Biochemical changes in the intestine associated with anoxia and reoxygenation: in vivo and in vitro studies

Propofol Attenuates Small Intestinal Ischemia Reperfusion Injury through Inhibiting NADPH Oxidase Mediated Mast Cell Activation

Both oxidative stress and mast cell (MC) degranulation participate in the process of small intestinal ischemia reperfusion (IIR) injury, and oxidative stress induces MC degranulation. Propofol, an anesthetic with antioxidant property, can attenuate IIR injury. We postulated that propofol can protect against IIR injury by inhibiting oxidative stress subsequent from NADPH oxidase mediated MC activation. Cultured RBL-2H3 cells were pretreated with antioxidant N-acetylcysteine (NAC) or propofol and subjected to hydrogen peroxide (H2O2) stimulation without or with MC degranulator compound 48/80 (CP). H2O2 significantly increased cells degranulation, which was abolished by NAC or propofol. MC degranulation by CP further aggravated H2O2 induced cell degranulation of small intestinal epithelial cell, IEC-6 cells, stimulated by tryptase. Rats subjected to IIR showed significant increases in cellular injury and elevations of NADPH oxidase subunits p47(phox) and gp91(phox) protein expression, increases of the specific lipid peroxidation product 15-F2t-Isoprostane and interleukin-6, and reductions in superoxide dismutase activity with concomitant enhancements in tryptase and β-hexosaminidase. MC degranulation by CP further aggravated IIR injury. And all these changes were attenuated by NAC or propofol pretreatment, which also abrogated CP-mediated exacerbation of IIR injury. It is concluded that pretreatment of propofol confers protection against IIR injury by suppressing NADPH oxidase mediated MC activation.

Danshen protects kidney grafts from ischemia/reperfusion injury after experimental transplantation

Danshen (DS) is used for treatment of various ischemic events in the traditional Chinese medicine. Hence, this study was designed to investigate its effect on ischemia/reperfusion injury (IRI) after experimental kidney transplantation (eKTx). Nephrectomized Sprague-Dawley rats underwent eKTx. Some animals were infused with 1.5 ml DS 10 min before surgery. Kidney grafts were transplanted after cold storage for 20 h in Histidine-Tryptophane-Ketoglutarate solution. After reperfusion blood samples were collected for blood urinary nitrogen (BUN), creatinine, lactate dehydrogenase (LDH), and alanine transaminase. Further, tissue was assessed for morphologic and pathophysiologic changes. Donor preconditioning with DS (DS-d) significantly decreased BUN, creatinine, LDH, and aspartate aminotransferase to 65-97% of controls while preconditioning of the recipient (DS-r) decreased values to 58-82% (P < 0.05). Tubular damage and caspase-3 decreased significantly in both DS-d and DS-r (DS-d: 96% and 67%, DS-r: 83% and 75% of controls) while heat shock protein 72 and superoxide dismutase increased significantly (DS-d: 143% and 173%, DS-r: 166% and 194% of controls). Further, inducible nitric oxide synthase and tumor necrosis factor-alpha decreased (DS-d: 84% and 61%, DS-r: 79% and 67% of controls) after DS. Preconditioning of both donors and recipients with DS significantly reduces IRI and thus improves graft function after eKTx.

Induction of LOX-1 and iNOS expressions by ischemia-reperfusion of rat kidney and the opposing effect of L-arginine

Lectin-like oxidized low-density lipoprotein receptor (LOX-1) is a newly identified endothelial cell surface major receptor for oxidatively modified low-density lipoprotein. Progression of arthrosclerosis in the donor organ after organ transplantation is a major problem. We hypothesized that ischemia-reperfusion induces LOX-1. After 1 h ischemia of bilateral kidneys plus 3, 6, or 12 h reperfusion, we first revealed that LOX-1 mRNA expression was increased in renal cortex and medulla at 6 h after reperfusion, which was decreased by L-arginine supplement. Plasma nitric oxide (NO) end-product nitrite plus nitrate and inducible nitric oxide synthase (NOS) expression were increased after reperfusion of 6 h. However, NOS substrate L-arginine did not augment but markedly decreased plasma NO end product, because L-arginine supplement suppressed inducible NOS expression in kidney. We hypothesized that available L-arginine is depleted by ischemia-reperfusion, leading to inducible NOS induction. Ischemia decreased L-arginine levels in kidney and L-arginine supplement increased NO end products in renal cortex in the earliest phase of reperfusion. These results disclosed for the first time that a deficiency in L-arginine by ischemia reperfusion causes uncoupling of constitutive NOS, which induces inducible NOS and LOX-1, implying why L-arginine is effective for stroke or transplantation in preventing atherosclerotic progress.

