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R S Britton

Publications and source records attributed to R S Britton.

At least 55 records · Page 3Linked to original sources
PubMed1994

Pathophysiology of iron toxicity.

There are several inherited and acquired disorders that can result in chronic iron overload in humans, and the major clinical consequences are hepatic fibrosis, cirrhosis, hepatocellular cancer, cardiac disease, and diabetes. It is clear that lipid peroxidation occurs in experimental iron overload if sufficiently high levels of iron within hepatocytes are achieved. Lipid peroxidation is associated with hepatic mitochondrial and microsomal dysfunction in experimental iron overload, and lipid peroxidation may underlie the increased lysosomal fragility that has been detected in liver samples from both iron-loaded human subjects and experimental animals. Reduced cellular ATP levels, impaired cellular calcium homeostasis, and damage to DNA may all contribute to hepatocellular injury in iron overload. Long-term dietary iron overload in rats can lead to increased collagen gene expression and hepatic fibrosis, perhaps due to activation of hepatic lipocytes. The mechanisms whereby lipocytes are activated in iron overload remain to be elucidated; possible mediators include aldehydic products of iron-induced lipid peroxidation produced in hepatocytes, tissue ferritin, and/or cytokines released by activated Kupffer cells.

Animals↗
PubMed1994

Determination of hepatic iron concentration in fresh and paraffin-embedded tissue: diagnostic implications.

BACKGROUND/AIMS: Determination of hepatic iron concentration (HIC) is essential for the evaluation of hereditary hemochromatosis. Occasionally, only paraffin-embedded liver biopsy specimens are available, or fresh biopsy specimens have been placed in saline for transport. This study aimed to describe a method for extraction of liver tissue from paraffin blocks, determine the accuracy of measurement of HIC in recovered tissue compared with fresh tissue, and determine the effect of immersion in saline on HIC. METHODS: HIC was measured in both fresh and deparaffinized liver specimens (n = 41). Accurate measurements were defined as either a normal result in both specimens or a result in the deparaffinized specimen that was within 30% of the fresh measurement. RESULTS: Measurements of HIC in fresh and deparaffinized tissue showed an excellent linear relationship (r = 0.95). In deparaffinized samples > or = 0.4 mg, accurate measurements were seen in 24 out of 29 specimens, compared with 6 out of 12 specimens weighing < 0.4 mg (P < 0.01). The hepatic iron index calculated from results in deparaffinized samples > or = 0.4 mg correctly classified all patients. Immersion of fresh biopsy specimens in saline for 1 hour resulted in up to 50% iron loss (P < 0.05). CONCLUSIONS: Accurate measurement of HIC in deparaffinized liver biopsy specimens is possible. Calculation of the hepatic iron index from deparaffinized liver tissue can facilitate diagnosis of hemochromatosis when fresh tissue is not available. Samples should not be transported in saline.

Animals↗
PubMed1994

Oxidant injury to hepatic mitochondria in patients with Wilson's disease and Bedlington terriers with copper toxicosis.

BACKGROUND/AIMS: Copper overload leads to liver injury in humans with Wilson's disease and in Bedlington terriers with copper toxicosis; however, the mechanisms of liver injury are poorly understood. This study was undertaken to determine if oxidant (free radical) damage to hepatic mitochondria is involved in naturally occurring copper toxicosis. METHODS: Fresh liver samples were obtained at the time of liver transplantation from 3 patients with Wilson's disease, 8 with cholestatic liver disease, and 5 with noncholestatic liver disease and from 8 control livers. Fresh liver was also obtained by open liver biopsy from 4 copper-overloaded and 4 normal Bedlington terriers and from 8 control dogs. Hepatic mitochondria and microsomes (humans only) were isolated, and lipid peroxidation was measured by lipid-conjugated dienes and thiobarbituric acid-reacting substances. In humans, liver alpha-tocopherol content was measured. RESULTS: Lipid peroxidation and copper content were significantly increased (P < 0.05) in mitochondria from patients with Wilson's disease and copper-overloaded Bedlington terriers. More modest increases in lipid peroxidation were present in microsomes from patients with Wilson's disease. Mitochondrial copper concentrations correlated strongly with the severity of mitochondrial lipid peroxidation. Hepatic alpha-tocopherol content was decreased significantly in Wilson's disease liver. CONCLUSIONS: These data suggest that the hepatic mitochondrion is an important target in hepatic copper toxicity and that oxidant damage to the liver may be involved in the pathogenesis of copper-induced injury.

