Calcium beta-hydroxy-beta-methylbutyrate. 1. Potential role as a phosphate binder in uremia: in vitro study

The binding capacity of calcium beta-hydroxy-beta-methylbutyrate (calcium HMB), compared to other binders, was investigated in an in vitro study. Fifty milliequivalents of either calcium HMB, calcium acetate, calcium carbonate, aluminum hydroxide gel or non-gel aluminum hydroxide was added to a phosphate solution, titrated (HCl or NaOH), shaken and centrifuged to four different pH levels at 37 degrees C (simulating the gastrointestinal milieu). The difference in phosphate concentration between that of the initial and that of the supernatant represented from the bound phosphate in the precipitate. After 4 h at a pH of 6 (representing the intestinal condition after a meal), the binding percentage was: calcium acetate = 95.6%, calcium HMB = 92.6%, calcium carbonate = 46.4%, aluminum hydroxide gel = 33.4% and non-gel aluminum hydroxide = 17.8%. There was no significant difference (p > 0.05) between calcium HMB and calcium acetate. These results suggest that calcium HMB is an efficient phosphate binder in vitro, which may predict its effective role in vivo.

Age and the effects of 2-D,L-amino-5-phosphonovalerate in an area of the chick forebrain which is essential for early learning

The intermediate, medial part of the hyperstriatum ventrale (IMHV) is a region of the avian forebrain which is known to be essential for early learning in the domestic chick. The IMHV in an in vitro slice preparation displays two forms of synaptic plasticity. The incidence of both varies with age and is maximal between 3 and 5 days post-hatch. Since NMDA receptors are critical for at least one of these plasticities, we have investigated the relationship between age and the contribution of NMDA receptors to the field response evoked by local, low-frequency stimulation and have found that the magnitude of the NMDA-dependent component of the response varies with age peaking between 3 and 5 days post-hatch. Spontaneous neural activity, recorded intracellularly, can be completely and reversibly silenced by NMDA receptor blockade and the incidence of spontaneous activity also varies with age, peaking between 3 and 5 days. These results suggest that the IMHV contains NMDA receptors which can be activated near resting membrane potential. Either the efficiency or the numbers of these receptors is maximal at a specific point in development and their peak activity coincides with a peak in synaptic plasticity. These characteristics are similar to those reported for young mammals.

Monoamine release in the rat striatum is induced by delta-guanidinovaleric acid and inhibited by GABA agonists

delta-Guanidinovaleric acid (GVA) is an endogenous convulsant and is thought to be a specific gamma-aminobutyric acid (GABA) antagonist. In this study, we examined the effects of GVA and GABA agonists, GABA, muscimol and baclofen, on the release of dopamine (DA) and serotonin (5-HT) in the rat striatum using a brain dialysis technique. GVA produced a significant increase in the amount of DA and 5-HT released compared with controls. Both GABA (10mM) and muscimol (10mM) inhibited the GVA-induced release of DA and 5-HT. Muscimol was a more potent inhibitor of 5-HT release than DA release. Baclofen (10mM) inhibited only the GVA-induced DA release. These results suggest that the activation of GABA receptors inhibits the release of DA and 5-HT in the striatum, and that the dopaminergic system regulates GABA-B receptors and the serotonergic system mainly regulates GABA-A receptors.

Treatment of immune cell-mediated liver damage by nonpeptidic mimetics of the extracellular matrix-associated Arg-Gly-Asp epitope

The etiology of T-cell-mediated liver injury involves the migration of immune cells, notably CD4+ T lymphocytes, into liver tissues. This process is mediated primarily by integrin-recognition of the sub-endothelium basement membranes and the extracellular matrix. The Arg-Gly-Asp-containing peptide, a major cell-adhesive ligand of extracellular matrix, is present in various plasma- and matrix-glycoproteins, such as fibronectin. Recently, we have described the design and usage of nonpeptide mimetics of Arg-Gly-Asp which bind specifically to integrins, and thereby, inhibit T cell immunity in vivo. We examined the efficacy of Arg-Gly-Asp-mimetics as potential therapeutic compounds for the treatment of experimental T-cell-mediated liver injury induced in mice by injection of Concanavalin-A. We now report that the Arg-Gly-Asp-mimetics specifically inhibited the binding of murine T cells to fibronectin, but did not affect the proliferative response of these cells in vitro. Intraperitoneal or oral administration of the Arg-Gly-Asp-mimetics but not the Arg-Gly-Asp-containing peptide, inhibited liver damage in mice if given before their inoculation with Con-A, as manifested by a lesser elevation in their serum levels of hepatic enzymes. The inhibitory effect of the Arg-Gly-Asp-mimetics was dose-dependent, the ED50 of the tested molecules being in the range of 100 micrograms per mouse and reaching maximal effect, e.g. approximately 95% inhibition, at 500 micrograms per mice. Thus, the Arg-Gly-Asp-mimetics described here may be used therapeutically to prevent immune-cell-mediated acute or chronic pathological reactions in the liver.

Colostral milk fat percentage and pig performance are enhanced by feeding the leucine metabolite beta-hydroxy-beta-methyl butyrate to sows

Three trials were conducted to test whether feeding the leucine metabolite beta-hydroxy-beta-methyl butyrate (HMB) would increase fat content of sows' milk and pig weight gain. All sows received a basal diet and were assigned at random to receive either 2 g of CaCO3/d (control) or 2 g of Ca(HMB)2/d (HMB), which was top-dressed to the basal diet. Treatment began 3 to 4 d before farrowing. In Trials 1, 2, and 3 there were 4, 19, and 11 pairs of sows, respectively. In a combined analysis that included all three trials, milk fat at d 1 was increased by 41% (P = .01) and pig weight at d 21 was increased by 7% (P = .01) for sows fed diets containing HMB compared with sows fed control diets. Sows fed HMB lost more backfat (P = .03); however, sows receiving HMB had more (P < .05) backfat depth at farrowing than control sows. At weaning there was no difference in backfat depth between the treatment groups. Sows fed HMB tended to consume less feed (P = .07) than control sows. In Trials 2 and 3, data were collected on the subsequent reproductive cycles of the sows. A combined analysis of the data revealed no differences in sow performance when sows previously fed the diet containing HMB were compared with sows previously fed the control diet. In conclusion, beta-hydroxy-beta-methyl butyrate, when fed to sows at 2 g/d, resulted in an increase in fat percentage of sow's milk and pig performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidation of human red blood cells by a free radical initiator and effects of radical scavengers

Haemolysis induced by a free radical initiator (4,4'azobis-(4-cyanovaleric acid) has been studied with transfusion blood. Azobis cyanovaleric acid caused an increase in haemolysis. The effect of alpha- and gamma-tocopherol, 2,2,5,7,8 pentamethyl-6-chromanol and 2,2,7,8 tetramethyl-6-chromanol on the red blood cell haemolysis was studied. There was little difference in the antioxidant action of four chromanols studied. Compounds without the side chain appeared to suppress haemolysis as well as alpha- and gamma-tocopherol. These results suggest that the long side chain of vitamin E has little or no effect on its antioxidant activity in red blood cells. However "protection against haemolysis" was related to total chromanol content of red blood cells. Therefore by dividing "protection" by "total chromanol content" it can be seen that alpha-tocopherol has the highest antioxidant potency.

