Specificity of prohormone convertase 2 on proenkephalin and proenkephalin-related substrates

In the central and peripheral nervous systems, the neuropeptide precursor proenkephalin must be endoproteolytically cleaved by enzymes known as prohormone convertases 1 and 2 (PC1 and PC2) to generate opioid-active enkephalins. In this study, we have investigated the specificity of recombinant mouse PC2 for proenkephalin-related internally quenched (IQ) peptides, for methylcoumarin amide-based fluorogenic peptides, and for recombinant rat proenkephalin. IQ peptides exhibited specificity constants (kcat/Km) between 9.4 x 10(4) M-1 s-1 (Abz-Val-Pro-Arg-Met-Glu-Lys-Arg-Tyr-Gly-Gly-Phe-Met-Gln-EDDnp+ ++; where Abz is ortho-aminobenzoic acid and EDDnp is N-(2, 4-dinitrophenyl)ethylenediamine)) and 0.24 x 10(4) M-1 s-1 (Abz-Tyr-Gly-Gly-Phe-Met-Arg-Arg-Val-Gly-Arg-Pro-Glu-EDDnp), with the peptide B to Met-enk-Arg-Phe cleavage preferred (Met-enk is met-enkephalin). Fluorogenic substrates with P1, P2, and P4 basic amino acids were hydrolyzed with specificity constants ranging between 2.0 x 10(3) M-1 s-1 (Ac-Orn-Ser-Lys-Arg-MCA; where MCA is methylcoumarin amide) and 1.8 x 10(4) M-1 s-1 (<Glu-Arg-Thr-Lys-Arg-MCA; where <Glu is pyroglutamic acid). Substrates containing only a single basic residue were not appreciably hydrolyzed, and substrates lacking a P4 Arg exhibited kcat of less than 0.05 s-1. Substitution of ornithine for Lys at the P4 position did not significantly affect the kcat but increased the Km 2-fold. Data from both sets of fluorogenic substrates supported the contribution of a P4 Arg to PC2 preference. Analysis of proenkephalin reaction products using immunoblotting and gel permeation chromatography demonstrated that PC2 can directly cleave proenkephalin and that the generation of small opioid peptides from intermediates is mediated almost entirely by PC2 rather than by PC1. These results are in accord with the analysis of PC2 knock-out brains, in which the amounts of three mature enkephalins were depleted by more than three-quarters.

Role of PC2 in proenkephalin processing: antisense and overexpression studies

The contribution of the prohormone-processing enzyme PC2 to the proteolytic maturation of proenkephalin was examined in three sets of studies. In the first, the processing of this precursor was compared in PC2-rich (Rin5f) and PC2-lacking (AtT-20) cell lines expressing proenkephalin by virtue of stable transfection. These studies showed that the time frame for processing of this precursor is cell line specific, with AtT-20 cells processing proenkephalin to peptide B much more rapidly than Rin cells. However, the latter cell line processed proenkephalin much more extensively, i.e., produced a greater proportion of the penta- to octapeptide enkephalins. The involvement of PC2 in these later processing events was analyzed by examining the processing of proenkephalin in PC2-overexpressing AtT-20 cell lines. These experiments yielded a processing profile similar to that observed for Rin cells, although the time frame of initial processing was similar to that found in AtT-20 cells. To confirm the physiological involvement of proenkephalin in the production of the small opioid peptides, we generated a Rin cell line in which the production of PC2 was impaired due to stable expression of antisense mRNA to this enzyme. These experiments provided conclusive evidence that the generation of Met-enkephalin-Arg-Phe and Met-enkephalin-Arg-Gly-Leu, but not the larger enkephalin-containing peptides, is mediated by PC2. Taken together, our data support the idea that PC2 is physiologically capable of mediating only the later processing steps of neuropeptide precursors. PC2 thus appears to be the primary enzyme responsible for the generation of bioactive opioid peptide species from proenkephalin.

Equal effects of gelatin and hydroxyethyl starch (6% HES 130/0.42) on modified thrombelastography in children

BACKGROUND

Artificial colloids are frequently used to prevent or treat circulatory failure due to hypovolaemia. Whereas gelatin has been shown not to affect coagulation besides its haemodilutional effect, hydroxyethyl starches (HES) have additional negative effects on haemostasis. The third-generation HES solutions have been developed to minimise these effects. We therefore conducted a prospective, randomised study, to verify the hypothesis that a 6% HES 130/0.42/6 : 1 and a 4% gelatin infusion influences modified thrombelastography (TEM) parameters in children in the same manner and to the same extent.

