Production of macrophage IL-1beta was inhibited both at the levels of transcription and maturation by caspase-1 following inhalation exposure to isobutyl nitrite.

Epidemiological studies have identified abuse of nitrite inhalants as an independent co-factor in HIV infection and in Kaposi's sarcoma (KS) in AIDS patients. In the present study we investigated the ability of macrophages from mice exposed to isobutyl nitrite to produce the inflammatory cytokine IL-1beta, upon stimulation with IFN-gamma and LPS. The production of IL-1beta was inhibited up to 55%. IL-1beta mRNA transcription was reduced by 35% following nitrite inhalant exposure, consistent with inhibition of activation-induced phosphorylation of macrophage mitogen-activated protein kinase p38. However, synthesis of the 31 kDa IL-1beta precursor protein was only marginally inhibited. Caspase-1, which cleaves the precursor IL-1beta into mature 17 kDa IL-1beta, was examined. Nitrite inhalant exposure blocked activation-induced increases in caspase-1 activity, consistent with a 50% reduction in 17 kDa IL-1beta shown in Western blots. Thus, exposure to nitrite inhalants reduced macrophage production of IL-1beta by reducing transcription, as well as post-translational processing mediated by caspase-1.

Inflammatory macrophage nuclear factor-kappaB and proteasome activity are inhibited following exposure to inhaled isobutyl nitrite.

A history of abuse of nitrite inhalants has been correlated with HIV seropositivity and Kaposi's sarcoma. A series of 14 daily, 45-min exposures of mice to 900-ppm isobutyl nitrite in an inhalation chamber reduced the number of peritoneal exudate macrophages (PEM) by 35% and the number of resident peritoneal macrophages (RPM) by 18%. Although the tumoricidal activity of RPM was not affected by the inhalant, the cytotoxicity of PEM was reduced by 26%. The induction of nitric oxide (NO) and the inducible NO synthase (iNOS) protein in PEM were inhibited by the inhalant to a similar extent. Inhibition of NF-kappaB activation in PEM from mice exposed to the inhalant corresponded to reduced degradation of the NF-kappaB inhibitor, IkappaB alpha. Proteasome-associated, enzymatic activity was compromised in PEM from inhalant-exposed mice, suggesting that inhaled isobutyl nitrite compromised macrophage, tumoricidal activity by inhibiting proteasomal degradation of the NF-kappaB inhibitor, IkappaB alpha.

Essential metalloelement chelates facilitate repair of radiation injury.

Treatment with essential metalloelement (Cu, Fe, Mn, and Zn) chelates or combinations of them before and/or after radiation injury is a useful approach to overcoming radiation injury. No other agents are known to increase survival when they are used to treat after irradiation, in a radiorecovery treatment paradigm. These chelates may be useful in facilitating de novo syntheses of essential metalloelement-dependent enzymes required to repair radiation injury. Reports of radioprotection, which involves treatment before irradiation, with calcium-channel blockers, acyl Melatonin homologs, and substituted anilines, which may serve as chelating agents after biochemical modification in vivo, as well as Curcumin, which is a chelating agent, have been included in this review. These inclusions are intended to suggest additional approaches to combination treatments that may be useful in facilitating radiation recovery. These approaches to radioprotection and radiorecovery offer promise in facilitating recovery from radiation-induced injury experienced by patients undergoing radiotherapy for neoplastic disease and by individuals who experience environmental, occupational, or accidental exposure to ultraviolet, x-ray, or gamma-ray radiation. Since there are no existing treatments of radiation-injury intended to facilitate tissue repair, studies of essential metalloelement chelates and combinations of them, as well as combinations of them with existing organic radioprotectants, seem worthwhile.

Acute exposure to the abused inhalant, isobutyl nitrite, reduced T cell responsiveness and spleen cellularity.

Isobutyl nitrite is an inhalant abused principally by male homosexuals. We have reported that subchronic inhalation exposure (45 min/day for 14 days) to 900 ppm isobutyl nitrite was immunosuppressive. In the present study, the effects of acute exposure to the inhalant were examined. Mice were exposed in an inhalation chamber to 900 ppm isobutyl nitrite for 45 min. One day later, spleen cellularity was reduced by 39% without selectively depleting CD4(+) or CD8(+) cells. The numbers of peripheral blood leukocytes and peritoneal cells were also reduced. Following acute inhalation exposure, T cell proliferative responses stimulated with allogeneic cells or anti-CD3 and anti-CD28 antibodies were inhibited, while mitogen-induced responses were not affected. Purified T cells exposed to the inhalant also had compromised responses, suggesting a direct effect on T cells. However, the cumulative effects of multiple exposures were necessary to inhibit T-dependent antibody responses or T cell or macrophage cytotoxicity.

