Citicoline Protects against Tramadol-Induced Oxidative Stress and Organ Damage

Tramadol is a common drug of abuse which has been shown to cause neurodegeneration in the rat brain. Cytidine-5'-diphosphocholine or citicoline is an intermediate in the synthesis of phosphatidylcholine and is in use in humans for the treatment of several brain pathologies. In this study, we aimed to investigate the effect of citicoline on oxidative stress and tissue injury caused by tramadol, an opioid drug. Rats were treated with tramadol at 30 mg/kg alone or in combination with citicoline at 50, 100, or 200 mg/kg orally, once a day, for 10 days. Other groups were treated with only 0.9% saline or only citicoline at 200 mg/kg. Lipid peroxidation (malondialdehyde), nitric oxide, reduced glutathione (GSH), and paraoxonase-1 (PON-1) activity were measured in the serum. Bone marrow DNA fragmentation assay and micronucleus test were also done. In addition, histopathological examination of the brain, liver, and kidney, and immunohistochemical staining for glial cell acidic fibrillary protein (GFAP) in the cerebral cortex were performed. Results indicated that compared to the saline-treated group, repeated tramadol administration led to significant increases in serum malondialdehyde and nitric oxide concentrations by 50.0% and 70.0%, respectively. There was also a decline in GSH content and PON-1 activity in the serum by 26.3% and 51.4%, respectively. Tramadol caused marked DNA fragmentation and increased the number of micronucleated polychromatic erythrocytes (MnPCE) in bone marrow by 192.8% and 876.3%, respectively, compared with the corresponding saline control values. Histopathological studies revealed neuronal degeneration (acidophilic cytoplasm and dark nuclei) and decreased GFAP immunostaining in the cerebral cortex of tramadol-treated rats. The liver exhibited fibrosis, apoptotic hepatocytes, and inflammatory cell infiltration. Vacuolar degeneration of the tubular lining epithelium and edema of glomeruli were observed in the kidney. Citicoline administered to saline-treated rats at a dose of 200 mg/kg showed no significant effect on serum malondialdehyde, nitric oxide, GSH concentrations, or PON-1 activity compared with the saline control group. Citicoline by itself had no effect on DNA fragmentation or the number of MnPCE in the bone marrow. In tramadol-treated rats, however, citicoline (50–200 mg/kg) resulted in a significantly decreased malondialdehyde by 23.8%–31.6%. Nitric oxide decreased by 29.2%–36.2% after citicoline at 50–200 mg/kg. There was also a significant increase in both GSH by 19.6%–33.6% and in PON-1 activity by 54.8%–125.7%. In addition, citicoline caused a significant decrease in DNA fragmentation (by 29.2%–52.4%) and the number of MnPCE in the bone marrow (by 20.5%–59.5%) in tramadol-treated rats. Histopathological changes caused by tramadol in the brain, liver, and kidney were ameliorated by treatment with citicoline. We conclude that citicoline treatment results in decreased lipid peroxidation and nitric oxide along with increased GSH content and PON-1 activity in the serum of rats treated with tramadol. These changes might account for the beneficial effect of citicoline in decreasing DNA fragmentation and tissue injury caused by tramadol.