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The blood-brain barrier (BBB) is the most important obstacle to delivery of therapeutics to the central nervous system. Low-intensity pulsed focused ultrasound (FUS) in combination with microbubbles applied under magnetic resonance imaging (MRI) control provides a non-invasive and safe technique for BBB opening (BBBo). In rodent models, however, settings and application protocols differ significantly. Depending on the strain and size, important variables include ultrasound attenuation and sound field distortion caused by the skull. We examined the ultrasound attenuation of the skull of Wistar rats using a targeted FUS system. By modifying the transducer elements and by varying and simulating the acoustic field of the FUS system, we measured a skull attenuation of about 60%. To evaluate potential application of the targeted FUS system in genetically modified animals with increased sensitivity to brain hemorrhage caused by vascular dysfunction, we assessed safety in healthy animals. Histological and MRI analyses of the central nervous system revealed an increase in the number and severity of hyperacute bleeds with focal pressure. At a pressure of 0.4 MPa, no bleeds were induced, albeit at the cost of a weaker hyperintense MRI signal post BBBo. These results indicate a relationship between pressure and the dimension of permeabilization., Competing Interests: Conflict of interest disclosure The authors declare no conflicts of interest., (Copyright © 2021. Published by Elsevier Inc.)

Beyond the crucial role of apolipoprotein A-I (ApoA-I) on peripheral cholesterol metabolism, this apolipoprotein has also been implicated in beta amyloid (Aβ)-related neuropathologies. ApoA-I-Milano (M) is a mutated variant, which showed increased vasoprotective properties compared to ApoA-I-wild type in models of atherosclerosis and cardiovascular damage. We speculated that ApoA-I-M may also protect Aβ-affected vasculature and reverse some of the pathological features associated with Alzheimer's disease (AD). For this purpose, we produced and characterized human recombinant ApoA-I-wild type and ApoA-I-M proteins. Both of them were able to avoid the aggregation of Aβ in vitro, even though recombinant ApoA-I-M was significantly more effective in protecting endothelial cells from Aβ(1-42)-toxicity. Next, we determined the effect of chronic intravenous administration of rApoA-I-M in the APP23-transgenic mouse model of AD. We found reduced cerebral Aβ levels in mice that received rApoA-I-M, which were accompanied by a lower expression of astrocyte and microglia neuroinflammatory markers. Our results suggest an applicability of this molecule as a therapeutic candidate for protecting the brain in AD., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: In the field of experimental stem cell therapy, intra-arterial (IA) delivery yields the best results concerning, for example, migrated cell number at the targeted site. However, IA application also appears to be associated with increased mortality rates and infarction. Since many rodent studies systemically apply 1 × 10 6 cells, this could also be a consequence of engrafted cell number. The aim of this study was therefore to investigate the effect of different doses of adipose tissue-derived stem cells (ASCs) on engraftment rates and stroke outcome measured in vivo using 9.4-T high-field magnetic resonance imaging (MRI)., Methods: Male Wistar rats (n = 43) underwent a middle cerebral artery occlusion (MCAo) for 45 or 90 min, followed by IA delivery of either saline or 1 × 10 6 , 3 × 10 5 , or 5 × 10 4 ASCs pre-labelled with very small superparamagnetic iron oxide particles (VSOPs). MRI (9.4-T) analysis was performed 48 h and 9 days post-MCAo. Lesion volumes were assessed by analysis of T2-weighted images and cell signal tracking showing cell engraftment and active cell migration by an improved T2*-analysis., Results: The ASC-derived signal intensity increased in the affected hemisphere 48 h post MCAo with injected cell number (p < 0.05). The analysis of stroke volumes revealed an increased infarction after injection of 1 × 10 6 ASCs compared to controls or application of 5 × 10 4 ASCs (p < 0.05). At 9 days post-MCAo, injection of 3 × 10 5 ASCs resulted in reduced infarct volumes (p < 0.05). Correspondingly, MRI analysis revealed no changes in cell numbers between both MRI examinations but showed active ASC migration to the site of infarction., Conclusion: Our results confirm that IA injection is an efficient way of targeting damaged brain tissue but its usefulness strongly depends on the right dose of delivered stem cells since this factor has a strong influence on migration rate and infarct volume, with better results for doses below 1 × 10 6 cells. Future challenges will include the determination of therapeutic doses for best cellular engraftment and stroke outcome.

