Inhibition of hepatocyte proteolysis and lactate gluconeogenesis by chloroquine

Chloroquine (50 μm) is rapidly taken up by isolated hepatocytes in a temperature-dependent manner. It inhibits glucose synthesis from lactate, but not from pyruvate or dihydroxyacetone. The inhibition is reversed by lysine or ammonia but not by oleate or carnitine. Ammonia inhibits chloroquine uptake by the hepatocytes but lysine does not. Chloroquine also inhibits urea synthesis, the release of ninhydrin-reacting substances, the accumulation of amino acids, and the lactate-dependent accumulation of glutamate. Ethanol oxidation in the presence of lactate is also inhibited, and this too is reversed by lysine. Chloroquine increases the redox state of the cytosolic compartment, as evidenced by lactate-to-pyruvate ratios, of hepatocytes prepared from both 48-h fasted and meal-fed rats. The above findings are consistent with chloroquine entering the lysosomes of the hepatocytes and inhibiting proteolysis by raising the lysosomal pH. Isolated hepatocytes are deficient in amino acids and, chloroquine inhibition of proteolysis prevents replenishment of the amino acid pools. Thus, chloroquine prevents reconstitution of the malate-aspartate shuttle required for the movement of reducing equivalents into the mitochondrion during lactate gluconeogenesis, ethanol oxidation, and glycolysis. The metabolic competency of freshly isolated hepatocytes, therefore, depends on the replenishment of amino acid pools by lysosomal breakdown of endogenous protein. Furthermore, chloroquine uptake may be an index of lysosomal function with isolated hepatocytes.     

Inhibition of hepatic gluconeogenesis and lipogenesis by benzoic acid,p-tert.-butylbenzoic acid,and a structurally related hypolipidemic agent SC-33459

Benzoic acid, p-tert.-butylbenzoic acid, and a structurally related hypolipidemic agent SC-33459 were found to inhibit glucose synthesis by hepatocytes isolated from 48-h fasted rats as well as fatty acid synthesis by hepatocytes isolated from meal-fed rats. Glucose synthesis was less sensitive than fatty acid synthesis. Benzoic acid was the least effective inhibitor of both processes; SC-33459 and p-tert.-butylbenzoic acid were very potent inhibitors with similar efficacy. Glycine prevented the inhibition of fatty acid synthesis caused by benzoic acid, but had no effect on that caused by p-tert.-butylbenzoic acid. Octanoate opposed the inhibitory effects of both benzoic acid and p-tert.-butylbenzoic acid. Oxidation of [1-¹⁴C]oleate to ketone bodies and acid-soluble radioactive products was inhibited by both p-tert.-butylbenzoic acid and SC-33459. Preincubation of hepatocytes with SC-33459 was required for the latter effect, suggesting catabolism of this compound may be involved. SC-33459 is a p-tert.-butylphenyl derivative which should be readily converted to p-tert.-butylbenzoic acid by β oxidation. Both p-tert.-butylbenzoic acid and SC-33459 decreased citrate levels dramatically. All three compounds reduced CoA and acetyl-CoA levels and increased medium-chain acyl-CoA ester levels. p-tert.-Butylbenzoic acid and SC-33459 also increased long-chain acyl-CoA ester levels. The increase in medium-chain acyl-CoA levels presumably reflects benzoyl-CoA formation from benzoic acid and p-tert.-butylbenzoyl-CoA formation from p-tert.-butylbenzoic acid and SC-33459. Inhibition of glucose and fatty acid synthesis by these compounds may be due to effects on specific enzymes or to CoA sequestration.     

Mechanism responsible for the hypoglycemic actions of dichloroacetate and 2-chloropropionate

Dichloroacetate, an activator of the pyruvate dehydrogenase complex, is known to lower blood glucose, lactate, pyruvate, and alanine when given to diabetic and 24 h fasted rats. Under certain conditions, especially when pyruvate carboxylase is made rate limiting for want of bicarbonate, dichloroacetate effectively inhibits glucose synthesis from lactate by isolated hepatocytes. 2-Chloropropionate also activates the pyruvate dehydrogenase complex, lowers blood glucose, lactate, and pyruvate in 24 h fasted rats, but stimulates gluconeogenesis from lactate or alanine by isolated hepatocytes. Dichloroacetate is catabolized to glyoxylate and thence to oxalate by liver cells, whereas 2-chloropropionate cannot be catabolized to these products. Glyoxylate and oxalate are potent inhibitors of glucose synthesis from lactate, pyruvate, and alanine, but not from dihydroxyacetone. Inhibition is much more pronounced in a bicarbonate-deficient medium, in which pyruvate carboxylase is probably rate limiting for gluconeogenesis. It seems likely, therefore, that the inhibition of lactate gluconeogenesis by dichloroacetate is actually caused by oxalate, which inhibits pyruvate carboxylation. Nevertheless, the major effect of dichloroacetate, and probably the sole effect of 2-chloropropionate, on blood glucose concentration is to limit substrate availability in the blood for hepatic gluconeogenesis. Since oxalic acid stone formation and renal dysfunction may prove to be side effects of any therapeutic application of dichloroacetate, we suggest that further studies on the treatment of hyperglycemia and lactic acidosis with pyruvate dehydrogenase activators be carried out with 2-chloropropionate rather than dichloroacetate.     

