Sharing Medical Big Data While Preserving Patient Confidentiality in Innovative Medicines Initiative: A Summary and Case Report from BigData@Heart

Sharing individual patient data (IPD) is a simple concept but complex to achieve due to data privacy and data security concerns, underdeveloped guidelines, and legal barriers. Sharing IPD is additionally difficult in big data-driven collaborations such as Bigdata@Heart in the Innovative Medicines Initiative, due to competing interests between diverse consortium members. One project within BigData@Heart, case study 1, needed to pool data from seven heterogeneous data sets: five randomized controlled trials from three different industry partners, and two disease registries. Sharing IPD was not considered feasible due to legal requirements and the sensitive medical nature of these data. In addition, harmonizing the data sets for a federated data analysis was difficult due to capacity constraints and the heterogeneity of the data sets. An alternative option was to share summary statistics through contingency tables. Here it is demonstrated that this method along with anonymization methods to ensure patient anonymity had minimal loss of information. Although sharing IPD should continue to be encouraged and strived for, our approach achieved a good balance between data transparency while protecting patient privacy. It also allowed a successful collaboration between industry and academia.

Environmental and genetic predictors of human cardiovascular ageing

Cardiovascular ageing is a process that begins early in life and leads to a progressive change in structure and decline in function due to accumulated damage across diverse cell types, tissues and organs contributing to multi-morbidity. Damaging biophysical, metabolic and immunological factors exceed endogenous repair mechanisms resulting in a pro-fibrotic state, cellular senescence and end-organ damage, however the genetic architecture of cardiovascular ageing is not known. Here we use machine learning approaches to quantify cardiovascular age from image-derived traits of vascular function, cardiac motion and myocardial fibrosis, as well as conduction traits from electrocardiograms, in 39,559 participants of UK Biobank. Cardiovascular ageing is found to be significantly associated with common or rare variants in genes regulating sarcomere homeostasis, myocardial immunomodulation, and tissue responses to biophysical stress. Ageing is accelerated by cardiometabolic risk factors and we also identify prescribed medications that are potential modifiers of ageing. Through large-scale modelling of ageing across multiple traits our results reveal insights into the mechanisms driving premature cardiovascular ageing and reveal potential molecular targets to attenuate age-related processes.

Genetic studies of paired metabolomes reveal enzymatic and transport processes at the interface of plasma and urine

The kidneys operate at the interface of plasma and urine by clearing molecular waste products while retaining valuable solutes. Genetic studies of paired plasma and urine metabolomes may identify underlying processes. We conducted genome-wide studies of 1,916 plasma and urine metabolites and detected 1,299 significant associations. Associations with 40% of implicated metabolites would have been missed by studying plasma alone. We detected urine-specific findings that provide information about metabolite reabsorption in the kidney, such as aquaporin (AQP)-7-mediated glycerol transport, and different metabolomic footprints of kidney-expressed proteins in plasma and urine that are consistent with their localization and function, including the transporters NaDC3 (SLC13A3) and ASBT (SLC10A2). Shared genetic determinants of 7,073 metabolite-disease combinations represent a resource to better understand metabolic diseases and revealed connections of dipeptidase 1 with circulating digestive enzymes and with hypertension. Extending genetic studies of the metabolome beyond plasma yields unique insights into processes at the interface of body compartments.

Deep learning on resting electrocardiogram to identify impaired heart rate recovery

Background and Objective

Postexercise heart rate recovery (HRR) is an important indicator of cardiac autonomic function and abnormal HRR is associated with adverse outcomes. We hypothesized that deep learning on resting electrocardiogram (ECG) tracings may identify individuals with impaired HRR.

Methods

We trained a deep learning model (convolutional neural network) to infer HRR based on resting ECG waveforms (HRR_pred) among UK Biobank participants who had undergone exercise testing. We examined the association of HRR_pred with incident cardiovascular disease using Cox models, and investigated the genetic architecture of HRR_pred in genome-wide association analysis.

Results

Among 56,793 individuals (mean age 57 years, 51% women), the HRR_pred model was moderately correlated with actual HRR (r = 0.48, 95% confidence interval [CI] 0.47-0.48). Over a median follow-up of 10 years, we observed 2060 incident diabetes mellitus (DM) events, 862 heart failure events, and 2065 deaths. Higher HRR_pred was associated with lower risk of DM (hazard ratio [HR] 0.79 per 1 standard deviation change, 95% CI 0.76-0.83), heart failure (HR 0.89, 95% CI 0.83-0.95), and death (HR 0.83, 95% CI 0.79-0.86). After accounting for resting heart rate, the association of HRR_pred with incident DM and all-cause mortality were similar. Genetic determinants of HRR_pred included known heart rate, cardiac conduction system, cardiomyopathy, and metabolic trait loci.

Conclusion

Deep learning-derived estimates of HRR using resting ECG independently associated with future clinical outcomes, including new-onset DM and all-cause mortality. Inferring postexercise heart rate response from a resting ECG may have potential clinical implications and impact on preventive strategies warrants future study.

