The Mechanisms Underlying The Modified Longdan Xiegan Tang-elicited Improvement Of Olanzapine-induced Hepatic Insulin Resistance In Rats

BackgroundInsulin resistance is closely associated with the occurrence and development of many major diseases.Hepatic insulin resistance is an important component of insulin resistance.Olanzapine is a representative new antipsychotic that can cause insulin resistance in the liver,but its pathological mechanisms remain largely unknown.Longdan Xiegan Tang(LXT)is a classic ancient Chinese medicine.Recently,it has been newly used to effectively treat hepatic insulin resistance-associated mental illness and abnormalities of glucose and lipid metabolism.However,the undelying mechanisms of action are still unknown.ObjectiveTo provide a scientific basis for the acient formula to treat hepatic insulin resistance-related diseases,this study first examined the molecular mechanism of olanzapine-induced hepatic insulin resistance.Then,the effects and underlying mechanisms of modified LXT(mLXT)on the hepatic insulin resistance.Methods1.Preparation of mLXTAccording to the requirements in the Chinese Pharmacopoeia,the relevant Chinese herbal medicines were selected and identified.The mLXT extract powder was prepared,and the contents of the main active ingredients was quantitatively analyzed by high performance liquid chromatography.2.Animal model and treatmentMale rats were randomly divided into four groups as follows:control,olanzapine model,olanzapine + low dose of mLXT(50 mg/kg),and olanzapine +high dose of mLXT(500 mg/kg).mLXT was intragastrically administered at different doses two hours after olanzapine(5 mg/kg)was orally given(the control group was given 5%gum Arabic solution),once daily for consecutive 8 weeks.Body weight and chow intake were recorded daily.An oral glucose tolerance test(OGTT)was performed at 7 weeks,and biochemical parameters were determined before glucose solution administration.Animals were sacrificed at week 8,and liver tissues were collected for determination of lipid contents and gene/protein expression.3.Determination of relevant parametersBlood biochemical parameters and liver lipid contents were determined by enzymatic or ELISA method,and HOMA-IR and Adipo-IR index were calculated.Pathology was examined by HE staining,and Oil Red O stained area was measured by ImageJ software for calculation of lipid droplet deposition.Hepatic gene and protein expression were analyzed by RT-PCR or/and Western blot.Results1.Olanzapine increased fasting plasma INS,HOMA-IR,liver tissue TG content and oil red staining area(P<0.05),suggesting that olanzapine induces hepatic insulin resistance and fatty liver in rats.The high dose of mLXT improved the above abnormalities,suggesting that mLXT can prevent hepatic insulin resistance and fatty liver.2.Olanzapine up-regulates expression of protein phosphorylation and its to total protein ratio in IRS-1 Ser307,IRS-2 Ser731,PI3K p85a Tyr607,Akt Ser473 and mTOR Ser24 8 sites(P<0.05).The high dose of mLXT inhibited the phosphorylation and ratio of these proteins induced by olanzapine(P<0.05).The results suggest that olanzapine induces hepatic insulin resistance through the IRS/PI3K/Akt/mTOR signaling pathway.mLXT regulates this signaling pathway.3.Olanzapine activated hepatic expression of the transcription factor SREBP-1c mRNA and protein,and its downstream genes ACC-1,FAS,SCD-1 mRNA(P<0.05).High doses of mLXT improved the above abnormalities,suggesting that olanzapine causes hepatic insulin resistance-associated fatty liver by activating SREBP-1c pathway.mLXT improves olanzapine-induced fatty liver by regulating the pathway.4.In addition,high doses of mLXT up-regulated the expression of PPAR-αmRNA and protein and its downstream genes CPT-1a and ACO mRNA(P<0.05).At the same time,the high dose of mLXT also increased the expression of AMPK-αThr172 phosphorylation protein and the ratio of AMPK-α Thr172 to AMPK-α total protein(P<0.05).The results suggest that the AMPK-α/PPAR-α signaling pathway is also involved in mLXT-elicited improvement of fatty liver.Conclusions1.Olanzapine causes hepatic insulin resistance via the IRS/PI3K/AKt signal axis in rats.2.mLXT improves hepatic insulin resistance by regulating IRS/PI3K/Akt signaling pathway in rats.3.Additionally,mLXT improves olanzapine-induced fatty liver through the AMPK-α/PPAR-α signaling pathway.