Formation of stacking complexes between caffeine (1,2,3-trimethylxanthine) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine may attenuate biological effects of this neurotoxin

Microbial metabolism of caffeine and potential applications in bioremediation

With increasing global consumption of caffeine-rich products, such as coffee, tea, and energy drinks, there is also an increase in urban and processing waste full of residual caffeine with limited disposal options. This waste caffeine has been found to leach into the surrounding environment where it poses a threat to microorganisms, insects, small animals, and entire ecosystems. Growing interest in harnessing this environmental contaminant has led to the discovery of 79 bacterial strains, eight yeast strains, and 32 fungal strains capable of metabolizing caffeine by N-demethylation and/or C-8 oxidation. Recently observed promiscuity of caffeine-degrading enzymes in vivo has opened up the possibility of engineering bacterial strains capable of producing a wide variety of caffeine derivatives from a renewable resource. These engineered strains can be used to reduce the negative environmental impact of leached caffeine-rich waste through bioremediation efforts supplemented by our increasing understanding of new techniques such as cell immobilization. Here, we compile all of the known caffeine-degrading microbial strains, discuss their metabolism and related enzymology, and investigate their potential application in bioremediation.

Interaction of CYP3A4 with caffeine: First insights into multiple substrate binding

Human cytochrome P450 3A4 (CYP3A4) is a major drug-metabolizing enzyme that shows extreme substrate promiscuity. Moreover, its large and malleable active site can simultaneously accommodate several substrate molecules of the same or different nature, which may lead to cooperative binding and allosteric behavior. Due to difficulty of crystallization of CYP3A4-substrate complexes, it remains unknown how multiple substrates can arrange in the active site. We determined crystal structures of CYP3A4 bound to three and six molecules of caffeine, a psychoactive alkaloid serving as a substrate and modulator of CYP3A4. In the ternary complex, one caffeine binds to the active site suitably for C8-hydroxylation, most preferable for CYP3A4. In the senary complex, three caffeine molecules stack parallel to the heme with the proximal ligand poised for 3-N-demethylation. However, the caffeine stack forms extensive hydrophobic interactions that could preclude product dissociation and multiple turnovers. In both complexes, caffeine is also bound in the substrate channel and on the outer surface known as a peripheral site. At all sites, aromatic stacking with the caffeine ring(s) is likely a dominant interaction, while direct and water-mediated polar contacts provide additional stabilization for the substrate-bound complexes. Protein-ligand interactions via the active site R212, intrachannel T224, and peripheral F219 were experimentally confirmed, and the latter two residues were identified as important for caffeine association. Collectively, the structural, spectral, and mutagenesis data provide valuable insights on the ligand binding mechanism and help better understand how purine-based pharmaceuticals and other aromatic compounds could interact with CYP3A4 and mediate drug-drug interactions.

Synergistic Effects of Caffeine in Combination with Conventional Drugs: Perspectives of a Drug That Never Ages

Plants have been known since ancient times for their healing properties, being used as preparations against human diseases of different etiologies. More recently, natural products have been studied and characterized, isolating the phytochemicals responsible for their bioactivity. Most certainly, there are currently numerous active compounds extracted from plants and used as drugs, dietary supplements, or sources of bioactive molecules that are useful in modern drug discovery. Furthermore, phytotherapeutics can modulate the clinical effects of co-administered conventional drugs. In the last few decades, the interest has increased even more in studying the positive synergistic effects between plant-derived bioactives and conventional drugs. Indeed, synergism is a process where multiple compounds act together to exert a merged effect that is greater than that of each of them summed together. The synergistic effects between phytotherapeutics and conventional drugs have been described in different therapeutic areas, and many drugs are based on synergistic interactions with plant derivatives. Among them, caffeine has shown positive synergistic effects with different conventional drugs. Indeed, in addition to their multiple pharmacological activities, a growing body of evidence highlights the synergistic effects of caffeine with different conventional drugs in various therapeutic fields. This review aims to provide an overview of the synergistic therapeutic effects of caffeine and conventional drugs, summarizing the progress reported to date.

