Manganese- and Platinum-Driven Oxidative and Nitrosative Stress in Oxaliplatin-Associated CIPN with Special Reference to Ca4Mn(DPDP)5, MnDPDP and DPDP

Platinum-containing chemotherapeutic drugs are efficacious in many forms of cancer but are dose-restricted by serious side effects, of which peripheral neuropathy induced by oxidative-nitrosative-stress-mediated chain reactions is most disturbing. Recently, hope has been raised regarding the catalytic antioxidants mangafodipir (MnDPDP) and calmangafodipir [Ca4Mn(DPDP)5; PledOx®], which by mimicking mitochondrial manganese superoxide dismutase (MnSOD) may be expected to overcome oxaliplatin-associated chemotherapy-induced peripheral neuropathy (CIPN). Unfortunately, two recent phase III studies (POLAR A and M trials) applying Ca4Mn(DPDP)5 in colorectal cancer (CRC) patients receiving multiple cycles of FOLFOX6 (5-FU + oxaliplatin) failed to demonstrate efficacy. Instead of an anticipated 50% reduction in the incidence of CIPN in patients co-treated with Ca4Mn(DPDP)5, a statistically significant increase of about 50% was seen. The current article deals with confusing differences between early and positive findings with MnDPDP in comparison to the recent findings with Ca4Mn(DPDP)5. The POLAR failure may also reveal important mechanisms behind oxaliplatin-associated CIPN itself. Thus, exacerbated neurotoxicity in patients receiving Ca4Mn(DPDP)5 may be explained by redox interactions between Pt2+ and Mn2+ and subtle oxidative-nitrosative chain reactions. In peripheral sensory nerves, Pt2+ presumably leads to oxidation of the Mn2+ from Ca4Mn(DPDP)5 as well as from Mn2+ in MnSOD and other endogenous sources. Thereafter, Mn3+ may be oxidized by peroxynitrite (ONOO-) into Mn4+, which drives site-specific nitration of tyrosine (Tyr) 34 in the MnSOD enzyme. Conformational changes of MnSOD then lead to the closure of the superoxide (O2•-) access channel. A similar metal-driven nitration of Tyr74 in cytochrome c will cause an irreversible disruption of electron transport. Altogether, these events may uncover important steps in the mechanism behind Pt2+-associated CIPN. There is little doubt that the efficacy of MnDPDP and its therapeutic improved counterpart Ca4Mn(DPDP)5 mainly depends on their MnSOD-mimetic activity when it comes to their potential use as rescue medicines during, e.g., acute myocardial infarction. However, pharmacokinetic considerations suggest that the efficacy of MnDPDP on Pt2+-associated neurotoxicity depends on another action of this drug. Electron paramagnetic resonance (EPR) studies have demonstrated that Pt2+ outcompetes Mn2+ and endogenous Zn2+ in binding to fodipir (DPDP), hence suggesting that the previously reported protective efficacy of MnDPDP against CIPN is a result of chelation and elimination of Pt2+ by DPDP, which in turn suggests that Mn2+ is unnecessary for efficacy when it comes to oxaliplatin-associated CIPN.

Exacerbated Neuropathy in POLAR A and M Trials Due to Redox Interaction of PledOx-Associated Mn2+ and Oxaliplatin-Associated Pt2+

Disappointing results from the POLAR A and M phase III trials involving colorectal cancer patients on chemotherapy with FOLFOX6 in curative (A) and palliative (M) settings have been reported by the principal investigators and the sponsor (PledPharma AB/Egetis Therapeutics AB). FOLFOX6, oxaliplatin in combination with 5-fluorouracil (5-FU), possesses superior tumoricidal activity in comparison to 5-FU alone, but suffers seriously from dose-limiting platinum-associated Chemotherapy-Induced Peripheral Neuropathy (CIPN). The aim of the POLAR trials was to demonstrate that PledOx [calmangafodipir; Ca4Mn(DPDP)5] reduced the incidence of persistent CIPN from 40% to 20%. However, this assumption was based on “explorative” data in the preceding PLIANT phase II trial, which did not mirror the expected incidence of unwanted toxicity in placebo patients. In POLAR A and M, the assessment of PledOx efficacy was conducted in patients that received at least six cycles of FOLFOX6, enabling analyses of efficacy in 239 A and 88 M patients. Instead of a hypothesized improvement from 40% to 20% incidence of persistent CIPN in the PledOx group, i.e., a 50% improvement, the real outcome was the opposite, i.e., an about 50% worsening in this bothersome toxicity. Mechanisms that may explain the disastrous outcome, with a statistically significant number of patients being seriously injured after having received PledOx, indicate interactions between two redox active metal cations, Pt2+ (oxaliplatin) and Mn2+ (PledOx). A far from surprising causal relationship that escaped prior detection by the study group and the sponsor. Most importantly, recently published data (ref 1) unequivocally indicate that the PLIANT study was not suited to base clinical phase III studies on. In conclusion, the POLAR and PLIANT trials show that PledOx and related manganese-containing compounds are unsuited for co-treatment with platinum-containing compounds. For use as a therapeutic adjunct in rescue treatment, like in ischemia-reperfusion of the heart or other organs, or in acetaminophen (paracetamol)-associated liver failure, there is little or nothing speaking against the use of PledOx or other PLED compounds. However, this must be thoroughly documented in more carefully designed clinical trials.

The Damaging Outcome of the POLAR Phase III Trials Was Due to Avoidable Time-Dependent Redox Interaction between Oxaliplatin and PledOx

On 2 July 2021, highly negative results were reported from the POLAR A and M phase III trials in patients with colorectal cancer, treated with an oxaliplatin-based regimen and co-treated with calmangafodipir (CaM; PledOx^®; PledPharma AB/Egetis Therapeutics AB) or placebo. The results revealed persistent chemotherapy-induced peripheral neuropathy (CIPN) in 54.8% of the patients treated with PledOx, compared with 40.0% of the patients treated with the placebo (p < 0.05), i.e., a 37% increase in incidence of the side effect that the trial was aimed to prevent. The damaging outcome of the trials differed diametrically from an in-parallel conducted mice study and from a clinical trial with mangafodipir, the active ingredient of CaM. According to the authors of the POLAR report, the etiology of the profound increase in CIPN in the PledOx arm is unclear. However, these devastating effects are presumably explained by intravenous administrations of PledOx and oxaliplatin being too close in time and, thereby, causing unfavorable redox interactions between Mn²⁺ and Pt²⁻. In the mice study as well as in the preceding phase II clinical trial (PLIANT), PledOx was administered 10 min before the start of the oxaliplatin infusion; this was clearly an administration procedure, where the devastating interactions between PledOx and oxaliplatin could be avoided. However, when it comes to the POLAR trials, PledOx was administered, for incomprehensible reasons, “on Top of Modified FOLFOX6” at day one, i.e., after the two-hour oxaliplatin infusion instead of before oxaliplatin. This is a time point when the plasma concentration of oxaliplatin and Pt²⁺-metabolites is at its highest, and where the risk of devastating redox interactions between PledOx and oxaliplatin, in turn, is at its highest.

