In Vitro Concentration Ranges
Most published in vitro peptide studies use concentration ranges between 1 nanomolar (nM) and 100 micromolar (uM), with the active range typically falling between 10 nM and 10 uM depending on the peptide and assay system. Starting with a broad range and narrowing based on initial results is standard practice.
BPC-157 has been studied in vitro at concentrations ranging from 1 nM to 10 uM. GHK-Cu is typically studied at 0.1-10 uM for collagen synthesis assays. TB-500 research commonly uses 0.1-100 ug/mL in cell culture models.
Designing Dose-Response Experiments
A well-designed dose-response experiment uses at least 5-8 concentrations spanning 2-3 orders of magnitude. Common dilution schemes include half-log dilutions (3.16-fold between concentrations) or serial 3-fold dilutions. Both provide sufficient resolution to define the response curve shape.
Always include: a zero-concentration control (vehicle only), concentrations below the expected active range (to confirm baseline), concentrations above the expected plateau (to confirm maximum response), and the concentration range where the response transitions from baseline to maximum.
Unit Conversions
Peptide concentrations can be expressed in mass/volume (mg/mL, ug/mL, ng/mL) or molar units (M, mM, uM, nM). Converting between them requires the molecular weight.
Molar concentration = Mass concentration / Molecular weight
Example: BPC-157 (MW 1419 Da) at 1 ug/mL = 1 mg/L / 1419 g/mol = 0.705 uM = 705 nM
Molar units are preferred for comparing potency across different peptides because they normalize for molecular weight differences.
Reconstitution for Target Concentrations
Work backward from your desired working concentrations to determine the stock concentration and reconstitution volume. A stock solution 100-1000x more concentrated than your highest working concentration is practical — it allows accurate dilution while minimizing the volume of peptide solution added to each well or sample.
Example: Highest working concentration needed is 10 uM. A 1 mM (1000 uM) stock provides 100x dilution. For BPC-157 at 1 mM: 1 mM x 1419 g/mol = 1.419 mg/mL. Reconstituting a 5 mg vial in 3.52 mL gives approximately 1.42 mg/mL = 1 mM stock.
Documentation
Record the exact stock concentration, date prepared, lot number, and dilution scheme used for each experiment. This documentation is essential for reproducibility and for troubleshooting if results vary between experiments. Small errors in concentration preparation can produce large differences in biological response, especially in the steep portion of a dose-response curve.
