Enoxaparin, a low molecular weight heparin decreases infarct size and improves sensorimotor function in a rat model of focal cerebral ischemia

Enoxaparin ameliorates post-traumatic brain injury edema and neurologic recovery, reducing cerebral leukocyte endothelial interactions and vessel permeability in vivo

BACKGROUND

Traumatic brain injury (TBI) confers a high risk of venous thrombosis, but early prevention with heparinoids is often withheld, fearing cerebral hematoma expansion. Yet, studies have shown heparinoids not only to be safe but also to limit brain edema and contusion size after TBI. Human TBI data also suggest faster radiologic and clinical neurologic recovery with earlier heparinoid administration. We hypothesized that enoxaparin (ENX) after TBI blunts in vivo leukocyte (LEU) mobilization to injured brain and cerebral edema, while improving neurologic recovery without increasing the size of the cerebral hemorrhagic contusion.

METHODS

CD1 male mice underwent either TBI by controlled cortical impact (CCI, 1-mm depth, 6 m/s) or sham craniotomy. ENX (1 mg/kg) or vehicle (VEH, 0.9% saline, 1 mL/kg) was administered at 2, 8, 14, 23, and 32 hours after TBI. At 48 hours, intravital microscopy was used to visualize live LEUs interacting with endothelium and microvascular leakage of fluorescein isothiocyanate-albumin. Neurologic function (Neurological Severity Score, NSS), activated clotting time, hemorrhagic contusion size, as well as brain and lung wet-to-dry ratios were evaluated post mortem. Analysis of variance with Bonferroni correction was used for statistical comparisons between groups.

RESULTS

Compared with VEH, ENX significantly reduced in vivo LEU rolling on endothelium (72.7 ± 28.3 LEU/100 μm/min vs. 30.6 ± 18.3 LEU/100 μm/min, p = 0.02) and cerebrovascular albumin leakage (34.5% ± 8.1% vs. 23.8% ± 5.5%, p = 0.047). CCI significantly increased ipsilateral cerebral hemisphere edema, but ENX treatment reduced post-CCI edema to near control levels (81.5% ± 1.5% vs. 77.6% ± 0.6%, p < 0.01). Compared with VEH, ENX reduced body weight loss at 24 hours (8.7% ± 1.2% vs. 5.8% ± 1.1%, p < 0.01) and improved NSS at 24 hours (14.5 ± 0.5 vs. 16.2 ± 0.4, p < 0.01) and 48 hours (15.1 ± 0.4 vs. 16.7 ± 0.5, p < 0.01) after injury. There were no significant differences in activated clotting time, hemorrhagic contusion size, and lung water content between the groups.

CONCLUSION

ENX reduces LEU recruitment to injured brain, diminishing visible microvascular permeability and edema. ENX may also accelerate neurologic recovery without increasing cerebral contusion size. Further study in humans is necessary to determine safety, appropriate dosage, and timing of ENX administration early after TBI.

Effect of heparin following cervical spinal cord injuries in rats

BACKGROUND

Risks of neurological deterioration after heparin administration following cervical spinal cord injury (SCI) in humans are unknown.

OBJECTIVE

To elucidate the safety of heparin following cervical SCI and investigate its potential neuroprotectant role.

METHODS

Sixty-two Sprague Dawley adult rats were subjected to mild (0.6 mm), moderate (0.9 mm), or severe (1.2 mm) C7-SCI. At each injury severity, intravenous heparin or saline was administered for 72 hours following SCI. Behavioral tests (Basso, Beattie, Bresnahan scores, Hargreave's) were performed before killing the rats at week 7. Half of the rats were killed at day 3, and the remainder at week 7 after SCI. Immunohistochemistry, Western blot analysis, and axonal retrograde tracing were conducted at both times.

RESULTS

Subpial hemorrhage was greater in heparin-treated animals compared with controls at all severities of SCI day 3 after injury. Counterintuitively, intraparencyhmal hemorrhage was minimal in the lesion epicenter following mild SCI in the heparin-treated animals compared with controls. India ink perfusion revealed greater preservation of microcirculation in heparin-treated animals compared with a reduction in control animals. A decrease in spinal cord perfusion correlated directly with an increase in hypoxia-inducible factor-1α expression. There was significant gray matter sparing, but no change in white matter volume after heparin treatment at week 7 in the mild SCI group. Beneficial effects on hemorrhagic volume, axon sparing, and functional recovery following heparin treatment were not observed in the moderate or severe SCI group.