May Mangafodipir or Other SOD Mimetics Contribute to Better Care in COVID-19 Patients?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is characterized by massive inflammation of the arterial endothelium accompanied by vasoconstriction and widespread pulmonary micro thrombi. As a result, due to the destruction of nitric oxide (^•NO) by inflammatory superoxide (O₂^•-), pulmonary ^•NO concentration ceases, resulting in uncontrolled platelet aggregation and massive thrombosis, which kills the patients. Introducing ^•NO by inhalation (INO) may replace the loss of endothelium-derived ^•NO. The first results from clinical trials with INO in SARS-CoV-2 patients show a rapid and sustained improvement in cardiopulmonary function and decreased inflammation. An ongoing phase III study is expected to confirm the method's efficacy. INO may hence become a first line treatment in SARS-CoV-2 patients. However, due to the rapid inactivation of ^•NO by deoxyhemoglobin to nitrate, pulmonary administration of ^•NO will not protect remote organs. Another INO-related pharmacological approach to protect SARS-CoV-2 patients from developing life-threatening disease is to inhibit the O₂^•--driven destruction of ^•NO by neutralizing inflammatory O₂^•-. By making use of low molecular weight compounds that mimic the action of the enzyme manganese superoxide dismutase (MnSOD). The MnSOD mimetics of the so-called porphyrin type (e.g., AEOL 10150), salen type (e.g., EUK-8) and cyclic polyamine type (e.g., M40419, today known as GC4419 and avasopasem manganese) have all been shown to positively affect the inflammatory response in lung epithelial cells in preclinical models of chronic obstructive pulmonary disease. The Manganese diPyridoxyL EthylDiamine (MnPLED)-type mangafodipir (manganese dipyridoxyl diphosphate-MnDPDP), a magnetic resonance imaging (MRI) contrast agent that possesses MnSOD mimetic activity, has shown promising results in various forms of inflammation, in preclinical as well as clinical settings. Intravenously administration of mangafodipir will, in contrast to INO, reach remote organs and may hence become an important supplement to INO. From the authors' viewpoint, it appears logical to test mangafodipr in COVID-19 patients at risk of developing life-threatening SARS-CoV-2. Five days after submission of the current manuscript, Galera Pharmaceuticals Inc. announced the dosing of the first patient in a randomized, double-blind pilot phase II clinical trial with GC4419 for COVID-19. The study was first posted on ClinicalTrials.gov (Identifier: NCT04555096) 18 September 2020.

Mangafodipir as a cardioprotective adjunct to reperfusion therapy: a feasibility study in patients with ST-segment elevation myocardial infarction

AIMS

The aim of the present study was to examine the feasibility of applying the catalytic antioxidant mangafodipir [MnDPDP, manganese (Mn) dipyridoxyl diphosphate] as a cardioprotective adjunct to primary percutaneous coronary intervention (pPCI) in patients with ST-segment elevation (STE) myocardial infarction (STEMI). Both MnDPDP and a metabolite (Mn dipyridoxyl ethyldiamine) possess properties as mitochondrial superoxide dismutase mimetics and iron chelators, and combat oxidative stress in various tissues and conditions.

METHODS AND RESULTS

The study tested MnDPDP (n = 10) vs. saline placebo (n = 10), given as a brief intravenous (i.v.) infusion prior to balloon inflation during pPCI in patients with STEMI. Mangafodipir was well tolerated and did not affect heart rate or blood pressure. Despite longer ischaemic time (205 vs. 144 min, P = 0.019) in the MnDPDP group, plasma biomarker releases were identical for the two groups. With placebo vs. MnDPDP, mean STE resolutions were 69.8 vs. 81.9% (P = 0.224) at 6 h and 73.1 vs. 84.3% (P = 0.077) at 48 h. Cardiac magnetic resonance revealed mean infarct sizes of 32.5 vs. 26.2% (P = 0.406) and mean left ventricular (LV) ejection fractions of 41.8 vs. 47.7% (P = 0.617) with placebo vs. MnDPDP. More LV thrombi were detected in placebo hearts (5 of 8) than MnDPDP-treated hearts (1 of 10; P = 0.011).

CONCLUSIONS

Mangafodipir is a safe drug for use as an adjunct to reperfusion therapy. A tendency to benefit of MnDPDP needs confirmation in a larger population. The study revealed important information for the design of a Phase II trial.

Mangafodipir a Selective Cytoprotectant - with Special Reference to Oxaliplatin and Its Association to Chemotherapy-Induced Peripheral Neuropathy (CIPN)

Oxaliplatin, in combination with 5-fluorouracil plus folinate (or capecitabine), has increased survival substantially in stage III colorectal cancer and prolonged life in stage IV patients, but its use is compromised because of severe toxicity. Chemotherapy-induced peripheral neuropathy (CIPN) is the most problematic dose-limiting toxicity of oxaliplatin. Oncologists included for years calcium and magnesium infusion as part of clinical practice for preventing CIPN. Results from a phase III prospective study published in 2014, however, overturned this practice. No other treatments have been clinically proven to prevent this toxicity. There is a body of evidence that CIPN is caused by cellular oxidative stress. Clinical and preclinical data suggest that the manganese chelate and superoxide dismutase mimetic mangafodipir (MnDPDP) is an efficacious inhibitor of CIPN and other conditions caused by cellular oxidative stress, without interfering negatively with the tumoricidal activity of chemotherapy. MnPLED, the metabolite of MnDPDP, attacks cellular oxidative stress at several critical levels. Firstly, MnPLED catalyzes dismutation of superoxide (O₂^•−), and secondly, having a tremendous high affinity for iron (and copper), PLED binds and disarms redox active iron/copper, which is involved in several detrimental oxidative steps. A case report from 2009 and a recent feasibility study suggest that MnDPDP may prevent or even cure oxaliplatin-induced CIPN. Preliminary results from a phase II study (PLIANT) suggest efficacy also of calmangafodipir, but these results are according to available data obscured by a surprisingly low number of adverse events and a seemingly lower than expected efficacy of FOLFOX.

Cardioprotective effects of the MR contrast agent MnDPDP and its metabolite MnPLED upon reperfusion of the ischemic porcine myocardium

Purpose: To evaluate whether manganese dipyridoxyl diphosphate (MnDPDP) or its metabolite manganese dipyridoxyl ethyldiamine (MnPLED) reduces post-ischemic myocardial injury.

Material and Methods: Left anterior descending artery (LAD) in anesthetized pigs was occluded (30 min) followed by reperfusion (120 min) during hemodynamic monitoring and infarct assessment. Three μmol/kg MnDPDP, 1 μmol/kg MnPLED (or a mixture of both) or saline was injected i.v. 10 min before reperfusion followed by infusion of either 3 μmol/kg/h MnDPDP, 1 μmol/kg/h MnPLED (or a mixture of both) or saline. The plasma concentrations of MnDPDP, MnPLED and other metabolites (e.g., ZnDPDP and ZnPLED) were analyzed.

Results: Femoral blood flow was reduced by 60% during early reperfusion in controls, whereas only 23 and 31% reductions were seen in animals treated with MnDPDP and MnPLED. During that time, +LV/dP and -LV/dP (maximum rate of left ventricular isovolumic contraction and relaxation, respectively), systolic pressure and diastolic pressure fell significantly less in animals treated with MnDPDP or MnPLED. Three out of 5 control animals experienced ventricular fibrillation (VF) during reperfusion, whereas VF was not seen in any of the pigs treated with MnPLED or/and MnDPDP. The infarct sizes in saline- and MnPLED-treated animals were 39±6 and 16±5%, respectively, of the occluded areas. MnDPDP did not reduce the infarct size. A mixture of MnDPDP and MnPLED significantly reduced infarct size (10±4%). When reperfusion started and throughout reperfusion, almost all injected MnDPDP was present as Zn-metabolites.

