A prolidase deficiency in man with iminopeptiduria

Quantitative analysis of the natural history of prolidase deficiency: description of 17 families and systematic review of published cases

PURPOSE

Prolidase deficiency is a rare inborn error of metabolism causing ulcers and other skin disorders, splenomegaly, developmental delay, and recurrent infections. Most of the literature is constituted of isolated case reports. We aim to provide a quantitative description of the natural history of the condition by describing 19 affected individuals and reviewing the literature.

METHODS

Nineteen patients were phenotyped per local institutional procedures. A systematic review following PRISMA criteria identified 132 articles describing 161 patients. Main outcome analyses were performed for manifestation frequency, diagnostic delay, overall survival, symptom-free survival, and ulcer-free survival.

RESULTS

Our cohort presented a wide variability of severity. Autoimmune disorders were found in 6/19, including Crohn disease, systemic lupus erythematosus, and arthritis. Another immune finding was hemophagocytic lymphohistiocytosis (HLH). Half of published patients were symptomatic by age 4 and had a delayed diagnosis (mean delay 11.6 years). Ulcers were present initially in only 30% of cases, with a median age of onset at 12 years old.

CONCLUSION

Prolidase deficiency has a broad range of manifestations. Symptoms at onset may be nonspecific, likely contributing to the diagnostic delay. Testing for this disorder should be considered in any child with unexplained autoimmunity, lower extremity ulcers, splenomegaly, or HLH.

PROLIDASE: A Review from Discovery to its Role in Health and Disease

Prolidase (peptidase D), encoded by the PEPD gene, is a ubiquitously expressed cytosolic metalloproteinase, the only enzyme capable of cleaving imidodipeptides containing C-terminal proline or hydroxyproline. Prolidase catalyzes the rate-limiting step during collagen recycling and is essential in protein metabolism, collagen turnover, and matrix remodeling. Prolidase, therefore plays a crucial role in several physiological processes such as wound healing, inflammation, angiogenesis, cell proliferation, and carcinogenesis. Accordingly, mutations leading to loss of prolidase catalytic activity result in prolidase deficiency a rare autosomal recessive metabolic disorder characterized by defective wound healing. In addition, alterations in prolidase enzyme activity have been documented in numerous pathological conditions, making prolidase a useful biochemical marker to measure disease severity. Furthermore, recent studies underscore the importance of a non-enzymatic role of prolidase in cell regulation and infectious disease. This review aims to provide comprehensive information on prolidase, from its discovery to its role in health and disease, while addressing the current knowledge gaps.

A targeted metabolomic procedure for amino acid analysis in different biological specimens by ultra-high-performance liquid chromatography-tandem mass spectrometry

INTRODUCTION

Amino acid analysis in biological fluids is essential for the study of inborn errors of metabolism (IEM) and other diseases.

OBJECTIVES

Our aim was to develop a UPLC-MS/MS procedure for the analysis of 25 amino acids and identification of 17 related compounds.

METHODS

Sample treatment conditions were optimized for plasma, urine, cerebrospinal fluid (CSF) and dried blood spots. Amino acids and related compounds were analyzed on a Waters ACQUITY UPLC H-class instrument with a reversed-phase C-18 column using water and acetonitrile with 0.1% formic acid as the mobile phases (run time = 9 min). The detection was performed with a Waters Xevo TQD triple-quadrupole mass spectrometer using positive electrospray ionization in the multiple reaction monitoring mode.

RESULTS

The method linearity, intra-assay and inter-assay precision, detection limit, quantification limit and trueness analysis displayed adequate results in both physiological and pathological conditions. Method comparison was performed between UPLC-MS/MS and ion exchange chromatography (IEC) with ninhydrin derivatization, and the methods showed good agreement, except for 4-hydroxyproline, aspartate and citrulline. Paediatrics age-related reference values in plasma, urine and CSF were established and patients with different IEM were easily identified.

CONCLUSION

We report a modified UPLC-MS/MS procedure for the analysis of 42 amino acids and related compounds in different specimens. The method is fast, sensitive and robust, and it has been validated to be an alternative to the traditional IEC procedure as the routine method used in metabolic laboratories. The method greatly decreases the run time of the analysis while displaying good metrological results.

Prolidase is a critical enzyme for complete gliadin digestion in Tenebrio molitor larvae

Prolidase is a proline-specific metallopeptidase that cleaves imidodipeptides with C-terminal Pro residue. Prolidase was purified and characterized from the Tenebrio molitor larval midgut. The enzyme was localized in the soluble fraction of posterior midgut tissues, corresponding to a predicted cytoplasmic localization of prolidase according to the structure of the mRNA transcript. Expression of genes encoding prolidase and the major digestive proline-specific peptidase (PSP)-dipeptidyl peptidase 4-were similar. The pH optimum of T. molitor prolidase was 7.5, and the enzyme was inhibited by Z-Pro, indicating that it belongs to type I prolidases. In mammals, prolidase is particularly important in the catabolism of a proline-rich protein-collagen. We propose that T. molitor larval prolidase is a critical enzyme for the final stages of digestion of dietary proline-rich gliadins, providing hydrolysis of imidodipeptides in the cytoplasm of midgut epithelial cells. We propose that the products of hydrolysis are absorbed from the luminal contents by peptide transporters, which we have annotated in the T. molitor larval gut transcriptome. The origin of prolidase substrates in the insect midgut is discussed in the context of overall success of grain feeding insects.

