Assessing the efficacy of a German-inspired intervention on occupational contact dermatitis in Denmark: A randomised controlled trial with 3-month follow-up

BACKGROUND

Occupational contact dermatitis (OCD) is a prevalent, often chronic disease that poses a risk for job loss and decreased quality of life. In Germany, a multi-step prevention programme emphasising early detection and highly specialised multidisciplinary treatment has been implemented with great success.

OBJECTIVES

To examine the effectiveness of a Danish-adapted version of the German prevention effort on OCD severity, quality of life and occupational consequences at 3-month follow-up.

METHODS

Randomised, controlled trial. Participants were recruited after the first referral from General Practitioner to Dermatologist with suspected OCD. The intervention group (IG) received a Danish-adapted, multidisciplinary intervention, while the control group (CG) navigated the Danish healthcare system without interference from the study. OCD severity, occupational consequences and quality of life were assessed at 3-month follow-up using self-reported questionnaires.

RESULTS

A statistically significant decrease in the severity of eczema was found at 3-month follow-up in the IG compared to the CG. The IG were statistically significantly more likely to have seen a dermatologist at 3-month follow-up. Higher treatment level in the IG was indicated by the results but was not statistically significant. No significant difference was found in quality of life or occupational consequences.

CONCLUSIONS

These initial findings suggest that early and specialised treatment of OCD improves OCD prognosis.

Impact of atopic dermatitis on occupational contact dermatitis among young people: A retrospective cohort study

BACKGROUND

Occupational contact dermatitis (OCD) is a common occupational disease. Atopic dermatitis (AD) is a known risk factor for OCD.

OBJECTIVES

To determine the prevalence of previously diagnosed AD among young workers with recognized OCD and assess its impact on OCD prognosis.

METHODS

A retrospective cohort study. A questionnaire was sent to 6251 workers with recognized OCD who were under 35 years at notification (response rate: 47%). Of the respondents, 2392 answered a question about previous doctor-diagnosed AD and were included in the study. Eczema severity, occupational consequences and quality of life were examined using statistical analyses comparing workers with and without previously diagnosed AD.

RESULTS

The prevalence of previously diagnosed AD was 41.8% (95% CI: 39.8-43.8). Women had a higher AD prevalence, and workers with AD reported OCD at a younger age. Workers with AD reported more frequent and severe eczema symptoms and had a higher risk of OCD negatively affecting job and occupation choices. Health-related quality of life was more adversely affected in workers with AD.

CONCLUSIONS

AD significantly impacts severity and has long-term consequences for young people with OCD. Targeted prevention strategies need to be developed.

Occupational contact dermatitis among young people in Denmark - A survey of causes and long-term consequences

BACKGROUND

Studies on the causes and consequences of occupational contact dermatitis (OCD) among young workers are non-existent.

OBJECTIVES

Determine causes and consequences of OCD among workers < 35 years.

METHODS

A questionnaire was sent to 6,251 workers < 35 years at notification with recognized OCD response rate 47%).

RESULTS

The most prevalent occupations were healthcare workers, kitchen workers, nursery teachers, and hairdressers and beauticians. 76% still had eczema, and 77% of these had eczema half to all the time the last 3 months, with 61% evaluating their eczema as moderate to very severe. 53% had changed occupation since notification, and 42.5% had lost their job because of OCD. Allergic OCD increased the odds ratio (OR) for facial or foot eczema, job loss, change in work tasks, difficulties finding work, decrease in income, and sick leave. Age at notification ≤ 25 years increased the risk of job loss and feeling restricted in choice of job. Workers in the food industry had a higher OR for job loss, while hairdressers and beauticians had a higher risk of job loss and a decrease in income.

CONCLUSIONS

The severe, long-term consequences of OCD notification signify the need for further preventive strategies among young workers. This article is protected by copyright. All rights reserved.

Asthma-inducing potential of 28 substances in spray cleaning products-Assessed by quantitative structure activity relationship (QSAR) testing and literature review

Exposure to spray cleaning products constitutes a potential risk for asthma induction. We set out to review whether substances in such products are potential inducers of asthma. We identified 101 spray cleaning products for professional use. Twenty‐eight of their chemical substances were selected. We based the selection on (a) positive prediction for respiratory sensitisation in humans based on quantitative structure activity relationship (QSAR) in the Danish (Q)SAR Database, (b) positive QSAR prediction for severe skin irritation in rabbits and (c) knowledge on the substances' physico‐chemical characteristics and toxicity. Combining the findings in the literature and QSAR predictions, we could group substances into four classes: (1) some indication in humans for asthma induction: chloramine, benzalkonium chloride; (2) some indication in animals for asthma induction: ethylenediaminetetraacetic acid (EDTA), citric acid; (3) equivocal data: hypochlorite; (4) few or lacking data: nitriloacetic acid, monoethanolamine, 2‐(2‐aminoethoxy)ethanol, 2‐diethylaminoethanol, alkyldimethylamin oxide, 1‐aminopropan‐2‐ol, methylisothiazolinone, benzisothiazolinone and chlormethylisothiazolinone; three specific sulphonates and sulfamic acid, salicylic acid and its analogue sodium benzoate, propane‐1,2‐diol, glycerol, propylidynetrimethanol, lactic acid, disodium malate, morpholine, bronopol and benzyl alcohol. In conclusion, we identified an asthma induction potential for some of the substances. In addition, we identified major knowledge gaps for most substances. Thus, more data are needed to feed into a strategy of safe‐by‐design, where substances with potential for induction of asthma are avoided in future (spray) cleaning products. Moreover, we suggest that QSAR predictions can serve to prioritise substances that need further testing in various areas of toxicology.

We reviewed whether substances in spray cleaning products constitute a potential risk for asthma induction. For this, we identified 101 spray cleaning products for professional use and prioritised their ingredient substances by use of quantitative structure activity relationship (QSAR). We provide a review of 28 selected substances: we give conclusions on their asthma induction potential, as well as a discussion on the use of QSAR for prioritisation of substances, and the major knowledge gaps we encountered.

Incidence rates of occupational contact dermatitis in Denmark between 2007 and 2018: A population-based study

BACKGROUND

Recent population-based studies on the incidence rates (IRs) of occupational contact dermatitis (OCD) are sparse.

OBJECTIVES

To determine the IRs of OCD and development thereof between 2007 and 2018 in known risk occupations.

METHODS

Data on all recognized cases of OCD were used to calculate IRs as the number of recognized OCD cases per 10 000 workers per year. Asymptotic chi-square test was used to compare the IRs between 2007-2012 and 2013-2018.

