Diagnostic area

APO A1

Hepatocellular carcinoma is the fifth most common neoplasm with more than 500.000 new cases diagnosed yearly. Although major risk factors of HCC are currently known, the identification of biological targets leading to an early diagnosis of the disease is considered one of the priorities of clinical hepatology. Mass spectrometry-based technologies contributes to the development of a new molecular medicine especially in the discovery of diagnostic biomarkers of human diseases. We have used a proteomic approach to identify markers of hepatocarcinogenesis in the serum of a knockout mice deficient in hepatic AdoMet synthesis (MAT1A -/-), as well as in patients with hepatocarcinoma. Three isoforms of Apolipoprotein AI (ApoA-I) with different pI were identified in murine serum. Isoform 1 is up-regulated in the serum of MAT1A-/- mice much earlier than any histological manifestation of liver disease. Further characterization of the differential isoform by electrospray tandem mass spectrometry revealed specific oxidation of methionine 86 and 116 to methionine sulfoxide while the sequence of the analogous peptides on isoforms 2 and 3 showed the non-oxidized methionine residues. Enrichment of an acidic isoform of apolipoprotein A-I was also assessed in the serum of HBV patients who developed hepatocarcinoma. Specific oxidation of methionine 112 to methionine sulfoxide and tryptophan 50 and 108 to formylkinurenine were identified selectively in the up-regulated isoform. This is the first time, to our knowledge, that specific oxidation of methionine and tryptophan residues of apolipoprotein A-I have been associated with hepatocarcinoma. Although it is not clear at present whether the occurence of these modifications has a causal role or simply reflects secondary epiphenomena this selectively oxidized Apo A-I isoform may be considered as a pathological hallmark that may help to the understanding of the molecular pathogenesis of this disease. We are currently producing antibodies to specifically recognize the oxidized Apo A-1 protein aiming at the development of detection/quantitation assays that may provide valuable information to improve the management of HCC patiens.