Evidence that the large loss of glutathione observed in ischemia/reperfusion of the small intestine is not due to oxidation to glutathione disulfide

Reperfusion injury following ischemia is thought to be the consequence of reactive oxygen species possibly generated either by xanthine oxidase activity or by processes associated with neutrophil activation in the affected organ or tissue. The conversion of xanthine dehydrogenase to the oxidase as well as the interactions between endothelium and neutrophils in the margination and activation of the latter are all considered to be results of conditions resulting from the ischemic episode. Determination of the redox status of glutathione in an ischemic/reperfused organ is frequently employed as an indicator of oxidative stress created by the production of oxygen free radicals during the reperfusion period. In this procedure, the ratio of oxidized glutathione (GSSG) to total glutathione (GSH + GSSG) is utilized to demonstrate the proportion of glutathione oxidized during reperfusion. We determined this ratio in the rat small intestine during ischemia and reperfusion and found that while the ratio of GSSG/(GSH + GSSG) does increase, this increase was the result of GSH disappearance rather than an increase in GSSG, and that essentially all of this loss occurred during the ischemic episode. We demonstrated that no oxidation of GSH occurred that was attributable to reperfusion per se; nor was there an increase of GSSG during this reoxygenation period.

Role of the epithelium in the control of intestinal motility: implications for intestinal damage after anoxia and reoxygenation

A vibration technique was used to dislocate the epithelium from the rat small intestine, in order to study the possible regulatory role of the epithelium on intestinal motility. Complete removal of the epithelium led to a slightly potentiated contraction of the longitudinal smooth muscle by the muscarinic agonist methacholine (pD2. 6.5 +/- 0.1 vs. 6.2 +/- 0.2). The maximal beta-adrenergic response expressed relative to the relaxation by 0.5 mM dibutyryl cyclic AMP increased from 55.9 +/- 9.0% to 72.6 +/- 9.1% by this treatment. Efforts were made to relate these observations to the endothelium-dependent relaxation in blood vessels, but no indication was found for a similar mechanism in the small intestine. Not only mechanical dislocation can be employed to affect the mucosal layer, but also intestinal ischemia has been reported to lead to mucosal damage. In this study we mimicked ischemia by applying in vitro anoxia and subsequent reoxygenation to isolated intestinal segments. When intestinal segments are isolated and kept in physiological buffer, xanthine dehydrogenase is converted slowly to xanthine oxidase, irrespective of whether the buffer is oxygenated or not. No evidence was found for oxygen radical damage after anoxia and reoxygenation. However, the intestinal mucosa was damaged both after normoxia, and after anoxia and reoxygenation. Anoxia and subsequent reoxygenation did not affect muscarinic contraction, but slightly increased the beta-adrenergic relaxation, which partly correlates with the effects of mechanical dislocation of the epithelium. The increased sensitivity of the smooth muscle after epithelial damage might be involved in motility changes during intestinal inflammatory diseases.

Role of reactive oxygen species in intestinal diseases

It is well known that reactive oxygen metabolites are generated during several pathologies, and that they are able to disturb many cellular processes and eventually lead to cellular injury. After intestinal ischemia, reactive oxygen species are produced when the ischemic tissue is reperfused. The enzyme xanthine oxidase is thought to play a key role in this process. As a result of this oxygen radical production, the permeability of the endothelium and the mucosa increases, allowing infiltration of inflammatory leukocytes into the ischemic area. Moreover, reactive oxygen species are also indirectly involved in leukocyte activation. In turn, these inflammatory cells respond with the production of oxygen radicals, which play an important role in the development of tissue injury. Thus, intestinal ischemia and reperfusion evokes an inflammatory response. Also during chronic intestinal inflammatory diseases, reactive oxygen metabolites are proposed to play an important role in the pathology. Scavenging of reactive oxygen species will thus be beneficial in these disorders.