Conclusion: MnPLED seems to reduce reperfusion-induced cardiac dysfunction and infarct size in pigs. MnDPDP does not reduce infarct size in the pig, probably because of the rapid exchange of Mn2+ for Zn2+ taking place in the pig.

Cardiovascular safety of MnDPDP and MnCl2

Purpose: To investigate the apparent discrepancy between expected basic physiological responses at the cellular level and the in vivo behaviour of both MnDPDP and MnCl2 adminstered i.v. prompted parallel investigations of these substances.

Material and Methods: Studies were performed in isolated perfused rat hearts, isolated bovine mesenteric arteries, conscious dogs, and dogs with acute ischaemic heart failure.

Results: These studies confirmed that Mn++ at high concentrations acted as a calcium antagonist inducing negative inotropy. Mn++ at low concentrations was an effective su-peroxide scavenger, conserving nitric oxide and facilitating vasodilation. Mn++ maintained or elevated heart rate (HR) and blood pressure (BP), and did not worsen existing cardiac failure. MnDPDP was about 10 times less potent than MnCl2 in eliciting these cardiovascular responses.

Conclusion: The ex vivo properties of Mn++, inducing vasodilation and negative inotropy, are counter-balanced in vivo through the action of 2 mechanisms: extensive plasma protein binding reducing active M++, and the release of catecholamines which maintain or even raise HR and BP. Taken together with pharmacokinetic factors, including maximal plasma concentrations in humans given the recommended 5 μmol/kg dose, it is concluded that MnDPDP in normal clinical use represents no safety risk to the cardiovascular system.

Calmangafodipir [Ca4Mn(DPDP)5], mangafodipir (MnDPDP) and MnPLED with special reference to their SOD mimetic and therapeutic properties

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) participate in pathological tissue damage. Mitochondrial manganese superoxide dismutase (MnSOD) normally keeps ROS and RNS in check. During development of mangafodipir (MnDPDP) as a magnetic resonance imaging (MRI) contrast agent, it was discovered that MnDPDP and its metabolite manganese pyridoxyl ethyldiamine (MnPLED) possessed SOD mimetic activity. MnDPDP has been tested as a chemotherapy adjunct in cancer patients and as an adjunct to percutaneous coronary intervention in patients with myocardial infarctions, with promising results. Whereas MRI contrast depends on release of Mn(2+), the SOD mimetic activity depends on Mn(2+) that remains bound to DPDP or PLED. Calmangafodipir [Ca4Mn(DPDP)5] is stabilized with respect to Mn(2+) and has superior therapeutic activity. Ca4Mn(DPDP)5 is presently being explored as a chemotherapy adjunct in a clinical multicenter Phase II study in patients with metastatic colorectal cancer.

Oxidative Stress and Myocardial Damage during Elective Percutaneous Coronary Interventions and Coronary AngiographyA Comparison of Blood-borne Isoprostane and Troponin Release

The role of oxidative stress in clinical cardiology is still controversial. The aims of the present study were to examine if minor ischaemic episodes as may occur during elective percutaneous coronary intervention (PCI) induce oxidative stress and, eventually, if oxygen stress correlates with myocardial injury. Thirty eight and nine patients underwent PCI and diagnostic coronary angiography, respectively. Peripheral blood was sampled at different time points for plasma analyses of: 8-iso-PGF2alpha (free radical-mediated oxidative stress); 15-keto-dihydro-PGF2alpha (cyclooxygenase-mediated inflammation); troponin-T (myocardial injury); hsCRP, vitamin A and vitamin E; and, total antioxidants status (TAS). In both groups 8-iso-PGF2alpha increased transiently by approximately 80% (p < 0.001) during the procedure. There was a minor troponin-T release (p < 0.001) after PCI, but no correlation with 8-iso-PGF2alpha. Troponin-T did not increase after angiography. 15-keto-dihydro-PGF2alpha decreased by 50% after ended procedure, but increased by 100% after 24 h compared to baseline. hsCRP increased significantly (p < 0.001) from baseline to the next day in the PCI-group, but not in the angiography group. Vitamins and TAS decreased slightly after the procedures. It is concluded that a moderate oxidative stress was induced by both elective PCI and coronary angiography but that no correlation was found between oxidative stress and myocardial injury in this setting. This indicates that other mechanisms than ischaemia-reperfusion episodes caused an elevation in plasma isoprostane such like the injury at a vascular site mutual for both procedures. A secondary finding from the study was elevated markers of early inflammatory response, not only after PCI, but also after angiography.

The effect of glucagon on plasma cyclic AMP and glucose concentrations in patients with alcoholic cirrhosis

Glucagon was infused intravenously into four patients with alcoholic cirrhosis and five healthy subjects and serial measurements were made of plasma cyclic AMP and glucose concentrations. The results in the cirrhotic patients did not differ significantly from those in healthy subjects.

Dynamic water changes in excised rat myocardium assessed by continuous distribution of T1 and T2

Ischemic changes in excised rat myocardium were followed by series of T1 or T2 measurements from 1 to 60 min after isolated perfusion cessation, and the influence of manganese enhancement was investigated. An inverse Laplace transformation (ILT) of T1 or T2 data was used to resolve the number, time constants, and fractions of tissue water components in a continuous distribution. For T1 distributions, one single tissue component approximately 900 ms was significantly shortened and dispersed by manganese enhancement (25 and 200 microM MnCl2). For T2 distributions, three tissue components (approximately 30, approximately 100, and approximately 350 ms) were obtained initially. The two shortest components merged after approximately 10 min to one component (approximately 40 ms). Both T1 and T2 tissue components became shorter with time. In particular, the T2 distribution dynamics might be compatible with complex sequential changes in tissue water fractions during ischemia.

Post-ischaemic restituted intestinal mucosa is more resistant to further ischaemia than normal mucosa in the pig

OBJECTIVE

Ischaemic preconditioning may protect the intestine from subsequent prolonged ischaemia. This study evaluates whether a much longer initial ischaemia, encountered clinically, may modify intestinal resistance to further ischaemia in a pig model.

MATERIAL AND METHODS

After cross-clamping of the superior mesenteric artery for 1 h, the intestine was either reperfused for 8 h or a second cross-clamping for 1 h was performed at 4 h of reperfusion. Based on microarray analysis of intestinal samples at 1, 4 and 8 h of reperfusion, mRNA of selected genes was measured with QRT-PCR.

RESULTS

The first ischaemic period caused exfoliation of surface epithelial cells from the basement membrane comprising about 90 % of the villi tips, a marked increase in permeability and depletion of ATP. The second ischaemic challenge caused about 30 % less denudation of the basement membrane (p = 0.008), no increase in permeability (p = 0.008) and less depletion of ATP (p = 0.039). mRNAs for superoxide dismutase 2, heat shock proteins and signal transducer and activator of transcription 3, which may protect against ischaemia/reperfusion injury, were up-regulated throughout the reperfusion period. mRNAs for matrix metalloproteinase 1, connexin 43 and peripheral myelin 22, which may be associated with cell migration or tight junctions, showed a particular up-regulation at 4 h of reperfusion.

CONCLUSION

One hour of initial ischaemia followed by 4 h of reperfusion is associated with increased intestinal resistance to further ischaemia. The differential regulation of genes identified in this study provides working hypotheses for mechanisms behind this observation.