Cohort design and natural language processing to reduce bias in electronic health records research

Electronic health record (EHR) datasets are statistically powerful but are subject to ascertainment bias and missingness. Using the Mass General Brigham multi-institutional EHR, we approximated a community-based cohort by sampling patients receiving longitudinal primary care between 2001-2018 (Community Care Cohort Project [C3PO], n = 520,868). We utilized natural language processing (NLP) to recover vital signs from unstructured notes. We assessed the validity of C3PO by deploying established risk models for myocardial infarction/stroke and atrial fibrillation. We then compared C3PO to Convenience Samples including all individuals from the same EHR with complete data, but without a longitudinal primary care requirement. NLP reduced the missingness of vital signs by 31%. NLP-recovered vital signs were highly correlated with values derived from structured fields (Pearson r range 0.95-0.99). Atrial fibrillation and myocardial infarction/stroke incidence were lower and risk models were better calibrated in C3PO as opposed to the Convenience Samples (calibration error range for myocardial infarction/stroke: 0.012-0.030 in C3PO vs. 0.028-0.046 in Convenience Samples; calibration error for atrial fibrillation 0.028 in C3PO vs. 0.036 in Convenience Samples). Sampling patients receiving regular primary care and using NLP to recover missing data may reduce bias and maximize generalizability of EHR research.

Genetic and environmental determinants of diastolic heart function

Diastole is the sequence of physiological events that occur in the heart during ventricular filling and principally depends on myocardial relaxation and chamber stiffness. Abnormal diastolic function is related to many cardiovascular disease processes and is predictive of health outcomes, but its genetic architecture is largely unknown. Here, we use machine learning cardiac motion analysis to measure diastolic functional traits in 39,559 participants of the UK Biobank and perform a genome-wide association study. We identified 9 significant, independent loci near genes that are associated with maintaining sarcomeric function under biomechanical stress and genes implicated in the development of cardiomyopathy. Age, sex and diabetes were independent predictors of diastolic function and we found a causal relationship between genetically-determined ventricular stiffness and incident heart failure. Our results provide insights into the genetic and environmental factors influencing diastolic function that are relevant for identifying causal relationships and potential tractable targets.

Self-Reported Medication Use and Urinary Drug Metabolites in the German Chronic Kidney Disease (GCKD) Study

BACKGROUND

Polypharmacy is common among patients with CKD, but little is known about the urinary excretion of many drugs and their metabolites among patients with CKD.

METHODS

To evaluate self-reported medication use in relation to urine drug metabolite levels in a large cohort of patients with CKD, the German Chronic Kidney Disease study, we ascertained self-reported use of 158 substances and 41 medication groups, and coded active ingredients according to the Anatomical Therapeutic Chemical Classification System. We used a nontargeted mass spectrometry-based approach to quantify metabolites in urine; calculated specificity, sensitivity, and accuracy of medication use and corresponding metabolite measurements; and used multivariable regression models to evaluate associations and prescription patterns.

RESULTS

Among 4885 participants, there were 108 medication-drug metabolite pairs on the basis of reported medication use and 78 drug metabolites. Accuracy was excellent for measurements of 36 individual substances in which the unchanged drug was measured in urine (median, 98.5%; range, 61.1%-100%). For 66 pairs of substances and their related drug metabolites, median measurement-based specificity and sensitivity were 99.2% (range, 84.0%-100%) and 71.7% (range, 1.2%-100%), respectively. Commonly prescribed medications for hypertension and cardiovascular risk reduction-including angiotensin II receptor blockers, calcium channel blockers, and metoprolol-showed high sensitivity and specificity. Although self-reported use of prescribed analgesics (acetaminophen, ibuprofen) was <3% each, drug metabolite levels indicated higher usage (acetaminophen, 10%-26%; ibuprofen, 10%-18%).

CONCLUSIONS

This comprehensive screen of associations between urine drug metabolite levels and self-reported medication use supports the use of pharmacometabolomics to assess medication adherence and prescription patterns in persons with CKD, and indicates under-reported use of medications available over the counter, such as analgesics.

Batch Selection via In Vitro/In Vivo Correlation in Pharmacokinetic Bioequivalence Testing

Pharmacokinetic differences between manufacturing batches, well established for inhaled drug products, preclude control of patient risk in the customary two-way (single batch) pharmacokinetic bioequivalence crossover design if batches are randomly chosen. European regulators have recommended selecting a "typical" in vitro batch to represent each product in pharmacokinetic bioequivalence testing. We explored the feasibility of this approach to control patient risk (the "false equivalence", or Type I, error rate). The probability of achieving a Test/Reference 90% confidence interval within (0.80, 1.25) for a true (non-equivalent) value of 1.25 was simulated for a two-way crossover design using the median in vitro batch across a range of number of in vitro batches, in vitro/in vivo correlation (IVIVC) quality (correlation coefficient, r, of zero to one), and within-subject between-batch pharmacokinetic variability. Even under extremely optimistic conditions, e.g., r=0.95 and >100 batches per product screened in vitro, patient risk for typical between-batch variability levels remained at least threefold higher than the 5% regulatory expectation for the significance level (the false equivalence error rate) of the pharmacokinetic bioequivalence test. This elevated error rate in bioequivalence decision-making occurs because of incomplete confidence that the true product average has been identified, and, importantly, omission of this uncertainty from the bioequivalence confidence interval.

