Chances and shortcomins of adenovirus-mediated ATP7B gene transfer in Wilson disease: proof of principle demonstrated in a pilot study with LEC rats

Long-Term Correction of Copper Metabolism in Wilson's Disease Mice with AAV8 Vector Delivering Truncated ATP7B

Wilson's disease (WD) is an autosomal recessive disorder of copper metabolism caused by mutations in the ATP7B gene encoding a liver active copper transport enzyme. Gene therapy with adeno-associated virus (AAV) carrying full-length ATP7B, which is about 4.4 kb, was shown to rescue copper metabolism disorder in WD mouse model. However, due to its relatively large size, the AAV vector containing full-length ATP7B could be oversized for its packaging capacity, which could lead to inefficient packaging. To this purpose, we engineered a truncated ATP7B mutant (tATP7B) that is about 3.3 kb in length and used for AAV gene therapy for WD mice. In vitro test showed that the excretion of copper outside the cells could be achieved with tATP7B as efficient as the full-length ATP7B. In vivo delivery of tATP7B to WD mice by AAV8 vectors corrected their copper metabolisms and significantly rescued copper accumulation-related syndromes, including reduced urinary copper excretion, increased serum ceruloplasmin, and improved liver damages. Thus, our study demonstrated that AAV gene therapy based on truncated ATP7B is a promising strategy in the treatment of WD.

Determination of copper poisoning in Wilson's disease using laser ablation inductively coupled plasma mass spectrometry

Copper (Cu) is an essential trace element that is vital to the health of all living organisms. As a transition metal, it is involved in a myriad of biological processes. Balance studies estimated that the adult human requirement for copper is in the range of 1.3 to 2 mg per day. Cu deficiency alters immune function, neuropeptide synthesis and antioxidant defense, while the excess in Cu results in oxidative stress and progressive structural damage of mitochondrial and clinically in hepatic and/or neurological symptoms. This becomes particularly visible in Wilson's disease (WD) representing a rare autosomal recessive inherited disorder with a disease prevalence of about 1 in 30,000 people. The affected gene, i.e., ATP7B, belongs to the class of ATP-dependent, P-type Cu-transporting ATPases. To understand the pathomechanism in WD, several experimental models for studying WD were established. Independent studies performed in these models showed that the inactivation of the Atp7b gene results in a gradual increase in Cu in many organs during life span. However, the exact distribution of Cu and the potential impact of elevated Cu concentrations on other metals within the tissue are only sparely analyzed. Recently, novel laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS)-based protocols for metal bio-imaging in liver and brain were established. In the present review, we will discuss the methodological background of this innovative technique and summarize our experiences using LA-ICP-MS imaging in biological monitoring, exact measurement, and spatial assignment of metals within tissue obtained from Atp7b null mice and clinical specimens taken from patients suffering from genetically confirmed WD. Using WD as an example, the data discussed demonstrates that LA-ICP-MS has multi-element capability, allowing precise measurement and visualization of metals in the tissue with high spatial resolution, sensitivity, quantification ability, and exceptional reproducibility.

Accuracy of the radioactive copper incorporation test in the diagnosis of Wilson disease

BACKGROUND & AIMS

In Wilson disease (WD), copper accumulates in the liver and other tissues because of mutations in the ATP7B copper transporter gene. Early and effective anticopper treatment is crucial. However, routine diagnostic methods based on clinical findings, copper metabolism tests, liver biopsies and DNA analyses do not always provide a conclusive diagnosis. The aim was to evaluate radioactive copper incorporation as a diagnostic test.

METHODS

We included cases with a diagnosis of WD supported by radiocopper testing and later, when available, confirmed by DNA analysis. Incorporation of ⁶⁴ Cu was measured at 2, 24 and 48 hours following intravenous injection. Diagnostic accuracy (area under the receiver operating characteristic curve [AUC]), sensitivity, specificity and predictive value were assessed for 24 hours/2 hours and 48 hours/2 hours ⁶⁴ Cu ratios and compared with serum measurements of ceruloplasmin, copper, non-ceruloplasmin-bound copper and urinary 24-hours copper excretion.

