A novel N-aryl tyrosine activator of peroxisome proliferator-activated receptor-gamma reverses the diabetic phenotype of the Zucker diabetic fatty rat.

The discovery that peroxisome proliferator-activated receptor (PPAR)-gamma was the molecular target of the thiazolidinedione class of antidiabetic agents suggested a key role for PPAR-gamma in the regulation of carbohydrate and lipid metabolism. Through the use of high-throughput biochemical assays, GW1929, a novel N-aryl tyrosine activator of human PPAR-gamma, was identified. Chronic oral administration of GW1929 or troglitazone to Zucker diabetic fatty (ZDF) rats resulted in dose-dependent decreases in daily glucose, free fatty acid, and triglyceride exposure compared with pretreatment values, as well as significant decreases in glycosylated hemoglobin. Whole body insulin sensitivity, as determined by the euglycemic-hyperinsulinemic clamp technique, was significantly increased in treated animals. Comparison of the magnitude of glucose lowering as a function of serum drug concentrations showed that GW1929 was 2 orders of magnitude more potent than troglitazone in vivo. These data were consistent with the relative in vitro potencies of GW1929 and troglitazone. Isolated perfused pancreas studies performed at the end of the study confirmed that pancreata from vehicle-treated rats showed no increase in insulin secretion in response to a step change in glucose from 3 to 10 mmol/l. In contrast, pancreata from animals treated with GW1929 showed a first- and second-phase insulin secretion pattern. Consistent with the functional data from the perfusion experiments, animals treated with the PPAR-gamma agonist had more normal islet architecture with preserved insulin staining compared with vehicle-treated ZDF rats. This is the first demonstration of in vivo efficacy of a novel nonthiazolidinedione identified as a high-affinity ligand for human PPAR-gamma. The increased potency of GW1929 compared with troglitazone both in vitro and in vivo may translate into improved clinical efficacy when used as monotherapy in type 2 diabetic patients. In addition, the significant improvement in daily meal tolerance may impact cardiovascular risk factor management in these patients.

Use of resampling techniques to estimate the variance of parameters in pharmacological assays when experimental protocols preclude independent replication: an example using Schild regressions.

Estimates of variance in pharmacological assays are usually made by repeating the experiment with different tissues. Biological factors, such as the inability to wash a drug from tissue, may preclude the type of replication that is appropriate for the statistics of interest. For example, in Schild regressions, replication is usually done at each concentration of antagonist. In some test systems, replication of dose-response curves is not possible. For example, some persistent agonists cannot be removed from tissues after exposure, while in other systems, rapid desensitization severely alters tissue sensitivity to repeated challenge with agonist. In this paper, we demonstrate how a statistical resampling method, bootstrapping, can be used to derive estimates of the confidence intervals for pA2, pKB, and slope from Schild plots. This method utilizes the speed of the computer to estimate variance by repeatedly resampling the data. The advantage to this method is that it can be used for many different experimental designs. For a data set obtained from a Schild regression of atenolol antagonism of isoproterenol in the guinea pig left atrium, bootstrap estimates of confidence limits were calculated for cases where dose ratios were derived from the same tissue and randomly paired tissues. These estimates showed good agreement with estimates obtained using conventional analytical methods, thus suggesting that this method may be useful in practice.

Inhibition of cartilage and bone destruction in adjuvant arthritis in the rat by a matrix metalloproteinase inhibitor.

