EC50 Values For Inhibition Research Articles

Evaluation of in vitro methods of anthelmintic efficacy testing against Ascaridia galli.

To investigate methods for in vitro assessment of anthelmintic efficacy against the chicken nematode Ascaridia galli this study firstly evaluated sample preparation methods including recovery of eggs from excreta using different flotation fluids and induced larval hatching by the deshelling-centrifugation method and the glass-bead method with or without bile. It then evaluated two in vitro assays, the in-ovo larval development assay (LDA) and larval migration inhibition assay (LMIA), for anthelmintic efficacy testing against A. galli using fresh eggs and artificially hatched larvae, respectively. Four anthelmintics, thiabendazole (TBZ), fenbendazole (FBZ), levamisole (LEV) and piperazine (PIP) were employed using an A. galli isolate of known susceptibility. The results suggested that the LDA and LMIA could successfully be used to generate concentration response curves for the tested drugs. The LDA provided EC50 values for inhibition of egg embryonation of 0.084 and 0.071 μg/ml for TBZ and FBZ, respectively. In the LMIA, the values of effective concentration (EC50) of TBZ, FBZ, LEV and PIP were 105.9, 6.32, 349.9 and 6.78 × 107 nM, respectively. For such in vitro studies, a saturated sugar solution showed high egg recovery efficiency (67.8%) and yielded eggs of the highest morphological quality (98.1%) and subsequent developmental ability (93.3%). The larval hatching assays evaluated did not differ in hatching efficiency but the deshelling-centrifugation method yielded larvae that had slightly better survival rates. For final standardization of these tests and establishment of EC50 reference values, tests using isolates of A. galli of defined resistance status need to be performed.

Phytotoxicity of Sodium Fluoride and Uptake of Fluoride in Willow Trees

The willow tree (Salix viminalis) toxicity test and a cress seed germination test (Lepidium sativum) were used to determine uptake of F and phytotoxicity of NaF. Concentrations in hydroponic solutions were 0–1000 mg F/L and 0–400 mg F/L in the preliminary and definitive test. A third test was done with soils collected from a fluoride-contaminated site at Fredericia, Denmark. The EC10, EC20 and EC50-values for inhibition of transpiration were determined to 38.0, 59.6 and 128.7 mg F/L, respectively. The toxicity test with soil showed strong inhibition for the sample with the highest fluoride concentration (405 mg free F per kg soil, 75 mg F per L soil solution). The seed germination and root elongation test with cress gave EC10, EC20 and EC50-values of 61.4, 105.0 and 262.8 mg F/L, respectively. At low external concentrations, fluoride was taken up more slowly than water and at high external concentrations at the same velocity. This indicates that an efflux pump becomes overloaded at concentrations above 210 mg F/L. Uptake kinetics were simulated with a non-linear mathematical model, and the Michaelis-Menten parameters were determined to half-saturation constant KM near 2 g F/L and maximum enzymatic removal rate vmax at 9 g/(kg d).

Distinct Relations Among Plasma Concentrations Required for Different Pharmacological Effects in Oxycodone, Morphine, and Fentanyl

ABSTRACTSeveral clinical reports showed that adverse effect profiles are not the same in morphine, oxycodone, and fentanyl. The authors investigated whether the relationship between plasma concentrations for antinociceptive effect and for various pharmacological effects differed among oxycodone, morphine, and fentanyl under controlled experimental setting using animal models. Oxycodone induced constipation and an antinociceptive effect in a similar concentration-dependent manner, whereas morphine required approximately 9-fold higher plasma concentration for antinociceptive effect compared with that for constipation when 50% effective plasma concentration (EC50) levels were compared. The EC50 values for inhibition of behavioral activity were 2.1-, 2.7-, and 1.3-fold higher than those for antinociceptive effect in oxycodone, morphine, and fentanyl, respectively. Respiratory inhibition was observed even at higher plasma concentrations in all three opioids, and the differences in the EC50 values compared with those for antinociceptive effects were 234.5-fold (oxycodone), 233.1-fold (morphine), or 104.2-fold (fentanyl). These results showed that oxycodone, morphine, and fentanyl exhibited unique patterns of plasma concentrations required for different pharmacological effects. The different adverse effect profiles observed in a clinical setting appear to be resulted from, at least in part, distinct intrinsic pharmacological profiles among these μ-opioid receptor agonists.

