A rapid assay of endotoxin in whole blood using autologous neutrophil dependent chemiluminescence

A rapid (30 min) whole blood assay for the detection of lipopolysaccharide (LPS) is described. This chemiluminescent (CL) assay utilizes the CR1 and CR3 receptor-induced oxidant production of polymorphonuclear leucocytes as a detection platform. The differential priming of neutrophils in whole blood by LPS-antibody complexes allows the specificity of the assay to be achieved. Oxidant released in response to complement opsonized zymosan results in luminol oxidation and subsequent light emission. This is dependent on heat labile putative complement proteins in the plasma. The assay consists of a control which measures baseline whole blood neutrophil oxidant production. The test assay contains murine monoclonal IgM antibody against the Lipid A epitope of LPS and measures the enhanced chemiluminescent response of the neutrophils in the presence of LPS-antibody complexes. Maximal sensitivity of the CL assay is dependent upon optimal antigen-antibody equivalence and duration of pre-incubation with the whole blood sample. The quantification of LPS is possible by inclusion of a positive control containing a maximally reactive LPS dose (800 pg/ml Escherichia coli 055:B5 LPS at an antibody concentration of 0.8 microg/assay). The CL assay is insensitive to variations in patient neutrophil concentration over a minimum range of 0.5 to 20 x 10(9) cells/l. The CL assay is widely reactive with the LPS of many strains of gram negative bacteria but not with the cell wall products of gram positive bacteria or Candida and Aspergillus. In comparison to acid extraction chromogenic LAL, the CL assay demonstrates superior recovery precision and accuracy in in vitro studies. This was reproducible over a wide range of LPS concentrations (0.017-1.6 EU/ml or 20-2000 pg/ml). This assay may be a clinically useful tool for the diagnosis of infection or endotoxin in patients.

Design and analysis of lipid tracer kinetic studies

A fundamental problem in lipid metabolism is designing experiments to quantitate the kinetics of the plasma lipids and lipoproteins in the body. Tracers have been used extensively. In this review, we will combine our knowledge of the theory and application of tracer kinetic studies to discuss current state of the art methodologies for lipid metabolism. We will review the use of stable and radioactive isotopes pointing out the importance of the measurement variables, and the theory and application of noncompartmental and compartmental models to interpret the data.

Prostatic acid phosphatase levels (enzymatic method) from completely sectioned, clinically benign, whole prostates

Clinically benign, whole untrimmed prostates were obtained from 104 patients at autopsy, completely sectioned, and examined microscopically. The histological and gross findings of the prostate were correlated with premortem prostatic acid phosphatase levels (PAP, enzymatic method, ACA, Dupont Co.) to determine how often carcinoma of the prostate (CAP) affected PAP levels and to identify other findings within the prostate associated with elevated PAP levels. Sixty (58%) prostates did not have CAP, 34 (33%) had CAP smaller than 1 ml in volume, and 10 (10%) had CAP larger than 1 ml in volume. PAP levels were elevated (greater than 1 U/L) in 8 of 60 (13%) prostates without CAP, in 2 of the 34 (6%) prostates with CAP smaller than 1 ml, and in 1 of the 10 (10%) prostates with CAP larger than 1 ml. These differences were not statistically significant. Likewise, a statistically significant correlation between PAP levels and patient age, patient race, severe inflammation, of high grade prostatic intraepithelial neoplasia (PIN) was not found. However, there was a statistically significant correlation between PAP levels and prostate weight (p < 0.0001). This study suggest that PAP cannot distinguish between patients with clinically undetected CAP and patients without CAP. Furthermore, elevated PAP levels are often not due to metastatic CAP and additional evidence should be present, even in patients with known CAP, before an elevated PAP level is considered to be conclusive evidence of metastatic CAP.

