Leukocytic .O2- and cardiac dysfunctions in isolated perfused rat hearts

Activation of renal haeme oxygenase-1 alleviates gentamicin-induced acute nephrotoxicity in rats

Objectives

This study aimed to investigate whether activation of haeme oxygenase (HO)-1 enzyme by haemin would have beneficial effects on the functional and histological outcome against gentamicin-induced renal damage in rats and sought to elucidate the underlying mechanisms of the therapeutic action.

Methods

Nephrotoxicity was induced by injection of gentamicin (80 mg/kg, i.p.) once daily for seven days. Haemin (50 μmol/kg, i.p.) was given to the control and gentamicin-treated rats in the presence or absence of a HO-1 inhibitor, zinc protoporphyrin IX (ZnPP, 50 μmol/kg per day, i.p.).

Key findings

Haemin treatment prevented gentamicin-induced elevated serum creatinine, urinary protein levels and ameliorated the impaired creatinine clearance. Haemin compensated the deficits in antioxidant enzyme activity and attenuated lipid peroxidation along with decreased reactive oxygen species (ROS) production in renal tissues due to gentamicin. Moreover, haemin pre-administration evoked increased renal HO-1 activity. Additionally, haemin significantly attenuated elevated renal tumour necrosis factor-α (TNF-α), nuclear factor-kappaB (NF-κB) levels and caspase-3 activity alongside ameliorating glomerular pathology. These therapeutic effects were abolished by ZnPP pretreatment.

Conclusions

Here is the first evidence demonstrating the protective effect of HO-1 against gentamicin-associated nephrotoxicity. Suppression of oxidative/inflammatory insults alongside the corresponding decline of apoptosis were presumably responsible for this renoprotection.

Biological role of the N-formyl peptide receptors

Ligation of N-formyl-methionyl-leucyl-phenylalanine (fMLP) to its specific cell surface receptors triggers different cascades of biochemical events, eventually leading to cellular activation. The formyl peptide receptors (FPRs) are members of the seven-transmembrane, G-protein coupled receptors superfamily, expressed at high levels on polymorphonuclear and mononuclear phagocytes. The main responses elicited upon ligation of formylated peptides, referred to as cellular activation, are those of morphological polarization, locomotion, production of reactive-oxygen species and release of proteolytic enzymes. FPRs have in recent years been shown to be expressed also in several non myelocytic populations, suggesting other unidentified functions for this receptor family, independent of the inflammatory response. Finally, a number of ligands acting as exogenous or host-derived agonists for FPRs, as well as ligands acting as FPRs antagonists, have been described, indicating that these receptors may be differentially modulated by distinct molecules.

Cellular responses to FMLP challenging: a mini-review

FMLP (N-formyl-methionyl-leucyl-phenylalanine) and other N-formylpeptides are powerful "activators" of polymorphonuclear and mononuclear phagocytes, but they are also active on other cell types. Present knowledge about formylpeptide receptors and the relevant tools for their imaging and the study of their dynamics are briefly discussed. The main responses elicited by FMLP in granulocytes are cell polarisation, the generation of reactive oxygen species, the production of arachidonic acid metabolites, and the release of lysosomal enzymes. The transduction cascades involved and the agents able to modulate these responses are reviewed. Homologous desensitization and heterologous desensitization of the FMLP-receptor following ligation of other chemokine receptors are also outlined. Finally, the receptor expression and the pharmacological and toxic actions of FMLP upon other tissues and organs, and its actions on the developing embryo, are illustrated.

Rabbit polymorphonuclear leukocytes release a factor that causes constriction of the coronary vasculature

Polymorphonuclear leukocytes (PMN) have been shown to have numerous vasoactive effects, particularly in large artery bioassays. This study shows that rabbit PMN passively release a contractile factor that constricts the coronary vasculature of isolated, Langendorff-perfused rabbit hearts. The mechanism of action of this factor does not involve inhibition of nitric oxide (NO), production of cyclooxygenase metabolites, 5-hydroxytryptamine, or endothelin, or the activation of alpha-adrenoceptors but is a Ca2+-dependent process, because the constriction is inhibited by the Ca2+-channel blocker amlodipine. The activity of this factor is significantly inhibited if it is pretreated with trypsin or heated to 90 degreesC for 10 min, and the active factor is concentrated in the retentate of 100-kDa cutoff centrifuge filters, indicating that the factor is a protein >100 kDa in size. This study shows that rabbit PMN spontaneously release a protein factor that causes constriction of isolated, perfused rabbit hearts by a NO-independent but Ca2+-dependent mechanism.

