Failure of ascorbic acid to prevent contrast-media induced nephropathy in patients with renal dysfunction.

AIMS: Contrast-media induced nephropathy (CIN) remains a common complication after contrast dye exposure especially in patients with chronic renal impairment (CRI). We sought to evaluate the efficacy of the antioxidant ascorbic acid as an adjunct to hydration in limiting the incidence of contrast induced nephrotoxicity after coronary procedures. MATERIALS AND METHODS: In a randomized, double-blind, prospective, single center-study, 143 consecutive patients with CRI (creatinine level > 120 micromol/l) referred to coronary angiography/intervention were randomly assigned to receive 1 g ascorbic acid or placebo in adjunct to saline hydration prior to and after angiography. Creatinine and urea nitrogen levels were measured prior to and up to 6 days after exposure to contrast agent. RESULTS: The development of CIN occurred totally in 8/143 (5.6%) patients. Between the two groups no significant difference was detected (Vitamin C 5/74 (6.8%) patients; placebo 3/69 (4.3%) patients). After adjusting for the amount of contrast dye, drug treatment, cardiovascular risk factors, ejection fraction, or sex, again no differences were detected. No patient required dialysis. More patients with diabetes had development of CIN (7/85; 8.2%) compared with nondiabetic patients (1/58; 1.7%), although not significant (p = 0.14). The incidence of CIN was elevated in patients with high amounts (> 140 ml) of contrast volume used (6/8). CONCLUSIONS: Our study does not support the prophylactic use of ascorbic acid in patients with renal dysfunction exposed to contrast dye.

[Thyroid hormone and the cardiovascular system]. / Schilddrüsenhormon und kardiovaskuläres System.

Thyroid hormone has many effects on the heart and vascular system. In hyperthyroidism changes in cardiovascular hemodynamics explain many of the clinical manifestations induced by thyroid hormones. In hypothyroidism the cardiovascular effects are opposite to those observed in hyperthyroidism, although the clinical manifestations are less obvious. This review will focus on the cardiovascular system in hyperthyroidism and hypothyroidism. In particular the subclinical dysfunctions of the thyroid gland, which occurs especially in older age, will be discussed. The clinical relevance and the necessity of diagnostic and therapy in subclinical thyroid disease are not clarified yet. In the United States an expert group has published a scientific review and guideline for the diagnosis and management of subclinical thyroid disease in 2004, which will also be outlined.

Two distinct mechanisms mediate a differential regulation of protein kinase C isozymes in acute and prolonged myocardial ischemia.

An activation of protein kinase C (PKC) in acute myocardial ischemia has been shown previously using its translocation to the plasma membrane as an indirect parameter. However, whether PKC remains activated or whether other mechanisms such as altered gene expression may mediate an isozyme-specific regulation in prolonged ischemia have not been investigated. In isolated perfused rat hearts, PKC activity and the expression of PKC cardiac isozymes were determined on the protein level using enzyme activities and Western blot analyses and on the mRNA level using reverse transcriptase-polymerase chain reaction after various periods of global ischemia (1 to 60 minutes). As early as 1 minute after the onset of ischemia, PKC activity is translocated from the cytosol to the particulate fraction without change in total cardiac enzyme activity. This translocation involves all major cardiac isozymes of PKC (ie, PKCalpha, PKCdelta, PKCepsilon, and PKCzeta). This rapid, nonselective activation of PKCs is only transient. In contrast, prolonged ischemia (>/=15 minutes) leads to an increased cardiac PKC activity (119+/-7 versus 190+/-8 pmol/min per mg protein) residing in the cytosol. This is associated with an augmented, subtype-selective isozyme expression of PKCdelta and PKCvarepsilon (163% and 199%, respectively). The specific mRNAs for PKCdelta (948+/-83 versus 1501+/-138 ag/ng total RNA, 30 minutes of ischemia) and PKCepsilon (1597+/-166 versus 2611+/-252 ag/ng total RNA) are selectively increased. PKCalpha and PKCzeta remain unaltered. In conclusion, two distinct activation and regulation processes of PKC are characterized in acute myocardial ischemia. The early, but transient, translocation involves all constitutively expressed cardiac isozymes of PKC, whereas in prolonged ischemia an increased total PKC activity is associated with an isozyme-selective induction of PKCepsilon and PKCdelta. Whether these fundamentally different activation processes interact remains to be elucidated.

