TRUU-Lab: Methods for Optimization of Test Names for Understanding and Utilization

Poor understandability of laboratory test names increases risk for inappropriate test utilization and medical errors. Yet, human understandability has not been a major consideration in existing laboratory test names or naming guidelines. TRUU-Lab (Test Renaming for Understanding and Utilization for Laboratory Test Names) is a national initiative that now has more than 45 members representing more than 20 academic and industry organizations, the CDC, the FDA, and organizations outside of the US. The goals of the initiative include: 1) Identify root causes and challenges in understanding and using laboratory test names; 2) Share resources related to potential solutions; 3) Develop consensus guidelines for laboratory test naming; 4) Establish consensus names for existing laboratory tests; and 5) Promote the adoption and implementation of consensus laboratory test names. Previous studies have addressed the first two goals of this initiative by identifying problematic test names and features of test names that contribute to misutilization. We also identified advantages and limitations of current test naming guidelines and previous standardization efforts. This study addresses goals 3 and 4 of the TRUU-Lab initiative. We have adopted an iterative process of guideline development, to make use of feedback from establishing consensus names to improve guidelines and vice versa. Preliminary work in this area has focused on definition of optimal laboratory test names from a human understandability perspective. By analysis of test characteristics through the process of test name redefinition, we found that the requirements for optimal understandability vary with respect to clinical scenario and provider background. This highlights the need for naming guidelines to permit flexibility in the components and presentation format for laboratory test display names. We are using results from this work to construct idealized candidate test names given an appropriate clinical scenario. Candidate names will be evaluated by survey studies through the Brand Institute, which offers expertise in pharmaceutical name and brand identity development. We are assessing different laboratory test names under controlled conditions, with studies conducted in two phases. The first phase, conducted through pilot surveys sent to primary care providers, assesses intuitive name preferences given a short and specific prompt. The second phase will use a simulated electronic medical record environment to present mock clinical scenarios, which surveyed physicians will use to select an appropriate test. We expect that results from survey studies will directly inform the development of TRUU-Lab naming guidelines, in turn permitting development of better optimized laboratory test names. This process represents a new strategy for intentional design of laboratory test names that are understandable and promote correct provider utilization.

What’s in a Name? Comparative Analysis of Laboratory Test Naming Guidelines as Applied to Common Confusing Test Names

Introduction/Objective

Laboratory test names frequently do not enable easy understandability or promote correct test utilization, which leads to difficulty for providers in finding the correct test and results in unnecessary cost and medical errors. Laboratory test names are also largely unstandardized and are not named by a consistent set of conventions. To address these issues, the TRUU-Lab (Test Renaming for Understanding & Utilization) initiative aims to generate a consensus test naming guideline for better human understandability of laboratory test names. These studies address the first aim of the TRUU-Lab initiative: to identify root causes and challenges in understanding and using laboratory test names.

Methods

We conducted survey studies to capture the most problematic laboratory test names, then performed analysis of these names to identify aspects of these names that led to confusion among providers. A subset of these test names were used to evaluate five existing laboratory test naming guidelines (LOINC, ONC TigerTeam, Pan- Canadian iEHR Viewer Name, Standards for Pathology Informatics (Australia), and ARUP Laboratories internal style guides) for their ability to produce understandable test names.

Results

274 survey responses yielded ~100 unique laboratory tests cited as confusing, and highlighted substantial diversity both in the names of these tests between institutions and in respondent opinion on the best alternative names. The top 10 most commonly-cited tests yielded ≥ 3 unique names, and the top 2 tests (Vitamin D and anti- factor Xa) yielded ≥ 10 unique names. Post-survey analysis identified eight characteristics associated with poor understandability of a test name, including ambiguity, abbreviations, homophones, multiple indications for a single test, proprietary names, synonyms, truncation, and “panels” where components are obfuscated. Existing guidelines produced highly variable names given the same prompt, and varied in their ability to avoid pitfalls associated with poor understandability.

Conclusion

These studies highlight aspects of existing laboratory test names that lead to confusion among ordering providers, and identify the inability of existing laboratory test naming practices to adequately address these issues. Efforts are ongoing within TRUU-Lab to use these results to inform novel laboratory test naming guidelines to promote universal human understandability.

