Free radicals and other reactive oxygen metabolites in inflammatory bowel disease: cause, consequence or epiphenomenon?

Oxygen-derived free radicals and other reactive oxygen metabolites have emerged as a common pathway of tissue injury in a wide variety of otherwise disparate disease processes. This has given rise to the hope that efforts directed towards the pharmacologic control of free radical-mediated tissue injury (Reilly, P.M., Schiller, H. J. and Bulkley, G. B. (1991) Pharmacologic approach to tissue injury mediated by free radicals and other reactive oxygen metabolites. Am. J. Surg. 161: 488-503) may have particular application to patients suffering from Crohn's disease and/or ulcerative colitis. However, because tissue injury by any mechanism, even direct mechanical trauma, can elicit an inflammatory response which entails the secondary generation of toxic oxidants by neutrophils and tissue macrophages, it is important that the evidence for this association be examined critically, so as to discriminate the possibility of an etiologic role for these toxic compounds from their presence as a reflection of injury caused primarily by other agents. Similarly, in considering the therapeutic potential of free radical ablation for the treatment of patients with IBD it is important to distinguish between interventions that might specifically block the fundamental injury mechanism from those which would act in a more nonspecific, anti-inflammatory role.

Evidence for an early free radical-mediated reperfusion injury in frostbite.

Frostbite is characterized by acute tissue injury induced by freezing and thawing. Initial complete ischemia is followed by reperfusion and later, tissue necrosis. These vascular events support the hypothesis that free radical-mediated reperfusion injury at thawing might contribute to tissue necrosis after frostbite in a manner similar to that seen after normothermic ischemia. To test this hypothesis, rabbit ears were frozen at -21 degrees C for 30, 60, 90, or 120 s and rewarmed at room temperature (22 degrees C). Rabbits were treated "blindly" with saline alone, highly purified, pharmaceutical grade superoxide dismutase (SOD), allopurinol, or deferoxamine. The area of ear necrosis was determined 3 weeks after frostbite by "blinded" morphometry. The administration of SOD at the time of thawing significantly improved viability in ears frozen for 60 and 90 s, but not in those frozen for 30 or 120 s. Deferoxamine also improved viability in ears frozen for 60 s. Allopurinol did not significantly affect ear survival. Electron micrographs showed the appearance of severe endothelial cell injury beginning during freezing and extending through early reperfusion. Later, neutrophil adhesion, erythrocyte aggregation, and microvascular stasis were seen. These findings suggest that free radical-mediated reperfusion injury has a role in frostbite, and quantitate the proportion of the injury that is due to this mechanism.

Allopurinol: discrimination of antioxidant from enzyme inhibitory activities.

This study was designed to quantitatively discriminate the specific xanthine oxidase (XO) inhibitory from the relatively nonspecific antioxidant activities of allopurinol, both in vitro and in vivo in the rat. XO activity, determined by the spectrophotometric assay for urate generation over time, was completely inhibited in vitro by allopurinol at concentrations > or = 200 microM. Allopurinol's antioxidant activity was determined in vitro using a linolenic acid peroxidation (LAP) assay. Although the known antioxidant butylated hydroxytoluene effectively inhibited LAP (80% inhibition of malondialdehyde generation at 10(1) microM), allopurinol (10(1)-10(3) microM) did not inhibit this LAP (p < .01). Rat serum obtained after oral administration of allopurinol (100 mg/kg x 2 doses) did not suppress LAP in vitro more than did control rat serum. Following oral administration of allopurinol (2-50 mg/kg x 2 doses), dose-dependent inhibition of XO activity was observed in the homogenates of the liver (to 5% of control level; p < .001) and the intestine (to 12% of control level; p < .001). We conclude that while 2-50 mg/kg of oral allopurinol effectively suppresses XO activity in the rat liver and intestine, antioxidant activity is not seen even in doses up to 100 mg/kg. The selective enzymatic inhibitory effect of allopurinol at these doses therefore should provide a useful tool to allow the discrimination of the effects of xanthine oxidase in particular from the effects of reactive oxygen metabolites in general.

Endothelial cells potentiate oxidant-mediated Kupffer cell phagocytic killing.

