Reduction of inflammatory response in composite flap transfer by local stress conditioning-induced heat-shock protein 32

Alendronate reduces periosteal microperfusion in vivo

Objectives

Bisphosphonates are known to induce a severe adverse effect known as medication-related osteonecrosis of the jaw (MRONJ). Previous studies have proven the impact of bisphosphonates on microperfusion; therefore, this study aimed to investigate alendronate-induced microcirculatory reactions in the calvarial periosteum of rats.

Study design

Bone chambers were implanted into 48 Lewis rats. Microhemodynamics, inflammatory parameters, functional capillary density and defect healing were examined after alendronate treatment for two and six weeks using repetitive intravital fluorescence microscopy for two weeks.

Results

Microhemodynamics remained unchanged. In alendronate-treated rats, inflammation was slightly increased, functional capillary density was significantly reduced (day 10: controls 100.45 ± 5.38 cm/cm2, two weeks alendronate treatment 44.77 ± 3.55 cm/cm2, six weeks alendronate treatment 27.54 ± 2.23 cm/cm2) and defect healing was decelerated. The changes in functional capillary density and defect healing were dose-dependent.

Conclusion

The bisphosphonate alendronate has a significant negative impact on periosteal microperfusion in vivo. This could be a promising target for the treatment of MRONJ.

Heme oxygenase‑1 improves the survival of ischemic skin flaps (Review)

Heat shock protein 32 (Hsp32), also known as heme oxygenase‑1 (HO‑1), is an enzyme that exists in microsomes. HO‑1 can be induced by a variety of stimuli, including heavy metals, heat shock, inflammatory stimuli, heme and its derivatives, stress, hypoxia, and biological hormones. HO‑1 is the rate‑limiting enzyme of heme catabolism, which splits heme into biliverdin, carbon monoxide (CO) and iron. The metabolites of HO‑1 have anti‑inflammatory and anti‑oxidant effects, and provide protection to the cardiovascular system and transplanted organs. This review summarizes the biological characteristics of HO‑1 and the functional significance of its products, and specifically elaborates on its protective effect on skin flaps. HO‑1 improves the survival rate of ischemic skin flaps through anti‑inflammatory, anti‑oxidant and vasodilatory effects of enzymatic reaction products. In particular, this review focuses on the role of carbon monoxide (CO), one of the primary metabolites of HO‑1, in flap survival and discusses the feasibility and existing challenges of HO‑1 in flap surgery.

Cell seeding accelerates the vascularization of tissue engineering constructs in hypertensive mice

Rapid blood vessel ingrowth into transplanted constructs represents the key requirement for successful tissue engineering. Seeding three-dimensional scaffolds with suitable cells is an approved technique for this challenge. Since a plethora of patients suffer from widespread diseases that limit the capacity of neoangiogenesis (e.g., hypertension), we investigated the incorporation of cell-seeded poly-L-lactide-co-glycolide scaffolds in hypertensive (BPH/2J, group A) and nonhypertensive (BPN/3J, group B) mice. Collagen-coated scaffolds (A1 and B1) were additionally seeded with osteoblast-like (A2 and B2) and mesenchymal stem cells (A3 and B3). After implantation into dorsal skinfold chambers, inflammation and newly formed microvessels were measured using repetitive intravital fluorescence microscopy for 2 weeks. Apart from a weak inflammatory response in all groups, significantly increased microvascular densities were found in cell-seeded scaffolds (day 14, A2: 192 ± 12 cm/cm², A3: 194 ± 10 cm/cm², B2: 249 ± 19 cm/cm², B3: 264 ± 17 cm/cm²) when compared with controls (A1: 129 ± 10 cm/cm², B1: 185 ± 8 cm/cm²). In this context, hypertensive mice showed reduced neoangiogenesis in comparison with nonhypertensive animals. Therefore, seeding approved scaffolds with organ-specific or pluripotent cells is a very promising technique for tissue engineering in hypertensive organisms.

Thermal Preconditioning for Surgery: A Systematic Review

BACKGROUND

Optimising patients pre-operatively reduces the chance of complications. This may be achieved by preconditioning. Thermal preconditioning refers to the supraphysiological heating of organisms or specific organs prior to an environmental insult. This review explores the current application and efficacy of thermal preconditioning for surgery.

METHODS

A comprehensive search of Medline (via PubMed), Embase and the Cochrane library was performed. Only articles evaluating the use of supraphysiological heating prior to a surgical intervention were included. Qualitative syntheses of data were undertaken due to the heterogeneity of the studies. The quality of each article was appraised using risk of bias tools (Cochrane and SYRCLE).

RESULTS

The primary literature search returned 3175 articles. After screening and reviewing reference lists, 28 papers met the inclusion criteria. The majority of studies were performed in animals, with only three clinical trials. Although there was broad coverage of different surgical techniques, flap transfer was the most commonly performed procedure. Most studies demonstrated a beneficial effect of thermal preconditioning, ranging from increased joint mobility to improved flap or organ transplant survival rates. The quality of evidence was variable, with experimental animal studies limited by a lack of methodological detail.

CONCLUSIONS

Thermal preconditioning for surgery has been primarily investigated using animal models. A beneficial effect has been demonstrated in most cases, across specialties ranging from plastic to general surgery. Future studies should aim to assess the clinical significance through large multicentre randomised controlled trials.

Targeting heme oxygenase-1 in early diabetic nephropathy in streptozotocin-induced diabetic rats

Diabetic nephropathy (DN) is one of the most common microvascular diabetic complications. This study was designed to evaluate the possible protective effect and underlying mechanisms of HO-1 induction in streptozotocin (STZ)-induced early DN in rats. The diabetic rats were divided into three groups: STZ-diabetic, cobalt protoporphyrin (CoPP)-treated diabetic, and zinc protoporphyrin IX (ZnPP)-treated diabetic groups. Compared to the STZ-diabetic group, CoPP-induced HO-1 upregulation improved the diabetic state and renal functional parameters, suppressed the renal proinflammatory marker, NF-κB, abrogated the elevated renal hydroxyprolin, and decreased the enhanced renal nicotinamide adenine dinucleotide phosphate oxidase activity with parallel reduction of urinary oxidative stress markers. On the contrary, treatment with ZnPP abrogated HO-1 levels, aggravated the diabetic condition with further increases in renal oxidative stress, fibrotic and inflammatory markers, and exacerbated renal dysfunction in diabetic animals. These findings suggest that the reduced diabetic renal injury upon HO-1 induction implicates the role of HO-1 induction as a potential treatment for DN.

