A review on biological sources, chemistry and pharmacological activities of pinostrobin

Abstract Pinostrobin, a dietary bioflavonoid discovered more than 6 decades ago in the heart-wood of pine (Pinus strobus), has depicted many pharmacological activities including anti-viral, anti-oxidant, anti-leukaemic, anti-inflammatory and anti-aromatase activities. It is an inhibitor of sodium channel and Ca2+ signalling pathways and also inhibits intestinal smooth muscle contractions. In spite of the fact that pinostrobin has an application as functional foods, till-to-date no comprehensive review on pinostrobin has been carried out. Hence, the present review deals with the biological sources, chemistry and pharmacological activities of pinostrobin. Graphical abstract

for their usage as functional foods. Among them, pinostrobin (5-hydroxy-7-methoxy flavanone), a dietary bioflavonoid, was discovered more than 6 decades ago in the heart-wood of pine (Pinus strobus l.). It is found to be present in edible food materials including Thai ginger (Boesenbergia pandurata Roxb.), honey, propolis, etc. Many pharmacological activities are attributed to pinostrobin, viz. anti-inflammatory activity, gastroprotective activity, quinone reductase inducer activity, anti-oxidant activity, anti-microbial activity, anti-viral activity, anti-nociceptive activity, anti-cancer, anti-fungal activity.
In spite of the fact that pinostrobin has an application as functional foods, till-to-date no comprehensive review on pinostrobin has been carried out. Hence, the present review deals with the biological sources, chemistry and pharmacological activities of pinostrobin.

Biological sources
Pinostrobin (2,3-dihydrotectochrysin) was previously isolated as a dextro-rotatory material from Salvia texana (Torr.) (González et al. 1989), levorotatory material and as an optically inactive form from Carya tonkinensis (lecomte) (Cuong et al. 1996). However, pinostrobin got its name due to its presence in Pinus strobus (l.) (Carvalho et al. 1996). In the past, various extraction and isolation methodologies have been applied for improving the yield of pinostrobin from different plant sources. There are more than 50 literature sources (not limited) that deal with the isolation strategies and content of pinostrobin from different biological sources (Supplementary Table 1). literature data reveal that the leaves of Cajanus cajan (l.) Millsp and rhizomes of Boesenbergia pandurata (Roxb.) are the best sources for the isolation of pinostrobin. Recently, Zhao et al. (2014) have developed a practicable method for the separation of pinostrobin from pigeon pea leaf extract by employing cation exchange resin (NKC-9) with a styrene-divinylbenzene matrix structure catalytic transformation combined with polyamide resin to transform pinostrobin chalcone into pinostrobin. They found that the dynamic transformation efficiency of pinostrobin was 97.67 ± 1.82% and pinostrobin adsorption on polyamide resin follows the Freundlich equation. Further, this leads to the improvement of production efficiency of pinostrobin from 2.32 to 57.23% with a recovery output of 151.12%.
In 2010, the Mitsunobu reaction, europium(III)-catalysed Claisen-Cope rearrangement and Claisen reaction coupled with cross-metathesis in a sealed-vessel microwave reactor was applied for the synthesis of prenylated pinostrobin (Poerwono et al. 2010). Mashentseva et al. (2011) have evaluated the biological activity of complex compounds of pinostrobin oxime with transition metals. Kul'magambetova et al. (2002) have prepared the corresponding oxime and hydrazone of pinostrobin with hydroxylamine and hydrazine without alteration of the γ-pyrone ring. Recently, pinostrobin was utilised as a starting material to synthesise coumarin-chalcone hybrids bearing a triazole linker (Mukusheva et al. 2015) ( Figure 1).

Pharmacokinetics studies
In the year 2011, Hua et al. developed a rapid and sensitive method for the determination of pinostrobin in rat plasma using liquid chromatography-tandem mass spectrometry (lC-MS/ MS) with isoliquiritigenin as an internal standard. They have applied this method to study the pharmacokinetics of pinostrobin. Results indicated that after an oral dose of 0.5 mg/ kg of pinostrobin, C max was found to be 615.35 ng/ml, t max = 4 h and t 1/2 = 4.34 min (Hua et al. 2011).

