Quercetin treatment changes fluxes in the primary metabolism and increases culture longevity and recombinant α₁-antitrypsin production in human AGE1.HN cells

Modulation of the structural and functional properties of α1-antitrypsin by interaction with flavonoid luteolin

α1-antitrypsin (A1AT) is a circulating serine protease inhibitor and an acute phase reactant, the deficiency of which can lead to liver failure and chronic lung disease. Flavonoid treatment may induce changes in α1-antitrypsin production in some human cells. The purpose of this study is to investigate the properties of the A1AT protein that interacts with the flavonoid luteolin, which exhibits numerous properties, including antioxidant properties. For this purpose, multi-spectroscopic (UV-Vis spectroscopy, fluorescence and FRET) methods and molecular docking were used. The intrinsic fluorescence of A1AT was quenched by luteolin through a static mechanism. Luteolin binds to one site of the A1AT protein, with a moderate binding constant, and the binding process was driven by entropy and hydrophobic interactions. Hydrophobicity around Trp decreased as a result of luteolin binding to the A1AT site and FRET occurred at a distance of 3.11 nm. Under the action of temperature, the stability of A1AT structure was decreased by the presence of luteolin. Molecular docking confirmed that luteolin binds to one site, with a moderate affinity. The results would give a better understanding of the functional changes that occurred in the structure of A1AT induced by luteolin binding, which may have implications in the field of pharmaceutical research.Communicated by Ramaswamy H. Sarma.

Quercetin-Induced Lifespan Extension in Podospora anserina Requires Methylation of the Flavonoid by the O-Methyltransferase PaMTH1

Quercetin is a flavonoid that is ubiquitously found in vegetables and fruits. Like other flavonoids, it is active in balancing cellular reactive oxygen species (ROS) levels and has a cyto-protective function. Previously, a link between ROS balancing, aging, and the activity of O-methyltransferases was reported in different organisms including the aging model Podospora anserina. Here we describe a role of the S-adenosylmethionine-dependent O-methyltransferase PaMTH1 in quercetin-induced lifespan extension. We found that effects of quercetin treatment depend on the methylation state of the flavonoid. Specifically, we observed that quercetin treatment increases the lifespan of the wild type but not of the PaMth1 deletion mutant. The lifespan increasing effect is not associated with effects of quercetin on mitochondrial respiration or ROS levels but linked to the induction of the PaMth1 gene. Overall, our data demonstrate a novel role of O-methyltransferase in quercetin-induced longevity and identify the underlying pathway as part of a network of longevity assurance pathways with the perspective to intervene into mechanisms of biological aging.

Road to the future of systems biotechnology: CRISPR-Cas-mediated metabolic engineering for recombinant protein production

The rising potential for CRISPR-Cas-mediated genome editing has revolutionized our strategies in basic and practical bioengineering research. It provides a predictable and precise method for genome modification in a robust and reproducible fashion. Emergence of systems biotechnology and synthetic biology approaches coupled with CRISPR-Cas technology could change the future of cell factories to possess some new features which have not been found naturally. We have discussed the possibility and versatile potentials of CRISPR-Cas technology for metabolic engineering of a recombinant host for heterologous protein production. We describe the mechanisms involved in this metabolic engineering approach and present the diverse features of its application in biotechnology and protein production.

Metabonomic analysis of quercetin against the toxicity of chronic exposure to a mixture of four organophosphate pesticides in rat plasma

1. A metabonomics approach was performed to investigate the effect of quercetin on the toxicity of chronic exposure to a mixture of four organophosphate pesticides (OPs) at their corresponding no-observed-adverse-effect level (NOAEL). The rats were divided into six groups (n = 10/group): control, two different doses of quercetin, OPs mixture and different doses of quercetin plus OPs mixture-treated groups. 2. Nine metabolites, including two quercetin metabolites and seven endogenous metabolites were identified in plasma. The intensities of metabolites significantly changed in the OP mixture-treated group compared with the control group (p < 0.01), such as lysoPE (16:0/0:0), lysoPC (17:0/0:0), lysoPC (15:0/0:0) and 4-pyridoxic acid, significantly increased; by contrast, the intensities of arachidonic acid and citric acid significantly decreased. Anomalous intensity changes in aforementioned metabolites were alleviated in the OP mixture plus 50 mg/kgċbw/d quercetin-treated group compared with the OP mixture-treated group (p < 0.05). 3. The results indicated that quercetin elicited partial protective effects against the toxicity induced by a mixture of OPs, which include regulation of lipid metabolism, improvement of tricarboxylic acid (TCA) cycle disorders, enhancement of antioxidant defence system to protect the liver.