Effects of beta-hydroxy-beta-methyl butyrate on performance and carcass quality of feedlot steers

Beta-hydroxy-beta-methyl butyrate (HMB), a compound formed during catabolism of leucine, was fed to 256 crossbred steers as 0 or .03% of diet dry matter. Effects on performance, carcass characteristics, and tissue composition were measured. Groups of 32 steers per diet were slaughtered after 105, 119, 133, and 147 d on feed. The HMB was fed to each group only during the final 82 d they were fed. Averaged across slaughter date, animal performance was not altered by HMB; however, an interaction between HMB and time on feed was detected. Feeding HMB increased (P < .01) daily gain of steers slaughtered at 105 d but decreased (P < .01) daily gain of steers slaughtered at 147 d. Steers fed HMB had numerically higher marbling scores that resulted in a trend toward higher carcass quality grades. Steers receiving HMB tended to have less (P < .08) s.c. fat and fewer steers with yield grades of 4 or greater (1.6 vs 4.7%). Supplementation of HMB to feedlot steers tended to increase (P < .07) the ratio of intramuscular fat to subcutaneous fat. Steers fed HMB had higher (P < .001) blood plasma concentrations of HMB (3.06 vs 1.70 mg/L) and lower (P < .03) blood plasma concentrations of cholesterol (108.4 vs 118.7 mg/dL). Feeding HMB tended to increase (P < .10) lipid content of the longissimus muscles of those steers slaughtered at 105 d.

Peroxisome proliferation of hepatocytes in rats by a microbial degradation product of cholic acid, 4-(decahydro-6-methyl-3-oxocyclopenta(f)quinoline-7-yl)valeric acid

Three-week oral administration of 4-(decahydro-6-methyl-3-oxo-cyclopenta(f)quinoline-7-yl)valeric acid (32-1328) in the diet supplemented at concentrations of 0.1% or 0.3% was associated with hepatomegaly and hypotriglyceridemia in male F344 rats. Electron microscopic examination of the liver revealed a remarkable increase of peroxisomes in hepatocytes both in number and size. Biochemically, there were increased activities of peroxisomal marker enzymes including the heat-labile enoyl-CoA hydratase and catalase while the mitochondrial enoyl-CoA hydratase activity was unchanged after feeding of 32-1328. These findings indicate that 32-1328 can exert peroxisome-proliferating activity to rat liver in a manner similar to typical peroxisome proliferators such as clofibrate or di(2-ethylhexyl)phthalate.

Synthesis of methyl 3-(2-octadecylcyclopropen-1-yl)propanoate and methyl 3-(2-octadecylcyclopropen-1-yl)pentanoate and cyclopropane fatty acids as possible inhibitors of mycolic acid biosynthesis

(Z)-Tetracos-5-enoic acid is a key intermediate in the biosynthesis of myocobacterial mycolic acids. Recently the methyl ester of its cyclopropene analogue, methyl 4-(2-octadecylcyclopropen-1- yl)butanoate, was shown to act as an inhibitor of mycolic acid biosynthesis. The related analogues methyl 5-(2-octadecylcyclopropen-1-yl)pentanoate and methyl 3-(2-octadecylcyclopropen-1-yl)propanoate have been synthesized, as well as the related cyclopropane esters methyl (Z)-4-(2-octadecylcyclopropan-1-yl)butanoate and methyl (Z)-5-(2-octadecylcyclopropan-1-yl)pentanoate. The synthesis of methyl 3-(2-octadecylcyclopropen-1-yl)propanoate involved protection of the cyclopropene ring by iodination to allow oxidation of an alcohol to a carboxylic acid; the diiodocyclopropane was deprotected by a new mild procedure using activated zinc.

Nonpeptidic analogues of the Arg-Gly-Asp (RGD) sequence specifically inhibit the adhesion of human tenon's capsule fibroblasts to fibronectin

PURPOSE

Scar formation from the process of wound healing is mediated primarily by fibroblasts and is a major problem in ophthalmology in general and in glaucoma therapy in particular. Interactions between fibroblasts and glycoprotein components of the extracellular matrix (ECM) are among the major causes of scar formation. Recognition of ECM glycoproteins occurs via cell surface integrins that are specific for adhesion epitopes, such as the Arg-Gly-Asp (RGD-) containing amino acid sequence. The RGD sequence, which is present in several matrix and plasma proteins, including fibronectin (FN) and vitronectin, is involved in cell-ECM interactions that occur during inflammatory and homeostatic reactions. The present study was designed to examine the possibility of using RGD-mimetics as inhibitors of fibroblasts-FN interactions.

METHODS

Two nonpeptidic mimetics of RGD were designed and constructed, and their inhibitory effect on the adhesion of human tenon's capsule fibroblasts to FN was examined. SF-6,5 consisting of the carboxylate group of Asp and the guanidinium group of Arg divided by a linear atom spacer and a newly designed mimetic, designated NS-11, were examined herein.

RESULTS

The RGD mimetics, SF-6,5 and NS-11, but not an Arg-Gly-Glu (RGE) mimetic inhibited the adhesion of ocular fibroblasts to immobilized FN. SF-6,5 and NS-11 did not inhibit adhesion of the fibroblasts to laminin or spontaneous proliferation of fibroblasts. Trypsin pretreatment of the nonpeptidic RGD mimetics did not affect their ability to inhibit adhesion of the ocular fibroblasts to FN, whereas that of the RGD-containing peptide was abolished by the pretreatment.

CONCLUSION

Nonpeptidic mimetics of RGD are attractive candidates for therapeutic agents to prevent the formation of scar tissue and related RGD-dependent pathologic events.

Inhibition of metastatic cell colonization in murine lungs and tumor-induced morbidity by non-peptidic Arg-Gly-Asp mimetics

The spreading and colonization of tumor cells require their migration to metastatic sites via blood vessels. To penetrate blood-vessel walls, cells, including malignant ones, must recognize and associate with the sub-endothelium extracellular matrix (ECM) and its glycoproteins. Recognition of ECM-glycoproteins, such as fibronectin (FN) and vitronectin (VN), is mediated by integrin receptors expressed on various cell types, including platelets, leukocytes and tumor cells. The Arg-Gly-Asp (RGD)-containing peptide, a major adhesive ligand of ECM, is present in various plasma and matrix glycoproteins, such as FN and VN. Non-peptidic mimetics of RGD, consisting of carboxylate and guanidinium groups of Asp and Arg divided by a linear atom spacer, express a high affinity for the alpha IIb-beta 3 integrin and inhibit platelet aggregation. Herein, the ability of RGD mimetics to inhibit adhesive interactions between tumor cells and RGD, and tumor progression in vivo, was examined. RGD-containing peptides and the RGD mimetic, compound SF-6,5, but not the Arg-Gly-Glu (RGE) peptide or the corresponding mimetic, specifically inhibited B16-F10 melanoma cell adhesion to immobilized VN and FN. Daily administration in vivo of SF-6,5 to mice inhibited the formation of B16-F10 colonies in experimental and spontaneous models of metastases. Moreover, SF-6,5 could prevent mouse death caused by massive colonization of tumor cells in the lungs. The therapeutic effect of RGD-containing peptides on tumor metastasis formation was marginal, probably due to the small amounts used, and its susceptibility to proteolysis in situ. Thus, non-peptidic mimetics of small adhesive epitopes may provide a novel therapeutic tool to prevent an adverse pathological event involving integrin-dependent cell-cell and cell-ECM interactions.

