antioxidative and antidiabetic effects of some african medicinal plants aminu mohammed

341 Pages·2016·12.08 MB·English

ANTIOXIDATIVE AND ANTIDIABETIC EFFECTS OF
SOME AFRICAN MEDICINAL PLANTS

BY

AMINU MOHAMMED

Student number: 212562498

MARCH, 2016
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ANTIOXIDATIVE AND ANTIDIABETIC EFFECTS OF
SOME AFRICAN MEDICINAL PLANTS

BY

AMINU MOHAMMED
Student number: 212562498

Submitted in fulfillment of the requirements for the award of Doctor of
Philosophy degree in Biochemistry
School of Life Sciences
College of Agriculture, Engineering and Science

As the candidate’s supervisor I have approved this thesis/dissertation for submission.

Signed: ……………………….. Name: Dr. M.S. Islam Date: …………………….
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COLLEGE OF AGRICLUTURE, ENGINEERING AND SCIENCE
DECLARATION I - PLAGIARISM

I, Aminu Mohammed…………………………….. declare that
1. The research reported in this thesis, except where otherwise indicated, is my original research.
2. This thesis has not been submitted for any degree or examination at any other university.
3. This thesis does not contain other persons’ data, pictures, graphs or other information, unless
specifically acknowledged as being sourced from other persons.
4. This thesis does not contain other persons' writing, unless specifically acknowledged as being
sourced from other researchers. Where other written sources have been quoted, then:
a. Their words have been re-written but the general information attributed to them has been
referenced
b. Where their exact words have been used, then their writing has been placed in italics and inside
quotation marks, and referenced
5. This thesis does not contain text, graphics or tables copied and pasted from the Internet, unless
specifically acknowledged, and the source being detailed in the thesis and in the references sections.

Signed: …………………………..
Declaration Plagiarism 22/05/08 FHDR Approved
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DECLARATION II
I, Aminu Mohammed hereby declare that the dissertation entitled “Antioxidative and antidiabetic effects
of some African medicinal plants” is the result of my own investigation and research and that it has not
been submitted in part or in full for any other degree or to any other university. Where use of the work of
others was made, it is duly acknowledged in the text.

Student: Mr. Aminu Mohammed Signature ……………………….

Supervisor: Dr. M.S. Islam Signature ……………………….
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PUBLICATIONS AND PRESENTATIONS
DETAILS OF CONTRIBUTION TO PUBLICATIONS that form part of and/or include research presented
in this thesis (include publication in preparation, submitted, in press and published and give details of the
contributions of each author to the experimental work and writing of each publication).

In all the publications included in this thesis, I designed the work, performed all the experiments and wrote
all the publications. The co-authors contributed by conducting an editorial work, checking the scientific
content of the work and the correctness of my statistical analysis of data and interpretation of the findings.

Published and/or accepted papers

Publication 1
Mohammed, A., Koorbanally, N.A., Islam, M.S. (2015). Ethyl acetate fraction of Aframomum melegueta
fruit ameliorates pancreatic β-cell dysfunction and major diabetes-related parameters in a type 2 diabetes
model of rats. Journal of Ethnopharmacology 175: 518-527.

Publication 2
Mohammed, A., Koorbanally, N.A., Islam, M.S. (2015). Phytochemistry, anti-oxidative and anti-diabetic
effects of various parts of Eugenia caryophyllata Thunb. in vitro. Acta Poloniae Pharmaceutica-Drug
Research 72: 1201-1215.

Publication 3
Mohammed, A., Koorbanally, N.A., Islam, M.S. (2015). Anti-oxidative activity, phytochemistry, and
inhibition of key enzymes linked to type 2 diabetes by various parts of Aframomum melegueta in vitro.
Acta Poloniae Pharmaceutica-Drug Research In press (Accepted on 28 March, 2015).

Publication 4
Mohammed, A., Ibrahim, M.A., Islam, M.S. (2014). African medicinal plants with anti-diabetic potentials:
a review. Planta Medica 80: 354-377.
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Publication 5
Mohammed A., Koorbanally N.A., Islam M.S. Anti-diabetic effect of Xylopia aethiopica (Dunal) A. Rich.
(Annonaceae) fruit acetone fraction in a type 2 diabetes model of rats. Journal of Ethnopharmacology
180: 131-139.

Papers are intended to submit:

Publication 6
Mohammed, A., Islam, M.S. Anti-oxidant potential of Aframomum melegueta fruit ethyl acetate fraction in
a type 2 diabetes model of rats (in preparation).

Publication 7
Mohammed, A., Koorbanally, N.A., Islam, M.S. Anti-oxidative activity, phytochemistry, and inhibition of
key enzymes linked to type 2 diabetes by various parts of Xylopia aethiopica in vitro (in preparation).

Publication 8
Mohammed, A., Koorbanally, N.A., Islam, M.S. Anti-oxidative action and inhibition of key enzymes linked
to type 2 diabetes of various solvent fractions from fruit ethanolic extract of Xylopia aethiopica in vitro (in
preparation).

Publication 9
Mohammed, A., Koorbanally, N.A., Islam, M.S. In vivo anti-oxidant potential of Xylopia aethiopica fruit
acetone fraction in a type 2 diabetes model of rats (in preparation).

Publication 10
Mohammed, A., Koorbanally, N.A., Islam, M.S. Anti-oxidative and anti-diabetic effects of various parts of
Capsicum annuum L. (Solanaceae) in vitro (in preparation).

Publication 11
Mohammed, A., Koorbanally, N.A., Islam, M.S. Acetone fraction from Capsicum annuum fruit possesses
anti-oxidative effects and inhibits the activities of carbohydrate digesting enzymes in vitro (in preparation).
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Publication 12
Mohammed, A., Islam, M.S. Anti-diabetic effects of Capsicum annuum L. fruit acetone fraction in a type
2 diabetes model of rats (in preparation).

