Emetine myopathy in the rat

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.

Muscle Toxicity of Drugs: When Drugs Turn Physiology into Pathophysiology

Drugs are prescribed to manage or prevent symptoms and diseases, but may sometimes cause unexpected toxicity to muscles. The symptomatology and clinical manifestations of the myotoxic reaction can vary significantly between drugs and between patients on the same drug. This poses a challenge on how to recognize and prevent the occurrence of drug-induced muscle toxicity. The key to appropriate management of myotoxicity is prompt recognition that symptoms of patients may be drug related and to be aware that inter-individual differences in susceptibility to drug-induced toxicity exist. The most prevalent and well-documented drug class with unintended myotoxicity are the statins, but even today new classes of drugs with unintended myotoxicity are being discovered. This review will start off by explaining the principles of drug-induced myotoxicity and the different terminologies used to distinguish between grades of toxicity. The main part of the review will focus on the most important pathogenic mechanisms by which drugs can cause muscle toxicity, which will be exemplified by drugs with high risk of muscle toxicity. This will be done by providing information on key clinical and laboratory aspects, muscle electromyography patterns and biopsy results, and pathological mechanism and management for a specific drug from each pathogenic classification. In addition, rather new classes of drugs with unintended myotoxicity will be highlighted. Furthermore, we will explain why it is so difficult to diagnose drug-induced myotoxicity, and which tests can be used as a diagnostic aid. Lastly, a brief description will be given of how to manage and treat drug-induced myotoxicity.

Proliferative and non-proliferative lesions of the rat and mouse soft tissue, skeletal muscle and mesothelium

The INHAND Project (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) is a joint initiative of the Societies of Toxicologic Pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP), and North America (STP) to develop an internationally accepted nomenclature for proliferative and nonproliferative lesions in laboratory animals. The purpose of this publication is to provide a standardized nomenclature for classifying lesions observed in the soft tissues including skeletal muscle as well as the mesothelium of rats and mice. The standardized nomenclature of lesions presented in this document is also available electronically on the Internet (http://www.goreni.org/). Sources of material included histopathology databases from government, academia, and industrial laboratories throughout the world. Content includes spontaneous developmental and aging lesions as well as those induced by exposure to test materials. A widely accepted and utilized international harmonization of nomenclature for lesions in soft tissues, skeletal muscle and mesothelium in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists. (DOI: 10.1293/tox.26.1S; J Toxicol Pathol 2013; 26: 1S-26S).

Praziquantel failure in the treatment of Fasciola hepatica

A case of human fascioliasis is presented in which the patient remained symptomatic after treatment with praziquantel and other agents but eventually responded to bithionol. The difficulties in finding an efficacious and tolerable drug therapy for this condition are reviewed with reference to the life cycle and pathogenesis of the parasite. It is concluded that while bithionol remains the current drug of choice, triclabendazole may play a dominant role in the near future.

Effects of myotoxins on skeletal muscle fibers

This review highlights various aspects of a number of experimental myological alterations, induced by different chemical toxicants, including anticholinesterase, colchicine, vincristine, chloroquine, tetanus toxin, botulinum toxin, reserpine and emetine. Despite their chemical diversity and mechanism(s) of action, it is evident from the data discussed here that remarkably different toxic agents exert quite similar effects and induce toxic myopathies. The latter include preferential involvement of slow-twitch red muscle, mitochondrial derangement, denervation-like alterations, formation of membranous whorls, tubular aggregates, autophagic vacuoles and axonal sprouts. The non-invasive experimental models discussed here are valuable in studying various aspects of myopathology in the absence of any mechanical damage to the innervating elements from neurons to axonal terminals.

