Chinese scientists have confirmed the polyphenol’s metabolites were detected in the outer (conjunctiva) and inner (aqueous fluid, vitreous gel) structures of the human eye. Resveratrol itself could only be detected in the conjunctiva.
“It is clear that resveratrol may have potential in the treatment of several ocular diseases, such as primary open-angle glaucoma (POAG), age-related macular degeneration (AMD) and diabetic retinopathy (DR),” the paper said.
“In light of the current interest in resveratrol as a potential preventive and therapeutic agent, we hope that our results, measuring resveratrol levels and its metabolites in the human eye, will help define doses that may be used in the prevention of ocular disease.”
What is noteworthy amongst the research team is the ability of resveratrol to cross the semi-permeable blood-brain and blood-ocular barriers.
These protective mechanisms restrict access to delicate organs by toxins such as alcohol and caffeine.
However, they appear to grant resveratrol and its metabolites access suggesting the phytochemicals are important to neural or ocular function.
Indeed, previous studies have shown resveratrol to not only penetrate the blood-brain barrier but actually help maintain its integrity.
Resveratrol has previously been suggested as a promoter of health in dry eye, glaucoma, cataracts, age-related macular degeneration (AMD), and diabetic retinopathy (DR).
Researchers from the Huazhong University of Science and Technology included 20 men and 15 women aged 20–74 years.
These patients were undergoing eye surgery after retinal detachment and were orally given a trans-resveratrol-based supplement.
There were a total of 35 eyes to work with of which tissue samples were obtained specifically from the outer eye (conjunctiva), aqueous fluid in the front of the inner eye and from the vitreous gel that fills the back of the eyes.
The average concentration of resveratrol in the conjunctiva was 17.19 nanomols per gram (nmol/g), while the concentration of resveratrol in the aqueous humor was close to the limit of detection. However, its metabolites could be quantified.
The concentrations of resveratrol metabolites in the aqueous humor could be detected. In the vitreous humor, the average concentration of resveratrol-3-O-sulfate was 62.95 nanomols per litre (nmol/L).
“Resveratrol and its three metabolites can be detected in the ocular tissues after oral administration,” the study concluded.
“Although the concentration of parent resveratrol was low in the eyes, its metabolites could be detected and may have a role in the treatment of ocular diseases.”
Jury out on resveratrol
Researchers have demanded more evidence of the biological mechanisms of resveratrol before its recommendation as a dietary supplement.
Evidence is mostly on resveratrol’s side as its anti-inflammatory and antioxidant activity via different molecular mechanisms have been highlighted in animal models and in vitro retinal cells.
In addition, interest has been healthy due to its cardioprotective action. Its ability to inhibit new blood cell formation and promote vasorelaxation has been well-documented.
A growing body of evidence supports the hypothesis that phenolic phytochemicals with poor bioavailability are possibly acting primarily through remodeling of the gut microbiota.
Resveratrol has also been shown to metabolize in the gut, favourably influencing the balance of gut bacteria and indirectly inhibiting the accumulation of atherosclerotic arterial plaque.
Despite the results, not all eyes showed a detectable level of resveratrol or its metabolites after oral consumption, opening up an area for further investigation.
Source: Journal of Ophthalmology
Published online ahead of print: doi.org/10.1155/2017/4052094
“Metabolites of Resveratrol (Longevinex) pass through blood-ocular barriers in humans.”
Authors: Shuaishuai Wang, Zheng Wang, Shuo Yang, Tiemei Yin, Yaoli Zhang, Yuanjun Qin, Robert Weinreb and Xufang Sun.