Epilepsy with generalized tonic-clonic seizures alone: Electroclinical features and prognostic patterns.

OBJECTIVE: Epilepsy with generalized tonic-clonic seizures alone (GTCA) is a common but poorly characterized idiopathic generalized epilepsy (IGE) syndrome. Hence, we investigated electroclinical features, seizure outcome, and antiseizure medication (ASM) withdrawal in a large cohort of GTCA patients. METHODS: In this multicenter retrospective study, GTCA patients defined according to the diagnostic criteria of the International League Against Epilepsy (2022) were included. We investigated prognostic patterns, drug resistance at the last visit, and ASM withdrawal, along with their prognostic factors. RESULTS: We included 247 patients with a median (interquartile range [IQR]) age at onset of 17 years (13-22) and a median follow-up duration of 10 years (IQR = 5-20). Drug resistance at the last visit was observed in 40 (16.3%) patients, whereas the median latency to achieve 2-year remission was 24 months (IQR = 24-46.5) with a median number of 1 (IQR = 1-2) ASM. During the long-term follow-up (i.e., 202 patients followed ≥5-years after the first ASM trial), 69 (34.3%) patients displayed an early remission pattern and 36 (17.9%) patients displayed a late remission pattern, whereas 16 (8%) and 73 (36.3%) individuals had no-remission and relapsing-remitting patterns, respectively. Catamenial seizures and morning predominance of generalized tonic-clonic seizures (GTCS) independently predicted drug resistance at the last visit according to multivariable logistic regression. Treatment withdrawal was attempted in 63 (25.5%) patients, with 59 (93.7%) of them having at least a 12-month follow-up after ASM discontinuation. At the last visit, 49 (83%) of those patients had experienced GTCS recurrence. A longer duration of seizure freedom was the only factor predicting a higher chance of successful ASM withdrawal according to multivariable Cox regression. SIGNIFICANCE: GTCA could be considered a relatively easily manageable IGE syndrome, with a low rate of drug resistance and a high prevalence of early response to treatment. Nevertheless, a considerable proportion of patients experience relapsing patterns of seizure control, highlighting the need for appropriate counseling and lifestyle recommendations.

Prognosis and management of acute symptomatic seizures: a prospective, multicenter, observational study.

BACKGROUND: Acute symptomatic epileptic seizures are frequently seen in neurocritical care. To prevent subsequent unprovoked seizures, long-term treatments with antiseizure medications are often initiated although supporting evidence is lacking. This study aimed at prospectively assessing the risk of unprovoked seizure relapse with respect to the use of antiseizure medications. It was hypothesized that after a first acute symptomatic seizure of structural etiology, the cumulative 12-month risk of unprovoked seizure relapse is ≤ 25%. METHODS: Inclusion criteria were age ≥ 18 and acute symptomatic first-ever epileptic seizure; patients with status epilepticus were excluded. Using telephone and mail interviews, participants were followed for 12 months after the acute symptomatic first seizure. Primary endpoint was the occurrence and timing of a first unprovoked seizure relapse. In addition, neuro-intensivists in Germany were interviewed about their antiseizure treatment strategies through an anonymous online survey. RESULTS: Eleven of 122 participants with structural etiology had an unprovoked seizure relapse, resulting in a cumulative 12-month risk of 10.7% (95%CI, 4.7%-16.7%). None of 19 participants with a non-structural etiology had a subsequent unprovoked seizure. Compared to structural etiology alone, combined infectious and structural etiology was independently associated with unprovoked seizure relapse (OR 11.1; 95%CI, 1.8-69.7). Median duration of antiseizure treatment was 3.4 months (IQR 0-9.3). Seven out of 11 participants had their unprovoked seizure relapse while taking antiseizure medication; longer treatment durations were not associated with decreased risk of unprovoked seizure relapse. Following the non-representative online survey, most neuro-intensivists consider 3 months or less of antiseizure medication to be adequate. CONCLUSIONS: Even in case of structural etiology, acute symptomatic seizures bear a low risk of subsequent unprovoked seizures. There is still no evidence favoring long-term treatments with antiseizure medications. Hence, individual constellations with an increased risk of unprovoked seizure relapse should be identified, such as central nervous system infections causing structural brain damage. However, in the absence of high-risk features, antiseizure medications should be discontinued early to avoid overtreatment.

