Abstracts of the 24th international isotope society (UK group) symposium: synthesis and applications of labelled compounds 2015

The 24th annual symposium of the International Isotope Society's United Kingdom Group took place at the Møller Centre, Churchill College, Cambridge, UK on Friday 6th November 2015. The meeting was attended by 77 delegates from academia and industry, the life sciences, chemical, radiochemical and scientific instrument suppliers. Delegates were welcomed by Dr Ken Lawrie (GlaxoSmithKline, UK, chair of the IIS UK group). The subsequent scientific programme consisted of oral presentations, short 'flash' presentations in association with particular posters and poster presentations. The scientific areas covered included isotopic synthesis, regulatory issues, applications of labelled compounds in imaging, isotopic separation and novel chemistry with potential implications for isotopic synthesis. Both short-lived and long-lived isotopes were represented, as were stable isotopes. The symposium was divided into a morning session chaired by Dr Rebekka Hueting (University of Oxford, UK) and afternoon sessions chaired by Dr Sofia Pascu (University of Bath, UK) and by Dr Alan Dowling (Syngenta, UK). The UK meeting concluded with remarks from Dr Ken Lawrie (GlaxoSmithKline, UK).

Indoor aerosols: from personal exposure to risk assessment

Motivated by growing considerations of the scale, severity, and risks associated with human exposure to indoor particulate matter, this work reviewed existing literature to: (i) identify state-of-the-art experimental techniques used for personal exposure assessment; (ii) compare exposure levels reported for domestic/school settings in different countries (excluding exposure to environmental tobacco smoke and particulate matter from biomass cooking in developing countries); (iii) assess the contribution of outdoor background vs indoor sources to personal exposure; and (iv) examine scientific understanding of the risks posed by personal exposure to indoor aerosols. Limited studies assessing integrated daily residential exposure to just one particle size fraction, ultrafine particles, show that the contribution of indoor sources ranged from 19% to 76%. This indicates a strong dependence on resident activities, source events and site specificity, and highlights the importance of indoor sources for total personal exposure. Further, it was assessed that 10-30% of the total burden of disease from particulate matter exposure was due to indoor-generated particles, signifying that indoor environments are likely to be a dominant environmental factor affecting human health. However, due to challenges associated with conducting epidemiological assessments, the role of indoor-generated particles has not been fully acknowledged, and improved exposure/risk assessment methods are still needed, together with a serious focus on exposure control.

Risk of ischemic stroke in patients with Crohn's disease: a population-based nested case-control study

BACKGROUND

Observational studies have linked Crohn's disease (CD) to an increased risk of venous thromboembolic complications. Case reports of ischemic stroke in CD patients have raised the question of a similar association, but data from observational studies are lacking.

METHODS

Using data from the UK General Practice Research Database we conducted a nested case-control analysis within a population-based cohort of 8054 patients with and 161,078 patients without CD. A total of 1748 cases of ischemic stroke were identified to whom 17,348 controls were matched on age, sex, and year of cohort entry. Adjusted odds ratios (ORs) of ischemic stroke associated with CD were calculated by conditional logistic regression. Stratified analyses were performed for age and sex.

RESULTS

While CD was not associated with an overall increased risk of ischemic stroke (OR 1.10, 95% confidence interval [CI] 0.85-1.43), stratified analyses revealed an increase in risk in younger patients (<50 years: OR 2.93; 95% CI 1.44-5.98) but not in elderly patients (> or =50 years: OR 0.99; 95% CI 0.75-1.30; P for interaction <0.01). The interaction with age remained statistically significant even after changing the cutoff value for the younger and older age group to 45, 55, or 60 years in a sensitivity analysis. There was no interaction with sex (P = 0.79).

CONCLUSIONS

The study indicates that younger patients with CD may be under an increased risk of ischemic stroke.

