A newly characterized opioid substance (Peak B) in human spinal fluid produced pain relief 10× more potent than morphine per weight, with both mu and delta receptor activity.
10× more potent than morphineBy weight, when injected into mouse brains
What the researchers found
Human cerebrospinal fluid (CSF) from pain-free surgery patients contained Peak B at a concentration equivalent to about 1.4 picomoles of morphine per milliliter.
Injected into mouse brains, Peak B produced dose-dependent pain relief at 0.06 and 0.12 picomoles of morphine equivalents. Naloxone (an opioid blocker) reversed this effect, confirming it works through opioid receptors.
In a muscle tissue assay (mouse vas deferens), Peak B's activity was blocked by low naloxone concentrations but not high ones. This unusual pattern suggests it interacts with opioid receptors differently than known opioids.
Most surprisingly, Peak B was not destroyed by trypsin or alpha-chymotrypsin, protein-digesting enzymes that break down all known opioid peptides. This means Peak B is either not a peptide or has an unusual structure that protects it from enzymes.
Why it matters
The human spinal fluid contains opioid substances we have not yet identified. Peak B correlates with pain status in chronic pain patients and resists enzymatic breakdown. If characterized, it could lead to new types of painkillers that last longer because they resist normal degradation.
How the study worked
Peak B was isolated from human CSF using gel filtration chromatography. Pain relief was tested in mice by intracerebroventricular injection with hot-plate and tail-flick tests. Opioid specificity confirmed with naloxone. Mouse vas deferens bioassay tested tissue-level effects. Enzyme resistance was tested with trypsin and chymotrypsin.
What this study cannot tell us
Peak B was not fully characterized or identified. The active component could be a modified peptide, a non-peptide opioid, or a mixture. The mouse pain tests may not predict human effects. The number of CSF samples was small.
How to read the evidence
Preliminary in-vitro/animal study characterizing a novel substance — identity not fully determined.
When this study was published
Published in 1987 — the full identity of Peak B remains an area of research.
The bigger picture
The human body may contain undiscovered natural painkillers more potent than morphine. Identifying and characterizing these could lead to new pain treatments with fewer side effects than synthetic opioids.
Questions still open
- What is the exact chemical identity of Peak B?
- Could synthetic analogs of Peak B serve as safer painkillers?
- Why is Peak B related to chronic pain patient status?
Common questions
What is Peak B?
Why is this substance important for pain treatment?
Read the original research
Partial characterization of a novel endogenous opioid in human cerebrospinal fluid.
Life sciences, 41(23), 2535-45
Citation
Miller, B E; Lipman, J J; Byrne, W L. (1987). Partial characterization of a novel endogenous opioid in human cerebrospinal fluid.. Life sciences, 41(23), 2535-45.