Phagocytosis and killing of circulating organisms by Kupffer cells (KCs) are discrete, important components of host defense. However, the killing mechanism(s) are not fully understood, and the potential role of adjacent nonparenchymal cells such as hepatic endothelial cells has not been defined. Rat KCs -/+ an hepatic endothelial cell enriched cellular fraction (HECEF) were incubated with Candida parapsilosis and assayed for phagocytosis and phagocytic killing by validated fluorochromatic vital staining. The role of reactive oxygen metabolites in KC phagocytic functions was examined by inhibition with superoxide dismutase and/or catalase. Diphenyleneiodonium and allopurinol were used to examine the potential roles of NADPH oxidase and xanthine oxidase, respectively, in generating these toxic oxidants. Coculture with HECEF increased KC phagocytic activity (from 75% to 88%) and candidacidal activity (from 20% to 31%). Superoxide dismutase, catalase, diphenyleneiodonium, or allopurinol caused inhibition of candidacidal activity, but did not affect phagocytosis, and did not block the potentiation of phagocytosis or of killing caused by coculture with HECEF. Reactive oxygen intermediates generated by both NADPH oxidase and xanthine oxidase-dependent pathways are important in KC killing of Candida parapsilosis. In vitro, KC phagocytosis and killing are potentiated (via a non-oxidant-mediated mechanism) by coculture with a preparation of hepatic non-parenchymal cells composed primarily of endothelial cells.

Ethane: a marker of lipid peroxidation during cardiopulmonary bypass in humans.

The goals of this study were to (1) determine the utility of quantification of ethane as a marker of ischemia-reperfusion during human cardiopulmonary bypass (CPB); and (2) determine, using an animal model for this surgical procedure, whether the mode of surgical approach produced increases the quantity of exhaled ethane. Human CPB was initiated following standard anesthetic and monitoring regimens. Samples of gas were collected at baseline and at multiple defined time points throughout the studies. Ethane was determined using cryogenic concentration and gas chromatography. Sternotomy increased exhaled ethane compared to baseline (p < .007; 5.8 +/- 1.7 vs. 3.0 +/- 0.7 nmol/m2 x min); ethane returned to baseline levels prior to the initiation of CPB. Aortic unclamping produced ethane elevation (p < .05; 2.3 +/- 0.8 vs. 1.5 +/- 0.4 nmol/m2 x min) with the levels being related to a lower cardiac index and a higher systemic vascular resistance post aortic unclamping. Termination of CPB significantly increased ethane levels compared to baseline (p < .002; 4.8 +/- 1.7 vs. 3.0 +/- 0.7 nmol/m2 x min). Independent variables that correlated with increased ethane measurements included a higher arterial blood pH on bypass and the change in hemoglobin pre- and post-CPB. Electrocautery, but not scalpel, incision of the porcine abdominal wall increased ethane levels significantly (p < .02). These results indicate that exhaled ethane may be a valuable marker of lipid peroxidation during and following CPB.

Breath ethane: a specific indicator of free-radical-mediated lipid peroxidation following reperfusion of the ischemic liver.

A major component of the organ injury mediated by toxic oxidants, such as seen following reperfusion of the ischemic liver, is due to the peroxidation of polyunsaturated fatty acids, especially of cell membranes. We utilized the measurement of exhaled breath ethane, a metabolic product unique to oxidant-mediated lipid peroxidation, as a noninvasive indicator of this process in swine liver subjected to warm ischemia/reperfusion. Under rigorously controlled anesthesia conditions, pig livers were subjected to 2 h of warm total ischemia, followed by reperfusion in situ. Expired air was collected and its ethane content quantitated by a novel gas chromatographic technique. The time course of breath ethane generation correlated closely with the appearance of hepatocellular injury as measured by impairment of Factor VII generation and other measures of liver integrity. Moreover, the administration of the specific superoxide free radical scavenger, superoxide dismutase (SOD), significantly attenuated both the elaboration of ethane and the hepatocellular injury. These findings not only provide confirmation of the previously reported link between hepatocellular injury by free radicals generated at reperfusion, but also establish the use of expired breath ethane analysis as a sensitive, specific, and noninvasive indicator of the injury process in real time.

Hemophilus aphrophilus meningitis followed by vertebral osteomyelitis and suppurative psoas abscess.

Hemophilus aphrophilus is an uncommon pathogen in man. It has rarely been reported as a cause of meningitis, exclusively in boys three years or younger. Osteomyelitis due to this organism is also rare. H. aphrophilus was responsible for meningitis, probable thoracic empyema, and ultimately vertebral osteomyelitis and suppurative psoas abscess formation in a woman following metrizamide myelography. The patient responded well to antibiotic treatment and surgical drainage. The organism was sensitive not only to chloramphenicol but also to newer cephalosporin antibiotics.