RESULTS

Patients having two pathogenic ATP7B mutations (homozygotes/compound heterozygotes) (n = 74) had significantly lower 24 hours/2 hours and 48 hours/2 hours ⁶⁴ Cu ratios than heterozygote controls (n = 21) (mean 0.14 and 0.12 vs 0.49 and 0.63, respectively; both P < .001). Of note, 24 hours/2 hours and 48 hours/2 hours ⁶⁴ Cu ratios had excellent diagnostic accuracy, with AUCs approaching 1, and only 24-hours urinary copper excretion displayed similar positive features. Other copper metabolism tests studied had lower accuracy, specificity and sensitivity.

CONCLUSIONS

The radioactive copper test had excellent diagnostic accuracy and may be useful in the evaluation of new therapies aimed at restoring ATP7B function.

Rare ER protein misfolding-mistrafficking disorders: Therapeutic developments

The presence of a functional protein at the appropriate location in the cell is the result of the processes of transcription, translation, folding and trafficking to the correct destination. There are numerous diseases that are caused by protein misfolding, mainly due to mutations in the respective gene. The consequences of this misfolding may be that proteins effectively lose their function, either by being removed by the cellular quality control machinery or by accumulating at the incorrect intracellular or extracellular location. A number of mutations that lead to protein misfolding and affect trafficking to the final destination, e.g. Cystic fibrosis, Wilson's disease, and Progressive Familial Intrahepatic 1 cholestasis, result in proteins that retain partial function if their folding and trafficking is restored either by molecular or pharmacological means. In this review, we discuss several mutant proteins within this class of misfolding diseases and provide an update on the status of molecular and therapeutic developments and potential therapeutic strategies being developed to counter these diseases.

Update on the clinical management of Wilson's disease

Wilson's disease (WD), albeit relatively rare, is an important genetic metabolic disease because of highly effective therapies that can be lifesaving. It is a great imitator and requires a high index of suspicion for correct and timely diagnosis. Neurologic, psychiatric and hepatologic problems in WD are very nonspecific, and we discuss the most common clinical phenotypes. The diagnosis remains laboratory based, and here we review the most important challenges and pitfalls in laboratory evaluation of WD, including the emerging role of genetic testing in WD diagnosis. WD is a monogenic disorder but has very high allelic heterogeneity with >500 disease-causing mutations identified, and new insights into phenotype-genotype correlations are also reviewed. The gold standard of therapy is chelation of excessive copper, but many unmet needs exist because of possible clinical deterioration in treated patients and potential adverse effects associated with currently available chelating medications. We also review the most promising novel therapeutic approaches, including chelators targeting specific cell types, cell transplantation and gene therapy.

Long-term metabolic correction of Wilson's disease in a murine model by gene therapy

BACKGROUND & AIMS

Wilson's disease (WD) is an autosomal recessively inherited copper storage disorder due to mutations in the ATP7B gene that causes hepatic and neurologic symptoms. Current treatments are based on lifelong copper chelating drugs and zinc salts, which may cause side effects and do not restore normal copper metabolism. In this work we assessed the efficacy of gene therapy to treat this condition.

METHODS

We transduced the liver of the Atp7b(-/-) WD mouse model with an adeno-associated vector serotype 8 (AAV8) encoding the human ATP7B cDNA placed under the control of the liver-specific α1-antitrypsin promoter (AAV8-AAT-ATP7B). After vector administration we carried out periodic evaluation of parameters associated with copper metabolism and disease progression. The animals were sacrificed 6months after treatment to analyze copper storage and hepatic histology.

RESULTS

We observed a dose-dependent therapeutic effect of AAV8-AAT-ATP7B manifested by the reduction of serum transaminases and urinary copper excretion, normalization of serum holoceruloplasmin, and restoration of physiological biliary copper excretion in response to copper overload. The liver of treated animals showed normalization of copper content and absence of histological alterations.

CONCLUSIONS

Our data demonstrate that AAV8-AAT-ATP7B-mediated gene therapy provides long-term correction of copper metabolism in a clinically relevant animal model of WD providing support for future translational studies.

