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Potential of Lichen Compounds as Antidiabetic Agents with Antioxidative Properties: A Review 时间:2017-06-13 12:08 来源:未知作者:admin 点击: 次 Abstract:The advancement in the knowledge of potent antioxidants has uncovered the way for greater insight in the treatment of diabetic complications. Lichens are a rich resource of novel bioactive compounds and their antioxidant potential is well documented. Herein we review the antidiabetic potential of lichens which have received considerable attention, in the recent past. We have correlated the antidiabetic and the antioxidant potential of lichen compounds. The study shows a good accordance between antioxidant and antidiabetic activity of lichens and points out the need to look into gathering the scarce and scattered data on biological activities for effective utilization. The review establishes that the lichen extracts, especially of Parmotrema sp. and Ramalina sp. have shown promising potential in both antidiabetic and antioxidant assays. Ubiquitous compounds, namely, zeorin, methylorsellinate, methyl-β-orcinol carboxylate, methyl haematommate, lecanoric acid, salazinic acid, sekikaic acid, usnic acid, gyrophoric acid, and lobaric acid have shown promising potential in both antidiabetic as well as antioxidant assays highlighting their potential for effective treatment of diabetic mellitus and its associated complications. The available compilation of this data provides the future perspectives and highlight the need for further studies of this potent herbal source to harvest more beneficial therapeutic antidiabetic drugs.
1. Introduction
Diabetes mellitus (DM) is an ever increasing global epidemic and one of the most challenging health problems of 21st century. In 2010, more than 285 million people around the world were afflicted with diabetes, and it was then estimated that the number of people with diabetes will increase to 439 million by 2030. Interestingly, the reports of 2015 show that globally 415 million (215.2 million men and 199.5 million women) had DM with a prevalence of 8.8%. In other words, one in eleven people have DM and global expenditure for treating it in 2015 alone was US$ 673 billion (12% of health expenditure) [1].
Two main groups of DM are distinguished: (1) autoimmune T1DM or insulin dependent DM or juvenile DM and (2) T2DM or noninsulin dependent DM or Maturity Onset DM. About 90% of people with DM around the world have type 2 DM (T2DM) [2].
In T1DM, β-cells in the pancreas are destroyed and do not secrete adequate insulin; treatment of T1DM requires insulin replacement via injection. T2DM is characterized by insulin resistance and a diminished capacity for insulin secretion by β-cells of the pancreas. T2DM is considerably more amenable to therapeutic drug intervention and is treated with insulin sensitizers, or through methods which reduce the plasma glucose levels. Natural products and herbal medicines that have claimed to be efficacious in the treatment of DM are thus most efficient in the treatment of T2DM [3].
Recent basic and clinical studies have exposed new understandings into the role of antioxidants to combat diabetic complications [4]. Oxidative stress plays a significant part in the pathogenesis of diabetes and its ramifications as it leads to the dysfunction of β-cells. Antioxidants on the other hand protect β-cells from apoptosis and preserve their function [5]. Therefore, if a compound shows good antioxidant activity, it is anticipated that it would show greater effects on diabetes and its complications as well. Thus antioxidant therapy recommends a different, innovative, and fundamental approach towards diabetes treatment [6, 7].
Lichens are composite organisms consisting of a symbiotic association between a fungal partner (mycobiont) and one or more photosynthetic partners (photobiont) usually either green algae or cyanobacterium or both. Lichens are found in all ecosystems, including the most extreme environments on earth-arctic tundra, hot deserts, icebergs, rocky coast, toxic heaps, and so on. Lichens produce characteristic and unique substances which may help them to survive in these extreme environments [8]. Around 1050 lichen metabolites are known up to date [9]. Importantly, the last decade witnessed renewed and growing interest in lichen substances as a source of novel, pharmacologically active biomolecules [10, 11]. Overall, tropical lichens are one of the least studied cryptogams. For example, in Sri Lanka, new species and new records of lichens are being discovered at a rapid rate and in the coming years the number of tropical lichens recorded will contribute to new knowledge of their pharmaceutical potential [12, 13]. Interestingly, wide array of biological activities have been reported revealing the pharmaceutical importance of Sri Lankan lichens [14–23].