Enkephalin binding systems in human plasma. III: Comparative protection of different peptides

Towards a possible aetiology for depressions?

BACKGROUND

Since a genetic disposition for depression is probable, there ought to be biochemical changes. Increased peptide levels with relevant bioactivities have been found in urine in a previous investigation, which may be such changes.

METHODS

Urine from patients with severe depression according to ICD 10 have been run on reversed phase High Performance Liquid Chromatography, and off line mass spectrometry was performed on some of these peptides.

RESULTS

We find overlapping patterns of peptide peaks in severe depression, but with considerable individuality. Mass spectrometry shows that some of these peptides are probably of dietary origin, because their sequences are found only in certain dietary proteins. Opioids from casein and gliadin are typical examples.

CONCLUSION

Our data show that the disposition must be polygenetic because some peptide peaks with the same bioactivity are of different length in different patients, but with the same diagnosis. However, some of the peaks are common Peptide increase in urine is found when break down is deficient, and the data presented agree with reports on peptidase deficiencies in depression. Antidepressant drugs decrease the peptide level after about 3 weeks.

Peripheral modulation of learning and memory: enkephalins as a model system

Extensive research on the effects of enkephalins on conditioning is reviewed and used as the basis for a model of peripheral modulation of learning and memory. An overall theme emphasized throughout our discussion is that these peptides can influence the strength with which a memory is acquired and stored by acting outside the blood-brain barrier. This assertion is supported by research on the behavioral effects of systemically administered enkephalins and opioid antagonists, the rapid hydrolysis of circulating enkephalins in vivo, and the limited ability of these peptides to penetrate the blood-brain barrier. A consideration of the extensive distribution of enkephalins throughout peripheral autonomic systems leads to the proposal that enkephalins may act to modulate learning and memory by altering peripheral autonomic function; autonomic afferents may then communicate with the memory trace in the CNS through a central modulatory pathway outlined herein. Evidence that some stressful experiences may lead to increases in circulating enkephalins also is discussed. The sites of action of these circulating enkephalins may involve peripheral autonomic sites, or additionally may involve the circumventricular organs. As a further regulatory mechanism, circulating enkephalin levels may be controlled by experience-dependent alterations of the activity of enzyme systems that participate in their breakdown. Finally, it is emphasized that the mechanisms of enkephalin action postulated herein may be applicable to the actions of other peripheral hormones, peptides, and neurotransmitters that participate in the modulation of learning and memory storage processes.

Gluten-free diet decreases urinary peptide levels in children with celiac disease

BACKGROUND

Increased urine secretion of peptides has been found in celiac disease, probably resulting from increased intestinal uptake of peptides caused by damage to the small gut mucosa.

METHODS

High-performance liquid chromatography of low-molecular-weight peptides in the urine was performed over 6 months, before and after a gluten-free diet was instituted in children who clinically improved while consuming the diet.

RESULTS

A significant decrease of peptide levels was observed in children consuming the gluten-free diet. Certain peptide peaks thought to be gluten related decreased the most after the patients began the diet.

CONCLUSIONS

Because the peptides decrease in patients consuming a gluten-free diet, it is reasonable to conclude that such peptides have a mostly dietary origin.

Serotonin uptake stimulating peptide found in plasma of normal individuals and in some autistic urines

We have isolated a tripeptide from normal plasma and autistic urines which stimulates the uptake of serotonin (5-HT) into platelets. This peptide was purified by high-performance liquid chromatography (HPLC) and characterized by sequenation and mass-spectrometry. Synthetic peptide showed co-chromatography with the biological sample in the HPLC systems used. Close to 60% of the autistic children diagnosed using the Diagnostic Statistical Manual III-R had an increased HPLC peak eluting like this peptide in their urines compared with controls.

