The Mechanism Underlying the Protective Effect of the Thearubigin Fraction of Black Tea (Camellia sinensis) Extract against the Neuromuscular Blocking Action of Botulinum Neurotoxins

Abstract: The aim of the present study was to elucidate the mechanism of the protective effect of black tea extract, the thearubigin fraction, against the neuromuscular blocking action of botulinum neurotoxin types A, B, and E. The effects of thearubigin fraction extracted from a black tea infusion were examined on the neuromuscular blocking action of botulinum neurotoxin types A, B, and E in mouse phrenic nerve‐diaphragm preparations and on the binding of these toxins to rat cerebrocortical synaptosomes. Botulinum neurotoxin type A (1.5 nM), B (6 nM), or E (5 nM) abolished indirect twitches in mouse phrenic nerve‐diaphragm preparations within 50, 90, 90 min., respectively. Thearubigin fraction mixed with each toxin blocked the inhibitory effect of the toxins. The specific binding of [ 125 I]botulinum neurotoxin type A, B, or E to rat cerebrocortical synaptosomes was inhibited by mixing iodinated toxin with thearubigin fraction. The elution profile of [ 125 I]botulinum neurotoxin type A, B, or E on Sephadex G‐50 column chromatography was different from that of toxin mixed with thearubigin fraction. These findings indicate that thearubigin fraction protects against the neuromuscular blocking action of botulinum neurotoxin types A, B, and E by binding with the toxins.