Jan Galle

Upregulation of Superoxide Dismutase and Nitric Oxide Synthase Mediates the Apoptosis-Suppressive Effects of Shear Stress on Endothelial Cells

Physiological levels of laminar shear stress completely abrogate apoptosis of human endothelial cells in response to a variety of stimuli and might therefore importantly contribute to endothelial integrity. We show here that the apoptosis-suppressive effects of shear stress are mediated by upregulation of Cu/Zn SOD and NO synthase. Shear stress-mediated inhibition of endothelial cell apoptosis in response to exogenous oxygen radicals, oxidized LDL, and tumor necrosis factor-alpha was associated with complete inhibition of caspase-3-like activity, the central effector arm executing the apoptotic cell death program in endothelial cells. Shear stress-dependent upregulation of Cu/Zn SOD and NO synthase blocks activation of the caspase cascade in response to apoptosis-inducing stimuli. These findings establish the upregulation of Cu/Zn SOD and NO synthase by shear stress as a central protective cellular mechanism to preserve the integrity of the endothelium after proapoptotic stimulation.

Reactive Oxygen Intermediates Are Involved in the Induction of CD95 Ligand mRNA Expression by Cytostatic Drugs in Hepatoma Cells

Oxidative stress has been associated with the induction of programmed cell death. The CD95 ligand/receptor system is a specific mediator of apoptosis. We have used the model of drug-induced apoptosis to assess whether the CD95 ligand mRNA is induced by reactive oxygen intermediates. Treatment of HepG2 hepatoma cells with bleomycin induced the production of reactive oxygen intermediates and, as an additional parameter of oxidative stress, resulted in glutathione (GSH) depletion. In parallel, CD95 ligand mRNA expression was induced. In a similar fashion CD95 ligand mRNA expression increased after treatment with H2O2. Additional treatment with the antioxidant and GSH precursor N-acetylcysteine resulted in partial restoration of intracellular GSH levels and in reduced induction of CD95 ligand mRNA. Induction of CD95 ligand mRNA by bleomycin was further reduced by combined treatment withN-acetylcysteine and deferoxamine. These data suggest a direct role of oxygen radicals in the induction of the CD95 ligand.

Cyclosporin A Inhibits Apoptosis of Human Endothelial Cells by Preventing Release of Cytochrome C From Mitochondria

BACKGROUND Several experimental and clinical studies suggest that cyclosporin A (CSA) treatment reduces transplant atherosclerosis. Because oxidized LDL (oxLDL) is believed to play a key role in the development of atherogenesis, causing injury to the endothelium, and has been shown to induce apoptosis of endothelial cells, we investigated whether CSA inhibits oxLDL-induced apoptosis. METHODS AND RESULTS Apoptosis was induced in human umbilical venous endothelial cells (HUVECs) by incubation of 10 microg/mL oxLDL for 18 hours. Coincubation with CSA dose dependently decreased oxLDL-induced apoptosis, with a maximal effect at 10 micromol/L. In addition, tumor necrosis factor-alpha- and angiotensin II-induced apoptosis was significantly prevented by CSA treatment, suggesting a general apoptosis-suppressive effect of CSA. CSA has been shown to inhibit disruption of the mitochondrial membrane function, which plays a key role in apoptosis induction. Indeed, oxLDL treatment triggered the release of cytochrome C from the mitochondria into the cytosol, indicating disturbance of the mitochondrial membrane. CSA (10 micromol/L) completely inhibited the oxLDL-induced release of cytochrome C. Moreover, tumor necrosis factor-alpha- and angiotensin II-induced cytochrome C release was prevented by CSA treatment. CONCLUSIONS OxLDL induces dysfunction of the mitochondrial membrane, leading to cytochrome C release into the cytosol, and thereby stimulates apoptosis of human endothelial cells. Apoptosis suppression by CSA correlates with the prevention of mitochondrial dysfunction and thus indicates the importance of mitochondrial destabilization in oxLDL-induced apoptosis signaling. The inhibition of apoptosis by CSA might preserve the function of the endothelium and may at least in part contribute to the antiatherogenic effects of CSA in transplant atherosclerosis.

Effects of the soluble guanylyl cyclase activator, YC-1, on vascular tone, cyclic GMP levels and phosphodiesterase activity.

