Distribution of hyaluronan in the middle and inner ear. A light microscopical study in the rat using a hyaluronan-binding protein as a specific probe

Hyaluronan up-regulation is linked to renal dysfunction and hearing loss induced by silver nanoparticles

Increased application of silver nanoparticles (AgNPs) has raised concerns on their potential adverse effects on human health. However, the precise toxicological mechanisms are not known in detail. The current study hypothesized that AgNPs induced glycosaminoglycan accumulation in the basement membrane that associated with the up-regulation of its component hyaluronic acid, known as a hydrophilic molecule of binding and retaining water, and caused toxicities in the kidney and cochlea. Rats administered AgNPs through either intravenous or intratympanic injection were observed at different time points after exposure. The concentrations of creatinine and urea in the serum were elevated remarkably, and proteins leaked into the urine were increased. A significant hearing loss over a broad range of frequencies was indicated. AgNP exposure induced glycosaminoglycan accumulation and hyaluronic acid up-regulation in the basement membrane. Abundant apoptotic cell death was demonstrated in the AgNP-exposed organs. Our results suggested that glycosaminoglycan accumulation associated with the up-regulation of hyaluronic acid was involved in the toxicities of kidney and cochlea caused by AgNPs.

TLR4-mediated induction of TLR2 signaling is critical in the pathogenesis and resolution of otitis media

Otitis media is the most prevalent childhood disease in developed countries. The involvement of Toll-like receptors (TLRs) in otitis media pathophysiology has been implicated by studies in cell lines and association studies of TLR gene polymorphisms. However, precise functions of TLRs in the etiology of otitis media in vivo have not been examined. We investigated the inflammatory response to nontypeable Haemophilus influenzae using a model of otitis media in wild-type, TLR2(- /-) and TLR4(-/ -) mice by gene microarray, qPCR, immunohistochemistry, Western blot analysis and histopathology. Toll-like receptor-2(- /-) and TLR4(- /-) mice exhibited a more profound, persistent inflammation with impaired bacterial clearance compared to controls. While wild-type mice induced tumor necrosis factor-a (TNF) after non-typeable H. influenzae challenge, TLR2(-/-) and TLR4(-/-) mice lack TNF induction in the early phase of otitis media. Moreover, lack of TLR2 resulted in a late increase in IL-10 expression and prolonged failure to clear bacteria. Toll-like receptor-4(-/- ) mice showed impaired early bacterial clearance and loss of TLR2 induction in early otitis media. Our results demonstrate that both TLR2 and TLR4 signalling are critical to the regulation of infection in non-typeable H. influenzae-induced otitis media. Toll-like receptor-4 signalling appears to induce TLR2 expression, and TLR2 activation is critical for bacterial clearance and timely resolution of otitis media.

Presence of glycosaminoglycans in the endolymphatic sac

Earlier morphological investigations have revealed that the endolymph, which is present in the endolymphatic sac (ES) seems to differ from that found elsewhere in the labyrinth, in that it contains a stainable substance. Histochemical investigations indicate that this substance is rich in glycosaminoglycans (GAGs). It has been speculated that the stainable substance might play a role in regulation of fluid and ions and also, possibly, the pressure within the endolymphatic sac compartment. Endolymphatic sac specimens obtained from adult guinea pigs, rats, mice and in vitro cultured fetal inner ears were incubated with monoclonal antibodies against epitopes, and after enzymatic digestion revealed five different GAGs: hyaluronan, chondroitin-4-sulphate+dermatan sulphate, chondroitin-6-sulphate and keratan sulphate. In order to verify the specificity of these antibodies, otocysts from fetal mice were incubated in the same way. These cartilaginous specimens are known to contain GAGs in abundance and served as positive controls. The results indicate that the hyaluronan visualized by the monoclonal antibody is present to a large extent in the lumen of the ES and in the epithelial cells. Keratan sulphate and chondroitin-4-sulphate+dermatan sulphate are present within the epithelial lining, in the subepithelial tissue, and to some minor extent in the lumen, while chondroitin-6-sulphate does not show any specific staining.

Inner ear content of glycosaminoglycans as shown by monoclonal antibodies

Inner ear cells are known to contain combinations of proteins and sugar, which histochemically have been identified to be proteoglycans. To visualize these components in the macula utriculi, crista ampullaris and in the cochlea four different monoclonal antibodies against hyaluronan (HA), keratan sulphate (KS), chondroitin-6-sulphate (C-6-S) and chondroitin-4-sulphate (C-4-S) were used. The results indicate that KS is predominantly present in the lining of the vestibular hair cells, in the otoconial layer and in nerve tissue. C-4-S is present in the sensory hairs as well as in the subepithelial layer but also in the tectorial and basilar membranes of the cochlea. HA is generally present in the surface area of vestibular hair cells, to some extent in the cochlear hair cells and in the stria vascularis. C-6-S is only present to a lesser degree in the inner ear.

Time-dependent alterations of 3-fucosyl-N-acetyl-lactosamine (CD15) expression in the endolymphatic sac of adult guinea pigs after glycerol administration

The present study examined the effect of glycerol administration on 3-fucosyl-N-acetyl-lactosamine (CD15) epitope expression in the endolymphatic sac (ES) of the guinea pig's inner ear. Adult guinea pigs were injected intravenously with glycerol (2 g/kg body wt.). CD15 expression was studied at 80 min up to 5 h after treatment. In untreated animals single cells and cell groups in the ES expressing CD15 epitope intra- and intercellularly were identified by immunohistochemistry to be mainly in the epithelial layer of the rugosal and distal part of the sac. Glycerol administration modulated the expression of CD15 epitope. In the epithelial layer, expression decreased and was nearly depleted after 3 h. After 4 h of glycerol administration, CD15 expression reappeared and reached the comparable level of controls. The numbers of CD15-positive cells in the lumen of the ES increased steadily and arrived at their the highest levels in 2-h specimens. The localization of CD15-epitope expression and its modulation after glycerol administration within the ES implies that this molecule may play a role in re-establishing the sac's normal function. In addition, we speculate that CD15 may be associated with processes of an immune response in the inner ear.

Localization and quantity of hyaluronan in urogenital organs of male and female rats

The histochemical distribution of hyaluronan was analysed in various urogenital organs of male and female (non-pregnant and pregnant) rats by use of a hyaluronan-binding protein and avidin biotin/peroxidase staining. Microwave-aided fixation was used to preserve the extracellular location of hyaluronan. The concentrations of hyaluronan in the different tissues were measured with a highly sensitive radio-assay. Hyaluronan accumulated predominantly in the connective tissue around smooth muscle fibres and in the subepithelial lamina propria. Abundant hyaluronan also occurred in perivascular and perineural connective tissue. In the female urogenital organs, hyaluronan content was high in the vagina and urinary bladder, and highest in the vagina during pregnancy. In the uterus, the surface epithelium of the endometrium stained intensely. In the ovary, the zona pellucida of the oocyte and the theca interna cell layer of the follicles and the follicular fluid of mature follicles exhibited prominent staining. The corpus luteum was devoid of hyaluronan, whereas enlarged corpora lutea of pregnancy exhibited weak, patchy staining. In male urogenital organs, staining for hyaluronan was absent from the testis and epididymis, whereas the erectile connective tissue of the penis stained intensely. The hyaluronan concentrations were high in penile tissue and urinary bladder, while testis, epididymis and the ductus deferens contained only little hyaluronan.