Modulation of CYP27B1 and CYP24 mRNA expression in bone is independent of circulating 1,25(OH)2D3 levels

Circulating levels of 1,25-dihydroxyvitamin D (1,25D) are determined by bioactivation catalyzed by the renal 25-hydroxyvitamin D 1alpha-hydroxylase (CYP27B1) and degradation through the action of the renal 25-hydroxyvitamin D 24-hydroxylase (CYP24). CYP27B1 and CYP24 are also present in bone cells, but little is known of their physiological role. The purpose of this study was to determine the changes that occur with aging on the expression of CYP27B1 and CYP24 mRNA in whole kidney and femora of female Sprague-Dawley rats. Real-time RT-PCR was used to measure CYP27B1, CYP24 and vitamin D receptor (VDR) mRNA levels in the kidneys and bones of animals aged between 3 weeks and 2 years. Circulating 1,25D levels decreased exponentially with age which was correlated with both reduced kidney CYP27B1 mRNA (R(2) = 0.72) and increased CYP24 mRNA levels (R(2) = 0.71). In the bone, CYP27B1 mRNA levels were maintained at their highest level throughout the ages of 3 to 15 weeks before decreasing in adult animals (P < 0.05). Bone CYP24 mRNA levels were positively correlated with bone CYP27B1 mRNA and not circulating 1,25D levels (R(2) = 0.74). Levels of bone CYP27B1 mRNA were positively correlated with distal femoral epiphyseal trabecular number (Tb.N) (R(2) = 0.74) and negatively with the trabecular thickness (Tb.Th) (R(2) = 0.56) in animals aged between 12 weeks and 2 years. These findings indicate that the regulation of CYP27B1 and CYP24 mRNA expression in the bone is unique from that in the kidney. The synthesis of 1,25D in bone tissue regulates bone CYP24 expression and is associated with bone mineralization suggesting that vitamin D metabolism has an autocrine or paracrine function.     

Novel mutations in the 1alpha-hydroxylase (P450c1) gene in three families with pseudovitamin D-deficiency rickets resulting in loss of functional enzyme activity in blood-derived macrophages.

Pseudovitamin D-defiency rickets (PDDR) is an autosomal recessive disorder characterized by hypocalcemia, rickets (which are resistant to treatment with vitamin D), and low or undetectable serum levels of 1,25-dihydroxyvitamin D (1,25(OH)2D). The symptoms are corrected with 1,25(OH)2D treatment, and the disease is now believed to result from a defect in the cytochrome P450 component (P450c1; CYP27B1) of the renal 25-hydroxyvitamin D-1alpha-hydroxylase (1-OHase). We have studied genomic DNA from three families with PDDR and have identified the same homozygous mutation in the P450c1 gene in two of the index cases, causing a frameshift in exon 8, resulting in a premature stop codon in the heme-binding domain. The two cases in the third kindred were compound heterozygotes with missense mutations in exons 6 and 9. We have also identified a C/T polymorphism in intron 6 of the P450c1 genomic DNA. Interferon gamma-inducible 1-OHase activity in blood-derived macrophages was shown by 1,25(OH)2D synthesis in all control cells tested (37-184 fmol/h/106 cells) and those from the PDDR family parents (34-116 fmol/h/106 cells) but was totally absent from the patients' cells, indicating a defect in their macrophage 1-OHase, similar to the presumed renal defect. The assumption of similarity between the renal and macrophage P450c1 was supported by our ability to clone a 514 bp sequence, including the heme-binding region of the macrophage P450c1 cDNA from controls, which was identical to that published for both the renal and keratinocyte P450c1 cDNAs.     

Oral cholecalciferol decreases albuminuria and urinary TGF-β1 in patients with type 2 diabetic nephropathy on established renin-angiotensin-aldosterone system inhibition

