Life-threatening infectious diseases are on their way to cause a worldwide crisis, as treating them effectively is becoming increasingly difficult due to the emergence of antibiotic resistant strains. Antimicrobial peptides (AMPs) form an ancient type of innate immunity found universally in all living organisms, providing a principal first-line of defense against the invading pathogens. The unique diverse function and architecture of AMPs has attracted considerable attention by scientists, both in terms of understanding the basic biology of the innate immune system, and as a tool in the design of molecular templates for new anti-infective drugs. AMPs are gene-encoded short (<100 amino acids), amphipathic molecules with hydrophobic and cationic amino acids arranged spatially, which exhibit broad spectrum antimicrobial activity. AMPs have been the subject of natural evolution, as have the microbes, for hundreds of millions of years. Despite this long history of co-evolution, AMPs have not lost their ability to kill or inhibit the microbes totally, nor have the microbes learnt to avoid the lethal punch of AMPs. AMPs therefore have potential to provide an important breakthrough and form the basis for a new class of antibiotics. In this review, we would like to give an overview of cationic antimicrobial peptides, origin, structure, functions, and mode of action of AMPs, which are highly expressed and found in humans, as well as a brief discussion about widely abundant, well characterized AMPs in mammals, in addition to pharmaceutical aspects and the additional functions of AMPs.

The aggregation of EOgg-POes-EOge (EO and PO being ethylene oxide and propylene oxide, respectively) in water has been studied. By gel permeation chromatography (GPC) and self-diffusion studies, it was found that micelles are formed in dilute solutions, but only at higher temperatures. The micelles formed have a hydrodynamic radius of approximately 10 nm over a wide temperature range. The residence time of the polymer molecules in the micelles is extremely long (~hours). At higher polymer concentrations, a clear isotropic gel is formed at intermediate temperatures. The extension of the gel region depends strongly on the presence of cosolutes, such as inorganic salts and hydrocarbons; detailed phase diagrams are presented and discussed. Furthermore, the self-diffusion of the polymer and of solubilized oil was studied. The diffusion of the polymer molecules is slow (Dp ~10'n-10~12 m2/s), decreasing with increasing polymer concentration (roughly as Dp ~c*1) up to 20 wt %. In the gel region, the echo-amplitude decay curves reveal a distribution of diffusion coefficients, precluding detailed analyses. The self-diffusion of the oil is comparable to that of the polymer (D0ii ~DP), and several orders of magnitude slower than the diffusion of water (Dw = 10~9 m2/s).

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The coagulation system is characterized by the sequential and highly localized activation of a series of serine proteases, culminating in the conversion of fibrinogen into fibrin, and formation of a fibrin clot. Here we show that C-terminal peptides of thrombin, a key enzyme in the coagulation cascade, constitute a novel class of host defense peptides, released upon proteolysis of thrombin in vitro, and detected in human wounds in vivo. Under physiological conditions, these peptides exert antimicrobial effects against Gram-positive and Gram-negative bacteria, mediated by membrane lysis, as well as immunomodulatory functions, by inhibiting macrophage responses to bacterial lipopolysaccharide. In mice, they are protective against P. aeruginosa sepsis, as well as lipopolysaccharide-induced shock. Moreover, the thrombin-derived peptides exhibit helical structures upon binding to lipopolysaccharide and can also permeabilize liposomes, features typical of “classical” helical antimicrobial peptides. These findings provide a novel link between the coagulation system and host-defense peptides, two fundamental biological systems activated in response to injury and microbial invasion.