The Experts below are selected from a list of 3 Experts worldwide ranked by ideXlab platform
Max Lakomek - One of the best experts on this subject based on the ideXlab platform.
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alkylglycerol opening of the blood brain barrier to small and large fluorescence markers in normal and c6 glioma bearing rats and isolated rat brain capillaries
British Journal of Pharmacology, 2003Co-Authors: Bernhard Erdlenbruch, Mehrnaz Alipour, Gert Fricker, David S Miller, Wilfried Kugler, Hansjorg Eibl, Max LakomekAbstract:The blood–brain barrier (BBB) represents the major impediment to successful delivery of therapeutic agents to target tissue within the central nervous system. Intracarotid alkylglycerols have been shown to increase the transfer of chemotherapeutics across the BBB. We investigated the spatial distribution of Intracarotid fluorescein sodium and intravenous lissamine-rhodamine B200 (RB 200)–albumin in the brain of normal and C6 glioma-bearing rats after Intracarotid co-Administration of 1-O-pentylglycerol (200 mM). To elucidate the mechanisms involved in the alkylglycerol-mediated BBB opening, intraluminal accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 was studied in freshly isolated rat brain capillaries using confocal microscopy during incubation with different alkylglycerols. Furthermore, 1-O-pentylglycerol-induced increase in delivery of methotrexate (MTX) to the brain was evaluated in nude mice. Microscopic evaluation showed a marked 1-O-pentylglycerol-induced extravasation of fluorescein and RB 200–albumin in the ipsilateral normal brain. In glioma-bearing rats, increased tissue fluorescence was found in both tumor tissue and brain surrounding tumor. Confocal microscopy revealed a time- and concentration-dependent accumulation of FITC–dextran 40,000 within the lumina of isolated rat brain capillaries during incubation with 1-O-pentylglycerol and 2-O-hexyldiglycerol, indicating enhanced paracellular transfer via tight junctions. Intracarotid co-Administration of MTX and 1-O-pentylglycerol (200 mM) in nude mice resulted in a significant increase in MTX concentrations in the ipsilateral brain as compared to controls without 1-O-pentylglycerol (P<0.005). In conclusion, 1-O-pentylglycerol increases delivery of small and large compounds to normal brain and brain tumors and this effect is mediated at least in part by enhanced permeability of tight junctions. Keywords: Alkylglycerol, blood–brain barrier, brain tumor, Drug delivery, fluorescence markers, methotrexate, rat brain capillaries, tight junction, confocal microscopy Introduction The brain capillary endothelium plays a key role in the pathophysiology of various diseases of the CNS such as inflammatory disorders, tumors, ischemia, and seizures (Pardridge, 1998). The mechanisms of functional regulation and transport at the blood–brain barrier (BBB) are not well understood, and further investigation is needed to clarify both how BBB dysfunction is mediated in disease states and how transport systems at the barrier can be altered for therapeutic purposes. Currently, successful treatment of many brain disorders seems to be impossible even though highly active Drugs exerting powerful effects at the target site have been developed. Their efficacy is limited by very low penetration across the BBB (Neuwelt et al., 1999). Thus, enhancing or targeting Drug delivery to the brain has become a major issue in experimental neurology. Chemical modification of Drugs and the use of transport mediating agents or vector systems are possible strategies for Drug targeting to the brain (Smith, 1993; Huwyler et al., 1996; Reszka et al., 1997; Kroll & Neuwelt, 1998; Jolliet-Riant & Tillement, 1999); however, the clinical benefit of such measures has still to be demonstrated. In contrast to this, methods to open the BBB such as hyperosmotic disruption of the BBB or bradykinin receptor-induced increase in barrier permeability have already been shown to be effective in the treatment of experimental brain tumors (Blasberg et al., 1990; Nomura et al., 1994; Elliott et al., 1996; Matsukado et al., 1996; Kroll et al., 1998). Chemotherapy of malignant brain tumors in conjunction with osmotic opening of the BBB has been advanced to the stage of clinical trials and tumor response has been documented in both adults and pediatric patients (Gumerlock et al., 1992; Dahlborg et al., 1996; 1998; Doolittle et al., 2000). The inadequate Drug delivery across the BBB is a major factor that explains the poor response rates of chemosensitive brain tumors (Siegal & Zylber-Katz, 2002). Consequently, there