LIST OF TABLES
2.5. Plant secondary metabolites: Source of herbal medicine
2.8.4. Neuroprotective and antioxidant activity
According to Cotran et al. (1995), neurodegeneration defined as the neuronal death condition due to the continuous disease progression for a longer period of time. Medically it involves the degradation of restricted set of neurons which may possibly be functionally or structurally linked with each other (Beal 1997). All the neural tissues undergo deterioration during the process of neurodegeneration. As a consequence, several diseases like Alzheimer’s and Parkinson’s disease and even loss of cognitive functions may arise as the degenerated neurons are not replaced by normal recovery process. Therefore, in recent years the field
related to neurodegeneration has become more serious concern where neuroprotection by therapeutic means has attracted much attention to add up some new insights into therapeutics and cell biology.
Neuroprotection collectively refers to prevention of neuron damage or dying by some therapeutic approach involving either any protective drug or other strategic treatment. The aim of neuroprotection is to reduce neuronal dysfunction of damaged or degenerated neurons and also it tries to retain the best possible integrity with other cellular interactions in brain ensuring normal functions of neurons. Several neuroprotective products are available in the market and many are under clinical trials. These drugs have similar mode of actions which can judicially be utilized in various types of neural disorders. The most promising type of drugs mainly includes antioxidative agents. Antioxidants are known to counterbalance free radicals and found successful in controlling or reducing the prevalence of these disorders.
According to Halliwell (1994), antioxidant agent refers to any molecules which in very dilute concentrations than any oxidizeable compound significantly slows or even prevents oxidation of the substrate. On the basis of origin, these antioxidants may be of endogenous or exogenous in nature. On the other hand, on the basis of their mechanism of actions, they have classified as preventive type and chain breaking type antioxidants. In the physiological system some key antioxidant enzymes are noteworthy, viz. superoxide dismutase, catalase and glutathione peroxidase which represents the key intracellular protection system as antioxidants by scavenging superoxide anion and hydrogen peroxide. Current research suggests that several natural products derived from plants showed antioxidant activities and in turn limit the serious consequences of neurodegeneration. Further, among the plant derived natural compounds, phenolic substances like flavonoids showed promising antioxidant
activities (Cao et al. 1997). Morel et al. (1993) described free radical scavenging activity of flavonoids which even can reduce the lipid peroxidation process.
In Ayurvedic system, two major approaches, viz. disease preventive and health promotive approach are gaining much attention due to its wide acceptability. The famous
‘Rasyanachikitsa’ of Ayurveda based on revitalization and rejuvenation therapy. The
“Rasayana drugs” known to function by modulating the nueral, endocrinal and immune systems in the body and have been identified as rich source of antioxidant molecules (Brahma and Debnath 2003; Pushpangadan 2005).
Recently, in this area Alpinia genus has showed remarkable contribution as herbal remedies. Report of Singh et al. (2011a) revealed the chloroform fraction of A. galanga as anti-amnesic where the active compound for this activity could be 1’S-1’-acetoxyeuginol acetate as it was found to be the lead compound in the fraction. On the other hand, A. galanga ethanol extract shows anti-amnesiac effect in Amyloid β induced neurodegeneration (Singh et al. 2011b). Likewise, A. oxyphylla fruit was found to have the neuroprotective activities (Koo et al. 2004) and subsequently many other Alpinia species have been reported till date (Table 2.4). Protocatechuic acid (PCA), a principal compound of the A. oxyphylla, protects against oxidative damage in vitro and reduces oxidative stress in vivo (Shi et al. 2006). It has been shown that PCA also reduces the hydrogen peroxide or sodium nitroprusside induced cell death in PC12 cells in dose-dependent manner (An et al. 2006) and this offers a valuable therapeutic strategy for the cure of oxidative stress-induced neurodegenerative disease like Parkinson’s disease. Other reports revealed that A. katsumadai seed extract protects neurons from ischaemic damage (Li et al. 2011a) and the treatment significantly decreased the activation of astrocytes and microglia in the hippocampal CA1 region (Li et al. 2011b).
