight per day) 4 weeks after the beginning of fructose feeding. Systolic blood pressure was measured twice a week by the tail-cuff method. Blood was examined for serum ionized calcium, phosphate, creatinine, glucose, triglycerides, and total cholesterol. Intra-peritoneal glucose intolerance test, aortic vascular reactivity, the weight of visceral fat pads, adipose size, and adipose angiotensin II levels were analyzed at the end of the study. The results showed that the fructose-fed rats significantly developed hypertension, impaired glucose tolerance, heavier weight and larger adipose size of visceral fat pads, and raised adipose angiotensin II expressions compared with the control rats. High- and low-dose calcitriol reduced modestly systolic blood pressure, increased endothelium-dependent aortic relaxation, ameliorated glucose intolerance, reduced the weight and adipose size of visceral fat pads, and lowered adipose angiotensin II expressions in the fructose-fed rats. However, high-dose calcitriol treatment mildly increased serum ionized calcium levels (1.44 ± 0.05 mmol/L). These results suggest a protective role of calcitriol treatment on endothelial function, glucose tolerance, and visceral adiposity in fructose-fed rats.