Selective inhibition of Src SH2 by a novel thiol-targeting tricarbonyl-modified inhibitor and mechanistic analysis by (1)H/(13)C NMR spectroscopy.

Detailed analysis of Src SH2 binding by peptides containing a novel tricarbonyl-modified pTyr moiety is described. We envisaged that Src SH2 selectivity might be obtained by exploiting the thiol group of Cys188 present in the pTyr binding pocket of the protein at the betaC3 position. Peptidyl as well as non-peptidyl compounds 1-4 possessing a 4-alpha,beta-diketoester-modified pTyr mimic exhibited micromolar affinity to Src SH2. Furthermore, these tricarbonyl compounds were selective for Src SH2 to the extent they showed no significant affinity for either Cys188Ser or Cys188Ala Src SH2 mutants. Upon closer examination of the binding of these tricarbonyls to Src SH2 using NMR of 13C-labeled compounds (6a, 6b, and 6c), we found that after the initial binding event the molecule disproportionated in a 'retro-Claisen' fashion to provide benzoic acid 16 and, following hydrolysis of the methyl ester 17, the hemiketal adduct of glyoxalic acid 18.

Effects of pharmacological interventions on emetine cardiotoxicity in isolated perfused rat hearts.

The cardiotoxicity of emetine continues to be a significant clinical problem. The purpose of this study was to investigate the effect of several mechanistic interventions, including ICRF-187, an iron-chelating agent which protects against doxorubicin toxicity, atropine, and fructose-1,6-bisphosphate (FBP) on the toxicity of emetine in our isolated, perfused rat heart model. The model includes functional, electrocardiographic, and biochemical determinations in the same preparation. Atropine and ICRF-187 had no effect on the time needed for emetine to induce ventricular asystole, while FBP significantly increased this time. Administration of 47 microM atropine, 300 microM FBP, or 1 mM FBP decreased the release of lactate dehydrogenase (LDH) into the coronary effluent, while ICRF-187 had no effect. These pharmacological interventions variably changed the amplitude of the biphasic response of the coronary flow to emetine. Finally, FBP was very effective in slowing the rate of QRS-waveform degeneration in the perfused hearts. Emetine caused PR- and QRS-prolongation which was not altered by FBP.

Emetine-induced lactate dehydrogenase release, functional changes and electrocardiographic changes in the rat heart in vitro.

Emetine is an old drug which is used primarily as a emetic in ipecac syrup and as an alternative amoebicide. The major problem with emetine is that chronic use causes severe cardiotoxicity. In order to explore the mechanism of emetine cardiotoxicity, simultaneous recordings of mechanical activity and electrocardiograms, and biochemical assays were performed on male Sprague-Dawley rat hearts perfused by the Langendorff technique. Emetine was perfused constantly at concentrations of 19 or 37 mum for 10 min. All of the effects of emetine were concentration dependent. The most significant toxicological effect was the large amounts of LDH which appeared in the coronary effluent. A significant degree of injury to the cardiac plasma membrane is indicated by this observation, since LDH normally is an intracellular enzyme. Such damage to the membrane might accumulate and lead to the chronic, cumulative cardiotoxicity observed clinically with emetine. The pharmacological effects of emetine perfusion included decreased contractility which occurred concurrently with P-R interval prolongation, QRS duration prolongation, and degeneration of the QRS waveform. Coronary flow increased early during emetine perfusion, but then dropped to below control levels. The atria were more delayed in their response to emetine and in their recovery following emetine than were the ventricles. The simultaneous measurement of several parameters is a useful technique for the study of cardiac toxicity.

Toxic mechanisms of the heart: a review.

