Nuclear-envelope nucleoside triphosphatase kinetics and mRNA transport following brain ischemia and reperfusion

Association between time to advanced airway management and neurologically favourable survival during out-of-hospital cardiac arrest

BACKGROUND

Advanced airway management (AAM) is commonly performed as part of advanced life support. However, there is controversy about the association between the timing of AAM and outcomes after out-of-hospital cardiac arrest (OHCA). This study aimed to determine whether time to AAM is associated with outcomes after OHCA.

METHODS

This was a nationwide population-based observational study using the Japanese government-led registry of OHCA. Adults who experienced OHCA and received AAM by EMS personnel in the prehospital setting from 2014 to 2017 were included. Multivariable logistic regression models were used to assess the associations between time to AAM (defined as time in minutes from emergency call to the first successful AAM) and outcomes after OHCA. Then, associations between early (≤ 20 min) vs. delayed (> 20 min) AAM and outcomes after OHCA were examined using propensity score-matched analyses. The primary outcome was one-month neurologically favourable survival.

RESULTS

A total of 164,223 patients (median [IQR] age, 80 [69-86] years; 57.7% male) were included. The median time to AAM was 17 min (IQR, 14-22). Longer time to AAM was significantly associated with a decreased chance of one-month neurologically favourable survival (multivariable adjusted OR per minute delay, 0.90 [95% CI, 0.90-0.91]). In the propensity score-matched cohort, compared with early AAM, delayed AAM was associated with a decreased chance of one-month neurologically favourable survival (516 of 50,997 [1.0%] vs. 226 of 50,997 [0.4%]; RR, 0.44; 95% CI, 0.37-0.51; NNT, 176).

CONCLUSIONS

Delay in AAM was associated with a decreased chance of one-month neurologically favourable survival among patients with OHCA.

Mechanism underlying carbon tetrachloride-inhibited protein synthesis in liver

AIM: To study the mechanism underlying carbon tetrachloride (CCl₄)-induced alterations of protein synthesis in liver.

METHODS: Male Sprague-Dawley rats were given CCl₄ (1 mL/100 g body weight) and ³H-leucine incorporation. Malondialdehyde (MDA) level in the liver, in vitro response of hepatocyte nuclei nucleotide triphosphatase (NTPase) to free radicals, and nuclear export of total mRNA with 3’-poly A⁺ were measured respectively. Survival response of HepG2 cells to CCl₄ treatment was assessed by methyl thiazolyl tetrazolium. Km and Vmax values of nuclear envelope NTPase activity in liver of rats treated with CCl₄ were assayed by a double-reciprocal plot.

RESULTS: The protein synthesis was inhibited while the MDA level was significantly increased in liver of rats treated with CCl₄. In addition, CCl₄ decreased the NTPase binding capacity of nuclear envelope (Km value) in cultured HepG2 cells. Moreover, in vitro ferrous radicals from Fenton’s system suppressed the NTPase activity of liver nuclear envelope in a dose-dependent manner. Down-regulation of the nuclear envelope NTPase activity indicated a lower energy provision for nucleocytoplasmic transport of mRNA molecules, an evidence in CCl₄-treated HepG2 cells correspondingly supported by the nuclear sequestration of poly (A)⁺ mRNA molecules in morphological hybridization research.

CONCLUSION: Inhibition of mRNA transport, suggestive of decreased NTPase activity of the nuclear envelope, may be involved in carbon tetrachloride-inhibited protein synthesis in liver.

Protective effect of taurine on hypochlorous acid toxicity to nuclear nucleoside triphosphatase in isolated nuclei from rat liver

AIM: Taurine has been shown to be an effective scavenger of hypochlorous acid (HOCl). The role of HOCl is well established in tissue damage associated with inflammation and injury. In the present study, the effect of HOCl on nuclear nucleoside triphosphatase of hepatocytes and the ability of taurine to prevent this effect were investigated.

METHODS: Isolated hepatic nuclei from rat liver were exposed to HOCl with or without taurine. The NTPase activity on nuclear envelope was assayed using ATP and GTP as substrates, respectively.

RESULTS: The first series of experiments evaluated the toxicity of HOCl and the efficacy of taurine to protect NTPase. HOCl at 10^-9-5 × 10^-6 mol/L reduced nuclear NTPase activities in a concentration dependent manner (ATP and GTP as substrates) (P < 0.01). HOCl at 10^-6 mol/L reduced the NTPase activity by 65% (ATP as substrate) and 76% (GTP as substrate). Taurine (10^-7 to 10^-4 mol/L) was tested for protection against HOCl at 10^-6 mol/L and the nuclei treated with 5 × 10^{- 4} mol/L taurine exhibited only 20% and 12% reduction in NTPase activities compared to untreated controls. A second study was performed comparing taurine to glutathione (GSH). GSH and HOCl at 10^-6 mol/L exhibited 46% and 67.4% reduction in NTPase activities compared with control. GSH (10^-4 mol/L) which was incubated with the nuclei and HOCl still exhibited 44.2% and 44.8% reduction in NTPase activities of untreated control. Taurine with HOCl only exhibited 15.2% and 17.1% reduction in NTPase activities, which provided more powerful protection against HOCl than GSH. The third experiment was undertaken to evaluate the specificity of taurine against HOCl. Incubation of rat hepatic nuclei with Fe³⁺/H₂O₂ (1 mmol/L vs 5 µmol/L) resulted in a decrease in nuclear NTPase activities (P < 0.01). When hepatic nuclei were incubated with Tau (10^-4 mol/L) and Fe³⁺/H₂O₂ (1mmol/L vs 5 µmol/L), nuclear NTPase activities were only slightly increased as compared with that of incubation with Fe³⁺/H₂O₂ alone. However, GSH failed to alter the NTPase activities induced by Fe³⁺/H₂O₂.

