Modulation of retinoid signalling through NGF-induced nuclear export of NGFI-B.

The retinoid-X receptor (RXR) regulates multiple hormonal pathways through heterodimerization with nuclear receptors such as the all-trans retinoic acid receptor (RAR). The orphan nuclear receptor NGFI-B (also called Nur77) can heterodimerize with RXR. Here we show that nerve growth factor (NGF) induces the phosphorylation of Ser 105 of NGFI-B in PC12 phaeochromocytoma cells, resulting in translocation of the NGFI-B-RXR heterodimer complex out of the nucleus using nuclear export signals within NGFI-B. As a consequence of the redistribution of RXR, the transcriptional activity of RXR-RAR is reduced. NGFI-B-mediated nuclear export of receptors may serve as a mechanism for crosstalk between NGF and retinoid pathways.

Dendritic cells with antigen-presenting capability reside in airway epithelium, lung parenchyma, and visceral pleura.

In this study, we identified a population of dendritic cells (DC) that exists throughout human and mouse pulmonary tissues, including the trachea, bronchi, alveoli, and visceral pleura. In human tissue, these DC were shown to be positive for HLA-DR and T200 antigens. In the mouse, the DC expressed not only Ia and the T200 antigen, but also Fc-IgG and C3bi receptors. Unlike alveolar macrophages, the DC were negative for nonspecific esterase staining and shared ultrastructural similarities with the DC described by Steinman (1), and with Langerhans' cells, even though they did not contain Birbeck granules. We were able to demonstrate that mouse pulmonary DC function in antigen presentation, as observed with the other DC. Thus, the respiratory tract contains DC that are capable of functioning in antigen presentation and that may be important in pulmonary immune responses.

Expression of the neutrophil elastase gene during human bone marrow cell differentiation.

Neutrophil elastase, a potent serine protease carried and released by activated neutrophils, is not synthesized by neutrophils, but by their bone marrow precursor cells. Using in situ hybridization with 35S-labeled antisense and sense neutrophil elastase cRNA probes, the present study demonstrates that expression of the neutrophil elastase gene is tightly controlled in bone marrow precursors and occurs during a very limited stage of differentiation of the neutrophil myeloid series, almost entirely at the promyelocyte stage. Neutrophil elastase mRNA transcript levels are detectable to a limited extent in blasts, increase markedly in the promyelocyte stage, and then disappear as promyelocytes further differentiate. Control probes specific for myeloperoxidase, lactoferrin, and beta-globin mRNA transcripts, respectively, demonstrated contrasting gene expression. Myeloperoxidase mRNA transcripts were also found almost exclusively at the promyelocyte stage, but myeloperoxidase mRNA levels disappeared earlier than do neutrophil elastase mRNA levels, suggesting that expression of these genes may be differently controlled. In comparison, lactoferrin mRNA transcripts were detected late in the neutrophil lineage, while beta-globin mRNA was detected only in cells of the erythroid lineage. Together these observations suggest that the expression of the neutrophil elastase gene is likely under very tight control, and is likely different than that for other constituents of the neutrophil granules.

Acidic fibroblast growth factor in the developing rat embryo.

Compared to basic fibroblast growth factor (bFGF), a widely distributed, broad spectrum mitogen and mesoderm inducer, acidic fibroblast growth factor (aFGF) is reported to have an essentially neural distribution and to be undetectable in the early embryo. In the present investigation, we used immunoblotting and immunochemistry to assess the cellular and tissue distributions of aFGF and bFGF in 11-20-d rat embryos. Immunoblotting of crude and heparin-bound embryo extracts revealed faint bands at the expected 17-18-kD and predominant bands at an apparent molecular mass of 26 to 28-kD (despite reducing conditions) using multiple specific antibodies for aFGF and bFGF. Pretreatment with 8 M urea yielded 18-20-kD aFGF and bFGF and some 24-26-kD bFGF. Immunoreactivity for both aFGF and bFGF was positive and similar in the cytoplasm, nuclei, and extracellular matrix of cells of neuroectodermal and mesodermal origin, while it was negative in endoderm-derived cells. The distribution of immunoreactive aFGF and bFGF also showed changes during development that were associated with the process of cellular and tissue differentiation. For example, intensity and extent of immunoreactivity for both peptides progressively increased in the middle layer of the spinal cord with increasing differentiation of the neural cells. The immunostaining patterns were very similar for aFGF and bFGF for each organ and at each stage. In conclusion, high molecular mass forms of immunoreactive aFGF and bFGF are present in the rat embryo. Acidic FGF and bFGF are both widely distributed in tissues of neuroectodermal and mesodermal origin, and their distribution was very similar.

