Ｒeview For Treatment Effect And Signaling Pathway Regulation Of Kidney-tonifying Traditional Chinese Medicine On Osteoporosis Ⅲ

2.4 Eucommia ulmoides

Eucommia ulmoides is sweet in taste and warm in nature. It enters the liver and kidney meridians. It has the effects of nourishing the liver and kidney, strengthening the tendons and bones, and calming the fetus. Zhang et al. [62] found that Eucommia ulmoides extract can improve the bone density, biomechanical properties, number and thickness of trabeculae in femurs, and reduce the content of bone turnover factor OPN in serum and Ca and phosphorus (P) in urine in castrated osteoporotic rats. It is proved that Eucommia ulmoides has a certain preventive and therapeutic effect on osteoporosis.

 

 

 

 

2.4.1 Regulation of Eucommia ulmoides and its active ingredients on pathways related to bone formation

2.4.1.1 Regulation of Eucommia ulmoides on Wnt/β-catenin signaling pathway

In the study of the changes in genes related to the Wnt signaling pathway during the osteogenic differentiation of BMSCs induced by Eucommia ulmoides alcohol extract, it was found that Eucommia ulmoides alcohol extract can significantly upregulate the expression of Fzd2, Fzd3 and β-catenin, and downregulate the expression of Wnt inhibitory factor (WIF1) [63]. This suggests that Eucommia ulmoides may induce osteogenic differentiation of BMSCs through the Wnt/β-catenin signaling pathway.

 

2.4.1.2 Regulation of Eucommia ulmoides on MAPK signaling pathway

Eucommia ulmoides leaf extract can increase the expression of phosphorylated AKT and ERK proteins in osteoblasts, promote the proliferation of rat osteoblasts, and activate Shp2 and ERK signaling pathways to promote the proliferation and osteogenic differentiation of rat BMSCs. It was found that it mainly plays a role by promoting the phosphorylation levels of ERK and AKT［64-65］.

 

2.4.2 Regulation of Eucommia ulmoides and its active ingredients on pathways related to inhibiting bone resorption

The main signaling pathway for Eucommia ulmoides to inhibit bone resorption is OPG/ＲANKL/ＲANK. Xu Xianghe et al. [66] found that Eucommia ulmoides can promote the proliferation and differentiation and maturation of osteoblasts by promoting the secretion of ALP and OPG by MC3T3-E1 osteoblasts, and upregulate the ratio of OPG/ＲANKL to inhibit the differentiation and maturation of osteoclasts, thereby inhibiting bone resorption. The lignans of Eucommia ulmoides act on osteoblasts, and the flavonoids of Eucommia ulmoides, astragaloside and baicalein, act on MC3T3-E1 osteoblasts to inhibit bone resorption, both of which act through the OPG/ＲANKL/ＲANK signaling pathway [67].

CISTANCH BENEFITS OF NOURISHING THE LIVER AND KIDNEY

 

2.5 Psoralea corylifolia

Psoralea corylifolia tastes bitter and pungent, is warm in nature, and enters the kidney and spleen meridians. It has the effects of tonifying the kidney and strengthening yang, consolidating essence and reducing urine. Leung et al. [68] found that psoralea corylifolia can increase the bone density of castrated osteoporotic rats, enhance biomechanical properties, and significantly increase the levels of estrogen and CT in serum. Psoralea corylifolia extract can increase the levels of Ca and OCN in the serum of castrated osteoporotic rats, increase bone density, and reduce the excretion of Ca in urine [69]. From the above, it can be seen that psoralea corylifolia can prevent and treat osteoporosis.

 

2.5.1 The regulatory effect of psoralen and its active ingredients on the signaling pathways related to bone formation

 

2.5.1.1 The regulation of psoralen on the BMP-Smads signaling pathway

 

Psoralen is the main component of the kidney-tonifying Chinese medicine psoralen. Psoralen can significantly promote the secretion of Collagen I, OCN, OPN and ALP in osteoblasts, upregulate the expression of BMP-2 and BMP-4 genes in a dose-dependent manner, and increase the protein levels of phosphorylated Smad1, Smad5 and Smad8 and the expression of Osterix, thereby promoting the osteogenic differentiation of osteoblasts. When the BMP-2 and BMP-4 genes were knocked out, the osteogenic differentiation effect of psoralen was also inhibited［70］. Therefore, it is speculated that psoralen may promote osteogenic differentiation by upregulating the expression of BMP-2 and activating the BMP-Smads signaling pathway.

