Abstract:
Alzheimer’s disease (AD) is a neurodegenerative disorder with clinical symptoms presenting as memory loss. There are no disease-modifying therapies to date as current therapies only provide symptomatic relief. Recently, the γ-aminobutyric acid (GABA) neurotransmitter system has been suggested to undergo remodelling in AD which disrupts the excitatory and inhibitory (E/I) balance in the brain. K-Cl-2 (KCC2) and N-K-Cl-1 (NKCC1) are cation chloride-cotransporters involved in GABA signalling, where NKCC1 promotes excitatory GABA activity in immature neurons and KCC2 promotes inhibitory GABA activity in mature neurons. High NKCC1 expression in mature neurons has been implicated in several neurological disorders and bumetanide, an NKCC1 inhibitor, might have a potential therapeutic benefit in these conditions. This study used primary mouse hippocampal neurons to explore the potential neuroprotective effects of bumetanide in an in vitro AD mouse model. Primary mouse hippocampal cultures were treated with amyloid beta (Aβ₁₋₄₂) alone or with various concentrations of bumetanide (1μM, 10μM, 100μM, 1mM) to investigate the effect of bumetanide on cell viability. Aβ₁₋₄₂ produced 53.1 ± 1.4% cell death after 5 days, and addition of bumetanide at all concentrations did not reduce this. Bumetanide at the lowest concentration (1μM) alone lead to 61.5 ± 1.2% cell death after 5 days, and at higher concentrations as well, suggesting bumetanide is neurotoxic. No change in KCC2 and NKCC1 expression was observed in the in vitro AD model, however localized upregulation of NKCC1 and downregulation of KCC2 was apparent in the CA1 subregion of the hippocampus in an in vivo mouse model of AD. Thirty day treatment with 3-(5-Methylisoxazol-3-yl)-6-[(1-methyl-1,2,3-triazol-4-yl)methyloxy]-1,2,4-triazolo[3,4-a]phthalazine (α5IA), an inverse agonist of α5-containing GABAA receptors with cognitive enhancing abilities, abolished the increase in NKCC1 expression. The research suggests bumetanide is not a suitable therapy for AD, but α5IA may be of therapeutic benefit by restoring the E/I balance in AD.