Proinflammatory Stimulation of Toll-Like Receptor 9 with High Dose CpG ODN 1826 Impairs Endothelial Regeneration and Promotes Atherosclerosis in Mice

Background

Toll-like receptors (TLR) of the innate immune system have been closely linked with the development of atherosclerotic lesions. TLR9 is activated by unmethylated CpG motifs within ssDNA, but also by CpG motifs in nucleic acids released during vascular apoptosis and necrosis. The role of TLR9 in vascular disease remains controversial and we sought to investigate the effects of a proinflammatory TLR9 stimulation in mice.

Methods and Findings

TLR9-stimulation with high dose CpG ODN at concentrations between 6.25nM to 30nM induced a significant proinflammatory cytokine response in mice. This was associated with impaired reendothelialization upon acute denudation of the carotid and increased numbers of circulating endothelial microparticles, as a marker for amplified endothelial damage. Chronic TLR9 agonism in apolipoprotein E-deficient (ApoE^-/-) mice fed a cholesterol-rich diet increased aortic production of reactive oxygen species, the number of circulating endothelial microparticles, circulating sca-1/flk-1 positive cells, and most importantly augmented atherosclerotic plaque formation when compared to vehicle treated animals. Importantly, high concentrations of CpG ODN are required for these proatherogenic effects.

Conclusions

Systemic stimulation of TLR9 with high dose CpG ODN impaired reendothelialization upon acute vascular injury and increased atherosclerotic plaque development in ApoE^-/- mice. Further studies are necessary to fully decipher the contradictory finding of TLR9 agonism in vascular biology.

[Principles of intervertebral disc assessment in private accident insurance]

Due to the spread of intervertebral disc degeneration, insurance companies and experts are regularly confronted with related assessments of insured persons under their private accident insurance. These claims pose a particular challenge for experts, since, in addition to the clinical assessment of the facts, extensive knowledge of general accident insurance conditions, case law and current study findings is required. Each case can only be properly assessed through simultaneous consideration of both the medical and legal facts. These guidelines serve as the basis for experts and claims.managers with respect to the appropriate individual factual assessment of intervertebral disc degeneration in private accident insurance.

Cardiovascular magnetic resonance feature-tracking assessment of myocardial mechanics: Intervendor agreement and considerations regarding reproducibility

Aim

To assess intervendor agreement of cardiovascular magnetic resonance feature tracking (CMR-FT) and to study the impact of repeated measures on reproducibility.

Materials and methods

Ten healthy volunteers underwent cine imaging in short-axis orientation at rest and with dobutamine stimulation (10 and 20 μg/kg/min). All images were analysed three times using two types of software (TomTec, Unterschleissheim, Germany and Circle, cvi⁴², Calgary, Canada) to assess global left ventricular circumferential (Ecc) and radial (Err) strains and torsion. Differences in intra- and interobserver variability within and between software types were assessed based on single and averaged measurements (two and three repetitions with subsequent averaging of results, respectively) as determined by Bland–Altman analysis, intraclass correlation coefficients (ICC), and coefficient of variation (CoV).

Results

Myocardial strains and torsion significantly increased on dobutamine stimulation with both types of software (p<0.05). Resting Ecc and torsion as well as Ecc values during dobutamine stimulation were lower measured with Circle (p<0.05). Intra- and interobserver variability between software types was lowest for Ecc (ICC 0.81 [0.63–0.91], 0.87 [0.72–0.94] and CoV 12.47% and 14.3%, respectively) irrespective of the number of analysis repetitions. Err and torsion showed higher variability that markedly improved for torsion with repeated analyses and to a lesser extent for Err. On an intravendor level TomTec showed better reproducibility for Ecc and torsion and Circle for Err.

Conclusions

CMR-FT strain and torsion measurements are subject to considerable intervendor variability, which can be reduced using three analysis repetitions. For both vendors, Ecc qualifies as the most robust parameter with the best agreement, albeit lower Ecc values obtained using Circle, and warrants further investigation of incremental clinical merit.

•

This is the first comparison of two types of CMR-FT software resulting in clinically valuable inter-vendor agreement data.

•

Assessment of myocardial strain and torsion is feasible with both types of software at rest and with dobutamine stimulation.

•

For both vendors, Ecc qualifies as the most robust parameter with the lowest variability.

The intravenous injection of oxidized LDL- or Apolipoprotein B100--Coupled splenocytes promotes Th1 polarization in wildtype and Apolipoprotein E--Deficient mice

BACKGROUND

Th1 responses in atherosclerosis are mainly associated with the aggravation of atherosclerotic plaques, whereas Th2 responses lead to a less pronounced disease in mouse models. The fixation of antigens on cells by means of ethylene carbodiimide (ECDI), and subsequent injection of these antigen-coupled splenocytes (Ag-SP) to induce tolerance against the attached antigens, has been successfully used to treat murine type 1 diabetes or encephalomyelitis in. We analyzed this approach in a mouse model for atherosclerosis.

