The effect of endotoxin on hepatocyte nuclear factor 1 nuclear protein binding: potential implications on CYP2E1 expression in the rat

The purpose of this study was to determine if changes in nuclear protein binding of hepatocyte nuclear factor 1 (HNF-1) occur after lipopolysaccharide (LPS) administration. In addition, the time-course of alterations in CYP2E1 regulation were evaluated. Rats were injected with 2.0 mg LPS and euthanized over a 72-h period. Nuclear protein binding to a consensus HNF-1 oligonucleotide was assessed by the electrophoretic mobility shift assay. CYP2E1 activity was analysed using chlorzoxazone as a substrate (60H-CLZ), and CYP2E1 protein concentration was determined by enzyme-linked immunosorbent assay. Endotoxin treatment resulted in decreased nuclear protein binding to an HNF-1 element as early as 1 h after treatment and returned to control levels by 72 h. This reduced binding persisted for 24 h and returned to control values 48 h after LPS administration. In addition, the reduction in binding was primarily attributable to a HNF-1alpha immunoreactive protein. The observed reduction in HNF-1 binding was followed in the time-course by decreases in CYP2E1 activity and protein content with maximal decreases to 50 and 67% of control, respectively, at 48 h after LPS administration. Endotoxin is a potent inducer of the acute phase response (APR). The APR stimulation by endotoxin administration reduced HNF-1alpha binding and decreased the expression of CYP2E1 in the rat liver. The time-course of alterations in HNF-1 and CYP2E1 lend support to the possibility that HNF-1alpha may play a role in the down-regulation of genes that require HNF-1alpha for their constitutive expression. These data serve as an important precedent for future studies evaluating the direct association of decreased HNF-1alpha binding and reduced gene expression after LPS administration.

Activities of conjugating and antioxidant enzymes following endotoxin exposure

Endotoxin exposure elicits various responses in mammals including the acute phase response that has been shown to cause changes in the activity of several forms of cytochrome P450s and other enzymes. Therefore, the hepatic conjugating enzyme, glutathione S-transferase (GST), and UDP-glucuronosyltransferase (UDPGT), the antioxidant enzymes, glutathione peroxidase (GSHPx), catalase, and superoxide dismutase (SOD), as well as lipid peroxidation were investigated following the administration of endotoxin to male Sprague-Dawley rats (8 mg/kg body weight). Rats were euthanized at various times following endotoxin administration and the livers removed and processed to assess various enzyme activities. Glutathione S-transferase, UDPGT, and GSHPx activity showed statistically significant decreases after 24 hours and remained lower than controls for the duration of the study. Decreases in total SOD and catalase activities were seen at 24, 48, and 72 hours following endotoxin administration; however, only catalase activity showed statistically significant differences between control and treated samples at those time points, and total SOD activity showed a statistically significant decrease at 24 hours. No statistically significant changes were seen in the level of lipid peroxidation in the liver microsomes from endotoxin-treated animals. Changes in the conjugative enzymes and the free-radical scavenging enzymes following endotoxin exposure may alter the host's metabolism and response to free radicals.

Depression of constitutive murine cytochromes P450 by staphylococcal enterotoxin B

Most in vivo studies demonstrating decreased activities of hepatic cytochromes P450 with inflammation have used Gram-negative bacterial lipopolysaccharide (LPS) as the inflammatory stimulant. But products of Gram-positive bacteria, such as staphylococcal enterotoxin B (SEB), also stimulate inflammatory mediators, albeit with a different pattern than LPS. Therefore, effects of SEB on the regulation of murine constitutive P450s were determined in this study and compared with those of LPS. LPS-responsive C3H/HeN and LPS-unresponsive C3H/HeJ mice were injected with either LPS (0.5 mg/kg) or SEB (0.66 to 6.6 mg/kg), and hepatic cytochromes P450 and serum tumor necrosis factor-alpha, interleukin-6, nitrate/nitrite, and serum amyloid A concentrations were determined up to 24 hr. HeJ mice were generally less responsive than HeN mice to both stimuli, with lower cytokine, nitrate/nitrite, and serum amyloid A responses. However, in both mouse strains SEB caused more prolonged cytokine, higher nitrate/nitrite, and lower serum amyloid A concentrations than LPS. Despite these differences, in HeN mice, after both SEB and LPS administration, total P450 concentrations were equally depressed by 40%. Both SEB and LPS depressed CYP1A1 and 1A2 microsomal protein concentrations by 45 and 30%, respectively; CYP2E1 by 64%; and CYP3A by 70%. There was comparable inhibition of enzymatic activities. In HeJ mice, SEB was only slightly more effective in depressing P450s than LPS, as might be expected. These data showed that the Gram-positive bacterial inflammatory stimulant SEB caused effects on murine hepatic cytochromes P450 similar to those of LPS, even though the pattern of inflammatory mediators induced after SEB exposure was different.

The effect of endotoxin administration on the pharmacokinetics of chlorzoxazone in humans

OBJECTIVE

Inflammation induced by Escherichia coli lipopolysaccharide alters the clearance of several hepatically eliminated drugs. Extensive rat liver research has shown CYP2E1 down-regulation after lipopolysaccharide administration. To further investigate this phenomenon in humans, lipopolysaccharide was administered to healthy male volunteers and chlorzoxazone was used as a CYP2E1 probe drug.

