Alvin Kamili

Role of ABCG1 and ABCA1 in regulation of neuronal cholesterol efflux to apolipoprotein-E discs and suppression of amyloid-β peptide generation

Maintenance of an adequate supply of cholesterol is important for neuronal function, whereas excess cholesterol promotes amyloid precursor protein (APP) cleavage generating toxic amyloid-β (Aβ) peptides. To gain insights into the pathways that regulate neuronal cholesterol level, we investigated the potential for reconstituted apolipoprotein E (apoE) discs, resembling nascent lipoprotein complexes in the central nervous system, to stimulate neuronal [3H]cholesterol efflux. ApoE discs potently accelerated cholesterol efflux from primary human neurons and cell lines. The process was saturable (17.5 μg of apoE/ml) and was not influenced by APOE genotype. High performance liquid chromatography analysis of cholesterol and cholesterol metabolites effluxed from neurons indicated that <25% of the released cholesterol was modified to polar products (e.g. 24-hydroxycholesterol) that diffuse from neuronal membranes. Thus, most cholesterol (∼75%) appeared to be effluxed from neurons in a native state via a transporter pathway. ATP-binding cassette transporters ABCA1, ABCA2, and ABCG1 were detected in neurons and neuroblastoma cell lines and expression of these cDNAs revealed that ABCA1 and ABCG1 stimulated cholesterol efflux to apoE discs. In addition, ABCA1 and ABCG1 expression in Chinese hamster ovary cells that stably express human APP significantly reduced Aβ generation, whereas ABCA2 did not modulate either cholesterol efflux or Aβ generation. These data indicate that ABCA1 and ABCG1 play a significant role in the regulation of neuronal cholesterol efflux to apoE discs and in suppression of APP processing to generate Aβ peptides.

Dietary Krill Oil Supplementation Reduces Hepatic Steatosis, Glycemia, and Hypercholesterolemia in High-Fat-Fed Mice

Krill oil (KO) is rich in n-3 fatty acids that are present in phospholipids rather than in triglycerides. In the present study, we investigated the effects of dietary KO on cardiometabolic risk factors in male C57BL/6 mice fed a high-fat diet. Mice (n = 6-10 per group) were fed for 8 weeks either: (1) a nonpurified chow diet (N); (2) a high-fat semipurified diet containing 21 wt % buttermilk + 0.15 wt % cholesterol (HF); (3) HF supplemented with 1.25 wt % KO (HFKO1.25); (4) HF with 2.5 wt % KO (HFKO2.5); or (5) HF with 5 wt % KO (HFKO5.0). Dietary KO supplementation caused a significant reduction in liver wt (i.e., hepatomegaly) and total liver fat (i.e., hepatic steatosis), due to a dose-dependent reduction in hepatic triglyceride (mean +/- SEM: 35 +/- 6, 47 +/- 4, and 51 +/- 5% for HFKO1.25, -2.5, and -5.0 vs HF, respectively, P < 0.001) and cholesterol (55 +/- 5, 66 +/- 3, and 71 +/- 3%, P < 0.001). Serum cholesterol levels were reduced by 20 +/- 3, 29 +/- 4, and 29 +/- 5%, and blood glucose was reduced by 36 +/- 5, 34 +/- 6, and 42 +/- 6%, respectively. Serum adiponectin was increased in KO-fed animals (HF vs HFKO5.0: 5.0 +/- 0.2 vs 7.5 +/- 0.6 microg/mL, P < 0.01). These results demonstrate that dietary KO is effective in improving metabolic parameters in mice fed a high-fat diet, suggesting that KO may be of therapeutic value in patients with the metabolic syndrome and/or nonalcoholic fatty liver disease.