CONCLUSION

Heparin treatment following SCI is safe at all degrees of injury. Heparin decreases platelet aggregation and microvascular occlusion, providing a potential neuroprotective effect following mild SCI.

Effects of enoxaparin in the rat hippocampus following traumatic brain injury

Purpose of this study was to investigate the effects of low molecular weight heparin, enoxaparin, on different parameters of the hippocampal damage following traumatic brain injury (TBI) in the rat. TBI of moderate severity was performed over the left parietal cortex using the lateral fluid percussion brain injury model. Animals were s.c. injected with either enoxaparin (1mg/kg) or vehicle 1, 7, 13, 19, 25, 31, 37, and 43 h after the TBI induction. Sham-operated, vehicle-treated animals were used as the control group. Rats were sacrificed 48h after the induction of TBI. Hippocampi were processed for spectrophotometric measurements of the products of oxidative lipid damage, thiobarbituric acid-reactive substances (TBARS) levels, as well as the activities of antioxidant enzymes, superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). Moreover, the Western blotting analyses of the oxidized protein levels, expressions of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), pro- and mature-interleukin-1β (pro-, and mature-IL-1β), and active caspase-3 were performed. COX-2 expressions were also explored by using immunohistochemistry. Glial fibrillary acidic protein immunochistochemistry was performed with the aim to assess the level of astrocytic activity. Fluoro-Jade B staining was used to identify the level and extent of hippocampal neuronal injury. TBI caused statistically significant increases of the hippocampal TBARS and oxidized protein levels as well as COX-2, pro-IL-1β, and active caspase-3 overexpressions, but it did not significantly affect the SOD and GSH-Px activities, the iNOS, and mature-IL-1β expression levels. TBI also induced hippocampal reactive astrocytosis and neurodegeneration. Enoxaparin significantly decreased the hippocampal TBARS and oxidized protein levels, COX-2 overexpression and reactive gliosis, but it did not influence the SOD and GSH-Px activities, pro-IL-1β and active caspase-3 overexpressions as well as neurodegeneration following TBI. These findings demonstrate that enoxaparin may reduce oxidative damage, inflammation and astrocytosis following TBI in the rat and could be a candidate drug for neuroprotective treatment of this injury.

An endogenously deposited fibrin scaffold determines construct size in the surgically created arteriovenous loop chamber model of tissue engineering

BACKGROUND

An arteriovenous loop (AVL) enclosed in a polycarbonate chamber in vivo, produces a fibrin exudate which acts as a provisional matrix for the development of a tissue engineered microcirculatory network.

OBJECTIVES

By administering enoxaparin sodium - an inhibitor of fibrin polymerization, the significance of fibrin scaffold formation on AVL construct size (including the AVL, fibrin scaffold, and new tissue growth into the fibrin), growth, and vascularization were assessed and compared to controls.

METHODS

In Sprague Dawley rats, an AVL was created on femoral vessels and inserted into a polycarbonate chamber in the groin in 3 control groups (Series I) and 3 experimental groups (Series II). Two hours before surgery and 6 hours post-surgery, saline (Series I) or enoxaparin sodium (0.6 mg/kg, Series II) was administered intra-peritoneally. Thereafter, the rats were injected daily with saline (Series I) or enoxaparin sodium (1.5 mg/kg, Series II) until construct retrieval at 3, 10, or 21 days. The retrieved constructs underwent weight and volume measurements, and morphologic/morphometric analysis of new tissue components.

RESULTS

Enoxaparin sodium treatment resulted in the development of smaller AVL constructs at 3, 10, and 21 days. Construct weight and volume were significantly reduced at 10 days (control weight 0.337 +/- 0.016 g [Mean +/- SEM] vs treated 0.228 +/- 0.048, [P < .001]: control volume 0.317 +/- 0.015 mL vs treated 0.184 +/- 0.039 mL [P < .01]) and 21 days (control weight 0.306 +/- 0.053 g vs treated 0.198 +/- 0.043 g [P < .01]: control volume 0.285 +/- 0.047 mL vs treated 0.148 +/- 0.041 mL, [P < .01]). Angiogenesis was delayed in the enoxaparin sodium-treated constructs with the absolute vascular volume significantly decreased at 10 days (control vascular volume 0.029 +/- 0.03 mL vs treated 0.012 +/- 0.002 mL [P < .05]).

