Socioeconomic factors and colorectal cancer incidence, stage and quality of care in Denmark during the COVID-19 pandemic

AIM

Efforts to control the COVID-19 pandemic might reduce accessibility for diagnostics and treatment of colorectal cancer. A universal public healthcare system may modify the availability of healthcare services. The aim of this study was to investigate changes in the quality of care for patients with colorectal cancer during the COVID-19 pandemic.

METHOD

Nationwide data from the Danish Colorectal Cancer database and Statistics Denmark on the number of new diagnoses, disease and health behaviour measures, socioeconomic measures, clinical quality measures and time to adjuvant chemotherapy were retrieved. Measures during the COVID-19 pandemic in 2020 and the different pandemic periods were compared to the pre-pandemic period.

RESULT

In 2020, 4035 patients were diagnosed with colorectal cancer, compared with 4346 in 2019 and 4496 in 2018. During the pandemic, patients were more likely to have UICC stage I disease (25.0% vs 23.4%; PR=1.07(95% confidence interval: 1.00;1.15)), belonging to the highest income quintile (PR=1.06(0.98;1.14), receive surgery with a curative aim (PR=1.02(1.01;1.03)), and to be operated on by a specialist (PR=1.07(1.06;1.08)), and less likely to be 60-69 years of age (PR=0.93(0.86;1.00)), non-western immigrants (PR=0.93(0.86;1.00)), diagnosed by screening (PR=0.79(0.73;0.86)) and receiving an acute operation (PR=0.77(0.66;0.91)). Furthermore, during the pandemic, 11.4% fewer patients waited 28 days or longer for initiation of adjuvant oncological treatment.

CONCLUSION

Based on nationwide data, we observed no major adverse effect on disease measures or clinical quality in a tax funded health care system. However, small changes in the socioeconomic composition of the patient population were observed.

Nationwide mammography screening participation in Denmark during the COVID-19 pandemic: An observational study

Background

In most of the world, the mammography screening programmes were paused at the start of the pandemic, whilst mammography screening continued in Denmark. We examined the mammography screening participation during the COVID-19 pandemic in Denmark.

Methods

The study population comprised all women aged 50-69 years old invited to participate in mammography screening from 2016 to 2021 in Denmark based on data from the Danish Quality Database for Mammography Screening in combination with population-based registries. Using a generalised linear model, we estimated prevalence ratios (PRs) and 95% confidence intervals (CIs) of mammography screening participation within 90, 180, and 365 d since invitation during the pandemic in comparison with the previous years adjusting for age, year and month of invitation.

Results

The study comprised 1,828,791 invitations among 847,766 women. Before the pandemic, 80.2% of invitations resulted in participation in mammography screening within 90 d, 82.7% within 180 d, and 83.1% within 365 d. At the start of the pandemic, the participation in screening within 90 d was reduced to 69.9% for those invited in pre-lockdown and to 76.5% for those invited in first lockdown. Extending the length of follow-up time to 365 d only a minor overall reduction was observed (PR = 0.94; 95% CI: 0.93-0.95 in pre-lockdown and PR = 0.97; 95% CI: 0.96-0.97 in first lockdown). A lower participation was, however, seen among immigrants and among women with a low income.

Conclusions

The short-term participation in mammography screening was reduced at the start of the pandemic, whilst only a minor reduction in the overall participation was observed with longer follow-up time, indicating that women postponed screening. Some groups of women, nonetheless, had a lower participation, indicating that the social inequity in screening participation was exacerbated during the pandemic.

Funding

The study was funded by the Danish Cancer Society Scientific Committee (grant number R321-A17417) and the Danish regions.

Diagnosis and treatment of lung cancer in Denmark during the COVID-19 pandemic

BACKGROUND

We examined the number of lung cancers diagnosed, the quality of care and the socio-economic and clinical characteristics among patients with lung cancer during the COVID-19 pandemic compared to previous years.

METHODS

We included all patients ≥ 18 years old diagnosed with lung cancer from 01 January 2018 to 31 August 2021 as registered in the Danish Lung Cancer Registry. Using a generalised linear model, we estimated prevalence ratios (PR) and 95% confidence intervals (CI) of the associations between the pandemic and socioeconomic and clinical factors, and indicators of quality.

RESULTS

We included 18,113 patients with lung cancer (82.0% non-small cell lung cancer (NSCLC)), which was similar to the preceding years, although a decline in NSCLC cases occurred during the first lockdown period in 2020. No difference in distribution of income or educational level was observed. No difference was observed in the quality of treatment - as measured by curative intent, proportion of patients resected or who died within 90 days of diagnosis.

CONCLUSION

Using nationwide population-based data, our study reassuringly shows no adverse effects of the COVID-19 pandemic on the diagnosis, socio-economic characteristics nor quality of treatment of lung cancer, as compared to the preceding years.

Nation-wide participation in FIT-based colorectal cancer screening in Denmark during the COVID-19 pandemic: An observational study

Background: Worldwide, most colorectal cancer screening programmes were paused at the start of the COVID-19 pandemic, whilst the Danish faecal immunochemical test (FIT)-based programme continued without pausing. We examined colorectal cancer screening participation and compliance with subsequent colonoscopy in Denmark throughout the pandemic.

