Understanding Chylomicron Retention Disease Through Sar1b Gtpase Gene Disruption: Insight From Cell Culture.

BACKGROUND: Understanding the specific mechanisms of rare autosomal disorders has greatly expanded insights into the complex processes regulating intestinal fat transport. Sar1B GTPase is one of the critical proteins governing chylomicron secretion by the small intestine, and its mutations lead to chylomicron retention disease, despite the presence of Sar1A paralog. OBJECTIVE: The central aim of this work is to examine the cause-effect relationship between Sar1B expression and chylomicron output and to determine whether Sar1B is obligatory for normal high-density lipoprotein biogenesis. APPROACH AND RESULTS: The SAR1B gene was totally silenced in Caco-2/15 cells using the zinc finger nuclease technique. SAR1B deletion resulted in significantly decreased secretion of triglycerides (≈40%), apolipoprotein B-48 (≈57%), and chylomicron (≈34.5%). The absence of expected chylomicron production collapse may be because of the compensatory SAR1A elevation observed in our experiments. Therefore, a double knockout of SAR1A and SAR1B was engineered in Caco-2/15 cells, which led to almost complete inhibition of triglycerides, apolipoprotein B-48, and chylomicron output. Further experiments with labeled cholesterol revealed the downregulation of high-density lipoprotein biogenesis in cells deficient in SAR1B or with the double knockout of the 2 SAR1 paralogs. Similarly, there was a fall in the movement of labeled cholesterol from cells to basolateral medium containing apolipoprotein A-I, thereby limiting newly synthesized high-density lipoprotein in genetically modified cells. The decreased cholesterol efflux was associated with impaired expression of ABCA1 (ATP-binding cassette subfamily A member 1). CONCLUSIONS: These findings demonstrate that the deletion of the 2 SAR1 isoforms is required to fully eliminate the secretion of chylomicron in vitro. They also underscore the limited high-density lipoprotein production by the intestinal cells in response to SAR1 knockout.

Apple peel polyphenols: a key player in the prevention and treatment of experimental inflammatory bowel disease.

Diets rich in fruits and vegetables may reduce oxidative stress (OxS) and inflammation via several mechanisms. These beneficial effects may be due to their high polyphenol content. The aims of the present study are to evaluate the preventive and therapeutic aspects of polyphenols in dried apple peel powder (DAPP) on intestinal inflammation while elucidating the underlying mechanisms and clinical benefits. Induction of intestinal inflammation in mice was performed by oral administration of the inflammatory agent dextran sulfate sodium (DSS) at 2.5% for 10 days. Physiological and supraphysiological doses of DAPP (200 and 400 mg/kg/day respectively) were administered by gavage for 10 days pre- and post-DSS treatment. DSS-mediated inflammation caused weight loss, shortening of the colon, dystrophic detachment of the epithelium, and infiltration of mono- and poly-morphonuclear cells in the colon. DSS induced an increase in lipid peroxidation, a down-regulation of antioxidant enzymes, an augmented expression of myeloperoxidase (MPO) and cyclooxygenase-2 (COX-2), an elevated production of prostaglandin E2 (PGE2) and a shift in mucosa-associated microbial composition. However, DAPP normalized most of these abnormalities in preventive or therapeutic situations in addition to lowering inflammatory cytokines while stimulating antioxidant transcription factors and modulating other potential healing pathways. The supraphysiological dose of DAPP in therapeutic situations also improved mitochondrial dysfunction. Relative abundance of Peptostreptococcaceae and Enterobacteriaceae bacteria was slightly decreased in DAPP-treated mice. In conclusion, DAPP exhibits powerful antioxidant and anti-inflammatory action in the intestine and is associated with the regulation of cellular signalling pathways and changes in microbiota composition. Evaluation of preventive and therapeutic effects of DAPP may be clinically feasible in individuals with intestinal inflammatory bowel diseases.

Glycomacropeptide as an Efficient Agent to Fight Pathophysiological Mechanisms of Metabolic Syndrome.