Desmin pathology in neuromuscular diseases

Desmin is an intermediate filament protein that in striated muscle is normally located at Z-bands, beneath the sarcolemma, and prominently at neuromuscular junctions. It is abundant during myogenesis and in regenerating fibers, but decreases in amount with maturation; in regenerating and denervated muscle fibers it is co-expressed with vimentin. Aggregates of desmin occur as nonspecific cytoplasmic bodies or cytoplasmic spheroid complexes, similar to the aggregates of keratin filaments in Mallory bodies or the neurofilament aggregates in Lewy bodies. In all three instances, alpha-B crystallin may be associated with desmin. There are now increasing numbers of neuromuscular disorders in which abnormal amounts of desmin, some abnormally phosphorylated, feature prominently in muscle fibres. Several of these diseases, including spheroid body myopathy, granulo-filamentous body myopathy and the dystrophinopathies, are familial. Ultrastructural and immunohistochemical studies of desmin have considerably broadened our understanding of the pathology of the cytoskeleton in muscle fibers and in certain hereditary neuromuscular diseases.

Experimental emetine myopathy: enzyme histochemical, electron microscopic, and immunomorphological studies

Ipecac, containing emetine hydrochloride, is used by patients with anorexia nervosa to induce vomiting. Its chronic usage may result in a myopathy and a cardiomyopathy, the former marked by cytoplasmic bodies. We studied myopathological changes after daily injections of female Wistar rats with emetine hydrochloride intraperitoneally for periods of 4, 5, 9, and 10 weeks. The extensor digitorum longus muscle and the soleus muscle showed core-like lesions, streaming of the z-discs, nemaline bodies, cytoplasmic bodies, and spheroid cytoplasmic bodies. Immunomorphological studies revealed increased amounts of desmin. During a period of repair, i.e., 2, 4, and 6 weeks after termination of emetine application, these myopathological alterations faded while proliferation of the T-tubular system, i.e., honeycomb structures, was more often prevalent. Pathological features completely disappeared between 6 and 12 weeks of recovery.

Abuse of drugs associated with eating disorders

Concomitant bulimia nervosa and drug abuse are common in women. Drugs used by this group include diuretics, emetics, laxatives, and diet pills, as well as alcohol, cigarettes, and illicit street drugs. This paper applies principles from behavioral pharmacology to the problem of drug use by women with bulimia nervosa. The prevalence of use, primary effects, toxicity, detection, tolerance, withdrawal, and effects on appetite and weight are discussed for drugs used by bulimic women to reduce appetite or weight or to induce purging (e.g., diuretics, emetics, laxatives, and diet aids). Alternatives in the diagnosis and treatment of drug use in women with eating disorders are discussed.

Reversible emetine-induced myopathy with ECG abnormalities: a toxic myopathy

A young anorexic woman is described with a history of progressive muscle weakness following chronic ingestion of syrup of ipecac that was used in an attempt at weight control. Electrocardiogram (ECG) showed T-wave inversion in all leads and prolongation of the Q-T interval. Electromyography was abnormal. Muscle biopsy revealed a randomized, generalized, predominantly type-2 fibre atrophy and structural alterations in oxidative enzyme stains, such as targetoid and moth-eaten fibres. A few necrotic cells were actively phagocytosed. Electron microscopy revealed severe sarcomeric abnormalities with Z-line streaming, myofibrillar disorganization and increased lysosomal activity. After discontinuation of ipecac syrup, the patient noted a gradual improvement in her condition. The ECG became normal. Emetine and related drug-induced myopathies are uncommon but are of experimental interest because of their effects on mitochondria and the light they shed on autophagic mechanisms in muscle.

Ultrastructural pathology in emetine-induced myopathy

Progressive myopathy developed in two women who consumed ipecac syrup containing emetine hydrochloride to induce vomiting as part of their anorexia nervosa. Muscle biopsy specimens were characterized by severe disruption of the sarcomeres. The ultrastructural spectrum extended from "Z-band streaming" to the formation of cytoplasmic bodies and also comprised abnormalities of the sarcotubular system, thus suggesting that muscle weakness may be related to both sarcomeric and sarcotubular lesions in this self-inflicted myopathy. It is tempting to suggest that muscle weakness may be correlated with or based on the pathology in sarcomeres and the sarcotubular system. As the myopathy is clinically reversible upon discontinuation of ipecac consumption the morphological findings should also be potentially reversible. Experimentally induced emetine myopathy may, thus, serve as a useful model to study morphological dynamics of sarcomeric lesions, which may be observed separately or simultaneously in a variety of spontaneously occurring human neuromuscular disorders.