The vasomotor and cyclic GMP‐elevating activity of YC‐1, a novel NO‐independent activator of soluble guanylyl cyclase (sGC), was studied in isolated rabbit aortic rings and compared to that of the NO donor compounds sodium nitroprusside (SNP) and NOC 18. Similarly to SNP and NOC 18, YC‐1 (0.3–300 μM) caused a concentration‐dependent, endothelium‐independent relaxation that was greatly reduced by the sGC inhibitor 1‐H‐[1,2,4]oxadiazole[4,3‐a]quinoxalin‐1‐one (ODQ 10 μM; 59% inhibition of dilation induced by 100 μM YC‐1) suggesting the activation of sGC as one mechanism of action. Preincubation with YC‐1 (3 and 30 μM) significantly increased the maximal dilator responses mediated by endogenous NO in aortic rings that was released upon exposure to acetylcholine, and enhanced the dilator response to the exogenous NO‐donors, SNP and NOC 18, by almost two orders of magnitude. Vasoactivity induced by SNP and YC‐1 displayed different kinetics as evidenced by a long‐lasting inhibition by YC‐1 (300 μM) on the phenylephrine (PE)‐induced contractile response, which was not fully reversible even after extensive washout (150 min) of YC‐1, and was accompanied by a long‐lasting elevation of intracellular cyclic GMP content. In contrast, SNP (30 μM) had no effect on the vasoconstrictor potency of PE, and increases in intravascular cyclic GMP levels were readily reversed after washout of this NO donor compound. Surprisingly, YC‐1 not only activated sGC, but also affected cyclic GMP metabolism, as it inhibited both cyclic GMP break down in aortic extracts and the activity of phosphodiesterase isoforms 1–5 in vitro. In conclusion, YC‐1 caused persistent elevation of intravascular cyclic GMP levels in vivo by activating sGC and inhibiting cyclic GMP break down. Thus, YC‐1 is a highly effective vasodilator compound with a prolonged duration of action, and mechanisms that are unprecedented for any previously known sGC activator.

Impairment of Endothelium-Dependent Dilation in Rabbit Renal Arteries by Oxidized Lipoprotein(a) Role of Oxygen-Derived Radicals

BACKGROUND Hyperlipoproteinemia is associated with impairment of nitric oxide (NO)-mediated, endothelium-dependent dilation in renal arteries. In the present study, we assessed and compared the effects of human lipoprotein(a) and LDL on endothelium-dependent and -independent dilation in vitro. METHODS AND RESULTS Dilator responses were detected in isolated, saline-perfused, preconstricted arterial segments by a photoelectric device. Acetylcholine-induced, endothelium-dependent dilator responses of rabbit renal arteries were not significantly attenuated after 150 minutes of incubation with native lipoprotein(a) (30 and 100 micrograms/mL). However, exposure to in vitro oxidized lipoprotein(a) (150 minutes, 30 and 100 micrograms/mL) suppressed acetylcholine-induced dilator responses in a dose-dependent manner. At similar concentrations, native and oxidized LDL had no effect. Endothelium-independent dilations induced by the NO-donor sodium nitroprusside were also impaired by oxidized lipoprotein(a), whereas forskolin-induced dilator responses were unaffected, indicating that smooth muscle dilator capacity was not impaired. Attenuation of dilator responses by oxidized lipoprotein(a) was potentiated in the presence of superoxide dismutase (SOD). The SOD effect was completely blunted by coincubation with catalase (100 U/mL) or deferoxamine. In the absence of SOD, catalase or deferoxamine had no effect on dilator responses. Using a chemiluminescence assay, we could detect increased O2- production by arteries pretreated with oxidized lipoprotein(a), which suggested that enhanced NO inactivation by O2- could be the underlying mechanism for impairment of endothelium-dependent dilations. CONCLUSIONS These data indicate that oxidized lipoprotein(a) impairs endothelium-dependent dilation and is more potent than oxidized LDL in this effect. The mechanism of the impairment may involve formation of O2- and inactivation of NO.

Native C-Reactive Protein Increases Whereas Modified C-Reactive Protein Reduces Atherosclerosis in Apolipoprotein E–Knockout Mice

