Progression of Alzheimer's disease and effect of scFv-h3D6 immunotherapy in the 3xTg-AD mouse model: An in vivo longitudinal study using Magnetic Resonance Imaging and Spectroscopy

Alzheimer's disease (AD) is an incurable disease that affects most of the 47 million people estimated as living with dementia worldwide. The main histopathological hallmarks of AD are extracellular β-amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau protein. In recent years, Aβ-immunotherapy has been revealed as a potential tool in AD treatment. One strategy consists of using single-chain variable fragments (scFvs), which avoids the fragment crystallizable (Fc) effects that are supposed to trigger a microglial response, leading to microhemorrhages and vasogenic edemas, as evidenced in clinical trials with bapineuzumab. The scFv-h3D6 generated by our research group derives from this monoclonal antibody, which targets the N-terminal of the Aβ peptide and recognizes monomers, oligomers and fibrils. In this study, 3xTg-AD mice were intraperitoneally and monthly treated with 100 μg of scFv-h3D6 (a dose of ~3.3 mg/kg) or PBS, from 5 to 12 months of age (-mo), the age at which the mice were sacrificed and samples collected for histological and biochemical analyses. During treatments, four monitoring sessions using magnetic resonance imaging and spectroscopy (MRI/MRS) were performed at 5, 7, 9, and 12 months of age. MRI/MRS techniques are widely used in both human and mouse research, allowing to draw an in vivo picture of concrete aspects of the pathology in a non-invasive manner and allowing to monitor its development across time. Compared with the genetic background, 3xTg-AD mice presented a smaller volume in almost all cerebral regions and ages examined, an increase in both the intra and extracellular Aβ_1-42 at 12-mo, and an inflammation process at this age, in both the hippocampus (IL-6 and mIns) and cortex (IL-6). In addition, treatment with scFv-h3D6 partially recovered the values in brain volume, and Aβ, IL-6, and mIns concentrations, among others, encouraging further studies with this antibody fragment.

Dilated cardiomyopathy and mitochondrial dysfunction in Sirt1-deficient mice: a role for Sirt1-Mef2 in adult heart

The deacetylase Sirtuin-1 (Sirt1) is involved in the cardiac hypertrophic responses and cardiac embryo morphogenesis. However, the physiological function of Sirt1 deficiency in the postnatal development of the heart remains to be characterized. The aim of the study was to investigate the relevance of Sirt1 in the development and function of the myocardium. Hearts from Sirt1-deficient mice partially or totally lacking Sirt1 protein activity were analyzed. Loss of Sirt1 activity led to dilated cardiomyopathy in adult hearts, a phenotype accompanied by reduced cardiomyocyte size and the absence of fibrosis. Morphological and functional mitochondrial abnormalities were observed in the adult hearts lacking Sirt1, suggesting that mitochondrial dysfunction contributes to the progression of the observed cardiomyopathy. Moreover, gene expression analyses revealed that mitochondrial genes were the most affected in Sirt1-deficient mice, showing a reduction in their expression. No overt cardiac dilatation was observed in neonates lacking Sirt1 activity, but first signs of mitochondrial alterations were already present. Immunoblot analyses revealed that Sirt1 is highly expressed in the heart after birth, indicating the importance of Sirt1 in the neonatal period. Finally, Sirt1 deficiency affected the acetylation pattern of the myocyte enhancer factor 2 (Mef2) transcription factors, which are critical for normal heart development and mitochondrial integrity. Collectively, our findings indicate that Sirt1 is essential for the maintenance of cardiac mitochondrial integrity and normal postnatal myocardium development.

Dimethyl sulfoxide (DMSO) as a potential contrast agent for brain tumors

Dimethyl sulfoxide (DMSO) is commonly used in preclinical studies of animal models of high-grade glioma as a solvent for chemotherapeutic agents. A strong DMSO signal was detected by single-voxel MRS in the brain of three C57BL/6 control mice during a pilot study of DMSO tolerance after intragastric administration. This led us to investigate the accumulation and wash-out kinetics of DMSO in both normal brain parenchyma (n=3 control mice) by single-voxel MRS, and in 12 GL261 glioblastomas (GBMs) by single-voxel MRS (n=3) and MRSI (n=9). DMSO accumulated differently in each tissue type, reaching its highest concentration in tumors: 6.18 ± 0.85 µmol/g water, 1.5-fold higher than in control mouse brain (p<0.05). A faster wash-out was detected in normal brain parenchyma with respect to GBM tissue: half-lives of 2.06 ± 0.58 and 4.57 ± 1.15 h, respectively. MRSI maps of time-course DMSO changes revealed clear hotspots of differential spatial accumulation in GL261 tumors. Additional MRSI studies with four mice bearing oligodendrogliomas (ODs) revealed similar results as in GBM tumors. The lack of T(1) contrast enhancement post-gadolinium (gadopentetate dimeglumine, Gd-DTPA) in control mouse brain and mice with ODs suggested that DMSO was fully able to cross the intact blood-brain barrier in both normal brain parenchyma and in low-grade tumors. Our results indicate a potential role for DMSO as a contrast agent for brain tumor detection, even in those tumors 'invisible' to standard gadolinium-enhanced MRI, and possibly for monitoring heterogeneities associated with progression or with therapeutic response.

1H-MRSI pattern perturbation in a mouse glioma: the effects of acute hyperglycemia and moderate hypothermia

MR spectroscopic Imaging (MRSI), with PRESS localization, is used here to monitor the effects of acute hyperglycemia in the spectral pattern of 11 mice bearing GL261 gliomas at normothermia (36.5-37.5 degrees C) and at hypothermia (28.5-29.5 degrees C). These in vivo studies were complemented by ex vivo high resolution magic angle spinning (HR-MAS) analysis of GL261 tumor samples from 6 animals sacrificed by focused microwave irradiation, and blood glucose measurements in 12 control mice. Apparent glucose levels, monitored by in vivo MRSI in brain tumors during acute hyperglycemia, rose to an average of 1.6-fold during hypothermia (p < 0.05), while no significant changes were detected at normothermia, or in control experiments performed at euglycemia, or in normal/peritumoral brain regions. Ex vivo analysis of glioma-bearing mouse brains at hypothermia revealed higher glucose increases in distinct regions during the acute hyperglycemic challenge (up to 6.6-fold at the tumor center), in agreement with maximal in vivo blood glucose changes (5-fold). Phantom studies on taurine plus glucose containing solutions explained the differences between in vivo and ex vivo measurements. Our results also indicate brain tumor heterogeneity in the four animal tumors investigated in response to a defined metabolic challenge.