Filip De Vos

Sizing Nanomatter in Biological Fluids by Fluorescence Single Particle Tracking

Accurate sizing of nanoparticles in biological media is important for drug delivery and biomedical imaging applications since size directly influences the nanoparticle processing and nanotoxicity in vivo. Using fluorescence single particle tracking we have succeeded for the first time in following the aggregation of drug delivery nanoparticles in real time in undiluted whole blood. We demonstrate that, by using a suitable surface functionalization, nanoparticle aggregation in the blood circulation is prevented to a large extent.

Encapsulation performance of layer-by-layer microcapsules for proteins

This study reports on the encapsulation efficiency of proteins in dextran sulfate/poly-L-arginine-based microcapsules, fabricated via layer-by-layer assembly (LbL). For this purpose, radiolabeled proteins are entrapped in CaCO(3) microparticles, followed by LbL coating of the CaCO(3) cores and subsequent dissolving of the CaCO(3) using EDTA. To allow to improve protein encapsulation in LbL microcapsules, we studied all steps in the preparation of the microcapsules where loss of protein load might occur. The encapsulation efficiency of proteins in LbL microcapsules turns out to be strongly dependent on both the charge and molecular weight of the protein as well as on the number of polyelectrolyte bilayers the microcapsules consist of.

PET with 18F-labelled choline-based tracers for tumour imaging: a review of the literature

PurposeTo give an up-to-date overview of the potential clinical utility of 18F-labelled choline derivatives for tumour imaging with positron emission tomography.MethodsA PubMed search for 18F-labelled choline analogues was performed. Review articles and reference lists were used to supplement the search findings.Results18F-labelled choline analogues have been investigated as oncological PET probes for many types of cancer on the basis of enhanced cell proliferation. To date, studies have focused on the evaluation of prostate cancer. Available studies have provided preliminary results for detecting local and metastatic disease. Experience with 18F-fluorocholine PET in other tumour types, including brain and liver tumours, is still limited. In the brain, excellent discrimination between tumour and normal tissue can be achieved due to the low physiological uptake of 18F-fluorocholine. In the liver, in which there is a moderate to high degree of physiological uptake in normal tissue, malignancy discrimination may be more challenging.ConclusionPET/CT with 18F-fluorocholine can be used to detect (recurrent) local prostate cancer, but seems to have limited value for T (tumour) and N (nodal) staging. In patients presenting with recurrent biochemical prostate cancer, it is a suitable single-step examination with the ability to exclude distant metastases when local salvage treatment is intended. In the brain, high-grade gliomas, metastases and benign lesions can be distinguished on the basis of 18F-fluorocholine uptake. Moreover, PET imaging is able to differentiate between radiation-induced injury and tumour recurrence. In the liver, 18F-fluorocholine PET/CT seems promising for the detection of hepatocellular carcinoma.

Role of Placental Growth Factor in Mesenteric Neoangiogenesis in a Mouse Model of Portal Hypertension

BACKGROUND & AIMS Portal hypertension is responsible for the major complications associated with cirrhosis. Angiogenesis has been associated with the pathophysiology of portal hypertension. We investigated the role of placental growth factor (PlGF) and tested the effects of monoclonal antibodies against PlGF (alphaPlGF) in a mouse model of portal hypertension. METHODS Using a mouse model of prehepatic portal hypertension, we measured PlGF levels in the mesenteric tissue at different time points. We used knockout mice and alphaPlGF to determine the role of PlGF in the splanchnic hyperdynamic system and portosystemic collateral formation, examining its effects before and after portal hypertension was induced. RESULTS PlGF was significantly up-regulated in the mesenteric tissue of mice with portal hypertension. Compared with wild-type animals, the vascular density in the mesentery was reduced in PlGF knockout hypertensive mice, preventing collateral formation and attenuation of mesenteric artery flow without affecting portal pressure. In the prevention study, alphaPlGF showed similar findings as in the knockout study. In mice with portal hypertension, administration of alphaPlGF resulted in a 32% decrease in portal pressure, compared with mice given immunoglobulin G(1) (control). CONCLUSIONS Pathologic angiogenesis in the mesenteric tissues of mice with portal hypertension is mediated by PlGF. Blocking PlGF could be an effective strategy for reducing collateral formation and lowering portal pressure; further research into the effects in cirrhosis is warranted.