Quercetin promotes the osteogenic differentiation of rat mesenchymal stem cells via mitogen-activated protein kinase signaling

The aim of the present study was to investigate the effects of quercetin on the mitogen-activated protein kinase (MAPK) signaling pathway in the osteogenic differentiation of rat mesenchymal stem cells (MSCs). A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and an alkaline phosphatase (ALP) assay were used to determine the effects of quercetin (concentrations of 0.1, 1 and 10 µmol/l) on the proliferation and differentiation of MSCs and the expression of ALP, respectively. In addition, through the introduction of inhibitors of p38 MAPK, extracellular signal-regulated kinase (ERK)1/2 and c-Jun NH₂-terminal kinase (JNK), the effects of quercetin on the proteins, ALP, collagen type I (COL I) and bone γ-carboxyglutamate protein (BGP), which are indicators of osteogenic differentiation, were investigated. Immunoblotting was performed to determine the phosphorylation levels of p38 MAPK, ERK1/2 and JNK, while fluorescent quantitative polymerase chain reaction was used to determine the mRNA expression levels of transforming growth factor (TGF)-β1, bone morphogenetic protein (BMP)-2 and core binding factor (CBF)α1. At all the concentrations tested, the concentrations of 10, 1 and 0.1 µmol/l quercetin were shown to promote the differentiation of MSCs and the expression of ALP, in which the concentration of 10 µmol/l was optimal. When compared with the control group, the phosphorylation levels of p38 MAPK, ERK1/2 and JNK, the protein expression levels of ALP, COL I and BGP, and the mNRA expression levels of TGF-β1, BMP-2 and Cbfα1 were increased in the quercetin-treated group. However, with the introduction of inhibitors, the levels of phosphorylated p38 MAPK, ERK1/2 and JNK, and the protein expression levels of ALP, COL I and BGP decreased. Furthermore, the mRNA expression levels of TGF-β1, BMP-2 and CBFα1 decreased in the quercetin + SP600125 (inhibitor of JNK) and quercetin + PD98059 (inhibitor of ERK1/2) groups. Therefore, quercetin was demonstrated to promote the osteogenic differentiation of MSCs by activating the MAPK signaling pathway. The ERK1/2 and JNK signaling pathways regulate the expression of TGF-β1, BMP-2 and CBFα1. Thus, activation of the ERK1/2 and JNK signaling pathways may play a leading role in the quercetin-promoted osteogenic proliferation and differentiation of MSCs.

Engineering the supply chain for protein production/secretion in yeasts and mammalian cells

Metabolic bottlenecks play an increasing role in yeasts and mammalian cells applied for high-performance production of proteins, particularly of pharmaceutical ones that require complex posttranslational modifications. We review the present status and developments focusing on the rational metabolic engineering of such cells to optimize the supply chain for building blocks and energy. Methods comprise selection of beneficial genetic modifications, rational design of media and feeding strategies. Design of better producer cells based on whole genome-wide metabolic network analysis becomes increasingly possible. High-resolution methods of metabolic flux analysis for the complex networks in these compartmented cells are increasingly available. We discuss phenomena that are common to both types of organisms but also those that are different with respect to the supply chain for the production and secretion of pharmaceutical proteins.

The influence of cell growth and enzyme activity changes on intracellular metabolite dynamics in AGE1.HN.AAT cells

