Human Serum Amyloid a Impaired Structural Stability of High-Density Lipoproteins (HDL) and Apolipoprotein (Apo) A-I and Exacerbated Glycation Susceptibility of ApoA-I and HDL

Abstract

Human serum amyloid A (SAA) is an exchangeable apolipoprotein (apo) in high-density lipoprotein (HDL) that influences HDL quality and functionality, particularly in the acute phase of inflammation. On the other hand, the structural and functional correlations of HDL containing SAA and apoA-I have not been reported. The current study was designed to compare the change in HDL quality with increasing SAA content in the lipid-free and lipid-bound states in reconstituted HDL (rHDL). The expressed recombinant human SAA1 (13 kDa) was purified to at least 98% and characterized in the lipid-free and lipid-bound states with apoA-I. The dimyristoyl phosphatidylcholine (DMPC) binding ability of apoA-I was impaired severely by the addition of SAA, while SAA alone could not bind with DMPC. The recombinant human SAA1 was incorporated into the rHDL (molar ratio 95:5:1, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC): cholesterol: apoA-I) with various apoA-I:SAA molar ratios from 1:0 to 1:0.5, 1:1 and 1:2. With increasing SAA1 content, the rHDL particle size was reduced from 98 Å to 93 Å, and the α-helicity of apoA-I:SAA was decreased from 73% to 40% for (1:0) and (1:2), respectively. The wavelength maximum fluorescence (WMF) of tryptophan in rHDL was red-shifted from 339 nm to 345 nm for (1:0) and (1:2) of apoA-I:SAA, respectively, indicating that the addition of SAA to rHDL destabilized the secondary structure of apoA-I. Upon denaturation by urea treatment from 0 M to 8 M, SAA showed only a 3 nm red-shift in WMF, while apoA-I showed a 16 nm red-shift in WMF, indicating that SAA is resistant to denaturation and apoA-I had higher conformational flexibility than SAA. The glycation reaction of apoA-I in the presence of fructose was accelerated up to 1.8-fold by adding SAA in a dose-dependent manner than that of apoA-I alone. In conclusion, the incorporation of SAA in rHDL impaired the structural stability of apoA-I and exacerbated glycation of HDL and apoA-I.

Synergistic Anti-Inflammatory Activity of Apolipoprotein A-I and CIGB-258 in Reconstituted High-Density Lipoproteins (rHDL) against Acute Toxicity of Carboxymethyllysine in Zebrafish and Its Embryo

“…The change in WMF originates from Trp in apoA-I because CIGB-258 has no Trp. Interestingly, an increase in SAA content in the rHDL containing apoA-I accelerated apoA-I glycation [ 14 ], but the current and previous results showed that an increase of CIGB-258 content in rHDL containing apoA-I resulted in the remarkable inhibition of apoA-I and HDL glycation [ 5 , 6 ]. As shown in Figure 5 , proteins and amino acids glycated through CML treatment exhibited dynamic characteristics, as microorganisms are capable of breaking down these compounds [ 31 , 32 ].…”

“…Interestingly, the incorporation of CIGB-258 could increase the particle size of rHDL with a more stabilizing tertiary structure of apoA-I against urea-induced denaturation, suggesting that adding the peptide could enhance the apoA-I stability. Many studies showed that the incorporation of apolipoproteins, such as apoA-II, apoC-III, serum amyloid A (SAA)-1, and α-synuclein (α-syn), in rHDL, resulted in a negative change in the structural stability and functionality [ 14 , 16 , 27 ]. The addition of apolipoprotein A-II (apoA-II) in rHDL containing apoA-I resulted in an almost 50% displacement of apoA-I, around an apoA-I:apoA-II molar ratio of 1:1, resulting in the destabilization of apoA-I and modulation of lecithin:cholesterol acyltransferase (LCAT) activity [ 28 ].…”

“…In addition, an increase in apoC-III in rHDL impaired several beneficial properties of HDL, including decreased particle size and apoA-I numbers in rHDL with a reduced antioxidant ability against LDL oxidation [ 30 ]. Furthermore, the co-presence of serum amyloid A (SAA) and apoA-I in rHDL resulted in a decrease in particle size and an impairment of the structural stability with a 3 nm red-shift of the WMF [ 14 ], indicating that Trp108 was more exposed to the polar phase. These reports suggest that the amphipathic a-helix domain of similar apolipoproteins could disturb the normal movement of the middle mobile helix domain.…”

“…The movement of an intrinsic fluorophore, especially Trp108, is essential for evaluating the conformational changes in apoA-I, whether enforcement of stability, amyloidogenesis, or proteolytic degradation [ 11 , 12 , 13 ]. This is because the structural stability of apoA-I is critical to HDL particle formation and HDL functionality, such as antioxidant activity and cholesterol efflux activity, upon binding with serum amyloid A and exchange of apoA-I [ 14 , 15 ]. The functionality of rHDLs was also compared individually regarding the antioxidant ability against LDL oxidation, anti-glycation activity against HDL glycation, and anti-inflammatory activity in zebrafish embryos in the presence of CML, according to previous reports [ 5 , 6 , 14 , 16 ].…”

A Current Update on the Role of HDL-Based Nanomedicine in Targeting Macrophages in Cardiovascular Disease

“…In case of an inflammatory response and in atherosclerosis, acute phase proteins such as serum amyloid a (particularly SAA-1), which is secreted by the liver, associates with HDL and modifies its function. Depending upon the concentration and the range of the acute phase response, SAA can displace ApoA-I from the HDL particles, thereby altering the structure and protective properties of HDL [ 112 ].…”