Epigallocatechin gallate: Phytochemistry, bioavailability, utilization challenges, and strategies

Abstract

Epigallocatechin gallate (EGCG), a green tea catechin, has gained the attention of current study due to its excellent health‐promoting effects. It possesses anti‐obesity, antimicrobial, anticancer, anti‐inflammatory activities, and is under extensive investigation in functional foods for improvement. It is susceptible to lower stability, lesser bioavailability, and lower absorption rate due to various environmental, processing, formulations, and gastrointestinal conditions of the human body. Therefore, it is the foremost concern for the researchers to enhance its bioactivity and make it the most suitable therapeutic compound for its clinical applications. In the current review, factors affecting the bioavailability of EGCG and the possible strategies to overcome these issues are reviewed and discussed. This review summarizes structural modifications and delivery through nanoparticle‐based approaches including nano‐emulsions, encapsulations, and silica‐based nanoparticles for effective use of EGCG in functional foods. Moreover, recent advances to enhance EGCG therapeutic efficacy by specifically targeting its molecules to increase its bioavailability and stability are also described. Practical applications The main green tea constituent EGCG possesses several health‐promoting effects making EGCG a potential therapeutic compound to cure ailments. However, its low stability and bioavailability render its uses in many disorders. Synthesizing EGCG prodrugs by structural modifications helps against its low bioavailability and stability by overcoming premature degradation and lower absorption rate. This review paper summarizes various strategies that benefit EGCG under different physiological conditions. The esterification, nanoparticle approaches, silica‐based EGCG‐NPs, and EGCG formulations serve as ideal EGCG modification strategies to deliver superior concentrations with lesser toxicity for its efficient penetration and absorption across cells both in vitro and in vivo. As a result of EGCG modifications, its bioactivities would be highly improved at lower doses. The protected or modified EGCG molecule would have enhanced potential effects and stability that would contribute to the clinical applications and expand its use in various food and cosmetic industries.

Flavonoids bridging the gut and the brain: Intestinal metabolic fate, and direct or indirect effects of natural supporters against neuroinflammation and neurodegeneration

“…EGCG and other catechins are highly enriched in green tea, and their daily intake is around 90-300 mg/day [81]. The beneficial effects of green tea on health have been known for millennia especially in Far East countries and modern science has demonstrated that EGCG is its predominant active molecule [82]. As for most flavonoids and polyphenols, it is nevertheless worth mentioning that their beneficial effects are not only a matter of ingested quantity, but rather of bioavailability.…”

“…Apart from more general beneficial effects on health of green tea extracts that are shared with other classes of flavonoids, such as the antioxidant, anti-inflammatory, antitumoral, antiviral, hypoglycemic and antiaging activities as recently summarized in details elsewhere [82], EGCG is endowed with positive outcomes on specific pathological mechanisms involved in neurodegeneration. Despite the very different clinical characteristics, AD and PD share many common pathological features, including the presence of a pro-inflammatory environment which is sustained and promoted by activated microglia and astrocytes, oxidative stress, the aggregation/precipitation/deposition of misfolded proteins, namely amyloidogenic -amyloid fragments (A1-42) and Tau protein in AD and -synuclein in PD, and dysregulation of the autophagy process, as recently brilliantly reviewed in [91].…”

“…Regretfully, these dosages appear to be very closed to the toxic ones. According to the European Food Safety Agency (EFSA) panel on Food Additives and Nutrient Sources added to Food, EGCG dosages above or equivalent to 800 mg/day caused acute liver inflammation, with increased transaminase level and other side effects such as anemia, hypoglycemia, dizziness, and kidney complications both in animals and in humans [81,82].…”

The Anticancer Potential of Plant-Derived Nutraceuticals via the Modulation of Gene Expression

“…EGCG metabolites are excreted through both bile and urine. EGCG can be further reabsorbed from the intestine through the enterohepatic recirculation process [ 233 , 234 , 235 ].…”

“…Likewise, it has been suggested that the ingestion of EGCG on an empty stomach may improve its systemic absorption [ 240 ]. Moreover, the structural modification of EGCG by methylation, acyclization, or glycoside modification seems to allow the management of its premature degradation and reduced absorption rate [ 228 , 233 ]. Finally, one promising approach to protect EGCG against unfavorable gastrointestinal conditions and improve its bioavailability includes the design of nanocarriers.…”