Serum markers of collagen type I metabolism in spontaneously hypertensive rats: relation to myocardial fibrosis

Markers of collagen synthesis is related to blood pressure and vascular hypertrophy: a LIFE substudy

Cardiac fibrosis and high levels of circulating collagen markers has been associated with left ventricular (LV) hypertrophy. However, the relationship to vascular hypertrophy and blood pressure (BP) load is unclear. In 204 patients with essential hypertension and electrocardiographic LV hypertrophy, we measured sitting BP, serum collagen type I carboxy-terminal telopeptide (ICTP) reflecting degradation, procollagen type I carboxy-terminal propeptide (PICP) reflecting synthesis and LV mass by echocardiography after 2 weeks of placebo treatment and after 1 year of antihypertensive treatment with a losartan- or an atenolol-based regimen. Furthermore, we measured intima-media thickness of the common carotid arteries (IMT), minimal forearm vascular resistance (MFVR) by plethysmography and ambulatory 24-h BP in around half of the patients. At baseline, PICP/ICTP was positively related to IMT (r=0.24, P<0.05), MFVR(men) (r=0.35, P<0.01), 24-h systolic BP (r=0.24, P<0.05) and 24-h diastolic BP (r=0.22, P<0.05), but not to LV mass. After 1 year of treatment with reduction in systolic BP (175+/-15 vs 151+/-17 mmHg, P<0.001) and diastolic BP (99+/-8 vs 88+/-9 mmHg, P<0.001), ICTP was unchanged (3.7+/-1.4 vs 3.8+/-1.4 microg/l, NS) while PICP (121+/-39 vs 102+/-29 microg/l, P<0.001) decreased. The reduction in PICP/ICTP was related to the reduction in sitting diastolic BP (r=0.31, P<0.01) and regression of IMT (r=0.37, P<0.05) in patients receiving atenolol and to reduction in heart rate in patients receiving losartan (r=0.30, P<0.01). In conclusion, collagen markers reflecting net synthesis of type I collagen were positively related to vascular hypertrophy and BP load, suggesting that collagen synthesis in the vascular wall is increased in relation to high haemodynamic load in a reversible manner.

Valsartan Decreases Type I Collagen Synthesis in Patients With Hypertrophic Cardiomyopathy

BACKGROUND

Fibrosis, as well as myocyte hypertrophy, is the major determinant of prognosis in hypertrophic cardiomyopathy (HCM). Valsartan, an angiotensin II type 1 receptor blocker, may improve myocardial fibrosis in patients with HCM.

METHODS AND RESULTS

Twenty-three patients with HCM were randomly divided into 2 groups: 11 patients had valsartan added to conventional treatment (V group) and 12 patients received the conventional therapy (C group). Plasma concentrations of brain natriuretic peptide (BNP), troponin T (TnT), aldosterone (ALDO), procollagen type I (PIP) and procollagen type III aminoterminal peptide (PIIINP) were measured before and 12 months after this study. Left ventricular wall thickness (LVWT) and ejection fraction (LVEF) were measured by echocardiography. PIP was decreased in the V group (123.2+/-63.1 ng/ml to 102.8+/-37.6, p<0.05), but unchanged in C group (110+/-40.5 ng/ml to 119.9+/-47.4, p=0.22). ALDO concentration was unchanged in the V group (88.5+/-26.2 pg/ml to 91.2+/-26.8, p=0.27), and increased in C group (92.6+/-36.6 ng/ml to 116.0+/-33.3, p<0.05). BNP, PIIINP, and TnT were unchanged by the treatment. There was no significant difference between the 2 groups in either LVWT or LVEF.

CONCLUSION

Valsartan suppresses the synthesis of type I collagen in patients with HCM and this was associated with suppression of the increase in ALDO.

Serum carboxyl-terminal propeptide of procollagen type I in exercise-induced left ventricular hypertrophy

BACKGROUND

Left ventricular hypertrophy (LVH) induced by exercise is considered to be a physiologic adaptive mechanism without fibrogenic hyperactivity, as occurs in pathologic hypertrophy.

HYPOTHESIS

This study investigated serum markers of collagen synthesis and echo parameters of left ventricular diastolic function (LVdf) in 22 male athletes.

METHODS

Twenty-two highly competitive male athletes (10 cyclists, 12 soccer players) were studied with full history, clinical examination, Doppler echocardiogram, and serum concentration of the carboxyl-terminal propeptide of collagen type I (PIP). They were divided into two groups: normal left ventricular mass (N) with left ventricular mass index (LVMI) < 125 g/m2 (14 athletes) and LVH with LVMI > 125 g/m2 (8 athletes).

