The Effect of REgulation of PArathyroId hoRmone in Patients With Chronic Kidney Disease to Investigate the Change in Bone Mineral Density

The prevalence of chronic kidney disease (CKD) is estimated to afflict 10 % of the adult population, and it is increasing world-wide. CKD is a devastating disease due to the risk of kidney failure and thereby the need for dialysis or transplantation, but also because the presence of CKD increases the risk of bone fracture, cardiovascular disease and mortality.

Parathyroid hormone (PTH) is a peptide hormone produced by the parathyroid glands(5). The main function of PTH is to regulate mineral metabolism, including the calcium and phosphate homeostasis. PTH increases as the kidney function declines, and at end stage kidney disease almost all patients have disturbances in the mineral metabolism. Treatment with activated vitamin D, phosphate binder and calcium supplementation has been used for more than 30 years to suppress hyperparathyroidism and keep calcium and phosphate within the normal range. Later calcimetics has been introduced as a treatment for secondary hyperparathyroidism.

The risk of bone fracture is increased in patients with CKD and the risk increases as the kidney function declines. A bone fracture leads to a direct burden on the individual. In addition, the risk of complications after a bone fracture is higher in the CKD population compared to the general population. A fracture also constitutes a significant cost for the society. The increased risk of fracture in patients with CKD is associated to the presence of hyperparathyroidism.

Bone mineral density (BMD) assessed by dual energy x-ray (DXA) scan is a highly used modality to diagnose osteoporosis and future fracture risk in the general population. Bone mineral density associates with the risk of future fracture in patients with CKD. In patients with CKD there is an association between decreasing eGFR and both low BMD and future fracture risk. It is unknown how elevated PTH associates with BMD and its changes at different stages of CKD, and it is unknown if treatment of hyperparathyroidism influence on BMD and fracture risk in patients with CKD.

The risk of cardiovascular mortality, coronary heart disease, heart failure, stroke and peripheral arterial disease increase as the kidney function declines. Elevated PTH associates with an increased risk of cardiovascular disease. However, hyperparathyroidism is tightly connected to the general disturbances in the mineral metabolism in CKD, i.e. hyperphosphatemia and elevated FGF-23, which associate with an increased risk of cardiovascular disease and mortality. Therefore, it is questioned if PTH is directly involved in the pathogenesis of cardiovascular disease, or if the increased risk of cardiovascular disease could be caused by other factors involved in the mineral metabolism. One way to approach precursors of vascular disease is measuring vascular stiffness with pulse wave velocity which is associated with cardiovascular outcomes in patients with CKD.

The active circulating form of vitamin D is 1,25 dihydroxy vitamin D (calcitriol). The level of calcitriol is regulated by the activity of the 1α hydroxylase enzyme located in the kidney. The 1α hydroxylase enzyme hydroxylate 25-hydroxy vitamin D at the 1-position. As kidney function declines the activity of 1α hydroxylase is reduced and thereby the circulating level of calcitriol is reduced. The reduced level of calcitriol, together with hypocalcaemia and hyperphosphatemia, leads to secondary hyperparathyroidism. Activated vitamin D is given to patients with hyperparathyroidism to try lowering PTH. In a randomized placebo-controlled trial with 36 patients with CKD G3-5 the intervention group were treated with active vitamin D, which resulted in a difference in BMD by +4.2% in the spine compared to controls after 18 months (P< 0.05). No clinical trials have aimed to explore the influence of targeting different levels of PTH and the influence on bone mineral density or bone fracture in patients with CKD.

Two randomized placebo-controlled trials aimed to address effect of 1 year of active vitamin D treatment on the left ventricular mass, a surrogate endpoint for development of heart failure. No difference between the treatment groups was found in any of the trials. Cohort studies in dialysis patients have found increased survival in patients treated with active vitamin D, but the result could be biased having the design in mind. One Japanese randomized controlled trial compared alfacalcidol with placebo in 976 patients on dialysis. Of importance, not all the included participants did have hyperparathyroidism. No difference was found in fatal and non-fatal cardiovascular events, additionally no difference was found in risk of fracture during the study. If this finding would have differed in patients with hyperparathyroidism or in patients with earlier stages of kidney disease and thereby preventable progression of vascular calcification, remains to be determined.

Treatment with active vitamin D, phosphate binders and calcimetics has been used for patients with CKD for decades. Recommendations regarding the appropriate dose and PTH target for different stages of CKD has varied during years and between guidelines, reflecting the lack of randomized clinical trials with clinical important end points.

In patients with CKD G3b-5, it is currently recommended to monitor the PTH every 3-6 month. As more than 50 % of the patients have elevated PTH already at CKD G3b, it is an everyday consideration for the clinician if the patients should be treated to reduce PTH. This is both time- and cost consuming. At present, there is no evidence to advise if secondary hyperparathyroidism should be treated in patients with CKD.

To improve knowledge about when secondary hyperparathyroidism should be treated, investigators want to conduct a randomized clinical trial with one group of patients being treated if PTH is elevated versus a second group of patients not being treated if PTH is elevated.

The investigators hypothesize that suppression of initially elevated PTH will improve BMD, arterial stiffness, muscle mass and muscle strength in patients with CKD.

Subjects will be recruited from the patient population in the outpatient clinic at the Department of Nephrology at Herlev and Gentofte Hospital, Herlev, Denmark.

Inclusion criteria

• ≥50 years of age at screening
• CKD G4-5nonD (eGFR < 30 mL/min/1.73m2) based on local laboratory assessment of serum creatinine and eGFR estimated by the CKD-EPI formula)
• Plasma PTH > upper normal limit of local laboratory reference range (> 8,5µmol/L) and/or treated with active vitamin D (Alphacalcidol) or calcimetics (Cinacalcet) initially
• Written informed consent

Exclusion criteria

• Patients who have received a kidney transplant
• Patients receiving treatment with specific anti-osteoporosis medication (denosumab/bisphosphonates) (because of the profound effect on calcium/phosphate fluxes and BMD)