Defect in assembly process of very-low-density lipoprotein in suncus liver: an animal model of fatty liver

Spontaneous Polycystic Kidneys with Chronic Renal Failure in an Aged House Musk Shrew (Suncus murinus)

Polycystic kidney disease is one of the most common inheritable renal diseases, characterized by the formation of multiple fluid-filled renal cysts. This disease is a progressive and unfortunately incurable condition. A case of polycystic kidney with chronic renal failure in house musk shrew (Suncus murinus) is described. At clinical presentation, a 16-month-old Suncus murinus showed weight loss and coarse fur. Regarding the biochemical profile, total protein concentrations increased, resulting in a declined albumin: globulin ratio. Blood urea nitrogen and creatinine concentrations were markedly elevated, indicating the end stage of chronic renal failure. Serum amyloid A levels increased and revealed inflammatory reaction during the cyst formation. Histopathologically, multiple cysts were lined by a single layer of epithelial cells or low cuboidal epithelium. The contents were homogenous eosinophilic materials (mucopolysaccharides or mucoproteins) and these cysts contained abundant macrophages. There were also regeneration and dilatation of renal tubes and interstitial fibrosis. The atrophic glomeruli and glomerular capsules were thickened and hyalinized by dense amorphous mucopolysaccharides. These histopathological findings suggested that the pathogenesis of polycystic kidney disease shared a common mechanistic feature across species.

Effects of dietary n-3 highly unsaturated fatty acids levels on growth, lipid metabolism and innate immunity in juvenile golden pompano (Trachinotus ovatus)

To investigate the effects of dietary n-3 highly unsaturated fatty acids (HUFA) levels on growth, lipid metabolism and innate immunity in juvenile golden pompano Trachinotus ovatus, a marine carnivorous teleost, a total of 450 fish (average body weight: 14.84 g) were randomly distributed into 18 cages at sea, each dietary group with three cages and respectively fed six diets (D1-D6) with 2.30% (D1), 0.64% (D2), 1.00% (D3), 1.24% (D4), 1.73% (D5), or 2.10% (D6) n-3 HUFA. Here, D1 with fish oil as lipid source was set as control, while D2-D6 used a mixed vegetable oil as lipid source and supplemented with docosahexaenoic acid- (DHA) and eicosapentaenoic acid- (EPA) enriched oils to adjust the n-3 HUFA levels. After 8 weeks feeding, the daily growth coefficient (DGC), specific growth rate (SGR) and feed efficiency ratio (FER) showed no significant difference among the six dietary groups (P > 0.05). The levels of EPA and DHA in serum and liver increased with the dietary n-3 HUFA levels. The activity of total superoxide disumutase (T-SOD) in serum of fish fed D4 and D5 were significantly higher than that of the other groups, whereas the opposite was true for serum IL-1β and IL-6 levels as well as liver malondialdehyde (MDA) content. The mRNA levels of genes related to hepatic lipid metabolism including sterol regulatory element-binding protein-1 (srebp-1), fatty acid binding protein 1 (fabp1), peroxisome proliferators-activated receptor alpha (pparα), elongase of very long-chain fatty acids 5 (elovl5) and fatty acyl desaturase 2 (fads2) were down-regulated in fish fed the diets with high n-3 HUFA levels, while those of apolipoprotein b 100 (aprob 100) and carnitine palmitoyl transferase 1 (cpt1) increased significantly as increasing n-3 HUFA levels up to 1.73% (D2-D5), but decreased in the 2.10% n-3 HUFA group (D6). In addition, the expression levels of genes related to innate immunity including interleukin-10 (il-10) and transforming growth factor β1 (tgf-β1) increased significantly when dietary n-3 HUFA increased from 0.64% to 1.73%, whereas the opposite was true for the expression levels of nuclear factor kappa-B (nf-κb), interleukin-1β (il-1β), interleukin-6 (il-6) and interleukin-8 (il-8). Overall, the results indicated that dietary n-3 HUFA at 1.24-1.73% (D4-D5) can effectively improve fatty acid profiles, lipid metabolism, antioxidant capacity and immune response of golden pompano.

