The molecular biology of bone resorption due to chronic otitis media

The Science of Cholesteatoma

Cholesteatoma is a potential end-stage outcome of chronic ear infections that can result in the destruction of temporal bone structures with potential resultant hearing loss, vertigo, and intracranial infectious complications. There is currently no treatment apart from surgery for this condition, and despite years of study, the histopathogenesis of this disease remains poorly understood. This review is intended to summarize our accumulated knowledge of the mechanisms of cholesteatoma development and the underlying molecular biology. Attention will be directed particularly to recent developments, covering many potential pharmacologic targets that could be used to treat this disease in the future.

Morphopathogenesis of Adult Acquired Cholesteatoma

Background and Objectives. The aim of this study was to compare the distribution of proliferation markers (Ki-67, NF-κβ), tissue-remodeling factors (MMP-2, MMP-9, TIMP-2, TIMP-4), vascular endothelial growth factor (VEGF), interleukins (IL-1 and IL-10), human beta defensins (HβD-2 and HβD-4) and Sonic hedgehog gene protein in cholesteatoma and control skin. Methods. Nineteen patient cholesteatoma tissues and seven control skin materials from cadavers were included in the study and stained immunohistochemically. Results. Statistically discernible differences were found between the following: the Ki-67 in the matrix and the Ki-67 in the skin epithelium (p = 0.000); the Ki-67 in the perimatrix and the Ki-67 in the connective tissue (p = 0.010); the NF-κβ in the cholesteatoma matrix and the NF-κβ in the epithelium (p = 0.001); the MMP-9 in the matrix and the MMP-9 in the epithelium (p = 0.008); the HβD-2 in the perimatrix and the HβD-2 in the connective tissue (p = 0.004); and the Shh in the cholesteatoma's perimatrix and the Shh in the skin's connective tissue (p = 0.000). Conclusion. The elevation of Ki-67 and NF-κβ suggests the induction of cellular proliferation in the cholesteatoma. Intercorrelations between VEGF, NF-κβ and TIMP-2 induce neo-angiogenesis in adult cholesteatoma. The similarity in the expression of IL-1 and IL-10 suggests the dysregulation of the local immune status in cholesteatoma. The overexpression of the Sonic hedgehog gene protein in the cholesteatoma proves the selective local stimulation of perimatrix development.

Perimatrix of middle ear cholesteatoma: A granulation tissue with a specific transcriptomic signature

OBJECTIVES/HYPOTHESIS

To establish comprehensive transcriptomic profiles of cholesteatoma perimatrix tissue and granulation tissue from chronic otitis media (COM) that did not develop cholesteatoma, which can indicate molecular pathways involved in the cholesteatoma perimatrix pathology and invasiveness.

STUDY DESIGN

Retrospective Case Series.

METHODS

Transcriptome data were obtained from cholesteatoma perimatrix tissue and COM granulation tissue by an Illumina iScan microarray. Differentially expressed genes (DEGs) were subsequently analyzed using both bioinformatical functional annotation and network analysis. Expression of candidate genes (MMP9 and LCN2) was validated by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) on a larger group of samples.

RESULTS

Analysis of the transcriptome led to the identification of 169 differentially expressed genes between investigated tissues. Bioinformatic analysis suggested that most significant biological processes involving DEGs were previously described in cholesteatoma pathology. Network analysis identified ERBB2, TFAP2A, and TP63 as major hubs of the DEGs molecular network. Furthermore, it was observed that the cellular component most significantly enriched in DEGs was extracellular space containing 47 DEGs. Using qRT-PCR, it was confirmed that mRNA levels of the major extracellular hub (MMP9) are increased, whereas its interacting molecule (LCN2) mRNA levels were decreased in cholesteatoma perimatrix tissue compared to COM granulation tissue.

