TatC-dependent translocation of pyoverdine is responsible for the microbial growth suppression.

Infections are often not caused by a colonization of Pseudomonas aeruginosa alone but by a consortium of other bacteria. Little is known about the impact of P. aeruginosa on the growth of other bacteria upon coinfection. Here, cell-ree culture supernatants obtained from P. aeruginosa suppressed the growth of a number of bacterial strains such as Corynebacterium glutamicum, Bacillus subtilis, Staphylococcus aureus, and Agrobacterium tumefaciens, but had little effect on the growth of Escherichia coli and Salmonella Typhimurium. The growth suppression effect was obvious when P. aeruginosa was cultivated in M9 minimal media, and the suppression was not due to pyocyanin, a well-known antimicrobial toxin secreted by P. aeruginosa. By performing transposon mutagenesis, PA5070 encoding TatC was identified, and the culture supernatant of its mutant did not suppress the growth. HPLC analysis of supernatants showed that pyoverdine was a secondary metabolite present in culture supernatants of the wild-type strain, but not in those of the PA5070 mutant. Supplementation of FeCl2 as a source of iron compromised the growth suppression effect of supernatants and also recovered biofilm formation of S. aureus, indicating that pyoverdine-mediated iron acquisition is responsible for the growth suppression. Thus, this study provides the action of TatC-dependent pyoverdine translocation for the growth suppression of other bacteria, and it might aid understanding of the impact of P. aeruginosa in the complex community of bacterial species upon coinfection.

Effect of Piperazine Dithioctate on the Oral Pharmacokinetics of Glimepiride in Rats.

The objective of the present work was to investigate the potential for pharmacokinetic drug-drug interactions between glimepiride (GMP) and piperazine dithioctate (PDT) in rats to support the development of an orally combined product of the two drugs. An LC-MS/MS bioanalytical method was developed for simultaneous quantification of GMP and thioctic acid (TA) in rat plasma. The accuracy, precision, linearity, selectivity, and recovery were all within an acceptable range. The oral plasma exposure of the GMP solution was more than 14-times greater than that of the GMP suspension at a dose of 0.5 mg/kg, suggesting a dissolution-limited absorption of the GMP suspension. Oral co-administration of PDT (72 mg/kg) with GMP suspension (0.5 mg/kg) reduced the plasma GMP exposure by approximately 80% without a significant change in t1/2 and tmax. Oral co-administration of PDT with GMP solution had no significant effect on the plasma pharmacokinetics of GMP. PDT lowered the pH (from ca. 7 to 5.6) and the dissolved GMP concentration in the GMP suspension. It was also shown that GMP was more soluble at pH 7 than at 5.7 in an aqueous solution, and the oral plasma exposure of a GMP suspension at pH 7.0 was substantially higher than that of a suspension at pH 5.7. These results suggest that the pH-dependent solubility of GMP was likely responsible for PDT's effect on the oral absorption of GMP. In conclusion, the current work suggests a possibility of drug-drug interaction between GMP and PDT upon oral co-administration.

Pharmacokinetics and metabolism of 4-O-methylhonokiol in rats.

The purpose of this study was to characterize the pharmacokinetics and metabolism of 4-O-methylhonokiol in rats. The absorption and disposition of 4-O-methylhonokiol were investigated in male Sprague-Dawley rats following a single intravenous (2 mg/kg) or oral (10 mg/kg) dose. Its metabolism was studied in vitro using rat liver microsomes and cytosol. 4-O-Methylhonokiol exhibited a high systemic plasma clearance and a large volume of distribution. The oral dose gave a peak plasma concentration of 24.1±3.3 ng/mL at 2.9±1.9 h and a low estimated bioavailability. 4-O-Methylhonokiol was rapidly metabolized and converted at least in part to honokiol in a concentration-dependent manner by cytochrome P450 in rat liver microsomes, predicting a high systemic clearance consistent with the pharmacokinetic results. It was also shown to be metabolized by glucuronidation and sulfation in rat liver microsomes and cytosol, respectively. 4-O-Methylhonokiol showed a moderate permeability with no apparent vectorial transport across Caco-2 cells, suggesting that intestinal permeation process is not likely to limit its oral absorption. Taken together, these results suggest that the rapid hepatic metabolism of 4-O-methylhonokiol could be the major reason for its high systemic clearance and low oral bioavailability.

