Exposure of Juvenile Mice to High-Dose Acetaminophen Confers Elevated Serum Cytokine Levels and Sociability Impairments in Adulthood

Background: Epidemiological evidence suggests that exposure of children younger than 5 years old to acetaminophen may be problematic for social brain development if it can’t be properly metabolized. Conjugative disposition pathways may be underdeveloped or compromised in some children treated with acetaminophen. Oxidative degradation pathways for acetaminophen are capable of triggering immune responses. We hypothesized that immune system activation could potentially disrupt juvenile brain development to produce autism-like behaviors in mice.  However, the specific factors mediating these effects have not been described, although parallels have been described for mice treated with valproic acid. We have used high dose acetaminophen exposures in juvenile mice (P18-21) to explore mechanisms that might compromise sociability in this population of acetaminophen sensitive children.

Objectives: The hypothesis underlying this study was that high-dose (>100 mg/kg) acetaminophen exposure in weanling (PD 18-21) mice might trigger unique and enduring immune responses that correspond with impairments in the social behavior of C57BL/6J mice, or worsening of them in socially deficient BTBR mice. These enduring changes in the immune system may persist and serve as biomarkers of such exposures.

Methods: Male C57BL/6 and BTBR mice were exposed for 4 days to injections of acetaminophen (400 mg/kg) or vehicle (saline + 10% DMSO), and matured to adulthood (PD 80). Three chamber sociability tests of C57BL/6 mice revealed a significant (p<0.05) reduction in social interaction relative to vehicle controls that was comparable to prenatal treatment with valproic acid. However, the social behavior of BTBR mice was unaffected. We postulated that persistent adverse immune responses might have contributed to this outcome. Serum collected after the behavior tests was used for cytokine and chemokine measurements performed using the Bio-plex mouse cytokine 23-plex panel on the Bio-plex 200 suspension array system. 

Results: Eotaxin levels were significantly higher in C57BL/6 adults treated as juveniles with high dose of acetaminophen. These mice also had high levels of TNF-α and G-CSF, both of which act as stimulation factors for granulocytes. In contrast, in BTBR mice, eotaxin levels were low and along with G-CSF, they remained unaffected by acetaminophen. TNF-α expression was reduced in acetaminophen treated BTBR relative to controls. Eotaxin can inhibit neurogenesis, particularly in the hippocampus. We therefore looked for evidence of reduced hippocampal serotonergic neuronal density based on saturated serotonin transporter binding by quantitative autoradiography, but we found no difference from control treatment values. However, the elevated eotaxin levels in C57BL/6 treated as juveniles with high-dose acetaminophen and differences among strains in their levels may relate in other ways to their sociability phenotypes.

Conclusions: The strain of mouse used in immune system challenge studies strongly influences the outcome of such studies and must be carefully considered. BTBR mice have impaired sociability that was not influenced by high dose acetaminophen. However, in C57BL/6 mice, social behavior was impaired and elevated eotaxin levels may be biomarkers of acetaminophen induced oxidative stress endured during juvenile development that can be measured in adulthood.