Etanercept protects myocutaneous flaps from ischaemia reperfusion injury: An experimental study in a rat tram flap model

Background Being an inevitable component of free tissue transfer, ischemia-reperfusion injury tends to contribute to flap failure. TNF-α is an important proinflammatory cytokine and a prominent mediator of the ischemia-reperfusion injury. Etanercept, a soluble TNF-α binding protein, has shown anti-inflammatory and anti-apoptotic effects in animal models of renal and myocardial ischemia-reperfusion injury. We have designed an experimental study to investigate the effect of etanercept on myocutaneous ischemia-reperfusion injury on transverse rectus abdominis myocutaneous flap model in rats. Methods Twenty-four male Sprague-Dawley rats were divided into 3 groups: In group 1 (sham), the TRAM flap was raised and sutured back without further intervention. In group 2 (control), the flap was raised and the ischemia-reperfusion protocol was followed. In group 3, etanercept (10 mg/kg, i.v.) was administered 10 minutes before reperfusion. At the end of the reperfusion period, biochemical and histolopathological evaluations were performed on serum and tissue samples. Results In the etanercept group the IMA and 8-OHdG levels (p = 0.005 and p = 0.004, respectively) were found significantly lower, and the GSH and SOD levels (p = 0.01 and p < 0.001, respectively) significantly higher in comparison to the control group. The histopathological analysis has revealed a lower degree of hyalinization, degenerated muscle fibers and nuclear change in the etanercept group compared to the control group. Conclusion The results of our experimental study indicate that etanercept offers protection against ischemia-reperfusion injury in skeletal muscle tissue, enhancing the TRAM flap viability. The ability of etanercept to induce ischemic tolerance suggests that it may be applicable in free-flap surgery.

Putative CD133+ melanoma cancer stem cells induce initial angiogenesis in vivo

Tumor angiogenesis is essential for tumor growth and metastasis, and is regulated by a complex network of various types of cells, chemokines, and stimulating factors. In contrast to sprouting angiogenesis, tumor angiogenesis is also influenced by hypoxia, inflammation, and the attraction of bone-marrow-derived cells. Recently, cancer stem cells have been reported to mimic vascularization by differentiating into endothelial cells and inducing vessel formation. In this study, the influence of cancer stem cells on initial angiogenesis was evaluated for the metastatic melanoma cell line D10. Following flow cytometry, CD133+ and CD133- cells were isolated using magnetic cell separation and different cell fractions were transferred to porcine gelatin sponges, which were implanted into the dorsal skinfold chamber of immunocompromised mice. Angiogenesis was analyzed based on microvessel density over a 10-day period using in vivo fluorescence microscopy, and the results were verified using immunohistology. CD133+ D10 cells showed a significant induction of early angiogenesis in vivo, contrary to CD133- D10 cells, unsorted D10 cells, and negative control. Neovascularization was confirmed by visualizing endothelial cells by immunohistology using an anti-CD31 antibody. Because CD133+ cells are rare in clinical specimens and hardly amenable to functional assays, the D10 cell line provides a suitable model to study the angiogenic potential of putative cancer stem cells and the leukocyte-endothelial cell interaction in the dorsal skinfold chamber in vivo. This cancer stem cell model might be useful in the development and evaluation of therapeutic agents targeting tumors.

Decelerated vascularization in tissue-engineered constructs in association with diabetes mellitus in vivo

AIMS

Rapid blood vessel ingrowth in transplanted tissue engineering constructs is the key factor for successful incorporation, but many potential patients who may use engineered tissues suffer from widespread diseases that limit the capacity of neovascularization (e.g. diabetes). Thus, in vivo vascularization analyses of tissue-engineered constructs in angiogenically affected organisms are required.

METHODS

We therefore investigated the in vivo incorporation of collagen-coated and cell-seeded poly-L-lactide-co-glycolide scaffolds in diabetic B6.BKS(D)-Lepr(db)/J mice using repetitive intravital fluorescence microscopy over a time period of two weeks. For this purpose, scaffolds were seeded with osteoblast-like or bone marrow mesenchymal stem cells and implanted into the dorsal skinfold chambers of diabetic and non-diabetic (C57BL/6) mice.

RESULTS

Apart from slightly increased inflammatory parameters, diabetic mice showed significantly reduced capillary densities compared with non-diabetic animals from day 6 onward. In line with previous studies, more densely meshed microvascular networks were demonstrated in cell-seeded than in collagen-coated scaffolds from day 6 onward within the single groups (diabetic and control).

CONCLUSIONS

A large number of patients who suffer from systemic diseases that affect angiogenesis would profit from tissue engineering. Therefore, the challenge for the clinical introduction of tissue-engineered constructs will be to overcome the decreased angiogenesis in diabetic organisms.

Association of heme oxygenase 1 with the restoration of liver function after damage in murine malaria by Plasmodium yoelii

The liver efficiently restores function after damage induced during malarial infection once the parasites are cleared from the blood. However, the molecular events leading to the restoration of liver function after malaria are still obscure. To study this, we developed a suitable model wherein mice infected with Plasmodium yoelii (45% parasitemia) were treated with the antimalarial α/β-arteether to clear parasites from the blood and, subsequently, restoration of liver function was monitored. Liver function tests clearly indicated that complete recovery of liver function occurred after 25 days of parasite clearance. Analyses of proinflammatory gene expression and neutrophil infiltration further indicated that hepatic inflammation, which was induced immediately after parasite clearance from the blood, was gradually reduced. Moreover, the inflammation in the liver after parasite clearance was found to be correlated positively with oxidative stress and hepatocyte apoptosis. We investigated the role of heme oxygenase 1 (HO-1) in the restoration of liver function after malaria because HO-1 normally renders protection against inflammation, oxidative stress, and apoptosis under various pathological conditions. The expression and activity of HO-1 were found to be increased significantly after parasite clearance. We even found that chemical silencing of HO-1 by use of zinc protoporphyrin enhanced inflammation, oxidative stress, hepatocyte apoptosis, and liver injury. In contrast, stimulation of HO-1 by cobalt protoporphyrin alleviated liver inflammation and reduced oxidative stress, hepatocyte apoptosis, and associated tissue injury. Therefore, we propose that selective induction of HO-1 in the liver would be beneficial for the restoration of liver function after parasite clearance.

