The Compound U18666A Inhibits the Intoxication of Cells by Clostridioides difficile Toxins TcdA and TcdB

The intestinal pathogen Clostridioides (C.) difficile is a major cause of diarrhea both in hospitals and outpatient in industrialized countries. This bacterium produces two large exotoxins, toxin A (TcdA) and toxin B (TcdB), which are directly responsible for the onset of clinical symptoms of C. difficile-associated diseases (CDADs), such as antibiotics-associated diarrhea and the severe, life-threatening pseudomembranous colitis. Both toxins are multidomain proteins and taken up into host eukaryotic cells via receptor-mediated endocytosis. Within the cell, TcdA and TcdB inactivate Rho and/or Ras protein family members by glucosylation, which eventually results in cell death. The cytotoxic mode of action of the toxins is the main reason for the disease. Thus, compounds capable of inhibiting the cellular uptake and/or mode-of-action of both toxins are of high therapeutic interest. Recently, we found that the sterol regulatory element-binding protein 2 (SREBP-2) pathway, which regulates cholesterol content in membranes, is crucial for the intoxication of cells by TcdA and TcdB. Furthermore, it has been shown that membrane cholesterol is required for TcdA- as well as TcdB-mediated pore formation in endosomal membranes, which is a key step during the translocation of the glucosyltransferase domain of both toxins from endocytic vesicles into the cytosol of host cells. In the current study, we demonstrate that intoxication by TcdA and TcdB is diminished in cultured cells preincubated with the compound U18666A, an established inhibitor of cholesterol biosynthesis and/or intracellular transport. U18666A-pretreated cells were also less sensitive against TcdA and TcdB variants from the epidemic NAP1/027 C. difficile strain. Our study corroborates the crucial role of membrane cholesterol for cell entry of TcdA and TcdB, thus providing a valuable basis for the development of novel antitoxin strategies in the context of CDADs.

Intraobserver, interobserver variation of sperm critical morphology: comparison of examiner and computer-assisted analysis

OBJECTIVE

To examine intraobservational and interobservational variation in sperm critical morphology analysis between trained andrologists and a computer over the range of 0% to 15% normal forms.

DESIGN

Retrospective.

SETTING

Fertility center.

PATIENTS

Twenty-four semen specimen slides were read five times in a randomized, blinded fashion by two andrologists and a computerized semen analyzer. Twenty-five samples were analyzed using a different stain and a centrifugation step.

MAIN OUTCOME MEASURE

Sperm strict morphology.

RESULTS

Mean average intraobserver deviation of normal forms was small (1.3% to 2.7%). Intraobserver deviation did not differ between andrologists, but both differed from the computer. Interobserver deviation for percent normal forms was similar for andrologists and computer. Mean average deviations were small over the variation was independent of the initial percent normal forms. The computer frequently evaluated significantly fewer cells than the andrologists. Updated software increased the number of cells read by the computer requiring more time than the andrologist.

CONCLUSIONS

Trained andrologists and a computer determine sperm critical morphology similarly over the range of 0% to 15% normal forms. A single evaluation is highly predictive of multiple evaluations. Improvements in the speed of computer assessment are still necessary.