Ablation of free radical-mediated reperfusion injury for the salvage of kidneys taken from non-heartbeating donors. A quantitative evaluation of the proportion of injury caused by reperfusion following periods of warm, cold, and combined warm and cold ischemia.

Postischemic renal failure is a severe problem following cadaveric renal transplantation, especially if the kidney has been harvested from a non-heartbeating donor, and thereby subjected to periods of both warm and cold ischemia. It is well established that a substantial component of postischemic injury is produced by oxygen-derived free radicals generated from xanthine oxidase at reperfusion. However, the clinical potential of free radical ablative therapy is dependent upon the proportion of the total injury caused by this reperfusion mechanism, compared with the proportion resulting from ischemic injury per se. Therefore, we quantitatively evaluated these proportions in porcine kidneys subjected to various periods of warm (renal artery occlusion in situ), cold (harvest, cold preservation, and allotransplantation), and combined warm and cold ischemia. Experiments were paired, one kidney treated with either superoxide dismutase (SOD) or allopurinol for free radical ablation, the contralateral kidney serving as a control. Creatinine clearance (Ccr) was measured separately for each kidney 48 hr after reperfusion. After 1 and 2 hr of warm ischemia, Ccr dropped to 50% and 36% of normal, respectively. This was improved to 110% and 55% when SOD was given into the renal artery at reperfusion. Similarly, after 24 and 48 hr of cold ischemia, kidney function was significantly improved from 30% and 18% to 72% and 47% of normal, respectively, when allopurinol was added to the preservation solution. SOD used at harvest and again at reperfusion was particularly effective following combined warm and cold ischemia, in a situation mimicking the harvest of cadaver kidneys from a non-heartbeating donor. These findings suggest that the ablation of free radical-mediated reperfusion injury may improve posttransplant renal function sufficiently to allow expansion of the cadaveric donor pool to include non-heartbeating donors.

The role of oxygen free radicals in mediating the reperfusion injury of cold-preserved ischemic kidneys.

We evaluated the hypothesis that postischemic renal failure is caused primarily at reperfusion by oxygen-derived free radicals in a swine model designed to realistically mimick human cadaveric renal transplantation. Both kidneys were removed, flushed with Euro-Collins solution, stored 24 hr at 4 degrees C, and then transplanted to a second pig. Experiments were paired, each pig receiving one treated and one control kidney. All pigs received the optimal conventional regimen of hydration, phenoxybenzamine, furosemide, and mannitol to allow assessment of free radical treatment superimposed thereupon. Two days later creatinine clearance (CCR) was measured from each kidney via separate ureterostomies. Untreated kidneys developed severe functional impairment, CCR falling from a normal level of 25.5 +/- 6.3 ml/min (n = 8) to 7.7 +/- 0.9 ml/min (n = 14, P less than .05 vs. control). The infusion of 20 mg of the free radical scavenger superoxide dismutase (SOD) into the renal artery at reperfusion substantially ameliorated this injury (CCR = 15.9 +/- 1.7 ml/min, n = 18, P less than 0.05 vs. control). A dose-response curve to SOD showed no effect of doses of 0.2 mg (CCR = 8.0 +/- 1.1 ml/min, n = 4) or 2 mg (CCR = 7.7 +/- 0.9, n = 5), and no greater benefit from 100 mg (CCR = 16.1 +/- 2.1 ml/min, n = 3, P less than 0.05 vs. control). Blocking the generation of superoxide radicals from xanthine oxidase with allopurinol (50 mg/kg) afforded similar protection (CCR = 18.2 +/- 1.8; n = 11, P less than 0.01 vs. control). On the other hand, following an 18-hr period of cold ischemia, little damage was sustained by the untreated (control) kidneys (CCR = 22.1 +/- 0.6 ml/min). Consequently, under these conditions the ablation of free radical generation with allopurinol provided no significant benefit. These findings suggest that after a critical period of cold ischemic preservation, metabolic changes take place within the kidney that lead to free radical generation and consequent tissue injury upon reperfusion, despite optimal preservation by conventional methods. This damage can be prevented by simple nontoxic measures--which, therefore, show great promise for use in the prevention of early renal failure following cadaveric renal transplantation.

Discriminant quantitation of posttransplant hepatic reticuloendothelial function. The impact of ischemic preservation.