New Life of an Old Drug: Caffeine as a Modulator of Antibacterial Activity of Commonly Used Antibiotics

With the rapid and continuous emergence of antimicrobial resistance, bacterial infections became a significant global healthcare concern. One of the proposed strategies to combat multidrug-resistant pathogens is to use additional compounds, such as natural biologically active substances, as adjuvants for existing antibiotics. In this study, we investigated the potential of caffeine, the widely consumed alkaloid, to modulate the antibacterial effects of antibiotics commonly used in clinical practice. We used disc diffusion assay to evaluate the effects of caffeine on 40 antibiotics in two Staphylococcus aureus strains (methicillin-resistant and methicillin-sensitive). Based on the results of this step, we selected five antibiotics for which the greatest caffeine-induced improvements in antibacterial activity were observed, and further analyzed their interactions with caffeine using a checkerboard approach. Caffeine at concentrations of 250 µg/mL or higher halved the MIC values of ticarcillin, cefepime, gentamycin, azithromycin, and novobiocin for all gram-negative species investigated (Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii). At the highest caffeine concentrations tested (up to 16 mg/mL), decreases in MIC values were 8- to 16-fold. The obtained results prove that caffeine modulates the activity of structurally diverse antibiotics, with the most promising synergistic effects observed for cefepime and azithromycin toward gram-negative pathogens.

Modulatory Effects of Caffeine and Pentoxifylline on Aromatic Antibiotics: A Role for Hetero-Complex Formation

Antimicrobial resistance is a major healthcare threat globally. Xanthines, including caffeine and pentoxifylline, are attractive candidates for drug repurposing, given their well-established safety and pharmacological profiles. This study aimed to analyze potential interactions between xanthines and aromatic antibiotics (i.e., tetracycline and ciprofloxacin), and their impact on antibiotic antibacterial activity. UV-vis spectroscopy, statistical-thermodynamical modeling, and isothermal titration calorimetry were used to quantitatively evaluate xanthine-antibiotic interactions. The antibacterial profiles of xanthines, and xanthine-antibiotic mixtures, towards important human pathogens Staphylococcus aureus, Enterococcus faecium, Escherichia coli, Acinetobacter baumannii, Klebsiella pneumoniae, and Enterobacter cloacae were examined. Caffeine and pentoxifylline directly interact with ciprofloxacin and tetracycline, with neighborhood association constant values of 15.8-45.6 M-1 and enthalpy change values up to -4 kJ·M-1. Caffeine, used in mixtures with tested antibiotics, enhanced their antibacterial activity in most pathogens tested. However, antagonistic effects of caffeine were also observed, but only with ciprofloxacin toward Gram-positive pathogens. Xanthines interact with aromatic antibiotics at the molecular and in vitro antibacterial activity level. Given considerable exposure to caffeine and pentoxifylline, these interactions might be relevant for the effectiveness of antibacterial pharmacotherapy, and may help to identify optimal treatment regimens in the era of multidrug resistance.

The theory of interceptor-protector action of DNA binding drugs

The review discusses the theory of interceptor-protector action (the IPA theory) as the new self-consistent biophysical theory establishing a quantitative interrelation between parameters measured in independent physico-chemical experiment and in vitro biological experiment for the class of DNA binding drugs. The elements of the theory provide complete algorithm of analysis, which may potentially be applied to any system of DNA targeting aromatic drugs. Such analytical schemes, apart from extension of current scientific knowledge, are important in the context of rational drug design for managing drug's response by changing the physico-chemical parameters of molecular complexation.

Comparative study of binding interactions between porphyrin systems and aromatic compounds of biological importance by multiple spectroscopic techniques: A review

The specific spectroscopic and redox properties of porphyrins predestine them to fulfill the role of sensors during interacting with different biologically active substances. Monitoring of binding interactions in the systems porphyrin-biologically active compound is a key question not only in the field of physiological functions of living organisms, but also in environmental protection, notably in the light of the rapidly growing drug consumption and concurrently the production of drug effluents. Not always beneficial action of drugs on natural porphyrin systems induces to further studies, with commercially available porphyrins as the model systems. Therefore the binding process between several water-soluble porphyrins and a series of biologically active compounds (e.g. caffeine, guanine, theophylline, theobromine, xanthine, uric acid) has been studied in different aqueous solutions analyzing their absorption and steady-state fluorescence spectra, the porphyrin fluorescence lifetimes and their quantum yields. The magnitude of the binding and fluorescence quenching constants values for particular quenchers decreases in a series: uric acid > guanine > caffeine > theophylline > theobromine > xanthine. In all the systems studied there are characters of static quenching, as a consequence of the π-π-stacked non-covalent and non-fluorescent complexes formation between porphyrins and interacting compounds, accompanied simultaneously by the additional specific binding interactions. The porphyrin fluorescence quenching can be explain by the photoinduced intermolecular electron transfer from aromatic compound to the center of the porphyrin molecule, playing the role of the binding site. Presented results can be valuable for designing of new fluorescent porphyrin chemosensors or monitoring of drug traces in aqueous solutions. The obtained outcomes have also the toxicological and medical importance, providing insight into the interactions of the water-soluble porphyrins with biologically active substances.

