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Megalin and Vitamin D Metabolism—Implications in Non-Renal Tissues and Kidney Disease. Nutrients 2022; 14:nu14183690. [PMID: 36145066 PMCID: PMC9506339 DOI: 10.3390/nu14183690] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 09/02/2022] [Accepted: 09/06/2022] [Indexed: 11/17/2022] Open
Abstract
Megalin is an endocytic receptor abundantly expressed in proximal tubular epithelial cells and other calciotropic extrarenal cells expressing vitamin D metabolizing enzymes, such as bone and parathyroid cells. The receptor functions in the uptake of the vitamin D-binding protein (DBP) complexed to 25 hydroxyvitamin D3 (25(OH)D3), facilitating the intracellular conversion of precursor 25(OH)D3 to the active 1,25 dihydroxyvitamin D3 (1,25(OH)2D3). The significance of renal megalin-mediated reabsorption of 25(OH)D3 and 1,25(OH)2D3 has been well established experimentally, and other studies have demonstrated relevant roles of extrarenal megalin in regulating vitamin D homeostasis in mammary cells, fat, muscle, bone, and mesenchymal stem cells. Parathyroid gland megalin may regulate calcium signaling, suggesting intriguing possibilities for megalin-mediated cross-talk between calcium and vitamin D regulation in the parathyroid; however, parathyroid megalin functionality has not been assessed in the context of vitamin D. Within various models of chronic kidney disease (CKD), megalin expression appears to be downregulated; however, contradictory results have been observed between human and rodent models. This review aims to provide an overview of the current knowledge of megalin function in the context of vitamin D metabolism, with an emphasis on extrarenal megalin, an area that clearly requires further investigation.
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Azer SM, Vaughan LE, Tebben PJ, Sas DJ. 24-Hydroxylase Deficiency Due to CYP24A1 Sequence Variants: Comparison With Other Vitamin D-mediated Hypercalcemia Disorders. J Endocr Soc 2021; 5:bvab119. [PMID: 34337279 PMCID: PMC8317629 DOI: 10.1210/jendso/bvab119] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Indexed: 11/26/2022] Open
Abstract
Context CYP24A1 encodes 24-hydroxylase, which converts 25(OH)D3 and 1,25(OH)2D3 to inactive metabolites. Loss-of-function variants in CYP24A1 are associated with 24-hydroxylase deficiency (24HD), characterized by hypercalcemia, nephrolithiasis, and nephrocalcinosis. We retrospectively reviewed laboratory, imaging, and clinical characteristics of patients with suspected or confirmed 24HD and patients with other vitamin D−mediated hypercalcemia disorders: sarcoidosis, lymphoma, and exogenous vitamin D toxicity (EVT). Objective To identify features that differentiate 24HD from other vitamin D-mediated hypercalcemia disorders. Methods Patients seen at the Mayo Clinic (Rochester, MN) from January 1, 2008, to 31 December, 2016, with the following criteria were retrospectively identified: serum calcium ≥9.6 mg/dL, parathyroid hormone <30 pg/mL, and 1,25(OH)2D3 >40 pg/mL. Patients were considered to have 24HD if they had (1) confirmed CYP24A1 gene variant or (2) 25(OH)D3:24,25(OH)2D ratio ≥50. Patients with sarcoidosis, lymphoma, and EVT were also identified. Groups were compared using the Fisher exact test (categorical variables) or the Wilcoxon rank sum test (continuous variables). Results We identified 9 patients with 24HD and 28 with other vitamin D−mediated disorders. Patients with 24HD were younger at symptom onset (median 14 vs 63 years; P = .001) and had positive family history (88.9% vs 20.8%; P < .001), nephrocalcinosis (88.9% vs 6.3%; P < .001), lower lumbar spine Z-scores (median −0.50 vs 1.20; P = .01), higher peak serum phosphorus (% of peak reference range, median 107 vs 84; P = .01), and higher urinary calcium:creatinine ratios (median 0.24 vs 0.17; P = .047). Conclusion Patients with 24HD had clinical and laboratory findings that differed from other vitamin D−mediated hypercalcemia disorders. 24HD should be suspected in patients with hypercalcemia who present at younger age, have positive family history, and have nephrocalcinosis.
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Affiliation(s)
- Sarah M Azer
- Mayo Clinic Alix School of Medicine-Minnesota Campus, Rochester, MN 55905, USA
| | - Lisa E Vaughan
- Division of Biomedical Statistics and Informatics, Mayo Clinic, Rochester, MN 55905, USA
| | - Peter J Tebben
- Division of Endocrinology, Diabetes, Metabolism, and Nutrition, Mayo Clinic, Rochester, MN 55905, USA.,Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN 55905, USA
| | - David J Sas
- Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN 55905, USA.,Division of Nephrology and Hypertension, Mayo Clinic, Rochester, MN 55905, USA
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Hypercalcemia is common during Pneumocystis pneumonia in kidney transplant recipients. Sci Rep 2019; 9:12508. [PMID: 31467367 PMCID: PMC6715728 DOI: 10.1038/s41598-019-49036-w] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 08/14/2019] [Indexed: 12/27/2022] Open
Abstract
A few cases of hypercalcemia related to Pneumocystis jirovecii pneumonia (PJP) have previously been described, supposedly associated with an 1α-hydroxylase enzyme-dependent mechanism. The prevalence and significance of hypercalcemia in PJP remain unclear, especially in kidney transplant recipients (KTR) who frequently display hypercalcemia via persisting hyperparathyroidism. We here retrospectively identified all microbiologically-proven PJP in adult KTR from 2005 to 2017 in the Lille University Hospital, and studied the mineral and bone metabolism parameters during the peri-infectious period. Clinical features of PJP-patients were analyzed according to their serum calcium level. Hypercalcemia (12.6 ± 1.6 mg/dl) was observed in 37% (18/49) of PJP-patients and regressed concomitantly to specific anti-infectious treatment in all cases. No other cause of hypercalcemia was identified. In hypercalcemic patients, serum levels of 1,25-dihydroxyvitamin D were high at the time of PJP-diagnosis and decreased after anti-infectious treatment (124 ± 62 versus 28 ± 23 pg/mL, p = 0.006) while PTH serum levels followed an inverse curve (35 ± 34 versus 137 ± 99 pg/mL, p = 0.009), suggesting together a granuloma-mediated mechanism. Febrile dyspnea was less frequent in hypercalcemic PJP-patients compared to non-hypercalcemic (29 versus 67%). In summary, hypercalcemia seems common during PJP in KTR. Unexplained hypercalcemia could thus lead to specific investigations in this particular population, even in the absence of infectious or respiratory symptoms.
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Mascia G, Argiolas D, Carta E, Michittu MB, Piredda GB. Acute Kidney Injury Secondary to Hypercalcemia in a Kidney Transplant Patient With Pneumocystis jirovecii Pneumonia: A Case Report. Transplant Proc 2018; 51:220-222. [PMID: 30736974 DOI: 10.1016/j.transproceed.2018.04.077] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2018] [Accepted: 04/13/2018] [Indexed: 10/28/2022]
Abstract
BACKGROUND Persistent hyperparathyroidism is one of the main causes of hypercalcemia following kidney transplantation; differential diagnosis is required. CASE PRESENTATION We report the case of a 61-year-old kidney transplant recipient who underwent transplant in September 2016. She was admitted in March 2017 presenting with a 3-week history of asthenia, hypotension, and cough. Laboratory analysis showed acute kidney injury with hypercalcemia and elevation of inflammatory markers. She was initially treated with hydration therapy. A few days after admission she developed respiratory failure: chest computed tomography showed a ground-glass pattern. A diagnosis of Pneumocystis jirovecii was made on bronchoalveolar lavage. A subsequent graft biopsy was performed that revealed intratubular calcium deposition without signs of rejection. The patient was given trimethoprim/sulfamethoxazole, with improvement in pulmonary and renal function as well as improvement in hypercalcemia. CONCLUSIONS P jirovecii infection can trigger activation of intra-alveolar macrophages that leads to extrarenal vitamin D production with subsequent hypercalcemia. This rare event should be considered in renal transplant patients with pulmonary infection accompanied by hypercalcemia. In our case, hypercalcemia also provoked acute kidney injury.