Dietary phospholipids, hepatic lipid metabolism and cardiovascular disease

Purpose of review An increasing number of studies in experimental animals suggest that dietary phospholipids might be of benefit in the treatment of fatty liver disease. This raises the possibility that synthetic or naturally occurring phospholipid isolates could be used as hepatoprotective nutraceuticals or functional foods. The aim of the present article is to review published data describing the beneficial effects of dietary phospholipids on hepatic lipid metabolism and their potential to affect atherosclerosis and cardiovascular disease. Recent findings Consistent results have been obtained supporting the concept that phospholipid from various sources (i.e., soybean, safflower, egg and fish roe) can reduce liver lipid levels. The primary site of action for this effect appears to be in the intestinal lumen, where dietary phospholipids are able to interfere with neutral sterol absorption. Results have also been obtained suggesting that dietary phospholipids can stimulate bile acid and cholesterol secretion. Additional work suggests that dietary phospholipids can have a beneficial effect on plasma lipid and lipoprotein levels. Summary The concept of using naturally occurring compounds such as phospholipid to treat or prevent hepatic steatosis is very attractive. Controlled human trials are, however, required to verify the efficacy of this approach. It is also important that additional research be conducted to determine the extent to which certain phospholipids have the ability to increase plasma HDL levels and potentially affect the onset or development of cardiovascular disease.

Dietary phospholipids and intestinal cholesterol absorption.

Experiments carried out with cultured cells and in experimental animals have consistently shown that phospholipids (PLs) can inhibit intestinal cholesterol absorption. Limited evidence from clinical studies suggests that dietary PL supplementation has a similar effect in man. A number of biological mechanisms have been proposed in order to explain how PL in the gut lumen is able to affect cholesterol uptake by the gut mucosa. Further research is however required to establish whether the ability of PLs to inhibit cholesterol absorption is of therapeutic benefit.

Dietary phospholipid-rich dairy milk extract reduces hepatomegaly, hepatic steatosis and hyperlipidemia in mice fed a high-fat diet

Recent studies have suggested that milk and certain dairy food components have the potential to protect against cardiovascular disease. In order to determine whether the addition of milk-derived phospholipids to the diet results in an improvement in metabolic and cardiovascular risk factors, we studied four groups (n=10) of C57BL/6 mice that were fed: (1) a normal non-purified diet (N); (2) the normal non-purified diet supplemented with phospholipid-rich dairy milk extract (PLRDME, 2.5% by wt) (NPL); (3) a high-fat semi-purified diet (HF) containing 21% butterfat+0.15% cholesterol by wt; or (4) HF supplemented with 2.5% by wt PLRDME (HFPL). Dietary PLRDME supplementation did not have a significant effect on metabolic parameters in mice fed the N diet. In contrast, in high-fat fed mice, PLRDME caused a significant decrease in: (a) liver wt (1.57+/-0.06 g vs. 1.20+/-0.04 g, P<0.001), (b) total liver lipid (255+/-22 mg vs. 127+/-13 mg, P<0.001, (c) liver triglyceride (TG) and total cholesterol (TC) 236+/-25 micromol/g vs. 130+/-8 micromol/g (P<0.01), 40+/-7 micromol/g vs. 21+/-2 micromol/g (P<0.05), respectively); and serum lipids (TG: 1.4+/-0.1 mmol/L vs. 1.1+/-0.1 mmol/L, P=0.01; TC: 4.6+/-0.2 mmol/L vs. 3.6+/-0.2 mmol/L, P<0.001; and PL: 3.3+/-0.1 mmol/L vs. 2.6+/-0.1 mmol/L, P<0.01). These data indicate that dietary PLRDME has a beneficial effect on hepatomegaly, hepatic steatosis and elevated serum lipid levels in mice fed a high-fat diet, providing evidence that PLRDME might be of therapeutic value in human subjects as a hepatoprotective or cardioprotective nutraceutical.

