Vitamin E Efficacy in HI/HA

Overview

Congenital hyperinsulinism (HI) is a rare disorder of pancreatic beta cell insulin secretion that causes persistent and severe hypoglycemia starting at birth. Hyperinsulinism/hyperammonemia (HI/HA) syndrome is the second most common type of congenital HI and is caused by activating mutations in glutamate dehydrogenase (GDH). Patients with HI/HA exhibit fasting hyperinsulinemic hypoglycemia, protein-induced hypoglycemia, hyperammonemia, seizures, and intellectual disability independent of hypoglycemia. These effects result from abnormal GDH activity in the beta cells, liver and kidney cells, neurons, and astrocytes. The only available treatment for HI/HA syndrome is diazoxide, which acts on the beta cells to decrease insulin secretion but has no effect on GDH activity itself or on other cell types. Thus, there remains a significant unmet need for improved therapies for this disorder. Pre-clinical data show that vitamin E inhibits GDH activity in human cell lines and improves fasting hypoglycemia in a GDH HI mouse model. Pilot study data show that vitamin E supplementation with a moderate dose is well-tolerated in children and adults with HI/HA syndrome, while continuing diazoxide treatment. However, most subjects continued to exhibit protein-induced hyperinsulinemic hypoglycemia. We hypothesize that a higher vitamin E dose will inhibit GDH over-activity in subjects with HI/HA syndrome, resulting in improved hyperinsulinemic hypoglycemia, reduced blood ammonia concentration, and decreased seizure activity.

The primary objective of this study is to determine an effective dose of vitamin E to reduce protein-induced hyperinsulinemia in subjects with HI/HA syndrome. Secondary objectives are to assess the effects of vitamin E on plasma C-peptide concentrations, serum alpha-tocopherol concentrations, blood ammonia concentrations, hypoglycemic events, and seizure frequency. The effect of vitamin E on brain glutamate levels and electroencephalogram findings will be explored. This single-group open-label dose-finding clinical study will use a before-and-after design to compare clinical and laboratory data before and after 2-3 weeks of escalating doses of oral vitamin E treatment in subjects with HI/HA syndrome. This single-site outpatient study will recruit up to 5 adult participants (18 years of age or older) with HI/HA syndrome. Each study visit will consist of blood tests, an IV leucine acute insulin response (AIR) test, home glucose meter and continuous glucose monitor (CGM) review, and a symptom questionnaire. The baseline and final visits will also include electroencephalogram (EEG) and brain magnetic resonance imaging (MRI) with glutamate chemical exchange saturation transfer (GluCEST) analysis. After baseline assessments, including a 2 week run-in period of CGM use, subjects will take twice daily oral vitamin E (alpha-tocopherol) at home. After steady-state of that dose of vitamin E has been achieved (i.e. at least 2 weeks on the dose of vitamin E), subjects will return for the next study visit. If there is no dose-limiting toxicity, then the twice daily vitamin E dose will be increased, and the subjects will return for a subsequent study visit after at least 2 weeks. If there is no dose-limiting toxicity at this visit, then the twice daily vitamin E dose will be increased again, and the subjects will return for a final study visit after at least 2 weeks. If toxicity is identified at any point, vitamin E will be discontinued and final study visit procedures will be performed.