Effects of isocaloric changes in dietary fat and carbohydrates on plasma lipids and apolipoproteins (Apo) A, A-I, and B were assessed in twenty-five healthy men. Initial diet provided 31% energy from fats and 53% from carbohydrates (Period 1). For a period of five weeks, subjects received a high fat diet with 44% energy from fats and 40% from carbohydrates (Period 2). They then returned to the initial normal fat diet (Period 3). Throughout the three periods, energy intake (mean±SD, 2, 761±491kcal/day), polyunsaturated to saturated fatty acid ratio (P/S ratio: 0.38 for Periods 1 and 3, and 0.35 for Period 2), and cholesterol intake (mean±SD, 298±132mg/day) were kept unchanged. At the end of each period, plasma lipids were measured by standard methods and apolipoproteins by laser immunonephelometry. During the high fat diet (Period 2), triglycerides (TG) and apolipoprotein B (Apo-B) increased, as did Apo-A, while the ratio of HDL-cholesterol (HDL-C) to Apo-A was statistically unchanged. However, total cholesterol (TC), HDL-C and LDL-C showed no consistent change. Once the initial normal fat diet was resumed (Period 3), TG and Apo-B decreased, and TG nearly returned to the initial values and Apo-B showed a marked decrease. HDL-C decreased, as did Apo-A-I, but the ratio of HDL-C/Apo-A-I remained unchanged. Levels of TC and LDL-C were not altered. Isocaloric changes in dietary lipids and carbohydrates affect TG and Apo-A and B synthesis and probably lead to consequent alterations in the composition of lipoproteins.
The effect of dietary fats on the low density lipoprotein (LDL) receptor activity of circulating blood mononuclear cells was investigated in 11 healthy women who consumed a 6-week normocaloric diet consisting of 54% of the calories as carbohydrate, 16% as protein, and 30% as fat. The tested fats were successively low erucic acid rapeseed (LEAR) oil, sunflower oil, peanut oil, and milk fats (butter and cream). Changes in total cholesterol levels according to the fat reflected changes in LDL-cholesterol but not in high density lipoprotein (HDL)-cholesterol. This effect was accompanied by modifications of the LDL receptor activity in freshly isolated blood mononuclear cells, quantified as the amount of [125I]LDL associated with cells: a negative correlation existed between total or LDL-cholesterol levels in plasma and LDL receptor activity (r=-0.35, p<0.05). Moreover, LDL receptor activity of cells was related to the daily intake of saturated fatty acids, particularly C16:0+C18:0. We conclude that a possible mechanism is a modification in the rate of endocytosis of LDL receptor due to changes in the membrane fluidity according to the dietary fat.
Since lipid peroxides (LPO) possess cytotoxic characteristics, a study of the influence that oxidized low density lipoprotein (LDL) has on insulin receptors was performed by employing human cultured lymphocytes (IM-9 cells). The oxidized LDL was produced by ultraviolet irradiation, and a 5-min irradiation resulted in an LPO concentration reaching 2.6 times that of the preirradiated value. The insulin binding for each concentration of oxidized LDL was as follows: the control (before ultraviolet irradiation) was 7.0±0.46% (mean±SE); while 2-min irradiated LDL gave 6.7±0.70%; 5-min irradiated, 4.9±0.69%; 10-min, 4.0±0.17%; 20-min, 4.5±0.24%. That is, a significant decrease in insulin binding was observed following treatment with LDL irradiated for 5, 10, or 20min (p<0.05, p<0.01, p<0.01, respectively). Scatchard analysis indicated that such a drop in insulin binding was not caused by any decrease in the number of receptors, but by a decrease in affinity. Preincubation of the cells with vitamin E showed an inhibitory trend against these decreases; furthermore, this drop in insulin binding was found to be irreversible when cells that had been incubated for 24h with fetal bovine serum-free, oxidized LDL had been washed and incubated for another 24h prior to binding assay. The above evidence suggests that the oxidized LDL acts directly on the membrane of IM-9 cells and causes a drop in the affinity of the insulin receptors.
