Retina, zinc

P2X2 Smooth muscle, CNS, retina, chromaffin cells, autonomic and sensory ganglia ATP>ATPyS>2- MeSATP > > a,p-meATP (pH + zinc sensitive) Suramin, isoPPADS, RB2, NF770, NF279 Intrinsic ion channel (particularly Ca2+)... 

Spiridon, M., Kamm, D Billups, B., Mobbs, P, and Attwell, D. (1998) Modulation by zinc of the glutamate transporters in glial cells and cones isolated from the tiger salamander retina../. Physiol. (Lond). 506, 363-376. 

In addition to its function in catalysis, zinc often plays an important structural role, e.g., in the zinc finger transcriptional regulators (Fig. 5-38).k Zinc ions bind to insulin and stabilize its hexameric structure (Fig. 7-18)/ Six Zn2+ ions are present in the hexagonal tail plate of the T-even bacteriophage (Box 7-C) and appear to be essential for invasion of bacteria.131 In carnivores, the tapetum, the reflecting layer behind the retina of the eye of many animals, contains crystals of the Zn2+-cysteine complex. 

Nevertheless, at least six randomized, double-blind, placebo-controlled, intervention trials have assessed the effect of vitamin or micronutrient supplements on AMD risk. The consensus from these and other trials seems to suggest a positive response of the retina as well as improved visual performance from vitamin and mineral supplementation such as the AREDS formulation (see above). Specifically, the AREDS results should be interpreted as understanding that the formulation was effective in slowing the risk of progression of AMD in persons 55 years of age and older who had some macular changes consistent with early age-related maculopathy. More recently, substantiation of these results was reported on a primarily white population as part of the Rotterdam Study. An above-median intake of beta-carotene, vitamin C, vitamin E, and zinc was associated with a 35% reduced risk of AMD. Still other clinical research has demonstrated shortterm beneficial effects in small populations for lutein and a combination of lutein and antioxidants in AMD. 

Biochemical research has shown the importance of zinc metabolism in the retina (9). Zinc is found in high concentrations in the choroid, the retina, and especially the ganglion cells. Retinol dehydrogenase, a zinc-containing enzyme, interferes with the transformation of retinol (vitamin Ai), which is essential for color sensation and conal vision. Furthermore, zinc is involved in the biosynthesis of the specific transport of retinol from the liver to the effector cells. Ethambutol is a chelating... 

It is estimated that the zinc content of a normal 70-kg male is approximately 1.5-2.0 gm. Liver, kidney, bone, retina, prostate, and muscle appear to be rich in zinc. In man, zinc content of testes and skin has not been determined accurately, although clinically it appears that these tissues are sensitive to zinc depletion. 

Total adult body content of zinc is about 2 to 2.5 g and the metal is present in the cells of aU metabolically active tissue and organs. About 55% of the total is found in muscle and approximately 30% in bone. The prostate, semen, and the retina have particularly high local concentrations of zinc. Almost aU zinc in a red cell is in the form of carbonic anhy-drase so that red cell zinc concentration is about 10 times higher than plasma. Hemolysates normally have about 50 fig Zn per g Hb, and total leukocyte zinc is normally about 100 25(J,g/10 cells. 

It has been reported (Leiner and Leiner, 1944) and confirmed (Bowness et al., 1952) that retina contains high concentrations of zinc. Horse liver ADH oxidizes vitamin Ai and reduces retinene, probably being identical with retinene reductase (Bliss, 1949 Theorell and Bonnichsen, 1951a). 

Since mammalian ADH has been found to be a zinc enzyme, enzymologicial and analytical observations on liver, retina and those of yeast ADH may be shown to have an analogous structural denominator. 

Nakamichi N, Chidlow G, Osborne NN. 2003. Effects of intraocular injection of a low concentration of zinc on the rat retina. Neuropharmacology 45 637-648. 

Ophir A, Berenshtein E, Kitrossky N, Averbukh E. 1994. Protection of the transiently ischemic cat retina by zinc-desferrioxamine. Invest Ophthalmol Vis Sci 35 1212-1222. 

Other Metal-Peptide and -Protein Interactions.—The determination of protein-bound trace elements in biological material by neutron activation analysis has been described Zn, Hg, Cu, and Se were accurately detected in human liver samples, provided that most of the element concerned was protein bound. An interaction of mercury with a protein or a protein-DNA complex has been invoked to explain the partitioning of the metal in euchromatin over heterochromatin (from mouse liver nuclei) by a 10 1 ratio. " Bovine retinas, isolated rod outer segments and emul-phogene extracts of rod outer segments have been shown to contain appreciable amounts of Zn ", Ca and the zinc levels being light sensitive. 

Zinc snlfate is absorbed poorly from the G1 tract only 20 to 30% of dietary zinc is absorbed. After administration, zinc resides in mnscle, bone, skin, kidney, liver, pancreas, retina, prostate, and, particnlarly, red and white blood cells. Zinc binds to plasma albnmin, alpha-2 macroglobulin, and some plasma amino acids inclnding histidine, cysteine, threonine, glycine, and asparagine. 

Zinc Retina and retinal pigment epithelium ( macular degeneration)... 

Among humans, abnormal dark adaptation is reported in both vitamin A deficiency and zinc deficiency and is especially prevalent in alcoholic cirrhotics (Patek and Haig, 1939 Russell et aL, 1973 Morrison et aL, 1978 McClain et aL, 1979). In the former but not in the latter deficiency, treatment with vitamin A reverses the abnormality (Russell et aL, 1978) only after correcting the zinc deficiency does dark adaptation become normal in the latter case (Morrison et aL, 1978 McClain et aL, 1979). The molecular basis for these observations may be associated, at least in part, with the activity of retinaldehyde reductase in the retina which, as already mentioned, Huber and Gershoff (1975) showed to be especially sensitive to the level of zinc nutriture and Mezey and Holt (1971) showed was competitively inhibited by the presence of ethanol. In the alcoholic cirrhotic, however, the zinc-vitamin A interaction may be further complicated by a defective hepatic synthesis of transport proteins (Mobarhan et aL, 1981) or failure to sequester or retain zinc Nutrition Reviews, 1982) and/or vitamin A (Sato and Lieber, 1981 Leo and Lieber, 1982) in the appropriate tissues. The implications for human nutrition of the interaction of vitamin A and zinc were reviewed by Solomons and Russell (1980). 

Main side effects Local reactions, auditory, retina, allergy, bone abnormalities, Yersinia infection Gastrointestinal (GI), neutropenia/ agranulocytosis, arthralgia, Uver enzyme rise, zinc deficiency GI, rash, renal, Uver... 

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