Anti-inflammatory activity of natural coumarin compounds from plants of the Indo-Gangetic plain

1.   Introduction

Coumarin nucleus is present in several plants. Studies have revealed that various phytoconstituents have been derived from coumarin nucleus that has pronounced anti-inflammatory activities. Certain coumarins-derived phytocompounds like columbiatnetin,visniadin, marmin, umbelliferon, scopoletin etc., have been reported to have potential anti-inflammatory activities. These compounds have also been reported to have potent antioxidant and radical scavenging potential which may complement their anti-inflammatory activities [1]. Coumarin derivatives which get synthesized naturally in various plants and also the compounds derived from coumarin and synthesized in laboratories, both are reported to have excellent anti-inflammatory effects. There have been several studies evaluating the anti-inflammatory and other pharmacological potential of natural and synthetic coumarin derivatives with the interest of developing useful and potent drugs for combating various pain and inflammatory conditions in animal bodies [2]. Studies show that the biological in vitro anti-inflammatory activities of coumarin derivatives are concentration-dependent [3].

Inflammation is an essential, immuno-protective physiological response to any kind of irritant or aggression [4]. The reaction of inflammation may be localized or may be generalised depending on the intensity of the stimulus exposed to. Inflammation can get triggered by various factors. Some of these include injury, trauma, exposure to toxins, pathogen attack etc., [5]. Several immune cells act together when our body encounters any kind of inflammation. In the process, various different types of chemicals are released which include substances like histamine and bradykinin. Together those substances are called as inflammatory mediators. They all act together with a goal of removing the cause of inflammation and promoting a healing process. Thus, in a nutshell, inflammation is a protective mechanism of our body and is inevitable to maintain a good health [6]. Besides, other events that occur during inflammation are alteration in vascular permeability and leukocyte recruitment and accumulation [7]. These cause dilatation of the blood vessels which in turn facilitates movement and accumulation of more and more leukocytes at the site of inflammation. Leukocyte chemotaxis occurs from circulation to the site of inflammation [8]. Leukocytes fight back the infection and devour the pathogens to reduce the cause of inflammation and thus help to mitigate the condition of inflammation. Also, leukocytes release inflammatory mediators at the site of inflammation which causes further inflammatory responses [7]. Dilation of blood vessels causes swelling of the site of inflammation. The inflammatory mediators irritate the nerve endings at the site of inflammation and send a pain signal to our central nervous system making us aware of the occurrence of inflammation at a particular site in our body and thus we tend to take care of the inflamed site. The prime inflammatory mediators other than histamine and bradykinin are neuropeptides, cytokines, growth factors and neurotransmitters. Any kind of pain is reported to be having an origin of inflammation or inflammatory response [9].

Studies conducted for several years reveal that coumarins and its derivatives can mitigate inflammation and inflammatory reactions by effecting different types of receptors like Toll-like receptors (TLR), and by effecting various signalling pathways and molecules which include the inflammasomes, Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT), mitogen-activated protein kinase (MAPK), nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κB) and transforming growth factor-β/small mothers against decapentaplegic (TGF-β/SMAD) pathways etc. [10]. Studies conducted using six different coumarins derivatives of plant source showed that they have potent anti-inflammatory effects against intestinal inflammation. The study further reveals that the anti-inflammatory activities of these six coumarin derivatives, namely scopoletin, scoparone, fraxetin, 4-methyl-umbelliferone, esculin and daphnetin had a correlation to their antioxidant properties [11]. Certain coumarins derived from natural plant products like esculetin, fraxetin, daphnetin etc., have been evaluated and are reported as inhibitors of lipoxygenase and cyclooxygenase (COX) enzymes [12]. COX plays an important role in the biosynthesis of prostaglandins H2 from arachidonic acid (AA). Prostaglandin H2 is a precursor for various molecules like prostaglandins, prostacyclins and thromboxanes which play crucial roles in the pathophysiology of pain and inflammation [13]. The natural coumarin derivatives have also been recognised to have inhibitory effects on neutrophil-dependent superoxide anion generation [12]. These findings show that the natural coumarin derivatives possess both anti-nflmmatory and antioxidant potential thus qualifying as them as excellent candidates for the development of anti-inflammatory drugs.