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Affiliation(s)
- G Mascia
- Renal Transplant Unit, AO Brotzu, Cagliari, Italy
| | - D Argiolas
- Renal Transplant Unit, AO Brotzu, Cagliari, Italy
| | - E Carta
- Renal Transplant Unit, AO Brotzu, Cagliari, Italy.
| | - M B Michittu
- Renal Transplant Unit, AO Brotzu, Cagliari, Italy
| | - G B Piredda
- Renal Transplant Unit, AO Brotzu, Cagliari, Italy
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Ling J, Anderson T, Warren S, Kirkland G, Jose M, Yu R, Yew S, Mcfadyen S, Graver A, Johnson W, Jeffs L. Hypercalcaemia preceding diagnosis of Pneumocystis jirovecii pneumonia in renal transplant recipients. Clin Kidney J 2017; 10:845-851. [PMID: 29225815 PMCID: PMC5716089 DOI: 10.1093/ckj/sfx044] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2017] [Accepted: 04/19/2017] [Indexed: 01/07/2023] Open
Abstract
BACKGROUND The overall incidence of Pneumocystis jirovecii pneumonia (PJP) in solid organ transplant recipients is 5-15%. A timely diagnosis of PJP is difficult and relies on imaging and detection of the organism. METHODS We present a case series of four patients displaying hypercalcaemia with an eventual diagnosis of PJP and document the management of the outbreak with a multidisciplinary team approach. We discuss the underlying pathophysiology and previous reports of hypercalcaemia preceding a diagnosis of PJP. We also reviewed the evidence concerning PJP diagnosis and treatment. RESULTS Within our renal transplant cohort, four patients presented within 7 months with hypercalcaemia followed by an eventual diagnosis of PJP. We measured their corrected calcium, parathyroid hormone (PTH), 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and 25-hydroxycholecalciferol [25(OH)D] levels at admission and following treatment of PJP. All four patients diagnosed with PJP were 4-20 years post-transplantation. Three of the four patients demonstrated PTH-independent hypercalcaemia (corrected calcium >3.0 mmol/L). The presence of high 1,25(OH)2D3 and low 25(OH)D levels suggest negation of the negative feedback mechanism possibly due to an extrarenal source; in this case, the alveolar macrophages. All four patients had resolution of their hypercalcaemia after treatment of PJP. CONCLUSIONS Given the outbreak of PJP in our renal transplant cohort, and based on previous experience from other units nationally, we implemented cohort-wide prophylaxis with trimethoprim-sulphamethoxazole for 12 months in consultation with our local infectious diseases unit. Within this period there have been no further local cases of PJP.
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Affiliation(s)
- Jonathan Ling
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Tara Anderson
- Department of Infectious Diseases, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Sanchia Warren
- Department of Infectious Diseases, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Geoffrey Kirkland
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Matthew Jose
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
- School of Medicine, University of Tasmania, Hobart, Tasmania, Australia
| | - Richard Yu
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Steven Yew
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Samantha Mcfadyen
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Alison Graver
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - William Johnson
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
| | - Lisa Jeffs
- Department of Nephrology, Royal Hobart Hospital, Hobart, Tasmania, Australia
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Ramakrishnan V, Yang QJ, Quach HP, Cao Y, Chow ECY, Mager DE, Pang KS. Physiologically-Based Pharmacokinetic-Pharmacodynamic Modeling of 1α,25-Dihydroxyvitamin D3 in Mice. ACTA ACUST UNITED AC 2015; 44:189-208. [PMID: 26586377 DOI: 10.1124/dmd.115.067033] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Accepted: 11/18/2015] [Indexed: 11/22/2022]
Abstract
1α,25-Dihydroxyvitamin D3 [1,25(OH)2D3] concentrations are regulated by renal CYP27B1 for synthesis and CYP24A1 for degradation. Published plasma and tissue 1,25(OH)2D3 concentrations and mRNA fold change expression of Cyp24a1 and Cyp27b1 following repetitive i.p. injections to C57BL/6 mice (2.5 μg × kg(-1) every 2 days for 4 doses) were fitted with a minimal and full physiologically-based pharmacokinetic-pharmacodynamic models (PBPK-PD). The minimal physiologically-based pharmacokinetic-pharmacodynamic linked model (mPBPK-PD) related Cyp24a1 mRNA fold changes to linear changes in tissue/tissue baseline 1,25(OH)2D3 concentration ratios, whereas the full physiologically-based pharmacokinetic-pharmacodynamic model (PBPK-PD) related measured tissue Cyp24a1 and Cyp27b1 fold changes to tissue 1,25(OH)2D3 concentrations with indirect response, sigmoidal maximal stimulatory effect/maximal inhibitory effect functions. Moreover, the intestinal segregated flow model (SFM) that describes a low and partial intestinal (blood/plasma) flow to enterocytes was nested within both models for comparison with the traditional model for intestine (TM) where the entire flow perfuses the intestine. Both the mPBPK(SFM)-PD and full PBPK(SFM)-PD models described the i.p. plasma and tissue 1,25(OH)2D3 concentrations and fold changes in mRNA expression significantly better than the TM counterparts with F test comparisons. The full PBPK(SFM)-PD fits showed estimates with good precision (lower percentage of coefficient of variation), and the model was more robust in predicting data from escalating i.v. doses (2, 60, and 120 pmol) and the rebound in 1,25(OH)2D3 tissue concentrations after dosing termination. The full PBPK(SFM)-PD model performed the best among the tested models for describing the complex pharmacokinetic-pharmacodynamic interplay among Cyp27b1, Cyp24a1, and 1,25(OH)2D3.
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Affiliation(s)
- Vidya Ramakrishnan
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada (Q.J.Y., H.P.Q., E.C.Y.C., K.S.P.); and Department of Pharmaceutical Sciences, University at Buffalo, SUNY, Buffalo, New York (V.R., Y.C., D.E.M.)
| | - Qi Joy Yang
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada (Q.J.Y., H.P.Q., E.C.Y.C., K.S.P.); and Department of Pharmaceutical Sciences, University at Buffalo, SUNY, Buffalo, New York (V.R., Y.C., D.E.M.)
| | - Holly P Quach
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada (Q.J.Y., H.P.Q., E.C.Y.C., K.S.P.); and Department of Pharmaceutical Sciences, University at Buffalo, SUNY, Buffalo, New York (V.R., Y.C., D.E.M.)
| | - Y Cao
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada (Q.J.Y., H.P.Q., E.C.Y.C., K.S.P.); and Department of Pharmaceutical Sciences, University at Buffalo, SUNY, Buffalo, New York (V.R., Y.C., D.E.M.)
| | - Edwin C Y Chow
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada (Q.J.Y., H.P.Q., E.C.Y.C., K.S.P.); and Department of Pharmaceutical Sciences, University at Buffalo, SUNY, Buffalo, New York (V.R., Y.C., D.E.M.)
| | - Donald E Mager
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada (Q.J.Y., H.P.Q., E.C.Y.C., K.S.P.); and Department of Pharmaceutical Sciences, University at Buffalo, SUNY, Buffalo, New York (V.R., Y.C., D.E.M.)
| | - K Sandy Pang
- Department of Pharmaceutical Sciences, Leslie Dan Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada (Q.J.Y., H.P.Q., E.C.Y.C., K.S.P.); and Department of Pharmaceutical Sciences, University at Buffalo, SUNY, Buffalo, New York (V.R., Y.C., D.E.M.)
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Zhao Y, Yu B, Mao X, He J, Huang Z, Zheng P, Yu J, Han G, Liang X, Chen D. Effect of 25-hydroxyvitamin D3 on rotavirus replication and gene expressions of RIG-I signalling molecule in porcine rotavirus-infected IPEC-J2 cells. Arch Anim Nutr 2015; 69:227-35. [PMID: 25897656 DOI: 10.1080/1745039x.2015.1034522] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The study evaluated whether a 25-hydroxyvitamin D3 (25D3) supplementation decreases the replication of rotavirus by the retinoic acid-inducible gene I (RIG-I) signalling pathway in a porcine small intestinal epithelial cell line (IPEC-J2). The results show that IPEC-J2 cells express high baseline levels of 1α-hydroxylase (CYP27B1), which converts inactive 25D3 to the active 1,25-dihydroxyvitamin D3 (1,25D3). Porcine rotavirus (PRV) infection alone resulted in a significant increase in CYP27B1 mRNA, which augmented the production of active vitamin D. Physiological concentrations of 25D3 were found to decrease PRV replication in IPEC-J2 cells. RIG-I plays an important role in the recognition of double-stranded RNA virus by host cells. Upon recognition, RIG-I triggers a series of signalling molecules such as interferon-β (IFN-β) promoter stimulator 1 (IPS-1) leading to the expression of type I interferons (IFN-β). Active 25D3 that was generated by PRV-infected IPEC-J2 cells led to an increased expression of toll-like receptors 3 (TLR3), RIG-I, IPS-1, IFN-β and IFN-stimulated genes 15 (ISG15) with important innate immune functions. Inhibiting CYP27B1 also failed to increase RIG-I, IPS-1, IFN-β and ISG15 mRNA expression. These observations suggest that 25D3 can directly inhibit PRV in IPEC-J2 cells, which requires this active form of vitamin D. The anti-rotavirus effect of 25D3 is mediated at least in part by RIG-I signalling pathways in IPEC-J2 cells.
