Reactive intermediates produced from the metabolism of the vanilloid ring of capsaicinoids by p450 enzymes

Bioactive Properties, Bioavailability Profiles, and Clinical Evidence of the Potential Benefits of Black Pepper (Piper nigrum) and Red Pepper (Capsicum annum) against Diverse Metabolic Complications

The consumption of food-derived products, including the regular intake of pepper, is increasingly evaluated for its potential benefits in protecting against diverse metabolic complications. The current study made use of prominent electronic databases including PubMed, Google Scholar, and Scopus to retrieve clinical evidence linking the intake of black and red pepper with the amelioration of metabolic complications. The findings summarize evidence supporting the beneficial effects of black pepper (Piper nigrum L.), including its active ingredient, piperine, in improving blood lipid profiles, including reducing circulating levels of total cholesterol, low-density lipoprotein cholesterol, and triglycerides in overweight and obese individuals. The intake of piperine was also linked with enhanced antioxidant and anti-inflammatory properties by increasing serum levels of superoxide dismutase while reducing those of malonaldehyde and C-reactive protein in individuals with metabolic syndrome. Evidence summarized in the current review also indicates that red pepper (Capsicum annum), together with its active ingredient, capsaicin, could promote energy expenditure, including limiting energy intake, which is likely to contribute to reduced fat mass in overweight and obese individuals. Emerging clinical evidence also indicates that pepper may be beneficial in alleviating complications linked with other chronic conditions, including osteoarthritis, oropharyngeal dysphagia, digestion, hemodialysis, and neuromuscular fatigue. Notably, the beneficial effects of pepper or its active ingredients appear to be more pronounced when used in combination with other bioactive compounds. The current review also covers essential information on the metabolism and bioavailability profiles of both pepper species and their main active ingredients, which are all necessary to understand their potential beneficial effects against metabolic diseases.

Capsaicin binds the N-terminus of Hsp90, induces lysosomal degradation of Hsp70, and enhances the anti-tumor effects of 17-AAG (Tanespimycin)

Heat shock protein 90 (Hsp90) and its co-chaperones promote cancer, and targeting Hsp90 holds promise for cancer treatment. Most of the efforts to harness this potential have focused on targeting the Hsp90 N-terminus ATP binding site. Although newer-generation inhibitors have shown improved efficacy in aggressive cancers, induction of the cellular heat shock response (HSR) by these inhibitors is thought to limit their clinical efficacy. Therefore, Hsp90 inhibitors with novel mechanisms of action and that do not trigger the HSR would be advantageous. Here, we investigated the mechanism by which capsaicin inhibits Hsp90. Through mutagenesis, chemical modifications, and proteomic studies, we show that capsaicin binds to the N-terminus of Hsp90 and inhibits its ATPase activity. Consequently, capsaicin and its analogs inhibit Hsp90 ATPase-dependent progesterone receptor reconstitution in vitro. Capsaicin did not induce the HSR, instead, it promoted the degradation of Hsp70 through the lysosome-autophagy pathway. Remarkably, capsaicin did not induce degradation of the constitutively expressed cognate Hsc70, indicating selectivity for Hsp70. Combined treatments of capsaicin and the Hsp90 inhibitor 17-AAG improved the anti-tumor efficacy of 17-AAG in cell culture and tridimensional tumor spheroid growth assays using breast and prostate cancer models. Consistent with this, in silico docking studies revealed that capsaicin binding to the ATP binding site of Hsp90 was distinct from classical N-terminus Hsp90 inhibitors, indicating a novel mechanism of action. Collectively, these findings support the use of capsaicin as a chemical scaffold to develop novel Hsp90 N-terminus inhibitors as well as its ability to be a potential cancer co-therapeutic.

A chemical probe unravels the reactive proteome of health-associated catechols

Catechol-containing natural products are common constituents of foods, drinks, and drugs. Natural products carrying this motif are often associated with beneficial biological effects such as anticancer activity and neuroprotection. However, the molecular mode of action behind these properties is poorly understood. Here, we apply a mass spectrometry-based competitive chemical proteomics approach to elucidate the target scope of catechol-containing bioactive molecules from diverse foods and drugs. Inspired by the protein reactivity of catecholamine neurotransmitters, we designed and synthesised a broadly reactive minimalist catechol chemical probe based on dopamine. Initial labelling experiments in live human cells demonstrated broad protein binding by the probe, which was largely outcompeted by its parent compound dopamine. Next, we investigated the competition profile of a selection of biologically relevant catechol-containing substances. With this approach, we characterised the protein reactivity and the target scope of dopamine and ten biologically relevant catechols. Strikingly, proteins associated with the endoplasmic reticulum (ER) were among the main targets. ER stress assays in the presence of reactive catechols revealed an activation of the unfolded protein response (UPR). The UPR is highly relevant in oncology and cellular resilience, which may provide an explanation of the health-promoting effects attributed to many catechol-containing natural products.

