Cell-Density Dependence of Host-Defense Peptide Activity and Selectivity in the Presence of Host Cells

Abstract

Host-defense peptides (HDPs) are promising compounds against multidrug-resistant microbes. In vitro, their bactericidal and toxic concentrations are significantly different, but this might be due to the use of separate assays, with different cell densities. For experiments with a single cell type, the cell-density dependence of the active concentration of the DNS-PMAP23 HDP could be predicted based on the water/cell-membrane partition equilibrium and exhibited a lower bound at low cell counts. On the basis of these data, in the simultaneous presence of both bacteria and an excess of human cells, one would expect no significant toxicity, but also inhibition of the bactericidal activity due to peptide sequestration by host cells. However, this inhibition did not take place in assays with mixed cell populations, showing that for the HDP esculentin-1a(1-21)NH, a range of bactericidal, nontoxic concentrations exists and confirming the effective selectivity of HDPs. Mixed-cell assays might be necessary to effectively asses HDP selectivity.

Antimicrobial peptides are degraded by the cytosolic proteases of human erythrocytes

“…In the in vitro experiments performed here, the concentration of RBCs was 1×10 8 RBCs/mL, 2% of human physiological concentration. It has been shown previously that both MIC values and hemolysis are directly dependent on cell density (38, 39). However, as cell counts are increased towards physiological concentrations, and fractional hemolysis decreases, the total pool of cytosolic proteases also increases.…”

“…At present, it may be more important than ever as the spread of antibiotic resistant pathogens accelerates and seriously threatens human health both inside and outside of the hospital (49). Recent research (17, 38), in which antimicrobial peptides are studied in the context of their interactions with both eukaryotic cells and prokaryotic cells, may suggest a critical paradigm shift that will bring antimicrobial peptides to the clinic. Taken together, our previous report (17) on erythrocyte-dependent AMP inhibition, and this work on erythrocyte intracellular proteases, reveal the dual effects of cell binding and proteolysis on AMP activity in the presence of erythrocytes.…”

From liposomes to cells: Filling the gap between physicochemical and microbiological studies of the activity and selectivity of host‐defense peptides

“… Inoculum effect on the activity of different HDPs. Data from references (blue), (green), (red). The continuous line is a prediction (not a fit) for the trend observed in reference, based on Equations 3 and 4, with values T B = 1.1 × 10 7 molecules/cell and = 1.8 × 10 8 cells/mL.…”

“…Data from references (blue), (green), (red). The continuous line is a prediction (not a fit) for the trend observed in reference, based on Equations 3 and 4, with values T B = 1.1 × 10 7 molecules/cell and = 1.8 × 10 8 cells/mL. Adapted with permission from references (copyright 1994 Wiley), (copyright 2016 Springer) and (copyright 2017 American Chemical Society).…”

“…In the last few years, some groups, including ours, have started trying to extend the powerful physicochemical approaches, normally applied to model membranes, to quantitative experiments on real cells, in order to tackle the questions discussed earlier. This review is devoted to the recent studies striving to fill the gap between microbiological and biophysical studies of HDPs.…”