N,N-diethylphenylacetamide, an insect repellent: absence of mutagenic response in the in vitro Ames test and in vivo mouse micronucleus test

Mosquito repellents: An insight into the chronological perspectives and novel discoveries

Mosquito being the major medically important arthropod vector; requires utmost attention to reduce the sufferings and economic consequences of those living in the endemic regions. This is only possible by minimising the human-mosquito contact by an absolute preventing measure. However, unfortunately, such absolute measures are yet to be developed despite enormous efforts and huge investments worldwide. In the absence of vaccines for number of mosquito-borne diseases, repellents could be an attractive option for both military personal and civilians to minimise the risk of contacting different mosquito-borne diseases. However, to achieve this golden goal, the detailed knowledge of a particular repellent is must, including its mode of repellency and other relevant informations. Here, in the present article, an effort has been made to convey the best and latest information on repellents in order to enhance the knowledge of scientific community. The review offers an overview on mosquito repellents, the novel discoveries, and areas in need of attention such as novel repellent formulations and their future prospective.

Evaluation of mutagenic and antimutagenic activities of neem (Azadirachta indica) seed oil in the in vitro Ames Salmonella/microsome assay and in vivo mouse bone marrow micronucleus test

AIM OF THE STUDY

The possible mutagenic and antimutagenic activity of neem oil (NO) and its DMSO extract (NDE) were, examined in the Ames Salmonella/microsome mutagenicity test and the mouse bone marrow micronucleus assay.

MATERIALS AND METHODS

Eight different strains of Salmonella typhimurium were, used to study the genotoxicity of neem oil both in the presence and absence of Aroclor-1254 induced rat liver homogenate (S9). Two-dose treatment protocol was, employed to study the cytogenetic activity in micronucleus assay. Similarly, the antimutagenic activity of neem oil and NDE was studied against mitomycin (MMC) and 7,12-dimethylbenz[a]anthracene (DMBA) in the above two test systems.

RESULTS

Neem oil was non-mutagenic in all the eight tester strains of Salmonella typhimurium both in the presence and absence of S9 mix. In the present study, there was no significant increase in the frequency of micronucleated polychromatic erythrocytes (MNPCEs) in neem oil treated groups over the negative control (DMSO) group of animals, indicating the non-clastogenic activity of neem oil in the micronucleus test. Neem oil showed good antimutagenic activity against DMBA induced mutagenicity compared to its DMSO extract. However, neem oil showed comparatively less antimutagenicity against MMC in the Ames assay. In vivo anticlastogenic assays shows that neem oil exhibited better activity against DMBA induced clastogenicity.

CONCLUSION

These results indicate non-mutagenic activity of neem oil and significant antimutagenic activity of neem oil suggesting its pharmacological importance for the prevention of cancer.

N,N-diethyl phenylacetamide (DEPA): A safe and effective repellent for personal protection against hematophagous arthropods

Repellents play an important role in protecting humans from the bites of insect pests. An effective and safe repellent will be useful in reducing human-vector contact and thereby help in the interruption of vector borne disease transmission. Because of the unavailability of m-toluic acid in India for the manufacture of N,N-diethyl m-toluamide (DEET), there is a need to develop an alternate effective and safe insect repellent. In total, 120 substituted amides were synthesized and tested for repellency at 1.0 mg/cm2 under laboratory conditions. Among these amides, N,N-diethyl phenylacetamide (DEPA), applied at 1.0 mg/cm2 in different oil bases, was found to exhibit promising repellency (6-8 h) in the laboratory when tested against Aedes aegypti (L.) The repellent DEPA was evaluated on army personnel in comparison with dimethylphthalate (DMP) and DEET against mosquitoes, black flies, and land leeches under field condition in the North-East Frontier area of India. Both DEPA and DEET displayed broad-spectrum repellency. DEPA was more effective than DMP against all test organisms. However, no significant difference was noticed between DEPA and DEET for repellency at 0.25 and 0.5 mg/cm2 against black flies and mosquitoes. DMP was the least effective among the three compounds in the field studies. The relative potency of DEPA in comparison with DEET and DMP for repellency against Phlebotomine sand flies also was determined. At 0.1 mg/cm2, both DEPA and DEET were found to be equally effective with a protection time from 4.37 +/- 0.08 to 4.45 +/- 0.15 h. Both compounds were significantly more effective than DMP. At 0.2 mg/cm2, DEPA and DEET provided protection times of 6.52 +/- 0.08 and 7.15 +/- 0.15 h, respectively. DEPA was formulated into a vanishing cream, a pharmacologically safe polymer-based liquid, and a liposphere lotion. The vanishing cream and the two-polymer liquid formulations enhanced protection times from 4.4 to 6.5 and 7.13 h, respectively, compared with an alcohol solution applied at 0.5 mg/cm2 on the forearm of human volunteers. Formulations of DEPA and DEET applied at 0.5 mg/cm2 on rabbits exposed to Ae. aegypti enhanced protection times compared with an alcohol solution and the liposphere lotion from 4.0 to 6.0 h and 4.0 to 5.0 h, respectively. Comparison of mean protection times of DEET and DEPA applied at a rate of 0.3 mg/cm2 to human volunteers exposed to Cx. quinque-fasciatus under field conditions indicated that the lotion formulations of DEET and DEPA provided significantly (Duncan's multiple-range test, P < 0.05) higher protection times than did alcohol solutions. Toxicological studies revealed that DEPA is safe.

