[Impact of perceived male infertility factors on penile erectile function]

OBJECTIVE

To evaluate the impact of the factors of perceived male infertility on men's penile erectile function.

METHODS

Using the 5-item version of the International Index of Erectile Function (IIEF-5), we investigated the penile erectile function among 245 infertile men (infertility group) and another 52 males having physical checkup for planned conception (checkup group), the former further divided into four subgroups according to the factors of infertility: male factor, female factor, bilateral factor, and unknown factor. We compared the total and item scores of IIEF-5 among different groups.

RESULTS

Mild or mild-moderate ED was found in 50.61% of the infertile men, with a total IIEF-5 score of 21.24 +/- 2.58. The total and item scores of IIEF-5 were markedly higher in the male factor than in the female factor subgroup (P < 0.01), but with no significant difference between the male factor subgroup and the bilateral and unknown factor subgroups (P > 0.05), except the score on confidence. The scores were significantly lower in the bilateral and unknown factor subgroups than in the female factor subgroup (P < 0.05), with no remarkable difference between the former two. In the infertility group, the total and item scores of IIEF-5 were markedly higher in those with education above high school than in those with high school or lower education (P < 0.01), but not correlated with age and infertility duration. After adjustment for education background, the total IIEF-5 score and the scores on confidence and satisfaction were significantly lower in the infertility than in the checkup group (P < 0.05), and 15.38% of the men in the latter group had mild ED, dramatically lower than in the former (P < 0.01).

CONCLUSION

Perceived infertility may cause ED in males, and a higher incidence rate is associated with lower education background of the men.

[Oral tadalafil on alternate days for erectile dysfunction that fails to respond to on-demand sildenafil: a report of 15 cases]

OBJECTIVE

To sum up the experience in administering oral tadalafil on alternate days for the treatment of erectile dysfunction (ED) that fails to respond to on-demand medication.

METHODS

We retrospectively analyzed the clinical data of 15 cases of ED treated with oral tadalafil on alternate days from September 2010 to March 2012. All the patients had failed to respond to on-demand medication of sildenafil previously.

RESULTS

After 4 weeks of tadalafil treatment, 11 (73.3%) of the cases were remarkably improved, with significant difference in IIEF-5 scores before and after treatment (P < 0.05). Transient adverse reactions were observed in the other 4 cases, including mild headache in 2, slight backache in 1, and facial flush in 1.

CONCLUSION

Oral tadalafil on alternate days is safe and effective in the treatment of ED that fails to respond to on-demand medication of sildenafil.

[Impact of male infertility on men's self-esteem and satisfaction with sexual relationship]

OBJECTIVE

To investigate the impact of infertility on men's self-esteem, self-confidence, sexual satisfaction and overall relationship with their spouses.

METHODS

Using Self-Esteem and Relationship questionnaire (SEAR), we conducted an investigation among 253 infertile men and 52 fertile male controls. We divided the infertile men into four subgroups according to their perceived causes of infertility: male (M) factors, female (F) factors, both M and F factors, and unknown factors, and compared the SEAR scores among different groups.

RESULTS

In the infertile men, the total SEAR score was significantly higher in those with < 3 years than in those with > or = 3 years of infertility duration (75.50 +/- 17.05 vs 68.66 +/- 17.19, P < 0.05) and so was it in those with above-high-school than in those with high-school or lower education background (81.42 +/- 13.99 vs 67.61 +/- 17. 8, P < 0.01), but showed no significant difference between the > or = 30- and < 30-year-olds (71.77 +/- 17.42 vs 72.74 +/- 18.38, P > 0.05). The total SEAR scores in the M factor, M & F factor, unknown factor and F factor groups were 65.69 +/- 18.68, 68.52 +/- 17.68, 74.85 +/- 15.19 and 83.21 +/- 12.61, respectively, with significant differences between the first two and the latter two groups (P < 0.05), as well as between the unknown factor and F factor groups (P < 0.05). In the fertile male controls, the total SEAR score and subdomain scores on sexual relationship, self-confidence, self-esteem and overall relationship were 90.04 +/- 9.85, 88.40 +/- 10.74, 92.23 +/- 9.41, 91.95 +/- 10.67 and 90.38 +/- 14.14, respectively, all remarkably higher than in the M factor, M&F factor and unknown factor groups of the infertile men after adjustment of their infertility duration and education levels (P < 0.05).

