Background: Previous studies of lipoproteins in patients with sepsis have been performed on density fractions isolated by conventional ultracentrifugation that are heterogeneous and provide no information about the cargo of apoproteins present in the immunochemically distinct subclasses that populate the density classes. Since apoproteins are now known to have important roles in host defense, we have separated these subclasses according to their apoprotein content and characterized their changes during experimental endotoxemia in human volunteers. Methods: We have studied apoB- and apoA containing lipoprotein subclasses in twelve healthy male volunteers before and for 8 h after a single dose of endotoxin (ET; 2 μg/kg) to stimulate inflammation. Results: After endotoxin, TG, TC, apoB and the apoB-containing lipoprotein cholesterol-rich subclass LpB and two of the three triglyceride-rich subclasses (TGRLP: Lp:B:C, LpB:C:E+ LpB:E) all declined. In contrast, the third TGRLP, LpA-II:B:C:D:E (“complex particle”), after reaching a nadir at 4 h rose 49% above baseline, p = .006 at 8 h and became the dominant particle in the TGRLP pool. This increment exceeds the threshold of > 25% change required for designation as an acute phase protein. Simultaneous decreases in LpA-I:A-II and LpB:C:E + LpB:E suggest that these subclasses undergo post-translational modification and contribute to the formation of new LpA-II:B:C:D:E particles. Conclusions: We have identified a new acute phase lipoprotein whose apoprotein constituents have metabolic and immunoregulatory properties applicable to host defense that make it well constituted to engage in the APR. Keywords: Endotoxin, Inflammation, Lipoprotein subclasses, TGLRP, triglyceride—rich lipoproteins, Innate immunity Background neutralizing microbial toxins and delivering vital nutrients The acute phase reaction (APR) is an integral compo- to cells actively engaged in the immune response and nent of host defense that contributes to the initiation, tissue repair [4, 5]. The fact that both the structural and activation, and propagation of events that are integral exchangeable apoprotein components of lipoproteins are features of innate immunity . This highly conserved now known to have a wide range of immunoregulatory transcriptional response is driven by inflammatory functions indicates that the protein moieties also serve to cytokines released from mononuclear cells that activate protect the host in the presence of infection and inflam- expression of multiple genes  that alter the hepatic se- mation [6–8]. cretion of a number of plasma proteins and lipoproteins Each lipoprotein density fraction isolated by conven- that have pathophysiological actions . One of these tional ultracentrifugation has been considered to be rela- many changes is a rise in triglyceride-rich lipoproteins tively homogeneous. Application of immune-based (TGRLP) that frequently is observed during sepsis. The lipoprotein separation methods has instead revealed a lipid contents of lipoproteins involved in this response more complex picture. Density fractions in fact are very are believed to protect the host both by sequestering and heterogeneous and contain several discrete subclasses that differ in their apoprotein and lipid composition, * Correspondence: email@example.com function, density, and metabolism and are not detected Deceased when conventional density fraction fractions are mea- Department of Human Physiology, University of Oregon, 122c Esslinger Hall, sured . Eugene, OR 97403, USA Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Bagdade et al. Lipids in Health and Disease (2018) 17:127 Page 2 of 9 Separating lipoproteins into immunochemically-defined placed at bed rest which was continued throughout the subclasses is feasible because their major apoproteins are entire study period. The twelve male participants in retained during intravascular lipolysis even though their Vienna (age 23 +/− 1 yr.; BMI 23.4 ± 0.5 kg/m ; mean ± physicochemical properties  and distribution within SEM) received a single i.v. bolus dose of endotoxin the conventional the density fractions changes. Lipopro- containing 2 ng/kg LPS (National Reference). Blood was teins containing apoB separated in this way have been obtained from these subjects at 0, 2, 4, 6, 8 h. Control grouped into two major subclasses – those that are subjects received an i.v. bolus dose of saline followed by TG-rich (LpB:C, LpB:C:E, LpAII:B:C:D:E) and those that saline infusions and were studied at three different sites: