Loss or Mislocalization of Aquaporin-4 Affects Diffusion Properties and Intermediary Metabolism in Gray Matter of Mice.

The first aim of this study was to determine how complete or perivascular loss of aquaporin-4 (AQP4) water channels affects membrane permeability for water in the mouse brain grey matter in the steady state. Time-dependent diffusion magnetic resonance imaging was performed on global Aqp4 knock out (KO) and α-syntrophin (α-syn) KO mice, in the latter perivascular AQP4 are mislocalized, but still functioning. Control animals were corresponding wild type (WT) mice. By combining in vivo diffusion measurements with the effective medium theory and previously measured extra-cellular volume fractions, the effects of membrane permeability and extracellular volume fraction were uncoupled for Aqp4 and α-syn KO. The second aim was to assess the effect of α-syn KO on cortical intermediary metabolism combining in vivo [1-13C]glucose and [1,2-13C]acetate injection with ex vivo 13C MR spectroscopy. Aqp4 KO increased the effective diffusion coefficient at long diffusion times by 5%, and a 14% decrease in membrane water permeability was estimated for Aqp4 KO compared with WT mice. α-syn KO did not affect the measured diffusion parameters. In the metabolic analyses, significantly lower amounts of [4-13C]glutamate and [4-13C]glutamine, and percent enrichment in [4-13C]glutamate were detected in the α-syn KO mice. [1,2-13C]acetate metabolism was unaffected in α-syn KO, but the contribution of astrocyte derived metabolites to GABA synthesis was significantly increased. Taken together, α-syn KO mice appeared to have decreased neuronal glucose metabolism, partly compensated for by utilization of astrocyte derived metabolites.

NG2 expression regulates vascular morphology and function in human brain tumours.

Tumour angiogenesis is a tightly regulated process involving cross-talk between tumour cells and the host tissue. The underlying mechanisms that regulate such interactions remain largely unknown. NG2 is a transmembrane proteoglycan whose presence on transformed cells has been demonstrated to increase proliferation in vitro and angiogenesis in vivo. To study the effects of NG2 during tumour growth and progression, we engineered an NG2 positive human glioma cell line (U251-NG2) from parental NG2 negative cells (U251-WT) and implanted both cell types stereotactically into immunodeficient nude rat brains. The tumours were longitudinally monitored in vivo using multispectral MRI employing two differently sized contrast agents (Gd-DTPA-BMA and Gadomer) to assess vascular leakiness, vasogenic oedema, tumour volumes and necrosis. Comparisons of Gd-DTPA-BMA and Gadomer revealed differences in their spatial distribution in the U251-NG2 and U251-WT tumours. The U251-NG2 tumours exhibited a higher leakiness of the larger molecular weight Gadomer and displayed a stronger vasogenic oedema (69.9 +/- 15.2, P = 0.018, compared to the controls (10.7 +/- 7.7). Moreover, immunohistochemistry and electron microscopy revealed that the U251-NG2 tumours had a higher microvascular density (11.81 +/- 0.54; P = 0.0010) compared to controls (5.76 +/- 0.87), with vessels that displayed larger gaps between the endothelial cells. Thus, tumour cells can regulate both the function and structure of the host-derived tumour vasculature through NG2 expression, suggesting a role for NG2 in the cross-talk between tumour-host compartments.

Uptake of IgG in osteosarcoma correlates inversely with interstitial fluid pressure, but not with interstitial constituents.

The uptake of therapeutic macromolecules in solid tumours is assumed to be hindered by the heterogeneous vascular network, the high interstitial fluid pressure, and the extracellular matrix. To study the impact of these factors, we measured the uptake of fluorochrome-labelled IgG using confocal laser scanning microscopy, interstitial fluid pressure by the 'wick-in-needle' technique, vascular structure by stereological analysis, and the content of the extracellular matrix constituents collagen, sulfated glycosaminoglycans and hyaluronan by colourimetric assays. The impact of the microenvironment on these factors was studied using osteosarcomas implanted either subcutaneously or orthotopically around the femur in athymic mice. The uptake of IgG was found to correlate inversely with the interstitial fluid pressure and the tumour volume in orthotopic, but not subcutaneous tumours. No correlation was found between IgG uptake and the level of any of the extracellular matrix constituents. The content of both collagen and glycosaminoglycans depended on the site of tumour growth. The orthotopic tumours had a higher vascular density than the subcutaneous tumours, as the vascular surface and length were 2-3-fold higher. The data indicate that the interstitial fluid pressure is a dominant factor in controlling the uptake of macromolecules in solid tumours; and the site of tumour growth is important for the uptake of macromolecules in small tumours, extracellular matrix content and vascularization.

Interstitial fluid pressure in human osteosarcoma xenografts: significance of implantation site and the response to intratumoral injection of hyaluronidase.

