Polynitroxyl albumin plus tempol attenuates liver injury and inflammation after hepatic ischemia and reperfusion.

PNA+Tempol, albumin containing conjugated (polynitroxyl albumin; PNA) and free (4-hydroxyl-2,2,6,6-tetramethyl-piperidinyl-1-oxyl; Tempol) nitroxide may protect against injury caused by reactive oxygen species. Therefore, the actions of PNA+Tempol on liver injury and inflammation induced by hepatic ischemia and reperfusion (I/R) were examined. Rats were subjected to 1 h ischemia followed by 24 h reperfusion in the absence (I/R) or presence of PNA+Tempol (25%; 15 mL/kg, i.v.) (I/R+PNA+Tempol) or human serum albumin (23%; 13.5 mL/kg, i.v.) (I/R+HSA). Test solutions were administered prior to and for 2 h during reperfusion. Sham-operated rats underwent surgery with neither ischemia nor infusion. I/R+PNA+Tempol rats had significantly less liver injury and inflammation than I/R rats. I/R+PNA+Tempol livers exhibited focal lesions whereas I/R livers exhibited global necrosis. Likewise, plasma ALT activity was significantly lower in I/R+PNA+Tempol rats. PNA+Tempol reduced I/R-induced neutrophil accumulation and intercellular adhesion molecule-1 (ICAM-1) expression. HSA did not alter I/R-induced liver injury or inflammation. Sham-operated rats exhibited normal liver morphology and no inflammation. Attenuation of I/R liver injury by PNA+Tempol may be mediated by its effect on inflammation, the major contributor to I/R injury. Reduction of inflammation by PNA+Tempol is most likely due to the antioxidative nature of the nitroxides.

Hepatic inflammatory responses to alphaalpha-cross-linked hemoglobin infusion in rats.

Cross-linked hemoglobin (alphaalpha-Hb) may be a useful red blood cell substitute if it can be administered safely. However, cell-free hemoglobin has inherent properties that may cause oxidant-mediated toxicity. We investigated whether alphaalpha-Hb induces oxidative or inflammatory responses that lead to liver damage. alphaalpha-Hb (0.5 or 1.0 gm/kg) was infused into rats, and indices of liver injury, inflammation, and oxidative stress were examined. Although focal hepatic necrosis was noted at 24 hours, plasma alanine aminotransferase activity was not increased and lesions were resolved by 48 hours. Modest neutrophil accumulation in hepatic vessels, but not sinusoids, occurred at 24 hours. Heme oxygenase-1 (HO-1) protein and activity were induced in a dose- and time-dependent manner, with maximal induction at 24 hours. Plasma tumor necrosis factor-alpha levels were not significantly increased. Additional cytokine- and oxidant-mediated events such as nuclear transcription factor-kappaB activation and nitric oxide synthase induction were not observed. These results suggest that alphaalpha-Hb-derived products such as heme and ferric iron (Fe3+), potent inducers of HO-1, are responsible for increasing HO-1. HO-1 induction may be a protective response by the liver to metabolize excess heme and Fe3+, thereby providing antioxidative products to counter the potentially damaging oxidants produced by Fe3+-catalyzed reactions.

A comparative study of the bronchodilator effect and duration of action of liposome encapsulated beta-2 adrenergic agonists in the guinea-pig.

The abilities of the adrenergic beta-2 agonists metaproterenol and albuterol in free and liposome encapsulated forms to prevent the bronchoconstrictor response to histamine (10 micrograms/kg i.v.) were compared in anesthetized guinea-pigs. Intratracheal instillation of the unencapsulated adrenergic agonists prevented the histamine bronchoconstriction in a dose dependent fashion. Liposomal metaproterenol was less effective in this regard than the same doses of free drug. In contrast, liposomal albuterol produced an initial bronchodilator effect which was similar to comparable doses of free albuterol but the effect was sustained for a longer duration. These data suggest that intratracheal liposome encapsulated bronchodilators were releashed slowly to the bronchi. This slow release rate reduced the available concentrations of metaproterenol below that required for bronchodilator effects, but the more potent albuterol achieved an active concentration and showed a more sustained duration of action. Further, studies showed that liposome encapsulated material could be aerosolized using a standard air blast nebulizer without significant difference (compared to free drug) in the mass of drug delivered or alteration in the percentage of the drug encapsulated within the liposomes.

Retention of topical liposomal formulations on the cornea.

The ability of liposomes composed of different kinds of phospholipid materials to adhere to the surface of the cornea was studied in the rabbit. The liposomes were labelled with tracer amounts of an I125-labelled phosphatidylethanolamine derivative and were instilled in 10 microliters drops onto the cornea. The retention of radioactivity was monitored. The results show that liposomes containing positively charged phospholipids are better retained than an albumin control. Thus, it may be possible to develop a drug delivery liposome system which would permit long-term sustained release of ophthalmic drugs onto the cornea.

The determination of myeloperoxidase activity in liver.

