Theory of Chirality Induced Spin Selectivity: Progress and Challenges.

A critical overview of the theory of the chirality-induced spin selectivity (CISS) effect, that is, phenomena in which the chirality of molecular species imparts significant spin selectivity to various electron processes, is provided. Based on discussions in a recently held workshop, and further work published since, the status of CISS effects-in electron transmission, electron transport, and chemical reactions-is reviewed. For each, a detailed discussion of the state-of-the-art in theoretical understanding is provided and remaining challenges and research opportunities are identified.

Single-molecule functionality in electronic components based on orbital resonances.

In recent years, a wide range of single-molecule devices has been realized, enabled by technological advances combined with the versatility offered by synthetic chemistry. In particular, single-molecule diodes have attracted significant attention with an ongoing effort to increase the rectification ratio between the forward and reverse current. Various mechanisms have been investigated to improve rectification, either based on molecule-intrinsic properties or by engineering the coupling of the molecule to the electrodes. In this perspective, we first provide an overview of the current experimental approaches reported in literature to achieve rectification at the single-molecule level. We then proceed with our recent efforts in this direction, exploiting the internal structure of multi-site molecules, yielding the highest rectification ratio based on a molecule-intrinsic mechanism. We introduce the theoretical framework for multi-site molecules and infer general design guidelines from this. Based on these guidelines, a series of two-site molecules have been developed and integrated into devices. Using two- and three-terminal mechanically controllable break junction measurements, we show that depending on the on-site energies, which are tunable by chemical design, the devices either exhibit pronounced negative differential conductance, or behave as highly-efficient rectifiers. Finally, we propose a design of a single-molecule diode with a theoretical rectification ratio exceeding a million.

Maintaining physiological testosterone levels by adding dehydroepiandrosterone to combined oral contraceptives: I. Endocrine effects.

OBJECTIVE: To determine whether adding dehydroepiandrosterone to combined oral contraceptives (COCs) maintains physiological levels of free testosterone. STUDY DESIGN: A randomized, double-blind, placebo-controlled, two-way crossover study conducted in 81 healthy women (age range: 20-35 years; Body mass index (BMI) range: 18-35 kg/m2) using oral contraceptives. Androgens, sex hormone-binding globulin (SHBG), estradiol (E2) and estrone (E1) were measured, and free testosterone and the free testosterone index were calculated. Subjects discontinued oral contraceptive use for at least one menstrual cycle before being randomized to receive five cycles of ethinyl estradiol (EE) combined with either levonorgestrel (EE/LNG group) or drospirenone (EE/DRSP group) together with either dehydroepiandrosterone (DHEA) (50 mg/day orally) or placebo. Subsequently, all subjects crossed over to the other treatment arm for an additional five cycles. RESULTS: Both COCs decreased the levels of all androgens measured. Significant decreases (p<.05) were found with EE/LNG and EE/DRSP for total testosterone (54.5% and 11.3%, respectively) and for free testosterone (66.8% and 75.6%, respectively). Adding DHEA to the COCs significantly increased all androgens compared to placebo. Moreover, including DHEA restored free testosterone levels to baseline values in both COC groups and total testosterone levels to baseline in the EE/LNG group and above baseline in the EE/DRSP group. SHBG concentrations were significantly higher with EE/DRSP compared to EE/LNG (p<.0001). The addition of DHEA did not affect the levels of SHBG. CONCLUSIONS: Taking COCs reduces total and free testosterone levels and increases SHBG concentrations. By coadministration with DHEA, physiological levels of total and free testosterone are restored while using EE/LNG. With EE/DRSP, only the free testosterone level is normalized by DHEA coadministration. IMPLICATIONS: A daily oral dose of 50-mg DHEA maintains physiological free and total testosterone levels in women who are using an EE/LNG-containing COC.

The use of high-dose estrogens for the treatment of breast cancer.

