Bernd van der Loo

High Glucose Causes Upregulation of Cyclooxygenase-2 and Alters Prostanoid Profile in Human Endothelial Cells Role of Protein Kinase C and Reactive Oxygen Species

Background—Prostaglandins generated by cyclooxygenase (COX) have been implicated in hyperglycemia-induced endothelial dysfunction. However, the role of individual COX isoenzymes as well as the molecular mechanisms linking oxidative stress and endothelial dysfunction in diabetes remains to be clarified. Methods and Results—Human aortic endothelial cells were exposed to normal (5.5 mmol/L) and high (22.2 mmol/L) glucose. Glucose selectively increased mRNA and protein expression of COX-2. Its upregulation was associated with an increase of thromboxane A2 and a reduction of prostacyclin (PGI2) release. Glucose-induced activation of PKC resulted in the formation of peroxynitrite and tyrosine nitration of PGI2 synthase. NO release was reduced despite 2-fold increase of endothelial NO synthase expression. Phorbol ester caused an increase of COX-2 and endothelial NO synthase expression similar to that elicited by glucose. These effects were prevented by the PKC inhibitor calphostin C. N-acetylcysteine, vitamin C, and calphostin C prevented ROS formation, restored NO release, and reduced colocalization of nitrotyrosine and PGI2 synthase. Expression of p22phox, a subunit of NAD(P)H oxidase, was increased, and diphenyleneiodonium inhibited ROS formation. By contrast, indomethacin did not affect glucose-induced ROS generation. Conclusions—Thus, high glucose, via PKC signaling, induces oxidative stress and upregulation of COX-2, resulting in reduced NO availability and altered prostanoid profile.

A Role for Changes in Platelet Production in the Cause of Acute Coronary Syndromes

Platelets are heterogeneous with respect to their size, density, and reactivity. Large platelets are more active hemostatically, and platelet volume has been found to be increased both in patients with unstable angina and with myocardial infarction. Furthermore, platelet volume is a predictor of a further ischemic event and death when measured after myocardial infarction. Platelets which are anucleate cells with no DNA are derived from their precursor, the megakaryocyte. Therefore, it is suggested that changes in platelet size are determined at thrombopoiesis in the megakaryocyte and that those changes might precede acute cardiac events. Understanding of the signaling system that controls platelet production may also further elucidate the cascade of events leading to acute vascular occlusion in some patients.

Vascular aging: Chronic oxidative stress and impairment of redox signaling—consequences for vascular homeostasis and disease

Characteristic morphological and molecular alterations such as vessel wall thickening and reduction of nitric oxide occur in the aging vasculature leading to the gradual loss of vascular homeostasis. Consequently, the risk of developing acute and chronic cardiovascular diseases increases with age. Current research of the underlying molecular mechanisms of endothelial function demonstrates a duality of reactive oxygen and nitrogen species in contributing to vascular homeostasis or leading to detrimental effects when formed in excess. Furthermore, changes in function and redox status of vascular smooth muscle cells contribute to age-related vascular remodeling. The age-dependent increase in free radical formation causes deterioration of the nitric oxide signaling cascade, alters and activates prostaglandin metabolism, and promotes novel oxidative posttranslational protein modifications that interfere with vascular and cell signaling pathways. As a result, vascular dysfunction manifests. Compensatory mechanisms are initially activated to cope with age-induced oxidative stress, but become futile, which results in irreversible oxidative modifications of biological macromolecules. These findings support the ‘free radical theory of aging’ but also show that reactive oxygen and nitrogen species are essential signaling molecules, regulating vascular homeostasis.

