| BackgroundPostoperative cognitive dysfunction(POCD)refers to a serious postoperative complication in which the ability of the brain to process information after anesthesia or surgery is impaired to varying degrees.After the occurrence of POCD,patients may have decreased function of attention,speech ability,thinking ability,and learning and memory ability.Often,patients experience cognitive dysfunction at one or several days after surgery,and some can even last for several months.The occurrence of POCD not only leads to prolonged hospitalization,worsening disease prognosis,increasing the incidence of postoperative complications and perioperative mortality,but also increasing the risk of long-term cognitive dysfunction(such as dementia)and death,seriously reducing the patients' long-term quality of life.POCD is a common neurological cognitive complication after surgery and anesthesia,especially in elderly patients.In recent years,with the aging process of Chinese society,there are more and more elderly patients,and more and more elderly patients would take general anesthesia and surgery to treat or alleviate diseases.However,due to the interaction of various factors such as preoperative factors and perioperative factors,the mechanism of the occurrence and development of POCD in elderly patients after anesthesia or surgery is still not fully understood.It has been reported that elderly patients themselves have a degraded central nervous system function due to aging,a weakened ability of the body to resist stress,and a combination of various factors such as surgical trauma and changes in the system function of the body caused by anesthesia.These factors lead to the occurrence and development of POCD in elderly patients More and more studies have shown that central and peripheral inflammatory reactions caused by surgical trauma,abnormal A(3 metabolism in brain tissue,oxidative stress damage in nerve cells,cholinergic neurotransmitter and receptor imbalance,blood-brain barrier damage which damages the stability of the micro-environment of the central nervous system play important roles in the occurrence and development of postoperative cognitive function complications.In addition,the roles of anesthetics,anesthesia,and depth of anesthesia in patients with POCD have increasingly attracted the attention of scholars.Studies have reported that general anesthesia may lead to early cognitive dysfunction in patients.Among them,inhalation anesthetics used in general anesthesia,such as isoflurane and sevoflurane,can cause neuropathological changes in the brain tissue of patients,neuronal apoptosis and increased ?-amyloid.In addition,studies have shown that certain cognitive dysfunctions in patients after anesthesia can last for a long time,may lead to long-term cognitive deficits and long-term brain structural changes.Therefore,clarifying the above pathogenesis is not only profound to reveal the underlying mechanism of general anesthesia,but also helps to reduce and prevent anesthesia and postoperative complications.How to reduce the incidence of POCD and prevent the occurrence of POCD has become a difficult point in clinical anesthesia work,and it is also a research hotspot of anesthesia in elderly patients.Nobiletin is a polymethoxyflavonoid extracted from the peel of citrus fruits.Because of its wide range of physiological effects beneficial to health,nobiletin has attracted more and more attention.More and more studies have confirmed that nobiletin can not only exert significant anti-inflammatory,anti-oxidant and anti-cancer biological activities,but also has anti-atherosclerosis,regulate blood sugar and protect liver effects.In addition,more and more researches have found that nobiletin also has significant functions in brain protection and improving learning and memory ability.Studies have shown that nobiletin can effectively alleviate memory deterioration and memory loss caused by Alzheimer's disease ?