Leukocyte recruitment and turnover in an experimental inflammatory exudate

Leukocyte hydrogen peroxide production in a surgical wound in mice. The effects of an amide local anaesthetic

The oxygen metabolism of polymorphonuclear leukocytes (PMN) is of importance in local tissue repair processes. Amide local anaesthetics are commonly used to relieve surgical wound pain. The cellular effects of local anaesthetics in vivo is poorly described in the literature. However, interactions between amide local anaesthetics and the oxygen metabolism of leukocytes have been reported. To extend that knowledge, this paper investigates the influence of lidocaine treatment on the production of hydrogen peroxide (H2O2) by leukocyte oxygen metabolism. A soft tissue chamber model in the mouse was used, allowing measurements of the H2O2 production spontaneously and after phorbol myristate acetate (PMA) addition, from two different leukocyte pools. Exudate leukocytes were generally more reactive to PMA stimulation in comparison to tissue chamber adherent leukocytes. Topically administered lidocaine significantly influenced the number of leukocytes in the wound exudate at 24 h postoperatively. Exudate leukocytes, topically exposed to lidocaine, showed an enhanced H2O2 production in comparison to leukocytes receiving lidocaine systemically. At 6 days, the viability and the H2O2 production differed significantly between the group receiving topically applied lidocaine in comparison to placebo. We conclude that the wound healing process may be effected by topically applied lidocaine, administered in clinical doses, at least via interference with leukocyte oxygen metabolism.

Ex vivo analysis of leukocyte hydrogen peroxide production using a bi-plate model in mice

Implantation of artificial materials is followed by inflammation and wound healing, where phagocytic cells play an important role. The mechanisms whereby the implant surface may elicit and modulate leukocyte functions in vivo are not understood, partly due to the technical difficulties of examining the local inflammatory events in vicinity of the material-tissue interface with conventional biochemical and immunological techniques. In the present study a newly developed biplate implant was inserted subcutaneously in the mouse. Leukocytes from the local inflammatory exudate and leukocytes associated to the surface of the implants were retrieved after 1 and 6 days and separately assayed with respect to hydrogen peroxide (H2O2) production ex vivo. Implantation caused a local accumulation of predominantly mononuclear cells in the surrounding subcutaneous tissue. The H2O2 production was found to be low in both the subcutaneous exudate and the implant-associated leukocytes, irrespective of implant material and implantation times. However, ex vivo-stimulation with phorbol myristate acetate (PMA) caused an enhanced H2O2 production. These observations show that biplate implants do not maximally activate the oxidative metabolism of the recruited leukocytes. The exudate leukocytes were more responsive to PMA stimulation in comparison with implant-associated leukocytes, indicating that properties of the implant surface and possibly surface-associated proteins could modify the responsiveness of the phagocytic cells at the implant site. Our results suggest that the present biplate model may be suitable for further studies on local production of oxygen metabolites and function of leukocytes at implanted biomaterials.