Silk fibroin (SF) nanofibers, formed through electrospinning, have attractive utility in regenerative medicine due to the biocompatibility, mechanical properties and tailorable degradability. The mechanism of SF electrospun nanofiber formation was studied to gain new insight into the formation and control of nanofibers. SF electrospinning solutions with different nanostructures (nanospheres or nanofilaments) were prepared by controlling the drying process during the preparation of regenerated SF films. Compared to SF nanospheres in solution, SF nanofilaments had better spinnability with lower viscosity when the concentration of silk protein was below 10%, indicating a critical role for SF morphology, and in particular, nanostructures for the formation of electrospun fibers. More interesting, the diameter of electrospun fibers gradually increased from 50 nm to 300 nm as the increase in concentration of SF nanofilaments in the solution from 6% to 12%, implying size control by simply adjusting SF nanostructure and concentration. Aside from process parameters investigated in previous studies, such as SF concentration, viscosity and electrical potential, the present mechanism emphasizes significant influence of SF nanostructure on spinnability and diameter control of SF electrospun fibers, providing a controllable option for the preparation of silk-based electrospun scaffolds for biomaterials, drug delivery and tissue engineering needs.

Vascularization is fundamental for bone formation and bone tissue homeostasis. However, in human subjects, a direct molecular relationship has not been identified between angiogenesis and agents that promote bone disease or factors related to age. Osteopenia is a condition in which bone mineral density is lower than normal, and it represents a sign of normal aging. Here we tested whether the type H vessel, which was recently identified as strongly positive for CD31 and Endomucin (CD31hiEmcnhi) in mice, is an important indicator of aging and osteopenia in human subjects. We found that age-dependent losses of type H vessels in human bone sections conform to the observations in aged mice. The abundance of human type H vessels and osteoprogenitors may be relevant to changes in the skeletal microarchitecture and advanced osteopenia. Furthermore, ovariectomized mice, a widely used model for postmenopausal osteoporosis, exhibited significantly reduced type H vessels accompanied by reduced osteoprogenitors, which is consistent with impaired bone microarchitecture and osteoporosis, suggesting that this feature is an indicator of bone mass independent of aging. More importantly, administration of desferrioxamine led to significantly increased bone mass via enhanced angiogenesis and increased type H vessels in ovariectomized mice. Altogether, these data represent a novel finding that type H vessels are regulated in aged and osteopenia subjects. The abundance of human type H vessels is an early marker of bone loss and represents a potential target for improving bone quality via the induction of type H vessels.

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Injectable hydrogels are an important class of biomaterials, and they have been widely used for controlled drug release. This study evaluated an injectable hydrogel formed in situ system by the reaction of a polyethylene glycol derivative with α,β-polyaspartylhydrazide for local cancer chemotherapy. This pH-responsive hydrogel was used to realize a sol-gel phase transition, where the gel remained a free-flowing fluid before injection but spontaneously changed into a semisolid hydrogel just after administration. As indicated by scanning electron microscopy images, the hydrogel exhibited a porous three-dimensional microstructure. The prepared hydrogel was biocompatible and biodegradable and could be utilized as a pH-responsive vector for drug delivery. The therapeutic effect of the hydrogel loaded with doxorubicin (DOX) after intratumoral administration in mice with human fibrosarcoma was evaluated. The inhibition of tumor growth was more obvious in the group treated by the DOX-loaded hydrogel, compared to that treated with the free DOX solution. Hence, this hydrogel with good syringeability and high biodegradability, which focuses on local chemotherapy, may enhance the therapeutic effect on human fibrosarcoma.

Great controversy exists regarding the biologic responses of osteoblasts to X-ray irradiation, and the mechanisms are poorly understood. In this study, the biological effects of low-dose radiation on stimulating osteoblast proliferation, differentiation and fracture healing were identified using in vitro cell culture and in vivo animal studies. First, low-dose (0.5 Gy) X-ray irradiation induced the cell viability and proliferation of MC3T3-E1 cells. However, high-dose (5 Gy) X-ray irradiation inhibited the viability and proliferation of osteoblasts. In addition, dynamic variations in osteoblast differentiation markers, including type I collagen, alkaline phosphatase, Runx2, Osterix and osteocalcin, were observed after both low-dose and high-dose irradiation by Western blot analysis. Second, fracture healing was evaluated via histology and gene expression after single-dose X-ray irradiation, and low-dose X-ray irradiation accelerates fracture healing of closed femoral fractures in rats. In low-dose X-ray irradiated fractures, an increase in proliferating cell nuclear antigen (PCNA)-positive cells, cartilage formation and fracture calluses was observed. In addition, we observed more rapid completion of endochondral and intramembranous ossification, which was accompanied by altered expression of genes involved in bone remodeling and fracture callus mineralization. Although the expression level of several osteoblast differentiation genes was increased in the fracture calluses of high-dose irradiated rats, the callus formation and fracture union were delayed compared with the control and low-dose irradiated fractures. These results reveal beneficial effects of low-dose irradiation, including the stimulation of osteoblast proliferation, differentiation and fracture healing, and highlight its potential translational application in novel therapies against bone-related diseases.

