Green tea polyphenol epigallocatechin 3-gallate in arthritis: progress and promise

Green tea's active ingredient, epigallocatechin 3-gallate (EGCG), has gained significant attention among scientists and has been one of the leading plant-derived molecules studied for its potential health benefits. In the present review I summarize the findings from some of the most significant preclinical studies with EGCG in arthritic diseases. The review also addresses the limitations of the dose, pharmacokinetics, and bioavailability of EGCG in experimental animals and findings related to the EGCG-drug interaction. Although these findings provide scientific evidence of the anti-rheumatic activity of EGCG, further preclinical studies are warranted before phase clinical trials could be initiated with confidence for patients with joint diseases.

Rheumatoid arthritis (RA) is a chronic infl ammatory disease characterized by the activation of synovial tissue lining the joint capsule, which results in the invasion of the cartilage and bone leading to the progressive joint dysfunction [1]. Severe morbidity and structural damage of joints caused by chronic infl ammation often lead to major personal, family, and fi nancial consequences, as well as increased mortality. Recent understanding of the RA pathogenesis has clarifi ed the role of cytokines and other infl ammatory mediators in this process and has provided a scientifi c rationale in the process of developing targeted therapies [2].
Osteoarthritis (OA) is a common disorder of synovial joints characterized pathologically by focal areas of damage to the articular cartilage, centered on load-bearing areas, which is associated with new bone formation at the joint margins (osteophytosis), changes in the subchondral bone, variable degrees of mild synovitis, and thickening of the joint capsule [3]. Th e severity of OA diff ers from patient to patient, but the very common clinical symptoms include pain, reduced range of motion, infl ammation, and deformity [4]. Th is condition is strongly age related, being less common before the age of 40 but showing a marked increase in frequency with age [3]. Although OA is considered the disease of the destruc tion of articular cartilage, recent evidence suggests that it may also damage bone and synovium in the arthritic joints [3,4]. Despite existing evidence of the crosstalk between tissues at the cellular and molecular levels, however, intertwined pathophysiological processes causing OA have reduced the focus in choosing from one of these three tissues -articular cartilage, bone, or synovium -to serve as the key therapeutic target [3].

Treatment of arthritis: approaches and options
Conventional disease-modifying anti-rheumatic drugs such as methotrexate have long been the mainstay of RA treatment and are still advocated as a fi rst-line option in newly diagnosed RA patients [5]. While a combination of good effi cacy and acceptable toxicity, in conjunction with low cost and patient convenience, has made methotrexate an increasingly favored drug for RA, recent studies suggest that patients lose effi cacy over time and only a minority of them achieve disease remission from its use [5]. TNFα inhibitors, as fi rst-generation biologics, have radically changed the treatment of patients with refractory RA. Among patients with RA who are unresponsive to methotrexate, however, only two-thirds respond to TNFα inhibitors -which opened the option of combi nation therapy (combining disease-modifying anti-rheumatic drugs with biological therapy) [5,6]. As a result, newer approaches have resulted in the development of next-generation biologics during the past few years, including abatacept, rituximab, and tocilizumab [2,6].
Pharmacological management of OA includes analgesics and nonsteroidal anti-infl ammatory drugs. Unfortunately, these medications can precipitate severe adverse reactions while providing only symptomatic relief from pain and no eff ect on the progress of OA in some patients [7]. In addition, increased rates of cardiovascular events associated with cyclooxygenase-2 (COX-2) inhibitors and some conventional nonsteroidal anti-infl ammatory drugs have made the treatments inappropriate for long-term use by OA patients with high risk of heart disease or stroke [8]. More recent emerging data from clinical trials conducted over nine clinical centers in the United States underlined the clinical effi cacy of a glucosamine and chondroitin sulfate combination on the progressive loss of cartilage, pain, and stiff ness in patients with knee OA [7].

