Effect of the first wave of COVID-19 on Poison Control Centre activities in 21 European countries: an EAPCCT initiative

BACKGROUND

Public health emergencies often affect Poison Control Centre (PCC) operations. We examined possible effects of the coronavirus disease 2019 (COVID-19) pandemic on call volume, call characteristics, and workload in European PCCs.

METHOD

All 65 individual European PCCs were requested to supply data on the number of calls and call characteristics (caller, age groups, reason and specific exposures) from March to June in 2018, 2019, and 2020 (Part 1). Number of calls with specific characteristics was normalised to all calls. Calls (N) and call characteristics (%) were compared between 2020 and 2018/2019 (average), within PCCs/countries and grouped. Correlation between call volume and COVID-19 cases per PCC/country was examined. All PCCs received a survey on workload (Part 2). Parts 1 and 2 were independent.

RESULTS

For Part 1, 36 PCCs (21 countries) supplied 26 datasheets. PCCs in the UK and in France merged data and supplied one datasheet each with national data. Summed data showed an increase of 4.5% in call volume from 228.794 in 2018/2019 (average) to 239.170 in 2020 (p < 0.001). Within PCCs/countries, calls significantly increased for 54% of PCCs/countries (N = 14/26) and decreased for 19% (N = 5/26), three of which (N = 3/5) only serve medical professionals. Correlation between call volume and COVID-19 cases was (non-significant) positive (Rho >0.7) in 5/26 PCCs/countries (19%), and negative in 6/26 (23%). Call characteristics (median proportion of grouped data in 2018/2019 vs. 2020) changed: fewer medical professionals called (40 vs. 34%, p < 0.001), calls on intentional exposures decreased (20 vs. 17%, p < 0.012), as did calls on patients between 13 and 17 years (5 vs. 4%, p < 0.05). Calls on specific exposures increased; disinfectants from 1.9 to 5.2%, and cleaning products from 4.4 to 5.7% (p < 0.001). For Part 2, 38 PCCs (24 countries) filled the survey on workload (number/length of shifts and time on PCC duties), which increased in 23/38 PCCs (61%), while 10/38 (26%) worked with fewer employees.

CONCLUSIONS

Obtaining aggregated European PCC data proved challenging but showed an increase in overall call volume and workload during the first COVID-19 wave. Call characteristics changed including fewer calls from professionals and more calls on specific exposures. Within single PCCs/countries a variety of effects was observed.

0768 A Million Dreams: Improving Compliance and Treatment of Obstructive Sleep Apnea via Upper Airway Stimulation Therapy. Real-World Outcomes

Introduction

Patient compliance to continuous positive airway pressure (CPAP) has been about 50% at 4-years despite numerous improvements in mask design, flow algorithms, education, and monitoring software. Compliance, however, is not equivalent to efficacy. Upper Airway Stimulation (UAS) is an alternative for select CPAP intolerant patients. We used a patient management platform to track UAS compliance and efficacy.

Methods

Anonymized, aggregated device usage and outcomes data was analyzed from a HIPAA compliant patient management platform (Inspire Cloud, Inspire Medical Systems, Golden Valley MN) through October 2021. Demographic data is not collected. We used this database to understand therapy outcomes. Data are presented as mean and standard deviation, unless otherwise noted.

Results

There were 1.74 million usage nights for 5,709 patients across 550 clinics. Patients increased median stimulation amplitude from 1.4 to 2.2 volts between activation to 90 days after activation. Typical therapy was activated at 11:44pm, and turned off at 5:51am, with one 13-minute pause per night, and therapy was on 89% of nights.Usage was 5.5 ± 1.8 hours per nights overall, and 6.0 ± 1.9 hours per night used. At 90 days, 90% of patients had usage &gt; 4 hours per nights overall, and 96% had usage &gt; 4 hours per night used.Average pre-implant AHI was reduced from 35 ± 15 events/hour (n=2760), to 9 ± 12 (n=1609) after therapy. ESS was reduced from 11 ± 5 (n=1254) to 7 ± 5 (n=1164).

Conclusion

This data represents the first big-data reporting of UAS therapy usage in general clinical practice including nightly data. It demonstrates high nightly usage with minimal pauses and marked improvement in symptoms. It demonstrates the potential that CPAP intolerant patients with can be fully adherent with alternative therapy.