CONCLUSION

Infertility reduces men's self-esteem, self-confidence, sexual satisfaction and relationship with their spouses, and the degree of its impact is correlated with the patients' infertility duration and education level.

[Detection of the mutation of all the exons of the CFTR gene in Chinese men with congenital bilateral absence of the vas deferens]

OBJECTIVE

To assess the necessity of detecting the gene of cystic fibrosis transmembrane conductance regulator factor (CFTR) in Chinese men with congenital bilateral absence of the vas deferens (CBAVD).

METHODS

We detected the mutation of all the 27 exons of the CFTR gene in 9 patients with CBAVD by DNA sequencing, and compared the results using NCBI and Cystic Fibrosis Mutation Database.

RESULTS

Four novel missense mutations/variants were found in the CFTR gene of the CBAVD patients, which were submitted and accepted in the Cystic Fibrosis Mutation Database.

CONCLUSION

There are mutations or variants in the CFTR gene in Chinese men with CBAVD, and the mutational distribution is different from that in Westerners.

Anxiety symptoms among Chinese nurses and the associated factors: a cross sectional study

BACKGROUND

Nurses are an indispensable component of the work force in the health care system. However, many of them are known to work in a stressful environment which may affect their mental well-being; the situation could be worse in rapidly transforming societies such as China. The purpose of this study was to investigate anxiety symptoms and the associated factors in Chinese nurses working in public city hospitals.

METHODS

A cross-sectional survey was performed for Chinese nurses in public city hospitals of Liaoning Province, northeast China. Seven hospitals in different areas of the province were randomly selected for the study. The Zung Self-Rating Anxiety Scale was used to measure anxiety symptoms. Effort-reward imbalance questionnaire and Job Content Questionnaire were used to assess the work stressors. Univariate analysis and stepwise multivariate logistic regression analysis were used to identify the factors associated with anxiety symptoms.

RESULTS

All registered nurses in the seven city hospitals, totaling 1807 registered nurses were surveyed. Of the returned questionnaires, 1437 were valid (79.5%) for analysis. Utilizing the total raw score ≥ 40 as the cut-off point, the prevalence of anxiety symptoms in these nurses was 43.4%. Demographic factors (education, chronic disease and life event), lifestyle factors (regular meals and physical exercise), work conditions (hospital grade, job rank, monthly salary, nurse-patient relationships, job satisfaction and intention of leaving), job content (social support and decision latitude), effort-reward imbalance and overcommitment were all significantly related to the anxiety symptoms. Multivariate logistic regression analysis showed main factors associated with anxiety symptoms were lower job rank (OR 2.501), overcommitment (OR 2.018), chronic diseases (OR 1.541), worse nurse-patient relationship (OR 1.434), higher social support (OR 0.573), lower hospital grade (OR 0.629), taking regular meals (OR 0.719) and higher level of job satisfaction (OR 0.722).

CONCLUSIONS

A large proportion of Chinese nurses working in public city hospitals had anxiety symptoms, which warrants immediate investigation and intervention from the hospital administrators. Meanwhile, results of the study suggest that proper counseling, promotion of healthy lifestyle behavior and improvements to the social environment in the work place may be helpful toward reducing or preventing the anxiety symptoms.