MO492SELF-REPORTED MEDICATION USE AND URINARY DRUG METABOLITES IN THE GERMAN CHRONIC KIDNEY DISEASE (GCKD) STUDY: A PHARMACOMETABOLOMIC APPROACH

Background and Aims

Chronic kidney disease (CKD) patients are prone to prescription of multiple medications. Medication adherence is a well-recognized problem in the management of patients with chronic diseases requiring polypharmacy. This study aimed to evaluate the connection between self-reported medication use and urine drug metabolite levels in a large cohort of CKD patients, the GCKD study, as a basis for future pharmacometabolomics studies.

Method

Self-reported medication use of 160 substances and 41 medication groups was ascertained at study baseline and coded according to the Anatomical Therapeutic Chemical classification system. A non-targeted mass spectrometry-based approach (Metabolon HD4™) was used for concomitant metabolite quantification in urine. Specificity, sensitivity and accuracy of medication use and the corresponding urine metabolite measurements were calculated. Multivariable regression models (adjusted to age, sex, eGFR, log(UACR), systolic blood pressure, LDL, log(triglycerides), log(HBA1c) were used to establish associations in prescription patterns.

Results

Among 4,885 participants, 78 drug metabolites were detected in urine (frequency range: 0.4-58%) and assigned into 110 medication – drug metabolite pairs (MMPs) based on reported individual substances and medication groups. For all 68 MMPs of individual substances, accuracy of medication use and the corresponding drug metabolite measurement was excellent (median 97.0%, range 43%-100%), as was measurement-based specificity (median 99.3%, range 73.3%-100%; Fig. 1). Median measurement-based sensitivity was 72.1% (range 1.1%-100%, Fig. 1). Sensitivity and specificity were especially high for angiotensin-II receptor blockers (92%-96%; 99-100%), calcium channel blockers (85-100%; 91-100%), and metoprolol (90%; 98% respectively) commonly prescribed and important medications for blood pressure control and cardiovascular risk reduction in CKD patients. MMPs showing sensitivity &lt;80% included several substances found in over-the-counter (OTC) analgesic medications, suggesting that their use is not always reported. While self-reported use of the OTC analgesics acetaminophen and ibuprofen was &lt;3% each, their corresponding drug metabolites indicated higher usage (acetaminophen: 10-26%; ibuprofen: 10-18%, depending on the number of evaluated drug metabolites). Typical examples of medication co-prescriptions (e.g., trimethoprim and sulfamethoxazole) were detected as the combined presence of their drug metabolites in urine. This result validates the abstraction of single substances from combination medications and this urine-based metabolomic approach.

Conclusion

This study provides a comprehensive screen of the associations between urine drug metabolite levels and self-reported medication use. It supports the usefulness of pharmacometabolomics to assess medication use, frequency of OTC analgesics use, and prescription patterns in persons with CKD.

Machine learning for subtype definition and risk prediction in heart failure, acute coronary syndromes and atrial fibrillation: systematic review of validity and clinical utility

BACKGROUND

Machine learning (ML) is increasingly used in research for subtype definition and risk prediction, particularly in cardiovascular diseases. No existing ML models are routinely used for cardiovascular disease management, and their phase of clinical utility is unknown, partly due to a lack of clear criteria. We evaluated ML for subtype definition and risk prediction in heart failure (HF), acute coronary syndromes (ACS) and atrial fibrillation (AF).

METHODS

For ML studies of subtype definition and risk prediction, we conducted a systematic review in HF, ACS and AF, using PubMed, MEDLINE and Web of Science from January 2000 until December 2019. By adapting published criteria for diagnostic and prognostic studies, we developed a seven-domain, ML-specific checklist.

RESULTS

Of 5918 studies identified, 97 were included. Across studies for subtype definition (n = 40) and risk prediction (n = 57), there was variation in data source, population size (median 606 and median 6769), clinical setting (outpatient, inpatient, different departments), number of covariates (median 19 and median 48) and ML methods. All studies were single disease, most were North American (n = 61/97) and only 14 studies combined definition and risk prediction. Subtype definition and risk prediction studies respectively had limitations in development (e.g. 15.0% and 78.9% of studies related to patient benefit; 15.0% and 15.8% had low patient selection bias), validation (12.5% and 5.3% externally validated) and impact (32.5% and 91.2% improved outcome prediction; no effectiveness or cost-effectiveness evaluations).

CONCLUSIONS

Studies of ML in HF, ACS and AF are limited by number and type of included covariates, ML methods, population size, country, clinical setting and focus on single diseases, not overlap or multimorbidity. Clinical utility and implementation rely on improvements in development, validation and impact, facilitated by simple checklists. We provide clear steps prior to safe implementation of machine learning in clinical practice for cardiovascular diseases and other disease areas.