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Affiliation(s)
- Ye Zhao
- a College of Animal Science and Technology , Sichuan Agricultural University , Ya'an , P.R. China
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Activation of vitamin D regulates response of human bronchial epithelial cells to Aspergillus fumigatus in an autocrine fashion. Mediators Inflamm 2015; 2015:208491. [PMID: 25960612 PMCID: PMC4413954 DOI: 10.1155/2015/208491] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2014] [Accepted: 02/10/2015] [Indexed: 01/04/2023] Open
Abstract
Aspergillus fumigatus (A. fumigatus) is one of the most common fungi to cause diseases in humans. Recent evidence has demonstrated that airway epithelial cells play an important role in combating A. fumigatus through inflammatory responses. Human airway epithelial cells have been proven to synthesize the active vitamin D, which plays a key role in regulating inflammation. The present study was conducted to investigate the impact of A. fumigatus infection on the activation of vitamin D and the role of vitamin D activation in A. fumigatus-elicited antifungal immunity in normal human airway epithelial cells. We found that A. fumigatus swollen conidia (SC) induced the expression of 1α-hydroxylase, the enzyme catalyzing the synthesis of active vitamin D, and vitamin D receptor (VDR) in 16HBE cells and led to increased local generation of active vitamin D. Locally activated vitamin D amplified SC-induced expression of antimicrobial peptides in 16HBE cells but attenuated SC-induced production of cytokines in an autocrine fashion. Furthermore, we identified β-glucan, the major A. fumigatus cell wall component, as the causative agent for upregulation of 1α-hydroxylase and VDR in 16HBE cells. Therefore, activation of vitamin D is inducible and provides a bidirectional regulation of the responses to A. fumigatus in 16HBE cells.
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Fibroblast growth factor 23, vitamin D, and health disparities among African Americans with chronic kidney disease. Semin Nephrol 2014; 33:448-56. [PMID: 24119850 DOI: 10.1016/j.semnephrol.2013.07.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Compared with Caucasians, African Americans have lower circulating concentrations of 25-hydroxyvitamin D (25(OH)D), the major storage form of vitamin D, leading to the widespread assumption that African Americans are at higher risk of vitamin D deficiency. However, the finding that African Americans maintain better indices of musculoskeletal health than Caucasians throughout their lifespan despite having lower circulating 25(OH)D concentrations suggests that the relationship between vitamin D deficiency and racial health disparities may not be so straightforward. The fairly recent emergence of fibroblast growth factor 23 (FGF23) may help resolve some of this uncertainty. FGF23 strongly modulates both systemic and local activation of 25(OH)D, playing a potentially important role in the degree to which lower 25(OH)D concentrations impact health outcomes, including differences in the incidence and rate of progression of chronic kidney disease by race. This review critically assesses ongoing controversies surrounding the relationship between vitamin D and racial disparities in chronic kidney disease outcomes, and how FGF23 may help to clarify the picture.
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Dietary vitamin D supplementation attenuates immune responses of pigs challenged with rotavirus potentially through the retinoic acid-inducible gene I signalling pathway. Br J Nutr 2014; 112:381-9. [PMID: 24833277 DOI: 10.1017/s000711451400097x] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
In the present study, twenty-four Duroc × Landrance × Yorkshire (initial body weight (BW) of 21·82 (sem 2·06) kg) cross-bred pigs were used to determine whether dietary vitamin D supplementation could confer protection against viral infections through the retinoic acid-inducible gene I (RIG-I) signalling pathway in pigs. Experimental treatments were arranged in a 2 × 2 factorial manner with the main effects of immune challenge (control v. porcine rotavirus (PRV) challenge) and dietary concentrations of vitamin D (200 and 5000 IU; where 1 IU of vitamin D is defined as the biological activity of 0.025 mg of cholecalciferol). The pigs were fed a diet containing 200 or 5000 IU vitamin D in the first week of the study period. On day 8, the pigs were orally dosed with 4 ml of Dulbecco's modified Eagle's medium/Ham's F-12 medium containing PRV or essential medium (control). Serum samples were collected on day 8 (pre-challenge), and 6 d after the PRV challenge, the pigs were killed to evaluate intestinal morphology and tissue gene expression following the last blood collection. Pigs challenged with PRV had decreased BW gain (P< 0·01), feed intake (P< 0·01), villus height (P< 0·01), faecal consistency (P< 0·05), and serum 1,25-dihydroxyvitamin D concentration (P< 0·01) and increased (P< 0·01) serum IL-2, IL-6 and interferon (IFN)-β concentrations. Vitamin D supplementation mitigated these effects. The mRNA expression of RIG-I (P< 0·01), IFN-β promoter stimulator 1 (P< 0·01), IFN-β (P< 0·01) and interferon-stimulated gene 15 (ISG 15 ) (P< 0·01) was up-regulated by the PRV challenge and vitamin D supplementation in the intestine. In conclusion, vitamin D supplementation could activate the RIG-I signalling pathway and thus alleviate the negative effects caused by PRV challenge.
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Genetic Influences on Circulating Vitamin D Level: A Review. CURRENT CARDIOVASCULAR RISK REPORTS 2012. [DOI: 10.1007/s12170-012-0278-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Proal AD, Albert PJ, Blaney GP, Lindseth IA, Benediktsson C, Marshall TG. Immunostimulation in the era of the metagenome. Cell Mol Immunol 2011; 8:213-25. [PMID: 21278764 PMCID: PMC4076734 DOI: 10.1038/cmi.2010.77] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Accepted: 12/15/2010] [Indexed: 12/15/2022] Open
Abstract
Microbes are increasingly being implicated in autoimmune disease. This calls for a re-evaluation of how these chronic inflammatory illnesses are routinely treated. The standard of care for autoimmune disease remains the use of medications that slow the immune response, while treatments aimed at eradicating microbes seek the exact opposite-stimulation of the innate immune response. Immunostimulation is complicated by a cascade of sequelae, including exacerbated inflammation, which occurs in response to microbial death. Over the past 8 years, we have collaborated with American and international clinical professionals to research a model-based treatment for inflammatory disease. This intervention, designed to stimulate the innate immune response, has required a reevaluation of disease progression and amelioration. Paramount is the inherent conflict between palliation and microbicidal efficacy. Increased microbicidal activity was experienced as immunopathology-a temporary worsening of symptoms. Further studies are needed, but they will require careful planning to manage this immunopathology.
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Abstract
Our understanding of vitamin D metabolism and biological effects has grown exponentially in recent years and it has become clear that vitamin D has extensive immunomodulatory effects. The active vitamin D generating enzyme, 1α-hydroxylase, is expressed by the airway epithelium, alveolar macrophages, dendritic cells, and lymphocytes indicating that active vitamin D can be produced locally within the lungs. Vitamin D generated in tissues is responsible for many of the immunomodulatory actions of vitamin D. The effects of vitamin D within the lungs include increased secretion of the antimicrobial peptide cathelicidin, decreased chemokine production, inhibition of dendritic cell activation, and alteration of T-cell activation. These cellular effects are important for host responses against infection and the development of allergic lung diseases like asthma. Epidemiological studies do suggest that vitamin D deficiency predisposes to viral respiratory tract infections and mycobacterial infections and that vitamin D may play a role in the development and treatment of asthma. Randomized, placebo-controlled trials are lacking but ongoing.
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Affiliation(s)
- Sif Hansdottir
- Department of Medicine, University of Iowa Carver College of Medicine and Veterans Administration Medical Center, Iowa City, IA 52242
| | - Martha M. Monick
- Department of Medicine, University of Iowa Carver College of Medicine and Veterans Administration Medical Center, Iowa City, IA 52242
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Autoimmune Disease and the Human Metagenome. METAGENOMICS OF THE HUMAN BODY 2011. [PMCID: PMC7121718 DOI: 10.1007/978-1-4419-7089-3_12] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Kawase T, Matsuo K, Suzuki T, Hirose K, Hosono S, Watanabe M, Inagaki M, Iwata H, Tanaka H, Tajima K. Association between vitamin D and calcium intake and breast cancer risk according to menopausal status and receptor status in Japan. Cancer Sci 2010; 101:1234-40. [PMID: 20151981 PMCID: PMC11159182 DOI: 10.1111/j.1349-7006.2010.01496.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Although several studies have investigated the possible association between elevated vitamin D and calcium intake and low breast cancer risk, findings have been inconsistent. We conducted a case-control study to clarify the association between vitamin D and calcium intake and breast cancer risk among pre- and post- menopausal women in Japan. We also investigated whether these effects were modified by tumor receptor status, specifically estrogen receptor (ER), progesterone receptor (PR), or human epidermal growth factor receptor-2 (HER2) status. We examined 1803 breast cancer patients and 3606 age- and menopausal status-matched noncancer controls. Among cases, 713 were assessed for ER, PR, and HER2 status. Odds ratios (ORs) with 95% confidence intervals (CIs) were estimated using conditional or unconditional logistic models adjusted for potential confounders. A significant inverse association was observed between vitamin D and calcium intake and breast cancer risk among all subjects, with top quartile ORs of 0.76 (95% CI, 0.63-0.90; trend P = 0.001) and 0.83 (95% CI, 0.69-0.99; trend P = 0.038), respectively. In analyses stratified by menopausal status, a significant association between risk and vitamin D was observed only among premenopausal women (trend P < 0.001), whereas that between risk and calcium intake was seen only among postmenopausal women (trend P = 0.022). Heterogeneity by menopausal status for these associations was statistically significant. This association was modified by tumor receptor status. These findings suggest that the protective effects of vitamin D and calcium intake against breast cancer risk may differ by menopausal status and receptor status.
