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.

Ionic currents of isolated retinal pacemaker neurons: projected daily phase differences and selective enhancement by a phase-shifting neurotransmitter

The eye of Aplysia expresses a robust circadian rhythm of neuronal activity. We dissociated the retinal cells in primary culture and studied isolated pacemaker neurons to identify ionic currents that may have roles in the circadian clock mechanism. Individual neurons were studied with perforated-patch whole cell recording techniques in current- and voltage-clamp modes. Pacemaker neurons had resting potentials near -40 mV and, if neurites had grown out, produced spontaneous action potentials in darkness at <1 Hz. Depolarizing current injections increased the rate of action potential firing. Hyperpolarizing current injections were followed by slowly decaying (1-3 s) afterhyperpolarizations. Four ionic currents were characterized under voltage-clamp, including a Ca current (I(Ca)), a voltage-gated potassium current (I(KV)), an A current (I(A)), and a hyperpolarization-activated Cl current (I(Cl)). I(Cl) was only seen using Cl(-)-filled electrodes when high concentrations of Cl- diffused from the electrode and is therefore unlikely to be important under physiological conditions. The magnitude of I(KV) was significantly larger during the projected zeitgeber predawn phase than during the postdawn phase, whereas the magnitude of I(A) was constant at these circadian phases, suggesting that only I(KV) is controlled by the circadian clock. Serotonin increased I(KV) by 29%, consistent with reports that serotonin suppresses optic nerve activity and phase shifts the circadian rhythm recorded from the intact eye. The enhancement of I(KV) likely contributes to membrane hyperpolarization, and it may be required for phase shifting. The phase-dependent changes in I(KV) provide evidence that each retinal pacemaker neuron contains a circadian clock, but confirmation must await further recordings made from individual pacemaker neurons that are isolated completely from all other cells in primary culture. From the present experiments, it appears that I(KV) is controlled by the circadian clock, in part, and it may be a required element in the pathway that is activated during serotonin-induced phase shifts.

Cloning, expression, and chromosomal localization of mouse liver bile acid CoA:amino acid N-acyltransferase

A mouse liver lambda Zap XR cDNA library was screened using the coding region of human bile acid CoA:amino acid N-acyltransferase (BAT) cDNA as a probe. Ten positive clones were isolated and purified, two of which apparently possessed complete open reading frames for BAT based on sequence analysis of the ends of the cDNAs. One clone (mBAT#9) was selected for sequence analysis and characterization. mBAT#9 is 1869 basepairs in length and the full-length cDNA possesses a 189 basepair 5'-nontranslated region, an open-reading frame of 1260 basepairs, and a 404 basepair 3'-nontranslated region followed by a poly(A) tail. The open-reading frame codes for a 420 amino acid protein with a calculated molecular mass of 46,525 daltons. The structural gene for mBAT was mapped to mouse Chromosome 4. The amino acid sequence of mBAT is 69% identical and 84% similar to that of hBAT, and 86% identical and 95% similar to that of kan-1, a putative rat liver BAT. Enzymatically active mBAT was expressed in E. coli using the bacterial expression vector pKK233-2. Immunoblot analysis of expressed mBAT with rabbit anti-human BAT polyclonal antibodies detected a single protein with a molecular mass of approximately 45,000 daltons. Cytosol from cells transformed with mBAT#9/pKK233-2 possessed significant amounts of BAT-catalyzed conjugating activity with taurine as substrate but the expressed enzyme did not use glycine or fluoro-beta-alanine as substrates. The K(m) value for taurine was 1.9 mM +/- 0.1 mM in reactions with cholyl CoA as a cosubstrate. The specificity of mBAT for taurine as a substrate was confirmed by the demonstration, using HPLC-electrospray ionization mass spectrometry, that mouse gallbladder bile contained only taurine conjugates of bile acids. The identification of the types of amino acid conjugates of bile acids present in mouse bile had not been previously reported. These results indicate that a taurine-specific form of BAT has been cloned and expressed from mouse liver.