The anti-inflammatory, antifibrotic, and antiproteinuric properties of vitamin D have been defined in studies using active vitamin D analogs. In this prospective observational study we determined whether nutritional vitamin D repletion can have additional beneficial effects in patients with type 2 diabetic nephropathy already established on renin-angiotensin-aldosterone system inhibition. During a 7-month period, 63 patients were enrolled and those with low levels of 25(OH)D were treated with oral cholecalciferol for 4 months. Baseline serum 25(OH)D and 1,25(OH)(2)D showed no significant correlation with baseline urinary MCP-1, TGF-β1, or albuminuria measured as the urinary albumin-to-creatinine ratio. Of the 63 patients, 54 had insufficient or deficient levels of serum 25(OH)D and 49 complied with cholecalciferol therapy and follow-up. Both 25(OH)D and 1,25(OH)(2)D were significantly increased at 2 and 4 months of treatment. Albuminuria and urinary TGF-β1 decreased significantly at both time points compared to their baseline values, while urinary MCP-1 did not change. Thus, in the short term, dietary vitamin D repletion with cholecalciferol had a beneficial effect in delaying the progression of diabetic nephropathy above that due to established renin-angiotensin-aldosterone system inhibition.     

Possible mechanism of impaired calcium and vitamin D metabolism in nephrotic rats.

Patients who have nephrotic syndrome and normal renal function are hypocalcemic in spite of the elevated levels of serum parathyroid hormone (PTH) caused by a low serum concentration of 1,25-dihydroxyvitamin D[1,25(OH)2D], presumably because of its loss in urine. However, it has not been established whether the conversion of 25-hydroxyvitamin D[25(OH)D] into 1,25(OH)2D is impaired in the kidney. In this study, we examined the serum levels of vitamin D metabolites, and kinetics of renal 25(OH)D-1-hydroxylase activity in vitro, and nephrogenous cyclic AMP excretion in response to exogenous PTH administration in puromycin aminonucleoside-induced nephrosis in rats. Plasma ionized calcium and the serum levels of vitamin D metabolites were lower, and conversely, the serum PTH level was higher, in nephrotic rats than in controls. Serum 1,25(OH)2D levels were higher in 25(OH)D3-treated nephrotic rats than in untreated nephrotic rats, indicating that the low 1,25(OH)2D level in nephrotic rats is partially due to the low concentration of 25(OH)D. Although PTH levels were higher in nephrotic rats than in control rats, the Vmax of renal 25(OH)D-1-hydroxylase and nephrogenous adenosine 3',5'-monophosphate (cyclic AMP) excretion in response to exogenous PTH were significantly lower in nephrotic animals than in controls. These results suggest that abnormalities in calcium and vitamin D metabolism in nephrotic rats are partially attributable to impaired proximal tubular function.     

Effect of long-term low-dose 1α, 25-dihydroxy vitamin D3 on the expression of aquaporin 2 in kidneys of uremic rats

Objective To investigate the effect of long-term low-dose 1α, 25-dihydroxy vitamin D3 [1,25(OH)2D3] on rat kidney aquaporin (AQP) 2 expression in 5/6 nephrectomized rats. Methods Twelve Sprague-Dawley rats underwent 5/6 nephrectomy surgery were divided into model group (n＝6) and 1,25(OH)2D3 group (n＝6) randomly; sham-operated rats only received the renal capsule stripping (control group, n＝6). Rats in 1,25(OH)2D3 group received 1,25(OH)2D3 (3 ng•100 g-1•d-1, ip) for 24 weeks. Serum and 24-hour urine specimens were collected for measurement of serum creatinine, arginine vasopressin (AVP) and urine protein. Animals were sacrificed at week 24 and kidneys were removed for routine pathological, immunohistochemistry and immunoblotting analysis. Results At week 24, plasma AVP level in 1,25(OH)2D3 and model group was much higher than that in control group (all P＜0.05), with no significant differences between the former two groups (P＞0.05). Lower serum creatinine and urinary protein were presented in 1,25(OH)2D3 group compared with the model group rats at week 24 (P＜0.05). Renal medullar fibrosis and inflammatory cell infiltration were improved significantly in 1,25(OH)2D3 group compared with model group (P＜0.01, P＜0.05). Immunohistochemistry analysis revealed abundant AQP2 and p-AQP2 expressed in the renal medulla of sham group, mainly in apical membrane of collecting duct cells. AQP2 expression in model group was down-regulated (P＜0.05) and p-AQP2 expression in apical membrane was reduced. AQP2 expression in 1,25(OH)2D3 group increased compared with model group, with increased p-AQP2 expression in apical membrane. Western blotting revealed same results of these expressions (all P＜0.05). Correlation analysis showed a negative correlation of AQP2 expression with urine volume, medullary fibrosis, and inflammatory cell infiltration (P＜0.05). Conclusion Long-term low-dose 1,25(OH)2D3 improves AQP2 expression and response to AVP in collecting duct, which may involve in the anti-polyuric effect of 1,25(OH)2D3 in uremic rat.     

