23 - Perinatal Exposure to Cyclohexanone Induces Profound Behavioral Deficits in Adulthood Including Hyperactivity and Disinhibition

The organic solvent cyclohexanone (CXO) is a sealer for polyvinyl chloride (PVC) IV bags and stopcocks. CXO leaches from plastic tubing, with high levels of CXO breakdown products in the urine of NICU patients. Use of cardiopulmonary bypass in cardiac surgery leads to a 3-fold increase in serum CXO levels in neonates. Elevated serum CXO levels in neonatal cardiac surgery with bypass are independently associated with poor neurodevelopment.

Objective:

Test the hypothesis that neonatal rat exposure to clinically relevant CXO levels is causal for functional neurodevelopmental deficits similar to those observed in children after neonatal cardiac surgery.

Design/Methods:

CXO concentrations were determined from 25 independent IV bags of total parenteral nutrition (TPN) with a median (IQR) concentration of 10.1 ug/mL (6.8-12.4 ug/mL).  On postnatal day 7 (P7, term equivalent) Sprague-Dawley rat littermates of both sexes were randomly allocated to receive intraperitoneal CXO injections (0.7ul/g body weight/day based on CXO concentrations in NICU TPN) or saline q12 hr for 7 days (P15, infantile equivalent).  Rats underwent behavioral testing by masked observers at P40 (young adult equivalent), including assessment of gait, coordination, and open field behavior. Comparisons were assessed with a student’s t-test with p< 0.05 considered statistically significant (n=6-8).

Results:

Rats exposed to CXO are hyperactive and hypermobile, with significant increases in distance traveled, time mobile, and center time during testing in an open field. Specifically, exposed rats travelled an average distance of 26.7 ± 2.1 meters compared to the 14.1± 1.9 meters by controls (p=0.02), had a mean mobile time of 222.4 ± 9.0 seconds vs. 153.6 ± 3.1 seconds (p=0.006), and mean center time of 21.1 ± 5.2 seconds vs. 6.0 ±1.5 seconds (P=0.04).

Exposed rats also showed significant abnormalities in gait, posture and balance, including impairments in stance, paw placement and break. Specifically, exposed rats had mean breaking time of 0.034 ± 0.005 seconds (p=0.02) compared to the 0.017 ± 0.001 seconds of controls, mean stance width of 3.3 ± 0.017 cm vs. 2.2 ± 0.05 cm (p=0.01), and mean angle of 8.1± 1.9 degrees vs 3.0 ± 0.29 degrees (p=0.01).

Conclusion(s):

CXO exposure for 7 days at equivalent levels to human neonatal exposure produced hyperactivity and motor abnormalities that persisted into adulthood and are common in 30% of children after neonatal cardiac surgery. Additional studies are needed to establish the mechanism of CXO-induced brain injury, and avenues for neurorepair and novel methods to reduce medical CXO exposures.