.European Journal of Pharmacology 347 1998 257260
Airway hyperresponsiveness to histamine in mycoplasmal infection: roleof histamine N-methyltransferase
Jun Tamaoki, Minako Araake, Atsushi Chiyotani, Kazuo Isono, Atsushi Nagai )First Department of Medicine and Department of Microbiology, Tokyo Womens Medical College, 8-1 Kawada-Cho, Shinjuku, Tokyo 162, Japan
Received 15 December 1997; revised 23 February 1998; accepted 27 February 1998
To elucidate the modulatory role of histamine-degrading enzymes in airway constrictor responses in mycoplasmal infection, westudied hamster tracheal segments under isometric conditions in vitro. Nasal inoculation with Mycoplasma pneumoniae potentiated thecontractile responses to histamine but not to methacholine. Pretreatment of tissues with the histamine N-methyltransferase inhibitor SKF91488 abolished the infection-induced potentiation, whereas, the diamine oxidase inhibitor aminoguanidine had no effect. The histamineN-methyltransferase but not diamine oxidase activity in tracheal tissues was decreased in infected animals. These results suggest that M.pneumoniae causes airway hyperresponsiveness to histamine probably through a reduction of endogenous histamine N-methyltransferaseactivity. q 1998 Elsevier Science B.V.
Keywords: Mycoplasmal infection; Histamine metabolism; Airway hyperreactivity; Asthma
.Mycoplasma pneumoniae M. pneumoniae continuesto be a common etiological organism of community-acquired respiratory tract infections. Although there isample evidence that M. pneumoniae infection frequently
.exacerbates asthma Seggev et al., 1986; Yano et al., 1994and airway hyperresponsiveness to histamine Boldy et al.,
.1990 , the mechanism for this remains uncertain.Histamine can be metabolized by two major pathways
.in the body Zeinger et al., 1976 : 50 to 70% of histamineis metabolized by histamine N-methyltransferase EC
.184.108.40.206 , located in the small intestine, liver, kidney andleukocytes, into N-methylhistamine, and the remaining 30
.to 45% is metabolized by diamine oxidase EC 220.127.116.11 ,also called histaminase, located in intestinal mucosa, pla-centa, liver, skin, kidney, neutrophils and eosinophils, toimidazole acetic acid. We and others have recently shownthat histamine N-methyltransferase plays a protective rolein the histamine-induced contraction in human bronchi . Tamaoki et al., 1994 and guinea pig trachea Ohrui et al.,
.1992 . Therefore, to determine whether M. pneumoniae
) Corresponding author. Tel.:q81-3-3353-8111; fax:q81-3-5379-5457.
infection modifies the contractile responses to histamineand, if so, whether this effect is associated with alterationsin histamine N-methyltransferase andror diamine oxidaseactivity, we studied hamster tracheal segments under iso-metric conditions in vitro.
2.1. M. pneumoniae infection
The experiments were approved by the Ethical Commit-tee of Tokyo Womens Medical College. Pathogen-freemale golden Syrian hamsters, weighing 6080 g, wereanesthetized with a gaseous mixture of nitrous oxide,halothane, and oxygen, and given an intranasal inoculation
7with M. pneumoniae FH strain 1.1=10 colony-forming.unitsrml, 500 ml or equivalent volume of sterile saline
.Cimolai et al., 1992 . These hamsters were housed sepa-rately for 10 days. In our separate experiment, we con-firmed that mycoplasmal infection was established basedon the increased antibody titers in serum samples, asdetermined by an indirect hemagglutinin test, and histo-logic findings including peribronchial and peribronchiolarinfiltration of lymphocytes and polymorphonuclear cells,perivascular edema, intraluminal exudate, and parenchy-
0014-2999r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. .PII S0014-2999 98 00177-0
( )J. Tamaoki et al.rEuropean Journal of Pharmacology 347 1998 257260258
mal pneumonia. However, apparent infiltration ofeosinophils or desquamation of epithelial cells was notobserved.
