Vitam Horm
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An estimated 25 million lives have been lost to acquired immune-deficiency syndrome (AIDS) since the immunodeficiency syndrome was first described in 1981. The progress made in the field of treatment in the form of antiretroviral therapy (ART) for HIV disease/AIDS has prolonged as well as improved the quality of life of HIV-infected individuals. However, access to such treatment remains a major concern in most parts of the world, especially in the developing countries. ⋯ Further, multivitamin supplementation reduces the rate of HIV disease progression among patients in early stage of disease, thus delaying the need for ART by prolonging the pre-ART stage. In brief, there is no evidence to recommend vitamin A supplementation of HIV-infected pregnant women; however, periodic vitamin A supplementation of HIV-infected infants and children is beneficial in reducing all-cause mortality and morbidity and is recommended. Similarly, multivitamin supplementation of people infected with HIV, particularly pregnant women, is strongly suggested.
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Retinol-binding protein (RBP) is the retinol-specific transport protein present in plasma. The available crystal structures of different forms of RBP have provided details of the interactions of this binding protein with retinol, retinoids, and transthyretin (TTR, one of the plasma carriers of thyroid hormones). The core of RBP is a beta-barrel, the cavity of which accommodates retinol, establishing with its buried portions apolar contacts. ⋯ Limited protein conformational changes affecting the entrance loops, which lead to a decrease or loss of the binding affinity of RBP for TTR, have been demonstrated for apo-RBP and RBP in complex with retinoids modified in the area of the retinol hydroxyl. A relatively small number of amino acid residues of RBP, essentially confined to the region of the entrance loops, and of TTR appear to play a critical role in the formation of the RBP-TTR complex, as established by crystallographic studies, mutational analysis, and amino acid sequence analysis of phylogenetically distant RBPs and TTRs. Overall, the available evidence indicates the existence of a high degree of complementarity between RBP and TTR, the contact areas of which are highly sensitive to conformational changes and amino acid replacements.
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The regulation of body weight in humans is coordinated by the interplay between food intake and energy expenditure. The identification of the adipocyte-secreted hormone leptin as a key regulator on both of these processes has shed new light on the pathways involved in their regulation. Indeed, mutations in the gene's encoding leptin and its cognate receptor cause severe obesity in humans. ⋯ Among these is the proopiomelanocortin (POMC)-derived peptide, alpha-melanocyte-stimulating hormone (alpha-MSH), which is produced in the arcuate nucleus and is a potent negative regulator of food intake. Like leptin, mutations in POMC or in central melanocortin receptors lead to obesity in humans. Thus, an understanding of the mechanisms by which the leptin and melanocortin pathways signal in the hypothalamus is critical in order to begin to clarify the pathways involved in regulating body weight in humans.