Requirement for generation of H2O2 for platelet-derived growth factor signal transduction.

Stimulation of rat vascular smooth muscle cells (VSMCs) by platelet-derived growth factor (PDGF) transiently increased the intracellular concentration of hydrogen peroxide (H2O2). This increase could be blunted by increasing the intracellular concentration of the scavenging enzyme catalase or by the chemical antioxidant N-acetylcysteine. The response of VSMCs to PDGF, which includes tyrosine phosphorylation, mitogen-activated protein kinase stimulation, DNA synthesis, and chemotaxis, was inhibited when the growth factor-stimulated rise in H2O2 concentration was blocked. These results suggest that H2O2 may act as a signal-transducing molecule, and they suggest a potential mechanism for the cardioprotective effects of antioxidants.

Thrombosis in association with atherosclerosis induced by dietary perturbations in dogs.

The distribution, severity, and complications of diet-induced atherosclerosis in dogs can be altered by changing the source of fat in the diet. Thrombosis and thromboembolic disease associated with atherosclerosis occurred with diets containing beef tallow and lard of coconut oil but were absent in dogs fed cottonseed oil as a source of fat. Experiemtnal animals with and without thrombosis are of value as models in elucidating the role of platelets and thrombostatic mechanisms in atherosclerosis.

Inhibition of intracellular degradation increases secretion of a mutant form of alpha1-antitrypsin associated with profound deficiency.

The mutant Z form of alpha1-antitrypsin (alpha1AT) is responsible for > 95% of all individuals with alpha1AT deficiency, an important inherited cause of emphysema and liver disease. Since secreted Z alpha1AT is a functional antiprotease, we hypothesized that interrupting catabolism of retained Z alpha1AT might increase its transport out of cells, causing an increase in extracellular protease protection. Both the protein translation inhibitor cycloheximide and the specific inhibitor of proteasome function, lactacystin, prevented intracellular degradation of Z alpha1AT. Moreover, this inhibition of degradation was associated with partial restoration of Z alpha1AT vesicular transport. This effect was observed in a model system of transfected CHO cells as well as in human alveolar macrophages synthesizing Z alpha1AT. This study supports the hypothesis that altering the intracellular fate of a mutant protein may be an option in the treatment of diseases associated with misfolded but potentially functional proteins.

Pertussis toxin-sensitive G proteins as mediators of the signal transduction pathways activated by cytomegalovirus infection of smooth muscle cells.

