HDL remodeling during the acute phase response

Abstract

Objective: The purpose of this study was to examine the interactive action of serum amyloid A (SAA), group IIA secretory phospholipase A(2) (sPLA(2)-IIA), and cholesteryl ester transfer protein (CETP) on HDL remodeling and cholesterol efflux during the acute phase (AP) response elicited in humans after cardiac surgery.

Methods and results: Plasma was collected from patients before (pre-AP), 24 hours after (AP-1 d), and 5 days after cardiac surgery (AP-5 d). SAA levels were increased 16-fold in AP-1 d samples. The activity of sPLA(2)-IIA was increased from 77.7+/-38.3 U/mL (pre-AP) to 281.4+/-57.1 U/mL (AP-1 d; P<0.001). CETP mass and activity reduction was commensurate to the reduction of HDL cholesterol levels. The combined action of SAA, sPLA(2)-IIA, and CETP in vitro markedly remodeled HDL with the generation of lipid-poor apoA-I from both pre-AP and AP-1 d HDL. The net result of this remodeling was a relative preservation of ABCA1- and ABCG1-dependent cholesterol efflux during the acute phase response.

Conclusions: Our results show that the many and complex changes in plasma proteins during the acute phase response markedly remodel HDL with functional implications, particularly the relative retention of cholesterol efflux capacity.

Figure 1

SAA (A) and sPLA₂ (B) concentrations in pre-AP, AP- 1d and AP- 5d plasma. Data is presented as mean ± SEM. n=12 (SAA); n=6 (sPLA₂); * p < 0.05 versus pre-AP by one way repeated measures ANOVA.

Figure 2

CETP, HDL cholesterol and apoA-I are reduced in AP- 1d plasma. (A) Plasma CETP concentrations were quantified by densitometric analysis of Western blots. (B) CETP activity (C) HDL-C concentrations and (D) apoA-I concentrations in pre-AP and AP- 1d plasma. ** p < 0.01, *** p < 0.001 by paired t-test.

Figure 3

Apolipoprotein characterization of pre-AP HDL, AP- 1d HDL and SAA-HDL. (A) SDS gel of HDL (5 μg total protein). (B) ¹²⁵I-pre-AP HDL (5 μg) was passed through an anti-apoA-II immunoaffinity column and fractions were electrophoresed and autoradiographed as outlined in the methods (ARG). (C) ¹²⁵I-AP HDL (10 μg) was passed through an anti-SAA immunoaffinity column with subsequent electrophoresis and ARG as described in (B). (D) ¹²⁵I-AP HDL (10 μg) was passed through an anti-apoA-II immunoaffinity column with subsequent electrophoresis and ARG as described in (B). Note: the gels in B–D were loaded on the basis of 2000 cpm per lane and since the majority of counts were present in E1 and E2, E3–E5 quantitatively represent a smaller percentage of total protein mass.

Figure 4

Dissociation of lipid-poor apoA-I from pre-AP and AP- 1d HDL following remodeling by CETP. HDLs were incubated with CETP in the presence of VLDL for 24 hr at 37°C as outlined in the methods. Reactions were analyzed by Western blot for (A) apoA-I and (B) SAA. The migration of lipid-poor apoA-I and SAA are marked with arrows.

Figure 5

The combined action of sPLA₂-IIA and CETP on HDL₂ and SAA-HDL. HDL were incubated with sPLA₂-IIA and CETP as set out in the methods. Reactions were analyzed by Western blot for apoA-I in (A) HDL₂ and (B) SAA-HDL and (C) SAA blot of SAA-HDL.