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Biomedical subjects

K A Nath

Publications and source records attributed to K A Nath.

At least 55 records · Page 3Linked to original sources
PubMed1995

Endothelial cell heme oxygenase and ferritin induction in rat lung by hemoglobin in vivo.

Iron-derived reactive oxygen species play an important role in the pathogenesis of various vascular disorders including vasculitis, atherosclerosis, and capillary leak syndromes such as the adult respiratory distress syndrome (ARDS). We have suggested that acute incorporation of the heme moiety of hemoglobin released from red blood cells into endothelium could provide catalytically active iron to the vasculature. Adaptation to chronic heme stress involves the induction of heme oxygenase and ferritin; the latter provides cytoprotection against free radicals in vitro. The present studies examine the bioavailability of heme, derived from hemoglobin, to induce heme oxygenase and ferritin in rat lungs in vivo. Intravenous injection of methemoglobin, but not oxyhemoglobin, increases total lung heme oxygenase mRNA approximately fivefold after 16 h. Accompanying this mRNA induction, expression of total lung heme oxygenase enzyme activity is also markedly enhanced. In situ hybridization for heme oxygenase reveals mRNA accumulation in the lung microvascular endothelium, implying incorporation of heme into endothelial cells. Similarly, methemoglobin significantly increases the ferritin protein content of rat lungs and in parallel, ferritin light-chain mRNA increases approximately 1.6-fold, whereas heavy-chain mRNA is upregulated by approximately 1.9-fold. Immunoreactive ferritin is present in lung microvascular endothelium after methemoglobin treatment, suggesting incorporation of heme iron into pulmonary vasculature. Subcutaneous injection of Sn-protoporphyrin IX, a competitive inhibitor of heme oxygenase, does not affect methemoglobin-induced ferritin synthesis in lungs. We speculate that methemoglobin, which might be generated by activated leukocytes in ARDS associated with disseminated interavascular coagulation, can provide heme iron to lung microvascular endothelium to induce heme oxygenase and ferritin.

Animals↗
PubMed1995

Recurrent hemolytic uremic syndrome in an adult renal allograft recipient: current concepts and management.

Acute renal insufficiency in the setting of hemolysis and thrombocytopenia, a triad that constitutes adult or pediatric hemolytic uremic syndrome, can be associated with or triggered by diverse conditions such as verocytotoxin-producing Escherichia coli, viral infections, pregnancy, malignant hypertension, scleroderma, renal radiation, allograft rejection, lupus erythematosus, and assorted medications such as mitomycin C, cyclosporine, and oral contraceptives. Recurrent and de novo hemolytic uremic syndrome occur after renal transplantation. Relapses are also common and probably reflect incomplete resolution of the initial episode. The major differential diagnoses of hemolytic uremic syndrome in the renal allograft include acute vascular rejection, cyclosporine, FK506 or antilymphocyte antibody nephrotoxicity, and malignant hypertension, all of which may display overlapping clinical and histologic features with primary hemolytic uremic syndrome; in such instances, the exact diagnosis may be quite difficult. It is possible that the risk of recurrence may be reduced by proper timing of transplantation and suitable choice of immunosuppressive agents. Intensive plasmapheresis in conjunction with fresh frozen plasma and supportive management of renal failure may lessen mortality and morbidity even in recurrent hemolytic uremic syndrome after transplantation.

Adult↗
PubMed1995

Acquired resistance to acute oxidative stress. Possible role of heme oxygenase and ferritin.

BACKGROUND: Prior administration of endotoxin has conferred resistance to tissue damage in a number of models of organ injury. The mechanisms by which this resistance is conferred are enigmatic. Recognizing that enhanced tissue oxidative stress may be a feature of endotoxin-associated injury and is present in many models of tissue injury, we questioned whether the beneficial effect conferred by endotoxin is dependent on the up-regulation of antioxidant defenses. EXPERIMENTAL DESIGN: We employed the glycerol model of acute renal failure (Gly-ARF), a model in which oxidant damage occurs in the kidney and other organs as a result of rhabdomyolysis and hemolysis. Rats were pretreated with endotoxin 24 hours before, or at the time of, induction of Gly-ARF. Renal functional studies and assessment of renal antioxidant status were performed. The effect of prior treatment with endotoxin was also examined in models of methemoglobin-induced and ischemic ARF. RESULTS: Renal function was improved in rats pretreated with endotoxin but worsened in rats subjected to Gly-ARF and endotoxin simultaneously. Endotoxin induced heme oxygenase activity and ferritin content in the kidney but did not induce other antioxidant systems such as catalase and glutathione peroxidase. Treatment with a competitive inhibitor of heme oxygenase blocked endotoxin-induced protection on days 2 and 3, while markedly attenuating the protective effect on day 1. Pretreatment with endotoxin reduced renal injury induced by methemoglobin, but not ischemia. CONCLUSIONS: The resistance to injury conferred by endotoxin in Gly-ARF involves induction of an antioxidant response, consisting of increased heme oxygenase and ferritin synthesis. This coupled response allows degradation of heme as well as chelation of iron, thus decreasing oxidant-mediated tissue injury. This novel mechanism of endotoxin-induced resistance may be applicable not only to Gly-ARF but also to other models of tissue injury in which enhanced oxidative stress is implicated.