Oxidative stress during coronary artery bypass operations: importance of surgical trauma and drug treatment

OBJECTIVE

To investigate oxidative stress and myocardial injury at different stages of coronary artery bypass grafting (CABG).

DESIGN

Twenty patients underwent CABG with use of cardiopulmonary bypass (CPB) and with intermittent sampling of plasma and urine. Main markers were: 8-iso-PGF2alpha (oxidative stress); troponin T (myocardial injury); and 15-keto-dihydro-PGF2alpha and hsCRP (inflammation).

RESULTS

Plasma 8-iso-PGF2alpha increased after start of surgery, but there was no further rise during CPB or after aortic cross-clamp release and no significant myocardial arterio-venous differences. An increase in troponin T was seen early after the operation, but no relationship was established between 8-iso-PGF2alpha and troponin T. 8-iso-PGF2alpha levels were elevated by preoperative withdrawal of acetylsalicylic acid (ASA) but reduced by intraoperative use of heparin. 15-keto-dihydro-PGF2alpha was elevated during operation and hsCRP following operation.

CONCLUSIONS

In the present study oxidative stress was multifactorial in origin with main impacts from surgical trauma, less from CPB and little if any from myocardial ischemia-reperfusion events. In addition, cardiovascular drugs in common use like ASA and heparin seemed to influence the pro- and antioxidant balance, a finding that has to be confirmed in future studies.

An apparent unidirectional influx constant for manganese as a measure of myocardial calcium channel activity

PURPOSE

To develop an in vivo MR method for evaluation of myocardial calcium channel activity through quantification of apparent unidirectional manganese influx constants following manganese dipyridoxyl-diphosphate (MnDPDP) infusions.

MATERIALS AND METHODS

A total of 10 healthy volunteers were divided in two groups, and received 5 micromol of MnDPDP per kg of body weight intravenously in a 1.5 Tesla scanner over five or 30 minutes, respectively. A fast inversion recovery gradient echo sequence was used to estimate pre- and postcontrast R1 values and to measure signal changes following infusions. By assuming equal longitudinal relaxivity (r1) of the contrast in all tissue compartments, signal changes in blood and myocardial tissue yielded temporal input and tissue contrast concentrations respectively. Through a two-tissue compartment model, apparent unidirectional influx constants (Ki) for myocardial manganese accumulation were estimated.

RESULTS

Consistent values for Ki in left ventricular wall were found, with a mean value of 5.96 mL/100 g/minute (SD=0.49; N=10). No statistical significant differences in Ki were found between the two infusion groups.

CONCLUSION

Since unidirectional manganese accumulation depends upon intact myocyte membranes with functioning calcium channels, the use of unidirectional manganese influx rates may be a valuable research tool for in vivo studies of myocyte functioning in myocardial disease.

Manganese dipyridoxyl-diphosphate (MnDPDP) as a viability marker in patients with myocardial infarction

PURPOSE

To evaluate contrast accumulation in left ventricular (LV) myocardium after manganese dipyridoxyl-diphosphate (MnDPDP) administration in patients with recent first time myocardial infarction.

MATERIALS AND METHODS

MnDPDP (5 micromol/kg) was administered to 10 patients with recent myocardial infarction (three to 12 weeks). One slice of interest (SOI) likely to traverse the infarction was chosen, and sectorial pre- and postcontrast longitudinal relaxivity rates (R(1)) and signal changes during infusion were estimated with a fast gradient echo sequence. LV volume and wall thickening were measured in short-axis cine recordings. Infarct localization from R(1) and wall thickening data were compared by vector analyses.

RESULTS

Reduced wall thickening was associated with reduced precontrast R(1) and reduced contrast enhancement. Both remote and infarcted regions showed rapid initial contrast accumulation. In remote regions, this was followed by a continuing slow increase. Mean precontrast R(1) was 0.87 +/- 0.06 second(-1) in infarcted regions and 0.96 +/- 0.03 second(-1) in remote regions (P < 0.001). Mean R(1) change over one hour was 0.24 +/- 0.07 second(-1) in infarcted regions and 0.38 +/- 0.03 second(-1) in remote regions (P < 0.0001).

CONCLUSION

Remote regions showed larger increases in R(1) than infarcted regions. This is most likely due to selective and slow Mn accumulation in viable myocytes.

Analyzing equilibrium water exchange between myocardial tissue compartments using dynamical two-dimensional correlation experiments combined with manganese-enhanced relaxography

Water compartments were identified and equilibrium water exchange was studied in excised rat myocardium enriched with intracellular manganese (Mn(2+)). Standard relaxographic measurements were supplemented with diffusion-T(2) and T(1)-T(2) correlation measurements. In nonenriched myocardium, one T(1) component (800 ms) and three T(2) components (32, 120, and 350 ms) were identified. The correlation measurements revealed fast- and slow-diffusing water fractions with mean diffusion coefficients of 1.2 x 10(-5) and 3.0 x 10(-5) cm(2) s(-1). The two shortest T(2) components, which had different diffusivities, both originated from water in intracellular compartments. A component with longer relaxation time (T(1) approximately equal 2200 ms; T(2) approximately equal 1200 ms), originating from extra-tissue water, was also observed. The presence of this component may lead to erroneous estimations of water exchange rates from multiexponential relaxographic analyses of excised tissues. The tissue T(1) value is strongly reduced with increasing enrichment of Mn(2+), and eventually a second tissue T(1) component emerges, indicating a shift in the equilibrium water exchange between intra- and extracellular compartments from the fast-exchange limit to the slow-exchange regime. Using a two-site water exchange analysis, the lifetime of intracellular water, T(ic), was found to be 475 ms, with a fraction, p(ic), of 0.71.

Oxidative stress and inflammatory response during and following coronary interventions for acute myocardial infarction

BACKGROUND

In acute myocardial infarction (AMI) treated with percutaneous coronary intervention (PCI), myocardial injury results from complex processes during both ischemia and reperfusion. Release of reactive oxygen species (ROS) may contribute to the accumulated myocardial damage.

AIMS

To examine by frequent sampling of peripheral blood oxidative stress and early inflammation in patients undergoing primary PCI for AMI. Secondly, to assess whether a correlation exists between these parameters and the extent of myocardial damage.

METHODS

Sixteen patients undergoing primary PCI within 6 h of AMI onset were included. Peripheral blood was sampled at start of procedure (t0) and repeatedly over 24 h following reperfusion. Main plasma analyses were: 8-iso-PGF2alpha (oxidative stress), 15-keto-dihydro-PGF2alpha (cyclooxygenase-mediated inflammation); and troponin-T (myocardial injury). Additional analyses included: total antioxidant status (TAS); vitamins; hsCRP and lipids.

RESULTS

8-Iso-PGF2alpha increased following restoration of blood flow, returned to t0 values after 3 h and was reduced below t0 the following day. TAS decreased significantly from t0 to the next day. There was no significant correlation between 8-iso-PGF2alpha and troponin T values. 15-Keto-dihydro-PGF2alpha was elevated during the first hour. There was a major rise in hsCRP after 24 h.

CONCLUSION

Following reperfusion by primary PCI in AMI, oxidative stress and an inflammatory response are induced immediately. A rise in 8-iso-PGF2a during ischemia indicate that ROS generation may also take place during severely reduced coronary blood flow and hypoxia. No direct relationship between 8-iso-PGF2alpha or 15-keto-dihydro-PGF2alpha and troponin T was evident. The present study adds to the increasingly complex pathophysiological roles of ROS acting both as signal molecules and as mediators of tissue injury.

