Plasma Triglyceride Determines Structure-Composition in Low and High Density Lipoproteins

Transcription

1 Plasma Triglyceride Determines Structure-Cmpsitin in Lw and High Density Lipprteins Richard J. Deckelbaum, Esther Grant, Yitzchak Oschry, Lynda Rse, and Shlm Eisenberg Because the assciatin f hypertriglyceridemia and premature athersclersis is nt due t the direct effects f the triglyceride mlecule itself, we studied the effects f increased plasma triglyceride-rich lipprteins n the cmpsitin and structure f lw density lipprtein (LDL) and high density lipprtein (HDL). We fund prfund changes in the cre and surface dmains f bth lipprteins with increasing triglyceridemia. Cre chlesterl esters were prgressively depleted and replaced by triglyceride mlecules. Highly significant negative crrelatins were fund between chlesterl ester/prtein ratis (r = fr LDL and fr HDL (p < 0.001); psitive crrelatins were fund fr triglyceride/prtein ratis (r = 0.62 fr LDL and 0.58 fr HDL) and fr triglyceride/chlesterl ester ratis (r = 0.70 fr LDL and 0.83 fr HDL) when these variables were assayed as a functin f plasma triglyceride cncentratins. With severe hypertriglyceridemia, triglyceride/chlesterl ester ratis f mre than 1.0 were cnsistently bserved (nrmal, <0.02). This leads t an underestimatin f LDL and HDL levels when chlesterl alne is measured. t the surface, LDL and HDL were depleted f phsphlipid and free chlesterl, with a relative enrichment f prtein. These changes can be explained n the basis f high levels f plasma triglyceride-rich lipprteins serving as acceptrs fr chlesterl esters and ther cnstituents frm LDL and HDL. Cncmitantly, triglycerides are transferred t LDL and HDL. These transfer prcesses are likely t be mediated by the activity f lipid transfer prteins present in human plasma. (rterisclersis 4: , May/June 1984) Increased levels f plasma lw density lipprtein (LDL) chlesterl 1 and very lw density lipprtein (VLDL) chlesterl and triglyceride 2 are risk factrs fr premature athersclersis. Cnversely, high levels f high density lipprtein (HDL) chlesterl have been crrelated with lngevity and freedm frm early crnary disease. 34 Fr example, high levels f LDL and nrmal levels f HDL are cnsidered a Frm the Departments f Gastrenterlgy, Pediatrics, and Medicine B, Hadassah University Hspital, Hebrew University- Hadassah Medical Schl, Jerusalem, Israel; and the Bistatistics Labratry, Bstn University Medical Center, Bstn, Massachusetts. Lynda Rse is at the Bistatistics Labratry, Bstn University Medical Center, Bstn, Massachusetts. This wrk was supprted by Grants 1901 and 3022 frm the United States-Israel Binatinal Science Fundatin, U.S. Public Health Service Grant HL-23864, and the Children's Nutritinal Disease Prject, Canadian Friends f the Hebrew University. ddress fr reprints: Dr. Richard J. Deckelbaum, Department f Gastrenterlgy, Hadassah University Hspital, P.O. Bx 12000, Jerusalem, Israel Received July 28, 1983; revisin accepted January 11, cause f accelerated crnary artery disease in familial hyperchlesterlemia. 5 The increased risk fr crnary artery disease bserved in hypertriglyceridemia, hwever, is prly understd and prbably des nt reflect the direct effects f the triglyceride mlecule itself. Recently, Hulley and assciates 6 have suggested that the lw HDL chlesterl levels fund in hypertriglyceridemic patients cntribute significantly t this phenmen. Such patients als have lw LDL chlesterl levels and high VLDL chlesterl and triglyceride levels. The metablic pathways respnsible fr these bservatins have nt been previusly elucidated. In this paper we suggest that these abnrmalities may merely reflect the state f hypertriglyceridemia. Specifically, we prpse that the replacement f chlesterl ester in HDL and LDL by triglycerides cntributes t the lw levels f chlesterl in these lipprteins. In recent in vitr experiments, 7 " 9 we shwed that chlesterl ester-triglyceride bidirectinal transfer prcesses, riginally bserved by Nichls and Smith, 10 play a majr rle in determining the structure and cmpsitin f LDL and HDL. We