RESULTS

The median age at notification of OCD was below 30 years for several of the examined occupations. Hairdressers and beauticians, bakers, dentists and dental assistants, and manufacturing of windmills had the highest overall IRs of OCD. We found a statistically significant increase in the IRs of OCD for child/nursery care workers.

CONCLUSIONS

The median age at notification of OCD was low for several of the occupations, signifying the need for further preventive strategies among young people. Based on the IRs of OCD, future preventive efforts should be directed at hairdressers and beauticians, bakers, dentists and dental assistants, and manufacturing of windmills. Furthermore, the statistically significant increase in IRs of OCD among child/nursery care workers highlights the need for further preventive strategies in this field.

Degree of employment, sick leave, and costs following notification of occupational contact dermatitis-A register-based study

BACKGROUND

Occupational contact dermatitis (OCD) is the most commonly recognized occupational disease in Denmark.

OBJECTIVES

To examine the impact of recognized OCD on degree of employment, sick leave, unemployment, and job change.

METHODS

Data on all recognized individuals with OCD notified in Denmark between 2010 and 2015 (n = 8940) were linked to information on social transfer payments in the years before and after notification. The number of weeks on unemployment benefits or sick leave and the degree of employment during the 2 years prior to notification was compared with the 2 years following notification.

RESULTS

The degree of employment decreased on average 8.9 work-hours/month, corresponding to an average annual loss of income per worker of approximately €1570. The average number of weeks that workers were receiving unemployment benefits and paid long-term sick leave rose by 2.5 and 3.4 weeks, respectively, corresponding to an average additional annual cost per worker of approximately €420 and €770, respectively. Longer case-processing time was significantly associated with lower degree of employment and higher levels of unemployment and sick leave.

CONCLUSIONS

OCD has a significant negative impact on employment and economics, thus highlighting the need for a national, strategic action plan for effective prevention of OCD.

Determinants of house dust, endotoxin, and β-(1→3)-D-glucan in homes of Danish children

Little is known about the geographic variation and determinants of bacterial endotoxin and β-(1,3)-D-glucan in Danish house dust. In a population of 317 children, we: (i) described loads and concentrations of floor dust, endotoxin, and β-(1→3)-D-glucan and (ii) their correlations and (iii) assessed their determinants; (iv) Finally, we compared our findings with previous European studies. Bedroom floor dust was analyzed for endotoxin content by the kinetic limulus amoebocyte lysate assay and for β-(1→3)-D-glucan by the inhibition enzyme immunoassay. The parents answered questions regarding potential determinants. We found: geometric means (geometric standard deviations) 186 mg/m(2) (4.3) for dust; 5.46 × 10(3) EU/m(2) (8.0) and 31.1 × 10(3) EU/g (2.6) for endotoxin; and 142 μg/m(2) (14.3) and 0.71 × 10(3) μg/g (7.3) for β-(1→3)-D-glucan. High correlations (r > 0.75) were found between floor dust and endotoxin and β-(1→3)-D-glucan loads, while endotoxin and β-(1→3)-D-glucan concentrations were moderately correlated (r = 0.36-0.41) with the dust load. Having a carpet was positively associated with dust load and with endotoxin and β-(1→3)-D-glucan concentrations. Pet keeping, dwelling type, and dwelling location were determinants of endotoxin concentrations. No other determinants were associated with β-(1→3)-D-glucan concentrations. Compared with other European studies, we found lower β-(1→3)-D-glucan loads and concentrations but higher endotoxin loads and concentrations suggesting a geographically determined different composition of Danish floor dust compared with other European regions.

Exposure to 27 polychlorinated biphenyls in the indoor environment of a workplace: a controlled bio-monitoring study

PURPOSE

To assess the exposure to a broad-spectrum of polychlorinated biphenyl congeners (PCBs) from the indoor environment through bio-monitoring of people working in a building with PCB-containing materials and elevated PCB levels in the indoor air.

METHODS

A cross-sectional study comparing the plasma concentration of 27 PCB congeners in 15 people working in a PCB-contaminated building and 30 matched controls.

RESULTS

Median concentration of eight low-chlorinated PCB congeners was significantly higher in the exposed than in the control group. The sum of median concentrations of tri + tetra-chlorinated PCB was almost ten times higher in the exposed group than in the unexposed, and sums of dioxin-like and non-dioxin-like PCB were both relatively increased by 60 % in the exposed group.

CONCLUSIONS

The occupational indoor environment may significantly add to PCB exposure, especially to the lower-chlorinated congeners. Health effect from this little-acknowledged exposure has not yet been documented, but data supporting lack of effect are sparse and research generating information on effect of exposure to specific congeners including at levels relevant for the indoor environment should be encouraged.

Polychlorinated biphenyls (PCBs) in indoor air originating from sealants in contaminated and uncontaminated apartments within the same housing estate

Twenty-four congeners of polychlorinated biphenyls (PCBs) were measured in 83 air samples and 20 elastic sealants samples of apartments with PCB-containing sealants. In addition, PCBs were measured in 21 air samples from reference apartments located in an uncontaminated section of the same estate. The PCB(tot) levels in the air of the contaminated section were 168-3843 ng m(-3) (mean: 1030 ng m(-3)), while the mean levels in the reference apartments were 6.03 ng m(-3). The sum of the 24 measured PCB congeners in sealants from the contaminated section was 187-221680 mg kg(-1). Principal component analysis revealed four groups among the sealant samples with different congener compositions, only two of which were clearly similar to known PCB mixtures, while two were not. Significant correlations and intercorrelations were observed between the lower chlorinated congeners in air and sealant, e.g. for PCB 28(air) and 28(seal) (p=0.04) and for PCB 28(air) and 52(air), 52(seal). However, no correlation was observed between the lower chlorinated congeners and the sums of PCB (∑PCB(6) or ∑PCB(24)) or the higher chlorinated congeners. Analysis of air concentrations in relation to questionnaire data indicated that the indoor air levels could be reduced by increased cleaning and airing frequencies.

Building-related symptoms and stress indicators

This study aims to study physiological stress indicators in relation to prevalence of building-related symptoms (BRS) among teachers employed in three selected schools in Copenhagen. Three hypotheses were studied: (i) Perceived psychosocial work environment was associated with BRS; (ii) Perceived psychosocial work environment (job strain) was associated with physiological strain; (iii) BRS was associated with physiological strain. We found a tendency among women of an association between job strain and being BRS positive. Also an association between job strain and physiological strain was observed among women. Being BRS positive was not associated with single physiological stress indicators with the exception of a higher level free testosterone in serum among BRS-positive women.

