Inhibition of redox cycling of methoxatin (PQQ), and of superoxide release by phagocytic white cells

Pyrroloquinoline quinone (PQQ) decreases myocardial infarct size and improves cardiac function in rat models of ischemia and ischemia/reperfusion

As pyrroloquinoline quinone (PQQ) is a redox cofactor in mammals, we asked if it is cardioprotective. Rats were subjected to 2 h of left anterior descending (LAD) coronary artery ligation without reperfusion (model 1, ischemia). In model 2 (ischemia/reperfusion), rats were subjected to 17 or 30 min of LAD occlusion and 2 h of reperfusion. PQQ (15-20 mg/kg) was given i.p., either 30 min before LAD occlusion (Pretreatment) or i.v. at the onset of reperfusion (Treatment). In model 1, PQQ reduced infarct size (10.0 +/- 1.5 vs 19.1 +/- 2.1%, P < 0.01). In model 2, either PQQ Pretreatment or Treatment also reduced infarct size (18.4 +/- 2.3 and 25.6 +/- 3.5% vs 38.1 +/- 2.6%, P < 0.01). PQQ resulted in higher LV developed pressure and LV (+)dP/dt after 1-2 h of reperfusion (P < 0.05), and fewer ventricular fibrillation episodes. PQQ dose (5-20 mg/kg) was inversely related to infarct size. PQQ reduced myocardial tissue levels of malondialdehyde (MDA), an indicator of lipid peroxidation (316 +/- 88 vs 99 +/- 14 nmol/g, P < 0.01). PQQ given either as Pretreatment or as Treatment at the onset of reperfusion is highly effective in reducing infarct size and improving cardiac function in a dose-related manner in rat models of ischemia and ischemia/reperfusion. The optimal dose in this study, which exhibited neither renal nor hepatic toxicity, was 15 mg/kg, but lower doses may also be efficacious. We conclude that PQQ, which appears to act as a free radical scavenger in ischemic myocardium, is a highly effective cardioprotective agent.

Inhibition of membrane-bound methane monooxygenase and ammonia monooxygenase by diphenyliodonium: implications for electron transfer

Diphenyliodonium (DPI) is known to irreversibly inactivate flavoproteins. We have found that DPI inhibits both membrane-bound methane monooxygenase (pMMO) from Methylococcus capsulatus and ammonia monooxygenase (AMO) of Nitrosomonas europaea. The effect of DPI on NADH-dependent pMMO activity in vitro is ascribed to inactivation of NDH-2, a flavoprotein which we proposed catalyzes reduction of the quinone pool by NADH. DPI is a potent inhibitor of type 2 NADH:quinone oxidoreductase (NDH-2), with 50% inhibition occurring at approximately 5 micro M. Inhibition of NDH-2 is irreversible and requires NADH. Inhibition of NADH-dependent pMMO activity by DPI in vitro is concomitant with inhibition of NDH-2, consistent with our proposal that NDH-2 mediates reduction of pMMO. Unexpectedly, DPI also inhibits pMMO activity driven by exogenous hydroquinols, but with approximately 100 micro M DPI required to achieve 50% inhibition. Similar concentrations of DPI are required to inhibit formate-, formaldehyde-, and hydroquinol-driven pMMO activities in whole cells. The pMMO activity in DPI-treated cells greatly exceeds the activity of NDH-2 or pMMO in membranes isolated from those cells, suggesting that electron transfer from formate to pMMO in vivo can occur independent of NADH and NDH-2. AMO activity, which is known to be independent of NADH, is affected by DPI in a manner analogous to pMMO in vivo: approximately 100 micro M is required for 50% inhibition regardless of the nature of the reducing agent. DPI does not affect hydroxylamine oxidoreductase activity and does not require AMO turnover to exert its inhibitory effect. Implications of these data for the electron transfer pathway from the quinone pool to pMMO and AMO are discussed.

Characterization of pyrroloquinoline quinone amino acid derivatives by electrospray ionization mass spectrometry and detection in human milk

We describe a HPLC method coupled to electrospray ionization mass spectrometry (ESI/MS) for quantification and identification of pyrroloquinoline quinone (PQQ) and condensation products formed upon incubation of PQQ with amino acids (IPQ; imidazolopyrroloquinoline and I/OPQ/R; imidazolopyrroloquinoline with attached R-group). More importantly, using these methods we demonstrate the presence of both PQQ and IPQ in human milk in nanomolar to micromolar concentrations. PQQ was incubated with amino acids and condensation products were separated by HPLC. Fractions corresponding to each product were collected and molecular masses were determined using ESI/MS. Ala, Asp, Arg, Cys, Gly, Glu, Ser, Thr, Trp, and Tyr form IPQ upon incubation with PQQ. Yields of IPQ were low (<5%) for Asp and Glu, yet high (>60%) for Thr. In addition to IPQ, Ala, Arg, Cys, Ser, Trp, and Tyr formed IPQ/R derivatives. His, Ile, Leu, Glu, Leu, Lys, Met, and Phe form only IPQ/R derivatives. Proline did not react with PQQ. Mass spectra indicate that PQQ forms stable hydrated carbonyls and decarboxylates easily. Although mass spectra were complicated by the oxidation state of the quinone and decarboxylation of PQQ, these methods are invaluable for the rapid detection of the full range of PQQ adducts in biological matrices.

Pyrroloquinoline quinone: a novel vitamin?

Pyrroloquinoline quinone (PQQ), otherwise known as methoxatin, is a water-soluble, redox-cycling orthoquinone that was initially isolated from cultures of methylotropic bacteria. It has been found to be a cofactor of some bacterial alcohol dehydrogenases, and is present in many animal tissues. It may be a novel vitamin because it has been shown to be essential for normal growth and development. The redox-cycling ability of PQQ enables it to scavenge or generate superoxide. When fed to animals as a supplement, PQQ prevents oxidative changes that would ordinarily occur. It has been reported to inhibit glutamate decarboxylase activity and protect against N-methyl-D-aspartate (NMDA) receptor-mediated neurotoxicity in the brain. It appears that in the whole animal, however, PQQ does not cross the blood-brain barrier. Furthermore, it increases nerve growth factor (NGF) synthesis in mouse astroglial cells, but has to be bound to glycine to penetrate and exert this effect in whole brain. It may therefore be regarded as a "Janus faced" molecule, with its potential for a therapeutic role in the brain still in question.

Reactive oxygen species and antioxidants in inflammatory diseases

This paper aims to review the rôle of free radical-induced tissue damage and antioxidant defence mechanisms in inflammatory diseases that involve pathogenic processes similar to the periodontal diseases. There is a clearly defined and substantial role for free radicals or reactive oxygen species (ROS) in periodontitis, but little research has been performed in this area. This paper reviews the considerable data available relating ROS activity and antioxidant defence to inflammatory diseases and attempts to draw parallels with periodontitis, in an effort to stimulate more periodontal research in this important area. The recent discovery of the transcription factor nuclear factor kappa B (NF-kappa B) is reviewed and several potential pathways for cytokine-induced periodontal tissue damage, mediated by NF-kappa B1 are discussed. Emphasis is placed on cytokines that have been studied in periodontitis, principally TNF-alpha, IL-1, IL-6, IL-8 and beta-interferon. The link between cellular production of such important mediators of inflammation and the antioxidant (AO) thiols, cysteine and reduced glutathione (GSH), is discussed and it is hypothesised that NF-kappa B antagonists may offer important therapeutic benefits.