Giovanni M. Puddu

Association of serum C3 levels with the risk of myocardial infarction

PURPOSE Serum complement and IgA levels have been found to be retrospectively associated with the presence of diffuse atherosclerosis. This study was performed to assess whether serum immunoglobulins and complement components are predictive of future ischemic events. PATIENTS AND METHODS The baseline values of IgG, IgA, IgM, C3, and C4 were measured in the sera from a cohort of 860 inhabitants of the town of Brisighella, Italy. They were 444 men and 416 women, mean age 53.9 years (SD 12.4, range 23 to 84), who had not had any ischemic events (myocardial infarction [MI], angina pectoris, stroke, transient ischemic attack, or intermittent claudication) at the time of blood sampling in 1984. Their baseline values for the main recognized risk factors for atherosclerosis were known at baseline and for 4 years of follow-up. Multiple logistic regression analysis was performed for associations between ischemic events and immunologic variables (including serum IgG, IgA, IgM, C3, and C4) and risk factors for atherosclerosis (including age, sex, diastolic blood pressure, cigarette consumption, Quetelet index, total cholesterol, HDL cholesterol, triglycerides and blood glucose). RESULTS During follow-up, 57 subjects experienced ischemic events, including 28 cases of coronary heart disease (17 MI and 11 angina pectoris). Of the immunologic variables studied, only serum C3 was found to be independently associated with ischemic events (P < 0.005 for any ischemic events, coronary heart disease, and MI). The population was divided into thirds according to C3 values. The cumulative incidence of MI was 7.1/1,000 in the low third, 10.6/1,000 in the middle third and 40.8/1,000 in the high third (risk ratio for high versus middle plus low = 4.2 after adjustment for age and sex; 95% CI 1.5 to 11.7). A separate analysis for the sexes showed that serum C3 was a particularly powerful predictor of MI in men. Men whose C3 levels were in the top third had a 72.6/1,000 incidence of MI while the incidence in the rest of the male population was 6.2/1,000 (risk ratio 10.7 after adjustment for age; 95% CI 2.3 to 49.0). When similar analyses were performed for angina pectoris, stroke, and intermittent claudication, no significant increase in risk was found to be associated with serum C3. CONCLUSION C3 levels measured in sera from male subjects without previous ischemic events are independently associated with the risk of MI.

The involvement of circulating microparticles in inflammation, coagulation and cardiovascular diseases

Microparticles (MPs) are small vesicles, ranging in size from 0.1 microm to 2 microm, originating from plasma membranes of endothelial cells, platelets, leukocytes and erythrocytes. MPs can transfer antigens and receptors to cell types that are different from their cell of origin. Circulating MPs provide a procoagulant aminophospholipid surface for the assembly of the specific enzymes of coagulation. Both tissue factor and phosphatidylserine are exposed on MP outer membranes. In addition, MPs can play a significant role in vascular function and inflammation by modulating nitric oxide and prostacyclin production in endothelial cells, and stimulating cytokine release and tissue factor induction in endothelial cells, as well as monocyte chemotaxis and adherence to the endothelium. Finally, increased levels of MPs have been found in the presence of acute coronary syndromes, ischemic stroke, diabetes, systemic and pulmonary hypertension, and hypertriglyceridemia. From a practical point of view, MPs could be considered to be important markers of cardiovascular risk, as well as surrogate end points for assessing the efficacy of new drugs and therapies.

Endothelial dysfunction in hypertension

Endothelial cells release both relaxing and contracting factors that modulate vascular smooth muscle tone and also participate in the pathophysiology of essential hypertension. Endothelium-dependent vasodilation is regulated primarily by nitric oxide but also by an unidentified endothelium-derived hyperpolarizing factor and by prostacyclin. Endothelium-derived contracting factors include endothelin-1, vasoconscrictor prostanoids, angiotensin II and superoxide anions. Under physiological conditions, there is a balanced release of relaxing and contracting factors. The balance can be altered in cardiovascular diseases such as hypertension, atherosclerosis, diabetes and other conditions, thereby contributing to further progression of vascular and end-organ damage. In particular, endothelial dysfunction leading to decreased bioavailability of nitric oxide impairs endothelium-dependent vasodilation in patients with essential hypertension and may also be a determinant for the premature development of atherosclerosis. Different mechanisms of reduced nitric oxide activity have been shown both in hypertensive states and several cardiovascular diseases, and endothelial dysfunction is likely to occur prior to vascular dysfunction. Thus, the strategies currently used to improve endothelial dysfunction may result in decreased morbidity and mortality in hypertensive patients.

