Vitamin A metabolism in rats chronically treated with 3,3',4,4',5,5'-hexabromobiphenyl

Chronic dietary administration of 3,3',4,4',5,5'-hexabromobiphenyl (HBB), 1 mg/kg diet, caused a decrease in retinol (20-fold) and retinyl esters (23-fold) in the livers of female rats, but resulted in a 6.4-fold increase in retinol and 7.4-fold increase in retinyl esters in the kidneys. Liver acyl-CoA:retinol acyltransferase and retinyl palmitate hydrolase activities were reduced while serum concentration of retinol was unaffected by HBB feeding. Metabolism of a physiological dose of [11-3H]retinyl acetate (10 micrograms), was examined in rats fed either vitamin A-adequate diet, or marginal amounts of vitamin A, or vitamin A-adequate diet containing HBB. A 13-fold greater amount of the administered vitamin A was found in kidneys of HBB-treated rats. In rats fed adequate or low amounts of vitamin A, kidney radioactivity was primarily in the retinol fraction, while in HBB-fed rats the radioactivity was associated mostly with retinyl esters. Fecal and urinary excretion of radioactivity was greatly increased in HBB-treated rats. Chronic HBB feeding results in a loss of ability of liver to store vitamin A, and severely alters the uptake and metabolism of vitamin A in the kidneys. We conclude that HBB causes major disturbances in the regulation of vitamin A metabolism.     

Changes in vitamin A status following prolonged immobilization (simulated weightlessness).

A study was conducted to investigate the effects of a simulated weightlessness induced by chronic immobilization on vitamin A status. To simulate the stress condition of weightlessness, rats were suspended for 10 days in a special jacket to which metal chains were attached. Animals received a commercial stock diet. Control rats were pair-fed in reference to the suspended rats. As compared with the control, prolonged immobilization resulted in a decrease in body weight gain and an increase in adrenal weight occurred. In the suspended rats, serum concentrations of retinol and retinol-binding protein (RBP) declined. Hepatic retinyl palmitate content increased, and the hepatic retinol level was decreased. The prolonged immobilization led to significantly reduced retinyl palmitate levels in the testis and lung as well as lowered testicular retinol levels. The results suggest that the stress state induced by prolonged immobilization caused accumulation of hepatic retinyl palmitate, decreasing the serum retinol concentration and retinyl ester content in the extrahepatic tissues.     

The effects of nonadecafluoro-n-decanoic acid on serum retinol and hepatic retinyl palmitate hydrolase activity in male Sprague-Dawley rats

The effects of nonadecafluoro-n-decanoic acid (NDFDA) on serum retinol levels and hepatic retinyl palmitate hydrolase (RPH) activity were investigated in male Sprague-Dawley rats given a single intraperitoneal (IP) dose of 0, 50, or 100 mg/kg NDFDA and sacrificed at two, eight, or 11 days. Treated animals exhibited depressed serum retinol levels, lymphoid involution, and failure to gain weight in proportion to the dose. Hepatic RPH activities were depressed in both treatment groups at all time points and correlated with serum retinol levels. Hepatic retinol levels were also depressed by Day 11. Extraction of hepatic homogenates with acetone removed NDFDA and increased RPH activities twofold and threefold for the low- and high-dose groups, respectively. Analysis of partially purified RPH showed both NDFDA and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to be noncompetitive inhibitors: KI = 450 and 750 microM, respectively. We conclude that NDFDA causes a decrease in the mobilization of vitamin A from the liver by noncompetitive inhibition of RPH.     

The effect of TCDD on acyl CoA:retinol acyltransferase activity and vitamin A accumulation in the kidney of male Sprague-Dawley rats

Previous studies have shown that rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) show signs of toxicity that are similar to the responses of animals to a vitamin A-deficient diet. These include hypophagia, loss of body weight, loss of hepatic vitamin A, and accumulation of renal retinoids. Male Sprague-Dawley rats treated with 10, 30, or 100 nmol/kg of TCDD accumulated renal vitamin A, with retinyl palmitate concentrations reaching 8 times those of control animals, similar to that of male rats fed a vitamin A-free diet for 26 days. Acyl CoA:retinol acyltransferase (ACARAT) activities in both TCDD-treated rats and rats fed a vitamin A-free diet for 26 days were similarly elevated, and were strongly and positively correlated with the renal retinyl palmitate concentrations. Retinol concentrations in the kidneys of rats treated with TCDD or fed a vitamin A-free diet were only slightly elevated when compared to control rats. We suggest that accumulation of retinyl esters in the kidneys of rats treated with TCDD or fed a vitamin A-free diet occurs as a result of increased rates of retinol esterification.     