Insulin transport from plasma into the central nervous system is inhibited by dexamethasone in dogs

We have previously shown that transport of plasma insulin into the central nervous system (CNS) is mediated by a saturable mechanism consistent with insulin binding to blood-brain barrier insulin receptors and subsequent transcytosis through microvessel endothelial cells. Since glucocorticoids antagonize insulin receptor-mediated actions both peripherally and in the CNS, we hypothesized that glucocorticoids also impair CNS insulin transport. Nine dogs were studied both in the control condition and after 7 days of high-dose oral dexamethasone (DEX) administration (12 mg/day) by obtaining plasma and cerebrospinal fluid (CSF) samples over 8 h for determination of immunoreactive insulin levels during a 90-min euglycemic intravenous insulin infusion (plasma insulin approximately 700 pmol/l). From these data, the kinetics of CNS insulin uptake and removal were determined using a mathematical model with three components (plasma-->intermediate compartment, hypothesized to be brain interstitial fluid-->CSF). DEX increased basal insulin levels 75% from 24 +/- 6 to 42 +/- 30 pmol/l (P < 0.005) and slightly increased basal glucose levels from 5.0 +/- 0.7 to 5.3 +/- 1.0 mmol/l (P < 0.05). DEX also lowered the model rate constant characterizing CNS insulin transport by 49% from 5.3 x 10(-6) +/- 4.0 x 10(-6) to 2.7 x 10(-6) +/- 1.2 x 10(-6) min-2 (P < or = 0.001). As glucocorticoids are known to reduce CSF turnover, we also hypothesized that the model rate constant associated with CSF insulin removal would be decreased by DEX. As expected, the model rate constant for CSF insulin removal decreased 47% from 0.038 +/- 0.013 to 0.020 +/- 0.088 min-1 (P < or = 0.0005) during DEX treatment. We conclude that DEX impairs CNS insulin transport. This finding supports our hypothesis that insulin receptors participate in the CNS insulin transport process and that this process may be subject to regulation. Moreover, since increasing brain insulin transport reduces food intake and body adiposity, this observation provides a potential mechanism by which glucocorticoid excess leads to increased body adiposity.

Evaluation of age-specific normal ranges for prostate-specific antigen

OBJECTIVES

To compare the traditional normal range (TNR) of 0.0 to 4.0 ng/mL for serum prostate-specific antigen (PSA) to age-specific normal ranges (ASNRs).

METHODS

An autopsy series of completely sectioned, clinically benign prostates from 171 consecutive Caucasian men over the age of 40 years was selected. These patients were divided into those having no prostate cancer at autopsy, prostate cancer less than 1 cc in volume, and prostate cancer at least 1 cc in volume. The PSA values of each group were compared using both the TNR and the ASNR.

RESULTS

Twenty-three of 105 (21.9%) patients with no cancer had elevated PSA values by the TNR, whereas only 18 (17.1%) were elevated using the ASNR. Nine of 54 (16.7%) with cancer less than 1 cc were elevated using the TNR, and 7 of 54 (13.0%) using the ASNR. Of 12 patients with cancer at least 1 cc, all had elevated PSA levels using the TNR and 11 (91.7%) were elevated using the ASNR. All discrepancies between the TNR and ASNR occurred in the 60- to 79-year age range.

CONCLUSIONS

Use of ASNRs appears helpful in increasing the specificity of PSA by eliminating some elevated values in patients in their 60s and 70s.

Characteristics of prostatic infarcts and their effect on serum prostate-specific antigen and prostatic acid phosphatase

OBJECTIVES

To determine how prostatic infarcts affect serum prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP) levels.

METHODS

Two hundred eighteen clinically benign, whole prostates were obtained at autopsy, completely sectioned, and examined histologically. PSA and PAP levels were determined from premortem serum.