Anti-ulcer study
At doses of 20 and 40 mg/kg body weight, pinostrobin was reported to reduce the incidence of ethanol induced ulcer by 83.40 and 92.03%, respectively, in Sprague dawley rats in comparison with omeprazole (76.77%, dose 20 mg/kg) (Abdelwahab et al. 2011). Recently, Jain (2015 has reviewed the potential of this molecule as an anti-ulcer agent (Table 1). Panthong et al. (1994) showed that at an oral dose of 300 mg/kg of pinostrobin has been an inhibition of 10.3% oedema. In the recent study, pinostrobin inhibited the production of TNF-α (IC 50 < 22 μM) and Il-1β (IC 50 < 40 μM) in murine macrophages and also in Sprague dawley rats (Patel & Bhutani 2014). The half maximal inhibitory concentration of pinostrobin for nitric oxide was found to be 43.2 μM (lee et al. 2013;Sudsai et al. 2014). Pinostrobin depicted the weak inhibitory effects on COX I and II enzymes at concentration of 100 μg/ ml (Wu et al. 2002) (Table 1).

Anti-viral activity
Pinostrobin inhibits herpes simplex virus-1 (HSV-1) replication with an EC 50 of 22.71 ± 1.72 μg/ ml via shedding and braking of the virus envelope (Wu et al. 2011). Pinostrobin was found to inhibit 88.7% of dengue-2 virus NS3 protease non-competitively at 400 ppm, while K i was found to be 345 μM (Kiat et al. 2006) (Table 1). Nicholson et al. (2010) demonstrated that pinostrobin exemplifies the pharmacological actions of anti-depressant drugs (sodium channel blockers) with half maximal concentration of 23 μM in comparison with the anti-convulsant and sodium channel inhibitor carbamazepine which exhibited an IC 50 of 299 μM in the same assay. However, they suggested that further exploration related to the specific binding of pinostrobin on the sodium channel complex is needed (Table 1).

Neuroactive properties and treatment of neurodegenerative disorders
In another study, pinostrobin (1-40 μM) depicted the protective effect against Aβ 25 − 35 -induced neurotoxicity in cultured rat pheochromocytoma (PC12) cells which demonstrate its anti-Alzheimer actions. This neuroprotection was facilitated by the inhibition of oxidative damage and calcium overload which was confirmed by an elevation of cell viability, depletion in lactate dehydrogenase activity, the levels of intracellular reactive oxygen species and calcium in Aβ 25 − 35 -treated PC12 cells. Further, pinostrobin was also found to significantly suppress the formation of dNA fragmentation with increase in the ratio of Bcl-2/Bax which suggests curtailment of mitochondrial pathway of cellular apoptosis (Xian et al. 2012).

Anti-oxidant activity
The anti-oxidant activity of pinostrobin was determined by investigating in vitro 2,2-diphenyl-1-picrylhydrazyl (dPPH) scavenging assay. The study shows that pinostrobin has anti-oxidant activity (IC 50 > 500 μg/ml) (Wu et al. 2009). Pinostrobin present in propolis from Canada was also found to exhibit anti-radical activity against dPPH (Christov et al. 2006). Pinostrobin exhibited ferric reducing/anti-oxidant power (FRAP) value of 116.11 ± 0.004 in comparison with ascorbic acid (915 ± 0.01562) (Abdelwahab et al. 2011). Pinostrobin, a prominent flavonoid found in honey, is able to induce mammalian phase 2 enzymes. The concentrations for doubling the quinine reductase (QR) activity of pinostrobin were found to be 0.5 μM in murine hepatoma cells (Fahey & Stephenson 2002). In another study, pinostrobin (circular dichroism [Cd] value < 0.56 mM) was found to have potent QR induction activity comparable to sulphoraphane (Cd value = 0.43 mM). Also, chemoprevention index (CI) of pinostrobin (>132) was found to be higher than that (25.0) of sulphoraphane (Su et al. 2003). Also, Gu et al. (2002) have reported the Cd values of 0.9 μg/ml for this compound with no cytotoxicity for induction of QR activity (Table 1).

