High plasma triglyceride (TG) level is a major independent risk factor of coronary heart disease. A newly identified Apolipoprotein A5 (Apoa5) gene has been shown to play an important role in determining plasma TG concentrations in humans and mice. Prague hereditary hypertriglyceridemic (HTG) rats are a useful model of human hypertriglyceridemia and other symptoms of metabolic syndrome. Thus, the variation of Apoa5 gene and its expression were studied in this strain under normal conditions and after chronic fructose loading. Lewis and Wistar rats served as normotriglyceridemic controls. Plasma TG were significantly higher in HTG rats in comparison with both control strains. Sequence analysis of the rat Apoa5 gene revealed the existence of two introns. However, screening of the coding regions and intron-exon boundaries of Apoa5 gene did not indicate any mutation of this gene in HTG rats in comparison with Lewis and Wistar ones. Under the basal conditions the expression of Apoa5 was lower in all age groups of HTG rats compared to Wistar animals. Furthermore, during chronic fructose loading there were no significant changes of Apoa5 expression in HTG rats, although plasma TG levels rose 3-4 times within first two days of fructose loading and were increased during the whole period of fructose treatment. In conclusion, Apoa5 does not seem to be a genetic determinant of hypertriglyceridemia in HTG rats. The absence of significant changes in Apoa5 gene expression during chronic fructose-induced TG elevation excludes its major role in mechanisms compensating severe hypertriglyceridemia.
The important role of APOAV gene variants in determination of plasma triglyceride levels has been shown in many population studies. Recently, an influence of APOAV T-1131>C polymorphism on C-reactive protein (CRP) in young Korean males has been reported. We have therefore analyzed a putative association between T-1131>C, Ser19>Trp and Val153>Met APOAV variants (PCR and restriction analysis) and CRP concentrations in 1119 Caucasian males, aged between 28 and 67 years (49.2±10.8 years). The frequency of C allele carriers was lower in Caucasians than in Koreans (15.5 % vs. 46.2 %). CRP levels did not differ between T/T homozygotes (n=946, 1.61±2.05 mg/l) and carriers of the C allele (n=173, 1.67±1.95 mg/l). Thus, in contrast to Korean males, T-1131>C APOAV variant has no effect on plasma concentrations of CRP in a large group of Caucasian males. Other APOAV variants (Ser19>Trp and Val153>Met) did not also influence plasma concentrations of CRP. APOAV variants are unlikely to be an important genetic determinant of plasma CRP concentrations in Caucasian males.
The ATP-binding cassette (ABC) superfamily of active transporters involves a large number of functionally diverse transmembrane proteins. They transport a variety of substrates including amino acids, lipids, inorganic ions, peptides, saccharides, metals, drugs, and proteins. The ABC transporters not only move a variety of substrates into and out of the cell, but also are also involved in intracellular compartmental transport. Energy derived from the hydrolysis of ATP is used to transport the substrate across the membrane against a concentration gradient. The typical ABC transporter consists of two transmembrane domains and two nucleotide-binding domains. Defects in 14 of these transporters cause 13 genetic diseases (cystic fibrosis, Stargardt disease, adrenoleukodystrophy, Tangier disease, etc.). Mutations in three genes affect lipid levels expressively. Mutations in ABCA1 cause severe HDL deficiency syndromes called Tangier disease and familial high-density lipoprotein deficiency, which are characterized by a severe deficiency or absence of high-density lipoprotein in the plasma. Two other ABCG transporters, ABCG5 and ABCG8, mutations of which cause sitosterolemia, have been identified. The affected individuals absorb and retain plant sterols, as well as shellfish sterols.
Animal studies (on transgenic and knock-out mice) and human association analysis assessed the importance of APOAV gene for plasma triglyceride determination. New APOAV missense variants (Val153 → Met and Cys185 → Gly) have been detected recently. We have analyzed these variants in 83 unrelated patients with extreme lipid parameters (triglycerides of 20.4±12.8 mmol/l and total cholesterol of 10.4±3.7 mmol/l) and in a control population group consisting of 2,559 unrelated Caucasians. In patients, the frequency of the Met153 carriers was slightly but not significantly higher (9.64 % vs. 6.49 %) compared to the population sample. This suggested that Val153 → Met polymorphism in the APOAV gene does not represent an important risk factor for developing the extreme levels of plasma triglycerides. We did not detect carriers of the Gly185 allele among patients or 420 healthy individuals. We suppose that this variant is probably not present in Caucasian populations.
