Indian Journal of Pharmacology Medknow Publications on behalf of Indian Pharmacological Society ISSN: 0253-7613 EISSN: 1998-3751 Vol. 38, Num. 3, 2006, pp. 185-189

Indian Journal of Pharmacology, Vol. 38, No. 3, May-June, 2006, pp. 185-189

Research Paper

Anticarcinogenic and antilipidperoxidative effects of Tephrosia purpurea (Linn.) Pers. in 7, 12-dimethylbenz(a)anthracene (DMBA) induced hamster buccal pouch carcinoma

Kavitha K, Manoharan S

Department of Biochemistry, Faculty of Science, Annamalai University, Annamalainagar - 608 002, Tamil Nadu
Correspondence Address:Department of Biochemistry, Faculty of Science, Annamalai University, Annamalainagar - 608 002, Tamil Nadu, manshisak@yahoo.com

Code Number: dv06045

Abstract

Keywords: Chemoprevention oral cancer, wild indigo.

Introduction

Oral squamous cell carcinoma, the fifth most common malignancy worldwide, is predominantly a disease of men, in the fifth to eighth decades of life. While it accounts for 3-4% of all malignancies in western countries, India has recorded the highest incidence, accounting about 30 - 40% of all cancers. Cancer of the oral cavity are frequently associated with chewing of betel quid containing tobacco, in addition to smoking and alcohol consumption.[1] 7,12-dimethylbenz(a)anthracene (DMBA)-induced hamster buccal pouch carcinogenesis, is a well suited model for studying precancerous and cancerous lesions of human oral squamous cell carcinoma, since it is morphologically and histologically similar to human tumors, as well as, it expresses many biochemical and molecular markers that are expressed in humans. [2]

Lipid peroxidation, a potent reactive oxygen species (ROS)- mediated chain reaction, has been implicated in the pathogenesis of several disorders, including oral carcinoma. Overproduction of reactive oxygen species within tissues can damage DNA and possibly contribute to mutagenesis and carcinogenesis. However organisms have an array of potent adaptive antioxidant defense mechanisms [enzymatic antioxidants: superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) and non-enzymatic antioxidants: reduced glutathione (GSH), vitamin C and vitamin E] within the cells, to combat the deleterious effects of reactive oxygen species- mediated oxidative damage.[3]

Cancer chemoprevention is a new promising strategy for prevention, inhibition or reversal of carcinogenesis, induced by specific natural or synthetic chemicals.[4] For a large number of the world′s rural population, medicinal plants are the only source for the prevention and treatment of various pathological diseases, from time immemorial. Several medicinal plants and their constituents have been reported, to prevent multistage carcinogenesis.[5]

Tephrosia purpurea is a wild plant known as "Sarapunkha" in Sanskrit, ′Purple tephrosia′ or ′Wild indigo′ in English and "Avuri" or "Kolinji" in Tamil. T. purpurea has been used for centuries in the Indian traditional medicine, for the treatment of various inflammatory disorders. It is considered beneficial for liver, spleen and kidney disorders. Also, it has the property to cure all types of wounds.[6] Experimental studies suggest that T. purpurea exerts antiulcer and antitumor promoting effects.[7],[8]

To our best knowledge, there is no scientific report on the chemopreventive efficacy and antilipidperoxidative effects of T. purpurea in DMBA-induced, hamster buccal pouch carcinogenesis. Hence, the present study is designed to evaluate the effectiveness of ethanolic root extract of Tephrosia purpurea (TpEt) in modifying the carcinogenic process, as well as oxidative alterations in DMBA- induced hamster buccal pouch carcinoma.

Materials and Methods

Chemicals
DMBA was obtained from Sigma-Aldrich Chemical Pvt. Ltd., Bangalore, India. All other chemicals used were of analytical grade.

Animals
Male, golden Syrian hamsters 8-10 weeks old, weighing 80-120 g, were purchased from National Institute of Nutrition, Hyderabad, India and maintained in the Central Animal House, Rajah Muthaiah Medical College and Hospital, Annamalai University. The animals were housed in groups of four or five in polypropylene cages and provided standard pellet diet and water ad libitum and maintained under controlled conditions of temperature and humidity, with a 12 h light/dark cycle.

Plant material
Tephrosia purpurea was collected in and around Annamalai University, Annamalai Nagar, Tamil Nadu, India, authenticated by Botanist, R. Panneer Selvam, Department of Botany, Annamalai University and a voucher specimen (AUO5102) was also deposited.

