Susceptibility of Different Mouse Wild Type Strains to Develop Diet-Induced NAFLD/AFLD-Associated Liver Disease.

Although non-alcoholic and alcoholic fatty liver disease have been intensively studied, concerning pathophysiological mechanisms are still incompletely understood. This may be due to the use of different animal models and resulting model-associated variation. Therefore, this study aimed to compare three frequently used wild type mouse strains in their susceptibility to develop diet-induced features of non-alcoholic/alcoholic fatty liver disease. Fatty liver disease associated clinical, biochemical, and histological features in C57BL/6, CD-1, and 129Sv WT mice were induced by (i) high-fat diet feeding, (ii) ethanol feeding only, and (iii) the combination of high-fat diet and ethanol feeding. Hepatic and subcutaneous adipose lipid profiles were compared in CD-1 and 129Sv mice. Additionally hepatic fatty acid composition was determined in 129Sv mice. In C57BL/6 mice dietary regimens resulted in heterogeneous hepatic responses, ranging from pronounced steatosis and inflammation to a lack of any features of fatty liver disease. Liver-related serum biochemistry showed high deviations within the regimen groups. CD-1 mice did not exhibit significant changes in metabolic and liver markers and developed no significant steatosis or inflammation as a response to dietary regimens. Although 129Sv mice showed no weight gain, this strain achieved most consistent features of fatty liver disease, apparent from concentration alterations of liver-related serum biochemistry as well as moderate steatosis and inflammation as a result of all dietary regimens. Furthermore, the hepatic lipid profile as well as the fatty acid composition of 129Sv mice were considerably altered, upon feeding the different dietary regimens. Accordingly, diet-induced non-alcoholic/alcoholic fatty liver disease is most consistently promoted in 129Sv mice compared to C57BL/6 and CD-1 mice. As a conclusion, this study demonstrates the importance of genetic background of used mouse strains for modeling diet-induced non-alcoholic/alcoholic fatty liver disease

Determination of hepatic lipid profile of regimen treated CD-1 and 129Sv mice.

<p>Hepatic lipid content was determined out of livers from regimen fed CD-1 and 129Sv mice by a semi-quantitative chromatographic method and is shown as relative amount compared to untreated counterparts. (A) TG levels were increased in both mouse strains, with elevated hepatic TG storage in 129Sv mice compared to CD-1 mice. (B) Free cholesterol was only altered in some of the regimen treated 129Sv mice, including decreased free cholesterol in feeding group EtOH 14 weeks and increased free cholesterol in HF + EtOH fed for 7 and 9 weeks. (C) CE as well as (D) CER levels were increased in all feeding groups of either strain, with higher CE content in 129Sv mice compared to CD-1 mice. (E) PC levels were not altered in CD-1 mice, while HF feeding for 7 weeks caused elevated PC content and HF + EtOH feeding for 7 weeks caused decreased PC levels. (F) PE content was similar in both strains, with no alterations between untreated and regimen treated mice. Values are given as means with standard deviations and relevant significant differences are marked by an asterisk (Mann-Whitney U test, <i>P</i> values of <0.05).</p

Medians and interquartile ranges of histopathological features of steatosis, ballooning, and inflammation as well as NAS of regimen treated C57BL/6, CD-1, and 129Sv mice.

<p>Medians and interquartile ranges of histopathological features of steatosis, ballooning, and inflammation as well as NAS of regimen treated C57BL/6, CD-1, and 129Sv mice.</p

Weight increase and adipose to body weight ratio of different dietary groups and mouse strains.

<p>(A-C) Weight increase of HF, EtOH, and HF + EtOH groups and different mouse strains was monitored twice a week, resulting in regimen induced weight increase in C57BL/6 and CD-1 but not in 129Sv mice. (D-F) Adipose to body weight ratios of respective strains and dietary groups, showing increased subcutaneous as well as total adipose to body weight ratio in C57BL/6 and 129Sv mice, while CD-1 mice exhibited only minor changes due to HF, EtOH, and HF + EtOH feeding. At the end of each experiment, subcutaneous as well as visceral adipose tissue was dissected, weighted and subcutaneous adipose, visceral adipose, and total adipose to body weight ratios were calculated. Shown are medians with interquartile ranges and relevant significant differences are marked by an asterisk (Kruskal-Wallis followed by Dunns test of selected pairs of columns, <i>P</i> values of <0.05).</p

FA composition of regimen treated 129Sv mice livers.