There is currently a growing interest in the use of nutraceuticals as a means of preventing the development of complex diseases. Given the considerable health potential of milk-derived peptides, the aim of this study was to investigate the protective effects of glycomacropeptide (GMP) on metabolic syndrome. Particular emphasis was placed on the potential mechanisms mitigating cardiometabolic disorders in high-fat, high-fructose diet-fed mice in the presence of GMP or Bipro, an isocaloric control. The administration of GMP for 12 weeks reduced obesity, hyperglycemia and hyperinsulinemia caused by a high-fat, high-fructose diet, resulting in a decline in insulin resistance. GMP also lessened systemic inflammation, as indicated by decreased circulating inflammatory cytokines. In the intestinal and hepatic tissues, GMP improved homeostasis by increasing insulin sensitivity and attenuating high-fat, high-fructose-induced inflammation, oxidative stress and endoplasmic reticulum stress. Biochemical and histological analyses revealed improved hepatic steatosis and fatty acid composition in the livers of high-fat, high-fructose diet-fed mice treated with GMP compared to Bipro. A trend toward a decrease in bile acids without any marked changes in intestinal microbiota composition characterized GMP-treated animals compared to those administered Bipro. GMP offers considerable potential for fighting metabolic syndrome-related components and complications given its beneficial effects on risk factors such as inflammation, oxidative stress and endoplasmic reticulum stress without involving the intestinal microbiota.

Cranberry Proanthocyanidins as a Therapeutic Strategy to Curb Metabolic Syndrome and Fatty Liver-Associated Disorders.

While the prevalence of metabolic syndrome (MetS) is steadily increasing worldwide, no optimal pharmacotherapy is readily available to address its multifaceted risk factors and halt its complications. This growing challenge mandates the development of other future curative directions. The purpose of the present study is to investigate the efficacy of cranberry proanthocyanidins (PACs) in improving MetS pathological conditions and liver complications; C57BL/6J mice were fed either a standard chow or a high fat/high sucrose (HFHS) diet with and without PACs (200 mg/kg), delivered by daily gavage for 12 weeks. Our results show that PACs lowered HFHS-induced obesity, insulin resistance, and hyperlipidemia. In conjunction, PACs lessened circulatory markers of oxidative stress (OxS) and inflammation. Similarly, the anti-oxidative and anti-inflammatory capacities of PACs were noted in the liver in association with improved hepatic steatosis. Inhibition of lipogenesis and stimulation of beta-oxidation could account for PACs-mediated decline of fatty liver as evidenced not only by the expression of rate-limiting enzymes but also by the status of AMPKα (the key sensor of cellular energy) and the powerful transcription factors (PPARα, PGC1α, SREBP1c, ChREBP). Likewise, treatment with PACs resulted in the downregulation of critical enzymes of liver gluconeogenesis, a process contributing to increased rates of glucose production in type 2 diabetes. Our findings demonstrate that PACs prevented obesity and improved insulin resistance likely via suppression of OxS and inflammation while diminishing hyperlipidemia and fatty liver disease, as clear evidence for their strength of fighting the cluster of MetS abnormalities.

Oxidative stress influences cholesterol efflux in THP-1 macrophages: role of ATP-binding cassette A1 and nuclear factors.

OBJECTIVES: Understanding the mechanisms involved in oxidative stress-induced foam cell formation is of fundamental importance for atherosclerosis. Our aim was to characterize the effects of oxidative stress on key receptors of macrophage cholesterol homeostasis, on the nuclear transcription factors PPAR and LXR regulating their expression, and on macrophage cholesterol handling. METHODS AND RESULTS: The incubation of macrophages derived from the human monocyte cell line THP-1 with iron (100 microm)/ascorbate (1000 microm) for a period of 4 h induced a strong peroxidation, as demonstrated by the elevation of malondialdehyde (220%, P < 0.001). The production of lipid peroxidation affected cholesterol efflux, which was probably due to decreased ABCAI gene and protein expression. On the other hand, cholesterol influx remained unchanged as did the mRNA and protein levels of SR-BI and CD36, important protein receptors that participate in cholesterol import. Experiments using RT-PCR showed that the ABCAI modulation was orchestrated by the nuclear receptors LXRalpha, LXRbeta, PPARalpha, and PPARgamma. Treatment with powerful antioxidants (Trolox and BHT) prevented the adverse effects of iron-ascorbate on cholesterol movement, conceivably supporting the role of oxidative stress. CONCLUSION: Our results show that oxidative stress can directly be induced in macrophages and concomitantly impairs the expression of receptors involved in cholesterol flux, which could influence foam cell formation and atherosclerosis development.

Targeted CFTR gene disruption with zinc-finger nucleases in human intestinal epithelial cells induces oxidative stress and inflammation.