METHODS

Twelve healthy men were given 500 mg oral chlorzoxazone after two daily lipopolysaccharide doses (20 endotoxin units/kg/day) and again after administration of saline solution in this balanced crossover study. Serum and urine chlorzoxazone and 6-hydroxychlorzoxazone were quantified, as well as cytokine and C-reactive protein levels.

RESULTS

Lipopolysaccharide produced the expected induction of the acute-phase response shown by elevations in tumor necrosis factor, interleukin-6, C-reactive protein, and temperature. Lipopolysaccharide treatment failed to produce a significant change in the chlorzoxazone oral clearance (4.4 +/- 0.9 mL/min/kg for lipopolysaccharide versus 4.2 +/- 1.4 mL/min/kg for control) or the 6-hydroxychlorzoxazone formation clearance (2.8 +/- 0.65 mL/min/kg for lipopolysaccharide versus 2.5 +/- 0.9 mL/min/kg for control). The high intersubject variabilities in oral clearance and formation clearance were not accounted for by changes in protein binding, cytokine, or C-reactive protein values. In contrast, a significant increase in the 6-hydroxychlorzoxazone glucuronide renal clearance was observed (7.5 +/- 1.37 mL/min/kg for lipopolysaccharide versus 6.1 +/- 1.7 mL/min/kg for control).

CONCLUSIONS

This study showed that the inflammatory response to lipopolysaccharide (20 endotoxin units/kg/day for 2 days) in humans does not consistently alter chlorzoxazone hepatic metabolism. However, the significant increase in renal clearance of the glucuronidated metabolite suggests that renal tubular secretion may be increased in humans with acute endotoxemia.

The effect of high dose endotoxin on CYP3A2 expression in the rat

PURPOSE

The purpose of our research was two-fold: 1) to further characterize the downregulation of CYP3A2 mRNA, protein, and activity during an acute phase response (APR); 2) most importantly, to relate the time-dependent activation of nuclear proteins to putative DNA binding sequences within the CYP3A2 5'-flanking region, with the loss in CYP3A2 expression.

METHODS

Rats were injected (2.0 mg/animal, i.p.) with LPS and sacrificed at 1, 2, 4, 6, 8, 24, 48, and 72 hours. Hepatic nuclear protein was isolated and analyzed for binding activity to AP-1, NFkappaB, and NF-IL6 consensus sequences. Hepatic CYP3A2 mRNA levels were determined by solution hybridization and CYP3A2 protein, CYP3A2 activity, and total P450 were measured in hepatic microsomes.

RESULTS

Computer analysis of the 5'-flanking region of CYP3A2 revealed the presence of 5 NF-IL6 and 4 AP-1 putative DNA binding sites. The strongest increase in AP-1 binding activity occurred between 6 and 24 hr, and the alteration in binding complexes to an NF-IL6 oligonucleotide occurred between 4 and 24 hr. Maximum loss in CYP3A2 mRNA occurred at 8 hr post-LPS injection and remained lowered at the 24 hr timepoint. CYP3A2 protein was significantly decreased at 24, 48, and 72 hours post-LPS treatment with corresponding decreases in CYP3A2 activity and total P450.

CONCLUSIONS

The changes in NF-IL6 and AP-1 binding after LPS treatment, which appears to correlate with the changes in CYP3A2 mRNA, combined with the presence of putative NF-IL6 and AP-1 sites located in the CYP3A25'-flanking region, may indicate a potential role for NF-IL6 and AP-1 in CYP3A2 downregulation during an APR.

Role of iron in the natural history and clinical course of hepatitis C disease

The following review evaluates the current data implicating a role for hepatic iron in enhancing the liver injury in patients with chronic hepatitis C infection. Iron removal lowers transaminases, but doesn't appear to improve responsiveness to interferon-alpha therapy. An important effect of iron removal might be to delay progression of liver injury to fibrosis and cirrhosis. Until such a hypothesis is disproven, phlebotomy therapy for even mildly iron-loaded HCV patients is recommended.

Ascorbic acid deficiency in porphyria cutanea tarda

Porphyria cutanea tarda (PCT), the most common form of porphyria, is manifested as skin photosensitivity caused by excess hepatic production of uroporphyrin and heptacarboxylporphyrin. In experimental animal models, ascorbic acid modulates chemically induced uroporphyrin accumulation. The purpose of this study was to determine whether ascorbic acid is decreased in the plasma of patients with PCT. Plasma was obtained after an overnight fast from 21 PCT patients, 16 of whom were infected with hepatitis C virus (HCV), and from a separate group of 9 patients with HCV infection but not PCT. Thirteen PCT patients were studied when they had active disease and 8 after treatment-induced remission. Plasma ascorbic acid was low (<23 micromol/L) in 11 (85%) of the 13 untreated PCT patients and deficient (<11 micromol/L) in 8 (62%). Two patients with normal ascorbic acid levels (45 and 62 micrommol/L) had consumed multivitamins. In 2 patients with deficient ascorbic acid, plasma levels returned to normal after phlebotomy treatment. Of the 8 patients studied during remission, 4 had normal ascorbic acid values and 4 were deficient (5 to 8 micromol/L). Plasma ascorbic acid values were normal for all patients who had HCV but no PCT. These data suggest that plasma ascorbic acid concentrations are commonly low in PCT, but this decrease is unrelated to HCV infection. Ascorbic acid deficiency may be one of the factors that contributes to the pathogenesis of PCT.

