RESUMEN
Kidney transplantation is the optimal treatment for children with end-stage renal disease. For children with undocumented immigration status, access to kidney transplantation is limited, and data on transplant outcomes in this population are scarce. The goal of the present retrospective single-center study was to compare outcomes after kidney transplantation in undocumented children with those of US citizen children. Undocumented residency status was identified in 48 (17%) of 289 children who received a kidney transplant between 1998 and 2010. In undocumented recipients, graft survival at 1 and 5 years posttransplantation was similar, and mean estimated glomerular filtration rate at 1 year was higher than that in recipients who were citizens. The risk of allograft failure was lower in undocumented recipients relative to that in citizens at 5 years posttransplantation, after adjustment for patient age, donor age, donor type, and HLA mismatch (p < 0.04). In contrast, nearly one in five undocumented recipients who reached 21 years of age lost their graft, primarily because they were unable to pay for immunosuppressive medications once their state-funded insurance had ended. These findings support the ongoing need for immigration policies for the undocumented that facilitate access to work-permits and employment-related insurance for this disadvantaged group.
Asunto(s)
Emigración e Inmigración/estadística & datos numéricos , Rechazo de Injerto/epidemiología , Supervivencia de Injerto , Fallo Renal Crónico/cirugía , Trasplante de Riñón , Obtención de Tejidos y Órganos/métodos , Adolescente , Adulto , Niño , Preescolar , Emigración e Inmigración/legislación & jurisprudencia , Femenino , Tasa de Filtración Glomerular , Política de Salud , Humanos , Incidencia , Lactante , Masculino , Estudios Retrospectivos , Medición de Riesgo , Factores Socioeconómicos , Donantes de Tejidos , Receptores de Trasplantes , Trasplante Homólogo , Resultado del Tratamiento , Estados Unidos/epidemiología , Adulto JovenRESUMEN
Islet transplantation after successful kidney transplantation is a recognized treatment for adults with diabetes and end-stage renal disease (ESRD), but has not been considered an option in the pediatric population. To our knowledge, we report the first combined islet and kidney transplant in a child. The patient was born with bilateral renal hypoplasia and was diagnosed with type 1 diabetes mellitus at age 13 months. He had erratic glycemic control and hypoglycemia unawareness. At 6 years of age, the child safely underwent simultaneous islet and live donor kidney transplantation. Although function of the islet graft was transient, the combined transplant provided significant benefits in terms of glucose control and overall growth and development. Such an approach represents a viable treatment option for pediatric patients with ESRD and unstable diabetes.
Asunto(s)
Glucemia/análisis , Diabetes Mellitus Tipo 1/cirugía , Fallo Renal Crónico/cirugía , Trasplante de Riñón , Trasplante de Páncreas , Adulto , Niño , Diabetes Mellitus Tipo 1/complicaciones , Femenino , Humanos , Fallo Renal Crónico/complicaciones , Masculino , PronósticoRESUMEN
Monitoring of renal graft status through peripheral blood (PB) rather than invasive biopsy is important as it will lessen the risk of infection and other stresses, while reducing the costs of rejection diagnosis. Blood gene biomarker panels were discovered by microarrays at a single center and subsequently validated and cross-validated by QPCR in the NIH SNSO1 randomized study from 12 US pediatric transplant programs. A total of 367 unique human PB samples, each paired with a graft biopsy for centralized, blinded phenotype classification, were analyzed (115 acute rejection (AR), 180 stable and 72 other causes of graft injury). Of the differentially expressed genes by microarray, Q-PCR analysis of a five gene-set (DUSP1, PBEF1, PSEN1, MAPK9 and NKTR) classified AR with high accuracy. A logistic regression model was built on independent training-set (n = 47) and validated on independent test-set (n = 198)samples, discriminating AR from STA with 91% sensitivity and 94% specificity and AR from all other non-AR phenotypes with 91% sensitivity and 90% specificity. The 5-gene set can diagnose AR potentially avoiding the need for invasive renal biopsy. These data support the conduct of a prospective study to validate the clinical predictive utility of this diagnostic tool.
