Induction of vascular endothelial growth factor-A165a in human retinal and endothelial cells in response to glyoxal

Low-density lipoprotein (LDL) apheresis is effective and safe for patients with diabetes, proteinuria, and dyslipidemia. Diabetes mellitus is accompanied by ocular microvascular complications like retinal neovascularization or diabetic macular edema. These are leading causes of blindness and can be mediated by abnormal vessel growth and increased vascular permeability due to elevated levels of vascular endothelial growth factor (VEGF) in diabetic patients. In this study, we established methods to study the expression of different VEGF isoforms in human retinal and endothelial cells. The VEGF-A_165a isoform is much higher expressed in retinal cells, compared to endothelial cells. Stimulation with glyoxal as a model of oxidative stress under diabetic conditions lead to a pronounced induction of VEGF-A_165a in human retinal and endothelial cells. These data suggest that diabetes and oxidative stress induce VEGF-A isoforms which could be relevant in regulating the ingrowths of novel blood vessels into the retina in diabetic patients.

ITN-VIROINF: Understanding (Harmful) Virus-Host Interactions by Linking Virology and Bioinformatics

Many recent studies highlight the fundamental importance of viruses. Besides their important role as human and animal pathogens, their beneficial, commensal or harmful functions are poorly understood. By developing and applying tailored bioinformatical tools in important virological models, the Marie Skłodowska-Curie Initiative International Training Network VIROINF will provide a better understanding of viruses and the interaction with their hosts. This will open the door to validate methods of improving viral growth, morphogenesis and development, as well as to control strategies against unwanted microorganisms. The key feature of VIROINF is its interdisciplinary nature, which brings together virologists and bioinformaticians to achieve common goals.

Implementing managed entry agreements in practice: The Dutch reality check

BACKGROUND

Conditional financing (CF) of expensive hospital drugs was applied in the Netherlands between 2006 and 2012; a 4-year coverage with evidence development (CED) framework for expensive hospital drugs. This study aims to evaluate the CF framework, focusing on Health Technology Assessment (HTA) procedures.

METHODS

Using a standardised data extraction form, researchers independently extracted information on procedural, methodological and decision-making aspects from HTA reports of drugs selected for CF.

RESULTS

Forty-nine drugs were chosen for CF, of which 12 underwent the full procedure. The procedure extended beyond the envisioned 4 years period for 11/12 drugs. Outcomes research studies conducted as part of CF provided insufficient scientific data to reach conclusions on appropriate use and cost-effectiveness of 5/12 drugs. After re-assessment, continuation of reimbursement was advised for 10/12 drugs, with 6 necessitating yet additional conditions for evidence generation. Notably, advice to discontinue reimbursement for 2/12 drugs has not yet been implemented in Dutch healthcare practice.

CONCLUSIONS

Theoretically, CF provided an option for quick but conditional access to drugs. However, numerous aspects related to the design and implementation of CF negatively affected its value in practice. Future CED schemes should aim to incorporate learnings from the CF example to increase their impact in healthcare practice.

Abstract 676: Hypoxia Upregulates NADPH Oxidase 4-Mediated Hydrogen Peroxide Release by a HIF-Independent Mechanism in Human Endothelial Cells

NADPH oxidases are important sources of reactive oxygen species in the vascular wall. Recent evidence supports a vasoprotective role of H 2 O 2 produced by the main endothelial isoform Nox4. The impact of hypoxia on NOX4 expression in human endothelial cells and the underlying mechanism remains to be elucidated. In this study, we show that NOX4 mRNA and protein expression was upregulated by hypoxia (1 % O 2 ) in human umbilical vein endothelial cells (HUVEC). Correspondingly, H 2 O 2 production was 2-fold elevated in HUVEC after hypoxia. In contrast to rotenone and oxypurinol, lentiviral downregulation via shNOX4 abolished the elevated hypoxic hydrogen peroxide levels to normoxic values. Hypoxia stabilized the hypoxia-inducible factor (HIF)-1α protein in endothelial cells. Furthermore, VEGF promoter activity and a control promoter containing 3 hypoxia-responsive elements (HRE) were induced by hypoxia. NOX4 promoter deletions up to -119/+239 had an increased basal activity compared to control vector. A full-length and a terminally deleted NOX4 promoter construct missing a putative HRE showed a comparable activity under hypoxic and normoxic conditions, suggesting that NOX4 is not induced on the transcriptional level by hypoxia in endothelial cells. In addition, stabilization of HIF-1α protein under normoxic conditions using DMOG did not change NOX4 mRNA expression in HUVEC. Furthermore, overexpression of HIF-1α did not alter NOX4 promoter activity. Blockade of active transcription by actinomycin D revealed an increased stability of the NOX4 mRNA under hypoxic conditions. In conclusion, this study demonstrates an HIF-independent upregulation of NOX4 as major source of endothelial hydrogen peroxide generation in response to hypoxia. Our data support as a novel mechanism an increased NOX4 mRNA stability under hypoxic conditions in human endothelial cells.

Increased gene expression of the cardiac endothelin system in obese mice

Obesity is a well-known risk factor of atherosclerosis and heart failure. In the human heart, a local endothelin system containing prepro-endothelin-1, endothelin-converting enzyme-1, and endothelin receptors A and B has been described. The endothelin system is activated in heart failure; however, the impact of obesity on the cardiac endothelin system is unknown. In this study, 18-week-old male C57BL/6 mice fed either a control diet or a high-fat diet for 10 weeks were analyzed. High-fat diet significantly increased the body weight of the animals and augmented low-density lipoprotein, high-density lipoprotein, and cholesterol plasma levels, compared to control. The animal groups showed no significant differences in left ventricular size or function (heart rate, ejection fraction, fractional shortening, left ventricular posterior wall thickness, cardiac output) after control or high-fat diet. We did not observe signs of cardiac hypertrophy or changes in markers of cardiac fibrosis in these heart samples. The cardiac expression of prepro-endothelin-1 mRNA, endothelin-converting enzyme-1 mRNA, and protein and endothelin receptors A and B mRNA was increased in 18-week-old obese C57BL/6 mice compared to animals with normal weight (p<0.05 vs. control). Furthermore, endothelin-1 plasma levels showed an increasing trend. In conclusion, an increased expression of genes of the endothelin system was observed in the hearts of 18-week-old mice after high-fat diet, possibly contributing to later cardiovascular complications of obesity.

