Hepatic metabolic alterations in rats treated with low-dose endotoxin and aspirin: an animal model of Reye's syndrome

Hypothesis: Induction of Autoimmunity in Type 1 Diabetes-A Lipid Focus

Several unrelated findings led us to hypothesize that induction of autoimmunity is a consequence of a prior major inflammatory event in individuals with susceptible HLA phenotypes and elevated sensitivity to cytokines and free fatty acids (FFA). We observed provocative enhanced responsiveness of cultured human fibroblasts from individuals with type 1 diabetes (T1D), but not control subjects, to FFA and the inflammatory cytokines TNFα and IL1-β. Major infections increase inflammatory cytokines as well as circulating FFA. Endotoxin-treated animal models of sepsis also exhibit elevated inflammatory cytokines that inhibit FFA oxidation and elevate FFA. The pancreatic β-cell possesses low reactive oxygen species (ROS) scavenging capacity and responds to both elevated FFA and cytokines with increased ROS production, a combination that increases exocytosis and trafficking of secretory vesicles to the plasma membrane. Increased trafficking is accompanied by increased cycling of secretory granule proteins and may be linked with increased surface presentation of granule proteins to the immune system. We propose that this ultimately targets β-cell granular proteins at the cell surface and is consistent with the preponderance of autoantibodies to granule proteins. Our hypothesis encourages testing of potential early therapeutic interventions to prevent progression of β-cell destruction.

Fibroblasts from type 1 diabetics exhibit enhanced Ca(2+) mobilization after TNF or fat exposure

The effects of cytokine and fatty acid treatment on signal transduction in dermal fibroblasts from type 1 diabetics and matched controls were compared. Chronic exposure to TNF, accentuated Ca²⁺ mobilization in response to bradykinin (BK) in cells from both controls and diabetics; responses were three-fold greater in cells from diabetics than in controls. Similarly, with chronic exposure to IL-1β, BK-induced Ca²⁺ mobilization was accentuated in cells from type 1 diabetics compared to the controls. Pretreatment with the protein synthesis inhibitor cycloheximide or the protein kinase C inhibitor calphostin C prior to the addition of TNF completely abrogated the TNF-induced increment in peak bradykinin response. Ca²⁺ transients induced by depleting endoplasmic reticulum (ER) Ca²⁺ with thapsigargin were also greater in TNF treated fibroblasts than in untreated cells, with greater increases in cells from diabetics. Exposing fibroblasts for 48 hours to 2 mM oleate also increased both the peak bradykinin response and the TNF-induced increment in peak response, which were significantly greater in diabetics than controls. These data indicate that cells from diabetic patients acquire elevated ER Ca²⁺ stores in response to both cytokines and free fatty acids,and thus exhibit greater sensitivity to environmental inflammatory stimuli and elevated lipids.

FGF21 is increased by inflammatory stimuli and protects leptin-deficient ob/ob mice from the toxicity of sepsis

The acute phase response (APR) produces marked alterations in lipid and carbohydrate metabolism including decreasing plasma ketone levels. Fibroblast growth factor 21 (FGF21) is a recently discovered hormone that regulates lipid and glucose metabolism and stimulates ketogenesis. Here we demonstrate that lipopolysaccharide (LPS), zymosan, and turpentine, which induce the APR, increase serum FGF21 levels 2-fold. Although LPS, zymosan, and turpentine decrease the hepatic expression of FGF21, they increase FGF21 expression in adipose tissue and muscle, suggesting that extrahepatic tissues account for the increase in serum FGF21. After LPS administration, the characteristic decrease in plasma ketone levels is accentuated in FGF21-/- mice, but this is not due to differences in expression of carnitine palmitoyltransferase 1α or hydroxymethyglutaryl-CoA synthase 2 in liver, because LPS induces similar decreases in the expression of these genes in FGF21-/- and control mice. However, in FGF21-/- mice, the ability of LPS to increase plasma free fatty acid levels is blunted. This failure to increase plasma free fatty acid could contribute to the accentuated decrease in plasma ketone levels because the transport of fatty acids from adipose tissue to liver provides the substrate for ketogenesis. Treatment with exogenous FGF21 reduced the number of animals that die and the rapidity of death after LPS administration in leptin-deficient ob/ob mice and to a lesser extent in control mice. FGF21 also protected from the toxic effects of cecal ligation and puncture-induced sepsis. Thus, FGF21 is a positive APR protein that protects animals from the toxic effects of LPS and sepsis.

