Anticitrullinated Protein Antibodies Induce Inflammatory Gene Expression Profile in Peripheral Blood Cells from CCP-positive Patients with RA.

OBJECTIVE: Anticitrullinated protein antibodies (ACPA) have major diagnostic significance in rheumatoid arthritis (RA). ACPA are directed against different citrullinated antigens, including filaggrin, fibrinogen, vimentin, and collagen. The presence of ACPA is associated with joint damage and extraarticular manifestations, suggesting that ACPA may have a significant role in the pathogenesis of RA. METHODS: To verify the effect of ACPA on RA-immune cells, peripheral blood mononuclear cells (PBMC) from cyclic citrullinated peptide (CCP)-positive patients with RA and healthy controls were cocultured in vitro with ACPA. ACPA-positive stained cells were analyzed by flow cytometry and the effect of ACPA on mRNA expression levels was evaluated by real-time PCR. We tested whether the stimulatory effects induced by ACPA could be inhibited by the addition of a new multiepitope citrullinated peptide (Cit-ME). RESULTS: We found that ACPA bind specifically to PBMC from CCP-positive patients with RA through the Fab portion. ACPA induce upregulation of pathogenic cytokine expression (4- to 13-fold increase) in PBMC derived from CCP-positive patients with RA. Moreover, ACPA upregulated IL-1ß and IL-6 mRNA expression levels by 10- and 6-fold, respectively, compared to control IgG. Cit-ME, a genuine ligand of ACPA, inhibited the ACPA-induced upregulation of IL-1ß and IL-6 by 30%. CONCLUSION: ACPA bind to a limited percentage of PBMC and upregulate inflammatory cytokine expression, suggesting that ACPA is involved in RA pathogenesis. Targeting ACPA to decrease their pathogenic effects might provide a novel direction in developing therapeutic strategies for RA.

Relatedness of Antibodies to Peptides Containing Homocitrulline or Citrulline in Patients with Rheumatoid Arthritis.

OBJECTIVE: Antibodies that target citrullinated protein/peptide (ACPA) and homocitrullinated/carbamylated protein/peptide (AHCPA) are associated with rheumatoid arthritis (RA). The relationship between ACPA and AHCPA remains unclear. We examined the expression and cross-reactivity of these antibodies using citrulline- and homocitrulline-containing synthetic peptides, CitJED and HomoCitJED, respectively, which have equal numbers of citrulline or homocitrulline residues on the same peptide backbone. METHODS: Serum from healthy subjects (n = 51) and patients with RA (n = 137), systemic lupus erythematosus (SLE; n = 37), and psoriatic arthritis (PsA; n = 37) were screened for IgG anti-CitJED and anti-HomoCitJED antibodies by ELISA. Cross-reactivity of these antibodies was examined by inhibition with various concentrations of CitJED and HomoCitJED. RESULTS: Out of 137 patients with RA, antibodies to CitJED and HomoCitJED were detected in 69 (50%) and 78 (57%), respectively. Anti-CitJED and HomoCitJED antibodies were 77% concordant and their levels were strongly correlated [Spearman correlation coefficient (rs) = 0.6676]. Sera from 25/27 patients (93%) with RA were inhibited by both CitJED and HomoCitJED with equal or higher affinity for the cognate (homologous) peptide. CONCLUSION: Antibodies to CitJED and HomoCitJED frequently occurred in RA, but were not found in SLE or PsA, suggesting that these antibodies are specific to RA. Cross-reactivity between anti-HomoCitJED and anti-CitJED antibodies suggests that ACPA and AHCPA are derived from the same B cell population and both may contribute to the pathogenesis of RA.

Oligonucleotide-peptide conjugates: solid-phase synthesis under acidic conditions and use in ELISA assays.

Here we used solid-phase methods to prepare oligonucleotides carrying fibrin/ filaggrin citrullinated peptides. Post-synthetic conjugation protocols were successfully applied for the synthesis of oligonucleotides carrying small peptides. A stepwise protocol using acid treatment for the final deprotection allowed the preparation of polypyrimidine oligonucleotides carrying longer and arginine-rich peptides. An ELISA-based test using the oligonucleotide-citrullinated peptide conjugates was developed for the detection of anti-citrullinated protein/peptide antibodies in human serum from rheumatoid arthritis patients.

A density functional theory investigation on the mechanism of the second half-reaction of nitric oxide synthase.

