Cationic Amphiphilic Drug-Induced Phospholipidosis
`
`Schering-Plough Research Institute, P.O. Box 32, Route 94 South, Lafayette, New Jersey 07848
`
`WILLIAM H. HALLIWELL
`
`ABSTRACT
`
`Phospholipidosis, a phospholipid storage disorder, defines an excessive accumulation of intracellular phospholipids. Phospholipids
`are structural components of mammalian cytoskeleton and cell membranes. The metabolism of this essential cell component is regulated
`by the individual cell and may be altered by drugs that interact with phospholipids or the enzymes that affect their metabolism.
`Xenobiotics or their metabolites that induce phospholipidosis include a wide variety of pharmacologic agents, including antibacterials,
`antipsychotics, antidepressants, antiarrhythmics, antianginals, antimalarials, anorexic agents, cholesterol-lowering agents, and others.
`Each of these drugs shares several common physiochemical properties: hydrophobic ring structure on the molecule and a hydrophilic
`side chain with a charged cationic amine group, hence the class term cationic amphiphilic drugs (CADs). This paper reviews the
`phospholipid metabolism, physiochemical characteristics of CADs, specificity of phospholipidosis in animals and humans, functional
`effects of phospholipidosis, interaction of CADs with biologic membranes and lysosome metabolism, influence of CADs on phos-
`pholipases and phospholipid synthesis, and a proposed mechanism for induction of phospholipidosis in the lung. In human risk
`assessment, investigators should consider the many factors in evaluating a drug that induces phospholipidosis in animals. These include:
`the therapeutic class of drug, presence of active metabolites, tissue or organ selectivity in animals and humans, influence of concurrently
`administered drugs, reversibility of effect, and other factors that increase or decrease the induction of phospholipidosis. Generalities
`regarding the etiology, incidence, and effect of the drug on a specific host may not be made. Each drug must be evaluated separately
`to identify the risk when administered for therapeutic effect in humans.
`Keywords. Phospholipidosis; cationic amphiphilic drugs; phospholipid storage disorder; foamy alveolar macrophages; lysosomal
`lamellar bodies
`
`INTRODUCTION
`In 1996, Greselin reported that a cholesterol synthesis-
`inhibiting drug trans-1,4-bis(2-chlorobenzylaminome-
`thyl) cyclohexane dichloride (AY-9944), induced in-
`creased numbers of foam cells in the pulmonary alveoli
`of rats (19). In 1971 there was the description of diethy-
`laminoethoxyhexestrol (DH)-induced foam cell lipidosis
`in humans (85). Since that time, there have been many
`reports of xenobiotic-induced phospholipid storage dis-
`orders. More than 50 cationic amphophilic drugs (CADs)
`administered to laboratory animals, humans, and cultured
`cells result in the induction of a generalized lipid storage
`disorder in many tissues of the body (39,47,48,50). Phos-
`pholipidosis describes the excessive accumulation of
`phospholipids in affected cell lysosomes that acquire a
`multilamellar morphologic appearance. Phospholipids are
`essential components of cell membranes. They contain a
`greater proportion of polar groups and are, therefore,
`partly soluble in water and partly soluble in nonpolar
`solvents. The bilayer of such polar lipids has been re-
`garded as a basic structure in biologic membranes. Their
`synthesis and metabolism are regulated by individual
`cells and tissues. Metabolic dysfunction associated with,
`or induced by, genetic disorders may produce lysosomal
`storage of phospholipids, such as Niemann-Pick and
`Tay-Sachs diseases (12). However, xenobiotic drugs and
`chemicals, as well as hormones, cofactors, and other
`agents, may alter the metabolism of the cell and result in
`phospholipidosis (39).
`
`*Address correspondence to: Dr. William H. Halliwell, Schering-
`Plough Research Institute, PO. Box 32, Route 94 South, Lafayette, New
`Jersey 07848.
`
`Phospholipidosis may be induced by the direct inter-
`action of xenobiotics with intracellular phospholipids or
`by the action of xenobiotics on the synthesis and metab-
`olism of phospholipids (36,39). The intracellular phos-
`pholipid content may increase to many times the normal
`content of the cell (23). Many factors contribute to the
`development of phospholipidosis including structural for-
`mula of the CAD, intra- and interspecies susceptibility,
`dose, duration of dosing (exposure) and mechanism of
`action of the CAD on the metabolism of specific phos-
`pholipids (39).
