Biomedical Engineering Reference
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Fig. 11
Confocal microscopy of HeLa cells treated with (
a
), FITC-dextran-loaded liposomes;
(
b
), RhB-modified FITC-dextran-loaded liposomes for 4 h. The treated cells were stained with
lysosomal markers and analyzed by confocal microscopy.
1
: FITC-dextran-loaded plain liposomes
(
green
),
2
: LysoTracker Red-stained lysosomes (
red
),
3
: Overlay of 1 and 2 images with their
respective DIC image.
4
: RhB (
red
),
5
: anti-Lamp2 mAb-stained lysosomes (
blue
),
6
: Overlay of
4 and 5 images with their respective DIC image. Bar = 10 mm. Cell incubation with RhB1-
modified FITC-dextran-loaded liposomes for 4 h led to the localization of RhB fluorescence
mostly in the lysosomes with a high rate of the co-localization with the lysosomal marker
(Pearson's correlation coefficient, PCC 0.7; Mander's overlap coefficient, MOP 0.8). The cells
treated with the same concentration of FITC-dextran-loaded liposomes demonstrated much lower
localization of FITC-dextran in the lysosomes (PCC − 0.1; MOP 0.2)
(Vult von Steyern et al.
1996
). Novel acidic fluorescent probes based on
rhodamine-B have also been described and used for the optical imaging of the
intracellular H
+
(Zhang et al.
2009
).
We prepared liposomes loaded with the model compound, FITC-dextran, and
modified with RhB (Koshkaryev et al.
2010
). Confocal microscopy demonstrated
that RhB-liposomes co-localize well with the specific lysosomal markers, unlike
plain liposomes (Fig.
11
). The comparison of the FITC fluorescence of the lyso-
somes isolated by subcellular fractionation also showed that the efficiency of FITC-
dextran delivery into lysosomes by RhB-modified liposomes was significantly
higher compared to plain liposomes.
This was confirmed using 5-dodecanoylamino fluorescein di-b-D-galactopyrano-
side (C
12
FDG)-loaded liposomes. C
12
FDG, is a lipophilic substrate for the lysosomal
b-galactosidase (Rotman et al.
1963
). It was assumed that upon undergoing the
endocytosis, C
12
FDG-loaded liposomes would eventually deliver their contents into
lysosomes, and the intra-lysosomal b-galactosidase will hydrolyze the non-fluorescent
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