Effects of trientine and penicillamine on intestinal copper uptake: A mechanistic 64 Cu PET/CT study in healthy humans

BACKGROUND AND AIMS

Trientine (TRI) and D-penicillamine (PEN) are used to treat copper overload in Wilson disease. Their main mode of action is thought to be through the facilitation of urinary copper excretion. In a recent study, TRI was noninferior to PEN despite lower 24-hour urinary copper excretion than PEN. We tested whether TRI and/or PEN also inhibit intestinal copper absorption.

APPROACH AND RESULTS

Sixteen healthy volunteers were examined with positron emission tomography (PET)/CT 1 and 15 hours after an oral Copper-64 ( 64 Cu) dose. They then received 7 days of either PEN or TRI (trientine tetrahydrochloride), after which the 64 Cu PET/CT scans were repeated. Venous blood samples were also collected. Pretreatment to posttreatment changes of the hepatic 64 Cu uptake reflect the effect of drugs on intestinal absorption. 64 Cu activity was normalized to dose and body weight and expressed as the mean standard uptake value. TRI (n=8) reduced hepatic 64 Cu activity 1 hour after 64 Cu dose from 6.17 (4.73) to 1.47 (2.97) standard uptake value, p <0.02, and after 15 hours from 14.24 (3.09) to 6.19 (3.43), p <0.02, indicating strong inhibition of intestinal 64 Cu absorption. PEN (n=8) slightly reduced hepatic standard uptake value at 15 hours, from 16.30 (5.63) to 12.17 (1.44), p <0.04.

CONCLUSIONS

In this mechanistic study, we show that TRI inhibits intestinal copper absorption, in addition to its cupriuretic effect. In contrast, PEN has modest effects on the intestinal copper absorption. This may explain why TRI and PEN are equally effective although urinary copper excretion is lower with TRI. The study questions whether the same therapeutic targets for 24-hour urinary excretion apply to both drugs.

Effects of tetrathiomolybdate on copper metabolism in healthy volunteers and in patients with Wilson disease

BACKGROUND & AIMS

In Wilson disease (WD), copper accumulates in the liver and brain causing disease. Bis-choline tetrathiomolybdate (TTM) is a potent copper chelator that may be associated with a lower risk of inducing paradoxical neurological worsening than conventional therapy for neurologic WD. To better understand the mode of action of TTM, we investigated its effects on copper absorption and biliary excretion.

METHODS

In a double-blind randomized setting, hepatic 64Cu activity was examined after orally administered 64Cu by PET/CT in 16 healthy volunteers before and after seven days of TTM treatment (15 mg/d) or placebo. Oral 64Cu was administered one hour after the final TTM dose. Changes in hepatic 64Cu activity reflected changes in intestinal 64Cu uptake. Additionally, in four patients with WD, the distribution of 64Cu in venous blood, liver, gallbladder, kidney, and brain was followed after i.v. 64Cu dosing for up to 68 hours before and after seven days of TTM (15 mg/day), using PET/MRI. Increased gallbladder 64Cu activity was taken as evidence of increased biliary 64Cu excretion.

RESULTS

In healthy volunteers, TTM reduced intestinal 64Cu uptake by 82% 15 hours after the oral 64Cu dose. In patients with WD, gallbladder 64Cu activity was negligible before and after TTM, while TTM effectively retained 64Cu in the blood, significantly reduced hepatic 64Cu activity at all time-points and significantly reduced cerebral 64Cu activity two hours after the intravenous 64Cu dose.

CONCLUSIONS

While we did not show an increase in biliary excretion of 64Cu following TTM administration, we demonstrated that TTM effectively inhibited most intestinal 64Cu uptake and retained 64Cu in the blood stream, limiting the exposure of organs like the liver and brain to 64Cu.

IMPACT AND IMPLICATIONS

Bis-choline tetrathiomolybdate (TTM) is an investigational copper chelator being developed for the treatment of Wilson disease. In animal models of Wilson disease, TTM has been shown to facilitate biliary copper excretion. In the present human study, TTM surprisingly did not facilitate biliary copper excretion but instead reduced intestinal copper uptake to a clinically significant degree. Our study builds on our understanding of human copper metabolism and the mechanism of action of TTM.

Distribution of non-ceruloplasmin-bound copper after i.v. 64Cu injection studied with PET/CT in patients with Wilson disease

Background & Aims

In Wilson disease (WD), copper accumulation and increased non-ceruloplasmin-bound copper in plasma lead to liver and brain pathology. To better understand the fate of non-ceruloplasmin-bound copper, we used PET/CT to examine the whole-body distribution of intravenously injected 64-copper (64Cu).

Methods

Eight patients with WD, five heterozygotes, and nine healthy controls were examined by dynamic PET/CT for 90 min and static PET/CT up to 20 h after injection. We measured 64Cu activity in blood and tissue and quantified the kinetics by compartmental analysis.

Results

Initially, a large fraction of injected 64Cu was distributed to extrahepatic tissues, especially skeletal muscle. Thus, across groups, extrahepatic tissues accounted for 45-58% of the injected dose (%ID) after 10 min, and 45-55% after 1 h. Kinetic analysis showed rapid exchange of 64Cu between blood and muscle as well as adipose tissue, with 64Cu retention in a secondary compartment, possibly mitochondria. This way, muscle and adipose tissue may protect the brain from spikes in non-ceruloplasmin-bound copper. Tiny amounts of cerebral 64Cu were detected (0.2%ID after 90 min and 0.3%ID after 6 h), suggesting tight control of cerebral copper in accordance with a cerebral clearance that is 2-3-fold lower than in muscle. Compared to controls, patients with WD accumulated more hepatic copper 6-20 h after injection, and also renal copper at 6 h.

