Polymethoxyflavones from Nicotiana plumbaginifolia (Solanaceae) Exert Antinociceptive and Neuropharmacological Effects in Mice

Abstract

Polymethoxylavones (PMFs) are known to exhibit significant anti-inflammatory and neuroprotective properties. Nicotiana plumbaginifolia, an annual Bangladeshi herb, is rich in polymethoxyflavones that possess significant analgesic and anxiolytic activities. The present study aimed to determine the antinociceptive and neuropharmacological activities of polyoxygenated flavonoids namely- 3,3',5,6,7,8-hexamethoxy-4',5'-methylenedioxyflavone (1), 3,3',4',5',5,6,7,8-octamethoxyflavone (exoticin) (2), 6,7,4',5'-dimethylenedioxy-3,5,3'-trimethoxyflavone (3), and 3,3',4',5,5',8-hexamethoxy-6,7-methylenedioxyflavone (4), isolated and identified from N. plumbaginifolia. Antinociceptive activity was assessed using the acetic-acid induced writhing, hot plate, tail immersion, formalin and carrageenan-induced paw edema tests, whereas neuropharmacological effects were evaluated in the hole cross, open field and elevated plus maze test. Oral treatment of compounds 1, 3, and 4 (12.5-25 mg/kg b.w.) exhibited dose-dependent and significant (p < 0.01) antinociceptive activity in the acetic-acid, formalin, carrageenan, and thermal (hot plate)-induced pain models. The association of ATP-sensitive K⁺ channel and opioid systems in their antinociceptive effect was obvious from the antagonist effect of glibenclamide and naloxone, respectively. These findings suggested central and peripheral antinociceptive activities of the compounds. Compound 1, 3, and 4 (12.5 mg/kg b.w.) demonstrated significant (p < 0.05) anxiolytic-like activity in the elevated plus-maze test, while the involvement of GABA_A receptor in the action of compound 3 and 4 was evident from the reversal effects of flumazenil. In addition, compounds 1 and 4 (12.5-25 mg/kg b.w) exhibited anxiolytic activity without altering the locomotor responses. The present study suggested that the polymethoxyflavones (1-4) from N. Plumbaginifolia could be considered as suitable candidates for the development of analgesic and anxiolytic agents.

Keywords: Nicotiana plumbaginifolia; antinociceptive; anxiolytic; benzodiazepine; opioid; polymethoxyflavone.

Figure 1

Polymethoxyflavones (PMFs) of N. plumbaginifolia. 1 = 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone; 2 = 3,3′,4′,5′,5,6,7,8-octamethoxyflavone (exoticin); 3 = 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone; 4 = 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone.

Figure 2

Effect of polymethoxyflavones (PMFs) of N. plumbaginifolia in acetic acid-induced writhing test. The panel shows effect on writhing onset (A), total number of writhing (B). Values are presented as median (n = 6) with range (min-max). 1 = 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone; 2 = exoticin; 3 = 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone; 4 = 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone, Gbc = glibenclamide. *p < 0.01 compared to control group; ^a,b,c,d,ep < 0.01 compared to 1 (25 mg/kg), 2 (25 mg/kg), 3 (25 mg/kg), and 4 (25 mg/kg), respectively.

Figure 3

Effect of compounds 1–4, morphine and pre-treatment of naloxone in hot plate test. (A) Maximal percent of analgesic effect (% MPE) of compounds 1–4, morphine and antagonist effect of naloxone. (B) Area under the curve (AUC _{0–120 min}) response of the compounds 1–4, morphine and pre-treatment of naloxone. Values are presented as median (n = 6) with range (min-max). 1 = 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone; 2 = exoticin; 3 = 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone; 4 = 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone, NLX = naloxone. ^*, ^**p < 0.05 and p < 0.01, compared to control group, respectively. ^a,b,c,d,ep < 0.05, compared to morphine (5 mg/kg), 1 (25 mg/kg), 2 (25 mg/kg), 3 (25 mg/kg), and 4 (25 mg/kg), respectively.

Figure 4

Effect of compounds 1–4, morphine and pre-treatment of naloxone in tail immersion test. (A) maximal percent of analgesic effect (% MPE) of compounds 1–4, morphine and antagonist effect of naloxone. (B) area under the curve (AUC _{0−120 min}) response of the compounds 1–4, morphine and pre-treatment of naloxone. Values are presented as median (n = 6) with range (min-max). 1 = 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone; 2 = exoticin; 3 = 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone; 4 = 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone, NLX = naloxone. ^*p < 0.01, compared to control group. ^a,bp < 0.01, compared to morphine (5 mg/kg) and 3 (25 mg/kg) respectively.

Figure 5

Ambulatory effect of compounds 1–4 and diazepam in open field test. (A–C) Represents effect of PMFs 1–4 and diazepam treatment on total number of central squares entries, percent of central squares entries and total number of squares crossed in open field, respectively. Values are presented as median (n = 6) with range (min-max). 1 = 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone; 2 = exoticin; 3 = 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone; 4 = 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone. ^*p < 0.05, compared to control group.

Figure 6

Effect of compounds 1–4, diazepam and pre-treatment of flumazenil in elevated plus maze test. The illustrations represent effect of PMFs 1–4 and diazepam treatment on (A) total number of open arms entries, (B) percent of central squares entries, (C) percent of open arm time, and (D) total number arm entries in elevated plus maze. Values are presented as median (n = 6) with range (min-max). 1 = 3,3′,5,6,7,8-hexamethoxy-4′,5′-methylenedioxyflavone; 2 = exoticin; 3 = 6,7,4′,5′-dimethylenedioxy-3,5,3′-trimethoxyflavone; 4 = 3,3′,4′,5,5′,8-hexamethoxy-6,7-methylenedioxyflavone, Flu, flumazenil. ^*p < 0.05, compared to control group. ^a,b,c,d,ep < 0.05, compared to diazepam (1 mg/kg), 3 (12.5 mg/kg), 3 (25 mg/kg), 4 (12.5 mg/kg), and 4 (25 mg/kg) respectively.