2.   Coumarin compounds rich Indo-gangetic plants

Coumrain compounds have been reported to be present in various plants naturally. These compounds are known to be present in a pretty high concentration in tonka bean i.e., Coumarouna odorata (Fabaceae) [14]. Other plants reported to be rich in coumarin compounds are cassia cinnamon and liquorice [15]. Licorice is known as liquorice, kanzoh in Japanese and is known as gancao in Chinese. It is actually the name applied to the roots and stolons of some Glycyrrhiza species (Leguminosae or Fabaceae). The genus Glycyrrhiza consists of almost 30 species [16]. Licorice is known to be used by human since ages. Vanilla grass, Anthoxanthum odoratum is also reported to be rich in coumarins compounds [17]. Sweet clover Melilotus sp. is also reported to be rich in coumarin compounds [18]. Besides these, Justicia pectoralis, Ferula L., Pachypleurum Hoff., Prangos Lindl., Heracleum L., Conioselinum Fisch., Libanotis L., Seseli L etc. were found to be containing various types of coumarins compounds [19]. Cherry blossoms, apricots and strawberries also contain coumarin compounds but in smaller quantities [19]. Studies reveal that more than one thousand and three hundred coumarins have been identified from various plant sources [20].

3.   Anti-inflammatory activities of Coumarin compounds

Coumarins are natural benzopyrone compounds (2H-1-benzopyran-2-one), widely and commonly distributed in many medicinal plants. These are actually fused benzene and α-pyrone rings. These compounds have been reported to have a wide variety of pharmacological potentials which include ani-inflammatory, anti-malarial, anti-viral, anti-fungal, neuro-protective, anti-convulsant, anti-hypertensive, antibacterial, anti-coagulant, anticancer etc. [14] Each of these bio-potential of coumarins have significant pharmacological value. Our aim in this review is to highlight the anti-inflammatory potential of the natural coumarins compounds from the plants of Indo-Gangetic plains.

Table 1 represents the list of some potent anti-inflammatory compounds and the plants they have been recognized to be present in. The mechanism of anti-inflammatory of these coumarins compounds isolated from plants of Indo-Gangetic plains are also mentioned in the table in brief.

Besides the plants mentioned in Table 1, cherry blossoms, apricots and strawberries also contain coumarin compounds in smaller quantities [19]. Studies reveal that more than one thousand and three hundred coumarins have been identified from various plant sources [20]. Studies reveal presence of coumarin compounds in plants like Hypericum perforatum (Saint John Wort), Uncaria tomentosa (Cat's Claw), Passiflora incarnata (Passion Flower), Aesculus hippocastanum (Horse-chestnut), Tilia cordata (Lime Tree), Lawsonia inermis (Henna) etc. [21].

Table 1.  Coumarin compounds, their source plants and brief mechanism of anti-inflammatory activities.

