Effects of icosapent ethyl according to baseline residual risk in patients with atherosclerotic cardiovascular disease: results from REDUCE-IT

BACKGROUND AND AIMS

Icosapent ethyl lowers triglycerides and significantly reduces major adverse cardiovascular events (MACE), though treatment effects may vary between individuals. This study aimed to determine the relative and absolute effects of icosapent ethyl on MACE according to baseline CVD risk in patients with atherosclerotic cardiovascular disease (ASCVD).

METHODS

Participants from REDUCE-IT with ASCVD were included (n = 5,785). The primary outcome was 3-point MACE, i.e. non-fatal myocardial infarction, non-fatal stroke, or cardiovascular death. Baseline 5-year risk of MACE was estimated using the ESC guideline-recommended SMART2 risk score. Modification of the relative treatment effects of icosapent ethyl by baseline risk was assessed using Cox proportional hazards models including a treatment-by-risk interaction. Next, treatment effects were assessed stratified by quartiles of baseline risk.

RESULTS

During a median follow-up of 4.8 years (interquartile range 3.2-5.3), MACE occurred in 361 vs 489 patients in the icosapent ethyl vs placebo group (95% confidence interval [CI]); hazard ratio (HR) 0.72 (0.63-0.82), absolute risk reduction (ARR) 4.4% (2.6-6.2%), number needed to treat (NNT) 23 (16-38), 5-year Kaplan-Meier estimated cumulative incidence reduction (CIR) 5.7% (3.5-7.9%). Icosapent ethyl significantly reduced MACE in all risk quartiles, with an HR (95% CI) of 0.62 (0.43-0.88), 0.66 (0.48-0.92), 0.69 (0.53-0.90), and 0.78 (0.63-0.96) respectively (p for treatment-by-risk interaction = 0.106). The ARR (95% CI) increased across risk quartiles, i.e. was 3.9% (1.0-6.8%), 4.3% (1.2-7.3%), 5.1% (1.4-8.7%), and 5.6% (1.3-10.0%) respectively. This translates to NNTs (95% CI) of 26 (15-98), 24 (14-84), 20 (11-70), and 18 (10-77). The 5-year CIR (95% CI) was 4.8% (1.3-8.2%), 5.0% (1.3-8.7%), 6.1% (1.7-10.5%), and 7.7% (2.3-13.2%) respectively. Consistent results were obtained for 5-point MACE, additionally including coronary revascularization and unstable angina.

CONCLUSIONS

Among patients with ASCVD and elevated triglyceride levels, icosapent ethyl significantly reduces the risk of MACE irrespective of baseline CVD risk, though absolute benefits are largest for patients at the highest risk.

Individual lifetime benefit from low-dose colchicine in patients with chronic coronary artery disease

AIMS

Low-dose colchicine reduces cardiovascular risk in patients with coronary artery disease (CAD), but absolute benefits may vary between individuals. This study aimed to assess the range of individual absolute benefits from low-dose colchicine according to patient risk profile.

METHODS AND RESULTS

The European Society of Cardiology (ESC) guideline-recommended SMART-REACH model was combined with the relative treatment effect of low-dose colchicine and applied to patients with CAD from the Low-Dose Colchicine 2 (LoDoCo2) trial and the Utrecht Cardiovascular Cohort-Second Manifestations of ARTerial disease (UCC-SMART) study (n = 10 830). Individual treatment benefits were expressed as 10-year absolute risk reductions (ARRs) for myocardial infarction, stroke, or cardiovascular death (MACE), and MACE-free life-years gained. Predictions were also performed for MACE plus coronary revascularization (MACE+), using a new lifetime model derived in the REduction of Atherothrombosis for Continued Health (REACH) registry. Colchicine was compared with other ESC guideline-recommended intensified (Step 2) prevention strategies, i.e. LDL cholesterol (LDL-c) reduction to 1.4 mmol/L and systolic blood pressure (SBP) reduction to 130 mmHg. The generalizability to other populations was assessed in patients with CAD from REACH North America and Western Europe (n = 25 812). The median 10-year ARR from low-dose colchicine was 4.6% [interquartile range (IQR) 3.6-6.0%] for MACE and 8.6% (IQR 7.6-9.8%) for MACE+. Lifetime benefit was 2.0 (IQR 1.6-2.5) MACE-free years, and 3.4 (IQR 2.6-4.2) MACE+-free life-years gained. For LDL-c and SBP reduction, respectively, the median 10-year ARR for MACE was 3.0% (IQR 1.5-5.1%) and 1.7% (IQR 0.0-5.7%), and the lifetime benefit was 1.2 (IQR 0.6-2.1) and 0.7 (IQR 0.0-2.3) MACE-free life-years gained. Similar results were obtained for MACE+ and in American and European patients from REACH.

