Endosomal pH modulation by peptide-gold nanoparticle hybrids enables potent anti-inflammatory activity in phagocytic immune cells.

Toll-like receptor (TLR) signaling plays a central role in the pathophysiology of many acute and chronic human inflammatory diseases, and pharmacological regulation of TLR responses is anticipated to be beneficial in many inflammatory conditions. Currently there are no specific TLR inhibitors in clinical use. To overcome this challenge, we have developed a nano-based TLR inhibitor (peptide-gold nanoparticle hybrids) that inhibits a broad spectrum of TLR responses. Through mechanistic studies, we established that specific peptide decorated-gold nanoparticles that display high cellular uptake in phagocytic immune cells modulate endosomal pH, leading to significant attenuation of signaling through multiple TLRs. Using a global transcriptomic approach, we defined the broad anti-inflammatory activity of the nanoparticle in human peripheral blood mononuclear cells. In vivo studies confirmed the beneficial immunomodulatory activity since treatment with the nanoparticle significantly reduced weight loss, improved the disease activity index, and ameliorated colonic inflammation in a murine model of intestinal inflammation. This work enhances our fundamental understanding of the role of peptide coatings on the nanoparticle surface in regulating innate immune signaling, and identifies specific peptide decorated nanoparticles that may represent a novel class of anti-inflammatory therapeutics for human inflammatory diseases.

The innate defense regulator peptides IDR-HH2, IDR-1002, and IDR-1018 modulate human neutrophil functions.

Although HDPs were originally hypothesized to act as antimicrobial agents, they also have been shown to broadly modulate the immune response through the activation of different cell types. We recently developed a series of novel, synthetic peptides, termed IDRs, which are conceptually based on a natural HDP, bovine bactenecin. We showed that IDR-1 and IDR-1002 protect the host against bacterial infections through the induction of chemokines. The objective of this study was to investigate the effects of the IDRs on various functions of human neutrophils. Here, we demonstrated that IDR-HH2, IDR-1002, and IDR-1018 modulated the expression of neutrophil adhesion and activation markers. Moreover, these IDRs enhanced neutrophil adhesion to endothelial cells in a ß2 integrin-dependent manner and induced neutrophil migration and chemokine production. The IDR peptides also increased the release of the neutrophil-generated HDPs (antimicrobial), human α-defensins, and LL-37 and augmented neutrophil-mediated killing of Escherichia coli. Notably, the IDRs significantly suppressed LPS-mediated neutrophil degranulation, the release of ROS, and the production of the inflammatory cytokines TNF-α and IL-10, consistent with their ability to dampen inflammation. As evidenced by the inhibitory effects of MAPK-specific inhibitors, IDRs activated the MAPK pathway that was required for chemokine production. In conclusion, our study provides novel evidence regarding the contribution of the IDR peptides to the innate immune response through the modulation of neutrophil functions. The results described here may aid in the development of IDRs as novel, anti-infective and immunomodulatory agents.

Synthetic cationic peptide IDR-1018 modulates human macrophage differentiation.

Macrophages play a critical role in the innate immune response. To respond in a rapid and efficient manner to challenges in the micro-environment, macrophages are able to differentiate towards classically (M1) or alternatively (M2) activated phenotypes. Synthetic, innate defense regulators (IDR) peptides, designed based on natural host defence peptides, have enhanced immunomodulatory activities and reduced toxicity leading to protection in infection and inflammation models that is dependent on innate immune cells like monocytes/macrophages. Here we tested the effect of IDR-1018 on macrophage differentiation, a process essential to macrophage function and the immune response. Using transcriptional, protein and systems biology analysis, we observed that differentiation in the presence of IDR-1018 induced a unique signature of immune responses including the production of specific pro and anti-inflammatory mediators, expression of wound healing associated genes, and increased phagocytosis of apoptotic cells. Transcription factor IRF4 appeared to play an important role in promoting this IDR-1018-induced phenotype. The data suggests that IDR-1018 drives macrophage differentiation towards an intermediate M1-M2 state, enhancing anti-inflammatory functions while maintaining certain pro-inflammatory activities important to the resolution of infection. Synthetic peptides like IDR-1018, which act by modulating the immune system, could represent a powerful new class of therapeutics capable of treating the rising number of multidrug resistant infections as well as disorders associated with dysregulated immune responses.

A systems biology approach to nutritional immunology - focus on innate immunity.

Innate immunity and nutrient metabolism are complex biological systems that must work in concert to sustain and preserve life. The effector cells of the innate immune system rely on essential nutrients to generate energy, produce metabolic precursors for macromolecule biosynthesis and tune their responses to infectious agents. Thus disruptions to nutritional status have a substantial impact on immune competence and can result in increased susceptibility to infection in the case of nutrient deficiency, or chronic inflammation in the case of over-nutrition. The traditional, reductionist methods used in the study of nutritional immunology are incapable of exploring the extremely complex interactions between nutrient metabolism and innate immunity. Here, we review a relatively new analytical approach, systems biology, and highlight how it can be applied to nutritional immunology to provide a comprehensive view of the mechanisms behind nutritional regulation of the innate immune system.

Therapeutic potential of host defense peptides in antibiotic-resistant infections.

The emergence of infections caused by multi-drug resistant (MDR) pathogens pose a major burden to modern healthcare. Exacerbating this issue is the substantial decline in development of new classes of antibiotics by pharmaceutical companies. This has led to renewed interest in the therapeutic potential of natural anti-infective agents such as host defense peptides (HDPs). The broad antimicrobial and immunomodulatory activities of HDPs and their synthetic derivatives, coupled with the fact that they do not readily induce microbial resistance, makes them extremely valuable leads in the development of new treatment strategies for MDR infections. This review examines our knowledge of the mechanisms behind multi-drug resistance as well as the properties of HDPs and their therapeutic potential, especially in the case of MDR infections. Challenges to their development as new therapeutics are also discussed.

Innate defense regulator peptide 1018 in wound healing and wound infection.

Innate defense regulators (IDRs) are synthetic immunomodulatory versions of natural host defense peptides (HDP). IDRs mediate protection against bacterial challenge in the absence of direct antimicrobial activity, representing a novel approach to anti-infective and anti-inflammatory therapy. Previously, we reported that IDR-1018 selectively induced chemokine responses and suppressed pro-inflammatory responses. As there has been an increasing appreciation for the ability of HDPs to modulate complex immune processes, including wound healing, we characterized the wound healing activities of IDR-1018 in vitro. Further, we investigated the efficacy of IDR-1018 in diabetic and non-diabetic wound healing models. In all experiments, IDR-1018 was compared to the human HDP LL-37 and HDP-derived wound healing peptide HB-107. IDR-1018 was significantly less cytotoxic in vitro as compared to either LL-37 or HB-107. Furthermore, administration of IDR-1018 resulted in a dose-dependent increase in fibroblast cellular respiration. In vivo, IDR-1018 demonstrated significantly accelerated wound healing in S. aureus infected porcine and non-diabetic but not in diabetic murine wounds. However, no significant differences in bacterial colonization were observed. Our investigation demonstrates that in addition to previously reported immunomodulatory activities IDR-1018 promotes wound healing independent of direct antibacterial activity. Interestingly, these effects were not observed in diabetic wounds. It is anticipated that the wound healing activities of IDR-1018 can be attributed to modulation of host immune pathways that are suppressed in diabetic wounds and provide further evidence of the multiple immunomodulatory activities of IDR-1018.