Fatty acid oxidation by human liver peroxisomes

Concomitant induction of cytosolic but not microsomal epoxide hydrolase with peroxisomal beta-oxidation by various hypolipidemic compounds

The effects of two cholesterol-lowering (probucol and 1-benzyl-imidazole), three triglyceride- and cholesterol-lowering (clofibrate, tiadenol and fenofibrate) and one triglyceride-lowering (acetylsalicylic acid) compounds on the specific activities of two lipid-metabolizing enzymes (cyanide-insensitive peroxisomal beta-oxidation and palmitoyl-CoA hydrolase) and two xenobiotic metabolizing enzymes (cytosolic (cEH) and microsomal epoxide hydrolase (mEHb] from the livers of male Fischer F-344 rats were investigated. With the exception of probucol and acetylsalicylic acid, all compounds tested caused a dose-dependent hepatomegaly. Taken on a weight basis fenofibrate was the most effective inducer, causing a 20-fold induction of peroxisomal beta-oxidation, a 13-fold induction of cEH activity and a 16-fold induction of palmitoyl-CoA hydrolase activity. The other compounds with triglyceride-lowering activity also induced cEH as well as peroxisomal beta-oxidation and palmitoyl-CoA hydrolase activity. The potency of each individual drug was similar for induction of cEH activity as compared with that of peroxisomal beta-oxidation and palmitoyl-CoA hydrolase activity, but very dissimilar for mEHb, which upon treatment with any of the triglyceride-lowering compounds was either not or only minimally (less than 1.5-fold) induced. 1-Benzylimidazole possessing exclusively cholesterol-lowering activity increased mEHb much more than either cEH or peroxisomal beta-oxidation. The absence of an enhancement of cEH activity in in vitro studies confirmed that the increase in enzyme activity by the test compounds is not caused by activation. cEH activity was also induced in the kidney but only about 2-fold by fenofibrate, tiadenol and acetylsalicylic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

A rapid method for the isolation of peroxisomes from rat liver

A preparative method for the isolation of peroxisomes from the liver of normal, untreated rats is described. The peroxisome-enriched "light mitochondrial" fraction is layered on a 30% Nycodenz (5-[N-2,3-dihydroxypropylacetamido]-2,4,6-triiodo-N,N'-bis[2, 3-dihydroxypropyl]isophthalamide) solution containing 1 mM tetrasodium EDTA and then centrifuged in an angular rotor for 1 h at 130,000gavg. Peroxisomes are sedimented to the bottom leaving other organelles at the top of the tube. On the basis of morphological and biochemical studies, it is found that the peroxisomes (marker-enzymes catalase and urate oxidase) obtained in this method are not contaminated with lysosomes (marker-enzyme acid phosphatase) and contained very few mitochondria (marker-enzyme succinate-cytochrome c reductase) and microsomal vesicles (marker-enzyme glucose-6-phosphatase).

Protein phosphorylation in peroxisomes

The possible presence of phosphorylated proteins in peroxisomes was studied in hepatocytes from nafenopin-treated and normal rats. A 63 kDa phosphorylated protein was consistently and exclusively found in the membrane of peroxisomes from hepatocytes incubated in the presence of 32P-phosphate. The peroxisomes were isolated in metrizamide isopycnic gradients of postnuclear supernatants and were subfractionated by alkaline extraction to separate the membrane and the matrix proteins. Polyacrylamide gel electrophoresis, autoradiography and densitometry were employed to characterize the proteins. The 63 kDa membrane protein copurifies with peroxisomes in metrizamide gradients and apparently can be phosphorylated, in purified peroxisomes, with ATP and catalytic subunit of cAMP-dependent protein kinase.

Large cation-selective pores from rat liver peroxisomal membranes incorporated to planar lipid bilayers

Fusion of a highly purified fraction of rat liver peroxisomal membranes to planar lipid bilayers incorporates large, cation-selective voltage-dependent pores. The PK/PCl ratio of these pores, estimated in KCl gradients, is close to 4. The pores display several conductance states and spend most of the time open at voltages near 0 mV, closing at more positive and negative voltages. At voltages near 0 mV the most frequent open state has a conductance of 2.4 nS in 0.3 M KCl. At voltages more positive and more negative than 10 mV the most frequent open state displays a conductance of 1.2 nS in 0.3 M KCl. With these results pore diameters of 3 and 1.5 nm, respectively, can be estimated. We suggest that these pores might account for the unusually high permeability of peroxisomes to low molecular weight solutes. Fusion also incorporates a perfectly anion-selective, two-open states channel with conductances of 50 and 100 pS in 0.1 M KCl.

Study of some factors controlling fatty acid oxidation in liver mitochondria of obese Zucker rats

Livers of genetically obese Zucker rats showed, compared with lean controls, hypertrophy and enrichment in triacylglycerols, indicating that fatty acid metabolism was directed towards lipogenesis and esterification rather than towards fatty acid oxidation. Mitochondrial activities of cytochrome c oxidase and monoamine oxidase were significantly lower when expressed per g wet wt. of liver, whereas peroxisomal activities of urate oxidase and palmitoyl-CoA-dependent NAD+ reduction were unchanged. Liver mitochondria were able to oxidize oleic acid at the same rate in both obese and lean rats. For reactions occurring inside the mitochondria, e.g. octanoate oxidation and palmitoyl-CoA dehydrogenase, no difference was found between both phenotypes. Total carnitine palmitoyl-, octanoyl- and acetyl-transferase activities were slightly higher in mitochondria from obese rats, whereas the carnitine content of both liver tissue and mitochondria was significantly lower in obese rats compared with their lean littermates. The carnitine palmitoyltransferase I activity was slightly higher in liver mitochondria from obese rats, but this enzyme was more sensitive to malonyl-CoA inhibition in obese than in lean rats. The above results strongly suggest that the impaired fatty acid oxidation observed in the whole liver of obese rats is due to the diminished transport of fatty acids across the mitochondrial inner membrane via the carnitine palmitoyltransferase I. This effect could be reinforced by the decreased mitochondrial content per g wet wt. of liver. The depressed fatty acid oxidation may explain in part the lipid infiltration of liver observed in obese Zucker rats.

Hepatic peroxisomes are deficient in infantile refsum disease: a cytochemical study of 4 cases

We examined liver biopsies from 4 patients with the infantile form of Refsum disease. No peroxisomes were visualized by light microscopy after cytochemical staining for catalase, a marker enzyme for this organelle. Absence of peroxisomes was confirmed by electron microscopy in 3 patients; in the 4th patient we observed organelles of peculiar size and structure and with minimal catalase activity. Light microscopy also showed birefringent macrophages containing P.A.S.-positive material; they were abundant in the 3 older children, and rare in the youngest (8 months). Peroxisomes and birefringent macrophages were absent in 2 patients with the cerebrohepatorenal syndrome of Zellweger. The simultaneous presence of these unique light microscopical characteristics may be of diagnostic value.