Asunto(s)
Rechazo de Injerto/diagnóstico , Trasplante de Riñón , Enfermedad Aguda , Rechazo de Injerto/sangre , Humanos , Reacción en Cadena de la Polimerasa , Sensibilidad y EspecificidadRESUMEN
To determine whether steroid avoidance in pediatric kidney transplantation is safe and efficacious, a randomized, multicenter trial was performed in 12 pediatric kidney transplant centers. One hundred thirty children receiving primary kidney transplants were randomized to steroid-free (SF) or steroid-based (SB) immunosuppression, with concomitant tacrolimus, mycophenolate and standard dose daclizumab (SB group) or extended dose daclizumab (SF group). Follow-up was 3 years posttransplant. Standardized height Z-score change after 3 years follow-up was -0.99 ± 2.20 in SF versus -0.93 ± 1.11 in SB; p = 0.825. In subgroup analysis, recipients under 5 years of age showed improved linear growth with SF compared to SB treatment (change in standardized height Z-score at 3 years -0.43 ± 1.15 vs. -1.07 ± 1.14; p = 0.019). There were no differences in the rates of biopsy-proven acute rejection at 3 years after transplantation (16.7% in SF vs. 17.1% in SB; p = 0.94). Patient survival was 100% in both arms; graft survival was 95% in the SF and 90% in the SB arms (p = 0.30) at 3 years follow-up. Over the 3 year follow-up period, the SF group showed lower systolic BP (p = 0.017) and lower cholesterol levels (p = 0.034). In conclusion, complete steroid avoidance is safe and effective in unsensitized children receiving primary kidney transplants.
Asunto(s)
Inmunosupresores/administración & dosificación , Trasplante de Riñón , Esteroides/administración & dosificación , Adolescente , Adulto , Niño , Preescolar , Femenino , Estudios de Seguimiento , Humanos , Lactante , Recién Nacido , Masculino , Adulto JovenRESUMEN
The principal hormone regulator of bone mineralization is vitamin D, which must be activated by a metabolic pathway consisting of a 25-hydroxylase and a 1alpha-hydroxylase to yield 1,25 (OH)(2)D. The hormonal regulation of vitamin D activation is at the level of the 1alpha-hydroxylase. We review the biology of vitamin D, the biochemistry of its activation and the molecular biology of the vitamin D-metabolizing enzymes. Recent advances have resulted in the cloning of the human vitamin D 1alpha-hydroxylase and the identification of mutations in its gene that cause Vitamin D Dependent Rickets type I.
Asunto(s)
Dieta/efectos adversos , Deficiencia de Vitamina D/etiología , Deficiencia de Vitamina D/genética , Vitamina D/biosíntesis , Vitamina D/genética , Sistema Enzimático del Citocromo P-450/metabolismo , Humanos , Mitocondrias/metabolismoRESUMEN
Several reports have suggested that the regulation of renal 1,25-dihydroxyvitamin D [1,25-(OH)(2)D] synthesis by extracellular phosphate (Pi) is dependent on normal transepithelial Pi transport by the renal tubule. Mice homozygous for the disrupted Na/Pi cotransporter gene Npt2 (Npt2(-/-)) exhibit renal Pi wasting, an approximately 85% decrease in renal brush border membrane Na/Pi cotransport, hypophosphatemia, and an increase in serum 1,25-(OH)(2)D concentration. We undertook 1) to determine the mechanism for the increased circulating levels of 1,25-(OH)(2)D in Npt2(-/-) mice and 2) to establish whether renal 1alpha-hydroxylase was appropriately regulated by dietary Pi in the absence of Npt2 gene expression. On a control diet, the 2.5-fold increase in the serum 1,25-(OH)(2)D concentration in Npt2(-/-) mice, relative to that in Npt2(+/+) littermates, is associated with a corresponding increase in renal mitochondrial 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) activity and messenger RNA (mRNA) abundance. A low Pi diet elicits an increase in serum 1,25-(OH)(2)D concentration, renal 1alpha-hydroxylase activity, and mRNA abundance in Npt2(+/+) and Npt2(-/-) mice to similar levels in both mouse strains. A high Pi diet has no effect on serum 1,25-(OH)(2)D concentration, renal 1 alpha-hydroxylase activity, or mRNA abundance in Npt2(+/+) mice, but normalizes these parameters in Npt2(-/-) mice. In addition, renal 24-hydroxylase mRNA abundance is significantly reduced in Npt2(-/-) mice compared with that in Npt2(+/+) mice under all dietary conditions. In summary, we demonstrate that 1) increased renal synthesis of 1,25-(OH)(2)D is responsible for the increased serum 1,25-(OH)(2)D concentration in Npt2(-/-) mice; and 2) renal 1alpha-hydroxylase gene expression is appropriately regulated by dietary manipulation of serum Pi in both Npt2(+/+) and Npt2(-/-) mice. Thus, intact renal Na/Pi cotransport is not required for the regulation of renal 1alpha-hydroxylase by Pi.
