Antiperoxynitrite strategies for the experimental therapy of shock

Mobilization of intracellular calcium by peroxynitrite in arteriolar smooth muscle cells from rats

The present study was designed to investigate the possible effects of peroxynitrite (ONOO(-)) on the intracellular calcium concentration ([Ca(2+)](i)) of mesenteric arteriolar smooth muscle cells (ASMCs), and to reveal the underlying mechanisms by using fluorescence imaging analysis. The results showed that ONOO(-) could exert a concentration- and time-dependent but also a dual effect on [Ca(2+)](i). Bolus administration with a low concentration of ONOO(-) (25 microM) decreased [Ca(2+)](i), whereas higher concentrations (50 or 100 microM) increased [Ca(2+)](i) persistently. Further experiments demonstrated that pretreatment of ASMCs with calcium-free medium completely abolished [Ca(2+)](i) increase by 100 microM ONOO(-). Additionally, nifedipine, an antagonist of selective L-type voltage-gated calcium channels (VGCCs), delayed the [Ca(2+)](i) response to ONOO(-), and ryanodine, an inhibitor of intracellular calcium release from the sarcoplasmic reticulum, effectively antagonized [Ca(2+)](i) increase during the late stage of ONOO(-) exposure. Furthermore, [Ca(2+)](i) alteration by ONOO(-) appeared to be intimately associated with the subsequent membrane potential changes. Although the mechanisms by which ONOO(-) alters [Ca(2+)](i) are complex, we conclude that a series of variables such as external calcium influx, activation of VGCCs, intracellular calcium release, and membrane potential changes are involved. The decrease of [Ca(2+)](i) in ASMCs by a low concentration of ONOO(-) may participate in the pathogenesis of low vasoreactivity in shock, and the increase of [Ca(2+)](i) by high concentrations of ONOO(-) may lead to calcium overload with cellular injury.

Differential effects of neonatal endotoxemia on heart and kidney carnitine palmitoyl transferase I

BACKGROUND/PURPOSE

The heart and kidney are both affected in sepsis-related multiple organ failure. Both utilize fatty acid substrates during the neonatal period, and impairment of oxidative metabolism during sepsis could lead to bioenergetic failure. The enzyme carnitine palmitoyl transferase I (CPT I) is important in the control of fat oxidation in the neonatal period. The aim of this study was to determine the effects of sepsis on neonatal cardiac and renal CPT I.

METHODS

Suckling rats received 300 microgram/kg lipopolysaccharide intraperitoneally. Mitochondria were isolated from the heart and kidney after 2 hours. CPT I and II activity were measured radiochemically. Protein levels of M- and L- isoforms of CPT I, both of which are present in heart, were determined by Western blotting.

RESULTS

CPT I activity was decreased significantly in the heart but not in the kidney by endotoxemia, whereas CPT II activity was the same in each organ. To investigate the mechanism of this decrease, we carried out Western blotting of the CPT I isoforms in heart mitochondria. Neither M- nor L- isoform was decreased in amount. To determine whether free-radical attack could directly inhibit CPT I activity, control heart mitochondria were incubated with free-radical generating systems. Although hydrogen peroxide had no effect on CPT I activity, the reactive oxygen species nitric oxide, superoxide, and peroxynitrite, all of which are generated in the heart during sepsis, significantly inhibited CPT I activity.

CONCLUSIONS

The activity of CPT I, a rate-controlling step of fat oxidation, is significantly impaired in heart but not in kidney during neonatal sepsis. This may be caused by direct attack by free radicals, suggesting that antioxidant strategies could be of use in preventing sepsis-related cardiac damage.