Abating progressive tissue injury and preserving function after CNS trauma: The role of inflammation modulatory therapies

Brain and spinal cord injuries result in cognitive and/or sensorimotor impairments that can significantly diminish the quality of life for the patient and their carers, and result in healthcare system costs totaling in the billions. The current gold-standard of acute care for spinal cord injury is to administer high doses of glucocorticoids within 8 h of injury; administration after 8 h may be without effect or detrimental to the outcome of the patient. Therefore, improved pharmacological approaches for limiting the extent of tissue damage and neurological dysfunction in the acute injury setting are urgently needed. Early intervention in CNS injury by antagonizing or controlling the post-injury inflammatory process with pharmaceutical agents is a major focus of current clinical and preclinical investigations. In this editorial overview, recent clinical trials and preclinical studies of brain and spinal cord injuries are discussed, including studies focusing on the use of broad-spectrum immunosuppressive drugs (eg, minocycline); growth factors (eg, erythropoietin); dual anti-inflammatory and anti-vasospasm drugs, such as Rho and ROCK kinase inhibitors; and broad-spectrum anti-inflammatory drugs, such as PDE4 inhibitors. These new approaches hold great promise to improve outcomes for patients with brain and spinal injuries.

Up-regulation of glomerular COX-2 by angiotensin II: role of reactive oxygen species

BACKGROUND

Prostaglandins such as prostaglandin E(2) (PGE(2)) and prostaglandin I(2) (PGI(2)) counteract the angiotensin II (Ang II)-induced vasoconstriction in the glomerular microcirculation. We have shown that Ang II promotes mesangial cell hypertrophy via reactive oxygen species (ROS), which originate from nicotinamide adenine dinucleotide phosphate and its reduced form (NADH/NADPH) oxidase. It has been reported that conditions associated with activation of the renin-angiotensin system result in increased glomerular cyclooxygenase-2 (COX-2) expression and activity.

METHODS

We designed studies to determine (1) whether Ang II induces COX-2 in the glomerulus in vivo in the glomerulus as well as in vitro in mesangial cells, (2) whether ROS originated from Ang II are involved, and (3) whether COX-2-derived prostaglandins modulate the growth promoting effects of Ang II in mesangial cells. Rats were infused with Ang II (0.7 mg/kg/day) for 5 days and glomerular COX-2 expression and activity assessed in isolated glomeruli.

RESULTS

Ang II increased glomerular PGE(2) production (100%) accompanied by a concomitant increase in glomerular COX-2 expression at the mRNA (1.7-fold) and protein level (sixfold). In mesangial cells, Ang II significantly increased mesangial cell PGE(2) (200%) and PGI(2) (100%) production as well as COX-2 mRNA that was prevented by the angiotensin type 1 (AT1) receptor blocker irbesartan and the COX-2 inhibitor NS-398. The NADPH oxidase inhibitor diphenyleneiodonium (DPI), the ROS scavenger tiron as well as catalase, inhibited Ang II-induced PGE(2) production suggesting that Ang II-induced ROS mediate COX-2 up-regulation. Strikingly, COX-2 inhibition as well as blockade of the type 1 PGE(2) receptor (EP1) prevented Ang II-induced mesangial cell hypertrophy suggesting that COX-2-derived prostaglandins, and specifically PGE(2), importantly contribute to the growth promoting effects of Ang II.

CONCLUSION

These studies suggest that blockade of specific PGE(2) receptors may be a novel strategy to modulate the pathologic effects of COX-2-derived prostaglandins without simultaneously affecting protective vasodilatory mechanisms.

Specific pathophysiological functions of JNK isoforms in the brain

We have investigated the effect of JNK1 ko, JNK2 ko, JNK3 ko, JNK2+3 ko and c-JunAA mutation on neuronal survival in adult transgenic mice following ischemia, 6-hydroxydopamine induced neurotoxicity, axon transection and kainic acid induced excitotoxicity. Deletion of JNK isoforms indicated the compartment-specific expression of JNK isoforms with 46-kDa JNK1 as the main phosphorylated JNK isoform. Permanent occlusion of the MCA significantly enlarged the infarct area in JNK1 ko, which showed an increased expression of JNK3 in the penumbra. Survival of dopaminergic neurons in the substantia nigra compacta (SNC) following intrastriatal injection of 6-hydroxydopamine was transiently improved in JNK3 ko and c-JunAA mice after 7 days, but not 60 days. Following transection of the medial forebrain bundle, however, JNK3 ko conferred persisting neuroprotection of axotomised SNC neurons. None of the JNK ko and c-JunAA mutation affected the survival of facial motoneurons following peripheral axotomy when investigated after 90 days. Finally, we determined the impact of JNK ko on the survival of animals and the degeneration of hippocampal neurons following kainic acid. JNK3 ko mice were substantially resistant against and survived kainic acid-induced seizures. JNK3 ko and JNK1 ko showed a nonsignificant tendency for decreased or increased death of hippocampal neurons, respectively. Surprisingly, the deletion of a single JNK isoform did not attenuate the immunocytochemical signal of phosphorylated c-Jun irrespective on the experimental set-up. This comprehensive study provides novel insights into the context-dependent physiological and pathological functions of JNK isoforms.