Regulation of hepatic genes related to lipid metabolism and antioxidant enzymes by sodium butyrate supplementation

Background

Rapid influx of energy caused by fasting/refeeding repeatedly enhances fatty acid synthesis leading to triacylglycerol accumulation and production of reactive oxygen species (ROS), increasing the risk of non-alcoholic steatohepatitis (NASH). Previous studies have reported that the ingestion of butyrate is effective at preventing hepatic disorders, which are accompanied by fat accumulation and inflammation. The aim of this study is to reveal the mechanism of action of butyrate, and thus we investigated the effects of dietary butyrate on the expressions of antioxidant enzymes in the livers of rats during refeeding following fasting.

Methods

Thirty-seven male rats were divided into six groups (6–7 animals per group): non-fasting, fasting, refeeding with a high sucrose diet as control for 12 or 24 h, and refeeding with a high sucrose diet containing 5% sodium butyrate (NaB) for 12 or 24 h. All groups except the non-fasting group were fasted for 72 h before refeeding. Statistical analysis was conducted among 4 refeeding groups (refeeding with the control diet for 12 or 24 h, and refeeding with a diet containing NaB for 12 or 24 h).

Results

Supplementation with NaB significantly reduced (p < 0.05) fatty acid synthase (Fas) gene expression and increased the expression of the carnitine palmitoyltransferase 1α (Cpt1a) gene, resulting in reduced triacylglycerol content in the livers of rats refed the NaB diet compared with controls at 24 h after the start of refeeding. The mRNA levels of the genes related to glutathione synthesis were significantly higher (p < 0.05) in the livers of the butyrate group than the control group. In addition, the mRNA level of Foxo3a, a transcription factor that regulates the expressions of antioxidant enzymes, was higher in the butyrate group than controls. The acetylation levels of histone H4 around the Foxo3a gene tended to be increased (p = 0.055) by refeeding with the NaB diet.

Conclusion

NaB supplementation in the diet for refeeding reduced the rate of lipid synthesis and stimulated fatty acid oxidation in the liver, which inhibited fat accumulation and the risk of NASH. The transcriptional regulation of Foxo3a involves histone acetylation around the gene.

Dietary conjugated linoleic Acid and hepatic steatosis: species-specific effects on liver and adipose lipid metabolism and gene expression

Objective. To summarize the recent studies on effect of conjugated linoleic acid (CLA) on hepatic steatosis and hepatic and adipose lipid metabolism highlighting the potential regulatory mechanisms. Methods. Sixty-four published experiments were summarized in which trans-10, cis-12 CLA was fed either alone or in combination with other CLA isomers to mice, rats, hamsters, and humans were compared. Summary and Conclusions. Dietary trans-10, cis-12 CLA induces a severe hepatic steatosis in mice with a more muted response in other species. Regardless of species, when hepatic steatosis was present, a concurrent decrease in body adiposity was observed, suggesting that hepatic lipid accumulation is a result of uptake of mobilized fatty acids (FA) from adipose tissue and the liver's inability to sufficiently increase FA oxidation and export of synthesized triglycerides. The potential role of liver FA composition, insulin secretion and sensitivity, adipokine, and inflammatory responses are discussed as potential mechanisms behind CLA-induced hepatic steatosis.

A novel pregnane X receptor-mediated and sterol regulatory element-binding protein-independent lipogenic pathway