Endotoxin depresses hepatic cytochrome P450-mediated drug metabolism in women

AIMS

In men, the inflammatory response to intravenous endotoxin depresses apparent oral clearances of antipyrine, hexobarbitone, and theophylline. The aim of this study was to investigate whether there might be gender differences in the regulation of hepatic cytochromes P450.

METHODS

Experiments were carried out in seven healthy women volunteers (ages 19-51, median 22 years). Each woman received a cocktail of the three drugs on two occasions, once after a saline injection and again after endotoxin.

RESULTS

Endotoxin injections, but not saline, caused the expected physiologic responses of inflammation including fever and increases in circulating tumor necrosis factor-alpha, interleukin-6, and C-reactive protein. When compared with the saline control studies, endotoxin significantly decreased clearances of all probes: antipyrine, 31% (95%CI 21%-41%); hexobarbitone, 20% (95%CI 10-31%); and theophylline, 20% (95%CI 10%-30%). The decreases were comparable with those found in the men previously studied (35%, 27%, and 22%, respectively).

CONCLUSIONS

These data show that endotoxin-induced inflammation decreases hepatic cytochrome P450-mediated metabolism of selected probe drugs in women as it does in men.

Effects of endotoxin on zinc metabolism in human volunteers

After stress or trauma, the serum zinc concentration decreases. This study evaluated possible mechanisms for hypozincemia with the use of a human endotoxemia model. Two doses of endotoxin [lipopolysaccharide (LPS)] were administered on consecutive mornings to 12 healthy volunteers, and each subject was also studied after saline injection. Blood was analyzed for zinc, cytokines (tumor necrosis factor-alpha and interleukin-6), albumin, albumin-zinc binding, and C-reactive protein (CRP). Serial 24-h urine collections were analyzed for zinc. Each LPS dose briefly increased plasma cytokine concentrations and decreased the serum zinc concentration. Serum albumin, the major zinc binding protein, did not decrease, but a progressive increase in CRP was found. LPS did not alter zinc binding affinity to serum albumin. Urine zinc losses were not increased. We conclude that hypozincemia in this model cannot be explained by decreased serum albumin, changes in serum albumin-zinc binding, or increased urinary zinc excretion. Because hypozincemia was transient and followed cytokine peaks, we postulate that LPS-stimulated hypozincemia is mediated, at least partly, by a cytokine-directed internal redistribution of zinc.

In vitro tumor necrosis factor cytotoxicity in Hep G2 liver cells

Tumor necrosis factor-alpha (TNF-alpha) is a mediator of liver injury. The objective of this study was to develop an in vitro model of TNF-mediated liver cell injury using the Hep G2 cell line. Hep G2 cells normally are insensitive to TNF cytotoxicity, but they were rendered susceptible, or sensitized, to TNF cytotoxicity by inhibitors of RNA and protein synthesis. The concentration of TNF required to kill 50% of Hep G2 cells sensitized with 0.8 mumol/L actinomycin D (Act D) was 35 pmol/L compared with 5 pmol/L for LM fibroblasts, a classic target cell used in TNF cytotoxicity bioassays. Similarly, TNF cytotoxicity occurred in Hep G2 cells sensitized with cycloheximide (CHX), and cytotoxicity to both inhibitors was dose dependent. Both protein and RNA synthesis were inhibited in Hep G2 cells by the concentrations of CHX and Act D associated with TNF cytotoxicity. Hep G2 cells pretreated with TNF alone and later exposed to normally toxic concentrations of TNF with DACT did not develop cytotoxicity. Thus, in vitro tolerance to TNF was induced. Cytotoxicity also was more severe at modestly increased temperatures (39 degrees C versus 37 degrees C), which may have clinical relevance to hepatic decompensation during febrile episodes. We suggest that the Hep G2 cell line sensitized by inhibiting RNA and protein synthesis is a useful in vitro model for evaluating mechanism(s) of TNF-mediated liver cell injury.

Endotoxin administration to humans inhibits hepatic cytochrome P450-mediated drug metabolism

In experimental animals, injection of gram-negative endotoxin (LPS) decreases hepatic cytochrome P450-mediated drug metabolism. To evaluate this phenomenon in a human model of gram-negative sepsis, LPS was administered on two consecutive days to healthy male volunteers during which time a cocktail of antipyrine (AP-250 mg), hexobarbital (HB-500 mg), and theophylline (TH-150 mg) was ingested and the apparent oral clearance of each drug determined. Each subject had a control drug clearance study with saline injections. In the first experiment, six subjects received the drug cocktail 0.5 h after the first dose of LPS. In the second experiment, another six subjects received the drug cocktail 0.5 h after the second dose of LPS. In both experiments, LPS caused the expected physiologic responses of inflammation including fever with increases in serum concentrations of TNF alpha, IL-1 beta, IL-6, and acute phase reactants. In the first experiment, only minor decreases in clearances of the probe drugs were observed (7-12%). However in the second experiment, marked decreases in the clearances of AP (35, 95% CI 18-48%), HB (27, 95% CI 14-34%), and TH (22, 95% CI 12-32%) were seen. The decreases in AP clearance correlated with initial peak values of TNF alpha (r = 0.82) and IL-6 (r = 0.86). These data show that in humans the inflammatory response to even a very low dose of LPS significantly decreases hepatic cytochrome P450-mediated drug metabolism and this effect evolves over a 24-h period. It is likely that septic patients with much higher exposures to LPS have more profound inhibition of drug metabolism.