Sl No.	Coumarin compounds	IUPAC name	Formula	Structure	Plant (common names)	Scientific names	Mode of anti-inflammatory action	References
1	Scopoletin	7-Hydroxy-6-methoxy-2H-1-benzopyran-2-one	C10H8O4		Datura or Indian thornapple	Datura metel	Works by inhibiting the pro-inflammatory cytokines	[22]–[25]
					Virgate wormwood	Artemisia scoparia
					Resinous kamala	Mallotus resinosus
					Fenugreek	Trigonella foenum-graecum
2	Scoparone	6,7-dimethoxychromen-2-one	C11H10O4		Virgate wormwood	Artemisia scoparia	Works primarily by suppressing the NF-κB signalling inflammatory pathway	[26]–[29]
					Wormwood	Artemisia absinthium
3	Fraxetin	7,8-Dihydroxy-6-methoxy-2H-1-benzopyran-2-one	C10H8O5		Thale cress, mouse-ear cress or arabidopsis	Arabidopsis thaliana	Works by suppressing pro-inflammatory cytokines induced NF-κB signalling inflammatory pathway	[30]–[33]
					Datura or trumpet flower	Datura stramonium
4	Fraxinol	6-hydroxy-5,7-dimethoxychromen-2-one	C11H10O5		Prostrate cherry, mountain cherry, Rock Cherry, Creeping Cherry, Spreading Cherry	Prunus prostrata	Works by by inhibiting T-cells and prostaglandin biosynthesis	[34]–[37]
5	Umbelliferone	7-hydroxychromen-2-one	C9H6O3		Coriander Toothbrush Tree, Miswak	Coriandrum sativum Salvadora persica	Works by suppressing and downregulating certain genes involved in inflammatory pathways like the genes of TLR4 and NF-κB	[38]–[41]
6	6-hydroxy-7-methoxy-4 methyl coumarin	6-hydroxy-7-methoxy-4-methylchromen-2-one	C11H10O4		Bishop's flower, false bishop's weed, laceflower, bullwort, lady's lace, false Queen Anne's lace	Ammi majus	Reported to exhibit anti-inflammatory activity in vivo in carrageenan-induced rat paw edema protocol	[42]–[45]
7	4-methyl-umbelliferone	7-hydroxy-4-methylchromen-2-one	C10H8O3		Bishop's flower, false bishop's weed, laceflower, bullwort, lady's lace, false Queen Anne's lace	Ammi majus	Works by inhibiting the pro-inflammatory cytokines	[46],[47]
8	Isofraxidin	7-hydroxy-6,8-dimethoxychromen-2-one	C11H10O5		Celery	Apium graveolens	Works by reducing pro-inflmmatory cytokines and by attenuating the increased expression of inflammatory enzymes	[48]–[51]
9	Esculin	7-hydroxy-6-[(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxychromen-2-one	C15H16O9		Barley	Hordeum spontaneum	Reported to work by reducing proinflammatory and inflammatory cytokines	[52]–[54]
10	Scopolin or Murrayin or Scopoletin 7-glucoside	6-methoxy-7-[(2S,3R,4S,5S,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)oxan-2-yl]oxychromen-2-one	C16H18O9		Thale cress, mouse-ear cress or arabidopsis	Arabidopsis thaliana	Reported to work by reducing proinflammatory and inflammatory cytokines	[55]–[63]
					Mugwort, wormwood,	Artemisia minor
					Orange berry and gin berry	Glycosmis pentaphylla
					Orange jasmine, orange jessamine, china box or mock orange	Murraya paniculata
11	Ostruthin	6-[(2E)-3,7-dimethylocta-2,6-dienyl]-7-hydroxychromen-2-one	C19H22O3		Kurantu Kuruntu Perum Kuruntu Kadanaathi	Pamburus missionis	Known to work by suppressing iNOS and COX-2 protein expression.	[64]–[67]
					Indian coffee plum, or scramberry	Flacourtia jangomas
12	3′,5,7-Trihydroxy-4-methoxyflavanone or 5-O-methylscutellarein	5,7-dihydroxy-2-(3-hydroxyphenyl)-4-methoxy-4H-chromen-3-one	C16H14O6		Turmeric	Curcuma zedoaria	Works by suppressing NF-κB activation, reduces cholesterol biosynthesis and Inhibits lipid peroxidation	[68]–[74]
13	7-methoxy coumarin (herniarin, 3) or Herniarin.	7-methoxychromen-2-one	C10H8O3		Turmeric	Curcuma zedoaria	Reported to work by inhbiting writhing and nociception	[75]–[78]
					White mugwort	Artemisia lactiflora
					Ruptureworts	Herniaria
					Ayapan	Eupatorium Triplinerve
14	Auraptene	7-[(2E)-3,7-dimethylocta-2,6-dienoxy]chromen-2-one	C19H22O3		Kaminmi, orange jasmine, orange jessamine, china box or mock orange	Murraya paniculata	Works by reducing oxidative stress, suppresses various proinflammatory cytokines, inflammatory mediators and the enzymes involved in inflammation	[61],[79]–[82]
15	Silibinin	(2R,3R)-3,5,7-trihydroxy-2-[(2R,3R)-3-(4-hydroxy-3-methoxyphenyl)-2-(hydroxymethyl)-2,3-dihydro-1,4-benzodioxin-6-yl]-2,3-dihydrochromen-4-one	C25H22O10		Milk thistle, blessed milkthistle, Marian thistle, Mary thistle, Saint Mary's thistle, Mediterranean milk thistle, variegated thistle and Scotch thistle	Silybum marianum	Reported to work by reducing proinflammatory and inflammatory cytokines	[83]–[89]
16	Murracarpin	8-(2-hydroxy-1-methoxy-3-methylbut-3-enyl)-7-methoxychromen-2-one	C16H18O5		Kaminmi, orange jasmine, orange jessamine, china box or mock orange	Murraya paniculata,	Works by inhibiting the elevation of IL-1β, TNF-α, and PGE2	[90]–[95]
					Curry patta, meetha neem	Murraya koenigii
					White Himalayan Rue	Boenninghausenia albiflora
					Orangeberry and gin berry	Glycosmis pentaphylla
17	Murrangatin	8-[(1R,2S)-1,2-dihydroxy-3-methylbut-3-enyl]-7-methoxychromen-2-one	C15H16O5		Curry patta, meetha neem	Murraya koenigii	Works by downregulation of IL-1β, TNFα, PGE2, and MMP-13 etc.	[96]–[100]
						Murraya paniculata,
18	Daphnetin	7,8-dihydroxychromen-2-one	C9H6O4		Indian Paper Plant, Indian paper tree, Nepali paper plant	Daphne papyracea	Suppresses activation of macrophages and proinflammatory cytokines and down-regulates NF-κB-dependent signalling events. Induces expression of anti-inflammatory cytokines	[101]–[106]
					Himalayan Stellera	Stellera chamaejasme
					sweet wormwood, sweet annie, sweet sagewort, annual mugwort	Artemisia annua
19	Marmin	7-[(E,6R)-6,7-dihydroxy-3,7-dimethyloct-2-enoxy]chromen-2-one	C19H24O5		bael (or bili) or bhel, also Bengal quince, golden apple, Japanese bitter orange, stone apple or wood apple	Aegle marmelos	Works by lowering nuclear factor kappa-B (NF-κB)	[107]–[112]
					Citron, rough lemon	Citrus medica
20	Psoralen	furo[3,2-g]chromen-7-one	C11H6O3		wood-apple and elephant-apple	Limonia acidissima	Works via estrogen receptor signalling pathway	[113]–[117]

