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

Abstract

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.Abbreviations: 3xTg-AD, triple-transgenic mouse model of AD.; 6E10+, mAb-6E10 immunoreactive

Cognitive Impairment in the 3xTg-AD Mouse Model of Alzheimer’s Disease is Affected by Aβ-ImmunoTherapy and Cognitive Stimulation

“…The effect of the treatment was not detected at 7 and 9 months of age, probably because training masked the effect of this low-doses treatment. Indeed, although a positive effect of scFv-h3D6 treatment at similar doses was observed in a longitudinal study followed by magnetic resonance imaging (MRI) [ 36 ], it is likely that the low dose used during both longitudinal studies could be increased to obtain more robust results, encouraging further studies with higher doses of this antibody fragment.…”

“…The anti-Aβ scFv-h3D6, derived from bapineuzumab, has been effective in the prevention of Aβ-induced toxicity in SH-SY5Y neuroblastoma cell-cultures [ 31 ] and in ameliorating AD histologically hallmarks, without eliciting any detectable inflammatory response in young 3xTgAD mice [ 32 , 33 , 34 , 35 ]. Interestingly, a longitudinal study using magnetic resonance imaging and spectroscopy showed the efficacy of scFv-h3D6 treatment in preventing loss of brain volume occurring in 3xTg-AD mice [ 36 ]. However, cognitive improvement through a chronic treatment has not ever been assessed.…”

Both Amyloid-β Peptide and Tau Protein Are Affected by an Anti-Amyloid-β Antibody Fragment in Elderly 3xTg-AD Mice

“…At this initial point in the discussion, an important methodological issue is worth mentioning. As we [18,[21][22][23][24][25] and other authors [39][40][41][42] have extensively argued, although 6E10 mAb is able to recognize Aβ, β-CTD, and APP, what we are measuring in the 3xTg-AD mouse with this mAb is nowadays agreed to be the Aβ peptide. The present work constitutes another demonstration of this fact since scFv-h3D6, which exclusively recognizes the Aβ peptide, promotes a comparable decrease in both 6E10-labeling and Aβ40-and Aβ42-specific signals by ELISA.…”

“…Treatment with scFv-h3D6 by some means affected the endogenous Aβ levels also in the non-transgenic mice. Although the significance found in the 3xTg-AD group was not reached, we observed a tendency for the protection from the loss of volume associated with aging in the cortex, cerebrum, and the whole brain, and diminished the 6E10+ intensity, amyloid load, and IL-6 values in both the hippocampus and, especially, the cortex [ 24 ]. Indeed, in our first study in vivo [ 21 ], the treatment was able to improve the performance of the non-transgenic animals in some learning tasks, although the overall effect on behavior/cognition was much less evident than in the 3xTg-AD mice.…”

Glial Cell-Based Vascular Mechanisms and Transplantation Therapies in Brain Vessel and Neurodegenerative Diseases

“…Some recent progresses of related antibody therapies may include: the catalytic immunoglobulin V domain (IgV) degrades and clears Aβ specifically with no evidence of microglial activation or microhemorrhages. Many monoclonal hAβ antibodies such as Bapineuzumab IgG1 and the single-chain variable fragment (scFv) fusion proteins such as scFv-h3D6 (derived from the IgG-h3D6) are effective in eliminating the most toxic species of hAβ-oligomers (üell-Bosch et al, 2020). The scFv is considered to clean without triggering Fcmediated effector functions.…”