The influence of environmental temperature, thyroid status and a synthetic oestrogen on the induction of fatty livers in chicks

Avian Liver: The Forgotten Organ

Simple Summary

The liver is a multi-purpose organ, with involvement in bile secretion, and lipid, carbohydrate and protein metabolism, as well as a number of other metabolic functions. This organ can adapt easily to changes in feed and the environment. Being at the centre of a number of digestive, metabolic and productive activities, it is essential to have a better understanding of this organ and the factors affecting liver functionality.

Abstract

Despite having huge responsibilities in avian species, published reports on the influence of dietary factors and other possible constraints on the size, development and function of liver are limited. Consideration of the factors that could influence and alter liver function is therefore of critical relevance. In the current review, aspects of liver structure and function, and the influence of feed restriction, anti-nutritional factors, structural components and feed additives on liver are discussed. Effects of feed technology techniques such as thermal treatment and pelleting, feed particle size and whole grain feeding on the liver are also reviewed. A discussion of lipogenesis and lipid storage in poultry is presented to provide a better understanding and to differentiate the normal pathways of lipid metabolism from abnormal (i.e., disordered) pathways. The liver is the main site of fat synthesis in poultry, but under certain conditions, excessive fat can accumulate in the liver and cause problems. Factors contributing to the fatty liver syndrome are also examined.

Emodin alleviates hepatic steatosis by inhibiting sterol regulatory element binding protein 1 activity by way of the calcium/calmodulin-dependent kinase kinase-AMP-activated protein kinase-mechanistic target of rapamycin-p70 ribosomal S6 kinase signaling pathway

AIM

To investigate the effects of emodin on the treatment of non-alcoholic fatty liver and the underlying mechanisms.

METHODS

In vitro, hepatocytes were treated with 1 mM free fatty acid together with various concentrations of emodin. In vivo, Sprague-Dawley rats were divided into a control group, high-fat diet (HFD) group, and three HFD groups treated with 40, 80, and 160 mg/kg emodin, respectively. After being fed a HFD for 4 weeks, rats were orally dosed with emodin once daily for 8 weeks. The biochemical parameters and histology features were examined. The expression of lipogenic and lipolytic gene and protein and the phosphorylation of calcium/calmodulin-dependent kinase kinase (CaMKK), AMP-activated protein kinase (AMPK), mechanistic target of rapamycin (mTOR) and p70 ribosomal S6 kinase (p70S6K) were measured in vitro and in vivo.

RESULTS

Emodin improved lipid accumulation in vitro and in vivo. Emodin downregulated the levels of sterol regulatory element binding protein 1 (SREBP1) and its target enzymes but increased lipolysis-related proteins and mRNA. Phosphorylation of AMPK was increased, while phosphorylation of mTOR and p70S6K were suppressed by emodin. The nuclear translocation of SREBP1 was inhibited by emodin by AMPK and mTOR. Emodin activated AMPK by CaMKK and reversed the reduction of CaMKK in HFD-fed rats.

CONCLUSION

Emodin effectively ameliorates hepatic steatosis through the CaMKK-AMPK-mTOR-p70S6K-SREBP1 signaling pathway.

Nutritional and Hormonal Induction of Fatty Liver Syndrome and Effects of Dietary Lipotropic Factors in Egg-type Male Chicks

This experiment was conducted with male chicks to investigate the influence of hormones and nutrients on the development of fatty liver syndrome (FLS) as well as the effects of dietary lipotropic factors on hepatic fat accumulation and lipogenic enzyme gene expression. A total of two-hundred sixteen 4-wk-old Hy-Line male chicks were divided into six groups and fed an experimental diet (T1, low-energy diet with low levels of lipotropic factors; T2, high-energy diet with low levels of lipotropic factors; T3 and T5, low-energy diet with high levels of lipotropic factors; T4 and T6, high-energy diet with high levels of lipotropic factors) for six weeks. The chicks in T5 and T6 groups were treated with intramuscular injections of estradiol benzoate for three days prior to biopsy and clinical analysis of FLS. Chicks treated with estrogen had significantly greater liver weights than untreated chicks. The abdominal fat contents were increased in chicks consuming high-energy diets as compared to those consuming low-energy diets. Treatment with estrogen significantly increased the concentrations of serum cholesterol, triacylglycerol and phospholipid (p<0.05). The hepatic triacylglycerol levels were tenfold higher in the estrogen treated chicks than in the untreated chicks. There were no significant differences in malondialdehyde levels between the treatment groups. Estrogen treatment dramatically increased the levels of fatty acid synthetase, acetyl-CoA carboxylase and ApoB mRNA. The results indicated that treatment with exogenous estrogen in growing male chicks induced hepatic fat accumulation, which might be partially due to increased lipogenic enzyme gene expression.

