Department of Pharmacy, University of Malakand, Chakdara, Dir (Lower), KPK, Pakistan.
Department of Pharmacy, University of Swabi, Swabi, KPK, Pakistan.
Naunyn Schmiedebergs Arch Pharmacol. 2021 May;394(5):929-940. doi: 10.1007/s00210-020-02021-x. Epub 2020 Nov 22.
Cisplatin-induced peripheral neuropathic pain is a common adverse effect of chemotherapy. The present study evaluated the effects of 2'-chloro-6-methylflavone (2'-Cl-6MF) at recombinant α1β2γ2L, α2β1-3γ2L, and α3β1-3γ2L GABA-A receptor subtypes expressed in Xenopus oocytes and subsequently evaluated its effectiveness in cisplatin-induced neuropathic pain. The results showed that 2'-Cl-6MF potentiated GABA-elicited currents at α2β2/3γ2L and α3β2/3γ2L GABA-A receptor subtypes. The potentiation was blocked by the co-application of flumazenil (a benzodiazepine (BDZs) site antagonist). In behavioral studies, mechanical allodynia was induced by intraplantar injection of cisplatin (40 μg/paw) in Sprague Dawley rats, and behavioral assessments were made 24 h after injection. 2'-Cl-6MF (1, 10, 30, and 100 mg/kg, i.p.), was administered 1 h before behavioral evaluation. Administration of 2'-Cl-6MF (30 and 100 mg/kg, i.p) significantly enhanced the paw withdrawal threshold and decreased mechanical allodynia. The standard drugs, gabapentin (GBP) at the dose of 70 mg/kg, and HZ 166 (16 mg/kg), i.p. also significantly enhanced the paw withdrawal threshold in mechanical allodynia. Pretreatment with pentylenetetrazole (PTZ) (15 mg/kg, i.p.) and flumazenil reversed the antinociceptive effect of 2'-Cl-6MF in mechanical allodynia indicating GABAergic mechanisms. Moreover, the binding mechanism of 2'-Cl-6MF was rationalized by in silico modeling tools. The 3D-coordinates of α2β2γ2L and α2β3γ2L were generated after homology modeling of the α2 subtype and 2'-Cl-6MF was at predicted binding sites of the developed models. The α2 model was compared with the α1 and α3 subunits via structural and sequence alignment. Molecular docking depicted that the compound binds efficiently at the neuromodulator binding site of the receptors. The findings of this study revealed that 2'-Cl-6MF ameliorated the manifestations of cisplatin-induced neuropathic pain in rats. Furthermore, we also conclude that GABAergic mechanisms may contribute to the antinociceptive effect of 2'-Cl-6MF. The molecular docking studies also confirm the involvement of the BDZs site of GABA-A receptors. It was observed that Ile230 of α2 stabilize the chlorophenyl ring of 2'-Cl-6MF through hydrophobic interactions, which is replaced by Val203 in α1 subunit. However, the smaller side chain of Val203 does not provide hydrophobic interaction to the compound due to high conformational flexibility of α1 subunit.
顺铂诱导的周围神经性疼痛是化疗的一种常见不良反应。本研究评估了 2'-氯-6-甲基黄酮（2'-Cl-6MF）在非洲爪蟾卵母细胞中表达的重组 α1β2γ2L、α2β1-3γ2L 和 α3β1-3γ2L GABA-A 受体亚型中的作用，随后评估了其在顺铂诱导的神经性疼痛中的有效性。结果表明，2'-Cl-6MF 增强了 α2β2/3γ2L 和 α3β2/3γ2L GABA-A 受体亚型中 GABA 诱发的电流。这种增强作用被氟马西尼（苯二氮䓬（BDZs）位点拮抗剂）的共同应用所阻断。在行为研究中，通过在 Sprague Dawley 大鼠足底注射顺铂（40μg/爪）诱导机械性痛觉过敏，并在注射后 24 小时进行行为评估。2'-Cl-6MF（1、10、30 和 100mg/kg，ip）在行为评估前 1 小时给药。2'-Cl-6MF（30 和 100mg/kg，ip）给药显著提高了爪回缩阈值并降低了机械性痛觉过敏。标准药物，加巴喷丁（GBP）剂量为 70mg/kg，和 HZ 166（16mg/kg，ip）也显著提高了机械性痛觉过敏时的爪回缩阈值。戊四氮（PTZ）（15mg/kg，ip）和氟马西尼预处理逆转了 2'-Cl-6MF 在机械性痛觉过敏中的抗伤害作用，表明 GABA 能机制。此外，通过计算建模工具合理化了 2'-Cl-6MF 的结合机制。通过同源建模生成了 α2 亚基的 3D 坐标，然后生成了 α2β2γ2L 和 α2β3γ2L 的 3D 坐标，并且 2'-Cl-6MF 位于开发模型的预测结合位点处。通过结构和序列比对将 α2 模型与 α1 和 α3 亚基进行比较。分子对接表明该化合物可有效地结合到受体的神经调节剂结合位点。这项研究的结果表明，2'-Cl-6MF 改善了顺铂诱导的大鼠神经性疼痛的表现。此外，我们还得出结论，GABA 能机制可能有助于 2'-Cl-6MF 的镇痛作用。分子对接研究还证实了 GABA-A 受体 BDZs 位点的参与。观察到 α2 中的 Ile230 通过疏水相互作用稳定 2'-Cl-6MF 的氯苯基环，而在 α1 亚基中则被 Val203 取代。然而，由于 α1 亚基的构象灵活性较高，Val203 的较小侧链不能与化合物提供疏水相互作用。
