Region-specific radioimmunoassay for human chromogranin A

A region-specific radioimmunoassay (RIA) for human chromograninA (CEA) was developed using synthetic CgA(344-374), based on the amino acid sequence re ported by Konecki et al. (19) and Mouland et al. (21). Anti-human CgA(344-3 74) serum raised in a rabbit, I-125-human CgA(344-374) as tracer and synthe tic human CgA(344-374) as standard were employed for development of the ass ay system. The standard displacement curve was parallel to the dose respons e curves of human plasma, urine, saliva and tissue extracts. The minimum de tectable limit of the assay system was approximately 1.80 fmol/tube. The im munoreactive (IR) CgA level of human normal plasma was 0.31 +/- 0.05 pmol/m L (mean +/- SD, n=25). Plasma IR-CgA levels in patients with renal failure (1.74 +/- 1.15 pmol/mL, n=28), pheochromocytoma (1.67 +/- 0.89 pmol/mL, n=4 ), thyroid carcinoma (1.90 +/- 0.72 pmol/mL, n=4), pituitary adenoma (2.71 +/- 0.90 pmol/mL, n=5) and rectal carcinoid tumour (2.70 pmol/mL, n=1) were significantly higher when compared to that in normal healthy subjects. Int ra-and inter-assay variances in the assay were 2.4-6.4% and 6.5-13.9%, resp ectively. Recovery of human CgA(344-374) added to plasma ranged from 85.4% to 99.3%. Gel filtrations of human plasma on Sephadex G-75 column using 1 M acetic acid as eluent revealed the existence of major IR-CgA having approx imately 58-60 kDa. These results indicate strongly that the present assay s ystem is valuable for the measurement of IR-CgA in human plasma. In additio n, the detectable amounts of IR-CgA were also found in human urine and sali va.