Methods: We used data from the Danish Colorectal Cancer Screening Database among individuals aged 50-74 years old invited to participate in colorectal cancer screening from 2018-2021 combined with population-wide registries. Using a generalised linear model, we estimated prevalence ratios (PR) and 95% confidence intervals (CI) of colorectal cancer screening participation within 90 days since invitation and compliance with colonoscopy within 60 days since a positive FIT test during the pandemic in comparison with the previous years adjusting for age, month and year of invitation.

Results: Altogether, 3,133,947 invitations were sent out to 1,928,725 individuals and there were 94,373 positive FIT tests (in 92,848 individuals) during the study period. Before the pandemic, 60.7% participated in screening within 90 days. A minor reduction in participation was observed at the start of the pandemic (PR=0.95; 95% CI: 0.94-0.96 in pre-lockdown and PR=0.85; 95% CI: 0.85-0.86 in 1^st lockdown) corresponding to a participation rate of 54.9% during pre-lockdown and 53.0% during 1st lockdown. This was followed by a 5-10% increased participation in screening corresponding to a participation rate of up to 64.9%. The largest increase in participation was observed among 55-59 year olds and among immigrants. The compliance with colonoscopy within 60 days was 89.9% before the pandemic. A slight reduction was observed during 1^st lockdown (PR=0.96; 95% CI: 0.93-0.98), where after it resumed to normal levels.

Conclusions: Participation in the Danish FIT-based colorectal cancer screening programme and subsequent compliance to colonoscopy after a positive FIT result was only slightly affected by the COVID-19 pandemic.

Funding: The study was funded by the Danish Cancer Society Scientific Committee (grant number R321-A17417) and the Danish regions.

Participation in the nationwide cervical cancer screening programme in Denmark during the COVID-19 pandemic: An observational study

Background

In contrast to most of the world, the cervical cancer screening programme continued in Denmark throughout the COVID-19 pandemic. We examined the cervical cancer screening participation during the pandemic in Denmark.

Methods

We included all women aged 23-64 y old invited to participate in cervical cancer screening from 2015 to 2021 as registered in the Cervical Cancer Screening Database combined with population-wide registries. Using a generalised linear model, we estimated prevalence ratios (PRs) and 95% CIs of cervical cancer screening participation within 90, 180, and 365 d since invitation during the pandemic in comparison with the previous years adjusting for age, year, and month of invitation.

Results

Altogether, 2,220,000 invited women (in 1,466,353 individuals) were included in the study. Before the pandemic, 36% of invited women participated in screening within 90 d, 54% participated within 180 d, and 65% participated within 365 d. At the start of the pandemic, participation in cervical cancer screening within 90 d was lower (pre-lockdown PR = 0.58; 95% CI: 0.56-0.59 and first lockdown PR = 0.76; 95% CI: 0.75-0.77) compared with the previous years. A reduction in participation within 180 d was also seen during pre-lockdown (PR = 0.89; 95% CI: 0.88-0.90) and first lockdown (PR = 0.92; 95% CI: 0.91-0.93). Allowing for 365 d to participation, only a slight reduction (3%) in participation was seen with slightly lower participation in some groups (immigrants, low education, and low income).

Conclusions

The overall participation in cervical cancer screening was reduced during the early phase of the pandemic. However, the decline almost diminished with longer follow-up time.

Funding

The study was funded by the Danish Cancer Society Scientific Committee (grant number R321-A17417) and the Danish regions.

Regional and socio-economic variation in survival after glioblastoma in Denmark, 2013-2018

INTRODUCTION

Glioblastoma is the most frequent primary brain tumour in adults. In Denmark, the treatment of glioblastoma is centralised to four neurosurgical and oncological departments located in four of the five Danish administrative regions. The aim of this study was to examine the regional and socioeconomic variation in survival after a diagnosis of glioblastoma in Denmark.

METHODS

We included 1,731 patients with histologically confirmed glioblastoma from 2013 to 2018 registered in the Danish Neuro-oncology Registry. The data sources were the Danish National Registries. The exposure was region of residence at diagnosis and household income in the year before diagnosis. Follow-up was initiated at diagnosis and concluded at death or end-of-follow-up on 15 July 2019. Cox regression was used to examine overall mortality by exposure.

RESULTS

With adjustment for age, sex, year of diagnosis and comorbidity, mortality rates of glioblastoma patients varied significantly between regions and were lowest in the Region of Southern Denmark and highest in the Capital Region (hazard ratio = 0.79; 95% confidence interval: 0.68-0.91, compared with the Capital Region). Further adjustment for surgical resection attenuated the regional differences in mortality. Income was not a predictor of survival.

CONCLUSIONS

We found significant regional variation in survival after a diagnosis of glioblastoma. Differences in treatment patterns between regions may explain part of this mortality variation. Household income and education level did not explain the regional differences.

FUNDING

none.

TRIAL REGISTRATION

not relevant.

The power of empirical data; lessons from the clinical registry initiatives in Scandinavian cancer care

BACKGROUND

In Scandinavia, there is a strong tradition for research and quality monitoring based on registry data. In Denmark, Norway and Sweden, 63 clinical registries collect data on disease characteristics, treatment and outcome of various cancer diagnoses and groups based on process-related and outcome-related variables.

