The Effects Of Obesity On Kainic Acid Induced Model Of Temporal Lobe Epilepsy In Mice And Preliminary Study On The Mechanism

Background:obesity is a major clinical risk factor for a series of human disease such as diabetes, cardiovascular disease, liver cancer and central nervous system injury. Epidemiological surveys have shown that the rates of being overweight or obese were higher in untreated patients with refractory than normal body mass; additionally, overweight or obesity rates were higher in patients with refractory than nonrefractory epilepsy. Epilepsy is a chronic central nervous system disorder with epileptic seizure, which is characterized by spontaneous repeatedly supersynchronous bioelectrical discharge in the nerve cells. Epilepsy is one of most common neurological diseases which severely affects life and work of patients. Temporal lobe epilepsy (TLE) accounting for 30-40% of all epilepsies, more than 30% of TLE will become refractory epilepsy. The role of obesity in epileptogenesis needs further research. Leptin is not only an important energy balance factor, but also play an important role in CNS injury. The increased levels of leptin caused by obesity may affect epileptogenic pathology, this may be the underlying mechanism of which obesity affects TLE.Methods:firstly, male C57BL/6J mice (4-5 weeks old) were randomly divided into two groups with similar body weights and assigned to receive two types of diets: a standard rodent chow and high fat-diet rodent chow. Mice’s body weightswere recorded weekly, body weight and serological indexes shows that high fat-diet induced obese model was successfully established in mice after 12 weeks. Based upon this model, kainic acid (KA) was microinjected into the right hippocampus to induce the model of TLE in mice. The normal weight mice were microinjected with saline (CS group), KA (CK group), leptin pretreatment (Lep+CK group), Nanobody pretreatment (Nanobody+CK group), AG490 (JAK2/STAT3 signaling pathway inhibitor) pretreatment (AG490+Lep+CK); the obese mice were microinjected with saline (OS group), KA (OK group), Nanobody pretreatment (Nanobody+CK group), leptin pretreatment (Lep+OK group), AG490 (JAK2/STAT3 signaling pathway inhibitor) pretreatment (AG490+Lep+OK). The behavior manifestations, serum bio-marker for judging the severity of injury and pathological change in right hippocampus of the mice were observed.Results:The first part:1 the mice model of obesity induced by a high fat-diet was successfully establishedCompared with mice fed on a standard rodent chow, mice fed on a high fat-diet have higher levels of fat mass, triglyceride, cholesterol and fatty acid (p<0.05), weight gain increased by more than 20%.2 Obesity aggravates KA-induced hippocampal injury inTLE model of mice1) A normal dose of KA (200 ng) was microinjected into the right hippocampus of the mice, the obese mice exhibited a very low survival rate over 24 hours’ observation compared with the lean mice (25% to 100%, respectively), differences are significant (p<0.05)2) A normal dose of KA (100 ng) was microinjected into the right hippocampus of the mice, Obese mice were more vulnerable to KA-induced seizure activity than normal mice, with mean peak seizure scores of 4.6 and 3.2, respectively, (p<0.05), (>3, TLE model of mice).3) After microinjection of KA, serum creatine kinase isoenzyme (CK-MB) and lactate dehydrogenase (LDH) increased significantly in mice (p<0.05). Comparing to mice of CK group, serum CK-MB and LDH levels are higher in mice of OK group, but differences are not significant (p>0.05).4) Neurons loss, glial fibers acidic protein (GFAP) and S-100β expression in mice’s hippocampus of OK group were more than that in mice’s hippocampus of CK group. KA cause a more pathological lesions in mice’s hippocampus of OK group than that in mice’s hippocampus of CK group.The second part:1 High levels of leptin caused by obesity may play an important role in that obesity aggravates pathological injury of TLE in mice.1) Exogenous leptin increased Racine score, exacerbated neurons loss, over-activated astrocytes, and increased S-100β expression in mice of CK group. The effects of exogenous leptin were reversed by Nanobody pretreatment.2) Serum leptin levels of obese mice are 2 times more than that of normal mice, differences are significant (p<0.05), and obese mice had not developed leptin resistance. Obesity increased Racine score, exacerbated neurons loss, over-activated astrocytes, and increased S-100β expression in mice of OK group, and these effects were reversed by Nanobody pretreatmentwhich blocked endogenous leptin.2 The underlying mechanism of astrocytes over-activation may be through JAK2/STAT3 signaling pathway activation by high level leptin.Exogenous leptin increased expression of p-STAT3 and GFAP, and the effects of exogenous leptin were reversed by AG490 pretreatment in both normal and obese mice.Conclusion:The levels of leptin increased significantly in high-fat diet induced obese C57BL/6J mice; obesity aggravated KA-induced injury of TLE in mice; the increased expression of leptin may contribute to that obesity aggravated KA-induced mice TLE; leptin exacerbated hippocampal injury may be through that leptin-JAK2/STAT3 signaling pathway over-activated astrocytes.