Soy intake and cancer risk: a review of the in vitro and in vivo data

International variations in cancer rates have been attributed, at least in part, to differences in dietary intake. Recently, it has been suggested that consumption of soyfoods may contribute to the relatively low rates of breast, colon, and prostate cancers in countries such as China and Japan. Soybeans contain a number of anticarcinogens, and a recent National Cancer Institute workshop recommended that the role of soyfoods in cancer prevention be investigated. In this review, the hypothesis that soy intake reduces cancer risk is considered by examining relevant in vitro, animal, and epidemiological data. Soybeans are a unique dietary source of the isoflavone genistein, which possesses weak estrogenic activity and has been shown to act in animal models as an antiestrogen. Genistein is also a specific inhibitor of protein tyrosine kinases; it also inhibits DNA topoisomerases and other critical enzymes involved in signal transduction. In vitro, genistein suppresses the growth of a wide range of cancer cells, with IC50 values ranging from 5 to 40 microM (1-10 micrograms/ml). Of the 26 animal studies of experimental carcinogenesis in which diets containing soy or soybean isoflavones were employed, 17 (65%) reported protective effects. No studies reported soy intake increased tumor development. The epidemiological data are also inconsistent, although consumption of nonfermented soy products, such as soymilk and tofu, tended to be either protective or not associated with cancer risk; however, no consistent pattern was evident with the fermented soy products, such as miso. Protective effects were observed for both hormone- and nonhormone-related cancers. While a definitive statement that soy reduces cancer risk cannot be made at this time, there is sufficient evidence of a protective effect to warrant continued investigation.

Noninvasive Doppler determination of cardiac output in man. Clinical validation

A noninvasive technique for assessing cardiac output (CO) was evaluated by comparing it with thermodilution determinations in patients in the intensive care unit. The new method uses pulsed ultrasound to measure aortic diameter and continuous-wave Doppler ultrasound to obtain aortic blood velocity. An initial study evaluating just the velocity measurement showed that changes of the Doppler index of output (DI) correlated well with those of thermodilution cardiac output (TDCO). Linear regression analysis yielded delta DI = 0.87 delta TDCO + 0.14 (r = 0.83, n = 95). Using a university research instrument these measurements were possible in 54 of 60 patients (90%). A second study using a prototype commercial device incorporated the diameter measurement. Ultrasonic cardiac output (UCO), calculated as the time integral of velocity multiplied by the aortic area, was compared to TDCO. The data, obtained from 45 of 53 patients (85%), are described by the linear regression UCO = 0.95TDCO + 0.38 (r = 0.94, n = 110) over a range of 2-11 l/min. Patients with aortic stenosis, aortic insufficiency or a prosthetic valve have been excluded from the second study due to conditions likely to violate the assumptions upon which the calculation of absolute cardiac output is based. These results indicate that accurate CO can be measured by noninvasive ultrasound in most patients. The technique may be useful for extended CO monitoring in acute care patients and for CO assessment in many other types of patients undergoing diagnostic studies and therapeutic interventions.

Antioxidant and antipromotional effects of the soybean isoflavone genistein

Antioxidant and antipromotional effects of the soybean isoflavone genistein have been studied in HL-60 cells and the mouse skin tumorigenesis model. Effects of structure-related flavone/isoflavones on hydrogen peroxide (H2O2) production by 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated HL-60 cells and superoxide anion (O2-) generation by xanthine/xanthine oxidase were compared. Of tested isoflavones, genistein is the most potent inhibitor among TPA-induced H2O2 formation by (dimethyl sulfoxide) DMSO-differentiated HL-60 cells, daidzein is second, and apigenin and biochanin A show little effect. In contrast, genistein, apigenin, and prunectin are equally potent in inhibiting O2- generation by xanthine/xanthine oxidase, with daidzein showing a moderate inhibitory effect and biochanin A exhibiting no effect. These results suggest that the antioxidant properties of isoflavones are structurally related and the hydroxy group at Position 4' is crucial in both systems. Dietary administration of 250 ppm genistein for 30 days significantly enhances the activities of antioxidant enzymes in the skin and small intestine of mice. Further studies show that genistein significantly inhibits TPA-induced proto-oncogene expression (c-fos) in mouse skin in a dose-dependent manner. In a two-stage skin carcinogenesis study, low levels of genistein (1 and 5 mumol) significantly prolong tumor latency and decrease tumor multiplicity by approximately 50%. We conclude that genistein's antioxidant properties and antiproliferative effects may be responsible for its anticarcinogenic effect. Its high content in soybeans and relatively high bioavailability favor genistein as a promising candidate for the prevention of human cancers.