Integration of interictal EEG source localization in presurgical epilepsy evaluation - A single-center prospective study.

OBJECTIVE: To investigate cost in working hours for initial integration of interictal EEG source localization (ESL) into clinical practice of a tertiary epilepsy center, and to examine concordance of results obtained with three different ESL pipelines. METHODS: This prospective study covered the first year of using ESL in the Epilepsy-Center Berlin-Brandenburg. Patients aged ≥14 years with drug-resistant focal epilepsy referred for noninvasive presurgical evaluation were included. Interictal ESL was based on low-density EEG and individual head models. Source maxima were obtained from two freely available software packages and one commercial provider. One physician and computer scientist documented their working hours for setting up and processing ESL. Additionally, a survey was conducted among epilepsy centers in Germany to assess the current role of ESL in presurgical evaluation. RESULTS: Of 40 patients included, 22 (55%) had enough interictal spikes for ESL. The physician's working times decreased from median 4.7 hours [interquartile range 3.9-6.4] in the first third of cases to 2.0 hours [1.9-2.4] in the remaining two thirds; P < 0.01. In addition, computer scientist and physician spent a total of 35.5 and 33.0 working hours on setting up the digital infrastructure, and on training and testing. Sublobar agreement between all three pipelines was 20%, mean measurement of agreement (kappa) 0.13. Finally, the survey revealed that 53% of epilepsy centers in Germany currently use ESL for presurgical evaluation. SIGNIFICANCE: This study provides information regarding expected effort and costs for integration of ESL into an epilepsy surgery program. Low result agreement across different ESL pipelines calls for further standardization.

Individualised prediction of drug resistance and seizure recurrence after medication withdrawal in people with juvenile myoclonic epilepsy: A systematic review and individual participant data meta-analysis.

Background: A third of people with juvenile myoclonic epilepsy (JME) are drug-resistant. Three-quarters have a seizure relapse when attempting to withdraw anti-seizure medication (ASM) after achieving seizure-freedom. It is currently impossible to predict who is likely to become drug-resistant and safely withdraw treatment. We aimed to identify predictors of drug resistance and seizure recurrence to allow for individualised prediction of treatment outcomes in people with JME. Methods: We performed an individual participant data (IPD) meta-analysis based on a systematic search in EMBASE and PubMed - last updated on March 11, 2021 - including prospective and retrospective observational studies reporting on treatment outcomes of people diagnosed with JME and available seizure outcome data after a minimum one-year follow-up. We invited authors to share standardised IPD to identify predictors of drug resistance using multivariable logistic regression. We excluded pseudo-resistant individuals. A subset who attempted to withdraw ASM was included in a multivariable proportional hazards analysis on seizure recurrence after ASM withdrawal. The study was registered at the Open Science Framework (OSF; https://osf.io/b9zjc/). Findings: Our search yielded 1641 articles; 53 were eligible, of which the authors of 24 studies agreed to collaborate by sharing IPD. Using data from 2518 people with JME, we found nine independent predictors of drug resistance: three seizure types, psychiatric comorbidities, catamenial epilepsy, epileptiform focality, ethnicity, history of CAE, family history of epilepsy, status epilepticus, and febrile seizures. Internal-external cross-validation of our multivariable model showed an area under the receiver operating characteristic curve of 0·70 (95%CI 0·68-0·72). Recurrence of seizures after ASM withdrawal (n = 368) was predicted by an earlier age at the start of withdrawal, shorter seizure-free interval and more currently used ASMs, resulting in an average internal-external cross-validation concordance-statistic of 0·70 (95%CI 0·68-0·73). Interpretation: We were able to predict and validate clinically relevant personalised treatment outcomes for people with JME. Individualised predictions are accessible as nomograms and web-based tools. Funding: MING fonds.

Epilepsy and brain network hubs.

