Ethyl acetate extract from black tea prevents neuromuscular blockade by botulinum neurotoxin type A in vitro

Review of the inhibition of biological activities of food-related selected toxins by natural compounds

There is a need to develop food-compatible conditions to alter the structures of fungal, bacterial, and plant toxins, thus transforming toxins to nontoxic molecules. The term 'chemical genetics' has been used to describe this approach. This overview attempts to survey and consolidate the widely scattered literature on the inhibition by natural compounds and plant extracts of the biological (toxicological) activity of the following food-related toxins: aflatoxin B1, fumonisins, and ochratoxin A produced by fungi; cholera toxin produced by Vibrio cholerae bacteria; Shiga toxins produced by E. coli bacteria; staphylococcal enterotoxins produced by Staphylococcus aureus bacteria; ricin produced by seeds of the castor plant Ricinus communis; and the glycoalkaloid α-chaconine synthesized in potato tubers and leaves. The reduction of biological activity has been achieved by one or more of the following approaches: inhibition of the release of the toxin into the environment, especially food; an alteration of the structural integrity of the toxin molecules; changes in the optimum microenvironment, especially pH, for toxin activity; and protection against adverse effects of the toxins in cells, animals, and humans (chemoprevention). The results show that food-compatible and safe compounds with anti-toxin properties can be used to reduce the toxic potential of these toxins. Practical applications and research needs are suggested that may further facilitate reducing the toxic burden of the diet. Researchers are challenged to (a) apply the available methods without adversely affecting the nutritional quality, safety, and sensory attributes of animal feed and human food and (b) educate food producers and processors and the public about available approaches to mitigating the undesirable effects of natural toxins that may present in the diet.

Inhibition in vivo of the activity of botulinum neurotoxin A by small molecules selected by virtual screening

To search for small molecular size inhibitors of botulinum neurotoxin A (BoNT/A) endopeptidase activity, we have screened the NCI library containing about 1 million structures against the substrate binding pocket of BoNT/A. Virtual screening (VS) was performed with the software Glide (Grid-based ligand docking energetics) and the findings were confirmed by AutoDock. Ten compounds were found that had favorable energetic and glide criteria and 5 of these compounds were selected for their ability to protect mice in vivo against a lethal dose of BoNT/A. Each compound was incubated at different molar excesses with a lethal dose of the toxin and then the mixture injected intravenously into mice. At 4690 M excess, compounds NSC94520 and NSC99639 protected all (100%) the mice from lethal toxicity. Compounds NSC48461 and NSC627733 gave 75% protection. Compound NSC348884 showed the least inhibition of toxicity allowing only a fraction (25%) of the mice to survive challenge with a lethal dose; and in the case of the mice that did not survive there was a considerable delay of mortality. At 2400 M excess compounds NSC94520 remained fully protective while and NSC99639 afforded 75% protection and at 1200 M excess each of these two compounds gave 50% protection. The two compounds gave no protection at 600 or less molar excess. When each compound was administered intravenously at 4690 M excess at different times (from 1 h to 6 h) after the intravenous injection of the active toxin, none of the compounds was able to protect the animals from toxicity. The findings show the value of VS in identifying potential inhibitors of the toxin for further development and improvement.

Use of a recombinant fluorescent substrate with cleavage sites for all botulinum neurotoxins in high-throughput screening of natural product extracts for inhibitors of serotypes A, B, and E

The seven serotypes of botulinum neurotoxin (BoNTs) are zinc metalloproteases that cleave and inactivate proteins critical for neurotransmission. The synaptosomal protein of 25 kDa (SNAP-25) is cleaved by BoNTs A, C, and E, while vesicle-associated membrane protein (VAMP) is the substrate for BoNTs B, D, F, and G. BoNTs not only are medically useful drugs but also are potential bioterrorist and biowarfare threat agents. Because BoNT protease activity is required for toxicity, inhibitors of that activity might be effective for antibotulinum therapy. To expedite inhibitor discovery, we constructed a hybrid gene encoding (from the N terminus to the C terminus, with respect to the expressed product) green fluorescent protein, then a SNAP-25 fragment encompassing residues Met-127 to Gly-206, and then VAMP residues Met-1 to Lys-94. Cysteine was added as the C terminus. The expressed product, which contained the protease cleavage sites for all seven botulinum serotypes, was purified and coupled covalently through the C-terminal sulfhydryl group to maleimide-activated 96-well plates. The substrate was readily cleaved by BoNTs A, B, D, E, and F. Using this assay and an automated 96-well pipettor, we screened 528 natural product extracts for inhibitors of BoNT A, B, and E protease activities. Serotype-specific inhibition was found in 30 extracts, while 5 others inhibited two serotypes.

Overview of antibacterial, antitoxin, antiviral, and antifungal activities of tea flavonoids and teas

Tea leaves produce organic compounds that may be involved in the defense of the plants against invading pathogens including insects, bacteria, fungi, and viruses. These metabolites include polyphenolic compounds, the six so-called catechins, and the methyl-xanthine alkaloids caffeine, theobromine, and theophylline. Postharvest inactivation of phenol oxidases in green tea leaves prevents oxidation of the catechins, whereas postharvest enzyme-catalyzed oxidation (fermentation) of catechins in tea leaves results in the formation of four theaflavins as well as polymeric thearubigins. These substances impart the black color to black teas. Black and partly fermented oolong teas contain both classes of phenolic compounds. A need exists to develop a better understanding of the roles of polyphenolic tea compounds in food and medical microbiology. This overview surveys and interprets our present knowledge of activities of tea flavonoids and teas against foodborne and other pathogenic bacteria, virulent protein toxins produced by some of the bacteria, virulent bacteriophages, pathogenic viruses and fungi. Also covered are synergistic, mechanistic, and bioavailability aspects of the antimicrobial effects. Further research is suggested for each of these categories. The herein described findings are not only of fundamental interest, but also have practical implications for nutrition, food safety, and animal and human health.