B-lymphocyte mitogenicity and adjuvanticity of an ornithine-containing lipid or a serine-containing lipid

An ornithine-containing lipid (Orn-L) or a serine-containing lipid (Ser-L) from Flavobacterium meningosepticum exhibited strong mitogenicity for the splenocytes from both LPS-responder C3H/HeSlc and LPS-low-responder C3H/HeJ mice. The potency of the lipoamino acids was the same as that of LPS for responder mice. The lipoamino acids were B-lymphocyte mitogens. Furthermore, Orn-L or Ser-L exhibited strong adjuvanticity. Compared with the adjuvanticity of LPS, the activity of Orn-L was rather high. Based on these data, together with the previously reported data of macrophage activation, we propose that the lipoamino acids are non-toxic, potent immunoactivators.

Coronary vasodilatation induced by endotoxin in the rabbit isolated perfused heart is nitric oxide-dependent and inhibited by dexamethasone

The coronary vasoconstriction induced by the thromboxane mimetic U46619 (9, 11 dideoxy methanoepoxy 9 alpha, 11 alpha prostaglandin F2 alpha, 3-30 nM) was significantly attenuated in hearts obtained from rabbits treated with endotoxin (lipopolysaccharide, LPS, 200 micrograms kg-1, i.v.) 4 h before isolation of the heart. Under these conditions the vasoconstriction induced by two inhibitors of nitric oxide (NO) synthase, NG-monomethyl-L-arginine (L-NMMA) and N-iminoethyl-L-ornithine (L-NIO) (1-100 microM for each) was significantly enhanced when compared to that induced in hearts from control animals. Both the decreased response to U46619 and the increased response to inhibitors of NO synthase were significantly attenuated by administration of dexamethasone (4 mg kg-1, i.v.) 90 min before treatment with LPS. These data are consistent with the induction, by LPS, of an NO synthase, and the inhibition of this induction by dexamethasone. The enhanced NO synthesis contributes to the haemodynamic changes known to occur in endotoxin shock.

Ornithine alpha-ketoglutarate in nutritional support

Ornithine alpha-ketoglutarate (OKG) is a salt formed of two molecules of ornithine and one molecule of alpha-ketoglutarate. OKG has been successfully used by the enteral and parenteral route in burn, traumatized, and surgical patients and in chronically malnourished subjects. According to the metabolic situation, OKG treatment decreases muscle protein catabolism and/or increases synthesis. In addition, OKG promotes wound healing. The mechanism of action of OKG is not fully understood, but the secretion of anabolic hormones (insulin, human growth hormone) and the synthesis of metabolites (glutamine, polyamines, arginine, ketoacids) may be involved.

Action of enterally administered ornithine alpha-ketoglutarate on protein breakdown in skeletal muscle and liver of the burned rat

Several studies concerning burn patients have shown that supplementation of enteral nutrition with ornithine alpha-ketoglutarate (OKG) favorably modifies protein metabolism. Therefore, the effect of OKG administration on muscular and hepatic protein catabolism was evaluated in burned rats. Four groups of six rats were used. Two groups were scalded by immersion of the dorsum in water at 90 degrees C for 10 seconds and then starved for 24 hours. Controlled enteral nutrition was then administered in three boluses daily (Osmolite, 210 kcal/kg/d, 1.2 g N/kg/d); one group was supplemented with OKG (5 g/kg/d, ie, 0.68 g N/kg/d), while the other group received an equivalent amount of nitrogen in the form of glycine. One group of healthy control rats received Osmolite supplemented with glycine and the last group was fed ad libitum. The animals were killed after 2 days of nutrition. Protein catabolism was assessed in vitro by measuring the amount of valine (liver catabolism) and phenylalanine (muscle catabolism) released into the incubation medium of isolated tissues. Tissular and serum glutamine were also assayed. Burn injury induced muscle hypercatabolism without affecting hepatic catabolism. The administration of OKG limited both muscle weight loss and muscle protein hypercatabolism and significantly improved the muscle glutamine pool. These results demonstrate the nitrogen-sparing effect of OKG in muscle in hypercatabolic states.