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4.   Molecular mechanism of the anti-inflammatory activity of coumarins

Coumarins exhibit their anti-inflammatory activities through various molecular mechanisms. Different coumarins compounds follow different molecular mechanisms to ultimately mitigate inflammation.

As evident from study conducted on mice, scopoletin is known to have inhibitory activity on PGE2 and TNF-α overproduction, and neutrophil infiltration. Also, it is reported that scopoletin significantly attenuates the malondialdehyde (MDA) level in the edema paw of experimental mice. Thus, scopoletin inhibits the pro-inflammatory cytokines and exhibits its anti-inflammatory activity [25]. Another coumarin named Scoparone, is reported to prevent IL-1β-induced inflammatory response in human osteoarthritis chondrocytes through the PI3K/Akt/NF-κB pathway. Scoparone is also known to suppressing the TLR4/NF-κB signalling pathway in mice which in turn mitigates inflammation, apoptosis and fibrosis associated with non-alcoholic steatohepatitis [28],[29]. The other coumarin, fraxetin is reported to exhibit its anti-inflammatory activity by the mechanism of suppressing IL-1β-induced inflammation via the TLR4/MyD88/NF-κB pathway in rat chondrocytes. Also,the other molecular mechanism of the anti-inflammatory activity of fraxetin is by imparting a suppression effect on microglia-mediated neuroinflammation, and this effect is associated with the PI3K/Akt/NF-κB signalling pathway [32],[33]. Fraxinol, another known coumarin compound with anti-inflammatory activity is known to reduce inflammation by the mechanism of inhibiting the T-cells and prostaglandin biosynthesis [37].