Estrogens are known to stimulate the growth of breast cancer but they are also an effective treatment for this disease (this has been termed the 'estrogen paradox'). The fact that estrogens can be an effective treatment for breast cancer is something that has almost been forgotten, whereas the fear for estrogens remains. This paper reviews the use of estrogens for the treatment of breast cancer and identifies possible applications. The data summarised in this review demonstrate that high-dose estrogens are effective for the treatment of advanced breast cancer, both as first-line treatment as well as for treatment after occurrence of endocrine resistance to TAM and AIs. Essential for efficacy is an extended period of estrogen deprivation before the tumour is subject to estrogen treatment (the gap hypothesis). Research on the mechanism of action has shown that apoptosis induced by estrogens is regulated via the estrogen receptor and growth factor signalling pathways. High-dose estrogens have a negative safety image, especially in terms of side-effects and increased rates of cardiovascular disease, but the safety data reviewed in this paper do not give rise to major concerns. Taking into account their side-effect profile together with their observed clinical efficacy, high-dose estrogens should be considered a valuable alternative to chemotherapy in selected patients.

Electric-Field Control of Interfering Transport Pathways in a Single-Molecule Anthraquinone Transistor.

It is understood that molecular conjugation plays an important role in charge transport through single-molecule junctions. Here, we investigate electron transport through an anthraquinone based single-molecule three-terminal device. With the use of an electric-field induced by a gate electrode, the molecule is reduced resulting into a 10-fold increase in the off-resonant differential conductance. Theoretical calculations link the change in differential conductance to a reduction-induced change in conjugation, thereby lifting destructive interference of transport pathways.

Report of the IFCC Working Group for Standardization of Thyroid Function Tests; part 3: total thyroxine and total triiodothyronine.

BACKGROUND: Because total thyroid hormone testing is performed on many automated clinical chemistry instruments, the IFCC Scientific Division commissioned the Working Group for Standardization of Thyroid Function Tests to include total thyroxine (TT4) and total triiodothyronine (TT3) in its standardization efforts. METHODS: Existing SI-traceable reference measurement procedures (RMPs) were used to assign TT4 and TT3 values to 40 single-donor serum samples for subsequent use in a method comparison study with 11 TT4 and 12 TT3 immunoassays. Data from comparison of each immunoassay with the RMPs provided a basis for mathematical assay recalibration. RESULTS: Seven TT4 assays had a mean bias within 10% of the RMP, but 2 deviated by an average of -12% and another 2 by +17%. All TT3 assays showed positive biases, 4 within and 8 outside 10%, up to 32%. Mathematical recalibration effectively eliminated assay-specific biases, but sample-related effects remained, particularly for TT3. Correlation coefficients with the RMPs ranged from 0.82 to 0.97 for TT4 and from 0.32 to 0.92 for TT3. The within-run and total imprecision ranges for TT4 were 1.4% to 9.1% and 3.0% to 9.4%, respectively, and for TT3 2.1% to 7.8% and 2.8% to 12.7%, respectively. Approximately one-half of the assays matched the internal QC targets within approximately 5%; however, we observed within-run drifts/shifts. CONCLUSIONS: The study showed that of the assays we examined, only 4 TT4 but the majority of the TT3 assays needed establishment of calibration traceability to the existing RMPs. Most assays performed well, but some would benefit from improved precision, within-run stability, and between-run consistency.

Report of the IFCC Working Group for Standardization of Thyroid Function Tests; part 2: free thyroxine and free triiodothyronine.

BACKGROUND: Free thyroxine (FT4) and free triiodothyronine (FT3) measurements are useful in the diagnosis and treatment of a variety of thyroid disorders. The IFCC Scientific Division established a Working Group to resolve issues of method performance to meet clinical requirements. METHODS: We compared results for measurement of a panel of single donor sera using clinical laboratory procedures based on equilibrium dialysis-isotope dilution-mass spectrometry (ED-ID-MS) (2 for FT4, 1 for FT3) and immunoassays from 9 manufacturers (15 for FT4, 13 for FT3) to a candidate international conventional reference measurement procedure (cRMP) also based on ED-ID-MS. RESULTS: For FT4 (FT3), the mean bias of 2 (4) assays was within 10% of the cRMP, whereas for 15 (9) assays, negative biases up to -42% (-30%) were seen; 1 FT3 assay was positively biased by +22%. Recalibration to the cRMP eliminated assay-specific biases; however, sample-related effects remained, as judged from difference plots with biologic total error limits. Correlation coefficients to the cRMPs ranged for FT4 (FT3) from 0.92 to 0.78 (0.88 to 0.30). Within-run and total imprecision ranged for FT4 (FT3) from 1.0% to 11.1% (1.8% to 9.4%) and 1.5% to 14.1% (2.4% to 10.0%), respectively. Approximately half of the manufacturers matched the internal QC targets within approximately 5%; however, within-run instability was observed. CONCLUSIONS: The study showed that most assays had bias largely correctable by establishing calibration traceability to a cRMP and that the majority performed well. Some assays, however, would benefit from improved precision, within-run stability, and between-run consistency.

