Serum prolidase enzyme activity and its relation to histopathological findings in patients with non-alcoholic steatohepatitis

Chronic Liver Disease in Patients with Prolidase Deficiency: A Case Series

Introduction

Prolidase deficiency is a rare autosomal recessive disorder caused by variants in the PEPD gene. Patients usually have multi-organ involvement and a wide range of clinical features including recurrent skin ulcers, dysmorphic facial features, recurrent infections, intellectual disability, and splenomegaly. Studies have shown that patients with prolidase deficiency may have hepatic manifestations including hepatomegaly and abnormal liver enzymes. However, there is no detailed description of liver disease in this patient population.

Case Presentation

Here, we present 3 patients with prolidase deficiency with varying extents of hepatic involvement.

Conclusion

Prolidase deficiency patients with liver disease should be followed up long term to understand more about the pathophysiology and the impact of liver disease on long-term outcomes.

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.

Current Understanding of the Emerging Role of Prolidase in Cellular Metabolism

Prolidase [EC 3.4.13.9], known as PEPD, cleaves di- and tripeptides containing carboxyl-terminal proline or hydroxyproline. For decades, prolidase has been thoroughly investigated, and several mechanisms regulating its activity are known, including the activation of the β₁-integrin receptor, insulin-like growth factor 1 receptor (IGF-1) receptor, and transforming growth factor (TGF)-β₁ receptor. This process may result in increased availability of proline in the mitochondrial proline cycle, thus making proline serve as a substrate for the resynthesis of collagen, an intracellular signaling molecule. However, as a ligand, PEPD can bind directly to the epidermal growth factor receptor (EGFR, epidermal growth factor receptor 2 (HER2)) and regulate cellular metabolism. Recent reports have indicated that PEPD protects p53 from uncontrolled p53 subcellular activation and its translocation between cellular compartments. PEPD also participates in the maturation of the interferon α/β receptor by regulating its expression. In addition to the biological effects, prolidase demonstrates clinical significance reflected in the disease known as prolidase deficiency. It is also known that prolidase activity is affected in collagen metabolism disorders, metabolic, and oncological conditions. In this article, we review the latest knowledge about prolidase and highlight its biological function, and thus provide an in-depth understanding of prolidase as a dipeptidase and protein regulating the function of key biomolecules in cellular metabolism.

Serum prolidase level in patients with brucellosis and its possible relationship with pathogenesis of the disease: a prospective observational study

Background/aim

Changes in collagen metabolism and fibroblastic activity may play a role in the pathogenesis of brucellosis. The prolidase enzyme plays an important role in collagen synthesis. We aimed to investigate the association of prolidase levels with brucellosis.

Materials and methods

Serum prolidase levels in 20 patients newly diagnosed with brucellosis were compared with levels in 30 healthy control subjects. Patients with brucellosis were reassessed 3 months later for prolidase, other laboratory measurements, and response to treatment.

Results

The levels of serum prolidase were significantly higher in brucellosis patients compared with those of healthy controls. Prolidase, sedimentation, and C-reactive protein levels were significantly lower after antibrucellosis treatment than before treatment.

Conclusion

The current study is the first to demonstrate significantly increased serum prolidase levels in patients with brucellosis compared with healthy controls. Prolidase levels also significantly decreased with antibrucellosis treatment. This finding provides a new experimental basis to understand the pathogenesis of brucellosis in relation to collagen metabolism. The increase in serum prolidase levels might be related to several factors such as tissue destruction, increased fibroblastic activity, and granuloma formation, all of which are involved in the natural history of brucellosis.

Serum prolidase level in ankylosing spondylitis: low serum levels as a new potential gold standard biomarker for disease activity

