Thursday, May 8, 2014

Coffee may prevent hypoxia-induced retinal degeneration

Retina is one of the most metabolically active tissues in the body, consuming oxygen more rapidly than any other tissues, including the brain. Therefore, it is susceptible to a variety of diseases caused by oxidative stress, including age-related macular degeneration, diabetic retinopathy, and glaucoma - all of which can lead to partial or complete blindness.

One mechanism of retinal degeneration is hypoxia, a reduction in retinal oxygen supply caused by pathologies such as central retinal artery occlusion, ischemic central retinal vein thrombosis, complications of diabetic eye disease, and some types of glaucoma that cause vascular eye diseases. Retinal hypoxia can negatively impact both tissue function and cell viability, and is a potential risk factor for sight-threatening disorders. Hence there has been a great interest in identifying neuroprotective compounds that inhibit hypoxia. Particularly promising in this capacity are natural products and phytochemicals that act as antioxidants and can be taken regularly without causing significant side effects.

One important group of neuroprotectants comprises derivatives of chlorogenic acid (CGA) found in a variety of edible plants, including tea, fruits, and vegetables, with the major source of intake in humans being coffee. Collectively, these phenolic phytochemicals are known to have hepatoprotective, antibacterial, anti-inflammatory, DNA protective, and anticancer activities, among others. Several studies have also suggested that the antioxidant properties of CGA make it a powerful neuroprotectant.

In raw coffee, CGA amounts to about 4–12% of raw coffee, while a 200 mL cup of prepared coffee contains 200 mg of total CGA. Coffee consumption appears to decrease the risk of developing chronic diseases such as Parkinson’s, prostate cancer, and diabetes. It also reduces the extent of cognitive declines associated with aging. The current study was designed to investigate whether coffee and, in particular, its main polyphenol, CGA, has protective effects against the degeneration of retinal ganglion cells (RGC), both in vitro and in vivo.

The researchers found that CGA significantly reduced the negative effect of the hypoxic agent on the cells being studied, with cell viability increasing with more CGA pretreatment. Also in animal models that mimic glaucoma, where the inner plexiform layer appears thinned, pretreatment with CGA reduced the amount of thinning seen. The authors also noted reduction in ganglion cell apoptosis.

This study demonstrates that CGA and coffee extract are responsible for reduction of the RGC apoptosis induced by hypoxia. Thus, coffee consumption may provide additional health benefits by preventing retinal degeneration.

Sources: Journal of Agricultural and Food Chemistry

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