Capsicum annuum L. and its bioactive constituents: A critical review of a traditional culinary spice in terms of its modern pharmacological potentials with toxicological issues

Capsicum annuum L., commonly known as chili pepper, is used as an important spice globally and as a crude drug in many traditional medicine systems. The fruits of C. annuum have been used as a tonic, antiseptic, and stimulating agent, to treat dyspepsia, appetites, and flatulence, and to improve digestion and circulation. The article aims to critically review the phytochemical and pharmacological properties of C. annuum and its major compounds. Capsaicin, dihydrocapsaicin, and some carotenoids are reported as the major active compounds with several pharmacological potentials especially as anticancer and cardioprotectant. The anticancer effect of capsaicinoids is mainly mediated through mechanisms involving the interaction of Ca²⁺ -dependent activation of the MAPK pathway, suppression of NOX-dependent reactive oxygen species generation, and p53-mediated activation of mitochondrial apoptosis in cancer cells. Similarly, the cardioprotective effects of capsaicinoids are mediated through their interaction with cellular transient receptor potential vanilloid 1 channel, and restoration of calcitonin gene-related peptide via Ca²⁺ -dependent release of neuropeptides and suppression of bradykinin. In conclusion, this comprehensive review presents detailed information about the traditional uses, phytochemistry, and pharmacology of major bioactive principles of C. annuum with special emphasis on anticancer, cardioprotective effects, and plausible toxic adversities along with food safety.

Research Trend and Detailed Insights into the Molecular Mechanisms of Food Bioactive Compounds against Cancer: A Comprehensive Review with Special Emphasis on Probiotics

In an attempt to find a potential cure for cancer, scientists have been probing the efficacy of the food we eat and its bioactive components. Over the decades, there has been an exponentially increasing trend of research correlating food and cancer. This review explains the molecular mechanisms by which bioactive food components exhibit anticancer effects in several cancer models. These bioactive compounds are mainly plant based or microbiome based. While plants remain the primary source of these phytochemicals, little is known about probiotics, i.e., microbiome sources, and their relationships with cancer. Thus, the molecular mechanisms underlying the anticancer effect of probiotics are discussed in this review. The principal mode of cell death for most food bioactives is found to be apoptosis. Principal oncogenic signaling axes such as Akt/PI3K, JAK/STAT, and NF-κB seem to be modulated due to these bioactives along with certain novel targets that provide a platform for further oncogenic research. It has been observed that probiotics have an immunomodulatory effect leading to their chemopreventive actions. Various foods exhibit better efficacy as complete extracts than their individual phytochemicals, indicating an orchestrated effect of the food components. Combining bioactive agents with available chemotherapies helps synergize the anticancer action of both to overcome drug resistance. Novel techniques to deliver bioactive agents enhance their therapeutic response. Such combinations and novel approaches are also discussed in this review. Notably, most of the food components that have been studied for cancer have shown their efficacy in vivo. This bolsters the claims of these studies and, thus, provides us with hope of discovering anticancer agents in the food that we eat.

Electrochemical Simulation of the Oxidative Capsaicin Metabolism

Capsaicin, primarily known as the pungent ingredient in hot peppers, is rapidly metabolized in the human body by enzymatic processes altering the pharmacological as well as toxicological properties. Herein, the oxidative transformation of capsaicin was investigated in vitro with electrochemistry as well as human liver microsomal incubations. The reaction mixtures were analyzed with liquid chromatography-mass spectrometry. Structure elucidation involved accurate mass measurements and multistage tandem mass spectrometry experiments. In total, 126 transformation products were detected. Electrochemistry provided evidence for 101 transformation products and the microsomal incubations for 46 species. 21 compounds were observed with both approaches. Identified oxidative pathways likely occurring during the phase I metabolism included dehydrogenation, O-demethylation, and hydroxylation reactions as well as combinations thereof. Furthermore, trapping of reactive intermediates either with glutathione or with electrochemically activated ribonucleosides provided evidence for the possible production of phase II metabolites and covalent adducts with a genetic material. Evidence for the occurrence of some capsaicin metabolites in humans was obtained by urine screening.

