Effect of nicotine on gene expression of angiogenic and osteogenic factors in a rabbit model of bone regeneration

Acute exposure to electronic cigarette components alters mRNA expression of pre-osteoblasts

The use of traditional nicotine delivery products such as tobacco has long been linked to detrimental health effects. However, little work to date has focused on the emerging market of aerosolized nicotine delivery known as electronic nicotine delivery systems (ENDS) or electronic cigarettes, and their potential for new effects on human health. Challenges studying these devices include heterogeneity in the formulation of the common components of most available ENDS, including nicotine and a carrier (commonly composed of propylene glycol and vegetable glycerin, or PG/VG). In the present study, we report on experiments interrogating the effects of major identified components in e-cigarettes. Specifically, the potential concomitant effects of nicotine and common carrier ingredients in commercial "vape" products are explored in vitro to inform the potential health effects on the craniofacial skeleton through novel vectors as compared to traditional tobacco products. MC3T3-E1 murine pre-osteoblast cells were cultured in vitro with clinically relevant liquid concentrations of nicotine, propylene glycol (PG), vegetable glycerin (VG), Nicotine+PG/VG, and the vape liquid of a commercial product (Juul). Cells were treated acutely for 24 h and RNA-Seq was utilized to determine segregating alteration in mRNA signaling. Influential gene targets identified with sparse partial least squares discriminant analysis (sPLS-DA) implemented in mixOmics were assessed using the PANTHER Classification system for molecular functions, biological processes, cellular components, and pathways of effect. Additional endpoint functional analyses were used to confirm cell cycle changes. The initial excitatory concentration (EC50) studied defined a target concentration of carrier PG/VG liquid that altered the cell cycle of the calvarial cells. Initial sPLS-DA analysis demonstrated the segregation of nicotine and non-nicotine exposures utilized in our in vitro modeling. Pathway analysis suggests a strong influence of nicotine exposures on cellular processes including metabolic processes and response to stimuli including autophagic flux. Further interrogation of the individual treatment conditions demonstrated segregation by treatment modality (Control, Nicotine, Carrier (PG+VG), Nicotine+PG/VG) along three dimensions best characterized by: latent variable 1 (PLSDA-1) showing strong segregation based on nicotine influence on cellular processes associated with cellular adhesion to collagen, osteoblast differentiation, and calcium binding and metabolism; latent variable 2 (PLSDA-2) showing strong segregation of influence based on PG+VG and Control influence on cell migration, survival, and cycle regulation; and latent variable 3 (PLSDA-3) showing strong segregation based on Nicotine and Control exposure influence on cell activity and growth and developmental processes. Further, gene co-expression network analysis implicates targets of the major pathway genes associated with bone growth and development, particularly craniofacial (FGF, Notch, TGFβ, WNT) and analysis of active subnetwork pathways found these additionally overrepresented in the Juul exposure relative to Nicotine+PG/VG. Finally, experimentation confirmed alterations in cell count, and increased evidence of cell stress (markers of autophagy), but no alteration in apoptosis. These data suggest concomitant treatment with Nicotine+PG/VG drives alterations in pre-osteoblast cell cycle signaling, specifically transcriptomic targets related to cell cycle and potentially cell stress. Although we suspected cell stress and well as cytotoxic effects of Nicotine+PG/VG, no great influence on apoptotic factors was observed. Further RNA-Seq analysis allowed for the direct interrogation of molecular targets of major pathways involved in bone and craniofacial development, each demonstrating segregation (altered signaling) due to e-cigarette-type exposure. These data have implications directed toward ENDS formulation as synergistic effects of Nicotine+PG/VG are evidenced here. Thus, future research will continue to interrogate how varied formulation of Nicotine+PG/VG affects overall cell functions in multiple vital systems.

