Image acquisition for intravoxel incoherent motion imaging of kidneys should be triggered at the instant of maximum blood velocity: evidence obtained with simulations and in vivo experiments.

PURPOSE: To demonstrate that diffusion-weighted images should be acquired at the instant of maximum blood velocity in kidneys to extract the perfusion fraction (PF) by the bi-exponential intravoxel incoherent motion model. METHODS: The PF values were measured in Monte-Carlo simulations corresponding to different blood velocities with a constant known PF. The distribution of the measured PF values (PF-distribution) was characterized quantitatively by 3 markers highlighting the deviation of the measurement from the true PF. Diffusion-weighted images of kidneys were acquired in 10 healthy volunteers at the instant of maximal respectively minimal blood velocity in the renal artery (Vmax versus Vmin acquisition). The PF-distributions measured from the Vmax and Vmin acquisitions were compared mutually and with simulated PF-distributions using the 3 markers. A radiologist evaluated the quality of the PF maps. RESULTS: The PF-distributions measured in the simulations were spread around the true PF value, and spreading was reduced as blood velocity increased. A comparison between simulated and in vivo PF-distributions suggests that a similar phenomenon is plausible in vivo. The quality of the PF maps of the Vmax -acquisition was scored higher by the radiologist than those of the Vmin -acquisition in 95% of cases (19 of 20). CONCLUSIONS: The PF maps are of better quality when the Vmax -acquisition is used. We show evidence supporting the hypothesis that the variation of PF along the cardiac cycle is due to oscillations between a poor estimation when the blood velocity is low, and a better estimation when blood velocity is higher.

Early postnatal migration and development of layer II pyramidal neurons in the rodent cingulate/retrosplenial cortex.

The cingulate and retrosplenial regions are major components of the dorsomedial (dm) limbic cortex and have been implicated in a range of cognitive functions such as emotion, attention, and spatial memory. While the structure and connectivity of these cortices are well characterized, little is known about their development. Notably, the timing and mode of migration that govern the appropriate positioning of late-born neurons remain unknown. Here, we analyzed migratory events during the early postnatal period from ventricular/subventricular zone (VZ/SVZ) to the cerebral cortex by transducing neuronal precursors in the VZ/SVZ of newborn rats/mice with Tomato/green fluorescent protein-encoding lentivectors. We have identified a pool of postmitotic pyramidal precursors in the dm part of the neonatal VZ/SVZ that migrate into the medial limbic cortex during the first postnatal week. Time-lapse imaging demonstrates that these cells migrate on radial glial fibers by locomotion and display morphological and behavioral changes as they travel through the white matter and enter into the cortical gray matter. In the granular retrosplenial cortex, these cells give rise to a Satb2+ pyramidal subtype and develop dendritic bundles in layer I. Our observations provide the first insight into the patterns and dynamics of cell migration into the medial limbic cortex.

Fibroblast growth factor-2 overexpression in transplanted neural progenitors promotes perivascular cluster formation with a neurogenic potential.

Stem/progenitor cell-based therapies hold promises for repairing the damaged nervous system. However, the efficiency of these approaches for neuronal replacement remains very limited. A major challenge is to develop pretransplant cell manipulations that may promote the survival, engraftment, and differentiation of transplanted cells. Here, we investigated whether overexpression of fibroblast growth factor-2 (FGF-2) in grafted neural progenitors could improve their integration in the host tissue. We show that FGF-2-transduced progenitors grafted in the early postnatal rat cortex have the distinct tendency to associate with the vasculature and establish multiple proliferative clusters in the perivascular environment. The contact with vessels appears to be critical for maintaining progenitor cells in an undifferentiated and proliferative phenotype in the intact cortex. Strikingly, perivascular clusters of FGF-2 expressing cells seem to supply immature neurons in an ischemic environment. Our data provide evidence that engineering neural progenitors to overexpress FGF-2 may be a suitable strategy to improve the integration of grafted neural progenitor cells with the host vasculature thereby generating neurovascular clusters with a neurogenic potential for brain repair.

Water-Soluble Vitamin Levels and Supplementation in Chronic Online Hemodiafiltration Patients.

INTRODUCTION: Supplementation of water-soluble vitamins is a common practice in hemodialysis patients, but dosages are largely based on conventional hemodialysis techniques. The aim of this study was to assess the status of water-soluble vitamins in patients on hemodiafiltration (HDF), and attempt to determine optimal dose of vitamin supplements. METHODS: This monocentric study included 40 patients on thrice-weekly chronic HDF. At baseline, all patients received 2 tablets of Dialvit containing B and C vitamins after each dialysis session. Predialysis samples of B and C vitamins were measured in both blood (n = 40) and a subgroup of dialysate (n = 6) samples. A second blood sample was obtained in 24 patients 3 months after dose adjustment of the vitamin supplement. RESULTS: At baseline, B-vitamin levels were high with, respectively, 0.4%, 10.0%, and 89.6% of patients in the low, normal, and high reference range. For vitamin C, most patients were in the normal range (5.0%, 82.5%, and 12.5% in low, normal, and high reference range). Three months after dose reduction, B vitamin levels decreased but stayed mostly at or above the normal range (1.4%, 25.7%, 72.9% in low, normal, and high reference range). Three patients (12.5%) developed vitamin C deficiency on low-dose substititon. CONCLUSION: This study shows that the levels of most vitamins are above the normal range in patients on HDF receiving a classic dose of vitamin supplements, vitamin C excepted. Our study suggests that the classic dose of postdialysis vitamin B supplements may be reduced.