Metabolism of [11-3H]retinyl acetate in liver tissues of vitamin A-sufficient, -deficient and retinoic acid-supplemented rats

A study was conducted on the incorporation of [11-3H]retinyl acetate into various retinyl esters in liver tissues of rats either vitamin A-sufficient, vitamin A-deficient or vitamin A-deficient and maintained on retinoic acid. Further, the metabolism of [11-3H]retinyl acetate to polar metabolites in liver tissues of these three groups of animals was investigated. Retinol metabolites were analyzed by high-performance liquid chromatography. In vitamin A-sufficient rat liver, the incorporation of radioactivity into retinyl palmitate and stearate was observed at 0.25 h after the injection of the label. The label was further detected in retinyl laurate, myristate, palmitoleate, linoleate, pentadecanoate and heptadecanoate 3 h after the injection. The specific radioactivities (dpm/nmol) of all retinyl esters increased with time. However, the rate of increase in the specific radioactivity of retinyl laurate was found to be significantly higher (66-fold) than that of retinyl palmitate 24 h after the injection of the label. 7 days after the injection of the label, the specific radioactivity between different retinyl esters were found to be similar, indicating that newly dosed labelled vitamin A had now mixed uniformly with the endogenous pool of vitamin A in the liver. The esterification of labelled retinol was not detected in liver tissues of vitamin A-deficient or retinoic acid-supplemented rats at any of the time point studied. Among the polar metabolites analyzed, the formation of [3H]retinoic acid from [3H]retinyl acetate was found only in vitamin A-deficient rat liver 24 h after the injection of the label. A new polar metabolite of retinol (RM) was detected in liver of the three groups of animals. The formation of 3H-labelled metabolite RM from [3H]retinyl acetate was not detected until 7 days after the injection of the label in the vitamin A-sufficient rat liver, suggesting that metabolite RM could be derived from a more stable pool of vitamin A.     

The effect of TCDD on Acyl CoA: Retinol acyltransferase activity and vitamin a accumulation in the kidney of male sprague-dawley rats

Previous studies have shown that rats treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) show signs of toxicity that are similar to the responses of animals to a vitamin A-deficient diet. These include hypophagia, loss of body weight, loss of hepatic vitamin A, and accumulation of renal retinoids. Male Sprague-Dawley rats treated with 10, 30, or 100 nmol/kg of TCDD accumulated renal vitamin A, with retinyl palmitate concentrations reaching 8 times those of control animals, similar to that of male rats fed a vitamin A-free diet for 26 days. Acyl CoA:retinol acyltransferase (ACARAT) activities in both TCDD-treated rats and rats fed a vitamin A-free diet for 26 days were similarly elevated, and were strongly and positively correlated with the renal retinyl palmitate concentrations. Retinol concentrations in the kidneys of rats treated with TCDD or fed a vitamin A-free diet were only slightly elevated when compared to control rats. We suggest that accumulation of retinyl esters in the kidneys of rats treated with TCDD or fed a vitamin A-free diet occurs as a result of increased rates of retinol esterification.     

Effects of emulsified perfluorochemicals on liver cytochromes P-450 in rats

1. The effects of intravenous (i.v.) injection of various perfluorochemical (PFC) emulsions or different fractions of the non-ionic poloxamer surfactant, Pluronic F-68, have been studied separately in male and female rats. 2. Injection of 10 ml/kg body wt of either Fluosol-DA 20% (F-DA) or a novel perfluorodecalin emulsion containing a C-16 oil additive in male rats increased liver weight up to 7 days later; no corresponding effect occurred in response to injection of Oxypherol (FC-43). 3. Liver weight was also increased in female rats at 72 hr after injection of the novel emulsion but this was less pronounced than in males; liver weight in female rats was unchanged in response to injection of either F-DA or FC-43. 4. Mean liver microsomal cytochromes P-450 concentrations in male rats were increased 2-3 fold at 72 hr after injection of either F-DA or the novel emulsion with a less pronounced increase also seen at 7 days in animals receiving the novel emulsion. No significant alterations in cytochrome concentration occurred in response to injection of FC-43 or either commercial grade or purified pluronic solution. 5. Liver cytochromes P-450 concentrations in female rats were unaffected by any of the experimental treatments. 6. These results show that injection of a single low dose of emulsified PFCs into male rats can increase hepatic microsomal cytochromes P-450 concentration but the response is highly variable, depending on composition of emulsion injected.     

Mixed-function oxygenase in juvenile rainbow trout exposed to hexachlorobenzene or 3,3',4,4'-tetrachlorobiphenyl.