Abstract 226: Neuronal Nitric Oxide Synthase Maintains Endothelial NO Release after Inhibition of NADPH Oxidase 4

The NADPH oxidase isoform NOX4 mainly produces H 2 O 2 . Previously we could show, that NOX4 is the major endothelial NOX isoform and constitutively active. Regulation of NOX4 and formation of reactive oxygen species is involved in NO release. The transcription factor NRF2 is a key mediator of cellular adaptation to redox stress. Therefore, regulation of NOX4 on the transcriptional level by NRF2 might be directly linked to NO release and endothelial function. Besides endothelial nitric oxide synthase (eNOS), a role of neuronal nitric oxide synthase (nNOS) in endothelial NO and H 2 O 2 release has been proposed. In this study, endothelial cells (HUVEC) were constantly exposed to high laminar shear stress (24 h, 30 dyn/cm°). Application of shear stress stimulated NO formation and induced elongation of endothelial cells in the direction of flow. Lentiviral overexpression of NOX4 strongly increased H 2 O 2 release, while downregulation using shNOX4 decreased H 2 O 2 release. Furthermore, application of shear stress caused downregulation of NOX4 as well as upregulation of eNOS and antioxidative response via NRF2 and its target genes NQO-1 and HMOX-1. H 2 O 2 can increase NO release by eNOS. We could show that downregulation of NOX4 leads to upregulation of eNOS mRNA and protein expression accompanied by attenuation of NRF2 pathway under flow conditions. Determination of NO release confirmed these results. This supports a compensatory mechanism maintaining a stable NO release after NOX4 inhibition in response to flow. Attenuation of NRF2 by shNRF2 inhibited shear stress-dependent induction of NRF2 and its target genes. In addition, shNRF2 enhanced the shear stress-dependent downregulation of NOX4. Finally, we detected a stable mRNA and protein expression of nNOS in endothelial cells, unaffected by flow. Interestingly, downregulation of NOX4 as well as of NRF2 resulted in strong induction of nNOS expression.

In conclusion, our data suggest an important role of H 2 O 2 production by NADPH oxidase 4 in maintaining NO release and endothelial function in response to flow. Inactivation of NADPH oxidase 4 attenuates NRF2 pathway and increases neuronal nitric oxide synthase as compensatory mechanisms.

From adaptive licensing to adaptive pathways: delivering a flexible life-span approach to bring new drugs to patients

The concept of adaptive licensing (AL) has met with considerable interest. Yet some remain skeptical about its feasibility. Others argue that the focus and name of AL should be broadened. Against this background of ongoing debate, we examine the environmental changes that will likely make adaptive pathways the preferred approach in the future. The key drivers include: growing patient demand for timely access to promising therapies, emerging science leading to fragmentation of treatment populations, rising payer influence on product accessibility, and pressure on pharma/investors to ensure sustainability of drug development. We also discuss a number of environmental changes that will enable an adaptive paradigm. A life‐span approach to bringing innovation to patients is expected to help address the perceived access vs. evidence trade‐off, help de‐risk drug development, and lead to better outcomes for patients.

Impact of Hey2 and COUP-TFII on genes involved in arteriovenous differentiation in primary human arterial and venous endothelial cells

Arteries and veins show marked differences in their anatomy, physiology and genetic expression pattern. In this study, we analyzed impact of overexpression or downregulation of arterial marker gene Hey2 and venous marker gene COUP-TFII in human venous and arterial endothelial cells on genes involved in arteriovenous differentiation. Lentiviral overexpression of venous marker gene COUP-TFII in arterial endothelial cells led to downregulation of NICD4, arterial marker gene Hey2 and EphrinB2. Downregulation of Hey2 could be mediated by direct binding of COUP-TFII to Hey2 promoter as shown by ChIP, EMSA and promoter analysis. Downregulation of Hey2 by shRNA causes downregulation of EphrinB2 expression. Overexpression of arterial marker Hey2 in venous endothelial cells did not change expression pattern of COUP-TFII. Downregulation of venous marker gene COUP-TFII in venous endothelial cells resulted in upregulation of VEGF-A, Dll4 and EphrinB2 expression. Our data support an important role of Hey2 and COUP-TFII in arteriovenous differentiation of human endothelial cells.

Abstract 395: Lipoprotein Apheresis of Hypercholesterolemic Patients Mediates Vasoprotective Gene Expression in Human Endothelial Cells

OBJECTIVE

Hypercholesterolemia is an important risk factor of cardiovascular diseases. Lipoprotein apheresis is an efficient strategy to reduce the serum low-density lipoprotein (LDL)-cholesterol and lipoprotein(a) levels and cardiovascular complications in patients with severe hypercholesterolemia. The underlying molecular mechanisms are not well-understood. In this study, we analyzed the impact of lipoprotein apheresis on gene expression in human endothelial cells.

METHODS

Human endothelial cells were stimulated with serum of hypercholesterolemic patients before and after lipoprotein apheresis. The expression of endothelial lipoprotein receptors, nitric oxide (NO) synthase and adhesion molecules was quantified by real-time PCR and Western blot.

RESULTS

Lipoprotein apheresis reduced the expression of the lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) in endothelial cells. Low-density lipoprotein (LDL) receptor expression remained unchanged. The mRNA expression of the endothelial nitric oxide synthase (eNOS) was increased with serum of hypercholesterolemic patients after lipoprotein apheresis. In contrast, endothelial expression of vascular cell adhesion molecule 1 (VCAM-1) was reduced in response to serum after lipoprotein apheresis.

CONCLUSION

Lipoprotein apheresis reduced the expression of the proatherosclerotic oxLDL receptor LOX-1 and adhesion molecule VCAM-1 and increased the expression of vasoprotective and NO generating eNOS in human endothelial cells in response to serum of hypercholesterolemic patients. These novel molecular mechanisms may account for the antiatherosclerotic and vasoprotective potential of lipoprotein apheresis in patients with hypercholesterolemia.

Abstract 480: Activation of NRF2/ARE Pathway Regulates Hydrogen Peroxide Releasing NADPH Oxidase NOX4 in Endothelial Cells

The NADPH oxidase isoform NOX4 produces mainly hydrogen peroxide (H 2 O 2 ). The transcription factor NRF2 is a key mediator of cellular adaptation to redox stress. Regulation of NOX4 and formation of H 2 O 2 might be directly linked to NO release. NOX4 is the major endothelial NOX isoform and considered to be constitutively active. Regulation of NOX4 on transcriptional level by NRF2 might be directly linked to NO release and endothelial function.

Endothelial cells (HUVEC) were constantly exposed to high laminar shear stress (24h, 30dyn/cm 2 ). This stimulates NO formation and leads to elongation of the cells in the direction of the flow. Previously, we could show that NOX4 is the major endothelial NOX isoform and downregulated by shear stress. Here we show that shear stress induces antioxidative response via upregulation of NRF2 which affects NOX4 expression. We transduced HUVEC with lentiviral particles containing short hairpin RNA (sh) against NRF2 and NOX4. Lentiviral downregulation of NOX4 using shNOX4 inhibited the shear stress-dependent elongation of cell shape in response to flow. Application of shear stress caused downregulation of NOX4 and upregulation of NRF2 and its target genes NQO-1 and HO-1. Attenuation of NRF2 by shNRF2 inhibited shear stress-dependent induction of NRF2 and its target genes. In addition, shNRF2 enhanced the shear stress-dependent downregulation of NOX4. Finally, we could show that downregulation of NOX4 is involved in the upregulation of eNOS and expression of NRF2 in response to flow. Nox4 overexpression had no effect on these processes. In conclusion, our data suggest a link between NOX4, NRF2-mediated antioxidative response and endothelial function.

