Oxidized- Low Density Lipoprotein Level Among Organophosphates (OPs) Pesticide Exposed Workers

1. Oxidized- Low Density Lipoprotein Level Among Organophosphates (OPs) • Pesticide Exposed Workers • Nor Zamzila Abdullah1,IshakaAminu1, Niza Samsuddin2, RazmanMohd Rus2 and Abdul Hadi Mohamed3 • 1Department of Basic Medical Sciences,2Department of Community Health and Family, Medicine, 3Department of Anesthesiology and Intensive Care, • International Islamic University Malaysia, Bandar Indera Mahkota, 25200 Kuantan, Pahang. Background Organophosphate (OP) is one of the widely used pesticides worldwide. It has been shown to induce oxidative stress in both animal and human. Oxidative stress may stimulate the oxidation of lipoprotein particularly the low density-lipoprotein (LDL) which is known to promote atherogenesis. Paraoxonase 1 (PON1) is high density-lipoprotein (HDL) related enzyme which is recognized for its function to hydrolyze OPs into a relatively less toxic substance and prevent atherosclerosis by hydrolyzing oxidized-LDL (ox-LDL). Low PON1 activities were reported in OPs exposed individuals, while in different studies it was associated with a higher risk of coronary artery disease (CAD). However, a link between chronic OP exposure, PON1 activity and ox-LDL which is known for its contribution in the development of atherosclerosis has not yet been reported. • Objective and Hypothesis • The aim of this report was to compare the level of PON 1 activities and ox-LDL level between workers who are exposed to OPs and the comparative non-exposed group. Our hypothesis is that OPs exposure will lead to decreased PON1 activities which will reduce the ability to hydrolyze OPs and oxidized-LDL, thus predispose an individual to atherosclerosis and CAD. • Method • In this cross-sectional study, 51 pesticide sprayers from 4 farms in Kuantan, Pahang who fulfilled the inclusion and exclusion criteria were recruited . Forty-eight (48) control subjects were selected based on matching process of age, ethnicity and income bracket. Serum samples were analyzed for PON1 activities towards substrates paraoxon, phenylacetate and diazoxon as well as for ox-LDL. The paraoxonase (PON), arylesterase (ARY) and diazoxonase (DZO) activities were determined spectrophotometrically according to methods described by Eckerson et al. (1983), Gan et al. (1990) and Davies et al. (1996) respectively. Enzyme activities were expressed as U/mL. The ox-LDL was determined by direct sandwich ELISA technique using Mercodia Ox-LDL ELISA kit. The ox-LDL was expressed in mU/L. Statistical Analysis The parametric data were presented as mean (SD) while the non parametric data were presented as median [interquartile range (IQR)]. The comparison of PON1 activities and the level of ox-LDL between the OPs exposed and the control groups were done by independent t-test (parametric data) and Mann-Whitney U test (non-parametric data). Results The demographic data were homogeneous between the OPs exposed and the control groups. There were no significant differences (p>0.05) between the two groups with regard to age, race, body mass index (BMI) Kg/m2 and smoking status. The period of exposure among the OPs exposed subjects ranged from 7-204 months. The diazoxonase activity was significantly lower in the exposed group (table 1). The ox-LDL was significantly higher while the ratio of PON1 activities per unit of ox-LDL was significantly lower among the OPs exposed group (table 2). Table 2: Comparison ofoxidized-LDL and the ratio of PON1 to oxidized-LDL between the OPs exposed and the control group Mann-Whitney U test, results presented as median (IQR), * significant difference Table 1: Comparison of PON1 activities between the OPs exposed and the control group Independent t-test, resultspresented as mean (SD),aMann-Whitney U test, +results presented as median (IQR),*significant difference (p<0.05) in the median diazoxonase activity between the exposed and the control groups • Discussion • The finding of lower PON1 activities among the OPs exposed group is similar to the report by Hernandez et al. (2004) and Sozmen et al (2007). This may occur as a result of inactivation of PON1 enzyme by the highly toxic oxons (Aviram et al, 1999).The higher ox-LDL level among the OPs exposed group is in line with animal study by Shih, et al. (1998) and in vitro study by Aviram (1999). The lower PON1 to ox-LDL ratio indicates that the OPs exposed subjects had a reduced PON1 antioxidant capacity to hydrolyze ox-LDL . The higher ox-LDL level and the lower PON1 to ox-LDL ratio among the OPs exposed worker may be explained by the lower PON1 activities among this group as low PON1 reduces the ability of HDL to prevent the oxidation of LDL and reduces the ability to hydrolyze the LDL that has been oxidized. Furthermore, the OPs themselves may also contribute to the higher ox-LDL as they have been shown to increase oxidative stress (Ranjbar, et al., 2002). Since ox-LDL contributes to the development of atherosclerosis, our findings provide evidences that OPs may predispose an individual to atherosclerosis and CAD. This may also explain the observation in some recent studies that the low PON1 activities are associated with CAD (Mackness et al., 2001; Singh et al., 2007). To our knowledge, this is the first study in human reporting the level of ox-LDL among chronic OPs exposed individuals. Conclusion In conclusion, our data demonstrated that the increased ox-LDL among the OPs exposed subjects may result from the reduced serum antioxidant capacity of PON1. This may contribute to the development of atherosclerosis among the subjects in this group. A larger scale study is required to confirm our observation. References Aviram, M, Rosenblatt, Billecke, S., Erogul, J., Sorenson, R., Bisgaire, C.L., Newton,R.S. and La Du,B. (1999). Human serum paraoxonase (PON1) is inactivated by oxidized low density lipoprotein and preserved by antioxidants. Free radical Biology Medicine.26, 892-904. Davies, H.G., Richter, R.J., Keifer, M., Broomfield, C.A., Sowalla, J., Furlong, C.E. (1996). The effects of the human paraoxonase (PON1) polymorphism is reversed with diazoxon,soman and sarin. Nature Genetics. 14:334-336. Eckerson, W.H., Wyte, M.C and La Du, B.N (1983). 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Induction of oxidative stress and acetylcholinesterase inhibition in organophosphorus pesticide manufacturing workers. Human Experimental Toxicology. 21, 179-182. Shih, D.M., Gu, L., Xia, Y.R., Navab., M., Li, W.F., Hama, S., Castellani, L.W., Furlong, C.E., Costa, L.G., Fogelman, A.M. et al. (1998). Mice lacking serum paraoxonase are susceptible to organophosphate toxicity and atherosclerosis. Nature. 394, 284-287. Singh, S., Venketesh, S., Verma, J.S., Verma, M., Lellamma, C.O. and Goel, R.C. (2007). Indian Journal of Medical Research. 125, 783-787. Sözmen ‌,B., Şule P .‌, Kaya ‌, U., Erkan, M ‌ and EserYildirimSözmen2007. Markers of Long-Term Exposure to Organophosphorus Pesticides in Farmers Who Work in Viniculture and Tobacco Production in Turkey. Toxicology Mechanisms and Method .17 (7), 379-384. Acknowledgement This work was supported by Research Endowment Fund (B), International Islamic University Malaysia (IIUM/504/RES/G/14/3/07/EDW B 0805-134). We would like to thank Sr. Syafini Ahmad Marzuki, Br. Awang Mat Zainal, Br. QusyairiAzliMohdAzhar, Br. AidilAzharDubi and all Medical Laboratory Technologists in the Biochemistry Unit, Department of Basic Medical Sciences and Community Health and Family Medicine Department, IIUM for their technical support. Correspondence: norzamzila@gmail.comorzamzila@iium.edu.my