Metabolic profile of opioid peptides differs in the hippocampus and striatum of seizure-susceptible E1 mice

Analytical characterization and comparison of the blood-brain barrier permeability of eight opioid peptides

Opioid drugs, including the newly developed peptides, should penetrate the blood-brain barrier (BBB) for pain management activity. Although BBB transport is fragmentarily described for some mu-opioid peptides, a complete and comparative overview is currently lacking. In this study, the BBB transport of eight opioid peptides (EM-1, EM-2, CTAP, CTOP, DAMGO, dermorphin, TAPP and TAPS) is described and compared. In addition, the metabolic stability in plasma and brain was evaluated. The highest influx rate was obtained for dermorphin (K(in)=2.18 microl/(g x min)), followed by smaller rates for EM-1, EM-2 and TAPP (K(in)=1.06-1.14 microl/(g x min)). Negligible influx was observed for DAMGO, CTOP and TAPS (K(in)=0.18-0.40 microl/(g x min)) and no influx for CTAP. Capillary depletion revealed that all peptides reached brain parenchyma for over 75%. Efflux was shown for TAPP (t(1/2)=2.82 min) and to a lesser extent for EM-1, EM-2 and DAMGO (t(1/2)=10.66-21.98 min), while no significant efflux was observed for the other peptides. All peptides were stable in mouse plasma and brain, with generally higher stability in brain, except for EM-1 and EM-2 which showed plasma half-life stabilities of a few minutes only.

Differential metabolism of dynorphins in substantia nigra, striatum, and hippocampus

To map the proteolytic enzymes metabolizing dynorphins in brain structures, size-exclusion chromatography linked to electrospray ionization mass spectrometry was used. Enzymes extracted from rat hippocampus, striatum, and substantia nigra were tested for their capability of converting dynorphin-related peptides. Dynorphin A was the most resistant to proteolytic conversion, whereas Big dynorphin and dynorphin B-29 were slowly converted to dynorphin A and dynorphins A and B, respectively. Dynorphin B and alpha-neoendorphin were the least resistant. Dynorphin B was rapidly converted to Leu-enkephalin in the striatum and hippocampus but to Leu-enkephalin-Arg6 in the substantia nigra. alpha-Neoendorphin was converted to Leu-enkephalin in all tissues investigated.

Plasma neuropeptide Y in patients with major depressive disorder

It has been suggested that neuropeptide Y (NPY) is involved in the pathophysiology of depression. Plasma peptide-rich fraction from patients with major depressive disorder and control subjects was eluted with high performance liquid chromatography (HPLC), followed by radioimmunoassay of NPY. The screening patterns of the NPY-like immunoreactivity in 50 fractions eluted by HPLC from the plasma peptide-rich fraction were different between the two groups. The values of NPY in the 16 controls and the 14 patients were 427 +/- 38 and 310 +/- 27 fmol/ml plasma (P < 0.05), respectively. These results suggest that impaired metabolism of plasma NPY and the reduced plasma NPY in patients with major depressive disorder could be involved in the pathogenesis or pathophysiology of major depressive disorder.

Endogenous opiates: 1995

This article is the eighteenth installment of our annual review of research concerning the opiate system. It includes articles published during 1995 reporting the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects. The specific topics covered this year include stress: tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.