Arterial flow reduces oxidative stress via an antioxidant response element and Oct-1 binding site within the NADPH oxidase 4 promoter in endothelial cells

The main sources of oxidative stress in the vessel wall are nicotine adenine dinucleotide phosphate (NADPH) oxidase (Nox) complexes. The endothelium mainly expresses the Nox4-containing complex; however, the mechanism by which shear stress in endothelial cells regulates Nox4 is not well understood. This study demonstrates that long-term application of arterial laminar shear stress using a cone-and-plate viscometer reduces endothelial superoxide anion formation and Nox4 expression. In primary human endothelial cells, we identified a 47 bp 5'-untranslated region of Nox4 mRNA by 5'-rapid amplification of cDNA ends (5'-RACE) PCR. Cloning and functional analysis of human Nox4 promoter revealed a range between -1,490 and -1,310 bp responsible for flow-dependent downregulation. Mutation of an overlapping antioxidative response element (ARE)-like and Oct-1 binding site at -1,376 bp eliminated shear stress-dependent Nox4 downregulation. Consistent with these observations, electrophoretic mobility shift assays (EMSA) demonstrated an enhanced shear stress-dependent binding of Nox4 oligonucleotide containing the ARE-like/Oct-1 binding site, which could be inhibited by specific antibodies against the transcription factors nuclear factor erythroid 2-related factor 2 (Nrf2) and octamer transcription factor 1 (Oct-1). Furthermore, shear stress caused the translocation of Nrf2 and Oct-1 from the cytoplasm to the nucleus. Knockdown of Nrf2 by short hairpin RNA (shRNA) increased Nox4 expression twofold, indicating a direct cross-talk between Nrf2 and Nox4. In conclusion, an ARE-like/Oct-1 binding site was noticed to be essential for shear stress-dependent downregulation of Nox4. This novel mechanism may be involved in the flow-dependent downregulation of endothelial superoxide anion formation.

Endothelial cells (EC) and endothelial precursor cells (EPC) kinetics in hematological patients undergoing chemotherapy or autologous stem cell transplantation (ASCT)

Our objective was to study the kinetics of circulating endothelial cells (EC) and endothelial precursor cells (EPC) in hematological patients during chemotherapy and autologous stem cell transplantion (ASCT). Eighteen newly diagnosed patients and 17 patients undergoing ASCT were studied and compared to healthy controls. ECs were evaluated as CD146+CD31+Lin- cells, while EPCs were evaluated as CD34+CD133+Lin-, or CD34+VEGFR2+Lin- cells, or CFU-En colony forming units. Numbers of these cells were evaluated before and after treatment, and, in patients treated with ASCT, during mobilization of hematopoietic progenitors. Both newly diagnosed patients and patients before ASCT had significantly higher number of CD146+CD31+Lin- cells and significantly lower number of CFU-En colonies than healthy controls. These parameters did not return to normal for at least 3 months after chemotherapy or ASCT. Numbers of CFU-En did not correlate either with numbers of CD34+CD133+Lin- cells or with numbers of CD34+VEGFR2+Lin- cells but they did correlate with numbers of CD4+ lymphocytes and NK cells. In conclusion, we have found that hematological patients have higher number of EC and lower numbers of CFU-En than healthy controls and that these parameters do not return to normal after short-term follow-up. Furthermore, our observations support emerging data that CFU-En represent cell population different from flowcytometrically defined EC and endothelial precursors and that their development requires cooperation of monocytes and CD4+ lymphocytes. However, cells forming CFU-En express endothelial surface markers and can contribute to proper endothelial function by NO production.

COUP-TFII is regulated by high glucose in endothelial cells

Diabetes mellitus is an important risk factor for cardiovascular diseases. Clinical evidence supports a link between hyperglycemia, endothelial dysfunction, and vascular disorders. However, the precise molecular mechanisms causing endothelial dysfunction in diabetic patients remain unclear. An interesting novel mediator could be chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII), which plays an essential role in glucose metabolism. COUP-TFII is known to be expressed in venous endothelial cells. In this study, we show COUP-TFII expression in human umbilical vein endothelial cells (HUVECs) and human coronary artery endothelial cells. HUVECs express glucose transporters 1, 3, 6, and 10, and the insulin receptor. Insulin in combination with glucose activates protein kinase B (PKB or Akt) phosphorylation via phosphoinositide 3-kinase (PI3-kinase). Short-term (60-240 min) stimulation of HUVECs with high glucose increased COUP-TFII expression independent of insulin. Long-term (48 h) stimulation of HUVECs with high glucose augmented expression of the insulin receptor and E-selectin, but downregulated COUP-TFII protein expression. Downregulation of COUP-TFII by shRNA leads to downregulation of E-selectin and upregulation of eNOS and glucose transporters. Our data suggest that COUP-TFII is regulated by glucose in a time- and dose-dependent manner in endothelial cells. COUP-TFII might affect endothelial function in a diabetic background.

Long-term cyclic strain downregulates endothelial Nox4

Endothelial cells in vivo are constantly exposed to mechanical forces such as cyclic strain. In endothelial cells, Nox4-containing NAD(P)H oxidase complexes have been identified as major sources of superoxide anion (.O(2)(-)) formation. In this study, we analyzed the effect of cyclic strain on endothelial ROS formation by electron paramagnetic resonance spectroscopy, cytochrome c assay, and dihydroethidium fluorescence, on NO formation by Griess reaction and on gene expression by RT-PCR and Western blot. Primary cultures of human umbilical vein endothelial cells were exposed to 2-18% cyclic strain for up to 24 h using the Flexercell system. Long-term application of 5-12% cyclic strain downregulated Nox4 expression and ROS formation in a time-dependent manner. Downregulation of Nox4 was further confirmed by promoter analysis using dual-luciferase assay. Cu/Zn SOD, MnSOD, and catalase expression was decreased after application of chronic 12% cyclic strain. In contrast, endothelial NO formation and eNOS were increased by cyclic strain. Strain-dependent Nox4 downregulation was abolished by eNOS inhibition with L-NAME. In conclusion, physiological levels of cyclic strain downregulate Nox4 expression and superoxide anion formation. This novel mechanism might contribute to a vasoprotective balance between NO and superoxide anions in response to physiological mechanical stimulation of endothelial cells.

Down-Regulation of Endothelial EphrinB2 Expression by Laminar Shear Stress

The EphB receptors and their ephrinB ligands are involved in vascular assembly and differentiation. In this study, the authors analyzed the regulation of ephrinB2 and EphB4 in response to laminar shear stress in human endothelial cells. In order to simulate different flow conditions in vitro, human endothelial cells were exposed to laminar shear stress (1 to 50 dyn/cm2 for up to 24 h) in a cone-and-plate viscometer. EphrinB2 mRNA expression is down-regulated by arterial, but not by venous, laminar shear stress in a dose-dependent manner in primary cultures of human umbilical vein endothelial cells (HUVECs) (maximum at 30 dyn/cm2, 24 h: 46% +/- 4%of internal control without shear stress, n = 16, p < .05). The down-regulation of ephrinB2 by arterial shear stress is blocked by the protein kinase C inhibitor RO-31-8220. A similar shear stress-dependent down-regulation of ephrin-B2 can be found in human coronary artery endothelial cells (HCAECs). Chronic application of laminar shear stress does not affect EphB4 expression in venous and arterial endothelial cells. The down-regulation of ephrinB2 in response to laminar shear stress may contribute to the differentiation of endothelial cells into a nonactivated phenotype.

