Chronic kidney disease and diabetes mellitus predict resistance to vitamin D replacement therapy

Study of the effect of vitamin D supplementation on glycemic control in type 2 diabetic prevalent hemodialysis patients

Vitamin D is claimed to have an adjuvant effect on glycemic control by dual action on pancreatic β-cells and insulin resistance. The aim of this study was to assess the possible effect of short-term alfacalcidol supply on glycemic control in type 2 diabetic hemodialysis (HD) patients. Twenty type 2 diabetic HD patients (using diet and oral drugs but not insulin) were randomly selected from our dialysis unit as well as 20 non-diabetic HD patients as control. A third group of 12 healthy subjects were studied as well. All three groups were similar in age, sex, and body mass index. Oral alfacalcidol therapy was administrated daily as recommended by Kidney Disease Outcomes Quality Initiative (K/DOQI) guidelines for 12 weeks guided by monthly serum phosphorus and Cax PO4 product. Corrected total calcium, phosphorus, intact parathyroid hormone, 25-hydroxy vitamin D (25[OH]D), and glucoparameters (fasting blood glucose, glycated hemoglobin [HbA1c%], insulin resistance by homeostatic model assessment, and β-cell function by HOMA-β%) were measured under basal conditions and after 3 months of therapy. 25(OH)D was non-significantly lower in diabetic than non-diabetic HD patients, but significantly lower than healthy subjects at the start of the study. However, vitamin D level increased significantly after 3 months of trial, although the levels did not reach normal values. This vitamin D rise was associated with highly significant improvement in concentrations of fasting blood sugar (FBS), fasting insulin, HbA1c%, and HOMA-β-cell function in diabetic and non-diabetic controls. However, there was a significant rise in insulin resistance after treatment. The percentage of change was evident more in diabetics regarding FBS and 25(OH)D concentration. Adjustment of 25(OH)D level in type 2 diabetic prevalent HD patients may improve, at least with short-term therapy, glycemic control mainly through improving β-cell function.

Vitamin D deficiency--prognostic marker or mortality risk factor in end stage renal disease patients with diabetes mellitus treated with hemodialysis--a prospective multicenter study

BACKGROUND

End stage renal disease (ESRD) patients on renal replacement therapy (RRT) with diabetes mellitus (DM) have a higher mortality rate and an increase prevalence of vitamin D deficiency compared to those without DM. It is still debated if vitamin D deficiency is a risk factor or a prognostic marker for mortality in these patients. This study investigated the prevalence of vitamin D deficiency and its impact on all-cause mortality in HD patients with DM.

METHODS

Our prospective non-interventional cohort study included 600 patients on hemodialysis therapy (HD) (median aged 56, interquartile range (19) years, 332 (55.3%) males) recruited from 7 HD centers, from all main geographical regions of Romania. The prevalence of DM was 15.3%. They were then followed regarding: dialysis duration, dialysis efficiency, renal anemia, CKD-MBD, inflammatory status and comorbidities: coronary artery disease (CAD), peripheral vascular disease (PVD) and stroke. The deficiency of 25-OH vitamin D was defined as a value lower than 12 ng/mL.

RESULTS

Patients were followed for 3 years. The overall 3 year mortality was 25.5% (153 individuals), being higher in patients with DM as compared to those without DM (33.7% vs. 24.0%; P = 0.049). The time-related prognosis was also influenced by the presence of DM, at the survival analysis resulting in a HR of 1.52 [1.03 to 2.26] 95% CI, P = 0.037, for death in dialyzed patients with DM. In DM patients, 25-OH vitamin D deficiency was significantly higher (37.0% compared to 24.0%, P = 0.009). Furthermore, in patients with DM we observed a shorter dialysis duration (2 vs. 3 years, P<0.001) and a lower intact parathyroid hormone (iPTH) (258.0 pg/ml vs. 441.9 pg/ml, P = 0.002). Regarding the presence of comorbidities at the inclusion in the study, the presence of diabetes in dialyzed patients was associated with increased prevalence of CAD (87.0% vs. 58.1%, P<0.001), PVD (67.4% vs. 17.3%, P<0.001) and history of stroke (29.3% vs. 14.0%, P<0.001). In patients with DM the presence of 25-OH vitamin D deficiency increased the probability of death (50.0% vs. 24.1%; P = 0.011). In multiple Cox proportional hazards analysis, vitamin D deficiency remained an independent predictor for mortality in dialysis patients with DM (HR = 1.71, 95% CI 1.21 to 2.43, P = 0.003). In the same time, multiple Cox proportional hazards analysis showed that age (HR = 1.02 per one year increase, P = 0.004), CAD (HR = 1.55, P = 0.046) and PVD (HR = 1.50, P = 0.029) were independent predictors for mortality in dialysis patients with DM.

