Enrichment of Triglyceride-Rich Lipoproteins with Apolipoprotein C-I Is Positively Associated with Their Delayed Plasma Clearance Independently of Other Transferable Apolipoproteins in Postmenopausal Overweight and Obese Women.

Background: The role of plasma apolipoprotein (apo) C-I in cardiometabolic risk in humans is unclear. However, in vitro studies showed a dual role for apoC-I, both protective and harmful, depending on the carrier lipoprotein.Objective: We tested the hypothesis that triglyceride (TG)-rich lipoprotein (TRL) apoC-I, not total or HDL apoC-I, is associated with delayed postprandial plasma clearance of TRLs, independently of apoC-II, apoC-III, and apoE.Methods: This cross-sectional study examines the plasma clearance of a 13C-triolein-labeled high-fat meal (68% fat energy) in 20 postmenopausal overweight and obese women [body mass index (in kg/m2) ≥27; aged 45-74 y] as the increment change in area under the 6-h postprandial curves (iAUC6h) of TRL parameters. Lipoproteins were fractionated by fast-protein LC. Transferable apolipoproteins were measured by ELISA. TRL enrichment with apolipoproteins was calculated by dividing their TRL concentrations by TRL apoB. The effects of human apoC-I and apoC-III on the hydrolysis and storage of 3H-triolein-labeled TRLs were tested in 3T3-L1 adipocytes.Results: TRL apoC-I was positively associated with plasma apo B-48 and total and non-HDL TGs, cholesterol, and apoB (r = 0.52-0.97) and negatively with HDL cholesterol (r = -0.52) and LDL diameter (r = -0.91) (P < 0.05). Total and HDL apoC-I were correlated only with total (r = 0.62) and HDL (r = 0.75) cholesterol. Women with high fasting TRL enrichment with apoC-I (99-365 µmol apoC-I/µmol apoB), but not apoC-II, apoC-III, or apoE, had higher iAUC6h for TGs (+195%), 13C-TGs (+319%), and apo B-48 (+186%) than those with low enrichment (14-97 µmol apoC-I/µmol apoB). The 4-h postprandial increase in TRL apoC-I was associated with a 4-h increase in TRL TGs and iAUC6h for TGs, 13C-TGs, and apo B-48 (r = 0.74-0.86, P < 0.001), independently of 4-h changes in TRL apoB, apoC-II, apoC-III, or apoE. ApoC-I and apoC-III inhibited 3H-TRL clearance by adipocytes by >75% (P < 0.001).Conclusions: TRL enrichment with apoC-I is positively associated with postprandial hypertriglyceridemia and remnant accumulation in postmenopausal overweight and obese women, independently of apoC-II, apoC-III, or apoE, which may be due to inhibiting TRL clearance by adipocytes. Reducing TRL apoC-I may ameliorate delayed postprandial plasma clearance of TRLs and associated risks in humans.

WAT apoC-I secretion: role in delayed chylomicron clearance in vivo and ex vivo in WAT in obese subjects.

Reduced white adipose tissue (WAT) LPL activity delays plasma clearance of TG-rich lipoproteins (TRLs). We reported the secretion of apoC-I, an LPL inhibitor, from WAT ex vivo in women. Therefore we hypothesized that WAT-secreted apoC-I associates with reduced WAT LPL activity and TRL clearance. WAT apoC-I secretion averaged 86.9 ± 31.4 pmol/g/4 h and 74.1 ± 36.6 pmol/g/4 h in 28 women and 11 men with BMI ≥27 kg/m(2), respectively, with no sex differences. Following the ingestion of a (13)C-triolein-labeled high-fat meal, subjects with high WAT apoC-I secretion (above median) had delayed postprandial plasma clearance of dietary TRLs, assessed from plasma (13)C-triolein-labeled TGs and apoB48. They also had reduced hydrolysis and storage of synthetic (3)H-triolein-labeled ((3)H)-TRLs in WAT ex vivo (i.e., in situ LPL activity). Adjusting for WAT in situ LPL activity eliminated group differences in chylomicron clearance; while adjusting for plasma apoC-I, (3)H-NEFA uptake by WAT, or body composition did not. apoC-I inhibited in situ LPL activity in adipocytes in both a concentration- and time-dependent manner. There was no change in postprandial WAT apoC-I secretion. WAT apoC-I secretion may inhibit WAT LPL activity and promote delayed chylomicron clearance in overweight and obese subjects. We propose that reducing WAT apoC-I secretion ameliorates postprandial TRL clearance in humans.