In vivo rodent erythrocyte micronucleus assay

The following summary represents a consensus of the working group except where noted. The items discussed are listed in the order in which they appear in the OECD guideline (474) for easy reference. Introduction, purpose, scope, relevance, application and limits of test. The analysis of immature erythrocytes in either bone marrow or peripheral blood is equally acceptable for those species in which the spleen does not remove micronucleated erythrocytes. In the mouse, mature erythrocytes are also an acceptable cell population for micronucleus analysis when the exposure duration exceeds 4 weeks. Test substances. Organic solvents such as DMSO are not recommended. Freshly prepared solutions or suspensions should be used unless stability data demonstrate the acceptability of storage. Vegetable oils are acceptable as solvents or vehicles. Suspension of the test chemicals is acceptable for p.o. or i.p. administration but not for i.v. injection. The use of any unusual solvent should be justified. Selection of species. Any commonly used laboratory rodent species is acceptable. There is no strain preference. Number and sex. The size of experiment (i.e., number of cells per animal, number of animals per group) should be finalized based on statistical considerations. Although a consensus was not achieved, operationally it was agreed that 2000 cells per animal and four animals per group was a minimum requirement. In general, the available database suggests that the use of one gender is adequate for screening. However, if there is evidence indicating a significant difference in the toxicity between male and female, then both sexes should be used. Treatment schedule. No unique treatment schedule can be recommended. Results from extended dose regimens are acceptable as long as positive. For negative studies, toxicity should be demonstrated or the limit dose should be used, and dosing continued until sampling. Dose levels. At least three dose levels separated by a factor between 2 and square root of 10 should be used. The highest dose tested should be the maximum tolerated dose based on mortality, bone marrow cell toxicity, or clinical symptoms of toxicity. The limit dose is 2 g/kg/day for treatment periods of 14 days or less and 1 g/kg/day for treatment periods greater than 14 days. A single dose level (the limit dose) is acceptable if there is no evidence of toxicity. Controls. Concurrent solvent (vehicle) controls should be included at all sampling times. A pretreatment sample, however, may also be acceptable only in the short treatment period peripheral blood studies. A concurrent positive control group should be included for each experiment.(ABSTRACT TRUNCATED AT 400 WORDS)

Bone marrow micronucleus assay: a review of the mouse stocks used and their published mean spontaneous micronucleus frequencies

We have examined published negative control data from 581 papers on micronucleated bone marrow polychromatic erythrocytes (mnPCE) for differences in mean frequency and the frequency distribution profile among the mouse stocks used with the bone marrow micronucleus assay. For the 55 mouse stocks with published micronucleus assay data, the overall mean frequency is 1.95 mnPCE/1,000 PCE (1.95 mnPCE/1,000); for the 13 stocks most commonly used in the assay, it is 1.88 mnPCE/1,000. During the last 5 years, the mnPCE rate for these 13 major stocks has been 1.74 mnPCE/1,000. This current mean frequency is a substantial decrease from the mean of 3.07 mnPCE/1,000 observed for these 13 stocks for data published prior to 1981. Of the major stocks, the highest mean mnPCE negative control frequencies were observed for MS/Ae > BALB/c > C57Bl/6, and the lowest for CD-1 < Swiss Webster. We note that hybrid mouse stocks appear to have lower and less variable negative control frequencies than either of their parent strains and that the negative control frequency for some progeny stocks have diverged significantly from that of the parent stocks. Overall mean negative control frequencies appear to be correlated with breadth of the frequency distribution profile of published mean negative control values. Furthermore, a possible correlation between negative control frequency in the micronucleus assay and sensitivity to clastogens of different mouse strains may be indicated. The databases generated here allow us to define a range of norms for both the historical mean frequency and individual experimental mean frequencies for most stocks, but in particular, for the more commonly used mouse stocks. Our analysis, for the most part, bears out the recommendation of the first Gene-Tox Report on the micronucleus assay that the historical negative control frequency for a mouse stock should fall between 1 and 3 mnPCE/1,000. Eighty-six percent of the most commonly used mouse stocks have historical mean frequencies within this range. Though individual experimental mean values would not necessarily be expected to fall within the 1-3.00 mnPCE/1,000 range, 65.3% of the 2,327 published negative control values do, and 83.5% are < 3 mnPCE/1,000. The frequency with which an individual experimental mean value lies outside the 1.00 to 3.00 mnPCE/1,000 range differs among stocks and appears related to the mouse mean frequency. We suggest that the recommended range for historical mean frequency be extended slightly, to approximately 3.4 mnPCE/1,000, to accommodate some commonly used strains with overall mean negative control frequencies just above 3.00 mnPCE/1,000.(ABSTRACT TRUNCATED AT 400 WORDS)

