Hepatic Lysosomal Acid Lipase Overexpression Worsens Hepatic Inflammation in Mice Fed a Western Diet

Nonalcoholic fatty liver disease (NAFLD) is characterized by the accumulation of lipid droplets in hepatocytes. NAFLD development and progression is associated with an increase in hepatic cholesterol levels and decreased autophagy and lipophagy flux. Previous studies have shown that the expression of lysosomal acid lipase (LAL), encoded by the gene LIPA, which can hydrolyze both triglyceride and cholesteryl esters, is inversely correlated with the severity of NAFLD. In addition, ablation of LAL activity results in profound NAFLD. Based on this, we predicted that overexpressing LIPA in the livers of mice fed a Western diet would prevent the development of NAFLD. As expected, mice fed the Western diet exhibited numerous markers of NAFLD, including hepatomegaly, lipid accumulation, and inflammation. Unexpectedly, LAL overexpression did not attenuate steatosis and had only minor effects on neutral lipid composition. However, LAL overexpression exacerbated inflammatory gene expression and infiltration of immune cells in mice fed the Western diet. LAL overexpression also resulted in abnormal phagosome accumulation and lysosomal lipid accumulation depending upon the dietary treatment. Overall, we found that hepatic overexpression of LAL drove immune cell infiltration and inflammation and did not attenuate the development of NAFLD, suggesting that targeting LAL expression may not be a viable route to treat NAFLD in humans.

Prebiotics Must Achieve a Threshold of Increase in Gut Probiotic Bacteria to Impart Beneficial Health Effects on the Host

Objectives

Prebiotic dietary fibers are dietary fibers that] are highly fermented in the large intestine, produce beneficial changes in the gut microbiome, and impart a health benefit to the host. Using reactive extrusion, we have synthesized a novel dietary fiber that is an oligosaccharide of polymerized lactose, which we term polylactose. Here we report on two studies feeding polylactose to rats to determine its prebiotic potential.

Methods

In Exp. 1, the polylactose preparation contained 51% dietary fiber, 20% free lactose, 5% glucose, and 24% other materials. Rats were fed high fat diets containing 9% total dietary fiber, including cellulose (control, CE, 9%), polylactose (PL, 6%), polydextrose (PD, 6%), and fructooligosaccharide (FOS, 6%). In Exp. 2, the polylactose preparation contained 75% dietary fiber, 9% lactose, 3% glucose, and 13% other materials. Rats were again fed high fat diets containing 9% total dietary fiber, including CE (9%), polylactose (6% or 3%), PD (6%), and galactooligosaccharide (GOS, 6%). In both experiments, rats were fed for 10 weeks, then cecums (empty), cecal contents, livers, and epididymal fat pads were collected. In addition, body composition was determined by MRI.

Results

In both experiments, final body weight and daily energy intake did not differ among the groups. In Exp. 1, feeding PL greatly increased cecum weight (an indicator of fermentation), cecal Bifidobacterium and Lactobacillus species abundance, increased cecal acetate and propionate, and reduced liver lipids and fat pad weight, compared to the CE group. While PD and FOS increased probiotic species and short chain fatty acids slightly (compared to CE), this was not to the same extent as PL and did not reduce fatty liver and adiposity. In Exp. 2, 6% PL increased cecum weight relative to 3% PF, PD and GOS, all of which were greater than CE. The cecal microbiome was similar among PL (both 3 and 6%), PD, and GOS, all of which differed from CE and were similar to PD and FOS from Exp. 1. Liver lipids, fat pad weight, and body composition did not differ among any of the groups.

Conclusions

The prebiotic activity of polylactose differed depending on the preparation, for unknown reasons. However, our results suggest there is a threshold of probiotic bacteria abundance that must be attained before beneficial effects are imparted on the host by prebiotics.

Funding Sources

Midwest Dairy Association.

Changes in the Gut Microbiome Contribute to Changes in Tissue Gene Expression in Rats Fed Prebiotic Dietary Fibers (P15-022-19)

Objectives

We investigated the intersection between the gut microbiome and gene expression of colon and liver tissues in rats, using prebiotic dietary fibers to modulate the gut microbiome and elicit health benefits to the host.

Methods

Male Wistar rats were fed normal fat (NF) or high fat (HF, 51% fat by kcal) diets containing various fibers (6% fiber + 3% cellulose, by weight); including cellulose (NFC and HFC, non-fermentable), polylactose (HFPL, a novel prebiotic), and polydextrose (HFPD, an established prebiotic). After 10 weeks, tissues were harvested. Transcriptome analysis was performed by RNA sequencing of colon and liver tissues, and cecal contents were utilized for 16S microbiome sequencing. Analyses were conducted in R using DESeq2, DADA2, and phyloseq.

