Factors associated with an increased risk of SARS-CoV-2 infection in healthcare workers in aerosol-generating disciplines

BACKGROUND

Healthcare workers (HCWs) are at a high risk of SARS-CoV-2 infection due to exposure to potentially infectious material, especially during aerosol-generating procedures (AGP). We aimed to investigate risk factors for SARS-CoV-2 infection among HCWs in medical disciplines with AGP.

METHODS

A nationwide questionnaire-based study in private practices and hospital settings was conducted between 12/16/2020 and 01/24/2021. Data on SARS-CoV-2 infections among HCWs and potential risk factors of infection were investigated.

RESULTS

2070 healthcare facilities with 25113 employees were included in the study. The overall infection rate among HCWs was 4.7%. Multivariate analysis showed that regions with higher incidence rates had a significantly increased risk of infection. Furthermore, hospital setting and HCWs in gastrointestinal endoscopy (GIE) had more than double the risk of infection (OR 2.63; 95% CI 2.50-2.82, p<0.01 and OR 2.35; 95% CI 2.25-2.50, p<0.01). For medical facilities who treated confirmed SARS-CoV-2 cases, there was a tendency towards higher risk of infection (OR 1.39; 95% CI 1.11-1.63, p=0.068).

CONCLUSION

Both factors within and outside medical facilities appear to be associated with an increased risk of infection among HCWs. Therefore, GIE and healthcare delivery setting were related to increased infection rates. Regions with higher SARS-CoV-2 incidence rates were also significantly associated with increased risk of infection.

One year of COVID-19 pandemic: Health care workers' infection rates and economical burden in medical facilities for oral and maxillofacial surgery

The aim of this study was to create an overview on the COVID-associated burdens faced by the oral and maxillofacial surgery (OMS) workforce during 1 year of the pandemic. OMS hospitals and private practices nationwide were surveyed regarding health care worker (HCW) screening, infection status, pre-interventional testing, personal protective equipment (PPE), and economic impact. Participants were recruited via the German Society for Oral and Maxillofacial Surgery. A total of 11 hospitals (416 employees) and 55 private practices (744 employees) participated. The HCW infection rate was significantly higher in private practices than in clinics (4.7% vs. 1.4%, p<0.01), although most infections in HCW occurred in private environment (hospitals 88.2%, private practice 66.7%). Pre-interventional testing was performed significantly less for outpatients in private practices than in hospitals (90.7% vs. 36.4%, p<0.01). Polymerase chain reaction (PCR) was used significantly more for inpatients in hospitals than in private practices (100.0% vs. 27.3%, p<0.01). FFP2/3 use rose significantly in hospitals (0% in second quarter vs. 46% in fourth quarter, p<0.05) and private practices (15% in second quarter vs. 38% in fourth quarter, p<0.01). The decrease in procedures (≤50%) was significantly higher in hospitals than in private practices (90.9% vs. 40.0%, p<0.01). Despite higher infection rates in private practices, declining procedures and revenue affected hospitals more. Future COVID-related measures must adjust the infrastructure especially for hospitals to prevent further straining of staff and finances.

SARS-CoV-2 Vaccination Rate and SARS-CoV-2 Infection of Health Care Workers in Aerosol-Generating Medical Disciplines

Healthcare workers (HCW) who perform aerosol-generating procedures (AGP) are at high risk of SARS-CoV-2 infection. Data on infection rates and vaccination are limited. A nationwide, cross-sectional study focusing on AGP-related specialties was conducted between 3 May 2021 and 14 June 2021. Vaccination rates among HCW, perception of infection risk, and infection rates were analyzed, focusing on the comparison of gastrointestinal endoscopy (GIE) and other AGP-related specialties (NON-GIE), from the beginning of the pandemic until the time point of the study. Infections rates among HCW developed similarly to the general population during the course of the pandemic, however, with significantly higher infections rates among the GIE specialty. The perceived risk of infection was distributed similarly among HCW in GIE and NON-GIE (91.7%, CI: 88.6−94.4 vs. 85.8%, CI: 82.4−89.0; p < 0.01) with strongest perceived threats posed by AGPs (90.8%) and close patient contact (70.1%). The very high vaccination rate (100−80%) among physicians was reported at 83.5%, being significantly more frequently reported than among nurses (56.4%, p < 0.01). GIE had more often stated very high vaccination rate compared with NON-GIE (76.1% vs. 65.3%, p < 0.01). A significantly higher rate of GIE was reported to have fewer concerns regarding infection risk after vaccination than NON-GIE (92.0% vs. 80.3%, p < 0.01).

Status quo after one year of COVID-19 pandemic in otolaryngological hospital-based departments and private practices in Germany

PURPOSE

The COVID-19 pandemic has affected healthcare systems worldwide. Data on the impact on otolaryngological clinics and private practices is sparse. This study aimed to present data on healthcare worker (HCW) screening, status of HCW, pre-interventional testing, the use of personal protective equipment (PPE) and the economic impact of the pandemic.