Low density lipoprotein delays clearance of triglyceride-rich lipoprotein by human subcutaneous adipose tissue.

Delayed clearance of triglyceride-rich lipoprotein (TRL) by white adipose tissue (WAT) promotes hypertriglyceridemia and elevated apoB-lipoproteins, which are primarily in the form of LDL. This study examines whether LDL promotes delayed clearance of TRL by WAT. Following the ingestion of a (13)C-triolein-labeled high-fat meal, obese women with high plasma apoB (> median 0.93 g/l, N = 11, > 98% as IDL/LDL) had delayed clearance of postprandial (13)C-triglyceride and (13)C-NEFA over 6 h compared with controls. AUC6 h of plasma (13)C-triglyceride and (13)C-NEFA correlated with plasma apoB but not with LDL diameter or adipocyte area. There was no group difference in (13)C-triolein oxidation rate, which suggests lower (13)C-NEFA storage in peripheral tissue in women with high apoB. Ex vivo/in vitro plasma apoB correlated negatively with WAT (3)H-lipid following a 4 h incubation of women's WAT with synthetic (3)H-triolein-TRL. LDL-differentiated 3T3-L1 adipocytes had lower (3)H-TRL hydrolysis and (3)H-NEFA storage. Treatment of women's WAT with their own LDL decreased (3)H-TRL hydrolysis and (3)H-NEFA uptake. Finally, LDL, although not an LPL substrate, reduced LPL-mediated (3)H-TRL hydrolysis as did VLDL and HDL. Exposure to LDL decreases TRL clearance by human WAT ex vivo. This may promote production of apoB-lipoproteins and hypertriglyceridemia through a positive-feedback mechanism in vivo.

White adipose tissue apolipoprotein C-I secretion in relation to delayed plasma clearance of dietary fat in humans.

OBJECTIVE: White adipose tissue (WAT) dysfunction is characterized by delayed clearance of dietary triglyceride-rich lipoproteins (TRL). We reported that apolipoprotein (apo) C-I, a transferable apolipoprotein that inhibits lipoprotein lipase activity when bound to TRL, was produced by a human adipocyte model. Thus, we aimed to determine whether increased WAT apoC-I secretion is related to delayed dietary fat clearance in humans. METHODS AND RESULTS: After the ingestion of a (13)C-triolein-labeled high-fat meal, postmenopausal obese women with high-fasting WAT apoC-I secretion (median >0.81 µmol/L per g/4 hours, n=9) had delayed postprandial plasma clearance of (13)C-triglyceride and (13)C-nonesterified fatty acids over 6 hours compared with controls. WAT apoC-I secretion over 4 hours correlated with fasting total and non-high-density lipoprotein apoC-I but not with high-density lipoprotein apoC-I and was the primary predictor of 4-hour postprandial increases in TRL apoC-I. Correction for TRL apoC-I eliminated the association of WAT apoC-I with 6-hour area under the curve of plasma (13)C-triglyceride; correction for insulin sensitivity or inflammation did not. Finally, in addition to apoC-I, WAT secreted considerable amount of apoC-II, apoC-III, and apoE over 24 hours; however, only WAT apoC-I secretion was associated with 6-hour area under the curve of plasma (13)C-triglyceride. CONCLUSIONS: Increased WAT apoC-I secretion in obese women is associated with delayed postprandial dietary fat clearance mediated by increased TRL apoC-I. Thus, we hypothesize that reducing WAT apoC-I secretion ameliorates WAT dysfunction and associated cardiometabolic risks in humans.

The loss-of-function PCSK9Q152H variant increases ER chaperones GRP78 and GRP94 and protects against liver injury.