Background—C-reactive protein (CRP) may have proatherogenic but also vasoprotective properties. We tested the hypothesis that the configuration of CRP (pentameric, or native [nCRP], versus monomeric, or modified [mCRP]) determines these different characteristics in an in vivo model. Methods and Results—We investigated the effects of human nCRP and mCRP on the development of atherosclerosis in apolipoprotein E–knockout (ApoE−/−) mice. Treatment with nCRP for 8 weeks (2.5 mg/kg SC weekly) resulted in a 4-fold-higher mean aortic plaque area in 14-week-old female ApoE−/− mice compared with the saline controls. In contrast, mean plaque size was decreased by ≈50% in mCRP-treated ApoE−/− mice (2.5 mg/kg SC weekly). Using immunohistochemistry, we report the natural presence of the mCRP antigen in saline controls. mCRP antigen was expressed in smooth muscle cells and extracellularly in the vicinity of the plaques to a similar level in both CRP-treated groups and saline controls. mCRP and ApoB colocalized with macrophages and were equally upregulated in all aortic plaques. Vascular cell adhesion molecule expression was increased, and CD154 and intercellular adhesion molecule showed a trend for higher expression in nCRP-treated compared with mCRP-treated mice. CD154 expression in the vessel wall and plaque size correlated significantly. mCRP-treated ApoE−/− exhibited higher serum levels of the antiinflammatory interleukin-10 compared with the other 2 groups. Conclusions—Here, we show that mCRP and nCRP have opposite effects on atherosclerosis in ApoE−/− mice. These data may explain in part the conflicting activities previously reported for CRP in models of atherogenesis.

Identification of a new tumor suppressor gene located at chromosome 8p21.3-22

Transformation of normal cells into malignant tumor cells, a process termed carcinogenesis, depends on progressive acquisition of genetic alterations. These result in activation of protooncogenes or inactivation of tumor suppressor genes responsible for the loss of proliferative control in tumor cells and the failure to undergo cellular differentiation. The aim of our study was the identification of molecular regulators of carcinogenesis by studying gene expression during induction of cellular differentiation and quiescence in a three‐dimensional (3D) cell culture model. Here, we report the discovery of a tumor suppressor gene located at chromosome 8p21.3–22 near marker D8S254. It is ubiquitously expressed in normal tissue and transiently up‐regulated during initiation of cellular differentiation and quiescence in 3D cell culture. In contrast, mRNA expression was not detectable in tissue from pancreatic tumor and the pancreatic tumor cell line MIA PaCa‐2. Recombinant expression in the tumor cell line MIA PaCa‐2 inhibited proliferation, as shown by a 30% reduction of BrdU uptake after recombinant expression. Immunocytochemistry and Western blot analysis of subcellular fractions demonstrated a mitochondrial localization for the mature protein. In conclusion, we identified a tumor suppressor gene at chromosome 8p21.3–22, encoding a mitochondrial protein, controlling cellular proliferation.

Antiproteinuric effects of angiotensin receptor blockers: telmisartan versus valsartan in hypertensive patients with type 2 diabetes mellitus and overt nephropathy

BACKGROUND Renin-angiotensin system blockade reduces proteinuria and prevents nephropathy progression in patients with type 2 diabetes mellitus (T2D). Experimental evidence demonstrates that angiotensin receptor blockers (ARBs) possess anti-inflammatory potential, which might contribute to reducing proteinuria and providing renoprotection. METHODS We conducted a multicentre, double-blind, prospective, parallel-group non-inferiority study of 885 hypertensive [systolic blood pressure/diastolic blood pressure (SBP/DBP) >130/80 mmHg] patients with T2D, proteinuria (> or =900 mg/24 h) and serum creatinine (< or =3.0 mg/dl) who were randomized to once-daily telmisartan 80 mg or valsartan 160 mg; additional antihypertensive therapy was permitted. The primary endpoint was the change from baseline in the 24-h proteinuria after 12 months. Secondary endpoints included changes in 24-h albuminuria, estimated glomerular filtration rate (eGFR) and inflammatory parameters asymmetrical dimethylarginine (ADMA), high-sensitivity C-reactive protein (CRP) and urinary 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)). RESULTS Telmisartan and valsartan produced comparable reductions in 24-h urinary protein excretion rates: geometric mean reduction (95% confidence interval) [telmisartan, 33% (27-39%); valsartan, 33% (27-38%)]. No significant differences between treatments were seen in changes from baseline in 24-h urinary albumin excretion rate and eGFR at 12 months. With both treatments, greater renoprotection was seen among patients with better blood pressure control. No significant changes in ADMA or CRP were noted in either group after 12 months, but urinary 8-iso-PGF(2alpha) levels decreased by 14% with telmisartan and by 7% with valsartan (P = 0.040). CONCLUSIONS In patients with T2D, hypertension and overt nephropathy, the renoprotection afforded by telmisartan and valsartan appears similar, and the study was unable to show any effect beyond that due to blood pressure control. At doses used to treat hypertension, there is no evidence of inflammatory parameters being modified by ARBs in patients with more advanced kidney disease due to T2D.

