16(R)-hydroxyeicosatetraenoic acid, a novel cytochrome P450 product of arachidonic acid, suppresses activation of human polymorphonuclear leukocyte and reduces intracranial pressure in a rabbit model of thromboembolic stroke.

OBJECTIVE: Activated polymorphonuclear leukocytes (PMNs) have been suggested to contribute to the development of increased intracranial pressure (ICP). We recently demonstrated that human PMNs produce a novel cytochrome P450-derived arachidonic acid metabolite, 1 6(R)-hydroxyeicosatetraenoic acid [16(R)-HETE], that modulates their function. It was thus of interest to examine this novel mediator in an acute stroke model. METHODS: 16-HETE was assessed initially in a variety of human PMN and platelet in vitro assays and subsequently in an established rabbit model of thromboembolic stroke. A total of 50 rabbits completed a randomized, blinded, four-arm study, receiving 16(R)-HETE, tissue plasminogen activator, both, or neither. Experiments were completed 7 hours after autologous clot embolization. The primary end point for efficacy was the suppression of increased ICP. RESULTS: In in vitro assays, 16(R)-HETE selectively inhibited human PMN adhesion and aggregation and leukotriene B4 synthesis. In the thromboembolic stroke model, animals that received 16(R)-HETE demonstrated significant suppression of increased ICP (7.7 +/- 1.2 to 13.1 +/- 2.7 mm Hg, baseline versus final 7-h time point, mean +/- standard error), compared with either the vehicle-treated group (7.7 +/- 0.9 to 15.8 +/- 2.6 mm Hg) or the tissue plasminogen activator-treated group (7.6 +/- 0.6 to 13.7 +/- 2.1 mm Hg). The group that received the combination of 16(R)-HETE plus tissue plasminogen activator demonstrated no significant change in ICP for the duration of the protocol (8.6 +/- 0.6 to 11.1 +/- 1.2 mm Hg). CONCLUSION: 16(R)-HETE suppresses the development of increased ICP in a rabbit model of thromboembolic stroke and may serve as a novel therapeutic strategy in ischemic and inflammatory pathophysiological states.

Complement depletion does not reduce brain injury in a rabbit model of thromboembolic stroke.

The contribution of the complement system to cerebral ischemic and ischemia/reperfusion injury was examined in a rabbit model of thromboembolic stroke by delivery of an autologous clot embolus to the intracranial circulation via the internal carotid artery. A two-by-two factorial design was employed to study the impact of complement depletion via pretreatment with cobra venom factor (CVF, 100 U/kg i.v.) in the setting of permanent (without tissue plasminogen activator; t-PA) and transient (with t-PA) cerebral ischemia. Thirty-two New Zealand white rabbits were assigned to one of four groups (n=8, each group): control without t-PA, control with t-PA, CVF without t-PA and CVF with t-PA. In the complement intact animals, t-PA administration resulted in an approximate 30% reduction in infarct size when compared to the group not receiving t-PA (20.4+/-6.6% of hemisphere area vs. 30.1+/-7.2%; mean+/-SEM). However, infarct sizes in the complement depleted rabbits, with (30.7+/-8.2%) or without (30.2+/-7.9%) t-PA, were no different from the control group receiving no therapy. Similarly, no difference in regional cerebral blood flow or final intracranial pressure values was noted between any of the four groups. Complement activation does not appear to be a primary contributor to brain injury in acute thromboembolic stroke.

Humanized anti-L-selectin monoclonal antibody DREG200 therapy in acute thromboembolic stroke.

