Die effek van organiese en anorganiese selenium op die immuunsisteem van skape

Abstract

AFRIKAANS: Die effek van die organiese en anorganiese vorme van selenium op sekere parameters van die immuunsisteem van skape, is ondersoek. Die potensiele gevaar wat die supplementering van hierdie twee seleniumbronne teen hoë vlakke in die dieet, op die immuunstelsel van skape inhou, is ook bestudeer. Daar is verder ook gekyk na die mate van akkumulering van selenium wat in verskillende weefsels in die liggaam, na supplementering van organiese en anorganiese selenium teen verskillende konsentrasies, plaasvind. 'n Seleniumryke gis is as bron van organiese selenium gebruik en aan drie groepe Vleismerino skape gesupplementeer teen vlakke van 6 mg/skaap/dag, 1.5 mg/skaap/dag en 0.75 mg/skaap/dag. Natriumseleniet is as bron van anorganiese selenium gebruik om drie ander groepe diere teen dieselfde vlakke te supplementeer. 'n Sewende groep, wat geen seleniumsupplementering ontvang het nie, het as kontrole gedien. Die supplementering van organiese selenium teen vlakke van 6 mg/skaap/dag, 1.5 mglskaap/dag en 0.75 mg/skaap/dag, het, in vergelyking met anorganiese selenium, tot 'n betekenisvolle hoër akkumulering van selenium in die skelet- en hartspier gelei. Selenium wat in 'n organiese vorm teen vlakke van 6 mg/skaap/dag en 1.5 mg/skaap/dag gesupplementeer is, het 'n betekenisvolle hoër akkumulering van selenium in die volbloed, plasma, nierkorteks en lewer, veroorsaak. Geen betekenisvolle verskille tussen organiese en anorganiese selenium is, in terme van seleniumakkumulering in die volbloed, plasma, nierkorteks en lewer, by 'n supplementeringsvlak van 0.75 mg/dag waargeneem nie. Daar is ook gevind dat die seleniumvlakke in die volbloed nie betekenisvol van mekaar verskil het wanneer die diere met 0.75 en 1.5 mg/dag anorganiese selenium gesupplementeer is nie. Dit dui daarop dat seleniumkonsentrasie in die volbloed moontlik nie 'n akkurate voorspeller van seleniuminname, wanneer diere anorganiese selenium in die dieet ontvang, is nie. Die gemiddelde superoksiedproduksie deur gestimuleerde neutrofiele was betekenisvol laer vir die groep met 'n 0.75 mg/dag anorganiese seleniumsupplementering. Hierdie resultate stel voor dat selenium, wat as natriumseleniet teen 'n vlak van 0.75 mg/dag aan skape gesupplementeer word, as antioksidant optree. Die antioksidatiewe eienskappe veroorsaak 'n opruiming van superoksied, wat deur die gestimuleerde neutrofiele geproduseer word. Die hoer T limfosietteIlings en laer kreatien fosfokinase aktiwiteit in die serum van hierdie groep dui op 'n beter membraanbeskerming van die T limfosietmembrane en spierselmembrane en steun die hipotese dat 'n inname van 0.75 mg/dag anorganiese selenium, bo-op die selenium wat natuurlik in die dieet teenwoordig is, as antioksidant in die liggaam optree. Die skape wat 1.5 mg/dag natriumseleniet as supplement ontvang het, het die hoogste primêre en sekondere antiliggaamproduksie teen perd eritrosiete getoon. Die gemiddelde primere antiliggaamproduksie teen perd eritrosiete van die groep diere wat 6 mgldag anorganiese selenium ontvang het, was betekenisvollaer as die gemiddelde primere antiliggaamproduksie van die ander groepe gewees. Hierdie onderdrukking van antiliggaamproduksie kan toegeskryf word aan 'n vergiftigingseffek van 'n hoë anorganiese seleniuminname, wat nie by organiese selenium waargeneem is nie. Dit is moontlik as gevolg van die pro-oksidant eienskappe van 'n hoë vlak van seleniet. Hierdie pro-oksidant eienskappe van hoë vlakke van natriumseleniet inname word ondersteun deur die definitiewe spierskade wat 'n supplementering van 6 mg/dag natriumseleniet veroorsaak het. 'n Inname van 6 mg/dag selenium, in beide organiese en anorganiese vorm, asook 1.5 mg selenium in anorganiese vorm, het tot 'n vergroting van die lewer gelei. Aangesien hierdie effek reeds by 'n veel laer vlak van aanvulling van anorganiese selenium gevind word, kan aangeneem word dat die inname anorganiese selenium 'n groter stremming op die lewer plaas. Daar word, na aanleiding van hierdie projek, aanvaar dat anorganiese selenium teen 'n supplementeringsvlak van 0.75 mg/dag/skaap, bo-op die selenium wat natuurlik in die dieet voorkom, voordelig vir die immuunsisteem is en membraanskade doeltreffend beperk. Hierdie vlak is ongeveer ekwivalent aan 'n totale seleniuminame van 0.44 mg selenium/kg gewig/dag, waarvan minstens 75% uit 'n anorganiese selenium bestaan. Geen toksiese effekte is by hierdie vlak waargeneem, soos in die geval by die hoër vlakke van anorganiese selenium, nie. Alhoewel die supplementering met hoër vlakke van organiese selenium nie werklik toksiese