Cell therapy to remove excess copper in Wilson's disease

To achieve permanent correction of Wilson's disease by a cell therapy approach, replacement of diseased hepatocytes with healthy hepatocytes is desirable. There is a physiological requirement for hepatic ATP7B-dependent copper (Cu) transport in bile, which is deficient in Wilson's disease, producing progressive Cu accumulation in the liver or brain with organ damage. The ability to repopulate the liver with healthy hepatocytes raises the possibility of cell therapy in Wilson's disease. Therapeutic principles included reconstitution of bile canalicular network as well as proliferation in transplanted hepatocytes, despite toxic amounts of Cu in the liver. Nonetheless, cell therapy studies in animal models elicited major differences in the mechanisms driving liver repopulation with transplanted hepatocytes in Wilson's disease versus nondiseased settings. Recently, noninvasive imaging was developed to demonstrate Cu removal from the liver, including after cell therapy in Wilson's disease. Such developments will help advance cell/gene therapy approaches, particularly by offering roadmaps for clinical trials in people with Wilson's disease.

PET with 64Cu-histidine for noninvasive diagnosis of biliary copper excretion in Long-Evans cinnamon rat model of Wilson disease

Excretion of copper into bile requires the copper transporter Atp7b, which is deficient in Wilson disease. We hypothesized that a radiocopper-histidine complex would be effective for diagnosing Wilson disease by molecular imaging and tested this hypothesis in the Long-Evans cinnamon (LEC) rat model with Atp7b deficiency.

METHODS

We complexed (64)Cu to l-histidine and analyzed clearance from blood, uptake in tissues, and excretion in bile of healthy Long-Evans agouti (LEA) rats versus LEC rats modeling Wilson disease. Sixty-minute dynamic PET recordings were obtained in LEA and LEC rats. Possible effects of acute and chronic liver injury induced by carbon tetrachloride were studied in LEA rats. Atp7b deficiency in LEC rats was reconstituted by transplantation of healthy cells to establish the specificity of findings.

RESULTS

Examination of blood, tissue, and bile showed that in healthy rats, radiocopper was incorporated in the liver, followed by rapid excretion in bile. Corresponding blood, tissue, and bile studies in LEC rats showed incorporation of radiocopper in the liver but without copper excretion in bile, leading to hepatic retention of the radiotracer. PET showed onset of copper clearance in the liver of LEA rats, whereas liver copper content progressively increased in LEC rats during the 1-h period. Hepatic radiocopper excretion was not altered by either acute or chronic liver injury. In LEC rats with liver repopulation by transplanted healthy hepatocytes, excretion of radiocopper confirmed that Atp7b was responsible for this effect.

CONCLUSION

Imaging with the radiocopper-histidine complex successfully identified Atp7b-dependent biliary copper excretion. This principle will advance molecular imaging for Wilson disease.

Wilson's disease

In the almost 100 years since Wilson's description of the illness that now bears his name, tremendous advances have been made in our understanding of this disorder. The genetic basis for Wilson's disease - mutation within the ATP7B gene - has been identified. The pathophysiologic basis for the damage resulting from the inability to excrete copper via the biliary system with its consequent gradual accumulation, first in the liver and ultimately in the brain and other organs and tissues, is now known. This has led to the development of effective diagnostic and treatment modalities that, although they may not eliminate the disorder, do provide the means for efficient diagnosis and effective amelioration if carried out in a dedicated and persistent fashion. Nevertheless, Wilson's disease remains both a diagnostic and treatment challenge for physician and patient. Its protean clinical manifestations make diagnosis difficult. Appropriate diagnostic evaluations to confirm the diagnosis and institute treatment can be confusing. In this chapter, the clinical manifestations, diagnostic evaluation, and treatment approaches for Wilson's disease are discussed.

Paediatric liver transplantation for metabolic disorders. Part 2: Metabolic disorders with liver lesions

Liver based metabolic disorders account for 10 to 15% of the indications for paediatric liver transplantation. In the last three decades, important progress has been made in the understanding of these diseases, and new therapies have emerged. Concomitantly, medical and surgical innovations have lead to improved results of paediatric liver transplantation, patient survival nowadays exceeding 80% 10 year after surgery with close to normal quality of life in most survivors. This review is a practical update on medical therapy, indications and results of liver transplantation, and potential future therapies, for the main liver based metabolic disorders in which paediatric liver transplantation may be considered. Part 1 focuses on metabolic based liver disorders without liver lesions, and part 2 on metabolic liver diseases with liver lesions.