CONCLUSIONS

The current study approach offers an overall look at molecular mechanisms that describe the cholesteatoma entity by focusing exclusively on the perimatrix processes in comparison to COM granulation tissue. The observed differences in gene expression between cholesteatoma perimatrix and COM granulation tissue could suggest novel markers potentially influenced by the perimatrix-matrix molecular interplay, which is not present in COM without cholesteatoma.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:E220-E227, 2020.

Outcomes Following Modified Tympanomastoidectomy With Soft-wall Reconstruction

OBJECTIVE

To report outcomes following modified tympanomastoidectomy with soft-wall reconstruction (MTMSWR).

STUDY DESIGN

Retrospective cohort.

SETTING

Tertiary referral center.

PATIENTS

Forty-seven patients (48 ears) with aggressive cholesteatoma undergoing MTMSWR.

INTERVENTIONS

Canal wall down (CWD) tympanomastoidectomy with temporalis fascia reconstruction of the posterior external auditory canal (EAC).

MAIN OUTCOME MEASURES

Cholesteatoma recidivism; hearing outcomes; degree of soft-wall retraction; time to epithelialization; otorrhea.

RESULTS

All ears had some form of ossicular compromise. There were 41 ears with completed surveillance of which 39% demonstrated recidivism for cholesteatoma. Of these, 68.8% had a small cholesteatoma foci averaging 3.7 mm. Air pure-tone average remained stable or improved for 60.0% and declined ≤ 20 dB for 85.7%. Excluding ears unable to undergo ossicular chain reconstruction, final air-bone gap was ≤ 30 dB for 66.7%. Retraction of the reconstructed wall was absent-to-mild in 34.7% and moderate-to-full in 52.1%. Thirteen percent had soft-wall breakdown. Average time to full epithelialization of the wall was 58.5 days.

CONCLUSIONS

MTMSWR is an option for restoring the posterior EAC wall following CWD surgery. Recidivism is comparable to canal wall up surgery, and hearing outcomes are generally better than CWD. Other advantages include rapid epithelialization, low rates of otorrhea, and restoration of a self-cleaning EAC regardless of retraction into the mastoid cavity.

Pathogenesis and Bone Resorption in Acquired Cholesteatoma: Current Knowledge and Future Prospectives

Cholesteatoma is a cystic non tumorous lesion of the temporal bone that has the ability to destroy nearby structures by its power to cause bone resorption and as a result, fatal complications prevail. We aimed to conduct a comprehensive review for pathogenesis of acquired cholesteatoma, bone resorption mechanisms, and offer a future vision of this serious disease. We have reviewed different theories for pathogenesis of acquired cholesteatoma including the most relevant and updated ones with special emphasis on the mechanisms of bone resorption through Medline/PubMed research using the keywords 'aetiopathogenesis, bone resorption, acquired cholesteatoma, temporal bone, and cytokines.' In order to strengthen our study, we searched the reference lists of identified reviews. Cholesteatoma is a subject of debate among otolaryngologists since it was prescribed firstly. Over many decades, several theories were postulated for aetiopathogenesis of cholesteatoma with a tendency to follow more than one theory to explain the proper nature of that disease. Until now, the mechanism of bone resorption has yet to be more clarified. In the last century, a leap has occurred in the field of biomolecular cholesteatoma research which improved our knowledge about its pathophysiology and bone destructive mechanism. However, surgery is still the only available treatment. We conclude that discovery of new therapeutic choices for cholesteatoma other than surgery by the use of anti-growth, anti-proliferative, apoptotic agents as well as medications that antagonize osteoclastogenesis should be the main concern in the future clinical and experimental research work. Also, searching for predictors of the aggressiveness of cholesteatoma can affect the timing of intervention and prevent occurrence of complications.

