Identification of two biologically crucial hydroxyl groups of (−)-epigallocatechin gallate in osteoclast culture

Planar catechin increases bone mass by regulating differentiation of osteoclasts in mice

OBJECTIVES

While catechins have been reported to exhibit potential to benefit osteoporosis patients, the effects of planar catechin (PCat), synthesized during the development of drugs for Alzheimer's disease, have not been clearly elucidated. Here, we examined the effects of PCat on mouse bone metabolism both in vivo and in vitro.

METHODS

Six week old female mice were orally administered PCat (30 mg/kg) every other day for four weeks, and their femurs were analyzed using micro-computed tomography imaging. Osteoclasts and osteoblasts were collected from mice and cultured with PCat. Subsequently, osteoclast formation and differentiation and osteoblast differentiation were observed.

RESULTS

Mice orally administered PCat displayed significantly increased femur bone mass compared to the control group. Quantitative polymerase chain reaction findings indicated that PCat addition to osteoclast progenitor cultures suppressed osteoclast formation and decreased osteoclast marker expression without affecting the proliferative potential of the osteoclast progenitor cells. Addition of PCat to osteoblast cultures increased osteoblast marker expression.

CONCLUSIONS

PCat inhibits osteoclast differentiation and promotes osteoblast differentiation, resulting in increased bone mass in mice. These results suggest that PCat administration is a promising treatment option for conditions associated with bone loss, including osteoporosis.

Tea-break with epigallocatechin gallate derivatives - Powerful polyphenols of great potential for medicine

Epigallocatechin gallate (EGCG) is a polyphenol present in green tea (Camellia sinensis), which has revealed anti-cancer effects toward a variety of cancer cells in vitro and protective potential against neurodegenerative diseases such as Alzheimer's and Parkinson's. Unfortunately, EGCG presents disappointing bioavailability after oral administration, primarily due to its chemical instability and poor absorption. Due to these limitations, EGCG is currently not used in medication, but only as a dietary supplement in the form of green tea extract. Therefore, it needs further modifications before being considered suitable for extensive medical applications. In this article, we review the scientific literature about EGCG derivatives focusing on their biological properties and potential medical applications. The most common chemical modifications of epigallocatechin gallate rely on introducing fatty acid chains or sugar molecules to its chemical structure to modify solubility. Another frequently employed procedure is based on blocking EGCG's hydroxyl groups with various substituents. Novel derivatives reveal interesting properties, of which, antioxidant, anti-inflammatory, antitumor and antimicrobial, are especially important. It is worth noting that the most promising EGCG derivatives present higher stability and activity than base EGCG.

Green tea polyphenol EGCg induces cell fusion via reactive oxygen species

Background

Osteoclasts are multinucleated cells formed by macrophage cell fusion that are responsible for bone resorption. Previously, we found that treating osteoclastic progenitor cells with (-)-epigallocatechin gallate (EGCg) increased cell fusion. In this study, we aimed to identify factors involved in the cell fusion induced by EGCg.

Methods

We hypothesized that EGCg-induced oxidative stress might be involved in cell fusion, and used macrophage cell line RAW264.7 cells. We evaluated cell fusion activity after adding the antioxidants N-acetyl-l-cysteine (NAC) or catalase in addition to EGCg. The mRNA expressions of genes related to cell fusion and bone resorption were quantified by real-time PCR. Finally, we added hydrogen peroxide and examined its effects on cell fusion and TRAP activity.

Results

EGCg-induced cell fusion was strongly inhibited by the addition of NAC in a dose-dependent manner (EGCg with 5 mM NAC; decreased to 1.5%; p < 0.05), while the inhibitory effect of catalase was limited (EGCg with 500 U/mL catalase; decreased to 27.7%; p < 0.05). DC-STAMP expression was significantly upregulated by EGCg compared with the untreated group, and the upregulation was significantly suppressed by 5 mM NAC. Conversely, Nfatc1 and TRAP expression were not upregulated by EGCg. These results suggest that EGCg induces DC-STAMP expression via reactive oxygen species production, which regulates cell fusion but does not affect the osteoclastic pathway. Although treatment with hydrogen peroxide promoted the formation of multinucleated cells, no increase in TRAP activity was observed, which was similar to EGCg treatment.