TRUU-Lab: Methods for Optimizing Test Names for Understanding and Utilization

Introduction/Objective

Poor understandability of laboratory test names increases the risk for inappropriate test utilization and medical errors. Yet, human understandability has not been a major consideration in existing laboratory test names or naming guidelines. TRUU-Lab (Test Renaming for Understanding and Utilization for Laboratory Test Names) is a national initiative that now has more than 45 members representing more than 20 academic and industry organizations, the CDC, and the FDA. The goals of the initiative include: 1) Identify root causes and challenges in understanding and using laboratory test names; 2) Share resources related to potential solutions; 3) Develop consensus guidelines for laboratory test naming; 4) Establish consensus names for existing laboratory tests; and 5) Promote the adoption and implementation of consensus laboratory test names.

Methods

We previously addressed the first two goals of this initiative by identifying problematic test names and features of test names that contribute to misutilization. We also identified the advantages and limitations of current test naming guidelines and previous standardization efforts. This current study addresses goals 3 and 4. We developed an iterative process of guideline development. This process includes collecting feedback on consensus names to improve guidelines, which then informs the improvement of the consensus names.

Results

By analyzing test name characteristics, we found that the requirements for understandability vary with respect to the clinical scenario and provider background. We have used these results to design a 30-min long survey to test candidate names. The survey will be distributed through the Brand Institute, which offers expertise in pharmaceutical name and brand identity development. This pilot survey will be sent to primary care providers to assesses intuitive name preferences given a short and specific prompt. The second phase will take place in a simulated electronic medical record environment to present clinical scenarios where physicians will select an appropriate test.

Conclusion

We expect that results from survey studies will directly inform the development of TRUU-Lab naming guidelines, in turn permitting development of better-optimized laboratory test names. This process represents a new strategy for the intentional design of laboratory test names that are understandable and promote correct provider utilization.

What’s in a Name? Comparative Analysis of Laboratory Test Naming Guidelines as Applied to Common Confusing Test Names

Laboratory test names frequently do not enable easy understandability or promote correct test utilization, which leads to difficulty for providers in finding the correct test and results in unnecessary cost and medical errors. As a further complication, laboratory test names are largely unstandardized and are not named based on a consistent set of conventions. To address these issues, the TRUU-Lab (Test Renaming for Understanding & Utilization) initiative aims to generate a consensus laboratory test naming guideline for better human understandability of laboratory test names. These studies address the first and second aims of the TRUU-Lab initiative: 1) to identify root causes and challenges in understanding and using laboratory test names, and 2) to share resources related to potential solutions. We initially conducted survey studies to capture the most commonly problematic laboratory test names, then performed analysis of these names to identify aspects of these names that led to confusion among providers. 274 survey responses yielded ~100 unique laboratory tests that respondents felt were confusing, and highlighted substantial diversity both in the names of these tests between institutions and in respondent opinion on the best alternative names, with the top 10 most commonly-cited tests having at least 3 unique names, and the top 2 tests (Vitamin D and anti-factor Xa) having at least 10 unique names. Post-survey analysis identified eight common characteristics associated with poor understandability of a test name, including ambiguity, abbreviations, homophones, multiple indications for a single test, non-descriptive proprietary names, synonyms, truncation due to software limitations, and €œpanels where test components are obfuscated. A subset of the survey-identified confusing test names were used to evaluate existing laboratory test naming guidelines for their ability to produce understandable test names. Five guidelines, including LOINC, ONC TigerTeam, Pan-Canadian iEHR Viewer Name, Standards for Pathology Informatics (Australia), and ARUP Laboratories internal style guides, were evaluated, and produced highly variable names given the same test name prompt. Further, existing guidelines also varied in their ability to avoid pitfalls previously identified as associated with poor understandability. Together, these studies highlight the aspects of existing laboratory test names that lead to confusion among ordering providers, and identify the inability of existing laboratory test naming practices to adequately address these issues. Efforts are ongoing within TRUU-Lab to use these results to inform novel laboratory test naming guidelines that promote universal human understandability. Work is also ongoing to apply these novel guidelines to generate new candidate test names, and conduct survey analysis to evaluate the effects of new test naming guidelines on understandability and correct test utilization.