Paradoxical effects of heme arginate on survival of myocutaneous flaps

Ischemia reperfusion injury (IRI) contributes to partial flap and solid organ transplant failure. Heme-oxygenase 1 (HO-1) is an inducible, cytoprotective enzyme which protects against IRI in solid organ transplant models. Heme arginate (HA), a HO-1 inducer, is a promising, translatable, preconditioning agent. This study investigated the effects of preconditioning with HA on the clinical outcome of a myocutaneous IRI model. Forty male Lewis rats were randomized to intravenously receive 1) Control-NaCl, 2) HA, 3) HA and tin mesoporphyrin (SnMP), a HO-1 inhibitor; and 4) SnMP alone. Twenty-four hours later, an in situ transverse rectus abdominis myocutaneous flap was performed under isoflurane anesthesia. Viability of flaps was measured clinically and by laser-Doppler perfusion scanning. In vitro work on human epidermal keratinocytes (HEKa) assessed the effects of HA, SnMP, and the iron chelator desferrioxamine on 1) cytotoxicity, 2) intracellular reactive oxygen species (ROS) concentration, and 3) ROS-mediated DNA damage. In contrast to our hypothesis, HA preconditioning produced over 30% more flap necrosis at 48 h compared with controls (P = 0.02). HA-containing treatments produced significantly worse flap perfusion at all postoperative time points. In vitro work showed that HA is cytotoxic to keratinocytes. This cytotoxicity was independent of HO-1 and was mediated by the generation of ROS by free heme. In contrast to solid organ data, pharmacological preconditioning with HA significantly worsened clinical outcome, thus indicating that this is not a viable approach in free flap research.

In situ transverse rectus abdominis myocutaneous flap: a rat model of myocutaneous ischemia reperfusion injury

Free tissue transfer is the gold standard of reconstructive surgery to repair complex defects not amenable to local options or those requiring composite tissue. Ischemia reperfusion injury (IRI) is a known cause of partial free flap failure and has no effective treatment. Establishing a laboratory model of this injury can prove costly both financially as larger mammals are conventionally used and in the expertise required by the technical difficulty of these procedures typically requires employing an experienced microsurgeon. This publication and video demonstrate the effective use of a model of IRI in rats which does not require microsurgical expertise. This procedure is an in situ model of a transverse abdominis myocutaneous (TRAM) flap where atraumatic clamps are utilized to reproduce the ischemia-reperfusion injury associated with this surgery. A laser Doppler Imaging (LDI) scanner is employed to assess flap perfusion and the image processing software, Image J to assess percentage area skin survival as a primary outcome measure of injury.

Heme oxygenase, inflammation, and fibrosis: the good, the bad, and the ugly?

Upon injury, prolonged inflammation and oxidative stress may cause pathological wound healing and fibrosis, leading to formation of excessive scar tissue. Fibrogenesis can occur in most organs and tissues and may ultimately lead to organ dysfunction and failure. The underlying mechanisms of pathological wound healing still remain unclear, and are considered to be multifactorial, but so far, no efficient anti-fibrotic therapies exist. Extra- and intracellular levels of free heme may be increased in a variety of pathological conditions due to release from hemoproteins. Free heme possesses pro-inflammatory and oxidative properties, and may act as a danger signal. Effects of free heme may be counteracted by heme-binding proteins or by heme degradation. Heme is degraded by heme oxygenase (HO) that exists as two isoforms: inducible HO-1 and constitutively expressed HO-2. HO generates the effector molecules biliverdin/bilirubin, carbon monoxide, and free iron/ferritin. HO deficiency in mouse and man leads to exaggerated inflammation following mild insults, and accumulating epidemiological and preclinical studies support the widely recognized notion of the cytoprotective, anti-oxidative, and anti-inflammatory effects of the activity of the HO system and its effector molecules. In this review, we address the potential effects of targeted HO-1 induction or administration of HO-effector molecules as therapeutic targets in fibrotic conditions to counteract inflammatory and oxidative insults. This is exemplified by various clinically relevant conditions, such as hypertrophic scarring, chronic inflammatory liver disease, chronic pancreatitis, and chronic graft rejection in transplantation.

Increase in periosteal angiogenesis through heat shock conditioning

Objective

It is widely known that stress conditioning can protect microcirculation and induce the release of vasoactive factors for a period of several hours. Little, however, is known about the long-term effects of stress conditioning on microcirculation, especially on the microcirculation of the periosteum of the calvaria. For this reason, we used intravital fluorescence microscopy to investigate the effects of heat shock priming on the microcirculation of the periosteum over a period of several days.

Methods

Fifty-two Lewis rats were randomized into eight groups. Six groups underwent heat shock priming of the periosteum of the calvaria at 42.5°C, two of them (n = 8) for 15 minutes, two (n = 8) for 25 minutes and two (n = 8) for 35 minutes. After 24 hours, a periosteal chamber was implanted into the heads of the animals of one of each of the two groups mentioned above. Microcirculation and inflammatory responses were studied repeatedly over a period of 14 days using intravital fluorescence microscopy. The expression of heat shock protein (HSP) 70 was examined by immunohistochemistry in three further groups 24 hours after a 15-minute (n = 5), a 25-minute (n = 5) or a 35-minute (n = 5) heat shock treatment. Two groups that did not undergo priming were used as controls. One control group (n = 8) was investigated by intravital microscopy and the other (n = 5) by immunohistochemistry.

Results

During the entire observation period of 14 days, the periosteal chambers revealed physiological microcirculation of the periosteum of the calvaria without perfusion failures. A significant (p < 0.05) and continuous increase in functional capillary density was noted from day 5 to day 14 after 25-minute heat shock priming. Whereas a 15-minute exposure did not lead to an increase in functional capillary density, 35-minute priming caused a significant but reversible perfusion failure in capillaries. Non-perfused capillaries in the 35-minute treatment group were reperfused by day 10. Immunohistochemistry demonstrated an increase in cytoprotective HSP70 expression in the periosteum after a 15-minute and a 35-minute heat shock pretreatment when compared with the control group. The level of HSP70 expression that was measured in the periosteum after 25 minutes of treatment was significantly higher than the levels observed after 15 or 35 minutes of heat shock exposure.

