AOBPreview originally published online on May 4, 2006
Annals of Botany 2006 98(1):57-65; doi:10.1093/aob/mcl089
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Identification of Oxalic Acid and Tartaric Acid as Major Persistent Pain-inducing Toxins in the Stinging Hairs of the Nettle, Urtica thunbergiana
1 Department of Life Science, College of Life Science, National Taiwan University, Taipei 106, Taiwan, 2 Department of Chemistry, College of Science, National Central University, Taoyuan 32054, Taiwan and 3 Department of Life Science, College of Science, National Central University and University System of Taiwan, Taoyuan 32054, Taiwan
* For correspondence. E-mail linglong{at}ntu.edu.tw or lsrong{at}cc.ncu.edu.tw
Received: 7 October 2005 Returned for revision: 4 January 2006 Accepted: 13 March 2006 Published electronically: 4 May 2006
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.
Key words: Formalin test, high-performance liquid chromatography (HPLC), oxalic acid, stinging hairs, tartaric acid, Urtica thunbergiana