The alveolar macrophage and its role in toxicology

Pulmonary clearance of Candida albicans: effect of exposure to native and metal-coated fly ash

The viability of Candida albicans was tested at various intervals in the lungs of rats following single intratracheal inoculation of the yeast cells. Most of the inoculated cells were cleared from lungs within 48 hr after exposure. Clearance was enhanced in lungs exposed to metal-coated fly ash than in those exposed to native fly ash. The validity of these studies was verified in vitro using peritoneal macrophages of mice exposed in vivo to native and metal-coated fly ash. An increase in phagocytic and intracellular killing of macrophages harvested from animals exposed to native or metal-coated fly ash was observed.

On the cytotoxicity of chrysotile asbestos fibers toward pulmonary alveolar macrophages. II. Effects of nicotinamide on the cell metabolism

Since it was recently shown that the addition of nicotinamide (NAM) to pulmonary alveolar macrophages (PAM) cell monolayers significantly altered their ATP pools (Nadeau and Lane, 1988), the effects of the vitamin on the metabolism of the cells, exposed or not to very short chrysotile asbestos fibers (VSF), were evaluated. First, it was found that the addition of NAM to the culture medium caused a dose-dependent (5-30 mM) decrease in the extracellular liberation of lactate and pyruvate by PAM. This is suggestive of a direct effect of NAM on the metabolism of glucose. A decrease in extracellular lactate was also observed when control PAM were exposed to 50 micrograms of VSF asbestos. This latter effect was however progressively abolished when the NAM was added to the asbestos-exposed cell monolayers. Second, contrary to the lactic acid production, the exposure to chrysotile caused an increase in the extracellular liberation of pyruvate by PAM. This cell response to the asbestos fibers could represent an antioxidative defense mechanism. Yet, interestingly enough, this effect of the VSF on PAM was not suppressed by the presence of the vitamin. The NAM also induced a dose-dependent decrease in the total lactate dehydrogenase content of PAM monolayers. By comparison, 3-aminobenzamide (up to 5 mM) did not appreciably modify these parameters. After an 18-hr incubation period with 20 mM NAM, the NAD+ pools of control PAM increased by approximately 300% comparatively to a approximately 40% increase for the NADP+ content. The exposure to the VSF asbestos caused a dose-dependent depletion of the cellular NAD+ and NADH pools. However, for the latter, the vitamin prevented the depletion effect of the asbestos fibers. Comparatively, the NADP(H) pools increased. This shift toward the phosphorylated pyridine nucleotide forms could also represent a defense of the cell against the oxygen radicals produced during the ingestion of the fibers. Overall, it is shown that changes in the energy metabolism could be implicated in the toxicity of chrysotile asbestos fibers toward PAM, and that the cells seem to be able to respond to an oxidant stress. Although not fully elucidated at the present time, these data tend nonetheless to point out that the protective effect of NAM could involve some modifications of the host defenses against prooxidants.

Changes in some histochemically demonstrable enzymes in macrophages exposed to quartz dust in vitro

Cytochemical studies were carried out on rat alveolar and peritoneal macrophage cultures following exposure to quartz and corundum dusts. Quartz increased the number of ATPase positive cells and brought about an enhancement in the peroxidase and diffusion of the acid phosphatase activity of the exposed cells. In unexposed cell cultures, acid phosphatase activity was higher in alveolar than in peritoneal macrophages and was dependent upon the duration of incubation. Corundum produced no significant effect on the enzyme activity. Quartz treatment did not alter esterase activity whereas corundum exposed cultures showed a decline. A significant increase in mitochondrial succinic dehydrogenase activity was observed in peritoneal macrophages after quartz treatment. The results demonstrate alteration in the marker enzymes of plasma membranes, mitochondria and lysosomes during phagocytosis of quartz dust as the key event of dust cell interaction in vitro.

Rabbit alveolar macrophage-mediated mutagenesis of polycyclic aromatic hydrocarbons in V79 Chinese hamster cells

Rabbit pulmonary alveolar macrophages (PAM) were used as a metabolizing device in combination with V79 Chinese hamster cells as a mutational indicator system. The capacity for metabolic activation of benzo[a]pyrene (B[a]P), its 7,8-diol and 2-aminoanthracene by PAM was investigated. Because of the high variation between different PAM preparations, a statistically significant effect of the 3 compounds could only be demonstrated in a series of 4 or 5 experiments. When the ability of PAM to metabolize B[a]P and the 7,8-diol to mutagenic products was compared with that of primary embryonic fibroblasts from Syrian hamsters, PAM were found to be one-tenth as efficient. Experiments were performed to find out how the phagocytic process could affect the metabolic activation of polycyclic aromatic hydrocarbons. The results showed that PAM-mediated mutagenesis of the 7,8-diol was enhanced 5-10-fold if PAM were fed with opsonized particles. The mechanism by which the phagocytosis of PAM enhanced the mutagenicity of 7,8-diol, as detected in co-cultivated V79 cells, can so far only be a matter for speculation.

