J Gonzalez-Christen | PubMed Health

PubMed1998

Adjuvant lipopeptide interaction with model membranes.

The cationic lipohexapeptide Pam3Cys-Ser-(Lys)4 is a synthetic model for the triacylated N-terminal part of bacterial lipoproteins, and it is used as an adjuvant and macrophage activator. The amphiphilic lipopeptide was injected below a phosphatidylserine monolayer at the air-water interface. It interacted with the interface, as seen by a decrease in the surface potential (deltaV), and it was inserted in the monolayer, until surface charge neutralization was reached, as seen by the parallel increases of deltaV and of the surface pressure. No insertion occurred above 29 mN/m. The interaction kinetics was sensitive to ionic strength and to the nature of acidic phospholipids and of their acyl chains, but the final equilibrium was independent of these factors. Addition of the lipopeptide to large unilamellar vesicles (LUVs) induced their aggregation, and an exchange of lipids between fluorophor-labelled and non-labelled LUVs. However, no fusion was observed, just as reported for polylysine. The lipopeptide strongly inhibited calcium-induced fusion of PS LUVs, in contrast to the published effect of polylysine. This was probably due to inhibition of calcium fixation on liposomes, since it was observed that the lipopeptide efficiently displaced 45Ca2+ from a PS monolayer. In addition, a phospholipid segregation was observed in SUVs for a few ten micromolar of the lipopeptide.

Lipoproteins↗

PubMed1997

Expression of NADPH oxidase is induced by all-trans retinoic acid but not by phorbol myristate acetate and 1,25 dihydroxyvitamin D3 in the human promyelocytic cell line NB4.

Human promyelocytic cells, NB4, differentiate into neutrophils in response to all-trans retinoic acid (ATRA). It has recently been proposed that NB4 cells have bilineage potential because these cells are also able to differentiate into monocyte/macrophages when exposed to a combination of 1,25-dihydroxyvitamin D3 (VD3) and phorbol myristate acetate (PMA). Differentiation of myeloid cells into neutrophils or monocytes is associated with the acquisition of the O2- producing enzyme, NADPH oxidase, which plays a critical role in microbial killing. In this study, the expression of the components of the NADPH oxidase complex during the differentiation of NB4 cells into neutrophils or macrophages has been investigated. Whereas cells exposed to ATRA were able to produce O2- after 2 days of differentiation, they remain unable to generate O2- when exposed to PMA or PMA + VD3. With the exception of p21rac, none of the other oxidase components was expressed in non-differentiated cells. Addition of ATRA induced the progressive expression and accumulation of p22phox, p91phox, p47phox and p67phox. Compared to the other components, p67phox was expressed late and its expression appeared to correlate most closely with the generation of O2- in the differentiation process. In PMA or PMA + VD3-differentiated NB4 cells, expression of the NADPH oxidase components was incomplete. Therefore, ATRA induced the expression of a functional NADPH oxidase complex in neutrophil-like NB4 cells. In contrast, when NB4 cells are exposed to monocytic differentiating agents, they acquire only part of the phenotypic characteristics of monocytes and lack one of the major phagocytic functionalities, the respiratory burst oxidase.

Calcitriol↗