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      Distúrbios do eixo cálcio-PTH-vitamina D nas doenças hepáticas crônicas Translated title: Disturbances of calcium-PTH-vitamin D axis in chronic liver diseases

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          Abstract

          Distúrbios no eixo cálcio-PTH-vitamina D são freqüentemente associados às doenças hepáticas crônicas (DHC). Já foi demonstrado que pacientes com DHC apresentam uma tendência à diminuição do cálcio e vitamina D, com aumento compensatório do PTH. Embora a diminuição da hidroxilação da vitamina D em 25 (OH) vitamina D fosse considerada o mecanismo principal destas alterações, estudos recentes vêm demonstrando que, mesmo nos estágios avançados de doença, o fígado ainda consegue manter níveis adequados de 25 (OH) vitamina D. Desta forma, outros fatores (ex: dieta inadequada, diminuição da exposição à luz solar) seriam os responsáveis pelas alterações no eixo cálcio-PTH-vitamina D. Além disso, o tratamento das DHC com glicocorticóides (fibrose cística) e ribavirina (Hepatite C) parece contribuir como agravante destes distúrbios. Por outro lado, parece ser a osteoporose, e não a osteomalácia ou o hiperparatireoidismo secundário, a principal alteração nas DHC. Assim, continua objeto de discussão o papel das alterações do eixo cálcio-PTH-vitamina D na osteodistrofia hepática.

          Translated abstract

          Disturbances in Calcium-PTH-Vitamin D axis are frequently associated with chronic liver diseases (CLD). In patients with CLD, a trend toward decreased serum calcium and vitamin D has already been demonstrated with compensatory increases in PTH levels. Even though reduced vitamin D hydroxylation has been considered the most important mechanism for these alterations, recent studies demonstrates an adequate production of 25(OH) Vitamin D even in end-stage liver disease. Therefore, other factors (i.e. inadequate diet, reduced exposure to sun light) would be responsible for the disturbances in calcium-PTH-vitamin D axis. Furthermore, antiviral drugs (such as ribavirin for hepatitis C) and glucocorticoids (cystic fibrosis) may also contribute to the worsening of these disturbances. On the other hand, osteoporosis, but not osteomalacia or secondary hyperparathyroidism, seems to be the main alteration in CLD. Thus, the clinical relevance of calcium-PTH-vitamin D disturbances in hepatic osteodistrophy is still under discussion.

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          Most cited references62

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          Intestinal absorption of cholecalciferol and 25-hydroxycholecalciferol in chronic cholestatic liver disease.

          We compared the absorption of cholecalciferol and 25-hydroxycholecalciferol in normal subjects and in patients with mild and severe cholestatic liver disease. 3H-cholecalciferol and 3H-25-hydroxycholecalciferol were given orally and serial blood samples were drawn for measurement of the serum level of radiolabeled vitamin. Absorption of 25-hydroxycholecalciferol peaked earlier and was greater than absorption of cholecalciferol at all times in all three groups. Patients with mild cholestasis (normal bilirubin and fecal fat excretion) absorbed both forms of the vitamin normally. Those with severe cholestasis (jaundice and steatorrhea) had minimal absorption of cholecalciferol but relatively preserved absorption of 25-hydroxycholecalciferol. Absorption of cholecalciferol and 25-hydroxycholecalciferol was inversely related to fecal fat excretion. The superior absorption of 25-hydroxycholecalciferol may partly explain its greater efficacy in oral treatment of vitamin D deficiency in patients with severe cholestasis.
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            Hepatic osteodystrophy in chronic cholestasis: evidence for a multifactorial etiology.