Spurious Elevation of Multiple Urine Amino Acids by Ion-Exchange Chromatography in Patients with Prolidase Deficiency

The enzyme prolidase cleaves dipeptides where the C-terminal amino acid corresponds to proline or hydroxyproline. As a consequence, a deficiency of this enzyme leads to accumulation of these dipeptides, which correspondingly are found to be elevated in urine. In fact, the absence of dipeptiduria is sufficient to rule out a diagnosis of prolidase deficiency. However, given the fact that these dipeptides elute at the same position as more common amino acids, the analyzer's software will instead call an elevation of these corresponding amino acids. Thus, an elevation of glycylproline, aspartylproline, glutamylproline, threonylproline and serylproline, valylproline, leucylproline, isoleucylproline, alanylproline, phenylalanylproline, and lysylproline will instead be interpreted as an elevation of leucine, citrulline, methionine, isoleucine, beta-aminoisobutyric acid, gamma-aminobutyric acid, ethanolamine, tyrosine, histidine, and anserine/carnosine, respectively. This particular profile of elevated amino acids, however, can easily be overlooked. We hope that the recognition of this characteristic pattern of falsely elevated urinary amino acids will aid in the recognition of prolidase deficiency.

Prolidase is required for early trafficking events during influenza A virus entry

Influenza A virus (IAV) entry is a multistep process that requires the interaction of the virus with numerous host factors. In this study, we demonstrate that prolidase (PEPD) is a cellular factor required by IAV for successful entry into target cells. PEPD was selected as a candidate during an entry screen performed on nonvalidated primary hits from previously published genome-wide small interfering RNA (siRNA) screens. siRNA-mediated depletion of PEPD resulted in the decreased growth of IAV during mono- and multicycle growth. This growth defect was independent of cell type or virus strain. Furthermore, IAV restriction was apparent as early as 3 h postinfection, and experiments in the absence of protein biosynthesis revealed that the nuclear import of viral ribonucleoprotein complexes (vRNPs) was already blocked in the absence of PEPD. These results led us to investigate which step during entry was affected. Receptor expression, IAV attachment, or IAV internalization was not dependent on the presence of PEPD. However, when looking at the distribution of incoming IAV particles in PEPD-knockdown cells, we found a localization pattern that differed from that in control cells: IAV mostly localized to the cell periphery, and consequently, viral particles displayed reduced colocalization with early and late endosome markers and fusion between viral and endosomal membranes was strongly reduced. Finally, experiments using a competitive inhibitor of PEPD catalytic activity suggested that the enzymatic function of the dipeptidase is required for its proviral effect on IAV entry. In sum, this study establishes PEPD as a novel entry factor required for early endosomal trafficking of IAV.

IMPORTANCE

Influenza A virus (IAV) continues to be a constant threat to public health. As IAV relies on its host cell for replication, the identification of host factors required by the virus is of importance. First, such studies often reveal novel functions of cellular factors and can extend our knowledge of cellular processes. Second, we can further our understanding of processes that are required for the entry of IAV into target cells. Third, the identification of host factors that contribute to IAV entry will increase the number of potential targets for the development of novel antiviral drugs that are of urgent need. Our study identifies prolidase (PEPD) to be a novel entry factor required by IAV for correct routing within the endosomal compartment following virus internalization. Thereby, we link PEPD, which has been shown to play a role during collagen recycling and growth factor signaling, to early events of viral infection.

Prolidase deficiency breaks tolerance to lupus-associated antigens

AIM

Prolidase deficiency is a rare autosomal recessive disease in which one of the last steps of collagen metabolism, cleavage of proline-containing dipeptides, is impaired. Only about 93 patients have been reported with about 10% also having systemic lupus erythematosus (SLE).

METHODS

We studied a large extended Amish pedigree with four prolidase deficiency patients and three heterozygous individuals for lupus-associated autoimmunity. Eight unaffected Amish children served as normal controls. Prolidase genetics and enzyme activity were confirmed. Antinuclear antibodies (ANA) were determined using indirect immunofluorescence and antibodies against extractable nuclear antigens were determined by various methods, including double immunodiffusion, immunoprecipitation and multiplex bead assay. Serum C1q levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Two of the four homozygous prolidase deficiency subjects had a positive ANA. One had anti-double-stranded DNA, while another had precipitating anti-Ro. By the simultaneous microbead assay, three of the four had anti-Sm and anti-chromatin. One of the three heterozygous subjects had a positive ANA and immunoprecipitation of a 75 000 molecular weight protein. The unaffected controls had normal prolidase activity and were negative for autoantibodies.

CONCLUSIONS

Prolidase deficiency may be associated with the loss of immune tolerance to lupus-associated autoantigens even without clinical SLE.