METHODS AND RESULTS

OTII-transgenic mice that were treated with a single dose of 5 × 10(7) OVA-coupled splenocytes (OVA-SP), had decreased splenocyte proliferation, and lower IFNγ production in vitro upon antigen recall. However, in vivo CD4 cell activation was increased. To try lipoprotein-derived, "atherosclerosis-associated" antigens, we first tested human oxidized LDL. In wild type mice, an increase of IFNγ production upon in vitro recall was detected in the oxLDL-SP group. In Apolipoprotein E - deficient (ApoE-/-) mice that received oxLDL-SP every 5 weeks for 20 weeks, we did not find any difference of atherosclerotic plaque burden, but again increased IFNγ production. To overcome xenogenous limitations, we then examined the effects of mouse Apolipoprotein B100 peptides P3 and P6. ApoB100-SP treatment again promoted a more IFNγ pronounced response upon in vitro recall. Flow cytometry analysis of cytokine secreting spleen cells revealed CD4 positive T cells to be mainly the source for IFNγ. In ApoE-/- mice that were administered ApoB100-SP during 20 weeks, the atherosclerotic plaque burden in aortic roots as well as total aorta was unchanged compared to PBS treated controls. Splenocyte proliferation upon antigen recall was not significantly altered in ApoB100-SP treated ApoE-/- mice.

CONCLUSION

Although we did not observe a relevant anti-atherosclerotic benefit, the treatment with antigen-coupled splenocytes in its present form already impacts the immune responses and deserves further exploration.

Probing Atmospheric Electric Fields in Thunderstorms through Radio Emission from Cosmic-Ray-Induced Air Showers

We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields.

Mobilization of sca1/flk-1 positive endothelial progenitor cells declines in apolipoprotein E-deficient mice with a high-fat diet

BACKGROUND

Atherosclerosis features a deterioration of the endothelial layer in all stages. Restoration of the endothelium is associated with circulating stem cell antigen 1 (sca1) and vascular endothelial growth factor receptor type 2 (flk-1) positive endothelial progenitor cells (EPCs). We investigated whether EPC production and/or a mobilization from bone marrow are reduced in severe atherosclerosis.

METHODS AND RESULTS

EPCs in peripheral blood were diminished in ApoE-/- mice with high-fat diet (HFD) whereas bone marrow levels of these cells were not significantly altered compared to controls. In situ perfusion of the hind limbs demonstrated that EPC mobilization was reduced compared to ApoE-/- mice with normal chow, although increased plasma stromal cell-derived factor (SDF) 1α and responsivity suggested a mobilizing stimulus. The proliferation of sca1/flk-1 positive cells showed no functional impairment. EPCs could not only be significantly mobilized from the bone marrow through the application of granulocyte colony stimulating factor (GCSF), but also led by trend to a depletion of the bone marrow pool. GCSF levels in plasma were equal in ApoE-/- mice with normal chow or HFD, which excluded a decline in GCSF production.

CONCLUSION

The capability of the bone marrow pool to adapt the proliferation and mobilization of sca1/flk-1 positive EPCs seems overstrained in ApoE-/- mice with a HFD.

Real-time phase-contrast flow MRI of haemodynamic changes in the ascending aorta and superior vena cava during Mueller manoeuvre

AIM

To evaluate the potential of real-time phase-contrast flow magnetic resonance imaging (MRI) at 40 ms resolution for the simultaneous determination of blood flow in the ascending aorta (AA) and superior vena cava (SVC) in response to reduced intrathoracic pressure (Mueller manoeuvre).

MATERIALS AND METHODS

Through-plane flow was assessed in 20 healthy young subjects using real-time phase-contrast MRI based on highly undersampled radial fast low-angle shot (FLASH) with image reconstruction by regularized non-linear inversion. Haemodynamic alterations (three repetitions per subject = 60 events) were evaluated during normal breathing (10 s), inhalation with nearly closed epiglottis (10 s), and recovery (20 s).

RESULTS

Relative to normal breathing and despite interindividual differences, reduced intrathoracic pressure by at least 30 mmHg significantly decreased the initial peak mean velocity (averaged across the lumen) in the AA by -24 ± 9% and increased the velocity in the SVC by +28 ± 25% (p < 0.0001, n = 23 successful events). Respective changes in flow volume per heartbeat were -25 ± 9% in the AA and +49 ± 44% in the SVC (p < 0.0001, n = 23). Flow parameters returned to baseline during sustained pressure reduction, while the heart rate was elevated by 10% (p < 0.0001) after the start (n = 24) and end (n = 17) of the manoeuvre.

CONCLUSIONS

Real-time flow MRI during low intrathoracic pressure non-invasively revealed quantitative haemodynamic adjustments in both the AA and SVC.