Conclusion

A few days after heat shock priming over an appropriate period of time, a continuous increase in functional capillary density is seen in the periosteum of the calvaria. This increase in perfusion appears to be the result of the induction of angiogenesis.

Effects of VEGF loading on scaffold-confined vascularization

Adequate vascularization of tissue-engineered constructs remains a major challenge in bone grafting. In view of this, we loaded ß-tricalcium-phosphate (ß-TCP) and porous poly(L-lactide-co-glycolide) (PLGA) scaffolds via collagen coating with vascular endothelial growth factor (VEGF) and studied whether the VEGF loading improves scaffold angiogenesis and vascularization. Dorsal skinfold chambers were implanted into 48 balb/c mice, which were assigned to 6 groups (n = 8 each). Uncoated (controls), collagen-coated, and additionally VEGF-loaded PLGA and ß-TCP scaffolds were inserted into the chambers. Angiogenesis, neovascularization, and leukocyte-endothelial cell interaction were analyzed repeatedly during a 14-day observation period using intravital fluorescence microscopy. Furthermore, VEGF release from PLGA und ß-TCP scaffolds was studied by ELISA. Micromorphology was studied from histological specimens. Unloaded ß-TCP scaffolds showed an accelerated and increased angiogenic response when compared with unloaded PLGA scaffolds. In vitro, PLGA released significantly higher amounts of VEGF compared with ß-TCP at the first two days resulting in a rapid drop of the released amount at the following days up to day 7 where the VEGF release was negligible. Nonetheless, in vivo VEGF loading increased neovascularization, especially in ß-TCP scaffolds. This increased vascularization was associated with a temporary leukocytic response with pronounced leukocyte-endothelial cell interaction at days 3 and 6. Histology revealed adequate host tissue response and engraftment of both ß-TCP and PLGA scaffolds. Our study demonstrates that ß-TCP scaffolds offer more suitable conditions for vascularization than PLGA scaffolds, in particular if they are loaded with VEGF.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.

Heme oxygenase in the regulation of vascular biology: from molecular mechanisms to therapeutic opportunities

Heme oxygenases (HOs) are the rate-limiting enzymes in the catabolism of heme into biliverdin, free iron, and carbon monoxide. Two genetically distinct isoforms of HO have been characterized: an inducible form, HO-1, and a constitutively expressed form, HO-2. HO-1 is a kind of stress protein, and thus regarded as a sensitive and reliable indicator of cellular oxidative stress. The HO system acts as potent antioxidants, protects endothelial cells from apoptosis, is involved in regulating vascular tone, attenuates inflammatory response in the vessel wall, and participates in angiogenesis and vasculogenesis. Endothelial integrity and activity are thought to occupy the central position in the pathogenesis of cardiovascular diseases. Cardiovascular disease risk conditions converge in the contribution to oxidative stress. The oxidative stress leads to endothelial and vascular smooth muscle cell dysfunction with increases in vessel tone, cell growth, and gene expression that create a pro-thrombotic/pro-inflammatory environment. Subsequent formation, progression, and obstruction of atherosclerotic plaque may result in myocardial infarction, stroke, and cardiovascular death. This background provides the rationale for exploring the potential therapeutic role for HO system in the amelioration of vascular inflammation and prevention of adverse cardiovascular outcomes.

Extracorporeal shock wave treatment modulates skin fibroblast recruitment and leukocyte infiltration for enhancing extended skin-flap survival

Extracorporeal shock wave (ESW) treatment has a positive effect of rescuing ischemic skin flaps. This study assessed whether ESW treatment rescues the compromised flap tissue by suppressing the apoptosis of ischemic tissue and recruiting tissue remodeling. We used a random-pattern extended dorsal-skin-flap (10 x 3 cm) rodent model. Thirty-six male Sprague-Dawley rats were divided into three groups. Group I, the control group, received no treatment. Group II received one session of ESW treatment (500 impulses at 0.15 mJ/mm(2)) immediately after surgery. Group III received two sessions of ESW treatment, immediately and the day after the surgery. Results indicated that the necrotic area in the flaps in group II was significantly smaller than that of the flaps in group I (p<0.01). Transferase dUTP-nick end labeling (TUNEL) analysis revealed a significant decrease in the number of apoptotic cells in group II. Hydrogen peroxide (H(2)O(2)) expression in circulation blood was significantly decreased in group II on the day after ESW treatment. Immunohistochemical staining indicated that compared with no treatment, ESW treatment could substantially increase proliferating cell nuclear antigen (PCNA), endothelial nitric oxide synthase, and prolyl 4-hydroxylase (rPH) expression, reduce CD45 expression, and suppress 8-hydroxyguanosine (8-OG) expression in the ischemic zone of the flap tissue. In conclusion, ESW treatment administered at an optimal dosage exerts a positive effect of rescuing ischemic extended skin flaps. The mechanisms of action of ESWs involve modulation of oxygen radicals, attenuation of leukocyte infiltration, decrease in tissue apoptosis, and recruitment of skin fibroblasts, which results in increased flap tissue survival.

Ischemia-induced up-regulation of heme oxygenase-1 protects from apoptotic cell death and tissue necrosis

BACKGROUND

Tissues are endowed with protective mechanisms to counteract chronic ischemia. Previous studies have demonstrated that endogenous heme oxygenase (HO)-1 may protect parenchymal tissue from inflammation- and reoxygenation-induced injury. Nothing is known, however, on whether endogenous HO-1 also plays a role in chronic ischemia to protect from development of tissue necrosis. The aim of this study is, therefore, to evaluate in vivo whether endogenous HO-1 exerts protection on chronically ischemic musculocutaneous tissue, and whether this protection is mediated by an attenuation of the microcirculatory dysfunction.

MATERIALS AND METHODS

In C57BL/6-mice, a chronically ischemic flap was elevated and fixed into a dorsal skinfold chamber. In a second group, tin-protoporphyrin-IX was administrated to competitively block the action of HO-1. Animals without flap elevation served as controls. With the use of intravital fluorescence microscopy, microcirculation, apoptotic cell death, and tissue necrosis were analyzed over a 10-day observation period. The time course of HO-1 expression was determined by Western blotting.