This study focuses upon two discrete components of posttransplant hepatic reticuloendothelial system (RES) function-phagocytosis and killing of bacteria-under various conditions of ischemic preservation. We had previously reported that, following intravenous injection of rats with 51Cr and 125I double-labeled Escherichia coli, hepatic 51Cr levels can be used to reliably quantify hepatic phagocytic clearance of the bacteria from the blood (HPC), while the subsequent release of 125I from the liver accurately parallels hepatic bacterial killing. Here, Wistar rats were transplanted with syngeneic livers perfused with either normal saline (NS) or University of Wisconsin solution (UW) and stored at 4 degrees C for 1, 2, or 3 hr prior to implantation. Control rats underwent laparotomy and hepatic artery ligation. Using the double-labeled E coli assay, HPC was decreased in all transplanted animals when compared with controls, reaching a nadir on the third postoperative day (P < 0.05). In rats transplanted with livers preserved in NS, the fraction of phagocytosed organisms that were subsequently killed (hepatic killing efficiency=HKE) was increased to 142%, 129%, or 112% of normal following 1, 2, or 3 hr of cold ischemia, respectively; P < 0.05). Conversely, preservation of donor allografts in UW was associated with marked depression of HKE. Moreover, rats receiving NS- or UW-preserved livers tolerated an intravenous challenge with Streptococcus pneumoniae poorly (50% mortality) compared with hepatic artery ligated controls (12% mortality) at 7 days. Ischemic preservation of rat livers in NS resulted in a dose (of ischemia)-dependent reduction of hepatic phagocytosis coupled with a potentiation of HKE. Preservation in UW, however, produced a striking suppression of both components of hepatic RES function. Following a septic challenge survival was reduced in both groups of transplanted rats.

Delayed "spontaneous" adhesion of leukocytes to rat mesenteric venules is dependent upon reactive oxidants.

We investigated the role of reactive oxygen metabolites (ROMs) as potential mediators of delayed "spontaneous" leukocyte adhesion to rat mesenteric venules after the manipulation for in vivo microscopy. Rats were anesthetized via tail vein and prepared for intravital microscopic viewing of a segment of mesenteric venule. Leukocyte rolling, adhesion, and emigration were quantitated every 30 min for 3 h. Intravital observation immediately after routine gentle manipulation revealed a substantial leukocyte rolling and a small number of adherent and emigrated leukocytes. This rolling leukocyte flux then declined to a minimal level for 60 min. The number of adherent and emigrated leukocytes did not change during the initial 90 min. After 120 min, the flux of rolling leukocytes, and adherent and emigrated leukocyte number began to increase and reached significant levels at 180 min. To determine the possible role of ROMs in this "spontaneous" adhesion, rats were treated continuously with superoxide dismutase (SOD) plus catalase given intravenously over 3 h. Rolling leukocyte flux after 120 min was significantly attenuated by SOD plus catalase. SOD + catalase also significantly inhibited delayed leukocyte adhesion and emigration. Allopurinol substantially inhibited xanthine oxidase activity but had no significant effects on the above parameters of neutrophil dynamics. These findings suggest that ROMs, probably derived from a source other than xanthine oxidase, constitute important mediators of "spontaneous" leukocyte adhesion in rat mesenteric venules.

Zonal heterogeneity of hepatic injury following shock/resuscitation: relationship of xanthine oxidase activity to localization of neutrophil accumulation and central lobular necrosis.

Post-ischemic hepatic injury is characterized by zonal heterogeneity of injury (central lobular necrosis), sinusoidal neutrophil accumulation, and injury generated by reactive oxygen metabolites. We evaluated the role of the heterogeneous distribution of hepatic xanthine oxidase in the generation of neutrophil accumulation and consequent hepatocellular injury in rats subjected to shock [controlled hemorrhagic hypotension (mean arterial pressure = 37.5 + or - 2.5 mmHg for 120 min)], with or without subsequent resuscitation and hemodynamic stabilization, compared with sham-operated rats. Shock/resuscitation produced striking neutrophil accumulation (assayed by esterase histochemistry) in the pericentral sinusoids, associated with centrolobular necrosis. This paralleled the pericentral distribution of xanthine oxidase (determined by histochemical assay of frozen sections) and its release from the liver into the circulation at resuscitation. Pretreatment with allopurinol inhibited hepatic xanthine oxidase activity, neutrophil accumulation, and pericentral hepatocyte necrosis in shock/resuscitation in rats. These findings suggest that reactive oxygen metabolites generated by heterogeneously distributed xanthine oxidase may contribute to the heterogeneity of hepatocellular injury in "ischemic hepatitis."

