Role of neighborhood context in ovarian cancer survival disparities: current research and future directions

Ovarian cancer is the fifth leading cause of cancer-associated mortality among US women with survival disparities seen across race, ethnicity, and socioeconomic status, even after accounting for histology, stage, treatment, and other clinical factors. Neighborhood context can play an important role in ovarian cancer survival, and, to the extent to which minority racial and ethnic groups and populations of lower socioeconomic status are more likely to be segregated into neighborhoods with lower quality social, built, and physical environment, these contextual factors may be a critical component of ovarian cancer survival disparities. Understanding factors associated with ovarian cancer outcome disparities will allow clinicians to identify patients at risk for worse outcomes and point to measures, such as social support programs or transportation aid, that can help to ameliorate such disparities. However, research on the impact of neighborhood contextual factors in ovarian cancer survival and in disparities in ovarian cancer survival is limited. This commentary focuses on the following neighborhood contextual domains: structural and institutional context, social context, physical context represented by environmental exposures, built environment, rurality, and healthcare access. The research conducted to date is presented and clinical implications and recommendations for future interventions and studies to address disparities in ovarian cancer outcomes are proposed.

Pembrolizumab plus Chemotherapy in Advanced Endometrial Cancer

BACKGROUND

Standard first-line chemotherapy for endometrial cancer is paclitaxel plus carboplatin. The benefit of adding pembrolizumab to chemotherapy remains unclear.

METHODS

In this double-blind, placebo-controlled, randomized, phase 3 trial, we assigned 816 patients with measurable disease (stage III or IVA) or stage IVB or recurrent endometrial cancer in a 1:1 ratio to receive pembrolizumab or placebo along with combination therapy with paclitaxel plus carboplatin. The administration of pembrolizumab or placebo was planned in 6 cycles every 3 weeks, followed by up to 14 maintenance cycles every 6 weeks. The patients were stratified into two cohorts according to whether they had mismatch repair-deficient (dMMR) or mismatch repair-proficient (pMMR) disease. Previous adjuvant chemotherapy was permitted if the treatment-free interval was at least 12 months. The primary outcome was progression-free survival in the two cohorts. Interim analyses were scheduled to be triggered after the occurrence of at least 84 events of death or progression in the dMMR cohort and at least 196 events in the pMMR cohort.

RESULTS

In the 12-month analysis, Kaplan-Meier estimates of progression-free survival in the dMMR cohort were 74% in the pembrolizumab group and 38% in the placebo group (hazard ratio for progression or death, 0.30; 95% confidence interval [CI], 0.19 to 0.48; P<0.001), a 70% difference in relative risk. In the pMMR cohort, median progression-free survival was 13.1 months with pembrolizumab and 8.7 months with placebo (hazard ratio, 0.54; 95% CI, 0.41 to 0.71; P<0.001). Adverse events were as expected for pembrolizumab and combination chemotherapy.

CONCLUSIONS

In patients with advanced or recurrent endometrial cancer, the addition of pembrolizumab to standard chemotherapy resulted in significantly longer progression-free survival than with chemotherapy alone. (Funded by the National Cancer Institute and others; NRG-GY018 ClinicalTrials.gov number, NCT03914612.).

Sociodemographic disparities in targeted therapy in ovarian cancer in a national sample

Background

The treatment landscape for ovarian cancer has changed in recent years with the introduction of targeted therapies to treat patients with advanced disease. We investigated patient demographic and clinical factors associated with use of targeted therapies as a part of the first-line treatment for ovarian cancer.

Methods

This study included patients diagnosed with stage I-IV ovarian cancer between 2012 and 2019 from the National Cancer Database. Information on demographic and clinical characteristics were collected and described using frequency and percent across receipt of targeted therapy. Logistic regression was used to compute the odds ratios (ORs) and 95% confidence intervals (CI) associating patient demographic and clinical factors with receipt of targeted therapy.