`The induction of phospholipidosis by the exposure to
`CADs results in the possible accumulation or retention
`of phospholipids in virtually every tissue or organ in the
`body. Commonly, excessive accumulation is seen in the
`lung, liver, brain, kidney, ocular tissues, heart, adrenal
`glands, hematopoietic tissue, and circulating lympho-
`cytes, but virtually all tissues of the body are capable of
`excessive phospholipid accumulation (3,32,47,50,55).
`Several excellent reviews of phospholipidosis induction
`by CADs have been published. (27,29,37,39,51,52,64).
`These publications span 20 yr of investigations into the
`etiology, mechanisms, effects, and reversibility of phos-
`pholipidosis in animals and its relevance in assessing hu-
`man risk assessment.
`There is a wide variation in the species susceptibility
`for animals and humans to phospholipidosis. It is not un-
`common to recognize different organ or tissue suscepti-
`bility and severity when comparisons are made between
`animals and humans. These features are particularly rel-
`evant in human risk assessment. The use of cell culture
`has become a useful tool in the evaluation of the potential
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`for a xenobiotic to induce phospholipidosis and to inves-
`tigate phospholipid metabolism (2,69).
`
`1. WHAT Is PHOSPHOLIPIDOSIS?
`Phospholipidosis is the excessive intracellular accu-
`mulation of phospholipids induced by the short-term or
`chronic administration of CADs. The induction time may
`be a few days to several months, depending on the affin-
`ity of the CAD for susceptible cells (25,34). In cell cul-
`tures, phospholipids can accumulate intracellularly and
`induce lysosomal lamellar body formation, within only a
`few hours of exposure (69).
`In the normal lung, production of surfactant is a dy-
`namic process. Type II pneumocytes synthesize surfac-
`tant in lamellar bodies and secrete it into the alveolar
`space by exocytosis. Surfactant is taken up by pinocytic
`action of alveolar macrophages, processed, and then ex-
`truded into the alveolar space. Some is then taken up by
`the type II pneumocytes and recycled (61,64). Although
`phospholipidosis may occur in almost any tissue in the
`body, the lung and the alveolar macrophages are usually
`prominent in their response to administration of most
`CADs.
`The experimental lung lesion is characterized by the
`excessive accumulation of foamy alveolar macrophages,
`mononuclear cells, and amorphous material in the alve-
`olar spaces of the lung (25,26,52). In pulmonary phos-
`pholipidosis, there is an increased amount of phospholip-
`id in the lung tissue and/or alveolar macrophages. Lungs
`from rats treated intraperitoneally with chlorphentermine
`(30 mg/kg) for 4 wk had: 1) marked accumulation of
`alveolar macrophages in the alveoli; 2) the alveolar mac-
`rophages were heterogeneous in size, with many up to
`10 times normal volume; and 3) the alveolar macro-
`phages became engorged with lysosomal lamellar bodies
`and granular material. Initially the lysosomes swell, some
`fragment, and others develop a lamellar pattern. The cell
`then becomes filled with lysosomal lamellar bodies and
`amorphous granular material derived from deterioration
`of the lysosomal lamellar bodies. Alveolar macrophages
`disintegrate and distribute the granular material to the ex-
`tracellular space (65). The increased total phospholipids
`in the alveolar macrophages of rats treated with chlor-
`phentermine are composed of phosphatidylcholine,
`sphingomyelin, phosphatidylserine, and phosphatidyleth-
`anolamine (65). The cellular changes induced by most
`CADs are generally reversible, but the effects on tissues
`do not return to control levels at the same time (65).
`
`II. DRUGS THAT INDUCE PHOSPHOLIPIDOSIS
`There are over 50 known CADs that induce phospho-
`lipidosis in one or more tissues in the body and they
`include many different therapeutic classes of drugs. Some
`of the classes of drugs are antidepressants, antiarrythm-
`ics, antianginals, antibacterials, antimalarials, anorexic
`agents, antipsychotics, cholesterol-reducing agents, and
`others (4,25,32,47,48,64) (Fig. 1).
