Experimental acute cerebral ischemia with reperfusion. Evaluation with gadolinium-texaphyrin

Behavior of new complexes of tetrakis(4-methoxylphenyl)porphyrin with heavy rare earth elements in reversed-phase high performance liquid chromatography

An HPLC method has been developed for the separation of new complexes of tetrakis(4-methoxylphenyl)porphyrin (TMOPP) with four heavy rare earth elements (RE = Y, Er, Tm, and Yb). The function of amine and acid in the mobile phase has been investigated and a reasonable explanation is presented. Successful separation of the RE-TMOPP-Cl complexes is accomplished in 10 min with a mobile phase consisting of methanol-water-acetic acid-triethanolamine. The detection limits (S/N= 3) for the four complexes are 0.01 microg/mL. This method is rapid, sensitive, and simple.

Magnetic resonance imaging and histologic findings of experimental cerebral fat embolism

RATIONALE AND OBJECTIVES

The purpose of this study was to determine whether cerebral fat embolism demonstrated reversible or irreversible findings in magnetic resonance (MR) imaging over time and to compare the features in MR images with histologic findings in a cat model.

MATERIALS AND METHODS

MR images were obtained serially at 2 hours, 1 and 4 days, and 1, 2, and 3 weeks after embolization with 0.05 mL of triolein into the internal carotid artery in 19 cats. Any abnormal signal intensity and change in the signal intensity were evaluated on T2-weighted images, T1-weighted images, diffusion-weighted images (DWIs; including apparent diffusion coefficient [ADC] maps), and gadolinium-enhanced T1-weighted images (Gd-T1WI) over time. After MR imaging at 3 weeks, brain tissue was obtained and evaluated for light microscopic (LM) examination using hematoxylin-eosin and Luxol fast blue staining. For electron microscopic examination, the specimens were obtained at the cortex. The histologic and MR findings were compared.

RESULTS

The embolization lesions showed hyperintensity on T2-weighted images, hyperintensity, or isointensity on DWIs, hypointensity, or isointensity on ADC maps and contrast enhancement on Gd-T1WIs at 2 hours. The T2-weighted hyperintensity extended to the white matter at day 1 and decreased thereafter. Contrast enhancement decreased continuously from day 1, and hyperintensity on DWI decreased after day 4. Hypointensity on ADC maps became less prominent after day 4. By week 3, most lesions had reverted to a normal appearance on MR images and were correlated with LM findings. However, small focal lesions remained in the gray matter of 8 cats and in the white matter of 3 cats on MR images, and this correlated with the cystic changes on LM findings. Electron microscopic examination of the cortical lesions that reverted to normal at week 3 in MR images showed that most of these lesions appeared normal but showed sporadic intracapillary fat vacuoles and disruption of the endothelial walls.

CONCLUSIONS

The embolized lesions of the hyperacute stage were of 2 types: type 1 lesions, showing hyperintensity on DWIs and hypointensity on ADC maps, have irreversible sequelae, such as cystic changes; whereas type 2 lesions, showing isointensity or mild hyperintensity on DWIs and ADC maps, reverted to a normal appearance in the subacute stage.

Dynamic enhancement features of gadophrin-2 on magnetic resonance imaging: an experimental model of VX2 carcinoma and bacterial abscess in rabbit thigh

RATIONALE AND OBJECTIVES

To determine the dynamic enhancement features of malignant tumor and bacterial abscess in rabbits on magnetic resonance imaging (MRI) after injection of gadolinium mesoporphyrin (gadophrin-2) and to correlate them with histopathologic findings.

METHODS

Six VX2 carcinomas and six bacterial abscesses were experimentally induced in either thigh of six rabbits. Dynamic T1-weighted MRI was performed before and 1, 3, 5, 10, 30 minutes and 16, 21, 72 hours after intravenous injection of gadophrin-2 (0.05 mmol/kg). The enhancement ratios of lesions were calculated for each time point. All tumors and abscesses were sectioned along the same plane of MR images for a detailed MRI-histopathologic correlation.

RESULTS

In tumors and abscesses, peripheral-rim enhancement appeared on MRI at 1, 3, 5, 10, 30 minutes after injection of gadophrin-2. The lesions showed peripheral enhancement with irregular central enhancement or diffuse enhancement after 16 and 21 hours, and there was diffuse enhancement of the entire lesion after 72 hours. Enhancement ratios in tumor-necrosis mixed area and the pure necrotic area in VX2 carcinoma and the central cavity in bacterial abscess were significantly lower than that in the compact cellular portion in VX2 carcinoma and the wall of abscess at early phase (P < 0.01). On delayed phase MRI, there was no statistical significance in enhancement ratio of three histologic parts of VX2 carcinoma (P > 0.05) and two histologic parts of abscess (P > 0.05). Rapid enhancement at early phase with diminishing signal intensity at delayed phase is indicative of viable compact tumor and delayed strong enhancement is indicative of necrosis.

CONCLUSION

It is difficult to distinguish an abscess from a tumor on gadophrin-2 enhanced MRI especially when intratumoral necrosis is prominent. However, the trend and degree of enhancement by gadophrin-2 could be helpful in discrimination between viable tumor and tumor necrosis.

Early development of vasogenic edema in experimental cerebral fat embolism in cats: correlation with MRI and electron microscopic findings

RATIONALE AND OBJECTIVES

To evaluate the magnetic resonance imaging and electron microscopic findings of the hyperacute stage of cerebral fat embolism in cats and the time needed for the development of vasogenic edema.