Perifused alveolar macrophages. A technique to study the effects of toxicants on prostaglandin release

A technique was developed for perfusing free airway cells (FAC) obtained by guinea-pig bronchoalveolar lavage. 10 x 10(6) FAC (mostly macrophages) were placed on the filter of a Nuclepore chamber perfused with Tyrode's solution or with Eagle's Minimal Essential Medium (MEM); the effluent was collected at intervals and te release of prostaglandin E2 by the perifused cells was used as an index of the inflammatory reaction to toxicants. Zymosan, asbestos fibers and soluble toxic agents stimulated the synthesis of prostaglandins while indomethacin abolished it. Our technique of FAC perifusion allows the sequential study of biochemical events involved in macrophage defense mechanisms as well as providing a simple test for the evaluation of various toxicants.

Drug-induced lipidosis and the alveolar macrophage

The alveolar macrophage is the principal component of the defense mechanisms of the lung. As a result, alterations in its function can predispose the host organism to pulmonary disease or damage. This cell shows toxic responses to a wide variety of chemicals which are delivered to the lungs by either inhalation or via the systemic circulation. In this regard, this review will focus on the effects of a group of cationic amphiphilic drugs which when administered to humans and animals causes a lysosomal storage disorder of lipids, principally phospholipids, in alveolar macrophages. The susceptibility to the disorder is species-dependent and can be induced in fetal, neonatal and adult animals. Evidence exists that the accumulation of lipids within the cells occurs as a result of an impairment in lipid catabolism, however, not all of the available data are consistent with this theory. In light of this, other mechanisms to explain the etiology of this lipidosis are discussed. Associated with the increase in lipid content within the cell, striking morphological, biochemical and functional changes occur to the alveolar macrophage. Available data indicate that afflicted cells have an increased phagocytic activity and exhibit enhanced killing of one strain of bacteria. While these data suggest an enhancement in certain cellular functions, inadequate information presently exists to allow conclusions to be drawn concerning the consequences of this disorder.

Phospholipase A activity and prostaglandin release from alveolar macrophages exposed to asbestos

The effect of asbestos (canadian chrysotile B) was studied on macrophages harvested by guinea-pig bronchoalveolar lavage. In short term incubation (3 hrs), asbestos (1 mg) induced a highly significant increase in macrophage phospholipase A activity and prostaglandin synthesis. At lower concentrations of the fibers (10 micrograms and 100 micrograms), no significant change of macrophage activity was noted following our incubation period. The modification by asbestos of membrane integrity and functions is suggested.

The biology of talc

Data are presented on the effects on health of talc dusts from exposure in industry and use of talc-containing health products. The mineralogy of talc and the composition of cosmetic and industrial grade talc dusts are described. Studies in animals are reviewed, and epidemiological data are considered in relation to exposures that occur during industrial and consumer uses of talc dusts. Hamsters exposed to 8 mg/m3 of respirable cosmetic grade talc dust for up to 150 minutes a day for 300 consecutive days showed no difference in incidence or nature of pathological lesions from those observed in a group of untreated animals. A retrospective study of the causes of death of 227 talc mine millers exposed to cosmetic grade talc at the threshold limit value for talc (20 million parts per cubic foot) for an average of 15-8 years showed that the causes of death were no different from those in a control cohort not exposed to talc dust. The available data indicate that talc dust exposure in the modern mining of cosmetic grade talc does not appear to be injurious to health. The significantly lower dust exposure in the normal use of cosmetic grade talc dusts in talc-containing health and cosmetic products confirms that their use is not a hazard to health.

The pulmonary macrophage

An overview of the pulmonary macrophage is provided, with particular emphasis on the origin of this cell and the adaptive mechanisms whereby the macrophagic system is able to respond to increased inhalant loads of organic and inorganic pollutants. Evidence is presented which favors an hematopoietic origin for the alveolar macrophage with a monocytic transportation compartment in the blood and an interstitial cell compartment in the lung in which cellular division and maturation may occur. Through the simple mechanism of increased cellular turnover this system of mononuclear phagocytes rapidly adapts to most inhalant challenges. In addition to its primary tasks phagocyte and destroyer of microorganisms the macrophage plays a pivotal role in the genesis of silicotic fibrosis, and it is possible that similar mechanisms may hold for a variety of cryptogenic fibroses. Paradoxically, destruction of collagen by the dual mechanisms of phagocytosis and the secretion of lytic enzymes may also occur. The relevance of this secretory function of the macrophage to the pathogenesis of destructive diseases of the lung such as emphysema remains to be determined.