METHODS

Otolaryngological private practices and hospital-based departments were surveyed nationwide using an online questionnaire. Participating facilities were recruited via the German Society for Oto-Rhino-Laryngology and the German Association for Otolaryngologists in Bavaria.

RESULTS

365 private practices (2776 employees) and 65 hospitals (2333 employees) were included. Significantly more hospitals (68.7%) than practices (40.5%) performed pre-interventional testing in their outpatients (p < 0.00). Most inpatients were tested in practices and hospitals (100.0% and 95.0%; p = 0.08). HCW screening was performed in 73.7% of practices and in 77.3% of hospitals (p = 0.54). Significantly more HCW infections were reported in private practices (4.7%) than in hospital (3.6%; p = 0.03). The private or home environment was the most frequent source of infection among HCW in hospitals (44%) and practices (63%). The use of PPE increased over the course of the pandemic. The number of procedures and the revenue decreased in 2020.

CONCLUSION

The rate of pre-interventional testing among outpatients in otolaryngological practices is low and HCW infections were found to be more frequent in practices than in hospitals. In addition, a high rate of infections in otolaryngological HCW seems to stem from the private or home environment.

One Year of the COVID-19 Pandemic in Dental Medical Facilities in Germany: A Questionnaire-Based Analysis

(1) Background: The COVID-19 pandemic forced healthcare workers to adapt to challenges in both patient care and self-protection. Dental practitioners were confronted with a potentially high possibility of infection transmission due to aerosol-generating procedures. This study aims to present data on healthcare worker (HCW) screening, infection status of HCWs, pre-interventional testing, the use of personal protective equipment (PPE) and the economic impact of the pandemic in dental facilities. (2) Methods: Dental facilities were surveyed nationwide using an online questionnaire. The acquisition of participants took place in cooperation with the German Society for Dentistry, Oral and Maxillofacial Medicine. (3) Results: A total of 1094 private practices participated. Of these, 39.1% treated fewer than 600 patients per quarter and 59.9% treated over 600 patients per quarter. Pre-interventional testing was rarely performed in either small (6.6%) or large practices (6.0%). Large practices had a significantly higher incidence of at least one SARS-CoV-2-positive HCW than small practices (26.2% vs.14.4%, p < 0.01). The main source of infection in small practices was the private environment, and this was even more significant in large practices (81.8% vs. 89.7%, p < 0.01). The procedure count either remained stable (34.0% of small practices vs. 46.2% of large practices) or decreased by up to 50% (52.6% of small practices vs. 44.4% of large practices). Revenue remained stable (24.8% of small practices vs. 34.2% of large practices) or decreased by up to 50% (64.5% of small practices vs. 55.3% of large practices, p = 0.03). Overall, employee numbers remained stable (75.5% of small practices vs. 76.8% of large practices). A vaccination readiness of 60-100% was shown in 60.5% (n = 405) of large practices and 59.9% (n = 251) of small practices. (4) Conclusion: Pre-interventional testing in dental practices should be increased further. Economic challenges affected small practices as well as large practices. Overall, a steady employee count could be maintained. Vaccination readiness is high in dental practices, although with some room for improvement.

[Impact of Covid 19 on endoscopy in Germany]

BACKGROUND

Practices and hospitals are facing great challenges in coping with the COVID-19-pandemic. So far, data on the impact of the pandemic on gastroenterological facilities are lacking, especially on a temporal course. A database is lacking, especially for the outpatient care sector. University Hospital of Augsburg was commissioned to generate data on this as a part of the collaborative project B-FAST of the Network of University Medicine (NUM).

METHODS

Gastroenterological institutions nationwide were surveyed by an online questionnaire. Recruitment was carried out via the German Society of Gastroenterology, Digestive and Metabolic Diseases (DGVS) and the Professional Association of Gastroenterologists in Private Practice (bng). This manuscript provides an overview of data on the use of protective equipment, pre-interventional testing of patients, staff screening and economic impact over the course of the pandemic.

RESULTS

429 facilities answered the questionnaire. Practices tested their patients pre-interventionally significantly less often than clinics (7.8% vs. 82.6%). In clinics, inpatients (93.1%) were tested significantly more often than outpatients (72.2%). The use of personal protective equipment (PPE) increased significantly during the pandemic. It was shown that over 70% of facilities screened their staff for SARS-CoV-2 without cause. Clinics cancelled elective procedures significantly more often than practices in quarter 4/2020. Procedures and turnover decreased in 2020 compared to the previous year. However, fewer facilities were affected by a loss of revenue than expected in previous studies.

CONCLUSION

Our data demonstrate the variable implementation of pre-interventional SARS-CoV-2 testing in outpatient and inpatient care. The use of adequate PPE and staff screening increased during the pandemic.

Gastrointestinal bleeding and endoscopic findings in critically and non-critically ill patients with corona virus disease 2019 (COVID-19): Results from Lean European Open Survey on SARS-CoV-2 (LEOSS) and COKA registries

BACKGROUND

Corona virus disease 2019 (COVID-19) patients are at increased risk for thromboembolic events. It is unclear whether the risk for gastrointestinal (GI) bleeding is also increased.

