FROM THE JOURNAL OF HEPATOLOGY
A new study has found that a strong association exists in adolescents who have obstructive sleep apnea, and their risks of developing more highly progressed forms of nonalcoholic fatty liver disease (NAFLD) or nonalcoholic steatohepatitis (NASH).
“Substantial evidence suggests oxidative stress is a central mediator in NAFLD pathogenesis and progression, although the specific trigger for reactive oxygen species (ROS) generation has not been clearly delineated,” wrote the authors, led by Shikha S. Sundaram, MD of the University of Colorado at Denver, Aurora, adding that “Emerging evidence demonstrates that obesity-related obstructive sleep apnea (OSA) and intermittent nocturnal hypoxia are associated with NAFLD progression.”
Dr. Sundaram and her coinvestigators looked at patients admitted to the Children’s Hospital Colorado Pediatric Liver Center from June 2009 through January 2014. Subjects included were children ages 8-18 years, male and female, who were classified as Tanner stage 2-4 with liver biopsy evidence of NAFLD.
“In our center, a clinical liver biopsy for suspected NAFLD is performed in overweight or obese children (body mass index greater than 85% for age and gender) with chronically elevated aminotransferases in whom a diagnosis is unclear based on serologic testing,” Dr. Sundaram and her coauthors clarified regarding the screening process.
Additionally, age-matched “lean” children, that is, those with a body mass index lower than 85%, were also enrolled as controls; these subjects were included if they had no evidence of hepatomegaly or liver disease – translated to AST and ALT levels of 640 IU/L – and were also Tanner stage 2-4. The authors explained that this Tanner stage range was chosen in order to “minimize variations in insulin sensitivity that may confound the interpretation of potential associations between OSA/hypoxia and NAFLD.”
Ultimately, 36 NAFLD adolescent subjects and 14 controls completed the study. A total of 25 of the 36 NAFLD subjects (69.4%) had OSA and/or nocturnal hypoxia; of these, 15 were classified as having isolated OSA, 9 had both OSA and hypoxia, and 1 had isolated hypoxia. Polysomnograms found that all NAFLD subjects spent more than 12% of their total time asleep in REM sleep, which was deemed adequate enough to consider the findings valid.
Based on liver histology scoring, laboratory testing, urine F2-isoprostanes, and 4-hydroxynonenal liver immunohistochemistry tests that were conducted on all subjects, Dr. Sundaram and her coinvestigators found that subjects with OSA or hypoxia had more severe fibrosis than did those without. While the latter cohort were 100% stage 0-2, only 64% of those with OSA/hypoxia were stage 0-2, while the remaining 36% were stage 3 (P = .03). Additionally, higher F2-isoprostanes – used to measure lipid peroxidation – correlated with apnea/hypoxia index (r = 0.39; P = .03), and the most severe OSA/hypoxia occurred in subjects that had the greatest 4-hydroxynonenal staining (P = .03). Furthermore, an increase in both F2-isoprostanes and 4-hydroxynonenal hepatic staining was shown to lead to a higher risk of worse steatosis: r = 0.32 and r = 0.47, respectively (P = .04 and P = .007).
“These data support sleep disordered breathing as an important trigger of oxidative stress that promotes progression of pediatric NAFLD to NASH,” the authors concluded, adding that “this study confirms that OSA/hypoxia is common in pediatric NAFLD and that more severe OSA/hypoxia is associated with elevated aminotransferases, hepatic steatosis, inflammation, NAS [NAFLD activity score], and fibrosis.”
Dr. Sundaram and her coauthors call for further research to examine if “prevention or reversal of NASH following effective therapy of OSA and nocturnal hypoxia in obese patients” is viable.
This study was supported by funding from the National Institutes of Health. Dr. Sundaram and her coinvestigators did not report any relevant financial disclosures.