Reduced diagnostic value of lactate dehydrogenase (LDH) in the presence of radiographic contrast media

Isoforms of the enzyme lactate dehydrogenase (LDH) were found in almost all cells of the organism and an elevated activity of LDH in the circulation is thought to be a clear indicator of elevated cell destruction coinciding with an increased release of components from the cellular cytoplasm, e.g. LDH. Here, we report on an in-vitro examination to test whether radiographic contrast media (RCM) could induce cell destruction followed by an increase in LDH release. The RCM were tested in non-flow cultures of human umbilical venous endothelial cells (HUVEC) of the fourth passage seeded on extracellular matrix and the results were compared to those from control cultures not exposed to contrast media. The examination revealed that the addition of contrast media to the cell culture media supplemented with pooled human serum (HSP) as source of exogenous LDH was followed by a strong decrease in LDH activity both in the absence and presence of HUVEC. Within 1.5 min after the addition of contrast media to the culture medium supplemented with HSP (30% vol of the culture medium were replaced by either of two contrast media, Iodixanol or Iopromide) the LDH activity decreased about 80% compared to the initial values. In contrast, the LDH activity did not change in cell culture media not supplemented with RCM. The partial replacement of HSP supplemented cell culture medium by RCM will cause a dilution of cell culture medium constituents. The decrease of LDH activity, however, was much stronger than the decrease thought to be attributable to the effects of dilution of cell culture medium, so that the role of dilution seems to be a minor one in this case. It has to be assumed that the RCM could interact with the LDH available in the culture medium as well as with the substrates delivered with the measurement system for the assessment of LDH activity, so that both, the amount of LDH and the activities of enzymes involved might be influenced. In the presence of HUVEC a similar effect was observed. Here, a little less strong decrease of LDH activity occurred compared to the decrease in cell culture medium without HUVEC. This was unexpected because a considerable amount of HUVEC were detached after the addition of contrast media and many of these cells were damaged seriously so that a significant amount of endogenous LDH should have been released. These unexpected results make it necessary to re-evaluate those past time examinations focussed on cell damage/destruction in the presence of contrast media, where the measurement of LDH activity was used as indicator or cell vitality and where cell decease rates were correlated to questionable toxic influences. According to the results of the examination reported here it is difficult to uphold the interpretation of recently published findings that contrast media almost exclusively induce cellular apoptosis and not necrosis.

Embedding of radiographic media molecules in the membrane of erythrocytes

The incubation of erythrocytes (RBC) or endothelial cells (HUVEC) in radiographic contrast media (RCM) could induce morphological alterations of or at the cell membranes, e.g. the generation of echinocytes or the formation of stress fibres coinciding with a massive buckling of HUVEC into the vascular lumen, as was demonstrated in several examinations in the recent years. The apposition or embedding of RCM at or in the cell membranes was discussed as possible causative mechanisms because the embedding of molecules into the internal leaflet of the cell membrane bilayer is expected to bulge the cell membrane to the outside, thus inducing e.g. the generation of echinocytes. The examination presented here is based therefore on high resolution scanning electron microscopy (SEM) analyses if iodine as marker element of RCM molecules can be found near the inside of or in RBC membranes (co-localisation study). Morphological analyses exploited secondary electron images (SE) while the analysis of elements exploited either back scattered electrons (BSE) or energy dispersive X-ray analysis (EDX) or the areal display of elements in high lateral resolution in the Bit-map modus. Even at the highest convenient magnification (1:40,000) it was impossible to detect RBC membrane associated iodine (I) after RBC incubation in RCM (Iodixanol, Iopromide) in vitro. Neither in the birds view on the samples nor looking from the side on the freeze fractured samples carrying the RBC was it possible to detect either the signal cohorts typical of I in the sum spectra or the main Lα1-peak in trace analysis.

Reversibility of echinocyte formation after contact of erythrocytes with various radiographic contrast media