Results

Among 99,286 ovarian cancer patients (mean age 62 years), 4.1% received targeted therapy. The rate of targeted therapy receipt across racial and ethnic groups over the study period was fairly similar; however, non-Hispanic Black women were less likely to receive targeted therapy than their non-Hispanic White counterparts (OR=0.87, 95% CI: 0.76-1.00). Patients who received neoadjuvant chemotherapy were more likely to receive targeted therapy than those who received adjuvant chemotherapy (OR=1.26; 95% CI: 1.15-1.38). Moreover, among patients who received targeted therapy, 28% received neoadjuvant targeted therapy, with non-Hispanic Black women being most likely to receive neoadjuvant targeted therapy (34%) compared with other racial and ethnic groups.

Conclusions

We observed differences in receipt of targeted therapy by factors such as age at diagnosis, stage, and comorbidities present at diagnosis, as well as factors related to healthcare access-including neighborhood education level and health insurance status. Approximately 28% of patients received targeted therapy in the neoadjuvant setting, which could negatively impact treatment outcomes and survival due to the increased risk of complications associated with targeted therapies that may delay or prevent surgery. These results warrant further evaluation in a cohort of patients with more comprehensive treatment information.

A New High Affinity Hemoglobin Variant: Hb San Francisco-KP (HBB: c.104T>C)

The evaluation of erythrocytosis can fail to detect hemoglobin (Hb) variants if a thorough and systemic investigation is not undertaken. Here we report the identification of a novel high-oxygen affinity Hb that was previously misclassified as polycythemia vera (PV). Given that treatment recommendations can vary significantly based on the etiology of erythrocytosis, familiarity with reference laboratories and their methodologies is of crucial importance to conducting a precise consultation, as in the case of our Hb variant, named Hb San Francisco-KP [β34(B16)Val→Ala, HBB: c.104T>C] for the city and medical center where it was discovered. The Mayo Clinic's (Rochester, MN, USA) Erythrocytosis Evaluation (REVE) panel was instrumental in establishing a final diagnosis. Of note, the patient's clinical response to phlebotomy distinguishes this subtype from many of the other high affinity Hbs where the erythrocytosis is primarily compensatory and not in need of venesection.

Abstract P15: Treatment (TX) of advanced melanoma during the Coronavirus Disease 2019 (COVID-19) pandemic in Kaiser Permanente Northern California (KPNC)

The COVID-19 pandemic brought with it TX changes for many patients (pts) with AMEL, as it did for other pts with cancer. The long-term impacts of mandated area lockdowns, social distancing, medical society guidelines, and patient preference will not be fully understood for some time. The first step to learning from the pandemic is to assess how AMEL care was rendered in 2020. We performed a retrospective analysis of systemic TX for AMEL in KPNC, an integrated community healthcare system with approximately 4 million pts and about 150 de novo diagnoses of AMEL annually. We performed a chart review of pts with AMEL who were treated with standard of care systemic therapy, either immune-checkpoint inhibitors (ICI) or BRAF/MEK inhibitors (BRAF/MEKi), from January 1 to March 15, 2020, as a control group, and between March 15 and May 20, during the first wave of the COVID-19 pandemic in California with follow-up through November 4, 2020. Between January 1 and March 15, 26 pts started palliative ICI of whom 11 started combination PD1 (PD1i) and CTLA4 inhibitors. Among 15 pts who started on single-agent PD1i, 14 pts received short-interval TX (SIT), while 1 started long-interval TX (LIT). All 21 pts who started perioperative PD1i pre-pandemic, started on SIT. Between March 15 and May 20, 21 pts started palliative ICI, of whom only 3 started combination TX. Among pts who started palliative single-agent PD1i 40% started on LIT in this initial phase of the pandemic. 27 pts started perioperative ICI during this time. We found 3 started with neoadjuvant therapy and 78% started on LIT. Among 78 pts who were already on palliative single-agent ICI at the start of the COVID-19 pandemic, 15% remained on SIT and 24% changed to LIT. Sixteen pts (21%) also interrupted palliative ICI between March 15 and April 15 after a median time on TX of 45 weeks and for 63% the cited reason for interruption on chart review was the COVID 19 pandemic. Three of these pts who stopped ICI changed to BRAF/MEKi, the remainder continue in active follow-up as of November 2020. Among 72 pts already receiving perioperative ICI in March 2020, 19% remained on SIT, 35% changed to LIT, and 11% were already on LIT. 39% of pts interrupted perioperative ICI after a median time of 20 weeks on TX and 46% of these cited COVID 19 as the reason for interruption. Three pts have since resumed peri-operative TX, but the others remain in active follow-up off therapy. Between 3/15 and 5/30/2020, we noted a 325% increase in pts started on BRAF/MEKi; 69% of pts received therapy for palliative intent. The start of the COVID-19 pandemic saw many different changes in AMEL TX in KPNC, with increased use of single-agent ICI, LIT, and oral therapy, in line with public health guidance, oncology societal guidelines and patient preference. It will be important to assess the long-term outcomes relating to these changes, including the impact of early discontinuation of ICI, to help guide future Melanoma care during and after the pandemic.