Effects of mono (2-ethylhexyl) phthalate and its straight chain analogues mono-n-hexylphthalate and mono-n-octyl phthalate on lipid metabolism in isolated hepatocytes

In cultured hepatocytes, as in vivo, mono-2-ethylhexyl phthalate (MEHP) and its straight chain analogues mono-n-hexyl phthalate (MnHP) and mono-n-octyl phthalate (MnOP) each cause accumulation of lipid but only MEHP produces significant induction of peroxisomal fatty acid oxidizing enzymes. To elucidate the mechanisms underlying this lipid accumulation we investigated the effects of these phthalates and the drug clofibric acid on fatty acid metabolism in suspensions of isolated hepatocytes. The effects were found to be markedly dependent on the nutritional state of the animals from which the hepatocytes were isolated. In hepatocytes isolated from animals fasted overnight, or animals fed ab libitum but killed at approximately 2.30 p.m., MEHP, MnHP, MnOP and clofibric acid each caused a marked rapid stimulation of fatty acid oxidation and the synthesis of triglycerides in hepatocytes when incubated in Hanks saline. Export of very low density lipoprotein (VLDL) from the cells was either unchanged or somewhat reduced. In contrast, in hepatocytes isolated from rats fed ad libitum but killed at approximately 9.30 a.m. MEHP and clofibric acid did not alter fatty acid oxidation or triglyceride synthesis, while MnOP and MnHP increased triglyceride synthesis but decreased fatty acid oxidation. The effects of fasting were largely abolished by incubations of the cells in a complete tissue culture medium (Liebowitz L-15). The results suggest that MEHP and its straight chain analogues can, either as the free acid or the CoA ester, mimic the action of fatty acids in the allosteric regulation of fatty acid metabolism.

3-Hydroxy-3-methylglutaryl coenzyme A reductase localization in rat liver peroxisomes and microsomes of control and cholestyramine-treated animals: quantitative biochemical and immunoelectron microscopical analyses

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a key regulatory enzyme involved in cholesterol biosynthesis, has recently been reported to be present in rat liver peroxisomes (Keller, G.A., M.C. Barton, D.J. Shapiro, and S.J. Singer, 1985, Proc. Natl. Acad. Sci. USA, 82:770-774). Immunoelectron labeling of ultrathin frozen sections of normal liver, using two monoclonal antibodies to purified rat liver microsomal HMG-CoA reductase, indicated that the enzyme is present in the matrix of peroxisomes. This study is a quantitative biochemical and immunoelectron microscopical analysis of HMG-CoA reductase in rat liver peroxisomes and microsomes of normal and cholestyramine-treated animals. Cholestyramine treatment produced a six- to sevenfold increase in the specific activity of peroxisomal HMG-CoA reductase, whereas the microsomal HMG-CoA reductase specific activity increased by about twofold. Using a computer program that calculates optimal linear combinations of marker enzymes, it was determined that between 20 and 30% of the total reductase activity was located in the peroxisomes of cholestyramine-treated animals. Less than 5% of the reductase activity was present in peroxisomes under control conditions. Quantitation of the immunoelectron microscopical data was in excellent agreement with the biochemical results. After cholestyramine treatment there was an eightfold increase in the density of gold particles per peroxisome, and we estimate about a threefold increase in the labeling of the ER.

Peroxisomal beta-oxidation of palmitoyl-CoA in human liver homogenates and its deficiency in the cerebro-hepato-renal (Zellweger) syndrome

The presence of a beta-oxidation system in peroxisomes has been well documented. Rather than a duplicate of the mitochondrial beta-oxidation system, peroxisomes seem specially equipped to initiate the oxidation of very-long-chain fatty acids. Thus, the accumulation of very-long-chain fatty acids in tissues and body fluids from patients with a limited (X-linked adrenoleukodystrophy) or generalized (cerebro-hepato-renal (Zellweger) syndrome, infantile Refsum disease, neonatal adrenoleukodystrophy) peroxisomal dysfunction probably results from an impairment in the peroxisomal beta-oxidation system. In order to study this, we have developed an original assay which allows measurement of the overall peroxisomal beta-oxidation activity in human liver homogenates. Compared to controls, a strong deficiency of this activity was detected in liver from Zellweger patients using palmitoyl-CoA as a substrate.

Conjugation of cholic acid with taurine and glycine by rat liver peroxisomes

We have previously shown that rat liver peroxisomes catalyze conversion of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholestanoic acid into cholic acid as the CoA-ester (1). In the present work it is shown that addition of taurine or glycine to the reaction mixture, choloyl-CoA is further converted to taurocholic or glycocholic acid, respectively. The identity of these products was verified by fast atom bombardment-mass spectrometry. The peroxisomal fraction catalyzed conjugation of cholic acid with taurine (22.3 nmol X mg-1 X h-1) or glycine (18.6 nmol X mg-1 X h-1) at rates twice those observed with the microsomal fraction. The results indicate that conjugation of newly formed bile acids may be an important function of liver peroxisomes.

Accumulation and defective beta-oxidation of very long chain fatty acids in Zellweger's syndrome, adrenoleukodystrophy and Refsum's disease variants

The accumulation of very long chain fatty acids in plasma and skin fibroblasts was measured in at least four separate inherited disease states. Both the magnitude and the nature of the fatty acid changes reflected the clinical status of individual patients. In Zellweger's syndrome, and to a lesser extent in infantile Refsum's disease, there was an increase in 24:0, 26:0, 26:1, and a number of even longer chain fatty acids, while in the X-linked form of adrenoleukodystrophy these changes were less pronounced. Zellweger fibroblasts in culture took up lignoceric, phytanic and stearic acids and incorporated them into a variety of lipids in a manner comparable to control fibroblasts. However, these cells were unable to convert phytanic or lignoceric acid to CO2. Infantile Refsum's and X-linked adrenoleukodystrophy fibroblasts showed normal conversion of these acids to CO2. Normal fibroblast homogenates produced radioactive acetate from [1-14C] stearic and [1-14C] lignoceric acids indicating that both substrates were beta-oxidised under these conditions. Homogenates of fibroblasts from all patients patients with biochemical evidence of accumulation of very long chain fatty acids showed normal or near-normal stearic acid beta-oxidation, but were deficient in lignoceric acid beta-oxidation. Residual lignoceric acid beta-oxidation activity varied from approximately 15% in Zellweger syndrome up to 50% in X-linked adrenoleukodystrophy. It is postulated that the accumulation of very long chain fatty acids results from defects in peroxisomal beta-oxidation. In Zellweger's syndrome, and possibly in infantile Refsum's disease, it is probable that this defect is secondary to a primary abnormality affecting the structure and/or function of peroxisomes, while the primary defect in X-linked adrenoleukodystrophy may be confined to a pathway specific for the oxidation of very long chain fatty acids.

