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Biomedical subjects

J L Boucher

Publications and source records attributed to J L Boucher.

At least 19 recordsLinked to original sources
PubMed2006

Mail and phone interventions for weight loss in a managed-care setting: weigh-to-be 2-year outcomes.

OBJECTIVE: Evaluate effectiveness of weight-loss interventions in a managed care setting. METHODS: Three-arm randomized clinical trial: usual care, mail, and phone intervention. Participants were 1801 overweight managed care organization (MCO) members. Measures included baseline height, weight at baseline and 24 months, self-reported weight at 18 months. Intervention and participation in other weight-related programs was monitored across 24 months. RESULTS: Weight losses were 2.2, 2.4, and 1.9 kg at 18 months in the mail, phone, and usual care groups, respectively. Mail and phone group weight changes were not significantly different from usual care (P<0.35). Weight losses at 24 months did not differ by condition (0.7 kg mail, 1.0 kg phone, and 0.6 kg usual care, P=0.55). Despite treatment availability over 24 months, participation diminished after 6 months. Participation was a significant predictor of outcomes in the mail and phone groups at 18 months and the mail group at 24 months. Cost-effectiveness of phone counseling was $132 per 1 kg of weight loss with mail and usual care achieving similar cost-efficiency of $72 per 1 kg of weight loss. CONCLUSION: Although mail- and phone-based weight-loss programs are a reasonably efficient way to deliver weight-loss services, additional work is needed to enhance their short- and long-term efficacy.

Adult↗
PubMed2003

Mail and phone interventions for weight loss in a managed-care setting: Weigh-To-Be one-year outcomes.

OBJECTIVE: To describe methods, recruitment success, and 1-y results of a study evaluating the effectiveness of phone- and mail-based weight-loss interventions in a managed care setting. DESIGN: Randomized clinical trial with three groups, that is, usual care, mail intervention, and phone intervention. SUBJECTS: In total, 1801 overweight members of a managed-care organization (MCO). MEASUREMENTS: Height, weight, medical status, and weight-loss history were measured at baseline. Participation in intervention activities was monitored for 12 months in the two active treatment groups. Self-reported weight was obtained at 6 and 12 months. RESULTS: More individuals assigned to mail treatment started it (88%) than did those assigned to phone treatment (69%). However, program completion rates were higher in the phone (36%) than mail (7%) intervention. The mean weight losses were 1.93, 2.38, and 1.47 kg at 6 months in the mail, phone, and usual care groups, respectively. The differences between the phone and usual care groups were statistically significant. The mean weight losses at 12 months did not differ by treatment group (2.28 kg mail, 2.29 kg phone, and 1.92 kg usual care). Greater weight loss was seen in men, older participants, and those with no prior experience in a weight-loss program. Heavier participants and those who reported current treatment for depression lost less weight. CONCLUSION: Although mail- and phone-based weight-loss programs can be delivered to large numbers of people in an MCO setting, additional work is needed to enhance their clinical efficacy as well as to assess their costs.

Female↗
PubMed2001

N-hydroxyguanidines as new heme ligands: UV-visible, EPR, and resonance Raman studies of the interaction of various compounds bearing a C=NOH function with microperoxidase-8.

Interaction between microperoxidase-8 (MP8), a water-soluble hemeprotein model, and a wide range of N-aryl and N-alkyl N'-hydroxyguanidines and related compounds has been investigated using UV-visible, EPR, and resonance Raman spectroscopies. All the N-hydroxyguanidines studied bind to the ferric form of MP8 with formation of stable low-spin iron(III) complexes characterized by absorption maxima at 405, 535, and 560 nm. The complex obtained with N-(4-methoxyphenyl) N'-hydroxyguanidine exhibits EPR g-values at 2.55, 2.26, and 1.86. The resonance Raman (RR) spectrum of this complex is also in agreement with an hexacoordinated low-spin iron(III) structure. The dissociation constants (K(s)) of the MP8 complexes with mono- and disubstituted N-hydroxyguanidines vary between 15 and 160 microM at pH 7.4. Amidoximes also form low-spin iron(III) complexes of MP8, although with much larger dissociation constants. Under the same conditions, ketoximes, aldoximes, methoxyguanidines, and guanidines completely fail to form such complexes with MP8. The K(s) values of the MP8-N-hydroxyguanidine complexes decrease as the pH of the solution is increased, and the affinity of the N-hydroxyguanidines toward MP8 increases with the pK(a) of these ligands. Altogether these results show that compounds involving a -C(NHR)=NOH moiety act as good ligands of MP8-Fe(III) with an affinity that depends on the electron-richness of this moiety. The analysis of the EPR spectrum of the MP8-N-hydroxyguanidine complexes according to Taylor's equations shows a strong axial distortion of the iron, typical of those observed for hexacoordinated heme-Fe(III) complexes with at least one pi donor axial ligand (HO(-), RO(-), or RS(-)). These data strongly suggest that N-hydroxyguanidines bind to MP8 iron via their oxygen atom after deprotonation or weakening of their O-H bond. It thus seems that N-hydroxyguanidines could constitute a new class of strong ligands for hemeproteins and iron(III)-porphyrins.