Losses of 1,25- and 24,25-dihydroxycholecalciferol in the peritoneal fluid of patients treated with continuous ambulatory peritoneal dialysis

We measured peritoneal losses of the active vitamin D metabolites 1,25(OH)2D3 and 24,25(OH)2D3 in patients receiving continuous ambulatory peritoneal dialysis (CAPD). The serum concentration of 24,25(OH)2D3 was considerably lower than in hemodialysis patients. The serum concentration of 1,25(OH)2D3 was undetectable and rose to levels similar to those in hemodialysis patients only after loading with much higher oral doses of 1-alpha-vitamin D3 than those received by hemodialysis patients. Losses of both metabolites in peritoneal fluid were considerable, averaging approximately 6-8% of the plasma pool per day. These losses lead to low serum levels of these active vitamin D metabolites in CAPD patients, which may be an important factor in exacerbating renal osteodystrophy. Our results indicate the need for increased replacement doses of vitamin D metabolites in CAPD patients.     

Effects of 25‐hydroxyvitamin D3 on proliferation and osteoblast differentiation of human marrow stromal cells require CYP27B1/1α‐hydroxylase

1,25‐Dihydroxyvitamin D₃ [1,25(OH)₂D₃] has many noncalcemic actions that rest on inhibition of proliferation and promotion of differentiation in malignant and normal cell types. 1,25(OH)₂D₃ stimulates osteoblast differentiation of human marrow stromal cells (hMSCs), but little is known about the effects of 25‐hydroxyvitamin D₃ [25(OH)D₃] on these cells. Recent evidence shows that hMSCs participate in vitamin D metabolism and can activate 25(OH)D₃ by CYP27B1/1α‐hydroxylase. These studies test the hypothesis that antiproliferative and prodifferentiation effects of 25(OH)D₃ in hMSCs depend on CYP27B1. We studied hMSCs that constitutively express high (hMSCs^hi‐1α) or low (hMSCs^lo‐1α) levels of CYP27B1 with equivalent expression of CYP24A1 and vitamin D receptor. In hMSCs^hi‐1α, 25(OH)D₃ reduced proliferation, downregulated proliferating cell nuclear antigen (PCNA), upregulated p21^Waf1/Cip1, and decreased cyclin D1. Unlike 1,25(OH)₂D₃, the antiapoptotic effects of 25(OH)D₃ on Bax and Bcl‐2 were blocked by the P450 inhibitor ketoconazole. The antiproliferative effects of 25(OH)D₃ in hMSCs^hi‐1α and of 1,25(OH)₂D₃ in both samples of hMSCs were explained by cell cycle arrest, not by increased apoptosis. Stimulation of osteoblast differentiation in hMSCs^hi‐1α by 25(OH)D₃ was prevented by ketoconazole and upon transfection with CYP27B1 siRNA. These data indicate that CYP27B1 is required for 25(OH)D₃'s action in hMSCs. Three lines of evidence indicate that CYP27B1 is required for the antiproliferative and prodifferentiation effects of 25(OH)D₃ on hMSCs: Those effects were not seen (1) in hMSCs with low constitutive expression of CYP27B1, (2) in hMSCs treated with ketoconazole, and (3) in hMSCs in which CYP27B1 expression was silenced. Osteoblast differentiation and skeletal homeostasis may be regulated by autocrine/paracrine actions of 25(OH)D₃ in hMSCs. © 2011 American Society for Bone and Mineral Research.     

Vitamin D–Dependent Rickets Type 1B (25‐Hydroxylase Deficiency): A Rare Condition or a Misdiagnosed Condition?