Plant-derived molecules for the treatment of arthritis
Th e past decade or two have seen a dramatic increase and growing interest in the use of alternative treatments and herbal therapies by arthritis patients [9][10][11]. Trustworthy documentation of traditional knowledge, together with extensive modern scientifi c/pharmaco logical experimentation, however, is necessary to validate or refute the purported medicinal value. In this regard, epigallocatechin-3-gallate (EGCG) has in the past decade been extensively evaluated by us and other researchers for its potential anti-rheumatic activity using in vitro experimen tations and animal models of arthritis. Th e following section of the present review highlights some of these major fi ndings and puts forward an argument for the future development of EGCG as a potential thera peutic entity for rheumatic diseases.

Epigallocatechin-3-gallate
Green tea (Camellia sinensis) is one of the most commonly consumed beverages in the world and is a rich source of polyphenols known as catechins (30 to 36% of dry weight) including EGCG, which constitutes up to 63% of total catechins [12]. EGCG has been shown to be 25 to 100 times more potent than vitamins C and E in terms of antioxidant activity [13]. A cup of green tea typically provides 60 to 125 mg catechins, including EGCG [14].

In vitro fi ndings Cartilage/chondrocyte protection
Extensive studies in the past decade have verifi ed the cartilage-preserving and chondroprotective action of EGCG. We pioneered research in this therapeutic area and studied the benefi ts of EGCG on progressive cartilage degradation, a hallmark of OA, using chondrocytes derived from OA cartilage. Proinfl ammatory cytokines such as IL-1β, TNFα, and IL-6 have been shown to modulate extracellular matrix turnover, to accelerate the degradation of cartilage, and to induce apoptosis in chondrocytes [3,4].
Besides promoting imbalance between excessive cartilage destruction and cartilage repair processes, IL-1β has been a potent inducer of reactive oxygen species, including nitric oxide and infl ammatory mediators such as prostaglandin E 2 , via enhanced expression of the enzymes inducible nitric oxide synthase and COX-2, respectively [15,16]. Preincubation of human chondrocytes derived from OA cartilage at diff erent micromolar concentrations of EGCG showed a marked inhibition in the IL-1β-induced inducible nitric oxide synthase and COX-2 expression and activity, which further resulted in the reduced nitric oxide and prostaglandin E 2 synthesis [15,16]. Defi ning the molecular mechanism of EGCG's effi cacy in regulating inducible nitric oxide synthase expression, the results showed that EGCG inhibits IL-1βinduced phosphorylation and proteasomal degradation of IκBα to suppress NF-κB nuclear translocation [16].
In a follow-up study to determine the eff ect of EGCG on other signaling pathways triggered by IL-1β, Singh and colleagues showed that EGCG selectively inhibited the p46 isoform of c-Jun-N-terminal kinase induced by IL-1β [17]. Th is resulted in the reduced accumulation of phosphorylated c-Jun and activation protein-1 DNA binding activity, and of activation protein-1-mediated infl ammatory responses in OA chondrocytes.
Under normal circumstances, chondrocytes in the cartilage make extracellular matrix components such as aggrecan and type II collagen as required in response to mechanical pressure [3]. Under abnormal or diseased conditions, however, chondrocyte metabolism is altered under the infl uence of the increased infl ux of pro infl ammatory cytokines that activate matrix-degrading enzymes termed matrix metalloproteinases (MMPs) and of reactive mediators that promote cartilage degradation [18]. MMPs are a large group of enzymes that play a crucial role in tissue remodeling as well as in the destruction of cartilage in arthritic joints due to their ability to degrade a wide variety of extracellular matrix components [19,20]. Interestingly, the collagenases among the MMP family are of particular importance in joint disorders due to their ability to effi ciently cleave type II collagen [19,20].
In another study, we evaluated the potential of EGCG to protect human cartilage explants from IL-1β-induced release of cartilage matrix proteoglycans and the induction and expression of MMP-1 and MMP-13 in human chondrocytes [21]. Our results showed that EGCG pretreatment of cultured human OA chondro cytes signifi cantly inhibited the expression and activities of MMP-1 and MMP-13 in a dose-dependent manner [21]. In a parallel observation, another study found that catechins from green tea inhibited the degradation of human cartilage proteoglycan and type II collagen, and selectively inhibited ADAMTS-1, ADAMTS-4, and ADAMTS-5 [22,23]. Further evaluation of the eff ect of EGCG on the anabolic pathways in chondrocytes showed that EGCG ameliorates IL-1β-mediated suppression of transforming growth factor β synthesis, and enhances type II collagen and aggrecan core protein synthesis in human articular chondrocytes [24]. Th ese results were further supported by a recent study showing the protective eff ect of EGCG on advanced glycation end productinduced MMP-13 production in human OA chondrocytes in vitro [25].
To further support the chondroprotective eff ects of EGCG in arthritis, a recent study conducted by the biomaterial testing group on collagen showed that collagen preincubated with EGCG demonstrated a remark able resistance against degradation by bacterial collagenase and MMP-1 [26]. A circular dichroism spectral analysis of the triple-helical structure of EGCGtreated collagen and untreated collagen showed a higher free-radical scavenging activity in EGCG-treated collagen [26]. Recent studies evaluating the cartilage-preserving property of EGCG showed that articular cartilages, preserved in a storage solution containing EGCG for up to 4 weeks, showed a higher degree of chondrocyte viability and proteoglycan (GAG) content of the extracellular matrix, at least in part, by reversibly regulating the cell cycle at the G 0 /G 1 phase and NF-κB expression [27,28]. Th ese fi ndings provide a scientifi c rationale for the effi cacy of EGCG in protecting cartilage breakdown during the progress of joint disorders and could be utilized in other chronic ailments where integrity of the collagen is compromised in tissue destruction or remodeling.