Background: Cerebral amyloid angiopathy (CAA) is characterized by extracellular deposition of amyloid β (Aβ) around cerebral arteries and capillaries and leads to an increased risk for vascular dementia, spontaneous lobar hemorrhage, convexal subarachnoid hemorrhage, and transient focal neurological episodes, which might be an indicator of imminent spontaneous intracerebral hemorrhage. In CAA cerebral microbleeds (cMBs) with a cortical/juxtacortical distribution are frequently observed in standard magnetic resonance imaging (MRI). In vivo MRI of transgenic mouse models of CAA may serve as a useful tool to investigate translational aspects of the disease., Materials and Methods: APP23-transgenic mice demonstrate cerebrovascular Aβ deposition with subsequent neuropathological changes characteristic for CAA. We performed a 9.4 Tesla high field MRI study using T2, T2* and time of flight-magnetic resonance angiograpy (TOF-MRA) sequences in APP23-transgenic mice and wildtype (wt) littermates at the age of 8, 12, 16, 20 and 24 months, respectively. Numbers, size, and location of cMBs are reported., Results: T2* imaging demonstrated cMBs (diameter 50-300 μm) located in the neocortex and, to a lesser degree, in the thalamus. cMBs were detected at the earliest at 16 months of age. Numbers increased exponentially with age, with 2.5 ± 2 (median ± interquartilrange) at 16 months, 15 ± 6 at 20 months, and 31.5 ± 17 at 24 months of age, respectively., Conclusion: We report the temporal and spatial development of cMBs in the aging APP23-transgenic mouse model which develops characteristic pathological patterns known from human CAA. We expect this mouse model to serve as a useful tool to non-invasively monitor mid- and longterm translational aspects of CAA and to investigate experimental therapeutic strategies in longitudinal studies.

Background and Purpose: The debate over the fact that experimental drugs proposed for the treatment of stroke fail in the translation to the clinical situation has attracted considerable attention in the literature. In this context, we present a retrospective pooled analysis of a large data set from preclinical studies, to examine the effects of early versus late administration of intravenous recombinant tissue-type plasminogen activator., Methods: We collected data from 26 individual studies from 9 international centers (13 researchers; 716 animals) that compared recombinant tissue-type plasminogen activator with controls, in a unique mouse model of thromboembolic stroke induced by an in situ injection of thrombin into the middle cerebral artery. Studies were classified into early (<3 hours) versus late (≥3 hours) drug administration. Final infarct volumes, assessed by histology or magnetic resonance imaging, were compared in each study, and the absolute differences were pooled in a random-effect meta-analysis. The influence of time of administration was tested., Results: When compared with saline controls, early recombinant tissue-type plasminogen activator administration was associated with a significant benefit (absolute difference, -6.63 mm(3); 95% confidence interval, -9.08 to -4.17; I(2)=76%), whereas late recombinant tissue-type plasminogen activator treatment showed a deleterious effect (+5.06 mm(3); 95% confidence interval, +2.78 to +7.34; I(2)=42%; Pint<0.00001). Results remained unchanged after subgroup analyses., Conclusions: Our results provide the basis needed for the design of future preclinical studies on recanalization therapies using this model of thromboembolic stroke in mice. The power analysis reveals that a multicenter trial would require 123 animals per group instead of 40 for a single-center trial., (© 2016 American Heart Association, Inc.)

Background: Cerebral amyloid angiopathy (CAA) is characterized by vascular deposition of amyloid β (Aβ) with a higher incidence of cerebral microbleeds (cMBs) and spontaneous hemorrhage. Since statins are known for their benefit in vascular disease we tested for the effect on CAA., Methods: APP23-transgenic mice received atorvastatin-supplemented food starting at the age of eight months (n = 13), 12 months (n = 7), and 16 months (n = 6), respectively. Controls (n = 16) received standard food only. At 24 months of age cMBs were determined with T2*-weighted 9.4T magnetic resonance imaging and graded by size., Results: Control mice displayed an average of 35 ± 18.5 cMBs (mean ± standard deviation), compared to 29.3 ± 9.8 in mice with eight months (p = 0.49), 24.9 ± 21.3 with 12 months (p = 0.26), and 27.8 ± 15.4 with 16 months of atorvastatin treatment (p = 0.27). In combined analysis treated mice showed lower absolute numbers (27.4 ± 15.6, p = 0.16) compared to controls and also after adjustment for cMB size (p = 0.13)., Conclusion: Despite to a non-significant trend towards fewer cMBs our results failed to provide evidence for beneficial effects of long-term atorvastatin treatment in the APP23-transgenic mouse model of CAA. A higher risk for bleeding complications was not observed.