is a need for new maneuvers designed to overcome the limited access of anticancer agents to the brain and to brain tumors. Recently, the transfer of a variety of chemotherapeutic Drugs across the BBB was shown to be increased dramatically by Intracarotid Drug Administration in the presence of short-chain alkylglycerols (Erdlenbruch et al., 2000; 2002). The Intracarotid injection of alkylglycerols resulted in a concentration-dependent accumulation of the coinjected Drugs within the brain. The effect was rapidly reversible and variations in the chemical structure of the alkylglycerols allowed for modulation of the extent of increased barrier permeability (Erdlenbruch et al., 2003). Of particular importance is the fact that there were no signs of toxicity in long-term experiments using Intracarotid 1-O-pentylglycerol and 2-O-hexyldiglycerol in rats (Erdlenbruch et al., 2003). In view of their low toxicity and the potent and well-controllable effects, Intracarotid alkylglycerols are thought to be a very promising principle to facilitate the transport of therapeutics across the BBB. However, little is known about the distribution of the delivered Drugs within the hemispheres and whether large compounds such as proteins will enter the brain after Intracarotid alkylglycerols. Furthermore, there are only marginal insights into the mechanisms involved in alkylglycerol-mediated BBB opening. Finally, nude mice represent the species mostly used for the treatment of experimental human brain tumor xenografts, but alkylglycerols were not administered in nude mice so far. Therefore, the purpose of the present study was (a) to estimate the 1-O-pentylglycerol-mediated increase in the penetration of small and large fluorescence markers into the brain of both normal and glioma-bearing rats and to investigate the spatial distribution of the different markers within the brain, (b) to elucidate the mechanisms of action of the alkylglycerols by studying the accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 (40 kDa) in freshly isolated rat brain capillaries using confocal microscopy and quantitative image analysis during incubation with different alkylglycerols, and (c) to demonstrate feasibility and effectivity of the permeabilizing effect of 1-O-pentylglycerol in nude mice by Intracarotid co-Administration with methotrexate (MTX).
Bernhard Erdlenbruch - One of the best experts on this subject based on the ideXlab platform.
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alkylglycerol opening of the blood brain barrier to small and large fluorescence markers in normal and c6 glioma bearing rats and isolated rat brain capillaries
British Journal of Pharmacology, 2003Co-Authors: Bernhard Erdlenbruch, Mehrnaz Alipour, Gert Fricker, David S Miller, Wilfried Kugler, Hansjorg Eibl, Max LakomekAbstract:The blood–brain barrier (BBB) represents the major impediment to successful delivery of therapeutic agents to target tissue within the central nervous system. Intracarotid alkylglycerols have been shown to increase the transfer of chemotherapeutics across the BBB. We investigated the spatial distribution of Intracarotid fluorescein sodium and intravenous lissamine-rhodamine B200 (RB 200)–albumin in the brain of normal and C6 glioma-bearing rats after Intracarotid co-Administration of 1-O-pentylglycerol (200 mM). To elucidate the mechanisms involved in the alkylglycerol-mediated BBB opening, intraluminal accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 was studied in freshly isolated rat brain capillaries using confocal microscopy during incubation with different alkylglycerols. Furthermore, 1-O-pentylglycerol-induced increase in delivery of methotrexate (MTX) to the brain was evaluated in nude mice. Microscopic evaluation showed a marked 1-O-pentylglycerol-induced extravasation of fluorescein and RB 200–albumin in the ipsilateral normal brain. In glioma-bearing rats, increased tissue fluorescence was found in both tumor tissue and brain surrounding tumor. Confocal microscopy revealed a time- and concentration-dependent accumulation of FITC–dextran 40,000 within the lumina of isolated rat brain capillaries during incubation with 1-O-pentylglycerol and 2-O-hexyldiglycerol, indicating enhanced paracellular transfer via tight junctions. Intracarotid co-Administration of MTX and 1-O-pentylglycerol (200 mM) in nude mice resulted in a significant increase in MTX concentrations in the ipsilateral brain as compared to controls without 1-O-pentylglycerol (P<0.005). In conclusion, 1-O-pentylglycerol increases delivery of small and large compounds to normal brain and brain tumors