Proceedings of the Association of American Physicians最新文献

Endothelin-1 (ET-1) is a potent molecule produced throughout the cardiovascular system; it can exert important effects on both the structure and function of vascular smooth muscle cells and cardiac myocytes. ET-1 appears to play a central role in the physiological regulation of cardiovascular function, particularly in the vasculature. The known actions of ET-1 and the demonstration that plasma ET-1 is elevated in patients with heart failure has raised the possibility that this molecule could play a role in the pathophysiology of heart failure. This thesis has been supported and furthered by studies in animal models of heart failure that demonstrate the salutary, short-term effects of ET-1 receptor antagonists on hemodynamic function, as well as improved ventricular remodeling and survival with long-term administration. Early clinical trials with these ET receptor blockers have demonstrated systemic vasodilation. Long-term trials to determine the effects of ET-1 blockade on symptoms and survival are under way.

Oral aspirin blocks cyclooxygenase in platelets, lowering serum thromboxane concentrations. Oral aspirin also blocks cyclooxygenase in the gastrointestinal mucosa, lowering prostaglandin production and increasing the risk of gastrointestinal ulceration and bleeding. Aspirin placed on the skin also inhibits cyclooxygenase in platelets, but aspirin absorption through skin is slow, which may minimize the gastrointestinal effects. Our objectives in this study were 1) to compare the pharmacokinetic and pharmacodynamic effects of cutaneous and oral aspirin in healthy volunteers and 2) to compare the effects of cutaneous aspirin on gastroduodenal mucosal prostaglandin E2 and F2 alpha content and on mucosal damage, using endoscopy. The bioavailability of cutaneous aspirin was 4%-8% that of oral aspirin. Cutaneous aspirin (750 mg/day for 10 days) significantly lowered serum thromboxane (by 85%) and gastric and duodenal prostaglandins (by 49%-71%); placebo had no effect. Moreover, cutaneous aspirin, but not placebo, resulted in significant gastric mucosal injury. These findings demonstrate that even tiny amounts of aspirin in the blood (2 microM) have inhibitory effects on prostaglandin production in the human stomach and duodenum that result in gastric mucosal damage, even without direct exposure of the stomach to aspirin.

Recent studies have shown that patients with heart failure overexpress a class of biologically active molecules, generically referred to as pro-inflammatory cytokines. This article will review recent clinical and experimental material that suggests that pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), and interleukin-6 (IL-6) may play a role in the pathogenesis of congestive heart failure. In addition, we will review recent studies that suggest that antagonizing cytokines may represent a novel target for heart failure therapy.

Polymorphonuclear leukocytes (PMNs) represent a prominent cellular element in the innate immune system, serving to ingest exogenous particles and microbes and to kill phagocytosed microorganisms. The microbicidal activity of PMNs depends on the interactions of a broad array of potent systems, including relatively stable degradative proteins as well as labile reactive radicals. These systems can be categorized as oxygen-dependent and nonoxidative mechanisms, although the physiologically relative activity depends on the precisely orchestrated interplay between both systems. The enzyme complex responsible for the activity of the oxygen-dependent system is the respiratory burst oxidase and its important contribution to host defense is best illustrated by the frequent and severe infections seen in individuals whose PMNs lack oxidase activity, namely patients with chronic granulomatous disease (CGD). Multiple elements comprise the oxygen-dependent system, and significant advances have been made in the past decade in understanding the protein components of the respiratory burst oxidase, their subcellular distribution in resting PMNs, and their agonist-dependent assembly into a functional system at phagosomal and plasma membranes. In parallel, substantial insights into the molecular bases of CGD have likewise been made. Nonetheless there remain significant gaps in our understanding of the precise functional contributions of particular components of the system, the molecular mechanisms that regulate their coordinated assembly, and the role of related proteins in nonphagocytic cells.

The natriuretic peptides are a group of structurally similar but genetically distinct peptides that have diverse actions in cardiovascular, renal, and endocrine homeostasis. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are of myocardial cell origin and C-type natriuretic peptide (CNP) is of endothelial origin. ANP and BNP bind to the natriuretic peptide-A receptor (NPR-A), which, via 3',5'-cyclic guanosine monophosphate (cGMP), mediates natriuresis, vasodilation, renin inhibition, antimitogenesis, and lusitropic properties. CNP lacks natriuretic actions but possesses vasodilating and growth-inhibiting actions via the guanylyl cyclase-linked natriuretic peptide-B receptor (NPR-B). All three peptides are cleared by the natriuretic peptide-C receptor (NPR-C) and are degraded by the ectoenzyme neutral endopeptidase 24.11 (NEP), both of which are widely expressed in the kidneys, lungs, and the vascular wall. Congestive heart failure (CHF) represents a pathological state in which the activation of the natriuretic peptides exceeds those of all other states. In this brief review, we will attempt to provide an update on important issues regarding natriuretic peptides in CHF, with a focus on their functional importance as a beneficial humoral response in asymptomatic left ventricular dysfunction (LVD), the mechanisms of natriuretic peptide hyporesponsiveness in severe heart failure, the diagnostic and prognostic significance of the natriuretic peptides in CHF, and the therapeutic potential of the natriuretic peptides in this multiorgan syndrome.

The beta-adrenergic signaling cascade is an important regulator of myocardial function. Significant alterations of this pathway are associated with several cardiovascular diseases, including congestive heart failure (CHF). Included in these alterations is increased activity and expression of G protein-coupled receptor kinases (GRKs), such as the beta-adrenergic receptor kinase (beta ARK1), which phosphorylate and desensitize beta-adrenergic receptors (beta ARs). A body of evidence is accumulating that suggests that GRKs, in particular beta ARK1, are critical determinants of cardiac function under normal conditions and in disease states. Transgenic mice with myocardial-targeted alterations of GRK activity have shown profound changes in the in vivo functional performance of the heart. Included in these studies is the compelling finding that inhibition of beta ARK1 activity or expression significantly enhances cardiac function and potentiates beta AR signaling in failing cardiomyocytes. This article summarizes the advances made in the study of beta ARK1 in the heart and addresses its potential as a novel therapeutic target for CHF.

A unique family of genes encoding serine endoproteases related to the Saccharomyces cerevisiae serine endoprotease kexin was identified in Pneumocystis carinii. Unlike previously described serine endoprotease genes that are single copies, multiple copies of the P. carinii serine endoprotease are distributed throughout the genome. The proteins predicted by these variant genes demonstrate sequence variability, but they retain the conserved active sites associated with endoprotease activity. The serine endoprotease was localized to the organism surface by immunohistochemical and immunofluorescence studies and to the electron lucent layer of the cyst wall by immunoelectron microscopy. The findings of multiple copies of the serine endoprotease gene in the P. carinii genome, and its localization to the cell surface, suggest that this protease plays an important role in the biology of P. carinii and that antigenic variation of the surface-expressed serine endoprotease may be a strategy for immune evasion. P. carinii serine endoprotease provides a novel target for chemotherapeutic and immune-based approaches to the treatment of P. carinii pneumonia.