Transferable tight-binding potential for germanium

We report a new tight-binding potential model for Ge. In this model, the bonding environment around each bond is taken into account. The features of this model are extensively examined using various structures, such as the diamond bulk with point defects, reconstructed surfaces, nanowires and small and medium-sized clusters. The resulting configurations, energies and the phonon dispersion as well as the electronic structures of the tested systems are in agreement with those predicted at the level of density functional theory. This indicates that the new model is able to handle complex Ge-based materials.

[Outcomes of IVF-ET and percentage of morphologically normal sperm before and after swim-up treatment]

OBJECTIVE

To study the relationship between sperm morphology and the outcomes of in vitro fertilization-embryo transfer (IVF-ET) before and after swim-up treatment of sperm on the day of oocyte retrieval.

METHODS

This study included 94 couples to be treated by IVF-ET for tubal factor infertility. Sperm samples were collected on the day of oocyte retrieval and sperm morphology evaluated according to the Kruger criteria before and after swim-up treatment. Based on the results of morphological evaluation, the sperm samples were divided into groups A1 (morphologically normal sperm > or = 10% after swim-up treatment), A2 (morphologically normal sperm < 10% after swim-up treatment), B1 (morphologically normal sperm > or = 10% before swim-up treatment) and B2 (morphologically normal sperm < 10% before swim-up treatment). The outcomes of IVF-ET treatment were compared between groups A1 and A2 as well as between B1 and B2.

RESULTS

After swim-up treatment, the rates of fertilization, cleavage, good quality embryo, clinical pregnancy and embryo implantation of group A1 were (72.72 +/- 3.35)%, (95.64 +/- 2.04)%, (24.39 +/- 4.57)%, 50.00% and 23.87%, respectively, while those of group A2 were (70.27 +/- 8.82)%, (94.82 +/- 4.94)%, (13.45 +/- 7.39)%, 9.52% and 6.25%, respectively, the latter three indexes remarkably higher in A1 than in A2 (P < 0.05), but the differences in the former two not statistically significant (P > 0.05). Before swim-up treatment, the above five indexes were (72.90 +/- 4.23)%, (95.20 +/- 2.61)%, (23.35 +/- 5.19)%, 39.58% and 18.35% in group B1, as compared with (71.33 +/- 5.10)%, (95.71 +/- 2.88)%, (20.18 +/- 6.15)%, 41.86% and 21.28% in group B2, with no statistically significant differences between the two groups (P > 0.05).

CONCLUSION

The percentage of morphologically normal sperm after swim-up treatment on the day of oocyte retrieval may be a valuable predictor of the outcomes of IVF-ET.

[Alternate-day oral tadalafil for erectile dysfunction with no successful intercourse at the baseline]

OBJECTIVE

To summarize the experience in the treatment of erectile dysfunction (ED) with no successful intercourse at the baseline with tadalafil.

METHODS

We retrospectively analyzed 21 cases of ED with no successful intercourse at the baseline treated with tadalafil on alternate days combined with sex guidance.

RESULTS

After 4 weeks of tadalafil treatment, 19 of the patients achieved successful sexual intercourse, and the IIEF-5 score was remarkably improved as compared with pre-medication (3.24 +/- 1.55 vs 18.95 +/- 3.02, P<0.0001). Mild adverse reactions were observed in 6 cases, including 2 cases of mild headache and 4 cases of facial blush.

CONCLUSION

Tadalafil on alternate days combined with sex guidance can significantly improve ED with no successful intercourse at the baseline.

Depressive symptoms among Chinese nurses: prevalence and the associated factors

AIM

  This article is a report of exploration of depressive symptoms and the associated factors among Chinese nurses working at public city hospitals.

BACKGROUND

  Hospital nurses are known to work in psychologically and physically demanding work environment, which may lead to depressive symptoms. However, little research has been done to address this problem in Chinese nurses.

METHODS

  A cross-sectional survey was carried out in seven randomly selected city hospitals of Liaoning Province, northeast of China in 2009. Depressive symptoms of the nurses were measured with the Chinese version of the Center for Epidemiologic Studies Depression Scale. Job Content Questionnaire and the effort-reward imbalance, demographic features, life style and work conditions were measured as the related factors.

