Remodeling pattern and ventricular function in rats exposed to cigarette smoke

Azevedo, Paula S.; Minicucci, Marcos F.; Matsubara, Beatriz B.; Matsubara, Luiz S.; Duarte, Daniella R.; Paiva, Sergio A. R.; Zornoff, Leonardo A. M.

doi:10.1590/S0066-782X2010005000004

Abstracts

BACKGROUND: The relevance of the remodeling pattern in the model of rats exposed to cigarette smoke is not known. OBJECTIVE: Analyzing the presence of different remodeling patterns in this model and its relation with the ventricular function. METHODS: Smoking rats (n=47) have been divided according to the geometry pattern, analyzed by echocardiogram: normal (normal mass index and normal relative wall thickness), concentric remodeling (normal mass index and increased relative wall thickness), concentric hypertrophy (increased mass index and increased relative wall thickness) and eccentric hypertrophy (increased mass index and normal relative wall thickness). RESULTS: Smoking rats presented one of the following geometry patterns: normal pattern, 51%; eccentric hypertrophy; 32%; concentric hypertrophy, 13% and concentric remodeling, 4%. The normal and eccentric hypertrophy groups presented smaller ejection fraction values and fractional shortening than the concentric hypertrophy group. Thirteen animals (28%) presented systolic dysfunction detected by the ejection fraction and by fractional shortening. In the single regression analysis, geometry patterns and mass index could not predict ventricular dysfunction (p<). On the other hand, the increased relative thickness of the wall could predict ventricular dysfunction in the single regression analysis (p<0,001) and in the multiple regression analysis after adjustment to the mass index (p=0,003). CONCLUSION: Rats exposed to cigarette smoke presented one of the four different remodeling patterns. Among the geometric variables analyzed, only the increased relative thickness of the left ventricle wall could predict ventricular dysfunction in this model.

Remodelling; geometry; ventricular function; smoking

FUNDAMENTO: A relevância do padrão de remodelação no modelo de ratos expostos à fumaça do cigarro não é conhecida. OBJETIVO: Analisar a presença de diferentes padrões de remodelação nesse modelo e sua relação com a função ventricular. MÉTODOS: Ratos fumantes (n=47) foram divididos de acordo com o padrão de geometria, analisado pelo ecocardiograma: normal (índice de massa normal e espessura relativa normal), remodelação concêntrica (índice de massa normal e espessura relativa aumentada), hipertrofia concêntrica (índice de massa aumentado e espessura relativa aumentada) e hipertrofia excêntrica (índice de massa aumentado e espessura relativa normal). RESULTADOS: Os ratos fumantes apresentaram um dos quatro padrões de geometria: padrão normal, 51%; hipertrofia excêntrica:,32%; hipertrofia concêntrica, 13% e remodelação concêntrica, 4%. Os grupos normal e hipertrofia excêntrica apresentaram menores valores de fração de ejeção e porcentagem de encurtamento que o grupo hipertrofia concêntrica. Treze animais (28%) apresentaram disfunção sistólica, detectada pela fração de ejeção e pela porcentagem de encurtamento. Na análise de regressão univariada, os padrões de geometria e o índice de massa não foram fator de predição de disfunção ventricular (p>0,05). Por outro lado, o aumento da espessura relativa da parede foi fator de predição de disfunção ventricular na análise univariada (p<0,001) e na análise multivariada, após ajuste para o índice de massa (p=0,003). CONCLUSÃO: Ratos expostos à fumaça do cigarro apresentam um dos quatro diferentes padrões de remodelação. Entre as variáveis geométricas analisadas, somente o aumento da espessura relativa da parede do ventrículo esquerdo foi fator de predição de disfunção ventricular nesse modelo.