The relationships among hyperuricemia,endothelial dysfunction,and cardiovascular diseases:Molecular mechanisms and clinical implications

Uric acid is the end product of purine metabolism. Its immediate precursor, xanthine, is converted to uric acid by an enzymatic reaction involving xanthine oxidoreductase. Uric acid has been formerly considered a major antioxidant in human plasma with possible beneficial anti-atherosclerotic effects. In contrast, studies in the past two decades have reported associations between elevated serum uric acid levels and cardiovascular events, suggesting a potential role for uric acid as a risk factor for atherosclerosis and related diseases. In this paper, the molecular pattern of uric acid formation, its possible deleterious effects, as well as the involvement of xanthine oxidoreductase in reactive oxygen species generation are critically discussed. Reactive oxygen species contribute to vascular oxidative stress and endothelial dysfunction, which are associated with the risk of atherosclerosis. Recent studies have renewed attention to the xanthine oxidoreductase system, since xanthine oxidoreductase inhibitors, such as allopurinol and oxypurinol, would be capable of preventing atherosclerosis progression by reducing endothelial dysfunction. Also, beneficial effects could be obtained in patients with congestive heart failure. The simultaneous reduction in uric acid levels might contribute to these effects, or be a mere epiphenomenon of the drug action. The molecular mechanisms involved are discussed.

Mitochondrial Dysfunction as an Initiating Event in Atherogenesis: A Plausible Hypothesis

It is now widely accepted that oxidant stress and the ensuing endothelial dysfunction play a key role in the pathogenesis of atherosclerosis and cardiovascular diseases. The mitochondrial respiratory chain is the major source of reactive oxygen species as byproducts of normal cell respiration. Mitochondria may also be important targets for reactive oxygen species, which may damage mitochondrial lipids, enzymes and DNA with following mitochondrial dysfunction. Free cholesterol, oxidized low-density lipoprotein and glycated high-density lipoprotein are further possible causes of mitochondrial dysfunction and/or apoptosis. Moreover, in patients with mitochondrial diseases, vascular complications are commonly observed at an early age, often in the absence of traditional risk factors for atherosclerosis. We propose that mitochondrial dysfunction, besides endothelial dysfunction, represents an important early step in the chain of events leading to atherosclerotic disease.

The molecular sources of reactive oxygen species in hypertension

In both animal models and humans, increased blood pressure has been associated with oxidative stress in the vasculature, i.e. an excessive endothelial production of reactive oxygen species (ROS), which may be both a cause and an effect of hypertension. In addition to NADPH oxidase, the best characterized source of ROS, several other enzymes may contribute to ROS generation, including nitric oxide synthase, lipoxygenases, cyclo‐oxygenases, xanthine oxidase and cytochrome P450 enzymes. It has been suggested that also mitochondria could be considered a major source of ROS: in situations of metabolic perturbation, increased mitochondrial ROS generation might trigger endothelial dysfunction, possibly contributing to the development of hypertension. However, the use of antioxidants in the clinical setting induced only limited effects on human hypertension or cardiovascular endpoints. More clinical studies are needed to fully elucidate this so called “oxidative paradox” of hypertension.

The emerging role of cardiovascular risk factor-induced mitochondrial dysfunction in atherogenesis

An important role in atherogenesis is played by oxidative stress, which may be induced by common risk factors. Mitochondria are both sources and targets of reactive oxygen species, and there is growing evidence that mitochondrial dysfunction may be a relevant intermediate mechanism by which cardiovascular risk factors lead to the formation of vascular lesions. Mitochondrial DNA is probably the most sensitive cellular target of reactive oxygen species. Damage to mitochondrial DNA correlates with the extent of atherosclerosis. Several cardiovascular risk factors are demonstrated causes of mitochondrial damage. Oxidized low density lipoprotein and hyperglycemia may induce the production of reactive oxygen species in mitochondria of macrophages and endothelial cells. Conversely, reactive oxygen species may favor the development of type 2 diabetes mellitus, mainly through the induction of insulin resistance. Similarly - in addition to being a cause of endothelial dysfunction, reactive oxygen species and subsequent mitochondrial dysfunction - hypertension may develop in the presence of mitochondrial DNA mutations. Finally, other risk factors, such as aging, hyperhomocysteinemia and cigarette smoking, are also associated with mitochondrial damage and an increased production of free radicals. So far clinical studies have been unable to demonstrate that antioxidants have any effect on human atherogenesis. Mitochondrial targeted antioxidants might provide more significant results.