Animals↗
PubMed2001

Coordination chemistry of the heme in cystathionine beta-synthase: formation of iron(II)-isonitrile complexes.

Interaction of rat and human cystathionine-beta-synthase (CBS) with various potential ligands has been studied by visible and EPR spectroscopy in order to explore the coordination chemistry of this atypical hemeprotein. Ferric CBS did not react with any classical hemeprotein ligands, such as various imidazole and pyridine derivatives, N(-)(3) and isonitriles RNC. Ferrous CBS also failed to bind these nitrogenous ligands or nitrosoalkanes. However, it reacts with various isonitriles RNC, leading to complexes characterized by a Soret peak at 433 +/- 2 nm. Binding of isonitriles to ferrous CBS is a relatively slow process; its rate markedly depends on the nature of R. It thus seems that the only exogenous ligands able to bind CBS iron are carbon-centered, very strong heme-Fe(II) ligands such as CNR, CO, and CN(-), presumably after dissociation of the CBS-iron(II)-cysteinate bond. Isonitriles appear as interesting tools for further studies on the topology of CBS active site.

Animals↗
PubMed2001

Mechanistic and metabolic inferences from the binding of substrate analogues and products to arginase.

Arginase is a binuclear Mn(2+) metalloenzyme that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. X-ray crystal structures of arginase complexed to substrate analogues N(omega)-hydroxy-L-arginine and N(omega)-hydroxy-nor-L-arginine, as well as the products L-ornithine and urea, complete a set of structural "snapshots" along the reaction coordinate of arginase catalysis when interpreted along with the X-ray crystal structure of the arginase-transition-state analogue complex described in Kim et al. [Kim, N. N., Cox, J. D., Baggio, R. F., Emig, F. A., Mistry, S., Harper, S. L., Speicher, D. W., Morris, Jr., S. M., Ash, D. E., Traish, A. M., and Christianson, D. W. (2001) Biochemistry 40, 2678-2688]. Taken together, these structures render important insight on the structural determinants of tight binding inhibitors. Furthermore, we demonstrate for the first time the structural mechanistic link between arginase and NO synthase through their respective complexes with N(omega)-hydroxy-L-arginine. That N(omega)-hydroxy-L-arginine is a catalytic intermediate for NO synthase and an inhibitor of arginase reflects the reciprocal metabolic relationship between these two critical enzymes of L-arginine catabolism.

Amino Acid Substitution↗
PubMed2001

Oxidations of N(omega)-hydroxyarginine analogues and various N-hydroxyguanidines by NO synthase II: key role of tetrahydrobiopterin in the reaction mechanism and substrate selectivity.

