Lysophosphatidic acid increased infarct size in the early stage of cerebral ischemia-reperfusion with increased BBB permeability.

BACKGROUND: We investigated whether exogenous lysophosphatidic acid (LPA), a phospholipid extracellular signaling molecule, would increase infarct size and blood-brain barrier (BBB) disruption during the early stage of cerebral ischemia-reperfusion, and whether it works through Akt-mTOR-S6K1 intracellular signaling. MATERIAL AND METHODS: Rats were given either vehicle or LPA 1 mg/kg iv three times during reperfusion after one hour of middle cerebral artery (MCA) occlusion. In another group, prior to administration of LPA, 30 mg/kg of PF-4708671, an S6K1 inhibitor, was injected. After one hour of MCA occlusion and two hours of reperfusion the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid and the volume of 3H-dextran distribution were determined to measure the degree of BBB disruption. At the same time, the size of infarct was determined and western blot analysis was performed to determine the levels of phosphorylated Akt (p-Akt) and phosphorylated S6 (pS6). RESULTS: LPA increased the Ki in the ischemic-reperfused cortex (+43%) when compared with Control rats and PF-4708671 pretreatment prevented the increase of Ki by LPA. LPA increased the percentage of cortical infarct out of total cortical area (+36%) and PF-4708671 pretreatment prevented the increase of the infarct size. Exogenous LPA did not significantly change the levels of p-Akt as well as pS6 in the ischemic-reperfused cortex. CONCLUSION: Our data demonstrate that the increase in BBB disruption could be one of the reasons of the increased infarct size by LPA. S6K1 may not be the major target of LPA. A decrease of LPA during early cerebral ischemia-reperfusion might be beneficial for neuronal survival.

Lysophosphatidic Acid Reduces Microregional Oxygen Supply/Consumption Balance after Cerebral Ischemia-Reperfusion.

BACKGROUND: Lysophosphatidic acid (LPA) is a small phospholipid-signaling molecule, which can alter responses to stress in the central nervous system. OBJECTIVE: We hypothesized that exogenous LPA would increase the size of infarct and reduce microregional O2 supply/consumption balance after cerebral ischemia-reperfusion. METHODS: This was tested in isoflurane-anesthetized rats with middle cerebral artery blockade for 1 h and reperfusion for 2 h with or without LPA (1 mg/kg, at 30, 60, and 90 min after reperfusion). Regional cerebral blood flow was determined using a C14-iodoantipyrine autoradiographic technique. Regional small-vessel (20-60 µm in diameter) arterial and venous oxygen saturations were determined microspectrophotometrically. RESULTS: There were no significant hemodynamic or arterial blood gas differences between groups. The control ischemic-reperfused cortex had a similar O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic-reperfused cortex with many areas of low O2 saturation (43 of 80 veins with O2 saturation below 50%). LPA did not significantly alter cerebral blood flow, but it did significantly increase O2 extraction and consumption of the ischemic-reperfused region. It also significantly increased the number of small veins with low O2 saturations in the reperfused region (76 of 80 veins with O2 saturation below 50%). This was associated with a significantly increased cortical infarct size after LPA administration (11.4 ± 0.5% control vs. 16.4 ± 0.6% LPA). CONCLUSION: This suggests that LPA reduces cell survival and that it is associated with an increase in the number of small microregions with reduced local oxygen balance after cerebral ischemia-reperfusion.

Improvement in Microregional Oxygen Supply/Consumption Balance and Infarct Size After Cerebral Ischemia-Reperfusion With Inhibition of p70 Ribosomal S6 Kinase (S6K1).

BACKGROUND: We tested the hypothesis that inhibition of p70 ribosomal S6 kinase (S6K1) would decrease infarct size and improve microregional O2 supply/consumption balance after cerebral ischemia-reperfusion. METHODS: This was tested in isoflurane-anesthetized rats with middle cerebral artery blockade for 1 hour and reperfusion for 2 hours with or without PF-4708671 (S6K1 inhibitor, 75 mg/kg, 15 minutes after blockade). Regional cerebral blood flow was determined using a C14-iodoantipyrine autoradiographic technique. Regional small vessel (20-60 µm diameter) arterial and venous oxygen saturations were determined microspectrophotometrically. RESULTS: There were no significant hemodynamic or arterial blood gas differences between groups. The control ischemic-reperfused cortex had a similar O2 consumption to the contralateral cortex. However, microregional O2 supply/consumption balance was significantly reduced in the ischemic-reperfused cortex with many areas of low O2 saturation (23 of 80 veins with O2 saturation below 45%). PF-4708671 did not significantly alter cerebral blood flow or O2 consumption. However, it significantly reduced the number of small veins with low O2 saturations in the reperfused region (6 of 80 veins with O2 saturation below 45%). This was associated with a significantly reduced cortical infarct size after S6K1 inhibition (12.9 ± .8% control versus 6.6 ± .3% PF-4708671). CONCLUSION: This suggests that S6K1 inhibition is important for cell survival and that it reduces the number of small microregions with reduced local oxygen balance after cerebral ischemia-reperfusion.