Umbelliferon, a very common coumarins compound with widely reported anti-inflammatory activity works by significantly suppressing the hepatic lipopolysaccharide binding protein, toll-like receptor 4 (TLR4), nuclear factor kappa B, and TNF-α gene expression in alcohol fed rats and thus prevents alcohol-induced inflammation in rat hepatic tissue [39]. Also, Umbelliferon is known to reduce lipopolysaccharide-induced inflammatory responses in acute lung injury by down-regulating TLR4/MyD88/NF-κB signalling [40]. Isofraxidin, another coumrin is reported to impart its anti-inflammatory activity by decreasing the lipopolysaccharide (LPS)-induced overproduction of nitric oxide (NO), prostaglandin E2 (PGE2), tumour necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). Isofraxidin is also nreported to mitigate the increased expression of inflammatory enzymes, like inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), in response to LPS stimulation and thus helps to reduce LPS-induced inflammation [50],[51].

Esculin, the coumarins is also a well reported anti-inflammatory coumarins. The basic molecular mechanism of action of this coumarin is reported to be by decreasing the cytokines IL-1, IL-6, ICAM-1, NO and NGAL levels in serum of diabetic rats in a dose dependent manner thus reducing the risks of microvascular complications associated with diabetes [54]. Scopolin, another aanti-inflammatory coumarins compound is known to exhibit its anti-inflammatory action by the molecular mechanism of inhibiting eicosanoid-release from ionophore-stimulated mouse peritoneal macrophages. Also, scopolin is known to reduce IL-6, VEGF and FGF-2 expressions in rat synovial tissue [62],[63]. The molecular mechanism of the anti-inflammatory activity of the coumarins, Ostruthin is reported to be by suppressing LPS-induced iNOS and COX-2 protein expressions [67]. 5-O-methylscutellarein, is known to impart its anti-inflammatory potential by suppressing the NF-κB [70]. Auraptene is also known to have anti-inflammatory activity. Studies show that treatment with auraptene (10-90 µM) significantly ameliorates ROS, MDA, IL-6, and TNF-α levels. Also, studies show that Auraptene, as a pre-treatment for five days before and another three days after ischemic surgery, suppressed microglial activation, cyclooxygenase (COX)-2 expression in astrocytes, and COX-2 mRNA expression in the hippocampus. Other underlying molecular mechanism of the anti-inflammatory activity of the coumarin auraptene is by suppressing the lipopolysaccharide-induced expression of COX-2 mRNA and the mRNA of pro-inflammatory cytokines in cultured astrocytes. It is also reported to have the capacity to interfere with inflammatory mediator secretion and to promote wound healing [81],[82].

Silibinin is known to have potent anti-inflammatory activity and the underlying molecular mechanism is reported to be by altering the level of various pro-inflammatory cytokines. Studies conducted in vitro using human fetal membranes reports that the coumarins, silibinin has the ability to significantly decrease LPS-stimulated expression of IL-6 and IL-8, COX-2, and prostaglandins PGE2 and PGF2α. In primary amnion and myometrial cells, silibinin is also reported to decrease the IL-1β-induced MMP-9 expression.Preterm fetal membranes with active infection treated with silibinin shows a decrease in IL-6, IL-8 and MMP-9 expression. Fetal brains from mice treated with silibinin shows a significant decrease in LPS-induced IL-8 and ninjurin, a marker of brain injury. Other studies show that Silibinin is capable of reducing, at least in part, the levels of NF-κB and cytokines TNF-α and IL-1β in preeclamptic women. Also, Silibinin alleviates inflammation and induces apoptosis in human rheumatoid arthritis fibroblast-like synoviocytes and has a therapeutic effect on arthritis in rats [88],[89]. Murracarpin is another potent anti-inflammatory coumarin. In carrageenin pleurisy model, murracarpin is reported to effectively inhibit the elevation of IL-1β, TNF-α, and PGE2 and thus mitigate inflammation therein [95].

