Inhibition of dioxin effects on bone formation in vitro by a newly described aryl hydrocarbon receptor antagonist, resveratrol

Endocrine Disruptor-Induced Bone Damage Due to Hormone Dysregulation: A Review

Hormones are indispensable for bone development, growth, and maintenance. While many of the genes associated with osteogenesis are well established, it is the recent findings in endocrinology that are advancing the fields of bone biology and toxicology. Endocrine-disrupting chemicals (EDCs) are defined as chemicals that interfere with the function of the endocrine system. Here, we report recent discoveries describing key hormone pathways involved in osteogenesis and the EDCs that alter these pathways. EDCs can lead to bone morphological changes via altering hormone receptors, signaling pathways, and gene expression. The objective of this review is to highlight the recent discoveries of the harmful effects of environmental toxicants on bone formation and the pathways impacted. Understanding the mechanisms of how EDCs interfere with bone formation contributes to providing a comprehensive toxicological profile of a chemical.

Assessment of Selected Morphological, Physical and Chemical Parameters of the Teeth of the Offspring of Female Rats Exposed to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), Taking into Account the Protective Role of Selected Antioxidants-Preliminary Study

The studies conducted so far indicate a negative effect of dioxins on the structure of the alveolar bone and teeth, especially in the developmental period in rats. The research aimed to analyze the indirect effect of dioxins contained in the body of female rats on the structure of the dental organ in their offspring in the neonatal period and to determine the possibility of reducing potential dioxin disorders of the structure of hard tissues in the offspring of intoxicated mothers by simultaneous administration of vitamin E or acetylsalicylic acid (ASA). Another goal of the research was to determine the level of magnesium, calcium and phosphorus contained in bone tissue as indicators of the mineralization process of hard tissues in rats, in the case of using 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and acetylsalicylic acid or α-tocopherol. The experiment was carried out on eight female rats of the Buffalo strain divided into four groups. From the offspring of eight females, the mandibles were removed from the mandibular joints, and then, after the removal of soft tissues, they were prepared for individual tests. Selected morphological, chemical and physical parameters of the teeth of the offspring of female rats from the experimental groups were analyzed. The analysis showed the effect of vitamin E and ASA on the content of Mg, Ca and P. In combination with TCDD, vitamin E and ASA, they positively inhibit the inflammatory process, preventing the leaching of Ca and Mg from the bones. ASA counteracted this phenomenon much more effectively than vitamin E. Detailed analysis of the tooth morphology showed that the molars' crowns exhibit shape disturbances under the influence of TCDD. Individual nodules in teeth T1, T2, T3 did not fuse, and the roots showed signs of hypertrophy. The study confirmed the negative effect of TCDD on tooth development. Teeth arising early in development are the most sensitive to the disorders, while the later ones are less exposed to the toxic effects of TCDD transmitted by the mother.

Nature-Derived and Synthetic Additives to poly(ɛ-Caprolactone) Nanofibrous Systems for Biomedicine; an Updated Overview

As a low cost, biocompatible, and bioresorbable synthetic polymer, poly (ɛ-caprolactone) (PCL) is widely used for different biomedical applications including drug delivery, wound dressing, and tissue engineering. An extensive range of in vitro and in vivo tests has proven the favourable applicability of PCL in biomedicine, bringing about the FDA approval for a plethora of PCL made medical or drug delivery systems. This popular polymer, widely researched since the 1970s, can be readily processed through various techniques such as 3D printing and electrospinning to create biomimetic and customized medical products. However, low mechanical strength, insufficient number of cellular recognition sites, poor bioactivity, and hydrophobicity are main shortcomings of PCL limiting its broader use for biomedical applications. To maintain and benefit from the high potential of PCL, yet addressing its physicochemical and biological challenges, blending with nature-derived (bio)polymers and incorporation of nanofillers have been extensively investigated. Here, we discuss novel additives that have been meant for enhancement of PCL nanofiber properties and thus for further extension of the PCL nanofiber application domain. The most recent researches (since 2017) have been covered and an updated overview about hybrid PCL nanofibers is presented with focus on those including nature-derived additives, e.g., polysaccharides and proteins, and synthetic additives, e.g., inorganic and carbon nanomaterials.

Bone toxicity induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the retinoid system: A causality analysis anchored in osteoblast gene expression and mouse data

Dioxin exposures impact on bone quality and osteoblast differentiation, as well as retinoic acid metabolism and signaling. In this study we analyzed associations between increased circulating retinol concentrations and altered bone mineral density in a mouse model following oral exposure to 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD). Additionally, effects of TCDD on differentiation marker genes and genes involved with retinoic acid metabolism were analysed in an osteoblast cell model followed by benchmark dose-response analyses of the gene expression data. Study results show that the increased trabecular and decreased cortical bone mineral density in the mouse model following TCDD exposure are associated with increased circulating retinol concentrations. Also, TCDD disrupted the expression of genes involved in osteoblast differentiation and retinoic acid synthesis, degradation, and nuclear translocation in directions compatible with increasing cellular retinoic acid levels. Further evaluation of the obtained results in relation to previously published data by the use of mode-of-action and weight-of-evidence inspired analytical approaches strengthened the evidence that TCDD-induced bone and retinoid system changes are causally related and compatible with an endocrine disruption mode of action.

Smoking and the patient with a complex lower limb injury

Smoking is known to increase the risk of peri-operative complications in Orthoplastic surgery by impairing bone and wound healing. The effects of nicotine replacement therapies (NRTs) and electronic cigarettes (e-cigarettes) has been less well established. Previous reviews have examined the relationship between smoking and bone and wound healing separately. This review provides surgeons with a comprehensive and contemporaneous account of how smoking in all forms interacts with all aspects of complex lower limb trauma. We provide a guide for surgeons to refer to during the consent process to enable them to tailor information towards smokers in such a way that the patient may understand the risks involved with their surgical treatment. We update the literature with recently discovered methods of monitoring and treating the troublesome complications that occur more commonly in smokers effected by trauma.

Resveratrol and Its Analogs as Functional Foods in Periodontal Disease Management

Periodontitis is a common chronic inflammatory disease driven by the interaction between a dysbiotic oral microbiome and the dysregulated host immune-inflammatory response. Naturally derived nutraceuticals, such as resveratrol and its analogs, are potential adjunctive therapies in periodontal treatment due to their antimicrobial and anti-inflammatory properties. Furthermore, different analogs of resveratrol and the choice of solvents used may lead to varying effects on therapeutic properties. This review presents the current findings and gaps in our understanding on the potential utility of resveratrol and its analogs in periodontal treatment.

Bone Disruption and Environmental Pollutants

BACKGROUND

Endocrine Disrupting Chemicals (EDCs) are ubiquitous and may significantly contribute in environmental pollution, thus contaminating humans and wildlife. Environmental pollutants could interfere with bone homeostasis by means of different mechanisms, which include hormonal imbalance, direct osteoblasts toxicity and enanchment of osteoclasts activity, thus leading to osteopenia or osteoporosis. Among these, bisphenols, dioxins, polycyclic aromatic hydrocarbons, polychlorobiphenyls, poly- and perfluoroalkyls, phthalates, parabens, organotins and cadmium may play a role in bone distuption.