Adolescent↗
PubMed1994

Differential production of TNF by Kupffer cells after phagocytosis of E. coli and C. albicans.

Tumor necrosis factor (TNF) of hepatic origin is thought to play a pivotal role early in the genesis of the septic shock syndrome, regardless of microbial etiology. To determine if production of TNF by Kupffer cells varies with microbial taxonomic class, we measured TNF secretory responses in primary cultures of rat Kupffer cells to numerically equivalent gram-negative bacterial or fungal phagocytic challenges. After a 30-min exposure to media, latex beads, soluble Escherichia coli lipopolysaccharide (LPS; serotype 055:B5), live or Formalin-fixed E. coli (serotype 055:B5), live or Formalin-fixed yeast-phase Candida albicans, or live hyphal-phase Candida, samples of culture supernatant were assessed at 30, 60, 120, and 240 min and at 24 h for TNF bioactivity by L929 cell cytotoxicity. Compared with media and latex bead controls, TNF levels progressively increased for up to 240 min after either LPS and equivalently in live E. coli or Formalin-fixed E. coli groups (P < 0.05). Formalin-fixed yeast-phase and live extracellular hyphal-phase C. albicans failed to stimulate production of TNF at any time point (6.9 +/- 0.7 and 8.7 +/- 0.4 U/ml, respectively, at t = 240 min; P < 0.05 vs. E. coli). In contrast, internalization of live yeast-phase C. albicans with subsequent hyphal formation and growth within Kupffer cells was accompanied by a rise in supernatant TNF levels (14.5 +/- 1.8 U/ml at t = 240 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

TNF-alpha and IL-6 expression in perfused rat liver after intraportal candidemia vs. E. coli or S. aureus bacteremia.

We tested the hypothesis that regulation of tumor necrosis factor-alpha (TNF-alpha) and IL-6 by the liver differs after intraportal challenge with Candida albicans spp. vs. gram-negative or gram-positive bacteria, independent of microbial clearance kinetics or hepatic O2 consumption (VO2). Buffer-perfused rat livers were infected with equivalent inocula (10(9) colony-forming units) of viable Escherichia coli serotype 055:B5 (EC), exotoxin C-producing Staphylococcus aureus (SA), or two strains of yeast phase C. albicans (CA-1 and CA-2). Microbial clearance and circulating cytokine levels were assessed over 180 min while monitoring VO2 and functional parameters, after which organ-based microbial killing, cell-associated TNF-alpha, and cytokine mRNA levels were determined. Compared with saline controls (normal saline solution; NSS), circulating and cell-associated TNF-alpha and TNF-alpha transcripts minimally increased after CA. In contrast, large increases in perfusate TNF-alpha occurred after EC, peaking at 180 min [135 +/- 32 U/ml (mean + SE)], concomitant with rises in cell-associated cytokine and TNF-alpha transcripts (P < 0.01 vs. NSS). Circulating TNF-alpha also rose after SA but neither cell-associated nor mRNA levels exceeded NSS values. There were no pathogen-specific differences in microbial clearance or VO2. IL-6 gene expression paralleled that for TNF-alpha, but IL-6 bioactivity in perfusates was inhibited by TNF-alpha-dependent and -independent mechanisms. We conclude that hepatic TNF-alpha and IL-6 expression are differentially regulated after taxonomically diverse microbial challenges, with E. coli eliciting the strongest and Candida spp. the weakest stimulatory responses.

Animals↗
PubMed1994

Identification and characterization of a receptor for tissue ferritin on activated rat lipocytes.

