Avermectin B1a

Avermectin B1a is a modulator of gamma-aminobutyric acid (GABA)-controlled chloride ion channels [1].
Avermectin B1a is a macrocyclic lactone derivative and possesses anthelmintic and insecticidal activities. It was obtained from the fermentation products of Streptomyces avermitilis. Avermectin B1a is usually worked as an anthelmintic and insecticidal agent. It suppresses the signal transmission of nematodes from the central command interneurons to the peripheral motoneurons. The mechanism of this action is that avermectin B1a can enhance the effects of glutamate on the gamma-aminobutyric acid (GABA)-controlled chloride ion channels, causing an influx of chloride ions into the cells. It subsequently leads to hyperpolarisation and subsequent paralysis of the neuromuscular systems. The excitatory effects can be reversed by the chloride ion channel blocker picrotoxin. Since mammals do not have this kind of ion channels, avermectin B1a has no toxicity for mammals [1 and 2].
In rat brain synaptic membranes, avermectin B1a significantly enhanced GABA binding up to 80% over control at concentration of 7 μM. Avermectin B1a also showed protection efficacy for GABA receptors from denaturation when the synaptic membranes were incubated at 60° C with 50 mM Tris-Cl. In the lobster stretcher muscle, treatment of avermectin B1a resulted in the block of IPSPs and the reduction of EPSPs. Besides that, avermectin B1a was found to have promoting effects on benzodiazepine binding. It enhanced flunitrazepan binding to synaptic membranes with EC50 value 50-fold lower than that of GABA [3 and 4].
When given to cattle, the oral administration of avermectin B1a at dose of 0.1 mg/kg reduced more than 95% of T. colubriformis, T. axei, Haemonchus placei, C. oncophora, Cooperia punctate, Ostertagia ostertagi, Oesophagostomum radiatum and Dictyocaulus viviparus. When given to sheep at the same dose, avermectin B1a administration caused also 95% above reduction of Trichostrongylus axei, Haemonchus contortus, Cooperia oncophora, Trichostrongylus colubriformis, Ostertagia circumcincta and Oesophagostomum columbianum [5].
References:
[1] Wang C C, Pong S S. Actions of avermectin B1a on GABA nerves. Progress in clinical and biological research, 1981, 97: 373-395.
[2] Bloomquist J R. Toxicology, mode of action and target site-mediated resistance to insecticides acting on chloride channels. Comparative Biochemistry and Physiology Part C: Pharmacology, Toxicology and Endocrinology, 1993, 106(2): 301-314.
[3] Pong S S, DeHaven R, Wang C C. A comparative study of avermectin B1a and other modulators of the gamma-aminobutyric acid receptor. chloride ion channel complex. The Journal of Neuroscience, 1982, 2(7): 966-971.
[4] Fritz L C, Wang C C, Gorio A. Avermectin B1a irreversibly blocks postsynaptic potentials at the lobster neuromuscular junction by reducing muscle membrane resistance. Proceedings of the National Academy of Sciences, 1979, 76(4): 2062-2066.
[5] Egerton J R, Ostlind D A, Blair L S, et al. Avermectins, new family of potent anthelmintic agents: efficacy of the B1a component. Antimicrobial Agents and Chemotherapy, 1979, 15(3): 372-378.

Significance of Heavy-Ion Beam Irradiation-Induced Avermectin B1a Production by Engineered Streptomyces avermitilis.[Pubmed:28243599]

Biomed Res Int. 2017;2017:5373262.