Optimization of bioprocesses with mammalian cells mainly concentrates on cell engineering, cell screening and medium optimization to achieve enhanced cell growth and productivity. For improving cell lines by cell engineering techniques, in-depth understandings of the regulation of metabolism and product formation as well as the resulting demand for the different medium components are needed. In this work, the relationship of cell specific growth and uptake rates and of changes in maximum in vitro enzyme activities with intracellular metabolite pools of glycolysis, pentose phosphate pathway, citric acid cycle and energy metabolism were determined for batch cultivations with AGE1.HN.AAT cells. Results obtained by modeling cell growth and consumption of main substrates showed that the dynamics of intracellular metabolite pools is primarily linked to the dynamics of specific glucose and glutamine uptake rates. By analyzing maximum in vitro enzyme activities we found low activities of pyruvate dehydrogenase and pyruvate carboxylase which suggest a reduced metabolite transfer into the citric acid cycle resulting in lactate release (Warburg effect). Moreover, an increase in the volumetric lactate production rate during the transition from exponential to stationary growth together with a transient accumulation of fructose 1,6-bisphosphate, fructose 1-phosphate and ribose 5-phosphate point toward an upregulation of PK via FBP. Glutaminase activity was about 44-fold lower than activity of glutamine synthetase. This seemed to be sufficient for the supply of intermediates for biosynthesis but might lead to unnecessary dissipation of ATP. Taken together, our results elucidate regulation of metabolic networks of immortalized mammalian cells by changes of metabolite pools over the time course of batch cultivations. Eventually, it enables the use of cell engineering strategies to improve the availability of building blocks for biomass synthesis by increasing glucose as well as glutamine fluxes. An additional knockdown of the glutamine synthetase might help to prevent unnecessary dissipation of ATP, to yield a cell line with optimized growth characteristics and increased overall productivity.

Metabolic control at the cytosol-mitochondria interface in different growth phases of CHO cells

Metabolism at the cytosol-mitochondria interface and its regulation is of major importance particularly for efficient production of biopharmaceuticals in Chinese hamster ovary (CHO) cells but also in many diseases. We used a novel systems-oriented approach combining dynamic metabolic flux analysis and determination of compartmental enzyme activities to obtain systems level information with functional, spatial and temporal resolution. Integrating these multiple levels of information, we were able to investigate the interaction of glycolysis and TCA cycle and its metabolic control. We characterized metabolic phases in CHO batch cultivation and assessed metabolic efficiency extending the concept of metabolic ratios. Comparing in situ enzyme activities including their compartmental localization with in vivo metabolic fluxes, we were able to identify limiting steps in glycolysis and TCA cycle. Our data point to a significant contribution of substrate channeling to glycolytic regulation. We show how glycolytic channeling heavily affects the availability of pyruvate for the mitochondria. Finally, we show that the activities of transaminases and anaplerotic enzymes are tailored to permit a balanced supply of pyruvate and oxaloacetate to the TCA cycle in the respective metabolic states. We demonstrate that knowledge about metabolic control can be gained by correlating in vivo metabolic flux dynamics with time and space resolved in situ enzyme activities.

Dynamics of growth and metabolism controlled by glutamine availability in Chinese hamster ovary cells

The physiology of animal cells is characterized by constantly changing environmental conditions and adapting cellular responses. Applied dynamic metabolic flux analysis captures metabolic dynamics and can be applied to industrially relevant cultivation conditions. We investigated the impact of glutamine availability or limitation on the physiology of CHO K1 cells in eight different batch and fed-batch cultivations. Varying glutamine availability resulted in global metabolic changes. We observed dose-dependent effects of glutamine in batch cultivation. Identifying metabolic links from the glutamine metabolism to specific metabolic pathways, we show that glutamine feeding results in its coupling to tricarboxylic acid cycle fluxes and in its decoupling from metabolic waste production. We provide a mechanistic explanation of the cellular responses upon mild or severe glutamine limitation and ammonia stress. The growth rate of CHO K1 decreased with increasing ammonia levels in the supernatant. On the other hand, growth, especially culture longevity, was stimulated at mild glutamine-limiting conditions. Flux rearrangements in the pyruvate and amino acid metabolism compensate glutamine limitation by consumption of alternative carbon sources and facilitating glutamine synthesis and mitigate ammonia stress as result of glutamine abundance.

Stable isotope-assisted metabolomics to detect metabolic flux changes in mammalian cell cultures

The determination of metabolic fluxes provides detailed information of cellular physiology, and the assessment of metabolic flux changes upon a certain perturbation can help to improve biotechnological and pharmaceutical processes. Stable isotope-assisted metabolomics using tracer-labeled substrates is the method of choice to determine the fluxes. Though well-established for microbial cultures, the application to mammalian cells is generally complex and still limited. However, there have been great achievements in recent years and it is now emerging that stable isotope-assisted metabolic flux analysis in mammalian cell cultures will help improving biotechnological production and will also support drug development and discovery.