RESULTS

  A total of 1592 nurses participated in the study and the effective response rate was 79·5%. The prevalence of depressive symptoms among the nurses was 61·7% (n = 886), of whom 74·9% (n = 664) had mild depressive symptoms. Multivariate logistic regression analysis showed that lower job rank, higher over commitment, alcohol consumption, worse nurse-patient relationship and higher education background were positively associated with depressive symptoms, whereas supervisor support, taking regular meals, doing physical exercises, higher skill discretion and higher job satisfaction were negatively associated with depressive symptoms.

CONCLUSION

  More than half of the Chinese nurses had depressive symptoms. As depressive symptoms may adversely affect quality of life and quality of care, consultation for the nurses with healthy life styles, work stress coping techniques and advice to administrator to improve social aspects of the work environment might be helpful to reduce the depressive symptoms in nurses.

Structures, stability, vibration entropy and IR spectra of hydrated calcium ion clusters [Ca(H(2)O)(n)](2+) (n = 1-20, 27): a systematic investigation by density functional theory

The low-lying candidates of hydrated calcium ion clusters, [Ca(H(2)O)(n)](2+) with n = 1-20 and 27, have been extensively sought by using density functional theory (DFT) at BLYP/6-311+G(d,p) level. The results showed that the first hydration shell around the calcium ion was fully occupied by six water molecules, whereas the second hydration shell might be fully occupied with different numbers of water molecules. This just corresponds to different growth patterns of the hydrated calcium ion clusters. Furthermore, we revealed that the vibration entropy contributed to the free energy of an isomer significantly. As a result, the stability of some low-lying candidates at zero-temperature was not maintained at finite temperatures. Therefore, we suggested that, at finite temperatures, the realistic products of [Ca(H(2)O)(n)](2+) should be a mixture of the best candidate and some of metastable isomers for a given cluster size. For a cluster having second and/or third shell of water molecules, we found structural transitions between a low-lying structure and the lowest-energy structure undergoing much lower energy barriers. In addition, the IR spectra of the best candidates were predicted, in which the evolution of hydrogen-bond configurations with the cluster size was revealed.

[Intracytoplasmic sperm injection for obstructive azoospermia]

OBJECTIVE

To sum up the experience in the treatment of obstructive azoospermia by intracytoplasmic sperm injection (ICSI).

METHODS

We retrospectively analyzed 107 cases of obstructive azoospermia treated by ICSI in our center from Jan. 2006 to Dec. 2008, and compared the rates of fertilization, cleavage and pregnancy between the patients with congenital bilateral absence of vas deferens (CBAVD) and those with non-CBAVD.

RESULTS

A total of 949 oocytes were injected for the 107 patients undergoing ICSI, of which 678 (71.4%) were fertilized and 605 (89.2%) cleaved, with 44 pregnancies (41.4%). Of the 442 oocytes injected for the 49 patients with CBAVD, 308 (69.6%) were fertilized and 279 (90.6%) cleaved, with 27 pregnancies (55.1%), and of the 507 oocytes injected for the 58 cases induced by inflammation or surgery, 370 (72.9%) were fertilized and 326 (88.1%) cleaved, with 17 pregnancies (29.3%). The rate of pregnancy was significantly higher in the CBAVD than in the non-CBAVD group (P < 0.01), but there were no significant differences in the rates of fertilization and cleavage between the two groups (P > 0.05).

CONCLUSION

PESA or TESE combined with ICSI is an effective approach to the treatment of male infertility induced by obstructive azoospermia, which may achieve a higher rate of pregnancy in patients with CBAVD than in those with non-CBAVD. Inflammation or surgery may not only cause the obstruction of the deferent duct, but also affect sperm quality, and consequently reduce the potentiality of embryonic development.