Obesity, genetics and the skin

The increasing problem of obesity in childhood is recognized as both a short-term and long-term serious public-health concern. Excess body weight may contribute to psychological morbidity; cancers; metabolic, cardiovascular and musculoskeletal disorders; and dermatological conditions. There is increasing recognition of the role of genetic factors in the aetiology of obesity. Although in the vast majority of cases these influences are polygenic, some obese children suffer from monogenic disorders, which may present with obesity alone. However, more often than not, they generally display other syndromic features. Some of these syndromes have a clear cutaneous phenotype, and these conditions will be the focus of this review.

Prolidase activity dysregulation and its correlation with oxidative-antioxidative status in chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is a consequence of an underlying chronic inflammatory disorder of the airways that is usually progressive and causes dysregulation in the metabolism of collagen. Prolidase has an important role in the recycling of proline for collagen synthesis and cell growth.

OBJECTIVE

We measured and compared prolidase activity in healthy individuals with COPD patients to find out that whether its activity might reflect disturbances of collagen metabolism in the patients. We also investigated oxidative-antioxidative status and its relationship with prolidase activity in this disease.

METHODS

Thirty voluntary patients with COPD and 30 healthy control subjects with similar age range and sex were included into the study. Plasma prolidase activities, total antioxidant capacity (TAC) and lipid peroxidation (LPO) levels were measured in the patient and control groups.

RESULTS

Plasma prolidase activity and TAC levels were significantly lower, and LPO levels were significantly higher in the patients than those in the control subjects (P<0.05, P<0.001, and P<0.001, respectively). Significant correlations were detected between plasma prolidase activity and TAC and LPO levels in the patients group (r=0.679, P<0.001; r=-426, P<0.05, respectively).

CONCLUSIONS

The results suggest that oxidative-antioxidative balance and collagen turnover are altered by the development of COPD in human lungs, and prolidase activity may reflect disturbances of collagen metabolism in this pulmonary disease. Monitoring of plasma prolidase activity and oxidative-antioxidative balance may be useful in evaluating fibrotic processes and oxidative damage in the chronic inflammatory lung disease in human.

Prolidase deficiency: it looks like systemic lupus erythematosus but it is not

Three siblings with recalcitrant leg ulceration, splenomegaly, photosensitive rash, and autoantibodies were suspected of having prolidase deficiency. Urine was checked for iminodipeptiduria, fibroblasts were cultured and analyzed for prolidase activity, and DNA was extracted for identifying the causative mutation. Glycyl proline was found as the dominant dipeptide in the urine. The activity of proline dipeptidase in fibroblasts was 2.5% of control fibroblasts. Sequence analysis of the PEPD gene revealed a homozygous nonsense C-->G transition at nucleotide 768. In conclusion, prolidase deficiency was diagnosed in siblings with skin ulceration autoantibodies and a lupus-like disease. A novel nonsense mutation was found, associated with the severe outcome of our patients.

Activity of prolidase isoenzymes in the rat brain: subcellular and regional distribution during development

Prolidase deficiency is characterized by chronic ulcerative dermatitis, mental retardation, and frequent infections. In the present study we examined the characteristics of rat brain prolidase isoenzymes. Prolidase isoenzymes (PD I and PD II) were isolated from the rat brain using DEAE cellulose column chromatography. PD I showed higher activity against seryl-proline and alanyl-proline, while PD II was particularly active against methionyl-proline. Prolidase activity in the whole brain and in the different brain regions showed higher activity against methionyl-proline and seryl-proline. PD II activity was highest in the hippocampus, followed by the cerebellum, cerebral cortex, caudatum, and the midbrain. The most rapid changes in the activities of PD I and PD II occurred perinatally, with a peak at three days before birth and a nadir at two days after birth, which then gradually increased until 21 days. N-benzyloxycarbonyl-l-proline inhibited PD I activity against various substrates in a dose-dependent manner. In contrast, there was no inhibition of PD II activity against methionyl-proline at low concentrations. In summary, these data suggest that maintenance of levels of proline, other amino acids and peptides containing proline in the rat brain is regulated by prolidase isoenzymes. The age-related alterations in PD I and PD II also may help to elucidate the fundation of prolidase isoenzymes in brain nervous system.

Characterization of prolidase I and II purified from normal human erythrocytes: comparison with prolidase in erythrocytes from a patient with prolidase deficiency

The effect of various sulfur-containing amino acids on the activities of prolidase isoenzymes I and II isolated from erythrocytes of healthy individuals, and erythrocyte lysates from a patient with prolidase deficiency was investigated. The activity of prolidase I against glycylproline was strongly enhanced by D: -methionine. L: -Methionine and D: ,L: -methionine slightly enhanced the activity at low concentration, but N-acetyl-L: -methionine had no effect. D: -Ethionine, L: -ethionine, and D: ,L: -ethionine also enhanced the activity of prolidase I. D: ,L: -Homocysteine enhanced the activity at low concentration, but inhibited the activity at 50 mM: . The activity of prolidase II against methionylproline was enhanced by D: -methionine, D: ,L: -methionine, and L: -methionine, but N-acetyl-L: -methionine had no effect. D: -Ethionine and D: ,L: -ethionine strongly enhanced the activity of prolidase II compared with L: -ethionine; D: ,L: -homocysteine weakly enhanced the activity. D: ,L: -Homocysteine-thiolactone inhibited the activities of prolidase I and II in a concentration-dependent manner. The effect of various sulfur-containing amino acids on prolidase activity against methionylproline in erythrocyte lysates from a patient with prolidase deficiency was almost the same as that on prolidase II. The kinetics of the activities of prolidase I, II, and patient prolidase were also studied. Their K (m) values were changed by adding sulfur-containing amino acids, but V (max) values were unchanged.