Report of the IFCC Working Group for Standardization of Thyroid Function Tests; part 1: thyroid-stimulating hormone.

BACKGROUND: Laboratory testing of serum thyroid-stimulating hormone (TSH) is an essential tool for the diagnosis and management of various thyroid disorders whose collective prevalence lies between 4% and 8%. However, between-assay discrepancies in TSH results limit the application of clinical practice guidelines. METHODS: We performed a method comparison study with 40 sera to assess the result comparability and performance attributes of 16 immunoassays. RESULTS: Thirteen of 16 assays gave mean results within 10% of the overall mean. The difference between the most extreme means was 39%. Assay-specific biases could be eliminated by recalibration to the overall mean. After recalibration of singlicate results, all assays showed results within the biological total error goal (22.8%), except for 1 result in each of 4 assays. For a sample with a TSH concentration of 0.016 mIU/L, 6 assays either did not report results or demonstrated CVs >20%. Within-run and total imprecision ranged from 1.5% to 5.5% and 2.5% to 7.7%, respectively. Most assays were able to match the internal QC targets within 5%. Within-run drifts and shifts were observed. CONCLUSIONS: Harmonization of TSH measurements would be particularly beneficial for 3 of the 16 examined assays. These data demonstrate that harmonization may be accomplished by establishing calibration traceability to the overall mean values for a panel of patient samples. However, the full impact of the approach must be further explored with a wider range of samples. Although a majority of assays showed excellent quality of performance, some would benefit from improved within-run stability.

On the possible role of mammary-derived growth hormone in human breast cancer.

The incidence of breast cancer has risen worldwide, especially in countries where it used to be low, very probably as a result of economic prosperity and changes in life-style. In women, the available data have resulted in the concept of progression from normal breast development to cancer through precursor lesions sensitive to hormones and growth factors that can be produced locally in the mammary gland, acting as paracrine or autocrine stimulating agents. The local endocrine environment in the breast can be different from the situation in the circulation. In the dog, growth hormone (GH) can be produced locally in the mammary glands and its production can be stimulated by progestins. This GH probably plays a paracrine role in the progesterone-induced proliferation and differentiation of mammary epithelium. There is increasing evidence that the local mammary progestin/GH-axis is operational not only in dogs but also in human breast cancer. No data are yet available on the production of mammary-derived GH in women.

Gene polymorphisms that may influence the biological effects of progestins.

Many of the biological actions of progestins depend on binding to intracellular receptors and through a long chain of events to subsequent stimulation of transcriptional activity and protein synthesis. This process requires at least a few hours in time and many different proteins called coregulators do play a role after binding to the receptor. Evidence for polymorphisms in the gene coding for the PR has been obtained and many studies have already attempted to show associations between particular polymorphisms and human diseases. However, at present no consistent and conclusive picture has emerged on clinically important associations. Studies on links between polymorphisms in genes coding for coregulators are just beginning. The second pathway, the so-called non-genomic actions, is related to rapid effects of progestins that occur within minutes. At this moment a number of different membrane bound receptors have been identified. No data are available yet on polymorphisms in genes coding for these proteins or to link any of these membrane receptors to specific human pathology.

Classification and pharmacology of progestins.

Besides the natural progestin, progesterone, there are different classes of progestins, such as retroprogesterone (i.e. dydrogesterone), progesterone derivatives (i.e. medrogestone) 17alpha-hydroxyprogesterone derivatives (i.e. chlormadinone acetate, cyproterone acetate, medroxyprogesterone acetate, megestrol acetate), 19-norprogesterone derivatives (i.e. nomegestrol, promegestone, trimegestone, nesterone), 19-nortestosterone derivatives norethisterone (NET), lynestrenol, levonorgestrel, desogestrel, gestodene, norgestimate, dienogest) and spironolactone derivatives (i.e. drospirenone). Some of the synthetic progestins are prodrugs, which need to be metabolized to become active compounds. Besides the progestogenic effect, which is in common for all progestins, there is a wide range of biological effects, which are different for the various progestins and have to be taken into account, when medical treatment is considered.

