Experimental Study On The Analgesic Effects Of Iridiod Glycosides From Paederia Scandens And Its Mechanisms

Pain accompanies surgery, various diagnostic procedures and dental care as well as acute injury (or trauma) and many other diseases. It not only makes patients feel unbearably distressful and anxious, but also makes them fall into a serious stress status, which secondarily resulting in functional disorders of many important organs. Iridiod glycosides from Paederia scandens (LOUR.) MERRILL (Rubiaceae) (IGPS) are paederoside, asperuloside, scandoside et al. Paederia scandens was described to use as analgesic, anti-inflammatory, and to treat bruise and rheumatism through eliminating heat and excreting dampness in terms of traditional Chinese medicine. It has not been reported about the analgesic effects of IGPS. This study is intended to investigate the analgesic effects of IGPS on different pain models. The main results are as follows:1 Experimental study on acute toxicity test of IGPSWe studied the acute toxicity effect of IGPS on healthy mice. The subject was administrated to mice once a day for 14 consecutive days by two ways: intragastric administration and intraperitoneal injection.After the preliminary experiment, we could not measure LD50 of IGPS, so we try to measure its maximum tolerated dose (MTD) and the result was 48.00g/kg by ig. Compared with the control the mice after administration large dose of IGPS by ig appeared no abnormalities in the succedent 14days.After the preliminary experiment, the dose levels of IGPS to be tested were 5.25, 4.72, 4.25, 3.83, 3.44g/kg body weight by ip respectively. Lethal dose (LD50) were measured by Bliss'method in the peritoneal injection. The results showed that LD50 was 4.12g/kg, 95% confidence limit of were (3.81～4.41)g/kg , suggesting IGPS have no apparently acute virulent function and safety extent is high.2 Effects of IGPS on pain response induced by formalin and acetic acid in miceThe analgesic effects of IGPS was studied by implanter injection (ipl) 2.5% formalin15μl to induce pain response of mice. The results showed that IGPS (360,180,90mg/kg, ig, qd×7d ) could markedly inhibit biphasic pain response of mice including restlessness, paw-flinching and licking or biting the injected paw as well as reduce the cumulative time spent for licking the injected paw in the formalin test, suggesting that the central and peripheral mechanism are at least involved in the analgesic effects of IGPS.The analgesic effects of IGPS was studied by ip 1% the acetic acid 0.2ml to induce writhing response of mice. The results showed that IGPS (360,180,90mg/kg, ig, qd×7d ) could significantly inhibit acetic acid-induce the number of writhing and writhing response in mice.3 Influence of naloxone, L-Arginine and L-NAME on analgesic effects of IGPSThe involvement of endor-phin and nitrogen monoxide were studied by naloxone antagonism test, peritoneal injection of L-Arginine (L-Arg,400mg/kg) or NG-Monomethy1-L-arginine (L-NAME, 37.5mg/kg) in advance in mice. The results showed that the inhibitory effects of IGPS on acetic acid-induce writhing response in mice could not be antagonized by naloxone(5mg/kg), in addition, antinociceptive effects of IGPS was patially blocked by L-Arginine but enhanced by L-NAME, suggesting analgesic action way of IGPS may be not related to the endogenous opioid system but partially related to its inhibitory effect on the production of nitric oxide (NO).4 Experimental study on addiction of IGPSThe mice tail-erecting test and jumping test were used to study the addiction of IGPS,The results showed that straub's tail and jumping reaction in mice would not be found while administrate IGPS(360mg/kg, sc, q12h×8d), suggesting addiction would not be found while administrate IGPS repeatedly and regularly.5 Effects of IGPS on neuropathic pain rat modelWe studied the effects of IGPS on neuropathic pain induced by spared nerve injury (SNI) in rats. The mechanical withdrawal threshold of rat hindpaw was determined by electronic Von Frey filaments; NOS activity and NO production in spinal cord were measured by spectrophotometry and its cyclic guanosine monophosphate (cGMP) content by radioimmunoassay, mRNA expression of inducible NOS (iNOS) and protein kinase G type I (PKGI, including PKGΙαand PKGIβ) of spinal cord in SNI rats were analyzed by RT-PCR. The results showed that IGPS (280,140,70mg/kg, ig, qd×15d ) significantly alleviated SNI-induced mechanical hypersensitivity behavior, which accompanied with an increased MWT, markedly decreased spinal NOS activity, NO production and cGMP content. At the same time, 280, 140, 70mg/kg of IGPS inhibited mRNA expression of iNOS and PKGΙαand PKGIβof the spinal cord tissue. The results suggested that IGPS possesses antinociceptive effects on SNI rats by inactivating NO/cGMP/PKC signal transduction pathway which plays a crucial role in pathogenesis of neuropathic pain.Conclusions:In summary, our results demonstrated that IGPS had antinociceptive effects on different animal pain models including the formalin test, acetic acid-induce writhing methods of mice and SNI model of neuropathic pain in rats. Furthermore, addiction would not be found while administrate IGPS repeatedly and regularly.The mechanisms of its abirritation may not be related to the endogenous opioid system but partially related to its inhibition of NO/cGMP/PKG signal pathway.