
<ArticleTitle>Characterization of serum and urinary <prot>chromogranin A</prot> by size exclusion chromatography: impact on calibrator selection and urinary assay.</ArticleTitle>
<AbstractText>Serum <prot>chromogranin A</prot> (<prot>CgA</prot>) is a useful marker for neuroendocrine tumors and is detectable in carcinomas at advanced stages. Elevated serum <prot>CgA</prot> is also an indicator of poor prognosis in prostate cancer and is useful for predicting the failure of hormonal therapy for prostate cancer patients. We found that <prot>CgA</prot> molecules with three different sizes could be detected in normal human serum. However, only the largest <prot>CgA</prot> molecule appears in patients with liver disease. Serum taken from cancer patients is composed predominantly of the middle-sized molecule, whereas the smallest <prot>CgA</prot> molecule was elevated in serum drawn from renal patients. Moreover, only the smallest <prot>CgA</prot> molecule was found in urine. We believe that the largest <prot>CgA</prot> molecule is metabolized by the liver, whereas the smallest <prot>CgA</prot> molecule is removed from the blood circulation via the kidney. Because the medium-sized <prot>CgA</prot> is the dominant molecule in both the cell medium of the tumor cell line SK-N-AS and sera from patients with malignant diseases, <prot>CgA</prot> from the cell medium was selected as the calibrator for the <prot>CgA</prot> ELISA assay. Our findings also suggest that it would not be possible to measure the urinary <prot>CgA</prot> to reflect the serum <prot>CgA</prot> concentration in order to detect pheochromocytoma among patients with hypertension.</AbstractText>
