Mark J. Reasor

Drug-Induced Phospholipidosis: Are There Functional Consequences?:

Phospholipidosis induced by drugs with a cationic amphiphilic structure is a generalized condition in humans and animals that is characterized by an intracellular accumulation of phospholipids and the concurrent development of concentric lamellar bodies. The primary mechanism responsible for the development of phospholipidosis is an inhibition of lysosomal phospholipase activity by the drugs. While the biochemical and ultrastructural features of the condition have been well characterized, much less effort has been directed toward understanding whether the condition has adverse effects on the organism. While there are a few cationic amphiphilic drugs that have been reported to cause phospholipidosis in humans, the principal concern with this condition is in the pharmaceutical industry during preclinical testing. While this class of drugs should technically be referred to as cationic lipophilic, the term cationic amphiphilic is widely used and recognized in this field, and for this reason, the terminology cationic amphiphilic drugs (CADs) will be employed in this Minireview. The aim of this Minireview is to provide an evaluation of the state of knowledge on the functional consequences of CAD-induced phospholipidosis.

Drug-induced phospholipidosis: issues and future directions

Numerous drugs containing a cationic amphiphilic structure are capable of inducing phospholipidosis in cells under conditions of in vivo administration or ex vivo incubation. The principal characteristics of this condition include the reversible accumulation of polar phospholipids in association with the development of unicentric or multicentric lamellated bodies within cells. There is an abundance of data providing an understanding of potential mechanisms for the induction of phospholipidosis; however, the process is likely to be complex and may differ from one drug to another. The functional consequences of the presence of this condition on cellular or tissue function are not well understood. The general consensus is that the condition is an adaptive response rather than a toxicological manifestation; however, additional studies to examine this question are needed. Until this issue is resolved, concerns about phospholipidosis will continue to exist at regulatory agencies. Procedures for the screening of potential phospholipogenic candidate compounds are available. In contrast, a clear need exists for the identification of valid biomarkers to assess the development of phospholipidosis in preclinical and clinical studies.

A review of the biology and toxicologic implications of the induction of lysosomal lamellar bodies by drugs

Over 30 drugs of differing pharmacologic action are capable of inducing lamellar bodies of lysosomal origin in cells of animals and humans. The structures develop because of a drug-induced impairment in lysosomal phospholipid catabolism. Toxicity frequently accompanies the induction of these bodies. However, little information exists as to whether their development or presence is causally linked to the cellular or tissue dysfunction. This review examines the biological aspects of the induction of lysosomal lamellar bodies by drugs and considers the toxicologic implications of their presence in cells.

AN EVALUATION OF POSSIBLE MECHANISMS UNDERLYING AMIODARONE-INDUCED PULMONARY TOXICITY

Abstract The effectiveness of amiodarone in the treatment of cardiac arrhythmias is limited due to the development of pulmonary toxicity. Although the biochemical and morphologic characteristics associated with amiodarone-induced pulmonary toxicity (AIPT) are well-defined, the mechanisms underlying this disorder remain unknown. This review focuses on proposed mechanisms of AIPT, in particular (i) direct cellular damage; (ii) the role of phospholipidosis; (iii) the correlation between drug burden and toxicity; (iv) the role of the immune system; (v) the generation of oxidants; (vi) changes in membrane properties; and (vii) miscellaneous biochemical considerations. Additional discussion of the role of amiodarones primary metabolite, desethylamiodarone, in AIPT and the involvement of preexisting lung dysfunction in the susceptibility to AIPT is included. With a clearer understanding of the possible contributions of these mechanisms to AIPT, it may be possible to develop strategies to alleviate toxicity and prolong the usefulness of amiodarone in the treatment of cardiac arrhythmias.

Role of phospholipase A inhibition in amiodarone pulmonary toxicity in rats

Amiodarone is effective in the treatment of ventricular and supraventricular arrhythmias. In man its clinical use is associated with the accumulation of phospholipid-rich multilamellar inclusions in various tissues including lung, liver and others. This report presents evidence showing that amiodarone is a potent inhibitor of lysosomal phospholipase A from rat alveolar macrophages, J-744 macrophages and rat liver. When compared with other cationic amphiphilic agents which are known to produce phospholipidosis, amiodarone is one of the most potent inhibitors yet discovered. The subcellular localization of amiodarone has been determined in lung and its distribution was consistent with a lysosomal localization. It is hypothesized that amiodarone causes cellular phospholipidosis by concentrating in lysosomes and inhibiting phospholipid catabolism.

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.

