The buildup of toxic aggregates formed by the amyloid-β peptide 1-42 (Aβ42) is a central process in Alzheimer's disease (AD) pathology. The peptide's self-assembly and toxicity are highly dependent on its primary amino acid sequence and can be altered by modifying key residues. Specifically, the single amino acid substitutions A30W, K28A, and M35C can reduce the aggregation and toxicity of the Aβ42 peptide. In this study, we further evaluated the effects of these mutations in a C6 rat glioma cell line and in the Caenorhabditis elegans strains CL2006 and CL4176, which express muscular Aβ42 as an in vivo model. Our results showed that the A30W, K28A, and M35C substitutions reduce apoptosis induction in cell culture, in contrast to the WT Aβ42 peptide. In C. elegans, the three variants extended the lifespan of CL2006 worms by reducing fibrillar aggregates or altering aging, whereas the M35C peptide delayed the paralysis of CL4176 worms. Additionally, the substitutions altered oxidative stress and autophagy in control worms. Taken together, these results suggest that the A30W, K28A, and M35C substitutions reduce Aβ42 toxicity in cell culture and in C. elegans and could protect the nematode against Aβ42 toxicity.