Manganese-calcium interactions with contrast media for cardiac magnetic resonance imaging: a study of manganese chloride supplemented with calcium gluconate in isolated Guinea pig hearts

OBJECTIVES

Manganese ions (Mn) enter cardiomyocytes via calcium (Ca) channels and enhance relaxation intracellularly. To prevent negative inotropy, new Mn-releasing contrast agents have been supplemented with high Ca. The study aim was to investigate how this affects cardiac function and magnetic resonance efficacy.

MATERIALS AND METHODS

MnCl2 based contrast agents, manganese and manganese-calcium (Ca:Mn 10:1), were infused during 4 repeated washin-washout sequences in perfused guinea pig hearts. [Mn] were 10, 50, 100 and 500 microM.

RESULTS

During washin, manganese depressed left ventricular developed pressure (LVDP) by 4, 9, 17, and 53% whereas manganese-calcium increased LVDP by 13, 18, 25, and 56%. After experiments, tissue Mn contents (nmol/g dry wt) were control <40, manganese 3720, and manganese-calcium 1620. T1 was reduced by 85-92% in Mn-enriched hearts.

CONCLUSIONS

High Ca supplements to Mn-releasing contrast agents may be counterproductive by inducing a strong positive inotropic response and by reducing the magnetic resonance efficacy.

Gut luminal microdialysis of glycerol as a marker of intestinal ischemic injury and recovery

OBJECTIVE

To evaluate microdialysis as a method to assess different degrees of intestinal damage and recovery during ischemia and reperfusion; to evaluate information obtained from microdialysis catheters in the peritoneum, the gut wall, and the gut lumen.

DESIGN

Randomized, controlled animal experiment.

SETTING

University laboratory animal center.

SUBJECTS

Twenty-seven domestic pigs.

INTERVENTIONS

The superior mesenteric artery was cross-clamped for 60 mins (n = 14) or 120 mins (n = 10) followed by 2 or 4 hrs of reperfusion. Three pigs served as controls.

MEASUREMENTS AND MAIN RESULTS

Intestinal mucosal integrity was assessed by morphometry, adenosine triphosphate in the gut wall, and permeability of C-polyethylene glycol. Lactate, glycerol, pyruvate, and glucose were measured by microdialysis. Changes in adenosine triphosphate, permeability, or lactate did not correlate to different extents of intestinal damage caused by 60 or 120 mins of ischemia. During the reperfusion period, pigs with 60 mins of intestinal ischemia showed a faster recovery of these variables than pigs with 120 mins of intestinal ischemia. Glycerol increased with increasing duration of the ischemic insult. After 60 mins of intestinal ischemia, glycerol in the gut lumen decreased toward baseline but remained high after 120 mins of intestinal ischemia. There was a good correlation between gut luminal glycerol and recovery of mucosal damage throughout the reperfusion period. In the peritoneal cavity, both glycerol and lactate decreased to baseline relatively shortly after onset of reperfusion independent of the duration of intestinal ischemia.

CONCLUSIONS

Microdialysis of glycerol provides information about the extent and severity of intestinal damage after ischemia and about the ensuing recovery. The gut lumen is to be preferred as a site for placement of microdialysis catheters.

Iodinated radiographic contrast media possess antioxidant properties in vitro

PURPOSE

To study potential properties of iodinated radiographic contrast media (IRCM) for intravascular use in in vitro free radical generating reactions.

MATERIAL AND METHODS

Superoxide (*O2-) and hydroxyl (*OH) radicals were generated in xanthine oxidase and Fenton reactions. *O2- was assayed by the nitroblue tetrazolium (NBT) method, whereas *OH was assayed by an aromatic hydroxylation (2-hydroxybenzoic acid) method. Total antioxidant status (TAS) of test substances was determined by a colorimetric assay. Finally, acetyl-cholinesterase (AChE) activity was measured in the absence and presence of IRCM.

RESULTS

High concentrations (>50 mM) of IRCM inhibited *O2- production, ionic more than non-ionic IRCM. Medium concentrations (25-50 mM) of IRCM reduced *OH production, and both types of IRCM were equally potent. Low concentrations (<25 mM) of non-ionic IRCM displayed higher antioxidant capacity than their ionic counterparts when tested in the TAS assay. Visipaque 320 (iodixanol) was found to have the highest TAS value, followed by Omnipaque 350 (iohexol), Hexabrix 320 (ioxaglate), and Urografin 370 (diatrizoate).

CONCLUSION

IRCM have in vitro antioxidant properties in concentrations relevant for their clinical application. These properties may therefore be of potential importance when evaluating IRCM effects in vivo, particularly those concerning cardiovascular and renal function.

Determination of water compartments in rat myocardium using combined D-T1 and T1-T2 experiments

We have used combined D-T1 and T1-T2 correlation experiments to explore water compartments in rat heart tissue (myocardium). The results show that two main compartments can be identified, which we assign to extracellular (ec) and intracellular (ic) water. The exchange rate of water across the cell membrane was found to be on the order of 0.1 Hz. In addition, the T1-T2 correlation measurements indicate that the ic compartment contain two T2 populations.

Relaxation enhancing properties of MnDPDP in human myocardium

PURPOSE

To assess magnitude and duration of changes in myocardial longitudinal relaxation rate (R1) in humans following infusion of the manganese (Mn) releasing contrast agent MnDPDP (Mn-dipyridoxyl-diphosphate).

MATERIALS AND METHODS

Fifteen healthy volunteers were divided into three groups. After initial myocardial and liver R1 measurements using an inversion recovery (IR) turbo fast low-angle shot (FLASH) sequence at 1.5 Tesla, the groups were given different doses of intravenous MnDPDP: 5, 10 and 15 micromol/kg body weight, respectively, over 30 minutes. R1 measurements were then repeated at 1, 2, 4, 8, and 24 hours after the infusion ended.

RESULTS

The left ventricular wall R1 prevalue was 0.98 second(-1) (+/-0.04). R1 increased on average (all 15 subjects) 0.41 second(-1) (+/-0.09). The increase was present one hour after the end of the infusion, remained relatively constant the next two hours, and then declined gradually. After 24 hours, there was still a moderate R1 elevation present, with an average R1-value of 1.16 (+/-0.05). There were only small differences in myocardial R1 responses between the three doses investigated, which was contrasted by a marked dose-response in liver tissue.

CONCLUSION

MnDPDP gave a significant and prolonged rise in myocardial R1 even at a dose of 5 micromol/kg. The R1-values in the myocardium did not increase linearly with higher doses.

Intracellular manganese ions provide strongT1relaxation in rat myocardium

The efficacy of manganese ions (Mn2+) as intracellular (ic) contrast agents was assessed in rat myocardium. T1 and T2 and Mn content were measured in ventricular tissue excised from isolated perfused hearts in which a 5-min wash-in with 0, 30, 100, 300, or 1000 microM of Mn dipyridoxyl diphosphate (MnDPDP) was followed by a 15-min wash-out to remove extracellular (ec) Mn2+. An inversion recovery (IR) analysis at 20 MHz revealed two T1 components: an ic and short T1-1 (650-251 ms), and an ec and longer T1-2 (2712-1042 ms). Intensities were about 68% and 32%, respectively. Tissue Mn content correlated particularly well with ic R1-1. A two-site water-exchange analysis of T1 data documented slow water exchange with ic and ec lifetimes of 11.3 s and 7.5 s, respectively, and no differences between apparent and intrinsic relaxation parameters. Ic relaxivity induced by Mn2+ ions in ic water was as high as 56 (s mM)(-1), about 8 times and 36 times higher than with Mn2+ aqua ions and MnDPDP, respectively, in vitro. This value is as high as any reported to date for any synthetic protein-bound metal chelate. The increased rotational correlation time (tauR) between proton and electron (Mn2+) spins, and maintained inner-sphere water access, might make ic Mn2+ ions and Mn2+ -ion-releasing contrast media surprisingly effective for T1-weighted imaging.

