Collagen remodelling in myocardia of patients with diabetes

Cardioprotective mechanisms of the kallikrein-kinin system in diabetic cardiopathy

PURPOSE OF REVIEW

Multiple pathogenic mechanisms contribute to the development of diabetic cardiopathy, including intramyocardial inflammation, cardiac fibrosis, abnormal intracellular Ca handling, microangiopathy and endothelial dysfunction. Moreover, the cardiac kallikrein-kinin system is thought to be altered under diabetic conditions and an improvement of this peptide system, e.g. by gene therapeutic approaches, has also been associated with an amelioration of the diabetic heart. In this review, we will discuss the hypothesis that the stimulation of the kallikrein-kinin system could be a promising target for the treatment of diabetic cardiopathy.

RECENT FINDINGS

The kallikrein-kinin system has cardioprotective properties, which may be particularly important under diabetic conditions. For example, its potential for endothelium-dependent vasodilation, and for improvement of glucose transport and utilization, make bradykinin an important mediator for reducing the consequences of diabetes-related oxidative stress on both the myocardium and vessels.

SUMMARY

The different synergistic cardioprotective effects of the kallikrein-kinin system in the diabetic heart suggest that the stimulation of the kallikrein-kinin system might open new avenues for the treatment of diabetic cardiopathy.

Left ventricular dysfunction and remodeling in streptozotocin-induced diabetic rats

BACKGROUND

It is not fully clarified how diabetes mellitus (DM)-induced cardiac dysfunction is associated with histopathological changes of the heart in a long lasting period of DM.

METHODS AND RESULTS

Eighteen weeks after a streptozotocin injection was given to Wistar - Kyoto rats (D rats), echocardiography and hemodynamic studies including the dobutamine infusion test were performed. After perfusion fixation, immunofluorescent staining and histopathology of the heart were analyzed, and analysis with electron microscopy was also conducted. Systolic blood pressure in the conscious state and left ventricular (LV) ejection fraction by 2-dimensional echocardiography were reduced in D rats. LV mechanical responses to dobutamine assessed by maximal LV pressure derivative (+LVdP/dt) also decreased with higher dobutamine doses in D rats. Although LV and right ventricular (RV) wall thickness were smaller in D rats, there were increased RV volumes, indicating LV and RV dilatational remodeling in D rats. The cardiomyocyte transverse diameter and actin staining in cardiomyocytes in both the LV and RV were significantly reduced, and capillary tortuosity and type IV collagen were increased, indicating microangiopathy in D rats.

CONCLUSIONS

Advanced insulin-dependent DM incurred not only RV remodeling but also overt resting LV systolic dysfunction and decreased LV responsiveness to beta adrenergic stimulation with dilatational remodeling, accompanied by pathological changes of capillaries and cardiomyocytes including actin filaments.

Myocardial collagen turnover in normotensive obese patients: relation to insulin resistance

OBJECTIVES

The present study was undertaken to assess the differential impact of insulin resistance, leptin and body composition on myocardial mass and serum markers of cardiac fibrosis in obese subjects, within a small range of elevated BMI (30-40 kg/m(2)), without pulmonary disease, cardiovascular disease, hypertension, cardiac hypertrophy or other cardiovascular disease.

BACKGROUND

Obesity is an independent predictor of left ventricular mass (LVM) and is associated with disturbances in cardiac structure. The extent of the interstitial fibrosis in obese patients is not known, especially in the absence of cardiac hypertrophy.

