Lipoteichoic acid synergizes with glycosphingolipids to potently stimulate secretion of interleukin-6 from human blood cells.

In the present study, we found that lipoteichoic acid (LTA) synergizes with glycosphingolipids to stimulate human blood cells to secrete cytokines. We employed globoside, kerasin, and lactosylceramide as representative neutral glycosphingolipids and mixed gangliosides GM(2) and GM(3) as representative acidic glycosphingolipids. LTA and the glycosphingolipids enhanced cytokine secretion by human whole blood, peripheral blood mononuclear cells, and purified monocytes in a dose-dependent manner. The level of synergy ranged up to approximately 10-fold greater than the additive stimulation caused by LTA and glycosphingolipid alone. The greatest synergy was observed with GM(3). We also found that LTA synergizes with the synthetic bacterial lipopeptide mimic Pam3CysK4. In contrast, the glycosphingolipids suppressed the stimulation caused by Pam3CysK4. The stimulation of human cells requires the simultaneous presence of LTA and the glycosphingolipids and probably requires their physical interactions, as shown by dot blotting and nondenaturing polyacrylamide gel electrophoresis experiments. We hypothesize that the enhanced stimulation is due to heterooligomers that form between LTA and glycosphingolipids at the subcritical micelle concentrations used in these experiments. Previous studies showed that LTA also synergizes with hemoglobin. The data taken together suggest that LTA may be a pathogen-associated molecular pattern, although its full activity requires the presence of a synergistic partner(s).

Neopeptide antibiotics that function as opsonins and membrane-permeabilizing agents for gram-negative bacteria.

We suggest a novel approach to enhancing antimicrobial drug action by utilizing engineered peptide conjugates. Our most potent conjugates, [fMLF]PMBN and [fMLF]PMEN, are nonapeptides derived from polymyxin B's (PMB's) cyclic moiety (Thr-Dab-cyclo[Dab-Dab-d-Phe-Leu-Dab-Dab-Thr], where Dab is 2,4-diaminobutyric acid) and polymyxin E's (PME's) cyclic moiety (Thr-Dab-cyclo[Dab-Dab-d-Leu-Leu-Dab-Dab-Thr]), respectively, attached to a linear tail comprised of formyl-Met-Leu-Phe (fMLF). The cyclic part binds to gram-negative lipopolysaccharides, rendering the bacterial outer membrane permeable to hydrophobic antibiotics. The tail confers chemotactic and opsonic activities upon the conjugates. These two activities appear to be the basis for the conjugates' antibacterial activities. The conjugates are 8 to 10 times less toxic than the parent PMB or PME antibiotics. Fourteen of 18 mice lethally challenged with erythromycin-resistant Klebsiella pneumoniae survived following intraperitoneal administration of erythromycin and [fMLF]PMBN, whereas erythromycin or the peptide conjugate alone had no effect. Moreover, the clearance of Klebsiella from blood was markedly enhanced by intravenous injection of the [fMLF]PMEN peptide conjugate compared to the clearance of the organism from the mice treated with buffer alone as a control and was similar to that achieved by the PME antibiotic. Blood clearance was also significantly enhanced by administration of PMEN either alone or in a mixture with fMLF, although the effect was less than that produced by the peptide conjugate. Since resistance to polymyxins, the parent molecules of the synthetic cyclic peptides, is rare, the emergence of bacteria resistant to the antimicrobial properties of the peptide conjugates may be precluded as well.

Rapid proliferation of prostatic epithelial cells in spontaneously hypertensive rats: a model of spontaneous hypertension and prostate hyperplasia.

Spontaneously hypertensive rats (SHRs), a commonly used model of genetic hypertension, exhibit features of glandular hyperplasia of the ventral prostate, including the narrowing of acini with epithelial protrusions into the lumen and the piling up of epithelial cells. These rats also have frequent urinary voiding. In order to define the fundamental processes that lead to prostatic hyperplasia in SHRs, we compared the proliferation rate of their prostatic epithelial cells (PECs) in primary culture and in vivo to that of Wistar-Kyoto rats (WKYs), their normotensive controls. In vitro, primary cultures of SHR PECs had a shorter doubling time than those of WKY (3.3 vs 8.0 days) and showed higher levels of bromodeoxyuridine (BrdU) incorporation into DNA. In vivo, the BrdU incorporation seen 48 hours following injection was observed primarily in areas of epithelial piling up, which are seen in SHRs but not in WKYs. We concluded that prostate hyperplasia in SHRs results from a genuine increase in the proliferation rate of PECs and that this rapid proliferation is a fundamental feature of SHR PECs, maintained both in vivo and in vitro. Thus, SHRs can serve as a model for glandular hyperplasia of the prostate, resulting from a genetic tendency for an increased rate of cell proliferation.