Carole Garofalo

A polyphenol-rich cranberry extract protects from diet-induced obesity, insulin resistance and intestinal inflammation in association with increased Akkermansia spp. population in the gut microbiota of mice

Objective The increasing prevalence of obesity and type 2 diabetes (T2D) demonstrates the failure of conventional treatments to curb these diseases. The gut microbiota has been put forward as a key player in the pathophysiology of diet-induced T2D. Importantly, cranberry (Vaccinium macrocarpon Aiton) is associated with a number of beneficial health effects. We aimed to investigate the metabolic impact of a cranberry extract (CE) on high fat/high sucrose (HFHS)-fed mice and to determine whether its consequent antidiabetic effects are related to modulations in the gut microbiota. Design C57BL/6J mice were fed either a chow or a HFHS diet. HFHS-fed mice were gavaged daily either with vehicle (water) or CE (200 mg/kg) for 8 weeks. The composition of the gut microbiota was assessed by analysing 16S rRNA gene sequences with 454 pyrosequencing. Results CE treatment was found to reduce HFHS-induced weight gain and visceral obesity. CE treatment also decreased liver weight and triglyceride accumulation in association with blunted hepatic oxidative stress and inflammation. CE administration improved insulin sensitivity, as revealed by improved insulin tolerance, lower homeostasis model assessment of insulin resistance and decreased glucose-induced hyperinsulinaemia during an oral glucose tolerance test. CE treatment was found to lower intestinal triglyceride content and to alleviate intestinal inflammation and oxidative stress. Interestingly, CE treatment markedly increased the proportion of the mucin-degrading bacterium Akkermansia in our metagenomic samples. Conclusions CE exerts beneficial metabolic effects through improving HFHS diet-induced features of the metabolic syndrome, which is associated with a proportional increase in Akkermansia spp. population.

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.

Localization of Microsomal Triglyceride Transfer Protein in the Golgi POSSIBLE ROLE IN THE ASSEMBLY OF CHYLOMICRONS

Although a critical role of microsomal transfer protein (MTP) has been recognized in the assembly of nascent apolipoprotein B (apoB)-containing lipoproteins, it remains unclear where and how MTP transfers lipids in the secretory pathway during the maturational process of apoB lipidation. The aims of this study were to determine whether MTP functions in the secretory pathway as well as in the endoplasmic reticulum and whether its large 97-kDa subunit interacts with the small 58-kDa protein disulfide isomerase (PDI) subunit and apoB, particularly in the Golgi apparatus. Using a high resolution immunogold approach combined with specific polyclonal antibodies, the large and small subunits of MTP were observed over the rough endoplasmic reticulum and the Golgi. Double immunocytochemical detection unraveled the colocalization of MTP and PDI as well as MTP and apoB in these same subcellular compartments. To confirm the spatial contact of these proteins, Golgi fractions were isolated, homogenized, and incubated with an anti-MTP large subunit antibody. Immunoprecipitates were applied on SDS-PAGE and then transferred on to nitrocellulose. Immunoblotting the membrane with PDI and apoB antibodies confirmed the colocalization of these proteins with MTP. Furthermore, MTP activity assay disclosed a substantial triglyceride transfer in the Golgi fractions. The occurrence of membrane-associated apoB in the Golgi, coupled with its interaction with active MTP, suggests an important role for the Golgi in the biogenesis of apoB-containing lipoproteins.

Apple Peel Polyphenols and Their Beneficial Actions on Oxidative Stress and Inflammation

Since gastrointestinal mucosa is constantly exposed to reactive oxygen species from various sources, the presence of antioxidants may contribute to the body’s natural defenses against inflammatory diseases. Hypothesis To define the polyphenols extracted from dried apple peels (DAPP) and determine their antioxidant and anti-inflammatory potential in the intestine. Caco-2/15 cells were used to study the role of DAPP preventive actions against oxidative stress (OxS) and inflammation induced by iron-ascorbate (Fe/Asc) and lipopolysaccharide (LPS), respectively. Results The combination of HPLC with fluorescence detection, HPLC-ESI-MS TOF and UPLC-ESI-MS/MS QQQ allowed us to characterize the phenolic compounds present in the DAPP (phenolic acids, flavonol glycosides, flavan-3-ols, procyanidins). The addition of Fe/Asc to Caco-2/15 cells induced OxS as demonstrated by the rise in malondialdehyde, depletion of n-3 polyunsaturated fatty acids, and alterations in the activity of endogenous antioxidants (SOD, GPx, G-Red). However, preincubation with DAPP prevented Fe/Asc-mediated lipid peroxidation and counteracted LPS-mediated inflammation as evidenced by the down-regulation of cytokines (TNF-α and IL-6), and prostaglandin E2. The mechanisms of action triggered by DAPP induced also a down-regulation of cyclooxygenase-2 and nuclear factor-κB, respectively. These actions were accompanied by the induction of Nrf2 (orchestrating cellular antioxidant defenses and maintaining redox homeostasis), and PGC-1α (the “master controller” of mitochondrial biogenesis). Conclusion Our findings provide evidence of the capacity of DAPP to reduce OxS and inflammation, two pivotal processes involved in inflammatory bowel diseases.