Studies on the regulation of leucine catabolism: Mechanism responsible for oxidizable substrate inhibition and dichloroacetate stimulation of leucine oxidation by the heart

In the absence of any other oxidizable substrate, the perfused rat heart oxidizes [1-¹⁴C]leucine to ¹⁴CO₂ at a rapid rate and releases only small amounts of α-[1-¹⁴C]ketoisocaproate into the perfusion medium. The branched-chain α-keto acid dehydrogenase complex, assayed in extracts of mitochondria prepared from such perfused hearts, is very active. Under such perfusion conditions, dichloroacetate has almost no effect on [1-¹⁴C]leucine oxidation, α-[1-¹⁴C]ketoisocaproate release, or branched-chain α-keto acid dehydrogenase activity. Perfusion of the heart with some other oxidizable substrate, e.g., glucose, pyruvate, ketone bodies, or palmitate, results in an inhibition of [1-¹⁴C]leucine oxidation to ¹⁴CO₂ and the release of large amounts of α-[1-¹⁴C]ketoisocaproate into the perfusion medium. The branched-chain α-keto acid dehydrogenase complex, assayed in extracts of mitochondria prepared from such hearts, is almost completely inactivated. The enzyme can be reactivated, however, by incubating the mitochondria at 30 °C without an oxidizable substrate. With hearts perfused with glucose or ketone bodies, dichloroacetate greatly increases [1-¹⁴C]leucine oxidation, decreases α-[1-¹⁴C]ketoisocaproate release into the perfusion medium, and activates the branched-chain α-keto acid dehydrogenase complex. Pyruvate may block dichloroacetate uptake because dichloroacetate neither stimulates [1-¹⁴C]leucine oxidation nor activates the branched-chain α-keto acid dehydrogenase complex of pyruvate-perfused hearts. It is suggested that leucine oxidation by heart is regulated by the activity of the branched-chain α-keto acid dehydrogenase complex which is subject to interconversion between active and inactive forms. Oxidizable substrates establish conditions which inactivate the enzyme. Dichloroacetate, known to activate the pyruvate dehydrogenase complex by inhibition of pyruvate dehydrogenase kinase, causes activation of the branched-chain α-keto acid dehydrogenase complex, suggesting the existence of a kinase for this complex.     

Inhibition of tropoelastin secretion by incorporation of DL-3,4-dehydroproline

Cells isolated from embryonic chick aorta were incubated in suspension culture with labeled amino acids and proline analogs. Incorporation of 4-cis-hydroxy-l-proline inhibited the secretion of labeled procollagen but not tropoelastin, while incorporation of dl-3,4-dehydroproline inhibited the secretion of both proteins and caused them to accumulate intracellularly. Protein synthesis did not appear to be significantly diminished during the 2-h incubation period. Incorporation of dl-3,4-dehydroproline may alter the conformation of tropoelastin leading to abnormal intracellular processing and a decreased rate of secretion.     

Role of fructose 2,6-bisphosphate in the regulation of glycolysis and gluconeogenesis in chicken liver

Glucagon and dibutyryl cyclic AMP inhibited glucose utilization and lowered fructose 2,6-bisphosphate levels of hepatocytes prepared from fed chickens. Partially purified preparations of chicken liver 6-phosphofructo-1-kinase and fructose 1,6-bisphosphatase were activated and inhibited by fructose 2,6-bisphosphate, respectively. The sensitivities of these enzymes and the changes observed in fructose 2,6-bisphosphate levels are consistent with an important role for this allosteric effector in hormonal regulation of carbohydrate metabolism in chicken liver. In contrast, oleate inhibition of glucose utilization by chicken hepatocytes occurred without change in fructose, 2,6-bisphosphate levels. Likewise, pyruvate inhibition of lactate gluconeogenesis in chicken hepatocytes cannot be explained by changes in fructose 2,6-bisphosphate levels. Exogenous glucose caused a marked increase in fructose 2,6-bisphosphate content of hepatocytes from fasted but not fed birds. Both glucagon and lactate prevented this glucose effect. Fasted chicken hepatocytes responded to lower glucose concentrations than fasted rat hepatocytes, perhaps reflecting the species difference in hexokinase isozymes.     

