Liver Gene Ces1 Identified as Major Genetic Driver of Cocaine Addiction
Summary: A large genetic study from the University of California San Diego reveals that a primary genetic influence on cocaine addiction lies in the liver, not the brain. Researchers mapped millions of genetic markers in nearly 900 genetically diverse rats and identified a cluster of liver metabolism genes, Ces1, that strongly predict compulsive cocaine use by altering how the body processes the drug.
Using N/NIH Heterogeneous Stock rats to better mirror human genetic diversity, the research team combined detailed behavioral data on cocaine self-administration with dense genome-wide analysis. Their work isolates metabolic pathways in the liver—particularly genes encoding carboxylesterase enzymes—as major contributors to whether an individual escalates drug intake into compulsive, addiction-like behavior.
Key Facts
- Addiction beyond the brain: While substance use disorders have traditionally been studied as neurocentric conditions—focused on reward circuits and dopamine—this study demonstrates a substantial role for peripheral metabolism. How the liver breaks down cocaine can shape the timing and intensity of drug-driven behaviors.
- The
Ces1gene cluster: The researchers pinpointed a set of carboxylesterase genes (Ces1) that encode enzymes directly responsible for metabolizing cocaine. Genetic variation in these genes affects drug clearance rates and is linked to the frequency and urgency of self-administration. - Diverse model: heterogeneous stock rats: Unlike inbred lab strains, heterogeneous stock rats carry wide genetic variation similar to human populations. This diversity enabled the team to detect genetic differences that predict susceptibility versus resistance to compulsive drug use.
- Six addiction-linked genomic regions: Genome-wide association across nearly 900 animals identified six chromosomal loci associated with addiction-like phenotypes, including escalation of intake and the intervals between self-administered doses.
- Translational validation with
Trak2: The study replicated a human-associated locus, theTrak2region, strengthening confidence that these rodent findings relate to human cocaine use disorder. - Therapeutic implications: Targeting liver carboxylesterase activity offers a new treatment strategy. Modifying peripheral drug metabolism could reduce the addictive impact of cocaine without directly altering brain chemistry, potentially avoiding neuropsychiatric side effects associated with central nervous system interventions.
- Preclinical Addiction Biobank: The project established a biobank of blood, urine, brain, and peripheral tissues to support biomarker discovery and translational studies aimed at predicting individual genetic risk before addiction develops.
Source: UCSD
Researchers at the University of California San Diego completed a large genome-wide study that identifies liver-based genetic drivers of cocaine self-administration and suggests new peripheral targets for treatment.
Published in Nature Communications, the study harnessed a cohort of 836 heterogeneous stock rats (415 females and 421 males) to evaluate cocaine-related behaviors—acquisition, escalation, and compulsive-like responding—while scanning millions of genetic markers per animal. Phenotypic correlations and modest SNP heritability guided discovery of statistically significant associations across the genome.
“Finding a liver enzyme that shapes cocaine-taking behavior was an ‘aha’ moment,” said co-corresponding author Olivier George, PhD, professor of psychiatry at UC San Diego School of Medicine. The finding highlights addiction as a whole-body problem in which peripheral drug processing interacts with brain circuits to determine behavioral outcomes.
Co-corresponding author Abraham A. Palmer, PhD, professor of psychiatry at UC San Diego School of Medicine, emphasized the translational value: identifying genes that drive risk allows drug development efforts to consider strategies that shift a genetically susceptible profile toward resistance, potentially by altering metabolism rather than central nervous system signaling.
The team found one notable locus on rat chromosome 19 that influences the post-infusion interval—the time between self-administered doses. This region contains several carboxylesterase genes orthologous to human CES1; carboxylesterases are known to metabolize cocaine. Three non-synonymous coding variants in Ces1c and Ces1d were found in perfect linkage with this locus, supporting a direct mechanistic role.
Other loci identified contain promising variants and gene candidates previously linked to substance use, including Trak2, Slc10a7, Plcl1, and Satb2—genes with prior associations to cocaine, alcohol, or tobacco use. Replicating Trak2 provides a cross-species validation that strengthens the study’s relevance for human addiction research.
First author Montana Kay Lara, PhD, noted that validating the Ces1 signal gives the team a concrete biochemical target to test whether modifying cocaine metabolism can blunt compulsive intake. The next research phase will investigate precisely how the identified genetic variants alter enzyme function and cocaine pharmacokinetics.
The research group is also leveraging the Preclinical Addiction Biobanks—extensive collections of blood, urine, brain, and peripheral tissues—to search for circulating biomarkers that predict genetic risk. These biomarker efforts aim to enable early identification and personalized prevention strategies before addiction develops.
This large-scale, collaborative effort combined behavioral neuroscience, quantitative genetics, and long-term cohort work across multiple institutions, showing the value of team science for uncovering complex biological drivers of addiction.
Additional coauthors on the study include a multidisciplinary team of investigators from UC San Diego, The Scripps Research Institute, and Wake Forest University School of Medicine.
Funding: The study was supported by the National Institute on Drug Abuse within the National Institutes of Health (P50DA037844, P30DA060810, U01DA051234, U01DA043799, and U01DA060810).
Key Questions Answered:
A: The liver determines how long and at what concentration a drug remains in the bloodstream. Carboxylesterase enzymes produced from Ces1 genes metabolize cocaine. Genetic variations that change metabolism speed or pathways can create rapid drops in drug levels that trigger urgent cravings and more frequent dosing, accelerating the transition to compulsive use.
A: Standard inbred laboratory rodents lack the genetic diversity necessary to model why individuals differ in addiction vulnerability. Heterogeneous stock rats capture wide genetic variation similar to human populations, enabling genomic mapping of risk and resistance factors that are more likely to translate to humans.
A: Targeting peripheral metabolism could blunt addictive drives by changing drug exposure without directly altering brain reward circuits. This approach may reduce the risk of neuropsychiatric side effects—like depressed mood or emotional blunting—that can accompany treatments that act on central nervous system pathways.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by staff.
About this genetics and addiction research news
Author: Miles Martin
Source: UCSD
Contact: Miles Martin – UCSD
Image: Image credited to Neuroscience News
Original Research: Open access. “Genome-wide association study of cocaine self-administration behavior in Heterogeneous Stock rats” by Montana Kay Lara et al., Nature Communications. DOI: 10.1038/s41467-026-73694-w.
Abstract
Genome-wide association study of cocaine self-administration behavior in Heterogeneous Stock rats
Cocaine use disorder (CUD) is a major public health problem and its genetic underpinnings remain incompletely understood. We performed a genome-wide association study in outbred N/NIH Heterogeneous Stock rats (n = 836; female = 415, male = 421) and measured phenotypes related to acquisition of self-administration, escalation of intake, and compulsive-like responding. These traits were correlated and showed modest SNP heritability (h2 = 0.07–0.16). Six genome-wide significant associations were identified. One locus on chromosome 19 was associated with variable time between cocaine infusions and contains several carboxylesterase genes orthologous to human CES1, enzymes known to metabolize cocaine. Three non-synonymous coding variants in Ces1c and Ces1d were in perfect linkage disequilibrium with this locus. Other loci include coding and expression variants in genes such as Trak2, Slc10a7, Plcl1, and Satb2, which have prior links to substance use. This largest genetic study of cocaine self-administration in rats replicates human loci and highlights carboxylesterases as potential pharmacological targets.