Residual ß-Cell Function Is Associated With Longer Time in Range in Individuals With Type 1 Diabetes.

OBJECTIVE: Little is known about the influence of residual islet function on glycemic control in type 1 diabetes (T1D). We investigated the associations between residual ß-cell function and metrics of continuous glucose monitoring (CGM) in individuals with T1D. RESEARCH DESIGN AND METHODS: In this cross-sectional cohort comprising 489 individuals (64% female, age 41.0 ± 14.0 years), T1D duration was 15.0 (interquartile range [IQR] 6.0-29.0) years. Individuals had a time in range (TIR) of 66% (IQR 52-80%) and a urinary C-peptide-to-creatinine ratio (UCPCR) of 0.01 (IQR 0.00-0.41) nmol/mmol. To assess ß-cell function, we measured UCPCR (detectable >0.01 nmol/mmol), and to assess α-cell function, fasting plasma glucagon/glucose ratios were measured. CGM was used to record TIR (3.9-10 mmol/L), time below range (TBR) (<3.9 mmol/L), time above range (TAR) (>10 mmol/L), and glucose coefficient of variance (CV). For CGM, 74.7% used FreeStyle Libre 2, 13.8% Medtronic Guardian, and 11.5% Dexcom G6 as their device. RESULTS: The percentage of patients with T1D who had a detectable UCPCR was 49.4%. A higher UCPCR correlated with higher TIR (r = 0.330, P < 0.05), lower TBR (r = -0.237, P < 0.05), lower TAR (r = -0.302, P < 0.05), and lower glucose CV (r = -0.356, P < 0.05). A higher UCPCR correlated negatively with HbA1c levels (r = -0.183, P < 0.05) and total daily insulin dose (r = -0.183, P < 0.05). Glucagon/glucose ratios correlated with longer TIR (r = 0.234, P < 0.05). CONCLUSIONS: Significantly longer TIR, shorter TBR and TAR, and lower CV were observed in individuals with greater UCPCR-assessed ß-cell function. Therefore, better CGM-derived metrics in individuals with preserved ß-cell function may be a contributor to a lower risk of developing long-term complications.

Effect of Fecal Microbiota Transplantation Combined With Mediterranean Diet on Insulin Sensitivity in Subjects With Metabolic Syndrome.

BACKGROUND: Recent studies demonstrate that a Mediterranean diet has beneficial metabolic effects in metabolic syndrome subjects. Since we have shown that fecal microbiota transplantation (FMT) from lean donors exerts beneficial effects on insulin sensitivity, in the present trial, we investigated the potential synergistic effects on insulin sensitivity of combining a Mediterranean diet with donor FMT in subjects with metabolic syndrome. DESIGN: Twenty-four male subjects with metabolic syndrome were put on a Mediterranean diet and after a 2-week run-in phase, the subjects were randomized to either lean donor (n = 12) or autologous (n = 12) FMT. Changes in the gut microbiota composition and bacterial strain engraftment after the 2-week dietary regimens and 6 weeks post-FMT were the primary endpoints. The secondary objectives were changes in glucose fluxes (both hepatic and peripheral insulin sensitivity), postprandial plasma incretin (GLP-1) levels, subcutaneous adipose tissue inflammation, and plasma metabolites. RESULTS: Consumption of the Mediterranean diet resulted in a reduction in body weight, HOMA-IR, and lipid levels. However, no large synergistic effects of combining the diet with lean donor FMT were seen on the gut microbiota diversity after 6 weeks. Although we did observe changes in specific bacterial species and plasma metabolites, no significant beneficial effects on glucose fluxes, postprandial incretins, or subcutaneous adipose tissue inflammation were detected. CONCLUSIONS: In this small pilot randomized controlled trial, no synergistic beneficial metabolic effects of combining a Mediterranean diet with lean donor FMT on glucose metabolism were achieved. However, we observed engraftment of specific bacterial species. Future trials are warranted to test the combination of other microbial interventions and diets in metabolic syndrome.

The Role of Heparan Sulfate and Neuropilin 2 in VEGFA Signaling in Human Endothelial Tip Cells and Non-Tip Cells during Angiogenesis In Vitro.

