Possible causes of excess sludge reduction adding metabolic uncoupler, 3,3',4',5-tetrachlorosalicylanilide (TCS), in sequence batch reactors

Two parallel sequence batch reactors (SBRs) were operated, with and without TCS addition, to research the causes of sludge reduction by uncouplers. Three possible mechanisms of sludge reduction by TCS were studied: (1) occurrence of metabolic uncoupling, (2) consumption of more energy to resist the infection of TCS, (3) promotion of lysis-cryptic growth by TCS addition. Results showed the remarkable reduction of electronic transport system (ETS) activity and specific cellular ATP (SATP) in TCS reactor, which proved the occurrence of metabolic uncoupling. The increasing amounts of extracellular polymeric substances (EPS), as measured by chemical methods and excitation-emission matrix (EEM) fluorescence spectra, implied microorganisms consumed more energy to resist TCS. The similar DNA concentrations of the effluents in two reactors indicated sludge lysis was not intensified by TCS. Therefore, uncoupler might not only cause metabolic uncoupling but also induce more energy consumption in the production of some substances to resist uncoupler.

The binding of closantel to ovine serum albumin, and homogenate fractions of Haemonchus contortus

Closantel binds to the serum proteins of the host and affects blood sucking parasites when they ingest the blood of treated hosts. Closantel binds specifically to ovine serum albumin (K(a) of 9. 3x10(6)M(-1)) at site I, the warfarin/phenylbutazone binding site of albumin Closantel also binds to invertebrate haemocyanin and haemolymph. The strongest binding of closantel in homogenates of H. contortus is found in fractions containing soluble proteins. This binding is of low affinity and, because the site itself is not fully denaturable, it may not be proteinaceous. There is no detectable difference in binding affinity between homogenate fractions from closantel susceptible and resistant isolates of adult or larval worms suggesting that closantel resistance is not due to changes in the closantel receptor or carrier.

The effect of feed intake level on the pharmacokinetic disposition of closantel in sheep

Closantel (CLS), containing a trace of [14C]CLS, was administered intraruminally to sheep whose feed intake was maintained at either 800 or 400 g day-1. The kinetic disposition of [14C]metabolites was determined in rumen and abomasal fluid and particulate digesta and of CLS per se in plasma. The slower digesta flow rate in the sheep on low, compared with high, feed intake resulted in the proportion of the dose passing through the abomasum being reduced from 60 to 45%. Increased absorption of CLS from the rumen of sheep on low feed intake resulted in both higher maximum CLS concentration and greater area under CLS plasma concentration versus time curve, although the elimination half-life was independent of feed intake. Not only are the higher plasma CLS concentrations likely to increase efficacy against Haemonchus contortus, the threshold concentrations that are considered to inhibit the establishment of ingested H. contortus larvae were extended by 10-14 days. The extended CLS presence after reduced feeding, when integrated with parasite treatment programmes, provides an opportunity to reduce the impact of H. contortus infection.

Haemonchus contortus: the uptake and metabolism of closantel

Closantel is an anthelmintic which associates with plasma albumin and is useful for the control of sheep parasites, such as Haemonchus contortus, that ingest blood. However, the utility of closantel for parasite control has been threatened by the emergence of resistance. The mechanisms of resistance are unknown. A closantel-resistant and a closantel-susceptible isolate of H. contortus were compared with respect to the distribution and metabolism of closantel. Neither strain appeared to metabolise closantel in vitro or in vivo. Following treatment of infected sheep with radioactively labelled closantel, isotope levels in closantel-resistant adult H. contortus were significantly lower than in susceptible worms. This reduced accumulation of drug could contribute to closantel resistance by mechanisms such as reduced feeding, failure to dissociate the drug-albumin complex in the gut or increased efflux of closantel from resistant worms.