Conclusions

This study suggests that the increased cell fusion by EGCg may be induced by oxidative stress due to reactive oxygen species production.

Anti-osteoclastogenic effect of epigallocatechin gallate-functionalized gold nanoparticles in vitro and in vivo

Background: Epigallocatechin gallate (EGCG), the major anti-inflammatory compound in green tea, has been shown to suppress osteoclast (OC) differentiation. However, the low aqueous solubility of EGCG always leads to poor bioavailability, adverse effects, and several drawbacks for clinical applications.

Purpose: In this study, we synthesized EGCG-capped gold nanoparticles (EGCG-GNPs) to solve the drawbacks for clinical uses of EGCG in bone destruction disorders by direct reduction of HAuCl₄ in EGCG aqueous solution.

Methods and Results: The obtained EGCG-GNPs were negatively charged and spherical. Theoretical calculation results suggested that EGCG was released from GNPs in an acidic environment. Cellular uptake study showed an obviously large amount of intracellular EGCG-GNPs without cytotoxicity. EGCG-GNPs exhibited better effects in reducing intracellular reactive oxygen species levels than free EGCG. A more dramatic anti-osteoclastogenic effect induced by EGCG-GNPs than free EGCG was observed in lipopolysaccharide (LPS)-stimulated bone marrow macrophages, including decreased formation of TRAP-positive multinuclear cells and actin rings. Meanwhile, EGCG-GNPs not only suppressed the mRNA expression of genetic markers of OC differentiation but also inhibited MAPK signaling pathways. Furthermore, we confirmed that EGCG-GNPs greatly reversed bone resorption in the LPS-induced calvarial bone erosion model in vivo, which was more effective than applying free EGCG, specifically in inhibiting the number of OCs, improving bone density, and preventing bone loss.

Conclusion: EGCG-GNPs showed better anti-osteoclastogenic effect than free EGCG in vitro and in vivo, indicating their potential in anti-bone resorption treatment strategy.

Influence of epigallocatechin-3-gallate in promoting proliferation and osteogenic differentiation of human periodontal ligament cells

BACKGROUND

Epigallocatechin-3-gallate (EGCG) was recently proposed to have the potential to regulate bone metabolism, however, its influence on osteogenesis remains controversial. The present study aimed to investigate the effects of EGCG on the proliferation and osteogenesis of human periodontal ligament cells (hPDLCs).

METHODS

Cells were cultured in osteogenic medium and treated with EGCG at various concentrations. Cell proliferation was analyzed using a CCK-8 assay and acridine orange (AO)/ethidium bromide (EB) staining. Flow cytometry was used to measure the intracellular reactive oxygen species (ROS) potential of hPDLCs. The expression levels of osteogenic marker genes and proteins in hPDLCs, including type I collagen (COL1), runt-related transcription factor 2 (RUNX2), osteopontin (OPN), and osterix (OSX), were determined by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot analysis. In addition, alkaline phosphatase (ALP) activity was monitored both quantitatively and qualitatively. Extracellular matrix mineralization was further analyzed by alizarin red S staining.

RESULTS

The results showed that EGCG concentrations from 6 to 10 μM increased the ROS level and inhibited the cell proliferation of hPDLCs. EGCG concentrations from 2 to 8 μM effectively increased extracellular matrix mineralization, in which 4 and 6 μM EGCG generated the most mineralizing nodules. The ALP activity and the mRNA and protein expression levels of the tested osteogenic markers were most strongly up-regulated by treatment with 4 and 6 μM EGCG.