Citation Format: Juraj Kavecansky, Nina Shah, Angeles Price, Frank Hsieh, Alice Kengla, Belinda Ark, Jahan Tavakoli, Christine Kaiser, Mingqing Li, Sejal Jhatakia, Mala Reddy, Dazhi Cen, Philip Sardar, Stephen Wang, Ashok Pai, Andrea Harzstark, Tatjana Kolevska, Thach-Giao Truong. Treatment (TX) of advanced melanoma during the Coronavirus Disease 2019 (COVID-19) pandemic in Kaiser Permanente Northern California (KPNC) [abstract]. In: Proceedings of the AACR Virtual Meeting: COVID-19 and Cancer; 2021 Feb 3-5. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(6_Suppl):Abstract nr P15.

Association of anticoagulation use with SARS-CoV2 detection

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Patients who warrant chronic warfarin can safely continue warfarin therapy with precautions during the COVID-19 pandemic.

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Chronic warfarin therapy is not associated with a higher rate of positively testing for SAR-CoV2.

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Patients on warfarin during the COVID-19 pandemic maintained TTR rates consistent with those prior to the COVID-19 pandemic.

Early case ascertainment and prospective multidisciplinary review for management of new melanoma diagnoses within an integrated healthcare system: The Kaiser Permanente Northern California experience

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Background: Appropriate surgical treatment of early-stage melanoma yields a high cure rate, but this management can be nuanced. In particular, surgical management, including sentinel lymph node biopsy (SLNB), of thin melanoma (≤1.0mm) is not well-defined. Methods: Biopsies with new melanoma diagnoses were identified electronically and manually reviewed. In a community oncology setting, we organized a review panel of physicians specialized in melanoma from dermatology, medical oncology, nuclear medicine, radiation oncology, and surgical subspecialties (oncology, plastics, head and neck). Patients were assigned to care pathways based on NCCN and ASCO guidelines, including guidance on SLNB for thin melanomas with high-risk features like lymphovascular invasion, high mitotic rate, positive deep margin, and ulceration. These recommendations were documented in the chart and communicated directly to the patient’s care team. Results: From 11/2016 through 10/2018, our multidisciplinary committee reviewed 3626 patients with new melanoma from 22 sites in our integrated, regional hospital system. Median age was 66 (range 19-99); 60% were male. cT2N0 tumors comprised 7%, cT3 3%, and cT4 2%. Thin melanomas ≤1.0mm represented 71% of cases, of which 34% were ≤0.5mm. SLNB was performed in 9.8% of thin melanomas, and 18% were positive, much higher than historical positive rates of 3-4%. Conclusions: Early case ascertainment and prospective multidisciplinary review in a community oncology setting resulted in increased identification of high-risk thin melanoma, and consequently increased identification of nodal disease through SLNB. Positive SLNB triggers important clinical decision-making regarding need for node dissection versus clinical surveillance, and need for adjuvant therapy, which have been shown to improve survival. This clinical practice structure improved risk-stratification and adherence to national guidelines. We plan to further study the impact of these improvements to melanoma care on disease-free survival and overall survival.