Crystal structure of caffeinium triiodide – caffeine (1/1), C16H21I3N8O4

C16H21I3N8O4, monoclinic, P21/n (no. 14), a = 14.7257(7) Å, b = 10.5712(5) Å, c = 16.7501(8) Å, β = 114.408(2)°, V = 2374.4(2) Å3, Z = 4, R gt(F) = 0.0254, wR ref(F 2) = 0.0760, T = 290(2) K.

Pentoxifylline as a modulator of anticancer drug doxorubicin. Part II: Reduction of doxorubicin DNA binding and alleviation of its biological effects

Anticancer drug doxorubicin is commonly used in cancer treatment. However, drug's severe side effects make toxicity reduction important matter. Another biologically active aromatic compound, pentoxifylline, can sequester aromatic compounds in stacking complexes reducing their bioactivity. This work deals with the problem of alleviating doxorubicin side effects by pentoxifylline. We employed a wide spectrum of prokaryotic and eukaryotic cellular assays. In addition, we used the doxorubicin-pentoxifylline mixed association constant to quantitatively assess pentoxifylline influence on the doxorubicin mutagenic activity. Obtained results indicate strong protective effects of pentoxifylline towards doxorubicin, observed on bacteria and human keratinocytes with no such effects observed on the cancer cells. It may be hypothesized that, considering much shorter half-life of pentoxifylline than doxorubicin, simultaneous administration of doxorubicin and pentoxifylline will lead to gradual release of doxorubicin from complexes with pentoxifylline to reach desired therapeutic concentration. Proposed results shed light on the possible doxorubicin chemotherapy modification and its side effects reduction without the loss of its therapeutic potential.

Pentoxifylline as a modulator of anticancer drug doxorubicin. Part I: Reduction of doxorubicin DNA binding

Pentoxifylline--biologically active aromatic compound--has a well established capability to sequester aromatic ligands, such as an anticancer drug--doxorubicin--in mixed stacking aggregates. Formation of such hetero-complexes may influence biological activity of secluded drug. Presented work shows assessment of pentoxifylline influence on doxorubicin direct interactions with DNA employing biophysical methods. Achievement of this goal required statistical-thermodynamical model allowing numerical four-parameter analysis of experimental mixture--an issue that was successfully tackled by merging McGhee--von Hippel and Kapuscinski--Kimmel models. Results obtained with new model are well in agreement with data obtained with separate experiments with each of these two models and show reduction of doxorubicin in free (monomeric, dimeric) and complexed with DNA forms in favor of doxorubicin-pentoxifylline complexes with increasing pentoxifylline concentration. Developed model appears to be a universal tool allowing numerical analysis of mixtures containing self-aggregating ligand, DNA, and modulating agent.

Antimutagenic compounds and their possible mechanisms of action

Mutagenicity refers to the induction of permanent changes in the DNA sequence of an organism, which may result in a heritable change in the characteristics of living systems. Antimutagenic agents are able to counteract the effects of mutagens. This group of agents includes both natural and synthetic compounds. Based on their mechanism of action among antimutagens, several classes of compounds may be distinguished. These are compounds with antioxidant activity; compounds that inhibit the activation of mutagens; blocking agents; as well as compounds characterized with several modes of action. It was reported previously that several antitumor compounds act through the antimutagenic mechanism. Hence, searching for antimutagenic compounds represents a rapidly expanding field of cancer research. It may be observed that, in recent years, many publications were focused on the screening of both natural and synthetic compounds for their beneficial muta/antimutagenicity profile. Thus, the present review attempts to give a brief outline on substances presenting antimutagenic potency and their possible mechanism of action. Additionally, in the present paper, a screening strategy for mutagenicity testing was presented and the characteristics of the most widely used antimutagenicity assays were described.

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.

