Testing the porphyrinogenicity of propofol in a primed rat model

We evaluated the porphyrinogenicity of propofol in a rat model. After a pilot study had been conducted to determine an optimal dose, 48 fasting male Sprague-Dawley rats were allocated randomly to six groups. The animals in groups 1-3 received saline i.p. In groups 4-6, the animals were given allylisopropylacetamide (AIA). Twelve hours later, animals in groups 1 and 4 received saline, groups 2 and 5 were given propofol 150 mg kg-1 i.p., followed by 75 mg kg-1 3 h later, and groups 3 and 6 received phenobarbitone 50 mg kg-1 i.p. and 25 mg kg-1 i.p. The animals were anaesthetized and killed 3 h after the second drug bolus and we measured the concentration of cytochrome P450, total porphyrin content and the activity of delta-aminolaevulinic acid synthase (ALAS) in the liver. Urinary delta-aminolaevulinic acid (ALA) and porphobilinogen (PBG) concentrations were measured. Analysis of variance and the t test with Bonferroni's correction were used to compare data. The hepatic cytochrome P450 concentration in the non-primed groups varied from 28.1 to 31.1 nmol g-1; administration of AIA decreased this to 20.1-20.9 nmol g-1. Total hepatic porphyrins were between 0.78 and 1.22 nmol g-1 in the non-primed groups and between 2.71 and 3.54 nmol g-1 in the AIA-primed groups. Hepatic ALAS activity was 29.2 and 35.5 nmol h-1 g-1 in groups 1 and 2. In the primed saline group, ALAS activity was measured at 134.5 nmol h-1 g-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental latent and acute porphyria in the non-fasted rat; preventive effect of propranolol

This study demonstrates an experimental model of the biochemical pattern of the 'latent phase' of hepatic porphyria subject to 'acute attack', upon application of prophyrinogenic stimuli. The 'latent phase' was achieved by administering 3,5-diethoxycarbonyl-1, 4-dihydrocollidine [DDC], 70 mg kg-1 day, orally to non-fasted rats. A two- and threefold increase in coproporphyrin in urine and protoporphyrin in faeces, respectively, were observed. An 'acute attack' was induced by phenobarbitone (PB), 100 mg kg-1, administered on the third day of treatment with DDC, followed by administration of 2-allyl-2-isopropylacetamide (AIA), 470 mg kg-1, on the fourth day. A fourfold elevation in urinary porphobilinogen (PBG) and delta-aminolevulinic acid (ALA) and further increase of three- and fourfold in urinary coproporphyrin and faecal protoporphyrin, respectively, was observed. The effect of DDC, AIA and PB on the excretion of PBG and porphyrins was found to be synergistic rather than additive. dl-Propranolol, 700 mg kg-1, given to DDC treated rats 'latent phase' reduced the amount of porphyrins excreted in urine and faeces to those observed in control dimethyl sulphoxide (DMSO) treated rats. It also prevented induction of 'acute attack' caused by the combination of PB and AIA. It is shown that dl-propranolol affects a few parameters in the haem biosynthetic pathway. Its beneficial effect in porphyria is probably the result of increasing the concentration of haem in the free haem pool.

Cimetidine suppresses chemically induced experimental hepatic porphyria

The ability of cimetidine to reduce the activity of hepatic aminolevulinic acid synthase (ALA-S) was examined in allylisopropyl acetamide (AIA) treated porphyric adult rats. A dose of 20 mg cimetidine/100 gm body weight resulted in a 50% decrease in the AIA-induced hepatic ALA-S activity compared to rats treated with AIA alone. Heme oxygenase activity was decreased 25% compared to rats treated with AIA alone. The effects of AIA and cimetidine on cytochrome P-450 were not additive, suggesting competition for a common site of interaction. The results suggest that cimetidine may prove to be useful in treating porphyria in humans.

The effects of haem arginate and haematin upon the allylisopropylacetamide induced experimental porphyria in rats

Biochemical disorders caused by allylisopropylacetamide in various animal species resemble human acute intermittent porphyria. The antiporphyrogenic efficacy and potency of haem arginate, a new haem compound, were compared with those of haematin in experimental porphyria of rats. Both haem arginate and haematin dose-dependently decreased the urinary excretions of porphyrin precursors. They inhibited significantly the induction of hepatic delta-aminola-evulinic acid synthase. Haem arginate and haematin could restore the activity of haem oxygenase and after higher doses they increased the activity. The dose-effect relationships of the two haem compounds were demonstrated.

Plasma lipoprotein pattern in relation to liver histology after toxic hepatitis and experimental biliary obstruction in rabbits

Plasma lipoproteins were studied in relation to liver histology in rabbits in the course of toxic hepatitis and compared to those after experimental biliary obstruction. The lipoprotein electrophoretic pattern became deeply abnormal during the acute phase of toxic hepatitis and correlated with the degree of liver injury, improving during recovery. Liver damage was more severe after carbon tetrachloride than after alcohol and milder after allylo-isopropyl-acetamide, a porphyrinogenic substance. Lipoprotein abnormalities were not followed by significantly reduced levels of cholesterol esters in the plasma. In comparison, animals with biliary obstruction developed milder liver damage presented gross abnormalities of plasma lipids and lipoproteins, followed by relative deficiency of cholesterol esterification. It is concluded that lipoprotein changes in acute liver injury, although non-specific, are a sensitive index of liver damage and recovery. Serious acute liver injury can exist without significant fall in cholesterol esters.