RESULTS

Chronic ischemia induced an increase of HO-1 expression, particularly at day 1 and 3. This was associated with arteriolar dilation and hyperperfusion, which was capable of maintaining an adequate capillary perfusion density in the critically perfused central part of the flap, demarcating the distal necrosis. Inhibition of endogenous HO-1 by tin-protoporphyrin-IX completely abrogated arteriolar dilation (44.6 +/- 6.2 microm versus untreated flaps: 71.3 +/- 7.3 microm; P < 0.05) and hyperperfusion (3.13 +/- 1.29 nL/s versus 8.55 +/- 3.56 nL/s; P < 0.05). This resulted in a dramatic decrease of functional capillary density (16 +/- 16 cm/cm(2)versus 84 +/- 31 cm/cm(2); P < 0.05) and a significant increase of apoptotic cell death (585 +/- 51 cells/mm(2)versus 365 +/- 53 cells/mm(2); P < 0.05), and tissue necrosis (73% +/- 5% versus 51% +/- 5%; P < 0.001).

CONCLUSION

Thus, our results suggest that chronic ischemia-induced endogenous HO-1 protects ischemically endangered tissue, probably by the vasodilatory action of the HO-1-associated carbon monoxide.

Extracorporeal Shock Wave Enhanced Extended Skin Flap Tissue Survival via Increase of Topical Blood Perfusion and Associated with Suppression of Tissue Pro-Inflammation

OBJECTIVE

Distal skin flap ischemic necrosis is a significant challenge in reconstructive surgery. This study assessed whether extracorporeal shock wave (ESW) treatment rescues compromised flap tissue by enhancing tissue perfusion and is associated with suppression of inflammatory response.

METHODS

This study used the dorsal skin random flap model in a rodent. Thirty-six male Sprague Dawley rats were divided into three groups. Group I, a control group, received no treatment. Group II was administrated 500 impulses of ESW treatment at 0.15 mJ/mm(2) as a single treatment immediately postoperatively. Group III received 500 impulses of ESW at 0.15 mJ/mm(2) applied immediately postoperatively and the day following surgery. Flap blood perfusion was detected by laser Doppler. Flap survival/necrosis area and histological staining of flap ischemia zone was performed on day 7 postoperatively. The tumor necrosis factor alpha, vascular endothelial growth factor, and proliferating cell nuclear antigen expression were evaluated with immunohistochemical staining.

RESULTS

Experimental results indicated that the necrotic area of the flaps in Group II was significantly reduced compared with that in the control group (13 +/- 2.6% versus 42 +/- 5.7%, P < 0.01). There was small and insignificant reduction in the necrotic area in Group III compared with the controls. Flap tissue blood perfusion was significantly increased postoperatively in Group II. Histological staining indicated that ESW treatment substantially increased vascular endothelial growth factor and proliferating cell nuclear antigen expressions, reduced leukocyte infiltration, and suppression of tumor necrosis factor alpha expression in flap tissue ischemic zones in Group II compared with that in controls.

CONCLUSION

Optimal dosage of ESW treatment has a positive effect in rescuing ischemic zone of flap by increasing tissue perfusion and is associated with suppressing inflammatory response.

Pathomechanisms of Ischemia-Reperfusion Injury as the Basis for Novel Preventive Strategies: Is It Time for the Introduction of Pleiotropic Compounds?

Ischemia-reperfusion-associated tissue dysfunction and organ failure still represent major complications in transplantation surgery. The pathomechanisms involve microvascular perfusion failure, ie, no-reflow and tissue hypoxia despite reperfusion and reoxygenation. However, postischemic reperfusion also provokes an inflammatory response, ie, reflow paradox, with activation of macrophages, recruitment of leukocytes, and accumulation of platelets, involving surface adhesion molecules such as P-selectin, P-selectin glycoprotein ligand (PSGL)-1, Mac-1, and intercellular adhesion molecule (ICAM)-1. These inflammatory cells produce cytokines, chemokines, lipid mediators, and oxygen radicals, which all may contribute to the manifestation of injury, including apoptosis, necrosis, and necrapoptosis. Although specific inhibition of single mediators, such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1, and oxygen radicals, or distinct molecules, such as P-selectin and ICAM-1, has been shown to be protective in the experimental setting, these single-agent antimediator and antimolecule approaches did not find their way into clinical practice. Clinically, University of Wisconsin (UW) solution for organ preservation is still the major milestone for prevention of ischemia- and reperfusion-associated injury. Characteristically, this treatment strategy does not represent an anti-single mediator approach, but exerts protection by influencing multiple pathways involved in hypoxic and inflammatory injury, potentially restoring the overall homeostasis. This type of pleiotropic action may also be achieved by single pharmacological compounds, such as statins, erythropoietin, hemoxygenase-1, and L-glycine. In recent experimental studies, these compounds have been shown to be effective to reduce post-ischemic-reperfusion injury, and, additionally, to be associated with less side effects. Accordingly, these pleiotropic substances may represent ideal candidates for pharmacological preconditioning in patient treatment, and, thus, should be further evaluated in clinical trials.

Angiogenic and inflammatory response to biodegradable scaffolds in dorsal skinfold chambers of mice

For tissue engineering, scaffolds should be biocompatible and promote neovascularization. Because little is known on those specific properties, we herein studied in vivo the host angiogenic and inflammatory response after implantation of commonly used scaffold materials. Porous poly(L-lactide-co-glycolide) (PLGA) and collagen-chitosan-hydroxyapatite hydrogel scaffolds were implanted into dorsal skinfold chambers of balb/c mice. Additional animals received cortical bone as an isogeneic, biological implant, while chambers of animals without implants served as controls. Angiogenesis and neovascularization as well as leukocyte-endothelial cell interaction and microvascular permeability were analyzed over 14 day using intravital fluorescence microscopy. PLGA scaffolds showed a slight increase in leukocyte recruitment compared to controls. This was associated with an elevation of microvascular permeability, which was comparable to that observed in isogeneic bone tissue. Of interest, PLGA induced a marked angiogenic response, revealing a density of newly formed capillaries almost similar to that observed in bone implants. Histology showed infiltration of macrophages, probably indicating resorption of the biomaterial. In contrast, hydrogel scaffolds induced a severe inflammation, as indicated by an approximately 15-fold increase of leukocyte-endothelial cell interaction and a marked elevation of microvascular permeability. This was associated by induction of apoptotic cell death within the surrounding tissue and a complete lack of ingrowth of newly formed microvessels. Histology confirmed adequate engraftment of PLGA and isogeneic bone but not hydrogel within the host tissue. PLGA scaffolds show a better biocompatibility than hydrogel scaffolds and promote vascular ingrowth, guaranteeing adequate engraftment within the host tissue.