Intestinal injury after thoracic aortic cross-clamping in the pig

BACKGROUND

The mucosal surface epithelium is an essential part of the functional intestinal barrier, but its structural response to ischemia/reperfusion is only partly characterized. The purpose of this study was to provide a detailed morphological evaluation of intestinal surface epithelium after aortic cross-clamping.

MATERIAL AND METHODS

Pigs were subjected to thoracic aortic cross-clamping for 60 min and subsequent reperfusion for 120 min. Tissue blood flow and high-energy phosphates were measured with microspheres and HPLC, respectively. Urinary excretion of (14)C polyethylene glycol (MW 4000 Da) (PEG-4000), loaded into an intestinal loop, provided an index of intestinal permeability.

RESULTS

Jejunal blood flow was restored at 10 min after aortic declamping. Denudation of the basement membrane of the intestinal villi tips, as a consequence of epithelial shedding, increased markedly during the initial 60 min of reperfusion (P = 0.002). During the following 45 min, the denuded basement membrane was partly covered with low cuboidal and squamous-shaped cells extending lamellipodia over a wavy basement membrane. Restoration of ATP at 60 min after aortic declamping correlated inversely to the extent of denuded basement membrane (r = 0.75, P = 0.032). Permeability of PEG-4000 increased markedly after aortic declamping and was linearly correlated to the area of denuded basement membrane (r = 0.87, P = 0.01).

CONCLUSIONS

Reperfusion for 2 h after aortic cross-clamping is associated with initial aggravation of ischemia-induced injury in the porcine jejunum, but thereafter with restitution of the surface epithelium. Restoration of ATP may be important to avoid intestinal injury after ischemia. Increased permeability of a macromolecule in response to reperfusion is closely correlated to injury of the surface epithelium.

Identification and regulation of the gastric H+/K+-ATPase in the rat heart

Previous reports indicate that H+/K+-adenosine triphosphatase (ATPase) might be expressed in the heart.

AIMS

The objectives of the present study were to explore the presence of H+/K+-ATPase protein and gene expression in the rat heart and to investigate whether the enzyme could contribute to potassium transport across the sarcolemma.

METHODS AND RESULTS

We performed reverse transcription-polymerase chain reaction (RT-PCR) on mRNA from myocardium and isolated cardiomyocytes using primers specific for the gastric H+/K+-ATPase alpha-subunit. The PCR products were sequenced and the predicted gastric H+/K+-ATPase sequence was verified. Western blots from myocardium detected a 34-kDa band and a 94-kDa band, indicating the beta-subunit and alpha-subunit of the gastric H+/K+-ATPase, respectively. Immunocytochemistry detected significant immunoreactivity of the beta-subunit in cardiomyocytes. H+/K+-ATPase-dependent potassium transport was assessed by 86Rb+-uptake in isolated cardiomyocytes. Both ouabain and the selective H+/K+-ATPase inhibitor Schering 28080 reduced 86Rb+-uptake at maximum specific inhibition, by 70 and 25%, respectively; the effects were additive. Competitive RT-PCR analysis indicated a significant upregulation of the myocardial H+/K+-ATPase in heart failure after myocardial infarction.

CONCLUSION

The gastric isoform of H+/K+-ATPase is expressed in rat cardiac myocytes, both at transcript and protein levels. Functional studies indicate that the enzyme could contribute to potassium and pHi regulation in cardiomyocytes.

Manganese ions as intracellular contrast agents: proton relaxation and calcium interactions in rat myocardium

Paramagnetic manganese (Mn) ions (Mn(2+)) are taken up into cardiomyocytes where they are retained for hours. Mn content and relaxation parameters, T(1) and T(2), were measured in right plus left ventricular myocardium excised from isolated perfused rat hearts. In the experiments 5 min wash-in of MnCl(2) were followed by 15 min wash-out to remove extracellular (ec) Mn(2+) MnCl(2), 25 and 100 micro M, elevated tissue Mn content to six and 12 times the level of control (0 micro M MnCl(2)). Variations in perfusate calcium (Ca(2+)) during wash-in of MnCl(2) and experiments including nifedipine showed that myocardial slow Ca(2+) channels are the main pathway for Mn(2+) uptake and that Mn(2+) acts as a pure Ca(2+) competitor and a preferred substrate for slow Ca(2+) channel entry. Inversion recovery analysis at 20 MHz revealed two components for longitudinal relaxation: a short T(1 - 1) and a longer T(1 - 2). Approximate values for control and Mn-treated hearts were in the range 600-125 ms for T(1 - 1) and 2200-750 ms for T(1 - 2). The population fractions were about 59 and 41% for the short and the long component, respectively. The intracellular (ic) R(1 - 1) and R(2 - 1) correlated best with tissue Mn content. Applying two-site exchange analyses on the obtained T(1) data yielded results in parallel to, but also differing from, results reported with an ec contrast agent. The calculated lifetime of ic water (tau(ic)) of about 10 s is compatible with a slow water exchange in the present excised cardiac tissue. The longitudinal relaxivity of Mn ions in ic water [60 (s mM)(-1)] was about one order of magnitude higher than that of MnCl(2) in water in vitro [6.9 (s mM)(-1)], indicating that ic Mn-protein binding is an important potentiating factor in relaxation enhancement.

Protective effects of repetitive injections of radiographic contrast media on the subsequent tolerance to ischemia in the isolated rat heart

PURPOSE

Despite detailed knowledge of the effects of X-ray contrast media on cardiac function, no studies have examined the effect of contrast media injections on the subsequent tolerance to ischemia in the heart.

METHODS

Isolated perfused rat hearts were exposed to repetitive injections of iohexol, iodixanol, or ioxaglate before 30 min of global ischemia and 120 min of reperfusion. These groups were compared with control (no pretreatment) and ischemic preconditioning known to reduce infarct size. Physiologic variables and infarct size were measured

RESULTS

Pretreatment with iodixanol reduced infarct size significantly compared with control and thus afforded protection against ischemia. Injections with iohexol and ioxaglate reduced infarct size, although not significantly, compared with control.

CONCLUSION

Pretreatment of the isolated rat heart with commonly used contrast media enhances the cardiac tolerance to subsequent ischemia. The mechanism behind this protective effect could not be determined, but could involve stretching of the heart and/or generation of nitric oxide.