Support (If Any)

Statistical support provided by Inspire Medical systems.

0772 Clusters of Upper Airway Stimulation Adherence Patterns in the First 90 Days

Introduction

Upper airway stimulation (UAS) therapy is effective for a subset of obstructive sleep apnea (OSA) patients with CPAP intolerance. While overall adherence is high, some patients have suboptimal adherence to UAS, which limits effectiveness. Our goal was to identify UAS therapy usage patterns during the first three months of therapy that affect adherence.

Methods

We retrieved anonymized UAS therapy usage data from 2,091 individuals stored in a cloud-based monitoring system during the first three months after device activation. We aggregated adherence data including mean and standard deviation (SD) of nightly hours of use, therapy pauses, hours from midnight when the therapy was turned ON and OFF, and percentage of missing days. We computed the difference of the stimulation amplitude between the first and last day. We performed cluster analysis with Gaussian mixture models and computed the centroids of each cluster highlighting their main differences.

Results

We identified six distinct clusters of UAS usage patterns. Clusters 1A (34% of the total cohort) and 1B (23%) had excellent therapy usage with 7.23h and 7.14h on days of use, respectively; with 1B distinguished by increased night-to-night variability. Clusters 2A (16%) and 2B (12%) had good mean therapy use of 6.63h and 6.21h, respectively, but their usage patterns were distinguished by a higher percentage of missing days (8% missing days in 2A and 23% in 2B) and less favorable therapy timing with an average therapy ON time after midnight. Clusters 3A (8%) and 3B (7%) were characterized by the lowest nightly use at 6.16h and 5.50h, respectively, and the highest night-to-night variability. 3A was further distinguished by the highest percentage of missing days (34%) while 3B was characterized by the frequent therapy pauses (mean 4.1 pauses per night) and the least increase in stimulation amplitude across the first 90 days.

Conclusion

Cluster analysis of UAS usage patterns identified six distinct groups that may enable custom interventions for improved long-term management. Differentiation of these groups may have clinical implications on conditions (e.g. therapy discomfort, comorbid insomnia, poor sleep hygiene) that impact adherence.

Support (If Any)

 

Cluster analysis of upper airway stimulation adherence patterns and implications on clinical care

Study Objectives

Upper airway stimulation (UAS) therapy is effective for a subset of obstructive sleep apnea (OSA) patients with continuous positive airway pressure (CPAP) intolerance. While overall adherence is high, some patients have suboptimal adherence, which limits efficacy. Our goal was to identify therapy usage patterns during the first 3 months of therapy to enable targeted strategies for improved adherence.

Methods

Therapy data was retrieved from 2098 patients for three months after device activation. Data included mean and standard deviation (SD) of hours of use, therapy pauses, hours from midnight the therapy was turned ON and OFF, percentage of missing days, and stimulation amplitude. Cluster analysis was performed using Gaussian mixture models that categorized patients into six main groups.

Results

The six groups and their prevalence can be summarized as Cluster 1A: Excellent Use (34%); Cluster 1B: Excellent Use with variable timing (23%); Cluster 2A: Good Use with missing days and late therapy ON (16%), Cluster 2B: Good Use with missing days, late therapy ON, and early therapy OFF (12%); Cluster 3A: Variable Use with frequent missing days (8%); Cluster 3B: Variable Use with frequent pauses (7%). Most patients (85%) are excellent or good users with mean therapy use &gt;6 hours per night.

Conclusions

Cluster analysis of early UAS usage patterns identified six distinct groups that may enable personalized interventions for improved long-term management. Differentiation of the patient clusters may have clinical implications with regard to sleep hygiene education, therapy discomfort, comorbid insomnia, and other conditions that impact adherence.