Density functional theory methods have been employed to systematically investigate the overall mechanism of the second half-reaction of nitric oxide synthases. The initial heme-bound hydrogen peroxide intermediate previously identified is found to first undergo a simple rotation about its O-O peroxide bond. Then, via a "ping-pong" peroxidase-like mechanism the -O(in)H- proton is transferred back onto the substrate's -NO oxygen then subsequently onto the outer oxygen of the resulting Fe(heme)-OOH species. As a result, O(out) is released as H2O with concomitant formation of a compound I-type (Fe(heme)-O) species. Formation of the final citrulline and NO products can then be achieved in one step via a tetrahedral transition structure resulting from direct attack of the Fe(heme)-O moiety at the substrate's guanidinium carbon center. The possible role of alternative mechanisms involving a protonated compound II-type species or an initial transfer of only the -NH- hydrogen of the =NHOH+ group of N(omega)-hydroxy-L-arginine is also discussed.

Synthetic approaches to N(delta)-methylated L-arginine, N(omega)-hydroxy-L-arginine, L-citrulline, and N(delta)-cyano-L-ornithine.

Nomega-Methylated arginines such as asymmetric dimethyl-L-arginine (ADMA) and monomethyl-l-arginine (NMMA) are known as potent physiological inhibitors of nitric oxide synthases (NOSs). To explore a possible physiological and pharmaceutical relevance of N(delta)-methylated analogues, a synthetic scheme had to be developed that would not lead to N(delta)-methyl-L-arginine only but also to its presumed metabolites of NOS catalysis. Two basic synthetic approaches have been pursued to obtain N(delta)-methylated derivatives of L-ornithine, L-citrulline, L-arginine, and N(omega)-hydroxy-L-arginine. A first attempt utilized conventionally protected L-ornithine, i.e., the tert-butyl ester and Boc-amine, and led to three end compounds in excellent yields. Simultaneous protection of the alpha-amino acid moiety by formation of boroxazolidinones, particularly by employing 9-borabicyclo[3.3.1]nonane (9-BBN-H), proved to be a convenient option to perform side chain modifications and led to all of the desired end compounds. Additionally, enantiomeric excess (ee, %) of crucial synthetic intermediates and end compounds was determined by chiral HPLC.

A conserved tryptophan 457 modulates the kinetics and extent of N-hydroxy-L-arginine oxidation by inducible nitric-oxide synthase.

In the oxygenase domain of mouse inducible nitric-oxide synthase (iNOSoxy), a conserved tryptophan residue, Trp-457, regulates the kinetics and extent of l-Arg oxidation to N(omega)-hydroxy-l-arginine (NOHA) by controlling electron transfer between bound (6R)-tetrahydrobiopterin (H(4)B) cofactor and the enzyme heme Fe(II)O(2) intermediate (Wang, Z. Q., Wei, C. C., Ghosh, S., Meade, A. L., Hemann, C., Hille, R., and Stuehr, D. J. (2001) Biochemistry 40, 12819-12825). To investigate whether NOHA oxidation to citrulline and nitric oxide (NO) is regulated by a similar mechanism, we performed single turnover reactions with wild type iNOSoxy and mutants W457F and W457A. Ferrous proteins containing NOHA plus H(4)B or NOHA plus 7,8-dihydrobiopterin (H(2)B), were mixed with O(2)-containing buffer, and then heme spectral transitions and product formation were followed versus time. All three proteins formed a Fe(II)O(2) intermediate with identical spectral characteristics. In wild type, H(4)B increased the disappearance rate of the Fe(II)O(2) intermediate relative to H(2)B, and its disappearance was coupled to the formation of a Fe(III)NO immediate product prior to formation of ferric enzyme. In W457F and W457A, the disappearance rate of the Fe(II)O(2) intermediate was slower than in wild type and took place without detectable build-up of the heme Fe(III)NO immediate product. Rates of Fe(II)O(2) disappearance correlated with rates of citrulline formation in all three proteins, and reactions containing H(4)B formed 1.0, 0.54, and 0.38 citrulline/heme in wild type, W457F, and W457A iNOSoxy, respectively. Thus, Trp-457 modulates the kinetics of NOHA oxidation by iNOSoxy, and this is important for determining the extent of citrulline and NO formation. Our findings support a redox role for H(4)B during NOHA oxidation to NO by iNOSoxy.

The design and synthesis of the high efficacy, non-peptide CCK1 receptor agonist PD170292.

The design, synthesis and biological actions of a novel, non-peptide CCK1 receptor agonist (PD 170292) which exhibits a similar pharmacological profile to the CCK analogue JMV180 is reported. PD 170292 was designed based on a consideration of the structures of a peptide based CCK1 receptor selective agonist and a peptoid CCK2 receptor selective antagonist.

Evaluation of new L-thiocitrulline derivatives as inhibitors of nitric oxide synthase.

New derivatives of L-thiocitrulline were prepared and assayed as inhibitors of the three isoforms of nitric oxide synthase. These compounds demonstrated weak inhibitory activity against the NOS isoforms and these results directly support a recently described model of the L-arginine binding site of NOS.