Clinical studies demonstrated favorable effects of statins in stroke beyond lipid-lowering effects. In acute stroke, the disruption of the blood-brain barrier (BBB) is mediated by matrix metalloproteinases (MMPs). A modified MMP metabolism may account for the beneficial effects of statins. Cultured human brain microvascular endothelial cells (BMECs) were pretreated with simvastatin and subjected to oxygen glucose deprivation (OGD). Gene expression and protein secretion of MMP-2 and MMP-9 and the tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 were measured by quantitative real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Simvastatin significantly dampened the expression but not secretion of MMP-2 under OGD. MMP-9 synthesis rate was low and unaffected by simvastatin treatment, while the gene expression and protein secretion of TIMP-1 and TIMP-2 were both strongly induced. Our results provide evidence for a positive effect of simvastatin on the MMP metabolism in human BMECs and experimental stroke mainly by means of the increased expression and secretion of TIMP-1 and TIMP-2.

Background and Purpose: Intracerebral hemorrhage (ICH) is the most adverse event of thrombolysis in ischemic stroke. Cerebral amyloid angiopathy increases the risk for spontaneous lobar ICH. Although thrombolysis may be performed in cerebral amyloid angiopathy-affected patients, there is still little knowledge available on the risk for secondary ICH., Methods: We investigated the effect of recombinant tissue-type plasminogen activator on experimental ischemic stroke in APP23 transgenic mice (n=18) and wild-type littermates (n=15). Focal ischemic stroke was induced in 26-month-old mice by temporal middle cerebral artery occlusion (filament model), followed by treatment with 10 mg/kg recombinant tissue-type plasminogen activator. Twenty-four hours later, a functional score was assessed and the mice were euthanized for histological analysis. ICH was classified as grades 1 to 3 depending on severity., Results: The groups did not differ regarding mortality (P=0.67) and functional deficit (P=0.18). Compared with wild-type mice, the APP23 genotype was associated with a higher appearance for ICH in the infarct area (P=0.05). ICH severity grades 2 and 3 correlated significantly with infarct size (P=0.004 and 0.008, respectively)., Conclusions: The APP23 genotype was not associated with increased mortality or worse functional outcome. Our results suggest an increased risk for ICH in the cerebral amyloid angiopathy-affected brain; however, no ICH was observed outside the ischemic area., (© 2014 American Heart Association, Inc.)

Object: A triple-resonant coil setup with an (1)H linear resonator and a double-tuned (23)Na/(35)Cl surface coil was used to study the evolution of T 2 (*) and M 0 for (35)Cl and (23)Na in a rat stroke model during the acute phase at 9.4 Tesla., Materials and Methods: In vivo measurements were performed 1.5-7 h after onset of stroke (n = 2), ten days after onset (n = 1) and on a healthy control rat by a chemical shift imaging sequence. Measurement times were 15 min ((23)Na) and 57 min ((35)Cl)., Results: The relaxation times ten days after onset [T 2 (*) = 14.3 ± 1.8 ms ((23)Na) and 6.0 ± 1.3 ms ((35)Cl)] are clearly prolonged in comparison to a healthy rat [T 2 (*) = 4.8 ± 0.6 ms ((23)Na) and 2.1 ± 0.3 ms ((35)Cl)] and the acute phase [T 2 (*) = 5.6 ± 0.2 ms ((23)Na) and 1.9 ± 0.1 ms ((35)Cl)]., Conclusion: M 0 in the infarcted region clearly rises later and slower for chlorine than for sodium. To the best of our knowledge, these are the first combined proton, sodium, and chlorine measurements in an animal stroke model during the acute phase.