Hepatic iron overload causes lipocyte activation with resultant fibrogenesis. This study examines whether rat lipocytes express ferritin receptors, which could be involved in paracellular iron movement and in cellular regulation. Lipocytes from normal rat liver were cultured on plastic and incubated with 125I-labeled rat liver ferritin (RLF) +/- a 100-fold excess of either unlabeled RLF or human heart ferritin, human liver ferritin, human recombinant H-ferritin, a mutant human recombinant L-ferritin, or a variety of nonspecific proteins. Specific binding sites for ferritin were demonstrated by displacement of 125I-RLF by RLF (64.5 +/- 4.3%) and by other ferritins (55-60%), but not by recombinant L-ferritin. Scatchard analysis demonstrated a single class of binding sites with a Kd of 5.1 +/- 2.9 x 10(-10) M, maximum binding capacity of 4.7 +/- 1.3 x 10(-12) M, and 5,000-10,000 receptor sites/cell. Ferritin receptor expression was observed only in activated lipocytes. Internalization of RLF was observed within 15 min using FITC-RLF and confocal microscopy. This study demonstrates that (a) activated lipocytes express a specific high affinity ferritin receptor; (b) the binding appears to be dependent on the H-ferritin subunit; and (c) lipocytes internalize ferritin. Expression of ferritin receptors in activated lipocytes suggests that the receptor may either be involved in the activation cascade or may be a marker of activation.

Actins↗
PubMed1994

Role of free radicals in liver diseases and hepatic fibrosis.

An increased production of free radicals in the liver has been implicated in a variety of liver diseases. Free radicals can damage cellular macromolecules and, therefore, may participate in hepatocellular injury when produced in excess. Strong evidence exists for hepatic free radical production in animal models of iron and copper overload, ethanol consumption, and ischemia-reperfusion. Although less is known about the situation in humans with liver diseases, the available evidence is consistent with the findings in animal experiments. Treatments that reduce free radical production and/or levels have protective effects in hepatic ischemia-reperfusion. Free radical-initiated lipid peroxidation may play a role in hepatic fibrogenesis, perhaps through an effect of aldehydic peroxidation products on Kupffer cells and lipocytes. This hypothesis is supported by the observation that dietary supplementation with vitamin E has a protective effect on carbon tetrachloride-induced hepatic fibrosis. While cellular damage in human liver diseases is probably multifactorial, free radicals may play important roles in initiating and/or perpetuating this damage.

Alcoholic Intoxication↗
PubMed1993

Hepatic mitochondrial energy production in rats with chronic iron overload.

BACKGROUND: Iron overload results in impaired hepatic mitochondrial oxidative metabolism. The current experiments evaluated the effects of iron overload on enzyme activities in the mitochondrial electron transport chain, on hepatic adenine nucleotide levels, and on hepatocellular oxygen consumption. METHODS: Hepatic iron overload was produced in rats using dietary carbonyl iron. Hepatic adenine nucleotides were assessed after freeze-clamping, mitochondrial enzyme activities and oxygen consumption were measured in isolated mitochondria, and oxygen consumption in isolated hepatocytes was determined. RESULTS: At a mean hepatic iron concentration of 4630 micrograms/g, there were no changes in reduced nicotinamide adenine dinucleotide (NADH)-cytochrome c reductase activity (complex I-III), but there was a 35% reduction in succinate-cytochrome c reductase activity (complex II-III), and a 70% decrease in cytochrome c oxidase activity (complex IV). With mild iron loading (2060 micrograms/g), there was a 28% decrease in hepatic adenosine 5'-triphosphate (ATP) levels with no change in adenosine 5'-diphosphate (ADP) or adenosine 5'-monophosphate (AMP) levels, whereas, at a higher hepatic iron concentration (3170 micrograms/g), there was a 40% reduction in ATP levels, a 22% decrease in ADP levels, with no change in AMP levels. There was a 48% reduction in oxygen consumption in isolated iron-loaded hepatocytes. CONCLUSIONS: Chronic iron overload decreases hepatic mitochondrial cytochrome c oxidase activity, hepatocellular oxygen consumption, and hepatic ATP levels.

Adenosine Diphosphate↗
PubMed1992

Increased 4-hydroxynonenal levels in experimental alcoholic liver disease: association of lipid peroxidation with liver fibrogenesis.

