Effects of nicomethanol hydrofluoride on dental enamel and synthetic apatites: a role for anti-caries protection.

AIM: To analyse the anti-caries properties of nicomethanol hydrofluoride (NH) and the benefit of its combination with siliglycol, a coating agent. METHODS: Fluoride (F) uptake by dental enamel and synthetic apatite treated with NH was measured in vitro and compared to treatment with mineral fluorides. The addition of siliglycol was also tested. The effect of NH (as a mouthwash) on salivary pH was also investigated in healthy human subjects and compared to the effect of a placebo and of nicomethanol alone. RESULTS: In vitro experiments showed a greater and faster F uptake on dental enamel or synthetic apatite treated with NH compared to sodium fluoride. F uptake was improved further by the addition of siliglycol. In healthy human subjects, pH reduction was strongly inhibited 5 min after two mouthrinses with NH. This effect was less pronounced but still statistically significant at 15 and 30 min (p < 0.05). CONCLUSIONS: NH was able to promote the fixation of F ions and strengthen the dental structure. Its combination with siliglycol further improved F uptake by the tooth and the control/inhibition of dental biofilm development.

Cytotoxic trans-platinum(II) complex with 3-hydroxymethylpyridine: Synthesis, X-ray structure and biological activity evaluation.

To assess the potential cytostatic properties of Pt(II) complexes with 3-hydroxymethylpyridine (3-hmpy) as the only carrier ligand, novel cis-[PtCl2(3-hmpy)2] (1) and trans-[PtCl2(3-hmpy)2] (2) have been prepared. Elemental analysis, FTIR spectroscopy, multinuclear NMR spectroscopy and X-ray crystallography were used to determine their structures. Based on the results obtained with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay and clonogenic assay on T24 human bladder carcinoma cells (T24), the most potent compound 2 was further tested for cytotoxicity in human ovarian carcinoma cell lines - cisplatin sensitive (IGROV 1) and its resistant subclone (IGROV 1/RDDP). The cytotoxicity of compound 2 in IGROV 1/RDDP is comparable to cisplatin. Furthermore, compound 2 induced severe conformational changes in plasmid DNA, which resulted in a delayed onset of apoptosis in T24 cells, and higher amounts of Pt in tumours and serum compared to cisplatin. In addition, in vivo antitumour effectiveness was comparable to that of cisplatin with a smaller reduction of animals' body weight, thus demonstrating that it is a promising transplatin analogue which deserves further studies.

Enzymatic oxidation of NADP+ to its 4-oxo derivative is a side-reaction displayed only by the adrenodoxin reductase type of ferredoxin-NADP+ reductases.

We have previously shown that Mycobacterium tuberculosis FprA, an NADPH-ferredoxin reductase homologous to mammalian adrenodoxin reductase, promotes the oxidation of NADP(+) to its 4-oxo derivative 3-carboxamide-4-pyridone adenine dinucleotide phosphate [Bossi RT, Aliverti A, Raimondi D, Fischer F, Zanetti G, Ferrari D, Tahallah N, Maier CS, Heck AJ, Rizzi M et al. (2002) Biochemistry41, 8807-8818]. Here, we provide a detailed study of this unusual enzyme reaction, showing that it occurs at a very slow rate (0.14 h(-1)), requires the participation of the enzyme-bound FAD, and is regiospecific in affecting only the C4 of the NADP nicotinamide ring. By protein engineering, we excluded the involvement in catalysis of residues Glu214 and His57, previously suggested to be implicated on the basis of their localization in the three-dimensional structure of the enzyme. Our results substantiate a catalytic mechanism for 3-carboxamide-4-pyridone adenine dinucleotide phosphate formation in which the initial and rate-determining step is the nucleophilic attack of the nicotinamide moiety by an active site water molecule. Whereas plant-type ferredoxin reductases were unable to oxidize NADP(+), the mammalian adrenodoxin reductase also catalyzed this unusual reaction. Thus, the 3-carboxamide-4-pyridone adenine dinucleotide phosphate formation reaction seems to be a peculiar feature of the mitochondrial type of ferredoxin reductases, possibly reflecting conserved properties of their active sites. Furthermore, we showed that 3-carboxamide-4-pyridone adenine dinucleotide phosphate is good ligand and a competitive inhibitor of various dehydrogenases, making this nucleotide analog a useful tool for the characterization of the cosubstrate-binding site of NADPH-dependent enzymes.