`It is important to recognize that each of these xeno-
`biotics possibly has a different species and tissue selec-
`tivity, affinity for phospholipids, metabolism or metabo-
`lites, and other biochemical or structural differences so
`
`that each will induce a slightly different manifestation of
`phospholipidosis.
`Despite the diverse pharmacologic activity, therapeutic
`indications, diversity of tissue selectivity, and distinct
`manifestations of phospholipidosis that each of these
`CADs can induce in different species of animals, they do
`share several common physiochemical similarities. The
`physiochemical properties most commonly shared by
`CADs are a hydrophobic ring structure on the molecule
`and a hydrophilic side chain with a charged cationic
`amine group. These two structural entities provide the
`amphiphilicity that is common to these drugs, and there-
`fore they are identified as cationic amphophilic amines
`(30,39).
`The hydrophobic structure enhances the molecule’s
`ability to pass through plasma membranes when they are
`not ionized. The ionized form of the molecule tends to
`remain with the membrane and contribute to membranous
`changes (30,39,76). Thus it can be visualized that cell
`membrane phospholipids and their charged ionic groups
`monitor CAD penetration and bonding in cells (39). The
`addition of a halogen group to the hydrophobic ring
`seems to enhance membrane penetrability (18,75).
`The diversity of the therapeutic activity of CADs is
`dependent on their effect on membrane composition,
`transition temperature, membrane fluidization, receptor
`site mediation, and other functions not yet well under-
`stood (9,44,46).
`Many of the antiarrhythmics, B blockers, and antip-
`sychotics affect ion channels and receptors (46,87).
`Amiodarone, an antiarrhythmic drug, inhibits Na+ pene-
`tration of cell membranes and also affects Ca2+ move-
`ment (77). Propanolol is a beta-adrenergic blocker that is
`primarily receptor site mediated (60). Neuroleptics and
`antipsychotics, for example promazine and chlorproma-
`zine, are lipid soluble and influence membrane perme-
`ability (74,76).
`Disobutamide induces clear cytoplasmic vacuoles that
`are indicative of intracellular drug storage and concentric
`lamellar bodies in multiple tissues and organs (68,70). It
`has been proposed that the unique structure of this CAD,
`with two basic amines on the hydrophobic chain, induces
`both clear cytoplasmic membrane-bound vacuoles that
`are storage sites of drug (disobutamide) and also induces
`lysosomal lamellar bodies typical of phospholipidosis
`(68,70). Chloroquine (Fig. 1) also contains two basic
`amines on the hydrophilic side chain and induces clear
`cytoplasmic vacuoles and lysosomal lamellar bodies (39).
`Two major concepts have been proposed for the mech-
`anism of CAD-induced phospholipidosis. The first pro-
`poses that CADs bind to phospholipids and the complex
`becomes more resistant to degradation by phospholipases
`(30,48). Secondly, is the hypothesis that CADs directly
`inhibit the enzymes responsible for phospholipid catab-
`olism (41). It is plausible that both mechanisms, or var-
`ious combinations of them, are responsible for the varied
`response seen in phospholipidosis in animals and humans
`(30).
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`FiG. 1.-Structural formulas and therapeutic use of various amphophilic drugs.
`
`III. SPECIFICITY OF PHOSPHOLIPIDOSIS: ANIMAL SPECIES,
`TISSUE, AND AGE SUSCEPTIBILITY
`The distribution of specific phospholipids in various
`tissues is dependent on the structure and function of each
`tissue and also the species and age of the animal. These
`factors and others determine the incidence and severity
`of phospholipidosis induced by CADs. Recognition of
`the ionic and hydrophobic interactions of CADs with
`phospholipids or phospholipases is important in recog-
`nizing the diversity of response of these molecules
`(30,49). Chlorphentermine reacts more vigorously with
`phospholipids that have polar ionic moieties; hydropho-
`bic interactions are minor (30). Chlorphentermine binds
`mainly to phosphatidylcholine and charged polar lipids.
`Surfactant in the lung contains high levels of disaturated
`
`phosphatidylcholine, therefore, it is not surprising that
`cholorphentermine produces dramatic pulmonary phos-
`pholipidosis in rats (30,66,79).
