The peroxisomal transporter ABCD3 plays a major role in dicarboxylic fatty acid metabolism

Peroxisomes metabolize a specific subset of fatty acids, which include dicarboxylic fatty acids (DCAs) generated by ω-oxidation. Data obtained in vitro suggest that the peroxisomal transporter ABCD3 (also known as PMP70) mediates the transport of DCAs into the peroxisome, but in vivo evidence to support this role is lacking. In this study, we studied an Abcd3 KO mouse model generated by CRISPR-Cas9 technology using targeted and untargeted metabolomics, histology, immunoblotting, and stable isotope tracing technology. We show that ABCD3 functions in DCA metabolism and uncover a novel role for this peroxisomal transporter in lipid metabolic homeostasis. The Abcd3 KO mouse presents with lipodystrophy, increased circulating free fatty acids, decreased ketone bodies, enhanced hepatic cholesterol synthesis and decreased hepatic de novo lipogenesis. Moreover, our study suggests that DCAs are metabolized by mitochondrial β-oxidation when ABCD3 is not functional, reflecting the importance of the metabolic compartmentalization and communication between peroxisomes and mitochondria. In summary, this study provides data on the role of the peroxisomal transporter ABCD3 in hepatic lipid homeostasis and DCA metabolism, and the consequences of peroxisomal dysfunction for the liver.

Flaxseed-Derived Peptide, IPPF, Inhibits Intestinal Cholesterol Absorption and Hepatic Cholesterol Synthesis in Caco-2 and HepG2 Cells

Background：Flaxseed peptide (FPs) showed serum cholesterol-lowering activity in SD rats fed a high-cholesterol diet, but the cholesterol-lowering amino acid sequences and mechanism of FPs were still unclear. Methods: FPs were separated via ultrafiltration, and the amino acid sequences of the selected fractions were determined via high-performance liquid chromatography- Electrospray Ionisation - Orbitrap- Mass spectrometry (HPLC-ESI-Orbitrap MS). These peptides then were synthesized by solid-phase synthesis (SPPS). IPPF with the highest CMSR was determined to exist in flaxseed protein by specific antibodies. The effects of IPPF on intestinal cholesterol absorption and hepatic cholesterol metabolism were investigated in Caco-2 cells and HepG2 cells.Results：1 kDa FP5 fraction had the highest cholesterol micelle solubility inhibition rate (CMSR) 72.39% compared with the other ultrafiltration fractions. Then Eleven peptides were identified from FP5. Ile-Pro-Pro-Phe (IPPF), with the highest CMSR 93.47%, was selected to research the cholesterol-lowering mechanism in Caco-2 and HepG2 cells. IPPF significantly reduces the amount of cholesterol transported in Caco2 cells and the amount of total cholesterol in HepG2 cells. IPPF significantly modulated the protein levels of NCP1L1 and ABCG5/8 in Caco2 cells and significantly reduced the mRNA levels of Srebp-2 and Hmgcr in HepG2 cells. Conclusion: IPPF inhibits cholesterol intestinal absorption through modulating the expression of cholesterol transporters in Caco-2 cells and reduces hepatic cholesterol synthesis through inhibiting the SREBP2-regulated mevalonate (HMGCR) pathway in HepG2 cells. IPPF is a new food-derived inhibitor of intestinal cholesterol absorption and hepatic cholesterol synthesis without side effects and provides a nutritional therapy component for hypercholesterolemia.

An Algorithmic Approach for Lipid Metabolism and Management of Patients with Xanthelasma Palpebrarum (XP)

Objectives XP (flat, yellowish plaques around the eyes) is difficult to treat and often recurs. We describe an algorithmic approach to explore the lipid metabolism and management of XP. Methods A 64 yo female with hypothyroidism, obesity, and metabolic syndrome was successful with weight loss and glycemia but noted recurrence of XP after a surgical excision. Her lipid profile (on rosuvastatin) revealed: total cholesterol 150 mg/dL, LDL 54 mg/dL, triglycerides 74 mg/dL, HDL 81 mg/dL. Apolipoprotein (Apo) A1 was 213 mg/dL (nl female > 140). Apo B100 was 63 mg/dL (nl < 130). Lp(a) was 29 mg/dL (nl < 30). LDL particles were 958 nmol/L (nl < 1000). LDL particle size was 20.9 nm (nl > 20.5). Small dense LDL particles were 598 nmol/L (nl < 528). There was presence of serum campesterol (3.7 mg/L; nl 0–7.0) and sitosterol (2.1 mg/L; nl 0–5.0), but not desmosterol or lathosterol. Oral ezetimibe (EZ), 10 mg/day was administered. After 8 months of therapy, campesterol and sitosterol dropped significantly (campesterol: 2.1, - 44%; sitosterol: 1.3, - 39%). XP lesions resolved completely. Results We developed an algorithmic approach to XP management. The sequence is as follows: 1) examine standard lipid levels, 2) examine levels of pro-atherogenic particles, 3) explore net cholesterol tissue transport, 4) confirm hepatic cholesterol synthesis suppression, 5) examine plant sterols, 6) treat the abnormalities detected. In this example case phytosterols were responsible for XP recurrence. Sitosterol and campesterol should be minimally absorbed by the gut through the Nieman Pick C1 Like 1 (NPC1L1) sterol influx transporter and eliminated by the sterol efflux transporters, adenosine triphosphate-binding cassette (ABC) ABCG5/ABCG8. If phytosterols are retained in the body, they may predispose to resistant XP. An algorithmic approach to XP suggested that hyper-absorption of plant sterols by the NPC1L1 transporter was present. This was clinically confirmed because inhibition of NPC1L1 transport (by EZ) significantly reduced plant sterol levels. Plant sterols were also clinically confirmed as the cause of her XP, since their reduction and led to XP resolution. Conclusions We present an algorithmic approach to help detail the metabolic etiology of XP and direct its management. The example case demonstrates its value to reduce XP recurrence and resolve XP in selected cases. Funding Sources None.

