Oxidant stress: the role of the glutathione redox cycle in skin preconditioning

Xenobiotica-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

Studies on the metabolic fate of medical drugs, skin care products, cosmetics and other chemicals intentionally or accidently applied to the human skin have become increasingly important in order to ascertain pharmacological effectiveness and to avoid toxicities. The use of freshly excised human skin for experimental investigations meets with ethical and practical limitations. Hence information on xenobiotic-metabolizing enzymes (XME) in the experimental systems available for pertinent studies compared with native human skin has become crucial. This review collects available information of which—taken with great caution because of the still very limited data—the most salient points are: in the skin of all animal species and skin-derived in vitro systems considered in this review cytochrome P450 (CYP)-dependent monooxygenase activities (largely responsible for initiating xenobiotica metabolism in the organ which provides most of the xenobiotica metabolism of the mammalian organism, the liver) are very low to undetectable. Quite likely other oxidative enzymes [e.g. flavin monooxygenase, COX (cooxidation by prostaglandin synthase)] will turn out to be much more important for the oxidative xenobiotic metabolism in the skin. Moreover, conjugating enzyme activities such as glutathione transferases and glucuronosyltransferases are much higher than the oxidative CYP activities. Since these conjugating enzymes are predominantly detoxifying, the skin appears to be predominantly protected against CYP-generated reactive metabolites. The following recommendations for the use of experimental animal species or human skin in vitro models may tentatively be derived from the information available to date: for dermal absorption and for skin irritation esterase activity is of special importance which in pig skin, some human cell lines and reconstructed skin models appears reasonably close to native human skin. With respect to genotoxicity and sensitization reactive-metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the Conclusions section in the end of this review.

Glutathione Depletion by L-Buthionine-S,R-Sulfoximine Induces Apoptosis of Cardiomyocytes through Activation of PKC-δ

In the present study, we investigated the effect of intracellular glutathione (GSH) depletion in heart-derived H9c2 cells and its mechanism. L-buthionine-S,R-sulfoximine (BSO) induced the depletion of cellular GSH, and BSO-induced reactive oxygen species (ROS) production was inhibited by glutathione monoethyl ester (GME). Additionally, GME inhibited BSO-induced caspase-3 activation, annexin V-positive cells, and annexin V-negative/propidium iodide (PI)-positive cells. Treatment with rottlerin completely blocked BSO-induced cell death and ROS generation. BSO-induced GSH depletion caused a translocation of PKC-δ from the cytosol to the membrane fraction, which was inhibited by treatment with GME. From these results, it is suggested that BSO-induced depletion of cellular GSH causes an activation of PKC-δ and, subsequently, generation of ROS, thereby inducing H9c2 cell death.

Inflammatory and oxidative stress after surgery for the small area corrections of burn sequelae

PURPOSE

To compare vitamin levels, inflammatory and oxidative stress markers before and after skin autograft surgery to correct burn scar areas.

METHODS

This prospective study was conducted with 8 patients with a median age of 28 years (range, 16 to 40 years) that had burn sequelae and were admitted to a Burn Unit for correction of small burn scar areas [3.3 (1.0-5.0) % of the corporal surface]. The volunteers were evaluated before and 48 hours after excision of scar tissue and skin autograft. Routine laboratory data, along with a food questionnaire and anthropometry were collected in the preoperative period. Serum vitamin A, C, E, B(12) and folic acid levels, inflammatory markers (C-protein reactive, alpha-1-acid glycoprotein, ferritin) and oxidative stress markers (reduced glutathione - GSH and Thiobarbituric Acid Reactive Substances - TBARS) were determined at preoperative and postoperative phases. Data were analyzed with two-sample Wilcoxon test.

RESULTS

All volunteers were clinically stable and had adequate nutritional status at admission. After surgery, C-reactive protein serum levels increased [0.4 (0.01-1.0) vs. 2.5 (0.6-4.7) mg/dL, p=0.01] and vitamin A levels decreased [3.4 (2.1-4.2) vs. 2.4 (1.6-4.1) µmol/L, p=0.01]. No changes occurred in other vitamins, ferrritin, alpha-1-acid glycoprotein, GSH and TBARS levels.

CONCLUSION

Minimal metabolic changes were produced after skin autograft in small areas of well-nourished patients without active infection or inflammation.

Investigation of reperfusion injury and ischemic preconditioning in microsurgery

Ischemia/reperfusion (I/R) is inevitable in many vascular and musculoskeletal traumas, diseases, free tissue transfers, and during time-consuming reconstructive surgeries in the extremities. Salvage of a prolonged ischemic extremity or flap still remains a challenge for the microvascular surgeon. One of the common complications after microsurgery is I/R-induced tissue death or I/R injury. Twenty years after the discovery, ischemic preconditioning has emerged as a powerful method for attenuating I/R injury in a variety of organs or tissues. However, its therapeutic expectations still need to be fulfilled. In this article, the author reviews some important experimental evidences of I/R injury and preconditioning-induced protection in the fields relevant to microsurgery.

