Binding of Perfluorooctanoic Acid to Rat Liver‐form and Kidney‐form α2u‐Globulins

Abstract

Perfluorooctanoic acid (PFOA) is an organic fluorochemical and is reported to have a long half‐life in human blood. Its urinary elimination in rats is markedly sex‐dependent, and characterized by significantly longer plasma half‐life of PFOA in male rats than in females. It has been postulated that male‐specific PFOA binding protein(s) is responsible for the long half‐life of PFOA in male rats. In this paper, two male rat specific proteins, liver‐ and kidney‐form α2u‐globulins (A2U_L and A2U_K), were purified from male rat urine and kidney, respectively. The binding of these two proteins to PFOA was investigated using ligand blotting, electrospray ionization mass spectrometry and fluorescence competitive binding assay. The results revealed that both A2U_L and A2U_K were able to bind PFOA in vitro under physiological conditions, and that PFOA and a fluorescent‐labeled fatty acid shared the same binding site on both A2U_L and A2U_K. The binding affinities, however, are relatively weak. The estimated dissociation constants are in the 10^{− 3} M range, indicating that bindings of PFOA to either A2U_L or A2U_K cannot adequately explain the sex‐dependent elimination of PFOA in rats, and it is unlikely that PFOA‐A2U_k binding would induce A2U nephropathy as seen with, for example, 1,4‐dichlorobenzene.

Key Words: :

• Perfluorooctanoic acid
• Protein binding
• α2u‐Globulin
• Organic fluorochemical

Notes

^aThe abbreviations used are: A2U, α2u‐globulin; A2U_K, kidney‐form α2u‐globulin; A2U_L, liver‐form α2u‐globulin; ADE, absorption, distribution, and elimination; ANS, 8‐anilino‐1‐naphthalenesulfonate; APFO, ammonium perfluorooctanoate; DAUDA, dansyl undecanoic acid; ESI, electrospray ionization; FABP, fatty acid binding protein; HSA, human serum albumin; OAT, organic anion transporter; PBS, phosphate buffered saline; PFOA, perfluorooctanoic acid; PVDF, polyvinylidene fluoride. RSA, rat serum albumin.

^bCalculated based on reported IC₅₀ value according to Eq. 2.