Bioactive profile, health benefits and safety evaluation of sea buckthorn (Hippophae rhamnoides L.): A review

Sea buckthorn (Hippophae rhamnoides L.) contains a large number of versatile compounds with antioxidant and hence medical properties that have been reported from time to time. Intensive work on the medical properties of sea buckthorn has concluded incredible results like the effects on atherosclerosis, anti-visceral obesity, platelet aggregation, inflammation, adverse stressful situations, and that of liver injury. Only a few studies have been conducted on the safety evaluation of the plant extract but importantly no study has deemed it unsafe for animal or human consumption till date. Considering the fact that no significant changes have been observed in organ weight/body weight ratios, of any vital organ studied (except liver and kidney in 1 g/kg and 2 g/kg body weight doses, respectively) and biochemical and hematological parameters in different animal trials with an lethal dose for 50% reduction of population (LD50) of >10 g/kg when given orally, there is scope for further investigations regarding its safety in the daily diet as a protective medicine. Subjects: Bioscience; Food Science & Technology; Health and Social Care

rapid growth, ability to act as protection against wind and sand drift, assistance in soil and water conservation, and improvement of soil by efficient nitrogen fixation allow sea buckthorn to be widely used in vegetation and restoration of degenerated ecosystems (Chen & Chen, 2003;Hou, Bai, & Cao, 1995;Li, 2004;Ruan & Li, 2002;Ruan, Xie, & Li, 2000;Wei, Yu, & Zhu, 1998). Sea buckthorn with diverse uses such as, controlling soil erosion, a source of horse fodder, nutritious foods, drugs, and skin-care products, also contains bioactive compounds with antioxidant properties that are preferred over the synthetic antioxidants simply because the latter have quite often been found to be carcinogenic (Fan, Ding, & Gu, 2007;Rodríguez-Meizoso et al., 2006). Oil from sea buckthorn has shown effectiveness in skin therapy for sunburns, chemical burns, radiation burns, and eczema (Goel et al., 2002;Seven et al., 2009;Yang et al., 2000;Zeb, 2004b). Furthermore, sea buckthorn oil has shown positive results in treating health problems related to damaged mucous membranes of the gastrointestinal tract including mouth ulcers, gastric ulcers, and stress ulcers Suleyman, Demirezer, et al., 2001;Xu et al., 2007). Of particular interest, the berries, the oil, and the seeds of sea buckthorn have been shown to possess antiatherogenic, hypocholesteromic, hypotensive, and anti-inflammatory properties (Eccleston et al., 2002;Ganju et al., 2005;Wu, Yu, Ma, Li, & Liu, 1994;Yang, 1995;Zhang, 1987) and could therefore be successfully exploited to prevent or treat cardiovascular disease.
Sea buckthorn has been used mostly in the Tibetian and Chinese traditional medicines for so long, which is supported by a lot of both ancient and recent literature on the use of different parts of sea buckthorn, such that the plant is also commonly known as Chinese medicinal plant. The fact that all parts of the plant possess bioactive compounds with antioxidant properties, the literature on its antioxidant activity, impact on the medical lines, and its safety evaluation are reviewed in the present manuscript.