Inhibition of p70 ribosomal S6 kinase 1 (S6K1) by PF-4708671 decreased infarct size in early cerebral ischemia-reperfusion with decreased BBB permeability.

It is not clear whether inhibition of p70 ribosomal S6 kinase 1 (S6K1) is neuroprotective in cerebral ischemia-reperfusion. Decreasing blood-brain barrier (BBB) disruption has been associated with a better neuronal outcome in cerebral ischemia. We hypothesized that inhibition of S6K1 would decrease BBB disruption and infarct size in the early stage of cerebral ischemia-reperfusion. Middle cerebral artery occlusion (MCAO) was performed in rats under isoflurane anesthesia with controlled ventilation. 75 mg/kg of PF-4708671, an S6K1 inhibitor, was administered intraperitoneally 15 min after MCAO. After 1 h of MCAO and 2 h of reperfusion, the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid and the volume of 3H-dextran distribution were determined to assess the degree of BBB disruption. At the same time point, phosphorylated Rictor (pT1135) and the infarct size were measured to evaluate S6K1 activity. In the PF-4708671 treated rats, the Ki of the ischemic-reperfused cortex was lower than the untreated rats (-22%, P < 0.05) and the volume of dextran distribution was significantly lower in most brain regions. With PF-4708671, a significant decrease in pT1135 Rictor was observed and the percentage of cortical infarct out of total cortical area was decreased (11.6 ±â€¯2.0% vs 7.2 ±â€¯1.1%, P < 0.0001). Our data demonstrate that PF-4708671 decreased the size of the cortical infarct in the ischemic-reperfused cortex with a decrease in BBB disruption suggesting that inhibition of S6K1 may induce neuronal survival in early cerebral ischemia-reperfusion and that a decrease of BBB disruption could be one of the contributing factors.

An Unusual Cause of Failure to Ventilate.

We report an unusual case of endotracheal tube failure. It was due to a manufacturing defect in the internal white plastic piece that is normally depressed by the luer-lock syringe within the blue pilot balloon. Prior to use, the endotracheal tube was tested and functioned normally. A 64-year-old patient in the intensive care unit with a history of hypertension was being mechanically ventilated after uneventful abdominal surgery. After several hours in the intensive care unit, he was noted to be suddenly no longer receiving adequate tidal volumes from the ventilator. It was found that the cuff on the endotracheal tube was not retaining air when it was filled with air from a syringe. This lead to a large "leak" around the endotracheal tube such that the intended tidal volumes set on the ventilator were not delivered to the patient. The patient was uneventfully reintubated and did well. Subsequent investigation revealed the cause to be a manufacturing defect in the internal white plastic piece that is normally depressed by the luer-lock syringe within the blue pilot balloon. Other mechanisms of cuff failure are reviewed in this case report. This case is an unusual reason for cuff failure. Illustrations supplied alert the reader how to identify the appearance of this manufacturing defect in a pilot balloon. This case illustrates the potential device malfunctions that can develop during a procedure, even when the equipment has been tested and previously functioned well. Even small defects developing in well-engineered products can lead to critical patient care emergencies.

Activation of Akt by SC79 decreased cerebral infarct in early cerebral ischemia-reperfusion despite increased BBB disruption.

