Biotransformation of melatonin in human breast cancer cell lines: role of sulfotransferase 1A1

Computational Analysis of Chemical Space of Natural Compounds Interacting with Sulfotransferases

The aim of this study was to investigate the chemical space and interactions of natural compounds with sulfotransferases (SULTs) using ligand- and structure-based in silico methods. An in-house library of natural ligands (hormones, neurotransmitters, plant-derived compounds and their metabolites) reported to interact with SULTs was created. Their chemical structures and properties were compared to those of compounds of non-natural (synthetic) origin, known to interact with SULTs. The natural ligands interacting with SULTs were further compared to other natural products for which interactions with SULTs were not known. Various descriptors of the molecular structures were calculated and analyzed. Statistical methods (ANOVA, PCA, and clustering) were used to explore the chemical space of the studied compounds. Similarity search between the compounds in the different groups was performed with the ROCS software. The interactions with SULTs were additionally analyzed by docking into different experimental and modeled conformations of SULT1A1. Natural products with potentially strong interactions with SULTs were outlined. Our results contribute to a better understanding of chemical space and interactions of natural compounds with SULT enzymes and help to outline new potential ligands of these enzymes.

Decreased phenol sulfotransferase activities associated with hyperserotonemia in autism spectrum disorders

Hyperserotonemia is the most replicated biochemical abnormality associated with autism spectrum disorders (ASD). However, previous studies of serotonin synthesis, catabolism, and transport have not elucidated the mechanisms underlying this hyperserotonemia. Here we investigated serotonin sulfation by phenol sulfotransferases (PST) in blood samples from 97 individuals with ASD and their first-degree relatives (138 parents and 56 siblings), compared with 106 controls. We report a deficient activity of both PST isoforms (M and P) in platelets from individuals with ASD (35% and 78% of patients, respectively), confirmed in autoptic tissues (9 pineal gland samples from individuals with ASD-an important source of serotonin). Platelet PST-M deficiency was strongly associated with hyperserotonemia in individuals with ASD. We then explore genetic or pharmacologic modulation of PST activities in mice: variations of PST activities were associated with marked variations of blood serotonin, demonstrating the influence of the sulfation pathway on serotonemia. We also conducted in 1645 individuals an extensive study of SULT1A genes, encoding PST and mapping at highly polymorphic 16p11.2 locus, which did not reveal an association between copy number or single nucleotide variations and PST activity, blood serotonin or the risk of ASD. In contrast, our broader assessment of sulfation metabolism in ASD showed impairments of other sulfation-related markers, including inorganic sulfate, heparan-sulfate, and heparin sulfate-sulfotransferase. Our study proposes for the first time a compelling mechanism for hyperserotonemia, in a context of global impairment of sulfation metabolism in ASD.

GPCRs in stem cell function

Many tissues of the body cannot only repair themselves, but also self-renew, a property mainly due to stem cells and the various mechanisms that regulate their behavior. Stem cell biology is a relatively new field. While advances are slowly being realized, stem cells possess huge potential to ameliorate disease and counteract the aging process, causing its speculation as the next panacea. Amidst public pressure to advance rapidly to clinical trials, there is a need to understand the biology of stem cells and to support basic research programs. Without a proper comprehension of how cells and tissues are maintained during the adult life span, clinical trials are bound to fail. This review will cover the basic biology of stem cells, the various types of stem cells, their potential function, and the advantages and disadvantages to their use in medicine. We will next cover the role of G protein-coupled receptors in the regulation of stem cells and their potential in future clinical applications.

Sulfation of fulvestrant by human liver cytosols and recombinant SULT1A1 and SULT1E1

Fulvestrant (Faslodex™) is a pure antiestrogen that is approved to treat hormone receptor-positive metastatic breast cancer in postmenopausal women. Previous studies have demonstrated that fulvestrant metabolism in humans involves cytochromes P450 and UDP-glucuronosyltransferases (UGTs). To date, fulvestrant sulfation has not been characterized. This study examined fulvestrant sulfation with nine recombinant sulfotransferases and found that only SULT1A1 and SULT1E1 displayed catalytic activity toward this substrate, with K(m) of 4.2 ± 0.99 and 0.2 ± 0.16 μM, respectively. In vitro assays of 104 human liver cytosols revealed marked individual variability that was highly correlated with β-naphthol sulfation (SULT1A1 diagnostic substrate; r = 0.98, P < 0.0001), but not with 17β-estradiol sulfation (SULT1E1 diagnostic substrate; r = 0.16, P = 0.10). Fulvestrant sulfation was correlated with both SULT1A1*1/2 genotype (P value = 0.023) and copy number (P < 0.0001). These studies suggest that factors influencing SULT1A1/1E1 tissue expression and/or enzymatic activity could influence the efficacy of fulvestrant therapy.