Regulation of M-like K+ current, IKx, by Ca(2+)-dependent phosphorylation in rod photoreceptors

An M-like K+ current (IKx) helps set the rod photoreceptor resting potential and accelerates the response to dim light. Recorded with ruptured-patch whole cell techniques, the amplitude of IKx diminished, and activation occurred at increasingly negative potentials as a function of time. In contrast, IKx was stable during nystatin perforated-patch recording. Stability during ruptured-patch recording could be induced by raising the intracellular Ca2+ concentration ([Ca2+]i) or by including caffeine or D-myo-inositol 1,4,5-trisphosphate in the pipette. This Ca(2+)-induced stability of IKx was blocked by inhibitors of Ca2+/calmodulin-dependent protein kinases, such as W-7, KN-62, chelerythrine, or H-7. Okadaic acid, an inhibitor of protein phosphatases, maintained IKx stability even at low [Ca2+]i. The requirement for phosphorylation was demonstrated by depleting MgATP or by providing 5'-adenylylimidophosphate, a nonhydrolyzable analog of ATP, either of which blocked the Ca(2+)-induced stability of IKx. These observations show that phosphorylation regulates IKx and that a stimulus controlling this action is [Ca2+]i. Should [Ca2+]i change during light adaptation, changes in IKx might alter the resting potential and temporal response properties of rod photoreceptors.

Urinary phytoestrogen levels in young women from a multiethnic population

Phytoestrogens include several classes of chemical compounds (i.e., isoflavones, coumestans, and lignans) which are structurally similar to endogenous estrogens. In biological systems, they have both estrogenic and antiestrogenic effects and may reduce the risk of developing certain types of hormonally related diseases. However, little information is available on population differences in exposure to phytoestrogens. To examine racial/ethnic differences in urinary phytoestrogen levels, 50 young women (ages 20-40 years) were randomly selected from participants in a previous epidemiological study in which 24-h urine specimens and a dietary assessment were obtained. Subjects were members of the Kaiser Permanente Medical Care Program of northern California. Selection was stratified on race/ethnicity. Urinary levels of seven phytoestrogens were measured using high-performance liquid chromatography-mass spectrometry. Substantial variation in phytoestrogen levels was observed and racial/ethnic differences are described. The highest levels of coumestrol and the lignans were observed in white women and the lowest levels in Latina and African American women. Genistein levels, however, were highest in Latina women; other isoflavone levels did not differ significantly by race/ethnicity.

The effect of treatment variables on mood and social adjustment in adult patients with pituitary disease

OBJECTIVE

Studies of mood in hypopituitary adults have yielded inconsistent results. This investigation was carried out to investigate whether treatment characteristics may be responsible for the inconsistent results.

DESIGN AND MEASUREMENTS

We compared three groups of patients with a group of matched healthy controls on self-report measures of mood and social adjustment (Beck depression inventory, State-trait anxiety inventory, Social adjustment scale (modified)) and a measure of quality of life (Nottingham health profile, NHP).

PATIENTS

The patient groups were those treated with transfrontal surgery (n = 23), transsphenoidal surgery (n = 23) or medication only (n = 23). In addition, a close informant of each subject was asked to complete a social adjustment measure about the subject's level of adjustment.

RESULTS

On the self-report mood and social adjustment measures and the emotion sub-scale of the NHP, the transsphenoidal and medication patient groups rated themselves as being more depressed, anxious and having poorer social adjustment than the transfrontal or control groups. The close informants, however, rated all three patient groups as having poorer social adjustment than the controls. Patients treated with surgery and without radiotherapy reported fewer symptoms of depression than those treated with radiotherapy. Realistic self-appraisal of social adjustment in surgical patients was found only in those treated with transsphenoidal surgery without radiotherapy.

CONCLUSIONS

Patients treated for pituitary tumour, excepting those treated with transfrontal surgery and to a lesser extent those treated with radiotherapy, suffer from mild mood disturbance and self-perceived decreased social adjustment. All patient groups are seen by others as having decreased social adjustment, raising the possibility that the transfrontal patients and possibly those who have had radiotherapy, lack insight. This may explain some of the discrepancies in the previous literature and needs to be taken into account when using self-report measures with these patients.

