Current perspectives on septic shock

Although septic shock may be initiated by invading microbes, it is the metabolic and immunologic host responses that determine the true pathophysiology of this common critical care illness. Currently, septic shock therapeutics emphasize empiric and symptomatic treatment. Biochemical elucidation of the septic process will ultimately result in specific interventions for this ominous intensive care syndrome.     

Species- and sex-specific variations in binding of ochratoxin A by renal proteins in vitro

The mycotoxin ochratoxin A (OTA) is a potent renal carcinogen in rodents and induces renal fibrosis in pigs. Furthermore, OTA has been associated with the development of renal tumors and nephropathies in humans. Large species- and sex-differences are observed in sensitivity toward OTA-mediated toxicity and carcinogenicity, yet neither the mechanism(s) resulting in OTA toxicity nor the reasons for the observed species- and sex-specificities are known. This paper investigated variations in OTA handling viz binding to renal proteins which could possibly explain the observed differences in OTA susceptibility in vivo and in vitro. The results obtained via a modification of a standard receptor-binding assay demonstrated the presence of at least one homogeneous binding component in renal cortical homogenates from pig, mouse, rat and humans. This component was shown to bind OTA in a specific and saturable manner. A range of compounds selected for their affinity for steroid receptors and/or for various known organic anion transporters were employed in a competition assay to answer the question whether this homogenous OTA binding component represents a steroid-like receptor component or one of the known organic anion transporters of the kidney. Although many of the compounds were able to compete with OTA for protein-binding, the competition patterns displayed a distinct species specificity and did not correspond to the competition patterns associated with presently known organic anion transporters of the kidney in the mouse, rat or human. The data thus suggests the presence of a new organic anion transporter or more likely, a cytosolic binding component of unknown function with high affinity and capacity for OTA binding in humans, rats, mice and possibly pigs.     

Post-traumatic brain hypothermia reduces histopathological damage following concussive brain injury in the rat

The purposes of this study were (1) to document the histopathological consequences of moderate traumatic brain injury (TBI) in anesthetized Sprague-Dawley rats, and (2) to determine whether posttraumatic brain hypothermia (30°C) would protect histopathologically. Twenty-four hours prior to TBI, the fluid percussion interface was positioned over the right cerebral cortex. On the 2nd day, fasted rats were anesthetized with 70% nitrous oxide, 1% halothane, and 30% oxygen. Under controlled physiological conditions and normothermic brain temperature (37.5°C), rats were injured with a fluid percussion pulse ranging from 1.7 to 2.2 atmospheres. In one group, brain temperature was maintained at normothermic levels for 3 h after injury. In a second group, brain temperature was reduced to 30°C at 5 min post-trauma and maintained for 3 h. Three days after TBI, brains were perfusion-fixed for routine histopathological analysis. In the normothermic group, damage at the site of impact was seen in only one of nine rats. In contrast, all normothermic animals displayed necrotic neurons within ipsilateral cortical regions lateral and remote from the impact site. Intracerebral hemorrhagic contusions were present in all rats at the gray-white interface underlying the injured cortical areas. Selective neuronal necrosis was also present within the CA3 and CA4 hippocampal subsectors and thalamus. Post-traumatic brain hypothermia significantly reduced the overall sum of necrotic cortical neurons (519±122 vs 952±130, mean ±SE, P=0.03, Kruskal-Wallis test) as well as contusion volume (0.50±0.14 vs 2.14±0.71 mm³, P=0.004). These data document a consistent pattern of histopathological vulnerability following normothermic TBI and demonstrate hypothermic protection in the post-traumatic setting.Supported by USPHS Grants NS30291 and NS27127     

A new model of embolic stroke produced by photochemical injury to the carotid artery in the rat

We report a new model of embolic stroke in the rat, based on endothelial disruption and platelet aggregation in the carotid artery, which leads to distal embolization and focal brain infarction. The common carotid artery was irradiated for 6.5 minutes with the focused beam of an argon laser operated at a wavelength of 514.5 nm with a peak power of 2 W and an average power of 400 mw. Ipsilateral cerebral infarcts, ranging in size from 0.1 to 1.7 mm, were produced by platelet emboli in 12 of 13 rats. A total of 44 infarcts were observed in the 12 rats: 29 in the cortex, 6 in the hippocampus, 5 in the thalamus, and 4 in the basal ganglia. Scanning electron microscopy identified platelet aggregates in the carotid artery and in a deep cortical arteriole 50 minutes after the photochemical lesion. Twenty-four hours after the experiment, scanning electron microscopy of the carotid artery revealed damaged endothelium but few remaining adherent platelets. More intense laser irradiation in 8 rats, leading to carotid occlusion, produced an infarct in only 1. This new model can be used to study the acute and chronic pathological changes in the brain associated with platelet embolism.     

Ischemia-induced extracellular release of serotonin plays a role in CA1 neuronal cell death in rats.

