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. 2022 Aug 12;27(16):5159.
doi: 10.3390/molecules27165159.

Anti-Obesity Evaluation of Averrhoa carambola L. Leaves and Assessment of Its Polyphenols as Potential α-Glucosidase Inhibitors

Nehal S Ramadan  1 , Nabil H El-Sayed  1 , Sayed A El-Toumy  1 , Doha Abdou Mohamed  2 , Zeinab Abdel Aziz  3 , Mohamed Sobhy Marzouk  1 , Tuba Esatbeyoglu  4 , Mohamed A Farag  3 , Kuniyoshi Shimizu  5
Affiliations

Anti-Obesity Evaluation of Averrhoa carambola L. Leaves and Assessment of Its Polyphenols as Potential α-Glucosidase Inhibitors

Nehal S Ramadan et al. Molecules. .

Abstract

Averrhoa carambola L. is reported for its anti-obese and anti-diabetic activities. The present study aimed to investigate its aqueous methanol leaf extract (CLL) in vivo anti-obese activity along with the isolation and identification of bioactive compounds and their in vitro α-glucosidase inhibition assessment. CLL improved all obesity complications and exhibited significant activity in an obese rat model. Fourteen compounds, including four flavone glycosides (1-4) and ten dihydrochalcone glycosides (5-12), were isolated and identified using spectroscopic techniques. New compounds identified in planta included (1) apigenin 6-C-(2-deoxy-β-D-galactopyranoside)-7-O-β-D-quinovopyranoside, (8) phloretin 3'-C-(2-O-(E)-cinnamoyl-3-O-β-D-fucopyranosyl-4-O-acetyl)-β-D-fucopyranosyl-6'-O-β-D fucopyranosyl-(1/2)-α-L arabinofuranoside, (11a) phloretin3'-C-(2-O-(E)-p-coumaroyl-3-O-β-D-fucosyl-4-O-acetyl)-β-D-fucosyl-6'-O-(2-O-β-D-fucosyl)-α-L-arabinofuranoside, (11b) phloretin3'-C-(2-O-(Z)-p-coumaroyl-3-O-β-D-fucosyl-4-O-acetyl)-β-D-fucosyl-6'-O-(2-O-β-D-fucosyl)-α-L-arabinofuranoside. Carambolaside M (5), carambolaside Ia (6), carambolaside J (7), carambolaside I (9), carambolaside P (10a), carambolaside O (10b), and carambolaside Q (12), which are reported for the first time from A. carambola L. leaves, whereas luteolin 6-C-α-L-rhamnopyranosyl-(1-2)-β-D-fucopyranoside (2), apigenin 6-C-β-D-galactopyranoside (3), and apigenin 6-C-α-L-rhamnopyranosyl-(1-2)-β-L-fucopyranoside (4) are isolated for the first time from Family. Oxalidaceae. In vitro α-glucosidase inhibitory activity revealed the potential efficacy of flavone glycosides, viz., 1, 2, 3, and 4 as antidiabetic agents. In contrast, dihydrochalcone glycosides (5-11) showed weak activity, except for compound 12, which showed relatively strong activity.

Keywords: Averrhoa carambola L.; Oxalidaceae; antidiabetic; dihydrochalcone; flavone glycosides; obesity; type 2 diabetes.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Body weight and biochemical parameters in the 4th week of treatment of experimental animals with Orly and CLL compared to normal and obese groups. (A) The initial, final body weights (BW) and BW gain (g). (B) The level of plasma total cholesterol (TCh mg/dL), triglycerides (TG mg/dL), high-density lipoprotein cholesterol (HDL-Ch mg/dL), and low-density lipoprotein cholesterol (LDL-Ch mg/dL). (C) The level of leptin (ng/mL), insulin (μg/L), glucose (mg/dL), and α-amylase (U/L). (D) The level of plasma butyrylcholinesterase (BChE (U/L)) and plasma catalase activity (CAT (U/L)). (E) The level of malondialdehyde (MDA (nmol/mL) and TCh/HDL. (F) The level of plasma uric acid (mg/dL) and plasma creatinine (mg/dL). (G) Calculated insulin resistance (IR). (H) The activity of aspartate transaminase (AST (IU/L)), alanine transaminase (ALT (IU/L)), and urea (mg/dL). Each bar graph represents the mean replicate measurement (n = 6) expressed as mean ± S.E. The bar graphs with a similar lower-case letter (such as ‘a’) among experimental groups are not significantly different from each other (p > 0.05). The bar graphs with different lower-case letters (such as a, b, c, d, and e) are statistically different from each other (p < 0.05).
Figure 2
Figure 2
Chemical structures of compounds 1–12 isolated from CLL extract.
Figure 3
Figure 3
Key HMBC correlations of compound 1, 8, and 11a.
Figure 4
Figure 4
(A) IC50 (µM) of tested compounds against α-glucosidase enzymes in vitro. (B) The potential sites of flavone C-glycosides affecting α-glucosidase inhibitory potential. (C) The potential sites of dihydrochalcone C-glycosides affecting the α-glucosidase inhibitory potential. The up arrows represent increased inhibition, whereas the down arrows represent decreased inhibition activity. Results are expressed as mean ± SE (n = 3).
Figure 5
Figure 5
Collective scheme for extraction, isolation, and biological activities performed on A. carambola leaves.
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