Vitronectin and fibronectin function as glucan binding proteins augmenting macrophage responses to Pneumocystis carinii

beta-glucans represent major structural components of fungal cell walls. We recently reported that Pneumocystis carinii beta-glucans stimulate alveolar macrophages to release proinflammatory cytokines. Macrophage activation by beta-glucan is augmented by serum, implying the presence of circulating factors that interact with beta-glucans and enhance their ability to stimulate macrophages. Using beta-glucan-enriched cell wall fractions from P. carinii and Saccharomyces cerevisiae, two prominent proteins were precipitated from serum and demonstrated to be vitronectin (VN) and fibronectin (FN) by immune analysis. Preincubation of beta-glucan with VN or FN enhanced macrophage activation in response to this cell wall component. Because VN and FN accumulate in the lungs during P. carinii pneumonia, we further investigated hepatic and pulmonary expression of VN and FN messenger RNA during infection. P. carinii pneumonia in rodents is associated with increased hepatic expression of VN and FN as well as increased local expression of FN in the lung. Because interleukin (IL)-6 represents the major regulator of VN and FN expression during inflammatory conditions, we measured macrophage IL-6 release in response to stimulation with P. carinii beta-glucan. Stimulation of macrophages with P. carinii beta-glucan induced significant release of IL-6. Elevated concentrations of IL-6 were noted in the blood of infected animals compared with uninfected control animals. These studies indicate that VN and FN bind to beta-glucan components of P. carinii and augment macrophage inflammatory responses. P. carinii cell wall beta-glucan stimulates secretion of IL-6 by macrophages, thereby enhancing hepatic synthesis of both VN and FN, and lung synthesis of FN during pneumonia.

Carbohydrate recognition domain of surfactant protein D mediates interactions with Pneumocystis carinii glycoprotein A

Pneumocystis carinii continues to cause severe pneumonia in immunocompromised patients. Surfactant protein D (SP-D), a lung collectin, markedly accumulates during P. carinii pneumonia and binds to glycoprotein A (gpA) on the surface of P. carinii, thereby enhancing interactions with alveolar macrophages. Herein, we report the structural basis of the interaction of SP-D with gpA. We demonstrate that natural SP-D binds to purified gpA in the presence of 2 mM calcium in a saturable, concentration-dependent manner, which is abolished by 10 mM ethylenediaminetetraacetic acid. Increasing concentrations of calcium under otherwise cation-free conditions significantly enhance SP-D binding to gpA, whereas manganese and magnesium cations have minimal effect. Maximal SP-D binding occurs at pH 7.4, with significant inhibition at pH 4. SP-D binding to gpA is also competitively inhibited by maltose>glucose>mannose>N-acetyl-glucosamine. Comparison of the binding of various natural and recombinant forms of SP-D to gpA reveals that the number of carbohydrate recognition domains (CRDs) in a given SP-D form determines the relative extent of binding to gpA. Maximal binding is observed with natural SP-D (dodecamers and higher order SP-D complexes) followed by recombinant dodecamers. In contrast, recombinant full-length trimers exhibit substantially less binding, which is similar to that observed with a recombinant truncated molecule consisting of the CRD and neck regions, and containing trimers of this portion of the molecule. Taken together, these findings strongly indicate that the CRD of SP-D mediates interaction with P. carinii gpA through its attached oligosaccharides and that the extent of SP-D binding to P. carinii is greatest with dodecamers and higher order forms of SP-D.

