High-Density Lipoprotein Function in Exudative Age-Related Macular Degeneration.

PURPOSE:High-density lipoproteins (HDL) have long been implicated in the pathogenesis of age-related macular degeneration (AMD). However, conflicting results have been reported with regard to the associations of AMD with HDL-cholesterol levels. The present study is the first to assess HDL composition and metrics of HDL function in patients with exudative AMD and control patients. METHODS:Blood samples were collected from 29 patients with exudative AMD and 26 age-matched control patients. Major HDL associated apolipoproteins were determined in apoB-depleted serum by immunoturbidimetry or ELISA, HDL-associated lipids were quantified enzymatically. To get an integrated measure of HDL quantity and quality, we assessed several metrics of HDL function, including cholesterol efflux capacity, anti-oxidative and anti-inflammatory activities using apoB-depleted serum from study participants. RESULTS:In our study, we observed that the HDL associated acute phase protein serum amyloid A (SAA) was significantly increased in AMD patients (p<0.01), whereas all other assessed apolipoproteins including ApoA-I, apoA-II, apoC-II, apoC-III and apoE as well as major HDL associated lipids were not altered. HDL efflux capacity, anti-oxidative capacity and arylesterase activity were not different in AMD patients when compared with the control group. The ability of apoB-depleted serum to inhibit monocyte NF-κB expression was significantly improved in AMD patients (mean difference (MD) -5.6, p<0.01). Moreover, lipoprotein-associated phospholipase A2 activity, a marker of vascular inflammation, was decreased in AMD subjects (MD -24.1, p<0.01). CONCLUSIONS:The investigated metrics of HDL composition and HDL function were not associated with exudative AMD in this study, despite an increased content of HDL associated SAA in AMD patients. Unexpectedly, anti-inflammatory activity of apoB-depleted serum was even increased in our study. Our data suggest that the investigated parameters of serum HDL function showed no significant association with exudative AMD. However, we cannot exclude that alterations in locally produced HDL may be part of the AMD pathogenesis

Serum amyloid a levels are increased in AMD patients.

Serum amyloid A (SAA) levels in apolipoprotein B (apoB)-depleted sera was quantified by ELISA. Values shown represent means of four independent experiments.</p

HDL serum levels, efflux capacity and HDL associated enzyme activities.

HDL serum levels, efflux capacity and HDL associated enzyme activities.</p

Cholesterol efflux capacity.

<p>Apolipoprotein B (apoB)-depleted sera of healthy subjects (control, n = 27) and patients with age-related macular degeneration (AMD, n = 29) were examined for (A) their ability to promote [³H]-cholesterol efflux from macrophages. [³H]-cholesterol-labeled RAW264.7 macrophages were incubated with 2.8% apoB-depleted sera for 4 hours. Cholesterol efflux is expressed as radioactivity in the supernatant relative to total radioactivity (in supernatant and cells). Values shown represent means of two independent experiments.</p

Clinical characteristics of study subjects.

Values are reported as median (±SD).</p

Paraoxonase activity.

<p>Activity of HDL-associated paraoxonase was measured using phenylacetate as substrate. Paraoxonase activity of apoB-depleted sera was calculated from the slopes of the kinetic chart. Values shown represent means of four independent experiments.</p

Lipoprotein associated phospholipase A2 (Lp-PLA2) activity.

<p>Lipoprotein associated phospholipase A2 (Lp-PLA2) activity of apoB-depleted sera was measured using 2-thio PAF as substrate. Lp-PLA2 activity of apoB-depleted sera was calculated from the slopes of the kinetic chart. Values shown represent means of two independent experiments.</p