Postmortem proteomic analysis in human amygdala of drug addicts: possible impact of tubulin on drug-abusing behavior

Besides the ventral tegmental area and the nucleus accumbens as the most investigated brain reward structures, several reports about the relation between volume and activity of the amygdala and drug-seeking behavior have emphasized the central role of the amygdala in the etiology of addiction. Considering its proposed important role and the limited number of human protein expression studies with amygdala in drug addiction, we performed a human postmortem proteomic analysis of amygdala tissue obtained from 8 opiate addicts and 7 control individuals. Results were validated by Western blot in an independent postmortem replication sample from 12 opiate addicts compared to 12 controls and 12 suicide victims, as a second control sample. Applying 2D-electrophoresis and MALDI-TOF-MS analysis, we detected alterations of beta-tubulin expression and decreased levels of the heat-shock protein HSP60 in drug addicts. Western blot analysis in the additional sample demonstrated significantly increased alpha- and beta-tubulin concentrations in the amygdala of drug abusers versus controls (P = 0.021, 0.029) and to suicide victims (P = 0.006, 0.002). Our results suggest that cytoskeletal alterations in the amygdala determined by tubulin seem to be involved in the pathophysiology of drug addiction, probably via a relation to neurotransmission and cellular signaling. Moreover, the loss of neuroprotection against stressors by chaperons as HSP60 might also contribute to structural alteration in the brain of drug addicts. Although further studies have to confirm our results, this might be a possible pathway that may increase our understanding of drug addiction.