Activation of a peroxisome-proliferating catabolite of cholic acid to its CoA ester

We have shown that a microbial cholic acid catabolite (4R)-4-(2,3,4,6,6a beta,7,8,9,9a alpha,9b beta-decahydro-6a beta-methyl-3-oxo- 1H-cyclopenta[f]quinolin-7 beta-yl)valeric acid (DCQVA), is a potent peroxisome proliferator. In this paper a possible key stage in DCQVA metabolism, the activation of DCQVA to its CoA ester, has been investigated in rat liver microsomes and particulate fractions. The microsomal reaction was dependent on CoA, ATP, DCQVA (0.2-1 mM) and protein content. The reaction was decreased by storage at 4 degrees C, preincubation of microsomes at 37 degrees C for 5 min, or inclusion of Triton X-100 in the reaction mixture. Such treatments also enhanced generation of long-chain fatty acyl-CoAs, as determined by h.p.l.c. analysis. The same effect was caused by exposing the microsomes to phospholipase A2, suggesting that endogenous fatty acids may compete with DCQVA for esterification with CoA. Subcellular fractionation of rat liver demonstrated that the activity of DCQVA-CoA synthesis was localized predominantly in the microsomal fraction, in contrast to long-chain fatty acyl-CoA synthetase, which was distributed among all particulate fractions. Administration of clofibrate of rats did not affect the distribution of DCQVA-CoA synthesis activity. In contrast to a 2-fold induction of long-chain fatty acyl-CoA synthetase by clofibrate treatment, the activity of DCQVA-CoA synthesis in the microsomal fraction decreased by 80%. These results suggest that DCQVA is activated by an enzyme distinct from long-chain fatty acyl-CoA synthetase. The resulting perturbation of fatty acid metabolism may be involved in the mechanism whereby DCQVA causes peroxisome proliferation.

Induction of peroxisomal beta-oxidation by a microbial catabolite of cholic acid in rat liver and cultured rat hepatocytes

The capability of (4R)-4-(2,3,4,6,6a beta,7,8,9,9a alpha,9b beta-decahydro-6a beta-methyl-3-oxo-1H-cyclopental[f]quinolin-7 beta-yl)valeric acid (DCQVA), a catabolite of cholic acid produced by enterobacteria, to induce peroxisome proliferation in vivo and in vitro was studied. Rats given 0.3% DCQVA in the diet for 2 weeks showed marked increases in peroxisomal beta-oxidation, mitochondrial 2,4-dienoyl-CoA reductase and microsomal laurate omega-oxidation activities in the liver compared with control rats given the diet without DCQVA. Cultured rat hepatocytes treated with DCQVA for 72 h also exhibited greatly enhanced beta-oxidation activity. The increased activity was concentration-dependent and the effective concentrations were comparable with those of clofibric acid that produced the same degree of induction in the assay. The results demonstrate that DCQVA is a potent peroxisome proliferator that occurs naturally in rat intestine.

Effects of isoacids, urea, and sulfur on ruminal fermentation in sheep fed high fiber diets

The effects of isoacids, urea N, and S on ruminal fermentation of sugarcane bagasse- or corn stover-based diets were studied in sheep. Acetate production was taken as a measure of the fermentation rate. For the sugarcane bagasse diet, neither urea nor S supplementation changed ruminal acetate production. When N and S were combined, acetate production was 44% higher (3.16 vs. 2.18 mol/d). Similar effects were noted for the corn stover diet. Increasing the level of isoacids from .1 to .2 g/kg BW per d in the diet did not change acetate production for either diet. However, N supplementation of the sugarcane bagasse diet containing the low level of isoacids resulted in a 49% greater acetate production (2.86 vs. 1.91 mol/d). Acetate production was 90% higher (3.74 vs. 1.97 mol/d) when the diet containing the high level of isoacids was supplemented with N. The corresponding increases for corn stover were 12% (2.64 to 2.95 mol/d) and 35% (2.88 to 3.87 mol/d). The results suggest that NH3 N provided by the basal diet was more limiting than isoacids. Once the N deficiency was corrected, isoacids became limiting. Ruminal digestion of high fiber diets low in N was improved by supplementation with urea, isoacids, and S.

Hydrophobic anion activation of human liver chi chi alcohol dehydrogenase

Class III alcohol dehydrogenase (chi chi-ADH) from human liver binds both ethanol and acetaldehyde so poorly that their Km values cannot be determined, even at ethanol concentrations up to 3 M. However, long-chain carboxylates, e.g., pentanoate, octanoate, deoxycholate, and other anions, substantially enhance the binding of ethanol and other substrates and hence the activity of class III ADH up to 30-fold. Thus, in the presence of 1 mM octanoate, ethanol displays Michaelis-Menten kinetics. The degree of activation depends on the size both of the substrate and of the activator; generally, longer, negatively charged activators result in greater activation. At pH 10, the activator binds to the E-NAD+ form of the enzyme to potentiate substrate binding. Pentanoate activates methylcrotyl alcohol oxidation and methylcrotyl aldehyde reduction 14- and 30-fold, respectively. Such enhancements of both oxidation and reduction are specific for class III ADH; neither class I nor class II shows this effect. The implications as to the nature of the physiological substrate(s) of class III ADH are discussed in light of the recent finding that this ADH and glutathione-dependent formaldehyde dehydrogenase are identical. A new rapid purification procedure for chi chi-ADH is presented.

Increased skin flap viability after treatment with forskolin or with ridogrel, a thromboxane synthesis inhibitor and receptor blocker

Two ventral skin flaps were raised in each of 60 rats and viability was assessed 48 h after operation. Twenty animals served as controls and immediately preoperatively 20 received an intraperitoneal injection of either 5 mg/kg body weight ridogrel, a combined thromboxane synthesis inhibitor and receptor blocker, or 4 mg/kg forskolin, a cAMP stimulator. The mean total and surviving flap areas measured 14.3 +/- 1.4 and 10.1 +/- 3.2 cm2 respectively for the control group. In the treated groups it was 16.4 +/- 1.3 cm2 and 15.6 +/- 2.6 cm2 for ridogrel and 17.8 +/- 1.1 cm2 and 15.8 +/- 4.3 cm2 for forskolin respectively. The differences between the areas of each treated group and the control group were statistically significant (p less than 0.0001). It can be concluded that both ridogrel and forskolin afford protection against skin necrosis probably because of improved conditions in the microcirculation due to reduced platelet aggregation in the vasculature of the distal part of the flap.

R68070, a combined thromboxane/endoperoxide receptor antagonist and thromboxane synthase inhibitor, inhibits human platelet activation in vitro and in vivo: a comparison with aspirin

We have investigated the effects of R68070 on platelet function in vitro and in vivo. The drug inhibits U46619-induced aggregation (IC50 = 1.2 x 10(-6) mol/L), blocks serum thromboxane formation (IC50 = 1 x 10(-7) mol/L), and increases serum prostaglandin (PG)E2 and 6-keto-PGF1 alpha levels, indicating that it combines thromboxane receptor blocking and thromboxane synthase inhibiting properties. The thromboxane-dependent aggregation of blood platelets is blocked by R68070, whereas no inhibition of thromboxane independent pathways occurs. A double-blind, randomized, cross-over study was performed on nine volunteers, comparing 400 mg placebo, 400 mg aspirin, and 400 mg R68070. Thromboxane-dependent aggregations were significantly inhibited by R68070 and by aspirin, the latter still having the most pronounced action. However, R68070 was clearly more powerful than aspirin (P less than .0005) in prolonging the bleeding time. Serum TxB2 formation was completely inhibited with both treatments, whereas serum 6-keto-PGF1 alpha and PGE2 and intralesional 6-keto-PGF1 alpha were inhibited after aspirin and stimulated after R68070. We conclude that R68070 inhibits platelet thromboxane synthase and its thromboxane receptor both in vitro and in vivo; local reorientation of cyclic endoperoxide metabolism toward prostacyclin induces a stronger inhibition of hemostasis than that produced by aspirin.

Effects of intravenous injection of butyrate, valerate and their isomers on endocrine pancreatic responses in conscious sheep (Ovis aries)

1. The effects of intravenous injection of n-butyrate, iso-butyrate, n-valerate and iso-valerate on insulin and glucagon secretion was examined in conscious sheep. 2. Each sodium salt of the short chain fatty acids increased plasma insulin and glucagon concentrations in a dose-dependent manner (312-1250 mumol/kg body wt). 3. Both butyrate and valerate isomers with branched carbon chains had larger insulin releasing activity than isomers with straight carbon chains. 4. The glucagon responses to butyrate or valerate did not differ between the isomers with straight carbon chains and those with branched carbon chains. 5. Our results suggest that the receptive mechanism to short chain fatty acids, which may involve the nervous system, differs between the A cell and the B cell in sheep in vivo.