The precise role of lipid peroxidation in the pathogenesis of alcoholic liver disease is still being debated. To explore the issue, this study was undertaken to investigate the status of lipid peroxidation, antioxidants and prooxidants at two discrete stages of experimental alcoholic liver disease. Male Wistar rats were intragastrically fed a high-fat diet plus ethanol for 5 or 16 wk (the duration that resulted in initiation of centrilobular liver necrosis or liver fibrosis, respectively). Lipid peroxidation was assessed in isolated microsomes and mitochondria with three parameters: malondialdehyde equivalents as determined by thiobarbituric acid assay, conjugated diene formation and 4-hydroxynonenal as a 2,4-dinitrophenylhydrazone derivative. To assess antioxidant systems, hepatic concentrations of glutathione, methionine and alpha-tocopherol were determined. The concentration of nonheme iron, a known prooxidant, was also measured. At wk 5, centrilobular liver necrosis was already evident in the ethanol-fed animals, with two- or threefold increases in plasma AST and ALT levels. At this stage, neither malondialdehyde equivalents nor conjugated diene values were elevated, and the 4-hydroxynonemal level was below 0.2 nmol/mg protein. Hepatic concentrations of methionine and alpha-tocopherol in these animals were increased two- and threefold, respectively, whereas the reduced glutathione level remained unchanged. When alcoholic liver disease had progressed to perivenular or bridging fibrosis at wk 16, all three parameters of lipid peroxidation showed consistent increases that were accompanied by significant reductions in the hepatic glutathione and methionine levels. Interestingly, the control animals pair-fed with the high-fat diet also had significantly elevated 4-hydroxynonenal levels at wk 16 compared to the wk 5 level.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldehydes↗
PubMed1991

Chronic dietary iron overload in rats results in impaired calcium sequestration by hepatic mitochondria and microsomes [corrected].

The purpose of these experiments was to determine whether chronic dietary iron overload causes impairment of hepatic mitochondrial and/or microsomal calcium sequestration. Experimental iron overload was produced by feeding three groups of rats a chow diet supplemented with 3.0% (wt/wt) carbonyl iron for up to 8 weeks achieving graded increases in hepatic iron concentrations ranging from 1360 to 3170 micrograms/g. At low levels of iron overload, there were no changes in mitochondrial oxidative metabolism or calcium sequestration, whereas at moderate and high degrees of iron loading, both of these parameters were significantly reduced. In contrast, there were significant decreases in microsomal cytochrome P450 levels and microsomal calcium sequestration at all three levels of iron loading. These abnormalities occurred at hepatic iron concentrations at which the authors have previously found evidence of hepatic organelle lipid peroxidation. These alterations in organelle calcium sequestration may impair intracellular calcium homeostasis in the liver and contribute to subsequent cellular injury.

Animals↗
PubMed1990

Hepatic mitochondrial malondialdehyde metabolism in rats with chronic iron overload.

Peroxidative decomposition of mitochondrial membrane phospholipids with subsequent mitochondrial dysfunction is a postulated mechanism of liver cell injury in parenchymal iron overload. Malondialdehyde is formed when polyunsaturated fatty acids of membrane phospholipids undergo peroxidative decomposition, and it is metabolized by aldehyde dehydrogenase. We studied mitochondrial metabolism of malondialdehyde in rats with chronic dietary iron overload. Hepatic malondialdehyde concentrations were significantly increased in iron-loaded livers, and mitochondrial respiratory control ratios using glutamate as a substrate were decreased by 47% largely owing to reductions in state 3 respiration. When exogenous malondialdehyde was added to mitochondrial fractions, there was significantly less metabolism of malondialdehyde in mitochondria of iron-loaded livers as compared with controls. In addition, there was a 28% decrease in mitochondrial aldehyde dehydrogenase in iron-loaded livers but no change in cytosolic aldehyde dehydrogenase. Increased hepatic malondialdehyde in chronic iron overload may result from a combination of increased production and decreased metabolism of malondialdehyde, both of which may be due to iron-induced mitochondrial lipid peroxidation.

Aldehyde Dehydrogenase↗
PubMed1990

Increased prooxidant action of hepatic cytosolic low-molecular-weight iron in experimental iron overload.

