Hanne H. Haukland

The antimicrobial peptides lactoferricin B and magainin 2 cross over the bacterial cytoplasmic membrane and reside in the cytoplasm

The localization of immunolabelled antimicrobial peptides was studied using transmission electron microscopy. Staphylococcus aureus and Escherichia coli were exposed to lactoferricin B (17–41), lactoferricin B (17–31) and D‐lactoferricin B (17–31). E. coli was also exposed to cecropin P1 and magainin 2. The lactoferricins were found in the cytoplasm of both bacteria. In S. aureus the amount of cytoplasmic lactoferricin B (17–41) was time‐ and concentration‐dependent, reaching a maximum within 30 min. Cecropin P1 was confined to the cell wall, while magainin 2 was found in the cytoplasm of E. coli. The finding of intracellularly localized magainin is not reported previously.

Lactoferricin B causes depolarization of the cytoplasmic membrane of Escherichia coli ATCC 25922 and fusion of negatively charged liposomes

Antimicrobial peptides have been extensively studied in order to elucidate their mode of action. Most of these peptides have been shown to exert a bactericidal effect on the cytoplasmic membrane of bacteria. Lactoferricin is an antimicrobial peptide with a net positive charge and an amphipatic structure. In this study we examine the effect of bovine lactoferricin (lactoferricin B; Lfcin B) on bacterial membranes. We show that Lfcin B neither lyses bacteria, nor causes a major leakage from liposomes. Lfcin B depolarizes the membrane of susceptible bacteria, and induces fusion of negatively charged liposomes. Hence, Lfcin B may have additional targets responsible for the antibacterial effect.

Antibacterial effects of lactoferricin B.

The antimicrobial peptide, lactoferricin, can be generated upon gastric pepsin cleavage of lactoferrin. We have examined the inhibitory efficacy of lactoferricin of bovine origin (Lf-cin B) on Escherichia coli, Proteus mirabilis and Staphylococcus aureus with or without a cell wall. We found that spheroplasts and protoplasts had a lower MIC than their counterparts with a cell wall. We also compared the efficacies of Lf-cin B (17-31) made of all L-amino acids and all D-amino acids. The peptide made of all D-amino acids was more active than the corresponding L-enantiomer. Furthermore, we examined the influence of Lf-cin B on the motility of E. coli and the influence of temperature on the susceptibility of bacteria exposed to Lf-cin B. Bacteria exposed to sub-MIC of Lf-cin B lost their motility. Bacteria exposed to Lf-cin B at 20 degrees C were more sensitive to Lf-cin B than when exposed at 37 degrees C. These findings indicate that the cell envelope is a limiting step for Lf-cin B to exert its antibiotic effect. We cannot rule out a receptor-mediated first step for Lf-cin B (17-31).

Induced resistance to the antimicrobial peptide lactoferricin B in Staphylococcus aureus

This study was designed to investigate inducible intrinsic resistance against lactoferricin B in Staphylococcus aureus. Serial passage of seven S. aureus strains in medium with increasing concentrations of peptide resulted in an induced resistance at various levels in all strains. The induced resistance was unstable and decreased relatively rapidly during passages in peptide free medium but the minimum inhibitory concentration remained elevated after thirty passages. Cross‐resistance to penicillin G and low‐level cross‐resistance to the antimicrobial peptides indolicidin and Ala3,13,18‐magainin was observed. No cross‐resistance was observed to the human cathelicidin LL‐37. In conclusion, this study shows that S. aureus has intrinsic resistance mechanisms against antimicrobial peptides that can be induced upon exposure, and that this may confer low‐level cross‐resistance to other antimicrobial peptides.

Changes in postprandial release patterns of gastrointestinal hormones in late pregnancy and the early postpartum period

Summary. Intestinal transit time increases and gastrointestinal incretin effect is reported to decrease in pregnancy. The release patterns of gastrointestinal hormones related to these functions were studied in eight women before and after ingestion of a standardized meal at 32–34 weeks gestation and at 4 days postpartum. Basal plasma motilin and the integrated meal response of motilin, pancreatic polypeptide (PP) and gastric inhibitory polypeptide (GIP) were significantly lower in pregnancy than postpartum. The meal‐induced rise of somatostatin and vasoactive intestinal polypeptide (VIP) was, however, absent in late pregnancy; whereas the somatostatin response recovered postpartum, and the plasma VIP concentrations stabilized at significantly higher levels postpartum without any meal response. Basal and meal‐induced plasma insulin were significantly higher in pregnancy.

The effect of severe pre‐eclampsia on the pancreas: changes in the serum cationic trypsinogen and pancreatic amylase

Summary. In 13 patients with severe pre‐eclampsia mean serum concentrations of cationic trypsinogen and amylase were statistically significantly higher at 64ng/ml and 1·6 μmol/1, respectively, than the corresponding mean serum concentrations in 30 normal pregnancies, 22 ng/ml and 1·1 μmol/1 respectively. These rises exceeded the expected increased values due to the slight reduction of the renal function in the pre‐eclamptic patients, and therefore indicate a concomitant injury of the pancreas.

Gastric Cancer after Vagotomy and Excision for Gastric Ulcer

A follow-up examination of 152 patients with gastric ulcer treated with vagotomy, ulcerectomy and drainage showed that 4 of the patients manifested gastric cancer 5–7 years after the operation. A simu

Characterization of secretin-like immunoreactivity in pregnancy.

The plasma secretin-like immunoreactivity (SLI) in 23 healthy females was elevated in late pregnancy (34 +/- 3 pmol/l) as compared with 23 non-pregnant female controls (12 +/- 2 pmol/l; p less than 0.01). The plasma SLI in pregnancy eluted close to albumin on a Sephadex G-200 column, whereas 50-75% of the recovered SLI was displaced to the elution volume of free secretin when plasma was exposed to 6 mol/l urea. When 125I-labelled secretin was incubated with plasma in the absence of secretin antibodies, 40% of the intact label eluted in the void volume of a Sephadex G-50 Fine column in pregnancy, compared with only 18% in the nonpregnant state. The present study supports the notion that secretin circulates bound to plasma proteins and suggests that the protein binding of secretin is enhanced in late pregnancy, a feature common to several classical hormones.