Increased Activity of the Diastrophic Dysplasia Sulfate Transporter in Otosclerosis and Its Inhibition by Sodium Fluoride

Brazilian Society of Otology task force - Otosclerosis: evaluation and treatment

OBJECTIVES

To review and provide evidence-based recommendations for the diagnosis and treatment of otosclerosis.

METHODS

Task force members were educated on knowledge synthesis methods, including electronic database search, review and selection of relevant citations, and critical appraisal of selected studies. Articles written in English or Portuguese on otosclerosis were eligible for inclusion. The American College of Physicians' guideline grading system and the American Thyroid Association's guideline criteria were used for critical appraisal of evidence and recommendations for therapeutic interventions.

RESULTS

The topics were divided into 2 parts: 1) Diagnosis - audiologic and radiologic; 2) Treatment - hearing AIDS, pharmacological therapy, stapes surgery, and implantable devices - bone-anchored devices, active middle ear implants, and Cochlear Implants (CI).

CONCLUSIONS

The pathophysiology of otosclerosis has not yet been fully elucidated, but environmental factors and unidentified genes are likely to play a significant role in it. Women with otosclerosis are not at increased risk of worsening clinical condition due to the use of contraceptives or during pregnancy. Drug treatment has shown little benefit. If the patient does not want to undergo stapedotomy, the use of hearing aids is well indicated. Implantable systems should be indicated only in rare cases, and the CI should be indicated in cases of profound deafness.

Differences in Otosclerotic and Normal Human Stapedial Osteoblast Properties Are Normalized by Alendronate in Vitro

Objective

Identify and compare phenotypic properties of osteoblasts from patients with otosclerosis (OSO), normal bones (HOB), and normal stapes (NSO) to determine a possible cause for OSO hypermineralization and assess any effects of the bisphosphonate, alendronate.

Study Design

OSO (n = 11), NSO (n = 4), and HOB (n = 13) cultures were assayed for proliferation, adhesion, mineralization, and gene expression with and without 10–10M-10–8M alendronate.

Setting

Academic hospital.

Methods

Cultures were matched for age, sex, and passage number. Cell attachment and proliferation + alendronate were determined by Coulter counting cells and assaying tritiated thymidine uptake, respectively. At 7, 14, and 21 days of culture + alendronate, calcium content and gene expression by quantitative reverse transcription-polymerase chain reaction (qRT-PCR) were determined.

Results

OSO had significantly more cells adhere but less proliferation than NSO or HOB. Calcification was significantly increased in OSO compared to HOB and NSO. NSO and HOB had similar cell adhesion and proliferation rates. A dose-dependent effect of alendronate on OSO adhesion, proliferation, and mineralization was found, resulting in levels equal to NSO and HOB. All cultures expressed osteoblast-specific genes such as RUNX2, alkaline phosphatase, type I collagen, and osteocalcin. However, osteopontin was dramatically reduced, 9.4-fold at 14 days, in OSO compared to NSO. Receptor activator of nuclear factor κB ligand/osteoprotegerin (RANKL/OPG), important in bone resorption, was elevated in OSO with decreased levels of OPG levels. Alendronate had little effect on gene expression in HOB but in OSO increased osteopontin levels and decreased RANKL/OPG.

Conclusions

OSO cultures displayed properties of hypermineralization due to decreased osteopontin (OPN) and also had increased RANKL/OPG, which were normalized by alendronate.

Homozygosity for a DTDST mutation in a child with multiple epiphyseal dysplasia

BACKGROUND

Multiple epiphyseal dysplasia (MED) is one of the common hereditary osteochondrodysplasias. Mutations in diastrophic dysplasia sulfate transporter gene (DTDST) result in recessive MED.

OBJECTIVE

To investigate the possible gene mutation in a recessive MED patient.

SUBJECTS

A boy with typical clinical features of recessive MED and his parents.

METHODS

Clinical and radiological evaluations, DTDST gene sequence analysis, and sulfate uptake assay were performed on the patient and his parents.

RESULTS

The patient showed typical symptoms of recessive MED. The radiological evaluation confirmed dysplasia in multiple epiphysis of the patient, while his parents did not show the similar clinical and radiological features. Gene sequence showed the patient was homozygous of A2092T (T689S) mutation, while his parents were both of heterozygous of the same mutation. No such mutation in DTDST gene was found in 81 normal control individuals. The patient showed reduced sulfate uptake ability in dermal fibroblast compared with his parents and normal controls.

CONCLUSION

The homozygous A2092T (T689S) mutation could be one of the mutations in the DTDST gene causing MED.

