What is the role of serology in assessing Helicobacter pylori eradication?

AIM

To assess the decline in Helicobacter pylori antibodies after eradication of infection.

METHODS

The H. pylori status was determined at entry (D0) by culture and histology performed on antral biopsies and after eradication treatment at day 42 (day 42) and after 6 months (M6) by the 13C-urea breath test. The EIA kits used to determine the anti-H. pylori antibody titre were HM-CAP (immunoglobulin-G) and PP-CAP (immunoglobulin-A) kits (Enteric Products, Inc.) and Pyloriset EIA-G (Orion Diagnostica).

RESULTS

Ninety-three patients were included. For 82 patients who were successfully treated, no kit was sufficiently accurate at D42 to show eradication. The antibody titre decreased for HM-CAP, PP-CAP and Pyloriset EIA-G by a mean of 35.6%, 41.2% and 64.7% between D0 and M6, respectively. According to the cut-off values defined by the manufacturers, 8.5% (PP-CAP, Pyloriset EIA-G) and 9.7% (HM-CAP) of the patients became H. pylori negative at M6. Using a 25% decrease in antibody titre between D0 and M6 as a threshold for H. pylori eradication, specificity was 100% for HM-CAP, 89.9% for Pyloriset EIA-G and 100% for PP-CAP, whereas the sensitivity was 76.8%, 98.8% and 72%, respectively.

CONCLUSION

An antibody titre decrease of 25% at M6 was found to be accurate in confirming H. pylori eradication.

The use of an oral fluid immunoglobulin G ELISA for the detection of Helicobacter pylori infection in children

BACKGROUND

Enzyme linked immunosorbent assay (ELISA) evaluation of oral fluid immunoglobulin G (IgG) antibodies to Helicobacter pylori is a unique approach for both epidemiological studies and the diagnosis of infection, especially in children. The use of oral fluid sampling to evaluate specific H. pylori IgG antibodies has advantages over serum, including reduced biohazard risk and noninvasive collection. Oral fluid sampling is fast and involves minimal patient discomfort. Since children facilitate transmission of H. pylori infection, a simple, accurate, noninvasive diagnostic test is necessary for large epidemiologic studies. The aim of our study was to evaluate a new oral fluid ELISA for detection of IgG antibodies to H. pylori in children.

MATERIALS AND METHODS

We compared this new oral fluid ELISA with the HM-CAPTM serum ELISA and gastric biopsy histology using 779 oral fluid samples from children collected at 11 clinical sites across the United States. This cohort included 315 children symptomatic for abdominal pain and 464 asymptomatic. All samples were evaluated in a double blind manner. The oral fluid ELISA demonstrated a sensitivity of 76.2% and a specificity of 94.0% in children 2 months old to 201/2 years, as compared with the HM-CAPTM serologic assay. The assay's sensitivity improved to 81.3% in children aged 5 or greater and the specificity remained at 94.0%. When compared with gastric biopsy histology in the same age group, the oral fluid ELISA demonstrated a sensitivity of 71.7% and a specificity of 90.4%.

RESULTS

This new oral fluid ELISA is moderately sensitive and offers a very specific method for detecting H. pylori infection in older children, but it is of little value in children under the age of 5 years.

CONCLUSIONS

Overall, we conclude that this oral fluid ELISA does not appear to be a helpful clinical tool for the diagnosis of H. pylori infection in children.

Diagnosis of Helicobacter pylori infection in children: comparison of a salivary immunoglobulin G antibody test with the [(13)C]urea breath test

The prevalence of Helicobacter pylori infection in a population-based sample of 477 children (mean age plus minus standard deviation, 5.8 plus minus 0.5 years) determined by the [(13)C]urea breath test ([(13)C]UBT) was 10.7% (95% confidence interval [CI], 8.1 to 13.8%), and that determined by salivary enzyme-linked immunosorbent assay (ELISA) was 11.9% (95% CI, 9.2 to 15.2%). Compared to the [(13)C]UBT, the sensitivity and specificity of the salivary ELISA were 80.9% (95% CI, 66.3 to 90.4%) and 95.3% (95% CI, 92.7 to 97.1%), respectively.