Long-term effects of progestins on bone quality and fractures.

The effects of progestins on the quality of bone and their influence on the risk of fractures are reviewed. Data discussed are based on experimental studies in vivo that generally lasted for longer than one year. Information is given on the background of osteoporosis and on several means of inducing changes in bone quality. In young women who start using oral contraceptives based on progestins alone shortly after pubertal development, a significant decrease in bone quality has been documented. World Health Organization experts have concluded that this is not a real argument for restrictions on the use of these contraceptives. In postmenopausal women, no evidence has been found for a bone-protective or an estrogen-antagonistic effect of progestins. A wide range of estrogens have been used that have shown positive effects on bone, which are not antagonized by progestins. The therapeutic use of high-dose megestrol acetate may result in marked negative effects on bone, leading to severe osteoporosis, possibly due to the inherent glucocorticoid activity of this progestin. Other pharmacotherapeutic agents that can be used in postmenopausal therapy, and that clearly have beneficial effects on bone, are discussed.

Proposal of a candidate international conventional reference measurement procedure for free thyroxine in serum.

In the present paper the IFCC WG-STFT recommends and provides the rationale to establish metrological traceability of serum free thyroxine (FT4) measurements to a candidate international conventional reference measurement procedure. It is proposed that this procedure be based on equilibrium dialysis combined with determination of thyroxine in the dialysate with a trueness-based reference measurement procedure. The measurand is thus operationally defined as "thyroxine in the dialysate from equilibrium dialysis of serum prepared under defined conditions". With regard to the trueness-based reference measurement procedure, the WG-STFT recommends use of an isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC/tandem MS) procedure for total thyroxine that has been optimized towards measurement at picomolar concentration levels and that is listed in the database of the Joint Committee for Traceability in Laboratory Medicine (JCTLM). For calibration, the purified thyroxine material IRMM-468 (resulting from a project funded by the European Commission and recently submitted to the JCTLM) is proposed. The WG-STFT stresses that according to this recommendation it is a prerequisite to strictly adhere to the defined equilibrium dialysis procedure, whereas it is permissible to introduce variants in the ID-LC/tandem MS procedure.

Gene polymorphisms involved in the regulation of bone quality.

Osteoporotic fractures in subjects at advanced age constitute a tremendous and growing problem. Established lifestyle risk factors can explain only a modest proportion of the liability to osteoporotic fractures. Bone mineral density (BMD) is considered the best established risk factor for osteoporotic fractures. The importance of genetic factors in the quality of bone is substantial, but no consensus exists yet on the genes that are involved. However, concomitant diseases, balance disorders and lifestyle habits are more important for fractures in elderly subjects. The abundance of common sequence variations, so-called polymorphisms, in the human genome and their high frequency in the population have made them targets to explain variation in the risk. Some genes have been identified that appear to be involved in the regulation of bone mass and in the pathogenesis of osteoporosis. Among these are those coding for the two estrogen receptors (ERalpha and ERbeta), the androgen receptor (AR) and the vitamin D receptor (VDR). In addition, enzymes involved in the biogenesis of estrone and estradiol have attracted attention as well as polymorphisms in the regulatory region of the type I collagen gene, COLIA1, affecting the binding site for the transcription factor Specificity protein 1 (Sp1). Although evidence suggests that the quality of bone is determined to a large extent by genetic factors, research so far has not been able to unequivocally identify genes involved in this matter. Over the last years a large number of studies have pointed to the variability in many genes and their relation with BMD, bone-related symptoms or specific therapies. The findings emphasize the complexity of the genetics of bone mass and bone loss.

Hormonal imbalance in two types of endometrial cancer and genetic polymorphism of steroidogenic enzymes.