Precision of intracellular calcium spike timing in primary rat hepatocytes

Extracellular stimuli are often encoded in the frequency, amplitude and duration of spikes in the intracellular concentration of calcium ([Ca2+]i). However, the timing of individual [Ca2+]i-spikes in relation to the dynamics of an extracellular stimulus is still an open question. To address this question, we use a systems biology approach combining experimental and theoretical methods. Using computer simulations, we predict that more naturalistic pulsed stimuli generate precisely-timed [Ca2+]i-spikes in contrast to the application of constant stimuli of the same dose. These computational results are confirmed experimentally in single primary rat hepatocytes upon alpha1-adrenergic stimulation. Hormonal signalling in analogy to neuronal signalling thus has the potential to make use of temporal coding on the level of single cells. The [Ca2+]i-signalling cascade provides a first example for increasing the information capacity of an intracellular regulatory signal beyond the known coding mechanisms of amplitude (AM) and frequency modulation (FM).

Palmitate-induced Ca2+-signaling in pancreatic beta-cells

Free fatty acids (FFA) have been proposed to participate in the regulation of insulin release from pancreatic beta-cells (beta-cells). As a rise in cytosolic free Ca2+ ([Ca(2+)]i) is a key event for the stimulation of insulin secretion, the effects of saturated FFA on [Ca2+]i were investigated. Palmitate was used as a reference compound and [Ca2+]i was measured in single fura-2 loaded HIT-T15 and in primary mouse beta-cells. Stimulation of single beta-cells with palmitate (100 microM) caused either repetitive Ca2+ transients or a plateau-like rise in [Ca2+]i. In HIT-T15 and in mouse beta-cells, the number of palmitate-responsive cells, and the amplitude of the palmitate-induced Ca2+-signals were dependent on the extracellular glucose concentration. In Ca2+-free medium palmitate (100 microM) caused only 1 or 2 Ca2+ transients indicating mobilization of Ca2+ from internal stores. Withdrawal of external Ca2+, the addition of voltage-sensitive Ca2+ channel (VSCC) blockers, as well as the K(ATP)-channel opener diazoxide (100 microM) reversibly blocked the palmitate-induced cytosolic Ca2+ responses. This demonstrates that Ca2+ influx through VSCC of the L-type coupled to membrane depolarization through closure of K(ATP)-channels are crucial for a sustained Ca2+-signal in response to palmitate. Methyl palmoxirate (100 microM) and 2-bromopalmitate (100 microM), which both inhibit transport of acyl-CoA into the mitochondria, reversibly blocked the palmitate-induced Ca2+-signals in HIT-T15 as well as in primary mouse beta-cells. By contrast, cerulenin (100 microM), an inhibitor of protein acylation, had no effect on the palmitate-induced changes in [Ca2+]i, which suggests that mitochondrial palmitate metabolism is required for eliciting the Ca2+-signals. Simultaneous measurement of [Ca2+]i and the mitochondrial membrane potential (DeltaPsi) revealed palmitate-induced depolarization of DeltaPsi which demonstrates that palmitate does not enhance mitochondrial ATP production. Therefore mitochondrial signals other than ATP appear to be generated from palmitate metabolism that underly the palmitate-induced Ca2+-signals in pancreatic beta-cells.

Long-term pharmacokinetics of an extract of isoflavones from red clover (Trifolium pratense)

OBJECTIVES

To study the pharmacokinetics of isoflavones from red clover (Trifolium pratense) after long-term administration as a once-daily dietary supplementary.

DESIGN

Fourteen (14) subjects who had been consuming a low-isoflavone diet for 2 weeks were given an oral dose of two isoflavone tablets (approximately 80 mg of total isoflavones) daily for 2 weeks and appeared for a study day at 9:00 AM after an overnight fast on the day that they were to receive the last dose. Plasma samples were collected for a 48-hour period after the last dose. Plasma isoflavones were assayed by high-performance liquid chromatography (HPLC).

