Cytotoxicity Testing of 9,667 Tox21 Compounds using Two Real-Time Assays by Promega

A recent paper in PLOS One demonstrated real-time cytotoxicity profiling of approximately 10,000 chemical compounds in the Tox21 compound library, using two Promega assays, RealTime-Glo™ MT Cell Viability Assay and CellTox™ Green Cytotoxicity Assay. This is exciting to me, a science writer working at Promega; exciting because it’s tricky figuring out how to write about the utility of our products without sounding like an evangelist.

I don’t know about you, but I tend to shut out evangelists and their messages.

Instead of me telling you about real-time viability and cytotoxicity assays from Promega, here is an example of their use in Tox21 chemical compound library research.

What is the Tox21 compound library?
As described in the article by Hsieh, J-H. et al. (2017) in PLOS One:
“The Toxicology in the 21st Century (Tox21) program is a federal collaboration among the National Institutes of Health, including the National Toxicology Program (NTP) at the National Institute of Environmental Health Sciences and the National Center for Advancing Translational Sciences, the Environmental Protection Agency, and the Food and Drug Administration. Tox21 researchers utilize a screening method called high throughput screening (HTS) that uses automated methods to quickly and efficiently test chemicals for activity across a battery of assays that target cellular processes. These assays are useful for rapidly evaluating large numbers of chemicals to provide insight on potential human health effects.” Continue reading

Real-Time Analysis for Cell Viability, Cytotoxicity and Apoptosis: What Would You Do with More Data from One Sample?

You are studying the effects of a compound(s) on your cells. You want to know how the compound affects cell health over a period of hours, or even days. Real-time assays allow you to monitor cell viability, cytotoxicity and apoptosis continuously, to detect changes over time.

Why use a real-time assay?
A real-time assay enables you to repeatedly measure specific events or conditions over time from the same sample or plate well. Repeated measurement is possible because the cells are not harmed by real-time assay reagents. Real-time assays allow you to collect data without lysing the cells.

Advantages of  Real-Time Measurement
Real-time assays allow you to: Continue reading

In Healthy Eating Less is More: The Science Behind Intermittent Fasting

Mix a love of eating with a desire to live a long, healthy life what do you get? Probably the average 21st century person looking for a way to continue enjoying food despite insufficient exercise and/or an age-related decline in caloric needs.

Enter intermittent fasting, a topic that has found it’s way into most news sources, from National Institutes of Health (NIH) and Proceedings of the National Academy of Sciences publications to WebMD and even the popular press. For instance, National Public Radio’s “The Salt” writers have tried and written about their experiences with dietary restriction.

While fasting has enjoyed fad-like popularity the past several years, it is not new. Fasting, whether purposely not eating or eating a restricted diet, has been practiced for 1,000s of years. What is new is research studies from which we are learning the physiologic effects of fasting and other forms of decreased nutrient intake.

You may have heard the claims that fasting makes people smarter, more focused and thinner? Researchers today are using cell and animal models, and even human subjects, to measure biochemical responses at the cellular level to restricted nutrient intake and meal timing, in part to prove/disprove such claims (1,2). Continue reading

Making BRET the Bright Choice for In vivo Imaging: Use of NanoLuc® Luciferase with Fluorescent Protein Acceptors

13305818-cr-da-nanoluc-application_ligundLive animal in vivo imaging is a common and useful tool for research, but current tools could be better. Two recent papers discuss adaptations of BRET technology combining the brightness of fluorescence with the low background of a bioluminescence reaction to create enhanced in vivo imaging capabilities.

The key is to image photons at wavelengths above 600nm, as lower wavelengths are absorbed by heme-containing proteins (Chu, J., et al., 2016 ). Fluorescent protein use in vivo is limited because the proteins must be excited by an external light source, which generates autofluorescence and has limited penetration due to absorption by tissues. Bioluminescence imaging continues to be a solution, especially firefly luciferase (612nm emission at 37°C), but its use typically requires long image acquisition times. Other luciferases, like NanoLuc, Renilla, and Gaussia, etc. either do not produce enough light or the wavelengths are readily absorbed by tissues, limiting their use to near- surface imaging.