Conclusion

Non-ceruloplasmin-bound copper is initially distributed into a number of tissues before being redistributed slowly to the eliminating organ, the liver. Cerebral uptake of copper is extremely slow and likely highly regulated. Our findings provide new insights into the mechanisms of copper control.

Impact and implications

Maintaining non-ceruloplasmin-bound copper within the normal range is an important treatment goal in WD as this "free" copper is considered toxic to the liver and brain. We found that intravenously injected non-ceruloplasmin-bound copper quickly distributed to a number of tissues, especially skeletal muscle, subcutaneous fat, and the liver, while uptake into the brain was slow. This study offers new insights into the mechanisms of copper control, which may encourage further research into potential new treatment targets.

Clinical trial number

2016-001975-59.

Positron Emission Tomography Using 64-Copper as a Tracer for the Study of Copper-Related Disorders

Copper is an essential trace element, functioning in catalysis and signaling in biological systems. Radiolabeled copper has been used for decades in studying basic human and animal copper metabolism and copper-related disorders, such as Wilson disease (WD) and Menke's disease. A recent addition to this toolkit is 64-copper (⁶⁴Cu) positron emission tomography (PET), combining the accurate anatomical imaging of modern computed tomography (CT) or magnetic resonance imaging (MRI) scanners with the biodistribution of the ⁶⁴Cu PET tracer signal. This allows the in vivo tracking of copper fluxes and kinetics, thereby directly visualizing human and animal copper organ traffic and metabolism. Consequently, ⁶⁴Cu PET is well-suited for evaluating clinical and preclinical treatment effects and has already demonstrated the ability to diagnose WD accurately. Furthermore, ⁶⁴Cu PET/CT studies have proven valuable in other scientific areas like cancer and stroke research. The present article shows how to perform ⁶⁴Cu PET/CT or PET/MR in humans. Procedures for ⁶⁴Cu handling, patient preparation, and scanner setup are demonstrated here.

Case report: Huppke–Brendel syndrome in an adult, mistaken for and treated as Wilson disease for 25 years

Background

Huppke–Brendel (HB) syndrome is an autosomal recessive disease caused by variants in the SLC33A1 gene. Since 2012, less than ten patients have been reported, none survived year six. With neurologic involvement and ceruloplasmin deficiency, it may mimic Wilson disease (WD).

Objectives and methods

We report the first adult patient with HB.

Results

The patient suffered from moderate intellectual disability, partial hearing loss, spastic ataxia, hypotonia, and unilateral tremor of parkinsonian type. At age 29, she was diagnosed with WD based on neurology, elevated 24H urinary copper, low ceruloplasmin, and pathological ⁶⁵Cu test. Approximately 25 years later, genetic testing did not support WD or aceruloplasminemia. Full genome sequencing revealed two likely pathogenic variants in SLC33A1 which combined with re-evaluation of neurologic symptoms and MRI suggested the diagnosis of HB.

Conclusion

Adult patients with HB exist and may be confused with WD. Low ceruloplasmin and the absence of ATP7B variants should raise suspicion.

Effect of oral zinc regimens on human hepatic copper content: a randomized intervention study

Zinc inhibits intestinal copper uptake, an effect utilized for treating Wilson’s disease (WD). We used copper-64 (⁶⁴Cu) PET/CT to examine how much four weeks of treatment with different zinc regimens reduced the hepatic ⁶⁴Cu content after oral ⁶⁴Cu administration and test if alternative regimens were noninferior to the standard regimen of zinc acetate 50 mg × 3 daily. Forty healthy persons were randomized to four different zinc protocols. The WD standard treatment zinc acetate 50 mg × 3 reduced the hepatic ⁶⁴Cu content from 26.9 ± 7.5% to 13.3 ± 5.6% of the administered ⁶⁴Cu. Zinc gluconate 50 mg × 3 was noninferior (P = 0.02) (35.8 ± 9.0% to 17.4 ± 7.5%). Zinc acetate 150 mg × 1 (33.1 ± 9.9% to 17.4 ± 7.5%) and zinc gluconate 150 mg × 1 (28.1 ± 6.7% to 22.0 ± 6.7%) were less effective. These effects were intra- and inter-individually highly variable, and 14% had no effect of any zinc regimen, which may explain disparities in zinc treatment efficacy in WD patients.

Cognitive impairment in stable Wilson disease across phenotype

In Wilson disease (WD), mutations in the gene encoding the ATP7B copper transport protein causes accumulation of copper especially in liver and brain. WD typically presents with hepatic and/or neuropsychiatric symptoms. Impaired cognition is a well-described feature in patients with neurological WD, while the reports on cognition in hepatic WD patients are fewer and less conclusive. We examined cognition in a cohort of WD patients with both phenotypes. In this cross-sectional pilot study, we investigated cognition in 28 stable Danish WD patients by the PortoSystemic Encephalopathy (PSE) and the Continuous Reaction Time (CRT) tests. Half of the patients were female, and their median age was 35.5 years (IQR 24.5). Their phenotype was hepatic in 14 (50%), neurologic in 10 (36%) and mixed in 4 (14%). The duration of treatment was > 2 year in all patients, and their condition was stable as judged by urinary copper excretion, liver enzymes, and clinical assessment. The hepatic patients did not show signs of liver failure. In total, 16 (57%) patients performed worse than normal in the PSE and/or the CRT tests. The two tests were correlated (rho = 0.60, p = 0.0007), but neither correlated with phenotype, MELD-, Child-Pugh score, 24 h-U-Cu, or treatment type. Measurable cognitive impairment was present in more than half of the stable WD patients independent of phenotype. Thus, our data questions the existence of a purely hepatic phenotype.