ABCG5 and ABCG8 transporters play an important role in the absorption and excretion of sterols. Missence polymorphisms (Gln604Glu in the ABCG5 and Asp19His, Tyr54Cys, Thr400Lys, and Ala632Val in the ABCG8) in these genes have been described. In 131 males and 154 females whose dietary composition markedly changed and lipid parameters decreased over an 8-year follow-up study (total cholesterol decreased from 6.21±1.31 mmol/l in 1988 to 5.43±1.06 mmol/l in 1996), these polymorphisms were investigated using PCR. Plasma lipid levels and changes in plasma lipid levels were independent of the Gln604Glu polymorphism in ABCG5 and Asp19His and the Ala632Val polymorphisms in ABCG8. The Tyr54Cys polymorphism influenced the degree of reduction in total plasma cholesterol (D –0.49 mmol/l in Tyr54 homozygotes vs. D +0.12 mmol/l in Cys54 homozygotes, p<0.04) and LDL-cholesterol (D –0.57 mmol/l in Tyr54 homozygotes vs. D +0.04 mmol/l in Cys54 homozygotes, p<0.03) levels between 1988 and 1996 in females, but not in males. Male Thr400 homozygotes exhibited a greater decrease in total cholesterol (D –0.90 mmol/l vs. D –0.30 mmol/l, p<0.02) and LDL-cholesterol (D –0.62 mmol/l vs. D –0.19 mmol/l, p<0.04) than Lys400 carriers. No such association was observed in females. We conclude that Tyr54Cys and Thr400Lys variations in the ABCG8 gene may play a role in the genetic determination of plasma cholesterol levels and could possibly influence the gender-specific response of plasma cholesterol levels after dietary changes. These polymorphisms are of potential interest as genetic variants that may influence the lipid profile.
Through the analysis of the common apolipoprotein (apo) E gene polymorphism in large Caucasian population study with the PCR and subsequent restriction analysis, we have identified carriers of mutant allele Arg136→Ser. Both of them (71-years-old female and her 43-years-old son) have normal lipid parameters. We suggest that Arg136→Ser mutation in apoE is not necessarily connected with elevated lipid levels in all cases. Furthermore, so far unidentified factors (environmental and/or genetic) are important for the development of lipid metabolism disorders in apoE Arg136→Ser mutation carriers.
The aim of the study was to ascertain whether the A-204C polymorphism in the cholesterol 7alfa-hydroxylase (CYP7A1) gene plays any role in determining LDL-cholesterol (LDL-C) concentration responsiveness to a high-fat diet. The concentrations of total cholesterol and LDL-cholesterol were measured in eleven healthy men (age: 30.9±3.2 years; BMI: 24.9±2.7 kg/m2) who were homozygous for either the -204A or -204C allele, after 3 weeks on a low-fat (LF) diet and 3 weeks on a high-fat (HF) diet. During both dietary regimens, the isocaloric amount of food was provided to volunteers; LF diet contained 22 % of energy as a fat and 2.2 mg of cholesterol/kg of body weight a day, HF diet 40 % of fat and 9.7 mg of cholesterol/kg of body weight a day. In six subjects homozygous for the -204C allele, the concentrations of cholesterol and LDL-cholesterol were significantly higher on HF than on LF diet (cholesterol: 4.62 vs. 4.00 mmol/l, p<0.05; LDL-C: 2.15 vs. 1.63 mmol/l, p<0.01, respectively); no significant change was observed in five subjects homozygous for the -204A allele. There were no other differences in lipid and lipoprotein-lipid concentrations. Therefore, the polymorphism in the cholesterol 7α-hydroxylase promotor region seems to be involved in the determination of cholesterol and LDL-C responsiveness to a dietary fat challenge.