Wilson disease

Wilson disease is an inherited autosomal recessive disorder of copper balance leading to hepatic damage and neurological disturbance of variable degree. The defective gene, ATP7B, encodes a hepatic copper-transporting protein, which plays a key role in human copper metabolism. Our knowledge of the genetic basis of Wilson disease has increased dramatically; however, understanding of genotype-phenotype correlation and multifarious effects of copper toxicity as basis for targeted and individualised therapy strategies is still insufficient. Clinical manifestations are related to copper accumulation predominantly in the liver and brain and include hepatic disease ranging from mild hepatitis to acute liver failure or cirrhosis and/or neurological symptoms such as dystonia, tremor, dysarthria, psychiatric disturbances. Mixed presentations occur frequently. Early recognition by means of clinical, biochemical or genetic examination and initiation of therapy with copper chelators, zinc salts or even liver transplantation in cases of acute and chronic liver failure are essential for favourable outcome.

Diagnosis of Wilson's disease: a comprehensive review

Wilson's disease is an autosomal recessive disorder of copper metabolism. The culprit gene is ATP7B. The worldwide prevalence is about 1 in 30,000, which may vary by population. Higher prevalence rates were reported using more sensitive screening techniques and pilot population screening. Typical presentations include neuropsychiatric and hepatic dysfunction, whereas atypical presentations are protean. Diagnosis relies on a high clinical suspicion, typical neurological symptoms, presence of Kayser-Fleischer rings, and reduced serum ceruloplasmin concentration. The conventional value of < 0.20 g/l is not a universal diagnostic value. Age of the subjects and analytical variations should be considered when interpreting these levels. Patients with inconclusive findings require further investigations such as 24 h urinary free-copper excretion, penicillamine challenge test, liver copper measurement, and detection of gene mutations. Direct molecular diagnosis remains the most decisive tool. Other tests such as non-ceruloplasmin-bound copper are unreliable. Potential pitfalls and limitations of these diagnostic markers are critically reviewed in this paper. The mainstays of therapy are trientine, penicillamine, and/or zinc. Liver transplantation is lifesaving for those with advanced disease. Ceruloplasmin oxidase activity and serum free-copper concentration should be monitored in patients on long-term de-coppering therapy to prevent iatrogenic copper deficiency.

Wilson's disease

Progressive hepatolenticular degeneration, or Wilson's disease, is a genetic disorder of copper metabolism. Knowledge of the clinical presentations and treatment of the disease are important both to the generalist and to specialists in gastroenterology and hepatology, neurology, psychiatry, and paediatrics. Wilson's disease invariably results in severe disability and death if untreated. The diagnosis is easily overlooked but if discovered early, effective treatments are available that will prevent or reverse many manifestations of this disorder. Studies have identified the role of copper in disease pathogenesis and clinical, biochemical, and genetic markers that can be useful in diagnosis. There are several chelating agents and zinc salts for medical therapy. Liver transplantation corrects the underlying pathophysiology and can be lifesaving. The discovery of the Wilson's disease gene has opened up a new molecular diagnostic approach, and could form the basis of future gene therapy.

Wilson's disease: an update

Wilson's disease (WD) is an inborn error of copper metabolism caused by a mutation to the copper-transporting gene ATP7B. The disease has an autosomal recessive mode of inheritance, and is characterized by excessive copper deposition, predominantly in the liver and brain. Diagnosis of the condition depends primarily on clinical features, biochemical parameters and the presence of the Kayser-Fleischer ring, and a new diagnostic scoring system has recently been proposed. Mutations in ATP7B can occur anywhere along the entire 21 exons, which makes the identification of gene defects particularly challenging. Identification of carriers and presymptomatic family members of affected individuals is achieved by polymerase-chain-reaction-based marker analysis. The traditional treatment for WD is based on copper chelation with agents such as D-penicillamine, but use of this drug has been questioned because of reported side effects. The use of agents such as trientine and ammonium tetrathiomolybdate has been advocated, although results of long-term trials are awaited. In selected cases, orthotropic hepatic transplantation can reverse the basic metabolic abnormality in WD and improve both hepatic and neurological symptoms. Studies of the underlying defects in ATP7B and its suspected modifiers ATOX1 and COMMD1 are expected to unravel the disease's genotype-phenotype correlation, and should lead to the design of improved drugs for ameliorating the suffering of patients.