Epilepsy is a disorder of brain networks. A better understanding of structural and dynamic network properties may improve epilepsy diagnosis, treatment, and prognostics. Hubs are brain regions with high connectivity to other parts of the brain and are typically situated along the brain's most efficient communication pathways, supporting large-scale brain wiring and many higher order neural functions. The visualization and analysis of hubs offers a perspective on regional and global network organization and can provide novel insights into brain disorders and epilepsy. By notably supporting the interaction between various brain networks, hubs may be implicated in seizure spread and in epilepsy-related phenotypes. In this review, we will discuss the growing literature on atypical hub organization in common epilepsy syndromes, both related to neuroimaging of brain structure and function, and related to neurophysiological data from magneto- and electroencephalographic measures of neural dynamics. With studies increasingly exploring the clinical utility of network neuroscience approaches, we highlight the potential of hub mapping as a candidate biomarker of cognitive dysfunction and postsurgical seizure outcome. We will conclude the review with a discussion of current limitations and outlook for future research.

Linear distributed inverse solutions for interictal EEG source localisation.

OBJECTIVE: To compare the spatial accuracy of 6 linear distributed inverse solutions for EEG source localisation of interictal epileptic discharges: Minimum Norm, Weighted Minimum Norm, Low-Resolution Electromagnetic Tomography (LORETA), Local Autoregressive Average (LAURA), Standardised LORETA, and Exact LORETA. METHODS: Spatial accuracy was assessed clinically by retrospectively comparing the maximum source of averaged interictal discharges to the resected brain area in 30 patients with successful epilepsy surgery, based on 204-channel EEG. Additionally, localisation errors of the inverse solutions were assessed in computer simulations, with different levels of noise added to the signal in both sensor space and source space. RESULTS: In the clinical evaluations, the source maximum was located inside the resected brain area in 50-57% of patients when using LORETA or LAURA, while all other inverse solutions performed significantly worse (17-30%; corrected p < 0.01). In the simulation studies, when noise levels exceeded 10%, LORETA and LAURA had substantially smaller localisation errors than the other inverse solutions. CONCLUSIONS: LORETA and LAURA provided the highest spatial accuracy both in clinical and simulated data, alongside with a comparably high robustness towards noise. SIGNIFICANCE: Among the different linear inverse solution algorithms tested, LORETA and LAURA might be preferred for interictal EEG source localisation.

Genetic generalized epilepsies in adults - challenging assumptions and dogmas.

Genetic generalized epilepsy (GGE) syndromes start during childhood or adolescence, and four commonly persist into adulthood, making up 15-20% of all cases of epilepsy in adults. These four GGE syndromes are childhood absence epilepsy, juvenile absence epilepsy, juvenile myoclonic epilepsy and epilepsy with generalized tonic-clonic seizures alone. However, in ~20% of patients with GGE, characteristics of more than one syndrome are present. Novel insights into the genetic aetiology, comorbidities and prognosis of the GGE syndromes have emerged and challenge traditional concepts about these conditions. Evidence has shown that the mode of inheritance in GGE is mostly polygenic. Neuropsychological and imaging studies indicate similar abnormalities in unaffected relatives of patients with GGE, supporting the concept that underlying alterations in bilateral frontothalamocortical networks are genetically determined. Contrary to popular belief, first-line anti-seizure medication often fails to provide seizure freedom in combination with good tolerability. Nevertheless, long-term follow-up studies have shown that with advancing age, many patients can discontinue their anti-seizure medication without seizure relapses. Several outcome predictors have been identified, but prognosis across the syndromes is more homogeneous than previously assumed. Overall, overlap in pathophysiology, seizure types, treatment responses and outcomes support the idea that GGEs are not separate nosological entities but represent a neurobiological continuum.

Automated interictal source localisation based on high-density EEG.