`In contrast, amiodarone binds most vigorously to the
`hydrophobic moiety of phospholipids, and ionic interac-
`tions of the polar moiety are minimal (29). Treatment
`with amiodarone produces a significant elevation of phos-
`phatidylcholine particularly in alveolar macrophages and
`type II pneumocytes (17). Amiodarone also induces phos-
`pholipidosis in the liver with large increases in phospha-
`tidylserine and phosphatidylethanolamine (62,86). It is
`noteworthy that amiodarone does not induce significant
`numbers of lysosomal lamellar bodies in the hepatocyte
`cytoplasm but does induce cytoplasmic vacuoles (43,62).
`Gentamicin is a CAD with a different affinity; it pro-
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`duces phospholipidosis predominantly in the kidney.
`Gentamicin, an aminoglycoside antibiotic, is predomi-
`nantly excreted by glomerular filtration and then binds to
`the brush-border membranes of the proximal tubule epi-
`thelial cells where it is adsorbed by endocytosis. Subse-
`quently, it accumulates in lysosomes of the proximal tu-
`bule epithelium (1,16,84). Analysis of homogenate and
`lysosomal fractions of kidney cortex reveals increases in
`concentration of total renal phospholipids including:
`phosphatidylserine, phosphatidylcholine, and phosphati-
`dylinositol. These changes are accompanied by a signif-
`icant reduction in phospholipase C, an enzyme with a
`high affinity for phosphatidylcholine and other phospho-
`lipids (35,84).
`The role of CADs in the alteration of cell-to-cell sig-
`naling has not been well defined; however, the alterations
`in levels of phosphatidylinositol, phosphatidylcholine,
`and others point to alterations in signal transduction
`(39,73).
`Even within species, there can be vast differences in
`the manifestation of phospholipidosis. McCloud et al
`have investigated the accumulation of amiodarone and its
`metabolites and its propensity to induce phospholipidosis
`in Fisher 344 rats and Sprague Dawley rats (56). In these
`studies, amiodarone was administered at 100 mg/kg/day
`for I wk or 4 wk. The results from these two studies
`were similar-phospholipidosis was induced in the lung
`tissues of the Fisher 344 rats but not significantly in the
`Sprague Dawley rats. It was concluded the strain differ-
`ences were related to the dispositional location of the
`drug (56).
`The role that age contributes to CAD-induced mor-
`phologic and metabolic response has also been investi-
`gated. Newborn rats treated with chlorphentermine or
`chlorcyclizine for 1 wk did not develop hypertrophic vac-
`uolated alveolar macrophages; however, adult rats treated
`with the same CADs at the same dose and for the same
`duration did develop hypertrophic vacuolated alveolar
`macrophages containing lysosomal lamellar bodies
`(33,34).
`There is significant evidence of pharmacologic manip-
`ulation of drug-induced phospholipidosis. Chlorphenter-
`mine-induced phospholipidosis of alveolar macrophages
`was reduced in incidence and severity when phenobar-
`bital was concurrently administered (33). Several related
`studies demonstrated that the concurrent administration
`of phenobarbital with chlorphentermine reduced the ac-
`cumulation of phospholipids in affected organs. These
`findings were attributed to the induction of specific drug-
`metabolizing enzymes by phenobarbital (33,36,80).
`It is apparent that many factors affect the ability of
`CADs to induce phospholipidosis. Included are species
`and strain differences, specific tissue affinity, structural
`and biochemical relationship, concurrent drug adminis-
`tration, age of the patient, metabolic rate of the drug and
`its metabolites, and pharmacokinetics of each of these
`components. In risk assessment to humans, these vari-
`ables must be assessed for each specific phospholipidosis-
`inducing drug.
`
`IV. FUNCTIONAL EFFECTS OF PHOSPHOLIPIDOSIS
`
`The dramatic morphologic changes induced in the
`lungs of some animals by CAD administration, and the
`known affinity of pulmonary tissue for CADs, has
`prompted investigations into the functionality of these or-
`gans (14). Camus et al investigated the changes in pul-
`monary respiratory function in rats treated with chlor-
`phentermine. They reported that despite massive induc-
`tion of pulmonary phospholipidosis, there were only mi-
`nor effects on lung function (5,6).
