[Free polyunsaturated fatty acids, estrogens and fetoproteins]

In the course of the foetal development of numerous animal species elevated serum concentrations of alpha-1-foetoprotein (AFP) are observed. The level of this foetal protein decreases after birth, but reappears in several pathological cases characterized by a cellular proliferation, in particular in neoplasia such as hepatoma and teratoblastoma. Little was known until 1971 on the biological role of this carcino-embryonic antigen. It has been since evidenced [Nunez and al., 1971, C.R. Acad. Sci., Paris, 273, 834-841]. That rat and mouse AFPs bind oestrogens with high affinity (Ka = 10(8) M-1) [Savu and al., 1972, F.E.B.S. Let., 22, 113-116]. Human AFP does not possess this property. We have recently shown [Benassayag and al., 1977, Steroids, 30, 771-785] that the sera from pregnant rats, rat and human foetuses contain compounds which behave as competitive inhibitors of the estrogen binding on rat or mouse AFP. We have subsequently identified this substances as a mixture of non-esterified fatty acids (NEFA) [Vallette and al., XXVII Colloquium "Protides of the biological fluids", Bruxelles, H. Peeters Ed., Pergamon Presse, 1979]. We have measured [BENASSAYAG and al., Oncodevelopmental biology and medicine, in press] the association constants of each NEFA of the serum mixture with rat AFP, the polyunsaturated fatty acids (PUFA) (C 20:4, C 22:4, C 22:6) show the highest association constants (Ka = 10(5)-10(6) M-1). We have also confirmed that human AFP binds the PUFA with high affinity. The biological perspectives opened up by these novel data will be discussed.