YFa, a chimeric opioid peptide, induces kappa‐specific antinociception with no tolerance development during 6 days of chronic treatment

Abstract

Our previous study showed that YGGFMKKKFMRFamide (YFa), a chimeric peptide of Met-enkephalin, and Phe-Met-Arg-Phe-NH2 induced naloxone-reversible antinociception and attenuated the development of tolerance to morphine analgesia. In continuation, the present study investigated which specific opioid receptors-mu, delta or kappa-mediate the observed YFa antinociception pharmacologically using specific antagonists and whether chronic administration of YFa at 26.01 micromol/kg per day induces tolerance and its effect on the expression of mu and kappa opioid receptors from day 4 to day 6, with endomorphine-1 (EM-1) and saline taken as positive and negative controls, respectively. Quantitative differential expression analysis was carried out by real-time reverse-transcriptase polymerase chain reaction, and the corresponding changes in protein levels were assessed by Western blot. A pharmacological investigation revealed that nor-binaltorphimine, a specific kappa opioid receptor-1 (KOR1) antagonist, completely antagonized the antinociception induced by 39.01 micromol/kg of YFa. Importantly, its chronic intraperitoneal administration did not result in significant tolerance over 6 days, whereas EM-1 induced significant tolerance after day 4. Differential expression analysis revealed that EM-1 caused up-regulation of mu opioid receptor-1 on day 4, followed by down-regulation on later days. Interestingly, YFa treatment caused a decrease on day 4, followed by an increase in the expression of KOR1 from day 5 onward. In conclusion, YFa induces kappa-specific antinociception, with no development of tolerance during 6 days of chronic treatment, which further articulates new directions for improved designing of peptide-based analgesics that may be devoid of adverse effects like tolerance.

Opioid peptides: potential for drug development

“…A dynorphin A-(1-7) analog stabilized to metabolism, SK-9709 (Figure 1), also exhibited antinociceptive activity following systemic (s.c.) administration (Table 2) [19]. In addition, YFa, designed as a chimeric peptide between Met 5 -enkephalin-Arg 6 -Phe 7 and FMRFa (Phe-Met-Arg-Phe amide) with structural similarities to dynorphin A, produced KOR-mediated antinociception in rats following i.p administration without producing tolerance [20], although large doses (≥40 mg/kg) were required. Structural modifications, i.e.…”

NPYFa, A Chimeric Peptide of Met‐Enkephalin, and NPFF Induces Tolerance‐Free Analgesia

“…In our previous study, we designed a chimeric peptide YFa (YGGFMKKKFMRFamide) (32,43) which demonstrated both analgesia and an attenuated morphine tolerance. Similar to YFa in the present study, we designed a chimera of both opioid and NPFF peptides, NPYFa (YGGFMKKKPQRFamide), which contains PQRF (a mammalian endogenous peptide having anti-opioid effects) in place of the FMRF (invertebrate anti-opiate) moiety.…”

Effect of chronic intra‐peritoneally administered chimeric peptide of met‐enkephalin and FMRFa‐[d‐Ala2]YFa‐on antinociception and opioid receptor regulation

“…Furthermore, a corresponding significant increase was observed in expression of DOR1 in brain and spinal cord from day 2 onward which could be attributed to the active opioid motif‐[Y‐(d‐A)‐GFM]‐present in [ d ‐Ala 2 ] YFa. This motif seems to prevent receptor downregulation by inhibiting the binding of endogenous ligands (Law et al, 1985; Bhargava et al, 1993; Lee and Yoburn, 2000; Clarke et al, 2003; Vats et al, 2008). Whereas decrease in DOR1 expression on subsequent days could be the result of desensitization or uncoupling of δ opioid receptors, a phenomenon which is well reported for endogenous as well as exogenous opioid peptide agonists (Burford et al, 1998; Mcconalogue et al, 1999; Horner and Zadina, 2004; Trafton and Basbaum, 2004).…”

“…Exact receptor specificity of [ d ‐Ala 2 ]YFa was determined using known antagonists namely naloxonazine, naltrindole and nor‐binaltorphimine to selectively antagonize μ,δ and κ opioid receptors, respectively. Rats were treated with previously standardized doses of antagonists (Vats et al, 2008) 5 min prior to i.p. injection of 25.7 μmol/kg [ d ‐Ala 2 ] YFa and tail‐flick latency was measured after 5, 15 and 30 min.…”

“…Moreover, its chronic intra‐peritoneal (i.p.) administration did not resulted in significant tolerance over 6 days which coincides with consequent increase in KOR1 expression whereas endomorphin‐1, a μ receptor agonist taken as positive control induced significant tolerance and subsequent downregulation in MOR1 expression after day 4 (Vats et al, 2008).…”