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Affiliation(s)
- Takakazu Kawase
- Division of Epidemiology and Prevention, Aichi Cancer Center Research Institute, Nagoya, Japan
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Petchey WG, Hickman IJ, Duncan E, Prins JB, Hawley CM, Johnson DW, Barraclough K, Isbel NM. The role of 25-hydroxyvitamin D deficiency in promoting insulin resistance and inflammation in patients with chronic kidney disease: a randomised controlled trial. BMC Nephrol 2009; 10:41. [PMID: 20003316 PMCID: PMC2804665 DOI: 10.1186/1471-2369-10-41] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2009] [Accepted: 12/10/2009] [Indexed: 12/24/2022] Open
Abstract
Background Approximately 50% of patients with stage 3 Chronic Kidney Disease are 25-hydroxyvitamin D insufficient, and this prevalence increases with falling glomerular filtration rate. Vitamin D is now recognised as having pleiotropic roles beyond bone and mineral homeostasis, with the vitamin D receptor and metabolising machinery identified in multiple tissues. Worryingly, recent observational data has highlighted an association between hypovitaminosis D and increased cardiovascular mortality, possibly mediated via vitamin D effects on insulin resistance and inflammation. The main hypothesis of this study is that oral Vitamin D supplementation will ameliorate insulin resistance in patients with Chronic Kidney Disease stage 3 when compared to placebo. Secondary hypotheses will test whether this is associated with decreased inflammation and bone/adipocyte-endocrine dysregulation. Methods/Design This study is a single-centre, double-blinded, randomised, placebo-controlled trial. Inclusion criteria include; estimated glomerular filtration rate 30-59 ml/min/1.73 m2; aged ≥18 on entry to study; and serum 25-hydroxyvitamin D levels <75 nmol/L. Patients will be randomised 1:1 to receive either oral cholecalciferol 2000IU/day or placebo for 6 months. The primary outcome will be an improvement in insulin sensitivity, measured by hyperinsulinaemic euglycaemic clamp. Secondary outcome measures will include serum parathyroid hormone, cytokines (Interleukin-1β, Interleukin-6, Tumour Necrosis Factor alpha), adiponectin (total and High Molecular Weight), osteocalcin (carboxylated and under-carboxylated), peripheral blood mononuclear cell Nuclear Factor Kappa-B p65 binding activity, brachial artery reactivity, aortic pulse wave velocity and waveform analysis, and indirect calorimetry. All outcome measures will be performed at baseline and end of study. Discussion To date, no randomised controlled trial has been performed in pre-dialysis CKD patients to study the correlation between vitamin D status with supplementation, insulin resistance and markers of adverse cardiovascular risk. We remain hopeful that cholecalciferol may be a safe intervention, with health benefits beyond those related to bone-mineral homeostasis. Trial registration Australian and New Zealand Clinical Trials Registry ACTRN12609000246280.
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Affiliation(s)
- William G Petchey
- Department of Nephrology, University of Queensland at Princess Alexandra Hospital, Brisbane, Australia.
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17
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Hansdottir S, Monick MM, Hinde SL, Lovan N, Look DC, Hunninghake GW. Respiratory epithelial cells convert inactive vitamin D to its active form: potential effects on host defense. THE JOURNAL OF IMMUNOLOGY 2008; 181:7090-9. [PMID: 18981129 DOI: 10.4049/jimmunol.181.10.7090] [Citation(s) in RCA: 401] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The role of vitamin D in innate immunity is increasingly recognized. Recent work has identified a number of tissues that express the enzyme 1alpha-hydroxylase and are able to activate vitamin D. This locally produced vitamin D is believed to have important immunomodulatory effects. In this paper, we show that primary lung epithelial cells express high baseline levels of activating 1alpha-hydroxylase and low levels of inactivating 24-hydroxylase. The result of this enzyme expression is that airway epithelial cells constitutively convert inactive 25-dihydroxyvitamin D(3) to the active 1,25-dihydroxyvitamin D(3). Active vitamin D that is generated by lung epithelium leads to increased expression of vitamin D-regulated genes with important innate immune functions. These include the cathelicidin antimicrobial peptide gene and the TLR coreceptor CD14. dsRNA increases the expression of 1alpha-hydroxylase, augments the production of active vitamin D, and synergizes with vitamin D to increase expression of cathelicidin. In contrast to induction of the antimicrobial peptide, vitamin D attenuates dsRNA-induced expression of the NF-kappaB-driven gene IL-8. We conclude that primary epithelial cells generate active vitamin D, which then influences the expression of vitamin D-driven genes that play a major role in host defense. Furthermore, the presence of vitamin D alters induction of antimicrobial peptides and inflammatory cytokines in response to viruses. These observations suggest a novel mechanism by which local conversion of inactive to active vitamin D alters immune function in the lung.
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Affiliation(s)
- Sif Hansdottir
- Department of Medicine, University of Iowa Carver College of Medicine, and Veterans Administration Medical Center, Iowa City, IA 52242, USA.
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18
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Chandra P, Binongo JNG, Ziegler TR, Schlanger LE, Wang W, Someren JT, Tangpricha V. Cholecalciferol (vitamin D3) therapy and vitamin D insufficiency in patients with chronic kidney disease: a randomized controlled pilot study. Endocr Pract 2008; 14:10-7. [PMID: 18238736 DOI: 10.4158/ep.14.1.10] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
OBJECTIVE To investigate the efficacy of cholecalciferol (vitamin D3) in raising serum 25-hydroxyvitamin D (25[OH)]D) levels and reducing parathyroid hormone (PTH) levels in patients with chronic kidney disease (CKD). METHODS In this double-blind, randomized controlled pilot study, participants with CKD stage 3 and 4 (estimated glomerular filtration rate, 15-59 mL/min/1.73 m2), vitamin D insufficiency (serum 25[OH]D <30 ng/mL), and serum intact PTH levels >70 pg/mL were randomly assigned to receive either 50 000 IU of cholecalciferol or placebo once weekly for 12 weeks. Primary outcomes (25[OH]D and PTH levels) were measured at baseline, week 6, and week 12. Secondary outcomes (1,25-dihydroxvitamin D and bone turnover markers) were measured at baseline and week 12. Because of skewed data distribution, statistical analyses were performed on a logarithmic scale. The difference between the group means was exponentiated to provide the geometric mean ratio. A linear mixed model using an unstructured variance-covariance matrix was used to examine change in the primary and secondary outcomes over time. RESULTS Geometric mean serum 25(OH)D concentrations of the study groups were similar at baseline (P = .77). At week 6, a significant difference between the treatment and placebo groups was detected (P = .001); this difference was maintained at week 12 (P = .002). Among cholecalciferol-treated participants, serum 25(OH)D concentration increased on average from 17.3 ng/mL (95% confidence interval [CI], 11.8-25.2) at baseline to 49.4 ng/mL (95% CI, 33.9-72.0) at week 12. As-treated analysis indicated a trend toward lower PTH levels among cholecalciferol-treated participants (P = .07). CONCLUSION Weekly cholecalciferol supplementation appears to be an effective treatment to correct vitamin D status in patients with CKD.
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Affiliation(s)
- Prakash Chandra
- Departments of Nutrition and Health Sciences, Emory University, Atlanta, Georgia 30322, USA
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19
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Miller RR, Hicks GE, Shardell MD, Cappola AR, Hawkes WG, Yu-Yahiro JA, Keegan A, Magaziner J. Association of Serum Vitamin D Levels With Inflammatory Response Following Hip Fracture: The Baltimore Hip Studies. J Gerontol A Biol Sci Med Sci 2007; 62:1402-6. [DOI: 10.1093/gerona/62.12.1402] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Bonjour JP, Chevalley T, Fardellone P. Calcium intake and vitamin D metabolism and action, in healthy conditions and in prostate cancer. Br J Nutr 2007; 97:611-6. [PMID: 17349071 DOI: 10.1017/s0007114507657961] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
An association between Ca intake and the risk of prostate cancer has been reported in some but not all epidemiological studies. Assuming that a pathophysiological relationship would underlie this association, a favoured hypothesis proposes that relatively high Ca consumption could promote prostate cancer by reducing the production of 1,25-dihydroxyvitamin D (1,25(OH)2D; calcitriol), the hormonal form of vitamin D. The present review analyses the plausibility of this hypothesis by considering the quantitative relationships linking Ca intake to 1,25(OH)2D production and action in healthy conditions and in prostate cancer. Changes in the plasma level of 1,25(OH)2D in response to Ca intake are of very small magnitude as compared with the variations required to influence the proliferation and differentiation of prostate cancer cells. In most studies, 1,25(OH)2D plasma level was not found to be reduced in patients with prostate cancer. The possibility that the level of 1,25(OH)2D in prostate cells is decreased with a high-Ca diet has not been documented. Furthermore, a recent randomised placebo-controlled trial did not indicate that Ca supplementation increases the relative risk of prostate cancer in men. In conclusion, the existence of a pathophysiological link between relatively high Ca intake and consequent low production and circulation level of 1,25(OH)2D that might promote the development of prostate cancer in men remains so far an hypothesis, the plausibility of which is not supported by the analysis of available clinical data.