Hydrolysis of peripheral leucine enkephalin in allergic asthma

Plasma hydrolysis of leucine enkephalin was studied in a group of patients affected by seasonal allergic asthma in acute and quiescent stage; data were compared with those obtained from a control group of healthy volunteers. Results obtained indicate a statistically significant reduction of leu-enkephalin hydrolysis in allergic subjects. In the quiescent stage, substrate degradation is reduced, and the pattern of the hydrolysis by-products is modified with respect to normal controls. In the acute stage, hydrolysis is further reduced, and the pattern of the hydrolysis by-products is further modified with respect to the quiescent stage. The variations of leu-enkephalin hydrolysis appear to be controlled by decreased activity of proteolytic enzymes and by increased activity of the low-molecular-weight plasma inhibitors active on these enzymes. The sum of these processes is conducive to a distribution of enkephalin-hydrolyzing enzymes, as well as a hydrolysis pattern, that appears to be specific for the allergic subjects and distinct from that seen in the controls.

Age-induced increase of leucine enkephalin enzyme degradation in human plasma

Possible age-induced variations of the hydrolysis of leucine enkephalin in the presence of plasma enzymes were studied by kinetic and chromatographic techniques in a group of elderly individuals. Results obtained indicate that in elderly individuals the activity of enkephalin-degrading plasma enzymes is greater than in the controls; ANOVA analysis of these data indicates that the dependency of the variation of hydrolysis upon the two age groups is statistically significant. Increased substrate hydrolysis, and a modified hydrolysis pattern, appear to be associated with increased activity of the enzymes involved, and with different distribution of the individual enzymes within each class, as well as with severely reduced activity of the low molecular weight plasma inhibitors. The combination of these factors defines a characteristic hydrolysis pattern for the elderly individuals, different from that found in the controls.

Interindividual variability of enkephalin-degrading enzymes in human plasma

The interindividual variability of the hydrolysis of leucine enkephalin, and of the formation of its hydrolysis by-products has been studied in human plasma. In agreement with known data, the data obtained indicate that Leu-enkephalin is degraded by several enzymes, belonging to three classes: aminopeptidases, dipeptidylaminopeptidases, and dipeptidylcarboxypeptidases. The relative ratio of the substrate degraded by each enzyme class-as well as the expression of the single enzyme species within each class-appears to be individually determined. Interindividual variability observed seems controlled by two main factors: the pattern of enkephalin-degrading enzymes and, more notably, the low molecular weight plasma inhibitors. Both these factors appear to be partially specific of each donor. Possibly because of the composition of these factors, the hydrolysis pattern of the substrate is characteristic of each donor, and constant in blood obtained from successive drawings, at least within a relatively short period of time.

Could schizophrenia be reasonably explained by Dohan's hypothesis on genetic interaction with a dietary peptide overload?

1. Dohan has proposed that schizophrenia is a genetic disposition which interacts with an overload of dietary proteins such as casein and gluten or gliadin. 2. A systematic attempt is made to see if this hypothesis is possible faced with aspects of schizophrenia that must be accounted for. 3. The authors conclusion is that it is possible, but more serious work in this field is urgently needed.

Positive and negative immunomodulation by opioid peptides

The data that follow review part of the existing evidence concerning the neuroimmune functions mediated by opioid peptides, with particular regard to dual immunomodulatory effects. Limited references to substances other than opioid peptides are included, mainly to emphasize the possible similarities in the mediation of neuroimmune interactions by different informational substances, while the interactions directed from the immune to the nervous system have deliberately been omitted.

Enzymes and inhibitors in leu-enkephalin in metabolism in human plasma

The enzymes degrading leucine enkephalin in human plasma and the inhibitors active on these enzymes were studied by kinetic and chromatographic techniques. Data obtained evidence the existence of complex kinetics of leu-enkephalin hydrolysis and of formation of its hydrolysis by-products. These appear to originate from the combined effect of further hydrolysis of the enkephalin's fragments after their release and of competition between the different enzymes present in plasma. Chromatographic separation of plasma proteolysis inhibitors indicates the existence of several pools of substances acting on all three enzyme groups that degrade leu-enkephalin. The partial specificity of these substances induces competition effects: consequently, the actual protection over leu-enkephalin is considerably lower that the total inhibitory activity. That notwithstanding, plasma inhibitors control enkephalin hydrolysis to a relevant extent, while they modify only slightly the ratio of hydrolysis between the different enzymes. This latter parameter--and specifically the large prevalence of aminopeptidases over dipeptidylaminopeptidases and dipeptidylcarboxypeptidases--appears controlled mainly by kinetic factors.