Purification and kinetic characterization of Haemophilus parasuis malate dehydrogenase.

Haemophilus parasuis malate dehydrogenase ((S)-malate:NAD+ oxidoreductase; EC 1.1.1.37) isolated from cell sonicates was purified 584-fold to electrophoretic homogeneity with a 19% recovery and a specific activity of 222 units/mg protein. SDS-polyacrylamide gel electrophoresis and molecular exclusion chromatography indicated the purified enzyme to be a dimer composed of 34,600 molecular weight subunits. Kinetic parameters for all four substrates in the forward and reverse reactions indicated a sequential mechanism for this enzymic process. Product and dead-end inhibition studies were consistent with an ordered bi-bi mechanism in which NAD is the first substrate bound to the enzyme and NADH the second product released. Protection against thermodenaturation of the enzyme by NAD and not by malate was supportive of this mechanism. A pronounced product inhibition by NADH (K(i) = 9.0 microM) was observed. Although NADP did not serve as a coenzyme, a number of analogs of NAD structurally altered in the nitrogen base moieties were observed to function as coenzymes in the oxidation of malate catalyzed by the purified malate dehydrogenase. Coenzyme-competitive inhibition of the malate dehydrogenase was observed with five adenosine derivatives and six structural analogs of NAD. Of the NAD analogs studied as inhibitors, 3-pyridylcarbinol adenine dinucleotide was the most effective (K(i) = 18 microM). Although inhibition of growth of H. parasuis by this analog was observed, it was less effective (K(i) = 136 microM) than the inhibition of the purified dehydrogenase.

In vitro acid decalcification of human surface enamel pretreated with toothpaste slurries.

An in vitro caries-like challenge of human tooth enamel treated with inorganic fluoride (NaF) and organic fluoride (aliphatic and aromatic amine fluorides) toothpaste slurries has been investigated. The results revealed that the organic fluoride-containing toothpastes affected positively the resistance of tooth enamel to demineralization.

Effects of nicotinic acid, nicotinamide, and pyridylcarbinol in pharmacological dosages on lipid metabolism in humans.

The clinical use of nicotinic acid, nicotinamide, and pyridylcarbinol as drugs against hypercholesterolemia is critically reviewed. Though several questions remain open as to the mode of action of these compounds, it is concluded that they indeed belong to the most useful drugs for the treatment of hypercholesterolemia and for the prevention of coronary disease.

Effects of the lipolysis inhibiting agent beta-pyridylcarbinol (Ronicol) in acute myocardial ischaemia.

The antilipolytic, nicotinic acid analogue beta-pyridylcarbinol (Ronicol) has previously been reported to decrease the free fatty acid (FFA) concentration of the arteria-blood, and to moderate the FFA-uptake and O2-consumption of the myocardium; on this basis, the drug may be expected to exert a cardioprotective action. The cardiac effects of Ronicol were therefore studied on a self-control, 'single-vessel' coronary artery ligature dog model. The left anterior descending coronary artery (LAD) was prepared in the in situ heart of anaesthetized, thoracotomized animals. Following the control ligation, a stabilization period and Ronicol infusion (1 mg/kg iv. during 10 minutes), the LAD was repeatedly ligated. The duration of the individual occlusions was 10 minutes. Ronicol significantly decreased the arterial FFA concentration and the epicardial ST segment elevation; its antilipolytic and anti-ischaemic effects were protracted and were still observed 120 minutes after pretreatment. The drug did not decrease the inhomogeneity of ventricular depolarization in the ischaemic myocardium and in the dose applied it had no influence on the heart rate, arterial blood pressure, left ventricular end-diastolic pressure and left ventricular contractility (LV dP/dtmax). In the canine myocardial infarction model employed it was observed that the duration of the anti-ischaemic effect of Ronicol (1 mg/kg iv.) is about 120 minutes. It has the advantage that it does not possess the unwanted cardiovascular side-effects displayed by nicotinic acid observed by us too in this model earlier (Cardiol. Hung. 13, 33-41, 1984).

Effect of beta-pyridyl-carbinol on platelet aggregation.

We studied the anti-platelet aggregation activity of beta-pyridyl-carbinol (b-PC) (Ronicol, Roche). This compound has a chemical structure similar to nicotinic acid and is therapeutically indicated in functional and organic circulatory processes. We determined the in vitro antiaggregation activity induced by ADP (4 microM) and collagen (20 micrograms/ml) using Cardinal and Flower's technique. Antithrombotic activity was assessed in rats by measuring the duration of ADP-induced (12.40 micrograms/kg i.v.) respiratory dysfunction in 2 groups: one given 17.14 mg/kg beta-pyridyl-carbinol for 8 consecutive days before testing and controls. In vitro and in vivo results were highly significant. Circulating platelet count increased in b-PC treated animals. Systolic and diastolic pressures remained unmodified during administration of b-PC.

