Current Vascular Pharmacology - Volume 3, Issue 2, 2005

This review demonstrates that oxidative stress, reactive oxygen species, and electron transfer can serve as unifying mechanistic themes for large numbers of cardiovascular toxins, both endogenous and exogenous. Lipid peroxidation is a prevalent insult. Common among the various conditions are atherosclerosis and arrhythmia. The preventive effects of antioxidants are documented.

The excessive contraction of small arteries under high blood pressure is the main contributor to the pathological change of hypertension. Current anti-hypertensive drugs, which lack a selective effect on small arteries in a hypertensive state, may cause many adverse effects. We have developed a novel opener of ATP-sensitive potassium channels, iptakalim, the vasorelaxing action of which is determined by the hypertensive status of small arteries. In conscious strokeprone, spontaneously hypertensive rats and “two-kidneys, one-clip” renal hypertensive dogs, this compound produced long-lasting hypotensive effects, with no tolerance. Furthermore, it exerted a protective effect against hypertensive damage to target organs. Given its potency and fewer side effects, iptakalim hydrochloride is a promising drug for the treatment of hypertension.

Somatostatin (somatotropin release inhibitory factor; SRIF) peptides are widely distributed throughout the mammalian body and act through a family of genetically distinct, guanine nucleotide regulatory protein coupled (Gprotein- coupled), cell surface receptors (sst1-5). Compelling evidence shows that SRIF and SRIF peptidyl analogs modulate vascular function, with actions upon smooth muscle and endothelium. SRIF receptors are known to exist in the carotid endothelium, a principal target for the pro-inflammatory cascade that accompanies coronary artery disease. SRIF- 14 and SRIF analogs are anti-inflammatory but the molecular mechanism involved remains unclear. Since crucial steps in the endothelial inflammation response include endothelial activation by cytokines, adhesion molecule expression and cellmonocyte interactions, peptide agents that inhibit these steps might provide a novel strategy for reducing vascular inflammation. SRIF, acting through its cognate receptors, modulates a variety of intracellular effectors that are linked to inflammation including phosphotyrosine phosphatases, the extracellular regulated protein kinase 1 and 2 (ERK1/2) cascade, adenylyl cyclase and endothelial nitric oxide synthase. Directly or indirectly, SRIF also functions to inhibit endothelial cell proliferation and induce apoptosis. A detailed understanding of SRIF actions could provide a rational basis for using SRIF ligands in controlling vascular inflammation and inhibiting cytokine signaling, critical events in atherogenesis.

The cardiovascular system is an important target for thyroid hormones (THs). Until recently, our understanding of the biological role of THs has been largely based on a catalog of effects observed in excess or deficiency of THs. In the last decades, however, some important progress has been done in defining the molecular and biochemical basis of thyroid hormone action at the cellular and nuclear level. Most of the molecular and cellular mechanisms responsible for the effects of THs on the heart have been clarified, whereas few data are available about the mechanisms of action of THs on the vasculature. Data reported so far describe the thyroid hormone effects on the vascular system as indirect consequences of thermogenic or hemodynamic derangements. The aim of this review is to focus on the direct role of THs in the vascular system, to analyze the main factors involved in this regulatory process, to evaluate the causes of imbalance, their relationships to some pathophysiological conditions, and, finally, to hypothesize effective therapeutic approaches. Our review considers data on the molecular and biochemical properties of iodothyronine deiodinases, with particular attention to D2, the enzyme for the local conversion of the precursor thyroxine (T4) into the biologically active triiodothyronine (T3). We summarize data on the deiodinase tissue distribution, subcellular localization, topology and structure-activity relationships. We also discuss the physiological role of deiodinases and their involvement in the THmediated regulation of vascular function.

The cellular role of mitochondria includes ATP generation and the modulation of cytosolic calcium signals, besides being the “crossroads” for several cell death pathways. The maintenance of optimal mitochondrial functioning during the disease process increases the chances for survival. For example, ischaemia followed by reperfusion is known to negatively affect mitochondrial function, namely by inducing a deleterious condition called mitochondrial permeability transition (MPT). The MPT is responsible for mitochondrial dysfunction and can ultimately lead to cell death. Therefore, it seems important to protect mitochondrial function in cardiac disease. Carvedilol, a β-adrenergic receptor antagonist with antioxidant properties, has a positive impact on cardiac mitochondria during in vitro, ex-vivo and in vivo models of cardiac dysfunction. Particularly, carvedilol was shown to inhibit MPT in isolated heart mitochondria and protect mitochondria against the oxidative damage induced by the xanthine oxidase / hypoxanthine pro-oxidant system. The observation that carvedilol acts as an inhibitor of mitochondrial complex-I is also of importance, since this mitochondrial system was proposed as cause of the cardiotoxicity associated with the antineoplasic drug doxorubicin. This review points out the major findings concerning the positive impact of carvedilol on mitochondrial function and its use in the treatment of myocardial diseases where oxidative stress is known to be involved.

Urotensin II is the most potent vasoconstrictor known. Paradoxically, urotensin II also possesses vasodilator activity in certain vascular beds. While much is still to be learnt regarding urotensin II's actions on vascular tone, it is now clear that it mediates its effects by interacting with a specific G-protein-coupled receptor. The presence of urotensin II and its receptor in both vertebrate and invertebrate species suggests an evolutionarily conserved role in normal physiology although evidence is mounting for both species-specific as well as disease-specific effects of this peptide. This somatostatin- like peptide was originally thought to reside solely in compartments of the central nervous system. However, recent evidence implicated urotensin II in the pathogenesis of a variety of disease processes ranging from hypertension to hepatic cirrhosis. Increased expression of this peptide has been noted in cardiac, renal and hepatic disease. While the contribution of urotensin II to these diseases remains unclear, the advent of urotensin II antagonists allows for not only the possibility of a new range of therapeutic drugs but also new avenues of investigation and further mechanistic insights into the pathophysiology of these disease processes.

