Correction: Impact of maintaining serum potassium concentration ≥ 3.6mEq/L versus ≥ 4.5mEq/L for 120 hours after isolated coronary artery bypass graft surgery on incidence of new onset atrial fibrillation: Protocol for a randomized non-inferiority trial

[This corrects the article DOI: 10.1371/journal.pone.0296525.].

Impact of maintaining serum potassium concentration ≥ 3.6mEq/L versus ≥ 4.5mEq/L for 120 hours after isolated coronary artery bypass graft surgery on incidence of new onset atrial fibrillation: Protocol for a randomized non-inferiority trial

BACKGROUND

Atrial Fibrillation After Cardiac Surgery (AFACS) occurs in about one in three patients following Coronary Artery Bypass Grafting (CABG). It is associated with increased short- and long-term morbidity, mortality and costs. To reduce AFACS incidence, efforts are often made to maintain serum potassium in the high-normal range (≥ 4.5mEq/L). However, there is no evidence that this strategy is efficacious. Furthermore, the approach is costly, often unpleasant for patients, and risks causing harm. We describe the protocol of a planned randomized non-inferiority trial to investigate the impact of intervening to maintain serum potassium ≥ 3.6 mEq/L vs ≥ 4.5 mEq/L on incidence of new-onset AFACS after isolated elective CABG.

METHODS

Patients undergoing isolated CABG at sites in the UK and Germany will be recruited, randomized 1:1 and stratified by site to protocols maintaining serum potassium at either ≥ 3.6 mEq/L or ≥ 4.5 mEq/L. Participants will not be blind to treatment allocation. The primary endpoint is AFACS, defined as an episode of atrial fibrillation, flutter or tachycardia lasting ≥ 30 seconds until hour 120 after surgery, which is both clinically detected and electrocardiographically confirmed. Assuming a 35% incidence of AFACS in the 'tight control group', and allowing for a 10% loss to follow-up, 1684 participants are required to provide 90% certainty that the upper limit of a one-sided 97.5% confidence interval (CI) will exclude a > 10% difference in favour of tight potassium control. Secondary endpoints include mortality, use of hospital resources and incidence of dysrhythmias not meeting the primary endpoint (detected using continuous heart rhythm monitoring).

DISCUSSION

The Tight K Trial will assess whether a protocol to maintain serum potassium ≥ 3.6 mEq/L is non inferior to maintaining serum potassium ≥ 4.5 mEq/L in preventing new-onset AFACS after isolated CABG.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04053816. Registered on 13 August 2019. Last update 7 January 2021.

Routine cerebral embolic protection in transcatheter aortic valve implantation: rationale and design of the randomised British Heart Foundation PROTECT-TAVI trial

Transcatheter aortic valve implantation (TAVI) is an established treatment for aortic stenosis. Cerebral embolic protection (CEP) devices may impact periprocedural stroke by capturing debris destined for the brain. However, there is a lack of high-quality randomised trial evidence supporting the use of CEP during TAVI. The British Heart Foundation (BHF) PROTECT-TAVI trial will address whether the routine use of CEP reduces the incidence of stroke in patients undergoing TAVI. BHF PROTECT-TAVI is a prospective, open-label, outcome-adjudicated, multicentre randomised controlled trial. The trial is open to all adult patients scheduled for TAVI at participating specialist cardiac centres across the United Kingdom who are able to receive the CEP device. The trial will recruit 7,730 participants. Participants will be randomised in a 1:1 ratio to undergo TAVI with CEP or TAVI without CEP (standard of care). The primary outcome is the incidence of stroke at 72 hours post-TAVI. Key secondary outcomes include the incidence of stroke and all-cause mortality up to 12 months post-TAVI, disability and cognitive outcomes, stroke severity, access site complications and a health economics analysis. The sample size of 7,730 participants has 80% power to detect a 33% relative risk reduction from a 3% incidence of the primary outcome in the controls. Trial recruitment commenced in October 2020. As of October 2022, 3,068 patients have been enrolled. BHF PROTECT-TAVI is designed to provide definitive evidence on the clinical efficacy and cost-effectiveness of using routine CEP with the SENTINEL device to reduce stroke in TAVI.

Behavioural intervention to reduce sexually transmitted infections in people aged 16–24 years in the UK: the safetxt RCT

Background

The prevalence of genital chlamydia and gonorrhoea is higher in the 16–24 years age group than those in other age group. With users, we developed the theory-based safetxt intervention to reduce sexually transmitted infections.

