Chronic intake of a high-cholesterol diet resulted in hepatic steatosis, focal nodular hyperplasia and fibrosis in non-obese mice

An overview of the cholesterol metabolism and its proinflammatory role in the development of MASLD

Cholesterol is an essential lipid molecule in mammalian cells. It is not only involved in the formation of cell membranes but also serves as a raw material for the synthesis of bile acids, vitamin D, and steroid hormones. Additionally, it acts as a covalent modifier of proteins and plays a crucial role in numerous life processes. Generally, the metabolic processes of cholesterol absorption, synthesis, conversion, and efflux are strictly regulated. Excessive accumulation of cholesterol in the body is a risk factor for metabolic diseases such as cardiovascular disease, type 2 diabetes, and metabolic dysfunction-associated steatotic liver disease (MASLD). In this review, we first provide an overview of the discovery of cholesterol and the fundamental process of cholesterol metabolism. We then summarize the relationship between dietary cholesterol intake and the risk of developing MASLD, and also the animal models of MASLD specifically established with a cholesterol-containing diet. In the end, the role of cholesterol-induced inflammation in the initiation and development of MASLD is discussed.

A Novel Sialoglycopeptide from Gadus morhua Eggs Prevents Liver Fibrosis Induced by CCl4 via Downregulating FXR/FGF15 and TLR4/TGF-β/Smad Pathways

Liver fibrosis plays a critical role in liver disease progression. A sialoglycopeptide from the Gadus morhua eggs (Gm-SGPP) was identified having a 7000 Da molecular weight with a core pentasaccharide structure and osteogenesis activity. However, whether Gm-SGPP is beneficial to liver fibrosis remains unknown. In this study, mice with liver fibrosis were intraperitoneally injected with 2.5% CCl₄ (10 mL/kg) and orally administered with Gm-SGPP (500 mg/kg) for 30 days. Results showed that Gm-SGPP alleviated oxidative liver damage and lipid metabolism disorder and reduced hepatocyte necrosis and lipid droplet accumulation. Notably, we found that Gm-SGPP increased the number and changed the composition of bile acids via increasing cholesterol 7a-hydroxylase (CYP7A1) and sterol 27-hydroxylase (CYP27A1) expression, which caused inhibition of ileum farnesoid X receptor (FXR) expression and accelerated the cholesterol conversion. Cholesterol accumulation is a risk factor for liver fibrosis. Masson staining showed that Gm-SGPP significantly reduced the degree of collagen deposition. Western blotting further suggested that Gm-SGPP downregulated the key gene of the toll-like receptor 4 (TLR4)-mediated transforming growth factor-β (TGF-β)/Smad pathway. To our best knowledge, this is the first report that Gm-SGPP prevented liver fibrosis via attenuating cholesterol accumulation. Our present results provide new ideas for the Gadus morhua egg's high-value utilization.

Role of Cholesterol-Associated Steatohepatitis in the Development of NASH

The rising prevalence of nonalcoholic fatty liver disease (NAFLD) and NAFLD-related cirrhosis in the United States and globally highlights the need to better understand the mechanisms causing progression of hepatic steatosis to fibrosing steatohepatitis and cirrhosis in a small proportion of patients with NAFLD. Accumulating evidence suggests that lipotoxicity mediated by hepatic free cholesterol (FC) overload is a mechanistic driver for necroinflammation and fibrosis, characteristic of nonalcoholic steatohepatitis (NASH), in many animal models and also in some patients with NASH. Diet, lifestyle, obesity, key genetic polymorphisms, and hyperinsulinemia secondary to insulin resistance are pivotal drivers leading to aberrant cholesterol signaling, which leads to accumulation of FC within hepatocytes. FC overload in hepatocytes can lead to ER stress, mitochondrial dysfunction, development of toxic oxysterols, and cholesterol crystallization in lipid droplets, which in turn lead to hepatocyte apoptosis, necrosis, or pyroptosis. Activation of Kupffer cells and hepatic stellate cells by hepatocyte signaling and cholesterol loading contributes to this inflammation and leads to hepatic fibrosis. Cholesterol accumulation in hepatocytes can be readily prevented or reversed by statins. Observational studies suggest that use of statins in NASH not only decreases the substantially increased cardiovascular risk, but may ameliorate liver pathology. Conclusion: Hepatic FC loading may result in cholesterol-associated steatohepatitis and play an important role in the development and progression of NASH. Statins appear to provide significant benefit in preventing progression to NASH and NASH-cirrhosis. Randomized controlled trials are needed to demonstrate whether statins or statin/ezetimibe combination can effectively reverse steatohepatitis and liver fibrosis in patients with NASH.

