Endogenous Sex Hormones Modulate the Analgesic Effect of Tramadol in Lean and High-Fat Diet-Induced Obese Wistar Rats: A Preclinical Molecular Approach.

INTRODUCTION: Differences in pain thresholds may have implications in pain management, as they may account in part for the variability in analgesic requirements between individuals. We planned to investigate the influence of endogenous sex hormones on the analgesic modulation of tramadol in lean and high-fat diet-induced obese Wistar rats. METHODS: The whole study was carried out on 48 adult Wistar rats (24 male: 12 obese and 12 lean and 24 female: 12 obese and 12 lean). Each male and female rat group was further subdivided into two groups (n = 6/group) and treated with normal saline/tramadol for 5 days. On the fifth day, 15 min after tramadol/normal saline treatment, animals were tested for pain perception toward noxious stimuli. Later, endogenous 17 beta-estradiol and free testosterone levels in serum were estimated through ELISA methods. RESULTS: The present study revealed that female rats experienced more pain sensitivity to noxious stimuli compared to male rats. High-fat diet-induced obese rats experienced more pain sensations to noxious stimuli than lean rats. Obese male rats were found to have significantly low free testosterone and high 17 beta-estradiol levels compared to lean male rats. An increase in serum 17 beta-estradiol level led to increased pain sensation to noxious stimuli. While an increase in free testosterone level resulted in the lowering of pain sensation to noxious stimuli. CONCLUSION: The analgesic effect of tramadol was more pronounced in male rats compared to female rats. The analgesic effect of tramadol was more marked in lean rats compared to obese rats. Additional research to elucidate obesity-induced endocrine changes and the mechanisms driving sex hormones in pain perception is needed to foster future interventions to reduce disparities in pain.

Possible new therapeutic strategy to regulate atopic dermatitis through upregulating filaggrin expression.

BACKGROUND: Nonsense mutations in filaggrin (FLG) represent a significant genetic factor in the cause of atopic dermatitis (AD). OBJECTIVE: It is of great importance to find drug candidates that upregulate FLG expression and to determine whether increased FLG expression controls the development of AD. METHODS: We screened a library of bioactives by using an FLG reporter assay to find candidates that promoted FLG mRNA expression using a human immortalized keratinocyte cell line (HaCaT). We studied the effect of the compound on keratinocytes using the human skin equivalent model. We examined the effect of the compound on AD-like skin inflammation in NC/Nga mice. RESULTS: JTC801 promoted FLG mRNA and protein expression in both HaCaT and normal human epidermal keratinocytes. Intriguingly, JTC801 promoted the mRNA and protein expression levels of FLG but not the mRNA levels of other makers for keratinocyte differentiation, including loricrin, keratin 10, and transglutaminase 1, in a human skin equivalent model. In addition, oral administration of JTC801 promoted the protein level of Flg and suppressed the development of AD-like skin inflammation in NC/Nga mice. CONCLUSION: This is the first observation that the compound, which increased FLG expression in human and murine keratinocytes, attenuated the development of AD-like skin inflammation in mice. Our findings provide evidence that modulation of FLG expression can be a novel therapeutic target for AD.

Nociceptin/orphanin FQ modulates energy homeostasis through inhibition of neurotransmission at VMN SF-1/ARC POMC synapses in a sex- and diet-dependent manner.

BACKGROUND: Orphanin FQ (aka nociceptin; N/OFQ) binds to its nociceptin opioid peptide (NOP) receptor expressed in proopiomelanocortin (POMC) neurons within the arcuate nucleus (ARC), a critical anorexigenic component of the hypothalamic energy balance circuitry. It inhibits POMC neurons by modifying neuronal excitability both pre- and postsynaptically. We tested the hypothesis that N/OFQ inhibits neurotransmission at synapses involving steroidogenic factor (SF)-1 neurons in the ventromedial nucleus (VMN) and ARC POMC neurons in a sex- and diet-dependent fashion. METHODS: Electrophysiological recordings were done in intact male and in cycling and ovariectomized female NR5A1-Cre and eGFP-POMC mice. Energy homeostasis was assessed in wildtype animals following intra-ARC injections of N/OFQ or its saline vehicle. RESULTS: N/OFQ (1 µM) decreased light-evoked excitatory postsynaptic current (leEPSC) amplitude more so in males than in diestrus or proestrus females, which was further accentuated in high-fat diet (HFD)-fed males. N/OFQ elicited a more robust outward current and increase in conductance in males than in diestrus, proestrus, and estrus females. These pleiotropic actions of N/OFQ were abrogated by the NOP receptor antagonist BAN ORL-24 (10 µM). In ovariectomized female eGFP-POMC mice, 17ß-estradiol (E2; 100 nM) attenuated the N/OFQ-induced postsynaptic response. SF-1 neurons from NR5A1-Cre mice also displayed a robust N/OFQ-induced outward current and increase in conductance that was sexually differentiated and suppressed by E2. Finally, intra-ARC injections of N/OFQ increased energy intake and decreased energy expenditure, which was further potentiated by exposure to HFD and diminished by estradiol benzoate (20 µg/kg; s.c.). CONCLUSION: These findings show that males are more responsive to the pleiotropic actions of N/OFQ at anorexigenic VMN SF-1/ARC POMC synapses, and this responsiveness can be further enhanced under conditions of diet-induced obesity/insulin resistance.