Objectives

To establish the effect of the safetxt intervention on the incidence of chlamydia/gonorrhoea infection at 1  year.

Design

A parallel-group, individual-level, randomised superiority trial in which care providers and outcome assessors were blinded to allocation.

Setting

Recruitment was from 92 UK sexual health clinics.

Participants

Inclusion criteria were a positive chlamydia or gonorrhoea test result, diagnosis of non-specific urethritis or treatment started for chlamydia/gonorrhoea/non-specific urethritis in the last 2 weeks; owning a personal mobile phone; and being aged 16–24 years.

Allocation

Remote computer-based randomisation with an automated link to the messaging system delivering intervention or control group messages.

Intervention

The safetxt intervention was designed to reduce sexually transmitted infection by increasing partner notification, condom use and sexually transmitted infection testing before sex with new partners. It employed educational, enabling and incentivising content delivered by 42–79 text messages over 1 year, tailored according to type of infection, gender and sexuality.

Comparator

A monthly message regarding trial participation.

Main outcomes

The primary outcome was the incidence of chlamydia and gonorrhoea infection at 12 months, assessed using nucleic acid amplification tests. Secondary outcomes at 1 and 12 months included self-reported partner notification, condom use and sexually transmitted infection testing prior to sex with new partner(s).

Results

Between 1 April 2016 and 23 November 2018, we assessed 20,476 people for eligibility and consented and randomised 6248 participants, allocating 3123 to the safetxt intervention and 3125 to the control. Primary outcome data were available for 4675 (74.8%) participants. The incidence of chlamydia/gonorrhoea infection was 22.2% (693/3123) in the intervention group and 20.3% (633/3125) in the control group (odds ratio 1.13, 95% confidence interval 0.98 to 1.31). There was no evidence of heterogeneity in any of the prespecified subgroups. Partner notification was 85.6% in the intervention group and 84.0% in the control group (odds ratio 1.14, 95% confidence interval 0.99 to 1.33). At 12 months, condom use at last sex was 33.8% in the intervention group and 31.2% in the control group (odds ratio 1.14, 95% confidence interval 1.01 to 1.28) and condom use at first sex with most recent new partner was 54.4% in the intervention group and 48.7% in the control group (odds ratio 1.27, 95% confidence interval 1.11 to 1.45). Testing before sex with a new partner was 39.5% in the intervention group and 40.9% in the control group (odds ratio 0.95, 95% confidence interval 0.82 to 1.10). Having two or more partners since joining the trial was 56.9% in the intervention group and 54.8% in the control group (odds ratio 1.11, 95% confidence interval 1.00 to 1.24) and having sex with someone new since joining the trial was 69.7% in the intervention group and 67.4% in the control group (odds ratio 1.13, 95% confidence interval 1.00 to 1.28). There were no differences in safety outcomes. Additional sensitivity and per-protocol analyses showed similar results.

Limitations

Our understanding of the mechanism of action for the unanticipated effects is limited.

Conclusions

The safetxt intervention did not reduce chlamydia and gonorrhoea infections, with slightly more infections in the intervention group. The intervention increased condom use but also increased the number of partners and new partners. Randomised controlled trials are essential for evaluating health communication interventions, which can have unanticipated effects.

Future work

Randomised controlled trials evaluating novel interventions in this complex area are needed.

Trial registration

This trial is registered as ISRCTN64390461.

Funding

This project was funded by the National Institute for Health and Care Research (NIHR) Public Health Research programme and will be published in full in Public Health Research; Vol. 11, No. 1. See the NIHR Journals Library website for further project information.

Effectiveness of a behavioural intervention delivered by text messages (safetxt) on sexually transmitted reinfections in people aged 16-24 years: randomised controlled trial

OBJECTIVE

To quantify the effects of a series of text messages (safetxt) delivered in the community on incidence of chlamydia and gonorrhoea reinfection at one year in people aged 16-24 years.

DESIGN

Parallel group randomised controlled trial.

SETTING

92 sexual health clinics in the United Kingdom.

PARTICIPANTS

People aged 16-24 years with a diagnosis of, or treatment for, chlamydia, gonorrhoea, or non-specific urethritis in the past two weeks who owned a mobile phone.

INTERVENTIONS

3123 participants assigned to the safetxt intervention received a series of text messages to improve sex behaviours: four texts daily for days 1-3, one or two daily for days 4-28, two or three weekly for month 2, and 2-5 monthly for months 3-12. 3125 control participants received a monthly text message for one year asking for any change to postal or email address. It was hypothesised that safetxt would reduce the risk of chlamydia and gonorrhoea reinfection at one year by improving three key safer sex behaviours: partner notification at one month, condom use, and sexually transmitted infection testing before unprotected sex with a new partner. Care providers and outcome assessors were blind to allocation.