Identifying atomic geometry and electronic structure of (2 x 3)-Sr/Si(100) surface and its initial oxidation

We present a joint experimental and theoretical study on the geometric and electronic states and the initial oxidation of the (2x3)-Sr/Si(100) surface. With scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS) measurements combined with ab initio calculations, the atomic geometry and the electronic states of the (2x3)-Sr/Si(100) surface are identified. The dimerization of the Si atoms in the single atom row based on a (1x3) Si substrate model plays a critical role in stabilization of the surface structure and in determining the electronic properties. At the very initial oxidation of the surface, four features corresponding to the primary adsorption and oxidation sites are determined. Three of them are corresponding to the most favored oxidation sites with single oxygen molecules, whose local density of states gives semiconducting behavior. One is corresponding to the oxidation site with two oxygen molecules, whose local density of states gives metallic behavior. These features all exhibit dark spots with different shapes in the occupied state images but display either dark spots or bright protrusions depending on the different oxidation sites in the empty state images. Compared with the theoretical calculations, the plausible adsorption and oxidation models are proposed.

A study of the size-dependent elastic properties of ZnO nanowires and nanotubes

We present our calculations of the Young's modulus of ZnO nanowires and nanotubes by using the empirical Buckingham-type potential. Our results indicate that the Young's moduli of ZnO nanowires increase as the diameters decrease, and the Young's moduli of ZnO nanotubes increase as the thicknesses decrease. Furthermore, we find that such size-dependent elastic properties mainly arise from the lateral facets of the nanowires and nanotubes. In particular, for a ZnO nanotube with a thin wall, the Coulomb interaction between the ions of the outer and inner atomic layers plays an important role in the Young's moduli of the surface atomic layers.

A comparative study on Pb2+, Zn2+ and Cd2+ sorption onto zirconium phosphate supported by a cation exchanger

In the present study, a novel hybrid sorbent ZrP-001 was prepared by loading zirconium phosphate (ZrP) onto a strongly acidic cation exchanger D-001. Sorption behavior of Pb(2+), Zn(2+), and Cd(2+) onto ZrP-001 was experimentally examined by comparing with the host exchanger D-001. ZrP-001 was characterized by scanning electron micrograph (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), pH-titration and pore size distribution analysis. Sorption of the heavy metals onto ZrP-001 was found to be pH-dependent due to the ion exchange mechanism. Compared to D-001, a smaller pore size of ZrP-001 due to the ZrP dispersion consequently resulted in a lower sorption rate. Competitive effect of Ca(2+) on sorption of heavy metals onto ZrP-001 and D-001 was compared to elucidate sorption preference of the hybrid sorbent towards heavy metals. More favorable sorption of ZrP-001 than D-001 was observed for all the three metals and their sorption preference onto ZrP-001 followed the order Pb(2+)>>Zn(2+) approximately Cd(2+). Fixed-bed sorption results and its efficient regeneration property further demonstrated that ZrP-001 is a potential candidate for removing heavy metals from contaminated water.

Interaction between gallium atoms and the inner walls of single-walled carbon nanotubes

The interaction between individual Ga atoms and the inner walls of both (8, 8) and (12, 0) carbon nanotubes (CNTs) is investigated using first principles calculations based on the density functional theory. We find that a single Ga atom favorably adsorbs at the center site (H) of a hexagonal ring and diffuses on the inner wall of a perfect CNT with very low energy barriers. In the case of CNTs containing monovacancies, a single Ga atom can heal the topological structure of a monovacancy in a (8, 8) CNT but not in a (12, 0) CNT. Our calculations show that the Ga atom adsorbed at the monovacancy in the CNT can alter the electronic structure of the tube significantly.