Effects of emetine and dehydroemetine at the frog neuromuscular junction

Emetine and dehydroemetine caused concentration-dependent reduction of the quantal content of the endplate potential (EPP) at the frog neuromuscular junction. At lower concentrations, the drugs had presynaptic action only, as they decreased the amplitude of the EPP without significantly affecting that of the spontaneous miniature EPP (MEPP). At higher concentrations, the drugs had postsynaptic effects as well. Studies of low frequency facilitation indicated that although at low concentrations the effect of emetine on quantal content was independent of frequency of stimulation, at higher concentrations the effect became markedly frequency-dependent and many of the stimuli (at 4 and 8 Hz) failed to evoke EPPs. In the voltage-clamped transected cutaneous pectoris muscle emetine (10(-4) M) depressed the peak amplitude of the endplate current (EPC). Emetine markedly shortened the time constant of decay of the EPC (tau) at more negative holding potentials but did not change the single exponential character of the decay. The results indicate that the acute effects of emetine involve blocking neuromuscular transmission by acting prejunctionally at low concentrations and pre- as well as postjunctionally at higher concentrations. The prejunctional effect is due to interference with evoked release and probably, mobilization of acetylcholine. The postjunctional effect is due to blockade of the acetylcholine-activated ionic channel.

Myopathy from surreptitious ipecac ingestion

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Emetine myopathy: two case reports with pathobiochemical analysis

We report two female patients with a history of alcohol abuse presenting with proximal painful muscle weakness following aversion therapy with emetine hydrochloride. Muscle biopsy of Case 1 showed a reversible floccular-shaped loss of myosin ATPase and dehydrogenase, an accumulation of PAS positive material, and a normal lipid content. Repeat biopsy showed core change with no focal loss of myosin ATPase. In Case 2, muscle biopsy was taken 1 month after commencement of emetine therapy and revealed similar but milder changes to Case 1. Electron microscopy revealed Z-band streaming with a decrease or loss of mitochondria. Sarcotubular systems appeared normal in shape and size. Anaerobic glycolysis on homogenate from the initial biopsy of Case 1 showed generalized reduction of lactate formation, which returned to normal in the repeat biopsy.

Adverse effects of drugs on muscle

A variety of drugs used in clinical practice may cause myopathy or interfere with neuromuscular transmission. The precise incidence of such disorders is not known, but it is almost certainly higher than is generally suspected. An important aspect of drug-induced muscular disorders is their reversibility if the offending agent is withdrawn, whereas failure to do so may lead to unnecessary morbidity. The study of drug effects on muscle provides a means of investigating the pathological reactions of muscle, and of producing experimental models of naturally occurring myopathies. Drug-induced myopathies may result from a direct toxic effect, which may be local when the drug is injected into a muscle or more diffuse when the drug is taken systemically, or may be secondary to electrolyte disturbances, muscle compression, ischaemia, neural activation or to the development of an immunological reaction directed against muscle. Repeated injections of antibiotics or drugs of addiction may lead to severe muscle fibrosis and contractures. A variety of drugs may cause an acute or subacute painful necrotising myopathy which may be associated with myoglobinuria, at times leading to acute renal failure. Clofibrate and epsilon aminocaproic acid are the drugs most frequently implicated, but a similar syndrome may occur in alcoholics and heroin addicts. Certain hypocholesterolaemic agents may induce myotonia by altering the sterol composition of the muscle cell membrane, while certain drugs including beta-adrenergic blockers and agonists, succinylcholine and diuretics may exacerbate or unmask pre-existing myotonia. In the syndrome of malignant hyperpyrexia, halothane, succinylcholine and various other agents may induce a potentially fatal state of muscular rigidity and hypermetabolism in susceptible individuals as a result of a defect in the calcium transport function of the sarcoplasmic reticulum and possibly of other cellular membranes. In corticosteroid myopathy, which is the most common form of drug-induced myopathy, there is selective atrophy of type 2 muscle fibres and the primary metabolic effect is an inhibition of RNA and protein synthesis, although protein degradation is also increased. Chloroquine and a number of related drugs with amphiphilic cationic properties may induce lysosomal storage myopathy, which may be associated with cardiomyopathy and with a more widespread form of lipidosis.