METHODS

We considered 4128 COVID-19 patients enrolled in the Lean European Open Survey on SARS-CoV-2 (LEOSS) registry. The association between occurrence of GI bleeding and comorbidities as well as medication were examined. In addition, 1216 patients from COKA registry were analyzed focusing on endoscopy diagnostic findings.

RESULTS

A cumulative number of 97 patients (1.8%) with GI bleeding were identified in the LEOSS registry and COKA registry. Of 4128 patients from the LEOSS registry, 66 patients (1.6%) had a GI bleeding. The rate of GI bleeding in patients with intensive care unit (ICU) admission was 4.5%. The use of therapeutic dose of anticoagulants showed a significant association with the increased incidence of bleeding in the critical phase of disease. The Charlson comorbidity index and the COVID-19 severity index were significantly higher in the group of patients with GI bleeding than in the group of patients without GI bleeding (5.83 (SD = 2.93) vs. 3.66 (SD = 3.06), p < 0.01 and 3.26 (SD = 1.69) vs. 2.33 (SD = 1.53), p < 0.01, respectively). In the COKA registry 31 patients (2.5%) developed a GI bleeding. Of these, the source of bleeding was identified in upper GI tract in 21 patients (67.7%) with ulcer as the most frequent bleeding source (25.8%, n = 8) followed by gastroesophageal reflux (16.1%, n = 5). In three patients (9.7%) GI bleeding source was located in lower GI tract caused mainly by diverticular bleeding (6.5%, n = 2). In seven patients (22.6%) the bleeding localization remained unknown.

CONCLUSION

Consistent with previous research, comorbidities and disease severity correlate with the incidence of GI bleeding. Also, therapeutic anticoagulation seems to be associated with a higher risk of GI bleeding. Overall, the risk of GI bleeding seems not to be increased in COVID-19 patients.

Evaluation of the ESGE recommendations for COVID-19 pre-endoscopy risk-stratification in a high-volume center in Germany

Background and study aims  The European Society of Gastrointestinal Endoscopy (ESGE) has defined COVID-19 infection prevention and control strategies within the endoscopy unit. These include pre-endoscopic questionnaire-based risk-stratification as well as pre-procedure viral testing. Real-life data on the effectiveness of these measures are presented here. Patients and methods  Data from the outpatient endoscopic unit of the University Hospital Augsburg between July 1, 2020 and December 31, 2020 including the second pandemic wave were reviewed retrospectively. All patients were assessed with a pre-endoscopic risk-stratification questionnaire as well as viral testing using an antigen point-of-care test (Ag-POCT) in conjunction with a standard polymerase chain reaction (PCR) test. Highly elective procedures were postponed. The theoretically expected number of SARS-CoV-2-positive patients was simulated and compared with the actual number. In addition, endoscopy staff was evaluated with a rapid antibody test to determine the number of infections among the personnel. Results  In total, 1029 procedures, 591 questionnaires, 591 Ag-POCTs, and 529 standard PCR tests were performed in 591 patients. 247 procedures in 142 patients were postponed. One Ag-POCT was positive but with a negative PCR test, while one PCR test was positive but with a negative Ag-POCT. This was lower than the theoretically expected number of COVID-19-positive patients (n = 15). One of 43 employees (2.3 %) in the outpatient endoscopy unit was seropositive. Conclusions  Pre-endoscopic risk management including questionnaire-based risk stratification and viral testing seems to be an effective tool in combination with personal protective equipment for SARS-CoV-2 infection prevention and control within the endoscopy unit even in a high-prevalence setting.

Performance of antigen testing for diagnosis of COVID-19: a direct comparison of a lateral flow device to nucleic acid amplification based tests

Objectives

The gold standard for diagnosing an infection with SARS-CoV-2 is detection of viral RNA by nucleic acid amplification techniques. Test capacities, however, are limited. Therefore, numerous easy-to-use rapid antigen tests based on lateral flow technology have been developed. Manufacturer-reported performance data seem convincing, but real-world data are missing.

Methods

We retrospectively analysed all prospectively collected antigen tests results performed between 23.06.2020 and 26.11.2020, generated by non-laboratory personnel at the point-of-care from oro- or nasopharyngeal swab samples at the University Hospital Augsburg and compared them to concomitantly (within 24 h.) generated results from molecular tests.

Results

For a total of 3630 antigen tests, 3110 NAAT results were available. Overall, sensitivity, specificity, NPV and PPV of antigen testing were 59.4%, 99.0%, 98.7% and 64.8%, respectively. Sensitivity and PPV were lower in asymptomatic patients (47.6% and 44.4%, respectively) and only slightly higher in patients with clinical symptoms (66.7% and 85.0%, respectively). Some samples with very low Ct-values (minimum Ct 13) were not detected by antigen testing. 31 false positive results occurred. ROC curve analysis showed that reducing the COI cut-off from 1, as suggested by the manufacturer, to 0.9 is optimal, albeit with an AUC of only 0.66.