2 226 RTERIOSCLEROSIS VOL 4, N 3, MY/JUNE 1984 nw prvide evidence that these prcesses als mediate structure-cmpsitin relatinships f LDL and HDL in viv. The metablic cnsequences f these pathways help in understanding the increased athergenicity assciated with hypertriglyceridemia. Methds LDL and HDL were islated frm the plasma f 43 male and female subjects with plasma triglyceride levels between 31 mg/dl and 2820 mg/dl and plasma chlesterl levels between 28 mg/dl and 494 mg/dl. These subjects were nt selected specifically fr this study but, rather, prvided plasma fr a variety f lipprtein-related studies being carried ut in ur labratries. The subject with the lwest plasma lipid levels (chlesterl 28 mg/dl and triglyceride 31 mg/dl) had abetalipprteinemia. One subject with plasma triglyceride levels ver 1000 mg/dl had Type IV hyperlipidemia, ne had apprtein C-ll deficiency, and the thers were children with Type I primary hypertriglyceridemias assciated with variable patterns f lipase deficiencies. ll ther bld dnrs were either nrmlipemic r phentypically Type IV hyperlipidemic adults. ll patients with hypertriglyceridemia had nrmal r lw LDL levels. We did nt differentiate between familial cmbined hyperlipprteinemia and familial hypertriglyceridemia because f lack f data n family members. Venus bld samples in disdium EDT (1 mg/ml) were btained after a 12- t 14-hur fast, and LDL and HDL were separated using either sequential salt density 11 r rate znal ultracentrifugatin. 12 With the first methd, LDL was recvered between the densities f and g/ml and HDL, between and 1.21 g/ml. With the secnd methd, LDL and HDL were btained directly frm the znal rtr effluent at the end f 140 minutes r 22 hurs f centrifugatin runs, respectively, in a 14Ti rtr, as previusly detailed. 13 The LDL and HDL were dialyzed against several changes f nrmal saline (0.15 M NaCI-1 mm EDT, ph 8.5, 100:1 (vl/vl). Lipids were extracted with chlrfrm/methanl 2:1 (vl/ vl). 14 The ttal phsphlipid cntent was determined using the methd f Bartlett. 15 The ttal chlesterl was determined using the methd f Chiamri and Henry, 16 and thin-layer chrmatgraphy was used t separate free and esterified chlesterl. 17 The triglyceride cntent was determined by the utnalyzer methd. 18 The prtein cntent was measured by the methd f Lwry et al. 19 Pearsn prduct-mment crrelatin and partial crrelatin analyses were perfrmed t determine the assciatins between individual lipprtein cnstituents and/r cmbinatins f cnstituents and plasma triglyceride and plasma chlesterl levels. T crrect the marked skew in plasma triglyceride levels at higher cncentratins, plasma triglyceride levels were transfrmed t lgarithmic scales (lg 10). Linear regressin analysis was perfrmed by the methd f least squares. nalysis f variance fr the regressin was perfrmed t btain the significance f F ratis. 20 ll 43 subjects had LDL analyzed; 40 subjects had HDL analyzed. LDL and HDL were separated frm the plasma f 20 subjects by salt density ultracentrifugatin; in the remaining subjects rate znal ultracentrifugatin was used. separate analysis f variables recrded with each centrifugatin methd shwed n significant differences; therefre, data frm bth grups, i.e., salt density and znal ultracentrifugatin grups, were pled. Results The cmpsitin f LDL and HDL in subjects were divided ver three ranges f plasma triglyceride levels (<250, , >1000 mg/dl) and demnstrated several cnsistent changes (Table 1). With increased triglyceridemia, the relative cntributin f prtein and triglyceride increases, and that f phsphlipid, free chlesterl, and chlesterl ester de- Table 1. Cmpsitin nalysis f LDL and HDL ver Three Ranges f Plasma Triglyceride Levels Plasma triglyceride cncentratin (mg/dl) Lw density < >1000 High density < >1000 lipprtein (18) (18) (5) lipprtein (19) (17) (4) Prtein (LDL) 22.9± ± ±6.1 (HDL) 51.5± ± ±5.1 Phsphlipid 22.4 ± ± ± ± ± ±4.8 Chlesterl, free 9.3±1.1.9± ± ± ± Chlesterl, ester 39.0 ± ± ± ± ±3.2 Triglyceride 6.5± ± ± ± ± ±1.7 Numbers in parentheses refer t the number f subjects studied in each grup. Since full cmpsitin analysis was available in nly 41 f the 43 subjects analyzed fr LDL, the ttal number in the three grups is 41 fr LDL. Cmpsitin is expressed as the relative percentage f weight cntributin t ttal lipprtein mass, mean ± SD.