Drug-metabolizing enzymes in the skin of man, rat, and pig

The mammalian skin has long been considered to be poor in drug metabolism. However, many reports clearly show that most drug metabolizing enzymes also occur in the mammalian skin albeit at relatively low specific activities. This review summarizes the current state of knowledge on drug metabolizing enzymes in the skin of human, rat, and pig, the latter, because it is often taken as a model for human skin on grounds of anatomical similarities. However only little is known about drug metabolizing enzymes in pig skin. Interestingly, some cytochromes P450 (CYP) have been observed in the rat skin which are not expressed in the rat liver, such as CYP 2B12 and CYP2D4. As far as investigated most drug metabolizing enzymes occur in the suprabasal (i.e. differentiating) layers of the epidermis, but the rat CYP1A1 rather in the basal layer and human UDP-glucuronosyltransferase rather in the stratum corneum. The pattern of drug metabolizing enzymes and their localization will impact not only the beneficial as well as detrimental properties of drugs for the skin but also dictate whether a drug reaches the blood flow unchanged or as activated or inactivated metabolite(s).

Effects of topical glutathione treatment in rat ischemic wound model

Oxidative stress secondary to ischemia can cause physiopathologic changes that adversely affect wound healing. In this experimental study, we hypothesized that the topical use of esterified glutathione, a well-known antioxidant, can minimize the effects of oxidative stress by an increase in intracellular glutathione and accelerate wound healing by increasing the contraction capacity of fibroblasts and preventing keratinocytes from apoptosis in a rat ischemic wound model. Experimental models were divided into 3 groups as treatment, control, and healthy. Bipedicled flaps were elevated from the dorsum of the rats, and 6-mm punch wounds were created at the end of the first day when the ischemia is most apparent. Wounds were followed histopathologically and immunohistochemically, and matrix metalloproteinase (MMP)-1 and tissue inhibitors of metalloproteinase (TIMP-1) levels were measured by ELISA. Samples were collected at 0, 5, 8, 10, and 12 days. Histopathologic evaluation revealed significant extracellular matrix deposition and reepithelization every fifth day in treatment and healthy groups when compared with control group. Immunohistochemical evaluation revealed increased apoptosis in basal keratinocytes in the control group when compared with the other groups. The evaluation of the samples collected at 5 and 8 days revealed increased MMP-1 levels in treatment and control groups, but the increase in TIMP-1 levels was more significant than MMP-1 levels in treatment group. MMP-1/TIMP-1 ratio was significantly low in the treatment group.Our results showed that topical GSH treatment can reduce oxidative stress, and the reestablishment of the MMP-1/TIMP-1 ratio gives way to adequate and regular extracellular matrix production and reepithelization. It is concluded that esterified GSH, which is experimentally shown to be effective in ischemic wound healing, can be used clinically in ischemic wounds.

Ischemic preconditioning: a defense mechanism against the reactive oxygen species generated after hepatic ischemia reperfusion

BACKGROUND

Preconditioning protects against both liver and lung damage after hepatic ischemia-reperfusion (I/R). Xanthine and xanthine oxidase (XOD) may contribute to the development of hepatic I/R.

OBJECTIVE

To evaluate whether preconditioning could modulate the injurious effects of xanthine/XOD on the liver and lung after hepatic I/R.

METHODS

Hepatic I/R or preconditioning previous to I/R was induced in rats. Xanthine and xanthine dehydrogenase/xanthine oxidase (XDH/XOD) in liver and plasma were measured. Hepatic injury and inflammatory response in the lung was evaluated.

RESULTS

Preconditioning reduced xanthine accumulation and conversion of XDH to XOD in liver during sustained ischemia. This could reduce the generation of reactive oxygen species (ROS) from XOD, and therefore, attenuate hepatic I/R injury. Inhibition of XOD prevented postischemic ROS generation and hepatic injury. Administration of xanthine and XOD to preconditioned rats led to hepatic MDA and transaminase levels similar to those found after hepatic I/R. Preconditioning, resulting in low circulating levels of xanthine and XOD activity, reduced neutrophil accumulation, oxidative stress, and microvascular disorders seen in lung after hepatic I/R. Inhibition of XOD attenuated the inflammatory damage in lung after hepatic I/R. Administration of xanthine and XOD abolished the benefits of preconditioning on lung damage.

CONCLUSIONS

Preconditioning, by blocking the xanthine/XOD pathway for ROS generation, would confer protection against the liver and lung injuries induced by hepatic I/R.

Protective effect of ozone treatment on the injury associated with hepatic ischemia-reperfusion: antioxidant-prooxidant balance

The effects of ozone treatment on the injury associated to hepatic ischemia-reperfusion (I/R) was evaluated. Ozone treatment (1 mg/kg daily during 10 days by rectal insufflation) is shown to be protective as it attenuated the increases in transaminases (AST, ALT) and lactate levels observed after I/R. I/R leads to a decrease in endogenous antioxidant (SOD and glutathione) and an increase in reactive oxygen species (H2O2) with respect to the control group. However, ozone treatment results in a preservation (glutathione) or increase (SOD) in antioxidant defense and maintains H2O2 at levels comparable to those in the control group. The present study reports a protective effect of ozone treatment on the injury associated to hepatic I/R. The effectiveness of ozone could be related to its action on endogenous antioxidants and prooxidants balance in favour of antioxidants, thus attenuating oxidative stress.