and this effect is mediated at least in part by enhanced permeability of tight junctions. Keywords: Alkylglycerol, blood–brain barrier, brain tumor, Drug delivery, fluorescence markers, methotrexate, rat brain capillaries, tight junction, confocal microscopy Introduction The brain capillary endothelium plays a key role in the pathophysiology of various diseases of the CNS such as inflammatory disorders, tumors, ischemia, and seizures (Pardridge, 1998). The mechanisms of functional regulation and transport at the blood–brain barrier (BBB) are not well understood, and further investigation is needed to clarify both how BBB dysfunction is mediated in disease states and how transport systems at the barrier can be altered for therapeutic purposes. Currently, successful treatment of many brain disorders seems to be impossible even though highly active Drugs exerting powerful effects at the target site have been developed. Their efficacy is limited by very low penetration across the BBB (Neuwelt et al., 1999). Thus, enhancing or targeting Drug delivery to the brain has become a major issue in experimental neurology. Chemical modification of Drugs and the use of transport mediating agents or vector systems are possible strategies for Drug targeting to the brain (Smith, 1993; Huwyler et al., 1996; Reszka et al., 1997; Kroll & Neuwelt, 1998; Jolliet-Riant & Tillement, 1999); however, the clinical benefit of such measures has still to be demonstrated. In contrast to this, methods to open the BBB such as hyperosmotic disruption of the BBB or bradykinin receptor-induced increase in barrier permeability have already been shown to be effective in the treatment of experimental brain tumors (Blasberg et al., 1990; Nomura et al., 1994; Elliott et al., 1996; Matsukado et al., 1996; Kroll et al., 1998). Chemotherapy of malignant brain tumors in conjunction with osmotic opening of the BBB has been advanced to the stage of clinical trials and tumor response has been documented in both adults and pediatric patients (Gumerlock et al., 1992; Dahlborg et al., 1996; 1998; Doolittle et al., 2000). The inadequate Drug delivery across the BBB is a major factor that explains the poor response rates of chemosensitive brain tumors (Siegal & Zylber-Katz, 2002). Consequently, there is a need for new maneuvers designed to overcome the limited access of anticancer agents to the brain and to brain tumors. Recently, the transfer of a variety of chemotherapeutic Drugs across the BBB was shown to be increased dramatically by Intracarotid Drug Administration in the presence of short-chain alkylglycerols (Erdlenbruch et al., 2000; 2002). The Intracarotid injection of alkylglycerols resulted in a concentration-dependent accumulation of the coinjected Drugs within the brain. The effect was rapidly reversible and variations in the chemical structure of the alkylglycerols allowed for modulation of the extent of increased barrier permeability (Erdlenbruch et al., 2003). Of particular importance is the fact that there were no signs of toxicity in long-term experiments using Intracarotid 1-O-pentylglycerol and 2-O-hexyldiglycerol in rats (Erdlenbruch et al., 2003). In view of their low toxicity and the potent and well-controllable effects, Intracarotid alkylglycerols are thought to be a very promising principle to facilitate the transport of therapeutics across the BBB. However, little is known about the distribution of the delivered Drugs within the hemispheres and whether large compounds such as proteins will enter the brain after Intracarotid alkylglycerols. Furthermore, there are only marginal insights into the mechanisms involved in alkylglycerol-mediated BBB opening. Finally, nude mice represent the species mostly used for the treatment of experimental human brain tumor xenografts, but alkylglycerols were not administered in nude mice so far. Therefore, the purpose of the present study was (a) to estimate the 1-O-pentylglycerol-mediated increase in the penetration of small and large fluorescence markers into the brain of both normal and glioma-bearing rats and to investigate the spatial distribution of the different markers within the brain, (b) to elucidate the mechanisms of action of the alkylglycerols by studying the accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 (40 kDa) in freshly isolated rat brain capillaries using confocal microscopy and quantitative image analysis during incubation with different alkylglycerols, and (c) to demonstrate feasibility and effectivity of the permeabilizing effect of 1-O-pentylglycerol in nude mice by Intracarotid co-Administration with methotrexate (MTX).
