Endotoxin Testing for Research Peptides: LAL, rFC and What an EU/mg Result Means

• ·Endotoxins are lipopolysaccharides from the outer membrane of Gram-negative bacteria. They are potent immune activators and can confound cell-based and animal research at very low levels.
• ·HPLC purity testing does not detect endotoxin. It takes a separate assay.
• ·The two main assay families are Limulus amebocyte lysate (LAL) and recombinant factor C (rFC).[1][2]
• ·Eppix commissions endotoxin screens on lots picked at random and publishes each result with the lot it was run on. Most lots are not screened, and a lot with no result was not tested.

Endotoxin activates Toll-like receptor 4 (TLR4) signaling in immune cells, triggering cytokine release.[3] In a research setting that is a confound: an inflammatory readout might reflect the peptide, the endotoxin riding along with it, or both.

It matters most for peptides studied in inflammation, tissue repair and immune models, such as KPV, BPC-157, TB-500 and thymosin-related compounds such as thymosin alpha-1. A contaminated lot can produce a strong "effect" that is really an endotoxin response.

Endotoxin is also heat-stable. It survives typical lyophilization and is not removed by sterile filtration, which removes bacteria but not the molecules they shed.

Research Material

Amino Acid Sequence

Chemical Structure

LAL is an extract of blood cells from the horseshoe crab. Endotoxin triggers an enzymatic cascade in the lysate, and that cascade can be read out in three ways.[1] The kinetic turbidimetric and chromogenic versions are quantitative and report a numeric result:

• ·Gel-clot: a pass/fail clot at a defined sensitivity.
• ·Turbidimetric: measures the increase in turbidity over time.
• ·Chromogenic: measures color released from a synthetic substrate.

rFC assays use a recombinantly produced version of factor C, the first enzyme in the LAL cascade, linked to a fluorescent readout. They avoid animal-derived reagents, and because they lack the alternate factor G pathway that lysates carry, they are not triggered by (1→3)-β-D-glucans, a known source of false positives in LAL.[4] USP has added a general chapter, <86>, for bacterial endotoxin testing with recombinant reagents, alongside its long-standing LAL chapter, <85>.[2]

FDA's guidance Pyrogen and Endotoxins Testing: Questions and Answers describes the compendial gel-clot, photometric and kinetic methods, and allows alternative methods provided they are validated and shown to achieve equivalent or better results.[1]

Results are reported in endotoxin units (EU), usually normalized to sample mass (EU/mg) or volume (EU/mL). Four things to read on the line:

• ·"< X EU/mg" means the result was below the assay's limit of detection for that sample. A lower X means a more sensitive test.
• ·A numeric value means endotoxin was detected and quantified.
• ·Spike recovery, sometimes shown as a positive product control, confirms the sample did not inhibit the assay. Test articles, peptides included, can interfere with the assay chemistry, so a valid result includes an inhibition/enhancement check.[1]
• ·What level is acceptable depends on the model. Primary immune cells and in vivo studies are far more sensitive than many biochemical assays. Define your threshold in the protocol before you look at the data.

• ·Use endotoxin-free consumables: pyrogen-free tubes, tips and water.
• ·Run a vehicle-only control prepared in the same solvent and consumables.
• ·Consider a polymyxin B control in cell assays. It neutralizes LPS and helps separate endotoxin effects from peptide effects.
• ·Record the batch ID, and keep the endotoxin result (where the lot has one) with the experimental record.

Every Eppix lot is tested for HPLC purity and measured content by an independent laboratory before it is sold (Janoshik Analytical for most lots), and the certificate is published. Most lots measure above 99% purity; an occasional lot comes back around 98% and is published as reported rather than left out.

Endotoxin works differently. It is one of three extra screens, with heavy metals and sterility, that Eppix orders on lots picked at random as quality control, so only a minority of lots carry one. When a lot was screened, the result appears on that lot's report page word for word as the laboratory printed it. When a lot shows no endotoxin result, it was not screened: the gap is a test that never ran, not a pass or a fail. All of it is on the certificates of analysis page.

A screen that a lot passed is a result about that lot. It is not a process control covering every lot, and it does not make research material suitable for use in people or animals.

Published Certificate

Select strength

10mg30mg

Batch

KPV-CA-26I-10

Purity (HPLC)

99.103%

Measured content

11.56 mglabeled 10 mg

Laboratory

Janoshik

Verify on the lab’s own databaseAll published certificates

Available at Eppix Labs

KPV

10mg · 30mg

Every batch tested by an independent laboratory, with the certificate published before sale.

From $49.99 USDIn stock