Another coumarins compound with reported anti-inflammatory potential is murrangatin. One of the reported molecular mechanism of the anti-inflammatory activity of murrangatin is by downregulation of IL-1β, TNFα, PGE2, and MMP-13. By this mechanism it the compound imparts chondroprotective activity, Other studies show that Murrangatin has anti-inflammatory activity against mouse RAW264.7 cells the underlying mechanism of which is by reduction of LPS-induced NO production after 24 hrs by the compound [99],[100]. Daphnetin, is also another reported anti-inflammatory coumarins. Studies show that one of the mechanisms of anti-inflammatory activity of the compound is by suppression of the activation of macrophage and human alveolar epithelial cells in response to lipopolysaccharide (LPS). This in turn is related to the down-regulation of NF-κB-dependent signalling events. Also, Daphnetin treatment is reported to significantly decrease the expression of pro-inflammatory cytokines and cause increased expression of anti-inflammatory cytokines in rat SAP. Molecular analysis reveals that daphnetin reduces TLR4 expression and inhibits NF-κB signalling pathway activation. These findings demonstrate that daphnetin attenuates acute pancreatic injury by regulating the TLR4/ NF-κB signalling pathway and inflammation in rat SAP model [102],[106]. Marmin is another reported coumarins compound with anti-inflammatory potential. Extracts of plants containing marmin have been reported to exhibit potent anti-inflammatory activities. Studies reveal that marmin works by lowering the nuclear factor kappa-B (NF-κB) and thus reduces inflammation[113]. The coumarin, psoralen is known to exhibit anti-inflammatory effects on synoviocytes, and mitigate monosodium iodoacetate-induced osteoarthritis. The mechanism of anti-inflammatory activity of psoralen in human periodontal ligament cells is reported to be via estrogenic receptor signalling pathway [114].

There are many more such coumarins compounds abundantly distributed in nature. The molecular mechanism of the anti-inflammatory activity of each of these coumarins are unique and varies from each other. The basic molecular mechanism of the anti-inflammatory activity of the coumarins seems to be by altering and effecting the anti-inflammatoy and pro-inflammatory cytokines associated with inflammation in various tissues.

5.   Extraction, purification, and isolation of coumarins from plant sources

Coumarins are widely distributed in nature in various plants. Theses potent phyto-constituents are extracted and purified by conventional methods of phytocompounds extraction. Various extraction techniques that are in use for isolating and purifying coumarins from plants are maceration, ultrasound maceration [118]. By these techniques, basically the plant material is macerated and the plant cells are broken down releasing the cellular content which includes the coumarins compounds along with many other compounds. In certain cases, the plant material in whole or after maceration or homogenization is infused with aqueous ethanol, water, methanol, ethyl acetate, chloroform, diethyl ether, or other solvents etc. [119],[120]. The coumarins compounds thus gets in dissolution into the suitable solvent and is then subjected to further purification process. The prime technique used commonly for purification and isolation of such phytocompounds as the coumarins is chromatography. Mostly various types of column chromatography is utilized coupled with or in some cases followed by high throughput liquid chromatography which is often coupled with fine analytical instruments like photodiode array detector (DAD) etc. After the purified fraction is compared against standards and collected from those analytical techniques, those are further subjected to finer analysis for understanding and interpretation of the composition and prediction of the molecular structure of the compounds. Techniques like MALDI TOFF, Scanning Electron microscopy, X-Ray Crystallography etc. are used for structural analysis of the purified coumarins. Some of the techniques used for purification and isolation of the coumarins involve utilization of various sophisticated analytical instruments like high performance liquid chromatography with UV detector (HPLC-UV) [121], reverse-phase high-performance liquid chromatographic method (RP-HPLC) coupled with a photodiode array detector (DAD) [122] etc., Also, other instruments like Scanning Electron Microscope (SEM)[123], Soxhelation, Ultrasonic-assisted response surface methodology (RSM) [123] etc. are used for extended procedures of extract1ion of coumarins from various plant sources.