Rare genetic variants affecting urine metabolite levels link population variation to inborn errors of metabolism

Metabolite levels in urine may provide insights into genetic mechanisms shaping their related pathways. We therefore investigate the cumulative contribution of rare, exonic genetic variants on urine levels of 1487 metabolites and 53,714 metabolite ratios among 4864 GCKD study participants. Here we report the detection of 128 significant associations involving 30 unique genes, 16 of which are known to underlie inborn errors of metabolism. The 30 genes are strongly enriched for shared expression in liver and kidney (odds ratio = 65, p-FDR = 3e-7), with hepatocytes and proximal tubule cells as driving cell types. Use of UK Biobank whole-exome sequencing data links genes to diseases connected to the identified metabolites. In silico constraint-based modeling of gene knockouts in a virtual whole-body, organ-resolved metabolic human correctly predicts the observed direction of metabolite changes, highlighting the potential of linking population genetics to modeling. Our study implicates candidate variants and genes for inborn errors of metabolism.

Leveraging Human Genetics to Estimate Clinical Risk Reductions Achievable by Inhibiting Factor XI

Supplemental Digital Content is available in the text.

Coagulation factor XI (FXI) is a novel target for antithrombotic therapy addressed by various therapeutic modalities currently in clinical development. The expected magnitude of thrombotic event reduction mediated by targeting FXI is unclear.

The Assessment of Quality Attributes for Biosimilars: a Statistical Perspective on Current Practice and a Proposal

Establishing comparability of the originator and its biosimilar at the structural and functional level, by analyzing so-called quality attributes, is an important step in biosimilar development. The statistical assessment of quality attributes is currently in the focus of attention because both the FDA and the EMA are working on regulatory documents for advising companies on the use of statistical approaches for strengthening their comparability claim. In this paper, we first discuss "comparable" and "not comparable" settings and propose a shift away from the usual comparison of the mean values: we argue that two products can be considered comparable if the range of the originator fully covers the range of the biosimilar. We then introduce a novel statistical testing procedure (the "tail-test") and compare the operating characteristics of the proposed approach with approaches currently used in practice. In contrast to the currently used approaches, we note that our proposed methodology is compatible with the proposed understanding of comparability and has, compared to other frequently applied range-based approaches, the advantage of being a formal statistical testing procedure which controls the patient's risk and has reasonable large-sample properties.

An update on the clinical evidence that supports biosimilar approvals in Europe

AIM

Sponsors and regulators have more than 10 years of experience with the development of biosimilars in Europe. However, the regulatory pathway is still evolving. The present article provides an update on biosimilar development in practice by reviewing the clinical development programmes of recently approved biosimilars in Europe.

METHODS

We used the European public assessment reports (EPARs) which are published by the European Medicines Agency (EMA) for a comparison of the clinical development programmes of the 37 approved biosimilars in Europe. Here, we present novel strategies in the development of biosimilars by focusing specifically on the 17 biosimilars that have gained approval in the last year, but we also compare additional key characteristics for all approved biosimilars.

RESULTS

The high variability of the clinical development strategies that we found previously was confirmed in the present analysis. Compared with earlier biosimilar applications, more nonstandard development strategies have been used recently. This includes, for example, applications without any studies in patients, and more complex study designs. During this study, we found that the EPARs for biosimilars seem to be improving; however, we identified important details which were still often missing. We provide a proposal for a checklist of the minimum information that should be included in biosimilar EPARs for giving the general public insights into the rationale for the approval of biosimilars.

CONCLUSIONS

European regulators still seem to be open to consider approaches that differ from the guidelines or previous applications, as long as justification is provided.

Incorporating historical information in biosimilar trials: Challenges and a hybrid Bayesian-frequentist approach

For the approval of biosimilars, it is, in most cases, necessary to conduct large Phase III clinical trials in patients to convince the regulatory authorities that the product is comparable in terms of efficacy and safety to the originator product. As the originator product has already been studied in several trials beforehand, it seems natural to include this historical information into the showing of equivalent efficacy. Since all studies for the regulatory approval of biosimilars are confirmatory studies, it is required that the statistical approach has reasonable frequentist properties, most importantly, that the Type I error rate is controlled-at least in all scenarios that are realistic in practice. However, it is well known that the incorporation of historical information can lead to an inflation of the Type I error rate in the case of a conflict between the distribution of the historical data and the distribution of the trial data. We illustrate this issue and confirm, using the Bayesian robustified meta-analytic-predictive (MAP) approach as an example, that simultaneously controlling the Type I error rate over the complete parameter space and gaining power in comparison to a standard frequentist approach that only considers the data in the new study, is not possible. We propose a hybrid Bayesian-frequentist approach for binary endpoints that controls the Type I error rate in the neighborhood of the center of the prior distribution, while improving the power. We study the properties of this approach in an extensive simulation study and provide a real-world example.