Protection of mice from lethal endotoxemia by use of an ornithine-containing lipid or a serine-containing lipid

The effects of an ornithine-containing lipid [alpha-N-(3-acyloxyacyl)-ornithine (Orn-L)] or a serine-containing lipid [alpha-N-(3-acyloxyacyl)-serine (Ser-L)] from Flavobacterium meningosepticum on lethal endotoxemia in mice were examined. When 500 micrograms of Orn-L was intravenously administered 1 h before intravenous administration of a lethal dose of endotoxin, none of the mice died. The protective effect of Ser-L was weaker than that of Orn-L. Light and electron microscopic studies demonstrated that necrosis of hepatocytes caused by endotoxin was prevented by pretreatment with Orn-L. Furthermore, Kupffer cells were activated morphologically 1 h after the administration of Orn-L or Ser-L, and the liposomes of the lipoamino acids were incorporated into phagolysosomes in activated Kupffer cells. The activity of tumor necrosis factor in sera of endotoxin-treated mice was decreased markedly by pretreatment of mice with Orn-L. In vitro, the lipoamino acids suppressed endotoxin-induced tumor necrosis factor generation but did not suppress tumor necrosis factor generation induced by zymosan and whole cells of Staphylococcus aureus. These results suggested that Orn-L and Ser-L can be used as specific blocking agents against endotoxin. The blocking mechanism may be antagonistic, because of the structural similarities between the lipoamino acids and endotoxin lipid A.

Early developmental profile of ornithine decarboxylase in the frog, Microhyla ornata and its regulation by polyamines

Ornithine decarboxylase (ODC) activity and polyamine levels were measured during early development of the frog, Microhyla ornata. ODC activity was found to be high and it showed three major peaks during the first 60 hr of development. Putrescine and spermidine levels increased gradually during the above period with little change in spermine. Treatment of developing embryos with exogenous putrescine and spermidine prevented the normal increase in ODC activity. Spermine did not have any significant effect. Addition of ornithine also prevented the increase in ODC activity. Experiment using exogenous ornithine and alpha-methylornithine revealed that formation of putrescine and/or spermidine from ornithine is necessary for the suppression of ODC to occur. Suppression of ODC takes place even if conversion of putrescine to spermidine is blocked, indicating that putrescine, independent of its conversion to spermidine, also plays a role in ODC regulation.

Development and mechanism of a specific supersensitivity to nitrovasodilators after inhibition of vascular nitric oxide synthesis in vivo

The mechanism of the increased sensitivity to nitrovasodilators after removal of endothelial nitric oxide (NO) was investigated in vitro and in vivo. The vasoconstrictor potency of phenylephrine and the force of contraction of rat isolated aortic rings were significantly enhanced after endothelium removal or treatment with inhibitors of endothelial NO synthase. Furthermore, these procedures led to a significant decrease in the basal levels of cGMP in the vascular rings. Moreover, the potency of glyceryl trinitrate (n3Gro) and sodium nitroprusside (SNP) as relaxing agents and the ability of SNP to induce increases in cGMP in aortic rings were significantly enhanced in those rings denuded of endothelium or treated with the inhibitors. These procedures did not affect the vasodilator actions of isoprenaline or 8-bromo-cGMP. In the anesthetized rat, treatment with the inhibitors enhanced significantly the hypotensive responses to n3Gro without affecting those to isoprenaline. These data indicate that the removal of the basal NO-mediated vasodilator tone in the cardiovascular system leads, at the level of the soluble guanylate cyclase, to a specific supersensitivity to nitrovasodilators in vivo. The existence of such a phenomenon has important implications for understanding the local physiological control of blood flow, its pathological disturbances, and the mechanism of action of nitrovasodilators.

Synthesis and siderophore activity of albomycin-like peptides derived from N5-acetyl-N5-hydroxy-L-ornithine

N5-Acetyl-N5-hydroxy-L-ornithine (1), the key constituent of several microbial siderophores, has been synthesized in 23% yield overall from N-Cbz-L-glutamic acid 1-tert-butyl ester (6) derived from L-glutamic acid. Reduction of 6 to 7 and treatment with N-[(trichloroethoxy)carbonyl]-O-benzylhydroxylamine (8), and diethyl azodicarboxylate and triphenylphosphine followed by deprotection produced the protected N5-acetyl-N5-hydroxy-L-ornithine derivatives 11 and 12 in large quantities (10-20 g). Following alpha-amino and alpha-carboxyl deprotections of 11 and 12, EEDQ [2-ethoxy-N-(ethoxycarbonyl)-1,2-dihydroquinoline] mediated peptide coupling and final deprotection provided amino acid 1 and six albomycin-like peptides (20, 23, 25, 28, 35, and 36). The growth-promoting ability of each was evaluated with the siderophore biosynthesis mutant Shigella flexneri SA240 (SA 100 iucD:Tn5). These results indicate that substantial modification of the framework of peptide-based siderophores can be tolerated by microbial iron-transport systems.