Synthesis and evaluation of new sulfur-containing L-arginine-derived inhibitors of nitric oxide synthase.

A series of compounds (7, 8, 10-17, 23) containing new functional groups derived by the combination of the substrate, intermediate, product, and known inhibitors of nitric oxide synthase (NOS) were prepared and evaluated against NOS. While none of the compounds assayed acted as a nitric oxide-producing substrate, the sulfur-containing arginine derivatives 10-12 were competitive inhibitors of iNOS with Ki's of 202, 7, and 58 microM, respectively. Compound 11 demonstrated the greatest potency against NOS-mediated citrulline formation for each of the three isoforms with IC50's of 6. 7, 19.7, and 13 microM for nNOS, eNOS, and iNOS, respectively. Compounds 10-12 each demonstrated a slight selectivity for inhibition of the neuronal isoform compared to the endothelial and inducible isoforms. These compounds also influenced the NADPH oxidase activity and heme iron spin state in a manner similar to structurally related compounds. Compound 10, a thiocarbonyl-containing compound, decreased the NADPH oxidase activity of the enzyme (EC50 = 190 microM) and shifted the heme iron spin state toward a low-spin configuration, similar to that of L-thiocitrulline. Compounds 11 and 12, S-alkylthiocitrulline derivatives, decreased the NADPH oxidase activity of the enzyme (EC50 = 6.6 and 180 microM, respectively) and shifted the heme iron spin state toward a high-spin configuration, similar to that of L-S-methylisothiocitrulline. Carbonyl-containing amino acid (7, 8, 23) and non-amino acid (13-17) analogues did not interact well with the enzyme.

Synthesis, in vivo evaluation and PET study of a carbon-11-labeled neuronal nitric oxide synthase (nNOS) inhibitor S-methyl-L-thiocitrulline.

UNLABELLED: Reports have implicated neuronal nitric oxide synthetase (nNOS) in the pathological effects of neurodegenerative diseases. S-Methyl-L-thiocitrulline (MTICU), a potent and selective nNOS inhibitor (Ki = 1.2 nM), was chosen as our initial target molecule for positron emitter labeling as a potential nNOS tracer. We report the synthesis, biological evaluation and primate brain images of S-[11C]methyl-L-thiocitrulline ([I11C]MTICU). METHODS: The two-step synthesis of [11C]MTICU consisted of the S-alkylation of alpha-N-Boc-L-thiocitrulline t-butyl ester with [11C]Mel followed by TFA hydrolysis and HPLC purification. The final product was obtained within 50 min (yield = 9.1%-12.5%, based on [11C]Mel S.A. = 27-680 Ci/mmol at end of synthesis). The lipophilicity of [11C]MTICU was determined by octanol/water partition coefficient (LogP). Blood stability of this tracer in vitro and in vivo was measured by HPLC analysis. Biodistribution using female Sprague-Dawley rats was performed, including examination of uptake in cerebellum and olfactory bulb (high nNOS) as well as cortex and brain stem (low nNOS). Carbon-11-MTICU was administered to a female baboon and brain images were obtained using a Siemens ECAT EXACT scanner for determination of brain regional uptake and blood-brain barrier permeability. RESULTS: At 30 min postinjection, [11C]MTICU remained 64% intact in vivo and 95% intact in vitro. Lipophilicity estimation gave Log p = 1.08 +/- 0.08 (n = 6). The brain (0.11% ID/g)-to-blood (0.20% ID/g) ratio was 1:2 at 30 min postinjection. Uptake in the cerebellum was 20% higher than in either the cortex or the brain stem (p < 0.05). Blockage using 1 mg/kg MTICU reduced uptake in the cerebellum and the cortex by 22%, but did not affect the brain stem. PET imaging showed that [11C]MTICU brain uptake, corrected for blood volume, was stable from 10 min to 1 hr at approximately 0.4% ID/organ. PET images of a baboon brain showed increased uptake in the region of the olfactory bulb compared to uniform biodistribution in the rest of the brain. CONCLUSION: The [11C]MTICU is a tracer that is potentially useful in determining nNOS levels in vivo.

S-alkyl-L-thiocitrullines. Potent stereoselective inhibitors of nitric oxide synthase with strong pressor activity in vivo.