Oxidations of L-arginine 2, homo-L-arginine 1, their N(omega)-hydroxy derivatives 4 and 3 (NOHA and homo-NOHA, respectively), and four N-hydroxyguanidines, N(omega)-hydroxynor-L-arginine 5 (nor-NOHA), N(omega)-hydroxydinor-L-arginine 6 (dinor-NOHA), N-(4-chlorophenyl)-N'-hydroxyguanidine (8), and N-hydroxyguanidine (7) itself, by either NOS II or (6R)-5,6,7,8-tetrahydro-L-biopterin (BH4)-free NOS II, have been studied in a comparative manner. Recombinant BH4-free NOS II catalyzes the oxidation of all N-hydroxyguanidines by NADPH and O2, with formation of NO2(-) and NO3(-) at rates between 20 and 80 nmol min(-1) (mg of protein)(-1). In the case of compound 8, formation of the corresponding urea and cyanamide was also detected besides that of NO2(-) and NO3(-). These BH4-free NOS II-dependent reactions are inhibited by modulators of electron transfer in NOS such as thiocitrulline (TC) or imidazole (ImH), but not by Arg, and are completely suppressed by superoxide dismutase (SOD). They exhibit characteristics very similar to those previously reported for microsomal cytochrome P450-catalyzed oxidation of N-hydroxyguanidines. Both P450 and BH4-free NOS II reactions appear to be mainly performed by O2(.-) derived from the oxidase function of those heme proteins. In the presence of increasing concentrations of BH4, these nonselective oxidations progressively disappear while a much more selective monooxygenation takes place only with the N-hydroxyguanidines that are recognized well by NOS II, NOHA, homo-NOHA, and 8. These monooxygenations are much more chemoselective (8 being selectively transformed into the corresponding urea and NO) and are inhibited by Arg but not by SOD, as expected for reactions performed by the NOS Fe(II)-O2 species. Altogether, these results provide a further clear illustration of the key role of BH4 in regulating the monooxygenase/oxidase ratio in NOS. They also suggest a possible implication of NOSs in the oxidative metabolism of certain classes of xenobiotics such as N-hydroxyguanidines, not only via their monooxygenase function but also via their oxidase function.

Antioxidants↗
PubMed2001

Microperoxidase 8 catalyzed nitration of phenol by nitrogen dioxide radicals.

Microperoxidase 8 (MP8) is a heme octapeptide obtained by hydrolytic digestion of horse heart cytochrome c. At pH below 9, the heme iron is axially coordinated to the imidazole side chain of His18 and to a water molecule. Replacement of this weak ligand by H2O2 allows the formation of high-valent iron-oxo species which are responsible for both peroxidase-like and cytochrome P450-like activities of MP8. This paper shows that MP8 is able to catalyze the nitration of phenol by nitrite. The reaction requires H2O2 and is inhibited by ligands having a high affinity for the iron, catalase and radical scavengers. This suggests that the nitrating species could be NO2* radicals formed by the oxidation of nitrite by high-valent iron-oxo species. This new activity of MP8 opens a new access to nitro-aromatic compounds under mild conditions and validates the use of this minienzyme to mimick heme peroxidases, especially in the reactions of NO-derived species with biomolecules under oxidative stress conditions.

Animals↗
PubMed2001

Cytochromes P450 and flavin monooxygenases--targets and sources of nitric oxide.

This article is a report on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the Experimental Biology 01 meeting in Orlando, FL. The presentations addressed the mechanisms of inhibition and regulation of cytochrome P450 and flavin monooxygenase enzymes by nitric oxide. They also highlighted the consequences of these effects on metabolism of drugs and volatile amines as well as on important physiological parameters, such as control of blood pressure, renal ion transport, and steroidogenesis. This is achieved via regulation of P450-dependent prostacyclin, hydroxyeicosatetraenoic acid, and epoxyeicosatrienoic acid formation. Conversely, the mechanisms and relative importance of nitric oxide synthases and P450 enzymes in NO production from endogenous and synthetic substrates were also addressed.

Animals↗
PubMed2000

Formation of iron(II)-nitrosoalkane complexes: a new activity of microperoxidase 8.

Microperoxidase 8 (MP8) is a heme octapeptide, obtained by enzymatic hydrolysis of heart cytochrome c, in which a histidine is axially coordinated to the heme iron, and acts as its fifth ligand. It exhibits two kinds of activities: a peroxidase-like activity and a cytochrome P450-like activity. We here show that MP8 is not only able to oxidize various aliphatic and aromatic hydroxylamines with the formation of MP8-Fe(II)-nitrosoalkane or -arene complexes absorbing around 414 nm, but also that these complexes can be obtained by reduction of nitroalkanes. This is the first example of fully characterized iron(II)-metabolite complexes of MP8. Such complexes constitute good models for those obtained upon oxidation of amphetamine or macrolids by cytochromes P450. In addition, this is a new catalytic activity of MP8, which validates the use of this mini-enzyme as a convenient model for hemoproteins of interest in toxicology and pharmacology such as cytochromes P450 and peroxidases.