Megakaryocytes and platelets in vascular disease

Platelets are anucleate cells with no DNA. They are derived from their precursor, the megakaryocyte (MK), whose differentiation is characterized by nuclear polyploidization through a process called endomitosis. Changes in the MK-platelet-haemostasis axis may precede acute thrombotic events. Changes in MK ploidy distribution may be associated with the production of large platelets. Mean platelet volume (MPV) is an important biological variable as it is a determinant of platelet reactivity. Large platelets are denser and more active haemostatically. MPV is increased in patients after myocardial infarction (MI) and is a predictor of a further ischaemic event and death when measured after MI. It has been suggested that changes not only in platelets but also in the parental MK are associated with chronic and acute vascular events. The regulation of megakaryocytopoiesis depends on several haematopoietic factors such as thrombopoietin. An understanding of the signalling system that controls platelet number and size might give insight into a role of platelet production in thrombogenesis and atherogenesis.

Decreased plasma and tissue levels of vitamin C in a rat model of aging: implications for antioxidative defense.

Aging is an independent risk factor for the development of cardiovascular and many other diseases. The aging process is known to be associated with increased oxidative stress, possibly related to an age-inherent loss of antioxidant capacity. Vitamin C is a major naturally occurring antioxidant. Thus, we investigated its role in a rat model of aging. Vitamin C in plasma and tissues as well as malondialdehyde in the heart were measured in young (6 months old) and old (27-30 months old) F1 (F344 x BN) healthy male rats fed a normal diet. In old rats, vitamin C plasma levels were found to be decreased (p<0.02) as compared with young animals. Furthermore, there was a tissue-specific distribution: in the heart, liver, kidney, lungs, and skeletal muscle, vitamin C decreased with age (p<0.005 to p<0.05), while no significant differences could be observed in the aortic wall and in the brain. Organs of the digestive tract rather showed an increase of vitamin C levels with age. Oxidative stress, determined representatively in the heart by measuring malondialdehyde tissue levels, exhibited an age-dependent increase (p<0.05). A distinct pattern of specific tissue distribution of vitamin C suggests a differential age-associated regulation. As vitamin C decreased concomitantly to an increase in cardiac lipid peroxidation, its supplementation may be useful to prevent age-related oxidative stress and tissue aging.

Cardiovascular Aging Is Associated With Vitamin E Increase

Background—Aging is an independent risk factor for the development of cardiovascular disease. Therefore, therapies to delay vascular aging may have enormous medical consequences. In this context, vitamin E is of particular interest, mainly because of its antioxidative properties. Methods and Results—In 3-year-old rats, which are not susceptible to atherosclerosis, vitamin E levels, as measured by reversed-phase high-performance liquid chromatography, were markedly increased both in plasma and in major organs (P <0.01 to P <0.0001). The highest increase (at least 70-fold) was found in the aortic wall. Conclusions—This unexpected accumulation of vitamin E appears to be a compensatory mechanism that attempts to counterbalance age-associated oxidative stress and that may represent a self-regulatory protective adaptation.

High-dose atorvastatin in peripheral arterial disease (PAD): Effect on endothelial function, intima-media-thickness and local progression of PAD - An open randomized controlled pilot trial

Beneficial effects of aggressive lipid-lowering with high-dose atorvastatin (80 mg/day) have been demonstrated in patients with coronary and cerebrovascular disease. The impact of such a therapy in patients with peripheral arterial disease (PAD) is less known so far. Here we studied the effects of high-dose atorvastatin on brachial artery endothelial function, common carotid intima-media thickness (IMT) and local progression of PAD in these patients. One hundred of 500 patients screened with documented PAD were randomly assigned to receive 80 mg of atorvastatin daily for six months or to continue on conventional medical treatment. Ninety-six percent of patients in the control group were on standard statin treatment. High resolution B-mode ultrasonography was used to study brachial artery flow-mediated dilation (FMD), IMT and ankle-brachial index (ABI) at baseline and at six months. FMD and IMT at baseline and at six months were 4.1 (0.06-8.6) versus 5.0 (0.76 vs. 8.1) %, p = 0.96, and 0.76 (0.66-0.82) versus 0.73 (0.63-0.81) mm, p = 0.41, respectively, in the atorvastatin group, and 2.66 (-1.9-6.9) versus 3.65 (0.0-8.6)%, p = 0.02, and 0.78 (0.71-0.90) versus 0.77 (0.70-0.90) mm, p = 0.48, in the control group. ABI at baseline and at six months was not different in either group. LDL cholesterol was reduced from 2.53 (2.21-3.28) to 1.86 (1.38-2.29) mM (p < 0.0001) in the atorvastatin group, whereas levels remained stable in the control group [2.38 (1.94-3.16) vs. 2.33 (1.82-2.84) mM, p = 0.61]. Major adverse cardiovascular events occurred in 2.1% in the atorvastatin group and 1.9% in the control group (p = 0.61). In conclusion, in this pilot trial aggressive lipid-lowering with 80 mg of atorvastatin daily for six months had no effect on brachial artery FMD in patients with PAD. IMT and ABI were also similar in patients with and without high-dose atorvastatin at six months.

