Composition of the otosclerotic stapes: electron microprobe analyses

For the first time, otosclerotic stapes have been distinguished from unafflicted controls at a high level of significance by using a spectrum of elements measured by energy-dispersive spectrometer-electron probe microanalyses (EDS/EPMA). Discriminant analyses of the maximum concentration of 13 elements measured at several sites within each of 32 stapes differentiated otosclerotic from unafflicted individuals well above the 95% confidence level. Eight of the 9 control (unafflicted) and 21 of the 23 afflicted stapes were correctly classified. In descending order of contribution to the discriminant function, the elements are Zn > Cr > K > Ca > Si > Mn > Na > Al > Mg > P > Fe > S > Ti. Zinc and chromium account for much of the difference, but discriminant analyses excluding them still distinguish the two groups at the 95% confidence level. These results are consistent with previous reports of high levels of alkaline phosphatase, a zinc-containing enzyme, in afflicted stapes. But the broad spectrum of elements capable of distinguishing otosclerotic stapes warrants study of additional zinc-containing and other metal-containing or metal-activated moieties.

Inner ear basic fibroblast growth factor in CBA/J, C3H/HeJ, and autoimmune Palmerston north mice

Basic fibroblast growth factor (bFGF) has a mitogenic effect on fibroblasts and osteoblasts for matrix proliferation and on endothelial cells for neovascularization. Because otic capsule osteogenesis in autoimmune disease subjects often involves abnormal matrix and vascular changes, bFGF may serve as a potential mediator for such bone disorders. To investigate this relationship, bFGF was evaluated in the Palmerston North autoimmune strain mouse, which develops otic capsule sclerotic lesions during the progression of its systemic disease. Inner ears from PN mice, along with control CBA/J and C3H/HeJ mice, were immunohistochemically stained with antibodies against bFGF to identify its presence and possible role in otic capsule disease. Although cells reactive for bFGF were observed along the lining of the otic capsule in all three strains, a significantly higher frequency was observed in the PN mice. Other sites of staining included connective tissue around the tensor tympani muscle and the geniculate ganglion. This identification of bFGF in the otic capsule raises the possibility that it may play some role in normal bone maintenance, as well as abnormal bone or connective tissue remodeling in autoimmune disease.

Synthesis and secretion of glycosaminoglycans and proteins in human normal and otosclerotic bone cells

Some biosynthetic activities of normal and otosclerotic temporal bone cultures have been studied. Bone cells were cultured for 24 hrs. in medium containing 3H-glucosamine, 35SO4 or 3H-proline. Labelled glycosaminoglycans (GAG) and proteins were precipitated from cells and media. In otosclerotic bone cells there was an evident reduction in the synthesis and secretion of radiolabelled macromolecules. The inhibitory effect was always greater in the extracellular than in the intracellular compartment. Some glycosidases were also studied. Otosclerosis decreased the activity of all enzymes examined, indicating that the lower GAG synthesis and secretion in otosclerotic bone cells were not due to an increased degradation.

Characterization of the cytoskeleton in human normal and otosclerotic osteoblast-like cells

The localization and distribution of some cytoskeletal protein components were studied by immunostaining methods in normal and ostosclerotic osteoblast-like cells. The protein components investigated were microtubules (beta-tubulin), intermediate filaments (vimentin), microfilaments (actin and myosin) and structural proteins (alpha-actinin and fibronectin). Although the mechanism is not yet clear, the alterations observed in the pathological cells could well play a role in the expression of otosclerosis.

Type II collagen distribution in the monkey ear

A possible role for type II collagen autoimmunity in the pathogenesis of Meniere's disease and otosclerosis was recently suggested by studies demonstrating anti-type II collagen antibody in the serum of humans with these disorders and by the induction of similar lesions in animals immunized with type II collagen. In light of these findings, we studied the anatomic distribution of type II collagen in the nonhuman primate ear by immunohistochemical techniques using defined monoclonal antibodies to type II collagen. Type II collagen was observed in the cartilage plate of the auricle and external auditory meatus, tympanic annulus, lamina propria of tympanic membrane (pars tensa), interossicular joints, stapes footplate, eustachian tube cartilage, enchondral layer and globuli interossei of the otic capsule, Rosenthal canal, cribriform base, osseous spiral lamina, spiral ligament, limbus, tectorial membrane, semicircular canal membrane and subepithelial layer of the ampullary crista, utricular and saccular maculae, and the endolymphatic duct and proximal part of the sac. Thus, type II collagen should be considered an important component of ear tissue.

