The endocytic pathway transports cargo from the plasma membrane to early endosomes, where certain cargoes are sorted to the late endosome/multivesicular body. Biosynthetic cargo destined for the lysosome is also trafficked through the multivesicular body. Once delivered to the multivesicular body, cargo destined for the interior of the lysosome is selectively sorted into vesicles that bud into the lumen of the multivesicular body. These vesicles are released into the lumen of the lysosome upon the fusion of the multivesicular body and lysosomal limiting membranes. The yeast protein Fab1, which catalyzes the production of phosphatidylinositol (3,5) bisphosphate [PtdIns(3,5)P 2 ], is necessary for proper sorting of biosynthetic cargo in the multivesicular body. Utilizing an endocytosis screen, we isolated a novel allele of FAB1 that contains a point mutation in the lipid kinase domain. Characterization of this allele revealed reduced PtdIns(3,5)P 2 production, altered vacuole morphology, and biosynthetic protein sorting defects. We also found that endocytosis of the plasma membrane protein Ste3 is partially blocked downstream of the internalization step, and that delivery of the dye FM4-64 to the vacuole is delayed in fab1 mutants. Additionally, Ste3 is not efficiently sorted into multivesicular body vesicles in fab1 mutants and instead localizes to the vacuolar limiting membrane. These data show that PtdIns(3,5)P 2 is necessary for proper trafficking and sorting of endocytic cargo through the late endosome/multivesicular body.

Overall, these analyses provide an example in which pediatric and adult exposure data alone are insufficient to adequately identify effective pediatric doses and raise questions about the appropriateness of exposure matching for other drugs in the same therapeutic class. In such cases, pediatric dose-ranging and efficacy studies are needed.

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BackgroundCardiopulmonary bypass (CPB) is associated with postoperative myocardial stunning, hypothermia, formation of microemboli, and systemic inflammatory response syndrome, all of which may prolong recovery from coronary artery bypass grafting (CABG) surgery. This study sought to compare outcomes in patients undergoing CABG off pump versus on pump.MethodsOutcomes, including mortality and several morbidities, were reviewed in 1,623 on-pump patients and 683 off-pump patients. Morbidities assessed included postoperative bleeding, incidence of multiorgan dysfunction, and neurologic complications. Chi-square and t-test analysis were used to determine statistical significance.ResultsMortality was 42% lower in the off-pump group than the on-pump group. Both critical care and total hospital length of stay were significantly shorter in the off-pump group. The incidence of postoperative bleeding requiring transfusion or a return to the operating room was reduced by 29% in the off-pump group and the incidence of multiorgan dysfunction was reduced by 31%. The off-pump patients also presented a significantly lower incidence of cerebral vascular accidents and seizures than on-pump patients.ConclusionsWe conclude that there is an association between improved patient outcome and off-pump CABG surgery. The outcomes of this study show a statistically significant decrease in mortality, critical care length of stay, total hospital stay, incidence of bleeding requiring transfusion or return to the operating room, amount of blood transfused, incidence of multiorgan dysfunction, cerebral vascular accidents, and seizures in off-pump patients when compared with on-pump patients. Such results support the use of myocardial revascularization off pump as an alternative to CABG surgery on pump. CABG surgery off pump may allow a better postoperative clinical course in patients who are candidates for the procedure.

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