General medical properties
The branches of sea buckthorn contain (-)-epigallocatechin and ursolic acid that exhibit anti-inflammatory effects and the leaves are used in the treatment of diarrhea, gastrointestinal, and dermatologic disorders (Yasukawa, Kitanaka, Kawata, & Goto, 2009). The leaf extracts of sea buckthorn are rich in flavonoids, tannins, and triterpenes , which as well as the extracts of its branches are used to treat colitis and enterocolitis in humans and animals in Mongolia (Tsybikova, Rasputina, Zalykeeva, Darzhapova, & Kundanova, 1983). The leaves have also been applied as compress form in rheumatoid arthritis in the Middle Asia. Flowers of sea buckthorn have been used as skin softener in Tajikistan. The extracts of whole fruit, fruit pulp, pulp oil, and seed oil of ripe fruits have been reported to be useful in treating various diseases such as gastric ulcers (Suleyman, Demirezer, et al., 2001;Xing et al., 2002), skin disorders (Yang et al., 2000), Sea buckthorn can increase the production of plasma leptin and of neuropeptide Y in children with functional dyspepsia. The overall effect of sea buckthorn is improvement of gastric emptying, gastric mobility, gastrointestinal digestive function, and promotion of children's growth (Xiao, Qiu, Yue, Cai, & Mo, 2013). Sea buckthorn berry oil is reported to play a potential role in treating atopic dermatitis and thrombosis (Cheng et al., 2003;Yang et al., 2000). Juice, syrup, and oil of the fruits have been used as pain killer, to heal wounds, in ulcer and other diseases of the stomach, disantheria, cancer, and as a metabolism regulator in traditional medicine. The freshly pressed juice is used in the treatment of colds, febrile conditions, and exhaustion (Yang et al., 2000). Oil from seeds and fruits is used in the treatment of eczema, lupus erythematosus, chronic wounds that are difficult to heal, inflammatory diseases, erosion of the cervix uteri, in the treatment of burns and frozen parts of the body, and in ophthalmology. Besides, they are used in the treatment of keratitis, trachoma, injuries or burns of eyelid, and conjunctivitis (Guliyev et al., 2004). Isorhamnetin isolated from sea buckthorn has been investigated for its cytotoxicity and its influence on human hepatocellular carcinoma cells. The cytotoxic effects of isorhamnetin showed dose and time dependency against hepatocellular carcinoma cells (IC 50 = 74.4 μg/ml) after treatment with isorhamnetin for 72 h. The cytotoxicity of isorhamnetin on tumor cells depends on cellular accumulation of the drug that permeates the cell membrane into the cell (Teng, Lu, Wang, Tao, & Wei, 2006). Cytotoxicity studied in murine macrophages induced by tertiary-butyl hydroperoxide was controlled up to >95% using a pretreatment of the cells with sea buckthorn extract of concentration as low as 25 μg/ml . Sea buckthorn leaf tea supplementation suppressed body weight gain in a dose-dependent manner and significantly reduced visceral fat, plasma levels of leptin, triglyceride and total cholesterol, and alanine aminotransferase activity as compared to high-fat-fed control mice studied for six weeks (Lee et al., 2011). The leaf tea supplementation also decreased hepatic triglyceride and cholesterol concentrations, and lipid accumulation, whereas fecal lipid excretion elevated. The hepatic cytochrome P450 2E1 activity and hepatic and erythrocyte lipid peroxides were significantly lowered with the leaf tea supplements. The hepatic and erythrocyte superoxide dismutase and catalase activities were also increased with the leaf tea supplements in a dose-dependent manner induced by high-fat feeding, which indicate that sea buckthorn leaf tea supplementation has potential anti-visceral obesity properties and antioxidant activity mediated by the regulation of lipid and antioxidant metabolism in high-fat diet-induced obese mice.

Anti-inflammatory properties
Sea buckthorn leaf extract acts as an immunosuppressant during the acute phase of inflammation by selectively inhibiting T-cell activation as a treatment against adjuvant-induced arthritis in rats (Ganju et al., 2005). The inducible nitric oxide synthase (iNOS) induced by microbial products like lipopolysaccharide accounts for the sustained generation of nitric oxide (NO) and is well known for its role in immunological responses such as inflammation and autoimmunity. Many flavanoids and phenylethanoids are antioxidants protecting biological system against oxidative stress. This is mainly due to their redox properties, which can play an important role in adsorbing and neutralizing free radicals, quenching singlet and triplet oxygen or decomposing peroxidase (Rice-Evans, Miller, & Pagana, 1996;Wang et al., 1996). Sea buckthorn leaf extract increased cell viability against dexamethasone (control) and NO scavenging activity as compared to four (amla, bahera, sacred basil, and shankhpushpi) extracts of known medicinal value. Pretreatment of macrophages with sea buckthorn leaf extract showed the maximum significant inhibition as compared to different extracts (Padwad et al., 2006). Treatment of cells with sea buckthorn leaf extract reduced iNOS expression with respect to the lipopolysaccharide-treated cells, whereas dexamethasone-treated cells showed almost a minimal expression (Wang et al., 1996). Sea buckthorn berries caused a reductive effect on C-reactive protein (marker of inflammation and a risk factor for cardiovascular diseases) in a study carried out as a randomized, double-blind, placebo-controlled trial, over an observation period of 90 days (Larmo, Alin, Salminen, Kallio, & Tahvonen, 2008). The branches of sea buckthorn contains (-)-epigallocatechin and ursolic acid that exhibit anti-inflammatory effects (Yasukawa et al., 2009).

