[Progress on perioperative monitoring of cerebral blood flow autoregulation].

Cerebral blood flow autoregulation is physiologically protective mechanism to maintain the stability of cerebral blood flow. Once autoregulation is impaired, the cerebral blood flow fluctuates with blood pressure, leading to the risk of brain ischemia or cerebral hyperemia. Multiple research results indicate that cerebral blood flow can be monitored indirectly and continuously with transcranial Doppler, near infrared spectroscopy or ICP. The correlation coefficient calculated by the surrogate for cerebral blood flow and blood pressure is used to judge cerebral blood flow autoregulation. When the correlation coefficient is close to 1, cerebral blood flow will be passively fluctuated by blood pressure, indicating autoregulation is impaired. When the coefficient is less than 0, cerebral blood flow will not be changed with blood pressure, indicating autoregulaiton is intact. The status of autoregualtion is closely associated with mortality or poor neurological outcomes in patients with cardiac surgery underwent cardiopulmonary bypass, liver transplantation patients or patients with deep trendelenburg position for long time or beach chair position. Continuous monitoring of cerebral blood flow autoregulation can identify the lower or the upper limit of autoregulation, and provide information to individualize the perioperative management of blood pressure.

[Expression of aquaporin-4 during brain edema in rats with thioacetamide-induced acute encephalopathy].

OBJECTIVE: To investigate the expression of aquaporin-4 (AQP4) during brain edema in rats with thioacetamide-induced acute liver failure and encephalopathy. METHODS: The rat model of acute hepatic failure and encephalopathy was induced by intraperitoneal injection of thioacetamide (TAA) at a 24-hour interval for 2 consecutive days. Thirty-two SD rats were randomly divided into the model group (n = 24) and the control group (normal saline, n = 8). And then the model group was further divided into 3 subgroups by the timepoint of decapitation: 24 h (n = 8), 48 h (n = 8) and 60 h (n = 8). Then we observed their clinical symptoms and stages of HE, indices of liver function and ammonia, liver histology and brain water content. The expression of AQP4 protein in brain tissues was measured with Western blot and the expression of AQP4mRNA with RT-PCR (reverse transcription-polymerase chain reaction). RESULTS: Typical clinical manifestations of hepatic encephalopathy occurred in all TAA-administrated rats. The model rats showed the higher indices of ALT (alanine aminotransferase), AST (aspartate aminotransferase), TBIL (total bilirubin) and ammonia than the control rats (P < 0.05). The brain water content was significantly elevated in TAA-administrated rats compared with the control (P < 0.05). The expressions of AQP4 protein and mRNA in brain tissues significantly increased in TAA-administrated rats (P < 0.05). In addition, the expressions of AQP4 protein and mRNA were positively correlated with brain water content (r = 0.536, P < 0.01; r = 0.566, P = 0.01). CONCLUSIONS: The high expression of AQP4 in rats with TAA-induced acute liver failure and encephalopathy plays a significant role during brain edema. AQP4 is one of the molecular mechanisms for the occurrence of brain edema in hepatic encephalopathy.

Ammonia induces upregulation of aquaporin-4 in neocortical astrocytes of rats through the p38 mitogen-activated protein kinase pathway.

BACKGROUND: Astrocyte swelling is an important consequence of hepatic encephalopathy, and aquaporin-4 has been reported to play a vital role in this swelling. Ammonia causes astrocyte swelling and is also known to modulate aquaporin-4 expression in the astrocyte foot processes. The purpose of this study was to explore the mechanism of ammonia-induced aquaporin-4 expression, which has been suggested to involve the p38 mitogen-activated protein kinase pathway. METHODS: We exposed cultured astrocytes to ammonium chloride, an in vitro model of hepatic encephalopathy. The purity of cultured astrocytes was evaluated by fluorescent glial fibrillary acidic protein labeling; cell morphology was assessed by light microscopy; the expression of aquaporin-4, phospho-p38, and p38 were detected by Western blotting analysis. Statistical analysis was performed by one-way factorial analysis of variance, and the relationship between variables was calculated by linear regression using SPSS version 13.0 program for Windows (SPSS, Chicago, IL, USA). RESULTS: The purity of cultured astrocytes was (96.6 +/- 1.4)%. Astrocytes swelled significantly when exposed to 5 mmol/L ammonium chloride for 24 hours as compared to non-exposed astrocytes. Co-treatment with 10 micromol/L SB203580 (an inhibitor of p38) attenuated the degree of ammonium chloride induced astrocyte swelling. Western blotting analysis revealed that the expression levels of phospho-p38 and aquaporin-4 in ammonium chloride treated cells were significantly increased relative to the control group (P < 0.001); SB203580 co-treatment inhibited the increased expression of phospho-p38 and aquaporin-4 relative to the ammonium chloride treated group (P = 0.002 and P = 0.015 respectively). The phosphorylation of p38 and upregulation of aquaporin-4 were highly correlated (r = 0.909). There were no significant differences in total p38 expression among the groups (P = 0.341). CONCLUSIONS: Ammonium chloride induced upregulation of aquaporin-4 in astrocytes is regulated by the p38 mitogen-activated protein kinase pathway. Inhibiting p38 activation prevented ammonium chloride induced aquaporin-4 protein upregulation.

