IDENTIFICATION OF ANTI-ATHEROGENIC AND ANTI-INFLAMMATORY EFFECTS OF WALNUTS AND PISTACHIOS
Open Access
- Author:
- Zhang, Jun
- Graduate Program:
- Nutrition
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 01, 2009
- Committee Members:
- Penny Kris Etherton And John Vanden Heuvel, Dissertation Advisor/Co-Advisor
Penny Margaret Kris Etherton, Committee Chair/Co-Chair
John Patrick Vanden Heuvel, Committee Chair/Co-Chair
Peter J Gillies, Committee Member
Kumble Sandeep Prabhu, Committee Member
Mosuk Chow, Committee Member - Keywords:
- farnesoid X receptor
cholesterol efflux
stearoyl coenzymeA desaturase
walnuts
alpha linolenic acid
atherosclerosis - Abstract:
- Tree nuts are low in saturated fatty acids and high in unsaturated fatty acids, and are rich sources of other nutrients including fiber, vitamin E, folate, phytosterols and potassium. While most tree nuts are rich in monounsaturated fatty acids (MUFA), walnuts contain high levels of polyunsaturated fatty acids (PUFA), both ¦Á-linolenic acid (ALA) and linoleic acid (LA). In addition, walnuts skins contribute 6.5 mmol antioxidants based on a one-ounce serving size, which is higher than other commonly consumed tree nuts. Pistachios, on the other hand, are relatively high in phytosterols compared with most other nuts. However, little is known about the effects of consuming tree nuts on the development of atherosclerosis, which is characterized by the formation of fatty streaks in the artery walls as well as a localized inflammation. In the in vitro and ex vivo studies presented herein, mouse and human macrophage cell lines were used as a model for foam cells to study the effects of walnuts, walnut components, and individual nutrients present on cholesterol storage and transport. ALA, a predominant n-3 fatty acid in walnuts, increased cholesterol efflux in the presence of various acceptor molecules. During gene expression profile studies, stearoyl CoA desaturase 1 (SCD1), a rate-limiting enzyme in MUFA synthesis, was decreased by ALA at both mRNA and protein levels in a dose-dependent manner. Repressing SCD1 by short interfering RNA vector led to a significant decrease in intracellular total cholesterol, cholesteryl ester, and free cholesterol. The converse was observed when SCD-1 expression was increased using an ectopic expression vector. After macrophage-derived foam cells were treated with lipid extracts from walnut skins, walnut oil, and whole walnuts, SCD1 expression was decreased with walnut oil treatment. In an ex vivo study, serum samples from subjects participating in a walnut components postprandial feeding study were applied as treatment to investigate the effects of bioactive molecules present in the nut on cholesterol efflux and gene expression. In foam cells treated with postprandial serum samples, regardless of the walnut component consumed, SCD1 mRNA was decreased. Bioactive compounds present in the serum from the walnut oil treatment were most efficacious. This ex vivo effect on SCD-1 expression was greater when subjects were categorized with low baseline C-reactive protein (CRP) (¡Ü 3 mg/L) compared to those who had high CRP (> 3 mg/L). A similar finding was observed during the cholesterol efflux assay, where serum from the walnut oil treatment (with lower basal CRP) had a significantly higher efflux than that of serum from the high basal CRP group. ALA and walnut extracts significantly activated farnesoid X receptor (FXR), which in turn interfered with liver X receptor (LXR) and its ability to affect sterol regulatory element binding protein 1c (SREBP1c) and ultimately SCD1. After cholesterol was transported and incorporated into the high-density lipoprotein (HDL) particle, the effects of walnut extracts on uptake and internalization of HDL in the hepatocyte was studied. Walnut extracts increased internalization of HDL collected from the efflux medium of foam cells. This effect was due to an activation of hepatocyte membrane receptor expression through a FXR-dependent pathway. Thus, bioactive molecules present in walnuts favorably decrease intracellular cholesterol storage and increase the removal of cholesterol out of lipid laden foam cells by inhibiting SCD1 through an FXR-dependent pathway. To investigate the anti-inflammatory effect of pistachios, lipopolysaccaride (LPS) was applied as an inflammation inducer to study the regulation of pistachios on inflammatory biomarker expression. Administration of pistachio oil (PO) to cultured macrophages affected a variety of genes associated with immune function. A novel biomarker, interferon-induced protein with tetratricopeptide repeats 2 (Ifit-2), was identified as being repressed by PO. A lipid extract of PO (PE) decreased LPS-induced Ifit-2 expression the most, compared with changes in TNF-¦Á, IL-6, and IL-1¦Â. The bioactive molecules that are present in PE, (e.g., linoleic acid and ¦Â-sitosterol) mimicked this inhibition. Two adjacent interferon-stimulated response elements (ISRE) were responsible for the regulation of Ifit-2 by PE. Taken together, walnuts and pistachios showed anti-atherogenic and anti-inflammatory effects on macrophage cholesterol transport, storage, and inflammatory biomarker expression, all of which are beneficial in the prevention and/or regression of atherosclerosis.