RESULTS

Age, body surface area, blood pressure, heart rate, and systolic function were not different between the groups. Serum concentration of PIP (N: 163 +/- 44.1 microg/l, LVH: 172.7 +/- 61.2 microg/l--NS) and LVdf (early to atrial peak mitral flow velocity ratio: [E/A] N: 1.77 +/- 0.47, LVH: 1.98 +/- 0.70--NS, and early to atrial peak mitral annulus velocity ratio: [Ea/Aa] N: 2.63 +/- 0.70, LVMI: 2.55 +/- 0.90 LV 1.61--NS) were similar in both groups.

CONCLUSIONS

Normal serum concentration of PIP in athletes with LVH in association with normal LVdf indicates the possibility that in this type of physiologic hypertrophy there is mainly an increase of myocyte size without interstitial fibrosis.

Hypertensive heart disease and fibrosis

PURPOSE OF REVIEW

The clinical importance of fibrosis in hypertensive heart disease is now well recognized. However, the precise mechanisms involved in the pathophysiology and therefore the potential cardioreparative strategies are still not fully understood. These areas continue to be the focus of extensive research. This review summarizes the work conducted in this field over the past 12 months.

RECENT FINDINGS

This article further confirms the involvement of the renin-angiotensin system in cardiac fibrosis and illustrates the supportive roles of mineralocorticoids, endothelin, and novel signaling pathways. It also summarizes the most recent data examining the genetic aspects of myocardial fibrosis and further clarifies potential cardioreparative strategies.

SUMMARY

Myocardial fibrosis in hypertensive heart disease remains an area of intensive research. Whereas recent work has expanded our knowledge of the underlying processes in the development of this fibrosis, additional scientific and clinical research is required to assist clinical risk assessment and to provide evidence that therapeutic intervention confers improved clinical outcome in hypertensive heart disease.

Polymorphism in gene coding for ACE determines different development of myocardial fibrosis in rats

In humans, the effect of angiotensin-converting enzyme (ACE) gene polymorphisms in cardiovascular disease is still controversial. In the rat, a microsatellite marker in the ACE gene allows differentiation of the ACE gene polymorphism among strains with different ACE levels. We tested the hypothesis that this ACE gene polymorphism determines the extent of cardiac fibrosis induced by isoproterenol (Iso) in the rat. We used a male F2generation (homozygous LL and BB ACE genotypes determined by polymerase chain reaction) derived from two rat strains [Brown-Norway (BB) and Lewis (LL)] that differ with respect to their plasma ACE activities. For induction of left ventricular (LV) hypertrophy (LVH) and cardiac fibrosis, rats were infused with Iso (5 mg·kg–1·day–1) or saline (control) for 10 days and euthanized at day 1 after the last injection. The interstitial collagen volumetric fraction (ICVF), collagen I, and fibronectin content, but not collagen III content, were significantly higher in the homozygous BB rats than in homozygous LL rats. Differences in metalloprotease (MMP)-9, but not in MMP-2 activities as well as in cardiac cell proliferation, were also detected between LL and BB rats treated with Iso. LV ACE activity was higher in BB rats than LL rats and correlated with ICVF ( r = 0.61, P < 0.002). No changes were observed in plasma ACE activities, ANG II plasma or LV levels, plasma renin activity, and ACE and ANG II type 1 receptor (AT1R) mRNA levels in the LV of rats with the two different ACE polymorphisms. Iso induced a similar degree of LVH [assessed by an increase in LV weight 100 per body weight, LV-to-right ventricle (RV) ratio, and LV protein content] in LL and BB rats. We concluded that rats in the F2generation with high plasma ACE activity developed more fibrosis but to a similar degree of LVH compared with rats with low plasma ACE activity.

Angiotensin-converting enzyme-gene polymorphism is associated with collagen I synthesis and QT dispersion in essential hypertension

AIM

This study tested the hypothesis that abnormal QT dispersion, an indicator of arrhythmogenic risk, is associated with angiotensin-converting enzyme (ACE) gene polymorphism and abnormalities of collagen metabolism.

METHODS

A total of 132 patients with untreated essential hypertension (EHT) were recruited. QT dispersion corrected by heart rate (QTc) on a 12-lead electrocardiogram, ACE genotype, left ventricular mass index (LVMI) and E/A ratio using echocardiogram, plasma ACE activity and serum propeptide type I C-terminal procollagen (PICP) concentration, a marker of myocardial fibrosis, were determined. A normal control group (NC) of 200 normotensive subjects was used for comparison of QT dispersion.

