Inhibition of transient receptor potential vanilloid type 1 through α2 adrenergic receptors at peripheral nerve terminals relieves pain.

The activation of α2 adrenergic receptors contributes to analgesia not only in the central nervous system but also in the peripheral nervous system. We reported that noradrenaline inhibits the activity of transient receptor potential vanilloid 1 (TRPV1) evoked by capsaicin through α2 receptors in cultured rat dorsal root ganglion (DRG) neurons. However, it is unclear whether activation of TRPV1 expressed in peripheral nerve terminals is inhibited by α2 receptors and whether this phenomenon contributes to analgesia. Therefore, we examined effects of clonidine, an α2 receptor agonist, on several types of nociceptive behaviors, which may be caused by TRPV1 activity, and subtypes of α2 receptors expressed with TRPV1 in primary sensory neurons in rats. Capsaicin injected into hind paws evoked nociceptive behaviors and clonidine preinjected into the same site inhibited capsaicin-evoked responses. This inhibition was not observed when clonidine was injected into the contralateral hind paws. Preinjection of clonidine into the plantar surface of ipsilateral, but not contralateral, hind paws reduced the sensitivity to heat stimuli. Clonidine partially reduced formalin-evoked responses when it was preinjected into ipsilateral hind paws. The expression level of α2C receptor mRNA quantified by real-time PCR was highest followed by those of α2A and α2B receptors in DRGs. α2A and α2C receptor-like immunoreactivities were detected with TRPV1-like immunoreactivities in the same neurons. These results suggest that TRPV1 and α2 receptors are coexpressed in peripheral nerve terminals and that the functional association between these two molecules causes analgesia.

Adrenergic receptors inhibit TRPV1 activity in the dorsal root ganglion neurons of rats.

Transient receptor potential vanilloid type 1 (TRPV1) is a polymodal receptor channel that responds to multiple types of stimuli, such as heat, acid, mechanical pressure and some vanilloids. Capsaicin is the most commonly used vanilloid to stimulate TRPV1. TRPV1 channels are expressed in dorsal root ganglion neurons that extend to Aδ- and C-fibers and have a role in the transduction of noxious inputs to the skin into the electrical signals of the sensory nerve. Although noradrenergic nervous systems, including the descending antinociceptive system and the sympathetic nervous system, are known to modulate pain sensation, the functional association between TRPV1 and noradrenaline in primary sensory neurons has rarely been examined. In the present study, we examined the effects of noradrenaline on capsaicin-evoked currents in cultured dorsal root ganglion neurons of the rat by the whole-cell voltage clamp method. Noradrenaline at concentrations higher than 0.1 pM significantly reduced the amplitudes of the inward capsaicin currents recorded at -60 mV holding potential. This inhibitory action was reversed by either yohimbine (an α2 antagonist, 10 nM) or propranolol (a ß antagonist, 10 nM). The α2 agonists, clonidine (1 pM) and dexmedetomidine (1 pM) inhibited capsaicin currents, and yohimbine (1 nM) reversed the effects of clonidine. The inhibitory action of noradrenaline was not seen in the neurons pretreated with pertussis toxin (100 µg/ml for 24 h) and the neurons dialyzed intracellularly with guanosine 5'- [ß-thio] diphosphate (GDPßS, 200 µM), the catalytic subunit of protein kinase A (250 U/ml) or okadaic acid (1 µM). These results suggest that noradrenaline directly acts on dorsal root ganglion neurons to inhibit the activity of TRPV1 depending on the activation of α2-adrenoceptors followed by the inhibition of the adenylate cyclase/cAMP/protein kinase A pathway.

Adenosine thiamine triphosphate (AThTP) inhibits poly(ADP-ribose) polymerase-1 (PARP-1) activity.

Overactivation of poly(ADP-ribose) polymerase-1 (PARP-1) has been demonstrated to result in various stress-related diseases, including diabetes mellitus. Deficiency of cellular nicotinamide adenine dinucleotide (NAD(+)) content, consumed by PARP-1 to add ADP-ribose moieties onto target proteins, contributes to pathophysiological conditions. Adenosine thiamine triphosphate (AThTP) exists in small amounts in mammals; however, the function(s) of this metabolite remains unresolved. The structure of AThTP resembles NAD(+). Recent experimental studies demonstrate beneficial impacts of high-dose thiamine treatment of diabetic complications. These findings have led us to hypothesize that AThTP may modulate the activity of PARP-1. We have chemically synthesized AThTP and evaluated the effect of AThTP on recombinant PARP-1 enzyme activity. AThTP inhibited the PARP-1 activity at 10 µM, and a structural model of the PARP-1-AThTP complex highlighted the AThTP binding site. The results provide new insights into the pharmacological importance of AThTP as an inhibitor of PARP-1.

Thiamine prevents obesity and obesity-associated metabolic disorders in OLETF rats.

We previously found that thiamine mitigates metabolic disorders in spontaneously hypertensive rats, harboring defects in glucose and fatty acid metabolism. Mutation of thiamine transporter gene SLC19A2 is linked to type 2 diabetes mellitus. The current study extends our hypothesis that thiamine intervention may impact metabolic abnormalities in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, exhibiting obesity and metabolic disorders similar to human metabolic syndrome. Male OLETF rats (4 wk old) were given free access to water containing either 0.2% or 0% of thiamine for 21 and 51 wk. At the end of treatment, blood parameters and cardiac functions were analyzed. After sacrifice, organs weights, histological findings, and hepatic pyruvate dehydrogenase (PDH) activity in the liver were evaluated. Thiamine intervention averted obesity and prevented metabolic disorders in OLETF rats which accompanied mitigation of reduced lipid oxidation and increased hepatic PDH activity. Histological evaluation revealed that thiamine alleviated adipocyte hypertrophy, steatosis in the liver, heart, and skeletal muscle, sinusoidal fibrosis with formation of basement membranes (called pseudocapillarization) which accompanied significantly reduced expression of laminin ß1 and nidogen-1 mRNA, interstitial fibrosis in the heart and kidney, fatty degeneration in the pancreas, thickening of the basement membrane of the vasculature, and glomerulopathy and mononuclear cell infiltration in the kidney. Cardiac and renal functions were preserved in thiamine treatment. Thiamine has a potential to prevent obesity and metabolic disorders in OLETF rats.

[Stapes surgery performed for congenital stapes foot plate fixation--comparison of prosthesis fixation to the malleus vs. the incus].

We report the surgical results of stapes surgery using the Schukneht-type wire piston prosthesis performed on 30 ears with fixation of the stapes footplate and absence of the long process of the incus. The prosthesis was reformed to avoid dislocation and fixed to the handle of the malleus. The surgical results in another 49 ears, the comparator group, in which the prosthesis was fixed to the long process of the incus because the anomaly was restricted to fixation of the footplate without other associated anomalies, were also analyzed for comparison. The mean postoperative air conduction hearing levels were 28.6dB in the subjects and 21.6dB in the comparator group, and the mean hearing improvements were 35.7dB and 29.7dB, respectively. The success rate of the operation, based on the criteria established by the Japan Otological Society, was 90% in the subjects and 98% in the comparator group. The mean postoperative air-bone gap in the subjects was 15.8dB, which was 4.3dB higher than that in the comparator group. The difference between the two groups was considered to be due to the difference in the effectiveness of the conduction mechanism after the surgery. We therefore concluded that the surgical procedure using the Schukneht-type wire piston prosthesis to fix the malleus handle is a useful surgical method that yields satisfactory results.