Molecular basis of the anaerobic response in plants

The response of plants to flooding is complex and involves the induction of specific gene sets. A multidisciplinary approach by several research teams has led to a reasonably good understanding of the low oxygen response, and many of the genes and proteins that are involved are known. But the factors that are critical in determining tolerance or intolerance remain unknown. Microarray technology offers renewed hope to unravel the complex changes in gene expression occurring in plants upon low oxygen treatment and what mechanisms are involved in the response.

Use of a dry-plasma collection device to overcome problems with storage and transportation of blood samples for epidemiology studies in developing countries

Studies are difficult in areas lacking modern facilities due to the inability to reliably collect, store, and ship samples. Thus, we sought to evaluate the use of a dry plasma collection device for seroepidemiology studies. Plasma was obtained by fingerstick using a commercial dry plasma collection device (Chemcard Plasma Collection Device) and serum (venipuncture) from individuals in Kazakhstan. Plasma samples were air dried for 15 min and then stored desiccated in foil zip-lock pouches at 4 to 6 degrees C and subsequently shipped to the United States by air at ambient temperature. Serum samples remained frozen at -20 degrees C until assayed. Helicobacter pylori status was determined by enzyme-linked immunosorbent assay (HM-CAP EIA) for the dry plasma and the serum samples. The results were concordant in 250 of the 289 cases (86.5%). In 25 cases (8.6%), the dry plasma samples gave indeterminate results and could not be retested because only one sample was collected. Five serum samples were positive, and the corresponding dry plasma samples were negative; one serum sample was negative, and the corresponding plasma sample was positive. The relative sensitivity and specificity of the Chemcard samples to serum were 97.6 and 97.9%, respectively, excluding those with indeterminate results. Repeated freeze-thawing had no adverse effect on the accuracy of the test. We found the dry plasma collection device to provide an accurate and practical alternative to serum when venipuncture may be difficult or inconvenient and sample storage and handling present difficulties, especially for seroepidemiologic studies in rural areas or developing countries and where freeze-thawing may be unavoidable.

Cellular radiosensitivity and complication risk after curative radiotherapy

PURPOSE

To test for an association between in vitro fibroblast radiosensitivity and complication risk in a case-control study of breast cancer patients treated under standard conditions in a clinical trial of radiotherapy dose fractionation.

PATIENTS AND METHODS

A cohort of patients participating in a randomised clinical trial of radiotherapy dose fractionation was selected on the basis of treatment-induced changes in the breast several years later. Thirty-nine cases with marked normal tissue changes were matched on several variables with 65 controls with no changes attributable to radiotherapy. Dermal fibroblast strains were established from duplicate skin biopsies, and clonogenic cell survival assays performed in triplicate after both high ( approximately 1.6 Gy/min) and low ( approximately 1 cGy/min) dose-rate irradiation. Laboratory studies were blind to patient identity, treatment outcome and radiotherapy schedule.

RESULTS

Analysis of 1128 clonogenic survival curves confirmed significant inter-patient variation in fibroblast radiosensitivity as measured by clonogenic survival. However, no association between fibroblast radiosensitivity and the development of late radiotherapy normal tissue effects was detected.

CONCLUSIONS

Inter-individual variation in cellular radiosensitivity may not be the main determinant of complication risk in patients undergoing radiotherapy for breast cancer. Other biological and technical factors may be more important in explaining the marked inter-patient differences in normal tissue damage evident several years after curative radiotherapy.

The chest radiograph appearances of very premature infants at 36 weeks post-conceptional age

