Study of the principles in the first phase of experimental pharmacology: the basic step with assumption hypothesis.

BACKGROUND: Experimental pharmacology deals with effects of various test substances studied on different animal species which is aimed at finding out safe therapeutic agent suitable for public health as well as mechanism and site of action of a test substance. It is the basic step in the discovery of new drugs or studying the pharmacological actions of already developed one using both preclinical and clinical study designs in a stepwise phase of investigations. However, the investigations in the first phase of experimental pharmacology are usually concluded with assumption hypothesis without any adequate validation of the scientific evidence. Single dose acute toxicology had been conducted on Balb c mice with three different level of doses prepared from each of three different test chemicals (Dichlorvos, Chlorpyrifos and Cypermethrin) with known median lethal dose (LD50) to define the fundamental principles, cause of toxicity and investigation timeframe in the first phase of experimental pharmacology. METHODS: The methods used for data collection were: procurement of test chemicals, investigation of single dose acute toxicity on Balb c mice and quantitative immunoglobulins test. Data was thematically compiled for validation of the findings from each of the sources. RESULTS: The result showed that the dose had never limited the toxic property of tested chemicals but the magnitude of adverse effect and length of time at which adverse effect was manifested on treated Balb c mice. The toxicity of tested chemicals was however limited by the toxic reaction rate of a dose in the biological process of exposed Balb c mice. The toxic effect of tested chemicals became magnified within a short period of time when large amount administered orally. It also remained after a long period of time when small amount administered in the same route. CONCLUSION: Adequate investigation time for acute toxicity study was therefore essential for comprehensive analysis of pharmacological property of tested chemicals at different level of doses.

Polyphenol-Rich Fraction of Parquetina nigrescens Mitigates Dichlorvos-Induced Cardiorenal Dysfunction Through Reduction in Cardiac Nitrotyrosine and Renal p38 Expressions in Wistar Rats.

Parquetina nigrescens is commonly used to treat diseases in humans and animals in developing countries, including Nigeria. This study evaluates the effects of its polyphenol-rich fraction (prf) on dichlorvos-induced cardio- and renal toxicity. There were several factors assessed during this study, including cardiac and renal markers, serum myeloperoxidase and xanthine oxidase, and electrocardiograph (ECG) changes. The changes in electrocardiograph (ECG) were recorded. Immunohistochemistry of cardiac and renal p38 and nitrotyrosine was determined. Dichlorvos exposure caused a significant decrease in L-glutathione (reduced glutathione) and other antioxidant enzymes with increases in malondialdehyde, myeloperoxidase, advanced oxidation protein products, and protein carbonyl levels. It also brought about alterations in microanatomy of the heart and kidneys accompanied by increases in serum creatinine and urea levels. Exposure to dichlorvos induced prolonged QRS interval and shortened QT durations in rats. Immunohistochemistry revealed lower expressions of cardiac nitrotyrosine and renal p38 (mitogen-activated protein kinase; MAPK) in rats treated with prf of P. nigrescens. Combining all, prf of P. nigrescens demonstrated antioxidant as well as protective properties in the heart and kidneys of rats exposed to dichlorvos. It ameliorated dichlorvos-induced cardio- and nephrotoxicity giving credence to its use in ethnomedicine.

A metabonomic analysis of the effect of quercetin on toxicity induced by chronic exposure to low-level dichlorvos in rat plasma.

A previous study of ours has reported that chronic exposure to low-level dichlorvos (DDVP, 7.2 mg per kg bw) damages the liver, interferes with fatty acid metabolism, and disturbs the antioxidant defense system in rats. This study aims to investigate whether or not quercetin can protect against DDVP-induced toxicity through metabonomics and to elucidate the mechanism underlying this protective effect. Rats were randomly assigned into the control group, DDVP-treated group, quercetin-treated group, and quercetin plus DDVP-treated group. DDVP and quercetin were administered to the rats daily via drinking water and gavage, respectively, continuously for 90 d. The metabonomic profiles of rat plasma were analyzed using ultra-performance liquid chromatography-mass spectrometry. Finally, 11 metabolites were identified, including those of quercetin, isorhamnetin, and quercetin-3-glucuronide. The 11 metabolites showed significant changes in some treatment groups compared with the control group. Arachidonic acid, phytosphingosine, and C16 sphinganine significantly decreased while p-cresol, lysoPE (16:0/0:0), lysoPC (15:0/0:0), lysoPC (16:0/0:0), lysoPC (0:0/18:0), and tryptophan significantly increased in the DDVP-treated group compared with the control group. The tendency of the aforementioned metabolites to change was significantly ameliorated in the high-dose quercetin (50 mg per kg bw per day) plus DDVP-treated group compared with the DDVP-treated group. However, the levels of these metabolites in the high-dose quercetin plus DDVP-treated group were still significantly different from those in the control group. The results indicate that high-dose quercetin (50 mg per kg bw per day) elicits a partial protective effect on DDVP-induced toxicity. The histopathology of the liver tissues was consistent with the above results. Quercetin demonstrated regulatory effects on the metabolism of lipids and amino acids, the antioxidant defense system, etc. Therefore, increasing the daily intake of quercetin can ameliorate the toxicity induced by chronic exposure to low-level DDVP residue in food and/or water.

