Juergen Graessler

SLC2A9 is a newly identified urate transporter influencing serum urate concentration, urate excretion and gout

Uric acid is the end product of purine metabolism in humans and great apes, which have lost hepatic uricase activity, leading to uniquely high serum uric acid concentrations (200–500 μM) compared with other mammals (3–120 μM). About 70% of daily urate disposal occurs via the kidneys, and in 5–25% of the human population, impaired renal excretion leads to hyperuricemia. About 10% of people with hyperuricemia develop gout, an inflammatory arthritis that results from deposition of monosodium urate crystals in the joint. We have identified genetic variants within a transporter gene, SLC2A9, that explain 1.7–5.3% of the variance in serum uric acid concentrations, following a genome-wide association scan in a Croatian population sample. SLC2A9 variants were also associated with low fractional excretion of uric acid and/or gout in UK, Croatian and German population samples. SLC2A9 is a known fructose transporter, and we now show that it has strong uric acid transport activity in Xenopus laevis oocytes.

Top-down lipidomics reveals ether lipid deficiency in blood plasma of hypertensive patients.

Background Dyslipoproteinemia, obesity and insulin resistance are integrative constituents of the metabolic syndrome and are major risk factors for hypertension. The objective of this study was to determine whether hypertension specifically affects the plasma lipidome independently and differently from the effects induced by obesity and insulin resistance. Methodology/Principal Findings We screened the plasma lipidome of 19 men with hypertension and 51 normotensive male controls by top-down shotgun profiling on a LTQ Orbitrap hybrid mass spectrometer. The analysis encompassed 95 lipid species of 10 major lipid classes. Obesity resulted in generally higher lipid load in blood plasma, while the content of tri- and diacylglycerols increased dramatically. Insulin resistance, defined by HOMA-IR >3.5 and controlled for BMI, had little effect on the plasma lipidome. Importantly, we observed that in blood plasma of hypertensive individuals the overall content of ether lipids decreased. Ether phosphatidylcholines and ether phosphatidylethanolamines, that comprise arachidonic (20∶4) and docosapentaenoic (22∶5) fatty acid moieties, were specifically diminished. The content of free cholesterol also decreased, although conventional clinical lipid homeostasis indices remained unaffected. Conclusions/Significance Top-down shotgun lipidomics demonstrated that hypertension is accompanied by specific reduction of the content of ether lipids and free cholesterol that occurred independently of lipidomic alterations induced by obesity and insulin resistance. These results may form the basis for novel preventive and dietary strategies alleviating the severity of hypertension.

Metagenomic sequencing of the human gut microbiome before and after bariatric surgery in obese patients with type 2 diabetes: correlation with inflammatory and metabolic parameters

Roux-en-Y gastric bypass (RYGB) has become a prominent therapeutic option for long-term treatment of morbid obesity and type 2 diabetes mellitus (T2D). Cross talk and pathogenetic consequences of RYGB-induced profound effects on metabolism and gut microbiome are poorly understood. The aim of the present study therefore was to characterize intra-individual changes of gut microbial composition before and 3 months after RYGB by metagenomic sequencing in morbidly obese patients (body mass index (BMI)>40 kg m−2) with T2D. Subsequently, metagenomic data were correlated with clinical indices. Based on gene relative abundance profile, 1061 species, 729 genera, 44 phyla and 5127 KO (KEGG Orthology) were identified. Despite high diversity, bacteria could mostly be assigned to seven bacterial divisions. The overall metagenomic RYGB-induced shift was characterized by a reduction of Firmicutes and Bacteroidetes and an increase of Proteobacteria. Twenty-two microbial species and 11 genera were significantly altered by RYGB. Using principal component analysis, highly correlated species were assembled into two common components. Component 1 consisted of species that were mainly associated with BMI and C-reactive protein. This component was characterized by increased numbers of Proteobacterium Enterobacter cancerogenus and decreased Firmicutes Faecalibacterium prausnitzii and Coprococcus comes. Functional analysis of carbohydrate metabolism by KO revealed significant effects in 13 KOs assigned to phosphotransferase system. Spearmen’s Rank correlation indicated an association of 10 species with plasma total- or low-density lipoprotein cholesterol, and 5 species with triglycerides. F. prausnitzii was directly correlated to fasting blood glucose. This is the first clinical demonstration of a profound and specific intra-individual modification of gut microbial composition by full metagenomic sequencing. A clear correlation exists of microbiome composition and gene function with an improvement in metabolic and inflammatory parameters. This will allow to develop new diagnostic and therapeutic strategies based on metagenomic sequencing of the human gut microbiome.