The influence of restrictive feeding of chickens on the microscopic structure of their liver

This paper describes the morphologic structure of chickens’ livers as a result of restrictive feeding in variable intensity. This experiment was performed on 96 chickens of two hybrids (Ross 308 and Cobb 500) of both sexes. The chickens were divided into 3 groups (control group and two groups with restricted feeding). There were 8 chickens in each group. After hatching, the control group was fed a standard mixture ad libitum. The first restricted group was fed 80% ad libitum from the age of 2 weeks. The second restricted group, from the age of 2 weeks, was fed 65% ad libitum. The experiment lasted for 5 weeks. The liver samples were obtained by necropsy, then weighed, and after this processed by standard histological methods. The slices of liver were stained with haematoxyline-eosin. The liver samples were evaluated both objectively and subjectively. In the control group, steatosis and marginal pathological acute venosis hyperaemia were found. In the group with 80% restriction, perilobular steatosis was observed. In the group with 65% restriction, centrolobular steatosis was observed. Controlled measurement of the average hepatocyte thickness in the individual sample groups was performed using an objective method. The hepatocyte diameter thickness of males was higher than the hepatocyte diameter thickness of females, which was significant (P < 0.001). This is the first work providing the possibility of morphometrical verification of the time factor including other morphological criteria.

A novel non-alcoholic steatohepatitis animal model featured with insulin resistance, hepatic inflammation and fibrosis

OBJECTIVE

There is no animal model that displays the features of non-alcoholic steatohepatitis (NASH) characterized by insulin resistance (IR) and fibrosing steatohepatitis. This study aimed to develop a novel IR-associated rat model of NASH.

MATERIAL AND METHODS

Male Sprague-Dawley rats were fed with the high-fat diet (HFD) supplemented with 0.25% propylthiouracil for 2, 4, 6, 8 and 12 weeks. The IR-associated metabolic parameters, histological assessment and the expression of key insulin signaling molecules were determined. The circulating and tissue pro-inflammatory factors and adipocytokines were examined.

RESULTS

In the HFD-fed rats, the systemic and multiple-organ IR was developed after 4 weeks, whereas the histological changes characterized by steatohepatitis, inflammatory response in the visceral adipose tissue and proliferative pancreatic islet β-cells appeared after 6 weeks, concomitant with altered expression of key insulin signaling molecules. In addition, the elevated levels of serum tumor necrosis factor α (TNF-α), soluble TNF receptor2, interleukin (IL)-6, CC-chemokine ligand (CCL)2 and resistin were parallel with the severity of hepatic inflammation, while the levels of serum adiponectin, leptin and TNF-α, but not resistin, were correlated with IR.

CONCLUSIONS

We have developed a systemic IR-associated NASH model of rats, with impaired insulin signaling, systemic inflammation and appropriate pathology characterized by human NASH, and provided a realistic experimental model for elucidating the association between IR and the pathogenesis of NASH.

Effect of dietary thyroxine on growth and muscle protein metabolism in broiler chickens

The effects of thyroxine (T4) on growth, feed efficiency, breast muscle (Musculus pectoralis profundus) weight, liver weight, abdominal fat content, and rates of muscle protein synthesis (Ks) and breakdown (Kd) estimated by N tau-methylhistidine excretion were investigated in broiler chickens of both sexes. Dietary inclusion of .4 ppm T4 resulted in a less abdominal fat content in female chickens and a higher muscle protein synthesis rate in male chickens. Administration of T4 at the level of 1.2 ppm produced higher feed efficiency in both sexes and greater muscle weight and muscle protein synthesis rate in male chickens. This treatment also produced less abdominal fat content in female chickens. Administration of T4 at the level of 3.6 ppm produced lower body weight gain, breast muscle weight, liver weight, and abdominal fat content in both sexes and both higher protein synthesis and breakdown in skeletal muscle in male chickens. These experiments demonstrated that the abdominal fat content could be successfully reduced by dietary inclusion of T4, especially in female broiler chickens. The findings in the present investigation suggested that the improved feed efficiency and muscle growth were largely accomplished by the increase in muscle protein synthesis induced by the dietary inclusion of thyroxine.