Asunto(s)
25-Hidroxivitamina D3 1-alfa-Hidroxilasa/metabolismo , Proteínas Portadoras/genética , Expresión Génica/fisiología , Riñón/fisiología , Fosfatos/farmacología , Simportadores , Vitamina D/análogos & derivados , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/genética , Animales , Sistema Enzimático del Citocromo P-450/genética , Dieta , Femenino , Riñón/enzimología , Masculino , Ratones , Ratones Noqueados/genética , Mitocondrias/enzimología , Fosfatos/administración & dosificación , ARN Mensajero/metabolismo , Proteínas Cotransportadoras de Sodio-Fosfato , Proteínas Cotransportadoras de Sodio-Fosfato de Tipo I , Proteínas Cotransportadoras de Sodio-Fosfato de Tipo III , Esteroide Hidroxilasas/genética , Vitamina D/sangre , Vitamina D3 24-HidroxilasaRESUMEN
The rate-limiting, hormonally regulated step in the bioactivation of vitamin D is renal 1 alpha-hydroxylation by P450c1 alpha. In late 1997, we reported the cloning of the human cDNA and gene from keratinocytes, and established that P450c1 alpha mutations cause vitamin D-dependent rickets, type I, while three other groups reported the cloning of the rodent enzyme. The genetics of P450c1 alpha are well established, with studies of over 30 patients, but the molecular mechanisms for the hormonal regulation of P450c1 alpha are still under investigation.
Asunto(s)
Esteroide Hidroxilasas/metabolismo , Animales , Regulación Enzimológica de la Expresión Génica , Humanos , Esteroide Hidroxilasas/biosíntesis , Esteroide Hidroxilasas/genéticaRESUMEN
The rate-limiting, hormonally regulated step in the bioactivation of vitamin D is the 1alpha-hydroxylation of 25-hydroxyvitamin D, which occurs in the kidney and other tissues and is catalyzed by the mitochondrial cytochrome P450 enzyme, P450c1alpha. After many years of effort, the cDNA and gene encoding this enzyme were cloned from mouse, rat, and human tissue in late 1997. The human gene encoding the 1alpha-hydroxylase is 5 kb in length, located on chromosome 12, and comprises nine exons and eight introns; its intron/exon organization is very similar to that of the other four mitochondrial P450 enzymes cloned to date. Mutations in P450c1alpha cause 1alpha-hydroxylase deficiency, also known as vitamin D-dependent rickets type 1, a rare autosomal recessive disease characterized by rickets and impaired growth due to failure of renal synthesis of 1,25(OH)2D. To date, 31 patients have been studied and 20 distinct mutations in the gene identified, including 13 mis-sense mutations, none of which encode a protein with significant enzyme activity. Recent studies in animals demonstrate that regulation of P450c1alpha gene expression by parathyroid hormone (PTH), low calcium diet, low phosphorus diet, and 1,25(OH)2D occurs at the level of its mRNA. Transcriptional activity of the mouse and human P450c1alpha gene promoters can be stimulated by PTH, cAMP, and forskolin and suppressed by 1,25(OH)2D.
