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Chapter 22

Effect of Hesperidin on Expression of Inducible Nitric Oxide Synthase in Cultured Rabbit Retinal Pigment Epithelial Cells

Luo Xiaoting, Zeng Xiangyun, Li Shumei, Dong Minghua, and Xiong Liang

Abstract

Objective: To study the effect of hesperidin on expression of inducible nitric oxide synthase (iNOS) in cultured rabbit retinal pigment epithelial (RPE) cells under the condition of high glucose in vitro.

Method: Hesperidin was extracted from Pericarpium Citri Reticulatae by ultrasound and ethanol precipitation and was detected qualitatively by high performance liquid chromatogram. The third to fifth primary cultured rabbit RPE were selected. The cells were divided into 6 groups including the control group cultured in DMEM, the model group cultured in DMEM containing 33 mmol/L glucose without any drug and four experimental groups which were exposed to hesperidin at the concentration of 10, 20, 40 and 80 mg/L at 37C under 5% CO2 for 2 h and then cultured in DMEM containing 33 mmol/L glucose. The proliferation of RPE was measured by the MTT assay. The levels of NO produced were measured by spectrophotometry. The changes of iNOS expressed in RPE cells were determined with immunohistochemistry.

Results: The growth rate of RPE cells was associated with the concentration of hesperidin. NO production induced by high glucose was significantly inhibited by hesperidin. iNOS expression in hesperidin-treated group was decreased compared with the control group (p <0.001).

Conclusion: Hesperidin can increase the proliferation of rabbit RPE cells, and inhibit the level of NO and iNOS expression, so hesperidin can protect rabbit RPE cells.

L. Shumei (B)

Department of Preventive Medicine, Gannan Medical College, Ganzhou, China e-mail: gnyxylsm@163.com

Supplied by: Department of Education of Jiangxi Province (NO.GJJ08401) and Gannan Medical College (NO.2006070). Brief introduction of author: Luo Xiaoting, female, born in 1976, is an associated professor. Her research field is mainly in molecular pharmacology. Tel: 0797-8657990; Fax: 0797-8200037; E-mail: xtluo76@yahoo.com.cn

R.E. Anderson et al. (eds.), Retinal Degenerative Diseases, Advances in Experimental

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Medicine and Biology 664, DOI 10.1007/978-1-4419-1399-9_22,C Springer Science+Business Media, LLC 2010

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L. Xiaoting et al.

22.1 Introduction

Diabetic retinopathy (DR), a principal cause of blindness, is characterized by increased retinal vascular permeability and progressive retinal vascular closure, resulting in tissue hypoxia and neovascularization, but the precise mechanisms are not fully understood. Glucose concentration, per se, is the critical risk factor in the pathogenesis of diabetic complications (Civan et al. 1994). Recently, those pathogenetic factors have been reported to be associated with the reninangiotensin system and vascular endothelial growth factor, probably via nitric oxide (NO). NO may be associated with the onset and development of DR (Izumi et al. 2006). Moreover, increasing evidence suggests that the inducible nitric-oxide synthase (iNOS) is associated with DR (Leal et al. 2007; Toda and Nakanishi-Toda 2007).

The retinal pigment epithelium (RPE) is a monolayer of cells that lies in the back of the vertebrate eye and transports metabolites, ions, and fluid between the neural retina and the choroidal blood supply. RPE, which forms a blood– retinal barrier between the neural retina and choriocapillaris, plays an important role in maintaining ocular homeostasis. High glucose can injury the RPE, influence the retinal function and have important effect on the development of DR (Roufail et al. 1998). High glucose could inhibit RPE cells proliferation. RPE cells cultured with high glucose could enhance expression of iNOS of the cells in vitro, at least in part, by activation of p38 MAPK pathway which suggested that RPE cells under the effecting of high glucose might participate in the pathological reaction of diabetic retinopathy (Hong et al. 2007). iNOS isoform plays a predominant role in leukostasis and blood-retinal barrier breakdown in DR and its mechanism involves ICAM-1 upregulation and tight junction protein down regulation.

Citrus fruit holds a unique place in plant kingdom and occupies a resulting solitary position in the human diet. However, most people always throw away Pericarpium Citri Reticulatae, the rind of citrus, after enjoying this fruit, which is a huge waste. In fact there are many uses for Pericarpium Citri Reticulatae. It is important for the preparation of traditional Chinese herbal medicines and foods in China. For instance, it has been used in the treatment of indigestion, cough and detoxification in China for thousands of years. Now Pericarpium Citri Reticulatae is acknowledged in the People’s Republic of China pharmacopoeia. The major components in Pericarpium Citri Reticulatae are flavonoids. Hesperidin (5,7,3 - trihydroxy-4 -methoxy-flavanone7-rhamnoglucoside) (Fig. 22.1), a flavanone-type flavonoid, is abundant in Pericarpium Citri Reticulatae and has been reported to exert a wide range of pharmacological effects (Tommasini et al. 2005). Hesperidin has a wide range of biological effects, such as inhibition of key enzymes in mitochondrial respiration, protection against coronary heart disease, and anti-spasmolytic, anti-inflammatory, antioxidative, vascular, estrogenic, cytotoxic antitumor, and antimicrobial activities (Luo and Li 2008). Hesperidin can improve venous tone, enhance microcirculation, assist healing of