PRACTICAL IMPLICATIONS

Including physiological stress indicators may be a supplementary measure to questionnaires when studying the association between the psychosocial work environment and building-related symptoms (BRS). In this study, job strain was associated with physiological strain among women. Being BRS positive was not associated with single physiological stress indicators with the exception of a higher level free testosterone in serum among BRS-positive women. This study should be regarded as a preliminary study because of its small number of participants.

The dustfall collector--a simple passive tool for long-term collection of airborne dust: a project under the Danish Mould in Buildings program (DAMIB)

A newly developed dustfall device that collects airborne dust by sedimentation has been evaluated in Danish schools. Dust collected over 140 days was compared with airborne dust sampled during single school days and settled floor dust sampled at the end of a school day. Measurements of culturable fungi in air samples corresponded well to those from the dustfall collector in mechanically but not naturally ventilated rooms. Levels of beta(1 --> 3)glucan and culturable fungi in dust from the dustfall collector and settled floor dust did not agree well. Up to 10 times more beta(1 --> 3)glucan per milligram dust was found in the dustfall collectors than in settled floor dust. Only in dust from the dustfall collector was the mass concentration of culturable fungi (cfu/mg) significantly correlated with the degree of dampness. The culturability of fungi in the 140-day dustfall samples tended to be lower than in other types of samples. Nonetheless, the results indicated that the dustfall collector can be used to estimate the median concentration of airborne culturable fungi, provided identical sampling periods are used for all samples. The collector is cost effective and simple to use.

PRACTICAL IMPLICATIONS

Traditional ways of assessing exposure to microorganisms by sampling airborne dust or dust from floors have several disadvantages. In the present paper, a new sampler, the dustfall collector, which collects airborne dust by sedimentation over a period of months, is introduced. Tests of this collector indicate that it can be used to estimate the mean concentration of airborne culturable fungi but not beta(1 --> 3)glucan over a long period and that the method can differentiate between buildings with different levels of water damage.

Molds in floor dust, building-related symptoms, and lung function among male and female schoolteachers

Five hundred and twenty-two teachers from 15 public schools, eight 'water-damaged' schools, and seven 'non-damaged' schools with no visible water damage were included in a cross-sectional design. Mold growth was assessed by recording the amount of dust on the floor and in the air in classrooms and the content of a number of mold species in the dust (CFU/g dust). The evaluation of health symptoms included symptoms recorded by questionnaire and spirometry, bronchial challenge, and CO-diffusion capacity. Nasal lavage fluid was analyzed for IL-8 and ECP. Personal and psychosocial factors were included as confounders. In this study population mucus membrane irritation symptoms (MMI) and general symptoms were reported more frequently by women than by men with odds ratios ranging from 1.4 to 2.1. Women's reports of symptoms from mucous membranes and skin and general symptoms were positively associated with mold exposure. Odds ratio for 'difficult to concentrate' after adjustment for confounders was 11.2 (1.4-90.1, 95% CI) at high levels of mold exposure. None of the lung function tests performed in this study were associated with mold exposure, to the 'water damaged' vs. 'non-damaged' classification, or to the symptoms reported. IL-8 and ECP were not associated either.

PRACTICAL IMPLICATIONS

Psychosocial and personal reasons dominate in MMI and general symptoms. Headache and difficulties to concentrate associated with indoor mold exposure, mainly for women. No lung function impairment associated with indoor mold exposure.

Double blind placebo controlled exposure to molds: exposure system and clinical results

The objective was to develop an experimental setup for human exposure to mold spores, and to study the clinical effect of this exposure in sensitive subjects who had previously experienced potentially building-related symptoms (BRS) at work. From three water-damaged schools eight employees with a positive histamine release test to Penicillium chrysogenum were exposed double- blinded to either placebo, approximately 600,000 spores/m3 air of P. chrysogenum or approximately 350,000 spores/m3 of Trichoderma harzianum for 6 min on three separate days. A statistically significant rise in symptoms from mucous membranes appeared from the 9-graded symptom scale after exposure to T. harzianum or placebo. Dichotomizing the data, whether the participants experienced at least a two-step rise on the symptom scale or not, gave borderline increase in mucous membrane symptoms after exposure to P. chrysogenum. In conclusion this is, to our knowledge, the first study to successfully conduct a human exposure to a highly controlled dose of fungal material aerosolized directly from wet building materials. This short-term exposure to high concentrations of two different molds induced no more reactions than exposure to placebo in eight sensitive school employees. However, a statistical type II error cannot be excluded because of the small sample size.

PRACTICAL IMPLICATIONS

In this double blind, placebo controlled study of mold exposure changes in symptoms, objective measurements and blood samples were small and mostly non-significant, and at the same level as after placebo exposure. The developed exposure system based on the Particle-Field and Laboratory Emission Cell (P-FLEC) makes it possible to deliver a precise and highly controlled dose of mold spores from water-damaged building materials, imitating realistic field exposure conditions. The present experiment is too small to rule out an effect of mold exposure; long-term experimental exposure studies on larger number of subjects are needed.

Molds in floor dust and building-related symptoms among adolescent school children: a problem for boys only?

In this stratified cross-sectional study in eight 'wet' and seven 'dry' schools, 1024 adolescent school children reported potentially building-related symptoms (BRS) in self-administrated questionnaires. From their classrooms dust samples were collected from floors, ventilation ducts, and air; settled dust was collected in cardboard boxes over a period of 5 months. Measurements of temperature, relative humidity and CO2 were performed. BRS were strongly associated with personal factors like recent airway infections, hay fever, asthma and psycho-social work load, but also to molds in floor dust and presence of mechanical ventilation. The association between molds in floor dust and BRS has in stratified analyses shown a strong association among adolescent school boys, and no association among adolescent school girls using multivariable analyses controlling for relevant confounders. In contrast to the menstruating school girls, the symptoms among the small group of not yet menstruating girls were associated with the levels of molds in floor dust. Their symptom prevalences were very similar to those of the boys. This finding makes us suggest a new hypothesis: The higher endogenous estrogen levels of sexually matured adolescent females seems to protect them from the effects of molds in dust, despite their overall higher symptom prevalence.

PRACTICAL IMPLICATIONS

In this cross-sectional epidemiological study of adolescent school children we found independent significant positive associations between building-related symptoms and viable molds in floor dust in boys and non-menstruating girls. In contrast, no such associations were seen among menstruating girls. The identification of these two susceptible groups adds further support the relevance of minimizing sources of dust and mold exposure.