Individuals harboring the loss-of-function (LOF) proprotein convertase subtilisin/kexin type 9 Gln152His variation (PCSK9Q152H) have low circulating low-density lipoprotein cholesterol levels and are therefore protected against cardiovascular disease (CVD). This uncleavable form of proPCSK9, however, is retained in the endoplasmic reticulum (ER) of liver hepatocytes, where it would be expected to contribute to ER storage disease (ERSD), a heritable condition known to cause systemic ER stress and liver injury. Here, we examined liver function in members of several French-Canadian families known to carry the PCSK9Q152H variation. We report that PCSK9Q152H carriers exhibited marked hypocholesterolemia and normal liver function despite their lifelong state of ER PCSK9 retention. Mechanistically, hepatic overexpression of PCSK9Q152H using adeno-associated viruses in male mice greatly increased the stability of key ER stress-response chaperones in liver hepatocytes and unexpectedly protected against ER stress and liver injury rather than inducing them. Our findings show that ER retention of PCSK9 not only reduced CVD risk in patients but may also protect against ERSD and other ER stress-driven conditions of the liver. In summary, we have uncovered a cochaperone function for PCSK9Q152H that explains its hepatoprotective effects and generated a translational mouse model for further mechanistic insights into this clinically relevant LOF PCSK9 variant.

White Adipose Tissue Surface Expression of LDLR and CD36 is Associated with Risk Factors for Type 2 Diabetes in Adults with Obesity.

OBJECTIVE: Human conditions with upregulated receptor uptake of low-density lipoproteins (LDL) are associated with diabetes risk, the reasons for which remain unexplored. LDL induce metabolic dysfunction in murine adipocytes. Thus, it was hypothesized that white adipose tissue (WAT) surface expression of LDL receptor (LDLR) and/or CD36 is associated with WAT and systemic metabolic dysfunction. Whether WAT LDLR and CD36 expression is predicted by plasma lipoprotein-related parameters was also explored. METHODS: This was a cross-sectional analysis of 31 nondiabetic adults (BMI > 25 kg/m2 ) assessed for WAT surface expression of LDLR and CD36 (immunohistochemistry), WAT function, WAT and systemic inflammation, postprandial fat metabolism, and insulin resistance (IR; hyperinsulinemic-euglycemic clamp). RESULTS: Fasting WAT surface expression of LDLR and CD36 was negatively associated with WAT function (3 H-triglyceride storage, r = -0.45 and -0.66, respectively) and positively associated with plasma IL-1 receptor antagonist (r = 0.64 and 0.43, respectively). Their expression was suppressed 4 hours postprandially, and reduced LDLR was further associated with IR (M/Iclamp , r = 0.61 women, r = 0.80 men). Plasma apolipoprotein B (apoB)-to-PCSK9 ratio predicted WAT surface expression of LDLR and CD36, WAT dysfunction, WAT NLRP3 inflammasome priming and disrupted cholesterol-sensing genes, and systemic IR independent of sex and body composition. CONCLUSIONS: Higher fasting and lower postprandial WAT surface expression of LDLR and CD36 is associated with WAT dysfunction, systemic inflammation, and IR in adults with overweight/obesity, anomalies that are predicted by higher plasma apoB-to-PCSK9 ratio.

Associations Between Soluble LDLR and Lipoproteins in a White Cohort and the Effect of PCSK9 Loss-of-Function.

Context: Elevated circulating cholesterol-rich low-density lipoprotein (LDL) particles increase coronary artery disease risk. Cell-surface hepatic LDL receptors (LDLRs) clear 70% of these particles from circulation. The ectodomain of LDLR is shed into circulation, preventing it from removing LDL particles. The role that LDLR ectodomain shedding plays as a regulatory mechanism is unknown. Objective: We describe LDLR shedding via the relationships between circulating soluble LDLRs (sLDLRs) and serum lipoproteins, serum proprotein convertase subtilin/kexin type 9 (PCSK9; a negative regulator of LDLR), and clinical parameters in a white Canadian population. Design: Population-based, cross-sectional study. Settings: Clinical Research Center, The Ottawa Hospital, and Faculty of Medicine, University of Ottawa. Participants: Two hundred seventy-three white Canadians. Intervention: None. Main Outcome Measures: sLDLR measured by ELISA; serum lipids and PCSK9, PCSK9 genotypes, and clinical parameters from previous analyses. Results: sLDLRs correlated strongly with triglycerides (TG; r = 0.624, P < 0.0001) and moderately with LDL cholesterol (r = 0.384, P < 0.0001), and high-density lipoprotein cholesterol (r = -0.307, P = 0.0003). Only TG correlations were unaffected by PCSK9 variations. sLDLR levels were significantly elevated in those with TG >50th or LDL cholesterol >75th percentiles. Conclusions: Serum sLDLR levels correlate with several lipoprotein parameters, especially TG, and the presence of PCSK9 loss-of-function variants alters sLDLR levels and correlations, except for TG. Ectodomain LDLR shedding has a role in LDL metabolism, distinct from PCSK9, with interplay between these two pathways that regulate cell-surface LDLRs. Findings suggest alteration of LDLR shedding could emerge as a target to treat dyslipidemia.

