Proteins & Peptides
Many recombinant proteins and peptides have short half-lives of elimination in vivo. After a single injection, the plasma concentration of protein rises to a peak and may then decline rapidly until the compound is eliminated. The duration of activity following a single injection can be limited to several minutes or hours, hence biological effects either fail to develop or develop poorly.
When testing a novel recombinant protein in vivo, rapid elimination following injection can result in a mistaken assessment of potential activity. If no effect is observed, it is difficult to determine whether the protein is inactive, or if it simply was not present in adequate concentration and for a sufficient duration to elicit an effect.
Prolonging exposure to recombinant proteins by multiple daily injections results in repeated fluctuations in the level of protein in plasma and tissues, and corresponding variations in protein effects over time. Because the protein concentration is constantly changing during the time course of the experiment, the resulting data can be misleading as to the nature of protein effects and the dose required to elicit them. Additionally, repeated injections are stressful to the animal and difficult to maintain around-the-clock.
To ensure continuous delivery, the activity of recombinant proteins must be stable at 37º C for the duration of infusion. DURECT recommends verification of protein stability prior to using ALZET pumps. In some cases, it is appropriate to add 1-5% protease-free serum albumin or protein-specific carrier molecules for enhanced protein stability.
Selecting an Optimum Vehicle
Careful selection of an optimum vehicle for solubilizing the recombinant protein during infusion can often improve results. The criteria for vehicle selection should include sterility, the solubility of the protein to be delivered, tissue compatibility, and pH considerations for protein stability and physiological compatibility.
DURECT recommends non-lactated Ringer’s solution as the vehicle for the delivery of proteins soluble in aqueous media, as it is sterile, particle- and pyrogen-free, and non-irritating.
Many proteins adsorb nonspecifically to plastic materials. ALZET pumps are manufactured from elastomers selected to minimize adsorption. However, if adsorption is a concern, DURECT recommends addition of 1-5% protease-free serum albumin to the vehicle for infusion. Since adsorption is greatest proportionally at concentrations below 100 µg/ml, it is best to choose the pump with the lowest flow rate for a particular duration, and to prepare a more concentrated solution for delivery. Since plastic labware may contain contaminants such as residual plasticizers or monomers, it is best to prepare peptide solutions in glassware that is chemically clean and rinsed in metal-free deionized water.
Bacterial contamination can compromise protein stability and result in tissue irritation. Sterile technique should be used in filling, handling, and implanting ALZET pumps. DURECT recommends filling ALZET pumps through a 0.22 µM filter to ensure the sterility of the infusate.
- Ensure around-the-clock exposure to test agents at predictable levels
- Permit continuous administration of short half-life proteins and peptides
- Provide a convenient method for the chronic dosing of laboratory animals
- Minimize unwanted experimental variables and ensure reproducible, consistent results
- Eliminate the need for nighttime or weekend dosing
- Reduce handling and stress to laboratory animals
- Small enough for use in mice or very young rats
- Allow for targeted delivery of agents to virtually any tissue
- Cost-effective research tool
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Researchers are saying...
“We administered nicotine to achieve a steady-state concentration, using subcutaneously implanted minipumps, a technique that avoids the episodic hypoxic-ischemic episodes that accompany nicotine injections, and that also sidesteps the inherent problems of repeated handling stress and episodic withdrawal between injections” Slotkin et al., Neurotoxicology and Teratology 2002; 24:369-384.