Effects Of Moderately Hyperkalemia On Ischemic Brain Injury And Its Mitochondrial Function

Background and objectiveGlobal cerebral ischemia reperfusion injury(IRI)is an important factor for mortality and disability in patients with cardiac arrest(CA)after successful cardiopulmonary resuscitation(CPR).Both hypothermia and hyperkalemia exert protective effects on myocardial ischemia-reperfusion injury.Hypothermia also plays protective roles on cerebral ischemia-reperfusion injury.However,the hypothesis that hyperkalemia has a protective effect on brain injury that still needs more research to confirm.This study aims to explore the effects of hyperkalemia on ischemic brain injury and its mitochondrial function from different perspectives of clinical observation and experimental research,and different levels of cytology and molecular biologyMethodFirst,a case of a patient with prolonged hypotension combined with hyperkalemia after cardiac surgery who was resuscitated without any neurological sequelae was reviewed.To discuss whether there is a correlation between hyperkalemia and ischemic-hypoxic tolerance of the body.Secondly,we searched the relevant literatures regarding the CA/CPR modeling using transesophageal electrical stimulation or potassium chloride injection,respectively,aiming to compare the rate of restoration of spontaneous circulation(ROSC)and long-term survival in different CA models which were subjected to similar CA duration.The criteria for inclusion were:1.The study subjects must be rats;2.Outcome measures must include CA time,ROSC rate,survival at 24h post ROSC or longer,and indicators with or without neural injury.CA was induced by potassium chloride or electrical stimulation for 5min in rat,and CA/CPR model was established.ROSC rate,ROSC time,mean arterial pressure(MAP)within 1h after ROSC and survival rate at 72h post ROSC were compared between the two groups.The Neurological Deficit Score(NDS)of two kinds of rats was compared at 24h,48h and 72h post ROSC,respectively.Fourth,the ventricular fibrillation(VF)was induced by transesophageal electrical stimulation in rats,and the CA/CPR model was established.The concentration of serum potassium was deliberately increased before routine CPR to verify whether high serum potassium can reduce the IRI of brain of the rats,that has surfferred systemic ischemic injury affter CA.Rats with CA were randomized into four groups and receive low dosage of potassium chloride(LK group,30μg/g),mid-dosage of potassium chloride(MK group,60μg/g),and high-dosage of potassium chloride(HK group,120μg/g)and equal volume of normal saline(NS group).The rats subjected to anesthesia without CA induction were defined as control group.The blood potassium concentration was detected at 1min and 10 min post ROSC,respectively.And the mean arterial pressure was monitored for 1 hour post ROSC.The NDS,neuron specific enolase and s-100βamong different groups were evaluated at 24 hours post ROSC,and the the Hippocampal tissues were stained with HE,then the changes of cell morphology evaluated were observed among different groups at the same time.At last,we used the same method to establish animal models aim to study the effect of hyperkalemia on mitochondrial function of hippocampal cells after ROSC.The content of adenosine-triphosphate and reactive oxygen spicy,the activity of Na+/K+-ATP enzymes,respiratory chain complex(I,II,III and IV)and reactive oxygen spices(ROS)content in the hippocampus tissue of brain were measured at 24hours post ROSC.ResultCase analysis showed that the patient was a 50-year-old female patient who has surffered repeated heart palpitations for 29 years,then aggravated for 1 week.The patient was diagnoses:rheumatic heart disease,severe mitral regurgitation,atrial fibrillation,heart function grade III,pneumonia.After admission,she underwent mitral valve replacement.After the condition was relatively stable,mitral valve replacement was performed.On the second day after the operation,malignant arrhythmias occurred repeatedly,resulting in low cardiac output and hypotension,accompanied by changes in consciousness.Her Glasgow coma score was 8T(GCS,E3VTM5),and the blood pressure was still low after high-dose vasoactive administration(MAP<56mm Hg,pulse pressure difference<18mm Hg)accompanied with oliguria.We provide extracorporeal membrane oxygenation(ECMO)support and continuous renal replacement therapy(CRRT)and other treatments to the patient.After ECMO support,The ECMO flow rate was maintained around 3.0L/min,however the maximum flow was only adjusted to3.2L/min.During ECMO treatment,continuous hypotension with MAP<60mm Hg was about 16h,of which MAP was 35-52mm Hg for about 9h.During the period of hypotension,the patients were combined with persistent hyperkalemia for 24h,up to 7.25mmol/L.There was no recurrence of malignant arrhythmia,heart function gradually recovered,vasoactive drugs gradually decreased,and oxygenation improved after ECMO support.On the 4th day after cardiac surgery,the patient’s condition improved with GCS 9T score(E4VTM5),MAP>70mm Hg,pulse pressure difference>38mm Hg,EF>25%),ECMO was successfully weaned.Then the EF returned to the preoperative level(57%)after2 weeks,and renal function returned to normal after 1 month.The mechanism of that the patients with long-term hypotension did not lead to organ function damage may be related to the enhancement of the body’s tolerance to ischemia and hypoxia by hyperpotassemia.A total of 14 literatures were screened to meet the inclusion criteria by searching for the CA/CPR model established by using potassium chloride or transesophageal electrical