Conclusion

In real life, performance of lateral-flow-based antigen tests are well below the manufacturer's specifications, irrespective of patient’s symptoms. Their use for detection of individual patients infected with SARS-CoV2 should be discouraged. This does not preclude their usefulness in large-scale screening programs to reduce transmission events on a population-wide scale.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06524-7.

A prospective whole-mixture approach to assess risk of the food and chemical exposome

Many widely used chemicals result in ubiquitous human exposure from multiple sources, including diet. Legislation mainly deals with the toxicological evaluation of single substances owing to a methodological and conceptual lack of alternatives, and does so within defined silos subject to over 40 distinct regulations in the EU alone. Furthermore, much of the research and many of the initiatives concerned with the assessment and evaluation of chemical mixtures and their potential effects on human health rely on retrospective analysis. Here we propose an approach for the prospective identification, assessment and regulation of mixtures relevant to human health. We address two distinct aspects of toxicology-which chemicals actually do occur together, and how potential mixture-related health hazards can be predicted-with an adapted concept of the exposome and large-scale hazard screens. The proactive use of the likelihood of co-exposure, together with the new approach of methods-based testing, may be a timely and feasible way of identifying those substances and mixtures where hazards may have been overlooked and regulatory action is needed. Ideally, we would generate co-exposure patterns for specific consumer groups, depending on lifestyle and dietary habits, to assess the specific risk of identified mixtures.

Ticagrelor or aspirin after coronary artery bypass in patients with chronic kidney disease

BACKGROUND

The optimal antiplatelet therapy for patients with chronic kidney disease (CKD) undergoing coronary artery bypass grafting (CABG) remains unknown.

METHODS

This post hoc analysis of the Ticagrelor in Coronary Artery Bypass (TiCAB) trial examined the efficacy and safety of ticagrelor versus aspirin in patients with or without CKD. Primary endpoint was the composite of cardiovascular death, stroke, myocardial infarction or revascularization (MACCE) at 1 year after CABG. Secondary endpoints included individual components of the primary endpoint, all-cause death, and major bleeding.

RESULTS

CKD was present in 276 of 1,843 randomized patients (15.0%). Patients with CKD versus those without CKD had higher 1-year rates of MACCE (13.0% vs. 8.3%, HR 1.63, 95% CI 1.12-2.39, P=0.01) and major bleeding (5.6% vs. 3.1%, HR 1.84, 95% CI 1.03-3.28, P=0.04). The 1-year rate of MACCE was increased with ticagrelor versus aspirin in patients with CKD (18.2% vs. 8.9%, HR 2.15, 95% CI 1.08-4.30, P=0.03), but not in patients without CKD (8.5% vs. 8.1%, HR 1.05, 95% CI 0.74-1.49, P=0.79) (P_interaction=0.067). There was no difference in the 1-year rate of major bleeding with ticagrelor versus aspirin in patients with CKD (6.6% vs. 4.7%, HR 1.44, 95% CI 0.52-3.97, P=0.48) and without CKD (3.3% vs. 2.9%, HR 1.14, 95% CI 0.64-2.01, P=0.65).

CONCLUSIONS

In patients with CKD and CABG, those who received ticagrelor had a higher incidence of MACCE but a similar incidence of major bleeding compared to those who received aspirin.

Minor structural modifications of bisphenol A strongly affect physiological responses of HepG2 cells

Bisphenols represent a large group of structurally similar compounds. In contrast to bisphenol A (BPA) and bisphenol S (BPS), however, toxicological data are usually scarce, thus making bisphenols an ideal candidate for read-across assessments. BPA, bisphenol C (BPC) and a newly synthesized bisphenol A/C (BPA/C) differ only by one methyl group attached to the phenolic ring. Their EC₅₀ values for cytotoxicity and logP_OW values are comparable. However, the estrogenic activities of these bisphenols are not comparable and among this group only BPC leads to a decrease of the mitochondrial membrane potential and ATP concentration in HepG2 cells. Conversely, the cell division rate was decreased by BPS, BPA, BPC and BPA/C at 10% toxicity (EC₁₀). At lower concentrations, only BPC significantly affected proliferation. The pro-inflammatory cytokines TGFB1 and TNF were significantly upregulated by BPC only, while SPP1 was upregulated by BPA, BPA/C and BPS. BPC led to the release of cytochrome c from mitochondria, indicating that this compound is capable of inducing apoptosis. In conclusion, the read-across approach revealed non-applicable in the case of the various structurally and physicochemically comparable bisphenols tested in this study, as the presence of one or two additional methyl group(s) attached at the phenol ring profoundly affected cellular physiology.