Hydroxylation, Epoxidation, and Dehydrogenation of Capsaicin by a Microbial Promiscuous Cytochrome P450 105D7

Cytochrome P450 enzymes (P450s) are versatile biocatalysts, which insert a molecular oxygen into inactivated C-H bonds under mild conditions. CYP105D7 from Streptomyces avermitilis has been reported as a bacterial substrate-promiscuous P450 which catalyzes the hydroxylation of 1-deoxypentalenic acid, diclofenac, naringenin, compactin and steroids. In this study, CYP105D7 catalyzes hydroxylation, epoxidation and dehydrogenation of capsaicin, a pharmaceutical agent, revealing its functional diversity. The kinetic parameters of the CYP105D7 oxidation of capsaicin were determined as K_m =311.60±87.30 μM and k_cat =2.01±0.33 min^-1 . In addition, we conducted molecular docking, mutagenesis and substrate binding analysis, indicating that Arg81 plays crucial role in the capsaicin binding and catalysis. To our best knowledge, this study presents the first report to illustrate that capsaicin can be catalyzed by prokaryotic P450s.

The Effects of Capsaicin on Gastrointestinal Cancers

Gastrointestinal (GI) cancers are a group of diseases with very high positions in the ranking of cancer incidence and mortality. While they show common features regarding the molecular mechanisms involved in cancer development, organ-specific pathophysiological processes may trigger distinct signaling pathways and intricate interactions with inflammatory cells from the tumoral milieu and mediators involved in tumorigenesis. The treatment of GI cancers is a topic of increasing interest due to the severity of these diseases, their impact on the patients' survivability and quality of life, and the burden they set on the healthcare system. As the efficiency of existing drugs is hindered by chemoresistance and adverse reactions when administered in high doses, new therapies are sought, and emerging drugs, formulations, and substance synergies are the focus of a growing number of studies. A class of chemicals with great potential through anti-inflammatory, anti-oxidant, and anti-tumoral effects is phytochemicals, and capsaicin in particular is the subject of intensive research looking to validate its position in complementing cancer treatment. Our paper thoroughly reviews the available scientific evidence concerning the effects of capsaicin on major GI cancers and its interactions with the molecular pathways involved in the course of these diseases.

Metabolic Forest: Predicting the Diverse Structures of Drug Metabolites

Adverse drug metabolism often severely impacts patient morbidity and mortality. Unfortunately, drug metabolism experimental assays are costly, inefficient, and slow. Instead, computational modeling could rapidly flag potentially toxic molecules across thousands of candidates in the early stages of drug development. Most metabolism models focus on predicting sites of metabolism (SOMs): the specific substrate atoms targeted by metabolic enzymes. However, SOMs are merely a proxy for metabolic structures: knowledge of an SOM does not explicitly provide the actual metabolite structure. Without an explicit metabolite structure, computational systems cannot evaluate the new molecule's properties. For example, the metabolite's reactivity cannot be automatically predicted, a crucial limitation because reactive drug metabolites are a key driver of adverse drug reactions (ADRs). Additionally, further metabolic events cannot be forecast, even though the metabolic path of the majority of substrates includes two or more sequential steps. To overcome the myopia of the SOM paradigm, this study constructs a well-defined system-termed the metabolic forest-for generating exact metabolite structures. We validate the metabolic forest with the substrate and product structures from a large, chemically diverse, literature-derived dataset of 20 736 records. The metabolic forest finds a pathway linking each substrate and product for 79.42% of these records. By performing a breadth-first search of depth two or three, we improve performance to 88.43 and 88.77%, respectively. The metabolic forest includes a specialized algorithm for producing accurate quinone structures, the most common type of reactive metabolite. To our knowledge, this quinone structure algorithm is the first of its kind, as the diverse mechanisms of quinone formation are difficult to systematically reproduce. We validate the metabolic forest on a previously published dataset of 576 quinone reactions, predicting their structures with a depth three performance of 91.84%. The metabolic forest accurately enumerates metabolite structures, enabling promising new directions such as joint metabolism and reactivity modeling.

