Gastrointestinal Tissue

Oxidative Stress and Dietary Antioxidants

Jordi Gracia-Sancho,M. Josepa Salvadó

• Publisher: Academic Press
• Year: 2017
• ISBN:
  9780128093009
• Topic: Medicine
• Subtopic: Gastroenterology & Hepatology

Gastrointestinal Tissue: Oxidative Stress and Dietary Antioxidants brings together leading experts from world renowned institutions, combining the basic mechanisms of gastrointestinal diseases with information regarding new and alternative treatments.

The processes within the science of oxidative stress are described in concert with other processes, including apoptosis, cell signaling and receptor mediated responses, further recognizing that diseases are often multifactorial with oxidative stress as a component. By combining the critical molecular processes underlying free radical mediated pathologies and the role of dietary antioxidant molecules, a connection is made that helps advance therapies and the prevention of gastrointestinal pathological processes.

This important reference is well designed with two complementary sections. Section One, Oxidative Stress and Gastroenterology, covers the basic processes of oxidative stress from molecular biology to whole organs, the gastrointestinal anatomy and sources of oxidative stress and free radicals and their products in gastrointestinal diseases. Section Two, Antioxidants and Gastroenterology covers antioxidants in foods, including plants and components.

• Covers the science of oxidative stress in gastrointestinal tissue and associated conditions and scenarios
• Provides information on optimal levels for human consumption of antioxidants, suggested requirements per day, recommended dietary allowances and curative/preventive effects of dietary antioxidants
• Presents an easy to reference guide with two complementary sections that discuss the pathophysiology of gastrointestinal diseases in relation to oxidative stress and antioxidant therapies

Section I

Oxidative Stress and Gastroenterology

Outline

Chapter 1 The Gastrointestinal System: Anatomy and Sources of Oxidative Stress

Chapter 2 Redox Mechanism of Reactive Oxygen Species in Gastrointestinal Tract Diseases

Chapter 3 Oxidative Stress and Gastrointestinal System Cancers

Chapter 4 The Role of Oxidative Stress in the Pathophysiology of Gastrointestinal Disorders

Chapter 5 Gastric Mucosal Injury and Oxidative Stress

Chapter 6 Helicobacter pylori and Reactive Oxygen Species

Chapter 7 Inflammatory Bowel Diseases: The Crosslink Between Risk Factors and Antioxidant Therapy

Chapter 8 Oxidative Stress and Gut Microbiota*

Chapter 9 Oxidative Stress in Liver Diseases

Chapter 10 Ischemia-reperfusion Injury and Oxidative Stress

Chapter 11 Role of Oxidative Stress in Portal Hypertension in Cirrhosis

Chapter 12 Role of Oxidative Stress in Necrotizing Enterocolitis: Advances and Possibilities for Future Therapy

Chapter 13 Pancreatic Cancer, Pancreatitis, and Oxidative Stress

Chapter 14 Gallbladder Disease: Relevance of Oxidative Stress

Chapter 1

The Gastrointestinal System

Anatomy and Sources of Oxidative Stress

José Miranda-Bautista, Rafael Bañares and Javier Vaquero, Gregorio Marañón University Hospital, Madrid, Spain

Summary

This chapter reviews the basic anatomy and histology of the gastrointestinal (GI) system as well as the main sources of oxidative stress. The GI tract, represents a major interface between the human body and its environment, harbors a large microbial community, and represents the first line of defense against potentially harmful effects of ingested materials. Although it is recognized as a major source of oxidative stress in the human body, the GI tract, and particularly its mucosa is endorsed with effective antioxidant defense systems that prevent injury. Excessive generation of oxidative stress, decrease of antioxidant defense systems, and microbiota dysregulation, however, may play a major role in various GI diseases.

Keywords

Oxidative stress; free radical; gastrointestinal tract; antioxidant; reactive oxygen species; reactive nitrogen species

Introduction

Oxidative stress is an unavoidable consequence of life in an oxygen-rich atmosphere. In living organisms, it is defined as the disturbance of the delicate balance between the oxidants and antioxidants in favor of the oxidants, leading to a disruption of redox signaling and control and/or to direct molecular damage (Fig. 1.1) [1]. Whereas an excessive amount of oxidative stress may cause damage of most cell constituents, a small or moderate amount of oxidative stress plays important roles in normal cell physiology by regulating redox-sensitive signaling pathways [2,3]. The OxyR and SoxR transcription factors in bacteria [4,5] and the NF-κB and Nrf2/Keap1 in higher organisms [6,7], are perfect examples of major oxidative stress-regulated signaling pathways. High amounts of oxidants can also be generated and released in a tightly controlled fashion by specialized immune cells as a defense mechanism against foreign pathogens [8].

Figure 1.1 The oxidant/antioxidant balance.
Living organisms are constantly exposed to oxidative stress. In normal conditions, a delicate balance between the generation of oxidants and free radicals and their detoxification exists that prevents injury. Small increases of oxidative stress result in compensatory mechanisms driven by redox-sensitive signaling pathways and compounds that allow restoration of the balance. When the imbalance is considerably larger, damage of cellular constituents may occur.