Yin and Yang Regulation of Liver X Receptor α Signaling Control of Cholesterol Metabolism by Poly(ADP-ribose) polymerase 1

Liver X receptor α (LXRα) controls a set of key genes involved in cholesterol metabolism. However, the molecular mechanism of this regulation remains unknown. The regulatory role of poly(ADP-ribose) polymerase 1 (PARP1) in cholesterol metabolism in the liver was examined. Activation of PARP1 in the liver suppressed LXRα sensing and prevented upregulation of genes involved in HCD-induced cholesterol disposal. Mechanistically, LXRα was poly(ADP-ribosyl)ated by activated PARP1, which decreased DNA binding capacity of LXRα, thus preventing its recruitment to the target promoter. Intriguingly, we found that unactivated PARP1 was indispensable for LXRα transactivation and target expression. Further exploration identified unactivated PARP1 as an essential component of the LXRα-promoter complex. Taken together, the results indicate that activated PARP1 suppresses LXRα activation through poly(ADP-ribosyl)ation, while unactivated PARP1 promotes LXRα activation through physical interaction. PARP1 is a pivotal regulator of LXRα signaling and cholesterol metabolism in the liver.

Understanding the Impact of Dietary Cholesterol on Chronic Metabolic Diseases through Studies in Rodent Models

The development of certain chronic metabolic diseases has been attributed to elevated levels of dietary cholesterol. However, decades of research in animal models and humans have demonstrated a high complexity with respect to the impact of dietary cholesterol on the progression of these diseases. Thus, recent investigations in non-alcoholic fatty liver disease (NAFLD) point to dietary cholesterol as a key factor for the activation of inflammatory pathways underlying the transition from NAFLD to non-alcoholic steatohepatitis (NASH) and to hepatic carcinoma. Dietary cholesterol was initially thought to be the key factor for cardiovascular disease development, but its impact on the disease depends partly on the capacity to modulate plasmatic circulating low-density lipoprotein (LDL) cholesterol levels. These studies evidence a complex relationship between these chronic metabolic diseases and dietary cholesterol, which, in certain conditions, might promote metabolic complications. In this review, we summarize rodent studies that evaluate the impact of dietary cholesterol on these two prevalent chronic diseases and their relevance to human pathology.

Non-alcoholic steatohepatitis-associated hepatic fibrosis and hepatocellular carcinoma in a combined mouse model of genetic modification and dietary challenge

AIM

Experimental models of non-alcoholic steatohepatitis (NASH) are still required for understanding the pathophysiology of this disease. This study aimed to examine whether disease progression is accelerated by combining dyslipidemic genetic modification and dietary challenges and develop NASH-associated hepatic fibrosis, cirrhosis, and carcinoma in a short period.

METHODS

Low-density lipoprotein receptor knockout mice were fed a modified choline-deficient amino acid-defined diet, including 1 w/w% cholesterol and 41 kcal% fat, and was comprehensively profiled over 1 year.

RESULTS

Microvesicular and macrovesicular steatosis in the liver was observed from the first week after starting the modified choline-deficient amino acid-defined diet. Macrovesicular steatosis was exacerbated with time and was observed in almost all hepatocytes at week 8, but slightly decreased at week 16. Infiltration of macrophages and neutrophils, and upregulation of hepatic inflammatory cytokines such as tumor necrosis factor-α and interleukin-1β were also observed from week 1. Plasma hepatic transaminase activities were increased at week 1, reached a peak at week 4, and gradually decreased thereafter. In parallel with increases in hepatic gene expression of collagen-I, the hepatic fibrosis area expanded after week 4 and massively spread all over the liver by week 8. Hepatocellular hyperplasia was observed from week 24. Hepatocellular adenoma and carcinoma were observed from week 31 and 39, respectively.

CONCLUSION

These results suggest that, in a rodent NASH model with the combination of genetic modification and dietary challenges, hepatic steatosis, inflammatory cell infiltration and hepatic injury, hepatic fibrosis, hepatocellular hyperplasia, adenoma, and carcinoma can be developed in a relatively short period.