Novel Homodimer Metabolites of GDC-0994 via Cytochrome P450-Catalyzed Radical Coupling

Two novel homodimer metabolites were identified in rat samples collected during the in vivo study of GDC-0994. In this study, we investigated the mechanism of the formation of these metabolites. We generated and isolated the dimer metabolites using a biomimetic oxidation system for NMR structure elucidation to identify a symmetric dimer formed via carbon-carbon bond between two pyrazoles and an asymmetric dimer formed via an aminopyrazole-nitrogen to pyrazole-carbon bond. In vitro experiments demonstrated formation of these dimers was catalyzed by cytochrome P450 enzymes (P450s) with CYP3A4/5 being the most efficient. Using density functional theory, we determined these metabolites share a mechanism of formation, initiated by an N-H hydrogen atom abstraction by the catalytically active iron-oxo of P450s. Molecular modeling studies also show these dimer metabolites fit in the CYP3A4 binding site in low energy conformations with minimal protein rearrangement. Collectively, the results of these experiments suggest that formation of these two homodimer metabolites is mediated by CYP3A, likely involving activation of two GDC-0994 molecules by a single P450 enzyme and proceeding through a radical coupling mechanism. SIGNIFICANCE STATEMENT: These studies identified structures and enzymology for two distinct homodimer metabolites and indicate a novel biotransformation reaction mediated by CYP3A. In it, two molecules may bind within the active site and combine through radical coupling. The mechanism of dimerization was elucidated using density functional theory computations and supported by molecular modeling.

Capsaicinoid metabolism by the generalist Helicoverpa armigera and specialist H. assulta: Species and tissue differences

Helicoverpa armigera and H. assulta are two of the few insects that can feed on hot pepper fruits. Capsaicin and dihydrocapsaicin (i.e., capsaicinoids) are the principal pungent compounds in hot peppers. To explore possible molecular mechanisms of adaptation that allow these two species to consume capsaicinoids, the capacity of the three detoxification tissues (fat body, midgut, and Malpighian tubule) of the two pests, to metabolically degrade capsaicin and dihydrocapsaicin, was compared. The results showed that capsaicin and dihydrocapsaicin were metabolized by crude enzyme preparations from all three tissues of the two pests. Five metabolites of capsaicin, and five metabolites of dihydrocapsaicin were identified. Tissue and species differences in the degree of capsaicin and dihydrocapsaicin metabolism were observed. The specialist H. assulta had an overall greater capacity to degrade the capsaicinoids compared to the generalist H. armigera. Further, the midgut was the most significant contributor to capsaicinoid metabolism. The notably high specific activity in Malpighian tubules of H. armigera also further highlights the significance of this organ in xenobiotic detoxification. Alkyl hydroxylation and dehydrogenation were the main pathways for the oxidative biotransformation of both capsaicin and dihydrocapsaicin by cytochrome P450s. This study provides evidence that enhanced metabolic decomposition of capsaicinoids may be an adaptation explaining dietary preferences for Capsicum fruits by these two pests.

Capsaicin metabolites and GSH-associated detoxification and biotransformation pathways in human liver microsomes revealed by LC-HRMS/MS with data-mining tools

Capsaicin (CAP) is a principal pungent ingredient in hot peppers, it is also employed as a common food additive, an efficient pharmaceutical component, or even a riot control agent. CAP exerts various pharmacological activities as well as associated adverse physiological responses and causes moderate toxicity if overused. A full screening and identification of CAP metabolites in combination with its main detoxification pathways are crucial for the clear demonstration on its pharmacological and toxicological significance. Here, we employed a post-acquisition data-mining metabolic screening approach to rapidly find and identify a broad range of CAP metabolites generated from in vitro human liver microsomes, based on an ultra-performance liquid chromatography-quadrupole orbitrap high resolution tandem mass spectrometric method. First, we collected full scan MS and MS/MS data sets by a data-dependent acquisition method in positive ion mode, and then we employed a modified mass defect filter and a diagnostic ion filter to screen and identify all the probable CAP metabolites, combining with information including retention time, accurate mass, characteristic fragments, and relevant drug biotransformation patterns. In comparison with the stable isotope-labeled CAP involved biotransformation products, we confirmed 19 functionalized metabolites and 13 glutathione (GSH) conjugates of CAP, in which 13 metabolites are reported for the first time. We then briefly depicted an overview metabolic pathway of CAP from the GSH detoxification viewpoint, revealed that various metabolites of CAP can be generated from single or multiple biotransformation and metabolic reactions. Both CAP and its reactive metabolites produced relevant GSH conjugates, which indicates a wide and important detoxification value of GSH conjugation way.

