Investigations of amitraz neurotoxicity in rats. III. Effects on motor activity and inhibition of monoamine oxidase

Amitraz toxicity to the midge Chironomus riparius: Life-history and biochemical responses

Acute and chronic toxicity of the formamidine pesticide amitraz to the midge Chironomus riparius was assessed using conventional ecotoxicological tests and biochemical approaches (biomarkers). Amitraz is mainly used as an ectoparasiticide in veterinary medicine, but also in agriculture and apiculture. However, information of amitraz toxicity to non-target invertebrates is limited. Besides the impairment of developmental and emergence rates (reduced larval growth, emergence, and delayed development time) caused by chronic exposure to amitraz, acute exposures induced alterations in the antioxidant enzymes glutathione peroxidase (GPx) and catalase (CAT), and in energetic metabolism biomarkers, lactate dehydrogenase (LDH) and electron transport system (ETS) activities. Moreover, lipid peroxidation (LPO) increased by amitraz exposure. Our results reveal potential secondary effects of amitraz to invertebrates and biomarkers that may aid in the interpretation of sub-lethal toxic responses to amitraz. These results add information concerning the potential outcomes of amitraz exposure to freshwater invertebrates underlining the importance of risk assessment studies of formamidine pesticides.

Pharmacokinetics and brain distribution of amitraz and its metabolites in rats

Amitraz is an acaricide and insecticide widely used in agriculture and veterinary medicine. Although central nervous system (CNS) toxicity is one of major toxicities following oral ingestion of amitraz, the understanding of the cause of the toxicity is limited. This study evaluated the systemic and brain exposure of amitraz and its major metabolites, BTS27271, 2',4'-formoxylidide, and 2,4-dimethylaniline following administration of amitraz in male Sprague-Dawley rats. Significant metabolism of amitraz was observed following the intravenous and oral administration. Amitraz related metabolites were majority of the total exposure observed, especially following oral administration. BTS27271 had higher brain exposure than amitraz and its other metabolites, which was due to low plasma protein binding but high brain tissue binding of BTS27271. Since BTS27271 has similar or higher toxicity and α₂-adrenoreceptor agonist potency than amitraz, its exposure in brain tissues may be the major cause of CNS toxicity of amitraz in animals and humans.

Amitraz changes NE, DA and 5-HT biosynthesis and metabolism mediated by alterations in estradiol content in CNS of male rats

Amitraz is a formamidine insecticide/acaricide that alters different neurotransmitters levels, among other neurotoxic effects. Oral amitraz exposure (20, 50 and 80 mg/kg bw, 5 days) has been reported to increase serotonin (5-HT), norepinephrine (NE) and dopamine (DA) content and to decrease their metabolites and turnover rates in the male rat brain, particularly in the striatum, prefrontal cortex, and hippocampus. However, the mechanisms by which these alterations are produced are not completely understood. One possibility is that amitraz monoamine oxidase (MAO) inhibition could mediate these effects. Alternatively, it alters serum concentrations of sex steroids that regulate the enzymes responsible for these neurotransmitters synthesis and metabolism. Thus, alterations in sex steroids in the brain could also mediate the observed effects. To test these hypothesis regarding possible mechanisms, we treated male rats with 20, 50 and 80 mg/kg bw for 5 days and then isolated tissue from striatum, prefrontal cortex, and hippocampus. We then measured tissue levels of expression and/or activity of MAO, catechol-O-metyltransferase (COMT), dopamine-β-hydroxylase (DBH), tyrosine hydroxylase (TH) and tryptophan hydroxylase (TRH) as well as estradiol levels in these regions. Our results show that amitraz did not inhibit MAO activity at these doses, but altered MAO, COMT, DBH, TH and TRH gene expression, as well as TH and TRH activity and estradiol levels. The alteration of these enzymes was partially mediated by dysregulation of estradiol levels. Our present results provide new understanding of the mechanisms contributing to the harmful effects of amitraz.

A study on immunotoxicological effects of subacute amitraz exposure in rats

The effects of amitraz, a formamidine pesticide, were investigated in four-week old outbred male Wistar rats on certain classic toxicological and haematological parameters as well as on specific immune functions. The animals were treated, per os by gavage for 28 days, in a five-day treatment two days break system, with 26.5, 21.1, 10.6 and 5.29 mg/kg/day amitraz. On the 29th day, organ weights of the thymus, heart, lung, spleen, liver, kidneys, adrenals, testicles and popliteal lymph node; WBC and RBC counts, Ht, MCV, haemoglobin; and cell content of the femoral bone marrow were determined. In two separate groups, the effects of amitraz on the PFC content of the spleen, and on the maximum level and time course of DTH reaction, were investigated.