Genistein inhibition of the growth of human breast cancer cells: independence from estrogen receptors and the multi-drug resistance gene

The effect of isoflavones on the growth of the human breast carcinoma cell lines, MDA-468 (estrogen receptor negative), and MCF-7 and MCF-7-D-40 (estrogen receptor positive), has been examined. Genistein is a potent inhibitor of the growth of each cell line (IC50 values from 6.5 to 12.0 micrograms/ml), whereas biochanin A and daidzein are weaker growth inhibitors (IC50 values from 20 to 34 micrograms/ml). The isoflavone beta-glucosides, genistin and daidzin, have little effect on growth (IC50 values greater than 100 micrograms/ml). The presence of the estrogen receptor is not required for the isoflavones to inhibit tumor cell growth (MDA-468 vs MCF-7 cells). In addition, the effects of genistein and biochanin A are not attenuated by overexpression of the multi-drug resistance gene product (MCF-7-D40 vs MCF-7 cells).

Genistein and biochanin A inhibit the growth of human prostate cancer cells but not epidermal growth factor receptor tyrosine autophosphorylation

The effect of the isoflavones, genistein, daidzein, and biochanin A on the growth of the LNCaP and DU-145 human prostate cancer cell lines has been examined. Genistein and biochanin A, but not daidzein, inhibit both serum and EGF-stimulated growth of LNCaP and DU-145 cells (IC50 values from 8.0 to 27 micrograms/ml for serum and 4.3 to 15 micrograms/ml for EGF), but have no significant effect of the EGF receptor tyrosine autophosphorylation. In contrast, tyrphostin 25, a specific EGF receptor tyrosine kinase inhibitor, inhibits EGF-stimulated growth and EGF receptor tyrosine autophosphorylation in these whole cells, but does not inhibit serum-stimulated growth. These data suggest that the mechanism of action of genistein and biochanin A does not depend on inhibition of EGF receptor tyrosine autophosphorylation, but on a more distal event in the EGF receptor-mediated signal transduction cascade.

Genistein suppresses mammary cancer in rats

Female Sprague-Dawley CD rats were injected s.c. with 5 mg genistein, a soy phytoestrogen, or 20 microliters of the vehicle, dimethylsulfoxide (DMSO), on days 2,4 and 6 postpartum. At day 50, they were exposed to 80 micrograms dimethylbenz[a]anthracene (DMBA)/g body wt. Animals treated neonatally with genistein as compared to DMSO had increased latency and reduced incidence and multiplicity of DMBA-induced mammary adenocarcinomas. Mammary whole mount analysis showed that 50 day old female rats treated neonatally with genistein had fewer terminal end buds. Cell proliferation studies revealed that 50 day old genistein-treated rats had lower percentages and total numbers of cells in the S-phase of the cell cycle in terminal end buds, terminal ducts, lobules I and lobules II. In genistein-treated as compared to vehicle-treated female rats, vaginal openings occurred earlier, the estrus cycle was disrupted and the uterine-ovarian weights were smaller. In 50 day old genistein-treated females there were atretic antral follicles, fewer corpora lutea, and lower circulating progesterone but not estradiol-17 beta concentrations. In 21 day old rats treated neonatally with genistein, mammary glands were larger and there were more terminal end buds and terminal ducts, and more proliferative activity in all terminal ductals structures. It appears that neonatal genistein-treatment exerted its chemoprevention action by acting directly to enhance maturation of terminal ductal structures and by altering the endocrine system to reduce cell proliferation in the mammary gland.