Optimization of the Order Menu in the Electronic Health Record Facilitates Test Patterns Consistent With Recommendations in the Choosing Wisely Initiative

OBJECTIVES

Thyroid and rheumatologic autoimmune testing are areas where evidence-based guidance from specialty organizations and Choosing Wisely support utilizing screening tests for autoimmune and thyroid disorders prior to more specialized testing. Adjustment of the orderable options in the electronic health record (EHR) can influence ordering patterns without requiring manual review or additional effort by the clinician.

METHODS

The menu was adjusted to reflect recommendations from Choosing Wisely to favor screening tests that automatically reflex to specialized testing on primary care providers' preference lists. Effectiveness was evaluated by reviewing total orders for individual tests.

RESULTS

Shifts in ordering from individual screening tests (antinuclear antibody and thyrotropin) to ones that reflexed to specialized testing were observed in parallel with significant reductions in the corresponding specialized testing.

CONCLUSIONS

Optimization of the EHR laboratory ordering menu can be used to shift ordering patterns toward Choosing Wisely recommendations.

Implementation of Laboratory Review of Test Builds Within the Electronic Health Record Reduces Errors

CONTEXT.—

As electronic health records (EHRs) become more ubiquitous, physicians have come to expect that laboratory data from a variety of sources will be incorporated into the EHR in a structured format. The Clinical Laboratory Improvement Amendments have standards for data transmission traditionally met by pathologist review of their own hospital laboratory information system transmissions. However, with third-party laboratory data now being sent through external (nonhospital laboratory) interfaces, ownership of this review is less clear. Lack of an expert laboratory review process prior to changes being implemented can result in mapping and interfacing errors that could lead to misinterpretation and diagnostic errors.

OBJECTIVE.—

To determine the impact of retrospective and prospective laboratorian-assisted review on the volume of interface errors and new builds.

DESIGN.—

A seminal event led to a restructuring of the process for review of EHR laboratory builds, using laboratory expertise.

RESULTS.—

A review of 26 500 test result fields found 61 of 4282 (1.4%) unique codes that could have led to misinterpretation. These were corrected and a process for proactive review and maintenance by laboratory experts was implemented. This resulted in monthly decreases in outbound error message from 4270 to 1820 (57.4%), in new test builds from 586 to 274 (53.2%), and in new result builds from 1116 to 552 (50.5%).

CONCLUSIONS.—

Regular review and maintenance of external laboratory test builds in EHRs by a laboratory review team reduces interface error messages and reduces the number of new builds required for results to file into the EHR.

Cost per Case Mix Index-Adjusted Hospital Day as a Measure of Effective Laboratory Utilization Efforts in a Growing Academic Medical Center

OBJECTIVES

Traditional laboratory utilization measures are unable to detect the results of small-scale utilization improvement efforts in a background of rising patient volumes and acuity. However, accurate assessment is necessary to document effectiveness of these efforts.

METHODS

Test menu changes, physician education, and laboratory utilization feedback were used to address costs and overused tests. Effectiveness was evaluated using cost/case mix index (CMI)-adjusted hospital day and inpatient tests/CMI-adjusted discharge. These metrics were compared with the more traditional measures of cost/test and inpatient tests/discharge.

RESULTS

Cost/CMI-adjusted hospital day and inpatient tests/CMI-adjusted discharge better demonstrated the impact of utilization improvement efforts compared with more traditional measures because they account for changes in patient volume and acuity.

CONCLUSIONS

Cost/CMI-adjusted hospital day and tests/CMI-adjusted discharge show the effectiveness of laboratory utilization efforts despite increasing patient volume and acuity.

Impact of weekly feedback on test ordering patterns

OBJECTIVES

We examined the impact of weekly feedback reports on the test-ordering behavior of internal medicine residents.

STUDY DESIGN

Retrospective analysis of a performance improvement effort.

METHODS

In a large, urban, academic medical center, we extracted raw data on every inpatient laboratory test ordered by all internal medicine residents during two 26-week time periods. The pre-intervention phase established baseline ordering volume as each resident rotated through the various clinical services. The intervention consisted of a 1-hour educational seminar detailing the potential harm and costs of laboratory overutilization followed by the post intervention phase, which consisted of weekly feedback reports graphically illustrating individual versus group ordering patterns, where the identity of individual residents was protected. The total numbers of tests ordered during the 2 phases were compared using an independent t test.

RESULTS

During the post intervention phase, we observed a net reduction of 21% in tests ordered-an average of 941 tests per week-with the greatest reduction in the chemistry section of the laboratory, followed by hematology, coagulation, and all others combined. This reduction in test volume corresponded to a $1.3 million reduction in charges.

