High-level production of pullulan from high concentration of glucose by mutagenesis and adaptive laboratory evolution of Aureobasidium pullulans

The cost of carbon sources and the low efficiency of the fermentation titer limit the industrial application of pullulan. In this study, a hypertonic-tolerant strain with efficient utilization of glucose was obtained using a double strategy. Initially, a strain for efficient synthesis of pullulan from glucose was generated by mutagenesis. Subsequently, the mutant was directionally evolved on the plate containing a high glucose concentration to enhance high osmotic resistance. The enzyme activities and the transcriptional levels involved in pullulan biosynthesis and high osmotic tolerance in mutants were increased. Nitrogen source and inorganic salts also significantly affected the production of pullulan by M233-20 from high concentration of glucose. The pullulan titer of 162.1 g/L was obtained using the response surface methodology in the flask. The strain M233-20 produced 162.3 g/L pullulan in a 30-L bioreactor with a yield of 0.82 g/g glucose. Hence, this work provides a potential industrial pullulan producer M233-20 and a strategy to develop excellent strain.

Imbalance in the antioxidant defence system and pro-genotoxic status induced by high glucose concentrations: In vitro testing in human liver cells

It has been hypothesized that high glucose concentrations might contribute to the overall intracellular oxidative stress either by the direct generation of reactive oxygen species (ROS) or by altering the redox balance. Moreover, it has also been suggested that high glucose concentration can increase the susceptibility of DNA to genotoxic effects of xenobiotics. The aim of this approach was to test high glucose concentrations for pro-genotoxicity in human liver cells by setting up an in vitro model for hyperglycaemia. The experimental design included performing of tests on both human HepG2 tumour cells and HepaRG immortalized cells. Increased cell susceptibility to genotoxic xenobiotics was tested by challenging cell cultures with 4-nitroquinoline-N-oxide (4NQO) and evaluating the extent of primary DNA damage by comet assay. Moreover, we evaluated the relationship between glucose concentration and intracellular ROS, as well as the effects of glucose concentration on the induction of Nrf2-dependent genes such as Glutathione S-transferases, Heme‑oxygenase-1, and Glutathione peroxidase-4. To investigate the involvement of ROS in the induced pro-genotoxic activity, parallel experimental sets were set up by considering co-treatment of cells with the model mutagen 4NQO and the antioxidant, glutathione precursor N-acetyl-L-cysteine. High glucose concentrations caused a significant increase in the levels of primary DNA damage, with a pro-genotoxic condition closely related to the concentration of glucose in the culture medium when cells were exposed to 4NQO. High glucose concentrations also stimulated the production of ROS and down-regulated genes involved in contrasting of the effects of oxidative stress. In conclusion, in the presence of high concentrations of glucose, the cells are in unfavourable conditions for the maintenance of genome integrity.

High Glucose-reduced Apoptosis in Human Breast Cancer Cells Is Mediated by Activation of NF-κB

Tumor cells rely on glycolysis for their energy supply with the production of lactate even in normoxia condition, which is named aerobic glycolysis or Warburg effect. Therefore, high glucose (HG) concentration provides a favorable condition for increasing proliferation, angiogenesis and decreasing apoptosis, but its molecular mechanisms are still unknown. The objective of this study is to investigate HG condition on tumor cells behavior including proliferation, apoptosis, and an angiogenesis mediator. In this study, MCF-7 derived from human breast adenocarcinoma, were cultured in DMEM with two different concentrations of glucose for 48 h (5.5 mM as normal glucose (NG) condition and 25 mM as HG condition). We used Zingiber officinale extraction for the inhibition of NF-κB. Cell proliferation assay was done by direct counting, cell viability by MTT method, bcl-2 by Immunocytochemistry, apoptosis by Hoechst/PI double staining and vascular endothelium growth factor (VEGF) by ELISA. Results showed that HG increased lactate production, significantly. HG increased cell proliferation, cell viability, VEGF secretion, and bcl-2 expression while it decreased apoptosis. However, when HG was combined with Zingiber officinale extraction, cell proliferation, cell viability, VEGF secretion and bcl-2 expression decreased and apoptosis increased significantly due to inhibition of NF-κB. Results revealed that HG increased cell proliferation, angiogenesis and decreased apoptosis due to activation of NF-κB pathway. Moreover, the probable mechanism of the activation of NF-κB in HG is increasing reactive oxygen species (ROS) in this condition that can activate NF-κB directly.

Viability of primary cultured podocytes is associated with extracellular high glucose-dependent autophagy downregulation

Structural and functional impairment of podocytes plays an important role in the development of diabetic nephropathy, a chronic complication of diabetes mellitus and leading cause of renal failure requiring renal replacement therapy. Autophagy plays a crucial role in podocyte viability and function, and its activity is modulated by a variety of pathophysiological factors found in diabetic milieu. Here we show that downregulation of autophagy is critical for podocyte survival in hyperglycemic environment. Moreover, long-term exposure to high glucose leads to inhibition of autophagy as well as to the development of insulin resistance in podocytes. Furthermore, impairment of autophagy is involved in alteration of insulin-dependent glucose uptake in podocytes, suggesting a relationship between these two processes. Taken together, our findings suggest that downregulation of podocyte autophagy, observed after long-term exposure to high glucose, results from their suppressed sensitivity to insulin, and may therefore lead to diminished podocyte cell viability as well as their reduced number in glomerulus.

Comparison of high glucose concentration blood and crystalloid cardioplegia in paediatric cardiac surgery: a randomized clinical trial

OBJECTIVES

This study investigates the effects of high glucose content on patients undergoing cold crystalloid versus cold blood cardioplegia in terms of early clinical results, functional myocardial recovery and ischaemia-reperfusion injury in patients undergoing repair of acyanotic cardiac lesions.