Cyclosporine A limits myocardial infarct size even when administered after onset of ischemia.

OBJECTIVE: The role of the immunosuppressant cyclosporine A as a preconditioning-mimetic in the rabbit heart was examined. METHODS: Cyclosporine A, a potent protein 2B or calcium/calmodulin-dependent phosphatase (PP) inhibitor, was administered isolated rabbit hearts starting either 15 min prior to or 10 or 20 min after the onset of a 30 min period of regional ischemia and continuing until the onset of reperfusion. The effect of pretreatment with a second PP2B antagonist, FK-506, was also examined. In an additional protocol L-NAME was perfused for 50 min starting 5 min before the 45-min infusion of cyclosporine A. After 2 h of reperfusion infarct size was measured with triphenyltetrazolium chloride. In a second study left ventricular biopsies of isolated rabbit hearts were obtained to measure the effect of cyclosporine A on dephosphorylation of [32P] phosphorylase kinase by calcium/calmodulin-dependent phosphatases. RESULTS: Pretreatment with cyclosporine A resulted in only 10.0%, infarction of the risk zone, significantly less than that in untreated control hearts (28.7%, p < 0.001) but comparable to the extent of infarction in ischemically preconditioned hearts (10.0% p < 0.001 vs. control). Equivalent protection was also observed in hearts with treatment delayed for 10 min following the onset of ischemia (10.4% infarction, p < 0.001 vs. control). However, protection waned when cyclosporine A was administered only during the last 10 min of the 30-min ischemic period (25.5% infarction, p = n.s. vs. control). Pretreatment with FK-506 also resulted in myocardial salvage (10.4% infarction, p < 0.001 vs. control). When hearts were exposed to a co-infusion of L-NAME and cyclosporine A, protection was still evident (18.1% infarction, p < 0.05 vs. L-NAME), although not as robust as that seen with the PP2B blocker alone. In hearts pretreated with cyclosporine A dephosphorylation of [32P] phosphorylase kinase by calcium/calmodulin-dependent phosphatases was inhibited by 67%. CONCLUSIONS: Cyclosporine A and FK-506, potent PP2B inhibitors, can protect the ischemic rabbit heart, and at least cyclosporine A continues to be effective when infusion is delayed until after the onset of ischemia. The mechanism of this protection may be related to inhibition of phosphatases and prolongation of the phosphorylation state of ischemic cells.

Fostriecin, an inhibitor of protein phosphatase 2A, limits myocardial infarct size even when administered after onset of ischemia.

BACKGROUND: The role of protein phosphatases (PPs) during ischemic preconditioning in the rabbit heart was examined. METHODS AND RESULTS: Fostriecin, a potent inhibitor of PP2A, was administered to isolated rabbit hearts starting either 15 minutes before or 10 minutes after the onset of a 30-minute period of regional ischemia and continuing until the onset of reperfusion. After 2 hours of reperfusion, infarct size was measured with triphenyltetrazolium chloride. In a second study with isolated rabbit cardiomyocytes, the effect of fostriecin pretreatment was assessed by measuring changes in cell osmotic fragility during simulated ischemia. PP1 and PP2A activities of isolated control and ischemically preconditioned cells were also measured. In a third series of experiments, left ventricular biopsies of isolated rabbit hearts were obtained before and at selected times during 60 minutes of global ischemia, and the tissue was assayed for PP1 and PP2A activities. In isolated hearts pretreated with fostriecin, only 8% of the ischemic zone infarcted, significantly less than that in untreated control hearts (33%; P<0.001) but comparable to that in ischemically preconditioned hearts (9%; P<0.001 versus control). Significant protection was also observed in the hearts treated only after the onset of ischemia (18% infarction; P<0.05 versus control). In isolated myocytes, fostriecin also provided protection comparable to that produced by metabolic preconditioning. Preconditioning had no apparent effect on the activity of either PP1 or PP2A in isolated ventricular myocytes or ventricular tissue obtained from heart biopsies. CONCLUSIONS: Fostriecin, a potent inhibitor of PP2A, can protect the rabbit heart from infarction even when administered after the onset of ischemia. But inhibition of either PP1 or PP2A does not appear to be the mechanism of protection from ischemic preconditioning.