Ethanol and High Cholesterol Diet Causes Severe Steatohepatitis and Early Liver Fibrosis in Mice

Background and Aim

Because ethanol consumption is commonly associated with a high cholesterol diet, we examined whether combined consumption of ethanol and high cholesterol increases liver injury and fibrosis.

Methods

Male C57BL/6J mice were fed diets containing: 1) 35% of calories from corn oil (CTR), 2) CTR plus 0.5% (w/v) cholesterol (Chol), 3) CTR plus ethanol (27% of calories) (EtOH), or 4) EtOH+Chol for 3 months.

Results

In mice fed Chol or EtOH alone, ALT increased to ~160 U/L, moderate hepatic steatosis occurred, and leukocyte infiltration, necrosis, and apoptosis increased modestly, but no observable fibrosis developed. By contrast in mice fed EtOH+Chol, ALT increased to ~270 U/L, steatosis was more extensive and mostly macrovesicular, and expression of proinflammatory molecules (HMGB-1, TLR4, TNFα, ICAM-1) and leukocyte infiltration increased substantially. Necrosis and apoptosis also increased. Trichrome staining and second harmonic generation microscopy revealed hepatic fibrosis. Fibrosis was mostly sinusoidal and/or perivenular, but in some mice bridging fibrosis occurred. Expression of smooth muscle α-actin and TGF-β1 increased slightly by Chol, moderately by EtOH, and markedly by EtOH+Chol. TGF-β pseudoreceptor BAMBI increased slightly by Chol, remained unchanged by EtOH and decreased by EtOH+Chol. MicroRNA-33a, which enhances TGF-β fibrotic effects, and phospho-Smad2/3, the down-stream signal of TGF-β, also increased more greatly by EtOH+Chol than Chol or EtOH. Metalloproteinase-2 and -9 were decreased only by EtOH+Chol.

Conclusion

High dietary cholesterol and chronic ethanol consumption synergistically increase liver injury, inflammation, and profibrotic responses and suppress antifibrotic responses, leading to severe steatohepatitis and early fibrosis in mice.

Effects of a High-Fat or High-Sucrose Diet on Ultraviolet B Irradiation-Induced Carcinogenesis and Tumor Growth in Melanin-Possessing Hairless Mice

We herein compared the effects of the chronic feeding of high-fat (HF), high-sucrose (HS), and low-fat/low-sucrose (control) diets on carcinogenesis following chronic ultraviolet B (UVB) irradiation in hairless mice. UVB irradiation-induced carcinogenesis was more prominent in HF diet-fed group than in control diet- and HS diet-fed groups. The HS diet group, as well as the HF diet one, showed tumor development and growth, increased skin matrix metalloproteinase (MMP) and blood plasminogen activator inhibitor-1 (PAI-1) levels, and decreased blood leptin and adiponectin levels after long-term UVB irradiation. These changes were smaller in the HS diet group than in the HF diet group. In addition, no difference was noted in the above changes between the control and HS diet groups. The increase induced in adipose tissue weight by the HF diet was markedly reduced by UVB irradiation. This result suggests that the abundant availability of lipids in hypertrophic adipose tissue may be related to tumor incidence and growth through increases in blood PAI-1 and skin MMP-9 expression levels and decreases in blood adiponectin levels by UVB irradiation. In conclusion, HF diet-induced hypertrophic adipose tissue is an important cancer risk factor that promotes UV irradiation-induced carcinogenesis and tumor growth.

Antibiotic-induced imbalances in gut microbiota aggravates cholesterol accumulation and liver injuries in rats fed a high-cholesterol diet

Increasing evidence suggests that maintenance of homeostasis between gut microbiota and host plays an important role in human health. Many diseases, such as those affecting the liver, have been linked to imbalances in gut microbial communities. However, it is not clear whether an imbalance in gut microbiota promotes the onset of liver injury or if the imbalance results from the pathological state. In the current study, antibiotics were used to disturb the gut microbiota of both rats fed a high-cholesterol diet and rats fed a normal diet (controls). The prevalence of Bacteroidetes and Firmicutes were reduced, and Proteobacteria was greatly increased in the guts of rats after antibiotic treatment. The antibiotic-induced perturbation of gut microbiota aggravated cholesterol accumulation and liver injury in rats fed a high-cholesterol diet. This may have been due to an increase in intestinal permeability and plasma lipopolysaccharide (LPS), which lead to an increase in LPS absorption and activation of TLR4 signaling, resulting in the synthesis of pro-inflammatory cytokines and chemokines in liver tissues. This study suggests that imbalances in gut microbiota may be a predisposing factor for the onset of metabolic diseases and liver injuries related to cholesterol and high-cholesterol diets. Modulation of gut microbiota could be a novel target for preventing cholesterol-related metabolic disorders.

