Current Medicinal Chemistry - Volume 15, Issue 22, 2008

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases which are involved in the proteolytic processing of several components of the extracellular matrix. As a consequence, MMPs are implicated in several physiological and pathological processes, like skeletal growth and remodelling, wound healing, cancer, arthritis, and multiple sclerosis, raising a very widespread interest toward this class of enzymes as potential therapeutic targets. Here, structure-function relationships are discussed to highlight the role of different MMP domains on substrate/inhibitor recognition and processing and to attempt the formulation of advanced guidelines, based on natural substrates, for the design of inhibitors more efficient in vivo.

Pre-eclampsia (PE), a characteristic hypertensive disorder of human pregnancy and a leading cause of maternal and fetal mortality and morbidity worldwide, shares some similarities with atherosclerosis, namely the involvement of oxidative stress and of endothelial dysfunction in their pathophysiologies, the presence of similar typical lesions and of common risk factors. Although it is widely accepted that regular physical exercise protects against cardiovascular events, few studies have addressed the impact of physical activity in reducing PE risk. In this paper, similarities between atherosclerosis and PE, involving pathogenic mechanisms, are described. This paper also reviews the studies performed until now that evaluated the impact of regular physical exercise (prenataly or during pregnancy) in reducing risk of PE. The potential mechanisms underlying physical activity as a prophylactic approach of PE, as observed with cardiovascular diseases, are discussed.

Literature publications reporting the development of organophosphorus compounds, targeting aspects of signal transduction to the titled therapeutic ends, are reviewed. With respect to extracellular targets, the development of ligands to purinergic (P2), and endothelial differentiation-gene receptors (of S1P- and LPA-receptor subtypes) is charted, along with inhibitors of the production and release of tumour necrosis factor-α (TNF-α). Reported also are inhibitors of the ectoenzymes aminopeptidase N, aminopeptidase A and dipeptidyl peptidase IV, the proteolytic enzyme thrombin, ligands to “apoptosis-receptors” and γδ T-cell activators. In addition, disruption of intracellular signalling chains mediated through reversible coupling of proteins via phosphorylation of Tyr residues and docking of pTyr residues in SH2-binding domains is covered. In particular, the development of ligands to SH2-binding domains in tyrosine kinases Src and lck, adaptor protein Grb2, and also ZAP70 protein are reported along with inhibitors to relevant phosphatases. SAR studies of ligands to Ins(1,4,5)-P3- and ryanodine-type receptors of intracellular Ca2+-storage organelles are described including analogues to secondary messengers cyclic-ADP-ribose (cADPR) and myo-inositol-1,4,5-triphosphate. Inhibitors of phosphatidyl inositol 3-kinase (PI3K) and sphingomyelinase are also reported, as are inhibitors of farnesyl transferase, the enzyme involved in protein-prenylation.

Scientific interest in defining the human body's ability to limit the effects of administered drugs and xenobiotics dates from the mid-19th century when developing knowledge and techniques in the field of organic chemistry first made such studies possible. The first experimental evidence documenting the existence of cytochrome p450 (CYP) dates to the year 1955, when an enzyme system capable of oxidizing xenobiotic compounds was identified in the endoplasmic reticulum of liver homogenates. From these days on several studies analyzed the expression and function of metabolizing phase I enzymes in liver cells. Due to the unique structural features of human skin, little was known about the expression and function of CYP enzymes in this tissue and their role in uptake, metabolism and elimination of xenobiotics as well as endogenous substrates. Lasting recent years it has become clear that human skin cells express various CYP enzymes, including CYP26AI which is responsible for the metabolism of retinoic acid in skin cells. It has been also shown that CYP enzyme expression patterns are cell type and tissue specific and that in skin cells this differs significantly from its expression in other environmental interfaces such as the liver, lung and gastrointestinal tract. Therefore knowledge of skinspecific CYP expression and function is a prerequisite for pharmacological studies of the skin.