Acute Kidney Injury↗
PubMed1994

Effect of pyruvate on oxidant injury to isolated and cellular DNA.

Drawing upon the capacity of pyruvate to detoxify H2O2, we demonstrate that pyruvate (i) protects against H2O2-dependent, hydroxyl radical-mediated degradation of isolated DNA; (ii) reduces the amount of 8-hydroxy-2-deoxyguanosine detected following oxidative injury to isolated DNA and (iii) diminishes the amounts of detectable hydroxyl radical generated by a H2O2-dependent system. Compared to mannitol, pyruvate protects weakly against oxidative degradation of DNA induced by a H2O2-independent, hydroxyl radical-generating system. The protective effects of pyruvate against H2O2-instigated DNA damage were also evinced in cells in culture exposed to H2O2. In contrast to its protective effects against H2O2-dependent injury to DNA, pyruvate failed to offer convincing protection to another intracellular, H2O2-vulnerable target, glyceraldehyde-3-phosphate dehydrogenase. The protection conferred by pyruvate to intracellular H2O2-vulnerable targets is thus influenced by the nature of the target exposed to H2O2. Pyruvate was markedly protective in a model of cytotoxicity induced by the concomitant depletion of cellular glutathione and inhibition of catalase activity; pyruvate can thus function as an intracellular antioxidant and in this latter model, no evidence of DNA damage was observed. Pyruvate, in contrast to catalase, is a potent protector against cytotoxicity induced by organic peroxides, a finding that cannot be explained by the scavenging of organic peroxides, differences in glutathione content or attenuation in oxidative injury to DNA. We conclude that while DNA damage is a key pathogenetic event in oxidative stress induced by H2O2, such nuclear changes may not universally subserve a critical role in models of H2O2-dependent cell death. We also conclude that the antioxidant capabilities of pyruvate extend beyond scavenging of H2O2 to include potent protection against cytotoxicity induced by organic peroxides.

Animals↗
PubMed1994

Physiological and structural responses to chronic experimental renal allograft injury.

Chronic rejection necessitates a return to dialysis or retransplantation for a significant number of patients with renal allografts. Although alloresponses between donor organ and recipient importantly determine this process, the detailed immunologic processes and organ physiology of chronic rejection are unclear; in consequence its mechanism and therapy are uncertain. A model of chronic rejection in the rat was used to examine several facets of this process. Fisher-to-Lewis (F-L), allogeneic, and Lewis-to-Lewis (L-L), syngeneic, renal transplants were performed in nephrectomized recipients. All rats were treated with cyclosporin A (5 mg.kg-1.day-1) for 10 days from the time of grafting. At 6 wk, allogeneically grafted animals had a higher protein excretion rate (F-L, 47 +/- 30 mg/day; L-L, 17 +/- 6 mg/day; P < 0.05) and an increase in glomerular capillary pressure (F-L, 69 +/- 5 mmHg; L-L, 58 +/- 8 mmHg; P < 0.05) and fractional cortical interstitial volume (F-L, 29.8 +/- 4.3%; L-L, 19.5 +/- 4.0%; P < 0.01). This model of chronic rejection is characterized by glomerular capillary hypertension, proteinuria, and cortical interstitial expansion. Because these findings are also present in other models of chronic renal injury, mechanisms in addition to alloresponses may operate in chronic rejection.

Animals↗
PubMed1994

Internucleosomal cleavage of DNA as the sole criterion for apoptosis may be artifactual.