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Affiliation(s)
- Jean-Philippe Bonjour
- Division of Bone Diseases (World Health Organization Collaborating Centre for Osteoporosis Prevention), Department of Rehabilitation and Geriatrics, University Hospitals of Geneva, Geneva 14, Switzerland.
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21
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Abstract
Vitamin D and calcium are metabolically interrelated and highly correlated dietary factors. Experimental studies have shown their anticarcinogenic effects due to their participation in regulating cell proliferation, differentiation, and apoptosis in normal and malignant breast cells. Given the emerging interest in their potential roles in the etiology of breast cancer, we review the current epidemiologic literature on dietary and/or supplemental intakes of vitamin D, endogenous circulating levels of vitamin D, and dietary and/or supplemental intakes of calcium in relation to breast cancer risk. To place these studies in context, we also provide a brief review of other supporting epidemiologic evidence. Despite inconsistent results from the epidemiologic studies, several lines of evidence suggest that vitamin D and calcium may be involved in the development of breast cancer. Specifically, (a) there is some epidemiologic evidence for inverse associations between vitamin D and calcium intakes and breast cancer; (b) serum, plasma, and/or blood levels of vitamin D metabolites have been inversely associated with breast cancer risk in some studies; (c) high sunlight exposure, presumably reflecting vitamin D synthesis in the skin, has been associated with a reduced risk of breast cancer; (d) vitamin D and calcium intakes have been inversely related to breast density, an intermediate end point for breast cancer; (e) calcium has been associated with a reduced risk of benign proliferative epithelial disorders of the breast, putative precursors of breast cancer; and (f) certain polymorphisms of the vitamin D receptor might modify breast cancer susceptibility. To further confirm the potential protective effects of calcium and vitamin D on breast cancer, well-designed cohort studies and clinical trials are warranted.
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Affiliation(s)
- Yan Cui
- Department of Epidemiology and Population Health, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Belfer 1301D, Bronx, NY 10461, USA.
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22
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Khadzkou K, Buchwald P, Westin G, Dralle H, Akerström G, Hellman P. 25-hydroxyvitamin D3 1alpha-hydroxylase and vitamin D receptor expression in papillary thyroid carcinoma. J Histochem Cytochem 2005; 54:355-61. [PMID: 16314444 DOI: 10.1369/jhc.5a6734.2005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Vitamin D receptor (VDR) and 25-hydroxyvitamin D3 1-alpha-hydroxylase expression have recently been shown to be upregulated in several tumors and thought to represent an important endogenous response to tumor progression. Little is known about the expression of these proteins in thyroid carcinoma, although previous reports have documented evidence of the biological effect of vitamin D in thyroid cells. Using paraffin-embedded and frozen sections of papillary thyroid carcinoma, we utilized real-time quantitative RT-PCR and immunohistochemistry to characterize the expression of VDR and 1-alpha-hydroxylase in thyroid follicular cells, with special emphasis on papillary thyroid carcinoma (PTC). VDR and 1-alpha-hydroxylase expression were increased in PTC compared with normal thyroid tissue and especially high in areas of lymphocyte infiltration. Expression of VDR and 1-alpha-hydroxylase in PTC may be compatible with an overall favorable prognosis for this tumor type and may constitute important prerequisites for using vitamin D and/or vitamin D analogs in the treatment of PTC.
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Affiliation(s)
- K Khadzkou
- Department of Surgical Sciences, University Hospital, Uppsala, Sweden
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23
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Rickels MR, Mandel SJ. Hypocalciuric hypercalcemia and autoantibodies against the calcium-sensing receptor. N Engl J Med 2004; 351:2237-8; author reply 2237-8. [PMID: 15548788 DOI: 10.1056/nejm200411183512120] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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24
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Lehmann B, Meurer M. Extrarenal sites of calcitriol synthesis: the particular role of the skin. Recent Results Cancer Res 2003; 164:135-45. [PMID: 12899518 DOI: 10.1007/978-3-642-55580-0_9] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Calcitriol (1alpha,25(OH)2D3), the hormonally active form of vitamin D3 (D3) is produced by a cascade of reactions, including photochemical D3 synthesis in the skin and subsequent hydroxylation at the C-25 atom in the liver and finally at C-1alpha position in the kidney. However, there is substantial evidence for additional extrarenal sites of calcitriol synthesis. In vitro, many nonrenal cells, including bone, placenta, prostata, keratinocytes, macrophages, T-lymphocytes and several cancer cells (e.g., from lung, prostata and skin) can enzymatically convert calcidiol (25OHD3) to 1alpha,25(OH)2D3. We have demonstrated that keratinocytes of the skin have unique properties in the D3 pathway; they are not only capable of producing D3 from 7-dehydrocholesterol (7-DHC), but also generate 1alpha,25(OH)2D3 from the substrates 25OHD3, lalpha-hydroxyvitamin D3 (1alpha-OHD3) and even D3. It is evident that keratinocytes possess at least 1alpha-OH-, 25OH- and 24OHase activity, which is necessary for enzymatic conversion of D3 to 1alpha,25(OH)2D3, and the 24OHase activity for initiation of catabolism of 1alpha,25(OH)2D3 to more polar metabolites. Thus, the skin is apparently the only extrarenal tissue where the complete UVB-induced pathway from 7-DHC to 1alpha,25(OH)2D3 takes place under physiological circumstances.
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Affiliation(s)
- Bodo Lehmann
- Department of Dermatology, Carl Gustav Carus Medical School, Dresden University of Technology, Fetscherstr. 74, 01307 Dresden, Germany.
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25
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Yokomura K, Suda T, Sasaki S, Inui N, Chida K, Nakamura H. Increased expression of the 25-hydroxyvitamin D(3)-1alpha-hydroxylase gene in alveolar macrophages of patients with lung cancer. J Clin Endocrinol Metab 2003; 88:5704-9. [PMID: 14671156 DOI: 10.1210/jc.2003-030537] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Abstract
25-Hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase) plays a central role in calcium metabolism by synthesizing the active hormone 1alpha,25-dihydroxyvitamin D(3) in the kidney. Its increased expression in the extrarenal tissues has been found in alveolar macrophages in sarcoidosis but not in any other pathological conditions. We found that 1alpha-hydroxylase-mRNA in alveolar macrophages measured by semiquantitative RT-PCR was 2-fold greater in patients with lung cancer than in control subjects (0.61 +/- 0.20 vs. 0.34 +/- 0.11, respectively; P < 0.0001). When the clinical stages of lung cancer were divided into early (stage IA-IIIA) and advanced (stage IIIB and IV) and the expression of 1alpha-hydroxylase gene was compared among the control, early, and advanced groups, the advanced group showed the highest expression, followed by the early group, then the control group (0.34 +/- 0.11, 0.52 +/- 0.11, and 0.69 +/- 0.23 for control, early, and advanced groups, respectively; P < 0.0001). The 1alpha-hydroxylase-mRNA level was well correlated with serum 1alpha,25-dihydroxylase D(3) concentration and the 1alpha,25-dihydroxylase D(3) to 25-hydroxyvitamin D(3) ratio, but none of the findings related to calcium metabolism among the patients with lung cancer. Increased local production of 1alpha,25-dihydroxyvitamin D(3) may be associated with the pathological conditions, such as immunosuppression, in lung cancer.
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Affiliation(s)
- Koushi Yokomura
- Department of Internal Medicine, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan
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26
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Takemoto F, Shinki T, Yokoyama K, Inokami T, Hara S, Yamada A, Kurokawa K, Uchida S. Gene expression of vitamin D hydroxylase and megalin in the remnant kidney of nephrectomized rats. Kidney Int 2003; 64:414-20. [PMID: 12846736 DOI: 10.1046/j.1523-1755.2003.00114.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
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.
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Abstract
The review provides an evaluation of the therapeutic potential of vitamin D analogues in the context of the current understanding of vitamin D biochemistry, molecular biology and physiology. Vitamin D activity results from several circulating and intracellular physiological metabolites acting simultaneously through at least three receptors. Common analogues are reviewed. Although most vitamin D analogues have traditionally been analogues of 1,25-dihydroxyvitamin D, it may be better to deliver high doses of base vitamin or (analogues) of 25-hydroxyvitamin D. This would permit physiological endocrine, paracrine and autocrine vitamin D metabolism. Agonists or antagonists of tissue-specific vitamin D metabolic pathways could be coadministered. The importance of measuring endogenous vitamin D metabolites during in vivo studies and the pitfalls of extending data across species and time are emphasised. Human vitamin D analogue trials should include direct comparison against the related endogenous metabolite.