Expression of human endothelin-converting enzyme isoforms: role of angiotensin II

A key step in endothelin-1 (ET-1) synthesis is the proteolytic cleavage of big ET-1 by the endothelin-converting enzyme-1 (ECE-1). Four alternatively spliced isoforms, ECE-1a to ECE-1d, have been discovered; however, regulation of the expression of specific ECE-1 isoforms is not well understood. Therefore, we stimulated primary human umbilical vein endothelial cells (HUVECs) with angiotensin II (Ang II). Furthermore, expression of ECE-1 isoforms was determined in internal mammary arteries of patients undergoing coronary artery bypass grafting surgery. Patients had received one of 4 therapies: angiotensin-converting enzyme inhibitors (ACE-I), Ang II type 1 receptor blockers (ARB), HMG-CoA reductase inhibitors (statins), and a control group that had received neither ACE-I, ARB (that is, treatment not interfering in the renin-angiotensin system), nor statins. Under control conditions, ECE-1a is the dominant isoform in HUVECs (4.5+/-2.8 amol/microg RNA), followed by ECE-1c (2.7+/-1.0 amol/microg), ECE-1d (0.49+/-0.17 amol/microg), and ECE-1b (0.17+/-0.04 amol/microg). Stimulation with Ang II did not change the ECE-1 expression pattern or the ET-1 release. We found that ECE-1 mRNA expression was higher in patients treated with statins than in patients treated with ARB therapy (5.8+/-0.76 RU versus 3.0+/-0.4 RU), mainly attributed to ECE-1a. In addition, ECE-1a mRNA expression was higher in patients receiving ACE-I therapy than in patients receiving ARB therapy (1.68+/-0.27 RU versus 0.83+/-0.07 RU). We conclude that ECE-1a is the major ECE-1 isoform in primary human endothelial cells. Its expression in internal mammary arteries can be regulated by statin therapy and differs between patients with ACE-I and ARB therapy.

Endothelin receptor B-mediated induction of c-jun and AP-1 in response to shear stress in human endothelial cellsThis article is one of a selection of papers published in the special issue (part 2 of 2) on Forefronts in Endothelin

In vivo, endothelial cells are constantly exposed to shear stress by flowing blood. Short-term exposure of endothelial cells to shear stress has been shown to induce endothelin-1 release. It is currently unknown, however, whether this shear stress-dependent endothelin-1 release affects the expression and activity of transcription factors. In this study, primary cultures of human endothelial cells from the umbilical vein were exposed to laminar shear stress in a cone-and-plate viscometer. Laminar shear stress for 30 min induced a 2-fold increase in mRNA expression of c-jun , but not c-fos, in human endothelial cells. Blockade of endothelin receptor subtype B (ETB) with BQ788 prevented this shear stress-dependent induction of c-jun expression. The induction of c-jun by shear stress involved protein kinase C and endothelial NO synthase. In addition, exposure of endothelial cells to arterial laminar shear stress for 1 h increased the binding of transcription factor AP-1 to its consensus sequence by 1.7-fold in electrophoretic mobility shift assays. This induction was also mediated by an ETB-dependent pathway. Supershift analysis supports an AP-1 complex containing c-jun, but not c-fos, in human endothelial cells. In conclusion, our data suggest endothelin-1-mediated induction of c-jun expression and activation of AP-1 (possibly as a c-jun homodimer) by laminar shear stress in human endothelial cells.

Flow-dependent regulation of angiopoietin-2

Endothelial cells are constantly exposed to high or low shear stress in arteries and veins by the flowing blood. Angiopoietin-2 (Ang-2) is acting as a critical regulator of vessel maturation and endothelial cell quiescence. In this study, flow-dependent regulation of Ang-2 was analyzed in vitro and in vivo. Ang-2 mRNA, protein expression and release was upregulated by 24 h of low (1 dyne/cm(2)), but downregulated by high flow (30 dyne/cm(2)) in human endothelial cells. Increased endothelial NO synthase expression and NO formation was not affecting regulation of Ang-2 by low or high flow. Low and high flow increased VEGF-A expression. Inhibition of VEGFR-2 prevented upregulation of Ang-2 by low flow, but not downregulation of Ang-2 by high flow. Furthermore, upregulation of Ang-2 by VEGF was reduced by application of high flow. Forkhead box O (FOXO) transcription factor FOXO1 has been shown to regulate Ang-2 expression in endothelial cells. FOXO1 binding activity was reduced by high flow. Nuclear localization of transcription factor FOXO1 was not changed by low flow, but reduced by high flow. In vivo, Ang-2 was higher expressed in veins compared to arteries. Arterial ligation augmented Ang-2 expression in distal arterial low flow areas. Our results support a VEGF-dependent induction of Ang-2 in low flow areas, and FOXO1-dependent downregulation of Ang-2 in high flow areas. These data suggest a new mechanism of flow-dependent regulation of vessel stability and differentiation.

Endothelial Protection, AT1 Blockade and Cholesterol-Dependent Oxidative Stress: The EPAS Trial

BACKGROUND

Statins and angiotensin type 1 (AT1) receptor blockers reduce cardiovascular mortality and morbidity. In the Endothelial Protection, AT1 blockade and Cholesterol-Dependent Oxidative Stress (EPAS) trial, impact of independent or combined statin and AT1 receptor blocker therapy on endothelial expression of anti-atherosclerotic and proatherosclerotic genes and endothelial function in arteries of patients with coronary artery disease were tested.

METHODS AND RESULTS

Sixty patients with stable coronary artery disease undergoing elective coronary artery bypass grafting (CABG) surgery were randomized 4 weeks before surgery to: (A) control without inhibition of renin-angiotensin system or statin; (B) statin (pravastatin 40 mg/d); (C) AT1 blockade (irbesartan 150 mg/d); or (D) combination of statin and AT1 blocker in same dosages. Primary end point was a priori therapy-dependent regulation of an anti-atherosclerotic endothelial expression quotient Q including mRNA expression (in arbitrary units measured by real-time polymerase chain reaction) of endothelial nitric oxide synthase and C-type natriuretic peptide, divided by expression of oxidized low-density lipoprotein receptor LOX-1 and NAD(P)H oxidase subunit gp91phox in left internal mammary arteries biopsies obtained by CABG surgery; 49 patients completed the study. Statin therapy increased lnQ from 3.2+/-0.4 to 4.4+/-0.4 significantly versus control. AT(1) blockade showed a trend to increase lnQ to 4.2+/-0.5. Combination of statin and AT1 blocker further increased lnQ to 5.1+/-0.6, but a putative interaction of both therapies in lnQ was not significant. Furthermore, preoperative therapy with statin, AT1 blocker and their combination improved endothelial function in internal mammary artery rings.

CONCLUSIONS

Statin and AT1 blocker therapy independently and in combination improve an anti-atherosclerotic endothelial expression quotient and endothelial function.

Endothelial EphrinB2 Is Controlled by Microenvironmental Determinants and Associates Context-Dependently With CD31

Objective— The EphB ligand ephrinB2 has been identified as a critical determinant of arterial endothelial differentiation and as a positive regulator of invading endothelial cells during angiogenesis. This study was aimed at identifying determinants of endothelial cell ephrinB2 expression.