Phosphorylation of tyrosine 182 of p38 mitogen-activated protein kinase correlates with the protection of preconditioning in the rabbit heart.

p38 mitogen-activated protein kinase (MAPK) is known to be activated after exposure to endotoxin, osmotic and environmental stress, and, most recently, during ischemia/reperfusion. We investigated whether ischemic preconditioning also causes phosphorylation of the activation sites on p38 MAPK. Three groups of isolated rabbit hearts were studied. Control hearts experienced 30 min of ischemia only. The second group was preconditioned with 5 min of global ischemia and 10 min of reperfusion. Group 3 was also ischemically preconditioned, but in the presence of 100 microM 8-(p-sulfophenyl)theophylline (SPT). Transmural left ventricular biopsies were taken before and during the long ischemic period. Western blot analysis with either p38 MAPK or phospho-specific p38 MAPK (Tyr-182) antibodies showed a decreased phosphorylation during ischemia in non-preconditioned hearts, but phosphorylation was enhanced several fold after 10 and 20 min of ischemia in preconditioned hearts. Furthermore, when protection from ischemic preconditioning was blocked by SPT, increased phosphorylation of p38 MAPK during ischemia was not present. Therefore the phosphorylation of p38 MAPK at tyrosine 182, which is required for the kinase's activation, occurred during ischemia only when protection from preconditioning was evident. In a second study, changes in osmotic fragility were measured during simulated ischemia in rabbit cardiomyocytes. Reduced fragility in ischemically preconditioned myocytes could be completely abolished by the specific p38 MAPK inhibitor SB-203580. In contrast, anisomycin, an activator of p38 MAPK and JUN kinase pathways, was found to be as protective as ischemic preconditioning. We conclude that p38 MAPK phosphorylation correlates with preconditioning's protection, and that its activation may be an important step in the signal transduction cascade of ischemic preconditioning.

Phospholipase D plays a role in ischemic preconditioning in rabbit heart.

BACKGROUND: Activation of protein kinase C (PKC) is thought to be a critical step in ischemic preconditioning. Many receptor agonists activate PKC via stimulation of phospholipase C (PLC), which degrades membrane phospholipids to diacylglycerol (DAG), an important PKC cofactor. However, adenosine receptors, critical components of the prototypical preconditioning pathway, are not thought to couple to PLC in the cardiomyocyte. We therefore tested whether ischemic preconditioning or adenosine might instead activate phospholipase D (PLD) to produce DAG. METHODS AND RESULTS: PLD activity was measured in isolated rabbit hearts. Ischemic injury was evaluated in either isolated rabbit hearts or dispersed myocytes. PLD activity doubled from a control level of 74.8 +/- 10.0 to 140.0 +/- 11.5 mumol.min-1.g-1 (P < .025) after two 5-minute periods of global ischemia separated by 5 minutes of reperfusion. A similar increase was noted after the heart had been exposed to (R)-N6-(2-phenylisopropyl)-adenosine [(R)-PIA] for 20 minutes. When sodium oleate, which activates PLD, was administered to isolated hearts before a 30-minute coronary occlusion, infarct size (15.6 +/- 2.0% of the risk zone) was significantly smaller than in untreated hearts (30.4 +/- 2.2%; P < .01). Exposure to sodium oleate significantly prolonged the rate of isolated myocyte survival during simulated ischemia. Propranolol 100 mumol/L, which blocks DAG production from metabolites produced by PLD catalysis, completely abolished the protective effects of both metabolic preconditioning and (R)-PIA exposure in myocytes. CONCLUSIONS: We conclude that PLD stimulation is involved in the protection of ischemic preconditioning in the rabbit heart.

Loss of glycogen during preconditioning is not a prerequisite for protection of the rabbit heart.