Post-implant care pathway: lessons learned and recommendations after 5 years of clinical implementation of hypoglossal nerve stimulation therapy

Hypoglossal nerve stimulation (HNS) therapy is now an established and widely-available obstructive sleep apnea (OSA) treatment alternative for continuous positive airway pressure (CPAP)-intolerant patients. Additionally, the HNS body of literature is robust with strong data on safety, efficacy, and durability-from the 5-year STAR Trial outcomes, to post-approval studies of independent institutions, to the multicenter ADHERE registry which recently reported outcomes on over 1,000 patients and is poised to enroll 5,000 HNS patients total. Nevertheless, now with thousands of implanted patients across hundreds of certified centers, and that number growing rapidly, the post-implant management of the HNS patient represents the next critical frontier. Post-implant patient management (therapy titration, troubleshooting, adjustments, and adherence monitoring) across a longitudinal care model is key to ensuring long-term therapy success and optimizing patient outcomes and health benefits. As with CPAP, patient education and close clinical monitoring are often essential to successful long-term management. Although many HNS patients are clear responders with excellent comfort and adherence as well as effective improvement in symptomatic and objective outcome measures, and even a smaller subset is clear non-responders, there is a growing body of patients somewhere in the middle: good outcomes but not great; partial but incomplete response. These are the patients in whom a standardized best-practice approach to treatment monitoring and targeted therapy modifications is likely critical to optimizing long-term outcomes.

Comparison of sporadic and familial behavioral variant frontotemporal dementia (FTD) in a North American cohort

INTRODUCTION

Behavioral variant frontotemporal dementia (bvFTD) may present sporadically or due to an autosomal dominant mutation. Characterization of both forms will improve understanding of the generalizability of assessments and treatments.

METHODS

A total of 135 sporadic (s-bvFTD; mean age 63.3 years; 34% female) and 99 familial (f-bvFTD; mean age 59.9; 48% female) bvFTD participants were identified. f-bvFTD cases included 43 with known or presumed chromosome 9 open reading frame 72 (C9orf72) gene expansions, 28 with known or presumed microtubule-associated protein tau (MAPT) mutations, 14 with known progranulin (GRN) mutations, and 14 with a strong family history of FTD but no identified mutation.

RESULTS

Participants with f-bvFTD were younger and had earlier age at onset. s-bvFTD had higher total Neuropsychiatric Inventory Questionnaire (NPI-Q) scores due to more frequent endorsement of depression and irritability.

DISCUSSION

f-bvFTD and s-bvFTD cases are clinically similar, suggesting the generalizability of novel biomarkers, therapies, and clinical tools developed in either form to the other.

Validation and determination of taselisib, a β-sparing phosphoinositide 3-kinase (PI3K) inhibitor, in human plasma by LC-MS/MS

A liquid chromatographic-tandem mass spectrometry (LC-MS/MS) method for the determination of taselisib (GDC-0032, RO5537381) concentrations in human plasma has been developed and validated to support bioanalysis of clinical samples. Solid phase extraction (SPE) was used to extract plasma samples (50μL) and the resulting samples were analyzed using reversed phase chromatography and mass spectrometry coupled with an atmospheric pressure chemical ionization interface. The mass analysis of taselisib was performed using multiple reaction monitoring transitions in positive ionization mode. The method was validated over the calibration curve range 0.400-400ng/mL using linear regression and 1/x(2) weighting. The within-run relative standard deviation (%RSD) ranged from 1.3 to 5.6%, while the between-run %RSD varied from 2.0 to 4.5% for LLOQ, low, medium, medium high and high QCs. The accuracy ranged from 94.7 to 100.3% of nominal for within-run and 96.0-99.0% of nominal for between-run for the same QCs. Extraction recovery of taselisib was between 83.8% and 92.9%. Stability of taselisib was established in human plasma for 977days at -20°C and -70°C and established in sample extracts for 96h when stored at 2 - 8°C. Stable-labeled internal standard was used to minimize matrix effects. Mean single dose pharmacokinetic parameters determined using this method for a phase I/II clinical trial were: Cmax=35.2ng/mL, AUC0-inf=1570ngh/mL, and T1/2=39.3h.