Emerging factors affecting peri-implant bone metabolism

Implant dentistry has evolved to the point that standard implant osseointegration is predictable. This is attributed in part to the advancements in material sciences that have led toward improvements in implant surface technology and characteristics. Nonetheless, there remain several cases where implant therapy fails (specifically at early time points), most commonly attributed to factors affecting bone metabolism. Among these patients, smokers are known to have impaired bone metabolism and thus be subject to higher risks of early implant failure and/or late complications related to the stability of the peri-implant bone and mucosal tissues. Notably, however, emerging data have unveiled other critical factors affecting osseointegration, namely, those related to the metabolism of bone tissues. The aim of this review is to shed light on the effects of implant-related factors, like implant surface or titanium particle release; surgical-related factors, like osseodensification or implanted biomaterials; various drugs, like selective serotonin reuptake inhibitors, proton pump inhibitors, anti-hypertensives, nonsteroidal anti-inflammatory medication, and statins, and host-related factors, like smoking, diet, and metabolic syndrome on bone metabolism, and aseptic peri-implant bone loss. Despite the infectious nature of peri-implant biological complications, these factors must be surveyed for the effective prevention and management of peri-implantitis.

The Effect of Waterpipe Tobacco Smoking on Bone Healing Following Femoral Fractures in Male Rats

Background: Given the increasing use of waterpipe tobacco smoking in the world and its unknown effects on bone healing, this study investigated the repairing of femoral bone fractures in rats exposed to waterpipe tobacco smoking (WTS).

Main Methods: This study involved 40 male Wistar rats that were divided into two groups, including the femoral fracture (Fx) and the Fx + WTS groups. Each group was divided into two subgroups that were evaluated for bone healing 28 and 42 days after femoral fracture. After fixing the fractured femur, the healing process was evaluated by radiography, pathological indicators, and a measurement of the blood levels of vascular endothelial growth factor (VEGF), parathyroid hormone (PTH), Ca ++, transforming growth factor-beta (TGF-β), and insulin-like growth factor 1 (IGF-1). Additionally, the density of VEGF and CD34 in fracture tissue was investigated by immunohistochemistry.

Key Findings: Radiographic findings showed that factors related to the earlier stages of bone healing had higher scores in the Fx + WTS28 and 42 subgroups in comparison to the Fx groups. The density of VEGF and CD34 showed that the angiogenesis processes were different in the bone fracture area and callus tissue in the Fx +WTS subgroups. The serum levels of VEGF, TGF-β, and IGF-1 were significantly lower in the Fx +WTS42 group, and PTH in the Fx +WTS28 group was higher than that in the other groups.

Significance: The findings showed the disturbance and delay in the femoral fracture union in rats exposed to hookah smoke. This is partly due to the reduction of molecular stimuli of bone synthesis and the attenuation of quantitative angiogenesis.

Tobacco and bone fractures: A review of the facts and issues that every orthopaedic surgeon should know

Objectives

The aim of this study was to review the impact of smoking tobacco on the musculoskeletal system, and on bone fractures in particular.

Methods

English-language publications of human and animal studies categorizing subjects into smokers and nonsmokers were sourced from MEDLINE, The Cochrane Library, and SCOPUS. This review specifically focused on the risk, surgical treatment, and prevention of fracture complications in smokers.

Results

Smokers have an increased risk of fracture and experience more complications with delayed bone healing, even if they have already stopped smoking, because some adverse effects persist for a prolonged period. Some risks can be reduced during and after surgery by local and general prevention, and smoking cessation is an important factor in lessening this risk. However, if a patient wants to stop smoking at the time of a fracture, the cessation strategies in reducing tobacco use are not easy to implement. The patient should also be warned that using e-cigarettes or other tobaccos does not appear to reduce adverse effects on health.

Conclusion

The evidence reviewed in this study shows that smoking has a negative effect in terms of the risk and treatment of fractures.

Cite this article: J. Hernigou, F. Schuind. Tobacco and bone fractures: A review of the facts and issues that every orthopaedic surgeon should know. Bone Joint Res 2019;8:255–265. DOI: 10.1302/2046-3758.86.BJR-2018-0344.R1.