From GWAS to GEMMs: Sestrin1 and cholesterol biosynthesis

Sestrin1 regulates hepatic cholesterol synthesis and circulating lipid concentrations.

The intestinal microbiota regulates host cholesterol homeostasis

Background Management of blood cholesterol is a major focus of efforts to prevent cardiovascular diseases. The objective of this study was to investigate how the gut microbiota affects host cholesterol homeostasis at the organism scale. Results We depleted the intestinal microbiota of hypercholesterolemic female Apoe−/− mice using broad-spectrum antibiotics. Measurement of plasma cholesterol levels as well as cholesterol synthesis and fluxes by complementary approaches showed that the intestinal microbiota strongly regulates plasma cholesterol level, hepatic cholesterol synthesis, and enterohepatic circulation. Moreover, transplant of the microbiota from humans harboring elevated plasma cholesterol levels to recipient mice induced a phenotype of high plasma cholesterol levels in association with a low hepatic cholesterol synthesis and high intestinal absorption pattern. Recipient mice phenotypes correlated with several specific bacterial phylotypes affiliated to Betaproteobacteria, Alistipes, Bacteroides, and Barnesiella taxa. Conclusions These results indicate that the intestinal microbiota determines the circulating cholesterol level and may thus represent a novel therapeutic target in the management of dyslipidemia and cardiovascular diseases.

54Role of the gut microbiome for the cholesterol lowering effect of atorvastatin

Background and aims Statins show interindividual differences in the extent of low-density lipoprotein cholesterol (LDL-C) reduction. The mechanisms of this interindividual variation are not fully understood. Here, we examined the potential role of the gut microbiome for the LDL-C lowering property of atorvastatin. Methods Mice (C57BL/6) with either intact (conventional mice, CONV, n=24) or with antiobiotic depleted gut microbiome (gnotobiotic, n=16), were put on standard chow diet (SCD) (n=11) or high fat diet (HFD) (n=29) for 6 weeks. During the last 4 weeks atorvastatin (Ator, 10mg/kg body weight/day) or control vehicle was orally applied via gavage. Blood levels of LDL-C and glucose and body weight after 6 weeks of treatment were compared between the groups. Expression of genes involved in hepatic and intestinal cholesterol-metabolism were examined. Faeces of CONV mice were analyzed for alteration of the gut microbiota profile upon atorvastatin treatment using 16S rRNA qPCR. Results HFD fed mice with intact gut microbiome showed significantly increased blood LDL-C levels as compared to SCD (HFD: 36.8±1.4 mg/dl vs. SCD: 22.0±1.8 mg/dl; P<0.01). Bodyweight gain or blood glucose levels after HFD were not significantly different between CONV and gnotobiotic mice. While in CONV mice atorvastatin significantly reduced LDL-C levels after HFD, in gnotobiotic mice the LDL-C lowering effect of atorvastatin was attenuated (CONV+HFD+Ator: 31.0±1.8 mg/dl vs. gnotobiotic mice+HFD+Ator: 46.4±3 mg/dl; P<0.01). The expression of genes involved in hepatic cholesterol synthesis was not significantly altered in gnotobiotic mice as compared to CONV mice. In CONV mice HFD decreased the relative abundance of the bacterial phyla Bacteroidetes and increased the abundance of Firmicutes as compared to SCD. The ratio between Firmicutes to Bacteroidetes was shifted towards control conditions upon atorvastatin treatment. Conclusions The results of this study suggest a regulatory impact of atorvastatin on the gut-microbial profile and, in turn, a crucial role of the gut-microbiome for the LDL-C lowering effect of atorvastatin independent of its regulation of hepatic cholesterol synthesis. Our findings provide novel insight into potential microbiota-related mechanisms causing interindividual variation in LDL-C lowering effects of statins. Acknowledgement/Funding German Heart Research Foundation

Modulating Sterol Concentrations in Infant Formula Influences Cholesterol Absorption and Synthesis in the Neonatal Piglet

Formula-fed infants present higher cholesterol synthesis rates and lower circulating cholesterol during the postnatal feeding period compared to breast-fed infants, though the mechanisms underlying this phenotype are not fully understood. Typical infant formulas contain vegetable-based fats, inherently including phytosterols (PS), which are structurally similar to cholesterol and may interfere with their absorption. A seven-day old piglets model was used to test the inhibitory effects of PS on cholesterol absorption during postnatal feeding. Following feeding for 21 days with milk-based formulas containing PS and cholesterol levels resembling those in formulas or human-milk, apparent cholesterol digestibility was analyzed in ileal digesta, and cholesterol, PS, and cholesterol synthesis markers were analyzed in plasma and liver samples. Ileal cholesterol digestibility content was increased in the piglets fed low PS formulas and the rate of the hepatic cholesterol synthesis, as determined by the lathosterol-to-cholesterol ratios (L:C), was decreased in the piglets fed LP-formulas and corresponded to reduced nuclear expression of SREBP2 relative to those fed HP-formulas. These results are consistent with the hypothesis that PS in formula can inhibit cholesterol absorption and enhance cholesterol synthesis. Whether or not this leads to entrainment of cholesterol synthesis later in life via early programming awaits further research.