CONCLUSION

The absolute benefits of low-dose colchicine vary between individual patients with chronic CAD. They may be expected to be of at least similar magnitude to those of intensified LDL-c and SBP reduction in a majority of patients already on conventional lipid-lowering and blood pressure-lowering therapy.

Personalized lifetime prediction of survival and treatment benefit in patients with heart failure with reduced ejection fraction: The LIFE-HF model

AIMS

Although trials have proven the group-level effectiveness of various therapies for heart failure with reduced ejection fraction (HFrEF), important differences in absolute effectiveness exist between individuals. We developed and validated the LIFEtime-perspective for Heart Failure (LIFE-HF) model for the prediction of individual (lifetime) risk and treatment benefit in patients with HFrEF.

METHODS AND RESULTS

Cox proportional hazards functions with age as the time scale were developed in the PARADIGM-HF and ATMOSPHERE trials (n = 15 415). Outcomes were cardiovascular death, heart failure (HF) hospitalization or cardiovascular death, and non-cardiovascular mortality. Predictors were age, sex, New York Heart Association class, prior HF hospitalization, diabetes mellitus, extracardiac vascular disease, systolic blood pressure, left ventricular ejection fraction, N-terminal pro-B-type natriuretic peptide, and glomerular filtration rate. The functions were combined in life-tables to predict individual overall and HF hospitalization-free survival. External validation was performed in the SwedeHF registry, ASIAN-HF registry, and DAPA-HF trial (n = 51 286). Calibration of 2- to 10-year risk was adequate, and c-statistics were 0.65-0.74. An interactive tool was developed combining the model with hazard ratios from trials to allow estimation of an individual's (lifetime) risk and treatment benefit in clinical practice. Applying the tool to the development cohort, combined treatment with a mineralocorticoid receptor antagonist, sodium-glucose cotransporter 2 inhibitor, and angiotensin receptor-neprilysin inhibitor was estimated to afford a median of 2.5 (interquartile range [IQR] 1.7-3.7) and 3.7 (IQR 2.4-5.5) additional years of overall and HF hospitalization-free survival, respectively.

CONCLUSION

The LIFE-HF model enables estimation of lifelong overall and HF hospitalization-free survival, and (lifetime) treatment benefit for individual patients with HFrEF. It could serve as a tool to improve the management of HFrEF by facilitating personalized medicine and shared decision-making.

C-Reactive Protein and Risk of Incident Heart Failure in Patients With Cardiovascular Disease

BACKGROUND

Patients with established cardiovascular disease (CVD) are at high risk of incident heart failure (HF), which may in part reflect the impact of systemic inflammation.

OBJECTIVES

The goal of this study was to determine the association between C-reactive protein (CRP) and incident HF in patients with established CVD.

METHODS

Patients from the prospective UCC-SMART (Utrecht Cardiovascular Cohort-Second Manifestations of ARTerial disease) cohort with established CVD, but without prevalent HF were included (n = 8,089). Incident HF was defined as a first hospitalization for HF. The association between baseline CRP and incident HF was assessed using Cox proportional hazards models adjusted for established risk factors (ie, age, sex, myocardial infarction, smoking, diabetes mellitus, body mass index, blood pressure, cholesterol, and kidney function).