3 PLSM TRIGLYCERIDES ND LDL-HDL COMPOSITION Deckelbaum et al. 227 Table 2. Relative Cntributin f Individual Cnstituents t Ttal LDL and HDL Mass Crrelated with Plasma Triglyceride Cncentratins Lw density lipprtein (LDL) Prtein Phsphlipid Free chlesterl Chlesterl ester Triglyceride N. High density lipprtein (HDL) Prtein Phsphlipid Free chlesterl Chlesterl ester Triglyceride N. < (N.S.) (N.S.) (N.S.) (N.S.) (0.035) (0.060) (N.S.) (0.002) (0.023) Crrelatin cefficients (r) Plasma triglyceride cncentratins (mg/dl) <1000 ll subjects (0.02) (N.S.) (0.007) (N.S.) (0.02) (N.S.) (N.S.) (0.002) ( (0.003) (0.040) 41 (0.020) (0.060) (0.013) r refers t the cefficient f crrelatin between the relative weight cntributin (percentage f ttal lipprtein mass) f an individual cmpsitinal cmpnent and lg 10 plasma triglyceride cncentratin fr each grup f subjects. Numbers in parentheses give the p value fr the cefficient f crrelatin. NS = nt significant, with p > creases. The crrelatin f individual cmpnents t the relative lipprtein mass ver the entire range f plasma triglyceride levels demnstrates similar significant trends (Table 2). In bth LDL and HDL, the decrease f chlesterl ester and the increase in triglyceride are highly significant. In lipprteins, phsphlipid, prtein, and free chlesterl make up the surface shell f the particle emulsifying the cre neutral lipids, chlesterl ester and triglyceride. T better understand the events that affect the structure, cmpsitin, and metablism f the particles, we crrelated the ratis f different cmpnents cntained in the tw dmains f the lipprtein with cntinually increasing plasma triglyceride (Table 3, Figure 1). In the cre, the amunt f triglyceride relative t chlesterl ester was highly crrelated t plasma triglyceride levels, and this rati increased very substantially with triglyceridemia (Figure 1, Table 3). Cnsidering the entire range f plasma triglycerides, we nted sme differences between LDL and HDL (Figure 1). In LDL, the increase f triglyceride/chlesterl ester rati was mderate at plasma triglyceride levels belw 1000 mg/dl, but increased steeply with mre severe hypertriglyceridemia. This was reflected in the crrelatin cefficients f LDL triglyceride/chlesterl ester ratis vs (lg) plasma triglyceride cncentratins: 0.37 (p < 0.020) at plasma triglyceride levels less than 1000 mg/dl and 0.70 (p < 0.001) fr the entire grup. By cntrast, in HDL the increase f the triglyceride/chlesterl ester rati was linear ver the entire range f plasma triglyceride levels with a crrelatin cefficient f 0.77 (p < 0.001) fr plasma triglyceride levels less than 1000 mg/dl and 0.83 (p < 0.001) fr all subjects. Table 3. Mass Ratis f Different Cnstltutents f LDL and HDL Crrelated with Plasma Triglyceride Cncentratins Mass rati LDL(r) Triglyceride/ chlesterl ester Triglyceride/ phsphlipid Triglyceride/prtein Triglyceride/ (phsphlipid + prtein + free chlesterl) Chlesterl ester/ phsphlipid Chlesterl ester/ prtein Chlesterl ester/ (phsphlipid + prtein + free chlesterl) Phsphlipid/prtein (Chlesterl ester + triglyceride)/ (phsphlipid + prtein + free chlesterl) (NS) (NS) (0.004) (0.017) (0.070) (NS) (NS) Mass ratis were calculated frm the relative cncentratins f individual lipprtein cnstituents n a weight/ weight basis, r refers t cefficient f crrelatin f the given rati and t lg- i plasma triglyceride cncentratin ver the entire range f plasma triglycerides in all subjects. Numbers in parentheses are the p values fr each crrelatin cefficient. NS = nt significant (p > 0.10).