Methods and Results— Arteriovenous asymmetrical endothelial cell ephrinB2 expression in vivo is lost on transfer into culture with aortic endothelial cells becoming partially ephrinB2-negative and saphenous vein endothelial cells becoming partially ephrinB2-positive. Contact with smooth muscle cells and angiogenic stimulation by vascular endothelial growth factor lead to an increased endothelial cell ephrinB2 expression. Quiescent, smooth muscle-contacting endothelial cells express ephrinB2 uniformly on their luminal surface. In contrast, monolayer endothelial cells translocate ephrinB2 to interendothelial cell junctions, which is strongly enhanced by EphB4-Fc-mediated receptor body activation. Junctional ephrinB2 colocalizes and coimmunoprecipitates with CD31.

Conclusions— This study identifies distinct regulatory mechanisms of endothelial ephrinB2 expression and cellular distribution in quiescent and activated endothelial cells. The data demonstrate that endothelial cell ephrinB2 expression is controlled by microenvironmental determinants rather than being an intrinsic endothelial cell differentiation marker.

Erythropoietin-induced excessive erythrocytosis activates the tissue endothelin system in mice

The endothelium controls blood flow and pressure by releasing several vasoactive factors, among them the vasodilator nitric oxide (NO) and the potent vasoconstrictor endothelin-1 (ET-1). Although increased NO levels have been found in excessive erythrocytosis, little is known concerning ET-1 expression in this condition. Thus, we examined the endothelin system in transgenic mice that due to constitutive overexpression of erythropoietin (Epo) reached hematocrit levels of approximately 80%. Surprisingly, despite generalized vasodilatation, polycythemic mice exhibited a two- to fivefold elevation in ET-1 mRNA levels in aorta, liver, heart, and kidney. In line with this, increased expression of ET-1 protein was detected in the pulmonary artery by immunohistochemical analysis. Compared with their wild-type littermates, aortic rings of Epo transgenic animals exhibited a marked reduction in vascular reactivity to ET-1 and big ET-1, but this effect was abrogated upon preincubation with the NO synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME). Pretreatment of polycythemic mice with the ET(A) receptor antagonist darusentan for 3 wk significantly prolonged their survival upon acute exposure to L-NAME. Taken together, these results demonstrate for the first time that excessive erythrocytosis induces a marked activation of the tissue endothelin system that results in increased mortality upon blockade of NO-mediated vasodilatation. Because ETA antagonism prolonged survival after acute blockade of NO synthesis, endothelin may be regarded as a contributor to the adverse cardiovascular effects of erythrocytosis and may thus represent a new target in the treatment of cardiovascular disease associated with erythrocytosis.

Obesity increases prostanoid-mediated vasoconstriction and vascular thromboxane receptor gene expression

OBJECTIVES

Vasoconstrictor prostanoids have been implicated in abnormal vasomotion in atherosclerosis and hypertension.

METHOD

Using lean and diet-induced obese mice, we investigated whether obesity affects vascular function or expression of genes involved in prostanoid action.

RESULTS

In lean C57BL/6J mice, at high concentrations acetylcholine caused endothelium-dependent contractions in the carotid artery but not in the aorta. Endothelium-dependent contractions to acetylcholine were blocked by the non-selective cyclooxygenase (COX) inhibitors indomethacin and meclofenamate, or a prostaglandin H2/thromboxane A2 receptor antagonist, but not by inhibitors of COX-2, thromboxane synthase or cytochrome P450 monooxygenase. Obesity increased endothelium-dependent contractions to acetylcholine in the carotid artery, and prostanoid-mediated vasoconstriction was now present in the aorta. Similarly, contractions to endothelin-1 were largely blocked by meclofenamate and were increased in the aorta of obese mice. Real-time quantitative polymerase chain reaction analysis of the thromboxane receptor gene in the carotid artery revealed a robust upregulation in obese animals (18-fold, 0.05); in comparison, obesity had a less pronounced effect on thromboxane synthase (2.1-fold increase, 0.05), or preproendothelin-1 gene expression (4.2-fold increase, 0.05).

CONCLUSIONS

These data demonstrate that obesity augments prostanoid-dependent vasoconstriction and markedly increases vascular thromboxane receptor gene expression. These changes are likely to promote the development of vascular disease, hypertension and thrombosis associated with obesity.

Angiotensin-converting enzyme inhibitor therapy prevents upregulation of endothelin-converting enzyme-1 in failing human myocardium

In this study, we investigated the role of the renin-angiotensin system in expression of the endothelin system in atrial myocardium of patients with congestive heart failure. Atrial myocardium of control patients without angiotensin-converting enzyme (ACE) inhibitor therapy and heart failure patients without or with ACE inhibitor therapy undergoing aorto-coronary bypass surgery was studied. Endothelin-converting enzyme-1 (ECE-1) expression and endothelin-1 peptide level was upregulated in myocardium of heart failure patients without ACE inhibition. ACE inhibitor therapy prevented upregulation of ECE-1 and endothelin-1 in failing myocardium. Prepro-endothelin-1 and endothelin receptor A expression were not affected by heart failure. Endothelin receptor B was downregulated in heart failure patients. Our data demonstrate an upregulation of ECE-1 mRNA expression in failing human myocardium. Inhibition of the renin-angiotensin system by ACE inhibitor treatment prevents upregulation of ECE-1, suggesting that angiotensin II regulates ECE-1 expression in vivo.

Increased expression of endothelin-converting enzyme-1 in failing human myocardium

Endothelin-1 (ET-1) is considered to be involved in the development and progression of heart failure. Therefore, we analysed the expression of endothelin-converting enzyme-1 (ECE-1), endothelin receptors A (ET(A)) and B (ET(B)) mRNAs by standard-calibrated, competitive reverse transcriptase-PCR using an internal-deleted in vitro-transcribed cRNA standard. ET-1 peptide levels were measured using isoform-specific rabbit antibodies against synthetic ET-1. mRNA and protein expression was determined in the right atrial myocardium of New York Heart Association class I patients and class IV patients undergoing aorto-coronary bypass surgery. ECE-1 mRNA was upregulated in failing atrial myocardium. Furthermore, ET-1 peptide levels were increased in failing atrial myocardium. Atrial ET(A) mRNA expression was not changed, while ET(B) mRNA was downregulated in the failing atrial myocardium. Our results support an upregulation of ET-1 synthesis by induction of ECE-1 in failing atrial myocardium. Pharmacological inhibition of augmented ECE-1 expression might provide a new therapeutic perspective in the treatment of heart failure.

Shear stress mediates tyrosylprotein sulfotransferase isoform shift in human endothelial cells

In this study, we examined expression of tyrosylprotein sulfotransferase (TPST) isoforms TPST1 and TPST2 in primary cultures of human umbilical vein endothelial cells. For the first time coexpression of both isoforms is shown in primary human cells. Application of physiological levels of shear stress regulates expression of TPST isoforms in a time- and dose-dependent manner. Sustained application of arterial laminar shear stress causes downregulation of TPST1 mRNA and protein expression, while TPST2 is upregulated. This TPST isoform shift is mediated by different signaling pathways. Shear stress-dependent downregulation of TPST1 involves tyrosine kinase, while upregulation of TPST2 is mediated by a protein kinase C-dependent pathway [corrected].

