Liposomal Gd-DTPA: preparation and characterization of relaxivity.

Abstract

Gadolinium diethylenetriaminepentaacetic acid (DTPA) has not proved particularly useful for hepatosplenic magnetic resonance imaging. However, by entrapping the Gd-DTPA within lipid vesicles, one may exploit the ability of the reticuloendothelial system to endocytose particulates, permitting passive delivery of contrast agent to the liver and spleen while decreasing the rate of clearance of Gd-DTPA from the vasculature. Liposomes of 70-400 nm diameter containing Gd-DTPA were prepared by a freeze-thaw extrusion process. These exhibited high trapping efficiencies and excellent stability during storage. For all sizes of liposomes, the relaxivity of the entrapped Gd-DTPA was less than that of free Gd-DTPA. Relaxivity varied linearly with the surface-area-to-volume ratio of the liposomes; the smaller the liposomes, the greater the relaxivity. Liposomes containing cholesterol had a lower relaxivity than liposomes without cholesterol. The authors suggest this reflects the decrease in the water permeability coefficient caused by the presence of cholesterol in the liposome membrane.

Targeted pharmaceutical nanocarriers for cancer therapy and imaging

“…First, the reporter metal is chelated into a soluble chelate (eg, diethylenetriamine pentaacetate [DTPA]) and then included in the interior of a liposome. 155 Alternatively, DTPA or a similar chelating compound may be chemically derivatized by the incorporation of a hydrophobic group, which can anchor the chelating moiety onto the liposome surface during or after liposome preparation. 156 Different chelators and different hydrophobic anchors were tried for the preparation of 111 In, 99m Tc, Mn-, and Gd-liposomes.…”

Size-Induced Enhancement of Chemical Exchange Saturation Transfer (CEST) Contrast in Liposomes

“…Under these two assumptions, the time-dependent PTR following a RF pulse duration of T sat is 21 (5) where r 1w = R 1w + k wl is the effective relaxation rate. R 1w represents the longitudinal relaxation of water in the presence of paramagnetic agents and can be calculated from the agentfree relaxation rate (R 1w,0 ) and the exchange rate 22 (6) The saturation efficiency α is determined by the power of the RF pulse and the exchange and relaxation rates of water protons: (7) where ω 1 is the power of the RF pulse, p = r 2l -k lw k wl /r 2w and q = r 1l -k lw k wl /r 1w , with r 1l = R 1l + k lw , r 2l = R 2l + k lw and r 2w = R 2w + k wl . Since R 2w in a dilute liposome sample does not affect the PTR as significantly as R 1w , as a good approximation, the transverse relaxation rate of water without liposomes can be used.…”

Intracerebral Diffusion of Paramagnetic Cationic Liposomes Containing Gd(DTPA)2- Followed by MRI Spectroscopy: Assessment of Patternc Diffusion and Time Steadiness of a Non-Viral Vector Model

“…The liposomes were prepared by the thin film hydration method (26). Briefly, chloroform/methanol solutions of the two lipids were rotary-evaporated to dryness and the resulting lipid film was further dried under vacuum for 2 h. Multilamellar liposomes were obtained by hydrating the lipid film with isotonic Gd(DTPA)"-complex solutions, giving a total liposome concentration of 4 mg/mL (27)(28). The liposomes were allowed to swell for two hours and were subjected to five freeze-thaw cycles in liquid nitrogen (29) according to reported procedures.…”