Influence of cycloheximide on normal and induced delta-aminolevulinic acid synthetase (aminoketone synthesis) of rat liver in vivo and in vitro

2 and 5 mg/kg cycloheximide given i.p. 30 minutes prior to the inducer allylisopropylacetamide (AIA) diminished or prevented the enhancement of delta-aminolevulinic acid synthetase (ALAS) activity in newborn rats. In adult rats the small AIA effect 24 hours after pretreatment was enhanced by 2 mg/kg cycloheximide i.p., when the inhibitor was injected 2 hours prior to the inducer. The basic aminoketone synthesis was inhibited by cycloheximide alone. 150-600 microgram/ml cycloheximide had no effect on the aminoketone synthesis of rat liver slices in vitro during 4 hours of incubation. The in vitro induction by 0.6 mg/ml AIA was enhanced by cycloheximide, if the inducer was added 1 hour after preincubation with cycloheximide. It is supposed, that the cytoplasmically localized precursor-ALAS is activated at the beginning of the induction process prior to the initiation of de novo enzyme synthesis, at least in vitro.

Hepatic heme metabolism and its control

This review summarizes heme metabolism and focuses especially upon the control of hepatic heme biosynthesis. Activity of δ-aminolevulinic acid synthetase, the first enzyme of heme biosynthesis, is of primary importance in controlling the overall activity of this biosynthetic pathway. Δ-aminolevulinic acid synthetase is subject to inhibition and repression by heme, and numerous basic and clinical studies support the concept that there exists within hepatocytes a "regulatory" heme pool which controls activity of δ-aminolevulinic acid synthetase. In addition, activity of this enzyme is repressed by feeding, especially by ingestion of carbohydrates (the so-called "glucose effect"). Studies pertaining to the mechanisms underlying this effect are also reviewed. The "glucose effect" appears to be mediated by glucose or perhaps by glucose-6-phosphate or uridine diphosphate glucose, rather than by metabolites further removed from glucose itself. Unlike the situation in E. coli, the "glucose effect" in liver of higher organisms is not mediated by alterations in intracellular concentrations of cyclic AMP. Effects of heavy metals, especially iron, on hepatic heme metabolism are also considered. Iron has been found to inhibit formation and utilization of uroporphyrinogen III and to lead to decreased concentrations of microsomal heme and cytochrome P-450. Administration of large amounts of iron is also associated with an increase in activity of heme oxygenase, a property shared by several other metal ions, most notably cobalt. This effect of iron or cobalt administration is similar to the effect of heme administration in increasing heme oxygenase activity; however, we believe it is unlikely that iron, rather than heme itself, is a physiologic regulator of hepatic heme metabolism, although this hypothesis has lately been proposed.

Decreased liver activity of porphyrin-metal chelatase in hepatic porphyria caused by 3,5-diethoxycarbonyl-1,4-dihydrocollidine. Studies in rats and mice

1. A difference has been found between rats and mice in their sensitivity to the porphyrogenic effect of drugs. Mice are more sensitive than rats to 3,5-diethoxycarbonyl-1,4-dihydrocollidine, but less sensitive than rats to 2-allyl-2-isopropylacetamide. 2. Use has been made of this difference in sensitivity to ascertain the importance of the decrease of liver porphyrin-metal chelatase activity in porphyria caused by 3,5-diethoxycarbonyl-1,4-dihydrocollidine. Mice, which are more sensitive than rats to the stimulation of 5-aminolaevulinate caused by this drug, are also more sensitive with respect to the decrease of chelatase activity. 3. In both species, after treatment with 3,5-diethoxycarbonyl-1,4-dihydrocollidine, the ratio between chelatase activity and 5-aminolaevulinate activity is linear with respect to the reciprocal of the liver porphyrin concentration. This suggests that under these conditions the degree of porphyrin accumulation depends on the balance between rate of porphyrin formation and rate of porphyrin utilization. 4. Compound SKF 525-A (2-diethylaminoethyl 3,3-diphenylpropylacetate) when given before 3,5-diethoxycarbonyl-1,4-dihydrocollidine prevents the appearance of porphyria in the rat and also largely prevents the decrease of chelatase activity. In the mouse it is much less effective in preventing porphyria and it is almost completely inactive in protecting the chelatase from a decrease in activity. 5. Cycloheximide, when given before 3,5-diethoxycarbonyl-1,4-dihydrocollidine also inhibits the induction of 5-aminolaevulinate synthetase and the appearance of porphyria in the rat, but does not prevent the decrease of chelatase activity. These results suggest that two successive stages can be distinguished in the induction process: a first stage leading to inhibition of haem synthesis and a second stage requiring synthesis of protein in the liver and leading to stimulation of 5-aminolaevulinate synthetase.