Expression of FGF-2 in neural progenitor cells enhances their potential for cellular brain repair in the rodent cortex.

Strategies to enhance the capacity of grafted stem/progenitors cells to generate multipotential, proliferative and migrating pools of cells in the postnatal brain could be crucial for structural repair after brain damage. We investigated whether the over-expression of basic fibroblast growth factor 2 (FGF-2) in neural progenitor cells (NPCs) could provide a robust source of migrating NPCs for tissue repair in the rat cerebral cortex. Using live imaging we provide direct evidence that FGF-2 over-expression significantly enhances the migratory capacity of grafted NPCs in complex 3D structures, such as cortical slices. Furthermore, we show that the migratory as well as proliferative properties of FGF-2 over-expressing NPCs are maintained after in vivo transplantation. Importantly, after transplantation into a neonatal ischaemic cortex, FGF-2 over-expressing NPCs efficiently invade the injured cortex and generate an increased pool of immature neurons available for brain repair. Differentiation of progenitor cells into immature neurons was correlated with a gradual down-regulation of the FGF-2 transgene. These results reveal an important role for FGF-2 in regulating NPCs functions when interacting with the host tissue and offer a potential strategy to generate a robust source of migrating and immature progenitors for repairing a neonatal ischaemic cortex.

EMMPRIN overexpression in SVZ neural progenitor cells increases their migration towards ischemic cortex.

Stimulation of endogenous neurogenesis and recruitment of neural progenitors from the subventricular zone (SVZ) neurogenic site may represent a useful strategy to improve regeneration in the ischemic cortex. Here, we tested whether transgenic overexpression of extracellular matrix metalloproteinase inducer (EMMPRIN), the regulator of matrix metalloproteinases (MMPs) expression, in endogenous neural progenitor cells (NPCs) in the subventricular zone (SVZ) could increase migration towards ischemic injury. For this purpose, we applied a lentivector-mediated gene transfer system. We found that EMMPRIN-transduced progenitors exhibited enhanced MMP-2 activity in vitro and showed improved motility in 3D collagen gel as well as in cortical slices. Using a rat model of neonatal ischemia, we showed that EMMPRIN overexpressing SVZ cells invade the injured cortical tissue more efficiently than controls. Our results suggest that EMMPRIN overexpression could be suitable approach to improve capacities of endogenous or transplanted progenitors to invade the injured cortex.

Matrix metalloproteinases and diseases of the central nervous system with a special emphasis on ischemic brain.

Matrix metalloproteinases (MMPs) are involved in the pathogenesis of several diseases of the CNS, that share common pathophysiological processes, such as blood-brain barrier (BBB) disruption, oxidative stress, remodeling of the extracellular matrix (ECM) and inflammation. In ischemic brain injury, MMPs are implicated in various stages of the disease. Early after the onset of ischemia, MMPs contribute to the disruption of the BBB leading to vasogenic edema and to the influx of leucocytes into the CNS. The ability of MMPs to digest the basal lamina of capillaries increases the risk of hemorrhagic transformation of the ischemic tissue. During the acute ischemic phase, maintenance of the ECM is essential for neuronal survival. However, ECM degradation and its reconstitution are critical to tissue recovery. MMPs as a key modulator of ECM homeostasis play a role in the cascades leading to neuronal cell death and tissue regeneration. This pleiotropic implication of MMPs in brain injury has open new areas of investigation, which should lead to innovative therapeutic strategies. Yet MMPs may have a detrimental or beneficial role depending on the stage of brain injury. Simple therapeutic strategies based on MMP inhibition have thus little chance to favorably alter prognosis.

Relationship of Grafted FGF-2-Overexpressing Neural Stem/Progenitor Cells With the Vasculature in the Cerebral Cortex.

Neural progenitor cells (NPCs) overexpressing fibroblast growth factor 2 (FGF-2) have the distinct tendency to associate with the vasculature and establish multiple proliferative clusters in the perivascular environment after transplantation into the cerebral cortex. Strikingly, the vascular clusters of progenitor cells give rise to immature neurons after ischemic injury, raising prospects for the formation of ectopic neurogenic niches for repair. We investigated the spatial relationship of perivascular clusters with the host vascular structures. FGF-2-GFP-transduced NPCs were transplanted into the intact somatosensory rat cortex. Confocal microscopic analysis revealed that grafted cells preferentially contacted venules at sites with aquaporin-4-positive astrocytic endfeet and avoided contacts with desmin-positive pericytes. Electron microscopic analysis confirmed that grafted cells preferentially made contact with astroglial endfeet, and only a minority of them reached the endothelial basal lamina. These results provide new insights into the fine structural and anatomical relationship between grafted FGF-2-transduced NPCs and the host vasculature.