Is the degeneration of aortic valve bioprostheses similar to that of native aortic valves? Insights into valvular pathology

Aortic stenosis (AS) is the most common valvular disease requiring valve replacement with a prevalence of 2-4% in adults greater than or equal to 65 years of age. There is increasing evidence that AS is an active inflammatory process that is highly regulated, displaying multiple hallmarks of atherosclerosis. Clinically, the definite therapy of advanced AS is prosthetic valve replacement. Herein, bioprosthetic tissue valves (BPs) possess superior thromboresistant and hemodynamic properties compared with mechanical valves. However, cusp degeneration and calcification also limit their long-term outcome. The pathogenesis of BP calcification as well as that of native valves is still poorly understood. Recent studies suggest a similar valvular pathology, that underlies both types of valvular degeneration, but also an even more important role of inflammatory and repair processes in the case of BP degeneration.

Atorvastatin-induced increase in progenitor cell levels is rather caused by enhanced receptor activator of NF-kappaB ligand (RANKL) cell proliferation than by bone marrow mobilization

BACKGROUND

Statins have been shown to increase the level of circulating progenitor cells in peripheral blood supposedly due to a mobilization of progenitor cells from the bone marrow niche. Osteoclast/osteoblast interaction has been associated with progenitor cell mobilization. Here, we investigated the role of statins on progenitor cell mobilization with a focus on bone metabolism.

METHODS AND RESULTS

FGF2(-/-) and wild type (wt) mice were treated with atorvastatin or placebo. In contrast to wt mice, the number of sca-1/flk-1 positive progenitor cells in peripheral blood (PB) of atorvastatin treated FGF2(-/-) mice did not increase, and was accompanied by a defective reendothelialization after perielectric injury of the common carotid artery. In wt, but not FGF2(-/-) mice, statin treatment was associated with increased levels of receptor activator of NF-κB ligand (RANKL) in bone marrow (BM) supernatant. Treatment with recombinant RANKL increased sca-1/flk-1 positive progenitors in FGF2(-/-) mice. Interestingly, osteoclast activation was not altered. To measure the egress of sca-1/flk-1 positive progenitor cells from the bone marrow, we performed in-situ perfusion experiments of isolated hind limbs. Mobilization was not significantly affected by atorvastatin in both wt and FGF2(-/-) mice. Furthermore, RANK - the specific receptor to RANKL - is expressed on progenitor cells, and RANKL stimulation increases cell proliferation in vitro and in vivo.

CONCLUSIONS

Atorvastatin treatment increases RANKL levels with no measurable effect on bone metabolism and mobilization of progenitor cells from BM to PB. RANKL is essential for the statin-mediated increase of progenitor cell levels but predominantly due to a RANKL-induced stimulation of cell proliferation.

[Christa Kohler's "communicative psychotherapy" as an integrated psychotherapeutic concept and its biographical, scientific and historical context]

"Communicative psychotherapy" was developed in the 1960s by the East German psychotherapist and psychiatrist Christa Kohler (1928-2004) for the treatment of "neuroses". Similar to established present-day psychotherapeutic methods, such as cognitive behaviour therapy, it combined diverse therapeutic approaches into an integrated treatment programme. This included individual and group therapy, exercise, work and occupational therapy. In contrast to modern psychotherapeutic practice, communicative psychotherapy was based on a firm system of values, namely socialist ideals. According to this system, psychological breakdown was viewed and treated ideologically. In addition, any lack of conformity with the East German system was likewise regarded as a psychopathological deviation, which should be subjected to psychological treatment. The latter concept requires a critical analysis from a current-day perspective. For the first time, this paper concentrates on Kohler's work on neuroses and the theory and practice of her communicative psychotherapy, albeit without neglecting Kohler's other scientific works, her biographical information and her Stasi documents.

Activation of endothelial toll-like receptor 3 impairs endothelial function

RATIONALE

Endothelial dysfunction and atherosclerosis are chronic inflammatory diseases characterized by activation of the innate and acquired immune system. Specialized protein receptors of the innate immune system recognize products of microorganisms and endogenous ligands such as nucleic acids. Toll-like receptor 3 (TLR3), for example, detects long double-stranded RNA and is abundantly expressed in endothelial cells. Whether innate immunity contributes to atherogenic mechanisms in endothelial cells is poorly understood.

OBJECTIVE

We sought to determine the effects of TLR3 activation in endothelial cells.

