Enzymatic hydrolysis of fractionated products from oils thermally oxidized in the laboratory

Effects of DNA polymerase inhibitory and antitumor activities of lipase-hydrolyzed glycolipid fractions from spinach

We succeeded in purifying the major glycolipid fraction in the class of sulfoquinovosyl diacylglycerol, monogalactosyl diacylglycerol and digalactosyl diacylglycerol (DGDG) from a green vegetable, spinach (Spinacia oleracea L.). This glycolipid fraction was an inhibitor of DNA polymerases and a growth inhibitor of NUGC-3 human gastric cancer cells, and, interestingly, the activities were much stronger when the fraction was hydrolyzed by lipase. Glycolipids in the hydrolyzed fraction consisted of sulfoquinovosyl monoacylglycerol (SQMG), monogalactosyl monoacylglycerol (MGMG) and DGDG. In the in vivo antitumor assay using Greene's melanoma, the fraction containing SQMG, MGMG and DGDG showed to be a promising suppressor of solid tumors. Spinach glycolipid fraction might be a potent antitumor compound if directly injected into a tumor-carrying body, and this fraction may be a healthy food material that has antitumor activity.

A novel DNA polymerase inhibitor and a potent apoptosis inducer: 2-mono-O-acyl-3-O-(alpha-D-sulfoquinovosyl)-glyceride with stearic acid

Sulfo-glycolipids in the class of sulfoquinovosyl diacylglycerol (SQDG) including the stereoisomers are potent inhibitors of DNA polymerase alpha and beta. However, since the alpha-configuration of SQDG with two stearic acids (alpha-SQDG-C(18)) can hardly penetrate cells, it has no cytotoxic effect. We tried and succeeded in making a permeable form, sulfoquinovosyl monoacylglycerol with a stearic acid (alpha-SQMG-C(18)) from alpha-SQDG-C(18) by hydrolysis with a pancreatic lipase. alpha-SQMG-C(18) inhibited DNA polymerase activity and was found to be a potent inhibitor of the growth of NUGC-3 cancer cells. alpha-SQMG-C(18) arrested the cell cycle at the G1 phase, and subsequently induced severe apoptosis. The arrest was correlated with an increased expression of p53 and cyclin E, indicating that alpha-SQMG-C(18) induced cell death through a p53-dependent apoptotic pathway.

Effects of glycolipids from spinach on mammalian DNA polymerases

We purified the major glycolipids in the class of monogalactosyl diacylglycerol (MGDG), digalactosyl diacylglycerol (DGDG) and sulfoquinovosyl diacylglycerol (SQDG) from a green vegetable, spinach (Spinacia oleracea L.). MGDG was an inhibitor of the growth of NUGC-3 human gastric cancer cells, but DGDG and SQDG had no such cytotoxic effect. Therefore, we studied MGDG and its monoacyglycerol-form, monogalactosyl monoacylglycerol (MGMG), in detail. MGMG with one fatty acid molecule was obtained from MGDG with two fatty acid molecules by hydrolyzing with a pancreatic lipase. MGMG was also found to prevent the cancer cell growth. MGDG was a potent inhibitor of replicative DNA polymerases such as alpha, delta and epsilon. MGMG inhibited the activities of all mammalian DNA polymerases including repair-related DNA polymerase beta with IC(50) values of 8.5-36 microg/mL, and the inhibition by MGMG was stronger than that by MGDG. Both MGDG and MGMG could halt the cell cycle at the G1 phase, and subsequently induced severe apoptosis. The relationship between the DNA polymerase inhibition and the cell growth effect by these glycolipids is discussed.

Column and high-performance size exclusion chromatography applications to the in vivo digestibility study of a thermoxidized and polymerized olive oil

This study aimed (i) to design an in vivo model to study fat digestibility, and (ii) to apply this design to test the in vivo digestibility of a highly thermoxidized olive oil. True digestibility of unheated olive oil was tested 2, 4, 6, and 7 h after administering 1 g of olive oil/100 g body weight to young adult Wistar rats by means of esophageal probes. Remaining gastrointestinal lumen fat showed an inversely linear relationship (r= -0.9932; P < 0.001) with the length of the experiment. A 4-h test was considered adequate because after this period, half of the oil administer still remains in the lumen, making it possible to accurately measure the different nondigested, nonabsorbed thermoxidized compounds. In a second experiment, fresh olive oil (3.6 mg polar content/100 mg oil) was heated at 180 degrees C for 50 h in the presence of air; the polar content in this oil rose to 46.0 mg/100 mg oil. After 4 h, the true digestibility coefficient of 50-h heated olive oil did not significantly change, although it tended to decrease (24%) with respect to the unheated oil. Silica gel column chromatography and high-performance size exclusion chromatography were used to quantify nonthermoxidized and thermoxidized products present in the oils and in the gastrointestinal lumen after these test periods. True digestibility of the different thermoxidized compounds from the heated oil was 30-40%, whereas that of thermoxidized compounds from the fresh oil was much higher (approximately 80%). Nonoxidized triacylglycerol hydrolysis was negatively affected by the presence of large amounts of thermoxidized compounds. The present proposed model seems to be a useful tool for the study of thermoxidized oils. Data also show that thermoxidized compounds from abused olive oil are poorly but actively hydrolyzed and absorbed in vivo.

