CEREBELLAR AND HIPPOCAMPAL AMMONIA ELEVATION ACROSS LIVER DISEASE STAGES: IMPLICATION OF GLUTAMINASE

Hyperammonemia and inflammation are major contributors to hepatic encephalopathy. Altered neurological function and neuroinflammation in cerebellum and hippocampus were reported in patients with steatotic liver disease (SLD) before reaching cirrhosis. In early stages of hepatic disease, some studies report unaltered blood ammonia, but brain levels in SLD patients remain unexamined. Neuroinflammation may increase brain ammonia by upregulating glutaminase, enzyme responsible for ammonia and glutamate production. This study aimed to assess ammonia and glutaminase levels in human cerebellum and hippocampus across liver disease stages. Brain samples from 40 deceased patients with chronic liver disease and matched controls were obtained from Spanish biobanks. Subjects were classified as control, steatohepatitis (SH1, SH2 or SH3 by severity) and cirrhosis. Cerebellum and hippocampus sections were stained with Nessler’s reagent for ammonia, and cerebellar glutaminase was analyzed by immunohistochemistry. Ammonia was increased in the cerebellum of SH1 patients; but not in more advanced stages; in the hippocampus, ammonia was elevated at all stages of liver disease. Glutaminase was increased in cerebellum of steatohepatitis and cirrhotic patients. An increase in glutaminase in the cerebellum of patients with SLD may contribute to increased ammonia levels. However, cirrhotic patients showed normal ammonia levels despite increased glutaminase. This suggests that ammonia is efficiently eliminated at that stage, whereas elevated glutaminase may also increase glutamate levels, contributing to altered neurotransmission and neurological dysfunction. Further studies are warranted to better understand the mechanisms underlying neurological alterations at different stages of liver disease leading to hepatic encephalopathy.
Funding: ISCIII(PI23/00062) cofunded FEDER; MICIU(JDC2024-054091-I); GVA(CIPROM2021/082).