Pharmacological basis for the use of Hypericum oblongifolium as a medicinal plant in the management of pain, inflammation and pyrexia

Pain, inflammation and pyrexia can result in unrelenting symptoms, misery, stress and sometimes disablement for the sufferer. Allopathic medicine uses drug treatments to decrease the inflammation and pyrexia as well as reduce the pain by blocking various inflammatory mediators especially the prostaglandins, leukotrienes, cytokines and histamine. However, these medications often cause side effects such as stomach bleeding, bone demineralisation, kidney damage and nutritional deficiencies [1, 2]. The use of complementary and alternative medicine has been shown to produce beneficial effect in the management of various painful inflammatory conditions [3, 4] and several natural remedies are available that are often as effective as drugs without the side effects [5, 6]. Thus there is an ample scope for new natural medicines to combat different pathological conditions associated with pain, inflammation and pyrexia.

Hypericum, is a large genus of the family Hypericacea and consists of herbs or shrubs that grow widely in the temperate regions. Useful drugs, dyes, pigments, timbers, gums and resins have been isolated from its different members [7]. This genus is widely studied for anti-depressant, anti-microbial, antioxidant, antiviral, anxiolytic, anticancer, anti-inflammatory and anti-ulcerogenic activities. Several species of this genus especially Hypericum perforatum [8], Hypericum caprifoliatum [9, 10], Hypericum polyanthemum [11, 12], and Hypericum grandifolium [13, 14] were extensively studied for their utility in different diseases like depression, seasonal effective disorder, HIV and hepatitis-C infection, obsessive compulsive disorder, as well as other pathological conditions associated with pain and inflammation. Their use in these conditions has been validated by using a number of different animal and in vitro models.

Hypericum oblongifolium Wall. (family: Hypericacea), is a 6–12 m high erect evergreen shrub that grows at an altitude of 5000-6000 ft and is common in China and Himalaya [15]. This plant has been traditionally used for the treatment of hepatitis, nasal hemorrhage, gastric ulcer, external wounds, sedative, antispasmodic, antiseptic and as a remedy for sting of bees and dog bites [16, 17]. H. oblongifolium has been tested for chymotrypsin [15] and urease inhibition [18], antioxidant, anti-glycation, anti-lipid peroxide inhibition [19], antispasmodic, bronchodilator, blood pressure lowering [16], anti-ulcer [20] and anti-proliferative activities [17]. Phytochemical analysis showed that H. oblongifolium contained flavonoids, saponins and tannins [16]. Recently, various chemical compounds have been isolated from this plant and include triterpenes like hyperinols A and B [15], flavonoids like quercetin, myricetin, rhamnetin, kaempferol, luteolin [21], 18-β-H-urs-20 (30)-en-3β-ol-28-oic acid, tetracosyl 3-(3,4-dihydroxyphenyl) acrylate, shikimic acid, 1-octatriacontanol, hexacosyl tetracosanoate, β-sitosterol and β-sitosterol 3-O-β-D-glucopyranoside [17], xanthones like hypericorin-C, hypericorin-D, 3,4-dihydroxy-5-methoxyxanthone, along with 2,3-dimethoxyxanthone, 3,4-dihydroxy-2-methoxyxanthone, 3,5-dihydroxy-1-methoxyxanthone, 3-acetylbetulinic acid, 10-H-1,3-dioxolo [4,5-b]-xanthen-10-one, 3-hydroxy-2-methoxyxanthone, 3,4,5-trihydroxyxanthone and betulinic acid [20]. More recently our research group reported a new antioxidant i.e. folicitin from H. oblongifolium [22].

Keeping in view the potential pain and inflammation relieving properties of the genus Hypericum, the present study has been attempted to explore the Hypericum oblongifolium methanol extract (HOME) for its prospective analgesic, anti-inflammatory and anti-pyretic activities.