Zonation of hepatic fatty acid metabolism - The diversity of its regulation and the benefit of modeling

A pronounced heterogeneity between hepatocytes in subcellular structure and enzyme activities was discovered more than 50years ago and initiated the idea of metabolic zonation. In the last decades zonation patterns of liver metabolism were extensively investigated for carbohydrate, nitrogen and lipid metabolism. The present review focuses on zonation patterns of the latter. We review recent findings regarding the zonation of fatty acid uptake and oxidation, ketogenesis, triglyceride synthesis and secretion, de novo lipogenesis, as well as bile acid and cholesterol metabolism. In doing so, we expose knowledge gaps and discuss contradictory experimental results, for example on the zonation pattern of fatty acid oxidation and de novo lipogenesis. Thus, possible rewarding directions of further research are identified. Furthermore, recent findings about the regulation of metabolic zonation are summarized, especially regarding the role of hormones, nerve innervation, morphogens, gender differences and the influence of the circadian clock. In the last part of the review, a short collection of models considering hepatic lipid metabolism is provided. We conclude that modeling, despite its proven benefit for understanding of hepatic carbohydrate and ammonia metabolisms, has so far been largely disregarded in the study of lipid metabolism; therefore some possible fields of modeling interest are presented.

Facile surface tailoring of metal oxide nanoparticles via a two-step modification approach

We present a versatile two-step approach that allows a rational tailoring of the surface properties of metal oxide nanoparticles, showing many benefits e.g. for the realization of optimized particle–matrix interfaces in nanocomposites.

Transfection of normal human epidermal keratinocytes with lipid/dna complexes in vitro

Highly proliferative normal human epidermal keratinocytes (NHK) were isolated from human foreskin biopsies, cultivated in serum-free medium and characterized by flow cytometry. The expression of cytokeratin 19, cytokeratin 14 and vimentin indicated that the suspension contained a high percentage of undifferentiated cells of the basal epidermal layer. The NHK were transfected in vitro with lipid/DNA complexes made of Effectene or Lipofectamine and different reporter genes. The transfection efficiency of Effectene/DNA complexes was 20fold higher compared to Lipofectamine. Transfected keratinocytes continued to grow and developed within 2 weeks a cellular multilayer (3-D culture). Areas of transfected cells were detected within this layer.

Primary mouse hepatocytes for systems biology approaches: a standardized in vitro system for modelling of signal transduction pathways

Complex cellular networks regulate regeneration, detoxification and differentiation of hepatocytes. By combining experimental data with mathematical modelling, systems biology holds great promises to elucidate the key regulatory mechanisms involved and predict targets for efficient intervention. For the generation of high-quality quantitative data suitable for mathematical modelling a standardised in vitro system is essential. Therefore the authors developed standard operating procedures for the preparation and cultivation of primary mouse hepatocytes. To reliably monitor the dynamic induction of signalling pathways, the authors established starvation conditions and evaluated the extent of starvation-associated stress by quantifying several metabolic functions of cultured primary hepatocytes, namely activities of glutathione-S-transferase, glutamine synthetase, CYP3A as well as secretion of lactate and urea into the culture medium. Establishment of constant metabolic activities after an initial decrease compared with freshly isolated hepatocytes showed that the cultured hepatocytes achieve a new equilibrium state that was not affected by our starving conditions. To verify the highly reproducible dynamic activation of signalling pathways in the in vitro system, the authors examined the JAK-STAT, SMAD, PI3 kinase, MAP kinase, NF-kappaB and Wnt/beta-catenin signalling pathways. For the induction of gp130, JAK1 and STAT3 phosphorylation IL6 was used, whereas TGFbeta was applied to activate the phosphorylation of SMAD1, SMAD2 and SMAD3. Both Akt/PKB and ERK1/2 phosphorylation were stimulated by the addition of hepatocyte growth factor. The time-dependent induction of a pool of signalling competent beta-catenin was monitored in response to the inhibition of GSK3beta. To analyse whether phosphorylation is actually leading to transcriptional responses, luciferase reporter gene constructs driven by multiple copies of TGFbeta-responsive motives were applied, demonstrating a dose-dependent increase in luciferase activity. Moreover, the induction of apoptosis by the TNF-like cytokine Fas ligand was studied in the in vitro system. Thus, the mouse hepatocyte in vitro system provides an important basis for the generation of high-quality quantitative data under standardised cell culture conditions that is essential to elucidate critical hepatocellular functions by the systems biology approach.

Long-term expression of foreign genes in normal human epidermal keratinocytes after transfection with lipid/DNA complexes

Normal human epidermal keratinocytes were isolated and cultivated in serum-free medium. The expression of the integrin subunits alpha6 and beta1 indicated that a high number of keratinocytes from the stem cell system was present. These cells were transfected with complexes made of different cationic lipids and marker genes. Effectene showed a 20-fold higher transfection efficiency, compared to Lipofectin and Lipofectamine, and a similar low toxicity. The transfection protocol was optimised. A DNA/lipid ratio of 0.133 showed the highest transfection efficiency. Keratinocytes expressed the marker gene luciferase for 20 days. The maximum expression occurred after 3-4 days, where individual patches of fluorescent keratinocytes were detected. Transfected keratinocytes, cultivated at the air-liquid interface, expressed the marker gene beta-galactosidase for at least 7 weeks.

