Onosma ambigens: Phytochemical composition, antioxidant and enzyme inhibitory activity

https://doi.org/10.1016/j.indcrop.2020.112651Get rights and content

Highlights

  • Chemical composition and biological activity of O. ambigens was studied.

  • Flavonoid glucosides and rosmarinic acid were found as the major compounds.

  • The methanol extract showed remarkable antioxidant activity.

  • Methanol and ethyl acetate extracts were the potent inhibitors of tyrosinase and α-amylase.

  • A significant correlation was determined between chemical composition and activity.

Abstract

Due to their medical importance, the number of studies on the enlightenment of the biological activities of Onosma species has been increasing over the years. In this study, besides the phytochemical composition of Onosma ambigens Lacaita (Boraginaceae), in vitro antioxidant, tyrosinase and α-amylase inhibitory activities of extracts obtained by using different solvents (ethyl acetate, methanol and water) were investigated. As a result of the spectrophotometric analysis, it was determined that methanol extract was rich in both phenolics (51.19 mg GAEs/g extract) and flavonoids (45.39 mg QEs/g extract). According to the results of liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) analysis, the major components of methanol extract were determined as rosmarinic acid (37670.55 μg/g), luteolin 7-glucoside (15756.40 μg/g), apigenin 7-glucoside (15080.34 μg/g), luteolin (2289.77 μg/g), apigenin (2240.38 μg/g), chlorogenic acid (2121.92 μg/g), vanillic acid (1179.66 μg/g), hesperidin (1038.38 μg/g), 4-hydroxybenzoic acid (961.97 μg/g) and pinoresinol (631.61μg/g). It was found that methanol extract showed remarkable activity in almost all antioxidant activity tests (except ferrous ion chelating test). The activity of this extract in the phosphomolybdenum, reducing power [cupric reducing antioxidant capacity (CUPRAC) and ferric reducing antioxidant power (FRAP)] and radical scavenging [on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)] assays were measured as 1.65, 0.95, 0.52, 1.86 and 1.45 mg/mL, respectively. Phenolic and flavonoid contents, especially chlorogenic acid, vanillic acid, luteolin 7-glucoside, hesperidin and rosmarinic acid, are thought to contribute significantly to the antioxidant activity of the extracts. In tyrosinase and α-amylase inhibitory activity tests, methanol (2.81 mg/mL) and ethyl acetate (2.64  mg/mL) extracts exhibited the best activity among the others, respectively. While it is thought that chlorogenic acid and rosmarinic acid may contribute to the tyrosinase inhibitory activity of methanol extract, it has been concluded that detailed chromatographic analyzes should be performed for detection of the compounds responsible for α-amylase inhibitory activity.

Introduction

The species belonging to the Boraginaceae family generally spread in the tropic and subtropic climate zone. According to the literature records, this family is known to be represented with approximately 100 genera and 200 species worldwide. While there are approximately 150 Onosma species in the Asian continent, the number of species in China alone is twenty-nine (El-Shazly et al., 1998; Özgen et al., 2004). Due to their medical importance, the number of studies on the enlightenment of the biological activities of Onosma species has been increasing over the years (Naz et al., 2006).

Plants are considered to be important natural resources in the production of pharmaceutical compounds. Today, rather than the production of chemical compounds, it has begun to turn to the production of plants rich in these compounds (Bagheri et al., 2011). The roots of Onosma members are known to be a rich source of shikonin-derived chemicals as well as their interesting pharmacological activities. This red-colored dye has been used frequently in various areas since ancient times (eg silk and food industries) (Pal and Chaudhury, 2010). This pigment is also among the popular phytochemicals in cosmetic and medical applications due to some pharmacological properties (eg anti-inflammatory, antimicrobial, etc.) (He, 2009; Noula et al., 2010). Therefore, production of these species both in the field and through tissue culture techniques is of great importance (Bagheri et al., 2011).