AIM

We describe the cancer-related clinical registries, compare organizational structures and quality indicators and provide examples of how these registries have been used to monitor clinical performance, develop prediction models, assess outcome and provide quality benchmarks. Further, we define unmet needs such as inclusion of patient-reported outcome variables, harmonization of variables and barriers for data sharing.

RESULTS AND CONCLUSIONS

The clinical registry framework provides an empirical basis for evidence-based development of high-quality and equitable cancer care. The registries can be used to follow implementation of new treatment principles and monitor patterns of care across geographical areas and patient groups. At the same time, the lessons learnt suggest that further developments and coordination are needed to utilize the full potential of the registry initiative in cancer care.

Regional and socio-economic variation in survival after a pancreatic cancer diagnosis in Denmark

INTRODUCTION

Pancreatic cancer is among the most lethal malignancies with a five-year survival of about 5%, and the only curative treatment is surgical resection. Denmark consists of five governmental regions and has four surgical centres. Our aim was to explore the regional and socio-economic differences in overall survival following a pancreatic cancer diagnosis in Denmark.

METHODS

We included a total of 5,244 pancreatic cancer patients (WHO International Classification of Diseases, tenth version C25) registered in the Danish Pancreatic Cancer Database during 2012-2017. The data sources used were the Danish Civil Registration System, the Danish National Patient Registry and the Danish national registers on education and income at Statistics Denmark. Cox regression analysis was used to examine all-cause mortality of pancreatic cancer patients by region of residence and socio-economic status.

RESULTS

Compared to The Capital Region, there was an excess mortality in the Central Denmark Region and the North Denmark Region in both men and women, whereas no increased mortality was observed in the Region of Southern Denmark or in Region Zealand. Estimates were adjusted for age, year of diagnosis and comorbidity. Adjustment for surgical resection greatly attenuated the variation in survival between the regions.

CONCLUSIONS

We found significant differences in overall survival across the five Danish regions following a diagnosis of pancreatic cancer. The regional variation in survival was largely attributable to differences in the propensity to use surgical resection.

FUNDING

none.

TRIAL REGISTRATION

not relevant.

Regional and socioeconomic variation in survival of melanoma patients in Denmark

INTRODUCTION

This article explores variation in survival and mortality of Danish melanoma patients from 2012 to 2017 in relation to their region of residence and socioeconomic status.

METHODS

Data were extracted from The Danish Melanoma Database, a clinical register, based on reports from hospital departments and dermatologists, and designed for quality improvement. The analysis included covariates at the person and tumour level. A cohort analysis was implemented to quantify the variations and identify the underlying mechanisms behind regional and socioeconomic variations in mortality of melanoma patients.

RESULTS

The mortality of melanoma patients varied between the five regions with mean hazard ratios (95% confidence interval) of 1.36 (1.07-1.74) in men and 1.44 (1.08-1.92) in women between the regions with highest and lowest mortality. Mortality was highest in the patients with the lowest income and shortest education. Regional variation in mortality was attributable to underlying variation in tumour stage and thickness, and it was not confounded by other covariates.

CONCLUSIONS

The two regions with the lowest mortality (highest survival) had high absolute incidence rates of stage IA and thin melanomas, indicating a high level of diagnostic activity in these regions. There was no regional variation in the incidence of advanced melanoma. The optimal level of diagnostic investigation of skin lesions has yet to be established.

FUNDING

none.

TRIAL REGISTRATION

not relevant.

Association Between Electronic Cigarette Use and Marijuana Use Among Adolescents and Young Adults: A Systematic Review and Meta-analysis

IMPORTANCE

Use of electronic cigarettes (often called e-cigarettes) has increased considerably among young people in the past 5 years. Use of e-cigarettes has been associated with higher rates of marijuana use, which is associated with several adverse health outcomes in youth.

OBJECTIVE

To characterize and quantify the association between e-cigarette and marijuana use among youth using a meta-analysis.

DATA SOURCES

PubMed, Embase, and Web of Science & ProQuest Dissertations and Theses were searched from inception to October 2018. A gray-literature search was also conducted on conference abstracts, government reports, and other sources.

STUDY SELECTION

Included studies compared rates of marijuana use among youth aged 10 to 24 years who had used e-cigarettes vs those who had not used e-cigarettes. Two reviewers independently assessed studies for inclusion; disagreements were discussed with a third reviewer and resolved by consensus.

DATA EXTRACTION AND SYNTHESIS

Data were extracted by 2 independent reviewers following Meta-analyses of Observational Studies in Epidemiology (MOOSE) reporting guidelines and pooled using a random-effects analysis. The Newcastle-Ottawa Scale was used to assess data quality and validity of individual studies.

MAIN OUTCOMES AND MEASURES

Adjusted odds ratios (AORs) of self-reported past or current marijuana use by youth with vs without past or current e-cigarette use.