CONCLUSIONS

ESRD patients with DM treated with HD have a higher overall mortality than non-DM patients. Vitamin D deficiency is significantly more prevalent in HD patients with DM. Low 25-OH vitamin D levels were associated with increased all-cause mortality in these patients. According to our data, in HD patients with DM, screening for vitamin D deficiency (and its correction) should be mandatory for an optimal risk reduction strategy.

Dietary resistant starch prevents urinary excretion of vitamin D metabolites and maintains circulating 25-hydroxycholecalciferol concentrations in Zucker diabetic fatty rats

BACKGROUND

Type 2 diabetes (T2D) is the leading cause of nephropathy in the United States. Renal complications of T2D include proteinuria and suboptimal serum 25-hydroxycholecalciferol (25D) concentrations. 25D is the major circulating form of vitamin D and renal reabsorption of the 25D-vitamin D-binding protein (DBP) complex via megalin-mediated endocytosis is believed to determine whether 25D can be activated to 1,25-dihydroxycholecalciferol (1,25D) or returned to circulation. We previously demonstrated that excessive urinary excretion of 25D-DBP and albuminuria occurred in rats with type 1 diabetes (T1D) and T2D. Moreover, feeding rats with T1D high-amylose maize partially resistant to digestion [resistant starch (RS)] prevented excretion of 25D-DBP without significantly affecting hyperglycemia.

OBJECTIVE

We used Zucker diabetic fatty (ZDF) rats, a model of obesity-related T2D, to determine whether feeding RS could similarly prevent loss of vitamin D and maintain serum 25D concentrations.

METHODS

Lean control Zucker rats (n = 8) were fed a standard semi-purified diet (AIN-93G) and ZDF rats were fed either the AIN-93G diet (n = 8) or the AIN-93G diet in which cornstarch was replaced with RS (550 g/kg diet; 35% resistant to digestion) (n = 8) for 6 wk.

RESULTS

RS attenuated hyperglycemia by 41% (P < 0.01) and prevented urinary DBP excretion and albuminuria, which were elevated 3.0- (P < 0.01) and 3.6-fold (P < 0.01), respectively, in control diet-fed ZDF rats. Additionally, urinary excretion of 25D (P = 0.01) and 1,25D (P = 0.03) was higher (89% and 97%, respectively), whereas serum 25D concentrations were 31% lower (P < 0.001) in ZDF rats fed the control diet compared with RS-fed ZDF rats. Histopathologic scoring of the kidney revealed that RS attenuated diabetes-mediated damage by 21% (P = 0.12) despite an ∼50% decrease in megalin protein abundance.

CONCLUSIONS

Taken together, these data provide evidence that suggests vitamin D balance can be maintained by dietary RS through nephroprotective actions in T2D, which are independent of vitamin D supplementation and renal expression of megalin.

Activation of FGF-23 mediated vitamin D degradative pathways by cholecalciferol

CONTEXT

The optimal circulating concentration of 25(OH) vitamin D is controversial.

OBJECTIVE

The aim was to investigate if FGF-23 and 24,25(OH)2D can guide cholecalciferol replacement.

DESIGN

Oral cholecalciferol (10,000 IU weekly) administered to subjects with 25(OH)D levels < 20 ηg/mL and eGFR > 60 mL/min/1.73 m(2) (n = 25), chronic kidney disease (CKD) (n = 27), or end stage renal disease (ESRD) (n = 14).

SETTING

The study was conducted at the Veterans Affairs clinics.

MAIN OUTCOME MEASURE

Serum FGF-23, PTH, 25(OH)D, 1,25(OH)2D, 24,25(OH)2D, calcium, and phosphorous concentrations, and urinary excretion of calcium and phosphorus at baseline and after 8 weeks of treatment.