Increased excretion of c4-carnitine species after a therapeutic acetylsalicylic Acid dose: evidence for an inhibitory effect on short-chain Fatty Acid metabolism

Acetylsalicylic acid and/or its metabolites are implicated to have various effects on metabolism and, especially, on mitochondrial function. These effects include both inhibitory and stimulatory effects. We investigated the effect of both combined and separate oral acetylsalicylic acid and acetaminophen administration at therapeutic doses on the urinary metabolite profile of human subjects. In this paper, we provided in vivo evidence, in human subjects, of a statistically significant increase in isobutyrylcarnitine after the administration of a therapeutic dose of acetylsalicylic acid. We, therefore, propose an inhibitory effect of acetylsalicylic acid on the short-chain fatty acid metabolism, possibly at the level of isobutyryl-CoA dehydrogenase.

Experimental models of Reye's syndrome

Intraperitoneal administration of 4-pentenoic acid (20 mg/kg/day for seven days or ten doses of 50 mg/kg with 4 h intervals) or acetylsalicylic acid (50 mg/kg 1 hour after single pyrogenal injection) to rats reproduced metabolic disorders characteristic of Reye's syndrome: hyperenzymemia, hyperbilirubinemia, decreased levels of ketone bodies and urea, hypoglycemia, hypoproteinemia, accumulation of ammonia and phenol, and acidosis. Necroses and microvesicular steatosis were found in the liver.

Acetylator phenotype and genotype in patients infected with HIV: discordance between methods for phenotype determination and genotype

The acetylator phenotype and genotype of AIDS patients, with and without an acute illness, was compared with that of healthy control subjects (30 per group). Two probe drugs, caffeine and dapsone, were used to determine the phenotype in the acutely ill cohort. Polymerase chain reaction amplification and restriction fragment length polymorphism analysis served to distinguish between the 26 known NAT2 alleles and the 21 most common NAT1 alleles. The distribution (%) of slow:rapid acetylator phenotype seen among acutely ill AIDS patients differed with the probe substrate used: 70:30 with caffeine versus 53:47 with dapsone. Phenotype assignment differed considerably between the two methods and there were numerous discrepancies between phenotype and genotype. The NAT2 genotype distribution was 45:55 slow:rapid. Control subjects, phenotyped only with caffeine, were 67:33 slow:rapid versus 60:40 genotypically. Stable AIDS patients, phenotyped only with dapsone, were 55:45 slow:rapid versus 46:54 genotypically. Following resolution of their acute infections, 12 of the acutely ill subjects were rephenotyped with dapsone. Phenotype assignment remained unchanged in all cases. The distribution of NAT1 alleles was similar in all three groups. It is evident from the amount of discordance between caffeine phenotype and dapsone phenotype or genotype that caution should be exercised in the use of caffeine as a probe for NAT2 in acutely ill patients. It is also clear that meaningful study of the acetylation polymorphism requires both phenotypic and genotypic data.

Sequestration of coenzyme A by the industrial surfactant, Toximul MP8. A possible role in the inhibition of fatty-acid beta-oxidation in a surfactant/influenza B virus mouse model for acute hepatic encephalopathy

We have investigated the mechanistic basis of our recent observation that exposing young mice to an industrial surfactant potentiates the inhibition of fatty-acid beta-oxidation that occurs with subsequent virus infection (Murphy et al., Biochim. Biophys. Acta 1315, 208-216, 1996). In our mouse model for acute hepatic encephalopathy (AHE), neonatal mice were painted on their abdomens from birth to postnatal day 12 with nontoxic amounts of the industrial surfactant, Toximul MP8 (Tox), and then infected with a sublethal dose (LD30) of mouse-adapted human Influenza B (Lee) virus (FluB). Mortality in mice treated with Tox + FluB was significantly higher than that in mice treated with FluB alone. In vitro assays of hepatic beta-oxidation of [1-(14)C]palmitic and [1-(14)C]octanoic acids in the presence or absence of exogenous coenzyme A (CoA) indicated that Tox-mediated inhibition of oxidation was masked when CoA was added to the assays. FluB also inhibited beta-oxidation by 20-30%, however this effect was independent of exogenous CoA which suggested that it involved a different mechanism. Tox-mediated potentiation of the inhibitory effect was most obvious (> 80% inhibition) when assays were done without added CoA. Analysis of hepatic CoA and its esters indicated that levels of both free CoA and acetyl-CoA were significantly lower in mice that were painted with Tox for 12 days. Tox-dependent reductions of acetyl-CoA were transient and returned to normal values after cessation of painting, whereas those of CoA persisted. FluB infection alone significantly reduced hepatic acetyl-CoA and the magnitude of this reduction (> 30%) was not affected by pre-exposing the mice to Tox. Relative to control mice, levels of acid insoluble acyl-CoA esters were elevated significantly in FluB and Tox + FluB treated mice. Activation of both [1-(14)C]palmitic and [1-(14)C]octanoic acids was reduced in Tox-exposed mice at experimental day 12, but only when exogenous CoA was not included in the assay media; this effect appeared to persist after cessation of painting. Collectively, these data support the concept that Tox and FluB have independent effects on hepatic CoA metabolism that are associated with abnormalities in fatty-acid beta-oxidation. However, these do not fully explain the synergistic effect of the virus and chemical on beta-oxidation inhibition, which is a candidate co-mechanism for potentiation of mortality in this mouse model of AHE.