Mutagenicity evaluation of riot control agent o-chlorobenzylidene malononitrile (CS) in the Ames Salmonella/microsome test

o-Chlorobenzylidene malononitrile (CS), a riot control agent, was evaluated for its possible mutagenic activity in the Ames Salmonella/mammalian microsome mutagenicity test. Five histidine-deficient (His-) mutant tester strains of Salmonella typhimurium--TA97a, TA98, TA100, TA102 and TA104--were used. The liquid preincubation procedure was used with metabolic activation (presence of S9 mixture) and without metabolic activation (absence of S9 mixture). For the experiments with metabolic activation, three different concentrations of S9 fraction (supernatant of Aroclor 1254-induced rat liver homogenate at 9000 g)--5%, 15% and 30% in S9 mixture--were used. Along with mutagenic activity, CS was also evaluated for cytotoxic activity in all the five tester strains of Salmonella typhimurium, both in the presence and absence of S9 mixture. The mutagenic and cytotoxic activities of CS were assessed by counting the His+ revertant colonies and by counting the microcolonies (His-, auxotrophs in the background lawn), respectively, and the respective mean values were compared with the relative negative (solvent) control. A dose range of 12.5-800 micrograms plate-1 for CS did not induce a mutagenic response either in the presence or absence of S9 mix. No change in the negative mutagenic response of CS has been observed even in the presence of an elevated level of S9 fraction in the S9 mix. A dose of 200 micrograms plate-1 for CS was found to be cytotoxic by decreasing the surviving cells as well as His+ revertant colonies; however, the effect was reduced in the presence of an elevated level of S9 fraction in the S9 mix.

Acute and subacute inhalation toxicity studies of a new broad spectrum insect repellent, N,N-diethylphenylacetamide

N,N-Diethylphenylacetamide (DEPA) is an inexpensive, long-acting and broad spectrum insect repellent. The acute LC50 for a 4-h exposure of DEPA aerosol was found to be 1.451 mg l-1 (1.290-1.633) in male and 1.375 mg l-1 (1.307-1.447) in female rats. DEPA did not cause delayed deaths. Acute exposure to 0.9 LC50 revealed that liver might be a target organ for DEPA toxicity. On subacute exposures to 0.2, 0.6 and 0.8 LC50 for 6 h per day, 5 days a week for 2 weeks, there was no significant change in the 0.2 LC50 group, as evaluated by the body weight gain and organ body weight ratio. The minimal changes observed in the 0.6 LC50 group were of reversible type as the animals recovered on cessation of exposure. A massive concentration of 0.8 LC50 produced lethal effects. The study shows that DEPA has a low mammalian toxicity by inhalation as was found earlier with cutaneous application of the insect repellent.

Distribution and metabolism of insect repellant N,N-diethylphenylacetamide on oral exposure in rats

Oral toxicity, distribution and metabolism of a new multi-insect repellant, N,N-diethylphenylacetamide (DEPA) was studied in rats. On administration of DEPA (851 mg/kg body wt.) labelled with 14C blood, liver, stomach and stomach contents had 2.65, 3.97, 12.07 and greater than 50.66% radioactivity, respectively, after 20 min. Gas chromatographic analysis showed presence of both DEPA and its metabolite N-ethylphenylacetamide (EPA) in blood, liver, kidneys and lungs while only DEPA was present in stomach and stomach contents. EPA, phenylacetamide and conjugated phenylacetic acid were excreted along with unmetabolized parent compound in urine of rats when a low oral dose of DEPA (70 mg/kg body wt.) was administered. Activities of erythrocyte cholinesterase and carbonic anhydrase did not change significantly upon acute oral exposure to DEPA.

Toxicity and metabolism of a new insect repellent N,N-diethylphenylacetamide in mice, rats and guinea pigs on cutaneous application

Cutaneous LD50 of N,N-diethylphenylacetamide (DEPA), a new multi insect repellent was 2200, 3200 and 7100 mg/kg body weight in female mice, rats and guinea pigs; and 1600 and 4000 mg/kg in male mice and rats indicating a high degree of safety on skin contact. Dermal application of DEPA to young growing rats for 21 days at a dose of 50 mg/kg did not exert any adverse effects while massive doses of 500 and 1000 mg/kg caused marked reduction of body weight gain and lowering of activities of serum alanine aminotransferase, aspartate aminotransferase and cholinesterase. Along with DEPA, N-ethylphenylacetamide, phenylacetamide and phenylacetic acid were detected in the urine of DEPA treated mice, rats and guinea pigs.