BAM 22P

IC50: 1.3 nM for opiate activity

Bovine adrenal medulla 22 peptide (BAM22P) is a peptide with 22 amino acids which is one of the cleavage products of proenkephalin A, the precursor of Leu- and Met-enkephalin, in the adrenal medulla, with very potent opiate activity.

In vitro: In the guinea-pig ileum assay, BAM-22P has been shown to have typical and extraordinarily potent opioid activities antagonized by naloxone. The potency of BAM-22P is 26 times that of Met-enkephalin and 22 times that of B hendorphin. IC50 value of BAM-22P in this tissue, 1.3 nM, makes it the most potent Met-enkephalin relatives that discoveried so far. [1].

In vivo: Intrathecal (i.t.) administration of BAM22 decreased nocifensive behavior scores, which measured as the sum of flinching and lifting/licking, in the first and second phases of the formalin test. Such decrease was partially attenuated by systemic injection of naloxone. [2].

Clinical trial: Up to now, BAM 22P is still in the preclinical development stage.

Reference:
[1] Mizuno K, Minamino N, Kangawa K, Matsuo H.  A new family of endogenous "big" Met-enkephalins from bovine adrenal medulla: purification and structure of docosa- (BAM-22P) and eicosapeptide (BAM-20P) with very potent opiate activity. Biochem Biophys Res Commun. 1980 Dec 31;97(4):1283-90.
[2] Hong Y, Dai P, Jiang J, Zeng X.  Dual effects of intrathecal BAM22 on nociceptive responses in acute and persistent pain--potential function of a novel receptor. Br J Pharmacol. 2004 Feb;141(3):423-30.

Adrenal secretion of BAM-22P, a potent opioid peptide, is enhanced in rats with acute cholestasis.[Pubmed:8141292]

Am J Physiol. 1994 Feb;266(2 Pt 1):G201-5.

The adrenal gland is known to produce and release endogenous opioids into the circulation. Bovine adrenal medulla docosapeptide (BAM-22P) is a potent opioid agonist, derived from the proenkephalin A gene, which is present in the adrenal medulla. This study was undertaken to determine whether BAM-22P is released into plasma during acute cholestatic liver injury, which increases plasma total opioid activity. Acute cholestasis was induced by bile duct ligation or administration of the hepatotoxin alpha-naphthylisothiocyanate. Plasma levels of BAM-22P were determined by a sensitive radioimmunoassay, and the specificity of the assay was confirmed using high-performance liquid chromatography. Plasma BAM-22P levels was cholestatic rats were significantly higher than those in control rats. This increase in plasma BAM-22P levels was completely prevented by adrenalectomy. Adrenal steady-state levels of proenkephalin mRNA, as determined by Northern blot hybridization analyses, were also increased significantly in cholestatic rats. These increases in proenkephalin mRNA levels were not paralleled by changes in adrenal BAM-22P peptide levels, which were similar in cholestatic rats and their respective controls. Similar levels of proenkephalin mRNA expression were observed in innervated and denervated adrenal glands from cholestatic rats, suggesting that the increase in adrenal proenkephalin mRNA levels in acute cholestasis is not due to splanchnic nerve activation. Thus acute cholestasis in the rat is associated with adrenal secretion and accumulation in plasma of the highly potent opioid peptide BAM-22P and an augmentation of adrenal proenkephalin mRNA expression. The increase in plasma BAM-22P levels may contribute substantially to the increase in total circulating opioid activity documented in cholestatic rats.

Opioid peptides in rat islets of Langerhans. Immunoreactive met- and leu-enkephalins and BAM-22P.[Pubmed:3510138]

Diabetes. 1986 Jan;35(1):52-7.

Previous studies have shown that met- and leu-enkephalins are present in extracts of whole pancreas obtained from guinea pigs and human cadavers. The present studies demonstrate that immunoreactive methionine (met)- and leucine (leu)-enkephalins present in rat pancreas are localized in islets of Langerhans. Immunohistochemical staining of fixed, whole pancreas indicated that only islet endocrine cells were heavily stained when any of four different met- and leu-enkephalin-directed antisera or an anti-BAM-22P (bovine adrenal medulla docosapeptide) antiserum was used. The peptides were characterized by a combination of gel-filtration chromatography, high-performance liquid chromatography (HPLC), and specific radioimmunoassay. Free met-enkephalin content in extracts of rat islets was 90-fold enriched over content in extracts of whole pancreas (1.72 +/- 0.35 versus 0.019 +/- 0.007 pmol/mg protein). Treatment with trypsin and carboxy-peptidase-B of high-molecular-weight peptides extracted from pancreas or islets resulted in release of additional met-enkephalin immunoreactivity, which was 39-fold enriched in islets compared with pancreas (5.90 +/- 0.58 and 0.153 +/- 0.032 pmol/mg protein, respectively). Total islet content (per milligram protein) of met-enkephalin-containing peptides was similar to that reported elsewhere for bovine hypothalamus. The immunohistochemical data as well as the enrichment of extractable enkephalins in islets compared with whole pancreas indicate that essentially all the met-enkephalin present in pancreas is localized in islets, while the presence of BAM-22P immunoreactivity in islets is consistent with biosynthesis of enkephalins in islet cells via a preprohormone, such as that described in the bovine adrenal medulla and rat brain.

A Met-enkephalin-containing-peptide, BAM 22P, as a novel substrate for glandular kallikreins.[Pubmed:6552186]

Biochem Biophys Res Commun. 1983 Apr 29;112(2):366-71.