Abnormalities in hepatic fatty-acid metabolism in a surfactant/influenza B virus mouse model for acute encephalopathy

Abnormalities in fatty-acid metabolism are believed to play a role in nonspecific acute encephalopathy (AE) with hepatomegaly, although the specific nature of these abnormalities and their temporal relationship to the pathology are not well defined. We have examined hepatic fatty-acid beta-oxidation and metabolism in a mouse model for AE in which neonatal mice were exposed dermally to nontoxic doses of the industrial surfactant, Toximul MP8 (Tox), daily from days 1 to 12 after birth, and then infected with a sublethal dose (LD30) of mouse-adapted human influenza B (Lee) virus (FluB). The number of deaths in the group treated with Tox + FluB were significantly higher than those in the group infected with virus alone. Under optimal in vitro assay conditions, beta-oxidation of [1-14C]palmitic acid was approximately 15% higher in liver homogenates from mice painted with Tox for 12 days (P < 0.02); catabolism of [1-14C]octanoic acid to 14C-labelled water-soluble products (14C-WSP) and 14CO2 was unaltered by Tox. Infecting Tox-free mice with FluB inhibited beta-oxidation of both [1-14C]palmitate and [1-14C]octanoate by 20-30% (P < 0.001). On days 18-19, when most Tox + FluB-dependent deaths occurred, the inhibition of oxidation was increased to approximately 50% in mice given the combined treatment. Treatment of the mice with Tox/FluB also altered the pattern of incorporation of fatty acids into complex lipids. Hepatic levels of thiobarbituric acid reactive substance (TBARS), a marker for lipid peroxides, were approximately 15% higher in Tox-painted than in control mice (P < 0.01); FluB alone had no effect. In Tox + FluB-treated animals, TBARS levels were > 2-fold higher than in any other experimental group (P < 0.001). These studies demonstrated that nasally-administered FluB has profound effects on hepatic fatty-acid metabolism, particularly beta-oxidation. Exacerbation of this and related effects by exposing young animals to xenobiotic surfactants could be the basis of surfactant-mediated potentiation of virus-induced mortality.

Alterations in hepatic production and peripheral clearance of IGF-I after endotoxin

Lipopolysaccharide (LPS) produces a rapid and sustained reduction in the circulating concentration of insulin-like growth factor I (IGF-I), which may be responsible, in part, for the alterations in protein metabolism observed in these animals. The purpose of the present study was to determine whether this drop was due to a decreased hepatic production of IGF-I and/or an increased clearance of the peptide from the blood. Four hours after intravenous injection of LPS the plasma IGF-I concentration was decreased 50%. IGF-I release by in situ perfused livers from control rats was constant throughout the 60-min perfusion period and averaged 111 +/- 3 ng/min. In contrast, hepatic IGF-I output was decreased 46% by in vivo LPS. In contrast, livers from LPS-injected rats released more IGF binding proteins-1, -2 and -4 than did control livers. Hepatic cell isolation indicated that LPS decreased the IGF-I content in Kupffer and parenchymal cells, but not endothelial cells, by approximately 45%. Pharmacokinetic analysis of blood 125I-IGF-I decay curves indicated that the half-life for whole body clearance of 125I-IGF-I from the circulation was not altered by LPS. However, LPS increased 125I-IGF-I uptake by spleen, liver, lung, and kidney while decreasing uptake by the pancreas and gastrointestinal tract. These results indicate that the LPS-induced decrease in blood IGF-I concentration is primarily due to a reduction in hepatic production, not a change in whole body peptide clearance, and that a decreased production by both parenchymal and Kupffer cells contributes to this alteration.