CONCLUSIONS

The present study demonstrated that EGCG might promote the osteogenesis of hPDLCs in a dose-dependent manner, with concentrations of 4 and 6 μM EGCG showing the strongest osteogenic enhancement without cytotoxicity, indicating a promising role for EGCG in periodontal regeneration in patients with deficient alveolar bone in the future.

Effect of Long-Term Green Tea Polyphenol Supplementation on Bone Architecture, Turnover, and Mechanical Properties in Middle-Aged Ovariectomized Rats

We investigated the effects of 6-month green tea polyphenols (GTP) supplementation on bone architecture, turnover, and mechanical properties in middle-aged ovariectomized (OVX) rats. Female rats were sham-operated (n = 39, 13/group) or OVX (n = 143, 13/group). Sham-control and OVX-control rats (n = 39) receiving no GTP were assigned for sample collection at baseline, 3, or 6 months. The remaining OVX rats (n = 104) were randomized to 0.15%, 0.5%, 1%, and 1.5% (g/dL) GTP for 3 or 6 months. Blood and bone samples were collected. Relative to the OVX-control group, GTP (1% and 1.5%) lowered serum procollagen type 1 N-terminal propeptide at 3 and 6 months, C-terminal telopeptides of type I collagen at 3 months, and insulin-like growth factor-I at 6 months. GTP did not affect bone mineral content and density. At 6 months, no dose of GTP positively affected trabecular bone volume based on microCT, but a higher cortical thickness and improved biomechanical properties of the femur mid-diaphysis was observed in the 1.5% GTP-treated group. At 3 and 6 months, GTP (0.5%, 1%, and 1.5%) had lower rates of trabecular bone formation and resorption than the OVX-control group, but the inhibitory effects of GTP on periosteal and endocortical bone mineralization and formation at the tibial midshaft were only evident at 3 months. GTP at higher doses suppressed bone turnover in the trabecular and cortical bone of OVX rats and resulted in improved cortical bone structural and biomechanical properties, although it was not effective in preventing the ovariectomy-induced dramatic cancellous bone loss.

Toxicological effects of Camellia sinensis (green tea): A review

Many scientific articles proved that green tea (GT), Camellia sinensis, has a great potential to manage central nervous system, cardiovascular, and metabolic diseases and treat cancer and inflammatory disorders. However, it is important to consider that "natural" is not always "safe." Some relevant articles reported side effects of GT, detrimental effects on health. The aim of this study is to provide a classified report about the toxicity of GT and its main constituents in acute, subacute, subchronic, and chronic states. Furthermore, it discusses on the cytotoxicity, genotoxicity, mutagenicity, carcinogenicity, and developmental toxicity of GT and its main constituents. The most important side effects have been reported hepatotoxicity and gastrointestinal disorders specially while consumed on an empty stomach. GT and its main components are not major teratogen, mutagen, or carcinogen substances. However, there is limited data in using them during pregnancy, and they should be used with caution in pregnancy, breast-feeding, and susceptible people. Because GT and its main components have a wide variety of drug interactions, consideration should be taken in coadministration of them with narrow therapeutic indexed drugs. Furthermore, they evoke selective cytotoxicity on cancerous cells that could engage them as an adjuvant substance in cancer therapy.

Synthesis and bioactivity of a conjugate composed of green tea catechins and hyaluronic acid

An amine-functionalized EGCG dimer was synthesized for the conjugation to HA. The resulting HA–EGCG conjugates could scavenge radicals effectively.