The effects of 4-pentenoic and pentanoic acid on the hypoxic rat atria

When exposed to hypoxia, the isolated rat atria released lactate into the bathing medium and underwent a rise in resting tension and a decline of the contractions frequency. In some of them, it also occurred a complete cessation of the pacemaker activity. Atria from 24-h fasted rats, when compared to those from fed ones, exhibited a lower lactate output, a higher rise in resting tension, a faster decay of the contraction frequency and an increased occurrence of atrial arrest. In both the fed and fasted rats atria, some triacylglycerol lipolysis remained throughout the hypoxic incubation. Addition of 2 mM 4-pentenoic acid abolished the lipolytic activity and reduced lactate output in both groups of atria. In the fed rats atria it also accelerated the decrease of the pacemaker frequency. Pentanoic acid reduced lactate output in both groups of atria and in those from fed rats it did not alter lipolysis but increased the rise in resting tension, the decline of the pacemaker frequency and the occurrence of atrial arrest. Present data indicate that although 4-pentenoic acid inhibits fatty acid oxidation and endogenous lipolysis, it was not able to reduce the noxious effects of hypoxia. Since the effects of 4-pentenoic acid were rather similar to those of fasting and pentanoic acid, they might be ascribed to the accumulation of its own oxidative metabolites which could be detrimental for the hypoxic atria.

Volatile fatty acid uptake and propionate metabolism in ruminant hepatocytes

Previous reports have demonstrated that butyrate inhibits metabolism of propionate by liver cells isolated from sheep and goats. Our objectives were to examine some possible mechanisms for this inhibition and to test for this inhibition in the bovine animal. Incorporation of label from 2.5 mM [2-(14)C]propionate into glucose (nmol propionate/mg cell DM/h) in the presence of 0, 1.25, and 2.5 mM butyrate was 107, 66, and 62 by goat hepatocytes and 79, 25, and 29 by calf hepatocytes; therefore, butyrate inhibited propionate metabolism at least as effectively in calves as in goats. In goat hepatocytes 1.25 mM butyrate reduced 1.25 mM propionate uptake to 46% of control, and 1.25 mM [2-(14)C] propionate incorporation into glucose to 44% of control. Propionate had no effect on butyrate uptake. Isovalerate and valerate tended to be cleared from the media to a greater extent than butyrate but had no effect on propionate uptake. Therefore, inhibition of propionate conversion to glucose by butyrate is specific and is not due to a general competition among VFA for metabolism. Butyrate inhibits hepatic propionate utilization generally, not specifically propionate conversion to glucose. Butyrate also inhibited propionate utilization by goat liver homogenates, indicating that butyrate inhibits propionate metabolism at a step subsequent to propionate transport across the hepatocyte plasma membrane.

R 68 070: thromboxane A2 synthetase inhibition and thromboxane A2/prostaglandin endoperoxide receptor blockade combined in one molecule--I. Biochemical profile in vitro

R 68 070 or (E)-5-[[[(3-pyridinyl)[3-(trifluoromethyl)phenyl]- methylen]amino]oxy] pentanoic acid (Janssen Research Foundation, Belgium) combines specific thromboxane A2 (TXA2) synthetase inhibition with TXA2/prostaglandin endoperoxide receptor blockade in one molecule. In vitro, the compound specifically inhibits the production of TXB2 from [14C] arachidonic acid by washed human platelets (IC50 = 8.2 X 10(-9) M) and by platelet microsomes (IC50 = 3.6 X 10(-9) M), of MDA (IC50 = 1.91 X 10(-8) M) and of TXB2 (IC50 = 1.47 X 10(-8) M) by thrombin-coagulated human platelet-rich plasma (P.R.P.) and whole blood respectively and increases the levels of PGD2, PGE2, PGF2 alpha and 6-keto-PGF1 alpha. The activity of cyclo-oxygenase-, prostacyclin synthetase-, 5-, 12- and 15-lipoxygenase-enzymes are not affected. Additionally, R 68 070 inhibits human platelet aggregation in P.R.P. induced by U 46619 3 X 10(-7) M to 2 X 10(-6) M (IC50 = 2.08 X 10(-6) M to 2.66 X 10(-5) M, collagen 0.5 to 2 micrograms/ml (IC50 = 2.85 X 10(-6) M to 4.81 X 10(-5) M), arachidonic acid 7.5 X 10(-4) M to 2 X 10(-3) M (IC50 = 2.1 X 10(-8) M to 3.3 X 10(-8) M) and the U 46619 (1 X 10(-7) M)-induced accumulation of [32P] phosphatidic acid (IC50 = 5.24 X 10(-7) M) in washed human platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

R 68 070: thromboxane A2 synthetase inhibition and thromboxane A2/prostaglandin endoperoxide receptor blockade combined in one molecule--II. Pharmacological effects in vivo and ex vivo

R 68 070 or (E)-5-[[[(3-pyridinyl)[3-(trifluoromethyl)phenyl]- methylen]amino]oxy] pentanoic acid (Janssen Research Foundation, Belgium), a newly developed compound, combining specific thromboxane A2 (TXA2) synthetase inhibition with TXA2/prostaglandin endoperoxide receptor blockade in one molecule, is active in vivo in man and in experimental animals. In man (n = 5), a single oral 400-mg dose of R 68 070 produces deep and protracted inhibition of platelet TXA2 synthetase activity (greater than or equal to 90% for 48 h), increases serum levels of immunoreactive 6-keto-PGF1 alpha, reduces platelet aggregation in P.R.P. induced by U 46619, collagen (greater than 70% for 8 h), arachidonic acid (greater than 90% for 18 h) and prolongs template bleeding times significantly, without affecting plasma coagulation or fibrinolysis. In rats, R 68 070 (1.25 mg/kg orally, -2 h) singly prolongs tail bleeding times as much as a combination of TXA2 synthetase inhibition (dazoxiben 10 mg/kg) and TXA2/prostaglandin endoperoxide receptor blockade (BM 13177 40 mg/kg). In dogs, the compound reduces coronary thrombosis induced by electrical damage (1.25 mg/kg i.v.) and prevents the evolution of occlusion/reperfusion-induced arrhythmias into ventricular fibrillation (2.5 mg/kg i.v.). R 68 070 thus may be an appropriate pharmacological tool to analyze the roles and interactions of agonistic (TXA2, prostaglandin endoperoxides) and antagonistic (PGD2, PGE2, PGI2) metabolites of arachidonic acid in experimental and human pathologies.

Correlation between selective inhibition of the cyclic nucleotide phosphodiesterases and the contractile activity in human pregnant myometrium near term

The present study was carried out to determine the ability of various pharmacological agents to selectively inhibit each cytosolic form of phosphodiesterase isolated from the longitudinal layer of human myometria near term. Among the drugs tested, zaprinast specifically inhibits the first form of PDE which hydrolyses both substrates (cAMP and cGMP) and is stimulated by the Ca2+-calmodulin complex. A second form of PDE specific for cAMP hydrolysis and Ca2+-calmodulin insensitive is only present during pregnancy. Rolipram is the most potent and selective inhibitor of this second form. It is also the most efficient compound to inhibit in vitro the spontaneous contractions of near term myometria. The double effect of rolipram suggests an important role of the second form of PDE in the mechanisms of contractility during the pregnancy. In addition rolipram or other derivatives might be of a therapeutic interest in the prevention of prematurity in so far as they are devoid of undesirable maternal and fetal side effects.