CONCLUSIONS

Providing physicians-in-training with a weekly feedback report detailing their test ordering volume in comparison with those of their peers is an effective method for reducing laboratory overutilization. Benefits to our approach include maintaining physician autonomy without alteration of existing infrastructure or disclosure of test fees.

Unbiased statistical analysis for multi-stage proteomic search strategies

"Multi-stage" search strategies have become widely accepted for peptide identification and are implemented in a number of available software packages. We describe limitations of these strategies for validation and decoy-based statistical analyses and demonstrate these limitations using a set of control sample spectra. We propose a solution that corrects the statistical deficiencies and describe its implementation using the open-source software X!Tandem.

Erythrocytosis-associated HIF-2alpha mutations demonstrate a critical role for residues C-terminal to the hydroxylacceptor proline

A classic physiologic response to hypoxia in humans is the up-regulation of the ERYTHROPOIETIN (EPO) gene, which is the central regulator of red blood cell mass. The EPO gene, in turn, is activated by hypoxia inducible factor (HIF). HIF is a transcription factor consisting of an alpha subunit (HIF-alpha) and a beta subunit (HIF-beta). Under normoxic conditions, prolyl hydroxylase domain protein (PHD, also known as HIF prolyl hydroxylase and egg laying-defective nine protein) site specifically hydroxylates HIF-alpha in a conserved LXXLAP motif (where underlining indicates the hydroxylacceptor proline). This provides a recognition motif for the von Hippel Lindau protein, a component of an E3 ubiquitin ligase complex that targets hydroxylated HIF-alpha for degradation. Under hypoxic conditions, this inherently oxygen-dependent modification is arrested, thereby stabilizing HIF-alpha and allowing it to activate the EPO gene. We previously identified and characterized an erythrocytosis-associated HIF2A mutation, G537W. More recently, we reported two additional erythrocytosis-associated HIF2A mutations, G537R and M535V. Here, we describe the functional characterization of these two mutants as well as a third novel erythrocytosis-associated mutation, P534L. These mutations affect residues C-terminal to the LXXLAP motif. We find that all result in impaired degradation and thus aberrant stabilization of HIF-2alpha. However, each exhibits a distinct profile with respect to their effects on PHD2 binding and von Hippel Lindau interaction. These findings reinforce the importance of HIF-2alpha in human EPO regulation, demonstrate heterogeneity of functional defects arising from these mutations, and point to a critical role for residues C-terminal to the LXXLAP motif in HIF-alpha.

Role of promoter polymorphisms in the plasma glutathione peroxidase (GPx-3) gene as a risk factor for cerebral venous thrombosis

BACKGROUND AND PURPOSE

Plasma glutathione peroxidase (GPx-3) is a major antioxidant enzyme in plasma and the extracellular space that scavenges reactive oxygen species produced during normal metabolism or after oxidative insult. A deficiency of this enzyme increases extracellular oxidant stress, promotes platelet activation, and may promote oxidative posttranslational modification of fibrinogen. We recently identified a haplotype (H(2)) in the GPx-3 gene promoter that increases the risk of arterial ischemic stroke among children and young adults.

METHODS

The aim of this study is to identify possible relationships between promoter haplotypes in the GPx-3 gene and cerebral venous thrombosis (CVT). We studied the GPx-3 gene promoter from 23 patients with CVT and 123 young controls (18 to 45 years) by single-stranded conformational polymorphism and sequencing analysis.

RESULTS

Over half of CVT patients (52.1%) were heterozygous (H(1)H(2)) or homozygous (H(2)H(2)) carriers of the H(2) haplotype compared with 12.2% of controls, yielding a more than 10-fold independent increase in the risk of CVT (OR=10.7; 95% CI, 2.70 to 42.36; P<0.0001). Among women, the interaction of the H(2) haplotype with hormonal risk factors increased the OR of CVT to almost 70 (P<0.0001).

CONCLUSIONS

These findings show that a novel GPx-3 promoter haplotype is a strong, independent risk factor for CVT. As we have previously shown that this haplotype is associated with a reduction in transcriptional activity, which compromises antioxidant activity and antithrombotic benefits of the enzyme, these results suggest that a deficiency of GPx-3 leads to a cerebral venous thrombophilic state.

