Green tea polyphenols mitigate deterioration of bone microarchitecture in middle-aged female rats

Exploring the Impact of Catechins on Bone Metabolism: A Comprehensive Review of Current Research and Future Directions

Background/Objectives: Degenerative musculoskeletal diseases represent a global health problem due to the progressive deterioration of affected individuals. As a bioactive compound, catechins have shown osteoprotective properties by stimulating osteoblastic cells and inhibiting bone resorption. Thus, this review aimed to address the mechanism of action of catechins on bone tissue. Methods: The search was applied to PubMed without limitations in date, language, or article type. Fifteen articles matched the topic and objective of this review. Results: EGCG (epigallocatechin gallate) and epicatechin demonstrated action on the osteogenic markers RANKL, TRAP, and NF-κβ and expression of BMPs and ALP, thus improving the bone microarchitecture. Studies on animals showed the action of EGCG in increasing calcium and osteoprotegerin levels, in addition to regulating the transcription factor NF-ATc1 associated with osteoclastogenesis. However, it did not show any effect on osteocalcin and RANK. Regarding human studies, EGCG reduced the risk of fracture in a dose-dependent manner. In periodontal tissue, EGCG reduced IL-6, TNF, and RANKL in vitro and in vivo. Human studies showed a reduction in periodontal pockets, gingival index, and clinical attachment level. The action of EGCG on membranes and hydrogels showed biocompatible and osteoinductive properties on the microenvironment of bone tissue by stimulating the expression of osteogenic growth factors and increasing osteocalcin and alkaline phosphate levels, thus promoting new bone formation. Conclusions: EGCG stimulates cytokines related to osteogenes, increasing bone mineral density, reducing osteoclastogenesis factors, and showing great potential as a therapeutic strategy for reducing the risk of bone fractures.

Nutraceuticals and Functional Foods: A Comprehensive Review of Their Role in Bone Health

Bone health is the result of a tightly regulated balance between bone modeling and bone remodeling, and alterations of these processes have been observed in several diseases both in adult and pediatric populations. The imbalance in bone remodeling can ultimately lead to osteoporosis, which is most often associated with aging, but contributing factors can already act during the developmental age, when over a third of bone mass is accumulated. The maintenance of an adequate bone mass is influenced by genetic and environmental factors, such as physical activity and diet, and particularly by an adequate intake of calcium and vitamin D. In addition, it has been claimed that the integration of specific nutraceuticals such as resveratrol, anthocyanins, isoflavones, lycopene, curcumin, lutein, and β-carotene and the intake of bioactive compounds from the diet such as honey, tea, dried plums, blueberry, and olive oil can be efficient strategies for bone loss prevention. Nutraceuticals and functional foods are largely used to provide medical or health benefits, but there is an urge to determine which products have adequate clinical evidence and a strong safety profile. The aim of this review is to explore the scientific and clinical evidence of the positive role of nutraceuticals and functional food in bone health, focusing both on molecular mechanisms and on real-world studies.

Study on the relationship between tea polyphenols alleviating osteoporosis and the changes of microorganism-metabolite-intestinal barrier

Tea polyphenols are known to alleviate osteoporosis; however, the role of intestinal flora in this process has not been studied. This research employed 16s rRNA sequencing and non-targeted metabonomics to investigate the potential link between osteoporosis mitigation and changes in intestinal flora. MicroCT and tissue staining results demonstrated that tea polyphenols improved bone microstructure, modulated bone metabolism, and significantly alleviated osteoporosis. The administration of tea polyphenols led to alterations in the intestinal flora's composition, marked by increased abundance of Firmicutes and Lactobacillus and decreased prevalence of Bacteroidetes and Bacteroides. Concurrently, the levels of serum metabolites such as Spermidine and 5,6-Dihydrouracil, associated with intestinal microorganisms, underwent significant changes. These variations in intestinal flora and metabolites are closely linked to bone metabolism. Furthermore, tea polyphenols partially repaired intestinal barrier damage, potentially due to shifts in intestinal flora and their metabolites. Overall, our findings suggest that tea polyphenol intervention modifies the intestinal flora and serum metabolites in osteoporotic mice, which could contribute to the repair of intestinal barrier damage and thereby mitigate osteoporosis. This discovery aids in elucidating the mechanism behind tea polyphenols' osteoporosis-relieving effects.

The entrancing role of dietary polyphenols against the most frequent aging-associated diseases

Aging, a fundamental physiological process influenced by innumerable biological and genetic pathways, is an important driving factor for several aging-associated disorders like diabetes mellitus, osteoporosis, cancer, and neurodegenerative diseases including Alzheimer's and Parkinson's diseases. In the modern era, the several mechanisms associated with aging have been deeply studied. Treatment and therapeutics for age-related diseases have also made considerable advances; however, for the effective and long-lasting treatment, nutritional therapy particularly including dietary polyphenols from the natural origin are endorsed. These dietary polyphenols (e.g., apigenin, baicalin, curcumin, epigallocatechin gallate, kaempferol, quercetin, resveratrol, and theaflavin), and many other phytochemicals target certain molecular, genetic mechanisms. The most common pathways of age-associated diseases are mitogen-activated protein kinase, reactive oxygen species production, nuclear factor kappa light chain enhancer of activated B cells signaling pathways, metal chelation, c-Jun N-terminal kinase, and inflammation. Polyphenols slow down the course of aging and help in combatting age-linked disorders. This exemplified in the form of clinical trials on specific dietary polyphenols in various aging-associated diseases. With this context in mind, this review reveals the new insights to slow down the aging process, and consequently reduce some classic diseases associated with age such as aforementioned, and targeting age-associated diseases by the activities of dietary polyphenols of natural origin.

Increased dosage and treatment time of Epigallocatechin-3-gallate (EGCG) negatively affects skeletal parameters in normal mice and Down syndrome mouse models

Bone abnormalities affect all individuals with Down syndrome (DS) and are linked to abnormal expression of DYRK1A, a gene found in three copies in people with DS and Ts65Dn DS model mice. Previous work in Ts65Dn male mice demonstrated that both genetic normalization of Dyrk1a and treatment with ~9 mg/kg/day Epigallocatechin-3-gallate (EGCG), the main polyphenol found in green tea and putative DYRK1A inhibitor, improved some skeletal deficits. Because EGCG treatment improved mostly trabecular skeletal deficits, we hypothesized that increasing EGCG treatment dosage and length of administration would positively affect both trabecular and cortical bone in Ts65Dn mice. Treatment of individuals with DS with green tea extract (GTE) containing EGCG also showed some weight loss in individuals with DS, and we hypothesized that weights would be affected in Ts65Dn mice after EGCG treatment. Treatment with ~20 mg/kg/day EGCG for seven weeks showed no improvements in male Ts65Dn trabecular bone and only limited improvements in cortical measures. Comparing skeletal analyses after ~20mg/kg/day EGCG treatment with previously published treatments with ~9, 50, and 200 mg/kg/day EGCG showed that increased dosage and treatment time increased cortical structural deficits leading to weaker appendicular bones in male mice. Weight was not affected by treatment in mice, except for those given a high dose of EGCG by oral gavage. These data indicate that high doses of EGCG, similar to those reported in some treatment studies of DS and other disorders, may impair long bone structure and strength. Skeletal phenotypes should be monitored when high doses of EGCG are administered therapeutically.