During angiogenesis, vascular endothelial growth factor A (VEGFA) regulates endothelial cell (EC) survival, tip cell formation, and stalk cell proliferation via VEGF receptor 2 (VEGFR2). VEGFR2 can interact with VEGFR2 co-receptors such as heparan sulfate proteoglycans (HSPGs) and neuropilin 2 (NRP2), but the exact roles of these co-receptors, or of sulfatase 2 (SULF2), an enzyme that removes sulfate groups from HSPGs and inhibits HSPG-mediated uptake of very low density lipoprotein (VLDL), in angiogenesis and tip cell biology are unknown. In the present study, we investigated whether the modulation of binding of VEGFA to VEGFR2 by knockdown of SULF2 or NRP2 affects sprouting angiogenesis, tip cell formation, proliferation of non-tip cells, and EC survival, or uptake of VLDL. To this end, we employed VEGFA splice variant 121, which lacks an HSPG binding domain, and VEGFA splice variant 165, which does have this domain, in in vitro models of angiogenic tip cells and vascular sprouting. We conclude that VEGFA165 and VEGFA121 have similar inducing effects on tip cells and sprouting in vitro, and that the binding of VEGFA165 to HSPGs in the extracellular matrix does not seem to play a role, as knockdown of SULF2 did not alter these effects. Co-binding of NRP2 appears to regulate VEGFA-VEGFR2-induced sprout initiation, but not tip cell formation. Finally, as the addition of VLDL increased sprout formation but not tip cell formation, and as VLDL uptake was limited to non-tip cells, our findings suggest that VLDL plays a role in sprout formation by providing biomass for stalk cell proliferation.

The effect of dapagliflozin on apolipoprotein B and glucose fluxes in patients with type 2 diabetes and well-controlled plasma LDL cholesterol.

AIM: To dissect the effects of the sodium-glucose linked transporter 2 inhibitor dapagliflozin on lipid metabolism and assess whether these effects could potentially offset cardiovascular benefit with this drug-class. MATERIALS AND METHODS: We assessed the effect of dapagliflozin on lipid metabolism in 11 adults with uncomplicated type 2 diabetes. After 4 weeks of statin wash-out and 4 weeks of rosuvastatin 10 mg treatment, participants were treated with dapagliflozin 10 mg once-daily for 5 weeks. Before and after dapagliflozin, plasma lipids were measured and very low-density lipoprotein (VLDL)-1 and VLDL-2 apolipoprotein (Apo)B fluxes were assessed using (5.5.5-2 H3 )-leucine tracer infusion. In addition, hepatic and peripheral insulin sensitivity as well as insulin-mediated inhibition of peripheral lipolysis were measured during a two-step hyperinsulinemic-euglycaemic clamp using (6,6-2 H2 )-glucose and (1,1,2,3,3-2 H5 )-glycerol tracers. RESULTS: Rosuvastatin decreased all plasma lipids significantly: total cholesterol from 4.5 (3.2-6.2) to 3.1 (2.5-3.8) mmol/L, LDL cholesterol from 2.6 (1.7-3.4) to 1.5 (1.1-2.2) mmol/L, HDL cholesterol from 1.34 (0.80-2.02) to 1.19 (0.74-1.89) mmol/L and triglycerides from 0.92 (0.31-3.91) to 0.79 (0.32-2.10) mmol/L. The addition of dapaglifozin to rosuvastatin did not raise either LDL cholesterol or total cholesterol, and only increased HDL cholesterol by 0.08 (-0.03-0.13) mmol/L (P = 0.03). In line with this, dapagliflozin did not affect VLDL-1 or VLDL-2 ApoB fluxes. Fasting endogenous glucose production tended to increase by 0.9 (-3.4-3.1) µmol kg-1 min-1 (P = 0.06), but no effect on hepatic and peripheral insulin sensitivity or on peripheral lipolysis was observed. CONCLUSIONS: Dapagliflozin has no effect on plasma LDL-cholesterol levels or VLDL-apoB fluxes in the context of optimal lipid-lowering treatment, which will thus not limit cardiovascular benefit when lipids are adequately controlled.

Donor metabolic characteristics drive effects of faecal microbiota transplantation on recipient insulin sensitivity, energy expenditure and intestinal transit time.

