Effect of Carica papaya on IRS-1/Akt Signaling Mechanisms in High-Fat-Diet-Streptozotocin-Induced Type 2 Diabetic Experimental Rats: A Mechanistic Approach

Abstract

Despite rigorous endeavors, existing attempts to handle type 2 diabetes (T2DM) are still a long way off, as a substantial number of patients do not meet therapeutic targets. Insulin resistance in skeletal muscle is discerned as a forerunner in the pathogenesis of T2DM and can be detected years before its progress. Studies have revealed the antidiabetic properties of Carica papaya (C. papaya), but its molecular mechanism on insulin receptor substrate-1 (IRS-1)/Akt signaling mechanisms is not yet known. The present study aimed to evaluate the role of C. papaya on IRS1 and Akt in high-fat-diet-streptozotocin-induced type 2 diabetic rats and also to analyze the bioactive compounds of C. papaya against IRS-1 and Akt via in silico analysis. Ethanolic extract of the leaves of C. papaya (600 mg/kg of body weight) was given daily for 45 days postinduction of T2DM up to the end of the study. Gluconeogenic enzymes, glycolytic enzymes, gene expression, and immunohistochemical analysis of IRS-1 and Akt in skeletal muscle were evaluated. C. papaya treatment regulated the levels of gluconeogenic and glycolytic enzymes and the levels of IRS-1 and Akt in skeletal muscle of type 2 diabetic animals. In silico studies showed that trans-ferulic acid had the greatest hit rate against the protein targets IRS-1 and Akt. C. papaya restored the normoglycemic effect in diabetic skeletal muscle by accelerating the expression of IRS-1 and Akt.

Keywords: Akt; Carica papaya; insulin receptor substrate-1; insulin signaling; molecular dynamics; skeletal muscle.

Figure 1

Outcome of ethanolic extract of C. papaya on (a) glucose-6-phosphatase and (b) fructose-1,6 bisphosphatase levels in control and diabetic rats. Each bar illustrates the mean ± SEM of eight rats, with p < 0.05 demonstrating significant differences between the groups: a—control; b—diabetes; c—diabetic rats administered with ethanolic extract of C. papaya; d—diabetic rats treated with metformin.

Figure 2

Outcome of ethanolic extract of C. papaya on (a) hexokinase and (b) pyruvate kinase levels in control and diabetic rats. Each bar illustrates the mean ± SEM of eight rats, with p < 0.05 demonstrating significant differences between the groups: a—control; b—diabetes; c—diabetic rats administered with ethanolic extract of C. papaya.

Figure 3

(a) IRS-1 mRNA expression levels in ethanolic extract of C. papaya in control and diabetic rats; (b) Akt mRNA expression levels in ethanolic extract of C. papaya in control and diabetic rats. Each bar demonstrates the mean ± SEM of eight rats, with p < 0.05 showing significant differences between the groups: a—control; b—diabetes.

Figure 4

Protein expression of IRS-1 using an immunohistochemical assay (magnification: ×100): (a) control rats; (b) type 2 diabetic rats; (c) type 2 diabetic rats treated with C. papaya (600 mg/kg b.wt); (d) type 2 diabetic rats treated with metformin (50 mg/kg, b.wt); (e) control rats treated with C. papaya (600 mg/kg b.wt).

Figure 5

Protein expression of Akt using an immunohistochemical assay (magnification: ×100): (a) control rats; (b) type 2 diabetic rats; (c) type 2 diabetic rats treated with C. papaya (600 mg/kg b.wt); (d) type 2 diabetic rats treated with metformin (50 mg/kg, b.wt); (e) control rats treated with C. papaya (600 mg/kg b.wt).

Figure 6

Molecular interaction of best three compounds with IRS-1; (a) trans-ferulic acid; (b) kaempferol; (c) quercetin.

Figure 7

Molecular interaction of best three compounds with Akt; (a) p-coumaric acid; (b) caffeic acid; (c) trans-ferulic acid.

Figure 8

(a) RMSD; (b) RMSF; (c) SASA; (d) RG of IRS-1 protein with the top three compounds. Kaempferol shown in red; quercetin (green); trans-ferulic acid (blue).

Figure 9

(a) RMSD; (b) RMSF; (c) SASA; (d) RG of Akt protein with the top three compounds. Caffeic acid shown in red; p-coumaric acid (green); trans-ferulic acid (blue).