Capsaicin: Effects on the Pathogenesis of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most frequent cancers, and to date, there have been very few drugs available that can improve survival, the most well-known being sorafenib. The pathogenesis of HCC is complex, involving multiple processes including abnormal cell and tissue regeneration, angiogenesis, genomic instability, cellular proliferation, and signaling pathway alterations. Capsaicin is a substance that holds increasingly high interest and is studied as a therapeutic option in a wide array of diseases. Several studies have investigated capsaicin roles in various stages of HCC oncogenesis. This paper aims to thoroughly detail the available information on the individual effects of capsaicin on the cellular mechanisms and pathways involved in HCC development, as well as investigate their possible cooperation and interferences. The synergistic antitumor effects of capsaicin and sorafenib are also addressed.

Capsaicin is efficiently transformed by multiple cytochrome P450s from Capsicum fruit-feeding Helicoverpa armigera

Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is the most abundant capsaicinoids found in hot peppers (Capsicum annum and Capsicum frutescens). It has been well documented that capsaicin plays an important role in the defense against the attack of herbivores or pathogens on Capsicum plants. A few insect herbivores such as Helicoverpa armigera and Helicoverpa assulta have been recorded to be capable of feeding on hot pepper fruits, suggesting that these insects evolve mechanisms against the toxicity of capsaicin. Although cytochrome P450-meidated detoxification is considered to be an important mechanism by which cotton bollworms cope with capsaicin, experimental evidence is lacking. In this study, we compared the capacity of four H. armigera P450s (CYP6B6, CYP9A12, CYP9A14 and CYP9A17) in capsaicin metabolism, and the capsaicin metabolites were screened and tentatively identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). HPLC analyses showed that depletion rates of capsaicin were 21.9 ± 0.1, 11.9 ± 1.5, 16.3 ± 1.4 and 14.8 ± 0.2 min^-1 for CYP6B6, CYP9A12, CYP9A14 and CYP9A17 respectively. The transformation of capsaicin was inhibited by the P450 inhibitor piperonyl butoxide. A total of seven products were detected, and hydroxylation (aromatic and aliphatic) and dehydrogenation were found to be two main pathways in capsaicin metabolism. In addition, capsaicin metabolism was enzyme selective: M1 (ω-hydroxylated N-macrocyclic metabolite) and M3 (ω-hydroxylated metabolite) were uniquely detected in the CYP6B6 catalytic reaction, while M4 (ω-n hydroxylated capsaicin), M5 (diene of capsaicin) and M6 (doubly oxidized metabolite of dehydrogenated capsaicin) were only detectable in CYP9A metabolisms. A capsaicin dimer (5, 5'-dicapsaicin) was found to be the major metabolite of CYP9A reactions, but the minor product produced by CYP6B6. An overall more similar behavior in capsaicin metabolism was observed among CYP9As than between CYP6B6 and CYP9As. Our data demonstrate that CYP6B6 and CYP9As have a potent capability to transform capsaicin, and individual P450 produce unique metabolite profile. These findings help us to understand the molecular basis of capsaicin adaptation in H. armigera.

Formation and biological targets of botanical o-quinones

The formation of o-quinones from direct 2-electron oxidation of catechols and/or two successive one electron oxidations could explain the cytotoxic/genotoxic and/or chemopreventive effects of several phenolic botanical extracts. For example, poison ivy contains urushiol, an oily mixture, which is oxidized to various o-quinones likely resulting in skin toxicity through oxidative stress and alkylation mechanisms resulting in immune responses. Green tea contains catechins which are directly oxidized to o-quinones by various oxidative enzymes. Alternatively, phenolic botanicals could be o-hydroxylated by P450 to form catechols in vivo which are oxidized to o-quinones. Examples include, resveratrol which is oxidized to piceatannol and further oxidized to the o-quinone. Finally, botanical o-quinones can be formed by O-dealkylation of O-alkoxy groups or methylenedioxy rings resulting in catechols which are further oxidized to o-quinones. Examples include safrole, eugenol, podophyllotoxin and etoposide, as well as methysticin. Once formed these o-quinones have a variety of biological targets in vivo resulting in various biological effects ranging from chemoprevention - > no effect - > toxicity. This U-shaped biological effect curve has been described for a number of reactive intermediates including o-quinones. The current review summarizes the latest data on the formation and biological targets of botanical o-quinones.