The effects of 4-pentenoic and pentanoic acids on the isolated rat atria

The peak developed tension and the pacemaker frequency of the isolated atria from fed and fasted rats, declined progressively during the incubation in a glucose-free medium containing 2-deoxyglucose. The atria from fed rats exhibited a faster decline than those from fasted rats, which was associated to a slower triacylglycerol lipolysis. 4-Pentenoic acid inhibited the lipolysis of both groups of atria but did not alter the atrial contractile performance. However, it enhanced the decline of the pacemaker frequency in the atria from fasted rats whereas, in contrast, it alleviated the decline in the fed atria. n-Pentanoic acid ameliorated the impairment of the contractile and pacemaker activities in both groups of atria, without affecting the lipolysis. It was concluded that, since the inhibition of the intramyocardial lipolysis did not correlate with changes of the atrial functions, 4-pentenoic acid was not appropriate to assess about the contribution of endogenous triacylglycerol to the maintenance of the atrial contractile and pacemaker activities.

Modulation of water transport in human red cells: effect of urea

We have studied the effect of urea on water flux in the human red cell and have found that 500 mosmolal urea inhibits osmotic water transport by 39%. The Ki for urea inhibition of water flux is 550 +/- 80 mosmolal, higher than, but comparable with, the Km of urea transport into the red cell of 220-330 mM given by Mayrand and Levitt (J. Gen. Physiol. 55 (1983) 427) and Brahm (J. Gen. Physiol. 82 (1983) 1). Other amides, such as propionamide and valeramide, as well as methyl-substituted ureas, have similar effects, although an indifferent molecule, such as 0.5 M creatinine, has no effect. Urea can be washed off the inhibition site with buffer, and the effects of urea concentrations as high as 1.2 osmolal are entirely reversible. 500 mosmolal urea also significantly increases the reflection coefficient for ethylene glycol, sigma eth gly, from 0.71 +/- 0.03 in control experiments to 0.86 +/- 0.04 (P less than 0.0005, t-test), and propionamide has a similar effect on sigma eth gly. These results show that urea can modulate ethylene glycol transport through the red cell membrane, and are consistent with, but not proof of, the presence of a single class of aqueous channels through which both ethylene glycol and urea enter the red cell. It is suggested that the physiological purpose of these low-affinity urea sites is to modulate water flow out of the red cell during passage through the regions of 0.5-0.6 M urea in the kidney.

Delta-aminovaleric acid antagonizes the pharmacological actions of baclofen in the central nervous system

The action of delta-aminovaleric acid (AVA) on the muscle relaxant properties of baclofen, a GABAB receptor agonist, was investigated in two experimental models: (1) the pathologically increased muscle tone of the gastrocnemius muscle in spastic mutant Han-Wistar rats and (2) the Hoffmann (H)-reflex recorded from plantar foot muscles after electrical stimulation of the tibial nerve in barbiturate (60 mg/kg) anaesthetized rats. In both paradigms coadministration of AVA (500 nmol/5 microliter) antagonized the muscle relaxant action of intrathecally applied baclofen (0.2-2 nmol), but failed to affect the muscle relaxant effects of intrathecally injected muscimol (2-20 nmol). In contrast, coadministration of bicuculline (1 nmol) did block the muscle relaxant action of muscimol, but failed to alter the effects of baclofen. When administered alone, bicuculline (1 nmol), or AVA (500 nmol-2 mumol) were without intrinsic action in both paradigms. In an additional series of experiments we investigated the action of AVA on a supraspinal effect of baclofen. Coadministration of AVA (12.5 nmol/0.5 microliter) in the ventromedial thalamic nucleus antagonized the catalepsy induced by baclofen (ED50 10 pmol/0.5 microliter), as indicated by an increase in ED50 of baclofen by a factor of 4.835 and a parallel shift of the probit-log dosage regression line to the right. The parallel shift seems to be consistent with a competitive mechanism of action of AVA. This study presents evidence that AVA antagonizes central pharmacological actions of baclofen at both spinal and supraspinal sites without affecting the actions of a GABAA agonist, muscimol.

Gemfibrozil decreases platelet reactivity in patients with hypercholesterolemia during physical stress

The effects of the lipid-lowering drug gemfibrozil on platelet reactivity at rest and during submaximal exercise were investigated in 10 patients with serum cholesterol levels greater than 270 mg/dl. No significant changes were observed in platelet reactivity at rest after gemfibrozil treatment. However, a marked decrease in platelet reactivity was seen in almost all patients treated with gemfibrozil during exercise. The adrenaline concentration necessary to induce secondary aggregation increased in eight patients during exercise after gemfibrozil and in two after placebo treatment. When adenosine diphosphatase (2 to 4 mumol/L) was used to induce aggregation, 5-hydroxytryptamine (serotonin) and thromboxane B2 secretion by platelets decreased by 35% and 67%, respectively, during exercise in patients treated with gemfibrozil. The area under the aggregation curve decreased by 28% during exercise after gemfibrozil. No significant changes occurred in these variables during exercise after placebo. Thus, gemfibrozil seems to have antiplatelet effects that might have importance in the prevention of acute complications of atherosclerosis in patients with hypercholesterolemia.

Effects of volatile fatty acids on propionate metabolism and gluconeogenesis in caprine hepatocytes

Isolated caprine hepatocytes were incubated with fatty acids of various chain lengths. Short-chain fatty acids effects on rates of gluconeogenesis and oxidation from [2-14C]propionate were determined. Additions of glucose (2.5 mM) had no effect on hepatic [2-14C]propionate metabolism in the presence and absence of amino acids. A complete mixture of amino acids increased label incorporation from [2-14C]propionate into [14C]glucose by 22%. Butyrate inhibited [2-14C]propionate metabolism and increased the apparent Michaelis constant for [2-14C]propionate incorporation into [14C]glucose from 2.4 +/- 1.5 to 5.6 +/- .9 mM. Butyrate's effects on propionate were similar in the presence and absence of L-carnitine (1 mM). Isobutyrate, 2-methylbutyrate, and valerate (1.25 mM) had no effect on [14C]glucose production but decreased 14CO2 production to 57, 61, and 54% of the control [2-14C]propionate (1.25 mM). This inhibition on 14CO2 production was not competitive. Isovalerate had no effect on either [2-14C]propionate incorporation into glucose or CO2. An increase in ratio of [14C]glucose to 14CO2 from [2-14C]propionate demonstrated that short-chain fatty acids other than butyrate do not inhibit gluconeogenesis from propionate. In addition, fatty acids that generate a net synthesis of intracellular oxaloacetate may partition propionate carbons toward gluconeogenic rather than oxidative pathways in goat hepatocytes.

Effects of gemfibrozil on plasma lipoprotein-apolipoprotein distribution and platelet reactivity in patients with hypertriglyceridemia

The effects of gemfibrozil on plasma lipoprotein distribution and composition and on platelet function were investigated in 11 patients with stable hypertriglyceridemia, six belonging to Fredrickson type IIb and five to type IV. Gemfibrozil (600 mg twice a day) significantly reduced total and very low density lipoprotein (VLDL)--associated triglyceridemia (respectively-32.4% and -40.4%, after 6 weeks of treatment). No significant variations were noted in the lipid components of low-density lipoproteins; by contrast, a marked increase (18%) was detected in high-density lipoprotein (HDL)--associated cholesterol. Comparison of the two patient groups (type IIb and type IV) showed that those with type IIb had both a more significant reduction of triglyceridemia and a more marked increase of HDL-cholesterol. Apolipoprotein B levels were reduced in both groups (-12%) with no change in apolipoprotein AI. The cholesterol content in the HDL subfractions, separated by rate zonal ultracentrifugation, was raised in HDL3 (18%) and in HDL2 (14%). Both particles also showed significant increases of the cholesterol/protein and the cholesterol/phospholipid ratios. A non-statistically significant decrease in collagen-induced aggregation and in the release of thromboxane B2 was noted after treatment. These findings suggest that, similar to what was recently reported in normal individuals and in laboratory animals, the probable mode of action of gemfibrozil is in reducing the secretion of atherogenic lipoproteins, particularly VLDL, while stimulating the production of small HDL particles.