METHODS AND RESULTS

We first investigated whether stimulation of TLR3 influences endothelial biology in mice. Intravenous injection of polyinosine polycytidylic acid, a synthetic double-stranded RNA analog and TLR3 ligand, impaired endothelium-dependent vasodilation, increased vascular production of reactive oxygen species, and reduced reendothelialization after carotid artery injury in wild-type mice compared with controls but had no effect in TLR3(-/-) animals. TLR3 stimulation not only induced endothelial dysfunction but also enhanced the formation of atherosclerotic plaques in apolipoprotein E-deficient mice. In vitro incubation of endothelial cells with polyinosine polycytidylic acid induced production of the proinflammatory cytokines interleukin-8 and interferon-γ-induced protein 10, increased formation of reactive oxygen species, diminished proliferation, and increased apoptosis, which suggests that endothelial cells are able to directly detect and respond to TLR3 ligands. Neutralization of interleukin-8 and interferon-γ-induced protein 10 antagonizes the observed negative effects of polyinosine polycytidylic acid. We found elevated levels of circulating endothelial progenitor cells in polyinosine polycytidylic acid-treated mice, although they displayed increased endothelial dysfunction. Stimulation of TLR3 in cultured endothelial progenitor cells, however, led to increased formation of reactive oxygen species, increased apoptosis, and reduced migration. Injection of endothelial progenitor cells that had been incubated with polyinosine polycytidylic acid ex vivo hindered reendothelialization after carotid artery injury. Therefore, endothelial progenitor cell function was affected by TLR3 stimulation. Finally, apolipoprotein E-deficient/TLR3-deficient mice exhibited improved endothelial function compared with apolipoprotein E-deficient/TLR3(+/+) littermates.

CONCLUSIONS

Immunorecognition of long double-stranded RNA by endothelial cells may be an important mechanism involved in endothelial cell activation and development of endothelial dysfunction.

Endothelial-regenerating cells: an expanding universe

Atherosclerosis is the most common cause for cardiovascular diseases and is based on endothelial dysfunction. A growing body of evidence suggests the contribution of bone marrow-derived endothelial progenitor cells, monocytic cells, and mature endothelial cells to vessel formation and endothelial rejuvenation. To this day, various subsets of these endothelial-regenerating cells have been identified according to cellular origin, phenotype, and properties in vivo and in vitro. However, the definition and biology, especially of endothelial progenitor cells, is complex and under heavy debate. In this review, we focus on current definitions of endothelial progenitor cells, highlight the clinical relevance of endothelial-regenerating cells, and provide new insights into cell-cell interactions involved in endothelial cell rejuvenation.

[Perspectives of regenerative mechanisms in cardiovascular disease spotlighting endothelial progenitor cells]

Cardiovascular diseases are the most common cause of death in the Western world. In general, the underlying disease is atherosclerosis, which is hallmarked by deterioration of the endothelial monolayer. Restoration of an intact endothelial monolayer for prevention and therapy of cardiovascular diseases is one key concept of regenerative medicine. This article offers a review of state-of-the-art regenerative mechanisms in cardiovascular disease spotlighting endothelial progenitor cells, and further features the perspectives of regenerative medicine in vascular biology.

Pathogen burden in degenerative aortic valves is associated with inflammatory and immune reactions

BACKGROUND AND AIM OF THE STUDY

The presence of five pathogens was assessed, together with a possible correlation of the total pathogen burden on inflammation and (auto)immunity in aortic stenosis (AS) and degenerative aortic valve bioprosthesis (BP).

METHODS

Diseased valve specimens from a total of 68 patients (52 with AS, 16 with BP) were studied. The presence and localization was assessed of Chlamydia pneumoniae (cHSP60), Helicobacter pylori (HP), cytomegalovirus (CMV), Epstein-Barr virus (EBV) and herpes simplex virus (HSV), as well as of macrophages (CD68), C-reactive protein (CRP) and human heat shock protein 60 (hHSP60), by using immunohistochemical and morphometric analyses.

RESULTS

In the majority of degenerative aortic valves, specific pathogens, inflammation and immunity were localized predominantly in the fibrosa of AS patients, and in superficial regions of the BP. The categorization of valves as having four or more pathogens (n = 37) or fewer pathogens (n = 31) demonstrated an increased signaling of CD68 (p = 0.03) and CRP (p = 0.02). Specifically, cHSP60, HP and hHSP60 levels were increased in valves where one or two bacteria were identified (n = 59) compared to those without bacterial presence (n = 9) (p = 0.04).

CONCLUSION

The pathogen burden may contribute to valvular degeneration by promoting further deleterious inflammatory and (auto)immune processes at the level of the valvular fibrosa.

Synergistic effects of telmisartan and simvastatin on endothelial progenitor cells