Molds in floor dust and building-related symptoms in adolescent school children

This stratified cross-sectional epidemiological study included 1053 school children aged 13-17 years. All pupils filled in a questionnaire on building-related symptoms and other relevant health aspects. The following exposure measurements were carried out: room temperature, CO2 level, and relative humidity; building characteristics including mold infestation were assessed, and dust was collected from floors, air, and ventilation ducts during a working day. Dust was examined for endotoxin level, and cultivated for viable molds. We did not find a positive association between building-related symptoms and extent of moisture and mold growth in the school buildings. Five of eight building-related symptoms were significantly and positively associated with the concentration of colony forming units of molds in floor dust: eye irritation, throat irritation, headache, concentration problems, and dizziness. After adjusting for different potentially confounding factors in separate analyses of each symptom, the above-mentioned associations between molds in dust and symptoms were still present, except for concentration problems. However, in none of the analyses was mold exposure the strongest covariate, being secondary to either asthma, hay fever, recent airway infection, or psychosocial factors.

Inflammatory potential of dust from schools and building related symptoms

AIMS

To test whether the inflammatory potential of dust samples might be used to differentiate schools with high and low prevalence of building related symptoms (BRS) among the occupants.

METHODS

Ten schools with high prevalence of BRS and 10 schools with low prevalence were selected. Dust collected from floors, horizontal surfaces, and exhaust outlets was tested at five concentrations on the lung epithelial cell line A549. The potency of the dust (PF) to stimulate IL-8 secretion was calculated from the initial linear part of the dose-response curves. The organic fraction of the dust samples was determined by incineration.

RESULTS

The schools with low prevalence of symptoms had a BRS% of 4.4-11.0 and the schools with high prevalence a BRS% of 19.6-31.9. The PF of floor dust and surface dust correlated, and the PF was associated with the organic content of the dust. The schools with low prevalence of symptoms had a significantly lower PF than the schools with high prevalence. Using the cut point value of 4.5 ng IL-8/mg floor dust, significantly more high prevalence schools were found above the cut point than below.

CONCLUSION

The PF of the floor dust samples correlated significantly with the prevalence of symptoms in the schools. The content of endotoxin and microorganisms did not seem to explain the inflammatory potential of the dust or BRS, and the substances in the dust causing the inflammatory potential are presently unknown.

Freeze-fracture studies on lipids and membranes

Freeze-fracture electron microscopy is especially useful for investigation of lipid structures by the advantageous fracture course within hydrophobic zones. Freezing is, on the other hand, a restriction because the structures of lamellar and non-lamellar phase states with disordered acyl chains (L(alpha), H(II,) cubic) are difficult to preserve. An important aspect of this method is therefore the lipid structure of phase states with ordered acyl chains (crystal, gel), and with a different degree of hydration. Freeze-fracture of pure lipid systems creates a valid representation of the structure of non-lamellar phases and of the general structure of the "lamellar" lipid bilayer, and lamellar phases with characteristic deformations (ripples, curvatures, plane sectors) can be identified. Fracture through the hydrophobic bilayer centre of biological membranes reveals characteristic protein components, the intramembraneous particles (IMPs). The lateral distribution of the IMPs is a helpful marker for fluid and rigid phase states, also without deformation of the lamella. The overall history and the present state of knowledge concerning the different structures revealed by the freeze-fracture and freeze-etch techniques in lipid systems, and to a limited extent in biological membranes, is reviewed, taking into account studies from our own laboratory.

Serum IgE specific to indoor moulds, measured by basophil histamine release, is associated with building-related symptoms in damp buildings

OBJECTIVE

To study the relationship between basophil histamine release (HRT) to indoor moulds, indicating specific IgE, and building-related symptoms (BRS), asthma, and hay fever in individuals working in damp and mouldy buildings.

METHODS

A cross-sectional study was performed among 86 school staff members, who on average had worked 143 months (range: 3-396) in moist buildings with mould growth in the constructions. A questionnaire concerning mucous membrane symptoms, facial skin symptoms, central nervous system symptoms, hay fever, and asthma was fulfilled by the participants, and blood samples were taken. Eight mould species growing on building constructions were identified and cultivated to obtain allergenic materials for testing. The presence in serum of IgE specific to moulds was verified by histamine release test (HRT) based on passive sensitization of basophil leukocytes. The validity of the method was confirmed by parallel testing of patients allergic to grass- and birch pollen and by the shift from positive to negative response after removal of serum IgE and by using sham sensitization.

RESULTS

The prevalence of most BRS was between 32% and 62%. Positive HRT, showing serum IgE specific to one or more of the moulds, was observed in 37% of the individuals. The highest frequency of positive HRT was found to Penicillium chrysogenum and then to Aspergillus species, Cladosporium sphaerospermum and Stachybotrys chartarum. A significant association was found between most BRS and positive HRT, whereas no association was observed between positive HRT to moulds and self reported hay fever or asthma.

CONCLUSION

Positive HRT to indoor moulds, showing the presence in serum of IgE specific to the fungi, was found to be related to BRS in individuals working in damp and mouldy buildings. Whether the association is of causal character is a question for further studies. The test may be useful in the evaluation and study of possible mould induced BRS.

Exposure to cold and draught, alcohol consumption, and the NS-phenotype are associated with chronic bronchitis: an epidemiological investigation of 3387 men aged 53-75 years: the Copenhagen Male Study

OBJECTIVES

This study was performed to estimate the strength of association between chronic bronchitis and lifetime exposure to occupational factors, current lifestyle, and the NS-phenotype in the MNS blood group among middle aged and elderly men.

METHODS

The study was carried out within the frameworks of the Copenhagen Male Study. Of 3387 men 3331 men with a mean age of 63 (range 53-75) years could be classified by prevalence of chronic bronchitis. As well as the completion of a large questionnaire on health, lifestyle, and working conditions, all participants had a thorough examination, including measurements of height and weight and blood pressure and a venous blood sample was taken for the measurement of serum cotinine and MNS typing; 16.5% of the men had the NS-phenotype. Chronic bronchitis was defined as cough and phlegm lasting 3 months or more for at least 2 years; 14.6% had chronic bronchitis.

RESULTS

Smoking and smoke inhalation were the factors most strongly associated with prevalence of chronic bronchitis. There were three major new findings: (a) long term (>5 years) occupational exposure to cold and draught was associated with a significantly increased prevalence of chronic bronchitis; compared with others, and adjusted for confounders, the odds ratio (OR) with 95% confidence interval (95% CI) was 1.4 (1.1 to 1.7), p=0.004; (b) a significant J shaped association existed between alcohol use and bronchitis, p<0.001, with the lowest prevalence found among moderate users; (c) a significant gene by environment association existed between smoking and the NS-phenotype in the MNS blood group; only among smokers was the NS-phenotype associated with a significantly decreased risk of chronic bronchitis, OR 0.67 (0.47-0.97), p=0.02. Other well known associations between dust, fumes, and even exposure to solvents and bronchitis were confirmed.

