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Multidrug resistance (MDR) is associated with the expression of P-glycoprotein (P-gp), an ATP-dependent transporter which expels anti-cancer drugs from cells. In the present study, MDR1 P-gp was immunodetected by Western blot analysis in 60 human brain tumors, including meningiomas, schwannomas, low-grade gliomas (astrocytomas, pilocytic astrocytomas) and high-grade gliomas (anaplastic astrocytomas, glioblastomas and anaplastic oligodendrogliomas). Most samples from primary tumors expressed P-gp at the same levels as normal brain tissue except for schwannomas, in which levels were reduced by 65%, and meningiomas, in which levels were more than 10-fold higher in 7 of 10 samples. P-gp levels were 70% and 95% lower in brain metastases from melanomas and lung adenocarcinomas, respectively, than in normal brain tissue. These results indicate that the majority of primary brain tumors express MDR1 P-gp and that its high expression levels in meningiomas may be a marker for this type of brain tumor., (Copyright 2001 Wiley-Liss, Inc.)

Endothelial cells (EC) were isolated from brain, lung, and renal cortex using magnetic microbeads cross-linked to an antibody directed against the platelet-endothelial cell adhesion molecule-1 (PECAM-1). Levels of endothelial nitric oxide synthase (eNOS) and PECAM-1 were measured by Western blots and both were enriched in the positively selected EC fractions. The multidrug resistance P-glycoprotein (P-gp) was strongly enriched (59-fold) in the EC fraction from brain and was absent in the negative fraction, in which the glial fibrillary acidic protein (GFAP), an astrocyte marker, was present. Lower P-gp levels were detected in EC from renal cortex and lung. Reverse transcription-polymerase chain reaction analysis showed that the mdr1a gene was preferentially expressed in EC fraction from the brain. The mdr1b gene was found in EC from renal cortex whereas both mdr1 genes were detected in EC from lung. Our results indicate that EC can be isolated using microbeads and that the isoform of P-gp found in brain is mostly mdr1a, associated with EC., (Copyright 2001 Academic Press.)

Malignant brain tumors and brain metastases present a formidable clinical challenge against which no significant advances have been made over the last decade. Multidrug resistance (MDR) is one of the main factors in the failure of chemotherapy against central nervous system tumors. The MDR1 gene encoding P-glycoprotein (P-gp), a drug efflux pump which plays a significant role in modulating MDR in a wide variety of human cancers, is highly expressed in the blood-brain barrier (BBB). The BBB controls central nervous system exposure to many endogenous and exogenous substances. The exact molecular mechanisms by which the BBB is involved in the resistance of brain tumors to chemotherapy remain to be identified. The purpose of this review is to summarize reports demonstrating that P-gp, one of the most phenotypically important markers of the BBB, is present in primary brain tumors and thus plays a crucial role in their clinical resistance to chemotherapy.

Sixty human brain tumors, classified according to the New World Health Organization (WHO) classification including, grade I schwannomas, meningiomas and pilocytic astrocytomas, grade II astrocytomas, grade III anaplastic astrocytomas, grade IV glioblastomas, grade III anaplastic oligodendrogliomas and grade IV glioblastomas and lung and melanoma metastases were analyzed for the expression of three matrix metalloproteinases (MMPs), two tissue inhibitors of MMPs (TIMPs) and for MMP activity. Some correlation was found between MMP expression and the degree of malignancy. Western blotting analysis revealed a more uniform pattern of distribution of MMP-2 (gelatinase A) than of MMP-9 (gelatinase B) and MMP-12 (metalloelastase) among tumors. MMP-9 levels were found to be significantly higher in grade III anaplastic astrocytomas and anaplastic oligodendrogliomas than those in grade I schwannomas and meningiomas. Anaplastic astrocytomas and Grade IV glioblastomas expressed significantly higher levels MMP-12 than grade I meningiomas. All sixty tumors showed a similar pattern of activity in zymography, proMMP-9 being the major species detected. Interestingly, TIMP-1 and TIMP-2 expression levels were especially low in tumors of grade II and grade III but significantly higher in tumors of grade I, particularly in schwannomas. Taken together, these data suggest that: 1) a balance between MMPs and TIMPs has an important role to play in human brain tumors; 2) TIMP expression may be valuable markers for tumor malignancy.

Sixty human brain tumors, including grade I meningiomas, schwannomas, and pilocytic astrocytomas, grade II astrocytomas, grade III anaplastic astrocytomas and oligodendrogliomas, and grade IV glioblastomas and lung and melanoma metastases were analyzed for expression of four matrix metalloproteinases (MMPs), two tissue inhibitors of MMPs (TIMPs), and MMP activity. No marked correlation was found between MMP expression and the degree of malignancy. Western blotting analysis revealed a more uniform pattern of distribution of MMP-2 (gelatinase A) than of MMP-9 (gelatinase B) and MMP-12 (metalloelastase) among tumors. All 60 tumors showed a similar pattern of activity in zymography, MMP-2 being the major species detected. Interestingly, TIMP-1 and TIMP-2 expression levels were low in tumors of grade III but significantly higher in tumors of grade I, particularly schwannomas. Altogether, these data suggest that: (1) the balance between MMP-2 and TIMP-2 is important in human brain tumors; and (2) TIMP expression may be a valuable marker for tumor malignancy.