Background: Matrix metalloproteinases (MMPs) are key players in proteolytic blood-brain barrier (BBB) disruption during ischemic stroke, leading to vascular edema, hemorrhagic transformation and infiltration by leukocytes. Their effect is dampened by the endogenous tissue inhibitors of metalloproteinases (TIMPs). The respective cellular source of specific MMPs and TIMPs during BBB breakdown is still under investigation., Methods: We analyzed the MMP and TIMP release of human brain microvascular endothelial cells (BMECs) under oxygen glucose deprivation (OGD). Cultured human BMECs (the hCMEC/D3 cell line) were subjected to OGD (6, 12, 18 and 24 h). Gene expression of MMP-2, MMP-9, TIMP-1 and TIMP-2 were serially measured by quantitative real time-PCR and compared to ELISA-detected cell culture medium levels., Results: OGD induced a significant and long-lasting increase in MMP-2 gene expression, reaching a plateau after 12 h. Medium protein levels of MMP-2 were correspondingly elevated at 12 h of OGD. The MMP-9 synthesis rate was detectable at very low levels and remained unaffected by OGD. TIMP-1 gene expression and secretion declined under OGD, whereas both expression and secretion of TIMP-2 remained stable. Contrary to the respective gene expression rate, medium levels of MMP-2, TIMP-1 and TIMP-2 started a simultaneous decline after 12 h of OGD. This is most likely due to an impaired synthesis and enhanced consumption rate under OGD., Conclusions: The objective of our study was to determine the contribution of human BMECs to the MMP metabolism under in vitro OGD conditions simulating ischemic stroke. Our results suggest that human BMECs switch to a proinflammatory state by means of an enhanced production of MMP-2, attenuated release of TIMP-1, and unaffected production of TIMP-2. Thus, human BMECs might participate in the MMP-mediated BBB breakdown during ischemic stroke. However, our data does not support human BMECs to be a source of MMP-9., (Copyright © 2013 S. Karger AG, Basel.)

Background: A new thromboembolic animal model showed beneficial effects of t-PA with an infarct volume reduction of 36.8% in swiss mice. Because knock-out animal experiments for stroke frequently used C57BL76 mice we evaluated t-PA effects in this mouse strain and measured infarct volume and vascular recanalisation in-vivo by using high-field 9.4 T MRI and a 1H surface cryo coil., Methods: Clot formation was triggered by microinjection of murine thrombin into the right middle cerebral artery (MCA). Animals (n = 28) were treated with 10 mg/kg, 5 mg/kg or no tissue plasminogen activator (t-PA) 40 min after MCA occlusion. For MR-imaging a Bruker 9.4 T animal system with a 1H surface cryo probe was used and a T2-weighted RARE sequence, a diffusion weighted multishot EPI sequence and a 3D flow-compensated gradient echo TOF angiography were performed., Results: The infarct volume in animals treated with t-PA was significantly reduced (0.67 ± 1.38 mm3 for 10 mg/kg and 10.9 ± 8.79 mm3 for 5 mg/kg vs. 19.76 ± 2.72 mm3 ; p < 0.001) compared to untreated mice. An additional group was reperfused with t-PA inside the MRI. Already ten minutes after beginning of t-PA treatment, reperfusion flow was re-established in the right MCA. However, signal intensity was lower than in the contralateral MCA. This reduction in cerebral blood flow was attenuated during the first 60 minutes after reperfusion. 24 h after MCA occlusion and reperfusion, no difference in signal intensity of the contralateral and ipsilateral MCAs was observed., Conclusions: We confirm a t-Pa effect using this stroke model in the C57BL76 mouse strain and demonstrate a chronological sequence MRI imaging after t-PA using a 1H surface cryo coil in a 9.4 T MRI. This setting will allow testing of new thrombolytic strategies for stroke treatment in-vivo in C57BL76 knock-out mice.

Purpose: To estimate changes in the (23)Na density and in the (23)Na relaxation time T(2) * in the anatomically small murine brain after stroke., Materials and Methods: Three-dimensional acquisition weighted chemical shift imaging at a resolution of 0.6 × 0.6 × 1.2 mm(3) was used for sodium imaging and relaxation parameter mapping. In vivo measurements of the mouse brain (n = 4) were performed 24 hours after stroke, induced by microinjection of purified murine thrombin into the right middle cerebral artery. The measurement time was 14 minutes in one mouse and 65 minutes in the other three. An exponential fit estimation of the free induction decay was calculated for each voxel enabling the reconstruction of locally resolved relaxation parameter maps., Results: The infarcted areas showed an increase in sodium density between 160% and 250%, while the T(2) * relaxation time increased by 5%-72% compared to unaffected contralateral brain tissue., Conclusion: (23)Na chemical shift imaging at a resolution of 0.6 × 0.6 × 1.2 mm(3) enabled sodium imaging of the anatomical small mouse brain and the acquired data allowed calculating relaxation parameter maps and hence a more exact evaluation of sodium signal changes after stroke., (Copyright © 2011 Wiley-Liss, Inc.)

