Transthyretin (TTR) is a plasmatic and cerebral spinal fluid homotetrameric protein, involved in Senile Systemic Amyloidosis (SSA) and Familial Amyloidotic Polyneuropathy (FAP), characterized by protein aggregation in amyloid fibril. In current study we are investigating the dissociation/unfolding and aggregation properties of an engineered dimer of TTR, named Bar-Dimer (BD-TTR) where residue Cys10 were replaced by Ala and residue Glu92 by Cys, allowing the formation of a disulphide bond between the A-B and C-D subunits, inhibiting monomer formation. Our data show that this dimer presents a higher thermodynamic stability than shown to wild type TTR (WT-TTR), in different pHs and temperatures tested. When treated with a reducing agent called DTT, which broke the disulfide bond, this thermodynamic stability is similar to WT-TTR. In previous studies we have shown that an alter tetramer of TTR can form amyloid fibrils after HHP treatment. Surprisingly, this dimer undergoes aggregation after HHP treatment even in the absence of DTT, suggesting that aggregation can proceed in the absence of any monomer, in opposite as previously suggested by other groups. The aggregation of BD-TTR is increased by HHP, for samples treated or not with DTT. Our thioflavin-T data shows that the aggregates of BD-TTR induced by HHP are amyloid fibrils. In our assay of cell viability with WT-TTR, V30M and L55P, we could verify that fibers formed by HHP treatment are toxic in a neuroblastoma cell line culture, so as the fibers formed by acid conditions. The samples aggregated in different pHs did not shown significant difference in cytotoxicity. Our MTT data shows that the supernatant of the samples are more cytotoxic than aggregate pellet to the cell line culture, indicating that the cytotoxic species are not only the fibers, but small species or pre-fibrillar structures. The L55P-TTR supernatant shown to be more cytotoxic than V30M-TTR and this more than WT-TTR. L55P-TTR shown to be cytotoxic in physiologic pH.