Strategies directed against activated neutrophils have reduced ischemia-induced brain injury. However, therapies targeted specially against the neutrophil adhesion protein L-selectin have not yet been examined in stroke. This study therefore examined the effects of a monoclonal antibody directed against L-selectin in a rabbit model of thromboembolic stroke with (n = 16) or without (n = 10) concomitant t-PA therapy. Rabbits received either the humanized monoclonal antibody DREG200 directed against the L-selectin receptor or humanized control monoclonal antibody HuDREG55 which does not bind to rabbit L-selectin in addition to t-PA therapy (n = 8, each group). HuDREG200 (2 mg kg-1 i.v.) was given as a bolus 3 h following clot embolization, followed immediately by a 2 h intravenous infusion of t-PA (6.3 mg kg-1. Without t-PA therapy rabbits received HuDREG200 (2 mgkg-1, i.v.; n = 5) or HuDREG55 (n = 5) 1 h following clot embolization. The group receiving HuDREG200 in addition to t-PA demonstrated a moderate improvement in brain infarct size (8.4 +/- 2.4 vs. 13.5 +/- 3.5, %hemisphere, mean +/- sem), ICP (final reading 10.0 +/- 1.6 vs. 12.4 +/- 3.0 torr) and restoration in regional cerebral blood flow (30.2 +/- 7.8 vs. 21.6 +/- 10.9 cc 100 g-1 min-1) when compared to t-PA therapy alone although statistical significance was not achieved. No efficacy was demonstrated in the group receiving HUDREG200 without concomitant t-PA therapy. The results suggest the addition of a humanized anti-L-selectin monoclonal antibody HuDREG200 in combination with t-PA may further improve outcome in acute thromboembolic stroke, although future studies are necessary to support these findings.

Peroxynitrite augments fMLP-stimulated chemiluminescence by neutrophils in human whole blood.

The neutrophil respiratory burst was examined by the technique of luminol-dependent chemiluminescence (LDCL) triggered by submaximal concentrations of N-formyl-methionyl-leucyl-phenylalanine (fMLP) in diluted whole blood. We sought to identify the chemical species responsible for LDCL in whole blood, to examine the role of leukotriene B4 (LTB4) and other arachidonic acid metabolites as mediators of the fMLP signaling pathway, and to investigate the effect of peroxynitrite on this response. Both sodium azide and taurine significantly inhibited LDCL (93% inhibition with 100 microM azide, 52% inhibition with 10 mM taurine). More modest inhibition was seen with superoxide dismutase (SOD), catalase, the nitric oxide synthase inhibitor monomethyl-L-arginine (L-NMMA), and with inhibitors of the cyclooxygenase (indomethacin), lipoxygenase (AA-861; no effect), and cytochrome P-450 (SKF 525-A) pathways of arachidonic acid metabolism. The nitric oxide donor SIN-1 (1-100 microM) and peroxynitrite (10-300 microM) also augmented fMLP-induced LDCL. The augmentation seen with peroxynitrite and SIN-1 was attenuated by SOD. Despite the increase in LDCL, peroxynitrite caused a dose-related inhibition of fMLP-stimulated LTB4 release. In summary, our results indicate that (1) LDCL elicited by fMLP in diluted whole blood appears primarily mediated by hypochlorous acid derived from myeloperoxidase; (2) pretreatment with the nitric oxide donor SIN-1 or with peroxynitrite augments LDCL; and (3) LTB4 release does not contribute to fMLP-stimulated LDCL or in the modulation of LDCL by SIN-1 or peroxynitrite.

The effect of oral antiplatelet agents on tissue plasminogen activator-mediated thrombolysis in a rabbit model of thromboembolic stroke.

