Structure and membrane interactions of the homodimeric antibiotic peptide homotarsinin

Antimicrobial peptides (AMPs) from amphibian skin are valuable template structures to find new treatments against bacterial infections. This work describes for the first time the structure and membrane interactions of a homodimeric AMP. Homotarsinin, which was found in Phyllomedusa tarsius anurans, consists of two identical cystine-linked polypeptide chains each of 24 amino acid residues. The high-resolution structures of the monomeric and dimeric peptides were determined in aqueous buffers. The dimer exhibits a tightly packed coiled coil three-dimensional structure, keeping the hydrophobic residues screened from the aqueous environment. An overall cationic surface of the dimer assures enhanced interactions with negatively charged membranes. An extensive set of biophysical data allowed us to establish structure-function correlations with antimicrobial assays against Gram-positive and Gram-negative bacteria. Although both peptides present considerable antimicrobial activity, the dimer is significantly more effective in both antibacterial and membrane biophysical assays.

Comparative Analysis of the Antimicrobial Activities of Plant Defensin-Like and Ultrashort Peptides against Food-Spoiling Bacteria

Antimicrobial peptides offer potential as novel therapeutics to combat food spoilage and poisoning caused by pathogenic and nonpathogenic bacteria. Our previous studies identified the peptide human beta-defensin 3 (HBD3) as a potent antimicrobial agent against a wide range of beer-spoiling bacteria. Thus, HBD3 is an excellent candidate for development as an additive to prevent food and beverage spoilage. To expand the repertoire of peptides with antimicrobial activity against bacteria associated with food spoilage and/or food poisoning, we carried out an in silico discovery pipeline to identify peptides with structure and activity similar to those of HBD3, focusing on peptides of plant origin. Using a standardized assay, we compared the antimicrobial activities of nine defensin-like plant peptides to the activity of HBD3. Only two of the peptides, fabatin-2 and Cp-thionin-2, displayed antimicrobial activity; however, the peptides differed from HBD3 in being sensitive to salt and were thermostable. We also compared the activities of several ultrashort peptides to that of HBD3. One of the peptides, the synthetic tetrapeptide O3TR, displayed biphasic antimicrobial activity but had a narrower host range than HBD3. Finally, to determine if the peptides might act in concert to improve antimicrobial activity, we compared the activities of the peptides in pairwise combinations. The plant defensin-like peptides fabatin-2 and Cp-thionin-2 displayed a synergistic effect with HBD3, while O3TR was antagonistic. Thus, some plant defensin-like peptides are effective antimicrobials and may act in concert with HBD3 to control bacteria associated with food spoilage and food poisoning.

IMPORTANCE

Food spoilage and food poisoning caused by bacteria can have major health and economic implications for human society. With the rise in resistance to conventional antibiotics, there is a need to identify new antimicrobials to combat these outbreaks in our food supply. Here we screened plant peptide databases to identify peptides that share structural similarity with the human defensin peptide HBD3, which has known antimicrobial activity against food-spoiling bacteria. We show that two of the plant peptides display antimicrobial activity against bacteria associated with food spoilage. When combined with HBD3, the peptides are highly effective. We also analyzed the activity of an easily made ultrashort synthetic peptide, O3TR. We show that this small peptide also displays antimicrobial activity against food-spoiling bacteria but is not as effective as HBD3 or the plant peptides. The plant peptides identified are good candidates for development as natural additives to prevent food spoilage.

A novel role for constitutively expressed epithelial-derived chemokines as antibacterial peptides in the intestinal mucosa

Intestinal-derived chemokines have a central role in orchestrating immune cell influx into the normal and inflamed intestine. Here, we identify the chemokine CCL6 as one of the most abundant chemokines constitutively expressed by both murine small intestinal and colonic epithelial cells. CCL6 protein localized to crypt epithelial cells, was detected in the gut lumen and reached high concentrations at the mucosal surface. Its expression was further enhanced in the small intestine following in vivo administration of LPS or after stimulation of the small intestinal epithelial cell line, mIC(c12), with IFNgamma, IL-4 or TNFalpha. Recombinant- and intestinal-derived CCL6 bound to a subset of the intestinal microflora and displayed antibacterial activity. Finally, the human homologs to CCL6, CCL14 and CCL15 were also constitutively expressed at high levels in human intestinal epithelium, were further enhanced in inflammatory bowel disease and displayed similar antibacterial activity. These findings identify a novel role for constitutively expressed, epithelial-derived chemokines as antimicrobial peptides in the intestinal mucosa.