1. 3,3',4,4'-tetrachlorobiphenyl (PCB 77), but not hexachlorobenzene, induced liver microsomal cytochrome P-450 (Cyt P-450), ethoxycoumarin-O-deethylase (ECOD) and ethoxyresorufin-O-deethylase (EROD) in rainbow trout. Maximum induction was observed in a PCB 77 injected group of fish (1.0 mg/kg, i.p. injection) 13 days after the injections being 2, 10 and 50 times the value of non-induced fish, respectively. 2. The apparent Km value of ethoxyresorufin of this induced group of fish differed only slightly from that of non-induced fish. The apparent Vmax value (EROD) was 50 times higher. 3. Freezing small pieces of liver in liquid nitrogen did not produce cytochrome P-420. 4. Fluorimetric and spectrophotometric measurements of EROD correlated.     

Effect of glycerol-induced acute renal failure and di-2-ethylhexyl phthalate on the enzymes involved in biotransformation of xenobiotixs.

The effects of di-(2-ethylhexyl)-phthalate (DEPH) on the levels of cytochrome P-450 and b5 monooxygenases were studied in the rat kidney and liver in acute renal failure induced by glycerol. Intramuscular injection of glycerol (50%,10 ml x kg(-1)) to rats produced proximal tubular damage and acute renal failure. The indicators of renal function, serum urea and creatinine significantly increased (480 and 350 percent, respectively). In control and glycerol-treated animals DEPH had no significant effect on the concentrations of serum urea and creatinine. Twenty-four hours after glycerol injection the total amount of cytochrome P-450 and b5 significantly decreased in renal but increased in liver microsomal fractions. Moreover, 48 and 72 hours after glycerol injection the level of cytochrome P-450 and b5 significantly increased in both organs. A single dose of DEPH (2 ml x kg(-1), i.p.) also elevated the total cytochrome P-450 and b5 in control animals. This enhancing effect of DEPH was additive to that of glycerol in glycerol-induced acute renal failure. These results indicate that DEPH and glycerol evoked pathological changes may affect the metabolism of xenobiotics plus endogenous hormones in the liver and in kidney.     

Induction of cytochrome P-450 forms by prolonged administration of nifedipine

In experiments on male Wistar rats it has been found that nifedipine applied in a dose of 10 mg/kg body weight i.p. daily for 20 days did not significantly increase the total amount of cytochrome P-450 but markedly increased the 7 alpha-, 16 beta- and 6 beta-hydroxylation of androstenedione in liver microsomes, suggesting the induction of cytochromes P-450a, P-450b and P-450p respectively. The induction of cytochrome P-450b was also confirmed immunochemically with polyclonal antibodies against cytochrome P-450b/e.     

Effects of inmecarb on alcohol intake and the state of hepatic cytochrome P-450 system during various stages of experimental alcoholism in rats

The influence of the new anti-alcohol drug Inmecarb on the alcohol consumption as well as on activity of the liver cytochrome P-450 system was studied in rats during chronic alcohol intoxication in the free choice situation between water and 15% ethanol solution. It was shown that voluntary alcohol consumption of different duration (10 days to 8 months) does not change the activity of liver cytochrome P-450 system. Inmecarb treatment (40 mg/kg, i.p. twice a day) during 14 days resulted in decrease of alcohol consumption in rats. This effect was most pronounced in late stages of experimental alcoholism. Inmecarb decreases the cytochrome P-450 content and suppresses the activity of aniline hydroxylase in rats with different duration of voluntary alcohol intoxication, but most pronounced effect was observed during the late stages of experimental alcoholism.     

Vitamin A metabolism in rats chronically treated with 3,3′,4,4′,5,′-hexabromobiphenyl

Chronic dietary administration of 3,3′,4,4′,5,5′-hexabromobiphenyl (HBB), 1 mg/kg diet, caused a decrease in retinol (20-fold) and retinyl esters (23-fold) in the livers of female rats, but resulted in a 6.4-fold increase in retinol and 7.4-fold increase in retinyl esters in the kidneys. Liver acyl-CoA: retinol acyltransferase and retinyl palmitate hydrolase activities were reduced while serum concentration of retinol was unaffected by HBB feeding. Metabolism of a physiological dose of [11-³H]retinyl acetate (10 μg), was examined in rats fed either vitamin A-adequate diet, or marginal amounts of vitamin A, or vitamin A-adequate diet containing HBB. A 13-fold greater amount of the administered vitamin A was found in kidneys of HBB-treated rats. In rats fed adequate or low amounts of vitamin A, kidney radioactivity was primarily in the retinol fraction, while in HBB-fed rats the radioactivity was associated mostly with retinyl esters. Fecal and urinary excretion of radioactivity was greatly increased in HBB-treated rats. Chronic HBB feeding results in a loss of ability of liver to store vitamin A, and severely alters the uptake and metabolism of vitamin A in the kidneys. We conclude that HBB causes major disturbances in the regulation of vitamin A metabolism.     