Vitamin D requires a two‐step activation by hydroxylation: The first step is catalyzed by hepatic 25‐hydroxylase (CYP2R1, 11p15.2) and the second one is catalyzed by renal 1α‐hydroxylase (CYP27B1, 12q13.1), which produces the active hormonal form of 1,25‐(OH)₂D. Mutations of CYP2R1 have been associated with vitamin D–dependent rickets type 1B (VDDR1B), a very rare condition that has only been reported to affect 4 families to date. We describe 7 patients from 2 unrelated families who presented with homozygous loss‐of‐function mutations of CYP2R1. Heterozygous mutations were present in their normal parents. We identified a new c.124_138delinsCGG (p.Gly42_Leu46delinsArg) variation and the previously published c.296T>C (p.Leu99Pro) mutation. Functional in vitro studies confirmed loss‐of‐function enzymatic activity in both cases. We discuss the difficulties in establishing the correct diagnosis and the specific biochemical pattern, namely, very low 25‐OH‐D suggestive of classical vitamin D deficiency, in the face of normal/high concentrations of 1,25‐(OH)₂D. Siblings exhibited the three stages of rickets based on biochemical and radiographic findings. Interestingly, adult patients were able to maintain normal mineral metabolism without vitamin D supplementation. One index case presented with a partial improvement with 1alfa‐hydroxyvitamin D₃ or alfacalcidol (1α‐OH‐D₃) treatment, and we observed a dramatic increase in the 1,25‐(OH)₂D serum concentration, which indicated the role of accessory 25‐hydroxylase enzymes. Lastly, in patients who received calcifediol (25‐OH‐D₃), we documented normal 24‐hydroxylase activity (CYP24A1). For the first time, and according to the concept of personalized medicine, we demonstrate dramatic improvements in patients who were given 25‐OH‐D therapy (clinical symptoms, biochemical data, and bone densitometry). In conclusion, the current study further expands the CYP2R1 mutation spectrum. We note that VDDR1B could be easily mistaken for classical vitamin D deficiency. © 2017 American Society for Bone and Mineral Research.     

Gene expression of vitamin D hydroxylase and megalin in the remnant kidney of nephrectomized rats

BACKGROUND: Regulation of vitamin D hydroxylase genes in the early stage of chronic renal failure is not fully understood. Using nephrectomized rats, we examined changes in mRNA levels of CYP27B1 (25-hydroxyvitamin D3-1 alpha-hydroxylase), CYP24 (25-hydroxyvitamin D3-24-hydroxylase), and vitamin D receptor in relation to megalin, recently found to participate in renal vitamin D metabolism. METHODS: A rat model of moderate renal failure was induced by 3/4 nephrectomy. Plasma parameters, including vitamin D metabolite concentrations, were measured at weeks 2, 4 and 8, and poly(A)+ RNA extracted from the remnant kidneys was subjected to Northern blot hybridization. RESULTS: Plasma creatinine concentration at week 2 was 0.40 +/- 0.02 mg/dL in the sham-operated and 0.93 +/- 0.15 mg/dL in the nephrectomized rats, and both values remained constant up to week 8. Plasma concentrations of 25(OH)D3, 1 alpha,25(OH)2D3, and 24,25(OH)2D3 were unchanged between nephrectomized and sham-operated rats at week 8. Intact parathyroid hormone (PTH) increased at week 8 in nephrectomized rats. CYP27B1 mRNA in nephrectomized rats did not vary at week 2, but increased approximately two- and four-fold at weeks 4 and 8, respectively, compared to the sham-operated rats. CYP24 and megalin mRNAs, on the other hand, began to decline as early as at week 2 in nephrectomized rats and kept decreasing throughout the experiment. The expression of vitamin D receptor was modestly but significantly decreased only at week 8. CONCLUSION: Coordinated and reciprocal alterations of the increase in CYP27B1 mRNA and the decrease in CYP24 mRNA may play a pivotal role in maintaining the plasma level of 1 alpha,25(OH)2D3 in the face of reduced nephron mass and/or megalin expression.     

Cholecalciferol Supplementation Alters Calcitriol-Responsive Monocyte Proteins and Decreases Inflammatory Cytokines in ESRD