Inhibitory effects of niacin and its analogues on induction of ornithine decarboxylase activity by diethylnitrosamine in rat liver.

Pharmacological doses of niacin and its analogues were given intraperitoneally to rats with and without coadministration of a hepatocarcinogenic dose of diethylnitrosamine (DEN), and their effects on the induction of ornithine decarboxylase (ODC, EC 4.1.1.17) activity in the rat liver were studied. The induction of ODC activity by DEN was inhibited by 74.3, 85.5, 94.6, 97.6, 72.6 and 55.2% by nicotinamide, nicotinic acid, 3-hydroxymethylpyridine, beta-picoline, pyridine-3-aldehyde and ethylnicotinate respectively. When given alone, these analogues did not induce ODC activity. All these compounds are known to have a niacin effect. DEN-induced ODC activity was also inhibited by 84.0, 93.3, 52.8 and 75.9% by 6-aminonicotinamide, picolinic acid, pyridine-3-sulfonic acid and thionicotinamide, respectively, but, peculiarly, they induced ODC activity by their administration alone. These niacin analogues are known to have anti-niacin effects. Tryptophan, N'-methylnicotinamide and isonicotinic acid hydrazide did not affect the DEN-induced ODC activity but could induce ODC by themselves. Tryptophan belongs to the former group and isonicotinic acid hydrazide to the latter group. The reason for these discrepancies is discussed.

Antihyperlipidemic properties of beta-pyridylcarbinol. A review of preclinical studies.

The available preclinical literature on the antihyperlipidemic properties of beta-pyridylcarbinol is reviewed. Similarities between the pharmacological profiles for beta-pyridylcarbinol and nicotinic acid, and evidence for the metabolic conversion of beta-pyridylcarbinol to nicotinic acid are discussed. Several reviews discussing the antihyperlipidemic effects of beta-pyridylcarbinol (beta-PC, nicotinyl alcohol, Roniacol) and nicotinic acid (NA) have appeared during the last 15 years (1-6). However, continuing clinical interest in the ability of nicotinic acid analogs to reduce plasma lipids indicated that an update and critical evaluation of the preclinical literature on this subject would be of value in order to permit a more complete assessment of the relevance of several animal models to effects in human subjects. The literature reviewed included (a) preclinical studies of beta-PC where it was the sole compound examined; (b) comparative studies of beta-PC and NA; and (c) studies relating to the metabolism of beta-PC. The literature chosen included experiments involving fasted animals, satiated animals, and effects of Triton-induced hyperlipidemia. Data on other pharmacological properties of beta-PC and/or NA that might contribute to antihyperlipidemic efficacy (e.g., fibrinolysis, inhibition of platelet aggregation, erythrocyte membrane changes) were also included where available.

Kinetic studies with the low-Km aldehyde reductase from ox brain.

Initial-rate studies of the low-Km aldehyde reductase-catalysed reduction of pyridine-3-aldehyde by NADPH gave families of parallel double-reciprocal plots, consistent with a double-displacement mechanism being obeyed. Studies on the variation of the initial velocity with the concentration of a mixture of the two substrates were also consistent with a double-displacement mechanism. In contrast, the initial-rate data indicated that a sequential mechanism was followed when NADH was used as the coenzyme. Product-inhibition studies, however, indicated that a compulsory-order mechanism was followed in which NADPH bound before pyridine-3-aldehyde with a ternary complex being formed and the release of pyrid-3-ylcarbinol before NADP+. The apparently parallel double-reciprocal plots obtained in the initial-rate studies with NADPH and pyridine-3-aldehyde were thus attributed to the apparent dissociation constant for the binary complex between the enzyme and coenzyme being finite but very low.

Release of disaggregatory prostanoids into circulation by nicotinic alcohol, nicotinic acid and nicotinamide.