The chest radiograph of very premature infants at 36 weeks post-conceptional age (PCA) was evaluated with regard to the degree of hyperinflation and cardiomegaly, and the presence of fibrosis/interstitial shadowing, cystic elements, air bronchograms and opacification. The evolution of abnormalities was assessed by comparing the radiograph appearance at 36 weeks PCA with that at 28 days post-natal age (PNA). Three scoring systems were used to determine how any abnormalities present could be best quantified to reflect disease severity as determined by chronic dependency upon supplementary oxygen status. Chest radiographs at 36 weeks PCA from 60 infants (median gestational age 26 weeks (range 24-28)) were studied. 47 infants also had radiographs at 28 days PNA. Only three infants had no chest radiograph abnormalities at 36 weeks PCA, although 24 infants were not dependent upon supplementary oxygen. The most common abnormalities were interstitial shadowing and hyperinflation, while cystic elements and cardiomegaly were rare. The radiographic appearance had deteriorated from 28 days PNA to 36 weeks PCA (p < 0.05); more infants at 36 weeks PCA were hyperinflated (p < 0.01). The chest radiograph appearances of infants who were dependent upon supplementary oxygen scored higher than those who were not (p < 0.01) using all three scoring systems. The system that assessed only the presence of interstitial shadowing, cystic elements and hyperinflation had the highest specificity in identifying oxygen dependency beyond 36 weeks PCA and had the highest area under the respective receiver operator characteristic curve. In conclusion, the majority of very immature infants have an abnormal chest radiograph appearance at 36 weeks PCA. The appearance can, however, be meaningfully scored by evaluating only three abnormalities.

Women's sexual health after childbirth

OBJECTIVE

To investigate the impact of childbirth on the sexual health of primiparous women and identify factors associated with dyspareunia.

DESIGN

Cross-sectional study using obstetric records, and postal survey six months after delivery.

SETTING

Department of Obstetrics and Gynaecology, St George's Hospital, London.

POPULATION

All primiparous women (n = 796) delivered of a live birth in a six month period.

METHODS

Quantitative analysis of obstetric and survey data.

MAIN OUTCOME MEASURES

Self reported sexual behaviour and sexual problems (e.g. vaginal dryness, painful penetration, pain during sexual intercourse, pain on orgasm, vaginal tightness, vaginal looseness, bleeding/irritation after sex, and loss of sexual desire); consultation for postnatal sexual problems.

RESULTS

Of the 484 respondents (61% response rate), 89% had resumed sexual activity within six months of the birth. Sexual morbidity increased significantly after the birth: in the first three months after delivery 83% of women experienced sexual problems, declining to 64% at six months, although not reaching pre-pregnancy levels of 38% . Dyspareunia in the first three months after delivery was, after adjustment, significantly associated with vaginal deliveries (P = 0 x 01) and previous experience of dyspareunia (P = 0 x 03). At six months the association with type of delivery was not significant (P = 0 x 4); only experience of dyspareunia before pregnancy (P < 0 x 0001) and current breastfeeding were significant (P = 0 x 0006). Only 15% of women who had a postnatal sexual problem reported discussing it with a health professional.

CONCLUSIONS

Sexual health problems were very common after childbirth, suggesting potentially high levels of unmet need.

Absence of Brca2 causes genome instability by chromosome breakage and loss associated with centrosome amplification

Women heterozygous for mutations in the breast-cancer susceptibility genes BRCA1 and BRCA2 have a highly elevated risk of developing breast cancer [1]. BRCA1 and BRCA2 encode large proteins with no sequence similarity to one another. Although involvement in DNA repair and transcription has been suggested, it is still not understood how loss of function of these genes leads to breast cancer [2]. Embryonic fibroblasts (MEFs) derived from mice homozygous for a hypomorphic mutation (Brca2(Tr2014)) within the 3' region of exon 11 in Brca2 [3], or a similar mutation (Brca2(Tr)) [4], proliferate poorly in culture and overexpress the tumour suppressor p53 and the cyclin-dependent kinase inhibitor p21(Waf1/Cip1). These MEFs have intact p53-dependent DNA damage G(1)-S [3] [4] and G(2)-M checkpoints [4], but are impaired in DNA double-strand break repair [3] and develop chromosome aberrations [4]. Here, we report that Brca2(Tr2014/Tr2014) MEFs frequently develop micronuclei. These abnormal DNA-containing bodies were formed through both loss of acentric chromosome fragments and by chromosome missegregation, which resulted in aneuploidy. Absence of Brca2 also led to centrosome amplification, which we found associated with the formation of micronuclei. These data suggest a potential mechanism whereby loss of BRCA2 may, within subclones, drive the loss of cell-cycle regulation genes, enabling proliferation and tumourigenesis.