Zoledronic Acid Inhibits Osteoclastogenesis in Vitro and in a Mouse Model of Inflammatory Osteolysis

This study assessed effects of the bisphosphonate zoledronic acid (ZLNA) on osteoclastogenesis. To assess the effect of ZLNA on osteoclast formation in vitro, we cultured mouse bone marrow cells under conditions that promote osteoclastogenesis. Administered at concentrations from 10−6 to 10−9 mol/L, ZLNA led to a dose-dependent inhibition of osteoclastogenesis. Combined TUNEL staining and histochemical staining for tartrate-resistant acid phosphatase showed that ZLNA induced apoptosis in osteoclasts and monocytic precursor cells. To study the effects of ZLNA in vivo, we placed keratin particles onto the surface of the parietal bone of mice to induce localized inflammatory bone resorption. Three experimental groups received daily subcutaneous injections of ZLNA (1, 3, or 10 μg/kg body weight) from 4 days before surgery until 5 days after keratin implantation. The ZLNA significantly reduced osteoclast recruitment in a dose-dependent manner, but did not affect the degree of inflammation or the mineral apposition rate.

Intercellular Communication between Keratinocytes and Fibroblasts Induces Local Osteoclast Differentiation: a Mechanism Underlying Cholesteatoma-Induced Bone Destruction

Bone homeostasis is maintained by a balance in activity between bone-resorbing osteoclasts and bone-forming osteoblasts. Shifting the balance toward bone resorption causes osteolytic bone diseases such as rheumatoid arthritis and periodontitis. Osteoclast differentiation is regulated by receptor activator of nuclear factor κB ligand (RANKL), which, under some pathological conditions, is produced by T and B lymphocytes and synoviocytes. However, the mechanism underlying bone destruction in other diseases is little understood. Bone destruction caused by cholesteatoma, an epidermal cyst in the middle ear resulting from hyperproliferation of keratinizing squamous epithelium, can lead to lethal complications. In this study, we succeeded in generating a model for cholesteatoma, epidermal cyst-like tissue, which has the potential for inducing osteoclastogenesis in mice. Furthermore, an in vitro coculture system composed of keratinocytes, fibroblasts, and osteoclast precursors was used to demonstrate that keratinocytes stimulate osteoclast differentiation through the induction of RANKL in fibroblasts. Thus, this study demonstrates that intercellular communication between keratinocytes and fibroblasts is involved in the differentiation and function of osteoclasts, which may provide the molecular basis of a new therapeutic strategy for cholesteatoma-induced bone destruction.

Increased Acquired Cholesteatoma Risk in Patients with Osteoporosis: A Retrospective Cohort Study

Objective

Clinically, we found the increased incidence of acquired colesteatoma in the patients with osteoporosis. In this study, we used a retrospective cohort to examine this association and to investigate the possible mechanism.

Methods

We conducted a population-based retrospective cohort study by using the National Health Insurance Research Database (NHIRD). We identified an osteoporosis cohort comprising 37 124 patients newly diagnosed with osteoporosis aged 20 years or older. Patients in the comparison cohort had no history of osteoporosis and were frequency matched with the patients in the osteoporosis cohort according to sex, age, and index year.

Results

The acquired cholesteatoma incidence rates for the osteoporosis and comparison cohorts were 1.12 and 0.83 per 1000 person-years, respectively. After we adjusted for confounding factors, the osteoporosis cohort exhibited a 1.32-fold increased acquired cholesteatoma risk relative to the comparison cohort (hazard ratio [HR] = 1.32, 95% confidence interval [CI] = 1.11–1.57). In addition, patients with no history of otitis media (HR = 1.33, 95% CI = 1.11–1.59), cancer (HR = 1.34, 95% CI = 1.12–1.60), or COPD (HR = 1.26, 95% CI = 1.05–1.52) in the osteoporosis cohort exhibited an increased risk of subsequent acquired cholesteatoma relative to those in the comparison cohort.

Conclusions

Our cohort study indicated that patients with osteoporosis had a 1.31-fold increased acquired cholesteatoma risk relative to the comparison cohort. This risk was further increased in patients with comorbid otitis media. Hence, we recommend that otolaryngologists evaluate the condition of the middle ear of patients with osteoporosis.