The terms oxidative damage, oxidants and free radicals are widely used in scientific and non-scientific forums, but it is important to remind that they are not synonymous nor they should be used indiscriminately (see definitions in Table 1.1). For example, free radicals can be neutral, negatively or positively charged, and their redox potential can range from oxidizing (e.g., hydroxyl radical) to reducing (e.g., superoxide radical). It should also be noted that there are oxidants, such as hydrogen peroxide, that are not free radicals and, therefore, oxidative damage does not need to proceed necessarily via a radical mechanism. In this line, it has been recommended to name the specific chemical reactants involved in particular processes whenever possible rather than to refer to more general terms such as “oxidative stress,” “reactive oxygen species,” (ROS) or “reactive nitrogen species” (RNS) [1].

Table 1.1

Definitions

Term	Definition
Oxidative stress	Imbalance between oxidants and antioxidants in favor of the former, leading to a disruption of redox signaling regulation or control and/or to direct molecular damage.
Oxidant	The electron acceptor in an oxidation-reduction reaction.
Oxidation	The increase of positive charges on an atom or the loss of negative charges.
Antioxidant	Substance that, when present at low concentrations compared to those of an oxidable substrate, significantly delays or prevents oxidation of that substance.
Reduction	The addition of hydrogen to a substance, or more generally, the gain of electrons.
Reductant	The electron donor in an oxidation-reduction (redox) reaction.
Free radical	A molecule or ion containing an unpaired valence electron.

Since the first report of the presence of free radicals in biological materials [9], extensive research has established an important role of oxidative stress and free radicals in normal cell physiology as well as in aging and a number of clinical disorders such as cancer, neurodegenerative diseases, atherosclerosis, or ischemia-reperfusion injury [2]. The gastrointestinal (GI) tract is receiving increasing attention as a major element for the maintenance of redox homeostasis in mammals, as it represents a major interface between the organism and the environment (both nutrients and intestinal microbiota are sources of oxidative stress). Furthermore, accumulating evidence shows that oxidative stress is an important player in the pathogenesis of various GI diseases [10]. In this chapter, we describe the basic anatomical and histological features of the GI tract and its associated organs, and provide a general overview of the main sources of oxidative stress with attention to those more relevant for the GI tract.

Anatomy and Histology of the Gastrointestinal Tract

The GI tract consists of a tubular organ that starts from the mouth and ends at the anus. Its main function is to digest and extract useful components from ingested materials and to expel the waste products at the end. This function is achieved by the progression of the alimentary bolus through different specialized sections of the GI tract together with the participation of accessory organs of the digestive system, which include the salivary glands, the liver, the pancreas, and the gall bladder (Fig. 1.2). Hormone-sensitive effector cells together with the neuro-vegetative system facilitate the autonomous progression of the alimentary bolus through the GI tract. Importantly, the GI tract also harbors a diverse and complex microbial community of about 1000 bacterial species, which has an immense impact on host metabolism, physiology, nutrition, and immune function [11].

Figure 1.2 Anatomy and histology of the gastrointestinal (GI) tract and its accessory organs.
The Eesophagus is mostly intrathoracic and impulses the alimentary bolus into the stomach. The stomach is an abdominal sac that changes the consistency of the bolus to semifluid and initiates the digestion. Pancreatic and biliary secretions subsequently converge in the duodenum to continue the digestion and to begin the absorption of nutrients and water along the small intestine. Once in the large intestine, water is further absorbed, and feces are compacted and stored until they are finally removed by defecation. The mucosa and glandular cells are essential elements responsible for all these functions. The drawings located beside the anatomic figure show the basic histological features of the mucosa and glandular cells that cover the different segments of the GI tract as well as those of the liver and pancreas.

In humans, the GI tract includes four major sections that can be individualized in terms of anatomy and histology: esophagus, stomach, small intestine, and large intestine. Although the histology varies with the anatomical region, all the sections have four histological layers that are called mucosa, submucosa, muscularis propria, and adventitia or serosa (from the lumen to the outer wall).

Esophagus

The esophagus in adults is a muscular tube of approximately 25 cm long that extends from the pharynx at the cricoid cartilage (at the level of the 6th cervical vertebra) to the cardia (at the level of the 10th or 11th thoracic vertebra). It pierces the left crus of the diaphragm and has an intra-abdominal portion of about 1.5 cm in length. The main function of the esophagus is to transport food, liquids, and saliva from the mouth to the stomach, which is achieved by the coordinated contractions of its muscular wall.

The esophagus is lined by a mucosa consisting of squamous epithelium, except for a small segment at its lower end that is lined by mucin-secreting columnar epithelium with underlying mucous glands. The latter segment continues into the stomach, which is also lined by columnar epithelium. The squamous-columnar junction occurs approximately at the level of the diaphragm. The squamous mucosa is composed of nonkeratinizing stratified squamous epithelium supported by the connective tissue of the lam...