METHODS AND RESULTS

We included 160 obese subjects. The LVM was obtained using the Devereux formula. Body composition was estimated from a total body scan. Insulin sensitivity was assessed by homeostasis model assessment (HOMA), and cardiac collagen turnover by measurement of procollagen type III aminopeptide (PIIINP). PIIINP was correlated to the E/A ratio (r=0.24; P=0.012), a marker of ventricular function. PIIINP was independently correlated with glucose concentration (r=0.27; P=0.004), indexes of insulin resistance (HOMA (r=0.27; P=0.003), insulin (r=0.24; P=0.008)), and parameters associated with the insulin-resistance syndrome (HDL-cholesterol r=-0.27; P=0.004) and fat trunk/fat leg ratio (r=0.24; P=0.053)). The variable most correlated with PIIINP was HDL-cholesterol, followed by HOMA (r (2)=0.13). When HOMA was substituted for blood glucose concentration and insulinemia (Model 2), HDL-cholesterol was strongly related to lower PIIINP levels, followed by higher glucose concentration (r (2)=0.21). Regression analyses showed that LVM had the strongest independent positive correlation with fat-free mass (FFM) (r=0.39; P=0.0002), followed by systolic blood pressure (r=0.19; P=0.034). Neither adipose mass nor height independently added information to multivariate models. The ratio leptin/fat mass was correlated with LVM (r=-0.27; P=0.004), but not independently of the FFM. Markers for fibrosis were not significantly correlated with LVM. As a result, FFM was the most predictive factor of LVM in obese subjects.

CONCLUSION

We found that serum levels of markers of cardiac collagen synthesis were significantly associated with insulin resistance in normotensive, nondiabetic obese subjects, and not related to the LVM. As a result, PIIINP could be a very early marker of ventricular dysfunction in these patients. Furthermore, we suggest that, for better detection of left ventricle hypertrophy in obese subjects, LVM should be indexed to FFM rather than to body surface area, or height.

The pathogenesis of myocardial fibrosis in the setting of diabetic cardiomyopathy

Diabetes has emerged as a major threat to worldwide health. The increasing incidence of diabetes in young individuals is particularly worrisome given that the disease is likely to evolve over a period of years. In 1972, the existence of a diabetic cardiomyopathy was proposed based on the experience with four adult diabetic patients who suffered from congestive heart failure in the absence of discernible coronary artery disease, valvular or congenital heart disease, hypertension, or alcoholism. The exact mechanisms underlying the disease are unknown; however, an important component of the pathological alterations observed in these hearts includes the accumulation of extracellular matrix (ECM) proteins, in particular collagens. The excess deposition of ECM in the heart mirrors what occurs in other organs such as the kidney and peritoneum of diabetics. Mechanisms responsible for these alterations may include the excess production, reduced degradation, and/or chemical modification of ECM proteins. These effects may be the result of direct or indirect actions of high glucose concentrations. This article reviews our state of knowledge on the effects that diabetes-like conditions exert on the cells responsible for ECM production as well as relevant experimental and clinical data.

Left ventricular diastolic dysfunction in diabetic patients: pathophysiology and therapeutic implications

Patients with signs and symptoms of heart failure and a preserved left ventricular (LV) systolic function may have significant abnormalities in diastolic function. This condition is called diastolic heart failure (DHF) and is observed in about 40% of patients with chronic heart failure (CHF). Diabetes mellitus is one of the major risk factors for DHF. Diastolic dysfunction is observed in about 40% of patients with diabetes mellitus and correlates with poor glycemic control. Suggested mechanisms for diastolic dysfunction in the diabetic heart are: (i) abnormalities in high-energy phosphate metabolism; (ii) impaired calcium transport; (iii) interstitial accumulation of advanced glycosylation end products; (iv) imbalance in collagen synthesis and degradation; (v) abnormal microvascular function, (vi) activated cardiac renin-angiotensin system; (vii) decreased adiponectin levels; and (viii) alteration in the metabolism of free fatty acids and glucose. Because most large, randomized clinical trials in CHF have enrolled only patients with systolic dysfunction, the specific management of diastolic dysfunction is largely unknown. The CHARM-Preserved (Candesartan in Heart Failure: Assessment of Reduction in Mortality and Morbidity-Preserved) trial, the only mega trial specific for DHF (LV ejection fraction >40%), showed that the angiotensin II type 1 receptor antagonist (angiotensin receptor blocker [ARB]) candesartan cilexetil reduced hospital admissions for CHF but not cardiovascular death. Currently, the pharmacologic treatment used in systolic heart failure is also recommended in DHF and includes administration of diuretics and nitrates for pulmonary congestion, and long-term management with ACE inhibitors, ARBs, aldosterone antagonists, and beta-adrenoceptor antagonists. Poor glycemic control is associated with a high incidence of heart failure in diabetic patients, but the preferable antihyperglycemic regimen for DHF in patients with diabetes mellitus needs to be determined in further studies.