Highly effective removal of heavy metals by polymer-based zirconium phosphate: A case study of lead ion

Zirconium phosphate (ZrP) has recently been demonstrated as an excellent sorbent for heavy metals due to its high selectivity, high thermal stability, and absolute insolubility in water. However, it cannot be readily adopted in fixed beds or any other flowthrough system due to the excessive pressure drop and poor mechanical strength resulting from its fine submicrometer particle sizes. In the present study a hybrid sorbent, i.e., polymer-supported ZrP, was prepared by dispersing ZrP within a strongly acidic cation exchanger D-001 and used for enhanced lead removal from contaminated waters. D-001 was selected as a host material for sorbent preparation mainly because of the Donnan membrane effect resulting from the nondiffusible negatively charged sulfonic acid group on the exchanger surface, which would enhance permeation of the targeted metal ions. The hybrid sorbent (hereafter denoted ZrP-001) was characterized using a nitrogen adsorption technique, scanning electron microscope (SEM), and X-ray diffraction (XRD). Lead sorption onto ZrP-001 was found to be pH dependent due to the ion-exchange mechanism, and its sorption kinetics onto ZrP-001 followed the pseudo-first-order model. Compared to D-001, ZrP-001 exhibited more favorable lead sorption particularly in terms of high selectivity, as indicated by its substantially larger distribution coefficients when other competing cations Na(+), Ca(2+), and Mg(2+) coexisted at a high level in solution. Fixed-bed column runs showed that lead sorption on ZrP-001 resulted in a conspicuous decrease of this toxic metal from 40 mg/L to below 0.05 mg/L. By comparison with D-001 and ZrP-CP (ZrP dispersion within a neutrally charged polymer CP), enhanced removal efficiency of ZrP-001 resulted from the Donnan membrane effect of the host material D-001. Moreover, its feasible regeneration by diluted acid solution and negligible ZrP loss during operation also helps ZrP-001 to be a potential candidate for lead removal from water. Thus, all the results suggested that ZrP-001 offers excellent potential for lead removal from contaminated water.

Modeling synergistic adsorption of phenol/aniline mixtures in the aqueous phase onto porous polymer adsorbents

The adsorption equilibria of phenol and aniline on nonpolar polymer adsorbents (NDA-100, XAD-4, NDA-16 and NDA-1800) were investigated in single- and binary-solute adsorption systems at 313 K. The results showed that all the adsorption isotherms of phenol and aniline on these adsorbents can be well fitted by Freundlich and Langmuir equations, and the experimental uptake of phenol and aniline in all binary-component systems is obviously higher than predicted by the extended Langmuir model, arising presumably from the synergistic effect caused by the laterally acid-base interaction between the adsorbed phenol and aniline molecules. A new model (MELM) was developed to quantitatively describe the synergistic adsorption behavior of phenol/aniline equimolar mixtures in the binary-solute systems and showed a marked improvement in correlating the binary-solute adsorption of phenol and aniline by comparison with the widely used extended Langmuir model. The newly developed model confirms that the synergistic coefficient of one adsorbate is linearly correlated with the adsorbed amount of the other, and the larger average pore size of adsorbent results in the greater synergistic effect of phenol/aniline equimolar mixtures adsorption.

Application of an effective method in predicting breakthrough curves of fixed-bed adsorption onto resin adsorbent

Removal of many organic pollutants including phenolic compounds from industrial wastewater can always be achieved by fixed-bed adsorption onto the polymeric resin adsorbent, and the relevant breakthrough curves would provide much valuable information to help to design a fixed-bed adsorption process in field application. In the present study, a model developed based on the constant-pattern wave approach theory and the Freundlich model was adopted to describe the breakthrough curves of phenol and p-nitrophenol adsorption onto a macroreticular resin adsorbent NDA-100 from aqueous solution. Column experiments were performed at different conditions to verify the model and the results proved that the model would describe the breakthrough curves well. Effect of the operation parameters on breakthrough curves was also discussed to get helpful information in choosing the adsorption process.

