Therapeutic concentration of morphine reduces oxidative stress in glioma cell line

Abstract

Morphine is a potent analgesic opioid used extensively for pain treatment. During the last decade, global consumption grew more than 4-fold. However, molecular mechanisms elicited by morphine are not totally understood. Thus, a growing literature indicates that there are additional actions to the analgesic effect. Previous studies about morphine and oxidative stress are controversial and used concentrations outside the range of clinical practice. Therefore, in this study, we hypothesized that a therapeutic concentration of morphine (1 μM) would show a protective effect in a traditional model of oxidative stress. We exposed the C6 glioma cell line to hydrogen peroxide (H2O2) and/or morphine for 24 h and evaluated cell viability, lipid peroxidation, and levels of sulfhydryl groups (an indicator of the redox state of the cell). Morphine did not prevent the decrease in cell viability provoked by H2O2 but partially prevented lipid peroxidation caused by 0.0025% H2O2 (a concentration allowing more than 90% cell viability). Interestingly, this opioid did not alter the increased levels of sulfhydryl groups produced by exposure to 0.0025% H2O2, opening the possibility that alternative molecular mechanisms (a direct scavenging activity or the inhibition of NAPDH oxidase) may explain the protective effect registered in the lipid peroxidation assay. Our results demonstrate, for the first time, that morphine in usual analgesic doses may contribute to minimizing oxidative stress in cells of glial origin. This study supports the importance of employing concentrations similar to those used in clinical practice for a better approximation between experimental models and the clinical setting.

Figure 1. Cell viability of C6 cell line exposed to increasing concentrations of hydrogen peroxide (H₂O₂) and/or 1 µM morphine for 24 h. Data are reported as means±SE. No significant differences were detected in groups incubated with the same concentration of H₂O₂ (ANOVA).

Figure 2. Lipid peroxidation of C6 cell line exposed to 0.0025% hydrogen peroxide (H₂O₂) and/or 1 µM morphine for 24 h. Data are reported as means±SE. *P<0.05 vs control and morphine groups; ^#P<0.05 vs peroxide group (ANOVA and Tukey test).

Figure 3. Content of sulfhydryl groups in the C6 cell line exposed to 0.0025% hydrogen peroxide (H₂O₂) and/or 1 µM morphine for 24 h. The insert shows levels of scavenged H₂O₂ in vitro in the presence of 1-100 µM morphine. Data are reported as means±SE. *P<0.05 vs all groups (ANOVA and Tukey test).