Acid Flux Research Articles

Free Amino Acid–Enriched Diets Containing Rapidly but Not Slowly Digested Carbohydrate Promote Amino Acid Absorption from Intestine and Net Fluxes across Skeletal Muscle of Pigs

The approach to matching appropriate carbohydrates alongside free amino acids to achieve optimal muscle growth remains unclear. We investigated whether the consumption of a diet containing rapidly digested carbohydrate and free amino acids can enhance intestinal absorption and muscular uptake of amino acids in pigs. Twelve barrows (28 kg; 11 wk old) with catheters installed in the portal vein, mesenteric vein, femoral artery, and femoral vein were randomly assigned to consume 1 of 2 free amino acid-enriched diets (3.34%) containing rapidly [waxy corn starch (WCS)] or slowly [pea starch (PS)] digested carbohydrate for 27 d. Blood was collected to determine the fluxes of plasma glucose and amino acids across the portal vein and the hindlimb muscle. Dietary in vitro carbohydrate digestive rates were also determined. Data were analyzed using repeated-measures (time × group) ANOVA. Carbohydrate in vitro cumulative digestibility at 30 and 240 min was 69.00% and 95.25% for WCS and 23.25% and 81.15% for PS, respectively. The animal experiment presented WCS increased individual amino acids (lysine, 0.67 compared with 0.53 mmol/min; threonine, 0.40 compared with 0.29 mmol/min; isoleucine, 0.33 compared with 0.22 mmol/min; glutamate, 0.51 compared with 0.35 mmol/min; and proline, 0.51 compared with 0.27 mmol/min), essential amino acid (EAA; 3.26 compared with 2.65 mmol/min), and branched-chain amino acid (BCAA; 0.86 compared with 0.65 mmol/min) fluxes across the portal vein during 8 h postprandial, as well as individual amino acids (isoleucine, 0.08 compared with 0.02 mmol/min; leucine, 0.06 compared with 0.02 mmol/min; and glutamine, 0.44 compared with 0.25 mmol/min), EAA (0.50 compared with 0.21 mmol/min), and BCAA (0.17 compared with 0.06 mmol/min) net fluxes across the hindlimb muscle during 8 h postprandial compared with PS (P < 0.05). A diet containing rapidly digested carbohydrate and free amino acids can promote intestinal absorption and net fluxes across hindlimb muscle of amino acids in pigs.

Upgrading the prediction model for Mn content in submerged arc welded metal via CALPHAD technology: Case study into typical acidic and basic fluxes

Fluxes (the granular materials containing oxides and CaF2) serve vital functions with respect to atmospheric shielding, arc stabilization, and weld metal composition control during the submerged arc welding process. Mn content must be carefully controlled since it dictates the toughness of the weldment. The slag-metal equilibrium model has been applied for decades to predict the Mn content in submerged arc welded metal, although there are several limitations regarding its application. With the aim of compensating for the limitations of the slag-metal equilibrium model, this study has been undertaken to upgrade the slag-metal equilibrium model to the gas-slag-metal equilibrium model via CALPHAD technology. Then, the Mn content in the weld metal is predicted by using both slag-metal and gas-slag-metal equilibrium models for typical acidic and basic fluxes. The capabilities of the models to predict Mn content is evaluated from the perspective of thermodynamics. It is concluded that the gas-slag-metal equilibrium model, which is independent of the basicity index model, possesses higher prediction accuracy than the slag-metal equilibrium model. Furthermore, the transfer direction of Mn, as well as Mn content are predictable even when no MnO is contained in the initial flux. Based on the measured and thermodynamic data, the mechanisms pertinent to Mn transfer in the welding process have been interpreted, and the limitations of the gas-slag-metal equilibrium model have been summarized.

On the Si content prediction for submerged arc welded metal via Calphad technique: a brief discussion

The slag-metal and gas-slag-metal equilibrium models have been employed via the Calphad technique to predict Si content in submerged arc welded metal. The investigated fluxes possess a wide range of basicity indices at full coverage with acidic, neutral, and basic fluxes. It is revealed that the gas-slag-metal equilibrium model offers better prediction accuracy for Si content than the slag-metal equilibrium model since the flux O potential is underestimated by the slag-metal equilibrium model. Especially, the gas-slag-metal equilibrium model is capable of predicting the transfer direction of Si between flux and weld metal, as well as Si content in submerged arc welded metal even when no SiO2 is contained in the initial flux. Additionally, the kinetic factors that influence the transfer behavior of Si have been evaluated to interpret the deviation between measured Si content and the value predicted from the equilibrium model. At last, we have proposed the limitations of the equilibrium models, as well as the models to be further developed with respect to improving the prediction accuracy.