Toxic injury is one of the many ways by which the functional integrity of the heart may become compromised. Any of the subcellular elements may be the target of toxic injury, including all of the various membranes and organelles. Understanding the mechanisms underlying cardiotoxicity may lead to treatment of the toxicity or to its prevention. Doxorubicin and its analogs are very important cancer chemotherapeutic agents that can cause cardiotoxicity. Other agents which are cardiotoxic and which have profound public health implications include the alkaloid emetine in ipecac syrup, cocaine, and ethyl alcohol. The most important cardiotoxic mechanisms proposed for doxorubicin include oxidative stress with its resultant damage to myocardial elements, changes in calcium homeostasis, decreased ability to produce ATP, and systemic release of cardiotoxic humoral mediators from tissue mast cells. Each of the first 3 mechanisms can lead to each of the other 2, and the causal relationships between all of these mechanisms are not clear. New evidence suggests that doxorubicinol, one of the metabolites of doxorubicin may be the moiety responsible for cardiotoxicity. Several other potential mechanisms also have been proposed for doxorubicin. Emetine in ipecac syrup is the first aid treatment of choice for many acute toxic oral ingestions and the alkaloid, itself, is used to treat amebiasis. Cardiotoxicity occurs following chronic exposure, such as occurs therapeutically in amebiasis and with ipecac abuse by bulemics. A number of mechanisms are proposed for emetine cardiotoxicity, but the current mechanistic literature is quite scarce. Cocaine abuse recently has caught the public interest, in particular because of the drug-related sudden deaths of certain athletes. Cocaine can cause hypertension, arrhythmias, and reduced coronary blood flow, each of which can contribute to its lethality. However, it may be possible that cocaine sudden death episodes are more related to hyperthermia and convulsive seizures, rather than to cardiovascular toxicity. Chronic alcohol use leads to dilated cardiomyopathy and failure as part of the general physical degeneration that occurs with alcoholism. Several mechanisms are proposed for the cardiomyopathy, but only 2 things seem clear. The cardiotoxicity is due to an intrinsic effect of alcohol, rather than to malnutrition or co-toxicity, and abstinence is the only effective treatment for the cardiomyopathy. Recent articles indicate that very moderate use of alcohol may be beneficial and protect against cardiovascular-related morbidity. One explanation for these findings seems to be that the non-drinking groups, against whom the moderate drinking comparisons were made, were enriched in former drinkers with significant alcohol-related cardiovascular pathology.

Prevention of acetaminophen-induced hepatotoxicity by dimethyl sulfoxide.

Dimethyl sulfoxide (DMSO) has previously been shown to protect against acetaminophen (APAP)-induced hepatotoxicity, but the mechanism of this effect was not clear. Treatment of mice with 1 mg/kg DMSO 4 h before 250 mg/kg APAP resulted in significantly less hepatotoxicity than with APAP alone, as measured by serum glutamic pyruvic transaminase (SGPT) content 24 h after APAP. Protection was also evident when 1 ml/kg DMSO was given 4, but not 8 h after 250 mg/kg APAP. The APAP-induced depletion of liver glutathione was prevented in mice pretreated with DMSO, although DMSO alone had no effect on liver glutathione levels. The hepatic concentration of cytochrome P-450 (P450) 4 h after treatment of mice with 1 ml/kg DMSO, was significantly decreased compared to saline-treated animals. However, while this DMSO pretreatment significantly decreased the activity of cytochrome P-450-linked aminopyrine-N-demethylase, it increased the activity of aniline hydroxylase. Covalent binding of [14C]APAP to hepatic protein in vivo was significantly decreased in mice pretreated with DMSO. Covalent binding of [14C]APAP to hepatic microsomal protein in vitro was not significantly altered after in vivo treatment with DMSO. However, the presence of DMSO in the in vitro incubation mixture significantly decreased covalent binding of [14C]APAP in a dose-dependent manner compared to microsomal fractions from untreated, saline-treated or DMSO pretreated animals. These data suggest that the DMSO-induced alterations in cytochrome P-450 content and activity may not be the cause of the observed protective action of this chemical. The ability to competitively inhibit APAP bioactivation or to directly scavenge free radicals produced during APAP metabolism, including the activated species which covalently binds to protein, may account for the hepatoprotection afforded by DMSO.

The toxicity of tetrahydrobiopterin: acute and subchronic studies in mice.

