Synthetic Peptides That Exert Antimicrobial Activities in Whole Blood and Blood-Derived Matrices

Peptides that exert antimicrobial activity in artificial media may lack activity within blood or other complex biological matrices. To facilitate the evaluation of antimicrobial peptides for possible therapeutic utility, an ex vivo assay was developed to assess the extent and durability of peptide antimicrobial activities in complex fluid biomatrices of whole blood, plasma, and serum compared with those in conventional media. Novel antimicrobial peptides (RP-1 and RP-11) were designed based in part on platelet microbicidal proteins. RP-1, RP-11, or gentamicin was introduced into biomatrices either coincident with, or 2 h prior to, inoculation with an Escherichia coli target organism. Antimicrobial activities of peptides were assessed by quantitative culture 2 h after bacterial inoculation and compared to those of peptide-free and gentamicin controls. In whole blood and homologous plasma or serum, introduction of RP-1 or RP-11 coincident with E. coli was associated with a significant reduction in CFU per milliliter versus the respective peptide-free controls. Moreover, substantial antimicrobial activity remained when RP-1 or RP-11 was placed into whole blood or plasma 2 h prior to E. coli inoculation. These results suggest that the peptides were not rapidly inactivated within these biomatrices. Peptide antimicrobial activities were negatively affected by preincubation in serum or in heat-inactivated serum, compared with those of the respective controls. Peptides RP-1 and RP-11 were consistently effective at lower concentrations in biomatrices than in artificial media, indicating favorable antimicrobial interactions with components of blood or blood fractions. Collectively, these findings support the concept that synthetic peptides can be designed to exert potent antimicrobial activities in relevant and complex biological matrices.

在人工培养基中展现出抗菌活性的多肽，在血液或其他复杂生物基质中可能丧失活性。为便于评估抗菌肽（antimicrobial peptides）的潜在治疗用途，研究人员开发了一种离体检测法（ex vivo assay），用于评估多肽在全血、血浆与血清等复杂流体生物基质中的抗菌活性范围及持久性，并与常规培养基中的活性进行对比。
新型抗菌肽RP-1与RP-11的设计部分借鉴了血小板杀菌蛋白。将RP-1、RP-11或庆大霉素，与大肠杆菌（Escherichia coli）靶标菌同时加入生物基质，或在靶标菌接种前2小时加入体系中。于细菌接种后2小时通过定量培养（quantitative culture）检测多肽的抗菌活性，并与无肽对照组及庆大霉素对照组的结果进行对比。
在全血及同源血浆与血清中，当RP-1或RP-11与大肠杆菌同时加入体系时，相较于各自的无肽对照组，每毫升菌落形成单位（Colony-Forming Units，CFU）数量显著降低。此外，若在大肠杆菌接种前2小时将RP-1或RP-11加入全血或血浆中，多肽仍可保留显著的抗菌活性。上述结果表明，此类多肽在这些生物基质中并未被快速灭活。
与各自对照组相比，在血清或热灭活血清中进行预孵育，会对多肽的抗菌活性产生负面影响。相较于人工培养基，RP-1与RP-11在生物基质中仅需更低浓度即可持续发挥抗菌效果，提示其与血液或血液组分的相互作用更具优势。
综上，这些研究结果支持如下理念：可通过设计合成肽类，使其在相关且复杂的生物基质中发挥强效抗菌活性。