Bone-preserving activity
In rheumatic diseases, loss of the intricate balance between bone formation and bone resorption activity leads to skeletal abnormalities that aff ect the quality of life [29]. In particular, three TNF family molecules -the receptor activator of NF-κB, its ligand RANKL, and the decoy receptor of RANKL, osteoprotegerin -have established their pivotal role as central regulators of osteoclast development and osteoclast function [29]. In 2006 Hafeez and colleagues showed that green tea poly phenols triggered caspase-3-dependent apoptosis in these cells by regulating the constitutively active NF-κBp65 to induce DNA fragmentation and apoptosis in osteocarcoma SaOS-2 cells [30]. Another recent study using human osteoblastic cells evaluated the eff ect of EGCG on oncostatin M-induced monocyte chemotactic protein-1 (MCP-1)/CCL2 synthesis [31]. Th e experi men tal fi ndings of the study suggested that EGCG inhibits oncostatin Minduced MCP-1/CCL2 synthesis in human osteoblastic and MG-63 cells by reducing c-Fos synthesis [31].
IL-6 -produced by both stromal cells and osteoblasts in response to several stimuli such as lipopolysaccharides, IL-1β, and TNFα -stimulates bone resorption and osteoclast formation [32,33]. Th e effi cacy of EGCG was evaluated against basic fi broblast growth factor-2induced IL-6 synthesis in osteoblast-like MC3T3-E1 cells [34]. EGCG inhibited basic fi broblast growth factor-2induced IL-6 synthesis dose dependently and, in part, via suppression of ERK1/2 and p38 mitogen-activated protein kinase pathways in osteoblast cells [34]. Further extending these fi ndings, a recent study by Kamon and colleagues showed that EGCG reduced osteoclast formation in these cells by inhibiting osteo blast diff erentiation without aff ecting their viability and proliferation [35]. Another recent study addressing the precise molecular mechanism through which EGCG inhibits osteoblast diff erentiation showed that EGCG produced an anti-osteoclastogenic eff ect by inhibiting RANKLinduced activation of c-Jun-N-terminal kinase and NF-κB pathways, thereby suppressing the gene expression of c-Fos and NFATc1 in osteoclast precursors [36].

