Your question about the bioavailability of peptide-mimic agents and the potential impact of pH on in vivo versus mammalian cell experiments is very pertinent, especially when considering the design of such agents for targeted organ delivery.

Here are a few thoughts on the key aspects:

pH Sensitivity in Biological Environments: Peptide-mimic agents, like peptides, often exhibit pH-dependent stability and functionality. The stability of these agents could be influenced by the pH of the environment they are exposed to, such as the acidic conditions in the stomach or the more neutral or slightly alkaline conditions in blood or tissues. pH can affect both the conformation and the charge state of the peptide, which in turn could influence its bioavailability, permeability, and ability to bind specifically to targeted organ cells.

pH Effects in Mammalian Cells vs. Animal Models: In vitro studies using mammalian cells generally have more controlled conditions, and pH can be tightly regulated within the cell culture medium. However, in vivo, pH can vary widely depending on the tissue, the presence of different metabolic environments, or even disease states. For example, tumors often have more acidic extracellular environments due to hypoxia, which could influence the behavior of peptide-mimic agents differently than under normal physiological conditions.

Cellular vs. Organ-Level pH: At the cellular level, mammalian cells can maintain a stable internal pH, but extracellular pH might still fluctuate. In vivo, however, you have not only cellular pH but also tissue and organ-level variations in pH. For example, the pH in the gastrointestinal tract (GIT) may influence the stability of oral peptide-mimic agents, while organs like the liver or kidneys may have their own pH gradients that impact drug uptake or clearance.

pH Stability of Peptide Mimics: The design of your peptide-mimic structure, particularly if it binds to specific organ cells, must take into account the pH variations within the target tissues. If the peptide-mimic agent is designed to be pH-sensitive (such as through pH-responsive linkers or groups), it might release its active compound only at specific pH levels. However, in animal models, these agents might face environments with pH fluctuations that are less easily controlled than in cell cultures. This could explain why the results from in vitro cell-based models might not always correlate with in vivo findings, particularly if the agent's stability is significantly influenced by pH.

Self-Stimulation Mechanisms: Some peptide-mimic agents, especially those designed with pH-sensitive groups, could exhibit self-stimulation mechanisms at particular pH ranges. These mechanisms could involve conformational changes, triggering the release of the drug or facilitating interaction with the target organ cells. The pH at which these transitions happen could be more easily controlled in vitro, but variations in tissue pH in vivo could lead to unpredictable responses, depending on how well the design adapts to physiological pH gradients.

Variable Results: You are absolutely correct that the variation in pH conditions between mammalian cells and animal models can lead to differences in experimental results. In mammalian cell cultures, a more controlled environment may reduce the variability seen in terms of pH stability and self-stimulation, while in animal models, tissue-specific pH gradients, metabolic variations, and systemic responses (such as blood flow and immune response) could all contribute to inconsistencies.

Key Factors to Consider for Your Experiment:

pH Stability of the Peptide Mimic: How stable is the peptide-mimic at different pH levels encountered in vivo? Consider designing the peptide to be stable in more acidic or neutral environments if it's targeting organs like the stomach, liver, or brain, where pH can differ from the typical neutral pH in blood.

pH-Responsive Linkers: If your peptide mimics have pH-sensitive linkers, consider testing these linkers in both cell-based models and in vivo models to see if their behavior is consistent across pH gradients.

In Vivo pH Mapping: To understand how tissue-specific pH could influence your results, performing studies where you map the pH across different organs or tissues could help explain discrepancies between mammalian cell data and in vivo data.

Testing Across Various Conditions: Consider evaluating the peptide-mimic under different conditions (different pH levels and environmental stresses) to see how its bioavailability, stability, and binding affinity vary.

In conclusion, the pH effect is indeed a crucial variable that can significantly influence the bioavailability and behavior of peptide-mimic agents, both in vitro and in vivo. Careful consideration of pH stability and design strategies to accommodate in vivo pH variations will be key in ensuring that your peptide-mimic agents perform as expected in a biological setting.

All respect..

Hezam Dhaifallah

Dear Mr Hezam Dhaifallah,

I think your comment is exactly which I am searching.

"Variable Results: You are absolutely correct that the variation in pH conditions between mammalian cells and animal models can lead to differences in experimental results. In mammalian cell cultures, a more controlled environment may reduce the variability seen in terms of pH stability and self-stimulation, while in animal models, tissue-specific pH gradients, metabolic variations, and systemic responses (such as blood flow and immune response) could all contribute to inconsistencies."

-> Essentially, we get the intention of testing by using spheroids and organoids to replace animal ultilization (you have known in advance). Obviously, variable results could be the hindrance shrinking back this evolution.

Thank you again for your suggestions and explanation. I am so looking forward to your answers on this topic in near future .

Best regardings,

Dear Hoang, while performing such experiments, always remember that pH governs the pKa and zwitter ion formation in polypeptides and demonstrates realistic changes in the overall functioning of peptides and proteins. Thus, any variation in pH stability or self-stimulation mechanisms in animal models definitely play a crucial role and bring variability in the experimental results.

So, first of all go through the requirements of experimental procedures from literature, only then design your experiment so that suitable outcomes can be obtained.

Thanks

Pawandeep Kour

Dear Mrs Pawandeep Kour,

I am really thankful for the reminder of "the pKa and zwitter ion formation in polypeptides and demonstrates realistic changes in the overall functioning of peptides and proteins" .

-> I guess it is required a full-text article for this evidential clarification; essentially for any specific case of peptides / proteins' functions changing accordingly .

Thank you again for your explanation. I have taken note this point carefully.

Best regardings,