Prolidase isoenzymes in the rat: their organ distribution, developmental change and specific inhibitors

Lack of prolidase I (PD I) leads to prolidase deficiency, a disease characterized by intractable skin lesions, recurrent respiratory infections, and mental retardation. The present study was undertaken to characterize and determine the physiologic roles of different prolidase isoenzymes. Two isoforms of prolidase were isolated from rat kidney. PD I showed higher activity against seryl-proline and alanyl-proline, whereas PD II was active especially against methionyl-proline. PD I was highly concentrated in the small intestine and kidney, whereas PD II was shown not to vary in the organs examined. Expression of PD I and PD II in the small intestine were maximal within 1 wk of birth, and then rapidly declined. The changes of prolidase in the kidney and heart were found to differ slightly. N-benzyloxycarbonyl-l-proline and captopril inhibited PD I dose-dependently, but showed no inhibition of PD II at low concentrations. NiCl2 inhibited PD II much more effectively than PD I. Our findings suggest that PD I functions by way of an intestinal peptide carrier, which may also be regulated by the uptake of various iminodipeptides. Similarly, age-related alterations of prolidase isoenzymes suggest that intestinal PD II also participates in absorption of proline and other amino acids early in life.

Different effects of sulfur amino acids on prolidase and prolinase activity in normal and prolidase-deficient human erythrocytes

BACKGROUND

Prolidase and prolinase activity is known to be enhanced significantly in some diseases. Recently, the effect of amino acids on prolidase and prolinase activity in normal and prolidase-deficient human erythrocytes was investigated. It was reported that both enzymes were enhanced by glycine and alanine in the presence of MnCl(2).

METHODS

Erythrocytes were isolated from heparinized blood from normal human and a patient with prolidase deficiency. Effects of various sulfur amino acids on prolidase and prolinase activities against iminodipeptides in the presence of 1 or 0.1 mmol/l MnCl(2) were investigated.

RESULTS

Prolinase activity against prolylglycine in normal and prolidase-deficient erythrocyte lysates was inhibited by L-methionine, NAc-L-methionine and D,L-methionine in a concentration-dependent manner, but D-methionine enhanced the activity in low concentrations (0-20 mmol/l). D,L-Homocysteine inhibited the activity more strongly than other sulfur amino acids tested in a concentration-dependent manner. On the other hand, prolidase activity against glycylproline was enhanced by L-methionine, D-methionine, D,L-methionine, D,L-homocysteine thiolactone and D,L-ethionine. The rates of enhancement by these sulfur amino acids were in the following order: D,L-ethionine>D,L-methionine, D-methionine, D,L-homocysteine thiolactone>L-methionine (10 mmol/l).

CONCLUSION

The prolinase activity in normal and prolidase-deficient erythrocyte lysates was inhibited by L-methionine, D,L-ethionine and D,L-homocysteine. On the other hand, prolidase activity in their erythrocyte lysates was enhanced by D,L-ethionine, D-methionine and L-methionine. These results indicate the effects of these sulfur amino acids on prolidase and prolinase activities were different.

A nonsense mutation of PEPD in four Amish children with prolidase deficiency

Encoded by the peptidase D (PEPD) gene located at 19q12-q13.11, prolidase is a ubiquitous cytosolic enzyme that catalyzes hydrolysis of oligopeptides with a C-terminal proline or hydroxyproline. We describe here four Amish children with a severe phenotype of prolidase deficiency in the Geauga settlements of Ohio as the first report of prolidase deficiency in the Amish population as well as in the United States. The patients presented with infection, hepatosplenomegaly, or thrombocytopenia, in contrast to most cases previously reported in the literature, presenting with skin ulcers. All four patients had typical facial features, classic skin ulcers, and multisystem involvement. Recurrent infections, asthma-like chronic reactive airway disease, hyperimmunoglobulins, hepatosplenomegaly with mildly elevated aspartate transaminase (AST), anemia, and thrombocytopenia were common and massive imidodipeptiduria was universal. Prolidase activity in our patients is nearly undetectable. Direct sequencing of PCR-amplified genomic DNA for all of the exons from the four patients revealed the same homozygous single nucleotide mutation c.793 T > C in exon 11, resulting in a premature stop-codon at amino acid residue 265 (p.R265X). It is speculated that the severe phenotype in these patients might be associated with the type of the PEPD gene mutation.

The role of emerging techniques in the investigation of prolidase deficiency: From diagnosis to the development of a possible therapeutical approach

The aim of the present article is to review the efforts performed in the past two decades by numerous research groups for the development of methods that allow a correct diagnosis of prolidase deficiency (PD), a rare autosomal recessive disorder and for the rationalization of a possible therapeutic intervention on these patients. In particular, the interest of the reader is focused on the application of capillary electrophoresis (i) for the detection of biological markers that reflect the pathological feature of the disease and (ii) for the determination of the efficiency of a carrier system in delivering prolidase inside cells in a possible therapy based on enzyme replacement.