Latex allergy and anaphylaxis in a child undergoing craniofacial surgery

This case report represents an example of latex anaphylaxis in a child with a history of multiple previous surgeries without any complications. Obviously, the patient had not shown evidence of being sensitized until this particular surgery, where she had multiple sources of latex exposure, e.g., Foley catheter, blood pressure cuff, rubber gloves, and clear adhesive tape. If a more careful history had been taken, the diagnosis of latex allergy might have been suspected, for upon further questioning after surgery, the mother reported multiple incidences of urticarial reactions to rubber gloves and clothes with elastic waist bands. In summary, this case report highlights the importance of a careful history and the need for a high index of suspicion of potential latex allergy in children who acquire sensitization to latex because they require multiple surgical procedures for anatomic correction of congenital abnormalities. One week after this episode, the patient returned to the operating room for completion of her surgery. All latex was avoided, and there were no complications.

Genistein inhibits both estrogen and growth factor-stimulated proliferation of human breast cancer cells

Genistein is a naturally occurring dietary protein tyrosine kinase (PTK) inhibitor that is hypothesized to be responsible for the lower rate of breast cancer observed in Asian women consuming soy. Although genistein is a potent in vitro PTK inhibitor, its mechanism of action in vivo is not known. In vivo, breast cancer growth is regulated by estrogens and peptide growth factors, such as epidermal growth factor (EGF), the receptor of which has intrinsic PTK activity. Therefore, genistein may block mammary epithelial cell growth by interfering with signal transduction events stimulated by estradiol or growth factors. The effect of genistein, related isoflavones, and other tyrosine kinase inhibitors on fetal bovine serum-, estradiol-, and EGF-stimulated cell growth and signal transduction pathways was examined in five human breast cancer cell lines. Genistein inhibited the growth of these cells by each of the growth stimuli with IC50 values ranging from 2.6 to over 20 micrograms/ml. Growth inhibition by genistein was cytostatic and reversible at IC50 concentrations. Related isoflavones were less potent growth inhibitors than genistein, whereas the synthetic PTK inhibitor tyrphostin A25 was an equally potent growth inhibitor. The mechanism of genistein growth inhibition in human breast cancer cells did not depend on the presence of functional estrogen receptor signaling pathways or on inhibition of EGF-receptor PTK activity. Furthermore, genistein (< or = 20 micrograms/ml) did not decrease constitutive or EGF-induced tyrosine phosphorylation as determined by Western blotting with antiphosphotyrosine antibodies. These data suggest that although genistein inhibits the growth of breast cancer cells in culture, it does so without gross inhibition of PTK activity.

Stimulatory influence of soy protein isolate on breast secretion in pre- and postmenopausal women