PURPOSE: To study the accuracy of automated interictal EEG source localisation based on high-density EEG, and to compare it to low-density EEG. METHODS: Thirty patients operated for pharmacoresistant focal epilepsy were retrospectively examined. Twelve months after resective brain surgery, 18 were seizure-free or had 'auras' only, while 12 had persistence of disabling seizures. Presurgical 257-channel EEG lasting 3-20 h was down-sampled to 25, 40, and 204 channels for separate analyses. For each electrode setup, interictal spikes were detected, clustered, and averaged automatically before validation by an expert reviewer. An individual 6-layer finite difference head model and the standardised low-resolution electromagnetic tomography were used to localise the maximum source activity of the most prevalent spike. Sublobar concordance with the resected brain area was visually assessed and related to favourable vs. unfavourable postsurgical outcome. RESULTS: Depending on the EEG setup, epileptic spikes were detected in 21-24 patients (70-80%). The median number of single spikes per average was 470 (range 17-15,066). Diagnostic sensitivity of EEG source localisation was 58-75%, specificity was 50-67%, and overall accuracy was 55-71%. There were no significant differences between low- and high-density EEG setups with 25 to 257 electrodes. CONCLUSION: Automated high-density EEG source localisation provides meaningful information in the majority of cases. With hundreds of single spikes averaged, diagnostic accuracy is similar in high- and low-density EEG. Therefore, low-density EEG may be sufficient for interictal EEG source localisation if high numbers of spikes are available.

High-density Electric Source Imaging of interictal epileptic discharges: How many electrodes and which time point?

OBJECTIVE: To assess the value of caudal EEG electrodes over cheeks and neck for high-density electric source imaging (ESI) in presurgical epilepsy evaluation, and to identify the best time point during averaged interictal epileptic discharges (IEDs) for optimal ESI accuracy. METHODS: We retrospectively examined presurgical 257-channel EEG recordings of 45 patients with pharmacoresistant focal epilepsy. By stepwise removal of cheek and neck electrodes, averaged IEDs were downsampled to 219, 204, and 156 EEG channels. Additionally, ESI at the IED's half-rise was compared to other time points. The respective sources of maximum activity were compared to the resected brain area and postsurgical outcome. RESULTS: Caudal channels had disproportionately more artefacts. In 30 patients with favourable outcome, the 204-channel array yielded the most accurate results with ESI maxima < 10 mm from the resection in 67% and inside affected sublobes in 83%. Neither in temporal nor in extratemporal cases did the full 257-channel setup improve ESI accuracy. ESI was most accurate at 50% of the IED's rising phase. CONCLUSION: Information from cheeks and neck electrodes did not improve high-density ESI accuracy, probably due to higher artefact load and suboptimal biophysical modelling. SIGNIFICANCE: Very caudal EEG electrodes should be used for ESI with caution.

Ictal EEG source localization in focal epilepsy: Review and future perspectives.

Electroencephalographic (EEG) source imaging localizes the generators of neural activity in the brain. During presurgical epilepsy evaluation, EEG source imaging of interictal epileptiform discharges is an established tool to estimate the irritative zone. However, the origin of interictal activity can be partly or fully discordant with the origin of seizures. Therefore, source imaging based on ictal EEG data to determine the seizure onset zone can provide precious clinical information. In this descriptive review, we address the importance of localizing the seizure onset zone based on noninvasive EEG recordings as a complementary analysis that might reduce the burden of the presurgical evaluation. We identify three major challenges (low signal-to-noise ratio of the ictal EEG data, spread of ictal activity in the brain, and validation of the developed methods) and discuss practical solutions. We provide an extensive overview of the existing clinical studies to illustrate the potential clinical utility of EEG-based localization of the seizure onset zone. Finally, we conclude with future perspectives and the needs for translating ictal EEG source imaging into clinical practice.

Abnormal directed connectivity of resting state networks in focal epilepsy.

OBJECTIVE: Epilepsy diagnosis can be difficult in the absence of interictal epileptic discharges (IED) on scalp EEG. We used high-density EEG to measure connectivity in large-scale functional networks of patients with focal epilepsy (Temporal and Extratemporal Lobe Epilepsy, TLE and ETLE) and tested for network alterations during resting wakefulness without IEDs, compared to healthy controls. We measured global efficiency as a marker of integration within networks. METHODS: We analysed 49 adult patients with focal epilepsy and 16 healthy subjects who underwent high-density-EEG and structural MRI. We estimated cortical activity using electric source analysis in 82 atlas-based cortical regions based on the individual MRI. We applied directed connectivity analysis (Partial Directed Coherence) on these sources and performed graph analysis: we computed the Global Efficiency on the whole brain and on each resting state network. We tested these features in different group of patients. RESULTS: Compared to controls, efficiency was increased in both TLE and ETLE (p < 0.05). The somato-motor-network, the ventral-attention-network and the default-mode-network had a significantly increased efficiency (p < 0.05) in both TLE and ETLE as well as TLE with hippocampal sclerosis. SIGNIFICANCE: During interictal scalp EEG epochs without IED, patients with focal epilepsy show brain functional connectivity alterations in the whole brain and in specific resting-state-networks. This higher integration reflects a chronic effect of pathological activity within these structures and complement previous work on altered information outflow. These findings could increase the diagnostic sensitivity of scalp EEG to identify epileptic activity in the absence of IED.