RESULTS

During a median follow-up of 9.7 years (IQR 5.4-14.1 years), 810 incident HF cases were observed (incidence rate 1.01/100 person-years). Higher CRP was independently associated with an increased risk of incident HF: HR per 1 mg/L: 1.10 (95% CI: 1.07-1.13), and for last vs first CRP quartile: 2.22 (95% CI: 1.76-2.79). The association was significant for both HF with reduced (HR: 1.09; 95% CI: 1.04-1.14) and preserved ejection fraction (HR: 1.12; 95% CI: 1.07-1.18) (P for difference = 0.137). Additional adjustment for medication use and interim myocardial infarction did not attenuate the association, and the association remained consistent beyond 15 years after the CRP measurement.

CONCLUSIONS

In patients with established CVD, CRP is an independent risk marker of incident HF. These data support ongoing trial efforts to assess whether anti-inflammatory agents can reduce the burden of HF.

C-Reactive Protein and Risk of Cardiovascular Events and Mortality in Patients with Various Cardiovascular Disease Locations

Anti-inflammatory drugs reduce the risk of cardiovascular events in patients with coronary artery disease (CAD), but less is known about the relation between inflammation and outcomes in patients with cerebrovascular disease (CeVD), peripheral artery disease (PAD), and abdominal aortic aneurysm (AAA). This study assessed the association between C-reactive protein (CRP) and clinical outcomes in patients with CAD (n = 4,517), CeVD (n = 2,154), PAD (n = 1,154), and AAA (n = 424) from the prospective Utrecht Cardiovascular Cohort-Second Manifestations of ARTerial disease study. The primary outcome was recurrent cardiovascular disease (CVD), defined as myocardial infarction, ischemic stroke, or cardiovascular death. Secondary outcomes were major adverse limb events and all-cause mortality. Associations between baseline CRP and outcomes were assessed using Cox proportional hazards models adjusted for age, sex, smoking, diabetes mellitus, body mass index, systolic blood pressure, non-high-density lipoprotein cholesterol, and glomerular filtration rate. Results were stratified by CVD location. During a median follow-up of 9.5 years, 1,877 recurrent CVD events, 887 major adverse limb events, and 2,341 deaths were observed. CRP was independently associated with recurrent CVD (hazard ratio [HR] per 1 mg/L 1.08, 95% confidence interval [CI] 1.05 to 1.10), and all secondary outcomes. Compared with the first quintile of CRP, HRs for recurrent CVD were 1.60 (95% CI 1.35 to 1.89) for the last quintile ≤10 mg/L and 1.90 (95% CI 1.58 to 2.29) for the subgroup with CRP >10 mg/L. CRP was associated with recurrent CVD in patients with CAD (HR per 1 mg/L 1.08, 95% CI 1.04 to 1.11), CeVD (HR 1.05, 95% CI 1.01 to 1.10), PAD (HR 1.08, 95% CI 1.03 to 1.13), and AAA (HR 1.08, 95% CI 1.01 to 1.15). The association between CRP and all-cause mortality was stronger for patients with CAD (HR 1.13, 95% CI 1.09 to 1.16) than for patients with other CVD locations (HRs 1.06 to 1.08; p = 0.002). Associations remained consistent beyond 15 years after the CRP measurement. In conclusion, greater CRP is independently associated with an increased risk of recurrent CVD and mortality, irrespective of previous CVD location.

Metabolic syndrome and risk of incident heart failure in non-diabetic patients with established cardiovascular disease

BACKGROUND

In patients with established cardiovascular disease (CVD), the relation between metabolic syndrome (MetS) and incident heart failure (HF) in the absence of diabetes mellitus (DM) is largely unknown. This study assessed this relation in non-diabetic patients with established CVD.

METHODS

Patients from the prospective UCC-SMART cohort with established CVD, but without DM or HF at baseline were included (n = 4653). MetS was defined according to the Adult Treatment Panel III criteria. Insulin resistance was quantified using the homeostasis model of insulin resistance (HOMA-IR). The outcome was a first hospitalization for HF. Relations were assessed using Cox proportional hazards models adjusted for established risk factors: age, sex, prior myocardial infarction (MI), smoking, cholesterol, and kidney function.

