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Structures of disease-specific serum alpha-fetoprotein isoforms.
P J Johnson1, T C Poon, N M Hjelm
1Department of Clinical Oncology, Chinese University of Hong Kong, Shatin, Hong Kong.
British Journal of Cancer
|October 25, 2000
Summary
Disease-specific alpha-fetoprotein (AFP) isoforms, crucial for diagnosing liver cancer and germ cell tumors, were analyzed using mass spectrometry. Differences in sialylation of AFP glycoforms distinguish between benign liver disease, HCC, and NSGCT.
Area of Science:
- Biochemistry
- Glycomics
- Cancer Biomarkers
Background:
- Alpha-fetoprotein (AFP) is a key serological marker for hepatocellular carcinoma (HCC) and non-seminomatous germ cell tumors (NSGCT).
- Isoelectric focusing (IEF) identifies disease-specific AFP isoforms: Band +I (benign liver disease), Band +II (HCC), and Band +III (NSGCT).
Purpose of the Study:
- To determine the glycan composition of AFP isoforms using electrospray ionization-mass spectrometry (ESI-MS).
- To correlate glycan structures with disease-specific AFP isoforms identified by IEF.
Main Methods:
- Purification of serum AFP from patients with HCC and NSGCT.
- Characterization of AFP glycoforms using ESI-MS to determine glycan structures and abundance.
- In vitro desialylation studies on purified AFP isoforms (Bands +I and +II).
Main Results:
- ESI-MS identified seven distinct AFP glycoforms in HCC patients and six in the NSGCT patient.
- Predominant glycoforms carried a single biantennary complex-type N-glycan; those with both N-glycan and O-glycan were minor.
- HCC-associated isoforms (Band +II) were predominantly mono-sialylated, benign liver disease isoforms (Band +I) were di-sialylated, and NSGCT isoforms (Band +III) were a-sialylated.
Conclusions:
- Differences in sialylation of AFP glycoforms are responsible for the formation of disease-specific isoforms.
- The characterized structures of tumor-specific AFP isoforms provide a basis for developing improved diagnostic assays.