Isolated Pneumocystis carinii cell wall glucan provokes lower respiratory tract inflammatory responses

Macrophage-induced lung inflammation contributes substantially to respiratory failure during Pneumocystis carinii pneumonia. We isolated a P. carinii cell wall fraction rich in glucan carbohydrate, which potently induces TNF-alpha and macrophage-inflammatory protein-2 generation from alveolar macrophages. Instillation of this purified P. carinii carbohydrate cell wall fraction into healthy rodents is accompanied by substantial increases in whole lung TNF-alpha generation and is associated with neutrophilic infiltration of the lungs. Digestion of the P. carinii cell wall isolate with zymolyase, a preparation containing predominantly beta-1,3 glucanase, substantially reduces the ability of this P. carinii cell wall fraction to activate alveolar macrophages, thus suggesting that beta-glucan components of the P. carinii cell wall largely mediate TNF-alpha release. Furthermore, the soluble carbohydrate beta-glucan receptor antagonists laminariheptaose and laminarin also substantially reduce the ability of the P. carinii cell wall isolate to stimulate macrophage-inflammatory activation. In contrast, soluble alpha-mannan, a preparation that antagonizes macrophage mannose receptors, had minimal effect on TNF-alpha release induced by the P. carinii cell wall fraction. P. carinii beta-glucan-induced TNF-alpha release from alveolar macrophages was also inhibited by both dexamethasone and pentoxifylline, two pharmacological agents with potential activity in controlling P. carinii-induced lung inflammation. These data demonstrate that P. carinii beta-glucan cell wall components can directly stimulate alveolar macrophages to release proinflammatory cytokines mainly through interaction with cognate beta-glucan receptors on the phagocyte.

Steady-state effects of vitronectin and fibronectin on the binding, uptake, and degradation of Pneumocystis carinii in rat alveolar macrophages

Pneumocystis carinii pneumonia remains a serious complication of immunodeficiency. Vitronectin (VN) and fibronectin (FN) accumulate in the lung during P. carinii infection and bind to the organism, thereby enhancing macrophage release of TNF alpha. It is not known whether VN and FN also regulate uptake and degradation of P. carinii by macrophage when present in concentrations similar to those in the lung during pneumonia. To address this, macrophages were cultured with 35S-radiolabeled P. carinii and organism binding, phagocytosis, and degradation determined in media alone (control), or in the presence of VN or FN (100 micrograms/ml each). Soluble VN and FN, in concentrations similar to those in the host, did not significantly affect binding uptake or degradation of P. carinii by alveolar macrophages. Thus, although VN and FN enhance macrophage activation during P. carinii pneumonia, phagocytosis of the organism is not increased by these host glycoproteins under steady-state conditions.

The role of alveolar macrophages in Pneumocystis carinii degradation and clearance from the lung

Although studies indicate that alveolar macrophages participate in host defense against Pneumocystis carinii, their role in organism degradation and clearance from the lung has not yet been established. We, therefore, quantified the uptake and degradation of 35S-labeled P. carinii by cultured macrophages, demonstrating significant degradation of P. carinii over 6 h. We further evaluated the role of macrophages in elimination of P. carinii from the living host. Rats received either intratracheal PBS, liposomal PBS (L-PBS), or liposomal dichloromethylene diphosphonate (L-Cl2MDP), a preparation which leads to selective depletion of macrophages. Over 72 h, L-Cl2MDP-treated animals had loss of > 85% of their alveolar macrophages. In contrast, L-PBS-treated rats had cellular differentials identical to rats receiving PBS. Macrophage-depleted rats and controls were next inoculated with P. carinii and organism clearance was determined after 24 h. P. carinii elimination was evaluated with both cyst counts and an ELISA directed against glycoprotein A (gpA), the major antigen of P. carinii. Both assays indicated that macrophage-depleted rats had substantial inpairment of P. carinii clearance compared to L-PBS- or PBS-treated rats. These data provide the first direct evidence that macrophages mediate elimination of P. carinii from the living host.

