Paclitaxel and docetaxel enhance the metabolism of doxorubicin to toxic species in human myocardium.

Doxorubicin cardiotoxicity is a multifactorial process in which the alcohol metabolite doxorubicinol mediates the transition from reversible to irreversible damage. We investigated whether the tubulin-active taxane paclitaxel increases conversion of doxorubicin to doxorubicinol, thus explaining the high incidence of congestive heart failure when doxorubicin is used with paclitaxel. Specimens of human myocardium from patients undergoing bypass surgery were processed to obtain cytosolic fractions in which doxorubicin was converted to doxorubicinol by NADPH-dependent aldo/keto or carbonyl reductases. In this model, clinically relevant concentrations of paclitaxel (1-2.5 microM) increased doxorubicinol formation by mechanisms consistent with allosteric modulation of the reductases. Stimulation was observed over a broad range of basal enzymatic activity, and was accompanied by a similar pattern of enhanced formation of doxorubicinol aglycone, a metabolite potentially involved in the reversible phase of cardiotoxicity. The closely related analogue docetaxel had effects similar to paclitaxel, but increased doxorubicinol formation over a narrower range of enzymatic activity. The unrelated tubulin-active alkaloid vinorelbine had no effect. These results demonstrate that taxanes have a unique potential for enhancing doxorubicin metabolism to toxic species in human myocardium. The effects on doxorubicinol formation provide clues to explain the clinical pattern of doxorubicin-paclitaxel cardiotoxicity and also caution against the potential toxicity of combining docetaxel with high cumulative doses of doxorubicin.

Anthracycline metabolism and toxicity in human myocardium: comparisons between doxorubicin, epirubicin, and a novel disaccharide analogue with a reduced level of formation and [4Fe-4S] reactivity of its secondary alcohol metabolite.

Secondary alcohol metabolites have been proposed to mediate chronic cardiotoxicity induced by doxorubicin (DOX) and other anticancer anthracyclines. In this study, NADPH-supplemented human cardiac cytosol was found to reduce the carbonyl group in the side chain of the tetracyclic ring of DOX, producing the secondary alcohol metabolite doxorubicinol (DOXol). A decrease in the level of alcohol metabolite formation was observed by replacing DOX with epirubicin (EPI), a less cardiotoxic analogue characterized by an axial-to-equatorial epimerization of the hydroxyl group at C-4 in the amino sugar bound to the tetracyclic ring (daunosamine). A similar decrease was observed by replacing DOX with MEN 10755, a novel anthracycline with preclinical evidence of reduced cardiotoxicity. MEN 10755 is characterized by the lack of a methoxy group at C-4 in the tetracyclic ring and by intercalation of 2, 6-dideoxy-L-fucose between daunosamine and the aglycone. Multiple comparisons with methoxy- or 4-demethoxyaglycones, and a number of mono- or disaccharide 4-demethoxyanthracyclines, showed that both the lack of the methoxy group and the presence of a disaccharide moiety limited alcohol metabolite formation by MEN 10755. Studies with enzymatically generated or purified anthracycline secondary alcohols also showed that the presence of a disaccharide moiety, but not the lack of a methoxy group, made the metabolite of MEN 10755 less reactive with the [4Fe-4S] cluster of cytoplasmic aconitase, as evidenced by its limited reoxidation to the parent carbonyl anthracycline and by a reduced level of delocalization of Fe(II) from the cluster. Collectively, these studies (i) characterize the different influence of methoxy and sugar substituents on the formation and [4Fe-4S] reactivity of anthracycline secondary alcohols, (ii) lend support to the role of alcohol metabolites in anthracycline-induced cardiotoxicity, as they demonstrate that the less cardiotoxic EPI and MEN 10755 share a reduction in the level of formation of such metabolites, and (iii) suggest that the cardiotoxicity of MEN 10755 might be further decreased by the reduced [4Fe-4S] reactivity of its alcohol metabolite.

Repeated stimulation of L-type calcium channels in the rat ventral tegmental area mimics the initiation of behavioral sensitization to cocaine.