6.   Benefits of the use of coumarin compounds

Natural Coumarin compounds come from plant sources and are thus devoid of much or any side effects unlike synthetic pharmaceutical compounds and formulations. These natural compounds can be used in combination with other pharmaceutical combinations. Studies reveal that most of the coumarins compounds exhibit anti-inflammatory as well as antioxidant activities. Hence, this makes these natural bioactive coumarins a perfect and potent candidate for developing potential anti-inflammatory drug formulations with dual benefits [124]. On one hand these act as effective anti-inflammatory agents impacting and regulating various pathways associated with pain and inflammation and on the other hand coumarins by virtue of their antioxidant potential reduces the oxidative stress mediated complications of inflammation and also is easy to be processed and metabolized by our liver. Overall, the properties of natural bioactive coumarins make them safer anti-inflammatory agents compared to other anti-inflammatory agents [124]. Studies show that non-steroidal anti-inflammatory drugs (NSAIDs) like piroxicam may be harsh on the gastric mucosal lining and may induce gastric ulcers. Whereas, these natural coumarin compounds from the plants of Indo-gangetic possess antioxidant potentials and they have been reported to be protective on gastric mucosa and are known not to induce oxidative stress there in unlike NSAIDs [124]. In addition to these magical miraculous properties of the natural coumarins compounds, they have been found to be adequately bio-available [124] which further qualifies them as suitable candidates for developing anti-inflammatory formulations. Coumarins are known to scavenge reactive oxygen species and thus are capable of effecting and influencing processes involving free radicals-induced injury and damages [125]. With all these benefits, coumarin compounds being available from natural resources can be easily isolated and can be used for developing better derivatives if needed and thus can be immensely utilised for developing potent anti-inflammatory pharmaceutical formulations with minimum side effects. Also, the lead coumarins compounds being mostly extracted from natural sources, it is expected that the anti-inflammatory drugs developed using natural coumarins and their derivatives will be potent, safer, better, cost effective and affordable.

7.   Coumarin compounds from plants of other regions

The micro and macronutrient composition of the soil varies as per the geographical regions. Thus, the plants growing in the indo-gangetic region and those growing in other regions vary in their composition. The potency of these bioactive phytocompounds are also reported to vary depending on the variation of the geographical region and soil composition. In vitro studies conducted on Murraya koenigi collected from different districts of the state of West Bengal, India is reported to have varied in their antioxidant potential [126]. Depending on the region , the climate and the soil composition, certain plants grow only in specific regions. Coumarins from those plants growing in other regions than the indo-gangetic plain have also been reported to exhibit potent anti-inflammatory activities. Thus, some of the coumarins compounds which are found in specific plants which do not grow in the indo-gangetic region are available in the plants which grow in other regions. High concentrations of coumarins are reported to be present in plants like Justicia pectoralis [127] which grows in the tropical areas of the Americas, including South and Central America and also grows in some Caribbean islands like Trinidad and Tobago [128], Dipteryx odorata (old name Coumarouna odorata) (tonka bean) (Fabaceae/Leguminosae) [129] which is also a tropical South American plant [130], Studies report high content of coumarins in plants like vanilla grass (Anthoxanthum odoratum) [131] which is native to acidic grassland in Eurasia and northern Africa [131] and many others. Studies also report abundant distribution of coumarins compounds in various plants from several plants grown exclusively in China and other parts of Eurasia. Those coumarins have potent bioactivities including anti-inflammatory activities. Phytoconstituents of plants like Cinnamomum cassia etc. has been evaluated to have potent anti-inflammatory activities in various experimental models and those plants have also been reported to be rich in coumarins [130]. Mostly, the type of coumarin compounds found in the plants from Indo-Gangetic region differ in their chemical structure from those obtained from the plants grown in other regions. Also, the biopotential of the same coumarins compounds obtained from same or different plant may vary depending on the composition of the soil the plant has grown in.

8.   Summary and conclusion

Investigations on the anti-inflammatory property of the natural coumarins compounds from various plants of the indo-gangetic plain delineated the basic mechanism to involve lowering of various pro-inflammatory cytokine levels including NF-κB and by altering the levels of prostaglandins [68],[78]. Some others alter the quantity of cytokines which are involved in the mechanism of inducing pain and inflammation [69]–[75]. Studies reveal that potent antioxidant activities complement the anti-inflammatory potential of the natural coumarins and their derivatives [124],[125]. Extensive research findings around the world involving investigations on the identification, isolation and anti-inflammatory potentials of the coumarin compounds from various regional endogenous plants and their derivatives, confirms the possibility of discerning coumarins as highly potent, cost effective and safe future anti-inflammatory therapeutic agents.