Department of Clinical Neuroscience, Karolinska Institute, 171 76 Stockholm, Sweden.
Department of Forensic Genetics and Forensic Toxicology, National Board of Forensic Medicine, 587 58 Linköping, Sweden.
Molecules. 2022 Apr 6;27(7):2350. doi: 10.3390/molecules27072350.
The importance of the dynamic interplay between the opioid and the serotonin neuromodulatory systems in chronic pain is well recognized. In this study, we investigated whether these two signalling pathways can be integrated at the single-cell level via direct interactions between the mu-opioid (MOP) and the serotonin 1A (5-HT1A) receptors. Using fluorescence cross-correlation spectroscopy (FCCS), a quantitative method with single-molecule sensitivity, we characterized in live cells MOP and 5-HT1A interactions and the effects of prolonged (18 h) exposure to selected non-peptide opioids: morphine, codeine, oxycodone and fentanyl, on the extent of these interactions. The results indicate that in the plasma membrane, MOP and 5-HT1A receptors form heterodimers that are characterized with an apparent dissociation constant Kdapp = (440 ± 70) nM). Prolonged exposure to all non-peptide opioids tested facilitated MOP and 5-HT1A heterodimerization and stabilized the heterodimer complexes, albeit to a different extent: Kd, Fentanylapp = (80 ± 70) nM), Kd,Morphineapp = (200 ± 70) nM, Kd, Codeineapp = (100 ± 70) nM and Kd, Oxycodoneapp = (200 ± 70) nM. The non-peptide opioids differed also in the extent to which they affected the mitogen-activated protein kinases (MAPKs) p38 and the extracellular signal-regulated kinase (Erk1/2), with morphine, codeine and fentanyl activating both pathways, whereas oxycodone activated p38 but not ERK1/2. Acute stimulation with different non-peptide opioids differently affected the intracellular Ca2+ levels and signalling dynamics. Hypothetically, targeting MOP−5-HT1A heterodimer formation could become a new strategy to counteract opioid induced hyperalgesia and help to preserve the analgesic effects of opioids in chronic pain.
阿片和 5-羟色胺能神经调质系统之间动态相互作用的重要性已得到充分认识。在这项研究中，我们研究了这两个信号通路是否可以通过μ-阿片（MOP）和 5-羟色胺 1A（5-HT1A）受体之间的直接相互作用在单细胞水平上整合。我们使用荧光相关光谱（FCCS）这一具有单分子灵敏度的定量方法，在活细胞中表征了 MOP 和 5-HT1A 相互作用以及延长（18 小时）暴露于选定非肽阿片类药物：吗啡、可待因、羟考酮和芬太尼对这些相互作用程度的影响。结果表明，在质膜中，MOP 和 5-HT1A 受体形成异二聚体，其特征为表观解离常数 Kdapp =（440±70）nM）。所有测试的非肽阿片类药物的延长暴露均促进 MOP 和 5-HT1A 异二聚化并稳定异二聚体复合物，但程度不同：Kd，芬太尼 app =（80±70）nM），Kd，吗啡 app =（200±70）nM，Kd，可待因 app =（100±70）nM 和 Kd，羟考酮 app =（200±70）nM。非肽阿片类药物在影响丝裂原激活蛋白激酶（MAPKs）p38 和细胞外信号调节激酶（Erk1/2）的程度上也存在差异，其中吗啡、可待因和芬太尼激活两条途径，而羟考酮仅激活 p38 而不激活 ERK1/2。不同的非肽阿片类药物急性刺激对细胞内 Ca2+水平和信号动力学有不同的影响。假设靶向 MOP-5-HT1A 异二聚体形成可能成为一种新策略，以对抗阿片类药物引起的痛觉过敏，并有助于在慢性疼痛中保留阿片类药物的镇痛作用。