Alkanes↗
PubMed2000

Recognition of alpha-amino acids bearing various C=NOH functions by nitric oxide synthase and arginase involves very different structural determinants.

Several alpha-amino acids bearing a C=NOH function separated from the Calpha carbon by two to five atoms have been synthesized and tested as substrates or inhibitors of recombinant nitric oxide synthases (NOS) I and II and as inhibitors of rat liver arginase (RLA). These include four N-hydroxyguanidines, N(omega)-hydroxy-L-arginine (NOHA) and its analogues homo-NOHA, nor-NOHA, and dinor-NOHA, two amidoximes bearing the -NH-C(CH(3))=NOH group, and two amidoximes bearing the -CH(2)-C(NH(2))=NOH group. Their behavior toward NOS and RLA was compared to that of the corresponding compounds bearing a C=NH function instead of the C=NOH function. The results obtained clearly show that efficient recognition of these alpha-amino acids by NOS and RLA involves very different structural determinants. NOS favors molecules bearing a -NH-C(R)=NH motif separated from Calpha by three or four CH(2) groups, such as arginine itself, with the necessary presence of delta-NH and omega-NH groups and a more variable R substituent. The corresponding molecules with a C=NOH function exhibit a much lower affinity for NOS. On the contrary, RLA best recognizes molecules bearing a C=NOH function separated from Calpha by three or four atoms, the highest affinity being observed in the case of three atoms. The presence of two omega-nitrogen atoms is important for efficient recognition, as in the two best RLA inhibitors, N(omega)-hydroxynorarginine and N(omega)-hydroxynorindospicine, which exhibit IC(50) values at the micromolar level. However, contrary to what was observed in the case of NOS, the presence of a delta-NH group is not important. These different structural requirements of NOS and RLA may be directly linked to the position of crucial residues that have been identified from crystallographic data in the active sites of both enzymes. Thus, binding of arginine analogues to NOS particularly relies on strong interactions of their delta-NH and omega-NH(2) groups with glutamate 371 (of NOS II), whereas binding of C=NOH molecules to RLA is mainly based on interactions of their terminal OH group with the binuclear Mn(II).Mn(II) cluster of the enzyme and on possible additional bonds between their omega-NH(2) group with histidine 141, glutamate 277, and one Mn(II) ion. The different modes of interaction displayed by both enzymes depend on their different catalytic functions and give interesting opportunities to design useful molecules to selectively regulate NOS and arginase.

Amino Acids↗
PubMed2000

Modulation of cholinergic airway reactivity and nitric oxide production by endogenous arginase activity.

Cholinergic airway constriction is functionally antagonized by agonist-induced constitutive nitric oxide synthase (cNOS)-derived nitric oxide (NO). Since cNOS and arginase, which hydrolyzes L-arginine to L-ornithine and urea, use L-arginine as a common substrate, competition between both enzymes for the substrate could be involved in the regulation of cholinergic airway reactivity. Using a perfused guinea-pig tracheal tube preparation, we investigated the modulation of methacholine-induced airway constriction by the recently developed, potent and specific arginase inhibitor N(Omega)-hydroxy-nor-L-arginine (nor-NOHA). Intraluminal (IL) administration of nor-NOHA caused a concentration-dependent inhibition of the maximal effect (E(max)) in response to IL methacholine, which was maximal in the presence of 5 microM nor-NOHA (E(max)=31.2+/-1.6% of extraluminal (EL) 40 mM KCl-induced constriction versus 51.6+/-2.1% in controls, P<0.001). In addition, the pEC(50) (-log(10) EC(50)) was slightly but significantly reduced in the presence of 5 microM nor-NOHA. The inhibition of E(max) by 5 microM nor-NOHA was concentration-dependently reversed by the NOS inhibitor N(Omega)-nitro-L-arginine methyl ester (L-NAME), reaching an E(max) of 89.4+/-7.7% in the presence of 0.5 mM L-NAME (P<0.01). A similar E(max) in the presence of 0.5 mM L-NAME was obtained in control preparations (85.2+/-9.7%, n.s.). In the presence of excess of exogenously applied L-arginine (5 mM), 5 microM nor-NOHA was ineffective (E(max)=33.1+/-5.8 versus 31.1+/-7.5% in controls, n.s.). The results indicate that endogenous arginase activity potentiates methacholine-induced airway constriction by inhibition of NO production, presumably by competition with cNOS for the common substrate, L-arginine. This finding may represent an important novel regulation mechanism of airway reactivity.