The heat shock proteins and plastic surgery

Heat shock proteins are diverse and essential components of cell physiology. Their expression is elevated in the cell undergoing stress, where they protect the cell from death by necrosis or apoptosis and accelerate recovery. Significant advances have been made in studies relevant to plastic surgery regarding these proteins and their manipulation. This review introduces the heat shock proteins and appraises these studies in skin, ultraviolet light exposure, neoplasia, wound healing, ageing, burns, and reconstructive surgery.

Endogenous carbon monoxide production correlates weakly with severity of acute illness

BACKGROUND AND OBJECTIVE

The enzyme haeme oxygenase-1 is highly inducible by oxidative agents. Its product carbon monoxide is thought to exert anti-inflammatory properties. We recently showed, that critically ill patients produce higher amounts of carbon monoxide compared to healthy controls. In the present study we compare endogenous carbon monoxide production with the severity of illness of intensive care unit patients.

METHODS

Exhaled carbon monoxide concentration was measured in 95 mechanically ventilated, critically ill patients (mean age +/- SD, 59.5 +/- 15.7) on a carbon monoxide monitor. Measurements were taken every hour for 24 h in each patient. Data were analysed using Mann-Whitney rank sum test. Correlation analysis was performed with the Spearman's rank order correlation.

RESULTS

Carbon monoxide production correlated weakly with the multiple organ dysfunction score (R = 0.27; P = 0.009). Patients suffering from cardiac disease (median 22.5, interquartile range 16.2-27.4 microL kg(-1) h(-1) vs. median 18.2, interquartile range 14.2-21.8 microL kg(-1) h(-1), P = 0.008) and critically ill patients undergoing dialysis (median 25.0, interquartile range 21.4-30.2 microL kg(-1) h(-1), vs. median 19.4, interquartile range 14.7-23.3 microL kg(-1) h(-1), P = 0.004) produced significantly higher amounts of carbon monoxide compared to critically ill controls.

CONCLUSION

The findings suggest that endogenous carbon monoxide production might reflect the severity of acute organ dysfunction.

Heme oxygenase-1 is a modulator of inflammation and vaso-occlusion in transgenic sickle mice

Transgenic sickle mice expressing betaS hemoglobin have activated vascular endothelium that exhibits enhanced expression of NF-kappaB and adhesion molecules that promote vascular stasis in sickle, but not in normal, mice in response to hypoxia/reoxygenation. Sickle mice hemolyze rbcs in vivo as demonstrated by increased reticulocyte counts, plasma hemoglobin and bilirubin, and reduced plasma haptoglobin. The heme content is elevated in sickle organs, which promotes vascular inflammation and heme oxygenase-1 expression. Treatment of sickle mice with hemin further increases heme oxygenase-1 expression and inhibits hypoxia/reoxygenation-induced stasis, leukocyte-endothelium interactions, and NF-kappaB, VCAM-1, and ICAM-1 expression. Heme oxygenase inhibition by tin protoporphyrin exacerbates stasis in sickle mice. Furthermore, treatment of sickle mice with the heme oxygenase enzymatic product carbon monoxide or biliverdin inhibits stasis and NF-kappaB, VCAM-1, and ICAM-1 expression. Local administration of heme oxygenase-1 adenovirus to subcutaneous skin increases heme oxygenase-1 and inhibits hypoxia/reoxygenation-induced stasis in the skin of sickle mice. Heme oxygenase-1 plays a vital role in the inhibition of vaso-occlusion in transgenic sickle mice.

Carbon Monoxide: Endogenous Production, Physiological Functions, and Pharmacological Applications

Over the last decade, studies have unraveled many aspects of endogenous production and physiological functions of carbon monoxide (CO). The majority of endogenous CO is produced in a reaction catalyzed by the enzyme heme oxygenase (HO). Inducible HO (HO-1) and constitutive HO (HO-2) are mostly recognized for their roles in the oxidation of heme and production of CO and biliverdin, whereas the biological function of the third HO isoform, HO-3, is still unclear. The tissue type-specific distribution of these HO isoforms is largely linked to the specific biological actions of CO on different systems. CO functions as a signaling molecule in the neuronal system, involving the regulation of neurotransmitters and neuropeptide release, learning and memory, and odor response adaptation and many other neuronal activities. The vasorelaxant property and cardiac protection effect of CO have been documented. A plethora of studies have also shown the importance of the roles of CO in the immune, respiratory, reproductive, gastrointestinal, kidney, and liver systems. Our understanding of the cellular and molecular mechanisms that regulate the production and mediate the physiological actions of CO has greatly advanced. Many diseases, including neurodegenerations, hypertension, heart failure, and inflammation, have been linked to the abnormality in CO metabolism and function. Enhancement of endogenous CO production and direct delivery of exogenous CO have found their applications in many health research fields and clinical settings. Future studies will further clarify the gasotransmitter role of CO, provide insight into the pathogenic mechanisms of many CO abnormality-related diseases, and pave the way for innovative preventive and therapeutic strategies based on the physiologic effects of CO.

Heme oxygenase modulates small intestine leukocyte adhesion following hindlimb ischemia/reperfusion by regulating the expression of intercellular adhesion molecule-1

OBJECTIVE

Heme oxygenase is the rate-limiting enzyme in the degradation of heme into carbon monoxide, iron, and bilirubin. Recent evidence suggests that the induction of heme oxygenase-1 is associated with potent anti-inflammatory properties. The objectives of this study were to determine the temporal, regional, and cellular distribution of heme oxygenase-1 within the small intestine and its role in modulating remote intestinal leukocyte recruitment following trauma induced by hindlimb ischemia/reperfusion.

DESIGN

Randomized, controlled, prospective animal study.

SETTING

Hospital surgical research laboratory.

SUBJECTS

Male C57BL/6 mice.

INTERVENTIONS

Mice underwent 1 hr of bilateral hindlimb ischemia, followed by 3, 6, 12, or 24 hrs of reperfusion.

