PREDICTION OF LD50 OF SOME COMMON PESTICIDES THROUGH QSAR (AN ALTERNATIVE METHOD TO SAVE EXPERIMENTAL ANIMALS)

PREDICTION OF LD₅₀ OF SOME COMMON PESTICIDES THROUGH QSAR (AN ALTERNATIVE METHOD TO SAVE EXPERIMENTAL ANIMALS)

S.P. Agrawal *¹ and V.L. Saxena ²

Lecturer, Department of Zoology ¹, D.A-V. (PG) College Kanpur, India

Head Dept. of Zoology ² and Co-ordinator Bioinformatics Infrastracture Facility Center of DBT, D.G. (PG) College Kanpur, India

ABSTRACT:The most common test of acute toxicity is the LD₅₀ test. LD₅₀ means, the lethal dose of a substance that will kills 50% of animals. But this requires large number of animals. To reduce the sacrifice of animals. In present study we are using QSAR based software T.E.S.T. (toxicity estimation search tool 4.1 version) for predicting oral LD₅₀. For prediction of oral LD₅₀ we have taken 100 insecticides, 40 fungicides and 40 herbicides. During our analysis we find that for experimental oral LD ₅₀, 27 insecticides are highly (value between 5-50) and 36 are moderate potent (value between 50-500). For predicted oral LD ₅₀ value, 24 insecticides are highly and 34 are moderate potent. For fungicides 3 experimental and 3 predicted are moderate potent. For herbicides 6 experimental and 7 predicted herbicides are moderate LD ₅₀ potent.

Toxicity, QSAR,

Pesticides, LD ₅₀

INTRODUCTION: Acute toxicity of a drug can be determined by the calculation of LD₅₀ i.e., the dose that will kill 50% of animals of a particular species. Many different substances are tested in this way, including all drugs, agricultural chemicals, cleaners some cosmetics and their ingredients¹. The smaller the LD₅₀ value, the more toxic is chemical. The opposite is also true: the larger the LD₅₀ value, the lower the toxicity. It was developed in 1920’s and called “classical LD50” involved 100 animals for 5 dose-groups, later in 1981 it was modified by the Organization for Economic Cooperation and Development (OECD) and reduced number upto 30 for 3 dose-groups. In 1987 further reduced to 20 animals ².

Mice, rats, rabbits, guinea pigs, cats, dogs, fish, monkeys and birds are used for LD₅₀ study³. The LD₅₀ values of a new drug are determined by various route of administration (intravenous, intraperitoneal, subcutaneous and oral) ⁴. Results of LD₅₀ study may affected by some factors which are - Species, Age, Sex, Amount of food, Social environment, Route of exposure (oral, dermal, inhalation) and Physical environment such as temperature and humidity.

FRAME (Fund for the Replacement of Animals in Medical Experiment) believes that the lethal dose test is unnecessarily cruel and scientifically invalid. The test involves giving groups of animal doses of a test substance until it kills half of them. Several countries, including the UK, have taken steps to ban the oral LD₅₀ and the OECD; the International Government’s advisory body abolished the requirement for the oral test in 2001⁵. Patricia et.al. predicted acute mammalian toxicity for sulphur mustard and its breakdown products with the help of QSAR.⁶

Quantitative Structure Activity Relationships (QSARs) are mathematical models that are used to predict measures of toxicity from physical characteristics of the structure of chemicals (known as molecular descriptors). Acute toxicities (such as the concentration which causes half of fish to die) are one example of toxicity measures which may be predicted from QSAR (http:// www.epa. gov/nrmrl/std/cppb/war/sim_war.htm).⁷

The QSAR models used for regulatory purposes should be associated with the following purposes.

• To defined end points
• An unambiguous algorithm
• Appropriate measures of goodness-of-fit robustness and predictability
• A mechanistic interpretation if possible.

Generally, the prime aim in developing QSAR is so that it can be used for predicting purposes. It is therefore important that the statistics given with the QSAR give an indication of its predictability.