Pomegranate flower extract diminishes cardiac fibrosis in Zucker diabetic fatty rats: modulation of cardiac endothelin-1 and nuclear factor-kappaB pathways

The diabetic heart shows increased fibrosis, which impairs cardiac function. Endothelin (ET)-1 and nuclear factor-kappaB (NF-kappaB) interactively regulate fibroblast growth. We have recently demonstrated that Punica granatum flower (PGF), a Unani anti-diabetic medicine, is a dual activator of peroxisome proliferator-activated receptor (PPAR)-alpha and -gamma, and improves hyperglycemia, hyperlipidemia, and fatty heart in Zucker diabetic fatty (ZDF) rat, a genetic animal model of type 2 diabetes and obesity. Here, we demonstrated that six-week treatment with PGF extract (500 mg/kg, p.o.) in Zucker diabetic fatty rats reduced the ratios of van Gieson-stained interstitial collagen deposit area to total left ventricular area and perivascular collagen deposit areas to coronary artery media area in the heart. This was accompanied by suppression of overexpressed cardiac fibronectin and collagen I and III mRNAs. Punica granatum flower extract reduced the up-regulated cardiac mRNA expression of ET-1, ETA, inhibitor-kappaBbeta and c-jun, and normalized the down-regulated mRNA expression of inhibitor-kappaBalpha in Zucker diabetic fatty rats. In vitro, Punica granatum flower extract and its components oleanolic acid, ursolic acid, and gallic acid inhibited lipopolysaccharide-induced NF-kappaB activation in macrophages. Our findings indicate that Punica granatum flower extract diminishes cardiac fibrosis in Zucker diabetic fatty rats, at least in part, by modulating cardiac ET-1 and NF-kappaB signaling.

Characterization of alterations in diabetic myocardial tissue using high resolution MRI

Cardiovascular complications, including diabetic cardiomyopathy, are the major cause of fatalities in diabetes. Diabetic cardiomyopathy is expressed in part through fibrosis and left ventricular hypertrophy, increasing myocardial stiffness leading to heart failure. In order to search for curative interventions, precise evaluation of the diabetic heart pathology is extremely important. Magnetic resonance imaging (MRI) is ideally suited for the assessment of heart disorders due to its high resolution, three-dimensional properties and dimensional accuracy. In this study streptozotocin injected Sprague-Dawley rats were used as a model of type 1 diabetes to characterize abnormalities in the diabetic left ventricle (LV). High resolution MRI using a 9.4 T horizontal bore scanner was performed on control and 7 weeks diabetic rats. In the diabetic rats as compared to controls, we found increased LV wall volume to body weight ratio, suggestive of LV hypertrophy; increased LV wall mean pixel intensity, and decreased T2 relaxation time, both suggestive of changes in the diabetic tissue properties, perhaps due to presence of fibrosis which was detected through increase in the collagen fractional area. In addition, changes in the LV cavity area were observed and quantified in post-mortem diabetic hearts indicative of stiffer and less resilient LV myocardial tissue with diabetes. Together the data suggest that LV hypertrophy and fibrosis may be a major factor underlying structural and functional abnormalities in the diabetic heart, and MRI is a valuable tool to non-invasively monitor the pathological changes in diabetic cardiomyopathy.

C16, a novel advanced glycation endproduct breaker, restores cardiovascular dysfunction in experimental diabetic rats

AIM

Advanced glycation endproducts (AGE) have been implicated in the pathogenesis of diabetic complications, including diabetic cardiovascular dysfunction. 3-[2-(4-Bromo-phenyl)-1-methyl-2-oxo-ethyl]-4,5,6,7-tetrahydro-benzothiazol-3-ium bromide (C16), a novel AGE breaker, was investigated for its effects on the development of cardiovascular disease in diabetic rats.

