Estrogen-mediated increases in LDL cholesterol and foam cell-containing lesions in human ApoB100xCETP transgenic mice.

The murine double transgenic mouse expressing both human apoB100 and cholesteryl ester transfer protein (CETP), has been used as a model to understand the effects mediated by various therapeutic modalities on serum lipoproteins and on atherosclerotic lesion progression. In the present study the effects of estrogen therapy on serum lipoproteins were investigated after mice were placed on an atherosclerotic diet. The daily oral administration of 20 or 100 microg/kg of 17 alpha-ethinyl estradiol resulted in a significant, dose-dependent increase in LDL cholesterol over a 20-week regimen. These differences were apparent by 6 weeks and further increases were observed through the 20-week period. Although CETP did result in a reduction in total HDL, estrogen did not have any impact on the amount of CETP activity associated with the HDL particles. The significant increase in LDL cholesterol was associated with increases in the amount of apoB100 and B48 and apoE-containing particles. Hepatic apoB message levels, however, were not different between the experimental groups. Although the extent of atherosclerotic lesions was modest, <0.5% of the aortic surface area in the vehicle group, the high-dose estrogen group, showed an increase in lesion area consistent with the elevation in LDL cholesterol. These lesions, primarily restricted to the aortic root and aortic semilunar valves, were more intensely stained with Oil Red O in the high-dose estrogen group when compared with the vehicle controls.

Inhibition of neutrophil oxidative burst and granule secretion by wortmannin: potential role of MAP kinase and renaturable kinases.

Exposure of neutrophils to a variety of agonists including soluble chemoattractant peptides and cytokines results in degranulation and activation of the oxidative burst (effector functions) that are required for bacterial killing. At present, the signaling pathways regulating these important functions are incompletely characterized. Mitogen-activated protein (MAP) kinases (MAPK) as well as members of a family of "renaturable kinases" are rapidly activated in neutrophils in response to diverse physiological agonists, suggesting that they may regulate cell activation. Antagonists of phosphatidyl inositol-3-(OH) kinase (PI3-kinase) such as wortmannin (Wtmn) inhibit these effector responses as well as certain of the above-mentioned kinases, leading to the suggestion that these enzymes lie downstream of PI3-kinase in the pathway regulating the oxidative burst and granule secretion. However, an apparent discrepancy exists in that, while virtually obliterating activity of PI3-kinase and the oxidase at low concentrations (ID50 < 20 nM), Wtmn has only variable inhibitory effects on MAPK even at substantially higher concentrations (75-100 nM). This raises the possibility that the inhibitory effects of Wtmn are mediated via other enzyme systems. The purpose of the current study was therefore to compare the effects of Wtmn on PI3-kinase activity and on the chemoattractant-activated kinases, and to determine the potential relationship of these pathways to microbicidal responses. In human neutrophils, both the oxidative burst and granule secretion induced by fMLP were inhibited by Wtmn but at markedly different concentrations: the oxidative burst was inhibited with an ID50 of < 5 nM while granule secretion was only partially inhibited at concentrations exceeding 75 nM. Activation of both MEK-1 and MAPK in response to fMLP was only partially inhibited by high doses of Wtmn (ID50 of > 100 nM and approximately 75 nM, respectively). In contrast, Wtmn potently inhibited fMLP-induced activation of the 63 and 69 kDa renaturable kinases (ID50 approximately 5-10 nM). We speculate that the renaturable kinases may be involved in the regulation of the oxidative burst, whereas the MAPK pathway may play a role in other neutrophil functions such as granule secretion.

Activated recombinant human protein C does not attenuate recruitment of neutrophils in rat models of acute inflammation.

It has been proposed that the reduction in mortality in animal models of sepsis by activated protein C (APC) is mediated by an antiinflammatory property rather than the well-characterized anticoagulant action. Human recombinant APC was examined for potential antiinflammatory activity in the pentobarbital-anesthetized rat. In the dermal reversed passive Arthus model, APC (20.0 mg/kg/h, i.v.) elevated clotting time 10-fold 3 h after the Arthus challenge, at which time, the wet-weights from Arthus dermal samples in APC rats (120.0 +/- 1.5 mg, n = 10) did not differ from controls (120.1 +/- 1.5 mg, n = 10) but were 30% heavier than remote noninflamed skin (92.0 +/- 2.0 mg, n = 10), indicating that APC treatment did not diminish tissue edema associated with immune-complex deposition. Skin-lesion myeloperoxidase (neutrophil marker enzyme) activities from APC rats were not significantly different from controls but was 21-fold more than remote noninflamed skin, indicating that APC treatment did not diminish dermal recruitment of neutrophils. In the intestinal ischemia/reperfusion model, 1 h complete occlusion of the superior mesenteric artery and an additional 4 h reperfusion was associated with a 2.87-fold increase in lung myeloperoxidase activity compared to sham-operated rats. APC (1.0 mg/kg/h, i.v.) did not diminish the elevation in this index of lung neutrophil sequestration. In conclusion, APC did not produce an antiinflammatory effect in the rat models used.

