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Biomedical subjects

R H Waring

Publications and source records attributed to R H Waring.

At least 19 recordsLinked to original sources
PubMed2005

Endocrine disrupters: a human risk?

Endocrine disrupters (EDs) alter normal hormonal regulation and may be naturally occurring or environmental contaminants. Classically, EDs act genomically, with agonistic or antagonistic effects on steroid receptors and may alter reproductive function and/or cause feminisation by binding to oestrogen or androgen receptors; their binding to the thyroid receptor may dysregulate the neuroendocrine system. Recently, it has been shown that EDs can also act by non-genomic mechanisms, altering steroid synthesis (inhibition of cytochrome P450 isoforms) or steroid metabolism. The alkylphenol and phthalate plasticisers inhibit the inactivation of oestrogens by sulphation (via SULT 1A1 and 1E1 isoforms) and so cause a rise in levels of the free active endogenous oestrogens. A range of ED effects have been shown in mammals, fish, birds, reptiles, amphibia and aquatic invertebrates but it is not yet clear whether these processes also occur in human beings. It is evident that EDs, as well as altering reproduction, can cause changes in neurosteroid levels and so have the potential to affect immune function, behaviour and memory. This may be of long-term concern since traces of EDs such as plasticisers, brominated fire retardants, sunscreen agents and cosmetic ingredients are widely distributed in the environment and in human biofluids.

Animals↗
PubMed2005

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.

Cells, Cultured↗
PubMed2005

The effect of plasticisers on "sulphate supply" enzymes.

Sulphation is important in xenobiotic detoxification and in steroid and thyroid hormones synthesis, transport and metabolism. Potential endocrine disrupting actions of plasticisers were assessed by studying effects on cell viability, cell proliferation and expression of enzymes (cysteine dioxygenase, sulphite oxidase, PAPS synthase I and II) involved in the synthesis of the cofactor, PAPS, for steroid sulphotransferases. TE 671 cells were used to study the effects of exposure to alkylphenols and alkylphenolethoxylates, bisphenol A, bisphenol A methacrylate, alkyladipates, dialkyl phthalates and resorcinol. The lactate dehydrogenase assay and CellTiter 96) AQ(ueous) One Solution Cell Proliferation Assay were used to measure cytotoxicity and cell proliferation, respectively. Steady-state mRNA was assessed by semi-quantitative RT-PCR and real time RT-PCR. None of the compounds tested was cytotoxic in TE 671 cells, however, cell proliferation was significantly increased with 0.005-0.5 microM dioctyl phthalate, diisodecyl phthalate (DIP) and butylbenzyl phthalate (P<0.05, n = 4). Real time RT-PCR showed dose-dependent decreases in steady-state mRNA levels of all the enzymes studied (P<0.05, n = 4) with 0.005-0.5 microM octylphenol, bis (2-ethylhexyl) phthalate and DIP treatment. Endocrine disrupting effects of some plasticisers may be a consequence of modulation of expression of enzymes supplying PAPS for hormone sulphation.

Cell Line↗
PubMed2005

Measurement of exogenous carbohydrate oxidation: a comparison of [U-14C]glucose and [U-13C]glucose tracers.