UNLABELLED: Cystic fibrosis (CF) is a multisystemic pathology caused by mutations of the CF transmembrane conductance regulator (CFTR) gene. OBJECTIVES: As the intestine harbors the greatest number of CFTR transcripts after birth and since CFTR plays a role in glutathione transport, we hypothesized that CFTR deletion might produce oxidative stress (OxS) and inflammation in CF intestinal epithelial cell. METHODS: CFTR gene was abrogated in Caco-2/15 enterocytes through the zinc-finger nuclease system. Their oxidative and inflammatory characteristics were appreciated under basal conditions and after the treatment with the pro-oxidant iron-ascorbate (Fe/Asc) complex and pro-inflammatory lipopolysaccharide (LPS). RESULTS: Intestinal epithelial cells with CFTR knockout spontaneously exhibited an increased lipid peroxidation level, reflected by malondialdehyde overproduction and reduced antioxidant defense characterized by low enzymatic activities of glutathione peroxidase and catalase. CFTR silencing also resulted in elevated protein expression of pro-inflammatory tumor necrosis Factor-α, interleukin-6, cyclooxygenase-2, and the transcription factor nuclear factor-κB. Moreover, exaggerated OxS and inflammation processes occurred in CFTR(-/-) cells in response to the addition of Fe/Asc and LPS, respectively. CONCLUSIONS: Intestinal Caco-2/15 cells with CFTR deletion, display innate oxidative and inflammatory features while being more sensitive to pro-oxidant and pro-inflammatory stimuli. These two pathophysiological processes could be implicated in CF-related intestinal disorders.

Activation and role of caspases in chemotherapy-induced apoptosis.

The importance of caspase activation during apoptosis has become eminently apparent in the last few years. The caspases participate in a proteolytic cascade activated in response to various stimuli, including anticancer drugs, that results in the systematic and orderly eradication of the cell. The core machinery of caspase activation is now emerging and involves multiple molecular complexes. We describe the two best-studied models of caspase activation, the mitochondrial pathway and the cell death receptor pathway, and discuss their involvement in caspase activation induced by various anticancer drugs used in chemotherapy. Defective apoptosis contributes to tumor growth and drug resistance. Understanding the activation and role of caspases in apoptosis may help develop new therapeutic strategies to circumvent drug resistance. Copyright 1999 Harcourt Publishers Ltd.

Ascorbate modulation of H(2)O(2) and camptothecin-induced cell death in Jurkat cells.

The effect of ascorbate on cell death was examined in Jurkat cells (human T-cell leukemia) by incubation with dehydroascorbate (DHA), which is rapidly taken up by cells and efficiently reduced to ascorbate. Apoptosis was evaluated by caspase-3 activity in cell extracts and flow cytometry of annexin V-labeled cells. In parallel, necrosis was estimated by the release of lactate dehydrogenase. Minor effects on cell death were observed when Jurkat cells were incubated with either DHA alone (100-1,000 microM) or a single dose of 10 microM H(2)O(2). However, pre-incubation with DHA followed by exposure to H(2)O(2) clearly stimulated both apoptosis and necrosis. In complete contrast, pre-incubation of cells with DHA significantly inhibited apoptosis, but did not affect necrosis, induced by the topoisomerase I inhibitor camptothecin. Our results indicate that intracellular ascorbate can modulate cell death in a manner which depends upon the nature of the apoptotic stimulus, which in turn has critical implications regarding the mechanism and potential application of ascorbate in cancer therapy.

PCSK9 plays a significant role in cholesterol homeostasis and lipid transport in intestinal epithelial cells.