Anti-Osteoporotic Mechanisms of Polyphenols Elucidated Based on In Vivo Studies Using Ovariectomized Animals

Polyphenols are widely known for their antioxidant activity, i.e., they have the ability to suppress oxidative stress, and this behavior is mediated by the autoxidation of their phenolic hydroxyl groups. Postmenopausal osteoporosis is a common health problem that is associated with estrogen deficiency. Since oxidative stress is thought to play a key role in the onset and progression of osteoporosis, it is expected that polyphenols can serve as a safe and suitable treatment in this regard. Therefore, in this review, we aimed to elucidate the anti-osteoporotic mechanisms of polyphenols reported by in vivo studies involving the use of ovariectomized animals. We categorized the polyphenols as resveratrol, purified polyphenols other than resveratrol, or polyphenol-rich substances or extracts. Literature data indicated that resveratrol activates sirtuin 1, and thereafter, suppresses osteoclastogenic pathways, such as the receptor activator of the nuclear factor kappa B (RANK) ligand (RANKL) pathway, and promotes osteoblastogenic pathways, such as the wingless-related MMTV integration site pathway. Further, we noted that purified polyphenols and polyphenol-rich substances or extracts exert anti-inflammatory and/or antioxidative effects, which inhibit RANKL/RANK binding via the NF-κB pathway, resulting in the suppression of osteoclastogenesis. In conclusion, antioxidative and anti-inflammatory polyphenols, including resveratrol, can be safe and effective for the treatment of postmenopausal osteoporosis based on their ability to regulate the imbalance between bone formation and resorption.

Drinking tea before menopause is associated with higher bone mineral density in postmenopausal women

BACKGROUND

Though tea drinking years and menopause stages have been indicated to be related with bone mineral density (BMD), most human studies have not considered the impact of tea drinking beginning time. Whether drinking tea before or after menopause plays a role in BMD is still unclear. This study aims to analyze whether drinking tea before or after menopause influences BMD in Chinese postmenopausal women.

METHODS

A total of 1377 postmenopausal women under 80 years were enrolled from the baseline survey of the Lanxi Cohort Study. Participants were initially categorized into non-tea drinking, tea drinking beginning after menopause and tea drinking beginning before menopause groups. Tea drinking groups were subdivided according to tea drinking frequency, concentration and type. Multiple linear regression models were applied to evaluate associations between tea drinking before or after menopause and BMD and the impacts of tea drinking frequency, concentration and type on their associations in analyses including all participants. Interactions of tea drinking frequency, concentration and type with drinking tea before or after menopause were further analyzed.

RESULTS

After adjusting for confounding factors, women who began drinking tea before menopause had significantly higher total and regional BMD than non-tea drinking participants and participants who began drinking tea after menopause. Differences in spine BMD were more significant among those who drank tea ≥four times per week. In addition, significant associations between tea drinking and BMD were found among participants who began drinking tea before menopause in both models, irrespective of the concentration and type of tea. No significant associations were found in subgroups of participants who began drinking tea after menopause in either model.

CONCLUSIONS

The results indicate that drinking tea before menopause is related to higher BMD in Chinese postmenopausal women. The relationship is independent of tea drinking concentration and type.

Polyphenols-loaded electrospun nanofibers in bone tissue engineering and regeneration

Bone is a complex structure with unique cellular and molecular process in its formation. Bone tissue regeneration is a well-organized and routine process at the cellular and molecular level in humans through the activation of biochemical pathways and protein expression. Though many forms of biomaterials have been applied for bone tissue regeneration, electrospun nanofibrous scaffolds have attracted more attention among researchers with their physicochemical properties such as tensile strength, porosity, and biocompatibility. When drugs, antibiotics, or functional nanoparticles are taken as additives to the nanofiber, its efficacy towards the application gets increased. Polyphenol is a versatile green/phytochemical small molecule playing a vital role in several biomedical applications, including bone tissue regeneration. When polyphenols are incorporated as additives to the nanofibrous scaffold, their combined properties enhance cell attachment, proliferation, and differentiation in bone tissue defect. The present review describes bone biology encompassing the composition and function of bone tissue cells and exemplifies the series of biological processes associated with bone tissue regeneration. We have highlighted the molecular mechanism of bioactive polyphenols involved in bone tissue regeneration and specified the advantage of electrospun nanofiber as a wound healing scaffold. As the polyphenols contribute to wound healing with their antioxidant and antimicrobial properties, we have compiled a list of polyphenols studied, thus far, for bone tissue regeneration along with their in vitro and in vivo experimental biological results and salient observations. Finally, we have elaborated on the importance of polyphenol-loaded electrospun nanofiber in bone tissue regeneration and discussed the possible challenges and future directions in this field.

Flavonoids as natural phenolic compounds and their role in therapeutics: an overview

BACKGROUND

Natural plants and plant-derived formulations have been used by mankind from the ancient period of time. For the past few years, many investigations elaborated the therapeutic potential of various secondary chemicals present in the plants. Literature revealed that the various secondary metabolites, viz. phenolics and flavonoids, are responsible for a variety of therapeutic action in humans.

MAIN BODY

In the present review, an attempt has been made to compile the exploration of natural phenolic compounds with major emphasis on flavonoids and their therapeutic potential too. Interestingly, long-term intake of many dietary foods (rich in phenolics) proved to be protective against the development and management of diabetes, cancer, osteoporosis, cardiovascular diseases and neurodegenerative diseases, etc.

CONCLUSION

This review presents an overview of flavonoid compounds to use them as a potential therapeutic alternative in various diseases and disorders. In addition, the present understanding of phenolics and flavonoids will serve as the basis for the next scientific studies.

Osteoprotective Roles of Green Tea Catechins

Osteoporosis is the second most common disease only secondary to cardiovascular disease, with the risk of fracture increasing with age. Osteoporosis is caused by an imbalance between osteoblastogenesis and osteoclastogenesis processes. Osteoclastogenesis may be enhanced, osteoblastogenesis may be reduced, or both may be evident. Inflammation and high reactive oxygen enhance osteoclastogenesis while reducing osteoblastogenesis by inducing osteoblast apoptosis and suppressing osteoblastic proliferation and differentiation. Catechins, the main polyphenols found in green tea with potent anti-oxidant and anti-inflammatory properties, can counteract the deleterious effects of the imbalance of osteoblastogenesis and osteoclastogenesis caused by osteoporosis. Green tea catechins can attenuate osteoclastogenesis by enhancing apoptosis of osteoclasts, hampering osteoclastogenesis, and prohibiting bone resorption in vitro. Catechin effects can be directly exerted on pre-osteoclasts/osteoclasts or indirectly exerted via the modulation of mesenchymal stem cells (MSCs)/stromal cell regulation of pre-osteoclasts through activation of the nuclear factor kB (RANK)/RANK ligand (RANKL)/osteoprotegerin (OPG) system. Catechins also can enhance osteoblastogenesis by enhancing osteogenic differentiation of MSCs and increasing osteoblastic survival, proliferation, differentiation, and mineralization. The in vitro effects of catechins on osteogenesis have been confirmed in several animal models, as well as in epidemiological observational studies on human subjects. Even though randomized control trials have not shown that catechins provide anti-fracture efficacy, safety data in the trials are promising. A large-scale, placebo-controlled, long-term randomized trial with a tea regimen intervention of optimal duration is required to determine anti-fracture efficacy.