Deprivation and excess winter mortality

OBJECTIVE

To investigate the effect of material deprivation on the winter rise in mortality and temperature dependent variations in mortality.

DESIGN

Ecological comparison of seasonal mortality at electoral ward level. Main outcome measures were ratios of winter to rest of the year mortality rates (seasonality ratios) and monthly deaths as the outcome variable in a model with monthly average temperature and Townsend score as main predictors.

SETTING

Croydon, London, United Kingdom.

SUBJECTS

All deaths of Croydon residents for the period 1990-1995.

MAIN RESULTS

There was a clear relation between overall mortality and deprivation. There was no evidence of a relation between age and sex standardised seasonality ratios and Townsend scores for all deaths (Kendall's tau = -0.066, p = 0.63) or cardiovascular deaths or respiratory deaths. There was no evidence of an interaction between Townsend score and temperature in the model of ward mortality rates (p = 0.73). These findings were not affected by exclusion of deaths of nursing and residential home residents.

CONCLUSION

This study provides no evidence of an effect of deprivation on excess winter mortality or temperature dependent variations in mortality. The findings question simple assumptions about the relation between deprivation and excess winter mortality and highlight the need for further study to guide interventions.

Usefulness of serological IgG antibody determinations for confirming eradication of Helicobacter pylori infection

OBJECTIVE

Prior studies have suggested that IgG antibody titers may be useful to confirm successful treatment of Helicobacter pylori (H. pylori) infection. However, the diagnostic value of decreasing IgG titers is limited by the necessity to perform pre and posttreatment tests in parallel which requires stored sera. Our objective was to assess the accuracy of IgG antibody titers using the HM-CAP IgG EIA kit (Enteric Products) in monitoring treatment of H. pylori infection and to compare the relative accuracy of parallel versus serial determinations.

METHODS

The 14C urea breath test (UBT) was used to confirm H. pylori infection in 83 dyspeptic patients and eradication of the organism at 4 wk and 6 months posttreatment. IgG titers pretherapy and 6 months posttherapy were determined either serially (separate EIA plates) or in parallel (same EIA plate), and the relative percent decline in antibody titer was calculated.

RESULTS

When a decline of > or = 25% at 6 months was used as the cut-off for H. pylori eradication, mean sensitivities of serial and parallel determinations were 87.5% and 86.8%, respectively, and mean specificities of both were 100%. In 68 of 75 patients in whom the organism was eradicated, the mean decrease in IgG titer at 6 months was 41.1% for serial determinations and 41.5% for parallel determinations.

CONCLUSIONS

Serial or parallel IgG titers offer equivalent diagnostic accuracy for confirming H. pylori eradication after therapy. A > or = 25% decline in titer 6 months after therapy is a sensitive and specific marker for eradication of the infection. Serial evaluation of IgG titers does not require serum storage, and is a cost-effective and accurate alternative to the UBT or endoscopy-based methods.

Social class and census-based deprivation scores: which is the best predictor of stillbirth rates?

This study investigates whether social class or a census-based deprivation score is a better predictor of stillbirth rates using data for 1993-5 for residents of South Thames (West) Region. Social class is routinely coded for 10% of live births and 100% of stillbirths. A Townsend deprivation score was assigned to each stillbirth and each live birth with a social class code, according to their electoral ward of residence. In unifactorial analyses of stillbirth rate the relationship was stronger with social class (P = 0.008) than with Townsend score (P = 0.11). Both relationships were strengthened by including those births recorded as social class 'other' ['other' vs. social class I odds ratio (OR) = 2.27, P < 0.001; lower vs. upper septile deprivation score OR = 1.45, P = 0.07)]. When social class and Townsend score were analysed together, the ORs for social class remained similar to before, but the Townsend ORs were reduced and non-significant overall. We conclude that social class, which is based on data on each individual, is a better predictor of stillbirth than Townsend score, which is based on data from the area of residence. We recommend further investigation of the stillbirth risk in the subgroups that make up the 'other' social class.

