Effects of human follicular fluid and high-density lipoproteins on early spermatozoa hyperactivation and cholesterol efflux.

The preovulatory human follicular fluid contains only HDLs as a lipoprotein class with a typically high proportion of prebeta HDL. We first examined the role of follicular fluid and HDL subfractions on human spermatozoa capacitation, a process characterized by a hyperactivation of the flagellar movement and a depletion of plasma membrane cholesterol. Whole follicular fluid and isolated HDL, used at constant free cholesterol concentration, were both able to promote an early flagellar hyperactivation. Moreover, incubation of [(3)H]cholesterol-labeled spermatozoa with follicular fluid induced a rapid cholesterol efflux from spermatozoa that was confirmed by mass measurements of cholesterol transfer. Using isolated HDL, the cholesterol efflux had a similar time course and represented 70% of that mediated by whole follicular fluid. We then analyzed the time course of radioactive labeling of HDL subfractions. In the first minute of incubation, we found that the prebeta HDL fraction incorporated the main part of the radioactivity (60%), with the rest being found in alpha-HDL, but strikingly, the labeling of alpha-HDL increased with time at the expense of prebeta HDL.Thus, our results indicate that HDLs are involved in both spermatozoa hyperactivation and cholesterol effl ux and suggest the role of prebeta-HDL particles as fi rst cellular cholesterol acceptors.

[Study on the protective effect of HDL subclasses against lipopolysaccharide].

AIM: To elucidate the anti-LPS effect of high-density lipoprotein (HDL) subclasses. METHODS: The pNF-kappaB-luc plasmid was transfected into HepG2 cells and the luciferase expression was obtained by the optimization of cell density, incubation time of transfected cells and stimulating concentration of LPS. The luciferase expression was examined in the cells treated with various stimulus including LPS, mixtures of HDL subclasses and LPS. The expression of TNF-alpha mRNA was detected RT-PCR. RESULTS: After LPS stimulation, HDL subclasses did not show obvious influence on the effect of LPS to stimulate the luciferase production. However, pre-incubation of cells or pre-incubation of LPS with large-sized HDL(2) strongly inhibited the effect of LPS to stimulate the luciferase production. When LPS was incubated with increased concentration of HDL(2), the LPS effect was decreased to a greater extent. Pre-incubation of LPS with HDL(2) before addition to the cells resulted in a significant decrease in the mRNA level of TNF-alpha. CONCLUSION: The largest HDL(2) has strong LPS-binding capacity and can inhibit the LPS induced TNF-alpha release in HepG2 cells; HDL(3) shows weak anti-LPS effect; small-sized prebeta(1)-HDL does not show anti-LPS effect.

A unique protease-sensitive high density lipoprotein particle containing the apolipoprotein A-I(Milano) dimer effectively promotes ATP-binding Cassette A1-mediated cell cholesterol efflux.

Carriers of the apolipoprotein A-I(Milano) (A-I(M)) variant present with severe reductions of plasma HDL levels, not associated with premature coronary heart disease (CHD). Sera from 14 A-I(M) carriers and matched controls were compared for their ability to promote ABCA1-driven cholesterol efflux from J774 macrophages and human fibroblasts. When both cell types are stimulated to express ABCA1, the efflux of cholesterol through this pathway is greater with A-I(M) than control sera (3.4 +/- 1.0% versus 2.3 +/- 1.0% in macrophages; 5.2 +/- 2.4% versus 1.9 +/- 0.1% in fibroblasts). A-I(M) and control sera are instead equally effective in removing cholesterol from unstimulated cells and from fibroblasts not expressing ABCA1. The A-I(M) sera contain normal amounts of apoA-I-containing prebeta-HDL and varying concentrations of a unique small HDL particle containing a single molecule of the A-I(M) dimer; chymase treatment of serum degrades both particles and abolishes ABCA1-mediated cholesterol efflux. The serum content of chymase-sensitive HDL correlates strongly and significantly with ABCA1-mediated cholesterol efflux (r = 0.542, p = 0.004). The enhanced capacity of A-I(M) serum for ABCA1 cholesterol efflux is thus explained by the combined occurrence in serum of normal amounts of apoA-I-containing prebeta-HDL, together with a unique protease-sensitive, small HDL particle containing the A-I(M) dimer, both effective in removing cell cholesterol via ABCA1.