Studies on tetrachloroethene respiration in Dehalospirillum multivorans

Tetrachloroethene (PCE) respiration was studied in the tetrachloroethene-utilizing anaerobe, Dehalospirillum multivorans, with respect to localization of the catabolic enzymes, the electron carriers potentially involved in electron transport, and the response to ionophores and specific inhibitors. Hydrogenase and formate dehydrogenase were recovered in the periplasmic cell fraction and were membrane-associated. Electron-accepting tetrachloroethene dehalogenase was found in the cytoplasmic fraction. In the PCE dehalogenase assay, only artificial electron donors with a standard redox potential of D. multivorans (Eo' = -445 mV) could serve as electron donor for PCE reduction. However, the reaction rate with ferredoxin was only 1% of that with methyl viologen, whereas the pyruvate-ferredoxin oxidoreductase exhibited almost the same reaction rates with methyl viologen and ferredoxin as electron acceptors for pyruvate oxidation. Reduced menadione (2-methyl-1, 4-naphthoquinone) did not serve as electron donor in the PCE dehalogenase reaction. 2-Heptyl-4-hydroxyquinoline-N-oxide (HOQNO) had no significant effect on PCE dechlorination in cell suspensions and in crude extracts. Whole cells catalyzed the reductive dechlorination of PCE with H2 or formate as electron donors. The dechlorination in cell suspensions rather than in cell extracts was inhibited by the ionophores carbonylcyanide-p-(trifluoromethoxy)phenylhydrazone (FCCP) and tetrachlorosalicylanilide (TCS), indicating that a membrane potential and/or a pH gradient may be required for the reaction in vivo.

Simultaneous determination of five fasciolicides in milk by liquid chromatography with electrochemical detection

A sensitive and specific method is described for determination of 5 fasciolicides in milk. The drugs are used to control liver flukes in cattle. The milk sample was homogenized with acetone and acetonitrile, sonicated, and centrifuged. The supernatant was extracted with dichloromethane. The extract was evaporated to dryness, dissolved in 1% sodium hydrogen carbonate, and purified on a C18 cartridge. The 5 drugs were separated from the matrix by reversed-phase liquid chromatography (LC) and determined by dual-electrode coulometric detection on a Kaseisorb LC ODS-300-5 column. The mobile phase was acetonitrile-0.05M potassium dihydrogen phosphate (55 + 45) at pH 3.0. The flow rate was 1 mL/min at 40 degrees C. The applied potentials of detectors 1 and 2 were set at 0.20 and 0.55 V, respectively. The average recovery of the drugs added to milk at 0.01 and 0.1 micrograms/mL was 89.6%, and the coefficient of variation was 4.7%. The detection limits of the drugs in milk were 4-20 ng/mL. The method is used to monitor commercial milk samples and to determine the residual levels of these drugs in milk from cows treated with a fasciolicide.

Closantel intoxication in a dog

A case of overdosage with closantel, a salicynalide derivative, in a dog is described. The dog received 6 times the recommended dosage. Closantel induced optic neuritis, retinal degeneration, partial deafness, hepatotoxicosis and myopathy. Only the blindness was irreversible. The therapy included albumin administration to reduce the acute toxicity of closantel.

Inhibitory effect of melanin pigment on sensitization and elicitation of murine contact photosensitivity: mechanism of low responsiveness in C57BL/10 background mice

We have shown that murine contact photosensitivity (CPS) to 3,3',4',5-tetrachlorosalicylanilide (TCSA) is genetically controlled mainly by the major histocompatibility complex. The H-2b,d haplotypes are closely associated with high responders, whereas mice with the H-2k are non-responders. Irrespective of their H-2 haplotypes, the C57BL/10 (B10) background strains, including B10, B10.D2, B10.A, and B10.BR, possessing black fur color, were low or nonresponders in CPS to TCSA. In B10 mice, however, high-sensitivity responses were induced when subcutaneous inoculation of epidermal cells (ECs) photomodified in vitro with TCSA was used for both immunization and challenge, suggesting that the epicutaneous route for induction and elicitation is defective in B10 background mice. F1 mice obtained by crossing high-responder BALB/c and low-responder B10 mice, possessing agouti fur color, were non-responders of CPS. The magnitude of CPS in the F2 mice derived from F1 (BALB/c X B10) siblings varied from low to high. When these F2 mice were divided into five groups with regard to fur color, the magnitude of reaction was correlated with the fur color and there was inverse relationship between the magnitude of CPS and the amount of melanin pigment in earlobe ECs. Furthermore, the in vivo formation of TCSA-EC photoadducts was negatively correlated to the melanin amount in earlobes. These observations suggested that the failure in CPS of the B10 background mice stems from inability of in vivo photocoupling of TCSA to ECs, presumably due to absorption of ultraviolet radiation by melanin pigment.