Effect of hexachlorobiphenyl on vitamin A homeostasis in the rat

Vitamin A status and turnover were examined in rats that had been exposed to chronic dietary treatment of 3,4,5,3',4',5'-hexachlorobiphenyl (HCB), 1 mg/kg diet. HCB caused hepatic depletion and renal accumulation of vitamin A, and a 1.7-fold increase in the serum retinol concentration. Intravenously administered [3H]retinol bound to retinol binding protein-transthyretin complex (RBP-TTR complex) was used to study the dynamics of circulatory retinol in these rats. In HCB-treated rats, the plasma turnover rate of retinol was increased compared to vitamin A-adequate untreated controls. HCB caused a 50% reduction of total radioactivity in liver, and, except for 0.5 h after the [3H]retinol-RBP-TTR dose, the specific activity of the hepatic retinyl ester pool was greater compared to control rats. The kidneys of HCB-treated rats accumulated radioactivity in the retinyl ester fraction. HCB also caused a 50% reduction in adrenal radioactivity compared with control rats. Urinary and fecal excretion of radioactivity was 3-fold higher in HCB-treated rats as compared to controls. Our findings demonstrate that chronic HCB feeding results in expansion of plasma vitamin A mass, in changes of liver and kidney retinol and retinyl ester pool dynamics and in an increased metabolism of vitamin A.     

Liver cytochrome P-450 induction in rats by drug preparations and the body vitamin A allowance

The content of P-450 cytochrome and vitamin A was determined in the liver of mature male rats who received for a month daily parenteral administrations of phenobarbital solutions (Pb; 40 mg/kg), rheopyrine (a mixture of equal aliquots of amidopyrine and butadione; 200 mg/kg), amidopyrine (100 mg/kg) or water (control). The animals were kept on a semisynthetic diet, receiving once, every week 400 IU of retinol-palmitate per rat. Pb administration markedly (more than threefold) increased P-450 cytochrome content in the liver. Rheopyrine and amidopyrine also elevated its level, but to a lesser extent than Pb. Pb and rheopyrine also depressed vitamin A levels in the liver and caused either a trend towards its decrease (Pb) or a significant decrease (rheopyrine) of its overall content in the liver. The effect of amidopyrine on the concentration and storage of retinol in the liver was less pronounced. The data obtained suggest that the drugs inducing P-450 cytochrome are capable of disturbing vitamin A content in the body.     

Potent induction of rat liver microsomal, drug-metabolizing enzymes by 2,3,3',4,4',5-hexabromobiphenyl, a component of fireMaster

The multistep synthesis and purification of 2,3,3',4,4',5-hexabromobiphenyl (HBBp) is described. Capillary gas chromatography revealed that HBBp comprises 0.05% of the industrial polybrominated biphenyl (PBB) mixture, fireMaster BP-6 (lot 7062). When administered to immature male Wistar rats, HBBp caused a dose-dependent increase in (a) the activity of benzo[a]pyrene (B[a]P) hydroxylase (AHH) and 4-chlorobiphenyl (4-CBP) hydroxylase and (b) the concentration of cytochrome P-450. Sodium dodecyl sulfate (SDS)-gel electrophoresis indicated that these increases in cytochrome P-450 and cytochrome P-450-dependent monooxygenase activities were accompanied by a dose-dependent intensification of a protein of relative molecular weight (Mr) 55 000 which comigrated with the major 3-methylcholanthrene(MC)-inducible form of cytochrome P-450 (i.e., cytochrome P-448). Like MC, but in contrast to phenobarbitone (PB), HBBp competitively displaced 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin ([3H]-TCDD) from the cytosolic protein thought to be the receptor for cytochrome P-448 induction. The results indicate that HBBp is a potent inducer of cytochrome P-448 and as such is the third MC-type inducer identified in fireMaster BP-6.     

