Structural and thermodynamic analysis of the hetero-association of theophylline with aromatic drug molecules

Pre-nucleation aggregation based on solvent microheterogeneity

The microheterogeneous region of aqueous acetonitrile leads to preferred localisation and aggregation of caffeine and theophylline on the interface.

NMR spectroscopy on flavins and flavoproteins

(1)H-, (11)B-, (13)C-, (15)N-, (17)O-, (19)F-, and (31)P-NMR chemical shifts of flavocoenzymes and derivatives of it, as well as of alloxazines and isoalloxazinium salts, from NMR experiments performed under various experimental conditions (e.g., dependence of the chemical shifts on temperature, concentration, solvent polarity, and pH) are reported. Also solid-state (13)C- and (15)N-NMR experiments are described revealing the anisotropic values of corresponding chemical shifts. These data, in combination with a number of coupling constants, led to a detailed description of the electronic structure of oxidized and reduced flavins. The data also demonstrate that the structure of oxidized flavin can assume a configuration deviating from coplanarity, depending on substitutions in the isoalloxazine ring, while that of reduced flavin exhibits several configurations, from almost planar to quite bended. The complexes formed between oxidized flavin and metal ions or organic molecules revealed three coordination sites with metal ions (depending on the chemical nature of the ion), and specific interactions between the pyrimidine moiety of flavin and organic molecules, mimicking specific interactions between apoflavoproteins and their coenzymes. Most NMR studies on flavoproteins were performed using (13)C- and (15)N-substituted coenzymes, either specifically enriched in the pterin moiety of flavin or uniformly labeled flavins. The chemical shifts of free flavins are used as a guide in the interpretation of the chemical shifts observed in flavoproteins. Although the hydrogen-bonding pattern in oxidized and reduced flavoproteins varies considerably, no correlation is obvious between these patterns and the corresponding redox potentials. In all reduced flavoproteins the N(1)H group of the flavocoenzyme is deprotonated, an exception is thioredoxin reductase. Three-dimensional structures of only a few flavoproteins, mostly belonging to the family of flavodoxins, have been solved. Also the kinetics of unfolding and refolding of flavodoxins has been investigated by NMR techniques. In addition, (31)P-NMR data of all so far studied flavoproteins and some (19)F-NMR spectra are discussed.

Caffeine and other methylxanthines as interceptors of food-borne aromatic mutagens: inhibition of Trp-P-1 and Trp-P-2 mutagenic activity

Caffeine is one of the most important biologically active food components. In this article, we demonstrate that caffeine and other methylxanthines significantly reduce the mutagenic activity of two food-derived heterocyclic aromatic amines, Trp-P-1 and Trp-P-2 in the Salmonella typhimurium TA98 strain. Moreover, protection against Trp-P-1-induced mutagenicity was independent of liver S9 enzymatic fraction, suggesting that mechanisms other than modulation of mutagen bioactivation can contribute to the observed protective effects. UV-vis spectroscopy and computational studies revealed that methylxanthines intercept Trp-P-1 and Trp-P-2 in noncovalent molecular complexes, with association constants (KAC) in the 10(2) M(-1) range. Enthalpy values (ΔH about -30 kJ·mol(-1)) of mutagen-methylxanthine heterocomplexation obtained microcalorimetrically correspond to stacking (π-π) interactions. Finally, we demonstrated that the biological activity of Trp-P-1 and Trp-P-2 is strictly dependent on the presence of the mutagen in a free (unbound with methylxanthine) form, suggesting that mutagen sequestration in stacking heterocomplexes with methylxanthines can decrease its bioavailability and diminish its biological effects.

Heterocyclic Aromatic Amines Heterocomplexation with Biologically Active Aromatic Compounds and Its Possible Role in Chemoprevention

Food-borne heterocyclic aromatic amines (HCAs) are known mutagens and carcinogens present especially in Western population diet, which contains large amount of meat and its products. HCAs are capable of interacting with DNA directly through the formation of covalent adducts, however this process requires biological activation in liver, mainly by cytochrome P450 enzymes. This process may produce mutations and in consequence may contribute to the development of cancer. However, there are many studies showing that several biologically active aromatic compounds (BACs) may protect against genotoxic effects of HCAs. Direct interactions and noncovalent heterocomplexes formation may be one of the most important mechanisms of such protection. This work describes several BACs present in human diet, which are capable of molecular complexes formation with HCAs and protect cells as well as whole organisms against HCAs action.

Physicochemical Mechanisms of Synergistic Biological Action of Combinations of Aromatic Heterocyclic Compounds

The mechanisms of synergistic biological effects observed in the simultaneous use of aromatic heterocyclic compounds in combination are reviewed, and the specific biological role of heteroassociation of aromatic molecules is discussed.

Caffeine, pentoxifylline and theophylline form stacking complexes with IQ-type heterocyclic aromatic amines

Methylxanthines (MTX), in particular caffeine (CAF), are known as the most widely consumed alkaloids worldwide. Many accumulated statistical data indicate the protective effect of CAF intake against several types of cancer. One of the possible explanations of this phenomenon is direct non-covalent interaction between CAF and aromatic mutagen/carcinogen molecules through stacking (π-π) complexes formation. Here we demonstrate that CAF and other MTX, pentoxifylline (PTX) and theophylline (TH), form stacking complexes with carcinogenic imidazoquinoline-type (IQ-type) food-borne heterocyclic aromatic amines (HCAs). We estimated neighborhood association constants (K(AC) of the order of magnitude of 10(2)M(-1)) in neutral and acidic environment and enthalpy changes (ΔH values between -15.1 and -39.8kJ/mol) for these interactions using UV-Vis spectroscopy, calculations based on thermodynamical model of mixed aggregation and titration microcalorimetry. Moreover, using Ames test with Salmonella typhimurium TA98 strain and recently developed mutagenicity assay based on bioluminescence of Vibrio harveyi A16 strain, we demonstrated a statistically significant reduction in HCAs mutagenic activity in the presence of MTX.