Avermectin B1b

Avermectin B1 is a mixture of avermectins containing >80% avermectin B1a and <20% avermectin B1b. B1a and B1b have very similar biological and toxicological properties.

In vitro: The avermectins are insecticidal and antihelmintic compounds derived from various laboratory broths fermented by the soil bacterium. Avermectin B1 is a natural fermentation product of this bacterium.

In vivo: Avermectin B1 therapy resulted in significant decreases in mean strongyle egg after treatment. All horses given ivermectin or avermectin B1 had zero strongyle egg counts 14 and 28 d after treatment. The oral administration of avermectin B1 appeared to be highly efficacious against intestinal strongyles and Onchocera microfilaria [1].

Clinical trial: Currently no clinical data are available

Reference:
[1] Mogg TD, Pollitt CC, Willmore JP, Thompson H.  Efficacy of avermectin B1 given orally against equine intestinal strongyles and Onchocera microfilaria. Aust Vet J. 1990;67(11):399-401.

Production and Screening of High Yield Avermectin B1b Mutant of Streptomyces avermitilis 41445 Through Mutagenesis.[Pubmed:25147669]

Jundishapur J Microbiol. 2014 Feb;7(2):e8626.

BACKGROUND: Secondary metabolite production from wild strains is very low for economical purpose therefore certain strain improvement strategies are required to achieve hundred times greater yield of metabolites. Most important strain improvement techniques include physical and chemical mutagenesis. Broad spectrum mutagenesis through UV irradiation is the most important and convenient physical method. OBJECTIVES: The present study was conducted for enhanced production of Avermectin B1b from Streptomyces avermitilis 41445 by mutagenesis using ultraviolet (UV) radiation, ethidium bromide (EB), and ethyl methanesulfonate (EMS) as mutagens. MATERIALS AND METHODS: S. avermitilis DSM 41445 maintained on yeast extract malt extract glucose medium (YMG) was used as inoculum for SM2 fermentation medium. Spores of S. avermitilis DSM 41445 were exposed to UV radiation for physical broad spectrum mutagenesis and to EMS and EB for chemical mutagenesis. For each mutagen, the lethality rate and mutation rate were calculated along with positive mutation rate. RESULTS: Avermectin B1b-hyper-producing mutant, produced using these three different methods, was selected according to the HPLC results. The mutant obtained after 45 minutes of UV radiation to the spores of S. avermitilis 41445, was found to be the best mutant for the enhanced production of Avermectin B1b component (254.14 mg/L). Other Avermectin B1b-hyper-producing mutants, were obtained from EMS (1 microL/mL) and EB (30 microL/mL) treatments, and yielded 202.63 mg/L and 199.30 mg/L of B1b, respectively. CONCLUSIONS: The hereditary stability analysis of the UV mentioning 45 minutes revealed the UV exposure time for mutants and 3 represented the colony taken from the plate irradiated for 45 minutes mutant showed that the production of Avermectin B1b remained constant and no reverse mutation occurred after 15 generations.

Measuring the effect of avermectins and milbemycins on somatic muscle contraction of adult Haemonchus contortus and on motility of Ostertagia circumcincta in vitro.[Pubmed:24576444]

Parasitology. 2014 Jun;141(7):948-56.

The mechanism of anthelmintic resistance against the widely used macrocyclic lactones (MLs) is still not fully understood. Pharyngeal, somatic body muscles and the ovijector have been proposed as putative sites of action as well as resistance. In the present study the effects of three avermectins and three milbemycins on adult parasitic nematodes were evaluated in vitro. The Muscle Transducer system was used to investigate the effects of MLs on muscle contraction in female Haemonchus contortus and effects on motility were measured in Ostertagia (Teladorsagia) circumcincta using the Micromotility Meter. Concentration-response curves for all substances in both systems shifted to the right in the resistant isolates. Resistance was present to ivermectin (IVM) and its components IVM B1a and IVM B1b, suggesting that both components are involved in the mode of action and resistance. No consistent patterns of potency and resistance of the substances were observed except that milbemycins generally showed lower resistance ratios (RRs) than IVM. IVM and IVM B1b were the most potent inhibitors of contraction and motility in both susceptible isolates and also showed the highest RR in both species. Low RRs for milbemycins recorded in vitro for highly resistant isolates in vivo suggest that other factors such as pharmacokinetics influence drug potency in vivo.