OBJECTIVE: The success of thrombolytic therapy in acute stroke relies on timely reperfusion. The current study examines the efficacy of antiplatelet agents as adjuvants for thrombolytic therapy. METHODS: Using an established rabbit model of clot embolization and a randomized blinded design, rabbits (n = 8 in each group) were orally pretreated daily for 5 days with adjuvant aspirin (1 mg/kg of body weight or 20 mg/kg), ticlopidine (100 mg/kg), or vehicle (sodium carbonate). On the 6th day, tissue plasminogen activator (6.3 mg/kg administered intravenously over 2 h), was initiated 1 hour after embolization. RESULTS: In all groups, cerebral blood flow (CBF) was reduced to < 10 ml/100 g/min immediately after clot embolization. After the initiation of tissue plasminogen activator (t-PA), there was significant restoration of CBF in the control (t-PA only) and ticlopidine groups (P < 0.05) only. Restoration of CBF generally correlated with brain infarct size (percent hemisphere, mean +/- standard error of the mean), which was 18.0 +/- 7.0 in the t-PA only group versus 11.0 +/- 3.3, 26.5 +/- 5.8, and 21.5 +/- 3.4 in the ticlopidine, low-dose aspirin, and high-dose aspirin groups, respectively (ticlopidine versus aspirin, P < 0.05). Clot lysis was identical in the control and ticlopidine groups, with 6 of 8 animals demonstrating complete clot lysis. Aspirin antagonized clot lysis in a dose-related manner, with low-and high-dose aspirin groups noting clot lysis in four of eight and two of eight animals, respectively. CONCLUSIONS: Pretreatment with ticlopidine significantly reduced brain infarct size when compared with aspirin treatment (P < 0.05). Moreover, whereas ticlopidine treatment did not affect clot lysis or CBF relative to t-PA alone, aspirin therapy resulted in antagonism of clot lysis and was associated with a more modest restoration of blood flow. This study provides a background for a more comprehensive understanding of the balance of thrombogenicity and thrombolysis and may assist in the development of novel therapies to expedite cerebrovascular patency and reduce ischemic and reperfusion-mediated neuronal injury.

Effects of low-protein diets on protein metabolism in insulin-dependent diabetes mellitus patients with early nephropathy.

The dietary protein requirements of patients with insulin-dependent diabetes mellitus (IDDM) are unknown. We studied the metabolic adaptation of IDDM patients with early nephropathy to therapeutic, low-protein diets. Six patients were studied at baseline and following 1 and 12 weeks of consuming 0.6 g/kg-1 ideal body weight.day-1 protein. Outcome variables included quadriceps muscle strength, body composition, nitrogen balance, and estimates of whole body protein turnover using an infusion of L-[1-13C]leucine. All subjects experienced decreased muscle strength (6.6% decline in maximal torque, P = 0.05) and increased body fatness (11% increase in fat mass, P = 0.03) with no change in total body weight. This was accompanied by an initial 40% decrease in the rate of whole-body leucine oxidation after 1 week of dietary restriction which returned almost to baseline rates by 12 weeks (P less than 0.001, 1 week vs. 12 weeks). Nitrogen balance remained negative throughout the period of protein restriction. We conclude that IDDM subjects with early nephropathy experience protein undernutrition during the first 3 months of the dietary protein restriction currently recommended for the treatment of nephropathy. This may result, in part, from an inability to conserve essential amino acids from oxidative loss over the time period of the study.

Exercise training increases the number of glucose transporters in rat adipose cells.

We studied the mechanism for the increase in glucose transport activity that occurs in adipose cells of exercise-trained rats. Glucose transport activity, glucose metabolism, and the subcellular distribution of glucose transporters were measured in adipose cells from rats raised in wheel cages for 6 wk (mean total exercise 350 km/rat), age-matched sedentary controls, and young sedentary controls matched for adipose cell size. Basal rates of glucose transport and metabolism were greater in cells from exercise-trained rats compared with young controls, and insulin-stimulated rates were greater in the exercise-trained rats compared with both age-matched and young controls. The numbers of plasma membrane glucose transporters were not different among groups in the basal state; however, with insulin stimulation, cells from exercise-trained animals had significantly more plasma membrane transporters than young controls or age-matched controls. Exercise-trained rats also had more low-density microsomal transporters than control rats in the basal state. When the total number of glucose transporters/cell was calculated, the exercise-trained rats had 42% more transporters than did either control group. These studies demonstrate that the increased glucose transport and metabolism observed in insulin-stimulated adipose cells from exercise-trained rats is due, primarily, to an increase in the number of plasma membrane glucose transporters translocated from an enlarged intracellular pool.