We demonstrated recently that the arachidonic acid (AA) cascade is involved in cytomegalovirus (CMV)-induced generation of reactive oxygen species (ROS) and the activation of nuclear factor (NF)-kappaB in human smooth muscle cells (SMCs). Since AA release from neutrophils is mediated by pertussis toxin (PTx)-sensitive guanine nucleotide-binding (G) proteins, we hypothesized by analogy that CMV stimulates ROS generation in SMCs and ultimately activates NF-kappaB via a PTx-sensitive G protein-coupled pathway. Our first test of this hypothesis demonstrated that PTx blocked AA release induced by CMV infection of SMCs, as well as blocked the terminal products of this reaction, ROS generation and NF-kappaB activation. More proximal components of the pathway were then examined. CMV infection increased phosphorylation and activity of cytosolic phospholipase A2 (cPLA2), an enzyme causing AA release; these effects were inhibited by PTx. CMV infection activated mitogen-activated protein (MAP) kinase, a key enzyme for cPLA2 phosphorylation, an effect also inhibited by PTx. Finally, inhibition of MAP kinase kinase (MAPKK), which phosphorylates and thereby activates MAP kinase, inhibited CMV-induced ROS generation. These data demonstrate that a PTx-sensitive G protein-dependent signaling pathway mediates cellular effects of CMV infection of SMCs. The downstream events include phosphorylation and activation of MAP kinase by MAPKK and subsequent phosphorylation and activation of cPLA2 (with its translocation to cell membranes), followed by stimulation of the AA cascade, which generates intracellular ROS and thereby activates NF-kappaB.

Alveolar macrophage replication. One mechanism for the expansion of the mononuclear phagocyte population in the chronically inflamed lung.

Within any chronically inflamed tissue, there is an increased number of macrophages, pluripotential phagocytic cells that, while critical to host defenses, are also able to profoundly damage parenchymal structure and function. Because of their central role in the inflammatory response, considerable attention has been focused on the mechanisms resulting in an expansion of the macrophage population within an inflamed tissue. Although recruitment of precursor monocytes from the circulation into inflamed tissues clearly plays an important role in macrophage accumulation, it is also possible that replication of tissue macrophages contributes to the expansion of macrophage numbers in inflammation. Because of the accessibility of tissue macrophages with the technique of bronchoalveolar lavage, the lung provides an ideal opportunity to test this hypothesis in humans. To accomplish this, bronchoalveolar lavage was performed to obtain alveolar macrophages from normals (n = 5) and individuals with chronic lung inflammation (normal smokers [n = 5], idiopathic pulmonary fibrosis [n = 13], sarcoidosis [n = 18], and other chronic interstitial lung disorders [n = 11]). Alveolar macrophage replication was quantified by three independent methods: (a) DNA synthesis, assessed by autoradiographic analysis of macrophages cultured for 16 h in the presence of [3H]thymidine; (b) DNA content, assessed by flow cytometric analysis of macrophages fixed immediately after recovery from the lower respiratory tract; and (c) cell division, assessed by cluster formation in semisolid medium. While the proportion of replicating macrophages in normals was very low, there was a 2- to 15-fold increase in this proportion in patients with chronic lung inflammation. In addition, morphologic evaluation demonstrated that individuals with chronic lung inflammation had alveolar macrophages undergoing mitosis. These results suggest that local tissue macrophage replication may play a role in the expansion of the macrophage population in chronic inflammation.

Acute tropical pulmonary eosinophilia. Characterization of the lower respiratory tract inflammation and its response to therapy.

Although acute tropical pulmonary eosinophilia (TPE) is well recognized as a manifestation of filarial infection, the processes that mediate the abnormalities of the lung in TPE are unknown. To evaluate the hypothesis that the derangements of the lower respiratory tract in this disorder are mediated by inflammatory cells in the local milieu, we utilized bronchoalveolar lavage to evaluate affected individuals before and after therapy. Inflammatory cells recovered from the lower respiratory tract of individuals with acute, untreated TPE (n = 8) revealed a striking eosinophilic alveolitis, with marked elevations in both the proportion of eosinophils (TPE 54 +/- 5%; normal 2 +/- 5%; P less than 0.001) and the concentration of eosinophils in the recovered epithelial lining fluid (ELF) (TPE 63 +/- 20 X 10(3)/microliter; normal 0.3 +/- 0.1 X 10(3)/microliter; P less than 0.01). Importantly, when individuals (n = 5) with acute TPE were treated with diethylcarbamazine (DEC), there was a marked decrease of the lung eosinophils and concomitant increase in lung function. These observations are consistent with the concept that at least some of the abnormalities found in the lung in acute TPE are mediated by an eosinophil-dominated inflammatory process in the lower respiratory tract.