OBJECTIVES: The proprotein convertase subtillisin/kexin type 9 (PCSK9) regulates cholesterol metabolism via degradation of low-density lipoprotein receptor (LDLr). Although PCSK9 is abundantly expressed in the intestine, limited data are available on its functions. The present study aims at determining whether PCSK9 plays important roles in cholesterol homeostasis and lipid transport in the gut. METHODS AND RESULTS: Caco-2/15 cells were used allowing the exploration of the PCSK9 secretory route through the apical and basolateral compartments corresponding to intestinal lumen and serosal circulation, respectively. The output of PCSK9 occurred through the basolateral membrane, a site characterized by the location of LDLr. Co-immunoprecipitation studies indicated an association between PCSK9 and LDLr. Addition of purified recombinant wild type and D374Y gain-of function PCSK9 proteins to the basolateral medium was followed by a decrease in LDLr concomitantly with the accumulation of both forms of PCSK9. Furthermore, the latter caused a significant enhancement in cholesterol uptake also evidenced by a raised protein expression of cholesterol transporters NPC1L1 and CD36 without changes in SR-BI, ABCA1, and ABCG5/G8. Moreover, exogenous PCSK9 altered the activity of HMG-CoA reductase and acylcoenzyme A: cholesterol acyltransferase, and was able to enhance chylomicron secretion by positively modulating lipids and apolipoprotein B-48 biogenesis. Importantly, PCSK9 silencing led to opposite findings, which validate our data on the role of PCSK9 in lipid transport and metabolism. Moreover, PCSK9-mediated changes persisted despite LDLr knockdown. CONCLUSIONS: These findings indicate that, in addition to its effect on LDLr, PCSK9 modulates cholesterol transport and metabolism, as well as production of apo B-containing lipoproteins in intestinal cells.

Intestinal fatty acid binding protein regulates mitochondrion beta-oxidation and cholesterol uptake.

The role of intestinal fatty acid binding protein (I-FABP) in lipid metabolism remains elusive. To address this issue, normal human intestinal epithelial cells (HIEC-6) were transfected with cDNA to overexpress I-FABP and compared with cells treated with empty pQCXIP vector. I-FABP overexpression stimulated mitochondrial [U-14C]oleate oxidation to CO2 and acid-soluble metabolites via mechanisms including the upregulation of protein expression and the activity of carnitine palmitoyltransferase 1, a critical enzyme controlling the entry of fatty acid (FA) into mitochondria, and increased activity of 3-hydroxyacyl-CoA dehydrogenase, a mitochondrial beta-oxidation enzyme. On the other hand, the gene and protein expression of the key enzymes FA synthase and acetyl-coenzyme A carboxylase 2 was decreased, suggesting diminished lipogenesis. Furthermore, I-FABP overexpression caused a decline in [14C]free cholesterol (CHOL) incorporation. Accordingly, a significant lessening was observed in the gene expression of Niemann Pick C1-Like 1, a mediator of CHOL uptake, along with an increase in the transcripts and protein content of ABCA1 and ABCG5/ABCG8, acting as CHOL efflux pumps. Furthermore, I-FABP overexpression resulted in increased levels of mRNA, protein mass, and activity of HMG-CoA reductase, the rate-limiting step in CHOL synthesis. Scrutiny of the nuclear receptors revealed augmented peroxisome proliferator-activated receptor alpha,gamma and reduced liver X receptor-alpha in HIEC-6 overexpressing I-FABP. Finally, I-FABP overexpression did not influence acyl-coenzyme A oxidase 1, which catalyzes the first rate-limiting step in peroxisomal FA beta-oxidation. Overall, our data suggest that I-FABP may influence mitochondrial FA oxidation and CHOL transport by regulating gene expression and interaction with nuclear receptors.

Localization and role of NPC1L1 in cholesterol absorption in human intestine.

Recent studies have documented the presence of Niemann-Pick C1-Like 1 (NPC1L1) in the small intestine and its capacity to transport cholesterol in mice and rats. The current investigation was undertaken to explore the localization and function of NPC1L1 in human enterocytes. Cell fractionation experiments revealed an NPC1L1 association with apical membrane of the enterocyte in human jejunum. Signal was also detected in lysosomes, endosomes, and mitochondria. Confirmation of cellular NPC1L1 distribution was obtained by immunocytochemistry. Knockdown of NPC1L1 caused a decline in the ability of Caco-2 cells to capture micellar [(14)C]free cholesterol. Furthermore, this NPC1L1 suppression resulted in increased and decreased mRNA levels and activity of HMG-CoA reductase, the rate-limiting step in cholesterol synthesis, and of ACAT, the key enzyme in cholesterol esterification, respectively. An increase was also noted in the transcriptional factor sterol-regulatory element binding protein that modulates cholesterol homeostasis. Efforts were devoted to define the impact of NPC1L1 knockdown on other mediators of cholesterol uptake. RT-PCR evidence is presented to show the significant decrease in the levels of scavenger receptor class B type I (SR-BI) with no changes in ABCA1, ABCG5, and cluster determinant 36 in NPC1L1-deficient Caco-2 cells. Together, our data suggest that NPC1L1 contributes to intestinal cholesterol homeostasis and possibly cooperates with SR-BI to mediate cholesterol absorption in humans.