Reviewing the use of carbon monoxide-releasing molecules (CO-RMs) in biology: implications in endotoxin-mediated vascular dysfunction.

The inducible stress protein heme oxygenase-1 (HO-1) has been linked to tissue and organ protection against the deleterious actions of many pathological conditions, including endotoxin challenge. Similar protection can be achieved by the main products of heme oxygenase activity, namely bilirubin and carbon monoxide (CO). Since the identification of novel chemical compounds that liberate CO in biological systems (CO-releasing molecules or CO-RMs), our group and others have had access to a convenient and simple pharmacological tool that enables to study the role of CO in physiological functions. This article will review the scientific literature published to date on CO-RMs, with emphasis on the in vitro, ex vivo and in vivo experimental models employed to determine the contribution of CO to cellular mechanisms. In addition, we will report on the effect of heme oxygenase-related substances, such as bilirubin, CORM-3 and hemin, in a model of endotoxin-induced hypotension. Among the three different approaches examined, CORM-3 proved the most effective agent in reducing the fall in blood pressure caused by endotoxin. Furthermore, heme oxygenase-related substances affected the endotoxin-stimulated induction and distribution of hepatic HO-1 and inducible nitric oxide synthase (iNOS). Thus, it emerges that CO-RMs could exert important biological actions in the context of endotoxic-mediated dysfunction.

The use of near-infrared spectroscopy for assessing flap viability during reconstructive surgery.

The ability to assess viability of tissues by monitoring changes in oxygenation and perfusion during harvesting and following transfer of free and pedicled flaps is potentially important in reconstructive surgery. Rapid detection of a critical change in tissue oxygenation could enable earlier and more successful surgical intervention when such problems arise. In this study near infra-red spectroscopy (NIRS) was used to assess changes in tissue oxygenation, haemoglobin oxygenation and blood volume in a porcine prefabricated myocutaneous flap model in response to pedicle manipulations. As far as we are aware this is the first usage of a NIRS instrument to assess changes in oxygenation in a flap model which closely simulates the clinical situation. A myocutaneous flap was raised (n = 9 pigs), tubed and the flap circulation allowed to readjust for periods between 7 and 9 days. The pedicle vessels were then subjected to arterial (n = 9), venous (n = 12) and total occlusion (n = 6). Repeatable and reproducible patterns of change were measured in each case. Comparison of mean values indicated that the differences between arterial and venous, and venous and total occlusions were significant for all NIRS parameters. The monitor was easily able to detect two additional features: (i) the presence of venous congestion indicated by raised levels of deoxygenated haemoglobin and an increase in blood volume; and (ii) the presence and magnitude of reactive hyperaemia. In two flaps release of arterial or total occlusion did not result in the expected reactive hyperaemia associated with an increase in blood volume (oxygenated haemoglobin) suggestive of possible damage to the vascular bed. NIRS proved able to detect and distinguish between microcirculatory changes occurring as a result of arterial, venous or total vascular occlusion. We believe that NIRS provides a sensitive and reliable postoperative monitor of tissue viability following transfer of free and pedicled flaps. It can accurately identify different types of problems with the pedicle vessels. In addition its predictive capabilities would allow assessment of flaps buried deep to the skin. This monitor is excellent for surgical and intensive care unit monitoring since it is unaffected by light, portable and is extremely easy to use.

Measurements of tissue viability in transplantation.

Near-infrared spectroscopy has primarily been used in monitoring changes in cerebral haemoglobin oxygenation and haemodynamics. However its use as a method for the assessment of tissue viability following transplantation has recently been explored experimentally in our laboratory. The ability to measure changes in oxygenation and perfusion during harvesting and following transplantation of organs or transfer of free and pedicled flaps potentially important in reconstructive surgery. We have found that near-infrared spectroscopy is extremely useful in detecting vaso-occlusive events and can accurately and reliably distinguish between arterial, venous or total occlusions. Venous congestion indicated by raised levels of deoxygenated haemoglobin with a concomitant increase in blood volume and the presence and magnitude of reactive hyperaemia are both easily recognizable features by near-infrared spectroscopy. We have shown that near-infrared spectroscopy measurements of venous congestion in kidneys (and other tissues) following prolonged storage correlate with medullary vascular congestion confirmed by angiographical and histological analysis of intrarenal perfusion. Clinically we have shown that flap perfusion can be improved by altering fluid replacement regimes and the addition of ionotropes. Cerebral near-infrared spectroscopy measurements in a liver transplant model showed statistically significant differences within minutes after the anhepatic phase in cerebral perfusion and oxygenation, between animals transplanted with ischaemically damaged livers compared to those isografted with minimally stored livers. Similarly we have found that near-infrared spectroscopy can be used as a monitor to assess the adequacy of fluid or blood replacement in haemorrhagic and hypovolaemic models. We believe that near-infrared spectroscopy provides a sensitive and reliable postoperative method for the assessment of tissue viability following the transfer of free and pedicled flaps and organs.