<p>FA were determined out of livers from regimen fed 129Sv mice by GC-MS. (A) Total hepatic cholesterol was significantly increased by feeding EtOH for 12 and 16 weeks. (B) Sum of FA was elevated in mice fed with EtOH for 16 weeks as well as in mice fed with HF + EtOH for 7 and 9 weeks. (C) Saturated FA and (D) unsaturated FA were increased in 129Sv mice fed with EtOH for 14 and 16 weeks. (E) MUFA elevated due to feeding EtOH for 16 weeks and HF + EtOH for 7 and 9 weeks respectively. (F) PUFA were only increased in 129Sv mice either receiving HF or HF + EtOH. (G) Ratios of saturated to unsaturated and (H) C18 to C16 FA were not affected by dietary regimens, while (I) ratio of n-6 to n-3 FA was increased due to HF and HF + EtOH feeding at all time points. Shown are medians with interquartile ranges and relevant significant differences are marked by an asterisk (Kruskal-Wallis followed by Dunns test of selected pairs of columns, <i>P</i> values of <0.05).</p

Measurement of inflammation markers IL-6, TNFα, and MCP-1.

<p>Inflammation markers were determined out of liver homogenates of all livers of the respective mouse strains and dietary groups. IL-6, TNFα, and MCP-1 levels of (A) C57BL/6 mice, (B) CD-1 mice, and (C) 129Sv mice, indicating inflammatory response in C57BL/6 and 129Sv mice by decreased hepatic IL-6 and increased hepatic TNFα and MCP-1 concentrations due to regimen feeding. Given are medians with interquartile ranges and relevant significant differences are marked by an asterisk (Kruskal-Wallis followed by Dunns test of selected pairs of columns, <i>P</i> values of <0.05).</p

Serum levels of TG, total cholesterol, FFA and liver function, transaminases AST and ALT of all regimen groups of C57BL/6, CD-1, and 129Sv mice.

<p>(A-E) Metabolic serum parameters and transaminase levels of C57BL/6 mice showed significant increases in total serum cholesterol of HF, EtOH 14 weeks, and HF + EtOH 9 weeks fed mice and a decrease of serum TG in mice fed with EtOH for 12 weeks compared to untreated mice. (F-J) Alterations in serum metabolic and hepatic parameters of regimen treated CD-1 mice led to significant elevated total cholesterol levels in mice fed with HF and EtOH for 14 weeks compared to untreated counterparts. (K-O) Serum concentrations of metabolic and hepatic parameters in 129Sv mice showed increased cholesterol level in the HF group and elevated AST in HF and EtOH 16 weeks fed mice compared to the untreated group. Shown are medians with interquartile ranges and relevant significant differences are marked by an asterisk (Kruskal-Wallis followed by Dunns test of selected pairs of columns, <i>P</i> values of <0.05).</p

Liver histology visualized by HE and Oil Red O staining as well as NAS quantification of dietary induced liver disease.

<p>(A) Mouse livers of different dietary groups and mouse strains were HE stained to show intracellular lipid accumulation, ballooning, and inflammation, with increases in hepatic lipid content and inflammation in HF and EtOH fed C57BL/6 and 129Sv mice. Shown are representative pictures of each group (magnification 200). Asterisks in each picture mark a central vein and black arrows indicate inflammatory cell infiltration. The enclosed box in C57BL/6 HF diet 7 weeks shows an enlarged image of cells resembling ballooning (magnification 600). (B) Oil Red O stained liver sections of regimen treated mouse strains, showing prominent lipid accumulation in regimen treated C57BL/6 and 129Sv mice, but none in CD-1 mice. Depicted are representative sections of each group (magnification 200). Asterisks in each picture mark a central vein. (C) Quantification of diet-induced steatosis, ballooning, and inflammation by NAS-scoring. NAS was significantly increased in C57BL/6 mice fed with HF and HF + EtOH 9 weeks compared to their untreated counterparts, while in CD-1 mice only EtOH fed for 16 weeks increased NAS. Feeding EtOH for 12 as well as 16 weeks and HF + EtOH for 9 weeks elevated NAS in 129Sv mice significantly compared to untreated mice. Given are medians with interquartile ranges and relevant significant differences are marked by an asterisk (Kruskal-Wallis followed by Dunns test of selected pairs of columns, <i>P</i> values of <0.05).</p