The purpose of this study was to assess the level of agreement between two techniques commonly used to measure exogenous carbohydrate oxidation (CHO(EXO)). To accomplish this, seven healthy male subjects (24 +/- 3 yr, 74.8 +/- 2.1 kg, V(O2(max)) 62 +/- 4 ml x kg(-1) x min(-1)) exercised at 50% of their peak power for 120 min on two occasions. During these exercise bouts, subjects ingested a solution containing either 144 g glucose (8.7% wt/vol glucose) or water. The glucose solution contained trace amounts of both [U-13C]glucose and [U-14C]glucose to allow CHO(EXO) to be quantified simultaneously. The water trial was used to correct for background 13C enrichment. 13C appearance in the expired air was measured using isotope ratio mass spectrometry, whereas 14C appearance was quantified by trapping expired CO(2) in solution (using hyamine hydroxide) and adding a scintillator before counting radioactivity. CHO(EXO) measured with [13C]glucose ([13C]CHO(EXO)) was significantly greater than CHO(EXO) measured with [14C]glucose ([14C]CHO(EXO)) from 30 to 120 min. There was a 15 +/- 4% difference between [13C]CHO(EXO) and [14C]CHO(EXO) such that the absolute difference increased with the magnitude of CHO(EXO). Further investigations suggest that the difference is not because of losses of CO2 from the trapping solution before counting or an underestimation of the "strength" of the trapping solution. Previous research suggests that the degree of isotopic fractionation is small (S. C. Kalhan, S. M. Savin, and P. A. Adam. J Lab Clin Med89: 285-294, 1977). Therefore, the explanation for the discrepancy in calculated CHO(EXO) remains to be fully understood.

Administration, Oral↗
PubMed2005

Induction of cysteine dioxygenase activity by oral administration of cysteine analogues to the rat: implications for drug efficacy and safety.

One of the major steps in the oxidation of the sulphur-containing amino acid, L-cysteine, is the production of cysteine sulphinic acid, catalysed by the enzyme cysteine dioxygenase. This enzyme plays a key role in the intermediary metabolism of sulphur-containing compounds. The activity of this crucial enzyme is known to be influenced by sulphur-compound intake, being increased in animals fed an excess of L-cysteine or methionine. However, the affects on this enzyme of the chronic administration of drugs similar in structure to cysteine are unknown. This has now been investigated using the anti-rheumatic agent, D-penicillamine, and the mucoactive compound, S-carboxymethyl-L-cysteine. Repeated oral administration of these sulphur-containing drugs to male Wistar rats for five consecutive days led to a significant increase in hepatic cysteine dioxygenase activity. This increase in the production rate of cysteine sulphinic acid remained evident until returning to control levels four days after cessation of drug administration. These observations provide evidence that these two drugs interact with the intermediary biochemistry of sulphur compounds and may provide hitherto unappreciated insights into mechanisms by which therapeutic effects and adverse reactions may occur.

Administration, Oral↗
PubMed2004

Effects of culture with TNF-alpha, TGF-beta and insulin on sulphotransferase (SULT 1A1 and 1A3) activity in human colon and neuronal cell lines.

The aim of the study was to determine whether the expression of sulphotransferase enzymes could be affected by the presence of cytokines or peptide hormones. The effects of cytokines (TNF-alpha and TGF-beta) and insulin on sulphotransferase (SULT 1A1 and 1A3) activity were studied in a human neuronal cell line (SK-N-SH) and a human gastrointestinal tract cell line (HT-29). Cells were cultured with varying concentrations of TNF-alpha, TGF-beta or insulin for 24 h; the SULT 1A1 isoform in the 2 cell lines showed different optimal substrate concentrations. There were no direct effects of cytokines on enzyme activity. Culture with TNF-alpha increased activity of both SULT 1A1 and 1A3 in the HT-29 cells; TGF-beta also increased activities of both isoforms but to a lesser extent; insulin increased activity of SULT 1A1 only. The cytokines and insulin had relatively little effect on sulphotransferase activity in the neuronal cell line. These results suggest that, unlike neuronal cells, gastrointestinal cells may respond to physiological states by altering sulphotransferase activity. As certain substrates such as diet-derived heterocyclic amines are bioactivated by sulphation to produce carcinogenic metabolites this may be a factor in the increased incidence of colorectal cancer in patients with inflammatory bowel disease or diabetes.

Arylsulfotransferase↗
PubMed2004

Phytoestrogens are potent inhibitors of estrogen sulfation: implications for breast cancer risk and treatment.