White and green tea polyphenols inhibit pancreatic lipase in vitro

Abstract Green, white and black teas were assayed for inhibition of pancreatic lipase activity in vitro. White tea proved to be more effective than green tea with black tea showing little inhibition even at 200 μg GAE/ml. The EC50 values for inhibition were 22 μg/ml for white tea and 35 μg/ml for green tea; both easily achievable from normal infusions of tea. Liquid chromatography-mass spectroscopy analysis showed that white and green teas had essentially equal amounts of flavan-3-ols but green tea had higher levels of flavonols. White tea had higher levels of 5-galloyl quinic acid, digalloyl glucose, trigalloyl glucose and the tannin, strictinin. After chromatography on Sephadex LH-20, the main inhibitory fraction was enriched in strictinin and fractions enriched in other components were ineffective. This suggests that strictinin content may be crucial for inhibition of pancreatic lipase. However, the possibility of synergies between the polyphenols cannot be disregarded.

Comparison of Tributyltin Compound Effects on the AlgaScenedesmus quadricaudaand the Benthic OrganismsTubifex tubifexandChironomus plumosus

The inhibitory and toxic effects of five tributyltin compounds and one dibutyltin compound were determined under standardized conditions on the freshwater plankton algaScenedesmus quadricaudaand the benthic organismsTubifex tubifexandChironomus plumosus. Observed were the mortality of benthos after 96 h and the inhibition of growth, photosynthesis, and chlorophyllacontent of the alga after 12 days of cultivation. The effects of the compounds were expressed as LC50values for mortality and EC50values for inhibition. Attention was focused on the influence of the bound X anion on the toxicological effects of the test compounds [dibutyltin bis(N,N-diethyldithiocarbamate (DBTC); bis(tributyltin 3,4,5,6-tetrachlorophthalate (TBTP); tributyltin sulfaminate (TBTS); tributyltinN,N-diethyldithiocarbamate (TBTC); tributyltin naphthenate (TBTN); bis(tributyltin) oxide) (TBTO)]. From the results obtained the following conclusions can be made: For benthic organisms the anionic groupN,N-diethyldithiocarbamate as well as the anionic inorganic group oxide had a very large toxic effect. The lowest efficiency was indicated for the 3,4,5,6-tetrachlorophthalate anion. When the positions of the tested compounds with respect to dependence of the bound anion were evaluated for the alga, it was concluded that the position of the anionic group in inhibitory rank orders depended on the parameter. The efficiency of the organic anionN,N-diethyldithiocarbamate was low in all divisions tested (especially for photosynthesis inhibition). Strong effects for all parameters tested were noted for the compound with organic anion 3,4,5,6-tetrachlorophthalate as well as the compound with the inorganic anion oxide, except for photosynthesis inhibition. From the results obtained the following rank orders of toxicity and/or inhibition are established:T. tubifex—TBTO>TBTC>TBTN>DBTC>TBTS>TBTP;Ch. plumosus—TBTS≥TBTC>TBTO>TBTN>DBTC>TBTP;S. quadricauda, growth inhibition—TBTO>TBTP>TBTN>TBTC>DBTC=TBTS;S. quadricauda, chlorophyllacontent—TBTO≥DBTC>TBTP=TBTC>TBTN=TBTS;S. quadricauda, photosynthesis inhibition—TBTP>TBTS≥TBTN>DBTC>TBTO>TBTC.

Comparative Study of Ecotoxicological Effect of Triorganotin Compounds on Various Biological Subjects

The toxic and inhibitory effect of 10 triorganotin compounds (triphenlyl-, tribenzyl-, and tributyltins) were determined under standardized conditions on four biological subjects:Tubifex tubifex, Chironomus plumosus, Sinapis albaseeds, and the algaScenedesmus quadricauda.Observed were the mortality ofT. tubifexandCh. plumosusafter 96 hr, the root growth inhibition ofS. albaseeds after 72 hr, and the inhibition of growth, photosynthesis, and chlorophyllacontent ofS. quadricaudaafter 12 days of cultivation. The effect of triorganotins was expressed as LC50values for mortality and EC50values for inhibition. For each subject and observed parameter the rank order of toxicity/or inhibition was arranged.

Alanine transport across the human placental brush border membrane and the role of SH groups in carrier function.