As a result of intensive studies on the biological activities of plants, many interesting activities have been revealed. Among these activities, perhaps the best known and most frequently studied is antioxidant activity (Madsen and Bertelsen, 1995; Schwarz et al., 2001; Tanabe et al., 2002). Many researchers working in this field agree that terpenoids, which are essential oil components, flavonoids and phenolic acids are compounds responsible for antioxidant activity (Madsen and Bertelsen, 1995). Since the millennium, consumers have begun to doubt the harmful effects of butylated hydroxyl anisole (BHA) and butylated hydroxyl toluene (BHT), which is used to extend the shelf life of foods, on human health. Some authorities consider these synthetic antioxidant substances to damage the DNA molecule (Sasaki et al., 2002). Therefore, interest in the use of plant species or spices, which are rich in antioxidant phytochemicals, as additives in foods has increased. Although it varies according to the herbal material, the application of the suitable extraction method can increase the antioxidant substance concentration in the extract obtained. Since the medium polarity or polar compounds show higher antioxidant activity than the non-polar ones, the differences between the antioxidant activity potentials of different extracts obtained from the same plant species can give an idea about the polarity of the components exhibiting the activity (Wangensteen et al., 2004).

Tyrosinase (EC 1.14.18.1), a polyphenol oxidase, is an important enzyme involved in melanin biosynthesis and is responsible for color formation in the skin and hair (El-Sayed et al., 2019). The first step of melanin production is the conversion of L-tyrosine by biochemical dihydrox-yphenylalanin (L-DOPA) by the tyrosinase enzyme. The same enzyme then oxidizes L-DOPA to dopakinone to obtain functional melanin pigment (Ai et al., 2014). Tyrosinase is an enzyme widely distributed in the plant kingdom. Tyrosinase causes browning during the processing and storage of some vegetables and fruits. As mentioned above, it is responsible for the production of melanin, the main pigment responsible for the formation of skin color in mammals, and disorders related to the activity of this enzyme cause various neurodegenerative diseases, especially Parkinson's disease (Asanuma et al., 2003). In some cases, inhibition of tyrosinase activity helps to eliminate the metabolic disorder caused by this metabolic pathway. Due to their importance in the agriculture, food and medical industries, there has been a great deal of interest in researching compounds with tyrosinase inhibitory activity in recent years. In addition to using tyrosinase inhibitors in the treatment of pigmentation related skin diseases, it is also of great importance for the prevention of browning in fruits and vegetables. Due to their pharmacological potential, there is a great interest in tyrosinase inhibitors in both the medical and cosmetic industries. A large number of tyrosinase inhibitors have been identified so far, both from natural sources and synthetic pathways (Loizzo et al., 2012). Some studies have shown that tyrosinase from mushrooms can be inhibited by some fruits, quercetin, kojic acid, flavonoids, pyridine derivatives and benzoic acids (Fan et al., 2017; Gheibi et al., 2015; Kamkaen et al., 2007; Kubo et al., 2000; Saghaie et al., 2013). Although a large number of tyrosinase inhibitors have been discovered, only a few of them can be used industrially due to safety concerns. For example, compounds containing sulfites have been traditionally used to prevent browning in fruits and vegetables. However, the use of these compounds have been banned by Food and Drug Administration since the application of them in freshly cut fruits and vegetables cause taste deterioration and allergies (El-Sayed et al., 2019).