Nitric oxide synthase catalyzes the oxidation of a guanidino nitrogen of L-arginine to nitric oxide with concomitant formation of citrulline. Enzyme activity is inhibited by a variety of N omega-monosubstituted L-arginine analogs including N omega-alkyl-, N omega-amino-, and N omega-nitro-L-arginine derivatives. We report here that both constitutive and inducible isoforms of nitric oxide synthase are strongly inhibited by S-alkyl-L-thiocitrullines (N delta-(S-alkyl)isothioureido-L-ornithines) with n-alkyl groups of one to three carbons. These compounds represent a novel class of inhibitors and are the most potent nitric oxide synthase-inhibiting amino acids described to date. Inhibition is reversible, stereoselective, and competitive with L-arginine. Spectral studies show no direct interaction of inhibitor sulfur with heme iron, a result in contrast to that seen previously with the parent compound, L-thiocitrulline. The S-alkyl-L-thiocitrullines have strong pressor activity in normotensive control rats; S-methyl-L-thiocitrulline reverses hypotension in a rat model of septic peritonitis and in dogs administered endotoxin. These latter findings suggest that the inhibitors may have therapeutic utility in treating hypotension due to the overproduction of nitric oxide.

Potent and selective inhibition of human nitric oxide synthases. Selective inhibition of neuronal nitric oxide synthase by S-methyl-L-thiocitrulline and S-ethyl-L-thiocitrulline.

Potent and selective inhibition of neuronal nitric oxide synthase (nNOS) compared to endothelial NOS (eNOS) and inducible NOS (iNOS) may be useful to treat cerebral ischemia (stroke) and other neurodegenerative diseases. S-Methyl-L-thiocitrulline (Me-TC) and S-ethyl-L-thiocitrulline (Et-TC) inhibited the oxidation of L-arginine and the L-arginine-independent oxidation of NADPH by nNOS from human brain. Me-TC and Et-TC were slow, tight binding inhibitors of nNOS with second-order association rate constants (kon) of 2.6 x 10(5) M-1 s-1 and 1.3 x 10(5) M-1 s-1, respectively. The respective dissociation rate constants (koff) were 3 x 10(-4) s-1 and 0.7 x 10(-4) s-1. Thus, the Kd values calculated from koff/kon were 1.2 and 0.5 nM, respectively. L-Arginine was a competitive inhibitor of Me-TC and Et-TC binding with competition constant (Ks) values of 2.2 and 2.7 microM, respectively. The Km of nNOS for L-arginine was 1.6 microM. The active site concentration of nNOS was estimated by titration with Et-TC. Based on this active site concentration, a kcat of 0.4 s-1 for the oxidation of L-arginine, was calculated. Me-TC and Et-TC were less potent inhibitors of human iNOS (Ki values of 34 and 17 nM, respectively) and human eNOS (Ki values of 11 and 24 nM). Thus, Me-TC and Et-TC were 10- and 50-fold, respectively, more potent inhibitors of nNOS than eNOS. Furthermore, Me-TC was also 17-fold selective for rat nNOS in neuronal tissue compared to rat eNOS in vascular endothelium, suggesting that Me-TC may be selective for nNOS in vivo and therefore, may be therapeutically useful to treat neurodegenerative diseases.

Synthesis of L-thiocitrulline, L-homothiocitrulline, and S-methyl-L-thiocitrulline: a new class of potent nitric oxide synthase inhibitors.

Nitric oxide synthase catalyzes the NADPH- and O2-dependent conversion of L-arginine to L-citrulline and nitric oxide. L-Thiocitrulline, L-homothiocitrulline, and S-methyl-L-thiocitrulline, novel citrulline analogs, have been synthesized and are shown to be potent inhibitors of both the constitutive brain and the inducible smooth muscle isoforms of nitric oxide synthase. Although many N omega-monosubstituted arginine derivatives inhibit nitric oxide synthase, inhibitory citrulline derivatives have not previously been reported. S-Methyl-L-thiocitrulline is significantly more potent than N omega-methyl-L-arginine, the prototypic nitric oxide synthase inhibitor.

Enzymatic syntheses of carbamyl phosphate, L-citrulline, and N-carbamyl L-aspartate labeled with either 13N or 11C.

[13N]- and [11C]carbamyl phosphate, L-[omega-13N]citrulline, L-[ureido-11C]citrulline, [carbamyl-13N]- and [carbamyl-11C]carbamyl-L-aspartate were synthesized using carbamyl phosphate synthetase co-immobilized with either aspartate transcarbamylase or ornithine transcarbamylase. Carbamyl L-[13N]aspartate was enzymatically prepared from carbamyl phosphate and L-[13N]aspartate. The tissue distribution of radioactivity in mice after injection of radiolabeled ammonia, carbamyl phosphate or citrulline was studied. The tissue distribution of isotope derived from [13N]carbamyl phosphate and [13N]ammonia were similar, with the exception of liver, brain and pancreas, in which 13NH3 uptake was higher after retroorbital injection. The distribution of label derived from L-[omega-13N]- and L-[ureido-11C]citrulline was similar. Substantial tumor (Sarcoma-180) uptake of label from L-citrulline was observed.