Promoter polymorphisms in the plasma glutathione peroxidase (GPx-3) gene: a novel risk factor for arterial ischemic stroke among young adults and children

BACKGROUND AND PURPOSE

Plasma glutathione peroxidase (GPx-3)-deficiency increases extracellular oxidant stress, decreases bioavailable nitric oxide, and promotes platelet activation. The aim of this study is to identify polymorphisms in the GPx-3 gene, examine their relationship to arterial ischemic stroke (AIS) in a large series of children and young adults, and determine their functional molecular consequences.

METHODS

We studied the GPx-3 gene promoter from 123 young adults with idiopathic AIS and 123 age- and gender-matched controls by single-stranded conformational polymorphism and sequencing analysis. A second, independent population with childhood stroke was used for a replication study. We identified 8 novel, strongly linked polymorphisms in the GPx-3 gene promoter that formed 2 main haplotypes (H1 and H2). The transcriptional activity of the 2 most prevalent haplotypes was studied with luciferase reporter gene constructs.

RESULTS

The H2 haplotype was over-represented in both patient populations and associated with an independent increase in the risk of AIS in young adults (odds ratio=2.07, 95% CI=1.03 to 4.47; P=0.034) and children (odds ratio=2.13, 95% CI=1.23 to 4.90; P=0.027). In adults simultaneously exposed to vascular risk factors, the risk of AIS approximately doubled (odds ratio=5.18, 95% CI=1.82 to 15.03; P<0.001). Transcriptional activity of the H2 haplotype was lower than that of the H1 haplotype, especially after upregulation by hypoxia (normalized relative luminescence: 3.54+/-0.32 versus 2.47+/-0.26; P=0.0083).

CONCLUSIONS

These findings indicate that a novel GPx-3 promoter haplotype is an independent risk factor for AIS in children and young adults. This haplotype reduces the gene's transcriptional activity, thereby compromising gene expression and plasma antioxidant and antithrombotic activities.

Diagnostic challenges for multiplexed protein microarrays

Multiplexed protein analysis using planar microarrays or microbeads is growing in popularity for simultaneous assays of antibodies, cytokines, allergens, drugs and hormones. However, this new assay format presents several new operational issues for the clinical laboratory, such as the quality control of protein-microarray-based assays, the release of unrequested test data and the use of diagnostic algorithms to transform microarray data into diagnostic results.

Antibody-mediated rejection in heart transplant recipients: potential efficacy of B-cell depletion and antibody removal

We present four patients with late AMR following cardiac transplantation, which was associated with de novo post-transplant anti-HLA class II antibody production. All patients had negative anti-HLA class I and class II antibodies prior to transplantation (as assessed by sensitive Flow PRA bead assays) and had a negative retrospective T- and B-cell flow cytometric cross-match. Upon presentation with late graft rejection due to AMR, all patients were treated with rituximab and serial plasmapheresis with IVIg plus triple-drug immunosuppression therapy. Despite initial responses to therapy, relapses occurred in all of the patients and necessitated prolonged or multiple hospital admissions and second transplants in two cases. Post-transplant serum antibody monitoring did not prove to be predictive of treatment success or failure. Serum anti-HLA antibodies should be monitored after heart transplantation. We recommend an assessment of anti-HLA antibodies following a decline in immunosuppressant drug levels or in the presence of heart failure symptoms. Anti-HLA antibody detection should be performed using very sensitive techniques such as microparticle-based assays.