Acyl-CoA: glycine N-acyltransferase: in vitro studies on the glycine conjugation of straight- and branched-chained acyl-CoA esters in human liver

Apparent kinetic constants (Km and Vmax values) were determined for human liver acyl-CoA: glycine acyltransferase (glycine-N-acylase) towards isobutyryl-CoA, 2-methyl butyryl-CoA, isovaleryl-CoA, butyryl-CoA, hexanoyl-CoA, octanoyl-CoA, and decanoyl-CoA. These acyl-CoA esters were selected because of their relevance to the human diseases with cellular accumulation of these esters, i.e., especially to metabolic defects in the acyl-CoA dehydrogenation steps of the branched-chain amino acids, lysine, 5-hydroxy lysine, tryptophan, and fatty acid oxidation pathways. With the acyl-CoA ester as the fixed substrate, the Km value for glycine ranged from 0.5 to 2.9 mole/liter, and with glycine as fixed substrate, the Km values for the acyl-CoA esters varied from 0.3 to 5.6 mmole/liter. It is concluded that the substrate concentration is decisive for the glycine conjugate formation and that the occurrence in urine of acylglycines reflects an intramitochondrial accumulation of the corresponding acyl-CoA ester.

Comparative pharmacokinetics and subacute toxicity of di(2-ethylhexyl) phthalate (DEHP) in rats and marmosets: extrapolation of effects in rodents to man

Certain phthalate esters and hypolipidemic agents are known to induce morphological and biochemical changes in the liver of rodents, which have been associated with an increased incidence of hepatocellular tumors in these species. There is evidence that hypolipidemic agents do not induce these effects in either subhuman primates or man. The oral and intraperitoneal administration of di(2-ethylhexyl) phthalate (DEHP) to the marmoset monkey at doses up to 5 mmole DEHP/kg body weight/day for 14 days did not induce morphological or biochemical changes in the liver or testis comparable with those obtained in rats given the same amount of DEHP. In the marmoset, the excretion profile of [14C]-DEHP following oral, IP, and IV administration and the lower tissue levels of radioactivity demonstrated a considerably reduced absorption in this species compared to the rat. The urinary metabolite pattern in the marmoset was in many respects qualitatively similar to but quantitatively different from that in the rat; the marmoset excreted principally conjugated metabolites derived from omega- 1 oxidation. The pharmacokinetic differences between these two species indicate that the tissues of the marmoset are exposed to a level of DEHP metabolites equivalent to the complete absorption of a dose of Ca. 0.1 to 0.25 mmole DEHP/kg body weight/day without significant toxicological effects. These exposure levels are at least 100-fold greater than the worst estimates of incidental human exposure (ca. 0.0015 mmole/kg/day). They are comparable with the human therapeutic dose of many hypolipidemic drugs (ca. 0.15 mmole/kg/day), a dose at which it is claimed that there is an absence of morphological or biochemical changes to human or subhuman primate liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Lignoceroyl-CoASH ligase: enzyme defect in fatty acid beta-oxidation system in X-linked childhood adrenoleukodystrophy

We have previously reported that the peroxisomal beta-oxidation system for very long chain fatty acids is defective in X-linked childhood adrenoleukodystrophy [(1984) Proc. Natl. Acad. Sci. USA 81, 4203-4207]. In order to elucidate the specific enzyme defect, we examined the oxidation of [1-14C]lignoceric acid, [1-14C]lignoceroyl-CoA and (1-14C)-labelled alpha,beta-unsaturated lignoceroyl-CoA (substrates for the 1st, 2nd, and 3rd steps of the beta-oxidation cycle, respectively). These studies suggest that the pathognomonic accumulation of very long chain fatty acids in X-linked childhood ALD may be due to the defective activity of peroxisomal very long chain (lignoceroyl-CoA) acyl-CoA ligase.

Peroxisomal fatty acid oxidation in rat and human tissues. Effect of nutritional state, clofibrate treatment and postnatal development in the rat

Oxidation of palmitate 14C-labeled in different positions was assayed in the absence and presence of antimycin and rotenone in homogenates of various rat and human tissues to determine total and peroxisomal oxidation and acetyl group production. Total and antimycin-insensitive palmitate oxidation rates were higher in rat heart, liver and quadriceps muscle than in the corresponding human tissues. The proportion of antimycin-insensitive oxidation of [1-14C]palmitate was 17-35% in tissues of starved rats and in human muscles and fibroblasts, but peroxisomal production of acetyl groups amounted only to 5-11% of that by mitochondria. The mean number of peroxisomal beta-oxidation cycles was 1.5-2.5 per palmitate molecule. The nutritional state markedly influenced the total oxidation rate and the antimycin-insensitive proportion in rat liver. Clofibrate feeding increased total and antimycin-insensitive oxidation rates in liver, heart and kidney, but not in quadriceps muscle. Total oxidation capacity was maximal in rat liver at weaning, and in rat heart at an age of 70 days. Antimycin-insensitive oxidation rates increased in rat liver and heart at postnatal development up to weaning. A marked proportion of lignocerate oxidation was antimycin-sensitive in rat tissues.

Characterization of peroxisomes in Chinese hamster ovary cells in culture

In order to explore the potential value of Chinese hamster ovary (CHO) cells for the isolation of peroxisomal mutants defective in the peroxisomal fatty acid oxidation system, some characteristics of their peroxisomes were studied. Catalase was detected biochemically and histochemically in peroxisome-like particles in cells or in subcellular fractions prepared by differential centrifugation or isopyknic equilibrium in Percoll or Metrizamide with catalase in the high density fractions of the isopyknic equilibrium gradients. By oxidation system, exhibited an unusually high specific activity, 2.46 +/- 1.09 mU/mg protein, in CHO cell homogenates, a value comparable to that of rat liver. This enzyme copurifies with catalase in the high density fractions of the isopycnic equilibrium gradients. By analogy with other cell types and from the ultrastructural analysis, it is concluded that these enzymes are contained in peroxisomes. These findings support the value of CHO cells for studies of peroxisomal function and organization.