Reye's and Reye-like syndromes, drug-related diseases? (causative agents, etiology, pathogenesis, and therapeutic approaches)

In the literature the separation between RS and RLS is confusing and makes it difficult to plan an appropriate preventive action or to develop new therapeutic approaches. We suggest that the generalized damage and encephalopathy seen in both RS and RLS may be due to a wide variety of causative agents that contribute to a common derangement, principally involving mitochondrial oxidative pathway. Fasting status and infections increase the catabolism and the subsequent flux of metabolites from peripheral tissues to the liver (FA and amino acids); cytokines (TNF, IL-1, and IL-6), in particular, mediate this effect during infection and experimental endotoxemia. Some drugs and other toxic compounds induce functional and morphological liver mitochondrial derangement. Oxidative metabolism is impaired, with subsequent stimulation of alternative pathways of oxidation, following production of unusual toxic acyl CoAs and dicarboxylic acids. Toxic compounds accumulate in the liver, deranging its functions and causing energy depletion, and are also released in the circulation from which they reach other tissues, including the brain. Neurons and astrocytes in the brain may be affected differently: Neurons suffer from the lack of energy and the effect of toxic compounds arriving from the bloodstream, and astrocytes may be directly affected by the beta-oxidation derangement. Very important may be genetic predisposition, which, by making the patient more sensitive to a particular causative agent, may facilitate the onset of RS and RLS. The therapeutic approach is, presently, mainly symptomatic, directed as it is to counteracting each alteration shown, depending by the clinical gravity. Other pharmacological approaches are only studied experimentally, like carnitine supplementation and PGE2 administration, or theoretically envisaged, like monoclonal antibody therapy directed at LPS or at pro-inflammatory cytokines or treatment with interferon-alpha.

Inhibition of mitochondrial beta-oxidation as a mechanism of hepatotoxicity

Severe and prolonged impairment of mitochondrial beta-oxidation leads to microvesicular steatosis, and, in severe forms, to liver failure, coma and death. Impairment of mitochondrial beta-oxidation may be either genetic or acquired, and different causes may add their effects to inhibit beta-oxidation severely and trigger the syndrome. Drugs and some endogenous compounds can sequester coenzyme A and/or inhibit mitochondrial beta-oxidation enzymes (aspirin, valproic acid, tetracyclines, several 2-arylpropionate anti-inflammatory drugs, amineptine and tianeptine); they may inhibit both mitochondrial beta-oxidation and oxidative phosphorylation (endogenous bile acids, amiodarone, perhexiline and diethylaminoethoxyhexestrol), or they may impair mitochondrial DNA transcription (interferon-alpha), or decrease mitochondrial DNA replication (dideoxynucleoside analogues), while other compounds (ethanol, female sex hormones) act through a combination of different mechanisms. Any investigational molecule should be screened for such effects.

The effect of treatment of the rat with bacterial endotoxin on gluconeogenesis and pyruvate metabolism in subsequently isolated hepatocytes

The effect of treatment of rats with bacterial endotoxin on gluconeogenesis and the flux through pyruvate kinase, phosphoenolpyruvate carboxykinase (PEPCK), pyruvate carboxylase and pyruvate dehydrogenase (PDH) was measured in isolated hepatocytes, prepared from animals starved for 18 h, incubated in the presence of 1 mM pyruvate. The lipopolysaccharide reduced gluconeogenesis by 50% and lowered the flux through pyruvate kinase, PEPCK and pyruvate carboxylase by comparable amounts. There was no effect of endotoxaemia on PDH flux, indicating that the lowered rate of gluconeogenesis is not the result of a redistribution of pyruvate metabolism between oxidation and carboxylation. The results confirm that a stimulation of pyruvate kinase activity following treatment with lipopolysaccharide is not involved in the inhibition of gluconeogenesis, but that the effect resides at the level of phosphoenolpyruvate formation. The most favoured mechanism for the inhibition of glucose synthesis is via an inhibition of PEPCK and subsequent feedback inhibition of pyruvate carboxylase, although a secondary effect at the level of the mitochondria and pyruvate carboxylase cannot be excluded.