Skin infections in renal transplant recipients

BACKGROUND

Skin infection is a frequent complication in renal transplant recipients. The purpose of the study was to acquire long-term, period-specific incidence data on the most commonly occurring skin infections in renal transplant recipients.

METHODS

A retrospective analysis was performed using medical records of 134 patients, covering a period between 10 and 29 yr. Cumulative incidences of the skin infections were calculated by counting the infections per patient for different time periods and were expressed as a percentage of the total group of patients. The incidence of the skin infections was determined for different post-transplant time periods.

RESULTS

A total of 340 skin infections in 105 out of 134 patients were recorded. Some infections, such as candidal infection, herpes simplex infection, and impetigo were most prominent during the first post-transplant year and did not affect many new patients after the first year. Other infections, such as dermatomycoses, herpes zoster, and folliculitis were also affecting a substantial number of new patients after the first post-transplant year.

CONCLUSIONS

This study confirms that skin infections among renal transplant recipients are very common and that the spectrum of skin infections differs according to the post-transplant time period.

Increased expression of endothelin-1 and inducible nitric oxide synthase isoform II in aging arteries in vivo: implications for atherosclerosis

We here report that aging increases expression of endothelin-1 and NO synthases in the vasculature and kidney of normotensive rats in vivo. Expression of preproendothelin-1 mRNA was quantified by RT-PCR and in situ hybridization, and endothelin-1 protein was determined by radioimmunoassay/HPLC. Vascular mRNA expression of NO synthase isoforms II and III was analyzed by RT-PCR. In young animals, vascular endothelin-1 protein was differentially expressed (aorta < renal artery < carotid artery) and increased with aging in all vascular beds (P < 0.05). In the intact aorta of aged rats, mRNA expression of preproendothelin-1, "inducible" NO synthase II, and endothelial cell NO synthase III gene was up-regulated (P < 0.05). Moreover, preproendothelin-1 mRNA expression increased in glomeruli and tubulointerstitial cells (P < 0.05). To our knowledge this is the first study demonstrating local vascular up-regulation of the trophic factor endothelin under physiological conditions. Activation of vascular endothelin and NO synthases may be important, pressure-independent factors contributing to structural and functional abnormalities of age-dependent diseases, including atherosclerosis.

Deloading of the left ventricle by ventricular assist device normalizes increased expression of endothelin ET(A) receptors but not endothelin-converting enzyme-1 in patients with end-stage heart failure

BACKGROUND

Ventricular assist devices (VAD) are implanted in patients with end-stage heart failure for bridging the time until heart transplantation, resulting in hemodynamic unloading of the failing heart, improved cardiac contractile and mitochondrial function, and reversal of cardiac hypertrophy. It is unknown whether VAD unloading may affect the cardiac endothelin (ET) system, which has been proposed as one of the putative pathomechanisms of heart failure.

METHODS AND RESULTS

With the use of standard-calibrated, competitive reverse-transcription-polymerase chain reaction mRNA expression of components of the ET system was analyzed in left ventricular myocardium from nonfailing donor hearts, from failing hearts without and with ACE inhibitor therapy, and from patients with end-stage heart failure at the time of VAD implantation and 103+/-15 days after VAD implantation during removal with subsequent heart transplantation. ET receptor A (ET(A)) was markedly upregulated in failing human myocardium. This increased ET(A) expression was not affected by ACE inhibitor treatment but was normalized by VAD unloading. ET(A) expression before or after VAD implantation did not correlate with duration of VAD implantation or suppression of Pro-ANP mRNA. ET(B) mRNA expression was unaffected by heart failure or VAD. In contrast, increased ET-converting enzyme-1 mRNA and ET-1 peptide levels in failing myocardium were partially normalized by ACE inhibition but not by VAD unloading.

CONCLUSIONS

We conclude that VAD implantation normalizes ET(A) expression in failing human left ventricular myocardium, probably as the result of the beneficial effects of VAD unloading.

Increasing resistance to fluoroquinolones in escherichia coli from urinary tract infections in the netherlands

In continuous surveillance of routine samples from five Dutch laboratories, we studied resistance to the antibiotics most commonly prescribed for urinary tract infections (UTI) in The Netherlands, namely norfloxacin, amoxycillin, trimethoprim and nitrofurantoin, from 1989 to 1998 in >90000 Escherichia coli isolates. Resistance to norfloxacin increased from 1.3% in 1989 to 5.8% in 1998. Multiresistance, defined as resistance to norfloxacin and at least two of the other three antibiotics, increased from 0.5% in 1989 to 4. 0% in 1998. Multivariate analysis of the norfloxacin resistance demonstrated that this yearly increase (the odds ratio was 1.0 in 1989, 1.6 in 1992, 2.9 in 1995 and 6.1 in 1998) was independent of other determinants of resistance to norfloxacin, such as age, gender and origin of the isolate. Analysis of strata, classified by year, age and gender, demonstrated an association between prescription of fluoroquinolones (defined daily doses per case of UTI) and resistance to norfloxacin in E. coli (P < 0.001). There was no significant association with the prescription of nitrofuran derivatives (nitrofurantoin) and trimethoprim with or without sulphamethoxazole. The yearly increase of resistance to fluoroquinolones in E. coli from UTI may stem from increased prescription of fluoroquinolones for UTI. Resistance of E. coli to these agents is likely to increase further as fluoroquinolone use increases in future.

Endothelin-1 induces NAD(P)H oxidase in human endothelial cells

Superoxide anions (O(*-)(2)) induce oxidative stress and reduce endothelial NO availability by peroxynitrite formation. In human endothelial cells gp91(phox) was identified as the limiting subunit of the forming NAD(P)H oxidase. Because endothelin-1 (ET-1) is considered as a pro-atherosclerotic stimulus, we analyzed the effect of ET-1 on gp91(phox) expression and O(*-)(2) generation in primary cultures of human umbilical vein endothelial cells (HUVECs). The gp91(phox) mRNA expression was quantified by standard calibrated competitive reverse transcriptase-polymerase chain reaction. ET-1 induces gp91(phox) mRNA expression in HUVEC (max. after 1 h). The induction of gp91(phox) expression was dose-dependent, reaching its maximum at 10 nmol/L ET-1. The increased gp91(phox) expression is mediated by endothelial receptor type B (ET(B)). Furthermore, ET-1 augments O(*-)(2) generation in human endothelial cells as measured by coelenterazine chemiluminescence. These data support a new mechanism: how ET-1 increases oxidative stress in the vessel wall leading to endothelial dysfunction and enhanced susceptibility to atherosclerosis.

MRSA in nursing homes in the Netherlands 1989 to 1998: a developing reservoir?