Regulation of synovial fi broblast activity
Under normal physiological conditions, synovial fi broblasts form a thin lining of synovial tissue surrounded by the fi brous capsule of the joint. Th e lining of synovial fi broblasts secretes synovial fl uid, which has both lubricat ing and immunomodulatory properties, and which promotes normal joint function. In diseased conditions such as RA, synovial fi broblasts in the RA synovium become hyperproliferative and secrete factors that promote infl ammation, neovascularization, and cartilage degradation.
In response to cytokines produced by macrophages such as TNFα and IL-1β, RA synovial fi broblasts secrete matrix-degrading enzymes such as MMPs, ADAMTS, and cathepsins. MMPs released from RA synovial fi broblasts can modulate activity of cytokines and chemo kines, release proapoptotic ligands from cell surfaces, and promote fi broblast invasion of the cartilage. RA synovial fi broblasts also attract leukocytes by expressing chemokines in response to cytokines via distinct signaling pathway, which provides an opportunity to target them for diff erent therapeutic approaches.
We and other workers have extensively evaluated the effi cacy of EGCG using the synovial fi broblasts isolated from human joints to provide the exact mechanism through which EGCG inhibits or suppresses arthritis. Our study showed that EGCG pretreatment signifi cantly inhibited both the constitutive and IL-1β-induced chemokine MCP-1/CCL2 production, regulated upon activation, normal T-cell expressed and secreted (RANTES/ CCL5) production, growth-regulated oncogene (Gro-α/ CXCL1) production, and epithelial neutrophil-activating peptide 78 (ENA-78/CXCL5) production, and MMP-2 activation by RA synovial fi broblasts [37]. Th is was achieved by EGCG via selective inhibition of the IL-1βinduced protein kinase Cδ and NF-κB pathways. One step further, we found that EGCG signifi cantly inhibited MMP-2 activity induced by RANTES/CCL5, Gro-α/ CXCL1, and ENA-78/CXCL5, suggesting a novel mechanism of MMP-2 regulation by EGCG in RA synovial fi broblasts [37]. In our follow-up study, we observed a similar inhibitory eff ect of EGCG-containing green tea extract (GTE) on chemokine synthesis in RA synovial fi broblasts [38]. GTE preincubation surprisingly induced the basal and IL-1β-induced chemokine receptor expression in these cells, however, which was also mimicked by the protein kinase Cδ inhibitor, Rottlerin [38]. Further studies are underway to clarify the signifi cance of these fi ndings in relation to GTE's antiarthritic property.
It has also been shown that EGCG was eff ective in inhibiting IL-1β-induced MMP-1, MMP-3, and MMP-13 in human tendon fi broblasts [39]. Synovial fi broblast IL-6 production has been shown to inhibit bone formation and to concomitantly stimulate bone resorption and pannus formation [40]. In this regard, we showed in our recent study that EGCG pretreatment inhibits IL-1βinduced IL-6 and vascular endothelial growth factor synthesis in RA synovial fi broblasts [41]. In a recent study, Yun and colleagues showed that EGCG treatment resulted in dose-dependent inhibition of TNFα-induced production of MMP-1 and MMP-3 at the protein and mRNA levels in RA synovial fi broblast by inhibiting activation protein-1 DNA binding activity [42].
In RA, the purposeful induction of apoptosis in activated synovial fi broblasts has emerged as a thera peutic strategy for halting deleterious tissue growth [1]. Th e constitutive activation of survival protein Akt and NF-κB in RA synovial fi broblasts makes these cells resis tant to both TNFα-mediated and Fas-mediated apoptosis [43,44]. In recent years, studies have linked the over expression of the anti-apoptotic myeloid cell leukemia-1 (Mcl-1) protein as a major cause of RA synovial fi broblast resistance to apoptosis [1,45]. Our recent study to evaluate the effi cacy of EGCG in downregulating Mcl-1 expression showed that, in RA synovial fi broblasts, EGCG inhibits constitutive and TNFα-induced Mcl-1 protein expression [46]. Importantly, EGCG specifi cally abrogated Mcl-1 expression in RA synovial fi broblasts and aff ected Mcl-1 expression to a lesser extent in OA synovial fi broblasts, normal synovial fi broblasts, and endo thelial cells. In this study, caspase-3 activation by EGCG also suppressed RA synovial fi broblast growth, and this eff ect was mimicked by Akt and NF-κB inhibitors. Interestingly, Mcl-1 degradation by EGCG sensitized RA synovial fi broblasts to TNFαinduced cleavage of poly ADP-ribose poly merase protein and apoptosis. Our fi nding suggests that EGCG may selectively induce apoptosis and further sensitize RA synovial fi broblasts to TNFα-induced apoptosis to regulate their invasive growth in RA.

