Original ArticleFibroblast growth factor-23, vitamin D and mineral metabolism in renal transplant recipients
Introduction
Kidney transplantation is the preferred treatment for patients with ESRD. Transplantation avoids the various complications associated with dialysis and is associated with a lower mortality and morbidity than is hemodialysis. The pathological link among infection, immune dysregulation, and cardiovascular disease, and the inflammatory response is being increasingly recognized in transplant recipients. Patients with CKD are known to be both 25-hydroxyvitamin D (25OHD3) and 1,25-dihydroxyvitamin D (1,25[OH]2D3) deficient. Several observational studies have shown that treatment of ESRD patients with vitamin D analogs is associated with improved survival. 1,25(OH)2-D3 has long been recognized to have an immune regulatory function besides its role in calcium homeostasis. There is evidence in literature that indicates that 1,25(OH)2-D3 could have an important role in the regulation of immune function. This could have important clinical implications. Transplant physicians and surgeons should understand that vitamin D has a variety of immunological actions which can have important effect on patient and graft survival after transplantation.1
Section snippets
Vitamin D physiology
Vitamin D2 (ergocalciferol) is obtained from various food and vitamin sources, whereas vitamin D3 (cholecalciferol) is generated for the most part after skin exposure to ultraviolet B radiation. The first step in the metabolic activation of vitamin D is hydroxylation of ergocalciferol and cholecalciferol in the liver, to form 25OHD3. Almost all 25OHD3 is bound to circulating vitamin D-binding protein, which is filtered by the kidney and reabsorbed by the proximal convoluted tubules via the
Vitamin D deficiency
In chronic kidney disease (CKD), vitamin D deficiency is increasingly recognized as a health problem as in the general population. It has been estimated that 1 billion individuals worldwide are vitamin D deficient or insufficient. Although no consensus exists on the optimal levels of 25OHD3 measured in the serum, the US Institute of Medicine has recommended after extensive investigations that mean 25OHD3 levels should be >50 nmol/l in the general population. It might be reasonable to suggest
Immune function in CKD
Vitamin D affects innate immune responses by enhancing the development of monocytes into macrophages. Vitamin D also influences chemotaxis and cytokine expression. It suppresses immunoglobulin production and B-cell proliferation and differentiation. Vitamin D has been reported to directly affect T-cell responses by inhibiting the release of Th1 and Th17 cytokines. It also induces Th2 cytokine production. Epidemiological and clinical evidence suggests significant association between vitamin D
Vitamin D deficiency and immune dysfunction
A high prevalence of vitamin D deficiency has been found in pre-dialysis patients with moderate and severe chronic kidney disease as well as in patients undergoing hemodialysis Analyses of pre-transplant 25-hydroxyvitamin D3 levels showed that only about 15% of kidney transplant recipients have adequate vitamin D levels at the time of transplantation.3
After kidney transplantation vitamin D deficiency remains a common problem. In a study of 31 kidney transplant recipients serum 25-hydroxyvitamin
Conclusions
We have also reported high prevalence of vitamin D deficiency in renal transplant recipients and its impact on post transplant graft outcome and function. There was high incidence of vitamin D deficiency and insufficiency in ESRD patients (69.2%) which increased further to 80.6% at 3 months after kidney transplant. 1,25(OH)2 D3 levels also decreased after transplant with concomitant increase in VDR activity but it was still less than normal controls. FGF-23 levels quickly came down to normal
Conflict of interest
No conflict of interest.
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