A simple chest radiograph score to predict chronic lung disease in prematurely born infants

A simple scoring system has been evaluated with regard to its ability to characterize the pre-term infant's chest radiograph appearance at 28 days and predict oxygen dependency beyond 36 weeks post-conceptional age (PCA). Chest radiographs taken at approximately 1 month of age in 42 infants (median gestational age 28 weeks) were assessed by the scoring system for the presence of fibrosis/interstitial shadows, cystic elements and degree of hyperinflation (maximum score 8). The system's results were then compared with those obtained using two previously published scoring systems. Using all three systems, there were significant differences in the scores of infants who were and were not oxygen dependent at 28 days (p < 0.001) and 36 weeks PCA (p < 0.001). For the three systems, the positive predictive values of a score of 3 or more to predict oxygen dependency at 36 weeks (PCA) were between 67% and 80% and similar receiver operating characteristic curves were obtained. We conclude that scoring only three abnormalities of the 28 day chest radiograph appearance of pre-term infants gives useful predictive information.

Serological discrimination of dogs infected with gastric Helicobacter spp. and uninfected dogs

Characterization of the humoral immune responses of people to Helicobacter pylori infection has facilitated the investigation of the host response to bacterial virulence factors and the development of sensitive and specific diagnostic tests. Dogs are commonly infected with gastric Helicobacter spp., but the presence of multiple Helicobacter spp. and possible coinfection in individual dogs have complicated serological evaluation. Evaluation of the antigenic homology of Helicobacter spp. revealed that the major protein bands of Helicobacter felis and Helicobacter bizzozeronii, two Helicobacter spp. that infect dogs, were very similar to UreA (29 to 31 kDa), UreB (63 to 66 kDa), and HSP (58 to 60 kDa) of H. pylori, and sera from infected and uninfected dogs bound in a similar way to each antigen. Immunoblotting and an enzyme-linked immunosorbent assay (ELISA) with H. felis ATCC 49179 antigen were performed with 101 serum samples (from 78 infected dogs and 23 uninfected dogs). Samples from uninfected dogs (median = 8) had fewer bands on immunoblotting than samples from infected dogs (median = 16) (P < 0.05). Combinations of the presence of any two of the low-molecular-mass bands (19, 25, 30, 32, and 37 kDa) or the high-molecular-mass bands (86 and 94 kDa) were found almost solely in samples from infected dogs (P < 0.0001). Kinetic ELISA results were significantly higher for samples from infected dogs (median = 0. 0802 optical density unit [OD]/min) than for samples from uninfected dogs (median = 0.01428 OD/min). The combination of ELISA and immunoblotting results gave a specificity of 95.6% and a sensitivity of 79.8%. No correlation between ELISA results, colonization density, degree of inflammation, and presence of lymphoid follicles was observed. The results indicate substantial antigenic homology between H. felis, H. pylori, and H. bizzozeronii. The combination of ELISA and immunoblotting was a highly specific and moderately sensitive indicator of infection. The degree of seropositivity assessed by ELISA was not related to bacterial colonization density, the degree of gastric inflammation, or the presence of lymphoid follicles.

Women's sexuality after childbirth: a pilot study

A pilot study was carried out investigating women's sexual health in the postnatal period. Postal questionnaires were sent to a cohort of 158 primiparous women approximately 7 months after delivery. Women who had resumed sexual intercourse were asked a detailed set of questions about problems experienced, sexual practices, frequency of intercourse, satisfaction with sex life, and consultation for postnatal sexual problems. All women were asked about the information they received on postnatal health prior to the birth and any information or help and advice they received from health professionals on the subject after the birth. Ninety-eight women (62%) responded. Women experienced significant levels of morbidity in the postnatal period; 3 months after delivery 58% experienced dyspareunia, 39% experienced vaginal dryness, and 44% suffered loss of sexual desire. These figures had reduced to 26, 22, and 35%, respectively, by the time of answering the questionnaire (approximately 8 to 9 months after delivery). Compared to before pregnancy, there was a decrease in frequency and satisfaction with sexual intercourse, although sexual practices changed little. Of the 67 women who reported a postnatal sexual problem, only 19% discussed this with a health professional. Conversations with health professionals in routine postnatal health contacts were mainly about contraception, and only rarely discussed problems with intercourse.