Quantification of lipids, liposomes, amino acids, and proteins by thermal ultramicrodigestion and an ultramicrocoulometric assay, based on the reaction of hypobromite with ammonia

The quantification of nitrogen in organic material is described. It is based on a novel thermal ultramicrodigestion in combination with an ultramicrocoulometric quantification. The lower detection limit of the coulometric measurement is 0.5 microg nitrogen, which corresponds to 20 microg lipid, 3 microg glycine, or 4 microg protein. Therefore it is as sensitive as the frequently used Lowry method. In contrast to the Lowry protein determination it is not disturbed by detergents and most other interfering substances.

Reconstructed human skin as model for liposome-skin interaction

Reconstructed human skin was prepared from human keratinoblasts. After 1 week of cultivation at the air-liquid interface a stratified layer developed, similar to native human epidermis. Liposomes with an average diameter of 50 nm, made of phosphatidylcholine (PC), phosphatidylserine (PS) and human stratum corneum lipids (hSCL) were applied on top of this culture system. The rate of penetration through the reconstructed human epidermis was 1.38, 0.55 and 0.013 ng lipidh-1cm-2 for PC, hSCL and PS liposomes, respectively. Electron microscopy and confocal laser scanning microscopy showed that PS and hSCL liposomes aggregated at the skin surface, while PC liposomes remained homogeneously dispersed. Fluorescence measurements demonstrated that vesicles, made of native human stratum corneum lipids rapidly mixed with PS liposomes, weakly with hSCL liposomes and did not mix with PC liposomes.

Physicochemical characterisation of human stratum corneum lipid liposomes

Liposomes were prepared from an extract of all human stratum corneum lipids (hSCL) and characterised in terms of temperature and the presence of Ca2+ by different physicochemical methods. Vesicle aggregation and lateral phase separation were induced by divalent cations with Ca2+ being more efficient than Mg2+. At 24.1 degrees C, i.e. well below physiological temperatures the suspensions consisted of a lamellar phase and crystalline cholesterol. At and above 37 degrees C, this cholesterol surplus was dissolved in the hSCL membranes. However, melting of the hSCL was not completed up to 60 degrees C. The presence of Ca2+ (> or = 9 mM) induced lateral phase separation and fusion of vesicles into extended multilamellar lipid sheets (MLLS) at and above 32.5 degrees C. Upon a subsequent cooling cycle recrystallisation of cholesterol occurred within the MLLS. Finally, membrane mixing of hSCL liposomes with vesicles made of synthetic lipids was investigated. No mixing was observed between either of DPPE/oleic acid, DPPC/DPPE, DPPC/lyso-PC and hSCL liposomes. Mixtures of DPPC/cholesterol hemisuccinate showed a temperature-dependent membrane mixing behaviour, whilst hSCL liposomes and phosphatidylserine liposomes fused temperature-independently with hSCL liposomes.

Aminopeptidase P--a cell-surface antigen of endothelial and lymphoid cells: catalytic and immuno-histotopical evidences

The physiological function of the GPI-anchored ectoenzyme aminopeptidase P (APP) is still elusive. Most researchers suppose that this enzyme inactivates biologically active peptides like bradykinin, neuropeptide tyrosine (NPY) and others (Vanhoof et al., 1995). We demonstrate by immunohistology with a specific antibody raised in rabbits and measurement of enzymatic activity in suspensions and of confluent monolayers on microscopic coverslips ('monolayer kinetics') that APP is a cell surface enzyme (ectoenzyme) of endothelial and lymphoid cells.

Oxidative damage of human skin lipids. Dependence of lipid peroxidation on sterol concentration

Photoprotection against sunburn and associated irradiation-induced damages of the human skin is mainly attributed to the darkening of the biochrome melanin by its oxidation. Human skin lipids were examined for an additional protection by sterols. Lipid vesicles prepared from extracted human skin lipids as well as from mixtures of typical lipids of the stratum corneum were irradiated by UV light in the presence and absence of oxygen. The oxidative degradation of various lipids was measured by quantitative HPTLC, by the dichlorofluorescein fluorescent assay, by the thiobarbituric acid assay and a novel luminol-based chemiluminescence technique. Electron spin resonance was used to look for certain radical intermediates. The results indicate, that sterols, mainly free cholesterol, with their high concentration in the lipid barrier of the stratum corneum (up to 50 mol%) effectively compete with the peroxidation of other human skin lipids (ceramides and free fatty acids).

Quantitative determination of thiolipids in organic solution, in membranes, and on HPTLC plates

In the presence of ortho-phthalaldehyde and glucosamine, thiolipids form fluorescent isoindole derivatives. This reaction can be used to quantify single- and double-chain mercaptans in membranes (liposomes) and micellar solutions. The lower detection limit is 100 pmol. In addition, the assay allows the detection of 1.9 nmol thiolipids on HPTLC plates and the fluorescence signal is stable for days. A minor modification of the commonly used DTNB (Ellman's) assay allows the quantification of thiolipids in organic solutions at a concentration down to 3 nmol.

