Activated Protein C Increases Fibrin Clot Lysis by Neutralization of Plasminogen Activator Inhibitor No Evidence for a Cofactor Role of Protein S

The effect of purified human activated protein G (APC) on fibrinolysis was studied using a clot iysis system consisting of purified glu-plasminogen, tissue-type plasminogen activator, plasminogen activator inhibitor (released from endothelial cells or blood platelets), fibrinogen, 125T-fibrinogen and thrombin. All proteins were of human origin.

In this system APC could increase fibrinolysis in a dose dependent way, without affecting fibrin formation or fibrin crosslinking. However, this profibrinolytic effect of APC could only be observed when plasminogen activator inhibitor (PAI-l) was present. The effect of APC was completely quenched by pretreatment of APC with anti-protein C IgG or di-isopropylfluorophosphate. Addition of the cofactors of APC:protein S, Ca2+-ions and phospholipid-alone or in combination did not enhance the profibrinolytic effect of APC. These observations indicate that human APC can accelerate in vitro clot lysis by the inactivation of PAI-1 activity. However, the neutralization of PAI-1 by APC is independent of the presence or absence of protein S, phospholipid and Ca2+-ions.

The Interaction of Activated Protein C and Thrombin with the Plasminogen Activator Inhibitor Released from Human Endothelial Cells

The effects of human activated protein C (APC) and thrombin on plasminogen activator inhibitor (PAI-1) released from cultured human umbilical endothelial cells, grown in serum-free 35S-methionine containing medium, were studied in two ways: 1) measurement of PAI-1 activity with an amidolytic assay, and 2) immunoprécipitation of the medium with anti-PAI-1 IgG, antiprotein C IgG or anti-thrombin IgG followed by SDS-PAGE and autoradiography.

Addition of APC or thrombin to the endothelial cell conditioned medium results in a time and concentration dependent loss of PAI-1 activity and in the degradation of PAI-1 from 46 kD into a 42 kD product.

After incubation of the medium with APC in the presence of cells, an additional band of 95 kD was found, which could be immunoprecipitated with both anti-PAI-1 IgG and anti-protein C IgG, indicating the formation of an APC-PAI-1 complex before degradation occurs. No complex could be detected after incubation of the medium with thrombin in the presence of endothelial cells.

Blocking the active sites of APC and thrombin prevented both the formation of APC-PAI-1 complexes and the inactivation and degradation of PAI-1. After removal of the active PAI-1 from the medium, no degradation of the inactive PAI-1 by APC or thrombin could be found.

It is concluded that both APC and thrombin react with the active PAI-1, resulting in inactivation and degradation of PAI-1.

FcgammaRI (CD64) contributes substantially to severity of arthritis, hypersensitivity responses, and protection from bacterial infection

The high-affinity receptor for IgG, FcgammaRI, shares its capacity to bind IgG2a immune complexes (IgG2a-IC) with the low-affinity receptor FcgammaRIII and complement factors, hampering the definition of its biological role. Moreover, in vivo, FcgammaRI is occupied by monomeric IgG2a, reducing its accessibility to newly formed IgG2a-IC. By using a variety of FcgammaR(-/-) mice, we demonstrate that in the absence of FcgammaRI, the IgG2a-IC-induced cellular processes of phagocytosis, cytokine release, cellular cytotoxicity, and antigen presentation are impaired. FcgammaRI(-/-) mice showed impaired hypersensitivity responses, strongly reduced cartilage destruction in an arthritis model, and impaired protection from a bacterial infection. We conclude that FcgammaRI contributes substantially to a variety of IgG2a-IC-dependent immune functions and immunopathological responses.

Effect of endurance training on the phospholipid content of skeletal muscles in the rat

Only few data are available on the effect of training on phospholipid metabolism in skeletal muscles. The aim of the present study was to examine the effect of 6 weeks of endurance training on the content of particular phospholipid fractions and on the incorporation of blood-borne [14C]-palmitic acid into the phospholipids in different skeletal muscles (white and red sections of the gastrocnemius, the soleus and the diaphragm) of the rat. Lipids were extracted from the muscles and separated using thin-layer chromatography into the following fractions: sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine, cardiolipin and neutral lipids (this fraction being composed mostly of triacylglycerols). It was found that training did not affect the content of any phospholipid fraction in soleus muscle. It increased the content of sphingomyelin in white gastrocnemius muscle, cardiolipin and phosphatidylethanolamine in red gastrocnemius muscle and phosphatidylinositol in white gastrocnemius muscle and diaphragm. The total phospholipid content in red gastrocnemius muscle of the trained group was higher than in the control group. Training reduced the specific activity of sphingomyelin and cardiolipin in all muscles, phosphatidylcholine in soleus, red, and white gastrocnemius muscles, phosphatidylserine in all muscles, phosphatidylinositol in all except the soleus muscle, and phosphatidylethanolamine in hindleg muscles, but not in the diaphragm compared to the corresponding values in the sedentary group. It was concluded that endurance training affects skeletal muscle phospholipid content and the rate of incorporation of the blood-borne [14C]palmitic acid into the phospholipid moieties.