Myeloperoxidase (MPO) is an enzyme found in granulocytes of neutrophils, but not in mammalian tissues. Previous studies have directly correlated MPO activity with neutrophil accumulation in tissues. This study presents a method for determining MPO activity in liver. Neutrophil accumulation in rat liver was provoked by creating partial ischemia followed by reperfusion. Liver homogenates prepared by a standard procedure showed no MPO activity. The homogenate was applied to Sephadex G100 and DEAE Sepharose CL6B columns which separated MPO activity from inhibitory activity. The inhibitor was identified as catalase based upon its elution from the columns and removal with 3-amino- 1,2,4-triazole (AT), a catalase inhibitor. Based upon these findings, it was determined that full MPO activity can be assayed in unfractionated liver homogenates by first inactivating catalase with AT.

Cerebrovascular autoregulation is resistant to calcium channel blockade with nimodipine.

In normal baboons cerebrovascular resistance changed along with blood pressure to maintain blood flow constant. This 'autoregulation' was not significantly altered in animals treated with a dose of the calcium channel blocker nimodipine causing selective cerebral vasodilation.

Mechanisms of vascular supersensitivity in hypercholesterolemia.

We have characterized in vitro, for the first time, the phenomenon of acute interaction between hypercholesterolemia and cerebrovascular function. We then used this model to investigate a number of mechanisms for the interaction. Rabbits fed a diet supplemented with 2% cholesterol developed hypercholesterolemia over 4 weeks with no histologically detectable atherosclerosis. This absence of anatomic change was reflected in normal biophysical elastic responses to graded radial stretch and normal optimum tension for responses to exogenous K+ in the selected arteries. However, basilar arteries removed from cholesterol-fed rabbits showed abolished myogenic responses to radial stretch and decreased median effective doses for added norepinephrine. These potentiated constrictor responses to norepinephrine were significantly correlated with increased plasma cholesterol concentration. A mechanism related to the opening of membrane calcium channels may be responsible for the supersensitivity.

Hypercholesterolemia and the baboon cerebral circulation.

We investigated cerebrovascular vasodilator responses to increased arterial CO2 and the cerebrovascular response to infused 5-hydroxytryptamine (5-HT) in normal and hypercholesterolemic baboons. After 6-8 weeks of feeding an atherogenic diet the plasma cholesterol levels were increased without change in the triglycerides. The hypercholesterolemic animals showed a higher basal systemic arterial blood pressure than the normal controls without significant decrease in cerebrovascular prostacyclin production, altered basal cerebral blood flow or altered cerebrovascular response to infused 5-HT. However, the vasodilator response to hypercapnia was significantly decreased from the control value of 2.78 ml/min per mmHg increase in PCO2, to 1.62 ml/min per mmHg. Thus functional impairment of cerebral hemodynamics occurred before atherosclerotic alteration in the cerebral vessels could have been present.

In vivo actions of a calcium channel blocker (nimodipine) on the cerebrovascular response to infused 5-hydroxytryptamine.

Previous in vitro studies show that the calcium channel blocker, nimodipine, inhibits the cerebrovascular contraction elicited by 5-hydroxytryptamine (5-HT). The present study determined if this effect was present in vivo in the baboon cerebral circulation rendered sensitive to infused 5-HT by prior intracisternal injection of autologous blood. Five to seven days after injection of this blood the five baboon displayed a vasoconstrictor response to intracarotid 5-HT at 10 micrograms/kg/min (cerebrovascular resistance increased from 2.19 +/- 0.16 to 2.75 +/- 0.30 mm Hg/ml X min-1). Subsequent i.v. infusion of nimodipine produced cerebral vasodilation with an efficacy similar to that in normal baboons. Reinfusion of 5-HT during nimodipine infusion caused a cerebrovascular resistance increase of similar magnitude to that in the prenimodipine test. These results suggest that nimodipine produces cerebral vasodilation after a mild cerebrovascular insult but did not significantly reduce the vasoconstrictor response to 5-HT.

The role of prostacyclin in the hypercapnic and hypoxic cerebrovascular dilations.

The cerebral blood flow (CBF H/A) and the production of a stable prostacyclin metabolite, 6-Keto PGF 1 alpha ( 6KPGF ) was studied in 5 baboons in control, hypercapnic and hypoxic conditions. In steady-state conditions CBF H/A was measured by the clearance of an intra-arterial bolus injection of 133xenon and arterial and cerebral venous blood was sampled for assay of 6KPGF by radioimmunoassay. Both hypercapnia and hypoxia significantly increased CBF H/A and both increments were abolished by indomethacin. However, only hypoxia showed an increased 6KPGF production. Thus, hypoxia, but not hypercapnia, appears to produce cerebral vasodilation by increasing prostacyclin production.

The effects of a calcium antagonist (nimodipine) on basal cerebral blood flow and reactivity to various agonists.

In vitro studies suggest that cerebrovascular contraction is more dependent on the influx of calcium to smooth muscle than general systemic arteries. The present study tested the in vivo effects of a calcium influx blocker (nimodipine) on cerebral blood flow and metabolism in 16 baboons. The 133xenon clearance technique was used together with careful control of EEG and blood gases. With normal blood gases intravenous nimodipine infusion (1 microgram/kg/min) produced an 18% increase in cerebral blood flow with no alteration in cerebral oxidative metabolism or blood pressure. Higher doses (above 10 micrograms/kg/min) resulted in a decreased arterial blood pressure and a return to control cerebral flow. Infusion of the dose producing maximal increase in flow, decreased the cerebral reactivity to altered PCO2 (n = 5). These results suggest that nimodipine may be a relatively selective cerebrovascular dilator.