Hormonal receptor site alterations in the etiopathogenesis of otosclerosis

The authors have studied calcium 45 uptake and cAMP intracellular levels in normal and otosclerotic bone cell cultures after stimulation with calcitonin in the presence or absence of propranolol. The results seem to demonstrate that poststimulatory 45Ca incorporation is slightly different in normal and otosclerotic cell cultures, being slower but longer lasting in the latter. Propranolol administration markedly inhibits 45Ca uptake in normal cells, while in otosclerotic cells a massive intracellular penetration becomes evident after an initial inhibitory phase. Also cAMP intracellular levels behave differently; a marked increase, followed by a rapid decrease, can be detected in normal cells after stimulation with calcitonin, while in otosclerotic cells, the increase is slower and followed by a long lasting reduction. Adding propranolol reduces cAMP levels in normal cells, while it increases levels in otosclerotic cells. The different behavior of calcium metabolism and cAMP levels after stimulation with calcitonin, depending upon the presence or absence of propranolol, seems to indicate an alteration of the transducing mechanism between stimulus, receptor, and cellular effector in otosclerotic cells.

Possible role of peptides derived from otosclerotic bone in the mechanism of sensorineural hearing loss

Otosclerotic stapes footplates, superstructures and temporal cortical bones were extracted with 0.25 M guanidine X HCl 0.5 M EDTA (pH 7.4) solution. The extracted non-collagenous peptides/proteins were separated chromatographically on a Sephadex G-25 microcolumn. The peptide composition of the bone samples were compared by capillary analytical isotachophoresis (ITP) in the molecular mass range 0.3-5 kD. The otosclerotic stapes footplate contained 13 ITP subfractions, while the stapes superstructures and cortical bone contained only 9 and 10, respectively. An otosclerosis-specific ITP subfraction was also detected in the stapes footplate, but not in the stapes superstructure or cortical bone. This subfraction was previously demonstrated in the otosclerotic perilymph as well. Four ITP subfractions occurred common in the otosclerotic stapes footplate, the superstructure and the cortical bone. Two of these common subfractions were not found in the cortical bone peptide extract, but all of them revealed higher than normal levels in the otosclerotic perilymph.

The effect of flavone treatment on human otosclerotic ossicle organ cultures

We studied the effect of 7-isopropoxy-isoflavone (Ipriflavone) on the collagen synthesizing activity in human otosclerotic auditory ossicle samples from whole organ cultures during incubation for 96 h, and compared this effect with that found in normal meatal cortical bone. Ipriflavone led to a dose-dependent increase in the collagen synthesizing activity in both the healthy and the otosclerotic bone samples. At the highest Ipriflavone concentration used (50 microM), collagen synthesis increased 6-fold in the cortical bone and 9-fold in the otosclerotic bone, as compared with untreated controls. These findings indicate that the otosclerotic bone cavities are filled in vitro with organic matrix.

Cyclic nucleotide and prostaglandin F2 alpha contents of otosclerotic auditory ossicles

We found that the cyclic-adenosine-3',5'-monophosphate (cAMP) contents of otosclerotic human ossicles were 40-50 times greater than basal levels. Cyclic-guanosine-3',5'-monophosphate (cGMP) levels were also found to be greater than in physiological conditions, but lower than in cortical bone. These findings suggest the extensive participation of these nucleotide coenzymes in effector cells during the process of bone resorption. This emphasizes the role of bone-resorbing cells in this process as well as the probable osteoclast progenitor role of vascular endothelial cells and their enhanced activity for differentiation. At the same time, the absence of prostaglandin F2 alpha content in the otosclerotic bone analyzed appears to exclude cartilage remnants as a source for inducing the changes in remodelling that occur.

Vitamin D deficiency and otosclerosis

A prospective study of 47 patients with otosclerosis was undertaken to investigate the possible etiologic role of vitamin D undernutrition. The population comprised 27 women and 20 men, with a mean age of 46.4 years (range 21 to 79). The disease was bilateral in 43 patients, and cochlear involvement was present in 84.4%. The mean duration of symptoms was 17.1 years. Vitamin D status was evaluated by measuring the plasma 25-hydroxy vitamin D3 (25-OHD), which is the main storage metabolite. Abnormally low 25-OHD levels were found in 10 patients (21.7%) and borderline low levels in another two. Raised serum alkaline phosphatase levels were present in 32.6%, calcium in 6.5%, and inorganic phosphate in 4.3%. Calcium and vitamin D replacement therapy resulted in significant hearing improvement in 3 of 16 patients; these data support a causal correlation. Vitamin D deficiency is probably a factor in the etiology of some cases of otosclerosis and is important, since the deafness resulting from cochlear involvement may be reversible.