Effect of dichloroacetate and glucagon on the incorporation of labeled substrates into glucose and on pyruvate dehydrogenase in hepatocytes from fed and starved rats

Dichloroacetate (2 mm) stimulated the conversion of [1-¹⁴C]lactate to glucose in hepatocytes from fed rats. In hepatocytes from rats starved for 24 h, where the mitochondrial $\text{NADH}\text{NAD}{}^{\mathrm{+}}$ ratio is elevated, dichloroacetate inhibited the conversion of [1-¹⁴C]lactate to glucose. Dichloroacetate stimulated ¹⁴CO₂ production from [1-¹⁴C]lactate in both cases. It also completely activated pyruvate dehydrogenase and increased flux through the enzyme. The addition of β-hydroxybutyrate, which elevates the intramitochondrial $\text{NADH}\text{NAD}{}^{\mathrm{+}}$ ratio, changed the metabolism of [1-¹⁴C]lactate in hepatocytes from fed rats to a pattern similar to that seen in hepatocytes from starved rats. Thus, the effect of dichloroacetate on labeled glucose synthesis from lactate appears to depend on the mitochondrial oxidation-reduction state of the hepatocytes. Glucagon (10 nm) stimulated labeled glucose synthesis from lactate or alanine in hepatocytes from both fed and starved rats and in the absence or presence of dichloroacetate. The hormone had no effect on pyruvate dehydrogenase activity whether or not the enzyme had been activated by dichloroacetate. Thus, it appears that pyruvate dehydrogenase is not involved in the hormonal regulation of gluconeogenesis. Glucagon inhibited the incorporation of 10 mm [1-¹⁴C]pyruvate into glucose in hepatocytes from starved rats. This inhibition has been attributed to an inhibition of pyruvate dehydrogenase by the hormone (Zahlten et al., 1973, Proc. Nat. Acad. Sci. USA70, 3213–3218). However, dichloroacetate did not prevent the inhibition of glucose synthesis. Nor did glucagon alter the activity of pyruvate dehydrogenase in homogenates of cells that had been incubated with 10 mm pyruvate in the absence or presence of dichloroacetate. Thus, the inhibition by glucagon of pyruvate gluconeogenesis does not appear to be due to an inhibition of pyruvate dehydrogenase.     

Studies on the relationship between glycolysis, lipogenesis, gluconeogenesis, and pyruvate kinase activity of rat and chicken hepatocytes.

Chicken hepatocytes synthesize glucose and fatty acids at rates which are faster than rat hepatocytes. The former also consume exogenous lactate and pyruvate at a much faster rate and, in contrast to rat hepatocytes, do not accumulate large quantities of lactate and pyruvate by aerobic glycolysis. α-Cyano-4-hydroxycinnamate, an inhibitor of pyruvate transport, causes lactate and pyruvate accumulation by chicken hepatocytes. Glucagon and N⁶,O²′-dibutyryl adenosine 3′,5′-monophosphate (dibutyryl cyclic AMP) convert pyruvate kinase (EC 2.7.1.40) of rat hepatocytes to a less active form. This effect explains, in part, inhibition of glycolysis, inhibition of lipogenesis, stimulation of gluconeogenesis, and inhibition of the transfer of reducing equivalents from the mitochondrial compartment to the cytoplasmic compartment by these compounds. In contrast, pyruvate kinase of chicken hepatocytes is refractory to inhibition by glucagon or dibutyryl cyclic AMP. Rat liver is known to have predominantly the type L isozyme of pyruvate kinase and chicken liver predominantly the type K. Thus, only the type L isozyme appears subject to interconversion between active and inactive forms by a cyclic AMP-dependent, phosphorylation-dephos-phorylation mechanism. This explains why the transfer of reducing equivalents from the mitochondrial compartment to the cytoplasmic compartment of chicken hepatocytes is insensitive to cyclic AMP. However, glucagon and dibutyryl cyclic AMP inhibit net glucose utilization, inhibit fatty acid synthesis, inhibit lactate and pyruvate accumulation in the presence of α-cyano-4-hydroxycinnamate, and stimulate gluconeogenesis from lactate and dihydroxyacetone by chicken hepatocytes. Thus, a site of action of cyclic AMP distinct from pyruvate kinase must exist in the glycolytic-gluconeogenic pathway of chicken liver.     