Hyperosmotic perfusion of the beating rat heart and the role of the Na+/K+/2Cl- co-transporter and the Na+/H+ exchanger

The aim of the present study was to investigate the role of the Na+/K+/2Cl- co-transporter and the Na+/H+ exchanger on contractile function and electrolyte regulation during hyperosmotic perfusion of the heart. Langendorff perfused rat hearts were subjected to hyperosmolal perfusion in 10-min intervals. Perfusates were made hyperosmotic by adding mannitol to the buffer (370, 450 and 600 mOsmol/kg H2O). Cardiac contractile function was monitored with a balloon in the left ventricle (LV) coupled to a pressure transducer. Cardiac effluent was sampled repeatedly throughout and after hyperosmotic perfusion and analysed for content of Na+, K+, and Cl-. All three hyperosmotic perfusates initially reduced LV developed pressure (LVDP), but for 370 and 450 mOsmol/kg H2O, LVDP recovered to baseline within 4 min of perfusion. With 600 mOsmol/kg H2O, LVDP recovered slowly and was 50% below baseline after 10 min of hyperosmotic perfusion. Inhibition of the Na+/H+ exchanger with 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and 3-methylsulfonyl-4-piperidinobenzoyl-guanidine methanesulfonate (HOE 694) abolished the recovery of LVDP to the 600 mOsmol/kg H2O perfusate, whereas inhibition of the Na+/K+/2Cl- co-transporter had no impact on LVDP. Potassium was taken up by the heart during hyperosmotic perfusion and this uptake was significantly reduced with inhibition of the Na+/H+ exchanger. Intracellular pH was assessed with 31p magnetic resonance spectroscopy and hyperosmolality induced a significant alkalosis that was dependent upon the Na+/H+ exchanger. The rat heart responds to moderate elevations in osmolality with a transient reduction in contractile function, whereas an elevation of 300 mOsmol/kg H2O persistently reduces contractile function. The Na+/H+ exchanger, but not the Na+/K+/2Cl- co-transporter, is of importance in contractile recovery and electrolyte regulation during hyperosmotic perfusion in the rat heart.

Hyperosmotic pretreatment reduces infarct size in the rat heart

Preconditioning of the heart can be achieved by an ischemia/reperfusion stimulus, but also by stretching of the heart by an acute volume overload. Since manipulations of the extracellular osmolality affects cell size, we hypothesized that hyperosmotic pretreatment of the isolated perfused rat heart could reduce infarct size following regional ischemia (RI). Langendorff perfused rat hearts were subjected to 30 min RI by ligature of the main branch of the left coronary artery followed by 120 min reperfusion (control group). Ischemic preconditioning (IP-5') was achieved by 5 min total global ischemia and 5 min reperfusion prior to RI. Hyperosmotic pretreatment was accomplished by perfusion with a hyperosmotic buffer (600 mOsm/kg H2O by adding mannitol) for 1 min, 2 min or 5 min. At the end of the experiments, the hearts were cut into 2 mm slices, incubated with triphenyltetrazoliumchloride before scanning and computerized for estimation of infarct size. The average infarct size (as percentage of area at risk) in the control group was 42% and was significantly reduced to 16% by ischemic preconditioning and to 17% by 2 min hyperosmotic pretreatment. Neither 1 min nor 5 min hyperosmotic pretreatment reduced infarct size as compared to the controls. The infarct reducing effect of 2 min hyperosmotic pretreatment was not blunted by inhibition of protein kinase C (chelerytrine chloride), the Na+/H+-exchanger (HOE 694) or stretch-activated anion channels (gadolinium chloride). The results indicate that short-lasting hyperosmotic perturbations of the extracellular environment may precondition the heart to a subsequent ischemic insult.

Beta-adrenergic signalling and threshold adrenaline concentration for induction of fibrillation in the perfused heart pretreated with antihypertensive drugs

Recent investigations have shown that antihypertensive drug treatment leads to enhanced myocardial beta-adrenoceptor sensitivity. This study was therefore conducted to establish whether or not such hypersensitivity might trigger myocardial arrhythmia subsequent to adrenaline exposure. Adult male Wistar rats (n = 6 per group) were treated with either placebo (vehicle), metoprolol (2.40 mg.kg-1.day-1), timolol (0.075 mg.kg-1.day-1), verapamil (5.50 mg.kg-1.day-1) or enalapril (0.50 mg.kg-1.day-1) for 20 consecutive days. Hearts were excised and perfused ad modum Langendorff in the presence of an adrenaline gradient (0-300 nM) for 20 min with either 3.0 mM or 5.9 mM of potassium in the perfusion buffer. Adrenaline threshold concentration (ATC, nanomolar) at myocardial fibrillation was recorded, as well as tissue cAMP contents, beta-adrenoceptor number, G-protein levels and signalling effector enzyme activities. The main findings were: (1) ATC and cAMP levels were affected in hearts perfused with low-concentration potassium buffer only. In terms of ATC, the beneficial effect of each drug regimen appeared to be in the rank order of: placebo = enalapril > verapamil > timolol > metoprolol. There was an inverse correlation between ATC and myocardial cAMP contents at the start of fibrillation; (2) Subsequent to fibrillation, beta-adrenoceptor number, hormone-elicited adenylate cyclase activities and Gs alpha:Gi2 alpha-ratio were no different from preperfusion values; (3) Significant inverse correlations between beta 1-adrenoceptor numbers and ATC were observed. We conclude that alterations in beta-adrenoceptor number, G proteins and cAMP induced by antihypertensive drugs are predictive of the myocardial sensitivity to adrenaline in terms of time to continuous and irrevocable fibrillation.

Myocardial manganese elevation and proton relaxivity enhancement with manganese dipyridoxyl diphosphate. Ex vivo assessments in normally perfused and ischemic guinea pig hearts

Manganese (Mn) dipyridoxyl diphosphate (MnDPDP) is the active component of a contrast medium for liver MRI. By being metabolized, MnDPDP releases Mn(2+), which is taken up and retained in hepatocytes. The study examined whether MnDPDP elevates Mn content and enhances proton relaxivity in normal myocardium, but not in ischemic myocardium with reduced coronary flow and impaired metabolism. Isolated guinea pig hearts were perfused at normal flow or low flow, inducing global subtotal ischemia. Ventricular ATP and Mn contents, T(1) and T(2) were measured. At normal flow tissue Mn content increased from the control level of 4.1 to 70.4 micromol/100g dry wt with MnDPDP (3000 microM), while low-flow perfusion with MnDPDP (3000 microM) resulted in a Mn content of 16.6 micromol/100 g dry wt. Prolonged ischemia (35 and 90 min) reduced tissue Mn down to the control level. T(1) shortening closely paralleled myocardial Mn elevations during both normal and low-flow perfusion. The use of a Mn(2+)-releasing contrast agent like MnDPDP may be a promising principle in MRI assessments of myocardial function and viability in coronary heart disease by revealing a differential pattern of changes in T(1) relative to coronary flow, cell Mn uptake and retention, ion channel function and metabolism.

Effect of magnesium infusion on bleeding time in healthy male volunteers

Intravenous magnesium has proved to be valuable in the treatment of cardiac arrhythmias and eclampsia, but the specific mode of action is not established. In this study the effect of magnesium sulphate (MgSO4) infusion on bleeding time and endogenous prostacyclin (PGI2) production in healthy male volunteers was investigated. Thirty-five males (age 18-30 years) randomized in a double-blind, placebo-controlled, cross-over study were investigated. MgSO4 was given as a bolus (8 mmol, 12 min) followed by continuous infusion (8 mmol in 108 ml saline, 120 min). Control was equal volumes of physiological saline. Heart rate, blood pressure and bleeding time (according to Ivy) were recorded as well as blood concentrations of magnesium and creatinine. Urine PGI2 was analysed as the stable metabolite 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha). Treatment with MgSO4 did not affect bleeding time (MgSO4; 8.4+/-3.5 vs. control 8.0+/-2.7 min) nor the production of PGI2 (MgSO4; 1.2 microg 6-keto-PGF1alpha/g creatinine vs. control; 1.1 microg 6-keto-PGF1alpha/g creatinine). Intravenous infusion of MgSO4 does not affect the PGI2/platelet axis in healthy male volunteers. Studies in patients with endothelium dysfunction and/or concomitant drug therapy are required before the anti-thrombogenic effect of MgSO4 in vivo is discarded.