Gene dosage affects the cardiac and brain phenotype in nonmuscle myosin II-B-depleted mice.

Complete ablation of nonmuscle myosin heavy chain II-B (NMHC-B) in mice resulted in cardiac and brain defects that were lethal during embryonic development or on the day of birth. In this paper, we report on the generation of mice with decreased amounts of NMHC-B. First, we generated B(DeltaI)/B(DeltaI) mice by replacing a neural-specific alternative exon with the PGK-Neo cassette. This resulted in decreased amounts of NMHC-B in all tissues, including a decrease of 88% in the heart and 65% in the brain compared with B(+)/B(+) tissues. B(DeltaI)/B(DeltaI) mice developed cardiac myocyte hypertrophy between 7 months and 11 months of age, at which time they reexpressed the cardiac beta-MHC. Serial sections of B(DeltaI)/B(DeltaI) brains showed abnormalities in neural cell migration and adhesion in the ventricular wall. Crossing B(DeltaI)/B(DeltaI) with B(+)/B(-) mice generated B(DeltaI)/B(-) mice, which showed a further decrease of approximately 55% in NMHC-B in the heart and brain compared with B(DeltaI)/B(DeltaI) mice. Five of 8 B(DeltaI)/B(-) mice were born with a membranous ventricular septal defect. Moreover, 5 of 5 B(DeltaI)/B(-) mice developed myocyte hypertrophy by 1 month; B(DeltaI)/B(-) mice also reexpressed the cardiac beta-MHC. More than 60% of B(DeltaI)/B(-) mice developed overt hydrocephalus and showed more severe defects in neural cell migration and adhesion than did B(DeltaI)/B(DeltaI) mice. These data on B(DeltaI)/B(DeltaI) and B(DeltaI)/B(-) mice demonstrate a gene dosage effect of the amount of NMHC-B on the severity and time of onset of the defects in the heart and brain.

Protection from reoxygenation injury by inhibition of rac1.

We demonstrate that adenoviral-mediated gene transfer of a dominant negative rac1 gene product (N17rac1) inhibits the intracellular burst of reactive oxygen species (ROS) that occurs after reoxygenation of vascular smooth muscle cells. In contrast, expression of a dominant negative ras gene (N17ras) had no effect. Challenge of control cells and cells expressing N17rac1 with a direct oxidant stress produced an equivalent increase in intracellular ROS levels and subsequent cell death. This suggests that N17rac1 expression appears to block production of harmful oxygen radicals and does not act directly or indirectly to scavenge ROS generated during reoxygenation. Expression of N17rac1 results in protection from hypoxia/reoxygenation-induced cell death in a variety of cell types including vascular smooth muscle cells, fibroblasts, endothelial cells, and ventricular myocytes. These results suggest that reoxygenation injury requires the activation of rac proteins, and that inhibition of rac-dependent pathways may be a useful strategy for the prevention of reperfusion injury in ischemic tissues.

Identification of lysosomal and Golgi localization signals in GAP and ARF domains of ARF domain protein 1.

ADP ribosylation factors (ARFs) are approximately 20-kDa guanine nucleotide-binding proteins that activate cholera toxin and phospholipase D and are critical components of vesicular trafficking pathways. ARF domain protein 1 (ARD1), a member of the ARF superfamily, contains a 46-kDa amino-terminal extension, which acts as a GTPase-activating protein (GAP) with activity towards its ARF domain. When overexpressed, ARD1 was associated with lysosomes and the Golgi apparatus. In agreement with this finding, lysosomal and Golgi membranes isolated from human liver by immunoaffinity contained native ARD1. ARD1, expressed as a green fluorescent fusion protein, was initially associated with the Golgi network and subsequently appeared on lysosomes, suggesting that ARD1 might undergo vectorial transport between the two organelles. Here we show by microscopic colocalization that GAP and ARF domains determine lysosomal and Golgi localization, respectively, consistent with the presence of more than one signal motif. Using truncated ARD1 molecules, expressed as green fluorescent fusion proteins, it was found that the signal for lysosomal localization was present in residues 301 to 402 of the GAP domain. Site-specific mutagenesis demonstrated that the sequence (369)KXXXQ(373) in the GAP domain was responsible for lysosomal localization. Association of ARD1 with the Golgi apparatus required tyrosine-based motifs. A green fluorescent fusion protein containing the QKQQQQF motif was partially associated with lysosomes, suggesting that this motif contains the information sufficient for lysosomal targeting. These results suggest that ARD1 is a multidomain protein with ARF and GAP regions, which contain Golgi and lysosomal localization signals, respectively, that could function in vesicular trafficking.