RESULTS

Twenty-one of 835 initially identified studies (2.5%) met selection criteria. The meta-analysis included 3 longitudinal and 18 cross-sectional studies that included 128 227 participants. Odds of marijuana use were higher in youth who had an e-cigarette use history vs those who did not (AOR, 3.47 [95% CI, 2.63-4.59]; I2, 94%). Odds of marijuana use were significantly increased in youth who used e-cigarettes in both longitudinal studies (3 studies; AOR, 2.43 [95% CI, 1.51-3.90]; I2, 74%) and cross-sectional studies (18 studies; AOR, 3.70 [95% CI, 2.76-4.96]; I2, 94%). Odds of using marijuana in youth with e-cigarette use were higher in adolescents aged 12 to 17 years (AOR, 4.29 [95% CI, 3.14-5.87]; I2, 94%) than young adults aged 18 to 24 years (AOR, 2.30 [95% CI, 1.40-3.79]; I2, 91%).

CONCLUSIONS AND RELEVANCE

This meta-analysis found a significant increase in the odds of past or current and subsequent marijuana use in adolescents and young adults who used e-cigarettes. These findings highlight the importance of addressing the rapid increases in e-cigarette use among youths as a means to help limit marijuana use in this population.

[Quality improvement in Danish healthcare services - status and recommendations]

In light of a 2018 report by WHO, OECD and World Bank, we provide a set of recommendations for quality improvement in Danish healthcare services, in this review: 1) Easily accessible decision-relevant local quality data should be provided. 2) The legal basis for quality development and research should be clarified. 3) The effort to develop patient-reported outcome measures should be intensified. 4) All clinicians should be involved in quality improvement, and quality improvement methods should be included in all healthcare professionals' training curricula.

[The patient's team and the responsible doctor as a condition for efficient patient courses]

In the healthcare system in The North Denmark Region the patient's team has been implemented in order to create and ensure efficient patient courses. Each patient has his or her own team, which is responsible for the entire patient course. As part of the team there is one doctor, who has the ultimate responsibility for the patient's treatment and pathway within the healthcare system. The patient's team is implemented in 2015-2017 in the healthcare system in The North Denmark Region.

[Research activities of junior physicians]

INTRODUCTION

Since 1991, the Danish Junior Doctors' Association has carried out annual investigations among its members in regard to education. In 2001, the questionnaire included a special section about scientific activities.

MATERIALS AND METHODS

The investigation included approximately 70 questions which were sent to all members of the Danish Junior Doctors' Association. A total of 76.2% answered the questionnaire. The age of the junior doctors and the year of graduating are comparable in the investigations from 1993 to 2001.

RESULTS

52.7% of the junior doctors make research in their spare time, and 47.1% have published at least once as primary researcher. The comparison of the investigations from 1993 to 2001 shows a significant fall in the average publications per doctor and in the number of doctors with at least one published paper. From 1999, there were 7% doctors less with one published paper (chi 2 = 53.4; p < 0.001). The average number of published articles per primary researcher has declined from 6.69/doctor in 1993 to 2.48/doctor in 2001 (t = -25.04, p < 0.001). As a whole, 11.9% of all junior doctors had a PhD-degree and 3.0% had a doctor's degree. 7.6% were in the process of a PhD-study. The number of junior doctors with a PhD is significantly rising. The number of doctors seeking positions at universities is less than 2%, the rest seek clinical education and work.

DISCUSSION

The publication rate has declined over the past ten years, which has many reasons. One reason is the increasing number of PhD-degrees and an increase in the impact factor, which means qualitative research improvement. A changed procedure in the postgraduate education is a factor as well. The low recruitment of junior doctors for pregraduate education seems to be a constant problem.

Expression of the Streptococcus pneumoniae type 3 synthase in Escherichia coli. Assembly of type 3 polysaccharide on a lipid primer

Synthesis of the type 3 capsular polysaccharide of Streptococcus pneumoniae is catalyzed by the membrane-localized type 3 synthase, which utilizes UDP-Glc and UDP-GlcUA to form high molecular mass [3-beta-d-GlcUA-(1-->4)-beta-d-Glc-(1-->](n). Expression of the synthase in Escherichia coli resulted in synthesis of a 40-kDa protein that was reactive with antibody directed against the C terminus of the synthase and was the same size as the native enzyme. Membranes isolated from E. coli contained active synthase, as demonstrated by the ability to incorporate Glc and GlcUA into a high molecular mass polymer that could be degraded by type 3 polysaccharide-specific depolymerase. As in S. pneumoniae, the membrane-bound synthase from E. coli catalyzed a rapid release of enzyme-bound polysaccharide when incubated with either UDP-Glc or UDP-GlcUA alone. The recombinant enzyme expressed in E. coli was capable of releasing all of the polysaccharide from the enzyme, although the chains remained associated with the membrane. The recombinant enzyme was also able to reinitiate polysaccharide synthesis following polymer release by utilizing a lipid primer present in the membranes. At low concentrations of UDP-Glc and UDP-GlcUA (1 microm in the presence of Mg(2+) and 0.2 microm in Mn(2+)), novel glycolipids composed of repeating disaccharides with linkages consistent with type 3 polysaccharide were synthesized. As the concentration of the UDP-sugars was increased, there was a marked transition from glycolipid to polymer formation. At UDP-sugar concentrations of either 5 microm (with Mg(2+)) or 1.5 microm (with Mn(2+)), 80% of the incorporated sugar was in polymer form, and the size of the polymer increased dramatically as the concentration of UDP-sugars was increased. These results suggest a cooperative interaction between the UDP-precursor-binding site(s) and the nascent polysaccharide-binding site, resulting in a non-processive addition of sugars at the lower UDP-sugar concentrations and a processive reaction as the substrate concentrations increase.

