Radiosynthesis and biological evaluation of [18F]AG-120 for PET imaging of the mutant isocitrate dehydrogenase 1 in glioma.

Glioma are clinically challenging tumors due to their location and invasiveness nature, which often hinder complete surgical resection. The evaluation of the isocitrate dehydrogenase mutation status has become crucial for effective patient stratification. Through a transdisciplinary approach, we have developed an 18F-labeled ligand for non-invasive assessment of the IDH1R132H variant by using positron emission tomography (PET) imaging. In this study, we have successfully prepared diastereomerically pure [18F]AG-120 by copper-mediated radiofluorination of the stannyl precursor 6 on a TRACERlab FX2 N radiosynthesis module. In vitro internalization studies demonstrated significantly higher uptake of [18F]AG-120 in U251 human high-grade glioma cells with stable overexpression of mutant IDH1 (IDH1R132H) compared to their wild-type IDH1 counterpart (0.4 vs. 0.013% applied dose/µg protein at 120 min). In vivo studies conducted in mice, exhibited the excellent metabolic stability of [18F]AG-120, with parent fractions of 85% and 91% in plasma and brain at 30 min p.i., respectively. Dynamic PET studies with [18F]AG-120 in naïve mice and orthotopic glioma rat model reveal limited blood-brain barrier permeation along with a low uptake in the brain tumor. Interestingly, there was no significant difference in uptake between mutant IDH1R132H and wild-type IDH1 tumors (tumor-to-blood ratio[40-60 min]: ~1.7 vs. ~1.3). In conclusion, our preclinical evaluation demonstrated a target-specific internalization of [18F]AG-120 in vitro, a high metabolic stability in vivo in mice, and a slightly higher accumulation of activity in IDH1R132H-glioma compared to IDH1-glioma. Overall, our findings contribute to advancing the field of molecular imaging and encourage the evaluation of [18F]AG-120 to improve diagnosis and management of glioma and other IDH1R132H-related tumors.

Identification of a Gain-of-Function LIPC Variant as a Novel Cause of Familial Combined Hypocholesterolemia.

BACKGROUND: Atherosclerotic cardiovascular disease is the main cause of mortality worldwide and is strongly influenced by circulating low-density lipoprotein (LDL) cholesterol levels. Only a few genes causally related to plasma LDL cholesterol levels have been identified so far, and only 1 gene, ANGPTL3, has been causally related to combined hypocholesterolemia. Here, our aim was to elucidate the genetic origin of an unexplained combined hypocholesterolemia inherited in 4 generations of a French family. METHODS: Using next-generation sequencing, we identified a novel dominant rare variant in the LIPC gene, encoding for hepatic lipase, which cosegregates with the phenotype. We characterized the impact of this LIPC-E97G variant on circulating lipid and lipoprotein levels in family members using nuclear magnetic resonance-based lipoprotein profiling and lipidomics. To uncover the mechanisms underlying the combined hypocholesterolemia, we used protein homology modeling, measured triglyceride lipase and phospholipase activities in cell culture, and studied the phenotype of APOE*3.Leiden.CETP mice after LIPC-E97G overexpression. RESULTS: Family members carrying the LIPC-E97G variant had very low circulating levels of LDL cholesterol and high-density lipoprotein cholesterol, LDL particle numbers, and phospholipids. The lysophospholipids/phospholipids ratio was increased in plasma of LIPC-E97G carriers, suggestive of an increased lipolytic activity on phospholipids. In vitro and in vivo studies confirmed that the LIPC-E97G variant specifically increases the phospholipase activity of hepatic lipase through modification of an evolutionarily conserved motif that determines substrate access to the hepatic lipase catalytic site. Mice overexpressing human LIPC-E97G recapitulated the combined hypocholesterolemic phenotype of the family and demonstrated that the increased phospholipase activity promotes catabolism of triglyceride-rich lipoproteins by different extrahepatic tissues but not the liver. CONCLUSIONS: We identified and characterized a novel rare variant in the LIPC gene in a family who presents with dominant familial combined hypocholesterolemia. This gain-of-function variant makes LIPC the second identified gene, after ANGPTL3, causally involved in familial combined hypocholesterolemia. Our mechanistic data highlight the critical role of hepatic lipase phospholipase activity in LDL cholesterol homeostasis and suggest a new LDL clearance mechanism.