Thiol Reactivity of Curcumin and Its Oxidation Products

The polypharmacological effects of the turmeric compound curcumin may be partly mediated by covalent adduction to cellular protein. Covalent binding to small molecule and protein thiols is thought to occur through a Michael-type addition at the enone moiety of the heptadienedione chain connecting the two methoxyphenol rings of curcumin. Here we show that curcumin forms the predicted thiol-Michael adducts with three model thiols, glutathione, N-acetylcysteine, and β-mercaptoethanol. More abundant, however, are respective thiol adducts of the dioxygenated spiroepoxide intermediate of curcumin autoxidation. Two electrophilic sites at the quinone-like ring of the spiroepoxide are identified. Addition of β-mercaptoethanol at the 5'-position of the ring gives a 1,7-dihydroxycyclopentadione-5' thioether, and addition at the 1'-position results in cleavage of the aromatic ring from the molecule, forming methoxyphenol-thioether and a tentatively identified cyclopentadione aldehyde. The curcuminoids demethoxy- and bisdemethoxycurcumin do not form all of the possible thioether adducts, corresponding with their increased stability toward autoxidation. RAW264.7 macrophage-like cells activated with phorbol ester form curcumin-glutathionyl and the 1,7-dihydroxycyclopentadione-5'-glutathionyl adducts. These studies indicate that the enone of the parent compound is not the only functional electrophile in curcumin, and that its oxidation products provide additional electrophilic sites. This suggests that protein binding by curcumin may involve oxidative activation into reactive quinone methide and spiroepoxide electrophiles.

Computational Approach to Structural Alerts: Furans, Phenols, Nitroaromatics, and Thiophenes

Structural alerts are commonly used in drug discovery to identify molecules likely to form reactive metabolites and thereby become toxic. Unfortunately, as useful as structural alerts are, they do not effectively model if, when, and why metabolism renders safe molecules toxic. Toxicity due to a specific structural alert is highly conditional, depending on the metabolism of the alert, the reactivity of its metabolites, dosage, and competing detoxification pathways. A systems approach, which explicitly models these pathways, could more effectively assess the toxicity risk of drug candidates. In this study, we demonstrated that mathematical models of P450 metabolism can predict the context-specific probability that a structural alert will be bioactivated in a given molecule. This study focuses on the furan, phenol, nitroaromatic, and thiophene alerts. Each of these structural alerts can produce reactive metabolites through certain metabolic pathways but not always. We tested whether our metabolism modeling approach, XenoSite, can predict when a given molecule's alerts will be bioactivated. Specifically, we used models of epoxidation, quinone formation, reduction, and sulfur-oxidation to predict the bioactivation of furan-, phenol-, nitroaromatic-, and thiophene-containing drugs. Our models separated bioactivated and not-bioactivated furan-, phenol-, nitroaromatic-, and thiophene-containing drugs with AUC performances of 100%, 73%, 93%, and 88%, respectively. Metabolism models accurately predict whether alerts are bioactivated and thus serve as a practical approach to improve the interpretability and usefulness of structural alerts. We expect that this same computational approach can be extended to most other structural alerts and later integrated into toxicity risk models. This advance is one necessary step toward our long-term goal of building comprehensive metabolic models of bioactivation and detoxification to guide assessment and design of new therapeutic molecules.

Biological Activities of Red Pepper (Capsicum annuum) and Its Pungent Principle Capsaicin: A Review

Capsaicin, the pungent alkaloid of red pepper (Capsicum annuum) has been extensively studied for its biological effects which are of pharmacological relevance. These include: cardio protective influence, antilithogenic effect, antiinflammatory, and analgesia, thermogenic influence, and beneficial effects on gastrointestinal system. Therefore, capsaicinoids may have the potential clinical value for pain relief, cancer prevention and weight loss. It has been shown that capsaicinoids are potential agonists of capsaicin receptor (TRPV1). They could exert the effects not only through the receptor-dependent pathway but also through the receptor-independent one. The involvement of neuropeptide Substance P, serotonin, and somatostatin in the pharmacological actions of capsaicin has been extensively investigated. Topical application of capsaicin is proved to alleviate pain in arthritis, postoperative neuralgia, diabetic neuropathy, psoriasis, etc. Toxicological studies on capsaicin administered by different routes are documented. Capsaicin inhibits acid secretion, stimulates alkali and mucus secretion and particularly gastric mucosal blood flow which helps in prevention and healing of gastric ulcers. Antioxidant and antiinflammatory properties of capsaicin are established in a number of studies. Chemopreventive potential of capsaicin is evidenced in cell line studies. The health beneficial hypocholesterolemic influence of capsaicin besides being cardio protective has other implications, viz., prevention of cholesterol gallstones and protection of the structural integrity of erythrocytes under conditions of hypercholesterolemia. Beneficial influences of capsaicin on gastrointestinal system include digestive stimulant action and modulation of intestinal ultrastructure so as to enhance permeability to micronutrients.

