Molecular insight on the binding of stevia glycosides to bovine serum albumin.

The interaction of the steviol and its glycosides (SG), steviolbioside, and rebaudioside A, with bovine serum albumin (BSA) was studied by absorption and fluorescence spectroscopy techniques alongside molecular docking. The stevia derivatives quenched the fluorescence of BSA by a dynamic quenching mechanism, indicating the interaction between the stevia derivatives and BSA. The binding constant (Kb) of steviol was 100-1000-fold higher than those of SG. The stevia derivative/BSA binding reaction was spontaneous and involved the formation of hydrogen bonds and van der Waals interactions between steviol and steviolbioside with BSA, and water reorganization around the rebaudioside A/BSA complex. Molecular docking pointed out the FA1 and FA9 binding sites of BSA as the probable binding sites of steviol and SG, respectively. In conclusion, steviol enhanced hydrophobicity and small size compared to SG may favor its binding to BSA. As steviol and its glycosides share binding sites on BSA with free fatty acids and drugs, they may be competitively displaced from plasma albumin under various physiological states or disease conditions. These findings are clinically relevant and provide an insight into the pharmacokinetics and pharmacodynamics of the stevia glycosides.

Glucocorticoids downregulate systemic nitric oxide synthesis and counteract overexpression of hepatic heme oxygenase-1 during endotoxin tolerance.

Heme oxygenase (HO)-1 has antioxidant and cytoprotective properties if properly expressed, whereas nitric oxide (NO) impairs tissue perfusion when greatly increased in the blood circulation. Here we hypothesized that the NO and HO-1 systems are altered during lipopolysaccharide (LPS) tolerance, and that glucocorticoids are crucial modulators of systemic NO production and hepatic HO-1 expression during this intriguing phenomenon of cellular reprogramming. Adrenalectomized (ADX) rats with or without administration of dexamethasone (DEX) were challenged with LPS for 3 consecutive days. The plasma levels of corticosterone and nitrate (NOx), and expression of HO-1 protein were assessed. During tolerance, corticosterone levels were elevated, NOx reduced, and HO-1 overexpressed. ADX rats challenged with LPS for 3 consecutive days exhibited a ~9-fold increase in NOx and a ~6-fold increase in HO-1, reverted by DEX. Our findings strongly support the fact that glucocorticoids downregulate systemic NO synthesis and counteract hepatic HO-1 overexpression during LPS tolerance.

Long-term antidepressant treatment inhibits neuropathic pain-induced CREB and PLCγ-1 phosphorylation in the mouse spinal cord dorsal horn.

UNLABELLED: The effect of long-term administration of imipramine, a tricyclic antidepressant, on the phosphorylation status of cyclic adenosine monophosphate-responsive element-binding protein (CREB), mitogen-activated protein kinase family members, and phospholipase γ-1 (PLCγ-1) was investigated in the dorsal horn of the spinal cord following peripheral nerve lesion. Nerve injury induced an ipsilateral long-lasting increased phosphorylation of CREB and PLCγ-1 but not extracellular signal-regulated kinase (ERK1,2), p38, and c-Jun N-terminal kinase. Daily administration of imipramine (5, 10, or 30 mg/kg) for 21 days progressively reduced both tactile-induced neuropathic pain hypersensitivity and thermal hyperalgesia. After withdrawal of treatment, the antinociceptive effect of imipramine was gradually abolished but still remained for at least 3 weeks. Conversely, no analgesic effect was observed with short-term imipramine treatment. Moreover, imipramine therapy reversed nerve injury-induced CREB and PLCγ-1 phosphorylation but had no effect on ERK1,2, p38, and c-Jun N-terminal kinase activity. These results indicate that long-term administration of imipramine may prevent some of the harmful changes in the spinal cord dorsal horn following nerve injury. However, imipramine analgesic effect takes time to develop and mature, which might explain in part why the clinical analgesic effect of tricyclic antidepressants develops with a delay after the beginning of treatment. Our data also provide evidence that prolonged imipramine treatment may induce antinociception in neuropathic pain conditions because of its action on the PLCγ-1/CREB-signaling pathway. PERSPECTIVE: This article demonstrates that long-term treatment with imipramine reverses some of the marked effects induced by peripheral nerve injury in the spinal dorsal horn that contribute to long-term maintenance of sensory disorder, providing a new view to the mechanisms of action of these drugs.

Differential expression of microRNAs in mouse pain models.

BACKGROUND: MicroRNAs (miRNAs) are short non-coding RNAs that inhibit translation of target genes by binding to their mRNAs. The expression of numerous brain-specific miRNAs with a high degree of temporal and spatial specificity suggests that miRNAs play an important role in gene regulation in health and disease. Here we investigate the time course gene expression profile of miR-1, -16, and -206 in mouse dorsal root ganglion (DRG), and spinal cord dorsal horn under inflammatory and neuropathic pain conditions as well as following acute noxious stimulation. RESULTS: Quantitative real-time polymerase chain reaction analyses showed that the mature form of miR-1, -16 and -206, is expressed in DRG and the dorsal horn of the spinal cord. Moreover, CFA-induced inflammation significantly reduced miRs-1 and -16 expression in DRG whereas miR-206 was downregulated in a time dependent manner. Conversely, in the spinal dorsal horn all three miRNAs monitored were upregulated. After sciatic nerve partial ligation, miR-1 and -206 were downregulated in DRG with no change in the spinal dorsal horn. On the other hand, axotomy increases the relative expression of miR-1, -16, and 206 in a time-dependent fashion while in the dorsal horn there was a significant downregulation of miR-1. Acute noxious stimulation with capsaicin also increased the expression of miR-1 and -16 in DRG cells but, on the other hand, in the spinal dorsal horn only a high dose of capsaicin was able to downregulate miR-206 expression. CONCLUSIONS: Our results indicate that miRNAs may participate in the regulatory mechanisms of genes associated with the pathophysiology of chronic pain as well as the nociceptive processing following acute noxious stimulation. We found substantial evidence that miRNAs are differentially regulated in DRG and the dorsal horn of the spinal cord under different pain states. Therefore, miRNA expression in the nociceptive system shows not only temporal and spatial specificity but is also stimulus-dependent.

Propyretic role of the locus coeruleus nitric oxide pathway.

Nitric oxide has been reported to modulate fever in the brain. However, the sites where NO exerts this modulation remain somewhat unclear. Locus coeruleus (LC) neurons express not only nitric oxide synthase (NOS) but also soluble guanylyl cyclase (sGC). In the present study, we evaluated in vivo and ex vivo the putative role of the LC NO-cGMP pathway in fever. To this end, deep body temperature was measured before and after pharmacological modulations of the pathway. Moreover, nitrite/nitrate (NOx) and cGMP levels in the LC were assessed. Conscious rats were microinjected within the LC with a non-selective NOS inhibitor (N(G)-monomethyl-l-arginine acetate), a NO donor (NOC12), a sGC inhibitor (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) or a cGMP analogue (8-bromo-cGMP) and injected intraperitoneally with endotoxin. Inhibition of NOS or sGC before endotoxin injection significantly increased the latency to the onset of fever. During the course of fever, inhibition of NOS or sGC attenuated the febrile response, whereas microinjection of NOC12 or 8-bromo-cGMP increased the response. These findings indicate that the LC NO-cGMP pathway plays a propyretic role. Furthermore, we observed a significant increase in NOx and cGMP levels, indicating that the febrile response to endotoxin is accompanied by stimulation of the NO-cGMP pathway in the LC.