MAIN OUTCOME MEASURES

The primary outcome was the cumulative incidence of chlamydia or gonorrhoea reinfection at one year, assessed by nucleic acid amplification tests. Safety outcomes were self-reported road traffic incidents and partner violence. All analyses were by intention to treat.

RESULTS

6248 of 20 476 people assessed for eligibility between 1 April 2016 and 23 November 2018 were randomised. Primary outcome data were available for 4675/6248 (74.8%). At one year, the cumulative incidence of chlamydia or gonorrhoea reinfection was 22.2% (693/3123) in the safetxt arm versus 20.3% (633/3125) in the control arm (odds ratio 1.13, 95% confidence interval 0.98 to 1.31). The number needed to harm was 64 (95% confidence interval number needed to benefit 334 to ∞ to number needed to harm 24) The risk of road traffic incidents and partner violence was similar between the groups.

CONCLUSIONS

The safetxt intervention did not reduce chlamydia and gonorrhoea reinfections at one year in people aged 16-24 years. More reinfections occurred in the safetxt group. The results highlight the need for rigorous evaluation of health communication interventions.

TRIAL REGISTRATION

ISRCTN registry ISRCTN64390461.

Tranexamic acid to reduce head injury death in people with traumatic brain injury: the CRASH-3 international RCT

BACKGROUND

Tranexamic acid safely reduces mortality in traumatic extracranial bleeding. Intracranial bleeding is common after traumatic brain injury and can cause brain herniation and death. We assessed the effects of tranexamic acid in traumatic brain injury patients.

OBJECTIVE

To assess the effects of tranexamic acid on death, disability and vascular occlusive events in traumatic brain injury patients. We also assessed cost-effectiveness.

DESIGN

Randomised trial and economic evaluation. Patients were assigned by selecting a numbered treatment pack from a box containing eight packs that were identical apart from the pack number. Patients, caregivers and those assessing outcomes were masked to allocation. All analyses were by intention to treat. We assessed the cost-effectiveness of tranexamic acid versus no treatment from a UK NHS perspective using the trial results and a Markov model.

SETTING

175 hospitals in 29 countries.

PARTICIPANTS

Adults with traumatic brain injury within 3 hours of injury with a Glasgow Coma Scale score of ≤ 12 or any intracranial bleeding on computerised tomography scan, and no major extracranial bleeding, were eligible.

INTERVENTION

Tranexamic acid (loading dose 1 g over 10 minutes then infusion of 1 g over 8 hours) or matching placebo.

MAIN OUTCOME MEASURES

Head injury death in hospital within 28 days of injury in patients treated within 3 hours of injury. Secondary outcomes were early head injury deaths, all-cause and cause-specific mortality, disability, vascular occlusive events, seizures, complications and adverse events.

RESULTS

Among patients treated within 3 hours of injury (n = 9127), the risk of head injury death was 18.5% in the tranexamic acid group versus 19.8% in the placebo group (855/4613 vs. 892/4514; risk ratio 0.94, 95% confidence interval 0.86 to 1.02). In a prespecified analysis excluding patients with a Glasgow Coma Scale score of 3 or bilateral unreactive pupils at baseline, the results were 12.5% in the tranexamic acid group versus 14.0% in the placebo group (485/3880 vs. 525/3757; risk ratio 0.89, 95% confidence interval 0.80 to 1.00). There was a reduction in the risk of head injury death with tranexamic acid in those with mild to moderate head injury (166/2846 vs. 207/2769; risk ratio 0.78, 95% confidence interval 0.64 to 0.95), but in those with severe head injury (689/1739 vs. 685/1710; risk ratio 0.99, 95% confidence interval 0.91 to 1.07) there was no apparent reduction (p-value for heterogeneity = 0.030). Early treatment was more effective in mild and moderate head injury (p = 0.005), but there was no obvious impact of time to treatment in cases of severe head injury (p = 0.73). The risk of disability, vascular occlusive events and seizures was similar in both groups. Tranexamic acid is highly cost-effective for mild and moderate traumatic brain injury (base case of £4288 per quality-adjusted life-year gained).

CONCLUSION

Early tranexamic acid treatment reduces head injury deaths. Treatment is cost-effective for patients with mild or moderate traumatic brain injury, or those with both pupils reactive.