Soy foods have been reported to have protective effects against premenopausal breast cancer in Asian women. No studies have been reported on potential physiological effects of dietary soy consumption on breast gland function. We evaluated the influence of the long-term ingestion of a commercial soy protein isolate on breast secretory activity. We hypothesized that the features of nipple aspirate fluid (NAF) of non-Asian women would be altered so as to resemble those previously found in Asian women. At monthly intervals for 1 year, 24 normal pre- and postmenopausal white women, ages 30 to 58, underwent nipple aspiration of breast fluid and gave blood and 24-h urine samples for biochemical studies. No soy was administered in months 1-3 and 10-12. Between months 4-9 the women ingested daily 38 g of soy protein isolate containing 38 mg of genistein. NAF volume, gross cystic disease fluid protein (GCDFP-15) concentration, and NAF cytology were used as biomarkers of possible effects of soy protein isolate on the breast. In addition, plasma concentrations of estradiol, progesterone, sex hormone binding globulin, prolactin, cholesterol, high density lipoprotein-cholesterol, and triglycerides were measured. Compliance was assessed by measurements of genistein and daidzein and their metabolites in 24-h urine samples. Excellent compliance with the study protocol was obtained. Compared with NAF volumes obtained in months 1-3, a 2-6-fold increase in NAF volume ensued during months 4-9 in all premenopausal women. A minimal increase or no response was found in postmenopausal women. No changes were found in plasma prolactin, sex hormone binding globulin, cholesterol, high density lipoprotein cholesterol, and triglyceride concentrations. Compared with concentrations found in months 1-3 (no soy), plasma estradiol concentrations were elevated erratically throughout a "composite" menstrual cycle during the months of soy consumption. No significant changes were seen in plasma progesterone concentrations. No significant changes were found in plasma estrogen levels in postmenopausal women. A moderate decrease occurred in the mean concentration of GCDFP-15 in NAF in premenopausal women during the months of soy ingestion. Of potential concern was the cytological detection of epithelial hyperplasia in 7 of 24 women (29.2%) during the months they were consuming soy protein isolate. The findings did not support our a priori hypothesis. Instead, this pilot study indicates that prolonged consumption of soy protein isolate has a stimulatory effect on the premenopausal female breast, characterized by increased secretion of breast fluid, the appearance of hyperplastic epithelial cells, and elevated levels of plasma estradiol. These findings are suggestive of an estrogenic stimulus from the isoflavones genistein and daidzein contained in soy protein isolate.

Rhythmic activities of isolated and clustered pacemaker neurons and photoreceptors of Aplysia retina in culture

Each eye of Aplysia contains a circadian clock that produces a robust rhythm of optic nerve impulse activity. To isolate the pacemaker neurons and photoreceptors of the eye and determine their participation in the circadian clock and its generation of rhythmic autoactivity, the retina was dissociated and its cells were placed in primary cell culture. The isolated neurons and photoreceptors survived and vigorously extended neurites tipped with growth cones. Many of the photoreceptors previously described from histological sections of the intact retina were identified in culture, including the large R-type photoreceptor, which gave robust photoresponses, and the smaller tufted, whorled, and flared photoreceptors. The pacemaker neurons responsible for the rhythmic impulse activity generated by the eye were identified by their distinctive monopolar morphology and recordings were made of their activity. Isolated pacemaker neurons produced spontaneous action potentials in darkness, and pacemaker neurons attached to fragments of retina or in an isolated cluster interacted to produce robust spontaneous activity. This study establishes that isolated retinal pacemaker neurons retain their innate autoactivity and ability to produce action potentials in culture and that clusters of coupled pacemaker neurons are capable of generating robust autoactivity comparable to pacemaker neuron rhythmic activity recorded in the intact retina, which was previously shown to correspond to 1:1 with the optic nerve compound action potential activity.

The role of metabolism in mammary epithelial cell growth inhibition by the isoflavones genistein and biochanin A

The basis for the differential sensitivity of cultured normal human mammary epithelial (HME) cells and a transformed human breast cancer MCF-7 cell line to growth inhibition by the isoflavone genistein and its 4'-methyl ether derivative, biochanin A, was examined. In HME cells genistein is 5-fold more potent as a growth inhibitor than biochanin A, whereas in MCF-7 cells biochanin A and genistein are equally potent as growth inhibitors. Based on its properties as an in vitro protein tyrosine kinase (PTK) inhibitor, biochanin A would be expected to be a less potent growth inhibitor than genistein. To determine whether isoflavone metabolism could account for the observed differences in growth inhibition, metabolism experiments were conducted with HME and MCF-7 cells using [4-14C]genistein and [4-14C]biochanin A. MCF-7 cells extensively metabolized both isoflavones, producing two genistein metabolites with molecular weights of 350 and 380 and three biochanin A metabolites with molecular weights of 270, 350 and 380. In contrast, significant genistein or biochanin A metabolism was not observed in HME cells. Using mass spectrometry and nuclear magnetic resonance analysis, metabolite 350 from genistein and biochanin A experiments was identified as genistein 7-sulfate; biochanin A metabolite 270 was identified as genistein. Metabolite 380 was not unequivocally identified, but appeared to be a hydroxylated and methylated form of genistein sulfate. In MCF-7 cells, genistein 7-sulfate and metabolite 380 were detected primarily in the cell media fraction, suggesting that once formed these polar metabolites were excreted from the cells. These data show that isoflavone metabolism by transformed breast epithelial cells modulates the growth inhibitory effects of genistein and biochanin A. In MCF-7 cells, genistein metabolism was correlated with a decrease in growth inhibition, whereas biochanin A metabolism was associated with an increase in growth inhibition.