Nitrite inhalants spontaneously liberate nitric oxide, which is not responsible for the immunotoxicity in C57BL/6 mice.

Nitrite inhalant abuse has been correlated epidemiologically with HIV seropositivity and with Kaposi's sarcoma. Using a mouse model, we have shown that inhaled isobutyl nitrite caused anemia and severely depressed immunity. In the present study, we showed that both isobutyl and cyclohexyl nitrites in air liberated nitric oxide (NO). An immunotoxic dose of 900 ppm isobutyl nitrite liberated 115 ppm NO. Mice were exposed in an inhalation chamber to 115 ppm NO, 900 ppm isobutyl nitrite, or 900 ppm cyclohexyl nitrite for 45 min/day. Following a single exposure, NO did not affect peripheral blood cell counts, while isobutyl and cyclohexyl nitrites reduced cell numbers. After 14 daily exposures, isobutyl nitrite, but not cyclohexyl nitrite or NO, reduced peritoneal macrophage tumoricidal activity. The nitrite esters likely caused immunotoxicity by mechanisms other than NO release.

Increased tumor growth in mice exposed to inhaled isobutyl nitrite.

Epidemiological studies have correlated the incidence of Kaposi's sarcoma (KS) in AIDS with a history of abuse of nitrite inhalants. To determine if exposure to nitrite inhalants could alter tumor growth, syngeneic PYB6 tumor cells were injected into groups of mice. Exposure of these mice to inhaled isobutyl nitrite increased both the tumor incidence and the tumor growth rate by almost 4-fold. Following only five daily exposures to the inhalant, the induction of specific T cell mediated cytotoxicity was inhibited by 36%. Similar inhalation exposures inhibited the tumoricidal activity of activated macrophages by 86%. The data suggest that exposure to abuser levels of a nitrite inhalant compromised tumor surveillance mechanisms.

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.

Acute blood toxicity of the abused inhalant, cyclohexyl nitrite.

Cyclohexyl nitrite is an abused nitrite inhalant. This is the first report of toxicity of cyclohexyl nitrite. Mice were exposed to 300-900 ppm cyclohexyl nitrite in an inhalation chamber for 45 min and then bled. Such treatment resulted in a 7-10% reduction in red blood cell counts, haemoglobin and haematocrit levels. Both blood leucocyte counts and spleen cellularity were reduced by 40%. Unlike isobutyl nitrite, subchronic treatment of mice with cyclohexyl nitrite did not impair macrophage tumoricidal activity or production of reactive nitrogen intermediates, but did modulate B and T cell mitogen responses. The data suggest that cyclohexyl nitrite had cytotoxic activity, comparable to that of isobutyl nitrite, which might be related to the anaemia reported in abusers. The immunomodulatory properties of cyclohexyl nitrite differed from those of isobutyl nitrite.

Elevated TNF-alpha and inducible nitric oxide production by alveolar macrophages after exposure to a nitrite inhalant.

Abuse of nitrite inhalants, widespread among male homosexuals, has been identified by epidemiological studies as an independent risk factor for AIDS and for Kaposi's sarcoma. Subchronic exposure of mice to inhaled isobutyl nitrite was previously found to impair the tumoricidal activity of peritoneal macrophages. Because inhalants would be expected to have the greatest effects on cells in the lung, alveolar macrophages from exposed mice were examined in this study. Mice were exposed to 900 ppm isobutyl nitrite in an inhalation chamber for 45 min/day for 14 days. Following this treatment, the lungs of exposed mice had large increases in cellularity, both in the alveolar septa and within the alveoli. Bronchoalveolar lavages also contained increased numbers of cells. Alveolar macrophages collected from treated mice had increased tumoricidal activity compared with controls and produced higher levels of inducible nitric oxide and tumor necrosis factor-alpha (TNF-alpha). The frequency of alveolar cells secreting TNF-alpha was increased ninefold in mice exposed to the inhalant. Cell influx into the lung, as indicated by the presence of red blood cells in lung lavages, was evident after only a single 45-min exposure to inhaled isobutyl nitrite at doses as low as 300 ppm.