New anesthetic kills pain without side effects

A research team, led by Clifford J. Woolf and Bruce Bean, tested the combination of capsaicin (the active ingredient in chilli peppers) and a drug called QX-314 (a derivative of lidocaine, the most commonly used local anesthetic) on rats, and showed that the combination was effective in alleviating pain without causing motor impairment. The drug combination took half an hour to fully block pain in the rats. However, once it began, the pain relief lasted for several hours.

Lidocaine relieves pain by blocking electric currents in all nerve cells. A lidocaine derivative, QX-314 alone cannot get through cell membranes to block their electrical activity. Capsaicin opens pores called TRPV1 channels found only within the cell membrane of pain sensing neurons. QX-314 can then pass through and selectively block the cells' activity thereby causing selective pain relief, without numbness or paralysis.

"Current nerve blocks cause paralysis and total numbness," Woolf said. "This new strategy could profoundly change pain treatment in the perioperative setting. Surgical pain is the obvious first application for this type of treatment." He added that similar therapies might eventually be useful for treating chronic pain and itch.

One problem with the combination treatment is that the capsaicin can cause unpleasant burning sensations until the QX-314 takes effect, Woolf said. Administering the QX-314 ten minutes before the capsaicin can minimize this problem in rats.

The investigators are now looking for ways to open the TRPV1 channels without the burning sensations, perhaps by finding an alternative to capsaicin. The study appears in Nature, dated October 4, 2007.

Reference:

Binshtok AM, Bean BP, Woolf CJ. Inhibition of nociceptors by TRPV1-mediated entry of impermeant sodium channel blockers. Nature, Oct 4, 2007, Vol. 449, No. 7162, pp. 607-610.

Written by Sunil Rangarajan.

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