are cholesterol-rich (LpB, LpB:E). Each of these is dis- four subjects were part of the Vienna cohort and had persed widely in VLDL, IDL, and LDL and has differing also received endotoxin; an additional six male subjects atherogenic properties and clinical relevance . The were studied at the University of Copenhagen (age 24 ± apoC-III-containing subclasses LpB:C and LpAII:B:C:D:E 1 yr.; BMI 23.5 ± 0.8 kg/m ); and six subjects studied at for example have been shown to be associated with Rockefeller University in New York (three males, three progression of coronary atherosclerosis  and the females (age 30+/− 1.9 yr.; BMI 25.0 +/− 1.0 kg/m ) that lipoprotein density classes (VLDL, LDL) containing these participated in earlier studies, in which lipoproteins had subclasses found to predict cardiovascular events [13, 14]. been isolated immunochemically and measured during Two major apoA-containing subclasses (LpA-I, LpA-I:A-II) saline infusion [19, 20]. In the subjects from populate the HDL2 and HDL3 subfractions . Copenhagen, blood was drawn at 0, 2, 3, 6 h. All When endotoxin (bacterial lipolysaccharide: LPS) is samples were processed immediately at each site by released from the cell walls of gram-negative bacteria centrifugation at 2000 g at 4 °C for 15 min and plasma into the circulation, it binds to the Toll-like receptor stored at − 80 °C before analysis. Since there was no (TLR4) on immune cells, which then release cytokines difference between the 3 h values in the Copenhagen and other inflammatory mediators that activate the APR subjects and the 4 h values in the New York and Vienna and initiate the host innate immune response . control subjects, the results were combined into a single For this reason, endotoxin has become a convenient 4 h measurement. experimental tool to investigate the APR . Most previous studies of lipoproteins from patients Analytical methods with sepsis [17, 18] and during experimental endotoxe- Total cholesterol (TC), TG and HDL-Cholesterol mia in human volunteers  have been performed on (HDL-C) were determined in frozen blood samples  lipoprotein density fractions. Since no information is and LDL-cholesterol (LDL-C) calculated using the available about the transport of apoprotein-defined lipo- Friedewald formula as previously described . Apolipo- protein subclasses during the APR, we have character- proteins (apo) A-I, A-II, B, C-III and E were determined ized these subclasses in a group of normal volunteers by employing the immunoturbidimetric procedure of following endotoxin exposure. Riepponon et al.  using corresponding monospecific polyclonal antisera. Quantitative determination of LpB, Methods LpB:C, LpB:E + LpB:C:E and LpA-II:B:C:D:E subclasses Study population was performed by sequential immunoprecipitation of Subjects were recruited for study in Vienna, whole plasma by polyclonal antisera to apoAII, apoE and Copenhagen, and New York. The study was performed apoCIII, respectively, as previously described . To according to the Declaration of Helsinki. Subjects were determine the distribution of apoC-III and apoE between informed about the possible risks and discomfort before the apoB- and apoA- lipoproteins following endotoxin or giving their written consent to participate. The protocol saline treatment, the binding of each was measured by was approved by the Ethical Committee(s) of the Medical electroimmunoassay in heparin soluble (HS; apoA) and University of Vienna, Austria and of Copenhagen and heparin precipitate (HP; apoB) fractions and changes in Fredriksberg Communities, DK and by the Institutional their apoE content expressed as apoE-HS (HDL)/HP Review Boards of Rockefeller University and the (VLDL+ LDL) ratios. LpA-I, LpA-I:A-II were measured Oklahoma Medical Research Foundation. Inclusion according to the method of Marz et al. . The between criteria: healthy young, non-obese, non-smoking sub- assay CVs for immunoprecipitation with anti-serum to jects. Exclusion criteria: recent intake of prescription apo CIII was 6–7%. or non-prescription medications. Statistical analysis Protocol Data were analyzed by 2-way ANOVA for main effect of All subjects were admitted to the clinical research unit time vs. ET treatment with posthoc analyses of signifi- at 0800 after an overnight fast. After voiding, they were cant main effects. A one-way ANOVA was used for Bagdade et al. Lipids in Health and Disease (2018) 17:127 Page 3 of 9 comparison of the changes in the apoB-subclasses within ApoB and apoB-subclasses each treatment group. In order to