CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 8, September 2012
466
AFRICA
Opuntia megacantha
leaf extract, which had hypoglycaemic
effects, reversed the inability of the kidney to excrete Na
+
in STZ
diabetes mellitus, suggesting that this plant may be beneficial.
17
We undertook a systematic survey of medicinal plants used
by rural communities in South Africa and have identified
several species with beneficial effects in the prevention of renal
complications in diabetes mellitus. These effects were observed
with both crude extracts and bioactive compounds isolated from
antidiabetic plants. In particular, we showed that plants such as
Sclerocarya
birrea
[(
A Rich) Hochst] [Anachardiaceae],
Persea
americana
(
Miller) [Lauraceae],
Ficus thonningii
(
Blume)
[
Moraceae] and
Helichrysium ceres
had reno-protective effects
(
Fig. 2).
17,32,38
Initial studies have shown that extracts from these
plants ameliorated renal dysfunction in experimental diabetes.
Subsequently, we isolated oleanolic acid as the bioactive
compound and have shown that it possesses reno-protective
effects in experimental diabetes mellitus. Therefore
S cordatum
-
derived oleanolic acid caused increased renal Na
+
excretion
in STZ-induced diabetic rats, which was mediated by an
improvement in glomerular filtration rate (Fig. 3).
63
Other
active agents identified in these plants include polysaccharides,
flavonoids, xanthones and peptides.
There are various mechanisms by which reno-protection
may be achieved, including modulation of AGEs, of the polyol
pathway, and of the PKC pathway, and anti-oxidative properties.
For example, morroniside isolated from
Corni fructus
has shown
reno-protection in experimental diabetes through a reduction in
the production of AGEs.
64
Additionally, some plants have been
shown to cause an improvement in renal function in experimental
diabetes mellitus through inhibition of ET-1 and TGF-
β
1
and the
endothelin-1 receptor A (ETRA).
65
Available evidence suggests that some herbal extracts interfere
with the concentrating and diluting mechanisms of tubular
transport processes in the proximal and distal tubules and/
or on other components of tubular cell membranes. Therefore
we speculate that oleanolic acid influences renal fluid and
electrolyte handling by altering the structural integrity and
function of tubular epithelial cells to affect reabsorption and
secretion.
Modification of risk factors in diabetes has an impressive
impact on morbidity and mortality in diabetic patients. An
overview of some of some medicinal plants currently used in
diabetic hypertension and kidney disease, together with the
possible mechanism(s) is summarised in Table 1.
Conclusion
We describe the therapeutic and pharmacological evidence in
support of some of the medicinal plant extracts used in the
management of hypertension and kidney disease in diabetes
mellitus. Some of these medicinal plant extracts are a potential
source of anti-diabetic drugs because of their therapeutic
efficacy and anti-diabetic mechanisms reported in experimental
animals. However, at present, the cellular/molecular mechanisms
of action of these plant extracts remain to be established.
Future research directed at the identification of active
components is the only viable option for supporting the efficacy
claims for all herbs. In the absence of such standardisation, health
practitioners and consumers alike should remain optimistic but
wary. Research funding to investigate potentially beneficial
effects of medicinal plants is critically important for optimal
patient care and safety.
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