A supported liquid extraction-LC-MS/MS method for determination of GDC-0980 (Apitolisib), a dual small-molecule inhibitor of class 1A phosphoinositide 3-kinase and mammalian target of rapamycin, in human plasma

A liquid chromatographic-tandem mass spectrometry (LC-MS/MS) method for the determination of GDC-0980 (Apitolisib) concentrations in human plasma has been developed and validated to support clinical development. Supported liquid extraction (SLE) was used to extract plasma samples (80μL) and the resulting samples were analyzed using reverse-phase chromatography and mass spectrometry coupled with a turbo-ionspray interface. The mass analysis of GDC-0980 was performed using multiple reaction monitoring (MRM) transitions in positive ionization mode. The method was validated over the calibration curve range 0.0500-25.0ng/mL using linear regression and 1/x(2) weighting. Within-run relative standard deviation (%RSD) ranged from 0.4 to 3.9%, while the between-run %RSD varied from 1.1 to 1.5% for QCs. The accuracy ranged from 96.1% to 106.7% of nominal for within-run and 96.7-106.7% of nominal for between-run at all concentrations including the LLOQ quality control at 0.0500ng/mL. Extraction recovery of GDC-0980 was between 72.4% and 75.5%. Stability of GDC-0980 was established in human plasma for 547 days at -20°C and -70°C and established in reconstituted sample extracts for 146h when stored at 2-8°C. Stable-labeled internal standard was used to minimize matrix effects. Mean pharmacokinetic parameters determined using this method for the day 1 control group in a phase I trial were: Cmax=11.1ng/mL, AUC0-inf=108ngh/mL, and T1/2=13.1h.

Idiopathic neuralgic amyotrophy in childhood

In addition to the review by van Alfen et al., which has been published in 2000, we would like to report a seven-week-old boy with bilateral idiopathic brachial plexus neuropathy that did not show any signs of osteomyelitis on repeated scintigraphy. To our knowledge this is the first child reported with bilateral plexus involvement.

Biocatalytic approaches for the quantitative production of single stereoisomers from racemates

Strategies for the chemoenzymatic transformation of a racemate into a single stereoisomeric product in quantitative yield have been developed. A range of industrially relevant alpha-hydroxycarboxylic acids was deracemized in a stepwise fashion via lipase-catalysed enantioselective O-acylation, followed by mandelate racemase-catalysed racemization of the remaining non-reacted substrate enantiomer. Alternatively, aliphatic alpha-hydroxycarboxylic acids were enzymatically isomerized using whole resting cells of Lactobacillus spp. Enantioselective hydrolysis of rac-sec-alkyl sulphate esters was accomplished using novel alkyl sulphatases of microbial origin. The stereochemical path of catalysis could be controlled by choice of the biocatalyst. Whereas Rhodococcus ruber DSM 44541 and Sulfolobus acidocaldarius DSM 639 act through inversion of configuration, stereo-complementary retaining sulphatase activity was detected in the marine planctomycete Rhodopirellula baltica DSM 10527.

Biomimetic approach toward the stereoselective synthesis of acetogenins

Acetogenins isolated from the Annonaceae family of tropical trees have drawn considerable attention owing to their broad spectrum of biological activities. They are structurally characterized by the presence of one to three tetrahydrofuran rings in the center of a long (partly hydroxylated) hydrocarbon chain that ends in a (functionalized) butenolide moiety. Here we describe some of our results toward the first asymmetric total synthesis of cis-gigantrionenin, a principal acetogenin. In this approach, an enzyme-catalyzed epoxide hydrolysis and an enzyme-triggered double cyclization are crucial and give stereoselective access to essential chiral building blocks.

Advances in biocatalytic synthesis. Enzyme-triggered asymmetric cascade reactions

Organic compounds can be transformed through enzyme-triggered domino (or cascade) reactions via several (inseparable) consecutive steps in an asymmetric fashion to yield nonracemic products. Despite the fact that these sequences often involve the occurrence of highly reactive unstable intermediates, the overall efficiency of these processes can be high, provided that the reaction rates of the individual steps match each other in order to minimize side reactions.

Non-sequential processes for the transformation of a racemate into a single stereoisomeric product: proposal for stereochemical classification

Non-sequential processes which allow the transformation of a racemate into a single stereoisomeric product without the occurrence of an "undesired" isomer are classified according to their underlying stereochemistry. A re-definition of the term "de-racemization" is proposed.

