molecules Review Endocannabinoid System Dysregulation from Acetaminophen Use May Lead to Autism Spectrum Disorder: Could Cannabinoid Treatment Be Efficacious? Stephen Schultz 1, Georgianna G. Gould 1, Nicola Antonucci 2, Anna Lisa Brigida 3 and Dario Siniscalco 4,* 1 Department of Cellular and Integrative Physiology, Center for Biomedical Neuroscience, University of Texas (UT) Health Science Center San Antonio, San Antonio, TX 78229, USA; [email protected] (S.S.); [email protected] (G.G.G.) 2 Biomedical Centre for Autism Research and Therapy, 70126 Bari, Italy; [email protected] 3 Department of Precision Medicine, University of Campania, 80138 Naples, Italy; [email protected] 4 Department of Experimental Medicine, University of Campania, 80138 Naples, Italy * Correspondence: [email protected] Abstract: Persistent deficits in social communication and interaction, and restricted, repetitive pat- terns of behavior, interests or activities, are the core items characterizing autism spectrum disorder (ASD). Strong inflammation states have been reported to be associated with ASD. The endocannabi- noid system (ECS) may be involved in ASD pathophysiology. This complex network of lipid signal- ing pathways comprises arachidonic acid and 2-arachidonoyl glycerol-derived compounds, their G-protein-coupled receptors (cannabinoid receptors CB1 and CB2) and the associated enzymes. Alter- Citation: Schultz, S.; Gould, G.G.; ations of the ECS have been reported in both the brain and the immune system of ASD subjects. ASD Antonucci, N.; Brigida, A.L.; Siniscalco, D. Endocannabinoid children show low EC tone as indicated by low blood levels of endocannabinoids. Acetaminophen System Dysregulation from use has been reported to be associated with an increased risk of ASD. This drug can act through the Acetaminophen Use May Lead to ECS to produce analgesia. It may be that acetaminophen use in children increases the risk for ASD by Autism Spectrum Disorder: Could interfering with the ECS.This mini-review article summarizes the current knowledge on this topic. Cannabinoid Treatment Be Efficacious?. Molecules 2021, 26, 1845. Keywords: autism; endocannabinoids; acetaminophen; endocannabinoid system https://doi.org/10.3390/ molecules26071845 Academic Editors: Alessandra Bisi 1. Introduction and Angela Rampa Autism spectrum disorder (ASD) is a life-long disability that manifests in early child- hood and continues throughout the lifespan, producing huge social and economic impacts Received: 26 February 2021 to society [1]. ASD is defined in the Diagnostic and Statistical Manual of Mental Disorders, Accepted: 22 March 2021 Published: 25 March 2021 5th edition [1], which combines the previously separate categories of autistic disorder, As- perger’s syndrome, and pervasive developmental delay—not otherwise specified. ASD’s Publisher’s Note: MDPI stays neutral core symptoms are deficits in social interactions and communication, along with repetitive with regard to jurisdictional claims in patterns of behavior. The core symptoms can range in severity along three defined levels published maps and institutional affil- indicating the spectrum of disability.ASD risk has been shown to be due to both genetic iations. and environmental risk factors in approximately equal proportions [2]. Early in 2008, we showed that acetaminophen use may increase the risk for ASD [3]. Since then, others have also shown an increased risk for ASD when children are given acetaminophen or are exposed to acetaminophen prenatally [4,5]. It has been shown that acetaminophen acts through the endocannabinoid system (ECS) to produce analgesia [6]. We have demon- Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. strated ECS dysregulation in ASD as shown by lower levels of cannabinoid receptor 2 This article is an open access article (CB2) in peripheral blood mononuclear cells [7]. ECS dysregulation may be the method by distributed under the terms and which acetaminophen use increases the risk for ASD and may point the way to a potential conditions of the Creative Commons treatment. There are currently no approved medications to treat the core symptoms of ASD. Attribution (CC BY) license (https:// In Section2, we will provide an overview of the ECS. In Section3, we will show creativecommons.org/licenses/by/ evidence for ECS disruption in ASD and in animal models for ASD. Section4 will provide 4.0/). chemical information for acetaminophen as well as mechanisms for its analgesic action. Molecules 2021, 26, 1845. https://doi.org/10.3390/molecules26071845 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x FOR PEER REVIEW 2 of 11 point the way to a potential treatment. There are currently no approved medications to treat the core symptoms of ASD. In Section 2, we