Nitensidine A, a guanidine alkaloid from Pterogyne nitens, induces osteoclastic cell death

Nitensidine A is a guanidine alkaloid isolated from Pterogyne nitens, a common plant in South America. To gain insight into the biological activity of P. nitens-produced compounds, we examined herein their biological effects on osteoclasts, multinucleated giant cells that regulate bone metabolism by resorbing bone. Among four guanidine alkaloids (i.e., galegine, nitensidine A, pterogynidine, and pterogynine), nitensidine A and pterogynine exhibited anti-osteoclastic effects at 10 μM by reducing the number of osteoclasts on the culture plate whereas galegine and pterogynidine did not. The anti-osteoclastic activities of nitensidine A and pterogynine were exerted in a concentration-dependent manner, whereas nitensidine A exhibited an approximate threefold stronger effect than pterogynine (IC50 values: nitensidine A, 0.93 ± 0.024 μM; pterogynine, 2.7 ± 0.40 μM). In the present study, the anti-osteoclastic effects of two synthetic nitensidine A derivatives (nitensidine AT and AU) were also examined to gain insight into the structural features of nitensidine A that exert an anti-osteoclastic effect. The anti-osteoclastic effect of nitensidine A was greatly reduced by substituting the imino nitrogen atom in nitensidine A with sulfur or oxygen. According to the differences in chemical structures and anti-osteoclastic effects of the four guanidine alkaloids and the two synthetic nitensidine A derivatives, it is suggested that the number, binding site, and polymerization degree of isoprenyl moiety in the guanidine alkaloids and the imino nitrogen atom cooperatively contribute to their anti-osteoclastic effects.

Homeostatic imbalance and colon cancer: the dynamic epigenetic interplay of inflammation, environmental toxins, and chemopreventive plant compounds

The advent of modern medicine has allowed for significant advances within the fields of emergency care, surgery, and infectious disease control. Health threats that were historically responsible for immeasurable tolls on human life are now all but eradicated within certain populations, specifically those that enjoy higher degrees of socio-economic status and access to healthcare. However, modernization and its resulting lifestyle trends have ushered in a new era of chronic illness; one in which an unprecedented number of people are estimated to contract cancer and other inflammatory diseases. Here, we explore the idea that homeostasis has been redefined within just a few generations, and that diseases such as colorectal cancer are the result of fluctuating physiological and molecular imbalances. Phytochemical-deprived, pro-inflammatory diets combined with low-dose exposures to environmental toxins, including bisphenol-A (BPA) and other endocrine disruptors, are now linked to increasing incidences of cancer in westernized societies and developing countries. There is recent evidence that disease determinants are likely set in utero and further perpetuated into adulthood dependent upon the innate and environmentally-acquired phenotype unique to each individual. In order to address a disease as multi-factorial, case-specific, and remarkably adaptive as cancer, research must focus on its root causes in order to elucidate the molecular mechanisms by which they can be prevented or counteracted via plant-derived compounds such as epigallocatechin-3-gallate (EGCG) and resveratrol. The significant role of epigenetics in the regulation of these complex processes is emphasized here to form a comprehensive view of the dynamic interactions that influence modern-day carcinogenesis, and how sensibly restoring homeostatic balance may be the key to the cancer riddle.

Green tea and bone health: Evidence from laboratory studies

Osteoporosis is a major health problem in the elderly. Epidemiological evidence has shown an association between tea consumption and the prevention of bone loss in the elderly population. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea with its bioactive components on bone health with an emphasis on the following: (i) the etiology of osteoporosis, (ii) evidence of osteo-protective impacts of green tea on bone mass and microarchitecture in various bone loss models in which induced by aging, sex hormone deficiency, and chronic inflammation, (iii) discussion of impacts of green tea on bone mass in two obesity models, (iv) observation of short-term green tea supplementation given to postmenopausal women with low bone mass, (v) possible mechanisms for the osteo-protective effects of green tea bioactive compounds, and (vi) a summary and future research direction of green tea and bone health.

Green tea polyphenols attenuate deterioration of bone microarchitecture in female rats with systemic chronic inflammation

Green tea polyphenols (GTP) are promising agents for preventing bone loss. GTP supplementation sustained microarchitecture and improved bone quality via a decrease in inflammation. Findings suggest a significant role for GTP in skeletal health of patients with chronic inflammation.