Extraction, bioavailability, and bioefficacy of capsaicinoids

Capsaicinoids are active constituents responsible for the pungent and spicy flavor in chili peppers. During the past few decades, various extraction methods of capsaicinoids from peppers have been developed with high yields. Through biological studies, pharmacological benefits have been reported such as pain relief, antiinflammation, anticancer, cardioprotection, as well as weight loss. In this paper, the extraction methods and bioavailability of capsaicinoids are reviewed and discussed. In addition, the pharmacological effects and their underlying mechanisms are also studied.

Modulation of signal transduction pathways by natural compounds in cancer

Cancer is generally regarded as the result of abnormal growth of cells. According to World Health Organization, cancer is the leading cause of mortality worldwide. Mother nature provides a large source of bioactive compounds with excellent therapeutic efficacy. Numerous phytochemicals from nature have been investigated for anticancer properties. In this review article, we discuss several natural compounds, which have shown anti-cancer activity. Natural compounds induce cell cycle arrest, activate intrinsic and extrinsic apoptosis pathways, generate Reactive Oxygen Species (ROS), and down-regulate activated signaling pathways, resulting in inhibition of cell proliferation, progression and metastasis of cancer. Several preclinical studies have suggested that natural compounds can also increase the sensitivity of resistant cancers to available chemotherapy agents. Furthermore, combining FDA approved anti-cancer drugs with natural compounds results in improved efficacy. On the basis of these exciting outcomes of natural compounds against several cancer types, several agents have already advanced to clinical trials. In conclusion, preclinical results and clinical outcomes against cancer suggest promising anticancer efficacy of agents from natural sources.

Feeling Nature's PAINS: Natural Products, Natural Product Drugs, and Pan Assay Interference Compounds (PAINS)

We have previously reported on classes of compounds that can interfere with bioassays via a number of different mechanisms and termed such compounds Pan Assay INterference compoundS, or PAINS. These compounds were defined on the basis of high-throughput data derived from vendor-supplied synthetics. The question therefore arises whether the concept of PAINS is relevant to compounds of natural origin. Here, it is shown that this is indeed the case, but that the context of the biological readout is an important factor that must be brought into consideration.

Characterization of glutathione conjugates derived from reactive metabolites of bakuchiol

Bakuchiol belongs to a family of monoterpene phenols occurring in plant Psoralea corylifolia L., a traditional herbal medicine. Bakuchiol has also demonstrated multiple pharmacologic activities. However, metabolism of bakuchiol had never been investigated. The major objective of the present study was to study the metabolic pathways of bakuchiol in order to identify potential reactive metabolites. A total of five glutathione (GSH) conjugates (M1-M5) were detected in rat/human liver microsomes containing NADPH, GSH, and bakuchiol. M1 and M2 resulted from GSH conjugated on the phenol ring. M3, M4, and M5 were derived from GSH adducted on the side chain. The results displayed that bakuchiol can be bioactivated by oxidation of the phenol moiety to the corresponding ortho-quinone and by epoxidation of the aliphatic side chain to epoxide metabolites. No bakuchiol-derived GSH conjugates were detected in urine of rats given bakuchiol, but six corresponding cysteinylglycine (Cys-Gly) conjugates and mercapturic acids were observed instead. A 2'-iodoxybenzoic acid-mediated oxidation reaction of bakuchiol in the presence of GSH produced M1 and M2, and m-chloroperoxybenzoicacid-mediated oxidation of bakuchiol trapped with GSH generated M3 and M4. The four synthetic metabolites were detected in microsomal incubations. In addition, recombinant P450 enzyme incubations showed that CYP 1A2 was the predominant P450 responsible for the metabolism of bakuchiol. In summary, our results demonstrated that bakuchiol can be bioactivated to quinone and epoxide metabolites. These findings facilitate the understanding of the mechanisms of bakuchiol-induced cytotoxicity.

Regioselective Enzymatic β-Carboxylation of para-Hydroxy- styrene Derivatives Catalyzed by Phenolic Acid Decarboxylases

We report on a 'green' method for the utilization of carbon dioxide as C1 unit for the regioselective synthesis of (E)-cinnamic acids via regioselective enzymatic carboxylation of para-hydroxystyrenes. Phenolic acid decarboxylases from bacterial sources catalyzed the β-carboxylation of para-hydroxystyrene derivatives with excellent regio- and (E/Z)-stereoselectivity by exclusively acting at the β-carbon atom of the C=C side chain to furnish the corresponding (E)-cinnamic acid derivatives in up to 40% conversion at the expense of bicarbonate as carbon dioxide source. Studies on the substrate scope of this strategy are presented and a catalytic mechanism is proposed based on molecular modelling studies supported by mutagenesis of amino acid residues in the active site.