In vitro, monocyte 1α-hydroxylase converts 25-hydroxyvitamin D [25(OH)D] to 1,25-dihydroxyvitamin D to regulate local innate immune responses, but whether 25(OH)D repletion affects vitamin D–responsive monocyte pathways in vivo is unknown. Here, we identified seven patients who had 25(OH)D insufficiency and were undergoing long-term hemodialysis and assessed changes after cholecalciferol and paricalcitol therapies in both vitamin D–responsive proteins in circulating monocytes and serum levels of inflammatory cytokines. Cholecalciferol therapy increased serum 25(OH)D levels four-fold, monocyte vitamin D receptor expression three-fold, and 24-hydroxylase expression; therapy decreased monocyte 1α-hydroxylase levels. The CD16⁺ “inflammatory” monocyte subset responded to 25(OH)D repletion the most, demonstrating the greatest increase in vitamin D receptor expression after cholecalciferol. Cholecalciferol therapy reduced circulating levels of inflammatory cytokines, including IL-8, IL-6, and TNF. These data suggest that nutritional vitamin D therapy has a biologic effect on circulating monocytes and associated inflammatory markers in patients with ESRD.There are two sources of vitamin D in humans: Dietary sources, including ergocalciferol (D₂) and cholecalciferol (D₃), and endogenous production by the skin in response to sunlight (D₃ only). To become active, vitamin D (D₂ and D₃) must undergo hydroxylation in the liver to form 25-hydroxyvitamin D [25(OH)D], a prehormone that is further hydroxylated via the 1α-hydroxylase (CYP27B1) enzyme in the kidney to generate 1,25-dihydroxyvitamin D [1,25(OH)₂D], the active form of this hormone.¹ A separate enzyme, 24-hydroxylase (CYP24), is a deactivating enzyme that forms an inactive metabolite of this hormone that is excreted in the bile.¹ As patients with chronic kidney disease (CKD) progress to ESRD, renal CYP27B1 activity decreases and the formation of 1,25(OH)₂D becomes impaired, resulting in hypocalcemia and secondary hyperparathyroidism in many of these patients. Previous attempts to counteract these changes in mineral metabolism with nutritional vitamin D therapy have been unsuccessful,^2–4 because these patients are expected to lack sufficient residual renal CYP27B1 activity to support circulating serum 1,25(OH)₂D levels. For this reason, therapeutic approaches to treat vitamin D deficiency in patients with ESRD have shifted away from the use of nutritional vitamin D forms to favor the use of calcitriol or its associated analogues.Although calcitriol and its analogues have proved to be important therapies for the treatment of disordered mineral metabolism in patients with ESRD, the sole use of these compounds for the correction of vitamin D deficiency in this setting has the potential for adverse effects and may be a fundamentally flawed treatment strategy.⁵ It is well established that vitamin D has both “classical” actions to affect mineral metabolism and “nonclassical” actions at various other tissues unrelated to mineral metabolism, including the heart, prostate, and monocytes, among others.^6,7 The existence of nonclassical actions of vitamin D is supported by the presence of vitamin D regulatory enzymes, such as CYP27B1 and CYP24, within these nonclassical tissues, where it is hypothesized that circulating 25(OH)D serves as a necessary substrate for the local generation of 1,25(OH)₂D and the regulation of tissue-specific, biologic pathways. It is believed that the local production of 1,25(OH)₂D in these nonclassical tissues forms a microenvironment for the regulation of vitamin D–responsive pathways at the cellular level, ultimately leading to biologic effects that are independent of circulating 1,25(OH)₂D. Existing associations between vitamin D deficiency and various disease processes, including cancer, diabetes, infection, and cardiovascular health, have provided evidence for nonclassical actions of 1,25(OH)₂D.^8–15An overwhelming amount of data supporting nonclassical actions of 1,25(OH)₂D exists, but it remains unclear whether these actions are related to the local production of this hormone or from circulating 1,25(OH)₂D produced by the kidneys. Despite an overwhelming amount of ex vivo data suggesting the importance of local vitamin D production by cells not involved in mineral metabolism, in vivo assessments of the autocrine and paracrine functions of these cells have been difficult and are confounded by the concurrent systemic generation of 1,25(OH)₂D by the kidneys with nutritional vitamin D therapy. This controversy of local versus systemic regulation of the nonclassical actions of vitamin D has the potential for profound consequences in patients who have chronic kidney disease (CKD) and are treated with calcitriol analogues, because these patients often have a deficiency of both 25(OH)D and 1,25(OH)₂D. Although this scenario poses a difficult problem for clinicians developing treatment strategies for these patients, it affords a unique opportunity to study the effects of extrarenal production of calcitriol in the setting of minimal renal CYP27B1 activity.Thus, there is a gap in our knowledge about the effects of nutritional vitamin D (D₂ or D₃) supplementation on cellular functions in peripheral tissues unrelated to mineral metabolism, and it remains unclear whether this supplementation has any measurable physiologic effects in the setting of ESRD. To address this question, we set out to investigate the physiologic impact of nutritional vitamin D repletion on monocyte protein expression and monocyte-derived inflammatory cytokine levels in patients who have ESRD and are on hemodialysis. Our findings demonstrate that the administration of nutritional vitamin D in the form of cholecalciferol to patients with nonfunctioning kidneys does indeed have biologic effects on circulating monocytes and decreases circulating levels of multiple inflammatory cytokines that have been linked to increased morbidity and mortality in this population. Our findings may serve as early evidence for in vivo, nonclassical effects of cholecalciferol therapy in patients with ESRD and suggest a potential benefit of 25(OH)D repletion in this patient population.     