INTRODUCTION

This study evaluated whether GTP can restore bone microstructure along with a molecular mechanism in rats with chronic inflammation. A 2 [placebo vs. lipopolysaccharide (LPS)]× 2 [no GTP vs. 0.5% GTP (w/v) in drinking water] factorial design was employed.

METHODS

Female rats were assigned to four groups: placebo, LPS, placebo + GTP, and LPS + GTP for 12 weeks. Efficacy was evaluated by examining changes in bone microarchitecture using histomorphometric and microcomputed tomographic analyses and by bone strength using the three-point bending test. A possible mechanism was studied by assessing the difference in tumor necrosis factor-α (TNF-α) expression in tibia using immunohistochemistry.

RESULTS

LPS lowered trabecular volume fraction, thickness, and bone formation in proximal tibia while increasing osteoclast number and surface perimeter in proximal tibia and eroded surface in endocortical tibial shafts. GTP increased trabecular volume fraction and number in both femur and tibia and periosteal bone formation rate in tibial shafts while decreasing trabecular separation in proximal tibia and eroded surface in endocortical tibial shafts. There was an interaction between LPS and GTP in trabecular number, separation, bone formation, and osteoclast number in proximal tibia, and trabecular thickness and number in femur. GTP improved the strength of femur, while suppressing TNF-α expression in tibia.

CONCLUSION

In conclusion, GTP supplementation mitigated deterioration of bone microarchitecture and improved bone integrity in rats with chronic inflammation by suppressing bone erosion and modulating cancellous and endocortical bone compartments, resulting in a larger net bone volume. Such a protective role of GTP may be due to a suppression of TNF-α.

Insights into the metabolism and microbial biotransformation of dietary flavan-3-ols and the bioactivity of their metabolites

Flavan-3-ols, occurring in monomeric, as well as in oligomeric and polymeric forms (also known as condensed tannins or proanthocyanidins), are among the most abundant and bioactive dietary polyphenols, but their in vivo health effects in humans may be limited because of their recognition as xenobiotics. Bioavailability of flavan-3-ols is largely influenced by their degree of polymerization; while monomers are readily absorbed in the small intestine, oligomers and polymers need to be biotransformed by the colonic microbiota before absorption. Therefore, phenolic metabolites, rather than the original high molecular weight compounds found in foods, may be responsible for the health effects derived from flavan-3-ol consumption. Flavan-3-ol phenolic metabolites differ in structure, amount and excretion site. Phase II or tissular metabolites derived from the small intestine and hepatic metabolism are presented as conjugated derivatives (glucuronic acid or sulfate esters, methyl ether, or their combined forms) of monomeric flavan-3-ols and are preferentially eliminated in the bile, whereas microbial metabolites are rather simple conjugated lactones and phenolic acids that are largely excreted in urine. Although the colon is seen as an important organ for the metabolism of flavan-3-ols, the microbial catabolic pathways of these compounds are still under consideration, partly due to the lack of identification of bacteria with such capacity. Studies performed with synthesized or isolated phase II conjugated metabolites have revealed that they could have an effect beyond their antioxidant properties, by interacting with signalling pathways implicated in important processes involved in the development of diseases, among other bioactivities. However, the biological properties of microbe-derived metabolites in their actual conjugated forms remain largely unknown. Currently, there is an increasing interest in their effects on intestinal infections, inflammatory intestinal diseases and overall gut health. The present review will give an insight into the metabolism and microbial biotransformation of flavan-3-ols, including tentative catabolic pathways and aspects related to the identification of bacteria with the ability to catabolize these kinds of polyphenols. Also, the in vitro bioactivities of phase II and microbial phenolic metabolites will be covered in detail.

Synergistic effects of green tea polyphenols and alphacalcidol on chronic inflammation-induced bone loss in female rats

Studies suggest that green tea polyphenols (GTP) or alphacalcidol is promising agent for preventing bone loss. Findings that GTP supplementation plus alphacalcidol administration increased bone mass via a decrease of oxidative stress and inflammation suggest a significant role of GTP plus alphacalcidol in bone health of patients with chronic inflammation.

