Peripheral endomorphins drive mechanical alloknesis under the enzymatic control of CD26/DPPIV

BACKGROUND

Mechanical alloknesis (or innocuous mechanical stimuli-evoked itch) often occurs in dry skin-based disorders such as atopic dermatitis and psoriasis. However, the molecular and cellular mechanisms underlying mechanical alloknesis remain unclear. We recently reported the involvement of CD26 in the regulation of psoriatic itch. This molecule exhibits dipeptidyl peptidase IV (DPPIV) enzyme activity and exerts its biologic effects by processing various substances, including neuropeptides.

OBJECTIVE

The aim of the present study was to investigate the peripheral mechanisms of mechanical alloknesis by using CD26/DPPIV knockout (CD26KO) mice.

METHODS

We applied innocuous mechanical stimuli to CD26KO or wild-type mice. The total number of scratching responses was counted as the alloknesis score. Immunohistochemical and behavioral pharmacologic analyses were then performed to examine the physiologic activities of CD26/DPPIV or endomorphins (EMs), endogenous agonists of μ-opioid receptors.

RESULTS

Mechanical alloknesis was more frequent in CD26KO mice than in wild-type mice. The alloknesis score in CD26KO mice was significantly reduced by the intradermal administration of recombinant DPPIV or naloxone methiodide, a peripheral μ-opioid receptor antagonist, but not by that of mutant DPPIV without enzyme activity. EMs (EM-1 and EM-2), selective ligands for μ-opioid receptors, are substrates for DPPIV. Immunohistochemically, EMs were located in keratinocytes, fibroblasts, and peripheral sensory nerves. Behavioral analyses revealed that EMs preferentially provoked mechanical alloknesis over chemical itch. DPPIV-digested forms of EMs did not induce mechanical alloknesis.

CONCLUSION

The present results suggest that EMs induce mechanical alloknesis at the periphery under the enzymatic control of CD26/DPPIV.

Inhibition of endothelin A receptor by a novel, selective receptor antagonist enhances morphine-induced analgesia: Possible functional interaction of dimerized endothelin A and μ-opioid receptors

BACKGROUND

The misuse of opioids has led to an epidemic in recent times. The endothelin A receptor (ETAR) has recently attracted attention as a novel therapeutic target to enhance opioid analgesia. We hypothesized that endothelin A receptors may affect pain mechanisms by heterodimerization with μ opioid receptors. We examined the mechanisms of ETAR-mediated pain and the potential therapeutic effects of an ETAR antagonist, Compound-E, as an agent for analgesia.

METHODS

Real-time in vitro effect of Compound-E on morphine response was assessed in HEK293 cells expressing both endothelin A and μ opioid receptors through CellKey™ and cADDis cAMP assays. Endothelin A/μ opioid receptor dimerization was assessed by immunoprecipitation and live cell imaging. The in vivo effect of Compound-E was evaluated using a morphine analgesia mouse model that observed escape response behavior, body temperature, and locomotor activity.

RESULTS

In CellKey™ and cAMP assays, pretreatment of cells with endothelin-1 attenuated morphine-induced responses. These responses were improved by Compound-E, but not by BQ-123 nor by bosentan, an ETAR and endothelin B receptor antagonist. Dimerization of ETARs and μ opioid receptors was confirmed by Western blot and total internal reflection fluorescence microscopy in live cells. In vivo, Compound-E potentiated and prolonged the analgesic effects of morphine, enhanced hypothermia, and increased locomotor activity compared to morphine alone.

CONCLUSION

The results suggest that attenuation by endothelin-1 of morphine analgesia may be caused by dimerization of Endothelin A/μ opioid receptors. The novel ETAR antagonist Compound-E could be an effective adjunct to reduce opioid use.

G Protein-Coupled Glutamate and GABA Receptors Form Complexes and Mutually Modulate Their Signals

Molecular networks containing various proteins mediate many types of cellular processes. Elucidation of how the proteins interact will improve our understanding of the molecular integration and physiological and pharmacological propensities of the network. One of the most complicated and unexplained interactions between proteins is the inter-G protein-coupled receptor (GPCR) interaction. Recently, many studies have suggested that an interaction between neurotransmitter GPCRs may mediate diverse modalities of neural responses. The B-type gamma-aminobutyric acid (GABA) receptor (GBR) and type-1 metabotropic glutamate receptor (mGluR1) are GPCRs for GABA and glutamate, respectively, and each plays distinct roles in controlling neurotransmission. We have previously reported the possibility of their functional interaction in central neurons. Here, we examined the interaction of these GPCRs using stable cell lines and rat cerebella. Cell-surface imaging and coimmunoprecipitation analysis revealed that these GPCRs interact on the cell surface. Furthermore, fluorometry revealed that these GPCRs mutually modulate signal transduction. These findings provide solid evidence that mGluR1 and GBR have intrinsic abilities to form complexes and to mutually modulate signaling. These findings indicate that synaptic plasticity relies on a network of proteins far more complex than previously assumed.

Synthesis and antileukemic activity of chymotrypsin-activated derivatives of 3'-amino-2',3'-dideoxycytidine. (Synthetic nucleosides and nucleotides. XXXIII

3'-Amino-2',3'-dideoxycytidine (8) was directly synthesized from 2'-deoxycytidine. 2',3'-Dideoxy-3'-(N-acyl-L-phenylalanylamino)cytidines (acyl = butoxycarbonyl (9a), acetyl (9b), benzoyl (9c), and n-hexanoyl (9d)) were synthesized as chymotrypsin-activated prodrugs of 8. This N-protection was required for activation by chymotrypsin to 8. In vitro, compound 8 showed high cytotoxic activity against P388 cells, but the prodrugs 9a-d were ineffective. In vivo, however, these prodrugs showed much higher activity than 8 in mice bearing P388 cells.