Die diffusionsgewichtete Magnetresonanztomographie in der Diagnostik retinaler Ischämien und ischämischer Optikusneuropathien

Die vorliegende Habilitationsschrift umfasst Arbeiten zur Anwendung der diffusionsgewichteten Magnetresonanztomographie im Bereich vaskulärer neuroophthalmologischer Erkrankungen. Sie thematisiert die systematischen Erstbeschreibungen retinaler Diffusionsrestriktionen im Rahmen des Zentralarterienverschlusses und Zentralarterienastverschlusses als Korrelate von Ischämien der Netzhaut. Darüber hinaus wird der diagnostische Nutzen der diffusionsgewichteten Magnetresonanztomographie in der Diagnostik arteriitischer ischämischer Optikusneuropathien im Rahmen der Riesenzellarteriitis behandelt

A Case-Control Study

Purpose: To evaluate diffusion abnormalities of the retina and optic nerve in patients with central retinal artery occlusion (CRAO) using standard stroke diffusion-weighted magnetic resonance imaging (DWI). Methods: In this case-control study, DWI scans of patients with nonarteritic CRAO were retrospectively assessed for acute ischemia of the retina and optic nerve. Two neuroradiologists, blinded for patient diagnosis, randomly evaluated DWI of CRAO patients and controls (a collective of stroke and transient ischemic attack [TIA] patients) for restrictions of the retina and optic nerve. We calculated statistical quality criteria and analyzed inter-rater reliability using unweighted Kappa statistics. Results: 20 CRAO patients (60,6 ± 17 years) and 20 controls (60,7 ± 17 years) were included in the study. Sensitivity, specificity, positive and negative predictive values for retinal DWI restrictions were 75%/80%/79%/76% (reader 1) and 75%/100%/100%/80% (reader 2), respectively. Unweighted Kappa was κ = 0,70 (95% CI 0,48‑0,92), indicating "substantial" interrater reliability. In comparison, sensitivity, specificity, PPV and NPV (positive and negative predictive values) for restrictions of the optic nerve in CRAO were 55%/70%/65%/61% (reader 1) and 25%/100%/100%/57% (reader 2). Inter-rater reliability was "fair" with unweighted Kappa κ = 0,32 (95% CI 0,09‑0,56). Conclusions: Retinal diffusion restrictions were present in a majority of CRAO patients and detectable with reasonable sensitivity, high specificity and substantial inter-rater reliability. Further studies are necessary to study time dependency of retinal diffusion restrictions, improve image quality and investigate the reliability of retinal DWI to discern CRAO from other causes of acute loss of vision

Retinal diffusion restrictions in acute branch retinal arteriolar occlusion

This study sought to investigate the occurrence of retinal diffusion restrictions (RDR) in branch retinal arteriolar occlusion (BRAO) using standard brain diffusion-weighted imaging (DWI). Two radiologists assessed DWI MRI scans of BRAO patients for RDR in a retrospective cohort study. Inter- and intrarater reliability were calculated using Kappa statistics. Detection rates of RDR were compared among MRI scans with varying field strength, sequence type and onset-to-DWI time intervals. 85 BRAO patients (63.1 +/- 16.5 years) and 89 DWI scans were evaluated. Overall sensitivity of RDR in BRAO was 46.1% with visually correlating low ADC signal in 56.1% of cases. Localization of RDR matched distribution of fundoscopic retinal edema in 85% of patients. Inter- and intra-rater agreement for RDR in BRAO was kappa(inter) = 0.64 (95% CI 0.48-0.80) and kappa(intra) = 0.87 (95% CI 0.76-0.96), respectively. RDR detection rate tended to be higher for 3T, when compared to 1.5T MRI scans (53.7% vs. 34.3%%; p = 0.07). RDR were identified within 24 h up to 2 weeks after onset of visual impairment. RDR in BRAO can be observed by means of standard stroke DWI in a substantial proportion of cases, although sensitivity and interrater reliability were lower than previously reported for complete central retinal artery occlusion

Clinical Course and Ophthalmologic Findings in Idiopathic Intracranial Hypertension and Pregnancy

Idiopathic intracranial hypertension (IIH) has its highest prevalence among women of childbearing age and therefore frequently coincides with pregnancy. This retrospective cohort study aimed to explore the impact of pregnancy on the clinical course, ophthalmologic findings and on the therapeutic management of IIH patients. Individual patient records were reviewed for neuro-ophthalmologic findings, treatment strategy, adherence to therapy and pregnancy complications. Sixteen patients with 19 documented pregnancies were identified. The visual acuity, visual field defects and the grade of papilledema at baseline and after pregnancy were compared. The visual acuity and visual field mean deviation at baseline and at follow-up after pregnancy did not significantly differ. Papilledema at baseline was more pronounced in patients who had been diagnosed with IIH during pregnancy than in patients with established IIH. In this cohort, the visual acuity and the visual field were not lastingly impacted by pregnancy. The adherence to therapy was low, with 69% discontinuing treatment or medication

Cerebral Ultrasound Time-Harmonic Elastography Reveals Softening of the Human Brain Due to Dehydration