Tetrahydrobiopterin (BH4) is presently being employed in clinical trials for the therapy of various neurological disorders. The toxicity of BH4 in mice was analyzed by acute and subchronic intraperitoneal and acute oral survival studies. Organ weight analysis and histopathology were performed after acute and subchronic i.p. administration. The effect of probenecid on BH4 toxicity was also tested. An LD50 of approximately 260 mg/kg was obtained from acute (14-day) intraperitoneal survival studies. A dose-dependent increase in kidney weights and histopathologic evidence of acute toxic tubular necrosis were noted in acute i.p. studies. Acute oral administration of up to 1318 mg/kg BH4 did not cause any significant morbidity or mortality, nor did subchronic (92-day) i.p. administration of 10 or 50 mg/kg BH4. Probenecid pretreatment did not decrease the toxicity of BH4. The importance of further evaluation of the potential toxicity of tetrahydrobiopterin in clinical utilization is emphasized.

Influence of in vitro ubiquinone antagonists on doxorubicin toxicity in vivo.

Doxorubicin is an anthracycline antibiotic with a very wide spectrum of anticancer activity. It has a great potential for clinical cardiotoxicity, however. One mechanism suggested for the cardiotoxicity is inhibition of ubiquinone-dependent enzymes. It was our purpose to study this possible mechanism using ubiquinone antagonists as probes. The effect on doxorubicin toxicity of three in vitro ubiquinone antagonists was tested in mice. Two of the antagonists, 2-hydroxy-3-n-dodecylmercapto-1,4-naphthoquinone and 2,3-dimethoxy-5-beta-naphthylmercapto-1,4-benzoquinone, enhanced doxorubicin toxicity in vivo as measured by survival. The latter was significantly toxic to mice, by itself. This effect was completely blocked by ubiquinone pretreatment, but only reduced by tocopherol pretreatment. Neither ubiquinone nor tocopherol was able to decrease the toxic interaction between doxorubicin and either of the ubiquinone antagonists. Cardiac and hepatic glutathione reductase and glutathione peroxidase activities were measured in studies using the 2,3-dimethoxy-5-beta-naphthylmercapto-1,4-benzoquinone. This compound appeared to cause a slight reduction in the activity of hepatic glutathione reductase. It appears that these antagonists are not useful to probe the relationship between doxorubicin cardiotoxicity and ubiquinone enzyme inhibition.

In vivo effects of 1,3-bis(2-chloroethyl)-1-nitrosourea and doxorubicin on the cardiac and hepatic glutathione systems.

Doxorubicin and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) are anti-cancer drugs which have been used together in combination therapy of certain cancers. Each drug has been reported to affect intracellular glutathione stores and together, doxorubicin and BCNU have been shown to exert synergistic toxicity and to deplete completely the glutathione content of isolated hepatocytes. Cardiac and hepatic glutathione reductase activity was significantly inhibited following treatment in vivo with BCNU. Treatment of mice with both doxorubicin and BCNU resulted in increased mortality compared to either drug alone. There was, however, no depletion of hepatic or cardiac glutathione levels in vivo beyond that seen with either BCNU or doxorubicin alone. Diethyl maleate, a known glutathione depletor whose effects are enhanced by BCNU in vitro, also was unable to increase GSH depletion after BCNU in vivo. These discrepancies between in vivo and in vitro studies may be due to the presence of more effective compensatory mechanisms in the whole animal, or to differences in the metabolism and inactivation of these drugs.

Role of calcium in isoproterenol cytotoxicity to cultured myocardial cells.

Primary cultures of rat myocardial cells were used to evaluate the cellular dynamics of calcium accumulation after exposure to isoproterenol (ISO). Non-toxic concentrations of ISO (2.4 X 10(-7) M) caused a gradual increase in myocyte calcium uptake. These effects peaked 3 min after exposure and returned to control levels within 2 min. Toxic concentrations of ISO caused a biphasic increase in calcium uptake. The initial phase peaked 1 min after exposure and returned to control levels by 3 min. A second phase was characterized by a progressive increase in calcium uptake that plateaued 10 min after exposure. Ascorbic acid (AA, 5 X 10(-3) M) and sodium bisulfite (SB, 9.6 X 10(-4) M) did not modify the calcium uptake of the initial phase, whereas propranolol (1 X 10(-6) M) and verapamil (1 X 10(-5) M) prevented the initial rise in calcium uptake. In contrast, the antioxidants prevented the the second phase of ISO-induced calcium uptake, whereas verapamil and propranolol did not. The toxic accumulation of calcium induced by ISO may be due to oxidative damage of the sarcolemma. Antioxidants may prevent the formation of oxidative metabolites from ISO and the subsequent calcium overload. Our results show that agents which modify slow calcium-channel transport do not prevent ISO-induced calcium overload in our cell culture system.