Monoclonal antibody therapy in the treatment of Reye's syndrome

A role for lipopolysaccharides (endotoxins, LPS) in 7 the pathogenesis of Reye's syndrome (RS) has previously been suggested. Impairment of hepatic LPS clearance can lead to systemic endotoxemia as previous studies by this and other laboratories have suggested for several hepatic disorders including RS. Systemic LPS may mediate many of the clinical findings associated with RS by eliciting monokines such as tumor necrosis factor-alpha, interleukin-1, interleukin-6, and interleukin-8. Monoclonal antibody therapy directed at LPS, and monokines may represent a novel approach to the treatment of RS.

Immunomodulation and drug acetylation: influence of the immunomodulator tilorone on hepatic, renal and blood N-acetyltransferase activity and on hepatic cytosolic acetyl coenzyme A content

The biochemical alteration responsible for immunomodulator enhancement of drug acetylation in vivo was probed ex vivo and in vitro in the rat. Rat liver or kidney cytosol, obtained by differential centrifugation, or whole blood served as the source of N-acetyltransferase (NAT). Addition of tilorone (0.5-8.0 mM) to incubation mixtures containing procainamide (PA, 0.6 mM) and acetyl coenzyme A (AcCoA, 0.42 mM) resulted in the inhibition of N-acetylprocainamide formation, while lower concentrations of tilorone had no effect. Pretreatment of rats with tilorone (50 mg/kg) administered orally 48 hr prior to sacrifice did not alter hepatic apparent Km and Vmax for NAT toward PA compared to control animals. Utilization of an AcCoA regenerating system in the incubation mixtures also resulted in no significant differences in the apparent Michaelis-Menten parameters obtained. Acetylation activity in kidney and whole blood also was not altered by immunomodulator pretreatment. Hepatic cytosolic AcCoA content was reduced significantly 48 hr after tilorone pretreatment (5.10 +/- 2.1 vs 11.97 +/- 2.2 nmol/mg protein) (P less than 0.05). These data indicate that an increase in NAT content or activity is not the biochemical alteration responsible for immunomodulator enhancement of drug acetylation, and that the required cofactor, cytosolic AcCoA, is decreased by immunomodulator pretreatment.

Ca2+ responses to interleukin 1 and tumor necrosis factor in cultured human skin fibroblasts. Possible implications for Reye syndrome

Elevated concentrations of cytokines were found in the plasma of patients acutely ill with Reye syndrome (RS) but not in control subjects or recovered RS patients. To determine whether this disorder involves a genetically determined abnormal response to cytokines, the effects of tumor necrosis factor (TNF) and IL-1 on intracellular free Ca2+ were compared in cultured skin fibroblasts from control subjects and patients with RS. IL-1 and TNF caused rapid, transient, and concentration-dependent increases in cytosolic free Ca2+. The peak cytosolic free Ca2+ was greater and occurred at higher concentrations of IL-1 and TNF in patient cells than in cells from age-matched controls. In control cells, the Ca2+ transient diminished sharply with increasing amounts of IL-1 or TNF above the maximum stimulatory concentration. In contrast, in patient fibroblast this bell-shaped curve of concentration dependency was much less apparent. Bradykinin-stimulated Ca2+ transients were similar in the two groups and did not exhibit the bell-shaped concentration dependency. Thus, plasma cytokine levels are elevated in RS patients and the Ca2+ response to cytokines is increased in cells derived from these patients. We propose that the increased response reflects a genetic defect in cytokine receptor-modulated signal transduction.

Role of glutamine and its analogs in posttraumatic muscle protein and amino acid metabolism

Skeletal muscle protein catabolism following trauma has until recently not been possible to counteract by intravenous nutritional means. The obligatory loss of nitrogen with concomitant reduction of skeletal muscle protein synthesis is also accompanied by a decrease of muscle free glutamine, the extent of which is proportional to the muscle protein catabolism. Serving as a human model of surgical trauma, patients undergoing elective cholecystectomy were given total parenteral nutrition including additions of either glutamine or its analogs (ornithine-alpha-ketoglutarate, alpha-ketoglutarate, or alanylglutamine) during 3 postoperative days. The polyribosome concentration and the intracellular glutamine concentration in skeletal muscle, as well as nitrogen balance, showed a less pronounced skeletal muscle catabolism in these groups than when conventional total parenteral nutrition was given. It is concluded that a support of either glutamine or its carbon skeleton, alpha-ketoglutarate, counteracts the postoperative fall of muscle free glutamine and of muscle protein synthesis. Furthermore, statistical correlations could be shown between the changes of muscle glutamine and muscle protein synthesis and the postoperative nitrogen losses.