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Abstract(s)
A vitamina D é uma hormona esteroide lipossolúvel sintetizada maioritariamente na pele pela
radiação ultravioleta (UVB) através do precursor 7-dehidrocolesterol ou de forma menos
frequente obtida pela dieta. A primeira hidroxilação ocorre no fígado com a formação da 25-
hidroxivitamina D, metabolito com pouca atividade, mas representativo das reservas desta
hormona. A segunda hidroxilação pode ocorrer nos rins pela CYP27B1 com formação da 1,25-
dihidroxivitamina D, metabolito ativo da vitamina D. A ação primária deste metabolito é
através do recetor nuclear da vitamina D, VDR, que se heterodimeriza com o recetor X
retinoide e se vai ligar a elementos responsivos da vitamina D próximos dos genes alvo. A
função mais conhecida da vitamina D é a homeostase dos níveis de cálcio e fósforo bem como
manter uma boa saúde óssea. Contudo há vários estudos que apontam para a associação da
vitamina D a várias patologias, como doenças cardiovasculares, doenças autoimunes e
doenças inflamatórias. Esta ampla distribuição clínica pode ser explicada pela expressão de
recetores VDR e da enzima CYP27B1 em vários órgãos além dos rins.
Para se dosear a vitamina D recorre-se ao 25-OHD havendo mais do que uma metodologia
aplicada a esta medição. Vários têm sido os problemas levantados na escolha da metodologia,
como a reatividade cruzada pelo 24,25-(OH)2D, um metabolito da vitamina D que permite que
haja um controlo adequado nos níveis das restantes formas. Existem ainda um conjunto de
fatores, para além do método usado, que podem interferir de forma negativa nos
doseamentos, realçando a necessidade crescente de estudos adicionais.
Neste projeto de investigação é feita uma análise estatística com base nos doseamentos dos
últimos 4 anos através de um imunoensaio de eletroquimioluminescência no equipamento
Cobas® 6000 (Roche). Este imunoensaio apresenta um anticorpo monoclonal que impede
reações cruzadas com o metabolito 24,25-(OH)2D.
Conclui-se assim nesta investigação que fatores como a estação do ano/meses interferem
significativamente no doseamento ainda que a maioria permaneça em hipovitaminose D.
Também o sexo parece ser um fator que intervém de forma significativa nos doseamentos,
apesar da contestação por parte de um elevado número de estudos. A avaliação dos
diagnósticos ainda carece de mais estudos, onde sejam avaliados outros parâmetros que
podem desfazer várias dúvidas até ao momento sentidas.
Vitamin D is a fat-soluble steroid hormone synthesized mostly in the skin by ultraviolet radiation (UVB) through the precursor 7-dehydrocholesterol or less commonly obtained by diet. The first hydroxylation occurs in the liver with the formation of 25-OHD, a metabolite with little activity, but representative of the hormone reserves. The second hydroxylation may occur in the kidneys by CYP27B1 with formation of 1,25-(OH)2D, active metabolite of vitamin D. The primary action of this metabolite is through the nuclear receptor of vitamin D, VDR, which is heterodimerized with the retinoid X receptor and whether it binds to vitamin D responsive elements near the target genes. The homeostasis of calcium and phosphorus levels as well as maintaining a good bone health are the most well known functions to Vitamin D. However, there are several studies that point to the association of this vitamin with various pathologies, such as cardiovascular diseases, autoimmune diseases and inflammatory diseases. This wide clinical distribution can be explained by the expression of VDR and CYP27B1 receptors in various organs aside from the kidneys. In order to provide a dosage of vitamin D one resorts to 25-OHD having in mind that there is more than one methodology to this measurement. Several problems have been raised regarding the choice of the methodology, such as the cross-reactivity for 24,25-(OH)2D, a metabolite of vitamin D that allows an adequate control of the levels of the remaining forms. There are still a set of factors, besides the method used, that can interfere negatively in the dosages, enhancing the increasing necessity of further studies. In this research project a statistical analysis is made based on the dosages of the last 4 years through an electrochemiluminescence immunoassay in the Cobas® 6000 equipment (Roche). This immunoassay presents a monoclonal antibody that prevents cross-reactions with the metabolite 24, 25-(OH)2D. It is concluded in this investigation that factors such as the season or certain months interfere significantly in the dosing even though most remain in hypovitaminosis D. Also, gender seems to be a factor that plays a significant role in the dosages, despite some challenge of a high number of studies. The evaluation of the diagnoses still lacks further studies, in which other parameters are evaluated and can undo several doubts felt so far.
Vitamin D is a fat-soluble steroid hormone synthesized mostly in the skin by ultraviolet radiation (UVB) through the precursor 7-dehydrocholesterol or less commonly obtained by diet. The first hydroxylation occurs in the liver with the formation of 25-OHD, a metabolite with little activity, but representative of the hormone reserves. The second hydroxylation may occur in the kidneys by CYP27B1 with formation of 1,25-(OH)2D, active metabolite of vitamin D. The primary action of this metabolite is through the nuclear receptor of vitamin D, VDR, which is heterodimerized with the retinoid X receptor and whether it binds to vitamin D responsive elements near the target genes. The homeostasis of calcium and phosphorus levels as well as maintaining a good bone health are the most well known functions to Vitamin D. However, there are several studies that point to the association of this vitamin with various pathologies, such as cardiovascular diseases, autoimmune diseases and inflammatory diseases. This wide clinical distribution can be explained by the expression of VDR and CYP27B1 receptors in various organs aside from the kidneys. In order to provide a dosage of vitamin D one resorts to 25-OHD having in mind that there is more than one methodology to this measurement. Several problems have been raised regarding the choice of the methodology, such as the cross-reactivity for 24,25-(OH)2D, a metabolite of vitamin D that allows an adequate control of the levels of the remaining forms. There are still a set of factors, besides the method used, that can interfere negatively in the dosages, enhancing the increasing necessity of further studies. In this research project a statistical analysis is made based on the dosages of the last 4 years through an electrochemiluminescence immunoassay in the Cobas® 6000 equipment (Roche). This immunoassay presents a monoclonal antibody that prevents cross-reactions with the metabolite 24, 25-(OH)2D. It is concluded in this investigation that factors such as the season or certain months interfere significantly in the dosing even though most remain in hypovitaminosis D. Also, gender seems to be a factor that plays a significant role in the dosages, despite some challenge of a high number of studies. The evaluation of the diagnoses still lacks further studies, in which other parameters are evaluated and can undo several doubts felt so far.
Description
Keywords
25-Dihidroxivitamina D 25-Hidroxivitamina D Eletroquimioluminescência Radiação Uvb Estação do Ano Hipovitaminose D