`Amiodarone is an iodinated antiarrhythmic drug that is
`reported to induce generalized phospholipidosis in sev-
`eral animal species as well as humans (21). It has been
`suggested that amiodarone interferes with phospholipase
`Al and A2 activity in the degradation of phospholipids
`(22,24,47). In humans and hamsters and other animals,
`administration of amiodarone is associated with gener-
`alized phospholipidosis, pulmonary fibrosis, and in-
`creased hepatic density (7,8). However, investigators are
`unsure if the phospholipidosis induces these changes in
`vital organs, or if the iodinated molecule depositing in
`these sites is responsible for some of the changes, or per-
`haps there is some other combination of factors inciting
`these changes (67).
`There are some situations in which phospholipidosis
`has been shown to have a definite functional effect. A
`common feature of CAD administration is the presence
`of lysosomal lamellar bodies in lymphocytes of some
`species. Mice treated with chlorphentermine in vivo had
`a significantly depressed ability to generate a delayed hy-
`persensitivity response or to produce antibody-secreting
`cells against de novo antigen (71,72). Mouse splenic lym-
`phocytes exposed to 10-7 M chlorphentermine for 3 days
`in vitro had a significantly depressed blastogenic re-
`sponse to the mitogens phytohemagglutinin, concanaval-
`in A, and lipopolysaccharide (71,72).
`
`V. INTERACTIONS OF CADs WITH BIOLOGIC MEMBRANES
`
`The biologic or pharmacologic activity of xenobiotics
`may occur at many sites, however, one of the more im-
`portant is the interaction with biologic membranes. In this
`context, drugs must penetrate the lipid bilayer and thus
`they affect the physiochemical properties of the lipid bi-
`layer (44).
`The presence of a halogen group on the hydrophobic
`portion of a molecule in some cases enhances the bio-
`logic and pharmacologic effects of the molecule, as in
`the comparison of phentermine and chlorphentermine or
`promazine and chlorpromazine (Fig. 1). The halogen
`group on the hydrophobic moiety increases the lipophil-
`icity and the phospholipidosis-inducing capacity of these
`CADs (75,76).
`The binding of CAD molecules to the hydrophobic and
`hydrophilic moieties of the phospholipids may affect the
`rate of metabolism of these molecules (39). The role that
`the structure of the CAD and its interaction with biologic
`membranes and other active sites on cells is complex and
`merits further investigation (11,39).
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`VI. THE EFFECT OF CADs ON LYSOSOME METABOLISM
`Alterations in lysosome metabolism by CADs and the
`development of lysosomal lamellar bodies are intimately
`related to the development of phospholipidosis. Several
`investigators have shown that xenobiotics are weak bases
`have an affinity for lysosomes (13,83). CADs that are
`basic and have a pKa higher than 7-8 preferentially con-
`centrate in the lysosomes (48). It follows then that CADs
`move toward and localize in lysosomes that contain an-
`ionic lipids (39).
`Some prominent CADs, such as amiodarone, have a
`lesser affinity for lysosomes (20). Amiodarone contains
`only one basic amine in the hydrophilic portion of the
`molecule and has limited reaction with polar phospholip-
`ids and storage in lysosomes yet does induce lysosomal
`lamellar bodies (39).
`The effect phospholipidosis has on lysosomal function
`has been addressed by several investigators. Lullmann-
`Rauch and Watermann investigated lysosomes that had
`been converted to lysosomal lamellar bodies in renal ep-
`ithelial cells and in hepatocytes of rats. These lysosomes
`retained their ability to fuse with autolysosomes and/or
`autophagosomes (53).
`
`VII. INHIBITION OF PHOSPHOLIPASES
`The mechanisms that produce phospholipidosis are dif-
`ficult to define because there are so many xenobiotics that
`when administered at the appropriate dose, duration, and
`multiple other factors already discussed can result in the
`accumulation of phospholipids and development of ly-
`sosomal lamellar bodies. It is simple to speculate on the
`factors that result in excessive phospholipids in the ly-
`sosomes :
`
`1. CADs bind to phospholipids and form complexes in
`lysosomes that become lysosomal lamellar bodies.