RESULTS

Trough plasma levels were significantly higher for daidzein and genistein after long-term dosing than levels taken prior to the commencement of the study and plasma levels of isoflavones after long-term dosing were in the range previously reported in populations that consume an isoflavone-rich diet. The plasma half-lives observed after long-term administration were, in most cases, consistent with once-daily administration.

CONCLUSIONS

Isoflavones have pharmacokinetic characteristics that suggest that once-daily administration is adequate when they are administered long-term as dietary supplements.

Cyclic-adenosine 3',5'-monophosphate-stimulated c-fos gene transcription involves distinct calcium pathways in single beta-cells

In beta-cells activation of the cyclic AMP (cAMP)-signaling cascade stimulates c-fos mRNA expression, which involves cAMP- and Ca(2+)-mediated mechanisms. To delineate potential crosstalk between both pathways at the transcriptional level we simultaneously measured c-fos promoter-driven enhanced green fluorescent protein (EGFP) expression and cytosolic free calcium ([Ca(2+)](i)) in single beta-cells (HIT-T15). Forskolin stimulated a rapid rise in cellular cAMP and in [Ca(2+)](i) through activation of voltage-sensitive Ca(2+)-influx and enhanced wild-type c-fos promoter-driven EGFP (pF711d2EGFP) expression about 4-fold after 6 h. The voltage-sensitive Ca(2+) channel (VSCC)-blocker nifedipine, which completely blocked the forskolin-induced rise in [Ca(2+)](i), partially inhibited the forskolin-induced increase in pF711d2EGFP expression, while it was completely abolished in Ca(2+)-free medium. VSCC-dependent Ca(2+)-influx per se when stimulated by K(+) (45 mM) increased pF711d2EGFP expression only minimally. No correlations could be delineated between the forskolin-induced amplitude of the Ca(2+) signal and the expression of pF711d2EGFP at the single cell level, which may indicate that small rises in [Ca(2+)](i) are sufficient to fully activate the Ca(2+)-dependent pathways required for cAMP-dependent c-fos promoter regulation. In experiments with various deletion constructs of the c-fos promoter, it could be shown that cAMP-mediated activation of the c-fos promoter involves both the cAMP-responsive element (CRE) and the serum-responsive element (SRE). While nifedipine completely abrogated the cAMP-dependent activation of c-fos transcription via the SRE, the CRE-mediated effect of cAMP on the c-fos promoter remained unaffected by nifedipine. Thus, cAMP and Ca(2+) are required for full c-fos promoter activation by the cAMP-signaling pathway in beta-cells. cAMP-dependent Ca(2+)-influx through VSCC is crucial for c-fos gene transcription via the SRE, whereas cAMP-mediated activation of the CRE demands Ca(2+)-influx, which is distinct from voltage-sensitive Ca(2+)-influx. This indicates a complex interplay between cAMP and Ca(2+) in controlling c-fos gene transcription and suggests that the mode of Ca(2+) entry may differentially act on signaling pathways leading to gene transcription in beta-cells.

Tolbutamide and diazoxide modulate phospholipase C-linked Ca(2+) signaling and insulin secretion in beta-cells