METHODS

PubMed/MEDLINE, ISI-web of knowledge and Google scholar databases were searched for medical subject headings terms and free-text word related to the aforementioned classes of chemicals and bone metabolism and remodelling for better clarifying and understanding the main mechanisms of bone disruption.

RESULTS

Several of EDCs act as xenoestrogens. Considering that estrogens play a significant role in regulating bone remodeling, most of these chemicals generate hormonal imbalance with possible detrimental consequences on bone tissue structure and its mechanical and non-mechanical properties.

DISCUSSION

A lot of evidences about bone distruptors came from in vitro studies or animal models, and conduct to equivocal results. In addition, a few data derived form humans and most of these data focused on the impact of EDCs on bone mineral density without considering their influence on long-term fracture risk. Moreover, it should be taken into account that humans are exposed to a mixture of EDCs and the final effect on bone metabolism might be the result of either a synergism or antagonist effects among them. Age of first exposure, cumulative dose exposure over time, and the usually observed non-monotonic dose-response curve for EDCs should be considered as other important variable influencing the final effect on bone metabolism.

CONCLUSION

Taking into account these variables, observational studies are needed to better analyze this issue both for echological purpose and to preserve bone health.

Endocrine Disruptors as a New Etiologic Factor of Bone Tissue Diseases (Review)

At present, diseases of bones and joints stand third after cardiovascular and oncological pathologies which demands the necessity of searching for new etiological factors and pathogenetical mechanisms of these illnesses. The accumulating data show the association between the impairment of bone tissue development and regeneration and endocrine disruptor impact. Endocrine disruptors are chemical substances, mainly of anthropogenic origin, capable of affecting endocrine system functioning and interfering with organ morphogenesis and physiological functions. The development and regeneration of bone tissues have a complex hormonal regulation and therefore bone tissue cells, osteoblasts, and osteoclasts can be considered as potential targets for endocrine disruptors. Endocrine disruptors have been established to be able to impair calcium metabolism which also contributes to the development of musculoskeletal system pathology. Data on histogenesis of bone tissue and regeneration, calcium metabolism as well as on hormonal regulation of bone growth and remodeling processes are presented in this work. Recent information on the effect of the main endocrine disruptor classes (diethylstilbestrol, organochlorine pesticides, alkylphenols, bisphenol A, dioxins, polychlorinated biphenyls, and phthalic acid esters) on the development and remodeling of bone tissues and calcium metabolism has been summarized. The established physiological and molecular mechanisms of their action have been also considered.

Benzo[a]pyrene injures BMP2-induced osteogenic differentiation of mesenchymal stem cells through AhR reducing BMPRII

Benzo[a]pyrene(BaP), a polycyclic aromatic hydrocarbons (PAH) of environmental pollutants, is one of the main ingredients in cigarettes and an agonist of the aryl hydrocarbon receptor (AhR). Mesenchymal stem cells (MSCs) including C3H10T1/2 and MEF cells, adult multipotent stem cells, can be differentiated toward osteoblasts during the induction of osteogenic induction factor-bone morphogenetic protein 2(BMP2). Accumulating evidence suggests that BaP decreases bone development in mammals, but the further mechanisms of BaP on BMP2-induced bone formation involved are unknown. Here, we researched the role of BaP on BMP2-induced osteoblast differentiation and bone formation. We showed that BaP significantly suppressed early and late osteogenic differentiation, and downregulated the runt-related transcription factor 2(Runx2), osteocalcin(OCN) and osteopontin (OPN) during the induction of BMP2 in MSCs. Consistent with in vitro results, administration of BaP inhibited BMP2-induced subcutaneous ectopic osteogenesis in vivo. Interestingly, blocking AhR reversed the inhibition of BaP on BMP2-induced osteogenic differentiation, which suggested that AhR played an important role in this process. Moreover, BaP significantly decreased BMP2-induced Smad1/5/8 phosphorylation. Furthermore, BaP significantly reduced bone morphogenetic protein receptor 2(BMPRII) expression and excessively activated Hey1. Thus, our data demonstrate the role of BaP in BMP2-induced bone formation and suggest that impaired BMP/Smad pathways through AhR regulating BMPRII and Hey1 may be an underlying mechanism for BaP inhibiting BMP2-induced osteogenic differentiation.

Periodontitis is an inflammatory disease of oxidative stress: We should treat it that way

Periodontitis is a highly prevalent disease. As it progresses, it causes serious morbidity in the form of periodontal abscesses and tooth loss and, in the latter stages, pain. It is also now known that periodontitis is strongly associated with several nonoral diseases. Thus, patients with periodontitis are at greater risk for the development and/or exacerbation of diabetes, chronic obstructive pulmonary disease, and cardiovascular diseases, among other conditions. Although it is without question that specific groups of oral bacteria which populate dental plaque play a causative role in the development of periodontitis, it is now thought that once this disease has been triggered, other factors play an equal, and possibly more important, role in its progression, particularly in severe cases or in cases that prove difficult to treat. In this regard, we allude to the host response, specifically the notion that the host, once infected with oral periodontal pathogenic bacteria, will mount a defense response mediated largely through the innate immune system. The most abundant cell type of the innate immune system - polymorphonuclear neutrophils - can, when protecting the host from microbial invasion, mount a response that includes upregulation of proinflammatory cytokines, matrix metalloproteinases, and reactive oxygen species, all of which then contribute to the tissue damage and loss of teeth commonly associated with periodontitis. Of the mechanisms referred to here, we suggest that upregulation of reactive oxygen species might play one of the most important roles in the establishment and progression of periodontitis (as well as in other diseases of inflammation) through the development of oxidative stress. In this overview, we discuss both innate and epigenetic factors (eg, diabetes, smoking) that lead to the development of oxidative stress. This oxidative stress then provides an environment conducive to the destructive processes observed in periodontitis. Therefore, we shall describe some of the fundamental characteristics of oxidative stress and its effects on the periodontium, discuss the diseases and other factors that cause oxidative stress, and, finally, review potentially novel therapeutic approaches for the management (and possibly even the reversal) of periodontitis, which rely on the use of therapies, such as resveratrol and other antioxidants, that provide increased antioxidant activity in the host.