Nicotinic alcohol, nicotinic acid and nicotinamide caused disaggregation of platelet clumps formed on collagen strip superfused with blood of anaesthetized cats. This effect was completely blocked by pretreatment of cats with 50 mg/kg of acetyl salicylic acid. Disaggregatory substance formed in cat's blood disappeared when blood had been passed through silicone coil warmed to 37 degrees C for 15 min. None of the tested substances had any disaggregatory activity when applied directly on collagen strip. It is postulated that the effect of nicotinic acid derivatives is mediated by prostacyclin which they release.

beta-Pyridylcarbinol (Ronicol) releases a prostacyclin-like substance into arterial blood of patients with arteriosclerosis obliterans.

Beta-pyridylcarbinol (Ronicol) when injected (1,2-1,4 mg/kg i.v.) into four patients with arteriosclerosis obliterans caused a release of an unstable disaggregatory substance into arterial blood of those patients. This release was not observed in other two patients who had been pretreated with aspirin (1,8 g p.o.daily). It is postulated that some of pharmacological properties of nicotinic acid derivatives are mediated through the release of endogenous PGI2-like substance.

Experimental atherosclerosis in hypercholesterolemic mini-pigs. Regression of cholesterol ester accumulation in aorta and coronary arteries after treatment with clofibrate, beta-pyridylcarbinol or a normo-lipidemic diet.

Studies have been performed on groups of mini-pigs 21-23 months of age, which after 18 months of hypercholesterolemia (approximately 10 mmol) had developed raised atherosclerotic lesions with high levels of cholesterol esters, especially in the abdominal aorta and the coronary arteries. If the hypercholesterolemia was continued for 18 months, no significant change in the cholesterol ester content in the aorta occurred; in the coronary arteries there was a significant decrease in these older pigs. If the hypercholesterolemic pigs also were treated with beta-pyridylcarbinol the findings were very similar to the first. When hypercholesterolemic pigs were treated with clofibrate, or when the hypercholesterolemic diet was replaced with the basal food for 18 months, the plasma cholesterol level was normalized (approximately 2 mmol) within 1-2 months. The cholesterol ester content in the thoracic aorta was reduced in both groups but not that in the abdominal aorta. Clofibrate decreased the cholesterol ester level in the coronary arteries when compared to the hypercholesterolemic group; the drug also reduced the free cholesterol level when compared to the basal group. We suggest that an increased plasma cholesterol level initiated the development of the atherosclerotic lesions; their later development was only partly dependent on the plasma cholesterol level.

Influence of myocardial substrate utilization on the oxygen consumption of the heart.

The effect of changing myocardial metabolism from predominantly lipid to predominantly carbohydrate utilization on myocardial oxygen consumption (MVO2) was studied in 10 closed-chest dogs. Oxygen saving potency of different metabolic interventions was quantified over a wide hemodynamic range by comparing the directly determined MVO2 with the hemodynamic parameter total left ventricular energy demand (Et), which correlates closely under control conditions with MVO2 (r = 0.98). Stimulation of carbohydrate metabolism by addition of glucose and beta-pyridyl carbinol or by activation of pyruvate dehydrogenase with dichloroacetate (DCA) shifted the cardiac respiratory quotient during beta-stimulation from 0.73 to 1.00 and 0.89, respectively, the nonesterified fatty acid/albumin ratio decreased from 4.0 to 0.5, or remained unchanged with DCA, and MVO2 was reduced by 25 and 16%, respectively. Therapeutic approaches aimed at decreasing MVO2 by changing substrate utilization are discussed.

[Validity of the transcutaneous PO2-measurement during pharmacologically induced changes of skin perfusion (author's transl)]. / Wertigkeit der transcutanen PO2-Messung bei unterschiedlicher Hautperfusion. Experimentelle Untersuchungen bei pharmakologisch induzierten Anderungen der Hautdurchblutung.

The validity of transcutaneous oxygen partial pressure (tcPO2) was tested during pharmacological vasodilatation and vasoconstriction of the skin. Measurements of transcutaneous oxygen partial pressure (tcPO2) were done on the hairless skin of the abdomen in 18 anaesthetized rabbits, when beta-pyridyl-carbonyl (Ronicol) was used as a vasodilator and vasopressin (Pitressin) as a vasoconstrictor. Vasodilation yielded no significant influence on the tcPO2-measurement. Vasoconstriction, however, resulted in a marked decrease of the tcPO2-signal (p less than 0.001). During this phase tcPO2 did no longer reflect arterial PO2 which remained nearly constant. In this experimental model vasoconstrictive drugs may cause a marked underestimation of the arterial oxygen tension. The dependence of the tcPO2-measurement on maximal local skin perfusion should be considered in intensive care patients.