Induction of cytokine production in cholesteatoma keratinocytes by extracellular high-mobility group box chromosomal protein 1 combined with DNA released by apoptotic cholesteatoma keratinocytes

High-mobility group box chromosomal protein 1 (HMGB-1), a nuclear DNA binding protein, was recently rediscovered as a new proinflammatory cytokine. The purpose of this study was to determine HMGB-1 expression in vivo and to identify the effect of extracellular HMGB-1 in inflammatory process associated with bone destruction in cholesteatoma. We investigated the expression and location of HMGB-1 in the cholesteatoma and healthy skin using an immunofluorescence assay. We also detected apoptosis and DNA fragments in the cholesteatoma by TUNEL staining. HMGB-1 concentration in apoptotic supernatants from UV light-treated cells, culture supernatants and its translocation in cholesteatoma keratinocytes stimulated by supernatants from UV light-treated cells were measured by immunoblot analysis and immunofluorescence assay. Cultures of human cholesteatoma keratinocytes were exposed to CpG-DNA, HMGB-1, or CpG-DNA complexed to HMGB-1 for 24 h. Cytokines in the culture supernatant were measured by ELISA. In addition, levels of proinflammatory cytokines released by cholesteatoma keratinocytes stimulated by supernatants from UV light-treated cells with or without anti-HMGB-1 antibodies and supernatants from UV light-treated cells with DNase 1 were measured by enzyme-linked immunosorbent assay. The expression of HMGB-1 in cholesteatoma increased and it translocated both to the cytoplasm and extracellular space. Furthermore, the HMGB-1 concentration in supernatants increased significantly after addition of supernatants from UV light-treated cells. TNF-α and IL-1β can be induced by purified HMGB-1 combined with CpG-DNA in the cholesteatoma keratinocytes. In addition, supernatants of apoptotic cells containing HMGB-1-DNA were effective in inducing TNF-α and IL-1β secretion. This study suggested that persistent expression of extracellular HMGB-1 and DNA fragments in cholesteatoma leads to TNF-α and IL-1β production, causing bone resorption and destruction. Thus, we have implicated that HMGB-1-DNA complexes might act as a key molecule involved in bone resorption associated with cholesteatoma.

Quantitative measurement of m-RNA levels to assess expression of cyclooxygenase-II, inducible nitric oxide synthase and 12-lipoxygenase genes in middle ear cholesteatoma

To assess expression of three main inflammatory genes, COX-II, ALOX-12 and i-NOS, quantitatively at transcriptional level in cholesteatoma matrix tissue. Ten patients who have chronic otitis media with primary acquired cholesteatoma were included in this study. Tissue samples obtained from cholesteatoma matrix and external ear canal skin (control tissue). Expression of the targeted genes (COX-II, i-NOS and LOX-12) was assessed using real-time quantitative polymerase chain reaction (RT-PCR) technique. The amount of COX2 mRNA was significantly higher in cholesteatoma matrix at transcriptional level (p = 0.038). There was no statistically significant difference regarding expression of iNOS and LOX12 mRNA levels (p > 0.05). There is a significant overexpression of the mRNA of COX-II in cholesteatoma matrix, which indicates a difference between the normal skin and cholesteatoma matrix at molecular level. COX-II gene overexpression seems to be associated with pathogenesis of cholesteatoma. This molecular change is similar to the molecular abnormalities observed in some benign and malignant neoplasms. Invasive and locally destructive nature of cholesteatoma may be due to COX-II overexpression. Absence of an increase in the gene expressions of i-NOS and LOX-12 in cholesteatoma matrix suggests that these mediators may not be related with the pathogenesis and evolution of cholesteatoma.

