N-isopropyl-4-[123I]iodoamphetamine (123I-IMP) products: a difference in radiochemical purity, unmetabolized fraction, and octanol extraction fraction in arterial blood and regional brain uptake in rats

Abstract

N-isopropyl-4-[123I]iodoamphetamine (123I-IMP) is a lipophilic compound utilized for cerebral blood flow (CBF) measurement with single photon emission computed tomography (SPECT). Two different 123I-IMP products (IMP(A) and IMP(B)) are commercially available. We examined the radiochemical purity, unmetabolized fraction, and octanol extraction fraction in arterial blood, and the regional brain uptake of IMP(A) and IMP(B) in a rat model. IMP(B) (96.4% +/- 0.08%, P < 0.05) showed significantly higher radiochemical purity than IMP(A) (95.5% +/- 0.20%). The mean unmetabolized fraction in arterial blood taken at 10 min after intravenous administration of IMP(B) (69.5% +/- 4.4%, P < 0.01) was significantly higher than that of IMP(A) (59.6% +/- 2.6%). The mean octanol extraction fraction of IMP(B) (75.0% +/- 1.3%, P < 0.01) was also significantly higher than that of IMP(A) (67.2% +/- 0.8%). The mean levels of radioactivity in arterial blood sampled at 10 min after injection and mean regional brain radioactivity (cerebral cortices, basal ganglia, brain stem, and cerebellum) at 10-12 min after injection were not significantly different between IMP(A) and IMP(B). The present study indicates differences in the radiochemical purity and the unmetabolized and octanol extraction fraction in arterial blood between the two commercially available 123I-IMP products. The appropriate octanol extraction fractions for IMP(A) and IMP(B) should be determined in humans and employed for quantitative CBF measurement in clinical SPECT.

Measurement of cerebral blood flow by the autoradiographic method with N-isopropyl-4-[I-123] iodoamphetamine: comparison of radiopharmaceuticals marketed by different companies in Japan

“…Mean ± SD are shown IMP B was significantly higher than those of IMP A, as in our previous studies [4,5,16]. We have measured the radiochemical purity of the two products each for several lots by TLC in the present and previous studies between 2005 and 2007 [4,5]. In both products, the radiochemical purity was similar among the lots.…”

“…Although no significant differences between the two products were observed in human whole body distribution, the octanolextracted fraction in whole blood differed significantly between the two products in both humans and rats perhaps because of the difference in radiochemical purity between the two products [4,5]. In the present study, the fraction of octanol-extracted components and radiochemical purity of Fig.…”

“…Radiochemical purity also differed significantly between the products [4]. Kanai et al [5] recently reported that slight but significant differences in the radiochemical purity of the two products resulted in differences in fractions of lipophilic and unmetabolized IMP in arterial blood in rats.…”

Development of an automated region-of-interest-setting program based on a deep neural network for brain perfusion single photon emission computed tomography quantification methods

“…As tracers that accumulate in brain tissue after passing through the Blood Brain Barrier (BBB), lipidsoluble substances such as N-isopropyl-p-[ 123 I]iodoamphetamine ( 123 I-IMP) and 99m Tc-ethyl cysteinate dimer ( 99m Tc-ECD) are widely used for cerebral blood ow single photon emission computed tomography (SPECT) [1][2][3][4][5][6][7]. Therefore, various regional cerebral blood ow quanti cation methods have been developed [8][9][10][11][12][13][14][15][16][17][18].…”