Apoptosis is a distinct form of cell death characterized by internucleosomal cleavage of DNA, cell membrane blebbing, condensation of nuclear chromatin in the nuclear periphery, and the formation of apoptotic, condensed nuclear bodies. The finding of internucleosomal cleavage of chromatin, perhaps caused by endonuclease activation, has become accepted as a hallmark of this form of cell death. We describe the incidental and artifactual finding of internucleosomal cleavage of chromatin from kidney tissue from normal animals. Nephrectomy was performed in living animals, and renal tissue was digested with proteinase K in 10 mmol/L Tris, 1 mmol/L ethylenediaminetetraacetic acid (EDTA), 10 mmol/L NaCl, and 0.5% sodium dodecyl sulfate. Agarose gel electrophoresis of extracted DNA showed internucleosomal cleavage. Internucleosomal cleavage of DNA was not tissue specific but was evident also in liver DNA from a number of animals. Histologic examination of kidney tissue where DNA exhibited internucleosomal cleavage showed normal morphology, with no evidence of either apoptotic or necrotic cell death. Cleavage was not completely prevented by immediate freezing of kidney tissue in liquid nitrogen before DNA extraction, nor was it prevented by the addition of spermidine, of ethyleneglycol-bis-(beta-aminoethylether)-N,N,N',N'-tetraace tic acid, of phenylmethylsulfonylfluride, or by an increased concentration of NaCl to 100 mmol/L in the digestion buffer. Internucleosomal cleavage of DNA was mostly, although not invariably, inhibited by the use of a digestion buffer containing 10 mmol/L Tris, 25 mmol/L EDTA, and 100 mmol/L NaCl. "Apoptotic" chromatin changes (internucleosomal fragmentation) are not always associated with histologic evidence of apoptosis and may occur artifactually.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Induction of clusterin in acute and chronic oxidative renal disease in the rat and its dissociation from cell injury.

BACKGROUND: Clusterin is a glycoprotein incriminated in diverse biologic processes including complement regulation, cell death, and tissue remodelling. Induction of clusterin occurs in renal and other tissue injuries. EXPERIMENTAL DESIGN: The purpose of this study was to determine the effect of prooxidant states, one acute (glycerol-induced acute renal failure) and the other chronic (vitamin E and selenium deficiency) on renal clusterin expression, and to attempt to delineate the signals which in these in vivo models can elicit expression of clusterin in vitro. RESULTS: In glycerol-induced acute renal failure, a model of rhabdomyolysis, clusterin mRNA was markedly increased 24 hours after injection of glycerol (control 97 +/- 21 versus glycerol 3644 +/- 134 optical density units; p < 0.001). Immunohistochemical clusterin was also increased in glycerol-treated rats with tubules in both cortex and medulla staining for clusterin. In vitamin E and selenium deficiency, clusterin mRNA was increased 9 weeks after initiation of the deficient diet (control 97 +/- 13 versus deficient 1137 +/- 403 optical density units; p < 0.04) as were the number of tubules staining for clusterin. Since renal injury is instigated in the glycerol model by muscle damage, we tested the effect of muscle extract on clusterin expression in vitro. A homogenate of skeletal muscle induced clusterin mRNA and this induction was not associated with disruption of cell membranes and was not inhibited by cycloheximide treatment, but was blocked by actinomycin D. Since increased generation of hydrogen peroxide is a pivotal biochemical lesion in both in vivo models, we tested the effect of peroxide to induce clusterin in vitro; no such induction occurred. CONCLUSIONS: Renal tubular clusterin expression was increased in both acute glycerol-induced renal failure and chronic vitamin E and selenium deficiency, two in vivo models of oxidant injury to the kidney. In vitro induction of clusterin can occur and can be dissociated from cell injury.

Acute Disease↗
PubMed1994

Therapeutic strategies in the prevention of acute renal failure.

The current management of acute renal failure rests largely on the avoidance of ischemic and nephrotoxic insults, attention to fluid and electrolyte balance, and the use of dialytic procedures when necessary. The efficacy of several strategies in experimental renal disease, reviewed in this article, raises the possibility that available to the clinician in the not-too-distant future would be analogous interventions that interrupt pathways of tissue injury and/or summon processes that attenuate the damaging effect of a given insult. The implementation of such therapeutic modalities would expand the management of acute renal failure from its current conservative approach to one encompassing therapeutic interventions that potentially prevent the occurrence of acute renal failure. Moreover, the remarkable and ever-increasing understanding of acute renal failure, in all its deranged cell biology and complex pathogenesis, offers the promise of discerning still better and more effective therapeutic interventions.

