Paul F. Shanley

Neutrophils contribute to TNF induced myocardial tolerance to ischaemia

Sublethal endotoxin (ETX) pretreatment of rats induces protection from cardiac ischaemia-reperfusion injury. This protective state is associated with increased endogenous myocardial catalase activity. Since tumour necrosis factor (TNF) is one mediator of ETX effects, we hypothesized that (TNF) pretreatment of the rat (30 micrograms/kg ip) 36 h prior to cardiac ischaemia-reperfusion could induce myocardial protection. We found that TNF administration increased both myocardial tolerance to ischaemia reperfusion injury (modified Langendorff, buffer perfusion, global, normothermic ischaemia) and myocardial catalase activity at 36 h. Moreover, we found that 6 h after TNF administration, myocardial hydrogen peroxide (H2O2, assessed by aminotriazole-H2O2 inactivation of catalase) and myocardial neutrophil accumulation (assessed by histology) were both increased. When neutrophil function was inhibited either by neutrophil depletion (vinblastine) or by ibuprofen treatments of the rat before TNF, the protection previously apparent at 36 h was blocked. We conclude that TNF can induce myocardial resistance to ischaemia reperfusion injury. This protection is related to prior tissue neutrophil accumulation and concomitant increases in H2O2 levels.

FNLP injures endotoxin-primed rat lung by neutrophil-dependent and -independent mechanisms

Bacterial lipopolysaccharide (LPS) and an N-formyl peptide, N-formyl-neoleucyl-leucyl-phenylalanine (FNLP), synergistically promote lung injury in rats as measured by 125I-labeled albumin flux. Concomitantly, neutrophils are sequestered in the lung. We hypothesized that LPS-FNLP-induced lung injury is mediated both by neutrophil-dependent and -independent mechanisms. Rats were depleted of circulating and marginating neutrophils with vinblastine. LPS-FNLP-induced lung protein leak was partially decreased in these neutrophil-depleted animals, although a component of lung injury remained. We hypothesized that LPS-FNLP-induced lung injury was also mediated by xanthine oxidase (XO). Rats were fed a tungsten-enriched diet that inactivates molybdenum-dependent oxidase systems. LPS-FNLP-induced lung leak was partially decreased in these animals as well. When tungsten-fed rats were also neutrophil depleted with vinblastine, no increase in 125I-albumin flux was observed in response to LPS-FNLP. In parallel experiments, lungs from vinblastine-pretreated rats were isolated and perfused. FNLP infusion into the LPS-primed, crystalloid-perfused lungs caused increased 125I-albumin flux, which was prevented by oxidase inhibition. We conclude that LPS-FNLP-induced lung injury is both neutrophil mediated and neutrophil independent. The nonneutrophil component of the LPS-FNLP-induced lung injury appears to be pulmonary XO derived and dependent.

Renal response to shock

Renal hypoperfusion such as occurs in shock creates an environment in which cellular injury and organ dysfunction can occur during the episode of shock as well as during reoxygenation and reperfusion. A severe decrement in oxygen delivery compromises energy (adenosine triphosphate) production, leading to various degrees of cell injury ranging from cell swelling to acute cortical necrosis. These different responses of the kidney to shock explain the multiple clinical presentations varying from an isolated loss of concentrating ability to prolonged anuria. Many cellular events contribute to renal cell injury, including cellular ATP depletion, cellular and mitochondrial calcium overload, and activation of phospholipases and oxygen radical formation. Recent clinical and experimental studies suggest that ATP-MgCl2, free radical scavengers, diuretics, vasodilators, and calcium channel blockers appear to be beneficial in preventing acute tubular necrosis after anoxic or severe hypoxic insults. Thus these agents may be helpful in altering the course of acute renal failure in shock patients and may decrease their morbidity and mortality.

Differential Susceptibility to Gentamicin Toxicity Within the Proximal Convoluted Tubule

The proximal convoluted tubule (PCT) is the major target for injury in gentamicin nephrotoxicity but the necrosis is often patchy and focal. The PCT is structurally, functionally, and metabolically heterogeneous, and the possibility of differential vulnerability to gentamicin-induced necrosis based on this heterogeneity has not been examined. A quantitative analysis comparing the extent of necrosis in the initial portion of the PCT (S1) to that in the more distal PCT (S2) and comparing necrosis in the PCT of superficial nephrons to that in juxtamedullary nephrons was done in rats after eight daily intraperitoneal doses of 100 mg gentamicin/kg rat weight. The results indicate that the PCT of superficial nephrons are more susceptible to necrosis than the PCT of juxtamedullary nephrons and that the initial S1 segment even in the superficial nephrons is remarkably resistant to injury. These findings suggest that some aspects of the functional or metabolic heterogeneity within the PCT may be related to either differential rates of uptake of the drug or to differences in intrinsic susceptibility to its toxic effects.

Oxygen metabolites and hypoxic renal injury: effect of mitochondrial electron transport blockade.

Isolated perfusion of the rat kidney causes hypoxic damage in the cells of the thick ascending limb of the loop of Henle. The cell damage is driven by active solute transport, which generates an imbalance of oxygen supply and demand. This injury is paradoxically prevented by adding the mitochondrial electron transport inhibitors rotenone or antimycin to the perfusion media. The present study shows that rotenone and antimycin decrease production of hydrogen peroxide in the thick ascending limb during perfusion. The findings support the hypothesis that the injury in this model is dependent on mitochondrial electron flow and suggest that mitochondrial electron flow, driven by the work of active solute transport in the presence of limited oxygen availability, may result in the generation of toxic oxygen metabolites.

Childhood membranoproliferative glomerulonephritis type I: limited steroid therapy

Nineteen patients with biopsy proven membranoproliferative glomerulonephritis type I (MPGN I) and a minimum of three years of follow-up (mean 6.5 +/- 0.7 years) have been treated with an uncontrolled regimen of limited corticosteroids. Initial therapy ranged from 20 mg per os (po) every other day to 30 mg/kg/day i.v. for three consecutive days, depending on clinical disease severity. Therapy was then decreased based on each patients improving clinical status. At diagnosis creatinine clearance (CCr) was less than 80 ml/min/1.73 m2 in 12 patients and less than 50 in 2. All patients had hematuria and proteinuria, with 15 in the nephrotic range. Hypertension, present at diagnosis in 13, developed in five others following institution of prednisone, and was controlled medically. Renal biopsy was repeated after two years of therapy prior to cessation of treatment (mean total treatment duration 38 +/- 3 months). Follow-up biopsy revealed decreased glomerular inflammatory activity in 88% of patients. All patients have now been off prednisone for 40 +/- 9 months. The mean CCr is 126 +/- 5 ml/min/1.73 m2. Eight patients have normal urinalyses. These data suggest that early therapy with a limited course of corticosteroids, and control of associated hypertension, may forestall progressive renal insufficiency in children with MPGN type I.