Mehrnaz Alipour - One of the best experts on this subject based on the ideXlab platform.
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alkylglycerol opening of the blood brain barrier to small and large fluorescence markers in normal and c6 glioma bearing rats and isolated rat brain capillaries
British Journal of Pharmacology, 2003Co-Authors: Bernhard Erdlenbruch, Mehrnaz Alipour, Gert Fricker, David S Miller, Wilfried Kugler, Hansjorg Eibl, Max LakomekAbstract:The blood–brain barrier (BBB) represents the major impediment to successful delivery of therapeutic agents to target tissue within the central nervous system. Intracarotid alkylglycerols have been shown to increase the transfer of chemotherapeutics across the BBB. We investigated the spatial distribution of Intracarotid fluorescein sodium and intravenous lissamine-rhodamine B200 (RB 200)–albumin in the brain of normal and C6 glioma-bearing rats after Intracarotid co-Administration of 1-O-pentylglycerol (200 mM). To elucidate the mechanisms involved in the alkylglycerol-mediated BBB opening, intraluminal accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 was studied in freshly isolated rat brain capillaries using confocal microscopy during incubation with different alkylglycerols. Furthermore, 1-O-pentylglycerol-induced increase in delivery of methotrexate (MTX) to the brain was evaluated in nude mice. Microscopic evaluation showed a marked 1-O-pentylglycerol-induced extravasation of fluorescein and RB 200–albumin in the ipsilateral normal brain. In glioma-bearing rats, increased tissue fluorescence was found in both tumor tissue and brain surrounding tumor. Confocal microscopy revealed a time- and concentration-dependent accumulation of FITC–dextran 40,000 within the lumina of isolated rat brain capillaries during incubation with 1-O-pentylglycerol and 2-O-hexyldiglycerol, indicating enhanced paracellular transfer via tight junctions. Intracarotid co-Administration of MTX and 1-O-pentylglycerol (200 mM) in nude mice resulted in a significant increase in MTX concentrations in the ipsilateral brain as compared to controls without 1-O-pentylglycerol (P<0.005). In conclusion, 1-O-pentylglycerol increases delivery of small and large compounds to normal brain and brain tumors and this effect is mediated at least in part by enhanced permeability of tight junctions. Keywords: Alkylglycerol, blood–brain barrier, brain tumor, Drug delivery, fluorescence markers, methotrexate, rat brain capillaries, tight junction, confocal microscopy Introduction The brain capillary endothelium plays a key role in the pathophysiology of various diseases of the CNS such as inflammatory disorders, tumors, ischemia, and seizures (Pardridge, 1998). The mechanisms of functional regulation and transport at the blood–brain barrier (BBB) are not well understood, and further investigation is needed to clarify both how BBB dysfunction is mediated in disease states and how transport systems at the barrier can be altered for therapeutic purposes. Currently, successful treatment of many brain disorders seems to be impossible even though highly active Drugs exerting powerful effects at the target site have been developed. Their efficacy is limited by very low penetration across the BBB (Neuwelt et al., 1999). Thus, enhancing or targeting Drug delivery to the brain has become a major issue in experimental neurology. Chemical modification of Drugs and the use of transport mediating agents or vector systems are