Differential expression and localization of annexin V in cardiac myocytes during growth and hypertrophy

Recently it was shown that annexin V is the most prominent member of the annexin family in the adult heart [1]. Amongst others, annexin V has been suggested to play a role in developmental processes. The aim of the present study was to explore whether in the heart annexin V content and localization change during maturational and hypertrophic growth, in order to obtain indications that annexin V is involved in cardiac growth processes. First, in the intact rat heart annexin V content and localization were studied during perinatal development. It was clearly demonstrated that annexin V content in total heart transiently increased in the first week after birth, from 0.79 +/- 0.06 microg/mg protein at 1 day before birth to a peak value of 1.24 +/- 0.08 microg/mg protein 6 days after birth, whereafter annexin V protein levels declined to a value of 0.70 +/- 0.06 microg/mg protein at 84 days after birth (p < 0.05). Differences in annexin V content were also observed between myocytes isolated from neonatal and adult hearts [0.81 +/- 0.09 and 0.17 +/- 0.08 microg/mg protein, respectively (p < 0.05)]. Moreover, during cardiac maturational growth the subcellular localization of annexin V might change from a cytoplasmic to a more prominent sarcolemmal localization. Second, in vivo hypertrophy induced by aortic coarctation resulted in a marked degree of hypertrophy (22% increase in ventricular weight), but was not associated with a change in annexin V localization or content. The quantitative results obtained with intact hypertrophic rat hearts are supported by findings in neonatal ventricular myocytes, in which hypertrophy was induced by phenylephrine (10(-5) M). In the latter model no changes in annexin V content could be observed either. In conclusion, the marked alterations in annexin V content during the maturational growth in the heart suggest a possible involvement of this protein in this process. In contrast, the absence of changes in annexin V content and localization in hypertrophied hearts compared to age matched control hearts suggests that annexin V does not play a crucial role in the maintenance of the hypertrophic phenotype of the cardiac muscle cell. This notion is supported by observations in phenylephrine-induced hypertrophied neonatal cardiomyocytes.

Saturated but not mono-unsaturated fatty acids induce apoptotic cell death in neonatal rat ventricular myocytes

The energy need of cardiac muscle cells in vivo is largely covered by the oxidation of saturated and mono-unsaturated fatty acids (FA). However, in vitro studies have shown that the saturated FA C16:0 at physiological concentrations exerts detrimental effects on primary cultures of neonatal rat ventricular myocytes by, as yet, unknown mechanisms. To evaluate the noxious effects of FA in more detail, neonatal cardiomyocytes were exposed to saturated (C16:0; C18:0) or mono-unsaturated (C16:1; cis-C18:1; trans-C18:1) FA, or combinations thereof for up to 48 h. FA (0.5 mM) complexed to bovine serum albumin (BSA) (0.15 mM) were added to a glucose-containing defined medium. Irrespective of the length and degree of unsaturation of the aliphatic chain, FA supplied to the cells were readily incorporated in the phospholipid pool. In the presence of mono-unsaturated FA, cardiomyocytes remained healthy and accumulated substantial amounts of triacylglycerol. In contrast, within 24 h after application of the saturated FA C16:0 or C18:0, cells had become irreversibly damaged, as evidenced by the presence of pyknotic nuclei and massive release of the cytosolic markers lactate dehydrogenase (LDH) and fatty acid-binding protein (FABP). Moreover, the occurrence of DNA-laddering indicated that apoptosis was involved. Induction of apoptotic cell death by C16:0 was counteracted by the co-administration of equimolar amounts of cis-C18:1, whereas trans-C18:1 delayed, but did not prevent, loss of cardiomyocyte viability. The present findings suggest that the incorporation of saturated, but not mono-unsaturated, fatty acids induces alterations in the phospholipid membrane, which initiate apoptotic cell death in neonatal cardiomyocytes.