FUTURE WORK

Further trials should examine early tranexamic acid treatment in mild head injury. Research on alternative routes of administration is needed.

LIMITATIONS

Time to treatment may have been underestimated.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN15088122, ClinicalTrials.gov NCT01402882, EudraCT 2011-003669-14, Pan African Clinical Trial Registry PACTR20121000441277.

FUNDING

The project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 26. See the NIHR Journals Library website for further project information. In addition, funding was provided by JP Moulton Charitable Trust, Joint Global Health Trials (Medical Research Council, Department for International Development and the Wellcome Trust). This project was funded by the NIHR Global Health Trials programme.

Patient and public involvement prior to trial initiation: lessons learnt for rapid partnership in the COVID-19 era

Patient and Public Involvement (PPI) describes the active involvement of patients and the public in the research process. Through PPI, patients and members of the public are increasingly involved in the design and conduct of clinical trials. PPI has been shown to improve the quality and relevance of research. During the COVID-19 pandemic, clinical trials have been playing a vital role in helping us find ways to prevent and treat the infection and improve our understanding of the virus. It is important that patients and the public are actively involved in deciding how COVID-19 research is carried out. Unfortunately, Research Ethics Committees in the UK have seen far less PPI for COVID-19 research studies compared with research before the pandemic. A key reason for this is that research is being designed much faster than normal and researchers may feel they do not have time to properly involve patients and the public. In this paper, we share our experiences of PPI for a COVID-19 clinical trial. We show that it is possible to rapidly involve patients and the public in COVID-19 clinical trials. We also explain how the design of the clinical trial was changed in response to feedback from public contributors. Lastly, we discuss the wider learning from this process which might be useful for researchers planning PPI activities for COVID-19 clinical trials in the future.

BACKGROUND

Clinical trials are playing a critical role in the global public health response to the COVID-19 pandemic. Despite the increasing recognition of the value of PPI in clinical trials, just 22% of the COVID-19 research proposals reviewed by Research Ethics Committees in the UK at the start of the pandemic reported PPI. There is a perception that PPI might result in delays in delivering research and therefore delays in obtaining important results. In this paper, we report our experience of rapid PPI for a COVID-19 clinical trial.

METHODS

RAPID-19 is a COVID-19 clinical trial which was planned to be submitted for fast-track ethics review in the United Kingdom. During the development of the trial protocol, the PPI Panel at the London School of Hygiene & Tropical Medicine Clinical Trials Unit was involved in the design of the study. The meeting with the PPI Panel lasted just over 1 h and was conducted by teleconference.

RESULTS

Although we only had a short period of time to explore the study with the PPI Panel, we were able to gain valuable insight into how the trial would be perceived by potential trial participants. Substantive changes were made to the trial to improve the acceptability of the research without compromising the study timelines. Having access to public contributors with relevant lived experience is an important resource for a Clinical Trials Unit and is critical for rapid PPI. The move to remote working due to lockdown required virtual discussions which helped to overcome some of the barriers to organising face-to-face meetings at short notice.

CONCLUSIONS

PPI for clinical trials can be conducted in a time-efficient manner within the pressured environment of a pandemic. Involving PPI contributors at an early stage in protocol development maximised the opportunity to shape and influence the trial as well as limited potential delays which could occur if changes to the protocol had to be made at a later stage.

The effect of statins on muscle symptoms in primary care: the StatinWISE series of 200 N-of-1 RCTs

BACKGROUND

Uncertainty persists about whether or not statins cause symptomatic muscle adverse effects (e.g. pain, stiffness and weakness) in the absence of severe myositis.

OBJECTIVES

To establish the effect of statins on all muscle symptoms, and the effect of statins on muscle symptoms that are perceived to be statin related.

DESIGN

A series of 200 double-blinded N-of-1 trials.

SETTING

Participants were recruited from 50 general practices in England and Wales.

PARTICIPANTS

Patients who were considering discontinuing statin use and those who had discontinued statin use in the last 3 years because of perceived muscle symptoms.

INTERVENTIONS

Participants were randomised to a sequence of six 2-month treatment periods during which they received 20 mg of atorvastatin daily or a matched placebo.

MAIN OUTCOME MEASURES

The primary outcome was self-reported muscle symptoms rated using a visual analogue scale on the last week of each treatment period. Secondary outcomes included the participant's belief about the cause of their muscle symptoms, the site of muscle symptoms, how the muscle symptoms affected the participant, any other symptoms they experienced, adherence to medication, the participant's decision about statin treatment following the trial, and whether or not they found their own trial result helpful.