4 228 RTERIOSCLEROSIS VOL 4, N 3, MY/JUNE 1984 LJJ O O LDL 1.60 r= 0.70 Intercept = Slp«: n u - i 0 I r, 0.83 Intercept = Slpe = OtO (1 ' 1 i LDL * 1 5 LU r= Intercept: 3 02 Slpes n -.,,...1 r=-0 58 Intercept 1069 Slpe =-0.16 UJ LL c Prtei _i Q. r^o Intercepts 0-57 Slpe « n Intercept = 0 35 Slpe = Plasma Triglyceridc (mg/d!) Figure 1. Mass ratis f LDL and HDL cnstituents cmpared t plasma tnglyceride cncentratins. Triglyceride/chlesterl ester ratis in LDL () and in HDL (B). Chlesterl ester/prtein ratis in LDL (C) and in HDL (D). (Triglyceride + chlesterl ester)/(phsphlipid + prtein + free chlesterl) ratis in LDL (E) and in HDL (F). Ratis are pltted as a functin f plasma triglyceride cncentratins. t the surface, the phsphlipid/prtein rati decreased with elevated plasma triglyceride cncentratins, but the degree f crrelatin reached statistical significance (p < 0.05) nly fr LDL. The ratis f cre cnstituents t individual r cmbined surface cnstituents changed accrdingly, i.e., highly significant psitive crrelatins were bserved fr triglyceride and negative crrelatins were seen fr chlesterl ester. Since neutral lipid transfers are nt significantly assciated with the transfer f LDL and HDL majr apprteins, 78 the lss f chlesterl ester mlecules frm bth LDL and HDL was substantiated by a decreasing chlesterl ester/prtein rati with increasing triglyceridemia (Figure 1). n exceptin, the chlesterl ester/phsphlipid rati, did nt seem t crrelate with plasma triglyceride levels (Table 3). These findings suggest that, as triglyceride increases in plasma, chlesterl ester leaves the cre f LDL and HDL and is replaced by triglyceride. If this assumptin is crrect, then the rati f the ttal cre cmpnents (triglyceride + chlesterl ester) t the ttal surface cmpnents (prtein + phsphlipid + free chlesterl) shuld change little ver the wide range f plasma triglyceride levels studied. The data in Table 3 and Figure 1 demnstrate that this is the case. In the subjects studied, plasma chlesterl levels crrelated with plasma triglyceride levels (r = 0.55, p < 0.001). Using Pearsn partial crrelatin cefficient analysis, we fund n significant crrelatin f any f the variables presented in Tables 1-3 with plasma chlesterl levels after an adjustment fr the effect f plasma triglyceride n chlesterl levels.