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Affiliation(s)
- Mark S Stein
- Department of Diabetes and Endocrinology, The Royal Melbourne Hospital, Parkville, Victoria 3050, Australia
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28
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Ogunkolade BW, Boucher BJ, Prahl JM, Bustin SA, Burrin JM, Noonan K, North BV, Mannan N, McDermott MF, DeLuca HF, Hitman GA. Vitamin D receptor (VDR) mRNA and VDR protein levels in relation to vitamin D status, insulin secretory capacity, and VDR genotype in Bangladeshi Asians. Diabetes 2002; 51:2294-300. [PMID: 12086963 DOI: 10.2337/diabetes.51.7.2294] [Citation(s) in RCA: 190] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Associations have been reported between vitamin D receptor (VDR) gene polymorphisms, type 1 diabetes, insulin secretion, and the insulin resistance syndrome. As VDR polymorphisms have no known functional significance, these findings may implicate a variant of the VDR gene or a locus in linkage disequilibrium with the VDR. We have examined VDR mRNA and VDR protein levels in relation to VDR polymorphisms (41 Bangladeshi subjects) and analyzed insulin secretory capacity (143 Bangladeshi subjects), allowing for other known determinants. Peripheral blood mononuclear cells (PBMCs) from subjects who had been genotyped for BsmI, ApaI, TaqI, and FokI VDR restriction fragment length polymorphisms were used for both total VDR mRNA quantitation (using TaqMan) and measurement of VDR protein levels (using a specific micro-immunoassay). Stepwise multiple regression analyses were used (to P < 0.05) to analyze the data. For the insulin secretion index, the best-fit model (n = 143, P < 0.0001) gave age (P = 0.002), TaqI (P < 0.0001), and BMI (P = 0.001) as independent determinants; with the inclusion of VDR mRNA and VDR protein levels, VDR mRNA was the sole independent determinant (n = 41, P = 0.024). However, the best-fit model for VDR mRNA (P = 0.004) gave FokI (P = 0.044) and TaqI (P = 0.04) genotypes and insulin secretory capacity (P = 0.042) as independent determinants. For VDR protein levels, the best-fit model (P = 0.006) gave TaqI genotype (P = 0.005) and circulating 1,25-dihydroxyvitamin-D levels (P = 0.03) as independent determinants. In conclusion, these studies confirm an association between VDR polymorphisms and insulin secretory capacity and demonstrate the VDR genotype to be a significant determinant of VDR mRNA and VDR protein levels in PBMCs, providing functional support to previously described genetic associations with the VDR gene. Furthermore, VDR expression has been shown to be a determinant of insulin secretory capacity.
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Affiliation(s)
- Babatunji-William Ogunkolade
- Department of Diabetes and Metabolic Medicine, Barts and the London Queen Mary's School of Medicine and Dentistry, University of London, Royal London Hospital, Whitechapel, London E1 1BB, UK
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Zehnder D, Evans KN, Kilby MD, Bulmer JN, Innes BA, Stewart PM, Hewison M. The ontogeny of 25-hydroxyvitamin D(3) 1alpha-hydroxylase expression in human placenta and decidua. THE AMERICAN JOURNAL OF PATHOLOGY 2002; 161:105-14. [PMID: 12107095 PMCID: PMC1850695 DOI: 10.1016/s0002-9440(10)64162-4] [Citation(s) in RCA: 175] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In addition to its classical calciotropic effects, the active form of vitamin D, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) is a potent anti-proliferative/immunomodulatory secosteroid. The enzyme that catalyzes the synthesis of 1,25(OH)(2)D(3), 1alpha-hydroxylase (1alpha-OHase), is expressed in many human tissues, highlighting its possible role as an autocrine/paracrine activator of vitamin D. Immunohistochemical and RNA analyses were used to characterize the ontogeny of 1alpha-OHase expression in human placenta and decidua. Protein for 1alpha-OHase was detectable in trophoblast and decidua; the latter being stronger in decidualized stromal cells than macrophages, with no staining of lymphocytes. Quantitative reverse transcriptase-polymerase chain reaction was used to assess changes in mRNA expression for 1alpha-OHase at different gestations: first (mean, 9.1 +/- 1.5 weeks); second (mean, 14 +/- 1.8 weeks), and third trimester (mean, 39.3 +/- 2.5 weeks). 1alpha-OHase expression in decidua was approximately 1000-fold higher in first (95% confidence limits, 611 to 1376) and second (95% confidence limits, 633 to 1623) trimester biopsies when compared with the third trimester (95% confidence limits, 0.36 to 2.81) (both P < 0.001). In placenta, 1alpha-OHase expression was 80-fold higher in the first (range, 42 to 137) and second (range, 30 to 199) trimester when compared with third trimester biopsies (0.6 to 1.6) (both P < 0.001). Similar results were obtained by semiquantitative IHC. Parallel analysis of the receptor for 1,25(OH)(2)D(3) (vitamin D receptor) indicated that, as with 1alpha-OHase, highest levels of expression occurred in first trimester decidua. However, changes in vitamin D receptor mRNA expression across gestation were less pronounced than 1alpha-OHase. These spatiotemporal data emphasize the potential importance of 1alpha-OHase during early fetoplacental life and, in particular, suggest an autocrine/paracrine immunomodulatory function for the enzyme.
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Affiliation(s)
- Daniel Zehnder
- Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham, UK
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Zehnder D, Bland R, Chana RS, Wheeler DC, Howie AJ, Williams MC, Stewart PM, Hewison M. Synthesis of 1,25-dihydroxyvitamin D(3) by human endothelial cells is regulated by inflammatory cytokines: a novel autocrine determinant of vascular cell adhesion. J Am Soc Nephrol 2002; 13:621-629. [PMID: 11856765 DOI: 10.1681/asn.v133621] [Citation(s) in RCA: 247] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
In addition to its calciotropic function, the secosteroid 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) has potent nonclassical effects. In particular, local production of 1,25D(3) catalyzed by the enzyme 1alpha-hydroxylase (1alpha-OHase) may act as an autocrine/paracrine immunomodulatory mechanism. To investigate the significance of this in vascular tissue the expression and function of 1alpha-OHase in human endothelial cells was characterized. Immunohistochemical and in situ hybridization analyses show, for the first time, the presence of 1alpha-OHase mRNA and protein in endothelial cells from human renal arteries as well as postcapillary venules from lymphoid tissue. Reverse transcription-PCR and Western blot analyses confirmed the presence of 1alpha-OHase in primary cultures of human umbilical vein endothelial cells (HUVEC). Enzyme activity in HUVEC (318 +/- 56 fmoles 1,25(OH)(2)D(3)/hr/mg protein) increased after treatment with tumor necrosis factor-alpha (1054 +/- 166, P < 0.01), lipopolysaccharide (1381 +/- 88, P < 0.01), or forskolin (554 +/- 56, P < 0.05). Functional studies showed that exogenously added 1,25(OH)(2)D(3) or its precursor, 25-hydroxyvitamin D(3) (25(OH)D(3)), significantly decreased HUVEC proliferation after 72 h of treatment (33% and 11%, respectively). In addition, after 24 h treatment, both 1,25(OH)(2)D(3) and 25(OH)D(3) increased the adhesion of monocytic U937 cells to HUVEC (159% and 153%, respectively). These data indicate that human endothelia are able to produce active vitamin D. The rapid induction of endothelial 1alpha-OHase activity by inflammatory cytokines suggests a novel autocrine/paracrine role for the enzyme, possibly as a modulator of endothelial cell adhesion.
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Affiliation(s)
- Daniel Zehnder
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
| | - Rosemary Bland
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
| | - Ravinder S Chana
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
| | - David C Wheeler
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
| | - Alexander J Howie
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
| | - Mary C Williams
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
| | - Paul M Stewart
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
| | - Martin Hewison
- *Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham; and Centre for Nephrology, Royal Free and University College Medical School, United Kingdom
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Bland R, Zehnder D, Hughes SV, Ronco PM, Stewart PM, Hewison M. Regulation of vitamin D-1alpha-hydroxylase in a human cortical collecting duct cell line. Kidney Int 2001; 60:1277-86. [PMID: 11576342 DOI: 10.1046/j.1523-1755.2001.00966.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND Recent studies have shown that renal expression of 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-OHase) is not restricted to proximal tubules. To investigate the significance of this expression, we characterized the regulation of 1alpha-OHase expression and activity in a human cortical collecting duct cell line (HCD). METHODS Expression of 1alpha-OHase mRNA and protein was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses. Enzyme activity was quantified using 25-hydroxyvitamin D3 as the substrate; conversion to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and 24,25-dihydroxyvitamin D3 was then determined by thin-layer chromatography. RESULTS HCD cells expressed mRNA and protein for 1alpha-OHase. However, basal 1,25(OH)2D3 production was lower than that observed in proximal tubule HKC-8 cells. In both cell lines, synthesis of 1,25(OH)2D3 was increased by forskolin, parathyroid hormone, and low calcium medium. Conversely, treatment with 1,25(OH)2D3 itself decreased 1alpha-OHase activity. This effect was more pronounced in HCD cells, which also demonstrated significantly higher levels of 24-hydroxylase activity. The most striking induction of 1alpha-OHase activity was observed in the HCD cells following incubation with lipopolysaccharide, which was coincident with the expression of mRNA for both CD14 and Toll-like receptor 4. CONCLUSIONS These results highlight the capacity for synthesis of 1,25(OH)2D3 in cells from more distal areas of the nephron. However, more sensitive feedback regulation and immune induction of 1alpha-OHase in the HCD cells suggest a more localized role for 1,25(OH)2D3 production in the distal nephron.
