Identification of oxalic acid and tartaric acid as major persistent pain-inducing toxins in the stinging hairs of the nettle, Urtica thunbergiana.

Abstract

BACKGROUND AND AIMS:

Once human skin contacts stinging hairs of Urtica spp. (stinging nettles), the irritant is released and produces pain, wheals or a stinging sensation which may last for >12 h. However, the existence of pain-inducing toxins in the stinging hairs of Urtica thunbergiana has never been systematically demonstrated. Experiments were therefore conducted to identify the persistent pain-inducing agents in the stinging hairs of U. thunbergiana.

METHODS:

The stinging hairs of U. thunbergiana were removed and immersed in deionized water. After centrifugation, the clear supernatants were then subjected to high-performance liquid chromatography (HPLC), enzymatic analysis and/or behavioural bioassays.

KEY RESULTS:

The HPLC results showed that the major constituents in the stinging hairs of U. thunbergiana were histamine, oxalic acid and tartaric acid. However, the well-recognized pain-inducing agents, serotonin and formic acid, existed at a low concentration as estimated by HPLC and/or enzymatic analyses. The behavioural tests showed that 2% oxalic acid and 10% tartaric acid dramatically elicited persistent pain sensations in rats. In contrast, 10% formic acid and 2% serotonin only elicited moderate pain sensation in the first 10 min. Moreover, no significant pain-related behavioural response was observed after injecting 10% acetylcholine and histamine in rats.

CONCLUSIONS:

Oxalic acid and tartaric acid were identified, for the first time, as major long-lasting pain-inducing toxins in the stinging hairs of U. thunbergiana. The general view that formic acid, histamine and serotonin are the pain-inducing agents in the stinging hairs of U. dioica may require updating, since their concentrations in U. thunbergiana were too low to induce significant pain sensation in behavioural bioassays.

• Authors: Han Yi Fu, Shiang Jiuun Chen, Ruei Feng Chen, Wang Hsien Ding, Ling Long Kuo-Huang, Rong Nan Huang
• Journal: Annals of botany (Ann Bot) Vol. 98 Issue 1 Pg. 57-65 (Jul 2006) ISSN: 0305-7364 [Print] England
• PMID: 16675601 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Tartrates
• Toxins, Biological
• Oxalic Acid
• tartaric acid

Topics

• Animals
• Chromatography, High Pressure Liquid
• Female
• Oxalic Acid (analysis, isolation & purification, toxicity)
• Pain (chemically induced)
• Pain Measurement
• Plants, Toxic (chemistry, metabolism)
• Rats
• Rats, Wistar
• Tartrates (analysis, isolation & purification, toxicity)
• Toxins, Biological (analysis, isolation & purification, toxicity)
• Urticaceae (chemistry, metabolism)