Peptide Conjugates of Benzene Carboxylic Acids as Agonists and Antagonists of Amylin Aggregation

Abstract

Human islet amyloid polypeptide (hIAPP), also known as amylin, is a 37 residue peptide hormone that is stored and co-secreted with insulin. hIAPP plays a pivotal role in type 2 diabetes and is the major component of amyloid deposits found in the pancreas of patients afflicted with the disease. The self-assembly of hIAPP and the formation of amyloid is linked to the death of insulin producing β-cells. Recent findings suggest that soluble hIAPP oligomers are the cytotoxic species responsible for β-cell loss whereas amyloid fibrils themselves may indeed be innocuous. Potential avenues of therapeutic intervention include the development of compounds that prevent hIAPP self-assembly as well as those that reduce or eliminate lag time and rapidly accelerate the formation of amyloid fibrils. Both of these approaches minimize temporal exposure to soluble cytotoxic hIAPP oligomers. Toward this end our laboratory has pursued an electrostatic repulsion approach to the development of potential inhibitors and modulators of hIAPP self-assembly. Peptide conjugates were constructed in which benzene carboxylic acids of varying charge were employed as electrostatic disrupting elements and appended to the N-terminal of the hIAPP22–29 (NFGAILSS) self-recognition sequence. The self-assembly kinetics of conjugates were characterized by turbidity measurements and the structure of aggregates probed by Raman and CD spectroscopy while the morphology was assessed using transmission electron microscopy. Several benzene carboxylic acid peptide conjugates failed to self-assemble and some were found to inhibit the aggregation of full-length amylin while others served to enhance the rate of amyloid formation and/or increase the yield of amyloid produced. Studies reveal that the geometric display of free carboxylates on the benzene ring of the conjugates plays an important role in the activity of conjugates. In addition, a number of free benzene carboxylic acids were found to modulate amylin self-assembly on their own. The results of these investigations confirm the viability of the electrostatic repulsion approach to the modulation of amyloid formation and may aid the design and development of potential therapeutic agents.

Conformational differentiation of α‐cyanohydroxycinnamic acid isomers: a Raman spectroscopic study

“…The incorporation of analyte within the MALDI matrix has been demonstrated to influence MALDI performance; thus, looking at solution properties of this class of compounds becomes relevant and highlights the advantage of Raman spectroscopy over X‐ray crystallographic techniques . We anticipate that these observations may as well be able to explain the slight difference in aggregation propensities of CHCA3‐hIAPP22‐29 and CHCA4‐hIAPP22‐29 conjugates . Parallel beta‐sheets associated with hIAPP22‐29 aggregation brings conjugated CHCA groups on a stacked orientation .…”

“…[39][40][41][42][43] We anticipate that these observations may as well be able to explain the slight difference in aggregation propensities of CHCA3-hIAPP22-29 and CHCA4-hIAPP22-29 conjugates. [15] Parallel beta-sheets associated with hIAPP22-29 aggregation brings conjugated CHCA groups on a stacked orientation. [44] The greater stability of stacking between CHCA4 may have led to the observed greater aggregation propensity of CHCA4-hIAPP22-29 conjugate over the former.…”

“…The larger presence of CHCA4 in biological studies has also led to its use as a scaffold for the development of novel small molecule inhibitors to protein activity such as those of aldose reductase . Our laboratory's recent study on CHCA3 and CHCA4 conjugated to the amyloidogenic hIAPP 22–29 showed slightly different aggregation behaviour, which perhaps can be attributed to the slight difference in structure that brings about different chemical properties between the two positional isomers …”

“…[14] Our laboratory's recent study on CHCA3 and CHCA4 conjugated to the amyloidogenic hIAPP [22][23][24][25][26][27][28][29] showed slightly different aggregation behaviour, which perhaps can be attributed to the slight difference in structure that brings about different chemical properties between the two positional isomers. [15] We measured the Raman spectra of the two isomers and assigned the observed peaks based on DFT calculations and by comparison to literature spectra of similarly structured compounds. [16] The Raman assignments expose very distinct vibrational modes for each compound that betrays the different types of interactions that exist in CHCA3 and CHCA4.…”

γ-AApeptides–based Small Molecule Ligands That Disaggregate Human Islet Amyloid Polypeptide

“…Hence, there is an urgent need for potent inhibitors of the process producing these pathogenic fibrils. In line with this, some inhibitors, including the peptides derived from the various secondary recognition elements along the amylin peptide chain [15][16][17] , engineered peptides [18][19][20] , constrained peptides [21][22][23][24][25][26][27] , small molecules 28,29 and natural products [30][31][32] , have been reported. Many of these inhibitors are specific in their activity; however, a good number of them have exhibited dual inhibitory activity such that they can inhibit amyloid aggregation of multiple classes of proteins non-specifically [32][33][34][35] .…”