How nature morphs peptide scaffolds into antibiotics

The conventional notion that peptides are poor candidates for orally available drugs because of protease-sensitive peptide bonds, intrinsic hydrophilicity, and ionic charges contrasts with the diversity of antibiotic natural products with peptide-based frameworks that are synthesized and utilized by Nature. Several of these antibiotics, including penicillin and vancomycin, are employed to treat bacterial infections in humans and have been best-selling therapeutics for decades. Others might provide new platforms for the design of novel therapeutics to combat emerging antibiotic-resistant bacterial pathogens.

Comprehensive defensin assay for saliva

Defensins are highly basic cationic peptides that are important components of the innate and adaptive immune response pathways. In addition, these peptides are involved in CD8+ T cell response to HIV-1, increased pulmonary infection risk among cystic fibrosis patients, upregulated levels of HNP-5 for patients with ulcerative colitis and Crohn's disease, and monitoring HNP-3 levels as a tumor classification scheme for cutaneous T cell lymphomas, and have promise in the pharmaceutical field as a new class of antibiotics. Here we present a parallel assay for the alpha (HNP1-3) and beta (HBD1-2) classes of defensins in saliva that are naturally observed in the concentration range of 1 ng/mL to 10 microg/mL. The method utilizes solid phase extraction of saliva samples combined with liquid chromatography-tandem mass spectrometry to identify and quantitate defensin targets. The approach involves limited sample manipulation and is easily amenable to automation. The saliva samples analyzed are derived from a large cohort study focused on examining the role of polymorphisms in genes of innate and adaptive immunity in modulating the response to vaccination for two gastrointestinal tract infections: typhoid and cholera. The alpha-defensin levels observed range from 1 to 10 microg/mL and correlate well with known active concentrations against a wide variety of pathogens. The observed concentration range for beta-defensins was between the detection limit and 33 ng/mL and had a sensitivity level that was comparable to immunoassay-based detection. This method is easily adapted for use in a clinical immunology setting and can be modified for other biological matrixes. This assay will facilitate examination of the production, secretion, and regulation of defensin peptides in a direct fashion to coordinate levels of these compounds with gender, age, response to vaccination, gene copy number, and oral health.

Effect of massive weight loss on inflammatory adipocytokines and the innate immune system in morbidly obese women

CONTEXT

Obesity may be regarded as a low-grade inflammatory state.

OBJECTIVE

The aim of this study was to evaluate changes in pro-inflammatory adipocytokines and the innate immune system, cardiovascular risk, and insulin sensitivity after massive weight loss.

DESIGN

This was a longitudinal study.

SETTING

The study was conducted at Catholic University, Rome.

SUBJECTS AND METHODS

There were 10 normoglucose-tolerant obese women evaluated before and 36 months after bilio-pancreatic diversion (BPD). Glucose sensitivity (M value) was estimated using the euglycemic-hyperinsulinemic clamp. Mannan-binding lectin (MBL), bactericidal/permeability increasing protein (BPI), alpha-defensins, soluble CD14 receptor (sCD14), C-reactive protein, adiponectin, leptin, visfatin, IL-6, and TNF-alpha were assayed.

RESULTS

After massive weight loss (53% of excess body weight), leptin (P <or= 0.0001), IL-6 (P <or= 0.0001), alpha-defensins (P <or= 0.001), and C-reactive protein (P <or= 0.0001) decreased significantly. Adiponectin increased significantly (P <or= 0.001). Of the nine subjects who lost more than 20% of body mass index, sCD14 (2.87 +/- 0.5 to 2.55 +/- 0.5; P = 0.016) and visfatin levels (12.20 +/- 0.93 to 10.63 +/- 1.93 ng/ml; P = 0.045) decreased significantly. No significant changes were observed in TNF-alpha, BPI, or MBL. Insulin sensitivity more than doubled after BPD (P <or= 0.0001). sCD14 changes were significantly associated with body mass index (r0 = 0.80; P = 0.003) and M changes (r0 = -0.59; P = 0.03). MBL correlated with insulin sensitivity in obese (r0 = 0.93; P = 0.0001) and post-BPD women (r(0) = 0.66; P = 0.038). Adiponectin correlated negatively with cardiovascular risk (r0 = -0.709; P = 0.02) and IL-6 (r0 = -0.634; P = 0.05). Multiple linear regression analysis showed that changes in sCD14 were also significantly related to changes in insulin sensitivity.

CONCLUSIONS

Surgically induced weight loss is capable of reversing low-grade inflammation, at least partially. The relationships between sCD14, MBL, BPI, and glucose sensitivity, and the role of TNF-alpha in obesity warrant further investigation.