Reduction in intestinal cholesterol absorption by various food components: Mechanisms and implications

A number of different food components are known to reduce plasma and LDL-cholesterol levels by affecting intestinal cholesterol absorption. They include: soluble fibers, phytosterols, saponins, phospholipids, soy protein and stearic acid. These compounds inhibit cholesterol absorption by affecting cholesterol solubilization in the intestinal lumen, interfering with diffusion of luminal cholesterol to the gut epithelium and/or inhibiting molecular mechanisms responsible for cholesterol uptake by the enterocyte. Cholesterol content of intestinal chylomicrons is subsequently reduced, less cholesterol is transported to the liver within chylomicron remnants, hepatic LDL-receptor activity is increased and plasma levels of LDL-cholesterol are decreased. Reduced hepatic VLDL production and less conversion of VLDL to LDL also contribute to lower LDL levels. Certain food components may also affect intestinal bile acid metabolism. Further investigation of the way in which these functional ingredients affect intestinal lipid metabolism will facilitate their use and application as cardiovascular nutraceuticals.

Dietary Sphingomyelin Lowers Hepatic Lipid Levels and Inhibits Intestinal Cholesterol Absorption in High-Fat-Fed Mice

Controlling intestinal lipid absorption is an important strategy for maintaining lipid homeostasis. Accumulation of lipids in the liver is a major risk factor for metabolic syndrome and nonalcoholic fatty liver disease. It is well-known that sphingomyelin (SM) can inhibit intestinal cholesterol absorption. It is, however, unclear if dietary SM also lowers liver lipid levels. In the present study (i) the effect of pure dietary egg SM on hepatic lipid metabolism and intestinal cholesterol absorption was measured with [14C]cholesterol and [3H]sitostanol in male C57BL/6 mice fed a high-fat (HF) diet with or without 0.6% wt/wt SM for 18 days; and (ii) hepatic lipid levels and gene expression were determined in mice given a HF diet with or without egg SM (0.3, 0.6 or 1.2% wt/wt) for 4 weeks. Mice supplemented with SM (0.6% wt/wt) had significantly increased fecal lipid and cholesterol output and reduced hepatic [14C]cholesterol levels after 18 days. Relative to HF-fed mice, SM-supplemented HF-fed mice had significantly lower intestinal cholesterol absorption (−30%). Liver weight was significantly lower in the 1.2% wt/wt SM-supplemented mice (−18%). Total liver lipid (mg/organ) was significantly reduced in the SM-supplemented mice (−33% and −40% in 0.6% wt/wt and 1.2% wt/wt SM, respectively), as were triglyceride and cholesterol levels. The reduction in liver triglycerides was due to inactivation of the LXR-SREBP-1c pathway. In conclusion, dietary egg SM has pronounced hepatic lipid-lowering properties in mice maintained on an obesogenic diet.

Hepatic accumulation of intestinal cholesterol is decreased and fecal cholesterol excretion is increased in mice fed a high-fat diet supplemented with milk phospholipids

BackgroundMilk phospholipids (PLs) reduce liver lipid levels when given as a dietary supplement to mice fed a high-fat diet. We have speculated that this might be due to reduced intestinal cholesterol uptake.MethodsMice were given a high-fat diet for 3 or 5 weeks that had no added PL or that were supplemented with 1.2% by wt PL from cows milk. Two milk PL preparations were investigated: a) a PL-rich dairy milk extract (PLRDME), and b) a commercially-available milk PL concentrate (PC-700). Intestinal cholesterol uptake was assessed by measuring fecal and hepatic radioactivity after intragastric administration of [14C]cholesterol and [3H]sitostanol. Fecal and hepatic lipids were measured enzymatically and by ESI-MS/MS.ResultsBoth PL preparations led to significant decreases in total liver cholesterol and triglyceride (-20% to -60%, P < 0.05). Hepatic accumulation of intragastrically-administered [14C]cholesterol was significantly less (-30% to -60%, P < 0.05) and fecal excretion of [14C]cholesterol and unlabeled cholesterol was significantly higher in PL-supplemented mice (+15% to +30%, P < 0.05). Liver cholesterol and triglyceride levels were positively correlated with hepatic accumulation of intragastrically-administered [14C]cholesterol (P < 0.001) and negatively correlated with fecal excretion of [14C]cholesterol (P < 0.05). Increased PL and ceramide levels in the diet of mice supplemented with milk PL were associated with significantly higher levels of fecal PL and ceramide excretion, but reduced levels of hepatic PL and ceramide, specifically, phosphatidylcholine (-21%, P < 0.05) and monohexosylceramide (-33%, P < 0.01).ConclusionThese results indicate that milk PL extracts reduce hepatic accumulation of intestinal cholesterol and increase fecal cholesterol excretion when given to mice fed a high-fat diet.

