# Effects of Epigallocatechin-3-O-Gallate on Bone Health
## 2 Functional Effects of EGCG
### Inhibition of Osteoclastogenesis and Osteoclast Differentiation  
According to conclusions drawn from studies by [PERSON] et al. [50] on mouse bone marrow cells, EGCG inhibited osteoclast differentiation from bone marrow cells and primary osteoblast co-cultures induced by IL-1, TNF-\(\alpha\), and vitamin D\({}_{3}\) plus PGE\({}_{2}\) by reducing \(c\)-Fos and the nuclear factor of activated T cells 1 NFATc1 expression, thereby inhibiting the RANKL-induced activation of the NF-\(\kappa\)B and JNK/\(c\)-Jun signalling pathways. Several years later, [PERSON] et al. [47] came to a similar conclusion that RANKL-induced osteoclastogenesis and F-actin ring formation were inhibited by EGCG through the downregulation of NFATc1 and \(c\)-Fos in mouse macrophage RAW 264.7 cells. They also found that the derivative of EGCG exerted a stronger effect than the parent molecule. The effects of RANKL are reversed by osteoprotegerin (OPG). [PERSON] et al. [19] showed that the co-culture of RAW 264.7 cells and the feeder cells ST2 treatment with EGCG resulted in an increase in OPG mRNA expression and a decrease in RANKL mRNA expression, and therefore, the RANKL/OPG ratio decreased. Moreover, a decrease in osteoclastogenesis by TRAP-positive (tarratte-resistant acid phosphatase) osteoclasts and TRAP activity, was noted.  
Osteoclast differentiation is physiologically stimulated by, among others, osteoblasts. The inhibition of this process may cause a reduction in the number of osteoclasts. [PERSON] et al. [38] reached this conclusion after observing that EGCG decreased ALP activity and suppressed the mRNA expression of ALP and osteoclast (OCN) in MC3T3-E1 cells, as well as in the co-cultures of osteoblasts from neonatal mouse calvaria and bone marrow cells. The treatment of pluripotent mesenchymal cells D1 with EGCG increased OPG expression and thus inhibited osteoclast differentiation and activity. Such conclusions were made by [PERSON] et al. [26; 42]. Several years later, [PERSON] et al. [43], using cloned osteoblast-like MC3T3-E1 cells derived from newborn mouse calvaria, showed an inhibition of osteoclast differentiation and activation by increasing OPG release and the levels of OPG mRNA expression. Many factors can influence the conversion of monocytes to osteoclasts. One of them is NFATc1. [PERSON] et al. [51] showed in the antibody-induced arthritis model of male mice that NFATc1 expression was limited by EGCG, which prevented the CD14+ monocytes from converting to osteoclasts. Simultaneously, catechin did not affect the expression of NF-\(\kappa\)B, \(c\)-Fos, and \(c\)-Jun. In turn, [PERSON] et al. observed on RAW 264.7 (a murine preosteoclast cell line) that osteoclast differentiation and bone resorption activity at an early stage of osteoclastogenesis were inhibited by EGCG in a dose-dependent manner through its effects on NF-\(\kappa\)B-mediated transactivation and RANKL signalling via intranuclear NF-\(\kappa\)B translocation [52]. In contrast, [PERSON] et al. found in rat osteoclast precursor cells and mature osteoclasts that EGCG had an inhibitory effect on osteoclast formation and differentiation by inhibiting the enzymatic activity of MMP-2 and MMP-9 and the levels of MMP-9 mRNA in osteoclast precursor cells [53].  
Major conclusions are as follows:  
* EGCG influences bone health by upregulating alkaline phosphatase to stimulate bone mineralisation [26].
* It modulates osteoblast function through MAP kinase inhibition, contributing to bone tissue formation [27].
* It can potentially induce bone regeneration by enhancing bone callus formation and modifying collagen membranes [21; 45].
* Concentration matters: high EGCG dosages inhibit mesenchymal cell proliferation in osteogenesis, while intermediate concentrations promote it [29].
* It also prevents the inhibition of osteogenic differentiation by affecting TNF-\(\alpha\), and it has various effects on bone microarchitecture and osteoclasts [33; 34; 35; 36; 37].