Various radiographic contrast media (RCM) significantly influence the morphology of erythrocytes, especially the formation of echinocytes [Scand. J. Clin. Lab. Invest. 35 (1975), 1-43; Microvasc. Res. 60 (2000), 193-200; Herz 23 (2003), 35-41]. Microscopic studies, however, have shown that these changes of erythrocyte morphology are possibly reversible [Acta Radiol. 37 (1996), 214-217]. The aim of this study was to proof if the RCM-induced echinocyte formation can be reversed by a resuspension in autologous plasma. In this study four RCMs were tested (Iodixanol, Iohexol, Iomeprol and Iopromide). These RCM induced echinocyte formation (after suspension of erythrocytes in plasma/RCM mixtures for 10 min at 37 degrees C), which was reversible after resuspension in autologous RCM-free plasma (resuspension time 5 min at 37 degrees C). Especially for Iomeprol and Iopromide - the RCMs which induced the strongest echinocyte formation - an echinocyte reduction from 94.2% to 44.5% and for Iopromide from 80.6% to 50.4% occurred. The echinocyte formation was influenced by the type of RCM as well as by the RCM concentration. The same was true for the reversibility of echinocyte formation due to resuspension in autologous plasma (type of RCM: p</=0.0001; concentration of RCM: p=0.0847). Iodixanol was associated with the least numbers echinocytes formed (after suspension in the plasma/RCM-mixture as well as after the resuspension in autologous plasma). A 100% reversibility back to discocytes was observed in none of the RCMs after resuspension in autologous RCM-free plasma.In conclusion, a significant reversibility of RCM-induced echinocyte formation in autologous plasma could be observed.

The effect of radiographic contrast media on the morphology of human erythrocytes

Echinocyte formation is associated with a rigidification of the cells that possibly affects capillary diffusion and, consequently, the tissue's oxygen supply. This study examines how many echinocytes appeared after the addition of various concentrations of radiographic contrast media (RCM) (Iodixanol 320, Iohexol 350, Iopromide 370, Iomeprol 350 and Iomeprol 400 mg Iodine/ml) compared to red blood cells in isotonic saline solution as well as in autologous plasma. Isotonic saline solution, Iodixanol, Iohexol, Iomeprol 350, Iomeprol 400 and Iopromide in concentrations of 10%, 20% or 40% were added to the plasma of six healthy subjects. Subsequently, the erythrocytes were resuspended in these RCM/plasma mixtures, incubated for 5 minutes at 37 degrees C and then examined under the microscope.The various mixtures and concentrations of the RCM in the mixture all had a significant effect on the number of discocytes (p<0.0001). The percentage of discocytes for all concentrations significantly depended on the RCM/plasma mixture (p=0.0097). Of all the RCM/plasma mixtures used as well as of the NaCl/plasma mixtures, the Iodixanol/plasma mixture showed the most similar discocyte fraction compared to red blood cells in the autologous plasma. At the same time, while Iodixanol in this respect differed from all other RCMs, the other RCMs only differed little from one another with respect to the discocyte fraction.

Influence of xantinole nicotinic acid on cutaneous microcirculation in patients with coronary artery disease and hyperlipoproteinemia

Xantinole nicotinic acid (NA) dose dependently lowers plasma levels of atherogenic lipoproteins and increases blood flow through vasodilation. The aim of this study was to evaluate the effect of NA on cutaneous microcirculation in patients with coronary artery disease and hyperlipidemia. In this open pilot study, five men and three women (74.2+/-9.1 yrs; 81.4+/-7.9 kg; 171.6+/-7.0 cm) with angiographically proven coronary artery disease and hyperlipidemia were included. Nailfold capillary microscopy was used for measurements of erythrocyte velocities at rest and after three minutes of ischemia, before and one hour after intake of 1000 mg of NA. The blood pressure (120+/-12/73+/-8 mmHg vs. 113+/-10/72+/-5 mmHg; p=0.19/0.83) and the heart rate (72+/-8/min vs. 70+/-7/min; p=0.38) remained unchanged. The mean capillary red blood cell velocity at rest (v(RBC); 0.27+/-0.23 mm/s vs. 0.32+/-0.18 mm/s; p=0.089) and the time to maximal post ischemia erythrocyte velocity (t(peak); 21.0+/-7.9 s vs. 24.3+/-15.5 s; p=0.49) did not change. The maximal post ischemic erythrocyte velocity (v(maxRBC); 0.93+/-0.33 mm/s vs. 1.19+/-0.19 mm/s; p=0.0096) raised slightly but significantly, the duration of post-ischemia hyperemia (DpH; 101+/-16 s vs. 127+/-15 s; p=0.0005) increased markedly. One patient reported about flush in the whole body. The administration of 1000 mg of NA resulted in a significant improvement of the cutaneous microcirculation in patients with coronary artery disease and hyperlipidemia.