Transcriptomic analysis of hepatic responses to testosterone deficiency in miniature pigs fed a high-cholesterol diet

Background

Recent studies have indicated that low serum testosterone levels are associated with increased risk of developing hepatic steatosis; however, the mechanisms mediating this phenomenon have not been fully elucidated. To gain insight into the role of testosterone in modulating hepatic steatosis, we investigated the effects of testosterone on the development of hepatic steatosis in pigs fed a high-fat and high-cholesterol (HFC) diet and profiled hepatic gene expression by RNA-Seq in HFC-fed intact male pigs (IM), castrated male pigs (CM), and castrated male pigs with testosterone replacement (CMT).

Results

Serum testosterone levels were significantly decreased in CM pigs, and testosterone replacement attenuated castration-induced testosterone deficiency. CM pigs showed increased liver injury accompanied by increased hepatocellular steatosis, inflammation, and elevated serum alanine aminotransferase levels compared with IM pigs. Moreover, serum levels of total cholesterol, low-density lipoprotein cholesterol, and triglycerides were markedly increased in CM pigs. Testosterone replacement decreased serum and hepatic lipid levels and improved liver injury in CM pigs. Compared to IM and CMT pigs, CM pigs had lower serum levels of superoxide dismutase but higher levels of malondialdehyde. Gene expression analysis revealed that upregulated genes in the livers of CM pigs were mainly enriched for genes mediating immune and inflammatory responses, oxidative stress, and apoptosis. Surprisingly, the downregulated genes mainly included those that regulate metabolism-related processes, including fatty acid oxidation, steroid biosynthesis, cholesterol and bile acid metabolism, and glucose metabolism. KEGG analysis showed that metabolic pathways, fatty acid degradation, pyruvate metabolism, the tricarboxylic acid cycle, and the nuclear factor-kappaB signaling pathway were the major pathways altered in CM pigs.

Conclusions

This study demonstrated that testosterone deficiency aggravated hypercholesterolemia and hepatic steatosis in pigs fed an HFC diet and that these effects could be reversed by testosterone replacement therapy. Impaired metabolic processes, enhanced immune and inflammatory responses, oxidative stress, and apoptosis may contribute to the increased hepatic steatosis induced by testosterone deficiency and an HFC diet. These results deepened our understanding of the molecular mechanisms of testosterone deficiency-induced hepatic steatosis and provided a foundation for future investigations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1283-0) contains supplementary material, which is available to authorized users.

L-serine supplementation attenuates alcoholic fatty liver by enhancing homocysteine metabolism in mice and rats

BACKGROUND

Hyperhomocysteinemia plays an important role in the development of hepatic steatosis, and studies indicate that homocysteine-lowering treatment inhibits the development of fatty liver.

OBJECTIVE

We evaluated the effects of L-serine on alcoholic fatty liver and homocysteine metabolism.

METHODS

In a binge ethanol study, male C57BL/6 mice were divided into 4 groups: control, ethanol + vehicle, and ethanol + 20 or 200 mg/kg L-serine. Mice were gavaged with ethanol (5 g/kg body weight) 3 times every 12 h with or without L-serine which was given twice 30 min before the last 2 ethanol doses. Control mice were fed isocaloric dextran-maltose. In a chronic ethanol study, male Wistar rats were divided into 3 groups: control, ethanol, and ethanol + L-serine. Rats were fed a standard Lieber-DeCarli ethanol diet (36% ethanol-derived calories) for 4 wk with or without dietary L-serine supplementation (1%; wt:vol) for the last 2 wk. In control rats, the ethanol-derived calories were replaced with dextran-maltose. The effects of L-serine were also tested in AML12 cells manipulated to have high homocysteine concentrations by silencing the genes involved in homocysteine metabolism.

