Reversible pancytopenia secondary to treatment with tetrathiomolybdate

Advances in Treatment of Wilson Disease

Background

Wilson disease (WD) is an inherited neurometabolic disorder that results in excessive copper deposition in the liver and the brain, affecting children and young adults. Without treatment the disease is invariably fatal. Though treatments for WD have been available since the 1950s, the disease continues to be associated with considerable morbidity and mortality because of missed diagnosis, and delayed or inadequate treatment. In this paper we survey WD-related literature in order to review recent advances in WD treatment.

Methods

We performed a literature search using the PubMed database for articles relating to WD and its medical treatment. We reviewed the articles, and cross-references of relevant articles, to summarize the current practices for treatment of WD.

Results

The survey shows that if WD is properly treated, in most patients the liver can be stabilized, even severe neurological disability reversed, and patients can resume normal lives.

Discussion

Medical treatment for WD includes use of copper chelators (penicillamine, trientine, dimercaprol, dimercaptopropane sulfonate, and ammonium tetrathiomolybdate) and drugs that decrease gastrointestinal copper absorption. Our knowledge of the treatment approaches has benefited from the large systematic clinical studies that have been conducted over the last decade. For each drug used to treat WD, we surveyed its development, indication for use, dosing, efficacy, and adverse effects.

Tetrathiomolybdate anticopper therapy for Wilson's disease inhibits angiogenesis, fibrosis and inflammation

The need for agents to lower body copper in Wilson's disease, a disease which results from copper toxicity has been the driving force for the development of the effective anticopper drugs penicillamine, trientine, zinc, and now tetrathiomolybdate (TM). Because of its rapid action, potency, and safety, TM is proving to be a very effective drug for initial treatment of acutely ill Wilson's disease patients. Beyond this, TM has antiangiogenic effects, because many proangiogenic cytokines require normal levels of copper. This has led to use of TM in cancer, where it is generally effective in animal tumor models, and has shown efficacy in preliminary clinical studies. Most recently, it has been found that TM has antifibrotic and antiinflammatory effects through inhibition of profibrotic and proinflammatory cytokines.

Recognition, diagnosis, and management of Wilson's disease

Wilson's disease is a relatively rare inherited disorder of copper accumulation and toxicity, caused by a defect in an enzyme that is part of the pathway of biliary excretion of excess copper. Clinically, patients usually present as older children or young adults with hepatic, neurologic, or psychiatric manifestations, or some combination of these. Wilson's disease is unusual among genetic diseases in that it can be very effectively treated. The prevention of severe permanent damage depends upon early recognition and diagnosis by the physician, followed by appropriate anticopper treatment. Anticopper treatments have evolved considerably since the days when the only drug available was penicillamine. Zinc is now the recommended therapy for long-term management of the disease.

Molybdenum

Molybdenum does not exist naturally in the pure metallic form and of the 5 oxidation states (2-6) the predominant species are Mo(IV) and Mo(VI). Molybdenum rapidly polymerizes to a wide variety of complex polymolybdate compounds in solution. The vast majority of molybdenum is used in metallurgical applications (stainless steel, cast-iron alloys). Ammonium tetrathiomolybdate is an experimental chelating agent for Wilson's disease. For the general population, the diet is the most important source of molybdenum and concentrations in water and air usually are negligible. The average daily dietary intake is about 0.1-0.5 mg m.o. Molybdenum is an essential element with relatively low toxicity. Enzymes containing molybdenum catalyze basic metabolic reactions in the carbon, sulfur, and nitrogen cycles. Elimination of molybdenum occurs via the kidney and usually is complete within several weeks. Molybdenosis (teart) is a form of molybdenum toxicity that produces a disease in ruminants similar to copper-deficiency. Little data are available on the human toxicity of molybdenum. A gout-like syndrome and pneumoconiosis have been associated with excessive concentrations of molybdenum, but the inadequate design of the studies prevents an adequate determination of the etiology of these effects.

Wilson disease

Wilson disease is a recessively inherited disorder of copper transport. Clinical features are highly variable, with any combination of neurological, hepatic or psychiatric illness. The age of onset varies from 3 to 50 years of age. Diagnosis is challenging because no specific combination of clinical or biochemical features is necessarily definitive. The genetic defect is due to a variety of abnormalities in a copper-transporting membrane ATPase. Most of the more than 80 mutations are present at a low frequency, and mutations differ between ethnic groups. At least two mutations are sufficiently common to aid in rapid diagnosis, in European and Asian populations respectively. Molecular analysis can provide a definitive diagnosis for asymptomatic sibs. Treatment, using chelating agents or zinc, is most effective when started before permanent tissue damage occurs.