Retrospective review of metastatic uveal melanoma (mUM) at NYU Perlmutter Cancer Center (NYU-PCC)

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Background: Uveal melanoma (UM) is the most common primary intraocular malignancy in adults, despite its rare incidence of 5 per 1,000,000. UM metastasis (mets) occurs in approximately 50% of patients (pts). The published median survival from the time of mets is only 6 to 12 months (mos). To date there is no curative therapy for pts with mUM. Methods: This is a retrospective review of pts evaluated at NYU-PCC with UM between January 1, 2011 and December 31, 2016. Data collected include: ophthalmic treatment, time from ophthalmic diagnosis, systemic metastatic sites, genetic mutations (muts), systemic treatment and survival. Results: During this 5-year interval, 100 UM pts were referred to NYU-PCC. 58 pts were diagnosed with high-risk primary T3/T4 sized tumors and remained disease-free during this period. For the remaining 42 pts that developed mUM, primary ophthalmic treatments included: 12 enucleations, 27 brachytherapy and 3 received none since they had synchronous UM and mUM. Therapy for mUM included liver-directed therapy (LDT) such as TACE, 90Y brachytherapy, or radiofrequency ablation; or systemic therapy. These mUM pts had a median survival of 17 mos. 20 mUM pts are male; 22 pts are female; Ages: 33-96; 24 deceased and 18 alive. Of the latter, 5 are NED and 13 are alive with disease on treatment. 24 deceased mUM pts treated initially with LDT lived on average 14 mos longer than those treated with any systemic therapy alone; pts with LDT had a median survival of 24 mos, compared to 10 mos for those treated only with systemic therapy (p = 0.0075). There was no correlation between time of ophthalmic diagnosis and time to onset of mets and survival (R2value 0.00243). Genetic analysis of met tumors was available on 9 pts. 3 of 5 pts with GNA11 muts are alive compared to 1 of 4 pts with GNAQ muts. Conclusions: Pts with mUM treated initially with LDT had significantly longer survival compared to pts treated with systemic therapy alone. Whether longer survival in these pts is an effect of LDT, earlier treatment of mets, or a more indolent disease remains to be determined. Our study demonstrates mUM pts survive an average of 17 mos, which is higher than historically reported. Significance of GNAQ or GNA11 requires further investigation.

Chromosome breakage is regulated by the interaction of the BLM helicase and topoisomerase IIalpha

Cells deficient in the recQ-like helicase BLM are characterized by chromosome changes that suggest the disruption of normal mechanisms needed to resolve recombination intermediates and to maintain chromosome stability. Human BLM and topoisomerase IIα interact directly via amino acids 489-587 of BLM and colocalize predominantly in late G2 and M phases of the cell cycle. Deletion of this region does not affect the inherent in vitro helicase activity of BLM but inhibits the topoisomerase IIα-dependent enhancement of its activity, based on the analysis of specific DNA substrates that represent some recombination intermediates. Deletion of the interaction domain from BLM fails to correct the elevated chromosome breakage of transfected BLM-deficient cells. Our results demonstrate that the BLM-topoisomerase IIα interaction is important for preventing chromosome breakage and elucidate a DNA repair mechanism that is critical to maintain chromosome stability in cells and to prevent tumor formation.

Telomerase-associated protein 1, HSP90, and topoisomerase IIalpha associate directly with the BLM helicase in immortalized cells using ALT and modulate its helicase activity using telomeric DNA substrates

The BLM helicase associates with the telomere structural proteins TRF1 and TRF2 in immortalized cells using the alternative lengthening of telomere (ALT) pathways. This work focuses on identifying protein partners of BLM in cells using ALT. Mass spectrometry and immunoprecipitation techniques have identified three proteins that bind directly to BLM and TRF2 in ALT cells: telomerase-associated protein 1 (TEP1), heat shock protein 90 (HSP90), and topoisomerase IIalpha (TOPOIIalpha). BLM predominantly co-localizes with these proteins in foci actively synthesizing DNA during late S and G(2)/M phases of the cell cycle when ALT is thought to occur. Immunoprecipitation studies also indicate that only HSP90 and TOPOIIalpha are components of a specific complex containing BLM, TRF1, and TRF2 but that this complex does not include TEP1. TEP1, TOPOIIalpha, and HSP90 interact directly with BLM in vitro and modulate its helicase activity on telomere-like DNA substrates but not on non-telomeric substrates. Initial studies suggest that knockdown of BLM in ALT cells reduces average telomere length but does not do so in cells using telomerase.