Acute Kidney Injury↗
PubMed1993

Autoxidation of cysteine generates hydrogen peroxide: cytotoxicity and attenuation by pyruvate.

The reactivity of cysteine presents a paradox: although regarded as an antioxidant, cysteine interacts with oxygen in a metal-catalyzed reaction to produce reactive species. Because ischemia provokes the appearance of millimolar amounts of cysteine and increased amounts of transition metals, we studied whether cysteine, in the presence of transition metals, consumes oxygen, generates hydrogen peroxide, and is toxic. Using fluorescence cytometry, we provide direct evidence that hydrogen peroxide is copiously generated during cysteine autoxidation. Pyruvate attenuates such generation of hydrogen peroxide and cytotoxicity. Cysteine oxidation is stimulated by an EDTA-chelatable diethyl-dithiocarbamate-chelatable constituent of kidney extract; this suggests that copper is the catalytically active metal. The toxicity resulting from cysteine oxidation is less than that induced by amounts of reagent hydrogen peroxide that produce comparable fluorescence. Cysteine also prevents hydrogen peroxide-induced toxicity. Thus, although cysteine generates hydrogen peroxide, it can guard against hydrogen peroxide toxicity, possibly by binding metals on which the toxicity of hydrogen peroxide is dependent. Thus the behavior of cysteine can be salutary or pernicious; the net effect of cysteine, within this wide ambit of actions, is decisively influenced by the conditions to which cysteine is exposed.

Amitrole↗
PubMed1993

Effect of proteinuria on renal interstitium: effect of products of nitrogen metabolism.

Tubulointerstitial disease is an invariant finding in proteinuric renal disease regardless of the underlying disease or the compartment in which the disease originates. Such histologic changes are functionally significant in that scores of such injury rather than glomerular histologic injury correlate with decrements in GFR. Proteinuria, the consequence of a loss of glomerular permselectivity incurred by glomerular diseases, also provides an index of renal functional decline. This review provides evidence that proteins leaked into the urinary space may directly or indirectly provoke tubulointerstitial injury, a linkage that may underlie the functional significance of proteinuria and tubulointerstitial disease. This review also highlights two products of nitrogen metabolism, ammonia and nitric oxide, in the pathogenesis of tubulointerstitial disease.

Ammonia↗
PubMed1993

Heme oxygenase is not expressed as a stress protein after renal ischemia.

Stressful stimuli such as heat, oxidative stress, heavy metals, and tissue trauma induce the expression of a family of proteins commonly referred to as stress proteins or heat shock proteins. The functions of these proteins are varied but include glycolysis, antioxidant defense, and several postulated "chaperone" functions involving the folding, unfolding, and translocation of other proteins. Heme oxygenase, the enzyme that catalyzes the degradation of heme to biliverdin, is also heat inducible and is, therefore, a heat shock protein. In the kidney, ischemia has been observed by several investigators to induce expression of the more commonly studied heat shock proteins HSP 70 and HSP 72. In addition, exposure of the kidney to myoglobin after glycerol injection induced heme oxygenase. The purpose of this study was to determine whether heme oxygenase is expressed as a stress protein after renal ischemia. Renal ischemia was induced in rats after right nephrectomy by clamping the renal artery for 40 minutes. Gene expression was evaluated after 60 minutes to 96 hours of postischemic reperfusion. There was essentially no expression of heme oxygenase at any of the time points evaluated. The absence of heme oxygenase expression was in striking contrast to the prompt and dramatic expression of HSP 70. This finding is consistent with the concept that all "stress proteins" are not equivalent and that, although there is considerable overlap between heat-sensitive gene promoters and oxidant stress-sensitive gene promoters, there is specificity for the type of stimulus that is able to activate any given stress protein gene.

Actins↗
PubMed1992

Tubulointerstitial changes as a major determinant in the progression of renal damage.

Tubulointerstitial injury is an invariant finding in the chronically diseased kidney, irrespective of the type of disease or the compartment in which the disease originates. Such histologic changes are functionally significant in that scores for such damage, rather than glomerular injury, correlate with decline of renal function. This review summarizes (1) clinical evidence attesting to tubulointerstitial changes as an index of functional impairment, (2) mechanisms by which tubulointerstitial injury impairs renal function, and (3) interactions of pathologic processes in the vascular, glomerular, tubular, and interstitial compartments that culminate in tubulointerstitial injury. This report concludes with a review of interstitial fibrosis, a pathologic process regarded as an irreversible outcome from tubulointerstitial injury.