Nitration of unsaturated fatty acids by nitric oxide-derived reactive nitrogen species peroxynitrite, nitrous acid, nitrogen dioxide, and nitronium ion

Reactive nitrogen species derived from nitric oxide are potent oxidants formed during inflammation that can oxidize membrane and lipoprotein lipids in vivo. Herein, it is demonstrated that several of these species react with unsaturated fatty acid to yield nitrated oxidation products. Using HPLC coupled with both UV detection and electrospray ionization mass spectrometry, products of reaction of ONOO- with linoleic acid displayed mass/charge (m/z) characteristics of LNO2 (at least three products at m/z 324, negative ion mode). Further analysis by MS/MS gave a major fragment at m/z 46. Addition of a NO2 group was confirmed using [15N]ONOO- which gave a product at m/z 325, fragmenting to form a daughter ion at m/z 47. Formation of nitrated lipids was inhibited by bicarbonate, superoxide dismutase (SOD), and Fe3+-EDTA, while the yield of oxidation products was decreased by bicarbonate and SOD, but not by Fe3+-EDTA. Reaction of linoleic acid with both nitrogen dioxide (*NO2) or nitronium tetrafluoroborate (NO2BF4) also yielded nitrated lipid products (m/z 324), with HPLC retention times and MS/MS fragmentation patterns identical to the m/z 324 species formed by reaction of ONOO- with linoleic acid. Finally, reaction of HPODE, but not linoleate, with nitrous acid (HONO) or isobutyl nitrite (BuiONO) yielded a product at m/z 340, or 341 upon reacting with [15N]HONO. MS/MS analysis gave an NO2- fragment, and 15N NMR indicated that the product contained a nitro (RNO2) functional group, suggesting that the product was nitroepoxylinoleic acid [L(O)NO2]. This species could form via homolytic dissociation of LOONO to LO* and *NO2 and rearrangement of LO* to an epoxyallylic radical L(O)* followed by recombination of L(O)* with *NO2. Since unsaturated lipids of membranes and lipoproteins are critical targets of reactive oxygen and nitrogen species, these pathways lend insight into mechanisms for the formation of novel nitrogen-containing lipid products in vivo and provide synthetic strategies for further structural and functional studies.

Ionic channels of the inner segment of tiger salamander cone photoreceptors

Cone photoreceptors were isolated enzymatically and their ionic currents studied by the whole-cell, gigaseal voltage-clamp technique. Five nonsynaptic currents were identified. A prominent, poorly selective cation current, Ih, activated after a delay during hyperpolarizations and then deactivated with a delay on return to potentials greater than -50 mV. An empirical model for Ih gating kinetics is developed with three open and two closed states. Depolarization elicits a small, voltage-gated calcium current (ICa). Block by nitrendipine, nickel, cadmium, and cobalt, increase of current with barium, lack of rapid inactivation, and relatively high threshold suggest an L-type Ca channel. No evidence was found for low-threshold Ca channels. An anion current ICl(Ca) was present after pulses that led to a significant inward ICa (but not IBa) and was not elicited when cobalt was present. Tails of ICl(Ca) were short (100 ms) after short depolarizations and were longer after longer depolarizations. Two TEA-sensitive K currents were also elicited by depolarizations. One, IK(Ca), was calcium sensitive. We looked for modulation of Ih, ICa, and ICl(Ca) by a number of neurotransmitters. No changes of Ih were seen, but ICa and ICl(Ca) were depressed in a few cones when GABA or adenosine were applied. We discuss how this modulation might contribute to the feedback effects of horizontal cells on cones when surrounding cones are illuminated.

Peroxynitrite-dependent tryptophan nitration

Peroxynitrite (ONOO-), the reaction product of superoxide (O2.-) and nitric oxide (.NO), nitrates tyrosine and other phenolics. We report herein that tryptophan is also nitrated by peroxynitrite in the absence of transition metals to one predominant isomer of nitrotryptophan, as determined from spectral characteristics and liquid chromatography-mass spectrometry analysis. At high peroxynitrite to tryptophan ratios, other oxidation products were detected as well. The amount of nitrotryptophan formed from peroxynitrite increased at acidic pH, with an apparent pKa of 7.8. High concentrations of Fe(3+)-EDTA were required to enhance peroxynitrite-induced nitrotryptophan formation, while addition of up to 15 microM Cu/Zn superoxide dismutase had a minimal effect on tryptophan nitration. Cysteine, ascorbate, and methionine decreased nitrotryptophan yield to an extent similar to that predicted by their reaction rates with ground-state peroxynitrite, and typical hydroxyl radical scavengers partially inhibited nitration. Plots of the observed rate constant of nitrotryptophan formation vs tryptophan concentration presented downward curvatures. Thus, the kinetics of metal-independent nitration reactions were interpreted in terms of two parallel mechanisms. In the first one, ground-state peroxynitrous acid nitrated tryptophan with a second-order rate constant of 184 +/- 11 M-1 s-1 at 37 degrees C. The activation enthalpy was 9.1 +/- 0.3 kcal mol-1, and the activation entropy was -19 +/- 1 cal mol-1 K-1. In the second mechanism, ONOOH*, an activated intermediate derived from trans-peroxynitrous acid formed in a steady state, was the nitrating agent.