Role for mitochondrial oxidants as regulators of cellular metabolism.

Leakage of mitochondrial oxidants contributes to a variety of harmful conditions ranging from neurodegenerative diseases to cellular senescence. We describe here, however, a physiological and heretofore unrecognized role for mitochondrial oxidant release. Mitochondrial metabolism of pyruvate is demonstrated to activate the c-Jun N-terminal kinase (JNK). This metabolite-induced rise in cytosolic JNK1 activity is shown to be triggered by increased release of mitochondrial H(2)O(2). We further demonstrate that in turn, the redox-dependent activation of JNK1 feeds back and inhibits the activity of the metabolic enzymes glycogen synthase kinase 3beta and glycogen synthase. As such, these results demonstrate a novel metabolic regulatory pathway activated by mitochondrial oxidants. In addition, they suggest that although chronic oxidant production may have deleterious effects, mitochondrial oxidants can also function acutely as signaling molecules to provide communication between the mitochondria and the cytosol.

rac1 regulates a cytokine-stimulated, redox-dependent pathway necessary for NF-kappaB activation.

The signal transduction pathway leading to the activation of the transcription factor NF-kappaB remains incompletely characterized. We demonstrate that in HeLa cells, transient expression of a constitutively active mutant of the small GTP-binding protein rac1 (V12rac1) leads to a significant increase in NF-kappaB transcriptional activity. In addition, expression of a dominant-negative rac1 mutant (N17rac1) inhibits basal and interleukin 1beta-stimulated NF-kappaB activity. Gel shift analysis using nuclear extract prepared from HeLa cells infected with a recombinant adenovirus encoding N17rac1 (Ad.N17racl) showed reduced levels of cytokine-stimulated DNA binding to a consensus NF-kappaB binding site. We demonstrate that rac proteins function downstream of ras proteins in the activation of NF-kappaB. In addition, V12rac1 stimulation of NF-kappaB activity is shown to be independent of the ability of rac proteins to activate the family of c-jun amino-terminal kinases. In an effort to further explore how rac proteins might regulate NF-kappaB activity, we demonstrate that expression of V12rac1 in HeLa cells or stimulation with cytokine results in a significant increase in intracellular reactive oxygen species (ROS). Treatment of cells with either of two chemically unrelated antioxidants inhibits the rise in ROS that occurs following V12rac1 expression as well as the ability of V12rac1 to stimulate NF-kappaB activity. These results suggest that in HeLa cells, rac1 regulates intracellular ROS production and that rac proteins function as part of a redox-dependent signal transduction pathway leading to NF-kappaB activation.

Competition for p300 regulates transcription by estrogen receptors and nuclear factor-kappaB in human coronary smooth muscle cells.

Previous studies suggest that estrogen may prevent expression of cell adhesion molecules implicated in vascular inflammation associated with atherosclerosis. We demonstrate the interaction and reciprocal interference of estrogen receptors (ERs) with p65, the nuclear factor-kappaB component, in smooth muscle cells that express ERalpha and ERss after exposure to 17ss-estradiol for 48 to 72 hours. ER and p65 do not associate directly, as shown by lack of coprecipitation, but instead compete for limiting amounts of p300, a close relative of the CREB-binding protein. Overexpressed p300 significantly reduced the inhibitory effect of ER on p65-dependent transcription as well as the inhibitory effect of p65 on ER-dependent transcription. These actions were ligand-dependent. The expression of both ER and nuclear factor-kappaB-dependent reporter genes was partially rescued from ER/p65 mutual inhibition by transient transfection of smooth muscle cells with a p300 expression vector. These actions of 17ss-estradiol may play an important role in the cytokine-induced expression of immune and inflammatory genes implicated in atherogenesis.

