The distribution of cystathionine beta-synthase (CBS) in the eye: implication of the presence of a trans-sulfuration pathway for oxidative stress defense.

Clinical abnormalities in cystathionine-beta-synthase (CBS) deficiency, a key enzyme in the trans-sulfuration pathway, associate with many eye disorders. However, little is known about this enzyme in the eye. The goal of this study is to examine the distribution of CBS in the various regions of the eye, including conjunctiva, cornea, iris, lens, vitreous, retina and optic nerve using fresh eyes from both pigs (6 months) and humans (4-82 years). We have found that pig eye showed the highest CBS protein presence in cornea, conjunctiva and iris, followed by retina and optic nerve. The whole lens had a relatively lower amount and vitreous body had none. CBS protein distribution in the human eyes showed a similar pattern, with high level in the anterior segments but much lower amount in retina and optic nerve. CBS in anterior segments remained high throughout the lifespan, but retinal CBS showed a trend of age-dependent increase. The presence of CBS in human and pig eye tissues was further confirmed by RT-PCR, CBS activity assay, both showed similar distribution profiles as the Western blot analysis. This is the first evidence of the presence of CBS enzyme in the eye outside of the lens, which indicates that a functional trans-sulfuration pathway may be present in various eye tissues.