Ghrelin Deacylase as a Treatment for Opioid Polysubstance Abuse

目前有治疗阿片使用障碍(OUD)的药物，复发率非常高。此外，共同- 使用阿片类药物和兴奋剂，如甲基苯丙胺(冰毒)，会破坏OUD治疗的成功。 人们非常希望开发新的治疗方案来治疗包括多物质使用在内的OUD 精神障碍(PSUD)。最近报道的研究揭示了Ghrelin在药物滥用和 与奖励相关的行为。Ghrelin是一种从胃中释放生长激素的酰化肽，是一种 28个氨基酸残基，第三个残基(Ser3)经正辛酸酰化。Ghrelin是在 胃，通过血液循环进入大脑，作用于生长激素释放素(或生长激素促分泌剂)。 受体(GHSR)刺激中脑边缘多巴胺奖赏通路并增加奖赏行为 啮齿动物。GHSR的拮抗作用已被证明可以减弱由各种物质引起的奖赏效应。 包括冰毒、安非他明、芬太尼、吗啡、海洛因、可卡因、尼古丁和酒精。例如, 给予选择性GHSR拮抗剂可显著减少芬太尼寻求/复发的行为 在老鼠身上。另一方面，GHSR具有与其构成活性(活性)相关的不同调节作用 在缺乏Ghrelin配体的情况下)，因此，GHSR拮抗也可能导致不想要的不良反应。 因此，针对Ghrelin本身的替代策略可能更有趣。然而，无论靶向Ghrelin Ghrelin本身会有效地减弱药物的奖赏作用，但在文献中仍存在争议 在之前针对Ghrelin本身的动物研究中，治疗前后的水平没有被测量。它是 不清楚以前使用的方法中是否有任何方法能够显著降低Ghrelin水平 足以减弱物质奖励。我们建议使用我们最近发现的Ghrelin脱酰酶(一种突变体 人丁酰胆碱酯酶(BChE)作为一种安全有效的Ghrelin调节剂来减弱物质 令人满意的效果。这种Ghrelin调节剂有望与GHSR拮抗剂一样有效地治疗 物质使用障碍(SOD)，包括PSUD，但不与任何大脑受体/转运体相互作用。 具体地说，在这项研究中，我们将首先评估BChE突变体在体内调节的效力 Ghrelin和减弱有代表性的阿片类药物(芬太尼和海洛因)的奖励和增强作用 它们在不同的啮齿动物模型中与冰毒的结合。然后，我们将设计并发现一个新的BChE突变体 作为一种更有效的Ghrelin脱酰酶，进一步提高了对Ghrelin二酰化的催化活性，开发其 长效融合蛋白的形成，并检测长效Ghrelin脱酰酶在体内的长期效果。 这项调查的完成将决定Ghrelin本身是否是一个真正有效的靶子，以及 一种有效的胃促生长素脱酰酶作为胃促生长素调节剂对PSUD的治疗是真正有效的。如果答案都是肯定的 阳性，待测试和开发的最有效的长效Ghrelin脱酰酶(重组蛋白)可能 也是治疗PSUDS的一种有前途的候选药物。

With currently available medications for opioid use disorder (OUD), the relapse rate is very high. Further, co- use of an opioid and a stimulant, such as methamphetamine (METH), undermines success in treatment for OUD. It is highly desired to develop novel therapeutic options for treatment of OUDs including polysubstance use disorders (PSUDs). Recently reported studies have revealed an interesting role of ghrelin in drug abuse and reward-relevant behaviors. Ghrelin is known as a “growth-hormone-releasing acylated peptide from stomach”, a 28 amino-acid peptide with the third residue (Ser3) acylated by n-octanoic acid. Ghrelin is produced in the stomach, travels to the brain through blood circulation, and acts on ghrelin (or growth hormone secretagogue) receptor (GHSR) to stimulate the mesolimbic dopamine reward pathway and increase rewarding behaviors in rodents. GHSR antagonism has been shown to attenuate rewarding effects induced by various substances including METH, amphetamine, fentanyl, morphine, heroin, cocaine, nicotine, and alcohol. For example, administration of a selective GHSR antagonist significantly reduced the fentanyl‐seeking/relapse‐like behavior in rats. On the other hand, GHSR has diverse regulatory roles associated with its constitutive activity (the activity in the absence of ghrelin ligand) and, hence, GHSR antagonism could also result in unwanted adverse effects. Thus, alternative strategies targeting ghrelin itself could be more interesting. However, whether targeting ghrelin itself would be effective to attenuate the drug rewarding effects remains controversial in literature as ghrelin levels before and after treatment were not measured in previous animal studies targeting ghrelin itself. It is unclear whether any of the previously used approaches was able to decrease the ghrelin level significantly enough to attenuate the substance reward. We propose to use our recently identified ghrelin deacylase (a mutant of human butyrylcholinesterase or BChE) as a safe and effective ghrelin modulator to attenuate substance rewarding effects. Such a ghrelin modulator is expected to be as effective as a GHSR antagonist in treatment of substance use disorders (SUDs) including PSUDs, but without interacting with any brain receptors/transporters. Specifically, in this investigation, we will first evaluate the BChE mutant for its in vivo potency in modulating ghrelin and attenuating the rewarding and reinforcing effects of representative opioids (fentanyl and heroin) and their combinations with METH in various rodent models. Then, we will design and discover a new BChE mutant as a more potent ghrelin deacylase with further improved catalytic activity for ghrelin diacylation, develop its long-acting fusion protein form, and examine the long-term in vivo effects of the long-acting ghrelin deacylase. Accomplishment of this investigation will determine whether ghrelin itself is a truly effective target and whether a potent ghrelin deacylase as a ghrelin modulator is truly effective for treatment of PSUDs. If the answers are all positive, the most effective long-acting ghrelin deacylase (recombinant protein) to be tested and developed may also serve as a promising therapeutic candidate for treatment of PSUDs.