Tumor cytokinetic effects of acute starvation versus polyamine depletion in tumor-bearing mice

Previous investigations in our laboratory have demonstrated that both acute host starvation and polyamine depletion by means of the irreversible ODC-inhibitor (ODC = ornithine-decarboxylase) fluoro-methylornithine (DFMO) lead to pronounced growth retardation of rapidly proliferating tumors. The aim of this investigation was to elucidate how these different interventions affect cell kinetics and cell cycle phases in vivo. Adult nongrowing mice (C57Bl/J) bearing a poorly differentiated rapidly growing methylcholanthrene induced sarcoma were used. Combined measurements of bromodeoxyuridine incorporation into DNA and flow cytometric techniques were used. Starvation and DFMO treatment resulted in a prolonged cell cycle transit compared to freely fed animals. Tumor cells from DFMO-treated mice demonstrated an increased time for DNA synthesis and a relatively larger accumulation of cells in the G2M phase, whereas tumor cells from starved animals were accumulated in the G0G1 phase. The fractional cell loss of tumor cell during proliferation was calculated to be around 18% higher in DFMO-treated animals compared to starved and freely fed tumor-bearing mice. This study demonstrates that different mechanisms are involved in tumor growth suppression from substrate deficiency (starvation) and from inhibition of polyamine synthesis.

Identification of N-iminoethyl-L-ornithine as an irreversible inhibitor of nitric oxide synthase in phagocytic cells

1. The synthesis of nitric oxide (NO) from L-arginine by rat peritoneal neutrophils (PMN) and the murine macrophage cell-line J774 and the inhibition of this synthesis by N-iminoethyl-L-ornithine (L-NIO), NG-monomethyl-L-arginine (L-NMMA), NG-nitro-L-arginine (L-NNA) and its methyl ester (L-NAME) were investigated. 2. L-NIO was the most potent inhibitor in both types of cells while L-NMMA was less active. L-NNA and L-NAME had no significant effect in PMN and L-NNA produced only approximately 40% inhibition of the generation of NO in the J774 cells at the highest concentration tested (300 microM). 3. The inhibitory effect of L-NIO was rapid in onset, requiring 10 min pre-incubation to achieve its full inhibitory activity, while the other compounds required 20-60 min pre-incubation to achieve their full effect. 4. The inhibitory effect of L-NIO (10 microM) on intact cells could not be reversed by L-arginine (300 microM) but could be prevented by concomitant incubation with this compound (300 microM), while the effect of the other inhibitors could be reversed by a 3-5 fold molar excess of L-arginine. 5. The NO synthase from both PMN and J774 cells was cytosolic and NADPH- but not Ca2(+)-dependent, with Km values for L-arginine of 3.3 +/- 0.8 and 4.2 +/- 1.1 microM respectively. 6. L-NIO was the most potent inhibitor of the neutrophil and J774 enzymes with IC50 values of 0.8 +/- 0.1 and 3 +/- 0.5 microM respectively. Furthermore, the effect of L-NIO was irreversible. The other three compounds were less potent, reversible inhibitors. 7. The inhibitory effects of all these compounds were enantiomerically specific. 8. These data indicate that L-NIO is a novel, potent, rapid in onset and irreversible inhibitor of NO synthase in phagocytic cells. The rapid uptake of L-NIO compared with the other compounds indicates that phagocytic cells have different uptake mechanisms for L-arginine analogues.