possible strategies for Drug targeting to the brain (Smith, 1993; Huwyler et al., 1996; Reszka et al., 1997; Kroll & Neuwelt, 1998; Jolliet-Riant & Tillement, 1999); however, the clinical benefit of such measures has still to be demonstrated. In contrast to this, methods to open the BBB such as hyperosmotic disruption of the BBB or bradykinin receptor-induced increase in barrier permeability have already been shown to be effective in the treatment of experimental brain tumors (Blasberg et al., 1990; Nomura et al., 1994; Elliott et al., 1996; Matsukado et al., 1996; Kroll et al., 1998). Chemotherapy of malignant brain tumors in conjunction with osmotic opening of the BBB has been advanced to the stage of clinical trials and tumor response has been documented in both adults and pediatric patients (Gumerlock et al., 1992; Dahlborg et al., 1996; 1998; Doolittle et al., 2000). The inadequate Drug delivery across the BBB is a major factor that explains the poor response rates of chemosensitive brain tumors (Siegal & Zylber-Katz, 2002). Consequently, there is a need for new maneuvers designed to overcome the limited access of anticancer agents to the brain and to brain tumors. Recently, the transfer of a variety of chemotherapeutic Drugs across the BBB was shown to be increased dramatically by Intracarotid Drug Administration in the presence of short-chain alkylglycerols (Erdlenbruch et al., 2000; 2002). The Intracarotid injection of alkylglycerols resulted in a concentration-dependent accumulation of the coinjected Drugs within the brain. The effect was rapidly reversible and variations in the chemical structure of the alkylglycerols allowed for modulation of the extent of increased barrier permeability (Erdlenbruch et al., 2003). Of particular importance is the fact that there were no signs of toxicity in long-term experiments using Intracarotid 1-O-pentylglycerol and 2-O-hexyldiglycerol in rats (Erdlenbruch et al., 2003). In view of their low toxicity and the potent and well-controllable effects, Intracarotid alkylglycerols are thought to be a very promising principle to facilitate the transport of therapeutics across the BBB. However, little is known about the distribution of the delivered Drugs within the hemispheres and whether large compounds such as proteins will enter the brain after Intracarotid alkylglycerols. Furthermore, there are only marginal insights into the mechanisms involved in alkylglycerol-mediated BBB opening. Finally, nude mice represent the species mostly used for the treatment of experimental human brain tumor xenografts, but alkylglycerols were not administered in nude mice so far. Therefore, the purpose of the present study was (a) to estimate the 1-O-pentylglycerol-mediated increase in the penetration of small and large fluorescence markers into the brain of both normal and glioma-bearing rats and to investigate the spatial distribution of the different markers within the brain, (b) to elucidate the mechanisms of action of the alkylglycerols by studying the accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 (40 kDa) in freshly isolated rat brain capillaries using confocal microscopy and quantitative image analysis during incubation with different alkylglycerols, and (c) to demonstrate feasibility and effectivity of the permeabilizing effect of 1-O-pentylglycerol in nude mice by Intracarotid co-Administration with methotrexate (MTX).
Gert Fricker - One of the best experts on this subject based on the ideXlab platform.