We have determined the kinetic characteristics of alanine transport into brush border membrane vesicles (BBMV) of human full term placenta and identified functional groups of the carrier proteins that are important for transport function. Alanine influx into BBMV was found to be mediated by two transport systems with different kinetic features and distinct substrate specificities. An uphill operating electrogenic Na(+)-dependent cotransport system could be kinetically separated from a Na(+)-independent facilitated diffusion system. The Na(+)-dependent transporter mediates Na(+)-alanine cotransport with a 1:1 flux coupling ratio (Hill coefficient 1.13 +/- 0.12) and a Km for alanine of 0.45 +/- 0.06 mmol/l. Half-maximal stimulation of Na(+)-dependent alanine influx was observed at a Na+ concentration (NaCl) of 51.4 +/- 1.3 mmol/l. A variety of group specific reagents were used to identify functional groups in the transport proteins. Only compounds reacting with SH-residues (NEM, DTNB, PCMBS) or NH2-groups (PITC) were found to affect Na+ dependent and Na+ independent alanine transport. The EC50 value for inhibition of alanine influx by PCMBS was 450 +/- 48 mumol/l. Chemical modifications of SH-groups by PCMBS caused a significant reduction (p < 0.005) in the Vmax for Na(+)-dependent alanine influx from 0.57 +/- 0.06 to 0.16 +/- 0.05 nmol.mg protein-1.10s-1 without affecting significantly the Km value. Inhibition by PCMBS was reversed by treatment of BBMV with DTT. When the substrate binding site of the transporter was protected by alanine or leucine, PCMBS still, blocked transport function, indicating that the crucial SH groups are not located within the substrate binding site of the transport proteins.

Effects of imazalil on sterol composition of sensitive and DMI-resistant isolates of Penicillium italicum

Imazalil differentially inhibited dry weight increase of 10-hour-old germlings of wild-type and DMI-resistant isolates ofPenicillium italicum in liquid malt cultures. EC50 values ranged from 0.005 to 0.27 μg ml−1. In all isolates ergosterol constituted the major sterol (over 95% of total sterols) in the absence of the fungicide. Therefore, DMI-resistance cannot be associated to a deficiency of the C-14 demethylation enzyme in the ergosterol biosynthetic pathway. Imazalil treatment at concentrations around EC50 values for inhibition of mycelial growth resulted in a decrease in ergosterol content and a simultaneous increase in 24-methylene-24,25-dihydrolanosterol content in all isolates. A correlation existed between the imazalil concentration necessary to induce such changes in sterol composition and the EC50 values for inhibition of mycelial growth of the different isolates. The reason for the differential effects of imazalil on sterol composition in the variousP. italicum isolates may be due to decreased accumulation of the fungicide in the mycelium and to other yet non-identified mechanisms of resistance.

Effects of fenflumizole on aggregation ex vivo of human platelets and formation of thromboxane B2 and 6-keto-prostaglandin-F1 alpha.

Fenflumizole (2-(2,4-difluorophenyl)-4,5-bis(4-methoxyphenyl)imidazole), a new non-steroidal anti-inflammatory drug, was given to healthy subjects in single oral doses of 0.1, 1 and 2 mg/kg. The effect of the drug was followed for up to 8 h by repeated tests of arachidonic acid-induced platelet aggregation and was related to its concomitant plasma concentration. Fenflumizole reversibly inhibited platelet aggregation and the degree of inhibition was found to be linearly correlated with the log plasma concentration. There was depression of the formation of thromboxane B2 and 6-keto-prostaglandin F1 alpha (the stable metabolites of thromboxane A2 and prostacyclin) in clotted whole blood measured by radioimmunoassay after fenflumizole 1 mg/kg. This effect was directly related to the concentration of the drug in plasma, the maximum effect being reached at fenflumizole concentrations greater than 200 ng/ml. EC50-values for inhibition of the formation of thromboxane B2 and 6-keto-prostaglandin F1 alpha were approximately 20 and 40 ng/ml, respectively. The results suggest that orally administered fenflumizole is a potent inhibitor of platelet aggregation and prostanoid formation.

Effects of two dithiocarbamates on the grass shrimp, Palaemonetes pugio: molt-related toxicity and inhibition of limb regeneration.

The effects of two dithiocarbamate formulations (Aquatreat® DNM-30 and Busan® 85) on the initiation and progression of limb regeneration following the removal of the left fifth walking leg (pereiopod) were studied with the estuarine grass shrimp,Palaemonetes pugio. Exposure to either Aquatreat DNM-30 or Busan 85 affected both the initiation and progression of limb regeneration; the shrimp exhibited dose-related inhibition of regenerative growth. The resultant EC50 values for inhibition of regenerative limb growth were well below the median lethal concentrations (LC50s) for grass shrimp. In tests with molting grass shrimp, Busan 85 was more acutely toxic than Aquatreat DNM-30.