Characterization of three inhibitors of endothelial nitric oxide synthase in vitro and in vivo

1. Three analogues of L-arginine were characterized as inhibitors of endothelial nitric oxide (NO) synthase by measuring their effect on the endothelial NO synthase from porcine aortae, on the vascular tone of rings of rat aorta and on the blood pressure of the anaesthetized rat. 2. NG-monomethyl-L-arginine (L-NMMA), N-iminoethyl-L-ornithine (L-NIO) and NG-nitro-L-arginine methyl ester (L-NAME; all at 0.1-100 microM) caused concentration-dependent inhibition of the Ca2(+)-dependent endothelial NO synthase from porcine aortae. 3. L-NMMA, L-NIO and L-NAME caused an endothelium-dependent contraction and an inhibition of the endothelium-dependent relaxation induced by acetylcholine (ACh) in aortic rings. 4. L-NMMA, L-NIO and L-NAME (0.03-300 mg kg-1, i.v.) induced a dose-dependent increase in mean systemic arterial blood pressure accompanied by bradycardia. 5. L-NMMA, L-NIO and L-NAME (100 mg kg-1, i.v.) inhibited significantly the hypotensive responses to ACh and bradykinin. 6. The increase in blood pressure and bradycardia produced by these compounds were reversed by L-arginine (30-100 mg kg-1, i.v.) in a dose-dependent manner. 7. All of these effects were enantiomer specific. 8. These results indicate that L-NMMA, L-NIO and L-NAME are inhibitors of NO synthase in the vascular endothelium and confirm the important role of NO synthesis in the maintenance of vascular tone and blood pressure.

Characterization of the L-arginine:nitric oxide pathway in human platelets

1. The activation of the L-arginine: nitric oxide (NO) pathway during aggregation of human platelets by adenosine 5'-diphosphate (ADP), arachidonic acid, thrombin and the calcium ionophore A23187 and its inhibition by NG-monomethyl-L-arginine (L-NMMA), NG-nitro-L-arginine methyl ester (L-NAME) and N-iminoethyl-L-ornithine (L-NIO) were studied. The inhibition of the cytosolic platelet NO synthase by these compounds was also examined. 2. Platelet aggregation induced by ADP (1-10 microM) and arachidonic acid (0.1-10 microM), but not that induced by thrombin (1-30 mu ml-1) or A23187 (1-10 nM), was inhibited by L-, but not D-arginine (1-30 microM). However, in the presence of a subthreshold concentration of prostacyclin (0.1 nM) or of M & B 22948 (1 microM), a selective inhibitor of guanosine 3':5'-cyclic monophosphate (cyclic GMP) phosphodiesterase, L-arginine caused concentration-dependent inhibition of aggregation induced by all of these aggregating agents. 3. L-NMMA, L-NAME and L-NIO (all at 1-30 microM), but not their D-enantiomers, enhanced to the same extent platelet aggregation induced by ADP, arachidonic acid and thrombin without affecting that induced by A23187. 4. In the presence of 300 microM L-arginine, the NO synthase in platelet cytosol was inhibited by L-NMMA, L-NAME and L-NIO with IC50s of 74 +/- 9, 79 +/- 8 and 8.5 +/- 1.5 microM (n = 3), respectively. 5. These results indicate that the L-arginine: NO pathway in human platelets plays a role in the modulation of platelet aggregation.

Ligand-induced isomerizations of Escherichia coli ornithine transcarbamoylase. An ultraviolet difference analysis

Ligand-induced ultraviolet difference spectra have been determined for Escherichia coli ornithine transcarbamoylase. The most prominent feature of the spectra is an absorbance difference which resembles a single period of a sine wave spanning the 245-320 nm region with a maximum at approximately 270 nm and a minimum at around 295-300 nm. This broad absorbance difference is typical of a blue-shift 1La band of tryptophan. Superimposed on the broad band in the 275-310 nm region is a series of smaller, narrow peaks resulted from red-shifted 1Lb bands of tryptophan and tyrosine residues. At pH 8.5, only carbamoyl phosphate and its analog phosphonacetamide yield a large ultraviolet difference absorbance (approximately 1800 M-1 cm-1) when bound to the enzyme. The spectra obtained are essentially the same in lineshape to and 80% in intensity of that produced by the bisubstrate analogy, N-(phosphonacetyl)-L-ornithine. In contrast, inorganic phosphate, a product of the reaction, induces small protein absorbance changes (approximately 300 M-1 cm-1) mainly in the 275-310 nm range. When complexed to the free enzyme, L-ornithine yields a marginally discernible ultraviolet difference spectrum in the 275-310 nm region, and its analogs L-norvaline and L-citrulline provide no absorbance change. However, inorganic phosphate in combination with any of the L-amino acids produces a difference spectrum similar to that given by carbamoyl phosphate alone. Collectively, these spectra suggest that carbamoyl phosphate elicits an isomerization required for the formation of the ternary complex and are consistent with the compulsory ordered mechanism of the enzyme at pH 8.5 with carbamoyl phosphate being the first substrate bound. Below pH 8, there is a kinetically discernible amount of random binding, but ordered addition is still the preferred pathway (Wargnies B., Legrain, C., and Stalon, V. (1978) Eur J. Biochem. 89, 203-212). Reflecting this change, the difference absorbance of the enzyme bound with carbamoyl phosphate is also pH dependent. The 1La band in the carbamoyl phosphate difference spectrum diminishes by approximately 20% at low pH. The PALO-induced changes, however, are pH invariant suggesting that full extent of the induced-fit isomerization is always reached in the ternary complex.