Olean-27-carboxylic acid-type triterpenes with potent antibacterial activity from Aceriphyllum rossii.

Aceriphyllum rossii Engler (Saxifragaceae) have been used as a nutritious food in Korea. We found that the methanol extract of the root portion of A. rossii potently inhibited the growth of Staphylococcus aureus , with a minimal inhibitory concentration (MIC) value of 8 microg/mL. Using mass spectrometry and nuclear magnetic resonance (NMR) studies, four active constituents were isolated and identified: aceriphyllic acid A, 3-oxoolean-12-en-27-oic acid, 3alpha-hydroxyolean-12-en-27-oic acid, and 3beta-hydroxyolean-12-en-27-oic acid. Aceriphyllic acid A and 3-oxoolean-12-en-27-oic acid showed a potent antibacterial activity against several strains of S. aureus , including methicillin-resistant S. aureus and quinolone-resistant S. aureus , with MIC values of 2-8 microg/mL, while 3alpha-hydroxyolean-12-en-27-oic acid and 3beta-hydroxyolean-12-en-27-oic acid exhibited a very weak activity, with MIC values of 128 microg/mL. The methyl ester derivative of aceriphyllic acid A lost its antibacterial activity. The time-kill study against S. aureus indicated that aceriphyllic acid A had rapid bactericidal activity. These results indicated that aceriphyllic acid A and 3-oxoolean-12-en-27-oic acid are the most active principles, and both the carboxylic group at C-27 and the hydroxyl group at C-24 in aceriphyllic acid A are critical for the rapid bactericidal activity.

Viridicatumtoxin B, a new anti-MRSA agent from Penicillium sp. FR11.

A new tetracycline-type antibiotic named viridicatumtoxin B along with the known compound viridicatumtoxin has been isolated from the mycelium of liquid fermentation cultures of Penicillium sp. FR11. The structure of viridicatumtoxin B was determined on the basis of MS and NMR data. Viridicatumtoxin B inhibited the growth of Staphylococcus aureus including methicillin-resistant S. aureus and quinolone-resistant S. aureus with MIC (microg/ml) of 0.5, which is similar with that of vancomycin, but 8-64 times higher activity than that of tetracycline.

Cyclo(Dehydrohistidyl-L-tryptophyl), an inhibitor of nitric oxide production from a fungal strain, Fb956.

In the course of screening for nitric oxide inhibitors in activated microglial BV-2 cells, cyclo(dehydrohistidyl-Ltryptophyl) was isolated from solid-state fermentation cultures of an unidentified fungal strain, Fb956. Its structure was determined by spectroscopic methods including 2D NMR and chiral TLC analyses. Cyclo(dehydrohistidyl-L-tryptophyl) was found to have an inhibitory activity on nitric oxide production with an IC50 of 6.5 muM in activated BV-2 cells. The structure determination and biological activity of cyclo(dehydrohistidyl- L-tryptophyl) was reported for the first time in this study.

Isolation and characterization of a novel glutathione S-transferase-activating peptide from the oriental medicinal plant Phellodendron amurense.

The aim of this study was to elucidate the characteristics of glutathione S-transferase (GST)-activating compounds from medicinal plants. Among 265 kinds of medicinal plants, Phellodendron amurense showed the highest GST activity at 174.8%. The GST-activating compound of P. amurense was maximally extracted when treated with distilled water at 30 degrees C for 12 h. The compound was purified by ultrafiltration, Sephadex G-10 gel filtration chromatography, and reverse-phase HPLC. The purified GST-activating compound from P. amurense was a novel tetrapeptide with an amino acid sequence of Ala-Pro-Trp-Cys and its molecular weight was estimated to be 476 Da. It also displayed a clear detoxicative effect in 1-chloro-2,4-dinitrobenzene treated mice at a dosage of mg/kg body weight.