OBJECTIVE: Bariatric surgery improves glucose metabolism. Recent data suggest that faecal microbiota transplantation (FMT) using faeces from postbariatric surgery diet-induced obese mice in germ-free mice improves glucose metabolism and intestinal homeostasis. We here investigated whether allogenic FMT using faeces from post-Roux-en-Y gastric bypass donors (RYGB-D) compared with using faeces from metabolic syndrome donors (METS-D) has short-term effects on glucose metabolism, intestinal transit time and adipose tissue inflammation in treatment-naïve, obese, insulin-resistant male subjects. DESIGN: Subjects with metabolic syndrome (n=22) received allogenic FMT either from RYGB-D or METS-D. Hepatic and peripheral insulin sensitivity as well as lipolysis were measured at baseline and 2 weeks after FMT by hyperinsulinaemic euglycaemic stable isotope (2H2-glucose and 2H5-glycerol) clamp. Secondary outcome parameters were changes in resting energy expenditure, intestinal transit time, faecal short-chain fatty acids (SCFA) and bile acids, and inflammatory markers in subcutaneous adipose tissue related to intestinal microbiota composition. Faecal SCFA, bile acids, glycaemic control and inflammatory parameters were also evaluated at 8 weeks. RESULTS: We observed a significant decrease in insulin sensitivity 2 weeks after allogenic METS-D FMT (median rate of glucose disappearance: from 40.6 to 34.0 µmol/kg/min; p<0.01). Moreover, a trend (p=0.052) towards faster intestinal transit time following RYGB-D FMT was seen. Finally, we observed changes in faecal bile acids (increased lithocholic, deoxycholic and (iso)lithocholic acid after METS-D FMT), inflammatory markers (decreased adipose tissue chemokine ligand 2 (CCL2) gene expression and plasma CCL2 after RYGB-D FMT) and changes in several intestinal microbiota taxa. CONCLUSION: Allogenic FMT using METS-D decreases insulin sensitivity in metabolic syndrome recipients when compared with using post-RYGB-D. Further research is needed to delineate the role of donor characteristics in FMT efficacy in human insulin-resistant subjects. TRIAL REGISTRATION NUMBER: NTR4327.

Reduced CETP glycosylation and activity in patients with homozygous B4GALT1 mutations.

The importance of protein glycosylation in regulating lipid metabolism is becoming increasingly apparent. We set out to further investigate this by studying the effects of defective glycosylation on plasma lipids in patients with B4GALT1-CDG, caused by a mutation in B4GALT1 with defective N-linked glycosylation. We studied plasma lipids, cholesteryl ester transfer protein (CETP) glyco-isoforms with isoelectric focusing followed by a western blot and CETP activity in three known B4GALT1-CDG patients and compared them with 11 age- and gender-matched, healthy controls. B4GALT1-CDG patients have significantly lowered non-high density lipoprotein cholesterol (HDL-c) and total cholesterol to HDL-c ratio compared with controls and larger HDL particles. Plasma CETP was hypoglycosylated and less active in B4GALT1-CDG patients compared to matched controls. Our study provides insight into the role of protein glycosylation in human lipoprotein homeostasis. The hypogalactosylated, hypo-active CETP found in patients with B4GALT1-CDG indicates a role of protein galactosylation in regulating plasma HDL and LDL. Patients with B4GALT1-CDG have large HDL particles probably due to hypogalactosylated, hypo-active CETP.

N-Glycosylation Defects in Humans Lower Low-Density Lipoprotein Cholesterol Through Increased Low-Density Lipoprotein Receptor Expression.

BACKGROUND: The importance of protein glycosylation in regulating lipid metabolism is becoming increasingly apparent. We set out to further investigate this by studying patients with type I congenital disorders of glycosylation (CDGs) with defective N-glycosylation. METHODS: We studied 29 patients with the 2 most prevalent types of type I CDG, ALG6 (asparagine-linked glycosylation protein 6)-deficiency CDG and PMM2 (phosphomannomutase 2)-deficiency CDG, and 23 first- and second-degree relatives with a heterozygous mutation and measured plasma cholesterol levels. Low-density lipoprotein (LDL) metabolism was studied in 3 cell models-gene silencing in HepG2 cells, patient fibroblasts, and patient hepatocyte-like cells derived from induced pluripotent stem cells-by measuring apolipoprotein B production and secretion, LDL receptor expression and membrane abundance, and LDL particle uptake. Furthermore, SREBP2 (sterol regulatory element-binding protein 2) protein expression and activation and endoplasmic reticulum stress markers were studied. RESULTS: We report hypobetalipoproteinemia (LDL cholesterol [LDL-C] and apolipoprotein B below the fifth percentile) in a large cohort of patients with type I CDG (mean age, 9 years), together with reduced LDL-C and apolipoprotein B in clinically unaffected heterozygous relatives (mean age, 46 years), compared with 2 separate sets of age- and sex-matched control subjects. ALG6 and PMM2 deficiency led to markedly increased LDL uptake as a result of increased cell surface LDL receptor abundance. Mechanistically, this outcome was driven by increased SREBP2 protein expression accompanied by amplified target gene expression, resulting in higher LDL receptor protein levels. Endoplasmic reticulum stress was not found to be a major mediator. CONCLUSIONS: Our study establishes N-glycosylation as an important regulator of LDL metabolism. Given that LDL-C was also reduced in a group of clinically unaffected heterozygotes, we propose that increasing LDL receptor-mediated cholesterol clearance by targeting N-glycosylation in the LDL pathway may represent a novel therapeutic strategy to reduce LDL-C and cardiovascular disease.