CONCLUSION: The present findings indicate that HOCl can act as an inhibitor of nuclear NTPase. Taurine can antagonistically reduce the toxicity of HOCl to NTPase.

Phospholipase A2 inhibits nuclear nucleoside triphosphatase activity and mRNA export in isolated nuclei from rat liver

The present study is undertaken to investigate whether the phospholipase A(2) (PLA(2)) influences mRNA nucleocytoplasmic transport evaluated by nucleoside triphosphatase (NTPase) activity and mRNA export in isolated hepatic nuclear envelope. Isolated hepatic nuclei from rat liver were exposed to PLA(2) (10(-5) approximately 10(-2)/ml) with or without incorporation of nuclei with phosphatidylcholine (PC) liposome. Messenger RNA exports and NTPase activities of nuclear membrane were assayed using ATP and GTP as substrates. We found that the RNA efflux, evaluated by [3H] uridine, was potently decreased in a concentration-dependent manner, by incubation of hepatic nuclei with PLA(2), regardless using ATP or GTP as substrates. The PC content in nuclear membrane was also decreased by PLA(2)-treatment. The PC was incorporated into the nuclear membrane by addition of phospholipid liposomes into the incubation mixture. PC incorporation into the nuclear membrane did not alter mRNA export. However this resulted in a significant increase in mRNA export rate in PLA(2)-treated group. Messenger RNA export rate in PLA(2) (10(-3) unit/mL)- treated nuclear membrane was positively correlated with level of PC incorporation, both using ATP and GTP as substrates. The activity of nucleoside triphosphatase, a nuclear membrane-associated enzyme, showed parallel variations with mRNA transport. It is concluded that nuclear PLA(2) plays a regulatory role in RNA transport, which can be antagonized by exogenous PC. These might be pathophysiologically significance, although the mechanisms by which this effect takes place remain to be clarified.

Brain ischemia and reperfusion: molecular mechanisms of neuronal injury

Brain ischemia and reperfusion engage multiple independently-fatal terminal pathways involving loss of membrane integrity in partitioning ions, progressive proteolysis, and inability to check these processes because of loss of general translation competence and reduced survival signal-transduction. Ischemia results in rapid loss of high-energy phosphate compounds and generalized depolarization, which induces release of glutamate and, in selectively vulnerable neurons (SVNs), opening of both voltage-dependent and glutamate-regulated calcium channels. This allows a large increase in cytosolic Ca(2+) associated with activation of mu-calpain, calcineurin, and phospholipases with consequent proteolysis of calpain substrates (including spectrin and eIF4G), activation of NOS and potentially of Bad, and accumulation of free arachidonic acid, which can induce depletion of Ca(2+) from the ER lumen. A kinase that shuts off translation initiation by phosphorylating the alpha-subunit of eukaryotic initiation factor-2 (eIF2alpha) is activated either by adenosine degradation products or depletion of ER lumenal Ca(2+). Early during reperfusion, oxidative metabolism of arachidonate causes a burst of excess oxygen radicals, iron is released from storage proteins by superoxide-mediated reduction, and NO is generated. These events result in peroxynitrite generation, inappropriate protein nitrosylation, and lipid peroxidation, which ultrastructurally appears to principally damage the plasmalemma of SVNs. The initial recovery of ATP supports very rapid eIF2alpha phosphorylation that in SVNs is prolonged and associated with a major reduction in protein synthesis. High catecholamine levels induced by the ischemic episode itself and/or drug administration down-regulate insulin secretion and induce inhibition of growth-factor receptor tyrosine kinase activity, effects associated with down-regulation of survival signal-transduction through the Ras pathway. Caspase activation occurs during the early hours of reperfusion following mitochondrial release of caspase 9 and cytochrome c. The SVNs find themselves with substantial membrane damage, calpain-mediated proteolytic degradation of eIF4G and cytoskeletal proteins, altered translation initiation mechanisms that substantially reduce total protein synthesis and impose major alterations in message selection, down-regulated survival signal-transduction, and caspase activation. This picture argues powerfully that, for therapy of brain ischemia and reperfusion, the concept of single drug intervention (which has characterized the approaches of basic research, the pharmaceutical industry, and clinical trials) cannot be effective. Although rigorous study of multi-drug protocols is very demanding, effective therapy is likely to require (1) peptide growth factors for early activation of survival-signaling pathways and recovery of translation competence, (2) inhibition of lipid peroxidation, (3) inhibition of calpain, and (4) caspase inhibition. Examination of such protocols will require not only characterization of functional and histopathologic outcome, but also study of biochemical markers of the injury processes to establish the role of each drug.