Hydration influences blood volume, blood viscosity, and water content in soft tissues - variables that determine the biophysical properties of biological tissues including their stiffness. In the brain, the relationship between hydration and stiffness is largely unknown despite the increasing importance of stiffness as a quantitative imaging marker. In this study, we investigated cerebral stiffness (CS) in 12 healthy volunteers using ultrasound time-harmonic elastography (THE) in different hydration states: (i) during normal hydration, (ii) after overnight fasting, and (iii) within 1 h of drinking 12 ml of water per kg body weight. In addition, we correlated shear wave speed (SWS) with urine osmolality and hematocrit. SWS at normal hydration was 1.64 ± 0.02 m/s and decreased to 1.57 ± 0.04 m/s (p < 0.001) after overnight fasting. SWS increased again to 1.63 ± 0.01 m/s within 30 min of water drinking, returning to values measured during normal hydration (p = 0.85). Urine osmolality at normal hydration (324 ± 148 mOsm/kg) increased to 784 ± 107 mOsm/kg (p < 0.001) after fasting and returned to normal (288 ± 128 mOsm/kg, p = 0.83) after water drinking. SWS and urine osmolality correlated linearly (r = -0.68, p < 0.001), while SWS and hematocrit did not correlate (p = 0.31). Our results suggest that mild dehydration in the range of diurnal fluctuations is associated with significant softening of brain tissue, possibly due to reduced cerebral perfusion. To ensure consistency of results, it is important that cerebral elastography with a standardized protocol is performed during normal hydration

In vitro screening for intrinsic activity of potential AT2R–agonists in differentiated THP-1-macrophages

Tierexperimentelle Evidenz deutet auf protektive Effekte der pharmakologischen Stimulation des AT2-Rezeptors des RAAS im Rahmen zerebraler und zerebrovaskulärer Erkrankungen. Die Evaluation neuroprotektiver Effekte wird jedoch dadurch erschwert, dass etablierte AT2-Agonisten wie CGP42112 und der Nicht-Peptid-Agonist Compound 21 die intakte Blut-Hirn-Schranke nicht überwinden können. Daher wird die Entwicklung neuer, ZNS-gängiger AT2-Agonisten angestrebt. Die durch strukturelle Alteration eines Ausgangsmoleküls gewonnenen, neuen Substanzen müssen auf ihre Affinität zum Zielrezeptor und ihre intrinsische Aktivität geprüft werden. Das bislang überwiegend verwendete Assay, das auf dem Auswachsen von Neuriten in vitro basiert, ist durch einen subjektiven Auswertungsprozess und schlecht quantifizierbare Ergebnisse benachteiligt. Ziel dieser Arbeit war die Etablierung eines zuverlässigen, gut quantifizierbaren und automatisiert auswertbaren in-vitro Screenings zur Prüfung der intrinsischen Aktivität potentieller AT2-Agonisten. Grundlage des Assays bildete die Bestimmung der Interleukin 6-Expression in THP-1-Makrophagen. Die Protein-Expression des AT2-Rezeptors wurde zwischen THP-1-Monozyten und PMA-differenzierten THP-1-Makrophagen mittels Western Blot verglichen. Des Weiteren wurden die Effekte einer Inkubation von THP-1-Makrophagen mit LPS (50 ng/ml) und/oder Compound 21 (1 µM) auf die AT2-Rezeptor-Protein-Expression untersucht. Die intrinsische Aktivität der Substanzen JS5090, L162-389 und VR0008 am AT2-Rezeptor wurde über die Hemmung der LPS-induzierten IL-6-mRNA- Expressionssteigerung in THP-1-Makrophagen mittels qPCR gemessen Als Referenzsubstanz diente der etablierte AT2-Agonist Compound 21. Die AT2 -Rezeptor-Spezifität etwaiger Effekte wurde mittels Hemmung der beobachteten Effekte durch den AT2-Antagonisten PD123319 sichergestellt. Die PMA-abhängige Differenzierung von THP-1-Monozyten zu -Makrophagen führte zu einer Verzehnfachung der AT2-Rezeptor-Protein-Expression im Western Blot (Einzelexperiment, p = 0,0002). Sowohl die direkte AT2-Rezeptor-Stimulation, als auch die LPS-Inkubation von THP-1-Makrophagen induzierten eine signifikante Absenkung der AT2-Rezeptor-Expression (Einzelexperiment, p = 0,0001; bzw. p = 0,0008). JS5090, L162-389, VR0008 und Compound 21 konnten keine reproduzierbare, signifikante Beeinflussung der LPS-induzierten IL-6 -mRNA-Expressionssteigerung in THP-1-Makrophagen bewirken. Die Substanzen JS5090, L162-389 und VR0008 konnten nicht als AT2-Agonisten verifiziert werden. Ferner zeigte die Referenzsubstanz Compound 21 keine konsistente Beeinflussung der LPS-induzierten IL-6-mRNA-Expression. Die Validität des verwendeten Assays wird somit am ehesten durch die interexperimentelle Heterogenität der Effekte der PMA-abhängigen Differenzierung von THP-1-Monozyten und der LPS-Stimulation von THP-1-Makrophagen eingeschränkt. Zukünftige Protokolle sollten daher mit dem Ziel optimiert werden, eine kontrollierte und interexperimentell konsistente PMA-abhängige Differenzierungen der THP-1-Monozyten zu gewährleisten. Aktuell ist das IL-6-THP-1-Assay als Screening-Verfahren für potentielle AT2-Rezeptor- Agonisten ungeeignet.Accumulating evidence suggests tissue-protective properties of pharmacological AT2R-stimulation in various animal models of cerebral and cerebrovascular disease. Further investigation of the neuroprotective properties of pharmacological AT2R-stimulation is hindered, because common AT2R-agonists like CGP42112 and the non-peptide agonist Compound 21 cannot penetrate the blood-brain barrier. Therefore, a new generation of blood-brain barrier- penetrating AT2R-agonists is being developed. New substances, designed through chemical alteration of established molecules, need to be reevaluated for AT2R–affinity and intrinsic activity. Common assays available, e. g. the Neurite-Outgrowth-assay are considered to be unreliable on the grounds of subjective analysis and imprecise quantification of results. Therefore, this project aimed at establishing a reliable and robust in vitro screening of potential AT2R–agonists for intrinsic activity at the AT2R based on determining interleukin 6 (IL-6) mRNA expression in THP-1-macrophages. AT2R- protein expression in THP-1-monocytes was compared with AT2R-protein expression in PMA-differentiated THP-1-macrophages using Western-Blot analysis. Effects of LPS- (50 ng/ml) and Compound 21- (1 µM) incubation on AT2R-protein-expression in THP-1-macrophages were evaluated. THP-1-macrophages were incubated with LPS (50 ng/ml), co-treated with the novel agents JS5090, L162-389 and VR0008 (1 µM each) for 6 hours and IL-6-mRNA expression determined by qPCR. AT2R-agonist Compound 21 was used for reference. AT2R- agonism was postulated if the substance in question attenuated the increase of LPS-induced IL-6-mRNA expression. The AT2R -antagonist PD123319 (10 µM) was used to confirm AT2R -specificity of observed effects. PMA-induced differentiation of THP-1 monocytes to macrophages increased expression of the AT2R-receptor-protein tenfold in Western Blot analysis (single experiment, p = 0,0002). Incubation with LPS and Compound 21 each significantly decreased AT2R-receptor-protein-expression (single experiment, p = 0,0001 and p = 0,0008 respectively). Treatment of THP-1 macrophages with JS5090, L162-389, VR0008, or Compound 21 did not result in consistent, significant effects on LPS- induced IL-6-mRNA-expression. JS5090, L162-389 and VR0008 could not be verified as AT2R-receptor agonists. Since the established AT2R-Agonist Compound 21 also did not elicit consistent effects on LPS-induced IL-6-mRNA- expression in our assay, we conclude that the tested assay was of limited validity probably due to unpredictable effects of PMA-induced differentiation and LPS-incubation of THP-1-macrophages. Future protocols should be optimized to achieve controlled and inter-experimentally consistent PMA-induced differentiation of THP-1-monocytes. In conclusion, the current IL-6-THP-1-assay has to be regarded as not suitable for the screening of potential AT2R-receptor agonists