METHODS

Rats that had streptozotocin-induced diabetes for 12 weeks were divided into groups receiving C16 or vehicle by gavage.

RESULTS

In hemodynamic studies of the left ventricle, C16 treatment (25 or 50 mg/kg) for 4 weeks resulted in a significant increase in left ventricular systolic pressure, +dp/dt(max), and -dp/dt(max) as compared with vehicle-treated diabetic rats. Furthermore, in hemodynamic studies of the cardiovascular system, C16 (12.5, 25, or 50 mg/kg) treatment for 4 weeks resulted in a dose-dependent and significant increase in cardiac output, a reduction of total peripheral resistance, and an increase in systemic arterial compliance when compared with vehicle-treated diabetic rats. Biochemical studies showed that C16 treatment also resulted in a significant decrease in immunoglobulin G-red blood cell surface crosslink content and an increase in collagen solubility. Morphological and immunohistochemical examinations indicated that C16 was able to prevent increases of the collagen type III/I ratio in the aorta and decrease the accumulation of AGE in the aorta.

CONCLUSION

C16 has the ability to reduce AGE accumulation in tissues in vivo, and can restore diabetes-associated cardiovascular disorders in rats. This provides a potential therapeutic approach for cardiovascular disease associated with diabetes and aging in humans.

Early changes in serum markers of cardiac extra-cellular matrix turnover in patients with uncomplicated hypertension and type II diabetes

AIMS

Extracellular matrix (ECM) turnover is a major determinant of diastolic dysfunction and pumping capacity, thus potentially contributing to the progression of congestive heart failure (CHF). Patients with both arterial hypertension and diabetes have a high risk of heart failure. Whether these patients have changes in cardiac ECM has not been studied previously. Our objective was to compare blood markers of collagen turnover among patients with CHF, patients with hypertension and type II diabetes (HD), and healthy individuals.

METHODS AND RESULTS

Measurements were performed in 239 CHF patients; 64 HD patients and 92 healthy subjects. We showed by adjusted ANOVA that PIIINP levels were significantly higher in CHF and HD patients than in controls, and higher in CHF patients than in HD patients. MMP1 levels were significantly lower in CHF and HD patients than in controls. Collagen type I markers (PICP and PINP) were not influenced by CHF but were lower in HD patients as compared to controls (p<0.05 for all comparisons).

CONCLUSION

In heart failure, markers of cardiac collagen synthesis are increased and markers of degradation are decreased, potentially contributing to cardiac fibrosis and thus to poor outcome. Changes in collagen turnover may also occur early in the disease process in high-risk patients before heart failure is clinically detectable.

Is the mitral valve passive flap theory overstated? An active valve is hypothesized

The concept that the mitral valve of the heart is a passive flap that opens and closes like a barn door has been emphasized for decades by medical and biology professors to their students. But experimental findings, which are outlined in this report, support the theory of an active valve. We hypothesize that the two leaflets of the mitral valve are actively contractile; that physical forces generated in the valve itself may stabilize and add precision to the sum of forces that regulate valve movement. This precision could be of critical significance both in the moments preceding, and during, valve opening and closing. Evidence supporting our active valve hypothesis includes the profuse innervation of motor and sensory nerves that are present in the mitral valves of all animals studied. In addition, multiple contractile cell types have been found in the mitral valve, including cardiac muscle cells, smooth muscle cells, and cardiac valvular interstitial cells. In vitro work in our laboratories using the rat mitral valve shows that not only are the valves capable of contraction and relaxation, but that the contractions and relaxations are nerve-mediated. We theorize that the rich innervation and contractile cells in the mitral valve work together to modulate fine-tuning of valve movements and tone, thereby ensuring the integrity of the valve seal. Other investigators have reported that the mitral valve demonstrates contractile activity and that denervation localized to the mitral valve affects valve competence. The evidence for an active mitral valve presented by these and other experimental studies warrant a reexamination of the validity of the passive valve concept. An accurate and full understanding of the precise movements of the valve leaflets and the mechanisms that regulate these movements is likely to provide the information needed to understand and develop treatments for many different cardiac valve problems, including mitral valve diseases such as prolapse and myxomatous degeneration. In view of the available experimental evidence, the concept that the mitral valve functions only as a passive structure is challenged by numerous anomalies. A reinterpretation of the concept of valve function that incorporates active as well as passive roles for the valve leaflets and other components of the valve apparatus would have significant implications both for the directions taken in research involving the cardiac valves and for the approaches to treatment.

