Amplex UltraRed

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Amplex UltraRed

Description

Amplex UltraRed (AmR) is used as an extrinsic fluorophore for measurement of hydrogen peroxide production (ROS) by cells or mitochondrial preparations. The reaction of H2O2 and AmR is catalyzed by horseradish peroxidase to produce the red fluorescent compound resorufin (excitation wavelength 563 nm, emission 587 nm). The change of emitted fluorescence intensity is directly proportional to the concentration of H2O2 added, whereby the H2O2 is consumed.

Abbreviation: AmR

Reference: Mohanty 1997 J Immunol Methods, Zhou 1997 Anal Biochem, Mishin 2010 Free Radical Biol Med, Towne 2004 Anal Biochem, Krumschnabel 2015 Methods Mol Biol


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Sources of AmR

Trade Mark Manufacturer/ Distributor
price [€/mg]
product id
Additional information
Amplex Red
Life Technologies
37.4
A12222
Amplex Ultra Red
Life Technologies
48.8
A36006
Ampliflu Red
Sigma
18.5
90101
Quanta Red
Thermo scientific
15150


Citation Amplex HRP pH Limit of detection
stock final unit definition stock final
mM
µM
U/ml
U/ml
BIOTEK
10
50
pyrogallol
10
0.1
7.4
4 nM (absorption 300 nm)
Life Technologies
10
50
10
0.1
6 to 7.5
<80 nM
Towne 2004
160
0.41
7.5 to 8.5
100 nM
Zhou1997
3 ?
0.3 to 1
50 nM (10 nM optimal)
Mohanty 1997
100
10 to 100
1
18 nM
Komary 2010
1
2.5


Amplex UltraRed in O2k-FluoRespirometry

In high-resolution respirometry HRR the Amplex Red method[1] is used with the O2k-FluoRespirometer (O2k-Series D-G: O2k-Fluo LED2-Module) selecting the Fluorescence-Sensor Green and Smart Fluo-Sensor for O2k-Series H. Use black stoppers with black cover-slips to exclude disturbances by external light sources. The fluorescence sensors are inserted though the windows of the O2k-Chambers[2]. The O2k has also been coupled to a fluorescence spectrophotometer with a light guide inserted through the black PEEK stopper.[3]
The use of AmR in HRR to simultaneously determine respiration and H2O2 flux has been intensively tested in the Oroboros lab (see references).

Preparation of AmR solution

  • Amplex UltraRed from Life Technologies (former Invitrogen): A36006; 6* 1 mg commercial vials, store at -20°C.
Preparation of 10 mM stock solution (dissolved in DMSO) - see also Manual Amplex UltraRed by Life Technologies.
  1. Dissolve one commercial vial of Ampler UltraRed (~1 mg) in 340 µL DMSO.
  2. Divide into 20 µL portions into 0.2 mL Eppendorf tubes.
  3. Store frozen at -20 °C in the dessicator.

Storage solution = stock solution

Prepare a 10 mM storage solution of Amplex® UltraRed reagent (AmR), which will also serve as stock solution, by adding 340 μL of fresh, high‑quality DMSO (Sigma D8418) to one commercial vial of Amplex® UltraRed reagent (1 mg). Vortex well to dissolve. Protect AmR from light and moisture. The storage solution should then be divided into 10 µl aliquots and stored in the dark, protected from moisture at –20°C for future use. When stored properly, the 10 mM storage solution is stable for 6 months. We have observed that after long-term storage AmR may exert a profound inhibitory effect on cell respiration.
Note: The preparation of the 10 mM storage solution follows the procedure suggested by the manufacturer. The manufacturer states only an approximate molecular weight for the Amplex® UltraRed formulation and does not publish details how the Amplex® UltraRed formulation deviates from the substance 10-acetyl-3,7-dihydroxyphenoxazine (CAS# 119171-73-2), known as Amplex® Red.

Final AmR concentration

Titration into into 2 mL O2k-Chamber: 2 µL of 10 mM AmR stock solution, final concentration of 10 µM AmR.
AmR, similar to other chemical probes, may exert an inhibitory effect on mitochondrial and cell respiration. AmR, therefore, should be used at the lowest concentration compatible with the total H2O2 production in an experimental run, including calibrations and chemical background conversion of AmR [4],[5].
You may add 1 µL of the 10 mM stock solution for brief measurements to obtain a final concentration of 5 µM. Optimize the final AmR concentration according to respiration media, sample type and concentration, and experimental protocol. These determine the total AmR consumption by H2O2 production during the experiment (check by initial and final H2O2 titrations for calibration). The final concentration of AmR becomes diminished during an experiment due to AmR consumption and dilution by titrations in a SUIT protocol. Check for any potential effects of the experimental AmR concentration on respiratory activity of cells or mt-preparations, by titration of AmR after a specific respiratory state has been reached in a control experiment.