Arginine vasopressin (AVP), bombesin, and ACh increase cytosolic free Ca(2+) and potentiate glucose-induced insulin release by activating receptors linked to phospholipase C (PLC). We examined whether tolbutamide and diazoxide, which close or open ATP-sensitive K(+) channels (K(ATP) channels), respectively, interact with PLC-linked Ca(2+) signals in HIT-T15 and mouse beta-cells and with PLC-linked insulin secretion from HIT-T15 cells. In the presence of glucose, the PLC-linked Ca(2+) signals were enhanced by tolbutamide (3-300 microM) and inhibited by diazoxide (10-100 microM). The effects of tolbutamide and diazoxide on PLC-linked Ca(2+) signaling were mimicked by BAY K 8644 and nifedipine, an activator and inhibitor of L-type voltage-sensitive Ca(2+) channels, respectively. Neither tolbutamide nor diazoxide affected PLC-linked mobilization of internal Ca(2+) or store-operated Ca(2+) influx through non-L-type Ca(2+) channels. In the absence of glucose, PLC-linked Ca(2+) signals were diminished or abolished; this effect could be partly antagonized by tolbutamide. In the presence of glucose, tolbutamide potentiated and diazoxide inhibited AVP- or bombesin-induced insulin secretion from HIT-T15 cells. Nifedipine (10 microM) blocked both the potentiating and inhibitory actions of tolbutamide and diazoxide on AVP-induced insulin release, respectively. In glucose-free medium, AVP-induced insulin release was reduced but was again potentiated by tolbutamide, whereas diazoxide caused no further inhibition. Thus tolbutamide and diazoxide regulate both PLC-linked Ca(2+) signaling and insulin secretion from pancreatic beta-cells by modulating K(ATP) channels, thereby determining voltage-sensitive Ca(2+) influx.

Modulation of neuronal phospholipase D activity under depolarizing conditions

Neuronal phospholipase D (PLD) activity was hypothesized to be involved in vesicle trafficking and endocytosis and, possibly, transmitter release. We here report that prolonged depolarization of rat hippocampal slices by potassium chloride (KCl) or 4-aminopyridine inhibited PLD activity. Similarly, PLD activity in rat cortical synaptosomes was significantly inhibited by depolarizing agents including veratridine and ouabain. Inhibition of calcium/calmodulin kinase II (CaMKII) which positively modulates synaptosomal PLD activity [Sarri et al. (1998) FEBS Lett. 440, 287-290] by KN-62 caused a further reduction of PLD activity in depolarized synaptosomes. Depolarization-induced inhibition of PLD activity was apparently not due to transmitter release or activation of other kinases. We observed, however, that KCl-induced depolarization caused an increase of inositol phosphates and a reduction of the synaptosomal pool of phosphatidylinositol-4, 5-bisphosphate (PIP(2)). Moreover, in synaptosomes permeabilized with Staphylococcus aureus alpha-toxin, PLD activation induced by calcium was abolished by neomycin, a PIP(2) chelator. We conclude that depolarizing conditions cause an inhibition of neuronal PLD activity which is likely due to breakdown of PIP(2), a required cofactor for PLD activity. Our findings suggest that neuronal PLD activity is regulated by synaptic activity.

Ca2+/calmodulin inhibition and phospholipase C-linked Ca2+ Signaling in clonal beta-cells

Neurotransmitters and hormones, such as arginine vasopressin (AVP) and bombesin, evoke frequency-modulated repetitive Ca2+ transients in insulin-secreting HIT-T15 cells by binding to receptors linked to phospholipase C (PLC). The role of calmodulin (CaM)-dependent mechanisms in the generation of PLC-linked Ca2+ transients was investigated by use of the naphthalenesulfonamide CaM antagonists W-7 and W-13 and their dechlorinated control analogs W-5 and W-12. W-7 (10-30 microM) and W-13 (30-100 microM), but not W-5 (100 microM) and W-12 (300 microM), reversibly inhibited the AVP- and bombesin-induced Ca2+ transients. As the generation of PLC-linked Ca2+ transients requires mobilization of internal Ca2+ and Ca2+ influx through voltage-sensitive (VSCC) and -insensitive (VICC) Ca2+ channels, the effects of the W compounds on these processes were further investigated. First, W-7 dose dependently diminished K+ (45 mM)-induced Ca2+ signals (IC50, approximately 25 microM), and W-13 (100 microM) reduced the K+ (45 mM)-induced [Ca2+]i rise by about 40-60%, whereas W-5 (100 microM) and W-12 (300 microM) had no effect. In addition, W-7 (100 microM) inhibited whole cell Ca2+ currents in mouse beta-cells by about 60%. Second, pretreatment of cells (5 min) with W-7 (30 microM), but not W-5 (30 microM), inhibited agonist-induced internal Ca2+ mobilization by about 75% in Ca2+-free medium. Neither W-7 (30 microM) nor W-5 (30 microM) affected AVP (100 nM)-stimulated formation of IP3. Third, capacitative Ca2+ influx through VICC activated by thapsigargin (2 microM) in the presence of verapamil (50 microM) was inhibited by W-7 (30 microM) but not by W-5 (30 microM). As all of the W compound effects corresponded well to their reported anticalmodulin activity, a specific anticalmodulin action can be assumed. Thus, Ca2+ via activation of CaM-dependent processes could provide positive feedback on the generation of PLC-linked Ca2+ transients in HIT-T15 cells. This appears to involve CaM-dependent regulation of both mobilization of internal Ca2+ and Ca2+ influx through VSCC and VICC.