Non-collagen proteins of stapedial bone matrix in perilymph of otosclerotic patients

Non-collagen proteins extracted from the otosclerotic stapes footplate, superstructure and temporal cortical bone were compared with the protein patterns of normal and otosclerotic perilymph by analytical isotachophoresis (ITP). Normal and otosclerotic perilymph yielded basically identical isotachophoretic subfractions. Thirteen subfractions were detected moving as anions at pH 9.6 in the normal perilymph, versus 16 subfractions of similar character in the otosclerotic perilymph. Of these 16 protein subfractions, one (which was not detected in the normal perilymph) could be found in the ITP-gram of the stapes footplate non-collagen proteins, but not of the stapes superstructure or temporal cortical bone. Our results support the concept that protein can enter the inner ear fluid spaces from the otosclerotic bone. The biological significance of these proteins has not yet been clarified.

Peptides of the otosclerotic perilymph examined by analytical isotachophoresis

Perilymphs of normal and otosclerotic origin were separated chromatographically on a Sephadex G-25 microcolumn. Peptide composition of the perilymphs was compared by capillary analytical isotachophoresis in the molecular mass range 0.3-5 kD. Otosclerotic perilymph samples contain a heterogeneous, UV-absorbing peptide subfraction which is not detected in the normal perilymph. Normal and otosclerotic perilymph, furthermore, contain four common subfractions detected in twice the normal concentration in the otosclerotic perilymph. These ITP subfractions are degraded during acid hydrolysis (6 M HCI). On the contrary, otosclerosis is a deficient state compared with the normal, as the number of peptides or oligoglycopeptides is twice as high in normal as in otosclerotic perilymph, beside the otosclerosis specific peptides.

Collagen fibres in otosclerosis and in osteogenesis imperfecta tarda. A light and electron microscopic study

Skin biopsies taken from patients with osteogenesis imperfecta tarda and otosclerosis were compared blind by light- and electron microscopy with similar biopsies taken from normal volunteers in an effort to find common pathological features in the collagen fibres from the two patient groups, thus corroborating the theory that osteogenesis imperfecta and otosclerosis might be due to a common genetic anomaly in the form of a mesenchymal hypoplasia. We were not able to find differences in structure or quantity of the collagen-, elastic- or reticular fibres between normals and the two patient groups. We cannot, on the basis of our previous work and on the present morphological investigation, give support to the above-mentioned theory.

Otosclerosis and otospongiosis: clinical and histological comparisons

The simultaneous occurrence of otosclerosis and otospongiosis in the same lesion is well documented. The logical sequence of events would seem to be softening and destruction of the bone by the otospongiotic lesion, which is subsequently converted to otosclerosis. Examination of 46 temporal bones has led us to further classify the lesion as: 1. an active lesion, both otospongiotic and otosclerotic, 2. an inactive lesion, also both otosclerotic and otospongiotic, or 3. a fibrous lesion. Hyalinization of the spiral ligament only occurs adjacent to active otospongiotic or very large otosclerotic lesions. If the lesion adjacent to the spiral ligament is inactive, there is no hyalinization. It seems illogical that a hyalinized spiral ligament will return to normal when the lesion changes from active otospongiosis to inactive otosclerosis. Otospongiotic and otosclerotic lesions are found side by side at the periphery of lesions, and both are adjacent to normal bone. These findings have implications concerning the mode of action of sodium fluoride and other medications that are under evaluation for the control of the sensorineural hearing loss due to otosclerosis.

Histomorphometric analysis of iliac trabecular bone in otosclerosis

With the aim of investigating whether patients with otosclerosis suffer from a generalized bone disorder, a histomorphometric analysis of trabecular bone from the iliac crest was performed. Iliac crest biopsies from 10 patients with otosclerosis and 20 normal controls were obtained after tetracycline double labelling and examined by histomorphometry. No significant differences were found in the estimates of density and remodeling of bone between patients and sex and age-matched normal controls. Qualitatively the bone specimens showed no signs of any generalized bone disorder.