Characterization of a new endogenous vitamin A metabolite

Here, we describe the discovery of a new major endogenous vitamin A metabolite with particularly high hepatic concentrations. This metabolite was isolated from mouse livers and was characterized as 9-cis-4-oxo-13,14-dihydro-retinoic acid (RA) based on mass spectral, ultraviolet, and nuclear magnetic resonance analyses. It was also detected in one human liver. To gain further insight into endogenous retinoid metabolism, mice were fed over a period of 14 days ad libitum with diets enriched with different amounts of retinyl palmitate [15,000, 45,000 or 150,000 international units (IU)/kg diet]. Higher retinyl palmitate amounts in the diet resulted surprisingly in a dose-dependent decrease in all-trans-RA levels in serum, kidney, and brain, whereas levels of 9-cis-4-oxo-13,14-dihydro-RA, retinol, and retinyl esters were dose-dependently elevated in serum, kidney, and liver. 13-cis-RA levels could be detected in serum, liver, and kidney, but were unaffected by the dietary vitamin A status. 9-cis-RA levels were below the detection limit of 0.2 ng/ml serum or 0.4 ng/g tissue. This study indicates that the oxidation at C4 of the cyclohexenyl ring, isomerization of the C9/C10 double bond, and reduction of the C13/C14 double bond are major endogenous metabolic pathways of vitamin A.     

Musk xylene is a novel specific inducer of cytochrome P-450IA2.

The effect of musk xylene on contents of both cytochrome P-450IA1 and cytochrome P-450IA2 in rat liver was investigated using Western blotting analysis. Rats were treated i.p. for five consecutive days with either 50, 100 or 200 mg musk xylene/kg body weight. Musk xylene increased both total cytochrome P-450 and cytochrome b5 contents in rat liver microsomes. Musk xylene induced cytochrome P-450IA2 (384 pmol/mg protein) strongly and preferentially and the ratio of cytochrome P450IA2/P-450IA1 was about 12 at the lowest dose tested. Musk xylene also induced the cytochrome P-450IA1 dose-dependently, but these extents were very small (32-174 pmol/mg protein). These results suggest that musk xylene may be a more specific inducer for cytochrome P-450IA2 than any other inducers reported.     

Precocious development of cytochrome P-450 in neonatal rat liver after glucocorticoid treatment.

Intraperitoneal injection of neonatal rats with glucocorticoid hormones causes precocious development of hepatic cytochrome P-450. Glucagon injection fails to stimulate this cytochrome P-450 development. Adult liver cytochrome P-450 is less responsive to glucocorticoid stimulation than is that of neonatal rat liver. Adrenalectomy of prematurely delivered neonatal animals prevents the early postnatal development of cytochrome P-450. Glucocorticoids failed to increase cytochrome P-450 concentrations in foetal rat liver. These findings imply that, although glucocorticoids are mandatory regulatory factors controlling cytochrome P-450 development, they are not themselves the 'trigger' initiating onset of that development.     

Distribution of cadmium in selected organs of mice: effects of cadmium on organ contents of retinoids and beta-carotene

Cadmium was administered to 32 adult ICR mice i.p. in two single doses (0.25 and 0.5 mg CdCl2, per kg of b.w.). After 48 hours concentrations of cadmium in kidneys, liver, spleen, muscle (m. quadriceps femoris), ovaries and testes and the concentration of retinyl palmitate, retinol and beta-carotene in kidney, liver and testes were determined. Significantly higher cadmium concentration was found in liver, kidney and ovary in both experimental groups in comparison with the control group (p<0.001). In muscle, spleen and testis the cadmium level was higher, however not significantly. No significant differences in the concentration of retinyl palmitate, retinol and alpha-carotene in liver were found. Concentration of alpha-carotene in kidney and testis was significantly decreased in both groups administered with cadmium (p<0.001). Concentration of retinyl palmitate was significantly lower in testis in the group with higher cadmium level (p<0.001) and the concentration of retinol significantly decreased in kidney and testis of mice after an administration of 0.5 mg CdCl2/kg b.w.     

The effects of malotilate on hepatic drug metabolizing systems in different strains of rats

1. In Sprague-Dawley (SD) rats treated for 7 days with malotilate (MAL:250 mg/kg, p.o.), cytochrome P-450 and b5 contents, aminopyrine N-demethylase and heme oxygenase activities were significantly increased. In Wistar rats, cytochrome b5 content and heme oxygenase and delta-aminolevulinic acid synthetase activities were found to be significantly increased. 2. Among the antipyrine metabolites excreted in urine during the 24 hr after antipyrine (100 mg/kg, i.p.) administration, norantipyrine increased significantly in Sprague-Dawley rats, while a significant increase of 4-hydroxyantipyrine was observed in Wistar rats. 3. The serum dimethadione/trimethadione ratio was only found to be significantly increased in Sprague-Dawley rats. 4. These results indicate that malotilate may have inducible effects on hepatic drug metabolizing enzymes, and that it affects the various cytochrome P-450 isozymes from different strains of rat in different ways.