METHODS

Magnetic resonance imaging was performed at 30 minutes (group 1, n = 9) and at 30 minutes and 1, 2, 4, and 6 hours after embolization with triolein (group 2, n = 10). As a control for group 2, the same acquisition was obtained after embolization with polyvinyl alcohol particles (group 3, n = 5). Magnetic resonance images were analyzed qualitatively and quantitatively. Electron microscopic examination was done in all cats.

RESULTS

In group 1, the lesions were iso- or slightly hyperintense on T2-weighted (T2W) and diffusion-weighted (DWIs) images, hypointense on the apparent diffusion coefficient (ADC) map image, and markedly enhanced on the gadolinium-enhanced T1-weighted images (Gd-T1WIs). In group 2 at 30 minutes, the lesions were similar to those in group 1. Thereafter, the lesions became more hyperintense on T2WIs and DWIs and more hypointense on the ADC map image. The lesions were enhanced on Gd-T1WIs at all acquisition times. In group 3, the lesions showed mild hyperintensity on T2WIs at 6 hours but hypointensity on the ADC map image from 30 minutes, with a tendency toward a greater decrease over time. The lesions were not enhanced on Gd-T1WIs at any time point. Electron microscopic findings revealed discontinuity of the capillary endothelial wall, perivascular and interstitial edema, and swelling of glial and neuronal cells in groups 1 and 2. Cellular swelling and interstitial edema were more prominent in group 2. In group 3, interstitial edema was seen; however, discontinuity of the endothelial wall was absent.

CONCLUSIONS

The lesions were hyperintense on T2WIs and DWIs, hypointense on the ADC map image, and enhanced on Gd-T1WIs. On electron microscopy, the lesions showed cytotoxic and vasogenic edema with disruption of the blood-brain barrier. Vasogenic edema seems to develop within 30 minutes in cerebral fat embolism in cats.

Sensitive high-performance liquid chromatographic assay for motexafin gadolinium and motexafin lutetium in human plasma

We present new HPLC methods for the quantitation in human plasma of two investigative metallotexaphyrin agents, motexafin gadolinium (Gd-Tex) and motexafin lutetium (Lu-Tex). Each assay uses: the other texaphyrin analogue as an internal standard; protein precipitation with acetonitrile:methanol (50:50, v/v); an ODS reversed-phase column; an isocratic mobile phase of 100 mM ammonium acetate, pH 4.3:acetonitrile:methanol (59:21:20, v/v/v); and absorbance detection at 470 nm. The Gd-Tex assay has a lower limit of quantitation (LLOQ) of 0.01 microM and is linear between 0.01 and 30 microM. The Lu-Tex assay has an LLOQ of 0.1 microM and is linear between 0.1 and 30 microM. The assays are suited for in vivo preclinical studies and clinical trials because they require minimal amounts of plasma, are sensitive, and involve a 30-mm run time. These assays are important tools for evaluating the potential of Gd-Tex and Lu-Tex as a radiation enhancer and photosensitizer, respectively.

Gadolinium mesoporphyrin as an MR imaging contrast agent in the evaluation of tumors: an experimental model of VX2 carcinoma in rabbits

OBJECTIVE

We determined the enhancement features of experimentally induced malignant tumors on MR imaging with the use of gadolinium mesoporphyrin, a recently developed MR contrast agent that may be necrosis-specific.

MATERIALS AND METHODS

VX2 carcinoma was inoculated into 24 rabbit thighs. T1-weighted contrast-enhanced MR imaging with IV gadopentetate dimeglumine (2-min delay) and gadolinium mesoporphyrin (20-hr delay) was performed 3-4 days (n = 6), 6-7 days (n = 6), 10-11 days (n = 5), and 13-14 days (n = 7) after the implantation of VX2 carcinoma. All tumors were sectioned along the same plane of MR images, and a detailed MR imaging-histopathologic correlation was performed.

RESULTS

Pathologically, areas enhanced with gadolinium mesoporphyrin included necrotic tissue, viable tumor, inflammatory granulation tissue, hemorrhage, and fibrosis. On gadopentetate dimeglumine-enhanced MR images, unenhanced areas of the tumor corresponded with intratumoral necrosis and hemorrhage.

CONCLUSION

Gadolinium mesoporphyrin enhances tumor necrosis on delayed phase MR imaging; however, it is impossible to specifically depict necrosis with gadolinium mesoporphyrin because it also enhances other parts of lesions, including viable tumor.

Delivery of diagnostic agents for magnetic resonance imaging

A review of contrast agents used for magnetic resonance imaging was made with regard to methods of drug delivery using published literature. Since the clinical approval of Gd-DTPA in 1988, there has been extensive research towards developing organ- and tissue-specific contrast agents. Targeting strategies have consistently improved along with improvements in nuclear medicine imaging, and a broad spectrum of potential agents has accumulated. Liver, blood-pool targeted, and, due to their inherent convenience of delivery, intraorally administered gastrointestinal agents have been developed or are being developed. For intravenous contrast agents, collective magnetic labels with modifications for some specificities results in the larger-sized agents which can be an obstacle for the agent in accessing the targeted cells. In conclusion, the next step in the development of specific contrast agents for clinical use is to improve non-specific delivery to the extra-capillary space adjacent to targeted cells.