Prevention of oxidative stress, inflammation and mitochondrial dysfunction in the intestine by different cranberry phenolic fractions

Cranberry fruit has been reported to have high antioxidant effectiveness that is potentially linked to its richness in diversified polyphenolic content. The aim of the present study was to determine the role of cranberry polyphenolic fractions in oxidative stress (OxS), inflammation and mitochondrial functions using intestinal Caco-2/15 cells. The combination of HPLC and UltraPerformance LC®-tandem quadrupole (UPLC-TQD) techniques allowed us to characterize the profile of low, medium and high molecular mass polyphenolic compounds in cranberry extracts. The medium molecular mass fraction was enriched with flavonoids and procyanidin dimers whereas procyanidin oligomers (DP > 4) were the dominant class of polyphenols in the high molecular mass fraction. Pre-incubation of Caco-2/15 cells with these cranberry extracts prevented iron/ascorbate-mediated lipid peroxidation and counteracted lipopolysaccharide-mediated inflammation as evidenced by the decrease in pro-inflammatory cytokines (TNF-α and interleukin-6), cyclo-oxygenase-2 and prostaglandin E2. Cranberry polyphenols (CP) fractions limited both nuclear factor κB activation and Nrf2 down-regulation. Consistently, cranberry procyanidins alleviated OxS-dependent mitochondrial dysfunctions as shown by the rise in ATP production and the up-regulation of Bcl-2, as well as the decline of protein expression of cytochrome c and apoptotic-inducing factor. These mitochondrial effects were associated with a significant stimulation of peroxisome-proliferator-activated receptor γ co-activator-1-α, a central inducing factor of mitochondrial biogenesis and transcriptional co-activator of numerous downstream mediators. Finally, cranberry procyanidins forestalled the effect of iron/ascorbate on the protein expression of mitochondrial transcription factors (mtTFA, mtTFB1, mtTFB2). Our findings provide evidence for the capacity of CP to reduce intestinal OxS and inflammation while improving mitochondrial dysfunction.

Maternal and fetal leptin, adiponectin levels and associations with fetal insulin sensitivity

It remains uncertain whether leptin and adiponectin levels are correlated in maternal vs. fetal circulations. Little is known about whether leptin and adiponectin affect insulin sensitivity during fetal life.

Modulation of intestinal and liver fatty acid-binding proteins in Caco-2 cells by lipids, hormones and cytokines

Intestinal and liver fatty acid binding proteins (I‐ and L‐FABP) are thought to play a role in enterocyte fatty acid (FA) trafficking. Their modulation by cell differentiation and various potential effectors was investigated in the human Caco‐2 cell line. With the acquisition of enterocytic features, Caco‐2 cells seeded on plastic progressively increased L‐FABP quantities, whereas I‐FABP was not detectable even very late in the maturation process. On permeable filters that improved differentiation markers (sucrase, alkaline phosphatase, transepithelial resistance), Caco‐2 cells furthered their L‐FABP content and expressed I‐FABP. Western blot analysis showed a significant increase in I‐ and L‐FABP expression following an 8‐hour incubation period with butyric acid, oleic acid, and phosphatidylcholine. However, in all cases, I‐FABP levels were higher than L‐FABP concentrations regardless of the lipid substrates added. Similarly, hydrocortisone and insulin enhanced the cellular content of I‐ and L‐FABP whereas leptin triggered I‐FABP expression only after an 8‐hour incubation. Finally, tumor necrosis factor‐α was more effective in increasing the cytosolic amount of I‐FABP levels. In conclusion, our data demonstrate that I‐FABP expression is limited to fully differentiated Caco‐2 cells and can be more easily regulated than L‐FABP by lipids, hormones, and cytokines. J. Cell. Biochem. 81: 613–620, 2001.

Circulating docosahexaenoic acid levels are associated with fetal insulin sensitivity.