Decreased GPIHBP1 protein levels in visceral adipose tissue partly underlie the hypertriglyceridemic phenotype in insulin resistance.

GPIHBP1 is a protein localized at the endothelial cell surface that facilitates triglyceride (TG) lipolysis by binding lipoprotein lipase (LPL). Whether Glycosyl Phosphatidyl Inositol high density lipoprotein binding protein 1 (GPIHBP1) function is impaired and may underlie the hyperTG phenotype observed in type 2 diabetes is not yet established. To elucidate the mechanism underlying impaired TG homeostasis in insulin resistance state we studied the effect of insulin on GPIHBP1 protein expression in human microvascular endothelial cells (HMVEC) under flow conditions. Next, we assessed visceral adipose tissue GPIHBP1 protein expression in type 2 diabetes Lepr db/db mouse model as well as in subjects with ranging levels of insulin resistance. We report that insulin reduces the expression of GPIHBP1 protein in HMVECs. Furthermore, GPIHBP1 protein expression in visceral adipose tissue in Lepr db/db mice is significantly reduced as is the active monomeric form of GPIHBP1 as compared to Leprdb/m mice. A similar decrease in GPIHBP1 protein was observed in subjects with increased body weight. GPIHBP1 protein expression was negatively associated with insulin and HOMA-IR. In conclusion, our data suggest that decreased GPIHBP1 availability in insulin resistant state may hamper peripheral lipolysis capacity.

ABCA8 Regulates Cholesterol Efflux and High-Density Lipoprotein Cholesterol Levels.

OBJECTIVE: High-density lipoproteins (HDL) are considered to protect against atherosclerosis in part by facilitating the removal of cholesterol from peripheral tissues. However, factors regulating lipid efflux are incompletely understood. We previously identified a variant in adenosine triphosphate-binding cassette transporter A8 (ABCA8) in an individual with low HDL cholesterol (HDLc). Here, we investigate the role of ABCA8 in cholesterol efflux and in regulating HDLc levels. APPROACH AND RESULTS: We sequenced ABCA8 in individuals with low and high HDLc and identified, exclusively in low HDLc probands, 3 predicted deleterious heterozygous ABCA8 mutations (p.Pro609Arg [P609R], IVS17-2 A>G and p.Thr741Stop [T741X]). HDLc levels were lower in heterozygous mutation carriers compared with first-degree family controls (0.86±0.34 versus 1.17±0.26 mmol/L; P=0.005). HDLc levels were significantly decreased by 29% (P=0.01) in Abca8b-/- mice on a high-cholesterol diet compared with wild-type mice, whereas hepatic overexpression of human ABCA8 in mice resulted in significant increases in plasma HDLc and the first steps of macrophage-to-feces reverse cholesterol transport. Overexpression of wild-type but not mutant ABCA8 resulted in a significant increase (1.8-fold; P=0.01) of cholesterol efflux to apolipoprotein AI in vitro. ABCA8 colocalizes and interacts with adenosine triphosphate-binding cassette transporter A1 and further potentiates adenosine triphosphate-binding cassette transporter A1-mediated cholesterol efflux. CONCLUSIONS: ABCA8 facilitates cholesterol efflux and modulates HDLc levels in humans and mice.

In Vivo Inflammation Does Not Impair ABCA1-Mediated Cholesterol Efflux Capacity of HDL.

HDL provides atheroprotection by facilitating cholesterol efflex from lipid-laden macrophages in the vessel wall. In vitro studies have suggested impaired efflux capacity of HDL following inflammatory changes. We assessed the impact of acute severe sepsis and mild chronic inflammatory disease on the efflux capacity of HDL. We hypothesize that a more severe inflammatory state leads to stronger impaired cholesterol efflux capacity. Using lipid-laden THP1 cells and fibroblasts we were able to show that efflux capacity of HDL from both patients with severe sepsis or with Crohn's disease (active or in remission), either isolated using density gradient ultracentrifugation or using apoB precipitation, was not impaired. Yet plasma levels of HDL cholesterol and apoA-I were markedly lower in patients with sepsis. Based on the current observations we conclude that inflammatory disease does not interfere with the capacity of HDL to mediate cholesterol efflux. Our findings do not lend support to the biological relevance of HDL function changes in vitro.

Restoration of high-density lipoprotein levels by cholesteryl ester transfer protein expression in scavenger receptor class B type I (SR-BI) knockout mice does not normalize pathologies associated with SR-BI deficiency.