OBJECTIVES: Modern data on endometrial cancer (EC) incidence demonstrate that it is one of the most prevalent gynecologic malignancies. It is possible that some allelic polymorphisms of the genes involved in steroidogenesis or steroid metabolism differently contribute into susceptibility to described types of this disease, namely to type I (which is considered to be hormone dependent) and type II. METHODS: Distribution of allelic polymorphisms of CYP17 (17alpha-hydroxylase/17,20-lyase), CYP19 (aromatase), catechol-O-methyltransferase (COMT) and CYP1B1 (primarily, estrogen 4-hydroxylase) genes was compared totally in 156 endometrial cancer patients, approximately two-third of who belonged (on the basis of case history and some characteristics of host and tumor) to type I of the disease, and one-third to type II. Blood leukocytes were used as source of normal DNA for PCR-genotyping. RESULTS: No differences were found in distribution of CYP17 and CYP1B1 genotypes between patients belonging to type I or II of the disease. On the other side, in case of CYP19, the ratio of incidence of A6A6 genotype to the frequency of A1A6 and A3A6 genotypes was higher in type II patients (1.0) than in type I patients (0.3). Besides, incidence of high activity (HH) COMT genotype was higher among patients with type I of disease than in patients with type II of it (33.3% versus 14.7%, OR=2.9, z=1.96, p=0.05) revealing tendency to the lower inactivation of catecholestrogens in the latter group. CONCLUSION: It may be suggested that more aggressive clinically and frequently receptor-negative type II of endometrial cancer is associated with indirect signs of mainly intratumoral hyperproduction of estrogens (excess of CYP19 A6A6 genotype) without their sufficient inactivation into methoxyderivatives that warrants further study.

Molecular three-terminal devices: fabrication and measurements.

Incorporation of a third, gate electrode in the device geometry of molecular junctions necessary to identify the transport mechanism. At present, the most popular technique fabricate three-terminal molecular devices makes use of electromigration. Although it statistical process, we show that control over the gap resistance can be obtained. A detailed analysis of the current-voltage characteristics of gaps without molecules, however, shows that they reveal features that can mistakenly be attributed to molecular transport. This observation raises questions about which gaps with molecules can be disregarded which not. We show that electrical characteristics can be controlled by the rational design of the molecular bridge and that vibrational modes probed by electrical transport are potential interest as molecular fingerprints.

Feasibility study of new calibrators for thyroid-stimulating hormone (TSH) immunoprocedures based on remodeling of recombinant TSH to mimic glycoforms circulating in patients with thyroid disorders.

BACKGROUND: Differences between the glycosylation patterns of a pituitary thyroid-stimulating hormone calibrator (pitTSH) and serum samples have been shown to be responsible for nonidentical epitope expression and for introducing discrepancies in TSH measurements. We studied the feasibility of developing new candidate reference materials by remodeling recombinant TSH (recTSH) to generate potential mimics of serum TSH. METHODS: Terminal sialylation and/or inner fucosylation of recTSH were remodeled by a combination of enzyme treatments followed (or not) by lentil lectin-Sepharose affinity chromatography. The resulting TSH preparations were screened for epitope similarity in 23 immunoassays mapping 3 antigenic clusters common to the pitTSH 2nd International Reference Preparation (IRP) and the recTSH 1st IRP and then challenged against a pool of 63 patients with increased serum TSH (>60 mIU/L). RESULTS: pitTSH was poorly correlated with serum TSH, with a mean (SD) slope of 2.124 (0.001), in contrast to recTSH [slope, 1.178 (0.056)]. Comparison of variably sialylated preparations with recTSH gave slopes of 0.860 (0.057) for desialylated TSH, 1.064 (0.057) for alpha2,3/6-oversialylated recTSH, and 0.953 (0.033) for alpha2,6-resialylated recTSH, indicating that TSH forms enriched in sialic acid closely resemble serum TSH. Further testing against serum TSH showed satisfactory agreement with both TSH preparations containing alpha2,6-sialic acid [slopes, 1.064 (0.057) and 0.953 (0.033)], particularly in the absence of nonfucosylated forms [0.985 (0.044)]. CONCLUSIONS: Glyco-engineered recTSH preparations enriched in sialic acid and inner fucose are promising candidates for future reference materials. These preparations may have advantages over existing preparations used for standardizing TSH measurements.