Differences in virulence between two Candida albicans strains in experimental keratitis.

PURPOSE: To study the differences in disease caused by two wild-type strains of Candida albicans in a model of contact lens-facilitated keratitis in rabbits. METHODS: Two strains, SC5314 and VE175, were examined. Standardized inocula were placed on the debrided corneal surface of one eye in Dutch belted rabbits and covered with a contact lens. A temporary tarsorrhaphy was opened after 24 hours with removal of the contact lens. Six days later, corneas were photographed and animals killed. Corneas were bisected with one half for quantitative isolate recovery and the other for stromal penetration by hyphae. RESULTS: Strain SC5314 was significantly more virulent. The mean hyphal penetration into the cornea was 24.4% +/- 8.5% of the corneal thickness, and in three of six corneas hyphae penetrated through the entire cornea. In contrast, for VE175, the mean hyphal penetration was 2.6% +/- 1.2%. The difference between these two strains was statistically significant (P = 0.0297). Hyphae did not penetrate into the deep layers of the cornea in any of the six rabbits infected with VE175. The grading of clinical disease was consistent with histology, in that strain SC5314 caused more severe infection than VE175 and the difference was statistically significant (P = 0.0048). There was no difference in isolate recovery. CONCLUSIONS: Wild-type strains of C. albicans can differ significantly in virulence as measured by depth of fungal invasion into corneas and clinical evaluation of infection. Further characterization of the intrinsic genetic differences between such strains may help identify factors responsible for fungal virulence.

Thioredoxin reductase activity is decreased by selenium deficiency.

Animal thioredoxin reductase is a selenoprotein. In this study, thioredoxin reductase activities in liver, kidney, and brain have been compared in rats fed selenium-deficient and control diets for 14 weeks following weaning. Selenium deficiency caused a decrease in thioredoxin reductase activity from control to 4.5% in liver and 11% in kidney. However, brain thioredoxin reductase activity was not affected by selenium deficiency of this severity. Gold inhibited thioredoxin reductase activity in the liver in a manner typical of its effect on selenoenzymes. Repletion of selenium-deficient rats with injections of selenium caused thioredoxin reductase activity to increase more rapidly in the liver than glutathione peroxidase activity but more slowly than selenoprotein P. These results indicate that thioredoxin reductase activity in liver and kidney is sensitive to selenium nutritional status but that brain thioredoxin reductase activity is less sensitive.

Cell density-dependent regulation of PLC gamma 1 tyrosine phosphorylation and catalytic activity in an intestinal cell line (IEC-6).

Administration of epidermal growth factor (EGF) to rats has been shown to induce both mitogenic and nonmitogenic responses in the intestine. The mechanisms to describe a multiplicity of hormonal responses within a single tissue are unclear but likely involve selectivity among receptor substrates. A nontransformed rat jejunal crypt intestinal epithelial cell line (IEC-6) was studied to determine if the regulation of receptor tyrosine kinase substrates is affected by cell population physiology. EGF stimulated a rapid increase in inositol trisphosphate in confluent but not subconfluent cells. Similarly, treatment of confluent IEC-6 cells with EGF provoked a significant increase in the hydrolysis of PtdIns 4,5-P2 by immunoisolated PLC gamma 1. The tyrosine phosphorylation state of PLC gamma 1 and the association of PLC gamma 1 with the EGF receptor were increased by EGF in confluent cells only. In contrast, the autophosphorylation state of the EGF receptor and the tyrosine phosphorylation state of another SH2-containing EGF receptor substrate SHC were increased by EGF regardless of cell density. Western blot analysis revealed equal protein expression of PLC gamma 1 in confluent and subconfluent cells. EGF receptor protein expression and ligand binding capacity were slightly increased in confluent compared to subconfluent cells. EGF regulation of PLC gamma 1, therefore, is regulated by physiological factors dependent on cell density in IEC-6 cells.

Synthesis of 15O-labeled butanol via organoborane chemistry.

Oxygen-15 labeled 1-butanol and 2-butanol were prepared by the reaction of O2-15O with tri-n-butylborane and tri-sec-butylborane in tetrahydrofuran. The reaction products were isolated and identified via reversed-phase high performance column chromatography and gas chromatography. Radiochemical yields of 50% (EOB) were obtained. The use of 15O-labeled butanol is suggested for cerebral blood flow measurements in conjunction with PET.