Tissues, selenomethionine

Selenium. Selenium, thought to be widely distributed throughout body tissues, is present mostly as selenocysteine in selenoproteins or as selenomethionine (113,114). Animal experiments suggest that greater concentrations are in the kidney, Hver, and pancreas and lesser amounts are in the lungs, heart, spleen, skin, brain, and carcass (115). 

Selenomethionine group had altered immune function, altered serum enzyme activities, and elevated concentrations of selenium in liver (4 times control values) and breast muscle (14 times). Sodium selenite-treated birds had normal immune function and selenium tissue burdens however, serum enzyme activity was disrupted in the 3.5 mg/L group Adults normal. Impaired reproduction (reduced survival of ducklings, increased developmental abnormalities) for selenomethionine occurs between 4 and 8 mg/kg ration selenocysteine did not impair reproduction at 16 mg Se/kg ration... 

Lorentzen, M., A. Maage, and K. Julshamn. 1994. Effects of dietary selenite or selenomethionine on tissue selenium levels of Atlantic salmon (Salmo salar). Aquaculture 121 359-367. 

Moksnes, K. 1983. Selenium deposition in tissues and eggs of laying hens given surplus of selenium as selenomethionine. Acta Vet. Scand. 24 34-44. 

In terms of human dietary requirements, much of the wheat for breadmaking in the United States is produced in selenium-adequate sections of the country. Bread is generally a good source of dietary selenium, Selenomethionine decomposes lipid peroxides and inhibits in vivo lipid peroxidation in tissues of vitamin-E-deficient chicks. Selenocysdne catalyzes the decomposition of organic hydroperoxides. Selenoproteins show a high degree of inhibition of lipid peroxidation in livers of sheep, chickens, and rats, Thus, some forms of selenium exhibit in vivo antioxidant behavior,... 

Deagen, J.T., Butler, J.A., Beilstein, M.A., and Whanger, P.D. 1987. Effects of dietary selenite, selenocysteine and selenomethionine on selenocysteine lyase and glutathione peroxidase activities in rat tissues. J. Nutr. 117, 91—98. 

Hansson, E. and Jacobsson, S.-O. 1966. Uptake of [75Se]selenomethionine in the tissues of the mouse studied by whole-body autoradiography. Biochim. Biophys. Acta 115, 285-293. 

Martin, J.L. and Hurlbut, J.A. 1976. Tissue selenium levels and growth responses of mice fed selenomethionine, Se-methylselenocysteine or sodium selenite. Phosphorus and Sulfur 1, 295-300. 

Waschulewski, I.H. and Sunde, R.A. 1988. Effect of dietary methionine on tissue selenium and glutathione peroxidase on tissue selenium and glutathione peroxidase (EC 1.11.1.9) activity given selenomethionine. Br. J. Nutr. 60, 57-68. 

Selenium Speciation in Edible Animal Tissues Reports on Se specia-tion analysis in edible animal tissues have been scarce. Speciation analysis of Se in cod muscle tissue was performed by separating the species using both RP- and SE-HPLC prior to ICP-MS detection. The main Se compound found in enzymatic hydrolysates was selenomethionine [42], This selenocompound was absent in MeOHDHCl extracts, indicating that Se was mainly incorporated into proteins. A number of unidentiFed Se species were also detected in cod muscle tissue, the separated Se compounds being quantised on-line by post-column isotope dilution [42], Soluble Se compounds extracted from muscles of chicken, turkey, duck, ostrich, lamb, cattle, and pig were separated by SEC with ICP-MS detection. Four peaks were observed, but distribution of Se among these peaks varied considerably in tissues from different animal species [86]. 

Enzymes such as protease in conjunction with pancreatin and amylase have been extensively used to liberate Se species from proteins for analysis [43, 57, 128, 133-136]. Relatively long times ( 24 h) are required to fully hydrolyze proteins using enzymes. However, not all Se is released as simple amino acids. Some peptides, and small molecular weight proteins remain. Thus, ultrafiltration (< 1 kDa) before analysis will be needed to separate amino acids from other material with higher molecular weight. In the presence of cysteine, selenomethionine and selenocysteine are stable to enzyme attack (Fig. 20.2). However, although large amounts of Se are released from marine tissues (30-60 percent), little (less than 10-20 percent) is characterizable by HPLC-ICP-MS. 

Figure 20.3. HPLC-ICP-MS separation of 6 M HCl-0.05% m/v cysteine hydrolyzed selenoamino acid standards and Mugil cephalus muscle tissue, (a) Cation exchange of hydrolyzed selenomethionine and muscle tissue, Supelcosil LC-SCX cation exchange column, 20 mM pyridine-formic acid, 1.5 ml min-1, 40°C, pH 2.5. (b) Anion exchange of hydrolyzed selenocystine and muscle tissue. Chromatography conditions as in Figure 20.1.

I opics of continuing concern in Se nutrition include the availability of Se when supplied as selenomethionine or sodium selenite and the definition of normal levels of tissue selenium and the normal activity of GSH peroxidase. In many tissues, the Se asst>ciated with GSH peroxidase accounts for only a small proportion of tissue Sc, This situation raises the question of whether values of tissue Se or of enzyme activity can more accurately define adequate or optimal Se status. 

Salbe, A. D., and Levander, O. A. (1990). Comparative toxicity and tissue retention of selenium in methionine-deficient rats fed sodium selenate or L-selenomethionine. /. Nutr. 120, 207-212. 

Selenium accumulates in many organ systems in the body in general, the highest concentrations are found in the liver and kidney (Table 3-6). Selenium concentrations in tissues do not seem to be correlated with effects. Tissue concentrations were highest in pigs fed D,L-selenomethionine, while a similar dose of selenium (form not stated) given as A. bisulcatus was a more potent neurotoxin. Blood, hair, and nails also contain selenium, and selenium has been found in human milk (Table 3-7). In addition, selenium is subject to placental transfer. 

The most important differences between the selenite and selenomethionine models lie in the turnover times. The estimated turnover times in the plasma, liver/pancreas, and tissues are shorter for selenomethionine than for selenite, but the estimated turnover time for the whole body is more than twice as long for selenomethionine as for selenite. This is probably because selenite is not recirculated, whereas selenomethionine is extensively recycled, passing through the individual organs and tissues many times before being excreted. 

Target tissues. The model is designed to simultaneously account for the appearance and disappearance of selenium in plasma, urine, and feces after administration of a single oral dose of 74Se as selenomethionine (Patterson et al. 1993 Swanson et al. 1991). 

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