ApoB-lipoproteins and dysfunctional white adipose tissue: Relation to risk factors for type 2 diabetes in humans.

BACKGROUND: Elevated plasma apoB is an independent predictor of T2D; however, underlying mechanisms remain unclear. Chronic reduction in white adipose tissue (WAT) function promotes T2D. We reported that differentiation of preadipocytes and acute incubation of human WAT with LDL induce their dysfunction (decreased hydrolysis and storage of triglyceride-rich lipoproteins [TRL]). OBJECTIVE: To examine the hypothesis that the association of plasma apoB with T2D risk factors, hypertriglyceridemia (hyperTG), insulin resistance (IR), and hyperinsulinemia, was dependent on WAT dysfunction. METHODS: Thirty normoglycemic subjects were enrolled (≥27 kg/m2, 45-74 years). Fasting gynoid WAT biopsy was obtained followed by the ingestion of a 13C-triolein-labeled-high-fat meal. WAT function was measured ex vivo as the hydrolysis and storage of 3H-triolein-labeled-TRL as 3H-lipids over 4 hours. Insulin sensitivity and secretion were measured by Botnia clamps. RESULTS: WAT function correlated with higher insulin sensitivity (M/Iclamp r = 0.60) and faster plasma clearance of chylomicrons in women (iAUC6hrs apoB48, r = -0.60). Plasma apoB correlated with WAT dysfunction (r = -0.52), postprandial hyperTG (iAUC6hrs-TG, r = 0.51, 13C-TG, r = 0.48), IR (M/Iclamp r = -0.38) and hyperinsulinemia (second phase-glucose-induced-insulin-secretion, r = 0.41). Co-incubation of subjects' WAT with their LDL increased medium accumulation of 3H-TRL and 3H-NEFA with no sex differences. Adjusting for WAT function eliminated the association of plasma apoB with IR independent of sex and body fat or adipocyte diameter. Its association with other risk factors was unaffected. CONCLUSIONS: Association of plasma apoB with IR in obese subjects is dependent on gynoid WAT dysfunction. We propose that targeting hyperapoB, without increasing their uptake into nonhepatic peripheral tissues, ameliorates WAT function and risk for T2D.

Statins upregulate PCSK9, the gene encoding the proprotein convertase neural apoptosis-regulated convertase-1 implicated in familial hypercholesterolemia.

OBJECTIVE: Neural apoptosis-regulated convertase (NARC)-1 is the newest member of the proprotein convertase family implicated in the cleavage of a variety of protein precursors. The NARC-1 gene, PCSK9, has been identified recently as the third locus implicated in autosomal dominant hypercholesterolemia (ADH). The 2 other known genes implicated in ADH encode the low-density lipoprotein receptor and apolipoprotein B. As an approach toward the elucidation of the physiological role(s) of NARC-1, we studied its transcriptional regulation. METHODS AND RESULTS: Using quantitative RT-PCR, we assessed NARC-1 regulation under conditions known to regulate genes involved in cholesterol metabolism in HepG2 cells and in human primary hepatocytes. We found that NARC-1 expression was strongly induced by statins in a dose-dependent manner and that this induction was efficiently reversed by mevalonate. NARC-1 mRNA level was increased by cholesterol depletion but insensitive to liver X receptor activation. Human, mouse, and rat PCSK9 promoters contain 2 typical conserved motifs for cholesterol regulation: a sterol regulatory element (SRE) and an Sp1 site. CONCLUSIONS: PCSK9 regulation is typical of that of the genes implicated in lipoprotein metabolism. In vivo, PCSK9 is probably a target of SRE-binding protein (SREBP)-2.

The apoB-to-PCSK9 ratio: A new index for metabolic risk in humans.