RESULTS

During a median follow-up of 8.0 years, 290 cases of incident HF were observed (0.81/100 person years). MetS was significantly related to an increased risk of incident HF independent of established risk factors (hazard ratio [HR] 1.32; 95% confidence interval [CI] 1.04-1.68, HR per criterion 1.17; 95% CI 1.06-1.29), as was HOMA-IR (HR per standard deviation [SD] 1.15; 95% CI 1.03-1.29). Of the individual MetS components, only higher waist circumference independently increased the risk of HF (HR per SD 1.34; 95% CI 1.17-1.53). Relations were independent of the occurrence of interim DM and MI, and were not significantly different for HF with reduced vs preserved ejection fraction.

CONCLUSION

In CVD patients without a current diagnosis of DM, MetS and insulin resistance increase the risk of incident HF independent of established risk factors.

Inflammation and risk of recurrent cardiovascular events according to prior vascular disease location

Background

In recent years, anti-inflammatory drugs have been shown to reduce the risk of recurrent cardiovascular disease (CVD) events in patients with coronary artery disease (CAD), but have not yet been tested in patients with other vascular disease locations. Whether the relation between inflammation and recurrent CVD is modified by prior vascular disease location is unknown.

Purpose

This study aimed to establish the relation between low-grade inflammation and recurrent CVD according to prior vascular disease location.

Methods

Inflammation was measured by plasma concentrations of high-sensitivity C-reactive protein (CRP). Patients from the UCC-SMART cohort with CAD (n=4,517), cerebrovascular disease (CeVD; n=2,154), peripheral artery disease (PAD, n=1,154), or abdominal aortic aneurysm (AAA, n=424), and CRP ≤10 mg/L were included in the main analysis (combined n=8,249). Patients with CRP >10 mg/L (n=756) were analysed separately. The primary outcome was a composite of myocardial infarction, ischemic stroke, or cardiovascular death. Secondary outcomes included the primary outcome components, major adverse limb events (MALE), and all-cause mortality. The relation between CRP and outcomes was assessed using Cox proportional hazard models stratified by prior vascular disease location, and adjusted for potential confounders.

Results

During a median follow-up of 9.5 years (interquartile range 5.1–13.9) 1,877 CVD events, 887 MALE events, and 2,341 deaths were observed. In the total population, CRP was related to recurrent CVD (hazard ratio [HR] per 1 mg/L 1.08; 95% confidence interval [CI] 1.05–1.10), and all secondary outcomes except for ischemic stroke (HR 1.03; 95% CI 0.99–1.08). Compared to the first quintile of CRP, HRs for recurrent CVD were 1.66 (95% CI 1.41–1.96) for the last quintile ≤10 mg/L, and 1.97 (95% CI 1.64–2.36) for the subgroup with CRP >10 mg/L. CRP was related to recurrent CVD in patients with CAD (HR per 1 mg/L 1.08; 95% CI 1.04–1.11), as well as CeVD (HR 1.05; 95% CI 1.01–1.10), PAD (HR 1.08; 95% CI 1.03–1.13), and AAA (HR 1.08; 95% CI 1.01–1.15; p for interaction 0.815). The relation between CRP and all-cause mortality was stronger for patients with CAD (HR 1.13; 95% CI 1.09–1.16) compared to other locations (HRs 1.06–1.08; p=0.002).

Conclusion

Inflammation is an independent risk factor of recurrent CVD and mortality, irrespective of prior vascular disease location. Trials of anti-inflammatory drugs in patients with CeVD, PAD, and AAA are warranted.

Funding Acknowledgement

Type of funding sources: None.

Standardized reporting of co-morbidity outcome after bariatric surgery: low compliance with the ASMBS outcome reporting standards despite ease of use

BACKGROUND

Despite the publication of the American Society for Metabolic and Bariatric Surgery (ASMBS) Outcome Reporting Standards in 2015, there is still a great variety in definitions used for reporting remission of co-morbidities after bariatric surgery. This hampers meaningful comparison of results.

OBJECTIVE

To assess compliance with the ASMBS standards in current literature, and to evaluate use of the standards by applying them in a report on the outcomes of 5 co-morbidities after bariatric surgery.

