Esma R. Isenovic

Oxidized low-density lipoprotein as a biomarker of cardiovascular diseases

Abstract Atherosclerosis is a life-long illness that begins with risk factors, which in turn contribute to the development of subclinical disease, followed by the establishment of overt cardiovascular disease (CVD). Thrombotic-occlusive complications of atherosclerosis are among the most widespread and costly health problems. Oxidized low-density lipoprotein (OxLDL) plays an important role in atherogenesis by promoting an inflammatory environment and lipid deposition in the arterial wall. As cardiovascular events occur in individuals without common risk factors, there is a need for additional tools that may help in CVD risk assessment and management. The use of biomarkers has improved diagnostic, therapeutic and prognostic outcome in cardiovascular medicine. This review elaborates on the value of circulating OxLDL as a biomarker of CVD. Three enzyme-linked immunosorbent assays (4E6, DLH3 and E06) using murine monoclonal antibodies for determination of OxLDL blood levels have been developed. However, none of these assays are currently approved for routine clinical practice. We identified studies investigating OxLDL in CVD (measured by 4E6, DLH3 or E06 assay) by searching the PubMed database. Circulating OxLDL was found to be associated with all stages of atherosclerosis, from early atherogenesis to hypertension, coronary and peripheral arterial disease, acute coronary syndromes and ischemic cerebral infarction. The results of studies investigating the usefulness of OxLDL for CVD prediction were also summarized. Furthermore, OxLDL was found to be associated with pathologic conditions linked to CVD, including diabetes mellitus, obesity and metabolic syndrome (MetS). In addition, we have addressed the mechanisms by which OxLDL promotes atherogenesis, and the effects of antiatherogenic treatments on circulating OxLDL. Finally, we highlight the evidence suggesting that lipoprotein (a) [Lp(a)] is the preferential carrier of oxidized phospholipids (OxPL) in human plasma. A strong association between OxPL/apoB level (representing the content of OxPL on apolipoprotein B-100 particles, measured by E06 assay) and Lp(a) has been determined.

Lipoprotein Subfractions in Metabolic Syndrome and Obesity: Clinical Significance and Therapeutic Approaches

Small, dense low density lipoprotein (sdLDL) represents an emerging cardiovascular risk factor, since these particles can be associated with cardiovascular disease (CVD) independently of established risk factors, including plasma lipids. Obese subjects frequently have atherogenic dyslipidaemia, including elevated sdLDL levels, in addition to elevated triglycerides (TG), very low density lipoprotein (VLDL) and apolipoprotein-B, as well as decreased high density lipoprotein cholesterol (HDL-C) levels. Obesity-related co-morbidities, such as metabolic syndrome (MetS) are also characterized by dyslipidaemia. Therefore, agents that favourably modulate LDL subclasses may be of clinical value in these subjects. Statins are the lipid-lowering drug of choice. Also, anti-obesity and lipid lowering drugs other than statins could be useful in these patients. However, the effects of anti-obesity drugs on CVD risk factors remain unclear. We review the clinical significance of sdLDL in being overweight and obesity, as well as the efficacy of anti-obesity drugs on LDL subfractions in these individuals; a short comment on HDL subclasses is also included. Our literature search was based on PubMed and Scopus listings. Further research is required to fully explore both the significance of sdLDL and the efficacy of anti-obesity drugs on LDL subfractions in being overweight, obesity and MetS. Improving the lipoprotein profile in these patients may represent an efficient approach for reducing cardiovascular risk.

Regulation of Inducible Nitric Oxide Synthase (iNOS) and its Potential Role in Insulin Resistance, Diabetes and Heart Failure.

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. NO is a reactive oxygen species as well as a reactive nitrogen species. It is a free radical which mediates several biological effects. It is clear that the generation and actions of NO under physiological and pathophysiological conditions are regulated and extend to almost every cell type and function within the circulation. In mammals 3 distinct isoforms of NOS have been identified: neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS). The important isoform in the regulation of insulin resistance (IR) is iNOS. Understanding the molecular mechanisms regulating the iNOS pathway in normal and hyperglycemic conditions would help to explain some of vascular abnormalities observed in type 2 diabetes mellitus (T2DM). Previous studies have reported increased myocardial iNOS activity and expression in heart failure (HF). This review considers the recent animal studies which focus on the understanding of regulation of iNOS activity/expression and the role of iNOS agonists as potential therapeutic agents in treatment of IR, T2DM and HF.

Human cytomegalovirus infection and atherothrombosis.