In the iron-loaded liver there may be an increase in the putative intracellular transit pool of iron, components of which could be catalytically active in stimulating lipid peroxidation. To study the levels of low-molecular-weight, catalytically active iron in the liver, cytosolic ultrafiltrates were tested in an assay containing rat liver microsomes and NADPH. Malondialdehyde production was used as an index of lipid peroxidation. This assay system was sensitive enough to detect 0.25 mumol/L ferrous iron; progressive but non-linear increases in malondialdehyde were produced as the iron concentration was increased to 5 mumol/L. Ultrafiltrates from hepatic cytosol of iron-loaded rats had greater prooxidant action than did those from controls. When added to the assay, deferoxamine, an iron chelator, completely suppressed the prooxidant action of hepatic ultrafiltrates, showing that this activity is iron-dependent. Deferoxamine administered intraperitoneally to control animals at a dose of 1 gm/kg completely inhibited the prooxidant effect of hepatic ultrafiltrates prepared from rats killed after 1, 2 and 3 hr. Partial inhibition was observed at 4 hr; by 6 hr the inhibitory effect of deferoxamine was completely lost. Administration of deferoxamine (1 gm/kg intraperitoneally, 1 hr before killing) completely inhibited the prooxidant action of hepatic ultrafiltrates in moderately iron-loaded rats and controls but had no protective effect in heavily iron-loaded rats. These results support the concept that iron overload results in an increase in a hepatic cytosolic pool of low-molecular-weight iron that is catalytically active in stimulating lipid peroxidation. This pool can be chelated transiently in vivo by deferoxamine in moderate, but not heavy, iron overload.

Animals↗
PubMed1990

Prevention of hepatocyte injury and lipid peroxidation by iron chelators and alpha-tocopherol in isolated iron-loaded rat hepatocytes.

These experiments were performed to characterize the relationship between lipid peroxidation and hepatocyte viability in iron overload. Hepatocytes were isolated from rats with chronic dietary iron overload and the effects of in vitro iron chelation on lipid peroxidation, cell viability and ultrastructure were studied over a 4-hr incubation period. Cell viability was significantly reduced at 3 and 4 hr in iron-loaded hepatocytes compared with controls and was preceded by an increase in iron-dependent lipid peroxidation. Similarly, extensive degenerative ultrastructural changes were observed in iron-loaded hepatocytes compared with controls after 4 hr of incubation. In vitro iron chelation with either deferoxamine or apotransferrin protected against lipid peroxidation, loss of viability and ultrastructural damage in iron-loaded hepatocytes. The addition of an antioxidant, alpha-tocopherol, also protected against lipid peroxidation and preserved cell viability over a 4-hr incubation. The protective effects of iron chelators and alpha-tocopherol support a strong association between iron-dependent lipid peroxidation and hepatocellular injury in iron overload.

Animals↗
PubMed1989

Effects of vitamin E deficiency on hepatic mitochondrial lipid peroxidation and oxidative metabolism in rats with chronic dietary iron overload.

Peroxidative decomposition of organelle membrane phospholipids with subsequent organelle dysfunction is a postulated mechanism of liver cell injury in parenchymal iron overload. We studied the effects of different alpha-tocopherol concentrations on hepatic mitochondrial lipid peroxidation and oxidative metabolism in rats with chronic dietary iron overload. There was no evidence of mitochondrial lipid peroxidation (conjugated dienes) or alteration in mitochondrial oxidative metabolism in alpha-tocopherol-deficient rats with normal hepatic iron levels. Significant reductions in mitochondrial respiratory control ratios and oxidative phosphorylation ratios were seen in association with increased conjugated dienes in all three groups of iron-loaded rats regardless of the alpha-tocopherol status (deficient, normal or excess); thus, the alpha-tocopherol deficiency associated with dietary iron overload in this experimental model is not responsible for the mitochondrial abnormalities observed. In addition, chronic parenteral administration of alpha-tocopherol to iron-loaded animals, which increased hepatic levels of this substance 3-fold, did not ameliorate the hepatic mitochondrial lipid peroxidation or the defects in mitochondrial oxidative metabolism resulting from iron overload.