SETTING

Two clinics of the Dutch Obesity Clinic, location Den Haag and Velp, and three affiliated hospitals: Haaglanden Medical Center in Den Haag, Groene Hart Hospital in Gouda, and Vitalys Clinic in Velp.

METHODS

A systematic search in PubMed was conducted to identify studies using the ASMBS standards. Besides, the standards were applied to a cohort of patients who underwent a primary bariatric procedure between November 2016 and June 2017. Outcomes of co-morbidities were determined at 6 and 12 months after surgery.

RESULTS

Ten previous studies applying ASMBS definitions were identified by the search, including 6 studies using portions of the definitions, and 4 using complete definitions for 3 co-morbidities or in a small population. In this study, the standards were applied to 1064 patients, of whom 796 patients (75%) underwent Roux-en-Y gastric bypass and 268 patients (25%) underwent sleeve gastrectomy. At 12 months, complete remission of diabetes (glycosylated hemoglobin <6%, off medication) was reached in 63%, partial remission (glycosylated hemoglobin 6%-6.4%, off medication) in 7%, and improvement in 28% of patients (n = 232/248, 94%). Complete remission of hypertension (normotensive, off medication) was noted in 8%, partial remission (prehypertensive, off medication) in 23% and improvement in 63% (n = 397/412, 96%). Remission rate for dyslipidemia (normal nonhigh-density lipoprotein, off medication) was 57% and improvement rate was 19% (n = 129/133, 97%). Resolution of gastroesophageal reflux disease (no symptoms, off medication) was observed in 54% (n = 265/265). Obstructive sleep apnea syndrome improved in 90% (n = 157/169, 93%).

CONCLUSIONS

Compliance with the ASMBS standards is low, despite ease of use. Standardized definitions provided by the ASMBS guideline could be used in future research to enable comparison of outcomes of different studies and surgical procedures.

Outcomes of second opinions in general internal medicine

BACKGROUND

To date, the outcomes of second opinions in internal medicine in terms of diagnostic yield and patient benefit have not been studied extensively. This retrospective study explores the outcomes of second opinions at a general internal medicine outpatient clinic in an academic hospital.

METHODS

A register of all patients referred to the general internal medicine outpatient clinic of the University Medical Center in Utrecht for a second opinion, was kept. All 173 patients referred between June 2016 and August 2018 were selected. Case records were analyzed for patient characteristics, referring doctor, chief complaint, performed investigations, follow-up time and, established diagnosis, additional diagnoses, initiated treatment and reported benefit.

RESULTS

A new diagnosis was established in 13% of all patients. A new treatment was initiated in 56% of all patients: 91% and 51% of patients with and without a new diagnosis respectively (p < 0.001). Of all patients, 19% received an effective treatment (52% vs 14% of patients with vs without a new diagnosis, p < 0.001). Regardless of treatment, resolution or improvement of the chief complaint was achieved in 28% of all patients (52% vs 25% of patients with vs without a new diagnosis, p = 0.006). Regarding diagnostics, 23-33% of radiology, endoscopy and pathology tests performed during second opinion were a repetition of previously conducted investigations. Conventional blood tests were a repetition in 89% of cases. Median time to diagnosis was 64 days (IQR: 25-128 days) and median time to discharge was 75 days (IQR: 31-144 days).

CONCLUSION

Second opinions in general internal medicine lead to the establishment of a new diagnosis in a small proportion of patients. However, the value of second opinions may not be limited to the establishment of diagnoses, as new treatments are often initiated and overall patients report improved symptomatology in 28% of cases.

[Measurement and evaluation of natural and artificial UV radiation]

Natural and artificial UV radiation are environmental factors with both beneficial and harmful biological effects. This article will explain the physical measurement quantities and their relation to the biologically effective dose and will summarize the present technical state of the art of personal UV monitoring. In practical use are dosimeters based on polysulphone, a polymer which undergoes changes in its optical properties upon irradiation with UV. Other systems determine the UV dose by quantifying damage induced in Bacillus subtilis spores upon UV exposure. An electronic UV sensor represents a new and interesting development. Personal UV dosimeters will become an useful tool in both clinical and scientific areas within dermatology.