MEASUREMENTS AND MAIN RESULTS

Heme oxygenase-1 messenger RNA, heme oxygenase-1 protein, and heme oxygenase activity were measured using reverse transcription polymerase chain reaction, Western blot, immunohistochemistry, and spectrophotometric assay, respectively. The jejunum was also exteriorized to quantify the flux of rolling and adherent leukocytes and R-Phycoerythrin conjugated intercellular adhesion molecule-1 monoclonal antibody fluorescence intensity in submucosal postcapillary venules with the use of intravital microscopy. Ischemia/reperfusion led to a significant increase in heme oxygenase-1 messenger RNA in the jejunum and ileum 3 hrs following limb reperfusion, with a subsequent increase in heme oxygenase-1 protein and heme oxygenase activity at 6 hrs. Ischemia/reperfusion also led to a significant 1.4-fold increase in leukocyte rolling, whereas inhibition of heme oxygenase via injection of tin protoporphyrin IX (20 micromol/kg intraperitoneally) resulted in a three-fold increase in leukocyte adhesion, compared with ischemia/reperfusion alone. This increase in adhesion was significantly reduced to baseline in mice treated with intercellular adhesion molecule-1 monoclonal antibody before heme oxygenase inhibition (40 microg/mouse), whereas inhibition of heme oxygenase activity following ischemia/reperfusion also led to a significant increase in R-Phycoerythrin intercellular adhesion molecule-1 monoclonal antibody fluorescence intensity.

CONCLUSIONS

Our data suggest that remote trauma induced by hindlimb ischemia/reperfusion leads to an increase in heme oxygenase activity within the small intestine, which modulates intercellular adhesion molecule-1 dependent intestinal leukocyte adhesion.

Novel lipid mediator aspirin-triggered lipoxin A4 induces heme oxygenase-1 in endothelial cells

Lipoxins (LX) and aspirin-triggered LX (ATL) are eicosanoids generated during inflammation via transcellular biosynthetic routes that elicit distinct anti-inflammatory and proresolution bioactions, including inhibition of leukocyte-mediated injury, stimulation of macrophage clearance of apoptotic neutrophils, repression of proinflammatory cytokine production, and inhibition of cell proliferation and migration. Recently, it was reported that aspirin induces heme oxygenase-1 (HO-1) expression on endothelial cells (EC) in a COX-independent manner, what confers protection against prooxidant insults. However, the underlying mechanisms remain unclear. In this study, we investigated whether an aspirin-triggered lipoxin A(4) stable analog, 15-epi-16-(para-fluoro)-phenoxy-lipoxin A(4) (ATL-1) was able to induce endothelial HO-1. Western blot analysis showed that ATL-1 increased HO-1 protein expression associated with increased mRNA levels on EC in a time- and concentration-dependent fashion. This phenomenon appears to be mediated by the activation of the G protein-coupled LXA(4) receptor because pertussis toxin and Boc-2, a receptor antagonist, significantly inhibited ATL-1-induced HO-1 expression. We demonstrate that treatment of EC with ATL-1 inhibited VCAM and E-selectin expression induced by TNF-alpha or IL-1beta. This inhibitory effect of the analog is modulated by HO-1 because it was blocked by SnPPIX, a competitive inhibitor that blocks HO-1 activity. Our results establish that ATL-1 induces HO-1 in human EC, revealing an undescribed mechanism for the anti-inflammatory activity of these lipid mediators.

Improvement of nutritive perfusion after free tissue transfer by local heat shock-priming-induced preservation of capillary flowmotion

BACKGROUND

Capillary flowmotion protects pedicled flaps during critical perfusion conditions. However, free tissue transfer, causing ischemia-reperfusion and surgical trauma, have been shown to blunt these protective blood flow fluctuations. Because heat shock priming protects tissue after transfer, we herein studied whether heat shock protein expression is capable to preserve critical perfusion-induced capillary flowmotion in transferred composite flaps.

METHODS

In Sprague Dawley rats (n = 16), osteomyocutaneous flaps were subjected to critical perfusion after harvest and 1 h and 4 h after free transfer. In eight animals additional heat shock priming was induced 24 h before flap harvest. Microcirculation including capillary flowmotion was analyzed using intravital fluorescence microscopy.

RESULTS

After harvest, critical perfusion induced capillary flowmotion in skeletal muscle tissue of all flaps. By this, functional capillary density (FCD), an indicator of nutritive perfusion, was maintained not only in muscle but also in periosteum, subcutis, and skin. In contrast, 1 h after flap transfer muscle capillary flowmotion was completely abrogated, resulting in a significant decrease of FCD in all tissues. Heat shock-priming completely restored capillary flowmotion, and, by this, maintained tissue FCD.

CONCLUSIONS

The loss of muscle capillary flowmotion after free tissue transfer-associated ischemia-reperfusion can be prevented by heat shock-priming. This may represent the mechanism of protection by local heat application.

Ketamine reduces mortality of severely burnt rats, when compared to midazolam plus fentanyl

Ketamine can provide protective effects, through its anti-inflammatory properties, as shown in animal models of septic shock and endotoxemia, and has elicited the heat-shock response (HSR) in experimental studies. The HSR has reduced the mortality after severe burns in rats. This study has tested the hypothesis that ketamine could be protective in experimental burns and that it could generate the HSR. One hundred and twenty adult male Fischer rats were randomly divided into five groups. Rats in the first group (n = 20) were sham-anesthetized. In the second group (n = 20), rats were anesthetized with ketamine and shaved. In the third group (n = 20) rats were anesthetized with midazolam plus fentanyl and shaved. In the fourth group (n = 30), rats were anesthetized with ketamine, shaved and submitted to 29% body surface third-degree burns using a brass bar. In the fifth group (n = 30), rats were anesthetized with midazolam plus fentanyl, shaved and submitted to 29% body surface third-degree burns using a brass bar. Mortality rates were measured at 1, 2, 3, 5, 7, 10, 15 and 25 days. Liver and lung samples were collected from all groups for heat-shock protein 70 (HSP70) detection. No animals died in the first, second or third group. Animals anesthetized with ketamine showed significantly decreased mortality, as compared to those anesthetized with midazolam plus fentanyl, from day 2 to day 10 (P < 0.01, Fischer's exact test) and from day 10 to day 25 (P < 0.05). HSP70 was positive in the lungs of animals from all groups, without any differences among them, and was found in none of the liver samples. In conclusion, the mortality was significantly lesser in ketamine-anesthetized burnt rats than in burnt animals anesthetized with midazolam plus fentanyl. Ketamine has not elicited the HSR in this model of experimental burns and, therefore, its protective effects were not shown to be mediated through this mechanism.