Deoxygenation-induced alterations in sickle cell membrane cholesterol exchange

Changes in a membrane sterol exchange of sickle red blood cells (SS RBC) induced by deoxygenation were studied using the fluorescent cholesterol analogue dehydroergosterol (DHE). DHE uptake by SS RBC membrane was measured by the incubation of SS RBC with small unilamellar vesicles (SUV) containing DHE. Deoxygenation of SS RBC, but not normal RBC, increased the rate of DHE uptake. DHE membrane content after 5 h of incubation with SUV in the cell-to-SUV ratio of 1:1 (mol lipid) was 16.25 +/- 0.94 and 12.22 +/- 0.85% of total sterol for deoxygenated and oxygenated cells, respectively. Membrane spicules isolated from these deoxygenated SS RBC had three-fold higher DHE content, suggesting that the increased sterol exchange was localized to spicules. When isolated spicules were incubated with DHE-SUV directly, 91 +/- 3% of membrane sterol was rapidly exchanged, in contrast to intact RBC, in which a maximum of 33% of sterol could be exchanged. The results suggest that spicule formation in SS RBC alters membrane cholesterol structure, such that a domain of cholesterol that is normally nonexchangeable becomes readily exchangeable with exogenous sterol.

Cholesterol domains in biological membranes

Membrane cholesterol is distributed asymmetrically both within the cell or within cellular membranes. Elaboration of intracellular cholesterol trafficking, targeting and intramembrane distribution has been spurred by both molecular and structural approaches. The expression of recombinant sterol carrier proteins in L-cell fibroblasts has been especially useful in demonstrating for the first time that such proteins actually elicit intracellular and intraplasma membrane redistribution of sterol. Additional advances in the use of native fluorescent sterols allowed resolution of transbilayer and lateral cholesterol domains in plasma membranes from cultured fibroblasts, brain synaptosomes and erythrocytes. In all three cell surface membranes, cholesterol is enriched in the inner, cytofacial leaflet. Up to three different cholesterol domains have been identified in the lateral plane of the plasma membrane: a fast exchanging domain comprising less than 10% of cholesterol, a slowly exchanging domain comprising about 30% of cholesterol, and a very slowly or non-exchangeable sterol domain comprising 50-60% of plasma membrane cholesterol. Factors modulating plasma membrane cholesterol domains include polyunsaturated fatty acids, expression of intracellular sterol carrier proteins, drugs such as ethanol, and several membrane pathologies (systemic lupus erythematosus, sickle cell anaemia and aging). Disturbances in plasma membrane cholesterol domains alter transbilayer fluidity gradients in plasma membranes. Such changes are associated with decreased Ca(2+)-ATPase and Na+, K(+)-ATPase activity. Thus, the size, dynamics and distribution of cholesterol domains within membranes not only regulate cholesterol efflux/influx but also modulate plasma membrane protein functions and receptor-effector coupled systems.

Regulation of membrane cholesterol domains by sterol carrier protein-2

Sterols are not randomly distributed in membranes but appear to be localized in multiple kinetic domains. Factors that regulate these sterol domains are not well-understood. A recently developed fluorescence polarization assay that measures molecular sterol transfer [Butko, P., Hapala, I., Nemecz, G., of Schroeder, F. (1992) J. Biochem. Biophys. Methods 24, 15-37] was used to examine the mechanism whereby anionic phospholipids and liver sterol carrier protein-2 (SCP2) enhance sterol transfer. Two exchangeable and one very slowly or nonexchangeable sterol domain were resolved in phosphatidylcholine (POPC)/sterol small unilamellar vesicles (SUV). Inclusion of 10 mol % anionic phospholipids enhanced sterol exchange primarily by redistribution of sterol domain sizes rather than by alteration of half-times of exchange. This effect was dependent primarily on the percent content rather than the net charge per anionic phospholipid. In contrast, SCP2 simultaneously altered both the distribution of sterol molecules between kinetic domains and the exchange half-times of exchangeable sterol domains. The effects of SCP2 were much more pronounced when 10% acidic phospholipid was incorporated in the SUV. Compared to spontaneous sterol exchange, in the presence of 1.5 microM SCP2, the rapidly exchanging pool was increased by 36 to 330%, depending on the SUV phospholipid composition. Concomitantly, exchange half-times for rapidly and slowly exchangeable sterol were reduced by 60 to 98% for 1t1/2 and 14 to 85% for 2t1/2, respectively. The stimulatory effect of SCP2 was saturable and dependent both on protein concentration and on content of acidic phospholipids in membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Erythrocyte membrane lateral sterol domains: a dehydroergosterol fluorescence polarization study