RATIONALE: A substantial body of evidence indicates that ion flux through L-type calcium channels and N-methyl-D-aspartate (NMDA) receptors contributes to behavioral sensitization to cocaine. OBJECTIVES: The following experiments were designed to evaluate the role of calcium influx through L-type calcium channels or NMDA receptors in the ventral tegmental area (VTA) in the initiation of behavioral sensitization to cocaine. METHODS: The L-type calcium channel agonist BayK 8644, the glutamate agonist NMDA, or vehicle was microinjected into the VTA on 3 consecutive days. Following a 2-week withdrawal period, all rats received a challenge injection of cocaine (15 mg/kg, i.p.) in order to assess potential cross-sensitization with the NMDA or BayK 8644 pretreatments. RESULTS: Repeated intra-VTA microinjections of BayK 8644, but not NMDA, resulted in an augmentation of the behavioral response to cocaine. CONCLUSIONS: These results indicate that calcium influx through L-type calcium channels produces neurophysiological adaptations that mimic those resulting from intermittent exposure to cocaine.

Doxorubicin metabolism and toxicity in human myocardium: role of cytoplasmic deglycosidation and carbonyl reduction.

The anthracycline doxorubicin (DOX) is an exceptionally good antineoplastic agent, but its use is limited by formation of metabolites which induce acute and chronic cardiac toxicities. Whereas the acute toxicity is mild, the chronic toxicity can produce a life-threatening cardiomyopathy. Studies in laboratory animals are of limited value in predicting the structure and reactivity of toxic metabolites in humans; therefore, we used an ethically acceptable system which is suitable for exploring DOX metabolism in human myocardium. The system involves cytosolic fractions from myocardial samples obtained during aorto-coronary bypass grafting. After reconstitution with NADPH and DOX, these fractions generate the alcohol metabolite doxorubicinol (DOXol) as well as DOX deoxyaglycone and DOXol hydroxyaglycone, reflecting reduction of the side chain carbonyl group, reductase-type deglycosidation of the anthracycline, and hydrolase-type deglycosidation followed by carbonyl reduction, respectively. The efficiency of each metabolic route has been evaluated at low and high DOX:protein ratios, reproducing acute, single-dose and chronic, multiple-dose regimens, respectively. Low DOX:protein ratios increase the efficiency of formation of DOX deoxyaglycone and DOXol hydroxyaglycone but decrease that of DOXol. Conversely, high DOX:protein ratios facilitate the formation of DOXol but impair reductase- or hydrolase-type deglycosidation and uncouple hydrolysis from carbonyl reduction, making DOXol accumulate at levels higher than those of DOX deoxyaglycone and DOXol hydroxyaglycone. Structure-activity considerations have suggested that aglycones and DOXol may inflict cardiac damage by inducing oxidative stress or by perturbing iron homeostasis, respectively. Having characterized the influence of DOX:protein ratios on deglycosidation or carbonyl reduction, we propose that the benign acute toxicity should be attributed to the oxidant activity of aglycones, whereas the life-threatening chronic toxicity should be attributed to alterations of iron homeostasis by DOXol. This picture rationalizes the limited protective efficacy of antioxidants against chronic cardiomyopathy vis-à-vis the better protection offered by iron chelators, and forms the basis for developing analogues which produce less DOXol.

Differential effects of morphine on histamine metabolism in brain and spinal cord of mice.

The effects of morphine on the levels of histamine (HA), its metabolite tele-methylhistamine (t-MH) and on t-MH synthesis rates (thought to be indicative of neuronal HA release) were investigated in brain regions and spinal cords of DBA/2J (DBA) and C57/BL6 (C57) mice, two strains known to differ in their sensitivity to morphine. In DBA (a strain highly sensitive to morphine antinociception), morphine (10 mg/kg, s.c.) had no effect on brain regional t-MH or HA levels, but produced a generalized inhibition of regional t-MH synthesis rates ranging from 11 to 53%. The monoamine oxidase (MAO) inhibitor pargyline (used to estimate t-MH synthesis rates) had no effect on HA or t-MH levels in the DBA or C57 spinal cord, indicating the absence of detectable spinal HA turnover. Morphine (10 mg/kg) had no effect on DBA or C57 spinal cord HA or t-MH levels, but significantly increased t-MH synthesis in the DBA but not in the C57 spinal cord. These results suggest that in DBA mice, antinociceptive doses of morphine inhibit HA release in brain, and promote the release of HA from spinal cord. Neither effect was found in C57 mice, which are resistant to morphine antinociception. The relevance of these actions to previous studies showing the blockade of opiate antinociception by H2 antagonists remains to be established.

A simple technique for preparation of bone marrow or peripheral blood buffy coat cells for electron microscopy.