The influence of lactate, pyruvate and glucose as exogenous substrates on free radical defense mechanisms in isolated rat hearts during ischaemia and reperfusion

Previous studies have shown that exogenous lactate impairs mechanical function of reperfused ischaemic hearts, while pyruvate improves post-ischaemic recovery. The aim of this study was to investigate whether the diverging influence of exogenous lactate and pyruvate on functional recovery can be explained by an effect of the exogenous substrates on endogenous protecting mechanisms against oxygen-derived free radicals. Isolated working rat hearts were perfused by a Krebs-Henseleit bicarbonate buffer containing glucose (5 mM) as basal substrate and either lactate (5 mM) or pyruvate (5 mM) as cosubstrate. In hearts perfused with glucose as sole substrate the activity of glutathione reductase was decreased by 32% during 30 min of ischaemia (p < 0.10 versus control value), while the activity of superoxide dismutase and catalase was reduced by 27 and 35%, respectively, during 5 min of reperfusion (p < 0.10 versus control value). The GSH level in the glucose group was reduced by 29% following 30 min of ischaemia and 35 min of reperfusion (p < 0.10). In lactate- and pyruvateperfused hearts there were no significant decreases of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase activity during 30 min of ischaemia, 5 min of reperfusion or 35 min of reperfusion. In pyruvate-perfused hearts the glutathione peroxidase activity was even increased by 43% during 30 min of ischaemia (p < 0.05). Glutathione levels (reduced and oxidized) did not markedly change in the lactate and pyruvate groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Annexin V in the adult rat heart: isolation, localization and quantitation

Annexins are a family of proteins with calcium- and phospholipid-binding properties. The present study was performed to identify which members of the annexin family are present in rat heart and to determine the cellular and subcellular distribution of annexin V, the most prominent annexin in rat cardiac tissue, in isolated ventricular myocytes and cultured endothelial and fibroblast-like cells. The presence of annexin I plus II, III, IV, V and VI in rat cardiac tissue was positively established with western blot analysis. Immunohistochemistry and western blot analysis revealed that annexin V is present in both cardiomyocytes and non-myocytal cells of the heart. In endothelial cells and fibroblast-like cells annexin V is predominantly localized in the cytoplasm and in cardiac myocytes in close vicinity of the sarcolemma. This last finding is confirmed by electron microscopy. Northern blot analysis demonstrated that all cell types investigated showed expression of annexin V. Annexin V mRNA levels were highest in the fibroblast-like cells, followed by the endothelial cells, and a weak signal was observed in the cardiomyocytes. By means of a sandwich-type enzyme-linked immunosorbent assay (ELISA) annexin V content in intact adult rat heart, isolated myocytes, cultured cardiac endothelial cells and fibroblast-like cells was found to be 0.70, 0.17, 1.63 and 3.84 micrograms/mg total protein, respectively. The differences in subcellular localization of annexin V in myocytes and non-myocytes suggest differences in biological function of annexin V in the various cell types.

The hydrolysis of glycerol-3-phosphate into glycerol in cardiac tissue: possible consequences for the validity of glycerol release as a measure of lipolysis

Glycerol release has been generally accepted as an index of lipolysis in the intact heart. The glycerol moiety of glycerol-3-phosphate (glycerol-3-P) is incorporated into triacylglycerols, which are then hydrolysed with release of glycerol. This study investigates the possibility that glycerol may be derived directly from glycerol-3-P instead of passing through the triacylglycerol pool. The cardiac capacity for hydrolysis of glycerol-3-P into glycerol was determined in homogenates of rat hearts. Glycerol-3-P hydrolysis activity in homogenates increased with decreasing pH. The activity was approximately four times higher at pH 5.0 than at pH 7.2 (0.94 +/- 0.11 and 0.25 +/- 0.03 mumol.g wet weight-1.min-1 respectively). The substrate concentration at which half-maximal glycerol-3-P hydrolysis activity was reached did not significantly differ at pH 5.0 and pH 7.2 (4.2 +/- 1.1 mM and 2.9 +/- 1.0 mM respectively). In the intact heart, the pH and substrate conditions found under ischaemia are favourable for direct conversion of glycerol-3-P into glycerol. The glycerol-3-P hydrolysis activity measured in vitro was sufficiently high to account for glycerol production in the ischaemia heart. However, the lack of a stoichiometric relation between cardiac glycerol-3-P and glycerol levels in ischaemia indicates that production of glycerol cannot be explained solely by hydrolysis.