Structural domains of cholesterol and their regulation in the erythrocyte membrane are poorly understood. Dehydroergosterol fluorescence polarization change was used to continuously monitor the kinetics of sterol exchange and sterol domain size in erythrocyte ghost membranes. Direct correlation between molecular sterol exchange and steady-state dehydroergosterol fluorescence polarization measurements was obtained without separation of donor and acceptor membranes. Three important observations were made. First, sterol exchange between small unilamellar vesicles (SUV) with the same cholesterol/phospholipid ratio as the erythrocyte membrane (1-palmitoyl-2-oleoylphosphatidylcholine/cholesterol = 1:1) was resolved into three kinetic cholesterol domains: 23 +/- 9% of total sterol was rapidly exchangeable, with t1/2 = 23 +/- 6 min; 59 +/- 9% of total sterol was slowly exchangeable, with t1/2 = 135 +/- 3 min; and 19 +/- 9% of total sterol was essentially nonexchangeable, with a t1/2 of days. Second, the substitution of erythrocyte ghosts for SUV as an acceptor significantly altered the kinetic parameters of sterol exchange from donor SUV, graphically showing that both the properties of the acceptor and spontaneous desorption of cholesterol from the donor SUV influenced spontaneous cholesterol transfer. Third, studies of exchange between erythrocyte ghosts revealed multiple kinetic pools of sterol differing from those in the SUV: 4 +/- 2% of total sterol was rapidly exchangeable, with t1/2 = 32 +/- 9 min; 29 +/- 3% of total sterol was very slowly exchangeable, with t1/2 = 23 +/- 7 h; and a surprisingly large 67 +/- 2% of total sterol was nonexchangeable, with a t1/2 of days.

Mechanistic studies of sterol carrier protein-2 effects on L-cell fibroblast plasma membrane sterol domains

The factors which regulate intermembrane sterol domains and exchange in biomembranes are not well understood. A new fluorescent sterol exchange assay allowed correlation of changes in polarization to sterol transfer. Analysis of spontaneous sterol exchange between L-cell plasma membranes indicated two exchangeable and one very slowly or nonexchangeable sterol domain. The exchangeable domains exhibited half-times of 23 and 140 min with fractional contributions of 5 and 30%, respectively. Sterol carrier protein-2 (SCP-2) enhanced sterol exchange between L-cell plasma membranes and altered sterol domain size in a concentration dependent manner. Previous model membrane studies indicate that SCP-2 alters sterol domains and exchange through interaction with anionic phospholipids. In contrast to these observations, the ionic shielding agents KCl, low pH, or neomycin were either totally or partially ineffective inhibitors of SCP-2 action in L-cell plasma membrane exchanges. Thus the mechanism of SCP-2 in sterol transfer appears to be less charge dependent in L-cell plasma membranes than in model membranes. The cholesterol lowering drug probucol was also capable of altering the sterol exchange kinetics.

Are membrane enzymes regulated by the viscosity of the membrane environment?

