Current Enzyme Inhibition - Volume 1, Issue 1, 2005

agr; bgr; Dgr; egr; Hsub2;Osub2 plus; plusmn; sim; percnt; clsup-;sup1;

Integrin-linked kinase (ILK) is a focal adhesion serine/threonine protein kinase that binds to the cytoplasmic domain of β1 integrin and has an important role in integrin and growth factor signaling pathways. Clustering of integrins on the cell surface in contact with the extracellular matrix induces focal adhesion that recruits numerous mitogenic signaling proteins other than ILK, such as growth factor receptors, mitogenactivated protein kinase, and small GTP-binding proteins, to integrin receptors and forms signaling centers where adhesive and mitogenic pathways can integrate. ILK is highly expressed in neuronal cells and its enzyme activity is activated by cell adhesion on the extracellular matrix in a phosphatidylinositol 3-kinasedependent manner. Recent studies demonstrated that ILK interacts with and regulates many different signaling pathways in neuronal cells, which implies an important role for ILK in a variety of neuronal functions. This article discusses the role of ILK in neuronal cells and also the possible involvement of ILK in neuronal disorders.

Sesame oil is commonly used as antioxidant. Sesamin (SA) and sesamolin (SO) are major lignans (a non-fat constituent) in sesame seed oil, inhibit Δ5-desaturase activity and cause accumulation of dihomo-γ- linolenic acid (DGLA), a precursor of 1-series prostaglandins, and the decreasing production of proinflammatory 2-series prostaglandins and 4-series leukotrienes. Diets supplemented with SA and/or SO, lower serum levels of interleukin (IL)-1β, IL-6 but elevate IL-10 in mice after lipopolysaccharide (LPS) exposure. Mice fed with sesame seed oil have a 65% survival rate after cecal ligation and puncture as compared with the 20% survival in the controls. SA and SO inhibit the IL-6, tumor necrosis factor (TNF)-α and nitric oxide (NO) productions from microglia under LPS stimulation. The protective effects of SA/SO to stroke-prone spontaneously hypertensive rats and hepatic ischemia-reperfusion injury have been attribute to their antioxidant and anti-inflammatory activities. The antioxidant activities of SA/SO are identified in their methylenedioxyphenyl moieties that can be changed into dihydrophenyl (catechol) moieties. Since reactive oxygen species (ROS) are mediators of a variety of pathological processes, including inflammation and ischemic/hypoxic injury, the ROS scavenging moiety may contribute as an important component to prevent cells from the free radical injury. Hypoxia or HO-induced cell injury are related with activated MAPKs and caspase-3 activities. Evidence suggests that the protective effects of SA and SO on hypoxic neuronal cells are related to suppression of ROS generation and mitogen-activated protein kinases (MAPKs). In addition, SA/SO significantly reduce LPS-activated p38 MAPK. Specific inhibitors of MAPKs dose-dependently inhibit NO and cytokine productions in LPS-stimulated microglia. Therefore, the inhibition of NO and cytokine productions may partly due to the reduction of LPS-induced p38 MAPK signal pathway by SA and SO.

While agents that cause carbonyl-induced modification include sugars, lipids and industrial and pyrogenic compounds, much of the existing literature describes the process of glycation. Protein glycation is recognized as a major post-translational modification that attends the pathogenesis of diverse diseases. Glycation arises from the reactivity of common carbohydrates, their metabolic intermediates and their oxidized byproducts. The hyperglycemia associated with diabetes and the life-long exposure to pro-glycating agents bring about an environment that favors the modification of diverse proteins resulting in macro- and microangiopathy and the neuropathy of misfolding disorders such as Alzheimer's disease. Numerous structural and catalytic proteins have been shown to be targets of glycation. The literature documents the potent inhibitory effects of glycation with very insightful suggestions on mechanisms of action. The current review describes the way carbonyl-containing (and particularly glycating) agents react with protein residues elucidating mechanisms that include two broad categories: direct reaction (1) with active site residues and (2) with residues distinct from the active site. The consequence of active site modification involves obvious steric and chemical changes that are likely to be prohibitive. The modification of residues distinct from the active site suggests inhibitory mechanisms more subtle and complex. The current review presents new perspectives in this emerging field that has implications beyond enzyme inhibition, such as the cellular impact of protein insolubility and aggregation.

