Radioimmunoassay of spermidine in human serum

Specific antispermidine antibodies were produced following immunization of New Zealand white rabbits with a spermidine-thyroglobulin conjugate of high (greater than 200:1) hapten-carrier molar ratio. The harvested antispermidine rabbit antiserum was characterized and a radioimmunoassay procedure developed. The specificity of this antibody was tested against cadaverine, putrescine, spermine, monoacetylputrescine, N-8-acetylspermidine and other compounds of similar molecular structure. Negligible cross-reactivity was observed with putrescine (2.1%), cadaverine (0.6%), spermine (0.3%), diaminopropane (less than 0.1%), and no cross-reaction was found with monoacetylputrescine, N-8-acetylspermidine, histamine, L-lysine and L-ornithine. The spermidine values on serum of five healthy volunteers were determined by RIA and compared with values by gas chromatographymass spectrometry. Statistical evaluation of the results were highly agreeable. Antibody titer, intra-assay precision and analytical accuracy were tested. The assay requires only 20 microliter of serum and has picomole sensitivity. The sensitivity, specificity and small sample requirement make this procedure an effective tool for spermidine analysis.