Synthesis of hyaluronan-amikacin conjugate and its bactericidal activity against intracellular bacteria in vitro and in vivo.

Aminoglycosides are often subtherapeutic to intracellular infections due to their high hydrophilicity. Here we used hyaluronic acid (HA) as a carbohydrate carrier of the aminoglycoside antibiotic, amikacin (AM) to deal with intracellular bacterial infections. The hyaluronan-amikacin conjugate (HA-AM) was synthesized by 'click' reaction between HA-propargyl amide (HAPA) and AM-azide. This conjugate with little cytotoxicity retained antibiotic effects on planktonic bacteria and showed better intracellular bactericidal activity than the antibiotic did. In addition, this conjugate was more efficient in reducing bacteria burden in an in vivo acute infection model than amikacin did. These results suggested that hyaluronic acid conjugation could reduce the dosage of antibiotic in treatment of intracellular bacterial infection, and further helping to alleviate the emergence of drug resistance in bacteria due to a long-term, high-dosage treatment.

Synthesis of 5-deoxy-5-epifluoro derivatives of arbekacin, amikacin, and 1-N-[(S)-4-amino-2-hydroxybutanoyl]tobramycin (study on structure--toxicity relationships).

As part of a study on fluorination--toxicity relationships for aminoglycoside antibiotics, 5,3'-dideoxy-5-epifluorokanamycin B (10), 5,3',4'-trideoxy-5-epifluorokanamycin B (11), 1-N-[(S)-4-amino-2-hydroxybutanoyl]-5-deoxy-5-epifluorotobramyc in (19), 5-deoxy-5-epifluoroarbekacin (20), and 5-deoxy-5-epifluoroamikacin (21) have been prepared. The acute toxicities of these three 5-deoxy-5-epifluoro compounds showed values almost identical or similar to those for arbekacin (ABK) and amikacin (15), making a sharp contrast with the toxicities of the corresponding 5-deoxy-5-fluoro derivatives. This fact is explained on the basis of basicity changes (retention for the 5-epifluoro derivatives and reduction for the 5-fluoro derivatives) at the H2N-3 groups of the fluorinated compounds compared to the parent compounds; this hypothesis was substantiated by the pKa values at the H3N(+)-1, 3 groups (determined by the shift changes depending on pD values at C-2 and C-4, 6 in their 13C NMR spectra) of 2,5-dideoxy-5-epifluorostreptamine (23) and 2,5-dideoxy-5-fluorostreptamine (24), chosen as model compounds, and 2-deoxystreptamine (DST).

Sulfated fucan as support for antibiotic immobilization.

Xylofucoglucuronan from Spatoglossum schröederi algae was tested as a support for antibiotic immobilization. The polysaccharide (20 mg in 6 ml) was first activated using carbodiimide, 1-ethyl-3-(3-dimethylamino-propyl)carbodiimide methiodide (20 mg in 2 ml), under stirring for 1 h at 25 masculine C and pH from 4.5 to 5.0. After adjusting the pH to 8.0, either gentamicin or amikacin (62.5 mg in 1.25 ml) was then immobilized on this chemically modified polysaccharide with shaking for 24 h in a cold room. Infrared spectra of the activated carbodiimide xylofucoglucuronan showed two bands to carbonyl (C=O at 1647.9 and 1700.7 cm(-1)) and to amide (C-NH2) groups (1662.8 and 1714.0 cm(-1)). Microbial characterization of the derivatives was carried out by the disk diffusion method using Staphylococcus aureus or Klebsiella pneumoniae incorporated in Müller Hinton medium. Inhibition halos of bacterial growth were observed for the antibiotics immobilized on this sulfated heteropolysaccharide before and after dialysis. However, the halos resulting from the samples after dialysis were much smaller, suggesting that dialysis removed either non-covalently bound antibiotic or other small molecules. In contrast, bacterial growth was not inhibited by either xylofucoglucuronan or its activated form or by gentamicin or amikacin after dialysis. An additional experiment was carried out which demonstrated that the sulfated heteropolysaccharide was hydrolyzed by the microorganism. Therefore, the antibiotic immobilized on xylofucoglucuronan can be proposed as a controlled drug delivery system. Furthermore, this sulfated heteropolysaccharide can be extracted easily from sea algae Spatoglossum schröederi.

[The fight against bacteria: the antibiotics policy]. / Baktérium elleni küzdelem és antibiotikum politika.

Development of bacterial resistance towards antibiotics is no longer a local phenomenon. It has by now become a European and global problem, as a result of unjustified and unprofessional administration of antibiotics in gratuitously high quantities, not only in the medicinal practice, but also in the agriculture. The resistant bacteria may spread from animals to humans, transmitted by the food-chain. A recent danger includes the appearance of the vancomycin-resistant strains (VRSA) besides the methycillin-resistant Staphylococcus aureus (MRSA) infections. The number of the vancomycin-resistant Enterococci (VRE) is also expected to grow in the future. The present paper reports the results of the international activities in the past decades, which is related to the fight against resistant bacteria. Such research involves the production of synthetic compounds, the development of semi-synthetic beta-lactam-, aminocyclitol-, macrolide-, and glycopeptide antibiotics, as well as the introduction of new enzyme-inhibitory substances. Elaboration of basic principles of the rational application of antimicrobial agents is an increasingly urgent need along with the establishment of national and European data bases in which the supply and consumption of related medicines are registered and kept under control.

Singly modified amikacin and tobramycin derivatives show increased rRNA A-site binding and higher potency against resistant bacteria.

Semisynthetic derivatives of the clinically useful aminoglycosides tobramycin and amikacin were prepared by selectively modifying their 6'' positions with a variety of hydrogen bond donors and acceptors. Their binding to the rRNA A-site was probed using an in vitro FRET-based assay, and their antibacterial activities against several resistant strains (e.g., Pseudomonas aeruginosa, Klebsiella pneumonia, MRSA) were quantified by determining minimum inhibitory concentrations (MICs). The most potent derivatives were evaluated for their eukaryotic cytotoxicity. Most analogues displayed higher affinity for the bacterial A-site than the parent compounds. Although most tobramycin analogues exhibited no improvement in antibacterial activity, several amikacin analogues showed potent and broad-spectrum antibacterial activity against resistant bacteria. Derivatives tested for eukaryotic cytotoxicity exhibited minimal toxicity, similar to the parent compounds.