Cancer cachexia, which encompasses a range of sickness behaviors such as anorexia, reduced locomotor activity, and depression, diminishes quality of life and increases mortality in cancer patients. Rubiscolin-6 is a hexapeptide derived from ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), a major plant leaf protein. Previous reports have demonstrated that rubiscolin-6 functions as an agonist of the δ opioid receptor, inducing diverse effects such as orexigenic, antinociceptive, and antidepressant-like effects. In this study, we investigated the effects of rubiscolin-6 on sickness behavior in colon26-bearing cachexia model mice. Intraperitoneal administration of rubiscolin-6 enhanced food intake in cachexic mice with chronic anorexia. It also increased locomotor activity, which decreased in cachexic mice, as assessed by the open field test. Moreover, the tail suspension test revealed that rubiscolin-6 alleviated depression-like behavior in mice with cachexia. These findings imply that rubiscolin-6 could be used to ameliorate the sickness behavior associated with cancer cachexia.
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