A milder variant of Zellweger syndrome

A 4.5-year-old male patient is described with chorioretinopathy, minor facial anomalies, delayed closure of the fontanel, mental retardation, moderate hypotonia, epilepsy and hepatic fibrosis. Postural control, intentional vocalising and manual dexterity were superior to the performance of patients with classical Zellweger syndrome (ZS). Morphologically distinct peroxisomes were absent in the liver. In blood elevated pipecolic acid levels and abnormal levels of bile acid intermediates were found. The plasmalogen content of erythrocytes was normal. In fibroblasts we found an accumulation of very long chain fatty acids, decreased activity of acyl CoA:dihydroxyacetone phosphate acyltransferase, and impaired de novo biosynthesis of plasmalogens. On the basis of these clinical, ultrastructural and biochemical characteristics we assume that this patient represents a milder variant of the classical cerebro-hepato-renal syndrome of Zellweger.

Identification of the proximate peroxisome proliferator(s) derived from di(2-ethylhexyl) phthalate

A primary rat hepatocyte culture system was utilized to determine the proximate peroxisome proliferator(s) derived from di(2-ethylhexyl) phthalate (DEHP). DEHP was administered to rats and the urinary metabolites were identified and isolated. The major metabolites were those resulting from initial omega- or omega - 1-carbon oxidation of the mono(2-ethylhexyl) phthalate (MEHP) moiety. These metabolites, together with MEHP and 2-ethylhexanol, were added to primary rat hepatocyte cultures and the effect on peroxisomal enzyme activity was determined. The omega-carbon oxidation products [mono(3-carboxy-2-ethylpropyl) phthalate (I) and mono(5-carboxy-2-ethylpentyl) phthalate (V)] and 2-ethylhexanol produced little or no effect on CN- -insensitive palmitoyl-CoA oxidation (a peroxisomal marker). MEHP and the omega - 1-carbon oxidation products [mono-(2-ethyl-5-oxohexyl) phthalate (VI) and mono(2-ethyl-5-hydroxyhexyl) phthalate (IX)] produced a large (7- to 11-fold) induction of peroxisomal enzyme activity. Similar structure-activity relationships were observed for the induction of cytochrome P-450-mediated lauric acid hydroxylase and increase in cellular coenzyme A content. This identification of the proximate proliferators will aid in the elucidation of the mechanism by which DEHP causes proliferation of peroxisomes in the rodent liver. Oral administration of MEHP (150 or 250 mg/kg) to male guinea pigs did not produce hepatic peroxisome proliferation. Addition of MEHP (0 to 0.5 mM) or one of the "active" proliferators in the rat (metabolite IX, 0 to 0.5 mM) to primary guinea pig hepatocyte cultures also failed to produce an induction of peroxisomal beta-oxidation. Possible reasons for this species difference are discussed.

The metabolism of di(2-ethylhexyl) phthalate (DEHP) and mono-(2-ethylhexyl) phthalate (MEHP) in rats: in vivo and in vitro dose and time dependency of metabolism

This study investigated the in vivo metabolism of di(2-ethylhexyl) phthalate (DEHP) and mono(2-ethylhexyl) phthalate (MEHP) in rats after multiple dosing, the metabolism of MEHP in primary rat hepatocyte cultures for periods of up to 3 days, and the biotransformation of some major metabolites of MEHP. Rats were orally administered [14C]DEHP or [14C]MEHP at doses of 50 and 500 mg/kg body wt for three consecutive days. Urine was collected at 24-hr intervals, and metabolite profiles were determined. After a single dose of either compound, urinary metabolite profiles were similar to those previously reported. However, after multiple administration of both DEHP and MEHP at 500 mg/kg, increases in omega-/beta-oxidation products [metabolites I and V, mono(3-carboxy-2-ethylpropyl) phthalate and mono(5-carboxy-2-ethylpentyl) phthalate, respectively] and decreases in omega - 1-oxidation products [metabolites VI and IX, mono(2-ethyl-5-oxohexyl) phthalate and mono(2-ethyl-5-hydroxyhexyl) phthalate, respectively] were seen. At the low dose of 50 mg/kg little or no alteration in urinary metabolite profiles was observed. At 500 mg/kg of MEHP a 4-fold stimulation of CN- -insensitive palmitoyl-CoA oxidation (a peroxisomal beta-oxidation marker) was seen after three consecutive daily doses. At the low dose of 50 mg/kg only a 1.8-fold increase was noted. Similar observations were made with rat hepatocyte cultures. MEHP at concentrations of 50 and 500 microM was extensively metabolized in the rat hepatocyte cultures. Similar metabolic profiles to those seen after in vivo administration of MEHP were observed. At the high (500 microM) concentration of MEHP, changes in the relative proportions of omega- and omega- 1-oxidized metabolites were seen. Over the 3-day experimental period, omega-/beta-oxidation products increased in a time-dependent manner at the expense of omega - 1-oxidation products. At a concentration of 500 microM MEHP, a 12-fold increase of CN- -insensitive palmitoyl CoA oxidation (a peroxisomal beta-oxidation marker) was observed. At the low concentration of MEHP (50 microM) only a 3-fold increase in CN- -insensitive palmitoyl-CoA oxidation was noted and little alteration in the metabolite profile of MEHP was observed with time. Biotransformation studies of the metabolites of MEHP confirmed the postulated metabolic pathways. Metabolites I and VI appeared to be endpoints of metabolism, while metabolite V was converted to metabolite I, and metabolite IX to metabolite VI. It was also possible to reduce the transformation of metabolite X [mono(2-ethyl-6-hydroxyhexyl) phthalate] to metabolite V.(ABSTRACT TRUNCATED AT 400 WORDS)

Purification of peroxisomes from livers of normal and clofibrate-treated mice

A method for the isolation of peroxisomes from livers of normal and clofibrate-treated mice is described. The method utilizes glutaraldehyde to stabilize peroxisomal membranes, and isopycnic centrifugation of a light mitochondrial fraction through a linear metrizamide gradient to achieve optimal resolution from other organelles. On the basis of the biochemical and morphological data, the peroxisomal preparations are indicated as of high purity: contamination by mitochondria, lysosomes, and plasma membranes is negligible, and the level of contaminating microsomes is around 5% for normal peroxisomes and 8% for peroxisomes from clofibrate-treated mice. Peroxisomal membranes prepared by carbonate extraction contain two major polypeptides of approximately 70,000 Da, and show 2 and 8% contamination by microsomal membrane protein for the preparations from normal and clofibrate-treated mice, respectively.