Effects on adverse stressful situations
Alcoholic leaf extract of sea buckthorn (70% ethanol) has been analyzed to inhibit hypoxia-induced cytotoxicity, mitochondrial integrity, reactive oxygen species (ROS) production, and DNA damage better than vitamin C (Narayanan et al., 2005). In a study of effect of dry sea buckthorn leaf (aqueous lyophilized) extract, untreated rats exposed to cold-hypoxia-restraint (C-H-R) up to fall of rectal temperature (T rec ) 23°C, blood hexokinase (HK) activity decreased, liver phosphofructokinase (PFK) activity increased, and muscle PFK activity decreased . During cold exposure of 20°C for 8 h in rat, liver glycolysis activated at the regulatory step catalyzed by PFK/fructose-1,6biphosphatase (Churchill et al., 1994). Acute hypoxic exposure of 7,000 m was found to increase heart HK activity in rats (Bass et al., 1989). Another study by Saggu and Kumar (2008) on the effect of sea buckthorn dry leaves (aqueous lyophilized extract) showed improvement in anaerobic generation of energy during C-H-R exposure and post-stress recovery, enabling the organism to adapt successfully in such a severe stressful situation (Table 3).

Safety evaluation
In rats exposed to C-H-R, aqueous extract of sea buckthorn leaf administered for 14 days (single oral dose of 1 g/kg and 2 g/kg once daily) and 30 days (single oral dose of 100 mg/kg once daily) showed that the maximal effective adaptogenic dose of the extract was 100 mg/kg body weight. No significant changes were observed in organ weight/body weight ratios, of any vital organ studied (except liver and kidney in 1 g/kg and 2 g/kg body weight doses, respectively) and biochemical and hematological parameters of the sub-acute drug-treated animals in comparison to control rats. In acute toxicity study, LD 50 of the extract was observed to be >10 g/kg when given orally . Safety and efficacy of supercritical CO 2 -extracted sea buckthorn seed oil on burn wound model revealed no adverse effects in acute and sub-acute oral toxicity (Upadhyay et al., 2009). Subchronic toxicity and efficacy study of sea buckthorn oil showed no significant changes in various physiological, hematological, biochemical (AST, ALT, ALP, uric acid, urea, and creatinine) and histopathological parameters in three groups of New Zealand white rabbits (0.5, 1, and 1.5 ml/kg body weight) with no mortality in any of the treatment groups (Rashid et al., 2011). Aqueous extract of sea buckthorn fruit administered in four groups of rats (0, 100, 250, or 500 mg/kg in a single dose/day for 90 days) showed no treatment-related change in mean body weight, organ/body weight ratio, histological, hematological, and biochemical parameters (Tulsawani, 2010).

Scope for further investigations
Analysis of the published literature on sea buckthorn reveals a lot of health-promoting properties in vitro and in vivo. However, the safety concerns regarding the use of sea buckthorn extract in the daily diet is still in its early days. Although only a few studies have been performed on the safety evaluation of different sea buckthorn extracts on different trial animals, yet no study has deemed its use deleterious for human consumption to the best of the knowledge of the authors. Therefore, further studies on the safety evaluation of sea buckthorn extracts find a great scope and are needed to authenticate the area of incorporation of sea buckthorn extracts in the daily diet of human beings as a protective medicine.

Conclusion
Different parts of sea buckthorn plant have been widely used in traditional medicine in various countries (India, China, Nepal, Pakistan, Myanmar, Russia, Britain, Germany, Finland, Romania, France, etc.) of the world. Among the various studies conducted on the effects of different parts of the plant are cardiovascular effects, effect on atherosclerosis and platelet aggregation, effect on diabetes, anti-inflammatory effect, antitumor effect, effect on clinical diseases of the liver, anti-visceral obesity, antiulcerogenic effect, effect on adverse stressful situations, etc. The different pharmacological effects of sea buckthorn are attributed to the various bioactive components with antioxidant properties of which sea buckthorn is a good source. These bioactive components include kaempferol, isorhamnetin, quercetin, catechin, epicatechin, gallocatechin, epigallocatechin, procyanidins, carotenoids, organic acids, etc. Sea buckthorn offers an excellent source of functional and therapeutic food whose safety evaluation although is in its infancy, yet the trails till date deem its use safe.