CONCLUSION

The results emphasise the multifactorial nature of chronic bronchitis, and show some hitherto unrecognised associations between cold and draught exposure, alcohol consumption, and the NS-phenotype and chronic bronchitis.

The structure and thermotropic phase behaviour of dipalmitoylphosphatidylcholine codispersed with a branched-chain phosphatidylcholine

The structure and thermotropic phase behaviour of a fully hydrated binary mixture of dipalmitoylphosphatidylcholine and a branched-chain phosphatidylcholine, 1, 2-di(4-dodecyl-palmitoyl)-sn-glycero-3-phosphocholine, were examined using differential scanning calorimetry, synchrotron X-ray diffraction and freeze-fracture electron microscopy. The branched-chain lipid forms a nonlamellar phase when dispersed alone in aqueous medium. Mixed aqueous dispersions of the two phospholipids containing less than 33 mol% of the branched-chain lipid form lamellar phases over the whole temperature range were studied (4 degrees C to 60 degrees C). When present in proportions greater than 33 mol% it induces a hexagonal phase in mixed aqueous dispersions with dipalmitoylphosphatidylcholine at temperatures above the fluid phase transition. At temperatures below 35 degrees C a hexagonal phase coexists with a gel bilayer phase. The lamellar<-->nonlamellar transition can be explained satisfactorily on the basis of the shape of the molecule expressed in terms of headgroup and chain cross-sectional areas. At temperatures below 35 degrees C macroscopic phase separation of two gel phases takes place. Freeze-fracture electron microscopy revealed that one gel phase consists of bilayers with a highly regular, periodic superstructure (macro-ripples) whereas the other phase forms flat, planar bilayers. The macro-ripple phase appears to represent a relaxation structure required to adapt to the packing constraints imposed by the incorporation of the branched-chain lipid into the dipalmitoylphosphatidylcholine host bilayer. The data suggest that structural changes that take place on cooling the mixed dispersion below the lamellar<-->nonlamellar phase transition temperature cannot be adequately described using the molecular form concept. Instead it is necessary to take into account the detailed molecular form of the guest lipid as well as its physical properties.

Hydration of DMPC and DPPC at 4 degrees C produces a novel subgel phase with convex-concave bilayer curvatures

Hydration of dimyristoyl- and dipalmitoylphosphatidylcholines at 4 degrees C results in the formation of a characteristic subgel phase designated Pcc. Examination of the phase by freeze-fracture electron microscopy shows convex-concave deformations of the planar bilayer which are of two types. A smaller type with a radius of curvature of about 20 nm predominates in DMPC, and a larger type with about 70 nm radii of curvatures dominates in DPPC. The Pcc phase can also be formed in samples hydrated at temperatures above the main phase transition if the dispersion is frozen slowly and subsequently incubated at 4 degrees C for several days. The subgel Pcc phase was distinguished from the subgel Lc phase by the temperature of transition, packing of the acyl chains on the basis of wide-angle X-ray diffraction, and 2H-NMR spectra characteristic of a 'solid-ordered' phase. Vibrational spectra of the carbonyl and phosphate regions are consistent with a partially reduced hydration state. The origin of the convex-concave bilayer deformation is believed to result from constraints imposed by limiting hydration of the headgroup and a frustration arising from the spontaneous curvature of both monolayers.

Ultrastructural characterization of peptide-induced membrane fusion and peptide self-assembly in the lipid bilayer

The peptide sequence B18, derived from the membrane-associated sea urchin sperm protein bindin, triggers fusion between lipid vesicles. It exhibits many similarities to viral fusion peptides and may have a corresponding function in fertilization. The lipid-peptide and peptide-peptide interactions of B18 are investigated here at the ultrastructural level by electron microscopy and x-ray diffraction. The histidine-rich peptide is shown to self-associate into two distinctly different supramolecular structures, depending on the presence of Zn(2+), which controls its fusogenic activity. In aqueous buffer the peptide per se assembles into beta-sheet amyloid fibrils, whereas in the presence of Zn(2+) it forms smooth globular clusters. When B18 per se is added to uncharged large unilamellar vesicles, they become visibly disrupted by the fibrils, but no genuine fusion is observed. Only in the presence of Zn(2+) does the peptide induce extensive fusion of vesicles, which is evident from their dramatic increase in size. Besides these morphological changes, we observed distinct fibrillar and particulate structures in the bilayer, which are attributed to B18 in either of its two self-assembled forms. We conclude that membrane fusion involves an alpha-helical peptide conformation, which can oligomerize further in the membrane. The role of Zn(2+) is to promote this local helical structure in B18 and to prevent its inactivation as beta-sheet fibrils.

Morphological transitions of brain sphingomyelin are determined by the hydration protocol: ripples re-arrange in plane, and sponge-like networks disintegrate into small vesicles

The phase transition of hydrated brain sphingomyelin occurs at around 35 degrees C, which is close to the physiological temperature. Freeze-fracture electron microscopy is used to characterize different gel state morphologies in terms of solid-ordered and liquid-ordered phase states, according to the occurrence of ripples and other higher-dimensional bilayer deformations. Evidently, the natural mixed-chain sphingomyelin does not assume the flat L beta, phase but instead the rippled P beta, phase, with symmetric and asymmetric ripples as well as macroripples and an egg-carton pattern, depending on the incubation conditions. An unexpected difference was observed between samples that are hydrated above and below the phase transition temperature. When the lipid is hydrated at low temperature, a sponge-like network of bilayers is formed in the gel state, next to some normal lamellae. The network loses its ripples during cold-incubation, which indicates the formation of a liquid-ordered (lo) gel phase. Ripples re-appear upon warming and the sponge-like network disintegrates spontaneously and irreversibly into small vesicles above the phase transition.