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Affiliation(s)
- R Bland
- Division of Medical Sciences, The University of Birmingham, Queen Elizabeth Hospital, Birmingham, England, United Kingdom
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Affiliation(s)
- M Hewison
- Division of Medical Sciences, Institute of Clinical Research, University of Birmingham, Birmingham B15-2TH, UK
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33
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Teegarden D, Nickel KP, Shi L. Characterization of 25-hydroxyvitamin D binding protein from intestinal cells. Biochem Biophys Res Commun 2000; 275:845-9. [PMID: 10973809 DOI: 10.1006/bbrc.2000.3397] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have previously purified a cytosolic vitamin D metabolite binding protein (cDBP) from rat enterocytes, which has characteristics distinct from other vitamin D binding proteins. In these studies, we demonstrate that cDBP in a semi-purified fraction from human intestinal cells (Caco-2 cells) binds 25-hydroxyvitamin D (25OHD) with at least a 1000-fold greater affinity than 1, 25-dihydroxyvitamin D (1,25(OH)(2)D) or 24,25-dihydroxyvitamin D. Treatment of cells with 1,25(OH)(2)D reduced 25OHD binding to approximately one third that of the untreated cells (0.42 CPM/mg total protein vs 1.34 CPM/mg total protein, respectively). Finally, the cDBP is not immunoreactive to antibodies prepared against the C-terminus of the nuclear vitamin D receptor (VDR). In summary, cDBP bound 25OHD with greater affinity than either 1,25(OH)(2)D or 24,25 dihydroxyvitamin D, the cytosolic binding activity was down-regulated by 1,25(OH)(2)D and cBDP is distinct from the nuclear VDR.
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Affiliation(s)
- D Teegarden
- Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana 47907, USA.
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34
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Bland R, Zehnder D, Hewison M. Expression of 25-hydroxyvitamin D3-1alpha-hydroxylase along the nephron: new insights into renal vitamin D metabolism. Curr Opin Nephrol Hypertens 2000; 9:17-22. [PMID: 10654820 DOI: 10.1097/00041552-200001000-00004] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Renal synthesis of the active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], is a pivotal step in calcium and phosphate homeostasis. Production of 1,25(OH)2D3 is catalyzed by the mitchondrial cytochrome P450, 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-HYD). As a consequence of the tight regulation of vitamin D metabolism during normal physiology, studies of the expression and regulation of 1alpha-HYD have proved remarkably difficult. However, the recent cloning of the gene for 1alpha-HYD has enabled a more comprehensive analysis of the tissue distribution of 1alpha-HYD, as well as the mechanisms involved in controlling 1,25(OH)2D3 production. In particular, an understanding of site-specific expression and regulation of 1alpha-HYD along the nephron might help to elucidate a more versatile role for 1,25(OH)2D3 in renal physiology.
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Affiliation(s)
- R Bland
- Division of Medical Sciences, The University of Birmingham, UK
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35
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Affiliation(s)
- D Feldman
- Endocrinology Division, Stanford University School of Medicine, California, USA
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36
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Zehnder D, Bland R, Walker EA, Bradwell AR, Howie AJ, Hewison M, Stewart PM. Expression of 25-hydroxyvitamin D3-1alpha-hydroxylase in the human kidney. J Am Soc Nephrol 1999; 10:2465-73. [PMID: 10589683 DOI: 10.1681/asn.v10122465] [Citation(s) in RCA: 128] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The secosteroid hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a vital role in calcium metabolism, tissue differentiation, and normal bone growth. Biosynthesis of 1,25(OH)2D3 is catalyzed by the mitochondrial cytochrome P450 enzyme 25-hydroxyvitamin D3 1alpha-hydroxylase (1alpha-hydroxylase). Although activity of this enzyme has been described in several tissues, the kidneys are recognized to be the principal site of 1,25(OH)2D3 production. To date, enzyme activity studies using vitamin D-deficient animals have suggested that 1alpha-hydroxylase is expressed exclusively in proximal convoluted tubules. With the recent cloning of 1alpha-hydroxylase, specific cRNA probes and in-house polyclonal antiserum have been used to determine the distribution of 1alpha-hydroxylase along the human nephron. Immunohistochemistry and in situ hybridization studies indicated strong expression of 1alpha-hydroxylase protein and mRNA in the distal convoluted tubule, the cortical and medullary part of the collecting ducts, and the papillary epithelia. Lower expression was observed along the thick ascending limb of the loop of Henle and Bowman's capsule. Weaker and more variable expression of 1alpha-hydroxylase protein and mRNA was seen in proximal convoluted tubules, and no expression was observed in glomeruli or vascular structures. These data show for the first time the distribution of alpha1-hydroxylase expression in normal human kidney. In contrast to earlier enzyme activity studies conducted in vitamin D-deficient animals, our data indicate that the distal nephron is the predominant site of 1alpha-hydroxylase expression under conditions of vitamin D sufficiency.
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Affiliation(s)
- D Zehnder
- Division of Medical Sciences, University of Birmingham, Queen Elizabeth Hospital, Edgbaston, United Kingdom
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37
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Jones G, Ramshaw H, Zhang A, Cook R, Byford V, White J, Petkovich M. Expression and activity of vitamin D-metabolizing cytochrome P450s (CYP1alpha and CYP24) in human nonsmall cell lung carcinomas. Endocrinology 1999; 140:3303-10. [PMID: 10385427 DOI: 10.1210/endo.140.7.6799] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Extrarenal 25-hydroxyvitamin D3-1alpha-hydroxylase is believed to play a major role in the pathogenesis of hypercalcemia associated with various types of granulomatous and lymphoproliferative diseases and certain solid tumors. In this paper, we describe the cloning of the cytochrome P450 component of the extrarenal enzyme from a human nonsmall cell lung carcinoma, SW 900. The cytochrome P450 for the extrarenal 1alpha-hydroxylase has an amino acid sequence identical to that of the cytochrome P450 component of the CYP1alpha, the renal form of the enzyme, and appears to be a product of the same gene. CYP1alpha messenger RNA (mRNA) and 1alpha-hydroxylase enzyme activity were detected in two (SW 900, SK-Luci-6) of a series of five nonsmall cell lung carcinoma cell lines. All five lung cell lines were cultured with the same medium under the same conditions, but only two of the five expressed 1alpha-hydroxylase enzyme; two others (WT-E, Calu-1) expressed high levels of the reciprocally regulated enzyme, 25-hydroxyvitamin D3-24-hydroxylase, with its specific cytochrome P450 component, CYP24. Although under basal conditions the lung cell line SW 900 expressed only CYP1alpha and showed 1alpha-hydroxylase enzyme activity, when treated with small concentrations of 1alpha,25-dihydroxyvitamin D3 or high concentrations of 25-hydroxyvitamin D3, it began to express CYP24 and exhibit 24-hydroxylase enzyme activity. Somewhat surprisingly, SW 900 cells still had detectable CYP1alpha mRNA some 24 h after vitamin D treatment despite the fact that 1alpha-hydroxylase enzyme activity was unmeasurable. These data are consistent with the emerging hypothesis that vitamin D through its active form does not directly turn off CYP1alpha mRNA production but, rather, strongly stimulates CYP24, thereby masking CYP1alpha activity. The factor(s) responsible for the basal expression of CYP1alpha in SW 900 and SK-Luci-6 is currently unknown.
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Affiliation(s)
- G Jones
- Cytochroma, Inc., Kingston, Ontario, Canada.
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38
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Abstract
The active, hormonal form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) has numerous pleiotropic actions including the regulation of calcium homeostasis, control of bone cell differentiation and modification of immune responses. Synthesis of 1,25(OH)2D3 from the major circulating metabolite, 25-hydroxyvitamin D3 (25(OH)D3), is catalysed by the mitochondrial cytochrome P450 enzyme 25-hydroxyvitamin D-1alpha-hydroxylase (1alpha-HYD). Although 1alpha-HYD activity has been demonstrated at several ectopic sites, circulating levels of 1,25(OH)2D3 appear to reflect the expression of this enzyme in the kidney. The tight regulation of 1alpha-HYD in both renal and ectopic tissues has made studies of the expression and regulation of this enzyme remarkably difficult. However, the recent cloning of mouse, rat and human cDNAs for 1alpha-HYD has stimulated renewed interest in the molecular endocrinology of 1,25(OH)2D3 production. Analysis of the 1alpha-HYD sequence has revealed homology with the liver enzyme vitamin D-25-hydroxylase, and the ubiquitously expressed vitamin D-24-hydroxylase. Furthermore, mutations causing the inherited disorder vitamin D-dependent rickets type 1, also known as pseudo-vitamin D deficiency rickets have been described for the 1alpha-HYD gene and these have been mapped to chromosome 12q14 by linkage analysis. The availability of sequence information for the 1alpha-HYD gene has also facilitated the development of new molecular tools which will help to clarify key functions of the enzyme. Specific issues such as tissue distribution and regulatory pathways are discussed in this review, with particular emphasis on the role of 1alpha-HYD in renal calcium/phosphate homeostasis.