A highly stable monolithic enhancement cavity for second harmonic generation in the ultraviolet

We present a highly stable bow-tie power enhancement cavity for critical second harmonic generation (SHG) into the UV using a Brewster-cut β-BaB₂O₄ (BBO) nonlinear crystal. The cavity geometry is suitable for all UV wavelengths reachable with BBO and can be modified to accommodate anti-reflection coated crystals, extending its applicability to the entire wavelength range accessible with non-linear frequency conversion. The cavity is length-stabilized using a fast general purpose digital PI controller based on the open source STEMlab 125-14 (formerly Red Pitaya) system acting on a mirror mounted on a fast piezo actuator. We observe 130 h uninterrupted operation without decay in output power at 313 nm. The robustness of the system has been confirmed by exposing it to accelerations of up to 1 g with less than 10% in-lock output power variations. Furthermore, the cavity can withstand 30 min of acceleration exposure at a level of 3 g_rms without substantial change in the SHG output power, demonstrating that the design is suitable for transportable setups.

A Longitudinal Item Response Theory Model to Characterize Cognition Over Time in Elderly Subjects

For drug development in neurodegenerative diseases such as Alzheimer's disease, it is important to understand which cognitive domains carry the most information on the earliest signs of cognitive decline, and which subject characteristics are associated with a faster decline. A longitudinal Item Response Theory (IRT) model was developed for the Basel Study on the Elderly, in which the Consortium to Establish a Registry for Alzheimer's Disease - Neuropsychological Assessment Battery (with additions) and the California Verbal Learning Test were measured on 1,750 elderly subjects for up to 13.9 years. The model jointly captured the multifaceted nature of cognition and its longitudinal trajectory. The word list learning and delayed recall tasks carried the most information. Greater age at baseline, fewer years of education, and positive APOEɛ4 carrier status were associated with a faster cognitive decline. Longitudinal IRT modeling is a powerful approach for progressive diseases with multifaceted endpoints.

Between-Batch Pharmacokinetic Variability Inflates Type I Error Rate in Conventional Bioequivalence Trials: A Randomized Advair Diskus Clinical Trial

We previously demonstrated pharmacokinetic differences among manufacturing batches of a US Food and Drug Administration (FDA)-approved dry powder inhalation product (Advair Diskus 100/50) large enough to establish between-batch bio-inequivalence. Here, we provide independent confirmation of pharmacokinetic bio-inequivalence among Advair Diskus 100/50 batches, and quantify residual and between-batch variance component magnitudes. These variance estimates are used to consider the type I error rate of the FDA's current two-way crossover design recommendation. When between-batch pharmacokinetic variability is substantial, the conventional two-way crossover design cannot accomplish the objectives of FDA's statistical bioequivalence test (i.e., cannot accurately estimate the test/reference ratio and associated confidence interval). The two-way crossover, which ignores between-batch pharmacokinetic variability, yields an artificially narrow confidence interval on the product comparison. The unavoidable consequence is type I error rate inflation, to ∼25%, when between-batch pharmacokinetic variability is nonzero. This risk of a false bioequivalence conclusion is substantially higher than asserted by regulators as acceptable consumer risk (5%).

Clinical trials for authorized biosimilars in the European Union: a systematic review

Aim

In 2006, Omnitrope (by Sandoz) was the first approved biosimilar in Europe. To date, 21 biosimilars for seven different biologics are on the market. The present study compared the clinical trials undertaken to obtain market authorization.

Methods

We summarized the findings of a comprehensive review of all clinical trials up to market authorization of approved biosimilars, using the European public assessment reports (EPARs) published by the European Medicines Agency (EMA). The features compared were, among others, the number of patients enrolled, the number of trials, the types of trial design, choice of endpoints and equivalence margins for pharmacokinetic (PK)/pharmacodynamic (PD) and phase III trials.

Results

The variability between the clinical development strategies is high. Some differences are explainable by the characteristics of the product; if, for example, the PD marker can be assumed to predict the clinical outcome, no efficacy trials might be necessary. However, even for products with the same reference product, the sample size, endpoints and statistical models are not always the same.

Conclusions

There seems to be flexibility for sponsors regarding the decision as to how best to prove biosimilarity.

Direct Observation of Photoinduced Tautomerization in Single Molecules at a Metal Surface

Molecular switches are of fundamental importance in nature, and light is an important stimulus to selectively drive the switching process. However, the local dynamics of a conformational change in these molecules remain far from being completely understood at the single-molecule level. Here, we report the direct observation of photoinduced tautomerization in single porphycene molecules on a Cu(111) surface by using a combination of low-temperature scanning tunneling microscopy and laser excitation in the near-infrared to ultraviolet regime. It is found that the thermodynamically stable trans configuration of porphycene can be converted to the metastable cis configuration in a unidirectional fashion by photoirradiation. The wavelength dependence of the tautomerization cross section exhibits a steep increase around 2 eV and demonstrates that excitation of the Cu d-band electrons and the resulting hot carriers play a dominant role in the photochemical process. Additionally, a pronounced isotope effect in the cross section (∼100) is observed when the transferred hydrogen atoms are substituted with deuterium, indicating a significant contribution of zero-point energy in the reaction. Combined with the study of inelastic tunneling electron-induced tautomerization with the STM, we propose that tautomerization occurs via excitation of molecular vibrations after photoexcitation. Interestingly, the observed cross section of ∼10(-19) cm(2) in the visible-ultraviolet region is much higher than that of previously studied molecular switches on a metal surface, for example, azobenzene derivatives (10(-23)-10(-22) cm(2)). Furthermore, we examined a local environmental impact on the photoinduced tautomerization by varying molecular density on the surface and find substantial changes in the cross section and quenching of the process due to the intermolecular interaction at high density.