METHODS

Patients were randomly assigned to receive either crystalloid (n = 31) or blood cardioplegia (n = 31). Early clinical results were assessed. Changes in left ventricular fractional shortening, arterial blood lactate levels, central venous saturation, cardiac Troponin I release and blood glucose concentration were measured during the first 24 h after ischaemia.

RESULTS

There was no significant difference in clinical outcomes and postoperative complication rates between groups. The postoperative changes in left ventricular function, lactate levels, central venous saturation and Troponin I were not significantly different between groups. The use of crystalloid cardioplegia was associated with significant increases in serum glucose compared with blood cardioplegia.

CONCLUSIONS

A high glucose content blood cardioplegia does not show any advantage compared with crystalloid cardioplegia in terms of clinical outcomes, functional recovery and the degree of ischaemic injury in infants and children undergoing repair of acyanotic heart lesions. High glucose concentration of the cardioplegic solution might potentiate ischaemia-reperfusion injury and diminish the beneficial effects of blood cardioplegia.

Combined effect of insulin and high glucose concentration on albumin permeability in cultured rat podocytes

Podocytes play a fundamental role in regulating glomerular permeability to albumin. This mechanism is disrupted in the course of diabetes. Both insulin and high glucose concentrations enhance the permeability of podocytes to albumin by stimulating oxygen free radical production, primarily by NAD(P)H oxidase-4 (NOX4), and by activating protein kinase G, isoform Iα (PKGIα). However, no study has investigated the combined effects of insulin and high glucose concentration. Here, we investigated the effects of applying insulin (INS, 300 nM) and high glucose (HG, 30 mM), both separately and combined, for 5 days, on cultured rat podocyte permeability to albumin. We measured podocyte permeability with a transmembrane albumin flux assay. We measured NOX4 and PKGIα mRNA expression with real-time PCR. We used Western blots to evaluate protein expression levels of NOX4, PKGIα, the myosin-binding subunit of myosin phosphatase 1, and myosin light chain. We found that INS and HG had a synergistic effect on podocyte permeability to albumin, and this synergy was not dependent on NOX4 or PKGIα. These results suggested that the combined action of INS and HG may exacerbate glomerular dysfunction in diabetes.

High glucose increases glomerular filtration barrier permeability by activating protein kinase G type Iα subunits in a Nox4-dependent manner

Hyperglycemia is a primary factor that disturbs podocyte function in the glomerular filtration process; this disturbance leads to the development of diabetic nephropathy, and ultimately, renal failure. Podocyte function may also be altered by biological agents that modify protein kinase activity, including the cGMP-activated protein kinase type Iα (PKGIα). We hypothesized that hyperglycemia-induced podocyte protein hyperpermeability was dependent on PKGIα activation, and that PKGIα was activated via dimerization induced by reactive oxygen species. This hypothesis was investigated in rat podocytes cultured in high glucose (HG, 30 mM). Protein expression was measured with Western blot and immunofluorescence. Podocyte permeability was measured with a transmembrane albumin flux assay. We found that HG increased podocyte permeability in long-term incubations (1, 3, and 5 days); permeability was increased by 66% on day 5. This effect was abolished with apocynin, a NAD(P)H inhibitor, and Rp-8-Br-cGMPS, a PKG inhibitor. It was also abolished by introducing small interfering RNAs (siRNAs) against Nox4 and PKGIα into cultured podocytes. Furthermore, HG increased PKGIα dimerization by 138% (0.23 ± 0.04 vs. 0.54 ± 0.09; P<0.05); this effect was abolished with a siRNA against Nox4. Our observations suggested that HG could increase albumin permeability across the podocyte filtration barrier via Nox4-dependent PKGIα dimerization.

An In Vitro Model to Probe the Regulation of Adipocyte Differentiation under Hyperglycemia

BACKGROUND

The aim of this study was an in vitro investigation of the effect of high glucose concentration on adipogenesis, as prolonged hyperglycemia alters adipocyte differentiation.

METHODS

3T3-L1 preadipocytes differentiated in the presence of varying concentrations of glucose (25, 45, 65, 85, and 105 mM) were assessed for adipogenesis using AdipoRed (Lonza) assay. Cell viability and proliferation were measured using MTT reduction and [(3)H] thymidine incorporation assay. The extent of glucose uptake and glycogen synthesis were measured using radiolabelled 2-deoxy-D-[1-(3)H] glucose and [(14)C]-UDP-glucose. The gene level expression was evaluated using reverse transcription-polymerase chain reaction and protein expression was studied using Western blot analysis.

RESULTS

Glucose at 105 mM concentration was observed to inhibit adipogenesis through inhibition of CCAAT-enhancer-binding proteins, sterol regulatory element-binding protein, peroxisome proliferator-activated receptor and adiponectin. High concentration of glucose induced stress by increasing levels of toll-like receptor 4, nuclear factor κB and tumor necrosis factor α thereby generating activated preadipocytes. These cells entered the state of hyperplasia through inhibition of p27 and proliferation was found to increase through activation of protein kinase B via phosphoinositide 3 kinase dependent pathway. This condition inhibited insulin signaling through decrease in insulin receptor β. Although the glucose transporter 4 (GLUT4) protein remained unaltered with the glycogen synthesis inhibited, the cells were found to exhibit an increase in glucose uptake via GLUT1.

CONCLUSION

Adipogenesis in the presence of 105 mM glucose leads to an uncontrolled proliferation of activated preadipocytes providing an insight towards understanding obesity.