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Affiliation(s)
- D Zehnder
- Institute of Clinical Research, The Queen Elizabeth Hospital, The University of Birmingham, UK
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39
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Murayama A, Takeyama K, Kitanaka S, Kodera Y, Kawaguchi Y, Hosoya T, Kato S. Positive and negative regulations of the renal 25-hydroxyvitamin D3 1alpha-hydroxylase gene by parathyroid hormone, calcitonin, and 1alpha,25(OH)2D3 in intact animals. Endocrinology 1999; 140:2224-31. [PMID: 10218975 DOI: 10.1210/endo.140.5.6691] [Citation(s) in RCA: 199] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Reflecting the prime role of 1alpha,25(OH)2D3 in calcium homeostasis, the activity of 25-hydroxyvitamin D3 1alpha-hydroxylase, a key enzyme for 1alpha,25(OH)2D3 biosynthesis, is tightly regulated by 1alpha,25(OH)2D3, PTH and calcitonin. Its significant activity is found in kidney, though the enzymatic activity is also reported in extra-renal tissues. In the present study, we found that the 1alpha-hydroxylase gene abundantly expresses in kidney, and at low levels in other tissues and in some cell lines. Positive and negative regulations of 1alpha-hydroxylase gene by PTH, calcitonin, or 1alpha,25(OH)2D3 were observed at transcriptional levels in kidneys of animals and in a mouse proximal tubule cell line. Moreover, the protein kinase A inhibitor abrogated the PTH-mediated positive regulation. In mice lacking the vitamin D receptor, the 1alpha-hydroxylase gene expression was overinduced, and the inducible effect of either PTH or calcitonin, but not the repression by 1alpha,25(OH)2D3, was evident. Thus, vitamin D receptor is essential for the negative regulation by 1alpha,25(OH)2D3. Moreover, we demonstrate that renal 1alpha-hydroxylase gene expression in chronic renal failure model rats was decreased and the positive effect by PTH and calcitonin was diminished. The present study demonstrates that PTH and calcitonin positively regulate renal 1alpha-hydroxylase gene expression via PKA-dependent and independent pathway, respectively, and that 1alpha,25(OH)2D3 negatively regulates it mediated by vitamin D receptor. Furthermore, in a moderate state of chronic renal failure, renal cells expressing the 1alpha-hydroxylase gene appear to have diminished potential in response to PTH and calcitonin.
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Affiliation(s)
- A Murayama
- The Institute of Molecular and Cellular Biosciences, The University of Tokyo, Japan
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40
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Abstract
For adults, the 5-microg (200 IU) vitamin D recommended dietary allowance may prevent osteomalacia in the absence of sunlight, but more is needed to help prevent osteoporosis and secondary hyperparathyroidism. Other benefits of vitamin D supplementation are implicated epidemiologically: prevention of some cancers, osteoarthritis progression, multiple sclerosis, and hypertension. Total-body sun exposure easily provides the equivalent of 250 microg (10000 IU) vitamin D/d, suggesting that this is a physiologic limit. Sailors in US submarines are deprived of environmentally acquired vitamin D equivalent to 20-50 microg (800-2000 IU)/d. The assembled data from many vitamin D supplementation studies reveal a curve for vitamin D dose versus serum 25-hydroxyvitamin D [25(OH)D] response that is surprisingly flat up to 250 microg (10000 IU) vitamin D/d. To ensure that serum 25(OH)D concentrations exceed 100 nmol/L, a total vitamin D supply of 100 microg (4000 IU)/d is required. Except in those with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25(OH)D concentrations <140 nmol/L, which require a total vitamin D supply of 250 microg (10000 IU)/d to attain. Published cases of vitamin D toxicity with hypercalcemia, for which the 25(OH)D concentration and vitamin D dose are known, all involve intake of > or = 1000 microg (40000 IU)/d. Because vitamin D is potentially toxic, intake of >25 microg (1000 IU)/d has been avoided even though the weight of evidence shows that the currently accepted, no observed adverse effect limit of 50 microg (2000 IU)/d is too low by at least 5-fold.
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Affiliation(s)
- R Vieth
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Mount Sinai Hospital, Ontario, Canada.
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41
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Bland R, Walker EA, Hughes SV, Stewart PM, Hewison M. Constitutive expression of 25-hydroxyvitamin D3-1alpha-hydroxylase in a transformed human proximal tubule cell line: evidence for direct regulation of vitamin D metabolism by calcium. Endocrinology 1999; 140:2027-34. [PMID: 10218951 DOI: 10.1210/endo.140.5.6683] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Circulating levels of the active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) are dependent on activity of the renal mitochondrial cytochrome P450 enzyme, 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-hydroxylase). Production of 1,25-(OH)2D3 occurs predominantly in the renal proximal tubule, with 1alpha-hydroxylase activity being impaired in renal insufficiency and renal disease. The expression and activity of 1alpha-hydroxylase are tightly regulated in response to serum levels of PTH, calcium, phosphate, and 1,25-(OH)2D3 itself. As a consequence of this, the characterization of 1alpha-hydroxylase in human renal tissue has proved difficult. In this study we have characterized constitutive 1alpha-hydroxylase expression in a simian virus 40-transformed human proximal tubule cell line, HKC-8. Initial analyses of [3H]25-hydroxyvitamin D3 (25OHD3) metabolism in these cells using straight and reverse phase HPLC revealed product peaks that coincided with authentic 1,25-(OH)2D3 as well as 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3). Enzyme kinetic studies indicated that the Km for synthesis of 1,25-(OH)2D3 in HKC-8 cells was 120 nmol/liter 25OHD3, with a maximum velocity of 21 pmol/h/mg protein. This activity was inhibited by treatment with ketoconazole, but not diphenyl phenylenediamine. RT-PCR analysis of RNA from HKC-8 cells revealed a transcript similar in size to that observed in keratinocytes and primary cultures of human proximal tubule cells, and protein was detected by Western blot analysis. Synthesis of 1,25-(OH)2D3 was up regulated by treatment with forskolin (10 micromol/liter, 24 h) and was down-regulated by 1,25-(OH)2D3 (10 nmol/liter, 24 h). 1Alpha-hydroxylase activity in HKC-8 cells was also sensitive to the concentration of calcium. Cells grown in low calcium (0.5 mmol/liter) showed a 4.8-fold induction of 1alpha-hydroxylase, whereas treatment with medium containing high levels of calcium (2 mmol/liter) significantly inhibited 1,25-(OH)2D3 production. These data suggest that direct effects of calcium on proximal tubule cells may be an important feature of the regulation of renal 1,25-(OH)2D3 production.
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Affiliation(s)
- R Bland
- Department of Medicine, Institute of Clinical Research, University of Birmingham, United Kingdom
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42
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Schütze N, Fritsche J, Ebert-Dümig R, Schneider D, Köhrle J, Andreesen R, Kreutz M, Jakob F. The selenoprotein thioredoxin reductase is expressed in peripheral blood monocytes and THP1 human myeloid leukemia cells--regulation by 1,25-dihydroxyvitamin D3 and selenite. Biofactors 1999; 10:329-38. [PMID: 10619700 DOI: 10.1002/biof.5520100403] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
1,25(OH)2 Vitamin D3 (1,25(OH)2D3) and adhesion propagate monocyte differentiation. We identified the selenoprotein thioredoxin reductase (TrxR) as a new molecular target for 1,25(OH)2D3 in monocytes during this process. In THP1 monocytic leukemia cells 1,25(OH)2D3 stimulated TrxR mRNA levels 2-4-fold by 4-8 h and enhanced TrxR activity (60%) (as measured by the dithionitrobenzole-assay) after 24 h, which declined below baseline after 96 h. The addition of 100 nM selenite enhanced (approx. 50%) basal and stimulated enzyme activity in THP1 cells. The relative stimulation by 1,25(OH)2D3 was very similar but peak levels were sustained in THP1 cells up to 48 h. Human peripheral blood monocytes (PBM) of different donors showed very low basal TrxR steady state mRNA levels which were markedly enhanced (as analyzed by Northern blotting) after 4 h of adherence to culture dishes. 1,25(OH)2D3 (100 nM) further stimulated TrxR mRNA expression (4 h, 3-fold). TrxR enzyme activity mirrored the mRNA changes. Basal activity was stimulated approx. 25% by adhesion in culture alone and was further stimulated (approximately 15%) by 1,25(OH)2D3 after 4 h. By 24 h similar results were achieved but the effect of 1,25(OH)2D3 could be seen in the presence of 100 nM selenium only. The expression of TrxR and its regulation by 1,25(OH)2D3 and selenite in monocytes might be important for their induction of differentiation and maintenance of function.
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Affiliation(s)
- N Schütze
- Klinische Forschergruppe, Medizinische Poliklinik, Universität Würzburg, Germany
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