INTRODUCTION

Studies have suggested that green tea polyphenols (GTP) or alphacalcidol are promising dietary supplements for preventing bone loss in women. However, the mechanism(s) related to the possible osteo-protective role of GTP plus D(3) in chronic inflammation-induced bone loss is not well understood.

METHODS

This study evaluated bioavailability, efficacy, and related mechanisms of GTP in combination with alphacalcidol in conserving bone loss in rats with chronic inflammation. A 12-week study of 2 (no GTP vs. 0.5% GTP in drinking water) × 2 (no alphacalcidol vs. 0.05 μg/kg alphacalcidol, 5×/week) factorial design in lipopolysaccharide-administered female rats was performed. In addition, a group receiving placebo administration was used to compare with a group receiving lipopolysaccharide administration only to evaluate the effect of lipopolysaccharide.

RESULTS

Lipopolysaccharide administration resulted in lower values for bone mass, but higher values for serum tartrate-resistant acid phosphatase (TRAP), urinary 8-hydroxy-2'-deoxyguanosine, and mRNA expression of tumor necrosis factor-α and cyclooxygenase-2 in spleen. GTP supplementation increased urinary epigallocatechin and epicatechin concentrations. Both GTP supplementation and alphacalcidol administration resulted in a significant increase in bone mass, but a significant decrease in serum TRAP levels, urinary 8-hydroxydeoxyguanosine levels, and mRNA expression of tumor necrosis factor-α and cyclooxygenase-2 in spleen. A synergistic effect of GTP and alphacalcidol was observed in these parameters. Neither GTP nor alphacalcidol affected femoral bone area or serum osteocalcin.

CONCLUSION

We conclude that a bone-protective role of GTP plus alphacalcidol during chronic inflammation bone loss may be due to a reduction of oxidative stress damage and inflammation.

Green tea and bone metabolism

Osteoporosis is a major health problem in both elderly women and men. Epidemiological evidence has shown an association between tea consumption and the prevention of age-related bone loss in elderly women and men. Ingestion of green tea and green tea bioactive compounds may be beneficial in mitigating bone loss of this population and decreasing their risk of osteoporotic fractures. This review describes the effect of green tea or its bioactive components on bone health, with an emphasis on (i) the prevalence and etiology of osteoporosis; (ii) the role of oxidative stress and antioxidants in osteoporosis; (iii) green tea composition and bioavailability; (iv) the effects of green tea and its active components on osteogenesis, osteoblastogenesis, and osteoclastogenesis from human epidemiological, animal, as well as cell culture studies; (v) possible mechanisms explaining the osteoprotective effects of green tea bioactive compounds; (vi) other bioactive components in tea that benefit bone health; and (vii) a summary and future direction of green tea and bone health research and the translational aspects. In general, tea and its bioactive components might decrease the risk of fracture by improving bone mineral density and supporting osteoblastic activities while suppressing osteoclastic activities.

Green tea and cardiovascular disease: from molecular targets towards human health

PURPOSE OF REVIEW

To summarize current knowledge of the protective effects of green tea and green tea constituents, particularly catechins, on the cardiovascular system.

RECENT FINDINGS

Consumption of green tea has been inversely associated with the development and progression of cardiovascular diseases and cardiovascular risk factors. Mechanisms that have been suggested as being involved in the antiatherosclerotic effects of green tea consumption primarily entail antioxidative, antiinflammatory, antiproliferative, and antithrombotic properties, as well as beneficial effects on endothelial function. Moreover, evidence exists for myocardial effects of tea constituents, including positive inotropic and antihypertrophic effects, and beneficial impact in myocardial ischaemia-reperfusion injury.

SUMMARY

Green tea represents a promising tool for the prevention of cardiovascular disorders.