Fungal beta-glucan interacts with vitronectin and stimulates tumor necrosis factor alpha release from macrophages

beta-Glucans are polymers of D-glucose which represent major structural components of fungal cell walls. It was shown previously that fungi interact with macrophages through beta-glucan receptors, thereby inducing release of tumor necrosis factor alpha (TNF-alpha). Additional studies demonstrated that vitronectin, a host adhesive glycoprotein, binds to fungi and enhances macrophage recognition of these organisms. Since vitronectin contains a carbohydrate-binding region, we postulated that vitronectin binds fungal beta-glucans and subsequently augments macrophage TNF-alpha release in response to this fungal component. To study this, we first determined the release of TNF-alpha from alveolar macrophages stimulated with fungal beta-glucan. Maximal TNF-alpha release occurred with moderate concentrations of beta-glucan (100 to 200 micrograms/ml), whereas higher concentrations of beta-glucan (> or = 500 micrograms/ml) caused apparent suppression of the TNF-alpha activity released. This suppression of TNF-alpha activity by high concentrations of beta-glucan was mediated by the particulate beta-glucan binding soluble TNF-alpha, through the lectin-binding domain of the cytokine, rendering the TNF-alpha less available for measurement. Next, we assessed the interaction of vitronectin with beta-glucan. Binding of 125I-vitronectin to particulate fungal beta-glucan was dose dependent and specifically inhibitable by unlabeled vitronectin. Furthermore, treatment of beta-glucan with vitronectin substantially augmented macrophage TNF-alpha release in response to this fungal component. These findings demonstrate that fungal beta-glucan can directly modulate TNF-alpha release from macrophages. Further, these studies indicate that the host adhesive glycoprotein vitronectin specifically binds beta-glucan and augments macrophage cytokine release in response to this fungal element.

Surfactant protein D interacts with Pneumocystis carinii and mediates organism adherence to alveolar macrophages

Pneumocystis carinii interacts with glycoproteins present in the lower respiratory tract through its mannose-rich surface antigen complex termed gpA. Surfactant protein D (SP-D) is a recently described component of the airspace lining material that possesses a calcium-dependent lectin domain capable of interacting with glycoconjugates present on microorganisms and leukocytes. Accordingly, we evaluated the extent and localization of SP-D in the lower respiratory tract during Pneumocystis pneumonia in an immunosuppressed rat model and examined its role in modulating interaction of P. carinii with macrophages. We report that SP-D is a major component of the alveolar exudates that typify P. carinii pneumonia and is present bound to the surface of P. carinii organisms in vivo. We further demonstrate that SP-D binds to P. carinii through saccharide-mediated interactions with gpA present on the surface of the organism. Lastly, we show that SP-D augments binding of P. carinii to alveolar macrophages, but does not significantly enhance macrophage phagocytosis of the organism. The interaction of SP-D with gpA represents an additional important component of the host-parasite relationship during P. carinii pneumonia.

Pneumocystis carinii glycoprotein A binds macrophage mannose receptors

Pneumocystis carinii causes life-threatening pneumonia in patients with impaired immunity. Recent studies suggest that alveolar macrophages interact with P. carinii through macrophage mannose receptors. However, the ligand(s) on P. carinii that is recognized by these receptors has not been fully defined. P. carinii contains a major mannose-rich surface antigen complex termed glycoprotein A (gpA). It was therefore hypothesized that gpA binds directly to macrophage mannose receptors and mediates organism attachment to these phagocytes. To assess this, gpA was purified from P. carinii by continuous-elution gel electrophoresis. 125I-labeled gpA bound to alveolar macrophages in a saturable fashion. In addition, gpA binding was substantially inhibited by both alpha-mannan and EDTA, further suggesting that gpA interacts with macrophage mannose receptors. Macrophage membrane proteins capable of binding to gpA were isolated with a gpA-Sepharose column. A 165-kDa membrane-associated protein was specifically eluted from the gpA-Sepharose column with EDTA (20 mM). This protein was identified as the macrophage mannose receptor by immunoprecipitation with a polyclonal anti-mannose receptor antiserum. To further investigate the role of gpA in P. carinii-macrophage interactions, 51Cr-labeled P. carinii cells were incubated with macrophages in the presence of increasing concentrations of soluble gpA, and organism attachment was quantified. Soluble gpA (2.5 mg/dl) competitively inhibited P. carinii attachment to alveolar macrophages by 51.3% +/- 3.7% (P = 0.01). Our findings demonstrate that gpA present on P. carinii interacts directly with mannose receptors, thereby mediating organism attachment to alveolar macrophages.

