Apoptosis during the development of the hepatic steatosis in force-fed ducks and cooking yield implications.

Mule ducks were force-fed for 12 d to determine whether or not signs of apoptosis could occur during the development of the hepatic steatosis induced by the huge quantities of corn ingested twice daily by the birds. Presence of apoptosis in hepatocytes was assessed through the measurements of increased activities of capsase-3 +-7, -8, and -9. From d 0 of the force-feeding period until d 8, activities of the different caspases remained at a low level. On the contrary, at d 10 and d 12, activities of all measured caspases dramatically increased, indicating that apoptosis occurred at this stage, which corresponds to the time of accumulation of large quantities of lipids in the hepatic cells.The melting level of the liver issued from force-feeding ("foie gras") during cooking is a point of interest for processors because it could degrade the quality of this delicate dish. In this study, we used the levels of caspases activities to improve the predictability of foie gras cooking, in addition to other parameters usually used, such as its weight or lipid content. From this improvement, we suggest that part of the variability of melting during cooking of fatty livers could reside in more or less intense activity of hepatic proteases.

Effect of different chilling rates on the quality parameters of mule duck fatty liver.

The aim of this experiment was to study the effect of chilling rates on the quality features of fatty livers. Three different chilling rates were applied: ultra-fast (UF), fast (FA), and slow (SL). Technological and proteomic results were compared at time T1 when the internal temperature of livers reached 10°C and at time T2=24 h post mortem. Samples from the UF group reached the T1 temperature at 50 min post mortem and had the least hard livers and the lowest cooking loss percentage (25±9%) at time T2=24 h post mortem (P-value of <0.01). The FA and SL groups reached the T1 temperature after 120 and 210 min post mortem and presented higher melting (36±9 and 41±9%, respectively, at time T2) and harder livers compared to the UF group. In parallel, we conducted semi-quantifications of proteins by electrophoresis and proteolytic activities by mono-dimensional zymography for three families of proteases: Matrix metalloproteases (MMP), Cathepsins, and Calpains. The proteomic assays revealed less modified proteolytic activities in samples from the UF group, and less associated proteins degradations than in samples from the FA and the SL groups. Effects of the different chilling rates were mainly significant at time T2 (24 h post mortem). As a conclusion we were able to highlight an indirect positive relation between proteolysis and melting yield in ducks' fatty liver.

Proteolytic activity alterations resulting from force-feeding in Muscovy and Pekin ducks.

We investigated liver protease activity in force-fed and non-force-fed ducks using zymography gels to better understand mechanisms underlying liver steatosis in palmipeds. Male Muscovy and Pekin ducks were slaughtered before and after a short period (13 d) while they were conventionally fed or force fed. The force-fed regimen contained a high level of carbohydrates and was delivered in large doses. Main hepatic proteases (matrix metalloprotease-2, calpains, and cathepsins) were extracted from raw liver and specifically activated within electrophoretic gels. Both force-fed Muscovy and Pekin ducks presented higher liver weights and BW associated with lower matrix metalloprotease-2 and m-calpain hepatic activities. On the other hand, hepatic cathepsin activity was not affected by force feeding. It was concluded that Muscovy and Pekin duck hepatic proteases are affected similarly by the force feeding. Thus, this cannot explain differences observed between Muscovy and Pekin ducks regarding their ability to develop hepatic steatosis generally reported in literature.

Current advances in proteomic analysis of (fatty) liver.

In this review, an overview on proteomic studies conducted in livers of farm animals is conducted with a special focus on liver steatosis in waterfowl. Several studies had interest in understanding liver metabolism in dairy cows under various conditions (e.g. fasting) or the evolution of liver proteome during embryonic phases or growing periods in chicken. Those studies provide interesting results leading to a better understanding of the liver metabolism. Liver steatosis development in waterfowl represents a special case and a focus on proteomic studies conducted in these birds will be done. Indeed, recent studies aimed at resolving protein evolution during overfeeding in duck. Proteomic analysis combining two complementary approaches (2-dimensional electrophoresis gels and shot gun strategy) in order to better understand the mechanisms underlying the variability of cooking yield of fatty liver will be presented.

Proteomic profile evolution during steatosis development in ducks.

We investigated a protein profile evolution during steatosis in ducks using 2-dimensional electrophoresis gels to better understand the mechanisms underlying liver steatosis at the level of hepatic proteins in waterfowl. Two-dimensional electrophoresis gels were performed in the liver at different stages of steatosis in the duck. Mule ducks were slaughtered after 0, 14, or 23 meals of overfeeding, according to commercial conditions. Thirty-one proteic spots were differentially expressed between 3 or 2 durations of overfeeding: 3 spots were differentially expressed between the 3 times and 28 spots were differentially expressed between 2 times. The identified proteins (14) could be regrouped into 5 categories: enzymes, translation factors, proteins involved in cell structure, proteins with antioxidant properties, and proteins that can link calcium. This study opens new research areas in the understanding of steatosis in waterfowl, such as cell structure and oxidative stress.