Remodelação; geometria; função ventricular; tabagismo

FUNDAMENTO: No se conoce la relevancia del estándar de remodelación en el modelo de ratones expuestos al humo del cigarrillo. OBJETIVO: Analizar la presencia de diferentes estándares de remodelación en este modelo y su relación con la función ventricular. MÉTODOS: Ratones fumadores (n=47) se dividieron según el estándar de geometría, analizado por el ecocardiograma: normal (índice de masa normal y espesor relativo normal), remodelación concéntrico (índice de masa normal y espesor relativo aumentado), hipertrofia concéntrica (índice de masa aumentado y espesor relativo aumentado) y hipertrofia excéntrica (índice de masa aumentado y espesor relativo normal). RESULTADOS: Los ratos fumadores presentaron uno de los cuatro estándares de geometría: estándar normal, el 51%; hipertrofia excéntrica: el 32%; hipertrofia concéntrica, el 13% y remodelación concéntrica, el 4%. Los grupos normal e hipertrofia excéntrica presentaron menores valores de fracción de eyección y porcentaje de acortamiento que el grupo hipertrofia concéntrica. Trece animales (28%) presentaron disfunción sistólica, detectada por la fracción de eyección y por el porcentaje de acortamiento. En el análisis de regresión univariado, los estándares de geometría y el índice de masa no fueron factor de predicción de disfunción ventricular (p > 0,05). Por otro lado, el aumento del espesor relativo de la pared fue factor de predicción de disfunción ventricular en el análisis univariado (p < 0,001) y en el análisis multivariado, tras ajuste para el índice de masa (p = 0,003). CONCLUSIÓN: Ratones expuestos al humo del cigarrillo presentan uno de los cuatro diferentes estándares de remodelación. Entre las variables geométricas analizadas, solamente el aumento del espesor relativo de la pared del ventrículo izquierdo del factor de predicción de disfunción ventricular en este modelo.

Remodelación; geometría; función ventricular; tabaquismo

ORIGINAL ARTICLE

Faculdade de Medicina de Botucatu - UNESP, Botucatu, SP - Brazil

Mailing address

ABSTRACT

BACKGROUND: The relevance of the remodeling pattern in the model of rats exposed to cigarette smoke is not known.

OBJECTIVE: Analisar a presença de diferentes padrões de remodelação nesse modelo e sua relação com a função ventricular. Analyzing the presence of different remodeling patterns in this model and its relation with the ventricular function.

METHODS: Smoking rats (n=47) have been divided according to the geometry pattern, analyzed by echocardiogram: normal (normal mass index and normal relative wall thickness), concentric remodeling (normal mass index and increased relative wall thickness), concentric hypertrophy (increased mass index and increased relative wall thickness) and eccentric hypertrophy (increased mass index and normal relative wall thickness).

RESULTS: Smoking rats presented one of the following geometry patterns: normal pattern, 51%; eccentric hypertrophy; 32%; concentric hypertrophy, 13% and concentric remodeling, 4%. The normal and eccentric hypertrophy groups presented smaller ejection fraction values and fractional shortening than the concentric hypertrophy group. Thirteen animals (28%) presented systolic dysfunction detected by the ejection fraction and by fractional shortening.

In the single regression analysis, geometry patterns and mass index could not predict ventricular dysfunction (p<). On the other hand, the increased relative thickness of the wall could predict ventricular dysfunction in the single regression analysis (p<0,001) and in the multiple regression analysis after adjustment to the mass index (p=0,003).

CONCLUSION: Rats exposed to cigarette smoke presented one of the four different remodeling patterns. Among the geometric variables analyzed, only the increased relative thickness of the left ventricle wall could predict ventricular dysfunction in this model.

Key Words: Remodelling; geometry ; ventricular function; smoking.

Introduction

Remodeling refers to gene, molecular, cellular and cardiac interstitial variations, which clinically manifest by changes in size, mass, geometry and heart function, in response to a given agression^1-3. The remodeling process plays a key role in the ventricular dysfunction physiopathology. By reacting to a given aggression, genetic, structural and biochemical changes result in a progressive deterioration of heart functions^4-6.

A relevant aspect is that in patients with high blood pressure, it was found that secondary remodeling to arterial hypertension may result in different geometry patterns. Using the mass index and the left ventricle (LV) wall relative thickness, the patients were divided into four different geometry patterns: normal (normal mass index and normal relative thickness), concentric remodeling (normal mass index and increased relative thickness), concentric hypertrophy (increased mass index and increased relative thickness) and eccentric hypertrophy (increased mass index and normal relative thickness). An important data to be considered is that the remodeling pattern predicted cardiovascular events⁷.

