Ginger Constituent 6-Shogaol Attenuates Vincristine-Induced Activation of Mouse Gastroesophageal Vagal Afferent C-Fibers

An overview of 6-shogaol: new insights into its pharmacological properties and potential therapeutic activities

Ginger (Zingiber officinale Roscoe) has traditionally been used as a cooking spice and herbal medicine for treating nausea and vomiting. More recently, ginger was found to effectively reduce the risk of diseases such as gastroenteritis, migraine, gonarthritis, etc., due to its various bioactive compounds. 6-Shogaol, the pungent phenolic substance in ginger, is the most pharmacologically active among such compounds. The aim of the present study was to review the pharmacological characteristic of 6-shogaol, including the properties of anti-inflammatory, antioxidant and antitumour, and its corresponding molecular mechanism. With its multiple mechanisms, 6-shogaol is considered a beneficial natural compound, and therefore, this review will shed some light on the therapeutic role of 6-shogaol and provide a theoretical basis for the development and clinical application of 6-shogaol.

Inflammation of some visceral sensory systems and autonomic dysfunction in cardiovascular disease

The sensitization and hypertonicity of visceral afferents are highly relevant to the development and progression of cardiovascular and respiratory disease states. In this review, we described the evidence that the inflammatory process regulates visceral afferent sensitivity and tonicity, affecting the control of the cardiovascular and respiratory system. Some inflammatory mediators like nitric oxide, angiotensin II, endothelin-1, and arginine vasopressin may inhibit baroreceptor afferents and contribute to the baroreflex impairment observed in cardiovascular diseases. Cytokines may act directly on peripheral afferent terminals that transmit information to the central nervous system (CNS). TLR-4 receptors, which recognize lipopolysaccharide, were identified in the nodose and petrosal ganglion and have been implicated in disrupting the blood-brain barrier, which can potentiate the inflammatory process. For example, cytokines may cross the blood-brain barrier to access the CNS. Additionally, pro-inflammatory cytokines such as IL-1β, IL-6, TNF-α and some of their receptors have been identified in the nodose ganglion and carotid body. These pro-inflammatory cytokines also sensitize the dorsal root ganglion or are released in the nucleus of the solitary tract. In cardiovascular disease, pro-inflammatory mediators increase in the brain, heart, vessels, and plasma and may act locally or systemically to activate/sensitize afferent nervous terminals. Recent evidence demonstrated that the carotid body chemoreceptor cells might sense systemic pro-inflammatory molecules, supporting the novel proposal that the carotid body is part of the afferent pathway in the central anti-inflammatory reflexes. The exact mechanisms of how pro-inflammatory mediators affects visceral afferent signals and contribute to the pathophysiology of cardiovascular diseases awaits future research.

Involvement of the Spinal Serotonergic System in the Analgesic Effect of [6]-Shogaol in Oxaliplatin-Induced Neuropathic Pain in Mice

Oxaliplatin is a chemotherapy drug that can induce severe acute neuropathy in patients within hours of treatment. In our previous study, 10 mg/kg [6]-shogaol (i.p.) significantly alleviated cold and mechanical allodynia induced by a 6 mg/kg oxaliplatin injection (i.p.); however, the precise serotonin-modulatory effect has not been investigated. In this study, we showed that intrathecal injections of NAN-190 (5-HT1A receptor antagonist, 1 µg) and MDL-72222 (5-HT3 receptor antagonist, 15 µg), but not ketanserin (5-HT2A receptor antagonist, 1 µg), significantly blocked the analgesic effect of [6]-shogaol (10 mg/kg, i.p.). Furthermore, the gene expression of the serotonin-synthesizing enzyme tryptophan hydroxylase 2 (TPH2) and serotonin levels in the spinal cord and serum were significantly downregulated (p < 0.0001 and p = 0.0002) and upregulated (p = 0.0298 and p = 0.0099) after oxaliplatin and [6]-shogaol administration, respectively. Moreover, both the gene and protein expression of the spinal serotonin receptors 5-HT1A and 5-HT3 significantly increased after [6]-shogaol injections (p < 0.0001). Finally, intrathecal injections of both receptor agonists (8-OH-DPAT; 5-HT1A receptor agonist, 10 µg and m-CPBG; 5-HT3 receptor agonist, 15 µg) mimicked the effects of [6]-shogaol in oxaliplatin-injected mice. Taken together, these results demonstrate that [6]-shogaol attenuates oxaliplatin-induced neuropathic pain by modulating the spinal serotoninergic system.

Synthesis of New Shogaol Analogues as NRF2 Activators and Evaluation of Their Anti-Inflammatory Activity, Modes of Action and Metabolic Stability

6-shogaol is a natural and the most potent bioactive vanilloid in dried Zingiber officinale rhizomes. Many scientific studies have reported the diverse biological activities of 6-shogaol. However, the major drawback of 6-shogaol is its instability at room temperature. We synthesised new shogaol thiophene compounds (STCs) by replacing the pentyl group in the sidechain with thiophene derivatives. The STCs were tested for their nuclear factor erythroid 2-related factor 2 (NRF2) activation ability in murine hepatoma cells (Hepa1c1c-7) by determining their NAD(P)H quinone oxidoreductase 1 (NQO1) inducing ability and expression of NRF2-associated antioxidant genes. The anti-inflammatory activity of STCs was determined in Escherichia coli lipopolysaccharide (LPS_Ec)-stimulated NR2-proficient and -silenced mouse microglial cells (BV-2) by measuring the inflammatory markers, cytokines, and mediators. The modes of action (interacting with the Kelch domain of KEAP1, covalent bonding with cysteines of KEAP1, and inhibition of GSK-3β enzyme activity) of NRF2 activation by STCs were determined using commercially available kits. The in vitro metabolic stability of the STCs in liver microsomes (humans, rats, and mice) was also investigated. The molecular docking and molecular dynamics studies were conducted to identify the binding poses, stability, and molecular interactions of the STCs in the binding pockets of Kelch and BTB domains of KEAP1 and GSK-3β enzyme. The new STCs were synthesised in good yields of > 85%, with a purity of about 95%, using a novel synthesis method by employing a reusable proline-proline dipeptide catalyst. The STCs are more potent than 6-shogaol in activating NRF2 and reducing inflammation. The nature of substituents on thiophene has a profound influence on the bioactivity of the STCs. Phenylthiophene STC (STC5) is the most potent, while thiophenes containing electron-withdrawing groups showed weaker bioactivity. The bioactivity of 6-shogaol is in the micromolar range, whereas STC5 showed bioactivity in the sub micromolar range. The STCs showed anti-inflammatory effects via NRF2-dependent and NRF2-independent mechanisms. The STCs improved NRF2 activity through multiple (KEAP1-independent and -dependent) mechanisms. The STCs showed decreased reactivity with thiols than 6-shogaol and thus may possess fewer side-effects than 6-shogaol. The STCs were more metabolically stable than 6-shogaol.