 

2.5.1.2 Regulation of Psoralea corylifolia on Wnt/β-catenin signaling pathway

Weng et al. [71] found in an in vitro experiment that both bakuchiol and psoralea corylifolia flavonoids could dose-dependently increase the expression of Wnt pathway-related proteins Wnt3a, LRP5 and β-catenin in osteoblasts, suggesting that bakuchiol may induce the differentiation of human primary osteoblasts by upregulating the Wnt/β-catenin signaling pathway.

 

2.5.2 Regulation of Psoralea corylifolia and its active ingredients on signaling pathways related to inhibition of bone resorption

The main signaling pathway for Psoralea corylifolia to inhibit bone resorption is OPG/ＲANKL/ＲANK. Tian Dan et al. [72] found that psoralea corylifolia aqueous extract could upregulate the expression of OPG and the OPG/ＲANKL mＲNA ratio in osteoblasts, and downregulate the expression of ＲANKL mＲNA, inhibiting the differentiation and maturation of osteoclasts, thereby inhibiting bone resorption.

 

2.6 Dipsacus root

Dipsacus root tastes bitter and pungent, is slightly warm in nature, and enters the liver and kidney meridians. It has the effects of nourishing the liver and kidney, strengthening tendons and bones, stopping bleeding and stabilizing pregnancy, and healing injuries and fractures. The Shennong's Herbal Classic records that it has the effects of "treating colds, replenishing deficiencies, wounds, carbuncles, fractures, healing tendons and bones, and treating breastfeeding difficulties in women". Niu et al. [73] showed that Dipsacus root can significantly increase the bone density of ovariectomized osteoporotic rats, improve the microstructure of trabecular bone, enhance its biomechanical properties, increase the expression of OPG and ALP in serum, and reduce the levels of Ca and P in urine, proving that Dipsacus root can improve the symptoms of osteoporosis in ovariectomized rats.

2.6.1 The regulatory effect of Dipsacus asper and its active ingredients on the signaling pathways related to bone formation

 

2.6.1.1 The regulatory effect of Dipsacus asper and its active ingredients on the Wnt/β-catenin signaling pathway

 

Dipsacus asper saponin VI is the main active ingredient of Dipsacus asper, a traditional Chinese medicine for strengthening the kidney and bones. The study by Li Jia et al. [74] showed that Dipsacus asper saponin VI can significantly increase the cell activity of BMSCs, promote their osteogenic differentiation and mineralization, and upregulate the expression of BMP-2, Runx2, β-catenin and OCN genes, but the Wnt signaling pathway blocker DKK-1 can significantly inhibit the upregulation of these osteogenic genes, which indicates that Dipsacus asper may promote the osteogenic differentiation of BMSCs by activating the Wnt/β-catenin signaling pathway.

 

2.6.1.2 Regulation of Dipsacus asper and its active ingredients on MAPK signaling pathway

 

Dipsacus asper saponin VI can significantly promote the proliferation, differentiation and mineralization of MC3T3-E1 and primary osteoblasts, increase the activity of ALP, and upregulate the expression of p38, ERK1/2, BMP-2 and phosphorylated p38 and ERK1/2［75］, which proves that Dipsacus asper may increase bone formation by activating the p38 and ERK1/2 signaling pathways and increasing the synthesis of BMP-2.

 

2.6.3 Regulation of Dipsacus asper and its active ingredients on signaling pathways related to inhibition of bone resorption

 

The main signaling pathway for Dipsacus asper to inhibit bone resorption is OPG/ＲANKL/ＲANK. Using a castrated osteoporotic rat model, Tao Yi et al. [76] found that Dipsacus root could significantly reduce the levels of Ca, ALP, and ＲANKL in the serum of the model group rats, increase the expression of OPG and ＲANK, and improve the symptoms of osteoporosis. In in vitro experiments, Dipsacus root extract can significantly promote the proliferation and mineralization of MC3T3-E1 and primary osteoblasts, increase the expression of OPG, and reduce the content of ＲANKL [73]. This result shows that Dipsacus root may inhibit bone resorption by upregulating the expression of OPG, thereby activating the OPG/ＲANKL/
ＲANK signaling pathway.

