Robert M. Harris

Sulfation of “Estrogenic” Alkylphenols and 17β-Estradiol by Human Platelet Phenol Sulfotransferases

We have investigated the ability of alkylphenols to act as substrates and/or inhibitors of phenol sulfotransferase enzymes in human platelet cytosolic fractions. Our results indicate: (i) straight chain alkylphenols do not interact with the monoamine-sulfating phenol sulfotransferase (SULT1A3); (ii) short chain 4-n-alkylphenols (C < 8) are substrates for the phenol-sulfating enzymes (SULT1A1/2), which exhibit two activity maxima against substrates with alkyl chain lengths of C1–2 and C4–5; (iii) long chain 4-n-substituted alkylphenols (C ≥ 8) are poor substrates and act as inhibitors of SULT1A1/2; (iv) human platelets contain two activities, of low and high affinity, capable of sulfating 17β-estradiol, and 4-n-nonylphenol is a partial mixed inhibitor of the low affinity form of this activity. We conclude that by acting either as substrates or inhibitors of SULT1A1/2, alkylphenols may influence the sulfation, and hence the excretion, of estrogens and other phenol sulfotransferase substrates in humans.

Environmental endocrine disrupters dysregulate estrogen metabolism and Ca2+ homeostasis in fish and mammals via receptor-independent mechanisms

Xenoestrogen endocrine disrupters (EDs) in the environment are thought to be responsible for a number of examples of sexual dysfunction that have recently been reported in several species. There is growing concern that these compounds may also cause abnormalities of the male reproductive tract and reduced spermatogenesis in man. Whilst some effects of EDs may be receptor-mediated, there is growing evidence that these compounds can exert potent effects in vivo by directly interacting with cellular enzyme targets. Here we report on, and review, the effects of alkylphenols and other EDs on two such enzymes: (1) sulfotransferases, which convert active estrogenic steroids to inactive steroid sulfates; and (2) Ca(2+)-ATPases, which are responsible for maintaining low, physiological, intracellular Ca(2+) concentrations. These enzymes are potently inhibited by EDs in both fish and mammalian species. The increased concentrations of active estrogens and the likely cytotoxic effects of elevated concentrations of intracellular Ca(2+) arising from these effects may underlie some of the endocrine disrupting potential of these widespread industrial pollutants.

Diethylstilboestrol—A long-term legacy

Diethylstilboestrol (DES) is an endocrine disrupter which causes cancer in rodents. It was prescribed in large amounts to treat women with gynaecological problems; some of the daughters of these women subsequently developed a rare cancer (vaginal clear cell adenocarcinoma) while genital abnormalities were found in some of the sons. It was used for decades in livestock feed and this may have contaminated the food chain leading to the exposure of the more general population. DES appears to cause epigenetic effects in animals and there is some evidence that this also occurs in man. The mechanisms of carcinogenesis are complex and the effects are difficult to prove due to the background of dietary and environmental phyto- and xenooestrogens. It has been suggested that, like other endocrine disrupters, DES may have acted as an obesogen in the human population.

Sulfur metabolism in ulcerative colitis: Investigation of detoxification enzymes in peripheral blood

Two enzymes of detoxification were studied inblood samples from 27 patients with ulcerative colitis(UC) and 18 controls to determine whether there is anabnormality in sulfur metabolism in UC. Thiolmethyltransferase (TMT) activity was measured in erythrocytemembranes as the extent of conversion of2-mercaptoethanol to S-methyl-2-mercaptoethanol with[3H]methyl-S-adenosyl methionine as methyldonor. Phenol sulfotransferase (PST) activity was measured in platelethomogenates as the extent of sulfation of p -nitrophenolwith 3-phosphoadenosine 5-phospho[35S]sulfate(PAPS) as sulfate donor. TMT activity was significantlyhigher in UC patients (27.0 vs 17.1 nmol/mgprotein/hr; P < 0.005). No difference in PST activitywas found. We conclude that TMT may be up-regulated inUC to detoxify excess hydrogen sulfide exposed to the peripheral blood compartment. This may arisefrom either increased luminal sulfide production orreduced colonic detoxification.

Endocrine disrupters—A threat to women's health?

Endocrine disruption has been a topic of public concern for many years and its study remains high on the scientific agenda. Endocrine disrupters (EDs) are compounds which may be of industrial or natural origin and which act to dysregulate steroid function and metabolism. As well as their actions on nuclear steroid receptors, EDs can inhibit the pathways of steroid synthesis and degradation. They not only affect reproductive function but also affect a range of tissues which are steroid sensitive such as the central nervous system and thyroid. Results from the latest studies suggest that EDs may also affect the immune system, glucose homeostasis and can act as epigenetic modulators resulting in transgenerational effects. Research in this area has led to the development of drugs used in the treatment of several types of hormone-sensitive cancer. However, despite many years of effort, the effects on human health of long-term environmental exposure to EDs, whether singly or as mixtures, remain unknown.

