Phytochemicals and biological studies of plants from the genus Balanophora

This review focus on the phytochemical progress and biological studies of plants from the genus Balanophora (Balanophoraceae) over the past few decades, in which most plants growth in tropical and subtropical regions of Asia and Oceania, and nearly 20 species ranged in southwest China. These dioeciously parasitic plants are normally growing on the roots of the evergreen broadleaf trees, especially in the family of Leguminosae, Ericaceae, Urticaceae, and Fagaceae. The plants are mainly used for clearing away heat and toxic, neutralizing the effect of alcoholic drinks, and as a tonic for the treatment of hemorrhoids, stomachache and hemoptysis. And it has been used widely throughtout local area by Chinese people. Cinnamic acid derivative tannins, possessing a phenylacrylic acid derivative (e. g. caffeoyl, coumaroyl, feruloyl or cinnamoyl), which connected to the C(1) position of a glucosyl unit by O-glycosidic bond, are the characteristic components in genus Balanophora. In addition, several galloyl, caffeoyl and hexahydroxydiphenoyl esters of dihydrochalcone glucosides are found in B. tobiracola, B. harlandii, and B. papuana. Other compounds like phenylpropanoids, flavonoids, terpenoids and sterols are also existed. And their biological activities, such as radical scavenging activities, HIV inhibiting effects, and hypoglycemic effects are highlighted in the review.


Introduction
Balanophora is a genus belonging to the family Balanophoraceae which possesses about 120 species all over the world. Many of them distribute in tropical and subtropical regions of Asia and Oceania, and nearly 20 species are widely ranged in southwest of China [1,2]. These types of dioeciously parasitic plants are normally growing on the roots of the evergreen broadleaf trees, especially in the family of Leguminosae, Ericaceae, Urticaceae, and Fagaceae [1,[3][4][5]. Species in this genus have miscellaneous biological properties such as clearing away heat and toxic, neutralizing the effect of alcoholic drinks, and used as a tonic for the treatment of hemorrhoids, stomachache and hemoptysis by local people in China. The plants of genus Balanophora have been recorded in the Compendium of Materia Medica and were called 'Gecaihua' or 'Geru' [3,5,6].
In this review, we mainly summarize the study progress of phytochemical over the past decades and list the entire chemical compounds isolated from the genus Balanophora. Meanwhile, the biological activities of the plant extracts and chemical constituents are highlighted as well.
The phytochemical studies of genus Balanophora Phytochemical Constituents. -There are several sorts of chemical constituents existing in genus Balanophora. The reported diverse chemical structures of tannins substances owe to their functional groups and the attended modes as well as linked locations of its substituting groups. Extensive studies have led to the identification of many other compounds, such as C 6 -C 3 and C 6 -C 3 -C 6 constituents, terpenoids, sterols and so forth. The structures of compounds in the Figure Table 1. 2.1 Tannins. There are abundant and varied tannins (1-61) in the genus Balanophora. The hydrolyzable tannins -one and / or several galloyls, HHDP, caffeoyl and coumaroyl groups attached to one glucosyl unit by ester linkage -were reported as predominant components from this genus.
3.1 Radical Scavenging Activities. Many studies had verified that lots of compounds from this genus were effective anti-oxidants, and the hydrolysable tannins exhibited higher activities than that of other compounds [1,5,15]. Especially, the compounds with more adjacent phenolic OH groups (galloyl, pyrogallol, or catechol group) had higher DPPH radical-scavenging activities [5,15].