Enkephalin-degrading dipeptidylcarboxypeptidases in human and Cavia porcellus plasma

1. The dipeptidylcarboxypeptidases that degrade leucine enkephalin in human and guinea pig plasma were studied by kinetic and chromatographic techniques. 2. The extremely rapid degradation of enkephalins in Cavia plasma seems to be caused by both increased activity of enzymes and reduced role of inhibitors. 3. The increased role of dipeptidylcarboxypeptidases in Cavia as compared to Homo appears prevalently caused by the presence in the former species of a considerable number of very active enzymes. 4. The sum of these data indicates the existence of noticeable intraspecific differences either in peptide-degrading enzymes present in plasma, or in plasma peptides, or in both.

Experience-dependent regulation of Leu-enkephalin hydrolysis in rat plasma

We examined experience-dependent alterations in the production of individual enkephalin metabolites during Leu-enkephalin hydrolysis in rat plasma in vitro. High performance liquid chromatography separation and electrochemical detection were used to quantify accumulation of the primary N-terminal products of enkephalin hydrolysis, Tyr and Tyr-Gly-Gly. Blood was sampled from rats through indwelling femoral artery catheters before, during, and after active avoidance training or appropriate control treatments. Avoidance training increased Tyr production, as did handling and exposing animals to the novel avoidance chamber without foot-shock training. On the other hand, Tyr-Gly-Gly production was elevated by blood sampling alone, by handling/novelty, and by training, but the effect of training was significantly greater than the effects of either of the other treatments. Interestingly, Tyr-Gly-Gly production was highly correlated (r = -0.885) with a measure of escape performance. Since the enzymes that participate in enkephalin hydrolysis act upon a number of peptides, regulation of enzyme activity may be one mechanism whereby an organism can modulate levels of circulating peptides in response to environmental experiences; this may contribute to the expression of appropriate behavioral responses to those environmental experiences.

Hydrolysis and binding of leucine enkephalin to lymphomic and erythroleukaemic cell lines

Hydrolysis and binding of labelled leucine enkephalin have been measured in the presence of cell lines of lymphoid and erythroid origin. The radioactive label was found to be associated to all lines studied. In the presence of these cells, enkephalin is rapidly hydrolyzed, forming three tyrosine-containing peptides: Tyr, Tyr-Gly and Tyr-Gly-Gly. Conversely, the presence of selective protease inhibitors reduces both enkephalin degradation and binding. Data obtained suggest the involvement in enkephalin hydrolysis of aminopeptidases, dypeptidylaminopeptidases and dypeptidylcarboxypeptidases. In addition, they suggest that the radioactive label associated to cells can be related to the peptides formed by the enzyme degradation of enkephalin and not to the intact pentapeptide.

Hydrolysis and protection from hydrolysis of enkephalins in human plasma

Seven groups of enkephalin-degrading enzymes and three groups of inhibitors active on these enzymes were separated from human plasma. The activity of the enzymes in hydrolyzing enkephalins and of the inhibitors in protecting enkephalins from proteolysis was measured. Results obtained with the endogenous inhibitors were compared to those relative to synthetic inhibitors. Data obtained indicate that all enkephalin-degrading enzymes found in plasma are significantly inhibited by the endogenous substances present in this tissue. The inhibition of the different classes of plasma enzymes by two of the three groups of endogenous substances is quite uniform, while one group of inhibitors appears specific to dipeptidylpeptidases. Results obtained are discussed in terms of the functional role of the inhibitory substances and of the possible pharmacological implication of their presence in human plasma.