Head injury and cytochrome P-450 enzymes. Differential effect on mRNA and protein expression in the Fischer-344 rat

Head trauma produces debilitating injuries that affect millions of people each year. Such injuries lead to a cascade of physiologic sequelae resulting in a hypercatabolic/hypermetabolic state. Current information describing changes in hepatic drug metabolism as a result of head trauma is limited. In this study, the effect of craniotomy and craniotomy plus cerebral percussive injury (impact) were investigated and compared with anesthesia control. Steady-state mRNA levels for CYP2C11 and CYP3A were suppressed to 50% of control values 24 hr following injury for the impact treatments. Craniotomy treatments also demonstrated a 50% decline in steady-state levels of mRNA for CYP3A 24 hr following injury. However, Western blot analysis of the CYP3A enzyme revealed no change at 6, 24, or 48 hr following injury. In addition, activities for 2 alpha- and 6 beta-testosterone hydroxylase did not differ from control values at any time point. Spectral analysis of total P-450 demonstrated a very small decline of 15% for the impact treatment 48 hr following injury. Total cytochrome P-450 content did not differ from control values at any other time point. Head injury produces a profound decline in steady-state mRNA concentrations for CYP2C11 and CYP3A that do not translate into altered protein expression.

Effects of interferon-alpha monotherapy on hepatic drug metabolism in cancer patients

1. The influence of interferon-alpha (IFN alpha) on the clearances of theophylline (TH), antipyrine (AP) and hexobarbitone (HB) was studied in seven cancer patients given IFN alpha as their only treatment. In addition, IFN alpha effects on drug clearance were correlated with changes in serum inflammatory cytokines and acute phase proteins. 2. A 'baseline' study was performed by administering an oral drug 'cocktail' of TH (150 mg), AP (250 mg) and HB (250 mg) with saline injected simultaneously and again 24 h later. One week later, an 'acute' study was performed at the initiation of IFN alpha therapy, 3 x 10(6) units injected with the drug cocktail and again 24 h later. After 2 weeks of IFN alpha treatment three times per week, a 'chronic' study was performed with IFN alpha injected the day prior to, simultaneously with, as well as 24 h after the drug cocktail. 3. Plasma samples were collected over 48 h and the clearances of TH, AP and HB were estimated. Serum samples were collected at various times for the measurement of tumor necrosis factor (TNF), interleukin-1 (IL-1), interleukin-6 (IL-6), C-reactive protein (C-RP) and alpha 1-acid glycoprotein (AGP). 4. IFN alpha caused a 33% decrease in the oral clearance of TH during the chronic study compared with baseline (P < or = 0.05). Although IFN alpha inhibited TH clearance by 16% during the acute study and AP clearance by 20-21% during both acute and chronic studies, these changes did not reach statistical significance. IFN alpha caused minimal changes in HB clearance. There were no chronic effects of IFN alpha on serum cytokines or acute phase proteins. 5. The findings confirm that the most commonly used dose of IFN alpha inhibits the hepatic clearance in humans of some but not all drugs and that this inhibition persists during IFN alpha therapy. Because inhibition was not associated with increases in serum cytokines or acute phase proteins, the mechanism by which IFN alpha inhibits cytochrome P450 activities in vivo does not appear to involve inflammatory mediators such as TNF. IL-1 or IL-6.

The calcium channel blocker nisoldipine minimizes the release of tumor necrosis factor and interleukin-6 following rat liver transplantation

Kupffer cells, when activated, release toxic cytokines such as tumor necrosis factor (TNF), which can cause tissue injury. Takei et al. have reported that nisoldipine, a calcium channel blocker which decreases phagocytotic activity by Kupffer cells, also diminishes liver and lung injury and dramatically improves survival following liver transplantation. Therefore, we studied the effect of nisoldipine on the time course of TNF and interleukin-6 (IL-6) release following cold storage and liver transplantation in the rat. Livers were stored under survival and non-survival conditions in cold Euro-Collins solution in the presence or absence of nisoldipine (1.4 microM). After storage, the effluent was collected for determination of cytokines. The liver was then transplanted orthotopically and serum was collected at various time intervals for up to 5 h. In the effluent, TNF levels were very low in both the control and nisoldipine-treated groups and IL-6 was not measurable. Furthermore, when livers were stored under survival conditions and transplanted (liver stored in the cold for 4 h), serum TNF (2 U/ml) and IL-6 (350 U/ml) values were minimal in both the control and nisoldipine-treated groups. In contrast, when livers were stored under non-survival conditions and transplanted (liver stored in the cold for 10 h), TNF levels increased to 15 +/- 2 U/ml, 150 min after graft reperfusion, an increase which was prevented by nisoldipine (6.5 U/ml). Serum IL-6 levels were also elevated 300 min after transplantation in livers stored for 10 h. Nisoldipine also reduced the release of this cytokine. Serum transaminases (SGOT) were elevated to values around 2000 U/l 5 h following transplantation. In the nisoldipine-treated group, values were lower between 60 and 300 min. In the lung, interstitial and alveolar edema and cellular infiltration were detectable 5 h postoperatively and were diminished by nisoldipine. These data confirmed that TNF and IL-6 release were minimal following cold storage and transplantation of livers stored under survival conditions, but were elevated transiently after transplantation under non-survival conditions. Nisoldipine prevented cytokine release, most likely by blocking the activation of Kupffer cells, which may explain how it decreases liver and lung injury very early following liver transplantation.