Cutaneous microcirculatory function predicts the responsiveness to tadalafil in patients with erectile dysfunction and coronary artery disease

Despite the proven clinical efficacy of phosphodiesterase inhibitors in the treatment of erectile dysfunction (ED), some patients do not respond to the medication. By means of nailfold capillary microscopy in patients with concomitant coronary artery disease (CAD) and ED, it was evaluated whether the extent of microvascular dysregulation predicts the responsiveness to tadalafil (TAD) in terms of erectile function. The ED of each patient was assessed by the International Index of Erectile Function (IIEF). Patients presenting both, documented CAD and ED, showed a significantly reduced capillary red blood cell velocity (v(RBC)) at rest and after 3 min of ischemia compared with age-matched controls. At 2 h after intake of 20 mg of TAD, a significant increase of v(RBC) at rest as well as during postischemic hyperemia was found. Patients who reported no improvement of their ED after the use of TAD demonstrated no changes in the duration of postischemic (DpH) hyperemia, or even a reduction of the DpH. The majority of the patients, who reported at least one successful sexual intercourse due to TAD, had a prolongation of DpH. We conclude that assessment of microvascular regulation by nailfold capillary microscopy can predict the probability of a treatment failure with phosphodiesterase inhibitors in patients with ED. Moreover, as endothelial dysfunction is the common underlying pathophysiological process of ED and cardiovascular diseases, the test may help to identify patients at risk for the development of atherosclerosis and following cardiovascular events.

Regulation of endothelial barrier function during flow-induced conversion to an arterial phenotype

OBJECTIVE

Flow-induced conversion of endothelial cells into an elongated arterial phenotype requires a coordinated regulation of cell junctions. Here we investigated the effect of acute and chronic flow on junction regulation.

METHODS AND RESULTS

Using an extended experimental setup that allows analyses of endothelial barrier function under flow conditions, we found a flow-induced upregulation of the transendothelial electrical resistance within minutes. This was accompanied by an increase in actin filaments along the junctions and vascular endothelial (VE)-cadherin clustering, which was identified at nanoscale resolution by stimulated emission depletion microscopy. In addition, a transient tyrosine phosphorylation of VE-cadherin and catenins occurred within minutes following the onset of flow. VE-cadherin and actin distribution were maintained under chronic flow over 24 h and associated with the upregulation of VE-cadherin and alpha-catenin expression, thus compensating for the cell elongation-mediated increase in cell border length. Importantly, all observed effects were rac1 dependent as verified by the inhibitory effect of dominant negative N17rac1.

CONCLUSION

These results show that flow-induced conversion of endothelial cells into an arterial phenotype occurs while intercellular junctions remain intact. The data place rac1 in a central multimodal regulatory position that might be important in the development of vascular diseases, such as arteriosclerosis.

Influence of radiographic contrast media on myocardial oxygen tension: a randomized, NaCl-controlled comparative study of iodixanol versus iomeprol in pigs

PURPOSE

To examine how a one-time bolus injection of radiographic contrast media (RCM; iodixanol 320 and iomeprol 350) into the left coronary artery of six pigs affects tissue oxygen tension in the artery's supply area (pO(2 )LAD) compared to a 0.9% sodium-chloride (NaCl) bolus.

MATERIAL AND METHODS

Each animal received a total of three boluses: one iodixanol, one iomeprol, and one NaCl (10 ml each). The radiographic contrast media and NaCl boluses were randomly assigned, and pO(2) profiles were recorded.

RESULTS

26.7+/-16.4 s after iodixanol injection, pO(2) LAD had declined by 3.5% from 42.2+/-5.6 mmHg to 40.7+/-5.9 mmHg (P = 0.0357). After 53+/-16.7 s, the initial value was restored. The pO(2) LAD was 41.9+/-7.4 mmHg before iomeprol injection, and, 303.3+/-58.9 s after injection, pO(2) LAD had declined by 13.1% to 36.4+/-7.5 mmHg (P = 0.0001). After 577+/-22 s, the initial value was restored. The bolus application of an isotonic NaCl solution resulted in no effect on pO(2) LAD. Immediately after injection, it increased by 3%. In the supply area of the right coronary artery and the peripheral skeletal muscle, no effect of the RCM or NaCl on tissue oxygen tension was observed. Furthermore, no effect on tissue temperature, heart rate, systolic and diastolic blood pressure, or cardiac output per minute occurred.

CONCLUSION

The injection of RCM in a coronary artery can result in a significant local contrast-medium-induced microcirculation disorder. The high viscosity of iodixanol led to a very short-term insignificant effect on the microcirculation, while iomeprol induced a slight time-delayed pO(2) decrease, which might be caused by the rigidification of erythrocytes. In comparison to a previous study with iopromide, the influence of iodixanol and iomeprol on myocardial oxygen tension was markedly less pronounced.

Influence of extra corporeal circulation on myocardial oxygen tension: results of an animal model

BACKGROUND

Experimental data have shown the potential risk of cellular damage of the myocardium during extra corporeal circulation (ECC). The influence of ECC on myocardial oxygen tension however remained unclear. Therefore, the influence of ECC on the oxygen tension in a beating heart was investigated.

METHODS

In a pig animal model flexible pO2 microcatheters were positioned in the midmyocardium of the left ventricle and the skeletal muscle and tissue oxygen tension during ECC were monitored and compared with data of a control group without ECC.