CONCLUSION

In this in vivo tissue engineering model, endogenous, extra-vascularly deposited fibrin volume determines construct size and vascular growth in the first 3 weeks and is, therefore, critical to full construct development.

Acute enoxaparin treatment widens the therapeutic window for tPA in a mouse model of embolic stroke

OBJECTIVES

The purpose of this experiment was to determine if the low molecular weight heparin (LMWH) enoxaparin could extend the treatment window for thrombolysis in a mouse model of embolic stroke.

METHODS

To establish the treatment window, mice were treated with tPA 2, 3 or 4 hours after clot insertion. Results showed that only the 2 hour treatment group exhibited infarct volumes significantly smaller than untreated controls. We attempted to widen this window by pre-treating mice with enoxaparin (10 mg/kg, s.c.; n=36) 1 hour before embolization. A control group (n=24) was given a saline injection. The enoxaparin-treated animals were subdivided and treated with tPA either 4 (n=12) or 6 hours (n=12) after clot insertion, while the third group (n=12) was given saline. The saline-pre-treated mice were dived into two groups: one group (n=12) received tPA and the other group (n=12) received saline 4 hours post-stroke. Embolization was confirmed by laser Doppler flowmetry and the effects of the resulting infarcts were evaluated by triphenyltetrazolium chloride staining and by behavioral testing.

RESULTS

Results showed large infarcts and impaired sensorimotor coordination in the saline pre-treated animals confirming the narrow treatment window. Enoxaparin pre-treatment produced significantly smaller infarcts and improved motor behavior in groups treated with tPA both 4 and 6 hours after embolization. Neither the 4 nor the 6 hour tPA-treated groups showed evidence of intracerebral hemorrhage or external bleeding.

CONCLUSION

These data indicate that the LMWH enoxaparin can significantly increase the therapeutic time window in a mouse model of embolic stroke.

Reproducible loss of CA1 neurons following carotid artery occlusion combined with halothane-induced hypotension

The 2-vessel occlusion approach to produce global ischemia in rats requires concomitant reduction of systemic blood pressure. We have utilized the hypotensive effect of halothane administrated by artificial respiration to prevent respiratory arrest and to ensure stable physiological conditions. Systemic blood pressure was reduced to 40-45 mmHg by instant adjustments of the halothane concentration. Bilateral occlusion of the carotid arteries caused a profound and reproducible ischemia, as analyzed by laser-Doppler flowmetry. In the rats exposed to 11, 12, or 13 min of ischemia, 5% died and 5% developed seizures. The extent of neuronal death in CA1 was highly correlated to the duration of ischemia. Following 11 min of ischemia, CA1 neuronal cell death, as analyzed by Fluoro-Jade, was absent 1 day after injury, variable at day 4, and consistent at day 7. The numbers of cresyl violet- and NeuN-positive neurons at day 7 were 8% and 20% of control, respectively. OX42 immunoreactivity was low and variable at day 4, but pronounced at day 7. In conclusion, this rat global ischemia model is relatively simple to perform, has a low mortality, and produces a profound and highly reproducible delayed cell death of hippocampal CA1 neurons.

Detection of chronic sensorimotor impairments in the ladder rung walking task in rats with endothelin-1-induced mild focal ischemia

A comprehensive evaluation of the effects of neuroprotection, neurogenesis, and compensatory mechanisms on the outcome of ischemic insults requires assessment of morphological and functional parameters. Behavioural tests are essential when recording performance throughout the time course of an experiment and the results bear predictive value in preclinical animal models. The goal of this study was to establish a behavioural test procedure for a model of transient focal ischemia induced by injection of endothelin-1 (eMCAO) that results in relatively mild behavioural deficits. The test protocol used in the present study allows evaluation of quantitative and qualitative impairments in skilled motor performance and is sensitive to detect chronic deficits at chronic post-ischemic time intervals. The ladder rung walking task [J. Neurosci. Methods 115 (2002) 169] is a motor test that assesses skilled walking and measures both forelimb and hindlimb placing, stepping and inter-limb co-ordination. In this study we tested the effect of two different technical variants of endothelin-1 application on infarct volume and motor skills (1) application via pre-implanted guiding cannula in awake animals and (2) via direct injection under halothane anaesthesia. We showed that the ladder rung walking task is sensitive in the assessment of loss of fine motor function after induction of relatively small lesions. In animals with implanted cannulas we found a smaller infarct area and an increase in placement errors prior to ischemia animals with eMCAO under anaesthesia showed a long lasting impairment of the contralateral forelimb up to 4 weeks post-eMCAO.