The two papers discussed here illustrate how researchers have combined NanoLuc® luciferase with a fluorescent protein to harness bioluminescent resonance energy transfer (BRET) for brighter in vivo imaging reporters. Continue reading

Don’t Let These Three Common Issues Hurt Your Luminescent Assay Results

4621CAThere is a lot riding on your luminescent assay results. Each plate represents precious time, effort and resources. Did you know that there are three things about your detection instrument that can impact how much useful information you get from each plate?  Instruments with poor sensitivity may cause you to miss low-level samples that could be the “hit” you are looking for.  Instruments with a narrow detection range limit the accuracy or reproducibility you needed to repeat your work.  Finally, instruments that let the signal from bright wells spill into adjacent wells allow crosstalk to occur and skew experimental results, costing you time and leading to failed or repeated experiments. Continue reading

Researchers Gather at Promega Madison Campus for Annual Stem Cell Symposium

stemcell header

Since the derivation of human-derived embryonic stem cells (ES cells) in the 1990’s, the world of stem cell biology and engineering has proceeded at an amazing pace. The isolation pluripotent cells (iPS) cells that have most of the properties of embryonic stem cells from somatic tissues has been possible for nearly a decade. Engineered human cells, tissues, and organ-like structures are becoming a reality and may soon play a part in treating diseases. ES and iPS cells are teaching us much about how cells become specialized during normal development and the pathologies that result when those specialization decisions go wrong.

At the 12th Annual Wisconsin Stem Cell Symposium held at the BioPharmaceutical Technology Center institute, leading researchers from around the world will be gathered to discuss the latest progress, roadblocks and issues around Engineering Cells and Tissues for Discovery and Therapy.

The Symposium is co-coordinated by the Stem Cell & Regenerative Medicine Center at the University of Wisconsin-Madison and the BioPharmaceutical Technology Center Institute and is open to the public. Registration is $100.00 ($50.00 for students and post-doctoral researchers). The Symposium will be held at Promega Corporation’s BioPharmaceutical Technology Center, 5445 E. Cheryl Parkway, Fitchburg, WI.

Topics to be discussed include: Continue reading

ViaFect™ Reagent: Building Assays in Difficult Cells

The story of ViaFect begins with Promega Custom Assay Services (CAS), a group that uses Promega technologies to construct made-to-order assays, typically in a cell line. Many projects from the CAS group involve transfecting cells with expression vectors and reporter vectors. In some instances, customers contact CAS to have an assay constructed in a difficult cell line, after attempting and failing, or experiencing difficulty building the assay themselves.

CAS projects start with a proof-of-concept experiment using transient transfection before moving on to production of a clonal, stable cell line. For difficult cell lines, the CAS group previously turned to electroporation after exhausting lipid-based transfection options. Electroporation often worked, but success came with a price—cytotoxicity. The CAS group challenged R&D to find a better solution—better transfection with low toxicity for difficult-to-use cells. The result of that challenge is the ViaFect™ Transfection Reagent. Continue reading

Improving the Success of Your Transfection

12150558-plasmid_with_cell_membrane3Not every lab has a tried and true transfection protocol that can be used by all lab members. Few researchers will use the same cell type and same construct to generate data. Many times, a scientist may need to transfect different constructs or even different molecules (e.g., short-interfering RNA [siRNA]) into the same cell line, or test a single construct in different cultured cell lines. One construct could be easily transfected into several different cell lines or a transfection protocol may work for several different constructs. However, some cells like primary cells can be difficult to transfect and some nucleic acids will need to be optimized for successful transfection. Here are some tips that may help you improve your transfection success.

Transfect healthy, actively dividing cells at a consistent cell density. Cells should be at a low passage number and 50–80% confluent when transfected. Using the same cell density reduces variability for replicates. Keep cells Mycoplasma-free to ensure optimal growth.

Transfect using high-quality DNA. Transfection-quality DNA is free from protein, RNA and chemical contamination with an A260/A280 ratio of 1.7–1.9. Prepare purified DNA in sterile water or TE buffer at a final concentration of 0.2–1mg/ml. Continue reading

Inflammasomes and Pyroptosis

In today’s post, guest blogger,  Martha O’Brien, PhD, provides a preview of her upcoming AAI poster and block symposium talk on the inflammasome, caspase-1 activity and pyroptosis.

Schematic of the Caspase-Glo 1 Inflammasome Assay.

Schematic of the Caspase-Glo 1 Inflammasome Assay.