Bioavailability of capsaicin and its implications for drug delivery

The dietary compound capsaicin is responsible for the "hot and spicy" taste of chili peppers and pepper extracts. It is a valuable pharmacological agent with several therapeutic applications in controlling pain and inflammation. Emerging studies show that it displays potent anti-tumor activity in several human cancers. On a more basic research level, capsaicin has been used as a ligand to activate several types of ion-channel receptors. The pharmacological activity of capsaicin-like compounds is dependent on several factors like the dose, the route of administration and most importantly on its concentration at target tissues. The present review describes the current knowledge involving the metabolism and bioavailability of capsaicinoids in rodents and humans. Novel drug delivery strategies used to improve the bioavailability and therapeutic index of capsaicin are discussed in detail. The generation of novel capsaicin-mimetics and improved drug delivery methods will foster the hope of innovative applications of capsaicin in human disease.

Quinone Methide Bioactivation Pathway: Contribution to Toxicity and/or Cytoprotection?

The formation of quinone methides (QMs) from either direct 2-electron oxidation of 2- or 4-alkylphenols, isomerization of o-quinones, or elimination of a good leaving group could explain the cytotoxic/cytoprotective effects of several drugs, natural products, as well as endogenous compounds. For example, the antiretroviral drug nevirapine and the antidiabetic agent troglitazone both induce idiosyncratic hepatotoxicity through mechanisms involving quinone methide formation. The anesthetic phencyclidine induces psychological side effects potentially through quinone methide mediated covalent modification of crucial macromolecules in the brain. Selective estrogen receptor modulators (SERMs) such as tamoxifen, toremifene, and raloxifene are metabolized to quinone methides which could potentially contribute to endometrial carcinogenic properties and/or induce detoxification enzymes and enhance the chemopreventive effects of these SERMs. Endogenous estrogens and/or estrogens present in estrogen replacement formulations are also metabolized to catechols and further oxidized to o-quinones which can isomerize to quinone methides. Both estrogen quinoids could cause DNA damage which could enhance hormone dependent cancer risk. Natural products such as the food and flavor agent eugenol can be directly oxidized to a quinone methide which may explain the toxic effects of this natural compound. Oral toxicities associated with chewing areca quid could be the result of exposure to hydroxychavicol through initial oxidation to an o-quinone which isomerizes to a p-quinone methide. Similar o-quinone to p-quinone methide isomerization reactions have been reported for the ubiquitous flavonoid quercetin which needs to be taken into consideration when evaluating risk-benefit assessments of these natural products. The resulting reaction of these quinone methides with proteins, DNA, and/or resulting modulation of gene expression may explain the toxic and/or beneficial effects of the parent compounds.

The potential antitumor effects of capsaicin

Capsaicin, one of the major pungent ingredients found in red peppers, has been recently demonstrated to induce apoptosis in many types of malignant cell lines including colon adenocarcinoma, pancreatic cancer, hepatocellular carcinoma, prostate cancer, breast cancer, and many others. The mechanism whereby capsaicin induces apoptosis in cancer cells is not completely elucidated but involves intracellular calcium increase, reactive oxygen species generation, disruption of mitochondrial membrane transition potential, and activation of transcription factors such as NFkappaB and STATS. Recently, a role for the AMP-dependent kinase (AMPK) and autophagy pathways in capsaicin-triggered cell death has been proposed. In addition, capsaicin shows antitumor activity in vivo by reducing the growth of many tumors induced in mice. In this chapter, we report the last advances performed in the antitumor activity of capsaicin and review the main signaling pathways involved.

Unusual cytochrome p450 enzymes and reactions

Cytochrome P450 enzymes primarily catalyze mixed-function oxidation reactions, plus some reductions and rearrangements of oxygenated species, e.g. prostaglandins. Most of these reactions can be rationalized in a paradigm involving Compound I, a high-valent iron-oxygen complex (FeO(3+)), to explain seemingly unusual reactions, including ring couplings, ring expansion and contraction, and fusion of substrates. Most P450s interact with flavoenzymes or iron-sulfur proteins to receive electrons from NAD(P)H. In some cases, P450s are fused to protein partners. Other P450s catalyze non-redox isomerization reactions. A number of permutations on the P450 theme reveal the diversity of cytochrome P450 form and function.