Melatonin receptors, melatonin metabolizing enzymes and cyclin D1 in human breast cancer

BACKGROUND

Melatonin suppresses breast cancer cell proliferation by inhibiting the upregulation of estrogen-induced cyclin D1 via its G-protein-coupled receptor MT1. Additionally, melatonin stimulates the expression of the estrogen sulfotransferase, SULT1E1. However, metabolism of melatonin via 6-hydroxylation by CYP1A1/1A2 and subsequent sulfonation by SULT1A1/1A3 decreases its intracellular concentration. This could have a negative impact on its oncostatic action in breast cancer.

PATIENTS AND METHODS

In this pilot study, we performed immunohistochemical (IHC) analysis of MT1 and cyclin D1 in breast cancer specimens from 33 patients. Also, we investigated the expression of CYP1A1/1A2, SULT1A1/1A3/1E1,and cyclin D1 in cancer (CANC) and adjacent non-cancer (NCANC) specimens from 10 representative breast cancer patients using quantitative real-time reverse transcription polymerase chain reaction.

RESULTS

CYP1A1-mRNA-expression was found only in three CANC and in one NCANC. CYP1A2 mRNA was below the detection limit in all patients. SULT1A1 was observed only in two of the 10 CANC and one of the 10 NCANC specimens. But, all 10 CANC and NCANC samples showed high SULT1A3 levels. Cyclin D1 mRNA levels were found in all 10 CANC and NCANC specimens. Furthermore, IHC-staining of cyclin D1 was observed in 27 of 33 CANC and correlated positively with estrogen receptor positivity (p = 0.015).

CONCLUSION

The low or even absent expression of CYP1A1 or CYP1A2 in breast cancer specimens suggested that melatonin might be involved in cell cycle arrest.

Sulfation of dietary flavonoids by human sulfotransferases

Dietary flavonoids catechin, epicatechin, eriodictyol, and hesperetin were investigated as substrates and inhibitors of human sulfotransferases (hSULTs). Purified recombinant proteins and human intestine cytosol were used as enzyme sources. hSULT1A1 and hSULT1A3 as well as human intestine cytosol can catalyse the sulfation of the investigated flavonoids. Sulfation of catechin, epicatechin, eriodictyol, and hesperetin by recombinant hSULTs showed substrate inhibition at high flavonoid concentrations. Hesperetin and eriodictyol are potent inhibitors of purified hSULT1A1, hSULT1A3, hSULT1E1, and hSULT2A1. Catechin and epicatechin inhibited hSULT1A1 and hSULT1A3, but not hSULT1E1 and hSULT2A1. The sulfation efficacy and potency of inhibition is related to the C-ring structure of flavonoids. These results suggest that dietary flavonoids may regulate human SULT activity and, therefore, affect the regulation of hormones and neurotransmitters, detoxification of drugs, and the bioactivation of pro- carcinogens and pro-mutagens.

Melatonin and breast cancer: cellular mechanisms, clinical studies and future perspectives

Recent studies have suggested that the pineal hormone melatonin may protect against breast cancer, and the mechanisms underlying its actions are becoming clearer. Melatonin works through receptors and distinct second messenger pathways to reduce cellular proliferation and to induce cellular differentiation. In addition, independently of receptors melatonin can modulate oestrogen-dependent pathways and reduce free-radical formation, thus preventing mutation and cellular toxicity. The fact that melatonin works through a myriad of signalling cascades that are protective to cells makes this hormone a good candidate for use in the clinic for the prevention and/or treatment of cancer. This review summarises cellular mechanisms governing the action of melatonin and then considers the potential use of melatonin in breast cancer prevention and treatment, with an emphasis on improving clinical outcomes.

