Kouichi Taira

Effect of apolipoprotein E3/4 phenotype on postprandial triglycerides and retinyl palmitate metabolism in plasma from hyperlipidemic subjects in Japan

In a previous study it was shown that postprandial lipid metabolism is delayed in individuals with intra-abdominal visceral fat accumulation. Population studies have shown that as compared with individuals with apolipoprotein (apo) E3/3, those with phenotype apo E3/4 phenotype have higher plasma and low density lipoprotein (LDL)-cholesterol (C) concentration and increased susceptibility to coronary heart disease. The aim of the present study is to determine how apo E4 affects postprandial lipid metabolism by comparing individuals with apo E3/4 to those with apo E3/3 phenotype matched for abdominal visceral fat. Sixty-two Japanese subjects (41 male, 21 female) [average age 48+/-14 years; mean body mass index (BMI) 25+/-5.6 kg/m2] were recruited for this study. The subjects were divided into two groups: those with apo E3/3 (n=43) and those with apo E3/4 phenotype (n=19), as determined by isoelectric focusing (IEF). Visceral fat accumulation was analyzed as area of fat deposition by computerized tomography at the umbilicus level. After a 12-h overnight fasting, an oral vitamin A and a fatty meal were administered to these subjects. The plasma triglyceride (TG) increased significantly hours after fat loading in both groups but the levels of TG were significantly higher in apo E3/4 than in apo E3/3 phenotype at 2, 4 and 6 h after fat loading. Plasma retinyl palmitate (RP) levels were also significantly higher in individuals with apo E3/4 than in those with apo E3/3 phenotype at 2, 4 and 6 h after fat loading. This investigation was then conducted in both genders separately, and found that these associations were statistically significant in men. Furthermore, after matching men for fasting TG levels, these associations did not persist for plasma TG levels at any time point, while plasma RP levels were still significantly higher in apo E3/4 group at 2 and 6 h after fat loading. These results indicate that in Japanese population especially for men apo E phenotype E3/4 is associated with an impaired postprandial TG-rich lipoprotein metabolism relative to apo E3/3 phenotype when matched for intra-abdominal visceral fat accumulation, which has a substantial effect on the metabolism of plasma TG-rich lipoproteins.

A novel frameshift mutation in exon 6 (the site of Asn 291) of the lipoprotein lipase gene in type I hyperlipidemia

A new heterozygous lipoprotein lipase gene defect has been identified in a type I hyperlipidemic patient at the position of notable amino acid Asn 291. The patient is a 33-year-old male. His body mass index (BMI) was 18.5 kg/m2. The total cholesterol (TC), triglycerides (TG) and high density lipoprotein-cholesterol (HDL-C) concentration from his fasting plasma were 4.8, 11.9 and 0.4 mmol/l, respectively. The lipoprotein lipase (LPL) activity and mass in the postheparin plasma (PHP) from the patient were 0.58 mmol/ml/h (normal range: 7.7+/-2.6) and 244 ng/ml (normal range: 192+/-30), respectively. The hepatic lipase activity of the PHP from the patient was 10.6 mmol/ml/h (normal range: 9.9+/-3.6). DNA analysis of the LPL gene revealed that this patient had a heterozygous one nucleotide deletion of A coding Asn 291, resulting in a premature termination of the LPL protein at amino acid residue 303. The other abnormality in the LPL gene of the proband was an amino acid residue 194 defect (Ile194-->Thr), which is known to cause a defective enzyme. A medium-chain triglyceride (MCT) loading test was conducted to find how this triglyceride affects plasma lipoprotein metabolism in this patient in a short term (Fig. 3). The plasma total cholesterol (TC) or high density lipoprotein (HDL)-C levels did not change significantly after oral administration of a fatty meal containing long chain triglycerides (LCT) or MCT. The plasma TG level, on the other hand, increased from 11.9 to 19.2 mmol/l (+61%) at 6 h after loading a fatty meal containing LCT, whereas the plasma TG levels tended to even decrease at 6 h after oral administration of an MCT, tricaprin (from 11.6 to 10.5 mmol/l (-9.4%)). These results suggest that MCT, as opposed to LCT, is useful for treatment of type I hyperlipidemia with a novel mutation at the notable amino acid Asn 291 of the LPL gene.

Marked elevation in serum apolipoprotein E in a case of heterozygous cholesteryl ester transfer protein deficiency.

The subject was a 57-year-old Japanese woman with a body mass index of 21.2 kgm(-2). Her serum total cholesterol (TC), triglycerides (TG) and HDL-cholesterol levels were 7.11 mmoll(-1), 0.53 mmoll(-1) and 2.05 mmoll(-1), respectively. She had a marked increase of serum apolipoprotein (Apo) E concentration of 25 mgdl(-1) with normal concentrations of serum Apo A-I, A-II, B, C-II and C-III. Polymerase chain reaction-restriction fragments length polymorphism analysis of the cholesteryl ester transfer protein (CETP) gene from this subject revealed the heterozygous nucleotide change causing a Asp442 to Gly substitution (D442G) in the CETP protein. For comparison, 11 unrelated female subjects with this mutation (age, 57+/-5.1 years; BMI, 22+/-1.5 kgm(-2); TC, 7.23+/-1.16 mmoll(-1); TG, 1.44+/-0.80 mmoll(-1); HDL-C, 2.47+/-0.53 mmoll(-1)) were found to have a serum Apo E concentration of 7+/-1.5 mgdl(-1), about a third of the patients concentration. The lipoprotein profile of the probands serum analyzed by disk polyacrylamide gel electrophoresis showed a trace amount of VLDL. A vitamin A fat-loading test showed little increase in serum triglycerides and retinyl palmitate levels compared with control subjects at 2, 4 and 6 h after fat loading. Ultracentrifugation analysis of her serum revealed no detectable Apo E in the VLDL fraction but showed a large amount of Apo E in the HDL fraction, in contrast to a normal control, who had Apo E in the VLDL fraction as well as in the HDL fraction. Sequence analysis of the Apo E gene from the subject showed no nucleotide changes in exon 3 and exon 4, which code the mature Apo E protein, indicating there is no structural abnormality in the Apo E protein. Direct sequence analysis of the LDL receptor gene also did not show any nucleotide change. Based on these findings, it was hypothesized that the marked increase of Apo E in the patients serum was caused by a decreased transfer of Apo E from HDL particles to TG-rich lipoproteins or impaired uptake of Apo E-containing HDL by LDL receptor or remnant receptor, due presumably to a dysfunction of these receptors in the patient.