 

3 Summary

3.1 Multi-pathway comprehensive regulation is a common feature of kidney-tonifying Chinese medicine for the treatment of osteoporosis

In summary, many kidney-tonifying Chinese medicines and their active ingredients can regulate the transcription and expression of target genes by regulating osteoporosis-related signaling pathways, especially intervening in the phosphorylation process of key signaling molecules in the signaling pathways, thereby achieving the purpose of preventing and treating osteoporosis. After a preliminary summary of the main signaling pathways of kidney-tonifying Chinese medicine regulating osteoporosis, it was found (Table 1) that kidney-tonifying Chinese medicine mainly acts on osteoblasts to promote bone formation through signaling pathways such as BMP-Smads, Wnt/β-catenin, MAPK, PI3K/AKT; and acts on osteoclasts to inhibit bone resorption through signaling pathways such as OPG/ＲANKL/ＲANK, estrogen, CTSK, etc., to achieve the purpose of treating osteoporosis.

Table 1 The regulation of kidney-tonifying traditional Chinese medicine on the signaling pathway of osteoporosis

 

Single Herb	Component	Target Cells or Model	Mechanism of Action	Related Pathway	References
Cistanche Extract	Water Extract	BMSCs	↑ Osteogenesis, ALP, Collagen I, OCN, TGF-β1, BMP-2	BMP-Smad	[22]
Cistanche Deserticola	Total Extract	BMSCs	↑ Osteogenesis, ALP, Collagen I, OCN, RUNX2, Osterix, BMP-2	BMP-Smad	[23]
Cistanche Tubulosa	MC3T3-E1	↑ BMP-2, Smad1, Smad5	BMP-Smad	[24-25]
	OB, hFOB1.19	↑ Osteogenesis, ALP, BMP-2, Smad4, RUNX2, OPG, RANKL	BMP-Smad	[26-27]
	BMSCs	↑ Wnt3a, β-catenin, Osteogenesis, GSK-3β, Phosphorylation of Cyclin D1, Runx2, OPN, DLX5, OCN, Collagen I, Lef1, TCF7, c-jun, c-myc, Cyclin D)	Wnt/β-catenin	[28-30]
OPC Gene Knockout Mice		↑ BMP-2, BMP-4, Runx2, OCN, Wnt1, Wnt3a, AXIN2, DKK1, TCF, LEF1)	Wnt/β-catenin	[31]
	OB, MC3T3-E1	↑ Osterix, Runx2, p38, Phosphorylation of Cbfα1, Cyclin E, PC-NA, Collagen I, ALP)	MAPK	[32-34]
		↓ (CTR, CAII, Cdk2n8, Caspase-3)
	BMSCs	↑ ALP, Phosphorylation of AKT, eNOS, iNOS	PI3K/AKT	[36-37]
	BMSCs	↑ Runx2, OPN, DLX5, OCN, Collagen I	Flavonoids	[30]
	BMSCs	↑ OPG, OPG/RANKL)	OPG/RANKL/RANK	[38]
Bone Remodeling System		↓ (NF-κB, RANK)	Flavonoids	[39]
Osteoclasts		↑ ERα	Flavonoids	[40]
	Osteoclasts	↓ (RANK, TRACP, MMP-9, Bone Resorption Pits)	CTSK	[41-42]
		↓ (RANK, TRACP, MMP-9, CTSK)
		↑ ALP, p38, Phosphorylation of p38, OPG	MAPK	[35]
Cistanche Salsa
Bone Marrow Supplement	Water Extract	OB	↑ IGF-1, BMP-2, BMP-4, ALP, OCN	BMP-Smad	[43]
	Total Extract	BMSCs	↑ ALP, Collagen I, Osteogenesis, TGF-β1, BMP-2)	BMP-Smad	[44-45]
		↓ (NF, Collagen I, Osteogenesis, Phosphorylation of Smad1/5/8)	BMP-Smad	[46]

 

 