Activation of mammalian folylpolyglutamate synthetase by sodium bicarbonate

NaHCO3 activated the folylpolyglutamate synthetase (FPGS) from rat liver and the human leukemia cell lines K562 and CCRF-CEM by 1.7- to 2.0-fold. Optimal activation was achieved by 10 mM NaHCO3 in all cases; NaCl, sodium formate, sodium acetate, NaN3, and Na2SO3 at 10 mM did not cause activation. Activation could be masked if assay solutions which had extensively absorbed atmospheric CO2 were used. Activation of the human CCRF-CEM FPGS was examined in detail. Km and Vmax values for pteroyl substrates (aminopterin or methotrexate) and L-glutamate increased proportionally in the presence of NaHCO3; there was thus no apparent change in the catalytic efficiency (Vmax/Km) of the FPGS reaction with these substrates. However, NaHCO3 increased the efficiency of the reaction with respect to ATP by decreasing its apparent Km while increasing the Vmax of the reaction. NaHCO3 also activated FPGS activity when folic acid, dihydrofolic acid and tetrahydrofolic acid were substrates. The relative distribution of products synthesized from methotrexate or tetrahydrofolate by FPGS was not altered by addition of NaHCO3. The potency of 5,8-dideazapteroylornithine, an FPGS-specific inhibitor, was not changed by the presence of NaHCO3 (IC50 = 0.4 microM). These results suggest that FPGS activity with folates and classical antifolates may be activated at physiological concentrations of NaHCO3. In addition, inadvertent contamination of assay solutions with bicarbonate from atmospheric CO2 may cause artifacts in the determination of activity levels and kinetic constants of FPGS.

Staphyloferrin A: a structurally new siderophore from staphylococci

Two ferric ion-binding compounds, designated staphyloferrin A and B, were detected in the culture filtrates of staphylococci grown under iron-deficient conditions. Staphyloferrin A was isolated from cultures of Staphylococcus hyicus DSM 20459. The structural elucidation of this highly hydrophilic, acid-labile compound revealed a novel siderophore, N2,N5-di-(1-oxo-3-hydroxy-3,4-dicarboxybutyl)-D-ornithine, which consists of one ornithine and two citric acid residues linked by two amide bonds. The two citric acid components of staphyloferrin A provide two tridentate pendant ligands, comprising of a beta-hydroxy, beta-carboxy-substituted carboxylic acid derivative, for octahedral metal chelation. The CD spectrum of the staphyloferrin A ferric complex indicates a predominant A configuration about the ferric ion center. The uptake of ferric staphyloferrin A by S. hyicus obeys Michaelis-Menten kinetics (Km = 0.246 microM; vmax = 82 pmol.mg-1.min-1), indicating active transport of this siderophore. The staphyloferrin A transport system is different from that of the ferrioxamines as shown by an antagonism test. Production of staphyloferrin A is strongly iron-dependent and is stimulated by supplementation of the medium with either D- or L-ornithine. DL-[5-14C]ornithine was incorporated into staphyloferrin A, demonstrating that ornithine is an intermediate in staphyloferrin A biosynthesis.

