Monotropein, a principal natural compound in iridoid glycosides extracted from Morindae officinalis radix, has potent pharmacological activities. To understand and utilize monotropein, we systematically summarized the studies on monotropein, including its biosynthetic pathway, physicochemical properties, pharmacokinetics, and pharmacology. Interestingly, we found that the multiple bioactivities of monotropein, such as anti-osteoporosis, anti-inflammation, anti-oxidation, anti-nociception, and hepatic or renal protection, are closely associated with its capability of downregulating the nuclear factor-κB signaling pathway, inhibiting the mitogen-activated protein kinase signaling pathway, attenuating the activation of nuclear factor E2-related factor 2/heme oxygenase-1 signaling pathway, and regulating the mammalian target of rapamycin/autophagy signaling pathway. However, the clinically therapeutic effects and the potential problems need to be addressed. This review highlights the current research progress on monotropein, which provides a reference for further investigation of monotropein.

Objective. Postmenopausal osteoporosis (PMOP) is a common age-associated disease in the life course. Clinically, Xiaozeng Qianggu Tablets (XQT) have a potent therapeutic effect on the PMOP. However, the bioactive components and the mechanism of XQT underlying the PMOP treatment were unclear and it should be explored to discover the scientific connotation in traditional medical practice. Methods. The components in XQT were identified by UPLC-Q-TOF/MS. The animal model of PMOP was established by surgical ovariectomy in the female Sprague-Dawley rats. After treatment of XQT, the therapeutic effect was assessed by the determination of bone metabolism biomarkers in serum and histopathological examination. The effect of XQT on the autophagy and bone micro-situation were tested using western blot, RT-qPCR, and transmission electron microscope. Results. There were 27 compounds identified in XQT, including catalpol, monotropein, verbascoside, cryptochlorogenic acid, 5,7-dihydroxychromone 7-rutinoside, biorobin, and so on. The bone metabolism markers (alkaline phosphatase, bone alkaline phosphatase, procollagen type I intact N-terminal propeptide, cross-linked carboxy-terminal telopeptide of type I collagen, and tartrate-resistant acid phosphatase) were significantly increased in the PMOP rats and reversed by XQT administration. Moreover, the width of bone trabeculae and the ratio of the area of calcium deposition to bone trabeculae were also improved after treating the middle dose of XQT. Meanwhile, the bone micro-structure was improved by XQT. The mRNA and protein expression of unc-51 like kinase 1, beclin-1, and microtubule-associated protein 1B-light chain 3 in PMOP rats were down-regulated and up-regulated by XQT administration. Conclusions. The compounds in XQT, including catalpol, monotropein, verbascoside cryptochlorogenic acid, and so on, were valuable for further pharmacy evaluation. The pathological changes and bone micro-structure were improved by XQT, and the down-regulated autophagy level was also restored, which suggested a potent effect of XQT on treating PMOP, corresponding to its clinic use.