Designing of amino silica covalently functionalized carboxylic multi-wall carbon nanotubes-based polyethersulfone membranes for enhancing oily wastewater treatment

The accumulation of oily wastewater is a critical issue that can cause environmental pollution. Membrane technology can play a vital role in the treatment of oily wastewater due to its productivity and economical cost. In this work, the amino silica covalently functionalized carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) nanohybrid was synthesized and blended with polyethersulfone (PES) membranes for oil/water separation to enhance the antifouling property. Membranes were fabricated with various loadings of SiO2-f-MWCNTs nanohybrid (0–2 wt%) using phase inversion technique. The incorporation of nanohybrid resulted in the enhancement of wettability and pore size distribution of nanocomposite membranes. The morphological structure, surface and chemical features of the synthesized membranes were examined using scanning electron microscopy, Fourier transform infrared spectroscopy, water contact angle and X-ray diffraction analyses. Furthermore, the impact of nanohybrid blending with PES membrane on water permeability and oil rejection was investigated. The water permeability enhanced from 188 ± 8 L/m2.h.bar, for the pristine PES membrane, to 293 ± 9 L/m2.h.bar for nanocomposite membrane blended with 2 % SiO2-f-MWCNTs nanohybrid. Similarly, the oil rejection was improved up to 97 ± 0.1 % using the same nanohybrid loading. The results revealed that using 2 % nanohybrid loading has increased the humic acid (HA) flux by 16 %, while the irreversible HA fouling was significantly reduced to 0.9 % compared to 9.9 % for the pristine PES.

Formate hydrogenlyase, formic acid translocation and hydrogen production: dynamic membrane biology during fermentation

Formate hydrogenlyase-1 (FHL-1) is a complex-I-like enzyme that is commonly found in gram-negative bacteria. The enzyme comprises a peripheral arm and a membrane arm but is not involved in quinone reduction. Instead, FHL-1 couples formate oxidation to the reduction of protons to molecular hydrogen (H2). Escherichia coli produces FHL-1 under fermentative conditions where it serves to detoxify formic acid in the environment. The membrane biology and bioenergetics surrounding E. coli FHL-1 have long held fascination. Here, we review recent work on understanding the molecular basis of formic acid efflux and influx. We also consider the structure and function of E. coli FHL-1, its relationship with formate transport, and pay particular attention to the molecular interface between the peripheral arm and the membrane arm. Finally, we highlight the interesting phenotype of genetic mutation of the ND1 Loop, which is located at that interface.

Evaluation of Flux Basicity Concept Geared toward Estimation for Oxygen Content in Submerged Arc Welded Metal

The present study has been undertaken to evaluate the basicity concept of oxygen content estimation subject to submerged arc welded metal. The investigated fluxes cover a wide range of basicity indices from 0.31 to 19.00 at full coverage with acidic, neutral, and basic fluxes. The oxygen content of the submerged arc welded metal (flux oxygen potential) is predicted by employing traditional flux basicity index models and the CALPHAD technique (gas–slag–metal equilibrium model). It is revealed that the gas–slag–metal equilibrium model in this study is capable of remedying the shortcomings of the basicity index models with respect to predicting the oxygen potentials of the fluxes with CaF2, CaO, SiO2, MnO, and FeO as major components. This study may provide a vital way to address technical difficulties in flux design. Based on the measured and thermodynamic data, thermodynamic parameters pertinent to flux oxygen potential have been systematically assessed.

Nonalcoholic fatty liver disease and diabetes.