effekte, buiten die vergroting van die lewer, getoon het nie, is daar ook geen positiewe effekte op die immuunsisteem en beskerming van selmembrane, by laer vlakke gevind nie. Organiese selenium blyk slegs doeltreffend te wees as voersupplement waar die doel is om dierlike produkte, vir mensegebruik, met selenium te verryk. Hierdie supplementering kan dan ook met 'n hoer mate van veiligheid uitgevoer word as wat die geval met anorganiese selenium is. ENGLISH: The effects of organic and inorganic forms of selenium on the immune system of sheep have been investigated and the potential danger of high dietary levels has also been studied. The extent by which the accumulation of selenium in various tissues occurs, after supplementation of either organic or inorganic selenium at differing concentrations was also investigated. Selenium rich yeast as a source of organic selenium was used as a supplement at, respectively, 6mg/sheep/day, 1.5mg/sheep/day and 0.75mg/sheep/day to three groups of Mutton Merino sheep. Sodium selenite as source of inorganic selenium was used to supplement another three groups of animals at the same levels. A seventh group who did not receive any selenium supplementation served as a control. Supplementation of organic selenium in a yeast form led to significantly higher levels of selenium in the skeletal muscles and heart compared to sodium selenite in all three groups whereas supplementation of organic selenium at 6mg and 1.5mg/sheep/day led to significantly higher selenium levels in whole blood, plasma and kidney cortex compared to the groups supplemented with inorganic selenium at the same concentrations. It was also found that the selenium levels in whole blood did not differ significantly between the animals on 0.75 and 1.5mg/day inorganic selenium indicating that the selenium concentration in whole blood is possibly not an accurate indicator of selenium intake in the case of animals receiving inorganic selenium in their diet. The mean superoxide production by stimulated neutrophils was significantly lower in the group supplemented with inorganic selenium at 0.75mg/day suggesting that selenium, at that concentration, can act as an antioxidant. The anti-oxidative properties of selenium caused a scavenging of neutrophil-derived superoxide. This group of sheep also had a higher T¬lymphocyte count and lower creatinine phosphokinase activity in serum indicating a protection of T-Iymphocyte membranes and support the hypothesis that 0.75mg/day inorganic selenium can act as an anti-oxidant in the body. The sheep on 1.5mg/day sodium selenite supplementation produced the highest primary and secondary antibodies against horse erythrocytes. On the other hand, animals receiving inorganic sodium selenite at 6mg/day produced significantly lower levels of primary antibodies than any of the other groups indicating the poisonous effect of high inorganic selenium supplementation that was not observed with the animals on organic selenium supplementation. This is possible because of the pro-oxidative properties of high selenium levels. These pro-oxidative properties of high selenium levels produced by the high intake of sodium selenite are supported by specific muscle damage caused by the supplementation of 6mglday sodium selenite. An intake of 6mglday of selenium in both forms, as well as l.5mg selenium in inorganic form, led to enlargement of the liver. Because this effect was found at a much lower level with inorganic selenium supplementation, it can be concluded that inorganic selenium places a greater stress on the liver. With these results in mind, the conclusion can be drawn that inorganic selenium supplemented at a level of 0.75 mg/day/sheep, together with the natural occuring feed selenium, can be advantageous for the immune system by effectively protecting cell membranes against neutrophil mediated oxidative damage. This level is approximately equal to a total selenium intake of 0.44mglkg live weight/day, of which at least 75% consists of inorganic selenium. No toxic effect was observed at this level, as was the case with higher levels of inorganic selenium. Supplementation with high levels of organic selenium did not lead to any definitive toxic effects, except enlargement of the liver, but there were also no positive effects on the immune system or protection of the cell membranes found at lower levels. Organic selenium seems to be effective only in the case where it is used as food supplement with the purpose to enrich animal products for human use. Thus it would appear from the results of the study, that organic selenium offers a safer method of dietary supplementation.