Evidence for peroxisomal hydroxylase activity in rat liver

This study presents evidence for the first time that rat liver peroxisomes contain a hydroxylase capable of converting 3 alpha, 7 alpha, 12 alpha,- trihydroxy-5 beta-cholestane to a cholestanetetrol. Furthermore, this hydroxylase differs from both the mitochondrial and microsomal enzymes in its response to various co-factors. Highly purified peroxisomal, mitochondrial, and microsomal fractions from cholestryamine-treated rats were incubated with [22(23)-3H]3 alpha,7 alpha,12 alpha,-trihydroxy-5 beta-cholestane under a variety of conditions. The products were acidified, extracted, and subjected to thin-layer chromatography to determine the amount of cholestanetetrol produced. The identification of the 25- and 26-hydroxylated products from the incubations with the microsomes was confirmed by gas chromatography-mass spectrometry. Peroxisomal fractions incubated with a NADPH-generating system, Mg2+, and ATP showed a rate of 40 pmol/min/mg conversion of 3 alpha,7 alpha,12 alpha,-trihydroxy-5 beta-cholestane to a cholestanetetrol. Co-factor studies indicated that both the peroxisomal and mitochondrial hydroxylase activities were dependent on NADPH, Mg2+, and ATP (with different concentration requirements) whereas the microsomal hydroxylase(s) required only NADPH. An abstract of this work has been published (1).

Biochemical, histological, and ultrastructural changes in rat and mouse liver following the administration of trichloroethylene: possible relevance to species differences in hepatocarcinogenicity

Trichloroethylene (TRI), administered by gavage for 10 consecutive days, at doses of 500 to 1500 mg/kg body wt increased liver weight (175% of control), decreased hepatic DNA concentration (66% of control), and increased the synthesis of DNA (500% of control; as measured by [3H]dT incorporation) in B6C3F1 mice and Alderley Park mice. Similar treatment of Osborne-Mendel rats or Alderley Park rats resulted in smaller increases in liver weight (130% of control) and decreases in DNA concentration (83% of control). No effect of TRI on DNA synthesis was seen in rats. The increased DNA synthesis in the mouse was not apparently due to regenerative hyperplasia since no signs of necrosis were seen. Furthermore the increased [3H]dT incorporation probably represented semiconservative replication of DNA and not repair, since a parallel increase of mitotic figures was observed. Hence, the liver growth noted after TRI administration appears to be due to liver cell enlargement (hypertrophy) in the rat, but both hypertrophy and hyperplasia (cell proliferation) in the mouse. An important observation has been that TRI induced the peroxisomal enzyme activities, catalase, and cyanide-insensitive palmitoyl-CoA oxidation (147 and 786% of control, respectively), in mice but not in rats. Furthermore, increases in peroxisome volume density (up to 1110% of control) were observed in mice receiving TRI. These observations lead us to suggest that the species difference in hepatocarcinogenicity of TRI, seen between the rat and mouse, is possibly due to a species difference in peroxisome proliferation and cell proliferation, the peroxisome proliferation leading to increased reactive oxygen species and DNA damage, and the cell proliferation then acting to promote this lesion.

Preparative isolation of peroxisomes from liver and kidney using metrizamide density gradient centrifugation in a vertical rotor

A method for the preparative isolation of peroxisomes from the livers of rat, guinea pig, and mouse, and also from rat kidney is described. The light mitochondrial fraction, i.e., particles sedimenting between 33,000 and 250,000g-min, or the postnuclear supernatant of liver or kidney, is subjected to a 20-50% Metrizamide density gradient ultracentrifugation in a vertical rotor. After centrifugation, the peroxisomes (marker enzyme catalase and dihydroxyacetone phosphate acyltransferase) sedimented as a band near the bottom of the tube (rho = 1.22 g/ml). From the distribution of different marker enzymes and also from the morphometric examinations, it was demonstrated that the isolated peroxisomes are not contaminated with lysosomes, mitochondria, or microsomes.

Isolation and characterization of peroxisomes from the liver of normal untreated rats

The classic method of Leighton et al. [(1968) J. Cell Biol. 37, 482-513] for the isolation of peroxisomes from rat liver involves the use of Triton WR-1339 which alters the biochemical properties of this organelle and requires the specialized type Beaufay-rotor which is not easily available. We have employed Metrizamide as the gradient medium and a commercial type vertical rotor to obtain highly purified and structurally well-preserved peroxisomes from normal untreated animals. The livers were homogenized in buffered 0.25 M sucrose and a slightly modified 'light mitochondrial fraction' was prepared by differential centrifugation. This was loaded on top of a linear Metrizamide gradient (1.12-1.26 g/cm3) and subjected to an integrated force of 1.252 X 10(6) X (g X min) using a Beckman VTi 50 vertical rotor. Peroxisomes banded at the density of 1.245 g/cm3. In the isolated fraction 95% of the protein was contributed by peroxisomes, which exhibited a strong activity for cyanide-insensitive lipid beta-oxidation. The purity of fractions was also confirmed by morphometry, which revealed that 98% of isolated particles consisted of peroxisomes. The latency for catalase was about 90% indicating a high degree of peroxisomal integrity. This corresponded to the low level of extraction of catalase in 3,3'-diaminobenzidine-stained filter preparations. The entire procedure took about five hours. Highly purified and structurally well preserved peroxisomes should be useful in further elucidation of the function of this organelle and especially in studies of peroxisomal enzymes with multiple intracellular localizations.

A sensitive spectrophotometric assay for peroxisomal acyl-CoA oxidase

A simple spectrophotometric assay was developed for peroxisomal fatty acyl-CoA oxidase activity. The assay, based on the H2O2-dependent oxidation of leuco-dichlorofluorescein catalysed by exogenous peroxidase, is more sensitive than methods previously described. By using mouse liver samples, cofactor requirements were assessed and a linear relationship was demonstrated between dye oxidation and enzyme concentration. By using this assay on subcellular fractions, palmitoyl-CoA oxidase activity was localized for the first time in microperoxisomes of rat intestine. The assay was also adapted to measure D-amino acid oxidase activity, demonstrating the versatility of this method for measuring activity of other H2O2-producing oxidases.

