Nutraceuticals and nootropics for anti-aging

How does curcumin prevent diabetes-related cataracts?

Curcumin — the yellow substance in the turmeric spice — has in recent years attracted attention as a treatment for medical conditions caused by free radicals, inflammation, viral infection, and protein handling. For example, in 2004 researchers reported that curcumin can compensate for the genetic defect that causes the symptoms of cystic fibrosis,¹ a disease resulting from faulty protein handling in secretory cells.

One of the many medical areas for which curcumin is being studied is the prevention of diabetic symptoms. It is widely believed that most of these symptoms ultimately stem from damage done to tissues by two processes:

• glycation — chemical reactions between sugar molecules and structural proteins or enzymes
• free radical damage to proteins and other components of tissues.

Glycation creates crosslinks between different protein molecules (or sometimes within a single protein), impairing the function of these proteins. Glycation is analogous to randomly splattering droplets of glue into a mechanical watch, bonding some of the cogs and structural parts together.

Free radical damage dramatically alters the structure and chemical nature of biological structures (such as enzymes) causing them to malfunction.

Glycation and free radical damage occur whether or not one has diabetes. But they happen faster in diabetics because hyperglycemic episodes raise sugar levels — more sugar → more bonding. As tissues become more damaged, they become stiffer and less functional. Antioxidant molecules are damaged, too, allowing still more free radical damage to take place.

In the lens of the eye, glycation and free radical damage affect an important protein called ‘alpha-crystallin’ which constitutes about 50% of all the protein in the lens. The function of alpha-crystallin is to keep the lens transparent. It does this by preventing other proteins in the lens from unraveling. Without alpha-crystallin, these other proteins would become disorganized and clump together, forming deposits that would scatter light and make the lens opaque. Such deposits are what cataracts are made of. But as long as alpha-crystallin performs its function, the other proteins are kept in line and the lens remains clear.

When alpha-crystallin molecules are bonded by glycation or damaged by free radicals, they can no longer perform their function. The other proteins that they should be monitoring are now free to unravel and clump together. This is why cataracts are one of the prominent symptoms of diabetes. Too much sugar → too much glycation → damaged alpha-crystallin → unmaintained lens proteins → cataracts.

Now for the exciting news... Recent work in India has shown that curcumin supplementation suppresses the formation of cataracts in diabetic rats,² and that the mechanism for this effect involves protecting alpha-crystallin from damage by glycation.^3a,3b There is no reason to doubt that the same effects hold in humans, as well. Furthermore, the anti-cataract effects of curcumin should not be limited to diabetics — ordinary cataracts are thought to arise by the same mechanism, but at a slower rate.

The main problem with curcumin in humans is its very low bioavailability — very little curcumin is absorbed from the digestive tract under normal conditions. For this reason, some suppliers of curcumin supplements have recently been adding piperine as a bioavailability enhancer to the product. Piperine not only improves the absorption of curcumin, it also inhibits some of the processes that would otherwise quickly convert curcumin to other substances. If a second bioavailability enhancer, such as quercetin, is added, an even greater increase in absorption is possible, as well as a further inhibition of the metabolic conversion of curcumin. In this way, by extending curcumin’s dwell time in the body, it has a much greater opportunity to enter hard-to-reach tissues such as the lens of the eye, and there do its work.

References

[1]  Curcumin, a major constituent of turmeric, corrects cystic fibrosis defects. Science. 2004 Apr 23;304(5670):600-2

[2]  Turmeric, curcumin could help delay cataract: Study The Hindu Business Line website

[3a]  Modulation of alpha-crystallin chaperone activity in diabetic rat lens by curcumin. [abstract] Mol Vis. 2005 Jul 26;11:561-8

[3b]  Modulation of alpha-crystallin chaperone activity in diabetic rat lens by curcumin. [full text] Mol Vis. 2005 Jul 26;11:561-8

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LifeLink carries curcumin in 333 mg capsules. This product, called ‘PriMeric’, utilizes both piperine and quercetin as bioavailability enhancers.