Chapter 12 - Nanotechnology-Based Approach for Enhanced Bioavailability and Stability of Tea Polyphenols—A Review

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Abstract

Tea, the most consumed nonalcoholic beverage is being used worldwide as a major health drink due to some of its important constituents like polyphenols, caffeine, theanine, saponin. Among these constituents, polyphenols are most important due to their potential applications related to human health. The major constituent of tea polyphenols, responsible for several health benefits, known as catechins constitute about 30–42% of the dry weight. Some of the major health benefits of tea polyphenols include their anticancer property, antioxidant activity, antimicrobial activity, effects in cardiovascular diseases, effects in neuroprotection, and antidiabetic and psychotropic effects. In spite of several impressive data on health benefits of tea polyphenols, there are certain constraints like bioavailability, stability, and metabolic transformation under physiological conditions which limit the application of tea polyphenols as a therapeutic agent. To overcome these limitations, certain approaches like prodrug approach and the nanoencapsulation have been attempted. Of these two approaches, use of nano-based carriers could be reliable for delivery of tea polyphenols. Nanoparticles, due to their small size could penetrate through small capillaries and are taken up by the cells allowing maximum drug accumulation at the target site and allow sustained release of drug at the target site over a period of time. Different types of nanoparticles have been used for this purpose which includes lipid-based nanomaterials, dendrimers, and polymeric nanoparticles including several proteins and copolymers. Among all these materials used, polymeric nanoparticles are widely used as nano-based carriers due to some of its properties such as biodegradability, nonantigenic, metabolizable, and easily modifiable for surface alterations. With these implications, several new formulations are being developed by encapsulating tea polyphenols in polymeric nanoparticles, thereby achieving increased bioavailability and stability. The application of nanotechnology for the delivery of tea polyphenols would serve as a promising tool in the field of medicine.

Introduction

Tea, the most consumed nonalcoholic drink, is produced from two leaves and a bud of the plant Camellia sinensis. The genus Camellia incorporates 325 species, belongs to the family Theaceae and is now cultivated in more than 30 nations around the world. Green tea (unfermented tea) is consumed in China, Japan, and the Middle East which constitute around 20–22% of the total tea consumption; people in the eastern part of China, China–Taiwan, and Japan prefer oolong tea (semifermented tea) comprising less than 2% while rest of the world drink black tea (fermented tea) that constitute 76–78% of the total tea consumption [1], [2].

The distinctive aroma and health benefits of green tea are mostly due to its polyphenolic compounds [3], along with other bioactive compounds such as caffeine, theanine, saponin. Catechins, the major constituent of green tea polyphenols (GTP) contribute to about 30–42% of the dry weight of tea leaves. Various forms of catechins which majorly constitute the polyphenols include (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin-3-gallate (ECG), and (−)-epigallocatechin-3-gallate (EGCG) (Fig. 12.1). Among these forms EGCG contributes to about 50–80% of the total catechins [4]. GTP as a whole demonstrated several profound biochemical and pharmacological activities [5].

Section snippets

Biosynthesis of Catechins

Catechins possess two benzene rings (A and B rings) and a dihydropyran heterocycle (C ring) with a hydroxyl group on carbon 3. A ring is similar to resorcinol moiety, while the B ring is similar to catechol moiety. The C6 (A) catechin ring is produced by the acetic–malonic acid pathway and C3–C6 (B) ring is produced by the shikimic–cinnamic acid pathway starting from the glucose pool. This fact was discovered during research in the synthesis of quercitin. When 14C-acetic acid is supplied,

Health Benefits of Tea

Tea is known to have several health benefits [7]. Compounds present in tea have an impact on a myriad of illness, a few of which include its immune functions, aging process, detoxification, and chemoprevention of some diseases. Compounds like flavonoids, amino acids, vitamins, caffeine, and polysaccharides are most important among more than 500 compounds present in tea. Tea flavonoids are 20-fold more capable antioxidants than vitamin C [8]. Among all these compounds, polyphenols, caffeine, and

Limitations of Tea Polyphenols

In spite of several impressive data available on health benefits of GTP, its application as a therapeutic agent is unsuccessful due to some of its limitations such as bioavailability, stability, and metabolic transformation under physiological conditions [22], [23], [24]. Despite exciting results obtained on efficacy of tea polyphenols against a number of diseases under in vitro conditions, its bioavailability poses a major challenge in reproducing these in vitro results under in vivo

Strategy to Overcome the Limitations

To overcome these limitations, several approaches have been put forth, of which the nanoparticulate approach has been widely attempted. Particles having a diameter of less than 200 nm are widely used in the field of medicine due to its several advantages, especially the small size of the particles. Several advances are being made to implement nanoparticles as a tool for the delivery of several drugs to the target site, thereby adapting a more effective drug delivery system. Several researchers

Nanoencapsulation of Green Tea Polyphenols

EGCG is one of the major constituent of GTP and is responsible for major health benefits. It has been reported that EGCG has the capability to obstruct tumor cell growth and induce DNA damage and apoptosis leading to chemotherapeutic action for colon cancer [50]. Though EGCG is known for its antioxidant activity, it was reported that nanoparticles containing EGCG showed promising antioxidant activity compared to free EGCG [51]. In another study, EGCG-encapsulated biopolymers showed potent

Conclusion

Drug delivery is a process or method to deliver a drug in human or animal to achieve its therapeutic effect. Selection of a drug delivery method has significant effect on the efficacy of the drug. Many important pharmacological properties of the drug, when used as free molecule, can be improved by using an appropriate drug delivery system. In the last few decades, methods of drug delivery have been changed dramatically and even much greater changes are expected in the near future. Among the new

Acknowledgments

We thank the management of VIT University for providing the facilities. Financial support from NTRF, Tea Board, Kolkata is also gratefully acknowledged.

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