Perspectives of pharmacological treatment in otosclerosis

To review our current knowledge of the pathologic bone metabolism in otosclerosis and to discuss the possibilities of non-surgical, pharmacological intervention. Otosclerosis has been suspected to be associated with defective measles virus infection, local inflammation and consecutive bone deterioration in the human otic capsule. In the early stages of otosclerosis, different pharmacological agents may delay the progression or prevent further deterioration of the disease and consecutive hearing loss. Although effective anti-osteoporotic drugs have become available, the use of sodium fluoride and bisphosphonates in otosclerosis has not yet been successful. Bioflavonoids may relieve tinnitus due to otosclerosis, but there is no data available on long-term application and effects on sensorineural hearing loss. In the initial inflammatory phase, corticosteroids or non-steroidal anti-inflammatory drugs may be effective; however, extended systemic application may lead to serious side effects. Vitamin D administration may have effects on the pathological bone loss, as well as on inflammation. No information has been reported on the use of immunosuppressive drugs. Anti-cytokine targeted biological therapy, however, may be feasible. Indeed, one study on the local administration of infliximab has been reported. Potential targets of future therapy may include osteoprotegerin, RANK ligand, cathepsins and also the Wnt-β-catenin pathway. Finally, anti-measles vaccination may delay the progression of the disease and potentially decrease the number of new cases. In conclusion, stapes surgery remains to be widely accepted treatment of conductive hearing loss due to otosclerosis. Due to lack of solid evidence, the place of pharmacological treatment targeting inflammation and bone metabolism needs to be determined by future studies.

The etiology of otosclerosis: a combination of genes and environment

Otosclerosis is a common form of hearing loss characterized by abnormal bone remodeling in the otic capsule. It is a complex genetic disease, caused by a combination of genetic and environmental factors. During the past decade, several attempts have been made to identify factors for otosclerosis. This review provides an overview of the current understanding of the etiology of otosclerosis and describes the genetic and environmental factors that have been implicated in the disease. Environmental factors include fluoride and viral factors, particularly measles. Genetic association studies for otosclerosis have reported several associations of genetic variants that influence the risk of disease, mainly involving bone remodeling pathways, although their individual risk contributions are small. Rare monogenic forms of otosclerosis also exist, which are caused by a mutation in a single gene leading to a clear familial segregation of the disease. Linkage analysis of large otosclerosis families has led to the identification of seven loci, and recently evidence was found that T cell receptor beta is a gene responsible for familial otosclerosis, suggesting an underlying immunological pathway. However, this might also represent an autoimmune process, a hypothesis that is supported by other data as well. In conclusion, a variety of pathways have been identified to be involved in the development of otosclerosis, showing that distinct mechanisms involving both genetic and environmental risk factors can influence and contribute to a similar disease outcome.

Genetics of otosclerosis

OBJECTIVES

Otosclerosis is a major cause of acquired hearing loss in adult life affecting exclusively the human temporal bone. Until recently, the etiopathogenesis of otosclerosis was still a matter of debate. Genetic research, however, has evolved enormously the last years and unveiled important clues regarding the cause of otosclerosis. The objective of this article is to review the genetics of otosclerosis with special attention for the links to the bone homeostasis of the otic capsule.

DATA SOURCES

A detailed literature study was performed focusing on the recent genetic findings in otosclerosis and the special bone turnover of the otic capsule. A PubMed search and own research data were used to bring the relevant information for this review together.

CONCLUSION

Unlike all other bones in the human skeleton, the otic capsule undergoes very little remodeling after development, possibly due to local inner ear factors. Otosclerosis is a process of pathologic increased bone turnover in the otic capsule, which in most cases leads to stapes fixation, resulting in a conductive hearing loss. Although environmental factors such as estrogens, fluoride, and viral infection have been implicated, it is clear that genetic factors play a significant role in the manifestation of otosclerosis. From a genetic viewpoint, otosclerosis is considered to be a complex disease with rare autosomal dominant forms caused by a single gene. Already, 7 monogenic loci have been published, but none of the genes involved have been identified. For the complex form of otosclerosis, caused by an interaction between genetic and environmental factors, the first susceptibility genes were identified by case-control association studies. All 3 replicated genes, TGFB1, BMP2, and BMP4, are a part of the transforming growth factor-beta1 pathway. Data from both genetic association studies and gene expression analysis of otosclerotic bone showed that the TGF-beta1 pathway is most likely an important factor in the pathogenesis of otosclerosis.