Vitronectin interacts with Candida albicans and augments organism attachment to the NR8383 macrophage cell line

Candida albicans is an increasingly important cause of mucocutaneous and bloodstream infections. The potential role of circulating adhesive glycoproteins such as vitronectin (Vn) in host defense against C. albicans is currently unknown. Accordingly, we investigated the binding of plasma-derived Vn with C. albicans strain 36082. Vn specifically bound to C. albicans in a concentration-dependent fashion. Higher affinity binding sites numbered 9.8 x 10(4) sites per organism, with a dissociation constant, Kd of 3.5 x 10(-7) M. Vn binding with C. albicans was significantly inhibited by heparin, suggesting interaction of the organism with Vn's glycosaminoglycan-binding region. To further determine which molecule(s) on the fungus interacted with Vn, C. albicans components were extracted, separated by SDS and blotted with radiolabeled Vn. These studies revealed that Vn binds to a 30 kDa molecule on C. albicans. Finally, we investigated the role of Vn in promoting interaction of C. albicans with phagocytic cells. Incubation of C. albicans in the presence of Vn significantly increased binding of the organism to cultured NR8383 macrophages compared to incubations performed in the absence of Vn. These data demonstrate that C. albicans interacts with the heparin-binding domain Vn and further suggest that Vn augments organism uptake by phagocytic cells.

Vitronectin, fibronectin, and gp120 antibody enhance macrophage release of TNF-alpha in response to Pneumocystis carinii

Alveolar macrophages (AMS) initiate inflammation during Pneumocystis carinii pneumonia by releasing cytokines including TNF-alpha. Recent studies suggest that macrophage responses to P. carinii are enhanced by serum opsonization, but the mechanisms of enhancement are not well defined. To determine whether macrophage release of TNF-alpha in response to P. carinii was augmented by immune opsonization, alveolar macrophages obtained from rabbits were cultured with P. carinii that had been opsonized with either nonimmune rabbit serum, immune serum generated against P. carinii, or an affinity-purified polyclonal Ab recognizing the major P. carinii surface Ag gp120. Each experiment also included organisms maintained in media alone (nonopsonized P. carinii). Opsonization of P. carinii with immune serum or gp120 Ab significantly enhanced macrophage TNF-alpha release. Interestingly, however, opsonization with nonimmune serum also increased TNF-alpha response to the organism. Because P. carinii is known to interact with the adhesive glycoproteins, vitronectin (VN) and fibronectin (FN), we hypothesized that they might also augment TNF-alpha release. Opsonization of P. carinii with VN or FN resulted in significant potentiation of macrophage TNF-alpha liberation. We further determined that VN and FN were present in increased quantities in the lower respiratory tract of patients with P. carinii pneumonia compared with normal volunteers. Additionally, VN and FN were demonstrated on the surface of freshly isolated P. carinii organisms by immunoblot analysis. Our study suggests that immune and nonimmune opsonins contribute to host defenses during P. carinii pneumonia by enhancing regional TNF-alpha release in response to the organism.