The Protective Effect of Xanthohumol on the Content of Selected Elements in the Bone Tissue for Exposed Japanese Quails to TCDD

Dioxins (including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are highly toxic and persistent chemicals widely distributed in the environment in trace amounts, and are side products of industrial and chemical processes. Exposure to dioxins leads to multiorgan morphological and functional abnormalities, including within the bone tissue, disrupting its microarchitecture and mechanical properties. Xanthohumol (XN) is a chemical compound classified as a prenylated flavonoid, distinguished by multidirectional biological action. The aim of the study is to assess whether xanthohumol, as a substance with strong antioxidant and anti-inflammatory properties, has the ability to eliminate the negative effects of TCDD on bone tissue. The experiment was conducted on adult Japanese quails. Two different doses of TCDD and xanthohumol were administered to birds. After euthanasia of animals, the research material in the form of cranial vault and hind limb bone was collected, and their mineral compositions of calcium, phosphorus, magnesium, zinc, and iron concentrations were determined using atomic emission spectrometry in an acetylene-air flame method. Our results indicate that the administration of TCDD at a low dose causes more dynamic changes in the concentration of elements in bone, in comparison to a higher dose of dioxin. Results show also that higher doses of the XN cause the linear increase in the concentration of phosphorus and iron in the bone of the hind limb, and calcium in the bones of the cranial vault. In conclusion, our experiment shows that the use of TCDD and XN in Japanese quails together in various doses influences the content of phosphorus, magnesium, zinc, and iron in the research material.

Molecular and cellular mechanisms linking air pollution and bone damage

Air pollution is the second most important risk factor associated with noncommunicable diseases after smoking. The effects of pollution on health are commonly attributable to particulate matter (PM), a complex mixture of particles suspended in the air. PM can penetrate the lower respiratory tract and has harmful direct and indirect effects on different organs and tissues. Direct effects are caused by the ability of PM components to cross the respiratory membrane and enter the bloodstream; indirect effects are systemic consequences of the local airway response. Recent work suggests that PM is an independent risk factor for low bone mineral density and osteoporosis-related fractures. Osteoporosis is a common age-related disease closely linked to bone fractures, with severe clinical consequences affecting quality of life, morbidity, and mortality. In this review, we discuss potential mechanisms behind the association between outdoor air pollution, especially PM, and bone damage. The discussion features four main mechanisms: 1) several different atmospheric pollutants can induce low-grade systemic inflammation, which affects bone metabolism through a specific effect of cytokines such as TNFα, IL-1β, IL-6, and IL-17 on osteoblast and osteoclast differentiation and function; 2) some pollutants, particularly certain gas and metal compounds, can cause oxidative damage in the airway and bone cells; 3) different groups of pollutants can act as endocrine disruptors when binding to the receptors in bone cells, changing their functioning; and 4) air pollution can directly and indirectly cause vitamin D deficiency. Characterizing these mechanisms will better define the physiopathology of bone damage, and recognizing air pollution as a modifiable risk factor for osteoporosis will inform environmental policies. Such knowledge will also guide the prevention of fractures due to fragility and help reduce health-related costs.

Immune Th17 lymphocytes play a critical role in the multiple beneficial properties of resveratrol

Modulation of the inflammatory response is one of the major issues of the 21st century due to its importance in the occurrence of various pathologies (cancer, autoimmune diseases, degenerative diseases) and their progression over time. Whether acute or chronic, the inflammatory response is directly related to the immune response through different subtypes of T lymphocytes. In addition, among the compounds capable of modulating the cells of the immune system, resveratrol, a polyphenol with pleiotropic biological properties, seems to be a good candidate. Indeed, resveratrol is able to alter the immune response by modulating the process of lymphocyte differentiation and subsequently diminishing the inflammatory-associated response. More specifically, thanks to its ability to act as a sirtuin-1 agonist, it can deacetylate the transcription factor STAT3 and alter nuclear factors essential to the process of lymphocyte differentiation. We present and discuss these different aspects in relation to various pathologies and how the alteration of the ratios between the different lymphocyte subtypes by resveratrol is an important element to take into account when studying its anti-inflammatory and immunomodulatory properties.

The Effects of Astaxanthin on Proliferation and Differentiation of MG-63 Osteosarcoma Cells via Aryl Hydrocarbon Receptor (AhR) Pathway: A Comparison with AhR Endogenous Ligand

Background: Osteosarcoma (OS) is the most prevalent bone-related malignancy with a high mortality rate among children and adolescents. In the present study, first we explored the effects of astaxanthin (AST) on proliferation and differentiation of the MG-63 osteosarcoma cell line, and then compared its effects with AhR endogenous ligand (FICZ).Methods: Cell proliferation and cytotoxicity assay were performed using MTT. To identify possible mechanisms underlying AST-induced changes in osteogenic metabolism via the AHR pathway, we defined changes in CYP1A1, osteocalcin, osteopontin, type I collagen, and Runx2 gene expression using RT-PCR.Results: AST upregulated CYP1A1, osteocalcin, osteopontin, type I collagen, and Runx2 expression in trends of increasing its concentration. FICZ showed a biphasic effect on MG-63 cell proliferation. At high concentrations, it significantly decreased the cell viability, while at lower concentrations it was increased as compared to the control. Increasing FICZ concentrations from 1 nm to 1 μM, down-regulated the expression of Runx2, osteopontin, osteocalcin and collagen type 1 at the transcriptional levels. It seems that AST can augment the proliferation and differentiation of MG-63 via the AhR-dependent pathway, while FICZ suppresses the proliferation and differentiation of MG-63.Conclusion: We concluded that various AhR ligands show different behaviors in the modulation of MG-63 cells.

The Protective Effect of α-Tocopherol on the Content of Selected Elements in the Calvaria for Exposed Hens to TCDD in the Early Embryonic Period

This paper focuses on negative effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on element content in male chicken calvaria and α-tocopherol (vitamin E) ability to reduce its toxic potential on bone mineralization in offspring. In the experiment carried out once, a solution containing only DMSO, TCDD, TCDD + α-tocopherol, and exclusively α-tocopherol was administrated. Subsequently, on the 5th day after hatching, the mineral composition of the chicken calvaria was evaluated. The results obtained suggest that the use of α-tocopherol contributes to the maintenance of the concentration of calcium, magnesium, and manganese in the chicken calvaria treated with TCDD in the embryonic period. In turn, vitamin E increases the level of zinc. It has been found that α-tocopherol in chicken embryos has a protective effect against disturbance of level of chosen trace elements in the bones of offspring caused by the TCDD.

The Effect of Proton Pump Inhibitors on Bone Formation in a Rat Spinal Arthrodesis Model

STUDY DESIGN

Rat posterolateral arthrodesis model.

OBJECTIVE

Quantify the impact of administration of a proton pump inhibitor on spine fusion.

SUMMARY OF BACKGROUND DATA

Proton pump inhibitors (PPIs) are widely used for gastrointestinal disorders and for ulcer prophylaxis in patients taking non-steroidal anti-inflammatory drugs. PPIs cause chronic acid suppression which has been found to result in decreased bone mineral density, increased fracture risk, and impaired fracture healing. Despite advances in surgical techniques, pseudarthrosis still occurs in up to 24% of patients requiring revision surgery following spinal fusion procedures. Thus, there are likely many unidentified risk factors. While PPIs have been hypothesized to impact fracture healing, no study has evaluated their effect on spine arthrodesis rates.