RESULTS

ECC and unload of the heart caused a significantly higher increase of myocardial pO2 than in a non-ECC control group.

CONCLUSION

Our findings show the beneficial effect of ECC on myocardial pO2. This may support the use of ECC in coronary artery bypass grafting because the potential myocardial injury due to ECC is not related to myocardial ischemia. On the contrary, myocardial pO2 was even increased during extracorporeal circulation in this study.

Use of the Platelet Reactivity Index by Grotemeyer, Platelet Function Analyzer, and Retention Test Homburg To Monitor Therapy with Antiplatelet Drugs

In 1974, Wu and Hoak described a method for determining circulating platelet aggregates. This method was modified by Grotemeyer in 1983. The platelet reactivity index (PR) is based on the ratio of platelet aggregates in blood samples obtained in different buffer solutions. Platelet aggregates are resolved when blood is sampled in EDTA-buffer, but remain fixed when EDTA-formalin-buffer is used. Generally, the PR is preferred, because in vitro manipulations of platelets are not necessary, and the results are calculated. PR values above 1.05 are suspicious for elevated platelet aggregation. PR values above 1.2 indicate pathological changes in platelet aggregation. The PR is inexpensive (4.0 euro dollars) and rapid to perform. PR values were used successfully to identify nonresponders to secondary prophylaxis with acetylsalicylic acid (ASA), that is, patients suffering from stroke (33%) and patients after cardiac ischemia (18%). Furthermore, elevated PR values correlated significantly with the incidence of arterial thromboembolic complications. The PR correlated well in our prospective study with values received from the retention test Homburg (RT-H) and the platelet function analyzer (PFA-100). The data indicate that the values of the PR seem to be highly predictive for the evaluation of the ASA therapy. However, the PR is not feasible for the determination of the ASA overdosage.

Haemocompatibility of polymer-coated stainless steel stents as compared to uncoated stents

Acute and subacute stent thrombosis still represent an unsolved problem in connection with endovascular stents. For this reason coatings are tested now with the intention to reduce thrombogenicity of stainless steel surfaces. This comparative study examined whether a polymeric stent coating affected the haemocompatibility of a stainless steel stent. For compatibility testing, coated and non-coated stents were implanted in a low-grade thrombogenic closed-loop system perfused with platelet rich plasma at shear rates far below the threshold value at which shear-rate-induced activation of thrombocytes occurs. After 21 circulations of the filling volume (exposure time: 6.2 min), the number of single circulating platelets in the perfusion system with uncoated stainless steel stents decreased almost twice as much as was the case with polymer-coated stents. This is thought to indicate that more thrombocytes had adhered to the uncoated stainless steel stent, or that the thrombocytes were clustered in circulating aggregates. Parallel to the platelet aggregation/adherence, a release reaction took place, as was evident from the TAT complexes indicating the generation of thrombin. In the case of the implantation of uncoated stainless steel stents, both the number of activated circulating thrombocytes and the level of platelet reactivity (number of thrombocytes circulating in the plasma as aggregates) were notably higher than in the system with polymer-coated stents. At the same time it should be noted that the activation or aggregation is almost wholly attributable to the exogenic surface of the implanted stent, since activation due to the tube system or to shear rate can be excluded (as shown by measurements of the system without a stent). In addition to activation of the thrombocytes, a notable increase in the number of receptors per platelet (significant only in the system with the uncoated stent) took place. This supports both the adherence of the thrombocytes and their readiness to aggregate, since more receptors (docking places for ligands) are available. The better haemocompatibility of the polymer-coated stents, as verified in the laboratory, was also evident under microscopic examination of the explanted stents following the perfusion tests.

Effect of desmopressin (DDAVP) on platelet membrane glycoprotein expression in patients with von Willebrand's disease

When patients with von Willebrand's disease were given a single injection of desmopressin (0.4 microg/kg body weight), there was a considerable increase in platelet reactivity (from 0.95 +/- 0.19 to 1.44 +/- 0.42; p = 0.0033). On flow cytometry, increased glycoprotein Ib/IX expression in the platelets was found after the desmopressin injection; when phycoerythrin-marked anti-CD62 antibodies were used, the mean fluorescence rose from 428.9 +/- 56.6 to 440.7 +/- 51.4 (p = 0.0056), and from 425.9 +/- 55.0 to 437.4 +/- 53.9 (p = 0.0018) when phycoerythrin-marked anti-thrombospondin antibodies were used. Apart from the rise in the von Willebrand factor, this could explain the increased platelet reactivity. However, the surface expression of CD62, CD63 and thrombospondin on platelets did not change following the desmopressin injection.