Determinants of Human Plasma Glutathione Peroxidase (GPx-3) Expression

Plasma glutathione peroxidase (GPx-3) is a selenocysteine-containing protein with antioxidant properties. GPx-3 deficiency has been associated with cardiovascular disease and stroke. The regulation of GPx-3 expression remains largely uncharacterized, however, and we studied its transcriptional and translational determinants in a cultured cell system. In transient transfections of a renal cell line (Caki-2), the published sequence cloned upstream of a luciferase reporter gene produced minimal activity (relative luminescence (RL) = 0.6 +/- 0.4). Rapid amplification of cDNA ends was used to identify a novel transcription start site that is located 233 bp downstream (3') of the published site and that produced a >25-fold increase in transcriptional activity (RL = 16.8 +/- 1.9; p < 0.0001). Analysis of the novel GPx-3 promoter identified Sp-1- and hypoxia-inducible factor-1-binding sites, as well as the redox-sensitive metal response element and antioxidant response element. Hypoxia was identified as a strong transcriptional regulator of GPx-3 expression, in part through the presence of the hypoxia-inducible factor-1-binding site, leading to an almost 3-fold increase in expression levels after 24 h compared with normoxic conditions (normalized RL = 3.5 +/- 0.3 versus 1.2 +/- 0.1; p < 0.001). We also investigated the role of the translational cofactors tRNA(Sec), SECIS-binding protein-2, and SelD (selenophosphate synthetase D) in GPx-3 protein expression. tRNA(Sec) and SelD significantly enhanced GPx-3 expression, whereas SECIS-binding protein-2 showed a trend toward increased expression. These results demonstrate the presence of a novel functional transcription start site for the human GPx-3 gene with a promoter regulated by hypoxia, and identify unique translational determinants of GPx-3 expression.

Cellular glutathione peroxidase deficiency and endothelial dysfunction

Cellular glutathione peroxidase (GPx-1) is the most abundant intracellular isoform of the GPx antioxidant enzyme family. In this study, we hypothesized that GPx-1 deficiency directly induces an increase in vascular oxidant stress, with resulting endothelial dysfunction. We studied vascular function in a murine model of homozygous deficiency of GPx-1 (GPx-1(-/-)). Mesenteric arterioles of GPx-1(-/-) mice demonstrated paradoxical vasoconstriction to beta-methacholine and bradykinin, whereas wild-type (WT) mice showed dose-dependent vasodilation in response to both agonists. One week of treatment of GPx-1(-/-) mice with L-2-oxothiazolidine-4-carboxylic acid (OTC), which increases intracellular thiol pools, resulted in restoration of normal vascular reactivity in the mesenteric bed of GPx-1(-/-) mice. We observed an increase of the isoprostane iPF(2alpha)-III, a marker of oxidant stress, in the plasma and aortas of GPx-1(-/-) mice compared with WT mice, which returned toward normal after OTC treatment. Aortic sections from GPx-1(-/-) mice showed increased binding of an anti-3-nitrotyrosine antibody in the absence of frank vascular lesions. These findings demonstrate that homozygous deficiency of GPx-1 leads to impaired endothelium-dependent vasodilator function presumably due to a decrease in bioavailable nitric oxide and to increased vascular oxidant stress. These vascular abnormalities can be attenuated by increasing bioavailable intracellular thiol pools.

Cellular redox state and endothelial dysfunction in mildly hyperhomocysteinemic cystathionine beta-synthase-deficient mice

Previous in vitro experiments have shown that hyperhomocysteinemia leads to oxidative inactivation of nitric oxide, in part by inhibiting the expression of cellular glutathione peroxidase (GPx-1). To elucidate the role of intracellular redox status on homocysteine-induced endothelial dysfunction and oxidant stress, heterozygous cystathionine beta-synthase-deficient (CBS(-/+)) and wild-type (CBS(+/+)) mice were treated with the cysteine donor L-2-oxothiazolidine-4-carboxylic acid (OTC). CBS(-/+) mice had significantly lower GPx-1 activity compared with their CBS(+/+) littermates, and OTC treatment led to a modest increase in tissue GPx-1 activity and significant increases in total thiols and in reduced glutathione levels in both CBS(+/+) and CBS(-/+) mice. Superfusion of the mesentery with beta-methacholine or bradykinin produced dose-dependent vasodilation of mesenteric arterioles in CBS(+/+) mice and in CBS(+/+) mice treated with OTC. In contrast, mesenteric arterioles from CBS(-/+) mice manifested dose-dependent vasoconstriction in response to both agonists. OTC treatment of CBS(-/+) mice restored normal microvascular vasodilator reactivity to beta-methacholine and bradykinin. These findings demonstrate that mild hyperhomocysteinemia leads to endothelial dysfunction in association with decreased bioavailable nitric oxide. Increasing the cellular thiol and reduced glutathione pools and increasing GPx-1 activity restores endothelial function. These findings emphasize the importance of intracellular redox balance for nitric oxide bioactivity and endothelial function.

