Pharmacological characterization of morphine-6-sulfate and codeine-6-sulfate

Morphine-6-sulfate (M6S) and codeine-6-sulfate (C6S) are mu-selective opiates which have been isolated from brain. M6S is an effective analgesic, with a 30-fold greater potency than morphine in the mouse radiant heat tailflick assay and similar to the active morphine metabolite morphine-6beta-glucuronide (M6G). M6S analgesia is reversed by 3-methoxynaltrexone at low antagonist doses which are inactive against morphine, suggesting that M6S may be acting through the same mechanisms as M6G. Consistent with this possibility, antisense mapping of the MOR-1 clone revealed that M6S analgesia was lowered by probes targeting exon 2 and not by targeting exon 1, a sensitivity profile similar to that of M6G and not morphine. C6S also has analgesic activity at doses approximately 10-fold greater than M6S. However, its characterization was impeded by the appearance of seizures at doses below full analgesic activity. Thus, M6S is a potent analgesic with pharmacological properties similar to M6G. C6S has limited utility due to its high level of toxicity.     

Spinal interleukin-6 (IL-6) inhibits nociceptive transmission following neuropathy

Interleukin-6 (IL-6) is a neuropoietic cytokine which is dramatically upregulated following peripheral nerve injury at the site of injury, in the dorsal root ganglion (DRG) and in the spinal cord. The functional effects of IL-6 in nociception in normal conditions and following nerve injury are unclear. Thus the aim of this study was to assess the effect of spinal IL-6 administration on nociceptive transmission in naive, sham-operated and neuropathic (spinal nerve ligation, SNL) rats using in vivo electrophysiology to elucidate the possible role of IL-6 in neuropathic pain. In anaesthetised rats, extracellular recordings were made from individual convergent dorsal horn neurones following electrical and natural (mechanical and thermal) stimulation of peripheral receptive fields. Exogenous spinal IL-6 (100-500 ng) had no significant effect on electrically evoked neuronal responses in naive rats. In contrast, following neuropathy, spinal IL-6 produced a dose-related inhibition of the electrically evoked C-fibre, initial C-fibre and measures of neuronal hyperexcitability (post discharge and wind-up). In addition, spinal IL-6 markedly inhibited mechanical neuronal responses in neuropathic rats. Higher doses of spinal IL-6 also inhibited, to a lesser degree, the initial C-fibre, post discharge and wind-up responses in sham-operated rats. These studies show that following nerve injury the actions of the cytokine alter so that spinal administration of IL-6 elicits anti-nociceptive effects not observed under normal conditions. Moreover, the inhibitory effects of IL-6 on C-fibre activity and neuronal hyperexcitability, suggest IL-6 to be a potential modulator of neuropathic pain.     

Infantile spinocerebellar ataxia type 6: relationship to episodic ataxia type 6

Spinocerebellar ataxia type 6 is one of the hereditary progressive cerebellar ataxias first described in 1997. Genetic studies have identified the defect as abnormal expansion of CAG trinucleotide repeat in 1 alpha subunit of the calcium channel gene located on chromosome 19p13. The symptomatic individuals have 20 or 23 repeats in contrast to normal individuals who manifest 19 or less CAG repeats. Most of the earlier reports indicate the age of onset of symptoms to be after the third decade. This report presents a patient with episodic symptoms soon after birth, which is unusual, and to our knowledge this is the youngest reported case. The clinical features of spinocerebellar ataxia type 6 are variable. The mode of inheritance and the common symptoms of this condition are also discussed.     

One-Electron Reduction of 6-Hydroxydopamine Quinone is Essential in 6-Hydroxydopamine Neurotoxicity

6-Hydroxydamine has widely been used as neurotoxin in preclinical studies related on the neurodegenerative process of dopaminergic neurons in Parkinson’s disease based on its ability to be neurotoxic as a consequence of free radical formation during its auto-oxidation to topaminequinone. We report that 50-µM 6-hydroxydopamine is not neurotoxic in RCSN-3 cells derived from substantia nigra incubated during 24 h contrasting with a significant sixfold increase in cell death (16 ± 2 %; P < 0.001) was observed in RCSN-3NQ7 cells expressing a siRNA against DT-diaphorase that silence the enzyme expression. To observe a significant cell death in RCSN-3 cells induced by 6-hydroxydopamine (24 ± 1 %; P < 0.01), we have to increase the concentration to 250 μm while a 45 ± 2 % cell death (P < 0.001) was observed at this concentration in RCSN-3NQ7 cells. The cell death induced by 6-hydroxydopamine in RCSN-3NQ7 cells was accompanied with a (i) significant increase in oxygen consumption (P < 0.01), (ii) depletion of reduced glutathione and (iii) a significant decrease in ATP level (P < 0.05) in comparison with RCSN-3 cells. In conclusion, our results suggest that one-electron reduction of 6-hydroxydopamine quinone seems to be the main reaction responsible for 6-hydroxydopamine neurotoxic effects in dopaminergic neurons and DT-diaphorase seems to play an important neuroprotective role by preventing one-electron reduction of topaminequinone.     

Interleukin-6 (IL-6) receptor/IL-6 fusion protein (Hyper IL-6) effects on the neonatal mouse brain: Possible role for IL-6 trans-signaling in brain development and functional neurobehavioral outcomes

Adverse neurodevelopmental outcomes are linked to perinatal production of inflammatory mediators, including interleukin 6 (IL-6). While a pivotal role for maternal elevation in IL-6 has been established in determining neurobehavioral outcomes in the offspring and considered the primary target mediating the fetal inflammatory response, questions remain as to the specific actions of IL-6 on the developing brain. CD-1 male mice received a subdural injection of the bioactive fusion protein, hyper IL-6 (HIL-6) on postnatal-day (PND)4 and assessed from preweaning until adulthood. Immunohistochemical evaluation of astrocytes and microglia and mRNA levels for pro-inflammatory cytokines and host response genes indicated no evidence of an acute neuroinflammatory injury response. HIL-6 accelerated motor development and increased reactivity to stimulation and number of entries in a light/dark chamber, decreased ability to learn to withhold a response in passive avoidance, and effected deficits in social novelty behavior. No changes were observed in motor activity, pre-pulse startle inhibition, or learning and memory in the Morris water maze or radial arm maze, as have been reported for models of more severe developmental neuroinflammation. In young animals, mRNA levels for MBP and PLP/DM20 decreased and less complexity of MBP processes in the cortex was evident by immunohistochemistry. The non-hydroxy cerebroside fraction of cerebral lipids was increased. These results provide evidence for selective effects of IL-6 signaling, particularly trans-signaling, in the developing brain in the absence of a general neuroinflammatory response. These data contribute to our further understanding of the multiple aspects of IL-6 signaling in the developing brain.     

Caspase-6 and neurodegeneration

Caspases are cysteine-aspartic proteases that post-translationally modify their substrates through cleavage at specific sites, which causes either substrate inactivation or a gain of function through the generation of active fragments. Currently, each caspase is categorized as either an initiator of apoptosis or an end-stage executioner. Caspase-6 was originally identified as an executioner caspase owing to its role in cleavage of nuclear lamins. However, it has since been shown that caspase-6 cleaves caspases-2, 3 and 8. Furthermore, active caspase-6 is present in post mortem brains of Huntington and Alzheimer disease subjects that do not yet display apoptotic morphology, which suggests a function distinct from its well-validated executioner role. In this review, we discuss evidence to date regarding the role of caspase-6 in neurodegeneration. The findings suggest that selective inhibitors of caspase-6 may have therapeutic potential for various neurodegenerative disorders.