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alkylglycerol opening of the blood brain barrier to small and large fluorescence markers in normal and c6 glioma bearing rats and isolated rat brain capillaries
British Journal of Pharmacology, 2003Co-Authors: Bernhard Erdlenbruch, Mehrnaz Alipour, Gert Fricker, David S Miller, Wilfried Kugler, Hansjorg Eibl, Max LakomekAbstract:The blood–brain barrier (BBB) represents the major impediment to successful delivery of therapeutic agents to target tissue within the central nervous system. Intracarotid alkylglycerols have been shown to increase the transfer of chemotherapeutics across the BBB. We investigated the spatial distribution of Intracarotid fluorescein sodium and intravenous lissamine-rhodamine B200 (RB 200)–albumin in the brain of normal and C6 glioma-bearing rats after Intracarotid co-Administration of 1-O-pentylglycerol (200 mM). To elucidate the mechanisms involved in the alkylglycerol-mediated BBB opening, intraluminal accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 was studied in freshly isolated rat brain capillaries using confocal microscopy during incubation with different alkylglycerols. Furthermore, 1-O-pentylglycerol-induced increase in delivery of methotrexate (MTX) to the brain was evaluated in nude mice. Microscopic evaluation showed a marked 1-O-pentylglycerol-induced extravasation of fluorescein and RB 200–albumin in the ipsilateral normal brain. In glioma-bearing rats, increased tissue fluorescence was found in both tumor tissue and brain surrounding tumor. Confocal microscopy revealed a time- and concentration-dependent accumulation of FITC–dextran 40,000 within the lumina of isolated rat brain capillaries during incubation with 1-O-pentylglycerol and 2-O-hexyldiglycerol, indicating enhanced paracellular transfer via tight junctions. Intracarotid co-Administration of MTX and 1-O-pentylglycerol (200 mM) in nude mice resulted in a significant increase in MTX concentrations in the ipsilateral brain as compared to controls without 1-O-pentylglycerol (P<0.005). In conclusion, 1-O-pentylglycerol increases delivery of small and large compounds to normal brain and brain tumors and this effect is mediated at least in part by enhanced permeability of tight junctions. Keywords: Alkylglycerol, blood–brain barrier, brain tumor, Drug delivery, fluorescence markers, methotrexate, rat brain capillaries, tight junction, confocal microscopy Introduction The brain capillary endothelium plays a key role in the pathophysiology of various diseases of the CNS such as inflammatory disorders, tumors, ischemia, and seizures (Pardridge, 1998). The mechanisms of functional regulation and transport at the blood–brain barrier (BBB) are not well understood, and further investigation is needed to clarify both how BBB dysfunction is mediated in disease states and how transport systems at the barrier can be altered for therapeutic purposes. Currently, successful treatment of many brain disorders seems to be impossible even though highly active Drugs exerting powerful effects at the target site have been developed. Their efficacy is limited by very low penetration across the BBB (Neuwelt et al., 1999). Thus, enhancing or targeting Drug delivery to the brain has become a major issue in experimental neurology. Chemical modification of Drugs and the use of transport mediating agents or vector systems are possible strategies for Drug targeting to the brain (Smith, 1993; Huwyler et al., 1996; Reszka et al., 1997; Kroll & Neuwelt, 1998; Jolliet-Riant & Tillement, 1999); however, the clinical benefit of such measures has still to be demonstrated. In contrast to this, methods to open the BBB such as hyperosmotic disruption of the BBB or bradykinin receptor-induced increase in barrier permeability have already been shown to be effective in the treatment of experimental brain tumors (Blasberg et al., 1990; Nomura et al., 1994; Elliott et al., 1996; Matsukado et al., 1996; Kroll et al., 1998). Chemotherapy of malignant brain tumors in conjunction with osmotic opening of the BBB has been advanced to the stage of clinical trials and tumor response has been documented in both adults and pediatric patients (Gumerlock et al., 1992; Dahlborg et al., 1996; 1998; Doolittle et al., 2000). The inadequate Drug delivery across the BBB is a major factor that explains the poor response rates of chemosensitive brain tumors (Siegal & Zylber-Katz, 2002). Consequently, there is a need for new maneuvers designed to overcome the limited access of anticancer agents to the brain and to