Effect of nitrendipine on renal function and on hormonal parameters after intravascular iopromide

PURPOSE

To evaluate the effect of the low-molecular nonionic radiographic contrast agent iopromide (Ultravist) on renal function, vasoactive peptides (angiotensin II, aldosterone, arginine vasopressin, and atrial natriuretic factor (ANF)), and blood pressure, and to evaluate the influence of the calcium antagonist nitrendipine on these parameters. The findings were evaluated in a prospective double-blind and placebo-controlled randomized study.

MATERIAL AND METHODS

Twenty-six patients undergoing routine aortofemoral arteriography for peripheral atherosclerotic disease were treated with nitrendipine tablets (10 mg) or placebo twice daily for a week. Angiography was performed on the fifth day of medication. Efficacy variables were determined on the day before and 2 days after arteriography. The glomerular filtration rate and renal plasma flow were measured by the constant infusion technique. Renal tubular function was estimated from the clearance of lithium. Hormones were measured by radioimmunoassays.

RESULTS

Arteriography with iopromide did not change renal function. No differences between the nitrendipine and placebo groups were found in renal hemodynamics, tubular sodium handling, or blood pressure. Nitrendipine changed ANF (26.1%) compared to placebo (1.5%), whereas the other hormones were not affected.

CONCLUSION

The use of iopromide for angiography did not affect renal function in normotensive patients with peripheral atherosclerotic disease. Short-term treatment with nitrendipine may lower the plasma levels of ANF but it had no effect on renal function or blood pressure. Treatment with calcium antagonists prior to arteriography with iopromide is not indicated in these patients.

Porous-coated metal-backed patellar components in total knee replacement. A postmortem retrieval analysis

The use of porous-coated metal-backed patellar components to achieve consistent fixation by bone ingrowth and to provide relief of pain warrants serious scrutiny. We conducted a quantitative postmortem investigation of eleven consecutively retrieved components with use of high-resolution contact radiographs, electron microscopy, and histological analysis. The implants had been in situ for a mean (and standard deviation) of 45+/-36 months (range, one to eighty-four months). Analysis of the high-resolution contact radiographs revealed that a mean of 86+/-12 per cent (range, 61 to 100 per cent) of the porous coating was in contact with the host bone. Backscattered electron imaging showed that the mean volume fraction of bone ingrowth was 13+/-9 per cent (range, 0 to 30 per cent). No significant difference was detected, with the numbers available, between the volume fraction of the bone ingrowth measured in the porous coating and that of the host cancellous bone in the patellae.

Postmortem analysis of consecutively retrieved asymmetric porous-coated tibial components

The objective of this investigation was to conduct a postmortem analysis of 8 porous-coated asymmetric tibial components to measure the extent of radiolucencies and bone ingrowth. With the use of radiographic, electron microscope, and histologic analysis techniques, a quantitative postmortem study of 8 consecutively retrieved porous-coated tibial components was conducted. Time in situ averaged 47+/-36 months. The components were secured with 4 pegs and 2 screws. Autograft bone chips were applied to the resected tibia during implantation. Contact radiographs of an average of 8 3-mm sections from each implant revealed that 73%+/-17% of the porous coating had no apparent radiolucencies present between the host bone and porous coating for the series. Backscattered electron imaging showed that the bone ingrowth averaged 6%+/-2%. Histologic analysis was unable to demonstrate any adverse cellular response. The analysis suggested that this asymmetric implant design is stable and biocompatible and has potential for long-term clinical durability.

Postmortem analysis of bone growth into porous-coated acetabular components

Microradiography, backscattered electron microscopy, and histological analysis were used to conduct a quantitative postmortem study of seven consecutively retrieved anatomical porous replacement acetabular components that had been inserted during total hip arthroplasties. Screws had been used for the initial fixation of six components. The microradiographic analysis of all seven components showed that an average (and standard deviation) of 84 +/- 9 per cent (range, 72 to 93 per cent) of the porous coating was in direct apposition to the periprosthetic bone. The backscattered electron images demonstrated that an average of 12 +/- 6 per cent (range, 4 to 21 per cent) of the space available in the porous coating was occupied by ingrown bone. The amount of bone ingrowth was not significantly different among the three zones delineated by DeLee and Charnley. Uniformity of bone growth into the porous coating suggests that the preferential loading that occurs in the superior region did not differentially affect the bone ingrowth. The present study showed that consistent bone growth into anatomical porous replacement acetabular components can be achieved.