 MATERIALS AND METHODS:

Materials: Tools and Databases

Tools: Toxicity Estimation Software Tool (T.E.S.T. Version 4.1) is used ⁸

Databases: Pubchem is used as a database

Methodology: A list of common pesticides is prepared and there structure files are derived from the database. QSAR methodology is used to determine the LD₅₀ of 180 pesticides. LD ₅₀ potent insecticides, fungicides and herbicides are selected and studied further and results are discussed.

 RESULTS AND DISCUSSIONS:

Prediction of LD₅₀ of 100 Insecticides 40 fungicides and 40 Herbicides are done with the help of T.E.S.T. (4.1 software).

TABLE 1: INSECTICIDE ORAL LD ₅₀ PREDICTION

Prediction of oral LD ₅₀ of 100 Insecticides were done with the help of T.E.S.T. (4.1) software. We have analysed that out of 100 insecticides, experimental value of 16 insecticides are not available. 63 Insecticides were found to be LD₅₀ potent. Out of 63 insecticides, experimental oral  LD₅₀ value of 27 insecticides were highly potent (Value from 5-50 mg/kg) and experimental LD₅₀ value of 36 insecticides are moderate potent (value between 50-500) and predicted oral LD₅₀ value of 24 insecticides are highly and 34 are moderate potent (value between 50-500 mg/kg).

Further we observed that out of 100 insecticides oral LD₅₀ value of 33 predicted and 18 experimental insecticides are non toxic because their values were greater than 500 mg/kg. It means that the possibility of being lethal of these insecticides are very less.

TABLE 2: FUNGICIDE ORAL LD50 PREDICTION

Further we have observed that out of 40 fungicides predicted oral LD₅₀ valuePrediction of oral L.D₅₀  of 40 fungicides were done with the help of T.E.S.T. (Toxicity Estimation Software Tool 4.1 version).We have analysed that out of 40 fungicides predicted oral LD 50 value of 34 fungicides and experimental oral LD₅₀ value of 29 fungicides are greater than  500 mg/kg (50-500 mg/kg – Moderate toxicity). It means that the possibility of being lethal of these fungicides are very less or not toxic.

of 3 fungicides (472.52, 195.88 and 285.83) and experimental oral LD₅₀ value of 3 fungicides (320.14, 430.21 and 363.10) were below 500 mg/kg (value between 50-500 mg/kg moderate) it means that these fungicides had moderate toxicity.

According to our T.E.S.T. analysis Predicted oral LD ₅₀ value of 3 fungicides and experimental oral LD₅₀ value of 12 fungicides are not available.

TABLE 3: HERBICIDE ORAL LD₅₀ PREDICTION

Prediction of oral LD ₅₀ of 40 Herbicides are done with the help of T.E.S.T 4.1 software. We have analysed that out of 40 herbicides predicted LD ₅₀ value of 7 herbicides (472.7, 81, 59, 139.81, 156.9, 360.16, 164.08 and 458.3) and experimental LD ₅₀ Value of 6 herbicides (357.3, 271.2, 189.92, 400.4, 469.7 and 511) are moderate LD ₅₀ potent (Value between 50-500 mg/kg).

Further we observed that out of 40 herbicides predicted LD ₅₀ of 31 herbicides and experimental LD₅₀ value of 22 herbicides are greater than 500 mg/kg body weight. It means that the possibility of being lethal of these herbicides are very less. The experimental value of 12 herbicides is not available. No valid structure and data is available for Imazamethabenz herbicide.

 DISCUSSIONS: Out of 100 insecticides, 51insecticides (experimental+ predicted) are LD₅₀ potent. Out of 51 insecticides, 24 predicted highly LD₅₀ potent insecticides are Parathion, Azinphosmethyl, Carbofuran, Diclorvos, Disulphoton, Ethoprop, Mathamidophos, Parathion

–methyl, Nailed, Oxydemeton- methyl, Phorate, Phosmet, Methidathion, Turbufos, Phenomiphos, Fenitrothion, Dieldrin, Fosthizale, Cyhazothrin, Mevinphos, Dicrotophos, Monocrotophos, Aldicarb, Eldrin (Table 1).

