Lipoamide dehydrogenase and diaphorase catalyzed conversion of some NO donors to NO and reduction of NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO).

One of the key functions of nitric oxide (NO) in human is to dilate blood vessels. We tested glycerol trinitrate (GTN) and other well-known NO donors together with those bearing a >C=N-OH group for possible conversion to NO (or nitrites, respectively) by diaphorase (DP) and lipoamide dehydrogenase (LAD). Both, DP and LAD were unable to convert formamidoxime (FAM), acetone oxime (AC), acetohydroxamic acid (AHA) and Nomega-hydroxy-L-arginine (L-NOHA). On the other hand, we observed good conversion of GTN without the requirement of superoxide anion. However, superoxide anion participated to a varying extent in the conversion of other donors (formaldoxime (FAL), acetaldoxime (AO), nitroprusside (NP), S-nitrosoglutathione (SNOG), S-nitroso-N-acetylpenicillamine (SNAP) and hydroxylamine (HA)). All DP- and LAD-mediated reactions were inhibited by diphenyleneiodonium chloride (DPI), (an inhibitor of flavine enzymes), in a concentration-dependent manner. For these inhibition reactions we determined Ki and IC50 values. In addition, we found that conversion of SNOG was significantly accelerated by glutathione reductase (GTR). Like with DP, 2-phenyl- 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) was reduced also by LAD and thioredoxin reductase (TRR). In summary, we found that LAD significantly accelerates the conversion of a defined subset of NO donors to NO, especially GTN, and eliminates the NO scavenging effect of PTIO.

Effect of drugs on cholesterol crystallization in an artificial bile model and relation of this effect to drug binding to albumin.

Substances that can affect the crystallization of cholesterol from human bile and consequently the gallstone formation have been given considerable attention. We improved the model system for testing cholesterol crystallization-affecting activity (promoting or inhibiting) of substances and used it for some drugs that are excreted into bile. Besides other factors natural lipid-protein complexes isolated from the native human bile have been shown to be responsible for nucleation and fast crystal growth in cholesterol supersaturated model bile. Artificial lipid-protein complex of taurolithocholate, human serum albumin and Ca2+ (TLTC-HSA-Ca2+) exhibited a lower crystallization activity than both the artificial lipid-protein complexes of taurodeoxycholate, human serum albumin and Ca2+ and the lipid-protein complex isolated from native human bile. The model bile supplemented with this artificial lipid-protein complex (TLTC-HSA-Ca2+) formed a convenient system for testing of various substances (drugs) for their crystallization-affecting activity. From the 20 tested drugs, which could occur at least in small amounts in human bile, the highest crystallization-promoting activity was found for complexes with ampicillin, butorphanol and colchicine. Complexes with tetracycline, thioridazine and doxycycline were the strongest inhibitors. The drugs, which had some effect on cholesterol crystallization, affected somehow the artificial lipid-albumin complex by displacing its components. Interactions of different drugs with HSA and its artificial complexes with the conjugated bile salt and Ca2+ ions were followed by absorption spectroscopy to observe displacement interactions. On the basis of these experiments we could classify drugs into four groups which differ by their effects on spectral characteristics of complexes.