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.

Variable effects of tyrosine kinase inhibitors on avian osteoclastic activity and reduction of bone loss in ovariectomized rats

We compared the effects of the tyrosine kinase inhibitor genistein, a naturally occurring isoflavone, to those of tyrphostin A25, tyrphostin A47, and herbimycin on avian osteoclasts in vitro. Inactive analogs daidzein and tyrphostin A1 were used to control for nonspecific effects. None of the tyrosine kinase inhibitors inhibited bone attachment. However, bone resorption was inhibited by genistein and herbimycin with ID50s of 3 microM and 0.1 microM, respectively; tyrphostins and daidzein were inactive at concentrations below 30 microM, where nonspecific effects were noted. Genistein and herbimycin thus inhibit osteoclastic activity via a mechanism independent of cellular attachment, and at doses approximating those inhibiting tyrosine kinase autophosphorylation in vitro; the tyrphostins were inactive at meaningful doses. Because tyrosine kinase inhibitors vary widely in activity spectrum, effects of genistein on cellular metabolic processes were compared to herbimycin. Unlike previously reported osteoclast metabolic inhibitors which achieve a measure of selectivity by concentrating on bone, neither genistein nor herbimycin bound significantly to bone. Osteoclastic protein synthesis, measured as incorporation of 3H-leucine, was significantly inhibited at 10 microM genistein, a concentration greater than that inhibiting bone degradation, while herbimycin reduced protein synthesis at 10 nM. These data suggested that genistein may reduce osteoclastic activity at pharmacologically attainable levels, and that toxic potential was lower than that of herbimycin. To test this hypothesis in a mammalian system, bone mass was measured in 200 g ovariectomized rats treated with 44 mumol/day genistein, relative to untreated controls. During 30 d of treatment, weights of treated and control group animals were indistinguishable, indicating no toxicity, but femoral weight in the treated group was 12% greater than controls (P < 0.05). Our data indicate that the isoflavone inhibitor genistein suppresses osteoclastic activity in vitro and in vivo at concentrations consistent with its ID50s on tyrosine kinases, with a low potential for toxicity.

The dihydropyridine-sensitive calcium channel subtype in cone photoreceptors

High-voltage activated Ca channels in tiger salamander cone photoreceptors were studied with nystatin-permeabilized patch recordings in 3 mM Ca2+ and 10 mM Ba2+. The majority of Ca channel current was dihydropyridine sensitive, suggesting a preponderance of L-type Ca channels. However, voltage-dependent, incomplete block (maximum 60%) by nifedipine (0.1-100 microM) was evident in recordings of cones in tissue slice. In isolated cones, where the block was more potent, nifedipine (0.1-10 microM) or nisoldipine (0.5-5 microM) still failed to eliminate completely the Ca channel current. Nisoldipine was equally effective in blocking Ca channel current elicited in the presence of 10 mM Ba2+ (76% block) or 3 mM Ca2+ (88% block). 15% of the Ba2+ current was reversibly blocked by omega-conotoxin GVIA (1 microM). After enhancement with 1 microM Bay K 8644, omega-conotoxin GVIA blocked a greater proportion (22%) of Ba2+ current than in control. After achieving partial block of the Ba2+ current with nifedipine, concomitant application of omega-conotoxin GVIA produced no further block. The P-type Ca channel blocker, omega-agatoxin IVA (200 nM), had variable and insignificant effects. The current persisting in the presence of these blockers could be eliminated with Cd2+ (100 microM). These results indicate that photoreceptors express an L-type Ca channel having a distinguishing pharmacological profile similar to the alpha 1D Ca channel subtype. The presence of additional Ca channel subtypes, resistant to the widely used L-, N-, and P-type Ca channel blockers, cannot, however, be ruled out.

