Interaction of chlorhexidine with biomembrane models on glass ionomer by using the Langmuir-Blodgett technique.

The antimicrobial property of chlorhexidine is believed to be associated with its interaction of bacterium membrane, which calls for research on the identification of membranes sites capable of drug binding. In this study, we investigated the interaction of chlorhexidine digluconate, a known agent with bactericidal and bacteriostatic activities employed in the treatment of periodontal diseases, with bacteria cell model systems by using Langmuir monolayers. The insertion of the drug caused the surface pressure-area isotherms for a mixed protein-lipid monolayer to be shifted to higher lipid molecular areas, which was the first indication of the action of chlorhexidine in the membrane model. Surface infrared spectroscopy pointed to intrinsic interactions of the drug with the hydrophobic part of the lipid, leading to a disruption of the lipid organization at the interface. Also, the secondary structure of the polypeptide model employed in this work has been changed, as a consequence of the drug interactions. Such change in the lipid-protein models could be confirmed when the membrane was transferred to glass ionomer cement as a solid support, which can be considered a model for dental surfaces. Therefore, chlorhexidine interacts with lipid and protein moieties supposed to be present in lipid membranes. This may have important implication in understanding how the drug acts on specific sites of the bacteria membrane.

Left ventricular mass reduction after aortic valve replacement: homografts, stentless and stented valves.

BACKGROUND: We studied the effect of four different types of prosthetic aortic valves on time course and extent of regression of left ventricular hypertrophy after aortic valve replacement for aortic stenosis. METHODS: Four groups of 10 patients each were randomly assigned to receive: (1) aortic homograft preserved in antibiotic solution at 4 degrees C, (2) Toronto stentless porcine valve, (3) Medtronic Freestyle stentless valve, or (4) Medtronic Intact aortic valve. The left ventricular mass index, effective orifice area index, and peak and mean transaortic gradients were measured by Doppler echocardiography before the operation and 8 months postoperatively. RESULTS: The hemodynamic performance indices were much better for the homograft and stentless valves than for the stented one. The absolute left ventricular mass index reduction was greater in the homograft group compared with the Intact (p = 0.0004) and Toronto (p = 0.007) groups. The extent of percent left ventricular mass index reduction was greater only in the homograft group versus Intact group (p = 0.005). The multilinear regression analysis showed that the only predictors of a larger percentage of left ventricular mass index reduction were the homograft type, a higher valve size index, and a higher preoperative left ventricular mass index. CONCLUSIONS: When a stentless or homograft aortic valve was used instead of a stented valve to replace a stenotic aortic valve there was more complete or at least faster regression of left ventricular hypertrophy. The hemodynamic performance of stentless porcine valves was similar to that of aortic homografts, nevertheless the aortic homografts preserved in antibiotic solution offered a faster regression of left ventricular hypertrophy during the same period of time.

Skeletal changes after burn injuries in an animal model.

Musculoskeletal deformities can develop after burn injuries. Seventy-five skeletally immature Sprague-Dawley rats were examined after infliction of full-thickness lower extremity scald burns to assess longitudinal growth, joint integrity, and bone composition. Longitudinal bone growth in the immediate postburn period was depressed. However, with the resumption of feeding and activity, normal growth ensued, unless the epiphyseal cartilage had been damaged by septic extension of the wound. Degenerative joint changes occurred in the burned limbs of six animals. Significant soft tissue contractures and collapse of the supporting subchondral bone were present in each of the affected knee joints. There was no evidence of joint sepsis. Large amounts of periosteal new bone consistently formed along the tibia beneath the burn wound. Sequential injections of fluorescent bone markers demonstrated that the stimulus for new bone formation corresponded with the presence of an open granulating burn wound. No further pathologic new bone formed after the wound had healed fully.

The inhibition of skeletal changes in a rat burn model with a local muscle flap.

The effects of early wound closure using a local muscle flap on the development of periosteal new bone formation in a rat burn model were studied. Following a full-thickness burn to one hind limb, periosteal new bone formation along the tibial diaphysis was measured by the use of the fluorochrome agent calcein and an image-analysis system. Prostaglandin E levels, a known inflammatory mediator, from the bone beneath the burn also were measured. Periosteal new bone formation was inhibited by 50 percent in animals that had debridement and wound closure with a gastrocnemius muscle flap and skin graft on postburn day 2 compared to untreated controls or animals closed with skin grafts only. There was a trend toward reduced prostaglandin E measurements from tibial sections in the early closure group compared to untreated controls. This study demonstrates that early wound closure using a local muscle flap inhibits the periosteal new bone formation which is possibly associated with the inflammation in a rat burn model.