Mean platelet volume (MPV) increase during acute non-lacunar ischemic strokes

INTRODUCTION Mean platelet volume (MPV) has been associated with the prognosis in stroke patients. However, its spontaneous variability during the acute phase of the disease is unknown. Materials and Methods - One hundred and thirty-seven patients with ischemic stroke, aged 75.4+/-11.0 (SD) years, were classified according to several criteria: National Institutes of Health Stroke Scale (NIHSS) score, maximum lesion diameter on CT scan, Oxfordshire Community Stroke Projects (OCSP) and Trial of ORG 10172 in Acute Stroke Treatment (TOAST) categories. Platelet parameters were determined 1.2 days after the onset of symptoms, and after 3.0 further days. RESULTS The initial MPV was higher in non-lacunar than lacunar strokes (8.30+/-1.10 vs. 7.95+/-0.79 fl, P=0.04), and correlated with the sampling delay with respect to the onset of symptoms, especially in the strokes with lesions >=4 cm (r=0.39, P=0.009), NIHSS >=11 (r=0.35, P=0.02) and of cardioembolic origin (r=0.35, P=0.01). Subsequently a late MPV increment was observed in the remaining categories: from 8.20 to 8.38 fl (P=0.02) in the strokes with lesions <4 cm, from 8.11 to 8.31 fl (P=0.01) in the presence of an NIHSS<11 and from 8.20 to 8.61 fl (P=0.03) when the occlusion of a large artery was involved. CONCLUSIONS Platelet volume is not stable during the acute phase in non-lacunar ischemic strokes, as it increases early in the most severe forms, and later in the remaining subtypes. The release of large and more reactive platelets may contribute to the thrombophilic state associated with ischemic events.

The Putative Role of Mitochondrial Dysfunction in Hypertension

Hypertension is a condition associated with oxidative stress, endothelial dysfunction, and increased vascular resistance, representing probably both a cause and a consequence of elevated levels of reactive oxygen (ROS) and nitrogen (RNS) species. Mitochondria are important sites of ROS production, and a mitochondrial dysfunction, preceding endothelial dysfunction, might favor the development of hypertension. ROS production may also be induced by RNS, which inhibit the respiratory chain and may be generated through the action of a mitochondrial NO synthase. Mitochondrial uncoupling proteins are involved in both experimental and human hypertension. Finally, an excessive production of ROS may damage mitochondrial DNA, with resultant impairment in the synthesis of some components of the respiratory chain and further ROS production, a vicious cycle that may be implicated in hypertensive states.

Peroxisome proliferator-activated receptors: are they involved in atherosclerosis progression?

Peroxisome proliferator-activated receptors (PPAR) are nuclear receptors present in several organs and cell types. They are subdivided into PPAR alpha, PPAR gamma and PPAR delta (or beta). PPAR alpha and gamma are the two main categories of these receptors, which are both characterized by their ability to influence lipid metabolism, glucose homeostasis, cell proliferation, differentiation and apoptosis, as well as the inflammatory response, by transcriptional activation of target genes. PPAR alpha are activated by fatty acids, eicosanoids and fibrates, while PPAR gamma activators include arachidonic acid metabolites, oxidized low density lipoprotein and thiazolidinediones. Atherosclerosis is now considered a chronic inflammatory condition. Thus, PPAR activation appears a promising approach to favorably affect atherosclerosis development through both metabolic and anti-inflammatory effects. However, the clinical data in favor of an anti-atherosclerotic action of PPAR agonists are still scanty, and some experimental data would even indicate possible pro-atherogenic effects, or a lack of effect in the female sex. New controlled clinical studies will provide the information necessary to understand the true significance and usefulness of PPAR alpha, gamma and delta activators in the control of atherosclerotic disease.