The pregnane X receptor (PXR) was isolated as a xenosensor regulating xenobiotic responses. In this study, we show that PXR plays an endobiotic role by impacting lipid homeostasis. Expression of an activated PXR in the livers of transgenic mice resulted in an increased hepatic deposit of triglycerides. This PXR-mediated lipid accumulation was independent of the activation of the lipogenic transcriptional factor SREBP-1c (sterol regulatory element-binding protein 1c) and its primary lipogenic target enzymes, including fatty-acid synthase (FAS) and acetyl-CoA carboxylase 1 (ACC-1). Instead, the lipid accumulation in transgenic mice was associated with an increased expression of the free fatty acid transporter CD36 and several accessory lipogenic enzymes, such as stearoyl-CoA desaturase-1 (SCD-1) and long chain free fatty acid elongase. Studies using transgenic and knock-out mice showed that PXR is both necessary and sufficient for Cd36 activation. Promoter analyses revealed a DR-3-type of PXR-response element in the mouse Cd36 promoter, establishing Cd36 as a direct transcriptional target of PXR. The hepatic lipid accumulation and Cd36 induction were also seen in the hPXR "humanized" mice treated with the hPXR agonist rifampicin. The activation of PXR was also associated with an inhibition of pro-beta-oxidative genes, such as peroxisome proliferator-activated receptor alpha (PPARalpha) and thiolase, and an up-regulation of PPARgamma, a positive regulator of CD36. The cross-regulation of CD36 by PXR and PPARgamma suggests that this fatty acid transporter may function as a common target of orphan nuclear receptors in their regulation of lipid homeostasis.

Association of liver steatosis with lipid oversecretion and hypotriglyceridaemia in C57BL/6j mice fed trans-10,cis-12-linoleic acid

Conjugated linoleic acids (CLA) have recently been recognized to reduce body fat and plasma lipids in some animals. This study demonstrated that the steatosis accompanying the fat loss induced by trans-10,cis-12-C(18:2) (CLA2) and not cis-9,trans-11-C(18:2) (CLA1) isomer in C57BL/6j mice was not due to an alteration of the liver lipoprotein production that was even increased. The 3-fold decrease in plasma triacylglycerol contents and the induction of mRNA expression of low-density lipoprotein receptors concomitantly observed in CLA2-fed mice suggested an increase in the lipoprotein clearance at the level of the liver itself. CLA1 feeding produced similar but attenuated effects on triglyceridaemia only.

Cardiorespiratory reflexes in a working heart-brainstem preparation of the house musk shrew, Suncus murinus

In this study, we adapted the working heart-brainstem preparation (WHBP) from rodents to the Insectivore, Suncus murinus. Suncus WHBPs had a baseline heart rate of 333 +/- 8 beats min(-1), a perfusion pressure of 69 +/- 2 mm Hg and a respiratory cycle length of 6.5 +/- 0.7 s. Administration of atropine produced an increase in heart rate of 26 +/- 9 beats min(-1) indicative of the presence of cardiac vagal tone. Activation of baroreceptors produced pressure-dependent reflex falls in heart rate and reduced respiratory cycle length. The baroreceptor reflex sensitivity in Suncus WHBP was a decrease in heart rate of 8.1 +/- 1.4 beats min(-1) mm Hg(-1). Activation of peripheral chemoreceptors with aortic injections of sodium cyanide (0.1-12.5 microg) produced a dose-dependent reflex fall in heart rate and reduced respiratory cycle length. The reflex falls in heart rate evoked by baroreceptor and peripheral chemoreceptor stimulation were both atropine-sensitive. We conclude that viable WHBP can be prepared from Suncus and that Suncus WHBP is a novel non-rodent model in which to study brainstem-mediated reflexes.

Ectopic expression of alpha1,6 fucosyltransferase in mice causes steatosis in the liver and kidney accompanied by a modification of lysosomal acid lipase

The alpha1,6 fucosyltransferase (alpha1,6 FucT) catalyzes the transfer of a fucose from GDP-fucose to the innermost GlcNAc residue of N-linked glycans via an alpha1,6 linkage. alpha1,6 FucT was overexpressed in transgenic mice under the control of a combined cytomegalovirus and chicken beta-actin promoter. Histologically numerous small vacuoles, in which lipid droplets had accumulated, were observed in hepatocytes and proximal renal tubular cells. Electron microscopic studies showed that the lipid droplets were membrane-bound and apparently localized within the lysosomes. Cholesterol esters and triglycerides were significantly increased in liver and kidney of the transgenic mice. Liver lysosomal acid lipase (LAL) activity was significantly lower in the transgenic mice compared to the wild mice, whereas LAL protein level, which was detected immunochemically, was increased, indicating that the specific activity of LAL was much lower in the transgenic mice. In all of the transgenic and nontransgenic mice examined, the activity of liver LAL was negatively correlated with the level of alpha1,6 FucT activity. As evidenced by lectin and immunoblot analysis, LAL was found to be more fucosylated in the transgenic mice, suggesting that the aberrant fucosylation of LAL causes an accumulation of inactive LAL in the lysosomes. Such an accumulation of inactive LAL could be a likely cause for a steatosis in the lysosomes of the liver and kidney in the case of the alpha1,6 FucT transgenic mice.