-amyloid;Through regulating the phosphorylation levels of ERK and CREB and CaMK in brain tissue,it can effectively improve the learning and memory dysfunction caused by cerebral ischemia;Through regulating the function of cholinergic nerves in brain tissue,it improves learning disorders;Through reducing the expression levels of HIF-la and cleaved caspase-3,increasing VEGF levels,and inhibiting neuronal apoptosis in rats with cerebral infarction;It regulates the activity of dopaminergic neurons in Parkinson's disease,inhibits the activation of microglia,promotes the expression of neurotrophic factors,and plays a significant role in preventing neurodegenerative changes in Parkinson's disease,it plays a significant role in brain protection.Oxidative stress and inflammation of the central nervous system are closely related to the processes of nervous system injury,learning and memory decline and cognitive impairment.The PI3K/Akt signaling pathway is one of the most important signal transduction pathways in the body and participates in a variety of important cell activities in the body,such as cell metabolism,inhibition of apoptosis and inflammatory response.PI3K is widely found in various cells of the body,and a variety of cytokines and stimulation factors can activate PI3K.Akt is an important downstream molecule of PI3K and an important hub of various signaling pathways in the body.It has been reported that PI3K/Akt is an important upstream activator of NF-kappab and plays a very important role in the activation of NF-kappab pathway.Nf-kappab is an important molecular pathway involved in regulating the release and activity of various cytokines and inflammatory mediators in the inflammatory response network system of the body.Both PI3K/Akt and nf-kappa B pathways play an important role in oxidative stress response.However,there are still few studies on whether nobiletin has effect on the prevention and treatment of postoperative cognitive dysfunction.In this study,old rats were anesthetized with isoflurane,and a rat model of postoperative cognitive dysfunction was established to investigate whether intraperitoneal injection of nobiletin can improve the learning and memory behavior of model rats,and explore the possible internal mechanism of this effect.ObjectiveThis study was designed to investigate whether pretreatment with nobiletin can improve learning and memory ability of aged rats after anesthesia.And we also explored whether its mechanism is related to the effects of regulating the inflammation and oxidative stress reaction which were mediated by PI3K/Akt-NF-?B passway.Methods1.Twenty-month-old healthy male Sprayer-Dawley rats,weighing between 480-550 g,were selected.The rats were randomly divided into four groups:1)isoflurane group(n=20,isoflurane+tween-80);(2)nobiletin(10)group(n=20,isoflurane+nobiletin)10 mg/kg);(3)Chuanzhongxin(25)group(n=20,isoflurane+nobiletin 25 mg/kg);(4)sham experimental group(n=20,oxygen+tween-80).2.Morris water maze training:Before the experiment,all rats were trained for 5 days in the Morris water maze to exclude rats that cann't swim,visually impaired,or mentally deficient and make a stable memory.The observation items of the Morris training include the escape latency and the length of the escape route on every day,and the time spent in the target quadrant and the number of times the rat crossed the platform on the next day after the end of the navigation test.3.Since the first day after the finish of Morris water maze training,rats in the nobiletin(10)group and the nobiletin(25)group were intraperitoneally injected with nobiletin 10 mg/kg/day or 25 mg/kg/day,respectively,for 3 days.The isoflurane group and the sham experimental group were given an equal volume of tween-80 by intraperitoneal injection for 3 days.The last drug injection was two hours after recovery from anesthesia.4.On the third day,rats were placed in a transparent sealed box(size:50 cm x 50 cm x 40 cm)connected to an anesthesia machine and administered isoflurane/oxygen.Rats in the isoflurane group,nobiletin(10)group and(25)group were given 2%isoflurane for 2 hours in an anesthesia chamber in a 100%oxygen environment;Rats in the sham experimental group only inhaled oxygen.After inhalation of isoflurane was finished,inhalation of 100%O2 was continued for 30 minutes.After recovery from anesthesia,rats were returned to the animal room.5.24 hours after complete recovery from anesthesia,10 rats in each groups were randomly selected and were performed with Morris water maze test to observe the escape latency and path length of the rats for 3 consecutive days,and the time spent in the target quadrant and the number of rats passing through the platform on the 3rd day after anesthesia.These results were used to determine the learning and memory function of rats in each group.6.After complete recovery of anaesthesia for 24 hours,the rest rats in eachgroups were sacrificed,and hippocampus tissues were collected.Enzyme-linked immunosorbent assays were performed to detect the protein levels of inflammatory factors(tumor necrosis factor-a(TNF-a),interleukin IL-1?,IL 6),oxidative stress