Research Article
Diets rich in fructose, fat or fructose and fat alter intestinal barrier function and lead to the development of nonalcoholic fatty liver disease over time,☆☆

https://doi.org/10.1016/j.jnutbio.2015.05.011Get rights and content

Abstract

General overnutrition but also a diet rich in certain macronutrients, age, insulin resistance and an impaired intestinal barrier function may be critical factors in the development of nonalcoholic fatty liver disease (NAFLD). Here the effect of chronic intake of diets rich in different macronutrients, i.e. fructose and/or fat on liver status in mice, was studied over time. C57BL/6J mice were fed plain water, 30% fructose solution, a high-fat diet or a combination of both for 8 and 16 weeks. Indices of liver damage, toll-like receptor 4 (TLR-4) signaling cascade, macrophage polarization and insulin resistance in the liver and intestinal barrier function were analyzed. Chronic exposure to a diet rich in fructose and/or fat was associated with the development of hepatic steatosis that progressed with time to steatohepatitis in mice fed a combination of macronutrients. The development of NAFLD was also associated with a marked reduction of the mRNA expression of insulin receptor, whereas hepatic expressions of TLR-4, myeloid differentiation primary response gene 88 and markers of M1 polarization of macrophages were induced in comparison to controls. Bacterial endotoxin levels in portal plasma were found to be increased while levels of the tight junction protein occludin and zonula occludens 1 were found to be significantly lower in the duodenum of all treated groups after 8 and 16 weeks. Our data suggest that chronic intake of fructose and/or fat may lead to the development of NAFLD over time and that this is associated with an increased translocation of bacterial endotoxin.

Introduction

Nonalcoholic fatty liver disease (NAFLD) is a disease comprising a continuum of liver damage ranging from simple steatosis to nonalcoholic steatohepatitis (NASH) and cirrhosis. A recent survey reviewing 260 epidemiological studies published in Europe in the last 5 years reported that NAFLD has to be accounted to the most frequent liver diseases in Europe [1]. Furthermore, results of Vernon et al. even suggest that NAFLD is the most common cause of elevated liver enzymes worldwide [2]. Also, it has been suggested that fatty livers, long thought to be a benign state of liver disease, are more vulnerable to injury from various causes increasing the probability to progress to later stages of the disease and further liver-related morbidity and mortality [3], [4]. However, despite intense research efforts during the last decades, molecular and pathological changes involved in the onset and even more so the progression of NAFLD are not yet fully understood and therapeutic options are still rather limited. Therefore, a better understanding of the alterations causally involved in the early stages of NAFLD is desirable to improve prevention and intervention strategies.

General overnutrition, particularly when being rich in fat and/or sugars like fructose, is being discussed to be key factors in the development of NAFLD [5]. However, results of not only animal-based studies but also some human studies suggest that not only the development of NAFLD in settings of overnutrition may result from the extra energy adding to an enhanced de novo synthesis and storage of lipids but also other factors may be involved. Indeed, we showed that the development of NAFLD in mice chronically fed a fructose-rich diet is associated with increased endotoxin levels in portal blood and an activation of the toll-like receptor TLR-dependent signaling cascades [6], [7]. Similar findings were also reported form NAFLD models exposing animals chronically to a high-fat diet [8], [9]. It was further shown that chronic intake of fat and fructose, respectively, is associated with a decrease in tight junction proteins in the small intestine [10], [11]. However, if the combination of a chronic exposure to a fat- and fructose-rich diet has an additive or even synergistic effect on the loss of tight junctions, the increased permeation of bacterial endotoxin and subsequently the development of liver damage and if these effects progress with time have not yet been systematically studied. Starting from this background, the aim of our study was to assess the effects of a chronic intake of a fructose, fat or fructose- and fat-enriched diet on intestinal tight junction proteins, portal endotoxin levels and the development of NAFLD over time in mice.

Section snippets

Animals and treatment

Six- to eight-week-old female C57BL/6J mice (Janvier Labs, Le Genest-Saint-Isle, France), shown before to be more susceptible to fructose-induced NAFLD than male mice [12], were housed in a specified and opportunistic pathogen-free (SOPF) barrier facility accredited by the Association for Assessment and Accreditation of Laboratory Animal Care. All procedures were approved by the local Institutional Animal Care and Use Committee. Mice (n=6 per group) had free access to plain tap water and

Effect of a diet rich in fructose, fat or fat and fructose on caloric intake and body weight

In Table 1 and Fig. 1A and B, intake of the different diets as well as body weight gain throughout the 8 and 16 weeks long feeding period, respectively, is summarized. Caloric intake and absolute body weight gain of mice fed standard chow and plain water did not differ from that of mice fed the high-fat diet. In line with earlier reports of our group [13], mice fed a 30% fructose solution reduced their caloric intake from chow significantly by ~45% in comparison to mice fed a standard chow.

Discussion

Worldwide, the number of individuals affected by NAFLD is still increasing. Results of several human studies suggest that lifestyle and herein particular physical activity and overnutrition are critical [5], [19]; however, in more recent years, it has been suggested that not only a general overnutrition but also dietary composition may be critical [20]. Indeed, epidemiological studies suggest that a diet rich in fat and cholesterol may increase the odds to develop NAFLD [21]. Similar data have

Conclusion

Taken together, our data suggest that chronic intake of fat, fructose and even more so a combined intake of fat and fructose leads to the development of NAFLD in mice, which progresses with time of intake. Our data further suggest that the development of NAFLD in feeding models using fat, fructose or a combination of both is associated with impairments of intestinal barrier function and an activation of TLR-4-dependent signaling cascades in the liver. However, further studies are needed to

Conflict of Interest

The authors declare that they have no competing interests or other interests that might be perceived to influence the results and discussion reported in this paper.

Acknowledgements

This work is funded by grants from Bundesministerium für Bildung und Forschung, FKZ: 01EA1305 and FKZ: 01KU1214A (both IB).

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    Funded by grants from Bundesministerium für Bildung und Forschung, FKZ: 01EA1305 and FKZ: 01KU1214A (both IB).

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    Conflicts of interest: None.

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