CHEMISTRY:

Evaluation of the traditional claims of Brahmi was initiated by investigating the effect of the ethanolic extract on the acquisition, consolidation and retention of three newly acquired behavioral responses in albino rats.⁴The activity was localized in a fraction containing dammarane type triterpenoid saponins, designated as bacosides A and B. Both bacosides A and B showed a single spot on TLC over silica gel.

Later investigations revealed that bacoside A was a mixture of three compounds, which were designated A2,A2’ and A3. The sugar moiety consisted of glucose and arabinose. Repeated chromatography of bacoside A over normal and reverse phases yielded two saponins, A2 and A3, in pure form. The structures of bacosides A2 and A3 were established.^5,6 Bacoside B was found to be a triglycoside having the same aglycone as A2 and two units of glucose and an arabinose as sugar moiety.

MECHANISM OF ACTION:

Since Bacopa's primary therapeutic use is to enhance cognitive function, most research has focused on the mechanism behind these properties. The triterpenoid saponins and their bacosides are responsible for Bacopa's ability to enhance nerve impulse transmission. The bacosides aid in repair of damaged neurons by enhancing kinase activity, neuronal synthesis, and restoration of synaptic activity, and ultimately nerve impulse transmission⁷. Loss of cholinergic neuronal activity in the hippocampus is the primary feature of Alzheimer's disease⁸. Based on animal study results, bacosides appear to have antioxidant activity in the hippocampus, frontal cortex, and striatum⁹. Animal research has shown Bacopa extracts modulate the expression of certain enzymes involved in generation and scavenging of reactive oxygen species in the brain¹⁰. In vitro research has shown Bacopa exerts a protective effect against DNA damage in astrocytes¹¹ and human fibroblasts¹².In animals Bacopa has a relaxant effect on pulmonary arteries, aorta, trachea, and ileal and bronchial tissue, possibly mediated by inhibition of calcium-ion influx into cell membranes¹³. Bacopa appears to stabilize mast cells in vitro¹⁴, and possesses anti-inflammatory activity via inhibition of prostaglandin synthesis and lysosomal membrane stabilization¹⁵. In vitro research suggests an anticancer effect for Bacopa extracts, possibly due to inhibition of DNA replication in cancer cell lines¹⁶.

SEASONAL VARIATION OF BACOSIDE:

Methods have been developed for a quantitative determination of bacoside A content in the extract by UV spectrophotometry¹⁷ and HPLC.¹⁸ To monitor seasonal variations of bacosides, fresh plant material was collected every month, extracted with ethanol and fractionated. This was carried out over a period of 14 months commencing March 1993. The TLC of the n-butanol fraction of the ethanolic extractives of the plant was used to monitor bacosides. From this study it was concluded that bacoside A (mixture of bacosides A2, A2’ and A3) predominates in March and April whereas both bacosides A and B are available in May. In the remaining months, other compounds appear and disappear.

PHARMACOLOGICAL EVALUTION:

Both the crude extract and the bacosides were evaluated for their nootropic activity. In adult male rats, the extract (40 mg/kg.p.s) was given 3 hours before the test in acute studies and every third day in chronic experiments.

A labile test utilized brightness discrimination reaction in a semi-automatic Y-maze. In this test significant effects were observed on all the three tempero-spatial parameters - acquisition, consolidation and retention. The initial test for stable behavior was an active conditioned flight reaction using a sound cue. In this test also the animal learnt to escape foot shock quickly (6 days versus 10 days in control) and the reaction time was significantly lower from day 4 onwards. The final test was the continuous avoidance test. A stable baseline behavior was achieved by day 20 in this test but did not happen in the control animals⁴. Detailed studies were carried out with bacosides A and a mixture of bacosides A and B¹⁹. The labile test was the brightness discrimination reaction for the Y-maze test as was done with the extract. The stable test included the active conditioned avoidance test used earlier and a conditioned aversion test employing aversion to lithium chloride in a water-deprived rat as the cue. The bacosides produced a dose-related effect similar to that of the extracts in all the three tests. The effect of 10 mg/kg bacosides was equal to that of 40 mg.kg of extract. A dose of 10 mg/kg of bacosides given orally 60 minutes prior to testing was able to abolish both the deficits of the W-shaped curve²⁰. These results suggested that the facilitatory effect of bacosides is mainly due to their ability to consolidate the retention of learnt behaviour of the earliest form, i.e. short term memory. This facilitatory effect persisted when the other two longer lasting forms of memory were getting consolidated. The anti-amnestic activity of bacoside was also evaluated. A significantly higher dose (20 mg/kg.p.c. for 3 days) was needed to prevent retrograde amnesia caused by electro-convulsive seizure, immobilization or scopolamine in the Y-maze test.²¹ The bacosides on the other hand exhibited significant anti-stress activity.