Fatty liver and hyperlipidemia in IDDM (insulin-dependent diabetes mellitus) of streptozotocin-treated shrews

Severe IDDM (insulin-dependent diabetes mellitus) was produced in the musk shrew (Suncus murimus, Insectivora) by a high dose (a single intraperitoneal injection of 100 mg/kg Body Weight) of streptozotocin (STZ) injection. All shrews that were administered a high dose of STZ exhibited hyperglycemia (449 +/- 16 mg/dl vs 73 +/- 4 mg/dl in controls) and hypoinsulinemia(0.25 +/- 0.07 ng/ml vs 10.96 +/- 1.97 ng/ml in controls) with ketosuria 10 days after injection. Their livers were enlarged and exhibited ayellowish-brown color with marked triglyceride (TG) accumulation (63.25 +/- 7.10 mg/g Liver vs 2.11 +/- 0.19 mg/g Liver in controls). It is probable that the increased influx of fatty acids into the liver induced by hypoinsulinemia and the low capacity of excretion of lipoprotein secretion from liver in the musk shrew resulting from a deficiency of apolipoprotein B synthesis play important roles in fatty liver formation. Hyperlipidemia was another feature in shrews with severe IDDM. The blood TG level was especially high in these shrews (899 +/- 178 mg/dl vs 23 +/- 5 mg/dl in controls). These results indicate that the IDDM shrew, induced by high doses of STZ, is a unique model characterized by fatty liver and hyperlipidemia and may be useful for studying lipid metabolism of IDDM.

Nutritional hepatic steatosis and mortality after burn injury in rats

AIMS

To investigate the effects of diet composition and starvation on hepatic steatosis and mortality after severe burn injury in rats.

METHODS

Experiment 1: rats received either normal chow (55 cent of energy carbohydrates, 14 cent fat, 31 cent protein), a high-fat (40 cent carbohydrates, 40 cent fat, 20 cent protein), or a high-carbohydrate diet (81 cent carbohydrates, 4 cent fat, 15 cent protein) ad libitum for 6 days. Another three groups received these diets ad libitum for 6 days after 48|h starvation. Experiment 2: mortality after 60 cent total body surface area scald burn was determined in a control group of rats and a group with nutritionally induced hepatic steatosis. Hepatic steatosis was induced by feeding the rats a high-fat diet (40 cent carbohydrates, 4 cent fat, 15 cent protein) ad libitum for 6 days.

RESULTS

Without starvation, liver triglyceride content (mg/g liver) increased in response to the high-fat diet (25.6'6.9) compared to normal chow (9.4'3.8; P < 0. 05); the high-carbohydrate diet had no influence on liver triglyceride content (12.4'3.7). Refeeding after starvation resulted in elevated (P < 0.05) liver triglyceride content in the high-fat (18.8'8.3) and the high-carbohydrate group (28.7'14.4 vs control 6. 7'3.7). Liver triglyceride content correlated (R2=0.72; P < 0.05) to non-protein energy intake but not to total energy intake. Burn caused 33 cent mortality in the hepatic steatosis group and no deaths in the control group (P < 0.05).

CONCLUSIONS

Diet composition and preceding starvation independently manipulate hepatic fat content in rats. Hepatic steatosis increases mortality after burn injury. Thus, nutritional interventions to reduce hepatic fat accumulation may be beneficial.