Circulating endothelial progenitor cells (EPC) contribute to endothelial replenishment. Telmisartan is an angiotensin-receptor blocker with PPARγ-agonistic properties. PPARγ-agonists and HMG-CoA reductase inhibitors have been shown to enhance EPC number and function. We focused on the effects of telmisartan alone or in combination with simvastatin on EPC. EPC were isolated from healthy human volunteers, cultured and stimulated with telmisartan, simvastatin, or the combination of telmisartan and simvastatin. Telmisartan significantly increased the number of acLDL/lectin double-positive early EPC, the number of colony forming units (EC-CFU) as well as EPC migratory capacity, inhibited TNFα-induced EPC apoptosis and reduced glucose-induced oxidative stress. The telmisartan effect was dose-dependent and could be inhibited by GW9662, indicating a PPARγ-dependent mechanism. The combination of telmisartan and simvastatin led to a significant additive increase in EPC count and function. In wild-type mice, systemic treatment with either telmisartan or simvastatin elevated the number of sca-1/flk-1-positive EPC in bone marrow and peripheral blood, spleen-derived acLDL/lectin double-positive EPC, EPC migration and EC-CFU. Consistent with the in vitro findings, the combination of telmisartan and simvastatin resulted in a further enhancement of EPC counts. Re-endothelialization after carotid injury was significantly enhanced by telmisartan, simvastatin and the combination. Telmisartan increases EPC number and function mediated by a PPARγ-dependent mechanism. This effect is further enhanced by combination with simvastatin, suggesting a synergistic activation of potentially diverse intracellular pathways.

Differential profile of the OPG/RANKL/RANK-system in degenerative aortic native and bioprosthetic valves

BACKGROUND AND AIM OF THE STUDY

Although degenerative calcific aortic valve stenosis is the most common valvular disease among the elderly, neither the etiology underlying the condition nor degeneration of the bioprostheses is yet fully understood. The study aim was to assess the expression profile of those OPG/RANKL/RANK-system determinants known to act as key regulators of bone metabolism and the immune system in calcific aortic valve stenosis and porcine aortic bioprostheses.

METHODS

Valve probes from a total of 69 patients (41 with end-stage aortic stenosis, 11 with mild-to-moderate aortic sclerosis, 17 with degenerative porcine aortic bioprostheses) were explanted either during surgery or at autopsy. The presence and localization of OPG, RANKL, RANK and NF-kappaB were analyzed by immunostaining and morphometry.

RESULTS

The majority of stenotic and sclerotic valves exhibited cell-bound signals of OPG, RANKL, RANK and NF-kappaB, while bioprostheses showed only sparse signaling. As key findings, the percentage of cells labeled by OPG, RANK and NF-kappaB was increased in sclerotic valves compared with stenotic valves (each p < 0.001), whereas the frequency of RANKL was higher in stenotic compared to sclerotic valves (p < 0.001). As a consequence, the OPG/RANKL ratio was decreased in stenotic (0.83) compared to sclerotic valves (20.2).

CONCLUSION

The differential expression profile of specific members of the OPG/RANKL/RANK axis suggests an involvement of their determinants in native valve calcification, but not in the degeneration of porcine bioprostheses. Thus, these mediators of bone homeostasis may represent new targets for a more specified prevention and/or therapy of native aortic stenosis.

Cells of primarily extra-valvular origin in degenerative aortic valves and bioprostheses

AIMS

We assessed aortic valves from patients with non-rheumatic aortic valve stenosis (AS) and with degenerative aortic valve bioprostheses (BP) for the presence of progenitor cell and leukocyte subtype-specific markers.

METHODS AND RESULTS

Diseased valve probes from a total of 87 patients (60 AS and 27 BP) were studied. We assessed presence and localization of endothelial progenitor cells (EPCs: CD34, CD133), dendritic cells (DCs: S100), T-lymphocytes (CD3), and macrophages (CD68) by immunohistochemical and morphometric analyses. In the majority of valves, we detected cell-bound signals of CD34 (48% of AS, 74% of BP, respectively), CD133 (58%/81%), S100 (58%/93%), CD3 (62%/81%), and CD68 (78%/93%). Labelled cells were predominantly localized within the valvular fibrosa. As key results, frequency of EPCs, DCs, macrophages, and lymphocytes was found significantly higher in BP when compared with AS (CD34: 19.2+/-23.2 vs. 5.7+/-13.0%; CD133: 13.7+/-12.4 vs. 5.5+/-8.3%; S100: 15.2+/-12.2 vs. 5.7+/-8.9%; CD3: 3.3+/-2.7 vs. 1.1+/-1.4%; CD68: 35.3+/-26.6 vs. 3.4+/-4.1%; each P<or=0.001).

CONCLUSION

EPCs and DCs were detected in a large collective of degenerative aortic valves, more frequently in bioprostheses than in native cusps. Aortoluminal presence of these primarily extra-valvular cells co-localized with inflammatory cells is a novel key feature involved in aortic valve degeneration.

