Serum and liver lipid composition and lecithin: cholesterol acyltransferase in horses, Equus caballus

Lipid classes in adipose tissues and liver differ between Shetland ponies and Warmblood horses

Fatty acids, as key components of cellular membranes and complex lipids, may play a central role in endocrine signalling and the function of adipose tissue and liver. Thus, the lipid fatty acid composition may play a role in health status in the equine. This study aimed to investigate the fatty acid composition of different tissues and liver lipid classes by comparing Warmblood horses and Shetland ponies under defined conditions. We hypothesized that ponies show different lipid patterns than horses in adipose tissue, liver and plasma. Six Warmblood horses and six Shetland ponies were housed and fed under identical conditions. Tissue and blood sampling were performed following a standardized protocol. A one-step lipid extraction, methylation and trans-esterification method with subsequent gas chromatography was used to analyse the total lipid content and fatty acid profile of retroperitoneal, mesocolon and subcutaneous adipose tissue, liver and plasma. Fatty acids were grouped according to their degree of saturation and their conjugated double bond into the respective lipid classes. In the adipose tissues, saturated fatty acids (SFAs) and n-9 monounsaturated fatty acids (n-9 MUFAs) were most present in ponies and horses. N-6 polyunsaturated fatty acids (n-6 PUFAs), followed by SFAs, were most frequently found in liver tissue and plasma in all animals. Horses, in comparison to ponies, had significantly higher n-6 PUFA levels in all tissues and plasma. In liver tissue, horses had significantly lower hepatic iso-branched-chain fatty acids (iso-BCFAs) than ponies. The hepatic fatty acid composition of selected lipid classes was different between horses and ponies. In the polar PL fraction, horses had low n-9 MUFA and n-3 PUFA contents but higher n-6 PUFA contents than ponies. Furthermore, iso-BCFAs are absent in several hepatic lipid fractions of horses but not ponies. The differences in fatty acid lipid classes between horses and ponies provide key information on the species- and location-specific regulation of FA metabolism, thus affecting health status such as inflammatory responses.

A fast method for the determination of the PC/LPC ratio in intact serum by MALDI-TOF MS: an easy-to-follow lipid biomarker of inflammation

The PC/LPC ratio of blood serum is increasingly considered to represent an important clinical parameter that reflects various kinds of diseases. Here, a simple and fast method of lipid analyses of "intact" blood serum (i.e. without extraction) by MALDI-TOF mass spectrometry is described. The novel procedure allows the accurate determination of the PC/LPC ratio, utilizing only a tiny amount of blood. The serum is diluted with distilled water and directly applied onto the MALDI target and, after drying, covered by a thin layer of the matrix solution (either 9-aminoacridine or 2,5-dihydroxybenzoic acid). Positive ion mass spectra acquired by using this procedure give similar peak patterns as the spectra of the lipid extracts of horse blood serum. Blood serum from fourteen different horses was used to set up and validate the new method of lipid analysis. The PC/LPC ratios determined with the fast "intact" method were compared with those obtained with classical MALDI-TOF MS and (31)P NMR analyses of the corresponding lipid extracts. As comparable data were obtained, this is a clear indication that extraction is not an absolute necessity.

High density lipoprotein cholesteryl ester metabolism in the pony, an animal species without plasma cholesteryl ester transfer protein activity: transfer of high density lipoprotein cholesteryl esters to lower density lipoproteins and the effect of the amount of fat in the diet

The metabolism of high density lipoprotein cholesteryl esters (HDL CE) was studied in the pony, an animal species without plasma cholesteryl ester transfer protein (CETP) activity. Studies were done in ponies fed a low- (1.5% fat, w/w) and a high-fat diet (11.5%, w/w fat). The ponies fed the high-fat diet had higher plasma HDL CE concentrations (1.08+/-0.15 vs. 0.84+/-0.11 mmol/l, mean+/-S.D., n=6, P<0.01) and plasma lipoprotein lipase (LPL) activities (14.3+/-4.0 vs. 5.7+/-3.4 micromol free fatty acids (FFA)/ml per h, P<0.05) than those on the low-fat diet. Plasma triacylglycerol (TAG) concentrations were lower on the high-fat diets (0.129+/-0.043 vs. 0.180+/-0.050 mmol/l), but these differences were not statistically significant. There was a negative correlation between the levels of plasma TAG (r=0.598, P<0.05) and VLDL CE (r=0.658, P<0.05) on the one hand and the HDL CE concentrations on the other hand. The transport rates of HDL CE were not significantly different between ponies fed high-fat (0.029+/-0.008 mmol HDL CE/h per l plasma) and those fed low-fat diets (0.024+/-0.004). HDL CE were transferred to low density lipoproteins (LDL) and we calculated that the percentage of LDL CE derived from HDL was 0.69+/-0.13 in the ponies fed the low-fat diet and 0.53+/-0.05 in the ponies fed the high-fat diet (P<0.05). The results of these in vivo studies suggest that in ponies, similarly as reported in rats and pigs, HDL CE can be transferred to LDL despite the absence of plasma CETP activity, and that the magnitude of this transfer is related to the levels of HDL CE as induced by the amount of fat in the diet.

In vitro Catabolism of very low density lipoproteins from horse (Equus caballus) by the action of autologous lipoprotein lipase

Incubation of equine very low density lipoproteins with lipoprotein lipase isolated from horse postheparin plasma resulted in the formation of lipoproteins of a higher density. Lipoproteins isolated after incubation and plasma lipoproteins had a different chemical composition and triacylglycerol fatty acid pattern. In vitro-obtained low density lipoproteins contained substantially more phospholipids and triacylglycerols but significantly less cholesteryl esters than native low density lipoproteins. Comparing the triacylglycerol fatty acid pattern of plasma very low density lipoproteins and in vitro--obtained low density lipoproteins, a drastic decrease in the proportion of linolenic acid was observed with increasing density.