Not a single dry eye in the house

Friday 31 July 1998

...after you try out medicine's latest recipe for killing pain -- red hot chilli peppers

-- have you ever had a mouthful of curry that had too much chilly powder and, two seconds later, felt your mouth explode in searing, white hot burn? Well, get used to the feeling because the chemicals that make your mouth explode are becoming increasingly fashionable in medical circles as pain killers.

The main burning chemical in chilli peppers, capsaicin, is a traditional remedy for pain. Now many pharmaceutical companies are including it in their recipes for their painkillers, mainly analgesic creams. At the same time, scientists are conducting more fundamental research that could lead to several new, more effective pain-killing drugs.

Capsaicin, being what scientists call a "counter-irritant", distracts attention of the patient from the old one. But there is much more to the story of its success than just that. Recent research has revealed that capsaicin controls pain at a molecular level, producing a genuine analgesia.

It seems that the chemical causes a burning sensation by binding to a molecular receptor on the nerve endings. This triggers the release of a chemical messenger, Substance P, which sends pain signals to the brain through the nerve fibres.

The nerves involved are the so-called type C fibres; they transmit slow throbbing pain that may take a few seconds to take effect but lasts a long while.

In 1997, David Julius and his team at the University of California, usa , discovered that the receptor that starts this process. vr 1, as they called it, is a nerve cell protein that binds to capsaicin and related compounds. vr 1 also responds to high temperatures and it seems that hot, spicy food triggers a reaction quite similar to that of overheated food.

How capsaicin works is still not very clear. By binding to vr 1, it somehow desensitises the nerve cells and reduces the amount of Substance P they produce. This makes them less sensitive to other painful stimuli.

And now that vr1 can be made in laboratories, scientists will be able to test many other chemicals for their effect on the receptor. Their aim is to look for ones that bind to it more effectively than capsaicin, without causing intense pain themselves. These could be the new painkillers of tomorrow.

The chilli-based creams available today contain less than 0.1 per cent of capsaicin. If they are applied to the affected area several times a day -- producing a transient, tolerable burning sensation -- they start to give substantial pain relief within a week.

Julius and his team are assessing a more drastic approach: creams with capsaicin concentrations of 5 to 10 per cent. At these levels, patients need local anaesthesia to tolerate the initial burning, followed by morphine for up to five days after treatment. But initial results suggest that high-strength capsaicin may offer better relief from chronic pain than anything else.

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