Regulation of cytosolic free calcium concentration by extracellular nucleotides in human hepatocytes

The effects of extracellular ATP and other nucleotides on the cytosolic free Ca2+ concentration ([Ca2+]i) have been studied in single primary human hepatocytes and in human Hep G2 and HuH-7 hepatoma cells. ATP, adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS), and UTP caused a concentration-dependent biphasic increase in [Ca2+]i with an initial peak followed by a small sustained plateau in most cells. In some cells, however, repetitive Ca2+ transients were observed. The rank order of potency was ATP >/= UTP > ATPgammaS, and complete cross-desensitization of the Ca2+ responses occurred between ATP and UTP. The initial transient peak in [Ca2+]i was resistant to extracellular Ca2+ depletion, which demonstrates mobilization of internal Ca2+ by inositol 1,4,5-trisphosphate whose formation was enhanced by ATP and UTP. In contrast, the sustained plateau phase required influx of external Ca2+. Ca2+ influx occurs most likely through a capacitative Ca2+ entry mechanism, which was shown to exist in these cells by experiments performed with thapsigargin. On the molecular level, specific mRNA coding for the human P2Y1, P2Y2, P2Y4, and P2Y6 receptors could be detected by RT-PCR in Hep G2 and HuH-7 cells. However, ADP and UDP, which are agonists for P2Y1 and P2Y6 receptors, respectively, caused no changes in [Ca2+]i, demonstrating that these receptors are not expressed at a functional level. Likewise, alpha,beta-methylene-ATP, beta,gamma-methylene-ATP, AMP, and adenosine were inactive in elevating [Ca2+]i, suggesting that the ATP-induced increase in [Ca2+]i was not caused by activation of P2X or P1 receptors. Thus, on the basis of the pharmacological profile of the nucleotide-induced Ca2+-responses, extracellular ATP and UTP increase [Ca2+]i by activating P2Y2 and possibly P2Y4 receptors coupled to the Ca2+-phosphatidylinositol signaling cascade in human hepatocytes. This suggests that extracellular nucleotides from various sources may contribute to the regulation of human liver cell functions.

The exocyclic groups of DNA modulate the affinity and positioning of the histone octamer

To investigate the nature of the chemical determinants in DNA required for nonspecific binding and bending by proteins we have created a novel DNA in which inosine-5-methylcytosine and 2, 6-diaminopurine-uracil base pairs are substituted for normal base pairs in a defined DNA sequence. This procedure completely switches the patterns of the base pair H bonding and attachment of exocyclic groups. We show that this DNA binds a histone octamer more tightly than normal DNA but, surprisingly, does not alter the orientation of the sequence on the surface of the protein. However, in general, the addition or removal of DNA exocyclic groups reduces or increases, respectively, the affinity for the histone octamer. The average incremental change in binding energy for a single exocyclic group is approximately 40 J/mol. The orientation of the DNA in core nucleosomes also is sensitive to the number and nature of the exocyclic groups present. Notably, substitution with the naturally occurring cytosine analogue, 5-methylcytosine, shifts the preferred rotational position by 3 bp, whereas incorporating 2,6-diaminopurine shifts it 2 bp in the opposite direction. These manipulations potentially would alter the accessibility of a protein recognition sequence on the surface of the histone octamer. We propose that exocyclic groups impose steric constraints on protein-induced DNA wrapping and are also important in determining the orientation of DNA on a protein surface. In addition, we consider the implications of the selection of A-T and G-C base pairs in natural DNA.