Expression of tumor necrosis factor-α, interleukin-1α, interleukin-6 and interleukin-10 in chronic otitis media with bone osteolysis

The purpose of this study was to evaluate the expression of proinflammatory and immunoregulatory cytokines in chronic otitis media. The expression levels of TNF-α, IL-1α, IL-6 and IL-10 were determined by Western blot analysis of tissue samples obtained during ear surgery. The expression levels of TNF-α, IL-1α and IL-6 in cholesteatoma tissues were substantially higher compared to those determined in the granulation tissue. The highest levels of TNF-α, IL-1 and IL-6 proteins were observed in patients with bone destruction. There were no significant differences in the expression of IL-10 levels in cholesteatoma and normal skin, but in the granulation tissue its level was substantially higher. The level of IL-10 in cholesteatoma tissues inversely correlated with the expression of proinflammatory cytokines, the degree of bone destruction and cholesteatoma invasion. Increased expressions of TNF-α, IL-1α and IL-6 in chronic otitis media and a strong positive correlation between these cytokine levels and the degree of bone destruction indicate the destructive behavior of cholesteatoma or granulation tissue.

Expression of the receptor activator for nuclear factor-κB ligand and osteoprotegerin in chronic otitis media

BACKGROUND

The receptor activator for nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) are the key factors controlling the osteoclast and osteoblast action in the bone.

PURPOSE

The study objective was to investigate the expression level of RANKL and OPG in cholesteatoma and granulation tissue, and to assess the relationship between their expression levels and osteolysis.

MATERIAL AND METHODS

Patients with chronic otitis media with cholesteatoma (n = 28) and without cholesteatoma (n = 24) treated surgically at the Department of Otolaryngology of the Medical University of Gdańsk were included in the study. RANKL and OPG expressions were analyzed by immunohistochemistry and Western blot.

RESULTS

RANKL and OPG were expressed in all cholesteatoma and granulation tissues. RANKL expression was mainly observed in cholesteatoma subepithelial stroma, whereas OPG-positive cells originated from the epithelium. The number of OPG-positive cells in the normal skin was significantly higher than in cholesteatoma tissues. The RANKL protein level in cholesteatoma tissues was 1.8- and 1.5-fold higher than in the auditory canal skin and granulation tissues, respectively. The number of RANKL-positive cells in cholesteatoma tissues was significantly higher than in the normal skin. No substantial differences were found in average OPG protein levels between cholesteatoma tissues and the normal auditory canal skin. The ratio of RANKL/OPG was significantly higher in cholesteatoma tissues (2.93 ± 0.79) than in the skin samples (1.36 ± 0.34).

CONCLUSIONS

Altered ratio of RANKL/OPG protein level in cholesteatoma tissues suggests that these proteins might be somehow involved in the pathogenesis of cholesteatoma. However, to resolve this issue a study on a larger group of patients should be conducted.

Hystology findings' correlation between the ossicular chain in the transoperative and cholesteatomas

Chronic otitis media is hystopathologycaly defined as the presence of irreversible inflammatory tissue changes in the middle ear. Ossicular lesions represent the most prevalent change.

AIM

to correlate the degree of ossicular chain changes seen during surgery with the inflammatory histological degree and the thickness of the cholesteatoma perimatrix.

STUDY DESIGN

Cross-sectional study.

METHODS

Seventy-one descriptions of surgeries done in patients submitted to tympanomastoydectomy were reviewed. Cholesteatoma were collected and fixed in 10% formaldehyde. Two slides were made for each cholesteatoma, one stained with HE and another with picrossirius. Images were obtained from light microscopy and digitally processed and "blindly" analyzed using Image Pro-Plus Software. For statistical analysis we used Spearman's coefficient. Differences were considered statistically significant if P< or =0.05.

RESULTS

the ossicular chain was involved in 65 cases. The incus was the most frequently affected bone, followed by the stapes and the malleus. When the Spearman's coefficient was employed considering ossicular chain change degree with patient's age by the time of surgery, perimatrix thickness and histological degree of inflammation, correlations were not established.

CONCLUSION

Our findings indicate that ossicular chain changes are practically universal when a cholesteatoma is present. We didn't find correlations related with bone erosion and cholesteatoma's histological findings.