Do nitroxides protect cardiomyocytes from hydrogen peroxide or superoxide?

The aim of the research was to study the role played by extracellular O2-radicals, which are implicated in cardiac cell damage and the protective effect by cell-permeable, nitroxide, superoxide dismutase-mimics. Cardiomyocytes cultures from 1-day-old rats served as the test-system. Experiments were performed since 5th day in culture when > 80% of the cells were beating myocardial cells. Oxidative damage was induced by 0.5 mM hypoxanthine and 0.06 U/ml xanthine oxidase or by 10 mM glucose and 0.15 U/ml glucose oxidase. The parameters used to evaluate damages were spontaneous beating, lactate dehydrogenase release and ATP level. The rhythmic pulsation was followed microscopically. To determine the kinetics of cytosolic enzyme release from the cells, media samples were collected at various points of time and assayed for enzyme activity. To determine the cellular ATP, cells were washed with sodium phosphate buffer, scraped off and boiled for 3 min with sodium phosphate buffer. Following centrifugation the supernatant was collected and ATP was determined by the chemiluminogenic assay using firefly tails. The present results indicate that nitroxide stable free radicals in the millimolar concentration range, provide full protection without toxic side-effect. Unlike exogenously added SOD that failed to protect, exogenous catalase provided almost full protection. In addition, the metal-chelating agent dipyridyl, but not diethylene-triamine-pentaacetate or desferrioxamine, protected the cultured cells. The present results suggest that H2O2 is the predominant toxic species mediating the oxidative damage whereas extracellular superoxide radical does not contribute to cultured cardiomyocyte damage.(ABSTRACT TRUNCATED AT 250 WORDS)

Postischemic dysfunction of the heart induced by small numbers of neutrophils via formation of hypochlorous acid

The role of polymorphonuclear neutrophils (PMN) in the injury of the heart following ischemia and reperfusion is still controversial. The aim of this study was to investigate whether small numbers of PMN may cause myocardial dysfunction in an isolated system, how the resulting loss of function can be characterized and whether the formation of hypochlorous acid (HOCl) can be responsible for the PMN-mediated effect. Isolated working guinea pig hearts were subjected to a 90% reduction of coronary flow for 30 min, with or without intracoronary infusion of homologous PMN (approximately 1-2 x 10(5) cells/min, i.e. about 5-10% of normal blood count). This ischemia was followed by a 15 min reflow period in a non-working ("Langendorff") mode before work was resumed. In hearts perfused only with buffer, post-hypoxic heart function recovered to 75-80% of the initial value. Inclusion of unstimulated PMN did not further attenuate cardiac function. However, cardiac output was decreased to 42% of the initial value, provided thrombin (0.3 U/ml) and H2O2 (10(-5) M) were also present, and the retained PMN (about 10% of those infused) were additionally stimulated during reflow by application of FMLP (10(-6) M for 1 min). In these instances, coronary flow at any time of the experiment and release of lactate or purines during ischemia and reflow did not differ significantly between hearts perfused with or without PMN. There was no substantial release of myoglobin in controls and in PMN-treated hearts. Inotropic stimulation of the hearts with noradrenaline or exogenous Ca2+ caused a sustained increase in contractile force. However, the response was significantly reduced in PMN-perfused hearts in comparison to control hearts. The myocardial contents of high-energy phosphates with and without inotropic stimulation proved to be identical irrespective of whether experiments had been performed in the absence or presence of PMN. A similar loss of myocardial function as mediated by PMN could be produced by infusing chemically generated hypochlorous acid (HOCl, 5 x 10(-7) M for 10 min). Strikingly, that portion of the infused HOCl which actually reacted with cardiac tissue was comparable to the amount shown to be generated by stimulating 10(6) PMN retained in the coronary system (about 7 nmoles). Supplementing the perfusate with the scavengers L-methionine (10(-4) M) or uric acid (5 x 10(-4) M) prevented the attenuation of heart function provoked by PMN. The results indicate that small numbers of PMN, sufficiently activated, can depress cardiac function after 30 min of ischemia.(ABSTRACT TRUNCATED AT 400 WORDS)