The Impact of Accelerated HF-rTMS on the Subgenual Anterior Cingulate Cortex in Refractory Unipolar Major Depression: Insights From 18FDG PET Brain Imaging

BACKGROUND Although one of the most frequent diagnosed mental illnesses worldwide, it appears to be challenging to successfully treat major depressive disorder (MDD). Although the phenomenon of treatment-resistant depression (TRD) still remains unclear, the subgenual anterior cingulate cortex (sgACC) has been put forward as a possible neurobiological marker to evaluate clinical effects of a variety of antidepressant treatments, including repetitive transcranial magnetic stimulation (rTMS). Accelerated high-frequency (HF)-rTMS may have the potential to rapidly result in beneficial clinical outcomes in TRD. No studies yet examined the clinical effects of such accelerated stimulation treatment paradigms on sgACC regional glucose metabolism (CMRglc), nor the predictive value of the latter for clinical outcome. OBJECTIVE First, we investigated the predictive value of baseline sgACC metabolic activity for clinical outcome. Second, we hypothesized that in clinical responders only accelerated HF-rTMS treatment would result in significant metabolic decreases. METHODS We recruited right-handed antidepressant-free unipolar melancholic TRD patients to participate in a two-week randomized sham-controlled crossover HF-rTMS treatment study. Stimulation was applied to the left dorsolateral prefrontal cortex (DLPFC). Fifteen patients underwent 18FDG PET (CMRglc) at baseline (T0), after the first week (T1) of accelerated HF-rTMS and at the end of the treatment after the second week (T2). RESULTS Higher baseline sgACC metabolic activity may indicate beneficial clinical outcome to this kind of accelerated HF-rTMS treatment. Moreover, clinical response resulted in a significant decrease in sgACC CMRglc. Non-response did not affect sgACC CMRglc. CONCLUSIONS Our results add to the sgACC as a specific neurobiological marker for anti-depressive response in accelerated HF-rTMS treatment paradigms. Such protocols may not only have the ability to result in fast clinical responses but they may also have potential to acutely modulate a dysfunctional sgACC.

Layer-by-Layer Incorporation of Growth Factors in Decellularized Aortic Heart Valve Leaflets

Aortic heart valve disease is a growing health problem and a tissue-engineered aortic heart valve could be a promising therapy. In this paper, decellularized porcine aortic heart valve leaflets are used as scaffolds and loaded with growth factor and heparin via layer-by-layer electrostatic deposition (LbL technique) with the final purpose to stimulate and control cellular processes. Binding and subsequent release of heparin and basic fibroblast growth factor (bFGF) from aortic valve leaflets were assessed qualitatively by immunohistochemistry and quantitatively by radioactive labeling methods. It was observed that the amount of heparin and bFGF bound to aortic heart valve leaflets was directly proportional to the concentration of heparin and bFGF in the incubation medium. Release of heparin and bFGF from the decellularized heart valve leaflets at physiological conditions was sustained over 4 days while preserving the biological activity of the released growth factor.

Affinity Study of Novel Gelatin Cell Carriers for Fibronectin

In the present work, the gelatin/fibronectin affinity was evaluated using SPR, QCM and radiolabelling. The results indicate that type A gelatin films possess a higher affinity for Fn compared to type B gelatin. This is due to a combined hydrophobic and electrostatic interaction between gelatin type A and Fn. In a second part, the affinity of Fn for porous gelatin scaffolds was evaluated. The scaffolds were prepared by a cryogenic treatment and subsequent freeze-drying yielding type I and type II scaffolds which possess different pore geometries/sizes. The results indicate that the Fn density on the scaffolds can be fine-tuned by varying the Fn concentration, the gelatin type (A vs. B), the pore size/geometry (type I vs. type II scaffolds).