Membrane structure of caveolae and isolated caveolin-rich vesicles

Caveolae are specialized invaginated domains of the plasma membrane. Using freeze-fracture electron microscopy, the shape of caveolae and the distribution of intramembrane particles (integral membrane proteins) were analyzed. The caveolar membrane is highly curved and forms flask-like invaginations with a diameter of 80-120 nm with an open porus of 30-50 nm in diameter. The fracture faces of caveolar membranes are nearly free of intramembrane particles. Protein particles in a circular arrangement surrounding the caveolar opening were found on plasma membrane fracture faces. For isolation of caveolin-enriched membrane vesicles, the method of Triton X-100 solubilization, as well as a detergent-free isolation method, was used. The caveolin-rich vesicles had an average size of between 100 and 200 nm. No striated coat could be detected on the surface of isolated caveolin-rich vesicles. Areas of clustered intramembrane particles were found frequently on membrane fracture faces of caveolin-rich vesicles. The shape of these membrane protein clusters is often ring-like with a diameter of 30-50 nm. Membrane openings were found to be present in the caveolin-rich membrane vesicles, mostly localized in the areas of the clustered membrane proteins. Immunogold labeling of caveolin showed that the protein is a component within the membrane protein clusters and is not randomly distributed on the membrane of caveolin-rich vesicles.

Minimal radius of curvature of lipid bilayers in the gel phase state corresponds to the dimension of biomembrane structures "caveolae"

Caveolae are membrane invaginations with a radius of curvature in the range of 40 nm for the bulb; 10-15 nm is the minimal radius for lipid bilayers in the liquid-crystalline Lalpha (liquid-disordered: ld) phase state. A minimal radius of 20-30 nm could be detected for the gel phase state by analysis of convex-concave bilayer deformations. Circular protrusions with a diameter in the range of only about 40 nm are closed by a flat lid, and those with diameters of 60 nm or more are closed by hemispherical caps. These structures are found primarily in phosphatidylcholine/sterol mixtures, where the gel phase state "liquid ordered" (lo) has been introduced. As a further example the mixture of dimyristoylphosphatidylcholine (DMPC) with an unusual sterol (diflucortolon-21-valerat) is presented. In the usual hydration at temperatures above the phase transition the deformation requires an incubation at 4 degrees C for several weeks or months to form. Using a low temperature hydration procedure (at 4 degrees C), surprisingly bilayers of pure DMPC and DPPC (dipalmitoylphosphatidylcholine) are found to deform in the same convex-concave manner, and this takes place within hours and days. The dependence on hydration protocol is also observed for formation of a sponge-like bilayer network with 30-35 nm radius of curvature in brain sphingomyelin and its mixtures with cholesterol. Caveolae are microdomains enriched in cholesterol and sphingomyelin and are simultaneously discussed to be in the lo state. Direct evidence by investigation of bilayers formed by the lipids isolated from caveolae is still lacking, but structures similar to caveolae which are in the gel phase state (very probably the lo state) are also formed by lipids extracted from bacterial membranes. A further analogy exists because both natural lipid mixtures (brain sphingomyelin and bacterial lipids) transform during heating from the curved bilayer structures into microvesicles above the phase transition. Internalization of caveolae is a process of vesicle formation.

High-pressure freezing causes structural alterations in phospholipid model membranes

The influence of high-pressure freezing (HPF) on the lipid arrangement in phospholipid model membranes has been investigated. Liposomes consisting of pure dipalmitoyl-phosphatidylcholine (DPPC) and of DPPC mixed with a branched-chain phosphocholine (1,2-di(4-dodecyl-palmitoyl)- sn-glycero-3-phosphocholine) have been analysed by freeze-fracture electron microscopy. The liposomes were frozen either by plunging into liquid propane or by HPF. The characteristic macroripple-phase of the two-component liposome system is drastically changed in its morphology when frozen under high-pressure conditions. The influence of ethanol which acts as pressure transfer medium was ruled out by control experiments. In contrast, no high-pressure alterations of the pure DPPC bilayer membrane have been observed. We assume that the modification of the binary system is due to a pressure-induced relaxation of a stressed and unstable lipid molecule packing configuration. HPF was performed with a newly designed sample holder, for using sandwiched copper platelets with the high-pressure freezing machine Balzers HPM010. The sandwich construction turned out to be superior to the original holder system with regard to freeze-fracturing of fluid samples. By inserting a spacer between the supports samples with a thickness of 20-100 microns can be high-pressure frozen. The sandwich holder is provided with a thermocouple to monitor cooling rates and allows exact sample temperature control. Despite a two-fold mass reduction compared to the original holder no HPF cooling rate improvement has been achieved (4000 degrees Cs-1). We conclude that the cooling process in high-pressure freezing is determined mainly by cryogen velocity.

DQAsomes: a novel potential drug and gene delivery system made from Dequalinium

PURPOSE

Dequalinium, a drug known for over 30 years, is a dicationic amphiphile compound resembling bolaform electrolytes. The purpose of our work was to determine the state of aggregation of dequalinium in aqueous medium and to investigate both, its ability to bind DNA and its potential to serve as a novel non-viral transfection vector.

METHODS

The form of aggregation was determined employing electron microscopic techniques. The DNA binding capacity of dequalinium was assayed using SYBR Green I stain. For in vitro cell transfection experiments plasmid DNA encoding for firefly luciferase was used.

RESULTS

Dequalinium forms in aqueous medium liposome-like aggregates, which we term DQAsomes. These dequalinium vesicles bind DNA and they are able to transfect cells in vitro with an efficiency comparable to Lipofectin.

CONCLUSIONS

Based on the intrinsic properties of dequalinium such as the in vivo selectivity for carcinoma cells and selective accumulation in mitochondria we propose DQAsomes as a novel and unique drug and gene delivery system.

Characterization of the nonlamellar cubic and HII structures of lipid A from Salmonella enterica serovar Minnesota by X-ray diffraction and freeze-fracture electron microscopy

The aggregate structures of lipid A, the 'endotoxic principle' of bacterial lipopolysaccharide (LPS), from rough mutant Salmonella enterica sv. Minnesota R595 was analyzed at different water content, cation (Mg2+) concentration, and temperature applying synchrotron radiation X-ray diffraction and, in selected cases, freeze-fracture electron microscopy. The X-ray diffraction spectra prove the existence of different lamellar, mixed lamellar/cubic, various cubic, and inverted hexagonal (HII) structures depending on ambient conditions. The three mainly bicontinuous cubic phases Q224, Q229, and Q230 can be observed between 30 and 50 degrees C in narrow water and cation concentration ranges. Above 50 degrees C, Q212 an intermediate phase between bicontinuous and micellar is adopted. In freeze-fracture electron microscopic experiments, cubic structures of these symmetries are not readily detected, which can be understood in the light of changes in hydration during freezing and the metastability of these phases. However, 'lipidic particles' closely related to cubic phases are observed. Above 65-70 degrees C, the existence of the HII phase with hexagonal periodicities dH between 4.0 and 6.0 nm for different hydration states is shown using both techniques. Possible biological implications for the preference of lipid A for nonlamellar structures are discussed.

