Is the lens canned?
The ocular lens somehow remains pellucid despite bombardment by ultraviolet radiation and endogenous hydrogen peroxide (present in the humoral fluids which bathe this tissue). The lens and adjacent aqueous and vitreous humors contain exceptionally high concentrations of reducing substances, particularly ascorbic acid, thought to be important in lenticular oxidant defense. However, in the presence of traces of transition metals, or when exposed to ultraviolet radiation, ascorbic acid readily reacts with oxygen, yielding hydrogen peroxide, and damaging lens crystallins. We propose the alternative hypothesis that the real antioxidant function of ascorbic acid, particularly that in the aqueous and vitreous humors, may be effecting the conversion of oxygen to water. Because the lens lacks a blood supply, coupled reactions of ascorbic acid with oxygen in the humoral fluid spaces should produce a metabolically sustained anaerobiosis. If so, nature may have preinvented the process of canning, wherein food (or in this case, the lens) is preserved by a combination of sterility and anoxia.
Eaton
J W
JW
Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis 55455.
D000818:Animals; D005609:Free Radicals; D007908:Lens, Crystalline / Q000502:physiology*; D010100:Oxygen / Q000502:physiology*
D005609:Free Radicals; D010100:Oxygen