Prior vasorelaxation enhances diadenosine polyphosphate-induced contractility of rat mesenteric resistance arteries

Low-threshold concentrations of diadenosine polyphosphates (ApnA: Ap3A, Ap4A, Ap5A, Ap6A) or ATP, which at basal vessel tone induce just measurable vasoconstrictions, induce up to ten times enhanced vasoconstrictions of previously relaxed (by acetylcholine or sodium nitroprusside or 8Br2 cGMP or isoproterenol or levcromakalim) pre-contracted rat mesenteric resistance arteries (MrA) in a microvessel-myograph. These enhanced vasoconstrictions were of similar magnitude for threshold concentrations of all ApnA.Possibly, the low concentrations of ApnA reverse the prior vasorelaxation by inhibiting a common vasorelaxation pathway, but obviously this is not due to inhibition of guanylate cyclase, which has been previously described to be inhibited by ApnA, because the enhanced vasoconstrictions can be observed with guanylate cyclase-independent vasorelaxants (8Br2 cGMP, isoproterenol or levcromakalim), too. The enhanced vasoconstrictions are endothelium-independent because after mechanical vascular de-endothelialization the results were identical. De-endothelialized vessels, which fail to relax by acetylcholine, showed no enhanced ApnA-induced vasoconstrictions, demonstrating that the mere prior vasorelaxation of the vessel is required to provide the enhanced vasoconstriction by ApnA. Furthermore, the enhanced contractility is not based on a potentiation of the phenylephrine contraction because it equally occurs with other agents used for arterial pre-contraction. Systemically applied ApnA considerably decrease arteriovascular resistance, resulting in hypotension. But here it is demonstrated that a preceding vasorelaxation enables the resistance arteries to generate a strong and persistent ApnA-induced vasoconstriction. Thus, in vivo at very low concentrations ApnA may serve to counteract severe conditions of hypotension (e.g., shock syndrome or anaphylaxis) by the constriction of resistance arteries.

Diverging vasorelaxing effects of C-type natriuretic peptide in renal resistance arteries and aortas of GC-A-deficient mice

This study aimed to characterize the vasorelaxing effects of ANP, BNP and CNP in isolated renal resistance arteries (RRA) from wild-type mice and mice with either systemic (GC-A -/-) or smooth muscle-restricted deletion of GC-A (SMC GC-A KO). In RRA from wild-type (GC-A +/+) mice natriuretic peptides (NP) induced concentration-dependent vasorelaxations with the rank order of potency ANP>BNP>CNP. In RAA obtained from mice with systemic or smooth muscle-restricted deletion of GC-A, the effects of ANP and BNP were abolished. In contrast, CNP induced concentration-dependent vasorelaxations of GC-A -/- and SMC GC-A KO RRA. However, the efficacy of CNP for vasorelaxation was markedly diminished compared with wild-type RRA. Such changes in CNP responsiveness did not affect large arteries as the aorta and they were not due to vascular changes secondary to chronic arterial hypertension in GC-A -/- mice. Unaltered vasorelaxing effects of acetylcholine and sodium nitroprusside demonstrated unaltered function of downstream targets regulated by cGMP in vascular smooth muscle. An increased expression of the clearance receptor (NPR-C) or diminished expression of GC-B were not found to account for the differences in CNP responsiveness. In conclusion, observations in isolated aortic rings do not necessarily allow conclusions concerning the physiology of natriuretic peptides in the smaller resistance size arteries. Changes at the GC-B receptor level are likely to explain the diminished responsiveness of GC-A-deficient RRA to CNP.

Vasoactivity of diadenosine polyphosphates in human small renal resistance arteries

BACKGROUND

We examined for the first time the vascular effects of purinergic agents that contribute to the regulation of peripheral vascular resistance in human small renal resistance arteries (hRRAs).

METHODS AND RESULTS

Diadenosine polyphosphates (ApnAs, n = 3-6) and ATP, mounted in a microvessel myograph, caused vasoconstriction in hRRAs (rank order of potency: Ap5A > Ap6A = Ap4A > Ap3A = ATP). ADP, AMP and adenosine had less contractile potency than ApnA, suggesting that the observed effects were not induced by ApnA degradation products. The ApnA agent, Ap5A, but not Ap4A, induced vasoconstrictions that were inhibited by pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS; a P2X purinoceptor antagonist), but not by ADP3'5' (a P2Y purinoceptor antagonist). In pre-contracted hRRAs, all of the ApnA agents caused vasorelaxation, and the potencies did not differ from each other. The ApnA degradation products had less vasorelaxing potencies than ApnA, suggesting that the vasorelaxation was caused by the ApnA agents themselves. Ap4A-induced vasorelaxation was inhibited by ADP3'5' and PPADS. In contrast, Ap5A-induced vasorelaxation was not antagonized by ADP3'5', but was antagonized more strongly by PPADS than was Ap4A.

CONCLUSIONS

We found that the tone of resistance arteries in human kidneys can be considerably influenced by these purinergic agonists, and most potently by ApnAs. Ap5A-induced vasoconstriction appeared to be mediated by P2X purinoceptors, whereas constriction due to Ap4A was caused by a different purinoceptor. Vasorelaxation due to Ap4A, but not Ap5A, appeared to be mediated by P2Y purinoceptors.

Impact of renal transplantation on small vessel reactivity

BACKGROUND

The function of large arteries is altered after renal transplantation. Whether transplantation also induces agonist-dependent functional changes in small arterial renal and extrarenal vessels has not yet been studied.