Otosclerosis 2: the medical management of otosclerosis

The rationale for medical therapy for otospongiosis is to slow down and eventually stop the phase of bone resorption. There is some increase in the incidence of stapedial otospongiosis in a low-fluoride area compared with a high-fluoride area. Sodium fluoride treatment has a role to play in preventing the onset and progression of hearing loss in patients suffering from otosclerosis. Sodium fluoride therapy has been shown to have some beneficial effect on dizziness associated with otosclerosis. In view of the possibility of systemic side effects of sodium fluoride therapy, a regular follow up of patients is warranted. Biphosphonates can be used as an alternative treatment to sodium fluoride in cases where the patient is intolerant to sodium fluoride therapy. Hearing aid is also a treatment option, but it does not halt the disease process.

Association of bone morphogenetic proteins with otosclerosis

We studied the role of polymorphisms in 13 candidate genes on the risk of otosclerosis in two large independent case-control sets. We found significant association in both populations with BMP2 and BMP4, implicating these two genes in the pathogenesis of this disease.

INTRODUCTION

Otosclerosis is a progressive disorder of the human temporal bone that leads to conductive hearing loss and in some cases sensorineural or mixed hearing loss. In a few families, it segregates as a monogenic disease with reduced penetrance, but in most patients, otosclerosis is more appropriately considered a complex disorder influenced by genetic and environmental factors.

MATERIALS AND METHODS

To identify major genetic factors in otosclerosis, we used a candidate gene approach to study two large independent case-control sets of Belgian-Dutch and French origin. Tag single nucleotide polymorphisms (SNPs) in 13 candidate susceptibility genes were studied in a stepwise strategy.

RESULTS

Two SNPs were identified that showed the same significant effect in both populations. The first SNP, rs3178250, is located in the 3' untranslated region of BMP2. Individuals homozygote for the C allele are protected against otosclerosis (combined populations: p = 2.2 x 10(-4); OR = 2.027; 95% CI = 1.380-2.979). The second SNP, rs17563, is an amino acid changing (p.Ala152Val) SNP located in BMP4. The G allele, coding for the amino acid alanine, confers susceptibility in both populations (combined populations: p = 0.002; OR = 1.209; 95% CI: 1.070-1.370).

CONCLUSIONS

These results indicate that polymorphisms in the BMP2 and BMP4 genes, both members of the TGF-beta superfamily, contribute to the susceptibility to otosclerosis and further strengthen the results from the recently reported association of TGFB1 with this disease.

Otosclerosis and measles virus - association or causation?

Otosclerosis is a frequent condition which occurs exclusively in the human temporal bone. This peculiar disease affects mainly Caucasians and Indians and may cause conductive, mixed conductive-sensorineural or occasionally merely sensorineural hearing loss. Morphological investigations of the otosclerotic focus show all three phases of a chronic inflammation with bone resorption, formation of new bone and finally eburnation. Various hypotheses about the cause of inflammation were proposed in the past. Immunological reactivity to collagen, the existence of otosclerosis genes (OTSC 1-5) including mutations of the collagen gene 1A1 and 1A2 or a measles virus (MV) infection were suggested. The existence of the MV proteins and RNA within the otosclerotic tissue has been shown by several authors. However, due to mainly technical problems, no further progress to elucidate the role of the virus could be made. Epidemiological studies revealed a dramatic decrease of measles and related diseases such as the subacute sclerosing panencephalitis since the introduction of MV vaccination programs in USA and Europe. Indeed, some surgeons reported decreasing numbers of stapes surgery and a shift towards elder patients. Our epidemiological survey of all patients hospitalized with otosclerosis in Germany between 1993 and 2004 demonstrates a highly significant decrease in otosclerosis among the population vaccinated against the MV. The strong correlation makes it most plausible that the MV is at least one triggering factor for the development of otosclerosis.

Surgical Findings and Long-Term Hearing Results in 3,050 Stapedotomies for Primary Otosclerosis

OBJECTIVE

To evaluate with a new otologic database the results of primary stapes surgery for otosclerosis with up to 14 years of follow-up in a consecutive series of 2,525 patients operated on by the same surgeon with the same technique (stapedotomy and vein graft interposition) and to provide online access to the complete data of this study for the reviewers. To study the effect of specific operative findings (obliterative otosclerosis and simultaneous malleus ankylosis) and age at the time of surgery on the long-term outcome.

STUDY DESIGN

Prospective clinical study using a new computerized otologic database.

SETTING

: Tertiary referral center.

PATIENTS

Two thousand five hundred twenty-five patients who underwent 3,050 stapedotomies for otosclerotic stapes fixation were enrolled in this study from January 1991 to December 2004. Separate analyses were made for two unique pathologies (92 cases of obliterative otosclerosis and 19 cases of simultaneous malleus ankylosis) diagnosed during surgery and for patients in two age brackets (<or=18 yr [28 patients] and >or=65 yr [302 patients]).

