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Haptoglobin inhibits lecithin‐cholesterol acyltransferase in human ovarian follicular fluid
Author(s) -
Balestrieri Marco,
Cigliano Luisa,
Simone Maria Laura De,
Dale Brian,
Abrescia Paolo
Publication year - 2001
Publication title -
molecular reproduction and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.745
H-Index - 105
eISSN - 1098-2795
pISSN - 1040-452X
DOI - 10.1002/mrd.1021
Subject(s) - follicular fluid , lecithin , sterol o acyltransferase , haptoglobin , cholesterol , apolipoprotein a1 , biology , cholesteryl ester , medicine , enzyme , size exclusion chromatography , apolipoprotein b , endocrinology , enzyme assay , follicular phase , lipoprotein , biochemistry , chemistry , embryo , oocyte , microbiology and biotechnology
The activity of the enzyme lecithin‐cholesterol acyltransferase (LCAT; E.C. 2.3.1.43) is involved in the removal of cholesterol excess from peripheral cells. This activity is stimulated by the HDL (high density lipoprotein) apolipoprotein A1 (ApoA1). Haptoglobin (Hpt) was previously found to be associated with ApoA1 in ovarian follicular fluid. LCAT activity was analyzed in follicular fluids, collected from an IVF program, containing different amounts of Hpt or Hpt/ApoA1 ratio. Addition of purified Hpt to follicular fluid caused a decrease in the enzyme activity, which was measured as the rate of synthesis of cholesteryl esters. In the fractions of fluid proteins, as obtained by gel filtration chromatography, Hpt and HDL were titrated by ELISA while the LCAT activity was assayed by using radioactive cholesterol and purified HDL. When isolated LCAT was incubated with fractions containing different Hpt/ApoA1 ratios, the enzyme activity was found negatively correlated with the Hpt/ApoA1 ratio ( P < 0.01). LCAT kinetic parameters were measured in two fractions with the same amount of ApoA1 (5 μg/ml) but different amounts of Hpt (0.69 or 3.77 μg/ml): the V max did not change while the K m values were 24.1 or 78.6 μM in the presence of the low or high Hpt level, respectively. The analysis of fluids associated with cytoplasmically mature MII oocytes, in a cross‐sectional study, confirmed that a negative correlation exists between the Hpt/ApoA1 ratio and the LCAT activity ( P < 0.01). The results suggest that Hpt inhibits the reverse transport of cholesterol by preventing ApoA1 stimulation of the LCAT activity. Mol. Reprod. Dev. 59:186–191, 2001. © 2001 Wiley‐Liss, Inc.