Microbial epoxide hydrolases for preparative biotransformations

Epoxide hydrolases from microbial sources are highly versatile biocatalysts for the asymmetric hydrolysis of epoxides on a preparative scale. Besides kinetic resolution, which furnishes the corresponding vicinal diol and remaining non-hydrolysed epoxide in nonracemic form, enantioconvergent processes are possible: these are highly attractive as they lead to the formation of a single enantiomeric diol from a racemic oxirane. The data accumulated over recent years reveal a common picture of the substrate structure selectivity pattern of microbial epoxide hydrolases and indicate that substrates of various structural types can be selectively hydrolysed with enzymes from certain microbial sources.

Assisted reproductive interventions and multiple birth

OBJECTIVE

To investigate the contributions of ovulation-inducing drugs and assisted reproductive technologies to multiple birth.

METHODS

This historic prospective study was conducted in a cohort of 13,151 women who delivered after 20 weeks' gestation between October 1996 and December 1999. The study setting was a Colorado health maintenance organization. Cases were women who were pregnant as a result of exposure to treatment with either assisted reproductive technologies or ovulation induction in the absence of assisted reproductive technologies. The main outcome measure was multiple birth.

RESULTS

There was a significant association between assisted conception and multiple birth. Compared with women with naturally conceived pregnancies, there was a 25-fold likelihood (95% confidence interval 18, 35, P <.001) of multiple birth among women exposed to any of those treatments. In the total cohort the proportion of multiple births attributable to those treatments was 33%. After adjusting for the use of assisted conception and other covariates, we found no association between advanced maternal age and multiple birth.

CONCLUSION

In this cohort, assisted reproductive interventions were strongly associated with multiple birth. Although a higher proportion of older women sought assisted reproductive technologies, we did not find an independent relationship between advanced maternal age and multiple birth. The increasing number of multiple births attributable to assisted conception raises public health concerns regarding multiple gestation-related maternal and infant morbidities.

Compartment pressure monitoring during anterior cruciate ligament reconstruction

A prospective double blind randomized study was carried out using 20 healthy males with anterior cruciate ligament (ACL) insufficiency undergoing bone-patellar tendon-bone ACL reconstruction. The subjects were randomized into either water or saline irrigation and then underwent identical reconstructive procedures using an arthroscopic pump. Continuous preoperative, intraoperative, and postoperative pressures were monitored using the slit catheter technique. Blood pressure and compartment pressure measurements were continuously recorded and noted at all stages of the procedure. Mean preoperative anterior and posterior compartment pressures were similar in both groups. No significant differences were noted between the anterior and posterior compartments of each group. No difference between water and saline irrigation was identified throughout the procedure. In both groups, postoperative pressures were slightly lower in the anterior and posterior compartments compared with preoperative pressures, but not significantly.

Determination of absolute configuration in 4-aryl-3, 4-dihydro-2(1H)-pyrimidones by high performance liquid chromatography and CD spectroscopy

The absolute configuration of three 4-aryl-3, 4-dihydro-2(1H)-pyrimidones (Biginelli compounds, DHPMs) was established by comparison of the typical circular dichroism (CD) spectra of individual enantiomers with reference samples of known absolute configuration. The enantiomers were obtained by semipreparative separation of racemic mixtures on a Chiralcel OD-H chiral stationary phase. The method was used to establish the enantiopreference of various lipases in biocatalytic kinetic resolution experiments employing activated DHPM esters.

Epoxide hydrolases and their synthetic applications

Chiral epoxides and 1,2-diols, which are central building blocks for the asymmetric synthesis of bioactive compounds, can be obtained by using enzymes--i.e. epoxide hydrolases--which catalyse the enantioselective hydrolysis of epoxides. These biocatalysis have recently been found to be more widely distributed in fungi and bacteria than previously expected. Sufficient sources from bacteria, such as Rhodococcus and Nocardia spp., or fungi, as for instance Aspergillus and Beauveria spp., have now been identified. The reaction proceeds via an SN2-specific opening of the epoxide, leading to the formation of the corresponding trans-configured 1,2-diol. For the resolution of racemic monosubstituted and 2,2- or 2,3-disubstituted substrates, various fungi and bacteria have been shown to possess excellent enantioselectivities. Additionally, different methods, which lead to the formation of the optically pure product diol in a chemical yield far beyond the 50% mark (which is intrinsic to classic kinetic resolutions), are discussed. In addition, the use of non-natural nucleophiles such as azides or amines provides access to enantiomerically enriched vicinal azido- and amino-alcohols. The synthetic potential of these enzymes for asymmetric synthesis is illustrated with recent examples, describing the preparation of some biologically active molecules.