Considerable evidence has associated the expression of matrix metalloproteinases (MMPs) with the degradation of cartilage and bone in chronic conditions such as arthritis. Direct evaluation of MMPs' role in vivo has awaited the development of MMP inhibitors with appropriate pharmacological properties. We have identified butanediamide, N4-hydroxy-2-(2-methylpropyl)-N1-[2-[[2-(morpholinyl)ethyl]-,[S- (R*,S*)] (GI168) as a potent MMP inhibitor with sufficient solubility and stability to permit evaluation in an experimental model of chronic destructive arthritis (adjuvant-induced arthritis) in rats. In this model, pronounced acute and chronic synovial inflammation, distal tibia and metatarsal marrow hyperplasia associated with osteoclasia, severe bone and cartilage destruction, and ectopic new bone growth are well developed by 3 wk after adjuvant injection. Rats were injected with Freund's adjuvant on day 0. GI168 was was administered systemically from days 8 to 21 by osmotic minipumps implanted subcutaneously. GI168 at 6, 12, and 25 mg/kg per d reduced ankle swelling in a dose-related fashion. Radiological and histological ankle joint evaluation on day 22 revealed a profound dose related inhibition of bone and cartilage destruction in treated rats relative to rats receiving vehicle alone. A significant reduction in edema, pannus formation, periosteal new bone growth and the numbers of adherent marrow osteoclasts was also noted. However, no significant decrease in polymorphonuclear and mononuclear leukocyte infiltration of synovium and marrow hematopoietic cellularity was seen. This unique profile of antiarthritic activity indicates that GI168 is osteo- and chondro-protective, and it supports a direct role for MMP in cartilage and bone damage and pannus formation in adjuvant-induced arthritis.

The effects of anorectic and aversive agents on deprivation-induced feeding and taste aversion conditioning in rats.

We compared the effects of intraperitoneally administered LiCl (0.5-2830 mumol/kg), sulfated cholecystokinin26-33 (10-1000 nmol/kg; CCK-8), nonsulfated CCK-8 (500 and 1000 nmol/kg), sulfated CCK26-29 (500 and 1000 nmol/kg), CCK30-33 (10-1000 nmol/kg) bombesin (10-1000 nmol/kg; BOM), (dl) fenfluramine HCl (0.9-37.3 mumol/kg; fenfluramine), fluoxetine HCl (2.9-86.7 mumol/kg; fluoxetine), and d-amphetamine sulfate (0.27-10.9 mumol/kg; AMPH) on both 18-hr deprivation-induced feeding and one-bottle, taste aversion conditioning in male, Long-Evans rats. Doses of LiCl > or = 177 mumol/kg (or 7.5 mg/kg) induced significant, dose-related taste aversions, but only doses of LiCl > or = 2123 mumol/kg (90 and 120 mg/kg) induced significant anorexia. CCK-8 induced marked anorexia (at doses > or = 25-50 nmol/kg), but only relatively mild taste aversions which were only statistically significant at the highest dose (1000 nmol/kg). The anorectic effects of CCK-8 at 500 and 1000 nmol/kg, but not at lower doses, lasted at least 3 hr. Sulfated CCK26-29, CCK30-33 and nonsulfated CCK-8 induced neither anorexia nor taste aversion. BOM induced marked anorexia at all doses tested, but did not induce statistically significant taste aversions. The nonpeptidal anorectic compounds, fenfluramine, fluoxetine, and AMPH, induced both dose-related anorexia and taste aversion conditioning. We focus on several issues concerning the interpretation of taste aversion conditioning. Our results challenge any simple relationship between the ability of a compound to induce taste aversion and to decrease feeding.

Anti-inflammatory activity of phosphodiesterase (PDE)-IV inhibitors in acute and chronic models of inflammation.