Vitronectin, fibronectin, and gp120 antibody enhance macrophage release of TNF-alpha in response to Pneumocystis carinii

Alveolar macrophages (AMS) initiate inflammation during Pneumocystis carinii pneumonia by releasing cytokines including TNF-alpha. Recent studies suggest that macrophage responses to P. carinii are enhanced by serum opsonization, but the mechanisms of enhancement are not well defined. To determine whether macrophage release of TNF-alpha in response to P. carinii was augmented by immune opsonization, alveolar macrophages obtained from rabbits were cultured with P. carinii that had been opsonized with either nonimmune rabbit serum, immune serum generated against P. carinii, or an affinity-purified polyclonal Ab recognizing the major P. carinii surface Ag gp120. Each experiment also included organisms maintained in media alone (nonopsonized P. carinii). Opsonization of P. carinii with immune serum or gp120 Ab significantly enhanced macrophage TNF-alpha release. Interestingly, however, opsonization with nonimmune serum also increased TNF-alpha response to the organism. Because P. carinii is known to interact with the adhesive glycoproteins, vitronectin (VN) and fibronectin (FN), we hypothesized that they might also augment TNF-alpha release. Opsonization of P. carinii with VN or FN resulted in significant potentiation of macrophage TNF-alpha liberation. We further determined that VN and FN were present in increased quantities in the lower respiratory tract of patients with P. carinii pneumonia compared with normal volunteers. Additionally, VN and FN were demonstrated on the surface of freshly isolated P. carinii organisms by immunoblot analysis. Our study suggests that immune and nonimmune opsonins contribute to host defenses during P. carinii pneumonia by enhancing regional TNF-alpha release in response to the organism.

Vitronectin binds to Pneumocystis carinii and mediates organism attachment to cultured lung epithelial cells

Pneumocystis carinii attaches to alveolar epithelial cells during the development of pneumonia. Adhesive proteins found within the alveolar space have been proposed to mediate P. carinii adherence to lung cells. Vitronectin (Vn), a 75-kDa glycoprotein present in the lower respiratory tract, has substantial cell-adhesive properties and might participate in the host-parasite interaction during P. carinii pneumonia. To address whether Vn binds to P. carinii, we studied the interaction of radiolabeled Vn with purified P. carinii organisms. Vn bound to P. carinii, occupying an estimated 5.47 x 10(5) binding sites per organism, with an affinity constant, Kd, of 4.24 x 10(-7) M. Interestingly, the interaction of Vn with P. carinii was not mediated through the Arg-Gly-Asp cell-adhesive domain of Vn. Addition of Arg-Gly-Asp-Ser (RGDS) peptides did not inhibit binding. In contrast, Vn binding to P. carinii was substantially inhibited by the addition of heparin or by digesting the organisms with heparitinase, suggesting that P. carinii may interact with the glycosaminoglycan-binding domain of Vn. To determine whether Vn might enhance P. carinii attachment to lung epithelial cells, we studied the binding of 51Cr-labeled P. carinii to cultured A549 lung cells. Addition of Vn resulted in significantly increased binding of P. carinii to A549 cells, whereas a neutralizing anti-Vn serum substantially reduced the binding of P. carinii to A549 cells. These data suggest that Vn binds to P. carinii and that Vn might provide an additional means by which P. carinii attaches to respiratory epithelial cells.

Pneumocystis carinii induces the release of arachidonic acid and its metabolites from alveolar macrophages

Pneumocystis carinii is an opportunistic organism that causes severe lung injury in immunocompromised hosts. Macrophage responses to P. carinii are poorly defined. Arachidonic acid (AA) and its metabolites are potent mediators of inflammation and have been implicated in host response to microorganisms. We therefore examined the production of eicosanoids from rat and rabbit alveolar macrophages stimulated with purified P. carinii. [14C]AA-labeled rabbit macrophages released 8.50 +/- 1.33% of the incorporated [14C]AA after 90 min in response to P. carinii (P = 0.0001 compared with unstimulated controls). In contrast, a similar number of rat alveolar macrophages exhibited a smaller but significant response to P. carinii, releasing 3.84 +/- 1.54% of their [14C]AA after 90 min (P = 0.001 compared with control). We further determined that P. carinii stimulated substantial production of prostaglandin E2 and concurrently a small amount of leukotriene B4 release from alveolar macrophages. To further investigate whether serum opsonization of P. carinii enhances these alterations in AA metabolism, we assessed the effect of P. carinii immune serum on P. carinii-induced AA release. P. carinii opsonized with this antiserum caused significantly greater AA release from rat alveolar macrophages than either unopsonized P. carinii or organisms opsonized with nonimmune serum. Previous studies suggest that P. carinii interacts with macrophage beta-glucan and mannose receptors. However, incubation of macrophages with P. carinii in the presence of either soluble beta-glucan or alpha-mannan failed to alter the release of AA from macrophages in response to P. carinii. Macrophage release of eicosanoids represents a potentially important host inflammatory response to P. carinii infection.