Mechanisms of action of the soy isoflavone genistein: emerging role for its effects via transforming growth factor beta signaling pathways

The soy isoflavone genistein attenuates growth factor- and cytokine-stimulated proliferation of both normal and cancer cells. This article reviews our current understanding of the potential mechanisms of action of genistein. In membrane preparations from mammalian cells, genistein is a potent and specific inhibitor of tyrosine autophosphorylation of the epidermal growth factor (EGF) receptor. However, in several cell systems in which it inhibits growth, genistein does not alter tyrosine phosphorylation of the EGF receptor or other tyrosine kinase substrates thought to be involved in signal transduction pathways, suggesting that other mechanisms may be responsible for its action. Alternatives include inhibition of DNA topoisomerase II activity, regulation of cell cycle checkpoints, and antiangiogenic and antioxidant activity. Experiments in our laboratory suggest a new concept, that genistein may inhibit cell growth by modulating transforming growth factor (TGF) beta1 signaling pathways. Such a link between genistein action and TGFbeta1 function is supported by preliminary results of studies in patients with hereditary hemorrhagic telangiectasia (a genetic disorder involving mutations in proteins that regulate TGFbeta receptor complex formation and signaling) in which several patients had dramatic attenuation of their symptoms after 1 wk of ingesting soy-based beverages. These preclinical studies in combination with our cell culture data suggest that the mechanism of genistein involves, if not requires, TGFbeta1-signaling.

Inhibition of tumor promoter-induced hydrogen peroxide formation in vitro and in vivo by genistein

Here we report that genistein, a soybean isoflavone, strongly inhibits tumor promoter-induced H2O2 formation both in vivo and in vitro. Genistein suppressed H2O2 production by 12-O-tetradecanoylphorbol-13-acetate- (TPA) stimulated human polymorphonuclear leukocytes (PMNs) and HL-60 cells in a dose-dependent manner over the concentration range 1-150 microM. Human PMNs were more sensitive to the inhibitory effect of genistein than HL-60 cells (50% inhibitory concentration 14.8 and 30.2 microM, respectively). In addition, genistein moderately inhibited superoxide anion formation by HL-60 cells and scavenged exogenously added H2O2 under the same conditions as in cell culture. However, the H2O2-scavenging effect of genistein was about 50% lower than its inhibition of cell-derived H2O2 formation at all concentrations. In the CD-1 mouse skin model, genistein strongly inhibited TPA-induced oxidant formation, edema, and PMN infiltration in mouse skin. Inhibition of TPA-mediated H2O2 in vivo may result from decreased cell-derived H2O2 formation, scavenging of H2O2 produced, and/or suppression of PMN infiltration into the dermis. The antioxidant properties of genistein may be responsible for its anticarcinogenic effects, and the dietary availability of genistein makes it a promising candidate for the prevention of human cancers.

Chemical modification of isoflavones in soyfoods during cooking and processing

The principal chemical forms of isoflavones in soybean are their 6''-O-malonyl-beta-glucoside (6OMalGlc) conjugates. Experiments were carried out to determine the best conditions for extraction of isoflavones from soyfoods and the effects of commercial processing procedures and of cooking on isoflavone concentrations and composition. Hot alcohol extraction of ground soybeans deesterified 6OMalGlc conjugates. Although room temperature extraction slowed the conversion, extraction at 4 degrees C for 2-4 h led to the highest yield of 6OMalGlc conjugates and the lowest proportion of beta-glucoside conjugates. Analysis of soyfood products by reversed-phase HPLC-mass spectrometry revealed that defatted soy flour that had not been heat treated consisted mostly of 6OMalGlc conjugates; in contrast, toasted soy flour contained large amounts of 6''-O-acetyl-beta-glucoside conjugates, formed by heat-induced decarboxylation of the malonate group to acetate. Soymilk and tofu consisted almost entirely of beta-glucoside conjugates; low-fat versions of these products were markedly depleted in isoflavones. Alcohol-washed soy-protein concentrates contained few isoflavones. Isolated soy protein and textured vegetable protein consisted of a mixture of all 3 types of isoflavone conjugates. Baking or frying of textured vegetable protein at 190 degrees C and baking of soy flour in cookies did not alter total isoflavone content, but there was a steady increase in beta-glucoside conjugates at the expense of 6OMalGlc conjugates. The chemical form of isoflavones in foods should be taken into consideration when evaluating their availability for absorption from the diet.

