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

Abstract

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.

Fig. 1

Body weight changes in female rats supplemented with green tea polyphenols (GTP) in drinking water or 1-α-OH-vitamin D₃ (D3) administration for 12 weeks. Values are mean (n=10) with their SEM represented by vertical bars. Throughout the study period, no significant difference was observed between the placebo-administered group (the P group) and the LPS-administered only group (the L group). Among the LPS-treated groups (the L, LD, LG, and LGD groups), data were evaluated by three-way ANOVA (GTP levels × D₃ administration × time interaction). Neither GTP supplementation nor D₃ administration affected body weight throughout the study period (P>0.05)

Fig. 2

Urinary (−)-epigallocatechin (EGC; a) and (−)-epicatechin (EC; b) concentrations in female rats supplemented with green tea polyphenols (GTP) in drinking water or 1-α-OH-vitamin D₃ (D3) administration for 12 weeks. Values are mean (n=10) with their SEM represented by vertical bars. Throughout the study period, no significant difference was observed between the placebo-administered group (the P group) and the LPS-administered only group (the L group). Among the LPS-treated groups (the L, LD, LG, and LGD groups), data were evaluated by three-way ANOVA (GTP levels × D₃ administration × time interaction). Urinary EGC and EC increased significantly in the GTP-supplemented group in a time-dependent manner (P<0.05). Urinary EGC and EC concentrations were not affected by D₃ administration (P>0.05). No interaction between GTP levels and D₃ administration was observed. Significantly different among the LPS-treated groups (the L, LD, LG, and LGD groups) at the same study period, ^a,bP<0.05

Fig. 3

Urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) in female rats supplemented with green tea polyphenols (GTP) in drinking water or 1-α-OH-vitamin D₃ (D3) administration for 12 weeks. Values are mean (n=10) with their SEM represented by vertical bars. At the baseline, there was no significant difference between the placebo-administered group (the P group) and the LPS-administered only group (the L group). After 6 and 12 weeks of study, the L group had significantly higher values for urinary 8-OHdG than those in the P group. Among the LPS-treated groups (the L, LD, LG, and LGD groups), data were evaluated by three-way ANOVA (GTP level × D₃ administration × time interaction). Urinary 8-OHdG decreased significantly in the GTP-supplemented groups in a time-dependent pattern (P<0.001). Urinary 8-OHdG also decreased significantly in the D₃-administered groups in a time-dependent manner (P<0.001). A significant interaction between GTP levels and D₃ administration was observed at the end of study (P<0.001). Significantly different from the P group (between the L group and the P group), *P<0.05. Significantly different among the LPS-treated groups (the L, LD, LG, and LGD groups) at the same study period, ^a,b,cP<0.05

Fig. 4

Relative mRNA expression of tumor necrosis factor-α (TNF-α; a) and cyclooxygenase-2 (COX-2; b) in spleen of female rats supplemented with green tea polyphenols (GTP) in drinking water or 1-α-OH-vitamin D₃ (D₃) administration for 12 weeks. Values are mean (n=10) with their SEM represented by vertical bars. The LPS-administered only group (the L group) had significantly higher values for both TNF-α and COX-2 mRNA expression in spleen than those in the placebo-administered group (the P group). Among the LPS-treated groups (the L, LD, LG, and LGD groups), data were evaluated by two-way ANOVA (GTP level × D₃ administration). mRNA expression of TNF-α in spleen decreased significantly in the GTP-supplemented groups (P<0.001) and in the D₃-administered groups (P=0.05). mRNA expression of COX-2 in spleen suppressed significantly in the GTP-supplemented groups (P=0.019) and in the D3-administered groups (P=0.01). An interaction between GTP levels and D₃ administration was observed in COX-2 mRNA expression (P= 0.001), but not in TNF-α mRNA expression (P=0.551). Significantly different from the P group (between the L group and the P group), *P<0.05. Significantly different among the LPS-administered groups (the L, LD, LG, and LGD groups), ^a,b,cP<0.05