A chlorhexidine-releasing epoxy-based coating on titanium implants prevents Staphylococcus aureus experimental biomaterial-associated infection

Prevention of biomaterial-associated infections (BAI) remains a challenging problem, in particular due to the increased risk of resistance development with the current antibiotic-based strategies. Metallic orthopaedic devices, such as non-cemented implants, are often inserted under high mechanical stress. These non-cemented implants cannot be protected by e.g. antibioticreleasing bone cement or other antimicrobial approaches, such as the use of bioactive glass. Therefore, in order to avoid abrasion during implantation procedures, we developed an antimicrobial coating with great mechanical stability for orthopaedic implants, to prevent Staphylococcus aureus BAI. We incorporated 5 and 10 wt % chlorhexidine in a novel mechanically stable epoxy-based coating, designated CHX5 and CHX10, respectively. The coatings displayed potent bactericidal activity in vitro against S. aureus, with over 80 % of the release (19 µg/cm2 for CHX5 and 41 µg/cm2 for CHX10) occurring within the first 24 h. In mice, the CHX10 coating significantly reduced the number of CFU (colony forming units), both on the implants and in the peri-implant tissues, 1 d after S. aureus challenge. The CHX10-coated implants were well-tolerated by the animals, with no signs of toxicity observed by histological analysis. Moreover, the coating significantly reduced the frequency of culture-positive tissues 1 d, and of culture-positive implants 1 and 4 d after challenge. In summary, the chlorhexidine-releasing mechanically stable epoxy-based CHX10 coating prevented implant colonisation and S. aureus BAI in mice and has good prospects for clinical development.

Mechanism for obesity-induced increase in myocardial lipid peroxidation

OBJECTIVE

To determine the mechanisms underlying the obesity-induced increase in myocardial lipid peroxidation in the fa/fa rat. We hypothesized that elevated heart work (ie rate-pressure product), an increased rate of superoxide (O2*-)) production, total myocardial lipid content, and/or insufficient antioxidant defenses are potential contributors to myocardial lipid peroxidation in obesity.

DESIGN

Comparative, experimental study of myocardial tissue in 16-week-old lean control (Fa/?, normal diet), obese high-fat fed (Fa/?, 45% dietary fat), and obese fatty (fa/fa, normal diet) Zucker rats.

MEASUREMENTS

Myocardial work (heart rate x systolic blood pressure), myocardial lipid content, oxidative and antioxidant enzyme activities (citrate synthase (CS), catalase (CAT), glutathione peroxidase (GPX), superoxide dismutase (SOD)), the rate of papillary muscle superoxide radical production in vitro, thiol content, basal and post-oxidative challenge myocardial lipid peroxidation levels using thiobarbituric reactive acid substances (TBARS) and lipid hydroperoxides (PEROX) as indices of lipid peroxidation.

RESULTS

Compared to lean controls, the high-fat fed and fatty animals had similar elevations (P<0.05) in myocardial TBARS and PEROX (23%, 25% and 29% 45%, respectively; P<0.05), and elevated susceptibilities to oxidative stress in vitro following exposure to oxidizing agents (P<0.05). Resting heart work was slightly higher (P<0.05) in both the high-fat fed and fatty animals compared to controls. Myocardial lipid content, SOD activities and non-protein thiol (glutathione) levels were elevated (P<0.05) in high-fat fed and fatty animals compared to controls. The rate of superoxide formation by isolated papillary muscles in vitro did not differ among groups (P<0.05). Regression analysis revealed that the myocardial lipid content contributed most to myocardial lipid peroxidation (R2=0.76, P<0.05).

CONCLUSIONS

Myocardial oxidative injury is closely associated with myocardial lipid content, but is not closely correlated with heart work, insufficient antioxidant defenses or a greater rate of superoxide production.