5 PLSM TRIGLYCERIDES ND LDL-HDL COMPOSITION Deckelbaum et al. 229 Discussin ssciatins between accelerated athersclersis, premature crnary heart diseases, and hypertriglyceridemia have been shwn in almst every study relating plasma lipids and athersclersis. Fr example, Hulley and clleagues 6 cite n less than 27 studies where significant crrelatins between these factrs were reprted using unadjusted plasma triglyceride levels. Whether it is the triglyceride mlecule itself, hwever, that is athergenic is nt knwn, and it is pssible that ther abnrmalities in plasma lipprteins r their cnstituents are respnsible fr the increased athergenicity (e.g., lw HDL levels). Hence, the imprtance f defining lipprtein systems in hypertriglyceridemia. bnrmal cmpsitin f lw and high density lipprteins has been previusly shwn in patients with unusually severe hypertriglyceridemia. 21 " 24 In the present study, we demnstrated that specific graded alteratins f cre and surface cnstituents in bth LDL and HDL are directly and cntinuusly related t plasma triglyceride levels. These changes especially affect the lipprtein cre lipids. Mdels fr lipprtein structure predict that the bulk f neutral lipids (chlesterl ester, triglyceride) are lcalized in the hydrphbic cre f the particle surrunded by mre hydrphbic surface cnstituents (phsphlipids, free chlesterl, and prtein). 25 We shw here that, in the frame f this general mdel, the cre f bth LDL and HDL underg cnsiderable alteratin in the prprtins f chlesterl ester and triglycerides. These changes ccur in a predictable fashin dependent n plasma triglyceride r VLDL levels, since VLDL carries mst f the triglyceride in plasma. These mdificatins can be explained by the activity f a prtein(s) present in human plasma that transfers chlesterl ester frm LDL and HDL t VLDL and, in the ppsite directin, triglyceride frm VLDL t LDL and HDL. 26 " 28 This suggestin is supprted by recent bservatins that, indeed, chlesterl ester-rich LDL and HDL are substantially mdified tward chlesterl ester-pr, triglyceride-rich particles in vitr after incubatin with high levels f VLDL and in the presence f lipid transfer prteins. 7 ' 8 These changes are directly related t the amunts f VLDL relative t LDL r HDL and the time f incubatin. 78 It seems, therefre, that the underlying pathways respnsible fr cre lipid alteratins in hypertriglyceridemia are similar transfers f cre lipids in subjects with high plasma triglyceride levels and prlnged circulating times f their triglyceride-rich lipprteins. 29 " 31 t the lipprtein surface, we fund a fall in free chlesterl and phsphlipids, with increased prtein crrelating t increasing triglyceridemia. Free chlesterl distributes between surface and cre dmains f lipprteins 32 and in the presence f high levels f VLDL, the free chlesterl plasma pl must redistribute tward a prepnderance in the large VLDL ppulatin. Our finding f a cnstant chlesterl ester/phsphlipid rati independent f plasma triglyceride levels is cnsistent with cupled transfer f these tw mlecules in viv as has been suggested in vitr. 33 Mrever, increases in chlesterl esterificatin via the lecithin chlesterl acyltransferase reactin, which cnsumes bth free chlesterl and phsphlipid, are described in hypertriglyceridemia. 34 Finally, since the majr LDL and HDL apprteins (B, -l, and -ll) d nt redistribute with these transfer prcesses, 78 they remain n the particles and their relative cntributin t the surface increases. practical cnsequence f ur bservatins is that LDL and HDL chlesterl measurements in the presence f increased plasma triglycerides d nt accurately reflect plasma LDL and HDL levels. This is in agreement with the cnclusins f Phillips et al. 35 wh reprted that falling HDL chlesterl with increasing plasma VLDL triglyceride was relatively much greater than cncmitant slight decreases in plasma's majr HDL prtein, ap -l. These authrs fund increasing abslute amunts f HDL triglycerides crrelating with plasma VLDL triglyceride. n earlier study by the same grup 36 reprted that the rati f ttal chlesterl t triglycerides in LDL and HDL decreased as serum triglyceride levels increased. In hypertriglyceridemic diabetics, decreasing HDL chlesterl and increasing HDL triglyceride crrelated with increasing ttal plasma triglyceride, but plasma apprtein -l levels did nt. 37 Our present study shws that the decrease f chlesterl in LDL and HDL in hypertriglyceridemia is due mainly t a decrease in chlesterl ester in the lipprtein particle, with a smaller decline in free chlesterl. Therefre, in bth LDL and HDL, we suggest that measurements f decreased chlesterl cntent may nt reflect a parallel decrease in the number f circulating particles. The pathways respnsible fr these lipprtein cmpsitinal changes als predict that in hypertriglyceridemia, bth LDL and HDL wuld be smaller and denser due t the lss f chlesterl esters fr triglyceride, cncmitant with LDL and HDL triglyceride hydrlysis. Cnversely, in a situatin such as abetalipprteinemia, where plasma is lacking in VLDL t accept chlesterl ester, ne culd predict that chlesterl ester accumulates in HDL. 9 Figure 2 illustrates that, indeed, this is the case in cntrasting znal ultracentrifugatin elutin prfiles f nrmal HDL with that f HDL in patients with severe hypertriglyceridemia r abetalipprteinemia. similar bservatin f small, dense HDL in hypertriglyceridemia has been reprted by Patsch and Gtt. 38 LDL, as well, has been decribed as smaller and denser in hypertriglyceridemia relative t nrmlipemic subjects. 39 Inspectin f the relative weight cmpsitin data presented in Table 1 des nt shw the bvius decreases in ttal cre/ttal surface cnstituent ratis that might be expected with decreasing particle size.

