Question (73949) | Complex I Enzyme Activity Microplate Assay Kit (Colorimetric) (ab109721)

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Question

Do you have any recommendations for OXPHOS assays made specifically for blood?

Answer

My guess is that the levels of OXPHOS proteins in whole blood are below the level of detection for activity assays. The activity assays for the most part require higher loading than the sandwich ELISA assays. We have tested Complex IV Quantity with whole blood with good results.



The caveat is that whole blood must be fresh or must be frozen viable (protocols can be found in the literature). Whole blood should not be loaded in terms of mg of protein as most of the protein present in whole blood is albumin, so using the loading guidelines for tissues to load whole blood will result in loading well below the detection level (OXPHOS proteins are present in leukocytes and platelets only). My suggestion for the customer (if they want to use the quantity dipstick kits) would be to mix 300uL of blood with 900uL of extraction buffer, follow the protocol in regards to the rest of the sample preparation (ice incubation, centrifugation, keeping the supernatant and discarding the pellet). I would advise to the customer to add protease inhibitors to the extraction buffer to prevent degradation of proteins after extraction as granulocytes from blood have high levels of proteases, which will be released once the detergent is added.



For loading on the dipsticks, the blocking buffer should be mixed with 50uL – 100uL of extracted blood so that the final concentration of blocking is 1X. This mixture can then be used to resuspend the gold conjugated antibody dried at the bottom of the well. Once the gold is resuspended the dipstick can be added to the well and allowed to wick the protein fully. Results will not be perfectly accurate (as loading cannot be done in terms of mg of protein), but will be more qualitative in terms of percent of signal from control mean or relative units. This approach will therefore require you to set up a control sample, which should be a pooled sample from several normal donors (10 – 20 donors would be ideal). From our experience, whole blood will not be as accurate as measuring isolated PBMCs only. But it will allow you to have a rough estimate of the trend.

The advantage of isolating PBMCs is that they could run both activity and quantity dipsticks/microplates by following the same guidelines of cultured cells.

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