INTERVENTION

Stapedotomy with vein graft interposition and reconstruction with either a Teflon piston, a bucket handle prosthesis, or a total prosthesis.

MAIN OUTCOME MEASURES

Preoperative and postoperative audiometric evaluation using conventional audiometry. Air-bone gap (ABG), bone-conduction thresholds, and air-conduction thresholds were all assessed. Postoperative audiometry was performed at 3, 6, 9, 12, 18, and 24 months and then annually for 14 years.

RESULTS

Overall, the postoperative ABG was closed to 10 dB in 94.2% of cases. The mean four-frequency postoperative ABG was 1.7 dB compared with 25.6 dB preoperatively. The mean four-frequency bone-conduction thresholds were unchanged postoperatively. A significant postoperative sensorineural hearing loss (SNHL; >15 dB) was seen in 0.5% of cases in this series. Postoperative ABG was achieved to within 10 dB in 95% of cases of obliterative otosclerosis and in 64.7% of cases of simultaneous malleus ankylosis. A significant postoperative SNHL (>15 dB) was seen in 4.8% of cases of obliterative otosclerosis and was not observed in any cases of simultaneous malleus ankylosis. Postoperative ABG was achieved to within 10 dB in 93.5% of cases in the pediatric series and in 94.5% of cases in the senior series. A significant postoperative SNHL (>15 dB) was seen in 0.7% of cases in the senior group but was not observed in the children.

CONCLUSION

Using a new otologic database, our series confirms that stapedotomy with vein graft interposition for otosclerotic stapes fixation is a safe and successful treatment for long-term hearing improvement. The deterioration in hearing with time after stapedotomy did not exceed the rate of hearing loss because of presbyacusis. Therefore, argon laser stapedotomy with vein graft interposition is our preferred surgical technique in the treatment of otosclerosis. Obliterative otosclerosis and simultaneous malleus ankylosis may be encountered during stapedotomy. Our study shows that reasonable success rates can still be expected in these situations. Stapedotomy results in the elderly and in children are comparable to those obtained in patients of other groups of age undergoing surgery for otosclerosis without an increased risk for complications.

Glucocorticoids Inhibit Diastrophic Dysplasia Sulfate Transporter Activity in Otosclerosis by Interleukin-6

HYPOTHESIS/OBJECTIVE

Otosclerosis is a bone remodeling disorder localized to the otic capsule and associated with inflammation. In vitro, increased activity of the diastrophic dysplasia sulfate transporter (DTDST), which is implicated in bone metabolism, has been reported. Because glucocorticoids modulate the bone turnover and inhibit inflammatory processes, we investigated the effect of dexamethasone (Dex) on interleukin-6 and DTDST in otosclerosis.

STUDY DESIGN

The authors conducted a prospective, case-control study.

MATERIALS AND METHODS

Primary cell cultures were obtained from stapes and external auditory canals in otosclerosis (n = 21) and control patients (n = 18). Assays with [H]Dex evaluated specific binding sites in otosclerotic and control stapes. The effects of Dex (10 to 10 M) and RU486 (10 M), a glucocorticoid antagonist, were studied on DTDST activity by sulfate uptake. IL-6 secretion was measured in culture media before and after Dex (10 M, 24 hours). The effect of IL-6 (10 M, 24 hours) was assessed on DTDST activity in control stapes.

RESULTS

: The number of specific Dex-binding sites was similar in all stapedial cultures. Dex inhibited DTDST activity (19.4 +/- 1.02 vs. 29.4 +/- 3.94 pmol/microg prot/5 minutes) only in otosclerotic stapes. This effect was dose-dependent, antagonized by RU 486 and only observed 24 hours after Dex exposure. Interleukin (IL)-6 stimulated DTDST activity in normal stapes, whereas Dex inhibited IL-6 production only in otosclerotic stapes.

CONCLUSION

Dex inhibits the DTDST activity, at least in part, through a reduction of IL-6 secretion only in otosclerotic cells. This effect is mediated through the glucocorticoid receptors and may lead to the reduction of bone turnover.

Activated Osteoclasts with CD51/61 Expression in Otosclerosis

HYPOTHESIS

Stapes ankylosis is supposed to be a disease with variable histopathology caused by otosclerosis or pseudo-otosclerosis. Persistent measles virus infection of the otic capsule could induce reactivation of quiescent embryonic osteoclasts in otosclerosis.