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease in the world and represents a clinical-histopathologic entity where the steatosis component may vary in degree and may or may not have fibrotic progression. The key concept of NAFLD pathogenesis is excessive triglyceride hepatic accumulation because of an imbalance between free fatty acid influx and efflux. Strong epidemiological, biochemical, and therapeutic evidence supports the premise that the primary pathophysiological derangement in most patients with NAFLD is insulin resistance; thus the association between diabetes and NAFLD is widely recognized in the literature. Since NAFLD is the hepatic manifestation of a metabolic disease, it is also associated with a higher cardio-vascular risk. Conventional B-mode ultrasound is widely adopted as a first-line imaging modality for hepatic steatosis, although magnetic resonance imaging represents the gold standard noninvasive modality for quantifying the amount of fat in these patients. Treatment of NAFLD patients depends on the disease severity, ranging from a more benign condition of nonalcoholic fatty liver to nonalcoholic steatohepatitis. Abstinence from alcohol, a Mediterranean diet, and modification of risk factors are recommended for patients suffering from NAFLD to avoid major cardiovascular events, as per all diabetic patients. In addition, weight loss induced by bariatric surgery seems to also be effective in improving liver features, together with the benefits for diabetes control or resolution, dyslipidemia, and hypertension. Finally, liver transplantation represents the ultimate treatment for severe nonalcoholic fatty liver disease and is growing rapidly as a main indication in Western countries. This review offers a comprehensive multidisciplinary approach to NAFLD, highlighting its connection with diabetes.

Photocatalytic TiO2@MIL-88A (Fe)/polyacrylonitrile mixed matrix membranes: Characterization, anti-fouling properties, and performance on the removal of natural organic matter.

Photocatalytic membrane reactors (PMRs), coupling photocatalysts and membranes in a single system, have shown a considerable potential to reduce membrane fouling, which is one of the major drawbacks of using membranes to treat water and wastewater. In this study, the visible light-activated photocatalysts were incorporated into the polyacrylonitrile (PAN) casting solution to synthesize the photocatalytic composite membranes. The physicochemical properties and the morphology of the membranes and photocatalysts were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction analysis (XRD), ultraviolet-visible diffuse reflectance spectroscopy (UV-visible DRS), photoluminescence (PL), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Brunauer-Emmett-Teller (BET), porosimetry, and contact angle analyses. The performance of the synthesized photocatalytic mixed matrix membranes (MMMs) in treating water containing humic acid, as one of the major components in natural organic matter (NOM) existing in drinking water sources, was investigated. Under visible light irradiation, the PAN/TiO2@MIL-88A (Fe) MMMs simultaneously adopted photocatalysis and membrane separation in the PMR and thereby enhanced humic acid removal and anti-fouling properties. The best synthesized photocatalytic membrane could remove 92.4% of the humic acid once exposed to visible light. The optimum membrane had suitable water permeability, a high flux recovery ratio (99.5%), and a 13.5% decline in the humic acid flux after a 10-h run, considerably lower compared to the corresponding decline of the pristine membrane (37.5% over the same period). The remarkable properties of the PAN/TiO2@MIL-88A (Fe) membrane, including its high anti-fouling specification, confirm the appropriateness of the synthesized MMM for treating water involving humic acid.

Fatty acid composition differs between emergent aquatic and terrestrial insects—A detailed single system approach

Emergent insects represent a key vector through which aquatic nutrients are transferred to adjacent terrestrial food webs. Aquatic fluxes of polyunsaturated fatty acids (PUFA) from emergent insects are particularly important subsidies for terrestrial ecosystems due to high PUFA contents in several aquatic insect taxa and their physiological importance for riparian predators. While recent meta-analyses have shown the general dichotomy in fatty acid profiles between aquatic and terrestrial ecosystems, differences in fatty acid profiles between aquatic and terrestrial insects have been insufficiently explored. We examined the differences in fatty acid profiles between aquatic and terrestrial insects at a single aquatic-terrestrial interface over an entire growing season to assess the strength and temporal consistency of the dichotomy in fatty acid profiles. Non-metric multidimensional scaling clearly separated aquatic and terrestrial insects based on their fatty acid profiles regardless of season. Aquatic insects were characterized by high proportions of long-chain PUFA, such as eicosapentaenoic acid (20:5n-3), arachidonic acid (20:4n-6), and α-linolenic acid (18:3n-3); whereas terrestrial insects were characterized by high proportions of linoleic acid (18:2n-6). Our results provide detailed information on fatty acid profiles of a diversity of aquatic and terrestrial insect taxa and demonstrate that the fundamental differences in fatty acid content between aquatic and terrestrial insects persist throughout the growing season. However, the higher fatty acid dissimilarity between aquatic and terrestrial insects in spring and early summer emphasizes the importance of aquatic emergence as essential subsidies for riparian predators especially during the breading season.