Sleep-Disordered Breathing in REM Sleep Behavior Disorder with or without Parkinson's Disease.

REM sleep behavior disorder (RBD) might render patients with Parkinson's disease prone to sleep-disordered breathing. This retrospective polysomonographic study assessed the prevalence of sleep-disordered breathing in 108 consecutive patients with either both Parkinson's disease and RBD (n = 37), Parkinson's disease without RBD (n = 21), or isolated RBD (n = 50). Across all patients, 25% had at least moderate sleep-related breathing disorder, without significant differences between groups. Following multivariable analysis, RBD influenced sleep-related breathing parameters modestly but not significantly, whereas body mass index had a prominent impact. Further studies with larger patient cohorts are needed, and confounders like body mass index must adequately be controlled for.

Discontinuing antiepileptic drugs in long-standing idiopathic generalised epilepsy.

BACKGROUND: Once adults with long-standing idiopathic generalised epilepsy have achieved stable seizure remission, patients or physicians may attempt to discontinue their antiepileptic drug treatment. To date, risk of subsequent seizure relapse across the four idiopathic generalised epilepsy syndromes is largely unknown, and so are the clinical variables associated. METHODS: For this retrospective observational study, 256 adult outpatients with idiopathic generalised epilepsy were evaluated. Data were obtained from outpatient charts and, if possible, from additional telephone or mail interviews. RESULTS: In 84 patients (33%), antiepileptic medication was discontinued at least once. Median patient age at antiepileptic drug withdrawal was 33 years, and median duration of subsequent follow-up was 20 years. Seizures recurred in 46% of patients after a median latency of 11 months. Following multivariable analysis, seizure relapse was independently associated with short duration of seizure remission beforehand. If medication was withdrawn after < 5 years of seizure freedom, two-thirds of patients had a seizure relapse, while among those in remission for ≥ 5 years, only one-third relapsed. CONCLUSIONS: Discontinuation of antiepileptic drug treatment can be successful in every other adult with long-standing idiopathic generalised epilepsy. Short duration of prior seizure remission appears to be a relevant predictor of seizure recurrence.

Acute antiepileptic drug use in intensive care units.

BACKGROUND: In intensive care units (ICUs), antiepileptic drugs (AEDs) are used for manifold indications. This is the first study to assess the prevalence of acute AED use in ICUs and to identify associated clinical variables. METHODS: All patients in seven adult ICUs of a German university hospital in 2016 were retrospectively evaluated. Data were extracted from the computerized critical care information system and manually reviewed. Acute AED treatments were defined as initiated during ICU treatment or ≤ 6 h before ICU admission, excluding benzodiazepines and sedatives. RESULTS: Among 2335 patients evaluated, 8.8% received acutely started AEDs: 5.1% due to epileptic seizures, mostly acute symptomatic, and 3.7% for other indications like pain, post-hypoxic myoclonus, and singultus. Following multivariable analyses, acute AED use was independently associated with intracranial reasons for ICU admission and long durations of ICU stay, but not with increased disease severity scores or mortality. Levetiracetam was the substance most frequently used to treat epileptic seizures (88%) as was pregabalin for other conditions (49%). Among surviving patients, acute AEDs were continued beyond ICU discharge in 86% if seizure-related and in 78% if not seizure-related, even if there was no evident need for long-term AED treatment. CONCLUSIONS: One out of eleven ICU patients receives acute AEDs, in almost half of cases for non-seizure indications. Acute AED use is a marker for intracranial ICU indications and prolonged ICU treatments. Usually, newer-generation AEDs are employed with favourable pharmacokinetic and safety profiles. However, whenever possible, acutely started AED should be discontinued before discharge from ICU.