Different faces of the heme-heme oxygenase system in inflammation

The heme-heme oxygenase system has recently been recognized to possess important regulatory properties. It is tightly involved in both physiological as well as pathophysiological processes, such as cytoprotection, apoptosis, and inflammation. Heme functions as a double-edged sword. In moderate quantities and bound to protein, it forms an essential element for various biological processes, but when unleashed in large amounts, it can become toxic by mediating oxidative stress and inflammation. The effect of this free heme on the vascular system is determined by extracellular factors, such as hemoglobin/heme-binding proteins, haptoglobin, albumin, and hemopexin, and intracellular factors, including heme oxygenases and ferritin. Heme oxygenase (HO) enzyme activity results in the degradation of heme and the production of iron, carbon monoxide, and biliverdin. All these heme-degradation products are potentially toxic, but may also provide strong cytoprotection, depending on the generated amounts and the microenvironment. Pre-induction of HO activity has been demonstrated to ameliorate inflammation and mediate potent resistance to oxidative injury. A better understanding of the complex heme-heme

The heme-heme oxygenase system: a molecular switch in wound healing

When cells are injured they release their contents, resulting in a local accumulation of free heme proteins and heme. Here, we investigated the involvement of heme and its degrading enzyme heme oxygenase (HO) in the inflammatory process during wound healing. We observed that heme directly accumulates at the edges of the wound after inflicting a wound in the palate of Wistar rats. This coincided with an increased adhesion molecule expression and the recruitment of leukocytes. To prove that heme is responsible for the recruitment of leukocytes, heme was administered intradermally 24 hours prior to injury. A clear heme-induced influx of both macrophages and granulocytes was observed. When examining the HO isoforms, HO-1 and HO-2, we found that HO-2 was present in the entire submucosa. Surprisingly, we observed also that HO-1 is significantly expressed in the epithelium of both the mucosa and the skin of animals without wounds. On inflammation, HO-1 expression increased, particularly in infiltrating cells during the resolution phase of inflammation. Interestingly, we observed that heme-induced influx of leukocytes was highly elevated after pharmacologic inhibition of HO activity. These observations suggest that the heme-HO system is closely involved in the control of wound healing. Our results demonstrate that the local release of heme may be a physiologic trigger to start inflammatory processes, whereas HO-1 antagonizes inflammation by attenuating adhesive interactions and cellular infiltration. Moreover, the basal level of HO expression in the skin may serve as a first protective environment against acute oxidative and inflammatory insults.

Pyrrolidine dithiocarbamate provides protection against hypothermic preservation and transplantation injury in the rat liver: the role of heme oxygenase-1

BACKGROUND

Pyrrolidine dithiocarbamate (PDTC) represents a class of antioxidants and is a potent inducer of the heme oxygenase-1 (HO-1) gene and an inhibitor of nuclear factor-kappa B (NF-kappa B). We examined the impact of PDTC preconditioning against cold ischemia and reperfusion injury in the rat liver.

METHODS

Lewis rats were treated subcutaneously with saline or PDTC solution 24 hours before harvesting. Some animals pretreated with PDTC were also given zinc protoporphyrin IX intravenously immediately after reperfusion. HO-1 expression and enzyme activity in liver tissues were analyzed at different time points after each treatment. After transplantation of 24-hour preserved livers, serum levels of transaminases and gene expression of tumor necrosis factor-alpha, interleukin-1 beta, and NF-kappa B were measured. Animal survival and cellular viability were monitored.

RESULTS

HO-1 gene expression and protein synthesis were enhanced in PDTC-treated livers, leading to increased enzyme activity (P <.05). The PDTC treatment group showed lower transaminase levels (P <.05), lower cytokine and NF-kappa B messenger RNA expression (P <.05), and fewer nonviable cells (P <.05) than did the control group, whereas these PDTC effects were abolished with zinc protoporphyrin injection after reperfusion (P <.05). The best animal survival rate was observed in the PDTC group (P <.05).

CONCLUSION

PDTC preconditioning reduces inflammatory responses during reperfusion. PDTC appears to exert this protective effect by induction of an antioxidative stress protein and inhibition of proinflammatory cytokines.

Prevention of kidney ischemia/reperfusion-induced functional injury, MAPK and MAPK kinase activation, and inflammation by remote transient ureteral obstruction

Protection against ischemic kidney injury is afforded by 24 h of ureteral obstruction (UO) applied 6 or 8 days prior to the ischemia. Uremia or humoral factors are not responsible for the protection, since unilateral UO confers protection on that kidney but not the contralateral kidney. Prior UO results in reduced postischemic outer medullary congestion and leukocyte infiltration. Prior UO results in reduced postischemic phosphorylation of c-Jun N-terminal stress-activated protein kinase 1/2 (JNK1/2), p38, mitogen-activated protein kinase (MAPK) kinase 4 (MKK4), and MKK3/6. Very few cells stain positively for proliferating cell nuclear antigen after obstruction, indicating that subsequent protection against ischemia is not related to proliferation with increased numbers of newly formed daughter cells more resistant to injury. UO increases the expression of heat shock protein (HSP)-25 and HSP-72. The increased HSP-25 expression persists for 6 or 8 days, whereas HSP-72 does not. HSP-25 expression is increased in the proximal tubule cells in the outer stripe of the outer medulla postobstruction, prior to, and 24 h after ischemia. In LLC-PK(1) renal epithelial cells, adenovirus-expressed human HSP-27 confers resistance to chemical anoxia and oxidative stress. Increased HSP-27 expression in LLC-PK(1) cells results in reduced H(2)O(2)-induced phosphorylation of JNK1/2 and p38. In conclusion, prior transient UO renders the kidney resistant to ischemia. This resistance to functional consequences of ischemia is associated with reduced postischemic activation of JNK, p38 MAP kinases, and their upstream MAPK kinases. The persistent increase in HSP-25 that occurs as a result of UO may contribute to the reduction in phosphorylation of MAPKs that have been implicated in adhesion molecule up-regulation and cell death.