Asunto(s)
25-Hidroxivitamina D3 1-alfa-Hidroxilasa/genética , Clonación Molecular , Expresión Génica , Mutación , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/deficiencia , Animales , Enzimas/metabolismo , Humanos , Biología Molecular , Vitamina D/biosíntesisRESUMEN
BACKGROUND: Little is known about parathyroid gland function in patients receiving total parenteral nutrition (TPN). OBJECTIVE: Our objective was to determine whether parathyroid gland function is abnormal in TPN recipients. DESIGN: Six patients with a mean (+/-1 SD) age of 45.5 +/- 8.0 y who had been receiving TPN for 18.7 +/- 2. 8 y underwent bone biopsy, bone mass measurements with dual-energy X-ray absorptiometry, and dynamic tests of parathyroid gland function. Diurnal variations in blood ionized calcium (iCa(2+)) and serum parathyroid hormone (PTH) concentrations were also assessed. Results were compared with those of healthy volunteers. RESULTS: Bone mass and bone formation were subnormal in all patients. Basal serum PTH concentrations were moderately higher in the TPN recipients than in healthy volunteers, and values obtained every 30 min over 24 h were significantly higher (P < 0.001) in TPN recipients (5.0 +/- 0.9 pmol/L) than in healthy volunteers (2.6 +/- 0.6 pmol/L). The percentage increase in serum PTH during citrate-induced hypocalcemia was lower in the TPN recipients, consistent with secondary hyperparathyroidism. Evening infusions of calcium-containing TPN eliminated the nocturnal rise in serum PTH, increased the amplitude of change for iCa(2+) and PTH over 24 h, increased the orderliness of change for iCa(2+) and PTH as measured by approximate entropy (ApEn), and enhanced the synchrony of change between iCa(2+) and PTH. Treatment for 10 d with calcium-free TPN restored the nocturnal rise in serum PTH and increased ApEn for PTH. ApEn for iCa(2+) remained low, suggesting that a component of nutrient solutions, but not calcium per se, enhances the regularity of PTH release in TPN recipients. CONCLUSION: Parathyroid gland function is abnormal in long-term TPN recipients, which may contribute to disturbances in bone metabolism.
Asunto(s)
Calcio/sangre , Glándulas Paratiroides/fisiopatología , Hormona Paratiroidea/sangre , Nutrición Parenteral Total , Adulto , Densidad Ósea , Remodelación Ósea , Calcio/orina , Ritmo Circadiano , Citratos , Femenino , Cuello Femoral , Humanos , Vértebras Lumbares , Masculino , Persona de Mediana Edad , Glándulas Paratiroides/metabolismo , Nutrición Parenteral Total/efectos adversos , Admisión del Paciente , Citrato de Sodio , Factores de Tiempo , Vitamina D/análogos & derivados , Vitamina D/sangreRESUMEN
The principal hormonal regulator of bone mineralization is vitamin D, which must be activated by a metabolic pathway consisting of a 25-hydroxylase and a 1 alpha-hydroxylase to yield 1,25 dihydroxy vitamin D. The hormonal regulation of vitamin D activation is at the level of the 1 alpha-hydroxylase. This article reviews the biology of vitamin D, and describes the biochemistry of its activation and the molecular biology of the vitamin D-metabolizing enzymes. Recent advances, principally in the authors' laboratories, have resulted in the cloning of the human vitamin D 1 alpha-hydroxylase and the identification of mutations in its gene that cause Vitamin D Dependent Rickets type I.
Asunto(s)
Vitamina D/biosíntesis , Vitamina D/genética , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/deficiencia , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/genética , Animales , Colestanotriol 26-Monooxigenasa , Sistema Enzimático del Citocromo P-450/deficiencia , Sistema Enzimático del Citocromo P-450/genética , Sistema Enzimático del Citocromo P-450/metabolismo , Humanos , Mutación , Esteroide Hidroxilasas/deficiencia , Esteroide Hidroxilasas/genética , Vitamina D3 24-HidroxilasaRESUMEN
Dietary deficiency of vitamin D, genetic disorders of its bioactivation to 1,25-dihydroxyvitamin D [1,25(OH)2D], or disorders of vitamin D action can cause rickets. The rate-limiting, hormonally-regulated, biologically activating step in the synthesis of 1,25(OH)2D is the 1 alpha-hydroxylation of 25-hydroxyvitamin D, which occurs in kidney and other tissues and is mediated by a mitochondrial cytochrome P450 enzyme, P450c1 alpha. After many years of effort, the cDNA and gene for this enzyme were cloned in late 1997. Mutations in the P450c1 alpha gene, located on chromosome 12, cause 1 alpha-hydroxylase deficiency, also known as vitamin D-dependent rickets type I, an autosomal recessive disease characterized by rickets and impaired growth due to failure of renal synthesis of 1,25(OH)2D. X-linked hypophosphatemic rickets, a dominantly inherited disease, is caused by mutations in the PHEX gene, whose function in regulating renal phosphate and vitamin D metabolism remains to be elucidated.
