Electrophysiological parameters that contribute to the pathogenesis of familial amyloid polyneuropathy caused by transthyretin mutations

Patisiran, an RNAi therapeutic for hereditary transthyretin-mediated amyloidosis: Sub-analysis in Taiwanese patients from the APOLLO study

BACKGROUND

To examine the efficacy and safety of patisiran, an RNA interference therapeutic, in patients from Taiwan with hereditary transthyretin-mediated (hATTR) amyloidosis with polyneuropathy.

METHODS

The APOLLO phase 3 trial included patients from Taiwan who received patisiran 0.3 mg/kg intravenously or placebo once every 3 weeks (q3w) for 18 months (18 M), followed by patisiran 0.3 mg/kg q3w in an ongoing global open-label extension (OLE) study. The primary endpoint was change from baseline in modified Neuropathy Impairment Score +7 (mNIS+7) at 18 M.

RESULTS

Eighteen Taiwanese patients were enrolled in APOLLO (patisiran, n = 8; placebo, n = 10; all A97S gene variant) and 14 continued in the global OLE. In this Taiwanese sub-population, beneficial treatment effects at 18 M were observed in mNIS+7 (least squares mean difference in change from baseline [patisiran-placebo], -26.5 points; 95% confidence interval: -45.5, -7.5). Patients who switched from placebo to patisiran demonstrated slowing of polyneuropathy progression at month 12 in the global OLE, while those who received patisiran in APOLLO maintained the beneficial treatment effects. Patisiran had an acceptable safety profile in the Taiwanese sub-population.

CONCLUSION

This analysis suggests that patisiran is well tolerated and may provide a substantial clinical benefit for Taiwanese patients with hATTR amyloidosis with polyneuropathy.

TRIAL REGISTRATION INFORMATION

The studies were registered on the ClinicalTrials.gov. The APOLLO study ClinicalTrials.gov identifier is NCT01960348 (https://clinicaltrials.gov/ct2/show/NCT01960348), with the registration date of October 10, 2013, and the first patient was enrolled on December 13, 2013. For the global OLE, the ClinicalTrials.gov identifier is NCT02510261 (https://clinicaltrials.gov/ct2/show/NCT02510261) with the registration date of July 29, 2015, and the first patient was enrolled on July 13, 2015.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that treatment with patisiran is safe and efficacious in Taiwanese patients with hereditary transthyretin-mediated amyloidosis with polyneuropathy.

Amyloid-β Effects on Peripheral Nerve: A New Model System

Although there are many biochemical methods to measure amyloid-β (Aβ)42 concentration, one of the critical issues in the study of the effects of Aβ42 on the nervous system is a simple physiological measurement. The in vitro rat sciatic nerve model is employed and the nerve action potential (NAP) is quantified with different stimuli while exposed to different concentrations of Aβ42. Aβ42 predominantly reduces the NAP amplitude with minimal effects on other parameters except at low stimulus currents and short inter-stimulus intervals. The effects of Aβ42 are significantly concentration-dependent, with a maximum reduction in NAP amplitude at a concentration of 70 nM and smaller effects on the NAP amplitude at higher and lower concentrations. However, even physiologic concentrations in the range of 70 pM did reduce the NAP amplitude. The effects of Aβ42 became maximal 5-8 h after exposure and did not reverse during a 30 min washout period. The in vitro rat sciatic nerve model is sensitive to the effects of physiologic concentrations of Aβ42. These experiments suggest that the effect of Aβ42 is a very complex function of concentration that may be the result of amyloid-related changes in membrane properties or sodium channels.

Motor excitability measurements in early stage familial amyloid polyneuropathy: The influence of tafamidis treatment

OBJECTIVE

To test motor fiber excitability in early affected patients with transthyretin (TTR)-type familial amyloid polyneuropathy (TTR-FAP) before and during tafamidis treatment.

METHODS

We examined the left median nerve of 21 healthy-matched controls and 10 early affected TTR-FAP patients using the automated threshold-tracking program, QTRAC. TTR-FAP patients were tested one day before the initiation of tafamidis treatment, 3 and 6 months later.

RESULTS

The drug was well-tolerated in all patients; there was no drop-out. No statistical difference was found between healthy controls and TTR-FAP patients at study entry. On treatment, both stimulus intensity for 50% of the maximal motor response and rheobase increased significantly from entry to the last evaluation at 6 months (P<0.05). Strength duration time constant decreased significantly from the 3rd to the 6th month of evaluation (P<0.05). There was also a "fanning-out" effect on the late depolarization phase (TEd 90-100ms) as well as a shortened relative refractory period from study entry to the 6th month of evaluation.

CONCLUSIONS

Threshold-tracking of median nerve motor fibers is not a helpful technique for the early diagnosis of TTR-FAP patients. Tafamidis was well-tolerated. We observed possible membrane hyperpolarization during treatment. Threshold tracking can contribute to documenting the action of new drugs to treat neuropathies. Tafamidis may change nerve electrical properties by reducing the burden of amyloid fibrils.