Influence of valproic acid on hepatic carbohydrate and lipid metabolism

Valproic acid (dipropylacetic acid), an antiepileptic agent known to be hepatotoxic in some patients, caused inhibition of lactate gluconeogenesis, fatty acid oxidation, and fatty acid synthesis by isolated hepatocytes. The latter process was the most sensitive to valproic acid, 50% inhibition occurring at ca. 125 microM with cells from meal-fed female rats. The medium-chain acyl-CoA ester fraction was increased whereas coenzyme A (CoA), acetyl-CoA, and the long chain acyl-CoA fractions were decreased by valproic acid. The increase in the medium chain acyl-CoA fraction was found by high-pressure liquid chromatography to be due to the accumulation of valproyl-CoA plus an apparent CoAester metabolite of valproyl-CoA. Salicylate inhibited valproyl-CoA formation and partially protected against valproic acid inhibition of hepatic metabolic processes. Octanoate had a similar protective effect, suggesting that activation of valproic acid in the mitosol is required for its inhibitory effects. It is proposed that either valproyl-CoA itself or the sequestration of CoA causes inhibition of metabolic processes. Valproyl-CoA formation also appears to explain valproic acid inhibition of gluconeogenesis by isolated kidney tubules. No evidence was found for the accumulation of valproyl-CoA in brain tissue, suggesting that the effects of valproic acid in the central nervous system are independent of the formation of this metabolite.     

Inhibition of in vitro biosynthesis of n-acetylneuraminic acid by n-acyl- and n-alkyl-2-amino-2-deoxyhexoses

The biosynthesis of N-acetylneuraminic acid is markedly inhibited by 2-deoxy-2-propionamido-d-glucose (GlcNProp) and to a much lesser extent by 2-deoxy-2-propionamido-d-mannose (ManNProp), but not by 2-deoxy-2-propionamido-d-galactose and N-methylated derivatives of 2-amino-2-deoxy-d-glucose. 2-Deoxy-2-trimethylamino-d-glucose is a weak inhibitor of 2-acetamido-2-deoxy-d-mannose metabolism. When incubated in a cell-free system from rat liver, GlcNProp gives the 6-phosphate, which is converted into N-propionylneuraminic acid. Evidence is presented which shows that it is the metabolites GlcNProp-6-P and ManNProp-6-P which are the competitive inhibitors, and not GlcNProp itself.     

Modification of electroplax excitability by veratridine

Veratridine influences membrane-potential changes arising both from the action potential and from the application of external cholinergic agonists in the isolated monocellular electroplax preparation. The action potential shows a long depolarizing after-potential in the presence of veratridine. The effects of various pharmacological agents and of external ion changes on this after-potential are similar to those reported for other nerve and muscle fibers and are consistent with the view that veratridine acts chiefly to increase the Na⁺ conductance.Membrane depolarizations by cholinergic agonists are inhibited by veratridine at pH 7 but strikingly amplified at pH 9. The former effect appears to involve interaction with the cholinergic receptor at the surface of the membrane, while the latter potentiation parallels the increase in the spike after-potential at pH 9 and presumably arises from a Na⁺ conductance increase.Veratridine appears to interact with the component involved in the Na⁺ conductance in the interior membrane phase. The possible localization of this component in both the conducting and synaptic membrane is discussed.     

Induction of male-typical aggression by androgens but not by estrogens in adult female mice

Ovariectomized adult CF-1 female mice were implanted with silastic capsules containing either testosterone (T), dihydrotestosterone (DHT), methyltrienolone (R1881), estradiol (E2), diethylstilbestrol (DES), or oil vehicle and were tested for aggressive behavior. The androgenic treatments (T, DHT, R1881) were highly effective in promoting male-like aggression while the estrogens (DES, E2) were completely ineffective. Subsequent receptor-binding studies confirmed assumptions about the specificity of DES, DHT, and R1881 binding to estrogen and androgen receptors in mouse hypothalamus.     

Stimulation of reduced lysozyme regeneration by transferrin and lactoferrin

Human serum transferrin, bovine lactoferrin, and hen conalbumin were investigated with respect to the ability of the bound metal to catalyze thiol oxidation. All three proteins were able to stimulate the oxidation of thiols in both reduced lysozyme and reduced glutathione. The efficiency of the metal in catalyzing thiol oxidation was not decreased by binding to transferrin, suggesting that transferrin-bound metals are completely available to both low and high molecular weight thiols. A 5 × 10^?7m concentration of transferrin isolated from serum was able to catalyze the formation of 70% of the theoretical lysozyme activity from reduced inactive lysozyme by 60 min. Increased rates of lysozyme activity formation were observed with copper-saturated transferrin. Decreased lysozyme regeneration rates were observed with the iron-saturated molecule compared to native transferrin. The results presented suggest that metalloproteins may aid in the maintenance of the steady-state cellular concentrations of low molecular weight disulfide by catalyzing the autooxidation of thiols.     

