Effects of chronic tramadol exposure on the zebrafish brain: A proteomic study

Tramadol hydrochloride (TH), has become the most prescribed opioid worldwide. However, its neurotoxicity and abuse potential are not well documented. In the present study, TH administration induced abnormal behavior and body and brain mean weight loss. Two principal metabolites O- and N-desmethyltramadol were detected in the brain tissue, and N-desmethyltramadol was the main metabolite produced. A total of 30 differential protein spots were identified using semi-quantitative 2D-PAGE and proteomic analyses, and classified into 13 categories, in which subtypes of 14-3-3 proteins, creatine kinase, ATP synthase beta chain, and tubulin were identified at the separated location on the gels 3, 3, 4, and 11 times respectively. Many TH responsive proteins have functions related to oxidative stress, including 14-3-3 proteins, creatine kinase BB, ubiquitin carboxy-terminal hydrolase L-1, ATP synthase, synaptosome-associated protein, tubulin and actin. Irrespective of oxidative damage, other pathways affected include apoptosis, energy metabolism, signal disorders, and cytoskeletal structure. Ultrastructural observation of mitochondria showed a series of morphological changes in the case of TH exposure. 2D-PAGE was performed with some modifications. The first dimension was performed on 18cm immobilized non-linear gradient strips at pH 5–8. After focusing, the strips were reduced and alkylated for 15min respectively. The strips were then cut into two portions from pH 8 to 5: 0–9cm (right map) and 9–18cm (left map), and the equal portions of gel strip from the control or tramadol administered group were recombined on the same SDS-PAGE (10%). Using the semi-quantitative 2D-PAGE, identical proteins from control and treatment were shown in one map with mirror symmetry passing through a central axis. [Display omitted] ► Tramadol induced abnormal behavior, both body and brain weight loss in zebrafish. ► The fish brain shows two metabolites N- and O-desmethyltramadol, which latter one is important. ► A proteomic study of zebrafish brain by tramadol has novel and significant characteristics. ► 30 differential protein spots were identified by proteomic analysis. ► Functional proteins of oxidative stress and apoptosis etc. are revealed exposed to tramadol.