Stereoselectivities of microbial epoxide hydrolases

Epoxide hydrolases from bacterial and fungal sources are highly versatile biocatalysts for the asymmetric hydrolysis of epoxides on a preparative scale. Besides kinetic resolution, which yields the corresponding enantiomerically enriched vicinal diol and the remaining nonconverted epoxide, enantioconvergent processes are also possible, which lead to the formation of a single enantiomeric diol from a racemic oxirane. The data available to date indicate that the enantioselectivities of enzymes from certain microbial sources can be correlated to the substitutional pattern of various types of substrates: red yeasts (e.g. Rhodotorula or Rhodosporidium sp.) give best enantioselectivities with monosubstituted oxiranes; fungal cells (e.g. from Aspergillus and Beauveria sp.) are best suited for styrene oxide-type substrates; bacterial enzymes, on the other hand (in particular from Actinomycetes such as Rhodococcus and Nocardia sp.) are the biocatalysts of choice for more highly substituted 2,2- and 2,3-disubstituted epoxides.

Detection of a new enzyme for stereoselective hydrolysis of linalyl acetate using simple plate assays for the characterization of cloned esterases from Burkholderia gladioli

Plate assays were developed for the identification of specific hydrolytic activities of esterases from Burkholderia gladioli, cloned and expressed in Escherichia coli. Clones showing different substrate specificities were identified by fluorescence or azo-dye formation caused by the released alcohol moiety of the hydrolyzed substrates, or by colour change of pH indicators mediated by decreased pH. The use of 1-hydroxypyrene-3,6,8-trisulfonic acid (HPTS-) esters and linalyl acetate for these assays clearly allowed to discriminate substrate specificities for two different cloned esterases, EP6 and EP10. Long chain fatty acid HPTS-esters were only hydrolyzed by the EP10 clone. On the other hand, the EP6 clone showed significant activity in hydrolysis of the sterically hindered ester linalyl-acetate. Enantioselective hydrolysis of linalyl acetate could be verified with a crude EP6 preparation on a preparative scale.

Purification and characterization of a highly selective epoxide hydrolase from Nocardia sp. EH1

A highly enantioselective, soluble epoxide from Nocardia sp. EH1 was purified to homogeneity via a four-step procedure: (i) hydrophobic interaction chromatography on Phenyl Sepharose CL-4B, (ii) anion exchange chromatography on SOURCE 30Q, followed by (iii) a second hydrophobic interaction chromatography on Phenyl Sepharose HP, and finally (iv) gel-filtration on Superdex 75 HR 10/30. The pure protein was shown to be a monomer of integral of 34 kDa possessing an optimum pH of 8-9. Neither UV-absorbing cofactors nor metal ions were required for activity. In contrast to whole-cell activity, the partially purified enzyme proved to be considerably less stable. Stabilization was achieved by addition of non-ionic detergents such as Tween 80 or Triton X-100, causing a shift of the temperature optimum from 35 to 40 degrees C. Both effects combined led to an enhancement of the relative activity of up to approximately 150% of that of the native enzyme.

Evaluation of the developmental neuroendocrine and reproductive toxicology of aluminium

Two experiments evaluating functional endpoints pertaining to the developmental neuroendocrine effects of aluminum in the rat are reported. A total of 31 timed mated dams were fed by daily gastric gavage 0, 5, 25, 50, 250, 500 or 1000 mg/kg body weight/day aluminum as a solution of aluminum lactate in distilled water from days 5 to 15 of gestation. The 390 offspring were evaluated for morphological and physiological parameters of reproductive functioning, including birth weight, anogenital distance (AGD), timing of vaginal opening, regularly of oestrous cycles, duration of pseudopregnancy (PSP), number of superovulated oocytes, and gonadal weight. No consistent or reproducible findings suggestive of toxic effect were found in the parameters of birth weight, AGD, timing of vaginal opening, duration of PSP, number of superovulated oocytes, and adult gonadal weight. A temporary increase in the proportion of aberrant oestrous cycles was detected during the first four cycles after vaginal opening, in the 250 mg/body weight/day group, with none by the fifth consecutive oestrous cycle. These results suggest that, apart from a transient disturbance of oestrous cycle regularity, aluminum does not have a developmental reproductive toxic effect.