Elevated interstitial fluid pressure (IFP) in solid tumors may reduce the effect of systemically administered anticancer drugs. Modulation of the tumor extracellular matrix might reduce the elevated IFP. To study the influence of the microenvironment, the IFP was measured in human osteosarcoma xenografts grown both subcutaneously and orthotopically. The IFP response was recorded in xenografts grown at both sites after direct intratumoral injection of bovine testicular hyaluronidase (500 or 1600 units in 50 microliters saline). Control tumors received 50 microliters saline alone or 10% bovine serum albumin in saline. IFP was measured centrally in the tumors using the wick-in-needle technique, and mean arterial blood pressure was monitored after carotid cannulation. Tumor tissue sections were stained with hyaluronectin and analyzed for hyaluronan content using confocal laser scanning fluorescence microscopy. The baseline IFP was significantly higher in orthotopic (30 +/- 9 mmHg, n = 30) compared with subcutaneous tumors (17 +/- 6 mmHg, n = 11) of comparable sizes (p < 0.001). Injection of hyaluronidase reduced the IFP in both tumor models to 61-81% compared with controls 1 h after injection (p < 0.05), without affecting the mean arterial blood pressure significantly. The hyaluronan staining intensity increased in subcutaneous tumor sections, but remained unchanged in orthotopic tumor sections 1 h after injection of 1600 units of hyaluronidase. The IFP was restored within 48 h after hyaluronidase injection. Interestingly, IFP increased with tumor volume in orthotopic tumors, but not in subcutaneous tumors. In conclusion, intratumoral hyaluronidase injection reduces the IFP transiently in solid osteosarcoma xenografts. Furthermore, this study emphasizes that physiological parameters might differ significantly between human osteosarcoma xenografts grown subcutaneously versus orthotopically in nude mice.

Hyaluronidase-induced periodic modulation of the interstitial fluid pressure increases selective antibody uptake in human osteosarcoma xenografts.

Periodic modulation of the elevated interstitial fluid pressure might improve filtration and uptake of tumor-targeting macromolecules (e.g. radioimmunoconjugates) in solid tumors. Cycling of the tumor interstitial fluid pressure was initiated by intratumoral injections of bovine testicular hyaluronidase (BTH, 1,600 U) in osteosarcoma-bearing nude mice. BTH injection was repeated at 3-day intervals up to 9 days, in conjunction with tail vein injections of 125I-labeled TP-3 monoclonal antibody against an osteosarcoma-associated antigen (n = 9) or non-specific 125I-labeled UPC-10 antibody (n = 9). Control mice received intratumoral injections of phosphate buffered saline (n = 18). The radioactivities of tumor and normal tissues (blood, liver, kidney and spleen) were measured and compared between the different groups. BTH injections increased the tumor uptake of specific 125I-labeled TP-3 significantly by approximately 70% in mice receiving 3 fractions compared to 1-2 fractions of the antibody (p < 0.05). The tumor/normal tissue ratio in mice receiving 3 fractions of 125I-labeled TP-3 (n = 5) was significantly higher for all tissues, compared with mice receiving 1-2 fractions (n = 4) (p < 0.05). Control injections did not affect the tumor/blood ratio, but increased the uptake of 125I-labeled TP-3 significantly in kidney and spleen (p < 0.05). Also, BTH reduced the uptake of 125I-labeled UPC-10 in tumor and liver by approximately 20% compared with controls (p < 0.05). The results indicate that periodic lowering of the tumor interstitial fluid pressure might increase the specificity of blood-borne monoclonal antibodies to solid tumors in vivo.

Mechanics of interstitial-lymphatic fluid transport: theoretical foundation and experimental validation.

Interstitial fluid movement is intrinsically linked to lymphatic drainage. However, their relationship is poorly understood, and associated pathologies are mostly untreatable. In this work we test the hypothesis that bulk tissue fluid movement can be evaluated in situ and described by a linear biphasic theory which integrates the regulatory function of the lymphatics with the mechanical stresses of the tissue. To accomplish this, we develop a novel experimental and theoretical model using the skin of the mouse tail. We then use the model to demonstrate how interstitial-lymphatic fluid movement depends on a balance between the elasticity, hydraulic conductivity, and lymphatic conductance as well as to demonstrate how chronic swelling (edema) alters the equipoise between tissue fluid balance parameters. Specifically, tissue fluid equilibrium is perturbed with a continuous interstitial infusion of saline into the tip of the tail. The resulting gradients in tissue stress are measured in terms of interstitial fluid pressure using a servo-null system. These measurements are then fit to the theory to provide in vivo estimates of the tissue hydraulic conductivity, elastic modulus, and overall resistance to lymphatic drainage. Additional experiments are performed on edematous tails to show that although chronic swelling causes an increase in the hydraulic conductivity, its greatly increased distensibility (due to matrix remodeling) dampens the driving forces for fluid movement and leads to fluid stagnation. This model is useful for examining potential treatments for edema and lymphatic disorders as well as substances which may alter tissue fluid balance and/or lymphatic drainage.

Taxane-induced apoptosis decompresses blood vessels and lowers interstitial fluid pressure in solid tumors: clinical implications.

