New prospects for the management of renal bone disease

Efficacy of early treatment with calcimimetics in combination with reduced doses of vitamin d sterols in dialysis patients

Vitamin D is an important physiologic regulator of bone and mineral metabolism. In chronic kidney disease, reduced renal production of calcitriol contributes to secondary hyperparathyroidism (SHPT). Consequently, supplementation with vitamin D sterols is an important treatment for SHPT and its associated mineral and bone disorders. However, doses of vitamin D sterols required to suppress parathyroid hormone (PTH) secretion often promote hypercalcaemia and hyperphosphataemia. Therefore, there is a trade-off between reduced serum PTH and increased levels of serum calcium, phosphorus and calcium–phosphorus product. It has been suggested that treatment of SHPT with cinacalcet, a type II calcimimetic, with reduced doses of vitamin D sterols could enhance achievement of calcium and phosphorus treatment targets while maintaining goals for PTH. Recent clinical trials have evaluated this hypothesis and demonstrated that treatment with cinacalcet in combination with reduced doses of vitamin D sterols is an effective treatment for the management of SHPT.

Bone status in patients with epilepsy: relationship to markers of bone remodeling

Patients with epilepsy and treated with antiepileptic drugs (AEDs) may develop metabolic bone disease; however, the exact pathogenesis of bone loss with AEDs is still unclear. Included were 75 adults with epilepsy (mean age: 31.90 ± 5.62 years; duration of treatment with AEDs: 10.57 ± 3.55 years) and 40 matched healthy controls. Bone mineral content (BMC) and bone mineral densities (BMD) of the femoral neck and lumbar spine were measured using dual-energy X-ray absorptiometry (DEXA). Blood samples were analyzed for calcium, magnesium, phosphate, alkaline phosphatase (ALP), 25-hydroxy vitamin D (25OHD), soluble receptor activator of nuclear factor-kappa B ligand (sRANKL), osteoprotegerin (OPG), and OPG/RANKL ratio (markers of bone remodeling). Compared to controls, patients had lower BMD, BMC, Z-score, and T-score at the femoral neck and lumbar spine (all p < 0.001). Seventy-two percent and 29.33% of patients had osteoporosis of the lumbar spine and femoral neck. Patients had significantly lower serum calcium, 25(OH)D, and OPG and higher ALP, sRANKL levels, and sRANKL/OPG (all p < 0.001). Fifty-two percent of patients had hypocalcemia, 93% had hypovitaminosis D, 31% had high levels of sRANKL, and 49% had low levels of OPG. No differences were identified between DEXA and laboratory results in relation to the type, dose, or serum levels of AEDs. BMD at the femoral neck and lumbar spine were found to be correlated with the duration of illness (p = 0.043; p = 0.010), duration of treatment with AEDs (p < 0.001; p = 0.012), and serum levels of 25(OH)D (p = 0.042; p = 0.010), sRANKLs (p = 0.005; p = 0.01), and OPG (p = 0.006; p = 0.01). In linear regression analysis and after adjusting for gender, age, weight, duration, and number of AEDs, we observed an association between BMD, 25(OH)D (p = 0.04) and sRANKL (p = 0.03) concentrations. We conclude that AEDs may compromise bone health through disturbance of mineral metabolism and acceleration of bone turnover mechanisms.

The efficacy of cinacalcet combined with conventional therapy on bone and mineral metabolism in dialysis patients with secondary hyperparathyroidism: a meta-analysis

Cinacalcet, the first calcimimetic to be approved for the treatment of secondary hyperparathyroidism (SHPT) in the chronic kidney disease patients, offers a novel therapeutic approach to SHPT. The aim of this meta-analysis is to access the efficacy and safety of cinacalcet on bone and mineral metabolism disorders in the dialysis patients with SHPT. Randomized controlled trials on cinacalcet combined with vitamin D and/or phosphate binders in the dialysis patients with SHPT were identified in Pubmed, Sciencedirect, and the Cochrane library. Data were analyzed with RevMan software. We compared the proportion of patients achieving the biochemical targets recommended by the Kidney Disease Outcomes Quality Initiative (KDOQI) guidelines and the incidence of adverse events between the cinacalcet and control groups. Six trials involving 2,548 patients were included. A greater proportion of patients in the cinacalcet group compared with the conventional group achieved the KDOQI targets. The relative risks (RRs) were parathyroid hormone (PTH) (RR = 3.51, 95 % CI: 2.38-5.17), calcium (RR = 2.04, 95 % CI: 1.76-2.37), phosphorus (RR = 1.15, 95 % CI: 0.83-1.60), and calcium-phosphorus product (Ca × P) (RR = 1.41, 95 % CI: 1.18-1.69), the number of patients simultaneously achieving the KDOQI targets for PTH + Ca × P was also greater (RR = 3.89, 95 % CI: 2.36-6.41), with p < 0.001 for each. The most common adverse events were nausea, vomiting, diarrhea, and hypocalcemia, which had a higher incidence in the cinacalcet group, but were usually mild to moderate in severity and transient. Compared with conventional therapy, treatment with cinacalcet results in more patients achieving KDOQI targets and offers an effective and safety therapeutic option for controlling mineral and bone disorders in the dialysis patients with SHPT.

Differential effects of oral doxercalciferol (Hectorol) or paricalcitol (Zemplar) in the Cyp27b1-null mouse model of uremia

BACKGROUND/AIMS

Kidney disease patients experience declining calcitriol levels and develop secondary hyperparathyroidism (SHPT). Animal models of uremia based on 5/6 nephrectomy (NTX) do not consistently reproduce this calcitriol deficiency. We developed an animal model, the NTX Cyp27b1-null mouse, which completely lacks endogenous calcitriol, and examined the suitability of this model for evaluation of treatment with vitamin D analogs in uremia.