Improved isolation and purification of rat liver peroxisomes by combined rate zonal and equilibrium density centrifugation

Two different peroxisome preparations were isolated from male rat liver by using total homogenate (TH) as the starting material for one and the light mitochondrial (L) fraction for the other. The technique worked out is based on rate zonal (RZ) centrifugation in a sucrose gradient and subsequent isopycnic centrifugation in a Nycodenz gradient. The peroxisome fraction isolated from the L fraction consisted of 97-98% peroxisomal protein with catalase activity 49-fold enriched over TH. The peroxisome preparation isolated directly from TH represented about 55% of the total liver peroxisome population and had catalase activity 43-fold enriched compared with TH. The contribution of peroxisome protein to the liver protein was calculated to be in the range 1.82-2.02%. Peroxisomes isolated from TH were considerably more heterogeneous in size than peroxisomes isolated from the L fraction. Comparison of the polypeptide patterns of both preparations by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed some quantitative differences. Several major polypeptides were found to be exclusively located in the peroxisome membrane. These polypeptides migrated in the gel with apparent molecular masses of 69, 42.5, 36, 26, 21, and 15 kDa.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase is present in peroxisomes in normal rat liver cells

The location inside rat liver parenchymal cells of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG-CoA reductase; EC 1.1.1.34), the key regulatory enzyme in cholesterol biosynthesis, has been examined by immunoelectron microscopy and by subcellular fractionation. Although HMG-CoA reductase is generally thought to be exclusively a microsomal enzyme, we find that a substantial portion of cellular HMG-CoA reductase is localized in peroxisomes. Immunoelectron microscopic labeling of ultrathin frozen sections of normal rat liver, using two monoclonal antibodies to purified HMG-CoA reductase, showed that the enzyme is present in the peroxisomes at a higher concentration than at any other site inside the hepatocytes. Subcellular fractionation studies using Percoll and metrizamide gradients demonstrated a close correspondence of peaks of HMG-CoA reductase activity and of catalase activity, again revealing the presence of the reductase enzyme in peroxisomes. HMG-CoA reductase is therefore localized in peroxisomes in addition to being in the microsomal fraction.

Ultrastructural localization of a peroxisomal protein in rat liver using the specific antibody against the non-specific lipid transfer protein (sterol carrier protein 2)

An antibody against the non-specific lipid transfer protein from rat liver was purified by immunoabsorbent affinity chromatography. This antibody in conjunction with protein A-colloidal gold was used to localize the transfer protein in rat liver by electron microscopy. Labeling by this immunocytochemical technique was found to be mainly restricted to the peroxisomes; low labeling was observed in the cytoplasm. Subsequent analysis of isolated peroxisomes by immunoblotting indicated that the non-specific lipid transfer protein (mol. wt. 14800) was absent from this organelle and that a protein of molecular weight 58000 was responsible for the immunological response. Immunoblotting of the membrane-free cytosol showed the presence of both proteins. It remains to be established to what extent the non-specific lipid transfer protein in the cytosol and the high-molecular weight protein in the peroxisomes are related.

Peroxisomal defects in neonatal-onset and X-linked adrenoleukodystrophies

Accumulation of very long chain fatty acids in X-linked and neonatal forms of adrenoleukodystrophy (ALD) appears to be a consequence of deficient peroxisomal oxidation of very long chain fatty acids. Peroxisomes were readily identified in liver biopsies taken from a patient having the X-linked disorder. However, in liver biopsies from a patient having neonatal-onset ALD, hepatocellular peroxisomes were greatly reduced in size and number, and sedimentable catalase was markedly diminished. The presence of increased concentrations of serum pipecolic acid and the bile acid intermediate, trihydroxycoprostanic acid, in the neonatal ALD patient are associated with a generalized diminution of peroxisomal activities that was not observed in the patient with X-linked ALD.

Comparison of the short-term effects of di(2-ethylhexyl) phthalate, di(n-hexyl) phthalate, and di(n-octyl) phthalate in rats

This study compares changes in the livers of rats treated with di(2-ethylhexyl) phthalate (DEHP) and its straight-chain analogs di(n-hexyl) phthalate (DnHP) and di(n-octyl phthalate (DnOP). Groups of rats were fed diets containing 20,000 ppm of one of these compounds. Subgroups were killed after 3, 10, and 21 days, and the livers were examined by histological, cytological, and biochemical methods. The results show considerable differences between the effects of the branched-chain phthalate ester DEHP and its straight-chain analogs. The major effects on the liver following administration of diets containing DEHP were midzonal and periportal accumulation of small droplets of lipid, hepatomegaly accompanied by an initial burst of mitosis, proliferation of hepatic peroxisomes and of smooth endoplasmic reticulum accompanied by induction of peroxisomal fatty acid oxidation, damage to the peroxisomal membranes as evidenced by increased leakage of catalase to the cytosol, and centrilobular loss of glycogen and falls in glucose-6-phosphatase activity and in low-molecular-weight reducing agents. In contrast, diets containing DnHP or DnOP induced accumulation of large droplets of fat around central veins leading, by 10 days, to mild centrilobular necrosis and a very slight induction of one peroxisomal enzyme and an increase in liver weight, but no significant changes in any other parameters which were affected by DEHP.

Chain-length specificities of mitochondrial and peroxisomal beta-oxidation of fatty acids in livers of rainbow trout (Salmo gairdneri)

Peroxisomes and mitochondria were prepared from livers of rainbow trout fed diets containing either 15% crude fish oil (CFO) or 11.5% partially hydrogenated fish oil (PHFO) plus 3.5% CFO. Peroxisomal preparations from the two dietary groups showed similar rates and substrate specificity patterns for acyl-CoA oxidation. The peroxisomal oxidation rate was highest with 12:0-CoA and decreased with increasing chain length, being negligible with 22-carbon acyl-CoA's. The trans isomer of 18:1(n-9) was oxidized at a higher rate than the cis isomer only by peroxisomes from the PHFO + CFO group. Mitochondria prepared from both groups of fish exhibited a broad chain-length specificity for the oxidation of acylcarnitines. Both polyunsaturated and trans monoenoic fatty acids were readily oxidized.

Species differences in carcinogenicity and peroxisome proliferation due to trichloroethylene: a biochemical human hazard assessment

Trichloroethylene (TRI) administered to mice by gavage for 10 consecutive days at doses of 50-2000 mg/kg body weight elicited dose-dependent increases (up to 700% of control values) of hepatic cyanide insensitive palmitoyl CoA oxidation (a marker of peroxisomal beta-oxidation). No effect was seen on catalase; the other peroxisomal marker examined. Similar experiments with rats demonstrated no effect of TRI on either cyanide insensitive palmitoyl CoA oxidation or catalase. A major metabolite of TRI, trichloroacetic acid (TCA) when administered by gavage for 10 consecutive days at doses of 10-200 mg/kg body weight, stimulated hepatic cyanide insensitive palmitoyl CoA oxidation in both mice (up to 500% of control) and rats (up to 650% of control). Again, no effect upon catalase activity was apparent. The kinetics of biotransformation of TRI to TCA in isolated hepatocytes was markedly species dependent. The 'intrinsic clearance' values (Vmax/Km) for TRI in mouse, rat and human hepatocytes were 3.8 X 10(-6), 1.2 X 10(-7) and 3.25 X 10(-8) L/min/10(6) cells respectively. TCA induced peroxisomal beta-oxidation in mouse and rat hepatocytes, but had no effect upon this enzyme activity in cultured human hepatocytes. It is postulated that the species difference in hepatocarcinogenicity of TRI (mouse positive; rat negative) is due to species differences in peroxisome proliferation which in turn is a result of differences in the rate of formation of TCA from TRI. On this basis it is proposed that TRI presents no significant human hepatocarcinogenic hazard since, human hepatocytes produced TCA at a rate even lower than that of the rat, and TCA was not a peroxisome proliferator in human hepatocytes.