Intestinal uptake and biliary excretion of the isoflavone genistein in rats

The intestinal absorption, biliary excretion and metabolism of genistein, a potent and specific protein tyrosine kinase inhibitor that occurs naturally in soy foods, was examined in anesthetized, adult female rats fitted with indwelling biliary cannulas. 4-14C-Genistein, when infused into the duodenum, was rapidly absorbed from the intestine, taken up by the liver and excreted into the bile as its 7-O-beta-glucuronide conjugate. Cumulative recovery of 14C-radioactivity in the bile over a 4-h period was 70-75% of the dose. When genistein was infused into the portal vein, it was also taken up efficiently by the liver, conjugated with glucuronic acid and transported into bile. However, portal blood collected after duodenal infusions of genistein contained mostly genistein 7-O-beta-glucuronide, suggesting that in vivo glucuronidation occurred in the intestinal wall rather than the liver. This was confirmed using everted intestinal sac preparations. Reinfusion of genistein 7-O-beta-glucuronide into the duodenum or into the mid small intestine resulted in its reappearance in the bile, albeit more slowly than when genistein was infused. Over a 4-h collection period, the cumulative recovery of 14C-radioactivity in bile was 27 and 70-75% of the administered dose for duodenal and ileal infusions, respectively. These data indicate that genistein is highly bioavailable in rats and because of its enterohepatic circulation may accumulate within the gastrointestinal tract.

Prepubertal genistein exposure suppresses mammary cancer and enhances gland differentiation in rats

Genistein, a component of soy, was administered to prepubertal female Sprague-Dawley CD rats and investigated for chemoprevention against mammary cancer. Genistein, at 500 microgram/g body wt or an equivalent volume of the vehicle, dimethylsulfoxide (DMSO), was injected (s.c.) on days 16, 18 and 20 post-partum. At day 50 post-partum all animals were exposed to 80 microgram dimethylbenz[a]anthracene (DMBA) per g body wt. Animals treated prepubertally with genistein as compared to DMSO had reduced incidence and significantly fewer adenocarcinomas per animal. Mammary whole mount analysis showed that prepubertal genistein treatment resulted in mammary glands of 50-day-old rats developing fewer terminal end buds and more lobules II. Cell proliferation studies with bromodeoxyuridine (BrdU) showed that terminal end buds from mammary glands of 50-day-old females treated prepubertally with genistein had significantly fewer cells in S-phase of the cell cycle. Serum genistein concentrations in 21- and 50-day-old females following prepubertal genistein treatment were 4.2 +/- 0.6 micromol and 102 +/- 30 nM, respectively. Animals treated prepubertally with genistein as compared to vehicle spent more time in the estrus phase of the estrus cycle, although all animals did cycle. In 50-day-old females, circulating estradiol-17 beta and progesterone concentrations were not significantly altered by the prepubertal genistein treatment. Oocyte/follicle counts and numbers of atretic follicles and corpora lutea were not significantly different between the genistein- and vehicle-treated animals. We conclude that genistein treatment during the prepubertal period can suppress the development of chemically-induced mammary cancer without significant toxicity to the endocrine/reproductive system.

