Subchronic inhalation toxicity of isobutyl nitrite in BALB/c mice. II. Immunotoxicity studies

Immunomodulation by nitrite inhalants may predispose abusers to AIDS and Kaposi's sarcoma

Epidemiological studies indicating that nitrite inhalant abuse is a co-factor in HIV infection and in Kaposi's sarcoma are supported by recent experimental studies, described in this review. Inhalation exposure to the nitrites produce a nonspecific cytotoxicity, depleting many cells of the immune system. Apparently distinct from this cytotoxicity, inhalation of the nitrites impairs a variety of immune mechanisms, affecting both humoral and cell-mediated immunity. In addition, the inhalant-increased macrophage production of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha), can directly stimulate HIV replication and can also stimulate the growth of Kaposi's sarcoma cells. Thus, nitrite inhalants may impair immune resistance to infection and actively promote viral replication and tumor growth.

T cell functions are impaired by inhaled isobutyl nitrite through a T-independent mechanism

Isobutyl nitrite is representative of a group of inhalants abused by male homosexuals and adolescents. Inhalation exposure of mice to isobutyl nitrite at 900 ppm for 45 min per day for 14 days caused serious deficits in T cell-mediated immune responses. Cytotoxic T lymphocyte (CTL) activity was reduced by 36% following the exposure. T cell proliferative responses to mitogenic and allogeneic stimulation were reduced by 37% and 51%, respectively. The exposure did not directly alter the ability of cells to synthesize or respond to IL-2. Accessory cell function in facilitating T cell activation was inhibited by about 50% following exposure to the inhalant.

Inhaled isobutyl nitrite compromises T-dependent, but not T-independent, antibody induction

Habitual abuse of nitrite inhalants has been linked in epidemiological studies with seropositivity to human immunodeficiency virus and, separately, with Kaposi's sarcoma among AIDS patients. Mice exposed to isobutyl nitrite in an inhalation chamber for 45 min/day for 14 days had depressed IgM and IgG antibody responses. The inhibition was dose-dependent at 750-900 ppm, but antibody responses were increased at an intermediate (600 ppm) dose. Gender differences in immunotoxicity were not observed. Antibody responses to a T-independent antigen (DNP-ficoll) were not affected by the immunotoxic exposure, suggesting that B-cells were refractory to the toxic exposure. Toxic exposure to isobutyl nitrite did not selectively deplete a particular spleen cell population, but caused equivalent reductions of T-cells and B-cells. Finally, exposed mice remained immunocompromised for 3-5 days after terminating exposures. Normal immune responses returned by 5-7 days, suggesting that inhibition of cellular function was reversible.

Subchronic inhalation toxicity of isobutyl nitrite in BALB/c mice. I. Systemic toxicity

The effects of subchronic inhalation exposure to isobutyl nitrite (IBN) on body weight, selected organ weights, hematology, and gross pathology and histopathology of BALB/c mice were evaluated. Mice of both sexes were exposed at 0, 20, 50, or 300 ppm IBN for 6.5 h/d, 5 d/wk for up to 18 wk. Most changes in measured indices occurred in mice exposed at 300 ppm IBN and included decreased thymus weight (females); decreased liver weight (males); decreased white blood cell counts (males); mild focal hyperplasia and vacuolization of the epithelium lining bronchi and bronchioles of the lungs (males and females). Organ weight and hematologic changes, however, were not accompanied by any observed histologic changes. In addition, elevated methemoglobin concentrations were detected in mice of both sexes exposed at 50 and 300 ppm IBN. Body weights were not adversely affected by exposure. These data suggest that mild tissue injury, restricted to the lung, and methemoglobinemia are the major toxic effects observed following exposures of mice to IBN at concentrations up to 300 ppm for 18 wk. No treatment-related effects were noted in mice exposed at 20 or 50 ppm IBN, except for slight elevations in methemoglobin concentrations in mice exposed at 50 ppm.