Bilayer membrane destabilization induced by dolichylphosphate

Small vesicles containing the fluorescent probe calcein were used to investigate the effect of dolichyl phosphate (Dol-P) on phospholipid bilayer stability. In the absence of Dol-P, phospholipid vesicles retained the fluorescent probe upon the addition of divalent cations. Small vesicles containing Dol-P, however, exhibited calcein leakage when incubated in the presence of divalent cations. This effect was observed in liposomes composed of a mixture of phosphatidylethanolamine (PE), phosphatidylcholine (PC) and Dol-P, but not in PC/Dol-P liposomes. The rate of calcein leakage was proportional to divalent cation concentration and to temperature, but was independent of vesicle concentration. These results demonstrate that Dol-P has significant effects on the stability of PE containing phospholipid bilayers. Vesicle leakage was also promoted by the addition of rat liver Dol-P-mannose synthase (EC 2.4.1.83) to intact PE/PC/Dol-P vesicles. Enzyme induced leakage from phospholipid vesicles required the presence of both unsaturated PE and Dol-P. The phospholipid composition of leaky vesicles could be correlated with the lipid matrix required for maximal transferase activity of the rat liver synthase. The destabilizing effects of Dol-P on phospholipid bilayers may therefore be involved in the translocation of activated sugars across biological membranes.

Phospholipase-induced modulation of dolichyl-phosphomannose synthase activity

Rat liver dolichyl-phosphomannose synthase is optimally active when the enzyme is reconstituted with lipids that prefer a nonlamellar macroscopic organization in isolation, such as phosphatidylethanolamine (PE), but the enzyme is only negligibly active in the presence of lipids that normally form stable bilayers, such as phosphatidylcholine (PC) [Jensen, J.W., & Schutzbach, J.S. (1985) Eur. J. Biochem. 153, 41-48]. We now report that the activity of the synthase can be modulated by incorporating diacylglycerol and lysophosphatidylcholine into the lipid matrix. Enzyme activity in PC bilayers was stimulated by the presence of diacylglycerol, a lipid that has a conical dynamic molecular shape and disrupts bilayer stability. In PC/diacylglycerol mixtures the apparent Km for dolichyl-P was 30-fold lower than the apparent Km for the polyprenol acceptor in PC membranes. Enzyme activity was also stimulated when diacylglycerol was generated in situ by incubation of PC vesicles with phospholipase C. In contrast, the activity of enzyme reconstituted in PE dispersions, or in PE/PC bilayers, was markedly inhibited by the presence of lysophospholipids. Enzyme activity was also reduced by the in situ generation of lysophospholipids in PE/PC vesicles by incubation with phospholipase A2. Since lysophospholipids and diacylglycerols arise in vivo as products of phospholipid metabolism, modulation of enzyme activity by these compounds may represent a potential regulatory mechanism for the synthesis of oligosaccharide lipids.

Modulation of dolichyl-phosphomannose synthase activity by changes in the lipid environment of the enzyme

Rat liver dolichyl-phosphomannose synthase (GDP mannose-dolicholphosphate mannosyltransferase; EC 2.4.1.83) was previously shown to catalyze optimal rates of mannosyl transfer to dolichyl-P when the polyprenol acceptor was incorporated into a phosphatidylethanolamine (PE) matrix that has a tendency to adopt a nonbilayer (hexagonal HII) phase [Jensen, J. W., & Schutzbach, J. S. (1985) Eur. J. Biochem. 153, 41-48]. The present investigations now further define the properties of the lipid environment that are essential for mannosyltransferase activity. Monogalactosyl diglyceride (MGDG), a glycoglycerolipid that prefers a nonbilayer-phase organization in isolation, was shown to provide a suitable lipid matrix for synthase activity. By comparison, the enzyme was not activated by digalactosyl diglyceride (DGDG), which forms stable bilayer structures upon hydration. Enzyme activity in MGDG/DGDG mixtures decreased as the proportion of DGDG in the dispersion was increased. Although bilayer-forming phospholipids supported low rates of mannosyl transfer, enzyme activity was stimulated by the addition of MGDG to either phosphatidylcholine (PC) or PE/PC (1:1) membranes. The incorporation of agents known to destabilize bilayer structures including dolichols, ubiquinone, dodecane, and cholesterol into PE/PC (1:1) membranes also increased the rate of mannosyl transfer. Enzyme activity in PC membranes was stimulated by the presence of gramicidin and also by greatly increased concentrations of the substrate, dolichyl-P. The results demonstrate that the enzyme does not have a requirement for PE and suggest that the physical state of the lipid matrix is an important determinant for reconstitution of the synthase and polyprenol phosphate substrate in a productive complex. The formation of an enzyme/lipid complex was demonstrated by sucrose density gradient centrifugation and could be correlated with the lipid requirements for enzyme activity.

Characterization of mannosyl-transfer reactions catalyzed by dolichyl-mannosyl-phosphate-synthase

Evidence suggesting that a single enzyme catalyzes mannosyl transfer from GDP-mannose to both dolichyl phosphate and to phenyl phosphate was obtained as follows: (a) The two activities were coeluted from columns of DEAE-cellulose and Sepharose CL-6B, (b) both reactions demonstrated similar kinetic constants for the glycosyl donor and for guanosine nucleoside inhibitors, (c) both reactions were sensitive to inhibition by low concentrations of nonionic detergents, and (d) both activities were found to be thermally inactivated at similar rates upon incubation at 55 degrees. The reaction conditions required for optimal mannosyl transfer by the purified enzyme preparation to the hydrophobic and water soluble acceptors, however, were found to be quite different. Whereas mannosyl transfer from GDP-mannose to dolichyl phosphate occurred at maximal rates only in the presence of specific phospholipids, the rate of mannosyl transfer to phenyl phosphate was essentially unaffected by the addition of phospholipid. These results indicate that dolichyl-mannosyl-phosphate-synthase, which has some of the properties of an intrinsic membrane protein, does not have an absolute requirement for phospholipid for catalytic activity, but rather that phospholipid is required for interaction of the enzyme with the long chain polyisoprenol substrate dolichyl phosphate.