Abstract. The purpose of the present study was to investigate the effects of bafilomycin A1 (BafA1) on proliferation, apoptosis and autophagy in MG63 osteosarcoma cells. The growth rate of MG63 cells was determined using a Cell Counting Kit-8 assay. The mitochondrial membrane potential (Δψ) was measured using a fluorescent probe, JC-1, and the inhibition of autophagy and apoptosis was monitored by transmission electron microscopy. In addition, the inhibition of autophagy was monitored by western blot analysis of microtubule-associated protein 1 light chain 3 (LC3), and the ratio of LC3-II/LC3-I protein levels was calculated as an indicator of the extent of autophagy. Furthermore, the expression levels of specific proteins associated with autophagy, including p53, Beclin1 and p62, were detected in cultured MG63 cells by western blotting. It was shown that the viability of MG63 cells was inhibited following the use of BafA1, and an induction in the expression levels of the apoptosis-related protein p53 and the autophagic protein Beclin1 was detected. Furthermore, a collapse in Δψ was observed, together with an induction of apoptotic cell death, following treatment with BafA1. Therefore, following BafA1-mediated inhibition of autophagy, the inhibition of MG63 cell proliferation and induction of apoptosis were observed.

Osteosarcoma (OS) is the most common type of bone cancer. Even with early diagnosis and aggressive treatment, the prognosis for OS is poor. In the present study, we investigated the proliferation and invasion inhibitory effect of apigenin on human OS cells and the possible molecular mechanisms involved. The cell viability of U2OS and MG63 human OS cell lines was detected by MTT assay. Cell cycle progression and invasion were assessed by flow cytometry and the Matrigel Boyden chamber assay, respectively, and the involvement of molecular mechanisms was examined by western blot analysis. We demonstrated that apigenin inhibited proliferation and reduced invasion in human OS cells, and downregulated the expression of β-catenin in OS cells. Furthermore, the inhibitory effect of apigenin on OS cells was reversed by overexpression of β-catenin, but enhanced by knockdown of β-catenin. Collectively, our results showed that apigenin inhibits the tumor growth of OS cells by inactivating Wnt/β-catenin signaling. Therefore, apigenin is a promising chemotherapeutic agent that may be used in the treatment of human OS.

It has been well documented that the inhibition of the mammalian target of rapamycin (mTOR) induces autophagy in proliferative cells. Therefore, mTOR inhibitors have been proposed for the treatment of cancer. As autophagy plays significant roles in tumor cell survival, the present study aimed to investigate the contribution of autophagy activation to the antitumor effects of cis-diamminedichloroplatinum (CDDP). An MTT assay was used to determine the cytotoxic effects of rapamycin on MG63 osteosarcoma cells. The cell cycle was assessed using a flow cytometry analysis subsequent to staining the DNA with propidium iodide. The mitochondrial membrane potential (Δψ) was measured using the fluorescent probe, JC-1. Western blot analysis was used to determine the expression of the proteins that are involved in apoptosis and autophagy, including p53, p62, light chain 3 (LC3) and Beclin-1. The viability of the MG63 cells was inhibited following rapamycin or CDDP treatment. The mitochondrial Δψ collapsed following treatment with rapamycin or CDDP. Rapamycin induced cell death and enhanced the effects of the induction of MG63 cell death by CDDP. Western blot analysis detected the induced expression of the p53 and Beclin-1 proteins and the autophagic proteins, LC3 and p62. Rapamycin was observed to induce the death of cancer cells through apoptotic and autophagic mechanisms. Rapamycin may enhance the effects of the activation of autophagy and the induction of apoptosis by CDDP.