Metabolism of resveratrol in breast cancer cell lines: impact of sulfotransferase 1A1 expression on cell growth inhibition

Resveratrol is a polyphenolic compound present in grapes and wine with anticancer activities that undergoes pronounced metabolism in humans. In order to determine whether metabolism of resveratrol also occurs in tumor cells and whether biotransformation has any impact on cytotoxicity, metabolism experiments were conducted with hormone-dependent ZR-75-1 and hormone-independent MB-MDA-231 human breast cancer cells. Along with resveratrol, it was possible to identify one metabolite, namely, resveratrol-3-O-sulfate in both cell lines. Its concentration in the cytoplasm and culture medium was 5.4- to 9-fold higher in ZR-75-1 cells than in MDA-MB-231 cells, concomitant with a 3.1-fold higher IC(50) value in the ZR-75-1 cell line (74 microM compared to 38 microM). By using RT-PCR, expression of sulfotransferase (SULT)1A1 mRNA, but not of other SULTs investigated, showed a close correlation with resveratrol 3-O-sulfate formation which was particularly high in ZR-75-1 and very low in MDA-MD-231 cells. In conclusion, we demonstrate that SULT1A1-based biotransformation reduces the anticancer activity of resveratrol in breast cancer cells, which must be considered in humans following oral uptake of dietary resveratrol as a chemopreventive agent.

One molecule, many derivatives: a never-ending interaction of melatonin with reactive oxygen and nitrogen species?

Melatonin is a highly conserved molecule. Its presence can be traced back to ancient photosynthetic prokaryotes. A primitive and primary function of melatonin is that it acts as a receptor-independent free radical scavenger and a broad-spectrum antioxidant. The receptor-dependent functions of melatonin were subsequently acquired during evolution. In the current review, we focus on melatonin metabolism which includes the synthetic rate-limiting enzymes, synthetic sites, potential regulatory mechanisms, bioavailability in humans, mechanisms of breakdown and functions of its metabolites. Recent evidence indicates that the original melatonin metabolite may be N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) rather than its commonly measured urinary excretory product 6-hydroxymelatonin sulfate. Numerous pathways for AFMK formation have been identified both in vitro and in vivo. These include enzymatic and pseudo-enzymatic pathways, interactions with reactive oxygen species (ROS)/reactive nitrogen species (RNS) and with ultraviolet irradiation. AFMK is present in mammals including humans, and is the only detectable melatonin metabolite in unicellular organisms and metazoans. 6-hydroxymelatonin sulfate has not been observed in these low evolutionary-ranked organisms. This implies that AFMK evolved earlier in evolution than 6-hydroxymelatonin sulfate as a melatonin metabolite. Via the AFMK pathway, a single melatonin molecule is reported to scavenge up to 10 ROS/RNS. That the free radical scavenging capacity of melatonin extends to its secondary, tertiary and quaternary metabolites is now documented. It appears that melatonin's interaction with ROS/RNS is a prolonged process that involves many of its derivatives. The process by which melatonin and its metabolites successively scavenge ROS/RNS is referred as the free radical scavenging cascade. This cascade reaction is a novel property of melatonin and explains how it differs from other conventional antioxidants. This cascade reaction makes melatonin highly effective, even at low concentrations, in protecting organisms from oxidative stress. In accordance with its protective function, substantial amounts of melatonin are found in tissues and organs which are frequently exposed to the hostile environmental insults such as the gut and skin or organs which have high oxygen consumption such as the brain. In addition, melatonin production may be upregulated by low intensity stressors such as dietary restriction in rats and exercise in humans. Intensive oxidative stress results in a rapid drop of circulating melatonin levels. This melatonin decline is not related to its reduced synthesis but to its rapid consumption, i.e. circulating melatonin is rapidly metabolized by interaction with ROS/RNS induced by stress. Rapid melatonin consumption during elevated stress may serve as a protective mechanism of organisms in which melatonin is used as a first-line defensive molecule against oxidative damage. The oxidative status of organisms modifies melatonin metabolism. It has been reported that the higher the oxidative state, the more AFMK is produced. The ratio of AFMK and another melatonin metabolite, cyclic 3-hydroxymelatonin, may serve as an indicator of the level of oxidative stress in organisms.

Melatonin and immunomodulation: connections and potential clinical applications

Melatonin is the main hormone secreted by the pineal gland in the human brain. It has a strong impact on the sleep-wake cycle and is considered a general modulator of the human circadian rhythm. Apart from these well-established properties, melatonin possesses immunomodulatory, antioxidative and antiinflammatory properties. The potential ability of this hormone to act synergistically with several cytokines by enhancing their antitumoral activity and dramatically decreasing their adverse effects has placed melatonin among the new and promising agents in cancer immunotherapy. The use of the neurohormone alone or in combination with cytokines and traditional chemotherapeutic drugs is currently under vigorous investigation. Experimental and clinical trials have already depicted some of the immunomodulatory and antitumor effects of melatonin, delineating the need for further research in this field.