Enantiomeric perylene-glycerolipids as fluorogenic substrates for a dual wavelength assay of lipase activity and stereoselectivity

A new type of fluorogenic alkyldiacyl glycerols was synthesized and used as fluorogenic substrates for the analysis of lipase activities and stereoselectivities. These compounds contain perylene as a fluorophore and the trinitrophenylamino (TNP) residue as a quencher. Both substituents are covalently bound to the omega-ends of the sn-2 and sn-1 (3) acyl chains, respectively. Upon glycerolipid hydrolysis, the residues are separated from each other thus allowing determination of lipase activity by the continuous increase in fluorescence intensity which is caused by dequenching. Using enantiomeric pairs of these compounds, we were able to analyze lipase stereoselectivity depending on the reaction medium. Mixtures of enantiomeric fluorogenic alkyldiacyl glycerols, selectively labelled with pyrene or perylene as fluorophores, can be used for a dual-wavelength "stereoassay" of lipases. Since absorption and emission maxima of both labels are clearly separated, hydrolysis of the respective enantiomeric substrates can be determined simultaneously, and the difference in the rates of hydrolysis can be taken as a parameter for the stereopreference of a lipase. Hydrolysis rates measured with perylene-substituted lipids are generally lower than those obtained with the pyrene analogs. Thus, with a mixture of perylene and pyrene-substituted lipids, we observe a higher apparent stereoselectivity of lipases since we measure a combination of stereo- and substrate selectivity. In the presence of albumin, all microbial lipases tested so far exhibit stereopreference for the sn-1 glycerol position. In our assay, the apparent stereoselectivities are highest if in the presence of albumin, the sn-1 position carries pyrene and the sn-3 position is substituted with perylene. The lipase stereoselectivity assay described here requires the simultaneous measurement of the fluorescence intensities at two different wavelengths in a single cuvette and can thus be carried out using existing and cheap instrumentation that was developed for the fluorimetric analysis of Ca+2 concentrations.

Inversion of lipase stereospecificity for fluorogenic alkyldiacyl glycerols. Effect of substrate solubilization

We synthesized enantiomeric 1-O-alkyl-2,3-diacyl-sn-glycerol and 3-O-alkyl-1,2-diacyl-sn-glycerol containing pyrene as a fluorescent reporter and the trinitrophenylamino residue as a fluorescence quencher; both reporter groups were covalently bound to the omega end of the acyl chains at positions sn-2 and sn-3(1), respectively. The fluorescence of the intact substrate molecules was very low. Chemical or enzymic release of the fatty acyl chains lead to fluorescence dequenching. The rate of lipolysis could be measured from the time-dependent increase in fluorescence intensity. We used the respective substrates for the continuous determination of activity and stereopreference of four different microbial lipases from Chromobacterium viscosum, Candida rugosa, Pseudomonas sp., Rhizopus arrhizus, as well as cutinase from Fusarium solani and lipoprotein lipase from bovine milk. The stereopreference of the lipases depended, in general, on how the substrate was solubilized in the reaction medium. All lipases under investigation preferentially hydrolysed the sn-1 acyl ester bond, if the lipid analog was dispersed in albumin-containing Tris/HCl buffer in the absence of detergent or organic solvent. In mixtures of 1:1 (by vol.) water/ethanol, the enzymes showed higher activity toward the sn-3 acyl ester bond, except for lipoprotein lipase which preferred the sn-1 acyl isomer under all conditions tested. Different stereopreferences were observed with the different lipases if the substrate was solubilized by amphiphiles (micelles of N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate). C. rugosa lipase and F. solani cutinase showed high stereopreference for the sn-3 acyl ester, whereas Pseudomonas sp. lipase and C. viscosum lipase hydrolysed both enantiomers at similar rates. From spectroscopic studies, it can be inferred that the conformation of the fluorescent lipids is probably similar in water, mixtures of water and organic solvents, and in micelles. The possible effects of reaction conditions on substrate accessibility and enzyme conformation on stereoselectivity of the respective lipases are discussed.