Mesenteric vasoconstriction in response to hemorrhagic shock.

Previous studies indicate that cardiogenic shock (tamponade) in swine produces selective mesenteric ischemia due to disproportionate mesenteric vasospasm mediated primarily by the renin-angiotensin axis. Here, we characterized the systemic and mesenteric hemodynamic responses to hypovolemic shock to better understand the neurohumoral mechanisms controlling this response. Varying degrees of hypovolemic shock were produced by graded levels of hemorrhage, from 12.5 to 50% of the calculated blood volume. Systemic and mesenteric pressures and blood flows were measured, and corresponding vascular resistances were calculated. The hemodynamic responses of the mesenteric vascular bed were compared with those of the systemic (nonmesenteric) vasculature. These experiments were then repeated after confirmed blockade either of the alpha-adrenergic nervous system (phenoxybenzamine), of vasopressin (Manning compound), or of the renin-angiotensin axis (enalapril). Graded levels of hemorrhage produced corresponding graded, reproducible, steady-state levels of systemic hypotension, hypoperfusion, and peripheral vasoconstriction, i.e., hemorrhagic shock. This was associated with disproportionate degrees of mesenteric ischemia due to disproportionate mesenteric vasoconstriction. The selective component of this mesenteric vasoconstrictive response was not attenuated by a-adrenergic blockade nor by vasopressin blockade but was blocked by ablation of the renin-angiotensin axis with enalapril. Like cardiogenic shock, hemorrhagic shock generates selective mesenteric ischemia by producing a disproportionate mesenteric vasospasm that is mediated primarily by the renin-angiotensin axis.

Effect of hemorrhagic shock and resuscitation upon hepatic phagocytic clearance and killing of circulating microorganisms.

We evaluated the effects of hemorrhagic shock/resuscitation (S/R) on hepatic reticuloendothelial system function, using an in vivo assay that discriminantly quantitates its two essential components, phagocytic clearance and phagocytic killing of double-labeled Escherichia coli injected intravenously. Rats were subjected to hemorrhagic shock at mean arterial pressure at 50 +/- 5 torr for 2 h, resuscitated, and survived. Hepatic phagocytic clearance was significantly decreased immediately following and 6 h after S/R, compared with sham-shocked rats, but recovered to normal levels after 24 h. Although hepatic killing efficiency was increased initially, and transiently depressed 6 h later, it was strikingly upregulated after 24 h. As a consequence, net hepatic killing was transiently suppressed at 0 and 6 h, but upregulated after 24 h. Pre-treatment with proinflammatory agonists, including endotoxin, IFN-gamma, or IFN-gamma + TNF-alpha enhanced both hepatic killing efficiency and net hepatic killing. These observations suggest that although hepatic killing function is initially impaired after the onset of S/R, it is strikingly upregulated 24 h later, simulating both the initial immunosuppression, and the later hyperinflammatory response to systemic S/R that could lead to multiple organ dysfunction syndrome.

The mesenteric hemodynamic response to circulatory shock: an overview.

The mesenteric hemodynamic response to circulatory shock is characteristic and profound; this vasoconstrictive response disproportionately affects both the mesenteric organs and the organism as a whole. Vasoconstriction of post-capillary mesenteric venules and veins, mediated largely by the alpha-adrenergic receptors of the sympathetic nervous system, can effect an "autotransfusion" of up to 30% of the total circulating blood volume, supporting cardiac filling pressures ("preload"), and thereby sustaining cardiac output at virtually no cost in nutrient flow to the mesenteric organs. Under conditions of decreased cardiac output caused by cardiogenic or hypovolemic shock, selective vasoconstriction of the afferent mesenteric arterioles serves to sustain total systemic vascular resistance ("afterload"), thereby maintaining systemic arterial pressure and sustaining the perfusion of non-mesenteric organs at the expense of mesenteric organ perfusion (Cannon's "flight or fight" response). This markedly disproportionate response of the mesenteric resistance vessels is largely independent of the sympathetic nervous system and variably related to vasopressin, but mediated primarily by the renin-angiotensin axis. The extreme of this response can lead to gastric stress erosions, nonocclusive mesenteric ischemia, ischemic colitis, ischemic hepatitis, ischemic cholecystitis, and/or ischemic pancreatitis. Septic shock can produce decreased or increased mesenteric perfusion, but is characterized by an increased oxygen consumption that exceeds the capacity of mesenteric oxygen delivery, resulting in net ischemia and consequent tissue injury. Mesenteric organ injury from ischemia/reperfusion due to any form of shock can lead to a triggering of systemic inflammatory response syndrome, and ultimately to multiple organ dysfunction syndrome. The mesenteric vasculature is therefore a major target and a primary determinant of the systemic response to circulatory shock.