METHODS

A total of 50 paediatric patients aged 0-12 years scheduled for surgery were assigned to receive either 10 ml/kg HES 130/0.42 or gelatin. Blood gas analysis, haemodynamic parameters and TEM measurements were performed before and after colloid administration.

RESULTS

Patient characteristics, indications/surgical procedures and the main results obtained from blood gas analysis were comparable between the two groups. After administration of either gelatin or HES, all TEM parameters, except for clotting time, indicated impaired coagulation whereas the mean values of all TEM parameters remained within the normal ranges. Comparing the gelatin and HES 130/0.42/6 : 1 groups, none of the measured TEM parameters was found to show between-group differences at baseline or after colloid infusion.

CONCLUSION

In conclusion, we could demonstrate that the investigational product, HES 130/0.42/6 : 1 solution, administered at a dosage of 10 ml/kg to children, had comparable effects on coagulation monitored with TEM as a gelatin solution. Perioperative administration of HES 130/0.42/6 : 1 does not alter coagulation to an extent above and beyond the effect of haemodilution.

Processing site blockade results in more efficient conversion of proenkephalin to active opioid peptides

Prohormones are known to be processed at various cleavage sites in a defined temporal order, suggesting the possibility of sequential unfolding of processing sites. In order to investigate whether sequential processing at predefined sites is in fact required for proper processing, site-directed mutagenesis was performed to block known initial cleavage sites within proenkephalin. Pulse-chase/immunoprecipitation experiments were employed to analyze the fate of mutant and native proenkephalins in stably transfected AtT-20 cells. While processing did not occur at blockaded sites, surprisingly, overall processing of mutant proenkephalins proceeded efficiently, and alternative sites were chosen. When compared with native proenkephalin, processing of mutant proenkephalins occurred more slowly at early stages and more quickly at later stages. Experiments employing endoglycosidase H indicated that the early slow processing of mutant proenkephalins may be due to delays in intracellular transport. Metabolic labeling studies showed that more efficient production of bioactive opioids occurred in all processing site blockade mutants examined; these results were confirmed using several different radioimmunoassays of stored peptide products. We conclude that efficient processing of prohormone precursors does not require a specific temporal order of processing events. The fact that mutant proenkephalins were more fully processed than native proenkephalin may provide a route for more efficient production of opioid peptides in applications for chronic pain treatment.

[Prehospital postcardiac-arrest-sedation and -care in the Federal Republic of Germany-a web-based survey of emergency physicians]

BACKGROUND

This study evaluates the implementation of postcardiac-arrest-sedation (PCAS) and -care (PRC) by prehospital emergency physicians in Germany.

MATERIALS AND METHODS

Analysis of a web-based survey from October to November 2022. Questions were asked about implementation, medications used, complications, motivation for implementing or not implementing PCAS, and measures and target parameters of PRC.

RESULTS

A total of 500 emergency physicians participated in the survey. In all, 73.4% stated that they regularly performed PCAS (hypnotics: 84.7%; analgesics: 71.1%; relaxants: 29.7%). Indications were pressing against the respirator (88.3%), analgesia (74.1%), synchronization to respirator (59.5%), and change of airway device (52.6%). Reasons for not performing PCAS (26.6%) included unconscious patients (73.7%); concern about hypotension (31.6%), re-arrest (26.3%), and worsening neurological assessment (22.5%). Complications of PCAS were observed by 19.3% of participants (acute hypotension [74.6%]); (re-arrest [32.4%]). In addition to baseline monitoring, PRC included 12-lead-electrocardiogram (96.6%); capnography (91.6%); catecholamine therapy (77.6%); focused echocardiography (20.6%), lung ultrasound (12.0%) and abdominal ultrasound (5.6%); induction of hypothermia (13.6%) and blood gas analysis (7.4%). An etCO2 of 35-45 mm Hg was targeted by 40.6%, while 9.0% of participants targeted an SpO2 of 94-98% and 19.2% of participants targeted a systolic blood pressure of ≥ 100 mm Hg.

CONCLUSIONS

Prehospital PRC in Germany is heterogeneous and deviations from its target parameters are frequent. PCAS is frequent and associated with relevant complications. The development of preclinical care algorithms for PCAS and PRC within preclinical care seems urgently needed.