Investigation of neutrophil signal transduction using a specific inhibitor of phosphatidylinositol 3-kinase.

Neutrophils contain a multicomponent NADPH oxidase system that is involved in the production of microbicidal oxidants. Stimulation of human neutrophils with the peptide FMLP activates this respiratory burst enzyme to produce superoxide and also has been shown to result in activation of phosphatidylinositol (Ptdlns) 3-kinase. Treatment of human neutrophils with 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), a potent and specific inhibitor of Ptdlns 3-kinase, resulted in complete inhibition of Ptdlns 3-kinase activity as well as in inhibition of superoxide production in FMLP-treated neutrophils in suspension; FMLP-stimulated oxidant production in adherent cells was also abolished. Treatment of human neutrophils with PMA resulted in production of superoxide without activation of Ptdlns 3-kinase; LY294002 did not block superoxide production in neutrophils exposed to PMA. In addition, LY294002 did not inhibit cellfree NADPH oxidase activation, CD11b-dependent adhesion, actin polymerization in response to FMLP, or FMLP-induced calcium flux. These results suggest that the signal transduction pathway of the FMLP-receptor involves activation of Ptdlns 3-kinase, which is required for subsequent superoxide production induced by the chemotactic peptide. Furthermore, Ptdlns 3-kinase may be located directly upstream of protein kinase C or other protein kinases, which in turn activate the NADPH oxidase system.

Effect of activation of ATP-dependent potassium channels with (-)-pinacidil and (-)-3-pyridyl pinacidil on infarct size in a canine model of ischemia-reperfusion injury.

We tested the hypothesis that opening myocardial ATP-dependent K+ (ATP-K) channels by administration of (-)-pinacidil or (-)-3-pyridyl pinacidil intracoronarily (i.c.) either during ischemia or as pretreatment could decrease infarct size in a canine model of ischemia-reperfusion injury in anesthetized male hounds subjected to 90-min left circumflex coronary artery (LCX) occlusion followed by 5-h reperfusion. Drugs were administered by one of two protocols. In the postocclusion treatment protocol (protocol post), either vehicle or (-)-3-pyridyl pinacidil [0.25 micrograms/kg/min (low dose) or 1 micrograms/kg/min (high dose)] was infused i.c. distal to the site of coronary artery occlusion, through LCX beginning 10 min after LCX occlusion and continuing until 10 min after the beginning of reperfusion. In the preocclusion treatment protocol (protocol pre), vehicle, low dose (-)-3-pyridyl pinacidil, or (-)-pinacidil (1 micrograms/kg/min) was infused i.c. distal to the site of coronary artery occlusion through the LCX beginning 10 min before occlusion and continuing until the end of the experiment. In both protocols, (-)-pinacidil and (-)-3-pyridyl pinacidil failed to demonstrate a decrease in infarct size from that of the vehicle-treated groups. In protocol post, the mean sizes of the infarcts in the vehicle, low-dose, and high-dose (-)-3-pyridyl pinacidil-treated groups were 26.4 +/- 5.0, 35.6 +/- 6.6, and 28.9 +/- 6.1% of the area at risk, respectively. In protocol pre, the mean sizes of the infarcts in the vehicle, (-)-pinacidil, and low dose (-)-3-pyridyl pinacidil-treated groups were 29.4 +/- 1.7, 27.0 +/- 3.9, and 35.6 +/- 4.1% of the area at risk, respectively. Neither subepicardial nor subendocardial blood flow in the ischemic zone, measured by radioactive microspheres, was significantly different among groups in either protocol. In protocol post, however, the endocardial/epicardial blood flow ration in the nonischemic zone was decreased by (-)-3-pyridyl pinacidil. In addition, the ischemic zone (LCX)/nonischemic left anterior descending coronary artery (LAD) zone blood flow ratio in the subepicardial region were decreased by (-)-3-pyridyl pinacidil. These observations suggest that the drug may shift blood flow away from the ischemic zone in general and away from the endocardium in particular. In protocol pre, the LCX/LAD ratio tended to decrease with both drugs, but the difference achieved statistical significance only with (-)-3-pyridyl pinacidil (low dose).(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of granulocyte cAMP-phosphodiesterase by rolipram in vivo is not sufficient to protect the canine myocardium from reperfusion injury.