RESULTS

Number of EHT patients with ACE genotype I/I, I/D and D/D was 61, 52 and 19, respectively. LVMI and E/A ratio were similar in the three groups. Compared with subjects with I/I or I/D genotype, subjects with D/D showed higher plasma ACE activity (I/I: 13 +/- 0.6, I/D: 17 +/- 0.9, and D/D: 21 +/- 1.1 nmol/min per ml, mean +/- SE, P05) and serum PICP concentration (I/I: 106 +/- 5.4, I/D: 106 +/- 4.9, D/D: 140 +/- 12.1 ng/ml, P < 0.01). QTc dispersion was larger in the three hypertensive subgroups than in NC, and was the largest in EHT with D/D (NC: 0.037 +/- 0.001, I/I: 0.056 +/- 0.003, I/D: 0.055 +/- 0.002, D/D: 0.069 +/- 0.004 s, P < 0.05).

CONCLUSION

ACE D/D genotype could be associated with an elevation of serum PICP concentration possibly leading to myocardial fibrosis and increased QT dispersion.

Doxycycline and tissue repair in rats

Iterations in collagen turnover are integral to tissue repair. Repair gone awry, as a result of excess collagen accumulation or degradation, can contribute to pathologic ventricular remodeling. Pharmacologic interventions that would attenuate either aspect of faulty repair have therefore attracted interest. Tetracyclines, which inhibit both collagen synthesis and degradation, as well as angiogenesis, may hold promise, unrelated to their antimicrobial properties, in this regard. Assessment of their potential in rodent hearts with experimental injury can be problematic, given the often microscopic nature of tissue repair and brief involvement of matrix metalloproteinases (MMPs). We therefore selected a subcutaneous model in which granulation and fibrous tissues form over several weeks in response to croton oil and where fibrous tissue is subsequently resorbed because of high levels of collagenolytic activity. Untreated rats were compared with those given daily oral doxycycline (40 mg/kg). We harvested pouch tissue and exudate weekly for 5 weeks to assess hydroxyproline concentration and MMP activity (gelatin substrate zymography) of pouch wall and mononuclear cell count of pouch exudate. At week 2, neovascularization in pouch wall was measured by means of intravenous infusion of carmine-red dye in gelatin. The resultant "vascular cast" was solubilized and dye content quantitated with the use of spectrophotometry. Serum was assayed weekly for type I collagen carboxyterminal telopeptide (ICTP), a marker of collagen degradation. During weeks 1 and 2 and compared with untreated controls, doxycycline-treated rats had attenuated pouch tissue weight, collagen concentration, MMP2 lytic activity and vascularity, and reduced exudate volume and mononuclear cells. In vitro, doxycycline inhibited tissue gelatinolytic activity in a dose-dependent manner. At weeks 4 and 5, pouches were larger and collagen concentration was higher in doxycycline-treated rats, and serum ICTP levels were reduced at weeks 3 and 4. During the initial phase of pouch development, doxycycline exerts an inhibitory effect on tissue formation, likely mediated through its attenuation of angiogenesis and modulations of collagen turnover. As repair proceeds in subsequent weeks, doxycycline retards collagen degradation and pouch resorption by inhibiting MMPs. Doxycycline offers a multifaceted pharmacologic profile with which to modify various aspects of tissue repair in the rat.

Clinical aspects of hypertensive myocardial fibrosis

Myocardial fibrosis is one of the histologic constituents of myocardial remodeling present in hypertensive patients with hypertensive heart disease. In fact, an exaggerated interstitial and perivascular accumulation of fibrillar collagens type I and type III has been found in the myocardium of patients with arterial hypertension and left ventricular hypertrophy. Hypertensive myocardial fibrosis has been shown to facilitate abnormalities of cardiac function, coronary reserve, and electrical activity that adversely affect the clinical outcome of hypertensive patients. Therefore, development of noninvasive tools for the monitoring of myocardial fibrosis and pharmacological strategies aimed to promote the regression of fibrosis could be of particular relevance in the clinical treatment of patients with hypertensive heart disease.

Low-dose ACE with alpha- or beta-adrenergic receptor inhibitors have beneficial SHR cardiovascular effects

BACKGROUND

There are no data regarding the prolonged effect of alpha-1 adrenergic receptor antagonists on ventricular collagen content and coronary hemodynamics in spontaneously hypertensive rats (SHR). This study, therefore, was designed to determine the effects of chronic treatment with the alpha-1 adrenergic receptor inhibitor doxazosin on SHR systemic and regional (especially coronary) hemodynamics, cardiovascular mass, and ventricular collagen. The effects of the combination of doxazosin with low-dose angiotensin-converting enzyme inhibitor were studied versus the alpha-1 antagonist alone. These effects were compared with those of a beta-1 adrenergic receptor inhibitor.

