Inhibition of IAPP amyloid formation by TTR as a function of TTR-stabilizing ligands at neutral and low pH. Amyloid formation of IAPP incubated in PBS (pH 7.5) or 25 mM citric acid pH 4.5, 150 mM NaCl, was probed against 500 nM of TTR-wt as well as TTR-M in the presence versus absence of the tetramer stabilizing drugs luteolin (1 μM) and diclofenac (5 μM). Figure (A) illustrates the result at neutral pH at 5 μM of IAPP. Figure (B) illustrates the results at pH 4.5 (note that 10 μM of IAPP was used in the setup at low pH). A significant reduction of the inhibiting propensity of the TTR stabilizing drugs was observed regarding the tetrameric TTR-wt, p-value < 0.005 (unpaired t-test), both at neutral and low pH. TTR-M, which is unable to bind to the ligands, was unaffected at neutral and low pH.