RESULTS

A total of 151 out of 200 (75.5%) randomised participants provided one or more visual analogue scale measurements in a placebo period and one or more measurements in a statin period, and were included in the primary analysis. There was no evidence of a difference in muscle symptom scores between statin and placebo periods (mean difference statin minus placebo -0.11, 95% confidence interval -0.36 to 0.14; p = 0.398). Withdrawals, adherence and missing data were similar during the statin periods and the placebo periods.

CONCLUSIONS

Among people who previously reported severe muscle symptoms while taking statins, this series of randomised N-of-1 trials found no overall effect of statins on muscle symptoms compared with the placebo. The slight difference in withdrawals due to muscle symptoms suggests that statins may contribute to symptoms in a small number of patients. The results are generalisable to patients who are considering discontinuing or have already discontinued statins because of muscle symptoms, and who are willing to re-challenge or participate in their own N-of-1 trial.

FUTURE WORK

We recommend that additional statins and doses are explored using N-of-1 trials. More broadly, N-of-1 trials present a useful tool for exploring transient symptoms with other medications.

LIMITATIONS

This study used 20-mg doses of atorvastatin only. Furthermore, a dropout rate of 43% was observed, but this was accounted for in the power calculations.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN30952488 and EudraCT 2016-000141-31.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 25, No. 16. See the NIHR Journals Library website for further project information.

HIV knowledge, sexual health and sexual behaviour among Black and minority ethnic men who have sex with men in the UK: a cross-sectional study

Background Black and minority ethnic (BME) men who have sex with men (MSM) face a major burden in relation to HIV infection. Using a cross-sectional correlational survey design, the present study explored the relationships between HIV knowledge and reported sexual health and sexual behaviour in this population.

METHODS

A convenience sample of 538 BME MSM was recruited in London, Leicester and Leeds: 346 (64%) self-identified as South Asian, 88 (16%) self-identified as Latin American, 76 (14%) self-identified as Black, 13 (2%) self-identified as mixed, and 15 (3%) self-identified as other.

RESULTS

HIV knowledge was low across the board, and South Asian MSM manifested the lowest scores. Respondents who perceived their HIV risk to be low possessed the least HIV knowledge. There were interethnic differences in the frequency of gay sauna visits, sex-seeking on mobile applications, drug use and attendance at sex parties. Respondents reported a high frequency of racism and discrimination, with Black MSM reporting highest frequency.

CONCLUSIONS

There is an urgent need to raise awareness of HIV in BME MSM, and a culturally competent approach to HIV awareness-raising in BME MSM is required. These findings shed light on the contexts in which HIV prevention efforts should be targeted to reach specific ethnic groups, as well as some of the potential syndemics that can increase HIV risk or undermine HIV outcomes in BME MSM patients.

The people living with HIV stigma survey UK 2015: HIV-related sexual rejection and other experiences of stigma and discrimination among gay and heterosexual men

We aim to understand the difference in stigma and discrimination, in particular sexual rejection, experienced between gay and heterosexual men living with HIV in the UK. The People Living with HIV StigmaSurvey UK 2015 recruited a convenience sample of persons with HIV through over 120 cross sector community organisations and 46 HIV clinics to complete an online survey. 1162 men completed the survey, 969 (83%) gay men and 193 (17%) heterosexual men, 92% were on antiretroviral therapy. Compared to heterosexual men, gay men were significantly more likely to report worrying about workplace treatment in relation to their HIV (21% vs. 11%), worrying about HIV-related sexual rejection (42% vs 21%), avoiding sex because of their HIV status (37% vs. 23%), and experiencing HIV-related sexual rejection (27% vs. 9%) in the past 12 months. In a multivariate logistic regression controlling for other sociodemographic factors, being gay was a predictor of reporting HIV-related sexual rejection in the past 12 months (aOR 2.17, CI 1.16, 4.02). Both gay and heterosexual men living with HIV experienced stigma and discrimination in the past 12 months, and this was higher for gay men in terms of HIV-related sexual rejection. Due to the high proportion of men reporting sexual rejection, greater awareness and education of the low risk of transmission of HIV among people on effective treatment is needed to reduce stigma and sexual prejudice towards people living with HIV.

