Screening the dermatological potential of plectranthus species components: antioxidant and inhibitory capacities over elastase, collagenase and tyrosinase

Abstract

A series of Plectranthus spp. plant extracts (aqueous, acetonic, methanolic and ethyl acetic) obtained from eight different species, and previously isolated compounds (ranging from polyphenols, diterpenes and triterpenes), were assayed for in vitro inhibition of the skin-related enzymes tyrosinase, collagenase and elastase, and for studying their antioxidant properties. The ethyl acetic extracts of P. grandidentatus and P. ecklonii registered the highest antioxidant activity, whereas acetonic, methanolic and ethyl acetic extracts of P. ecklonii, P. grandidentatus, P. madagascariensis and P. saccatus concerning the enzymatic inhibition assays revealed high anti-tyrosinase and anti-collagenase activities. From the isolated compounds tested, abietane diterpenes and triterpenes were highly active against tyrosinase and elastase activity. Overall, the experimental results showed the powerful antioxidant and inhibitory action on skin-related enzymes tyrosinase, collagenase and elastase of Plectranthus spp. extracts and/or isolated compounds, supporting their further research as bioactive metabolites against skin sagging and hyperpigmentation in cosmetic and pharmaceutical formulations.

Keywords: Plectranthus; antioxidant; collagenase; elastase; tyrosinase.

Graphical abstract

Figure 1.

Signalling pathway induced by ultraviolet (UV) radiation causing skin damage. Radical oxygen species (ROS) up-regulated mitogen activated protein kinases (MAPK) cascades enhance transcriptional activity of activator protein 1 (AP-1) heterodimer (comprised of c-Jun and c-Fos) thus increasing metalloproteinases (MPPs) expression. Additionally, transforming growth factor (TGF)-/Smad signalling pathway is down-regulated by over-accumulation of ROS, decreasing the synthesis of extracellular matrix (ECM) proteins such as collagenase and elastin.

Figure 2.

Studied natural compounds isolated from Plectranthus spp: 7-acetoxy-6-hydroxyroyleanone (1), 6,7-dihydroxyroyleanone (2), 6,7-dehydroroyleanone (3), Parvifloron D (4), -sitosterol (5), stigmasterol (6), oleanolic acid (7), ursolic acid (8), (13S,15S)-6,7,12,19-tetrahydroxy-13,16-cyclo-8-abietene-11,14-dione (9), (11 R*,13E)-11-acetoxyhalima-5,13-dien-15-oic acid (10), Plectrornatin C (11), 1,6-di-O-acetylforskolin (12), 1,6-di-O-acetyl-9-deoxyforskolin (13), -amyrin (14), -amyrin (15), chlorogenic acid (16) and rosmarinic acid (17).

Figure 3.

In vitro antioxidant activity of Plectranthus spp. organic extracts at 100 g/mL measured as percentage of DPPH radical scavenging activity. The results are presented as means percentage values, considering the absorbance of quercetin as the positive control. Data are expressed as the mean ± SD (n = 3) **p < 0.005 ***p < 0.0001 vs negative control (DPPH in ethanol). DPPH: 2,2-diphenyl-1-picrylhydrazyl; ns: not significant; SD: Standard Desviation. Values were determined by one-way ANOVA followed by Tukey HSD comparison test.

Figure 4.

In vitro anti-tyrosinase activity of Plectranthus spp. (A) Organic extracts at 50 g/mL. (B) Aqueous extracts at 50 g/mL. (C) Isolated compounds at 50 g/mL. The results are presented as means percentage values, considering the absorbance of kojic acid as the positive control. Data are expressed as the mean ± SD (n = 3) *p < 0.05 **p < 0.005 ***p < 0.0001 vs negative control (DMSO 0.5% (v/v) in PBS buffer). DMSO: dimethyl sulfoxide; ns: not significant; PBS: phosphate-buffered saline; SD: Standard Deviation. Values were determined by one-way ANOVA followed by Tukey HSD comparison test.

Figure 5.

In vitro anti-collagenase activity of Plectranthus spp. (A) Organic extracts at 100 g/mL. (B) Aqueous extracts at 100 g/mL. (C) Isolated compounds at 100 g/mL. The results are presented as means percentage values, considering the absorbance of EGCG as the positive control. Data are expressed as the mean ± SD (n = 3) ***p < 0.0001 vs negative control (DMSO 0.3% (v/v) in Tricine buffer). DMSO: dimethyl sulphoxide; EGCG: epigallocatechin gallate; ns: not significant; SD: Standard Deviation. Values were determined by one-way ANOVA followed by Tukey HSD comparison test.

Figure 6.

In vitro anti-elastase activity of Plectranthus spp. (A) Organic extracts at 100 g/mL. (B) Aqueous extracts at 100 g/mL. (C) Isolated compounds at 100 g/mL. The results are presented as means percentage values, considering the absorbance of ursolic acid as the positive control. Data are expressed as the mean ± SD (n = 3) ***p < 0.0001 vs negative control (DMSO 1% (v/v) in Tris-HCl buffer). DMSO: dimethyl sulphoxide; HCl: Hydrochloride; ns: not significant; SD: Standard Deviation; Tris: tris(hydroxymethyl) aminomethane. Values were determined by one-way ANOVA followed by Tukey HSD comparison test.