Certain Zinc Metallopeptidases, such as Angiotensin Converting Enzyme (ACE), Neutral Endopeptidase (NEP) and Endothelin Converting Enzyme (ECE), play a key role in vascular homeostasis through their proteolytic activity in various vasoactive peptides. Effective inhibitors for these enzymes were until recently designed in the absence of the X-ray structure of these enzymes, and a variety of ACE inhibitors are commercially available. A new class of promising compounds, namely vasopeptidase inhibitors, have emerged and they represent a new concept in hypertension and cardiovascular disease therapeutics. They contemporarily inhibit the catalytic function of more than one of the above enzymes and they are undergoing extensive clinical trials exhibiting increased efficacy in hypertension treatment and higher risk for side effects such as angioedema when compared to ACE inhibitors. The determination of the substrate-free and substrateloaded X-ray models of NEP and ACE provides valuable insight of the structure determinants in enzymesubstrate interaction and it is believed that new more selective inhibitors could be afforded through structurebased drug design process. Selectivity towards target enzyme even in simultaneous inhibition could modify the breakdown of vasodilator and vasoconstrictor peptides and could therefore modulate the balance of the risk-benefit profile.

Activation-induced cell death (AICD) is an active process. T and B lymphocytes undergo AICD as an auto-regulatory mechanism for the body to remove unwanted activated cells after making appropriate use of them. Recent studies have shown that brain microglia and astrocytes also undergo apoptosis upon inflammatory activation. Caspase-11 has been demonstrated to play a central role in the apoptosis of both microglia and astrocytes following inflammatory activation; inflammatory stimuli induce neuroglial apoptosis through caspases-11, -1, and -3. Thus, inflammatory signals that activate neuroglia may also initiate internal death program, in which caspases play a crucial role. Caspases may be a target for the modulation of neuroglial AICD that has implications in neurodegenerative diseases.

The traditional linear model of the RAS has now been replaced by a dynamic system than includes a number of new components. Among them the angiotensin converting enzyme type 2 has recently become recognized as an important homeostatic factor and counterbalance to ACE, modulating the balance between vasoconstrictors and vasodilators within the heart and kidney, and playing a significant role in regulating cardiovascular and renal function. However, ACE2 also has a number of important independent actions as evidence by its differential distribution in both development and in adult tissues. Studies from knockout mice suggest that ACE2 is involved in both cardiac and renal development. ACE2 is also involved in a number of disease processes, most notably ACE2 has been reported recently to be the functional receptor for the severe acute respiratory syndrome (SARS) coronavirus. A reduction in ACE2 in diabetes may also contribute to endorgan damage. ACE2 may also have important functional consequences in heart failure and pre-eclampsia. In this context, selective inhibitors of ACE2 will provide important tools for exploring the physiology and pathology of the enzyme in both heath and disease states.

A novel approach for treatment of type 2 diabetes is based on the gut hormone glucagon-like peptide-1 (GLP- 1), which is antidiabetic due to its combined action to stimulate insulin secretion, increase beta-cell mass, inhibit glucagon secretion, reduce the rate of gastric emptying and induce satiety. A problem is, however, that the peptide is rapidly inactivated by the enzyme dipeptidyl peptidase-4 (DPP-4), resulting in a half-life of active GLP-1 of only approximately 1-2 minutes. To overcome this inconvenient drawback for the treatment of diabetes, two strategies have been successful; one strategy uses DPP-4 resistant GLP-1 receptor agonists whereas the other strategy uses inhibition of DPP-4. Such inhibition will increase the levels of endogenous active GLP-1 and prolong its half-life. The rationale behind the strategy is evident from studies in animals with genetic deletion of DPP-4, which have improved glucose tolerance and increased insulin secretion in response to oral glucose. Furthermore, in experimental animals, different pharmacological DPP-4 inhibitors are antidiabetic. Recently also studies in subjects with type 2 diabetes have shown that prolonged DPP-4 inhibition for up to 1 year is antidiabetogenic because fasting and postprandial glucose as well as HbA1c levels are reduced. This is seen in association with good tolerability and weight neutrality. Hence, DPP-4 inhibition has the potential to be a novel, efficient and tolerable approach to treat type 2 diabetes.

Protein phosphorylation plays a central role in cellular processes. Recently, a considerable interest in the development of inhibitors of protein kinase has been taken. Mitogen activated protein kinases (MAPKs), a group of Ser/Thr protein kinases, are activated by a wide spectrum of extracellular stimuli. Extensive literature reports have indicated the key role of these kinases in inflammatory processes and in immune response. This review outlines relevant aspects on the development of MAPK inhibitors that could form the molecular basis for a new class of anti-inflammatory and immunoregulatory agents. Particular focus is given to their role in regulating the dysfunction of innate immunity. Also, concepts as docking interactions, participation of scaffold proteins in MAPK cascades and its importance in the design of more specific inhibitors are discussed.

The recent description of the crystal structures of rat MAO-A and human MAO-B provides an unprecedented framework to elucidate the mechanisms underlying the selective interactions between these proteins and their ligands. The analysis of previous and emerging data, in the light of the structural similarities and differences between both isozymes, allows a better understanding of the requirements that determine the affinity and selectivity of substrates and inhibitors. This augurs a new impulse for the rational design of potent and selective MAO inhibitors with therapeutic potential.