Elevated tumor interstitial fluid pressure (IFP) is partly responsible for the poor penetration and distribution of therapeutic agents in solid tumors. The etiology of tumor interstitial hypertension is poorly understood. We have postulated that the solid stress generated by tumor cells growing in a confined space compresses blood vessels and increases tumor microvascular pressure and IFP. To test the hypothesis that neoplastic cell loss would decompress blood vessels and lower IFP, we induced apoptosis in tumors with paclitaxel and docetaxel. Taxanes inhibited the growth of the murine mammary carcinoma (MCa-IV) and of the human soft tissue sarcoma (HSTS-26T). Taxanes induced apoptosis and reduced the density of intact neoplastic cells in both MCa-IV and HSTS-26T. To determine whether neoplastic cell loss decompressed blood vessels, we measured the diameter of tumor vessels in HSTS-26T tumors implanted in transparent dorsal skin fold chambers. At 48 and 96 h after paclitaxel, the diameter of tumor vessels was significantly increased. The increase in vascular diameters was associated with reductions in microvascular pressure and IFP. The changes in neoplastic cell density and IFP were also correlated. In the human glioblastoma U87, which is resistant to paclitaxel, the IFP and cellular density were not modified by paclitaxel treatment. Collectively, these results support the hypothesis that solid stress generated by neoplastic cell proliferation increases vascular resistance and IFP. The increase in vessel diameter induced by paclitaxel and docetaxel suggests that taxanes could improve tumor response by increasing the vascular surface area for delivery of therapeutic agents.

Hyaluronidase reduces the interstitial fluid pressure in solid tumours in a non-linear concentration-dependent manner.

Hyaluronidase has gained increasing interest as an adjuvant in local and systemic cancer therapy, despite the incomplete knowledge of its physiological function. To this end, direct intratumoral injection of bovine testicular hyaluronidase (500, 1600 or 7500 U in 50 microl phosphate-buffered saline (PBS)) was performed in orthotopic (o.t.) osteosarcoma xenografts grown in the hind leg of nude mice. Control tumours received 50 microl PBS alone or supplemented with 10% bovine serum albumin (BSA). Central tumour interstitial fluid pressure (IFP) and mean arterial blood pressure (MABP) were measured using the wick-in-needle technique and after cannulation of the carotid artery, respectively. IFP was 32 +/- 8 mmHg (n = 44, mean +/- SD) in untreated tumours and there was a significant correlation between tumour IFP and volume (P < 0.01). The hyaluronidase injection reduced IFP to 63-84% after 1 h compared with controls (P < 0.05) and in a non-linear concentration-dependent manner. MABP was not affected significantly. In conclusion, an intratumoral hyaluronidase injection might reduce IFP temporally in solid osteosarcoma xenografts.

Intratumoral infusion of fluid: estimation of hydraulic conductivity and implications for the delivery of therapeutic agents.

We have developed a new technique to measure in vivo tumour tissue fluid transport parameters (hydraulic conductivity and compliance) that influence the systemic and intratumoral delivery of therapeutic agents. An infusion needle approximating a point source was constructed to produce a radially symmetrical fluid source in the centre of human tumours in immunodeficient mice. At constant flow, the pressure gradient generated in the tumour by the infusion of fluid (Evans blue-albumin in saline) was measured as a function of the radial position with micropipettes connected to a servo-null system. To evaluate whether the fluid infused was reabsorbed by blood vessels, infusions were also performed after circulatory arrest. In the colon adenocarcinoma LS174T with a spherically symmetrical distribution of Evans blue-albumin, the median hydraulic conductivity in vivo and after circulatory arrest at a flow rate of 0.1 microl min(-1) was, respectively, 1.7x10(-7) and 2.3x10(-7) cm2 mmHg(-1) s. Compliance estimates were 35 microl mmHg(-1) in vivo, and 100 microl mmHg(-1) after circulatory arrest. In the sarcoma HSTS 26T, hydraulic conductivity and compliance were not calculated because of the asymmetric distribution of the fluid infused. The technique will be helpful in identifying strategies to improve the intratumoral and systemic delivery of gene targeting vectors and other therapeutic agents.

Penetration and binding of monoclonal antibody in human osteosarcoma multicell spheroids. Comparison of confocal laser scanning microscopy and autoradiography.

Penetration and binding of monoclonal antibody (MAb) in multicell osteosarcoma spheroids have been studied by autoradiography and confocal laser scanning microscopy (CLSM). Optical sectioning of the 3-dimensional spheroids was performed by CLSM. Owing to attenuation of fluorescence intensity, FITC-labelled MAb could not be detected at depths greater than 60 microm within the spheroids. The antibody uptake seen in autoradiographs and CLSM images 60 microm within the spheroids were essentially identical. MAb had reached all parts of the spheroids within 6 h. Quantitative measurements of the fluorescence intensity of FITC-labelled MAb seen in confocal images and measurements of MAb bound per cell using flow cytometry, showed that maximum uptake was reached after 6 h. The possibility to perform both quantitative and qualitative measurements makes CLSM a promising method for studying antibody uptake in thick tissue samples.