Green Tea Catechin (-)-Epigallocatechin-3-Gallate (EGCG) Facilitates Fracture Healing

Green tea drinking can ameliorate postmenopausal osteoporosis by increasing the bone mineral density. (-)-Epigallocatechin-3-gallate (EGCG), the abundant and active compound of tea catechin, was proven to be able to reduce bone loss and ameliorate microarchitecture in female ovariectomized rats. EGCG can also enhance the osteogenic differentiation of murine bone marrow mesenchymal stem cells and inhibit the osteoclastogenesis in RAW264.7 cells by modulation of the receptor activator of nuclear factor-kB (RANK)/RANK ligand (RANKL)/osteoprotegrin (OPG) (RANK/RANKL/OPG) pathway. Our previous study also found that EGCG can promote bone defect healing in the distal femur partially via bone morphogenetic protein-2 (BMP-2). Considering the osteoinduction property of BMP-2, we hypothesized that EGCG could accelerate the bone healing process with an increased expression of BMP-2. In this manuscript, we studied whether the local use of EGCG can facilitate tibial fracture healing. Fifty-six 4-month-old rats were randomly assigned to two groups after being weight-matched: a control group with vehicle treatment (Ctrl) and a study group with 10 µmol/L, 40 µL, EGCG treatment (EGCG). Two days after the operation, the rats were treated daily with EGCG or vehicle by percutaneous local injection for 2 weeks. The application of EGCG enhanced callus formation by increasing the bone volume and subsequently improved the mechanical properties of the tibial bone, including the maximal load, break load, stiffness, and Young’s modulus. The results of the histology and BMP-2 immunohistochemistry staining showed that EGCG treatment accelerated the bone matrix formation and produced a stronger expression of BMP-2. Taken together, this study for the first time demonstrated that local treatment of EGCG can accelerate the fracture healing process at least partly via BMP-2.

Red Rooibos Tea Stimulates Osteoblast Mineralization in a Dose-Dependent Manner

Most studies show a positive association between higher tea intake and bone mineral density (BMD), while associations with fracture are inconclusive. Although a few studies have investigated the potential effects of rooibos tea on the bone cell metabolism, only 1 or 2 doses were tested or specific flavonoids were evaluated in isolation. A dose-response study is needed to comprehensively identify whether a level that modulates bone cell activity is associated with dietary or supplemental levels of red rooibos (RR) tea. We investigated if RR tea stimulates mineralization in a dose-dependent manner. Mineralization was induced in Saos-2 cells in the presence of RR tea (0.1–10 µg/mL of polyphenols) or control (dH2O) for 5 days. Cell activity, mRNA, protein expression and activity of key regulators of mineralization were measured. A positive dose-dependent relationship was observed between RR tea concentration and mineralization accompanied with similar trends in cell activity. With high concentrations of tea, protein expression of enzymes directly regulating mineralization (ALP and NPP1) were unchanged but ALP activity was significantly elevated. Osteopontin (OPN) was significantly downregulated midway through mineralization while sclerostin (SOST) was upregulated in response to higher concentrations of RR tea. In conclusion, RR tea stimulated osteoblast mineralization in a dose-dependent manner and were accompanied with downregulation of OPN, increased ALP activity, and increased cell activity.

(-)-Epigallocatechin-3-gallate (EGCG) enhances healing of femoral bone defect

BACKGROUND

Previously, we found that (-)-epigallocatechin-3-gallate (EGCG) enhanced osteogenic differentiation of murine bone marrow mesenchymal stem cells by increasing the mRNA expression of osteogenesis-related genes, alkaline phosphatase activity and eventually mineralization. We further found EGCG supplementation preserved bone mass and microarchitecture in female rats during estrogen deficiency in the proximal tibia and lumbar spine at least in part by increasing bone morphogenetic protein-2 (BMP2). BMP2 can enhance de novo bone formation.

PURPOSE

In this study, we evaluate the effect of local EGCG application in de novo bone formation in bone defect healing.

METHODS

Twenty-four rats aged 4 months were weight-matched and randomly allocated to 2 groups: defect control with vehicle treatment (control) and defect with 10 µM EGCG treatment (EGCG). Daily vehicle and EGCG were applied locally by percutaneous local injection 2 days after defect creation for 2 weeks. Four weeks after treatment, animals were sacrificed for micro-computed tomography (μ-CT) and biomechanical analysis.

RESULTS

Local EGCG at femoral defect can enhance de novo bone formation by increasing bone volume and subsequently improve mechanical properties including max load, break point, stiffness, area under the max load curve, area under the break point curve and ultimate stress.

CONCLUSIONS

Local EGCG may enhance bone defect healing via at least partly by the de novo bone formation of BMP-2.

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.

(-)-Epigallocatechin-3-Gallate Decreases Osteoclastogenesis via Modulation of RANKL and Osteoprotegrin

Osteoporosis is the second most common epidemiologic disease in the aging population worldwide. Previous studies have found that frequent tea drinkers have higher bone mineral density and less hip fracture. We previously found that (-)-epigallocatechin gallate (EGCG) (20⁻100 µmol/L) significantly suppressed receptor activator of nuclear factor-kB ligand (RANKL)-induced osteoclastogenesis and pit formation via inhibiting NF-κB transcriptional activity and nuclear transport of NF-κB in RAW 264.7 cells and murine primary bone marrow macrophage cells. The most important regulation in osteoclastogenesis is the receptor activator of nuclear factor-kB/RANKL/osteoprotegrin (RANK/RANKL/OPG) pathway. In this study, we used the coculture of RAW 264.7 cells and the feeder cells, ST2, to evaluate how EGCG regulated the RANK/RANKL/OPG pathway in RAW 264.7 cells and ST2 cells. We found EGCG decreased the RANKL/OPG ratio in both mRNA expression and secretory protein levels and eventually decreased osteoclastogenesis by TRAP (+) stain osteoclasts and TRAP activity at low concentrations-1 and 10 µmol/L-via the RANK/RANKL/OPG pathway. The effective concentration can be easily achieved in daily tea consumption. Taken together, our results implicate that EGCG could be an important nutrient in modulating bone resorption.

Modulatory Effects of Plant Polyphenols on Bone Remodeling: A Prospective View From the Bench to Bedside

During the past, a more comprehensive knowledge of mechanisms implicated in bone resorption processes has driven researchers to develop a compound library of many small molecules that specifically interfere with the genesis of osteoclast precursors cells. Natural compounds that suppress osteoclast commitment may have therapeutic value in treating pathologies associated with bone resorption like osteoporosis, rheumatoid arthritis, bone metastasis, and periodontal disease. The present review is focused on the current knowledge on the polyphenols derived from plants that could be efficacious in suppressing osteoclast differentiation and bone resorption.