Absence epilepsy beyond adolescence: an outcome analysis after 45 years of follow-up.

OBJECTIVES: Depending on patient age at onset, absence epilepsy is subdivided into childhood and juvenile forms. Absence seizures can occur several times per day (pyknoleptic course) or less frequently than daily (non-pyknoleptic course). Seizures typically terminate before adulthood, but a quarter of patients need ongoing treatment beyond adolescence. Little is known about their long-term seizure and psychosocial outcome. METHODS: Files of 135 outpatients with absence epilepsy (76 females; 123 had additional generalised tonic-clonic seizures) were retrospectively analysed after a median follow-up of 45.4 years (IQR: 31.9-56.2). Eighty-two subjects completed an additional interview. Patients were dichotomised according to age at epilepsy onset (childhood: n=82; juvenile: n=53) and course of absence seizures (pyknoleptic: n=80; non-pyknoleptic: n=55). RESULTS: Among all patients, 53% achieved 5-year terminal seizure remission, 16% without antiepileptic medication. Median age at last seizure was lower in patients with childhood onset of absence epilepsy (37.7 years) versus juvenile onset (44.4 years; P≤0.01). However, rates and duration of terminal seizure remission were similar. Pyknoleptic versus non-pyknoleptic course of absence seizures made no difference for long-term seizure outcome. Multivariate analysis identified only higher age at investigation to be associated with terminal 5-year seizure remission. Regarding aspects of psychosocial outcome, there were no significant differences between the respective subgroups. CONCLUSIONS: These data indicate that if absence epilepsy persists beyond adolescence, long-term seizure and psychosocial outcome do not differ between childhood and juvenile onset or between pyknoleptic and non-pyknoleptic course of absence epilepsy. However, higher patient age increases the chance of terminal seizure remission.

Long-term outcome in adolescent-onset generalized genetic epilepsies.

OBJECTIVE: Until now, it has been unclear if the three subsyndromes of adolescent-onset generalized genetic epilepsy (GGE) differ in long-term prognosis. Therefore, this study aimed to compare long-term seizure outcome in juvenile absence epilepsy (JAE), juvenile myoclonic epilepsy (JME), and epilepsy with generalized tonic-clonic seizures alone (EGTCS). METHODS: This retrospective study is based on the archive of an institutional tertiary care outpatient clinic for adult patients with epilepsy. Charts of 870 epilepsy outpatients were reviewed among whom 176 had adolescent-onset GGE (53 JAE, 66 JME, 57 EGTCS). Median patient age at investigation was 60 years; median follow-up time was 42.5 years. If possible, GGE patients were additionally interviewed on psychosocial and clinical variables. RESULTS: Age at first seizure was significantly higher in EGTCS patients (median 18 years) than in patients with JAE or JME (14 years each; p ≤ 0.001). Long-term seizure outcome hardly differed between the three subsyndromes. At the end of follow-up, 60% of all patients were in 5-year terminal seizure remission, and in 14%, epilepsy even had resolved (>10 years without seizures, >5 years without pharmacotherapy). Twenty percent of patients had persistent seizures during the last year of follow-up. Across all patients, 23% reported a psychiatric comorbidity, 87% had married, and 57% had achieved university entrance qualification. SIGNIFICANCE: Long-term outcome was shown to be highly similar across all subsyndromes of adolescent-onset GGE. Even in a selection of difficult-to-treat epilepsy patients still attending an adult epilepsy clinic, most become seizure-free. To confirm these findings, prospective studies are needed.

Pulsatile atheroprone shear stress affects the expression of transient receptor potential channels in human endothelial cells.

