IntroductionAlpha-mangostin is a bi

Introduction
Alpha-mangostin is a biosynthetic di-prenylated tetra-oxygenated
xanthone derivatives [1] which was firstly isolated from the fruit rind
of Garcinia mangostana GM by Schmid in 1855 [2]. Its chemical
structure of 1,3,6-trihydroxy-7-methoxy-2,8-bis(3-methyl-2-butenyl)-
9H-xanthen-9-one (Figure 1) was elucidated by Yates et al. [3]. Alphamangostin
represented the major active constituent among the detected
xanthones and therefore, it has been considered as analytical marker for
the quality control of GM products [4,5]. Recently, alpha-mangostin
has been commonly employed as ingredient in nutritional supplements,
herbal cosmetics [4] and some topical pharmaceutical preparations [6]
owing to its previously investigated multi-pharmacological activities
that were previously reviewed by Pedraza-Chaverri et al. [7]. It is well
known that alpha-mangostin exhibited a broad spectrum of biological
effects including anti-oxidant [8], anti-inflammatory [9], anti-allergic
[10], analgesic [11], neuro-protective [12], anti-mycobacterial [1], antifungal
[13], anti-bacterial [14] and anti-proliferative [15,16] activities.
In addition, recent studies have indicated that alpha-mangostin
had anti-metastatic effect against various cancer cell lines [17-19].
Nevertheless, the results of pharmacokinetic study of pure alphamangostin
revealed its low oral bioavailability attributed to the first
pass metabolism beside its non-selective distribution into the rat tissue
[20]. As such, we had previously encapsulated the alpha-mangostin into
poly (lactic-co-glycolic acid) PLGA nanospheres in order to enhance
its bioavailability through selective targeting of the compound into
specific tissue. The selectivity is envisaged to be achieved based on
“enhanced permeability and retention” (EPR) effect duly caused by
its size that passively distributed and retained within porous vascular
structure of tumor sites. In addition, the drug delivery employing
PLGA co-polymer that was fabricated into microspheres had long been
used clinically. Zoladex and Lupron were among the popular drugs.
The carrier system was also employed here due to its ability to provide
controlled-release of drugs apart from its biodegradability that do not
warrant second surgery to remove the carrier. Although biodegradable
PLGA microparticles have been widely employed as delivery vehicles
for various macromolecules such as protein [21], peptides [22] and
plasmid DNA [23], numerous small molecules were encapsulated in
order to enhance their therapeutic activities and to minimize their
adverse effects [24].
As part of routine characterization, encapsulation efficiency
of alpha-mangostin was required to be determined and can only
be accomplished following complete dissolution of the polymeric
microsphere. Previously described method [4] for the assay of pure
alpha-mangostin using methanol as solvent could not be applied to
quantify alpha-mangostin from the PLGA microspheres. This was due
to poor solubilising property of the methanol to completely dissolve the
polymeric PLGA. Another study had employed acetonitrile as solvent
to solubilise xanthone and 3-methoxyxanthone encapsulated-PLGA
nanocapsules but there was no report on the analytical validation
[25]. Further analytical methods were established and validated