A Quantitative Systems Pharmacology Model of Liver Lipid Metabolism for Investigation of Non-Alcoholic Fatty Liver Disease.

Non-alcoholic fatty liver disease is a metabolic and inflammatory disease that afflicts many people worldwide and presently has few treatment options. To enhance the preclinical to clinical translation and the design of early clinical trials for novel therapeutics, we developed a Quantitative Systems Pharmacology model of human hepatocyte lipid metabolism. The intended application of the model is for simulating anti-steatotic therapies for reversing fatty liver. We parameterized the model using literature data from humans with both normal and elevated liver fat. We assessed that the model construct was sufficient to generate a virtual population of NAFLD patients that matched relevant statistics of a published clinical cohort, and then validated the model response to treatment by simulating pioglitazone and diet intervention in the virtual population. Finally, a sensitivity analysis was performed to determine the best points of intervention for reducing hepatic steatosis. Analysis of the model suggests the most potent method for reducing hepatic steatosis is by limiting non-esterified fatty acid flux from the adipose to the liver.

Enhanced diffusion dialysis performance of cross-linked poly(aryl piperidine) anion exchange membranes by thiol-ene click chemistry for acid recovery

A series of cross-linked QPBP-HT/OT-X% anion exchange membranes (AEMs) were prepared by introducing unsaturated olefins during the quaternization of poly(biphenyl piperidine) polymers (QPBP), followed by a thiol-ene “Click” reaction with a dithiol cross-linker for diffusion dialysis. In particular, the ethoxy (EO) group in 3,6-dioxa-1,8-octanedithiol (OT) can enhance the hydrophilicity of AEM and the ion-dipole interactions existing with cationic groups can effectively tune the nanostructure within AEM, which is jointly verified by AFM and SAXS. Compared with the original QPBP AEM, the ion exchange capacity of cross-linked QPBP-HT/OT-X% AEMs did not change significantly, but the water uptake and swelling rate showed a decreasing trend, which led to an obvious improvement in dimensional stability. Diffusion dialysis tests showed that QPBP-OT-5% AEM containing EO groups achieved a better dialysis coefficient (UH+) of 41.72 × 10−3 m h−1 and an excellent separation factor (S) of 103.56, which was significantly superior than QPBP-HT-X% AEMs containing hydrophobic crosslinkers and commercial DF-120 AEM (UH+ = 9 × 10−3 m h−1, S = 18.5). These results show that the “trade-off” effect between acid flux and ion selectivity can be effectively balanced by introducing hydrophilic EO groups into the cross-linked network of the polymer, which is a perspective design strategy.

To evaluate the efficacy and safety profile of rosuvastatin, simvastatin and atorvastatin in newly diagnosed type 2 diabetic patients with dyslipidaemia

Dyslipidemia is one of the major risk factors for cardiovascular disease in diabetes mellitus. The lipid changes associated with diabetes mellitus are attributed to increased free fatty acid flux secondary to insulin resistance. Newly diagnosed 90 cases of patients of Type II Diabetes Mellitus well controlled on oral hypoglycemic drugs were randomly divided into 3 groups of 30 each. The mean difference of Triglycerides between baseline versus after 6 months was 65.04 mg/dl in Group A, 39.99 mg/dl in Group B and 37.04 mg/dl in Group C. The mean difference of HDL between baseline versus after 6 months was 10.04 mg/dl in Group A, 10.26 mg/dl in Group B and 9.13 mg/dl in Group C. The mean difference of LDL between baseline versus after 6 months was 79.4 mg/dl in Group A, 67.6 mg/dl in Group B and 33.82 mg/dl in Group C. The mean difference of VLDL between baseline versus after 6 months was 13.01 mg/dl in Group A, 7.58 mg/dl in Group B and 7.41 mg/dl in Group C.

