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The global market for drugs for the central nervous system (CNS) is greatly under-penetrated, and would have to grow by >500% just to equal the cardiovascular drug market.
More than 98% of the newly developed agents for CNS do not cross BBB.
Molecules should possess low molecular weight (<500 Da) and high lipophilicity in order to cross blood-brain barrier (BBB).
There are only a few diseases of the brain that are currently treated by CNS drugs.› Only affective disorders, insomnia, pain, and epilepsy respond to
small molecules › Most other brain diseases such as Alzheimer’s,Parkinson’s,Brain
Cancer, Stroke, Neuro-AIDS etc do not respond to small molecules.
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Recently developed large molecules such as therapeutic proteins, peptides, genes, monoclonal antibodies, cannot cross BBB.
Development of drugs for brain is incomplete without a parallel approach in brain drug delivery.
Ref: Pardridge, W.M. Brain Drug Targeting: The Future of Brain Drug Development, Cambridge University Press, 1, (2001), pp 3-9.
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Oral bioavailability of proteins and peptides is severely limited due to the epithelial barriers of the GIT and degradation by digestive enzymes.
GI passage of particles can be achieved by formulation of fine size ranges of approximately below 200 nm.
A Nano-size range favors uptake through› Absorptive Enterocytes› Intestinal M cells
Also, a size range below 200 nm favors escape from spleenic filtration effects thereby enhancing circulation half-life of nanoparticles.
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Polymeric nanoparticles can allow loading of such molecules within a polymeric matrix, protecting from enzymatic degradation and hydrolysis, as well as targeting to brain tissue.
However, application of nanoparticles as oral drug delivery systems are restricted due to their› Limited absorption across GIT.› Short circulation half-life.
(The peptide drug chosen for this study is dalargin, a hexapeptide with amino acid sequence Tyr-D-Ala-Gly-Phe-Leu-Arg which does not cross the BBB. It is an Leu-Enkephalin analog which binds with opioid receptors in brain and causes central analgesia)
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Nanoparticles can be “double-coated” with a combination of Tween 80 and PEG 20,000 successively to achieve “stealth” targeting properties.
Role of Tween 80
A Tween 80 coating over a polymeric nanoparticle leads to the adsorption of Apo lipoprotein E (Apo E) from plasma upon the nanoparticle surface.
Such nanoparticles interacts with Low Density Lipoproteins (LDL) receptors in BBB and reaches the brain interior by endocytic uptake mechanism.
Nanoparticles degrade in brain interior and peptide is released.
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Role of PEG 20,000
Poly (ethylene) glycol (PEG) is known to protect labile drugs against enzymatic degradation in GIT.
Higher molecular weight PEGs such as PEG 20,000, forms a protective “brush” against the digestive enzymes.
High molecular weight PEGs also provides “dysopsonic” effect against macrophageal clearance in the blood circulation.
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Emulsion (Anionic) polymerization
Medium (pH 2.5, 0.01N HCl) containing Dextran 70 (1.5%) as an emulsifier.
Polymerization for 4 hours with constant magnetic stirring at 8,000 rpm.
Medium was neutralized using 0.1 N NaOH until the final pH reached 7.0
Size excluded by multi-filtration steps using successive filters of 5 µ, 1.2 µ and 0.7 µ pore size diameters.
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Unreacted monomers and agglomerations removed by 3 cycles of washing and ultracentrifugation at 76,500 g for 1 hour.
Nanoparticles collected as wet pellets.
Immediately kept in lyophilizer at -40ºC and 130 × 10-4 mbar for 12 hours for freeze drying.
Finally, nanoparticles were obtained as free flowing, white powder and stored at 4ºC for further use.
The nanoparticle yield was 23% w/w.
Entrapment efficiency (EE %) was found to be 39.84 ± 4 % w/w
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Formulation Codes:
Coatings with:Tween 80 (%)
Coatings with:PEG 20,000 (%)
T0P0 0 0
T2P0 2 0
T1.5P0.5 1.5 0.5
T1P1 1 1
T0.5P1.5 0.5 1.5
T0P2 0 2
T2P2 2 2
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An average diameter of 100 nm with a polydispersity index of 0.018 obtained for the optimum formulation.
-25
-20
-15
-10
-5
0T0P0 T2P0 T1.5P0.5 T1P1 T0.5P1.5 T0P2 T2P2
PBCA-NDS Formulations
Zet
a P
oten
tials
(m
V)
14
0
10
20
30
40
50
60
70
80
90
100
0 10 20 30 40 50
Time (hours)
% D
rug
Re
lea
se
T0P0
T2P0
T1.5P0.5
T1P1
T0.5P1.5
T0P2
T2P2
15
16
0
10
20
30
40
50
60
70
80
90
100
T0P0 T2P0 T1.5P0.5 T1P1 T0.5P1.5 T0P2 T2P2
PBCA-NDS Formulations
% Dru
g Rem
aining
40
50
60
70
80
90
100
0 0.5 1 1.5 2 2.5 3
Time (hours)
% D
rug
Rem
aing
T2P2
T0P0
0
1020
30
4050
60
70
8090
100
T0P0 T2P0 T1.5P0.5 T1P1 T0.5P1.5 T0P2 T2P2
PBCA-NDS Formulations
% Dru
g Rem
aining
17
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8 10 12
Time (hours)
% D
rug
Rem
aining
T2P2
T0P0
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Formulation Code SummaryC1 PBS solution {Control 1}
C2 PBS + Tween (2%) {Control 2}
C3 PBS + PEG (2%) {Control 3}
C4 PBS + Tween (2%) + PEG (2%) {Control 4}
C5 PBS + Drug {Control 5}
C6 PBS + Drug + Tween (2%) {Control 6}
C7 PBS + Drug + PEG (2%) {Control 7}
T2P2-N PBS + Drug + Tween (2%) + PEG (2%) + No nanoparticles present
T0P0 PBS + Drug + Nanoparticles + Tween (0%) + PEG (0%)
T2P0 PBS + Drug + Nanoparticles + Tween (2%) + PEG (0%)
T1.5P.5 PBS + Drug + Nanoparticles + Tween (1.5%) + PEG (0.5%)
T1P1 PBS + Drug + Nanoparticles + Tween (1%) + PEG (1%)
T.5P1.5 PBS + Drug + Nanoparticles + Tween (0.5%) + PEG (1.5%)
T0P2 PBS + Drug + Nanoparticles + Tween (0%) + PEG (2%)
T2P2 PBS + Drug + Nanoparticles + Tween (2%) + PEG (2%)
T2P2 + A PBS + Drug + Nanoparticles + Tween (2%) + PEG (2%) + Naltrexone HCl
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0
20
40
60
80
100
0 15 30 45 60 75 90 105 120
Time Points (mins)
% M
PE
T2P2T2P2+AntaT0P2T.5P1.5T1P1T1.5P.5T2P0T0P0T2P2-Nano
(*) = p < 0.05, compared with T0P0
*
*
*
0
20
40
60
80
100
7.5 15 22.5 30 37.5 45 52.5
Dose (mg/kg)
% M
PE
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Double-coated PBCA-NDSs with overcoats of Tween 80 and PEG 20,000 represent a feasible method to deliver and target peptides to brain via the oral route.
Coating of nanoparticles with 2% Tween and 2% PEG represents the optimal formulation for PBCA nanoparticulate system.
PBCA-NDSs with average diameter of 100 nm represents a satisfactory size for oral and targeted peptide delivery to the brain.
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