Activation of Akt has been suggested to produce neuronal protection in cerebral ischemia. Decreasing blood-brain barrier (BBB) disruption has been associated with a better neuronal outcome in cerebral ischemia. We hypothesized that activation of Akt would decrease BBB disruption and contribute to decreasing the size of infarct in the early stage of cerebral ischemia-reperfusion within the therapeutic window. Transient middle cerebral artery occlusion (MCAO) was performed in rats under isoflurane anesthesia with controlled ventilation. Rats were treated with SC79 (a selective Akt activator which is cell and BBB permeable) 0.05 mg/kg × 3 i.p. or vehicle i.p. perioperatively. After one hour of MCAO and two hours of reperfusion, the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid (14C-AIB, molecular weight 104 Da) and the volume of 3H-dextran (molecular weight 70,000 Da) distribution were determined to measure the degree of BBB disruption. At the same time point, the size of infarction was determined using tetrazolium staining. In an additional group of rats, a higher dose of SC79 (0.5 mg/kg × 3) was administered to determine the size of infarct. Administration of SC79 increased the Ki in the ischemic-reperfused cortex (IR-C, +32%, p < 0.05) as well as in the contralateral cortex (CC, +35%, p < 0.05) when compared with the untreated animals with MCAO/reperfusion. The volume of dextran distribution was not significantly changed by SC79. SC79 treatment significantly produced a decrease in the percentage of cortical infarct out of total cortical area (12.7 ±â€¯1.7% vs 6.9 ±â€¯0.9%, p < 0.001). Increasing the dose of SC79 by ten times did not significantly affect the size of cortical infarct. Contrary to our hypothesis, our data demonstrated that SC79 decreased the size of the infarct in the ischemic-reperfused cortex despite an increase in BBB disruption. Our data suggest the importance of activation of Akt for neuronal survival in the early stage of cerebral ischemia-reperfusion within the therapeutic window and that the mechanism of neuroprotection may not be related to the BBB effects of SC79.

Varicella Pneumonia: Case Report and Review of a Potentially Lethal Complication of a Common Disease.

Varicella zoster virus causes varicella (chickenpox). It can be reactivated endogenously many years later to cause herpes zoster (shingles). Although varicella is usually a benign disease in healthy children, it resulted in over 11 000 hospitalizations and over 100 deaths every year, in all ages, in the United States. Morbidity was considerably worse in older teenagers and adults. Between 5% and 15% of cases of adult chickenpox will produce some form of pulmonary illness. Progression to pneumonia risk factors include pregnancy, age, smoking, chronic obstructive pulmonary disease, and immunosuppression. Typically, pulmonary symptoms occur 1 to 6 days after varicella zoster infection. They often include cough, fever, and dyspnea. Treatment is a 7-day course of intravenous acyclovir for varicella pneumonia. Early intervention may modify the course of this complication. This review illustrates practical features with a case of a 34-year-old female with severe varicella pneumonia. Despite the lack of significant past medical history and absence of immunosuppression, her pneumonia worsened and by using continuous positive airway pressure mask, intubation was avoided. More important, the radiographic progression of severe varicella pneumonia is shown. This highlights how a common disease of varicella can progress in an adult and manifest with significant organ malfunction.

Rapamycin decreased blood-brain barrier permeability in control but not in diabetic rats in early cerebral ischemia.

Diabetes causes functional and structural changes in blood-brain barrier (BBB). The mammalian target of rapamycin (mTOR) has been associated with glucose metabolism, diabetes, and altering BBB permeability. Since there is only a narrow therapeutic window (3h) for stroke victims, it is important to investigate BBB disruption in the early stage of cerebral ischemia. We compared the degree of BBB disruption in diabetic and in control rats at two hours of reperfusion after one hour of middle cerebral artery (MCA) occlusion with or without inhibition of mTOR. Two weeks after streptozotocin ip to induce diabetes, MCA occlusion was performed. In half of the rats, an mTOR inhibitor, rapamycin was given for 2days before MCA occlusion. After one hour of MCA occlusion and two hours of the reperfusion, the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid was determined to quantify degree of BBB disruption. Ischemia-reperfusion increased the Ki in the control animals. Streptozotocin increased the Ki in the ischemic-reperfused (IR-C, +22%) as well as in the contralateral cortex (CC, +40%). Rapamycin decreased the Ki in the IR-C (-32%) as well as in the CC (-26%) in the control rats. However, rapamycin did not affect Ki in the IR-C or in the CC in the diabetic rats. Our data demonstrated a greater BBB disruption in diabetes in the ischemic as well as non-ischemic cortex even in the early stage of cerebral ischemia-reperfusion and that acute administration of rapamycin did not significantly affect BBB permeability in diabetes. From our quantitative analysis of BBB disruption, the vulnerability of BBB in diabetes has been emphasized in the early stage of cerebral ischemia-reperfusion and a less important role of the mTOR pathway is suggested in altering BBB permeability in diabetes.

Blood -brain barrier disruption was less under isoflurane than pentobarbital anesthesia via a PI3K/Akt pathway in early cerebral ischemia.