Discharge and temperature effects on weathering fluxes in alpine and perialpine basins in Switzerland

• Influence of discharge and temperature on weathering loads and fluxes in Switzerland has been studied. • Weathering loads depend mostly on discharge. • Multiple linear regression reveals the real influence of temperature, which differs from that obtained from simple regression. • The effect of temperature on weathering loads is mostly indirect, via its influence on discharge. • Runoff and lithology are the main positive factors on silicic acid fluxes, whereas temperature is the main positive factor in Ca car fluxes. Chemical weathering exerts a key control on atmospheric CO 2 and hence on Earth’s temperature. Knowledge of the influence of discharge and temperature on weathering product loads and fluxes through rivers is important to evaluate the possible influence of climate change on weathering. The role of hydrology on such loads and fluxes is clear, but the effect of temperature is difficult to investigate, particularly in big rivers. We use long term (1974–2015) measurements of hydrological and chemical parameters in 20 Swiss stations in large, median-sized, and small rivers. This is to calculate the effect of discharge and temperature on annual loads in each station and in mean fluxes of silicic acid (SA) and calcium linked to carbonate (Ca car ) considering all 20 stations together. SA and Ca car loads are good proxies of carbonate and silicate weathering. Mean annual loads of SA and Ca car depend mostly on discharge. They decrease with temperature when the dependence is evaluated by univariate linear regression. Multiple linear regression analysis, however, reveals that the real influence of temperature, when taking into account discharge, is positive in several cases for SA and is mostly non-significant for Ca car . Runoff and lithology are the main positive factors on SA fluxes, whereas temperature is the main positive factor in Ca car fluxes. In both cases, the fraction of impounded water in the catchment is the main negative influence. No significant temporal trend in loads are detected in 18 out of the 20 stations despite the general increase of water temperature, which is consistent with the small effect of temperature on loads found in the present work.

Technological aspects of innovative milk-based bioproducts

The strategic goal of modern food technology is to create complete and safe products enriched with biologically active components that ensure the maintenance and activation of vital human functions, and increase the body’s general resistance to aggressive living conditions. The development of functional food products, including bioproducts, is one of the most affordable and effective ways to correct the nutrition and health of modern people. The scientific understanding of a positive effect of functional food products on the human body, on its physiological functions is the most important task of researchers, since this not only makes it possible to clarify the mechanism of favorable action of functional food products on the body, but also to purposefully design new products of this type. One representative of functional food products is probiotics. According to the World Health Organization (WHO), probiotics are living microorganisms or products fermented by them that have a beneficial effect on human health mainly revealed in the gastrointestinal tract [1]. The greatest interest in probiotics arose in the early 70s, when the excessive use of antibiotics, the deterioration of the environmental situation led to violations of human microbiocenosis, as well as the phenomena of antibiotic resistance. In this regard, the strategic task of dairy specialists is to create fermented dairy products with high probiotic properties, which have a diverse positive effect on human health. Currently, various researchers have proposed new methods for the production of kefir using microorganisms with a pronounced probiotic effect. Kefir fungi as a representative of protosymbiotic microbial associations, as well as propionic bacteria, are considered as promising probiotics which positive impact on human health is generally recognized. A biological feature of classical propionic bacteria (compared, for example, with lactic bacteria) is the ability to produce a number of metabolites, including B vitamins, including folic acid, vitamin B12 and bifidogenic factors, the flux of propionic acid (propionates) and polypeptides with antimicrobial and antimutagenic properties, the presence of antioxidant enzymes in cells. The relevant direction of this study is the creation of fermented milk bioproducts based on a consortium of propionic and lactic bacteria of kefir fungal starter enriched with a high number of viable microorganism cells, vitamin B12 having antimutagenic and antioxidant properties. A new microbial consortium based on lactic and propionic bacteria was experimentally created. This paper presents the experimental data on technological features of new milk-based bioproducts taking into account the biochemical activity of a combined starter. The effect of inulin prebiotic on biochemical and rheological properties of bioproducts was studied. The study also shows the characteristics of finished bioproducts, and justifies their high biological value.