Ionizing radiation (IR) induces a variety of DNA lesions among which DNA double-strand breaks (DSBs) are the biologically most significant. It is currently unclear if DSB repair is equally efficient after low and high doses. Here, we use gamma-H2AX, phospho-ATM (pATM), and 53BP1 foci analysis to monitor DSB repair. We show, consistent with a previous study, that the kinetics of gamma-H2AX and pATM foci loss in confluent primary human fibroblasts are substantially compromised after doses of 10 mGy and lower. Following 2.5 mGy, cells fail to show any foci loss. Strikingly, cells pretreated with 10 microM H(2)O(2) efficiently remove all gamma-H2AX foci induced by 10 mGy. At the concentration used, H(2)O(2) produces single-strand breaks and base damages via the generation of oxygen radicals but no DSBs. Moreover, 10 microM H(2)O(2) up-regulates a set of genes that is also up-regulated after high (200 mGy) but not after low (10 mGy) radiation doses. This suggests that low radical levels induce a response that is required for the repair of radiation-induced DSBs when the radiation damage is too low to cause the induction itself. To address the in vivo significance of this finding, we established gamma-H2AX and 53BP1 foci analysis in various mouse tissues. Although mice irradiated with 100 mGy or 1 Gy show efficient gamma-H2AX and 53BP1 foci removal during 24 h post-IR, barely any foci loss was observed after 10 mGy. Our data suggest that the cellular response to DSBs is substantially different for low vs. high radiation doses.

Objectives: Purpose of this study was to compare the effect of high-pitch spiral data acquisition with prospective electrocardiography (ECG)-triggering on the x-ray induced DNA damages to blood lymphocytes with commonly used low-pitch spiral scans., Materials and Methods: Thirty four patients underwent coronary computed tomography angiography either using high-pitch spiral data acquisition (n = 15; dual-source computed tomography (CT) scanner, 38.4 mm collimation, 100-120 kV, 320-456 mAs/rotation, pitch value 3.2-3.4) or using a low-pitch protocol (n = 19; dual-source CT scanner, 19.2 mm collimation, 120 kV, 330-438 mAs/rotation, pitch 0.2-0.39, ECG-based tube current modulation). Blood samples were obtained before and 30 minutes after CT. Lymphocytes were isolated, stained against the phosphorylated histone variant gammaH2AX, and DNA double-strand breaks (DSBs) were visualized using fluorescence microscopy. Radiation dose to the blood was estimated by relating in vivo DSB levels to values of in vitro irradiated blood samples (50 mGy). Dose length product was registered as provided by the patient protocol., Results: Total dose length product ranged from 101 to 237 (median 112) mGy cm in high-pitch and from 524 to 1283 (median 1025) mGy cm in low-pitch scans (P < 0.0001). The median CT induced DSB level 30 minutes after exposure was significantly lower after high-pitch (0.04 DSBs/cell, range 0.02-0.10 DSBs/cell) compared with low-pitch scans (0.39 DSBs/cell, 0.22-0.71 DSBs/cell, P < 0.0001). Both DSB levels and radiation dose to the blood showed a significant correlation to the dose length product (r = 0.82, P < 0.0001). The radiation dose to the blood was significantly reduced in the high-pitch (median 3.1, range 2.0-8.1 mGy) compared with the low-pitch group (median 26.9; range 14.2-44.9 mGy, P < 0.0001)., Conclusions: Prospectively ECG-triggered high-pitch spiral data acquisition can considerably reduce the radiation dose to the blood in coronary CT angiography as compared with low pitch protocols.