Activation of dolichyl-phospho-mannose synthase by phospholipids

Dolichyl-phospho-mannose synthase, or GDPmannose:dolichyl-phosphate mannosyltransferase (EC 2.4.1.83), was solubilized from rat liver microsomes with 1.0% Nonidet P-40 and the enzyme was further purified by column chromatography on DEAE-cellulose in the presence of 0.1% Nonidet P-40. The purified enzyme preparation (880-fold over microsomes) was unstable in the presence of detergent and had no activity in the presence of Nonidet P-40, Triton X-100, octyl beta-glucoside, or deoxycholate. Detergent-free enzyme was active in the presence of phosphatidylethanolamine (PtdEtn) and in the presence of phospholipid mixtures of PtdEtn and phosphatidylcholine (PtdCho) when the molar proportion of PtdCho was 70% or less. The enzyme was inactive in the presence of PtdCho alone. Unsaturated species of PtdEtn have a tendency to destabilize membrane bilayers [Cullis, P. R. & de Kruijff, B. (1978) Biochim. Biophys. Acta 507, 207-218] and we have shown that dolichol promotes the destabilizing effect of PtdEtn on membranes composed of PtdCho and PtdEtn [Jensen, J. W. & Schutzbach, J. S. (1984) Biochemistry 23, 115-1119]. These results suggest that dolichyl-P-mannose synthase is optimally active in a phospholipid matrix that contains some component phospholipids that prefer non-bilayer structural organization in isolation. Heat-inactivation and sedimentation experiments demonstrated that the synthase associated with PtdEtn in the presence of dolichyl-P. The PtdEtn-reconstituted enzyme catalyzed the reversible transfer of mannose from GDP-mannose to dolichyl-P. The Km for GDP-mannose was found to be 0.69 microM and the apparent Km for dolichyl-P was 0.3 microM. GMP, GDP, and GTP inhibited mannosyl transfer 50% at concentrations of 16 microM, 1.3 microM and 3 microM respectively.

Induction of cellular efflux by a galactosamine polymer from Neurospora crassa

A cationic polymer of D-galactosamine was isolated from culture filtrates of a colonial temperature-sensitive strain of Neurospora crassa. Adsorption of the polymer to the cell surface initiated immediate efflux of low molecular weight metabolites and subsequent loss of viability. The polymer appeared to bind to those sites on the cell surface that normally bind calcium ions. Chemical analysis of the polymer showed it to be partially N-acetylated. The polymer had an isoelectric point of 8.4. Thirty percent of the D-galactosamine residues contained free amino groups. A rapid assay that has potential application for monitoring the effect of a variety of other membrane-active factors on membrane permeability has been developed.

Biosynthesis of heparin. Substrate specificity of heparosan N-sulfate D-glucuronosyl 5-epimerase

The substrate specificity of heparosan N-sulfate D-glucuronosyl 5-epimerase from a mouse mastocytoma was examined to determine the effects of N-acetyl and O-sulfate groups on substrate recognition by the enzyme. [5-3H]Glucuronosyl-labeled heparosan N-sulfate was prepared enzymatically and was modified chemically by partial N-desulfation and N-acetylation. After enzymatic release of tritium, the location of remaining label was determined by deaminative cleavage and analysis of resulting di-, tetra-, and higher oligosaccharides. This analysis indicated that a D-glucuronosyl residue is recognized as a substrate if it is linked at C-1 to an N-acetylated glucosamine residue and at C-4 to an N-sulfated unit. However, the reverse structure, in which the D-glucuronosyl moiety is bound at C-1 to an N-sulfated residue and at C-4 to N-acetylated glucosamine, is not a substrate. Similar studies with O-sulfated heparin intermediates showed that O-sulfate groups either at C-2 of the L-iduronosyl moieties or at C-6 of vicinal D-glucosaminyl moieties prevent 5-epimerization. These findings were confirmed by studies of the reverse reaction, in which tritium was incorporated from 3H2O into partially O-desulfated heparin and the location of incorporated radioactivity was determined. These and more direct experiments corroborated the previous conclusion that the L-iduronosyl moieties are formed after N-sulfation but before O-sulfation. Assessment of the influence of substrate size on the reaction further showed that a large substrate is preferred; an octasaccharide released tritium at a rate approximately 10% of that observed for the parent polysaccharide, and some release occurred also with smaller oligosaccharides.