Asunto(s)
Avitaminosis/genética , Cromosomas Humanos Par 12/genética , Sistema Enzimático del Citocromo P-450/genética , Mutación/genética , Raquitismo/genética , Vitamina D/metabolismo , Avitaminosis/diagnóstico , Avitaminosis/metabolismo , Genes Recesivos , Pruebas Genéticas , Humanos , Biología Molecular , Raquitismo/clasificación , Raquitismo/diagnóstico , Raquitismo/metabolismoRESUMEN
BACKGROUND: Children with primary hyperoxaluria type 1 (PH 1) are at great risk to develop systemic oxalosis in end-stage renal disease (ESRD), as endogenous oxalate production exceeds oxalate removal by dialytic therapy. As oxalate accumulates, calcium oxalate (CaOx) tissue deposition occurs. Children with other causes of ESRD, however, are not prone to CaOx deposition despite elevated plasma oxalate (POx) levels. METHODS: Our study objective was to examine the potential mechanisms for these observations. We measured POx, sulfate, citrate, and calculated CaOx saturation (betaCaOx) in 7 children with ESRD caused by PH 1 and in 33 children with non-PH-related ESRD. Maintenance hemodialysis (HD) was performed in 6 PH 1 and 22 non-PH patients: Pre- and post-HD levels were analyzed at this point and were repeated twice within 12 months in 5 PH 1 and 14 non-PH patients. Samples were obtained only once in 12 patients (one PH 1) on peritoneal dialysis (PD). After liver-kidney or kidney transplantation, plasma levels were measured repetitively. RESULTS: The mean POx was higher in PH 1 (125.7 +/- 17.9 micromol/liter) than in non-PH patients (44.2 +/- 3.3 micromol/liter, P < 10(-4)). All other determined anions did not differ between the two groups. betaCaOx was higher in PH 1 (4.71 +/- 0.69 relative units) compared with non-PH children (1.56 +/- 0.12 units, P < 10(-4)). POx and betaCaOx were correlated in both the PH 1 (r = 0.98, P < 2 x 10(-4)) and the non-PH group (r = 0.98, P < 10(-4)). POx and betaCaOx remained stable over time in the non-PH children, whereas an insignificant decline was observed in PH 1 patients after six months of more aggressive dialysis. betaCaOx was supersaturated (more than 1) in all PH 1 and in 25 out of 33 non-PH patients. Post-HD betaCaOx remained more than 1 in all PH 1, but in only 2 out of 22 non-PH patients. In non-PH children, POx and betaCaOx decreased to normal within three weeks after successful kidney transplantation, whereas the levels still remained elevated seven months after combined liver-kidney transplantation in two PH 1 patients. CONCLUSION: Systemic oxalosis in PH 1 children with ESRD is due to higher POx and betaCaOx levels. As betaCaOx remained supersaturated in PH 1 even after aggressive HD, oxalate accumulation increases, and CaOx tissue deposition occurs. Therefore, sufficient reduction of POx and betaCaOx is crucial in PH 1 and might only be achieved by early, preemptive, combined liver-kidney transplantation or liver transplantation alone.
Asunto(s)
Oxalato de Calcio/sangre , Hiperoxaluria Primaria/sangre , Hiperoxaluria Primaria/complicaciones , Fallo Renal Crónico/sangre , Fallo Renal Crónico/etiología , Huesos/metabolismo , Oxalato de Calcio/metabolismo , Niño , Femenino , Humanos , Lactante , Fallo Renal Crónico/terapia , Trasplante de Riñón , Masculino , Oxalatos/sangre , Diálisis Renal , Retina/metabolismoRESUMEN
Vitamin D-dependent rickets type I (VDDR-I), also known as pseudo-vitamin D-deficiency rickets, appears to result from deficiency of renal vitamin D 1alpha-hydroxylase activity. Prior work has shown that the affected gene lies on 12q13.3. We recently cloned the cDNA and gene for this enzyme, mitochondrial P450c1alpha, and we and others have found mutations in its gene in a few patients. To determine whether all patients with VDDR-I have mutations in P450c1alpha, we have analyzed the P450c1alpha gene in 19 individuals from 17 families representing various ethnic groups. The whole gene was PCR amplified and subjected to direct sequencing; candidate mutations were confirmed by repeat PCR of the relevant exon from genomic DNA from the patients and their parents. Microsatellite haplotyping with the markers D12S90, D12S305, and D12S104 was also done in all families. All patients had P450c1alpha mutations on both alleles. In the French Canadian population, among whom VDDR-I is common, 9 of 10 alleles bore the haplotype 4-7-1 and carried the mutation 958DeltaG. This haplotype and mutation were also seen in two other families and are easily identified because the mutation ablates a TaiI/MaeII site. Six families of widely divergent ethnic backgrounds carried a 7-bp duplication in association with four different microsatellite haplotypes, indicating a mutational hot spot. We found 14 different mutations, including 7 amino acid replacement mutations. When these missense mutations were analyzed by expressing the mutant enzyme in mouse Leydig MA-10 cells and assaying 1alpha-hydroxylase activity, none retained detectable 1alpha-hydroxylase activity. These studies show that most if not all patients with VDDR-I have severe mutations in P450c1alpha, and hence the disease should be referred to as "1alpha-hydroxylase deficiency."