RESULTS

Six of the 218 (2.8%) prostates had infarcts. The infarcts were usually multiple and usually located in the central and/or middle concentric zones of the middle third of the prostate without a preference for a particular lobe. Serum PSA by immunoradiometric assay were elevated in all 6 cases. Serum PAP by both enzymatic assay (ACA), and immunoradiometric assay were available for 5 cases and were elevated by both methods in 2 cases, approached elevated levels by both methods in 1 case, and were normal by both methods in 2 cases. The PSA and PAP levels appeared to be affected more by the age than by the size of the infarct.

CONCLUSIONS

Prostatic infarcts elevate PSA levels more frequently than PAP levels, and prostatic infarcts may be responsible for some unexplained elevations of serum PSA and PAP levels.

Estimating the fractional synthetic rate of plasma apolipoproteins and lipids from stable isotope data

The use of isotopic tracer studies to quantitate parameters characterizing apolipoprotein metabolism is enjoying a resurgence. This is due in large part to the availability of a number of stable isotopes and methods to measure them accurately in small quantities. Most experimental protocols in which stable isotopes are used call for endogenous labeling of the apolipoprotein of interest by an infusion of a labeled amino acid. Unlike the radioactively labeled amino acid counterpart in which turnover studies have traditionally been carried out for 72 hours to 14 days, the duration of the stable isotope experiment is normally less than 24 hours. This has contributed to some problems related to estimating the kinetic parameters because simplistic formulas whose underlying assumptions are not applicable to the lipoprotein system under study are often invoked. This is particularly true for the fractional synthetic rate (FSR). The purpose of this review is to address some of these problems. We derive the formula commonly used to estimate the FSR. In so doing, the underlying assumptions are carefully delineated. We then discuss several ways in which the formula is applied. Finally, we discuss the implications of these assumptions when the formula is applied to specific lipoprotein systems.

Articular pharmacokinetics of protein-bound antirheumatic agents

By what mechanism do nonsteroidal anti-inflammatory drugs (NSAIDs) move from plasma into synovial fluid and back, and how does binding to plasma albumin in vitro relate to articular transport in vivo? To evaluate these issues, concurrent plasma and synovial fluid data of 8 different NSAIDs from 10 single-dose trials were analysed by a simple compartmental model incorporating intra-articular volume, synovial plasma flow rates and protein transport. All pharmacological and physiological data were taken from published studies of chronic knee effusions in patients with rheumatoid arthritis. The analysis shows that these protein-bound NSAIDs readily leave the vasculature and enter synovial fluid during each transit of synovial microvessels. The mean rate of transport, 0.23 min-1, is consistent with passive diffusion at rates far in excess of those attributable to movement of albumin-bound drug or of the small, free-drug fraction found by equilibrium dialysis. These findings are explained by association and dissociation of NSAIDs and albumin that occur far more rapidly than vascular transit. Ongoing dissociation makes bound drug available for transvascular exchange and thereby diminishes the pharmacokinetic significance of binding data obtained in vitro.

Saturable transport of insulin from plasma into the central nervous system of dogs in vivo. A mechanism for regulated insulin delivery to the brain

By acting in the central nervous system, circulating insulin may regulate food intake and body weight. We have previously shown that the kinetics of insulin uptake from plasma into cerebrospinal fluid (CSF) can best be explained by passage through an intermediate compartment. To determine if transport kinetics into this compartment were consistent with an insulin receptor-mediated transport process, we subjected overnight fasted, anesthetized dogs to euglycemic intravenous insulin infusions for 90 min over a wide range of plasma insulin levels (69-5,064 microU/ml) (n = 10). Plasma and CSF samples were collected over 8 h for determination of immunoreactive insulin levels, and the kinetics of insulin uptake from plasma into CSF were analyzed using a compartmental model with three components (plasma-->intermediate compartment-->CSF). By sampling frequently during rapid changes of plasma and CSF insulin levels, we were able to precisely estimate three parameters (average standard deviation 14%) characterizing the uptake of insulin from plasma, through the intermediate compartment and into CSF (k1k2); insulin entry into CSF and insulin clearance from the intermediate compartment (k2 + k3); and insulin clearance from CSF (k4). At physiologic plasma insulin levels (80 +/- 7.4 microU/ml), k1k2 was determined to be 10.7 x 10(-6) +/- 1.3 x 10(-6) min-2. With increasing plasma levels, however, k1k2 decreased progressively, being reduced sevenfold at supraphysiologic levels (5,064 microU/ml). The apparent KM of this saturation curve was 742 microU/ml (approximately 5 nM). In contrast, the rate constants for insulin removal from the intermediate compartment and from CSF did not vary with plasma insulin (k2 + k3 = 0.011 +/- 0.0019 min-1 and k4 = 0.046 +/- 0.021 min-1). We conclude that delivery of plasma insulin into the central nervous system is saturable, and is likely facilitated by an insulin-receptor mediated transport process.

