## 4 Discussion  
SC has been effectively applied for the treatment of diseases, such as edema, gonorrhea, jaundice, and inflammation. In our previous study, SCE treatment was shown to increase bone mineral density, decrease separation of the bone trabecula, and positively regulate the biomarkers in OVX rat models, which is in agreement with the results of the present study [8; 31]. In the present study, serum biomarkers in an estrogen deficiency-induced osteoporosis model and effects of SCE on the metabolites of OVX rats were analyzed by UPLC/Q-TOF MS-based metabolomics analysis. Changes in metabolites, potential biomarkers, and related pathways were observed. Estrogen deficiency induces bone loss, changes in lipid profiles, and bone mineral density [32]. Bone metabolism, bone formation, and bone resorption have a complex relationship with lipid metabolism. Blood lipid level is increased in osteoporoprotein postmenopausal women and significantly increased in OVX-induced osteopororotic rats [33]. [PERSON] et al. reported that lipid accumulation increases oxidation, not only inhibiting the differentiation of osteoblasts but also promoting bone marrow stromal cell differentiation into adipogenic cells [34]. Most lipids, including fatty acids, glycerophospholipids (PC, PE, PA, phosphatidylserine (PS), phosphatidylglycerol (PG), and phosphatidylinositol (PI)), and sphingolipids, are components of the animal cell membrane and lipoproteins. LysoPCs, which result from the hydrolysis of PCs, are bioactive pro-inflammatory lipids generated through pathophysiological activities [35]. Increases in LysoPCs and PCs are suggestive of an oxidative stress response, and they are reportedly significantly upregulated in the plasma of osteopororotic mice; moreover, increases in reactive oxygen species lead to oxidative stress damage [36]. Oxidative stress may lead  
Figure 4: The pathway analysis with MetPA of SCE treatment effect: (**A**) including glycerophospholipid metabolism; (**B**) the compounds of the red boxes are LysoPE, LysoPC, and LysoPC(18:1) by serum metabolomics. to increase bone mass loss and skeletal friability, resulting in aggravation of osteoporosis progression [37]. In this study, compared with that in the sham group, most of LysoPC, LysoPE, PC, and PA levels in the OVX groups significantly increased, suggesting that abnormal metabolism of glycerophospholipids was related to osteoporosis and was likely to enhance oxidative stress by generating reactive oxygen species [30]. In our current study, SCE showed the most significant effect on glycerophospholipid metabolism compared to that of other metabolic pathways, and SCE effectively reversed decreases in LysoPC, LysoPE, PC, and PA levels in the OVX group, which can be used as targets for the future clinical treatment of osteoporosis [38]. In a study by [PERSON] et al., a high level of tryptophan in bone marrow mesenchymal stem cells due to the osteogenic induction associated with alkaline phosphatase protein expression was reported to be a risk marker for osteoblastic differentiation [39]. Aging negatively affects bone marrow mesenchymal stem cells by depleting normal anabolic tryptophan signals. Glutaryl-coenzyme A is an intermediate in the metabolism of lysine and tryptophan [40]. Mainly, glutaryl-CoA dehydrogenase converts tryptophan into glutararic acid and glutarylcarnitine in the catabolic pathways of tryptophan. In our model, the levels of tryptophan and glutarylcarnitine, which indicated the involvement of the catabolic pathways of tryptophan, were significantly upregulated in the OVX group. The levels of these metabolites were restored to normal level after treatment with SCE. Carnitine transports long-chain fatty acids for oxidation, thus directly promoting the metabolism of osteoblasts. Moreover, increasing acetyltransferase in aging rats leads to improved mitochondrial energy metabolism and reduced oxidative stress [32].