N-methyl-N-nitrosourea에 의한 백내장 유발 흰쥐에서 수정체 상피 자멸사에 대한 카테킨의 보호효과 : The Protective Effect of Catechin on Apoptosis of the Lens Epithelium in Rats with N-methyl-N-nitrosourea-Induced Cataract

다국어 초록 (Multilingual Abstract)

A cataract is an opacity that develops in the crystalline lens of the eye or in its envelope; it varies in degree from slight to completely opaque, obstructing the passage of light. The lens epithelium covers the anterior surface of the lens. Epithelial cells near the lens equator divide and differentiate into lens fibers. This process continues at a constant, slow rate throughout adult life, resulting in steady growth of the lens fiber mass.1The mitotically quiescent central region of the epithelium is thought to protect the underlying fibers from various insults, to transportions to and from the deeper layers of the lens, and perhaps to provide nutrients to elongating lens fibers. 2 Damage to the lens epithelium has been the focus of investigators in the identification of causes of cataract formation.3
Apoptosis, also known as programmed cell death, is a form of cell death that serves to eliminate dying cells in proliferating or differentiating cell populations. Thus, apoptosis plays a crucial role in normal development and tissue homeostasis. 4,5 Previous studies have shown that apoptosis of lens epithelial cells plays ani mportant role in the development of several types of cataract.6-8 These studies have suggested that apoptosis of lens epithelial cells appears as a common cellular mechanism mediating stress-induced noncongenital cataractogenesis.9,10
Apoptosis can be detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, a measure of DNA fragmentation in tissue sections, and by observation of a DNA ladder, a measure of fragmentation in DNA extracted from cells or tissues.11,12 In human cataract research, TUNEL-positive cells indicate apoptotic cell death in the lens epithelium.1,13 Another important characteristic of apoptosis is caspase activation. Caspase-3 is one of the most widely studied caspases, and it is a key executor of apoptosis.14 In addition to caspases, Bcl-2 family proteins also play a pivotal role in the regulation of apoptosis. The Bcl-2 family is classified into anti-apoptotic and pro-apoptotic proteins according to function. The balance between pro-apoptotic and anti-apoptotic Bcl-2 family members determines the mitochondrial response to apoptotic stimuli.15
Catechin is a naturally occurring polyphenolic compound found abundantly in green tea. Polyphenolic compounds include (-)-epgallocathechin-3-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin-3-gallate (ECG), and (-)-epicatechin (EC), and these are the main constituents of catechin.16 Previous studies have shown that catechin has diverse health benefits, including anti-oxidant, anti-hyperglycemic, anti-cancer, and anti-apoptosis effects.17-20 Catechin has also been reported to exert a protective effect on UV radiation-induced epithelial cell damage of the retina21 and lens.22
The functional roles of catechin have been well documented. However, its effects on the lens epithelium following cataract formation are not well known. Although great advances have been made in surgical treatment, the incidence of cataracts in developing countries is so high that it overwhelms the capacity of surgical intervention. Thus, we investigated the effect of catechin on apoptosis in the lens epithelium following cataract formation in rats. In this study, we performed TUNEL assay, Western-blot for Bcl-2 and Bax, and immunohistochemistry for caspase-3.

목차 (Table of Contents)

• 차례 i
• 그림차례 ii
• Ⅰ. Introduction 1
• Ⅱ. Mathods and meterials 3
• Ⅲ. Results 8
• Ⅳ. Discussion 17
• 참고문헌 20
• 국문초록 25