Characterization of prolidase activity in erythrocytes from a patient with prolidase deficiency: Comparison with prolidase I and II purified from normal human erythrocytes

OBJECTIVES

The purpose of this study was to investigate the effect of various amino acids and their metabolites on the activities of prolidase I and II from human erythrocytes compared to those in a patient with prolidase deficiency.

DESIGN AND METHODS

Prolidase I and II from human erythrocytes were purified by using column chromatography. Prolidase activity against various iminodipeptides was determined by spectrophotometry using Chinard's method.

RESULTS

The activities of prolidase I and II against glycylproline and methionylproline were enhanced by glycine, L- and D-isoforms of alanine and serine and D-isoforms of valine, leucine and isoleucine. L-isoforms of branched amino acids inhibited the activity of prolidase I. On the other hand, the activity of prolidase II was enhanced by all of these L-branched amino acids. The patient's prolidase activity was also enhanced by all the L- and D-branched amino acids.

CONCLUSION

The activities of prolidase I and II against various iminodipeptides were prominently enhanced by glycine, but the effect of L-valine differed between the two enzymes. Enzymatic properties of the patient's prolidase were essentially the same as those of prolidase II.

Effects of amino acids and its metabolites on prolidase activity against various iminodipeptides in erythrocytes from normal human and a patient with prolidase deficiency

BACKGROUND

The characteristics of prolidase in erythrocytes from controls and patient with prolidase deficiency were investigated.

METHODS

The erythrocytes were isolated from the heparinized blood of normal human and a patient with prolidase deficiency. Effects of various amino acids and their metabolites on prolidase activity against iminodipeptides in presence of 1 mmol/l MnCl(2) were investigated.

RESULTS

Prolidase activity against glycylproline in erythrocytes from normal human was strongly enhanced by glycine, L-alanine, L-serine with MnCl(2), but the activity was strongly inhibited by L-valine, and L-leucine. However, the stereoisomers, D-leucine and D-valine enhanced the activity. The prolidase activity against methionylproline in erythrocytes from the patient with prolidase deficiency was also enhanced by glycine, L-alanine and L-serine. The activity was inhibited by l-leucine, but D-leucine and L-valine enhanced the activity against various iminodipeptides.

CONCLUSION

Prolidase activity against glycylproline in normal human erythrocytes and against methionylproline from the prolidase-deficient patient was enhanced strongly by glycine, alanine and serine with MnCl(2). However, this activity was inhibited by L-leucine, but was enhanced by D-leucine.

Determination of prolidase activity using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Proline-containing peptides of the X-proline type are cleaved by the dipeptidase prolidase. The classical method of prolidase assay relied on the colorimetric estimation of the liberated proline with ninhydrin using acidic media and heat. This method, however, gave inconsistent results due to the nonspecificity of the ninhydrin color reaction. We report here a method for the detection of the liberated proline using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Human sera were incubated with a mixture containing the dipeptide glycyl-proline in Tris-HCl supplemented with manganese at 37 degrees C for 24h. The samples were precipitated with trifluoroacetic acid and centrifuged. An aliquot of the supernatant was mixed with an equal volume of ferulic acid solution. An aliquot from this mixture was spotted on a stainless steel mass spectrometry grid and analyzed using MALDI-TOF mass spectrometry. The activity of the enzyme was determined by the complete disappearance of the glycyl-proline peak with the concomitant appearance of the proline peak and can be expressed in terms of the ratio of the area beneath the proline to the area beneath the glycyl-proline peak. Subjects homozygous for prolidase deficiency had a ratio ranging from 0.006 to 0.04 while obligatory heterozygotes had a ratio ranging from around 1.1 to 2.4. Normal subjects had ratios ranging from 9 to 239. Using this method we have unambiguously identified subjects with homozygous or heterozygous prolidase deficiency. In addition to the advantage of rapid sample preparation time, this method is highly specific, reproducible, and sensitive.

Characteristics of prolinase against various iminodipeptides in erythrocyte lysates from a normal human and a patient with prolidase deficiency

The effect of various amino acids and MnCl

The kinetics of prolinase activity in the erythrocytes from both the normal individual and the prolidase-deficient patient were also studied. Their K

Characteristics of Prolidase from the Erythrocytes of Normal Humans and Patients with Prolidase Deficiency and Their Mother

Prolidases I and II were highly purified from human erythrocytes. The effects of various amino acids, MnCl2 and mercaptoethanol, on these two enzymes were investigated. Normal prolidase II was very labile in the absence of MnCl2 or mercaptoethanol. The activity of prolidase II was maintained at about 76% by pre-incubation with MnCl2; it was then activated up to 140% by treatment with mercaptoethanol for 60 minutes at 37 degrees C. Normal prolidases I and II showed the highest activity against glycylproline or methionylproline in the presence of MnCl2. The activity of prolidase I against glycylproline was enhanced strongly by glycine and MnCl2, but not activated in the absence of MnCl2. The activity of prolidase II against methionylproline was enhanced three-fold in the presence of glycine and MnCl2, but its activity against glycylproline was very low even in the presence of MnCl2. A stronger enhancement of this activity was found in normal erythrocytes, and a lower level of this activity was found in erythrocytes of patients treated with glycine, MnCl2 and mercaptoethanol compared to those treated with glycine and MnCl2. The activity of prolidase II against methionylproline in all erythrocytes, of normal humans and of patients, was strongly activated by the addition of glycine with MnCl2 but suppressed by the addition of mercaptoethanol.

