New insights into the pathogenesis of primary biliary cholangitis asymptomatic stage

Primary biliary cholangitis(PBC)is a chronic cholestatic progressive liver disease and one of the most important progressive cholangiopathies in adults.Damage to cholangiocytes triggers the development of intrahepatic cholestasis,which progresses to cirrhosis in the terminal stage of the disease.Accumulating data indicate that damage to biliary epithelial cells[(BECs),cholangiocytes]is most likely associated with the intracellular accumulation of bile acids,which have potent detergent properties and damaging effects on cell membranes.The mechanisms underlying uncontrolled bile acid intake into BECs in PBC are associated with pH change in the bile duct lumen,which is controlled by the bicarbonate(HCO3-)buffer system“biliary HCO3-umbrella”.The impaired production and entry of HCO3-from BECs into the bile duct lumen is due to epigenetic changes in expression of the X-linked microRNA 506.Based on the growing body of knowledge on the molecular mechanisms of cholangiocyte damage in patients with PBC,we propose a hypothesis explaining the pathogenesis of the first morphologic(ductulopenia),immunologic(antimitochondrial autoantibodies)and clinical(weakness,malaise,rapid fatigue)signs of the disease in the asymptomatic stage.This review focuses on the consideration of these mechanisms.

Catalytic domain of PDC-E2 contains epitopes recognized by antimitochondrial antibodies in primary biliary cirrhosis

AIM:To search for further immunodominant peptides of the pyruvate dehydrogenase complex E2-component (PDC-E2) recognized by antimitochondrial antibodies (AMA) in primary biliary cirrhosis (PBC). METHODS:Sera from 95 patients with PBC were tested by enzyme-linked immunosorbent assay against 33 synthetic overlapping peptides (25 amino acids; aa) covering the entire length of the E2-subunit of PDC-E2. Furthermore,the inner lipoyl peptide 167-184 was used in an unlip oylated and a lipoylated form as well as coupled to ovalbumin. Sera from 11 AMA negative/ANA posit ive PBC patients,63 patients with other liver disorders and 22 healthy blood donors served as controls.RESULTS:Of the 95 PBC-sera,74% reacted with the peptide 475-499 and 58% with the pept ide 407-431 located within the catalytic domain of PDC-E2. Patients with other disorders or healthy controls were positive in only up to 18%. Antibodies to the unlipoylatedand lip oylated pept ide 167-184 within the inner lipoyl domain were found in only 5% and 11% of the PBC sera,respectively; using ovalbumin-coupled peptides,the incidence increased up to 57% (unlipoylated form). CONCLUSION:Peptides within the catalytic site of PDC-E2 rather than the previously reported lipoyl binding peptide 167-184 may represent major immunodomin ant epitopes recognized by AMA in PBC.

Targeting metabolic vulnerability in mitochondria conquers MEK inhibitor resistance in KRAS-mutant lung cancer

MEK is a canonical effector of mutant KRAS;however,MEK inhibitors fail to yield satisfactory clinical outcomes in KRAS-mutant cancers.Here,we identified mitochondrial oxidative phosphorylation(OXPHOS)induction as a profound metabolic alteration to confer KRAS-mutant non-small cell lung cancer(NSCLC)resistance to the clinical MEK inhibitor trametinib.Metabolic flux analysis demonstrated that pyruvate metabolism and fatty acid oxidation were markedly enhanced and coordinately powered the OXPHOS system in resistant cells after trametinib treatment,satisfying their energy demand and protecting them from apoptosis.As molecular events in this process,the pyruvate dehydrogenase complex(PDHc)and carnitine palmitoyl transferase IA(CPTIA),two rate-limiting enzymes that control the metabolic flux of pyruvate and palmitic acid to mitochondrial respiration were activated through phosphorylation and transcriptional regulation.Importantly,the co-administration of trametinib and IACS-010759,a clinical mitochondrial complex I inhibitor that blocks OXPHOS,significantly impeded tumor growth and prolonged mouse survival.Overall,our findings reveal that MEK inhibitor therapy creates a metabolic vulnerability in the mitochondria and further develop an effective combinatorial strategy to circumvent MEK inhibitors resistance in KRAS-driven NSCLC.