BACKGROUND: Proprotein convertase subtilisin/kexin type 9 (PCSK9) shuttles low-density lipoprotein (LDL) receptors for degradation, thus upregulates LDL plasma clearance. Although PCSK9 loss of function is cardioprotective, its role in metabolic risks remains unknown. Increased apoB-lipoproteins uptake into nonhepatic tissues such as white adipose tissue (WAT) induces their dysfunction, which may be favored by lower plasma PCSK9. We hypothesized that lower plasma PCSK9 relative to apoB, or higher apoB-to-PCSK9 ratio, is a better predictor of metabolic disturbances than PCSK9 alone in humans. METHODS: Thirty-three men and 48 postmenopausal women (>27 kg/m(2), aged 45-74 years, normoglycemic) underwent in-depth assessment of glucose and fat metabolism using high-fat meals, WAT biopsies, intravenous glucose-tolerance tests, and hyperinsulinemia clamps. RESULTS: Plasma apoB correlated positively with fasting and postprandial triglycerides and chylomicron clearance (R = 0.44-0.66) and glucose-stimulated insulin secretion (R = 0.24) and negatively with insulin sensitivity (R = -0.28) and gynoid WAT in situ lipoprotein lipase activity (ie, ex vivo WAT function, R(2) = 0.34). Neither PCSK9 nor LDL cholesterol associated with these risks. In regression analysis that adjusted for body mass index, lower plasma PCSK9 strengthened the association of apoB to WAT dysfunction and insulin resistance. Moreover, plasma apoB-to-PCSK9 ratio correlated positively with all these metabolic risks and further associated positively with android-to-gynoid fat ratio (R = 0.41) and negatively with gynoid fat mass (R = -0.23, all P ≤ .05). No significant sex differences existed in these associations. CONCLUSIONS: Lower plasma PCSK9 relative to apoB associates with metabolic risks and WAT dysfunction in normoglycemic obese subjects. We hypothesize that the plasma apoB-to-PCSK9 ratio provides a better clinical index than PCSK9 alone for monitoring early metabolic disturbances that may be promoted by reduction in plasma PCSK9.

Changes in total and central fat mass after a hypocaloric diet associate with changes of apoC-I in postmenopausal obese women.

BACKGROUND: We previously reported the secretion of apolipoprotein apoC-I, apoC-II, apoC-III, and apoE from adipose tissue in postmenopausal obese women, suggesting their potential regulation by energy balance in humans. OBJECTIVE: We examined the changes of these apolipoproteins, in relation to changes in cardiometabolic risks, following a hypocaloric diet in overweight/obese women. METHODS/RESULTS: A total of 137 postmenopausal overweight/obese women who were free of chronic disease were examined at baseline, 56 women of whom were reevaluated following a 6-month hypocaloric diet. At baseline, there was no association between the plasma transferable apolipoproteins with any index of adiposity, insulin sensitivity, lipids, or inflammation, except for apoE with peripheral fat mass (r = 0.18, P < .05), and apoC-II and apoC-III with cholesterol (r = 0.23 and r = 0.20 respectively, P < .05). The hypocaloric diet reduced adiposity, insulin resistance, and inflammatory markers but had no significant effects on plasma transferable apolipoproteins or lipids, whose average concentrations were within normal range at baseline. The changes in total and central, but not peripheral, fat mass associated with changes of apoC-I only (r = 0.28 and r = 0.43; respectively, P < .05). Post-weight-loss apoC-I increased in some women (52%) yet it decreased in others, however there were no differences in cardiometabolic risk factors between the 2 groups. CONCLUSIONS: Plasma apoC-I, apoC-II, apoC-III, and apoE are not associated with adiposity, insulin sensitivity, or inflammation in obese but healthy postmenopausal women. Post-weight-loss changes of total and central fat mass associate with changes of apoC-I.

Annexin A2 is a natural extrahepatic inhibitor of the PCSK9-induced LDL receptor degradation.

Proprotein convertase subtilisin/kexin-9 (PCSK9) enhances the degradation of hepatic low-density lipoprotein receptor (LDLR). Deletion of PCSK9, and loss-of-function mutants in humans result in lower levels of circulating LDL-cholesterol and a strong protection against coronary heart disease. Accordingly, the quest for PCSK9 inhibitors has major clinical implications. We have previously identified annexin A2 (AnxA2) as an endogenous binding partner and functional inhibitor of PCSK9. Herein, we studied the relevance of AnxA2 in PCSK9 inhibition and lipid metabolism in vivo. Plasma analyses of AnxA2(-/-) mice revealed: i) a ∼1.4-fold increase in LDL-cholesterol without significant changes in VLDLs or HDLs, and ii) a ∼2-fold increase in circulating PCSK9 levels. Western blotting and immunohistochemistry of AnxA2(-/-) tissues revealed that the LDLR was decreased by ∼50% in extrahepatic tissues, such as adrenals and colon. We also show that AnxA2-derived synthetic peptides block the PCSK9≡LDLR interaction in vitro, and adenoviral overexpression of AnxA2 in mouse liver increases LDLR protein levels in vivo. These results suggest that AnxA2 acts as an endogenous regulator of LDLR degradation, mostly in extrahepatic tissues. Finally, we identified an AnxA2 coding polymorphism, V98L, that correlates with lower circulating levels of PCSK9 thereby extending our results on the physiological role of AnxA2 in humans.