Endothelial disruptive proinflammatory effects of nicotine and e-cigarette vapor exposures

The increased use of inhaled nicotine via e-cigarettes has unknown risks to lung health. Having previously shown that cigarette smoke (CS) extract disrupts the lung microvasculature barrier function by endothelial cell activation and cytoskeletal rearrangement, we investigated the contribution of nicotine in CS or e-cigarettes (e-Cig) to lung endothelial injury. Primary lung microvascular endothelial cells were exposed to nicotine, e-Cig solution, or condensed e-Cig vapor (1-20 mM nicotine) or to nicotine-free CS extract or e-Cig solutions. Compared with nicotine-containing extract, nicotine free-CS extract (10-20%) caused significantly less endothelial permeability as measured with electric cell-substrate impedance sensing. Nicotine exposures triggered dose-dependent loss of endothelial barrier in cultured cell monolayers and rapidly increased lung inflammation and oxidative stress in mice. The endothelial barrier disruptive effects were associated with increased intracellular ceramides, p38 MAPK activation, and myosin light chain (MLC) phosphorylation, and was critically mediated by Rho-activated kinase via inhibition of MLC-phosphatase unit MYPT1. Although nicotine at sufficient concentrations to cause endothelial barrier loss did not trigger cell necrosis, it markedly inhibited cell proliferation. Augmentation of sphingosine-1-phosphate (S1P) signaling via S1P1 improved both endothelial cell proliferation and barrier function during nicotine exposures. Nicotine-independent effects of e-Cig solutions were noted, which may be attributable to acrolein, detected along with propylene glycol, glycerol, and nicotine by NMR, mass spectrometry, and gas chromatography, in both e-Cig solutions and vapor. These results suggest that soluble components of e-Cig, including nicotine, cause dose-dependent loss of lung endothelial barrier function, which is associated with oxidative stress and brisk inflammation.

Cigarette smoking and its impact on fracture healing

In this review, we discuss current knowledge and studies concerning the pathophysiology of cigarette smoking and its impact on fracture healing. We include studies on the biology of fracture healing and more specifically how smoking affects oxygenation in tissues, serum concentrations of important growth factors, collagen synthesis, and bone mineralization. Also mentioned are clinical studies showing that smoking impacts soft tissue regeneration and the healing of tibial fractures and open fractures, as well as articles discussing the apparent benefits and limitations of presurgical smoking cessation. Our review of the current literature suggests that it is necessary to inform smokers with fractures about their increased risk for impaired fracture healing. They should be closely monitored and additional therapies such as the use of BMP-7, BMP-2, or low-intensity ultrasound should be considered in early stages after trauma.

Effects of chronic passive smoking on the regeneration of rat femoral defects filled with hydroxyapatite and stimulated by laser therapy

Defects associated with bone mass loss are frequently treated by autogenous bone grafting. However, synthetic biomaterials such as calcium phosphate ceramics can substitute autologous grafts as long as they are biocompatible with bone tissue. In addition, low-level laser therapy (LLLT) is used to enhance bone regeneration by stimulating the local microcirculation and increasing the synthesis of collagen by bone cells. However, bone health is fundamental for osseointegration of the graft and bone repair. In this respect, excessive tobacco consumption can compromise expected outcomes because of its deleterious effects on bone metabolism that predispose to the development of osteoporosis. The objective of this study was to evaluate the regeneration of bone defects implanted with biomaterial and stimulated by LLLT in rats submitted to passive cigarette smoking. Porous hydroxyapatite granules were implanted into critical-size defects induced experimentally in the distal epiphysis of the right femur of 20 female Wistar rats submitted to passive smoking for 8 months in a smoking box. The defect site was irradiated with a gallium-arsenide laser at an intensity of 5.0 J/cm2. The animals were divided into four groups: control (non-smoking) rates submitted (G2) or not (G1) to laser irradiation, and smoking rats submitted (G4) or not (G3) to laser irradiation. The animals were sacrificed 8 weeks after biomaterial implantation. The right femurs were removed for photodocumentation, radiographed, and processed for routine histology. The results showed good radiopacity of the implant site and of the hydroxyapatite granules. Histologically, formation of new trabecular bone was observed adjacent to the hydroxyapatite granules in G1 and G2. In G3 and G4, the granules were surrounded mainly by connective tissue. In conclusion, passive smoking compromised bone neoformation in the defects and the LLLT protocol was not adequate to stimulate local osteogenesis.