Interleukin-1beta, tumor necrosis factor-alpha, and LPS enhance calcium channel current in isolated vascular smooth muscle cells of rat tail artery

Cytokines, such as interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha), are thought to be responsible for the compromised blood pressure regulation after systemic infection or other antigenic challenge. Because Ca homeostasis is critical for the maintenance of vascular tone, we hypothesized that cytokines may contribute to alterations in blood pressure by a mechanism involving the voltage-sensitive Ca channel in vascular smooth muscle (VSM) cells. Using nystatin-permeabilized patch techniques we examined the effects of IL-1 beta, TNF-alpha, and lipopolysaccharide (LPS) on the Ca channel of VSM cells isolated from rat tail artery. Both IL-1 beta (0.05--1 nM) and TNF-alpha (0.1--1 nM) increased, dose-dependently, the Ba2+ current carried in VSM Ca channels, whereas heat-denatured IL-1 beta was without significant effect on the channel. LPS (0.01--1.0 ng/ml) also increased the Ba2+ current with onset kinetics similar to the two cytokines. Prostaglandins were ruled out as an intermediary in VSM Ca channel modulation, as prostaglandin E2 had no effect and indomethacin (1 microM) failed to block TNF-alpha-induced Ca channel enhancement. The role of cyclic nucleotides in mediating TNF-alpha-induced changes in Ca channel activity was also assessed. Increasing intracellular cAMP via forskolin (1 microM) did not affect the response to TNF-alpha, but pretreatment with the membrane-permeant analog of cGMP, dibutyryl cGMP (100 microM), inhibited the response to TNF-alpha. These data demonstrate that IL-1 beta, TNF-alpha, and LPS have immediate effects on VSM cells via an interaction with the voltage-sensitive Ca channel, and these effects may he regulated by intracellular cGMP. Immunomodulation of Ca channels may represent an early signaling step in VSM cells mediating kinetically slower events, such as changes in gene transcription.

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.

Low-calcium-induced enhancement of chemical synaptic transmission from photoreceptors to horizontal cells in the vertebrate retina

According to the classical calcium hypothesis of synaptic transmission, the release of neurotransmitter from presynaptic terminals occurs through an exocytotic process triggered by depolarization-induced presynaptic calcium influx. However, evidence has been accumulating in the last two decades indicating that, in many preparations, synaptic transmitter release can persist or even increase when calcium is omitted from the perfusing saline, leading to the notion of a "calcium-independent release" mechanism. Our study shows that the enhancement of synaptic transmission between photoreceptors and horizontal cells of the vertebrate retina induced by low-calcium media is caused by an increase of calcium influx into presynaptic terminals. This paradoxical effect is accounted for by modifications of surface potential on the photoreceptor membrane. Since lowering extracellular calcium concentration may likewise enhance calcium influx into other nerve cells, other experimental observations of "calcium-independent" release may be reaccommodated within the framework of the classical calcium hypothesis without invoking unconventional processes.

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.

Selective detection and site-analysis of O-GlcNAc-modified glycopeptides by beta-elimination and tandem electrospray mass spectrometry