Absorption in rats of rapeseed, soybean, and sunflower oils before and following moderate heating

Rapeseed, soybean, and sunflower oil were heated for 15 min in a 5-mm oil layer in a pan at 180 degrees C. The fatty acid composition was almost unaffected by heating, while the polymer content rose slightly and the tocopherol content decreased, except in soybean oil. The absorption of oils before and after heating was investigated in lymph-cannulated rats. Oils were administered as emulsions through a gastrostomy tube and lymph was collected during the next 24 h. The highest accumulated lymphatic transport of total fatty acids was observed after administration of rapeseed oil, and the lowest after heated sunflower oil. The accumulated transport was similar for all unheated oils. The transport of fatty acids was significantly lower in rats receiving heated oil compared to those receiving the corresponding unheated oil. Small increases in polymers may have contributed to the decreased lymphatic transport of oil following heating, although this probably does not fully explain the effect. The absorption of sunflower oil was more affected by heating than the absorption of soybean or rapeseed oil. Furthermore, the largest decrease in total activity of tocopherols following heating was observed in sunflower oil. Overall, these results demonstrate that the absorption of vegetable oils is affected by moderate heating.

Hydrolysis of used frying palm olein and sunflower oil catalyzed by porcine pancreatic lipase

The enzymatic hydrolysis of frying used vegetable oils with different degrees of alteration were measured using porcine pancreatic lipase (acylglycerol acylhydrolase EC 3.1.1.3). Successive frying of potatoes significantly increased the level of total polar lipid content in the palm olein from 9.3 +/- 0.1 mg/100 mg oil to 26.4 +/- 0.3 mg/100 mg oil after 90 fryings, and from 4.0 +/- 0.1 mg/100 mg oil to 27.7 +/- 0.3 mg/100 mg oil in sunflower oil after 60 fryings. Triacylglycerol polymers, triacylglycerol dimers, and oxidized triacylglycerols also increased 37-, 7.9-, and 7.5-times in palm olein, respectively, and 56-, 22-, and 4.7-times in sunflower oil, respectively. However, diacylglycerols and free fatty acid levels related to hydrolytic alteration did not increase with the number of fryings in both oils. The substrate concentration in the reactor was determined by calculating the molecular weight of each oil showing a different degree of alteration. We compared the methodology used by us and that used by other authors. The results show that the methods are reproducible and that the values obtained are in concordance with theoretical values. The kinetic parameters apparent Michaelis-Menten constant (KMapp) and apparent maximum velocity of hydrolysis (Vmaxapp) were different in unused palm olein (5.1 +/- 0.7 and 166 +/- 7.6, respectively) than in sunflower oil (2.2 +/- 0.3 and 62 +/- 2.2, respectively). However, changes in KMapp and Vmaxapp were not related to the degree of alteration of the oils.

Hydrolysis of fish oils containing polymers of triacylglycerols by pancreatic lipase in vitro

Fish oils containing different levels of polymers of triacylglycerols formed during autoxidation were incubated with pancreatic lipase to establish whether these polymers are substrates for lipase hydrolysis. With oils containing low amounts (less than 4%) of triacylglycerol polymers as substrates, both triacylglycerols and polymers of triacylglycerols were almost completely hydrolyzed, and fatty acid monomers and monoacylglycerols were the major lipid products. Under the same incubation conditions, some triacylglycerols remained intact when highly oxidized oils containing 20 or 30% triacylglycerol polymers were the substrate. The fatty acid composition of these residual triacylglycerols was almost identical to that of triacylglycerols present at the start of the assay. When fish oil containing 30% triacylglycerol polymers was incubated with the lipase, the component triacylglycerols and polymers of triacylglycerols were hydrolyzed at similar rates, and fatty acid dimers were detected as a product. It is concluded that the high molecular weight polymers of triacylglycerols present in oxidized fish oils can be hydrolyzed by pancreatic lipase in vitro.

Cyclic fatty esters: synthesis, characterization, and lipolysis of isomeric triglycerides of 9-(6-propyl-3-cyclohexenyl)-(Z)8-nonenoic acid

Triglycerides of a model cyclic fatty acid (CFA) 9-(6-propyl-3-cyclohexenyl)-(Z)8-nonenoic acid (Ia) were synthesized for biological and toxicity evaluations. The monoacid triglyceride II (CyCyCy) was interesterified with triolein (OOO) to obtain mixtures of diacid triglycerides: III (OOCy), IV (OCyO), V (OCyCy), and VI (CyOCy). The interesterification mixtures were separated by preparative HPLC into two 'critical pairs' of isomeric triglycerides. Triglycerides III-VI were synthesized and a 13C-NMR method was developed to estimate 'critical pairs'. CFA-triglycerides were characterized by IR, NMR, HPLC and capillary GLC, and their relative rates of hydrolysis by lipase were compared. Although tricyclin (II) was completely resistant to lipolysis, triglycerides III and VI hydrolyzed significantly slower than triolein, and the 'critical pairs' hydrolyzed as readily as triolein. Therefore, partial CFA-triglycerides formed in heat-abused fats can undergo lipolysis and likely be absorbed like normal dietary fats.

Enzymatic hydrolysis in vitro of thermally oxidized sunflower oil

The hydrolysis of thermally oxidized sunflower oil by pancreatic lipase was studied in relation to chemical changes in the acylglycerols. Four classes of compounds (monomers, dimers, trimers and polymers) formed from the acylglycerols were separated from the heated oils by column chromatography on silica gel, and further verified by thin layer chromatography. Each fraction, after analyses for generaly properties, was subjected to a time course study of hydrolysis by pancreatic lipase over a 30-min period. After 70 hr of heating, the amount of hydrolysis for the acylglycerol dimers was only about half that of the monomers, and that for the trimers was, in turn, about one-third that of the monomers. The polymers were the least hydrolyzed and showed no further reaction after 5 min. The reduction in enzymatic hydrolysis of isolated fractions from the thermally oxidized oils indicates structural differences, related to formation of polar compounds and polymerization products. Adverse effects on animals from feeding these materials can be attributed partly to inhibition of hydrolysis resulting in less available energy.