Experiences of stigma and discrimination in social and healthcare settings among trans people living with HIV in the UK

The People Living with HIV StigmaSurvey UK 2015 was a community led national survey investigating experiences of people living with HIV in the UK in the past 12 months. Participants aged 18 and over were recruited through over 120 cross-sector community organisations and 46 HIV clinics to complete an anonymous online survey. Trans is an umbrella term which refers to individuals whose current gender identity is different to the gender they were assigned at birth. Trans participants self-identified via gender identity and gender at birth questions. Descriptive analyses of reported experiences in social and health care settings were conducted and multivariate logistic regression analyses were used to identify sociodemographic predictors of reporting being treated differently to non-HIV patients, and being delayed or refused healthcare treatment in the past 12 months. 31 out of 1576 participants (2%) identified as trans (19 trans women, 5 trans men, 2 gender queer/non-binary, 5 other). High levels of social stigma were reported for all participants, with trans participants significantly more likely to report worrying about verbal harassment (39% vs. 23%), and exclusion from family gatherings (23% vs. 9%) in the last 12 months, compared to cisgender participants. Furthermore, 10% of trans participants reported physical assault in the last 12 months, compared to 4% of cisgender participants. Identifying as trans was a predictor of reporting being treated differently to non-HIV patients (48% vs. 30%; aOR 2.61, CI 1.06, 6.42) and being delayed or refused healthcare (41% vs. 16%; aOR 4.58, CI 1.83, 11.44). Trans people living with HIV in the UK experience high levels of stigma and discrimination, including within healthcare settings, which is likely to impact upon health outcomes. Trans-specific education and awareness within healthcare settings could help to improve service provision for this demographic.

Phosphatidate phosphohydrolases in liver, heart and adipose tissue of the JCR:LA corpulent rat and the lean genotypes: implications for glycerolipid synthesis and signal transduction

The activities of two distinct phosphatidate phosphohydrolases (PAP) were measured in livers, hearts and adipose tissues of the JCR:LA corpulent rat which is hyperphagic, hypertriglyceridaemic and insulin resistant. The specific activity of PAP-1, which requires Mg2+, was similar in the livers of lean and corpulent female rats and in male corpulent rats, but these activities were about 1.6-fold higher than in lean males. There was a correlation between the specific activity of PAP-1 and the concentrations of hepatic and serum triacylglycerols in the males, but not in the females. Chronic treatment of the corpulent rats with ethanol did not significantly alter the hepatic activity of PAP-1, or the concentrations of hepatic or serum triacylglycerols. Specific activities of PAP-1 in the heart were higher in the lean compared to the corpulent males. There was no significant difference for the females. Specific activities of PAP-1 were over 5-fold higher in the subcutaneous adipose tissue of the corpulent males and females compared to the lean genotypes. The differences were smaller (1.6-1.9-fold) in the gonadal adipose tissue of both sexes and in the peri-renal depot for the males. PAP-1 activity in the peri-renal depots of corpulent females was 23% lower than in lean females. PAP-2 activity was insensitive to N-ethylmaleimide and did not require Mg2+ for activity. Its activity was 1.5-2.0-fold higher in the livers and hearts of the lean male and female rats than in the corpulent genotypes. Chronic treatment with ethanol increased the activity of PAP-2 in the hearts of the corpulent males, but had no effect in the corpulent females. The specific activity of PAP-2 was higher in subcutaneous, gonadal and peri-renal adipose depots in the females and in the peri-renal depot of the corpulent males compared with the lean genotypes. Lean males had higher specific activities in all three depots compared to lean females. The tissue specificity and the sex differences in the specific activities of PAP-1 and PAP-2 are discussed in terms of their proposed functions in glycerolipid biosynthesis and signal transduction. It is proposed that a decreased activity of PAP-2 could be involved in the insulin insensitivity in the corpulent rats.

Effects of okadaic acid on the activities of two distinct phosphatidate phosphohydrolases in rat hepatocytes

Incubation of hepatocytes with okadaic acid displaced the N-ethylmaleimide-sensitive phosphatidate phosphohydrolase from the membrane fraction into the cytosol and partially prevented the oleate-induced movement of phosphohydrolase from cytosol to membranes. However, higher concentrations of oleate still caused translocation and activation of the phosphohydrolase. This enzyme is stimulated by Mg2+, and is probably involved in glycerolipid synthesis. Okadaic acid also decreased the concentration of diacylglycerol within the hepatocytes. Okadiac acid had no observable effect on the activity of an N-ethylmaleimide-insensitive phosphatidate phosphohydrolase which remained firmly attached to membranes. This activity is not stimulated by Mg2+ and is probably involved in signal transduction by the phospholipase D pathway.

