Spinal Mechanism Of Itch Via A NMR-mediated Metabolomics Study

Background: Itch is the cardinal symptom of many diseases and a severe side effect of many drugs. Itch has brought tremendous negative effects on our health and living conditions and added a heavy finance burden to the society. However, there is no effective treatments currently. Spinal cord has been demonstrated to play a key role in modifying the itch signals transition from peripheral sensory receptors to the center neural system. Some progresses have been made recently, but whether there are correlations between spinal metabolites and itch still remain unknown.Objective: To explore the spinal metabolites changes of itch induced by α-Me-5-HT through a metabolomics method and try to illuminate the mechanism of itch.Methods: Eighteen C57BL/6 mice were randomly divided into 2 groups: saline group(n = 9) and α-Me-5-HT group(n = 9). The saline(50 μL) or α-Me-5-HT(30 μg/50 μL) was microinjected intradermally, respectively. The scratch number was obtained then. Two hours after injection, the bottom half of the spinal cords(C5~C8) were quickly removed from the vertebral cervicales. The extractants of the C5~C8 were explored by the NMR tool and raw data of the specimen was collected. The quantity of metabolites and correlation of metabolites were analyzed between two groups.Results: Compared with the saline group, the scratch number increased swiftly after the injection of pruritogen(α-Me-5-HT) and there was significant difference between the two groups(p<0.05). Specifically, the scratch number within 30 min after the injection was: saline group(33.33 ± 7.74), α-Me-5-HT group(157.55 ± 30.90). The results of NMR study of the spinal cord extracts shown that the concentration of NAA of α-Me-5-HT group was greatly increased(4.375 ± 0.057μmol/g VS 4.743 ± 0.051 μmol/g, increased 8.42%, p = 0.0002), the concentrations of alanine, taurine and GABA were significantly decreased, especially for GABA(3.114 ± 0.069 μmol/g VS 2.671 ± 0.065 μmol/g, decreased 14.2%, p = 0.0002). Moreover, we found that the ratio of NAA/myo of α-Me-5-HT treated group was also statistical higher than that of saline group. Finally the spinal metabolites of two groups(saline and α-Me-5-HT) were completely separated with the Principal Components Analysis study.Conclusion: The metabolite of NAA, GABA, taurine and alanine may take part in the progress of itch signal transition induced by α-Me-5-HT; the ratio of NAA/myo may serve as a marker of the severity of itch condition.Highlights: To our knowledge, this is the first description:(1) studying the change of spinal amino acids after pruritogens α-Me-5-HT injection;(2) employing NMR tool to explore and study the spinal metabolomics of itch;(3) predicting the severity of itch.