Oxidized lipoproteins inhibit endothelium-dependent vasodilation. Effects of pressure and high-density lipoprotein.

Hypertension and atherogenic low-density lipoproteins cause attenuation of endothelium-dependent dilations in vivo. We investigated a potential interference of high transmural pressure with the effects of low-density lipoproteins on endothelium-dependent dilation in vitro. Furthermore, we determined whether high-density lipoproteins preserve endothelial function. Endothelium-intact rabbit renal arteries were isolated, placed in an organ bath, perfused intraluminally with Tyrodes solution, and exposed to different degrees of transmural pressure and native or oxidized low-density lipoproteins. In preconstricted arteries perfused under low-pressure conditions (30 mm Hg), acetylcholine dose dependently elicited endothelium-dependent dilations that were not altered by increasing the perfusion pressure to 100 mm Hg for 90 minutes (high-pressure conditions). Incubation of the arteries with native or oxidized low-density lipoproteins (0.2 and 1 mg/mL for 60 minutes, respectively) under low-pressure conditions did not attenuate acetylcholine-induced dilations. However, under high-pressure conditions dilations were dose dependently attenuated by oxidized but not by native low-density lipoproteins. Endothelium-independent dilations to glyceroltrinitrate (0.001 to 3 mumol/L) were not affected. Preincubation of the segments with high-density lipoproteins (0.5 mg/mL, 30 minutes) prevented attenuation of dilator responses. The attenuation of endothelium-dependent dilations by oxidized low-density lipoproteins under high-pressure conditions was accompanied by a transmural, dose-dependent infiltration of the vessel wall with lipoprotein, as detected by light microscopy of cryostat sections stained with Sudan III. This infiltration was prevented by high-density lipoprotein. Under low-pressure conditions no lipoprotein infiltration was visible. In segments incubated with native low-density lipoprotein, no lipoprotein infiltration was detectable.(ABSTRACT TRUNCATED AT 250 WORDS)

Glyc-oxidized LDL impair endothelial function more potently than oxidized LDL: role of enhanced oxidative stress.

Hypercholesterolemia is associated with impairment of endothelial function due to increased levels of LDL. In diabetic patients, however, attenuation of endothelial function occurs even under normocholesterolemic conditions. Here we assessed whether glycation of LDL potentiates their influence on endothelial function, with particular emphasis on the oxidizability of LDL and the role of O2-. Human LDL was glycated by dialyzation for 7 days against buffer containing 200 mmol/l glucose, or sham-treated without glucose, and oxidized by incubation with Cu2+. Glycation significantly enhanced the oxidizability of LDL, as detected by diene formation and by electrophoretic mobility (27.5 mm for oxidized LDL vs. 34 mm for oxidized glycated LDL at 20 h of oxidation). Isolated rings of rabbit aorta were superfused with physiological salt solution, and isometric tension was recorded. Incubation of the aortic rings with sham-treated or with glycated LDL, not oxidized, had no influence on acetylcholine-induced, endothelium-dependent relaxation. Exposure of the aortic rings to oxidized non-glycated LDL caused a significant inhibition (30% at 1 microM acetylcholine) of the endothelium-dependent relaxation only in the presence of diethyl-dithiocarbamate (DDC), an inhibitor of the endogenous superoxide dismutase (SOD). Incubation of aortic rings with oxidized glycated LDL attenuated endothelium-dependent relaxation even in the absence of DDC (by 31% at 1 microM acetylcholine). The presence of DDC potentiated the inhibition of relaxation (65% inhibition at 1 microM acetylcholine), and co-incubation with exogenous SOD and catalase prevented the inhibition of relaxation, indicating a mediator role of O2-. Endothelium-independent relaxation induced by forskolin was unaffected by any of the lipoproteins. Using a chemiluminescence assay, significantly increased O2- production of aortic rings pretreated with oxidized glycated LDL (4101 +/- 360 counts/s) in comparison to control rings (753 +/- 81 counts/s) or arteries pretreated with oxidized non-glycated LDL (2358 +/- 169 counts/s) could be detected, suggesting that enhanced NO-inactivation by O2- could be the underlying mechanism for the stronger impairment of endothelium-dependent dilations by oxidized glycated LDL. Glycation increases the oxidizability of LDL and potentiates its endothelium-damaging influence. The likely mechanism for attenuation of endothelium-dependent dilations is increased formation of O2-, resulting in inactivation of nitric oxide. This mechanism may play an important role in diabetic patients and may contribute to disturbed organ perfusion.