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In the news: Role of DHA in Future Survival of Retinal Cells; Progress in Eye Scans For Alzheimer's

DHA Preconditions Future Survival of Retinal Cells

A team of researchers from the Neuroscience Center at Louisiana State University Health New Orleans, reports that the omega-3 fatty acid DHA not only protects photoreceptor and retinal pigment epithelial (RPE) cells from potentially lethal initial insults, but also from future insults. The study, through in vitro and in vivo experiments, showed that the omega-3 fatty acid, DHA, and its derivatives “precondition” these cells to survive future injury (1).

The study’s authors define preconditioning as an acquired protection or resilience by a cell, tissue, or organ to a lethal stimulus enabled by previous sub- lethal stressors or stimuli (2). Preconditioning takes place, for example, when the blood supply to an organ is interrupted for a short time and then reestablished. The protective response from that first injury would carry over to a subsequent blood supply shortage, much like the immunity a vaccine confers against future exposures to disease.

According to the researchers, “This [preconditioning] happens in the heart, brain and retina, as well as other organs. To harness the therapeutic potential of preconditioning, it is very important to identify the molecules directly involved.”

DHA is the precursor of docosanoids, mediators that are made ‘on demand’ when factors threaten to disrupt cellular homeostasis. Docosanoids include molecules such as resolvins and neuroprotectin D1, regulators of neuroprotective, anti-inflammatory, and anti-angiogenic activity. In contrast, eicosanoid derivatives of omega-6 arachidonic acid have pro-inflammatory actions.

The research team showed that the protective actions of oxidative stress preconditioning require DHA and docosanoid synthesis, while also showing that DHA and docosanoids are involved in both ischemic preconditioning and light exposure preconditioning protection. They found that the free pool size of DHA is increased to form docosanoids, which play a critical role in survival signaling.

Although they are released concomitantly from phospholipids in cellular membranes, DHA can alter the action of arachidonic acid. When DHA was supplemented prior to the oxidative stress insult, the synthesis of protective DHA derivatives increased while arachidonic acid synthesis decreased over time. “Our findings demonstrate that DHA and the induction of docosanoid synthesis is necessary for preconditioning protection, and thus daily survival, of photoreceptor and RPE cells,” the authors conclude

Curcumin & Eye Scans for Alzheimer's

According to Cedars-Sinai Medical Center neuro-scientists, Alzheimer's disease (AD) essentially starts about 20 years prior to patients developing symptoms. And by the time one becomes symptomatic, significant loss of brain weight, brain cells and connectivity has already occurred. It’s therefore important to develop means of early detection so that the disease can be treated early through drugs and lifestyle interventions.

While PET scans are used to detect amyloid plaques, they are expensive and require injecting tracers into patients’ brains. However, it was discovered that curcumin - the dark yellow component of turmeric spice - floresces when it binds to the amyloid-beta plaques of AD. Additionally, animal studies have shown that the amount of plaques present in the retina correlates with levels in brain tissue. This has led to the development of curcumin-florescence eye scans for AD detection, though further testing is needed before it is approved for clinical use.

A new study by Cedar-Sinai investigators is a promising step in this direction. The researchers examined the brains and eyes from human cadavers with and without AD, finding that plaques tend to congregate in the superior quadrant of the retina. They next fed enhanced bioavailable curcumin to AD patients and healthy volunteers. Using a modified ophthalmoscope to detect fluorescence, they found that AD patients had about twice the level of amyloid-beta plaques as the controls.

References

1. Knott EJ, et al. Retinal pigment eipithelium and photo-receptor preconditioning protection requires docosanoid signaling. Cellular and Molecular Neurobiology. Published online