Inhibitors of cyclic nucleotide phosphodiesterases are known to suppress lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) production in vitro in human monocytes. The most potent of these have selectivity for type IV PDEs, suggesting that this class of PDE is the major type involved in the regulation of human TNF-alpha production. Using compounds of two distinct chemical structural classes, a quinazolinedione (CP-77059) and a 4 arylpyrrolidinone (rolipram), we show here that PDE-IV-specific inhibitors are also potent in suppressing LPS-induced TNF-alpha production in vitro in sodium periodate-elicited murine macrophages (IC50s of 1 and 33, respectively). We then report the in vivo anti-inflammatory effect of PDE-IV inhibition in five murine models of inflammation: (i) elevation of serum TNF-alpha induced by a sublethal LPS injection; (ii) LPS-induced endotoxic shock; (iii) LPS/galactosamine-induced endotoxic shock; (iv) carrageenan-induced paw oedema; and (v) adjuvant arthritis. Following a sublethal (5 micrograms/mouse) injection of LPS, serum TNF-alpha levels in mice peaked sharply, reaching concentrations of 3-12 ng/ml 90 min after injection. In this sublethal LPS assay, CP-77059 was about 30 times more potent than rolipram, with a minimum effective dose of 0.1 mg/kg versus 3 mg/kg for rolipram. This rank order is in keeping with the relative in vitro IC50s for CP-77059 and rolipram, as well as their relative Ki against the human PDE-IV enzyme (46 nM and 220 nM, respectively). In LPS-induced endotoxic shock, rolipram and CP-77059 at relatively high doses of 30 and 10 mg/kg, respectively, significantly reduced serum TNF-alpha levels, and also inhibited mortality 66%. In the LPS/galactosamine shock model, in which mice are rendered exquisitely sensitive to LPS by co-injection with galactosamine, only 0.1 microgram of LPS/mouse is necessary for serum TNF-alpha elevation and death. Both rolipram and the CP-77059 caused dose-dependent reduction of serum TNF-alpha and lethality. In the carrageenan-induced paw oedema model, in which there is a pronounced local TNF-alpha response (without a serum TNF-alpha elevation), rolipram significantly inhibited paw swelling as well as localized TNF-alpha levels in the paw. In the adjuvant arthritis model, a chronic model of inflammation also possessing localized TNF-alpha elevation in the inflamed paw, rolipram and CP-77059 suppressed ankle swelling and radiological evidence of joint damage. These data are consistent with a major role for PDE-IV in regulation of TNF-alpha production and inflammatory responses in murine systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Anti-inflammatory activity of salmeterol: down-regulation of cytokine production.

Elevation of intracellular cAMP levels has been shown previously to inhibit cytokine secretion by various cell types in vitro. Since salmeterol is a beta 2-agonist which activates adenylate cyclase, its ability to inhibit cytokine production was evaluated. Though salmeterol, and the related drug albuterol, did not inhibit IL-1 beta production in vitro, both drugs did inhibit tumour necrosis factor-alpha (TNF-alpha) secretion by lipopolysaccharide (LPS)-activated THP-1 cells with similar IC50s of approximately 0.1 microM. This inhibition was effectively reversed by the beta 2-antagonist oxprenolol, indicating that the inhibition was mediated through the beta 2-adrenergic receptor. A strikingly different reactivity profile was seen with T cells. Salmeterol was able to inhibit the activation of both mouse and human T cells, as measured by proliferation and IL-2 secretion in response to anti-CD3 antibody, whereas albuterol was completely inactive in these assays. This T cell inhibition by salmeterol was about 10-fold less potent than that for TNF-alpha production, and was not reversed by a beta 2-antagonist, indicating that a different mechanism was involved in the effect of salmeterol on T cells. Paralleling the TNF-alpha inhibitory activity in vitro, oral dosing of salmeterol and albuterol inhibited LPS-induced increase in murine serum TNF level in vivo, with ED50s of approximately 0.1 mg/kg. This inhibition could be abrogated by dosing orally with the beta-blocker propranolol. The long-acting pharmacological profile of salmeterol was apparent in that it maintained its efficacy for 3 h, while albuterol had a much shorter duration of action. Salmeterol also had some protective effects in the galactosamine/LPS model of endotoxic shock, which is dependent upon TNF-alpha production. Though salmeterol inhibited serum TNF-alpha levels by up to 94% in this assay, it protected less than 50% of the animals from the lethal effects of the LPS/galactosamine mixture. This observation suggests that functional levels of TNF-alpha localized in tissues may not be accurately reflected by serum levels.

Evaluation of the significance of elevated levels of systemic and localized tumor necrosis factor in different animal models of inflammation.

