Radioassay of Serum Folate with Use of Pig Plasma Folate Binders

Abstract

Pig plasma has been used as a source of specific folate binders for the development of a rapid radioassay to measure the concentration of folate in serum. The assay uses ³H-pteroylglutamic acid as tracer and N-5-methyltetrahydrofolic acid for the construction of the standard curve. The assay is run in a two-step incubation system of 15 min each at room temperature. Comparison between the results obtained with this method and a microbiological one indicated that for sera with relatively high folate levels there was a good agreement between the two methods, whereas for sera with low folate levels the present method produces lower values than the microbiological one. The diagnostic value of the results obtained by the two methods is discussed on the basis of the availability to the tissues of the folates which are firmly bound to specific folate binders of human serum.

Determination of Blood Folate Using Acid Extraction and Internally Standardized Gas Chromatography–Mass Spectrometry Detection

“…The myriad forms of folates have hindered development of analytic techniques that detect specific congeners and the majority of measurements are reported as total folate. Popular methods for folate measurement include microbiological growth assays that use folate-responsive microorganisms (8 -11) or radiolabeled folate binder assays that operate on the principle of competitive binding between endogenous and exogenous (radiolabeled folate) folates for a limited amount of a protein binder (12)(13)(14)(15)(16)(17)(18). Folate assays that involve the use of HPLC (19 -22) and GCMS (23) methods for blood and tissues are less commonly used, but have the potential for providing superior specificity and analytic precision.…”

Measurement of serum folate: experience with 75Se-selenofolate radioassay.

“…Radioisotopic assays for folate measurement have been explored since folate binders were identified in milk (Ghitis, 1967) and in animal (especially porcine) sera (Mantzos et al, 1974). A variety of methods have been documented (Waxman et al, 1971;Rothenberg et al, 1972;Dunn and Foster, 1973;Mantzos, 1975) recently, all of which suffer from the shortcomings of scintillation counting associated with the use of tritiated folic acid, which appears to prohibit their widespread application for clinical diagnostic purposes (Coulson and Rose, 1974;International Society of Haematology, London, 1975). Further development of a method, using a gamma-emitting radiofolate adhering to basic principles of saturation analysis, has yielded a simple, reliable, and effective method which has a number of advantages compared with the L. casei assay.…”

“…Then 100 ,A of porcine serum in the same buffer is added. Porcine serum provides plentiful and avid folate binding proteins (Mantzos, 1975). The folate binding behaviour of porcine serum is more reproducible than milk or milk extracts.…”

Radioassay of Folacin in Foodstuffs

“…Recently, binding protein from porcine blood serum has been successfully used because of its higher binding capacity and broader affinity for folate derivatives (Mantzos 1975;Johnson et al 1977). In order to increase the specific radioactivity (i.e., assay sensitivity) and to remove the difficulties associated with 3H radioactivity measurements, NS-methyl-3'-'251-tetrahydrofolate and pter~yl-L-methyl-~~Se-cysteine were introduced into the radioassay of folacin (Johnson et al 1977).…”