The pharmacodynamics of the flukicidal salicylanilides, rafoxanide, closantel and oxyclosanide

The pharmacokinetics of oxyclosanide, rafoxanide and closantel were investigated in sheep (n = 5). All three drugs were extensively (greater than 99%) bound to plasma proteins and the plasma concentration/time curve was best described by a tri-exponential equation. Closantel and rafoxanide had long terminal half-lives (mean 14.5 and 16.6 days, respectively) compared with oxyclosanide (mean 6.4 days). In a study of the efficacy of rafoxanide against Fasciola hepatica, a dose rate of 7.5 mg kg-1 against 6-week-old flukes appeared to be similarly effective to a dose rate of 2.5 mg kg-1 against 10-week-old flukes (86% and 88% efficacy, respectively), as assessed at autopsies carried out on all sheep when the flukes were 14 weeks old. Part of this putative efficacy against immature flukes may be due to rafoxanide persisting in the plasma and affecting the mature flukes when they reach the bile ducts.

The metabolism and fate of closantel (Flukiver) in sheep and cattle

Closantel was reasonably well absorbed in sheep and cattle. After oral (10 mg/kg) or parenteral (5 mg/kg) administration, similar peak times (8-48 h) and peak plasma levels (45-55 micrograms/mL) are observed. Plasma level-time curves are superimposable for either route and increase linearly with the dose. The elimination half-life of closantel is 2 to 3 weeks. The relative bioavailability of 50% of oral closantel can partly be explained by incomplete absorption. Experiments in sheep with 14C-closantel revealed that the plasma radioactivity is almost exclusively due to the unmetabolized drug, metabolites accounting for less than 2%. At least 80% of the dose was excreted with the feces over the investigational period of 8 weeks, and less than 0.5% with the urine. Closantel was only poorly metabolized. Over 90% of the fecal radioactivity was due to the parent compound. Two monoiodoclosantel isomers were the only fecal metabolites detected with radio-HPLC. The distribution of closantel to tissues was limited by its high protein binding. Closantel bound strongly (greater than 99.9%) and almost exclusively to plasma albumin. Accordingly, tissue concentrations were many times lower than the corresponding plasma levels. Residual radioactivity in sheep in all tissues but liver was entirely due to closantel. About 30% to 40% of the liver radioactivity could be attributed to monoiodoclosantel. In both sheep and cattle, residual tissue concentrations decline parallel to the plasma concentrations. Consequently, the plasma kinetics of closantel reliably reflect its depletion from tissues. Independently of the dosing scheme and route of administration, the maximum daily intake by the consumer was always below the acceptable daily intake within 4 weeks after the last dose.

A comparison of the metabolism and elimination of benzanilide and salicylanilide in the rat

1. The metabolism and elimination of benzanilide and salicylanilide in rats were compared. 2. For both compounds, greater than 70% dose was excreted in urine with 20% in faeces, in 3 days. 3. With [14C]benzanilide and [14C]salicylanilide, 40% and 35% respectively of the 14C was excreted in the bile in 24 h. 4. Benzanilide was metabolized to 4'-hydroxybenzanilide (24%), 2-hydroxybenzanilide (salicylanilide, 19%) and 2'-hydroxybenzanilide (13%), with small amounts of 4-hydroxybenzanilide. 5. Salicylanilide was excreted unchanged (56%) with small amounts of the 5-hydroxy and 4'-hydroxy-derivatives. 6. All metabolites were present as glucuronide conjugates; the free aglycones were not found.

