Mutagenicity: Assays and Applications

Ashutosh Kumar, Vasily N. Dobrovolsky, Alok Dhawan, Rishi Shanker

• Publisher: Academic Press
• Year: 2017
• Print ISBN: 9780128092521
• eBook ISBN: 9780128092606
• Topic: Biological Sciences
• Subtopic: Toxicology
• Index: Biological Sciences

Mutagenicity: Assays and Applications presents an extensive examination of the detection, assessment and future of mutagenicity, particularly as it concerns human health and the environment. Chapters focused on specific types of mutagens or testing methods for their detection collectively explore the current state of human and environmental mutagenesis, future perspectives and regulatory needs. The test procedures for measuring mutagenicity, their advantages and limitations are described with practical and procedural detail, along with their presentation and data processing aspects. It is an essential reference covering the breadth and depth of the field of mutagenicity studies and regulation.By providing both important introductory material and practical assays and applications, this book is useful to graduate students, academic and industry researchers and regulators at various stages of their careers, leading to improved risk assessment and regulation.- Presents an up-to-date and in-depth review of the current state of mutagenesis research- Draws upon the combined experience and expertise of an international group of highly respected editors and chapter authors- Provides an introduction to the concept of mutagenesis with particular consideration given to novel chemicals and materials

Chapter One

Mutagenesis, Genetic Disorders and Diseases

Manisha Dixit^1,2, and Amit Kumar^{3 1}Institute of Toxicology Research (CSIR-IITR), Lucknow, India ²Academy of Scientific and Innovative Research (AcSIR), Chennai, India ³CSIR-Indian Institute of Toxicology Research, Lucknow, India

Abstract

The human genome is made up of the DNA molecule that encodes the genetic makeup of the cell. Often this DNA is subjected to several extrinsic and intrinsic insults and renders incorporation of faulty base pairing among the nucleotides. The faulty base pairing can change the coding sequence of genome and can disrupt the entire machinery of the cell, which results in deadly consequences ranging from neurodegenerative disorders to carcinomas and developmental anomalies in the individual. Here, in this chapter, we would be highlighting the various mutagens, the changes that they introduce to the DNA base pairing, their repairing machinery pathway, and diseases that are caused by faulty repair machinery.

Keywords

Cancer; DNA damage; DNA repair; Mutagen; Mutation

1. Introduction

We are subjected to continuous genotoxic insults every day by environmental factors that include harmful UV rays from sunlight or carcinogens in our food consumables, which potentially could be harmful to the human body. Even in the presence of multiple mechanisms devised to efficiently cope with these insults, very often failures occur in the exhaustive defensive strategies of the cell leading to a number of diseases such as cancers, developmental disorders, and neurodegeneration. The changes in DNA, due to exposure to certain insults (such as harmful radiations, chemicals, or biological agents) or the inability of the cells to repair damaged chromosomes, is referred as mutagenesis; while the physical, chemical, or biological entities that are able to mutagenize are called mutagens (Fig. 1.1). There are around 20,000 genes in the human body [1], and they often undergo alterations due to endogenous or exogenous DNA damage as stated above. Although the efficient repair system is competent enough to protect the cells from such damage, at times it fails to repair the chromosomes efficiently, and this leads to changes in the DNA sequence and exome readout through phenotypic and genotypic alterations, which are referred as mutations.

Although mammalian DNA replication is meticulous and tightly controlled owing to its complexity (although all DNA replications are tightly regulated, the mammalian one is more complex), there remains a possibility of 10⁻⁸ error per base pair (bp) [2]. Mutations are imperative to evolution and form the basis of incorporation of new alleles, which pass to subsequent generations. They serve as the reason for variation among individuals. These new alleles or variants could be envisioned as the reason behind how eukaryotes have survived so far in the course of time and fought to cope against diseases that were once considered deadly. In this chapter, we will elaborate on various mutagens, their role in causing mutations, molecular mechanisms of repair pathways, and some rare and common diseases arising from distinct mutations.

Figure 1.1 Type of mutagens.