Correlação da cadeia ossicular no transoperatório com achados histológicos de colesteatomas

A Otite Média Crônica é definida pela presença de alterações teciduais inflamatórias irreversíveis na fenda auditiva. As lesões ossiculares são as mais prevalentes. OBJETIVO: Correlacionar o grau de comprometimento da cadeia ossicular, visualizada no transoperatório, com o grau histológico de inflamação e com a espessura da perimatriz de colesteatomas. TIPO DE ESTUDO: Estudo transversal. MÉTODOS: Descrições cirúrgicas de 71 pacientes foram revisadas. Colesteatomas coletados e fixados em formol 10% e preparadas uma lâmina em Hematoxilina-Eosina e outra em Picrossírios. A leitura foi "cega", através de imagens digitais, no ImageProPlus. A análise estatística foi realizada através do coeficiente de Spearman, sendo considerados como estatisticamente significativos os valores de P<0,05. RESULTADOS: Havia algum envolvimento da cadeia ossicular em 65 casos. O ossículo mais freqüentemente afetado era a bigorna, seguida pelo estribo e pelo martelo. Ao aplicarmos o coeficiente de Spearman entre o grau de comprometimento da cadeia ossicular com a idade do paciente à cirurgia, a espessura da perimatriz e o grau histológico de inflamação não foram detectadas correlações. CONCLUSÃO: Os nossos achados indicam que é praticamente universal o acometimento da cadeia ossicular na presença de colesteatoma. Não foi encontrada correção entre a erosão ossicular e os achados histológicos.

Expression of RANKL and OPG in Middle Ear Cholesteatoma Tissue

OBJECTIVES

The objective of this study was to investigate how the expression of the RANK-RANKL-OPG system mediates the formation and differentiation of osteoclasts and causes bone resorption in cholesteatoma.

METHODS

An immunohistochemical analysis was carried out in 22 cholesteatoma tissues obtained during middle ear surgery and 15 normal postauricular skin tissues to examine the expression of RANKL and OPG.

RESULTS

All 22 cases of cholesteatoma and the 15 cases of normal postauricular skin expressed RANKL and OPG. The count and rate of RANKL-positive cells in cholesteatoma was significantly higher than in normal postauricular skin. The count and rate of OPG-positive cells in normal postauricular skin was significantly higher than in cholesteatoma. The ratio of the positive expression rates of RANKL and OPG in cholesteatoma was statistically higher than in normal postauricular skin.

CONCLUSIONS

We provide evidence suggesting that RANKL, which activates osteoclasts, plays a significant role in the mechanism of bone destruction in cholesteatoma, and that the ratio of RANKL to OPG may be a reliable indicator of bone destruction in cholesteatoma.

Algumas considerações sobre colesteatomas adquiridos pediátricos e adultos

Neste artigo, os autores dissertam sobre o tema colesteatoma, desde a primeira vez em que foi utilizada a palavra por Mueller (1838), até informações atuais. Fazem uma abordagem de sua definição, passam pela etiopatogênese e apresentam noções básicas sobre sua biologia. Ainda realizam uma ampla revisão sobre colesteatoma pediátrico, apresentam dados clínicos epidemiológicos e biológicos e mostram um paralelo com o colesteatoma em adultos. Para finalizar, descrevem alguns trabalhos sobre erosão da cadeia ossicular correlacionando-a com dados sobre a perimatriz, colágeno e colagenase.

Some considerations about acquired adult and pediatric cholesteatomas

Authors debate about cholesteatomas, from the first time this word was employed, by Muller, in 1838, until the recent updates. They dissert about its definition, etiology and pathology and present basic concepts about its biology. They also make a wide review about pediatric cholesteatoma, its epidemiology and biology, and compare it with adult cholesteatoma. Finally, they describe some articles about ossicle chain erosion and its correlation with cholesteatoma perimatrix, collagen and collagenase.

