Journal of the Anatomical Society of India

M. Azim Khan, Aijaz A. Khan and Nafis A. Faruqi - JNMC, AMU, Aligarh

Abstract: Topical nasal decongestants and intranasal antihistamines are effective for treatment of vasomotor and allergic rhinitis. Protracted use of such drugs may lead to aggravation of the symptoms. One group of albino rats received azelastine nasal sprays and another group xylometazoline nasal drops, once daily for one month. Light microscopy of the haematoxylin-eosin stained, azelastine exposed, respiratory mucosa revealed congested capillaries with leucocyte margination in lamina propria, while glomerular and external plexiform layers of olfactory bulb showed mild inflammatory exocytosis with vascularization and vacuolar degeneration of neural bundles. Xylometazoline exposed respiratory and olfactory mucosa showed epithelial cell disarray and basal cell proliferation with cytoplasmic homogenization and hyperaemic subepithelium, while the glomerular layer of the olfactory bulb showed oedematous, homogenized nerve bundles, periglomerular hypercellularity and lateralization of nuclei with chronic inflammatory cells. It was concluded that olfactory mucosa and olfactory bulb are much more susceptible to xylometazoline than to azelastine and therapeutic usage of azelastine appears safer than xylometazoline for a given period of time.

Key Words: Azelastine, xylometazoline, nasal mucosa, olfactory bulb.

Introduction:

Intranasal antihistamines have been approved as the first line treatment for the symptoms of seasonal allergic rhinitis such as rhinorrhea, sneezing and nasal pruritis. Classical or 1st generation H1 (Histamine receptor) antagonists when used systemically, cross the blood-brain barrier, produce sedation and other nonspecific events, while intranasal azelastine (IInd generation H1 antagonist) does not produce sedation and non-specific symptoms. Azelastine HCl, is the first intranasal antihistamine preparation approved for use in the United states Newson Smith et al. (1997); Ratner et al. (1994); Laforce et al. (1996). Topical nasal decongestants are mainly vasoconstrictors that contain oxy-or xylometazoline Malm (1994). Vasoconstrictors temporarily induce vasoconstriction resulting into decongestion due to reduction in the thickness of the nasal mucosa. Detailed histological changes in nasal mucosa after exposure to azelastine nasal spray or xylometazoline nasal drop are lacking. Moreover, the effects on the olfactory mucosa and olfactory bulb could not be found. Therefore, the present study was conducted to find out the azelastine and xylometazoline induced microscopic changes in the nasal mucosa and the olfactory bulb and also to compare the relative susceptibility of respiratory and olfactory mucosa to azelastine (nasal sprays) and xylometazoline (nasal drops).

Materials and Methods

Material And Method 24 young adult albino rats weighing 120 gm (±10 gm) of Charles Foster strain were obtained from the Central Animal House, J.N. Medical College, AMU, Aligarh. Animals were divided into 3 groups (A, B and C) of 8 rats each. Group A received azelastine nasal sprays (0.1% aqueous solution in a metered spray delivery device), 1 spray daily in each nostril for 1 month.- Group B received xylometazoline nasal drops (0.1 %) 1 drop daily in each nostril for 1 month. Group C consisted of control against A and B and received no medication but were maintained in similar environment and food. The animals were sacrificed at the end of the experiment. The nasal mucosa and olfactory bulb were immersion-fixed in 10% buffered formalin. Tissue samples, were processed for 8-10µ thick paraffin sections. Light microscopic observations were made on H&E stained sections.

Observations:

Control Group: Respiratory mucosa consisted of pseudostratified ciliated columnar epithelium interspersed with goblet and basal cells lying on a thin basal lamina and beneath the basal lamina were clustered groups of serous and mucous glands. (Fig. 1) Olfactory mucosa consisted of thick pseudostratified ciliated columnar epithelium, within its thickness there were many layers of nuclei, although towards the free surface, there was a nucleus free zone. The epithelium was lying on basal lamina, underlying lamina propria contained numerous olfactory nerve fascicles and subepithelial olfactory glands (of Bowman) (Fig. 2). Olfactory bulb on coronal sections revealed laminar structure. From superficial to deep it had olfactory nerve fibre layer, glomerular layer penetrated by the incoming olfactory nerve fibres, the external plexiform layer comprised of the principal and secondary dendrites of mitral and tufted cells, the mitral cell layer consisted of somata of large mitral cells, the internal plexiform composed of axons, and granule cell layer contained the majority of granule cells together with their superficial and deep processes (Fig. 3)

Fig. 1: Photomicrograph of the nasal mucosa of albino rat showing characteristic respiratory epithelium (pseudostratified ciliated) with sub epithelial serous and mucous glands in the lamina propria (–>) H/E, X 40

Fig. 2: Photomicrograph of the olfactory mucosa of albino rat showing characteristic olfactory epithelium (pseudostratified, considerably thicker than respiratory epithelium) with dead cell in the superficial Zone (–>) and olfactory nerve fascicles in subepithelial connective tissue (<–>) H/E, X 400

Fig. 3: Olfactory bulb from control showing laminar organization in coronal section. 1. Olfactory nerve fibre layer, 2. Layer of synaptic gloeruli, 3. External plexiform layer, 4. Mitral cell layer, 5. Internal plexiform layer, 6. Granule cell layer. H & E, X 200

Fig. 4: Photomicrograph of azelastine treated respiratory mucosa. Note the congested capillary with leucocyte margination (–>), epithelial spongiosis (t) and infiltration of mononuclear cells in lamina propria (). H/E stain, x 400.

