Silvia S. Fojo

Effectiveness of mevinolin on plasma lipoprotein concentrations in type II hyperlipoproteinemia.

Patients with low-density lipoprotein (LDL) concentrations in the top 10th percentile of the population (type II hyperlipoproteinemia [HLP]) are at increased risk for premature cardiovascular disease; however, the incidence of myocardial infarction and death can be decreased by LDL cholesterol reduction. Mevinolin, an inhibitor of endogenous cholesterol synthesis, has been shown to reduce LDL cholesterol concentrations in a subset of type II patients with heterozygous familial hypercholesterolemia (FH). Using a double-blind, randomized, crossover, placebo-controlled trial, the safety and efficacy of mevinolin were compared in 24 patients with type II HLP with heterozygous FH (n = 6) or without FH type II HLP (n = 18). Compared with placebo treatment, both apolipoprotein B and LDL cholesterol levels were reduced (p less than 0.01) in both FH and non-FH patients by 28 to 34% with mevinolin treatment. In addition, high-density lipoprotein cholesterol levels were significantly increased (p less than 0.001) in both patients with FH (16%) and those with non-FH type II HLP (14%). Patients had no serious or clinically significant adverse effects. Thus, mevinolin is a useful drug for treatment of most patients with elevated plasma LDL cholesterol concentrations.

Analysis of the apoC-II gene in apoC-II deficient patients

Apolipoprotein C-II (apoC-II), a 79 amino acid protein, is a cofactor for lipoprotein lipase, the enzyme which catalyzes the lipolysis of triglycerides on plasma chylomicrons and VLDL. Patients with apoC-II deficiency have marked elevations in plasma triglycerides, chylomicrons, VLDL, and a type I hyperlipoproteinemia. In order to evaluate the molecular defect in apoC-II deficiency, genomic DNA was analyzed using Southern Blot from 2 independent apoC-II deficient patients and compared to normal controls. Restriction digests of genomic DNA were performed with five different enzymes and the restriction fragments analyzed utilizing a 354 base pair nick-translated apoC-II probe for hybridization following Southern blotting. The restriction fragments varied from 0.8 to 21 Kb, and the pattern with normal DNA was identical to that of the two apoC-II deficient patients. The present study reveals that the apoC-II gene is present in patients with apoC-II deficiency. In addition, no insertional or deletional polymorphism was detected in the apoC-II gene of apoC-II deficient patients.

Apolipoprotein C-ll deficiency syndrome due to apo C-IIHamburg: clinical and biochemical features and Hphl restriction enzyme polymorphism

Abstract. We have characterized the clinical and biochemical features of three siblings of a kindred with severe hypertriglyceridaemia due to apolipoprotein C‐II (apo C‐II) deficiency caused by the mutation described as apo C‐IIHumburg. The clinical syndrome is characterized by recurrent pancreatitis in two of three affected individuals, with discrete hepatosplenomegaly in all three patients and cholelithiasis in one. Eruptive xanthomas and lipemia retinalis were absent.

The localization of the gene for apolipoprotein C-II to chromosome 19

Human apolipoprotein (apo) C-II, a 79 amino acid protein, functions as a cofactor for lipoprotein lipase, the enzyme which catalyzes the hydrolysis of plasma triglycerides. The chromosomal location of apoC-II has been determined by filter hybridization analysis of human-mouse hybrid cells. Southern blots of DNA from 21 human-mouse hybrid cells were hybridized with a 190 base pair nick translated probe prepared from a Hinf I digest of an apoC-II cDNA clone. Without exception, ApoC-II segregated with chromosome 19 thus establishing synteny with the apoE and LDL receptor genes known to be localized to this chromosome. The localization of the apoC-II gene to chromosome 19 will permit more detailed analysis of the genomic organization and linkages of the apolipoprotein genes.

Molecular Genetics of ApoC-II and Lipoprotein Lipase Deficiency

Apolipoprotein (apo) C-II plays a central role in normal triglyceride metabolism as cofactor for the enzyme lipoprotein lipase (LPL). Patients with a deficiency of either apoC-II or LPL have marked derangements in triglyceride metabolism which include an elevation of plasma triglycerides, fasting chylomicrons and VLDL (1). Clinical features of this syndrome, which is inherited as an autosomal recessive trait, include hepatosplenomegaly, eruptive xanthomas and an increased risk of pancreatitis. The diagnosis of apoC-II or LPL deficiency is established by finding a reduced post-heparin lipoprotein lipase activity which in apoC-II deficiency is corrected by the addition of normal apoC-II containing plasma.

The Molecular Biology of Human ApoA-I, ApoA-II, ApoC-II and ApoB

The application of molecular biology techniques has enabled us to determine the gene sequence, organization, transcription and processing of apolipoprotein genes. Consequently, new insights have been gained in the biosynthesis and processing of these proteins. In addition to apoA-I, apoA-II and apoC-III reported here, other apolipoprotein genes such as apoC-II and apoE genes were found to share common intron-exon organizations. The results suggest that these genes most probably arise from a common ancestral gene. Utilizing cDNA as hybridization probes, we have localized apoA-I, apoA-II, apoC-II, apoC-III, apoE and apoB to specific locations of individual chromosomes (for review, see ref. 6). There is no clear relationship between currently known physiological function and the organization of the apolipoproteins in the chromosomes with the exception of the LDL receptor and its ligand, apoE which are localized to chromosome 19. However, apoB-100, the major ligand for the LDL receptor is on chromosome 2 and not in synteny with the apoE and the LDL receptor genes. The cloning of the major human apolipoprotein genes have also allowed us to initiate studies on the molecular defects leading to various dyslipoproteinemias including Tangier disease and abetalipoproteinemia. Undoubtedly, information derived from these studies will provide the basis for future in vitro and in vivo studies on patients with dyslipoproteinemia and premature atherosclerosis.