Long-Term Intake of Green Tea Extract Causes Mal-Conformation of Trabecular Bone Microarchitecture in Growing Rats

The purpose of this study was to examine the effects of green tea extract (GTE) intake on bone structural and physiological properties, such as bone mass, trabecular bone microarchitecture, cortical bone geometry, and bone mechanical strength, in growing rats. Four-week-old male Wistar rats were divided into the following four groups: standard diet feeding for 85 days (S-CON) or 170 days (L-CON), and GTE diet feeding for 85 days (S-GTE) or 170 days (L-GTE). At the end of the experiment, in addition to measurement of circulating bone formation/resorption markers, bone mass, trabecular bone microarchitecture, and cortical bone geometry were analyzed in the left femur, and bone mechanical strength of the right femur was measured. There was no difference in all bone parameters between the S-CON and S-GTE groups. On the other hand, the L-GTE group showed the decrease in some trabecular bone mass/microarchitecture parameters and no change in cortical bone mass/geometry parameters compared with the L-CON group, and consequently the reduction in bone weight corrected by body weight. There was no difference in bone formation/resorption markers and bone mechanical strength between the S-CON and S-GTE groups and also between the L-CON and L-GTE groups. However, serum leptin levels were significantly lower in the L-GTE group than in the L-CON group. Thus, the long-term GTE intake had negative effects on bone, especially trabecular bone loss and microarchitecture mal-conformation, in growing rats.

Safety Evaluation of Green Tea Polyphenols Consumption in Middle-aged Ovariectomized Rat Model

This work evaluates chronic safety in middle-aged ovariectomized rats supplemented with different dosages of green tea polyphenols (GTP) in drinking water. The experiment used 6-mo-old sham (n = 39) and ovariectomized (OVX, n = 143) female rats. All sham (n = 39) and 39 of the OVX animals received no GTP treatment and their samples were collected for outcome measures at baseline, 3 mo, and 6 mo (n = 13 per group for each). The remaining OVX animals were randomized into 4 groups receiving 0.15%, 0.5%, 1%, and 1.5% (n = 26 for each) of GTP (wt/vol), respectively, in drinking water for 3 and 6 mo. No mortality or abnormal treatment-related findings in clinical observations or ophthalmologic examinations were noted. No treatment-related macroscopic or microscopic findings were noted for animals administered 1.5% GTP supplementation. Throughout the study, there was no difference in the body weight among all OVX groups. In all OVX groups, feed intake and water consumption significantly decreased with GTP dose throughout the study period. At 6 mo, GTP intake did not affect hematology, clinical chemistry, and urinalysis, except for phosphorus and blood urea nitrogen (increased), total cholesterol, lactate dehydrogenase, and urine pH (decreased). This study reveals that the no-observed-adverse-effect level (NOAEL) of GTP is 1.5% (wt/vol) in drinking water, the highest dose used in this study.

ClC-7/Ostm1 contribute to the ability of tea polyphenols to maintain bone homeostasis in C57BL/6 mice, protecting against fluorosis

Epidemiological investigations indicate that certain ingredients in tea bricks can antagonize the adverse effects of fluoride. Tea polyphenols (TPs), the most bioactive ingredient in tea bricks, have been demonstrated to be potent bone-supporting agents. ClC‑7 is known to be crucial for osteoclast (OC) bone resorption. Thus, in this study, we investigated the potential protective effects of TPs against fluorosis using a mouse model and explored the underlying mechanisms with particular focus on ClC‑7. A total of 40, healthy, 3‑week‑old male C57BL/6 mice were randomly divided into 4 groups (n=10/group) by weight as follows: distilled water (control group), 100 mg/l fluoridated water (F group), water containing 10 g/l TPs (TP group) and water containing 100 mg/l fluoride and 10 g/l TPs (F + TP group). After 15 weeks, and after the mice were sacrificed, the long bones were removed and bone marrow-derived macrophages were cultured ex vivo in order to perform several experiments. OCs were identified and counted by tartrate‑resistant acid phosphatase (TRAP) staining. The consumption of fluoride resulted in severe fluorosis and in an impaired OC function [impaired bone resorption, and a low mRNA expression of nuclear factor of activated T-cells 1 (NFATc1), ATPase H+ transporting V0 subunit D2 (ATP6v0d2) and osteopetrosis‑associated transmembrane protein 1 (Ostm1)]. In the F + TP group, fluorosis was attenuated and OC function was restored, but not the high bone fluoride content. Compared with the F group, mature OCs in the F + TP group expressed higher mRNA levels of ClC‑7 and Ostm1; the transportation and retaining of Cl‑ was improved, as shown by the fluorescence intensity experiment. On the whole, our findings indicate that TPs mitigate fluorosis in C57BL/6 mice by regulating OC bone resorption. Fluoride inhibits OC resorption by inhibiting ClC‑7 and Ostm1, whereas TPs attenuate this inhibitory effect of fluoride.

Updated association of tea consumption and bone mineral density: A meta-analysis

BACKGROUND

Current studies evaluating the association of tea consumption and bone mineral density (BMD) have yielded inconsistent findings. Therefore, we conducted a meta-analysis to assess the relationship between tea consumption and BMD.

METHODS

The PubMed, Embase, and Cochrane Library databases were comprehensively searched, and a meta-analysis performed of all observational studies assessing the association of tea consumption and BMD. Forest plots were used to illustrate the results graphically. The Q-test and I statistic were employed to evaluate between-study heterogeneity. Potential publication bias was assessed by the funnel plot.

RESULTS

Four cohort, 1 case-control, and 8 cross-sectional studies including a total of 12,635 cases were included. Tea consumption was shown to prevent bone loss [odds ratio (OR): 0.66; 95% confidence interval (CI), 0.47-0.94; P = 0.02], yielding higher mineral densities in several bones, including the lumbar spine [standardized mean difference (SMD): 0.19; 95% CI, 0.08-0.31; P = 0.001], hip (SMD: 0.19; 95% CI, 0.05-0.34; P = 0.01), femoral neck [mean difference (MD): 0.01; 95% CI, 0.00-0.02; P = 0.04], Ward triangle (MD: 0.02; 95% CI, 0.01-0.04; P = 0.001), and greater trochanter (MD: 0.03; 95% CI, 0.02-0.04; P < 0.00001), than the non-tea consumption group.

CONCLUSION

This meta-analysis provided a potential trend that tea consumption might be beneficial for BMD, especially in the lumbar spine, hip, femoral neck, Ward triangle, and greater trochanter, which might help prevent bone loss.

Comparison of black, green and rooibos tea on osteoblast activity

Globally, tea is the second most consumed beverage after water. Habitual tea intake has been associated with higher bone mineral density, particularly in postmenopausal women. This association may be due to its polyphenols and resulting protective antioxidant effects. While in vivo studies have shown improved bone outcomes with a consumption of individual purified tea polyphenols, it is unclear if a particular tea - due to its different profiles of polyphenols - is more beneficial than others. Therefore, we compared three different types of commercially available teas on osteoblasts: green, black and rooibos tea. Tea was normalized to 1 or 10 μg per mL gallic acid equivalents to assess differences in outcomes based on tea profiles rather than the quantity of polyphenol naturally present. The lower level of polyphenols (1 μg per mL gallic acid equivalents) - regardless of tea type and thus polyphenol profile - resulted in greater mineral content as well as cellular and alkaline phosphatase activity in Saos2 cells. Moreover, this was associated with higher markers of differentiation (osteopontin, sclerostin) and reduced cellular toxicity and pro-inflammatory markers (IL6, TNFα). Green, black and rooibos tea improved osteoblast activity at the low level and support epidemiological evidence suggesting tea consumption may benefit bone heath.