We investigated the ability of 37 flavonoids and flavonoid sulfoconjugates, including some abundant dietary constituents, to act as substrates and/or inhibitors of the sulfotransferase and sulfatase enzymes that interconvert active estrogens and inactive estrogen sulfates in human tissues. The enzymes studied include estrogen sulfotransferase, the thermostable phenolsulfotransferase that acts on a range of substrates including estrogens; steroid sulfatase; and two related enzymes, monoamine phenolsulfotransferase and arylsulfatase A. Several dietary flavonoids, including the soy isoflavones genistein and daidzein, were sulfated by these human sulfotransferases. Many flavonoids were potent inhibitors of thermostable phenolsulfotransferase. Genistein and equol were potent mixed inhibitors of hepatic estrogen sulfotransferase, with inhibitory constant values of 500 nM and 400 nM, respectively. Monoamine phenolsulfotransferase activity was relatively unaffected by flavonoids, but this enzyme was mainly responsible for the sulfation of flavonoids at concentrations greater than 1 micro M. Of the compounds tested, only daidzein 4,7-bisulfate, a trace metabolite in humans, significantly inhibited steroid sulfatase in the micromolar concentration range. Hence, dietary flavonoids may be able to influence the bioavailability of endogenous estrogens, and disrupt endocrine balance, by increasing the ratio of active estrogens to inactive estrogen sulfates in human tissues.

Arylsulfotransferase↗
PubMed2004

The effect of cysteine analogues on the excretion of urinary sulphate in the rat following cysteine administration.

A major pathway for the production of sulphate within the mammalian body is known to be via the oxidative degradation of the sulphur moiety within the amino acid, L-cysteine. The ability of two structurally similar sulphur-containing drugs, the anti-rheumatic agent, D-penicillamine, and the mucoactive compound, S-carboxymethyl-L-cysteine, to interfere with this sulphate production was investigated. Co-administration to the male rat of D-penicillamine (p.o.) and S-carboxymethyl-L-cysteine (p.o.) with [35S]-L-cysteine (i.p.) led to a significant decrease in the subsequent urinary elimination of inorganic sulphate whilst having no measurable effect on organic sulphate excretion. The co-administration of L-valine, an amino acid not containing sulphur, had no effect. It is not known where, within the complex sequence of events surrounding the degradation of cysteine to sulphate, that D-penicillamine or S-carboxymethyl-L-cysteine may interact.

Animals↗
PubMed2003

Expression of cysteine dioxygenase (EC 1.13.11.20) and sulfite oxidase in the human lung: a potential role for sulfate production in the protection from airborne xenobiotica.

AIMS: The lung is one of the major sites of phase I cytochrome P450 enzyme and phase II sulfotransferase expression, which together are thought to act as an enzymic barrier against the unimpeded transfer of airborne xenobiotics into the lung parenchyma and systemic circulation. Sulfate for conjugation is produced primarily from the oxidation of cysteine, begun by cysteine dioxygenase (CDO), and completed with the conversion of sulfite to sulfate via sulfite oxidase (SO). Little is known about the site of expression of these two enzymes in the alveoli of the human lung. METHODS: Antibodies and oligonucleotide probes raised against both CDO and SO were used for immunohistochemistry and in situ hybridisation, respectively, to investigate the expression of CDO and SO in human lung alveoli. RESULTS: CDO and SO were expressed in alveolar epithelial cells, which is also the site of expression of cytochrome P450 1B1. CONCLUSIONS: These results demonstrate that the two key enzymes in sulfate production are expressed in the same locale as phase I and phase II enzymes, and that these two enzymes may be involved in the production of sulfate for the maintenance of a metabolic barrier against the entry of airborne xenobiotics and the synthesis of important structural proteins and proteoglycans.

Air Pollutants↗
PubMed2003

Degradation to sulphate of S-methyl-L-cysteine sulphoxide and S-carboxymethyl-L-cysteine sulphoxide in man.