Novel Radioiodinated and Radiofluorinated Analogues of FT-2102 for SPECT or PET Imaging of mIDH1 Mutant Tumours.

Isocitrate dehydrogenases (IDHs) are metabolic enzymes commonly mutated in human cancers (glioma, acute myeloid leukaemia, chondrosarcoma, and intrahepatic cholangiocarcinoma). These mutated variants of IDH (mIDH) acquire a neomorphic activity, namely, conversion of α-ketoglutarate to the oncometabolite D-2-hydroxyglutarate involved in tumourigenesis. Thus, mIDHs have emerged as highly promising therapeutic targets, and several mIDH specific inhibitors have been developed. However, the evaluation of mIDH status, currently performed by biopsy, is essential for patient stratification and thus treatment and follow-up. We report herein the development of new radioiodinated and radiofluorinated analogues of olutasidenib (FT-2102) as tools for noninvasive single photon emission computed tomography (SPECT) or positron emission tomography (PET) imaging of mIDH1 up- and dysregulation in tumours. Nonradiolabelled derivatives 2 and 3 halogenated at position 6 of the quinolinone scaffold were synthesised and tested in vitro for their inhibitory potencies and selectivities in comparison with the lead compound FT-2102. Using a common organotin precursor, (S)-[125I]2 and (S)-[18F]3 were efficiently synthesised by radio-iododemetallation and copper-mediated radiofluorination, respectively. Both radiotracers were stable at room temperature in saline or DPBS solution and at 37 °C in mouse serum, allowing future planning of their in vitro and in vivo evaluations in glioma and chondrosarcoma models.

PCSK9 is not secreted from mature differentiated intestinal cells.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes lysosomal degradation of the LDL receptor and is a key regulator of cholesterol metabolism. After the liver, the small intestine is the second organ that highly expresses PCSK9. However, the small intestine's ability to secrete PCSK9 remains a matter of debate. While liver-specific PCSK9-deficient mice present no PCSK9 in systemic blood, human intestinal Caco-2 cells can actively secrete PCSK9. This raises the possibility for active intestinal secretion via the portal blood. Here, we aimed to determine whether enterocytes can secrete PCSK9 using in vitro, ex vivo, and in vivo approaches. We first observed that PCSK9 secretion from Caco-2 cells was biphasic and dependent on Caco-2 maturation status. Transcriptional analysis suggested that this transient reduction in PCSK9 secretion might be due to loss of SREBP2-mediated transcription of PCSK9. Consistently, PCSK9 secretion was not detected ex vivo in human or mouse intestinal biopsies mounted in Ussing chambers. Finally, direct comparison of systemic versus portal blood PCSK9 concentrations in WT or liver-specific PCSK9-deficient mice confirmed the inability of the small intestine to secrete PCSK9 into the portal compartment. Altogether, our data demonstrate that mature enterocytes do not secrete PCSK9 and reinforce the central role of the liver in the regulation of the concentration of circulating PCSK9 and consequently of cellular LDL receptors.

Circulating Rather Than Intestinal PCSK9 (Proprotein Convertase Subtilisin Kexin Type 9) Regulates Postprandial Lipemia in Mice.