Antiepileptic drugs modulate P-glycoproteins in the brain: a mice study with 11C-desmethylloperamide

P-glycoprotein transporters (P-gp) located at the blood-brain barrier (BBB) are likely to play a role in refractory epilepsy. In vitro studies already pointed out that several antiepileptic drugs (AEDs) are substrate of P-gp. This study proposes a new in vivo approach to investigate the interaction between some AEDs and P-gp located at the BBB. (11)C-desmethylloperamide ((11)C-dLop), a radiolabelled substrate of P-gp, was intravenously administrated after pretreatment with saline or AEDs (sodium valproate, levetiracetam, topiramate and phenytoin) at their human therapeutic and four times their therapeutic dose. The effect of the different pretreatment on the intracerebral concentration of (11)C-dLop was determined to indirectly investigate possible in vivo interactions between AEDs and P-gp. Pretreatment with levetiracetam, topiramate and phenytoin at therapeutic doses significantly decreased intracerebral concentration of (11)C-dLop. Pretreatment with a therapeutic dose of sodium valproate did not influence brain uptake of (11)C-dLop. In case of pretreatment with supratherapeutic doses of AED, (11)C-dLop brain uptake was not different compared to pretreatment with saline. The metabolisation rate of (11)C-dLop in plasma was unaltered, indicating that observed differences in brain uptake of the tracer were not due to pharmacokinetic changes. The following conclusion can be made: levetiracetam, topiramate and phenytoin demonstrate biphasic modulation of the BBB P-gp. At therapeutic doses they act as inducers of efflux, at supratherapeutic doses they have no effect on the efflux rate. Sodium valproate does not interact with P-gp at therapeutic nor at higher doses.

Synthesis, In Vitro and In Vivo Evaluation, and Radiolabeling of Aryl Anandamide Analogues as Candidate Radioligands for In Vivo Imaging of Fatty Acid Amide Hydrolase in the Brain

Fatty acid amide hydrolyase (FAAH) is one of the main enzymes responsible for terminating the signaling of endocannabinoids in the brain. Imaging FAAH in vivo using PET or SPECT is important to deeper understanding of its role in neuropsychiatric disorders. However, at present, no radioligand is available for mapping the enzyme in vivo. Here, we synthesized 18 aryl analogues of anandamide, FAAHs endogenous substrate, and in vitro evaluated their potential as metabolic trapping tracers. Interaction studies with recombinant FAAH revealed good to very good interaction of the methoxy substituted aryl anandamide analogues 17, 18, 19, and 20 with FAAH and they were identified as competing substrates. Compounds 17 and 18 did not display significant binding to CB1 and CB2 cannabinoid receptors and stand out as potential candidate metabolic trapping tracers. They were successfully labeled with 11C in good yields and high radiochemical purity and displayed brain uptake in C57BL/6J mice. Radioligands [11C]-17 and [11C]-18 merit further investigation in vivo.

Vaginal distribution and retention of a multiparticulate drug delivery system, assessed by gamma scintigraphy and magnetic resonance imaging.

BACKGROUND For any new vaginal dosage form, the distribution and retention in the vagina has to be assessed by in vivo evaluation. We evaluated the vaginal distribution and retention of starch-based pellets in sheep as live animal model by gamma scintigraphy (using Indium-111 DTPA as radiolabel) and in women via magnetic resonance imaging (MRI, using a gadolinium chelate as contrast agent). A conventional cream formulation was used as reference in both studies. METHOD Cream and pellets were administered to sheep (n=6) in a two period-two treatment study and to healthy female volunteers (n=6) via a randomized crossover trial. Pellets (filled into hard gelatin capsule) and cetomacrogol cream, both labeled with Indium-111 DTPA (for gamma scintigraphy) or with gadolinium chelate (for MRI) were evaluated for their intravaginal distribution and retention over a 24h period. Spreading in the vagina was assessed based on the part of the vagina covered with formulation (expressed in relation to the total vaginal length). Vaginal retention of the formulation was quantified based on the radioactivity remaining in the vaginal area (sheep study), or qualitatively evaluated (women study). RESULTS Both trials indicated a rapid distribution of the cream within the vagina as complete coverage of the vaginal mucosa was seen 1h after dose administration. Clearance of the cream was rapid: about 10% activity remained in the vaginal area of the sheep 12h post-administration, while after 8h only a thin layer of cream was detected on the vaginal mucosa of women. After disintegration of the hard gelatin capsule, the pellet formulation gradually distributed over the entire vaginal mucosa. Residence time of the pellets in the vagina was longer compared to the semi-solid formulation: after 24h 23 ± 7% radioactivity was detected in the vaginal area of the sheep, while in women the pellet formulation was still detected throughout the vagina. CONCLUSION A multi-particulate system containing starch-based pellets was identified as a promising novel vaginal drug delivery system, resulting in complete coverage of the vaginal mucosa and long retention time.