The present study was carried out to study medicinal plants of Arabian origin as anti-glycation agents. In this study, we systematically evaluated 26 medicinal plants for their anti-glycation activity potential (Table 1). Results revealed that out of 26 medicinal plants, five (i.e. Sida cordifolia, Plumbago zeylanica, Tribulus terrestris, Glycyrrhiza glabra, and Rosa indica) were found active against the in-vitro protein glycation. Among five active plants, Glycyrrhiza glabra L. (Voucher number: 37999) was found to be the most potent one. G. glabra belongs to the Fabaceae/Leguminosae family. It is famous for underground stems, which is widely used in flavor confectionery [21]. This plant is also known for its diverse biological activities, such as anti-inflammatory, anti-microbial, hepatoprotective properties. It is also used as folk remedy for sore throats, mouth ulcers, stomach ulcers, inflammatory stomach conditions, and indigestion [22–26]. G. glabra was also reported for hypoglycemic activity in rats [27]. G. glabra- based herbal formulations are known to exhibit anti-AGEs activities. Additionally a pure substance (glycyrrhizic acid) from the roots of this plant showed anti-glycation potential in high fat diet treated rats [14, 28, 29]. Major constituents of G. glabra include flavonoids, isoflavonoids, saponins, and tripentenes [30]. Literature has no report describing the in-vitro anti-glycation activity of root extracts of G. glabra. In our study methanolic extracts of G. glabra showed 63.42 % inhibition (IC50 = 0.408 ± 0.027 mg/mL) in BSA-MG glycation assay (Table 1; Fig. 1). Therefore in view of these results, G. glabra may be used as a therapeutic agent to reduce AGEs formation in diabetes.
Rosa indica L. (Voucher number: 91863) is an ornamental plant, known for perfuming effect. It possess pharmacological properties such as antioxidant, anti-fungal, anti-bacterial and urease inhibitory activities [31–33]. Manikandan et al. reported the synthesis of silver nanoparticles using extract of the petals of Rosa indica (ethanolic extract), and its in-vitro antibacterial, anticancer and anti-inflammatory activities. Different parts of R. indica (e.g. petals and buds) are known to treat runny nose, blocked bronchial tubes, asthma, and chest problems [34]. The bioactive compounds isolated, from Rosa indica, include flavonoids, alkaloids, phenols, saponins, and steroids [35]. There is no report describing the anti-glycation activity of R. indica. In our in-vitro experimental assay, R. indica showed a good anti-glycation potential with 78.56 % inhibition (IC50 = 0.596 ± 0.0179 mg/mL) (Table 1; Fig. 2).
The third most potent plant Sida cordifolia L. (Voucher number: 12135) belongs to Malvaceae family. Roots of S. cordifolia are used in coryza, pain, cardiac diseases, nervous disorders, and for anti-inflammatory, analgesic, hypoglycemic, antimicrobial, anti-hypercholesterolemic, antioxidant activities [36–40]. In addition, the extract of S. cordifolia has shown the anti-aging properties [41]. Major phytoconstituents of Sida cordifolia include alkaloids, flavonoids, steroids, phytoecdysteroids, and fatty acids [42]. As per literature survey, this is the first report describing the anti-glycation potential of the methanolic extracts of the seeds of S. cordifolia. In the present study, S. cordifolia showed 81.98 % inhibition of BSA-MG glycation with IC50 = 0.63 ± 0.009 mg/mL (Table 1; Fig. 3).
Crude extract of Plumbago zeylanica L. (voucher No. 24177) and Tribulus terrestris L. (voucher No. 53177) showed a week anti-glycation potential (IC50 = 1.300 ± 0.033, and 1.690 ± 0.020 mg/mL, respectively), when compared with the other active plants of this study (Table 1; Fig. 4 and 5).
The plant P. zeylanica showed many biological properties, such as anti-inflammatory, hypolipidimic, wound healing, antidiabetic, memory-inducing, blood coagulation, anti-malarial, anti-fertility, anti-microbial, anticancer, antiviral, antioxidant, and anti-larvicidal activities. The phytochemical investigation showed that these biological activities are due to the presence of compounds, such as elliptinone, zeylanone, sistosterol and plumbagin [43]. Tribulus terrestris L. is known for several pharmacological properties, and its use in folk medicine for the treatment of impotence, edema, rheumatism, kidney stones, and hypertension. T. terrestris contains phenols, saponins, alkaloids and sterols as active constituents [44].
Oxidative reactions are known to be involved in the protein glycation cascade. Most importantly, AGEs via their receptors (RAGEs), inactivate the enzymes and promote the formation of reactive oxygen species. Dual activity, i.e. antioxidant and anti-glycation, is therefore a valid approach for the treatment of complications resulting from hyperglycemia [11, 12]. The antioxidant activities of plants are mainly due to two mechanisms, i.e. scavenging the free radicals produced in the body or by chelating the transition metal [45]. Keeping this in view, all active plants (i.e. Sida cordifolia, Plumbago zeylanica, Tribulus terrestris, Glycyrrhiza glabra, and Rosa indica) were evaluated for their DPPH, superoxide anion radical scavenging and iron-chelating activities.
DPPH (2,2-diphenyl-1-picrylhydrazyl) is a stable free radical, in which electronic delocalization resulted in deep violet coloration. Certain plant extracts are able to donate hydrogen atoms and convert the DPPH radical into its reduced and stable form, and hence resulted in fading of violet color into pale yellow [45]. The in-vitro DPPH radical scavenging assay was performed with gallic acid as a positive control. Results revealed that all plants were active (Table 2; Fig. 6).
Glycation reaction, and AGEs are known to produce reactive oxygen intermediates (mainly superoxide anion and hydrogen peroxide) both in-vitro as well as in-vivo. In the in-vivo system, once generated, H2O2 can quickly enter inside the cell, while other activated oxygen species cannot. Within the cell, H2O2 can react with iron or copper in the Fenton reaction, and leads to the formation of hydroxyl radicals. These hydroxyl radicals contribute factors in diabetes-related oxidative stress [46]. Therefore metal chelators (e.g. Fe-chelators) can effectively serve as AGE-inhibitors. Interestingly when we evaluated the five active plants (i.e. S. cordifolia, P. zeylanica, T. terrestris, G. glabra, and R. indica) for iron chelating ability, all were found to be inactive, showing that they do not have ability to chelate with the iron at 2 mg/mL concentration.
Superoxide radical anion is formed from the reduction (i.e. one-electron) of free molecular oxygen by membrane-bound enzyme i.e. nicotinamide adenine dinucleotide phosphate Oxidase (NADPH). Ortwerth et al. reported that in glycation reaction, superoxide anion is formed by superoxide dismutase-dependent reduction of ferricytochrome C. They reported that Amadori products (formed from the reaction of lysine and small sugars) can generate superoxide anion even in the absence of metals [47]. Therefore, scavenging of superoxide anion was identifying as useful approach to inhibit the glycation mediated complications. In the final step of this study, we subjected all five plants for superoxide anion radical scavenging assay. Results showed that except G. glabra, all four plants scavenge the superoxide anion radicals effectively (Table 2, Figs. 7, 8, 9, and 10).