Isolated Cleft in the Posterior Mitral Valve Leaflet: A Congenital Form of Mitral Regurgitation

Isolated congenital cleft of the posterior leaflet of the mitral valve is a rare cause of mitral regurgitation (MR). This study describes the clinical, echocardiographic, and intraoperative findings as well as treatment options.

Signalling processes in endothelial ageing in relation to chronic oxidative stress and their potential therapeutic implications in humans.

Ageing is an important risk factor for the development of cardiovascular diseases. Vascular ageing is mainly characterized by endothelial dysfunction, an alteration of endothelium‐dependent signalling processes and vascular remodelling. The underlying mechanisms comprise increased production of reactive oxygen species (ROS), inactivation of nitric oxide (·NO) and subsequent formation of peroxynitrite (ONOO−). Elevated ONOO− may exhibit new messenger functions by post‐translational oxidative modification of intracellular regulatory proteins. Mitochondria are a major source of age‐associated superoxide formation, as electrons are misdirected from the respiratory chain. Manganese superoxide dismutase (MnSOD), a mitochondrial antioxidant enzyme, is an integral part of the nucleoids and may protect mitochondrial DNA from ROS. A model linking ·NO, mitochondria, MnSOD and its acetylation/deacetylation by sirtuins (NAD+‐dependent class III histone deacetylases) may be the basis for a potentially new powerful therapeutic intervention in the ageing process.

A New “Sunshine” in the Vasculature?

The discovery of vitamin D (calciol) was one of the great achievements in medicine and helped to eliminate rachitis in children and osteomalacia in adults. Vitamin D systemically acts on calcium homeostasis in parallel with parathyrin (parathyroid hormone [PTH]) and calcitonin to maintain serum calcium levels within the physiologically acceptable range. Vitamin D controls calcium and phosphate absorption in the intestine, calcium reabsorption in the kidney, and mineralization of bone. See p 1666 Synthesis of vitamin D requires UVB irradiation of the skin, which promotes the metabolism of its precursor, 7-dehydrocholesterol, to previtamin D3, which then slowly isomerizes to form vitamin D3. Because exposure to sunlight is necessary for its synthesis, vitamin D has also been called the “sunshine” vitamin. Vitamin D has also been identified in archaic phytoplankton and zooplankton, where it is synthesized after solar UV exposure. Its function in these organisms is poorly understood, but it probably serves as a photosensor. This would imply an evolutionarily conserved cellular signal transduction pathway, mediating autocrine, paracrine, and endocrine signals. Vitamin D3 is biologically inactive and must be hydroxylated, first in the liver to 25-hydroxyvitamin D3, and finally in the kidney by the 25-hydroxyvitamin D3-1α-hydroxylase (CYP24) enzyme system, to form the active metabolite 1α,25-dihydroxyvitamin D3 [1α,25-(OH)2D3; calcitriol].1 This also suggests that the term “vitamin” is possibly inappropriate, because its actions represent a classic steroidal hormone endocrine system. Vitamin D (for simplicity, the term “vitamin D” is used to indicate its active metabolite) regulates myocyte proliferation and induces hypertrophy.2 Vitamin D may also cause calcification of vascular smooth muscle cells (VSMCs)3 in a dose-dependent manner. Its influence on peripheral arteries has recently been reviewed,4 and its role can be considered at least partly …