In vivo morphine treatment synergistically increases LPS-induced caspase activity in immune organs

Caspases are a family of proteins important for the elimination of infected cells through the induction of apoptosis as well as the initiation of inflammatory cytokines including IL-1β and IL-18. Morphine exposure to animals and/or cells has been associated with the induction of apoptosis. The most common practices of apoptosis detection have involved removing tissues from animal or humans and the analysis of apoptosis on cells or tissues. These methods can potentially induce spontaneous apoptosis that is unrelated to the actual treatment. The objective of this study was to develop an in vivo detection method for assessing caspase activity induced both by morphine directly and by morphine combined with lipopolysaccharide (LPS)-immune activation. Mice were administered saline, morphine, LPS, or a combination of morphine and LPS. Prior to sacrifice, mice were injected with a polycaspase-specific apoptosis detection probe to detect internal caspase activity in vivo. Results revealed that morphine alone did not directly induce caspase activity. However, morphine significantly enhanced the LPS-induced caspase activity in spleen, thymus, and bone marrow-derived immune cells. The use of a poly-caspase detection probe methodology to label caspase activity in vivo provides a powerful quantitative tool for the in vivo analysis of caspase activity.