stimulation,which included 5 studies related to the establishment of CA/CPR model in rats by potassium chloride injection-induced CA and 9 studies related to CA/CPR by transesophageal electrical stimulation-induced ventricular fibrillation(VF).Compared with the electrical stimulation group,the CA time was significantly longer in the KCL group(5.56±0.72 min vs.8.18±2.85 min,P<0.01)and the ROSC rate was significantly higher(82%vs56%).In studies regrading to CA period<8 min,the survival rate post ROSC was increased in the potassium chloride group compared with the electrical stimulation group at 72 h post ROSC(74%vs 32%).It was speculated that the potassium chloride group had better CA ischemia tolerance based on the fact that the potassium chloride group had similar ROSC 24h NDS to the electrical stimulation group under the condition of longer CA time in the related studies of CA time>8min.Under the premise of the same CA time,the long-term prognosis of CPR was better in the potassium chloride group.Although the ROSC rate in the potassium chloride group was similar to that in the electrical stimulation group(57.1%Vs64%),the ROSC duration in the potassium chloride group was longer(222.00±31.95s Vs 193.78±26.95s),and the early blood pressure after ROSC was lower.Howere the higher survival rate of 72h post ROSC(P<0.05)and significant improved NDS at 24h,48h,and 72h(P<0.05)were observed in the potassium group compared with the stimulation group.Deliberately raising serum potassium before CPR can reduce reperfusion injury.Compared with the sham-operated group,blood K+was significantly higher 1min after ROSC(4.50±0.53mmol/L Vs 3.93±0.39 mmol/L,P<0.05),but there was no statistical difference at 10min post ROSC in the NS group;compared with the NS group,blood potassium was significantly higher in the animals receiving different dosages of potassium chloride group at 1min post ROSC(LK group 5.18±0.47 mmol/L,MK group 5.76±0.51 mmol/L,and HK group6.63±0.44 mmol/L Vs NS group 4.50±0.53 mmol/L)and blood potassium was significantly higher in the MK group and HK group at 10min after ROSC(MK group 4.96±0.52 mmol/L,HK group 5.65±0.37 mmol/L Vs NS group 4.19±0.28mmol/L).The blood K~+level of rats in LK,MK and HK groups increased after potassium solution administration in a dose-dependent manner,but the difference of blood potassium within groups narrowed over time at 10 min post ROSC.The MAP level within 10 min post ROSC presented with the trend that LK group>NS group>MK group>HK group,indicating a dose-dependent.Compared with the SH group,the NS group exhibited obviously lower NDS(71.57±1.61 VS 80.0,P<0.01),significantly increased NSE(5.28±0.24 ng/ml VS 2.83±0.21 ng/ml,P<0.01)and S-100β(2.98±0.39pg/ml VS2.37±0.39pg/ml,P<0.01)at 24h post ROSC.Compared with the NS group,the MK group exhibited obviously higher NDS(76.40±1.57 Vs 71.57±1.61,P<0.01)、decreased NSE(3.71±0.34ng/ml Vs 5.28±0.24ng/ml,P<0.01)and decreased S-100β(2.61±0.27pg/ml Vs2.98±0.39pg/ml,p<0.05);the LK group(5.02±0.28ng/ml Vs 5.28±0.24ng/ml,P<0.01)and HK group(4.96±0.29ng/ml Vs 5.28±0.24ng/ml p<0.05)exhibited obviously decreased NSE.The degree of cell morphology changes did not follow the dose-dependent.Of all the groups receiving potassium solution,the MK group presented with the best cell morphology in hippocampus compared with the other group.Studies on molecular biology level have shown that high serum potassium can improve mitochondrial function of ischemic brain cells.Compared with the sham group,the NS group presented with the lower activity of respiratory chain complex I(4.12±0.35nmol/min/mg,P<0.01),II(4.32±0.32nmol/min/mg,P<0.01)and III(2.62±0.13nmol/min/mg,P<0.01),increased the content of ATP(291.40±11.37umol/mg.prot,P<0.01),decreased activity of Na~+/K~+-ATP enzyme(5.28±0.24U/mg.prot,P<0.01),and increased ROS level(602.85±22.886),but no significant change was observed regarding to the respiratory chain complex IV(3.44±0.32 nmol/min/mg).Compared with the NS group,In the LK group,the activity of respiratory chain complex III(2.89±0.20 nmol/min/mg,P<0.05),and the ROS level(574.87±16.32,P<0.05)was lower than that in the NS group.the MK group showed obvious increased activity of respiratory chain complex I(4.83±0.40nmol/min/mg,P<0.01),II(5.02±0.25nmol/min/mg,P<0.01),III(3.71±0.34nmol/min/mg,P<0.01),increased activity of Na~+/K~+-ATP enzyme(22.48±2.17U/mg.prot,P<0.01)improved activity of Na~+/K~+-ATP enzyme(22.48±2.17U/mg.prot,P<0.01)and decreased ROS level(503.60±17.39,P<0.01).The HK group yield the similar imporved results regarding to the activity of respiratory chain complex III(2.90±0.12nmol/min/mg,P<0.05),the activity of Na~+/K~+-ATP enzyme(20.20±1.36 U/mg.prot,P<0.05)and decreased ROS level(576.85±24.44,P<0.05)compared with the NS group.The activity of respiratory chain complex IV in all group were similar at 24-hour post ROSC(p>0.05).The results of hoc comparison among groups receiving potassium chloride solution,the MK group showed the best improvement in each evaluation index.ConclusionHyperkalemia may play a protective role to increase the tolerance against the hypotension-derived ischemic injury in patients with prolonged hypotension after cardiac surgery.The animals subjected to CA induced by potassium chloride exhibited better long-term survival and neural function post ROSC.Elevating blood potassium at onset of CPR exerted cerebral protection.And the underlying mechanism may relate to the inhibition of intracellular potassium efflux,increased activity of respiratory chain complex,improved mitochondrial function and decreased ROS production,which contributing to reduce IRI in rat experienced CA/CPR.