Animal studies Collagen-induced arthritis
Th e potential disease-modifying eff ect of EGCG on arthritis was fi rst discovered in a study in which the consumption of EGCG-containing GTE in drinking water ameliorated collagen-induced arthritis (CIA) in mice [47]. Th e reduced CIA incidence and severity was refl ected in a marked inhibition of the infl ammatory mediators COX-2, IFNγ, and TNFα in arthritic joints of green tea-fed mice. Additionally, total immunoglobulins (IgG) and type II collagen-specifi c IgG levels were found to be lower in serum and arthritic joints of green tea-fed mice [47].
Interestingly, some recent pharmacological studies using EGCG or green tea to suppress arthritis have focused equally on bone resorption observed in RA [31,[48][49][50][51]. A recent study by Morinobu and colleagues showed that EGCG treatment reduced bone resorption as determined by tartrate-resistant acid phosphatasepositive multinucleated cells, bone resorption activity, and osteoblast-specifi c gene expression of the transcription factor NF-ATc1, but not of NF-κB, c-Fos, and c-Jun [49]. Th e in vivo eff ect of osteoclast diff erentiation in CIA mice was not clear, however, as intraperitoneal administration of EGCG (20 mg/kg) inhibited infl ammation in experimental arthritis [49]. Using in vivo testing conducted in mouse CIA model, another study showed that EGCG (20 mg/kg, intraperitoneally daily) ameliorated arthritis and macrophage infi ltration, and caused a reduction in the amount of MCP-1/CCL2-synthesizing osteoblasts [31].

Adjuvant-induced arthritis
Recent advances in understanding the pathogenic eff ects of IL-6 provide evidence of its central role in promoting acute infl ammation [32,33]. Further studies related to the mechanisms through which EGCG inhibits infl ammation and tissue destruction in RA were studied by us and others. Our novel fi ndings showed that EGCG selectively inhibits IL-6 synthesis in rat adjuvant-induced arthritis, thus providing a missing link to the reduction in infl ammation observed in earlier studies [41]. Administration of EGCG (100 mg/kg, intraperitoneally daily) during the onset of arthritis in rats resulted in a specifi c inhibition of IL-6 levels in the serum and joints of EGCG-treated animals. Our study also showed that EGCG enhances the synthesis of soluble gp130 protein, an endogenous inhibitor of IL-6 signaling and trans-signaling [41]. Th e inhibition of arthritis in EGCG-treated rats correlated to the reduction in MMP-2 activity in the joints compared with the activity level in arthritic rats [41]. A recent study testing a possible immunomodulatory activity of GTE in arthritis showed that GTE administration in drinking water ameliorated rat adjuvantinduced arthritis via the inhibition of serum IL-17 levels, with a concomitant upregulation of serum IL-10 levels [52]. In our recent study, a daily per oral adminis tration of GTE (200 mg/kg) modestly ameliorated rat adjuvantinduced arthritis, which was accompanied by a decrease in MCP-1/CCL2 and GROα/CXCL1 levels and enhanced CCR-1, CCR-2, CCR-5, and CXCR1 receptor expression in the joints of GTE-administered rats [38]. Th is suggests that chemokine receptor overexpression with reduced chemokine production by GTE may be one potential mechanism to limit the overall infl ammation and joint destruction in RA. Further studies may be designed to improve the clinical outcome in animal models of RA through modifi cation of the dose and frequency of GTE administration, which may provide a better outcome and benefi ts of GTE in RA.