Horseradish peroxidase

Titration into into 2 mL O2k-chamber: 4 µL of HRP stock solution, final concentration 1 U/mL.
Horse radish peroxidase (Sigma-Aldrich P 8250 - 5 kU): Prepare a stock solution with 500 U HRP/mL in MiR05 or MiR05Cr; the solution can be used as storage solution at -20 °C.

Superoxide dismutase

Superoxide dismutase (SOD) is included to generate H2O2 from superoxide.
(Sigma-Aldrich S 8409-15KU): Depending on the batch the SOD preparation may contain a specific activity of 2,000–6,000 units/mg protein. We recommend to use the enzyme at 5 U/mL, the final volume to be added to the respiratory chamber has thus to be adjusted accordingly.
Experiments can be performed in the absence of SOD.

Calibration with H2O2

Calibration standards of H2O2: Commercial solution (Sigma-Aldrich 323381 - 25 mL hydrogen peroxide solution 3 wt.%; stabilized with acetanilide, c. 200 ppm) = 880 mM H2O2.
  1. Prepare a HCl stock solution of 10 µM HCl.
  2. H2O2 dilution 1 (1:88): add 10 µL of a commercial stock solution of 3 wt. H2O2 to 870 µL 10 µM HCl solution, to obtain a 10 mM H2O2 solution.
  3. H2O2 dilution 2 (1:250):add 4 µL of 10 mM H2O2 solution to 996 µL 10 µM HCl solution, to obtain the H2O2 stock solution of 40 µM.
The H2O2 calibration solution has to be prepared fresh everyday, kept away from light exposure and avoid freezing it.
Titration into into 2 mL O2k-Chamber: 5 µL of the 40 µM H2O2 stock, step increase of 0.1 µM H2O2. One to three subsequent steps. Titrations are peformed after addition of respiration medium, HRP and Amplex UltraRed to the O2k-Chamber. We suggest to perform calibrations at the beginning (sample already present), intermittently at various respiratory states, and near the end of an experiment (but before cytochrome c, catalase or other substances are added that interfer with the H2O2 measurement).
DatLab supports automatic H2O2 calibration by calculating the calibration parameters by linear regression and graphical display of the calibration regression.
Since part of the signal change is caused by an ongoing H2O2 production of the biological sample, the calibration is corrected for the slope.


Experimental media for the AmR assay

Media with high antioxidant activity compete with HRP and partially consume H2O2 before it can react with AmR to form the active fluorophore UltroxRed (similar to resorufin). This was shown by comparing the resorufin-sensitivity and H2O2-sensitivity [6],[7].
  • H2O2-sensitivity: the change of fluorescence signal per µM H2O2 added in calibrations with H2O2 titration in media containing HRP and AmR.
  • Resorufin-sensitivity: the change of fluorescence signal per µM resorufin added in calibrations with resorufin titration in media containing HRP and AmR.
The H2O2-sensitivity is much higher in a simple phosphate buffer compared to media with strong antioxidant capacity. In contrast, this is not the case for the resorufin-sensitivity.


HRP-independent background AmR flux

In the absence of sample, there is a spontaneous increase of the ultroxred fluorescence signal over time, the extent of which depends on components of the respiration medium (Krumschnabel et al 2015). The sensitivity – the change in fluorescence per unit of H2O2 produced in or added to the chamber – depends on the medium and tends to decline over time. Both the background change in fluorescence and the change in assay sensitivity over time need to be corrected for in data analysis, for which DatLab-Analysis templates are available.


A study by Miwa et al 2016 (Free Radical Bio Med 90:173) suggests that this phenomenon is related to a mitochondrially expressed carboxylesterase which converts Amplex Red to resorufin at a high rate. The issue can be relatively easily solved by adding a protease inhibitor to various mitochondrial preparations as described here.
For further informaton see the Discussion page.

Artefacts

Votyakova TV and Reynolds IJ (Archives of Biochemistry and Biophysics 431(1):138-44. 2014) revealed that NADH and the reduced glutathione is able to react with AmR in the presence of O2 and HRP and create a background in the absence of mitochondria. If the mitochondria remain intact, this above-mentioned reaction is negligible. If you add SOD (superoxide dismutase),you can avoid this side-effect of the AmR assay.