Superoxide dismutase catalyzes nitration of tyrosines by peroxynitrite in the rod and head domains of neurofilament-L

Superoxide dismutase (SOD) catalyzes the nitration of specific tyrosine residues in proteins by peroxynitrite (ONOO-), which may be the damaging gain-of-function resulting from mutations to SOD associated with familial amyotrophic lateral sclerosis (ALS). We found that disassembled neurofilament-L (light subunit) was more susceptible to tyrosine nitration catalyzed by SOD in vitro. Neurofilament-L was selectively nitrated compared with the majority of other proteins present in brain homogenates. Assembled neurofilament-L was more resistant to nitration, suggesting that the susceptible tyrosine residues were protected by intersubunit contacts in assembled neurofilaments. Electrospray mass spectrometry of trypsin-digested neurofilament-L showed that tyrosine 17 in the head region and tyrosines 138, 177, and 265 in alpha-helical coil regions of the rod domain of neurofilament-L were particularly susceptible to SOD-catalyzed nitration. Nitrated neurofilament-L inhibited the assembly of unmodified neurofilament subunits, suggesting that the affected tyrosines are located in regions important for intersubunit contacts. Neurofilaments are major structural proteins expressed in motor neurons and known to be important for their survival in vivo. We suggest that SOD-catalyzed nitration of neurofilament-L may have a significant role in the pathogenesis of ALS.

Nitric oxide inhibition of lipoxygenase-dependent liposome and low-density lipoprotein oxidation: termination of radical chain propagation reactions and formation of nitrogen-containing oxidized lipid derivatives

Lipoxygenase-induced lipid oxidation contributes to plasma lipoprotein oxidation and may be an underlying pathogenic mechanism of atherogenesis. Since inactivation of the vasorelaxant actions of nitric oxide (.NO) plays a critical role in the impaired function of atherosclerotic vessels and because .NO reacts rapidly with other radical species, we assessed the influence of .NO on lipoxygenase-catalyzed oxidation of linoleic and linolenic acid, 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphocholine (PC) liposomes, hypercholesterolemic rabbit beta-very-low-density lipoprotein, and human low-density lipoprotein. Soybean lipoxygenase (SLO)-induced lipid oxidation was assessed by accumulation of conjugated dienes, formation of lipid hydroperoxides, oxygen consumption, and liquid chromatography-mass spectrometry. Different rates of delivery of .NO to lipid oxidation systems were accomplished either by infusion of .NO gas equilibrated with anaerobic buffer or via .NO released from S-nitrosoglutathione. Nitric oxide alone did not induce lipid peroxidation, while exposure to SLO yielded significant oxidation of fatty acids, PC liposomes, or lipoproteins in a metal ion-independent mechanism. Low concentrations of .NO, which did not significantly inhibit the activity of the iron-containing lipoxygenase, induced potent inhibition of lipid peroxidation in a dose-dependent manner. Mass spectral analysis of oxidation products showed formation of nitrito-, nitro-, nitrosoperoxo-, and/or nitrated lipid oxidation adducts, demonstrating that .NO serves as a potent terminator of radical chain propagation reactions. The formation of Schiff's base fluorescent conjugates between SLO-oxidized linoleic or linolenic acid and bovine serum albumin (BSA) was also inhibited by .NO via reaction with lipid hydroperoxyl radicals (LOO.), thus preventing the reaction of LOO. with polypeptide amino groups. Mass spectrometry analysis showed that both lipid peroxidation products and nitrogen-containing oxidized lipid species decreased in the presence of BSA. We conclude that .NO can play a potent oxidant-protective role in the vessel wall by inhibiting lipoxygenase-dependent lipid and lipoprotein oxidation. This occurs via termination of lipid radical chain propagation reactions catalyzed by alkoxyl (LO.) and LOO. intermediates of lipid peroxidation rather than by inhibition of lipoxygenase-catalyzed initiation reactions.

Rationale for the use of genistein-containing soy matrices in chemoprevention trials for breast and prostate cancer

Pharmacologists have realized that tyrosine kinase inhibitors (TKI) have potential as anti-cancer agents, both in prevention and therapy protocols. Nonetheless, concern about the risk of toxicity caused by synthetic TKIs restricted their development as chemoprevention agents. However, a naturally occurring TKI (the isoflavone genistein) in soy was discovered in 1987. The concentration of genistein in most soy food materials ranges from 1-2 mg/g. Oriental populations, who have low rates of breast and prostate cancer, consume 20-80 mg of genistein/day, almost entirely derived from soy, whereas the dietary intake of genistein in the US is only 1-3 mg/day. Chronic use of genistein as a chemopreventive agent has an advantage over synthetic TKIs because it is naturally found in soy foods. It could be delivered either in a purified state as a pill (to high-risk, motivated patient groups), or in the form of soy foods or soy-containing foods. Delivery of genistein in soy foods is more economically viable ($1.50 for a daily dose of 50 mg) than purified material ($5/day) and would require no prior approval by the FDA. Accordingly, investigators at several different sites have begun or are planning chemoprevention trials using a soy beverage product based on SUPRO, an isolated soy protein manufactured by Protein Technologies International of St. Louis, MO. These investigators are examining the effect of the soy beverage on surrogate intermediate endpoint biomarkers (SIEBs) in patients at risk for breast and colon cancer, defining potential SIEBs in patients at risk for prostate cancer, and determining whether the soy beverage reduces the incidence of cancer recurrence.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclic-nucleotide-gated channels mediate synaptic feedback by nitric oxide

