Potential of N-acetylated-para-aminosalicylic acid to accelerate manganese enhancement decline for long-term MEMRI in rodent brain

Abstract

Background: Manganese (Mn(2+))-enhanced MRI (MEMRI) is a valuable imaging tool to study brain structure and function in normal and diseased small animals. The brain retention of Mn(2+) is relatively long with a half-life (t1/2) of 51-74 days causing a slow decline of MRI signal enhancement following Mn(2+) administration. Such slow decline limits using repeated MEMRI to follow the central nervous system longitudinally in weeks or months. This is because residual Mn(2+) from preceding administrations can confound the interpretation of imaging results. We investigated whether the Mn(2+) enhancement decline could be accelerated thus enabling repeated MEMRI, and as a consequence broadens the utility of MEMRI tests.

New methods: We investigated whether N-acetyl-para-aminosalicylic acid (AcPAS), a chelator of Mn(2+), could affect the decline of Mn(2+) induced MRI enhancement in brain.

Results and conclusion: Two-week treatment with AcPAS (200mg/kg/dose×3 daily) accelerated the decline of Mn(2+) induced enhancement in MRI. In the whole brain on average the enhancement declined from 100% to 17% in AcPAS treated mice, while in PBS controls the decline is from 100% to 27%. We posit that AcPAS could enhance MEMRI utility for evaluating brain biology in small animals.

Comparison with existing methods: To the best of our knowledge, no method exists to accelerate the decline of the Mn(2+) induced MRI enhancement for repeated MEMRI tests.

Keywords: Chelation; Manganese enhanced MRI (MEMRI); N-acetylated-para-aminosalicylic acid (AcPAS); Repeated MEMRI.

Figure 1

Study design. Mice were first administrated with MnCl₂, followed with PBS (n =3), low dose (n = 3, 100 mg/kg), medium dose (n = 3, 150 mg/kg) or high dose AcPAS (n = 3, 200 mg/kg) for two weeks. MRI was performed on the mice at one and two weeks after MnCl₂ administration. After the second MRI, the mice were immediately euthanized for ICP/MS analysis of brain Mn²⁺ concentrations.

Figure 2

AcPAS concentrations measured by HPLC in plasma (blue line) and in the brain regions (red lines). The concentrations in plasma were measured in ng/ml (left vertical axis), and in brain were measured in ng/mg (right vertical axis). The error bar at each time point shows the mean standard error of the measurement.

Figure 3

(A) MRI data. (a) Averaged MRI of mice (n = 9) at 24 hours after MnCl₂ administration. (b) Averaged MRI of PBS controls (n = 3, top panel) and high dose AcPAS treated mice (n = 3, bottom panel) at one week after MnCl₂ administration. (c) Averaged MRI of PBS controls (n = 3, top panel) and high dose AcPAS treated mice (n = 3, bottom panel) at two weeks after MnCl₂ administration. (B) Manganese enhancement maps corresponding to Figure 3A.

Figure 4

Brain regions with significantly less enhancement in mice after one (A) and two (B) weeks high dose AcPAS treatment compared to in PBS controls. The regions are shown in coronal slices, whose locations are indicated using red lines on the sagittal slices in the leftmost column.