Over the past decade, a number of nuclear and cytoplasmic proteins have been identified that are modified by single N-acetylglucosamine residues attached to the hydroxyl side chain of serines or threonines (O-GlcNAc). O-GlcNAc is a dynamic modification and therefore may act in a regulatory capacity analogous to phosphorylation. To undertake site-directed mutagenesis studies of O-GlcNAc's function, it is necessary to identify the sites of glycosylation on various proteins. The current method of site mapping, which involves galactosyltransferase labeling, generation of glycopeptides by proteolysis, purification by several rounds of HPLC, and gas-phase and manual Edman sequencing, is very tedious and requires about 10 pmol of pure, labeled glycopeptide. In this report, synthetic glycopeptides were generated and used to demonstrate that O-GlcNAc-modified peptides can be rapidly identified in complex mixtures by HPLC-coupled electrospray mass spectrometry due to the partial loss of the O-linked glycan (204 amu) at a modest orifice potential. Furthermore, the exact site of glycosylation was directly identified in the low picomole range by collision-induced dissociation (CID) of the glycopeptide after removal of the O-GlcNAc by alkaline beta-elimination. The conversion of glycosylserine to 2-aminopropenoic acid (2-ap) by beta-elimination both decreased the mass of the glycopeptide by 222 amu and resulted in a CID fragment ion representing the loss of 69 amu (2-ap) instead of 87 amu (Ser) at the position of the glycosylserine. Finally, we tested this method on an identical synthetic, alpha-linked O-GalNAc-modified peptide. Like O-GlcNAc, the O-GalNAc moiety was selectively removed at a modest orifice potential; however, the beta-elimination conditions that efficiently removed the O-GlcNAc only liberated about 20% of the O-GalNAc. We conclude that the selectivity and the sensitivity of this method will make it a powerful tool for determining the sites of O-GlcNAc modification on proteins of low abundance such as transcription factors and oncogenes.

Acute lymphoblastic leukemia, hypercalcemia, and pseudohyperkalemia in a dog

A 5-month-old sexually intact male Chesapeake Bay Retriever was evaluated for lameness of 2 weeks' duration and lymphocytosis. Acute lymphoblastic leukemia was diagnosed on the basis of results of cytologic and cytochemical evaluation of a bone marrow aspirate. Serum biochemical abnormalities included hypercalcemia and hyperkalemia. Hypercalcemia was likely paraneoplastic; hyperkalemia was believed to be a result of release of potassium from large numbers of lymphocytes in vitro (pseudohyperkalemia). The dog was euthanatized, and necropsy revealed infiltration of the hepatic vasculature and sinusoids, renal parenchyma, mesenteric and peripheral lymph nodes, bone marrow, and iridial tissue with neoplastic cells. Unique features of this case include the young age of the dog and the hypercalcemia and hyperkalemia associated with acute lymphoblastic anemia.

Soy isoflavonoids and cancer prevention. Underlying biochemical and pharmacological issues

The isoflavonoids in soy, genistein and daidzein, have been proposed to contribute an important part of the anti-cancer effect of soy. Although there have been many interesting studies on the effects of isoflavones on biochemical targets in tissue culture experiments, in most cases the concentrations used by investigators have exceeded 10 microM. However, based on simple pharmacokinetic calculations involving daily intake of isoflavones, absorption from the gut, distribution to peripheral tissues, and excretion, it is unlikely that blood isoflavone concentrations even in high soy consumers could be greater than 1-5 microM. Experiments designed to evaluate these pharmacological principles were carried out in anesthetized rats with indwelling biliary catheters and in human volunteers consuming soy beverages. The data from these experiments indicate that genistein is efficiently absorbed from the gut, taken up by the liver and excreted in the bile as its 7-O-beta-glucuronide. Re-infused genistein 7-O-beta-glucuronide was also well absorbed from the gut, although this occurred in the distal small intestine. In human subjects fed a soy beverage for a period of two weeks, plasma levels of genistein and daidzein, determined by HPLC-mass spectrometry, ranged from 0.55-0.86 microM, mostly as glucuronide and sulfate conjugates. In summary, genistein is well absorbed from the small intestine and undergoes an enterohepatic circulation. Although the plasma genistein levels achievable with soy food feeding are unlikely to be sufficient to inhibit the growth of mature, established breast cancer cells by chemotherapeutic-like mechanisms, these levels are sufficient to regulate the proliferation of epithelial cells in the breast and thereby may cause a chemopreventive effect.