Patients with fractures of the zygomatic bone were treated with high molecular weight poly(L-lactic) acid (PLLA) bone plates and screws. Three years after implantation four patients returned to our department with a swelling at the site of implantation. At the recall of the remaining patients we found an identical type of swelling after the same implantation period. To investigate the nature of the tissue reaction, eight patients were reoperated for the removal of the swelling. The implantation period of the PLLA material varied from 3.3 to 5.7 years. Microscopic evaluation and molecular weight measurements were performed. The excised material showed remnants of degraded PLLA material surrounded by a dense fibrous capsule. Ultrastructural investigation showed crystal-like PLLA material internalized by various cells. The results of this investigation suggest that the PLLA material slowly degrades into particles with a high crystallinity. The intra-and extracellular degradation rate of these particles is very low. After 5.7 years of implantation, these particles were still not fully resorbed.

The virulence of the opportunistic human pathogen Pseudomonas aeruginosa PAO1 is controlled by an N-acyl-homoserine lactone (AHL)-dependent quorum-sensing system. During functional analysis of putative acylase genes in the P. aeruginosa PAO1 genome, the PA2385 gene was found to encode an acylase that removes the fatty acid side chain from the homoserine lactone (HSL) nucleus of AHL-dependent quorum-sensing signal molecules. Analysis showed that the posttranslational processing of the acylase and the hydrolysis reaction type are similar to those of the beta-lactam acylases, strongly suggesting that the PA2385 protein is a member of the N-terminal nucleophile hydrolase superfamily. In a bioassay, the purified acylase was shown to degrade AHLs with side chains ranging in length from 11 to 14 carbons at physiologically relevant low concentrations. The substituent at the 3 position of the side chain did not affect activity, indicating broad-range AHL quorum-quenching activity. Of the two main AHL signal molecules of P. aeruginosa PAO1, N-butanoyl-Lhomoserine lactone (C 4 -HSL) and N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C 12 -HSL), only 3-oxo-C 12 -HSL is degraded by the enzyme. Addition of the purified protein to P. aeruginosa PAO1 cultures completely inhibited accumulation of 3-oxo-C 12 -HSL and production of the signal molecule 2-heptyl-3-hydroxy-4(1H)-quinolone and reduced production of the virulence factors elastase and pyocyanin. Similar results were obtained when the PA2385 gene was overexpressed in P. aeruginosa. These results demonstrate that the protein has in situ quorum-quenching activity. The quorum-quenching AHL acylase may enable P. aeruginosa PAO1 to modulate its own quorum-sensing-dependent pathogenic potential and, moreover, offers possibilities for novel antipseudomonal therapies.Pseudomonas aeruginosa PAO1 is an opportunistic pathogen which causes disease mainly in individuals who are immunocompromised, have cystic fibrosis, or suffer from serious burn wounds. It utilizes two N-acyl-homoserine lactone (AHL)-dependent quorum-sensing systems, termed las and rhl, which together regulate an extensive set of cell population density and growth-phase-dependent virulence factors (7,22). The las and the rhl quorum-sensing systems employ N-(3-oxododecanoyl)-L-homoserine lactone (3-oxo-C 12 -HSL) and N-butanoyl-L-homoserine lactone (C 4 -HSL), which function by activating the response regulator proteins LasR and RhlR, respectively. In diverse gram-negative bacteria, many different AHL signal molecules have been characterized. These all consist of a homoserine lactone (HSL) ring or nucleus which is connected via an amide bond to a fatty acid side chain of 4 to 14 carbon atoms in length that may contain an oxo or hydroxyl group at the 3Ј position and unsaturated bonds (Fig. 1).In P. aeruginosa PAO1, swarming motility, biofilm maturation, and the expression of virulence factors such as exoproteases, hemolysins, exotoxin A, exoenzyme S, pyocyanin, cyanide, and the cytotoxic lectins PA-IL and PA-IIL, as w...

No abstract

The degradation of high molecular weight as-polymerized poly(L-lactide) (PLLA) is very slow; it takes more than 5.6 yr for total resorption. Moreover, the degradation products of as-polymerized PLLA bone plates, consisting of numerous stable particles of high crystallinity, are related with a subcutaneous swelling in patients 3 yr postoperatively. In order to avoid these complications, polymers were developed that are anticipated to have comparable mechanical properties but a higher degradation rate and do not degrade into highly stable particles that can induce a subcutaneous swelling. On chemical grounds it can be expected that copolymerization of PLLA with 4% D-lactide (PLA96) or by modifying PLLA through cross-linking (CL-PLLA) will lead to less stable particles and a higher degradation rate. To evaluate the long-term suitability of these as-polymerized polymers, the biocompatibility of the degradation products should be studied. Considering the very slow degradation rate of as-polymerized PLLA, in vitro pre-degradation at elevated temperatures was used to shorten the in vivo follow-up periods. In this study, the biocompatibility and degradation of as-polymerized PLLA, PLA96 and CL-PLLA were investigated by implanting pre-degraded particulate materials subcutaneously in rats. Animals were killed after a postoperative period varying from 3 to 80 wk. Light and electron microscopical analysis and quantitative measurements were performed. The histological response of all three pre-degraded materials showed a good similarity with in vivo implanted material. Pre-degraded PLLA induced a mild foreign body reaction and showed a slow degradation rate.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract