Abstract
Retinitis pigmentosa (RP) is an inherited retinal dystrophy characterized by progressive degeneration of the visual cells and abnormalities in retinal pigment epithelium, the vision is lost slowly, and the final outcome is total blindness. RP primarily affects rods, but cones can also be affected as a secondary effect. Photoreceptor cell death is usually triggered by apoptosis, however the molecular mechanisms linking the rod degeneration to the secondary cone death are poorly understood. Possible causes of the secondary cone death are oxidative stress and/ or the release of toxic factors from dying rods. The aim of this study is to analyze the effect of nutraceutical molecules with antioxidant properties, on the progression of the disease in an established animal model of RP, and rd10 mice. We show that chronic treatment per os with a flavanone (naringenin) or a flavonol (quercetin) present in citrus fruits, grapes and apples, preserves retinal morphology, and ameliorates functionality. These actions are associated with a significant reduction of stress-oxidative markers, such as the detoxifying enzymes Sod1 and Sod2. In addition, naringenin and quercetin treatment reduces the levels of acrolein staining associated with a reduction of ROS in the cellular environment. The study demonstrates the beneficial effects of naringenin and quercetin, two molecules that possess antioxidant properties, limiting neurodegeneration, and thus preventing cone damage.
Highlights
Retinitis pigmentosa (RP) is a group of inherited retinal diseases in which a mutation causes the death of rod photoreceptors
The lack of factors secreted by rods that are essential to the cone viability may lead to cone death (Roque et al, 1996)
It has been suggested that the migration of microglial cells into the outer retina could contribute to photoreceptor degeneration in RP (Leveillard et al, 2004; Peng et al, 2014)
Summary
Retinitis pigmentosa (RP) is a group of inherited retinal diseases in which a mutation causes the death of rod photoreceptors. While genetic mutations are the primary cause of the rod degeneration, cone death is possibly the consequence of the release of toxic substances, either released by a dying rod into the retinal milieu, or diffused to coupled cones through gap junctions (Ripps, 2002). The upregulation of the genes involved in the insulin/mTOR pathway supports the notion that metabolic stress is a contributing factor to the secondary death of cones (Punzo et al, 2009; Venkatesh et al, 2015). Emerging studies show that all these factors contribute to making cones in RD retinas much more sensitive to oxidative stress than their counterpart in healthy retinas, triggering processes of cell death (Campochiaro and Mir, 2018)
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