Met-enkephalin modulates lipid peroxidation and total sialic acid level in CBA mice in age- and sex-dependent manners.

Age- and sex-associated differences in lipid peroxidation (LPO), and total sialic acid content (TSA) in response to abuse of drugs have been reported both in humans and experimental animals. However, no data on the influence of gender and age on these parameters have been reported for methionine-enkephalin (MENK). In this study we examined the influence of age and gender on MENK-induced LPO levels in the liver and TSA content in splenocytes of CBA mice. LPO production, which was age- and gender-associated was differentially regulated by MENK at a dose of 10 mg or 2.5 mg/kg body weight. At the higher dose, MENK stimulated LPO production in younger males and females but suppressed only in older male mice. At the lower dose, MENK induced strong suppression in males while being without any effect in females. In TSA levels, the age-associated increase was greater in males and much lower in females, with higher TSA levels in younger (2.5, 4.5 months) and decreased levels in older female mice (9 months) being observed. Contrary to the effect on LPO level, TSA level in MENK-treated mice was suppressed in both sexes but only in young 2.5-month-old mice. These data provide evidence that some immunomodulatory properties of MENK are age- and gender-associated which may be relevant to the potential use of MENK as adjuvant therapy in patients with immunocompromised status.