Estimation of protein fractional synthetic rate from tracer data

The fractional synthetic rate (FSR) is a key parameter characterizing protein turnover that is estimated from tracer kinetic data. Formulas to estimate this parameter usually assume a precursor-product model. Assuming this model is correct, we discuss these formulas to estimate the FSR in the steady and non-steady state both for the radioactive and stable isotope tracer. Then we deal with the non-steady-state case where the FSR becomes time varying and derive formulas for its estimation. A non-steady-state case study on the flooding-dose technique for measuring protein turnover is presented.

Protein transfer between A-I-containing lipoprotein subpopulations: evidence of non-transferable A-I in particles with A-II

Transfer of apolipoproteins (apo) between the two subpopulations of apo A-I-containing lipoproteins in human plasma: those with A-II [Lp(AI w AII)] and those without [Lp(AI w/o AII)], were studied by observing the transfer of 125I-apo from a radiolabeled subpopulation to an unlabeled subpopulation in vitro. When Lp(AI w AII) was directly radioiodinated, 50.3 +/- 7.4 and 19.5 +/- 7.7% (n = 6) of the total radioactivity was associated with A-I and A-II, respectively. In radioiodinated Lp(AI w/o AII), 71.5 +/- 6.8% (n = 6) of the total radioactivity was A-I-associated. Time-course studies showed that, while some radiolabeled proteins transferred from one population of HDL particles to another within minutes, at least several hours were necessary for transfer to approach equilibrium. Incubation of the subpopulations at equal A-I mass resulted in the transfer of 51.8 +/- 5.0% (n = 4) of total radioactivity from [125I]Lp(AI w/o AII) to Lp(AI w AII) at 37 degrees C in 24 h. The specific activity (S.A.) of A-I in the two subpopulations after incubation was nearly identical. Under similar incubation conditions, only 13.4 +/- 4.6% (n = 4) of total radioactivity was transferred from [125I]Lp(AI w AII) to Lp(AI w/o AII). The S.A. of A-I after incubation was 2-fold higher in particles with A-II than in particles without A-II. These phenomena were also observed with iodinated high-density lipoproteins (HDL) isolated by ultracentrifugation and subsequently subfractionated by immunoaffinity chromatography. However, when Lp(AI w AII) radiolabeled by in vitro exchange with free [125I]A-I was incubated with unlabeled Lp(AI w/o AII), the S.A. of A-I in particles with and without A-II differed by only 18% after incubation. These data are consistent with the following: (1) in both populations of HDL particles, some radiolabeled proteins transferred rapidly (minutes or less), while others transferred slowly (hours); (2) when Lp(AI w AII) and Lp(AI w/o AII) were directly iodinated, all labeled A-I in particles without A-II were transferable, but some labeled AI in particles with A-II were not; (3) when Lp(AI w AII) were labeled by in vitro exchange with [125I]A-I, considerably more labeled A-I were transferable. These observations suggest the presence of non-transferable A-I in Lp(AI w AII).