Adsorption of phenolic compounds from aqueous solution onto a macroporous polymer and its aminated derivative: isotherm analysis

Adsorption of phenolic compounds from aqueous solution to a macroporous polymeric adsorbent (CHA-111), its animated derivative (MCH-111) and a reference weakly anion exchanger (ND-900) was studied. Experimental results indicated that amino functional groups on the polymeric matrix play an important role in phenol adsorption by MCH-111 and ND-900, which was attributed to the formation of hydrogen bonding between the phenol molecule and the amino group on the polymeric matrix. The semi-empirical Freundlich isotherm equation and its reduced form were employed to interpret the adsorption behavior. A site energy distribution model based on the Polanyi adsorption potential theory can elucidate the adsorption mechanism reasonably.

Nature of single vacancy in achiral carbon nanotubes

We have performed systematic calculations for single vacancies and their related point defects in achiral carbon nanotubes using a tight-binding model. Our calculations clarify that the local structures around single vacancies in such tubes do reconstruct with no constraint. We find that the structural configuration and formation energy of the resulting point defect are dependent on the radius and chirality, as well as the electric properties of a tube. The electronic structures of the single vacancies also depend strongly upon the chirality of the carbon nanotubes.

Role of amination of a polymeric adsorbent on phenol adsorption from aqueous solution

Adsorption of seven phenols, one aromatic carboxylic acid and one sulfonated aromatic acid from aqueous solution, by a hypercrosslinked polymeric adsorbent (CHA-111) and the derivative animated by dimethylamine was compared. The results of different adsorption isotherms indicated that amino group on the polymeric matrix played a significant role on adsorption of almost all the employed compounds. For most employed compounds adsorption capacities increase to different degree and significantly for those with lower value of pK(a). It may be attributed to the enhanced adsorbent-adsorbate interaction for amino group introduced on the polymeric matrix. The empirical Freundlich isotherm equation was employed to interpret the adsorbent-adsorbate interaction. The adsorption enthalpy change indicated the uptake of phenols on MCH-111 to be an enhanced physical adsorption because of the hydrogen-bonding interaction. Adsorption kinetic study of phenols on CHA-111 and MCH-111 was also conducted and amino group on the matrix will reduce the adsorption rate for change of pore size distribution and loss of macroprous volume as well as the hydration effect on the surface partly.

Metastability of amorphous silicon from silicon network rebonding

We propose a network rebonding model for light-induced metastability in amorphous silicon, involving bonding rearrangements of silicon and hydrogen atoms. Nonradiative recombination breaks weak silicon bonds and generates dangling bond-floating bond pairs, with very low activation energies. The transient floating bonds annihilate, generating local hydrogen motion. Charged defects are also found. Support for these processes is found with tight-binding molecular dynamics simulations. The model accounts for major experimental features of the Staebler-Wronski effect including electron-spin resonance data, the t(1/3) kinetics of defect formation, two types of metastable dangling bonds, and hysteretic annealing.

Benzylacyclouridine enhances 5-fluorouracil cytotoxicity against human prostate cancer cell lines

At a nontoxic growth inhibitory concentration benzyloxyacyclouridine (BAU), a potent and specific inhibitor of uridine phosphorylase (UrdPase), enhanced 5-fluorouracil (5-FU) cytotoxic activity against human prostate cancer PC-3 and DU-145 cell lines. The BAU/5-FU combination exhibited greater antitumor activity in vivo using PC-3 human xenografts compared to 5-FU alone, with no associated increase in animal host toxicity. The mechanism(s) responsible for the enhanced in vitro and in vivo activity of this combination may involve enhanced formation of the 5-FU nucleotide metabolites FdUMP, FdUTP, and FUTP resulting in enhanced inhibition of thymidylate synthase (TS) and increased incorporation of fluoropyrimidine metabolites into tumoral RNA and DNA.