Results

Analysis of the gut microbiome revealed an increased abundance of probiotic genera, Bifidobacterium and Lactobacillus, in HFPL fed animals when compared to all other groups. These species are galactose fermenters which synthesize short chain fatty acids (SCFAs). This increased taxonomical abundance correlated with an increased FFar3 (SCFA receptor) expression in the colon. This suggests increased FFar3 signaling, leading to increased energy expenditure and GLP-1 and PYY secretion. Additionally, HFPL and HFPD groups had a decreased Firmicutes: Bacteroidetes ratio, which is associated with reduced adiposity due to the Bacteroidetes phylum being poor carbohydrate metabolizers, resulting in reduced energy uptake, yet increased SCFA synthesis.

Bacteriodetes are also able to survive in SCFA and bile acid rich environments and are involved in the recycling of bile acids which negatively regulates cholesterol synthesis. This corresponds to reduced liver cholesterol and cholesterol synthesis pathway expression in the HFPL group. Further, liver gene expression revealed reduced lipid synthesis and increased lipid oxidation pathway gene expression in the HFPL group, corresponding to the reduction in fatty liver found in this group.

Conclusions

Prebiotic dietary fibers elicit changes in the gut microbiome and gene expression in liver and colon. Changes in gene expression correlated with the abundance of beneficial gut bacteria, providing a connection between the gut microbiome and health benefits to the host.

Funding Sources

Midwest Dairy Association.

Supporting Tables, Images and/or Graphs

Polylactose, a Novel Prebiotic Dietary Fiber, Reduces Adiposity and Hepatic Lipid Accumulation (P20-027-19)

Objectives

Polylactose is a novel dietary fiber, synthesized by extrusion of lactose. To evaluate its potential as a prebiotic, we determined its fermentability, effect on the microbiome, and its effects on adiposity, fatty liver, and liver cholesterol in a diet-induced obesity animal model.

Methods

72 male Wistar rats were fed normal fat (NF) or high fat (HF, 51% fat by kcal) diets containing various fibers (6% fiber of interest and 3% cellulose, by weight); including cellulose (NFC and HFC), polylactose (HFPL), matched lactose (HFML), matched to the residual lactose in the HFPL diet, and two established prebiotic fibers, polydextrose (HFPD) and fructooligosaccharides (HFFOS). After 10 weeks on experimental diets, organs were harvested and cecal contents collected for analysis.

Results

There were no significant differences in final body weights among the groups, nor did average daily food intake differ significantly among the HF-fed groups. HFPL animals had greater cecal weight (empty) and lower cecal contents pH when compared to all other groups, suggesting that polylactose is much more vigorously fermented than the other prebiotic fibers. This was also indicated by an increase in taxonomical abundance of probiotic species in the cecum. Epididymal fat pad weight was significantly decreased in the HFPL animals compared to all other HF groups (P < 0.05) and did not differ from the normal fat control (NFC). Liver lipids and cholesterol were significantly reduced in HFPL fed animals when compared to HFC fed animals and were numerically lower than all other HF groups. Transcriptome analysis of the liver revealed increased lipid oxidation and decrease lipid synthesis pathway expression, providing insights into mechanisms of reduction of lipid accumulation in the liver.

Conclusions

Polylactose is a vigorously fermentable fiber and elicits a beneficial change in the gut microbiome. We also demonstrate that consuming polylactose, in the context of a high fat diet, prevents the accumulation of body fat normally seen with this diet, as well as reduced lipid and cholesterol accumulation in the liver. As these effects of polylactose were greater than those of two established prebiotics, fructooligosaccharides and polydextrose, this suggests that polylactose is a potent prebiotic.

Funding Sources

Midwest Dairy Association.

Mechanism of the increased venous return and cardiac output caused by epinephrine

The effect of epinephrine on venous return has been measured in 11 dogs under total spinal anesthesia. The mechanism by which epinephrine increases venous return seems to be to increase the tone of the vascular walls thereby increasing the mean circulatory pressure. This in turn increases the pressure gradient forcing blood from the systemic vessels toward the right atrium. By equating the recorded venous return curves with curves that depict the effect of epinephrine on the heart's ability to pump blood, it is shown that under normal operating conditions cardiac output is determined far more by the tendency for blood to return to the heart than by the heart's ability to pump blood.