Effects of pantethine supplementation to diets with different energy cereals on hepatic lipogenesis of laying hens

Effects on dietary pantethine supplementation on hepatic lipid accumulation and on the activities of lipogenic-related enzymes in the liver were studied in Single Comb White Leghorn laying hens fed isocaloric and isonitrogenous diets containing corn or barley as the carbohydrate source. Addition of 200 ppm pantethine to the corn-soy (CS) basal diet significantly reduced abdominal fat weight, liver triglyceride, as well as total cholesterol and 17 beta-estradiol concentrations in the plasma. Activities of citrate cleavage enzyme (EC 4.1.3.8; CCE) and fatty acid synthetase (FAS) in the liver were significantly reduced when the CS basal diet was supplemented with pantethine, but the activities of nicotinamide adenine dinucleotide phosphate-malate dehydrogenase (EC 1.1.1.40; NADP-MDH) and glucose-6-phosphate dehydrogenase (EC 1.1.1.49; G6PDH), were not significantly affected. However, liver triglyceride, total cholesterol, and 17 beta-estradiol concentrations in plasma as well as the activities of CCE, FAS, and NADP-MDH in liver were significantly lower in laying hens fed the barley-soy (BS) basal diet than in those fed the CS basal diet. Pantethine supplementation to the BS diet failed to show any significant effect on liver triglyceride content and on the hepatic activities of lipogenic-related enzymes. There were no significant differences in liver weight, rate of egg production, and egg weight among dietary treatments. these results suggest that dietary pantethine is effective in reducing the accumulation of liver and abdominal fat in laying hens fed a CS diet.

Genetic variation of liver lipid content of coturnix quail

Two experiments were conducted to elucidate the genetic variation in the liver lipid content of coturnix quail. In Experiment 1, the change of the liver lipid content with advancing age was studied. In Experiment 2, the genetic variation of the liver lipid content at 4 weeks of age was analyzed. Liver lipid was extracted with ethanol-ether solution and weighed. Genetic parameters of liver lipid content, body weight, and liver weight were estimated from sib analysis. The means of liver lipid content at 2 and 4 weeks of age were approximately 25% on a dry weight basis in both sexes. After 6 weeks of age, the liver lipid content of the female was higher than that of the male. The liver lipid content of the egg-laying female was slightly higher than that of the nonlaying female. Heritability (h2sire) of liver lipid content from 4-week-old coturnix quail was estimated as h2sire: .62 +/- .73.

Diet composition, environmental temperature, and exogenous estradiol effects on hepatic lipid deposition in growing chicks

The interrelationships among dietary composition, environmental temperature, and level of estradiol (E2) administration on hepatic lipid deposition in chicks were studied. Two levels of E2 were injected at three intervals over a 4-day period, in 3-week-old male Leghorn chicks fed either a corn-soybean meal (CS) diet or a diet containing fish meal (FM) after 2 days fasting. The chicks were subjected to temperature ranges of 15 to 24 C (low) or 24 to 35 C (high) at 2 weeks of age. The E2 (in silastic tubes) was also implanted subcutaneously in 3-week-old broiler chicks fed either the CS diet or a diet containing fish meal, alfalfa meal, and torula yeast (FAY) from day of age to 6 weeks. They were subjected to the high and low temperature ranges at 3 weeks. Liver lipid deposition markedly increased with E2 administration among chicks fed all diets within both temperature ranges. Liver lipid was significantly greater at 24 to 35 C than at 15 to 24 C among estrogenized chicks. Feeding the FM or the FAY diet decreased hepatic lipid accumulation as compared to feeding the CS diet, but the ameliorative effect of the FM diet on hepatic lipid deposition was not observed at the low temperature or at the lower level of implantation. It was concluded that a range for estrogen administration exists wherein dietary effects are expressed. These data indicate that environmental temperature, dietary composition, estrogen level, and their interactions influence hepatic lipid deposition and also suggest that high temperature augments liver response to estrogen.

Effect of diisopropyl 1,3-dithiolan-2-ylidenemalonate on experimental fatty livers in chicks

The effect of diisopropyl 1,3-dithiolan-2-ylidenemalonate (NKK-100) on experimental fatty livers was investigated in chicks administered an antithyroid agent plus synthetic estrogen or in estrogenized, starved-refed chicks. NKK-100 was added at levels of 250, 500, 1000, and 1500 mg/kg diet. Liver weight was significantly decreased by administration of NKK-100 at 1500 mg/kg diet in the estrogen-administered chicks. Liver lipid content and liver lipid deposition were significantly and inversely decreased with increasing NKK-100 concentration in the diet in the estrogen administered chicks. Plasma transaminase activity, which was elevated by the estrogen administration, was reduced by the administration of NKK-100. These results suggest that NKK-100 may be of value in preventing fatty livers in poultry.