Role of Influenza B virus in hepatic steatosis and mitochondrial abnormalities in a mouse model of reye syndrome

The hepatic steatosis observed in the influenza B virus mouse model of Reye syndrome has been attributed to infectious virus or, alternately, to decreased food intake in the virus-treated mice or impurities in the virus preparation. To resolve this issue, 4- to 6-wk-old male Balb C mice were given, by intravenous injection, 12,800 hemagglutination units of influenza B Lee/40 virus in phosphate buffered saline/1% bovine serum albumin using virus prepared by ultracentrifugation from infected allantoic fluid, by sucrose density-gradient purification of virus prepared by ultracentrifugation from infected allantoic fluid or by irradiation of virus prepared by ultracentrifugation from infected allantoic fluid to inactivate virus. The infectivity titer of virus prepared by ultracentrifugation from infected allantoic fluid was much higher than that of sucrose density-gradient purified virus prepared from infected allantoic fluid: 50% egg infectious dose for virus prepared by ultracentrifugation from infected allantoic fluid was 3.9 × 10⁴/hemagglutination unit vs. 8.7 50% egg infectious dose/hemagglutination unit for sucrose density-gradient purified virus prepared from infected allantoic fluid. Control mice received phosphate-buffered saline/1% bovine serum albumin or uninfected allantoic fluid diluted in phosphate-buffered saline/1% bovine serum albumin. Mice were fasted to eliminate dietary variation, and livers were obtained 36 hr after virus administration. Of the above treatments, only virus prepared by ultracentrifugation from infected allantoic fluid caused clinical illness and increased hepatic triglycerides (p < 0.02) compared with controls. Hepatic triglycerides in virus prepared by ultracentrifugation from infected allantoic fluid correlated with histopathological vacuolization scores (r = 0.5773; p < 0.03).

Hepatic mitochondrial enzymes succinate dehydrogenase and glutamate dehydrogenase were decreased (p < 0.003) in mice given virus prepared by ultracentrifugation from infected allantoic fluid compared with mice given phosphate-buffered saline/1% bovine serum albumin. Two mechanisms that could explain this finding—peroxidation of and changes in the composition of mitochondrial membrane lipids—were investigated. Treatment with virus prepared by ultracentrifugation from infected allantoic fluid did not result in increased mitochondrial lipid peroxidation, as measured by conjugated dienes, but was associated with a 27% increase in hepatic mitochondrial cholesterol compared with treatment with phosphate-buffered saline/1% bovine serum albumin (p < 0.05).

We conclude that treatment of young mice with virus prepared by ultracentrifugation from infected allantoic fluid leads to hepatic steatosis and illness resulting from the high titer of infectious virus in the preparation and not from viral proteins or nonviral components of the infected or uninfected allantoic fluid or from dietary factors. Administration of virus to young mice results in depression of hepatic mitochondrial enzymes, similar to findings in children with Reye syndrome. The possibility that these abnormalities are the consequence of increased hepatic mitochondrial cholesterol deserves further investigation. (HEPATOLOGY 1991;13:96–103).