Oxidative modification of low density lipoprotein (LDL) has been implicated as a factor in the generation of macrophage-derived foam cells, the hallmark of atherosclerotic plaques. Because LDL consists of discrete subtractions with different physicochemical characteristics, the question arises as to whether these LDL subtractions differ in their susceptibility to oxidative modification. To answer this question, three LDL subtractions, LDL,, LDL 2 , and LDL 3 , were isolated from the plasmas of 11 healthy volunteers by density gradient ultracentrifugation. The LDL subtractions were oxidatively modified by incubation with copper ions. Differences in the subtractions' susceptibilities to lipid peroxidation were studied by measuring the formation of the 234-nm-absorbing oxidation products every 3 minutes on an ultraviolet spectrophotometer. are positively correlated with the incidence of coronary artery disease (CAD). 1 In the last decade, evidence has accumulated that human plasma LDL comprises discrete subtractions, varying in size, density, and lipid content.2 -6 Two to three LDL subtractions can be detected and isolated from normolipidemic plasma by density gradient ultracentrifugation.7 These LDL subtractions have been found to differ in chemical composition and molecular size.7 Several lines of evidence suggest that the

Lipoproteins can bind lipopolysaccharide (LPS) and decrease the LPS-stimulated production of pro-inflammatory cytokines. We investigated the effect of increased plasma concentrations of low-density-lipoproteins (LDL) on survival and cytokine production after a lethal challenge with either LPS or live Gram-negative bacteria in LDL receptor deficient mice (LDLR Ϫ / Ϫ ). The LDLR Ϫ / Ϫ mice challenged with LPS had an eightfold increased LD 50 when compared with the wild type controls (C57Bl/6J), while tumor necrosis factor ␣ (TNF ␣ ) and interleukin-1 ␣ (IL-1 ␣ ) plasma concentrations were decreased twofold. LDLR Ϫ / Ϫ mice had significantly lower and delayed mortality than control mice after infection with Klebsiella pneumoniae. No differences in the outgrowth of bacteria in the organs were present between the two groups, while circulating cytokine concentrations were decreased twofold in LDLR Ϫ / Ϫ mice. In contrast, the LPS-stimulated in vitro production of cytokines by peritoneal macrophages of LDLR Ϫ / Ϫ mice was significantly increased compared with controls. This increase was associated with enhanced specific binding of LPS to the macrophages of LDLR Ϫ / Ϫ mice. In conclusion, endogenous LDL can protect against the lethal effects of endotoxin and Gram-negative infection. At least part of this protection is achieved through decreased in vivo production of pro-inflammatory cytokines, in spite of increased cytokine production capacity. ( J. Clin. Invest. 1996. 97:1366-1372). Key words: lipopolysaccharide • gram-negative infection • tumor necrosis factor • interleukin-1 • low-density lipoproteins.

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Familial combined hyperlipidemia (FCH) is characterized by a variable expression of hypercholesterolemia and/or hypertriglyceridemia. We evaluated the variability in lipid phenotype expression over a 5-year period and studied factors affecting the lipid phenotype expression. A total of 32 families (299 subjects) were studied in 1994 and in 1999. Subjects were classified as having FCH when total cholesterol and/or triglyceride levels exceeded the 90th percentile adjusted for age and sex. In 1994, 93 (31%) of the 299 subjects were affected, whereas 206 (69%) of the subjects were unaffected relatives. In 1999, a diagnosis of FCH was consistent in 69 (74%) of the 93 subjects. So, 26% of the FCH subjects in 1994 showed a sporadic normolipidemic pattern (ie, total cholesterol and/or triglycerides <90th percentile) in 1999. Among the 206 unaffected relatives in 1994, 178 (86%) remained unaffected in 1999, and 28 (14%) developed an FCH lipid phenotype. Multiple regression analysis showed that sex (odds ratio 2.03, 95% CI 1.09 to 3.87; P =0.03) and body mass index (odds ratio 1.14, 95% CI 1.05 to 1.24; P <0.01) significantly contributed to the variability in lipid phenotype expression. Thus, a diagnosis of FCH, based on plasma total cholesterol and/or triglyceride levels, is consistent in only 74% of the subjects over a 5-year period. Two other major characteristics of our FCH group, compared with the unaffected relatives, included elevated apolipoprotein B (apoB) levels and the presence of small dense low density lipoprotein (LDL), as reflected by a low value of the parameter K (apoB 1461±305 versus 997±249 mg/L, respectively [ P <0.001]; K value −0.22±0.19 versus −0.02±0.19, respectively [ P <0.001]). We now report that the apoB concentration and the K value show less variability in time and are more consistently associated with FCH, inasmuch as affected FCH subjects, compared with the unaffected relatives, persistently show a higher apoB level and a lower value of parameter K , reflecting small dense LDL, even when they present a sporadic normolipidemic pattern. In conclusion, our results emphasize the need for reevaluation of the diagnostic criteria for FCH. We demonstrate that apoB and small dense LDL are attractive new candidates for defining FCH. Further studies are indicated to evaluate the role of apoB and small dense LDL as diagnostic criteria for FCH.

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Low-density-lipoprotein (LDL) oxidation may provide the crucial link between plasma LDL and atherosclerotic-lesion formation. Oxidation can be induced in vitro by incubating LDL with cells or metal ions and can be measured by continuously monitoring conjugated-diene absorbance at 234 nm. Measurement of LDL oxidizability was improved by performing the assay with 0.05 g of LDL-protein per liter of phosphate buffer containing 1 mumol of EDTA, by initiating oxidation by adding CuCl2 (5 mumol/L) at 30 degrees C, and by using a short-run ultracentrifugation method for isolating LDL, which reduced the time needed for obtaining purified LDL and thus reduced in vitro oxidation. LDL apolipoprotein analysis and oxidizability determination showed that this method is better than the longer sequential-isolation procedure. Adding butylated hydroxytoluene (BHT) to plasma as an antioxidant unpredictably increased the LDL oxidation lag time, making BHT unsuitable as an antioxidant. Adding EDTA appeared to be sufficient to prevent in vitro oxidation. Additionally, the diene production correlated highly with the concentration of thiobarbituric acid-reactive substances (r = 0.97). No relation between the vitamin E content of LDL and the oxidation lag time was found.

Background: Defects in the biosynthesis of N-glycans may be found by isoelectric focusing (IEF) of plasma transferrin. No test is available to demonstrate O-glycan biosynthesis defects. Methods: We used isoforms of apolipoprotein C-III (apoC-III) as a marker for the biosynthesis of core 1 mucin type O-glycans. Plasma samples from patients with primary defects and secondary alterations in Nglycan biosynthesis were studied by apoC-III isofocusing. Results: Age-related reference values for apoC-III were determined. Plasma samples from patients with the primary congenital disorders of glycosylation (CDG) types Ia-Ic, Ie, If, IIa, and IId all showed a normal apoC-III isofocusing profile. Plasma from two patients with CDG type IIx were tested: one showed a normal apoC-III distribution, whereas the other showed a hypoglycosylation profile. In plasma from patients with hemolytic uremic syndrome (HUS), a hypoglycosylation profile was obtained. Conclusions: IEF of apoC-III is a rapid and simple technique that may be used as a screening assay for