Enkephalin hydrolysis by human serum biotinidase

Evaluation of dynorphin and kappa-opioid receptor level in the human blood lymphocytes and plasma: Possible role as a biomarker in severe opioid use disorder

BACKGROUND

The dynorphin (DYN)/kappa opioid receptor (KOR) system plays an important role in the development of addiction, and dysregulation of this system could lead to abnormal activity in the reward pathway. It has been reported that the expression state of the neurotransmitters and their receptors in the brain is reflected in peripheral blood lymphocytes (PBLs).

METHODS

We have evaluated the PBLs and plasma samples of four groups: 1) subjects with severe opioid use disorder (SOD), 2) methadone-maintenance treated (MMT) individuals, 3) long-term abstinent subjects having former SOD, and 4) healthy control subjects (n = 20 in each group). The mRNA expression level of preprodynorphin (pPDYN) and KOR in PBLs has been evaluated by real-time PCR. Peptide expression of PDYN in PBLs has been studied by western blot, and DYN concentration in plasma has been measured by ELISA.

RESULTS

The relative expression level of the pPDYN mRNA and PDYN peptide in PBLs were significantly up-regulated in SOD, MMT, and abstinent groups compared to control subjects. No significant difference was found in the plasma DYN concentration between study groups. The expression level of the KOR mRNA in PBLs was significantly decreased in all three study groups compared to the control subjects.

CONCLUSION

the expression changes in the DYN/KOR system after chronic exposure to opioids, including methadone, seems to be stable and does not return to normal levels even after 12 months abstinence. These long-time and permanent changes in PBLs may serve as a biomarker and footprint of SOD development in the periphery.

Triazole biotin: a tight-binding biotinidase-resistant conjugate

The natural amide bond found in all biotinylated proteins has been replaced with a triazole through CuAAC reaction of an alkynyl biotin derivative. The resultant triazole-linked adducts are shown to be highly resistant to the ubiquitous hydrolytic enzyme biotinidase and to bind avidin with dissociation constants in the low pM range. Application of this strategy to the production of a series of biotinidase-resistant biotin-Gd-DOTA contrast agents is demonstrated.

Characterization of immunoreactive dynorphin B and beta-endorphin in human plasma

Dynorphins and beta-endorphin in human plasma were characterized and studied quantitatively using radioimmunoassay, high-performance liquid chromatography (HPLC), and mass spectrometry. Most immunoreactive (ir) dynorphin B and beta-endorphin in human plasma coeluted with authentic peptides in analysis. Dynorphin A was not detected. Added to human plasma it was rapidly converted into Leu-enkephalin-Arg6 followed by elimination of the C-terminal arginine after prolonged incubation. The rate of dynorphin A conversion was estimated at 40 pmol/min/microl plasma. This process was inhibited by the thiol protease inhibitor, PHMB and by EDTA. Dynorphin B, alpha-neoendorphin and big dynorphin were virtually not metabolized by plasma proteases under the same conditions. beta-endorphin was processed into beta-endorphin(1-19) and the corresponding C-terminal counterpart beta-endorphin(20-31) at a rate of about 25 pmol/min/microl of plasma. Based on the above data, a reliable strategy was established to measure dynorphin B- and beta-endorphin-ir in human plasma samples. The basal levels in a male control group were 0.99 +/- 0.11 (n = 11) and 16.3 +/- 1.5 (n = 11) fmol/ml plasma, respectively.

Urinary biotinidase and alanine excretion in patients with insulin-dependent diabetes mellitus

Twenty-four-hour urine specimens from 21 juvenile insulin-dependent diabetics and 10 healthy controls were compared with respect to biotinidase activity and alanine content. Urinary biotinidase activity was analysed by a newly developed high-performance liquid chromatography (HPLC) method. It was found that the excretion of biotinidase in urine was elevated in diabetics (7.02 mU/d; p < 0.005) as compared with controls (not detectable). Alanine excretion was also found to increase (p < 0.01) in diabetics. Biotinidase excretion in diabetics was correlated with alanine excretion (rS = 0.667; p < 0.01), but not with protein, albumin or N-acetyl-beta-glucosaminidase excretion. The simultaneous elevation of urinary biotinidase and alanine excretion in juvenile diabetics suggests that changes in kidney metabolism arise in the early stages of diabetes.

Changes in cerebrospinal fluid biotinidase activity in Staphylococcus aureus meningitis

An early increase in activity of biotinidase in the cerebrospinal fluid (CSF) during the course of acute Staphylococcus aureus meningitis in a subject with subacute sclerosing panencephalitis (SSPE) is reported. A possible role of CSF biotinidase in the hydrolysis of specific opioid neuropeptides during acute inflammatory processes involving the CSF-central nervous system compartment is suggested.

Biocytin-specific 110-kDa biotinidase from human serum

Biotinidase purification from human serum was performed under new protocol. With HPLC biotinidase assay instead of colorimetric method and using non-ionic surfactant, 110-kDa biotinidase was discovered and co-purified in addition to the previously identified 76-kDa biotinidase. This newly identified enzyme accounted for 5% of the total biotinidase activity. Protein core of 110 kDa was estimated as 72 kDa by use of N-glycanase and SDS-PAGE analysis, while that of the 76-kDa enzyme was estimated as 59 kDa. Total amino acid analysis indicated 30% higher absolute amounts of amino acids in 110-kDa enzyme. The following differences were observed from kinetic study: the 110-kDa enzyme showed a 10-fold lower Km value and a 9-fold higher kcat/Km value for biocytin than those of 76-kDa enzyme. Thus, 110-kDa enzyme is more likely to be the physiological biocytin hydrolase (biocytinase), since the biocytin concentration in human serum is extremely low. The pathogenesis of an inborn error of the metabolism such as a variant form of biotinidase deficiency, which presented an atypical clinical course, might be related to these isoenzymes in terms of their different roles in the body.