Reduced Dietary Omega-6 to Omega-3 Fatty Acid Ratio and 12/15-Lipoxygenase Deficiency Are Protective against Chronic High Fat Diet-Induced Steatohepatitis

Abstract

Obesity is associated with metabolic perturbations including liver and adipose tissue inflammation, insulin resistance, and type 2 diabetes. Omega-6 fatty acids (ω6) promote and omega-3 fatty acids (ω3) reduce inflammation as they can be metabolized to pro- and anti-inflammatory eicosanoids, respectively. 12/15-lipoxygenase (12/15-LO) enzymatically produces some of these metabolites and is induced by high fat (HF) diet. We investigated the effects of altering dietary ω6/ω3 ratio and 12/15-LO deficiency on HF diet-induced tissue inflammation and insulin resistance. We examined how these conditions affect circulating concentrations of oxidized metabolites of ω6 arachidonic and linoleic acids and innate and adaptive immune system activity in the liver. For 15 weeks, wild-type (WT) mice were fed either a soybean oil-enriched HF diet with high dietary ω6/ω3 ratio (11∶1, HFH), similar to Western-style diet, or a fat Kcal-matched, fish oil-enriched HF diet with a low dietary ω6/ω3 ratio of 2.7∶1 (HFL). Importantly, the total saturated, monounsaturated and polyunsaturated fat content was matched in the two HF diets, which is unlike most published fish oil studies in mice. Despite modestly increased food intake, WT mice fed HFL were protected from HFH-diet induced steatohepatitis, evidenced by decreased hepatic mRNA expression of pro-inflammatory genes and genes involved in lymphocyte homing, and reduced deposition of hepatic triglyceride. Furthermore, oxidized metabolites of ω6 arachidonic acid were decreased in the plasma of WT HFL compared to WT HFH-fed mice. 12/15-LO knockout (KO) mice were also protected from HFH-induced fatty liver and elevated mRNA markers of inflammation and lymphocyte homing. 12/15-LOKO mice were protected from HFH-induced insulin resistance but reducing dietary ω6/ω3 ratio in WT mice did not ameliorate insulin resistance or adipose tissue inflammation. In conclusion, lowering dietary ω6/ω3 ratio in HF diet significantly reduces steatohepatitis.

The contribution of arachidonate 15-lipoxygenase in tissue macrophages to adipose tissue remodeling

“…40 However, in this study, we found that the pro-inflammatory Alox15 products 12-HETE and 15-HETE, were not upregulated after CL treatment, suggesting that the pro-inflammatory role of Alox15 is induced by high-fat diet feeding, but not by β -adrenergic stimulation. Thus, key factors that may regulate this dual role of Alox15 include diet, 41 and lipid metabolites generated by the enzyme. 37 Further investigation of Alox15 function in adipose tissue biology is needed in the context of adipose tissue remodeling, including chronic effects of defects in efferocytosis of apoptotic adipocytes.…”

Induction of Steatohepatitis (NASH) with Insulin Resistance in Wild-type B6 Mice by a Western-type Diet Containing Soybean Oil and Cholesterol

“…Neither TNFα nor cholesterol alone enhanced actinomycin D-stimulated caspase 3 activity significantly. However, if mouse hepatocytes were exposed to a combination of TNFα and cholesterol, the actinomycin D-dependent caspase 3 activity was significantly increased about two-fold ( Figure 6C) and there was a significant interaction between cholesterol and TNFα (two-way analysis of variance, obesogenic, diabetogenic and proinflammatory than fat sources such as lard or coconut oil with saturated fatty acids or fish oil with a different PUFA composition (13,14,(37)(38)(39). The high content of n-6-PUFA in soybean oil exaggerated insulin resistance and increased liver steatosis and inflammation in mice (38,14), while a high n-3/n-6-PUFA ratio in the diet reduced hepatic steatosis in humans and mice (39)(40)(41).…”

“…n-6-fatty acids can be metabolized to arachidonic acid derivatives such as prostanoids (2-series) with proinflammatory properties, whereas n-3-fatty acids serve as substrates for less inflammatory prostanoids (3-and 5-series) or antiinflammatory metabolites (38,42). Serum levels of oxidized metabolites of the n-6 fatty arachidonic and linoleic acids were increased in mice fed a soybean oil-rich high-fat diet compared with mice fed a fish oil-rich high-fat diet (37). Furthermore, oxidized LDL caused Kupffer cell activation in a transgenic mouse model and thus might trigger hepatic inflammation (43).…”

Molecular mechanisms of nonalcoholic fatty liver disease: Potential role for 12-lipoxygenase

“…Also, in the Apoe −/− mouse, 5-LOX deficiency protected mice from macrophage infiltration in the liver with decreased hepatic expression of pro-inflammation cytokines (IL-18 and MCP-1) (Martínez-Clemente, Clària, & Titos, 2011). Along similar lines, whole-body genetic knockout of Alox15 in HFD-fed mice resulted in decreased hepatic steatosis, decreased macrophage infiltration, decreased mRNA expression levels of proinflammatory cytokine genes in the liver (IFN-γ, TNF-α and IL-10), and decreased immune cell chemoattractants (Cxcl2/3) (Lazic et al, 2014b). The liver includes multiple different cell types such as hepatocytes, cholangiocytes, Kupffer cells and stellate cells.…”

“…Both 12-LOX and 5-LOX are expressed in normal mouse hepatocytes and upon liver damage via acetaminophen the transcript and expression levels of both are increased (Suciu et al, 2016). Likewise, upon HFD-feeding, 12-HETE and 5-HETE is increased compared chow-fed control mice (Lazic et al, 2014a). 5-LOX has been shown to be elevated in the liver of ob/ob mice and 5-LOX inhibition downregulated genes involved in hepatic fatty acid uptake and acyl-CoA oxidase expression, restored hepatic microsomal triglyceride transfer protein activity and hepatic VLDL-triglyceride and Apo-B secretion, suggesting a steatogenic role of 5-LOX.…”