Clinical studies
Th e effi cacy of EGCG or GTE in human RA or OA using the phase-controlled trials is yet to be tested. Several phase I and phase II cancer chemoprevention trials, however, have been performed using EGCG or GTE. A study by Elmets and colleagues showed that EGCG provided photoprotection to the skin from ultraviolet radiation on topical application in healthy human volunteers [53]. In another study, patients suff ering from chronic lymphocytic leukemia showed an improvement in their clinical, laboratory, and radiographic outcomes and objective responses [54] after oral ingestion of EGCG. Th e results of a recent open-label, phase II clinical trial using EGCG in prostate cancer patients showed a signifi cant decrease in the serum levels of prostate-specifi c antigen, hepatocyte growth factor, and vascular endothelial growth factor after 6 weeks of treatment [55]. A phase I trial on EGCG, with a 400 to 2,000 mg dose taken by mouth twice a day for month, was well tolerated by chronic lymphocytic leukemia patients, the majority of whom showed a decline in lymphocyte count and lymphadenopathy [56]. Th is has encouraged the investigators of the study to initiate a phase II trial to evaluate EGCG effi cacy using a 2,000 mg dose twice daily [56].
Th e effi cacy of EGCG in human metabolic disorders has been a topic of clinical interest. A randomized, controlled clinical trial using EGCG on insulin resistance and associated metabolic risk factors in obese men showed that 400 mg EGCG treatment twice daily for 8 weeks showed no eff ect on insulin sensitivity or secretion and glucose tolerance, but caused a moderate reduction in blood pressure and a positive eff ect on mood [57]. In another study by Maki and colleagues, the consumption of 625 mg EGCG-containing catechins daily for 12 weeks caused a greater loss of body weight and a decrease in the fasting serum triglyceride levels in the catechin-administered group [58]. In a double-blind, placebo-controlled trial, intake of GTE (containing 302 mg EGCG) for 12 weeks showed a signifi cant reduction in the levels of low-density lipoprotein and triglyceride, and markedly increased the high-density lipoproteins and adiponectin levels [59].

Pharmacokinetics of EGCG
Th e pharmacokinetics and bioavailability of EGCG in rodents and humans is well studied. An acute and shortterm toxicity study on EGCG preparations showed that the dietary consumption of EGCG by rats for 13 weeks was nontoxic at doses up to 500 mg/kg/day [60]. A study by Chen and colleagues showed that administration of pure EGCG or EGCG in the form of decaff einated GTE to rats via intravenous or intragastric administration showed diff erences in the pharmacokinetic patterns, favoring the intravenous route when given as an extract [61]. Studies also revealed that EGCG possesses a longer half-life and a smaller clearance rate, suggesting a slower rate of elimination of EGCG as compared with epigallocatechin and epi catechin [61]. A study by Kim and colleagues, in which subjects consumed GTE at 0.6% in drinking water over 28 days, showed that EGCG is more available in free form as compared with other catechins [62]. Th ese studies also showed that the highest concen tration of EGCG was found in the large intestine, suggesting a higher absorption rate but less clearanceas demonstrated by the lower levels of EGCG detected in plasma and distributed in the kidney, liver, lungs, and prostate of rats [61,62]. In contrast to the results with rats, however, the level of EGCG in mice was much higher than that of epigallocatechin and epicatechin, suggesting a high bioavailability of EGCG in mice [62]. In addition, it was reported that the intraperitoneal administration of green tea containing EGCG showed much higher tissue and plasma concentration of EGCG than that obtained intragastrically [62]. Although other chemical processes such as peracetylation and glucuronidation have been shown to enhance the bioavailability of EGCG, not much is known about the distribution and its bioactivity in diseased conditions.
In humans, EGCG has been extensively studied for its acute and long-term toxicity studies [63][64][65][66]. A standardized capsule of polyphenon E containing 400 mg, 800 mg, or 1,200 mg EGCG was used to study the pharmacokinetics of EGCG in humans [63,64]. Th e pharmaco kinetic analysis from the study showed that the average plasma area under the curve, the maximum concentration, and the half-life increased with an increase in the dosages given in the capsules of 400 mg, 800 mg, and 1,200 mg EGCG [64]. Th is study also showed that administration of EGCG capsules to human subjects under fasting conditions signifi cantly enhanced the pharmacokinetic profi le and bioavailability of EGCG, possibly due to reduced conversion by glucuronidation process [64]. A 4-week clinical study carried out to determine the safety and pharmacokinetics of EGCG at doses of 400 and 800 mg/day in healthy participants showed no signifi cant adverse eff ects, and investigators observed a signifi cant (>60%) increase in EGCG bioavailability by the 800 mg/day dose, when compared with the 400 mg/day dose, in these participants [63]. Th ere are, however, limited numbers of studies suggesting that the EGCG plasma concentration may reach up to ~1 μM when consumed by drinking green tea [67,68]. Further studies are required to optimize the circulating and synovial concentrations of EGCG to avail benefi ts similar to those observed in vitro and in preclinical studies.