New assay for uronosyl 5-epimerases

Simple assays have been developed for the two uronosyl 5-epimerases which participate in the biosynthesis of heparin and dermatan sulfate (heparosan N-sulfate D-glucuronosyl 5-epimerase and chondroitin D-glucuronosyl 5-epimerase, respectively). Following previously published procedures, substrates labeled with tritium in the C-5 positions of the D-glucuronosyl and L-iduronosyl residues were prepared enzymatically by incubation of O-desulfated heparin and dermatan with 3H2O and crude epimerase preparations from bovine liver and human skin fibroblasts, respectively. In the new assays, 3H2O generated from these substrates during the epimerase reactions was quantitated by the method of Pollard et al. (Anal. Biochem. (1981) 110, 424-430). In this procedure, 3H2O in the aqueous reaction mixture is extracted into a toluene-based organic phase containing 25% isoamyl alcohol, while the polysaccharide substrate remains in the aqueous phase and does not generate scintillations. This procedure is much simpler than that used previously which involves distillation of each reaction mixture and quantitation of the radioactivity in the distillate. The new assays have been validated by the demonstration that conditions of linearity with time and enzyme concentration can be established for both epimerase reactions. Assays of this type should be useful in the study of any enzymatic reaction where 3H2O is formed from a 3H-labeled substrate and the unreacted substrate is not appreciably soluble in the organic phase.

The biosynthesis of oligosaccharide-lipids. Activation of mannosyltransferase II by specific phospholipids

Mannosyltransferase II catalyzes transfer directly from GDP-mannose to an oligosaccharide-lipid resulting in the formation of the alpha-1,3-mannosyl linkage in Man alpha 1-3(Man alpha 1-6)Man beta-GlcNAc beta-GlcNac-P-P-lipid. The enzyme has been solubilized and purified 660-fold from rabbit liver microsomes (Jensen, J. W., and Schutzbach, J. S. (1981) J. Biol. Chem. 256, 12899-12904). Enzyme activity was reconstituted in the presence of specific phospholipids and evidence for the formation of an enzyme-phospholipid complex was obtained from kinetic studies, by the stabilization of the enzyme by phosphatidylethanolamine, and by co-sedimentation of the enzyme with phospholipid. Maximal activity was restored only when the enzyme was reconstituted in the presence of synthetic or naturally occurring phosphatidylethanolamine which contained unsaturated acyl chains. Investigation of the phospholipid specificity required for activation of the enzyme and results obtained with phospholipid vesicles of mixed composition suggest that the enzyme may have a requirement for phospholipids that can associate to form nonbilayer lipid structures in aqueous environments.

The biosynthesis of oligosaccharide-lipids. Partial purification and characterization of mannosyltransferase II

A mannosyltransferase that catalyzes transfer from GDP-mannose to tetrasaccharide-pyrophosphoryl-lipid with the formation of the alpha-1,3-mannosyl-mannose linkage in Man alpha 1-3(Man alpha 1-6)Man beta-GlcNAc beta-GlcNAc-P-P-lipid has ben purified 660-fold from rabbit liver microsomes. The enzyme was completely separated from mannosyltransferases that synthesize alpha-1,2-mannosyl-mannose linkages, but the purified preparation still contained some activity which synthesized alpha-1,6-mannosyl linkages. The enzyme has a requirement for divalent cations and a pH optimum between 6.8 and 7.3, and the purified enzyme was very sensitive to detergent concentration with optimal activity at 0.0225% Nonidet P-40. The extent of purification of the enzyme and its resistance to inhibition by amphomycin strongly suggest that the enzyme catalyzes direct transfer from nucleotide-sugar to the oligosaccharide-lipid acceptor.

The biosynthesis of oligosaccharide-lipids. Isolation of an oligosaccharide-P-P-lipid acceptor

An oligosaccharide-P-P-lipid has been isolated from porcine liver by extraction with organic solvents and purified by chromatography on silica gel and DEAE-cellulose. The purified oligosaccharide-lipid was shown to contain mannose and N-acetylglucosamine in an approximate ratio of 1:1 and our results suggest that the major oligosaccharide component in the preparation was a tetrasaccharide with the composition (Man)2 (GlcNAc)2. When the oligosaccharide-lipid was incubated with GDP-[14C]mannose and a solubilized enzyme preparation from rabbit liver in the presence of MgCl2, three radioactive products could be isolated. The oligosaccharides in the products could be identified as a penta-, a hexa-, and a heptasaccharide. These products were formed by the stepwise addition of mannose to the growing oligosaccharide chain and GDP-mannose was indicated as the glycosyl donor in each reaction.

The biosynthesis of oligosaccharide-lipids. Formation of an alpha-1,2-mannosyl-mannose linkage

An enzyme present in rabbit liver microsomes has been found to catalyze mannosyltransfer from GDP-mannose to exogenously added oligosaccharide-lipid acceptor resulting in the formation of an alpha-1,2-mannosyl-mannose linkage. Several lines of evidence suggest that the product is a heptasaccharide containing a single 1,6-linked branched glycosyl unit with 65% of the newly added mannosyl units in a terminal nonreducing position. The enzyme has been solubilized with non-ionic detergents and was partially purified on DEAE-cellulose and hydroxylapatite. The partially purified enzyme no longer catalyzed the formation of dolichol-P-mannose indicating a direct transfer from GDP-mannose to oligosaccharide-lipid acceptor.