METHODS

NTX was performed at 2 months of age. One week post-NTX, animals were treated for 4 weeks with vehicle; doxercalciferol at 30, 100 or 300 pg/g body weight (b.w.); or paricalcitol at 100, 300 or 1,000 pg/g b.w. by gavage 3 times per week.

RESULTS

Serum blood urea nitrogen and creatinine were elevated. Vehicle-treated NTX null mice had hypocalcemia and SHPT. Doxercalciferol at 100 or 300 pg/g b.w. normalized serum calcium and parathyroid hormone (PTH) levels. Paricalcitol at 300 or 1,000 pg/g normalized serum calcium, but PTH levels remained elevated. Osteomalacia was corrected by 100 pg/g b.w. of doxercalciferol or 1,000 pg/g b.w. of paricalcitol. The highest dose of doxercalciferol, but not of paricalcitol, significantly reduced osteitis fibrosa.

CONCLUSION

Our results reveal the differential efficacy of doxercalciferol and paricalcitol in this novel animal model incorporating both calcitriol deficiency and renal insufficiency.

Iron chelation therapy in Upper Egyptian transfusion-dependent pediatric homozygous beta-thalassemia major: impact on serum L-carnitine/free fatty acids, osteoprotegerin/the soluble receptor activator of nuclear factor-kappabeta ligand systems, and bone mineral density

Bone disease in beta-thalassemia major (betaTM) remains poorly understood. Receptor activator of nuclear factor-kappabeta ligand (RANKL) regulates osteoclast formation and function. RANKL activity is balanced by interaction with its receptor (RANK) and binding to osteoprotegerin (OPG). L-Carnitine (LC) enhances osteoblastic activity by furnishing fuel. This study hypothesized that abnormal bone metabolism in betaTM involves imbalanced RANKL/OPG and LC/free fatty acids (FFAs) metabolism. Sixty-nine transfusion-dependent betaTM patients and 15 healthy controls were enrolled. One group of patients (n=34) received desferrioxamine (DFO) and the other (n=35) did not. Serum OPG, soluble RANKL (sRANKL), FFAs, LC [total LC (TC), free LC (FC), and esterified LC (EC)], calcium, and inorganic phosphate were measured by specific immuno and colorimetric assays; bone mineral density was examined by dual x-ray absorptiometry. Patients showed lower levels of OPG, TC, FC, EC and higher levels of sRANKL, sRANKL/OPG ratio, and FFAs than controls. Patients on DFO showed lower levels of OPG, TC, FC and higher levels of sRANKL, sRANKL/OPG ratio, and FFAs than those without chelation. In patients, sRANKL correlated negatively with TC and OPG and FC correlated positively with OPG and negatively with sRANKL, sRANKL/OPG ratio, and FFAs. In conclusion, altered bone metabolism owing to imbalanced osteoclastic bone resorption versus constructive osteoblastic activities in betaTM pediatric patients could be due to abnormal sRANKL-OPG and LC-FFAs systems that were worsened by DFO.

A new paradigm for the treatment of secondary hyperparathyroidism

The global rise in chronic kidney disease makes secondary hyperparathyroidism (SHPT) a growing medical concern. Conventional therapies for treating SHPT are limited and include calcium-based and calcium-free phosphate binders for reducing serum phosphorus and vitamin D or its analogues for simultaneous stimulation of calcium absorption and suppression of parathyroid hormone (PTH) gene expression. Control of SHPT using these therapies has typically been poor. Recent studies have demonstrated that use of calcimimetics that reduce PTH secretion by increasing the sensitivity of the parathyroid gland calcium-sensing receptor to circulating calcium allow improved control of serum PTH, calcium, phosphorus and calcium-phosphorus product. This review describes experimental data and the clinical rationale supporting novel strategies for the integration of calcimimetics with conventional therapies to improve control of SHPT.

Effect of L-carnitine supplementation on secondary hyperparathyroidism and bone metabolism in hemodialyzed patients

The aim of our work was to test the influence of L-carnitine supplementation on secondary hyperparathyroidism and bone metabolism in hemodialyzed patients in a randomized study. Eighty-three chronically hemodialyzed patients were observed; 44 were supplemented with L-carnitine (15 mg/kg intravenously after each hemodialysis for 6 months), while 39 took placebo. Levels of free carnitine (CAR), calcium (Ca), inorganic phosphate (P), Ca x P product, parathormone (PTH), bone-specific alkaline phosphatase (b-ALP), osteocalcin (OC), and osteoprotegerin (OPG) were monitored. In comparison with pretreatment values, changes of some selected parameters occurred in the supplemented patients after 6 months (data are expressed as medians; NS, nonsignificant change): PTH, 186.0 vs. 135.5 ng/L (NS); b-ALP, 13.9 vs. 13.2 microg/L (P < 0.05); OC, 78.3 vs. 68.8 microg/L (NS); OPG, 144.0 vs. 182.0 ng/L (P < 0.05). In the controls, there were the following changes: PTH, 148.0 vs. 207.0 ng/L (NS); b-ALP, 15.2 vs. 13.2 microg/L (P < 0.05); OC, 62.7 vs. 79.8 microg/L (P < 0.05); OPG, 140.0 vs. 164.0 ng/L (NS). A significant correlation was found between CAR and OPG changes (r = 0.51, P < 0.001) in the supplemented patients. The supplementation led to a significant increase of serum OPG concentration. Nevertheless, we observed only nonsignificant tendencies to correction of secondary hyperparathyroidism and reduction of bone turnover in hemodialyzed patients supplemented with L-carnitine in contrast to controls. At this point, the use of L-carnitine does not seem to be justified.