SAFETY EVALUTION:

The LD50 of the ethanolic extract has been determined in rats and mice by the oral and IP routes. It was greater than 3g/kg by the oral route in the species. The LD50 by the IP route was 205 mg.kg (range 230-182) in rats and 224mg/kg (range 260-135) in mice. The oral LD50 of bacosides in mice was 774 mg/kg. It was evident that the extract had less acute toxicity bacosides. Further studies have therefore been performed with the standardized preparation. Chronic toxicity studies have been performed following oral administration of 2.5, 5 and 10 times the effective nootropic dose of the preparation in a rodent (rat) and a non-rodent species for 90 days. Various hematological, biochemical and gross behavioral changes were regularly recoded. Terminal autopsy was followed by gross and microscopic examination of all viscera as per regulatory requirements. The preparation was found to be safe and devoid of any teratological effects in 2 species (rat and rabbit) and mutagenicity in in vitro and in vivo tests. Pre-clinical neuropharmacological studies demonstrated that both Brahmi extract and bacosides improved short term and intermediate memory, thus improving long-term memory. Based on these wide-rang-granted CDRI permission to conduct Phase I clinical trials in healthy human volunteers. The Institute has assessed the safety and tolerability of the standard preparation in 51 healthy human volunteers.²² Single oral doses of 20-200 mg or 100 and 200 mg once daily for four weeks were found to be safe, and did not produce any reaction or side effects. Subsequently a placebo-controlled double-blind phase II clinical trial in 36 children of Attention Deficit Hyperactivity Disorder (ADHD) was conducted. The children received either a placebo or 50 mg of the preparation twice daily for 12 weeks. The children receiving the preparation showed significant improvement in scores in several test systems and there were no side effects.

IMPORTANT EFFECTS ON THE CENTRAL NERVOUS SYSTEM:

Bacopa meditates the GABAergic system.²³ Gamma-aminobutyric acid is an inhibitory neurotransmitter that has been shown to possess anticonvulsive, antinociceptive (prevention of pain due to hypersensitive nerve endings), locomotor, and sedative effects. Because Bacopa also has all these properties, it is reasonable to speculate that a similar mechanism of action explains its effects on the brain and the body. Like some other GABAergic agents, Bacopa may be able to help protect against epilepsy by regulating the memory-transmission molecules that govern motor mechanisms and potentiate neuronal signaling: dopamine and acetylcholine.

ANXIETY AND DEPRESSION:

Bacopa’s traditional use as an anti-anxiety remedy in Ayurvedic medicine is supported by both animal and clinical research. Research using a rat model of clinical anxiety demonstrated a Bacopa extract of 25-percent bacoside A exerted anxiolytic activity comparable to Lorazepam, a common benzodiazapene anxiolytic drug. Importantly, the Bacopa extract did not induce amnesia, side effects associated with Lorazepam, but instead had a memory-enhancing effect.²⁴A one-month, limited clinical trial of 35patients with diagnosed anxiety neurosis demonstrated that administration of Brahmi syrup (30 mL daily in two divided doses, equivalent to 12 g dry crude extract of Bacopa) resulted in a significant decrease in anxiety symptoms, level of anxiety, level of disability, and mental fatigue, and an increase in immediate memory span. Other changes noted were increased body weight, decreased respiration rate, and decreased systolic blood pressure.²⁵For four weeks, 35 patients were treated for anxiety neurosis.²⁶After treatment, they were assessed for clinical anxiety levels, maladjustment level, mental fatigue rate, and immediate memory span. In those patients receiving Bacopa: Anxiety levels were lowered by about 20%,Maladjustment was significantly lower than its corresponding pretreatment value, Mental fatigue, as determined in total daily work output, was lower, Immediate memory-span scores were significantly increased.

EPILEPSY:

Although Bacopa has been indicated as a remedy for epilepsy in Ayurvedic medicine, research in animals shows anticonvulsant activity only at high doses over extended periods of time. Early research in India demonstrated that hersaponin (an active constituent) exhibited protection against seizures in mice.²⁷A more recent Indian study also examined the anticonvulsant properties of Bacopa extracts in mice and rats. Researchers determined that intraperitoneal injections of high doses of Bacopa extract (close to 50percent of LD50) given for 15 days demonstrated anticonvulsant activity. When administered acutely at lower doses (approaching 25 percent of LD50), anticonvulsant activity was not observed.²⁸

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Received on 26.02.2010

Accepted on 29.04.2010

Research Journal of Pharmacognosy and Phytochemistry. 2(3): May-June 2010, 181-184