Recently, various studies reported that the exposure to cigarette smoke causes cardiac remodeling in rats, damaging their ventricular function^8-15. Nevertheless, the importance of the cardiac remodeling pattern, in this model, is not known. Hence, the purpose of this study was to analyze the presence of different remodeling patterns ventricular functions in the model rats exposed to cigarette smoke.

Methods

The experimental protocol of this paper has been approved by the Ethics Commission on Animal Experimentation (CEEA) of our institution. It complies with the Ethic Principles on Animal Experimentation adopted by the Brazilian Board of Animal Experimentation.

Protocol and experimental groups

Male Wistar rats weighing 200g to 230g were divided into 2 experimental groups: 1) group C, n=30 - composed of animals not exposed to cigarette smoke; 2) group F, n=47 - composed of animals exposed to cigarette smoke for a period of 2 months.

Later, the animals of group F have been classified according to the remodeling pattern: normal (normal mass index and normal relative thickness), concentric remodeling (normal mass index and increased relative thickness), concentric hypertrophy (increased mass index and increased relative thickness) and eccentric hypertrophy (increased mass index and normal relative thickness).

To expose the animals to cigarette smoke, we used a method standardized in our laboratory^8-13. During the first week, the smoke was released at a rate of 5 cigarettes, twice a day in the afternoon with resting intervals of 10 minutes. The number of cigarettes was increased to a rate of 10 cigarettes/30 minutes, twice in the morning and twice in the afternoon, until the completion of the study.

Morphologic and functional evaluation by echocardiogram

Twenty-four hours past the end of the observation period, the animals underwent echocardiographic study. A Philips equipment (model TDI 5500) provided with multifrequency transducer was used up to 12 MHz. Cardiac structures were measured according to the recommendations of the American Society of Echocardiography/ European Association of Echocardiography¹⁶. The measurements were made by the same observer, who did not know which groups the animals belonged to. For the relative wall thickness of the LV, the following formula was used: (RWT= 2 x posterior wall thickness (WT)/diastolic diameter). The relative wall thickness was considered increased when > 0.42¹⁶. For the mass index (LVMI), the following formula was used: LVMI = LVM/BW, considering LVM = {[LVDD + (2 x WT)³ - (LVDD)³] x 1.04}/1000 and BW is the body weight of the animal. The mass index was considered increased when > 1.733. This value corresponds to the values above the percentile 75% found in the control animals. To issue a diagnosis on systolic ventricular dysfunction, we considered the values below 49% for the shortening percentage and below 0.87 for the ejection fraction. These values correspond to the values below the percentile 25% found in the control animals.

Statistic method

The comparisons were made by one-way ANOVA, complemented by Tukey test, when the data presented normal distribution. When the data did not present normal distribution, the comparisons between the groups were made by Kruskal-Wallis test. The data were expressed in mean ± standard deviation (for normal distribution) or average with percentiles 25 and 75 (for non normal distribution). The analysis of ventricular dysfunction prediction factors was made by simple regression analysis. The significance level was 5%. Statistic analysis were made with the program SigmaStat for Windows v3.5 (SPSS Inc, Chicago, IL).

Results

Considering the geometric pattern of control animals, 20 animals presented normal pattern, 5 had eccentric hypertrophy , 2 presented concentric hypertrophy and 3 had concentric remodeling. Concerning the cardiac dimension measures, the results of control animals were: LVDD (7.13 ± 0.68 mm), posterior wall thickness (1.39 ± 0.27 mm) relative wall thickness (0.40 ± 0.14) and mass index (1.5 ± 0.31 g/kg).

Considering our rats exposed to cigarette smoke, the animals presented one of the four geometry patterns, in the following percentages: normal pattern, 51%; eccentric hypertrophy; 32%; concentric hypertrophy, 13% and concentric remodeling, 4%. As only two animals presented the concentric remodeling pattern, these animals were not included in the other analyses.