Acetic acid induced abdominal constriction assay is a well recommended protocol in evaluating medicinal agents for their peripheral analgesic activity [26, 27]. In this paradigm, pain is induced by the liberating endogenous substances especially the prostaglandins through the action of the constitutive enzyme cyclooxygenase-1 (COX-1) and its isoform COX-2. Induction of this mechanism through COX enzymes and stimulation of these sensory pathways in the mouse peritoneum incites a viscero-somatic reflex and the abdominal constrictions (writhing) [28]. The acetic acid induced writhing method is sensitive to analgesics and sensory afferents in the peritoneum carry α1/2-adrenoceptors, β-adrenoceptors and opioid receptors on their terminals. When activated by appropriate agonists, these receptors depress the generation of pain impulses [29, 30]. Regarding the results of our extract in acetic acid-induced abdominal constriction assay, a prominent inhibition of writhing reflex was observed. These findings strongly recommend that HOME has peripheral analgesic activity and their mechanisms of action might be mediated through inhibition of local peritoneal receptors or inhibition of cyclooxygenase enzymes. The writhing test however is non-specific in nature as it does not exactly indicate the involvement of central or peripheral mechanism. On the other hand, the hot plate method involves spinal reflex and may be considered as a suitable model for the determination of central anti-nociceptive mechanism [31‐33]. Although, in this study, HOME produce significant analgesic effect in the hot plate test only at a dose of 200 mg/kg after 60 min (P < 0.05), however, a non-statistical significant protection against thermal induced nociception was observed at doses of 300 mg/kg (35.9 %) after 30 min, 100 mg/kg (13.9 %) and 300 mg/kg (34.9 %) after 60 min and for all the tested doses after 90 min i.e. 100 mg/kg (47.9 %), 200 mg/kg (71.8 %) and 300 mg/kg (51.6 %) (Fig. 2). In comparison the standard opioid analgesic i.e. tramadol produced significant analgesic effect (P < 0.001) after 30, 60 and 90 min.

Carrageenan-induced paw edema is a well established animal model to assess the anti-inflammatory effect of natural products as well as synthetic chemical compounds. Carrageenan-induced edema in paw is a biphasic event; the initial phase (1 or 1.5 h) is predominately a non-phagocytic edema followed by a second phase (2–5 h) with increased edema formation that remained up to 5 h. The initial phase has been attributed to the release of various mediators including histamine, serotonin and bradykinin while the late phase or second phase edema has been shown to be caused by overproduction of prostaglandins [34‐36]. The result of pre-treatment of HOME demonstrated that the extract is effective in alleviating inflammation during the entire study duration. Significant protection against carragennan induced paw edema was afforded by the 100, 200 and 300 mg/kg doses of HOME after 1 h (10 %, 13.5 %, 21.4 %), 2 h (21 %, 30.8 %, 38.3 %), 3 h (30.6 %, 50.6 %, 66.2 %) and 4 h (28.8 %, 43.6 %, 54.1 %) of treatment. The ability to decrease paw inflammation in mice by all the tested doses of HOME was significantly (P < 0.001) comparable to that of the standard, diclofenac sodium (10 mg/kg) (Fig. 3).

Subcutaneous injection of Brewer’s yeast induces pyrexia by increasing the synthesis of prostaglandins and is considered as a useful test for screening of plants materials as well as synthetic drugs for their antipyretic effect [37, 38]. The inhibition of prostaglandin synthesis among other mediators can be regarded as a possible mechanism of antipyretic action like that of paracetamol which inhibits the synthesis of prostaglandin by blocking the COX enzyme activity [39, 40]. In this study, the intraperitoneal administration of HOME significantly attenuated the hyperpyrexia induced by yeast in mice. All the doses of HOME (100, 200 and 300 mg/kg) were able to reduced the febrile response and the protection is comparable to the standard paracetamol especially after 2 h and remained effective throughout the study duration (4 h).

Studies showed that H. oblongifolium contains xanthones which possess strong in vitro anti-inflammatory [41] and anti-ulcer [20] activities by inhibiting the respiratory burst of neutrophils and urease respectively. Luteolin and myricetin, which are the most abundant flavonoid aglycones along with quercetin, rhamnetin, and kaempferol present in H. oblongifolium [21] are known to have analgesic [42], anti-inflammatory [43] and antipyretic [44] activities. Moreover, strong antioxidants including folicitin [22] and quercetin have been isolated from H. oblongifolium and antioxidants are able to reduce pain, pyrexia and inflammation in both animal models [45‐47] as well as in humans [48, 49]. Furthermore, other Hypericum species including the widely used official medicine, Hypericum perforatum are reported to have strong antidepressant, antinociceptive, antiviral, antimicrobial, antipyretic, anti-inflammatory and healing properties [50].