A possible role for nitric oxide in osteoclastogenesis associated with cholesteatoma

HYPOTHESIS

This study was designed to investigate the potential role of nitric oxide in cholesteatoma-induced bone resorption, in vitro and in vivo.

BACKGROUND

Cholesteatoma is a disease of inflammatory bone resorption in the middle ear leading to hearing loss and vestibular dysfunction. Inappropriate activation of osteoclasts causes the morbidity associated with this disease. Previous studies suggest nitric oxide may be an important mediator of osteoclast function.

METHODS

A murine model of cholesteatoma induced bone resorption was used to demonstrate nitric oxide synthase (NOS) gene expression and the effect of a NOS inhibitor. An in vitro osteoclast culture method was used to demonstrate the effect of nitric oxide on isolated osteoclasts. Osteoclast development was assayed by counting the number of mature osteoclasts; activity was assayed by measuring the amount of resorbed bone.

RESULTS

Quantitative reverse transcriptase-polymerase chain reaction results demonstrated the temporal expression of all three NOS isoforms in vivo. NOS I demonstrated very low levels of expressions throughout the duration of the study with no change in expression in response to keratin implant. Similarly, NOS III also demonstrated low levels of expression and no change in response to keratin. NOS II was highly upregulated in response to keratin throughout the duration of the study. In vitro, pharmacological nitric oxide donors--sodium nitroprusside and S-nitroso-N-acetyl-D,L-penicillamine--dose-dependently stimulated osteoclast resorption. Alone, interferon gamma (IFNgamma)--but not IL-1beta or TNFalpha--generated nitrite in vitro. A cytokine cocktail of IL-1beta, TNFalpha, and IFNgamma synergistically enhanced nitrite production. Nitrite production was blocked by the addition of aminoguanidine (AG), suggesting that AG-inhibited cytokine mediated nitrite production. However, in an in vivo model of cholesteatoma-induced bone resorption, the osteoclast response of AG-treated mice was not statistically different from untreated controls.

CONCLUSIONS

All three NOS isoforms were expressed in an in vivo model of cholesteatoma-induced bone resorption with significant upregulation of NOS II throughout the study. Exogenously administered nitric oxide dose-dependently enhanced osteoclast activation in vitro. The pro-inflammatory cytokines, IL-1beta, TNFalpha, and IFNgamma, synergistically induce nitrite production, which was abrogated by treatment with the nitric oxide synthase inhibitor, AG. Although AG suppresses nitrite production in vitro, treatment had no effect on osteoclast response in vivo, suggesting that the effects of inflammatory cytokines on osteoclast response were mediated through other pathways.

A murine model of cholesteatoma-induced bone resorption using autologous dermal implantation

OBJECTIVE

To investigate a novel murine model for dermal implant-induced osteolysis analogous to bone resorption observed in middle ear cholesteatoma.

STUDY DESIGN

Animal experiment.

METHODS

We placed autologous dermal implants on the surface of mouse calvaria. The calvaria were examined at days 1, 3, 5, 7, and 14 after implantation by histological study and tartrate-resistant acid phosphatase immunohistochemical processing to detect osteoclasts.

RESULTS

Dermal implants showed a significantly increased osteoclast density compared with control samples. The dermal implant tissue remained viable and produced a robust, localized inflammatory osteolytic response on the adjacent calvarial surface. Osteoclasts were predominantly found on the surface of the calvarium with the greatest osteoclast density seen at 5 to 7 days after implantation.

CONCLUSION

The mouse model is expected to be a useful tool for investigating the pathogenesis of localized inflammatory bone resorption related to cholesteatoma.