Age-dependent stereoselective increase in the oral clearance of hexobarbitone isomers caused by rifampicin

1. The disposition of hexobarbitone enantiomers before and after rifampicin treatment (600 mg daily for 14 days) was investigated in six young (29 +/- 3 years old) and six elderly (71 +/- 4 years old) healthy male volunteers. Hexobarbitone was given as a single 500 mg oral dose of the racemate. 2. The mean (+/- s.d.) oral clearance of S-(+) hexobarbitone was 1.9 +/- 0.3 and 1.8 +/- 0.2 ml min-1 kg-1, respectively, in young and elderly subjects and increased approximately six fold following 14 days of rifampicin treatment in both young (to 11.9 +/- 2.2 ml min-1 kg-1) and elderly (to 10.7 +/- 2.8 ml min-1 kg-1) subjects. 3. In contrast, rifampicin treatment produced a larger and a differential increase in the oral clearance of R-(-) hexobarbitone in young and elderly subjects; an 89 fold change in the young (15.6 +/- 16.4 to 1146.7 +/- 1478.0 ml min-1 kg-1) and a 19 fold change (10.3 +/- 3.0 to 199.9 +/- 98.1 ml min-1 kg-1) in the elderly.

3,3',4,4'-Tetrabromobiphenyl sensitizes rats to the hepatotoxic effects of endotoxin by a mechanism that involves more than tumor necrosis factor

To determine whether the cytokine tumor necrosis factor/cachectin might be a mediator of hepatotoxicity seen after exposure to polyhalogenated aromatic hydrocarbons, rats treated with a single dose of 3,3',4,4'-tetrabromobiphenyl (150 mumol/kg intraperitoneally) or corn oil vehicle were studied. The 3,3',4,4'-tetrabromobiphenyl caused the expected anorexia, alterations in organ weights and changes in cytochromes P-450 over 21 days. Although tumor necrosis factor could not be detected in the serum of rats at any time after 3,3',4,4'-tetrabromobiphenyl treatment alone (from 90 min to 21 days), 3,3',4,4'-tetrabromobiphenyl treatment significantly increased peak serum tumor necrosis factor concentrations after intravenous bacterial endotoxin (lipopolysaccharide, 1 mg/kg). This effect was seen with lipopolysaccharide given 24 hr, 48 hr, and 20 days after 3,3',4,4'-tetrabromobiphenyl treatment and increases in peak serum tumor necrosis factor levels ranged from threefold to eightfold over controls in various experiments with no significant differences between the three time points. However, a synergistic increase in hepatic damage (assessed by serum enzymes and liver histological findings 24 hr after lipopolysaccharide injection) was seen in rats given lipopolysaccharide 24 hr and 48 hr after 3,3',4,4'-tetrabromobiphenyl administration, with 75% and 25% lethality, respectively. There was no lethality with lipopolysaccharide given 20 days after 3,3',4,4'-tetrabromobiphenyl administration or with simultaneous administration. A lower dose of lipopolysaccharide (0.1 mg/kg) given 24 hr after 3,3',4,4'-tetrabromobiphenyl also enhanced hepatotoxicity and serum tumor necrosis factor but without lethality. Lipopolysaccharide decreased cytochromes P-450 concentrations and activities to similar extents at all time points tested in both control and 3,3'4,4'-tetrabromobiphenyl-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of a novel serum amyloid A protein in BALB/c mice

Four serum amyloid A protein (SAA) genes and two SAA gene products, SAA1 and SAA2, were identified in BALB/c mice. Using analytical isoelectric focusing we have identified a quantitatively significant new member of the SAA family and designated it 'SAA5'. This protein has characteristics never before described for any SAA molecule. In the highly conserved region between amino acids 33 and 44, identical in all SAAs from all species examined, SAA5 had four amino acid substitutions. In addition, the induction of SAA5 by lipopolysaccharide had different kinetics from that of the other mouse SAAs. Our data suggest that the mouse SAA gene family is more complex in composition and regulation than previously surmised.