METHODS

Thirty-eight female rats underwent posterolateral lumbar spinal fusion. Rats were divided into two groups: normal saline control and pantroprazole, which was administered by daily intraperitoneal injections. At 8 weeks postoperative spines were evaluated with manual palpation, microCT, histologic analysis, and biomechanical testing.

RESULTS

Fusion rates of the control group and PPI group were not significantly different (100% vs. 94%). Average fusion scores were significantly lower in the pantoprazole group. New bone formation identified on microCT imaging of bilaterally fused specimens demonstrated a lower average volume of newly generated bone in the PPI group, but this difference was not significant. Biomechanical testing demonstrated no significant difference in strength or stiffness of the fusion mass between the groups.

CONCLUSION

This study demonstrates that administration of PPIs does not inhibit fusion rates, bone formation, or affect biomechanical integrity of fusion. However, lower fusion scores in the PPI group suggest that a negative impact may still exist. Future studies will explore growth factor and protein expression in the fusion masses as well as utilize higher doses of PPI to fully discern their effect on spine fusion.

LEVEL OF EVIDENCE

N/A.

Indirect study of the effect of α-tocopherol and acetylsalicylic acid on the mineral composition of bone tissue in the offspring of female rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin: long-term observations

This paper discusses problems related to the influence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the mineral composition of the calvaria in the offspring of female rats. The female rats were administered with a single dose of TCDD and subsequently, after three-weeks, with α-tocopherol or acetylsalicylic acid. The research focused on analysis of the main mineral elements (Ca, Mg, Fe, Zn). The aim of the study was to determine the effect of dioxins and various doses of drugs on bone mineral composition in a six-month observation period. The mineral composition was analyzed using an atomic spectrometry method. Data were statistically analyzed and verified at a significance level of p = 0.05. The use of α-tocopherol normalizes bone resorption and formation disturbed by TCDD, maintaining the content of the studied elements at the physiological level. In turn, administration of acetylsalicylic acid limits the bone resorption process, which affects the element content.

Resveratrol attenuates oxidative stress during experimental periodontitis in rats exposed to cigarette smoke inhalation

OBJECTIVES

This study aimed at investigating the effect of the systemic administration of resveratrol (RESV) on oxidative stress during experimental periodontitis in rats subjected to cigarette smoke inhalation.

MATERIAL AND METHODS

Experimental periodontitis (EP) was induced in 26 male Wistar rats by the insertion of a ligature around one of the first mandibular and maxillary molars. The animals were assigned randomly to the following groups: cigarette smoke inhalation (CSI; 3 times/d, 8 minutes/d) + resveratrol (10 mg/Kg), that is, SMK + RESV (n = 13) and cigarette smoke inhalation + placebo, that is, SMK + PLAC (n = 13). The substances were administered daily for 30 days (19 days prior and 11 days following EP induction), and then, the animals were euthanized. The maxillary specimens were processed for morphometric analysis of bone loss, and the tissue surrounding the first maxillary molars was collected for mRNA quantification of Sirtuin 1 (SIRT1) by real-time PCR. The gingival tissues surrounding the mandibular first molars were collected for quantification of superoxide dismutase 1 (SOD1) and nicotinamide adenine dinucleotide phosphatase oxidase (NADPH) using an ELISA assay.

RESULTS

Reduced bone loss was demonstrated in animals in the SMK + RESV group as compared to those in the SMK + PLAC (P < 0.05) group on the basis of morphometric analysis. Resveratrol promoted higher levels of SIRT and SOD (P < 0.05) as well as reduced levels of NADPH oxidase (P < 0.05) were found in tissues derived from animals in the SMK + RESV group when compared to those in the SMK + PLAC group.

CONCLUSION

Resveratrol is an efficient therapeutic agent that reduces exacerbation of bone loss found in animals with EP that were also exposed to smoke. The results suggest that its effects could be mediated, at least in part, by its antioxidant and anti-inflammatory properties which attenuate the effects of oxidative stress on EP in the presence of cigarette smoke.

Osteotoxicity of 3-methylcholanthrene in fish

Many chemicals produced by human activities end up in the aquatic ecosystem causing adverse developmental and reproductive effects in aquatic organisms. There is evidence that some anthropogenic chemicals disturb bone formation and skeletal development but the lack of suitable in vitro and in vivo systems for testing has hindered the identification of underlying mechanisms of osteotoxicity. Several fish systems - an in vitro cell system to study extracellular matrix mineralization and in vivo systems to evaluate bone formation and skeletogenesis - were combined to collect data on the osteotoxic activity of 3-methylcholanthrene (3-MC), a polycyclic aromatic hydrocarbon. Anti-mineralogenic effects, increased incidence of skeletal deformities and reduced bone formation and regeneration were observed in zebrafish upon exposure to 3-MC. Pathway reporter array revealed the role of the aryl hydrocarbon receptor 2 (Ahr2) in the mechanisms underlying 3-MC osteotoxicity in mineralogenic cell lines. Analysis of gene expression in zebrafish larvae confirmed the role of Ahr2 in the signaling of 3-MC toxicity. It also indicated a possible complementary action of the pregnane X receptor (Pxr) in the regulation of genes involved in bone cell activity and differentiation but also in xenobiotic metabolism. Data reported here demonstrated the osteotoxicity of 3-MC but also confirmed the suitability of fish systems to gain insights into the toxic mechanisms of compounds affecting skeletal and bone formation.

Resveratrol restores the level of key inflammatory cytokines and RANKL/OPG ratio in the femur of rat osteoporosis model

Resveratrol's effect on bone mineral density (BMD) and expression of cytokines in ovariectomized rats (postmenopausal osteoporosis model) was studied. The study was conducted on 3-month-old Sprague-Dawley rats that were (a) sham-operated, (b) ovariectomized, (c) ovariectomized and treated with β-estradiol (487.5 µg/kg weight/day), and (d) ovariectomized and treated with resveratrol (625 µg/Kg body weight/day). The treatment was for 4 weeks. After sacrifice BMD and gene expression (RANKL, OPG, IL-23, and IL-17A, IL-1β, and TNFα) were measured in tibia and femur respectively. Resveratrol could restore RANKL/OPG ratio, slightly increase BMD, and moderately but significantly reduce IL-23, IL-17A, IL-1β, and TNF-α cytokine expression levels.

Resveratrol Reverts Epigenetic and Transcription Changes Caused by Smoke Inhalation on Bone-Related Genes in Rats

We investigated the effects of cigarette smoke (CS) and resveratrol intake on the modulation of bone repair-related genes through epigenetic mechanisms at the global and gene-specific levels, after 30 days of calvarial defects were created, in rats. The samples were assigned to three groups as follows: no CS, CS, and CS/resveratrol. After evaluation of global (5 hmC) changes and epigenetic and transcription regulation at gene-specific levels, CS group showed increased 5 hmC and Tets transcripts with demethylation at Rankl and Trap promoters (p ≤ 0.01), linked to their increased gene expression (p ≤ 0.001). These modifications were reverted in the CS/resveratrol group. Opposite patterns were observed among CS and CS/resveratrol for epigenetic enzyme transcripts with higher levels of Dnmts in the CS/resveratrol (p ≤ 0.01). No CS and CS/resveratrol demonstrated similar gene expression levels for all Tets and bone-related genes. Resveratrol reverts epigenetic and transcription changes caused by CS at both global and gene-specific levels in bone-related and epigenetic machinery genes, emphasizing the resveratrol as biological modulator for CS in rats.

