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L. D. Marchette, M. A. Babizhayev, A. Kasus-Jacobi; The Pseudodipeptide Carcinine Protects Photoreceptors From Toxic Products of Oxidative Stress. Invest. Ophthalmol. Vis. Sci. 2009;50(13):688.
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© ARVO (1962-2015); The Authors (2016-present)
Toxic aldehydes such as 4-hydroxynonenal (4-HNE) are produced in photoreceptor cells by lipid peroxidation induced during exposure to bright light. If not detoxified, they disrupt photoreceptor functions and induce apoptosis. The dipeptide L-carnosine (β-alanyl-L-histidine) has been shown to quench 4-HNE. We investigated whether carcinine, a derivative of L-carnosine offering the advantage of being more resistant to enzymatic hydrolysis, had the same ability to quench 4-HNE, therefore protecting cells against its toxic effects.
Our experiments were conducted in cultured cells and in mice. The photoreceptor cell line 661W was pre-incubated with 0, 2, and 20 mM carcinine for 2, 4, 6, and 24 h. After removing extracellular carcinine, cells were treated with increasing concentrations of 4-HNE and cell death was quantified using an LDH assay. Balb/C mice were injected intravitrealy with carcinine in one eye and PBS in the other eye. Two days after injection, mice were exposed to bright light (4,000 lux, 5 h) to induce oxidative stress and endogenous production of 4-HNE. Protection of photoreceptors by carcinine was quantified by histology.
Carcinine protects 661W cells against 4-HNE-induced apoptosis in a time- and dose-dependent manner. This suggests that carcinine can be transported inside the cells and quench 4-HNE. Carcinine did not protect when pre-incubated only 2 h, suggesting an additional mechanism of action, by induction of protective genes. Carcinine significantly protected photoreceptors against light-induced apoptosis, suggesting that this compound is sufficiently resistant to degradation to be used in vivo, representing new strategies in anti-apoptotic drug discovery.
The biological properties of carcinine offer a potential strategy for treatment of a wide range of eye diseases linked to oxidant stress. For example, we have shown that the photoreceptor-specific enzyme RDH12 offers endogenous protection against 4-HNE. In absence of a functional RDH12 gene, an early onset vision loss occurs. We will further explore possibilities of replacing the disrupted activity of RDH12 with a similar functioning molecule such as carcinine.
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