Preparation of plant extract
500 g of dried finely powdered T. purpurea roots were soaked with 1500 ml of 95% ethanol, overnight. The residue obtained was again resuspended in equal volume of 95% ethanol for 48 h and filtered again. The above two filtrates were mixed and the solvents were evaporated in a rotovapour at 40-50°C, under reduced pressure. A dark semisolid material (13%) obtained, was stored at -4°C, until use. For experimental studies, a known volume of the extract was suspended in distilled water and orally administered to the experimental animals by gastric intubation, using force-feeding needle.

Experimental protocol
The institutional animal ethics committee approved the experimental design. The hamsters were randomized into four groups of 10 animals each. Group I served as untreated control. Groups II and III were painted with 0.5% DMBA in liquid paraffin thrice a week, for 14 weeks on the left buccal pouches. Group II received no other treatment. Group III were administered TpEt (300 mg/kg, b.w.) orally starting 1 week before the exposure to the carcinogen and continued on days alternate to DMBA painting, until the animals are sacrified. Group IV received oral TpEt, only throughout the experimental period. The experiment was terminated at the end of 14 weeks and all the animals were sacrificed by cervical dislocation. Biochemical studies were conducted on blood and buccal mucosa of control and experimental animals, in each group. For histopathological examination, buccal mucosal tissues were fixed in 10% formalin and embedded with paraffin, 2-3 µm sections were cut in a rotary microtome and stained with haematoxylin and eosin.

Biochemical analysis
The erythrocyte membrane was prepared by the method of Dodge et al,[9] modified by Quist.[10] Thiobarbituricacid reactive substances (TBARS) was assayed in plasma, erythrocytes and buccal mucosa, according to the methods of Yagi,[11] Donnan[12] and Ohkawa et al,[13] respectively. Reduced glutathione (GSH) was determined by the method of Beutler and Kelley.[14] Vitamin C and E were measured according to the methods of Omaye et al[15] and Desai,[16] respectively. The enzymatic antioxidant activities were estimated by the methods of Kakkar et al ,[17] (SOD), Sinha[18] (CAT) and Rotruck et al [19] (GPx), respectively.

Statistical analysis
Values are expressed as mean±SD. Statistical analysis was performed by one-way analysis of variance (ANOVA), followed by Duncan′s multiple range test (DMRT). The values were considered statistically significant, if P was less than 0.05.

Results

[Table - 1] depicts the effect of TpEt on the incidence, volume and burden of tumor in DMBA- induced hamster buccal pouch carcinoma. In DMBA- painted hamsters (Group II), a 100% tumor formation with mean tumor volume (472 mm ³) and tumor burden (2029 mm ³), was observed. Oral TpEt (300 mg/kg, b.w.) significantly prevented the incidence, volume and burden of tumor in DMBA- painted hamsters (Group III). No tumor was observed in control (Group I) as well as TpEt alone- treated animals (Group IV).

[Table - 2] shows the histopathological features of control and experimental animals in each group. A myriad of histopathological changes (severe keratosis, hyperplasia, dysplasia and squamous cell carcinoma of the epithelium), were observed in hamsters painted with DMBA alone (Group II). A mild to moderate preneoplastic lesions [hyperplasia (++), keratosis (+) and dysplasia (+)], were noticed in Group III animals (DMBA + TpEt).

[Table - 3] and [Table - 4] show the status of TBARS and antioxidant in plasma and erythrocytes of the control and experimental groups. The concentration of TBARS was increased, whereas the levels of nonenzymatic antioxidants (GSH, Vitamin C and Vitamin E) and activities of enzymatic antioxidants (SOD, CAT and GPx), were significantly decreased in group II (DMBA alone), as compared to control animals. Oral administration of TpEt significantly decreased the levels of TBARS and improved the antioxidants status in DMBA- painted hamsters. TpEt alone- treated hamsters showed no significant difference in TBARS and antioxidants status, as compared to control animals.

[Table - 5] indicates the concentration of TBARS and antioxidants status, in the buccal mucosa of all animal groups. Decrease in TBARS concentration and alterations in the antioxidant status (Vitamin E, GSH and GPx were increased; SOD and CAT were decreased), were noticed in cancer animals (Group II) as compared to control (Group I). However oral administration of TpEt (Group III), reverted the concentration of TBARS and antioxidants to near normal range in DMBA- painted animals.Hamsters treated with TpEt alone (Group IV) showed no significant difference in TBARS and antioxidants status, as compared to control animals.