Modulating effect of selected pharmaceuticals on bone in female rats exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

This paper discusses the problems connected with the influence of TCDD on the mechanical properties and structure of the bone tissue in female rats treated with the dioxin. Moreover an analysis of the protective role of tocopherol, acetylsalicylic acid, dexamethazone and levamisol was performed. Rat tibiae were assessed by mechanical testing, and histological and trace element analysis. It was proved that TCDD has negative effect on bone mechanical properties, histological microstructure and trace element content. The results indicate that usage of both steroid and non-steroid anti-inflammatory medicaments, along with tocopherol and levamisol, modulating their activity, can reduce the negative effect of dioxin activity on the bone tissue of female rats intoxicated with TCDD.

Actein alleviates 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated cellular dysfunction in osteoblastic MC3T3-E1 cells

The environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is known to affect bone metabolism. We evaluated the protective effects of the triterpene glycoside actein from the herb black cohosh against TCDD-induced toxicity in MC3T3-E1 osteoblastic cells. We found that TCDD significantly reduced cell viability and increased apoptosis and autophagy in MC3T3-E1 osteoblastic cells (P < .05). In addition, TCDD treatment resulted in a significant increase in intracellular calcium concentration, mitochondrial membrane potential collapse, reactive oxygen species (ROS) production, and cardiolipin peroxidation, whereas pretreatment with actein significantly mitigated these effects (P < .05). The effects of TCDD on extracellular signal-related kinase (ERK), aryl hydrocarbon receptor, aryl hydrocarbon receptor repressor, and cytochrome P450 1A1 levels in MC3T3-E1 cells were significantly inhibited by actein. The levels of superoxide dismutase, ERK1, and nuclear factor kappa B mRNA were also effectively restored by pretreatment with actein. Furthermore, actein treatment resulted in a significant increase in alkaline phosphatase (ALP) activity and collagen content, as well as in the expression of genes associated with osteoblastic differentiation (ALP, type I collagen, osteoprotegerin, bone sialoprotein, and osterix). This study demonstrates the underlying molecular mechanisms of cytoprotection exerted by actein against TCDD-induced oxidative stress and osteoblast damage.

Impact of resveratrol on bone repair in rats exposed to cigarette smoke inhalation: histomorphometric and bone-related gene expression analysis

This study investigated the effect of resveratrol on bone healing and its influence on the gene expression of bone-related markers in rats exposed to cigarette smoke. Two calvarial defects were created in each of 60 rats, which were assigned equally (n=20) to three groups: (1) resveratrol (10mg/kg)+smoke exposure (SMK+RESV); (2) placebo+smoke exposure (SMK+PLA); or (3) placebo+no smoke exposure (NS+PLA). Substances were administered daily for 30days following surgery. Smoke inhalation was started 7days before surgery and continued for 30days after surgery. One defect was processed for histomorphometric analysis and the other was used for mRNA quantification of bone-related gene expression by qPCR. The remaining defect was smaller in the SMK+RESV (2.27±0.61mm, P=0.0003) and NS+PLA (2.17±0.74mm, P=0.0005) groups than in the SMK+PLA group (3.12±0.47mm). Higher levels of Runx2 were observed in the NS+PLA group than in the smoke exposure groups (vs. SMK+PLA, P=0002; vs. SMK+RESV, P=0.052); levels of Lrp-5 were also higher in the no smoke exposure group (vs. SMK+RESV, P=0.009; vs. SMK+PLA, P=0.003). Resveratrol therapy decreased RANKL/OPG expression when compared to placebo (SMK+RESV vs. SMK+PLA, P=0.017). Dkk1 levels were decreased in the SMK+RESV group when compared to the SMK+PLA (P=0.006) and NS+PLA groups (P=0.005). In conclusion, resveratrol optimizes the repair of critical-sized bone defects, up-regulating the gene expression of important bone remodelling markers in rats exposed to cigarette smoke inhalation.

Effect of Resveratrol on Critical-Sized Calvarial Defects of Diabetic Rats: Histometric and Gene Expression Analysis

PURPOSE

This study investigated the influence of resveratrol (RESV) on the repair of bone critical defects in calvaria of animals with induced diabetes mellitus (DM).

MATERIAL AND METHODS

One hundred rats were divided into 5 groups: induced DM + RESV administration (DM + RESV; n = 20); induced DM plus placebo solution administration (DM + PLAC; n = 20); induced DM plus insulin therapy (DM + INS; n = 20); induced DM plus administration of RES and INS (DM + RESV + INS; n = 20); and nondiabetic controls (NDM; n = 20). DM was induced by intraperitoneal injection of streptozotocin 50 mg/kg 3 days before the surgical procedures. Two critical calvarial defects were created in each animal at the start of the study (day 0). Treatments were administered from day 0 to day 30 of the experiment, when animals were euthanized. One defect was processed for histometric analysis to measure closure of the bone defect. The tissue of the other defect was analyzed for quantification of bone morphogenetic protein-2 (BMP-2), osteopontin, osteoprotegerin, receptor activator of nuclear factor-κB ligand, runt-related transcription factor-2, osterix (Osx), β-catenin, lipoprotein receptor-related protein-5, and dikkop-1 mRNA by quantitative polymerase chain reaction.

RESULTS

Histometric results showed that the DM + RESV, DM + RESV + INS, and NDM groups exhibited greater closure of the bone defects compared with the PLAC- or INS-treated groups (P < .05). Diabetic animals treated with RESV plus INS showed higher levels of BMP-2 and Osx; Osx also was positively increased in animals treated with INS alone (P < .05).

CONCLUSIONS

The use of RESV, regardless of the presence of INS, positively influenced bone repair in animals with induced DM. Further, the combination of INS plus RESV was necessary for the modulation of BMP-2 gene expression.