Anti-malarial activity
The study shows that pinostrobin has anti-malarial activity but exact mechanism of anti-malarial action is not clear but some flavonoids are shown to inhibit the influx of l-glutamine and myoinositol into infected erythrocytes. Pinostrobin (IC 50 > 100 μM) possess weak anti-malarial activity (Kaur et al. 2009). duker-Eshun et al. (2004 have reported the weak anti-plasmodial activity with an IC 50 > 100 μM (Table 1).

Anti-protozoal activity
Pinostrobin was found to be moderately inhibiting E. histolytica and G. lamblia with an IC 50 of 184.0 and 80.8 μg/ml, respectively (Calzada et al. 2003) (Table 1). Bail et al. (2000) was the first to study the interaction between pinostrobin and the oestrogen receptor in the presence or absence of 17β-estradiol (E 2 ) or dehydroepiandrosterone sulphate (dHEAS), respectively, in a stably transfected human breast cancer cell line (MVlN). They successively found out that pinostrobin depicted an anti-aromatase activity (IC 50 = 10 μM) without decreasing dHEAS-or E 2 -stimulated cell proliferation and without binding to the oestrogen receptor (Bail et al. 2000). Further, pinostrobin showed an IC 50 value of 4 μM for the inhibition of 17β-estradiol formation in JEG-3 cells and in Arom + HEK 293 cells and 29 μM for anti-oxidative capacity (inhibition of t-BuOOH-lP) (Saarinen et al. 2001). (S)-(-)-Pinostrobin was found to be moderately active (IC 50 > 116.41 μM) towards sensitive and drug-resistant cancer cell lines and normal cells when determined by the resazurin assay (Kuete et al. 2014). However, pinostrobin was found to be most active against the adriamycin-sensitive acute T-lymphoblastic leukaemia cell line (CCRF-CEM, IC 50 = 10.2 μg/ml) and its multidrug-resistant sub-line CEM/AdR5000 (IC 50 = 10.5 μg/ml) (Ashidi et al. 2010) (Table 1). Pinostrobin also demonstrated anti-tumour activity against Hela and HepG2 cell lines (Cao et al. 2012).

Anti-diarrhoeal actions
The pharmacological effect of pinostrobin was evaluated using isolated in vitro guinea-pig ileal smooth muscle. It inhibited the contractions evoked by high concentrations of potassium. The potency of the relaxant effect was determined by measuring the capacity of each product in reducing the phasic (16.6 ± 1.29 μM) and the slower sustained tonic (13.49 ± 0.80 μM) contractile responses induced by depolarisation with 60 mM K + (Meckes et al. 1998) (Table 1).

Trypanocidal activity
Trypanocidal activity was used as screening criteria to prevent the transmission of Chagas disease in blood banks. Pinostrobin depicted the lysis of 14.7 trypanocides of Trypanosoma cruzi at dose of 500 μg/ml (Takeara et al. 2003) (Table 1).

Toxicity studies
Pinostrobin exhibited non-toxic and non-genotoxic effects to male Wistar rats at higher dose of 500 mg/kg and ld 50 of pinostrobin was found to be more than 500 mg/kg. The relative organ weights and biochemical parameters, such as albumin, albumin-globulin ratio (A/G), alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase and total protein, and urea concentration were found to remain unaffected by pinostrobin. Pinostrobin did not present clastogenicity in rat liver when examined by a micronucleus assay in regenerating livers of rat (Charoensin et al. 2010).

Conclusions and future directions
Pinostrobin, a bioflavanone present in many plant sources, has depicted many pharmacological activities. In addition, the protein binding rate, the pharmacokinetic and safety profile of pinostrobin are already reported. There is availability of many plant sources specifically Cajanus cajan (l.) Millsp can be employed for the industrial separation of pinostrobin with good yield. Interestingly, some researchers have developed a feasible method for improving the yield of this compound. However, an environmental friendly, simple, economic and highyield method needs to develop in the future. Also, it is important to know the exact form (R/S/RS) of pinostrobin when addressing its biological activity or pharmacokinetic parameters. Although, some modification on pinostrobin has been carried out in the past; however, further more is required to develop the structure activity relationship (SAR) to develop this compound into successful drug lead.

Disclosure statement
No potential conflict of interest was reported by the authors.