Positive biochemical effects of a bioartificial liver support system (BALSS) in a porcine fulminant hepatic failure (FHF) model

This study describes biochemical changes in the plasma and blood of pigs with devascularised livers treated in a bioartificial liver support system (BALSS). Porcine hepatic cells were incubated with collagen-coated dextran microspheres (CDM) for 3 hours and the medium tested to determine cellular metabolic activity. Incubation continued for a further 18 hours during which the hepatic cells attach to the CDM. The CDM-attached cells were inoculated into a hollow fibre bioreactor which was part of an extracorporeal support system. Hepatic cell content of the bioreactor was 6 x 10(9) cells. The system was tested in a controlled trial in pigs prepared in a surgical model of fulminant hepatic failure (FHF). When plasma from FHF pigs was circulated through the device containing hepatic cells, there was significantly less increase in the accumulation of ammonia and most amino acids, together with a decrease in plasma lactate and of one amino acid, compared to control experiments when hepatic cells were excluded. We conclude that primary porcine hepatocytes can contribute beneficial metabolic function in a BALSS.

DNA sequence- and structure-selective alkylation of guanine N2 in the DNA minor groove by ecteinascidin 743, a potent antitumor compound from the Caribbean tunicate Ecteinascidia turbinata

Ecteinascidin 743 is one of several related marine alkaloids isolated from the Caribbean tunicate Ecteinascidia turbinata. It is remarkably active and potent in a variety of in vitro and in vivo systems and has been selected for development as an anticancer agent. The present study investigates the interactions of ecteinascidin 743 with DNA. Ecteinascidin 743 retarded the electrophoretic migration of both supercoiled and relaxed simian virus 40 DNA even in the presence of sodium dodecyl sulfate and after ethanol precipitation, consistent with covalent DNA modifications. Similar results were obtained in a DNA oligonucleotide derived from ribosomal DNA. However, DNA denaturation reversed the DNA modifications. The homopolymeric oligonucleotide dG/dC was modified while neither the dI/dC nor the dA/dT oligonucleotides were, consistent with covalent attachment of ecteinascidin 743 to the exocyclic amino group at position 2 of guanine. Ecteinascidin 743 was then compared to another known DNA minor groove alkylating agent, anthramycin, which has also been shown to alkylate guanine N2. Footprinting analyses with DNase I and 1,10-phenanthroline-copper and exonuclease III digestions showed that ecteinascidin 743 covers three to five bases of DNA and exhibits a different sequence specificity than anthramycin in the Escherichia coli tyrosine tRNA promoter (tyrT DNA). The binding of ecteinascidin to DNA was abolished when guanines were substituted with inosines in this promoter. A band shift assay was designed to evaluate the influence of the bases flanking a centrally located guanine in an oligonucleotide containing inosines in place of guanines elsewhere. Ecteinascidin 743 and anthramycin showed similarities as well as differences in sequence selectivity. Ecteinascidin 743-guanine adducts appeared to require at least one flanking guanine and were strongest when the flanking guanine was 3' to the targeted guanine. These data indicate that ecteinascidin 743 is a novel DNA minor groove, guanine-specific alkylating agent.

Preclinical trial of a bioartificial liver support system in a porcine fulminant hepatic failure model

BACKGROUND

This study describes the pre-clinical trials of an extracorporeal bioartificial liver support system (BALSS). It includes the biochemical changes which occur in the plasma and blood of pigs with devascularized livers when the plasma is treated in a BALSS, and the testing of the system for presence or absence of infective agents, pyrogens and for toxicity.