Cyclosporin A, FK506 and dithranol after tyrosine-specific protein phosphorylation in HaCaT keratinocytes

Protein tyrosine kinases (PTKs) are closely related to cell growth, proliferation and differentiation. In keratinocytes, various growth factor receptors and cytosolic proteins, including the EGF and IGF receptors, the proteins of the src family and others, exhibit PTK activity. In psoriatic epidermis an increased level of EGF receptors and their ligand TGF-alpha has been found, and this is thought to be one reason for the pathological hyperproliferation of keratinocytes in this disease. Oral treatment with cyclosporin A (CsA) and FK506 or topical treatment with dithranol lead to an improvement in psoriasis. In the present study we examined the effect of these three drugs on the cellular content of phosphorylated tyrosines in highly proliferative HaCaT keratinocytes. HaCaT keratinocytes can be used as a model for highly proliferative epidermis, e.g. psoriatic epidermis. CsA had no effect whereas FK506 and dithranol reduced the phosphorylation of tyrosine residues in HaCaT keratinocytes. The activation of serine/threonine protein kinase C (PKC) is known to downregulate PTKs. Therefore we incubated keratinocytes with the selective PKC inhibitor Ro 31-8220 in addition to the other drugs. Only after the addition of Ro 31-8220 to FK506-treated keratinocytes was the phosphotyrosine (p-tyr) level elevated, but this was only one-third of the increase measured without additional therapeutic drugs. We assume that an induction of PKC alone is not responsible for the reduced p-tyr level after treatment with dithranol and FK506.(ABSTRACT TRUNCATED AT 250 WORDS)

GABA and glycine in synaptic vesicles: storage and transport characteristics

gamma-Aminobutyric acid (GABA) and glycine are major inhibitory neurotransmitters that are released from nerve terminals by exocytosis via synaptic vesicles. Here we report that synaptic vesicles immunoisolated from rat cerebral cortex contain high amounts of GABA in addition to glutamate. Synaptic vesicles from the rat medulla oblongata also contain glycine and exhibit a higher GABA and a lower glutamate concentration than cortical vesicles. No other amino acids were detected. In addition, the uptake activities of synaptic vesicles for GABA and glycine were compared. Both were very similar with respect to substrate affinity and specificity, bioenergetic properties, and regional distribution. We conclude that GABA, glycine, and glutamate are the only major amino acid neurotransmitters stored in synaptic vesicles and that GABA and glycine are transported by similar, if not identical, transporters.

P29: a novel tyrosine-phosphorylated membrane protein present in small clear vesicles of neurons and endocrine cells

A novel membrane protein from rat brain synaptic vesicles with an apparent 29,000 Mr (p29) was characterized. Using monospecific polyclonal antibodies, the distribution of p29 was studied in a variety of tissues by light and electron microscopy and immunoblot analysis. Within the nervous system, p29 was present in virtually all nerve terminals. It was selectively associated with small synaptic vesicles and a perinuclear region corresponding to the area of the Golgi complex. P29 was not detected in any other subcellular organelles including large dense-core vesicles. The distribution of p29 in various subcellular fractions from rat brain was very similar to that of synaptophysin and synaptobrevin. The highest enrichment occurred in purified small synaptic vesicles. Outside the nervous system, p29 was found only in endocrine cell types specialized for peptide hormone secretion. In these cells, p29 had a distribution very similar to that of synaptophysin. It was associated with microvesicles of heterogeneous size and shape that are primarily concentrated in the centrosomal-Golgi complex area. Secretory granules were mostly unlabeled, but their membrane occasionally contained small labeled evaginations. Immunoisolation of subcellular organelles from undifferentiated PC12 cells with antisynaptophysin antibodies led to a concomitant enrichment of p29, synaptobrevin, and synaptophysin, further supporting a colocalization of all three proteins. P29 has an isoelectric point of approximately 5.0 and is not N-glycosylated. It is an integral membrane protein and all antibody binding sites are exposed on the cytoplasmic side of the vesicles. Two monoclonal antibodies raised against p29 cross reacted with synaptophysin, indicating the presence of related epitopes. P29, like synaptophysin, was phosphorylated on tyrosine residues by endogenous tyrosine kinase activity in intact vesicles.