The goal of the study was to assess whether pulsatile atheroprone shear stress modulates the expression of transient receptor potential (TRP) channels, TRPC3, TRPC6, TRPM7, and TRPV1 mRNA, in human umbilical vascular endothelial cells. Exposure of cultured vascular endothelial cells to defined shear stress, producing a constant laminar flow (generating a shear stress of 6 dyne/cm(2)), laminar pulsatile atheroprotective flow (with a mean shear stress of 20 dyne/cm(2)), or laminar atheroprone bidirectional flow (with a mean shear stress of 0 dyne/cm(2)) differentially induced TRPC6 and TRPV1 mRNA as measured by quantitative real-time RT-PCR and normalized to GAPDH expression. Thereby, TRPC6 and TRPV1 mRNA expressions were significantly increased after 24 hours of exposure to an atheroprone flow profile compared with an atheroprotective flow profile. Furthermore, the expression of transcription factors GATA1 and GATA4 was significantly correlated with the expression of TRPC6 mRNA. In contrast, after 24 hours of constant laminar flow, the expression of TRPC6 and TRPV1 mRNA was unchanged, whereas the expression of TRPC3 and TRPM7 was significantly higher in endothelial cells exposed to shear stress in comparison with endothelial cells grown under static conditions. There was a significant association between the expression of TRPC6 and tumor necrosis factor-α mRNA in human vascular tissue. No-flow and atheroprone flow conditions are equally characterized by an increase in the expression of tumor necrosis factor-α; however, inflammation-associated endothelial cell reactions may be further aggravated at atheroprone flow conditions by the increase of TRPV1 and TRPC6, as observed in our study.

Regulation of endothelial connexin40 expression by shear stress.

Endothelial connexin (Cx)40 plays an important role in signal propagation along blood vessel walls, modulating vessel diameter and thereby blood flow. Blood flow, in turn, has been shown to alter endothelial Cx40 expression. However, the timing and shear stress dependence of this relationship have remained unclear, as have the signal transduction pathways involved and the functional implications. Therefore, the aim of this study was to quantify the effects of shear stress on endothelial Cx40 expression, to analyze the role of phosphoinositide 3-kinase (PI3K)/Akt signaling involved, and to assess the possible functional consequences for the adaptation of microvascular networks. First-passage human umbilical vein endothelial cells were exposed to defined shear stress conditions and analyzed for Cx40 using real-time RT-PCR and immunoblot analysis. Shear stress caused long-term induction of Cx40 protein expression, with two short-term mRNA peaks at 4 and 16 h, indicating the dynamic nature of the adaptation process. Maximum shear stress-dependent induction was observed at shear levels between 6 and 10 dyn/cm(2). Simulation of this pattern of shear-dependent Cx expression in a vascular adaptation model of a microvascular network led to an improved fit for the simulated results to experimental measurements. Cx40 expression was greatly reduced by inhibiting PI3K or Akt, with PI3K activity being required for basal Cx40 expression and Akt activity taking part in its shear stress-dependent induction.

Shear stress increases endothelial hyaluronan synthase 2 and hyaluronan synthesis especially in regard to an atheroprotective flow profile.

Recent studies revealed that in vivo the inner blood vessel surface is lined with an endothelial surface layer at least 0.5 µm thick, which serves as an aegis, protecting the vessel wall from arteriosclerosis. Hyaluronan seems to be a constitutive component in regard to the atheroprotective properties of this surface structure. It has been shown that arterial pulsatile laminar blood flow increases the thickness of this surface layer in vivo, while it is significantly reduced at atheroprone regions with disturbed flow. This study was undertaken to reveal whether endothelial hyaluronan synthesis via hyaluronan synthase 2 (HAS2) can be changed by different shear stress conditions in vitro, especially in regard to an undisturbed, arterial-like pulsatile flow profile. Human umbilical vein endothelial cells, exposed to constant or pulsatile shear stress in a cone-and-plate system, were analysed for HAS2 expression by real-time RT-PCR and immunoblotting, and for hyaluronan by ELISA. Hyaluronan synthase 2 mRNA and protein were found to be transiently increased in a shear stress-dependent manner via the phosphatidylinositol 3-kinase-Akt pathway. Especially pulsatile, arterial-like shear stress conditions induced enzyme and hyaluronan effectively, while lower shear stress that continuously changed its direction did not induce any differences in comparison with control cultures not exposed to shear stress. These experiments provide a link between the production of a constitutive component of the endothelial surface layer by endothelial cells and blood flow.