The effect of sterols on structures formed in the gel/subgel phase state of dipalmitoylphosphatidylcholine bilayers

The effect of cholesterol and lanosterol on the formation of structures in the gel/subgel phase of 1,2-dipalmitoylphosphatidylcholine was investigated using freeze-fracture electron microscopy and X-ray diffraction. Mixtures with up to 25 mol% sterol were analysed after annealing for between several days and some months at 4 degrees C. Bilayers of DPPC with 5 or 10 mol% sterol showed a domain structure in the gel state. There are rounded or lens-like and often inclined plates within less smooth either plane or striped bilayer areas. The stripes are formed by parallel lines separated by a distance of 30-60 nm. Parallel lines can be induced also in the less smooth but plane areas by warming up to 25 degrees C. X-ray diffraction showed two lamellar repeat spacings at 6.45 and 8.3 nm in both 5 and 10 mol% samples. The plates are interpreted as domains of (nearly) pure DPPC within the sterol containing bilayer. Stripes are present if the concentration of cholesterol is below a critical value (approx. 15 mol%). With time of incubation at 4 degrees C curved deformations appear in parts of the bilayers. Two main types are formed. The small type has a repeat distance of about 100 nm and the large type of about 400 nm. The curved deformations were progressively flattened by warming up to 25-32 degrees C with an accompanying reappearance of stripes but no plates. After prolonged annealing at 4 degrees C there is also the formation of regular ripples. It is concluded that in presence of 5 and 10 mol% sterol in bilayers of 1,2-dipalmitoy-phosphatidylcholine the immiscibility of gel phase and subgel phase changes during prolonged annealing at 4 degrees C. We assume a rearrangement of the molecules into a homogeneous phase state with liquid-ordered properties.

Pulsed Field Gradient NMR Self-Diffusion Study in Distinct Phases of the Ternary System Water/n -Heptane/Igepal CA-520

We report on self-diffusion measurements of all the components in distinct phases of the ternary system water/n -heptane/Igepal CA-520 with pulsed field gradient NMR. The phases are also investigated with electron microscopy. The observed self-diffusion coefficients are discussed in comparison with the structural data obtained from the micrographs. They intimately reflect the effect of the phase state and phase boundaries on the molecular transport in this system.

Pretransition-ripples in bilayers of dipalmitoylphosphatidylcholine: undulation or periodic segments? A freeze-fracture study

Freeze-fracture analysis of ripple structures of 1,2-dipalmitoylphosphatidylcholine bilayers leads to the conclusion that the asymmetric ripple is the basic structure formed by periodic segments with different tilt direction. The molecules are tilted by about 30 degrees from the bilayer normal but arranged in two positions. Symmetric ripples are also formed by an alternation in tilt direction of the segments but the succession is more complex. A ridge in their valleys or a cleft at their crests may indicate structures formed or deformed during preparation (replication, etching). The freeze-fracture method reveals transition structures in ripple formation which are helpful in interpretation, but does not support a model consisting of an undulation of the bilayer by periodic fluid-like and gel-like domains.

The appearance of cytoplasmic membranes of Escherichia coli cells in freeze-fracture electron microscopy after stringent and relaxed response

Guanosine-5'-diphosphate-3'-diphosphate (ppGpp), an effector for many metabolic pathways, is synthesized by the relA gene product after amino acid limitation. Studies of stringent controlled Escherichia coli CP78 (relA+) and relaxed controlled E. coli CP79 (relA-) were carried out to test whether these strains differ in the appearance of their cytoplasmic membranes after induction of stringent and relaxed response. Cytoplasmic membrane structures of the cells were investigated by freeze-fracture electron microscopy after cooling the cells. The obtained micrographs showed a net-like distribution of the particles in the cytoplasmic membranes of relaxed controlled cells whereas such a pattern was not detectable in the stringent controlled counterparts.

Is the brush border membrane of the intestinal mucosa a generator of "chymosomes"?

1. The microvilli of enterocytes in calf intestine demonstrate high levels of vesiculation activity at the top and at the basal region. 2. The morphology of the vesicles associated with microvilli (100-500 nm diameter, unilamellar, few intramembraneous particles, high AP activity) is very similar to the morphology of vesicles found in the chyme. 3. Vesicles can be purified 6-10 fold from chyme of the calf intestine applying a Mg(++)-precipitation method, used for brush border membrane preparation. 4. Specific activities of alkaline phosphatase and disaccharidases were found to be much higher in chyme vesicles than in the mucosa. 5. Phospholipid content and phospholipid composition is in chyme vesicles different from brush border membrane vesicles. 6. The characterized chyme vesicles are referred to as chymosomes. We consider the mucosa as a large-scale generator of chymosomes, i.e. digestive enzymes bearing vesicles.

Convex-concave curvatures in bilayers of dipalmitoylphosphatidylcholine and cholesterol induced by amphotericin B/deoxycholate after prolonged storage

Freeze-fracture investigations on the influence of amphotericin B/deoxycholate on multilamellar vesicles (MLV) of DPPC containing cholesterol have revealed a new phase structure. Alternating convex and concave curvatures are observed after storage of the vesicles at temperatures below 25 degrees C for at least 4 weeks. Three types of these patterns occur, a small-dimensional (repeat distance approximately 100 nm), an intermediate-dimensional (repeat distance approximately 400 nm) and a large-dimensional (repeat distance approximately 700 nm). The types can be formed on the same bilayer side by side. Additionally, the types differ in the morphology of the tops. In the case of the small-dimensional type the shape of the top can be described as a circular flat plane or opening and in the other cases as a hemispherical cap. The large dimensional type differs from the others by involvement of bilayer stacks. The formation of this new phase after prolonged storage could be confirmed by DSC measurements. The new structure can be explained in the framework of bicontinuous cubic phases and periodically curved bilayer structures. From the electron micrographs a lo (liquid ordered) phase is suggested.

Membrane topology of microsomal cytochrome P-450: saturation transfer EPR and freeze-fracture electron microscopy studies

The rotation of cytochrome P-450 LM2 (CYPIIB4) incorporated into large microsomal-like lipid vesicles was investigated by saturation transfer EPR using 15N- and 2H-substituted spin labels. In combination with rotational diffusion, the distribution and size of protein particles in the bilayer were studied by freeze-fracture electron microscopy. The data from both methods suggest an oligomeric and membrane-spanning aggregate for the topology of microsomal cytochrome P-450.