Resistance to 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine derivatives is generated by mutations at multiple sites in the HIV-1 reverse transcriptase

Virus isolates resistant to 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) and a highly potent HEPT derivative, [1-benzyloxymethyl-5-ethyl-6-(alpha-pyridylthio)uracil] (NSC 648400, E-BPTU), were selected in cell culture. Cross-resistance evaluation indicated that the two drug-resistant virus isolates were phenotypically distinct from one another although each of the virus isolates was resistant to both of the HEPT derivatives. The virus isolate resistant to NSC 648400 had a single amino acid change in the reverse transcriptase (Y181C) which resulted in cross-resistance to all of the nonnucleoside reverse transcriptase inhibitors evaluated, with the exception of calanolide A. The NSC 648400-resistant virus isolate exhibited 15-fold enhanced sensitivity to calanolide A. The virus isolate selected in the presence of HEPT exhibited a single amino acid change (P236L) which was not cross-resistant to other nonnucleoside RT inhibitors tested with the exception of the two HEPT derivatives. This HEPT-resistant virus isolate exhibited enhanced sensitivity (5- to 10-fold) to thiazolobenzimidazole. We have used both virus isolates with defined single amino acid changes in the RT and bacterially expressed RTs with site-directed amino acid substitutions to test the effects of a wide variety of mutations on the activity of NSC 648400. Single mutations at amino acids 101, 103, 106, 181, or 236 yielded virus with high resistance (> 20-fold) to NSC 648400, while lower levels of resistance were seen with mutations at amino acids 98, 100, or 108. These results suggest that several changes in the conformation of the nonnucleoside inhibitor binding site of the HIV-1 reverse transcriptase can affect the inhibitory activity of the HEPT class of compounds.

Overexpression of ribonucleotide reductase in transfected human KB cells increases their resistance to hydroxyurea: M2 but not M1 is sufficient to increase resistance to hydroxyurea in transfected cells

Ribonucleotide reductase (RR) is a rate-limiting enzyme in DNA synthesis. The enzyme consists of two subunits, M1 and M2. Hydroxyurea (HU) is an M2-specific inhibitor. It has been shown that a HU-resistant clone derived from stepwise exposure to HU overexpresses the M2 mRNA and the RR protein (Y. Yen et al., Cancer Res., 54: 3868-3691, 1994). In this study, we established stable clones by transfecting human KB cells with the cDNA of human wild-type RR in which each subunit was overexpressed by a SV40 promoter. The mammalian cell expression vector ph beta APr-1 was used for constructing M1, M2, and M1/M2 subunit cDNA. The transfected cells were selected with G418. The clones designated M2-D, M1-D, X-D, and KB-V represent transfectant clones which contain M2 cDNA, M1 cDNA, M1/M2 cDNA, and vector alone, respectively. The parental KB cells and clones containing vector plasmid KB-V express equally low amounts of M2 and M1 mRNA from the endogenous genes. The expression of M2 mRNA and M1 mRNA is elevated 2-3 fold in the X-D transfectants. M2-D clone demonstrated a 6-fold higher M2 mRNA level although the M1 mRNA expression remains the same as parental cells. M1-D transfectants have a 3-fold increase in M1 mRNA expression relative to parental cells, but reveal no alteration of M2 mRNA. Southern analysis of genomic DNA suggested the incorporation of the plasmid into the genome. The X-D clone revealed both integration of the M2 and M1 gene while the M2-D clone only showed M2 gene integration. The M1-D clone revealed M1 gene integration relative to the parental cells. The Western blot of M2 protein showed a 3-fold increase in the X-D and M2-D clones whereas the M2 protein level in M1-D was the same as it was in parental cells. The M1 protein was increased 3-fold in X-D and 1.5-fold in M1-D over that of parental cells. However, lower M1 protein levels were identified in the M2-D clone. The specific activity of the RR enzyme from each transfectant showed a 3-fold increase in both the X-D and M2-D clones and slightly increased in M1-D clone over that of parental cells. However, X-D and M2-D both demonstrated a 3-fold increase in resistance to HU as compared to M1-D which showed the same sensitivity as the parental enzyme.(ABSTRACT TRUNCATED AT 400 WORDS)