Rat heart fatty acid-binding protein content is increased in experimental diabetes

Cytoplasmic fatty acid-binding protein (FABP) was assayed immunochemically in hearts from rats with insulin-dependent (IDDM) or non-insulin-dependent diabetes mellitus (NIDDM). FABP contents were 34% higher in IDDM and 103% higher in NIDDM hearts than in respective age-matched controls. FABP levels returned to control values when islets of Langerhans were transplanted into diabetic IDDM animals. In the diabetic hearts the activity of fructose-6-phosphate kinase decreased (IDDM and NIDDM animals), while that of 3-hydroxyacyl-CoA dehydrogenase increased (NIDDM animals only). These data indicate that experimental diabetes induces a marked increase of the FABP content of rat heart and suggests that this protein is involved in the enhanced fatty acid utilization by the diabetic heart.

Modulation of fatty acid-binding protein content of adult rat heart in response to chronic changes in plasma lipid levels

The aim of this work was to study in the adult rat heart the effect of modifications of fatty acid (FA) supply on the content of cytoplasmic fatty acid-binding protein (H-FABPc). To modify the amount of circulating lipids, three different treatments were chosen: (i) an hypolipidemic treatment with Clofibrate, administered daily through a gastric tube at a dose of 250 mg/kg per day for one week, (ii) a continuous intravenous infusion of 20% Intralipid, a fat emulsion, for one week at a dose of 96 ml/kg per day, and (iii) a normobaric hypoxia exposure (pO2 = 10%) for three weeks. At the end of each treatment plasma lipids, myocardial H-FABPc content and the activities of three key enzymes (citrate synthase, CS, fructose-6-phosphate kinase, FPK and hydroxy-acyl CoA-dehydrogenase, HAD) were assessed. With each of the three treatments a decrease of plasma cholesterol and phospholipid levels was observed. Plasma FA concentration increased with Intralipid infusion and decreased with chronic hypoxia. The heart H-FABPc content was increased by 20% with Clofibrate, decreased by 20% with chronic hypoxia and remained unaltered upon Intralipid treatment. The induced changes in H-FABPc content were not related directly to changes in plasma lipid levels. CS activity was slightly decreased in the hypoxia group, FPK activity decreased in the Clofibrate group, and HAD activity decreased in the Intralipid group. Among the various groups heart H-FABPc content was related to HAD activity. In conclusion, the H-FABPc content of adult rat heart appears responsive to changes in plasma lipid levels.

Differences in metabolic response of dog and goat latissimus dorsi muscle to chronic stimulation

The latissimus dorsi (LD) muscle is considered suitable to assist ventricular mechanical function in either cardiomyoplasty or extra-aortic-assist devices. Such application requires that this mixed-type skeletal muscle be transformed into a fatigue-resistant muscle, the adaptation of which can be elicited by chronic stimulation. In this study the LD muscles of dog and goat were subjected in situ to 12 wk of continuous electrical stimulation through intramuscular electrodes, and their myofibrillar and metabolic adaptations were compared. A gradual increase in the contraction rate of the muscle (in 10 wk from 30 to 80 contractions/min) caused the proportion of immunohistochemically identified type I fibers to increase in dog muscle from 30 to 74% and in goat muscle from 21 to 99%. Correspondingly, the anaerobic-glycolytic activity (fructose-6-phosphate kinase and lactate dehydrogenase activities) decreased by approximately 75% in both dog and goat muscles, whereas the oxidative capacity (fatty acid oxidation and citrate synthase activity) increased two- to threefold in goat LD muscle but remained unaltered in dog LD muscle. Muscular contents of high-energy phosphates and endogenous substrates were maintained, but the L-carnitine content decreased by 43% in both dog and goat. Our data further indicate that, for the monitoring of the metabolic adaptation of skeletal muscle, the ratio of activities of the oxidative and anaerobic-glycolytic pathways (e.g., citrate synthase to fructose-6-phosphate kinase activities) is a useful parameter in both dog and goat.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of fatty-acid-binding protein content of rat heart and skeletal muscle by endurance training and testosterone treatment