RESULTS

Binge ethanol treatment increased serum homocysteine and hepatic triglyceride (TG) concentrations by >5-fold vs. controls, which were attenuated in the 200-mg/kg L-serine treatment group by 60.0% and 47.5%, respectively, compared with the ethanol group. In the chronic ethanol study, L-serine also decreased hepatic neutral lipid accumulation by 63.3% compared with the ethanol group. L-serine increased glutathione and S-adenosylmethionine by 94.0% and 30.6%, respectively, compared with the ethanol group. Silencing betaine homocysteine methyltransferase, cystathionine β-synthase, or methionine increased intracellular homocysteine and TG concentrations by >2-fold, which was reversed by L-serine when L-serine-independent betaine homocysteine methyltransferase was knocked down.

CONCLUSION

These results demonstrate that L-serine ameliorates alcoholic fatty liver by accelerating L-serine-dependent homocysteine metabolism.

Oils rich in α-linolenic acid independently protect against characteristics of fatty liver disease in the Δ6-desaturase null mouse

Alpha-linolenic acid's (ALA) biological activity is poorly understood and primarily associated with its conversion to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Delta-6 desaturase (D6D) initiates the metabolism of linoleic acid (LA) and ALA to arachidonic acid, EPA, and DHA, respectively. In this study, D6D knock-out (D6KO) mice were used to evaluate the effects of ALA-rich oils in preventing hepatic steatosis and inflammation. D6KO and wild-type mice were fed 1 of 4 high-fat (14% w/w) diets: (i) lard (LD, 0% n-3 PUFA), (ii) canola oil + ARASCO (CD, 8% ALA), (iii) flax seed oil + ARASCO (FD, 55% ALA), (iv) menhaden oil (MD, 30% EPA/DHA) for 8 or 20 weeks. Livers of D6KO mice consuming CD and FD were depleted of EPA/DHA, and enriched in ALA. Markers of fat accumulation and inflammation were lowest in the MD-fed mice, at 8 and 20 weeks, regardless of genotype. CD- and FD-fed D6KO groups were found to have lower liver lipid accumulation and lower hepatic inflammation relative to the LD-fed mice at 8 weeks. In conclusion, while MD was the most protective, this study shows that ALA can act independently on risk factors associated with the development of fatty liver disease.

Comparative histomorphological review of rat and human hepatocellular proliferative lesions

In this comparative review, histomorphological features of common nonneoplastic and neoplastic hepatocyte lesions of rats and humans are examined using H&E-stained slides. The morphological similarities and differences of both neoplastic (hepatocellular carcinoma and hepatocellular adenoma) and presumptive preneoplastic lesions (large and small cell change in humans and foci of cellular alteration in rats) are presented and discussed. There are major similarities in the diagnostic features, growth patterns and behavior of both rat and human hepatocellular proliferative lesions and in the process of hepatocarcinogenesis. Further study of presumptive preneoplastic lesions in humans and rats should help to further define their role in progression to hepatocellular neoplasia in both species.

A high-cholesterol diet exacerbates liver fibrosis in mice via accumulation of free cholesterol in hepatic stellate cells

BACKGROUND & AIMS

Some studies have indicated that dietary cholesterol has a role in the progression of liver fibrosis. We investigated the mechanisms by which dietary cholesterol might contribute to hepatic fibrogenesis.

METHODS

C57BL/6 mice were fed a high-cholesterol diet or a control diet for 4 weeks; liver fibrosis then was induced by bile-duct ligation or carbon tetrachloride administration. Hepatic stellate cells (HSCs) were isolated from mice fed high-cholesterol diets or from Niemann-Pick type C1-deficient mice, which accumulate intracellular free cholesterol.

RESULTS

After bile-duct ligation or carbon tetrachloride administration, mice fed high-cholesterol diets had significant increases in liver fibrosis and activation of HSCs compared with mice fed control diets. There were no significant differences in the degree of hepatocellular injury or liver inflammation, including hepatocyte apoptosis or Kupffer cell activation, between mice fed high-cholesterol or control diets. Levels of free cholesterol were much higher in HSCs from mice fed high-cholesterol diets than those fed control diets. In cultured HSCs, accumulation of free cholesterol in HSCs increased levels of Toll-like receptor 4 (TLR4), leading to down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor (a pseudoreceptor for transforming growth factor [TGF]β); the HSCs became sensitized to TGFβ-induced activation. Liver fibrosis was not aggravated by the high-cholesterol diet in C3H/HeJ mice, which express a mutant form of TLR4; HSCs that express mutant TLR4 were not activated by accumulation of free cholesterol.