Animals↗
PubMed1992

Hyperosmolality impairs ammonia-mediated inflammation: implications for the renal medulla.

Although ammonia modifies the third component of complement (C3) and activates the alternative pathway, inflammation is not seen in the renal medulla where ammonia concentrations are normally elevated. We examined the effect of the unique hyperosmolar milieu of the renal medulla on the interaction of ammonia with C3 and the capacity of ammonia-modified C3 (NH3.C3) to induce cytolytic injury and stimulate neutrophils (PMN). Incubation of purified human C3 with ammonia in concentrations found in urine results in significant disruption of the C3 thiolester bond compared with ammonia-free controls. Coincubation with urinary osmolytes and hyperosmolar NaCl and urea does not impair thiolester disruption over a range of ammonia concentrations. However, hyperosmolar NaCl and urea virtually abolish cytolytic injury mediated by the alternative pathway. Coincubation with the organic osmolytes betaine, sorbitol, and inositol fails to reverse this inhibitory effect of hyperosmolar NaCl and urea. Hyperosmolar NaCl and urea also suppress lytic injury mediated by ammonia and complement in MDCK, a cell line derived from canine distal tubular epithelium. Both PMN degranulation and respiratory burst responses to NH3.C3 are significantly blunted in the presence of hyperosmolar NaCl and urea. Hyperosmolality also impairs PMN responses to the formyl peptide N-formyl-Met-Leu-Phe and phorbol 12-myristate 13-acetate (PMA). Therefore, in an in vitro setting of hyperosmolar NaCl and urea, amidation of C3 occurs, but subsequent membrane-directed and receptor-mediated functions of NH3.C3 are markedly impaired.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗
PubMed1992

Induction of heme oxygenase is a rapid, protective response in rhabdomyolysis in the rat.

Heme proteins such as myoglobin or hemoglobin, when released into the extracellular space, can instigate tissue toxicity. Myoglobin is directly implicated in the pathogenesis of renal failure in rhabdomyolysis. In the glycerol model of this syndrome, we demonstrate that the kidney responds to such inordinate amounts of heme proteins by inducing the heme-degradative enzyme, heme oxygenase, as well as increasing the synthesis of ferritin, the major cellular repository for iron. Prior recruitment of this response with a single preinfusion of hemoglobin prevents kidney failure and drastically reduces mortality (from 100% to 14%). Conversely, ablating this response with a competitive inhibitor of heme oxygenase exacerbates kidney dysfunction. We provide the first in vivo evidence that induction of heme oxygenase coupled to ferritin synthesis is a rapid, protective antioxidant response. Our findings suggest a therapeutic strategy for populations at a high risk for rhabdomyolysis.

Animals↗
PubMed1992

Interaction of complement and clusterin in renal injury.

Clusterin is a heterodimeric glycoprotein that has been associated with such diverse biologic functions as reproduction, cell regression, cell aggregation, and regulation of the cytolytic activity of the membrane attack complex of complement. Clusterin is a component of glomerular immune deposits in the kidney, and increased clusterin expression occurs in a number of renal injury states. To further explore the interaction between clusterin and complement, the requirement for an intact complement system for renal clusterin induction in an acute (folic acid nephropathy) and a chronic (subtotal renal ablation) model of renal injury was examined. After it was first demonstrated that folic acid increased renal clusterin mRNA in the rat, a species in which renal clusterin was highly inducible by other stimuli, the effects of folic acid (250 mg/kg ip) on clusterin mRNA and immunoreactivity were examined in mice sufficient and deficient for the fifth component of complement. Similar increases in clusterin mRNA and immunoreactivity were seen in both the C5-sufficient and C5-deficient mice compared with their respective vehicle-injected control groups. Renal clusterin mRNA was also increased to a similar extent in the remaining kidney of both C5-sufficient and C5-deficient mice 10 days after subtotal nephrectomy. In conclusion, the induction of clusterin after folic acid administration or subtotal nephrectomy was independent of the presence of an intact complement system, because similar increases in clusterin expression were observed in C5-sufficient and C5-deficient mice.

Acute Disease↗