Pneumocystis carinii stimulates tumor necrosis factor-alpha release from alveolar macrophages through a beta-glucan-mediated mechanism

Recent studies suggest that TNF-alpha plays a central role in host defenses during Pneumocystis carinii pneumonia. To determine whether P. carinii directly stimulates TNF-alpha secretion, rat alveolar macrophages were cultured in the presence of purified P. carinii. Whereas unstimulated alveolar macrophages released only 13.0 +/- 2.7 pg/ml of TNF-alpha into the medium, macrophages stimulated with P. carinii released 108.2 +/- 20.4 pg/ml of TNF-alpha after overnight culture (p = 0.0001). Maximal TNF-alpha release was observed after 8 h of incubation and required a P. carinii: macrophage ratio of at least 2.5:1. Autoclaved P. carinii were also able to trigger TNF-alpha release from macrophages albeit at a reduced level. In view of recent evidence that P. carinii is phylogenetically related to the fungi and contains a beta-glucan-rich cell wall, we hypothesized that TNF-alpha release might in part be mediated by this cell wall component. Preincubation of macrophages with particulate beta-glucan derived from Baker's yeast resulted in complete inhibition of TNF-alpha release in response to P. carinii. In addition, digestion of P. carinii with zymolyase, a preparation containing predominantly beta-glucanase activity, substantially reduced the ability of P. carinii to cause TNF-alpha release from macrophages. In a similar manner, macrophages incubated with P. carinii in the presence of laminariheptaose, an oligosaccharide that binds to macrophage beta-glucan receptors, also displayed decreased TNF-alpha release. Interestingly, TNF-alpha release may not be completely linked to the adherence of the organism to macrophages. Particulate beta-glucan significantly reduced P. carinii adherence to macrophages and also impaired TNF-alpha release. However, yeast mannan also significantly reduced P. carinii adherence to macrophages and also impaired TNF-alpha release. However, yeast mannan also significantly reduced P. carinii adherence but had no effect on TNF-alpha release. These data demonstrate that P. carinii can directly stimulate the secretion of TNF-alpha from alveolar macrophages and that this effect is largely mediated by beta-glucan components of the P. carinii cell wall.

Pneumocystis carinii stimulates tumor necrosis factor-alpha release from alveolar macrophages through a beta-glucan-mediated mechanism

Recent studies suggest that TNF-alpha plays a central role in host defenses during Pneumocystis carinii pneumonia. To determine whether P. carinii directly stimulates TNF-alpha secretion, rat alveolar macrophages were cultured in the presence of purified P. carinii. Whereas unstimulated alveolar macrophages released only 13.0 +/- 2.7 pg/ml of TNF-alpha into the medium, macrophages stimulated with P. carinii released 108.2 +/- 20.4 pg/ml of TNF-alpha after overnight culture (p = 0.0001). Maximal TNF-alpha release was observed after 8 h of incubation and required a P. carinii: macrophage ratio of at least 2.5:1. Autoclaved P. carinii were also able to trigger TNF-alpha release from macrophages albeit at a reduced level. In view of recent evidence that P. carinii is phylogenetically related to the fungi and contains a beta-glucan-rich cell wall, we hypothesized that TNF-alpha release might in part be mediated by this cell wall component. Preincubation of macrophages with particulate beta-glucan derived from Baker's yeast resulted in complete inhibition of TNF-alpha release in response to P. carinii. In addition, digestion of P. carinii with zymolyase, a preparation containing predominantly beta-glucanase activity, substantially reduced the ability of P. carinii to cause TNF-alpha release from macrophages. In a similar manner, macrophages incubated with P. carinii in the presence of laminariheptaose, an oligosaccharide that binds to macrophage beta-glucan receptors, also displayed decreased TNF-alpha release. Interestingly, TNF-alpha release may not be completely linked to the adherence of the organism to macrophages. Particulate beta-glucan significantly reduced P. carinii adherence to macrophages and also impaired TNF-alpha release. However, yeast mannan also significantly reduced P. carinii adherence to macrophages and also impaired TNF-alpha release. However, yeast mannan also significantly reduced P. carinii adherence but had no effect on TNF-alpha release. These data demonstrate that P. carinii can directly stimulate the secretion of TNF-alpha from alveolar macrophages and that this effect is largely mediated by beta-glucan components of the P. carinii cell wall.

