Inhibition of rat liver microsomal fatty acid chain elongation by gemfibrozil in vitro

Gemfibrozil inhibits Legionella pneumophila and Mycobacterium tuberculosis enoyl coenzyme A reductases and blocks intracellular growth of these bacteria in macrophages

We report here that gemfibrozil (GFZ) inhibits axenic and intracellular growth of Legionella pneumophila and of 27 strains of wild-type and multidrug-resistant Mycobacterium tuberculosis in bacteriological medium and in human and mouse macrophages, respectively. At a concentration of 0.4 mM, GFZ completely inhibited L. pneumophila fatty acid synthesis, while at 0.12 mM it promoted cytoplasmic accumulation of polyhydroxybutyrate. To assess the mechanism(s) of these effects, we cloned an L. pneumophila FabI enoyl reductase homolog that complemented for growth an Escherichia coli strain carrying a temperature-sensitive enoyl reductase and rendered the complemented E. coli strain sensitive to GFZ at the nonpermissive temperature. GFZ noncompetitively inhibited this L. pneumophila FabI homolog, as well as M. tuberculosis InhA and E. coli FabI.

Malonyl-CoA decarboxylase is present in the cytosolic, mitochondrial and peroxisomal compartments of rat hepatocytes

A role for cytosolic malonyl-CoA decarboxylase (MCD) as a regulator of fatty acid oxidation has been postulated. However, there is no direct evidence that MCD is present in the cytosol. To address this issue, we performed cell fractionation and electron microscopic colloidal gold studies of rat liver to determine the location and activity of MCD. By both methods, substantial amounts of MCD protein and activity were found in the cytosol, mitochondria and peroxisomes, the latter with the highest specific activity. MCD species with different electrophoretic mobility were observed in the three fractions. The data demonstrate that active MCD is present in the cytosol, mitochondria and peroxisomes of rat liver, consistent with the view that MCD participates in the regulation of cytosolic malonyl-CoA levels and of hepatic fatty acid oxidation.

Effect of hypolipidemic drugs on key enzyme activities related to lipid metabolism in normolipidemic rabbits

The effect of atorvastatin (3 mg kg(-1) day(-1)), simvastatin (3 mg kg(-1) day(-1)) and bezafibrate (100 mg kg(-1) day(-1)) administered for 4 weeks to male New Zealand white rabbits on enzyme activities related to lipid metabolism has been studied. Only the statins reduced plasma cholesterol values, while none of the drugs modified plasma triglyceride or high density lipoprotein (HDL)-cholesterol concentrations, nor the activity of enzymes such as hepatic diacylglycerol acyltransferase, lipoprotein lipase or hepatic lipase, directly involved in triglyceride metabolism. Both statins elicited similar increases in the hepatic microsomal 3-hydroxy-3-methyl-glutaryl Coenzyme A (CoA) reductase activity (147 and 109% induction for simvastatin and atorvastatin, respectively), and none of the drugs assayed modified hepatic acyl-coenzyme A:cholesterol acyltransferase activity significantly. Only bezafibrate induced a significant 57% reduction in the activity of hepatic microsomal cholesterol 7alpha-hydroxylase. Regarding the rate limiting enzyme of phosphatidylcholine biosynthesis, CTP:phosphocholine cytidylyl transferase, atorvastatin and bezafibrate behaved similarly, decreasing the enzyme activity in the liver by 45% and 54%, respectively; simvastatin induced no modification of this activity. The reduction of CTP:phosphocholine cytidylyl transferase activity is not caused by a direct inhibition of the enzyme by bezafibrate and atorvastatin. Further, the inhibitory effect of atorvastatin appears to be unrelated to the inhibition of 3-hydroxy-3-methyl-glutaryl CoA reductase elicited in vivo.

Different effects of fibrates on the microsomal fatty acid chain elongation and the acyl composition of phospholipids in guinea-pigs

