Síntese química da dienantina e da trienantina e avaliação toxicológica do consumo crônico em ratos

Abstract

Medium chain triacylglycerols (MCT), as found in milk fat and coconut and palm oil, are recommended as a source of rapidly available energy for pre- and postchirurgical patients, and for those with burns, cancers or presenting disorders associated with the absorption and/or metabolism of long chain triacylglycerols. Typically, however, short and medium chain fatty acids contribute only ca. 3% of the total daily dietary intake of lipids. Synthetic MCT have been obtained from glycerol and medium chain fatty acids by esterification or trans-esterification either chemically or enzimatically. The aim of the present study was chemically to synthesize esters of glycerol with enantic acid, and evaluate the possible toxic effects of the long term consumption of these esters on growth, lipid metabolism, and the integrity of the tissues of the liver, kidney and small intestine of rats. For the esterification reaction, glycerol (365 mmol) and enantic acid (1415 mmol) were mixed continuously for 100h in a round bottom flask held at 130°C under vacuum (10 mmHg). The product thus obtained was alkali-refined by the addition of aqueous sodium carbonate solution (5%) followed by extraction with dichloromethane. The esters were characterized by infra-red, 1H- and 13C-NMR spectroscopy and mass spectrometry. The yield of the esterification reaction was 65%, and the product oil (TAGC7) contained 2% of monoacylglycerol, 34% of diacylglycerol and 64% of triacylglycerol; NMR data indicated that the diacyl product was 1,3-dienantin. For the biological study, 30 newly weaned male Wistar rats were divided into 3 groups of 10 animals. Over a 9 month period, the control group received a diet containing soya oil as lipid source, whilst the two experimental groups (TAGC7 30% and TAGC7 50%) received diets in which either 30 or 50%, respectively, of the soya oil was substituted with the oil product TAGC7. A fourth group of 7 animals, each being 10 months old and with the same provenance and characteristics as the previous groups, was used as a further control in order to verify the biochemical and histological results. For the evaluation of growth, protein efficiency ratio and feed efficiency were determined during the first 28 days of experimentation. The coefficient of lipid digestibility was assessed during the period of growth and in the adult animals. For the evaluation of hepatic and renal function and the profile of circulating lipids, serum biochemical proofs of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, γ-glutamyl transferase, albumin, total protein, urea, creatinin, uric acid, triacylglycerides, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, very low-density lipoprotein cholesterol, glucose and total iron were determined. For this purpose, blood was collected from the retro-orbital plexus at the end of the experimental period. Histological analyses of the liver, kidney and small intestine were made using the light microscope. The null hypothesis (that all diets were equal) was tested statistically at p<0.05 using analyses of variance, Tukey and Kruskal-Wallis tests, method of the multiple comparisons, test for rations, coefficients of correlation and Student’s test. All diets were equally efficient in the promotion of growth in young rats, but in the adult phase the coefficient of lipid digestibility for TAGC7 50% diet was significantly greater than that of the control diet. Long term consumption of the experimental oil, as substituted for soya oil at the levels employed in this study, did not induce significant differences in the biochemical parameters analyzed in relation to the control group. All animals in the control and experimental groups presented some degree of liver steatosis but, since the TAGC7 50% group showed a smaller number of serious cases compared with the control group (p<0.05). However, the experimental oil exerts a hepatoprotective effect. Hyaline-type material was observed in the lumen of the glomerular tubules in all animals, and this was compatible with the physiological proteinuria associated with this species. Abnormalities observed in the small intestine, ie atrophy or hyperplasia of the villus, and non-specific alterations in the duodenum were similarly distributed in all of the groups. Such alterations were not related to the presence of the experimental oil in the diet and their cause remains obscure. It is concluded that the long term consumption of the experimental oil, under the conditions employed in the present study, did not exert any toxic effect in rats.