OBJECTIVE: Increased postprandial lipemia (PPL) is an independent risk factor for atherosclerotic cardiovascular diseases. PCSK9 (Proprotein convertase subtilisin kexin type 9) is an endogenous inhibitor of the LDLR (low-density lipoprotein receptor) pathway. We previously showed that PCSK9 inhibition in mice reduces PPL. However, the relative contribution of intracellular intestinal PCSK9 or liver-derived circulating PCSK9 to this effect is still unclear. Approach and Results: To address this issue, we generated the first intestine-specific Pcsk9-deficient (i-Pcsk9-/-) mouse model. PPL was measured in i-Pcsk9-/- as well as in wild-type and streptozotocin-induced diabetic mice following treatment with a PCSK9 monoclonal antibody (alirocumab). Blocking the circulating form of PCSK9 with alirocumab significantly reduced PPL, while overexpressing human PCSK9 in the liver of full Pcsk9-/- mice had the opposite effect. Alirocumab regulated PPL in a LDLR-dependent manner as this effect was abolished in Ldlr-/- mice. In contrast, i-Pcsk9-/- mice did not exhibit alterations in plasma lipid parameters nor in PPL. Finally, PPL was highly exacerbated by streptozotocin-induced diabetes mellitus in Pcsk9+/+ but not in Pcsk9-/- mice, an effect that was mimicked by the use of alirocumab in streptozotocin-treated Pcsk9+/+ mice. CONCLUSIONS: Taken together, our data demonstrate that PPL is significantly altered by full but not intestinal PCSK9 deficiency. Treatment with a PCSK9 monoclonal antibody mimics the effect of PCSK9 deficiency on PPL suggesting that circulating PCSK9 rather than intestinal PCSK9 is a critical regulator of PPL. These data validate the clinical relevance of PCSK9 inhibitors to reduce PPL, especially in patients with type 2 diabetes mellitus.

Single-anastomosis duodeno-ileal bypass with sleeve gastrectomy improves lipid and glucose homeostasis in ob/ob mice.

OBJECTIVE: The objective of this study was to compare the general and metabolic impact of single-anastomosis duodeno-ileal bypass with sleeve gastrectomy (SADI-S) with Roux-en-Y gastric bypass (RYGB) in an obese (ob/ob) mouse model. METHODS: 10-week-old male ob/ob mice underwent either SADI-S, RYGB, or laparotomy surgery (Sham group). General and metabolic parameters were assessed during a 5-week period thereafter. RESULTS: SADI-S induced a deeper weight loss ([mean ± SEM] -41.2% ± 3.3%) than RYGB (-5.6% ± 3.5%, p < 0.001) compared with the Sham group (+6.3% ± 1.0%, p < 0.05). A significant food restriction was observed after SADI-S only (-31%, 117.4 ± 10.3 g vs. 170.2 ± 5.2 g of food at day 35 in Sham group mice, p < 0.001). Random-fed glycemia and glucose tolerance were more improved after SADI-S than RYGB. SADI-S decreased plasma cholesterol concentration by 60% (0.49 ± 0.04 g/L vs. 1.40 ± 0.10 g/L in the Sham group at day 35, p < 0.01), significantly more than RYGB (1.04 ± 0.14 g/L, p = 0.018). Plasma sitosterol/cholesterol and campesterol/cholesterol ratios were decreased after SADI-S, suggesting a reduced intestinal cholesterol absorption. SADI-S increased exogenous plasma cholesterol-D7 clearance and fecal elimination, also indicating an increased plasma cholesterol excretion. Studying a pair-fed group demonstrated that calorie restriction alone did not explain the beneficial impact of SADI-S. CONCLUSIONS: SADI-S is associated with a greater improvement in lipid and glucose homeostasis than RYGB in ob/ob mice.

PCSK9 regulates the NODAL signaling pathway and cellular proliferation in hiPSCs.

Proprotein convertase subtilisin kexin type 9 (PCSK9) is a key regulator of low-density lipoprotein (LDL) cholesterol metabolism and the target of lipid-lowering drugs. PCSK9 is mainly expressed in hepatocytes. Here, we show that PCSK9 is highly expressed in undifferentiated human induced pluripotent stem cells (hiPSCs). PCSK9 inhibition in hiPSCs with the use of short hairpin RNA (shRNA), CRISPR/cas9-mediated knockout, or endogenous PCSK9 loss-of-function mutation R104C/V114A unveiled its new role as a potential cell cycle regulator through the NODAL signaling pathway. In fact, PCSK9 inhibition leads to a decrease of SMAD2 phosphorylation and hiPSCs proliferation. Conversely, PCSK9 overexpression stimulates hiPSCs proliferation. PCSK9 can interfere with the NODAL pathway by regulating the expression of its endogenous inhibitor DACT2, which is involved in transforming growth factor (TGF) ß-R1 lysosomal degradation. Using different PCSK9 constructs, we show that PCSK9 interacts with DACT2 through its Cys-His-rich domain (CHRD) domain. Altogether these data highlight a new role of PCSK9 in cellular proliferation and development.