Nitric oxide synthase I mediates osteoclast activity in vitro and in vivo

Bone resorption is responsible for the morbidity associated with a number of inflammatory diseases such as rheumatoid arthritis, orthopedic implant osteolysis, periodontitis and aural cholesteatoma. Previous studies have established nitric oxide (NO) as a potentially important mediator of bone resorption. NO is a unique intercellular and intracellular signaling molecule involved in many physiologic and pathologic pathways. NO is generated from L-arginine by the enzyme nitric oxide synthase (NOS). There are three known isoforms of NOS with distinct cellular distributions. In this study, we have used mice with targeted deletions in each of these isoforms to establish a role for these enzymes in the regulation of bone resorption in vivo and in vitro. In a murine model of particle induced osteolysis, NOS I-/- mice demonstrated a significantly reduced osteoclast response. In vitro, osteoclasts derived from NOS I-/- mice were larger than wild type controls but demonstrated decreased resorption. Although NOS I has been demonstrated in osteoblasts and osteocytes as a mediator of adaptive bone remodeling, it has not previously been identified in osteoclasts. These results demonstrate a critical role for NOS I in inflammatory bone resorption and osteoclast function in vitro.

Osteoclast stimulating and differentiating factors in human cholesteatoma

OBJECTIVES

To investigate the expression of osteoclast-activating and differentiating factors and to study the occurrence of osteoclast precursor cells and osteoclasts in acquired human cholesteatoma tissue.

METHODS

We examined 21 cholesteatoma samples versus 18 normal auditory canal skin specimens for the expression of osteoprotegerin ligand (OPGL), osteoprotegerin (OPG), and macrophage-colony stimulating factor (M-CSF) using reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. Immunohistochemistry and computer-assisted microscopy using markers CD4, CD11a, CD11b, CD14, CD51, CD68, and TRAP obtained the detection of osteoclast cell lineage.

RESULTS

An increased expression of the investigated cytokines M-CSF, OPG, and OPGL was demonstrated by immunohistochemistry and RT-PCR in cholesteatoma tissue compared with normal external meatal skin. Several CD4-positive cells exhibited a co-expression for OPGL within the perimatrix of cholesteatoma. The presence of osteoclast precursor cells was confirmed in all samples of cholesteatoma tissue.

CONCLUSIONS

This study reveals that the number of osteoclast precursor cells is markedly increased in the perimatrix of cholesteatoma tissue. Our results support a concept described for inflammatory arthritis: the inflammation related to cholesteatoma induces bone resorption by release of OPGL from activated T-cells and triggers osteoclastogenesis. This could be a major target for drugs to inhibit osteoclast formation and bone resorption and may be an adjunct in cholesteatoma management.

Expression of bone morphogenetic protein-2 messenger ribonucleic acid in cholesteatoma fibroblasts

HYPOTHESIS

The aim of the study was to evaluate the role of bone morphogenetic protein-2 (BMP-2) in the pathology of middle ear cholesteatoma.

BACKGROUND

Middle ear cholesteatoma is a chronic inflammatory disease associated with destruction of the temporal bone and marked by increased expression levels of diverse cytokines. Bone remodeling associated with this disease is mainly caused by the action of osteoclasts. It has been shown that BMP-2 expression is inducible by interleukin 1 in synovial fibroblasts and that BMP-2 in combination with interleukin 1alpha is able to stimulate the formation of osteoclast-like multinucleated cells in co-cultures of osteoblast-like cells and hematopoietic cells.

METHODS

By using Northern hybridizations, we examined the messenger ribonucleic acid expression of BMP-2 in keratinocytes and fibroblasts derived from normal external ear canal skin (EACS) and from cholesteatoma, respectively.

RESULTS

We show that normal EACS fibroblasts do not express BMP-2, whereas keratinocytes of both EACS and cholesteatoma origin are positive for the BMP-2 transcript. In contrast to EACS fibroblasts, BMP-2 is clearly expressed in cholesteatoma perimatrix fibroblasts. Incubation of normal fibroblasts with cholesteatoma extracts caused the transcription of BMP-2. Interleukin 1alpha, bacterial endotoxin, or bovine keratin, however, were not able to initiate BMP-2 expression in normal fibroblasts.

CONCLUSION

In view of the above data, it is tempting to speculate that BMP-2 expression might play a role in cholesteatoma pathology.