Extensive Taurine Depletion and Retinal Degeneration in Cats Treated with β-Alanine for 40 Weeks
It has now been established that cats are dependent on dietary sources of taurine to maintain their body reserve, and when deprived, they develop a variety of disorders including retinal degeneration, myocardial failure, depressed immune responsiveness and extensive reproductive deficits37,38,39. Feline central retinal degeneration, a photoreceptor degenerative condition originally described as bilaterally symmetrical generalized focal lesions of unknown etiology3,4,26, was among the first to be clearly linked to taurine deficiency16. The small incipient lesions visible by fundus ophthalmoscope as hyper-reflective round or oval foci in the area centralis, extend nasally and temporally in advanced stages of taurine deprivation accompanied by significant reductions in rod and cone ERG amplitudes5,6,34. The progression of retinal degeneration, however inevitable, is a relatively slow process and takes at least 6 to 12 months for cats fed a completely taurine-free diet to show the first signs. Moreover, tissue taurine levels are lowered only to the point that equilibrium with biosynthesized taurine is reached, with considerable individual variation, no matter how long cats are maintained on such a diet. In an attempt to reduce tissue taurine levels further, we provided adult female cats with β-alanine which competes with taurine for the same transport system, thereby limiting taurine uptake21,25. Previously, we reported that tissue taurine concentrations were greatly reduced while large amounts of β-alanine accumulated in visceral tissues and neural tissues of acutely taurine-depleted cats after 20 weeks of ß-alanine treatment42. The morphological changes associated with photoreceptor degeneration in the retinas of these cats were considerably more extensive and widespread than any described in cats rendered taurine-deficient by means of taurine-free diet alone17,40. In the present report we describe the consequence of extreme taurine depletion attained by extending the period of ß-alanine treatment to 40 weeks.
KeywordsOuter Segment Retinal Degeneration Outer Nuclear Layer Photoreceptor Degeneration Taurine Concentration
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