Antioxidant and antiproliferative activities of methanolic extract from a neglected agricultural product: corn cobs

Abstract

Neglected agricultural products (NAPs) are defined as discarded material in agricultural production. Corn cobs are a major waste of agriculture maize. Here, a methanolic extract from corn cobs (MEC) was obtained. MEC contains phenolic compounds, protein, carbohydrates (1.4:0.001:0.001). We evaluated the in vitro and in vivo antioxidant potential of MEC. Furthermore, its antiproliferative property against tumor cells was assessed through MTT assays and proteins related to apoptosis in tumor cells were examined by western blot. MEC showed no hydroxyl radical scavenger capacity, but it showed antioxidant activity in Total Antioxidant Capacity and DPPH scavenger ability assays. MEC showed higher Reducing Power than ascorbic acid and exhibited high Superoxide Scavenging activity. In tumor cell culture, MEC increased catalase, metallothionein and superoxide dismutase expression in accordance with the antioxidant tests. In vivo antioxidant test, MEC restored SOD and CAT, decreased malondialdehyde activities and showed high Trolox Equivalent Antioxidant Capacity in animals treated with CCl4. Furthermore, MEC decreased HeLa cells viability by apoptosis due an increase of Bax/Bcl-2 ratio, caspase 3 active. Protein kinase C expression increased was also detected in treated tumor cells. Thus, our findings pointed out the biotechnological potential of corn cobs as a source of molecules with pharmacological activity.

Figure 1

In vitro DPPH activity scavenging of MEC. The activity of Methanolic Extract is represented by the continuous line. The dashed line expresses activity of the known antioxidant α-tocopherol. MEC and positive control were used at the same concentrations (0; 0.5; 1.0; 2.5; 5.0; 10; 15 µg/mL). Letters ^a,b,c,d,e Indicate significantly differences between different concentrations of the same sample. ^x,y Represent significantly difference between different samples at similar concentrations. Student-Newman-Keuls test (p < 0.05).

Figure 2

In vitro reducing power effect of MEC. The test expresses sample ability to reduce the iron ions Fe³⁺ to Fe²⁺. The activity of methanolic extract has been represented to continuous line. The dashed line expresses activity to already known antioxidant (ascorbic acid). MEC and ascorbic acid were used in the follow concentrations 0; 20; 40; 80; 120; 160; 300 µg/mL. ^a,b,c,d,e Indicate significantly differences between different concentrations of the same sample. ^x,y Represent significantly difference between different samples at similar concentrations. Student-Newman-Keuls test (p < 0.05) Absorbance at 700 nm.

Figure 3

In vitro superoxide radicals scavenging activity of MEC. The methanolic extract reaches maximum activity with 40 µg/mL of sample. Sample concentrations used were 0; 2.5; 5.0; 10; 20; 40; 50 µg/mL. Letters ^a,b,c,d,e Indicate significantly differences between different concentrations of the same sample. Student-Newman-Keuls test (p < 0.05).

Figure 4

Effect of MEC on level of CAT, SOD and MT in HeLa cells. Graphic represents the relation of protein normalized to actin. (A) Catalase enzyme; (B) MT—Metallothionein; (C) SODMn—Superoxide dismutase. In the upper right are the images of the western blot of proteins involved. Letters ^a,b,c,d Indicate significantly differences between different concentrations of the same sample. Student-Newman-Keuls test (p < 0.05).

Figure 5

Effect of MEC on HeLa cell proliferation measured by MTT test. HeLa cells proliferation was carry out in the presence or absence of MEC (0; 2.5; 5.0; 10; 20; 40; 50 µg/mL). Letters ^a,b,c,d Indicate significantly differences between different concentrations of the same sample. Student-Newman-Keuls test (p < 0.05).

Figure 6

Effect of MEC on several proteins levels involved in cell death. Graphic represents the relation of protein normalized to actin. (A) Bcl-2 protein; (B) Bax protein; (C) pro-Caspase 3; (D) PKC – Protein kinase; (E) in the box, Bax/Bcl-2 ratio. In the upper right are the images of the western blot of proteins involved. Letters ^a,b,c,d Indicate significantly differences between different concentrations of the same sample. Student-Newman-Keuls test (p < 0.05).