Chlorhexidine: beta-cyclodextrin inhibits yeast growth by extraction of ergosterol

Chlorhexidine (Cx) augmented with beta-cyclodextrin (β-cd) inclusion compounds, termed Cx:β-cd complexes, have been developed for use as antiseptic agents. The aim of this study was to examine the interactions of Cx:β-cd complexes, prepared at different molecular ratios, with sterol and yeast membranes. The Minimal Inhibitory Concentration (MIC) against the yeast Candida albicans (C.a.) was determined for each complex; the MICs were found to range from 0.5 to 2 µg/mL. To confirm the MIC data, quantitative analysis of viable cells was performed using trypan blue staining. Mechanistic characterization of the interactions that the Cx:β-cd complexes have with the yeast membrane and assessment of membrane morphology following exposure to Cx:β-cd complexes were performed using Sterol Quantification Method analysis (SQM) and scanning electron microscopy (SEM). SQM revealed that sterol extraction increased with increasing β-cd concentrations (1.71 × 10³; 1.4 × 10³; 3.45 × 10³, and 3.74 × 10³ CFU for 1:1, 1:2, 1:3, and 1:4, respectively), likely as a consequence of membrane ergosterol solubilization. SEM images demonstrated that cell membrane damage is a visible and significant mechanism that contributes to the antimicrobial effects of Cx:β-cd complexes. Cell disorganization increased significantly as the proportion of β-cyclodextrin present in the complex increased. Morphology of cells exposed to complexes with 1:3 and 1:4 molar ratios of Cx:β-cd were observed to have large aggregates mixed with yeast remains, representing more membrane disruption than that observed in cells treated with Cx alone. In conclusion, nanoaggregates of Cx:β-cd complexes block yeast growth via ergosterol extraction, permeabilizing the membrane by creating cluster-like structures within the cell membrane, possibly due to high amounts of hydrogen bonding.

Antitumor effects of rhodium (II) complexes on mice bearing Ehrlich tumors

Rhodium (II) trifluoracetate (TFARh), rhodium (II) trifluoracetate adduct with sulfadiazine (TFARh.Sd) and rhodium (II) acetate adduct with sulfisoxazole (RhSx) were tested in mice for acute toxicity, antitumoral activity against Ehrlich ascites carcinoma and for viability of Ehrlich tumor cells in culture. At ip doses up to 60 µmg/kg (40-70 and 59 mg/kg, respectively), these coumpounds had no toxic effects up to 14 days. At ip doses of 10 µmol Kg-1 day-1 for 5 days, TFARh and TFARh.Sd significantly increased the survival rate of mice bearing Ehrlich ascites cells (probability of survival to the end of 34th day, controls = 0.23, TFARh = 0.85, TFARh.Sd = 0.74). No significant effect was observed for RhSx. In vitro, these rhodium complexes at 40 µM significantly increased the number of dead cells in cultured Ehrlich tumor cells