Evaluation of mutagenic and antimutagenic properties of new derivatives of pyrrolidine-2,5-dione with anti-epileptic activity, by use of the Vibrio harveyi mutagenicity test

The Vibrio harveyi test was used to evaluate mutagenic and antimutagenic properties of nineteen new derivatives of pyrrolidine-2,5-dione (compounds 1-19) with antiepileptic activity. Four V. harveyi strains were used: BB7 (wild type) and the genetically modified strains BB7M, BB7X and BB7XM (i.e. strains with additional mucA and mucB genes, UV hypersensitivity, and UV hypersensitivity with plasmid pAB91273, respectively). None of the derivatives of 2-ethyl-2-methylsuccinic acid (compounds 1-7) had mutagenic activity against the tester strains of V. harveyi, but this set had strong or moderate antimutagenic activity against 4-nitroquinoline-N-oxide (NQNO) in the tester strains BB7, BB7X, and BB7M. This antimutagenic activity ranged from 51% to 67%, through 51-66% to 71-83% for V. harveyi BB7, BB7X and BB7M strains, respectively. Mutagenic activities in the group of 2,2-diphenyl-succinic acid derivatives (compounds 8-19) were variable and depended on the tester strain used. Compounds 8-19 were devoid of mutagenic properties against BB7 (wild-type strain). Among this group only compound 9, with the fluorine substituent in position 2 of the aromatic system, was devoid of mutagenic potential against all tester strains. The compounds in this group (8-19) demonstrated strong antimutagenic activity only against strain BB7 (inhibition ranging from 51% to 71%). We conclude that there are various mutagenic and antimutagenic activities of derivatives of pyrrolidine-2,5-dione. Moreover, our studies have proven that the V. harveyi test can be applied for primary mutagenicity and antimutagenicity assessment of these new compounds.

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.

Spectroscopic study of porphyrin-caffeine interactions

The association between water-soluble porphyrins: 4,4′,4″,4‴-(21 H,23 H-porphine-5,10,15,20-tetrayl)tetrakis-(benzoic acid) (H₂TCPP), 5,10,15,20-tetrakis(4-sulfonatophenyl)-21 H,23 H-porphine (H₂TPPS₄), 5,10,15,20-tetrakis[4-(trimethylammonio)phenyl]-21 H,23 H-porphine tetra-p-tosylate (H₂TTMePP), 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21 H,23 H-porphine tetra-p-tosylate (H₂TMePyP), the Cu(II) complexes of H₂TTMePP and H₂TMePyP, as well as chlorophyll a with caffeine (1,3,7-trimethylxanthine) has been studied analysing their absorption and emission spectra in aqueous (or acetone in case of chlorophyll a) solution. During the titration by caffeine the porphyrins absorption spectra undergo the evolution – the bathochromic effect can be observed as well as the hypochromicity of the Soret maximum. The association constants were calculated using curve-fitting procedure (K_AC of the order of magnitude of 10³ mol^-1). Whereas the emission spectra point at the presence of the fluorescence quenching effect testifying for the partial inactivation of the porphyrin molecule. The fluorescence quenching constants were calculated from Stern-Volmer plots. The results obtained show that caffeine can interact with water-soluble porphyrins and through formation of stacking complexes is able to quench their ability to emission.

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.

Mutagenicity evaluation of metal oxide nanoparticles by the bacterial reverse mutation assay

Nanomaterials have been emerging as a new group of contaminants in the environment. We reported the use of a bacterial reverse mutation assay (Ames assay) to evaluate the mutagenicity of five metal oxide nanoparticles Al(2)O(3), Co(3)O(4), CuO, TiO(2), and ZnO in this study. Results showed the mutagenicity was negative for four nanoparticles (Al(2)O(3), Co(3)O(4), TiO(2), and ZnO) up to 1000mug/plate to all three tested strains without S9 metabolic activation. Using a preincubation procedure and high S9 (9%) activation, TiO(2) and ZnO induced marginal mutagenesis to strain Escherichia coli WP2 trp uvrA. CuO displayed low mutagenic potential to Salmonella typhimurium TA97a and TA100 at specific concentrations. However, the colony inhibition effect of CuO was predominant to the strain E. coli WP2 trp uvrA. A dose-dependent inhibition of Escherichia coli WP2 colony was found under CuO exposure at concentration range of 100-1600mug/plate. No growth inhibition of tested bacterial strains by Al(2)O(3), Co(3)O(4), and ZnO was observed at the concentrations used.