Elevated tumor necrosis factor (TNF) levels have been reported in various models of acute and chronic inflammation and used by many investigators to determine the stage of disease and effectiveness of treatment. Because of the documented involvement of TNF in the mechanism of septic shock, experiments were done to determine whether serum TNF levels paralleled the pathology in endotoxic shock and other models of inflammation. When mice received an intraperitoneal injection of lipopolysaccharide, serum TNF levels increased dramatically, peaking 90 minutes after injection. In a dose-response experiment with lipopolysaccharide alone, we found no correlation between serum levels of TNF and survival rate of mice. All three lipopolysaccharide concentrations resulted in comparable elevations of serum TNF, yet only in the high-dose group did the animals die. In a second model of endotoxic shock, TNF-alpha levels in serum were again compared with the survival rate of mice receiving lipopolysaccharide plus galactosamine. As in the first model, we found no relationship between the level of TNF in mouse serum and mouse survival rate. The two lowest concentrations of lipopolysaccharide/galactosamine induced identically low levels of serum TNF, yet in one group all of the animals survived and in the other all died. Discrepancies between serum TNF level and mortality rate were also seen in drug treatment experiments. GI 147404X, a standard phosphodiesterase type IV inhibitor, inhibited lipopolysaccharide/galactosamine-induced elevation of serum TNF by 90% at doses of 1 and 10 mg/kg. However, the high dose resulted in 66% protection while the low dose afforded no protection.(ABSTRACT TRUNCATED AT 250 WORDS)

Improved donor myocardial recovery with a new lazaroid lipid antiperoxidant in the isolated canine heart.

U74006F is a new 21-amino steroid (lazaroid) that prevents lipid peroxidation without glucocorticoid or mineralocorticoid side effects. Reperfusion injury has been reduced by the addition of various free radical scavengers and antiperoxidants to the reperfusate. To assess the effect of U74006F on reperfusion of donor hearts subjected to prolonged hypothermic ischemia, 21 isolated canine hearts were divided into three groups: control (group 1), drug (2 mg/kg) injected into the oxygenated blood perfusate immediately before 4 hours of preservation (group 2), and drug (2 mg/kg) injected 1 hour before heart isolation and again 15 minutes before reperfusion (group 3). After control left ventricular function studies (with an intraventricular balloon) and biopsy for high-energy phosphates and dry/wet ratios, the hearts were arrested with cold cardioplegia and cooled for 4 hours then reperfused for 3 hours. Left ventricular work was calculated by systolic and diastolic pressure curves, which showed a better return of function in group 3 hearts (1625, 2150, and 3493 mm Hg/ml in groups 1, 2, and 3, respectively, at 180 minutes of reperfusion; p = 0.02). This was likely the result of improved diastolic compliance in group 3. Dry/wet ratios showed increased tissue edema in all hearts at the end of reperfusion. Although high-energy phosphate concentrations were not different between groups, adenosine was best preserved in group 3 (p = 0.03), suggesting reduced washout of this precursor. In conclusion, administration of U74006F before preservation and reperfusion may be useful for donor heart protection.

Pulsatile reperfusion after cardiac arrest improves neurologic outcome.

Cardiopulmonary bypass (CPB) using nonpulsatile flow (NPF) is advocated for refractory cardiac arrest. This study examined cerebral outcome after resuscitation with pulsatile flow (PF) versus NPF. Dogs arrested for 12.5 minute were reperfused with NPF (n = 11) using roller pump CPB or PF (n = 11) using mechanical biventricular cardiac massage. Pump flows were similar between groups; however early arterial pressures were greater during PF versus NPF, *p less than 0.05. Circulatory support was weaned at 60 minutes' reperfusion. Neurologic recovery of survivors (n = 16) was significantly better after PF versus NPF, *p = 0.01. The presence of brain lesions on magnetic resonance images did not significantly differ between groups at 7 days. Brain then were removed and regions examined for ischemic changes. Loss of CA1 pyramidal neurons was more severe after NPF versus PF, +p = 0.009. Ischemic changes were more frequent after NPF in the caudate nucleus (+p = 0.009) and watershed regions of the cerebral cortex (+p = 0.062), compared with PF. These results demonstrate that PF improves cerebral resuscitation when treating cardiac arrest with mechanical circulatory support (* = MANOVA with repeated measures, + = categorical data analysis.

Myocardial tolerance to ischemia after resuscitation. Direct mechanical ventricular actuation versus cardiopulmonary bypass.

This study assessed myocardial ischemia after resuscitation from cardiac arrest using direct mechanical ventricular actuation (DMVA) or cardiopulmonary bypass (CPB). Myocardial ischemic tolerance was better after DMVA resuscitation. Resuscitation using DMVA, when compared with CPB, may improve outcome when subsequent coronary artery bypass grafting (CABG) is required.