better visualize a full In the ET group apoB, LpB, and LpB:C declined within 8 h pattern of changes in the TGRLP subclasses in the 6 h to levels significantly less than baseline (Figs. 2a-c) saline-infused controls in whom these parameters were and their pattern of change differed from those of the measured from 0 to 6 h only, regression lines were saline group. The behavior of LpA-II:B:C:D:E in the ET determined by least squares estimation for the plasma group, however, differed from that of apoB and other of lipids and each subclass from 0 to 6 h and from each their apoB- containing subclasses. After declining to a line values were estimated at 8 h . nadir at 4 h, Lp-AII:B:C:D:E then increased progressively over the next 4 h and reached a level at 8 h that was almost two-fold above baseline (p = .006); Fig. 2e). While Results the plasma TG declined from baseline and the All subjects who received endotoxin manifested one or TGRLP pool size contracted in the ET group, the more of its side effects: typical flu-like symptoms, chills, number of Lp-AII:B:C:D:E particles relative to LpB:C fever, headache, nausea, and myalgia [27, 28]. and LpB:C:E + LpB:E increased and LpA-II:B:C:D:E: became the predominant TGRLP subclass at 6 h and Baseline measures and changes from baseline 8h (p = .001; Fig. 2f). The percentage of each TGRLP The physical characteristics of the two experimental subclass in the saline group was unchanged through- groups are indicated in the Methods section. At baseline out the study. the subjects who received ET had significantly lower TG (p = .003; Fig. 1a), LpAII:B:C:D:E (p = .016; Fig. 2e), and ApoA-I and apoA-subclasses apoE levels (p = .004; Fig. 4a) than the saline controls. The From 0 to 6 h, there was no significant change in apoA-I directional changes in TG, TC, LDL-C, and HDL-C, how- and LpA-I in either group. (Fig. 3a, b). At 8 h, however, ever, were similar in the two groups until 6 h (Fig. 1)when both apoA-I and LpA-I:A-II in the ET subjects declined TG in the ET subjects had declined significantly from significantly from baseline (p = .0001). Since LpA-I levels baseline and was significantly less than the TG in the remained stable from 6 to 8 h, these findings indicate saline controls (p =.0001; Fig. 1a) and HDL-C was lower that the decrease in apoA-I was due to a specific decline overall with time in the ET group (p =.003). in the LpA-I:A-II subclass. Saline ab Time P<0.0001 100 Endotoxin 200 LPS P<0.0001 Interaction P=0.007 80 + 0 120 02468 02468 Hours Hours cd Time P=0.02 120 70 LPS n.s. 70 30 02468 02468 Hours Hours Fig. 1 Changes in plasma lipids in response to endotoxin. Fasting plasma (a) triglycerides, (b) total cholesterol, (c) LDL-cholesterol, and (d) HDL-cholesterol concentrations (mean +/− SE) were measured in subjects at baseline and for 8 h after an intravenous dose of endotoxin (closed circles, n =7–12) or saline (open circles, n =4–9). Data were analyzed by 2-way repeated measures ANOVA (time x LPS treatment) with Dunnett’s posthoc analysis for time points compared to group baseline with saline (+; p < 0.05) or LPS (#; p < 0.05). A Sidak’s multiple comparison test was used to compare treatment groups at each time point (*; p < 0.05) LDL-C (mg/dL) Trigylcerides (mg/dL) Total Cholesterol (mg/dL) HDL-C (mg/dL) Bagdade et al. Lipids in Health and Disease (2018) 17:127 Page 4 of 9 ab c 90 60 10 Interaction P=0.03 LPS n.s. LPS n.s. Saline Time P=0.006 Time P<0.001 Endotoxin 85 8 80 6 75 4 70 2 # # 65 40 0 02468 02468 02468 Hours Hours Hours Interaction P=0.03 de f % Composition P=0.001 Interaction P=0.002 40 LPS n.s. (0.06) Time P=0.01. Saline Endotoxin (6h) # Endotoxin (8h) 10 15 b b * b -20 0 5 -40 02468 02468 LpAII:B LpB:C:E+LpB:E LpB:C Hours Hours Fig. 2 Endotoxin alters the quantity and distribution of apo B-containing lipoprotein subclasses. Plasma (a) apoB and apoB-containing lipoprotein subclasses: (b) LpB, (c) LpB:C, (d) LpB:C + LpB:E and (e) LpA-II:B:C:D:E concentrations measured at baseline and for 8 h after an intravenous dose of endotoxin (closed circles, n = 11) or saline (open circles, n = 9). Data were analyzed by 2-way repeated measures ANOVA (time x LPS treatment) with Dunnett’s posthoc analysis for time points compared to baseline in saline (+; p < 0.05) or LPS (#; p < 0.05) groups. A Sidak’smultiple comparison test was used to compare treatment groups at each time point (*; p <0.05). (f) The percent change from baseline in TGRLP subclass distribution at 6 h and 8 h after an intravenous dose of LPS or saline. To compare group