Effects of heavy metal ions on selected oxidative metabolic processes in rat alveolar macrophages

The effects of four heavy metal cations, Cd2+, Hg2+, Ni2+, and Pb2+, on oxygen consumption, glucose metabolism, and the release of active oxygen species (as measured by chemiluminescence) were studied in rat alveolar macrophages at rest (no phagocytosis) and during phagocytosis. All four heavy metals depress the oxygen consumption and glucose metabolism which occurs in alveolar macrophages at rest by about 60–95%. During phagocytosis there is release of reactive forms of oxygen from the cells, a two- to threefold increase in oxygen consumption, but no change in glucose metabolism from that which occurs in resting cells. The metals inhibit the release of active oxygen from the cells and the oxygen consumption which occurs during phagocytosis by 75–85%. The ED50 values, i.e., the concentrations of metals which produce one-half of the maximal effects, indicate that the mechanism for release of active oxygen is affected by much lower concentrations of metals than is oxygen consumption. Also, experiments with trypan blue provide evidence that the metals can affect oxidative metabolism without causing gross membrane damage. The results of these experiments indicate that heavy metals inhibit oxidative metabolic processes in alveolar macrophages and, thus, may diminish the antibacterial activity of these cells.

The response of rat alveolar macrophages to chronic inhalation of coal dust and/or diesel exhaust

The use of diesel-powered equipment in underground mines has raised questions regarding possible synergistic effects of coal dust and diesel emissions. Therefore, the effects of chronic exposure of rats to coal dust and/or diesel exhaust on various properties of alveolar macrophages were investigated. Inhalation exposure of rats was 7 hr/day, 5 days/week for 2 years. Exposure groups were: filtered air controls, 2 mg/m3 coal dust, 2 mg/m3 diesel particulate, and 1 mg/m3 coal dust plus 1 mg/m3 diesel exhaust. Exposure to coal dust and/or diesel exhaust had little effect on oxygen consumption, membrane integrity, lysosomal enzyme activity, or protein content of alveolar macrophages. However, exposure to coal dust increased macrophage yield, enhanced chemiluminescence, and increased the activity of the cell membrane (i.e., increased cellular spreading and surface ruffling). In contrast, diesel emissions depressed chemiluminescence and decreased the ruffling of the cell membrane. Therefore, the data suggest that exposure to coal dust and/or diesel exhaust does not affect the viability of alveolar macrophages. However, coal dust may activate alveolar macrophages while diesel emissions may depress the phagocytic activity of these cells. The combination of exposures to coal dust and diesel exhaust results in a phagocytic activity which is an average of the effects of separate exposures.

Macrophage regulation of myelopoiesis is altered by exposure to the benzene metabolite hydroquinone

Hydroquinone, a myelotoxic metabolite of benzene, decreases the ability of murine bone marrow stromal cells to support myelopoiesis in vitro. Bone marrow stroma consists of macrophages and fibroblastoid stromal cells that participate coordinately in regulating myelopoiesis. The goal of this study was to determine if macrophage or fibroblastoid cell function is more sensitive to the myelotoxic actions of hydroquinone. To address this question, we developed purified populations of macrophages and fibroblastoid stromal cells and treated each population with hydroquinone. These cells were reconstituted together with nontreated cells of the opposite type and assayed for their ability to support the formation of granulocyte and macrophage colonies in an agar overlay. Reconstituted cultures containing hydroquinone-treated macrophages supported fewer colonies than did corresponding cultures containing untreated macrophages. Reconstituted cultures containing hydroquinone-treated fibroblastoid stromal cells were not affected. Moreover, hydroquinone reduced detectable interleukin-1 activity in purified macrophage cultures stimulated with lipopolysaccharide. These results indicate that hydroquinone selectively interferes with macrophage function possibly, in part, via alteration of macrophage interleukin-1 secretion.

Amiodarone-induced pulmonary toxicity in rats: Biochemical and pharmacological characteristics

Treatment of humans with the antiarrhythmic drug, amiodarone (AD), may result in the development of pulmonary toxicity. To characterize this response, male Fischer 344 rats were treated with AD for 1, 3, 9, and 16 weeks. AD induces a twofold increase in the level of pulmonary phospholipid after 3 weeks of treatment. Continued administration results in only a small increase above this level. All classes of phospholipids are elevated; phosphatidylcholine displays the largest increase, both quantitatively and as a relative increase over the control level. Both AD and its principal metabolite, desethylAD, are sequestered in the lungs following AD treatment. The relative levels are similar at all time points except 16 weeks, where the relative amount of AD is decreased. After 3 weeks of AD, female 344 rats show the same increase in pulmonary phospholipid as males. While similar levels of desethyAD are sequestered in the lungs of both sexes, AD levels are much lower in female lungs. Evidence is presented to suggest that desethylAD may play an important role in the induction of the phospholipidosis. The activity of Na+,K+-ATPase in the lungs is inhibited by 75% after 9 weeks of AD while the activity of the acid hydrolase, beta-N-acetylglucosaminidase is increased significantly at this time point. All biochemical changes are reversible with values returning to control levels 2 weeks after termination of a 3-week AD treatment protocol. Measurable levels of AD and desethylAD are present in lung tissue after 5 weeks of recovery.