Background:  HIV infection is associated with increased serum levels of inflammatory markers, endothelial dysfunction, and cardiovascular events. In a recent pilot trial of HIV-infected patients not requiring ART, we showed that the anti-inflammatory drug pentoxifylline (PTX) improves in vivo endothelial function, possibly by inhibiting the leukocyte adhesion pathway. We used cellular models to investigate further the mechanistic roles of HIV infection, inflammation, and PTX on endothelial cell activation.

Methods:  Recombinant tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ), either alone or together with HIV Tat or gp120, were added to primary human endothelial cells. Additionally, Jurkat T cells (either HIV-infected or not) were co-cultured with endothelial cells. Endothelial cell supernatants were collected and analyzed for secretion of the inflammatory chemokine MCP-1, while endothelial cells were harvested for quantitative real-time polymerase chain reaction (qRT-PCR) gene expression analysis of MCP-1 and the leukocyte adhesion molecules IP-10 and VCAM-1. Surface marker evaluations were performed using flow cytometry. Endothelial cells were also treated with PTX, at concentrations achieved in vivo in our clinical trial, to assess modulation of gene and protein expression. Significance testing was performed using ANOVA.

Results:  Gene expression of IP-10 was significantly (p <0.05) enhanced when IFN-γ (but not TNF-α) was combined with either gp120 or Tat. VCAM-1 gene expression was significantly (p <0.05) enhanced by TNF-α (but not with IFN-γ) in combination with either HIV protein. On the other hand, MCP-1 regulation was not affected by these HIV proteins. However, we did find that that endothelial MCP-1 production ELISA was significantly up-regulated (p = 0.0009) when in close contact with HIV-infected Jurkat cells. PTX significantly (p = 0.048) reduced this heightened endothelial MCP-1 production.

Conclusions:  These in vitro results demonstrate that HIV proteins, when combined with inflammatory mediators, synergistically and differentially enhance endothelial gene expression of leukocyte adhesion molecules. We further show that PTX can reduce the heightened production of endothelial cell MCP-1 which is induced by cellular contact with HIV-infected T cells. These results extend our understanding of the roles of HIV and systemic inflammatory mediators on endothelial inflammation and may explain the beneficial effects of PTX found in vivo.