[Effect of propofol upon ammonia-induced neocortical astrocyte swelling and aquaporin-4 expression].

OBJECTIVE: To investigate the effect of propofol upon ammonia-induced neocortical astrocyte swelling and aquaporin-4 expression in rat astrocyte. METHODS: Methods Astrocytes were isolated from newborn Sprague Dawley rats. After a 3-week culture, cell immunofluorescence was employed to label glial fibrillary acidic protein, the specific protein of astrocyte. Astrocytes were cultured with NH4Cl (5 mmol/L) for 6, 12, 24 and 48h. Astrocytes were pretreated by propofol and DMSO respectively for 30 min and then exposed to NH4Cl for 24h. The expression of AQP4 was detected by the Western blot; cell morphology assessed by light microscopy and cell viability measured by MTF reduction assay. RESULTS: The expression of AQP4 was elevated after a 12h exposure to ammonia, lasted to 48h and peaked at 24h. Astrocytes were found significantly swelling in the NH4Cl-24h and DMSO pretreated groups as compared with the propofol pretreated group. The over-expression of aquaporin-4 was attenuated by propofol pretreatment and the cell viability of astrocytes in the propofol pretreated group was higher than that in the NH4Cl-24h group (P < 0.05). CONCLUSION: Pretreatment of astrocytes with propofol can inhibit the over-expression of AQP4, relieve cellular swelling and reduce the ammonia-induced decline in cell viability of astrocytes.

Propofol inhibits aquaporin 4 expression through a protein kinase C-dependent pathway in an astrocyte model of cerebral ischemia/reoxygenation.

BACKGROUND: Aquaporin 4 (AQP4) plays a key role in maintaining water balance in the central nervous system, and its dysfunction may lead to brain edema. Previous studies have suggested that propofol may be involved in neuroprotection by preventing brain edema. In this study, we examined the effects of propofol on edema and assessed its neuroprotective actions in an oxygen and glucose deprivation (OGD) model of cultured rat astrocytes. We assessed the effects of propofol on AQP4 expression and the possible role of the protein kinase C (PKC) pathway on this effect. METHODS: Neocortical astrocytes were exposed to OGD in an anaerobic chamber. After 6 h of OGD exposure, astrocytes were subsequently subjected to 24 h of reoxygenation. Propofol was added during the OGD phase of the model. Cell morphology was assessed by light microscopy. Astrocyte viability was assessed by measuring 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide absorbency (optical density value) and the percentage of lactate dehydrogenase released by injured astrocytes. AQP4 expression was evaluated with Western blot analysis. To investigate the possible mechanism of propofol's effects on AQP4 expression, cultured astrocytes were pretreated for 24 h with the PKC activator, 12-O-tetradecanoylphorbol 13-acetate, before the propofol treatment/OGD 6 h/reoxygenation 24 h. RESULTS: We found by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide testing that astrocyte viability began to decrease after about 4 h of OGD exposure and decreased to 60% after 6 h of OGD. When 6 h of OGD was followed by 24 h of reoxygenation, cell viability was further decreased. AQP4 expression was attenuated after 6 h of OGD exposure but was reversed and exceeded baseline levels after 24 h of reoxygenation. Propofol dose-dependently reduced cell death assessed by lactate dehydrogenase test (P < 0.05), and 10 muM propofol significantly down-regulated AQP4 expression in astrocytes after 6 h of OGD followed by 24 h of reoxygenation (P < 0.01). Prolonged (24 h) pretreatment with the phorbol ester, 12-O-tetradecanoylphorbol 13-acetate before OGD significantly reversed the effect of propofol on AQP4 expression (P < 0.01). CONCLUSION: Propofol, administered during OGD, provided neuroprotective effects and down-regulated AQP4 expression in the OGD/reoxygenation model of cultured rat astrocytes. Activation of the PKC pathway may block the effects of propofol.