Attenuation by antioxidants of Na+/K+ ATPase inhibition by toxic concentrations of isoproterenol in cultured rat myocardial cells.

We have reported previously that toxic concentrations of isoproterenol caused severe alterations in the structural integrity of the sarcolemma and mitochondria found in primary cultures of rat myocardial cells [8, 9]. Mitochondrial injury was observed 1.5 h after exposure to isoproterenol, whereas leakage of intracellular ions and enzymes was observed only after prolonged exposures (greater than 4 h). Ascorbic acid and sodium bisulfite prevented the cytotoxic effects of isoproterenol in our cell culture system. Takeo et al. [13] suggested that adrenochrome (an oxidative metabolite of epinephrine) specifically inhibits the activity of the sodium/potassium ATPase. Other investigators have shown that an indole metabolite of epinephrine inhibited actomyosin ATPase [1, 4]. These inhibitory actions may result from an interaction between the oxidative metabolites and sulfhydryl groups present in the enzyme [13]. Inhibition of the sodium/potassium ATPase is associated with an increase in the intracellular concentration of Na+ and Ca2+ and a decrease in intracellular K+. Changes in the intracellular concentration of these ions are commonly seen in heart cell damage and contractile failure [2]. The present study was designed to determine if isoproterenol, a synthetic catecholamine, inhibits the sodium/potassium ATPase activity in a primary culture system of rat myocardial cells.

Effect of formulation factors on the matrix pH of nylon microcapsules.

The application of nylon microencapsulation as a drug delivery system inherently demands that the microencapsulated matrix should not cause degradation of the encapsulated drug. The presence of alkaline hexamethylenediamine (HMD) in the microcapsule core will affect the final pH of the microcapsules and may influence the stability of some drugs. To follow the pH within the microcapsule core during manufacture, pH indicators were encapsulated. The final pH was found to depend on the formulation used and could be controlled by the addition of acid. Several other variables affecting the nylon wall formation were examined to determine optimum processing conditions. Increased agitation produced a decrease in microcapsule size. This cause an increase in nylon weight recovered. The increased recovery of nylon was due in part to nylon formation over a larger surface area. Varying the amounts of HMD and sebacyl chloride (SC) used also affected the total weight of nylon formed. In general, more nylon is recovered as the level of each reactant increases. However, the molar ratio of HMD:SC determined the total amount of nylon formed when SC was present in excess.

Study of tetrahydrobiopterin and 6-methyltetrahydropterin on alcohol dependence in mice.

The literature establishes a potential link between the function of tetrahydroisoquinolines in the biological actions of alcohol and the reduced pterin cofactor needed for synthesis of certain neurotransmitters. The effect of the administration of 6-methyltetrahydropterin and tetrahydrobiopterin upon alcohol withdrawal in mice was tested. Dependence was produced by ip administration of alcohol, supplemented by alcohol delivered by a subcutaneously implanted silastic tube. Administration of the reduced pterins at relatively high doses did not reduce the magnitude of the alcohol withdrawal syndrome.

Cytotoxicity of isoproterenol to cultured heart cells: effects of antioxidants on modifying membrane damage.

Primary cultures of rat myocytes were used to study the cardiac damage induced by toxic doses of L-isoproterenol (ISO). Cultures were exposed to varying concentrations of ISO (2.4 X 10(-5), 1 X 10(-4), and 5 X 10(-4) M) for 0.5, 1.5, 4, and 12 hr. Mitochondrial membrane fragility, myocyte potassium content (as an index of sarcolemmal damage), and cellular glutathione content were used to evaluate cellular injury. A significant increase in mitochondrial fragility was observed 0.5 hr after treatment with 5 X 10(-4) M ISO. Lower doses caused an increase in mitochondrial fragility 1.5 hr after exposure. Longer durations of ISO exposure (4 and 12 hr) were necessary to decrease cellular potassium content. Glutathione levels were minimally affected by ISO. L-Ascorbic acid (5 X 10(-3) M) or sodium bisulfite (9.6 X 10(-4) M) were added to the cultures to determine if antioxidants prevent the toxicity caused by ISO. The presence of L-ascorbic acid or sodium bisulfite in ISO-treated myocyte cultures prevented the toxic changes in mitochondrial fragility and myocyte potassium content. The data indicate that antioxidants may be useful in reducing injury induced by toxic doses of ISO. Furthermore, mitochondrial injury may be involved significantly with the development of ISO-induced cardiotoxicity.