Asunto(s)
25-Hidroxivitamina D3 1-alfa-Hidroxilasa/deficiencia , Mutación , Raquitismo/genética , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/genética , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/metabolismo , Adolescente , Adulto , Alelos , Secuencia de Aminoácidos , Animales , Niño , Preescolar , Cromosomas Humanos Par 12/genética , Etnicidad/genética , Salud de la Familia , Femenino , Ligamiento Genético , Haplotipos/genética , Humanos , Lactante , Células Intersticiales del Testículo , Masculino , Ratones , Repeticiones de Microsatélite/genética , Mitocondrias/enzimología , Mitocondrias/genética , Datos de Secuencia Molecular , Polimorfismo de Longitud del Fragmento de Restricción , Raquitismo/diagnóstico , Raquitismo/enzimología , Raquitismo/patologíaRESUMEN
Chronic renal insufficiency is associated with elevated serum parathyroid hormone (PTH) levels (2 degrees HPT), deficiency of 1,25-dihydroxyvitamin D (1,25(OH)2D), and hypocalciuria. In chronic renal insufficiency, the 2 degrees HPT may result from reduced expression of the parathyroid gland extracellular Ca(2+)-sensing receptor (CaSR). Since the CaSR was cloned from rat and human kidney, this study examined in rats whether expression of the renal CaSR is altered in experimental chronic renal insufficiency. Four weeks after chronic renal insufficiency was induced by 5/6 nephrectomy (Nx) in Sprague Dawley rats, the serum creatinine concentration was 0.96+/-0.06 mg/dl compared with 0.35+/-0.02 mg/dl in sham-operated animals (P < 0.05). The serum total Ca2+ and phosphorus concentrations were not different. In the Nx group, the serum concentration of amino-PTH was higher (65+/-8 pg/ml), and the concentration of 1,25(OH)2D was significantly lower (47+/-5 pg/ml) compared with 45+/-5 pg/ml and 61+/-4 pg/ml (P = 0.05) in the sham group, respectively. In a subset of rats studied, the Nx group was hypocalciuric (1.4+/-0.5 mg/kg per d) compared with the sham group (3.7+/-0.5 mg/kg per d) (P < 0.05). In the Nx rats, CaSR mRNA expression and CaSR protein levels were found to be reduced by 35 and 38%, respectively, than those observed in controls. These results suggest that reduced renal CaSR expression in chronic renal insufficiency may play a role in disordered mineral ion homeostasis, including hypocalciuria.
Asunto(s)
Fallo Renal Crónico/metabolismo , Riñón/metabolismo , Receptores de Superficie Celular/metabolismo , Animales , Western Blotting , Hibridación de Ácido Nucleico , ARN Mensajero/metabolismo , Ratas , Ratas Sprague-Dawley , Receptores Sensibles al Calcio , Receptores de Superficie Celular/genética , RibonucleasasRESUMEN
We examined the effect of aging on the relationship between the concentrations of blood ionized calcium and of serum parathyroid hormone (PTH) in 22 healthy men [9 elderly (age 74 +/- 2 yr) and 13 young (age 39 +/- 1 yr)] in whom the glomerular filtration rate was > 70 ml/min. Throughout a 24-h period, serum concentrations of PTH in the elderly men were twice those in the young men, whereas blood ionized calcium did not differ between the two groups. With intravenous infusion of calcium gluconate, the minimum PTH concentration was two- to threefold higher in the elderly men. With infusion of NaEDTA. the maximum PTH concentration was 20% higher in the elderly men. The calcium set point for PTH release was higher in the elderly than in the young men (4.71 +/- 0.04 vs. 4.54 +/- 0.03 mg/dl, respectively, P < 0.005). In these healthy men, the age-related increase in serum PTH could not be attributed to a sustained decrease in concentration of either blood ionized calcium or 1,25-hydroxyvitamin D. These findings suggest that, with aging, the relationship between calcium and PTH is altered such that at any given level of calcium, the concentration of PTH is higher.