1. The effects in vitro and in vivo of three fibric acid derivatives, clofibrate (CFB), bezafibrate (BFB) and gemfibrozil (GFB) on some enzyme activities related to fatty acid biosynthesis, namely palmitoyl-CoA synthetase and hydrolases (microsomal and cytosolic), NADH and NADPH cytochrome c reductases and acyl-CoA elongases were investigated in guinea-pigs. 2. The three fibrates inhibited acyl-CoA elongation in vitro, irrespective of the substrate of elongation used (saturated, monounsaturated, polyunsaturated) and with an order of potency GFB > BFB > CFB. In the case of GFB, inhibition occurred at concentrations that can be reached in vivo. 3. Microsomal palmitoyl-CoA hydrolase and synthetase were also inhibited in vitro (GFB > or = BFB > CFB), whereas NADH cytochrome c reductase activity was increased by GFB. Nevertheless, the magnitude of changes were lower than those observed in elongation activities. 4. Treatment with fibrates did not produce peroxisomal proliferation in guinea-pigs, as measured by peroxisomal beta-oxidation activity and liver weight/body weight ratio. Nevertheless, fibrates provoked a reduction in plasma cholesterol and triglycerides, at least in GFB- and BFB-treated animals. 5. Fatty acid elongation was significantly modified by GFB treatment in vivo. The remaining enzyme activities studied were only slightly changed by fibrate treatment. 6. Treatment with BFB and to a lesser extent with CFB, increased the relative proportion of MUFA (palmitoleic and oleic acids) in microsomal phospholipids, whereas PUFA (mainly linoleic acid) decreased. GFB behaved differently, increasing palmitic and linoleic acids and decreasing stearic and oleic acids. The latter changes are attributable to an inhibition of elongation activity by GFB. 7. The changes observed after fibrate treatment in both rats and guinea-pigs, as they are not directly related to peroxisome proliferation, could be more reliably extrapolated to man than those observed only in rats.

Differential effects of fibrates on the acyl composition of microsomal phospholipids in rats

1. The time-course and comparative effects of treatment with clofibrate (CFB), bezafibrate (BFB), and gemfibrozil (GFB) on the acyl composition of the main microsomal phospholipids, i.e. phosphatidylcholine and phosphatidylethanolamine, have been studied in male Sprague-Dawley rats. 2. The administration of the three fibrates caused a strong peroxisomal induction and a hypolipidaemic effect. Concerning the changes in acyl composition, CFB and BFB behaved in a similar way, with differences which could be attributed to their different potency as peroxisome inducers, whereas GFB showed a somewhat distinct profile. 3. The three drugs increased the relative content of palmitic, palmitoleic and oleic acids, whereas the levels of stearic acid and also those of long chain, highly unsaturated fatty acids docosatetraenoic, docosapentaenoic and docosahexaenoic acids were reduced. In general, these effects appeared from the first day of treatment and were highly correlated with peroxisomal proliferation. In addition, they were more evident in the phosphatidylcholine than in the phosphatidylethanolamine fraction. 4. Fibrates increased total monounsaturated fatty acids, whereas a decrease in total polyunsaturated fatty acids in the phosphatidylcholine fraction was observed in CFB- and BFB-, but not in GFB-treated rats. Clear differences appeared between CFB and BFB on the one hand, and GFB on the other when the influence of fibrate treatment on the molar percentages of linoleic, eicosatrienoic, arachidonic and mead acids was analyzed. 5. GFB increased linoleic acid content in phosphatidylethanolamine, whereas CFB and BFB decreased its level in both phospholipid fractions. In contrast, CFB and BFB enhanced eicosatrienoic and mead acids in both fractions and arachidonic acid in phosphatidylethanolamine, whereas GFB had practically no effect.

Selective modification of rat hepatic microsomal fatty acid chain elongation and desaturation by fibrates: relationship with peroxisome proliferation

1. The time-course of the effect of clofibrate (CFB), bezafibrate (BFB) and gemfibrozil (GFB) on lipid plasma levels and palmitoyl-, palmitoleoyl- and gamma-linolenoyl-CoA elongase, delta-9, delta-6 and delta-5 desaturase activities, and microsomal electron transport chains, as well as the correlation with the peroxisomal proliferation phenomenon have been studied in male Sprague-Dawley rats. 2. As reported in our previous work, the three drugs behave as peroxisomal proliferators (the order of potency was BFB > CFB > or = GFB) and induced a clear reduction in both plasma cholesterol and triglyceride levels. 3. Palmitoyl-CoA elongation activity was increased by the three drugs (BFB = GFB > CFB), whereas palmitoleoyl-CoA elongation activity was only enhanced by GFB. Elongation activity was not modified by fibrates when gamma-linolenoyl-CoA was used as substrate. These results are in accordance with the existence of three different elongation systems for saturated, mono- and polyunsaturated fatty acids. 4. delta-9, delta-6 and delta-5 desaturase activities were increased by the three fibrates, with an order of potency BFB > CFB = GFB for delta-9 and delta-5, and GFB > BFB = CFB for delta-6. 5. Of the enzyme activities integrated in the microsomal electron transport chains, NADH cytochrome b5 reductase was not affected by fibrate treatment, NADPH cytochrome c reductase activity was enhanced (BFB = GFB > CFB), whereas NADH cytochrome c reductase activity was reduced by CFB and BFB. 6. The increase in Delta-9 and Delta-5 desaturase activities was highly dependent on the peroxisomal proliferation phenomena, whereas the increase in Delta-6 desaturase activity and the decrease in NADH cytochromec reductase was mainly independent. The modifications of palmitoyl-CoA elongase and NADPH cytochrome c reductase activities, as well as plasma lipid levels, were partially correlated with peroxisomal beta-oxidation, but the r2 values obtained point to the existence of additional independent mechanisms.7. As man is assumed to be a species refractory to peroxisomal proliferation, only those fibrate effectsnot absolutely related to this phenomenon are expected to appear after fibrate therapy.