2.2. Contractile responses
The trachea was removed under general anesthesia .sodium pentobarbital, 35 mgrkg, iv and mounted in 5-mlorgan chambers containing KrebsHenseleit solution con-
.sisting of the following composition in mM : NaCl, 118;KCl, 5.9; MgSO , 1.2; CaCl , 2.5; NaH PO , 1.2;4 2 2 4NaHCO , 25.5; and D-glucose, 5.6, gassed with a mixture3of 95% O 5% CO at 378C. Contractile responses were2 2continuously measured isometrically with a force-displace-
.ment transducer Nihon Kohden, JB-652T, Tokyo, Japanand were recorded on a pen recorder Nihon Kohden,
.WT-685G . The tissues were allowed to equilibrate for 60min while they were washed with KrebsHenseleit solu-tion every 15 min, and the resting tension was adjusted to1 g. A contractile response was determined as the differ-ence between peak tension developed and resting tension.All experiments were conducted in the presence of indo-
y6 .methacin 3=10 M to avoid prostaglandin release.Following the equilibration period, histamine Sigma,
. .St. Louis, MO, USA or methacholine Wako Pure, Tokyowas added to the chamber in a cumulative manner atconcentrations ranging from 10y8 to 10y3 M in half-molarincrements at 5-min intervals or 2 min after stable plateauwas achieved, whichever was the longer period. Becausethe contractile responses to methacholine were not alteredby M. pneumoniae infection, we studied only histamine-induced contractions in the following experiments. Tostudy the role of histamine-degrading enzymes, the tissues
w were incubated for 20 min with SKF 91488 S- 4- N,N-di-. x y4methylamino -butyl isothiourea, 10 M, a gift from
.Smith Kline, Philadelphia, PA, USA , an inhibitor of
.histamine N-methyltransferase Beaven and Shaff, 1979 , y4 .or aminoguanidine 10 M , an inhibitor of diamine
.oxidase Schuler, 1952 , and the histamine concentration-response curves were generated in a similar manner.
At the end of these experiments, each tracheal segmentswas blotted on a gauze pad and weighed. Active tensionswere normalized for tissue weight and expressed as gramstension per gram of tissue weight. To characterize theconcentration-response curves, we determined the maximal
.contractile response E and the negative logarithm ofmaxmolar concentration of agonist required to produce 50% of
.E pD by linear regression analysis.max 2
2.3. Measurement of histamine N-methyltransferase anddiamine oxidase actiities
The activity of histamine N-methyltransferase was mea-sured in tracheal tissues according to the method by Fukuda
.et al. 1991 . Briefly, tissues were homogenized with fourvolumes of ice-cold phosphate-buffered saline PBS, 0.05
.M, pH 7.4 containing 1-mM dithiothreitol and 1%polyethyleneglycol with a glass homogenizer. The ho-
.mogenate was centrifuged at 48C 120 000=g, 1 h , andthe supernatant was dialyzed three times for 8 h against100 volumes of the buffer. The reaction of histamineN-methyltransferase was carried out at 378C for 20 min in0.5 ml of a mixture of 0.1 ml of the supernatant, 0.3 ml of0.1 M PBS containing 0.1-mM pargyline and 0.1-mM
.aminoguanidine pH 7.4 , 0.05 ml of 1 mM histamine and0.05 ml of S-adenosyl-L-methionine. After incubation,Nt-methylhistamine was separated from histamine by ahigh-performance liquid chromatography on a weak cation
.exchanger Toyo-Soda, TSKgel CM2SW, Tokyo , with37.5-mM citric acid, 1.25% imidazole and 20% aceto-nitrile, as the mobile phase at a flow rate of 1.0 mlrmin.The fluorescence intensity of the reaction mixture was then
.Fig. 1. Contractile responses of tracheal segments to histamine in M. pneumoniae-infected hamsters closed symbols and saline-treated control hamsters . . y4 . y4 .open symbols in the absence left panel and presence of aminoguanidine 10 M, middle panel or SKF 91488 10 M, right panel . Responses areexpressed as grams tension per gram of tissue weight. Values are means"S.E.; ns11 for each point.
( )J. Tamaoki et al.rEuropean Journal of Pharmacology 347 1998 257260 259
measured using a post-column derivatization with o-phthalaldehyde and 2-mercaptoethanol, and the histamineN-methyltransferase activity was expressed as pmol ofNt-methylhistamine formed per hour per milligram of pro-tein.
w 14 xTo assay diamine oxidase activity, 1,4- C putrescine . Amersham, Tokyo was used as a substrate Kusche and
. w14 xLorenz, 1983 . C Putrescine was mixed with unlabeledputrescine to yield a specific activity of 0.22 mCirmmol,and this was then mixed with PBS to form a 4.5-mMputrescine solution. The reaction of diamine oxidase wascarried out at 378C for 30 min in a mixture of 0.1 ml of thesupernatant of the tracheal homogenate and 0.05 ml of theputrescine solution. After incubation, 1 ml of 1 M NaOHwas added and the mixture was extracted with 6-ml tolueneincluding 0.35% 2,5-diphenyloxazole. The toluene phasewas then counted in a liquid scintillation spectrometer .Packard Instruments, 460 CD, Downers Grove, IL, USA .
All values were expressed as means"S.E. Compara-tive statistical analysis was performed using analysis ofvariance followed by either Turkeys test for multiplecomparisons or by Students t-test; n refers to the numberof hamsters from which the tissues were taken, and P-0.05 was considered statistically significant.
As demonstrated in Fig. 1, contractile responses oftracheal segments to histamine were greater in the ham-sters infected with M. pneumoniae than in those receivedsaline alone. M. pneumoniae infection caused a leftwarddisplacement of the histamine concentration-responsecurves, so that the pD values increased from 4.9"0.2 to2
.5.7"0.2 P-0.01, ns11 , but the difference in themaximal contracti