`These lysosomal lamellar bodies are variably resistant
`to phospholipase enzyme activity. Concerning recov-
`ery, the complexes are unstable and become more sus-
`ceptible to phospholipase activity after cessation of
`CAD administration (29,31,48,50). Recovery from
`phospholipidosis after drug discontinuance may be a
`couple of weeks to months depending on the CAD
`administered and multiple host factors.
`2. The second theory implies that CADs inhibit phos-
`pholipase activity. This theory has been investigated
`by many researchers (22,24,40,42,78). Critics of this
`theory state that most tests are conducted in vitro and
`it is difficult to detect if the CAD binds to the phos-
`pholipid or if it inhibits the phospholipase in the in-
`cubation medium. A good discussion of these vagaries
`of activity is presented in a paper by Kodavanti and
`Mehendale (39).
`Probably the best support for the theory that CADs in-
`hibit phospholipase activity is a series of in vitro studies
`with amiodarone (24,54).
`The mechanism of phospholipidosis remains unsettled.
`The wide spectrum of xenobiotics that induce phospho-
`lipidosis, the difficulty in isolating specific substrates and
`enzymes, and the variable recovery times after withdraw-
`al remain as obstacles to a comprehensive explanation.
`
`57
`
`In the evaluation of risk assessment, individual drugs
`should be investigated and assessed with more certainty
`than the entire class of CADs that induce phospholipi-
`dosis.
`
`VIII. PHOSPHOLIPID SYNTHESIS-THE EFFECTS OF CADs
`Some researchers have also investigated the plausibil-
`ity that administration of CADs can increase the synthesis
`of phospholipids resulting in phospholipidosis. Some in
`vitro and in vivo studies do support this theory. In cul-
`tures of skin fibroblasts, chloroquine stimulated phospho-
`lipid and cholesterol synthesis (10). Chlorpromazine has
`also been reported to increase cellular synthesis of phos-
`pholipids in vitro (45).
`It is apparent from these observations and those in the
`previous section that CADs do have an influence on
`phospholipid metabolism. The influence may depend on
`binding to phospholipids and inhibiting breakdown, in-
`fluencing enzymes, resulting in reduced catabolism or in-
`fluencing the synthesis of phospholipids. In each case,
`researchers have demonstrated by in vivo and/or in vitro
`techniques support for their theories. However, the vast
`array of CADs, the species, strain, and age variation, and
`a host of other factors suggest that each CAD and host
`have unique interactions and that in risk assessment for
`humans one should focus on the molecule under inves-
`tigation and conduct the studies necessary to provide an-
`swers relevant to human risk.
`
`IX. THE MECHANISM OF CAD-INDUCED
`PHOSPHOLIPIDOSIS
`Induction of phospholipidosis has been attributed to a
`multitude of factors. There are features that are common
`to most of these pathways at the organ, tissue, cell, en-
`zyme system, and molecular level. From these features
`and others, Joshi and Mehendale (30) have proposed the
`following generalized mechanism of phospholipidosis in
`the lung (Fig. 2).
`
`X. PHOSPHOLIPID METABOLISM AND EFFECTS ON
`CELL FUNCTION
`The various cellular lipids and their influence on cell
`metabolism have been investigated for many years. These
`products influence regulation of cell function, cell-to-cell
`signaling, cell growth, receptor sites, and other mem-
`brane-associated events. Most of these activities appear
`to be active at the molecular level and vary with the CAD
`under investigation.
`The effects of CADs on receptor-mediated events have
`been reported to be attributed to influences of CAD-
`membrane interactions (41). The role of phosphatidylino-
`sitol, arachadonic acid, prostaglandins, interleukins,
`platelet-activating factors, and others in cell-to-cell sig-
`naling is becoming a feature that can be investigated and
`identified and utilized in drug development (15,38,81).
`The role of CADs and their effects on cell metabolism
`through alterations in phospholipids remain to be iden-
`tified and understood, but it is certain that they are able
`to influence a wide variety of cell-to-cell interactions
`(31). Protein kinases catalyze phosphorylation reactions
`but are influenced by endogenous regulatory products re-
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`FIG. 2.-Mechanism of phospholipidosis in vivo-reproduced with
`permission of the publisher (32).
