Vitamin B12 and Cobalt Deficiency in Sheep

Cobalt-Induced Ototoxicity in Rat Postnatal Cochlear Organotypic Cultures

Cobalt (Co) is a required divalent metal used in the production of metal alloys, batteries, and pigments and is a component of vitamin B12. Excessive uptake of Co is neurotoxic causing temporary or permanent hearing loss; however, its ototoxic effects on the sensory hair cells, neurons, and support cells in the cochlea are poorly understood. Accordingly, we treated postnatal day 3 rat cochlear organotypic cultures with various doses and durations of CoCl2 and quantified the damage to the hair cells, peripheral auditory nerve fibers, and spiral ganglion neurons (SGN). Five-day treatment with 250 μM CoCl2 caused extensive damage to hair cells and neurons which increased with dose and treatment duration. CoCl2 caused greater damage to outer hair cells than inner hair cells; damage was greatest in the base of the cochlea and decreased towards the base. CoCl2 increased expression of superoxide radical in hair cells and SGNs and SGN loss was characterized by nuclear condensation and fragmentation, morphological features of apoptosis. CoCl2 treatment increased the expression of caspase-3 indicative of caspase-mediated programmed cell death. These results identify hair cells and spiral ganglion neurons as the main targets of Co ototoxicity in vitro and implicate the superoxide radical as a trigger of caspase-mediated ototoxicity.

The chemistry of anti-pernicious anaemia factors; 5:6-disubstituted benziminazoles as products of acid hydrolysis of vitamin B12

Evidence is presented for the presence of three chemically related substances, components α, β, and γ, in acid hydrolysates of vitamin B12. Spectroscopic examination of these components has led to their classification as benziminazole derivatives. Spectroscopic comparison with 22 methylated benziminazoles synthesised to serve as model compounds, has resulted in the identification of components α and β as 1:5:6-trisubstituted benziminazoles, and of component γ as a 5:6-disubstituted benziminazole. Preliminary paper chromatographic studies point to the identity of component γ with 5:6-dimethylbenziminazole; from which it is concluded that components α and β are both 1-substituted 5:6-dimethyl-benziminazoles. Spectroscopic and chemical evidence leads to the conclusion that only one 5:6-dimethylbenziminazole residue is released from vitamin B12 on acid hydrolysis and that the benziminazole nucleus exists preformed in the vitamin. It is, therefore, concluded that components α, β, and γ represent successive stages of degradation of a common precursor. The bearing of these results on the biogenesis and structure of vitamin B12 is briefly discussed. It is a pleasure to acknowledge the encouragement of the Directors of The British Drug Houses, Ltd., in this work. Footnote. While preparing this paper for publication we became aware at the meeting of the First International Congress of Biochemistry held at Cambridge in August, 1949, of the findings of Dr. K. Folkers and his colleagues, and at the same session we announced the conclusions we had reached in the work now reported (Holiday and Petrow, J. Pharm. Pharmacol, 1949, 1, 734).