6 230 RTERIOSCLEROSIS VOL 4, N 3, MY/JUNE V c re r beta Nrmal Type IV HM) Effluent Vlume (ml) 500 Figure 2. Separatin by rate znal ultracentrifugatin f HDL in a nrmal subject ( ), a patient with abetalipprteinemia ( ), and a patient with Type IV hyperlipidemia ( ). The plasma triglyceride cncentratins were 130,31, and 927 mg/dl in each subject, respectively. Flatatin is frm the left t the right, with the lighter and larger particles eluting earlier than the denser and smaller particles. In abetalipprteinemia, the majr HDL peak elutes earlier than in nrmal HDL. Cnversely, in the subject with hypertriglyceridemia, HDL elutes later than in nrmal HDL. When we calculated* lipprtein partial specific vlumes, 40 hwever, bth LDL and HDL shwed a tendency tward denser particles. In LDL, partial specific vlume fell frm ml/g t ml/g, mving frm the <250 mg/dl plasma triglyceride grup t the mg/dl grup. In the severe hypertriglyceridemic grup (>1000 mg/dl), LDL partial specific vlume was ml/g. Similarly in HDL, partial specific vlumes decreased frm t ml/g between the lwest and highest plasma triglyceride level grups, respectively. We believe these differences wuld be greater if a mre hmgeneus grup f hypertriglyceridemic subjects were studied. The grup with plasma triglyceride levels ver 1000 mg/dl, fr example, cntained mainly patients with severe Type l-like hyperlipprteinemia; ne patient had a deficiency f lipprtein lipase activatr, apprtein C-ll, while thers were children in whm classificatin f their severe primary hypertriglyceridemia was difficult because f a heterge- *LDL and HDL partial specific vlumes were calculated by summing the partial specific vlume cntributin f individual particle cnstituents where the partial specific vlumes were as fllws: prtein, ml/g; phsphlipid, ml/g; free chlesterl, ml/g; chlesterl ester, ml/g; and triglyceride, ml/g. neus pattern f lipase deficiencies. 41 Indeed, in an nging evaluatin f a hmgeneus grup f nrmal and hypertriglyceridemic subjects (nne with lipase deficiencies) befre and after treatment with lipid lwering agents, bth LDL and HDL were clearly smaller and denser with increasing triglyceridemia (S. Eisenberg, Y. Oschry, R. Deckelbaum, and D. Gavish, unpublished data). The effects f deficiencies f different lipases cncmitant with hypertriglyceridemia, n lipprtein structure-cmpsitin remains t be determined. D the lipprtein cmpsitinal changes that ccur with increasing plasma triglyceride have metablic cnsequences? Mst likely, yes. ccelerated catablism f LDL prtein (apprtein B) has been described in patients with hypertriglyceridemia. 42 This may reflect the lw chlesterl cntent f such LDL with diminished dwn-regulatin f the LDL receptr catablic pathway 43 due t the delivery f smaller amunts f chlesterl int cells per LDL particle. Indeed, using cultured fibrblasts, recent data 44 shw less dwn-regulatin f cellular chlesterl synthesis by triglyceride-enriched LDL mdified in vitr. We cnclude, therefre, that nt nly d plasma triglyceride levels determine the structurecmpsitin relatinships in LDL and HDL, but prbably als affect their bilgic behavir. References 1. Kannel WB, Castelll WP, Grdn T. Chlesterl in the predictin f athersclertic disease: new perspectives based