A nearly complete recovery of radioactivity was achieved over 14 days following the oral administration of [35S]-S-methyl-L-cysteine sulphoxide and [35S]-S-carboxymethyl-L-cysteine sulphoxide to four healthy male volunteers. The urine was the major pathway of excretion of radioactivity (c. 96% in 0-14 days; c. 59% in 0-24 hours), with the faecal route being relatively unimportant (c. 1.7% in 0-3 days). Inorganic sulphate was an important degradation product, incorporating a substantial proportion of radioactive sulphur derived from these molecules (c. 40% in 0-14 days; c. 20% in 0-24 hours). Subtle differences were noted in the pattern of radioactive sulphate excretion following administration of the two cysteine-sulphoxide compounds, suggesting that their sulphur-containing moieties may enter different catabolic routes.

Administration, Oral↗
PubMed2002

Cysteine dioxygenase: modulation of expression in human cell lines by cytokines and control of sulphate production.

Cysteine dioxygenase (CDO) is the initial and rate-limiting enzyme involved in the oxidative degradation of cysteine to inorganic sulphate. It is believed to be the major source of sulphate in vivo. Inflammatory conditions such as rheumatoid arthritis have been linked with high plasma cysteine:sulphate ratios in patients. The cytokines tumour necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) have been shown to inhibit the expression of CDO in neuronal (TE671) and hepatic (Chang) human cell lines at nanomolar concentrations. Cytokine release may therefore modulate sulphate production and hence regulate formation of sulphated biocomponents.

Antineoplastic Agents↗
PubMed2002

Fate of the anthelmintic, phenothiazine, in man.

1. Radiolabelled [(35)S]-phenothiazine has been administered orally to two healthy adult male volunteers (6 mg kg(-1) body weight). Faeces were the major route of excretion of radioactivity (68%), the remainder being eliminated via the urine (32%) with an estimated urinary half-life (biphasic) of 6-16 h. Over the 5 days of the study a complete recovery of radioactivity was achieved. 2. From urinary data, it was shown that metabolism occurred via ring carbon oxidation to form phenothiazone and thionol and via ring sulphur oxidation to form phenothiazine sulphoxide. The majority of urinary material (92%) was present in the form of conjugates of phenothiazine and phenothiazone. Only unchanged phenothiazine was detected in the faeces. Phenothiazine sulphoxide was reduced to phenothiazine during incubation with faecal homogenates.

Adult↗
PubMed2002

Use of a physiological process model with forestry yield tables to set limits on annual carbon balances.

We present an approach that sets limits on annual carbon fluxes for different aged forests by using a simple process-based model (3-PG) and information derived from yield tables and local weather stations. Given a measure of height-growth potential, model predictions are constrained to match stand dynamics described in yield tables. Thus constrained, the model can provide reasonable annual estimates of gross photosynthesis under a specified climate, even with inexact knowledge of soil properties. If we assume that leaf litterfall and fine-root turnover approach equilibrium at canopy closure, maximum net annual ecosystem exchange can also be predicted from modeled estimates of these two detrital components and estimates of foliage, branch, stem and coarse-root production. The latter four components of production are predicted from allometric relationships with mean stem diameter. The approach is demonstrated for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands between Ages 20 and 150 years growing under conditions typical of those at Wind River, Washington, USA. Gross photosynthesis (Pg) by Douglas-fir at Ages 20, 70 and 150 years with leaf area indices (L) of 8.1, 6.9 and 4.0 was predicted at 1630, 1580 and 1160 g C m-2 year(1, respectively. Maximum net ecosystem production (Pe) for the same range in age classes was predicted to average 275, 294 and 207 g C m-2 year-1, respectively. The predicted reductions in L for older stands do not occur because other species fill the canopy gaps created by natural mortality of Douglas-fir. As a result of the development of an understory, total Pg is predicted to decrease only slightly with the aging of the overstory. Estimates of Pe exclude respiration from coarse woody debris, although additions of this component are provided annually by the model. The process-based modeling approach, constrained by yield table estimates of stand properties, sets reasonable limits on annual carbon exchange and suggests which environmental variables deserve careful monitoring to refine estimates of carbon fluxes.

