Differential effects of isoflurane and CO2 inhalation on plasma levels of inflammatory markers associated with collagen-induced arthritis in DBA mice

Abstract Inhalation of CO 2 or isoflurane is a commonly used method of euthanasia with mice, but information related to their effects on serum inflammatory markers in chronic models of inflammation is limited. In the current study, nineteen-week old DBA female mice with ( n  = 53) or without ( n  = 51) collagen-induced arthritis were randomly assigned to euthanization with CO 2 ( n  = 55) or isoflurane ( n  = 49. Plasma was collected for the measurement of soluble intercellular adhesion molecule-1 (sICAM-1), tumor necrosis factor alpha (TNF-α), and interleukin-6 (IL-6) by ELISA. When mice without and with collagen-induced arthritis were pooled, compared to CO 2 , administration of isoflurane was associated with lower production of the pro-inflammatory cytokines TNF-α (pg/ml, mean ± SEM) (26.1 ± 2.82 versus 48.1 ± 7.99) and IL-6 (25.18 ± 2.73 versus 48.1 ± 6.82) (ANOVA, p 2 decreased the plasma sICAM-1 level (1170 ± 50 versus 758 ± 24 for CO 2 ) ( p 2 and isoflurane persisted. Low plasma sICAM-1 levels found in CO 2 euthanasia group may be due to degradation. Since mice are the most common animal model for studying inflammation, researchers should be aware of these iatrogenic experimental variables before interpreting their data.