Animals↗
PubMed1989

Hepatic injury in chronic iron overload. Role of lipid peroxidation.

In both hereditary hemochromatosis and in the various forms of secondary hemochromatosis, there is a pathologic expansion of body iron stores due mainly to an increase in absorption of dietary iron. Excess deposition of iron in the parenchymal tissues of several organs (e.g. liver, heart, pancreas, joints, endocrine glands) results in cell injury and functional insufficiency. In the liver, the major pathological manifestations of chronic iron overload are fibrosis and ultimately cirrhosis. Evidence for hepatotoxicity due to iron has been provided by several clinical studies, however the specific pathophysiologic mechanisms for hepatocellular injury and hepatic fibrosis in chronic iron overload are poorly understood. The postulated mechanisms of liver injury in chronic iron overload include (a) increased lysosomal membrane fragility, perhaps mediated by iron-induced lipid peroxidation, (b) peroxidative damage to mitochondria and microsomes resulting in organelle dysfunction, (c) a direct effect of iron on collagen biosynthesis and (d) a combination of all of the above.

Animals↗
PubMed1987

Potentiation of carbon tetrachloride hepatotoxicity by chlordecone: dose-response relationships and increased covalent binding in vivo.

Chlordecone greatly potentiates carbon tetrachloride (CCl4) hepatotoxicity. In order to quantitate the degree of this potentiation, the effects of a range of doses of CCl4 on two microsomal enzymatic functions and liver enzyme release were examined in chlordecone-treated and control rats. Male Sprague-Dawley rats were pretreated with 15 mg chlordecone per kilogram body weight (BW) intragastrically or with vehicle. After 48 hours, 0 to 250 microliters CCl4 per 100 g body weight were given intraperitoneally (IP), and the rats were killed 24 hours later. Chlordecone treatment produced approximately a 17-fold potentiation of the CCl4-dependent loss of cytochrome P-450 and glucose-6-phosphatase activity, so that a dose of 6 microliters CCl4 per 100 g body weight in the chlordecone-treated animals resulted in a similar amount of damage as observed with 100 microliters CCl4 per 100 g body weight in controls. A similar potentiation by chlordecone was seen with CCl4 induced increases in serum glutamic-oxaloacetic transaminase (SGOT) levels. Chlordecone treatment also increased hepatic cytochrome P-450 levels by 67% and resulted in an increase in the covalent binding of [14-C]-CCl4-derived metabolites to microsomal protein and lipid in vivo.

Animals↗
PubMed1987

Chlordecone does not interfere with hepatic repair after carbon tetrachloride or partial hepatectomy.

The effect of chlordecone (CD) on hepatic repair, measured either as recovery of microsomal enzymatic functions or as the induction of cytosolic thymidine kinase (TK) activity, was evaluated in rats given carbon tetrachloride (CCl4). Carbon tetrachloride was administered to CD-potentiated and control animals using doses of this hepatotoxin which produce similar degrees of damage at 24 hours in both groups of animals (6 and 100 microliters CCl4 per 100 g body weight, respectively). Chlordecone had no significant effect on the time course of recovery of microsomal cytochrome P-450 content or glucose-6-phosphatase activity following CCl4 administration. Hepatic TK activity was measured 48 hours after CCl4 administration as a biochemical index of the hepatic regenerative response. Thymidine kinase activity was increased eightfold in CD-treated rats receiving 6 microliters CCl4 per 100 g body weight, whereas in controls a similar induction of TK activity was produced by 100 microliters CCl4 per 100 g body weight. Therefore, the TK response in CD-treated rats receiving CCl4 is appropriate for the amount of damage produced, suggesting that CD does not inhibit the hepatic regenerative response to CCl4-induced injury. The effect of CD on hepatic repair was also examined in rats receiving a two-thirds partial hepatectomy. Pretreatment of animals with CD had no significant effect on the increase in TK activity produced 24 hours after partial hepatectomy. These results offer no support for the idea that CD impairs hepatic repair after either partial hepatectomy or CCl4 administration.

Animals↗