The Effects of Oleoyl Alanine and Oleoyl Glycine on Affective and Somatic Opiate Withdrawal Behaviours in Male Sprague Dawley Rats

Abstract

Opiate use continues to rise worldwide, leading to a record number of opiate-dependent individuals seeking detoxification treatment. Opiate withdrawal produces a syndrome of physiological and psychological disturbances, poorly managed by currently available treatment options. Preclinical research suggests that the endocannabinoid system, and related fatty acids, play an essential role in the regulation of opiate withdrawal behavioural and neurobiological responses in rodents. N-Oleoyl glycine (OlGly) is a N-acyl amino acid that interacts with the cannabinoid-1 receptor (CB1) and peroxisome proliferator-activated receptor alpha (PPAR) to attenuate somatic and affective behavioural responses produced by acute naloxone-precipitated morphine withdrawal (NPMWD) in rats. However, several fatty acids, including OlGly, are short-lived in the body due to rapid enzymatic degradation, thus, limiting their therapeutic potential. Consequently, a methylated version of OlGly, N-Oleoly alanine (OlAla), was synthesized because methylation of fatty acids can provide compound stability. In Chapter 2, using multiple behavioural paradigms in male rats, intraperitoneal OlAla reduced acute NPMWD affective and somatic responses through CB1 and PPAR mechanisms, consistent with previous findings using the structurally similar OlGly compound. OlAla produced longer-lasting attenuation of opiate withdrawal behaviour than OlGly, consistent with the use of methylation to increase the stability of the fatty acid stability in-vivo. The experiments in Chapter 3 evaluated the potential of OlGly and OlAla to attenuate withdrawal following chronic opiate exposure. In each experiment, OlAla reduced somatic withdrawal-induced behaviours, while OlGly was without effect. Also, OlAla pretreatment reversed molecular changes in the gut and brain induced by chronic opiate administration followed by withdrawal. In Chapter 4, to provide enhanced translational appeal of this work to clinical populations, orally administered OlAla was tested on opiate withdrawal behaviour. Oral OlAla maintained its ability to reduce withdrawal following acute and chronic opiate exposure, signifying that multiple routes of administration are compatible with our observed effects. The results are discussed within the context of opiate withdrawal neurobiology and the use of OlAla for the treatment of opiate withdrawal in clinical populations. Overall, these data support the continued investigation of fatty acid compounds as potential treatment options for opiate withdrawal.