Psyllium husk. I: Effect on plasma lipoproteins, cholesterol metabolism, and atherosclerosis in African green monkeys

Psyllium's effects on plasma and lipoprotein cholesterol concentrations, cholesterol metabolism, and diet-induced atherosclerosis were studied in adult male African green monkeys (Cercopithecus aethiops). Animals were fed for 3.5 y one of three experimental diets: low-cholesterol cellulose (LCC), high-cholesterol cellulose (HCC), or high-cholesterol psyllium (HCP). The LCC and HCP groups had significantly (P less than 0.05) lower plasma cholesterol concentrations (39% lower) at 1 mo than did the HCC group. These responses persisted throughout the study. Plasma cholesterol changes were due to a reduction in intermediate-density and low-density lipoproteins; very-low and high-density-lipoprotein concentrations were similar among groups. Aortic atherosclerosis, evaluated as percent sudanophilia at 3.5 y, was lowest in the LCC group, intermediate in the HCP group, and highest in the HCC group. Cholesterol absorption, neutral steroid and fat excretion, HMGCoA reductase activity (in intestine and liver), and body weight were unrelated to psyllium's hypocholesterolemic effects.

Psyllium husk. II: Effect on the metabolism of apolipoprotein B in African green monkeys

Dietary psyllium's ability to reduce low-density-lipoprotein (LDL) cholesterol is presumably mediated by increased LDL catabolism and/or reduced LDL synthesis. To distinguish between these possibilities, apolipoprotein B (apo B) metabolism was studied in adult male African green monkeys consuming one of three semipurified diets: low-cholesterol cellulose (LCC), high-cholesterol cellulose (HCC), or high-cholesterol psyllium (HCP). 131I-labeled LDL and 125I-labeled VLDL were injected simultaneously into animals; blood samples were drawn at selected times and apo B specific activity determined in VLDL, IDL, and LDL. Based on a multicompartmental model, LDL apo B pool size and de novo apo B transport were elevated significantly in HCC animals compared with HCP and LCC animals. Differences in LDL transport, although not significant, paralleled differences observed in LDL apo B pool size. Fractional catabolic rates were similar among groups (HCC 0.040 +/- 0.010; HCP 0.042 +/- 0.009, and LCC 0.043 +/- 0.004 pools/h). These data suggest that dietary psyllium reduces plasma cholesterol concentrations by decreasing LDL synthesis.

Tracer-to-tracee ratio for analysis of stable isotope tracer data: link with radioactive kinetic formalism

A kinetic formalism for the analysis of stable isotope transient tracer data is developed by establishing the link with the formalism available for radioactive tracer data. The crucial variable is the tracer-to-tracee ratio. By expressing the measurements in terms of this ratio, the conventional kinetic formalism used for radioactive data can be applied to estimate noncompartmental parameters using stable isotope tracer data. The tracer-to-tracee ratio also plays an important role in compartmental modeling. By considering the tracer masses in the compartments as state variables the system-experiment model can be written in a format analogous to that usually adopted for the radioactive tracer. Finally, it is shown that the tracer-to-tracee ratio also plays a role in a test of the endogenous steady-state assumption.

Role of modeling in the design of experiments in carbohydrate metabolism

Most publications on modeling present only the final product without describing the details as to how they were developed and tested. It is, however, by model development and testing that the true power of modeling as a research tool reveals itself. The purpose of this paper is to present a "behind the scenes" look at a set of experiments designed to study carbon atom transport in gluconeogenesis. In particular, it will be shown how the development of one model led to hypotheses for which another set of experiments was designed. The model which resulted from the second study contained in turn a number of new hypotheses for which further experiments remain to be designed. The second model supported the findings of the first, and yielded deeper insights into the exchange of carbon atoms among three metabolites. It is hoped this illustration will encourage other investigators to take advantage of the utilitarian value of modeling not only as a parameter generating tool, but also as a true research tool which can aid significantly to extract more information from available data.