rab3 is a small GTP-binding protein exclusively localized to synaptic vesicles

rab3, a low molecular weight GTP-binding protein, is primarily expressed in brain, where it is present in soluble and membrane-bound forms. Membrane-bound rab3 in brain is exclusively localized on synaptic vesicles, the secretory organelles of the synapse that store and release neurotransmitters. rab3 is also expressed in endocrine tissues such as the adrenal medulla, where it is found together with other synaptic vesicle proteins on microvesicles distinct from chromaffin granules. The tight binding of rab3 to membranes correlates with hydrophobic modifications that are different in the membrane-bound and soluble forms of rab3. The results demonstrate the exclusive targeting of a small GTP-binding protein to secretory vesicles of a subset of the regulated pathway of secretion.

Synaptic vesicles immunoisolated from rat cerebral cortex contain high levels of glutamate

L-Glutamate is regarded as the major excitatory neurotransmitter in the mammalian CNS. However, whether the released transmitter originates from a cytosolic pool or is discharged from synaptic vesicles by exocytosis (vesicle hypothesis) remains controversial. A problem with the general acceptance of the vesicle hypothesis is that the enrichment of glutamate in synaptic vesicles has not been convincingly demonstrated. In the present study, we have analyzed the glutamate content of synaptic vesicles isolated from rat cerebral cortex by a novel immunobead procedure. A large amount of glutamate was present in these vesicles when a proton electrochemical gradient was maintained across the vesicle membrane during isolation. Compared with the starting fraction, glutamate was enriched more than 10-fold relative to other amino acids. Addition of N-ethylmaleimide prevented glutamate loss during isolation. Isotope exchange experiments revealed that exchange or re-uptake of glutamate after homogenization is negligible. We conclude that rat brain synaptic vesicles contain high levels of glutamate in situ.

Interaction of far- and near-ultraviolet radiation. The occurrence of photo-augmentation and photo-recovery in cultured mammalian cells

Guided by the phenomena of photo-augmentation and photo-recovery, which have been described with respect to the induction of erythema in human skin, experiments were undertaken with cultured mammalian cells to study whether irradiation with far- and near-ultraviolet radiation results in an interaction at the cellular level with respect to cell survival and induction of mutations. Evidence was found for both photo-augmentation and photo-recovery. Photo-augmentation (more than an additive effect) was observed for cell survival when the long-wave ultraviolet irradiation (UVA) preceded the short-wave ultraviolet irradiation (UVB). Photo-recovery (less than an additive effect) was observed for cell survival if the UVA was given after or simultaneously with the UVB. The latter effect, however, was strongly influenced by dose: doses of UVA higher than 20 000 J/m2 no longer lead to photo-recovery in cell survival. For mutation induction, reduction in mutant frequency appears indicated for both combinations of UVA and UVB and for high and low doses of UVA.

Mutagenicity of 8-methoxypsoralen and long-wave ultraviolet irradiation in diploid human skin fibroblasts: an improved risk estimate in photochemotherapy

Cell killing and the induction of mutation were studied in dividing and non-dividing human skin fibroblasts as a result of treatment by 8-methoxypsoralen (8-MOP) and long-wave UV irradiation (UVA). The cytotoxic effect was highly dependent upon the duration of the UVA exposure. The frequency of mutations increased linearly with the UVA dose at concentrations of 10 and 0.25 microliter 8-MOP/ml, the latter representing the concentration in the skin during PUVA treatment. The number of mutations induced per unit dose (= per microgram 8-MOP/ml per joule UVA/m2) was calculated: for dividing cells this value was 3.3 X 10(-8) per cell and for non-dividing cells 0.6 X 10.8(-8) per cell. On the basis of these values the expected number of induced mutants in the human skin per session of photochemotherapy is 1.2 X 10(-5), and per 30 years of maintenance therapy 1.3 X 10(-2) per cell. A comparison was made between this frequency and the frequency to be expected from spontaneous mutation. In addition the significance of absence in patients of SCE induction by photochemotherapy is discussed.