Abstract:
Oxidative stress-induced conditions and bacterial diseases constitute some of the major
causes of mortality worldwide. Their treatment is becoming a challenge due to
antimicrobial resistance, prohibitive costs, inaccessibility and side effects of the
conventional drugs. Thus, traditional medicine is becoming popular in the treatment of
these diseases in various parts of the world. The objectives of this study were to;(1)
identify the secondary metabolites in extracts of Albizia coriaria leaves (EOACL), (2)
determine the total phenolic and total flavonoid contents of EOACL, (3) establish the
antioxidant activity of EOACL, (4) evaluate the antibacterial activity of EOACL, and
(5) characterize the phytochemicals in the most active EOACL used in traditional
treatment of oxidative stress-induced conditions and bacterial diseases in Uganda. The
leaves were sampled from Jinja, Kole and Mbarara districts of Uganda, representing
the South East, Mid Northern and Southern drylands agroecological zones,
respectively. Shade-dried samples were ground into powder and successively extracted
with ethyl acetate, ethanol and distilled water. The extracts were chemically profiled
using classical phytochemical screening, ultraviolet-visible (UV-Vis) spectroscopy,
Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass
spectrometry (GC-MS). The total phenolic content, total flavonoid content, antioxidant
and antibacterial activities were determined using; Folin-Ciocalteu method, aluminum
chloride assay, 1,1-diphenyl-2-picrylhydrazyl assay and culture-based agar disc
diffusion method, respectively. The results obtained varied for the three agroecological
zones; Mbarara leaf extracts had many secondary metabolites and exhibited the highest
bioactivities, followed by Kole and Jinja extracts. Phytochemical screening results
indicated that phenols, alkaloids, saponins, flavonoids, cardiac glycosides and tannins
were the major secondary metabolites in EOACL. These results were confirmed by
UV-Vis spectra (with absorption maxima of 338 nm, 470 nm, 534 nm, 607 nm and 664
nm) and FTIR spectra which indicated the presence of O−H stretch (3370.27 cm -1 ),
C=O (1739.70 cm -1 ), N−H (3261.46 cm -1 ) and aromatic−C=C (1454.48 cm -1 ). Total
phenolic and flavonoid contents, and antioxidant activity were found to be highest for
ethanolic extracts, with the highest contents (101.72 ± 0.22 mg GAE/ g DW and 13.23
± 0.03 mg QE/ g DW) and antioxidant potential (IC 50 = 18.65 ± 0.06 mg/mL) being for
EOACL from Mbarara district. The high antioxidant potential of EOACL suggests their
potential role in the prevention of oxidative stress-induced conditions. Antibacterial
screening indicated that ethanolic extracts had the highest antibacterial activities with
mean zones of inhibition of 6.00 ± 1.73 to 10.00 ± 1.73 mm, 5.00 ± 1.00 to 12.30 ±
1.53 mm, 17.00 ± 0.00 to 25.00 ± 2.65 mm and 9.00 ± 1.73 to 16.00 ± 1.73 mm for
Escherichia coli (E. coli), Staphylococcus aureus, Pseudomonas aeruginosa and
Salmonella typhi, respectively. Ethyl acetate EOACL from Kole and Mbarara were
active against E. coli with inhibition zones of 3.00 ± 0.00 mm and 4.00 ± 2.00 mm
respectively. Ethyl acetate EOACL from Jinja and all the aqueous extracts showed no
antibacterial activity. Characterization of fractions of the most active (ethanolic)
EOACL using GC-MS led to the identification of nine compounds: lupeol (7), lupenone
(8), betulinic acid (9), benzyl alcohol (12), betulin (13), oleanolic acid (14), oleanolic
acid acetate (15), undecanol (16) and pterin-6-carboxylic acid (17) of which compounds
13-17 are being reported for the first time in Albizia coriaria. In conclusion, EOACL
were established to have compounds with antioxidant and antibacterial activities,
giving credence to their use in traditional management of oxidative stress-induced
conditions and bacterial diseases. Clinical trials using the active EOACL and the
identified compounds should be done.