A simple and rapid method of processing ethylene-diamine-tetra-acetic acid anticoagulated peripheral blood or aspirated bone marrow for electron microscopy is described. The resultant buffy coat pellet is easily processed into epoxy resin. Semithin sections (1 mu) stained with 1% toluidine blue reveal the various stratified cell layers allowing convenient selection for ultramicrotomy and ultrastructural evaluation.

Cimetidine-sensitive analgesia: investigation of the importance of stress-induced changes in arterial pressure.

Because previous studies have suggested that activation of baroreceptors could mediate stress-induced analgesia, the effect of acute exposure to footshock on mean arterial pressure (MAP) and pain sensitivity was simultaneously determined in conscious rats receiving the histamine H2 receptor antagonist cimetidine or vehicle. Continuous exposure to 3 min of inescapable footshock (3.5 mA) dramatically decreased pain sensitivity, with no increase in post-stress MAP, when compared to no shock controls. The histamine H2-antagonist cimetidine (100 mg/kg, IP) had no significant effect on MAP in resting or stressed animals, but inhibited the stress-induced analgesia, showing that the antagonism of the analgesia is not mediated by modulation of post-stress MAP. Although footshock failed to elicit a significant increase in MAP, a highly significant correlation was found between individual analgesic scores and shock-induced pressure changes in animals treated with cimetidine; in animals receiving vehicle, no such correlation was observed, although the use of a cutoff in analgesic testing may explain this. These results suggest the existence of a stress-induced analgesic mechanism resistant to cimetidine, but associated with elevated MAP.

Age, dementia, dyskinesias, and lithium response.

Nineteenth-century neuropsychiatrists felt that the aged bipolar patient usually developed chronic mania, which eventually turned into dementia. The authors' elderly patients seemed to experience few such denouements, so they evaluated the course and treatment response of 81 bipolar patients over the age of 55. Fifty-six responded well to lithium. Advanced age had no effect on course or outcome. However, with increased clinical evidence of neurological illness there was an increased incidence of chronic mania, a poorer response to lithium, and more frequent and severe neurotoxicity. Extrapyramidal syndromes were particularly devastating.

The homosexual rights movement in the United States: a traditionally overlooked area of American history.

In this short account, the homosexual rights movement in the United States, traditionally overlooked by historians, is presented as a minority movement. References are made to the European origins and the early efforts in America. The author sees eight stages in the growth of the movement. In Stage 1, from 1908 through 1945, there were sporadic individual attempts to defend the rights of homosexual men and women. In the years immediately following World War II, Stage 2 witnessed the dawning of a minority consciousness among gay people living in the cities. Stage 3, from 1950 to 1952, represented a search for identity. During the years 1952-1953, Stage 4, righteous indignation flared up within the movement. In Stage 5, from 1953 to 1960, the movement emphasized information and educational approaches. The decade of the sixties, Stage 6, brought civil-rights activism to the homophile movement. In Stage 7, beginning in 1969, gay liberation emerged. Finally, in Stage 8 (1973-1979), the movement and the government responded to each other through institutional channels. The 1970s ended with two major confrontations, giving the decade of 1969 to 1979 a unity and sense of accomplishment.

The collection and analysis of documents for the Civil Liberties and Sexual Orientation Project.

This article shows how documents are collected and analyzed as part of a complex methodology to supplement and verify data gathered for the Civil Liberties and Sexual Orientation Project. During interviews, respondents are shown a checklist and asked if they have documents that may support their belief that they have experienced discrimination. Interviews are considered fully documented if materials are obtained which demonstrate that action was taken against a respondent and that the action was based on sexual orientation or on departures from social sex-role stereotypes. Documents are also collected to see if other attributes of a respondent were involved in the action. In addition, supplemental information is obtained that augments interview data.

Emergence of myasthenia gravis during treatment with lithium carbonate.

In a patient with recurrent episodes of severe mania, classical manifestations of myasthenia gravis developed for the first time during treatment with lithium carbonate. Four episodes were recorded in which the appearance of progressive weakness coincided with subacute or long-term lithium carbonate administration during periods of psychiatric remission. In each instance, neurologic symptoms were ameliorated or disappeared shortly after the drug was discontinued or its dosage was reduced. There was no evidence of lithium carbonate toxicity or electrolyte disturbances at any time during treatment. Based on a literature review of animal studies and related clinical reports, a mechanism of peripherally mediated neuromuscular cholinergic insufficiency is proposed. In addition, the differential diagnosis of muscle weakness during lithium carbonate administration is discussed.