Ammonia is a constituent of body fluids generated in the intestine by bacterial hydrolysis of nitrogen compounds, muscular amino acid transamination, purine nucleotide cycle and metabolic processes mainly in the kidneys and liver . Ammonia and bicarbonate are condensed in the hepatic mitochondria to produce carbamoyl phosphate to initiate urea cycle, the most important mechanism of blood ammonium removal . When the blood level of ammonia increases, it enters the central nervous system (CNS) in excessively and becomes toxic to the brain .
Astroglial cells are the only CNS cells that metabolize ammonia . Ammonia is condensed with glutamate to form glutamine. As the level of glutamine increases, it results in astrocyte swelling, cerebral edema and intracranial hypertension . When astrocytes are continuously exposed to ammonia, they may undergo phenotypic transformation into Alzheimer´s type II astrocytes with reduced proliferative activity [6, 7]. Moreover, elevated concentrations of ammonia in CNS promote oxidative stress [8–9]. Glutamine and ammonia exposure to astrocytes increases reactive oxygen species production , another possible cause of astrocyte swelling responsible for neurotoxicity .
Liver failure is the cause of 90% of hyperammonemia cases in adults. Those not related to liver failure may be divided in two groups: cases with increased ammonia production and cases with decreased elimination .
Increased ammonia production may occur in progressive multiple myeloma  and infections by urea-producing bacteria . Rare causes include starvation, total parenteral nutrition, gastrointestinal bleeding and seizures . Reduced elimination occurs mainly in metabolic disorders like urea-cycle disorders, pyruvate metabolism errors, organic acidurias, impaired fatty acid oxidation, dibasic aminoaciduria and congenital portosystemic shunt [15–18].
Since 2009, reports have demonstrated the association of fibrolamellar hepatocellular carcinoma (FLHCC) with hyperammonemia [19–25]. Nevertheless, none of those articles reached a definite explanation to hyperammonemia in FLHCC patients. Berger et al. theorized that portosystemic shunts were accountable . Alsina et al. suggested that intrahepatic shunting and lack of clearance of nitrogenous compounds by tumor cells were responsible .
In 2017, Surjan et al. proposed a new physiopathological pathway to hyperammonemia in patients with FLHCC . According to the theory, all FLHCC present a single and recurrent heterozygous deletion in chromosome 19 that results in a chimeric protein DNAJB1-PRKACA (a catalytic subunit of protein kinase A) [27–28]. The DNAJB1-PRKACA kinase is probably both necessary and sufficient to the carcinogenesis of FLHCC [29–30], and results in Aurora kinase A (AURKA) overexpression within the tumor, as previously demonstrated .
Elevated levels of AURKA upregulates c-Myc transcription affecting cellular proliferation and ATP production, important factors on FLHCC tumorigenesis [32, 33]. c-Myc overexpression leads to increased ornithine decarboxylase (ODC) activity . This results in increased ornithine consumption to polyamines synthesis , reducing ornithine bioavailability that results in urea cycle disorder due to ornithine transcarboxylase (OTC) dysfunction and consequent hyperammonemia .
The proposal of this physiopathological pathway to HE in a FLHCC patient allowed an innovative treatment with complete neurocognitive recovery. However, the described process was not proved by analysis of involved enzymes activities and RNA expression.
In this study, fresh frozen tissue samples of non-tumor liver parenchyma, FLHCC and one hepatic adenomatosis in a patient that developed HE without liver dysfunction were submitted to analysis of expression of ODC, c-Myc, OTC and AURKA and tested for the chromosome 19 deletion.