Non-invasive measurement of cardiac oxygenation and haemodynamics during transient episodes of coronary artery occlusion and reperfusion in the pig.

1. The non-invasive method of near-infrared spectroscopy was used to measure myocardial oxygenation and haemodynamics in response to left anterior descending coronary artery occlusion in a porcine model. 2. Near-infrared spectroscopy measures changes in haemoglobin (and myoglobin) oxygenation and blood volume to yield information on tissue perfusion and flow. It also measures the redox state of cytochrome aa3, thus providing information about intracellular oxygen utilization. 3. Left anterior descending coronary artery occlusion was induced to produce periods of ischaemia lasting between 24s and 13.5 min (n = 13). The changes in deoxyhaemoglobin, oxyhaemoglobin and cytochrome aa3 measured during occlusion were all highly significant compared with baseline variation. In all occlusions (n = 13) a rapid decrease in oxyhaemoglobin concentration (-75.83 +/- 3.27 mumol/l, mean +/- SEM) with a simultaneous increase in deoxyhaemoglobin of 9.27 +/- 1.69 mumol/l was measured. The total haemoglobin concentration also fell by -71.3 +/- 5.32 mumol/l. Cytochrome aa3 was also reduced during occlusion (-8.35 +/- 1.044) mumol/l. 4. Over the range 24-60s occlusion, the magnitude of the fall in total haemoglobin and oxyhaemoglobin correlated with the duration of occlusion (P < 0.003 and 0.013 respectively). For total haemoglobin only the magnitude of the fall correlated with the increase upon release of occlusion (r = 0.89, P < 0.003). 5. Release of occlusion (n = 8) resulted in an immediate increase in the concentration of deoxyhaemoglobin at 9.88 +/- 1.06s, then total haemoglobin at 13.62 +/- 1.23s and finally oxyhaemoglobin at 29.75 +/- 5.96s. The difference between the timing of the maxima after reperfusion is significant (P < 0.002 and P < 0.007 respectively). Moreover, the time for the deoxyhaemoglobin signal to reach maximum values was found to correlate with the duration of occlusion (P < 0.04). This could be indicative of the PO2 of the ischaemic tissues and an immediate off-loading of oxygen from oxyhaemoglobin. The results are reliable, reproducible and sensitive enough to detect the kinetics of haemoglobin oxygenation from a beating heart in situ.

Angiogenesis and reinnervation in skin flaps: the effects of ischaemia examined in an animal model.

In clinical flap transplantation, ischaemia may alter reinnervation patterns either directly or by affecting angiogenesis. This study presents the effects of ischaemia on innervation in totally denervated, transiently (30 minutes) or prolongedly ischaemic skin flaps studied immunohistochemically with antisera to PGP 9.5, CGRP and VWF. Following transient ischaemia, an increase in PGP-immunoreactive (PGP-IR) and CGRP-IR nerve fibres in distant skin by day 12 was followed by increased innervation in immediately adjacent skin. The latter increase was maintained up to 24 days which allowed near normal innervation at the suture margin and in adjacent flap tissue, 0.5 cm from the margin. There was concomitant reinnervation from the pedicle by day 24. In prolongedly ischaemic flaps, an earlier and more prolonged increase in innervation was seen in the entire surrounding skin, with innervation around the suture line at 24 days resembling that in the transiently ischaemic flaps despite initial complete nerve fibre depletion in this area. Hypertrophic nerve fibre clusters were seen in fibrotic areas overlying the pedicle. Vascular changes were similar in both groups with vascularization preceding reinnervation. There were no significant differences in reinnervation between the transiently and prolongedly ischaemic flaps at 24 days, despite considerable initial variations. Ischaemia, CGRP, mediators of chronic inflammation and epidermal factors appeared to stimulate angiogenesis and reinnervation.