BACKGROUND

Presence of measles virus RNA was demonstrated in the footplates of otosclerotic patients by reverse-transcription polymerase chain reaction (RT-PCR). Histology of active otosclerosis is featured by the presence of numerous osteoclasts with unknown phenotype.

METHODS

Nucleic acid was extracted from stapes footplates of clinically otosclerotic patients (n = 261). Genomic RNA of measles virus was amplified by RT-PCR. Amplification results were correlated to postoperative histologic and CD51/61 specific immunohistologic findings. A parallel alcalic phosphatase activity assessment was performed to evaluate the metabolic activity of osteoclasts in each section.

RESULTS

Among 261 stapes fixation cases, 175 otosclerotic stapes contained measles virus RNA. Histology for virus negative stapes (n = 86) represented nonotosclerotic, degenerative disorders. Histologically confirmed otosclerosis was featured by the presence of osteoclasts with renewed, embryonic phenotype. In otosclerosis, alcalic phosphatase activity was significantly higher compared with nonotosclerotic stapes ankylosis (P < .001).

CONCLUSION

The presence of CD51/61 positive osteoclasts in otosclerotic bone containing viral sequences provides the basis for an inflammatory bone remodeling disorder. Otosclerosis is a disease caused by persistent measles virus infection and reactivation of resting embryonic osteoclasts in the otic capsule.

Mechanisms in protein O-glycan biosynthesis and clinical and molecular aspects of protein O-glycan biosynthesis defects: a review

BACKGROUND

Genetic diseases that affect the biosynthesis of protein O-glycans are a rapidly growing group of disorders. Because this group of disorders does not have a collective name, it is difficult to get an overview of O-glycosylation in relation to human health and disease. Many patients with an unsolved defect in N-glycosylation are found to have an abnormal O-glycosylation as well. It is becoming increasingly evident that the primary defect of these disorders is not necessarily localized in one of the glycan-specific transferases, but can likewise be found in the biosynthesis of nucleotide sugars, their transport to the endoplasmic reticulum (ER)/Golgi, and in Golgi trafficking. Already, disorders in O-glycan biosynthesis form a substantial group of genetic diseases. In view of the number of genes involved in O-glycosylation processes and the increasing scientific interest in congenital disorders of glycosylation, it is expected that the number of identified diseases in this group will grow rapidly over the coming years.

CONTENT

We first discuss the biosynthesis of protein O-glycans from their building blocks to their secretion from the Golgi. Subsequently, we review 24 different genetic disorders in O-glycosylation and 10 different genetic disorders that affect both N- and O-glycosylation. The key clinical, metabolic, chemical, diagnostic, and genetic features are described. Additionally, we describe methods that can be used in clinical laboratory screening for protein O-glycosylation biosynthesis defects and their pitfalls. Finally, we introduce existing methods that might be useful for unraveling O-glycosylation defects in the future.

Effect of 17 beta-estradiol on diastrophic dysplasia sulfate transporter activity in otosclerotic bone cell cultures and SaOS-2 cells

OBJECTIVE

Diastrophic dysplasia sulfate transporter (DTDST) is involved in the regulation of bone turnover, and its activity in otosclerosis has been shown to be abnormally high. Taking into account the role of estrogens in the progression of otosclerosis, the possible effect of estrogens on DTDST was investigated in otosclerotic bone cell cultures and in SaOS-2, a human osteoblastic cell line.

MATERIAL AND METHODS

Primary bone cell cultures of stapes and external auditory canal (EAC) bone were obtained from 33 patients with otosclerosis and 18 control patients undergoing cerebellopontine angle tumor surgery. These cultures were assessed in parallel with SaOS-2 cells. Estrogen receptors (ERs) were detected using reverse transcriptase polymerase chain reaction. DTDST activity was assessed by sulfate uptake at baseline and after 24 h of incubation with 17 beta-estradiol at concentrations ranging from 10(-12) to 10(-6) M.

RESULTS

Stapes and EAC cultures predominantly expressed mRNA of ER alpha, while ER beta expression was predominant in SaOS-2 cells. In stapes and EAC cultures no modification of DTDST activity was observed with 10(-8) M 17 beta-estradiol. In SaOS-2 cells, DTDST activity was inhibited by 17 beta-estradiol (93.5+/-9.21 vs 83.6+/-8.83 pmol/mg protein/5 min, n=29; mean of differences=10.0+/-3.22, paired t-test, p<0.01).

CONCLUSION

DTDST activity is regulated by estrogens in SaOS-2 cells, but not in primary cell cultures from stapes and EAC. This difference in the regulation mechanisms may be related to the type of estrogen receptor expressed.