Perilymph oxygenation in sudden and progressive sensorineural hearing loss

The perilymphatic oxygen tension of the vestibular perilymph of 34 patients with different inner ear losses were measured with the polarographic method before and after inhalation with carbogen. Two patterns of disturbed perilymphatic oxygenation were observed: 1) Characterized by low initial values of perilymphatic oxygenation and normal response to carbogen inhalation was present in sudden deafness and sudden cochleovestibular loss of inner ear function. 2) Characterized by normal initial values of perilymphatic oxygenation and a low response to carbogen, was found in presence of a slowly progressive sensorineural hearing loss. The significance of the obtained results in regard to the possible vascular pathology of the inner ear is discussed.

Otosclerosis: relationship of spiral ligament hyalinization to sensorineural hearing loss

The sensorineural component of a mixed hearing loss due to otosclerosis is generally accepted as due to the otosclerotic lesion. The existence of pure cochlear otosclerosis without stapes fixation has been questioned. However, we are documenting 7 such cases in a separate publication. Results of this study, which evaluates 46 temporal bones with clinical or cochlear otosclerosis, demonstrate that the degree of sensorineural loss is directly related to the amount of hyalinization of the spiral ligament. The hyalinization occurs adjacent to active otospongiotic lesions but not next to inactive otosclerotic lesions. Both types of lesions may involve the cochlear endosteum. Small channels through the endosteal bone from the lesion to the spiral ligament have been found. The hyalinization spreads laterally from these channels. The hyalinization is presumably a result of the passage of toxic substances (proteolytic enzymes) from the lesion to the ligament. Strial atrophy is most pronounced on ligaments with the greatest degree of hyalinization. Hyalinization in only one ear produces decreased hearing compared to the other ear.

Examination of noncollagen protein composition of the footplate and superstructure of the otosclerotic stapes

We have differentially precipitated 2 fractions of noncollagen proteins extracted from separately pooled superstructure and footplate of surgically removed stapes of patients from both sexes, who have suffered from otosclerosis. The two fractions were: EDTA-soluble, CaCl2 precipitable (Fraction-1) and EDTA-soluble, CaCl2 non-precipitable proteins. The protein pattern of these two fractions was compared by isoelectric focusing and two-dimensional gel electrophoresis. The phosphoprotein fraction (Fraction-1) of the otosclerotic stapes footplate contained acidic (pI 3-6), low molecular weight (20-40 kD) proteins, which were not detected in the superstructure and temporal cortical bone. Two-dimensional mapping of the Fraction-2 showed predominantly acidic proteins in the footplate and some basic minor components in the superstructure. The lack of the low molecular weight proteins in the superstructure proves the localisation of the otosclerotic process only in the footplate.

Fragile bones and fragile ears

Conductive, sensorineural and mixed hearing loss occur in osteogenesis imperfecta in autosomal dominant inheritance pattern. Hearing loss is generally due to the middle and inner ear pathology of osteogenesis imperfecta and only occasionally to the coincidental association of otosclerosis and osteogenesis imperfecta. Two lesions cause the conductive hearing loss of osteogenesis imperfecta: (1) functional ossicular discontinuity due either to stapes superstructure fracture or fibrous replacement, or (2) thick, crumbly, lightly fixed stapes footplate. Cochlear hair cell loss, stria vascularis atrophy and calcification, tectorial membrane distortion and perilymph hemorrhage are autopsy findings that could account for sensorineural hearing loss, which occurs in a surprisingly high percentage of osteogenesis imperfecta patients. Hearing loss occurs earlier in osteogenesis imperfecta than in otosclerosis. Distinctive acoustic impedance and X-ray abnormalities occur in osteogenesis imperfecta. Other otologic findings may include lopped pinna, notching of the helix of the pinna, rosy flush of the medial wall of the middle ear and vestibular abnormalities.

Mineral content of skeletal bones in otosclerosis

In 63 patients with otosclerosis confirmed by operation, the bone mineral content was determined by photon absorptiometry. The bone mineral content and bone mineral concentration were found to be normal, which lends support to the assumption that otosclerosis is a localized disease and not a manifestation of a generalized disorder of the skeletal system.

Bone mineral content in osteogenesis imperfecta tarda and in otosclerosis

In 22 patients with osteogenesis imperfecta and in 63 patients with otosclerosis the bone mineral content in peripheral bones was determined by photon absorptiometry. The bone mineral content proved significantly reduced in patients with osteogenesis imperfecta as compared with normals and with patients with otosclerosis. In the latter patients the bone mineral content was normal. These findings support the assumption that stapedial fixation in otosclerosis and in osteogenesis imperfecta is of different aetiology.