Out of 51 insecticides, 27 insecticides with highly potent experimental LD₅₀ values are Parathion, Pentachlorophenol, Azinphosmethyl, Bendiocarb, Carbofuran, Dichlorvos, Disulphoton, Ethoprop, Heptachlor, Methamidophos, Parathion- methyl, Oxydemeton-methyl, Phorate, Methidathion, Omethoate, Dioxacarb,  Terbufos, Fenaniphos, Dieldrin, Chlorithoxyfos, Methomyl,  Mevinphos, Dicrotophos, Monocrotophos, Aldicarb, Aldrin, Eldrin (Table 1).

The insecticides whose both experimental and predicted LD₅₀ values are highly potent – Parathion, Azinphosmethyl, Bendiocarb, Carbofuran, Dichlorvos, Disulphoton, Ethoprop, Methamidophos, Parathion- methyl, Oxydemeton-methyl, Phorate, Methidathion, Terbufos, Fenaniphos, Dieldrin, Mevinphos, Dicrotophos, Monocrotophos, Eldicarb, Eldrin (Table 1). These 20 insecticides are highly potent both in experimental and predicted value. So it is strongly recommended to check its mutagenicity and LD₅₀ in vivo and in vitro.

Out of 40 fungicides 6 moderate LD₅₀ potent fungicides are Thiabendazole, Etridiazale, Diazomet (3 predicted fungicides) and Carbathilin, Triadiamet, Diazomet (3 experimental fungicides). One fungicide with both experimental and predicted LD₅₀  potent is Diazomet (Table 2).

In herbicides 13 are moderate LD₅₀ potent. 7 Predicted LD₅₀ potent  herbicides are  Dichlobenil, Bensulide, Bromoxynil, Amitraz, Fluroxypyr, Isoxaben, Imazamethabenz   and 6 experimental LD₅₀ potent herbicides are 2,4-Dichlorophenoxy, Bensulide, Bromoxynil Amitraz, Difenzoquate, Diclofop-methyl .Both experimental and predicted  moderate LD₅₀ potent herbicides are Bensulide, Bromoxinil and Amitraz (Table 3).

CONCLUSION: QSAR have long been used for predicting wide range of endpoints. In present analysis 180 pesticides were taken. We found that out of 180 pesticides (100 insecticides, 40 fungicides and 40 herbicides), value of experimental oral LD 50 for 27 insecticides are highly (value between 5-50) and 36 are moderate potent (value between 50-500). For predicted oral LD₅₀ value, 24 insecticides are highly and 34 are moderate potent. For 40 fungicides, 3 experimental and 3 predicted fungicides are moderate LD ₅₀ potent. For 40 herbicides, 6 experimental and 7 predicted herbicides are moderate LD ₅₀ potent. Now we conclude that pesticides which has potent potential value should analyze with more than two predictor (Topkat, Admet) also for more reliability.

 ACKNOWLEDGEMENT: We are thankful to BIFC DG (PG) College Kanpur, for providing laboratory facilities & encouragement during the study.

REFERENCES:

1. Turner, R.: “Acute toxicity: The determination of LD50”. In Screening Methods in Pharmacology, Academic Press, New York, 1965; pp.300.
2. Botham, P.A.: Toxicology in Vitro 2004; 18:227-230.
3. Fifth Report on the Statistics on the Number of Animals used for Experimental and other Scientific Purposes in the Member States of the European Union Commission of the European Communities, published 2007.
4. Ghosh M N, Toxicity studies. In Fundamentals of Experimental Pharmacology, Scientific Book Agency, Calcutta, 1984; 153–158.
5. www.frame.org.uk ) 2001.
6. Ruiz, P.; Begluitti. G.; Tincher, T.; Wheeler, J. and Mumtaz, M.:”Prediction of acute mammalion toxicity using QSAR” Molecules 2012:17, 8982-9001.
7. http://www.epa.gov/nrmrl/std/cppb/war/sim_war.htm 2012.
8. US Environmental Protection Agency: A program to estimate toxicity from molecular structure. (http://www.epa.gov/nrmrl/std/cppb/war/sim_war.htm) 2012.
   

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   How to cite this article:

   Agrawal SP and Saxena VL:Prediction of LD₅₀ of Some Common Pesticides through QSAR (An Alternative Method to Save Experimental Animals).Int J Pharm Sci Res2014; 5(12): 5356-73. doi: 10.13040/IJPSR.0975-8232.5 (12).5356-73.

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