Differential potency of atropisomers of polychlorinated biphenyls on cytochrome P450 induction and uroporphyrin accumulation in the chick embryo hepatocyte culture

The atropisomers of 2,2',3,4,6-pentachlorobiphenyl (PeCB), 2,2',3,4,4',6-hexachlorobiphenyl (HeCB), and 2,2',3,3',4,4',6,6'-octachlorobiphenyl (OCB) were studied in the chick embryo hepatocyte culture to determine if chirality plays a role in the recognition events associated with the induction of cytochromes P450 and the accumulation of uroporphyrin (URO). Concentration-related induction of cytochrome P450 content, ethoxyresorufin-O-deethylase (EROD) and benzphetamine N-demethylase (BPDM) activities were measured. The rank order of potency for total cytochrome P450 induction was HeCB greater than OCB greater than or equal to PeCB. The (+)- and (-)-enantiomers of PeCB and OCB were of equal potencies as inducers of cytochromes P450, whereas the (+)-HeCB was greater than the (-)-HeCB. HeCB was a much more potent inducer of EROD activity than was either PeCB or OCB. EROD activity was induced to a much greater extent by the (+)-enantiomers of all compounds, with the (-)-enantiomers of PeCB and OCB being inactive. BPDM activity was induced by all three compounds in the order of OCB greater than or equal to HeCB greater than PeCB. The (-)-enantiomers were more potent inducers of BPDM activities than were the (+)-enantiomers, except for HeCB, in which the (+)- was more potent than the (-)-enantiomer. Analysis of porphyrin accumulation in cultures treated with delta-aminolevulinic acid revealed that (+)-HeCB caused the greatest percent URO accumulation, which also correlated with the greatest increase in EROD activity. All other enantiomers caused up to 47% URO accumulation, which did not correlate with an increase in EROD activity.

Effects of polychlorinated biphenyls on cytochrome P450 induction in the chick embryo hepatocyte culture

The effects of pure synthetic polychlorinated biphenyl (PCB) congeners on the induction of cytochrome P450 and associated activities were examined in cultured chick embryo hepatocytes. Dose-response effects for the induction of total cytochrome P450 ethoxyresorufin-O-deethylase (EROD) activity, and benzphetamine demethylase (BPDM) activity were studied using 10 selected tetra- to hexachlorinated PCB congeners. These studies revealed that PCBs caused effects in the chick hepatocyte culture different from previously observed effects in rat liver. Based on their effects in chick hepatocytes, the PCBs could be categorized into two groups. The first group (consisting of 3,3',4,4'-PCB, 3,3',4,4',5-PCB, 3,3',4,4',5,5'-PCB, 2',3,3',4,5-PCB, 2,3,3',4,4',5'-PCB, and 2,3,4,4',5-PCB) induced total cytochrome P450 2.4- to 2.9-fold and EROD activity from 1-2 pmol/min/mg protein to 162-247. There was marked variation in potency, but all these congeners had a maximal inducing dose above which cytochrome P450 concentrations and EROD activities declined. BPDM activities were increased only slightly (1.2- to 1.6-fold) at the maximal cytochrome P450 inducing dose. The second group of congeners (consisting of 2,2',4,5,5'-PCB. 2,2',4,4',5,5'-PCB, and 2,2',3,4,4',6-PCB) induced total cytochrome P450 concentrations 4.0-fold and BPDM activities 2.2- to 2.6-fold with greatest activity occurring at the highest doses which could be added (10-50 microM). However, EROD activities were also increased by these congeners to 60-112 pmol/min/mg protein with declining activities seen at the highest PCB doses (i.e., resembling EROD induction patterns of the first group). The EROD induction patterns with these latter PCB congeners are noteworthy since these PCBs do not induce EROD activity in the rat. For both groups of PCB congeners, EROD induction was associated with increased accumulation of uroporphyrin in cultures exposed to exogenous 5-aminolevulinate. Studies investigating the reason for the depression of cytochrome P450 concentrations and/or EROD activities by high doses of the PCBs revealed that with the first group there was slightly decreased total protein synthesis, decreased total cell heme concentrations, and decreased accumulation of radiolabeled heme synthesized from 5-[14C]aminolevulinate. These changes might represent nonspecific toxic effects of the first group of PCBs. However, since these changes were not seen with the second group of PCBs, it is unlikely that either inhibition of heme synthesis or toxicity cause the depression of EROD activity with high PCB doses.