Relationship between plasma lipids and palmitoyl-CoA hydrolase and synthetase activities with peroxisomal proliferation in rats treated with fibrates

1. The time-course of the effect of clofibrate (CFB), bezafibrate (BFB) and gemfibrozil (GFB) on lipid plasma levels and palmitoyl-CoA hydrolase and synthetase activities, as well as the correlations with the peroxisomal proliferation phenomenon have been studied in male Sprague-Dawley rats. 2. The administration of the three drugs caused a significant reduction in body weight gain, accompanied with a paradoxical increase in food intake in groups treated with BFB and GFB. 3. Drug treatment produced gross hepatomegaly and increase in peroxisomal beta-oxidation, and these parameters were strongly correlated. The order of potency was BFB > CFB > or = GFB. 4. Both plasma cholesterol (BFB approximately CFB > GFB) and triglyceride (BFB approximately GFB > CFB) levels were reduced in treated animals. There was an inverse correlation between these parameters and peroxisomal beta-oxidation, although the peroxisomal proliferation seemed to explain only a small part of the hypolipidemic effect observed. 5. Cytosolic and microsomal (but not mitochondrial) palmitoyl-CoA hydrolase activities were increased by the three drugs (BFB > CFB > GFB), probably by inducing the hydrolase I isoform, which is insensitive to inhibition by fibrates in vitro. The increased hydrolase activities were directly and strongly correlated with peroxisomal beta-oxidation. 6. Palmitoyl-CoA synthetase activity was also increased by the treatment with fibrates (BFB > CFB > GFB), probably as a consequence of the enhancement of hydrolase activities. 7. Some of the effects of fibrate treatment can be explained, at least in part, in terms of peroxisomal induction and caution should be exercised in the extrapolation of these results to species, such as man,that are insensitive to peroxisomal proliferation.

Increase in intracellular triglyceride synthesis induced by gemfibrozil

Gemfibrozil is an effective hypotriglyceridemic agent. Its mechanism of action has not been determined with certainty, but it is generally thought to act by virtue of an effect on lipoprotein lipase. However, this study was designed to test the hypothesis that gemfibrozil directly affects intracellular triglyceride synthesis in peripheral cells, and indeed, when added to the medium, gemfibrozil markedly stimulated triglyceride synthesis in cultured human skin fibroblasts. The effect was concentration-dependent, with a maximum effect at a gemfibrozil concentration of 40 micrograms/mL. A marked increase in triglyceride synthesis was observed when either labeled glucose or labeled fatty acid were added to the medium, indicating that the stimulation was substrate-coordinated. The effect was sustained for hours, with an onset of action within minutes. Lineweaver-Burk plots were constructed, and these revealed no apparent change in Km for either oleate or glucose (8.18 +/- 2.97 v 6.40 +/- 2.10 mumol/L for oleate and 0.113 +/- 0.004 v 0.107 +/- 0.051 mmol/L for glucose, control v gemfibrozil, P = NS). By contrast, there was a significant increase in the maximum triglyceride synthetic rate (Vmax) for both oleate and glucose (14.57 +/- 0.01 v 32.66 +/- 1.85 nmol/mg/4 h for oleate and 67.72 +/- 1.22 v 156.77 +/- 17.61 nmol/mg/4 h for glucose, control v gemfibrozil, P < .025). Given the rapid onset in action, these data suggest that gemfibrozil altered the active state of a limiting step in the triglyceride synthetic pathway. The effect of gemfibrozil on triglyceride synthesis was also determined on differentiated human preadipocytes and HepG2 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Lovastatin increases arachidonic acid levels and stimulates thromboxane synthesis in human liver and monocytic cell lines

