Calcium balance during pulse alfacalcidol therapy for secondary hyperparathyroidism in CAPD patients treated with 1.0 and 1.25 mmol/L dialysate calcium

Evaluation of the association of Wnt signaling with coronary artery calcification in patients on dialysis with severe secondary hyperparathyroidism

BACKGROUND

Patients with end-stage renal disease have a higher risk of death from cardiovascular events, which can be mainly attributed to coronary artery calcification (CAC). Wnt signaling is involved in vascular development and may play a role in vascular calcification. This study aimed to evaluate CAC prevalence in patients on dialysis with severe secondary hyperparathyroidism (SHPT) and identify CAC risk factors.

METHODS

The study is a retrospective analysis of the severe hyperparathyroidism registration study that prospectively recruited patients on dialysis with severe SHPT who were candidates for parathyroidectomy, from October 2013 to May 2015. CAC and bone mineral density (BMD) were measured. Demographic and clinical data including calcium, phosphorus, alkaline phosphatase, intact parathyroid hormone, Dickkopf-related protein 1 (DKK1), and sclerostin levels were analyzed. CAC scores were reported in Agatston units (AU).

RESULTS

A total of 61 patients were included in this study. No CAC, mild CAC (<100 AU), moderate CAC (>100 AU), and severe CAC (>400 AU) were observed in 4.9%, 11.4%, 14.8%, and 68.9% of patients, respectively. DKK1 and sclerostin were not associated with CAC. In univariate analysis, CAC was significantly correlated with age, sex (male), total cholesterol, and intravenous pulse calcitriol (p<0.05). CAC was not inversely correlated with the BMD, T scores, or Z scores of the femoral neck (p>0.05). In multivariate analysis, the stepwise forward multiple linear regression revealed that CAC was associated with age, male sex and intravenous pulse calcitriol (p<0.05). Furthermore, serum sclerostin was positively correlated with the BMD of the femoral neck but negatively associated with intact parathyroid hormone (p<0.05). Serum sclerostin was significantly associated with severely low bone mass with Z-scores<-2.5 of the femoral neck, even when adjusted for serum intact parathyroid hormone, vitamin D status, dialysis pattern, sex, and DKK-1 (p<0.05).

CONCLUSIONS

The patients on dialysis with severe SHPT have a high prevalence of vascular calcification. Although the Wnt signaling pathway could play a role in hyperparathyroid bone disease, CAC may be mainly due to the treatment modality rather than the Wnt signaling pathway associated bone metabolism in patients on dialysis with severe SHPT.

Effects of vitamin D on parathyroid hormone and clinical outcomes in peritoneal dialysis: a narrative review

Vitamin D deficiency is very prevalent in dialysis and peritoneal dialysis (PD) patients show lower levels of cholecalciferol (25(OH)D3) than hemodialysis patients. We conducted a systematic narrative review to assess the effects of vitamin D therapy on control of secondary hyperparathyroidism and clinical outcomes induced by vitamin D pleiotropic effects. Medline database was searched for cohort and intervention studies reporting data on vitamin D (all sterols including synthetic analogs) and peritoneal dialysis without language restriction. Two authors independently extracted data. Twenty-nine observational and eleven interventional studies were identified for inclusion (1,036 subjects). PTH levels decreased in twenty-nine studies, increased in one study and remained stable in ten studies. Thirty-three studies analyzed the oral route for vitamin D administration, ten the intraperitoneal, one the subcutaneous and one the intravenous. A significant decrease of peritonitis risk was observed in two studies. Proteinuria decreased in four studies and remained stable in one study. Peritoneal protein loss decreased in one study and was stable in two studies. Studies on the therapeutic effects of vitamin D in PD are limited and describe small population samples. Moreover, vitamin D compounds do not consistently reduce PTH levels. The administration of active vitamin D in PD may have interesting pleiotropic effects such as decreasing proteinuria and peritoneal protein loss. According to these effects, vitamin D could help to preserve residual renal function and ensure efficient peritoneal membrane dialysance.

Reversal of adynamic bone disease by lowering of dialysate calcium

Adynamic bone disease (ABD) is increasingly recognized, especially in dialysis patients treated with oral calcium carbonate, vitamin D supplements, or supraphysiological dialysate calcium. We undertook this study to assess the effect of lowering dialysate calcium on episodes of hypercalcemia, serum parathyroid hormone (PTH) levels as well as bone turnover. Fifty-one patients treated with peritoneal dialysis and biopsy-proven ABD were randomized to treatment with control calcium, 1.62 mM, or low calcium, 1.0 mM, dialysate calcium over a 16-month period. In the low dialysate calcium group, 14 patients completed the study. This group experienced a decrease in serum total and ionized calcium levels, and an 89% reduction in episodes of hypercalcemia, resulting in a 300% increase in serum PTH values, from 6.0+/-1.6 to 24.9+/-3.6 pM (P<0.0001). Bone formation rates, all initially suppressed, at 18.1+/-5.6 microm2/mm2/day rose to 159+/-59.4 microm2/mm2/day (P<0.05), into the normal range (>108 microm2/mm2/day). In the control group, nine patients completed the study. Their PTH levels did not increase significantly, from 7.3+/-1.6 to 9.4+/-1.5 pM and bone formation rates did not change significantly either, from 13.3+/-7.1 to 40.9+/-11.9 microm2/mm2/day. Lowering of peritoneal dialysate calcium reduced serum calcium levels and hypercalcemic episodes, which resulted in increased PTH levels and normalization of bone turnover in patients with ABD.

Calcium Loading, Calcium Accumulation, and Associated Cardiovascular Risks in Dialysis Patients

Calcium and phosphate imbalances are important mutable risk factors for cardiovascular disease in chronic kidney disease (CKD). Nearly all dialysis patients require phosphate binders. These include traditional calcium-based compounds and, more recently, the calcium-free, metal-free, non-absorbed agent, sevelamer hydrochloride. Both binder types reduce serum phosphorus, but differ with respect to calcium load and metabolism. Absorption from calcium-based agents very likely promotes positive total calcium balance in many patients. Positive calcium balance is inappropriate in adults and may promote or accelerate soft-tissue and vascular calcification even in the absence of hypercalcemia. Calcium accumulation in heart and vascular tissues contributes to rapidly progressive cardiovascular calcification - a strong predictor of cardiovascular and all-cause mortality in stage 5 CKD. More than two-thirds of stage 5 CKD patients have calcification scores above the 75th percentile for matched controls -- scores associated with extremely high risk of cardiovascular events and death.