METHODS AND RESULTS

Systemic and regional hemodynamics (radionuclide-labeled microspheres), left and right ventricular weight, hydroxyproline concentration, and aortic weight were measured at age 35 weeks. Doxazosin reduced arterial pressure and total peripheral resistance without changing left ventricular mass and collagen content, whereas monotherapies with the beta-1 antagonist metoprolol or a subdepressor dose of the ACE inhibitor enalapril were effective in reducing left ventricular mass and hydroxyproline without altering pressure. Doxazosin combined with the same low-dose ACE inhibitor reduced left ventricular mass and hydroxyproline without potentiating the hypotensive effect of doxazosin. By contrast, the combination of beta-1 antagonist with the low-dose ACE inhibitor reduced pressure, unlike either agent alone. Aortic weight index was significantly reduced only by doxazosin whether when used alone or with the ACE inhibitor. Low-dose ACE inhibitor with doxazosin or the beta-1 receptor antagonist as well as doxazosin alone decreased renal vascular resistance.

CONCLUSION

These data show that the low subdepressor dose ACE inhibitor with an alpha- or beta-adrenergic receptor antagonist provides beneficial cardiovascular effects in SHR.

Fibrosis and hypertensive heart disease

The normal myocardium is composed of a variety of cells: cardiac myocytes and noncardiomyocytes, which include endothelial and vascular smooth muscle cells and fibroblasts. Hypertensive heart disease involves a structural remodeling of muscular and nonmuscular compartments. It is not the quantity but rather the quality of myocardium that accounts for pathologic hypertrophy and predisposes to ventricular dysfunction and arrhythmias, which, in turn, confer increased risk of adverse cardiovascular events. Herein, factors regulating growth of these compartments are reviewed and in particular signals involved in promoting adverse remodeling of intramyocardial coronary arteries and arterioles by fibrous tissue.

Angiotensin II and connective tissue: homeostasis and reciprocal regulation

As a concept traditionally applied to integrative organ physiology, homeostasis likewise applies to self-regulated growth and structure of loose, dense and specialized connective tissues. De novo generation and co-induction of signals, either stimulatory or inhibitory to the formation of these tissues, provide for a reciprocal regulation of their composition; angiotensin (Ang) II is a growth stimulator. Components involved in AngII generation and its biological activity, including angiotensin converting enzyme (ACE) and AngII receptors, are expressed by mesenchymal cells responsible for connective tissue turnover. ACE inhibition or AT1 receptor antagonism attenuate the formation of these connective tissues. The concept of circulatory homeostasis, and the endocrine properties of plasma AngII involved in maintaining same, need each be broadened to encompass auto- and paracrine effects of AngII produced within connective tissues, where it contributes to their homeostatic regulation of structure and composition.

Losartan inhibits the post-transcriptional synthesis of collagen type I and reverses left ventricular fibrosis in spontaneously hypertensive rats

OBJECTIVE

Previous studies have shown that as well as left ventricular hypertrophy, myocardial fibrosis develops early in rats with spontaneous hypertension (SHR). The present study was designed to investigate whether chronic treatment with the angiotensin II type 1 (AT1) receptor antagonist losartan modifies collagen type I metabolism and reverses left ventricular fibrosis in young SHR with left ventricular hypertrophy.

DESIGN

The study was performed in 30-week-old normotensive Wistar-Kyoto (WKY) rats, untreated SHR and SHR treated with losartan (20 mg/mg per day, orally) for 14 weeks before they were killed.

METHODS

Ventricular pro-alpha 1 (I) collagen messenger RNA was analyzed by Northern blot. Serum levels of the carboxy-terminal propeptide of procollagen type I (PIP) and the pyridoline cross-linked telopeptide domain of collagen type I (CITP) were determined by specific radioimmunoassays as markers of collagen type I synthesis and degradation, respectively. Collagen volume fraction was determined in the left ventricle by quantitative morphometry.

RESULTS

Compared with WKY rats, SHR exhibited increased (P < 0.05) mean arterial pressure, pro-alpha 1 (I) collagen messenger RNA, PIP and left ventricular collagen volume fraction, and similar CITP values. After the treatment period, mean arterial pressure was higher (P < 0.05) in losartan-treated SHR than in WKY rats. Compared with untreated SHR, treated SHR showed no left ventricular hypertrophy and diminished (P < 0.05) values of mean arterial pressure, PIP and left ventricular collagen volume fraction. No changes in pro-alpha 1 (I) collagen messenger RNA and CITP values were observed with treatment in SHR. No significant differences in the left ventricular collagen volume fraction were observed between treated SHR with normal blood pressure and treated SHR with abnormally high blood pressure at the end of the treatment period.

CONCLUSIONS

These results suggest that chronic AT1 blockade with losartan decreases the post-transcriptional synthesis of fibril-forming collagen type I molecules in young SHR. This effect may be involved in the ability of this drug to reverse left ventricular fibrosis in young rats with genetic hypertension. Apart from its antihypertensive action, other mechanisms may mediate the antifibrotic effect of losartan in this animal model.