The effect of different bypass flow rates and low-dose dopamine on gut mucosal perfusion and outcome in cardiac surgical patients

The aim of this double-blind, randomized, placebo-controlled trial was to investigate the effects of different cardiopulmonary bypass flow rates and low-dose dopamine on gastric mucosal pH (pHi) and outcome. We hypothesized that by minimizing gut mucosal hypoperfusion during and after cardiac surgery endotoxin translocation may be prevented, resulting in an improved clinical outcome. Four groups of 25 patients each receiving high or low flows during bypass and low-dose dopamine or saline for 24 hours after induction of anaesthesia were studied. The pHi was measured at six time intervals over 24 hours. The combination of low-dose dopamine and a low bypass flow rate was associated with a significantly greater frequency and severity of low pHi. This group also demonstrated a significantly lower vascular resistance on admission to the intensive care unit. There may be an association between low pHi and low vascular resistance.

How to make nutrition education more meaningful through facilitated group discussions

Facilitated group discussions provide an alternative method to lecture and one-on-one approaches for conducting educational interventions at clinic sites. They are an interactive form of education wherein learners generate the specific topics to be addressed and share their knowledge and experience with other group members through discussion. In brief, the educator becomes a facilitator who, rather than lecturing, encourages clients to discuss freely among themselves their own approach to the nutrition problems posed during the session. As a facilitator, the nutritionist strives to create a comfortable atmosphere for discussion, encourages participation, and interjects only to correct misinformation and manage group dynamics. Facilitated group discussions allow nutrition practitioners to deliver meaningful nutrition education in a manner that helps empower their clients to improve their dietary habits; at the same time such discussions meet the increased public administrative demands for efficiency. Possible benefits to clients include more confidence, better communication skills, improved thinking skills, and increased motivation and commitment to improving nutrition behavior. We recommend that nutrition educators try facilitated group discussions in their clinics.

Are women who have abortions different from those who do not? A secondary analysis of the 1990 national survey of sexual attitudes and lifestyles

Studies of women undergoing termination of a pregnancy are often used to make recommendations about family planning and health education policy. However, it is not clear how similar the women in these studies are to the general population of women of childbearing age. Our secondary analysis of the National Sexual Attitudes and Lifestyles Survey allowed us to test the hypothesis that women who have undergone an abortion are the same as those who have not (in terms of socio-demographic characteristics, lifestyles, and attitudes). Our findings show significant differences between these two groups of women, particularly regarding ethnicity, marital status, number of natural children, lifetime number of sexual partners, and attitudes to abortion. We conclude that family planning/reproductive health services and health education policies need to take these differences into account and that further research is required to explain why these differences arise.

Radioresistant MTp53-expressing rat embryo cell transformants exhibit increased DNA-dsb rejoining during exposure to ionizing radiation

Recent data suggest that aberrant function of the wild type p53 protein (WTp53) may alter cellular survival following DNA damage through cellular pathways involving apoptosis and cell-cycle checkpoints, but little is known concerning it's possible role in DNA repair. In the present study, the ionizing radiation sensitivity was determined for a series of rat embryo fibroblast (REF) cell lines transfected with an activated form of the H-ras oncogene alone, or in combination with a variety of missense-mutant p53 (MTp53) alleles. Transformed REF clones which expressed exogenous MTp53 and p21ras proteins (CLASS II clones) were generally radioresistant in culture as determined by higher values for the surviving fraction after 2 Gy (SF2 value) and the radiation dose required to reduce survival to a fraction of 0.1 (D10 value), compared either to transformed REF clones expressing p21ras protein alone (CLASS I clones), or to non-transfected REF control cell lines expressing baseline endogenous levels of p21ras and WTp53 protein. The increased radioresistance observed in the CLASS II clones (following both HDR- and LDR-irradiation), was significantly correlated with increased expression of MTp53 protein, and a decreased radiation-induced G1 arrest response. The variability observed in clonogenic radiosensitivity among REF clones was not explained by differential radiation-induced apoptosis. Using the Comet assay performed after continuous low dose-rate (LDR)-irradiation, MTp53-expressing REF clones were also found to be more proficient at the rejoining of DNA double-strand breaks (DNA-dsb), compared to WTp53-expressing REF clones. These results suggest that an enhanced DNA and cellular repair capacity may, in part, explain the increased radiation survival observed in some MTp53-expressing transformed fibroblasts and tumours.