Thiol depletion induces apoptosis in cultured lung fibroblasts

Thiol antioxidants are implicated in the protection of cells from oxidative injury. We studied the role of thiols in the regulation of apoptosis in cultured lung fibroblasts. Thiol depletion by culturing fibroblasts in cystine-free medium or with thiol-depleting agents induced oxidant accumulation and cell death by apoptosis. The cell death was prevented by the antioxidants ascorbic acid (AA) and catalase. Thiol depletion also induced leukotriene (LT) C4, LTD4, and LTE4 production and selective phosphorylation of p38-mitogen-activated protein kinase (MAPK) and its nuclear substrate ATF2. LT production and p38-MAPK phosphorylation were required for induction of apoptosis because thiol depletion-induced apoptosis was completely blocked by the 5-lipoxygenase inhibitor AA861, the LT antagonists FPL55712 and ONO1078, and the p38-MAPK inhibitor SB203580. LT production was inhibited by AA and p38-MAPK phosphorylation was inhibited by AA, AA861, and FPL55712. In an in vitro scratch wound model, repopulating fibroblasts at the wound margin, but not quiescent cells at the intact site, selectively underwent thiol depletion- induced apoptosis that was completely blocked by AA861, FPL55712, and SB203580. Thus, thiol depletion induces apoptosis through an ordered pathway involving oxidant accumulation, LT production, and p38-MAPK activation. Apoptosis of wound fibroblasts may be responsible for impaired wound healing in various organs, including the lung.

Effects of glutathione depletion on oxidant-induced endothelial cell injury

Ischemia-reperfusion produces edema in vivo by disrupting endothelial cell junctional integrity. A cultured rat pulmonary artery endothelial cell (RPAEC) model was used to analyze the effects of oxidants and ischemic plasma in vitro. RPAEC cultures were treated with ischemic human plasma from transverse rectus abdominis musculocutaneous (TRAM) flaps following mastectomy or with an equal quantity of nonischemic plasma taken peripherally. Endothelial cells treated with ischemic plasma rounded and formed gaps within 5 min, then ruffled and blebbed after 10 min. Cultures treated with human nonischemic plasma had no gross morphological changes. Additionally, cultures treated with human ischemic plasma demonstrated an increase in diffusion rate of 125I-albumin across monolayers while monolayers treated with human nonischemic plasma had no increase in diffusion rate. RPAEC monolayers were treated with malic acid diethyl ester (DEM) or L-buthionine-[S, R]-sulfoximine (BSO) to decrease cellular stores of glutathione before exposure to oxidant stress. Cultures depleted of cellular glutathione stores were significantly (P < 0.05) more susceptible to 50 microM H2O2 than controls, as determined by an increase in diffusion rate of 125I-albumin across monolayers. To determine if ischemic plasma effects were mediated by oxidants, cultures were depleted of glutathione by DEM or BSO pretreatment before exposure to plasma from the ischemic hind limbs of Sprague-Dawley rats. Glutathione-depleted RPAEC monolayers were significantly (P < 0.05) and substantially (2-3 X) more susceptible to the effects of ischemic plasma than were cultures with normal glutathione levels. Glutathione depletion had no effect on cultures treated with an equal amount of nonischemic plasma from sham-operated rats. These data strongly suggest that ischemic plasma in the absence of any cellular component are able to induce an oxidant injury in endothelial cells and thereby compromise junctional integrity.

The effect of cobalt chloride on skin flap survival

The effects of cobalt chloride on ischaemia-reperfusion injury were evaluated in skin flaps. Groin neurovascular island flaps, 3 x 6 cm, were elevated in rats and subjected to primary and secondary ischaemia. Primary ischaemia was produced by 1 hour occlusion of the femoral artery and vein and, 22 hours later, secondary ischaemia was produced by 3 hours venous occlusion. The treatment group received intraperitoneal cobalt chloride (5 or 10 mg/kg) at the time of secondary ischaemia. Flap survival was 80% in the control, 10 to 20% in the cobalt chloride treated, and 20% in the cobalt plus mannitol group. Mannitol (100 mg/kg) failed to prevent the harmful effects of cobalt. Skin flaps exposed to cobalt chloride exhibited increased thiobarbituric acid reactant (TBAR) levels of 20 to 30 times normal. Of the antioxidant enzymes, glutathione peroxidase activity increased by 40% (P < 0.01), whereas glutathione reductase activity decreased by 40% (P < 0.01) in the cobalt exposed groups. Glucose 6-phosphate dehydrogenase activity was not affected.