The influence of glutathione on the photoreaction of 3,4',5-tribromosalicylanilide alone and in the presence of serum albumin

Glutathione is known to play a prominent detoxifying role in the organism. In this study attention has been paid to the possible occurrence of a detoxifying action of glutathione on the photoreaction of 3,4',5-tribromosalicylanilide (tbsa), which is notorious for causing photoallergy. It was found that tbsa forms stable photoconjugates on irradiation with glutathione: 3-glutathyl-4',5-dibromosalicylanilide and 5-glutathyl-4'-bromosalicylanilide. The rate of the photoreaction of tbsa in the presence of glutathione, resulting in photostable products, is increased. Furthermore, covalent binding with serum albumin appeared to be decreased in the presence of glutathione.

The metabolism and disposition of 3,5-dibromosalicylanilide in male and female rats

1. The metabolism of the pesticide, 3,5-dibromosalicylanilide, has been studied following oral administration to rats. 2. This compound is more toxic than other brominated salicylanilides, some fatalities being recorded at an oral dose of 100 mg/kg. 3. 3,5-Dibromosalicylanilide is well absorbed, and excreted in urine and bile as sulphate and glucuronide conjugates of the parent compound and of several phenolic metabolites. Radioactivity was present in tissues (blood, kidney, liver, fat) six days after dosing with 3,5-dibromosalicyl[14C]anilide. 4. Sex-differences occur, both in excretion route and in the proportions of urinary metabolites.

The disposition and metabolism of 3,4',5-tribromosalicylanilide and 4'5-dibromosalicylanilide in the rat

1. The metabolism of two pesticides, 3,4',5-tribromosalicylanilide (TBS) and 4',5-dibromosalicylanilide (DBS) has been studied after oral administration to rats. 2. Approximately 65% of the dose of TBS is absorbed, and then excreted as glucuronide and sulphate conjugates of two hydroxylated metabolites. One of these has been identified as 4'-hydroxy-3,5-dibromosalicylanilide, while evidence suggests that the other metabolite is 5-hydroxy-3,4'-dibromosalicylanilide. 3. In contrast, only 11% of the dose of DBS is absorbed; it is then excreted mainly as glucuronide and sulphate conjugates of the parent molecule.

The metabolism of the anthelmintics clioxanide and resorantel and related compounds in vitro by Moniezia expansa, Ascaris suum and mouse- and sheep-liver enzymes

1. Clioxanide and related compounds were deacetylated by the cestode Moniezia expansa, the nematode Ascaris suum, by enzymes prepared from these species and by mouse- and sheep-liver homogenates. Deacetylase activity was found in the cytosol of cestode proglottids throughout the strobila, and in the cytosol of nematode intestinal cells and reproductive tract. 2. The O-deacetylases from both helminths showed similar pH optima of about 7.0. Activity was enhanced by Ca2+ and low molecular weight thiols. Cu2+, Cd2+, Hg2+, Zn2+, and La2+ inhibited the deacetylation of clioxanide. 3. Resorantel and clioxanide were not hydrolysed at the amide bond by helminth or mammalian enzymes. 4. Resorantel was hydroxylated by mammalian microsomal enzymes, but helminths did not modify the molecule.

Photoreactions of 3,3',4',5-tetrachlorosalicylanilide with proteins

The photoreactions of 3,3',4',5-tetrachlorosalicylanilide anion (TCSA-) with two serum proteins were studied. TCSA- and anions of two similar compounds, N-ethyl-3,5-dichlorosalicylamide and salicylanilide, bind noncovalently to human serum albumin (HSA) without irradiation in aqueous pH 7.4 buffered solutions. TCSA- noncovalently bound to HSA yields three types of photoproducts when irradiated with ultraviolet light (lambda greater than 360 nm). A covalently bonded photoadduct between TCSA- and HSA is formed and histidines in HSA are chemically modified. In addition to these two types of photoproducts which involve HSA, two of the four TCSA- photoproducts which form when HSA is absent are also formed when the TCSA-/HSA complex is irradiated. The results presented indicate that not all proteins in the skin are capable of being the carrier protein in photoallergy of TCSA- and that cross reactivity to other halogenated salicylanilides can be explained by further photochemical reactions of TCSA- photoproducts.