Vascular endothelium, as a key regulator of hemostasis, mediates vascular dilatation, prevents platelet adhesion, and inhibits thrombin generation. Endothelial dysfunction caused by acute or chronic inflammation, such as in atherosclerosis, creates a proinflammatory environment which supports leukocyte transmigration toward inflammatory sites, and at the same time promotes coagulation, thrombin generation, and fibrin deposition in an attempt to close the wound. Life-long persistent infection with human cytomegalovirus (HCMV) has been associated with atherosclerosis. In vivo studies have revealed that HCMV infection of the vessel wall affects various cells including monocytes/macrophages, smooth muscle cells (SMCs) and endothelial cells (ECs). HCMV-infected SMCs within vascular lesions display enhanced proliferation and impaired apoptosis, which contribute to intima-media thickening, plaque formation and restenosis. Monocytes play a central role in the process of viral dissemination, whereas ECs may represent a viral reservoir, maintaining persistent infection in HCMV-infected atherosclerotic patients following the primary infection. Persistent infection leads to dysfunction of ECs and activates proinflammatory signaling involving nuclear factor κB, specificity protein 1, and phosphatidylinositol 3-kinase, as well as expression of platelet-derived growth factor receptor. Activation of these pathways promotes enhanced proliferation and migration of monocytes and SMCs into the intima of the vascular wall as well as lipid accumulation and expansion of the atherosclerotic lesion. Moreover, HCMV infection induces enhanced expression of endothelial adhesion molecules and modifies the proteolytic balance in monocytes and macrophages. As a consequence, infected endothelium recruits naive monocytes from the blood stream, and the concomitant interaction between infected ECs and monocytes enables virus transfer to migrating monocytes. Endothelial damage promotes thrombin generation linking inflammation and coagulation. HCMV, in turn, enhances the thrombin generation. The virus carries on its surface the molecular machinery necessary to initiate thrombin generation, and in addition, may interact with the prothrombinase protein complex thereby facilitating thrombin generation. Thus, infection of endothelium may significantly increase the production of thrombin. This might not only contribute to thrombosis in patients with atherosclerosis, but might also induce thrombin-dependent proinflammatory cell activation. This review summarizes the existing evidence on the role of HCMV in vascular inflammation.

AMP-activated protein kinase-dependent and -independent mechanisms underlying in vitro antiglioma action of compound C.

We investigated the effect of compound C, a well-known inhibitor of the intracellular energy sensor AMP-activated protein kinase (AMPK), on proliferation and viability of human U251 and rat C6 glioma cell lines. Compound C caused G(2)/M cell cycle block, accompanied by apoptotic glioma cell death characterized by caspase activation, phosphatidylserine exposure and DNA fragmentation. The mechanisms underlying the pro-apoptotic action of compound C involved induction of oxidative stress and downregulation of antiapoptotic molecule Bcl-2, while no alteration of pro-apoptotic Bax was observed. Compound C diminished AMPK phosphorylation and enzymatic activity, resulting in reduced phosphorylation of its target acetyl CoA carboxylase. AMPK activators metformin and AICAR partly prevented the cell cycle block, oxidative stress and apoptosis induced by compound C. The small interfering RNA (siRNA) targeting of human AMPK mimicked compound C-induced G(2)/M cell cycle arrest, but failed to induce oxidative stress and apoptosis in U251 glioma cells. In conclusion, our data indicate that AMPK inhibition is required, but not sufficient for compound C-mediated apoptotic death of glioma cells.

Thrombin and vascular inflammation

Vascular endothelium is a key regulator of homeostasis. In physiological conditions it mediates vascular dilatation, prevents platelet adhesion, and inhibits thrombin generation. However, endothelial dysfunction caused by physical injury of the vascular wall, for example during balloon angioplasty, acute or chronic inflammation, such as in atherothrombosis, creates a proinflammatory environment which supports leukocyte transmigration toward inflammatory sites. At the same time, the dysfunction promotes thrombin generation, fibrin deposition, and coagulation. The serine protease thrombin plays a pivotal role in the coagulation cascade. However, thrombin is not only the key effector of coagulation cascade; it also plays a significant role in inflammatory diseases. It shows an array of effects on endothelial cells, vascular smooth muscle cells, monocytes, and platelets, all of which participate in the vascular pathophysiology such as atherothrombosis. Therefore, thrombin can be considered as an important modulatory molecule of vascular homeostasis. This review summarizes the existing evidence on the role of thrombin in vascular inflammation.