One of the important factors altering the degree of blood-brain barrier (BBB) disruption in cerebral ischemia is the anesthetic used. The phosphoinositide 3-kinase (PI3K)/Akt signaling pathway has been reported to be involved in modulating BBB permeability and in isoflurane induced neuroprotection. This study was performed to compare the degree of BBB disruption in focal cerebral ischemia under isoflurane vs pentobarbital anesthesia and to determine whether inhibition of PI3K/Akt would affect the disruption in the early stage of focal cerebral ischemia. Permanent middle cerebral artery (MCA) occlusion was performed in rats under 1.4% isoflurane or pentobarbital (50mg/kg i.p.) anesthesia with controlled ventilation. In half of each group LY294002, which is a PI3K/Akt inhibitor, was applied on the ischemic cortex immediately after MCA occlusion. After one hour of MCA occlusion, the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid (14C-AIB) was determined to quantify the degree of BBB disruption. MCA occlusion increased the Ki both in the isoflurane and pentobarbital anesthetized rats. However, the value of Ki was lower under isoflurane (11.5±6.0µL/g/min) than under pentobarbital (18.3±7.1µL/g/min) anesthesia. The Ki of the contralateral cortex of the pentobarbital group was higher (+74%) than that of the isoflurane group. Application of LY294002 on the ischemic cortex increased the Ki (+99%) only in the isoflurane group. The degree of BBB disruption by MCA occlusion was significantly lower under isoflurane than pentobarbital anesthesia in the early stage of cerebral ischemia. Our data demonstrated the importance of choice of anesthetics and suggest that PI3K/Akt signaling pathway plays a significant role in altering BBB disruption in cerebral ischemia during isoflurane but not during pentobarbital anesthesia.

Hypoxic Preconditioning Increases Blood-Brain Barrier Disruption in the Early Stages of Cerebral Ischemia.

Even though hypoxic preconditioning has been reported to produce neuroprotection, its effect on blood-brain barrier (BBB) disruption in the early stages of cerebral ischemia within the therapeutic window is not clear. Since hypoxic preconditioning increases expression of vascular endothelial growth factor (VEGF) that modulates vascular permeability, the effects of hypoxic preconditioning and VEGF on BBB permeability were investigated after one hour of focal cerebral ischemia. Rats were exposed to 8% of oxygen for two hours or room air and then 24 hours later, permanent middle cerebral artery (MCA) occlusion was performed. In some of the hypoxic preconditioned rats, a VEGF-A antibody was applied to the ischemic cortex one hour before MCA occlusion. One hour after MCA occlusion, the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid was determined to measure the degree of BBB disruption. MCA occlusion increased the Ki when compared with the contralateral cortex (14.1 ± 4.0 vs 4.2 ± 1.9 µL/g/min, p < 0.0001). Hypoxic preconditioning further increased the Ki in the ischemic cortex when compared with the control rats (25.1 ± 8.7 µL/g/min, p < 0.01). Application of VEGF antibody to the ischemic cortex of the hypoxic preconditioned animals reduced the Ki to the level of the control rats (13.6 ± 5.1 µL/g/min, p < 0.01). Our data demonstrated that hypoxic preconditioning increased BBB disruption through a VEGF related pathway and suggest the possibility of aggravation of brain edema by hypoxic preconditioning in the early stages of cerebral ischemia.

Effects of rapamycin pretreatment on blood-brain barrier disruption in cerebral ischemia-reperfusion.

The mammalian target of rapamycin (mTOR) pathway is essential in neuronal survival and repair in cerebral ischemia. Decreases in blood-brain barrier (BBB) disruption are associated with a decrease in neuronal damage in cerebral ischemia. This study was performed to investigate how pre-inhibition of the mTOR pathway with rapamycin would affect BBB disruption and the size of the infarcted cortical area in the early stage of focal cerebral ischemia-reperfusion using quantitative analysis of BBB disruption. Rats were treated with 20mg/kg of rapamycin i.p. once a day for 2days (Rapamycin Group) or vehicle (Control Group) before transient middle cerebral artery (MCA) occlusion. After one hour of MCA occlusion and two hours of reperfusion, the transfer coefficient (Ki) of (14)C-α-aminoisobutyric acid ((14)C-AIB) to measure the degree of BBB disruption and the size of the cortical infarct were determined. Ischemia-reperfusion increased the Ki in the Rapamycin treated (+15%) as well as in the untreated control group (+13%). However, rapamycin pretreatment moderately decreased Ki in the contralateral (-30%) as well as in the ischemic-reperfused (-29%) cortex when compared with the untreated control group. Rapamycin pretreatment substantially increased the percentage of cortical infarct compared with the control group (+56%). Our data suggest that activation of mTOR pathway is necessary for neuronal survival in the early stage of cerebral ischemia-perfusion and that the reason for the enlarged cortical infarct by rapamycin pretreatment may be related to its non-BBB effects on the mTOR pathway.