Tea flavonoids for bone health: from animals to humans

Osteoporosis is a skeletal disease characterized by a deterioration of bone mass and bone quality that predisposes an individual to a higher risk of fragility fractures. Emerging evidence has shown that the risk for low bone mass and osteoporosis-related fractures can be reduced by nutritional approaches aiming to improve bone microstructure, bone mineral density, and strength. Tea and its flavonoids, especially those of black tea and green tea, have been suggested to protect against bone loss and to reduce risk of fracture, due to tea's antioxidant and anti-inflammatory properties. Based on the results of animal studies, moderate intake of tea has shown to benefit bone health as shown by mitigation of bone loss and microstructural deterioration as well as improvement of bone strength and quality. Epidemiological studies have reported positive, insignificant, and negative impacts on bone mineral density at multiple skeletal sites and risk of fracture in humans with habitual tea consumption. There are limited human clinical trials that objectively and quantitatively assessed tea consumption and bone efficacy using validated outcome measures in a population at high risk for osteoporosis, along with safety monitoring approach. This review summarizes the current state of knowledge of laboratory animal research, epidemiological observational studies, and clinical trials assessing the skeletal effects of tea and its active flavonoids, along with discussion of relevant future directions in translational research.

Differential effects of Epigallocatechin-3-gallate containing supplements on correcting skeletal defects in a Down syndrome mouse model

SCOPE

Down syndrome (DS), caused by trisomy of human chromosome 21 (Hsa21), is characterized by a spectrum of phenotypes including skeletal abnormalities. The Ts65Dn DS mouse model exhibits similar skeletal phenotypes as humans with DS. DYRK1A, a kinase encoded on Hsa21, has been linked to deficiencies in bone homeostasis in DS mice and individuals with DS. Treatment with Epigallocatechin-3-gallate (EGCG), a known inhibitor of Dyrk1a, improves some skeletal abnormalities associated with DS in mice. EGCG supplements are widely available but the effectiveness of different EGCG-containing supplements has not been well studied.

METHODS AND RESULTS

Six commercially available supplements containing EGCG were analyzed, and two of these supplements were compared with pure EGCG for their impact on skeletal deficits in a DS mouse model. The results demonstrate differential effects of commercial supplements on correcting skeletal abnormalities in Ts65Dn mice. Different EGCG-containing supplements display differences in degradation, polyphenol content, and effects on trisomic bone.

CONCLUSION

This work suggests that the dose of EGCG and composition of EGCG-containing supplements may be important in correcting skeletal deficits associated with DS. Careful analyses of these parameters may lead to a better understanding of how to improve skeletal and other deficits that impair individuals with DS.

Green tea supplementation benefits body composition and improves bone properties in obese female rats fed with high-fat diet and caloric restricted diet

This study investigated the effects of green tea polyphenols (GTP) supplementation on body composition, bone properties, and serum markers in obese rats fed a high-fat diet (HFD) or a caloric restricted diet (CRD). Forty-eight female rats were fed an HFD ad libitum for 4 months, and then either continued on the HFD or the CRD with or without 0.5% GTP in water. Body composition, bone efficacy, and serum markers were measured. We hypothesized that GTP supplementation would improve body composition, mitigate bone loss, and restore bone microstructure in obese animals fed either HFD or CRD. CRD lowered percent fat mass; bone mass and trabecular number of tibia, femur and lumbar vertebrae; femoral strength; trabecular and cortical thickness of tibia; insulin-like growth factor-I and leptin. CRD also increased percent fat-free mass; trabecular separation of tibia and femur; eroded surface of tibia; bone formation rate and erosion rate at tibia shaft; and adiponectin. GTP supplementation increased femoral mass and strength (P = .026), trabecular thickness (P = .012) and number (P = .019), and cortical thickness of tibia (P < .001), and decreased trabecular separation (P = .021), formation rate (P < .001), and eroded surface (P < .001) at proximal tibia, and insulin-like growth factor-I and leptin. There were significant interactions (diet type × GTP) on osteoblast surface/bone surface, mineral apposition rate at periosteal and endocortical bones, periosteal bone formation rate, and trabecular thickness at femur and lumbar vertebrate (P < .05). This study demonstrates that GTP supplementation for 4 months benefited body composition and improved bone microstructure and strength in obese rats fed with HFD or HFD followed by CRD diet.

Role of (-)-epigallocatechin-3-gallate in the osteogenic differentiation of human bone marrow mesenchymal stem cells: An enhancer or an inducer?

Epidemiological investigations have revealed that the consumption of green tea, which is a rich source of (-)-epigallocatechin-3-gallate (EGCG), is associated with a reduced risk of osteoporosis. A number of in vitro and in vivo studies have also demonstrated that EGCG exerts a significant positive effect on osteogenesis; however, the single effect of EGCG on osteogenic differentiation has been seldom studied. EGCG was hypothesized to function as an enhancer or an inducer. In the present study, the effect of EGCG on the osteogenic differentiation of primary human bone marrow mesenchymal stem cells (hBMSCs), without other additives, was investigated. Three groups of stem cells were analyzed, which included a negative control group (hBMSCs cultured with culture medium only), an experimental group (cells treated with culture medium containing 2.5, 5 and 10 µM EGCG), and a positive control group (cells cultured with osteogenesis-induced culture medium). After 3, 7, 14 and 21 days, cell proliferation, alkaline phosphatase (ALP) activity and the expression of associated osteogenic genes were analyzed. The results revealed that ALP activity and the expression of associated osteogenic genes, with the exception of bone morphogenetic protein 2 (BMP2), were not affected by EGCG treatment alone. These results indicated that EGCG itself had little effect on the osteogenic differentiation of MSCs; however, EGCG was able to enhance osteogenesis in the presence of osteoinductive agents through the upregulation of BMP2 expression. Additionally, EGCG was shown to promote cell growth, demonstrating its safety as a therapeutic agent. Therefore, the present study indicated that treatment with EGCG was dependent on other osteogenic inducers.

Green Tea Extract (GTE) improves differentiation in human osteoblasts during oxidative stress

Background

Oxidative stress is involved in the pathogenesis of bone diseases such as osteoporosis, which has a high coincidence with fractures in elderly. Several studies showed positive effects of herbal bioactive substances on oxidative stress. This study analyses the effect of green tea extract (GTE) Sunphenon 90LB on primary human osteoblasts differentiation and viability during H₂O₂-induced oxidative stress. Moreover, it was analyzed, whether GTE acts during the HO-1 signaling pathway.

Methods

Human osteoblasts were isolated from femoral heads of patients undergoing total hip replacement. Beneficial effects of GTE on osteoblasts were examined in a dose- and time-dependent manner. Furthermore, GTE was given before, simultaneous with and after induction of oxidative stress with 1 mM H₂O₂ to simulate prophylactic, acute and therapeutic use, respectively. Cell damage was measured by LDH leakage and cell viability by MTT assay. Flow cytometry was applied to measure formation of Reactive Oxygen Species by using 2`7`-dichlorofluorescein-diacetate. The formation of Extracellular Matrix after differentiation with GTE supplementation during oxidative stress was visualized with von Kossa and Alizarin Red staining. Last one was additionally photometrically quantified. To assess the effects of H₂O₂ and GTE on the osteogenic genes, RT-PCR was performed. To evaluate the intramolecular influence of GTE after the stimulation the protein levels of HO-1 were analyzed.