Evaluate the efficacy and safety profile of Rosuvastatin, Simvastatin and Atorvastatin in newly diagnosed type 2 diabetic patients with dyslipidaemia

Dyslipidemia is one of the major risk factors for cardiovascular disease in diabetes mellitus. The lipid changes associated with diabetes mellitus are attributed to increased free fatty acid flux secondary to insulin resistance. This is prospective, comparative, open label, randomized and parallel group. The subjects enrolled for this study were selected from the Out-Patient Department of Medicine collaboration with Department of Pharmacology, Tertiary care teaching hospital over a period of month. Newly diagnosed 90 cases of patients of Type II Diabetes Mellitus well controlled on oral hypoglycemic drugs were randomly divided into 3 groups of 30 each. Group A was received Rosuvastain 10 mg O.D for 3 months, Group B: Simvastatin 10 mg O.D and Group C was received Atrovastatin 10 mg O.D. In Group ‘A’ the mean difference of Total Cholesterol between baseline versus after 6 months was 82.37 mg/dl, 64.92 mg/dl and 52.23 mg/dl in Group B and Group C respectively. The mean difference of Triglycerides between baseline versus after 6 months was 65.04 mg/dl in Group A, 39.99 mg/dl in Group B and 37.04 mg/dl in Group C.

Pancreatic Dysfunction and Duodenal Inflammatory Responses Coordinate with Refractory Epigastric Pain Including Functional Dyspepsia: A Narrative Review.

Some patients with functional dyspepsia (FD) have abnormalities in pancreatic enzymes and chronic pancreatitis. Since 2009, when the idea of early chronic pancreatitis (ECP) first emerged, the utility of endoscopic ultrasonography gained attention, as it can help identify early chronic pancreatitis in patients with dyspepsia. Although the symptoms associated with pancreatic enzyme abnormalities and pancreatic dysfunction overlap with those of dyspepsia, no available data explain the direct relationships and linkages between pancreatic dysfunction and dyspeptic symptoms. Disturbance of exocrine pancreatic enzyme function and reduction in pancreatic endocrine levels, such as insulin, may be associated with dyspeptic symptoms through impaired gastric emptying and duodenal inflammation. Some recent studies have examined the role of duodenal pathophysiology in gastric motility, bicarbonate secretion, and digestion. Because reduced bicarbonate secretion, which is caused by pancreatic dysfunction, leads to a failure to neutralize gastric acid in the proximal duodenum, impaired bicarbonate secretion in turn fails to protect the duodenal mucosa against gastric acid influx, thereby inducing duodenal inflammation. In addition, elevated trypsin levels might be associated in part with duodenal inflammatory responses through PAR2-related immunomodulatory cells. This review describes how duodenal inflammation might affect the pathogenesis of FD and examines whether pancreatic dysfunction is associated with FD through intestinal inflammation.

Arginine Catabolism and Polyamine Biosynthesis Pathway Disparities Within Francisella tularensis Subpopulations.

Francisella tularensis is a highly infectious zoonotic pathogen with as few as 10 organisms causing tularemia, a disease that is fatal if untreated. Although F. tularensis subspecies tularensis (type A) and subspecies holarctica (type B) share over 99.5% average nucleotide identity, notable differences exist in genomic organization and pathogenicity. The type A clade has been further divided into subtypes A.I and A.II, with A.I strains being recognized as some of the most virulent bacterial pathogens known. In this study, we report on major disparities that exist between the F. tularensis subpopulations in arginine catabolism and subsequent polyamine biosynthesis. The genes involved in these pathways include the speHEA and aguAB operons, along with metK. In the hypervirulent F. tularensis A.I clade, such as the A.I prototype strain SCHU S4, these genes were found to be intact and highly transcribed. In contrast, both subtype A.II and type B strains have a truncated speA gene, while the type B clade also has a disrupted aguA and truncated aguB. Ablation of the chromosomal speE gene that encodes a spermidine synthase reduced subtype A.I SCHU S4 growth rate, whereas the growth rate of type B LVS was enhanced. These results demonstrate that spermine synthase SpeE promotes faster replication in the F. tularensis A.I clade, whereas type B strains do not rely on this enzyme for in vitro fitness. Our ongoing studies on amino acid and polyamine flux within hypervirulent A.I strains should provide a better understanding of the factors that contribute to F. tularensis pathogenicity.

Plasma Metabolic Signatures of Healthy Overweight Subjects Challenged With an Oral Glucose Tolerance Test.

