Discussion
Patient noncompliance is a significant barrier to successful TB
management. According to a recent meta-analysis, patients who missed
10% or more of their doses contributed to poor treatment outcomes
(113). The risk of mortality, morbidity, and drug resistance increases
dramatically in those who do not show adherence to the TB
treatment15. Noncompliance with TB treatment is
multifaceted, but pill burden and dosing frequency play a significant
role (114). As a result, there is an urgent need for new formulations
and fixed dose combinations (FDC) that can provide all drugs in one pill
with reduced dosing frequency.
Our center has worked on PLGA nano-formulation of anti-tubercular drugs
for the treatment of pulmonary tuberculosis10. The
nanoformulation has been evaluated for oral and inhalation
administration in animals and a phase one ascending dose study is
ongoing 14. A sustained release profile and better
therapeutic effect were been seen 14. However, there
is not a single human study of this or similar formulation for the
evaluation of pharmacokinetics, pharmacodynamics and biodistribution
profile. Before conducting Pharmacodynamics studies in humans, we
require complete evaluation of safety, pharmacokinetics and
biodistribution profile in humans16. Therefore, we
have elucidated the biodistribution pattern of PLGA loaded rifampicin
nanoparticles in humans under gamma camera by using radiolabeled
rifampicin. We exclusively tested rifampicin in this investigation
because we wanted to get accurate results free from drug interference.
Another reason for using only rifampicin was that it is used to treatMeningococcal meningitis, Methicillin-Resistant Staphylococcus
Aureus (MRSA), Neisseria gonorrhoeae, Haemophilus influenzae, and
Legionella pneumonia infections in addition to tuberculosis.
Radio-pharmaceuticals have an emerging role in diagnosis, therapeutic,
or in both (theranostics). They have also been used in biodistribution
and mass-balance studies to see the fate of a drug in a living system
non-invasively. In this study, we labeled rifampicin by indirect method
with 99mTc to track the distribution of nanoparticles
in healthy human volunteers. The various parameters have been
standardized to obtain the highest radiochemical purity. When 500µg of
rifampicin, 15mCi activity, pH ranges between 6.5-7, was incubated at
80oC for 30 minutes in step one and at
100oC for 40 minutes in step two, more than 97 percent
radio-labeling yield was obtained. Animals were used to evaluate the
labeled rifampicin for polarity and distribution pattern changes. The
labeled rifampicin was found in every organ, with the highest
concentration in the stomach, followed by the lungs, liver, and
intestines, which is consistent with previous findings17.
In our study, we have evaluated rifampicin PLGA nanoparticles because we
wanted to study how the drug will behave when given as a
nano-formulation. This information would be applicable to other
anti-tubercular drugs too. A significant difference in plasma level of
rifampicin between the 5 to 15 hours of oral administration in
nanoformulation of rifampicin group compared to conventional group
(Fig.7). In nanoformulation group, the plasma levels of rifampicin were
detectable over five days but were below the limit of quantification
(BLQ) of 250 ng/ml. We have done the confirmatory animal PK and
biodistribution studies, in which, again, we got the plasma level of the
drug in BLQ. The reason for limited sustained release could be
dissipation of nanoparticles with feces after 24 hours which is average
gut transit time18. In addition to this, significant
drug concentration was observed in lymph nodes and spleen on the day
sixth after administration. This presence of drug could be attributed to
the smaller sized (100 nm or less) nanoparticles, absorbed through the
para-cellular spaces from GI track1920. Further in
lymph nodes the drug concentrations detected was also high i.e. up to 12
µg/ml on 6th-day. The possible explanation could be
the denominator effect as the lymph nodes harvested from each animal
were 200-300 µgs of weight. A significant difference in the PK
parameters in the two groups have been found, as elimination constant in
nanoformation has been decreased, which could have increased the other
parameters like t1/2, AUC, AUMC, and
MRT21. The significant difference in AUC/MIC and
percentage T>MIC could be because of sustained release
behavior of nanoformulation.
The free movement of nanoparticles throughout the GIT indicates major
proportion of nanoparticles remained un-absorbed. Nanoparticles were
started to get accumulated in the distal parts of the GI tract from the
5th hour of oral administration, which is in
concordance with gastro-illic transit time. Lucia et al. 2019 have done
an ex-vivo study of PLGA-PEG nanoparticles loaded with a
fluorescent dye, rhodamine B, and the anti-cancerous drug paclitaxel. In
that study, they saw the nanoparticles were in the gut lumen and started
accumulating in the large intestine as time increased after oral
administration.
They have also explored the absorption pattern of nanoparticles in the
GI track, persistent luminal localization of nanoparticles has been seen
at different time points 22. Same pattern has been
seen in our study, we found nanoparticles were get accumulated in large
intestines gamma camera and showed the release of drugs from there. The
higher counts in the intestines and lower counts in blood and urine over
the 24 hours in the nano-formulation group as compared to the
conventional group confirm the accumulation of nanoparticles in the
large intestines.
In conclusion, our study has shown the bio-distribution and
pharmacokinetic profile of PLGA nanoparticles in humans. Nanoparticles
get accumulated into distal parts of the gut from where the encapsulated
drug is released in a sustained release manner. Although the sustained
release of seven days was not observed in healthy human volunteers, an
increase in pharmacokinetic parameters in the nanoformulation group
could be utilized to decrease the dose of ATT for the treatment of
pulmonary tuberculosis.
Acknowledgment:
This work was funded by ICMR, New Delhi, India.
Conflict of interest
We don’t have any conflict of interest.
Data availability and statement
Research data are not shared
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