Circulating PCSK9 levels are not associated with the severity of hepatic steatosis and NASH in a high-risk population.

BACKGROUND AND AIMS: Some studies suggested that proprotein convertase subtilisin kexin type 9 (PCSK9) is linked to liver steatosis severity and non-alcoholic steatohepatitis (NASH). We aimed to assess whether circulating PCSK9 levels are associated with either liver fat content (LFC) or histological markers of NASH in high-risk patients. METHODS: We present results from three cross-sectional studies from two French Hospitals: Dijon and Numevox (departments of Endocrinology) and Angers (department of Hepatology). Only patients without lipid-lowering therapy were included. All 132 patients had type 2 diabetes in Dijon, compared to 55/224 in Numevox (25%) and 39/122 in Angers (32%). LFC was assessed on MRI (Dijon and Numevox), and NASH lesion on liver biopsy (Angers). Additionally, we included mRNA results from 138 overweight patients of a Belgian Hospital (Antwerp). RESULTS: While circulating levels of PCSK9 were positively correlated with total cholesterol, LDL-C, triglycerides and non-HDL-C in all 3 cohorts, no significant association was found between PCSK9 and transaminases. Furthermore, no association was found between plasma PCSK9 levels and LFC in both Numevox (ßadjusted = 0.71 ±â€¯1.33, p = 0.60) and Dijon (ßadjusted = -1.03 ±â€¯0.90, p = 0.25). There was no correlation between circulating PCSK9 and histological liver lesions: steatosis severity (ßadjusted = -3.95 ±â€¯2.75, p = 0.15), NASH activity score (ßadjusted = -0.31 ±â€¯0.17, p = 0.082), lobular (ß = -0.067 ±â€¯0.055, p = 0.22) or portal inflammation (ß = -0.088 ±â€¯0.079, p = 0.27), ballooning (ß = -0.025 ±â€¯0.065, p = 0.70) and fibrosis (ß = -0.17 ±â€¯0.11, p = 0.12). Finally, hepatic PCSK9 mRNA levels were not correlated with NASH histological severity. CONCLUSIONS: Circulating PCSK9 concentrations are not associated with the severity of liver steatosis or histological markers of NASH. These data are reassuring regarding the clinical use of PCSK9 inhibitors in cardiovascular diseases.

Sleeve Gastrectomy Alters Intestinal Permeability in Diet-Induced Obese Mice.

BACKGROUND: Increased lipopolysaccharide (LPS) translocation due to altered intestinal permeability has been suggested as a mechanism for obesity-associated insulin resistance. The goal of this study was to assess the effect of sleeve gastrectomy (SG) on intestinal barrier permeability in diet-induced obese mice. MATERIALS AND METHODS: Four weeks after surgery, the effects of SG on intestinal permeabilities were assessed ex vivo and in vivo in male C57Bl/6J mice fed a high-fat diet. Gene expression of tight junction proteins and inflammatory cytokines was measured in jejunum, colon, liver, and inguinal adipose tissue. Plasma LPS was quantified by HPLCMS/MS spectrometry. RESULTS: SG significantly reduced body weight and improved glucose homeostasis, as expected. SG decreased paracellular (p = 0.01) and transcellular permeability (p = 0.03) in the jejunum; and increased mRNA levels of the tight junction proteins Jam A (p = 0.02) and occludin (p = 0.01). In contrast in the distal colon, paracellular permeability tended to be increased (p = 0.07) while transcellular permeability was significantly induced (p = 0.03) after SG. In vivo, the paracellular permeability was significantly increased 3 weeks after SG (p = 0.02). Plasma LPS level were increased after SG (p = 0.03), as well as mRNA levels of adipose and hepatic inflammatory markers (p = 0.02). CONCLUSIONS: SG significantly modifies intestinal permeability in a differential manner between the proximal and distal intestine. These changes promote LPS translocation in plasma, induce a low-grade pro-inflammatory state in adipose tissue and liver, but do not impair the SG-induced glucose homeostasis improvement.