The effects of training and/or testosterone treatment and its aromatization to oestradiol on fatty-acid-binding protein (FABP) content and cytochrome c oxidase activity in heart, soleus and extensor digitorum longus (EDL) muscles were studied in intact adult female rats. One group of rats remained sedentary, whereas the others were trained for 7 weeks. Thereafter the trained rats were divided into control and testosterone-treated groups, with or without an aromatase inhibitor. Testosterone was administered by a silastic implant. Training was continued for 2 weeks. In untreated sedentary rats the immunochemically assayed FABP contents were 497 +/- 28, 255 +/- 49 and 58 +/- 17 micrograms/g wet weight for the heart, soleus, and EDL respectively. In the heart the FABP content was increased after training (29%), testosterone treatment (33%) or both manipulations (53%). In soleus muscle FABP increased only after testosterone treatment (16%), whereas in EDL no changes were found. Inhibiting the aromatase enzyme complex abolished the testosterone-induced effect on FABP content in soleus (suggesting an oestradiol effect) but not in heart muscle. Among the three muscles studied the FABP content was found to be related to the cytochrome c oxidase activity in a non-linear way. In conclusion, it is shown that the FABP contents and mitochondrial activities of heart and skeletal muscle are affected by training and sex hormones and that these effects are different for heart and skeletal muscles.

Fatty acid oxidation capacity and fatty acid-binding protein content of different cell types isolated from rat heart

Heart tissue contains appreciable amounts of fatty acid-binding protein (FABP). FABP is thought to play a crucial role in the transport of fatty acids from the cellular membrane to the intracellular site of oxidation and also, in case of endothelial cells, in the transfer of fatty acids from the vascular to the interstitial compartment through the endothelial cytoplasm. The present study was designed to delineate a possible quantitative relationship between the capacity of different cell types in the heart to oxidize fatty acids and the presence of FABP. Palmitate oxidation capacity, measured in homogenates of cells isolated from adult rat hearts, was 2 nmol/min per mg tissue protein in freshly isolated cardiomyocytes (CMC), but only 0.09 and 0.31 nmol/min per mg tissue protein in cultivated endothelial (CEC) and fibroblast-like cells (CFLC), respectively. Palmitate oxidation rates were closely related to the cytochrome C oxidase activity and, hence, to the mitochondrial density in the cells under investigation. In CMC the content of cytosolic H-FABP (H-FABPc) was about 4.5 micrograms/mg tissue protein. However, in CEC and CFLC the FABP content was less than 0.01 and 0.004 micrograms/mg tissue protein, respectively, corresponding to at maximum 0.2% of the FABP content of CMC. These findings indicate a marked difference between CMC and non-myocytal cells in the heart regarding their capacity to oxidize fatty acids, and a marked disproportion between the fatty acid oxidation capacity and immunochemically determined FABP content in both CEC and CFLC. The functional implication of these observations remains to be elucidated.

The interaction of activated protein C and thrombin with the plasminogen activator inhibitor released from human endothelial cells

The effects of human activated protein C (APC) and thrombin on plasminogen activator inhibitor (PAI-1) released from cultured human umbilical endothelial cells, grown in serum-free 35S-methionine containing medium, were studied in two ways: measurement of PAI-1 activity with an amidolytic assay, and immunoprecipitation of the medium with anti-PAI-1 IgG, anti-protein C IgG or anti-thrombin IgG followed by SDS-PAGE and autoradiography. Addition of APC or thrombin to the endothelial cell conditioned medium results in a time and concentration dependent loss of PAI-1 activity and in the degradation of PAI-1 from 46 kD into a 42 kD product. After incubation of the medium with APC in the presence of cells, an additional band of 95 kD was found, which could be immunoprecipitated with both anti-PAI-1 IgG and anti-protein C IgG, indicating the formation of an APC-PAI-1 complex before degradation occurs. No complex could be detected after incubation of the medium with thrombin in the presence of endothelial cells. Blocking the active sites of APC and thrombin prevented both the formation of APC-PAI-1 complexes and the inactivation and degradation of PAI-1. After removal of the active PAI-1 from the medium, no degradation of the inactive PAI-1 by APC or thrombin could be found. It is concluded that both APC and thrombin react with the active PAI-1, resulting in inactivation and degradation of PAI-1.

Quantitative analysis of the composition of mixtures of one-chain and two-chain tissue-type plasminogen activator with a spectrophotometric method

Tissue-type plasminogen activator (t-PA) exists in two active forms, one-chain t-PA and two-chain t-PA. These two forms differ in their kinetic constants for certain substrates. An assay has been devised to determine the composition of unknown mixtures of both t-PA forms, using the activity measurement on two different substrates. The best results are obtained using plasminogen and less than Glu-Pro-Arg-pNA as substrates.