Amitraz in 26.5 mg/kg dose increased relative adrenal weight, and decreased relative liver weight, MCV value, PFC content of the spleen, and the maximum level of DTH reaction. The 21.1 mg/kg dose decreased only MCV value, while 10.6 mg/kg elevated the liver-to-brain weight ratio. Based of these findings, a NOEL dose of 5.29 mg/kg was determined for amitraz in this experimental system; while the LOEL doses were 10.6 mg/kg for the general toxicological, 21.1 mg/kg for the haematological and 26.5 mg/kg for the immune function parameters. The results show that the exposure sensitivity of these immune functions to amitraz is lower than that of some other toxicological and haematological parameters. Human & Experimental Toxicology ( 2007) 26 , 441—445

Production of date palm fruits free of acaricides residues by ozone technology as post-harvest treatment

Distilled water and ozonated water as postharvest wash treatments for 15-60 min as dipping times were tested to remove two acaricides namely, dicofol and amitraz from different varieties of date fruits. Recovered amount of the acaricides was extracted using solid phase extraction (SPE) and then analyzed by gas chromatography-mass spectrometry (GC-MS). Dicofol removal percentages in the presence of ozone increased in the order of Nabtet Aly > Nabout Seif > Khalas > Sakay, while amitraz removal increased in the order of Nabtet Aly > Nabout Seif > Sakay > Khalas, respectively, and the percentages of residues on date fruits depended on the dipping time. Kinetic studies revealed that dicofol and amitraz were easily removable from date fruits treated with ozonated water. Ozone-treated date palm fruits were not associated with significant changes in antioxidant capacity, and phenolic and sugar contents. Due to the large amount of dates consumed by Saudi residents, a higher risk of exposure to pesticides, especially in children and other vulnerable individuals may occur and the search for safety methods to remove pesticides with negligible residual deposits has always been preferred. Therefore, the present study validated that ozone technology as wash treatments is safe and promising processes for the removal of acaricides from date fruits surface under domestic conditions to reduce the impact over consumer's health.

Effects of amitraz on motor function

The effects of amitraz, a formamidine derivative, on motor function were studied in rats. Behavioural and neurochemical studies were performed. Results show that amitraz was able: 1) to decrease locomotion and rearing frequencies of rats and to increase their immobility time in an open-field; 2) to displace to the left the control dose-response curve constructed to apomorphine-induced stereotyped behavior; 3) to potentiate both pentobarbital sleeping time and amphetamine effects on open-field behaviour of rats and 4) to increase not only the whole brain levels of noradrenaline but also the striatal levels of dopamine. In relation to control animals, the pesticide also induced 5) a decrease in the striatal levels of homovanillic acid, 6) pesticide effects on open-field behaviour of rats were not antagonized by yohimbine administration, and 7) metoclopramide administration on amitraz pretreated rats antagonized not only amphetamine effects on open-field behaviour, but also apomorphine-induced stereotypy. These results are discussed in the light of the actions of amitraz on biogenic amines. It is suggested that the pesticide effects on motor function are consequences of the inhibitory effects on MAO activity, most probably through the increases produced on catecholamine levels within the central nervous system.

Hepatotoxic interactions of ethanol with allyl alcohol or carbon tetrachloride in rats

To assess whether potential toxic interactions occur between ethanol and allyl alcohol or carbon tetrachloride following subacute, concurrent chemical exposure, male Fischer 344 rats, approximately 70 d of age, were given ethanol at 0, 0.05, 0.1, 0.2, or 0.5 ml/kg in corn oil daily by gavage for 14 d (ETOH group), or the same levels of ethanol with 21 mg allyl alcohol/kg (ALAC group), or the same levels of ethanol with 20 mg carbon tetrachloride/kg (CCL4 group). Hepatic response was assessed 24 h after the last dose. Interactions were evaluated by comparing the ETOH group with either the ALAC group or the CCL4 group using multivariate analysis of variance procedures. No statistically significant interaction was seen between the ETOH group and the ALAC group at the dosages used. Although an interaction between ethanol and carbon tetrachloride given simultaneously was not statistically significant, a small interactive effect on weight gain from d 0 to termination was apparent (p = .057). Exposure to ethanol alone resulted in a concentration-dependent decrease in absolute and relative liver weight, with a threshold between 0.05 and 0.1 ml/kg. There was no histopathological evidence of hepatic damage with ethanol alone, and no effect on hepatic cytochrome P-450 and glutathione levels or on serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALK). Exposure to allyl alcohol alone resulted in significant increases in absolute and relative liver weights, liver glutathione, and periportal hepatocellular vacuolar degeneration. Exposure to carbon tetrachloride alone resulted in significant increases in absolute and relative liver weight, serum levels of ALT, AST, and ALK, and centrilobular hepatocellular vacuolar degeneration and necrosis. These observations indicate that subacute, concurrent exposure of ethanol with carbon tetrachloride or allyl alcohol at ethanol levels comparable to those reported in gavage vehicles did not result in interactive toxicity.

Rat strain and stock comparisons using a functional observational battery: baseline values and effects of amitraz

A functional observational battery (FOB) was utilized to assess the effects of 3-day exposure to the formamidine pesticide amitraz in outbred Sprague-Dawley-derived and inbred Fischer-344-derived (F344) rats (both from Charles River Laboratories) and in outbred Long-Evans rats obtained from two commercial suppliers (Charles River Breeding Laboratories and Blue Spruce Farms). Significant strain and stock differences were obtained in baseline values for one-third of the FOB measures. In most cases, F344 rats were different from the others. Characteristic signs of amitraz exposure consisting of increased excitability, hyper-reactivity, and physiological and autonomic changes were evident in all treated rats. These effects increased with repeated dosing, and many were still present 6 days after dosing. On individual measures, there were differences between the strains and stocks in terms of sensitivity and time course of amitraz effects. In general, Blue Spruce Long-Evans rats displayed more effects of amitraz and F344 rats recovered more quickly than others. Although Sprague-Dawley rats showed the least effect overall, they displayed the largest increases in the sensorimotor responses to stimuli. These data indicate that although some behavioral and physiological parameters showed strain and supplier differences, in both baseline values and the effects of amitraz, conclusions concerning its neurotoxic potential in a screening context would be similar.