The prevalence of methicillin resistant Staphylococcus aureus (MRSA) in Dutch nursing homes in 1998 was higher than that found in 1989 to 1997. The increased prevalence of MRSA could lead to colonisation outside these nursing homes. A study of the prevale

Obesity is associated with tissue-specific activation of renal angiotensin-converting enzyme in vivo: evidence for a regulatory role of endothelin

In the C57BL/6J mice model, we investigated whether obesity affects the function or expression of components of the tissue renin-angiotensin system and whether endothelin (ET)-1 contributes to these changes. ACE activity (nmol. L His-Leu. mg protein(-1)) was measured in lung, kidney, and liver in control (receiving standard chow) and obese animals treated for 30 weeks with a high-fat, low cholesterol diet alone or in combination with LU135252, an orally active ET(A) receptor antagonist. ACE mRNA expression was measured in the kidney, and the effects of LU135252 on purified human ACE were determined. Aortic and renal tissue ET-1 protein content was measured, and the vascular contractility to angiotensin II was assessed. Obesity was associated with a tissue-specific increase in ACE activity in the kidney (55+/-4 versus 33+/-3 nmol/L) but not in the lung (34+/-2 versus 32+/-2 nmol/L). Long-term LU135252 treatment completely prevented this activation (13.3+/-0.3 versus 55+/-4 nmol/L, P<0.05) independent of ACE mRNA expression, body weight, or renal ET-1 protein but did not affect pulmonary or hepatic ACE activity. Obesity potentiated contractions in response to angiotensin II in the aorta (from 6+/-2% to 33+/-5% KCl) but not in the carotid artery (4+/-1% to 3.6+/-1% KCl), an effect that was completely prevented with LU135252 treatment (6+/-0.4% versus 33+/-5% KCl). No effect of LU135252 on purified ACE was observed. Thus, obesity is associated with the activation of renal ACE in vivo independent of its mRNA expression and enhanced vascular contractility to angiotensin II. These effects are regulated by ET in an organ-specific manner, providing novel mechanisms by which ET antagonists may exert organ protection.

Broader vaccination of expatriates against HBV infection: do we reach those at highest risk?

BACKGROUND

The effects of the implementation of a new Dutch hepatitis B virus (HBV) vaccination strategy (1991) for expatriates on HBV vaccination status and HBV infection prevalence were evaluated in a group of 864 expatriates returning from HBV-endemic areas.

METHODS

During a routine medical examination at the participating medical centres Dutch expatriates were asked to complete a questionnaire and to donate a serum sample for HBV testing. Blood was tested for antibodies against the hepatitis B core (anti-HBc) and surface antigens (anti-HBs). The serological data were related to information gathered on aspects of residence, sexual risk behaviour and occupational risks.

RESULTS

A significantly higher percentage of expatriates (37%) were vaccinated compared to a previous study in 1987-1989 (14%). However, the percentage of expatriates with HBV infection markers (5%) had not decreased significantly. Moreover, the risk for HBV infection, as determined with a questionnaire, was still affected by well-known risk factors such as homosexual contacts (odds ratio [OR] = 6.6, 95% CI: 1.7-26), more than five casual local partners (OR = 3.6, 95% CI: 1.2-11) and more than five occupational accidents in the last 3 years (OR = 20, 95% CI: 2-187). Detailed analysis of the vaccination status indicated that especially young female expatriates with low risk behaviour (65%) were protected, while older male expatriates with high risk behaviour were less protected (20%).

CONCLUSION

We conclude that the new vaccination strategy has resulted in a higher percentage of expatriates protected. However, only a small proportion was reached of those at highest risk for HBV infection.

European Antimicrobial Resistance Surveillance System (EARSS): objectives and organisation

Effective European surveillance must have the agreement and active involvement of all participants, concluded a European Union (EU) conference on the need for surveillance of resistant microorganisms (the microbial threat), held in September 1998 in De

[Health council report: "Antimicrobial growth promoters"]

The Health Council of the Netherlands has issued a report on the risk of development of resistance among bacteria as result of the use of antibiotics as growth promotors in livestock farming. The committee appointed by the Health Council conclude that the use of antimicrobial growth promotors contributes to the problem of resistance among human pathogens. The conclusions are based on evidence regarding the development of resistance in livestock as the result of the use of antimicrobial growth promotors, the possibility of colonisation/infection of humans with resistant bacteria from the intestinal flora of productive livestock, and the transfer of resistance genes from livestock bacteria to human pathogenic microorganisms. Effective measures for the limitation of the public health risk should focus on termination of the use of antimicrobial growth promotors that confer resistance to (related) antibiotics currently used (or which will be available) to treat patients suffering from bacterial infections. In addition, the committee advised ending the use of antimicrobial growth promotors in 3 years.

Methods for exposure of laboratory animals to ultraviolet radiation

Two different sources of ultraviolet B (UVB) radiation, an electronically controlled UVB exposure unit, containing FS40 tubes, and a hand-held Kromayer lamp, were evaluated for actual irradiance in W/m2 and spectra (physical dosimetry and biological dosimetry (skin effects in rodents)). The technical studies of the FS40 sources demonstrated that the flux intensity of the lamps could be changed electronically, without affecting the spectrum. Thus it was possible to standardize UVB exposure electronically. The biologically effective doses of these sources were analysed in RIV-Tox Wistar rats and BALB/c mice. After low doses of UVB radiation, histopathological changes such as acanthosis, hyperkeratosis and dermal inflammation were observed in the skin without the presence of major side effects such as erythema and oedema. After higher doses of UVB radiation erythema and oedema were clearly visible. Quantitative studies showed that the minimal erythema dose, as a biological parameter, correlated well to the emission in J/m2. In addition, biological parameters such as acanthosis and inflammation in the skin correlated well to the actual exposure in J/m2 and were sensitive biomarkers for UVB-induced skin toxicity. Thus, in addition to minimal erythemal doses, acanthosis and inflammation may also be applied as biologically relevant doses for studies of the biological effects of UVB radiation.

Comparative immunotoxicology of ultraviolet B exposure I. Effects of in vitro and in situ ultraviolet B exposure on the functional activity and morphology of Langerhans cells in the skin of different species

Ultraviolet (UV) B-induced morphological and functional changes in the skin of mice, rats and humans were investigated. Changes in the morphological structure of Langerhans cells (LC), the major antigen-presenting cells in the skin, using confocal laser scanning microscopy, were found in mouse and rat skin after in situ exposure to high doses of UVB radiation (FS40) (3-9 kJ/m2). Similar UVB doses failed to induce alterations in the morphological structure of human LC. Alterations in the function of epidermal cells (especially LC) were studied, using the mixed skin lymphocyte response (MSLR). In vitro UVB exposure of epidermal cells (EC), derived from the skin of the different species, revealed that low doses of UVB radiation impaired the stimulatory capacity of these cells dose-dependently; mouse epidermal cells were most UVB-susceptible, while human cells were least UVB susceptible. For suppression of the stimulatory capacity of EC after in situ UVB exposure of skin tissue, higher doses of UVB radiation than the in vitro UVB exposure were needed in all species tested. Also in this in situ set-up mouse epidermal cells were most UVB-susceptible, and human epidermal cells were least UVB-susceptible. The magnitude of differences in susceptibility for UVB-induced changes in the stimulatory capacity of EC after in situ and after in vitro exposure experiments was similar. Firstly, it may be concluded that UVB impairs the functional activity of LC at a lower dose than that which alters the morphology of these cells. Secondly, it is clear that epidermal cells, especially LC, from the skin of rodents are more susceptible to UVB than epidermal cells derived from human skin. It is important to account for these differences in susceptibility when data on the effects of UVB radiation on the immune system in rodents are extrapolated to humans.