Plasma PCSK9 concentrations during the course of nondiabetic chronic kidney disease: Relationship with glomerular filtration rate and lipid metabolism.

BACKGROUND: The association between proprotein convertase subtilisin/kexin type 9 (PCSK9), a critical regulator of low-density lipoprotein (LDL) metabolism, and kidney function is a matter of debate. OBJECTIVE: We aimed to assess the association of circulating PCSK9 concentrations with both glomerular filtration rate (eGFR) and serum lipid parameters in nondiabetic patients with chronic kidney disease (CKD). METHODS: Fasting plasma PCSK9 concentrations were measured by ELISA in 94 nondiabetic nondialysis CKD (ND-CKD) patients not receiving statins, at different stages of CKD. RESULTS: Plasma PCSK9 levels were associated neither to eGFR (P = .770) nor to proteinuria (P = .888) at several stages of CKD. In addition, plasma PCSK9 levels did not vary significantly between the different CKD stages. Plasma PCSK9 concentrations were positively correlated with apolipoprotein B (r = 0.221; P = .03) and triglycerides (r = 0.211; P = .04) but not with total cholesterol, calculated LDL-cholesterol, HDL cholesterol, lipoprotein(a), or CRP. CONCLUSION: In a homogeneous population of nondiabetic subjects without lipid-lowering therapy, plasma PCSK9 concentrations are not associated to eGFR at several stages of CKD. These data suggest that kidney function per se does not impact significantly PCSK9 metabolism.

Urine-sample-derived human induced pluripotent stem cells as a model to study PCSK9-mediated autosomal dominant hypercholesterolemia.

Proprotein convertase subtilisin kexin type 9 (PCSK9) is a critical modulator of cholesterol homeostasis. Whereas PCSK9 gain-of-function (GOF) mutations are associated with autosomal dominant hypercholesterolemia (ADH) and premature atherosclerosis, PCSK9 loss-of-function (LOF) mutations have a cardio-protective effect and in some cases can lead to familial hypobetalipoproteinemia (FHBL). However, limitations of the currently available cellular models preclude deciphering the consequences of PCSK9 mutation further. We aimed to validate urine-sample-derived human induced pluripotent stem cells (UhiPSCs) as an appropriate tool to model PCSK9-mediated ADH and FHBL. To achieve our goal, urine-sample-derived somatic cells were reprogrammed into hiPSCs by using episomal vectors. UhiPSC were efficiently differentiated into hepatocyte-like cells (HLCs). Compared to control cells, cells originally derived from an individual with ADH (HLC-S127R) secreted less PCSK9 in the media (-38.5%; P=0.038) and had a 71% decrease (P<0.001) of low-density lipoprotein (LDL) uptake, whereas cells originally derived from an individual with FHBL (HLC-R104C/V114A) displayed a strong decrease in PCSK9 secretion (-89.7%; P<0.001) and had a 106% increase (P=0.0104) of LDL uptake. Pravastatin treatment significantly enhanced LDL receptor (LDLR) and PCSK9 mRNA gene expression, as well as PCSK9 secretion and LDL uptake in both control and S127R HLCs. Pravastatin treatment of multiple clones led to an average increase of LDL uptake of 2.19 ± 0.77-fold in HLC-S127R compared to 1.38 ± 0.49 fold in control HLCs (P<0.01), in line with the good response to statin treatment of individuals carrying the S127R mutation (mean LDL cholesterol reduction=60.4%, n=5). In conclusion, urine samples provide an attractive and convenient source of somatic cells for reprogramming and hepatocyte differentiation, but also a powerful tool to further decipher PCSK9 mutations and function.