慢性肾脏病患者血清1,25（OH）2D水平与蛋白尿及尿炎症细胞因子相关性研究

目的：探讨慢性肾脏病（CKD）1～4期患者血清1,25（OH）2D水平与蛋白尿、尿炎症细胞因子的关系。方法：对我科115例CKD1～4期患者及20例健康对照者进行血清1,25（OH）2D、血CRP,尿TGF-β1、MCP-1、TNF、IL-6,24h尿蛋白定量检测;分析血清1,25（OH）2D水平与以上指标相关性。结果：（1）CKD组患者血清1,25（OH）2D水平低于对照组（P〈0.05）;血CRP,尿MCP-1、TGF-β1、IL-6、TNF水平,24h尿蛋白定量高于对照组（P〈0.05）。（2）与GFR≥60ml·min^-1·1.73m^-2患者比较：GFR〈44ml·min^-1·1.73m^-2患者CRP,尿MCP-1、TGF-β1、IL-6、TNF水平、24h尿蛋白定量升高（P〈0.05）;血清1,25（OH）2D水平降低（P〈0.05）;而GFR45～59ml·min^-1·1.73m^-2患者与GFR≥60ml·min^-1·1.73m^-2患者比较,两组间差异无统计学意义（P〉0.05）;（3）单因素相关分析显示CKD患者血清1,25（OH）2D与年龄（r=-0.442）、收缩压（r=-0.464）、舒张压（r=-0.399）、GFR（r=0.902）、Scr（r=-0.430）、PTH（r=-0.341）、UA（r=0.237）、24h尿蛋白定量（r=-0.372）及尿TGF-β1（r=-0.894）、MCP-1（r=-0867）、TNF（r=-0.899）、IL-6（r=-0.934）水平相关（P〈0.05）。多元回归分析显示血清1,25（OH）2D与GFR呈正相关;与24h尿蛋白定量,尿MCP-1、IL-6,血Scr、PTH呈负相关。结论：CKD1～4期患者存在1,25（OH）2D水平降低,并与蛋白尿及尿炎症细胞因子水平密切相关。     

Hypercalcemia and Overexpression of CYP27B1 in a Patient With Nephrogenic Systemic Fibrosis: Clinical Vignette and Literature Review

Nephrogenic systemic fibrosis (NSF) is a disease of thickened, hard, hyperpigmented skin lesions with or without systemic fibrosis occurring in patients with renal insufficiency and associated with the administration of gadolinium‐containing contrast. The pathogenesis of this disease is unclear, and there is no definitive treatment. We describe a 71‐yr‐old patient with stable chronic lymphocytic leukemia (CLL), end‐stage renal disease (ESRD), and NSF who presented with hypercalcemia in 2006. Before onset of renal insufficiency in 2002, serum calcium, phosphorus, and PTH levels were normal. In 2004, the patient began hemodialysis, and he was diagnosed with NSF in 2005, shortly after undergoing an MRI with gadolinium contrast administration. Over the next 6 mo, albumin‐corrected serum total calcium levels rose from 9.9 to 13.1 mg/dl (normal range, 8.5–10.5 mg/dl) with normal serum phosphorus levels. On admission in September 2006, 1,25‐dihydroxyvitamin D [1,25(OH)₂D] levels were elevated at 130.7 pg/ml (normal range, 25.1–66.1 pg/ml). Biopsy of an NSF lesion showed increased 25‐hydroxyvitamin D₃–1‐α hydroxylase (CYP27B1) immunostaining compared with the biopsy from a normal control. This is the first reported association of NSF with hypercalcemia caused by elevated 1,25(OH)₂D levels. This metabolic disturbance should be sought in future cases to determine a connection between NSF, 1,25(OH)₂D metabolism, and CYP27B1 activation in the skin, which may shed light on the pathogenesis of this unusual local and systemic fibrosing disorder.     