METHODS

Chronic rejection was induced by grafting Lewis rats with kidneys from Fischer rats (FL). Rats that underwent transplantation were bilaterally nephrectomized. Rats that underwent syngeneic transplantation, uninephrectomized rats, uninephrectomized rats with denervated kidneys or with kidneys made ischemic, and native rats served as controls. All animals were treated with cyclosporine for 10 days. Eighteen weeks after surgery, the reactivity of small arteries (220-270 microm) was tested by myography.

RESULTS

Weight gain, glomerular filtration rate, and arterial pressure were similar in all groups, whereas proteinuria was elevated in FL. Only kidneys from FL showed glomerular lesions, tubular atrophy, and vasculopathy. Responsiveness of coronary, mesenteric, and femoral resistance vessels to both constrictor and dilator agonists was similar in transplanted and nontransplanted animals. Resistance vessels obtained from both allogeneically and syngeneically transplanted kidneys were more sensitive to norepinephrine, phenylephrine, angiotensin II, and vasopressin than renal vessels from weight-matched controls. Vasodilation in response to acetylcholine and sodium nitroprusside was mitigated in transplanted versus nontransplanted kidneys.

CONCLUSIONS

In rat renal transplantation, renal resistance vessel responsiveness to constrictor or dilator stimuli is altered. Extrarenal small vessel function is not affected. The changes in function of renal resistance vessels are not explained by reduction of nephron mass, denervation, ischemia, or chronic rejection.

Mesenteric and renal vascular effects of diadenosine polyphosphates (APnA)

Diadenosine polyphosphates (APnA) are endogenous dinucleoside molecules consisting of two adenosine moieties linked via their 5'-ribose positions by a variable number of phosphate groups. APnA have been shown to be present in different cell types and to be released from platelets as well as co-released with catecholamines and ATP from bovine adrenal medulla. Candidate metabolites of APnA are ATP, ADP, AMP and adenosine. Vascular effects induced by APnA and their metabolites in several models have been reported to be mediated by A1- and A2-adenosine receptors as well as P2-purinoceptors. APnA have been demonstrated to differentially affect regional perfusion, to influence cardiac output and blood pressure as well as the reactivity of isolated blood vessels and vascular beds. Vascular effects of APnA vary with the number of phosphate groups linking the adenosine molecules. This review outlines the effects of APnA on mesenteric and renal circulation. The effects of the antagonists varying with the type of vascular bed and the heterogeneous and dynamic vascular effects of diadenosine polyphosphates indicate a regionally different distribution of P2X and of P2Y purinoceptors in resistance arteries from different vascular beds. Although APnA have vasoconstrictor effects on the local level, it was repeatedly confirmed that systemically applied APnA induce hypotensive effects. The vasoconstrictor effects of APnA in isolated vessels are most prominent under resting tone conditions. In vivo, the vasculature exhibits a vasotone which makes dilatory effects more likely. Information on effects of APnA in vivo is still limited despite the fact that these compounds already have been used in man.

Vasoactivity of diadenosine polyphosphates in human small mesenteric resistance arteries

Diadenosine polyphosphates (ApnA) (n = 3-6) induced vasoconstrictions in isolated human mesenteric resistance arteries (hMRAs) mounted in a microvessel myograph (rank order of potency: Ap5A > Ap6A > Ap4A > Ap3A). The contractile effects of ApnA in hMRA were similar to their effects in rat MRA investigated previously. ATP, ADP, AMP, and adenosine had less contractile potency than ApnA, suggesting that the observed effects were not induced by the degradation products of ApnA. Ap4A- and Ap5A-induced vasoconstriction was inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) (P2X purinoceptor antagonist) but not by ADP3'5' (P2Y purinoceptor antagonist). Thus, this purinergic vasoconstriction of hMRA seems to be P2X but not P2Y purinoceptor-mediated. In precontracted hMRA all ApnA caused vasorelaxations but (in contrast to rat MRA) the potencies of the ApnA did not differ significantly from each other. The ApnA degradation products had less vasorelaxing potency than ApnA, demonstrating that the vasorelaxations can be ascribed to the ApnA themselves. Ap5A-induced vasorelaxation of hMRA could neither be inhibited with ADP3'5' nor with PPADS, which reveals a decisive difference to the rat MRA where the inhibitory profile demonstrated the importance of the P2Y purinoceptor for Ap5A-induced vasorelaxation. However, Ap4A-induced vasorelaxation in hMRA could be inhibited by ADP3'5'. These findings show that Ap4A-induced vasorelaxation in hMRA is due to P2Y purinoceptor activation, that Ap5A evokes vasorelaxation in hMRA via another mechanism than Ap4A, and that data derived from the animal model cannot be simply transferred to human conditions.