Pediatric gastroenterology. Update on metabolic liver disease

Wilson's disease, genetic and neonatal hemochromatosis, protoporphyria, tyrosinemia, and alpha1-antitrypsin deficiency are updated. Cost effectiveness of screening is discussed. Current therapies are evaluated, including the role of transplantation. The molecular biologic technique PCR is covered. Gene therapy is introduced.

Practical recommendations and new therapies for Wilson's disease

Wilson's disease is an inherited disorder of copper accumulation. The basic defect is a failure of excretion of excess copper in the bile by the liver for loss in the stool. The accumulating copper causes damage primarily to the liver and the brain. Patients typically present in the second to the fourth decades of life with liver disease, a neurological disease of the movement disorder type, or a wide array of behavioural disturbances. Because the manifestations of Wilson's disease are so protean, and the disease masquerades so well as something else, recognition of the possibility of Wilson's disease is a major problem, leading to serious underdiagnosis of the disease. Excellent therapies exist for both the prophylaxis and treatment of Wilson's disease. The longer recognition and diagnosis are delayed, the greater the risk of permanent damage to liver and/or brain. The availability of effective therapy and the risks in delay or therapy make the earliest possible diagnosis critical. Once the disease comes under consideration, a series of diagnostic steps can be undertaken which almost always establish or rule out the diagnosis of Wilson's disease. These include urine copper, blood ceruloplasmin, slit lamp examination for Kayser-Fleischer rings, and liver biopsy with quantitative copper assay. Currently, there are 4 drugs being used as anticopper agents in Wilson's disease. These are zinc, which blocks intestinal absorption of copper, penicillamine and trientine, both of which are chelators that increase urinary excretion of copper, and tetrathiomolybdate which forms a tripartite complex with copper and protein, and can block copper absorption from the intestine, or render blood copper non-toxic. Zinc is clearly the treatment of choice, in our opinion, for maintenance therapy, for the treatment of the presymptomatic patient from the beginning and for the treatment of the pregnant patient, because of its complete efficacy and lack of toxicity. For the initial treatment of the patient presenting with mild liver failure, we empirically use a combination of trientine and zinc. Trientine gives a strong, fast, negative copper balance, and zinc induces hepatic metallothionein, which sequesters hepatic copper. For the initial treatment of patients presenting with neurological disease we use an experimental drug, tetrathiomolybdate, which provides rapid, safe control of copper. These latter patients are at great risk of serious permanent neurological worsening with penicillamine, and zinc is too slow-acting, in our judgment, to be optimal.

Thiotungstate-copper interactions II. The effects of tetrathiotungstate on systemic copper metabolism in normal and copper-treated rats

The intraperitoneal administration of tetrathiotungstate to rats (6-17.4 mg W/Kg BW) caused profound changes in copper metabolism in both normal rats and in rats pretreated with copper. Plasma copper associated with albumin increased, liver copper, particularly cytosol copper, was depleted, and biliary excretion was increased. There was also a movement of copper to higher molecular weight proteins in both liver cytosol and bile. In contrast to penicillamine, tetrathiotungstate did not increase liver cytosolic apometallothionein levels and reduced the rise provoked by copper. Metallothionein-bound copper was removed. Ceruloplasmin oxidase activity was inhibited and there was evidence for increased movement of copper into subcellular organelles, probably lysosomes. It is concluded that tetrathiotungstate has a genuine "decoppering" effect and could be considered as an alternative to thiomolybdates in the treatment of copper storage diseases.

Copper and liver disease

There has been some limited progress in the understanding of the basic defect in Wilson disease and the gene concerned has been located to the chromosome region 13q14. Treatment with zinc has emerged as a definite alternative to penicillamine administration and some shortcomings and/or hazards of both forms of therapy have emerged as their modes of action have been studied more carefully. Tetrathimolybdate may have a place in treatment, especially when rapid complexing of copper is important. Hepatic copper accumulation occurs in a number of cholestatic diseases and they play an important part in pathogenesis and can occasionally lead to neurologic toxic effects. Copper overload in the newborn period when biliary excretion of copper is inefficient may establish a vicious cycle of copper accumulation and liver damage in Indian childhood cirrhosis and less frequently in babies in other countries.