Natural hydroxytyrosol and eye protection

Ultraviolet radiation (UVR) is not known to contribute to visual perception but to mainly damage multiple structures. Excessive exposure to UVR through live may seriously contribute to increase in OS of various eye tissues and thus lead to the advancement of serious ocular pathologies (“Ultraviolet radiation oxidative stress affects eye health”; Iliya V Ivanov ET AL.; J Biophotonics 2018)

One of the eye major threats could be oxidation and the diminishment of internal antioxidant defenses. This drives to endogenous end products of lipid oxidation like acrolein.

The age-related macular degeneration (AMD) is the leading cause of vision loss in the Western world among people over 65 years of age. It causes degeneration of retinal pigment epithelium and photoreceptors in the macular area of the retina.

Oxidative- and inflammatory-related ocular surface diseases have high prevalence and are an emerging issue in ophthalmology. According to a 2010 study (“Hydroxytyrosol protects against oxidative damage by simultaneous activation of mitochondrial biogenesis and phase II detoxifying enzyme systems in retinal pigment epithelial cells; Lu Zhua et al; Journal of Nutritional Biochemistry”), dietary supplementation of hydroxytyrosol may contribute to eye health by preventing the degeneration of retinal pigment epithelial cells induced by oxidative stress.

The hydroxytyrosol protection can come from third sources, as an inducer of phase II detoxifying enzymes, antioxidant booster and enhancer of miochondrial biogénesis.

Our aging population is growing at a remarkable rate with the population aged 60 years or over predicted to double to 2.1 billion by 2050. Age is major risk factor for cataracts with the current estimate of cataracts to afflict more than 20 million people worldwide. Given our globally aging population, the social and economic costs of lens cataract are quite staggering and the demand for cataract surgery far exceeds limited public health resources. In the USA alone, cataract surgery is the most commonly performed surgical procedure and costs around $3.5 billion per year. In Australia, where it has been estimated that the population will increase by 22% between 1996 and 2021, the incidence of age-related cataract will disproportionately increase by 76% during the same period (“Nutritional Strategies to Prevent Lens Cataract: Current Status and Future Strategies”; Andrea J. Braakhuis et al.; Nutrients).

Population growth, sedentary lifestyles, unhealthy diets and an increasing prevalence of obesity are increasing the number of people with diabetes mellitus. Worldwide more than 285 million people are affected by diabetes mellitus with the number expected to increase to 439 million by 2030. A frequent complication of both type 1 and type 2 diabetes is diabetic cortical cataracts which occur 2–5 times more frequently in patients with diabetes, and occur at an earlier age.

In 2018, José A. González-Correa et al. (“Neuroprotective Effect of Hydroxytyrosol in Experimental Diabetic Retinopathy: Relationship with Cardiovascular Biomarkers”; J Agric Food Chem) concluded that, hydroxytyrosol exerted a neuroprotective effect on diabetic retinopathy, and this effect correlated significantly with changes in some cardiovascular biomarkers.

The aim of such study was to test the neuroprotective effect of hydroxytyrosol on experimental diabetic retinopathy. Animals were divided in four groups: (1) control nondiabetic rats, (2) streptozotocin-diabetic rats (DR), (3) DR treated with 1 mg/kg/day p.o. HT, and (4) DR treated with 5 mg/kg/day p.o. HT. Treatment with HT was started 7 days before inducing diabetes and was maintained for 2 months.

In the DR group, total area occupied by extracellular matrix was increased, area occupied by retinal cells was decreased; both returned to near-control values in DR rats treated with HT. The number of retinal ganglion cells in DR was significantly lower (44%) than in the control group, and this decrease was smaller after HT treatment (34% and 9.1%). Linear regression analysis showed that prostacyclin, platelet aggregation, peroxynitrites, and the dose of 5 mg/kg/day HT significantly influenced retinal ganglion cell count.

Hydroxytyrosol has a singular advantage, it can cross the blood brain barrier (“Pharmacokinetics and metabolism of hydroxytyrosol, a natural antioxidant from olive oil”; Stefania D´Angelo et al. 2001; Drug Metabolism and Disposition). It is true that the lens could utilize a unique internal microcirculation system to actively deliver antioxidants to these different regions, and that selecting antioxidants that can utilize this system is the key to developing novel nutritional therapies to delay the onset and progression of lens cataract (Andrea J. Braakhuis et al. 2019). More clinical studies should be carried out to confirm antioxidants activity on eye care but the chemical structure of hydroxytyrosol makes it an ideal candidate.

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