Previously we reported that human breast cancer cell strain MCF-7 released an extremely large amount of a human epidermal growth factor (hEGF)-like immunoreactive factor (designated as MCF-7 EGF) into the culture medium. In this paper, we examined in detail the synthesis and secretion of MCF-7 EGF by the cells. Our enzyme immunoassay system for hEGF distinguished MCF-7 EGF from hEGF or transforming growth factor type-α. The amount of MCF-7 EGF secreted increased linearly up to 24h. Secretion of the molecule was inhibited by cycloheximide and actinomycin D, but not by cytosine arabinoside, suggesting that synthesis of MCF-7 EGF requires DNA transcription but not DNA replication. A significant amount of MCF-7 EGF was detected in the cells. Intracellular MCF-7 EGF showed the same properties as the extracellular form in its antigenicity, molecular weight, and isoelectric point. In the presence of the ionophore monensin, the amount of extracellular MCF-7 EGF decreased greatly and that of intracellular MCF-7 EGF increased, indicating that MCF-7 EGF is secreted from its intracellular site via the Golgi apparatus into the culture medium. β-Estradiol specifically stimulated production of MCF-7 EGF, revealing hormonal regulation of synthesis of the factor. Possible involvement of MCF-7 EGF in the development and progress of mammary tumors is also discussed.
Plasma lipoprotein lipid, triglyceride clearance, and post-heparin lipolytic activity were measured in young (2 months old) and aged (24 months old) male Wistar-King rats. Very low density lipoprotein and low density lipoprotein lipids (cholesterol, triglyceride, and phospholipid) and high density lipoprotein cholesterol were increased significantly in aged rats compared with the levels in young rats. Oral oil loading increased the plasma triglyceride levels to a greater extent in aged rats, and the clearance of plasma triglyceride following intravenously administered lipid occurred at a lower rate in the old rats. Lipoprotein lipase activities in post-heparin plasma and adipose tissue were higher in the young than that in the aged. These results suggest that hypertriglyceridemia in aged rats might be partly due to the delayed clearance of triglyceride by lipoprotein lipase.
Nerve growth factors (NGF's) were purified from mouse submaxillary gland, guinea pig prostate gland, bovine seminal plasma, and venom of Naja naja atra, and their biochemical and immunological properties were compared. The NGF's from the four sources stimulated the maximal response of nerve fiber outgrowth from chick dorsal root ganglia at 10ng/ml. Two-site enzyme immunoassay (EIA) systems for these NGF's showed that mouse NGF, guinea pig NGF, and bovine NGF were similar in immunological properties and that the crossreactivity was less than 1% between snake NGF and mammalian NGF's. However, pretreatment with anti-snake NGF antibody inhibited the biological activity of mammalian NGF's even when their immunological activity was not completely inhibited. These results suggest that snake NGF and mammalian NGF's are similar in their biological activity but not in their immunological activity and that anti-snake NGF antibody recognizes the parts of mammalian NGF's essential for the biological activity.
In the previous paper, the content of prostaglandin D2 (PGD2) was found to be five times higher than that of PGF2α or PGE2 in rat gastric mucosa. Thus, the effect of exogenous PGD2 on ethanol-induced gastric mucosal lesions was studied. Intragastric administration of 500μg/kg of PGD2, which did not inhibit gastric acid secretion, but did stimulate pepsin secretion, significantly prevented ethanol-induced ulcer formation compared with the control group. Although 100μg/kg of PGD2, also given intragastrically, prevented ethanol-induced ulcer formation compared with the control group, the difference was not statistically significant. Gastric mucosal blood flow (GMBF) in the corpus ventriculi measured by the hydrogen gas clearance technique was significantly increased when PGD2 was given intragastrically at 100 or 500μg/kg. These results suggest that PGD2 has anti-ulcerogenic effect in the stomach and that an increase in GMBF might be one of factors by which this effect is mediated.
The effects of oleic acid and the serum from two patients with Reye's syndrome (RS-serum) on the respiratory control ratio (RCR) of rat liver mitochondria were studied; the reaction site of each reagent was determined by using various substrates for the respiratory chain. The results were as follows: 1. Pre-incubation of rat liver mitochondria with oleic acid induced a decrease in RCR when succinate or ascorbate+cytochrome c were employed as substrates. 2. Under the identical conditions, RS-serum induced a significant decrease in RCR with ascorbate+cytochrome c. 3. When KCN was added to the assay medium, both oxygen consumption rate and RCR were decreased as expected in oxidizing ascorbate+cytochrome c. But the effect of KCN was less obvious when pyruvate+L-malate were employed as substrates. The latter phenomenon might suggest that the rate-limiting step in the electron transport system from NADH to O2 resided on the substrate side and not on the side between coenzyme Q and O2. Among the substrates (succinate, pyruvate+L-malate, ascorbate+N, N, N′, N′-tetramethyl-phenylenediamine, ascorbate+cytochrome c) tested, the strongest effect was observed when ascorbate+cytochrome c were employed as substrates. These results suggest that both oleic acid and RS-serum showed similar substrate-specific inhibition of RCR, predominantly at the site of cytochrome c oxidase. Thus, a localized effect of oleic acid or RS-serum on the mitochondrial respiratory chain became apparent.