Carbon↗
PubMed2001

Cysteine dioxygenase: regional localisation of protein and mRNA in rat brain.

Cysteine dioxygenase (CDO) converts cysteine to cysteinesulphinic acid and is the rate-limiting step in sulphate production. Most studies have centred upon the hepatic form of the enzyme, but several studies have investigated brain CDO using activity assays and western blotting. The aim of this study was to investigate the expression of CDO in the rat brain using a combination of immunohistochemistry and in situ hybridisation. Affinity-purified anti-R and anti-H CDO antibodies were immunoprecipitated using rat brain homogenate to determine whether the antibodies could remove enzyme activity. Immunohistochemistry and in situ hybridisation were then used to determine the cellular and regional expression of both CDO protein and mRNA. Immunoprecipitation of rat brain homogenate removed up to 98% and 70% (anti-R and anti-H, respectively) of enzyme activity. Nonimmune sheep serum had no effect upon enzyme activity. CDO protein and mRNA was localised solely to the neurones of the brain, including the pyramidal cells of the hippocampus and the Purkinje cells of the cerebellum. Regional localisation varied, with high levels of expression in the hippocampus, the dentate gyrus, the outer cortices of the brain, and the substantia nigra. The relative expression of CDO activity and protein in these regions is most probably a result of the relative abundance of neurones in these regions. CDO expression in the brain may have several possibilities functions, the most likely being the prevention of free radical production by the autoxidation of cysteine and dopamine.

Animals↗
PubMed2001

Do dietary phytoestrogens influence susceptibility to hormone-dependent cancer by disrupting the metabolism of endogenous oestrogens?

Phytoestrogens are natural constituents of our diets that have been suggested to protect against hormone-dependent breast cancer. Some of the diverse effects of these compounds may be attributed to ligand-dependent differences in their interaction with oestrogen receptor sub-classes. However, phytoestrogens can also inhibit enzymes that are involved in the generation and removal of endogenous steroid hormones. Among the most potent effects of dietary phytoestrogens is their ability to inhibit the sulphotransferases that sulphate both oestrogenic steroids and a variety of environmental chemicals, including dietary pro-carcinogens. Circulating steroid sulphates are thought to be the major source of oestradiol in post-menopausal breast tumours and sulphation is a key step in the activation of some dietary pro-carcinogens. Hence the inhibition of sulphotransferases by dietary phytoestrogens may have complex effects upon human susceptibility to breast cancer.

3-Hydroxysteroid Dehydrogenases↗
PubMed2001

Renal localisation of rat cysteine dioxygenase.

BACKGROUND/AIMS: Cysteine dioxygenase (CDO, EC 1.13.11.20) catalyses the conversion of cysteine to cysteine sulphinic acid and controls the rate-limiting step of sulphate production. Many neurological and non-neurological diseases are associated with abnormalities in CDO activity, giving rise to reduced availability of sulphate. The importance of the kidney in the sulphation of xenobiotics has long been recognised, but little is known about the renal expression of key enzymes in this pathway. In order to address this, this report demonstrates the expression of CDO in the kidney. METHODS: Two previously characterised antibodies were used to investigate the localisation and expression of CDO using immunohistochemistry, in-situ hybridisation and Western blotting. RESULTS: Renal CDO was shown to exist as a 68-kDa protein, which was unaffected by levels of cysteine and methionine that had been previously shown to induce hepatic CDO. CDO protein expression was present in the proximal convoluted tubules of the cortex and the collecting ducts of both the medulla and papilla. DISCUSSION: These results suggest that renal CDO is immunologically identical to that of the liver. Its expression in the kidney tubules, the major site of sulphation in the kidney, suggests that CDO in the kidney may play a role in both xenobiotic metabolism and sodium and water homeostasis.

Animals↗