Results

Stimulation of primary human osteoblasts with low doses of GTE during oxidative stress over 21 days improved mineralization. Furthermore, GTE supplementation in combination with H₂O₂ leads to a higher gene expression of osteocalcin and collagen1α1 during osteoblasts differentiation. Both are important for bone quality. Pre-incubation, co-incubation and post-incubation of osteoblasts with high doses of GTE protect the osteoblasts against acute oxidative stress as shown by increased cell viability, decreased LDH leakage, and reduced production of intracellular free radicals. Functional analysis revealed an increased HO-1 protein synthesis after stimulation with GTE.

Conclusions

Incubation of human primary osteoblasts with GTE significantly reduces oxidative stress and improves cell viability. GTE also has a beneficial effect on ECM production which might improve the bone quality. Our findings suggest that dietary supplementation of GTE might reduce inflammatory events in bone-associated diseases such as osteoporosis.

Effects of dried plum supplementation on bone metabolism in adult C57BL/6 male mice

Dietary supplementation of dried plum (DP) prevents bone loss and restores bone mass in osteopenic animal models. This study was designed to determine the effects of DP supplementation on bone metabolic activity over time using adult (6-month-old) male C57BL/6 mice (n = 40) receiving control (CON = AIN93 M) or CON+DP 25 % (w/w) diets for 4 or 12 weeks. After 4 weeks of treatment, animals consuming the DP diet had a higher whole-body bone mineral density, vertebral trabecular bone volume (BV/TV), and femoral cortical thickness compared to the CON animals. In the distal metaphysis of the femur, BV/TV was increased in the DP-treated animals, but only after 12 weeks. Bone histomorphometric analyses revealed that DP decreased osteoblast surface (67 %) and osteoclast surface (62 %) at 4 weeks, but these surfaces normalized to the CON animals by 12 weeks. Coincident with these changes, the mineralizing surface (MS/BS) and cancellous bone formation rate (BFR/BS) were reduced at 4 weeks in the DP group compared to the CON, but by 12 weeks of DP supplementation, BFR/BS (~twofold) and MS/BS (~1.7-fold) tended to be increased (p < 0.10). The relative abundance of RNA for key regulators of osteoblast and osteoclast differentiation and indicators of osteoblast activity were reduced in the DP group at 4 weeks with no difference between groups at 12 weeks. These results indicate that supplementing the diet with DP initially suppressed cancellous bone turnover, but a biphasic response occurs over time, resulting in a positive effect on bone mass and structure.

Promoting osteoblast differentiation by the flavanes from Huangshan Maofeng tea is linked to a reduction of oxidative stress

Epidemiological evidence has shown an association between tea consumption and the prevention of bone loss in the elderly. Previous studies indicated that green tea exerted osteoprotective effect in vivo. This study aims to investigate the constituents in Huangshan Maofeng tea and systemically evaluate their antioxidative and osteogenic effects in vitro. Five flavanes, isolated from Huangshan Maofeng tea, showed effects on proliferation of osteoblastic cells and ameliorated H2O2-induced C2C12 mouse myoblast cell apoptosis at 3.125-50 μg/ml. (-)-Epicatechin observably increased alkaline phosphatase (ALP) activity and hydroxyproline content. (-)-Epiafzelechin at 25 μg/ml significantly increased the area of mineralized bone nodules. The activities of flavanes in promoting osteblastic proliferation and differentiation are positively correlated with activities in protecting against apoptosis in C2C12 cells. It indicates that anti-osteoporosis effect of these flavanes may be linked to their antioxidative activity. The observed effects of these flavanes suggest that these flavanes may have beneficial effects on bone health.

Tea and bone health: steps forward in translational nutrition

Osteoporosis is a major health problem in the aging population worldwide. Cross-sectional and retrospective evidence indicates that tea consumption may be a promising approach in mitigating bone loss and in reducing risk of osteoporotic fractures among older adults. Tea polyphenols enhance osteoblastogenesis and suppress osteoclastogenesis in vitro. Animal studies reveal that intake of tea polyphenols have pronounced positive effects on bone as shown by higher bone mass and trabecular bone volume, number, and thickness and lower trabecular separation via increasing bone formation and inhibition of bone resorption, resulting in greater bone strength. These osteoprotective effects appear to be mediated through antioxidant or antiinflammatory pathways along with their downstream signaling mechanisms. A short-term clinical trial of green tea polyphenols has translated the findings from ovariectomized animals to postmenopausal osteopenic women through evaluation of bioavailability, safety, bone turnover markers, muscle strength, and quality of life. For future studies, preclinical animal studies to optimize the dose of tea polyphenols for maximum osteoprotective efficacy and a follow-up short-term dose-response trial in postmenopausal osteopenic women are necessary to inform the design of randomized controlled studies in at-risk populations. Advanced imaging technology should also contribute to determining the effective dose of tea polyphenols in achieving better bone mass, microarchitecture integrity, and bone strength, which are critical steps for translating the putative benefit of tea consumption in osteoporosis management into clinical practice and dietary guidelines.

Effect of dimethyl sulfoxide on inhibition of post-ovariectomy osteopenia in rats

There is increasing evidence that oxidative stress, due to estrogen deficiency, leads to osteopenia. In this study, dimethyl sulfoxide (DMSO), an antioxidant solvent, was used against post-ovariectomy osteopenia (PO) in rats. Forty female rats were divided into 5 groups randomly as follows: Sham, control group; OVX, ovariectomized group; DMSO1, ovariectomized injected DMSO (0.5 ml/kg/d ip); DMSO2, ovariectomized injected DMSO (1 ml/kg/day ip) and DMSO3, ovariectomized injected DMSO (2 ml/kg/d ip). DMSO therapy started 1 week after ovariectomy and continued for 13 weeks. After 13th weeks, sera were prepared, and then L4 vertebrae and right tibial bones rinsed in fixative. Serum bone alkaline phosphatase (BALP), osteocalcin, pyridinoline, malondialdehyde (MDA) and glutathione (GSH) were measured. Trabecular volume density, trabecular and cortex thickness were estimated. Osteoclast and osteoblast numbers were counted morphometrically. The data were analyzed by ANOVA and then post hoc Tukey test at p < 0.05. The increase of pyridinoline and decrease of BALP in DMSO injected groups were inhibited compared with OVX group (p < 0.05). In DMSO injected groups, decrease of bone density, trabecular volume density, thickness of trabecular and tibial cortex were inhibited compared with OVX group (p < 0.05). MDA decreased significantly in DMSO injected groups compared with OVX group. Osteoclast number decreased in DMSO injected groups compared with OVX group (p < 0.05). Osteoblast number did not show significant change in DMSO groups compared with OVX group. In conclusion, DMSO ameliorates PO through decrease of osteoclast number, osteoclast inhibition and osteoblast activation. These effects may probably be mediated via antioxidant property of DMSO.

