Figure 5.

Kinetics of luciferase knockdown by siRNA in nondividing hepatocytes in BALB/c mice. Experimental and predicted results are shown for luciferase knockdown after hydrodynamic tail-vein co-injection of 5 µg pApoEHCRLuc and 50 µg siRNA per 20 g mouse on day 0. Circles represent the ratio of the average luciferase signal intensity from three mice receiving plasmid + siRNA to the luciferase signal intensity from three mice receiving plasmid alone. The predicted luciferase knockdown, given by the solid line, was calculated using the baseline in vivo parameters given in Table 2 with the following modifications to account for hydrodynamic injection of naked siRNA without a delivery vehicle: eliminate steps involving the complexes (kescendvec, kunpackend, kunpackcyt), modify uptake and intracellular trafficking to match observed kinetics (partition = 1 × 10⁻², ktransblood = 1, kint = 1 ×10⁻³ h⁻¹, kescendna = 1 × 10⁻² h⁻¹, kdegendna = 5 × 10⁻³ h⁻¹), and modify extracellular volume (Ve = 1.5 × 10⁻⁵ L). The kescendna and kdegendna may no longer represent endosomal processes as hydrodynamically injected naked siRNA may be internalized through different vesicles or partitioned into a separate intracellular compartment (e.g. nucleus) that exhibits different degradation and release kinetics than in standard or receptor-mediated endocytosis of siRNA-containing complexes. The total number of hepatocytes was chosen to be 5 × 10⁷, on the same order of magnitude as the number of hepatocytes in a mouse liver (40,41).