[Dopamine receptors of the corneal epithelium and endothelium]

BACKGROUND

Dopamine is a major neurotransmitter and its two receptor subgroups, termed D1-like and D2-like receptors, are found both in the central and peripheral nervous systems. D1-like receptors signal through increases, D2-like receptors through decreases in cAMP production. Reports about the presence of dopamine receptors in the cornea are rare and inconsistant. The aim of this study was to examine if native bovine corneal epithelial and endothelial cells express dopamine receptors and whether these receptors belong to the D1-like or D2-like group.

MATERIALS AND METHODS

Dopamine receptors were studied using polyclonal antibodies. The cAMP concentration after receptor stimulation with dopamine was determined by means of an enzyme immunoassay.

RESULTS

In bovine corneal epithelium and endothelium immunohistochemical staining was positive for D1-like receptors but not for D2-like receptors. Stimulation of corneal D1-like receptors with dopamine revealed a dose-dependent increase of the intracellular cAMP concentration which was blocked by SCH23 390 (a selective D1-like antagonist).

CONCLUSION

Our data demonstrate that bovine corneal epithelium and endothelium express a functional D1-like receptor positively coupled to adenylyl cyclase and cAMP production. However, at the present time the physiological role of this receptor remains a matter of speculation.

[m4 muscarinic receptors of the cornea : muscarinic cholinoceptor-stimulated inhibition of the cAMP-PKA pathway in corneal epithelial and endothelial cells]

BACKGROUND

Muscarinic cholinoceptors have been found in all types of ocular tissue, e.g. in corneal epithelium and endothelium. Latest research has focused only on the m5 cholinoceptor subtype. However, previous studies have also indicated the presence of m2 or m4 receptor subtypes in corneal tissue. The aim of this study was to show the decrease of intracellular cAMP formation and protein kinase A (PKA) activity after stimulation of m2 or m4 cholinoceptors in bovine corneal epithelial and endothelial cells. MATERIALS UND METHODS: Muscarinic cholinoceptors were studied using polyclonal antibodies. The cAMP concentration was determined with an enzyme immunoassay and PKA activity was estimated by the consumption of ATP.

RESULTS

Immunocytochemistry, immunofluorescence and immunoblotting revealed the presence of the m4 muscarinic cholinoceptor subtype but not of the m2 receptor subtype in bovine corneal epithelial and endothelial cells. In bovine corneal epithelium and endothelium protein cAMP formation was decreased and PKA activity was inhibited by acetylcholine in a dose-dependent manner (p<0.001).

CONCLUSION

The findings indicate that stimulation of m4 muscarinic cholinoceptors inhibits the cAMP-PKA pathway in corneal epithelial and endothelial cells resulting in decreased protein kinase A activity. Further work will be needed to clarify the physiological role of this signaling pathway in corneal epithelium and endothelium.

Mechanical behavior of nanocrystalline NaCl islands on Cu(111)

The mechanical response of ultrathin NaCl crystallites of nanometer dimensions upon manipulation with the tip of a scanning tunneling microscope (STM) is investigated, expanding STM manipulation to various nanostructuring modes of inorganic materials as cutting, moving, and cracking. In the light of theoretical calculations, our results reveal that atomic-scale NaCl islands can behave elastically and follow a classical Hooke's law. When the elastic limit of the nanocrystallites is reached, the STM tip induces atomic dislocations and consequently the regime of plastic deformation is entered. Our methodology is paving the way to understand the mechanical behavior and properties of other nanoscale materials.

Alcohol in the South Pacific: the mid-1990s

In the mid-1990s data were obtained on alcohol consumption in the Cook Islands, Fiji, Kiribati, Samoa, the Solomon Islands and Tonga. These data are reported together with a discussion of the nature of alcohol related problems in the island nations. Per capita consumption is highest in the Cook Islands, which compared with other countries has the highest ratio of liquor outlets and lowest alcohol taxation regime. As an alcohol problem prevention measure, it is concluded that the promotion of responsible consumption, together with the option of abstinence for those who wish it, is an acceptable strategy for the Pacific.

Medications for chronic pain practical review

This review is confined to the drug management of chronic pain, and is specifically adapted to the resource-poor environment and the HIV pandemic of sub-Saharan Africa. A brief classification of chronic pain is followed by a discussion of the different classes of medications in use, including those used in migraine. An approach to the rational drug management of neuropathic pain is presented. In conclusion some general principles for prescribing in this setting are derived.