Animals↗
PubMed2000

L-Arginine availability modulates local nitric oxide production and parasite killing in experimental trypanosomiasis.

Nitric oxide (NO) is an important effector molecule of the immune system in eliminating numerous pathogens. Peritoneal macrophages from Trypanosoma brucei brucei-infected mice express type II NO synthase (NOS-II), produce NO, and kill parasites in the presence of L-arginine in vitro. Nevertheless, parasites proliferate in the vicinity of these macrophages in vivo. The present study shows that L-arginine availability modulates NO production. Trypanosomes use L-arginine for polyamine synthesis, required for DNA and trypanothione synthesis. Moreover, arginase activity is up-regulated in macrophages from infected mice from the first days of infection. Arginase competes with NOS-II for their common substrate, L-arginine. In vitro, arginase inhibitors decreased urea production, increased macrophage nitrite production, and restored trypanosome killing. In vivo, a dramatic decrease in L-arginine concentration was observed in plasma from infected mice. In situ restoration of NO production and trypanosome killing were observed when excess L-arginine, but not D-arginine or L-arginine plus N(omega)-nitro-L-arginine (a NOS inhibitor), was injected into the peritoneum of infected mice. These data indicate the role of L-arginine depletion, induced by arginase and parasites, in modulating the L-arginine-NO pathway under pathophysiological conditions.

Animals↗
PubMed1999

Microsomal formation of nitric oxide and cyanamides from non-physiological N-hydroxyguanidines: N-hydroxydebrisoquine as a model substrate.

The microsomal oxidative transformation of a non-physiological N-hydroxyguanidine was demonstrated for the first time for N-hydroxydebrisoquine as a model substrate (Clement et al., Biochem Pharmacol 46: 2249-2267, 1993). The objective of the present work was to further compare this reaction with the analogous oxidation of arginine via N-hydroxyarginine to citrulline and nitric oxide. The oxidation of N-hydroxydebrisoquine by liver microsomes from rats pretreated with dexamethasone not only produced nitric oxide and the urea, but also the cyanamide derivative as the main metabolite. The low stability of the cyanamide derivative, which easily hydrolyzed to the urea derivative, was noted. The formation of all compounds required cosubstrate and the enzyme source. Experiments with catalase, superoxide dismutase, and H2O2 showed that the O2- formed from the enzyme and the substrate apparently participated in the reaction. While the N-hydroxylation of the guanidine involves the usual monooxygenase activity of cytochrome P-450 (Clement et al., Biochem Pharmacol 46: 2249-2267, 1993), the resultant N-hydroxyguanidine decoupled the monooxygenase. Nitric oxide was detected by the oxyhemoglobin assay. To examine the influence of enzymatically formed nitric oxide on the formation of the metabolites, the N-hydroxydebrisoquine was incubated with SIN-1 as nitric oxide donor under aerobic conditions. It was again possible to detect the cyanamide and urea derivatives, with the latter as main metabolite. It was concluded that the microsomal transformation of N-hydroxydebrisoquine produces a cyanamide and nitric oxide which reacts with N-hydroxydebrisoquine to form the urea derivative. The purely chemical reaction of the unsubstituted N-hydroxyguanidine with nitric oxide gave similar results (Fukuto et al., Biochem Pharmacol 43: 607-613, 1992). In conclusion, similarities (formation of a urea derivative) and differences (formation of a cyanamide derivative) between the physiological oxidation of N-hydroxy-L-arginine by nitric oxide synthases and non-physiological N-hydroxyguanidines by cytochrome P-450 were observed. Furthermore, non-physiological N-hydroxyguanidines can be regarded as nitric oxide donors.

Animals↗
PubMed1999

Efficient formation of nitric oxide from selective oxidation of N-aryl N'-hydroxyguanidines by inducible nitric oxide synthase.

