Morphine-induced tolerance in the ileum and colon

吗啡和其他阿片类药物仍然是治疗中重度疼痛，包括癌症或手术引起的疼痛的最常开出的药物。本研究的总体目标是阐明吗啡和其他阿片类药物诱导回肠和脑耐受的机制，而不是结肠耐受，这会导致便秘，并限制这些优秀止痛药在人类的长期使用。这项提议是两个高级实验室的合作，一个在胃肠生理学方面有专门知识，另一个在利用分子、细胞和整体动物方法研究吗啡和其他阿片类药物的急性和慢性影响方面具有丰富的经验。需要检验的主要假设是，结肠和回肠之间细胞信号特性的差异导致吗啡诱导回肠耐受，而不是结肠。我们进一步提出，这些组织对各种阿片类药物的耐受率是相同的。我们的初步数据表明，在小鼠慢性给药后，显著的耐受性发展到吗啡的抗伤害效应，耐受性不会发展到便秘效应。第一年提出的工作的主要目标是阐明在不同组织中观察到的吗啡耐受性差异是否适用于体内和体外的其他阿片类药物。在第二年，我们建议进一步评估我们有趣的发现，烟酰胺，一种内源性CD-38抑制剂，诱导结肠对吗啡的耐受，这一现象以前没有报道过。我们将测试这一假设，即CD-38途径阻止结肠耐受发展，并且其通过化学手段或基因敲除动物的阻断允许耐受发生。我们建议调查回肠或脑等其他组织中的CD38是否也对这些组织中耐受性的发展起到调节作用。进一步，我们将研究信号转导过程中的其他步骤，如Mu阿片受体的磷酸化，蛋白激酶C和A的活性，GRK是否会在不同组织中类似或不同地改变阿片耐受的发展。我们的初步数据表明，烟酰胺或8-溴环ADPribose抑制CD38通路会导致结肠对吗啡的耐受。我们将在分离的结肠肌条上测试烟酰胺、兰诺定和cADPribose对耐受性形成和对吗啡依赖的影响，并确定抑制CD38通路是否会导致肠神经元Mu受体磷酸化的变化。这项研究的长期重大公共健康影响是利用这些信息开发治疗没有便秘的慢性疼痛的药物。这些研究还将增加我们对大脑中对阿片类药物的耐受性和最终身体依赖的潜在机制的理解。

Morphine and other opioids remain the most frequently prescribed drugs for the treatment of moderate to severe pain, including pain due to cancer or surgery. The overall goal of this study is to elucidate the mechanisms of morphine and other opioid-induced tolerance in the ileum and brain but not in the colon which leads to constipation and limits the chronic use of these excellent pain relievers in man. This proposal represents a collaboration of two senior laboratories, one with expertise in gastrointestinal physiology and the other with extensive experience in studying the acute and chronic effects of morphine and other opioids, utilizing molecular, cellular and whole animal approaches. The main hypothesis to be tested is that differences in the cellular signaling properties between the colon and ileum result in morphine-induced tolerance in the ileum but not the colon. We further propose that the ratio of tolerance to various opioids is the same across these tissues. Our preliminary data demonstrate that as marked tolerance develops to the antinociceptive effects of morphine following chronic administration in mice, tolerance does not develop to its constipating effects. The major objective of the work proposed in year 1 is to elucidate whether this difference in tolerance in different tissues observed for morphine is the same for other opioids both in vivo and in vitro. In the second year we propose to further evaluate our interesting finding that nicotinamide, an endogenous CD-38 inhibitor, induces tolerance to morphine in the colon, a phenomenon not previously reported. We will test the hypothesis that the CD-38 pathway prevents tolerance development in the colon and that its blockade by either chemical means or genetically in knock out animals allows tolerance to occur. We propose to investigate whether CD38 in other tissues such as the ileum or brain causes a regulatory effect on the development of tolerance in these tissues as well. Further, we will investigate whether additional steps in the signal transduction process such as the phosphorylation of mu opioid receptors, the activity of protein kinase C and A, GRK alter opioid tolerance development similarly or differently in various tissues. Our preliminary data demonstrate that inhibition of the CD38 pathway by either nicotinamide or 8-bromo cyclic ADPribose results in the induction of tolerance to morphine in the colon. We will test the effects of nictoinamide, ryanodine and cADPribose on tolerance development and on dependence to morphine in the isolated colonic muscle strips and determine if inhibition of the CD38 pathways results in changes in mu receptor phosphorylation in enteric neurons. The long-term major public health implication of this research is the use of this information to develop medications to treat chronic pain that are devoid of constipation. These studies will also increase our understanding of the potential mechanisms in the development of tolerance and ultimately physical dependence to opioids in the brain.