Plasma membrane fractions from rat liver contain a phosphatidate phosphohydrolase distinct from that in the endoplasmic reticulum and cytosol

Assays for two distinct phosphatidate phosphohydrolase activities were established based upon a differential inhibition by N-ethylmaleimide (NEM). The activity that is insensitive to this reagent in rat liver is predominantly in the plasma membrane fraction, whereas the NEM-sensitive activity is in the cytosolic and microsomal fractions. The NEM-insensitive activity is further distinguished from the NEM-sensitive phosphohydrolase by: (a) being relatively stable to heat; (b) not being inhibited by phenylglyoxal, butane-2,3-dione, cyclohexane-1,2-dione, 2,4-dinitrofluorobenzene, 7-chloro-4-nitrobenz-2-oxa-1,3-diazole, and diethyl pyrocarbonate; (c) being inhibited by NaF and phosphatidylcholine; and (d) not being stimulated by Mg2+. The NEM-insensitive activity was specific for phosphatidate. Both phosphohydrolase activities could be inhibited by chlorpromazine, propranolol, sphingosine, and spermine. The NEM-sensitive phosphatidate phosphohydrolase activity was increased by incubating hepatocytes for 12 h with glucagon and dexamethasone, and this effect was antagonized by insulin. The NEM-sensitive phosphohydrolase is concluded to be involved in glycerolipid synthesis. The activity of the NEM-insensitive phosphohydrolase was not altered by preincubation of rat hepatocytes in the short or long term with vasopressin, glucagon, insulin, triiodothyronine, or dexamethasone, but it might be modulated indirectly by sphingosine. The NEM-insensitive enzyme of the plasma membranes could be involved in signal transduction via the agonist-stimulated degradation of phosphatidylcholine through the phospholipase D pathway.

Differences in the properties of A1-type adenosine receptors in rat white and brown adipocytes

1. White adipocytes were found to be more responsive than brown adipocytes to inhibition of lipolysis by the A1 adenosine receptor agonist phenylisopropyladenosine. 2. Radioligand binding studies with plasma membranes isolated from the two adipocyte types indicated differences in the properties of the A1 receptors. Kd values (high and low affinity) for phenylisopropyladenosine were higher in membranes from brown adipocytes. The Kd values for the antagonist dipropylcyclopentylxanthine were also higher in brown adipocyte membranes. 3. The effects of guanine nucleotides in converting adipocyte A1 receptors into a low-affinity state were enhanced by dithiothreitol.

Changes in brown-adipose-tissue mitochondrial processes in streptozotocin-diabetes

Diabetic rats were used as a source of brown-adipose-tissue mitochondria 2 days after a single subcutaneous injection of streptozotocin (100 mg/kg). Diabetes caused an 80% decrease in carnitine-dependent oxidation of palmitoyl-CoA and a 50-60% decrease in overt carnitine palmitoyltransferase activity. An additional lesion in brown-adipose-tissue mitochondrial oxidative capacity was also indicated, since diabetes increased by 30-50% the rate of oxidation under uncoupled conditions of several respiratory substrates (i.e. malate + palmitoylcarnitine, malate + pyruvate, succinate, NNN'N'-tetramethyl-p-phenylenediamine + ascorbate). This decrease in mitochondrial function was accompanied by an approx. 30% decrease in the abundance of cytochromes (a + a3) and total cytochromes b.

A novel assay for 5'-nucleotidase using 1,N6-etheno-AMP as substrate, and comments on the properties of the reaction product, ethenoadenosine

A novel assay for 5'-nucleotidase is described in which 1,N6-etheno-AMP is converted into ethenoadenosine. The product ethenoadenosine is neither a substrate for nor an inhibitor of adenosine deaminase. Ethenoadenosine appears to have little effect at adenosine receptors on adipose-tissue cells.

Factors influencing the altered thermogenic response of rat brown adipose tissue in streptozotocin-diabetes