Similarly, methanolic extract of A. officinarum rhizome showed protection against oxidative
damage in PC12 cells (Chang et al. 2011). Essential oil of A. zerumbet has strong potential as antipsychotic and antioxidant agent (de Arau´jo et al. 2011) which may have promising efficacy for the treatment of schizophrenia. Members of the genus Alpinia are found to have a remarkable antioxidant activity which in turn gives more biological efficacy towards the development of therapeutics. The neuroprotective and antioxidant activities of the genus are enlisted in Table 2.6.
Table 2.6 List of neuroprotective and antioxidant activities exhibited by various natural bioactive compounds and crude fractions of Alpinia species
Species Name Parts used Bioactive fractions/compounds Bioactivity References
A. galanga Rhizome n-hexane, chloroform and ethyl acetate Neuroprotective Singh et al. 2011a
A. galanga Rhizome Ethanolic extract Neuroprotective Singh et al. 2011b
A. katsumadai Seeds 70% ethanolic extract Neuroprotective Li et al. 2011a
A. katsumadai Seeds Ethanolic extract Neuroprotective Li et al. 2011b
A. officinarum Rhizome Methanolic extract Neuroprotective Chang et al. 2011
A. oxyphylla Fruits 80% ethanolic extract Neuroprotective Zhang et al. 2011a
A. oxyphylla Kernel Protocatechuic acid Neuroprotective An et al. 2006
A. oxyphylla Fruits Protocatechuic acid Neuroprotective Shi et al. 2006
A. oxyphylla Fruits Water extract Neuroprotective Koo et al. 2004
A. oxyphylla Fruits 94% ethanolic extract Neuroprotective Yu et al. 2003
A. oxyphylla Fruits Ethanolic extract Neuroprotective Yu et al. 2003
A. mutica Rhizome 5,6-dehydrokawain, flavokawin B,
pinostrobin, β-sitosterol and pinocembrin
Antioxidant Mustahil et al. 2013
A. oxyphylla Fruits 1-(3',5'-dihydroxy-4'-methoxyphenyl)-7- phenyl-3-heptanone and 1-(2',4'-dihydroxy- 3'-methoxyphenyl)-7-(4’-methoxyphenyl)-3- heptanone
Antioxidant Bian et al. 2013
A. oxyphylla Seeds Yakuchinone A Antioxidant Lin et al. 2013
A. oxyphylla Fruits Ethanol extract Antioxidant Wang et al. 2013b
A. zerumbet Leaves Hydroethanolic extract Antioxidant Roman Junior et al. 2013
A. galanga Rhizome Ethanol extract Antioxidant Singh et al. 2011b
A. officinarum Rhizome Methanolic extract Antioxidant Chang et al. 2011
A. oxyphylla Fruits Protocatechuic acid Antioxidant Zhang et al. 2011b
Table 2.6 (Continued)
Species Name Parts used Bioactive fractions/compounds Bioactivity References
A. calcarata Rhizome Hydrodistilled n-pentane and ether extract Antioxidant Arambewela et al.
2010
A. officinarum Rhizome Hydro alcoholic extract Antioxidant Srividya et al. 2010a
A. densespicata Stem and leaves Ethanol extract Nitric oxide
inhibitory
Kuo et al. 2009
A. zerumbet Leaves and rhizome dihydro-5,6-dehydrokawain and other ethyl acetate and hexane extract
Antioxidant Elzaawely et al.
2007a A. zerumbet Flowers and seeds Ethyl acetate and hexane extract Antioxidant Elzaawely et al.
2007b A. galanga and
A. allughas
Rhizome Dichloromethane and methanol extract Antioxidant Vankar et al. 2006
A. katsumadai Seeds Epigallocatechine-3-gallate, resveratrol and total extract
Antioxidant Lee et al. 2003
A. speciosa Rhizome Feruloyl esters with epicatechin Antioxidant Masuda et al. 2000