[Effect of timolol on central corneal thickness and endothelial cell density]

BACKGROUND

The measurement of corneal thickness plays an increasing role in glaucoma screening and diagnosis. The influence of a variety of drugs on corneal thickness is well established. Especially for antiglaucomateous drugs this effect seems to be important. However, little is known about the influence of beta receptor antagonists on corneal thickness. The aim of this study was to provide evidence of the effect of timolol on central corneal thickness and endothelial cell density.

MATERIALS AND METHODS

Ten healthy volunteers (five women and five men) with a mean age of 29 years (range 25 to 56 years) were examined in a double-blind, prospective and randomised pilot study. Intraocular pressure, corneal thickness and endothelial cell density was estimated before as well as fifteen minutes, 24, 48, 72 and 96 hours after application of timolol 0.5 % eye drops twice daily. The partner eye received sodium hyaluronate eye drops twice daily and served as a control.

RESULTS

The application of timolol showed a decrease of intraocular pressure from initially 12 mmHg to 9 mmHg after four days (p = 0,0188) as well as an increase of corneal thickness from 537 microm to 557 microm after four days (p = 0,0659). There was no change of intraocular pressure (p = 0,9935) or corneal thickness (p = 0,9998) in the control eyes. There was also no effect of timolol (p = 0,2782) or sodium hyaluronate (p = 0,1940) on endothelial cell density.

CONCLUSIONS

The study provides evidence of the influence of beta receptor antagonists on corneal thickness. This effect may be caused by receptor mediated influences on corneal ion and fluid transport. Further studies are needed to show if the increase of corneal thickness after application of topical timolol has clinical importance.

[Protein kinase C isoforms in corneal epithelium and endothelium]

BACKGROUND

Protein kinase C (PKC) plays a key role in cell metabolism. Three subgroups and 12 isoforms have been isolated so far, catalysing specific functions in cell metabolism. The demonstration of PKC subtypes in corneal tissue has been inconsistent. The aim of this study was to verify the expression of several PKC subgroups and isoforms in human and bovine corneal epithelial and endothelial cells.

MATERIALS AND METHODS

PKC subgroups and isoforms were studied using polyclonal antibodies.

RESULTS

Antibodies to PKC-alpha, -delta, -epsilon and -zeta, representing all three PKC subgroups, bound in human and bovine corneal epithelium and endothelium. No binding was found for antibodies to PKC-beta2.

CONCLUSIONS

For the first time the presence of all three PKC subgroups was demonstrated in human and bovine corneal epithelial and endothelial cells. Further studies are needed to show the role of these subgroups in cellular functions such as cell proliferation and differentiation.

[Choroidal effusion syndrome after embolization of an indirect cavernous sinus fistula via the superior ophthalmic vein]

Embolization of a cavernous sinus fistula (SCF) via the superior ophthalmic vein (SOV) was reported to be an almost uncomplicated procedure, even after ligature of the vein at the end of the procedure. We report about a complication of this therapy. A 58-year-old female had a successful embolization of a right indirect cavernous sinus fistula via the SOV. At the end of the operation the SOV was ligated because of the danger of bleeding. Directly after surgery she experienced general worsening of the right eye with signs of venous congestion and marked effusion syndrome. The patient underwent total heparinization to achieve an opening of venous collaterals. Under local therapy with atropine 1% eye drops a decrease of the intraocular pressure was observed. The effusion syndrome was completely resolved within 1 month. If embolization of a cavernous sinus fistula is performed via the SOV, the ligature of the vein at the end of the procedure leads to thrombosis, which can reduce the venous stream from the eye and orbit. A secondary effusion syndrome with ocular hypertension because of a ciliolenticular block situation is possible and requires appropriate therapy. It is not possible to assess the capacity and time of opening of the venous collateral system before surgery. Therefore a transient outflow disturbance should be considered.

Epilepsy in sub-Saharan Africa: its socio-demography, aetiology, diagnosis and EEG characteristics in Harare, Zimbabwe

OBJECTIVE

To assess epileptics with regard to socio-demographic characteristics, aetiology, EEG results and classification.

DESIGN

A descriptive cohort study from 1997 to 2001.

SETTING

Parirenyatwa Group of Hospitals in Harare, Zimbabwe.

SUBJECTS

A total of 229 consecutive epileptic subjects.