Characterization of a new LCAT mutation causing familial LCAT deficiency (FLD) and the role of APOE as a modifier gene of the FLD phenotype.

Familial LCAT deficiency (FLD) is a disease characterized by a defect in the enzyme lecithin:cholesterol acyltransferase (LCAT) resulting in low HDL-C, premature corneal opacities, anemia as well as proteinuria and renal failure. We have identified the first French Canadian kindred with familial LCAT deficiency. Two brothers, presenting classical signs of FLD, were shown to be homozygous for a novel LCAT mutation. This c.102delG mutation occurs at the codon for His35 and causes a frameshift that stops transcription at codon 61 abolishing LCAT enzymatic activity both in vivo and in vitro. It has a dramatic effect on the lipoprotein profile, with an important reduction of HDL-C in both heterozygotes (22%) and homozygotes (88%) and a significant decrease in LDL-C in heterozygotes (35%) as well as homozygotes (58%). Furthermore, the lipoprotein profile differs markedly between the two affected brothers who had different APOE genotypes. We propose that APOE could be an important modifier gene explaining heterogeneity in lipoprotein profiles observed among FLD patients. Our results suggest that a LCAT-/- genotype associated with an APOE epsilon2 allele could be a novel mechanism leading to dysbetalipoproteinemia.

Apolipoprotein E limits oxidative stress-induced cell dysfunctions in human adipocytes.

Oxidative stress in adipose tissue constitutes a pathological process involved in obesity-linked metabolic disorders. Apolipoprotein E (apoE), which exhibits antioxidant properties in plasma and brain, is highly produced by adipose tissue and adipocytes. In this study, we investigated the role of apoE in the human adipocyte response to oxidative stress. We first demonstrated that apoE secretion by adipocytes was stimulated by oxidative stress. We also observed that apoE overexpression protected adipocytes from hydrogen peroxide-induced damages, by mitigating intracellular oxidation and exerting extracellular antioxidant properties. Our findings clearly show a novel antioxidant role for apoE in adipose tissue.

Synthesis and secretion of apoC-I and apoE during maturation of human SW872 liposarcoma cells.

Little is known about the regulation of apolipoprotein (apo) C-I production by human adipocytes. The aim of the present study, therefore, was to investigate the effect of different tissue culture conditions on the synthesis and secretion of apoC-I and apoE in human SW872 liposarcoma cells. After 3-4 d in culture (0.5 x 10(6) cells/well, DMEM/F-12 medium with 10% fetal calf serum), cells reached confluence and became growth arrested. The molar ratio of apoE:apoC-I in the cell was 8.9 +/- 0.6 and in the medium was 6.6 +/- 0.5. After 17 d in culture, SW872 cells contained significantly more cholesterol (100%) and triglyceride (3-fold) and secreted more apoC-I [4 vs. 17 d: 0.11 +/- 0.01 vs. 0.23 +/- 0.01 pmol/(10(6) cells . 24 h), P < 0.001] and apoE [0.7 +/- 0.1 vs. 3.1 +/- 0.3 pmol/(10(6) cells . 24 h), P < 0.001]. Cellular apoC-I increased 7-fold and apoE increased 16-fold. Cell maturation was associated with significantly higher levels of apoE mRNA but not apoC-I mRNA. Increases in cell lipids, apoC-I, and apoE were not dependent on the presence of extracellular lipids because similar changes occurred in cells incubated with lipoprotein-deficient serum or in cells incubated without serum. Treatment (7 d) of cells during maturation with insulin (10 or 1000 nmol/L) significantly reduced the secretion of apoC-I and apoE. These results demonstrate that in maturing SW872 cells, cholesterol and triglyceride accumulation in the presence or absence of extracellular lipids, is associated with increased apoC-I and apoE production. Furthermore, apoC-I and apoE production are differentially regulated at the transcriptional level, and long-term treatment with insulin has an inhibitory rather than stimulatory effect on apoC-I and apoE production.