2. Mutagens

2.1. Physical Mutagens

Physical mutagens include various kinds of ionizing and nonionizing radiations such as ultraviolet (UV) rays, infrared (IR) rays, X-rays, gamma rays, alpha particles, beta particles, or fast moving neutrons (Fig. 1.1) [3], which can be emitted either by natural or artificial sources. These particles possess enough energy to free atoms or molecules from their electronic orbits and induce reactive oxygen species (ROS) formation. Cobalt⁶⁰, a sterilizing agent, and cesium¹³⁷ are few examples of ionizing agents.

2.2. Chemical Mutagens

Chemical mutagens react with DNA and lead to faulty base pairing that can be classified into different categories (Fig. 1.1). Base analogues mimic a particular nucleobase in nucleic acid and are misread by the replicating machinery as a normal base. Following incorporation into DNA, they form non-Watson pairing with the DNA. The most studied base analogues are halouracils and uridine derivatives that include 5-bromodeoxyuridine (BrdU). This potent mutagen is capable of inducing point mutations by substituting thymine residues and pairing with guanine instead of adenine. Such base pair changes are deleterious and are more prone to alterations by physical mutagens such as X-rays, UV rays, or gamma rays relative to normal DNA [4]. Certain chemicals such as nitrous acid, hydroxyl amine, and sodium azide can modify the bases by deamination, thus modifying the regular base pairing. Nitrous acid deaminates adenine, guanine, and cytosine substituting adenine to hypoxanthine, guanine to xanthine, and cytosine to uracil [5]. These substitutions induce AT to GC transitions leading to faulty base pairing. Chemical mutagens are also comprised of alkylating agents and DNA intercalating agents. Ethyl methyl sulfate, nitrogen mustards, mitomycin, methyl methane sulfonate (MMS), diethyl sulfate, and nitrosoguanidine (NTG, NG, MNNG) are few examples of alkylating agents as well as DNA-intercalating agents, which include acridine orange, ethidium bromide (EtBr), proflavin, daunorubicin, among others.

Acridine orange or EtBr introduces frameshift mutations either by addition or deletion of base pairs. Certain pesticides such as rotenone, paraquat, or maneb have the capacity to induce mutations such as base pair changes in genes and could lead to neurodegenerative diseases such as Parkinson disease (PD) [6].

2.3. Biological Mutagens

Biological mutagens include agents such as transposons, viruses, or bacteria (Fig. 1.1). Both transposons and viral DNA may integrate into the human genome and change the genetic composition during cell division [7]. Upon incorporation into DNA, they can cause change in normal functioning of gene and can lead to several disorders.

3. Mutations

Mutations can be spontaneous or induced; spontaneous mutations arise de novo and include mutations due to DNA replication or lesions, whereas induced mutations occur upon interaction with mutagens. Mutations are classified into three broad categories: gene mutation, chromosomal mutation, and genome mutation (Fig. 1.2). Gene mutations include transition, transversion, frameshift mutation [8], neutral mutation, silent mutation, and missense or nonsense mutation [9]. Chromosomal mutations involve deletion, duplication, inversion, or translocation of a group of genes. Genome mutations include aneuploidy such as monosomic, nullisomic, double monosomic, trisomic, double trisomic, and tetrasomic...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Foreword
• Preface
• Acknowledgments
• Chapter One. Mutagenesis, Genetic Disorders and Diseases
• Chapter Two. Detection of Mutation in Prokaryotic Cells
• Chapter Three. Detection of Gene Mutation in Cultured Mammalian Cells
• Chapter Four. Chromosomal Aberrations
• Chapter Five. In Vivo Cytogenetic Assays
• Chapter Six. Mutagenicity and Genotoxicity Testing in Environmental Pollution Control
• Chapter Seven. Mutagens in Food
• Chapter Eight. Emerging Computational Methods for Predicting Chemically Induced Mutagenicity
• Chapter Nine. Overview of Nonclinical Aspects for Investigational New Drugs Submission: Regulatory Perspectives
• Chapter Ten. Mutagenicity Testing: Regulatory Guidelines and Current Needs
• Chapter Eleven. Detecting Mutations In Vivo
• Chapter Twelve. An In Vitro Male Germ Cell Assay and Its Application for Detecting Phase Specificity of Genotoxins/Mutagens
• Chapter Thirteen. Fluorescence In Situ Hybridization in Genotoxicity Testing
• Chapter Fourteen. DNA Damage, Repair, and Maintenance of Telomere Length: Role of Nutritional Supplements
• Index