Endocrine disrupting alkylphenols: Structural requirements for their adverse effects on Ca2+pumps, Ca2+ homeostasis & Sertoli TM4 cell viability

Alkylphenols such as nonylphenol are pollutants that are widely dispersed within our environment. They bio-accumulate within man, with levels in the muM concentration range reported in human tissues. These chemicals act as endocrine disruptors, having xenoestrogenic activity. More recently alkylphenols have also been shown to affect Ca2+ signalling pathways. Here we show that alkylphenols are potent inhibitors of sarcoplasmic-endoplasmic reticulum Ca2+-ATPase (SERCA) activity. For linear chain alkylphenols the potency of inhibition is related to chain length, with the IC50 values for inhibition ranging from 8 microM for 4-n-nonylphenol (C9) to 1.3 mM for 4-n-propylphenol (C3). Branched chain alkylphenols generally had lower potencies than their linear chain counterparts, however, good correlations for all alkylphenols were observed between their Ca2+ pump inhibition and hydrophobicity, molecular volume and flexibility, indicating that these parameters are all important factors. Alkylphenols cause abnormal elevations of intracellular [Ca2+] within TM4 Sertoli cells (cells involved in sperm maturation) depolarise their mitochondria and induce cell death in these cells, in an alkyl chain size-dependent manner.

Non-genomic effects of endocrine disrupters: inhibition of estrogen sulfotransferase by phenols and chlorinated phenols.

Phenols are used world-wide and their presence in the environment is a cause of increasing concern. Despite evidence to suggest that, in general, they bind poorly to estrogen receptors, they are suspected of being endocrine disrupters. Here, we show that 2, x-substituted phenols are potent inhibitors of estrogen sulfotransferase with IC(50) values at low- or sub-micromolar levels. Our results demonstrate a potential non-genomic mechanism of action for these compounds and suggest that, where viable alternatives exist, both phenols substituted in the 2-position and their metabolic precursors should be avoided.

Inhibition of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase by flavonoids: A quantitative structure-activity relationship study

Flavonoids are commonly found in fruit and vegetables and have been shown to reach concentrations of several micromolars in human blood plasma. Flavonoids are also believed to have cancer chemoprotective properties. One hypothesis is that flavonoids are able to initiate apoptosis, especially in cancer cells, via a Ca2+‐dependent mitochondrial pathway. This pathway can be activated through an exaggerated elevation of cytosolic [Ca2+], and sarcoplasmic/endoplasmic reticulum Ca2+‐ATPases (SERCA) play an essential role in ameliorating such changes. In this study, we demonstrate that flavonoids (especially flavones) can inhibit the activity of Ca2+‐ATPases isoforms SERCA1A and SERCA2B in the micromolar concentration range. Of the 25 flavonoids tested, 3,6‐dihydroxyflavone (IC50, 4.6 μM) and 3,3′,4′,5,7‐pentahydroxyflavone (quercetin) (IC50, 8.9 μM) were the most potent inhibitors. We show that polyhydroxylation of the flavones are important for inhibition, with hydroxylation at position 3 (for SERCA1A) and position 6 (for SERCA2B) being particularly relevant.

In utero exposure to carcinogens: Epigenetics, developmental disruption and consequences in later life

The uterine environment is often viewed as a relatively safe haven, being guarded by the placenta which acts as a filter, permitting required materials to enter and unwanted products to be removed. However, this defensive barrier is sometimes breached by potential chemical hazards to which the mother may be subjected. Many of these toxins have immediate and recognisable deleterious effects on the embryo, foetus or neonate, but a few are insidious and leave a legacy of health issues that may emerge in later life. Several substances, falling into the categories of metals and metalloids, endocrine disruptors, solvents and other industrial chemicals, have been implicated in the development of long-term health problems in the offspring following maternal and subsequent in utero exposure. The mechanisms involved are complex but often involve epigenetic changes which disrupt normal cell processes leading to the development of cancers and also dysregulation of biochemical pathways.

Molecular basis of carcinogenicity of tungsten alloy particles.

The tungsten alloy of 91% tungsten, 6% nickel and 3% cobalt (WNC 91-6-3) induces rhabdomyosarcoma when implanted into a rat thigh muscle. To investigate whether this effect is species-specific human HSkMc primary muscle cells were exposed to WNC 91-6-3 particles and responses were compared with those from a rat skeletal muscle cell line (L6-C11). Toxicity was assessed by the adenylate kinase assay and microscopy, DNA damage by the Comet assay. Caspase 3 enzyme activity was measured and oligonucleotide microarrays were used for transcriptional profiling. WNC 91-6-3 particles caused toxicity in cells adjacent to the particles and also increased DNA strand breaks. Inhibition of caspase 3 by WNC 91-6-3 occurred in rat but not in human cells. In both rat and human cells, the transcriptional response to WNC 91-6-3 showed repression of transcripts encoding muscle-specific proteins with induction of glycolysis, hypoxia, stress responses and transcripts associated with DNA damage and cell death. In human cells, genes encoding metallothioneins were also induced, together with genes related to angiogenesis, dysregulation of apoptosis and proliferation consistent with pre-neoplastic changes. An alloy containing iron, WNF 97-2-1, which is non-carcinogenic in vivo in rats, did not show these transcriptional changes in vitro in either species while the corresponding cobalt-containing alloy, WNC 97-2-1 elicited similar responses to WNC 91-6-3. Tungsten alloys containing both nickel and cobalt therefore have the potential to be carcinogenic in man and in vitro assays coupled with transcriptomics can be used to identify alloys, which may lead to tumour formation, by dysregulation of biochemical processes.