The protective effects of HDL and its constitutents against neutrophil respiratory burst activation by hypochlorite-oxidized LDL

Hypochlorite-oxidized low-density lipoprotein (oxLDL) possesses a substantial proinflammatory potential by modulating respiratory burst activities of polymorphonuclear neutrophils (PMN). As evaluated by luminol-amplified chemiluminescence (CL) incubation of 106 PMN/ml with 70 nM oxLDL was followed by substantial induction of neutrophil oxidant (ROS) generation. We evaluated the inhibitory capacity of high-density lipoprotein (HDL) and its lipid and protein constituents against the activating effects of oxLDL. At a HDL or apolipoprotein AI/LDL protein ratio of 1.0, native HDL decreased the respiratory burst activation by 64%, followed by trypsinized HDL (57%) and native apoAI (43%). The inhibitory effects of native HDL did not require prior incubation with PMN or with oxLDL suggesting an instantaneously acting protective mechanism in the minute range. OxLDL modulated ROS production not only of resting PMN but also that of activated PMN, as indicated by a 14-fold increase in FMLP-stimulated CL response and a 50% decrease in zymosan-mediated CL answer. HDL itself did not protect PMN from activation by FMLP and zymosan. However, it clearly reduced effects of oxLDL on FMLP-activation and slightly counteracted the oxLDL-mediated decrease in zymosan-induced ROS generation. Taken together, these findings may offer new insight into atheroprotective mechanisms of HDL.

Gender, Contraceptives and Individual Metabolic Predisposition Shape a Healthy Plasma Lipidome.

Lipidomics of human blood plasma is an emerging biomarker discovery approach that compares lipid profiles under pathological and physiologically normal conditions, but how a healthy lipidome varies within the population is poorly understood. By quantifying 281 molecular species from 27 major lipid classes in the plasma of 71 healthy young Caucasians whose 35 clinical blood test and anthropometric indices matched the medical norm, we provided a comprehensive, expandable and clinically relevant resource of reference molar concentrations of individual lipids. We established that gender is a major lipidomic factor, whose impact is strongly enhanced by hormonal contraceptives and mediated by sex hormone-binding globulin. In lipidomics epidemiological studies should avoid mixed-gender cohorts and females taking hormonal contraceptives should be considered as a separate sub-cohort. Within a gender-restricted cohort lipidomics revealed a compositional signature that indicates the predisposition towards an early development of metabolic syndrome in ca. 25% of healthy male individuals suggesting a healthy plasma lipidome as resource for early biomarker discovery.

Lipidomic profiling before and after Roux-en-Y gastric bypass in obese patients with diabetes

Bariatric surgery is a well-established approach to improve metabolic disease in morbidly obese patients with high cardiovascular risk. The post-operative normalization of lipid metabolism has a central role in the prevention of future cardiovascular events. The aim of the present study therefore was to characterize changes of plasma lipidomic patterns, consisting of 229 lipid species of 13 lipid classes, 3 months after Roux-en-Y gastric bypass (RYGB) in morbidly obese patients with and without diabetes. RYGB resulted in a 15–32% decrease of body mass index, which was associated with a significant reduction of total cholesterol (TC, −28.3%; P=0.02), LDL-cholesterol (LDL-C, −26.8%; P=0.03) and triglycerides (TGs, −63.0%; P=0.05) measured by routine clinical chemistry. HDL-cholesterol remained unchanged. The effect of RYGB on the plasma lipidomic profile was characterized by significant decreases of 87 lipid species from triacylglycerides (TAGs), cholesterol esters (CholEs), lysophosphatidylcholines (LPCs), phosphatidylcholines (PCs), phosphatidylethanolamine ethers (PEOs), phosphatidylinositols (PIs) and ceramides (Cers). The total of plasma lipid components exhibited a substantial decline of 32.6% and 66 lipid species showed a decrease by over 50%. A direct correlation with HbA1C values could be demonstrated for 24 individual lipid species (10 TAG, three CholE, two LPC, one lysophosphatidylcholine ethers (LPCO) (LPC ether), one PC, two phosphatidylcholine ethers (PCO) and five Cer). Notably, two lipid species (TAG 58:5 and PEO 40:5) were inversely correlated with HbA1C. LPCO, as single whole lipid class, was directly related to HbA1C. These data indicate that RYGB-induced modulation of lipidomic profiles provides important information about post-operative metabolic adaptations and might substantially contribute to improvements of glycemic control. These striking changes in the human plasma lipidome may explain acute, weight independent and long-term effects of RYGB on the cardiovascular system, mental status and immune regulation.

Hypochlorite-oxidized low-density lipoprotein upregulates CD36 and PPARγ mRNA expression and modulates SR-BI gene expression in murine macrophages

The uptake of oxidized low-density lipoprotein (oxLDL) by scavenger receptors of macrophages with resulting foam cell formation is considered a critical event in atherogenesis. Since hypochlorite-oxidized LDL (HOCl-LDL) has been shown to be recognized by macrophages and evidence was provided that HOCl-LDL is internalized via class B scavenger receptors CD36 and SR-BI, the regulatory relationships between CD36, SR-BI, and the nuclear transcription factor PPARγ in murine macrophages (RAW 264.7) on exposure to HOCl-LDL were examined. Using the highly sensitive real-time RT-PCR we could demonstrate that HOCl-LDL upregulated CD36 and PPARγ levels dose- and time dependently while modulating SR-BI message levels differently in dependence on HOCl-LDL concentration and incubation time. On exposure of macrophages to HOCl-LDL but not native LDL in varying concentrations, a significant positive correlation between CD36 and PPARγ (ρ = 0.603, p = 0.001) was observed indicating the presence of a positive feedback mechanism by which HOCl-LDL could promote its own uptake. The transcriptional expression of SR-BI in macrophages was not significantly related to PPARγ mRNA levels after treatment with HOCl-LDL suggesting a differential regulation of the two members of the scavenger receptor class B family in response to HOCl-LDL.