Green tea polyphenols improve bone microarchitecture in high-fat-diet-induced obese female rats through suppressing bone formation and erosion

This study evaluates the effects of green tea polyphenols (GTPs) on bone microarchitecture in high-fat-diet (HFD)-induced obese female rats. Thirty-six 3-month-old female rats were fed either a control diet or a HFD for 4 months. Animals in the control group continued on the control diet for another 4 months. Animals in the HFD group were divided into two groups, with 0.5 g/100 mL GTP (the HFD+GTP group) or without GTP (the HFD group) in drinking water, in addition to the HFD for another 4 months. Compared to the control group, the HFD group increased bone formation and erosion rates at the tibia, decreased trabecular volume and thickness, but had no impact on bone mineral density (BMD), trabecular number (Tb.N), and separation. Compared to the control group, the HFD+GTP group demonstrates a greater Tb.N at the proximal tibia, and a greater trabecular thickness at the femur and the lumbar vertebrae, but a smaller trabecular separation (Tb.Sp) and mineralizing surface at the proximal tibia, and a reduced endocortical mineral apposition rate (MAR) at the tibia shaft. Relative to the HFD group, the HFD+GTP group demonstrates (1) a higher BMD at the femur, a greater trabecular volume, thickness, and number at the proximal tibia, a larger cortical area and thickness at the tibial shaft, and a greater trabecular volume and thickness at the femur and the lumbar vertebrae, (2) a smaller Tb.Sp, MAR, bone formation rate, and eroded surface at the tibia. We concluded that GTP supplementation in drinking water improves bone microarchitecture in the HFD-induced obese female rats, possibly through suppressing bone turnover, resulting in a larger net bone volume.

Phytonutrients for bone health during ageing

Osteoporosis is a skeletal disease characterized by a decrease in bone mass and bone quality that predispose an individual to an increased risk of fragility fractures. Evidence demonstrating a positive link between certain dietary patterns (e.g. Mediterranean diet or high consumption of fruits and vegetables) and bone health highlights an opportunity to investigate their potential to protect against the deterioration of bone tissue during ageing. While the list of these phytonutrients is extensive, this review summarizes evidence on some which are commonly consumed and have gained increasing attention over recent years, including lycopene and various polyphenols (e.g. polyphenols from tea, grape seed, citrus fruit, olive and dried plum). Evidence to define a clear link between these phytonutrients and bone health is currently insufficient to generate precise dietary recommendations, owing to mixed findings or a scarcity in clinical data. Moreover, their consumption typically occurs within the context of a diet consisting of a mix of phytonutrients and other nutrients rather than in isolation. Future clinical trials that can apply a robust set of outcome measurements, including the determinants of bone strength, such as bone quantity (i.e. bone mineral density) and bone quality (i.e. bone turnover and bone microarchitecture), will help to provide a more comprehensive outlook on how bone responds to these various phytonutrients. Moreover, future trials that combine these phytonutrients with established bone nutrients (i.e. calcium and vitamin D) are needed to determine whether combined strategies can produce more robust effects on skeletal health.

Green tea polyphenols reduce body weight in rats by modulating obesity-related genes

Beneficial effects of green tea polyphenols (GTP) against obesity have been reported, however, the mechanism of this protection is not clear. Therefore, the objective of this study was to identify GTP-targeted genes in obesity using the high-fat-diet-induced obese rat model. A total of three groups (n = 12/group) of Sprague Dawley (SD) female rats were tested, including the control group (rats fed with low-fat diet), the HF group (rats fed with high-fat diet), and the HF+GTP group (rats fed with high-fat diet and GTP in drinking water). The HF group increased body weight as compared to the control group. Supplementation of GTP in the drinking water in the HF+GTP group reduced body weight as compared to the HF group. RNA from liver samples was extracted for gene expression analysis. A total of eighty-four genes related to obesity were analyzed using PCR array. Compared to the rats in the control group, the rats in the HF group had the expression levels of 12 genes with significant changes, including 3 orexigenic genes (Agrp, Ghrl, and Nr3c1); 7 anorectic genes (Apoa4, Cntf, Ghr, IL-1β, Ins1, Lepr, and Sort); and 2 genes that relate to energy expenditure (Adcyap1r1 and Adrb1). Intriguingly, the HF+GTP group restored the expression levels of these genes in the high-fat-induced obese rats. The protein expression levels of IL-1β and IL-6 in the serum samples from the control, HF, and HF+GTP groups confirmed the results of gene expression. Furthermore, the protein expression levels of superoxide dismutase-1 (SOD1) and catechol-O-methyltransferase (COMT) also showed GTP-regulated protective changes in this obese rat model. Collectively, this study revealed the beneficial effects of GTP on body weight via regulating obesity-related genes, anti-inflammation, anti-oxidant capacity, and estrogen-related actions in high-fat-induced obese rats.

Green tea polyphenols benefits body composition and improves bone quality in long-term high-fat diet-induced obese rats

This study investigates the effects of green tea polyphenols (GTPs) on body composition and bone properties along with mechanisms in obese female rats. Thirty-six 3-month-old Sprague Dawley female rats were fed either a low-fat (LF) or a high-fat (HF) diet for 4 months. Animals in the LF diet group continued on an LF diet for additional 4 months, whereas those in the HF diet group were divided into 2 groups: with GTP (0.5%) or without in drinking water, in addition to an HF diet for another 4 months. Body composition, femur bone mass and strength, serum endocrine and proinflammatory cytokines, and liver glutathione peroxidase (GPX) protein expression were determined. We hypothesized that supplementation of GTP in drinking water would benefit body composition, enhance bone quality, and suppress obesity-related endocrines in HF diet-induced obese female rats and that such changes are related to an elevation of antioxidant capacity and a reduction of proinflammatory cytokine production. After 8 months, compared with the LF diet, the HF diet increased percentage of fat mass and serum insulin-like growth factor I and leptin levels; reduced percentage of fat-free mass, bone strength, and GPX protein expression; but had no effect on bone mineral density and serum adiponectin levels in the rats. Green tea polyphenol supplementation increased percentage of fat-free mass, bone mineral density and strength, and GPX protein expression and decreased percentage of fat mass, serum insulin-like growth factor I, leptin, adiponectin, and proinflammatory cytokines in the obese rats. This study shows that GTP supplementation benefited body composition and bone properties in obese rats possibly through enhancing antioxidant capacity and suppressing inflammation.

Effect of green tea and Tai Chi on bone health in postmenopausal osteopenic women: a 6-month randomized placebo-controlled trial

Postmenopausal women with osteopenia received green tea polyphenols (GTP) supplement and/or Tai Chi exercise for 6 months. Bone turnover biomarkers, calcium metabolism, and muscle strength were measured. This study showed that GTP supplementation and Tai Chi exercise increased bone formation biomarkers and improved bone turnover rate. Tai Chi exercise increased serum parathyroid hormone. GTP supplementation, Tai Chi exercise, and the combination of the two all improved muscle strength in postmenopausal women with osteopenia.

INTRODUCTION

This study evaluated the effect of GTP supplementation and Tai Chi (TC) exercise on serum markers of bone turnover (bone-specific alkaline phosphatase, BAP, and tartrate-resistant acid phosphatase, TRAP), calcium metabolism, and muscle strength in postmenopausal osteopenic women.

METHODS

One hundred and seventy-one postmenopausal osteopenic women were randomly assigned to four groups: (1) placebo (500 mg starch/day), (2) GTP (500 mg GTP/day), (3) placebo + TC (placebo plus TC training at 60 min/session, three sessions/week), and (4) GTP + TC (GTP plus TC training). Overnight fasting blood and urine samples were collected at baseline, 1, 3, and 6 months for biomarker analyses. Muscle strength was evaluated at baseline, 3, and 6 months. One hundred and fifty subjects completed the 6-month study.

