Summary Tpk1p, Tpk2p and Efg1p are members of the Rasprotein kinase A pathway that governs the yeast-tohyphal transition in Candida albicans

Candida albicans must penetrate the endothelial cell lining of the vasculature to invade the deep tissues during a hematogenously disseminated infection. We compared 27 C. albicans mutants with their wild-type parent for their capacity to damage endothelial cells in vitro and cause a lethal infection in mice following tail vein inoculation. Of 10 mutants with significantly impaired capacity to damage endothelial cells, all had attenuated virulence. Therefore, the endothelial cell damage assay can be used as a screen to identify some virulence factors relevant to hematogenously disseminated candidiasis.During the initiation of hematogenously disseminated candidiasis, blood-borne organisms must adhere to and penetrate the endothelial cell lining of the blood vessels to invade the deep tissues. One mechanism by which Candida albicans can penetrate the vascular endothelium is by damaging and eventually killing the endothelial cells. Damaged endothelial cells detach from the basement membrane, leaving gaps through which the organism can invade. Also, the exposed basement membrane can be avidly bound by additional organisms (18).C. albicans damages human vascular endothelial cells in vivo and in vitro (5,10,17,25). Maximal endothelial cell damage (ECD) occurs in vitro when C. albicans adheres to and invades the endothelial cells and then secretes lytic enzymes (2,10,11,13,16). Moreover, some C. albicans mutants with filamentation defects cause significantly less ECD than the wild-type parent strain (24). These filamentation mutants also have attenuated virulence in various experimental models of infection (reviewed in reference 23). We hypothesized that the in vitro assay for C. albicans-induced ECD (ECD assay) can serve as a model for certain aspects of host-pathogen interactions in vivo, such as the ability of the organism to adhere to, invade, and injure host cells. This hypothesis predicts that some mutants with virulence defects will be defective in the ECD assay. The goal of the present study was to investigate this prediction.C. albicans strains. The genotypes and sources of the C. albicans strains used here are listed in Tables 1 and 2. Each strain was grown overnight in yeast nitrogen base broth (Difco, Detroit, Mich.) supplemented with 2% glucose (wt/vol) at 20°C on a rotating drum. The blastospores were harvested by centrifugation, washed with phosphate-buffered saline, enumerated with a hemacytometer, and suspended in RPMI 1640 medium (Irvine Scientific, Santa Ana, Calif.).ECD assay. We used our standard 51 Cr release ECD assay to determine the abilities of mutants of C. albicans to damage endothelial cells in vitro (24). The ECD assay was performed in 96-well tissue culture plates (Corning Inc., Acton, Mass.) with endothelial cells isolated from human umbilical cord veins, as described previously (24). The inoculum was 4 ϫ 10 4 organisms per well, and the organisms were incubated with the endothelial cells for 3 h in 5% CO 2 at 37°C. At the end of the incubation period, the wells were examined with an inv...

Racemic ketoconazole (KTZ) was the first orally active azole antifungal agent used in clinical practice and has become widely used in the treatment of mucosal fungal infections associated with AIDS immunosuppression and cancer chemotherapy. However, the use of KTZ has been limited because of adverse drug-drug interactions. KTZ blocks ergosterol biosynthesis by inhibiting the fungal cytochrome P450 (CYP51). KTZ is also a potent inhibitor of human cytochrome P450 3A4 (CYP3A4) enzyme, the major drug-metabolizing CYP isozyme in the human liver. We examined the enantioselective differences of KTZ in the inhibition of human CYP3A4 and in antifungal action. Dextro- and levo-KTZ exhibited modest enantioselective differences with respect to CYP3A4 inhibition of testosterone and methadone metabolism. For both substrates levo-KTZ was approximately a 2-fold more potent inhibitor. We examined the enantioselective differences in the in vitro activity of KTZ against medically relevant species of Candida and Aspergillus, as well as Cryptococcus neoformans. Overall, levo-KTZ was 2-4-fold more active than dextro-KTZ. Therefore, levo-KTZ is a more potent inhibitor of CYP3A4 and has stronger in vitro antifungal activity. Chirality 16:79-85, 2004.