1. Adipocytes were isolated from the interscapular brown fat of male rats maintained at 21 degrees C. These animals were controls, streptozotocin-diabetics or 2-day insulin-treated diabetics. 2. With adipocytes from diabetic animals, maximum rates of noradrenaline-stimulated O2 uptake were decreased by 58%, and the Bmax. of [3H]GDP binding to mitochondria was decreased by 55%. Insulin administration reversed both of these changes. 3. Streptozotocin-diabetes increased basal lipolysis in adipocytes incubated with adenosine deaminase (1 unit/ml), decreased the EC50 (concn. giving 50% of maximum effect) for noradrenaline, but did not change the maximum rate of noradrenaline-stimulated lipolysis. Except for some small differences at very low concentrations (10-100 pM), diabetes or insulin treatment did not alter the sensitivity of noradrenaline-stimulated lipolysis or O2 uptake to the inhibitory effect of N6-phenylisopropyladenosine. It is therefore concluded that the lesion(s) in thermogenesis in diabetes are not attributable to any changes in lipolysis. 4. Blood flow through interscapular brown fat, measured by accumulation of [14C]DDT [14C-labelled 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane] was increased by 2.3-fold 70 min after a single administration of insulin to diabetic rats. This treatment decreased blood flow through epididymal white fat by 58%. 5. Propranolol treatment of diabetic rats muted the ability of insulin treatment to increase the maximum rate of noradrenaline-stimulated O2 uptake, suggesting that this action of insulin may be a secondary one rather than a direct effect of the hormone on the adipocytes.

Enzymes involved in adenosine metabolism in rat white and brown adipocytes. Effects of streptozotocin-diabetes, hypothyroidism, age and sex differences

1. Adipocytes were isolated from epididymal white fat and interscapular brown fat of male rats, and activities of 5'-nucleotidase, adenosine deaminase and adenosine kinase were measured in cell extracts. 2. 5'-Nucleotidase activity in white adipocytes was increased in streptozotocin-diabetes, decreased in hypothyroidism and increased with age. That activity in brown adipocytes was unchanged in diabetes, decreased in hypothyroidism and increased with age. 5'-Nucleotidase activity was higher in white adipocytes from female rats. 3. Adenosine deaminase activity in white adipocytes was increased in diabetes, decreased in hypothyroidism and increased with age. That activity in brown adipocytes was decreased in diabetes and hypothyroidism. 4. Adenosine kinase activity in both cell types was unchanged in diabetes or hypothyroidism, but increased with age.

Effects of 2-mercaptopropionyl glycine on radiation-induced lipid peroxidation in liposomes and in rat liver microsomal suspensions

gamma-Irradiation of rat liver microsomal suspensions resulted in the accumulation of both malondialdehyde (MDA) and lipid hydroperoxides. The presence of 2-mercaptopropionylglycine (MPG) during the irradiation period decreased the formation of MDA and lipid hydroperoxides in a dose (MPG)-dependent manner. This may be attributed to the ability of MPG to scavenge the free radicals produced by irradiation. Post-irradiation incubation of microsomes further enhanced the production of both MDA and lipid hydroperoxides; when high concentrations of MPG were present during the incubations the production of MDA and lipid hydroperoxides was substantially decreased. This antioxidant role of MPG was demonstrated for both pre-irradiated microsomes and liposomes and is thought to be due to the conversion of the hydroperoxy to hydroxy fatty acids within the lipid bilayer, as well as the scavenging action on initiating free radicals.

Separation of plasma from whole blood by membrane filtration in oscillatory flows

This paper describes the performance of a microfiltration plasmapheresis unit operating with reversing oscillatory flows. The device consists of a flat channel duct between cellulose nitrate membranes and was used to extract plasma from anticoagulated fresh whole bovine blood. Measurements were made of plasma flux, haematocrit concentration, haemolysis and protein sieving coefficients. The effects on plasma flux are reported for alterations in the stroke and frequency of flow pulsations, transmembrane pressure, membrane properties and blood throughput. It was found that the imposition of oscillatory flows enhanced the plasma extraction rate by a factor of 3, producing about 0.9 litre/min/m2 membrane.

Metabolism of cholesteryl ester in monolayers of bovine adrenal cortical cells. Effect of an inhibitor of acyl-CoA: cholesterol acyltransferase

The effect of Sandoz compound 58-035 on cholesterol metabolism in monolayers of bovine adrenal cortical cells was studied. 58-035 did not inhibit cholesterol ester hydrolase, cholesterol side-chain cleavage, cholesterol synthesis from acetate, or cortisol synthesis in cells stimulated with ACTH or in unstimulated cells. It was, however, an effective inhibitor of formation of cholesteryl ester. The rate of formation of cholesteryl ester in the cells was increased by additional cholesterol derived from mevalonic acid or from the hydrolysis of intracellular lipid droplets. 58-035 caused an increase in the secretion of cortisol from cells maintained on a limited supply of cholesterol from bovine lipoproteins added to the medium when the cells were not stimulated with ACTH. This effect was not observed in stimulated cells. The results suggest that the bovine adrenal cortical cell can direct the flux of exogenous cholesterol very precisely according to its metabolic state.