changes within each subclass, data were analyzed by 2-way ANOVA (TGLRP composition vs. time) with Tukey post hoc analysis. * p < 0.05 compared to saline within subclass. Significant difference (P < 0.05) between subclasses letters at 6 or 8 h are marked with different letter Distribution of apoE and apoC-III p = .0001; Fig. 4d). In both the saline and ET-treated Apo E concentration at 0 h in the ET subjects was subjects, the apoE content of apoE-HP (VLDL+LDL) significantly lower than in the saline-treated controls declined from baseline from 4 to 8 h (Fig. 4c). and levels in both groups were stable until 6 h after ET. ApoC-III levels at baseline were similar in the two At 8 h, however, total apoE in the ET group trended groups (Fig. 5a), thereafter declining in plasma and in upward from baseline and this small increment (+ 10%) the apoB-containing lipoproteins (apoC-III HP; Fig. 5c) was reflected by increases in the apoE content of HDL and increasing at 8 h in HDL (apoC-III HS; Fig. 5b)ina (apoE-HS; Fig. 4b) which rose significantly (+ 27%; p =.01) pattern similar to that of apoE. These changes, however, abovebaselineand in theapoE HS/HPratio(+40%; were not statistically significant. 150 120 a b 34 c LPS n.s. LPS n.s. Saline Time P=0.004 Time P=0.005 Endotoxin 32 110 28 90 # # 24 70 02468 02468 Hours Hours Hours Fig. 3 Endotoxin reduces the quantity of apo A-containing particles. The concentration of plasma (a) apoA-I and apoA-I containing lipoprotein subclass, (b) LpA-I, (c) LpA-I:A-II were measured in subjects at baseline and for 8 h after an intravenous dose of endotoxin (closed circles, n = 12) or saline (open circles, n = 4) groups. Data were analyzed by 2-way repeated measures ANOVA (time x LPS) LpB:C:E+LpB:E (mg/dL) ApoB (mg/dL) ApoA-I (mg/dL) LpB (mg/dL) LpA-II:B:C:D:E (mg/dL) LpA-I (mg/dL) LpB:C (mg/dL) % Change in TGLRP LpA-I:A-II (mg/dL) Bagdade et al. Lipids in Health and Disease (2018) 17:127 Page 5 of 9 Interaction P=0.009 Saline ab 5.0 3 LPS P=0.005 Endotoxin 4.0 3.0 * * 2.0 1.0 0.0 0 02468 02468 Hours Hours cd # 3 Interaction P=0.03 3 Interaction P=0.0065 LPS P<0.0001 LPS P<0.0001 Time P<0.0001 Time P=0.001 2 2 * * * * 1 1 # # 0 0 02468 02468 Hours Hours Fig. 4 Endotoxin alters distribution of ApoE among plasma lipoproteins. The concentration of (a) apoE in plasma, (b) apoE associated with HDL (ApoE heparin soluble [HS]), (c) apoE associated with apoB-containing lipoproteins (ApoE-heparin precipitate [HP]) was measured at baseline and for 8 h after an intravenous dose of endotoxin (closed circles, n = 11) or saline (open circles, n = 4). (d) Changes in distribution of apoE in heparin soluble (HS) and heparin precipitate (HP) is expressed as the apoE HS/apoE HP ratio. Data were analyzed by 2-way repeated measures ANOVA (time x LPS treatment) with Dunnett’s posthoc analysis for time points compared to baseline in saline (+; p < 0.05) or LPS (#; p < 0.05). A Sidak’s multiple comparison test used to compare treatment groups at a single time point (*p < 0.05) Discussion Except for the lack of an early increase in plasma TG, Disturbances in plasma lipids have been observed for the directional changes we observe in the major plasma many years in patients during sepsis [17, 18, 28]. In the lipids and apoB in the ET group from 0 to 6 h resemble most comprehensive sepsis-related study of lipoprotein those described by Hudgins et al. . As previously re- transport to date, sequential changes in the concentra- ported, we too find that individual TG responses during tion of lipoprotein density fractions were measured and systemic inflammation and sepsis are variable [1, 18, 30]. correlated with levels of cytokines, inflammatory While the changes in the apoB-subclasses from 0 to 4 h markers, and acute phase reactants during experimental did not differ in our two experimental groups, their sub- endotoxemia in human volunteers . Hudgins et al. sequent responses differed significantly. Notably, as the  observed an early and rapid increase in TG and plasma TG and the TGRLP subclasses LpB:C and LpB:C: VLDL lipids that peaked at 3 h and was synchronous E continued to decline in the ET subjects, their LpA-II: with maximum levels of IL-6 and TNF-alpha. B:C:D:E (LpA-II:B complex) particle number increased Previously, we examined immunochemically-defined progressively and this particle which normally is only a lipoprotein subclasses in human volunteers during an minor component (7%) of the TGRLP pool [9, 10] IL-6 infusion to investigate lipoprotein subclasses during became the most