We have examined the idea that membrane enzymes are regulated by the viscosity of surrounding lipids using data compiled from the literature for the effect of the change in membrane viscosity ([symbol: see text]) at the gel- to liquid-crystal-phase transition on the activities of several enzymes. The analysis was not extended explicitly to the problem of viscosity-dependent regulation of membrane enzymes in liquid-crystalline lipids because of the absence of exact data for values of [symbol: see text] in liquid-crystalline phases of variable composition. For most membrane enzymes studied, energies of activation are discontinuous, while kcat is continuous, at the main-phase transition. We consider that the energy of activation contains terms related to the height of the chemical barrier to reaction and terms due to the mechanical properties of the bilayer, such as the work of expansion during the catalytic cycle and the temperature dependence of [symbol: see text]. We find that the differences in energies of activation, above and below the break points in Arrhenius plots, are orders of magnitude larger than can be accounted for by the above mechanical factors. Thus, discontinuities in energies of activation at the phase transition appear to reflect changes in the chemical barrier to reaction, which is independent of [symbol: see text]. The theorectical analysis indicates too that values of [symbol: see text] for bilayers in the liquid-crystalline phase would have to be several orders of magnitude larger than those for gel phases in order to provide a basis for viscosity-dependent regulation of membrane enzymes in liquid-crystalline phases.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of high pressure on the catalytic and regulatory properties of UDP-glucuronosyltransferase in intact microsomes

The effects of high pressure on the kinetic properties of microsomal UDP-glucuronosyltransferase (assayed with 1-naphthol as aglycon) were studied in the range of 0.001-2.2 kbar to clarify further the basis for regulating this enzyme in untreated microsomes. Activity changed in a discontinuous manner as a function of pressure. Activation occurred at pressure as low as 0.1 kbar, reaching one of two maxima at 0.2 kbar. As pressure was increased above 0.2 kbar, activity decreased, reaching a minimum at about 1.4 kbar followed by a second activation. The pathway for activation at pressure greater than 1.4 kbar was complex. The immediate effect of 2.2 kbar was nearly complete inhibition of activity. The inhibited state relaxed, however, over about 10 min (at 10 degrees C), to a state that was activated as compared with enzyme at 0.001 kbar or enzyme at pressures between 1.4 and 2.2 kbar, which was the highest pressure we could test. Examination of the detailed kinetic properties of UDP-glucuronosyltransferase indicated that the effects of pressure were due to selective stabilization of unique functional states of the enzyme at 0.2 and 2.2 kbar. Activation at 0.2 kbar was reversible when pressure was released. This was true as well as for activation at pressure greater than 1.4 kbar, but after prolonged treatment at 2.2 kbar, UDP-glucuronosyltransferase became activated irreversibly on release of pressure. The process by which prolonged treatment at 2.2 kbar led to permanent activation of UDP-glucuronosyltransferase after release of pressure was not reflected, however, by time-dependent changes in the functional state of UDP-glucuronosyltransferase at this pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Organization of microsomal UDP-glucuronosyltransferase. Activation by treatment at high pressure

Treatment of microsomes at pressures as high as 2.25 kbar led to an apparent irreversible activation of UDP-glucuronylsyltransferase when pressure was released. The response of the enzyme to pressure, as reflected by activity measured after release of pressure, appeared to be discontinuous in that no activation was seen for any preparation at pressures less than 1.2 kbar. In addition, activation was temperature dependent. Maximum activation at 2.25 kbar occurred at about 12 degrees C; the extent of activation in 10 min was less for either higher or lower temperatures. Activation was also time dependent. Maximum activation at 2.25 kbar and 9 degrees C required 90 min of pressure treatment. Activation appeared to occur more slowly at lower pressure. Pressure-induced activation was associated with a loss of sensitivity of the enzyme to allosteric activation by UDP-N-Ac-Glc and a conversion of the kinetic pattern from non-Michaelis-Menten to Michaelis-Menten. Pressure did not activate enzyme that had previously been activated maximally by adding detergent to microsomes. Pressure also did not activate pure UDP-glucuronosyltransferase reconstituted into unilamellar vesicles of dioleoylphosphatidylcholine. Pressure treatment did not release UDP-glucuronosyltransferase from microsomes into water. Pressure had a continuous effect on the polarization and excimer/monomer formation of fluorescent probes incorporated into microsomes, and the properties returned essentially to their values at 1 atm when pressure was released. Measurements of activity at 2.2 kbar showed that pressure-induced activation of UDP-glucuronosyltransferase in microsomes occurred via two intermediates that were inactive and that the activated state of the enzyme was generated during/after release of pressure.(ABSTRACT TRUNCATED AT 250 WORDS)