Depletion of glycogen has been proposed as the mechanism of protection from ischemic preconditioning. The hypothesis was tested by seeing whether pharmacological manipulation of preconditioning causes parallel changes in cardiac glycogen content. Five groups of isolated rabbit hearts were studied. Group 1 experienced 30 min of ischemia only. Group 2 (PC) was preconditioned with 5 min of global ischemia followed by 10 min of reperfusion. Group 3 was preconditioned with 5 min exposure to 400 nM bradykinin followed by a 10 min washout period. Group 4 experienced exposure to 10 microM adenosine followed by a 10 min washout period, and the fifth group was also preconditioned with 5 min ischemia and 10 min reperfusion but 100 microM 8-(p-sulfophenyl)theophylline (SPT), which blocks adenosine receptors, was included in the buffer to block preconditioning's protection. Transmural biopsies were taken before treatment, just prior to the 30 min period of global ischemia, and after 30 min of global ischemia. Glycogen in the samples was digested with amyloglucosidase and the resulting glucose was assayed. Baseline glycogen averaged 17.3 +/- 0.6 mumol glucose/g wet weight. After preconditioning glycogen decreased to 13.3 +/- 1.3 mumol glucose/g wet weight (p < 0.005 vs. baseline). Glycogen was similarly depleted after pharmacological preconditioning with adenosine (14.0 +/- 1.0 mumol glucose/g wet weight, p < 0.05 vs. baseline) suggesting a correlation. However, when preconditioning was performed in the presence of SPT, which blocks protection, glycogen was also depleted by the same amount (13.3 +/- 0.7 mumol glucose/g wet weight, p = ns vs. PC). Bradykinin, which also mimics preconditioning, caused no depletion of glycogen (16.3 +/- 0.8 mumol glucose/g wet weight, p = ns vs. baseline). Because preconditioning with bradykinin did not deplete glycogen and because glycogen continued to be low when protection from preconditioning was blocked with SPT, we conclude that loss of glycogen per se does not cause the protection of preconditioning.

Impaired function of inhibitory G proteins during acute myocardial ischemia of canine hearts and its reversal during reperfusion and a second period of ischemia. Possible implications for the protective mechanism of ischemic preconditioning.

A brief antecedent period of myocardial ischemia and reperfusion can delay cellular injury during a subsequent ischemic condition. Recent observations suggest that this protective mechanism depends on the continued activation of adenosine A1 receptors and Gi proteins. During acute myocardial ischemia, sufficient amounts of adenosine for maximal activation of adenosine A1 receptors are released, independent of a preconditioning ischemia. Hence, the protective mechanism of ischemic preconditioning may not exclusively be explained by activation of adenosine A1 receptors. As a working hypothesis, an increased responsiveness of Gi proteins toward receptor-mediated activation, leading to an increased response of Gi-regulated effectors, was tested in this study. In 47 anesthetized dogs, ischemia was induced by proximal ligation of the left anterior descending coronary artery. Animals underwent either a single period of 5 minutes of ischemia (n = 9), a single period of 15 minutes of ischemia (n = 10), 5 minutes of ischemia followed by 15 minutes of reperfusion (n = 8), 15 minutes of ischemia followed by 60 minutes of reperfusion (n = 5), or 5 minutes of ischemia followed by 15 minutes of reperfusion and a second period of 5 minutes of ischemia (n = 15). Sarcolemmal membranes were prepared from the central ischemic area and from the posterior left ventricular wall, which served as the control. During ischemia, carbochol-stimulated GTPase decreased by 38% (control, 33.5 +/- 17.7; ischemia, 24.2 +/- 15 pmol.min-1.mg protein-1; n = 9; P < .001). The decrease in carbachol-stimulated GTPase activity was associated with a 45% decrease in carbachol-mediated inhibition of adenylyl cyclase (control, 28.9 +/- 2.4% maximal inhibition; ischemia, 15.1 +/- 2.6% maximal inhibition; n = 5; P < .001). Prolongation of the ischemic period to 15 minutes did not lead to a further reduction of the Gi-mediated signal transduction. The binding properties of muscarinic receptors were not affected by ischemia. Furthermore, as demonstrated by carbachol-stimulated binding of [gamma-35S]GTP to sarcolemmal membranes, high- and low-affinity binding sites for the muscarinic antagonist carbachol, the EC50 for carbachol-stimulated GTPase activity and the substrate dependency of the high-affinity GTPase, the interaction between muscarinic receptors and inhibitory G proteins, and GTP binding to G proteins were not altered (n = 14). Immunoblotting with alpha 1- and alpha 2-specific antibodies did not indicate a loss of Gi proteins during ischemia that could explain the reduced GTPase activity.(ABSTRACT TRUNCATED AT 400 WORDS)