Elevated levels of endogenous adenosine alter metabolism and enhance reduction in contractile function during low-flow ischemia: associated changes in expression of Ca(2+)-ATPase and phospholamban

Adenosine has several potentially cardioprotective effects including vasodilatation, reduction in heart rate and alterations in metabolism. Adenosine inhibits catecholamine-induced increase in contractile function mainly through inhibition of phosphorylation of phospholamban (PLB), the main regulatory protein of Ca(2+)-ATPase in sarcoplasmic reticulum (SR), and during ischemia it reduces calcium (Ca2+) overload. In this study we examined the effects of endogenous adenosine on contractile function and metabolism during low-flow ischemia (LFI) and investigated whether endogenous adenosine can alter expression of the Ca(2+)-ATPase/PLB-system and other Ca(2+)-regulatory proteins. Isolated blood-perfused piglet hearts underwent 120 min 10% flow. Hearts were treated with either saline, the adenosine receptor blocker (8)-sulfophenyl theophylline (8SPT, 300 micromol/l) or the nucleoside transport inhibitor draflazine (1 micromol/l). During LFI, 8SPT did not substantially influence metabolic or functional responses. However, draflazine enhanced the reduction in heart rate, contractile force and MVO(2), with less release of H+ and CO2. Before LFI there were no significant differences between groups for any of the proteins (Ca(2+)-ATPase, ryanodine-receptor, Na+/K(+)-ATPase) or mRNAs (Ca(2+)-ATPase, PLB, calsequestrin, Na+/Ca(2+)-exchanger) measured. At end of LFI mRNA-level of PLB was higher in draflazine-treated hearts compared to both other groups (P<0.01 vs both). Also, at end of LFI protein-level of Ca(2+)-ATPase was lower in draflazine-treated hearts (P<0.05 vs both), and a parallel trend towards a lower mRNA-level was seen (P=0.11 vs saline and P=0.43 vs 8SPT). During LFI tissue Ca2+ tended to rise in saline- and 8SPT-treated hearts but not in draflazine-treated hearts (at end of LFI, P=0.01 vs 8SPT). We conclude that the amount of adenosine normally produced during LFI does not substantially influence function and metabolism. However, increased endogenous levels by draflazine enhance downregulation of function and reduce signs of anaerobic metabolism. At end of LFI associated changes in expression of PLB and Ca(2+)-ATPase were seen. The functional significance was not determined in the present study. However, altered protein-levels might influence Ca(2+)-handling in sarcoplasmic reticulum and thus affect contractile force and tolerance to ischemia.

Cardiac metal contents after infusions of manganese. An experimental evaluation in the isolated rat heart

RATIONALE AND OBJECTIVES

Manganese dipyridoxyl diphosphate (MnDPDP), a contrast agent for liver MRI, releases free Mn2+ in a graded manner. The aim of the study was to compare the effects of brief versus prolonged infusions of MnDPDP and manganese chloride (MnCl2) on cardiac function, metabolism, Mn accumulation, and tissue metal content.

METHODS

Isolated perfused rat hearts received 1-minute or 10-minute infusions of MnDPDP (100 microM, 1000 microM) or of MnCl2 (10 microM, 100 microM). Physiologic indices were measured intermittently, and tissue high-energy phosphate compounds and Ca/Fe/Mg/Mn/Zn contents were measured after a standardized Mn washout.

RESULTS

One-minute and 10-minute infusions induced, respectively, minor and marked depressions of contractile function and corresponding elevations in myocardial Mn content. MnCl2 was markedly more potent than MnDPDP. Ten-minute infusions of the highest concentration of MnDPDP and MnCl2 lowered tissue Mg and elevated tissue Ca (MnCl2), whereas high-energy phosphates were unaffected.

CONCLUSIONS

Mn uptake after Mn infusion is strongly related to the duration, concentration, and dose of free Mn ions. Differences in Mn accumulation between MnDPDP and MnCl2 were more pronounced after the 10-minute infusion.

Cardiac contractile function and electrolyte regulation during hyperosmolal stress: an experimental study in the isolated rabbit heart

Perturbations of the extracellular osmotic environment leads to cell volume changes. The aim of the present study was to evaluate the effects of hyperosmolality on cardiac contractile function and in particular the role of ionic mechanisms anticipated to be operative during hyperosmolal exposure. Paced rabbit hearts were perfused in the Langendorff mode and were exposed to 330, 370, 410, 450 and 600 mOsm kg-1 in 10 min. intervals intervened by 15 min. isosmolal buffer perfusion (by adding mannitol). Thereafter, 370 and 600 mOsm kg-1 perfusates were chosen for investigation of the effects of inhibition of the Na-K-2Cl co-transporter (bumetanide 1 microM and 10 microM), the Na+/H+ exchanger (5-(N-ethyl-N-isopropyl amiloride (EIPA) 100 nM) and the Na+/K(+)-ATPase (ouabain 50 nM). After a rapid and transient decrease in left ventricular developed pressure, all perfusates up to 450 mOsm kg-1 increased LVDP. The 600 mOsm kg-1 perfusate initially reduced LVDP by 50%, but LVDP increased to 85% of initial value at the end of the 10 min. perfusion. EIPA attenuated the recovery of LVDP during perfusion with 600 mOsm kg-1, whereas bumetanide did not affect cardiac contractile function. A net uptake of potassium was observed during hyperosmolal perfusion. Inhibition of the Na+/H+ exchanger resulted in a continued release of cardiac water throughout hyperosmolal perfusion. Isolated perfused rabbit hearts tolerate considerable elevations in perfusate osmolality. Our results suggest that the Na+/H+ antiporter is activated on hyperosmolal exposure with a secondary activation of the Na+/K(+)-ATPase. Since inhibition with bumetanide did not affect contractility or electrolyte movements, the Na-K-2Cl co-transporter does not seem to play an important role in cardiac response to hyperosmolality in rabbits.

Manganese dipyridoxyl diphosphate: MRI contrast agent with antioxidative and cardioprotective properties?

Manganese dipyridoxyl diphosphate (MnDPDP) is a contrast agent for magnetic resonance imaging (MRI) of the liver. Aims of the study were to examine if MnDPDP possesses superoxide dismutase (SOD) mimetic activity in vitro, and if antioxidant protection can be demonstrated in an ex vivo rat heart model. Superoxide (*O-2) and hydroxyl radicals (*OH-) were generated in xanthine oxidase and Fenton reactions. Spin adducts with 5,5-dimethyl-1-pyrroline-N-oxide were detected by electron spin resonance spectroscopy. Contractile function and enzyme release were monitored in rat hearts during hypoxia-reoxygenation. Low microM concentrations of MnDPDP and its metabolite Mn dipyridoxyl ethylene-diamine (MnPLED) dismutated *O-2, but showed no activity in Fenton or catalase reactions. MnDPDP 30 microM improved contractile function and reduced enzyme release in rat hearts during reoxygenation. It is concluded that MnDPDP and MnPLED possess SOD mimetic activities and may thereby protect the heart in oxidative stress.