Hydrogenated phosphatidylcholine supplementation reduces hepatic lipid levels in mice fed a high-fat diet.

The ability of the fatty acid composition of dietary phosphatidylcholine (PC) to affect hepatic lipid levels was investigated in C57BL/6 mice (n=8-10 per group) by feeding: (1) a high-fat semi-purified diet (HF), (2) HF diet supplemented with 1.25 wt% soy PC (SPC), (3) HF with 1.25 wt% hydrogenated soy PC (SPCH), (4) HF with 1.25 wt% egg PC (EPC), and (5) HF with 1.25 wt% hydrogenated egg PC (EPCH). The polyunsaturated fatty acid content (C18:2+C18:3+C20:4) of soy, egg and hydrogenated PC was 70%, 20% and 0%, respectively. Total liver lipid was significantly lower in SPCH and EPCH vs. HF (8.7 ± 0.1 and 8.5 ± 0.5 vs. 11.8 ± 0.6g/100, P<0.05), but not in SPC or EPC. SPCH and EPCH had significantly lower levels of hepatic cholesterol (-52% and -53% vs. HF, respectively). Bioactive lipids (i.e., sphingomyelin and ceramide) were also lower in the liver of SPCH and EPCH rather than in SPC or EPC. Hepatic expression of genes controlling fatty acid synthesis and catabolism were not significantly affected by dietary PC. However, hepatic expression of HMGCR, LDLR and SREBP2 was higher and that of ABCA1, ABCG5 and ABCG8 was reduced in SPCH and EPCH vs. HF. These results demonstrate that hydrogenated PC supplementation reduces hepatic lipid levels in mice fed a high-fat diet supporting the concept that the ability of dietary PC to lower hepatic lipid levels is not due to its content of polyunsaturated fatty acids.

Tumor protein D52 represents a negative regulator of ATM protein levels.

Tumor protein D52 (TPD52) is a coiled-coil motif bearing hydrophilic polypeptide known to be overexpressed in cancers of diverse cellular origins. Increased TPD52 expression is associated with increased proliferation and invasive capacity in different cell types. Recent studies have reported a correlation between TPD52 transcript levels and G2 chromosomal radiosensitivity in lymphocytes of women at risk of hereditary breast cancer, and that TPD52 knockdown significantly reduced the radiation sensitivity of multiple cancer cell lines. In this study, we investigated possible roles for TPD52 in DNA damage response, and found that increased TPD52 expression in breast cancer and TPD52-expressing BALB/c 3T3 cells compromised ATM-mediated cellular responses to DNA double-strand breaks induced by γ-ray irradiation, which was associated with downregulation of steady-state ATM protein, but not transcript levels, regardless of irradiation status. TPD52-expressing 3T3 cells also showed significantly increased radiation sensitivity compared with vector cells evaluated by clonogenic assays. Furthermore, direct interactions between exogenous and endogenous ATM and TPD52 were detected by GST pull-down and co-immunoprecipitation assays. We also identified the interaction domains involved in this binding as TPD52 residues 111–131, and ATM residues 1–245 and 772–1102. Taken together, our results suggest that TPD52 may represent a novel negative regulator of ATM protein levels.