Substances incompatible with the Amplex Red method

The following substances/ classes of substances are strictly incompatible with the Amplex Red method for theoretical reasons:
  • Strongly redox-active substances, e.g. cytochrome c, TMPD/Ascorbate
  • Catalase and other substances consuming or scavenging H2O2. The effect of substances in the medium that consumes H2O2 slowly is taken account of by the calibration procedure. However, such substances decrease the sensitivity of the method. Note that catalase can be a valuable tool for checking for artifacts.


The effect of other substances should be checked by blank experiments, including comparing the sensitivity (result of calibration) before and after injecting the substances.
In preliminary experiments Oroboros Instruments evaluated small amounts (as typically used in SUIT protocols) of the following substances as compatible with the method:
DMSO, ethanol, malate, glutamate, pyruvate (a strong scavanger of H2O2), succinate, (ADP + Mg2+), (ATP + Mg2+), rotenone, FCCP, CCCP, oligomycin, antimycin A, malonate, myxothiazol

Avoiding artefacts

The Amplex method is based on the H2O2 dependent oxidation of AmR to UltroxRed by HRP. Under unfavorable conditions AmR may be oxidized even in the absence of H2O2. At a small rate such an oxidation occurs in the presence of HRP even without any sample present. The magnitude of this background signal ("drift") depends, among other things, on the light intensity used and can therefore be minimized by using the suggested or lower light intensity. Components of the sample may however induce a far higher, non H2O2 related rate of AmR oxidation. Therefore, especially when applying the method on new types of samples the method should be checked for artifacts. A few approaches are listed here:
Sequential addition of HRP and AmR: This method is particular easy to implement if AmR and HRP have to be added to the chamber already containing the sample anyway: First, inject Amplex Red and wait a few minutes for flux stabilization. The Amp slope has to stay near zero. Then add HRP. The Amp slope should increase and correspond to the H2O2 production. If a significant Amp slope is detected before the addition of HRP this increase in fluorescence is not caused by H2O2 production. The experiment can be continued as usual after this test. If the sample is injected routinely into the chamber already containing AmR and HRP the method can not be applied. In this case it is suggested to change this sequence at least for one experiment.
Addition of catalse: After a H2O2 flux (production) is established, a high dose (e.g. 10 µL of a 280,000 U/mL stock solution) of catalase is injected. Catalase competes with HRP for the available H2O2. Then the apparent H2O2 production (the Amp slope) should be reduced to near zero as a control for distinguishing an unspecific chemical background slope from H2O2 dependent Amplex Red oxidation.
Note: The experiment cannot be continued afterwards for measurement of hydrogen peroxide production, whereas respiration can be recorded onwards.

Nitrogen injection

  • Injection of nitrogen to decrease the oxygen concentration in the O2k-Chamber.
  1. Open chamber: Before injecting nitrogen gas, opening of the O2k-Chamber is needed to obtain a defined gas volume above the aqueous phase.
  2. Using the Syringe\60 mL\Gas-Injection nitrogen is injected into the gas phase of the O2k-Chamber.
  3. Close the chamber when the O2 concentration approaches the desired O2 level.

Experimental SOP

H2O2 flux analysis

References

  1. Mohanty 1997 J Immunol Methods
  2. Hickey 2012 J Comp Physiol B
  3. Anderson 2011 Am J Physiol Heart Circ Physiol
  4. Makrecka-Kuka M, Krumschnabel G, Gnaiger E (2015) High-resolution respirometry for simultaneous measurement of oxygen and hydrogen peroxide fluxes in permeabilized cells, tissue homogenate and isolated mitochondria. Biomolecules 5:1319-38. - »Bioblast link«
  5. Komlodi T, Sobotka O, Krumschnabel G, Bezuidenhout N, Hiller E, Doerrier C, Gnaiger E (2018) Comparison of mitochondrial incubation media for measurement of respiration and hydrogen peroxide production. Methods Mol Biol 1782:137-55. - »Bioblast link«
  6. Krumschnabel G, Fontana-Ayoub M, Sumbalova Z, Heidler J, Gauper K, Fasching M, Gnaiger E (2015) Simultaneous high-resolution measurement of mitochondrial respiration and hydrogen peroxide production. Methods Mol Biol 1264:245-61. - »Bioblast link«
  7. Komlodi T, Sobotka O, Krumschnabel G, Bezuidenhout N, Hiller E, Doerrier C, Gnaiger E (2018) Comparison of mitochondrial incubation media for measurement of respiration and hydrogen peroxide production. Methods Mol Biol 1782:137-55. - »Bioblast link«
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