BACKGROUND AND PURPOSE: Serotonin, via 5-HT2 receptors, exerts an excitatory effect on CA1 neurons and may play a role in ischemia-induced excitotoxic damage. To evaluate the role of serotonin in ischemia, both neurochemical and histopathological studies were performed. METHODS: Neurochemical studies included rats that were subjected to 12.5 or 20 minutes of normothermic ischemia by two-vessel occlusion plus hypotension, and extracellular serotonin levels were measured in the hippocampus (12.5 minutes' ischemia, n = 5) or striatum (20 minutes' ischemia, n = 13) by microdialysis. In the histopathological study the effect of 8 mg/kg ritanserin, a 5-HT2 antagonist, administered continuously from 30 minutes prior to ischemia until 1 hour of recirculation was evaluated in five rats subjected to 10 minutes of ischemia. After 3 days, the numbers of normal-appearing neurons in the CA1 subregions were counted. RESULTS: Ischemia of 12.5 minutes' duration induced a fourfold increase in serotonin in the hippocampus (mean +/- SEM baseline, 1.86 +/- 0.25 pmol/ml perfusate; during ischemia, 8.14 +/- 0.89 pmol/ml; p < 0.05 by analysis of variance). Twenty minutes of ischemia induced a 25-fold increase in serotonin in the dorsolateral striatum (baseline, 0.98 +/- 0.15 pmol/ml; ischemia, 24.4 +/- 5.93 pmol/ml; p < 0.001). The histopathological study demonstrated severe ischemic damage in all CA1 subregions of nontreated animals (medial, 34 +/- 16 normal-appearing neurons, middle, 52.2 +/- 22.9 neurons; lateral, 56.6 +/- 21.8 neurons). Treatment with ritanserin significantly attenuated ischemic damage (medial, 117.6 +/- 6.5 neurons; middle, 131.4 +/- 4.9 neurons; lateral, 130 +/- 7.5 neurons; p < 0.01 different from nontreated). CONCLUSIONS: Taken together, these results suggest that serotonin plays a detrimental role, mediated by 5-HT2 receptors, in the development of ischemic damage.     

Spectrometric investigations in ocular hypertension and early stages of primary open angle glaucoma and of low tension glaucoma — multisubstance analysis

The approximation of logarithmic difference spectra between the reflectance of the normal fundus and the fundus reflectance in different stages of glaucoma is demonstrated by a model. The influences of fundus pigments like oxihemoglobin, melanin, xanthophyll and rhodopsin as well as the intensity and the exponent of the scattered light are optimized. Glaucomatous alterations in the extinction of these pigments and of the scattering parameters are different in the macula, in the papillo-macular bundle and in the parapapillary region temporal to the optic disc. A lack of oxihemoglobin only in the papillo-macular bundle in first relative losses in the visual field function points to a damaged microcirculation in early POAG. In progressive glaucoma the extinction spectrum of xanthophyll is detectable in the papillo-macular bundle. A decreased intensity of the scattered light and an altered scattering exponent are suggestive of a damage in the nerve fiber layer at early stages of glaucoma.     

Alterations in mammalian target of rapamycin signaling pathways after traumatic brain injury.

In response to traumatic brain injury (TBI), neurons initiate neuroplastic processes through the activation of intracellular signaling pathways. However, the molecular mechanisms underlying neuroplasticity after TBI are poorly understood. To study this, we utilized the fluid-percussion brain injury (FPI) model to investigate alterations in the mammalian target of rapamycin (mTOR) signaling pathways in response to TBI. Mammalian target of rapamycin stimulates mRNA translation through phosphorylation of eukaryotic initiation factor 4E binding protein-1 (4E-BP1), p70 ribosomal S6 kinase (p70S6K), and ribosomal protein S6 (rpS6). These pathways coordinate cell growth and neuroplasticity via dendritic protein synthesis. Rats received sham surgery or moderate parasagittal FPI on the right side of the parietal cortex, followed by 15 mins, 30 mins, 4 h, 24 h, or 72 h of recovery. Using Western blot analysis, we found that mTOR, p70S6K, rpS6, and 4E-BP1 phosphorylation levels were significantly increased in the ipsilateral parietal cortex and hippocampus from 30 mins to 24 h after TBI, whereas total protein levels were unchanged. Using confocal microscopy to localize these changes, we found that rpS6 phosphorylation was increased in the parietal cortex and all subregions of the hippocampus. In accordance with these results, eIF4E, a key, rate-limiting mRNA translation factor, was also phosphorylated by mitogen-activated protein kinase-interacting kinase 1 (Mnk1) 15 mins after TBI. Together, these results suggest that changes in mRNA translation may be one mechanism that neurons use to respond to trauma and may contribute to the neuroplastic changes observed after TBI.     

Effect of early and late antibiotic treatment in experimental acute pancreatitis in rats

Background The clinical course in acute necrotizing pancreatitis is mainly determined by bacterial infection of pancreatic and peripancreatic necrosis. The effect of two antibiotic regimens for early and late treatment was investigated in the taurocholate model of necrotizing pancreatitis in the rat. Materials and methods Seventy male Wistar rats were divided into five pancreatitis groups (12 animals each) and a sham-operated group (10 animals). Pancreatitis was induced by intraductal infusion of 3% taurocholate under sterile conditions. Animals received two different antibiotic regimes (20 mg/kg imipenem or 20 mg/kg ciprofloxacin plus 20 mg/kg metronidazole) early at 2, 12, 20, and 28 h after induction of pancreatitis or late at 16 and 24 h after induction of pancreatitis or no antibiotics (control). Animals were examined after 30 h for pancreatic and extrapancreatic infection. Results Early and late antibiotic treatment with both regimes could significantly reduce pancreatic infection from 58 to 8–25%. However, extrapancreatic infection was only reduced by early antibiotic therapy. While quinolones also reduced bacterial counts in small and large bowel, imipenem did not. Conclusions In our animal model of necrotizing pancreatitis, early and late treatment with ciprofloxacin/metronidazole and imipenem reduce bacterial infection of the pancreas. Extrapancreatic infection, however, is reduced significantly only by early antibiotic treatment. The effectivity of early antibiotic treatment in the clinical setting should be subject to further investigation with improved study design and sufficient patient numbers.