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.

Verifying Protein Stability

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.

Minimizing Absortion

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 0.1 to 1% 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.

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.

Maintaining Sterility

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.