A porcine model using skin graft chambers for studies on cultured keratinocytes.

In wound healing research, animal models permit an extensive tissue analysis which is not normally possible in clinical studies. A morphological comparison of human and porcine skin was made in order to identify those aspects of the wound healing process where a porcine model may help our understanding of clinical problems. We describe a porcine model for evaluating the growth of cultured keratinocytes on a variety of wound beds. Polytetrafluoroethylene skin graft chambers were used to isolate wounds and prevent epidermal healing from the skin edge. The chambers remained in situ for 5-7 weeks. We detail the surgical technique, the method of porcine keratinocyte culture and highlight some practical measures that were taken to optimise the "take" of the cultured keratinocyte grafts.

Neovascularisation precedes neural changes in the rat groin skin flap following denervation: an immunohistochemical study.

We have employed immunohistochemical techniques to study neural and vascular changes in rat skin flaps. Following partial or total denervation, flaps were studied at 4, 7 or 12 days using antisera to PGP 9.5 (panneural marker), the neuropeptides CGRP (sensory nerves) and CPON (adrenergic nerves) and an endothelial marker VWF. In partially denervated flaps, moderate increases in PGP-immunoreactive (PGP-IR) and CGRP-IR nerves and a mild increase in CPON-IR nerves in immediate surrounding skin preceded smaller increases in similar nerves around the pedicle. Following total denervation, mild increases in all nerve types at these locations were accompanied by a marked increase of these nerves in distant surrounding skin, 1-2 cm from the suture line. A gradual increase in endothelial cell staining (VWF) of blood vessels was seen in surrounding skin, flap beds and pedicles. Angiogenesis preceded flap reinnervation which occurred initially from surrounding skin, and later from the base, with sensory fibres appearing first.

Is early vascularization of nerve grafts necessary?

Revascularization and regeneration through vascularized and non-vascularized nerve grafts were compared on optimal and adverse graft beds in 76 rabbit sciatic nerves. A delay in revascularization of more than 14 days was found to occur in 30 mm long, non-vascularized nerve grafts placed on completely avascular graft graft beds. However, over a period of 44 weeks, this prolonged ischaemia did not adversely affect nerve regeneration. The vascularized nerve grafts did not differ significantly with respect to the rate of regeneration, motor conduction velocity, fibre diameter and thickness of myelin sheath. In rabbits, the provision of early vascularity does not appear to confer superior regeneration through nerve grafts. The clinical use of vascularized nerve grafts is discussed in the light of these results.

The effect of desferrioxamine on lipid peroxidation and survival of ischaemic island skin flaps in rats.

To produce total necrosis, it was found necessary to subject pedicled groin flaps in rats to 16 hours of warm ischaemia (WI) (whether clamped in situ or removed and maintained at 37 degrees C ex vivo before replantation). Biochemical markers of lipid peroxidation (Schiff bases and thiobarbituric acid (TBA)-reactive material) in homogenates of full thickness skin or of subcutaneous fat rose significantly (p less than 0.001) after 14 hours of WI and reperfusion in vivo. Desferrioxamine (15 mg/kg i.v.) administered systemically either before 14 h WI only, before reperfusion only after 14 h WI or in both circumstances inhibited these rises to near-control (fresh tissue) levels. In survival experiments, this treatment also protected these flaps from necrosis (p less than 0.01).

Neuroleptanalgesia in the rabbit.

The efficacy of the neuroleptanalgesic combinations of fentanyl-fluanisone with diazepam; and etorphine-methotrimeprazine, either alone, or with diazepam, was investigated in the rabbit. The effects of these drugs on some cardiovascular variables were studied in chronically catheterized rabbits. Fentanyl-fluanisone and diazepam produced good surgical anaesthesia. Although respiratory depression occurred, this had little effect on blood gas values. In contrast, etorphine-methotrimeprazine and diazepam produced severe respiratory depression with consequent hypercapnia and acidosis.

Injectable anaesthetic techniques in 2 species of gerbil (Meriones libycus and Meriones unguiculatus).

The effects of a range of injectable anaesthetic agents were assessed in two species of gerbil (M. libycus and M. unguiculatus). The drug combination of metomidate and fentanyl was the only preparation that consistently produced surgical anaesthesia. Considerable species variation in drug response was noted, indicating that caution should be exercised in recommending standard anaesthetic dose rates for these animals.