The effect of stimulation of calcium sensing receptors via cinacalcet on renal and bone histomorphometry

Aim: To evaluate the effect of stimulation of calcium sensing receptors via cinacalcet on renal tubular functions, renal histology in terms of particularly mesangial cell proliferation and bone histomorphometry.Methods: Two groups, each including seven female, 6-week-old Sprague-Dawley rats with a mean body weight of 120-130gr were included into the study. The first group received cinacalcet (25mg/kg) by p.o. gavage and the control group received distillated water by the same method for 21 days. At the end of the study, renal tubular functions were evaluated by serum and urine biochemical analyses. Renal and bone histological investigations were performed via light microscopy. Glomerular mesangial cell numbers were determined by counting total mesangial cell numbers in five renal sections of 0.7 ?m. Extraglomerular mesangial cells were evaluated in approximately ten sections with a thickness of 5 ?m crossing both afferent and efferent arterioles. Histomorphometric analyses of bone were performed by using image analysis system. Histomorphometric analysis parameters were growth plate thickness, cortical thickness, osteoid volume, trabecular bone volume, osteoblast and osteoclast number per 1mm of osteoid surface. Glomerular and extraglomerular mesangial cell numbers, histomorphometric bone analyses were compared between the two groups.Results: At the end of study, body weight gains per 100 g body weights were similar between the two groups (p>0.05). Serum ionized calcium (0.86±0.08 vs. 1.22±0.15 mmol/L), total calcium (9.17±0.61 vs. 11.30±0.46 mg/dL) and paratiroid hormone (14.6±7.5 vs. 64.9±31.4 pg/mL) levels were statistically lower in rats receiving cinacalcet (p=0.001 for each). However, no statistically significant difference was determined in the levels of serum phosphorus, sodium, potassium, blood urea nitrogen, creatinine, magnesium, total protein and 25-OH vitamin D levels between the two groups (p>0.05). Daily urine volumes of the rats under cinacalcet treatment were significantly higher than the control group (65.6±18.9 vs. 31.7±9.1 mL/kg/day, p=0.001). Although Tmp/GFR and daily calcium excretion levels of the rats in the study group were higher when compared with the control group, the differences were not statistically significant (p>0.05). However, daily calcium excretion/serum calcium ratio in study group were higher when compared with control group (8.73±5.25 vs. 4.64±2.84 p=0,006). There was a linear correlation between the daily urine volume and calcium excretion levels (r2= 0.399, p=0.001). The comparison of fractional sodium and chloride excretion between the two groups revealed increase in favour of the study group (respectively 1.82±0.42 vs. 1.28±0.35, p = 0.026 and 3.22±0.87 vs. 2.27±0.43, p = 0.053), while urinary excretion of magnesium, phosphorus and protein levels were similar between the two groups (p>0.05).There was a significant increase in renal glomerular (7.42±0.32 vs. 4.87±0.34, p=0.001) and ekstraglomerular (4.28±0.94 vs. 2.15±0.58 p=0.001) mesangial cell counts in the study group . Mononuclear cell infiltration was demonstrated in renal sections of 4 rats in study group and 1 rat in control group. Nevertheless, this difference was not statistically significant (p>0.05). When histomorphometric parameters were evaluated, a significant increase was demonstrated in total growth plate thickness (209.61±3.63 vs. 200.64±6.58 µm, p<0.001) and cortical thickness (105.05±10.69 vs. 81.87±11.04 µm, p<0.001) in the study group. Trabecular bone volumes (19.75±2.68 vs. 23.36±5.79, p=0.007), osteoblast (4.16±0.34 vs. 5.47±0.19, p<0.001)and osteoclast (0.35±0.12 ve 0.60±0.13, p<0.001) counts were significantly lower in the study group . However, there was no significant difference in osteoid volume between the two groups (0.66±0.41 vs. 1.18±0.90%, p=0,056).Conclusion: Calcium sensing receptor stimulation via cinacalcet in healthy rats resulted in a decrease in PTH levels upon induction of parathyroid glands, proliferation of renal mesangial cells and bone histomorphometric changes compatible with low turnover bone disease.Keywords: Mesangial cell proliferation, cinacalcet, bone histomorphometry