The Roles of Long-Term Hyperhomocysteinemia and Micronutrient Supplementation in the AppNL-G-F Model of Alzheimer's Disease

Hendrik Nieraad; Natasja de Bruin; Olga Arne; Martine C J Hofmann; Nina Pannwitz; Eduard Resch; Sonja Luckhardt; Ann-Kathrin Schneider; Sandra Trautmann; Yannick Schreiber; Robert Gurke; Michael J Parnham; Uwe Till; Gerd Geisslinger

doi:10.3389/fnagi.2022.876826

The Roles of Long-Term Hyperhomocysteinemia and Micronutrient Supplementation in the App^NL-G-F Model of Alzheimer's Disease

Front Aging Neurosci. 2022 Apr 26:14:876826. doi: 10.3389/fnagi.2022.876826. eCollection 2022.

Authors

Hendrik Nieraad¹, Natasja de Bruin¹, Olga Arne¹, Martine C J Hofmann¹, Nina Pannwitz¹, Eduard Resch¹, Sonja Luckhardt¹, Ann-Kathrin Schneider¹, Sandra Trautmann², Yannick Schreiber¹, Robert Gurke^{1

2}, Michael J Parnham^{1

3}, Uwe Till⁴, Gerd Geisslinger^{1

2}

Affiliations

¹ Fraunhofer Institute for Translational Medicine and Pharmacology, Frankfurt am Main, Germany.
² Pharmazentrum Frankfurt/ZAFES, Institute of Clinical Pharmacology, Goethe University, Frankfurt am Main, Germany.
³ EpiEndo Pharmaceuticals, Reykjavík, Iceland.
⁴ Former Institute of Pathobiochemistry, Friedrich-Schiller-Universität Jena, Jena, Germany.

Abstract

A causal contribution of hyperhomocysteinemia to cognitive decline and Alzheimer's disease (AD), as well as potential prevention or mitigation of the pathology by dietary intervention, have frequently been subjects of controversy. In the present in vivo study, we attempted to further elucidate the impact of elevated homocysteine (HCys) and homocysteic acid (HCA) levels, induced by dietary B-vitamin deficiency, and micronutrient supplementation on AD-like pathology, which was simulated using the amyloid-based App^NL-G-F knock-in mouse model. For this purpose, cognitive assessment was complemented by analyses of ex vivo parameters in whole blood, serum, CSF, and brain tissues from the mice. Furthermore, neurotoxicity of HCys and HCA was assessed in a separate in vitro assay. In confirmation of our previous study, older App^NL-G-F mice also exhibited subtle phenotypic impairment and extensive cerebral amyloidosis, whereas dietary manipulations did not result in significant effects. As revealed by proximity extension assay-based proteome analysis, the App^NL-G-F genotype led to an upregulation of AD-characteristic neuronal markers. Hyperhomocysteinemia, in contrast, indicated mainly vascular effects. Overall, since there was an absence of a distinct phenotype despite both a significant amyloid-β burden and serum HCys elevation, the results in this study did not corroborate the pathological role of amyloid-β according to the "amyloid hypothesis," nor of hyperhomocysteinemia on cognitive performance. Nevertheless, this study aided in further characterizing the App^NL-G-F model and in elucidating the role of HCys in diverse biological processes. The idea of AD prevention with the investigated micronutrients, however, was not supported, at least in this mouse model of the disease.

Keywords: Alzheimer’s disease; amyloid betapeptides; hyperhomocysteinemia; memory and learning tests; proteomics; vitamin B deficiency.