Malathion induced cancer-linked gene expression in human lymphocytes

Highlights

• Higher concentration of malathion is cytotoxic to human lymphocytes.

• Low concentration of malathion induces differentially regulated gene expression.

• 659 and 3729 genes were up and down regulated in malathion treated lymphocytes.

• 57 differentially regulated genes are involved in the etiology of cancer.

• Malathion is carcinogenic in human lymphocytes.

Abstract

Background

Malathion is the most widely used organophosphate pesticide in agriculture. Increasing cancer incidence in agricultural workers and their children links to the exposure of malathion. Identification of genes involved in the process of carcinogenesis is essential for exploring the role of malathion. The alteration in gene expression by malathion in human lymphocytes has not been explored yet, although hematological malignancies are rampant in humans.

Objective

This study investigates the malathion induced expression of cancer associated genes in human lymphocytes.

Methods

Human lymphocyte viability and colony-forming ability were analyzed in malathion treated and control groups. Gene expression profile in control and malathion treated human lymphocytes were performed using a microarray platform. The genes which have significant functions and those involved in different pathways were analyzed using the DAVID database. Differential gene expression upon malathion exposure was validated by quantitative real-time (qRT)-PCR.

Results

Malathion caused a concentration-dependent reduction in human lymphocyte viability. At low concentration (50 μg/mL) of malathion treatment, human lymphocytes were viable indicating that low concentration of malathion is not cytotoxic and induces the colony formation. Total of 659 genes (15%) were up regulated and 3729 genes (85%) were down regulated in malathion treated human lymphocytes. About 57 cancer associated genes related to the growth and differentiation of B and T cells, immunoglobulin production, haematopoiesis, tumor suppression, oncogenes and signal transduction pathways like MAPK and RAS were induced by malathion.

Conclusion

This study evidences the carcinogenic nature of malathion. Low concentration of this pesticide is not cytotoxic and induces differentially regulated genes in human lymphocytes, which are involved in the initiation, progression, and pathogenesis of cancer.

Introduction

Malathion (Diethyl 2-[(dimethoxyphosphorothioyl)sulfanyl] butanedioate) is a non-systemic broad-spectrum organophosphate pesticide used for controlling insect pests of agricultural crops, gardens, house hold products, ectoparasites on animals, fumigation, veterinary practices and in public health pest-eradication programmes (ATSDR, 2003). Malathion residues have been frequently detected in the agroecosystem sediment (2.62–129 μg/kg); water (0.699–298 μg/L); ground water near industrial area (0.855–16.24 μg/L); rain water (0.900–1.500 μg/L); river surface water (2.618 μg/L); unfiltered water (0.1–3.3 μg/L); drinking water pipes (0.2–1.0 mg/g); urine (1.3–4.1 μg/L); fruits and vegetables (0.04 ng/g) (Rao and Pillala, 2001; Varca, 2012; Agarwal et al., 2015; Harper et al., 2017; IARC , 2017). Malathion exposure can cause acute and chronic toxicity, disturbance in metabolism, induce oxidative stress, decrease in AChE activity, hepatotoxicity, neurotoxicity, immunotoxicity, cytotoxicity and genotoxicity in target and non-target species including humans (Windham et al., 1998; Gurushankara et al., 2007a; 2007b; Muniz et al., 2008; Kalender et al., 2010; Moore et al., 2010; Nain et al., 2011; Akbel et al., 2018; Selmi et al., 2018).

Cancer is the most common malignant disease, causing major morbidity and mortality in the world. It is a genetic disease, i.e., the initiation of cancer occurs at the molecular level due to alterations in genes, proteins and the signal transduction pathways that control the way our cells function, specifically how they grow and divide (Hanahan and Weinberg, 2000). The causative factors for carcinogenesis remain an enigma. Pesticides are considered as carcinogens and appear to be involved in the etiology of cancer (Mitra et al., 2012; Goodson et al., 2015). But, there is no report to propose how pesticides may influence gene expression in carcinogenesis. Identification of genes involved in the process of carcinogenesis upon pesticide exposure is essential for exploring the role of environmental agent(s) in cancer development. Studies have substantiated that malathion induces DNA and chromosomal damages in humans (Moore et al., 2010; Navarrete-Meneses et al., 2018). Increased cancer (particularly leukemia and lymphoma) incidence in agriculture workers and their children was linked to malathion exposure (Cabello et al., 2001; Bonner et al., 2007; Lerro et al., 2015). Malathion could be a carcinogen as its exposure was found to elevate the risk of cancer (Reuber, 1985; Cabello et al., 2001). International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) has classified malathion as ‘probably carcinogenic to humans’ (Group 2A) (IARC , 2017). However, the alteration in the gene expression by malathion has not been explored so far, although hematological malignancies are prevalent in humans. In order to understand the genes involved in carcinogenesis, we have employed the gold standard in vitro model system, human lymphocytes. The profile of malathion induced cancer related gene expression in human lymphocytes were made using microarray platform and differential gene expressions were confirmed by quantitative real time (qRT)-PCR.