METHODS

Hepatic cells were prepared from littermate juvenile white landrace pigs with a double-step collagenase digest technique. The cell preparations were incubated with collagen-coated dextran microspheres (CDM) for 3 h and the medium was tested to determine cellular metabolic activity. Incubation continued for a further 20 h during which the hepatic cells attach to the CDM. The CDM-attached cells were inoculated into a hollow fibre bioreactor which was part of an extracorporeal liver support system.

RESULTS

Hepatic cell content of the bioreactor was 6 x 10(9) +/- 3 x 10(8) cells, equivalent to those present in half a pig's liver. The system was tested in a controlled trial with the plasma of pigs with fulminant hepatic failure (FHF) due to devascularized livers. When plasma from FHF pigs was circulated through the device there was significantly less of an increase in the accumulation of ammonia, lactate and most amino acids when hepatic cells were included in the circuit compared with those in control experiments when they were excluded. Similar changes occurred in procine blood. There were few infections diagnosed and an absence of pyrogens, endotoxins and toxicity in the bioreactor contents or in the terminating reservoir or animal blood samples.

CONCLUSIONS

We believe that the results, demonstrating function of the porcine hepatic cells in the circuit, together with low risks, justify a clinical trial of use of the BALSS in Australia.

A urinary profile study of dietary phytoestrogens. The identification and mode of metabolism of new isoflavonoids

The metabolic fate of the dietary isoflavones daidzein and genistein was investigated in human volunteers challenged with soya. Urinary diphenols, isolated by partition chromatography on Sephadex LH-20, were characterized and identified by profile capillary gas chromatography (GC) and electron ionization mass spectrometry (GC-EIMS) analysis of the trimethylsilyl ether (TMS) derivatives. Novel isoflavonic phytoestrogens found in the urine of volunteers were those of tetrahydrodaidzein, dihydrogenistein, 6'-hydroxy-O-demethylangolesin and 2-dehydro-O-demethylangolensin. Other known diphenols identified were those of equal, dehydrodaidzein, O-demethylangolensin, daidzein, genistein, glycitein, and the lignan enterolactone. Two other urinary isomers with a fragmentation pattern closely resembling that of the persilylated TMS ethers of cis/trans-isomers of tetrahydrodaidzein, were characterized based on the elucidation of fragments associated with the loss of a non-phenolic-OTMS functional group in ring-C. These are fragments presented in the persilylated mass spectra of isoflavan-4-ols and isoflav-3-ene-4-ols, demonstrated here by a combination of simple and tandem mass spectrometry study of the deuterated persilylated TMS ethers of dihydrodaidzein. In a similar study we also present the data on the structural identification and fragment elucidation of the keto/enol tautomers of the TMS ether derivatives of the dihydro derivatives of daidzein and genistein, observed in the urine of volunteers and considered probable products of the derivatization process. Finally, the GC and GC-MS data of two unknown isoflavonoids and that of a lignan-like compound are presented together with those of dihydrodaidzein, dihydrogenistein, tetrahydrodaidzein and 2-dehydro-O-demethylangolensin. The latter four were obtained here as products of small scale chemical synthesis in a preliminary study on the tentative identification of urinary isoflavonoids in human volunteers challenged with soya.

Absence of both auditory evoked potentials and auditory percepts dependent on timing cues