Precise knowledge of the ultrastructural features and interneuronal relationships of dopaminergic (DA) axon terminals or varicosities in neostriatum is still lacking. This ignorance is due to current limitations of the methods applicable to their specific visualization at electron microscopic level. High resolution radioautography, in particular, has not yet permitted a clearcut identification of the DA nerve endings which take up and store exogenous catecholamines in vivo, due to an apparent mobilization of tracer during standard histological preparative procedures for light and electron microscopy (Fig. 1 A). In this context, histological processing of the central nervous system by vascular perfusion, tested in adult rats subjected to prolonged lateroventricular instillation of [3H]DA, led to the following results and conclusions: 1 Axonal varicosities having accumulated [3H]DA in vivo may be detected in great number in the ipsilateral paraventricular neostriatum (Figs. 1 B and 1 C). 2 The specificity of this radioautographic labelling is evidenced by: (a) its disappearance or persistance, depending on the addition of a high concentration of non-radioactive noradrenaline or serotonin to the [3H]DA solution (Fig. 1 C); (b) the absence of labelled axonal varicosities in the supraependymal region (Figs. 2 E and 2 F) and suprachiasmatic nucleus (Fig. 1 E to be compared with 1 F) after administration of [3H]DA alone; (c) the absence of any localized accumulation of [3H]DA in neostriatum following prior destruction of the nigro-striatal DA system by 6-hydroxydopamine (Fig. 1 D). 3 It seems that carrying out the double fixation with glutaraldehyde and osmium by vascular perfusion is the prerequisite for retaining in situ the [3H]DA accumulated in vivo by neostriatal nerve endings. 4 Preliminary ultrastructural examination shows that the DA axonal varicosities of paraventricular neostriatum are of small caliber (mean diameter: 0.5 micron) and mostly contain clear synaptic vesicles, occasionally associated with a few larger dense-core vesicles (figs. 2 A-D). Several of these nerve endings establish axo-dendritic synaptic junctions (Fig. 2 C) and a few, perhaps, axo-somatic contacts (Fig. 2 D).

Isosmotic fluid absorption carried out by many mammalian epithelia appears to be similar to the isosmotic secretion of insect epithelia such as the Malpighian tubules, which are responsible for urine formation and osmoregulation. We have studied by electron microscopy (80 kV) the three-dimensional characteristics of organelles in the Malpighian tubules of Rhodnius prolixus using thick sections (0.3-0.5 microns) and uranyl and lead impregnation. The ER presents a different organization in the upper (distal) and lower (proximal) segments of the Malpighian tubule. In distal secretory segment, the ER forms a network made of chains of vesicles having irregular shapes (ca. 0.06 micron in diameter) connected to each other by canaliculi while in the lower absorptive segment, the ER is made of parallel saccules arranged in stacks or whorls in the central region of the cytoplasm. In both segments, the ER network extends throughout the cytoplasm from the basolateral infoldings to the apex between the many mitochondria present in these two areas. A unique feature of these cells, revealed by thick sections, is the presence in each microvillus of either a mitochondrion or an ER canaliculus in continuity with the ER network. The ER does not seem to have any specific association with mitochondria or other organelles. As in the mammalian nephron, this ER organization is most likely related to specific segmental functions and adds support to its potential role as a transcellular epithelial route.

The morphologic interrelationships between mitochondria, the endoplasmic reticulum (ER) and other organelles were examined in rat kidney cells by stereomicroscopy of thick sections (0.3-1.0 micron) using either standard transmission (80-100 kV) or high voltage (1 mEV) electron microscopy. Mitochondria fit into three different categories: (1) elongated cylinders observed in S1 and S2 segments; (2) irregular lamina in the cortical ascending limb or plates in the distal straight and convoluted segments; (3) small spheres or short rods mostly in intercalated and principal cells of the collecting tubule. The chondrioma occupies a large volume in all cells except in the thin limb and in principal cells of the collecting tubule. This volume occupied by the chondrioma is likely to be related to metabolic functions, but its polymorphic configuration could also be explained by a passive adaptation of the mitochondria to the space left by the basilar membrane infoldings and the ER network, which was found to have an extensive three-dimensional organization which varies, as for the mitochondria, with the cell type. In fact, in the proximal nephron, mitochondria surrounded by the ER and the plasma membranes appear to form a functional unit. Organelle interrelationship is extensively modified during ontogeny or under hormonal influence. Disruption in organelle relationships or in their motility could probably have far reaching consequences which would be more deleterious than the pathological lesions observed at the level of a single organelle. The extent of the disassembly can be fully explored only with thick sections and stereomicroscopy.