Apolipoprotein C-II deficiency: Identification of a structural variant apoC-IIPadova

Apolipoprotein(apo) C-II DNA, RNA and protein from a patient with a familial deficiency of apoC-II were evaluated and compared to normal individuals. No major defect of the apoC-II gene could be detected by Southern blot hybridization. Northern and slot blot analyses of total liver RNA documented normal levels of a normal sized apoC-II mRNA. Immunohistochemical studies of the liver of the apoC-II deficient patient revealed a normal to slightly elevated intracellular content of the C-II apolipoprotein. Plasma apoC-II was 3 to 5% of normal apoC-II levels and exhibited abnormal electrophoretic mobility on two dimensional gel electrophoresis and immunoblotting. We postulate that at the molecular level, the deficiency of apoC-II in the plasma of this patient results from a structural defect in the coding portion of the apoC-II gene leading to either defective secretion of cellular apoC-II or increased catabolism of a structurally defective apoC-II in plasma.

The Molecular Basis of ApoC-II Deficiency

The genetic defect that leads to deficiency of apoC-II in 2 patients with apoC-II deficiency from independent kindreds has been defined.

Mevinolin and Neomycin in the Treatment of Type II Hyperlipoproteinemia

The reduction of elevated low-density lipoprotein (LDL) cholesterol concentrations in patients with type II hyperlipoproteinemia leads to improved cardiovascular morbidity and mortality. Two agents that may be of value in treating hypercholesterolemia are mevinolin and neomycin. Since these drugs lower cholesterol levels through complementary mechanisms, we evaluated the effects of mevinolin and combined mevinolin-neomycin treatment on plasma lipoprotein concentrations in 21 type II hyperlipoproteinemic patients. Mevinolin reduced total and LDL cholesterol concentrations by 24% and 31%, respectively, and 81% of the patients reduced their LDL cholesterol levels to less than 200 mg/dl. Both familial hypercholesterolemic heterozygotes and nonfamilial hypercholesterolemic type II hyperlipoproteinemic patients responded to mevinolin treatment with comparable degrees of cholesterol and LDL cholesterol reduction expressed as percentage reduction. Although the addition of neomycin to mevinolin treatment further lowered total (5%) and LDL (4%) cholesterol concentrations, it also reduced HDL cholesterol levels by 19%. Therefore, mevinolin effectively alters the plasma lipoprotein concentrations in patients with type II hyperlipoproteinemia but, despite the theoretical advantage of combined treatment, mevinolin and neomycin combination treatment offers no advantage over mevinolin-only therapy.

Genomic Structure, Biosynthesis, and Processing of Preproapolipoprotein C-II

Apolipoprotein C-II plays a major role in lipid metabolism as a cofactor for lipoprotein lipase, the enzyme involved in the hydrolysis of plasma triglycerides. Patients with deficiency of apo C-II have marked elevations of plasma triglyceride-rich lipoproteins and are at increased risk of pancreatitis. Apolipoprotein C-II has been cloned, and the complete genomic structure elucidated. The apo C-II gene consists of four exons interrupted by three introns and encodes a 22-amino-acid signal peptide that undergoes cotranslational cleavage. The posttranslational processing of apo C-II was analyzed by two-dimensional gel electrophoresis followed by immunoblotting of apo C-II isoforms in the media of Hep G2 cells and in plasma. Four major isoforms have been identified and designated apo C-II-2, apo C-II-1, apo C-II-1/2, and apo C-II0. Neuroaminidase studies have shown that apo C-II-2 and apo C-II-1 are sialic-acid-containing glycoproteins. There is a relative enrichment of these two isoforms of apo C-II in Hep G2 cell media, but they represent minor apo C-II isoforms in normal fasting plasma. Apolipoprotein C-II0, the major plasma isoform of apo C-II, is a proprotein that undergoes proteolytic cleavage of the amino-terminal hexapeptide to form mature apo C-II (apo C-II-1/2)-Amino acid composition and amino-terminal analysis of apo C-II-1/2 confirms the loss of the six terminal amino acids of apo C-II0. In summary: (1) apo C-II has been cloned, and its complete genomic sequence determined; (2) apo C-II is synthesized as preproapo C-II, which undergoes cleavage of a 22-amino-acid signal peptide to form proapo C-II; (3) proapo C-II is glycosylated to generate the sialic-acid-containing glycoproteins apo C-II-2 and apo C-II-1; (4) apo C-II-2 and apo C-II-1 are deglycosylated to form apo C-II0; (5) apo C-II0, the major plasma isoform of apo C-II, is a proprotein; (6) proteolytic processing of apo C-IIo results in the loss of six amino terminal residues to form apo C-II-1/2, the mature apo C-II isoform. A better understanding of the structural relationship of the various plasma isoforms of apo C-II will help to elucidate the mechanisms involved in normal as well as defective processing of apo C-II.