RESULTS

Significant increases in BAP level due to GTP intake (at 1 month) and TC (at 3 months) were observed. Significant increases in the change of BAP/TRAP ratio due to GTP (at 3 months) and TC (at 6 months) were also observed. Significant main effect of TC on the elevation in serum parathyroid hormone level was observed at 1 and 3 months. At 6 months, muscle strength significantly improved due to GTP, TC, and GTP + TC interventions. Neither GTP nor TC affected serum TRAP, serum and urinary calcium, and inorganic phosphate.

CONCLUSION

In summary, GTP supplementation and TC exercise increased BAP and improved BAP/TRAP ratio. TC exercise increased serum parathyroid hormone. GTP supplementation, TC exercise, and the combination of the two all improved muscle strength in postmenopausal women with osteopenia.

(-)-Epigallocathechin-3-gallate, an AMPK activator, decreases ovariectomy-induced bone loss by suppression of bone resorption

Previously, we showed that AMP-activated protein kinase (AMPK) negatively regulates receptor activator of nuclear factor-κB ligand-induced osteoclast formation in vitro. The present study investigated the effect of (-)-epigallocathechin-3-gallate (EGCG), an AMPK activator, on ovariectomy (OVX)-induced bone loss in mice. Female mice subjected to OVX were administered EGCG for 8 weeks. We measured total-body bone mineral density (BMD) before and after the operation at an interval of 4 weeks. We performed micro-computed tomography (micro-CT) of the tibia and bone histomorphometric examination of the femur. Western blot analysis was additionally performed, to detect levels of the phosphorylated and total forms of AMPK-α in calvarial extracts. EGCG prevented OVX-induced body weight gain. The OVX control did not show a significant increase in BMD values at baseline and after treatment, unlike the sham control. EGCG attenuated OVX-induced bone loss. Micro-CT experiments revealed that EGCG induced a significant increase in trabecular bone volume and trabecular number and a decrease in trabecular spacing compared to the OVX control. Histomorphometric analyses further showed that EGCG suppressed osteoclast surface and number. Phosphorylated AMPK expression was significantly elevated in bone following EGCG treatment. Our findings collectively indicate that EGCG decreases OVX-induced bone loss via inhibition of osteoclasts.

A novel quercetin analogue from a medicinal plant promotes peak bone mass achievement and bone healing after injury and exerts an anabolic effect on osteoporotic bone: the role of aryl hydrocarbon receptor as a mediator of osteogenic action

We recently reported that extracts made from the stem bark of Ulmus wallichiana promoted peak bone mass achievement in growing rats and preserved trabecular bone mass and cortical bone strength in ovariectomized (OVX) rats. Further, 6-C-β-D-glucopyranosyl-(2S,3S)-(+)-3',4',5,7-tetrahydroxyflavanol (GTDF), a novel flavonol-C-glucoside isolated from the extracts, had a nonestrogenic bone-sparing effect on OVX rats. Here we studied the effects of GTDF on osteoblast function and its mode of action and in vivo osteogenic effect. GTDF stimulated osteoblast proliferation, survival, and differentiation but had no effect on osteoclastic or adipocytic differentiation. In cultured osteoblasts, GTDF transactivated the aryl hydrocarbon receptor (AhR). Activation of AhR mediated the stimulatory effect of GTDF on osteoblast proliferation and differentiation. Furthermore, GTDF stimulated cAMP production, which mediated osteogenic gene expression. GTDF treatments given to 1- to 2-day-old rats or adult rats increased the mRNA levels of AhR target genes in calvaria or bone marrow stromal cells. In growing female rats, GTDF promoted parameters of peak bone accrual in the appendicular skeleton, including increased longitudinal growth, bone mineral density, bone-formation rate (BFR), cortical deposition, and bone strength. GTDF promoted the process of providing newly generated bone to fill drill holes in the femurs of both estrogen-sufficient and -deficient rats. In osteopenic OVX rats, GTDF increased BFR and significantly restored trabecular bone compared with the ovaries-intact group. Together our data suggest that GTDF stimulates osteoblast growth and differentiation via the AhR and promotes modeling-directed bone accrual, accelerates bone healing after injury, and exerts anabolic effects on osteopenic rats likely by a direct stimulatory effect on osteoprogenitors. Based on these preclinical data, clinical evaluation of GTDF as a potential bone anabolic agent is warranted.

Supplementation with green tea polyphenols improves bone microstructure and quality in aged, orchidectomized rats

Recent studies show that green tea polyphenols (GTPs) attenuate bone loss and microstructure deterioration in ovariectomized aged female rats, a model of postmenopausal osteoporosis. This study evaluated the efficacy of GTPs at mitigating bone loss and microstructure deterioration along with related mechanisms in androgen-deficient aged rats, a model of male osteoporosis. A 2 (sham vs. orchidectomy) × 2 (no GTP and 0.5% GTP in drinking water) factorial design was studied for 16 weeks using 40 aged male rats. An additional 10 rats (baseline group) were killed at the beginning of study to provide baseline parameters. There was no difference in femoral mineral density between baseline and the sham only group. Orchidectomy suppressed serum testosterone and tartrate-resistant acid phosphatase concentrations, liver glutathione peroxidase activity, bone mineral density, and bone strength. Orchidectomy also decreased trabecular bone volume, number, and thickness in the distal femur and proximal tibia and bone-formation rate in trabecular bone of proximal tibia but increased serum osteocalcin concentrations and bone-formation rates in the endocortical tibial shaft. GTP supplementation resulted in increased serum osteocalcin concentrations, bone mineral density, and trabecular volume, number, and strength of femur; increased trabecular volume and thickness and bone formation in both the proximal tibia and periosteal tibial shaft; decreased eroded surface in the proximal tibia and endocortical tibial shaft; and increased liver glutathione peroxidase activity. We conclude that GTP supplementation attenuates trabecular and cortical bone loss through increasing bone formation while suppressing bone resorption due to its antioxidant capacity.

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.

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.

Protective actions of green tea polyphenols and alfacalcidol on bone microstructure in female rats with chronic inflammation

This study investigated the effects of green tea polyphenols (GTP) and alfacalcidol on bone microstructure and strength along with possible mechanisms in rats with chronic inflammation. A 12-week study using a 2 (no GTP vs. 0.5%, w/v GTP in drinking water)×2 (no alfacalcidol vs. 0.05 μg/kg alfacalcidol orally, 5×/week) factorial design was employed in lipopolysaccharide (LPS)-administered female rats. A group receiving placebo administration was used to compare with a group receiving LPS administration only to evaluate the effect of LPS. Changes in tibial and femoral microarchitecture and strength of femur were evaluated. Difference in expression of tumor necrosis factor-α (TNF-α) in proximal tibia using immunohistochemistry was examined. Compared to the placebo group, the LPS-administered-only group had significantly lower femoral mass, trabecular volume, thickness and number in proximal tibia and femur, and lower periosteal bone formation rate in tibial shafts but had significantly higher trabecular separation and osteoclast number in proximal tibia and eroded surface in endocortical tibial shafts. Both GTP and alfacalcidol reversed these LPS-induced detrimental changes in femur, proximal tibia and endocortical tibial shaft. Both GTP and alfacalcidol also significantly improved femoral strength, while significantly suppressed TNF-α expression in proximal tibia. There were significant interactions in femoral mass and strength, trabecular separation, osteoclast number and TNF-α expression in proximal tibia. A combination of both showed to sustain bone microarchitecture and strength. We conclude that a protective impact of GTP and alfacalcidol in bone microarchitecture during chronic inflammation may be due to a suppression of TNF-α.