Antitumor activity of liposome-encapsulated doxorubicin in advanced breast cancer: phase II study.

Previous studies in animals have demonstrated liposome-encapsulated doxorubicin (LED) has substantially less cardiac toxicity than free doxorubicin but retains antitumor activity. In a phase I clinical study of LED, the maximum tolerated dose was 90 mg/m2 and dose-limiting toxicity was considered to have been reached when granulocytopenia was produced. We used LED to treat 20 patients with advanced, measurable breast cancer. LED was given at doses of 60-75 mg/m2 every 3 weeks as an intravenous infusion. Regression of disease was objectively measured in nine patients; in five of these patients, complete regression of the index lesion occurred. The mean duration of the responses was 7 months. Hematologic toxicity consisted of grade 1-2 leukopenia in some patients. Gastrointestinal toxicity and mucositis were generally mild and tolerable. Alopecia occurred in all patients and usually was complete. Twelve patients received cumulative doses of LED of greater than 400 mg/m2 and were evaluated with radionuclide ventriculograms. In eight patients, the cumulative dose was greater than 500 mg/m2, and five had endomyocardial biopsies. Four of these biopsy results were Billingham grade 0, while one (cumulative LED dose, 750 mg/m2) showed grade 1 changes with mild myofibrillar loss and dilatation of the sarcoplasmic reticulum involving less than 5% of cardiac myocytes. Two patients had decreases in left ventricular ejection fraction. One of these patients had received a total dose of LED of 630 mg/m2 and had a decline of 13% in left ventricular ejection fraction, but had no clinical evidence of congestive heart failure and had a Billingham grade 0 endomyocardial biopsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of chronic doxorubicin cardiotoxicity in dogs by pretreatment with (+/-)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane (ICRF-187).

Adult beagle dogs were given doxorubicin (1.0 mg/kg body weight i.v.) either alone or 30 min after ICRF-187 (NSC 169780) (12.5 mg/kg body weight i.p.) at weekly intervals. Control dogs received 0.9% NaCl solution i.v. 30 min after ICRF-187 i.p. (12.5 mg/kg body weight). One week after the 15th injection (300 mg/sq m total dose), the animals were sacrificed. The frequency and extent of cellular lesions were graded on a scale of 0 to 4+. Such lesions, consisting mainly of vacuolization and myofibrillar loss, were noted in the hearts of all six dogs given doxorubicin alone. The lesions were severe (4+) in five of these animals and moderate (2+) in one. In contrast, no abnormalities were noted in the hearts of four of the six dogs pretreated with ICRF-187 before doxorubicin administration; the remaining two animals in this group had minimal alterations (1+). At the dosage regimen used in the present experiments, doxorubicin did not induce lesions in lungs, liver, kidney, diaphragm, small intestine, or skeletal muscles. Comparable decreases in white blood cell count, red blood cell count, hemoglobin, and serum iron concentration were found in animals receiving doxorubicin with or without ICRF-187. Concurrent administration of ICRF-187 offers a promising means of reducing the chronic cardiotoxicity induced by doxorubicin.

Effect of pretreatment with ICRF-187 on the total cumulative dose of doxorubicin tolerated by beagle dogs.

