Stoffwechselverhalten des anorganischen Kobalts und des in der Vitamin B12- bzw. Vitamin B12-Coenzym-Struktur organisch gebundenen Kobalts im Säugetier-Organismus

Abstract

Chromatographically pure, vitamin B12-free 60CoCl2 as well as 60Co-vitamin B12 (60Co-cyanocobalamin and 60Co-aquocobalamin) and 60Co-vitamin B12-coenzyme (60Co-5.6-dimethylbenzimidazol-C5′-deoxyadenosyl-cobamid) were given orally and by injection in smallest amounts (10 — 100 pMol = 0.59-5.9 ng Co2®, 100 pMol = 136 ng vitamin B12 and 100 pMol = 158 ng vitamin B12-coenzyme) to female Sprague-Dawley rats. The whole body retention and excretion of the 60Co label was measured in a large volume radioactivity detector with liquid organic scintillators and 4 π-geometry. The biological half life and whole body metabolic turnover rate were calculated for the inorganic and organic cobalt from the kinetics of the 60Co whole body retention. After oral application of 100 pMol 60Co2® nearly all the 60Co is excreted already after 2 days within the faeces (90%), and the urine (15%). Only about 0.9% of the 60Co2⊕ leaves the rats with a biological half life of 18 days. After intramuscular injection of 100 pMol 60Co2⊕ about 91% of the 60Co are excreted in the urine and 10% in the faeces within four weeks. Only 4.6% of the 60Co2⊕ were eliminated with a biological half life of 28 days. The intramuscular injection of only 10 pMol 60Co2⊕ resulted in a faecal excretion of 82%, and an urinary excretion of 21% of the 60Co. A biological half life of 23 days was calculated for 8.6% of the 60Co2⊕. Inorganic cobalt is therefore practically not retained in the body and rapidly excreted mainly with the urine after injection and mainly within the faeces after oral uptake. In contrast to the inorganic cobalt a completely different metabolic behaviour is typical for the cobalt, which is incorporated in the organic structure of the vitamin B12- and vitamin B12-coenzyme molecules. This organic cobalt accumulates in the storage organs and tissues (kidney, liver etc.) after absorption as well as after injection of 100 pMol 60Co-vitamin B12 and 60Co-vitamin B12coenzyme. Only 15% of the 60Co-cyanocobalamin and 9—10% of the 60Co-aquocobalamin and 60°Covitamin B12-coenzyme are excreted within 48 hours after injection. The organ and tissue incorporated 60Co-vitamin B12 and 60Co-vitamin B12-coenzyme is metabolized with a biological half life of about 52 days. From the whole body pool size of 20 μg vitamin B12 and the biological half life a metabolic turnover rate of 0.27 μg vitamin B12/day or 1.34% of the vitamin-B12-pool per days was calculated for the whole body of the rat. The lacking organ and tissue retention of absorbed and injected 60Co2⊕ and its short biological half life in rats (if compared with the organic cobalt in the vitamin B12-structure) as well as the comparison of the total cobalt content of human liver (measured by physical techniques) with the cobalt content calculated from the vitamin B12-content of human liver (measured by microbiological assay) do not support a biological significance and function of inorganic cobalt in mammals. There is no evidence at the moment that any cobalt besides the cobalt in the vitamin B12 and vitamin B12-coenzymes is existing and biochemically active in humans or animals.