Delta-guanidinovaleric acid as an endogenous and specific GABA-receptor antagonist: electroencephalographic study

Sporadic spike discharges recorded on EEGs from epidural electrodes appeared 5-10 min after topical application of 0.3 nmol delta-guanidinovaleric acid (DGVA) on the pia mater of the sensorimotor cortex, on the same side as the application. Spike discharges induced by DGVA were completely suppressed within 10 min of supplementary application of GABA (50 nmol), (3R)-(-)-4-amino-3-hydroxybutanoic acid (L-GABOB) (5 nmols) or muscimol (5 nmols) on the pia mater, but the discharges were not affected by supplementing with 500 nmol of alpha-amino-DGVA, i.e., arginine (Arg). Whereas spike discharges were not induced by DGVA together with L-GABOB or muscimol, DGVA applied together with Arg induced spike discharges. Neither phenobarbital (PB) (20 mg/kg, i.m.), diazepam (DZ) (10 mg/kg, i.p.), sodium valproate (200 mg/kg, i.p.) nor diphenylhydantoin (20 mg/kg, i.p.) showed any suppressive effects on spike discharges induced by DGVA. DGVA induced spike discharges 20 min after pre-injection of PB or DZ. These electroencephalographic findings suggest that DGVA, which has one more carbon in its chain than N-amidino-GABA, might act directly on the GABA-receptor to induce spike discharges and might be a specific GABA-receptor antagonist.

Mechanism of inactivation of gamma-aminobutyrate aminotransferase by 4-amino-5-fluoropentanoic acid. First example of an enamine mechanism for a gamma-amino acid with a partition ratio of 0

The mechanism of inactivation of pig brain gamma-aminobutyric acid aminotransferase (GABA-T) by (S)-4-amino-5-fluoropentanoic acid (1, R = CH2CH2COOH, X = F) previously proposed [Silverman, R. B., & Levy, M. A. (1981) Biochemistry 20, 1197-1203] is revised. apo-GABA-T is reconstituted with [4-3H]pyridoxal 5'-phosphate and inactivated with 1 (R = CH2CH2COOH, X = F). Treatment of inactivated enzyme with base followed by acid denaturation leads to the complete release of radioactivity as 6-[2-hydroxy-3-methyl-6-(phosphonoxymethyl)-4-pyridinyl]-4-oxo-5-+ ++hexenoic acid (4, R = CH2CH2COOH). Alkaline phosphatase treatment of this compound produces dephosphorylated 4 (R = CH2CH2COOH). These results support a mechanism that was suggested by Metzler and co-workers [Likos, J. J., Ueno, H., Feldhaus, R. W., & Metzler, D. E. (1982) Biochemistry 21, 4377-4386] for the inactivation of glutamate decarboxylase by serine O-sulfate (Scheme I, pathway b, R = COOH, X = OSO3-).

The effects of short-chain fatty acids on the neuronal membrane functions of Helix pomatia. I. Electrical properties

The effects of short-chain fatty acids on the membrane excitability, current-voltage (I-V) characteristics, and cell volume of Helix pomatia neurons were studied. 2-Decenoic acid (DA), having 10 carbon atoms in the hydrocarbon chain, suppressed the excitability of bursting neurons RPa1 (Sakharov and Salanki, 1969) for 30-60 min, while valeric acid (VA), having 5 carbon atoms, had no significant effect on excitability. DA had three different effects on the excitability of beating neurons: in some neurons DA suppressed excitability as in bursting neurons; in a second type of neuron DA had a negligible effect on excitability; and in the neuron located near RPa1 DA had a pentylentetrazol (PTZ)-like effect, i.e., it converted the discharge of the neuron from beating to bursting. DA decreased the peak value of the current, inducing a negative-resistance region in the I-V curve of the bursting neuron without any change in the level of the voltage at which the current reaches its maximal value. DA inhibited the hyperpolarization induced by activation of the Na+ pump, tested after preliminary enrichment of neurons with Na+ ions by incubation in a potassium-free solution for 20 min. DA caused a swelling of the neuron by about 10% which was independent of the Na+ pump. In all the above-mentioned cases VA had no significant effect.

The effects of short-chain fatty acids on the neuronal membrane functions of Helix pomatia. II. Cholinoreceptive properties

We have examined the effects of short-chain fatty acids on acetylcholine (ACh)-induced transmembrane currents using internally dialyzed neurons of Helix. Decenoic acid, which increased the fluidity of excitable membranes, caused dramatic changes in the voltage sensitivity of ACh currents consisting of an ACh-induced increase in membrane permeability for K+ and Na+ ions and a shift of the Erev of these ACh responses to more positive potentials. Valeric acid, which did not change the membrane fluidity, had no effect on this type of ACh response. Changes of the ENa and ECl had no effect on the size of the decenoic acid-induced shift of the Erev. But the influence of decenoic acid on the voltage sensitivity of ACh-induced currents almost disappeared after the change of the EK by the reduction of the internal K concentration. Decenoic acid had no effect on ACh responses in which K+ ions were not involved in the generation of ACh-induced currents. The results suggest that decenoic acid-induced changes in membrane fluidity modulate cholinoreceptive properties of the neuronal membrane by the inhibition of the K+ carrier involved in the generation of ACh responses.

Effect of gemfibrozil on lipids, apoproteins, and postheparin lipolytic activities in normolipidemic subjects

The lipid lowering agent Gemfibrozil was tested in 8 normolipidemic subjects during a three-month intake. Plasma triglycerides decreased by 41% and Very Low Density Lipoprotein (VLDL) triglycerides decreased by 54%. The reduction of plasma cholesterol, less marked (by 10%), was due to a decrease of Low Density Lipoprotein by 20% while High Density Lipoprotein (HDL) increased up to 30%. The separation of HDL demonstrated that only HDL3 were increased. The determination of the apoproteins in plasma and lipoprotein fractions showed similar results with a decrease of apo B (by 20%) and an increase of apo A-I and apo A-II, mainly in the HDL3 fraction. Plasma postheparin lipolytic activities (PHLA) were not influenced by the therapy and no correlation was found between these activities and any of the plasma or lipoprotein lipids. The apo C-III/apo C-II ratio in VLDL decreased by 30%; however, no correlation was found between this ratio in plasma as well as VLDL and triglycerides. In addition, the Intra Venous Fat Tolerance Test did not demonstrate any improvement of the clearance of exogenous fat. The lipid lowering efficacy of Gemfibrozil, its collateral effects, and the possible mechanisms of action are discussed.

Effects of valerate and isobutyrate on fatty acid secretion by the isolated perfused mammary gland of the lactating goat

The isolated mammary glands of six lactating goats were perfused with heparinized and oxygenated blood for 8 to 11 h. Adequate quantities of glucose, acetate and amino acids (including valine) were added to the perfusate. Either unlabelled valerate or unlabelled isobutyrate was added in excess to the perfusate of one gland, while the respective symmetrical gland was used as a control. After the administration of valerate, the proportions of the odd-numbered fatty acids (C11:0, C13:0, C15:0) in the milk fat, collected every hour during perfusion, rose progressively after 5 h until the end. The synthesis of milk fatty acids from valerate is discussed. After isobutyrate was added to the perfusate, isoC12:O, isoC14:0 and isoC16:0 in the milk fat increased as compared to the control. The effect of isobutyrate indicated that valine acted as a precursor of milk iso-branched fatty acids after its metabolisation to isobutyryl-CoA. During perfusion in the presence of the complete substrate mixture, the proportion of certain major milk fatty acids (C10:0, C12:0, C14:0 and C16:0) increased, whereas the proportion of C18:0 and C18:1 decreased. These effects have been ascribed to the presence of acetate and beta-hydroxybutyrate in the substrate mixture.