Corticosteroid treatment of prolidase deficiency skin lesions by inhibiting iminodipeptide-primed neutrophil superoxide generation

We studied the pathogenetic role of iminodipeptides, and the effects of corticosteroids on the skin lesions of two adult female siblings with prolidase deficiency. The elder sister had had severe skin ulcers and mental retardation since childhood, while the younger sister had shown milder clinical manifestations since late adolescence. The ulcers showed vascular wall thickening and neutrophil infiltration. Oral prednisolone at moderate doses was not effective, but corticosteroid pulse therapy followed by a moderate dose of prednisolone improved the preulcerative indurated lesions and ulcers. A 2-year follow-up of the younger patient indicated that N-formyl methionyl leucyl phenylalanine-induced neutrophil superoxide generation was elevated, in parallel with an increase in the serum iminodipeptide level, when the skin ulcers and preulcerative indurated lesions were most active. Corticosteroid pulse therapy downregulated the superoxide generation by neutrophils. The serum iminodipeptide level, however, did not decrease during 25 days after pulse therapy. These findings suggest that iminodipeptides may play an important part in aggravating the skin lesions by priming neutrophil superoxide generation, and that high-dose corticosteroids improve the skin lesions, probably by inhibiting the infiltration, and superoxide generation by, neutrophils. Neutrophil superoxide generation was more prominent in the elder sister, suggesting that clinical severity may depend on the response of neutrophils to the iminodipeptides. Chronic stimulation by superoxide may cause thickening of cerebral blood vessels and eventual mental retardation.

The effects of serum iminodipeptides and prednisolone on superoxide generation and tyrosyl phosphorylation of proteins in neutrophils from a patient with prolidase deficiency

The aim of this study was to examine the effects of serum iminodipeptides and prednisolone on superoxide generation and tyrosyl phosphorylation of proteins in neutrophils from a patient with prolidase deficiency, and also to find the causative effects of superoxide on inflammatory skin lesions. When the neutrophils from a patient with prolidase deficiency (PDPPMN) were preincubated with prolyl-proline (Pro-Pro), which is one of the iminodipeptides found at high concentration in the serum of patients with prolidase deficiency, the N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced superoxide generation was enhanced in a concentration-dependent manner, although the extent of enhancing effect was lower than that in neutrophils from healthy humans (HPPMN). Pro-Pro also enhanced superoxide generation induced by opsonized zymosan (OZ) in PDPPMN but not that induced by arachidonic acid or phorbol 12-myristate 13-acetate. Herbimycin A and genistein decreased the fMLP- and OZ-induced superoxide generations after priming by Pro-Pro. 1-(5-isoquinoline-sulfonyl)-2-methyl-piperazine (H-7) and staurosporine did not decrease, but rather enhanced, the superoxide generation in a low concentration range. When PDPPMN were prepared, tyrosyl phosphorylation of 45 kDa protein in PDPPMN had already occurred. The phosphorylation was scarcely increased by incubation of the cells with Pro-Pro, in contrast to that in HPPMN. Genistein decreased the phosphorylation of 45 kDa protein in both PDPPMN and HPPMN. These results suggest that the priming effect of iminodipeptides on superoxide generation in PDPPMN is coupled with phosphorylation of 45 kDa protein by protein tyrosine kinase. Protein tyrosine kinase may play a critical role(s) in the regulatory mechanism of priming by iminodipeptides and activation of NADPH oxidase in the patient's neutrophils. In prolidase deficiency, the characteristic skin manifestations are inflammatory indurations and chronic leg ulcers. Prednisolone improves the ulcers, and this compound decreased the fMLP- and OZ-induced superoxide generation and tyrosyl phosphorylation of 45 kDa protein in the patient's neutrophils after priming by Pro-Pro. When inflammatory skin lesions were present, the levels of iminodipeptides in the patient's serum were elevated and the superoxide generation by neutrophils was up-regulated. When skin lesions were healing or absent, the levels of iminodipeptides in the patient's serum and superoxide generation by neutrophils were higher than those of healthy controls but lower than those in the inflammatory stages. Thus, the enhancement of superoxide generation by neutrophils via serum iminodipeptides would be one of the inducers of inflammatory skin lesions. Corticosteroid administration might be a therapeutic modality of choice for skin lesions.