Epidemiological studies show that high density lipoprotein cholesterol (HDL-C) levels are inversely related to the risk of vascular events. Statins are the most widely prescribed drugs for the treatment of dyslipidaemias and their use for the prevention of vascular events is evidence based. Statins raise HDL-C but this effect seems to vary considerably between studies. We searched the literature to assess the relationship between statin-induced increases in HDL-C levels and surrogate and/or clinical endpoints. Based on the existing evidence, it is difficult to determine how much reduction, if any, in vascular risk is attributable to a statin-induced increment in HDL-C levels. Whether a statin that beyond its LDL-C lowering effect also raises HDL-C has additional benefits in the prevention of vascular events remains to be established.

The liver plays a central role in the regulation of cholesterol homeostasis. Hepatic cholesterol content is maintained by a complex interplay between input and output pathways; alterations in the balance among these processes may lead to accumulation of excess cholesterol in body compartments with potentially deleterious consequences at the level of blood vessels (atherosclerosis) and biliary tract (gallstone disease). Molecular biology has brought new insights into this field. Nuclear receptors have been shown to play a key role in the “sensing” of intracellular cholesterol levels and in the triggering of metabolic responses via the sterol regulatory element binding protein (SREBP) cascade. A nuclear receptor for bile acids, farnesoid X receptor (FXR), has been identified and the molecular pathways underlying feedback inhibition of bile acid synthesis, the main mechanism of irreversible degradation of cholesterol, have been clarified. Such regulation involves a number of additional coactivators/corepressors of the transcription of the limiting enzyme of bile acid synthesis, cholesterol 7α-hydroxylase. Finally, the main transporters of biliary lipids (bile acids, phospholipids and cholesterol) have been described; most of them undergo transcriptional control by nuclear receptors, allowing regulation of biliary lipid efflux in conditions of different intracellular availability. Despite a body of evidence coming from experimental models the intimate mechanisms of regulation have not been clearly defined and direct evidence in humans is rather limited. This review will focus on the role of nuclear receptors in the regulation of hepatic cholesterol degradation and biliary lipid secretion, and on the theoretical applications from a pharmacotherapeutic perspective.

Characterization of liver-specific autoantigens has given a fresh impetus to research in the pathogenesis of autoimmune liver diseases, viral-triggered and drug-induced autoimmunity affecting the liver. Intriguing is the fact that most of the liver-specific autoantigens are enzymes of key importance for cell's homeostasis. Detection of autoantibodies against the respective antigens is carried out for diagnostic and research purposes using indirect immunofluorescence, immunoblotting, enzyme-linked immunosorbent assays, radioimmunoassay, immunoprecipitation or assays determining inhibition of enzyme activity. In patients with autoimmune hepatitis, a liver disorder of unknown etiology and pathogenesis, disease-specific autoantibodies are frequently directed against drug metabolizing enzymes of phase 1, namely cytochrome P450 2D6 (CYP2D6). The same and other members of these families of enzymes (CYPs) have also been described as targets of liver-specific autoimmunity in chronic hepatitis C virus (HCV)-infected patients, patients with autoimmune hepatitis as part of the autoimmune polyglandular syndrome type-1 (APS-1) and drug-induced autoimmunity. How these enzymes become ‘self targets’ is not yet established. An antigen release following hepatocyte injury could provide the stimulus for an immune response towards epitopes on these enzymes but the highly-specific, antigenrestricted initiation of the observed autoimmune response is against such an explanation. Accordingly, in this review we will focus on the pathogenic role -if any- of autoimmune responses against liver-related CYPs in autoimmune hepatitis, HCV infection, APS-1 and drug-induced autoimmunity. Learning more about the specificity of antibody responses against these enzymes may help us better understand the mechanisms underlying liver autoimmunity and may facilitate the development of therapeutic and preventive interventions.

Arsenic, a known human carcinogen, can induce tumors of the skin, urinary bladder, liver and lung etc.. On the other hand, arsenic is also a novel promising anticancer agent, and can be used effectively to treat acute promyelocytic leukemia (APL) and some other tumors. These paradoxical effects of arsenic not only result from direct or indirect influences on the genetic and epigenetic levels, but are also closely correlated with unique arsenic metabolism. This article reviews our recent studies as well as other reports on arsenic metabolism and epigenetic changes of DNA methylation during its metabolism. We also summarize the clinical use of arsenic trioxide (As2O3) to date and discuss new therapeutic strategies such as concurrent arsenic-radiation therapy to achieve local tumor control and enhance the radiosensitivity of solid tumors.