The echocardiogram results, according to the remodeling pattern, are shown in Table 1. We can observe that the left atrium diameter was bigger in the eccentric hypertrophy than in the normal pattern. The normal and eccentric hypertrophy patterns presented higher ventricular cavity values than the concentric hypertrophy group, both in the systole and in the diastole. Concerning the LV mass index, the animals belonging to the hypertrophy group (concentric and eccentric hypertrophy) presented higher values than the normal group. Concerning the LV wall relative thickness, the animals falling under the normal pattern presented lower values than the concentric hypertrophy pattern. Considering the systolic function, the normal and eccentric hypertrophy groups presented smaller ejection fraction values and fractional shortening than the concentric hypertrophy group. There were no differences between the groups related to the diastolic function.

Thumbnail

Considering the smoking animals, thirteen (13) animals (13) presented systolic dysfunction detected by the ejection fraction and by fractional shortening. These animals presented only two geometry patterns: 61% presented normal geometry pattern and 39% presented eccentric hypertrophy pattern.

As to the ventricular dysfunction prediction factors, we analyzed the influence of the mass index, the wall relative thickness and the geometry pattern. In the single regression analysis, geometry patterns and mass index could not predict ventricular dysfunction (p<). On the other hand, the increased relative thickness of the wall could predict ventricular dysfunction in the single regression analysis (p<0.001) and in the multiple regression analysis after adjustment to the mass index (p=0,003).

Discussion

Several studies showed that the exposure to cigarette smoke results in cardiac remodeling, in the rat model, with a drop in the systolic function indexes^8-15. Considering the lack of information on the relevance of remodeling pattern in the model of rats exposed to cigarette smoke, the purpose of this study was to analyze the presence of different remodeling patterns and its relation with ventricular function in this model.

The first relevant information of our study was that animals exposed to cigarette smoke presented one of the four geometry patterns described: normal pattern, eccentric hypertrophy, concentric hypertrophy, and concentric remodeling. Nevertheless, we should consider that the mechanisms involved in the geometry pattern variability are not known.

Considering the presence of one of the four different remodeling patterns, an aspect that is worthy of note is that the same phenomenon was observed in clinical studies, in arterial hypertension models^7,17. In the case of arterial hypertension, although the mechanisms are not completely clear, the different geometry patterns are explained by the different physiopathological mechanisms for hypertension, with different hemodynamic patterns. Hence, the geometry would depend on the vasoconstriction degree, the intensity of activation of neurohumoral factors and the presence of volume overcharge¹⁷. In our study, however, the animals exposed to cigarette smoke present the same characteristics. Then, our results suggest that in the model of exposure to cigarette smoke, animals with the same characteristics may present different morphological adaptations even if submitted to the same aggression.

Concerning the relevance of the ventricular remodeling patterns, in the Jackson Cohort of the Atherosclerosis Risk in Communities (ARIC) Study, the type of hypertrophy was associated to the type of ventricular dysfunction. Eccentric hypertrophy was associated to a systolic dysfunction, while concentric hypertrophy was associated to diastolic dysfunction. On the other hand, concentric remodeling was not associated to ventricular dysfunction¹⁸. In the MESA study, however, patients with concentric remodeling presented systolic dysfunction, assessed by means of magnetic resonance¹⁹. Therefore, the association between the geometry and the ventricular dysfunction is still controversial. In our study, only the animals with normal geometry patterns and eccentric hypertrophy presented systolic dysfunction. Another aspect to be considered is that different authors showed that the remodeling poattern may have prognostic implications. This way, in patients with hypertension, the concentric hypertrophy pattern was associated with increased risk of cardiovascular events compared to other geometry patterns²⁰. Additionally, studies suggest that the concentric remodeling is associated to an increased risk of cardiovascular events^21-26. On the other hand, other studies found that geometry was not associated to a worse prognosis^27-29, suggesting that the relevance of the remodeling pattern in patients with high blood pressure remains undetermined. In our study, the geometry patterns were not factors of prediction of systolic ventricular dysfunction. Therefore, in the model of rats exposed to cigarette smoke, the remodeling pattern did not present relevance in relation to cardiac function.