Carnitine acyltransferase and acyl-coenzyme A hydrolase activities in human liver. Quantitative analysis of their subcellular localization

The subcellular localizations of carnitine acyltransferase and acyl-CoA hydrolase activities with different chain-length substrates were quantitatively evaluated in human liver by fractionation of total homogenates in metrizamide density gradients and by differential centrifugation. Peroxisomes were found to contain 8-37% of the liver acyltransferase activity, the relative amount depending on the chain length of the substrate. The remaining activity was ascribed to mitochondria, except for carnitine octanoyltransferase, for which 25% of the activity was present in microsomal fractions. In contrast with rat liver, where the activity in peroxisomes is very low or absent, human liver peroxisomes contain about 20% of the carnitine palmitoyltransferase. Short-chain acyl-CoA hydrolase activity was found to be localized mainly in the mitochondrial and soluble compartments, whereas the long-chain activity was present in both microsomal fractions and the soluble compartment. Particle-bound acyl-CoA hydrolase activity for medium-chain substrates exhibited an intermediate distribution, in mitochondria and microsomal fractions, with 30-40% of the activity in the soluble fraction. No acyl-CoA hydrolase activity appears to be present in human liver peroxisomes.

Acyl-CoA synthetase and the peroxisomal enzymes of beta-oxidation in human liver. Quantitative analysis of their subcellular localization

The presence of acyl-CoA synthetase (EC 6.2.1.3) in peroxisomes and the subcellular distribution of beta-oxidation enzymes in human liver were investigated by using a single-step fractionation method of whole liver homogenates in metrizamide continuous density gradients and a novel procedure of computer analysis of results. Peroxisomes were found to contain 16% of the liver palmitoyl-CoA synthetase activity, and 21% and 60% of the enzyme activity was localized in mitochondria and microsomal fractions respectively. Fatty acyl-CoA oxidase was localized exclusively in peroxisomes, confirming previous results. Human liver peroxisomes were found to contribute 13%, 17% and 11% of the liver activities of crotonase, beta-hydroxyacyl-CoA dehydrogenase and thiolase respectively. The absolute activities found in peroxisomes for the enzymes investigated suggest that in human liver fatty acyl-CoA oxidase is the rate-limiting enzyme of the peroxisomal beta-oxidation pathway, when palmitic acid is the substrate.

A direct comparison between peroxisomal and mitochondrial preferences for fatty-acyl beta-oxidation predicts channelling of medium-chain and very-long-chain unsaturated fatty acids to peroxisomes

A well-characterized crude peroxisomal fraction from brown adipose tissue was used to compare peroxisomal beta-oxidation with beta-oxidation in isolated mitochondria. The apparent Km and chain-length specificity for peroxisomal (acyl-CoA) and mitochondrial (acyl-carnitine) beta-oxidation were determined with saturated C4-C22 fatty acyls and some unsaturated fatty acyls. Peroxisomes showed the lowest Km for medium-chain (9:0-10:0) and mono-unsaturated long-chain (16:1-22:1) fatty acids, and highest oxidation rates with lauroyl-CoA (12:0). Mitochondria showed the lowest Km for long-chain fatty acids (16:0-18:0) and highest oxidation rates with 12:0-16:0 and with 18:2. These in vitro results offer an explanation of previous results obtained in situ by Foerster et al. (Foerster, E.-C., Fährenkemper, T., Rabo, U., Graf, P. and Sies, H. (1981) Biochem. J. 196, 705-712) and indicate a role for peroxisomes in degradation of medium-chain and mono-unsaturated long-chain fatty acids. It is concluded that no mechanism, other than relative preferences, needs to be suggested for channelling of fatty acids between the two subcellular organelles.

Factors influencing peroxisome proliferation in cultured rat hepatocytes

A primary rat hepatocyte culture system has been developed for the study of peroxisome proliferation. Maximal induction of peroxisomal activity requires supplementation of the culture medium with hydrocortisone. The addition of clofibric acid (0.01-1 mM), mono-(2-ethylhexyl)phthalate (0.01-0.5 mM) and trichloroacetic acid (0.1-5 mM) to cultured rat hepatocytes resulted in a time- and dose-related increase in CN- insensitive palmitoyl CoA oxidation (maximal increases: 27-, 15.5-, and 5-fold respectively) and mitochondrial alpha-glycerophosphate dehydrogenase activity (maximal increases: 7.3-, 5.8-, and 1.6-fold respectively). Electron microscopic examination revealed smooth endoplasmic reticulum proliferation and morphometric analysis indicated an increase in fractional peroxisomal volume of X 8 and X 4 for clofibric acid (1 mM) and trichloroacetic acid (2.5 mM), respectively. SDS-PAGE of cell homogenates revealed an intensified protein band of mol. wt. 76-78,000. The induction of peroxisomal beta-oxidation by clofibric acid was elevated from 9- to 12-fold by supplementation of the medium with L-carnitine (2 mM).

Reversible, highly localized alterations in fatty acid metabolism in the chronically ischemic canine myocardium

Acute myocardial ischemia is accompanied by a marked decrease in the oxidation of fatty acids. Whether similar changes occur during chronic ischemia was studied in 13 beagles. In 10 dogs, an ameroid constrictor was implanted about the left circumflex artery; 3 others served as sham-operated controls. Mitochondrial and peroxisomal fatty acid oxidation of (1-14C)oleate were measured and compared in affected (posterobasal left ventricular endocardial [posterior LV endo]) and unaffected (anteroapical LV epicardial [anterior LV epi]) tissues of control and experimental dogs. Five experimental and 3 control dogs were killed after 3 weeks. The posterior LV endo sections of experimental dogs at 3 weeks showed increased fatty acid oxidation due to peroxisomal (KCN-insensitive) beta oxidation (p less than 0.01). The anterior LV epi sections showed no difference in fatty acid oxidation between sham-operated and experimental dogs. Five dogs were studied after 3 months; fatty acid oxidation of the posterior LV endo section was normal. Thus, under a slowly evolving state of myocardial ischemia, highly localized and reversible adaptive changes in fatty acid oxidation occur that enable the affected tissue to cope with a fatty acid load. When collateralization is accomplished, fatty acid metabolism reverts to normal.