Individual variation of human plantar stratum corneum lipids, determined by automated multiple development of high-performance thin-layer chromatography plates

The stratum corneum lipids are unique in composition and have been used frequently as a model system of the skin's lipid barrier. Automated multiple development (AMD) of high-performance thin-layer chromatography plates in combination with a 25-step gradient, based on methanol, diethyl ether and n-hexane separated the six major human plantar stratum corneum lipids. Post-chromatographic staining of these lipids with a solution of MnCl2-H2SO4 at 130 degrees C or a solution of CuSO4-H3PO4 at 140 degrees C allowed visualization of the lipids and quantification. The MnCl2-H2SO4 solution stained saturated fatty acids less intensely. Therefore, the CuSO4-H3PO4 solution was used for quantification and we found, on average, 2.06% (w/w) cholesterol 3-sulphate, 20.16% (w/w) free fatty acids, 20.25% (w/w) ceramides, 43.53% (w/w) non-esterified sterols, 4.56% (w/w) triacylglycerols and 9.4% (w/w) sterolesters in the human plantar stratum corneum extracts. The concentration of phospholipids was less than 1% (w/w). In addition, the lipid composition of twenty different human plantar stratum corneum extracts was determined. Statistics revealed a correlation between the ratio of free fatty acids and non-esterified sterols (r=0.832, p<0.01, n=20). Several control experiments proved that this correlation is not due to the extraction method, the post-chromatographic staining procedure or bacterial contamination of the stratum corneum.

Tumor targeting in vivo by means of thermolabile fusogenic liposomes

Thermolabile fusogenic liposomes were devised based on the stoichiometric 1/2 mixtures of dipalmitoylphosphatidylcholine (DPPC) and elaidic acid (ELA) and from the similar stoichiometric mixtures of DPPC, dipalmitoylphosphatidylglycerol (DPPG) and elaidoyl alcohol (EL-OH) or palmitelaidoyl alcohol (PEL-OH). The resulting vesicle suspensions are fusogenic in the region of hyperthermia (> or = 42 degrees C) and can be targeted selectively to the heated tumor tissue. Incorporation of DPPG or fatty alcohols into the vesicle membranes also leads to a non-specific, temporary vesicle material accumulation in the lung, however, probably due to platelet activation. Vesicle material accumulation in A-431 tumors, xenotransplanted in nude mice, after 30 min of local hyperthermia (42 degrees C) is 4-fold higher for the DPPC/ELA (1/2), 2.8-fold higher for the DPPC/DPPG/EL-OH (0.8/0.2/2) and 3.7-fold higher for the DPPC/ELA/EL-OH (1/1/1) mixtures than for similar vesicles used at the physiological temperature. Extension of hyperthermia to 60 min induces a 7.8-fold relative material accumulation in the tumor tissue when the thermolabile, fusogenic DPPC/ELA/EL-OH (1/1/1) vesicles are used. Simple DPPC vesicles only reach concentrations in the heated tumor or muscle tissue that are 1.85-fold and 1.38-fold higher than in the normothermic control, respectively. This is probably a consequence of simple vasodilatation. In vitro experiments revealed that the adsorption of serum proteins to the vesicle membrane decreases the chain-melting phase transition temperature and the transition enthalpy of vesicle suspension. Adsorption is most prominent at the chain-melting phase transition temperature of the mixed lipid bilayers, which is also the critical temperature for the induction of liposome fusion. This hampers the practical use of the resulting vesicle suspension in vivo. The serum-induced decrease of the chain-melting phase transition temperature, which is likely to change as a function of time in vivo, depends on the lipid composition and on the local surface charge density of vesicles. Incorporation of ELA and DPPG concentrations above 15 mol-%, for example, reduce the extent of protein adsorption onto vesicles. This has to be borne in mind when devising vesicles for practical applications.

Interaction of phosphatidylcholine liposomes with the human stratum corneum

The interaction of dimyristoylphosphatidylcholine liposomes with the human stratum corneum was investigated by confocal laser scanning microscopy and differential scanning calorimetry. Human skin is characterized by a high autofluorescence. By introducing appropriate optical filters the autofluorescence of the skin was depressed and the penetration profile of fluorescence labelled vesicles was investigated. From optical sectioning it was obvious that neither the vesicles nor the fluorophore N-(lissamine rhodamine B sulfonyl)diacylphophatidylethanolamine (Rho-PE) penetrates in detectable amounts into the human skin. Differential scanning calorimetry of human stratum corneum revealed, that the peak positions of the human stratum corneum specific endothermic transitions at 10 degrees C, 35 degrees C, 50 degrees C, 62 degrees C, 73 degrees C and 81 degrees C did not change significantly after 18 h of non-occlusive vesicle application. However, the enthalpy of the transitions at 35 degrees C, 50 degrees C, 62 degrees C and 73 degrees C, estimated through peak heights increased, relative to the protein related peak at 81 degrees C. A novel transition at 10 degrees C was observed. From these data we conclude that DMPC liposomes do not penetrate intact into the human skin. We deduce, however, that the vesicles disintegrate at the surface of stratum corneum after non-occlusive application. The individual lipid molecules then interact with the lipid barrier of the stratum corneum and penetrate into the latter, which results in an increase of the enthalpy, related to the lipid components of the SC.