The effect of lovastatin (LOV), the inhibitor of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase, on linoleic acid (LA, 18:2n-6) metabolism was examined in human monocytic Mono Mac 6 (MM6) and hepatoma Hep G2 cells. The desaturation of LA was examined after LOV (72 h, 10 microM) or dimethylsulfoxide (LOV carrier, < 0.1%) and [14C]LA (last 18 h, 0.3 microCi, 5 microM). In both cell lines, LOV reduced the percentage of 14C label associated with LA and increased the percentage of label in the 20:4n-6 and the 22:5n-6 fractions. In Hep G2 but not MM6 cells, this effect was fully reversible by means of coincubation with mevalonic acid (500 microM), but not with cholesterol or lipoproteins. In both cell lines, the LOV-mediated increase in LA desaturation resulted in dose-dependent reductions of LA and elevations of AA in cellular phospholipids. The lipids secreted by LOV-treated Hep G2 cells were also enriched in arachidonic acid (AA). In the MM6 cells, LOV increased release of thromboxane upon stimulation with the calcium ionophore A23187. In summary, our findings of higher LA desaturation and AA enrichment of lipids secreted by the Hep G2 cells suggest that LOV treatment may increase the delivery of AA from the liver to extrahepatic tissues. The changes in membrane fatty acid composition can influence a variety of cellular functions, such as eicosanoid synthesis in monocytic cells. The mechanism appears to be related to the reduced availability of intermediates of cholesterogenesis.

Fibrates modify rat hepatic fatty acid chain elongation and desaturation in vitro

Three fibric acid derivatives, clofibric acid (CFB), bezafibrate (BFB), and gemfibrozil (GFB), mainly used in the treatment of hypertriglyceridaemic or mixed hyperlipidaemic states, have been tested for their ability to modify fatty acid chain elongation and desaturation in vitro. Both endogenous and exogenous (saturated, monounsaturated and polyunsaturated) fatty acid elongations were inhibited by fibrates at concentrations well within the physiological range (IC50 values for GFB were between 0.1 and 0.3 mM). The potency order was GFB > BFB > CFB. Inhibition was not due to an impairment of the activation step from free fatty acids to acyl-CoAs, as palmitoyl-CoA synthetase was only slightly inhibited (IC50 value for GFB = 2.8 mM). Fibrates (GFB) appeared to behave as mixed non-competitive inhibitors with respect to malonyl-CoA when the rate limiting step of elongation, the condensing enzyme, is assayed. Further, delta 6 and delta 5 desaturates were inhibited by the three drugs (GFB > BFB > CFB), although not to the same extent as the elongation system. In contrast, delta 9 desaturase activity was not affected by fibrates.

Gemfibrozil modifies acyl composition of liver microsomal phospholipids from guinea-pigs without promoting peroxisomal proliferation

Treatment with gemfibrozil modifies acyl composition of hepatic microsomal phosphatidylcholine and phosphatidylethanolamine in guinea-pigs. Palmitic (16:0) and palmitoleic (16:1) fatty acids are increased, and stearic (18:0) and oleic (18:1) are decreased; further, while linoleic acid [18:2 (n-6)] is increased by gemfibrozil treatment, the other constituents of the n-6 fatty acids family, including arachidonic acid [20:4 (n-6)], are decreased. As gemfibrozil is a potent inhibitor of fatty acid elongation in vitro (Sánchez et al., FEBS Lett 300: 89-92, 1992), the inhibition of this enzyme system by gemfibrozil treatment could be responsible for the observed results in vivo. These changes in fatty acid composition are accompanied by a decrease in serum lipids and, more important, are independent of peroxisomal proliferation.

Cytosolic lipogenic enzymes: effect of fibric acid derivatives in vitro

The effect of fibric acid derivatives, clofibric acid (CFB), bezafibrate (BFB), and gemfibrozil (GFB) on hepatic cytosolic enzymatic activities involved in saturated fatty acid synthesis has been estudied in vitro. From all the activities tested (fatty acid synthetase, acetyl-CoA carboxylase, ATP-citrate lyase, malic enzyme, malic dehydrogenase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase), only acetyl-CoA carboxylase and glucose-6-phosphate dehydrogenase were significantly inhibited by fibrates, with the following order of potency: GFB > BFB > > CFB. The characteristics of the inhibition phenomena (IC50, kinetic analysis, time and protein dependence, etc) and their transcendence to the effects of fibric acid derivatives in vivo are discussed.