The in vitro and in vivo effects of nicotine on bone, bone cells and fracture repair

INTRODUCTION

Cigarette smoke has negative effects on bone metabolism and fracture repair. However, no study has reviewed effects of nicotine on bone and fracture repair independent of other constituents of cigarette smoke. The authors review the existing evidence of the effect of nicotine on 'bone' and 'bone cells' and fracture repair, drawing conclusions relevant to clinical practice and future research.

AREAS COVERED

A literature review was conducted using PRISMA guidelines and PubMed, Cochrane, MEDLINE/OVID, EMBASE, NHS Evidence and Google scholar databases. Articles were included if they specifically investigated the effects of nicotine on 'bone' or fracture repair in animal or human models or in vitro effects on 'bone cells'. A total of 64 papers were included in this review, of which 15 were human in vitro studies and 49 animal studies wherein 9 were in vitro and 40 in vivo. In vivo studies of the effects of nicotine in animals demonstrated widespread effects on bone including osteoneogenesis, osseointegration, steady-state skeletal bone and genes and cytokines relevant to bone cell physiology and bone homeostasis. In these studies, nicotine's effects are predominately negative, inhibiting bone cell metabolism and fracture repair, whereas most in vitro studies reported biphasic responses in all bone cells except osteoclastic cells.

EXPERT OPINION

The review suggests that nicotine has effects on osteoneogenesis, osseointegration and steady-state skeletal bone in animal in vivo models, as well as effects on all 'bone cells', via several mechanisms in both animal and human cell in vitro studies. The effect of nicotine is dose-dependent, with higher concentrations having predominantly negative effects, whereas at low concentrations a stimulatory effect is seen. Stimulatory effects on certain cells may indicate a possible, limited therapeutic role; advice regarding smoking cessation perioperatively should remain due to the other harmful components of cigarette smoke, but there may be scope for allowing the use of nicotine patches instead of complete abstention. Further research into clinical outcomes is required before the exact response of bone and fracture repair in humans to nicotine is known.

Influence of nicotine on the biological activity of rabbit osteoblasts

OBJECTIVES

To assess the influence of nicotine on the proliferation and gene expression of osteogenic and angiogenic mediators of osteoblasts.

MATERIAL AND METHODS

Rabbit primary osteoblasts were exposed to various concentrations of nicotine (0.001, 0.1 and 10 μmol/l). The cell proliferation was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. The gene expression of transforming growth factor (TGF)-β(1), bone morphogenetic protein (BMP)-2, platelet-derived growth factor (PDGF)-AA and vascular endothelial growth factor (VEGF) was evaluated using real-time reverse transcription - polymerase chain reaction.

RESULTS

The osteoblast proliferation was inhibited by nicotine at the concentration of 0.001-10 μM at 48 and 72 h of culture, but with no significant effect at 24 h. The expression of TGF-β(1), BMP-2, PDGF-AA and VEGF was inhibited by nicotine at the concentrations of 0.1 and 10 μM, but with no significant difference at the low concentration of 0.001 μM.

CONCLUSIONS

Nicotine suppresses osteoblast proliferation and inhibits the expression of some key osteogenic and angiogenic mediators in the in vitro experimental model. These inhibitory effects of nicotine on the osteoblast activity may reflect, to a certain degree, the overall detrimental effects of tobacco use on the survival rate of dental implants.