Dana E. Wilson

Metabolic relationships among the plasma lipoproteins: Reciprocal changes in the concentrations of very low and low density lipoproteins in man

The changes in other plasma lipoproteins which accompany alterations in very low density lipoproteins (VLDL) were studied in 31 normal and hyperlipidemic men and women who underwent weight reduction, carbohydrate induction, or clofibrate treatment. Plasma lipids and individual lipoprotein cholesterol concentrations were measured serially during control and treatment periods. Low density lipoprotein (LDL) protein was determined by radial immunodiffusion. Oppositely directed changes in VLDL and LDL were found with each of the three metabolic perturbations. Changes in high density lipoprotein (HDL) cholesterol generally paralleled those in LDL but were less consistent. Two patients with type III hyperlipoproteinemia failed to demonstrate reciprocal increases in LDL despite more than 40% reduction in plasma glycerides or VLDL with weight reduction or clofibrate therapy. After clofibrate therapy, LDL increased in proportion to the absolute decrease in VLDL cholesterol during treatment. LDL protein changed relatively less than did LDL cholesterol. The mechanism for the interdependency of plasma VLDL and LDL concentrations over the long term is not known and may be the result of altered rates of interconversion of these lipoproteins, or to feedback inhibition by VLDL of LDL production and release.

Phenotypic expression of heterozygous lipoprotein lipase deficiency in the extended pedigree of a proband homozygous for a missense mutation.

Familial lipoprotein lipase (LPL) deficiency is a rare genetic disorder accompanied by well-characterized manifestations. The phenotypic expression of heterozygous LPL deficiency has not been so clearly defined. We studied the pedigree of a proband known to be homozygous for a mutation resulting in nonfunctional LPL. Hybridization of DNA from 126 members with allele-specific probes detected 29 carriers of the mutant allele. Adipose tissue LPL activity, measured previously, was reduced by 50% in carriers, but did not reliably distinguish them from noncarriers. Carriers were prone to the expression of a form of familial hypertriglyceridemia characterized by increased plasma triglyceride, VLDL cholesterol and apolipoprotein B, and decreased LDL and HDL cholesterol concentrations. These manifestations were age modulated, with conspicuous differences between carriers and noncarriers observed only after age 40. Several noncarriers exhibited similar lipid abnormalities, but without the inverse relationship between VLDL cholesterol and LDL cholesterol noted among carriers. In addition to age and carrier status, the potentially reversible conditions, obesity, hyperinsulinemia and lipid-raising drug use were contributory. Thus heterozygous lipoprotein lipase deficiency, together with age-related influences, may account for a form of familial hypertriglyceridemia.

Self-regulated glycosylated insulin delivery

Abstract A self-regulating insulin delivery system, based on the concept of competitive binding between synthetic glycosylated insulin (G-insulin) and glucose to concanavalin A (Con A) ligand substrate, has been designed. The competitive binding of the two ligands for the substrate regulates G-insulin release in relation to the outside glucose concentration, while a polymeric membrane, serving as a peritoneal implant pouch containing G-insulin and Con A, is used to control the permeability of glucose influx and G-insulin efflux. Mono-, di- and tri-sugar substituted insulins have been characterized. The nonimmunogenicity, bioactivity and pharmacodynamic activity of succinyl amidophenyl glucopyranoside insulin (SAPG-insulin) and succinyl amidophenyl mannopyranoside insulin (SAPM-insulin) were found to be comparable to unsubstituted bovine insulin. Initial systems were based on SAPG- or SAPM-insulin with water soluble Con A tetramer contained in pouches of porous ρ-HEMA or cellulose acetate. A second system was designed with Con A immobilized beads (to prevent Con A leakage) and cellulose acetate or Nucleopore ® membranes. A new system was designed by crosslinking the Con A molecules to create a gel and enclosing the insulin and gel in a pouch of Durapore ® membrane (heat sealable and having comparable permeability to G-insulins andglucose). The fabricated pouch in vitro showed a short lag time in response to glucose with no leakage of Con A molecules. An alternative system of Con A and SAPG-insulin loaded into microcapsules demonstrated a short lag time for insulin release due to the large surface area of the microcapsules.

Mutations in exon 3 of the lipoprotein lipase gene segregating in a family with hypertriglyceridemia, pancreatitis, and non-insulin-dependent diabetes.

A proband with chylomicronemia, pancreatitis, and non-insulin-dependent diabetes (NIDDM) bears two different mutations in exon 3 of the lipoprotein lipase (LPL) gene: a missense mutation, 75Arg-->Ser, inherited through the paternal line and a truncation, 73Tyr-->Ter, through the maternal line. NIDDM appeared to be independently segregating. The R75S mutant was studied in extracts and media from transfected COS-1 cells. Detectable amounts of catalytically competent R75S LPL suggested destabilization of the active homodimer as with exon 5 mutants (Hata et al. 1992. J. Biol. Chem. 267:20132-20139). Hydrolysis of a short-chain fatty acid ester indicated that R75S does not directly affect activation of LPL by apoC-II. Subjects with NIDDM and wild-type LPL, and nondiabetic middle-aged carriers of the 73Tyr-->Ter truncation had moderate hypertriglyceridemia (260-521 mg/dl) and reduced high density lipoprotein cholesterol. A maternal aunt with NIDDM carried the truncation. Her phenotype (triglycerides of 5,300 mg/dl, eruptive xanthomatosis, and recurrent pancreatitis) was as severe as that in homozygotes or compound heterozygotes. We conclude: (a) diabetic carriers of dysfunctional LPL alleles are at risk for severe lipemia; and (b) the physiologic defects in NIDDM may be additive or synergistic with heterozygous LPL deficiency.

