The genus Morinda is pan tropical in its distribution with about 80 species. This genus includes trees, shrubs and vines. In the Western Pacific region, vines are most common while the trees are only a few, including Morinda citrifolia which typically have “vine-like” characteristics of their branches and stems [1,2]. The tree belongs to the family Rubiaceae. It has different local names in various geographical locations. Some commonly used names include noni in Hawaii, nono in Tahiti, Indian Mulberry in India, Ba ji tian in China and cheese fruit in Australia [3]. Morinda citrifolia has been used by humankind both as food and medicine for millennia [4-6]. Due to its traditional and current use, a number of biological and chemical studies have been performed on this species dating back more than 100 years. Literature survey however reveals that the leaves have the most prevalent traditional use and were usually used topically. On the other hand, in the current practice the fruit juice and less commonly the leaves or other parts are used and these are primarily given orally [3,7]. Hence in the present preliminary studies three parts namely fruits, leaves and stem were separately evaluated for different biological activities namely, anti-leishmanial, spasmolytic and spasmogenic, antioxidant and antimicrobial activities. It may be noted that in earlier studies the parts of the plant mainly used for these activities were roots [8], fruits and roots [9,10] and fruit juice [11]. The present results provide a direction regarding the selection of particular part for studying any specific biological activity referred to above in future.

Aerial parts of Morinda citrifolia were collected from the University of Karachi campus Pakistan in the month of August. The plant was identified by Dr. Surayya Khatoon, Department of Botany, University of Karachi, and a voucher (specimen No. 67344) has been deposited in the Herbarium of the same department. The fruits (2 kg), leaves (1.5 kg) and stem (3 kg)) were manually separated and extracted with MeOH (x3) at room temperature. The fruits (1 kg) and leaves (1 kg) were also extracted with 70% aqueous ethanol (x3) at room temperature. The solvent was removed from each extract under reduced pressure to yield a thick syrupy extract of fruits (133.0 g), leaves (114.0 g) and stem (198.0 g).

The extracts from the three parts referred to above were screened in different biological assays and the observations are noted below.

Anti-leishmanial activity

A preparation of the methanol extracts of fruits, leaves and stem at 1% concentration in ointment base was applied in clinical patients suffering from cutaneous leishmaniasis. Lesions were dry, ulcerative and size of lesion was measured in mm at clinical observation. Marked improvement and cure was observed in 50% patients treated with stem extract whereas 30% patients showed moderate improvement and 20% patients showed insignificant improvement. The leaves and fruit extracts were not much effective.

Spasmolytic and spasmogenic activities

The 70% aqueous-ethanol extracts of fruits and leaves of M. citrifolia showed relaxant effect on isolated spontaneously contracting rabbit jejunum preparation at a dose range of 0.3-5.0 mg/ml and 0.1-3.0 mg/ml respectively according to the procedure reported earlier [12]. The same preparations were also tested in the presence of atropine (0.3 μM). Fruits extract caused the relaxation at two fold less dose (0.3-3.0 mg/ml) while, the leaves extract did not show any significant effect as shown in Figure 1. The fruits and leaves extracts also inhibited the potassium (80 mM) induced contractions at the same dose range of 0.3-1.0 mg/ml. These results indicated the presen ce of calcium channel blocking, cholinergic type and relaxant constituents in the fruits and leaves extract of the plant as shown in Figure 2. The graphs were prepared using Graph Pad Prism software version 4.00 for Windows, (Graph Pad Software, San Diego California USA, www.graphpad.com).

Figure 1: Inhibitory effect of the Morinda citrifolia 70% aqueous-ethanolic fruits (Mc.Cr.F) (A) and leaves extract (Mc.Cr.L) (B) on spontaneous and high K+- induced contractions and concentration-response curves of Ca++ in isolated rabbit jejunum. The symbols represent mean ± S.E.M, n= 4-6.

Figure 2: Typical tracing showing the inhibitory effect of Morinda citrifolia 70% aqueous-ethanolic leaves and fruits extracts on the spontaneous contractions in isolated rabbit jejunum preparation.

Antioxidant activity

The fruits, leaves and stem methanol extracts were assayed for antioxidant activity at 200 μg/ml dose in diphenylpicryl hydrazine (DPPH) assay by the method described earlier [13]. The leaves and stem methanol extracts showed almost similar activity (18.13% and 19.23% inhibition respectively) while the fruit extract was significantly (>3 times) more active than the leaves and stem methanol extracts and showed 57.69% inhibition.

Antibacterial activity

The disc diffusion method [14] was used to determine the antibacterial and antifungal activities of the three extracts referred to above. The stem methanol extract was most active and showed inhibition of all the 12 Gram-positive bacteria (Table 1) and was significantly effective against 8 bacteria at 200 μg /disc concentration with inhibition zone ranging from 10 to 14 mm; 8 out of 12 Gramnegative bacteria with inhibition zone ranging from 9 to 12 mm at the same concentration (Table 2). It was further observed that the stem extract inhibited the growth of 7 out of 13 fungi tested (Table 3) at the same concentration.

Table 1: Antimicrobial activity of the leaves, fruits and stem methanol extracts against Gram-positive bacteria.

Table 2: Antimicrobial activity of the extracts against Gram-negative bacteria.

Table 3: Antimicrobial activity of the extracts against Fungi.

The methanol/70% aqueous ethanol extracts of three parts used in this study showed varying extent of activities for each evaluated activity. The stem methanol extract was most active against leishmania, Gram+ve and Gram-ve bacteria, and fungi. For spasmolytic/spasmogenic activity both fruits and leaves 70% ethanolic extracts showed similar order of activity. Both the fruits and stem methanol extracts showed almost equal order of antioxidant activity. These observations provide a direction for future work and can help in selection of specific plant part for carrying out studies on any particular biological activity.