Resveratrol has anti-thyroid effects both in vitro and in vivo

Resveratrol is a natural polyphenol with antioxidant, anti-inflammatory, and antiproliferative properties. We have shown previously that resveratrol decreases sodium/iodide symporter expression and iodide uptake in thyrocytes, both in vitro and in vivo. In the present study, we further investigated the effects of resveratrol, with evaluation of the expression of additional thyroid-specific genes in the FRTL-5 rat thyroid cell line: thyroglobulin, thyroid peroxidase, TSH receptor, Nkx2-1, Foxe1 and Pax8. We observed decreased expression of these genes in FRTL-5 cells treated with 10 μM resveratrol. The effects of resveratrol was further evaluated in vivo using Sprague-Dawley rats treated with resveratrol 25 mg/kg body weight intraperitoneally, for 60 days. No clinical signs of hypothyroidism were seen, although the treated rats showed significant increase in thyroid size. Serum TSH and thyroid hormone levels were in the normal range, with significantly higher TSH seen in resveratrol-treated rats, compared with control rats. Histological and immunohistochemical analyses confirmed increased proliferative activity in the thyroid from resveratrol-treated rats. These data suggest that resveratrol acts as a thyroid disruptor and a goitrogen, which indicates the need for caution as a supplement and for therapeutic uses.

Benzo[a]pyrene impedes self-renewal and differentiation of mesenchymal stem cells and influences fracture healing

Mesenchymal stem cells (MSCs) are implicated in the bone-forming process during fracture repair. Benzo[a]pyrene (BaP)-a cigarette smoke component and powerful motivator of the aryl hydrocarbon receptor (Ahr)-unfavorably influences bone condition and osteoblast differentiation. The first thing we noticed decreases self-renewal and differentiation of human bone marrow mesenchymal stem (hBM-MSCs) from smokers and activates Ahr signaling in MSCs by up-regulating the Ahr target gene cytochrome P450 (CYP) 1B1 expression. In vitro studies, we employed C3H10T1/2 and bone marrow mesenchymal stem cells (BM-MSCs) with BaP and discovered that BaP impaired innate properties of MSCs. Further investigation into MSCs showed that exposure to BaP activated Ahr signaling and inhibited TGF-β1/SMAD4 and TGF-β1/ERK/AKT signaling pathways. Corresponding with the outcomes, tibial fracture calluses produced by BaP-administered rats appeared to delay healing. This effect of BaP was abrogated by resveratrol, a natural Ahr antagonist, in vitro and in vivo. These data demonstrated that Ahr may play a key role in BaP-impaired innate properties by inhibiting SMAD-dependent signaling pathways TGF-β1/SMAD4 and SMAD-independent TGF-β1/ERK/AKT signaling pathways. Furthermore, resveratrol inhibited MSCs from adverse effects caused by BaP.

Janus-faced Acrolein prevents allergy but accelerates tumor growth by promoting immunoregulatory Foxp3+ cells: Mouse model for passive respiratory exposure

Acrolein, a highly reactive unsaturated aldehyde, is generated in large amounts during smoking and is best known for its genotoxic capacity. Here, we aimed to assess whether acrolein at concentrations relevant for smokers may also exert immunomodulatory effects that could be relevant in allergy or cancer. In a BALB/c allergy model repeated nasal exposure to acrolein abrogated allergen-specific antibody and cytokine formation, and led to a relative accumulation of regulatory T cells in the lungs. Only the acrolein-treated mice were protected from bronchial hyperreactivity as well as from anaphylactic reactions upon challenge with the specific allergen. Moreover, grafted D2F2 tumor cells grew faster and intratumoral Foxp3+ cell accumulation was observed in these mice compared to sham-treated controls. Results from reporter cell lines suggested that acrolein acts via the aryl-hydrocarbon receptor which could be inhibited by resveratrol and 3′-methoxy-4′-nitroflavone Acrolein- stimulation of human PBMCs increased Foxp3+ expression by T cells which could be antagonized by resveratrol. Our mouse and human data thus revealed that acrolein exerts systemic immunosuppression by promoting Foxp3+ regulatory cells. This provides a novel explanation why smokers have a lower allergy, but higher cancer risk.

Mechanistic insight into the effects of Aryl Hydrocarbon Receptor activation on osteogenic differentiation

While inhibition of bone healing and increased rates of pseudarthrosis are known adverse outcomes associated with cigarette smoking, the underlying mechanisms by which this occurs are not well understood. Recent work has implicated the Aryl Hydrocarbon Receptor (Ahr) as one mediator of the anti-osteogenic effects of cigarette smoke (CS), which contains numerous toxic ligands for the Ahr. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) is a high-affinity Ahr ligand frequently used to evaluate Ahr pathway activation. The purpose of this study was to elucidate the downstream mechanisms of dioxin action on bone regeneration and investigate Ahr antagonism as a potential therapeutic approach to mitigate the effects of dioxin on bone. Markers of osteogenic activity and differentiation were assessed in primary rat bone marrow stromal cells (BMSC) after exposure to dioxin, Ahr antagonists, or antagonist + dioxin. Four Ahr antagonists were evaluated: α-Naphthoflavone (ANF), resveratrol (Res), 3,3′-Diindolylmethane (DIM), and luteolin (Lut). Our results demonstrate that dioxin inhibited ALP activity, migratory capacity, and matrix mineralization, whereas co-treatment with each of the antagonists mitigated these effects. Dioxin also inhibited BMSC chemotaxis, while co-treatment with several antagonists partially rescued this effect. RNA and protein expression studies found that dioxin down-regulated numerous pro-osteogenic targets, whereas co-treatment with Ahr antagonists prevented these dioxin-induced expression changes to varying degrees. Our results suggest that dioxin adversely affects bone regeneration in a myriad of ways, many of which appear to be mediated by the Ahr. Our work suggests that the Ahr should be investigated as a therapeutic target to combat the adverse effects of CS on bone healing.

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Dioxin, a potent Ahr ligand, inhibits osteogenic differentiation of BMSC.

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“Nutraceutical” Ahr antagonists found in red wine and broccoli protected against dioxin action.

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Targets of dioxin action included Collagens, MMPs, Phex, CXCR4/CXCL12 axis.

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The Ahr may in part mediate the adverse effects of cigarette smoke on osteogenic differentiation and bone healing.

From the Cover: Embryonic Exposure to TCDD Impacts Osteogenesis of the Axial Skeleton in Japanese medaka, Oryzias latipes

Recent studies from mammalian, fish, and in vitro models have identified bone and cartilage development as sensitive targets for dioxins and other aryl hydrocarbon receptor ligands. In this study, we assess how embryonic 2,3,7,8-tetrachlorochlorodibenzo-p-dioxin (TCDD) exposure impacts axial osteogenesis in Japanese medaka (Oryzias latipes), a vertebrate model of human bone development. Embryos from inbred wild-type Orange-red Hd-dR and 3 transgenic medaka lines (twist:EGFP, osx/sp7:mCherry, col10a1:nlGFP) were exposed to 0.15 nM and 0.3 nM TCDD and reared until 20 dpf. Individuals were stained for mineralized bone and imaged using confocal microscopy to assess skeletal alterations in medial vertebrae in combination with a qualitative spatial analysis of osteoblast and osteoblast progenitor cell populations. Exposure to TCDD resulted in an overall attenuation of vertebral ossification characterized by truncated centra, and reduced neural and hemal arch lengths. Effects on mineralization were consistent with modifications in cell number and cell localization of transgene-labeled osteoblast and osteoblast progenitor cells. Endogenous expression of osteogenic regulators runt-related transcription factor 2 (runx2) and osterix (osx/sp7), and extracellular matrix genes osteopontin (spp1), collagen type I alpha I (col1), collagen type X alpha I (col10a1), and osteocalcin (bglap/osc) was significantly diminished at 20 dpf following TCDD exposure as compared with controls. Through global transcriptomic analysis more than 590 differentially expressed genes were identified and mapped to select pathological states including inflammatory disease, connective tissue disorders, and skeletal and muscular disorders. Taken together, results from this study suggest that TCDD exposure inhibits axial bone formation through dysregulation of osteoblast differentiation. This approach highlights the advantages and sensitivity of using small fish models to investigate how xenobiotic exposure may impact skeletal development.