abundant TGRLP particle. systemic inflammation . In that project, we found By increasing more than 25% above its baseline value that the concentration of the TGRLP subclasses LpB:E + (+ 27% at 6 h and + 48% at 8 h), the LpAII:B complex LpB:C:E,which are distributed in the apoB-containing particle meets the definition of an acute phase reactant VLDL, IDL, and LDL density classes increased signifi- [1, 29] and therefore is a previously unrecognized cantly at 30 min and 60 min with no change in plasma positive acute phase protein. Even though the overall TG. Since IL-6 is only one of several inflammatory me- changes in plasma TG and TGRLP pool size after diators released during the acute phase reaction , endotoxin were modest, we believe that the increase in this observation suggested that simulating inflammation number of this specific particle is biologically significant with endotoxin may impact the transport of this and other because it contains several multifunctional apolipopro- immunochemically-separated lipoprotein subclasses. Our teins that have immunomodulatory properties. There- current results confirm this hypothesis. fore, the fact that these particles increase in number ApoE (mg/dL) ApoE-HP (mg/dL) ApoE Ratio (HS/HP) ApoE-HS (mg/dL) Bagdade et al. Lipids in Health and Disease (2018) 17:127 Page 6 of 9 ab 10 6 Saline Endotoxin 8 4 6 2 4 0 02468 02468 Hours Hours cd 6 4 LPS P=0.02 LPS P=0.02 Time P=0.03 Time n.s. (0.06) 02468 02468 Hours Hours Fig. 5 Endotoxin does not significantly change the distribution of ApoC-III among plasma lipoproteins. The concentration of (a) apo C-III in plasma, (b) apo C-III associated with HDL (C-III heparin soluble [HS]), (c) apo C-III associated with apo B-containing lipoproteins (C-III heparin precipitate [HP]) was measured at baseline and for 8 h after an intravenous dose of endotoxin (closed circles, n = 11) or saline (open circles, n = 4). (d) Changes in the distribution of apo C-III in HS and HP expressed as the C-III HS/C-III HP ratio (apo C-III R) after the intravenous injection of endotoxin (LPS). Data were analyzed by 2-way repeated measures ANOVA (time x LPS treatment) with Dunnett’s posthoc analysis for time points compared to baseline in saline (+; p < 0.05) or LPS (#; p < 0.05). A Sidak’s multiple comparison test was used to compare treatment groups within each time point (*; p < 0.05) during inflammation makes it likely that they contribute well suited to engage in the APR and plays an important actively to host defense. Alaupovic first identified the role in host defense. Being resistant to lipolysis and hav- LpAII:B complex particle in the plasma of patients with ing a prolonged residence time in plasma during inflam- Tangier disease and showed that it differed metabolically mation may be useful because this property enhances its from other TGRLP by being lipolysis resistant and a capacity to deliver nutrients and apoproteins to immune poor substrate for LPL . More recent kinetic studies cells that support their activation . For example, showing that it has a prolonged residence time in plasma apoA-II can upregulate and then modulate the host are consistent with his earlier observations . response during sepsis . Although better known for The concentration of most acute phase proteins is its role in cholesterol transport and macrophage biology, regulated by APR genes  at the transcriptional level apoB-100 also can act as an immune suppressor by lim- through changes in hepatic production . The alter- iting the release of cytokines . Because LpA-II:B:C:D: ations we observe in lipoproteins, however, are too rapid E, has apoB-100 as its major structural apoprotein, it to be ascribed to changes in production. Rather, our would under normal circumstances facilitate its internal- findings suggest that changes in LpA-II:B particle num- ization by LDL B,E receptors in both hepatic and extra- ber was a post-translational event involving the coordi- hepatic tissues throughout the body. During infection, nated activity of lipases and lipid transfer proteins that however, LDL receptors are down-regulated in the liver normally play integral roles in the remodeling of TGRLP and upregulated in macrophages , changes thought and HDL . Indeed, Alaupovic et al. speculated earlier to benefit the host by promoting the uptake of apoB- that LpA-II:B particles were formed in plasma by the containing subclasses by immune cells. Not surprisingly, transfer of apoA-II from the HDL subclass LpA-I:A-II two of the three apoC isoforms present on LpA-II:B:C:D: particles to LpB:C:E . The concomitant increase we E also are involved in host defense (7). Quite apart from observe in LpA-II:B and decline in both the LpA-I:A-II their regulatory roles in lipoprotein transport , and LpB:C:E + LpB:E from 4 to 8 h after endotoxin sup- apoC-I has been shown to enhance the inflammatory ports this mechanism. response to LPS  and apoC-III to actively participate Based on its apoprotein content and kinetic behavior in the inflammatory components of atherosclerosis , we suggest that the LpAII:B complex particle is development . ApoC-III (mg/dL) ApoC-III-HP (mg/dL) ApoC-III Ratio (HS/HP) ApoC-III-HS (mg/dL) Bagdade et al. Lipids in Health and Disease (2018) 17:127 Page 7 of 9 Despite apoD being structurally dissimilar from other associated proteins having immunomodulatory properties apolipoproteins , it too has immunoregulatory, anti- (A-IV, C-III, C-IV, L-I, M, F, H, J [clusterin]) play in host stress, and antioxidant properties that contribute to host defense, their distribution among the HDL subclasses and defense . Alaupovic suggested earlier that apoD was fate during the APR require further study . acquired from LpA-I:A-II HDL particles when LpAII:B The strength of our study is that we have employed an complex particles are formed from the interaction of underutilized immunochemical method of measuring LpA-I:A-II with LpB:C:E . While apoE is a key ligand lipoproteins to demonstrate for the first time changes in that facilitates transport of the apoE-containing apoB the TGRLP subclasses during inflammation that are not subclasses, most apoE (50–75%) in humans is associated revealed by conventional methods of lipoprotein isolation. with circulating HDL . Like many other HDL con- A limitation of this study is that our measurements stituents , apoE is involved in both immunoregulation are limited to the first 8 h after ET. While a longer and host defense . During infection, for example, period of observation would be desirable, it was still pos- apoE can multi-task and simultaneously neutralize LPS sible within this time to discern changes in lipoproteins and modulate lipoprotein trafficking . during the APR with a new level of precision and to Since atherosclerosis is accelerated in a number of identify LpA-II:B:C:D:E as a new acute phase reactant. chronic inflammatory diseases , it is relevant to the Longer studies are needed to determine the duration of present study that LpA-II:B:C:D:E particle number is LpAII:B:C:D:E elevation, the extent to which it and other increased and associated with progression of atheroscler- immunochemically-defined lipoprotein subclasses con- osis in patients with rheumatoid arthritis . Because tribute to the APR, and the degree to which changes our study indicates that this particle is an acute phase in their concentration correlate with inflammatory reactant closely linked to inflammation, it seems likely mediators. that it poses a similar risk in patients with Tangier dis- Other concerns are that our control subjects were ease who also develop cardiovascular disease prema- studied at different sites, their 8 h data was incomplete, turely . and some of their baseline lipid measures differed from The behavior we observe of the two major those of the ET group. While demographic differences immunochemically-defined HDL subpopulations, LpA-I likely account for the disparity in baseline lipids, the and LpA-I:A-II, after endotoxin add to the growing body changes exhibited in their plasma lipids during saline of information about the changes that HDL undergoes infusion correspond closely to those reported by during inflammation [49, 50]. Despite the extensive re- Hudgins under identical experimental conditions . modeling of HDL surface and core constituents and the Importantly, neither these site differences or our esti- decline in HDL-C and apoA-I that is known to occur dur- mating 8 h TG and TGRLP subclass values influenced ing the APR [19, 50], we show that the same percentage our conclusions. distribution of 25% LpA-I and 75% LpA-I:A-II present at baseline was maintained for 8 h after endotoxin. Conclusion We also provide preliminary information about the Employing an underutilized immunochemical method of transport of the exchangeable apoproteins apoE and measuring lipoproteins according to their apoprotein apoC-III during the APR. For the first 6 h, apoE asso- content, we have identified a new acute phase lipopro- ciated with HDL and the apoB lipoproteins (VLDL, IDL, tein whose apoprotein constituents have