Inactivation of staphylococcal enterotoxin A by chemical modification

(3-¹⁴C)-serine was fed through cut ends of 10-day-old shoots of normal (Ganga-2) and opaque (opaque-2) maize ($\text{Zea}\text{mays}$ L.) and allowed to be metabolized in light for 24 hours. Subsequent methanolic extraction, radiochromatographic separation and radioautographic analysis showed that 10.4 and 10.3 percent of the absorbed ¹⁴C-serine activity was incorporated into L-tryptophan by the shoot tissues of the normal and opaque maize respectively.By coupling extraction of the enzyme with ammonium sulfate precipitation (75% saturation) it was possible to show a serine-dependent indole utilization by the enzyme preparations from coleoptiles (4-day-old), kernels (18 and 28 days after anthesis) and first nodal callus tissues (one-month-old) of the two corn varieties. Furthermore, the indole disappearance from reaction mixture occurred with a concomitant transfer of (3-¹⁴C)-serine appearance into tryptophan.     

In situ activation of murine macrophages by liposomes containing lymphokines

Murine alveolar and peritoneal macrophages harvested after injection of lymphokines encapsulated within multilamellar phospholipid vesicles (liposomes) were tumoricidal in vitro. The state and degree of activation depended on the route of liposome administration. Activation of peritoneal macrophages was achieved by intraperitoneal injection of liposomes and alveolar macrophages were activated by injecting liposomes intravenously but not intraperitoneally. The in vivo rendering of macrophages with tumoricidal properties might be useful toward destruction of tumor cells in vivo.     

Ultrasonic degradation of schizophyllan, an antitumor polysaccharide produced by Schizophyllum commune Fries

Schizophyllan, a water-soluble beta-D-glucan elaborated by Schizophyllum commune Fries, was partially depolymerized by ultrasonic irradiation to a low-molecular-weight polysaccharide, designated "sonic-degraded schizophyllan". Both native and degraded polysaccharides exhibited essentially the same antitumor activities against Sarcoma-180 ascites. Both glucans are comprised solely of D-glucose residues and have a main chain of (1 leads to 3)-beta-D-glucopyranosyl residues, one out of three glucose residues being attached as single, (1 leads to 6)-beta-D-glucopyranosyl groups. Although both glucans have similar structural features, significant differences are observed in such physical properties as molecular weight and intrinsic viscosity. End-group analysis by using radioisotope-labeled glucans suggests that ultrasonic degradation occurs mainly by cleavage of glycosidic bonds of the main chain of schizophyllan. The molecular weights of the native and sonic-degraded schizophyllan were shown to be 75% of those of corresponding, original schizophyllan preparations, suggesting that there is no anomalous linkage sensitive to periodate oxidation, and ultrasonic irradiation may cause random hydrolysis of (1 leads to 3)-beta-D-glucosidic linkages in the main chain.     

Direct augmentation of cytolytic activity of tumor-derived macrophages and macrophage cell lines by muramyl dipeptide.

Macrophages derived from MSV-induced tumors and several macrophage cell lines showed direct cytolytic activity in an 18-hr ⁵¹Cr release assay against tumor target cells. The cytolytic activity of these macrophages was augmented by the addition of muramyl dipeptide (MDP) to the cytotoxicity assay, an effect similar to that observed with bacterial lipopolysaccharide. The stimulation of macrophage-mediated cytotoxicity by MDP appeared to be under genetic control since macrophages from BALB/c mice were augmented with MDP while those from C57BL/6 animals were not. MDP appears to act directly on the macrophage without the participation of any other cell type, since MDP increased the activity of the macrophage cell lines.     

Stimulation of human granulocyte elastase by platelet factor 4 and heparin

Highly purified platelet factor 4 (PF₄) was found to be a potent stimulator of human granulocyte elastase activity against native elastin and solubilized α elastin. Heparin neutralized this stimulation of elastolysis by PF₄, but independently stimulated granulocyte elastase activity. Chondroitin sulfate, a constituent of the PF₄ carrier molecule, also stimulated granulocyte elastase activity. The stimulation of granulocyte elastase by PF₄ occurs at known serum concentrations of PF₄.