RESULTS

Cholecalciferol treatment increased concentrations of serum 25(OH)D by (19.3 ± 8 ηg/mL, P = .001; 12.2 ± 9 ηg/mL, P = .0001) and 24,25(OH)2D (1.14 ± 0.89 ηg/mL, P = .0024; 1.0 ± 0.72 ηg/mL P = .0002), and reduced serum PTH (-11 ± 21 pg/mL, P = .0292; -42 ± 68 pg/mL, P = .0494) in normal and CKD subjects, respectively. Cholecalciferol increased serum FGF-23 levels only in normal subjects (44 ± 57 ηg/mL, P = .01). Increments in serum 25(OH)D positively correlated with serum FGF-23 and 24,25(OH)2D and negatively correlated with PTH. In ESRD, cholecalciferol administration increased 25(OH)D by (16.6 ± 6.6 ηg/mL P ≤ .05) without changing 24,25(OH)2D, FGF-23 or PTH levels.

CONCLUSION

Modest elevations of serum 25(OH)D levels after cholecalciferol treatment are sufficient to induce compensatory degradative pathways in patients with sufficient renal reserves, suggesting that optimal circulating 25(OH)D levels are approximately 20 ηg/mL. In addition, catabolism of 25(OH)D may also contribute to the low circulating vitamin D levels in CKD, since elevations of FGF-23 in CKD are associated with increased 24,25(OH)2D after cholecalciferol administration.

The effect of calcium with or without calcitriol supplementation on renal function in patients with hypovitaminosis d and chronic kidney disease

Background:

Hypovitaminosis D (serum 25-OHD < 30 ng/mL) is common in patients with chronic kidney disease (CKD). Vitamin D is believed to involve in the regulation of renin-angiotensin system and may be renoprotective.

Objectives:

To compare the effects of calcium with or without calcitriol on renal function in patients with CKD.

Patients and Methods:

A prospective randomized trial was performed involving patients with stages 2-4 CKD and hypovitaminosis D. Baseline demographics data were taken at baseline. Patients were randomized equally into oral calcitriol plus calcium carbonate (calcitriol group) or calcium carbonate alone (non-calcitriol group). Serum levels of 25-hydroxyvitamin D (25-OHD), 1,25-dihydroxyvitamin D3 (1,25-(OH)2D), creatinine, calcium and urine protein creatinine index (uPCI) were measured at 6 and 12 weeks.

Results:

Fifty (21 Female: 29 Male) patients with CKD with a median age of 53 (22-65) years were recruited. Their median MDRD eGFR (modification of diet in renal disease, estimation of glomerular filtration rate) was 36.0 (15-89) mL/min/1.73 m² with the CKD stage 2 (n = 8, 16%), stage 3 (n = 29, 58%), and stage 4 (n = 13, 26%) respectively. In both study groups serum 25-OHD levels were increased at 12 weeks (P = 0.001), in contrast to serum 1,25-(OH)2D levels which remained unchanged (P > 0.05), serum creatinine and uPCI were also remained unchanged until the end of study (P > 0.05 each). Patients with diabetes had higher serum creatinine (P = 0.01) and lower serum 1,25-(OH)2D (P = 0.02) at baseline. Regardless of the diabetics status, the serum 25-OHD was increased, and 1,25-(OH)2D remained unchanged at 12 weeks in both study groups. At 12 weeks, serum creatinine was decreased in patients with diabetes in the noncalcitriol group (P = 0.03) compared to stabilization of creatinine in the calcitriol group (P > 0.05). Serum calcium was increased, though it was still within the normal range in the calcitriol group (P < 0.001); whereas, in the noncalcitriol group, there was an initial reduction but increased back to baseline (P = 0.007). Urine PCI remained unchanged in both groups.

Conclusions:

We have demonstrated that calcitriol supplementation did not offer any additional benefit to reduce 25-OHD and 1,25-(OH)2D levels over calcium carbonate alone in patients with CKD in this short term study. Overall renal function remained unchanged. However, we found that calcitriol at 0.5 mg daily plus calcium carbonate 500 mg daily could be reno-protective in diabetic nephropathy regardless of their serum 25-OHD levels.