Direct monitoring of prolidase activity in cultured skin fibroblasts using capillary electrophoresis

Capillary electrophoresis (CE) was used as an alternative to current analysis schemes for detecting prolidase activity in erythrocytes and skin fibroblast cultures because of its unique selectivity and high resolving power. Kinetic measurement of peptide bond hydrolysis was performed using porcine kidney prolidase on different substrates (Gly-Pro, Leu-Pro and Ala-Pro) and by following the disappearance of the peptide-substrate's peak. The K(m) values obtained were in agreement with those previously reported. Interestingly, in the case of Phe-Pro as the substrate, simultaneous analysis of the product and parent peptide was possible, thus showing the superiority of the capillary electrophoresis (CE) assay with respect to the standard spectrophotometric method. The application of the CE technique to the characterization of prolidase activity in control and prolidase-deficient skin cultured fibroblasts was successful. Enzyme activity was easily calculated in all controls tested and the K(m) values determined were slightly lower than those obtained with the colorimetric reaction, thus confirming our assumption that the CE assay shows higher specificity than the ninhydrin technique. Our results demonstrate the feasibility of using CE as a simple and reliable technique for determining prolidase activity.

Measurement of iminodipeptides in the serum of patients with prolidase deficiency using liquid chromatography-mass spectrometry

Iminodipeptides containing C-terminal proline or hydroxyproline were determined in sera from patients with prolidase deficiency, in their mother's serum, and in the sera of unrelated controls, using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. The separation was carried out on a reversed phase column using 1 g/l aqueous trifluoroacetic acid-methanol (75 + 25, by vol.). The quasi-molecular ions ([M + H])+ of various iminodipeptides containing C-terminal proline and hydroxyproline were observed in the sera of patients with prolidase deficiency, using selected ion monitoring. The quasi-molecular ions ([M + H])+ of iminodipeptides containing C-terminal proline were not observed in the sera of normal subjects or the patients' mother, but the latter did contain various iminodipeptides with C-terminal hydroxyproline. This method proved useful for the determination of iminodipeptides in the sera of patients with prolidase deficiency.

Prolidase deficiency: a multisystemic hereditary disorder

Prolidase deficiency is a rare hereditary disorder with a wide spectrum of clinical manifestations including skin ulcers, eczematous eruptions, characteristic facies, mental retardation, splenomegaly, and susceptibility to infections. We report two new cases of prolidase deficiency. Our patients had the typical manifestations of prolidase deficiency. One also had lupus erythematosus. Prolidase activity was either normal or half-normal in all family members. The skin disease in our patients did not respond to topical glycine/proline ointment or to oral vitamin C.

Liquid chromatography-mass spectrometry for simultaneous analyses of iminodipeptides containing an N-terminal or a C-terminal proline

Simultaneous analyses of synthetic iminodipeptides containing an N-terminal proline or a C-terminal proline have been demonstrated using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. The separation of iminodipeptides was carried out on a reversed-phase high-performance liquid chromatographic column using 0.1% aqueous trifluoroacetic acid-methanol (75:25, v/v, pH 2.0) as mobile phase. Very intense protonated molecular ions [M + H]+ of various synthetic iminodipeptides, Pro-Gly, Gly-Pro, Pro-Ala, Ala-Pro, Pro-Val, Val-Pro, Pro-Leu and Leu-Pro, were observed. Pro-Gly (Pro-X) and Gly-Pro (X-Pro) have the same protonated molecular ion (m/z 173), but the peaks of these compounds on the mass chromatograms were clearly distinguished by the differences of the retention times and mass spectra. The synthetic iminodipeptides containing an N-terminal proline added to urine samples from a patient with prolidase deficiency were also distinguished from iminodipeptides containing a C-terminal proline in urine samples from a patient with prolidase deficiency by scanning the [M + H]+ ion of each iminodipeptide. We established the method to measure simultaneously the various iminodipeptides containing an N-terminal or a C-terminal proline in biological samples.

Liquid chromatography-mass spectrometry for the qualitative analyses of iminodipeptides in the urine of patients with prolidase deficiency

Analyses of standard iminodipeptides and iminodipeptides in the urine of patients with prolidase deficiency have been demonstrated using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system. The separation was carried out on a reversed-phase column using 0.1% aqueous trifluoroacetic acid-methanol (70:30 or 80:20). Very intense quasi-molecular ions [( M + H]+) of various standard iminodipeptides were observed by this method. The quasi-molecular ions [M + H]+ of various iminodipeptides were also observed in the urine samples of patients with prolidase deficiency, and Gly-Pro, Ala-Pro, Val-Pro, Leu-Pro, Ile-Pro, Ser-Pro, Thr-Pro, Glu-Pro, Asp-Pro, His-Pro, Lys-Pro, Pro-Pro and Tyr-Pro as iminodipeptides containing proline with C-terminal residue and Glu-Hyp, Pro-Hyp, Ile-Hyp and Gly-Hyp as iminodipeptides containing hydroxyproline with C-terminal residue were identified in the urine of patients with prolidase deficiency.