Inflammation and apoptosis in aortic tissues of aged type II diabetes: Amelioration with α-lipoic acid through phosphatidylinositol 3-kinase/Akt- dependent mechanism

AIMS Endothelial dysfunction is a key triggering event in the development of cardiovascular diseases and the current study explored this phenomenon in the context of inflammation, apoptosis, reactive oxygen species (ROS) and the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway during chronic diabetes. MAIN METHODS alpha-Lipoic acid (ALA) and wortmannin (WM) were chronically administered to aged Goto Kakizaki (GK) rats, a genetic model of non-obese type II diabetes. Key indices of inflammation, apoptosis and oxidative stress were assessed using western blotting, real-time PCR and immunofluoresence-based techniques. KEY FINDINGS A chronic inflammation (e.g., increased mRNA/protein levels of TNF-alpha, ICAM, fractalkine, CD-68, myeloperoxidase) in connection with increased caspase-based apoptotic cell death and heightened state of oxidative stress (HSOS)- appear to exist in diabetic cardiovascular tissues. An assessment of NF-kappaB dynamics in aged diabetic vessels revealed not only a marked increase in cytosolic phosphorylated levels of IkappaB-alpha, NIK, IKK but also an enhancement in nuclear localization of p65 concomitantly with augmented NF-kappaB-DNA binding activity. Most of the aforementioned cardiovascular-based diabetic abnormalities including reduced activities of PI3K and Akt kinase were ameliorated following chronic ALA therapy. WM, given to GK rats negated the anti-inflammatory and anti-apoptotic actions of ALA. SIGNIFICANCE Our data highlight a unifying mechanism whereby HSOS through an induction of NF-kappaB activity together with an impairment in PI3K/Akt pathway favors pro-inflammatory/pro-apoptotic diabetic vascular milieu that culminate in the onset of endothelial dysfunction, a phenomenon which appears to be amenable to treatment with antioxidants and/or PI3/Akt mimetics (e.g., ALA).

PCSK9 Inhibition - A Novel Mechanism to Treat Lipid Disorders?

Plasma low-density lipoprotein cholesterol (LDL-C) is one of the biomarkers of cardiovascular disease (CVD) risk. LDL is cleared from the circulation preferentially through the LDL receptor (LDLR) pathway. Proprotein convertase subtilisin/kexin 9 (PCSK9) promotes the degradation of the LDLR. PCSK9 inhibition is attractive as a new strategy for lowering LDL-C levels, especially in combination with lipid lowering drugs such as statins. We review data from the available studies which focus on PCSK9 as a potential target in the treatment of hyperlipidemia. Further studies are still necessary to investigate the potential underlying mechanisms involved.

Role of PI3K/AKT, cPLA2 and ERK1/2 Signaling Pathways in Insulin Regulation of Vascular Smooth Muscle Cells Proliferation

Vascular smooth muscle cells (VSMCs) respond to arterial wall injury by intimal proliferation and play a key role in atherogenesis by proliferating and migrating excessively in response to repeated injury, such as hypertension and atherosclerosis. In contrast, fully differentiated, quiescent VSMCs allow arterial vasodilatation and vasoconstriction. Exaggerated and uncontrolled VSMCs proliferation appears therefore to be a common feature of both atherosclerosis and hypertension. Phosphorylation/dephosphorylation reactions of enzymes belonging to the family of mitogen-activated protein kinases (MAPKs), phosphatidylinositol 3-kinase (PI3K) and protein kinase B (Akt) play an important role in the transduction of mitogenic signal. We have previously shown that among extracellular signal-regulated protein kinases (ERKs), the 42 and 44 kDa isoforms (ERK1/2) as well as Akt and cytosolic phospholipase 2 (cPLA2) participate in the cellular mitogenic machinery triggered by several VSMCs activators, including insulin (INS). The ability of INS to significantly increase VSMCs proliferation has been demonstrated in several systems, but understanding of the intracellular signal transduction pathways involved is incomplete. Signal transduction pathways involved in regulation of the VSMCs proliferation by INS remains poorly understood. Thus, this review examines recent findings in signaling mechanisms employed by INS in modulating the regulation of proliferation of VSMCs with particular emphasis on PI3K/Akt, cPLA2 and ERK1/2 signaling pathways that have been identified as important mediators of VSMCs hypertrophy and vascular diseases. These findings are critical for understanding the role of INS in vascular biology and hyperinsulinemia.

Link between oxidative stress and acute brain ischemia.

The pathogenesis of acute brain ischemia (ABI) is highly complex and involves multiple mechanisms including free radical generation. Imbalance between the cellular production of free radicals and the ability of cells to defend against them is referred to as oxidative stress. Oxidative stress is one of the mechanisms contributing to neuronal damage, potentially induced through the ABI. Through interactions with a large number of molecules, reactive oxygen species may irreversibly destroy or alter the function of the cellular lipids, proteins, and nucleic acids and initiate cell signaling pathways after cerebral ischemia. Future investigations should focus on the understanding of oxidative stress mechanisms and neuroprotection in order to discover new treatment targets.