3D Environment Is Required In Vitro to Demonstrate Altered Bone Metabolism Characteristic for Type 2 Diabetics

Aggregation of human osteoblasts unlocks self-reliant differentiation and constitutes a microenvironment for 3D-co-cultivation with other bone marrow cells

Skeletal bone function relies on both cells and cellular niches, which, when combined, provide guiding cues for the control of differentiation and remodeling processes. Here, we propose an in vitro 3D model based on human fetal osteoblasts, which eases the study of osteocyte commitment in vitro and thus provides a means to examine the influences of biomaterials, substances or cells on the regulation of these processes. Aggregates were formed from human fetal osteoblasts (hFOB1.19) and cultivated under proliferative, adipo- and osteoinductive conditions. When cultivated under osteoinductive conditions, the vitality of the aggregates was compromised, the expression levels of the mineralization-related gene DMP1 and the amount of calcification and matrix deposition were lower, and the growth of the spheroids stalled. However, within spheres under growth conditions without specific supplements, self-organization processes occur, which promote extracellular calcium deposition, and osteocyte-like cells develop. Long-term cultivated hFOB aggregates were free of necrotic areas. Moreover, hFOB aggregates cultivated under standard proliferative conditions supported the co-cultivation of human monocytes, microvascular endothelial cells and stromal cells. Overall, the model presented here comprises a self-organizing and easily accessible 3D osteoblast model for studying bone marrow formation and in vitro remodeling and thus provides a means to test druggable molecular pathways with the potential to promote life-long bone formation and remodeling.

Tobacco heating system has less impact on bone metabolism than cigarette smoke

Cigarette smoking promotes osteoclast activity, thus increasing the risk of secondary osteoporosis, leading to osteoporosis-associated fracture and impaired fracture healing. Heated tobacco products (HTP) are considered potential reduced-risk alternatives to cigarettes. However, their impact on bone metabolism remains to be elucidated. We developed an in vitro model that mimics in vivo bone cell interactions to comparatively evaluate the effects of HTPs and cigarette smoke on bone cell functionality and viability. We generated an in vitro coculture system with SCP-1 and THP-1 cells (1:8 ratio) cultured on a decellularized Saos-2 matrix with an optimized coculture medium. We found that, following acute or chronic exposure, particulate matter extract from the aerosol of an HTP, the Tobacco Heating System (THS), was less harmful to the bone coculture system than reference cigarette (1R6F) smoke extract. In the fracture healing model, cultures exposed to the THS extract maintained similar osteoclast activity and calcium deposits as control cultures. Conversely, smoke extract exposure promoted osteoclast activity, resulting in an osteoporotic environment, whose formation could be prevented by bisphosphonate coadministration. Thus, THS is potentially less harmful than cigarette smoke to bone cell differentiation and bone mineralization - both being crucial aspects during the reparative phase of fracture healing.

Maqui Berry and Ginseng Extracts Reduce Cigarette Smoke-Induced Cell Injury in a 3D Bone Co-Culture Model

Cigarette smoking-induced oxidative stress has harmful effects on bone metabolism. Maqui berry extract (MBE) and ginseng extract (GE) are two naturally occurring antioxidants that have been shown to reduce oxidative stress. By using an osteoblast and osteoclast three-dimensional co-culture system, we investigated the effects of MBE and GE on bone cells exposed to cigarette smoke extract (CSE). The cell viability and function of the co-culture system were measured on day 14. Markers of bone cell differentiation and oxidative stress were evaluated at gene and protein levels on day 7. The results showed that exposure to CSE induced osteoporotic-like alterations in the co-culture system, while 1.5 µg/mL MBE and 50 µg/mL GE improved CSE-impaired osteoblast function and decreased CSE-induced osteoclast function. The molecular mechanism of MBE and GE in preventing CSE-induced bone cell damage is linked with the inhibition of the NF-κB signaling pathway and the activation of the Nrf2 signaling pathway. Therefore, MBE and GE can reduce CSE-induced detrimental effects on bone cells and, thus, prevent smoking-induced alterations in bone cell homeostasis. These two antioxidants are thus suitable supplements to support bone regeneration in smokers.

Smoking Impairs Hematoma Formation and Dysregulates Angiogenesis as the First Steps of Fracture Healing

Bone fracture healing is an overly complex process in which inflammation, osteogenesis, and angiogenesis are tightly coupled, and delayed fracture repair is a very common health risk. One of the major causes of delayed healing is the formation of insufficient vasculature. Precise regulation of blood vessels in bone and their interplay with especially osteogenic processes has become an emerging topic within the last years; nevertheless, regulation of angiogenesis in (early) diseased fracture repair is still widely unknown. Here, we aim to develop an in vitro model for the analysis of early fracture healing which also enables the analysis of angiogenesis as a main influencing factor. As smoking is one of the main risk factors for bone fractures and developing a delay in healing, we model smoking and non-smoking conditions in vitro to analyze diverging reactions. Human in vitro fracture hematomas mimicking smokers’ and non-smokers’ hematomas were produced and analyzed regarding cell viability, inflammation, osteogenic and chondrogenic differentiation, and angiogenic potential. We could show that smokers’ blood hematomas were viable and comparable to non-smokers. Smokers’ hematomas showed an increase in inflammation and a decrease in osteogenic and chondrogenic differentiation potential. When analyzing angiogenesis, we could show that the smokers’ hematomas secrete factors that drastically reduced HUVEC proliferation and tube formation. With an angiogenesis array and gene expression analysis, we could identify the main influencing factors: Anpgt1/2, Tie2, and VEGFR2/3. In conclusion, our model is suitable to mimic smoking conditions in vitro showing that smoking negatively impacts early vascularization of newly formed tissue.

Altered Secretome of Diabetic Monocytes Could Negatively Influence Fracture Healing-An In Vitro Study

Diabetes mellitus is a main risk factor for delayed fracture healing and fracture non-unions. Successful fracture healing requires stimuli from different immune cells, known to be affected in diabetics. Especially, application of mononuclear cells has been proposed to promote wound and fracture healing. Thus, aim was to investigate the effect of pre-/diabetic conditions on mononuclear cell functions essential to promote osteoprogenitor cell function. We here show that pre-/diabetic conditions suppress the expression of chemokines, e.g., CCL2 and CCL8 in osteoprogenitor cells. The associated MCP-1 and MCP-2 were significantly reduced in serum of diabetics. Both MCPs chemoattract mononuclear THP-1 cells. Migration of these cells is suppressed under hyperglycemic conditions, proposing that less mononuclear cells invade the site of fracture in diabetics. Further, we show that the composition of cytokines secreted by mononuclear cells strongly differ between diabetics and controls. Similar is seen in THP-1 cells cultured under hyperinsulinemia or hyperglycemia. The altered secretome reduces the positive effect of the THP-1 cell conditioned medium on migration of osteoprogenitor cells. In summary, our data support that factors secreted by mononuclear cells may support fracture healing by promoting migration of osteoprogenitor cells but suggest that this effect might be reduced in diabetics.