will provide an overview of the ECS.In Section 3, we will show ev- Molecules 2021, 26, 1845 2 of 11 idence for ECS disruption in ASD and in animal models for ASD.Section 4 will provide chemical information for acetaminophen as well as mechanisms for its analgesic ac- Sectiontion.Section5 will 5 introduce will introduce animal animal models models of ASD of andASD show and show evidence evidence that acetaminophen that acetamino- mayphen change may change behavior behavior in these in animals these animals through th therough ECS. the In Section ECS.In6 ,Section we will 6, show we will evidence show thatevidence acetaminophen that acetaminophen use may increase use may ASD increa risk.se ASD Currently risk.Currently used medical used treatments medical treat- for ASDments will for be ASD discussed will be in discussed Section7. Sectionin Section8 will 7. provideSection 8 evidence will provide that cannabinoids evidence that may can- benabinoids useful in may treating be useful ASD in through treating the ASD ECS. through The discussion the ECS. andThe summarydiscussion of and these summary topics willof these be in topics Section will9. be in Section 9. 2.2. OverviewOverview ofof thethe EndocannabinoidEndocannabinoid SystemSystem WeWe havehave reviewedreviewed thethe linklink between between thethe endocannabinoid endocannabinoid systemsystem andand ASDASD [ 8[8].]. AsAs shownshown inin Figure1 1 fromfrom ourour 2013 paper, the the EC ECSS consists consists of of the the classical classical cannabinoid cannabinoid re- receptorsceptors 1 1and and 2 2 (CB1 (CB1 and and CB2) CB2) along with the endocannabinoidsendocannabinoids thatthat activateactivate them,them, primarilyprimarily anandamideanandamide andand 2-arachidonylglycerol2-arachidonylglycerol (2-AG),(2-AG), andand thethe enzymesenzymes responsibleresponsible forfor theirtheir synthesissynthesis andand degradation. degradation.Diacylglycerol Diacylglycerol lipaselipase (DAG(DAG lipase)lipase) isis responsibleresponsible forfor thethe synthesissynthesis ofof 2-AG,2-AG, and andN N-acyl-acyl phosphatidylethanolamine-specific phosphatidylethanolamine-specific phospholipasephospholipase DD (NAPE-PLD)(NAPE-PLD) is is the the key key enzyme enzyme for for the the synthesis synthesis of anandamide.of anandamide.The The enzyme enzyme responsible responsi- forble 2-AGfor 2-AG degradation degradation is monoacylglycerol is monoacylglycer lipaseol lipase (MAGL), (MAGL), and the and enzyme the enzyme that degrades that de- anandamidegrades anandamide is fatty acidis fatty amide acid hydrolase amide hydrolase (FAAH). The(FAAH).The endocannabinoid endocannabinoid receptors recep- regu- latetors cells regulate by reducing cells by the reducing activation the ofactivation adenylyl of cyclase, adenylyl thereby cyclase, decreasing thereby thedecreasing production the ofproduction cyclic adenosine of cyclic monophosphate adenosine monophosph (cAMP). Theate ECS (cAMP). provides The regulation ECS provides for the regulation immune systemfor the throughimmune CB2system receptors through on CB2 immune receptors system on cells.immune CB1 system receptors cells. are CB1 found receptors atthe highestare found concentration atthe highest in the concentration brain and the in peripheralthe brain nervousand the systems,peripheral where nervous they systems, provide awhere regulatory they functionprovide thata regulatory is required function for proper that synaptogenesis, is required for axon proper growth synaptogenesis, and position- ing,axon and growth neuronal and positioning, cell fate [9]. Theand lackneuronal of proper cell fate control [9]. The over lack axon of growth proper couldcontrol result over inaxon improper growth development could result ofin theimproper corpus deve callosum,lopment which of the provides corpus acallosum, pathway which for axons pro- traversingvides a pathway the brain for fromaxons one traversing hemisphere the brain to the from other. one hemisphere to the other. FigureFigure 1.1. EndocannabinoidEndocannabinoid system system workflow workflow in in peripheral peripheral blood blood mononuclear mononuclear cells cells of of patients patients with autismwith autism spectrum spectrum disorder disorder (ASD). (ASD). The cannabinoid The cannabino receptorid receptor 2 (CB2) 2 (CB2) gene isgene over-expressed, is over-expressed, as well as well as protein levels. The anandamide synthesis enzyme N-acyl phosphatidylethanola- as protein levels. The anandamide synthesis enzyme N-acyl phosphatidylethanolamine-specific mine-specific phospholipase D (NAPE-PLD) gene is slightly decreased. Reprinted from [7], with phospholipase D (NAPE-PLD) gene is slightly decreased. Reprinted from [7], with permission from permission from Springer (Berlin/Heidelberg,