Modulation of murine hematopoiesis in vivo with recombinant murine interleukin-1

Interleukin-1 (IL-1), a cytokine, primarily produced by monocytes, is the molecule involved in mediating many of the body's responses associated with infection and inflammation. More recently, IL-1 has been shown to sustain elevated levels of circulating granulocytes, stimulate the production of granulocyte-macrophage colony stimulating factors (CSFs) in vitro, increase plasma levels of CSF, and act synergistically with CSFs to increase the number of granulocyte-macrophage progenitors (colony-forming units) (CFU-GM) in vitro. The purpose of this study was to investigate the effect of murine IL-1 on steady-state hematopoiesis in vivo. C3H/HeJ or its normal littermate C3H/HeN male mice were administered either murine recombinant IL-1 at 45, 50, 200, 225, or 900 units (0.0125-0.25 micrograms)/animal, or 200 units (0.05 micrograms) of semipurified IL-1 derived from P388D1 cell culture supernatants. Because one of the responses to IL-1 is increased prostaglandin (PG) production and with the known activity of PGs on hematopoiesis, additional studies incorporated the cyclooxygenase inhibitor indomethacin (IM) (10 mg/kg body weight). In order to study the effect of IL-1 in vivo on pluripotential progenitors (CFU-S), IL-1 was compared with recombinant murine GM-CSF (50, 200, and 900 units; 0.0125, 0.05, and 0.25 micrograms). Control groups consisted of animals receiving either lipopolysaccharide (0.5 mg/kg body weight) or phosphate-buffered saline where appropriate. After 24 h, animals were sacrificed, and their peripheral blood indices and stem cell content of both bone marrow and spleen were evaluated for various committed hematopoietic progenitors: CFU-GM, CFU-Meg, CFU-E, BFU-E, and CFU-DG. Circulating neutrophils were increased following IL-1; however, this increase was reduced following IM. IL-1 marrow-derived CFU-GM, CFU-E, BFU-E, and CFU-Meg were below controls. In contrast, splenic CFU-GM and CFU-Meg were significantly elevated with increasing IL-1 concentrations. Erythroid progenitors were increased following low IL-1 concentrations and reduced in animals receiving IM, thus indicating a role for prostaglandins in the mechanism of IL-1 for influencing hematopoiesis. CFU-DG were increased, however, only when animals were pretreated with IL-1 and their cells implanted into normal hosts, not when normal cells were implanted into animals pretreated with IL-1, indicating a potential target cell effect rather than an indirect, factor-related response.(ABSTRACT TRUNCATED AT 400 WORDS)

Haem synthesis from exogenous 5-aminolaevulinate in cultured chick-embryo hepatocytes. Effects of inducers of cytochromes P-450

The effects of inducers of cytochrome P-450 on haem biosynthesis from 5-aminolaevulinate were examined by using cultured chick-embryo hepatocytes. Cultures treated with either 2-propyl-2-isopropylacetamide or 3-methylcholanthrene contained increased amounts of cytochrome P-450 and haem. After treatment for 3 h with 5-amino[4-14C]laevulinate, the relative amounts of radioactivity accumulating as haem corresponded to the relative amounts of total cellular haem, but not to increases in the amounts of cytochrome P-450. Treatment with 5-aminolaevulinate did not alter cellular haem or cytochrome P-450 concentrations in either control or drug-treated cultures. The mechanism of the enhanced accumulation of radioactivity in haem was investigated. Although 2-propyl-2-isopropylacetamide enhanced the uptake of 5-aminolaevulinate and increased the cellular concentration of porphobilinogen 1.5-fold, these changes did not account for the increases in haem radioactivity. The inducing drugs had no effect on the rates of degradation of radioactive haem, but appeared to enhance conversion of protoporphyrin into haem. This latter effect was shown by: (1) a decreased accumulation of protoporphyrin from 5-aminolaevulinate in cells treated with inducers, and (2) complete prevention of this decrease if the iron chelator desferrioxamine was present. We conclude that inducers of cytochrome P-450 may increase haem synthesis not only by increasing activity of 5-aminolaevulinate synthase, but also by increasing conversion of protoporphyrin into haem.

Interleukin-1 (IL-1) depresses cytochrome P450 levels and activities in mice

Endotoxin depresses cytochrome P450 levels when injected into animals. The purpose of this study was to determine whether endotoxin itself, or monokine(s) released in response to endotoxin administration are responsible for this effect. Cytochrome P450 levels and drug metabolizing activities were measured in endotoxin resistant C3H/HeJ mice 24h after single intraperitoneal injections of either lipopolysaccharide (LPS), a semipurified murine monokine preparation containing interleukin-1 (IL-1), or murine recombinant IL-1. In endotoxin sensitive C3H/HeN mice, LPS (0.5 mg/Kg) decreased total cytochrome P450 levels, benzphetamine demethylase activities, and ethoxyresorufin-0-deethylase activities. This dose of LPS did not alter cytochrome P450 levels or activities in the C3H/HeJ mice. However, after injection of the semipurified monokine preparation or the recombinant IL-1, there were significant decreases in cytochrome P450 levels and activities similar to the decreases observed with LPS in the C3H/HeN mice. These findings suggest that the alterations in hepatic cytochrome P450 seen with endotoxin injection are mediated, at least in part, by IL-1.

Zinc metabolism in alcoholic liver disease

Alterations in zinc metabolism or zinc deficiency frequently occur in patients with alcoholic liver disease. Potential manifestations of zinc deficiency include skin lesions, hypogonadism, impaired night vision, impaired immune function, anorexia, altered protein metabolism, diarrhea, and depressed mental function. Because of the variety of ways in which zinc deficiency may present in alcoholic liver disease, clinicians must maintain a high index of suspicion for this nutrient deficiency when caring for these patients. Not only may zinc deficiency occur with alcoholic liver disease, but there also may be altered zinc metabolism. Recent data from alcoholic hepatitis patients demonstrate increased serum levels of the monokine interleukin 1, which is known to cause hypozincemia and an internal redistribution of zinc. This monokine has a host of metabolic functions other than its effect on mineral metabolism that have relevance for alcoholic liver disease such as fever production, neutrophilia, and muscle catabolism. We suggest that the patient with alcoholic liver disease frequently has problems with either zinc deficiency or altered zinc metabolism and the potential implications of this are discussed.