Effects of resveratrol and cigarette smoking onbone healing: histomorphometric evaluation

BACKGROUND/AIM

The aim of the present study is to investigate the effects of cigarette smoke (CS) and simultaneous application of resveratrol on bone healing histomorphometrically and to evaluate the effects of resveratrol on negative effects of CS.

MATERIALS AND METHODS

For 4 weeks, Sprague Dawley rats were exposed to cigarette smoke at the equivalent of 6 cigarettes per day. After this period, monocortical defects were created in femurs by a trephine bur on day 28. Starting from the day of defect creation to the 28th postoperative day, rats were given 20 mg/kg body weight resveratrol. Histomorphometric examination of the number of osteoblasts and osteoclasts, as well as new bone area, was conducted.

RESULTS

Investigations were carried out on 33 rats. Differences between osteoblast numbers in the control and CS groups were significant, and CS caused a reduction in the number of osteoblasts. Areas of new bone formation in the resveratrol and control groups were higher than in the smoking and smoking+resveratrol groups.

CONCLUSION

Smoking appeared to have adverse effects upon bone healing and resveratrol administration helped to reduce these effects.

Benzo[a]pyrene/aryl hydrocarbon receptor signaling inhibits osteoblastic differentiation and collagen synthesis of human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Cigarette smoking has detrimental effects on periodontal tissue, and is known to be a risk factor for periodontal disease, including the loss of alveolar bone and ligament tissue. However, the direct effects of cigarette smoking on periodontal tissue remain unclear. Recently, we demonstrated that benzo[a]pyrene (BaP), which is a prototypic member of polycyclic aryl hydrocarbons and forms part of the content of cigarettes, attenuated the expression of extracellular matrix remodeling-related genes in human periodontal ligament (PDL) cells (HPDLCs). Thus, we aimed to examine the effects of BaP on the osteoblastic differentiation and collagen synthesis of HPDLCs.

MATERIAL AND METHODS

HPDLCs were obtained from healthy molars of three patients, and quantitative reverse transcription-polymerase chain reaction were performed for gene expression analyses of cytochrome P450 1A1 and 1B1, alkaline phosphatase, bone sialoprotein and aryl hydrocarbon receptor (AhR), a receptor for polycyclic aryl hydrocarbons. We have also analyzed the role of the AhR, using 2-methyl-2H-pyrazole-3-carboxylic acid (2-methyl-4-o-tolylazo-phenyl)-amide (CH-223191), which is an AhR antagonist.

RESULTS

The treatment of HPDLCs with BaP reduced mRNA expression of osteogenic genes, alkaline phosphatase activity, mineralization and collagen synthesis. The treatment with CH-223191 subsequently restored the observed suppressive effects of BaP on HPDLCs.

CONCLUSIONS

The present results suggest that BaP exerts inhibitory effects on the maintenance of homeostasis in HPDL tissue, such as osteoblastic differentiation and collagen synthesis of HPDLCs, and that this signaling pathway could be suppressed by preventing the transactivity of AhR. Future studies may unveil a role for the inhibition of AhR as a promising therapeutic agent for periodontal disease caused by cigarette smoking.

Skeletal Effects of Smoking

Smoking is a leading cause of preventable death and disability. Smoking has long been identified as a risk factor for osteoporosis, with data showing that older smokers have decreased bone mineral density and increased fracture risk compared to nonsmokers, particularly at the hip. The increase in fracture risk in smokers is out of proportion to the effects on bone density, indicating deficits in bone quality. Advanced imaging techniques have demonstrated microarchitectural deterioration in smokers, particularly in the trabecular compartment. The mechanisms by which smoking affects skeletal health remain unclear, although multiple pathways have been proposed. Smoking cessation may at least partially reverse the adverse effects of smoking on the skeleton.

Premature aging in bone of fish from a highly polluted marine area

Fish species have attracted considerable interest in studies assessing biological responses to environmental contaminants. In this study, the attention has been focussed on fishbone of selected fish species from a highly polluted marine area, Augusta Bay (Italy, Central Mediterranean) to evaluate if toxicant elements had an effect on the mineralogical structure of bones, although macroscopic deformations were not evident. In particular, an attempt was made to evaluate if bone mineral features, such as crystallinity, mineral maturity and carbonate/phosphate mineral content, determined by XR-Diffraction and FT-IR Spectroscopy, suffered negative effects due to trace element levels in fishbone, detected by ICP-OES. Results confirmed the reliability of the use of diffractometric and spectroscopic techniques to assess the degree of crystallinity and the mineral maturity in fishbone. In addition, in highly polluted areas, Hg and Cr contamination induced a process of premature aging of fishbone, altering its biochemical and mineral contents.

Non-Nutrient, Naturally Occurring Phenolic Compounds with Antioxidant Activity for the Prevention and Treatment of Periodontal Diseases

One of the main factors able to explain the pathophysiological mechanism of inflammatory conditions that occur in periodontal disease is oxidative stress. Given the emerging understanding of this relationship, host-modulatory therapies using antioxidants could be interesting to prevent or slow the breakdown of soft and hard periodontal tissues. In this context, non-nutrient phenolic compounds of various foods and plants have received considerable attention in the last decade. Here, studies focusing on the relationship between different compounds of this type with periodontal disease have been collected. Among them, thymoquinone, coenzyme Q (CoQ), mangiferin, resveratrol, verbascoside and some flavonoids have shown to prevent or ameliorate periodontal tissues damage in animal models. However evidence regarding this effect in humans is poor and only limited to topical treatments with CoQ and catechins. Along with animal experiments, in vitro studies indicate that possible mechanisms by which these compounds might exert their protective effects include antioxidative properties, oxygen and nitrogen scavenging abilities, and also inhibitory effects on cell signaling cascades related to inflammatory processes which have an effect on RNS or ROS production as well as on antioxidant defense systems.

Dioxin Exposure Impairs BMP-2-Mediated Spinal Fusion in a Rat Arthrodesis Model

BACKGROUND

Cigarette smoking inhibits bone-healing and leads to increased rates of pseudarthrosis. However, the mechanisms behind these effects are controversial. Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin)--a cigarette smoke constituent and potent activator of the aryl hydrocarbon receptor (Ahr)--negatively impacts bone quality and osteoblast differentiation. We hypothesized that activation of the Ahr by dioxin would inhibit bone morphogenetic protein (BMP)-2-mediated spinal fusion in a rat arthrodesis model.