Comparison of vitamin D metabolism in early healthy and late osteoporotic postmenopausal women

Summary We studied 20 healthy premenopausal women aged 36.5±4.0 years (mean±1 SD), 123 healthy postmenopausal women aged 50.0±2.4 years, and 103 postmenopausal women aged 65.1±5.6 years with symptomatic osteoporosis (forearm and spinal fracture). Serum levels of vitamin D metabolites [25(OH)D, 24,25(OH)₂D₃, and 1,25(OH)₂D] were compared with (1) bone mass in the forearm (single photon absorptiometry) and in the spine (dual photon absorptiometry); (2) biochemical indices of bone formation (serum alkaline phosphatase, plasma bone Gla protien), and bone resorption (fasting urinary hydroxyproline); and (3) other biochemical estimates of calcium metabolism (serum calcium, serum phosphate, 24-hour urinary calcium, intestinal absorption of calcium). The present study revealed no difference in any of the vitamin D metabolites between the premenopausal women, the healthy postmenopausal women and the osteoporotic women as a group. The concentrations of 1,25(OH)₂D and 25(OH)D were significantly lower in patients with spinal fracture than in those with forearm fracture. In the early postmenopausal women, serum 1,25(OH)₂D was related to forearm bone mass (r=−0.20;P<0.05), intestinal calcium absorption (r=0.18;P<0.05), and 24-hour urinary calcium (r=0.21;P<0.05); serum 25(OH)D was related to spinal bone mass (r=0.23;P<0.01). In the osteoporotic women, serum vitamin D metabolites were not related to bone mass, but 1,25(OH)₂D was related to bone Gla protein (r=0.33;P<0.001), serum phosphate (r=−0.27;P<0.01), and 24-hour urinary calcium (r=0.43;P<0.001). The present study demonstrates that in a population that is apparently not deficient in vitamin D, a disturbance of the vitamin D metabolism is not likely to play a pathogenetic role in early postmenopausal bone loss. Patients with spinal fractures have low levels of vitamin D metabolites, which may aggravate their osteoporosis.     

Serum levels of 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D, and 25-hydroxyvitamin D in nondialyzed patients with chronic renal failure

BACKGROUND: In patients with chronic renal failure (CRF), abnormalities in vitamin D metabolism are known to be present, and several factors could contribute to the abnormalities. METHODS: We measured serum levels of three vitamin D metabolites, 1,25(OH)2D, 24, 25(OH)2D and 25(OH)D, and analyzed factors affecting their levels in 76 nondialyzed patients with CRF (serum creatinine> 1.6 and < 9.0 mg/dl), 37 of whom had diabetes mellitus (DM-CRF) and 39 of whom were nondiabetic (nonDM-CRF). RESULTS: Serum levels of 1,25(OH)2D were positively correlated with estimated creatinine clearance (CCr; r = 0.429; P < 0.0001), and levels of 24,25(OH)2D were weakly correlated with CCr (r = 0.252, P < 0.05); no correlation was noted for 25(OH)D. Serum levels of all three vitamin D metabolites were significantly and positively correlated with serum albumin. Although there were no significant differences in age, sex, estimated CCr, calcium and phosphate between DM-CRF and nonDM-CRF, all three vitamin D metabolites were significantly lower in DM-CRF than in nonDM-CRF. To analyze factors influencing vitamin D metabolite levels, we performed multiple regression analyses. Serum 25(OH)D levels were significantly and independently associated with serum albumin, presence of DM and serum phosphate (R2 = 0.599; P < 0.0001). 24,25(OH)2D levels were significantly and strongly associated with 25(OH)D (beta = 0.772; R2 = 0.446; P < 0.0001). Serum 1,25(OH)2D levels were significantly associated only with estimated CCr (R2 = 0. 409; P < 0.0001). CONCLUSIONS: These results suggest that hypoalbuminemia and the presence of DM independently affect serum 25(OH)D levels, probably via diabetic nephropathy and poor nutritional status associated with diabetes, and that 25(OH)D is actively catalyzed to 24,25(OH)2D in CRF, probably largely via extrarenal 24-hydroxylase. Serum levels of 1,25(OH)2D were significantly affected by the degree of renal failure. Thus, this study indicates that patients with CRF, particularly those with DM, should receive supplements containing the active form of vitamin D prior to dialysis.