Borneol inhibits TRPA1, a proinflammatory and noxious pain-sensing cation channel

Borneol, a natural product isolated from several species of Artemisia, Blumea and Kaempferia, has a widespread use in traditional medicine. TRP ion channels are a class of nonselective cation channel proteins involved in a variety of physiological and pathological processes in mammals. TRPA1, a member of TRP family of cation channels, is involved in plethora of processes including noxious-cold, noxious-pain sensations, inflammation and the detection of irritant chemicals. Borneol is chemically related to camphor [a known inhibitor of TRPA1 ion channels]; therefore, it is beneficial to investigate the effects of borneol on TRPA1. In the present investigation it was found that borneol inhibits TRPA1 mediated cationic currents in low millimolar range [IC[so] 0.3mM] in heterologous expression systems like Xenopus oocytes and in neurons cultured from trigeminal ganglia. Effects of nicotine, a known chemical irritant and agonist of TRPA1 are also inhibited by borneol in both systems. It is concluded that borneol, being an inhibitor of TRPA1, could be a safer therapeutic-combination in clinical situations where TRPA1 channelopathies like neuropathic-pain, trigeminal neuralgia or nicotine withdrawal treatments are involved

Camphor modulates TRPV3 cation channels activity by interacting with critical pore-region cysteine residues

TRPV3 ion channels mediate thermo-transduction, nociception, inflammation and dermatitis in mammals. TRPV1-4 proteins have been shown to have conserved cysteine-residues in the pore-forming regions. These residues participate in channel activation via S-nitrosylation of channel proteins. Camphor is a commonly used ligand for TRPV3 channels. Thus the knowledge about the potential binding/interacting site[s] for camphor will help to design effective and potent analgesic compounds. In an overlap-extension PCR method, following primer-pairs were used to mutate conserved cysteine-residues in the pore-region of TRPV3 channels; GATTGAGAATcCTCCAAGGACAAAAAGGAC, TRPV3-C612S-Fw and GTCCTTGGAGgACTTCTCAATCAGTCAGTGAGG, TRPV3-C612S-Rv primers pair. And for TRPV3-C619S: GGACTCcAGTTCCTATGGCCAGC, TRPV3-C619S-Fw and GCTGGCCATAgGAACTGGAGTCC, TRPV3-C619S-Rv respectively. All cDNA constructs were confirmed by DNA-sequencing and used to make cRNAs. Oocytes expressing mTRPV3-C619S and mTRPV3-C612S mutant channels were challenged with 2-APB [1 mM], camphor [10 mM] and dihydrocarveol [10 mM] either at -40 mV or +40 mV holding potentials in voltage-clamp experiments. Responses of both mutants to 2-APB were similar to wild-type mTRPV3. Interestingly, responses to camphor were totally lost in mTRPV3-C619S mutant, while responses to dihydrocarveol remained intact. In contrast mTRPV3-C612S displayed slightly altered [16 +/- 2% reduction] phenotype with respect to camphor sensitivity. It is concluded that pore-region cysteines play critical role in camphor sensitivity of TRPV3 ion channels

Inhibition of tryptophan-pyrrolase activity and elevation of brain tryptophan concentration by fluoxetine in rats

To investigate in-vitro as well as in-vivo effects of various doses of fluoxetine [SSRI] on tryptophan metabolism in rats. Design: A pre-clinical study. Place and Duration of Study: Clinical Biochemistry Research Laboratory, Department of Biochemistry, University of Karachi. The investigation was carried out during 2000 to 2001. Subjects and Male Wistar rats [150-200 g body wt] were selected and divided into control and test groups [n = 5] for comparison. In in-vitro [10 - 1000mM] as well in-vivo [0.5 ' 30 mg/kg body wt.] studies, fluoxetine showed a statistically significant inhibition of rat liver tryptophan pyrrolase [tryptophan-2,3-dioxygenase; EC 1.13.11.11] activity. Significant increases were noted at 10 and 30 mg/kg doses in brain, serum [total and free] and liver L-tryptophan concentrations. Similarly, serum non-estrified free fatty acids showed a significant increase at both doses. There was no effect on serum glucose and albumin concentrations. It is suggested that major mechanism of action of fluoxetine is that of elevating brain tryptophan concentration and hence 5-HT synthesis by increasing the availability of circulating tryptophan to the brain secondarily to inhibition of major tryptophan degrading enzyme, hepatic tryptophan pyrrolase. It is assumed that fluoxetine inhibits the binding of apoenzyme form of tryptophan pyrrolase with its cofactor haem. The results are discussed in relation to possible involvement of disturbed hepatic tryptophan metabolism in depressive illness