TB-500: what product testing can and cannot tell you

When it comes to the TB-500, the question of "quality or fake" is more complicated than it seems. TB-500 is not an approved human medicine; retail claims of “pharmaceutical grade” do not establish an authorized, regulated product. The editors explain what parameters determine the quality of a peptide, what can actually be checked and what cannot, and what alarm signals should be paid attention to.

What does a "quality" peptide even mean

In pharmaceuticals, the quality of a medicinal product is described by a set of specifications — requirements that each batch must meet. For biotechnological and peptide products, these requirements are summarized, in particular, in the ICH Q6B guideline. Quality is not a single number of "purity", but a combination of several independent characteristics.

• Identity — the vial contains exactly the declared molecule.
• Purity is the proportion of the target peptide among all peptide components.
• Quantitative content — exactly how much peptide is in the bottle.
• Sterility is the absence of viable microorganisms.
• Bacterial endotoxins — content of pyrogenic substances within permissible limits.
• Foreign substances — residual solvents, reagents, heavy metals.

The product may meet some requirements and not others. For example, a peptide of high chromatographic purity may be non-sterile or contain endotoxins. Conversely, a sterile solution may contain the wrong molecule. Therefore, it is necessary to evaluate everything in a complex.

For registered medicines, compliance with specifications is the responsibility of the good manufacturing practice (GMP) manufacturer, and the regulator inspects production. There is no such system for "research" peptides. The buyer actually relies only on the seller's word.

That is why the editors emphasize: even the "best" TB-500 from the unofficial market cannot be considered high-quality in the pharmaceutical sense. You can only reduce the probability of the worst problems, but not guarantee safety.

Which molecule is in the bottle: the problem of identity

The first and most important problem is the ambiguity of the name itself. At least two different substances are sold under the brand TB-500. In doping analysis, TB-500 was identified as a synthetic N-acetylated fragment 17–23 of thymosin beta-4 with the sequence LKKTETQ (Esposito et al., 2012). At the same time, some sellers claim a full-sized protein of 43 amino acids.

These molecules differ fundamentally. Complete thymosin beta-4 has a molecular weight of about 4.9 kDa, and the acetylated heptapeptide - about 890 Da, that is, about five and a half times less. Mass spectrometry makes it easy to tell them apart, but the label often doesn't show the difference at all.

In addition to the declared options, there are products with another peptide, with a small amount of the active substance or without it at all. In the illegal market of doping drugs, in general, the inconsistency of the content of the label was described repeatedly - from an understated amount to a complete substitution.

A separate problem is related impurities: peptides with missing or extra amino acids, incompletely removed protective groups, racemized residues. They are formed during solid-phase synthesis and, with poor purification, can make up a significant proportion of the product.

Laboratory control methods

The main method for evaluating the purity of peptides is high-performance liquid chromatography (HPLC). The sample is separated on the column, and each component gives a peak in the chromatogram. Purity is expressed as a fraction of the area of ​​the main peak from the total area of ​​all peaks. However, HPLC alone does not prove that the main peak is the correct molecule.

To confirm the identity, mass spectrometry is used, most often in combination with chromatography (LC-MS). It determines the molecular weight of the components and allows you to confirm that the main peak corresponds to the declared molecule. For more complex cases, fragmentation and sequence analysis are used.

Quantitative peptide content is a different indicator than purity. The lyophilisate contains, in addition to the peptide, counterions (for example, trifluoroacetate remaining after purification), water and other excipients. Therefore, the actual content of the peptide in the powder is usually lower than the declared mass. It is determined by amino acid analysis or quantitative chromatography with a standard.

Sterility and endotoxins are checked by separate pharmacopoeial tests: the sterility test (inoculation on nutrient media) and the bacterial endotoxin test (LAL test based on horseshoe crab amebocyte lysate). None of the chemical analyzes replaces these indicators.

Certificate of analysis: how to read and where the catch is

Peptide sellers often add a Certificate of Analysis (CoA) to the product with impressive purity. The very fact of its presence means little: the document can easily be forged, copied from another batch, or produced based on the analysis of a completely different sample.

The editors highlight typical "red flags" in the following documents:

1. The name and contact details of the laboratory that performed the analysis are missing, or the laboratory cannot be located and verified.
2. The batch number in the certificate does not match the number on the bottle or is missing.
3. Only "HPLC purity" is given without mass spectrometric confirmation of identity.
4. It is not specified which molecule was analyzed - a fragment or a complete protein, and its expected mass.
5. There are no data on endotoxins and sterility, which are critical for an injectable product.
6. Identical chromatograms or purity values ​​for different lots and even different peptides.

Even an impeccably designed certificate from a real laboratory characterizes only a specific sample at a specific moment. It does not guarantee that all vials of the batch are the same, that the product was stored correctly and that sterility was not violated during packaging.

Independent testing of an individual vial by a third-party laboratory provides more information than a vendor's certificate, but even that usually only covers identity and purity. Full pharmacopoeial control, including sterility, for one bottle is practically impossible.

What can be evaluated independently

Without a laboratory, the buyer's options are limited to a visual inspection. It does not confirm quality, but it is able to detect gross problems. The lyophilisate should look like a uniform white or almost white "tablet" or powder, without spots, clumps, or drops of moisture. The bottle is whole, with an intact stopper and aluminum cap.

The absence of a batch number and production dates, blurred or inconsistent labels on bottles of the same batch, foreign particles, very small or, on the contrary, disproportionately large volume of powder for the declared quantity should be alarming. After dissolution, the product should be transparent, without turbidity and flakes.

Price can also be a signal: synthesis and purification of peptides, especially long ones, cost a lot of money. Suspiciously cheap "full-size thymosin beta-4" is most likely not what it claims to be. However, a high price also does not guarantee anything.

The most important limitation: no visual test will detect peptide replacement, insufficient content, chemical impurities or endotoxins. Therefore, the "good look" of the product should not create a sense of security.

Editorial conclusions

Peptide quality is determined by identity, purity, quantitative content, sterility and level of endotoxins. For the TB-500, none of these parameters are controlled by an independent regulator.

Different molecules are sold under the name TB-500 - a short fragment and a complete protein - which differ in mass several times and have a different evidence base. They can be distinguished only by mass spectrometry.

Certificates of analysis from vendors are easily forged and usually do not include data on sterility and endotoxins, the most important parameters for an injectable product. A visual inspection reveals only the grossest defects.

We also recommend that you read our materials on the storage and stability of TB-500, its side effects and the status of thymosin beta-4 on the WADA list and legislation.

References

1. Esposito S, Deventer K, Goeman J, et al. Synthesis and characterization of the N-terminal acetylated 17–23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. Drug Test Anal. 2012;4(9):733–738.
2. International Council for Harmonisation. ICH Q6B: Specifications: Test Procedures and Acceptance Criteria for Biotechnological/Biological Products. 1999.
3. Manning MC, Chou DK, Murphy BM, et al. Stability of protein pharmaceuticals: an update. Pharm Res. 2010;27(4):544–575.
4. United States Pharmacopeia. General Chapter <71> Sterility Tests. Rockville, MD: USP.
5. United States Pharmacopeia. General Chapter <85> Bacterial Endotoxins Test. Rockville, MD: USP.
6. Goldstein AL, Hannappel E, Kleinman HK. Thymosin β4: actin-sequestering protein moonlights to repair injured tissues. Trends Mol Med. 2005;11(9):421–429.