Determination of epidermal transpiration in four cultivars of Nicotiana tabacum L. using epidermal strips in a quasi-steady state system

A quasi-steady state method is presented for quantifying epidermal transpiration of epidermal strips where simple relations between transmembrane fluxes and parameters of diffusibility of penetrating compounds hold. Contrary to most permeability studies, we did not use astomatous, enzymatically isolated, or dried cuticular membranes, because these procedures are largely responsible for the problems cited in the literature. Instead, we used freshly harvested stomatous epidermal strips, thus avoiding the sorption of lipids by the cuticular membranes during enzymatic isolation. Our approach allowed estimation of amounts and composition of intracuticular soluble lipids. Diffusion coefficients (D-values) were calculated with smaller associated standard deviations and an order of magnitude lower than previously reported; the fresh material sorption of the diffusing compound by the membrane and hydration of the cuticular pores was greatly reduced. In the present study the hold-up time (te) ranged from 66.2+/-0.3 to 110.3+/-0.9 sec. Furthermore, 0.1 microm thick membranes were used, contrary to previous studies of water permeability that used cuticles more than 2 microm thick. Because a small but constant flow of penetrant could be detected during the first half of the steady flow to te, small holes probably did not influence the reported permeability. Permeability coefficients (Pd) in the order of 0.65 x 10(-9) ms(-1) were calculated. Pd values in the order of 5.68 x 10(-3) ms(-1) were calculated when incomplete stomatal closure occurred, while when areas of mass flow were detected, Pd values in the order of 1.26 x 10(-2) ms(-1) were calculated. The degree of contamination of the epidermal strips by cellular debris was quantified and expressed as the total chlorphyll content per exposed surface area of the epidermal strip, and an average of 8.7% contamination was observed compared to the total leaf chlorophyll content. Leakage from the system was calculated to be approximately 0.18 x 10(-10) ms(-1), which represents an average 2.7% experimental variability. These results are discussed in terms of the limitations associated with using composite membranes that are stomatous and have trichomes, for possible application in drought tolerance selection.

Mutator phenotype in Msh2-deficient murine embryonic fibroblasts

Embryonic fibroblast cell lines were established from mice deficient, heterozygous, or proficient for Msh2, one of the three known DNA mismatch repair genes involved in hereditary nonpolyposis colon cancer (HNPCC). Cell lines were established by transfection of primary mouse embryo fibroblasts with E7 and Ras oncogenes or mutant p53. Spontaneously immortalized cells derived from the primary cultures were also studied. To determine whether these cells developed a mutator phenotype similar to that found in colon cancer cells deficient in mismatch repair, we measured mutation rates, microsatellite instability, and sensitivities to a range of DNA-damaging agents. The mutator phenotype detected in the E7 and Ras or mutant p53-immortalized Msh2-/- mouse cells was similar to that found in human mismatch repair-deficient colorectal carcinoma cell lines. Mutation rates to ouabain resistance were increased 8-12-fold relative to lines from Msh2+/+ mice, and microsatellite instability was detectable in 12-18% of subclones derived from the Msh2-/- line but was undetectable in subclones developed from the Msh2+/+ line. Furthermore, E7 and Ras or spontaneously immortalized Msh2-/- cells were significantly more resistant to the cytotoxic effects of 6-thioguanine relative to Msh2+/+ cells. In contrast, these lines showed various responses to UV light and cis-platinum, suggesting that mismatch repair deficiency was not the sole determinant for sensitivity to these DNA-damaging agents. Particular attention was paid to the properties of cells heterozygous for the Msh2 mutant gene, which would mimic the situation of an HNPCC carrier. However, our studies failed to reveal any properties of these cells that might provide a growth advantage or predispose them for the acquisition of further mutations. This observation is consistent with the model that inactivation of the wild-type Msh2 allele is a critical step for tumorigenesis in HNPCC patients.