substances(glutathione(GSH),Glutathione peroxidase(GSH-Px),superoxide dismutase(SOD)and malondialdehyde(MDA)).Western blot was used to determine apoptosis-related protein(Bcl-2?Bax?cleaved caspase-3),and channel protein(NF-?B and p-Akt)expression levels.RT-PCR was performed to determine the mRNA expressions of NF-?B and p-Akt in hippocampusResults1.Compared with the sham experimental group,the escape latency and path length of the rats in the isoflurane group increased significantly on the 1-3rd day after anesthesia,the difference was statistically significant(P<0.01,P<0.01);Compared with the isoflurane group,the escaping latency and path length of rats in the nobiletin(10)and(25)groups on days 1-3 after anesthesia were significantly lower,and the difference was statistically significant(P<0.05,P<0.05;P<0.01,P<0.01).In addition,compared with the sham group,the time spent in the target quadrant of the isoflurane group and the number of times the rat crossed the platform on the fourth day significantly decreased,and the difference was statistically significant(P<0.01,P<0.01);Compared with the isoflurane group,the time spent in the target quadrant and the number of rats crossing the platform on the fourth day increased significantly in the nobiletin(10)and(25)groups,and the difference was statistically significant(P<0.05,P<0.05;P<0.01,P<0.01)2.Compared with the sham experimental group,the concentration of MDA in the isoflurane group was significantly increased,and the concentration of GSH?GSH-Px and SOD were significantly decreased,the difference was statistically significant(each P<0.01);Compared with the isoflurane group,the concentrations of MDA in the nobiletin(10)and(25)groups were significantly decreased,and the GSH?GSH-Px and SOD concentrations were significantly increased(each P<0.05 in NOB-10 group;each P<0.01 in NOB-25 group);The differences of the above indicators were not statistically significant when comparing the nobiletin(10)grope and(25)group,each P>0.053.Compared with the sham experimental group,the concentrations of TNF-a,IL-1?,and IL-6 in the isoflurane group were significantly increased,each P<0.01;In comparison with the isoflurane group,the concentrations of TNF-?,IL-1?,and IL-6 in the nobiletin(10)and(25)groups were significantly lower(each P<0.05 in NOB-10 group;each P<0.01 in NOB-25 group),and the difference was statistically significant;The above indicators were compared between the two doses of nobiletin,the difference was not statistically significant(each P>0.05).4.Compared with the sham experimental group,the expression apoptosis-related protein of Bax?cleaved caspase-3 in the isoflurane group was significantly increased,the level of Bcl-2 was markedly decreased(each P<0.01);Compared with the isoflurane group,the protein expressions of Bax?cleaved caspase-3 in the nobiletin(10)and(25)groups were significantly decreased,and the expression of Bcl-2 was significantly increased(each P<0.05 in NOB-10 group;each P<0.01 in NOB-25 group);Comparing the two groups with different doses of nobiletin,the differences of the above indicators were statistically significant,each P<0.05.5.Compared with the sham experimental group,the protein level of NF-?B was markedly increased and the level of p-Akt was markedly decreased in the isoflurane group(both P<0.01);Compared with the isoflurane group,the protein expression of NF-?B was significantly decreased and the protein level of p-Akt was significantly increased in nobiletin(10)and(25)groups(both P<0.05 in NOB-10 group;both P<0.01 in NOB-25 group).The differences of the above indicators between the two groups of nobiletin were statistically significant,both P<0.05.6.Compared with the sham experimental group,the mRNA level of NF-?B was markedly increased and the mRNA level of p-Akt was decreased in the isoflurane group(both P<0.01);Compared with the isoflurane group,the mRNA level of NF-?B was significantly decreased and the mRNA level of p-Akt was significantly increased in nobiletin(10)and(25)groups(both P<0.05 in NOB-10 group;both P<0.01 in NOB-25 group).The differences of the above indicators between the two groups of nobiletin were statistically significant,both P<0.05.Conclusion1.Nobiletin can significantly improve cognitive impairment after anesthesia in aged rats,and large doses of nobiletin work better.2.Nobiletin may improve cognitive dysfunction through regulating oxidative and inflammatory reaction in the central nervous system related with PI3K/Akt-NF-?B passway. |
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