Salacia oblonga improves cardiac fibrosis and inhibits postprandial hyperglycemia in obese zucker rats

Diabetes has a markedly greater incidence of cardiovascular disease than the non-diabetic population. The heart shows a slowly developing increase in fibrosis in diabetes. Extended cardiac fibrosis results in increased myocardial stiffness, causing ventricular dysfunction and, ultimately, heart failure. Reversal of fibrosis may improve organ function survival. Postprandial hyperglycemia plays an important role in the development of type 2 diabetes and cardiovascular complications, and has been proposed as an independent risk factor for cardiovascular diseases. Salacia oblonga (S.O.) is traditionally used in the prevention and treatment of diabetes. We investigated the effects of its water extract on cardiac fibrosis and hyperglycemia in a genetic model of type 2 diabetes, the obese Zucker rat (OZR). Chronic administration of the extract markedly improved interstitial and perivascular fibrosis in the hearts of the OZR. It also reduced plasma glucose levels in non-fasted OZR, whereas it had little effect in the fasted animals, suggesting inhibition of postprandial hyperglycemia in type 2 diabetic animals, which might play a role in improvement of the cardiac complications of OZR. Furthermore, S.O. markedly suppressed the overexpression of mRNAs encoding transforming growth factor betas 1 and 3 in the OZR heart, which may be an important part of the overall molecular mechanisms. S.O. dose-dependently inhibited the increase of plasma glucose in sucrose-, but not in glucose-loaded mice. S.O. demonstrated a strong inhibition of alpha-glucosidase activity in vitro, which is suggested to contribute to the improvement of postprandial hyperglycemia.

Diabetic cardiomyopathy: evidence, mechanisms, and therapeutic implications

The presence of a diabetic cardiomyopathy, independent of hypertension and coronary artery disease, is still controversial. This systematic review seeks to evaluate the evidence for the existence of this condition, to clarify the possible mechanisms responsible, and to consider possible therapeutic implications. The existence of a diabetic cardiomyopathy is supported by epidemiological findings showing the association of diabetes with heart failure; clinical studies confirming the association of diabetes with left ventricular dysfunction independent of hypertension, coronary artery disease, and other heart disease; and experimental evidence of myocardial structural and functional changes. The most important mechanisms of diabetic cardiomyopathy are metabolic disturbances (depletion of glucose transporter 4, increased free fatty acids, carnitine deficiency, changes in calcium homeostasis), myocardial fibrosis (association with increases in angiotensin II, IGF-I, and inflammatory cytokines), small vessel disease (microangiopathy, impaired coronary flow reserve, and endothelial dysfunction), cardiac autonomic neuropathy (denervation and alterations in myocardial catecholamine levels), and insulin resistance (hyperinsulinemia and reduced insulin sensitivity). This review presents evidence that diabetes is associated with a cardiomyopathy, independent of comorbid conditions, and that metabolic disturbances, myocardial fibrosis, small vessel disease, cardiac autonomic neuropathy, and insulin resistance may all contribute to the development of diabetic heart disease.

