Monitoring stroke progression: in vivo imaging of cortical perfusion,blood–brain barrier permeability and cellular damage in the rat photothrombosis model

Focal cerebral ischemia is among the main causes of death and disability worldwide. The ischemic core often progresses, invading the peri-ischemic brain; however, assessing the propensity of the peri-ischemic brain to undergo secondary damage, understanding the underlying mechanisms, and adjusting treatment accordingly remain clinically unmet challenges. A significant hallmark of the peri-ischemic brain is dysfunction of the blood–brain barrier (BBB), yet the role of disturbed vascular permeability in stroke progression is unclear. Here we describe a longitudinal in vivo fluorescence imaging approach for the evaluation of cortical perfusion, BBB dysfunction, free radical formation and cellular injury using the photothrombosis vascular occlusion model in male Sprague Dawley rats. Blood–brain barrier dysfunction propagated within the peri-ischemic brain in the first hours after photothrombosis and was associated with free radical formation and cellular injury. Inhibiting free radical signaling significantly reduced progressive cellular damage after photothrombosis, with no significant effect on blood flow and BBB permeability. Our approach allows a dynamic follow-up of cellular events and their response to therapeutics in the acutely injured cerebral cortex.     

The Effect of Weight-Loss Interventions on Cervical and Chin Subcutaneous Fat Depots; the CENTRAL Randomized Controlled Trial

Accumulation of cervical and chin subcutaneous adipose tissues (SAT) represent known phenotypes of obesity. We aimed to evaluate the sensitivity of these fat storages to long-term weight-loss directed lifestyle-intervention and to assess their relations to bodily-adiposity, insulin-resistance, and cardiometabolic risk; We randomly assigned 278 participants with abdominal-obesity/dyslipidemia to low-fat or Mediterranean/low-carbohydrate diets +/− physical-activity. All participants underwent an 18 month whole-body magnetic resonance imaging follow-up, from which we assessed cervical and chin SAT-areas; Participants (age = 48 years; 90% men; body-mass-index = 30.9 kg/m²) had an 18-month adherence-rate of 86%. Cervical-SAT and chin-SAT decreased after 6-months (−13.1% and −5.3%, respectively, p < 0.001). After 18-months only cervical-SAT remained decreased compared to baseline (−5%, p < 0.001). Cervical and chin-SAT 18-month changes were associated with changes in weight (r = 0.70, r = 0.66 respectively; <0.001 for both) and visceral-adipose-tissue (VAT; r = 0.35, r = 0.42 respectively; <0.001 for both). After adjustment to VAT, waist-circumference, or weight-changes, chin-SAT 18-month reduction was associated with favorable changes in fasting-glucose (β = 0.10; p = 0.05), HbA1c (β = 0.12; p = 0.03), and homeostasis-model-assessment-of-insulin-resistance (β = 0.12; p = 0.03). Cervical-SAT 18-month reduction was associated with decreased triglycerides (β = 0.16; p = 0.02) and leptin (β = 0.19; p = 0.01) independent of VAT; Cervical and chin-SATs are dynamic fat depots that correspond with weight-loss and are associated with changes in cardiometabolic profile. In long-term, chin-SAT displays a larger rebound compared with cervical-SAT. Chin-SAT accumulation is associated with in insulin-resistance, independent of central obesity. (ClinicalTrials identifier {"type":"clinical-trial","attrs":{"text":"NCT01530724","term_id":"NCT01530724"}}NCT01530724)     

Dynamic in vivo imaging of cerebral blood flow and blood–brain barrier permeability

The brain is characterized by an extremely rich blood supply, regulated by changes in blood vessel diameter and blood flow, depending on metabolic demands. The blood–brain barrier (BBB)—a functional and structural barrier separating the intravascular and neuropil compartments—characterizes the brain's vascular bed and is essential for normal brain functions. Disruptions to the regional cerebral blood supply, to blood drainage and to BBB properties have been described in most common neurological disorders, but there is a lack of quantitative methods for assessing blood flow dynamics and BBB permeability in small blood vessels under both physiological and pathological conditions. Here, we present a quantitative image analysis approach that allows the characterization of relative changes in the regional cerebral blood flow (rCBF) and BBB properties in small surface cortical vessels. In experiments conducted using the open window technique in rats, a fluorescent tracer was injected into the tail vein, and images of the small vessels at the surface of the cortex were taken using a fast CCD camera. Pixel-based image analysis included registration and characterization of the changes in fluorescent intensity, followed by cluster analysis. This analysis enabled the characterization of rCBF in small arterioles and venules and changes in BBB permeability. The method was implemented successfully under experimental conditions, including increased rCBF induced by neural stimulation, bile salt-induced BBB breakdown, and photothrombosis-mediated local ischemia. The new approach may be used to study changes in rCBF, neurovascular coupling and BBB permeability under normal and pathological brain conditions.