Direct maxacalcitol injection into hyperplastic parathyroids improves skeletal changes in secondary...

Area of Science:

• Nephrology and Endocrinology
• Bone Biology and Mineral Metabolism

Background:

• Secondary hyperparathyroidism (s-HPT) is a common complication of chronic kidney disease.
• Current treatments for s-HPT face challenges with resistance, partly due to altered vitamin D receptor (VDR) and Ca-sensing receptor (CaSR) expression and parathyroid gland (PTG) hyperplasia.
• Direct maxacalcitol injection into PTGs shows promise in addressing these underlying factors.

Purpose of the Study:

• To evaluate the long-term effects of direct maxacalcitol injection into PTGs on bone histomorphology in advanced s-HPT.
• To assess the impact of this treatment on PTG hyperplasia, VDR and CaSR expression, and serum parathyroid hormone (PTH) levels.

Main Methods:

• A rat model of advanced s-HPT was established using five/six nephrectomy and a high-phosphorus, low-calcium diet.
• Rats received either direct maxacalcitol injection into PTGs followed by intravenous administration (DI-OCT+IV-OCT), direct vehicle injection with IV-OCT, IV-OCT alone, or no treatment.
• Serum PTH, PTG weight, VDR/CaSR expression, and bone histomorphometric parameters were analyzed.

Main Results:

• The DI-OCT+IV-OCT group showed sustained reduction in serum intact-PTH levels.
• Significant decreases in PTG weight and increased VDR and CaSR expression were observed in the DI-OCT+IV-OCT group.
• Bone histomorphometric analysis revealed significant improvements in osteitis fibrosa in both cancellous and cortical bones in the DI-OCT+IV-OCT group.

Conclusions:

• Direct maxacalcitol injection into PTGs, combined with intravenous administration, effectively controls PTH levels by reducing PTG hyperplasia.
• This therapeutic approach successfully reverses osteitis fibrosa in advanced s-HPT.
• The findings suggest a promising strategy for managing complex secondary hyperparathyroidism and its skeletal complications.