Single Herb	Component	Target Cells or Model	Mechanism of Action	Related Pathway	References
BMSCs		↑ β-catenin, LEF-1, Cyclin D	Wnt/β-catenin	[50]
		↑ OPG, RANKL	OPG/RANKL	[52-53]
		↓ RANK, TRACP, ALP	RANK
		↓ CTSK	CTSK	[54]
	MC3T3-E1	↑ ALP, OCN, BMP-2	BMP-Smad	[49]
	BMSCs	↑ p38, Phosphorylation of JNK, TGF-β1, Cbfα1	MAPK	[55]
Citrus Peel	Total Extract	BMSCs	↑ BMP-2, Collagen I, OPN, OCN, ALP, ↓ Smad1/5/8	BMP-Smad	[56]
	BMSCs, hFOB	↑ ALP, Ca, Runx2, Collagen I, BMP-2, Osterix	BMP-Smad	[57]
	BMSCs	↑ OCN, OPN, Smad1/5/8, ↓ Phosphorylation of Smad1/5/8	BMP-Smad	[57, 59]
	BMSCs	↑ Collagen I, OPN, OCN, ALP	Wnt/β-catenin	[57, 59]
Osteoclasts		↑ OPG, RANKL, OPG/RANKL	OPG/RANKL	[60]
	Osteoclasts	↓ TRACP, CTSK, Bone Resorption Pits	CTSK
	Enzyme Extract	BMSCs	↑ Fzd2, Fzd3, β-catenin	Wnt/β-catenin	[63]
Water Extract	OB	↑ AKT, ERK, Phosphorylation of AKT, Phosphorylation of ERK	MAPK	[64-65]
	MC3T3-E1	↑ ALP, OPG, OPG/RANKL	OPG/RANKL/RANK	[66]
	OB, MC3T3-E1 Subclone 1	↑ OPG, OPG/RANKL	OPG/RANKL/RANK	[67]
Bone Marrow Supplement	Total Extract		↑ Collagen I, OCN, OPN, ALP, BMP-2, BMP-4, Smad1/5/8, Osterix	BMP-Smad	[70]
		↑ Wnt3a, LRP5, β-catenin	Wnt/β-catenin	[71]
		↑ OPG, OPG/RANKL	OPG/RANKL	[72]
Water Extract	BMSCs	↑ BMP-2, Runx2, β-catenin, OCN	Wnt/β-catenin	[73]
	MC3T3-E1, OB	↑ ALP, ERK1/2, BMP-2, p38, Phosphorylation of p38	MAPK	[75]
	Osteoporotic Mice	↑ Ca, ALP, RANKL	RANK
Water Extract	MC3T3-E1, OB	↑ OPG, OPG/RANKL	OPG/RANKL/RANK	[73]

 

 

Icariin in Epimedium, naringin in Drynaria, osthole in Cnidium monnieri, and psoralen in Psoralea corylifolia can promote bone formation by regulating signaling pathways such as BMPSmads and Wnt/β-catenin, and can also activate signaling pathways such as OPG/ＲANKL/ＲANK and CTSK to inhibit bone resorption, indicating that kidney-tonifying Chinese medicine can act on multiple signaling pathways simultaneously in regulating the dynamic balance of osteoblastic bone formation and osteoclast bone resorption. Each signaling pathway is not independent of each other in the process of preventing and treating osteoporosis, but crosses and interacts with each other, forming a complex biomolecular network system. Traditional Chinese medicine has the advantages of overall regulation and comprehensive treatment, so the multi-target and multi-pathway mechanisms of kidney-tonifying Chinese medicine in regulating osteoporosis-related pathways should be explored in depth, so that kidney-tonifying Chinese medicine can play a greater role in preventing and treating osteoporosis.

 

3.2 Comprehensive regulation of osteoporosis-related signals by kidney-tonifying Chinese medicine needs further study

Osteoporosis is a systemic bone metabolic disease with complex pathogenesis and clinical difficulty in cure. Kidney-tonifying Chinese medicine and its preparations have good clinical efficacy in preventing and treating osteoporosis, and have the advantages of multiple pathways, multiple targets, and low toxicity and side effects. However, how to develop more effective osteoporosis treatment drugs based on known disease mechanisms is a question worth considering by researchers. There are some problems in the research on the regulation of osteoporosis-related signal pathways by kidney-tonifying Chinese medicine at home and abroad:

① At present, the research on the regulation of osteoporosis-related signal pathways by kidney-tonifying Chinese medicine is still in its infancy. In addition to the signal pathways mentioned above, there are also multiple signal pathways such as IGF, PTH, and FGF. Moreover, the bone metabolism-related signal pathways do not exist independently. The pathways overlap and interact with each other. Research on a single target only has many limitations. Therefore, the crosstalk between bone metabolism signal pathways should become one of the hot spots and focuses of future research.

②The research on the signal pathways related to osteoporosis by kidney-tonifying Chinese medicine is currently mainly focused on the cellular level, with low-level duplication, and further in-depth research is still needed in animal experiments. ③The animal model of the research is relatively simple, mainly the osteoporosis model of ovariectomized rats. For other osteoporosis models caused by symptoms such as kidney deficiency, further research is needed.