Risk assessment for the harmful effects of UVB radiation on the immunological resistance to infectious diseases

Risk assessment comprises four steps: hazard identification, dose-response assessment, exposure assessment, and risk characterization. In this study, the effects of increased ultraviolet B(UVB, 280-315 nm) radiation on immune functions and the immunological resistance to infectious diseases in rats were analyzed according to this strategy. In a parallelogram approach, nonthreshold mathematical methods were used to estimate the risk for the human population after increased exposure to UVB radiation. These data demonstrate, using a worst-case strategy (sensitive individuals, no adaptation), that exposure for approximately 90 min (local noon) at 40 degrees N in July might lead to 50% suppression of specific T-cell mediated responses to Listeria monocytogenes in humans who were not preexposed to UVB (i.e., not adapted). Additionally, a 5% decrease in the thickness of the ozone layer might shorten this exposure time by approximately 2.5%. These data demonstrate that UVB radiation, at doses relevant to outdoor exposure, may affect the specific cellular immune response to Listeria bacteria in humans. Whether this will also lead to a lowered resistance (i.e.,increased pathogenic load) in humans is not known, although it was demonstrated that UVB-induced immunosuppression in rats was sufficient to increase the pathogenic load. Epidemiology studies are needed to validate and improve estimates for the potential effects of increased UVB exposure on infectious diseases in humans.

Risk assessment for the harmful effects of immunotoxic agents on the immunological resistance to infectious diseases: ultraviolet light as an example

Risk assessment comprises four steps: hazard identification, dose-response assessment, exposure assessment and risk characterization. As an example we have assessed the risk of decreased host resistance to infections due to effects of the immunotoxic agent - ultraviolet light. We have analysed effects of UVB radiation on basal immune functions in rats and man, and the immunological resistance to infectious diseases in rats. Non-threshold mathematical methods were used in order to estimate the risk for the human population after increased exposure to UVB radiation. These data demonstrate that UVB radiation, at doses relevant to outdoors exposure, may affect the immunological resistance to infectious diseases in human individuals. This study may also provide a basis for a strategy to assess the risk of adverse effects of exposure to immunotoxic agents.

Quercetin prevents UV-induced local immunosuppression, but does not affect UV-induced tumor growth in SKH-1 hairless mice

Ultraviolet is thought to induce skin tumors by its dual activity as a mutagenic agent and a suppressor of cell-mediated immunity. In the present study the effects of quercetin, a flavonoid-containing compound, on carcinogenesis and immunosuppression were studied in SKH hairless mice exposed to suberythemal doses of UV for up to 17 weeks. It was found that quercetin did not affect the onset or growth of non-melanoma skin tumors resulting from UV exposure. In contrast, it prevented the suppression in contact hypersensitivity (CHS) to picryl chloride induced by UV. The mechanism of this prevention might be explained by the observation that the decreased number of epidermal Langerhans' cells is partly prevented by the quercetin. Quercetin did not alter the effects of UV in increasing numbers of spleen and lymph node cells, only partly in decreasing the CD8-positive cells in spleen cell populations and decreasing the lymphoproliferative response of spleen cells to the mitogens concanavalin A and phytohemagglutinin. Thus oral quercetin did not prevent UV-induced carcinogenesis although it restored the skin-associated CHS response probably by protecting the antigen-presenting cells in the skin.

UVB-induced decreased resistance to Trichinella spiralis in the rat is related to impaired cellular immunity

Our laboratory has demonstrated in preliminary experiments that UVB exposure using the Kromayer lamp can induce increased numbers of Trichinella spiralis larvae in carcasses of infected Wistar rats, without affecting specific antibody titers to this parasite. In this study, orally T. spiralis-infected Wistar rats were exposed to suberythemal doses of UVB radiation using FS40 lamps during different time periods before or after infection. A significant increase in the number of T. spiralis larvae was found in the carcasses of rats that were UVB irradiated daily for 7 consecutive days in the second week after infection. Additionally, increased numbers of larvae were also detected histologically in the tongue of rats that were exposed the first and the second week after infection. Lymphocyte stimulation assays using mesenteral lymph node cells indicated that UVB exposure also impaired the specific lymphocyte response to T. spiralis. Moreover, DTH responses to T. spiralis were severely impaired in rats that were UVB irradiated daily for 7 consecutive days in the second week after infection. Thus, these data combined with the data of the Kromayer study indicate that exposure of rats to FS40 irradiation following oral infection with T. spiralis leads to increased numbers of larvae in systemic sites and impaired T-cell immunity to the parasite.

Risk assessment of UVB effects on resistance to infectious diseases

The aim of this study was to develop a quantitative risk assessment of lowered resistance to infections in humans due to (solar) ultraviolet B (UVB) exposure. We followed the steps for risk assessment as defined by the U.S. National Academy of Sciences: (1) hazard identification, (2) dose-response assessment, (3) exposure assessment, and (4) risk characterization. For step 1, the suppressory effects of UVB radiation on the immune system have been reviewed, supplemented with new data, and analyzed. Experiments on UV-induced immunosuppression cannot be performed with humans for ethical reasons, but herpes simplex virus infection appears to be the human paradigm. Thus, UVB radiation appears to be a potential hazard to immunologic functions. Step 2 is crucial, but dose-response relationships for infections have never been measured in humans. We used our earlier dose-response rat data for suppression of lymphocyte stimulation and computed that the UVB dose resulting in a 50% reduction of lymphocyte stimulation by Listeria monocytogenes is 6.800 J/m2. Using mixed skin lymphocyte response assays we found that humans are 3.8 times less sensitive than rats (interspecies variation [IEV]). To account for the 2.5 percentile of most susceptible individuals in a population, an additional factor (intraspecies variation [IAV]) was introduced (0.5 for humans). Using these data, we computed that 13.100 J/m2 of UVB radiation emitted by FS40 lamps would suppress 50% of the proliferative response of lymphocytes to L. monocytogenes in most sensitive skin type 2 humans. In step 3, we assumed the action spectrum for the responses analyzed by us as identical to an action spectrum for suppression of contact hypersensitivity that is available in the literature. This led us to step 4, where we calculated that approximately 100 min of solar exposure at around noon in Italy or Spain would suppress the resistance to infections by L. monocytogenes in the most sensitive humans.

Effects of ultraviolet-B exposure on the resistance to Listeria monocytogenes in the rat

A rat infection model using the bacterial pathogen Listeria monocytogenes was employed to analyze the immunosuppressive activity of UVB radiation. Rats were exposed to suberythemal doses of UVB radiation for 5 or 7 consecutive days, using Kromayer or FS40 lamps respectively. Subsequently, the rats were infected subcutaneously or intravenously with Listeria. Exposure to UVB resulted in an increased number of bacteria in the spleen 4 days after infection. Listeria-specific lymphocyte proliferation assays as well as delayed-type hypersensitivity reactions demonstrated that T cell-mediated immunity to Listeria was impaired by UVB as measured 4 and 8 days after infection. In addition, UVB exposure decreased phagocytotic activity of peripheral blood macrophages. This study demonstrated that suberythemal doses of UVB radiation caused a delay in the clearance of Listeria bacteria from the spleen of the rats and that this was probably caused by impaired nonspecific phagocytosis of Listeria by macrophages in addition to an impaired activity of Listeria-specific T cells.