Temperature- and pH-controlled fusion between complex lipid membranes. Examples with the diacylphosphatidylcholine/fatty acid mixed liposomes

The fusion capability of complex lipid bilayers and its pH as well as temperature sensitivity have been studied by optical and spectroscopic means. The aggregation and fusion efficiency of such lipid membranes can be optimized by controlling the phase characteristics of the individual membrane components. For a practically relevant illustration, the stoichiometric 1:2 (mol/mol) mixtures of phosphatidylcholines and fatty acids are used. Perhaps the most interesting liposomes of this kind, which are made of dipalmitoylphosphatidylcholine/elaidic acid (DPPC/ELA-COOH (1:2)), undergo a chain-melting phase transition between 42 degrees C and 48 degrees C, depending on the bulk pH value. The highest chain-melting phase transition temperatures are measured with the fully protonated fatty acids at pH < or = 5.5 and involve a change into the non-bilayer high-temperature state. Upon increasing pH, this transition reverts into an ordinary gel-to-fluid lamellar phase change and occurs at 42 degrees C, by and large. Simultaneously, the rate and the efficacy of fusion between the PC/FA and PC/FA- mixed vesicles decreases. The fusion efficacy of the PC/FA(-) mixed liposomes at pH > or = pK(FA) approximately 7.5 is practically negligible. This is largely due to the increased interbilayer repulsion and to the relatively high water-solubility of the deprotonated fatty acid molecules at high pH. While the pH-variability chiefly affects the efficacy of the intermembrane aggregation, the vesicle fusion itself is more sensitive to temperature variations. It is more likely that the temperature dependence of the intramembrane defect density is chiefly responsible for this. Optimal conditions for the fusion between DPPC/ELA-COOH (1:2) mixed vesicles are thus 3.5 < or = pH < or = 5.5 (6.3) (aggregation maximum) and T > or = 41.5 degrees C = Tm(DPPC) (defect density and fusion maximum). Under such conditions the average size of PC/FA (1:2) mixed vesicles in a 1 mM suspension increases by a factor of 10 over a period of 10 min. Interbilayer fusion can also be catalyzed by the mechanically induced local membrane defects. Freshly made liposomes thus always fuse more avidly than aged vesicles. This permits estimates of the kinetics of membrane defects annihilation based on the measured temporal dependence of the maximum fusion-rate. From such studies, a quasi-exponential decay on the time scale of 1.2 h is found for the thermolabile fusogenic DPPC/ELA-COOH liposomes.

Hemodynamic findings during exercise on a bicycle ergometer following balloon valvuloplasty of pulmonary stenosis in children and adolescents

Eleven patients (4 female, 7 male), age range 3.3 to 24.8 years (mean 11.10 years) treated for isolated pulmonary stenosis underwent cardiac catheterization and percutaneous transluminal balloon valvuloplasty (PTVP). The right ventricular systolic pressure (RVSP) before valvuloplasty ranged from 31 to 127 mmHg (mean 79 mmHg) decreasing to 28 to 62 mmHg (mean 42 mmHg) immediately after the dilatation. The peak systolic gradient of the pulmonary valve (delta p RV-PA) before valvuloplasty ranged from 22 to 107 mmHg (mean 61 mmHg) and decreased to a range of 14 and 45 mmHg (mean 23 mmHg) immediately after the dilatation. Balloon valvuloplasty was performed using balloons of 13 to 31 mm in diameter. On 11 patients cardiac catheterization and Doppler echocardiography were repeated between 11 months and 5.3 years (mean 3.11 years) after the balloon valvuloplasty showed a further significant fall in the gradient of pressure. The right ventricular systolic pressure ranged from 20 to 51 mmHg (mean 31.7 mmHg) while the transpulmonary gradient varied from 3 to 24 mmHg (mean 11.6 mmHg). At the time of follow-up examination the patients were aged between 7.2 and 25.7 years (mean 15.9 years). On average the second catheterization was performed 3.11 years following the first hemodynamic study. The follow-up examination encompassed clinical examination, electrocardiogram, Doppler echocardiography, and right heart cardiac catheterization. During right heart cardiac catheterization the children exercised on a bicycle ergometer for three min at 50 or 100 W depending on their body surface area. During this exertion, pressures of the right ventricle and the pulmonary artery as well as heart rate and oxygen saturation were recorded.(ABSTRACT TRUNCATED AT 250 WORDS)