Mechanism of lipid radical formation following exposure of epidermal homogenate to ultraviolet light

It has been suggested that oxygen free radicals are important mediators of lipid peroxidation in the epidermis exposed to ultraviolet (UV) light. However, it is not clear whether it is the superoxide anion radical (O2-.) or the hydroxyl radical (.OH) that plays the major role in producing the lipid radicals (L.) following UV exposure. In this study, we used electron spin resonance (ESR) technique with the spin trap (5,5-dimethyl-1-pyrroline-N-oxide [DMPO]) to determine which active oxygen species is involved in the UV-induced lipid radical formation (DMPO-L.: aN = 15.5 G, aH = 22.7 G). In the presence of superoxide dismutase or the metal-chelating agent, the DMPO-spin adduct spectrum of lipid radicals was reduced remarkably. The lipid radicals were formed by the hydroxyl radical generation system, not the superoxide anion generation system. The hydroxyl radical was found to be the direct active oxygen species that can generate lipid radicals as a result of .OH-mediated hydrogen atom abstraction. Superoxide anion radical stimulated the generation of hydroxyl radical via the iron-catalyzed reaction.

The toxicity of flavonoids to guinea pig enterocytes

Flavonoids, a group of compounds found primarily in vegetables and fruits, are generally believed to be beneficial to biological systems. Isolated guinea pig enterocytes were exposed to three of these compounds (kaempferol, quercetin, and myricetin) in concentrations of 50-450 microM. Toxicity was examined using trypan blue exclusion and lactic dehydrogenase (LDH) leakage. All three flavonoids produced cellular damage at 450 microM: compared with a control incubation, cellular viability was 12-60% lower and LDH leakage 28-41% greater after a 3-hr incubation. In addition, as assessed by trypan blue exclusion, quercetin and myricetin, both of which produce superoxide on autoxidation, appeared to be more toxic than kaempferol. These results suggest that dietary flavonoids may have the potential for producing intestinal injury.

Superoxide dismutase conjugated to polyethylene glycol provides sustained protection against myocardial ischemia/reperfusion injury in canine heart

Disagreement regarding the cardioprotective role of superoxide dismutase may relate to the use of different durations for induction of ischemic injury and reperfusion. The present study employed superoxide dismutase conjugated to polyethylene glycol (PEG-SOD), which has a half-life greater than 30 hours. Two protocols differing in the mode of administration and the duration of the reperfusion interval were used. Dogs were subjected to occlusion of the circumflex coronary artery for 90 minutes, then reperfused for 6 hours (Protocol A) or 4 days (Protocol B). The dogs received either polyethylene glycol conjugated to albumin (PEG-ALB) or PEG-SOD (1,000 U/kg). In Protocol A, treatment was administered starting 15 minutes before coronary occlusion and continued for 2 hours, terminating 15 minutes after reperfusion. Infarct size was determined 6 hours later. In Protocol B, the conjugated proteins were given 15 minutes before reperfusion and ended simultaneously with reperfusion. Infarct size was measured after 4 days. Infarct size (percentage of area at risk) in control (n = 9) and treated (n = 9) dogs in Protocol A differed between groups: 46.7 +/- 3.5% versus 28.3 +/- 2.9%, respectively (p less than or equal to 0.005); risk regions did not differ: 42.8 +/- 1.5% versus 43.8 +/- 2.1%, respectively. Myocardial salvage also was observed in Protocol B. Infarct size in control (n = 13) and treated (n = 13) groups was 44.2 +/- 2.6% versus 29.2 +/- 1.6%, respectively (p less than or equal to 0.005), with risk regions being 44.4 +/- 1.4% versus 46.0 +/- 1.6% (p = NS). Hemodynamic variables did not differ during the period of coronary artery occlusion. The respective collateral blood flows to the inner two thirds of the ischemic myocardium determined 60 minutes after occlusion were 0.05 +/- 0.01 ml/min/g and 0.06 +/- 0.04 ml/min/g (p = 0.806) for the PEG-ALB and PEG-SOD treated groups, respectively. Infarct size was related inversely to collateral blood flow in the PEG-ALB treated group. This relation shifted downward (analysis of covariance, p = 0.017). Plasma SOD activity in Protocols A sustained for 6 hours. Significant enzymatic activity was present after 4 days in Protocol B. Previous negative studies with native SOD may be related to the short half-life of its free-radical scavenging capacity, which compromises the chances of observing a protective effect after 4 days of reperfusion. The present results support our previous observations, as well as those of other investigators, demonstrating that superoxide dismutase can reduce that component of myocardial injury associated with reperfusion.

Spin trapping: ESR parameters of spin adducts

Spin trapping has become a valuable tool for the study of free radicals in biology and medicine. The electron spin resonance hyperfine splitting constants of spin adducts of interest in this area are tabulated. The entries also contain a brief comment on the source of the radical trapped.