`
`sulting from phospholipid metabolism (15,58,82). Chlor-
`promazine has been demonstrated to inhibit phospholi-
`pase activity (42,78). It is also an inhibitor of protein
`kinase C (28,59). The role of chlorpromazine and phos-
`pholipid metabolism in relation to other cell functions
`remains to be identified (42).
`
`XI. INFLUENCE OF CADs ON CELL MEMBRANES
`Cationic amphilic drugs influence bilayer cell mem-
`branes. In this role, they may influence a wide variety of
`cell functions, including: phosphorylation pathways, ion
`transport, and other metabolic pathways. In rat lung,
`amiodarone inhibits Mg2+-ATPase and Na+,K+-ATPase
`in areas where phospholipid is located (64). In this lo-
`cation and probably in others, CADs may affect ion trans-
`port and oxidative phosphorylation. These effects may be
`due to the increasing intracytoplasmic Ca2+ as presented
`by Powis et al (63).
`Chloroquine, another CAD, has shown inhibition of
`calmodulin stimulation of phosphodiesterases and
`Ca2+,Mg2+-ATPase activities in investigations into the
`shape and change of erythrocyte ghosts (57). These ex-
`amples indicate that CADs may have an effect on recep-
`tor-mediated reactions by altering the bilamellar mem-
`brane and phospholipases.
`
`CONCLUSIONS
`The influence of cationic amphophilic drugs have been
`known for 30 yr: the administration of these drugs results
`in an excessive accumulation of intracellular phospholip-
`ids and CADs in the tissue. These xenobiotics share
`structural and physiochemical similarities of a hydropho-
`bic moiety and a hydrophilic moiety. A halogen ion on
`the hydrophobic moiety seems to enhance the membrane
`permeability in some cases. These drugs are recognized
`in a wide spectrum of therapeutic categories including
`
`antivirals, antiarrythmics, antibacterials, antihistamines,
`antimalarials, antipsychotics, antidepressants, anorexics,
`antilipemics, and others.
`In each of these categories, the CAD molecule seems
`to have an affinity for a particular tissue(s). This affinity
`is modulated by species, strain, age, concurrently admin-
`istered drugs, dose, duration, and other factors. The af-
`finity is lysomorphotrophic so that CAD administration
`results in morphologic changes in lysosomes that can eas-
`ily be recognized by ultrastructural techniques. The lung
`and alveolar macrophages are affected by most CADs,
`but occasionally the effect on the lung is minor and ef-
`fects on other tissues predominate. In most cases, the re-
`versal of phospholipidosis is expected shortly after ces-
`sation of drug administration.
`The physiologic effects of phospholipidosis have rarely
`been demonstrated to match the morphologic effects of
`CAD administration. Chlorphentermine, a drug that pro-
`duces dramatic lysosomal lamellar bodies in alveolar
`macrophages and other tissues of rats, when tested, has
`proved to have little effect on respiratory function or me-
`chanics.
`The mechanism of how CADs induce phospholipidosis
`is complex and probably unique to each molecule and the
`species/strain treated. Three concepts are considered par-
`amount : (1) CADs bind with phospholipids and render
`them more resistant to phospholipase activity; (2) CADs
`interact with phospholipases and limit their ability to af-
`fect phospholipid metabolism and (3) CADs influence the
`synthesis of phospholipids. Each of these mechanisms
`and others may be active in the production of phospho-
`lipidosis in a specific species, strain, and tissue in animals
`or humans.
`There has been limited work, but there is evidence that
`phospholipid metabolism can be influenced by CAD ad-
`ministration and may have effects on immune function,
`ion transport, receptor-mediated events, signal transduc-
`tion pathways, and other cell functions.
`The use of CADs in greater than 50 therapeutic agents
`and their diversity of activity in various tissues and or-
`gans in the body provides a ready opportunity to assess
`their risk for human use. It seems appropriate, recogniz-
`ing this diversity of influence on cell function, to evaluate
`each therapeutic agent in its effect in laboratory animals,
`in vitro cell culture, and its effect in humans, as well as
`its therapeutic goals and the benefit produced.
`
`ACKNOWLEDGMENT
`The author gratefully acknowledges the assistance of
`Ms. Diane McGreen for manuscript preparation.
`
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