Hemodynamic pathogenesis of ischemic hepatic injury following cardiogenic shock/resuscitation.

Post-ischemic hepatic injury is observed commonly following cardiogenic or hypovolemic shock. We evaluated the putative roles of the alpha-adrenergic sympathetic nervous system and the renin-angiotensin axis in the pathogenesis of hepatic injury following cardiogenic shock. Previous studies have characterized the hepatic hemodynamic response to shock, while the relationship of these hemodynamic changes to ischemic hepatic injury has not been defined. Sustained (4 h) periods of pericardial tamponade (after mild hemorrhage) followed by 2 h of resuscitation generated a reproducible model of cardiogenic shock and consequent post-ischemic hepatic injury in anesthetized pigs. In a separate group of pigs, the alpha-adrenergic component of the sympathetic nervous system was ablated with phenoxybenzamine or, in other groups, the renin-angiotensin axis was ablated by either prior nephrectomy or, separately, by confirmed angiotensin converting enzyme inhibition with teprotide. The hepatic injury response in each case was reevaluated. Compared to sham-shocked pigs, those subjected to tamponade alone manifested selective splanchnic vasospasm and consequent biochemical and histological evidence of classic post-ischemic liver injury (centrilobular necrosis involving about a third of each hepatic lobule). These manifestations of splanchnic vasospasm and the consequent ischemic injury were not ameliorated by confirmed alpha-adrenergic blockade, but significantly attenuated by either method of prior ablation of the renin-angiotensin axis. This model of sustained cardiogenic shock and resuscitation generates the manifestations of ischemic hepatic injury associated with selective splanchnic vasospasm, findings consistent with previous, short-term, hemodynamic studies. The major mediator of this response, and the consequent hepatic injury, is the selective hypersensitivity of the mesenteric vasculature to the renin-angiotensin axis.

Partial T-cell receptor gene rearrangement. A source of pseudo-clonal populations in thymomas and other thymic tissues.

The differentiation of thymocytes into mature post-thymic T cells requires rearrangement of T-cell antigen receptor genes from germline to a spectrum of spliced configurations encoding functional receptors. In the T-cell receptor beta chain locus, this process occurs via a hierarchical series of recombination events, linking "diversity" and "joining" segments, then "variable" and "diversity" segments. The authors report Southern blot analysis of the T-cell receptor beta locus in normal human thymic tissue after restriction digestion with Bam HI identifying rearranged DNA fragments in 5 of 6 samples, which probably represent an intermediate deletion joining D beta 1 to a J beta 2 segment without rearrangement of the upstream V region. Hybridization intensity was in the range of 5% to 30% of represented DNA. Reduction of signal from bands containing C beta 1 and J beta 2 sequences after Eco RI and Hind III digestion was consistent with this model. A probe specific for J beta 1 did not hybridize with the rearranged fragment while J beta 2 specific sequences did not hybridize with the rearranged fragment while J beta 2 specific sequences did, indicating a deletion of the region of J beta 1, but limited to sequences upstream of J beta 2. Most peripheral lymphoid specimens do not demonstrate similar rearranged DNA fragments, however T-cell-rich populations may do so. Analysis of 31 additional surgically resected thymic tissues and three polyclonal T-cell-rich peripheral lymphoid specimens revealed a similarly rearranged fragment in 13 of 14 thymuses with follicular hyperplasia; 6 of 9 thymomas; 5 of 6 malignant (invasive) thymomas; 0 of 2 thymic carcinomas; and, at very low abundance, in 3 of 3 peripheral T-cell populations. Because this nongermline T-cell receptor gene apparently reflects polyclonal incomplete rearrangement, rather than clonality, awareness of this phenomenon may help prevent erroneous diagnosis of T-cell lymphoma for mediastinal lymphoid lesions with an apparent "clonal" T-cell receptor gene rearrangement. If the intermediate deletion is derived from an ongoing process, the data suggest that in many cases neoplastic thymic epithelium may retain functions necessary not only to support a resident thymocyte population, but also to activate ongoing T-cell differentiation. Alternatively, the intermediate deletion may derive from abandoned non-productive rearrangements.