Evaluation of mutagenic and antimutagenic properties of some bioactive xanthone derivatives using Vibrio harveyi test

AIMS

Drug safety evaluation plays an important role in the early phase of drug development, especially in the preclinical identification of compounds' biological activity. The Vibrio harveyi assay was used to assess mutagenic and antimutagenic activity of some aminoalkanolic derivatives of xanthone (1-5), which were synthesized and evaluated for their anticonvulsant and hemodynamic activities.

METHODS AND RESULTS

A novel V. harveyi assay was used to assess mutagenic and antimutagenic activity of derivatives of xanthone 1-5. Two V. harveyi strains were used: BB7 (natural isolate) and BB7M (BB7 derivative containing mucA and mucB genes on a plasmid pAB91273, products of these genes enhance error-prone DNA repair). According to the results obtained, the most beneficial mutagenic and antimutagenic profiles were observed for compounds 2 and 3. A modification of the chemical structure of compound 2 by the replacement of the hydroxy group by a chloride improved considerably the antimutagenic activity of the compound. Thus, antimutagenic potency reached a maximum with the presence of tertiary amine and chloride atom in the side chain.

CONCLUSIONS

Among the newly synthesized aminoalkanolic derivatives of xanthone with potential anticonvulsant properties, there are some compounds exhibiting in vitro antimutagenic activity. In addition, it appears that the V. harveyi assay can be applied for primary mutagenicity and antimutagenicity assessment of compounds.

SIGNIFICANCE AND IMPACT OF THE STUDY

The obtained preliminary mutagenicity and antimutagenicity results encourage further search in the group of amino derivatives of xanthone as the potential antiepileptic drugs also presenting some antimutagenic potential. Furthermore, V. harveyi test may be a useful tool for compounds safety evaluation.

Complexation of biologically active aromatic compounds with DNA in the presence of theophylline

(1)H NMR measurements (500 MHz) have been used to determine the equilibrium hetero-association constants of theophylline (THP) with various biologically active aromatic compounds (daunomycin, novantrone, ethidium bromide, proflavine, norfloxacin) and the complexation constants of THP with both single- and double-stranded oligonucleotides in solution. The results provide a quantitative estimation of the effect of THP on the binding of aromatic ligands with DNA, and a determination of the fraction of aromatic ligand removed from DNA on addition of THP.

Impaired mutagenic activities of MPDP(+) (1-methyl-4-phenyl-2,3-dihydropyridinium) and MPP(+) (1-methyl-4-phenylpyridinium) due to their interactions with methylxanthines

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) is a neurotoxin causing symptoms that resemble those observed in patients suffering from Parkinson's disease. However, in animal or human organisms, MPTP is converted to MPDP(+) (1-methyl-4-phenyl-2,3-dihydropyridinium) and further to MPP(+) (1-methyl-4-phenylpyridinium); the latter compound is the actual neurotoxin. In this report, we demonstrate that MPDP(+) and MPP(+) can form stacking complexes with methylxanthines (caffeine and penthoxifylline), which leads to significant impairment of the biological activity of these toxins (as measured by their mutagenicity).

Complexation of anthracycline drugs with DNA in the presence of caffeine

The competitive binding of anthracycline antitumour drugs, [daunomycin (DAU), doxorubicin (DOX) or nogalamycin (NOG)], with caffeine (CAF) to a model DNA oligomer has been investigated by 500 MHz 1H NMR spectroscopy under physiological solution conditions. The method depends on the stepwise analysis of one-component (self-association), two-component (hetero-association and DNA complexation) and three-component interactions, in order to de-convolute the overall binding of the anthracycline antibiotic and CAF to DNA into two competing processes, viz. hetero-association of the antibiotic-CAF ('interceptor' action of CAF) and CAF-DNA complexation ('protector' action of CAF). It is found that the complexation of DAU with DNA in the presence of CAF is mainly affected by the CAF-DNA complexation, whereas the binding of either DOX or NOG to DNA is affected approximately equally by both the CAF-DNA complexation and CAF-antibiotic hetero-association. Quantitative evaluation of the three-component mixture of drug-CAF-DNA has enabled the proportion of the antibiotic displaced from DNA on addition of CAF to be calculated over a large range of CAF concentration, which may provide a quantitative basis for the change in anthracycline-related toxicity on addition of CAF.