RESULTS

The mean (s.d.) follow-up was 3.2 (1.14) years. The mean (s.d.) age of subjects was 23.4(11.8) years and 56% of them were males, over one third (43.1%) were unemployed and had secondary education (48%). Over one fourth (26.6%) of the subjects were first borns and had a family history of epilepsy (25.8%). Most of the subjects had Generalised Tonic Clonic Seizures (TCS). Over half (51.5%) of the subjects had their first onset of seizures after the age of 20 years. Lack of sleep (7.9%) and emotional disturbance (5.4%) were described by subjects as the frequent provoking factors for epileptic attacks. One hundred and fourteen subjects had electroencephalogram (EEG) results. Of these, 96 (41.9%) subjects had abnormal EEG results and only 18 (7.9%) had normal EEG results a majority (43.8%) of whom were of generalised slow waves. Majority of the subjects (52.8%) sought treatments from biomedical drugs, but some started with traditional herbs (20.5%) and then biomedical drugs, whereas others sought biomedical drugs then resorted to traditional herbs (20.1%). Phenobarbital and carbamazepine were taken by over 40% of the subjects.

CONCLUSION

The findings of this study seem to suggest that these referrals to a specialised epilepsy outpatient clinic for further management may be attributed to socio cultural issues in our African settings about the actual nature of the condition, hence the delay in treatments and diagnosis of seizures as well as under diagnoses of non-epileptic seizure disorders that may lead to the condition becomes uncontrollable. Inexpensive drugs such as phenobarbital and phenytoin can be able to control most of the epileptic seizures, if they can be made available in primary health care centres.

Keratoconjunctivitis epidemica

OBJECTIVE

The validity of the 15-min adenovirus assay SAS Adenotest was evaluated compared with virus detection by polymerase chain reaction (PCR) from conjunctival swabs.

METHODS

In 75 patients with assumed epidemic keratoconjunctivitis, adenovirus detection from conjunctival swabs was performed by the immunochromatographic assay SAS Adenotest and PCR.

RESULTS

In 25 patients adenovirus was detected by PCR, 18 of whom were detected by the SAS Adenotest and 7 of whom were not. No false positive results occurred. Sensitivity was 72% and specificity was 100%.

CONCLUSIONS

The results indicate that rapid adenovirus detection with the SAS Adenotest is a useful tool in early epidemic keratoconjunctivitis. An additional PCR should be performed when clinical symptoms persist for 5 days or more.

Breaking the silence: an HIV-related educational intervention for medical students in Zimbabwe

PROBLEM

A culture of silence surrounding HIV is a major contributor to continued HIV transmission and poor care for people living with HIV/AIDS.

AIM

To encourage medical leadership in addressing stigma and fear related to HIV at individual and community levels

OBJECTIVE

To pilot a mini-course for final year medical students in Zimbabwe that demonstrates stigma-reduction knowledge and skills needed to communicate information about HIV to patients, to address ethical implications of testing versus not testing for HIV, to increase awareness of the medical and preventive benefits of knowing one's HIV status and showing people how to cope with the emotional burden of dealing with HIV everyday.

DESIGN

Methods of proven effectiveness for training medical students in ethics and communication skills were used such as presentations by well respected role models and opinion leaders, role-playing, small group discussions, accompanied by materials indicating local resources, in three afternoon teaching sessions.

SETTING

University of Zimbabwe College of Medicine.

PARTICIPANTS

60 medical students, six lecturers, two facilitators and a group of actors.

MAIN OUTCOME MEASURES

Evaluation of the course by students showed appreciation of the course as measured on a scale of one to five for content and usefulness with requests for further inputs into the curriculum; model of mini-course that can be used by other medical schools in the southern Africa region and other areas of emerging HIV epidemics.

CONCLUSIONS

A brief educational intervention can help medical students to cope with the extraordinary challenge of providing care in high HIV prevalence countries and may contribute towards better leadership in addressing HIV epidemics.

Making research ethics review work in Zimbabwe--the case for investment in local capacity

OBJECTIVE

To describe the status of ethics review as pertaining to medical research in Zimbabwe, to compare this with international guidelines, and thus to identify potential improvements in the process.

DESIGN

The description includes background about the national review body, the Medical Research Council of Zimbabwe (MRCZ), and the findings of an analysis of institutional ethics review performed by the MRCZ liaison office.

RESULTS

Discrepancies with international guidelines include application of the concepts of independent and competent review, monitoring of ongoing studies, and ensuring appropriate membership of institutional ethics review committees (IRECs).

CONCLUSION

A focus on research ethics education for researchers and IREC members, as well as ensuring appropriate respect for IREC review, are opportunities for improvement in the process.

Kammerwasserdynamik

Intraocular pressure is mainly controlled by the rate of aqueous humor production and the resistance to its outflow. Aqueous humor formation is the result of fast unidirectional secretion and slow contradirectional reabsorption. The most striking evidence of endogenous regulation of the ciliary epithelial secretion is provided by the observation of the circadian rhythm. Aqueous humor formation is mainly controlled by the interaction of inhibiting alpha(2)-adrenoreceptors and stimulating beta-adrenoceptors. The role of the central nervous system in the regulation of this process remains unclear and the precise mechanism of outflow regulation is not fully understood. The aqueous humor passes into the anterior chamber and leaves the eye by two routes: the direct outflow pathway through the trabecular meshwork or the indirect outflow pathway through the ciliary muscle. Further biochemical, biological and pharmacological investigations are necessary to determine the fundamental process of aqueous humor formation, outflow and regulation.