Kinetic characteristics of nitric oxide synthase from rat brain

The relationship between the rate of synthesis of nitric oxide (NO) and guanylate cyclase stimulation was used to characterize the kinetics of the NO synthase from rat forebrain and of some inhibitors of this enzyme. The NO synthase had an absolute requirement for L-arginine and NADPH and did not require any other cofactors. The enzyme had a Vmax. of 42 pmol of NO formed.min-1.mg of protein-1 and a Km for L-arginine of 8.4 microM. Three analogues of L-arginine, namely NG-monomethyl-L-arginine, NG-nitro-L-arginine and NG-iminoethyl-L-ornithine inhibited the brain NO synthase. All three compounds were competitive inhibitors of the enzyme with Ki values of 0.7, 0.4 and 1.2 microM respectively.

Isolation and characterization of the gene from Pseudomonas syringae pv. phaseolicola encoding the phaseolotoxin-insensitive ornithine carbamoyltransferase

The gene coding for the phaseolotoxin-insensitive ornithine carbamoyltransferase (OCTase) from Pseudomonas syringae pv. phaseolicola has been cloned and sequenced. The gene has a deduced coding capacity for a polypeptide with a calculated Mr of 36,520 daltons. Comparison of the amino acid sequence of the OCTase enzymes encoded by the P. aeruginosa argF and the Escherichia coli argI and argF genes with the deduced sequence of the newly identified gene shows that 79 amino acid residues are strictly conserved in all four polypeptides; among these 7 out of 9 residues are involved in enzyme function. Of three amino acid regions that have been implicated in substrate binding or catalysis, two are strictly conserved, and the third involved in carbamoylphosphate binding differs. This correlates well with published data showing that phaseolotoxin competes for the carbamoylphosphate binding site in the phaseolotoxin-sensitive OCTases. We propose that the gene be named argK.

Novel type of ornithine-glutathione double conjugate excreted as a major metabolite into the bile of rats administered clebopride

Rats orally given radioactive Clebopride [[14C]CP; N-(1'-benzyl-4'-piperidyl)-2-[14C]methoxy-4-amino-5-chlorobenzamide++ +], an antiulcer agent, excreted a novel type of ornithine (Orn)-GSH double conjugate in the bile as a major metabolite [( 14C]BMCP), corresponding to 18% of the dose. The present study provides the first evidence for Orn conjugation of a xenobiotic in mammals and demonstrates that the structure of the radioactive conjugate differs fundamentally from those known in birds and reptiles. The structure of the biliary metabolite, [14C]BMCP, purified to homogeneity by silica gel thin layer and reverse phase high pressure liquid chromatography, was elucidated as S-[2-ornithylamino-4-[14C]methoxy-5-(1'-methyl-4'-piperidylamin o) carboxyphenyl]glutathione, based mainly on the following facts: 1) BMCP showed a protonated molecular ion (M + H)+ peak at m/z 683 in the secondary ion mass spectrum and 2) [14C]BMCP afforded Orn, glutamic acid, glycine, S-(2-amino-4-[14C]methoxy-5-carboxyphenyl)cysteine [( 14C]AMCC), and 1-methyl-4-aminopiperidine (MAP) quantitatively, in an equal molar ratio, by complete hydrolysis with peptidase. Thus, BMCP was a metabolite with three enzymatically hydrolyzable amide bonds in addition to the one existing originally in the parent structure of the drug, which produces MAP by peptic digestion. Of the three additional amide bonds of BMCP, one was a novel type of bond formed by condensation of the alpha-carboxylic acid group of Orn with the primary aromatic amino group of the drug and the other two were in the S-glutathionyl residue, substituted for the chlorine atom vicinal to the Orn-conjugating primary amino group in the aromatic ring and affording glutamic acid, glycine, and the S-cysteine conjugate AMCC by hydrolysis of BMCP with the peptidase. Substitution of a methyl group for the benzyl group at the piperidine ring nitrogen atom, leading to the formation of MAP by peptic digestion, also occurred during metabolism of CP to BMCP.