Insulin secretion following ingestion of a carbohydrate load affects a multitude of metabolic pathways that simultaneously change direction and quantity of interorgan fluxes of sugars, lipids and amino acids. In the present study, we aimed at identifying markers associated with differential responses to an OGTT a population of healthy adults. By use of three metabolite profiling platforms, we assessed these postprandial responses of a total of 202 metabolites in plasma of 72 healthy volunteers undergoing comprehensive phenotyping and of which half enrolled into a weight-loss program over a three-month period. A standard oral glucose tolerance test (OGTT) served as dietary challenge test to identify changes in postprandial metabolite profiles. Despite classified as healthy according to WHO criteria, two discrete clusters (A and B) were identified based on the postprandial glucose profiles with a balanced distribution of volunteers based on gender and other measures. Cluster A individuals displayed 26% higher postprandial glucose levels, delayed glucose clearance and increased fasting plasma concentrations of more than 20 known biomarkers of insulin resistance and diabetes previously identified in large cohort studies. The volunteers identified by canonical postprandial responses that form cluster A may be called pre-pre-diabetics and defined as “at risk” for development of insulin resistance. Moreover, postprandial changes in selected fatty acids and complex lipids, bile acids, amino acids, acylcarnitines and sugars like mannose revealed marked differences in the responses seen in cluster A and cluster B individuals that sustained over the entire challenge test period of 240 min. Almost all metabolites, including glucose and insulin, returned to baseline values at the end of the test (at 240 min), except a variety of amino acids and here those that have been linked to diabetes development. Analysis of the corresponding metabolite profile in a fasting blood sample may therefore allow for early identification of these subjects at risk for insulin resistance without the need to undergo an OGTT.

Inhibition of MAP4K4 signaling initiates metabolic reprogramming to protect hepatocytes from lipotoxic damage

The primary hepatic consequence of obesity is non-alcoholic fatty liver disease (NAFLD), affecting about 25% of the global adult population. Non-alcoholic steatohepatitis (NASH) is a severe form of NAFLD characterized by liver lipid accumulation, inflammation, and hepatocyte ballooning, with a different degree of hepatic fibrosis. In the light of rapidly increasing prevalence of NAFLD and NASH, there is an urgent need for improved understanding of the molecular pathogenesis of these diseases. The aim of this study was to decipher the possible role of STE20-type kinase MAP4K4 in the regulation of hepatocellular lipotoxicity and susceptibility to NAFLD. We found that MAP4K4 mRNA expression in human liver biopsies was positively correlated with key hallmarks of NAFLD (i.e., liver steatosis, lobular inflammation, hepatocellular ballooning, and fibrosis). We also found that the silencing of MAP4K4 suppressed lipid deposition in human hepatocytes by stimulating β-oxidation and triacylglycerol secretion, while attenuating fatty acid influx and lipid synthesis. Furthermore, downregulation of MAP4K4 markedly reduced the glycolysis rate and lowered incidences of oxidative/endoplasmic reticulum stress. In parallel, we observed suppressed JNK and ERK and increased AKT phosphorylation in MAP4K4-deficient hepatocytes. Together, these results provide the first experimental evidence supporting the potential involvement of STE20-type kinase MAP4K4 as a component of the hepatocellular lipotoxic milieu promoting NAFLD susceptibility.

Photocontrol of Itaconic Acid Synthesis in Escherichia coli.

Metabolic engineering aims to control cellular metabolic flow and maximize the production of a product of interest. Photocontrol of the activities of proteins is an effective method for accurately regulating metabolic pathways. In this study, we inserted the photosensor light-oxygen-voltage-sensing domain 2 of Avena sativa (AsLOV2) into selected sites of isocitrate dehydrogenase (IDH), the key enzyme in the competitive pathway of itaconic acid (ITA) synthesis, to construct photoswitchable IDH-AsLOV2 (ILOVs). These engineered light-sensitive proteins were used to regulate the metabolic flux of the tricarboxylic acid (TCA) cycle in Escherichia coli to improve ITA production. The engineered fusion proteins ILOV2, ILOV3, ILOV6, and ILOV7 exhibited effective reversibility under the oscillation of darkness and blue light illumination in vitro. The efficacies of the intracellular photoswitches were evaluated, and an optimal photocontrol strategy was established in vivo. The ITA titer was significantly enhanced to 3.30 g/L for strain ITAΔ43, which displayed superior photoswitchable potency for ITA production compared with the strains that completely deleted the icd gene. The photocontrol strategy developed here can be extended for process optimization and titer improvement of other high-value bioengineering chemicals.