Free radicals and other reactive oxygen metabolites: clinical relevance and the therapeutic efficacy of antioxidant therapy.

As in any new field, justifiable enthusiasm for the potential for antioxidant therapy has led to hyperbole, hastily designed, poorly conceived clinical trials, and premature reporting of uncontrolled, anecdotal indicators of efficacy that have not held up when subjected to close scrutiny or more careful, controlled trial design. This tendency has been augmented by strong pressure for early positive results from a few, but not most, members of the pharmaceutical industry and by a few clinicians in highly competitive fields who were anxious not to be left behind. The sobering reality of negative or, even worse, indeterminate clinical trials has culled the field and educated those that remain. As a result, we are beginning to see the publication of quite promising results from large, well-controlled, carefully designed clinical studies, many, but not all, of which are quite promising. This has been associated with a much better understanding of the basic mechanism of free radical-mediated human disease, without which further substantial progress would be quite limited. Because the manipulation of oxidant-mediated tissue injury represents treating disease at its most basic level, the therapeutic potential of this approach remains not only promising but exciting.

The role of leukocytes in the production of oxygen-derived free radicals in acute experimental pancreatitis.

Oxygen-derived free radicals mediate an important step in the initiation of experimental acute pancreatitis in the ex vivo perfused canine pancreas model. In other organ systems, circulating leukocytes may serve as one source of oxygen-derived free radical production. The current experiments were designed to evaluate the role of circulating leukocytes in the generation of injury in this model. Four experimental groups of animals were studied: group I consisted of controls (n = 6); group II had white blood cell (WBC) depletion (n = 4) in which the recirculating whole blood perfusate was depleted of 98% of its circulating leukocytes; group III had oleic acid infusion (FFA) alone (n = 9), which induced pancreatitis; group IV had WBC depletion and FFA (n = 6), in which oleic acid was infused after depletion of the circulating leukocytes in the perfusate. During the 4-hour perfusion period, the pancreatic preparations were monitored hourly for the development of edema, weight gain, and release of alpha-amylase into the perfusate. Animals in groups I and group II manifested no gross edema, gained minimal weight, and did not manifest hyperamylasemia. Leukocyte depletion alone had no effect. In group IV animals marked edema, significant weight gain, and hyperamylasemia developed to the same extent as in group III animals. These results demonstrate that circulating leukocytes are not essential to the development of pancreatitis in this model and suggest that another source of oxygen-derived free radicals mediates this injury.

Temporal efficacy of allopurinol during the induction of pancreatitis in the ex vivo perfused canine pancreas.

Oxygen-derived free radicals play an important role in the pathogenesis of experimental acute pancreatitis in the isolated perfused canine pancreas. We have previously found that pretreatment with allopurinol inhibits xanthine oxidase--apparently the primary source of free radical generation in this model--and prevents the initial development of pancreatitis. In these experiments, we evaluated whether allopurinol administered after the onset of pancreatitis would arrest the progression of the disease process. Edema formation, weight gain, and the release of amylase activity into the perfusate in the ex vivo perfused canine pancreas model were monitored during a 4-hour perfusion period. There were six experimental groups: Group I (control) received no treatment, group II (allopurinol alone) received only allopurinol (100 mg) at the start of perfusion, and groups III through VI were each given an infusion of 0.3 ml of oleic acid (FFA) over a 1-hour period to initiate acute pancreatitis. Group III (FFA alone) received no other treatment. In group IV (pretreatment with allopurinol), group V (concurrent treatment with allopurinol), and group VI (posttreatment with allopurinol), allopurinol (100 mg) was administered 1 hour before, concurrent with, or at the end of the FFA infusion, respectively. Pretreatment with allopurinol prevented edema formation, markedly attenuated weight gain, and the release of amylase caused by the FFA infusion. Administration of allopurinol concurrent with the FFA infusion provided only partial protection, whereas posttreatment with allopurinol failed to arrest the progression of the injury process. Therefore, the use of allopurinol to inhibit oxygen-derived free radical production from xanthine oxidase prevented the development of acute pancreatitis in this model; however, treatment with allopurinol after initiation of the disease process failed to arrest the progression of acute pancreatitis.