Heavy-ion irradiation technology has advantages over traditional methods of mutagenesis. Heavy-ion irradiation improves the mutation rate, broadens the mutation spectrum, and shortens the breeding cycle. However, few data are currently available regarding its effect on Streptomyces avermitilis morphology and productivity. In this study, the influence of heavy-ion irradiation on S. avermitilis when cultivated in approximately 10 L stirred-tank bioreactors was investigated. The specific productivity of the avermectin (AVM) B1a-producing mutant S. avermitilis 147-G58 increased notably, from 3885 to 5446 mug/mL, approximately 1.6-fold, compared to the original strain. The mycelial morphology of the mutant fermentation processes was microscopically examined. Additionally, protein and metabolite identification was performed by using SDS-PAGE, 2- and 3-dimensional electrophoresis (2DE and 3DE). The results showed that negative regulation gene deletion of mutants led to metabolic process upregulating expression of protein and improving the productivity of an Avermectin B1a. The results showed that the heavy-ion beam irradiation dose that corresponded to optimal production was well over the standard dose, at approximately 80 Gy at 220 AMeV (depending on the strain). This study provides reliable data and a feasible method for increasing AVM productivity in industrial processes.

Quantitative determination and validation of avermectin B1a in commercial products using quantitative nuclear magnetic resonance spectroscopy.[Pubmed:24943110]

Magn Reson Chem. 2014 Sep;52(9):480-5.

Nuclear magnetic resonance is defined as a quantitative spectroscopic tool that enables a precise determination of the number of substances in liquids as well as in solids. There is few report demonstrating the application of NMR in the quantification of Avermectin B1a (AVB1a ); here, a proton nuclear magnetic resonance spectroscopy ((1) H NMR) using benzene [1-methoxy-4-(2-nitroethyl) (PMN)] as an internal standard and deuterochloroform as an NMR solvent was tested for the quantitative determination of AVB1a . The integrated signal of AVB1a at 5.56 ppm and the signal of PMN at 8.14 ppm in the (1) H NMR spectrum were used for quantification purposes. Parameters of specificity, linearity, accuracy, precision, intermediate precision, range, limit of detection (LOD), limit of quantification (LOQ), stability and robustness were validated. The established method was accurate and precise with good recovery (98.86%) and relative standard deviation (RSD) of assay (0.34%) within the linearity of the calibration curve ranging from 5.08 to 13.58 mg/ml (R(2) = 0.9999). The LOD and LOQ were 0.009 and 0.029 mg/ml, which indicated the excellent sensitivity of the method. The stability of the method was testified by a calculated RSD of 0.11%. The robustness was testified by modification of four different parameters, and the differences among each parameter were all less than 0.1%. Comparing with the assay described by the manufacturer of avermectin tablets, there was no significant difference between the assay obtained by HPLC and quantitative NMR (qNMR), which indicated qNMR was a simple and efficient method for the determination of AVB1a in commercial formulation products.

Medium optimization for the production of avermectin B1a by Streptomyces avermitilis 14-12A using response surface methodology.[Pubmed:19356927]

Bioresour Technol. 2009 Sep;100(17):4012-6.

Response surface methodology was employed to optimize the composition of medium for the production of Avermectin B1a by Streptomyces avermitilis 14-12A in shaker flask cultivation. Corn starch and yeast extract were found to have significant effects on Avermectin B1a production by the Plackett-Burman design. The steepest ascent method was used to access the optimal region of the medium composition, followed by an application of response surface. The analysis revealed that the optimum values of the tested variables were 149.57 g/l corn starch and 8.92 g/l yeast extract. A production of 5128 mg/l, which was in agreement with the prediction, was observed in verification experiment. In comparison to the production of original level (3528 mg/l), 1.45-fold increase had been obtained.

Total synthesis of avermectin B1a revisited.[Pubmed:26350782]

J Antibiot (Tokyo). 2016 Jan;69(1):31-50.

Avermectins were isolated as compounds possessing anthelmintic activity from the culture broth of Streptomycesavermitilis by Omura and co-workers. Owing to their potent anthelmintic and insecticidal activities, as well as their unique pentacyclic architecture, the avermectin family attracted keen interest from synthetic organic chemists. We have recently completed a more efficient and straightforward total synthesis of Avermectin B1a, as compared with previous syntheses.