Cyclic-nucleotide-gated (CNG) channels in outer segments of vertebrate photoreceptors generate electrical signals in response to changes in cyclic GMP concentration during phototransduction. CNG channels also allow the influx of Ca2+, which is essential for photoreceptor adaptation. In cone photoreceptors, cGMP triggers an increase in membrane capacitance indicative of exocytosis, suggesting that CNG channels are also involved in synaptic function. Here we examine whether CNG channels reside in cone terminals and whether they regulate neurotransmitter release, specifically in response to nitric oxide (NO), a retrograde transmitter that increases cGMP synthesis and potentiates synaptic transmission in the brain. Using intact retina, we show that endogenous NO modulates synapses between cones and horizontal cells. In experiments on isolated cones, we show directly that CNG channels occur in clusters and are indirectly activated by S-nitrosocysteine (SNC), an NO donor. Furthermore, both SNC and pCPT-cGMP, a membrane-permeant analogue of cGMP, trigger the release of transmitter from the cone terminals. The NO-induced transmitter release is suppressed by guanylate cyclase inhibitors and prevented by direct activation of CNG channels, indicating that their activation is required for NO to elicit release. These results expand our view of CNG channel function to include the regulation of synaptic transmission and mediation of the presynaptic effects of NO.

Barriers to advance care planning in chronic obstructive pulmonary disease

The English End of Life Care Strategy promises that all patients with advanced, life limiting illness will have the opportunity to participate in Advance Care Planning (ACP). For patients with Chronic Obstructive Pulmonary Disease (COPD), the barriers to this being achieved in practice are under-explored. Five focus groups were held with a total of 39 health care professionals involved in the care of patients with COPD. Participants reported that discussions relating to ACP are very rarely initiated with patients with COPD and identified the following barriers: inadequate information provision about the likely course of COPD at diagnosis; lack of consensus regarding who should initiate ACP and in which setting; connotations of comparing COPD with cancer; ACP discussions conflicting with goals of chronic disease management; and a lack of understanding of the meaning of 'end of life' within the context of COPD. The findings from this study indicate that, for patients with COPD, significant service improvement is needed before the objective of the End of Life Care Strategy regarding patient participation in end of life decision-making is to be achieved. Whilst the findings support the Strategy's recommendations regarding an urgent for both professional education and increased public education about end of life issues, they also indicate that these alone will not be enough to effect the level of change required. Consideration also needs to be given to the integration of chronic disease management and end of life care and to developing definitions of end of life care that fit with concepts of 'continuous palliation'.

Analysis of plasma isoflavones by reversed-phase HPLC-multiple reaction ion monitoring-mass spectrometry

A HPLC-MS procedure for the rapid, sensitive and specific measurement of the isoflavones, daidzein, dihydrodaidzein, O-desmethylangolensin and genistein, in human plasma has been developed. Synthetic radiolabeled genistein conjugates were used for evaluation of optimum conditions for solid phase extraction. Biochanin A was added to plasma as a recovery marker for isoflavones and phenolphthalein glucuronide and 4-methylumbelliferone sulfate were added to ensure completeness of hydrolysis with beta-glucuronidase/sulfatase. Isoflavones in plasma extracts were separated using an isocratic HPLC method and analyzed by negative ion multiple reaction ion monitoring-mass spectrometry using a heated nebulizer-atmospheric pressure chemical ionization interface. Using plasma samples from four subjects consuming two servings a day of an isolated soy protein beverage for 14 days, the mean plasma genistein and daidzein concentrations were 556 and 345 nM, respectively. Within assay and between assay coefficients of variation for measurement of daidzein and genistein in five aliquots of the same plasma sample were 8.51% and 7.76%, and 5.98% and 6.12%, respectively.