Drug interaction
Th ere have been limited data available to validate or reject the potential benefi t of EGCG in RA patients. Studies conducted recently, however, evaluate the effi cacy of EGCG in combination with conventional medicine, which could be extrapolated for possible interaction with anti-rheumatic drugs. Th e initial observation came from the anti-cancer studies using EGCG, wherein the administration of EGCG was shown to enhance the apoptosis-inducing property of COX-2 inhibitors on the growth of human prostate cancer cells in vitro and in vivo [69]. In another related study, EGCG sensitized human prostate carcinoma LNCaP cells to TNF-related apoptosisinducing ligand-induced apoptosis and synergistic inhibition of the biomarkers of angiogenesis and metastasis [70]. Similar outcomes on the sensitization of RA synovial fi broblasts for TNF-related apoptosis-inducing ligand-induced apoptosis were observed with trichostatin A, suggesting a common mechanism of regulating invasive growth of synovial tissue in RA [71].
Another unique mechanism through which EGCG leaves a positive impact as a potential therapeutic option comes from its property of inducing pretranscriptional modifi cation, termed alternative splicing. In addition to our study, where EGCG enhanced the synthesis of soluble gp130 at least in part by this mechanism, recent reports suggest that EGCG modulates alternative splicing to correct mutated proteins to normal forms, as observed for survival motor neuron-1 protein in neurodegenerative disorder, or to produce spliced variants of Mcl-1 and Bcl-X proteins in combination with ibuprofen that may inhibit the functionality of these anti-apoptotic proteins in prostate cancer cells [41,72,73]. More recently, confl icting results have emerged from the studies related to the eff ect of EGCG on clinical effi cacy of the chemotherapeutic agent Bortezomib as a proteasome inhibitor in cancer-related studies [74,75]. More elaborative and rigorous studies are awaited, however, to verify the possible interaction of EGCG with current treatment modalities for rheumatic diseases -in particular, biological therapies and metho trexate treatment.

Development of synthetic analogs of EGCG: future implications
Th e growing interest of pharmacologists in studying EGCG was never hidden from medicinal chemists, which led to the development of synthetic analogs of EGCG [76]. Zaveri and colleagues reported the synthesis of a trimethoxybenzoyl ester (D-ring) analog of EGCG, which was found to be equally as potent as natural EGCG for its effi cacy as an anti-carcinogenic agent [77]. In addition, there have been some recent eff orts to enhance its bioavailability by delivering EGCG using lipid nanocapsules and liposome encapsulation, suggesting the possibility of this molecule being developed further by medicinal chemists [78]. In this direction, there has been a successful in vitro and in vivo testing of delivering EGCG in polylactic acid-polyethylene glycol nanoparticles to inhibit angiogenesis and induce apoptosis [79]. Similarly, the results from a recent study suggest that nanolipidic EGCG particles signifi cantly improved the neuronal α-secretase enhancing ability and possessed the oral bioavailability more than twofold over free EGCG for the treatment of Alzheimer's disease [80].

Conclusions and future implications
Th e present review summarizes the translational research for the validation of the purported benefi ts of EGCG in preclinical and clinical settings. An extensive evaluation of the potential risks or benefi ts of using EGCG alone or together with anti-rheumatic drugs may open a new area of research wherein EGCG or its synthetic analogs could be developed to enhance its clinical appeal. Extensive research on the benefi ts of EGCG in other chronic ailments such as carcinogenesis and cardiovascular diseases using clinical trials has shown promise [81,82]. With the availability of the safety profi le and pharmacokinetics of EGCG in phase I trials in humans, the window of opportunity is even wider to test EGCG for its potential therapeutic effi cacy as an anti-rheumatic entity in human RA or OA. In conclusion, for the scientists and clinicians in the research area of drug discovery, EGCG represents a much safer molecule worth testing in humans, as the positive outcomes of such studies may have potential for its rapid clinical development and application.

Competing interests
The author declares that he has no competing interests.