The Expressing Patterns of Opioid Peptides, Anti-opioid Peptides and Their Receptors in the Central Nervous System Are Involved in Electroacupuncture Tolerance in Goats.

To investigate dynamic processes of enkephalin (ENK), cholecystokinin octapeptide (CCK-8), orphanin FQ (OFQ) and their receptors (µ opioid receptor, MOR; CCK B type receptor, CCKBR and opioid receptor-like 1 receptor, OPRL1) in the central nerve system (CNS) during electroacupuncture (EA) tolerance, EA of Sixty Hz was used to stimulate goats for 6 h. Pain threshold was measured using potassium iontophoresis. The expression levels of ENK, CCK-8, and OFQ and their receptors were determined with ELISA and qPCR, respectively. The results showed that the change rates of pain threshold in EA-treated goats decreased from 89.9 ± 11.7% at 0.5 h to -11.4 ± 8.9% at 6 h. EA induced the decreased ENK and increased CCK-8 and OFQ in the most measured nuclei. EA caused decreased preproenkephalin mRNAs in ACB, CAU, PVH, and PAG at 4 h, and decreased or unchanged MOR mRNAs at 2-6 h, but increased CCK mRNAs in CAU, PVT, PVH, PAG, and SCD at 4-12 h. Increased prepronociceptin mRNAs and fluctuated CCKBR and OPLR1 mRNAs were found in the most measured nuclei. ENK levels were positively correlated (p < 0.01) with the change rates of pain thresholds in the measured nuclei or areas while CCK-8 levels (or OFQ levels) were negatively correlated (p < 0.01) with the pain thresholds in CAU (or CAU and ACB). These results suggest that the development and recovery of EA tolerance may be associated with the specific expression patterns of opioid peptides, anti-opioid peptides and their receptors in the analgesia-related nuclei or areas.

Nociceptin effect on intestinal motility depends on opioid-receptor like-1 receptors and nitric oxide synthase co-localization.

AIM: To study the effect of the opioid-receptor like-1 (ORL1) agonist nociceptin on gastrointestinal (GI) myenteric neurotransmission and motility. METHODS: Reverse transcriptase - polymerase chain reaction and immunohistochemistry were used to localize nociceptin and ORL1 in mouse tissues. Intracellular electrophysiological recordings of excitatory and inhibitory junction potentials (EJP, IJP) were made in a chambered organ bath. Intestinal motility was measured in vivo. RESULTS: Nociceptin accelerated whole and upper GI transit, but slowed colonic expulsion in vivo in an ORL1-dependent manner, as shown using [Nphe(1)]NOC and AS ODN pretreatment. ORL1 and nociceptin immunoreactivity were found on enteric neurons. Nociceptin reduced the EJP and the nitric oxide-sensitive slow IJP in an ORL1-dependent manner, whereas the fast IJP was unchanged. Nociceptin further reduced the spatial spreading of the EJP up to 2 cm. CONCLUSION: Compounds acting at ORL1 are good candidates for the future treatment of disorders associated with increased colonic transit, such as diarrhea or diarrhea-predominant irritable bowel syndrome.

Activation of membrane estrogen receptors attenuates opioid receptor-like1 receptor-mediated antinociception via an ERK-dependent non-genomic mechanism.

To our knowledge, the present data are the first to demonstrate that activation of membrane estrogen receptors (mERs) abolishes opioid receptor-like 1 (ORL1) receptor-mediated analgesia via extracellular signal-regulated kinase (ERK)-dependent non-genomic mechanisms. Estrogen was shown previously to both attenuate ORL1-mediated antinociception and down-regulate the ORL1 gene expression. The present study investigated whether non-genomic mechanisms contribute to estrogen-induced attenuation of ORL1-mediated antinociception by the mERs GPR30, Gq-coupled mER, ERα, and ERß. E2BSA [ß-estradiol-6-(O-carboxymethyl)oxime: bovine serum albumin] (0.5mM), a membrane impermeant analog of estradiol, injected intrathecally immediately prior to orphanin FQ (OFQ;10 nmol), the endogenous ligand for the ORL1 receptor, abolished OFQ's antinociceptive effect in both male and ovariectomized (OVX) female rats, assessed using the heat-induced tail-flick assay. This effect was not altered by protein synthesis inhibitor, anisomycin (125 µg), given intrathecally 15 min prior to E2BSA and OFQ. Intrathecal application of selective receptor agonists permitted the relative contributions of various estrogen receptors in mediating this blockade of the antinociceptive response of OFQ. Activation of GPR30, Gq-mER, ERα, but not ERß abolished ORL1-mediated antinociception in males and OVX females. E2BSA produced a parallel and significant increase in the phosphorylation of ERK 2 only in OVX females, and pre-treatment with MEK/ERK 1/2 inhibitor, U0126 (10 µg), blocked the mER-mediated abolition of ORL1-mediated antinociception in OVX females. Taken together, the data are consistent with the interpretations that mER activation attenuates ORL1-mediated antinociception through a non-genomic, ERK 2-dependent mechanism in females.