Prevention of cardiac fibrosis and left ventricular dysfunction in diabetic cardiomyopathy in rats by transgenic expression of the human tissue kallikrein gene

Diabetic cardiomyopathy includes fibrosis. Kallikrein (KLK) can inhibit collagen synthesis and promote collagen breakdown. We investigated cardiac fibrosis and left ventricular (LV) function in transgenic rats (TGR) expressing the human kallikrein 1 (hKLK1) gene in streptozotocin (STZ) -induced diabetic conditions. Six weeks after STZ injection, LV function was determined in male Sprague-Dawley (SD) rats and TGR(hKLK1) (n=10/group) by a Millar tip catheter. Total collagen content (Sirius Red staining) and expression of types I, III, and VI collagen were quantified by digital image analysis. SD-STZ hearts demonstrated significantly higher total collagen amounts than normoglycemic controls, reflected by the concomitant increment of collagen types I, III, and VI. This correlated with a significant reduction of LV function vs. normoglycemic controls. In contrast, surface-specific content of the extracellular matrix, including collagen types I, III, and VI expression, was significantly lower in TGR(hKLK1)-STZ, not exceeding the content of SD and TGR(hKLK1) controls. This was paralleled by a preserved LV function in TGR(hKLK1)-STZ animals. The kallikrein inhibitor aprotinin and the bradykinin (BK) B2 receptor antagonist icatibant reduced the beneficial effects on LV function and collagen content in TGR(hKLK1)-STZ animals. Transgenic expression of hKLK1 counteracts the progression of LV contractile dysfunction and extracellular matrix remodeling in STZ-induced diabetic cardiomyopathy via a BK B2 receptor-dependent pathway.

A breaker of advanced glycation end products attenuates diabetes-induced myocardial structural changes

The formation of advanced glycation end products (AGEs) on extracellular matrix components leads to accelerated increases in collagen cross linking that contributes to myocardial stiffness in diabetes. This study determined the effect of the crosslink breaker, ALT-711 on diabetes-induced cardiac disease. Streptozotocin diabetes was induced in Sprague-Dawley rats for 32 weeks. Treatment with ALT-711 (10 mg/kg) was initiated at week 16. Diabetic hearts were characterized by increased left ventricular (LV) mass and brain natriuretic peptide (BNP) expression, decreased LV collagen solubility, and increased collagen III gene and protein expression. Diabetic hearts had significant increases in AGEs and increased expression of the AGE receptors, RAGE and AGE-R3, in association with increases in gene and protein expression of connective tissue growth factor (CTGF). ALT-711 treatment restored LV collagen solubility and cardiac BNP in association with reduced cardiac AGE levels and abrogated the increase in RAGE, AGE-R3, CTGF, and collagen III expression. The present study suggests that AGEs play a central role in many of the alterations observed in the diabetic heart and that cleavage of preformed AGE crosslinks with ALT-711 leads to attenuation of diabetes-associated cardiac abnormalities in rats. This provides a potential new therapeutic approach for cardiovascular disease in human diabetes.

Extracellular matrix maturation in the left ventricle of normal and diabetic swine

The main objective of this study is to determine the transmural distribution of extracellular matrix (ECM) collagen and maturation in non-diabetic and diabetic hearts. The Yucatan miniature swine heart ECM was analyzed in eight streptozotocin (STZ) induced diabetic pigs (Diabetic-Swine) and age matched normal control pigs (Nondiabetic-Swine). After 12 weeks of STZ induced diabetes, transmural biopsies were obtained from the left ventricular free wall divided into subendocardial, mid- and subepicardial layers. Collagen concentration and maturation were measured by RP-HPLC determination of hydroxyproline (Hyp) and content of hydroxylysylpyridinoline (HP) cross-links, respectively. Results showed a significant elevation in arterial glucose (P<0.05) and reduction in arterial plasma insulin levels in the Diabetic-Swine. Hyp concentration was significantly greater (P<0.05) in the subendocardial layers in both the Diabetic and Nondiabetic animals. The HP cross-link content was significantly greater (17%) in the Diabetic-swine subendocardial layer compared to Nondiabetic-Swine (P<0.05), but not in other layers. In summary, the accumulation and/or increase in HP cross-link content in the Diabetic-Swine subendocardial layer suggests that myocardial fibrosis may be greater in this specific region.

