Background:  Monocytes and macrophages (M/M) are a strategic reservoir of HIV-1. Once infected by HIV-1 monocytes and macrophages survive for a long time, produce and release a large amount of new HIV-1 particles, spread the virus to other cells, and induce apoptosis in T-lymphocytes, astrocytes, and neurons. M/M are commonly infected by strains of HIV-1 that use CCR5 as co-receptor (R5). D-ala-peptide T-amide (DAPTA) is an octapeptide derived from a V2 region of the HIV-1 gp120, able to bind CCR5. We thus analyzed the effect of DAPTA upon virus replication and cellular damage induced by HIV-1 gp120 protein.

Methods:  HIV-1 gag production was assessed in M/M infected by different HIV-1 strains during treatment with several concentrations of DAPTA. A polymerase chain reaction (PCR) analysis of HIV-1 proviral DNA was performed on HIV-1-infected M/M in the presence of DAPTA at different doses. The specificity of DAPTA-CCR5 binding was assessed in M/M and in human neuronal cell line SK-N-SH with flow cytometry (FACS). Programmed cell death was evaluated in SK-N-SH incubated with supernatants from HIV-1-infected M/M in the presence or absence of DAPTA by FACS and by nuclear staining (DAPI). Student t test was used for statistical analysis.

Results:  Very low concentrations of DAPTA (10^-4 nM) inhibited HIV-1 replication in M/M (>80% compared to control), as measured by the p24 gag antigen released in the cell culture supernatants. A PCR analysis of HIV-1 proviral DNA on cultured M/M showed a remarkable decrease (up to 70%) of HIV-1 DNA in DAPTA-treated M/M and suggests that the DAPTA-mediated inhibition occurs at very early stages of HIV-1 replication, probably at entry. HIV-1 R5 strains produced and released by infected M/M-induced apoptosis in CCR5-expressing SK-N-SH. DAPTA, at concentration of 10^­3 and 10^­4 nM, strongly inhibited this apoptosis in SK-N-SH of 58% and 56%, respectively, compared to control. Surprisingly, this effect is more than double than that induced by TAK-779 (a non-peptidic CCR5 antagonist with potent anti-HIV-1 activity).

Conclusions:  The mechanisms of DAPTA inhibition may include suppression of HIV-1 R5 strains in the brain, direct inhibition of HIV-1 replication in M/M and containment of damage related to gp120-CCR5 binding. The development of anti HIV-1 compounds acting through new mechanisms, such as DAPTA, could be important in synergistic combination with other ART in preventing both central nervous system HIV-1 infection and the consequent neural damage.