DL-canaline and 5-fluoromethylornithine. Comparison of two inactivators of ornithine aminotransferase

5-Fluoromethylornithine (5FMOrn) is an enzyme-activated irreversible inhibitor or ornithine aminotransferase (L-ornithine:2-oxo-acid 5-aminotransferase, OAT). For purified rat liver OAT, Ki(app.) was found to be 30 microM. and tau 1/2 = 4 min. Of the four stereomers of 5FMOrn only one reacts with OAT. The formation of a chromophore with an absorption maximum at 458 nm after inactivation of OAT by 5FMOrn suggests the formation of an enamine intermediate, which is slowly hydrolysed to release an unsaturated ketone. L-Canaline [(S)-2-amino-4-amino-oxybutyric acid] is a well-known irreversible inhibitor of OAT. Not only the natural L-enantiomer but also the D-enantiomer reacts by oxime formation with pyridoxal 5'-phosphate in the active site of the enzyme, although considerably more slowly. This demonstrates that the stereochemistry at C-2 of ornithine is not absolutely stringent. In vitro, canaline reacted faster than 5FMOrn with OAT. In vivo, however, only incomplete OAT inhibition was observed with canaline. Whereas intraperitoneal administration of 10 mg of 5FMOrn/kg body wt. to mice was sufficient to inactivate OAT in brain and liver by 90% for 24 h, 500 mg of DL-canaline/kg body wt. only produced a transient inhibition of 65-70%. The accumulation of ornithine in these tissues was considerably slower and the maximum concentrations lower than were achieved with 5FMOrn. It appears that DL-canaline, in contrast with 5FMOrn, is not useful as a tool in studies of biological consequences of OAT inhibition.

Action of ornithine alpha ketoglutarate on DNA synthesis by human fibroblasts

Ornithine alpha ketoglutarate (OKG) is largely used in clinical nutrition for its anabolic effects. However, the mechanism of its action remains questionable. We investigated the effect of OKG on the rate of DNA synthesis in human fibroblasts. The in vitro experimental procedure required to demonstrate in cell culture the anabolic effects of OKG observed in vivo was found to be glutamine-free and serum-poor medium with sparse cells. In these conditions, OKG induced a significant increase in [3H]thymidine incorporation compared to untreated control cells. This effect was dose-dependent and was observed in all the cultures tested. Taken individually, the two constituents of OKG, i.e. alpha KG and Orn, also showed a stimulatory effect, but did not demonstrate a dose-dependent response. Concomitant analysis of extracellular aminoacids showed in alpha KG-treated cultures an increase in glutamate and a decrease in aspartate, suggesting a cellular transamination of alpha KG. Glutamine, which is the preferential energetic substrate of fibroblasts, can be produced from glutamate and might play a role in the action of OKG. Moreover, OKG induced a rise in the cellular polyamine content. This, in association with the inhibitory effect on OKG action of difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, suggests a link between the polyamine biosynthesis pathway and the anabolic effect of OKG.

Effects of an amino acid solution enriched with either branched chain amino acids or ornithine-alpha-ketoglutarate on the postoperative intracellular amino acid concentration of skeletal muscle

Patients undergoing elective cholecystectomy provide a highly reproducible model of the effects of trauma on intermediary metabolism. Three parenteral nutrition regimens were given to groups of eight such patients. An isonitrogenous total parenteral nutrition, including a commercially available amino acid solution, an amino acid solution enriched with branched chain amino acids or one supplemented with ornithine-alpha-ketoglutarate, was given after operation. The intra cellular free amino acid concentrations of skeletal muscle were determined in tissue specimens obtained before operation and on the third postoperative day using a percutaneous needle biopsy technique. The mean (s.e.m.) decrease in the concentrations of free intracellular glutamine on the third postoperative day was less pronounced (P less than 0.05) in the ornithine-alpha-ketoglutarate group (18.8(7.5)per cent) than in the control group (39.4(5.1)per cent) or the branched chain amino acid group (45.3(6.1)per cent). In conclusion, in the immediate postoperative period total parenteral nutrition supplemented with ornithine-alpha-ketoglutarate countered the decline in the muscle free glutamine. No difference in this parameter was seen between the control group and the branched chain amino acid group.

Isolation and characterization of staphyloferrin A, a compound with siderophore activity from Staphylococcus hyicus DSM 20459

A highly hydrophilic compound was isolated from low iron culture broth of Staphylococcus hyicus DSM 20459 which exhibits siderophore activity to the producer and 37 other staphylococci. The previously unknown metabolite was designated staphyloferrin A and consists of two molecules of citric acid, each linked to D-ornitine by an amide bond. Using an ion-pair HPLC-system we detected staphyloferrin A and a second iron regulated compound (staphyloferrin B) in the culture fluid of several Staphylococcus strains. We found no evidence that staphylococci synthesize catecholor hydroxamate-type siderophores.