Asunto(s)
Envejecimiento/sangre , Envejecimiento/fisiología , Calcio/fisiología , Hormona Paratiroidea/sangre , Adulto , Anciano , Calcio/sangre , Calcio/orina , Gluconato de Calcio/farmacología , Ácido Edético/farmacología , Humanos , Masculino , Concentración Osmolar , Fósforo/sangre , Fósforo/orina , Valores de Referencia , Vitamina D/sangreRESUMEN
The rate-limiting, hormonally regulated step in the biosynthesis of the biologically active form of vitamin D, 1,25(OH)2D, is its 1alpha-hydroxylation in the kidney by the mitochondrial P450 enzyme, P450c1alpha. We have recently cloned the human P450c1alpha cDNA and shown that this enzyme is the factor disrupted in vitamin D-dependent rickets, type 1 (VDDR-1). To facilitate the analysis of further patients with VDDR-1 and to permit studies of the regulation of the gene for P450c1alpha, we have used PCR-based tactics to clone the gene. Southern blotting studies indicate that there is only one copy of this gene in the human genome. The complete sequence of all exons and introns show that the gene consists of 9 exons spanning only 5 kb; the entire protein-coding region can be PCR-amplified as a single 4-kb fragment. The transcriptional start site, located by primer extension and S1 nuclease protection, lies 62-bp upstream from the ATG transitional start codon. Analysis of rodent/human somatic cell hybrid DNAs show that this gene lies on chromosome 12. Although the gene is substantially smaller than the human genes for other mitochondrial enzymes, its intron/exon organization is very similar, especially to that of P450scc. This indicates that although the mitochondrial P450 enzymes retain only 30%-40% amino acid sequence identity, they all belong to a single evolutionary lineage.
Asunto(s)
25-Hidroxivitamina D3 1-alfa-Hidroxilasa/genética , Sistema Enzimático del Citocromo P-450/genética , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/metabolismo , Secuencia de Aminoácidos , Secuencia de Bases , Mapeo Cromosómico , Cromosomas Humanos Par 12 , Clonación Molecular , Sistema Enzimático del Citocromo P-450/metabolismo , Dosificación de Gen , Humanos , Datos de Secuencia Molecular , Análisis de Secuencia de ADN , Transcripción GenéticaRESUMEN
The secosteroid hormone, 1,25-dihydroxyvitamin D [1,25(OH)2D], plays a crucial role in normal bone growth, calcium metabolism, and tissue differentiation. The key step in the biosynthesis of 1,25(OH)2D is its 1 alpha-hydroxylation from 25-hydroxyvitamin D (25-OHD) in the kidney. Because its expression in the kidney is very low, we cloned and sequenced cDNA for 25-OHD-1 alpha-hydroxylase (P450c1 alpha) from human keratinocytes, in which 1 alpha-hydroxylase activity and mRNA expression can be induced to be much greater. P450c1 alpha mRNA was expressed at much lower levels in human kidney, brain, and testis. Mammalian cells transfected with the cloned P450c1 alpha cDNA exhibit robust 1 alpha-hydroxylase activity. The identity of the 1,25(OH)2D3 product synthesized in transfected cells was confirmed by HPLC and gas chromatography-mass spectrometry. The gene encoding P450c1 alpha was localized to chromosome 12, where the 1 alpha-hydroxylase deficiency syndrome, vitamin D-dependent rickets type 1 (VDDR-1), has been localized. Primary cultures of human adult and neonatal keratinocytes exhibit abundant 1 alpha-hydroxylase activity, whereas those from a patient with VDDR-1 lacked detectable activity. Keratinocyte P450c1 alpha cDNA from the patient with VDDR-1 contained deletion/frameshift mutations either at codon 211 or at codon 231, indicating that the patient was a compound heterozygote for two null mutations. These findings establish the molecular genetic basis of VDDR-1, establish a novel means for its study in keratinocytes, and provide the sequence of the key enzyme in the biological activation of vitamin D.