Characterization of prolidase I and II from erythrocytes of a control, a patient with prolidase deficiency and her mother

Prolidase I (EC 3.4.13.9) was purified to homogeneity from the erythrocytes of a normal human (control) and the patient's mother, and prolidase II from erythrocytes of a control and the patient's mother, and prolidase from the patient's erythrocytes was also highly purified. The various properties of the patient's prolidase were compared to those of prolidase from a control and the patient's mother. Prolidase I from a control and the patient's mother had a molecular weight of about 112,000, and was composed of two subunits with an identical molecular weight of 56,000. The Km values for Gly-Pro of the control's and the patient's mother's prolidase I were 2.90 +/- 0.22 and 2.88 +/- 0.27 mM, but the Vmax values for Gly-Pro of the mother's enzyme was reduced about 30% compared to that of control enzymes (mother: 6.02 units/mg protein, control: 22.21 units/mg protein). Isoionic points of these enzymes by chromatofocusing were pH 4.6 approximately 4.7. Prolidase II from the control and the patient's mother, and the patient's prolidase had a molecular weight of about 185,000, and was composed of two subunits with an identical molecular weight of 95,000. The Km and Vmax values for various substrates of prolidase II from a control and the patient's mother, and the patient's prolidase were almost the same.

Biochemical basis of prolidase deficiency. Polypeptide and RNA phenotypes and the relation to clinical phenotypes

Cultured skin fibroblasts or lymphoblastoid cells from eight patients with clinical symptoms of prolidase deficiency were analyzed in terms of enzyme activity, presence of material crossreacting with specific antibodies, biosynthesis of the polypeptide, and mRNA corresponding to the enzyme. There are at least two enzymes that hydrolyze imidodipeptides in these cells and these two enzymes could be separated by an immunochemical procedure. The specific assay for prolidase showed that the enzyme activity was virtually absent in six cell strains and was markedly reduced in two (less than 3% of controls). The activities of the labile enzyme that did not immunoprecipitate with the anti-prolidase antibody were decreased in the cells (30-60% of controls). Cell strains with residual activities of prolidase had immunological polypeptides crossreacting with a Mr 56,000, similar to findings in the normal enzyme. The polypeptide biosynthesis in these cells and the controls was similar. Northern blot analyses revealed the presence of mRNA in the polypeptide-positive cells, yet it was absent in the polypeptide-negative cells. The substrate specificities analyzed in the partially purified enzymes from the polypeptide-positive cell strains differed, presumably due to different mutations. Thus, there seems to be a molecular heterogeneity in prolidase deficiency. There was no apparent relation between the clinical symptoms and the biochemical phenotypes, except that mental retardation was present in the polypeptide-negative patients. The activities of the labile enzyme may not be a major factor in modifying the clinical symptoms.

Prolidase deficiency: a case report and literature review

We describe a patient in whom chronic leg ulceration was due to prolidase deficiency. The clinical features of this condition are described and we discuss the metabolic abnormality and the treatment regimes which have been employed. We also report the further finding of erosive cystitis, which we consider should be added to the list of clinical features of prolidase deficiency.

Biochemical studies on prolidase in sera from control, patients with prolidase deficiency and their mother

Prolidase activity in serum from normal subjects and the mother of two patients was readily detected without adding Mn2+ to the assay, and the activity was increased by addition of Mn2+ to the assay or preincubation with Mn2+. However, the activity in serum from patients with prolidase deficiency against gly-pro, leu-pro and val-pro could not be detected irrespective of Mn2+ conditions and activity against met-pro, ala-pro and phe-pro also showed a marked reduction compared to controls. Both normal and the patients' mother's prolidase activity against gly-pro was reduced about 20% at 60 degrees C compared to the activity at 37 degrees C, but the addition of Mn2+ at 55 degrees C increased the activity about 1.8-fold, whereas prolidase activity of patients could not be increased by the addition of Mn2+. The addition of Co2+ increased prolidase activity in serum from control and the patients' mother but did not increase the heat stability. These results indicate that prolidase in serum from patients with prolidase deficiency is altered rather than markedly reduced in amount.

Prolidase deficiency: a patient without hydroxyproline-containing iminodipeptides in urine

A 17-year-old girl was shown to have prolidase deficiency on the basis of the presence of large amounts of proline-containing dipeptides in urine and an almost complete absence of prolidase in plasma and erythrocytes. Unlike most earlier cases of this genetic defect our patient did not excrete hydroxyproline-containing dipeptides in her urine.

Intestinal hydrolysis of aspartylphenylalanine--the metabolic product of aspartame

Aspartame [Nutrasweet, Equal (Searle Consumer Products, Chicago, Ill.)] is the methyl ester of the dipeptide aspartylphenylalanine (Asp-Phe). After hydrolysis of the ester bond in the intestinal lumen, the dipeptide is apparently absorbed and digested in the same manner as dipeptides derived from protein digestion. We observed that Asp-Phe is hydrolyzed approximately equally well by three previously reported brush border dipeptidases. However, these enzymes have very low affinity for Asp-Phe, and a substantial amount of the dipeptide may be transported intact and hydrolyzed in the cytosol. Starch gel electrophoresis and ion-exchange chromatography of the cytosol of intestinal mucosa and of red blood cell lysate revealed only one peak with Asp-Phe hydrolase activity. This activity was distinct from the seven cytosolic peptidases that have been described previously. The reduction in Asp-Phe hydrolase activity in the brush border and cytosol of diseased intestinal mucosa was similar to the reduction in levels of other brush border and cytosol enzyme activities. If double-blind studies confirm that some people have symptoms caused by aspartame ingestion, it would be appropriate to test such individuals for deficiency of cytosolic Asp-Phe hydrolase activity.