The purpose of this study was to determine whether the selective type IV cAMP-phosphodiesterase inhibitor rolipram could reduce the reperfusion injury that occurs during myocardial infarction in the anesthetized dog. This question was tested in pentobarbital-anesthetized dogs subject to 90 min of regional myocardial ischemia and 5 h of reperfusion. Dogs were treated with 1 mg/kg of rolipram (i.v., 15 min before reperfusion) followed by a 1 mg/kg/h infusion over the duration of the 5 h of reperfusion. Rolipram was tested in vitro for efficacy in inhibition of isolated human neutrophil superoxide generation. Rolipram produced significant inhibition of superoxide production over the concentration range of 0.1-100 microM rolipram when neutrophils were stimulated with a 10(-7) M concentration of the chemotactic peptide f-Met-Leu-Phe. Rolipram significantly inhibited superoxide generation from human and canine granulocytes in whole blood stimulated by zymosan. Therapeutic concentrations of rolipram in the blood of dogs were achieved during the course of the experiments with a plasma concentration of 0.761 +/- 0.095 micrograms/ml (2.76 +/- 0.34 microM) at the time of reperfusion, and 0.574 +/- 0.098 micrograms/ml (2.08 +/- 0.36 microM) at the end of the reperfusion period. The relative severity of myocardial ischemia between the two treatment groups was similar as assessed with radiolabeled microsphere measurement of myocardial blood flow. Transmural myocardial blood flows were not significantly different between the two groups after coronary occlusion (control, 0.05 +/- 0.01 ml/min/g, n = 6, vs. rolipram, 0.18 +/- 0.07 ml/min/g, n = 6; p = 0.48).(ABSTRACT TRUNCATED AT 250 WORDS)

The role of serotonin (5HT2) receptor blockade in myocardial reperfusion injury: effects of LY53857 in a canine model of myocardial infarction.

The potential protective effects of serotonin receptor antagonism during the process of acute myocardial infarction were studied in anesthetized male dogs, which were subjected to a 90-min left circumflex coronary artery occlusion followed by 5 h of reperfusion. Either vehicle (0.9% NaCl) or the serotonin (5HT2) receptor antagonist LY53857 was infused i.v. at a dose of 0.5 mg/kg, followed by a constant infusion of 2 mg/kg/min beginning 5 min before left circumflex coronary artery occlusion and continuing throughout the duration of the ischemia and subsequent reperfusion. Verification of functional 5HT2 receptor antagonism in the circulating blood of the LY53857-treated dogs was monitored throughout the experiments by periodic assessment of ex vivo platelet reactivity to exogenous serotonin. After 5 h of reperfusion, the hearts were excised and analyzed utilizing histochemical staining with triphenyltetrazolium, which demarcates myocardial infarct size and anatomical area of myocardium at risk of infarction. There was not a significant reduction of infarct size with LY53857 treatment: control infarct/area at risk = 38.6 +/- 4.7%, n = 9 LY53857 infarct/area at risk = 33.4 +/- 3.8%, n = 6. Similarly, when myocardial infarct size was analyzed as a function of myocardial collateral blood flow, there were no significant effects of drug treatment on the relationship between collateral blood flow and infarct size. The effects of 5HT on neutrophil activation were determined by measuring the potential ability of 5HT to enhance the chemotactic peptide-induced production of superoxide. 5HT did not activate human neutrophils in vitro and LY53857 had no effect on neutrophil superoxide production.(ABSTRACT TRUNCATED AT 250 WORDS)

Therapeutic defibrination with ancrod does not protect canine myocardium from reperfusion injury.

The purpose of this study was to determine whether normal fibrinogen contributes to the development of myocardial reperfusion injury by acting as a substrate in vivo for neutrophil adhesion. This was tested in a dog model of acute myocardial infarction that used pentobarbital anesthetized dogs subjected to 90 min regional myocardial ischemia and 5 h reperfusion. Dogs were treated with 1 unit/kg Ancrod (venom from the Malayan pit viper, Agkistrodon rhodostoma) or vehicle i.v. 60 min after left circumflex coronary artery occlusion. Therapeutic defibrination was verified in Ancrod-treated dogs by measurements of clottable fibrinogen, alpha-2 antiplasmin and plasminogen, by the activated partial thromboplastin time and by immunoelectrophoresis. Fibrinogen was depleted to below detectable limits of the assay (less than 0.05 mg/ml) after treatment with Ancrod. The defibrination effect was accomplished by the expected activation of the fibrinolytic system: alpha-2 antiplasmin was decreased by 10% and plasminogen activity was decreased by 30% with Ancrod treatment. There were no measureable differences between the two treatment groups in heart rate, mean arterial blood pressure, rate pressure product or circumflex coronary blood flow throughout the 90 min of regional ischemia or during the 5 h of reperfusion. The relative severity of ischemia between the two treatment groups was similar when assessed with radiolabeled microsphere measurement of myocardial blood flow. The accumulation of neutrophils (measured by myeloperoxidase activity) within the myocardium after reperfusion was not reduced by prior depletion of fibrinogen.(ABSTRACT TRUNCATED AT 250 WORDS)