Assessing phytoestrogen exposure in epidemiologic studies: development of a database (United States)

BACKGROUND AND OBJECTIVE

Phytoestrogens (weak estrogens found in plants or derived from plant precursors by human metabolism) have been hypothesized to reduce the risk of a number of cancers. However, epidemiologic studies addressing this issue are hampered by the lack of a comprehensive phytoestrogen database for quantifying exposure. The purpose of this research was to develop such a database for use with food-frequency questionnaires in large epidemiologic studies.

METHODS

The database is based on consumption patterns derived from semistructured interviews with 118 African-American, Latina, and white women residing in California's San Francisco Bay Area. HPLC-mass spectrometry was used to determine the content of seven specific phytoestrogenic compounds (i.e. the isoflavones: genistein, daidzein, biochanin A, and formononetin; the coumestan: coumestrol; and the plant lignans: matairesinol and secoisolariciresinol) in each of 112 food items/groups.

RESULTS

Traditional soy-based foods were found to contain high levels of genistein and daidzein, as expected, as well as substantial amounts of coumestrol. A wide variety of "hidden" sources of soy (that is, soy protein isolate, soy concentrate, or soy flour added to foods) was observed. Several other foods (such as various types of sprouts and dried fruits, garbanzo beans, asparagus, garlic, and licorice) were also found to be substantial contributors of one or more of the phytoestrogens analyzed.

CONCLUSIONS

Databases, such as the one described here, are important in assessing the relationship between phytoestrogen exposure and cancer risk in epidemiologic studies. Agencies, such as the United States Department of Agriculture (USDA), that routinely provide data on food composition, on which epidemiologic investigations into dietary health effects are based, should consider instituting programs for the analysis of phytochemicals, including the phytoestrogens.

Evolution of the health benefits of soy isoflavones

Soy is a unique dietary source of the isoflavones, genistein and daidzein. It has been part of the Southeast Asian diet for nearly five millenia, whereas consumption of soy in the United States and Western Europe has been limited to the 20th century. Heavy consumption of soy in Southeast Asian populations is associated with reduction in the rates of certain cancers and cardiovascular disease. Recent experimental evidence suggests that phytochemicals in soy are responsible for its beneficial effects, which may also include prevention of osteoporosis, a hereditary chronic nose bleed syndrome, and autoimmune diseases. Exposure of soy formula-fed infants to the potential estrogenizing effects of the isoflavones is limited by the first pass effect of the liver following the uptake of isoflavones from the gut. Several mechanisms of action of isoflavones have been proposed-both through estrogen-dependent and estrogen-independent pathways.

Antioxidant mechanisms of isoflavones in lipid systems: paradoxical effects of peroxyl radical scavenging

Oxidation of lipids has been implicated in the pathophysiology of atherosclerosis. It has been suggested that scavenging of lipid peroxyl radicals contribute to the antiatherosclerotic effects of naturally occurring compounds such as the isoflavones. This group of polyphenolics includes genistein and is present in relatively high concentrations in food products containing soy. Soy isoflavones are capable of inhibiting lipoprotein oxidation in vitro and suppressing formation of plasma lipid oxidation products in vivo. However, key aspects of the antioxidant mechanisms remain unknown. In this study the antioxidant effects of genistein and other soy isoflavones on lipid peroxidation initiated by mechanistically diverse oxidants was investigated. Although isoflavones inhibited lipid peroxidation stimulated by both metal-dependent and independent processes, the concentration required for these effects were relatively high compared to those found in vivo. Interestingly, however, isoflavones were not consumed and remained in the native state over the time during which inhibition of lipid peroxidation was observed. This was also the case under conditions where synergistic inhibition of LDL oxidation was observed with ascorbate. Furthermore, in an oxidation system driven solely by peroxyl radicals, isoflavones were found to be relatively poor peroxyl radical scavengers. Consistent with the apparent lack of reactivity with lipid-derived oxidants, isoflavones were also relatively resistant to oxidation mediated by the potent oxidant peroxynitrite. The potential antioxidant mechanisms of isoflavones are discussed in the context of possible reactivities of isoflavone-derived phenoxyl radicals.