Homogeneous preparations of two well-characterized glandular kallikreins have been examined for their ability to hydrolyze BAM 22P, a methionine-enkephalin-containing-peptide found in the adrenal medulla. Both enzymes cleaved preferentially the Arg6-Arg7 bond in this substrate. The specificity constant (kcat/Km) for this cleavage was 86 mM-1 sec-1 for horse urinary kallikrein and 566 mM-1 sec-1 for porcine pancreatic kallikrein. These results demonstrate a previously undescribed specificity for glandular kallikreins and suggest a possible role for these widely distributed enzymes in prohormone processing.

Opioid peptides (DAGO-enkephalin, dynorphin A(1-13), BAM 22P) microinjected into the rat brainstem: comparison of their antinociceptive effect and their effect on neuronal firing in the rostral ventromedial medulla.[Pubmed:2572306]

Brain Res. 1989 Oct 30;501(1):116-28.

The highly mu-selective agonist Tyr-D-Ala-Gly-MePhe-Gly-ol-enkephalin (DAGO) produces potent, dose-dependent naloxone-reversible antinociception when microinjected into the ventrolateral periaqueductal gray (PAG) (ED50 = 0.72 nmol) or rostral ventromedial medulla (RVM) (ED50 = 0.05 nmol) as measured on the rat tail flick (TF) assay. In single-unit recording experiments, DAGO microinjected into the PAG also affected On- and Off-Cell firing in the RVM in the same way as previously demonstrated by our group for morphine. PAG-microinjected DAGO inhibits spontaneous and noxious-evoked On-Cell firing (attenuating the characteristic On-Cell burst) (n = 19), and excites spontaneous Off-Cell firing, preventing the characteristic Off-Cell pause (n = 12) at doses which suppress the TF. These results support a major role for the mu receptor in PAG and RVM mechanisms of opiate antinociception. In our experiments using BAM22P, an endogenous weakly mu-selective opioid peptide, we could not demonstrate a dose-dependent antinociceptive effect, whether the peptide was microinjected supraspinally into the PAG (n = 9) or RVM (n = 11), or intrathecally at the lumbar cord (n = 4). In two animals, a naloxone-reversible antinociceptive effect was observed following the microinjection of 10 nmol BAM 22P into the RVM; however, no effect was seen in 3 animals microinjected with 20 nmol. Dyn A(1-13), a putative endogenous ligand for the kappa receptor, had no antinociceptive effect when microinjected into the ventrolateral PAG, and no effect on the firing (spontaneous or noxious-evoked) of RVM On (n = 3)- or Off (n = 2)-Cells.

Dual effects of intrathecal BAM22 on nociceptive responses in acute and persistent pain--potential function of a novel receptor.[Pubmed:14718254]

Br J Pharmacol. 2004 Feb;141(3):423-30.

Bovine adrenal medulla 22 (BAM22) peptide is one of the cleavage products of proenkephalin A. It binds with high affinity to both opioid receptors and a newly discovered receptor in vitro. This latter receptor was first named sensory neuron-specific receptor and is here named BAM peptide-activated receptor with non-opioid activity (BPAR). BPAR is uniquely distributed in small-diameter DRG neurons, most of which are associated with the IB4 class of nociceptor afferent. The present study examined the effects of intrathecal administration of BAM22 on formalin-induced nocifensive behaviors and tail-withdrawal latency in the rat. Intrathecal (i.t.) administration of BAM22 decreased nocifensive behavior scores, measured as the sum of flinching and lifting/licking, in the first and second phases of the formalin test. This decrease was partially attenuated by systemic injection of naloxone. In the presence of naloxone, i.t. BAM22 produced a dose-dependent suppression of the nocifensive behaviors observed during the formalin test. The ratio of the efficacy of BAM22 (5 nmol) in the presence of naloxone over that in the absence of naloxone was 0.65 for flinching and 0.74 for lifting/licking in the second phase. BAM22 at a dose of 5 nmol increased the tail-withdrawal latency by 193 and 119% of baseline in the absence and presence of naloxone, respectively. Systemic administration of naloxone alone enhanced the nocifensive behaviors in the second, but not in the first phase of the formalin test. Naloxone treatment did not alter the tail-withdrawal latency. These data confirm earlier in vitro data showing that BAM22 has both opioid and non-opioid biological actions. The non-opioid action of BAM22 involves inhibition of acute and persistent nociceptive behaviors at the spinal level, presumably mediated via BPAR. The name suggested for this novel receptor, its potential physiological function and its ligand are discussed. British Journal of Pharmacology (2004) 141, 423-430. doi:10.1038/sj.bjp.0705637

Proenkephalin A gene products activate a new family of sensory neuron--specific GPCRs.[Pubmed:11850634]

Nat Neurosci. 2002 Mar;5(3):201-9.

Several peptide fragments are produced by proteolytic cleavage of the opioid peptide precursor proenkephalin A, and among these are a number of enkephalin fragments, in particular bovine adrenal medulla peptide 22 (BAM22). These peptide products have been implicated in diverse biological functions, including analgesia. We have cloned a newly identified family of 'orphan' G protein--coupled receptors (GPCRs) and demonstrate that BAM22 and a number of its fragments bind to and activate these receptors with nanomolar affinities. This family of GPCRs is uniquely localized in the human and rat small sensory neuron, and we called this family the sensory neuron--specific G protein--coupled receptors (SNSRs). Receptors of the SNSR family are distinct from the traditional opioid receptors in their insensitivity to the classical opioid antagonist naloxone and poor activation by opioid ligands. The unique localization of SNSRs and their activation by proenkephalin A peptide fragments indicate a possible function for SNSRs in sensory neuron regulation and in the modulation of nociception.