Cell Analysis on Microfluidics Combined with Mass Spectrometry

Metabolites from scutellarin alleviating deferoxamine-induced hypoxia injury in BV2 cells cultured on microfluidic chip combined with a mass spectrometer

The changes of metabolites of tricarboxylic acid (TCA) cycle in cells under hypoxia play a key role in drug screening. In order to dynamically monitor the drug metabolism changes of Scutellarin in the hypoxia environment induced by deferoxamine (DFO), a microfluidic-chip mass spectrometry method was used to study the real-time monitoring of drug metabolism changes under hypoxia conditions. This system has six drug-loading units, cell culture chamber, metabolite collection, filtration, HPLC separation and mass spectrometer. The cells in each microchannel were incubated with continuous flow of culture medium, metabolites will be collected by the fixed card slot, automatic sampling needle will be precise positioned and sampled. Through this new system combined with molecular biological methods, the changes of metabolites in TCA cycle of BV2 cells and drug metabolism of Scutellarin can be determined in real-time. In general, we illustrated a new mechanism of Scutellarin for reducing BV2 cell hypoxia injury and presented a novel analysis strategy that opened a way for real-time online monitoring of the energy metabolic mechanism of the effect of drugs on cells and further provided a superior strategy to screen natural drug candidates for hypoxia-related brain disease treatment.

Pollution-Free and Highly Sensitive Lactate Detection in Cell Culture Based on a Microfluidic Chip

Cell metabolite detection is important for cell analysis. As a cellular metabolite, lactate and its detection play an important role in disease diagnosis, drug screening and clinical therapeutics. This paper reports a microfluidic chip integrated with a backflow prevention channel for cell culture and lactate detection. It can effectively realize the upstream and downstream separation of the culture chamber and the detection zone, and prevent the pollution of cells caused by the potential backflow of reagent and buffer solutions. Due to such a separation, it is possible to analyze the lactate concentration in the flow process without contamination of cells. With the information of residence time distribution of the microchannel networks and the detected time signal in the detection chamber, it is possible to calculate the lactate concentration as a function of time using the de-convolution method. We have further demonstrated the suitability of this detection method by measuring lactate production in human umbilical vein endothelial cells (HUVEC). The microfluidic chip presented here shows good stability in metabolite quick detection and can work continuously for more than a few days. It sheds new insights into pollution-free and high-sensitivity cell metabolism detection, showing broad application prospects in cell analysis, drug screening and disease diagnosis.

Neurotoxicity mechanism of aconitine in HT22 cells studied by microfluidic chip-mass spectrometry

Aconitine, a common and main toxic component of Aconitum, is toxic to the central nervous system. However, the mechanism of aconitine neurotoxicity is not yet clear. In this work, we had the hypothesis that excitatory amino acids can trigger excitotoxicity as a pointcut to explore the mechanism of neurotoxicity induced by aconitine. HT22 cells were simulated by aconitine and the changes of target cell metabolites were real-time online investigated based on a microfluidic chip-mass spectrometry system. Meanwhile, to confirm the metabolic mechanism of aconitine toxicity on HT22 cells, the levels of lactate dehydrogenase, intracellular Ca²⁺, reactive oxygen species, glutathione and superoxide dismutase, and ratio of Bax/Bcl-2 protein were detected by molecular biotechnology. Integration of the detected results revealed that neurotoxicity induced by aconitine was associated with the process of excitotoxicity caused by glutamic acid and aspartic acid, which was followed by the accumulation of lactic acid and reduction of glucose. The surge of extracellular glutamic acid could further lead to a series of cascade reactions including intracellular Ca²⁺ overload and oxidative stress, and eventually result in cell apoptosis. In general, we illustrated a new mechanism of aconitine neurotoxicity and presented a novel analysis strategy that real-time online monitoring of cell metabolites can provide a new approach to mechanism analysis.

Highly sensitive monitoring of telomerase activity in living cells based on rapidly triggered cascade amplification reaction

Telomerase is an important potential biomarker for the study of tumor progression. Herein, we designed a cascade-amplification-reaction-based nanoprobe for intracellular telomerase detection based on the integration of rolling circle amplification (RCA) and catalytic hairpin assembly (CHA) onto MnO₂ nanosheets. Firstly, MnO₂ nanosheets rapidly delivered and released signal amplification units into cells, and very short telomerase extension products formed RCA circular templates and initiated the exponential RCA, producing enriched telomere sequence amplification products. Then the amplification products specifically triggered the CHA process and numerous H1/H2 complexes were formed, realizing the exponential amplification of fluorescence signals. The detection limit is as low as 1 LoVo cell for telomerase activity in cell extract. We further designed a microfluidic chip with six independent cell culture regions for in situ fluorescence imaging. Simultaneous detection of six types of cells was realized on the chip, and only 1-2 μL of cell suspension and reagents are needed. Our detection method features faster response speed and stronger fluorescence signal. Telomerase in living cells showed strong fluorescence signal within 1.5 h, and tumor cells were effectively distinguished from normal cells. Telomerase activities of different types of tumor cells and activity changes were both monitored conveniently. These results demonstrate that this method holds the potential for the sensitive detection of low abundance biomarkers in living cells, and will contribute to cancer diagnosis, cancer treatment and telomerase-related drug screening.

Recent advances of integrated microfluidic suspension cell culture system

Microfluidic devices with superior microscale fluid manipulation ability and large integration flexibility offer great advantages of high throughput, parallelisation and multifunctional automation. Such features have been extensively utilised to facilitate cell culture processes such as cell capturing and culturing under controllable and monitored conditions for cell-based assays. Incorporating functional components and microfabricated configurations offered different levels of fluid control and cell manipulation strategies to meet diverse culture demands. This review will discuss the advances of single-phase flow and droplet-based integrated microfluidic suspension cell culture systems and their applications for accelerated bioprocess development, high-throughput cell selection, drug screening and scientific research to insight cell biology. Challenges and future prospects for this dynamically developing field are also highlighted.

Uncovering the Metabolic Mechanism of Salidroside Alleviating Microglial Hypoxia Inflammation Based on Microfluidic Chip-Mass Spectrometry

Microglia are the main immune cells in the brain playing a critical role in neuroinflammation, and numerous pieces of evidence have proved that energy metabolism is closely associated with inflammation in activated microglia. Salidroside (Sal) isolated from Tibetan medicine Rhodiola crenulate can inhibit microglial hypoxia inflammation (HI). However, whether the inhibition is due to the intervening energy metabolic process in microglia is not clear. In this work, the hypoxic microenvironment of BV2 microglial cells was simulated using deferoxamine (DFO) in vitro and the change of cell metabolites (lactate, succinate, malate, and fumarate) was real-time online investigated based on a cell microfluidic chip-mass spectrometry (CM-MS) system. Meanwhile, for confirming the metabolic mechanism of BV2 cells under hypoxia, the level of HI-related factors (LDH, ROS, HIF-1α, NF-κB p65, TNF-α, IL-1β, and IL-6) was detected by molecular biotechnology. Integration of the detected results revealed that DFO-induced BV2 cell HI was associated with the process of energy metabolism, in which cell energy metabolism changed from oxidative phosphorylation to glycolysis. Furthermore, administration of Sal treatment could effectively invert this change, and two metabolites of Sal were identified: tyrosol and 4-hydroxyphenylacetic acid. In general, we illustrated a new mechanism of Sal for reducing BV2 cell HI injury and presented a novel analysis strategy that opened a way for real-time online monitoring of the energy metabolic mechanism of the effect of drugs on cells and further provided a superior strategy to screen natural drug candidates for HI-related brain disease treatment.