Serum interleukin-1 (IL-1) activity in alcoholic hepatitis

Interleukin-1 (IL-1) is a monokine which has been demonstrated to produce a variety of seemingly diverse metabolic events including fever, neutrophilia, anorexia, altered mineral metabolism, muscle catabolism, and fibroblast proliferation. Because many of the clinical features of alcoholic hepatitis are metabolic abnormalities that have been shown to be caused by IL-1, we questioned whether patients with alcoholic hepatitis had elevated serum levels of IL-1. Six patients with alcoholic hepatitis had serum IL-1 activity measured by the thymocyte costimulator assay after serum inhibitors were removed. Their values were compared to those of 6 age and sex-matched healthy controls. Patients with alcoholic hepatitis had markedly elevated serum IL-1 activity, with the integrated value of all fractions having serum IL-1 activity being 9.8 times that of controls. IL-1 activity in serum from alcoholic hepatitis patients also was blocked by antibody to IL-1. We conclude that patients with alcoholic hepatitis have increased serum IL-1 activity which may play a role in certain of the metabolic complications of alcoholic hepatitis.

Increased glutathione in cultured hepatocytes associated with induction of cytochrome P-450. Lack of effect of glutathione depletion on induction of cytochrome P-450 and delta-aminolevulinate synthase

Cellular glutathione concentrations in primary cultures of chick embryo hepatocytes were 15.3 +/- 5.3 nmoles/mg protein (mean +/- S.D.) and remained stable for up to 3 days in culture. The presence of insulin was not essential for the maintenance of glutathione concentrations. Induction of cytochrome P-450 by phenobarbital-like inducers (2-propyl-2-isopropylacetamide, 2-allyl-2-isopropylacetamide, and 2,4,5,2',4',5'-hexabromobiphenyl) was accompanied by 2- to 3-fold increases in glutathione concentrations and by increased glucuronidation of phenol red. The 3-methylcholanthrene-like inducers of cytochrome P-450 (beta-naphthoflavone and 3,4,3',4'-tetrachlorobiphenyl) did not have these effects. Glutathione was rapidly depleted to 15-30% of control levels in hepatocytes treated with buthionine sulfoximine, an inhibitor of gamma-glutamylcysteine synthase. No toxicity was observed with glutathione depletion. Glutathione depletion did not affect the ability of 2-propyl-2-isopropylacetamide to induce cytochrome P-450, glucuronidation of phenol red, or delta-aminolevulinate synthase.

Iron loading of cultured hepatocytes. Effect of iron on 5-aminolaevulinate synthase is independent of lipid peroxidation

Cultured chick embryo hepatocytes were iron-loaded with ferric nitrilotriacetate. Iron-loading was confirmed by both quantitative cellular iron determinations and ultrastructural studies. With iron-loading, lipid peroxidation, as detected by malonaldehyde released into the medium, occurred at a linear rate for 12h, after which time the rate of malonaldehyde production decreased. No cell toxicity, as detected by lactate dehydrogenase release, was noted. The amount of malonaldehyde recovered in the medium after 18h of exposure to iron represented 24-33% of the total malonaldehyde that could be produced by incubating lysed cells with iron and ascorbate. Cellular glutathione was not affected by iron-stimulated lipid peroxidation, but was increased by allylisopropylacetamide. Although iron-loading by itself had no effect on activity of 5-aminolaevulinate synthase, the first and rate-limiting step in haem synthesis, iron-loading in the presence of the porphyrogenic drug allylisopropylacetamide increased levels of 5-aminolaevulinate synthase 6-fold over levels induced by the drug alone. The antioxidant, butylated hydroxytoluene, totally inhibited iron-stimulated lipid peroxidation, but did not interfere with the effect of iron-loading to potentiate an increase in 5-aminolaevulinate synthase. After 18h of exposure to iron, followed by a change to fresh medium, the iron remaining within the cells did not stimulate further lipid peroxidation over the following 18h, but did potentiate an increase in 5-aminolaevulinate synthase on exposure to allylisopropylacetamide. It therefore appears that lipid peroxidation is not the mechanism by which iron potentiates induction of hepatic 5-aminolaevulinate synthase.

Iron and the liver: acute effects of iron-loading on hepatic heme synthesis of rats. Role of decreased activity of 5-aminolevulinate dehydrase

Acute iron loading of rats, by intraperitoneal administration of iron-dextran (500 mg Fe/kg body wt 18-20 h before killing) decreased by 30% the rate of conversion of 5-amino-[14C]levulinate ([14C]ALA) into heme as measured with a recently described procedure for liver homogenates (1981. Biochem. J. 198: 595-604). The decrease in conversion of labeled ALA into heme caused by iron loading was shown to be due to a 70-80% decrease in activity of ALA dehydrase. The decrease in activity of ALA dehydrase caused by iron loading was not associated with a decrease in hepatic concentrations of GSH, nor could it be reversed by addition of dithiothreitol, Zn2+ or chelators of Fe2+ and Fe3+. Addition of FeSO4, ferric citrate, or ferritin to homogenates of control liver had no effect of activity of ALA dehydrase. The decrease in activity of ALA dehydrase, caused by iron-dextran, was mirrored by a reciprocal increase in ALA synthase. Iron-dextran potentiated the induction of ALA synthase by allylisopropylacetamide. However, this potentiation could be dissociated from the decrease in ALA dehydrase caused by iron loading.