Smooth muscle-selective deletion of guanylyl cyclase-A prevents the acute but not chronic effects of ANP on blood pressure

Atrial natriuretic peptide (ANP) is an important regulator of arterial blood pressure. The mechanisms mediating its hypotensive effects are complex and involve the inhibition of the sympathetic and renin-angiotensin-aldosterone (RAA) systems, increased diuresis/natriuresis, vasodilation, and enhanced vascular permeability. In particular, the contribution of the direct vasodilating effect of ANP to the hypotensive actions remains controversial, because variable levels of the ANP receptor, guanylyl cyclase A (GC-A), are expressed in different vascular beds. The objective of our study was to determine whether a selective deletion of GC-A in vascular smooth muscle would affect the hypotensive actions of ANP. We first created a mutant allele of mouse GC-A by flanking a required exon with loxP sequences. Crossing floxed GC-A with SM22-Cre transgene mice expressing Cre recombinase in smooth muscle cells (SMC) resulted in mice in which vascular GC-A mRNA expression was reduced by approximately 80%. Accordingly, the relaxing effects of ANP on isolated vessels from these mice were abolished; despite this fact, chronic arterial blood pressure of awake SMC GC-A KO mice was normal. Infusion of ANP caused immediate decreases in blood pressure in floxed GC-A but not in SMC GC-A knockout mice. Furthermore, acute vascular volume expansion, which causes release of cardiac ANP, did not affect resting blood pressure of floxed GC-A mice, but rapidly and significantly increased blood pressure of SMC GC-A knockout mice. We conclude that vascular GC-A is dispensable in the chronic and critical in the acute moderation of arterial blood pressure by ANP.

[understanding and radiation hygiene assessment of solar UV exposure in Germany]

In order to monitor the natural ultraviolet (UV) radiation and to assess it from the point of view of radiation hygiene, the Federal Office for Radiation Protection (BfS) and the Federal Environmental Agency (UBA) have built up a common network for UV monitoring. Since 1993, the ground-level solar UV radiation has been measured at four sites in Germany every 6 minutes, with spectroradiometers in the wavelength range between 290 and 400 nm. Because erythema (sunborn) is of special interest in terms of radiation hygiene, the erythemal weighted irradiance was used as a measure for the biological effect of UV exposure. For this purpose, the measured spectral irradiance was multiplied by the relative erythemal weighting function, and the resulting function integrated from 290 to 400 nm. In the summer months of June and July 1999, the erythemal irradiance exceeded regularly the value of 175 mW/m2 in the south of Germany. In the north, values of not less than 160 mW/m2 were measured during this period. These values correspond to an UV index of more than 7 or 6, respectively--a high exposure regarding to the classification of the German Radiation Protection Commission (SSK), for which (absolute) sun protection is recommend. Between 1995 and 1999, the four sites were characterized by a small increase of the ground-level UV exposure of approx. 10%. Nevertheless, in consideration of the manifold factors affecting the acquired data, the measuring period of 5 years is still insufficient to demonstrate an ozone-dependent effect.

Heterogenous vascular effects of AP5A in different rat resistance arteries are due to heterogenous distribution of P2X and P2Y(1) purinoceptors

In the accompanying article, we showed that AP5A displayed heterogenous vasoactive effects in rat resistance arteries. It induced a stable vasoconstriction in the superior epigastric artery (SEA) and a transient vasoconstriction in the mesenteric resistance artery (MrA). In the phenylephrine-precontracted MrA AP5A induced a marked vasorelaxation. In this study the noncompetitive inhibition of the AP5A-induced vasoconstriction with pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid was found to be significantly stronger in MrA than in SEA. The nonselective P2 purinoceptor antagonist suramin inhibited AP5A-induced vasoconstriction in MrA only. The vasoconstriction by the P2X purinoceptor agonist alpha,beta-methylene ATP was inhibited by with pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid and suramin similarly to that induced by AP5A. Thus, the AP5A-induced vasoconstriction is due to P2X receptor activation, but two different P2X receptors seem to be operational in the two different vessels. The AP5A-induced vasorelaxation of phenylephrine-precontracted MrA was inhibited by the P2Y(1) receptor antagonist ADP3'5'. The vasorelaxation induced by ADPbetaS (P2Y(1) agonist) also was inhibited by ADP3'5'. These findings suggest that AP5A-induced vasorelaxation of MrA is caused by P2Y(1) receptor activation. The P1 (A(2)) receptor antagonist 3, 7-dimethyl-1-propargylxanthine only slightly inhibited AP5A-induced vasorelaxation at high concentrations. Adenosine and the A(2) receptor agonist CGS21680 failed to produce significant vasorelaxation. Therefore, vasorelaxation in MrA does not involve A(2) purinoceptor activation. AP5A-induced vasorelaxation was not inhibited by Ca(2+)- or ATP-dependent K(+) channel blockade with clotrimazole, apamin, or glibenclamide. These data indicate that vasoconstriction in MrA and SEA by AP5A is due to different P2X receptors, and vasorelaxation in precontracted MrA is due to P2Y(1) receptor activation.