Periodically curved bilayer structures observed in hyphal cells or stable L-form cells of a Streptomyces strain, and in liposomes formed by the extracted lipids

Periodically curved bilayer structures showing a tetragonal pattern were revealed by freeze-fracture electron microscopy in hyphal cells, stable L-form cells, and liposomes prepared from extracted lipids of Streptomyces hygroscopicus NG 33-354. The pattern is formed by alternating convex and concave curvatures of the bilayer. It has been found with different repeat distances (multiples of about 15 nm) and with a different degree of expression (from just visible to very pronounced). An interpretation as infinite periodic minimal surface (IPMS) structures is more probable than an inducement of the pattern by underlying small vesicles. The occurrence of nonbilayer textures and the similarity of the tetragonal pattern with a 'bilayer sector' from a cubic phase structure (Anderson, S. et al. (1988) Chem. Rev. 88, 221-242) support such an interpretation.

Hyperosmotic relaxation lysis of chromaffin granules is caused by interactions between the granular membrane and intragranular vesicles

Bovine chromaffin granules undergo irreversible structural changes during osmotic shrinkage in hypertonic sucrose and salt solutions, such that, on reexposure to isoosmotic conditions they do not regain their original morphology, but undergo lysis ('hyperosmotic relaxation lysis'). Irreversible alterations of granules were induced by hypertonic incubations lasting for as little as 1 min. Fluorescence and EPR membrane labelling experiments showed that hypertonicity did not induce membrane loss for instance by inwardly or outwardly directed pinching off of membrane material. The mean sizes of chromaffin granules as a function of increasing and subsequently decreasing osmotic pressure were measured by photon correlation spectroscopy; there was no significant difference in sizes of hyperosmotically pretreated granules as compared with controls. Freeze-fracture electron micrographs showed the formation of 'twins' and 'triplets' under hypertonic conditions. They also revealed intragranular vesicles of 50-200 nm in diameter in both hypertonically and isotonically suspended granules. 'Twin' and 'triplet' granules were formed by the attachment of intragranular vesicles to the granule membranes. We suggest that hyperosmotic relaxation lysis is caused by the fact that this adhesion partly prevents the granule membrane from reexpanding, thus, leading to its rupture.

[Extracorporeal shockwave lithotripsy in chronic pancreatitis]

Extracorporeal shock wave lithotripsy was performed on eight patients (six men, two women; mean age 46.3 years, range 36-58) with predominantly stone-induced obstructive pancreatitis. Stones in the pancreatic duct were smashed in one session to such an extent that the fragments were eliminated spontaneously via the ostium which had previously been split endoscopically. Repeat lithotripsy to achieve complete removal was necessary in only two patients. In one there were multiple concrements along the entire length of the main pancreatic duct; the other had a cherry-sized stone near the bifurcation of the accessory pancreatic duct. There were no serious complications. After successful removal of the stones all patients were free of pain which before had required strong analgesics to control. Six patients remained pain-free during a follow-up period of two eight months. Pain again occurred in the other two, but it was less frequent and milder.

The influence of poly(ethylene glycol) on the molecular dynamics within the glycocalyx

Interaction of polymers with cell surfaces is a question of general interest for cell aggregation and fusion. The molecular dynamics within the surface coat of human erythrocytes as well as alterations of membrane protein arrangement (IMPs) in the presence of poly(ethylene glycol) (PEG) were investigated by EPR spin labeling techniques and freeze-fracture electron microscopy, respectively. AT PEG concentrations which induce aggregation of erythrocytes the surface coat and the protein arrangement is not disturbed by the polymer. This implicate an exclusion of the polymer from the cell surface.

The phase diagram of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/sucrose in the dry state. Sucrose substitution for water in lamellar mesophases

The phase diagram of the binary system, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)/sucrose, was determined by DSC. In contrast to dry DPPC, which exhibits chain melting at 342.5 K, the main feature of the DPPC/sucrose system is eutectic melting at 320 K. This was supported earlier by Crowe, J.H., Crowe, L.M. and Chapman, D. (Science 223 (1984) 701-703), who reported a drastic decrease in the chain-melting temperature of the dry lipid in the presence of some mono- and disaccharides. Electron microscopy suggests that the phase structures on either side of the phase transition are of the lamellar type. Definite sugar saturation concentrations can be derived from this phase diagram. Up to about 17 mol% sucrose, i.e., 1 mol of sucrose per 5 mol of lipid is adopted by DPPC in the low-temperature phase Lc. In the high-temperature phase Lm the saturation concentration is well above 90 mol% sucrose at 320 K (eutectic point) but decreases with increasing temperature. The lower limit of 50 mol% sucrose is reached at 455 K. At this temperature, peritectic melting of sucrose occurs. Because of some similarities in the phase diagrams of DPPC/sucrose and DPPC/water, it is possible to understand the sucrose substitution for water in dry lamellar mesophases.

The preparation and characterization of lipid vesicles containing esters of sucrose and fatty acids

Encapsulation and electron microscopy studies have shown that aqueous dispersions of several nonionic emulsifiers with sucrosepalmitatestearate (SPS) structure and cholesterol (Chol) result in synthetic lipid vesicles. This was demonstrated for the commercial emulsifier sucrosepalmitatestearate for the first time. Such vesicles were able to entrap aqueous solutes, for instance the fluorescence marker carboxyfluorescein (CF) for a period of more than 10 weeks with latencies of about 90 per cent. Though SPS/Chol-vesicles tended to flocculate--especially in concentrated solutions--the efflux of entrapped solutes after storage was lower in these vesicles compared with liposomes consisting of natural egg phosphatidylcholine (EPC) and cholesterol.

Spatially periodic discrete contact regions in polylysine-induced erythrocyte-yeast adhesion

Cell-cell adhesion occurs when human erythrocytes and yeast cells are suspended together in suprathreshold concentrations of polylysine in saline. The threshold polycation concentration for adhesion depends on cell concentration and decreases with increasing polycation molecular weight. The threshold concentration was similar for erythrocyte-erythrocyte adhesion and for yeast-erythrocyte adhesion. Transmission electron micrographs show that the erythrocytes adhere to yeast as if to engulf the cell. The regions of close contact between the erythrocyte membrane and the yeast cell walls are spatially discrete. The contact separation distance for the asymmetric erythrocyte-yeast adhesion is very similar to that (0.83 micron) observed when polylysine-induced adhesion occurs in the symmetrical erythrocyte-erythrocyte system. The spacing is attributed to the growth of a squeezing wave as an interfacial instability, on the intercellular aqueous layer. Freeze-fracture electron microscopy of cells that were not fixed during preparation for microscopy confirms the discrete nature of contacts between polylysine treated erythrocytes.