METHODS

Female Long-Evans rats were pretreated with dioxin or vehicle in six weekly doses, followed by bilateral posterior lumbar spinal fusion across the L4-L5 transverse processes using recombinant human BMP (rhBMP)-2. Treatments continued until sacrifice at four weeks postoperatively. A third group was treated with dioxin for six weeks, followed by a recovery period of four elimination half-lives to assess the reversible effects of dioxin exposure on spinal fusion capacity. Bone formation and fusion capacity were evaluated using fusion scoring, radiography, micro-computed tomography, and histologic analysis.

RESULTS

Fusion scores for dioxin-treated and dioxin-recovery rats were significantly lower than those for controls. Although fusion rates were also significantly reduced in dioxin-treated animals relative to controls (50% versus 100%, respectively), rates were not significantly reduced in dioxin-recovery animals (80%).

CONCLUSIONS

Dioxin treatment significantly inhibited spinal fusion in a rat arthrodesis model, and a prolonged cessation of dioxin exposure facilitated only a partial recovery of bone-healing capacity. This finding indicates that, although the effects of dioxin are persistent, an extended recovery from exposure could potentially restore bone regeneration in vivo.

CLINICAL RELEVANCE

Development of a pharmacologic agent that reduces the adverse effects of cigarette smoke on bone-healing could prove useful to orthopaedic surgeons. Since dioxin and other similar cigarette smoke toxins exert their effects through Ahr pathway activation, the receptor represents a potential therapeutic target to improve spinal fusion rates in patients who smoke.

Histopathological, ultrastructural, and immunohistochemical assessment of hippocampus structures of rats exposed to TCDD and high doses of tocopherol and acetylsalicylic acid

The effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on central nervous system consists of changing expression of estrogen receptors, whereas the result of chronic inflammatory reaction caused by dioxin is occurrence of destructive changes in various organs connected with disturbed metabolism of connective tissue and damage of cells. The aim of the study was to determine the effect of dioxins on function, ultrastructure, and cytological and histological structure of hippocampus, particularly on expression of estrogen receptors in central nervous system as well as to define protective influence of tocopherol (TCP) and acetylsalicylic acid (ASA) on the decrease in activity of proinflammatory effects in central nervous system. It was shown that TCDD contributes to destructive and inflammatory changes along with demyelization of myelin sheaths and atrophy of estrogen receptors in hippocampus. Dioxin contributes to atrophy of estrogen receptors in hippocampus, in which also destructive and inflammatory changes were found along with demyelination of myelin sheaths. Histopathological and ultrastructural image of hippocampus areas in rats, in which both TCP and ASA were used, is characterized by poorly expressed degenerative changes and smaller inflammatory reactivity. Using both TCP and ASA has a protective effect on functions of central nervous system.

New insights to the role of aryl hydrocarbon receptor in bone phenotype and in dioxin-induced modulation of bone microarchitecture and material properties

Bone is a target for high affinity aryl hydrocarbon receptor (AHR) ligands, such as dioxins. Although bone morphology, mineral density and strength are sensitive endpoints of dioxin toxicity, less is known about effects on bone microarchitecture and material properties. This study characterizes TCDD-induced modulations of bone tissue, and the role of AHR in dioxin-induced bone toxicity and for normal bone phenotype. Six AHR-knockout (Ahr(-/-)) and wild-type (Ahr(+/+)) mice of both genders were exposed to TCDD weekly for 10 weeks, at a total dose of 200μg/kgbw. Bones were examined with micro-computed tomography, nanoindentation and biomechanical testing. Serum levels of bone remodeling markers were analyzed, and the expression of genes related to osteogenic differentiation was profiled using PCR array. In Ahr(+/+) mice, TCDD-exposure resulted in harder bone matrix, thinner and more porous cortical bone, and a more compact trabecular bone compartment. Bone remodeling markers and altered expression of a number of osteogenesis related genes indicated imbalanced bone remodeling. Untreated Ahr(-/-) mice displayed a slightly modified bone phenotype as compared with untreated Ahr(+/+) mice, while TCDD exposure caused only a few changes in bones of Ahr(-/-) mice. Part of the effects of both TCDD-exposure and AHR-deficiency were gender dependent. In conclusion, exposure of adult mice to TCDD resulted in harder bone matrix, thinner cortical bone, mechanically weaker bones and most notably, increased trabecular bone volume fraction in Ahr(+/+) mice. AHR is involved in bone development of a normal bone phenotype, and is crucial for manifestation of TCDD-induced bone alterations.

Smoke carcinogens cause bone loss through the aryl hydrocarbon receptor and induction of Cyp1 enzymes

Smoking is a major risk factor for osteoporosis and fracture, but the mechanism through which smoke causes bone loss remains unclear. Here, we show that the smoke toxins benzo(a)pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interact with the aryl hydrocarbon receptor (Ahr) to induce osteoclastic bone resorption through the activation of cytochrome P450 1a/1b (Cyp1) enzymes. BaP and TCDD enhanced osteoclast formation in bone marrow cell cultures and gavage with BaP stimulated bone resorption and osteoclastogenesis in vivo. The osteoclastogenesis triggered by BaP or RANK-L was reduced in Ahr(-/-) cells, consistent with the high bone mass noted in Ahr(-/-) male mice. The receptor activator of NF-κB ligand (RANK-L) also failed to induce the expression of Cyp1 enzymes in Ahr(-/-) cells. Furthermore, the osteoclastogenesis induced by TCDD was lower in Cyp1a1/1a2(-/-) and Cyp1a1/1a2/1b1(-/-) cultures, indicating that Ahr was upstream of the Cyp enzymes. Likewise, the pharmacological inhibition of the Cyp1 enzymes with tetramethylsilane or proadifen reduced osteoclastogenesis. Finally, deletion of the Cyp1a1, Cyp1a2, and Cyp1b1 in triple knockout mice resulted in reduced bone resorption and recapitulated the high bone mass phenotype of Ahr(-/-) mice. Overall, the data identify the Ahr and Cyp1 enzymes not only in the pathophysiology of smoke-induced osteoporosis, but also as potential targets for selective modulation by new therapeutics.

The musculoskeletal effects of cigarette smoking

➤ Cigarette smoking decreases bone mineral density and increases the risk of sustaining a fracture or tendon injury, with partial reversibility of these risks with long-term cessation of smoking. ➤ Cigarette smoking increases the risk for perioperative complications, nonunion and delayed union of fractures, infection, and soft-tissue and wound-healing complications. ➤ Brief preoperative cessation of smoking may mitigate these perioperative risks. ➤ Informed-consent discussions should include notification of the higher risk of perioperative complications with cigarette smoking and the benefits of temporary cessation of smoking.