Another aspect to be considered in our study refers to the importance of the LV relative thickness. In clinical trials with patients with high blood pressure, the mass index was more important than the relative thickness of wall as a prognostic factor²⁹. In patients with acute myocardial infarction, the geometry pattern, the mass index and the relative thickness of the wall were independent prediction factors of death³⁰. In our study, among the geometric variables analyzed, the relative thickness of the wall was the only variable that could predict ventricular dysfunction, emphasizing the importance of such variable in the model of smoking rats.

The conclusion we have drawn is that rats exposed to cigarette smoke presented one of the four different remodeling patterns. Among the geometric variables analyzed, only the increased relative wall thickness of the left ventricle could predict ventricular dysfunction in this model.

Potential Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Sources of Funding

There were no external funding sources for this study.

Study Association

This study is not associated with any post-graduation program.

References

1. Pfeffer MA, Braunwald E. Ventricular remodeling after myocardial infarction: experimental observations and clinical implications. Circulation. 1990; 81: 1161-72.
2. Pfeffer JM, Pfeffer MA, Braunwald E. Influence of chronic captopril therapy on the infarcted left ventricle of the rat. Circ Res. 1985; 57: 84-95.
3. Cohn JN, Ferrari R, Sharpe N. Cardiac remodeling- concepts and clinical implications: a consensus paper from an international forum on cardiac remodeling. J Am Coll Cardiol. 2000; 35: 569-82.
4. Zornoff LAM, Paiva SAR, Duarte DR, Spadaro J. Ventricular remodeling after myocardial infarction: concepts and clinical implications. Arq Bras Cardiol. 2009; 92: 150-6.
5. Francis GS. Pathophysiology of chronic heart failure. Am J Med. 2001; 110: 37S-46S.
6 Swynghedauw B. Molecular mechanisms of myocardial remodeling. Physiol Rev. 1999; 79: 215-62.
7. Ganau A, Devereux RB, Roman MJ, de Simone G, Pickering TG, Saba PS, et al. Patterns of left ventricular hypertrophy and geometric remodeling in essential hypertension. J Am Coll Cardiol. 1992; 19: 1550-8.
8. Paiva SAR, Zornoff LAM, Okoshi MP, Okoshi K, Cicogna AC, Campana AO. Behavior of cardiac variables in animals exposed to cigarette smoke. Arq Bras Cardiol. 2003; 81: 221-8.
9. Castardeli E, Paiva SAR, Matsubara BB, Matsubara LS, Minicucci MF, Azevedo PS, et al. Chronic cigarette smoke exposure results in cardiac remodeling and impaired ventricular function in rats. Arq Bras Cardiol. 2005; 84: 320-4.
10. Zornoff LAM, Matsubara LS, Matsubara BB, Okoshi MP, Okoshi K, Dal Pai-Silva, et al. Beta-carotene supplementation attenuates cardiac remodelling induced by one-month tobacco-exposure in rats. Tox Sci. 2006; 90: 259-66.
11. Zornoff LAM, Matsubara BB, Matsubara LS, Minicucci MF, Azevedo PS, Campana AO, et al. Cigarette smoke exposure intensifies ventricular remodelling process following myocardial infarction. Arq Bras Cardiol. 2006; 86: 276-82.
12. Castardeli E, Duarte DR, Minicucci MF, Azevedo PS, Matsubara BB, Matsubara LS, et al. Tobacco smoke-induced left ventricular remodelling is not associated with metalloproteinase-2 or -9 activation. Eur J Heart Fail. 2007; 9: 1081-5.
13. Castardeli E, Duarte DR, Minicucci MF, Azevedo PS, Matsubara BB, Matsubara LS, et al. Exposure time and ventricular remodeling induced by tobacco smoke exposure in rats. Med Sci Monit. 2008; 14: BR62-66.
14. Houdi AA, Dowell RT, Diana JN. Cardiovascular responses to cigarette smoke exposure in restrained conscious rats. J Pharmacol Exp Ther. 1995; 275: 646-53.
