Molecular mechanisms involved in the adverse effects associated with the chronic use of morphine: role of the TRPA1 receptor and the aldehyde dehydrogenase-2 enzyme

• Grant number: 23/14271-8
• Support Opportunities: Scholarships in Brazil - Master
• Start date: May 01, 2024
• End date: April 30, 2026
• Field of knowledge: Biological Sciences - Pharmacology - Biochemical and Molecular Pharmacology
• Principal Investigator: Vanessa Olzon Zambelli
• Grantee: Natalia Pressuto Pennachioni
• Host Institution: Instituto Butantan. Secretaria da Saúde (São Paulo - Estado). São Paulo , SP, Brazil
• Associated scholarship(s): 25/05902-0 - Role of TRPA1 channels in hyperalgesia and tolerance induced by chronic morphine administration, BE.EP.MS

Abstract

Opioids are currently the most widely used drugs in clinical practice for the treatment of moderate to severe pain. However, chronic use of these analgesics triggers adverse effects, such as tolerance to their analgesic effect and a decrease in nociceptive threshold, a phenomenon known as hyperalgesia. These effects generally lead to the need for dose escalation during treatment to achieve the initial analgesic effect. Therefore, a better understanding of the molecular mechanisms by which opioids induce tolerance and hyperalgesia is crucial for the development of more efficient therapies with fewer adverse effects. The mitochondrial enzyme aldehyde dehydrogenase 2 (ALDH2) metabolizes reactive aldehydes produced from oxidative stress, such as 4-hydroxynonenal (4-HNE), into less reactive acids. About 8% of the global population, particularly in East Asia, carries a point mutation (E487K) in ALDH2, known as ALDH2*2. This mutation reduces the enzyme's activity by up to 100% in homozygous individuals. Initial studies from our group have shown that this mutation is associated with increased sensitivity to adverse effects of opioids, such as tolerance, hyperalgesia, and respiratory depression in rodents. However, the mechanisms by which ALDH2 regulates the deleterious effects of morphine are unknown. It is known that impaired ALDH2 activity elevates 4-HNE levels, inducing hypernociception by activating TRPA1 receptors. Still, the role of this aldehyde in the adverse effects induced by chronic morphine use remains unclear. Therefore, the aim of this study is to investigate the role of ALDH2 and 4-HNE in the cellular and molecular mechanisms involved in the development of analgesic tolerance and hyperalgesia induced by chronic morphine use. The specific objectives include characterizing the chronic effect of morphine in wild-type and ALDH2*2 animals on: a) 4-HNE levels in the dorsal root ganglia (DRG) using the western blot technique; b) the involvement of TRPA1 receptors in this effect using selective antagonists for these receptors; c) TRPA1 receptor signaling by assessing neuropeptide levels (substance P and CGRP) and calcium influx-regulated proteins in the DRG in the presence or absence of the antagonist. The results will be validated using the small molecule Alda-1, which selectively activates both wild-type and mutant enzymes, reducing 4-HNE levels. This project could provide relevant information about the mechanism by which morphine triggers adverse effects such as tolerance and hyperalgesia. If this mechanism is elucidated, this study will contribute to pain management and provide scientific knowledge for better nociception management using opioid analgesics.