Figures & data
Figure 1. Illustration of the pathophysiology of CKD-MBD according to GFR value and CKD stage. The more recent data from literature suggest the first abnormality to be a decrease in klotho expression. This determines a progressive peripheral resistance to FGF23 and an increase in its serum levels. By inhibiting 1α-hydroxylase, FGF23 reduces 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] production with consequent secondary hyperparathyroidism, enhanced bone remodeling, increased serum phosphorus and calcium levels, vascular smooth muscle cell calcifications and further increase in FGF23 expression.
![Figure 1. Illustration of the pathophysiology of CKD-MBD according to GFR value and CKD stage. The more recent data from literature suggest the first abnormality to be a decrease in klotho expression. This determines a progressive peripheral resistance to FGF23 and an increase in its serum levels. By inhibiting 1α-hydroxylase, FGF23 reduces 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] production with consequent secondary hyperparathyroidism, enhanced bone remodeling, increased serum phosphorus and calcium levels, vascular smooth muscle cell calcifications and further increase in FGF23 expression.](/cms/asset/56576102-70e9-4ff9-a688-0fd233093b60/ieid_a_962652_f0001_b.jpg)
Figure 2. Illustration of vitamin D metabolism. In the skin, 7-dehydrocholesterol is converted to cholecalciferol (vitamin D3) by ultraviolet B (UVB) rays. Then, a 25-hydroxylase present in the liver transforms cutaneous cholecalciferol and the one deriving from diet and supplements in 25-hydroxyvitamin D3, which in turn is converted to 1,25-dihydroxyvitamin D3 by the renal 1α-hydroxylase. 1,25-dihydroxyvitamin D3 is the active form of vitamin D and, by binding to its related receptor (vitamin D receptor [VDR]), exerts the hormone effects on different target tissues. The physiological role played by vitamin D in calcium/phosphate balance justifies the use of the drugs listed in the table at the top right of the picture in CKD patients.
![Figure 2. Illustration of vitamin D metabolism. In the skin, 7-dehydrocholesterol is converted to cholecalciferol (vitamin D3) by ultraviolet B (UVB) rays. Then, a 25-hydroxylase present in the liver transforms cutaneous cholecalciferol and the one deriving from diet and supplements in 25-hydroxyvitamin D3, which in turn is converted to 1,25-dihydroxyvitamin D3 by the renal 1α-hydroxylase. 1,25-dihydroxyvitamin D3 is the active form of vitamin D and, by binding to its related receptor (vitamin D receptor [VDR]), exerts the hormone effects on different target tissues. The physiological role played by vitamin D in calcium/phosphate balance justifies the use of the drugs listed in the table at the top right of the picture in CKD patients.](/cms/asset/b5f17912-6de0-4c39-81f1-1c48eabcb9ea/ieid_a_962652_f0002_b.jpg)