Overexpression of cellular glutathione peroxidase rescues homocyst(e)ine-induced endothelial dysfunction

Homocyst(e)ine (Hcy) inhibits the expression of the antioxidant enzyme cellular glutathione peroxidase (GPx-1) in vitro and in vivo, which can lead to an increase in reactive oxygen species that inactivate NO and promote endothelial dysfunction. In this study, we tested the hypothesis that overexpression of GPx-1 can restore the normal endothelial phenotype in hyperhomocyst(e)inemic states. Heterozygous cystathionine beta-synthase-deficient (CBS((-/+))) mice and their wild-type littermates (CBS((+/+))) were crossbred with mice that overexpress GPx-1 [GPx-1((tg+)) mice]. GPx-1 activity was 28% lower in CBS((-/+))/GPx-1((tg-)) compared with CBS((+/+))/GPx-1((tg-)) mice (P < 0.05), and CBS((-/+)) and CBS((+/+)) mice overexpressing GPx-1 had 1.5-fold higher GPx-1 activity compared with GPx-1 nontransgenic mice (P < 0.05). Mesenteric arterioles of CBS((-/+))/GPx-1((tg-)) mice showed vasoconstriction to superfusion with beta-methacholine and bradykinin (P < 0.001 vs. all other groups), whereas nonhyperhomocyst(e)inemic mice [CBS((+/+))/GPx-1((tg-)) and CBS((+/+))/GPx-1((tg+)) mice] demonstrated dose-dependent vasodilation in response to both agonists. Overexpression of GPx-1 in hyperhomocyst(e)inemic mice restored the normal endothelium-dependent vasodilator response. Bovine aortic endothelial cells (BAEC) were transiently transfected with GPx-1 and incubated with dl-homocysteine (HcyH) or l-cysteine. HcyH incubation decreased GPx-1 activity in sham-transfected BAEC (P < 0.005) but not in GPx-1-transfected cells. Nitric oxide release from BAEC was significantly decreased by HcyH but not cysteine, and GPx-1 overexpression attenuated this decrease. These findings demonstrate that overexpression of GPx-1 can compensate for the adverse effects of Hcy on endothelial function and suggest that the adverse vascular effects of Hcy are at least partly mediated by oxidative inactivation of NO.

Mechanism of nitric oxide-induced vasodilatation: refilling of intracellular stores by sarcoplasmic reticulum Ca2+ ATPase and inhibition of store-operated Ca2+ influx

The precise mechanisms by which nitric oxide (NO) decreases free [Ca2+]i, inhibits Ca2+ influx, and relaxes vascular smooth muscle are poorly understood. In rabbit and mouse aorta, agonist-induced contractions and increases in [Ca2+]i were resistant to nifedipine, suggesting Ca2+ entry through non-L-type Ca2+ channels. Relaxations to NO were inhibited by thapsigargin (TG) or cyclopiazonic acid (CPA) indicating the involvement of sarcoplasmic reticulum ATPase (SERCA). Studies of the effect of NO on [Ca2+]i and the rate of Mn2+ influx with fura-2 fluorometry in rabbit aortic smooth muscle cells in primary culture were designed to test how SERCA is involved in mediating the response to NO. When cells were stimulated with angiotensin II (AII), NO accelerated the removal of Ca2+ from the cytoplasm, decreased [Ca2+]i, and inhibited Ca2+ and Mn2+ influx. Inhibition of SERCA abolished all the effects of NO. In contrast, inhibition of the Na+/Ca2+exchanger or the plasma membrane Ca2+ ATPase had no influence on the ability of NO to decrease [Ca2+]i. NO maximally decreased [Ca2+]i within 5 s, whereas significant inhibition of AII-induced Ca2+ and Mn2+ influx required more than 15 s. The inhibition of cation influx strictly depended on [Ca2+]o and functional SERCA, suggesting that during the delay before NO inhibits Ca2+ influx, the influx of Ca2+ and the uptake into intracellular stores are required. In the absence of [Ca2+]o, NO diminished the AII-induced [Ca2+]i transient by a SERCA-dependent mechanism and increased the amount of Ca2+ in the stores subsequently released by ionomycin. The present study indicates that the initial rapid decrease in [Ca2+]i caused by NO in vascular smooth muscle is accounted for by the uptake of Ca2+ by SERCA into intracellular stores. It is proposed that the refilling of the stores inhibits store-operated Ca2+ influx through non-L-type Ca2+ conducting ion channels and that this maintains the decrease in [Ca2+]i and NO-induced relaxation.