Influences of matrixes on nylon-encapsulated pharmaceuticals.

The preparation and properties of nylon microcapsules containing three different matrixes (formalized gelatin, calcium alginate, and calcium sulfate) are described. Microcapsules containing each matrix were dense and free flowing and could be made of very small diameter by controlling the stirring speed during nylon formation. The preparation of microcapsules containing calcium alginate employed freeze-drying procedures. Lyophilization was not necessary with the formalized gelatin and calcium sulfate systems. Various representative drugs (anionic, cationic, nonionic, quaternary, and amphoteric compounds) were used in the formulation studies. The effects of pH, matrix, and encapsulated species on retention of drug in the microcapsules are described. In addition, the surface morphology of the microcapsules was examined using scanning electron microscopy.

Study of the combined and separate administration of doxorubicin and coenzyme Q10 on mouse cardiac enzymes.

Administration of an acutely toxic dose of doxorubicin to mice did not increase, but rather decreased the percent deficiency of coenzyme Q10 (CoQ10) as calculated according to the coenzyme-apoenzyme system principle. The date indicate that doxorubicin may occupy CoQ10-empty receptors on the apoenzyme, with or without some destruction of enzyme-menbrane structure close to the receptor. Data from mice receiving both CoQ10 and doxorubicin indicated that CoQ10 may protect against doxorubicin. CoQ10 alone corrected the pre-existing deficiency found in control mice.

High steady-state levels of uric acid produced in rats by dietary training and potassium oxonate.

To reduce the inherent variability in serum uric acid levels of animals allowed ad libitum exposure to food containing potassium oxonate and uric acid, male Sprague-Dawley rats were trained to eat their daily food allotment in a 1.25-hr period each morning. After training the rats were fed a food mixture containing 5% potassium oxonate and 2% uric acid (w/w each). Serum blood levels of uric acid reached a steady state within 2 hr; these levels were maintained for an additional 4 hr. It is believed that the stomach emptying rate is a zero-order process under these experimental conditions.

Effect of water-soluble carriers on morphine sulfate release from a silicone polymer.

The influence of gelatin, sodium lauryl sulfate, lactose, and sodium alginate on morphine sulfate diffusion from cylindrical silicone polymer pellets was examined in isotonic pH 7.4 phosphate buffer. These water-soluble carriers caused the pellets to swell in aqueous media. Sodium alginate exerted the greatest influence on drug release. The morphine sulfate diffusion rate from the cylindrical pellets increased as the matrix alginate content increased up to 20%. Water-soluble carrier incorporation into silicone polymeric matrixes permits controlled release of water-soluble drugs that otherwise would be released extremely slowly from the polymer. Drug diffusion from the silicone matrix containing sodium alginate followed second-order kinetics. The release mechanism probably involves the creation of pores or pathways through the matrix secondary to the swelling.

Effect of exercise stress upon the acute toxicity of adriamycin in mice.

The effect of an acute exercise stress upon the acute toxicity of adriamycin was tested. Mice were forced to swim for 30 min following 18 or 23 mg/kg ip of adriamycin. Survival was checked daily for 30 days. The exercise stress did not appear to increase the toxicity of adriamycin in these animals.

Prevention by coenzyme Q10 of the electrocardiographic changes induced by adriamycin in rats.

The administration of adriamycin (ADM) to rats has consistently caused a widening of the QRS complex of the electrocardiogram. When coenzyme Q10 was also administered, beginning two days before ADM, this widening of the QRS complex and the elongation of the Q-T interval were reduced or totally prevented, depending upon conditions. ADM alone or with coenzyme Q10 did not alter the P-R interval. Some control by coenzyme Q10 of the cardiotoxicity of adriamycin in cancer patients is promising.