n the Framingham Study. nn Intern Med 1979;90: Carlsn L, Bttlger LE, hfeldt PE. Risk factrs fr mycardial infarctin in the Stckhlm prspective study: a 14- year fllw-up fcusing n the rle f plasma triglycerides and chlesterl. cta Med Scand 1979;206: Miller GJ, Miller NE. Plasma high density lipprtein cncentratin and develpment f ischaemic heart disease. Lancet 1975;1: Yard S, Gldburt U, Even-Zhar S, Neufeld HN. ssciatin f serum high density lipprtein and ttal chlesterl with ttal, cardivascular, and cancer mrtality in a 7-year prspective study f 10,000 men. Lancet 1981 ;1: Kannel WB, Castelll WP, Grdn T, McNamara PM. Serum chlesterl, lipprteins, and the risk f crnary heart disease: the Framingham Study. nn Intern Med 1971 ;74: Hulley SB, Rsenman RH, Bawl RD, Brand RJ. Epidemilgy as a guide t clinical decisins: the assciatin between triglyceride and crnary heart disease. N Engl J Med 1980;302: Deckelbaum RJ, Eisenberg S, Oschry Y, Butbul E, Sharn I, Ollvecrna T. Reversible mdificatin f human plasma lw density lipprteins tward triglyceride-rich precursrs: a mechanism fr lsing excess chlesterl esters. J Bil Chem 1982:257: Deckelbaum R, Eisenberg S, Grant E, Oschry Y, Ollvecrna T. Cre lipid exchange and lipprtein lipase in mdelling human high density lipprtein [abstr]. rterisclersis 1982;2:437a 9. Deckelbaum RJ, Eisenberg S, Oschry Y, Cper M, Blum C. bnrmal high density lipprteins f abetalipprteinemia: relevance t nrmal HDL metablism. J Lipid Res 1982;23: Nichls V, Smith L. Effect f very lw density lipprteins n lipid transfer in incubated serum. J Upid Res 1965;6:

7 PLSM TRIGLYCERIDES ND LDL-HDL COMPOSITION Deckelbaum et al Hatch FT, Lees RS. Practical methds fr plasma lipprtein analysis. dv Lipid Res 1966;6: Patsch JR, Sailer S, Kstner G, Sandhfer F, Hlasek, Braunsteiner H. Separatin f the main lipprtein density classes frm human plasma by rate-znal ultracentrifugatin. J Lipid Res 1974;15: Oschry Y, Eisenberg S. Rat plasma lipprteins: re-evaluatin f a lipprtein system. J Lipid Res 1982;23: Flch J, Lees M, Slane-Stanley GH. simple methd fr the islatin and purificatin f ttal lipids frm animal tissues. J Bil Chem 1957;226: Bartlett GR. Phsphrus assay in clumn chrmatgraphy. J Bil Chem 1959;234: Chiamri N, Henry RJ. Study f the ferric chlride methd fr determinatin f ttal chlesterl and chlesterl esters. m J Clin Pathl 1959;31: Eisenberg S, Rachmilewltz D. Interactin f rat plasma very lw density lipprtein with lipprtein lipase-rich (pstheparin) plasma. J Lipid Res 1975;16: ut nalyzer Methdlgy N-78. Tarrytwn, New Yrk: Technicn Crpratin, Lwry OH, Rsebrugh NJ, Farr L, Randall RJ. Prtein measurement with the Flin phenl reagent. J Bil Chem 1951:193: Snedecr GW, Cchran WG. Statistical methds. 6th ed. mes, Iwa: Iwa State University Press, Breckenridge WC, Little J, Steiner G et al. Hypertriglyceridemia assciated with deficiency f aplipprtein C-ll. N Engl J Med 1978;298: Musliner T, Herbert PN, Kingstn MJ. Lipprtein substrates f lipprtein and hepatic triacylglycerl lipase frm human pst-heparin plasma. Bichim Biphys cta 1979; 575: Carlsn L, Ericssn M. Quantitative and qualitative serum lipprtein analysis: Part 2. Studies in male survivrs f mycardial infarctin. thersclersis 1975;21: Packard CJ, Shepherd J, Jerns