Enhancement of antibody production by lysophosphatidylcholine and alkylglycerol

Inflammation products of normal and cancerous tissues, lysophosphatidylcholine and dodecylglycerol, were tested for their adjuvant effect on the antibody response. Mice treated with these agents and immunized with sheep erythrocytes simultaneously or at 3 days posttreatment developed a greatly enhanced antibody production as demonstrated by the Jerne plaque assay. Mice immunized at 3 days postadministration of agents did not significantly produce enhanced antibody-secreting cells as compared with those of mice simultaneously immunized. Since the mechanism of macrophage activation by lysophospholipids requires contribution of B and T cells, BALB/c-nu/nu mice treated with these agents and subsequently immunized with sheep erythrocytes did not produce antibodies. However, conditioned medium of in vitro-treated BALB/c-nu/nu B cells efficiently transmitted a signal to untreated BALB/c +/+ T cells for enhanced macrophage ingestion activity. This observation suggests that lysophospholipid-activated macrophages and T cells efficiently transmitted antigenic signal to the antibody-producing B cell population. Therefore, we conclude that these lipid metabolites have dual beneficial effects for the host by enhancing phagocytosis and antibody production. Thus, lysophosphatidylcholine and dodecylglycerol have potential practical application as adjuvants that could be administered separately or in combination with antigens.

Metabolic regulation of plasma apolipoprotein E by estrogen and progesterone in the baboon (Papio sp)

Apolipoprotein (apo) E plays an important role in the metabolism of lipoproteins. To determine the effects of estrogen and progesterone on plasma levels and metabolism of apo E, we used 12 ovariectomized baboons fed a cholesterol- and fat-enriched diet. These baboons were divided into four groups and treated with estrogen, progesterone, estrogen + progesterone, and a placebo control. After 10 months, although the lipid levels were not different among the treatment groups, low-density lipoprotein (LDL)/high-density lipoprotein (HDL) ratios in the estrogen + progesterone group were significantly lower than those in the control and progesterone groups. Estrogen alone or in combination with progesterone decreased plasma apo E levels significantly compared with those in the control group. Plasma apo E levels in the progesterone group were similar to those in the control group. In all groups, most (greater than 60%) of the apo E was present in HDL. HDL apo E concentrations in the estrogen and estrogen + progesterone groups were significantly lower than those in the control and progesterone groups. To determine the metabolic mechanisms of these changes in apo E levels, turnover studies were conducted by injection of iodinated apo E-labeled very-low-density lipoprotein (VLDL) and HDL. Residence times were calculated using multicompartment modeling. Progesterone alone and in combination with estrogen decreased residence times of apo E injected in both HDL and VLDL compared with estrogen alone and control groups. Progesterone alone also increased the apo E production rate compared with other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of fish oil on VLDL triglyceride kinetics in humans

Dietary n-3 fatty acids (FAs) found in fish oils markedly lower plasma triglyceride (TG) and very low density lipoprotein (VLDL) levels in both normal and hypertriglyceridemic subjects. The present study examined the mechanism of this effect. Ten subjects with widely different plasma triglyceride levels (82 to 1002 mg/dl) were fed metabolically controlled diets containing 20% fat. The control diet contained a blend of cocoa butter and peanut oil (P/S = 0.8). The test diet contained fish oil (P/S = 1.1) and provided 10-17 g of n-3 FAs per day (depending on calorie intake). After 3 to 5 weeks of each diet, the kinetics of VLDL-TG were determined over a 48-h period after the injection of [3H]glycerol. The fish oil diet reduced the VLDL-TG synthetic rate from 23 +/- 14.3 (mean +/- SD) to 12.6 +/- 7.5 mg/h per kg ideal weight (P less than 0.005) and increased the fractional catabolic rate (FCR) for VLDL-TG from 0.23 +/- 0.12 to 0.38 +/- 0.16 h -1 (P less than 0.005). At the same time, there was a 66% reduction of plasma triglyceride levels, resulting largely from a 78% decrease in VLDL-TG levels (398 +/- 317 to 87 +/- 77 mg/dl; P less than 0.005). There was a strong correlation (r = 0.83; P less than 0.01) between the change in synthetic rates and pool sizes, but there was no correlation (r = 0.24; NS) between changes in FCRs and pool sizes. The VLDL cholesterol: triglyceride ratio increased during the n-3 diet suggesting that smaller VLDL particles were present. These particles would be expected to leave the VLDL fraction more rapidly than larger particles producing a higher FCR. We conclude that the hypotriglyceridemic effect of fish oil appears to be caused primarily by an inhibition of very low density lipoprotein-triglyceride synthesis, but an additional, independent effect upon VLDL catabolism cannot be ruled out.