Tongue protrusion: a simple test for neurological recovery in rats following focal cerebral ischemia

A simple tongue protrusion (TP) test is described for rats following focal ischemia induced by middle cerebral artery occlusion (MCAO). MCAO resulted in a dramatic decrease in TP that correlated with a concomitant decline in neurological performance in standard 5- and 20-point tests and deficits in performance in the Morris water maze and the accelerating rotarod. TP values also correlated with infarct size at 7 and 24 days following MCAO. This simple and inexpensive test, that monitors the ability of rats to lick food out of a glass tube, is easily administered, can be administered frequently without changing baseline performance, is not susceptible to behavioral compensation and should not interfere with other tests used concurrently to evaluate neurological deficit. The TP test may, therefore, serve as a useful addition to the battery of tests commonly used to assess neurological damage in rats, particularly in models of stroke.

Examination of sensorimotor performance following middle cerebral artery occlusion in rats

Middle cerebral artery occlusion (MCAO) in rats is the most commonly used stroke model. Besides the infarct size, assessment of sensorimotor performance has become increasingly important in neuroprotective drug research. However, contradictions exist about procedures for testing functional outcome following MCAO. The aim of the present study was to evaluate a relatively simple set of neurological tests based on the most commonly used scoring systems, and to describe the functional recovery and correlation with the infarct size in rats sacrificed 2 or 14 days after permanent or transient MCAO. The smaller infarct size of rats with transient occlusion was reflected in the neurological scores only during the first 6h. By day 14, no recovery occurred in postural signs, lateral resistance and spontaneous activity, other signs showed different degrees of recovery. Correlation with the infarct size was found only on certain days in gait disturbance, placing reactions, daily body weight and spontaneous activity. According to our observations, the most commonly used sensorimotor tests provide a useful initial screening of functional deficits, but these tests most probably measure deficits caused by infarction of the core area. It is suggested that these tests should be completed by more refined tests when testing a neuroprotective drug which reduces the infarct size in penumbral areas.

Low molecular weight heparin versus aspirin for acute ischemic stroke: A systematic review

Aspirin is the standard treatment for acute ischemic stroke, although heparins are widely prescribed. We performed a systematic review of randomized controlled trials to compare the safety and efficacy of low molecular weight heparins (LMWH) with aspirin in acute ischemic stroke. Two completed randomized controlled trials involving 1,933 patients were identified; 1 trial only included patients with presumed cardioembolic stroke. As compared with aspirin, treatment with heparin was associated with a significant reduction in symptomatic venous thromboembolism (odds ratio [OR]--0.29, 95% confidence interval [CI]--0.12-0.66) and an increase in major extracranial hemorrhage (OR--2.57, 95% CI--1.01-6.52). Nonsignificant increases in end-of-treatment case fatality (OR--1.35, 95% CI--0.87-2.08) and symptomatic intracranial haemorrhage (OR--1.82, 95% CI--0.68-4.87) were seen; symptomatic intracranial haemorrhage was significantly raised (OR--4.26, 95% CI--1.04-17.4) with heparin in patients treated within 24 hours of stroke onset. Stroke recurrence (OR--1.24, 95% CI--0.79-1.94) and deterioration (OR--1.13, 95% CI--0.85-1.50) during treatment and end-of-trial death (OR--1.00, 95% CI--0.77-1.30) or dependency and case fatality (OR--1.03, 95% CI--0.85-1.25) did not differ between the 2 treatments. No benefit of LMWH over aspirin was seen in patients with presumed cardioembolic stroke. Low molecular weight heparin should not replace aspirin in the routine management of patients with ischemic stroke, including those with presumed cardioembolic stroke.

Inhibition of factor IX(a) is protective in a rat model of thromboembolic stroke

BACKGROUND AND PURPOSE

Although used clinically to prevent stroke, there are few examples of anticoagulant investigations in the treatment of acute thromboembolic stroke in animal models. The treatment of thromboembolic stroke in experimental models has been investigated almost exclusively around the use of tissue plasminogen activator (tPA). In this study, using a rat thromboembolic stroke model, we investigated the use of an inhibitory anti-factor IX(a) monoclonal antibody (SB 249417) for the treatment of thromboembolic stroke and compared its efficacy to that of tPA.