S, Gtt M, Tauntn OD. Very lw density and lw density in type III and type IV hyperlipprteinemia: chemical and physical prperties. Bichim Biphys cta 1979;572: Mrrisett JD, Jacksn RL, Gtt M. Lipid-prtein interactin in the plasma lipprteins. Bichim Biphys cta 1977;472: Zilversmit DB, Hughes LB, Balmer V. Stimulatin f chlesterl ester exchange by lipprtein free rabbit plasma. Bichim Biphys cta 1975;409: Chajek T, Fielding CJ. Islatin and characterizatin f a human serum chlesteryl ester transfer prtein. Prc Natl cad Sci US 1978:75: Hpkins GJ, Barter PJ. Transfer f esterified chlesterl and triglyceride between high density and very lw density lipprteins: In vitr studies f rabbits and humans. Metablism 1980;29: Sigurdssn G, Nicll, Lewis B. The metablism f very lw density lipprteins in hyperlipidemia: studies f aplipprtein B kinetics in man. Eur J Clin Invest 1976:6: Reardn MF, Fidge NH, Nestel PJ. Catablism f very lw density lipprtein B apprtein in man. J Clin Invest 1978:61: Berman M, Eisenberg S, Hall MH et al. Metablism f ap B and ap C lipprteins in man: kinetic studies in nrmals and hyperlipprteinemics. J Lipid Res 1978;19: Deckelbaum RJ, Shipley GG, Small DM. Structure and interactin f lipids in human plasma lw density lipprteins. J Bil Chem 1977:252: Ihm J, Quinn DM, Busch SJ, Chataing B, Harmny JK. Kinetics f plasma prtein-catalyzed exchange f phsphatidylchline and chlesterl ester between plasma lipprteins. J Lipid Res 1982:23: Rse HG, Julian J. Regulatin f plasma lecithirvchlesterl acyltransferase in man. I. Increased activity in primary hypertriglyceridemia. J Lab Clin Med 1976:88: Phillips NR, Havel RJ, Kane JM. Serum aplipprtein -l levels: relatinship t lipprtein lipid levels and selected demgraphic variables. m J Epidemilgy 1982;116: Myers LH, Phillips NR, Havel RJ. Mathematical evaluatin f methds fr estimatin f the cncentratin f the majr lipid cmpnents f human serum lipprteins. J Lab Clin Med 1976:88: Biesbreck RC, lbers JJ, Wahl PW, Weinberg CR, Bassett ML, Bierman EL. bnrmal cmpsitin f high density lipprteins in nninsulin-dependent diabetes. Diabetes 1982:31: Patsch JR, Gtt M. Separatin and analysis f HDL subclasses by znal ultracentrifugatin. In: Reprts f the High Density Lipprtein Methdlgy Wrkshp, DHEW-NIH Publicatin N Washingtn DC: Natinal Institutes f Health, 1979: Vakakis N, Redgrave TG, Small DM, Castelli WP. Chlesterl cntent f red bld cells and lw density lipprtein in hypertriglyceridemia. Bichim Biphys cta 1983:751: Sata T, Havel RJ, Jnes L. Characterizatin f subtractins f triglyceride-rich lipprteins separated by gel chrmatgraphy frm bld plasma f nrmlipemic and hyperlipemic humans. J Lipid Res 1972:13: Deckelbaum RJ, Dupnt C, LeTarte J, Pencharz P. Primary hypertriglyceridemia in childhd. m J Dis Child 1983; 137: Sigurdssn G, Nicll, Lewis B. The metablism f lw density lipprtein in endgenus hypertriglyceridemia. Eur J Clin Invest 1976:6: Brwn MS, Kvanen PT, Gldstein JL. Regulatin f plasma chlesterl by lipprtein receptrs. Science 1981; 212: Eisenberg S, Chait, Steinmetz et al. LDL mdificatin by chlesterl ester transfer prteins alters cell interactins [abstr]. rterisclersis 1983;3:490a Index Terms: lw density lipprtein high density lipprtein plasma triglyceride hyperlipidemia