An 11-yr-old girl had an absence of sensory components of auditory evoked potentials (brainstem, middle and long-latency) to click and tone burst stimuli that she could clearly hear. Psychoacoustic tests revealed a marked impairment of those auditory perceptions dependent on temporal cues, that is, lateralization of binaural clicks, change of binaural masked threshold with changes in signal phase, binaural beats, detection of paired monaural clicks, monaural detection of a silent gap in a sound, and monaural threshold elevation for short duration tones. In contrast, auditory functions reflecting intensity or frequency discriminations (difference limens) were only minimally impaired. Pure tone audiometry showed a moderate (50 dB) bilateral hearing loss with a disproportionate severe loss of word intelligibility. Those auditory evoked potentials that were preserved included (1) cochlear microphonics reflecting hair cell activity; (2) cortical sustained potentials reflecting processing of slowly changing signals; and (3) long-latency cognitive components (P300, processing negativity) reflecting endogenous auditory cognitive processes. Both the evoked potential and perceptual deficits are attributed to changes in temporal encoding of acoustic signals perhaps occurring at the synapse between hair cell and eighth nerve dendrites. The results from this patient are discussed in relation to previously published cases with absent auditory evoked potentials and preserved hearing.

Polarized beam splitting effect in inhomogeneously magnetized magnetooptic films

Linearly polarized light passing through a several micron thick magnetooptic film in the inhomogeneous magnetization state is split into a linearly polarized central beam and linearly polarized first and higher order diverging rings. The polarization of the central output beam lies in the same direction as the linearly polarized input, while the polarization of the diverging rings lies in a direction orthogonal to the input plane of polarization. The effect is described, and applications of the effect are discussed.

Objective detection of averaged auditory brainstem responses

Detection of an auditory brainstem response, ABR, usually relies on visual evaluation of two or more data acquisition runs of a fixed number of sweeps to determine if there is sufficient replication of the averaged waveforms to indicate a response. Visual interpretation can be difficult when the signal-to-noise ratio is poor because of either a small response or high levels of physiological background noise. Moreover, variations in the background noise from run to run can result in poor or spurious replications of component peaks and troughs in the waveform. A previous study (Elberling & Don, 1984) described a statistical approach for objective evaluation of the quality of an ABR recording. The method uses variance analysis in calculating the ratio of the magnitude of the ABR to the estimated averaged background noise. This study further applies this method to obtain a quantitative definition of the ABR threshold, to demonstrate its application in automatic threshold detection, and to estimate the number of sweeps required to reach detection criterion. Application of this method is valuable in reducing the variability of test interpretation and in maximizing the efficiency of recording ABRs by avoiding the averaging of excessive or insufficient numbers of sweeps. These improvements enhance the cost-benefit of ABR testing to the patient.

Conformation dependent binding of netropsin and distamycin to DNA and DNA model polymers

The binding of the antibiotics netropsin and distamycin A to DNA has been studied by thermal melting, CD and sedimentation analysis. Netropsin binds strongly at antibiotic/nucleotide ratios up to at least 0.05. CD spectra obtained using DNA model polymers reveal that netropsin binds tightly to poly (dA) . poly (dT), poly (dA-dT) . poly(dA-dT) and poly (dI-dC) . poly (dI-dC) but poorly, if at all, to poly (dG) . poly (dC). Binding curves obtained with calf thymus DNA reveal one netropsin-binding site per 6.0 nucleotides (K(a)=2.9 . 10(5) M(-1)); corresponding values for distamycin A are one site per 6.1 nucleotides with K(a)= 11.6 . 10(5) M(-1). Binding sites apparently involve predominantly A.T-rich sequences whose specific conformation determines their high affinity for the two antibiotics. It is suggested that the binding is stabilized primarily by hydrogen bonding and electrostatic interactions probably in the narrow groove of the DNA helix, but without intercalation. Any local structural deformation of the helix does not involve unwinding greater than approximately 3 degrees per bound antibiotic molecule.

Nucleotide sequence repetition: a rapidly reassociating fraction of mouse DNA

The separated complemnentary strands of a minor component in mouse DNA reassociate with each other much more rapidly than do the complementary strands of other DNA's including those of the principal part of mouse DNA. This difference in capacity of the strands to reassociate can be used to effect a preparative separation of the minor component from the principal fraction. The rate constant for reassociation of the minor component, compared with those of viral and bacterial DNA's, indicates that the minor component consists of a short nucleotide sequence present in about one million copies.