Asunto(s)
25-Hidroxivitamina D3 1-alfa-Hidroxilasa/genética , Trastorno Mineral y Óseo Asociado a la Enfermedad Renal Crónica/enzimología , Trastorno Mineral y Óseo Asociado a la Enfermedad Renal Crónica/genética , Clonación Molecular , Mutación , 25-Hidroxivitamina D3 1-alfa-Hidroxilasa/fisiología , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Línea Celular , Células Cultivadas , Trastorno Mineral y Óseo Asociado a la Enfermedad Renal Crónica/congénito , ADN Complementario/biosíntesis , ADN Complementario/aislamiento & purificación , Femenino , Humanos , Lactante , Queratinocitos , Células Intersticiales del Testículo , Masculino , Ratones , Datos de Secuencia Molecular , Especificidad de Órganos/genética , ARN Mensajero/biosíntesisRESUMEN
To determine whether aging impairs renal responsiveness to PTH, we studied the ability of the kidney to respond to infusion of human PTH-(1-34) for 24 h in 16 healthy men, 9 young (39 +/- 1 yr) and 7 elderly (70 +/- 1 yr), free of any conditions known to influence mineral metabolism and in whom the glomerular filtration rate was greater than 1.17 mL/s.1.73 m2. Basal concentrations of blood ionized calcium, serum 1,25-dihydroxyvitamin D [1,25-(OH)2D], and urinary calcium and phosphorus were similar in both age groups, but basal serum PTH (+148%), plasma cAMP (+44%), nephrogenous cAMP (+56%), and fractional excretion of phosphorus (+44%) were higher in the elderly. PTH infusion increased serum 1,25-(OH)2D to the same maximum level in the young (113 +/- 10 pmol/L) and the elderly (106 +/- 11 pmol/L) men, but the response in the elderly was delayed. Urinary cAMP, nephrogenous cAMP, and fractional excretion of phosphorus increased, and neither the time course nor the increment was significantly different between age groups. The phosphate threshold concentration decreased in response to PTH to the same extent in both age groups. The results demonstrate that although the increment in serum 1,25-(OH)2D in the elderly may be delayed relative to that in the young, renal responsiveness to a 24-h PTH infusion is similar in healthy young and elderly men in whom glomerular filtration rate is normal or near normal.
Asunto(s)
Envejecimiento/fisiología , Riñón/efectos de los fármacos , Teriparatido/farmacología , Adulto , Anciano , Calcio/orina , AMP Cíclico/sangre , AMP Cíclico/orina , Tasa de Filtración Glomerular , Humanos , Masculino , Hormona Paratiroidea/sangre , Fosfatos/orina , Proteínas Recombinantes , Valores de Referencia , Vitamina D/análogos & derivados , Vitamina D/sangreRESUMEN
We tested the hypothesis that aging alters physiological regulation of the serum concentration of 1,25-dihydroxyvitamin D [1,25(OH)2D] by inorganic phosphorus. In seven elderly men [age 71 +/- 1 (SE) yr] and 9 young men (29 +/- 2 yr), dietary phosphorus was first normal, then increased and decreased within its normal range. At each intake of phosphorus, serum concentrations of 1,25(OH)2D in the elderly did not differ from those in young men, but fasting and 24-h mean serum concentrations of phosphorus were lower in elderly men. With phosphorus restriction, in each group serum 1,25(OH)2D increased by 47%, and 24-h mean serum phosphorus decreased by 0.6 +/- 0.1 mg/dl. Serum concentrations of 1,25(OH)2D varied inversely with 24-h mean serum phosphorus (R= -0.92, P<0.0001). Thus, in healthy elderly men in whom glomerular filtration rate is normal or near normal, serum concentrations of 1,25(OH)2D increase when dietary phosphorus is restricted; the magnitude of response at steady state is unaffected by aging, but the time course of response is delayed. At any level of serum phosphorus, serum 1,25(OH)2D is lower than that in young men, as reflected by a lower intercept of regression of serum 1,25(OH)2D on 24-h mean phosphorus.