METHODS

Stroke was initiated by delivering 6 clots into the internal carotid artery. After 2, 4, or 6 hours, rats received either intravenous vehicle, 10.0 mg/kg tPA, or 1.0, 2.0, or 3.0 mg/kg SB 249417. At 24 hours after stroke, infarct volumes and neurological deficits were assessed.

RESULTS

Treatment with tPA 2, 4, or 6 hours after stroke reduced infarct volumes by 35% (P=NS), 45%, and 39%, respectively. tPA treatment did not improve neurological deficits at any time point. Treatment with SB 249417 (3.0 mg/kg) 2, 4, or 6 hours after stroke reduced infarct volumes by 44%, 50%, and 13% (P=NS), respectively. Neurological deficits were reduced by 49%, 42%, and 13% (P=NS), respectively. Neither mortality nor hemorrhage was affected by either treatment.

CONCLUSIONS

The data indicate that the inhibition of factor IX(a) within 4 hours of thromboembolic stroke produced a more favorable outcome than tPA. When treatment was initiated 6 hours after stroke, the benefits of factor IX(a) inhibition were lost, whereas tPA continued to suppress lesion development, albeit without a corresponding improvement in functional deficits. This study suggests that cerebral ischemia and the resultant perfusion deficit are exacerbated by the activation of blood coagulation and that anticoagulants like SB 249417 may find utility in the treatment of ischemic stroke.

Intrathecal administration of liposomal neostigmine prolongs analgesia in mice

BACKGROUND

There is substantial evidence that cholinomimetic drugs increase pain threshold. However, the profound side effects of these agents have limited their clinical use either as analgesics or as analgesic adjuncts. A delivery system that would assure a slow and sustained drug release may be of value in ameliorating the problem of untoward effects.

METHODS

The acetylcholinesterase inhibitor neostigmine was encapsulated into multilamellar lipid vesicles composed of phosphocholine and cholesterol. Three doses of plain or liposomal neostigmine were administered by the intrathecal route to mice (n=8-10/group), and analgesic duration was quantified by tail flick test. The doses were chosen based on preliminary experiments, which showed the maximum tolerated intrathecal doses of plain and liposomal neostigmine formulation were 0.625 microg and 80 microg, respectively. Two other doses for each formulation were then derived by 1:1 serial dilutions. Results were compared using survival analysis.

RESULTS

The median antinociceptive duration for plain neostigmine was 0.33, 0.99 and 1.0 h for the 0.115, 0.312 and 0.625 microg doses, respectively. For the liposomal formulation, the median antinociceptive duration was 1.0, 1.5 and 6.0 h for the 20, 40 and 80 microg doses, respectively.

CONCLUSIONS

Liposomal neostigmine provides prolonged spinal antinociception, and permits the safe administration of a relatively large dose, because drug is gradually released from the liposomal depot. This technology holds promise for the development of a clinically useful neostigmine formulation to provide spinal analgesia.

Elements of cerebral microvascular ischaemia

Although neuronal cells have long been thought to be the prime target of ischaemic insults, events which occur at the blood-vascular-parenchymal interface are necessary for the initiation of ischaemic tissue injury. This cascade of microvascular events includes fibrin accumulation, endothelium expression of leukocyte adhesion receptors, breakdown of the basal laminae with loss of astrocyte and endothelial cell contacts leading to blood-brain barrier disruption and consequently oedema formation and haemorrhagic transformation. Potential stroke treatments have been studied in the clinic and many have not been particularly successful, probably due to the delicate balance between improved outcome and adverse reactions as well as the window of opportunity for drug treatment after symptom onset. The only acute intervention trial demonstrating any benefit in patients was that of intravenous tissue plasminogen activator (tPA), administered within 3 h of the onset of symptoms of ischaemic stroke. Such treatment improved clinical outcome at 3 months, although there was an increased incidence of symptomatic haemorrhage [New Engl. J. Med. 333 (1995) 1581]. The recent progress made in defining the mechanisms involved in the initiation of ischaemic events, as described in this review, may lead to the identification of new strategies for intervention in the ischaemic cascade.