Elsevier

Toxicology

Volume 278, Issue 2, 5 December 2010, Pages 242-248
Toxicology

Mechanisms and genes involved in enhancement of HIV infectivity by tobacco smoke

https://doi.org/10.1016/j.tox.2010.09.010Get rights and content

Abstract

HIV infection is more common among smokers than nonsmokers, and, remarkably, HIV-infected individuals are about 3 times more likely to smoke than the uninfected general population. However, the relationship between tobacco smoking and HIV/AIDS disease progression remains controversial.

In this study, we demonstrate a potent enhancing effect of aqueous tobacco smoke extract (TSE) on HIV infectivity that is nicotine-independent. This increased infectivity is neither NF-κB mediated nor a direct result of oxidative stress, as it cannot be blocked by antioxidants. On the contrary, TSE itself was found to possess significant antioxidant potential, enabling it to protect the viability of both infected cells and HIV virions in the presence of peroxide. Assessment of TSE-induced alterations in cellular gene expression that may be involved in increasing HIV infectivity in T cells showed that TSE up-regulates some genes known to be capable of enhancing HIV and HCV infection, or protecting HIV, but down-regulates several genes involved in cellular defense and antigen presentation.

These results demonstrate that tobacco smoke can enhance HIV infectivity, possibly by a combination of direct (antioxidant) and indirect (gene-based) mechanisms. This raises the concern that smoking may thereby increase the risk of acquisition or progression of HIV infection.

Introduction

The relationship between tobacco smoking and HIV/AIDS progression still remains controversial (Furber et al., 2007). Some studies suggest that tobacco smoking by HIV-1-seropositive individuals is associated with a more rapid progression to AIDS (Crothers et al., 2005, Nieman et al., 1993). In contrast, a survey that enrolled 2499 HIV-1-seropositive men for up to 9 years found that tobacco smoking does not have a major effect on the progression of HIV-1 infection to AIDS (Galai et al., 1997). However, one of the stronger conclusions presented recently is that smoking increases the risk of becoming infected with HIV (Furber et al., 2007). Evidence also suggests that AIDS patients who smoke have a higher incidence of dementia (Burns et al., 1996).

Perhaps partly because of these controversies and inconsistencies in study results, and because the life expectancies of AIDS patients have been increased dramatically since highly active antiretroviral therapy (HAART) became the standard of care, comparatively little attention has been paid to the interactions between tobacco smoking and HIV/AIDS. A decreased awareness among health care providers of current smoking behaviors of HIV-positive compared to HIV-negative veterans has been reported (Crothers et al., 2007). However, it would be unwise to ignore studies suggesting that HIV/AIDS patients who are smokers suffer more clinical complications such as pneumonia, oral candidiasis, hairy leukoplakia, vascular diseases, AIDS-related malignancies and neuropathy (Conley et al., 1996, Elzi et al., 2006). At the same time, some of the benefits provided by HAART are negated in tobacco smokers (Feldman et al., 2006). Patients with HIV infection who smoke also have poorer health-related quality of life than nonsmokers (Turner et al., 2001). During pregnancy, tobacco smoking can increase risk of maternal-child HIV transmission and complications (Kalish et al., 1998, Turner et al., 1997).

In defining the relation between tobacco smoking and HIV/AIDS, most research has been done based on epidemiological profiles; few studies have explored the possibility of direct interactions between tobacco constituents and/or smoking and actual viral replication in HIV/AIDS.

Nicotine is the single tobacco constituent demonstrated to have at least the potential to stimulate the production of HIV-1, as has been shown using in vitro-infected alveolar macrophages (Abbud et al., 1995). Pretreatment of microglia with nicotine (300 μM) was shown to increase HIV-1 expression (Abbud et al., 1995). However, the median concentration of nicotine in the plasma of smokers does not usually exceed about 0.23 μM (Taylor et al., 1986), and at this concentration, nicotine showed no effect on HIV infection (Rock et al., 2008).

Tobacco smoking is widely viewed as a source of oxidative stress. Significantly, oxidative stress can induce HIV replication, resulting in disease progression (Boelaert et al., 1996, Miller et al., 1997). Smoking can induce the NF-κB activation pathway in lymphocytes via intracellular formation of peroxynitrite, through a reaction between smoke-derived NO and endogenously produced superoxide (Hasnis et al., 2007). However, when samples of alveolar air from smokers and non-smokers were analyzed for ethane using mass spectrometry, they showed no evidence that cigarette smoking is related to increased n-3 lipid peroxidation (Puri et al., 2008). Similarly, blood samples from clinically stable smoking and nonsmoking men with HIV/AIDS showed no striking differences in oxidative stress or antioxidant capacity (Cole et al., 2005).

Here, an aqueous tobacco smoke extract (TSE) was used to study the direct effect of smoking on HIV infection and its effects on gene expression in human T cells. The data demonstrate that TSE can enhance HIV infectivity in a nicotine-independent manner, and, surprisingly, that TSE has significant antioxidant potential, capable of protecting cells and virions from oxidative damage. An mRNA microarray analysis of TSE-treated human T-cells suggests that a number of genes that are up-regulated can be related to HIV infection, whereas several genes involved in cell defense or redox functions are down-regulated by TSE treatment.

Section snippets

Preparation of aqueous tobacco smoke extract (TSE)

Into 40 mL of sterile saline (PBS) in a water pipe-like apparatus (sidearm conical flask), 5 cigarettes (Marlboro Light brand, Philip Morris, USA) were puffed through the PBS solution. The nicotine concentration in this TSE is typically around 100 μM, as measured with a standard method based on bromination of nicotine (Rai et al., 1994). This TSE is used throughout all these studies. Note that when diluted 100-fold in culture media (e.g., 2 μL TSE in 200 μL final volume of media), this would give a

Toxicity of TSE on TZM-BL cells

As assessed by the MTT cell viability assay, TSE shows dose dependent cellular toxicity in TZM-bl cells (Fig. 1). At dilutions as low as 0.15 μL of TSE in 200 μL of cell culture medium, TSE shows a mild proliferative effect, whereas amounts larger than 5 μL of TSE per 200 μL of culture medium show increasing toxicity to cells. Therefore, a dose of 2 μL per 200 μL microplate well (i.e., 1% TSE in culture media) was used as the standard dose for HIV stimulation in later experiments.

TSE enhances HIV virion production/infectivity in both T cells and CD4+ Hela (TZM-bl) cells

As shown in Fig. 2A,

Discussion

Few studies have explored the possibility of direct interactions between non-nicotine tobacco constituents and viral replication in HIV/AIDS. The current study has identified direct interactions between tobacco constituents and HIV/AIDS infection at both the virion and cellular levels. The data show that as-yet unidentified non-nicotine smoke constituents are involved in enhancing HIV infectivity/virus production. We propose here that the mechanism involved in smoke-enhanced stimulation of HIV

Conflict of interest

The authors declare no conflict of interest with the study or preparation of the manuscript.

Acknowledgments

This study was supported by the UNCG Office of Research and Economic Development (to Ethan W. Taylor) and by the Fundamental Research Funds for the Central Universities of China, to Lijun Zhao (GK200901012).

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