Purpose: To assess the effect of iodinated contrast medium (CM) on the induction and repair of DNA double-strand breaks (DSBs) in peripheral blood lymphocytes after computed tomographic (CT) examinations., Materials and Methods: This prospective study was approved by the institutional ethics committee; written informed patient consent was obtained from 37 patients. Venous blood samples were taken from patients before and at 30 minutes, 1 hour, 2.5 hours, and 5 hours after performing CT with (n = 18) or without (n = 19) intravenous administration of CM (iopromide or iomeprol). DSBs were assessed in lymphocytes by enumerating gammaH2AX foci. DSB levels after CT were compared with those obtained after in vitro irradiation. Cell culture experiments with peripheral lymphocytes and fibroblasts were performed with iopromide, iomeprol, or the control substance mannitol added before or immediately after x- or gamma-ray irradiation. DSBs were assessed at 5 minutes, 30 minutes, 2.5 hours, and 5 hours after irradiation. Data were analyzed by using linear regression and the one-tailed Welch and paired sample t tests., Results: The presence of CM during CT increases DSB levels in peripheral lymphocytes by approximately 30%. Cell culture experiments confirmed this effect and further showed that CM administered prior to x-ray irradiation increases the initial DSB yield but has no effect if added after irradiation or when gamma-rays are used instead of x-rays., Conclusion: The highly sensitive gammaH2AX foci assay shows that CM-enhanced radiation damage incurred in peripheral lymphocytes during CT. However, it is unknown whether long-term bioeffects of low-dose ionizing radiation from CT examinations, such as cancer, are increased by using CM.

Objectives: To adapt gamma-H2AX immunofluorescence microscopy to assessment of induction and repair of DNA double-strand breaks (DSBs) in peripheral blood lymphocytes in patients undergoing angiographic procedures., Materials and Methods: The study was approved by the institutional ethics committee. After written informed patient consents were obtained, venous blood samples were taken from 19 patients (age 23-88 years) undergoing different angiographic procedures before, during, and after (10 minutes-24 hours) the examination. Individual DSB yields were visualized by detecting the phosphorylated variant of the histone H2AX (gamma-H2AX) in lymphocytes using fluorescence microscopy. Values were correlated with dose area product. Single in vitro irradiation with 50 mGy was performed in 14 and additional fractionated irradiation with 10 x 5 mGy over a time period corresponding to the angiography duration in 4 patients. The radiation doses to the blood delivered during angiography were estimated by comparing the number of DSBs after angiography with DSB yields obtained after in vitro irradiation., Results: In all patients in vivo and in vitro irradiation increased the number of DSBs (0.03-1.50 per cell), even if very small doses were applied (minimum 338 microGy x m). Thereafter in both in vitro and in vivo a rapid loss of gamma-H2AX foci was observed. The number of DSBs showed a linear correlation to dose area product for specific examination regions (eg, R = 0.85, pelvic and leg arteries). Calculated radiation doses to blood delivered during angiography ranged from 2.2 to 99.9 mGy and increased if fractioned in vitro samples were used as calibration instead of single in vitro irradiations at the same total dose., Conclusions: gamma-H2AX immunofluorescence microscopy is a reliable and sensitive method for measuring the induction and repair of DNA damage caused by ionizing radiation during angiography. To estimate radiation doses delivered during procedures and to consider patients individual repair capacity, postangiography DSB-yields should be compared with DSB-yields after fractioned in vitro irradiation imitating examination conditions.

Purpose: Radiotherapy is an effective cancer treatment, but a few patients suffer severe radiation toxicities in neighboring normal tissues. There is increasing evidence that the variable susceptibility to radiation toxicities is caused by the individual genetic predisposition, by subtle mutations, or polymorphisms in genes involved in cellular responses to ionizing radiation. Double-strand breaks (DSB) are the most deleterious form of radiation-induced DNA damage, and DSB repair deficiencies lead to pronounced radiosensitivity. Using a preclinical mouse model, the highly sensitive gammaH2AX-foci approach was tested to verify even subtle, genetically determined DSB repair deficiencies known to be associated with increased normal tissue radiosensitivity., Experimental Design: By enumerating gammaH2AX-foci in blood lymphocytes and normal tissues (brain, lung, heart, and intestine), the induction and repair of DSBs after irradiation with therapeutic doses (0.1-2 Gy) was investigated in repair-proficient and repair-deficient mouse strains in vivo and blood samples irradiated ex vivo., Results: gammaH2AX-foci analysis allowed to verify the different DSB repair deficiencies; even slight impairments caused by single polymorphisms were detected similarly in both blood lymphocytes and solid tissues, indicating that DSB repair measured in lymphocytes is valid for different and complex organs. Moreover, gammaH2AX-foci analysis of blood samples irradiated ex vivo was found to reflect repair kinetics measured in vivo and, thus, give reliable information about the individual DSB repair capacity., Conclusions: gammaH2AX analysis of blood and tissue samples allows to detect even minor genetically defined DSB repair deficiencies, affecting normal tissue radiosensitivity. Future studies will have to evaluate the clinical potential to identify patients more susceptible to radiation toxicities before radiotherapy.