Responding rapidly to microbial pathogens and damage-associated molecular markers is critical to our innate immune system. Caspase-1 is pivotal in this process leading to processing and release of essential cytokines and an immunogenic form of cell death, termed pyroptosis. Upon sensing pathogen-associated and damage-associated molecular patterns (PAMPs and DAMPs), innate immune cells form inflammasome protein complexes that recruit and activate caspase-1 (canonical inflammasomes). In addition, other inflammatory caspases, 4 and 5 in humans and 11 in mice, directly bind bacterial lipopolysaccharides (LPS), triggering pyroptosis (non-canonical inflammasome). LPS-triggered non-canonical inflammasomes in mice and humans ultimately lead to canonical inflammasome engagement and caspase-1 activation (1–3).  Caspase-1 was originally termed interleukin converting enzyme (ICE) for its well-established role in processing IL-1ß and IL-18, two important inflammation cytokines. How caspase-1 mediates pyroptosis is less well understood, but is beginning to be delineated. Recently, a substrate of the inflammatory caspases, gasdermin D, was identified and its processed fragment, gasdermin-N domain, was shown to be required for pyroptosis in non-canonical inflammasome circumstances (4, 5). The precise role of gasdermin D in canonical inflammasome-triggered pyroptosis is still under investigation. Linking inflammatory caspases directly to pyroptosis is a notable step in understanding the mechanism of this important form of cell death.

Pyroptosis is clearly one means of releasing processed IL-1ß and IL-18 from the cell. However depending on the cell type and stimulus, there is evidence for inflammasome engagement, caspase-1 activation, and release of IL-1ß in the absence of cell death (6, 7). On the flip-side there is also evidence for caspase-1 mediated pyroptosis that helps clear bacteria, independent of IL-1ß and IL-18 involvement (8). To enable further studies on the inflammasome and in particular, assessing the connections between caspase-1 activation, pyroptosis, and cytokine release, Promega developed a new tool to conveniently monitor caspase-1 activation, the Caspase-Glo® 1 Inflammasome Assay.  This bioluminescent, plate-based assay is used to measure caspase-1 activity directly in cell cultures or to monitor released caspase-1 activity in culture medium from treated cells. This flexibility allows easy multiplexing to monitor all three outcomes of inflammasome stimulation; caspase-1 activity, pyroptosis, and release of IL-1ß and IL-18. Caspase-1 activation typically is monitored indirectly with western blots of processed caspase-1. Now the activity of the enzyme can be monitored directly, providing accurate information on temporal aspects of the inflammasome. The assay can be readily combined with real-time measures of cell death (e.g., CellTox™ Green Cytotoxicity Assay) and some of the culture medium can be removed for IL-1ß/IL-18 assessment, leaving the cells and remaining culture medium for caspase-1 activity measurements. At the upcoming meeting of the American Association of Immunologists (AAI) in Seattle, May 13th-17th, oral and poster presentations will highlight use of the Caspase-Glo® 1 Inflammasome Assay and its value for exploring the relationship between inflammasomes and pyroptosis.

References

  1. Schmid-Burgk et al. (2015) Caspase-4 mediates non-canonical activation of the NLRP3 inflammasome in human myeloid cells. J. Immunol. 45, 2911–7.
  2. Baker et al. (2015) NLRP3 inflammasome activation downstream of cytoplasmic LPS recognition by both caspase-4 and caspase-5. J. Immunol. 45, 2918–26.
  3. Ruhl, S. and P. Broz (2015) Caspase-11 activates a canonical NLRP3 inflammasome by promoting K+ Eur. J. Immunol. 45, 2927–36.
  4. Shi et al. (2015) Cleavage of GSDMD by inflammatory caspases determines pyroptotic cell death. Nature 526, 660–5.
  5. Kayagaki et al. (2015) Caspase-11 cleaves gasdermin D for non-canonical inflammasome signaling. Nature 526, 666–71.
  6. Gaidt et al. (2016) Human monocytes engage an alternative inflammasome pathway. Immunity 44, 833–46.
  7. Chen et al. (2014) The neutrophil NLRC4 inflammasome selectively promotes IL-1ß maturation without pyroptosis during acuteSalmonella Cell Reports 8, 570–82.
  8. Miao et al. (2010) Caspase-1-induced pyroptosis is an innate immune effector mechanism against intracellular bacteria. Nature Immunology 11, 1136–42.

Inflammasome Research: A Tool to Aid Progress

Inflammasomes: A Few Basics

Inflammasomes are protein complexes composed of immune system receptors and sensor molecules. These complexes can respond to both infectious organisms and molecules derived from host proteins. When activated, a series of receptors and molecules signal via either pathogen-associate molecular patterns (PAMPs) induced by microbial pathogens, or danger-associated molecular patterns (DAMPs) induced as a result of endogenous stressors; the common next step in signaling is through pattern recognition receptors (PRR).

Inflammasome diagram.

Innate immune response in inflammation; a basic diagram.

Inflammasome activation is integral to the host immune response in mice and humans (1). The activation results in signaling that activates the caspase-1 scaffold, causing release of immune mediators such as interleukins IL-1β and IL-18. So, whether inflammation is host tissue- or pathogen-induced, inflammasome activation results in a cascade of receptor signaling and mediator release, of which caspase-1 is a critical component.

Continue reading