Evaluating the Use of Sacran, a Polysaccharide Isolated from Aphanothece sacrum, as a Possible Microbicide for Preventing HIV-1 Infection

Abstract

Since combination antiretroviral therapy (cART) was introduced to treat human immunodeficiency virus type-1 (HIV-1)/acquired immunodeficiency syndrome (AIDS), the AIDS mortality rate has markedly decreased, and convalescence in individuals with HIV has improved drastically. However, sexual transmission has made HIV-1 a global epidemic. Sacran is a megamolecular polysaccharide extracted from cyanobacterium Aphanothece sacrum that exhibits numerous desirable characteristics for transdermic applications, such as safety as a biomaterial, a high moisture retention effect, the ability to form a film and hydrogel, and an anti-inflammatory effect. In this study, we evaluated the anti-HIV-1 effects in sacran as a barrier to HIV-1 transmission. Sacran inhibited HIV-1 infection and envelope-dependent cell-to-cell fusion. Moreover, we used a Transwell assay to confirm that sacran inhibited viral diffusion and captured viruses. The synergistic effects of sacran and other anti-HIV infection drugs were also evaluated. HIV-1 infections can be reduced through the synergistic effects of sacran and anti-HIV-1 drugs. Our study suggests using sacran gel to provide protection against HIV-1 transmission.

Keywords: HIV-1; microbicide; sacran.

Figure 1

HIV-1_LAI-infected PM1-CCR5 cells were analyzed using flow cytometry 48 h post-infection. (A) HIV-1 infection was induced in all three experimental settings. (a) Target cells, sacran gel, and HIV-1 were cultured with a triple-layered gel for 48 h at 37 °C. (b) Sacran gel and HIV-1 were co-treated to target cells and cultured for 48 h at 37 °C. (c) Sacran gel and HIV-1 were mixed in a 1.5 mL tube. Then, sacran and HIV-1 mix solution were added to target cells and cultured for 48 h at 37 °C. (B) Intracellular p24 (HIV-1 Gag) levels in sacran-treated PM1-CCR5 cells. (C–E) Summary of intracellular p24 levels in three experimental settings (a–c), respectively. Data represent the mean ± SD. Representative results from three independent experiments are shown. * p < 0.05, ** p < 0.01.

Figure 2

Sacran inhibited env-dependent cell-to-cell fusion. (A) Inhibition of cell fusion was analyzed using flow cytometry. (B) Summary of (A). Data represent the mean ± SD. One representative result from three independent experiments is shown.

Figure 3

Sacran inhibited viral diffusion and captured HIV-1. (A) Experimental design. The Transwell system simulates HIV-1 transmission in the presence of a vaginal gel. A thin gel layer was applied to the Transwell membrane. A suspension of HIV-1 was then added to the upper compartment. After incubation, the levels of HIV-1 in the upper and lower chambers were quantified using p24 ELISA. (B) Viral loads in the lower chamber. (C) Viral load in the upper chamber. Data represent the mean ± SD. Representative results from three independent experiments are shown.

Figure 4

Synergistic HIV-1 inhibition of sacran and HIV-1 entry inhibitors. (A) HIV-1 inhibitory activity of sacran, plerixafor, enfuvirtide, and sacran with plerixafor or enfuvirtide. Combination indices of sacran with plerixafor (B) and sacran with enfuvirtide (C). The synergy between sacran and HIV-1 entry inhibitors was calculated using CompuSyn software based on the Chou–Talalay method [26,27]. Data represent the mean ± SD. Representative results from three independent experiments are shown.

Figure 5

Synergistic HIV-1 inhibition of sacran and EFV. (A) HIV-1 inhibitory activity of sacran, EFV, and sacran with EFV. (B) Combination indices of sacran with EFV. The synergy between sacran and HIV-1 entry inhibitors was calculated using CompuSyn software based on the Chou–Talalay method [26,27]. Data represent the mean ± SD. Representative results from three independent experiments are shown.