Novelties in the field of antimicrobial compounds for the treatment of lower respiratory tract infections

On the physiology and pathophysiology of antimicrobial peptides

Antimicrobial peptides (AMP) are a heterogeneous group of molecules involved in the nonspecific immune responses of a variety of organisms ranging from prokaryotes to mammals, including humans. AMP have various physical and biological properties, yet the most common feature is their antimicrobial effect. The majority of AMP disrupt the integrity of microbial cells by 1 of 3 known mechanisms--the barrel-stave pore model, the thoroidal pore model, or the carpet model. Results of growing numbers of descriptive and experimental studies show that altered expression of AMP in various tissues is important in the pathogenesis of several gastrointestinal, respiratory, and other diseases. We discuss novel approaches and strategies to further improve the promising future of therapeutic applications of AMP. The spread of antibiotic resistance increases the importance of developing a clinical role for AMP.

Collectins and cationic antimicrobial peptides of the respiratory epithelia

The respiratory epithelium is a primary site for the deposition of microorganisms that are acquired during inspiration. The innate immune system of the respiratory tract eliminates many of these potentially harmful agents preventing their colonization. Collectins and cationic antimicrobial peptides are antimicrobial components of the pulmonary innate immune system produced by respiratory epithelia, which have integral roles in host defense and inflammation in the lung. Synthesis and secretion of these molecules are regulated by the developmental stage, hormones, as well as many growth and immunoregulatory factors. The purpose of this review is to discuss antimicrobial innate immune elements within the respiratory tract of healthy and pneumonic lung with emphasis on hydrophilic surfactant proteins and beta-defensins.

Alternative and/or integrative therapies for pneumonia under development

PURPOSE OF REVIEW

Increasing antimicrobial resistance among common respiratory bacteria has created challenges in selecting appropriate therapy for pneumonia. Fortunately, the analysis of genome sequences has allowed us to find novel, nontraditional targets that are involved in disease pathogenesis or in adaptation and growth in infection sites. The advantage of the nonclassical targets is that targeting these sites could ablate infection without inducing resistance. Interfering with bacterial adhesion, inhibiting, neutralizing and clearing endotoxin, and administering cytokines as immunoadjuvants are the most promising alternative or integrative treatments for pneumonia that are under development.

RECENT FINDINGS

Interference with bacterial adhesion is possible using inhibitors of sortase or inactivators of the srtA gene against gram-positive bacteria, inhibitors of the periplasmic chaperone or those of usher function against gram-negative bacteria, novel polysaccharides that are present on echinoderm surfaces, antiadhesin vaccines, or the passive administration of antiadhesin antibodies. Inhibition, neutralization, and clearance of endotoxin possibly interferes in the lipid A biosynthetic pathway or using lipid A analogues with reduced or lack of ability to activate the major endotoxin receptors or proteins such as recombinant Limulus antilipopolysaccharide factor, bactericidal/permeability increasing protein, or lipopolysaccharide binding protein. Tumor necrosis factor 70-80, an adenoviral vector that encodes murine tumor necrosis factor alpha, and recombinant interferon gamma seem to be the most promising cytokines for use as immunoadjuvants for the treatment of pneumonia.

SUMMARY

Ideally, potential treatment of life-threatening bacterial pneumonia will combine immunoadjuvant and conventional antibiotic therapy. Compounds capable of stimulating early host defense and microbial clearance, but not the later phases of inflammatory tissue injury associated with sepsis, may be advantageous.