CONCLUSIONS

Dietary cholesterol aggravates liver fibrosis because free cholesterol accumulates in HSCs, leading to increased TLR4 signaling, down-regulation of bone morphogenetic protein and activin membrane-bound inhibitor, and sensitization of HSC to TGFβ. This pathway might be targeted by antifibrotic therapies.

Is platelet-derived growth factor-BB expression proportional to fibrosis in the hypertrophied lumber ligamentum flavum?

STUDY DESIGN

A clinical and experimental assessment using human samples of lumbar ligamentum flavum (LF).

OBJECTIVE

To identify platelet-derived growth factor-BB (PDGF-BB) expression in hypertrophied LF of patients with lumbar spinal canal stenosis (LSS) and relate it to fibrosis.

SUMMARY OF BACKGROUND DATA

Recent studies showed that fibrosis in LF hypertrophy was due to accumulation of inflammation-related scar tissue. PDGF-BB participates in scar formation and collagen development in wound healing and fibrosis diseases. However, it is unclear whether PDGF-BB expression is associated with fibrosis of the hypertrophied LF in LSS.

METHODS

In all, 10 patients of LSS was enrolled in this study, while 10 patients of lumbar disc herniation (LDH) as a control group. LF thickness was measured by axial T1-weighted magnetic resonance imaging. Fibrosis was graded and type of collagen was identified. The location and the expression of PDGF-BB were analyzed using immunohistochemical stains, real-time polymerase chain reaction, and Western Blotting. Correlation among LF thickness, fibrosis, and PDGF-BB expression was analyzed.

RESULTS

LF thickness was 5.3 ± 1.0 mm (range from 3.9 to 7.5 mm) in the LSS group and 2.8 ± 0.7 mm (range from 1.69 to 3.8 mm) in the LDH group. Obvious fibrosis was observed in all samples of the LSS group, and correlated to LF thickness of the dural, middle, and dorsal layers (P < 0.05), respectively. PDGF-BB was detected in the hypertrophied LF, particularly in the dorsal layer. PDGF-BB expression was higher in the LSS group than that in the LDH group (P < 0.05), and in the dorsal layer than the dural layer in the LSS group (P < 0.05). PDGF-BB mRNA correlated significantly to thickness of LF (r = 0.41) and the severity of fibrosis (r = 0.69) (P < 0.05).

CONCLUSION

A higher PDGF-BB expression existed in the hypertrophied LF of patients with LSS and could be a risk factor of the fibrosis.

Age and diet affect gene expression profiles in canine liver tissue

Background

The liver plays a central role in nutrient and xenobiotic metabolism, but its functionality declines with age. Senior dogs suffer from many of the chronic hepatic diseases as elderly humans, with age-related alterations in liver function influenced by diet. However, a large-scale molecular analysis of the liver tissue as affected by age and diet has not been reported in dogs.

Methodology/Principal Findings

Liver tissue samples were collected from six senior (12-year old) and six young adult (1-year old) female beagles fed an animal protein-based diet (APB) or a plant protein-based diet (PPB) for 12 months. Total RNA in the liver tissue was extracted and hybridized to Affymetrix GeneChip® Canine Genome Arrays. Using a 2.0-fold cutoff and false discovery rate <0.10, our results indicated that expression of 234 genes was altered by age, while 137 genes were differentially expressed by diet. Based on functional classification, genes affected by age and/or diet were involved in cellular development, nutrient metabolism, and signal transduction. In general, gene expression suggested that senior dogs had an increased risk of the progression of liver disease and dysfunction, as observed in aged humans and rodents. In particular for aged liver, genes related to inflammation, oxidative stress, and glycolysis were up-regulated, whereas genes related to regeneration, xenobiotic metabolism, and cholesterol trafficking were down-regulated. Diet-associated changes in gene expression were more common in young adult dogs (33 genes) as compared to senior dogs (3 genes).

Conclusion

Our results provide molecular insight pertaining to the aged canine liver and its predisposition to disease and abnormalities. Therefore, our data may aid in future research pertaining to age-associated alterations in hepatic function or identification of potential targets for nutritional management as a means to decrease incidence of age-dependent liver dysfunction.