Ultrafiltration of lipoproteins through a synthetic membrane: Implications for the filtration theory of atherogenesis

To investigate the interaction of lipoproteins with semipermeable membranes, solutions of low density lipoproteins (LDL), very low density lipoproteins (VLDL), mixtures of the two, and diluted, normal, and hyperlipidemic serum were ultrafiltered through a synthetic membrane (500 A nominal pore diameter) using a stirred laboratory ultrafiltration cell. The pressure dependence of ultrafiltrate flux showed that a concentrated layer of lipoproteins was built up at the membrane surface (concentration polarization) and that VLDL was more subject to polarization than LDL. This phenomenon controlled the observed lipoprotein transport behavior. Whereas true membrane rejection (the fraction of the solute on the membrane surface which does not pass through the membrane) was greater than 0.95 for both LDL and VLDL, observed solute rejection varied from nearly 0 to 1.0, depending upon experimental conditions. If concentration polarization occurs in the arterial system, these results suggest that lipoprotein transport into arterial wall may be influenced not only by arterial blood pressure and the properties of the arterial wall, but also by local hemodynamic conditions and by the relative as well as absolute magnitudes of LDL and VLDL concentration.

Lipoprotein lipase and hepatic triglyceride lipase: molecular and genetic aspects

Lipoprotein lipase and hepatic triglyceride lipase exert their actions at critical stages of the catabolism of plasma lipoproteins. Structural or biochemical studies of normal enzymes and molecular analyses of enzyme deficiencies unraveling a growing number of lesions should ultimately help clarify

Plasma lipoprotein retinoids after vitamin A feeding in normal man: minimal appearance of retinyl esters among low-density lipoproteins.

Retinyl esters have been thought to be carried solely by lipoproteins of intestinal origin (chylomicrons and their catabolic derivatives). Recent reports, however, have indicated that there may be significant transfer of retinyl esters from chylomicrons to low-density lipoproteins (LDL) in vitro, and that in other species, substantial amounts of retinyl esters may appear in LDL. Since in man lipoproteins of intestinal origin are not considered to contribute to a quantitatively significant extent to circulating LDL, we have examined this issue further. The distribution of retinol and retinyl esters within the plasma lipoproteins of eight normal human volunteers was measured following the ingestion of vitamin A along with a mixed meal. Retinyl esters appeared in the chylomicrons and very-low-density lipoproteins. Small amounts of retinyl esters were also detected in the intermediate- and low-density lipoprotein (LDL) classes. Estimates of the masses of retinyl esters, however, indicated that 5% or less of chylomicron retinyl esters appeared in the LDL. These observations are consistent with orderly chylomicron delipidation and provide further evidence that chylomicron-derived components do not contribute directly or to a quantitatively significant extent to circulating LDL.

The inheritance of high density lipoprotein cholesterol and apolipoproteins A-I and A-II.

A large pedigree was ascertained through cases of early myocardial infarction. High density lipoprotein cholesterol and apolipoproteins A-I and A-II were measured on family members. Likelihood analysis, using the polygenic/major gene mixed model, provided no evidence that major loci play a role in determining the levels of any of the three measurements. Heritability estimates, assuming polygenic inheritance, were 0.59 and 0.26 for HDL-C level and A-II level, respectively. No evidence of genetic transmission of A-I level was found.

Estrogen treatment and gonadal function in the regulation of lipoprotein lipase

Lipoprotein lipase (LPL) activity was measured in adipose tissue, heart and diaphragm in Sprague--Dawley rats after estrogen therapy or orchiectomy. Enzyme activity was measured by incubation of tissue fragments with a triolein emulsion in the presence of serum and heparin. In confirmation of other work, depression of adipose tissue LPL followed estradiol treatment in pharmacologic or near-physiologic doses. Cardiac and diaphragmatic muscle LPL were increased. Estrogen-treated male animals showed growth retardation. However, they gained weight steadily and did not show significant differences in serum insulin, glucose of D-beta-hydroxybutyrate. The effects of estradiol in male animals were reversed by sequential fasting and re-feeding. At times during growth and aging in normal female rats, adipose tissue activity was decreased while cardiac and skeletal muscle activities were increased relative to males of the same age or body weight. Castration of male rats failed to reproduce the effect of estrogens on tissue lipoprotein lipase. These in vitro data suggest that exogenous estrogens may shift the flux of triglyceride fatty acids from storage in the adipose organ toward incorporation by muscle. These, and other data, raise the possibility that physiological estrogen secretion exerts a tonic influence over the synthesis and ultimate destination of triglyceride fatty acids.

Intraperitoneal insulin administration produces a positive portal-systemic blood insulin gradient in unanesthetized, unrestrained swine

The present study was performed to evaluate the porto-systemic insulin gradient in response to (1) glucose feeding (2) intramuscular insulin administration, and (3) peritoneal insulin administration in unanesthetized swine. The experiment was designed to verify the hypothesis that intraperitoneal insulin administered might lead to a more physiologic portal vein insulin concentration than systemic administration of a similar insulin dose. Studies were performed in 4 domestic swine with chronic, indwelling catheters in the inferior vena cava and portal vein. Unpaired studied of the absolute portal venous and systemic venous insulin concentrations were performed in response to glucose prn(n = 4), 1 unit regular insulin/kg i.m.(n = 4), and 1 unit regular insulin/kg i.p.(n = 5). Timed blood samples were obtained and serum insulin concentrations determined by RIA. Portal and caval serum insulin concentrations following intramuscular insulin injection showed no significant difference. A significant portal vein insulin excess (p less than 0.001) was demonstrated following both feeding and intraperitoneal insulin.