GENOME-WIDE DNA METHYLATION ANALYSIS IN THE SALIVA OF CRACK COCAINE DEPENDENTS

Background DNA methylation has been increasingly recognized in the etiology of drug dependence. Due to the difficulties in assessing brain tissue in living humans, peripheral cells such as blood and saliva have been explored as alternatives to explore the involvement of DNA methylation in drug dependency. Here, we characterized DNA methylation changes in the saliva from crack cocaine users compared to health controls. Methods DNA was extracted from saliva of 128 crack cocaine dependents and 109 health controls (males, age 34.8 +/- 9.9 years). Bisulfite converted DNA was hybridized in the Illumina Infinium MethylationEPIC BeadChip arrays. Cellular composition heterogeneity was corrected using RefFreeEwas followed identification of differentially CpG sites using limma (DMSs). Using DMSs with pvalue Results Comparison between crack cocaine dependents and controls revealed 3,857 DMRs which were involved with metabolic processes related to nucleic acid, ncRNA and rRNA processing, gene expression and protein-DNA complex assembly. The gene-gene interaction analysis revealed three networks: one containing 11 genes, which were enriched for biological processes related to mitochondrial function; a second network composed by 36 genes which was enriched mainly for glycosylphosphatidylinositol (GPI) activity and extracellular membrane interaction biological processes; and a third network with 22 genes that was enriched for synapse related processes (GABaergic, serotononergic and cholinergic synapses) and, interestingly, biological processes related to visual perception. Discussion These results suggest that the use of saliva may help to understand the mechanisms underlying the pathology of drug abuse. Changes in DNA methylation found in the saliva revealed perturbation in pathways related to the reward system, often found affected in drug dependents. Moreover, the enrichment analysis of the networks replicated our previous study performed in peripheral blood where molecular functions related to protein activity were associated with cocaine and crack dependency.