15. Gu L, Pandey V, Geenen DL, Chowdhury SAK, Piano MR. Cigarette smoke-induced left ventricular remodelling is associated with activation of mitogen-activated protein kinases. Eur J Heart Fail. 2008; 10: 1057-64.
16. Lang RM, Bierig M, Devereaux RB, Flachskampf FA, Foster E, Pellikka PA, et al. Recommendations for chamber quantification: a report from the American Society of Echocardiography's Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology. J Am Soc Echocardiogr. 2005; 18: 1440-63.
17. Dávila DF, Donis JH, Odreman R, Gonzalez M, Landaeta. Patterns of left ventricular hypertrophy in essential hypertension: should echocardiography guide the pharmacological treatment? Int J Cardiol. 2008; 124: 134-8.
18. Fox E, Taylor J, Taylor H, Han H, Samdarshi T, Arnett D, et al. Left ventricular geometric pattern in the Jackson Cohort of the Atherosclerosis Risk in Communities (ARIC) Study: clinical correlates and influences on systolic and diastolic dysfunction. Am Heart J. 2007; 153: 238-44.
19. Rosen BD, Edvardsen T, Lai S, Castillo E, Pan L, Jerosch-Herold M, et al. Left ventricular concentric remodeling is associated with decreased global and regional systolic function: the Multi-Ethinic Study of Atherosclerosis. Circulation. 2005; 112: 936-8.
20. Koren MJ, Devereux RB, Casale PN, Savage DD, Laragh JH. Relation of left ventricular mass and geometry to morbidity and mortality in uncomplicated essential hypertension. Ann Intern Med. 1991; 114: 345-52.
21. de Simone G, Kitzman DW, Chinali M, Oberman A, Hopkins PN, Rao DC, et al. Left ventricular concentric geometry is associated with impaired relaxation in hypertension: the HyperGEN study. Eur Heart J. 2005; 26: 1039-45.
22. Gardin JM, McClellan R, Kitzman D, Lima JA, Bommer W, Klopfenstein HS, et al. M-mode echocardiographic predictors of six-to-seven year incidence of coronary heart disease, stroke, congestive heart failure, and mortality in an elderly cohort. Am J Cardiol. 2001; 87: 1051-7.
23. Verdecchia P, Schillaci G, Borgioni C, Ciucci A, Battistelli M, Bartoccini C, et al. Adverse prognostic significance of concentric remodeling of the left ventricle in hypertensive patients with normal left ventricular mass. J Am Coll Cardiol. 1995; 25: 871-8.
24. Muiesan ML, Salvetti M, Monteduro C, Bonzi B, Paini A, Viola S, et al. Left ventricular concentric geometry during treatment adversely affects cardiovascular prognosis in hypertensive patients. Hypertension. 2004; 43: 731-8.
25. Pierdomenico SD, Lapenna D, Bucci A, Manente BM, Cuccurullo F, Mezzetti A. Prognostic value of left ventricular concentric remodeling in uncomplicated mild hypertension. Am J Hypertens. 2004; 17: 1035-9.
26. Di Tullio MR, Zwas DR, Sacco RL, Sciacca RR, Homma S. Left ventricular mass and geometry and the risk of ischemic stroke. Stroke. 2003; 34: 2380-4.
27. Verdecchia P, Schillaci G, Borgioni C, Ciucci A, Gattobigio R, Zampi I, et al. Prognostic value of left ventricular mass and geometry in systemic hypertension with left ventricular hypertrophy. Am J Cardiol. 1996; 78: 197-202.
28. Krumholz HM, Larson M, Levy D. Prognosis of left ventricular geometric patterns in the Framingham Heart Study. J Am Coll Cardiol. 1995; 25: 879-84.
29. Ghali JK, Liao Y, Cooper RS. Influence of left ventricular geometric patterns on prognosis in patients with or without coronary artery disease. J Am Coll Cardiol. 1998; 31: 1635-40.
30. Verma A, Meris A, Skali H, Ghali JK, Arnold JM, Bourgoun M, et al. Prognostic implications of left ventricular mass and geometry following myocardial infarction: the VALIANT (VALsartan In Acute myocardial iNfarcTion) Echocardiographic Study. JACC Cardiovasc Imaging. 2008; 1: 582-91.