Turbidimetric Limulus Amoebocyte Lysate Assay: A Technique to Detect and Quantify Endotoxin Contamination in Nano-Formulated Drugs

Abstract

Source: Neun, B. W. et al., Detection of Endotoxin in Nano-formulations Using Limulus Amoebocyte Lysate (LAL) Assays. J. Vis. Exp. (2019)

This video describes the turbidimetric format of the Limulus amoebocyte lysate, or LAL, assay to estimate endotoxin contamination in PEGylated liposomal doxorubicin nano-formulations. The turbidity of the solution following the reaction of the endotoxin with the LAL reagent helps to estimate the endotoxin in the sample.

Protocol

1. Preparation of Nanoparticle Samples

1. Prepare the study sample in LAL grade water.
2. If the sample pH is outside of the 6-8 range, adjust the pH by using pyrogen-free sodium hydroxide or hydrochloric acid.
3. Using LAL grade water prepare several dilutions of the study sample. Make sure that the highest dilution does not exceed maximum valid dilution (MVD).

2. Preparation of Reagents Common Between LAL Formats

1. Dilute concentrated sodium hydroxide stock using pyrogen-free LAL reagent water to prepare a working solution at a concentration of 0.1 N.
2. Dilute concentrated hydrochloric acid ....

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Sodium Hydroxide	Sigma	S2770	When needed, it is used to adjust sample pH to be between 6-8
Hydrochloric acid	Sigma	H9892	When needed, it is used to adjust sample pH to be between 6-8
LAL Reagent	Associates of Cape Cod	T0051	This reagent can be used with turbidity assay only
Control Endotoxin Standard	Associates of Cape Cod	E0005	This reagent can be used with turbidity and gel-clot assays
LAL grade water	Associates of Cape Cod	WP0501	This reagent can be used with any LAL format
Glucashield Buffer	Associates of Cape Cod	GB051-25	Used to prevent false-positive response from beta-glucans
Disposable endotoxin-free glass dilution tubes 12 x 75 mm	Associates of Cape Cod	TB240	These tubes can be used with all three assays
Disposable endotoxin-free glass reaction tubes 8 x 75 mm	Associates of Cape Cod	TK100	These tubes can be used with turbidity and chromogenic assays
Pyrogen-free tips with volumes 0.25 and 1.0 mL	RAININ	PPT25, PPT10	Tips and pipettes may adsorb endotoxin and release leachables which interfere with LAL assay. These RAININ tips are used because their optimal performance in the LAL assay was verified and confirmed
Pyrogen-free microcentrifuge tubes, 2.0 mL	Eppendorf	22600044	Other equivalent supplies can be used
Pyrogen-fee combitips, 5mL	Eppendorf	30089669	Other equivalent supplies can be used
Repeat pipettor	Eppendorf	4982000020	Other equivalent supplies can be used
Microcetrifuge	any brand		Any brand can be used
Refrigerator, 2-8 C	any brand		Any brand can be used
Vortex	any brand		Any brand can be used
Freezer, -20 C	any brand		Any brand can be used
Pyros Kinetix or Pyros Kinetix Flex reader	Associates of Cape Cod	PKF96	Other instruments can be used. However, LAL reagents and endotoxin standards used in this assay may require optimization. When other instrumentation is used, please refer to the instrument and LAL kit manufacturers for instructions