Jun, Fos and Krox in the hippocampus after noxious stimulation: simultaneous-input-dependent expression and nuclear speckling

Stimulation of sensory C-fibres produces extensive expression of the Fos, Jun and Krox families of inducible transcription factors (ITFs) in many nociceptive CNS areas [28]. In the hippocampus, however, c-Fos is only weakly induced by such stimulation, and expression of the other ITFs has not been studied. Here we examine the effects of single, repeated and simultaneous C-fibre inputs on ITF expressions in the rat hippocampus. A brief, strong electrical stimulation of sciatic nerve C-fibres induced little or no expression of c-Fos or Krox-20. In contrast, FosB was induced and continued to rise in all areas, whereas the basal expressions of c-Jun and Krox-24 were initially reduced but then returned during the subsequent 36 h. A weak noxious cutaneous stimulus applied to one hindpaw induced only weak expressions of the ITFs. However, if the sciatic stimulation was applied contralaterally and 6 h beforehand, this weak stimulus strongly induced Krox-24, but not other ITFs, i.e. there was a potentiation of Krox-24 expression. When these two stimuli were applied simultaneously a few c-Fos labelled cells did appear, and there was and an increased Krox-24 expression. There was also a strong potentiation of FosB and a strong reduction in c-Jun expression. This simultaneous stimulation was the only type of stimulation to induce expression of Krox-20. Also after simultaneous stimulation the majority of the nuclear labelling for FosB, but not of the other ITFs, had a speckled appearance. MK-801 blocked these changes in ITF expressions, but it could also cause the C-fibre stimulations to induce c-Fos and c-Jun in specific areas of the hippocampus. Thus C-fibre stimulation does affect transcription factor activity in the hippocampus; and the strong responses of some ITFs to simultaneous inputs points to their having a role as 'genetic coincidence detectors' in the hippocampus.

Accuracy of hemodynamic measurements during partial liquid ventilation with perflubron

Patients undergoing partial liquid ventilation (PLV) are often monitored with pulmonary artery catheters and receive positive end-expiratory pressure (PEEP). PEEP can dissociate wedge pressure (Pcw) from transmural left atrial pressure (Platm) by elevating pleural pressure and can dissociate Pcw from Pla by elevating alveolar pressure, PLV, like PEEP, also elevates pleural and alveolar pressures. However, the artifacts PLV may cause in measured vascular pressures are unknown. In 6 anesthetized, paralyzed healthy adult sheep, we compared effects of gas ventilation (GV) and PLV with 10 and 30 ml/kg perflubron on pericardial pressure (Pperi), Pcw, Pla, thermodilution cardiac output, and pulmonary artery flow measured with a doppler probe. PEEP was applied from 0-15 mm Hg during GV and PLV. PLV changed pericardial pressure or cardiac output minimally (at PEEP(0), GV: Pperi = -1.7 +/- 0.6 mm Hg, CO = 3. 2 +/- 0.1 L/m; 10 ml/kg perflubron: Pperi = -1.3 +/- 0.6 mm Hg, CO = 3.4 +/- 0.2 L/m; 30 ml/kg perflubron: Pperi = -1.6 +/- 0.7 mm Hg, CO = 3.4 +/- 0.2 L/m; all mean +/- SEM). On PEEP, Pcw agreed with Pla and Platm as well or better during PLV as during gas ventilation. Cardiac output by thermodilution and probe agreed equally well under all conditions. We conclude that hemodynamic values are as accurate during PLV as during gas ventilation.

Measurements of free radicals in isolated, ischemic lungs and lung mitochondria

Previous studies in isolated, ventilated lungs have demonstrated by indirect measurements that oxidant generation occurs during pulmonary ischemia before reperfusion. To identify and quantify the types of free radical species generated during ischemia, we used electron paramagnetic resonance (EPR) spectroscopy in the presence and absence of the spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). EPR spectra obtained from the vascular effluent of isolated ferret lungs, contained a doublet signal (g = 2.005) indicative of ascorbyl radical. This signal doubled in magnitude after 180 min of ischemia, providing evidence of oxidant formation during ischemia. When DMPO, which reacts with radicals including superoxide anions and hydroxyl radicals, was added to the perfusate, the spectra contained ascorbyl radical signals but no DMPO-adducts. To clarify the relationship between ascorbyl radical and DMPO-adduct formation, additional studies were conducted in the presence and absence of ascorbate with isolated lung mitochondria as the source of free radicals. The results showed that in the presence of ascorbate, oxygen free radicals were not detected by EPR spin trapping with DMPO because of the formation of prominent ascorbyl radical signals. These data suggest that DMPO may be useful for the detection of reactive oxygen species in isolated lungs, provided the ascorbate can be sufficiently depleted. Alternatively, as shown by our results, EPR studies that directly monitor ascorbyl radical formation may be used as a marker of oxidative stress in the lung.