Myocardial remodelling: pharmacological targets

Despite considerable progress in therapy, the progressive augmentation of lifespan makes cardiac remodelling and its consequence, heart failure, a major cause of mortality and morbidity. Heart failure is consequently becoming a major goal in pharmacological research. New approaches include converting enzyme inhibitors, beta-blockers and anti-aldosterones and have demonstrated that cardiac remodelling is, at least partly, a reversible process. This review aims to establish a strategy for therapeutic research which is based on the recent advances on the molecular mechanisms of cardiac remodelling, and also to evaluate some of the new developments which are presently in progress, including new inotropic drugs, new receptors or signals blockers, nitric oxide donors, metalloproteinases and apoptotic inhibitors. Our view is clearly evolutionary and several of our conclusions may contradict current opinions, such as those which consider hypertrophy a detrimental process, hormones as a primary cause of cardiac remodelling or inotropic interventions as beneficial.

Molecular mechanisms of myocardial remodeling

"Remodeling" implies changes that result in rearrangement of normally existing structures. This review focuses only on permanent modifications in relation to clinical dysfunction in cardiac remodeling (CR) secondary to myocardial infarction (MI) and/or arterial hypertension and includes a special section on the senescent heart, since CR is mainly a disease of the elderly. From a biological point of view, CR is determined by 1 ) the general process of adaptation which allows both the myocyte and the collagen network to adapt to new working conditions; 2) ventricular fibrosis, i.e., increased collagen concentration, which is multifactorial and caused by senescence, ischemia, various hormones, and/or inflammatory processes; 3) cell death, a parameter linked to fibrosis, which is usually due to necrosis and apoptosis and occurs in nearly all models of CR. The process of adaptation is associated with various changes in genetic expression, including a general activation that causes hypertrophy, isogenic shifts which result in the appearance of a slow isomyosin, and a new Na+-K+-ATPase with a low affinity for sodium, reactivation of genes encoding for atrial natriuretic factor and the renin-angiotensin system, and a diminished concentration of sarcoplasmic reticulum Ca2+-ATPase, beta-adrenergic receptors, and the potassium channel responsible for transient outward current. From a clinical point of view, fibrosis is for the moment a major marker for cardiac failure and a crucial determinant of myocardial heterogeneity, increasing diastolic stiffness, and the propensity for reentry arrhythmias. In addition, systolic dysfunction is facilitated by slowing of the calcium transient and the downregulation of the entire adrenergic system. Modifications of intracellular calcium movements are the main determinants of the triggered activity and automaticity that cause arrhythmias and alterations in relaxation.

Cellular mechanisms of diabetic vascular hypertrophy

Mesenteric vascular hypertrophy occurs in experimental diabetes. The present study examines whether this medial hypertrophy originates via cellular hyperplasia or hypertrophy of smooth muscle cells or an increase in collagen content. Male Sprague-Dawley diabetic (streptozotocin, 50 mg/kg, i.v.) rats were compared with control rats after 3 weeks in order to study mesenteric and aortic smooth muscle cell size and degree of cellular polyploidy. Collagen content in the mesenteric vessels was examined via staining with Sirius red. Further groups of control and diabetic animals were studied after 7 and 14 days of diabetes to assess proliferation in the various layers of the vessel wall using incorporation of [3H]thymidine (0.5 mCi/kg, i.p.). Smooth muscle cell size was measured by a Coulter counter and polyploidy assessed using flow cytometry measurement of cellular DNA content. Diabetic smooth muscle cell size was reduced in both the aorta and the mesenteric vessels and polyploidy was increased in these cells. The collagen content of diabetic mesenteric media was proportionally increased. At day 7, diabetic mesenteric endothelial and adventitial layers showed increased [3H]thymidine labeling of cells and this was not observed in the media of these vessels. These findings indicate that increased endothelial and adventitial cell proliferation are early events in diabetes associated vascular hypertrophy. Furthermore, an increase in extracellular matrix within the media is an important feature of diabetes associated vascular hypertrophy.