Efficacy of trimedoxime in mice poisoned with dichlorvos, heptenophos or monocrotophos.

The aim of the study was to examine antidotal potency of trimedoxime in mice poisoned with three direct dimethoxy-substituted organophosphorus inhibitors. In order to assess the protective efficacy of trimedoxime against dichlorvos, heptenophos or monocrotophos, median effective doses and efficacy half-times were calculated. Trimedoxime (24 mg/kg intravenously) was injected 5 min. before 1.3 LD50 intravenously of poisons. Activities of brain, diaphragmal and erythrocyte acetylcholinesterase, as well as of plasma carboxylesterases were determined at different time intervals (10, 40 and 60 min.) after administration of the antidotes. Protective effect of trimedoxime decreased according to the following order: monocrotophos > heptenophos > dichlorvos. Administration of the oxime produced a significant reactivation of central and peripheral acetylcholinesterase inhibited with dichlorvos and heptenophos, with the exception of erythrocyte acetylcholinesterase inhibited by heptenophos. Surprisingly, trimedoxime did not induce reactivation of monocrotophos-inhibited acetylcholinesterase in any of the tissues tested. These organophosphorus compounds produced a significant inhibition of plasma carboxylesterase activity, while administration of trimedoxime led to regeneration of the enzyme activity. The same dose of trimedoxime assured survival of experimental animals poisoned by all three organophosphorus compounds, although the biochemical findings were quite different.

Fumigant activity of (E)-anethole identified in Illicium verum fruit against Blattella germanica.

The insecticidal activities of materials derived from the fruit of star anise, Illicium verum, against adults of Blattella germanica were examined by direct contact application and fumigation methods, and compared with those of DDVP, deltamethrin and hydramethylnon. The biologically active constituent of the Illicium fruit was characterized as the phenylpropene, (E)-anethole, by spectroscopic analysis. In a filter paper diffusion test with females, (E)-anethole caused 80.3% mortality at 0.159 mg cm-2 at 1 and 3 days after treatment (DAT), whereas 16.7% mortality at 3 DAT was achieved at 0.079 mg cm-2. DDVP and deltamethrin gave > 90% mortality at 0.019 mg cm-2 at 1 DAT. At 0.009 mg cm-2, DDVP and deltamethrin showed 73.3 and 60% mortality at 1 DAT, respectively, but 93.3 and 76.7% mortality at 3 DAT. Hydramethylnon exhibited 0 and 93.3% mortality at 0.159 mg cm-2 at 1 and 3 DAT, respectively, whereas 6.7% mortality at 3 DAT was observed at 0.079 mg cm-2. In a fumigation test with females, (E)-anethole was much more effective in closed cups than in open ones, indicating that the insecticidal activity of the compound was largely attributable to fumigant action. (E)-Anethole and DDVP caused 100% mortality at 0.398 and 0.051 mg cm-2 4 and 1 h after treatment, respectively. (E)-Anethole showed 46.7% mortality at 0.199 mg cm-2 at 3 DAT, whereas deltamethrin and hydramethylnon at 0.796 mg cm-2 was ineffective for 3-day period. As naturally occurring insect-control agents, the I verum fruit-derived materials described could be useful for managing populations of B germanica.

Malathion and dichlorvos toxicokinetics after the oral administration of malathion and trichlorfon.

We studied the distribution and persistence of malathion and dichlorvos in the Wistar rat and established their toxicokinetics with the help of the PCNONLIN software program.

Pathological changes in testes and liver of male albino rats after dermal exposure to DDVP insecticide.

Exposure of male albino rats to DDVP insecticide at sublethal dose of 30 mg/kg/day through dermal painting for a period of 90 days didn't show any intoxication symptoms or mortality. However, cytopathological changes in testicular and liver tissues were evident. There was a positive correlation between the degree of cellular damage and the period of insecticide administration. In general, damages were prominent in rats treated for 30 days or more. Histological examination of testes showed degenerative seminiferous tubules and fewer leydig cells. Hepatic cells were congested, atrophied and showed different stages of necrobiotic changes. This suggests a great care and caution for workers during different phases of DDVP insecticide handling.

Teratogenic potential of dichlorvos given by inhalation and gavage to mice and rabbits.

Dichlorvos (2,2-dichlorovinyl dimethyl phosphate) is an important organophosphate insecticide and anthelmintic with widespread use. The purpose of this study was to evaluate the teratogenic potential of dichlorvos given orally at the maximum tolerated dose to mice (60 mg/kg/day) and rabbits (5 mg/kg/day) and by inhalation in both species at a concentration of 4 microgram/l seven hours daily. Dichlorvos was not found to be teratogenic in either species by either route of administration.