Background Arachidonic acid (AA; C20∶4 n-6) and docosahexaenoic acid (DHA; C22∶6 n-3) are important long-chain polyunsaturated fatty acids (LC-PUFA) in maintaining pancreatic beta-cell structure and function. Newborns of gestational diabetic mothers are more susceptible to the development of type 2 diabetes in adulthood. It is not known whether low circulating AA or DHA is involved in perinatally “programming” this susceptibility. This study aimed to assess whether circulating concentrations of AA, DHA and other fatty acids are associated with fetal insulin sensitivity or beta-cell function, and whether low circulating concentrations of AA or DHA are involved in compromised fetal insulin sensitivity in gestational diabetic pregnancies. Methods and Principal Findings In a prospective singleton pregnancy cohort, maternal (32-35 weeks gestation) and cord plasma fatty acids were assessed in relation to surrogate indicators of fetal insulin sensitivity (cord plasma glucose-to-insulin ratio, proinsulin concentration) and beta-cell function (proinsulin-to-insulin ratio) in 108 mother-newborn pairs. Cord plasma DHA levels (in percentage of total fatty acids) were lower comparing newborns of gestational diabetic (n = 24) vs. non-diabetic pregnancies (2.9% vs. 3.5%, P = 0.01). Adjusting for gestational age at blood sampling, lower cord plasma DHA levels were associated with lower fetal insulin sensitivity (lower glucose-to-insulin ratio, r = 0.20, P = 0.036; higher proinsulin concentration, r = −0.37, P <0.0001). The associations remained after adjustment for maternal and newborn characteristics. Cord plasma saturated fatty acids C18∶0 and C20∶0 were negatively correlated with fetal insulin sensitivity, but their levels were not different between gestational diabetic and non-diabetic pregnancies. Cord plasma AA levels were not correlated with fetal insulin sensitivity. Conclusion Low circulating DHA levels are associated with compromised fetal insulin sensitivity, and may be involved in perinatally “programming” the susceptibility to type 2 diabetes in the offspring of gestational diabetic mothers.

Oxidized low-density lipoproteins in cord blood from neonates with intra-uterine growth restriction

OBJECTIVE We verified whether oxidative stress indices (oxidized low-density lipoproteins and malondialdehyde) and inflammatory biomarkers (circulating C-reactive protein, interleukin-6, tumour necrosis factor-α, serum amyloid A and soluble intercellular vascular cell adhesion molecule) are increased in the umbilical vein of placental insufficiency induced intra-uterine growth restricted neonates. STUDY DESIGN The prospective cohort study, involving 3 tertiary care centers, consists of 200 consecutively recruited pregnant women carrying twins. We chose the twin pregnancy model because both fetuses share the same maternal environment, thereby avoiding potential confounding factors when comparing oxidative stress and inflammation biomarkers. We analysed only twin pairs with one with intra-uterine growth restriction (N=38) defined as fetal growth<10th percentile with abnormal Doppler of the umbilical artery. Blood samples were taken at birth from the umbilical vein. Intra-pair comparisons on the biomarkers were performed using the Student paired t-test. RESULTS We observed increased cord blood levels of oxidized low-density lipoproteins, (2.394 ± .412 vs 1.296 ± .204, p=.003) but not of malondialdehyde in growth restricted neonates when compared to their normal counterparts. Although indices of inflammation tended to be increased in cord blood from growth restricted newborns, the difference did not reach statistical significance. CONCLUSION In the twin model, intra-uterine growth restriction is associated with low-density lipoprotein oxidation without apparent dysregulation of inflammation biomarkers. CONDENSATION Increased oxidized low-density lipoproteins are observed in growth restricted twins compared to their co-twins with normal growth at birth.

Receptor-Mediated Transcytosis of Leptin through Human Intestinal Cells In Vitro

Gastric Leptin is absorbed by duodenal enterocytes and released on the basolateral side towards the bloodstream. We investigated in vitro some of the mechanisms of this transport. Caco-2/15 cells internalize leptin from the apical medium and release it through transcytosis in the basal medium in a time- temperature-dependent and saturable fashion. Leptin receptors are revealed on the apical brush-border membrane of the Caco-2 cells. RNA-mediated silencing of the receptor led to decreases in the uptake and basolateral release. Leptin in the basal medium was found bound to the soluble form of its receptor. An inhibitor of clathrin-dependent endocytosis (chlorpromazine) decreased leptin uptake. Confocal immunocytochemistry and the use of brefeldin A and okadaic acid revealed the passage of leptin through the Golgi apparatus. We propose that leptin transcytosis by intestinal cells depends on its receptor, on clathrin-coated vesicles and transits through the Golgi apparatus.