Myopathy due to epsilon amino-caproic acid

A subacute necrotizing myopathy developed in a patient treated with epsilon amino-caproic acid (EACA) for subarachnoid hemorrhage. The muscle biopsy showed features suggesting that the muscle fiber necrosis might have been due to capillary damage. An attempt to induce EACA myopathy in the rat was made, but no abnormality developed.

Experimental (-) emetine myopathy. Ultrastructural and morphometric observations

The ultrastructural changes induced by (-) emetine hydrochloride were studied in two skeletal muscles of the rat. (-) Emetine was administered at a dose level of 2 mg/kg for periods ranging from one to four weeks. Changes were noted after the one week stage and were progressive with all muscle components appearing to be affected. Myofibrillar changes included Z line streaming, rod formation, myofilament loss and contraction clumping. Mitochondrial degeneration was detected, but the most striking feature of the induced myopathy was the extensive membrane proliferation. The membranes were considered to be involved in the isolation of sarcoplasmic constitutents in the production of autophagic vacuoles. Morphometry was carried out in order to quantify some of the changes in the fibre components.

Drug-induced myopathies in man

Drug-induced diseases constitute up to 5% of hospital admissions,a figure which almost certainly understates the total morbidity due to drugs1. Sever drug-induced myopathies are uncommon, but milder forms may be more prevalent than is generally appreciated, since skeletal muscle constitutes some 45% of total body-weight and has a major metabolic role in addition to its mechanical function2. Knowledge of possible effects of drugs on the neuromuscular system is of increasing importance both because the range of therapeutic agents continues to expand and because the resulting syndromes, through usually reversible at the outset, may progress and lead to grave consequences if the drug responsible is not stopped. Drug-induced neuropathies3 will not be considered here, but it will be appreciated that muscle weakness may also be feature of such disorders and that some drugs may cause both a neuropathy and a myopathy. The features of the main drug-induced syndromes are summarised in the table. To these one could justifiably add the unwanted effects of srugs given for the treatment of central-nervous-system or neuromuscular disorders per se-e.g., the cholinergic block which may be produced by anticholinesterases alone or with corticosteroids in the myasthenic,4 and the profound weakness which may supervene after relief of spasticity with dantrolene sodium5.

Becker-type muscular dystrophy

This is a review of clinical, cardiologic, electrophysiologic, pathologic, and serum creatine kinase changes in eight families with slowly progressive X-linked Becker-type muscular dystrophy. All but one of the patients were able to walk until the age of 16 years, and most lived beyond 20. In every family, electromyography and muscle biopsy showed features which, on the basis of classical criteria, were interpreted as those of both myopathy and denervation, although among patients and among families, one or the other of these processes predominated. The most frequent biopsy picture was of fiber atrophy and hypertrophy, with many split and angulated fibers, and clumps of pyknotic nuclei. Necrosis, phagocytosis, regeneration, endomysial fibrosis, and some fatty infiltration were commonly seen. Review of a family originally described by Becker showed a similar biopsy picture; These pathologic changes are separable from those of Duchenne muscular dystrophy, but they often overlap with those seen in other chronic neuromuscular diseases.