Studies were made of the influence of ICRF-187 on the functional and morphological effects of very large cumulative doses of doxorubicin given over a prolonged period of time. Adult beagles of either sex (6.2-11.6 kg) were given doxorubicin (1.75 mg/kg i.v.) either alone or 15 min after ICRF-187 (25 mg/kg, i.v.) at 3-week intervals. Control dogs received ICRF-187 (25 mg/kg, i.v.) or 0.9% saline without doxorubicin. Of eight animals receiving doxorubicin alone, five died; two after a total dose of 12.25 mg/kg and three after 14 mg/kg; three others were in poor condition at the time of euthanasia after 14 mg/kg. Of eight animals receiving both ICRF-187 and doxorubicin, four died; two after 35 mg/kg, one after 43.75 mg/kg, and one after 52.5 mg/kg; two other dogs were euthanized after 43.75 mg/kg because of difficulties encountered in giving i.v. injections, and two dogs survived a total dose of 52.5 mg/kg. All control dogs survived. None of the treatment or control groups developed consistent echocardiographic changes or alterations in mean arterial pressure. By 300 days after onset of treatment, dogs given ICRF-187 and doxorubicin developed significant prolongation of the PQ interval; by 550 days, surviving dogs in this group developed ventricular premature contractions. Each animal receiving doxorubicin alone had severe myocardial lesions (lesion score 3+). Of the animals given ICRF-187 and doxorubicin, one that received 35 mg/kg doxorubicin had no lesions; of four given 43.75 mg/kg, three had no lesions and one had minimal lesions (lesion score 1+); of three given 52.5 mg/kg, one had minimal (lesion score 1+), and two had moderate (lesion score 2+) lesions. Control animals had no myocardial lesions. Thus, ICRF-187 provided significant protection when administered with doxorubicin over a period of 90 weeks, and made it possible to give doses of doxorubicin which otherwise would have been lethal.

Comparison of the effectiveness of (+/-)-1,2-bis(3,5-dioxopiperazinyl-1-yl)propane (ICRF-187) and N-acetylcysteine in preventing chronic doxorubicin cardiotoxicity in beagles.

This investigation examined the potential of N-acetylcysteine (NAC) and ICRF-187, alone and in combination, to protect against chronic doxorubicin cardiotoxicity. Adult beagles of either sex (7.3 to 12.5 kg) were given doxorubicin (1.75 mg/kg i.v.) either alone or 30 min after either ICRF-187 (25 mg/kg i.p.), NAC (200 mg/kg i.p.), or ICRF-187 (25 mg/kg i.p.) and NAC (200 mg/kg i.p.) at 3-week intervals. Control dogs received ICRF-187 (25 mg/kg i.p.), NAC (200 mg/kg i.p.), ICRF-187 (25 mg/kg i.p.) and NAC (200 mg/kg i.p.), or 0.9% NaCl solution without doxorubicin. The experiment was terminated 3 weeks after the seventh injection (total doxorubicin dose, 12.25 mg/kg). Three animals pretreated with NAC and one pretreated with ICRF-187 before receiving doxorubicin died or were in poor condition and were killed before the end of the study. The frequency and extent of myocardial lesions (vacuolization and myofibrillar loss) were assessed on a scale of 0 to 4+. Such lesions were present in all six dogs given doxorubicin alone and were marked to severe (3+ to 4+) in five of these dogs and moderate (2+) in one. Lesions of comparable severity (2+ to 4+) were also apparent in the hearts of dogs given the combination of NAC and doxorubicin. In contrast, no abnormalities (lesion score 0) were found in the hearts of three of six dogs given doxorubicin and ICRF-187 and in four of six dogs given doxorubicin following the combination of ICRF-187 and NAC; the remaining animals in these two groups had minimal lesions. At the dosage regimen used in the present experiments, doxorubicin, NAC, or ICRF-187 alone or in combination did not cause alterations in lungs, liver, kidney, or small intestine. Decreases in WBC count, RBC count, and hemoglobin occurred in dogs given doxorubicin with or without the various pretreatments. Thus, pretreatment with ICRF-187 was effective and pretreatment with NAC was ineffective in reducing chronic doxorubicin cardiotoxicity.