Inhibition of P-glycoprotein in the blood-brain barrier alters avermectin neurotoxicity and swimming performance in rainbow trout.[Pubmed:24316435]

Aquat Toxicol. 2014 Jan;146:176-85.

The importance of the blood brain barrier (BBB) and the contribution to its function by the efflux transporter P-glycoprotein (P-gp) in teleosts were examined using the P-gp substrates and central nervous system neurotoxins ivermectin (22,23-dihydroavermectin B1a+22,23-dihydroAvermectin B1b) [IVM]) and emamectin benzoate (4''-deoxy-49''epimethylaminoavermectin B1 benzoate [EB]). Trout were injected intraperitoneally with 0.01-1.0 and 1-50mg/kg of IVM or EB, respectively either alone or in combination with cyclosporin A (CsA: a P-gp substrate) at 1mg/kg. IVM affected the swimming performance (critical swimming speed, burst swimming distance, and schooling) at significantly lower concentrations than EB. When fish were exposed to IVM or EB in the presence of CsA, alterations to swimming were increased, suggesting that competition for P-gp in the BBB by CsA increased IVM and EB penetration into the CNS and decreased swimming capabilities. The effect of co-administration of CsA on swimming-related toxicity was different between IVM and EB-treated fish; EB toxicity was increased to a greater extent than IVM toxicity. The greater chemosensitization effect of EB vs. IVM was examined using a P-gp competitive inhibition assay in isolated trout hepatocytes with rhodamine 123 as a substrate. At the cellular level, IVM was a more potent inhibitor of P-gp than EB, which allowed for a greater accumulation of R123 in hepatocytes. These results provide evidence for a role of P-gp in the BBB of fish, and suggest that this protein protects fish from environmental neurotoxins.

Preliminary resistance screening on abamectin in pear psylla (Hemiptera: Psyllidae) in northern Italy.[Pubmed:17972642]

J Econ Entomol. 2007 Oct;100(5):1637-41.

In northern Italy (Emilia-Romagna region), integrated pest management has been used for several years against pear psylla, Cacopsylla pyri L. (Hemiptera: Psyllidae), a relevant pest of pear (Pyrus spp.) trees. After the outlawing of amitraz in 2005, the most common active ingredient involved is abamectin, a mixture of avermectin B1a and Avermectin B1b. After the development of C. pyri resistance to azinphos methyl in southern France, we evaluated, by topical application, the different sensitivities to abamectin on C. pyri populations collected in orchards from Emilia-Romagna, where different field strategies were used, with alternative success in terms of pest management. The LC50 values ranged between 1.61 and 28.37 mg/liter, and they revealed variations more related to collection time than to field strategies. The failure of abamectin treatments against C. pyri in some Emilia-Romagna locations is probably unrelated to resistance development, but rather it is related to incorrect pest defense management, which could interfere with pest parasitoids and predators.

Antiviral effect of theaflavins against caliciviruses.[Pubmed:27756911]

J Antibiot (Tokyo). 2017 Apr;70(4):443-447.

Caliciviruses are contagious pathogens of humans and various animals. They are the most common cause of viral gastroenteritis in humans, and can cause lethal diseases in domestic animals such as cats, rabbits and immunocompromised mice. In this study, we conducted cytopathic effect-based screening of 2080 selected compounds from our in-house library to find antiviral compounds against three culturable caliciviruses: feline calicivirus, murine norovirus (MNV) and porcine sapovirus (PoSaV). We identified active six compounds, of which two compounds, both related to theaflavins, showed broad antiviral activities against all three caliciviruses; three compounds (abamectin, a mixture of avermectin B1a and B1b; avermectin B1a; and (-)-epigallocatechin gallate hydrate) were effective against PoSaV only; and a heterocyclic carboxamide derivative (BFTC) specifically inhibited MNV infectivity in cell cultures. Further studies of the antiviral mechanism and structure-activity relationship of theaflavins suggested the following: (1) theaflavins worked before the viral entry step; (2) the effect of theaflavins was time- and concentration-dependent; and (3) the hydroxyl groups of the benzocycloheptenone ring were probably important for the anti-calicivirus activity of theaflavins. Theaflavins could be used for the calicivirus research, and as potential disinfectants and antiviral reagents to prevent and control calicivirus infections in animals and humans.