metabolic and and LDL) declined to a similar degree in both the ET immunoregulatory properties applicable to host defense and saline groups. By 8 h, however, the apoE present in that make it well constituted to engage in the APR. HDL in the ET group increased 28% above baseline as first reported in septic patients and identified as an acute Abbreviations APR: Acute phase response; BMI: Body mass index; ET: Endotoxin; HDL: High phase protein by Li et al. . In contrast to most other density lipoprotein; IDL: Intermediate density lipoprotein; LDL: Low density acute phase proteins that involve de novo hepatic syn- lioprotein; LPL: Lipoprotein lipase; LPS: Bacterial lipopolysaccharride; thesis, these workers found that the increase in apoE TG: Triglyceride; TGRLP: Triglyceride-rich lipoprotein; TLR: Toll-like receptor; TNF: Tumor necrosis factor; VLDL: Very-low density lipoprotein during sepsis resulted from a combination of inhibition of apoE degradation and down-regulation of hepatic Acknowledgements LDL receptors [38, 51]. The authors are grateful for the technical assistance of Carmen Quiroga and The movement of apoC-III from the apoB lipoproteins Carolyn Knight-Gibson and the facilities provided to the Lipid Research Laboratory by the Oklahoma Medical Research Foundation. (HP) to HDL (HS) resembled that of apoE but the mag- nitude was small, the number of observations limited, Funding and the changes were not statistically significant. In light CEM is supported by NIH grant R01 DK095926. BJ has been supported by of heightened awareness of the proinflammatory proper- the Austrian Science Funds (FWF SFB54–04). LCH was supported by the NIH ties of apoC-III and the key role that it and other HDL- GCRC Grant M01-RR00102. The content is solely the responsibility of the Bagdade et al. Lipids in Health and Disease (2018) 17:127 Page 8 of 9 authors and does not necessarily represent the official views of the National 9. Alaupovic P. Apolipoprotein composition as the basis for classifying plasma Institutes of Health. lipoproteins. Characterization of ApoA- and ApoB-containing lipoprotein families. Prog Lipid Res. 1991;30:105–38. 10. Alaupovic P. The concept of apolipoprotein-defined lipoprotein families and Availability of data and materials its clinical significance. Curr Atheroscler Rep. 2003;5:459–67. The data that support the results of this study are available from the 11. Agnani G, Bard JM, Candelier L, Delattre S, Fruchart JC, Clavey V. Interaction corresponding author on reasonable request. of LpB, LpB:E, LpB:C-III, and LpB:C-III:E lipoproteins with the low density lipoprotein receptor of HeLa cells. Arterioscler Thromb. 1991;11:1021–9. Authors’ contributions 12. Alaupovic P, Mack WJ, Knight-Gibson C, Hodis HN. The role of triglyceride- JB conceived the design of the study and bears primary responsibility for the rich lipoprotein families in the progression of atherosclerotic lesions as manuscript’s contents and drafting. CEM contributed to the analysis and determined by sequential coronary angiography from a controlled clinical display of the data and review of the manuscript. BJ provided blood samples trial. Arterioscler Thromb Vasc Biol. 1997;17:715–22. and LCH data from saline-infused control subjects obtained in Vienna and 13. Lee SJ, Campos H, Moye LA, Sacks FM. LDL containing apolipoprotein CIII is New York respectively. PA was responsible for all the lipid and lipoprotein an independent risk factor for coronary events in diabetic patients. analyses and preliminary data analysis. All authors have read and approved Arterioscler Thromb Vasc Biol. 2003;23:853–8. the content of the manuscript. 14. Sacks FM, Alaupovic P, Moye LA, Cole TG, Sussex B, Stampfer MJ, Pfeffer MA, Braunwald E. VLDL, apolipoproteins B, CIII, and E, and risk of recurrent Ethics approval and consent to participate coronary events in the cholesterol and recurrent events (CARE) trial. The protocol was approved by the Ethical Committee(s) of the Medical Circulation. 2000;102:1886–92. University of Vienna, Austria and of Copenhagen and Fredriksberg 15. Wheeler DS, Zingarelli B, Wheeler WJ, Wong HR. Novel pharmacologic Communities, DK and by the Institutional Review Boards of Rockefeller approaches to the management of sepsis: targeting the host inflammatory University and the Oklahoma Medical Research Foundation. Subjects were response. 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Lipids in Health and Disease – Springer Journals
Published: May 28, 2018
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