Diabetes is an important metabolic disorder that can occur in two different ways, congenital or acquired. Congenital diabetes is also called type I, and these patients are dependent on insulin injection. Acquired diabetes is also known as type II and insulin intake is not required in these patients. In either case, the transport of glucose from the bloodstream to the cells cannot be performed (Abesundara et al., 2004). Diabetes causes various levels of organ failure/dysfunctions in the long term (Funke and Melzig, 2006). Currently, it is estimated that 150 million people worldwide suffer from diabetes. However, this number is expected to reach 220 million in 2010 and 300 million in 2050 (Li et al., 2005). It is known that type II diabetes accounts for about 90 % of all diabetes patients (Abesundara et al., 2004). Many clinical approaches have been used in the treatment of diabetes so far. Inhibition of glucose absorption from intestine, inhibiting the metabolic pathway of gluconeogenesis, increasing the number of glucose transporters in membranes, and promoting insulin secretion are just a few of these approaches (Youn et al., 2004). One of the most effective ways to deal with type II diabetes is reported to be keeping postprandial hyperglycemia under control immediately after meal (Kim et al., 2005). It is very important to keep the blood glucose level stable in diabetic patients, as this helps to eliminate hyperglycemia and associated complications (Mai and Chuyen, 2007). In fact, the most effective way to control glucose levels in the bloodstream is to prevent glucose production by inhibiting the activity of enzymes involved in carbohydrate digestion in the digestive organs (Kim et al., 2005). α-Amylase is one of the enzymes that catalyze the hydrolysis of starch first to maltose and then glucose, which is the basic sugar form that can be used in the body (Kotowaroo et al., 2006). If this enzyme is inhibited, the increase in blood glucose level is prevented since the production of monosaccharides that are absorbed from the intestines into the bloodstream will be eliminated (Funke and Melzig, 2006). Plants are natural sources rich in effective α-amylase inhibitors. Researchers are increasingly releasing new data on the inhibitory activity of a new and alternative phytochemicals available in the plant species (Kim et al., 2005).

In this study, antioxidant, tyrosinase and  α-amylase inhibitory activities of extracts obtained from Onosma ambigens Lacaita (Boraginaceae) using solvents with different polarity were investigated. In order to reveal the relationship between the biological activities of the extracts and their phytochemical compositions, total phenolic/flavonoid contents were determined and the amounts of some standard phytochemicals were analyzed by using LC-ESI-MS/MS system. Pearson Correlation Coefficient test was performed to statistically make sense of the activity-composition relationship. In this study, the relative antioxidant capacity index (RACI) values of the extracts (including phenolics) were calculated to compare the results obtained from each antioxidant activity tests system in a standard form. Since there are no studies in literature regarding the phytochemical composition and biological activities of O. ambigens, the data presented here can be considered as the first record.

Section snippets

Plant material and extract preparation

The aerial parts of O. ambigens were collected from Sincan–Divriği highway, Sivas-Turkey on July 1, 2016 (6.−8. km, 1292 m., 39° 28′ 57″N 37° 55′ 14″E). The plant was identified by Dr. Olcay Ceylan from the Department of Biology, Mugla Sitki Kocman University, Mugla-Turkey and deposited at the herbarium of Mugla Sitki Kocman University (Herbarium number: O.5005). Details of the extraction process were included in the supplementary file.

Identification of phenolic compounds by liquid chromatography–electrospray tandem mass spectrometry (LC–ESI–MS/MS)

The phytochemical compositions of the extracts were

Phytochemical compositions of the extracts

Since one of the main objectives of this study is to establish a relationship between the phytochemical compositions and biological activities of the extracts, firstly, the phytochemical composition data were discussed. For this purpose, the total phenolic and flavonoid contents of the extracts were determined qualitatively (Fig. 1). All of the extracts were found richer in phenolics than flavonoids. Among the extracts, methanol extract was found to be the richest in terms of both compound

Conclusions

As given above, in this study, antioxidant, tyrosinase and α-amylase inhibitory activities of ethyl acetate, methanol and water extracts from O. ambigens were tested. As a result of the antioxidant activity tests carried out, it has been concluded that methanol extract is an effective antioxidant and can be used in food industry to prolong the shelf-life of foods. Phenolic and flavonoid contents, especially chlorogenic acid, vanillic acid, luteolin 7-glucoside, hesperidin and rosmarinic acid,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement

Cengiz Sarikurkcu: Conceptualization, Investigation, Data curation, Writing - original draft, Supervision. Saliha Seyma Sahinler: Resources, Conceptualization, Visualization, Formal analysis, Investigation, Methodology. Olcay Ceylan: Resources, Formal analysis, Investigation. Bektas Tepe: Conceptualization, Writing - review & editing.

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