Azelastine exposure revealed that the olfactory mucosa remained-relatively unaffected in terms of thickness and cellular architecture, while the respiratory mucosa showed mild epithelial spongiosis and increased mononuclear cells with congested capillaries in lamina propria (Fig.4). Olfactory bulb showed increased vascularity and vacuolar degeneration of neural bundles with mild inflammatory exocytosis of mononuclear cells in glomerular and external plexiform layers (Fig. 5). Occasionally, eosinophils were also observed.

Xylometazoline exposure revealed that both olfactory and respiratory mucosa were equally affected. Basal cell proliferation of epithelium and cytoplasmic homogenization (cytoplasmic boundaries merging with each other resulting into homogenous hyaline pattern) with obtunded cell boundaries were the most characteristic feature (Fig. 6). Subepithelial blood vessels showed vascular dilatation and congestion with sub-epithelial lymphatic infiltration, indicating chronic inflammation. Epithelial cells showed cellular disarrangement and degenerative changes in the form of nuclear damage and loss of cilia. Olfactory bulb showed homogenized nerve bundles with separation of oedematous fascicles. Increased perineuronal spaces, periglomerular hypercellularity, lateralization of nuclei, mild to moderate inflammation and occasional infiltration of mononuclears and eosinophils (Fig. 7).

Fig. 5: Photomicrograph of azelastine treated olfactory bulb (outer 3 layers). Note the vascularization and vacuolar degeneration ( ) of neural bundles with mild inflammatory exocytosis (?). H/E stain, x 400.

Fig. 6: Photomicrograph of xylometazoline treated olfactory mucosa. Note the marked cytoplasmic homogenization (–>)in superficial layer of epithelium with disarray and basal cell proliferation and sub epithelial hyperaemia ( ). H/E stain, x 400.

Fig. 7: Photomicrograph of xylometazoline treated olfactory bulb. Note the oedematous homogenized nerve-bundles ( ) with lateralization of nuclei () and chronic inflammatory cells (mononuclears ( ) and eosinophils (–>). H/E stain, x 400.

Discussion:

The regular use of topical (intranasal) azelastine is effective in getting symptomatic relief and reduction of the symptoms of seasonal allergic rhinitis after 4 weeks of therapy, Siegel (1988). The apparently unaffected olfactory mucosa and minimally affected respiratory mucosa in the form of microvascular congestion and mononuclear infiltration observed in the present study were comparable with studies of Thomas et al. (1992) and Peucchi et al. (1995). These workers have further shown that topical azelastine is better tolerated and has no side-effects. According to McTavish and Sorkin (1989) azelastine has an antiinflammatory activity, however in the present study increased number of mononuclear cells in the respiratory mucosa and olfactory bulb clearly indicated that it induces inflammation. The presence of eosinophils and mononuclears cells in the olfactory bulb observed in the present study finds support from the study of Saengpanich et al. (2002), wherein after methacholine challenge eosinophils were neither inhibited nor reduced by azelastine. Increased nasal congestion are also in agreement with the study conducted by Golden et al. (2000) in which they reported that azelastine is effective in reducing rhinorrhea and non-effective in reducing the severity of nasal congestion. They also emphasized that azelastine can aggravate nasal congestion. While the finding of nasal congestion in present study does not match with the study conducted by Saengpanich et al. (2002) in which they reported that treatment with intranasal azelastine results in significant reductions of allergen-induced sneezing, rhinorrhea, itching and nasal congestion.

Xylometazoline has been shown to induce a pronounced decongestion that lasts for 6 to 8 hours Akerlund et al. (1989). In the present study after one month exposure to xylometazoline, dilatation of blood vessels and vascular congestion were comparable with the past studies. In one of these studies, Graf et al. (1995), reported that healthy subjects complained of nasal stuffiness from the 2nd week of receiving the medication. By rhinostereometric study, Graf and Juto (1994) reported that after 10 days use of oxymetazoline nasal spray no rebound swelling occurs, but after 30 days use of oxymetazoline nasal spray a pronounced rebound swelling with clinical symptom of nasal stuffiness appears. They also reported that rhinitis medicamentosa develops after a relatively short time on oxymetazoline exposure, even in healthy volunteers, and that the swelling is due to a vasodilatation rather than an edema. In the present study increased mucosal swelling associated chronic inflammation (infiltration of chronic inflammatory cells in the lamina propria) were comparable to those reported by Elwany et al. (1983). The oedematous homogenized epithelial cytoplasm with oedematous nerve bundles observed in the nasal mucosa and olfactory bulb clearly indicated that xylometazoline causes rebound or compensatory vasodilation with subsequent swelling of nasal mucosa as reported by Baldwin (1977) as well as in olfactory bulb. It is also believed by some workers like Rijntjes (1985), Graf and Juto (1994 and 1995) that rebound nasal congestion may be produced by protracted use of xylometazoline. The histological findings of the present study can also be compared with the findings of Suh et al. (1995). They reported that intranasal administration of oxymetazoline for more than 2 weeks causes ciliary loss, epithelial ulceration, inflammatory cell infiltration and subepithelial edema in respiratory mucosa. They also reported their electronmicroscopic findings as dilatation or vacuolization of mitochondria and endoplasmic reticula, vesicle formation in cytoplasm and widening of the intercellular spaces in 2-4 weeks oxymetazoline exposed respiratory mucosa of rabbits. In the absence of specific references with respect to effect of xylometazoline and azelastine on olfactory mucosa and olfactory bulb the observations in the present study on olfactory mucosa and olfactory bulb remained to be compared. It was concluded that olfactory mucosa and olfactory bulb are much more susceptible to xylometazoline than to azelastine. Therefore, medication by azelastine appears safer than xylometazoline in symptomatic treatment of vasomotor and allergic rhinitis.

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