Gemfibrozil increases both apo A-I and apo E concentrations. Comparison to other lipid regulators in cholesterol-fed rats

HDL cholesterol (HDL-C) was increased by gemfibrozil (+3.6-fold), fenofibrate (+1.3-fold) and ciprofibrate (+1.2-fold) but not clofibrate or bezafibrate when dosed PO at 50 mg/kg for 2 weeks in cholesterol-fed rats. Cholesterol in apo B-containing lipoproteins decreased with gemfibrozil (-76%), clofibrate (-12%) and ciprofibrate (-12%). Plasma apo B decreased to the greatest extent with gemfibrozil (-86%) followed by ciprofibrate (-47%), fenofibrate (-40%), clofibrate (-24%) and bezafibrate (-20%). Only gemfibrozil increased plasma apo E levels which are characteristically low in this rat model. Gemfibrozil, fenofibrate and ciprofibrate increased apo A-I concentrations. It is concluded that plasma lipid regulators which elevate HDL in this model might do so by altering the metabolism and hence plasma concentration of apoAI (fenofibrate, ciprofibrate) or both apo E and A-I (gemfibrozil). It is hypothesized that drugs which alter the metabolism of both HDL peptides result in the greatest HDL-C elevation in the rat.

Evidence of hemin as an end product inhibitor of L-alanine: 4,5-dioxovalerate transaminase in rat liver mitochondria

This study describes the in vitro and in vivo effect of hemin on L-alanine:4,5-dioxovalerate transaminase activity. Hemin was shown to be an inhibitor of the purified enzyme and this inhibition was proportional to the concentration of hemin. The examined kinetic data with hemin showed uncompetitive inhibition for both alanine and 4,5-dioxovalerate. An apparent Ki of 30 and 42 microM for hemin were obtained with both alanine and 4,5-dioxovalerate, respectively. Moreover, the enzyme activity in liver was considerably decreased after the intravenous hemin administration and such an inhibition is dose and time dependent. Furthermore, maximum inhibition of the enzyme was observed 30 min after hemin injection and 60% enzyme inhibition was achieved with a dose of 1.2 mg/kg body wt of rat. Thus is suggests the important role of this enzyme on heme biosynthesis.

Apolipoprotein changes associated with the plasma lipid-regulating activity of gemfibrozil in cholesterol-fed rats

Gemfibrozil (Lopid) is a new plasma lipid-regulating drug that decreases very low and low density lipoprotein (VLD/LDL) and increases high density lipoprotein (HDL) concentrations in man. The present experiments tested the effects of gemfibrozil on plasma lipoproteins and apolipoproteins in rats fed high fat/high cholesterol diets. Compared to chow-fed rats, cholesterol feeding for 2 weeks (20% olive oil/2% cholesterol) produced the expected increases in VLDL and intermediate density lipoprotein (IDL) while lowering plasma HDL. This was documented by using three methods of lipoprotein isolation: sequential ultracentrifugation, density gradient ultracentrifugation, and agarose gel filtration. Gemfibrozil gavaged at 50 mg/kg per day for 2 weeks during cholesterol feeding prevented these changes such that lipoprotein patterns were similar to those in chow-fed animals. Whole plasma apoE and apoA-I concentrations were decreased and apoB increased due to cholesterol feeding as determined by electroimmunoassay, but again gemfibrozil treatment prevented these diet-induced alterations. Gradient polyacrylamide gel electrophoresis patterns of the total d less than 1.21 g/ml lipoprotein fractions reflected the changes in apolipoprotein concentrations and further demonstrated a greater increase of apoBl compared to apoBh in cholesterol-fed rats. Gemfibrozil lowered the concentration of both apoB variants and prevented the shift of apoE from HDL to lower density lipoproteins. Changes in the distribution of apoE were confirmed using agarose gel column chromatography followed by electroimmunoassay. These methods also revealed a shift of apoA-IV from HDL to the d greater than 1.21 g/ml, lipoprotein-free fraction with gemfibrozil treatment when blood was taken from fasted or postabsorptive animals. Since it was also noted that in chow-fed rats more apoA-IV was present in the d greater than 1.21 g/ml fraction in the postabsorptive or fed state compared to fasted animals, it could be postulated that the shift of apoA-IV into this fraction in gemfibrozil-treated rats is related to an accelerated clearance of chylomicrons. It is concluded that gemfibrozil largely prevents the accumulation of abnormal lipoproteins in this model of dyslipoproteinemia, and that apoE may play a critical role in this normalization process.

Mechanism of action of gemfibrozil on lipoprotein metabolism

Gemfibrozil is a potent lipid regulating drug whose major effects are to increase plasma high density lipoproteins (HDL) and to decrease plasma triglycerides (TG) in a wide variety of primary and secondary dyslipoproteinemias. Its mechanism of action is not clear. Six patients with primary familial endogenous hypertriglyceridemia with fasting chylomicronemia (type V lipoprotein phenotype) with concurrent subnormal HDL cholesterol levels (HDL deficiency) were treated initially by diet and once stabilized, were given gemfibrozil (1,200 mg/d). Each patient was admitted to the Clinical Research Center with metabolic kitchen facilities, for investigation of HDL and TG metabolism immediately before and after 8 wk of gemfibrozil treatment. Gemfibrozil significantly increased plasma HDL cholesterol, apolipoprotein (apo) AI, and apo AII by 36%, 29%, and 38% from base line, respectively. Plasma TG decreased by 54%. Kinetics of apo AI and apo AII metabolism were assessed by analysis of the specific radioactivity decay curves after injection of autologous HDL labeled with 125I. Gemfibrozil increased synthetic rates of apo AI and apo AII by 27% and 34%, respectively, without changing the fractional catabolic rates. Stimulation of apo AI and apo AII synthesis by gemfibrozil was associated with the appearance in plasma of smaller (and heavier) HDL particles as assessed by gradient gel electrophoresis and HDL composition. Postheparin extra-hepatic lipoprotein lipase activity increased significantly by 25% after gemfibrozil, and was associated with the appearance in plasma of smaller very low density lipoprotein particles whose apo CIII:CII ratio was decreased. These data suggest that gemfibrozil increases plasma HDL levels by stimulating their synthesis. Increased transport (turnover) of HDL induced by gemfibrozil may be significant in increasing tissue cholesterol removal in these patients.

3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors. 1. Structural modification of 5-substituted 3,5-dihydroxypentanoic acids and their lactone derivatives

A series of 5-substituted 3,5-dihydroxypentanoic acids and their derivatives have been prepared and tested for inhibition of HMG-CoA reductase in vitro. In general, unless a carboxylate anion can be formed and the hydroxy groups remain unsubstituted in an erythro relationship, inhibitory activity is greatly reduced. Furthermore, only one enantiomer of the ring-opened form of lactone 6a(+/-) possesses the activity displayed by the racemate. Insertion of a bridging unit other than ethyl or (E)-ethenyl between the 5-carbinol moiety and an appropriate lipophilic moiety (e.g., 2,4-dichlorophenyl) attenuates activity.

