3-Methylindole-Induced Nasal Mucosal Damage in Mice

Abstract

Abstract. 3-Methylindole (3MI) damages nasal olfactory epithelium in mice. Lesions were studied histologically from 30 minutes to 28 days after intraperitoneal injection of 400 mg 3MI/kg. Cellular swelling was apparent in olfactory epithelium by 6 hours after injection of 3M1, while respiratory epithelium was normal. Necrosis of olfactory epithelium and subepithelial glands was diffuse by 48 hours. Subsequent ulceration resulted in epithelial hyperplasia, squamous metaplasia, fibroplasia, and ossification. Partially occlusive intranasal fibrous and osseous tissue persisted through 28 days after 3MI injection.3-Methylindole (3MI), a ruminal metabolite of tryptophan, is a cause of acute bovine pulmonary edema and interstitial emphysema (ABPE).8 Experimentally, 3MI also induces pulmonary edema in ~h e e p ,~.~ rats,21 and mice.Io In small ruminant^,^ mice,10,24 and 3MI selectively damages nonciliated bronchiolar epithelial (Clara) cells. Olfactory epithelium in the nasal mucosa of mice is also selectively injured by 3MI.25 3-Methylindole is thought to be metabolized by mixed function oxidases (MFO).6J3J7-20 In the nasal cavity, olfactory epithelium is the major site of MFO activity in rats, mice, hamsters, guinea pigs, rabbits, and dogs.I2 In the present study, C57BL mice were chosen as an inbred strain with inducible MFO l 6 to facilitate further study of 3MI toxicosis. This paper describes 3MI-induced nasal mucosal damage in mice. Materials and MethodsA total of 65 C57BW6N 35-day-old male mice (Hilltop Lab Animals, Inc.) were divided into 13 groups. The mice were housed five per cage, with 12 hour light : dark cycle, and maintained on Purina Rat Chow and water ad libitum from 1 week before treatment to the end of the experiment. A 4% solution of 3MI in corn oil was injected intraperitoneally in four mice per group at a dose of 400 mg 3MI/kg. The fifth mouse in each group received a comparable volume of corn oil by the same route and served as a control.Mice were killed by cervical dislocation %, 1, 6, 12, and 24 hours, and 2,3,5,7, 10, 14,2 1, and 28 days after injection of 3MI. Tissues were fixed by perfusion of 5 to 6 ml of cacodylate-buffered 2% formaldehyde1 Yo glutaraldehyde via the right cardiac ventricle. The head was removed and the nasal cavity flushed with the same fixative through a 20-gauge cannula inserted 2-3 mm into the nasopharynx. The skin and mandibles were removed, and the head was immersed in fixative for at least 48 hours. To decalcify bone, the head was immersed in equal volumes of 20% sodium citrate and 50% formic acid for approximately 24 hours, then transferred to a saturated solution of sodium bicarbonate and washed in running tap water overnight to return pH to neutral. Frontal sections of the head through the plane of the first molar tooth were embedded in methacrylate. Sections cut at 2-3 bm were stained with hematoxlyin and eosin (HE) for light microscopy. ResultsWithin 30 minutes of 3MI injection, mice were lethargic with slowed respiratory rate. By 24 hours, mice were huddled and c...

Respective Roles of CYP2A5 and CYP2F2 in the Bioactivation of 3-Methylindole in Mouse Olfactory Mucosa and Lung: Studies Using Cyp2a5-Null and Cyp2f2-Null Mouse Models

“…3MI can selectively induce necrosis in the bronchiolar epithelial (Clara) cells in the mouse lung (Turk et al, 1984) and necrosis in epithelial cells of Bowman's glands and olfactory sustentacular cells in mouse nasal olfactory mucosa (OM) (Turk et al, 1987;Miller and O'Bryan, 2003). Cytochrome P450 (P450)-mediated metabolic activation is believed to play a major role in 3MI-induced toxicity (Yost, 1989).…”

Heat shock protein 70 in the rat nasal cavity: localisation and response to hyperthermia

“…A wide variety of compounds cause toxicity within the nasal cavity, including environmental pollutants (Turk et al 1987;Johnson et al 1990;Bascom et al 1995), industrial chemicals (Gaskell et al 1988;Keenan et al 1990;Reed et al 1995;Morgan 1997), herbicides (Brandt et al 1990; Morgan et al 1997), wood dust (Feron et al 2001) and drugs (Johansson 1981;Hart et al 1995). Thus, the nasal passages are now routinely investigated during toxicity studies, and there is a need for robust in vitro model systems for screening for nasal toxins.…”

3-Methylindole Induces Transient Olfactory Mucosal Injury in Ponies

“…6 Cytochrome P-450 isoenzymes of goats, mice, rabbits, and human beings convert 3MI to its reactive intermediate, 3methyleneindolenine, which damages cells by forming protein adducts, particularly in the lungs. 28,31,36 In the nasal cavity, 3MI selectively injures olfactory mucosa, sparing respiratory mucosa, at least at lower doses, in mice 39,40 and rats. 1,25,26 In mice, 40 mucosal injury is evident under light microscopy within 6 hours of intraperitoneal injection of 3MI and progresses to diffuse mucosal necrosis by 48 hours.…”

“…28,31,36 In the nasal cavity, 3MI selectively injures olfactory mucosa, sparing respiratory mucosa, at least at lower doses, in mice 39,40 and rats. 1,25,26 In mice, 40 mucosal injury is evident under light microscopy within 6 hours of intraperitoneal injection of 3MI and progresses to diffuse mucosal necrosis by 48 hours. Although mice recover from the bronchiolar epithelial necrosis induced by nonfatal doses, olfactory mucosal injury progresses to epithelial metaplasia, fibrosis, and ossification that persist through 28 days after 3MI injection.…”

“…Although mice recover from the bronchiolar epithelial necrosis induced by nonfatal doses, olfactory mucosal injury progresses to epithelial metaplasia, fibrosis, and ossification that persist through 28 days after 3MI injection. 40 Olfactory mucosal damage also persists in rats and is accompanied by a sensory deficit. 26 3MI-induced epithelial necrosis is attributed to a reactive intermediate that binds cell proteins, 28,31,36 but the pathogenesis of the ensuing nasal fibrosis in rodents is obscure.…”