The absence of testicular atrophy and in vivo and in vitro effects on hepatocyte morphology and peroxisomal enzyme activities in male rats following the administration of several alkanols

Previous studies have shown that ethylhexanol (2-EH) and its oxidation products, but not n-hexanol, produce hepatomegaly, peroxisomal proliferation and hypotriglyceridaemia. In the present studies we have confirmed that at 1 mmol/kg doses, neither the linear nor branched chain alcohols induce testicular atrophy, hepatomegaly, peroxisome proliferation or hypolipidaemia. In vivo, neither the free alcohols nor their metabolic products seem to be responsible for the activity of the parent plasticiser. The released monoesters are probably the more potent metabolic products responsible for the hepatomegaly, peroxisomal proliferation and hypolipidaemia. This contention is supported by the in vitro hepatocyte data which demonstrate the induction of peroxisomal oxidative enzymes by MEHP whereas the alcohols were without effects.

Fatty acyl-CoA dehydrogenase deficiency: enzyme measurement and studies on alternative metabolism

Fatty acyl-CoA dehydrogenase deficiencies are defined as disorders of the metabolism of straight chain acyl-CoA esters at the level of short chain acyl-CoA, general (medium chain) acyl-CoA and long chain acyl-CoA dehydrogenases. Patients with proven or indicated defects in either general (medium chain) or long chain acyl-CoA dehydrogenase have been reported. In recent years assays for the enzymatic diagnosis in cells, especially cultured skin fibroblasts, from such patients have been developed. The different methods are reviewed. The urinary excretion profile of organic acids from patients with fatty acyl-CoA dehydrogenase deficiencies are characterized by the presence of different compounds originating from the primary accumulated acyl-CoA ester(s). The most important biochemical processes involved in the formation of these compounds are glycine conjugation and omega/omega-1 oxidation. The biochemistry of these pathways is discussed and the knowledge gained from in vitro and in vivo studies is used to explain the excretion pattern in some of the patients with general (medium chain) acyl-CoA dehydrogenase deficiency.

Incomplete palmitate oxidation in cell-free systems of rat and human muscles

The palmitate oxidation capacity was determined in whole homogenates, postnuclear fractions and mitochondrial fractions of various rat and human muscles and in rat liver, kidney, brain and lung. The oxidation rate (production of 14CO2 and 14C-labeled acid-soluble intermediates) was [1-14C]palmitate greater than [U-14C]palmitate greater than [16-14C]palmitate in all cell-free systems. Oxidation rates were highest in rat heart and liver, intermediate in kidney, diaphragm and m. quadriceps, and low in brain and lung. The capacity of human heart was much lower than that of rat heart and about twice that of human skeletal muscles. Omission of L-carnitine and addition of malonyl-CoA, KCN or antimycin A decreased the oxidation rates in whole homogenates and mitochondrial fractions. Antimycin or KCN increased and malonyl-CoA decreased the ratio of the oxidation rates with [1-14C]- and [16-14C]palmitate. The carnitine concentration had no significant effect on the ratio. 14C-labeled dodecanoic and tetradecanoic acids were identified in homogenates and mitochondrial fractions of m. quadriceps and liver of rat as acid-insoluble intermediates of [16-14C]palmitate oxidation in the presence and absence of antimycin A. Their amounts recovered can account for the differences in oxidation rates found with [1-14C]- and [16-14C]palmitate. The incomplete palmitate oxidation in cell-free systems appears to be mainly caused by an inadequate mitochondrial degradation of peroxisomal oxidation products.

General (medium-chain) acyl-CoA dehydrogenase deficiency (non-ketotic dicarboxylic aciduria): quantitative urinary excretion pattern of 23 biologically significant organic acids in three cases

Urinary analysis of the pattern of 23 organic acid metabolites derived from fatty acids in three patients with general (medium-chain) acyl-CoA dehydrogenase deficiency was performed. Although there exist quantitative differences in the excreted amounts of the different metabolites in the three patients the qualitative picture was the same. The excretion of adipic, suberic and sebacic acids was substantial, whereas that of dodecanedioic acid was within or just above control limit. The monounsaturated C6-C10-dicarboxylic acid excretion was only marginally or not increased. 5-OH-hexanoic acid and hexanoylglycine were excreted in excessive amounts, whereas 7-OH-octanoic acid, 9-OH-decanoic acid, octanoylglycine and decanoylglycine were excreted in limited amounts. The excreted amounts of 6-OH-hexanoic, 8-OH-octanoic and 10-OH-decanoic acids were not or only marginally elevated compared to controls. In one of the patients the excretion of ethylmalonic and methylsuccinic acids was enhanced, whereas the excretion of these two acids in the two other patients was comparable to that in controls. The urinary excretion of hexanoic, octanoic, decanoic and dodecanoic acids was just a little above the control limit, whereas the esterified hexanoic and octanoic acids were excreted in appreciable amounts. It is argued that the microsomal omega- and omega-1-oxidation systems are involved in the dicarboxylic and omega-1-OH-monocarboxylic acids formation at C10 and C12 level and that the C8-C6-dicarboxylic and omega-1-OH-monocarboxylic acids are formed from higher chained acids by beta-oxidation in both mitochondria and peroxisomes.

Increase of muscle peroxisomal enzymes and myotonia induced by nafenopin, a hypolipidemic drug

The chronic administration of nafenopin, a hypolipidemic drug, induced an increase in catalase and acyl-CoA oxidase activities in various skeletal muscles, including the gracilis, diaphragm, soleus, and extensor digitorum longus. The magnitude of the increase was around 100% for both enzymes in each of the muscles studied in spite of the different basal level. These changes seem to be specific of the peroxisomal enzymes because acetylcholinesterase, which is not peroxisomal, did not follow the same pattern in all the muscles. Concomitant with the increase in muscle peroxisomal enzymes, the skeletal muscles presented an altered electromyogram with prolonged insertional activity, repetitive firing of action potentials, and myotonic runs characteristic of myotonia. Our results suggest a role for peroxisomes in the myotonic disorder.

Carcinogenesis by hepatic peroxisome proliferators: evaluation of the risk of hypolipidemic drugs and industrial plasticizers to humans

In this critical review, I would like to provide a brief outline of the morphology, biochemical composition, distribution, and functions of peroxisomes. The induction of peroxisome proliferation and peroxisome-associated enzymes in the rodent liver by two classes of chemicals (hypolipidemic drugs and the industrial plasticizers) will be considered. The role of peroxisomes in lipid metabolism will be discussed. Carcinogenicity studies in rats and mice with these peroxisome proliferators will be evaluated critically. Careful consideration will be given to the hypothesis that "potent hepatic peroxisome proliferators as a class are carcinogenic." The possible mechanism(s) by which peroxisome proliferators induce liver tumors will be outlined. Particular attention will be paid to the possible role of peroxisome proliferation-mediated radical toxicity and generation of endogenous initiators of carcinogenesis.