Effect of gemfibrozil on biliary lipid metabolism in normolipemic subjects

The mechanisms of the lipid-lowering agent gemfibrozil on biliary lipid metabolism were studied in eight normolipemic male volunteers. These measurements were performed before and after 3 months of administration. During administration of gemfibrozil, plasma cholesterol decreased by 19% (P less than 0.01) and triglycerides by 46% (P less than 0.01), and HDL cholesterol increased by 10% (P less than 0.01). The lithogenic index in gallbladder bile increased from 0.73 to 1.37 (P less than 0.05) and in hepatic bile from 0.86 to 1.42 (P less than 0.01). The increase in lithogenicity of gallbladder bile and hepatic bile was due to an increased biliary output of cholesterol from 47 to 70 mg/h (P less than 0.01) and a decreased output of bile acids from 943 to 694 mg/hr (P less than 0.01), whereas phospholipid output was not altered. The reduction in bile acid output was a result of a significant decrease in chenodeoxycholic acid secretion (r = 0.852; P less than 0.01). Cholic acid output was not affected by gemfibrozil. These results suggest that administration of gemfibrozil enhances the possible risk of gallstone formation like clofibrate.

Quantitative microscopy comparison of peroxisome proliferation by the lipid-regulating agent gemfibrozil in several species

Peroxisome proliferation, a well-documented subcellular reaction which follows the administration of hypolipidemic agents, has been well studied in rodents. However, quantitative studies of this phenomenon in other species of laboratory animals are not readily available even though these species are commonly used as predictors of tolerance or safety in humans. The quantitative stereologic studies reported here compared the effects of the new hypolipidemic agent gemfibrozil on hepatic peroxisomes of monkeys, dogs, hamsters and rats of both sexes under several treatment schedules. Gemfibrozil was administered to rats at 300 mg per kg per day for 1 year in the diet; to hamsters at 400 mg per kg per day for 2 weeks by diet admixture; to dogs at 300 mg per kg per day in gelatin capsules for 1 year; and to monkeys at 300 mg per kg day for 3 months by gavage. These dose levels were selected on the basis of tolerance from preliminary studies in each species. At the end of each experimental interval, liver samples were processed for quantitative microscopy. Peroxisomes from male rats were enlarged and the number of peroxisomes per cell were increased 7-fold over controls, resulting in a 20-fold increased peroxisome volume per cell. Statistically, significant increases also occurred in female rats and the difference between treated and controls was 3-fold for both number and volume of peroxisomes per cytoplasmic unit volume. In hamsters, peroxisomes were proliferated and were of significantly smaller size to the extent that the volume of cytoplasm occupied by peroxisomes was not significantly changed. In dogs, the number of peroxisomes per cell was increased and the volume fraction was significantly increased in females only. The number of peroxisomes in young monkeys did not change after treatment, and the peroxisome volume was decreased in males and increased in females. Aged monkeys had increased number of peroxisomes per hepatocyte with increased volume fraction. These results indicate significant differences in the magnitude and direction of peroxisome changes, reflecting species-dependent organelle response to hypolipidemic agents. The order of susceptibility of peroxisome proliferation in laboratory animals is dog less than monkey less than hamster less than rat.

Role of N-acetylglutamate and acetyl-CoA in the inhibition of ureagenesis by isovaleric acid in isolated rat hepatocytes

1 and 10 mmol/l isovalerate strongly inhibited urea synthesis in isolated rat hepatocytes incubated with 10 mmol/l alanine and 3 mmol/l ornithine. Isovalerate also markedly decreased N-acetylglutamate levels, and the decrease correlated with the inhibition of urea synthesis by isovalerate. This compound also lowered cellular levels of acetyl-CoA, a substrate of N-acetylglutamate synthase (EC 2.3.1.1). Isovalerate did not significantly affect the cellular levels of ATP and had no direct effect on N-acetylglutamate synthase activity. These results suggest that the inhibition of urea synthesis by isovalerate is due to decrease in N-acetylglutamate levels.

Some comparative effects of gemfibrozil, clofibrate, bezafibrate, cholestyramine and compactin on sterol metabolism in rats

Liver cholesterogenesis in rats was measured by giving [l-14C]octanoate i.p.; 1 h later digitonin-precipitable sterols were isolated and counted. In rats fed normal chow and given 7 daily p.o. doses of compounds and then fasted, at 20 h after the last dose, clofibrate or bezafibrate had no effect at lower doses or inhibited incorporation at higher doses, while compactin or gemfibrozil caused increases; cholestyramine added to the diet also caused marked increases. When rats were fed chow containing 0.1% cholesterol and 5.5% peanut oil, again at 20 h following the last of 7 daily doses, gemfibrozil caused increases of incorporation which diminished at higher levels of dosage, while clofibrate caused only inhibition. A single dose of gemfibrozil caused inhibition at 3 h postdose followed by increases over control at 36 and 48 h; a single dose of compactin caused inhibition at 3 h but not subsequent increase, and a single dose of clofibrate had no effect over the entire period. In rats fed chow containing 1.5% cholesterol and 5.5% peanut oil, gemfibrozil given orally or cholestyramine in the diet prevented the diet-induced decreases of plasma HDL cholesterol and increases of liver cholesterol content, while bezafibrate treatment did not have those effects. The effects of cholestyramine rapidly disappeared when it was withdrawn from the diet, while the effects of gemfibrozil persisted after dosage was stopped. These results suggest that some of the actions of gemfibrozil on rat sterol metabolism are quantitatively different from those of the other agents tested.

Influence of gemfibrozil on high-density lipoproteins

In animal studies, gemfibrozil markedly elevates high-density lipoprotein (HDL) cholesterol levels. In humans with primary hyperlipoproteinemia and lipoprotein phenotypes IIA, IIB and IV, gemfibrozil, 1,200 mg/day, was associated with a 25%, 20% and 17% increase in HDL cholesterol, respectively. Gemfibrozil also substantially increased the ratio of HDL to total cholesterol, reflecting both an increase in HDL cholesterol and a decrease in very low density lipoprotein cholesterol and low-density lipoprotein cholesterol. Compared with a placebo in subjects with types IIA, IIB and IV lipoprotein phenotypes, therapy with gemfibrozil led to an increase of 33%, 34% and 23%, respectively, in the ratio of HDL cholesterol to total cholesterol. With gemfibrozil therapy, about 80% of subjects with hypertriglyceridemia had a reduction in triglycerides of 35% or a return to normal levels; 50% of subjects with hypercholesterolemia had a cholesterol reduction of 20% or a return to normal levels.

In vitro and in vivo effects on brain GABA metabolism of (S)-4-amino-5-fluoropentanoic acid, a mechanism-based inactivator of gamma-aminobutyric acid transaminase

The effects of intraperitoneal administration of (S)-4-amino-5-fluoropentanoic acid, a mechanism-based covalent inactivator of gamma-aminobutyric acid transaminase (GABA-T), on whole brain GABA metabolism in mice were investigated. A dose-dependent and time-dependent irreversible inactivation of GABA-T was observed with a concomitant increase in whole brain GABA levels. The compound exhibited no in vitro nor in vivo time-dependent inhibition of glutamate decarboxylase (GAD), alanine transaminase, or aspartate transaminase (Asp-T). It was, however, a potent competitive reversible inhibitor of GAD and a weak competitive inhibitor of Asp-T. The chloro analogue, (S)-4-amino-5-chloropentanoic acid, was ineffective.

A steady-state random-order mechanism for the oxidative deamination of norvaline by glutamate dehydrogenase

The kinetic mechanism of glutamate dehydrogenase with the monocarboxylic substrate norvaline was examined by using initial-rate steady-state kinetics and inhibition kinetics. To a first approximation the reaction mechanism can be described as a rapid-equilibrium random-order one. Binding synergism between the monocarboxylic substrate and coenzyme is not observed. Dissociation constants for NAD+ and 2-oxoglutarate calculated from the kinetic data assuming a rapid-equilibrium random-order model are in good agreement with independently obtained estimates. Lineweaver-Burk plots with varied norvaline concentration are not strictly linear, and it is concluded that a steady-state random-order model more accurately reflects the observed kinetics with norvaline as substrate.