brain tumors. Recently, the transfer of a variety of chemotherapeutic Drugs across the BBB was shown to be increased dramatically by Intracarotid Drug Administration in the presence of short-chain alkylglycerols (Erdlenbruch et al., 2000; 2002). The Intracarotid injection of alkylglycerols resulted in a concentration-dependent accumulation of the coinjected Drugs within the brain. The effect was rapidly reversible and variations in the chemical structure of the alkylglycerols allowed for modulation of the extent of increased barrier permeability (Erdlenbruch et al., 2003). Of particular importance is the fact that there were no signs of toxicity in long-term experiments using Intracarotid 1-O-pentylglycerol and 2-O-hexyldiglycerol in rats (Erdlenbruch et al., 2003). In view of their low toxicity and the potent and well-controllable effects, Intracarotid alkylglycerols are thought to be a very promising principle to facilitate the transport of therapeutics across the BBB. However, little is known about the distribution of the delivered Drugs within the hemispheres and whether large compounds such as proteins will enter the brain after Intracarotid alkylglycerols. Furthermore, there are only marginal insights into the mechanisms involved in alkylglycerol-mediated BBB opening. Finally, nude mice represent the species mostly used for the treatment of experimental human brain tumor xenografts, but alkylglycerols were not administered in nude mice so far. Therefore, the purpose of the present study was (a) to estimate the 1-O-pentylglycerol-mediated increase in the penetration of small and large fluorescence markers into the brain of both normal and glioma-bearing rats and to investigate the spatial distribution of the different markers within the brain, (b) to elucidate the mechanisms of action of the alkylglycerols by studying the accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 (40 kDa) in freshly isolated rat brain capillaries using confocal microscopy and quantitative image analysis during incubation with different alkylglycerols, and (c) to demonstrate feasibility and effectivity of the permeabilizing effect of 1-O-pentylglycerol in nude mice by Intracarotid co-Administration with methotrexate (MTX).
David S Miller - One of the best experts on this subject based on the ideXlab platform.
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alkylglycerol opening of the blood brain barrier to small and large fluorescence markers in normal and c6 glioma bearing rats and isolated rat brain capillaries
British Journal of Pharmacology, 2003Co-Authors: Bernhard Erdlenbruch, Mehrnaz Alipour, Gert Fricker, David S Miller, Wilfried Kugler, Hansjorg Eibl, Max LakomekAbstract:The blood–brain barrier (BBB) represents the major impediment to successful delivery of therapeutic agents to target tissue within the central nervous system. Intracarotid alkylglycerols have been shown to increase the transfer of chemotherapeutics across the BBB. We investigated the spatial distribution of Intracarotid fluorescein sodium and intravenous lissamine-rhodamine B200 (RB 200)–albumin in the brain of normal and C6 glioma-bearing rats after Intracarotid co-Administration of 1-O-pentylglycerol (200 mM). To elucidate the mechanisms involved in the alkylglycerol-mediated BBB opening, intraluminal accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 was studied in freshly isolated rat brain capillaries using confocal microscopy during incubation with different alkylglycerols. Furthermore, 1-O-pentylglycerol-induced increase in delivery of methotrexate (MTX) to the brain was evaluated in nude mice. Microscopic evaluation showed a marked 1-O-pentylglycerol-induced extravasation of fluorescein and RB 200–albumin in the ipsilateral normal brain. In glioma-bearing rats, increased tissue fluorescence was found in both tumor tissue and brain surrounding tumor. Confocal microscopy revealed a time- and concentration-dependent accumulation of FITC–dextran 40,000 within the lumina of isolated rat brain capillaries during incubation with 1-O-pentylglycerol and 2-O-hexyldiglycerol, indicating enhanced paracellular transfer via tight junctions. Intracarotid co-Administration of MTX and 1-O-pentylglycerol (200 mM) in nude mice resulted in a significant increase in MTX concentrations in the ipsilateral brain as compared to controls without 1-O-pentylglycerol (P<0.005). In conclusion, 1-O-pentylglycerol increases delivery of small and large compounds to normal brain and brain tumors and this effect is mediated at least in part by enhanced permeability