Amiodarone-mediated increase in intracellular free Ca2+ associated with cellular injury to human pulmonary artery endothelial cells

The cardiac antidysrrhythmic drug amiodarone can give rise to potentially fatal pulmonary toxicity in large numbers of patients. The effect of amiodarone on Ca2+ homeostasis and cell injury has been studied using human pulmonary artery endothelial (HPAE) cells in vitro. Amiodarone produced a concentration-dependent increase in intracellular free Ca2+ concentration ( [Ca2+]i) to micromolar levels that are similar to those seen with physiological stimuli that increase [Ca2+]i. Unlike physiological stimuli, the rise in [Ca2+]i produced by amiodarone developed slowly and was maintained over at least 30 min. Omitting Ca2+ from the external medium reversibly prevented the amiodarone-induced rise in [Ca2+]i. Amiodarone treatment increased the apparent first order rate constants for 45Ca2+ influx and efflux in intact HPAE cells. 45Ca2+ accumulation into the endoplasmic reticulum of saponin-permeabilized HPAE cells was decreased by amiodarone treatment. The release of 45Ca2+ from the endoplasmic reticulum stores by the putative intracellular second messengers inositol-1,4,5-trisphosphate, arachidonic acid, and Ca2+ was blocked by amiodarone treatment. The changes in Ca2+ homeostasis coincide with an increase in [3H]deoxyglucose release as a measure of early cell injury by amiodarone. It is concluded that amiodarone can produce an increase in [Ca2+]i by an action on the plasma membrane that allows the influx of external Ca2+. This increase in [Ca2+]i, together with other changes in Ca2+ homeostasis, may be responsible for the early cell injury associated with amiodarone toxicity.

Amiodarone pulmonary toxicity: biochemical evidence for a cellular phospholipidosis in the bronchoalveolar lavage of human subjects

Amiodarone pulmonary toxicity represents an example of a life-threatening adverse drug reaction. Our study examined 10 subjects with amiodarone pulmonary toxicity by bronchoalveolar lavage (BAL) and determined that cells obtained by BAL demonstrated marked increases in various phospholipids compared to control subjects (n = 7). Bis monoacylglycerol phosphate and phosphatidylglycerol were significantly increased in both relative and absolute amounts (P less than .01). Several other phospholipids also were significantly increased in absolute amounts within the cell fraction. In contrast, the cell-free BAL fluid revealed only minor differences in phospholipid content. There was a strong direct correlation between concentration of amiodarone and its primary metabolite, desethylamiodarone in BAL cells (r = 0.98), and also a direct correlation between either the concentration of amiodarone or desethylamiodarone and the accumulation of phospholipids in the cells (r = 0.97, both determinations). This study indicates that findings from BAL in human subjects may provide specific and quantifiable evidence of pulmonary phospholipidosis, and suggests the concentration of the drug or its primary metabolite in BAL cells is a major determinant for the degree of phospholipid accumulation in the lung.