Hepatic apo B-100 lipoproteins and plasma LDL heterogeneity in African green monkeys

The contribution of hepatic apolipoprotein (apo) B-100 lipoproteins to plasma low-density lipoprotein (LDL) metabolic heterogeneity was examined in African green monkeys. Hepatic 3H-labeled very low-density lipoproteins (VLDL) (d less than 1.006, where d is density in g/ml) or hepatic 131I-labeled LDL (1.030 less than d less than 1.063) were isolated from perfused livers and injected simultaneously with autologous plasma 125I-LDL into African green monkeys. Serial blood samples were taken, and the distribution of radioactivity among various subfractions of apo B-100 lipoproteins was determined using density-gradient ultracentrifugation. Compartmental models were developed to describe simultaneously the kinetics of hepatic lipoproteins and plasma LDL. In five of seven studies, the metabolic behavior of LDL derived from radiolabeled hepatic lipoprotein precursors differed from the metabolic behavior of radiolabeled autologous plasma LDL. These differences could be described by different models supporting two hypotheses with different physiological interpretations: 1) lipoproteins of donor and recipient animals are kinetically distinct, and/or 2) plasma LDL derived from various potential sources are kinetically distinct. Compartmental modeling was used to test these hypotheses, which were not accessible to testing by conventional experimental methodologies. The kinetic analyses of these studies suggest that plasma LDL may be derived from a variety of precursors, including hepatic VLDL and hepatic LDL, with each source giving rise to metabolically distinct plasma LDL.

Conversion of plasma VLDL and IDL precursors into various LDL subpopulations using density gradient ultracentrifugation

The contribution of very low density lipoproteins (VLDL) and intermediate density lipoproteins (IDL) to various low density lipoprotein (LDL) subfractions was examined in three normal subjects and two with familial combined hyperlipidemia. Autologous VLDL + IDL (d less than 1.019 g/ml) or VLDL only (d less than 1.006 g/ml; one subject only) were isolated by sequential ultracentrifugation, iodinated, and injected into each subject. The appearance, distribution, and subsequent disappearance of radioactivity into LDL density subpopulations was characterized using density gradient ultracentrifugation. These techniques help determine the contribution of precursors to various LDL subpopulations defined uniquely for each subject. The results from these studies have suggested: 1) it took up to several days of intravascular processing of precursor-derived LDL before it resembled the distribution of the 'steady-state' plasma LDL protein; 2) plasma VLDL and IDL precursors contributed rapidly to a broad density range of LDL; 3) the radiolabeled plasma precursors did not always contribute to all LDL density subfractions within an individual in proportion to their relative LDL protein mass as determined by density gradient ultracentrifugation; 4) with time, the distribution of the precursor-derived LDL became more buoyant or more dense than distribution of the LDL protein mass; and 5) the kinetic characteristics of precursor-derived particles within LDL changed within a relatively narrow density range and were not always related to the LDL density heterogeneity of each subject. These studies emphasize the complexities of apoB metabolism and the need to design studies to carefully examine the production of various LDL subpopulations, the kinetic fate and interconversions among the subpopulations, and ultimately, their relationship to the development of atherosclerosis.