OBJECTIVE: Disruption of scavenger receptor class B type I (SR-BI) in mice impairs high-density lipoprotein (HDL)-cholesterol (HDL-C) delivery to the liver and induces susceptibility to atherosclerosis. In this study, it was investigated whether introduction of cholesteryl ester transfer protein (CETP) can normalize HDL-C transport to the liver and reduce atherosclerosis in SR-BI knockout (KO) mice. METHODS AND RESULTS: Expression of human CETP in SR-BI(KO) mice resulted in decreased plasma HDL-C levels, both on chow diet (1.8-fold, P<0.001) and on challenge with Western-type diet (1.6-fold, P<0.01). Furthermore, the presence of CETP partially normalized the abnormally large HDL particles observed in SR-BI(KO) mice. Unexpectedly, expression of CETP in SR-BI(KO) mice did not reduce atherosclerotic lesion development, probably because of consequences of SR-BI deficiency, including the persistence of higher VLDL-cholesterol (VLDL-C) levels, unchanged elevated free cholesterol/total cholesterol ratio, and the increased oxidative status of the animals. In addition, CETP expression did not normalize other characteristics of SR-BI deficiency, including female infertility, reticulocytosis, thrombocytopenia, and impaired platelet aggregation. CONCLUSIONS: CETP restores HDL-C levels in SR-BI(KO) mice, but it does not change the susceptibility to atherosclerosis and other typical characteristics that are associated with SR-BI disruption. This may indicate that the pathophysiology of SR-BI deficiency is not a direct consequence of changes in the HDL pool.

Chylomicronemia with low postheparin lipoprotein lipase levels in the setting of GPIHBP1 defects.

BACKGROUND: Recent studies in mice have established that an endothelial cell protein, glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1), is essential for the lipolytic processing of triglyceride-rich lipoproteins. METHODS AND RESULTS: We report the discovery of a homozygous missense mutation in GPIHBP1 in a young boy with severe chylomicronemia. The mutation, p.C65Y, replaces a conserved cysteine in the GPIHBP1 lymphocyte antigen 6 domain with a tyrosine and is predicted to perturb protein structure by interfering with the formation of a disulfide bond. Studies with transfected Chinese hamster ovary cells showed that GPIHBP1-C65Y reaches the cell surface but has lost the ability to bind lipoprotein lipase (LPL). When the GPIHBP1-C65Y homozygote was given an intravenous bolus of heparin, only trace amounts of LPL entered the plasma. We also observed very low levels of LPL in the postheparin plasma of a subject with chylomicronemia who was homozygous for a different GPIHBP1 mutation (p.Q115P). When the GPIHBP1-Q115P homozygote was given a 6-hour infusion of heparin, a significant amount of LPL appeared in the plasma, resulting in a fall in the plasma triglyceride levels from 1780 to 120 mg/dL. CONCLUSIONS: We identified a novel GPIHBP1 missense mutation (p.C65Y) associated with defective LPL binding in a young boy with severe chylomicronemia. We also show that homozygosity for the C65Y or Q115P mutations is associated with low levels of LPL in the postheparin plasma, demonstrating that GPIHBP1 is important for plasma triglyceride metabolism in humans.

Absence of mutations in the PCI gene in subfertile men.

The molecular aetiology of male subfertility is still unknown in the majority of cases and it is thought that multiple genes are involved. One of the genes that might play a role in male reproductive function is the protein C inhibitor (PCI) gene. In mice the presence of PCI is an absolute requirement for reproduction. In this study we performed a mutation screen of the PCI gene in subfertile men with severe teratozoospermia or idiopathic azoospermia. Male partners of subfertile couples with idiopathic azoospermia (n = 27) or teratozoospermia (n = 34) and men with normozoospermia (n = 34) were screened for mutations in the PCI gene by direct sequencing. Nine nucleotide variants found in the patients were not present in the initial control group and were therefore screened in an additional control group of 80 men with normozoospermia by restriction fragment length polymorphism analysis. In addition, PCI antigen levels were measured in the seminal plasma of the patients in which a potential mutation was found. In total, three new variants were exclusively present in men with idiopathic azoospermia, but are not likely to have caused the patients' phenotypes. In addition, the PCI antigen levels in seminal plasma of these three patients were not decreased. The fact that we were not able to detect causal mutations in the PCI gene does not necessarily lead to the conclusion that the PCI protein is not involved in human male fertility, but the results of our study indicate that mutations in the human PCI gene are not a common cause of reduced semen parameters in men.