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Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

Saunders NR, Dziegielewska KM, Møllgård K, Habgood MD - Front Neurosci (2015)

Bottom Line: The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations.There is no single marker suitable for all purposes.A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Developmental Neurobiology and Neurotrauma, Department of Pharmacology and Therapeutics, University of Melbourne Parkville, VIC, Australia.

ABSTRACT
In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

No MeSH data available.


Related in: MedlinePlus

Evans blue. As used at University College London, Department of Physiology circa 1960 for in vivo plasma volume estimation.
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Figure 1: Evans blue. As used at University College London, Department of Physiology circa 1960 for in vivo plasma volume estimation.

Mentions: The realization that brain barriers may play a critical role in a wide range of neurological disorders prompted a renewed interest in studies of their function and integrity (Saunders et al., 2008). Such studies require suitable models and especially markers to demonstrate integrity of the interfaces between the blood, the brain and the cerebrospinal fluid, CSF. Similarly markers are also required for the study of barriers in the developing brain and in its evolution, which are the main focus of the Frontiers Topic “Ontogeny and Phylogeny of Brain Barrier Mechanisms.” Dyes have a venerable history dating back to the end of the nineteenth-century, in studies of brain barrier mechanisms in both the developing and adult brain, although many ascribe incorrectly the first use of dyes for this purpose to Ehrlich in the mid nineteenth-century or to Goldmann (1909, 1913), in the early twentieth century (see Saunders et al., 2014). In times when there were no alternatives it seems reasonable that dyes should have been used as markers for brain barrier integrity, similar to their use in cardiovascular studies for measurement of plasma volume (Dawson et al., 1920). Particularly in the latter field scientists were well aware of the limitations of dyes and as soon as more satisfactory alternatives became available, notably radiolabeled proteins such as albumin, dyes were rapidly abandoned. In striking contrast, the use of dyes remained widespread in blood-brain barrier field in spite of their limitations, which have been well described since the mid twentieth-century. One dye in particular, Evans blue (Figure 1) is still the most commonly used marker of brain barrier integrity (Figure 2) and its use has increased substantially in recent years (Figure 3). Limitations of Evans blue as applied to studies of brain barriers, as well as of other dyes, will be reviewed here together with their properties. Another commonly used marker for brain barrier integrity is HRP (introduced in mid twentieth-century for electron microscopy studies by Straus (1959), Reese and Karnovsky (1967), and Brightman and Reese (1969) will also be discussed in this review.


Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

Saunders NR, Dziegielewska KM, Møllgård K, Habgood MD - Front Neurosci (2015)

Evans blue. As used at University College London, Department of Physiology circa 1960 for in vivo plasma volume estimation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4624851&req=5

Figure 1: Evans blue. As used at University College London, Department of Physiology circa 1960 for in vivo plasma volume estimation.
Mentions: The realization that brain barriers may play a critical role in a wide range of neurological disorders prompted a renewed interest in studies of their function and integrity (Saunders et al., 2008). Such studies require suitable models and especially markers to demonstrate integrity of the interfaces between the blood, the brain and the cerebrospinal fluid, CSF. Similarly markers are also required for the study of barriers in the developing brain and in its evolution, which are the main focus of the Frontiers Topic “Ontogeny and Phylogeny of Brain Barrier Mechanisms.” Dyes have a venerable history dating back to the end of the nineteenth-century, in studies of brain barrier mechanisms in both the developing and adult brain, although many ascribe incorrectly the first use of dyes for this purpose to Ehrlich in the mid nineteenth-century or to Goldmann (1909, 1913), in the early twentieth century (see Saunders et al., 2014). In times when there were no alternatives it seems reasonable that dyes should have been used as markers for brain barrier integrity, similar to their use in cardiovascular studies for measurement of plasma volume (Dawson et al., 1920). Particularly in the latter field scientists were well aware of the limitations of dyes and as soon as more satisfactory alternatives became available, notably radiolabeled proteins such as albumin, dyes were rapidly abandoned. In striking contrast, the use of dyes remained widespread in blood-brain barrier field in spite of their limitations, which have been well described since the mid twentieth-century. One dye in particular, Evans blue (Figure 1) is still the most commonly used marker of brain barrier integrity (Figure 2) and its use has increased substantially in recent years (Figure 3). Limitations of Evans blue as applied to studies of brain barriers, as well as of other dyes, will be reviewed here together with their properties. Another commonly used marker for brain barrier integrity is HRP (introduced in mid twentieth-century for electron microscopy studies by Straus (1959), Reese and Karnovsky (1967), and Brightman and Reese (1969) will also be discussed in this review.

Bottom Line: The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations.There is no single marker suitable for all purposes.A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Developmental Neurobiology and Neurotrauma, Department of Pharmacology and Therapeutics, University of Melbourne Parkville, VIC, Australia.

ABSTRACT
In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

No MeSH data available.


Related in: MedlinePlus