Long-term effects of delapril hydrochloride on procollagen type III amino-terminal peptide, left ventricular mass and left ventricular function in hypertensive patients

The long-term effect of delapril hydrochloride, a non-sulfhydryl angiotensin converting enzyme inhibitor, on serum concentrations of procollagen type III amino-terminal peptide (PIIIP) and left ventricular mass (LVM) and function were investigated in 15 hypertensive patients. Patients were treated with delapril hydrochloride 30 mg/day po for 12 months. Blood samples and an echocardiogram were obtained before treatment and after 6 and 12 months of treatment. Blood pressure, PIIIP, and LVM significantly decreased associated with an increase in left ventricular fractional shortening and mean systolic and diastolic posterior wall velocity at 6 and 12 months of treatment. Positive correlations between PIIIP and LVM (r=0.49, p<0.005) and negative correlations between PIIIP and left ventricular fractional shortening (r=-0.31, p<0.05) were found. Delapril hydrochloride reduced PIIIP and LVM and improved cardiac function in hypertensive patients.

Quantitative evaluation of the rate of myocardial interstitial fibrosis using a personal computer

We investigated the reliability and reproducibility of an image-analyzing system run on a personal computer for measurement of myocardial interstitial fibrosis. Measurements of myocardial interstitial fibrosis in right ventricular endomyocardial biopsies obtained from patients with hypertrophic cardiomyopathy determined by this image-analyzing system were compared with measurements determined by the point-counting method. We also investigated the correlation between measurements of interstitial fibrosis obtained by image analysis and biochemical measurements of myocardial levels of hydroxyproline in normal and cardiomyopathic hamsters. The intra- and interobserver variability were significantly lower for measurements obtained by the image-analyzing system than for measurements obtained by the point-counting system. Reproducibility was superior with the image-analyzing method. The rate of myocardial interstitial fibrosis determined by the computer image-analyzing method was positively correlated with the hydroxyproline measurement (r = 0.89). Our results suggest that an image-analyzing system using a personal computer provides reproducible results with a high level of reliability.

Prognostic significance of diabetes mellitus in patients with acute myocardial infarction after recanalization

Although diabetic patients are at high risk for ischemic heart disease, the effect of diabetes mellitus on the prognosis of patients with acute myocardial infarction after recanalization therapy is controversial. In this study 255 patients with acute myocardial infarction admitted to CCU for coronary recanalization therapy were studied. In 95 diabetic patients, in-hospital mortality (26% for 4 weeks), complication of heart failure (35%) were significantly higher than in 160 non-diabetic patients (mortality 5%, and heart failure 11%), whereas incidence of post-infarction angina is not different between the two groups. Mortality in diabetic patients was not influenced by previous history of myocardial infarction and the number of diseased vessels. Multivariate analysis of risk factors showed that among non-cardiac risk factors, diabetes mellitus is a most important risk factor for short-term prognosis of patients with acute myocardial infarction.

Correlation between myocardial dysfunction and changes in myosin isoenzymes in diabetic rat hearts

We investigated the relationship between papillary muscle function and the myosin isoenzyme pattern, collagen content, and the type of myocardial collagen in diabetic rats to elucidate the mechanism of short-term myocardial dysfunction in diabetes. Diabetes was induced in 9-week-old male Wistar rats with a single intravenous injection of streptozotocin. One-half of the diabetic rats were treated with insulin. Age-matched control rats were also studied. The time to peak tension (TPT) of isometric papillary muscle contraction, time to 1/2 relaxation, and time from the peak tension to the peak decrease in tension (TPN) were significantly prolonged in diabetic rats at 4, 8, and 12 weeks. The peak increase and decrease in tension were slower in the diabetic rats compared with control rats. The level of the myocardial myosin isoenzyme V3 was greater in diabetic rats than in control rats at each interval. Findings in insulin-treated rats were similar to those in controls. The collagen content and the ratio of type I collagen to type III collagen were similar in all groups. The V3 level was significantly correlated with mechanical parameters (TPT versus %V3: r = 0.81, p < 0.01; TPN versus % V3: r = 0.78, p < 0.01). Our findings suggest that short-term myocardial dysfunction in diabetic rats is related to changes in the myosin isoenzyme pattern.