She et al. reported the acetone extract of the fresh female plant of B. laxiflora had obviously radical scavenging activity in DPPH assay (IC 50 = 16.4 μg/ml). All the isolated compounds (8-10, 13-15, 53-54, 59, 70, 82, 91-92, 94, 98 and 100) from the plants were evaluated the free-radical-scavenging activities by DPPH assay with ascorbic acid as positive control. In this assay, the hydrolysable tannins presented higher activities than the other kinds of the phenolic compounds, and the balaxiflorin A (98) and balaxiflorin B (82), with galloyl or caffeoyl groups attached, showed stronger activity than matching phenol compounds [5]. Ho and others convinced the IC 50 values of 6.0, 3.0, 6.4, and 15.7 μg/ml of the crude extract, its derived soluble fractions, EtOAc fraction, BuOH fraction, and water fraction from male flowers of aforementioned plant in DPPH test, (+) -catechin as the reference control. And their IC 50 values were 5.4, 4.1, 5.8, 20.4 μg/ml in superoxide radical scavenging assay (NBT assay), while the IC 50 of (+)-catechin is 9.0 μg/ml. Meanwhile, the methanolic extract of the male flower showed stronger DPPH radical scavenging activity and superoxide radical scavenging assay than that of female flower's extract [20].
The free radical scavenging rate of 4 mg/ml crude extract of B. involucrata was 94.34%. Wang et al. reported that the 80% acetone extract of B. polyandra displayed high free radical scavenging activity with IC 50 = 14.48 μg/ ml [15]. Then, bioassay-guided chemical investigation of the crude extract led to the isolation of 22 phenolic compounds, and they showed striking radical-scavenging activities. The dihydrochalcones 44, 45, 47, 112 and 114, which were found from the 80% watery acetone extract from the fresh rhizome of B. harlandii, with a catechol (= benzene-1,2-diol) moiety as ring B exhibited higher activities than ascorbic acid [1,52].
DPPH free radical scavenging assay and ferric reducing power assay of the plant B. spicata by Deng et al. revealed that the ethyl acetate extract, n-butanol extract, ethanol extract and water-soluble crude polysaccharides had similar anti-oxidatant activities compared with vitamin C. The DPPH experiment (18.91%) indicated that the scavenging rate was relatively stronger than that of vitamin C (13.25%) while the content of ethyl acetate extract was lower than 0.02 mg/ml. When the content of water fraction was 0.06 mg/ml, the scavenging rate of it was 91.08%, which closed to the 95.44% of vitamin C. The IC 50 of B. spicata ethyl acetate extracts was 6.0 μg/ml, while the chloroform extract was the highest [10].
3.3 Hypoglycemic Effects. The literature 50 showed that the 95% ethanol extract of B. polyandra could decrease both the fasting and no fasting blood glucose concentrations of ICR mice. The glucose tolerance was improved remarkably in both normal and alloxan-induced diabetic mice. Compared with normal mice, the blood glucose peak of the ethanol extract of B. polyandra processed retroposited and declined 40%, the area under the blood glucose-time curve (AUC) declined about 26%. Trace it to its cause, the inhibition of α-glucosidase might be one of its major mechanisms [6,49].
3.4 Anti-inflammatory and Analgesic Effects. Literatures about anti-inflammatory and analgesic effects of plant Balanophora are few. The methanol extracts of B. involucrata had significant anti-inflammatory and analgesic effect. The MTD of it in mice was more than 75 g/(kgÁd). Hot plate test indicated the healing effect of it was stronger and better than that of diclofenac -a positive control, and the acting time was more durable than morphine's. Acetic acid writhing test showed that both the two doses (20 g/kg, 12.5 g/kg) could reduce the number of writhing mice (P < 0.01) with the analgesic rates 46.9% and 39.4%. Meanwhile, it could prolong the time the writhing appeared. According to the result of the experiment, the effect of it was equal to the drug hydrocortisone [42,47] 50) showed moderate vasodilator effect on rat aorta, while papuabalanols B (51) had potent inhibition effect of mushroom tyrosinase and anti-melanogenesis in B16 mouse melanoma cells [9]. The (−) -pinoresinol from B. abbreviata had inhibitory activities on the lipopolysaccharide (LPS)-induced inducible nitric oxide synthase (iNOS) expression in RAW 246.7 cells [31]. And extract of B. polyandra could improve the high-fat-diet-induced metabolic syndrome by inhibiting the activity of enzyme PTP1B in mice [13].