Mechanical myocardial actuation during ventricular fibrillation improves tolerance to ischemia compared with cardiopulmonary bypass.

Direct mechanical ventricular actuation (DMVA) is a unique non-blood-contacting biventricular assist device that provides circulatory support during ventricular fibrillation without demonstrating adverse effects on the myocardium. The purpose of this study was to assess the preservation of myocardial energy stores and myocardial responses to ischemia after circulatory support during ventricular fibrillation with direct mechanical ventricular actuation versus cardiopulmonary bypass. Twenty adult mongrel dogs were randomized to receive circulatory support with either cardiopulmonary bypass or direct mechanical ventricular actuation. After 4 hours of ventricular fibrillation, hearts were defibrillated and left ventricular transmural biopsies were obtained. Hearts were then excised and subjected to 90 minutes of normothermic total ischemia. Serial biopsies were obtained at 15-minute intervals to determine regional depletion of high energy phosphates. The time-to-peak ischemic contracture was recorded by using needle-tipped Millar catheters placed in the left ventricular endocardium, epicardium, septum, and right ventricle. Time-to-peak ischemic contracture of the endocardium (62.6 +/- 1.4 vs. 58.8 +/- 1.0 minutes, p less than 0.05) and septum (61.1 +/- 6.9 vs. 46.9 +/- 6.2 minutes, p less than 0.004) were significantly prolonged after direct mechanical ventricular actuation versus cardiopulmonary bypass, respectively. Similar trends were noted in the epicardium and right ventricular regions; however, these differences were not statistically significant. Left ventricular adenosine triphosphate (ATP) levels were better preserved after direct mechanical ventricular actuation (22 +/- 1.5 mumols/g dry wt) compared with cardiopulmonary bypass (17 +/- 1.9 mumols/g dry wt). The depletion of left ventricular endocardium ATP during normothermic ischemia was significantly delayed after direct mechanical ventricular actuation compared with cardiopulmonary bypass.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimal temperature for preservation of donor myocardium.

The ideal method for the preservation of donor hearts for transplantation is unclear. To assess the optimal temperature for donor myocardium preservation, the recovery of isolated canine hearts (n = 20) exposed to 4 hours of either standard ice-chest hypothermia (0-4 degrees C) or constant moderate hypothermia (12 degrees C) were compared. Functional and metabolic data were acquired before hypothermia and every 30 minutes during 3 hours of reperfusion with oxygenated blood. Mean end-systolic pressure-volume slopes were 2.11 +/- 0.06 and 2.09 +/- 0.06 mm Hg/ml for ice-chest hypothermia and constant moderate hypothermia, respectively (p = NS), which were unchanged from control. All y intercepts during reperfusion were decreased compared with control (p = 0.002) without any differences between groups. End-diastolic pressures were greater than control throughout the reperfusion period for both groups (p = 0.02), but there was a difference in change of end-diastolic pressures with time between groups (p = 0.04). Dry/wet ratios were similar after preservation and reperfusion in both groups. ATP recovered to control levels during reperfusion for both groups although energy charge ratios were greater for hearts exposed to constant moderate hypothermia (p = 0.007). These data indicate that intracellular energy stores are well maintained by preservation using either technique. Changes in function appear to be related to altered compliance irrespective of preservation temperature. These data suggest that a wide range of temperatures may be acceptable for donor heart preservation.

Mechanical cardiac actuation achieves hemodynamics similar to cardiopulmonary bypass.