            Children with cholestatic liver disease have been thought to develop hepatic osteodystrophy resulting from vitamin D and calcium malabsorption, resulting in secondary hyperparathyroidism and osteomalacia or rickets. However, treatment with vitamin D has not always proven successful in improving the bone disturbance. The aim of our study was to determine the role of vitamin D deficiency in the pathogenesis of hepatic osteodystrophy. We studied five patients, three female and two male, ages 0.9-19 yr, with biopsy-proven chronic cholestatic liver disease and previously low serum levels of vitamin D despite oral intake of vitamin D preparations. Patients were admitted to the Clinical Research Center for 8 days for sunlight deprivation and ultraviolet light substitution and for determinations of serum 25-hyroxyvitamin D(25(OH)) D2 and -D3, osteocalcin, and type I collagen telopeptide (ICTP), the last two being markers of bone formation and resorption, respectively. Samples were taken on admission, at discharge, and 1 month later. Results demonstrated low serum levels of osteocalcin and normal circulating levels of ICTP. Admission serum 25(OH)D2 levels were uniformly low or undetectable and remained so. Admission levels of circulating 25(OH)D3 were normal or low and did not rise during ultraviolet light therapy or subsequent resumption of oral vitamin D therapy and remained low 1 month later. These results indicate that in the face of low-normal to low total 25(OH)D levels, the low osteocalcin and normal ICTP levels suggest that decreased bone formation and not increased bone resorption is the main determinant of bone loss in a subset of children with chronic cholestatic liver disease.
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              Subcutaneous administration of insulin-like growth factor (IGF)-II/IGF binding protein-2 complex stimulates bone formation and prevents loss of bone mineral density in a rat model of disuse osteoporosis.

              Elevated serum levels of insulin-like growth factor binding protein-2 (IGFBP-2) and a precursor form of IGF-II are associated with marked increases in bone formation and skeletal mass in patients with hepatitis C-associated osteosclerosis. In vitro studies indicate that IGF-II in complex with IGFBP-2 has high affinity for bone matrix and is able to stimulate osteoblast proliferation. The purpose of this study was to determine the ability of the IGF-II/IGFBP-2 complex to increase bone mass in vivo. Osteopenia of the femur was induced by unilateral sciatic neurectomy in rats. At the time of surgery, 14-day osmotic minipumps containing vehicle or 2 microg IGF-II+9 microg IGFBP-2/100g body weight/day were implanted subcutaneously in the neck. Bone mineral density (BMD) measurements were taken the day of surgery and 14 days later using a PIXImus small animal densitometer. Neurectomy of the right hindlimb resulted in a 9% decrease in right femur BMD (P<0.05 vs. baseline). This loss in BMD was completely prevented by treatment with IGF-II/IGFBP-2. On the control limb, there was no loss of BMD over the 14 days and IGF-II/IGFBP-2 treatment resulted in a 9% increase in left femur BMD (P<0.05). Bone histomorphometry indicated increases in endocortical and cancellous bone formation rates and in trabecular thickness. These results demonstrate that short-term administration of the IGF-II/IGFBP-2 complex can prevent loss of BMD associated with disuse osteoporosis and stimulate bone formation in adult rats. Furthermore, they provide proof of concept for a novel anabolic approach to increasing bone mass in humans with osteoporosis.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Journal
                abem
                Arquivos Brasileiros de Endocrinologia & Metabologia
                Arq Bras Endocrinol Metab
                Sociedade Brasileira de Endocrinologia e Metabologia (São Paulo )
                1677-9487
                August 2004
                : 48
                : 4
                : 443-450
                Affiliations
                [1 ] Universidade Federal do Rio de Janeiro Brazil
                Article
                S0004-27302004000400004
                10.1590/S0004-27302004000400004
                c1d3647d-234f-4cd9-966e-9a86716feee4

                http://creativecommons.org/licenses/by/4.0/

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                Product

                SciELO Brazil

                Self URI (journal page): http://www.scielo.br/scielo.php?script=sci_serial&pid=0004-2730&lng=en
                Categories
                ENDOCRINOLOGY & METABOLISM

                Endocrinology & Diabetes
                Chronic liver diseases,Calcium,Vitamin D,Parathyroid hormone,Hepatic osteodistrophy,Doenças hepáticas crônicas,Cálcio,Vitamina D,PTH,Osteodistrofia hepática

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