Standard Diffusion-weighted MRI for the Diagnosis of Central Retinal Artery Occlusion

Purpose!#!To evaluate diffusion abnormalities of the retina and optic nerve in patients with central retinal artery occlusion (CRAO) using standard stroke diffusion-weighted magnetic resonance imaging (DWI).!##!Methods!#!In this case-control study, DWI scans of patients with nonarteritic CRAO were retrospectively assessed for acute ischemia of the retina and optic nerve. Two neuroradiologists, blinded for patient diagnosis, randomly evaluated DWI of CRAO patients and controls (a collective of stroke and transient ischemic attack [TIA] patients) for restrictions of the retina and optic nerve. We calculated statistical quality criteria and analyzed inter-rater reliability using unweighted Kappa statistics.!##!Results!#!20 CRAO patients (60,6 ± 17 years) and 20 controls (60,7 ± 17 years) were included in the study. Sensitivity, specificity, positive and negative predictive values for retinal DWI restrictions were 75%/80%/79%/76% (reader 1) and 75%/100%/100%/80% (reader 2), respectively. Unweighted Kappa was κ = 0,70 (95% CI 0,48‑0,92), indicating 'substantial' interrater reliability. In comparison, sensitivity, specificity, PPV and NPV (positive and negative predictive values) for restrictions of the optic nerve in CRAO were 55%/70%/65%/61% (reader 1) and 25%/100%/100%/57% (reader 2). Inter-rater reliability was 'fair' with unweighted Kappa κ = 0,32 (95% CI 0,09‑0,56).!##!Conclusions!#!Retinal diffusion restrictions were present in a majority of CRAO patients and detectable with reasonable sensitivity, high specificity and substantial inter-rater reliability. Further studies are necessary to study time dependency of retinal diffusion restrictions, improve image quality and investigate the reliability of retinal DWI to discern CRAO from other causes of acute loss of vision