Publication 13
Mohammed, A., Islam, M.S. Anti-oxidant action of Capsicum annuum fruit acetone fraction in in a type 2
diabetes model of rats (in preparation).

Publication 14
Mohammed, A., Koorbanally, N.A., Islam, M.S. Anti-diabetic action of some African natural products
(Aframomum melegueta, Xylopia aethiopica and Capsicum annuum) in vitro and and isolation of bioactive
compounds (in preparation).

Presentions:

Presention 1
Mohammed, A., Islam, M.S. Anti-diabetic effect of acetone fraction from Xylopia aethiopica fruit in a type
2 diabetes model of rats. A poster presentation at the 23rd World Diabetes Congress 2015 (30th November,
2015 to 4th December, 2015) at Vancouver, Canada. I have been awarded one of the 100 prestigious
IDF Travel Grants to present the work at the conference.

Presention 2
Mohammed, A., Islam, M.S. Ethyl acetate fraction of Aframomum melegueta fruit ameliorates pancreatic
β-cell dysfunction and major diabetes-related parameters in a type 2 diabetes model of rats. A poster
presentation at the 15th Congress of International Society for Ethnopharmacology, (5-8 May, 2015) at
BeitZaman Hotel & Resort, Petra, Jordan.

Presention 3
Mohammed, A., Islam, M.S. Anti-diabetic effect of Xylopia aethiopica (Dunal) A. Rich. fruit acetone
fraction in a type 2 diabetes model of rats. An oral presentation at the College of Agriculture, Engineering
and Sciences Research Day (22nd September 2015) at C Block Lecture Theatre Complex, University of
KwaZulu-Natal, Pietermaritzburg Campus, Durban 4000, South Africa.
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Presention 4
Mohammed, A., Islam, M.S. Anti-diabetic effect of Aframomum melegueta ethyl acetate fraction from fruit
in type 2 diabetes model of rats. An oral presentation at the College of Agriculture, Engineering and
Sciences Research Day (27th October 2014) at T Block Lecture Theatre Complex, University of KwaZulu-
Natal, Westville Campus, Durban 4000, South Africa.

Presention 5
Mohammed, A., Islam, M.S. Anti-oxidative potential and inhibition of key enzymes linked to type-2
diabetes mellitus of various fractions from sweet pepper (Capsicum annuum L.) in vitro. A poster
presentation at the School of Life Sciences Research Day (26th May, 2014) at T Block Lecture Theatre
Complex, University of KwaZulu-Natal, Westville Campus, Durban 4000, South Africa.

Student: Mr. Aminu Mohammed Signature ……………………….
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ABSTRACT
Three (3) medicinal plants [Aframomum melegueta K. Schum., Xylopia aethiopica (Dunal.) A. Rich. and
Capsicum annuum L.] were selected based on their traditional uses in the treatment of diabetes in Africa.
Various crude extracts and fractions from different parts of the plants were screened using several anti-
oxidative and anti-diabetic tests in vitro. Most active fractions from each plant were used to examine in vivo
anti-diabetic activity in type 2 diabetes (T2D) rat model. Additionally, possible bioactive compounds from
most active extracts and fractions were analyzed by using GC-MS, TLC and NMR spectroscopy. The results
showed that ethanolic extracts derived from the fruits of the plants demonstrated excellent anti-oxidative
and anti-diabetic activities in vitro compared to other extracts from the same or different parts of these
plants. After fractionation, ethyl acetate fraction from A. melegueta and acetone fractions from
X. aethiopica and C. annuum exhibited strong radical scavenging (IC : 1-120 µg/mL) activity, inhibition
50
of hemoglobin glycation (IC : 100-150 µg/mL), α-amylase (IC : 50-170 µg/mL) and α-glucosidase (IC :
50 50 50
40-87 µg/mL) activities hence were used for the in vivo study. The GC-MS analysis of the three (3) most
active fractions revealed the presence of mostly phenolic compounds of 4-hydroxy-3-methoxyphenyl
derivatives. Furthermore, the data of the in vivo study showed that oral intervention of the fractions (150
and 300 mg/kg bw) for 4 weeks demonstrated potent anti-diabetic actions via improving body weight gain,
reducing feed and fluid intake and hyperglycemia, improving glucose tolerance ability, insulin sensitivity,
amelioration of pancreatic β-cell histology and β-cell functions, improving dyslipidemia in a T2D rat model.
Additionally, the pancreatic histopathological damages and other oxidative damages caused by the
induction of diabetes were attenuated to near normal in the liver, kidney, heart and pancreas of the treated
animals. The bioassay-guided fractionations lead to the isolation of 3 arylalkanes (6-paradol (1), 6-shagaol
(2), and 6- gingerol (3)) and oleanolic acid (4) from A. melegueta fruits, when oleanolic acid (4) was the
first to be isolated from A. melegueta. Moreover, 6-gingerol (3) and oleanolic acid (4) were similarly
isolated for the first time from X. aethiopica fruits as well. These compounds have exhibited significant
inhibitions against the α-amylase and α-glucosidase actions and thus are possible anti-diabetic agents and
the anti-diabetic action of A. melegueta and X. aethiopica fruits is attributed to the presence of these
compounds. This study also confirmed the use of these plants in African anti-diabetic traditional medicines
by traditional healers. However, further clinical study is required to confirm these effects in human subjects.
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DEDICATION
To my parent Alhaji Abubakar Mohammed and Hajiya Hauwa’u Aminu for their guidance, support and
wisdom.