Disscusion

The incidence and mortality rates of oral cancer vary widely across the world, but the highest rates were reported every year from developing countries, particularly from India. Oral cancer is one among the few human cancers, with the vast potential for prevention. A major target of reactive oxygen species is cell membrane, due to the high content of polyunsaturated fatty acids. Reactive oxygen species mediated lipid peroxidation causes damage to cellular DNA, membrane structure and inhibition of functions several enzymes and alterations in the immune system.[20] In cancer, enormous production of free radicals in the system has been reported. A close relationship between free radical activity and neoplastic transformation, has been shown.[21] Antioxidants (enzymatic and non-enzymatic) play a vital role in scavenging reactive oxygen species and protect the cells from oxidative damage. Vitamin E, Vitamin C and reduced glutathione, are primary defense antioxidants. They provide protection against several reactive oxygen species, development of cancer and other oxidative stress- mediated dysfunctions.[3] SOD, CAT and GPx, are important antioxidant enzymes that protect cell and tissue damage from enhanced lipid peroxidation, via elimination of reactive oxygen species.

Elevated lipid peroxidation and poor antioxidant systems, have been reported in oral cancer patients. Sabitha and Shyamaladevi[22] have suggested, that a lack of antioxidant defense is responsible for the elevated lipid peroxidation in erythrocytes. Altered activities of enzymatic antioxidants are reported during carcinogenesis or after tumor formation. Hence, the elevated lipid peroxidation in the circulation of cancer animals, is due to poor antioxidant defense mechanism. Lowered nonenzymatic antioxidants (Vitamin C, Vitamin E and GSH) in the circulation, are probably due to elevated lipid peroxidation or sequestration by the tumor tissues for their rapid growth.

Diminished lipid peroxidation and disturbed antioxidants status (GSH and GPx were increased, whereas SOD and CAT were decreased), were observed in tumor tissues, as compared to normal tissues. Cancer cells showed decreased susceptibility to lipid peroxidation, compared to normal tissues. An inverse relationship between the lipid peroxidation process and the rate of cell proliferation, has been reported.[23] Glutathione, a biologically important tripeptide, is essential for maintaining cell integrity, due to its reducing properties and participation in the cell metabolism. Glutathione peroxidase and its co-substrate glutathione, are reported to have regulatory effects on cell proliferation. Elevated glutathione and GPx activity, have been demonstrated in several tumor tissues, including oral cancer. Subapriya et al [23] have postulated that diminished lipid peroxidation combined with enhanced glutathione-dependent antioxidant capacity of oral tumors, facilitates cell- proliferation, offering selective growth advantage in tumor cells over their surrounding normal cells. Our results lend credibility to the above observations. Decrease in SOD and catalase activities described in tumors, is regarded as markers of malignant transformation. Lowered activities of SOD and CAT were reported in several cancers, including oral cavity cancer. [22],[23] Our results corroborate these observations.

The painting of 0.5% DMBA in liquid paraffin thrice a week, for 14 weeks to the hamster buccal pouch, induced oral carcinoma. We have also noticed the precancerous lesions in DMBA- painted hamsters, from the 10th week of the experimental period. In the present study oral administration of TpEt at a dose of 300 mg/kg, b.w., reduced tumor incidence, volume, burden and the number in DMBA- painted hamsters. Our results thus indicate, that TpEt possess significant chemopreventive potential against DMBA- induced buccal pouch carcinoma.

Furthermore, TpEt significantly reduced the levels of TBARS and enhanced the status of antioxidants in the circulation of DMBA- painted hamsters. We also noticed an elevation of TBARS level and improvement in antioxidant defense system in the buccal mucosa of DMBA-painted hamsters, after treatment with TpEt. Johnson[24] reported that the chemopreventive properties of plant anticarcinogens are either due to antilipidperoxidative action, modulating carcinogen detoxification or by improving the antioxidant defense system. Sharma et al,[25] have proposed that several medicinal plants and their constituents, probably exert their chemopreventive effect, by scavenging reactive oxygen species and improving the antioxidant defense systems. The present study reveals, that the chemopreventive effect of TpEt in DMBA- painted animals, is probably due to its antilipidperoxidative and antioxidant properties.

Acknowledgments

References

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