Different effects of exogenous horseradish peroxidase on luminol-amplified chemiluminescence induced by soluble and particulate stimuli in human neutrophils

The chemiluminescence (CL) technique with scavengers for superoxide anion (superoxide dismutase) and hydrogen peroxide (catalase) was used to characterize the generation of reactive oxygen species (ROS) inside and outside the human neutrophil after stimulation with both soluble (formyl-methionyl-leucyl-phenylalanine, FMLP) and particulate (urate crystals, zymosan, oxidized LDL) stimuli. Depending on the stimulus used, ROS generation differed in composition and absolute amounts. The ratio between extracellularly and intracellularly produced ROS ranged from 0.3 (zymosan) to 4.2 (FMLP). While enhancing substantially FMLP-stimulated CL, horseradish peroxidase inhibited CL induced by particulate stimuli by 40-80%. Furthermore, an azide-insensitive and therefore peroxidase-independent part of CL was found in FMLP-, LDL- and zymosan-stimulated cells. The results indicate that different agonists may lead through distinct chemical pathways to neutrophil luminol-amplified light generation.

Type 2 Diabetes in Octogenarians Is Associated with Decreased Low Molecular Weight Adiponectin

Background: Adiponectin circulates in the blood in three different multimer isoforms, of which the high molecular weight form (HMW) is presumed to mediate insulin sensitivity. We examined whether adiponectin oligomer distribution is associated with aging and type 2 diabetes (T2D) in octogenarians without characteristic features of metabolic syndrome. Methods: The study included 154 octogenarians (58 men, 96 women), 24 normoglycemic middle-aged controls (11 men, 13 women; mean age 44 years), and 33 middle-aged individuals (14 men, 19 women; mean age 55 years) with T2D. Based on oral glucose tolerance test 62 octogenarians had normal, 63 impaired glucose tolerance, and 29 octogenarians had newly detected T2D. Serum adiponectin multimer isoforms were measured after overnight fast by enzyme-linked immunosorbent assays. Results:Compared to the normoglycemic middle-aged control group, male normoglycemic octogenarians revealed significantly higher total adiponectin and all adiponectin isoforms. The same was true for females with the exception of low molecular weight (LMW) adiponectin, which was not statistically higher in octogenarians. Male and female octogenarians with T2D had significantly higher levels of total, HMW, and middle molecular weight (MMW) adiponectin, but not LMW adiponectin, than middle-aged individuals with T2D. Female, but not male, octogenarians revealed significantly lower total adiponectin than normoglycemic octogenarians. Compared with normoglycemic octogenarians, male and female octogenarians with T2D were characterized by significantly lower LMW adiponectin. In male and female octogenarians, total adiponectin and all multimer isoforms were directly correlated with HDL cholesterol. LMW adiponectin in octogenarians of both sexes was inversely correlated with glucose level at 2-hour oral glucose tolerance test. Conclusions: Serum levels of total adiponectin as well as its HMW and MMW isoforms were significantly higher in octogenarians with normoglycemia or T2D than in corresponding middle-aged control groups. In male and female octogenarians without metabolic syndrome, T2D was associated with lower LMW adiponectin, while the HMW and MMW isoforms were not statistically different.

Beyond lowering circulating LDL: Apheresis-induced changes of systemic oxidative stress markers by four different techniques

OBJECTIVE AND METHODS Dyslipidemia and oxidative stress are causally related to atherogenesis and cardiovascular disease. We assessed acute changes of systemic oxidative stress biomarkers in thirty-two patients undergoing regular apheresis using four different techniques: heparin-induced extracorporeal LDL precipitation (HELP), direct adsorption of lipoproteins (DALI), lipidfiltration (LF), and immunoadsorption of lipoproteins (IA). RESULTS All apheresis procedures were similarly effective in lowering LDL cholesterol (-2.5+/-0.2 mmoL/L), oxidized LDL (-52.4+/-4.4 U/L), and levels of antioxLDL antibodies (-59.5+/-15.1 U/L). Among the LDL-apheresis methods investigated, only the DALI technique without prior separation of blood plasma led to a decline in leukocyte count (p=0.01 vs. LF post apheresis) and to decreased phagocyte oxidant-generating activity as evaluated by chemiluminescence. Moreover, DALI was followed by a smaller decrease of blood total antioxidant capacity than the other techniques (p<0.01 vs. HELP post apheresis). CONCLUSION Together, our data suggest that compared with other common techniques, the DALI apheresis system is accompanied by the lowest systemic oxidative burden evoked by a single apheresis treatment.