Leptin and ghrelin are novel peptide hormones which are counter-regulatory in the central control of appetite. More recently, it has become clear that these hormones have a range of effects on the cardiovascular system. Leptin increases sympathetic activity, producing a pressor effect when acting on the central nervous system. However, leptin produces vasodilation by an endothelium-dependent mechanism peripherally. Ghrelin decreases sympathetic activity and has a depressor effect when acting on the central nervous system. Peripherally, ghrelin produces vasodilation by an endothelium- independent mechanism. Ghrelin improves left ventricular function and cardiac cachexia in heart failure. Leptin may contribute to cardiac cachexia, and to obesity-related cardiomyopathy by a variety of mechanisms. Leptin has proinflammatory, proliferative and calcification promoting effects in the vasculature. Ghrelin has recently been shown to be anti-inflammatory in the vasculature. Leptin may also produce a pro-thrombotic state through stimulation of platelet aggregation and inhibition of coagulation and fibrinolysis. The evidence for and against these effects as well as their pathophysiological significance in obesity hypertension, heart failure, atherosclerosis and thrombosis are discussed.

Cardiovascular disease is extremely common in patients with end-stage renal disease (ESRD) and accounts for at least 50% of deaths among these patients. Vascular calcifications (VC) have been recently implicated as a possible cause of this excess cardiovascular mortality. Medial calcification is a striking feature of vascular disease in patients with ESRD. The traditional view that VC is a degenerative and passive process has been seriously challenged , based on strong evidence suggesting that VC is an active and highly regulated process similar to bone formation. Different data support the notion that elevated levels of phosphorus and/or other uremic toxins may play an important role by transforming vascular smooth muscle cells into osteoblast-like cells, which can produce bone matrix proteins. This nidus can then mineralize if the balance of pro-mineralizing factors outweighs inhibitory factors. The advent of newer noninvasive screening tests have generated great interest for screening patients with ESRD for vascular calcifications. Control of serum phosphorus with sevelamer, a recently developed non-calcium, non-aluminum phosphate binder, have attenuated or arrested progression of coronary artery and aortic calcifications compared to treatment with calcium-based binders. Amino bisphosphonates, have shown to completely inhibit soft tissue calcifications, calciphylaxis and prevent death in animal models. The first generation bisphosphonate, etidronate, reduces the progression of coronary artery calcifications patients receiving long-term hemodialysis and intravenous pamidronate has produced a rapid improvement of calciphylaxis. In conclusion, VC is a widespread phenomenon in patients with ESRD with important cardiovascular consequences. A better understanding of the processes of VC is leading to therapies to retard or improve this phenomenon and will probably have an important impact on patient mortality.

The increase in obesity prevalence is problematic as this condition is associated with health complications such as diabetes and cardiovascular diseases, more particularly when the excess body fat is stored in the deep abdominal region. The mainstay of therapy consists of behavior modification related to obesity such as overeating and physical inactivity. When these lifestyle modifying attempts fail, the use of anti-obesity drugs is warranted. Drug treatment is often indicated but is somewhat limited by the minimal number of well tolerated drugs that have proven to have long-term efficacy in maintaining body weight loss. The currently available drugs, sibutramine and orlistat, appear modestly effective in promoting weight loss. Ongoing studies continue to evaluate other drug treatments that may result in body weight reduction through a number of different mechanisms. Thus, the aim of this review is to present an overview of the current drugs available (particularly sibutramine and orlistat) as well as potential future candidates, and the impact of these agents on obesity and cardiovascular physiology. Furthermore, the therapeutic paradox of sibutramine in preventing obesity will be discussed as well as the beneficial impact of physical exercise on cardiac economy.

For more than decades calcium antagonists (CEBs) have been widely used for the treatment of myocardial ischaemia (angina pectoris). Among the classes of CEBs, the 1,4-dihidropyridine (DHPs) have been used for this indication because of their haemodynamic and electrophysiological properties. In particular, DHPs are compounds capable of vascular protection on both smooth muscle and endothelium. The main protective activity is related to their calcium antagonist activity. In addition, they present vascular dilatation function, which has been related to an anti-endothelin efficacy. The newer DHPs are endowed with slow onset and long duration of vasodilator activity and reduce coronary resistance with little or no effect on heart rate. The more lipophilic DHP, lacidipine, is also able to reduce the formation of atheroma plaque in animal models at therapeutic doses. It has potent and long-lasting antihypertensive properties and appears to protect the arterial wall against the development of atherosclerotic lesions in animal models or human subjects with severe and multiple risk factors. Additionally, it has been observed that: i) NO/cyclic GMP pathway facilitates the inhibitory effect of Ca++ antagonists on KCl-evoked contraction in rat aorta; ii) Vasodilator effect of lacidipine was significantly attenuated in the presence of NO-synthase inhibitors; iii) DHPs stimulate an electrochemical activity related to the nitric oxide (NO) system within the aortic vessel tissue, in rats and mice. In particular, they implement endothelial NO at “useful” and not toxic nanomolar levels. These activities join the already described positive effects of these compounds upon vascular functions.