The disadvantages of blood/interface interactions and difficult installation are common to current circulatory support devices. Direct mechanical ventricular actuation (DMVA) is a method of biventricular cardiac massage that avoids contact of blood with various surfaces. The purpose of this study was to compare hemodynamic responses and organ perfusion between DMVA and cardiopulmonary bypass (CPB). Twenty adult mixed-breed dogs randomized for DMVA or CPB were anesthetized with alpha-chloralose. During 4 hours of ventricular fibrillation, animals received either DMVA or CPB with aortic arch perfusion (90 to 120 ml/kg/min), bicaval venous return, and full left ventricle venting. Hemodynamics and organ perfusion were assessed by multivariant analysis of variance with repeated measures. Blood flow was similar to normal sinus rhythm (control) with either method; however, average CPB flows (control, 110%) were increased significantly over DMVA flows (control, 75%) (p = 0.016). The resulting mean arterial pressures were significantly greater during DMVA (control, 66%) compared to CPB (control, 49%) (p = 0.0011). Radiolabeled microspheres were the measure of organ perfusion during sinus rhythm and at 2 and 4 hours of circulatory support. Myocardial blood flow was equal to control in all regions during DMVA; CPB resulted in increased flows to the left ventricular epicardium, septum, and right ventricle. DMVA generated significantly greater flows to the renal cortex. All other organs demonstrated similar perfusion with either method. However, CPB displayed declining cerebral flows at 4 hours compared to DMVA (42% vs 55% control, respectively). Overall, DMVA provided hemodynamic stability equal to that of CPB. Rapid application and avoidance of blood/surface contact make DMVA a favorable method of temporary circulatory support.

Comparison of direct mechanical ventricular actuation and cardiopulmonary bypass.

Direct mechanical ventricular actuation (DMVA) is a non-blood-contacting method for biventricular support. To compare effects of DMVA and cardiopulmonary bypass (CPB), 13 swine were supported by DMVA or CPB during 4 hours of ventricular fibrillation. Hearts were then rapidly excised and sectioned into right ventricular (RV) and left ventricular (LV) free wall slabs and subjected to total normothermic ischemia. Time to peak ischemic contracture (TIC) of LV endocardium (endo), LV epicardium (epi) and RV were determined using Millar needle transducers. Mean TIC was compared between DMVA (n = 6), CPB (n = 7), and control (n = 18). Significant decreases in LV endo TIC were found after DMVA (53.3 +/- 3.3 min) and CPB (56.2 +/- 2.4 min) compared with control (62.5 +/- 1.0), p less than 0.05. Myocardial blood flow was measured using microspheres during normal sinus rhythm and after 2 and 4 hr of circulatory support. Nonsignificant decreases in endo flow occurred during CPB and DMVA compared with control. LV endo adenosine triphosphate (ATP) levels (mumol/g dry weight) were significantly decreased after DMVA (9.0 +/- 2.5) and CPB (4.0 +/- 2.7) compared with control (17.8 +/- 0.6), p less than 0.05. Although CPB maintained mean arterial pressure by increased pump flows (mean, 129 ml/kg/min) and LV intracavitary pressures were kept below 5 mmHg with LV venting, resulting endo flows and ATP levels were decreased. DMVA generated decreased cardiac outputs (mean, 67 ml/kg/min) under these vasodilated states, yet maintained endo flow and ATP levels as well as CPB. These experimental data show that different mechanisms of myocardial perfusion and metabolism result from CPB and DMVA.

Myocardial tolerance to total ischemia in the dog anesthetized with halothane or isoflurane.

Myocardial tolerance to total ischemia was compared in animals anesthetized with halothane or isoflurane by measuring the time required for development of cardiac rigor in the absence of coronary circulation or wall stress. Sixteen dogs, eight in each group, were anesthetized with equally potent inspired concentrations of either halothane (2 MAC) or isoflurane (2 MAC), intubated, and ventilated. Thirty minutes later, the heart was rapidly excised. A left ventricular slab was prepared and maintained at 37 degrees C. A portion of each slab was placed in a compressibility gauge that detects rigor onset by an abrupt increase in resistance to tissue deformation. Subendocardial tissue pressure was continuously measured in a second slab using needle-tipped Millar pressure transducers. A third slab was used for intermittent tissue sampling and HPLC assay of high-energy nucleotide levels. There were no differences in pre-ischemic heart rate, mean arterial pressure, glucose, lactate, PO2, PCO2, pH, plasma epinephrine, or norepinephrine levels between the two groups. The onset of rigor as measured by the compressibility gauge was delayed in the halothane group (68 +/- 7.2 vs. 60 +/- 5.0 min; P less than .05). Tissue ATP and ADP levels declined throughout the period of ischemia, with a trend towards preservation in the halothane group. The data show that myocardial tolerance to total normothermic ischemia is improved in animals anesthetized with halothane compared to isoflurane, independent of the effects on hemodynamics or collateral coronary circulation.