Lentiviral gene transfer ameliorates disease progression in Long-Evans cinnamon rats: an animal model for Wilson disease

OBJECTIVE

Wilson disease is a copper storage disorder caused by mutations in the ATP7B gene leading to liver cirrhosis. It has previously been shown that lentiviral vectors can govern an efficient delivery and stable expression of a transgene. The aim of this pilot study was to prove the principle of a lentiviral gene transfer in the Long-Evans cinnamon (LEC) rat, an animal model of Wilson disease.

MATERIAL AND METHODS

LEC rats were treated either by systemic application of lentiviral vectors or by intrasplenic transplantation of LEC-rat hepatocytes lentivirally transduced with ATP7B. The ATP7B gene expression was analyzed by RT-PCR and immunofluorescence analysis. The therapeutic effect was assessed by analysis of liver histology, serum ceruloplasmin oxidase activity, and liver copper content.

RESULTS

Hepatic expression of the transgene was detected at different time-points post-treatment and lasted for up to 24 weeks (end of experiment). Liver copper levels were lowered in all treatment groups compared to untreated LEC rats. Twenty-four weeks after treatment, the area of the examined liver-tissue sections occupied by fibrosis was 48.3-57.9% in untreated LEC rats and 10.7-19.8% in rats treated with cell therapy. In systemically treated rats, only small fibrous septa could be observed.

CONCLUSIONS

These data prove for the first time that lentiviral ATP7B gene transfer is feasible in Wilson disease. In our pilot study the systemic approach was more promising in ameliorating disease progression than the transplantation of lentivirally transduced hepatocytes.

Morbus Wilson

Wilson disease is an autosomal recessive inherited disorder of human copper metabolism that leads to neurological symptoms and hepatic damage of variable degree. The affected gene ATP7B encodes a hepatic copper transport protein, which plays a key role in human copper metabolism. Clinical symptoms are complex with neurologic symptoms such as tremor, dysarthria, psychiatric disorders etc., predominant hepatic disease or mixed forms. Copper deposition in the liver results in acute liver failure, chronic hepatitis or liver cirrhosis. Early recognition by means of clinical, biochemical or genetic examination and early initiation of therapy with chelators or zinc-salts are essential for outcome and prognosis. Liver transplantation is an alternative in cases with acute and chronic liver failure and cures the hepatic disease. Frequent monitoring of drug therapy, adverse effects, and compliance is critical for the prognosis of the disease.

Wilson disease: new insights into pathogenesis, diagnosis, and future therapy

Wilson disease is caused by disease-specific mutations of the copper transporting ATPase, ATP7B. The diagnosis is established by clinical and biochemical means, though advances in molecular diagnostics will someday permit de novo diagnosis. The patient may present with hepatic, neurologic, or psychiatric symptoms, or a combination of these. Both environmental and extragenic effects contribute to the varied phenotypic presentations of this disease. Patients can be treated effectively with chelating agents or zinc salts, or with liver transplantation. Liver cell transplant and gene therapy offer potential cures for this disorder, but at present only data from preclinical studies on animal models are available. Future advances in immunotolerization and gene therapy will likely enable human trials for treatment of this disorder and other genetic disorders of hepatic metabolism.

Wilson disease: pathophysiology, diagnosis, treatment, and screening

Wilson disease is an autosomal recessive condition of copper metabolism that was once considered fatal. The identification of the gene for Wilson disease has led to a better understanding of the molecular defect underlying this disorder and has impacted on disease diagnosis for some individuals. Medical therapy with chelating agents or zinc salts remains the mainstay of therapy for most patients, and liver transplant is lifesaving for those with advanced disease refractory to medical therapy or with fulminant hepatic failure. Future cell-based and genetic therapies may provide a cure for this disorder.