Inducible nitric oxide synthase (NOS II) efficiently catalyzes the oxidation of N-(4-chlorophenyl)N'-hydroxyguanidine 1 by NADPH and O2, with concomitant formation of the corresponding urea and NO. The characteristics of this reaction are very similar to those of the NOS-dependent oxidation of endogenous Nomega-hydroxy-L-arginine (NOHA), i.e., (i) the formation of products resulting from an oxidation of the substrate C=N(OH) bond, the corresponding urea and NO, in a 1:1 molar ratio, (ii) the absolute requirement of the tetrahydrobiopterin (BH4) cofactor for NO formation, and (iii) the strong inhibitory effects of L-arginine (L-arg) and classical inhibitors of NOSs. N-Hydroxyguanidine 1 is not as good a substrate for NOS II as is NOHA (Km = 500 microM versus 15 microM for NOHA). However, it leads to relatively high rates of NO formation which are only 4-fold lower than those obtained with NOHA (Vm = 390 +/- 50 nmol NO min-1 mg protein-1, corresponding roughly to 100 turnovers min-1). Preliminary results indicate that some other N-aryl N'-hydroxyguanidines exhibit a similar behavior. These results show for the first time that simple exogenous compounds may act as NO donors after oxidative activation by NOSs. They also suggest a possible implication of NOSs in the oxidative metabolism of certain classes of xenobiotics.

Biopterins↗
PubMed1999

Effects of the new arginase inhibitor N(omega)-hydroxy-nor-L-arginine on NO synthase activity in murine macrophages.

In stimulated murine macrophage, arginase and nitric oxide synthase (NOS) compete for their common substrate, l-arginine. The objectives of this study were (i) to test the new alpha-amino acid N(omega)-hydroxy-nor-l-arginine (nor-NOHA) as a new selective arginase inhibitor and (ii) to elucidate the effects of arginase inhibition on l-arginine utilization by an inducible NOS. Nor-NOHA is about 40-fold more potent than N(omega)-hydroxy-l-arginine (NOHA), an intermediate in the l-arginine/NO pathway, to inhibit the hydrolysis of l-arginine to l-ornithine catalyzed by unstimulated murine macrophages (IC(50) values 12 +/- 5 and 400 +/- 50 microM, respectively). Stimulation of murine macrophages with interferon-gamma and lipopolysaccharide (IFN-gamma + LPS) results in clear expression of an inducible NOS (iNOS) and to an increase in arginase activity. Nor-NOHA is also a potent inhibitor of arginase in IFN-gamma + LPS-stimulated macrophage (IC(50) value 10 +/- 3 microM). In contrast to NOHA, nor-NOHA is neither a substrate nor an inhibitor for iNOS and it appears as a useful tool to study the interplays between arginase and NOS. Inhibition of arginase by nor-NOHA increases nitrite and l-citrulline accumulation for incubation times higher than 12 h, under our conditions. Our results allow the determination of the kinetic parameters of the two competitive pathways and the proposal of a simple model which readily explains the differences observed between experiments. This model readily accounts for the observed effects and should be useful to predict the consequences of arginase inhibition in the presence of an active NOS on l-arginine availability.

Animals↗
PubMed1999

Nitric oxide biosynthesis, nitric oxide synthase inhibitors and arginase competition for L-arginine utilization.

Nitric oxide (NO) is a recently discovered mediator produced by mammalian cells. It plays a key role in neurotransmission, control of blood pressure, and cellular defense mechanisms. Nitric oxide synthases (NOSs) catalyze the oxidation of L-arginine to NO and L-citrulline. NOSs are unique enzymes in that they possess on the same polypeptidic chain a reductase domain and an oxygenase domain closely related to cytochrome P450s. NO and superoxide formation as well as NOS stability are finely regulated by Ca2+/calmodulin interactions, by the cofactor tetrahydrobiopterin, and by substrate availability. Strong interactions between the L-arginine-metabolizing enzymes are clearly demonstrated by competition between NOSs and arginases for L-arginine utilization, and by potent inhibition of arginase activity by N(omega)-hydroxy-L-arginine, an intermediate in the L-arginine to NO pathway.

Animals↗