of tight junctions. Keywords: Alkylglycerol, blood–brain barrier, brain tumor, Drug delivery, fluorescence markers, methotrexate, rat brain capillaries, tight junction, confocal microscopy Introduction The brain capillary endothelium plays a key role in the pathophysiology of various diseases of the CNS such as inflammatory disorders, tumors, ischemia, and seizures (Pardridge, 1998). The mechanisms of functional regulation and transport at the blood–brain barrier (BBB) are not well understood, and further investigation is needed to clarify both how BBB dysfunction is mediated in disease states and how transport systems at the barrier can be altered for therapeutic purposes. Currently, successful treatment of many brain disorders seems to be impossible even though highly active Drugs exerting powerful effects at the target site have been developed. Their efficacy is limited by very low penetration across the BBB (Neuwelt et al., 1999). Thus, enhancing or targeting Drug delivery to the brain has become a major issue in experimental neurology. Chemical modification of Drugs and the use of transport mediating agents or vector systems are possible strategies for Drug targeting to the brain (Smith, 1993; Huwyler et al., 1996; Reszka et al., 1997; Kroll & Neuwelt, 1998; Jolliet-Riant & Tillement, 1999); however, the clinical benefit of such measures has still to be demonstrated. In contrast to this, methods to open the BBB such as hyperosmotic disruption of the BBB or bradykinin receptor-induced increase in barrier permeability have already been shown to be effective in the treatment of experimental brain tumors (Blasberg et al., 1990; Nomura et al., 1994; Elliott et al., 1996; Matsukado et al., 1996; Kroll et al., 1998). Chemotherapy of malignant brain tumors in conjunction with osmotic opening of the BBB has been advanced to the stage of clinical trials and tumor response has been documented in both adults and pediatric patients (Gumerlock et al., 1992; Dahlborg et al., 1996; 1998; Doolittle et al., 2000). The inadequate Drug delivery across the BBB is a major factor that explains the poor response rates of chemosensitive brain tumors (Siegal & Zylber-Katz, 2002). Consequently, there is a need for new maneuvers designed to overcome the limited access of anticancer agents to the brain and to brain tumors. Recently, the transfer of a variety of chemotherapeutic Drugs across the BBB was shown to be increased dramatically by Intracarotid Drug Administration in the presence of short-chain alkylglycerols (Erdlenbruch et al., 2000; 2002). The Intracarotid injection of alkylglycerols resulted in a concentration-dependent accumulation of the coinjected Drugs within the brain. The effect was rapidly reversible and variations in the chemical structure of the alkylglycerols allowed for modulation of the extent of increased barrier permeability (Erdlenbruch et al., 2003). Of particular importance is the fact that there were no signs of toxicity in long-term experiments using Intracarotid 1-O-pentylglycerol and 2-O-hexyldiglycerol in rats (Erdlenbruch et al., 2003). In view of their low toxicity and the potent and well-controllable effects, Intracarotid alkylglycerols are thought to be a very promising principle to facilitate the transport of therapeutics across the BBB. However, little is known about the distribution of the delivered Drugs within the hemispheres and whether large compounds such as proteins will enter the brain after Intracarotid alkylglycerols. Furthermore, there are only marginal insights into the mechanisms involved in alkylglycerol-mediated BBB opening. Finally, nude mice represent the species mostly used for the treatment of experimental human brain tumor xenografts, but alkylglycerols were not administered in nude mice so far. Therefore, the purpose of the present study was (a) to estimate the 1-O-pentylglycerol-mediated increase in the penetration of small and large fluorescence markers into the brain of both normal and glioma-bearing rats and to investigate the spatial distribution of the different markers within the brain, (b) to elucidate the mechanisms of action of the alkylglycerols by studying the accumulation of fluorescein isothiocyanate (FITC)–dextran 40,000 (40 kDa) in freshly isolated rat brain capillaries using confocal microscopy and quantitative image analysis during incubation with different alkylglycerols, and (c) to demonstrate feasibility and effectivity of the permeabilizing effect of 1-O-pentylglycerol in nude mice by Intracarotid co-Administration with methotrexate (MTX).