Ankylosing spondylitis (AS) is a chronic inflammatory disorder that mainly affects the sacroiliac joints and axial skeleton. The aim of this study was to assess serum prolidase level (SPL) and its association with disease activity in patients with AS. This prospective study included 75 AS patients. Thirty age- and gender-matched healthy controls were enrolled. AS patients were considered as active if BASDAI score was ≥4 or inactive if BASDAI score was <4. There were 34 AS patients in the active group and 41 AS patients in the inactive group. Anti-TNF-monoclonal antibody treatment was started in patients in the active group. These active patients were reassessed 6 months later. BASDAI, ASDAS, visual analogue scale, short-form-general health survey questionnaire, C-reactive protein, erythrocyte sedimentation rate and SPL were measured in all AS patients before and after treatment. The SPL was significantly lower in inactive AS patients than in control group, and also, SPL was significantly lower in active AS patients than in inactive patients. All activity parameters were successful in separating active and inactive AS patients. However, the only parameter that could distinguish active patients from inactive patients was prolidase. The optimum cutoff point of SPL to identify patients with active AS was 23.13 ng/mL with sensitivity, specificity, positive predictive value and negative predictive value of 100 %. Serum prolidase level was successful in measuring disease activity and had as high sensitivity and specificity as BASDAI and was superior to other activity parameters.

The Value of Serum Prolidase Activity in Progression of Microalbuminuria in Patients With Type 2 Diabetes Mellitus

BACKGROUND

Prolidase is a cytosolic exopeptidase that plays a pivotal role in collagen turnover. Diabetic nephropathy (DN) is associated with structural changes in glomerular basement membrane accompanied with increased amounts of collagen. Prolidase is known to be abundant in kidney and collagen accumulation is increased in DN, so we aimed to determine the value of serum prolidase activity (SPA) in predicting the progression of nephropathy in type 2 diabetes mellitus (DM).

METHODS

Thirty type 2 DM patients having microalbuminuria (microalbuminuric group), 30 type 2 DM patients without albuminuria (normoalbuminuric group), and 28 healthy controls (control group) were enrolled. Study groups had similar age, sex distribution, and body mass index (BMI).

RESULTS

Metabolic parameters, SPA and urinary microalbumin were determined. SPA was significantly higher in microalbuminuric group when compared with normoalbuminuric and control groups (P = 0.05 and P < 0.001, respectively). Triglyceride levels were significantly higher and high density lipoprotein cholesterol (HDL-C) levels were significantly lower in microalbuminuric group compared to control group (Both P < 0.05). SPA showed a negative correlation with HDL-C level and a positive correlation with urinary albumin excretion (r = -0.219, P < 0.05 and r = 0.39, P < 0.001 respectively). In regression analysis, albumin excretion was the sole parameter influencing SPA.

CONCLUSION

SPA appears to be higher in type 2 DM patients having microalbuminuria compared to patients without microalbuminuria and healthy controls. The pathophysiological role and the significance of SPA in predicting DN need to be further evaluated.

Serum prolidase levels in Graves' disease without ophthalmopathy and its association with oxidative status

OBJECTIVE

The aim of this study was to evaluate serum prolidase levels and its association with oxidative stress in autoimmune thyroid disease (AITD).

MATERIALS AND METHODS

25 with Hashimoto thyroiditis (HT) and 25 patients Graves' disease (GD), and 27 healthy controls were enrolled in the study. The patients with signs of Graves' ophthalmopathy were excluded from the study. Serum samples were obtained in euthyroid period at the third month of treatment. Serum prolidase, total antioxidant status (TAS), total oxidative stress (TOS), and total free sulfhydryl (-SH) levels were measured.

RESULTS

Serum prolidase levels were significantly higher in the patients with GD compared to the HT and the healthy control group. Oxidative stress index (OSI) and TOS levels of the patients with both GD and HT were significantly higher compared to those of the control group (p < 0.001, for each), while -SH levels were significantly lower (p < 0.001, for each). There was no significant difference between the patients with HT and healthy control group in terms of prolidase levels (p = 0.580). Prolidase levels were positively correlated with TOS and OSI and negatively correlated with -SH (r = 0.565, p = 0.003; r = 0.604, p = 0.001; r = -0.532, p = 0.006).

CONCLUSION

Serum prolidase activity is increased in GD patients without signs of ophthalmopathy, and showed a positive correlation with oxidative stress parameters.

Assessment of the correlation between serum prolidase and alpha-fetoprotein levels in patients with hepatocellular carcinoma

AIM: To determine the predictive value of increased prolidase activity that reflects increased collagen turnover in patients with hepatocellular carcinoma (HCC).

METHODS: Sixty-eight patients with HCC (mean age of 69.1 ± 10.1), 31 cirrhosis patients (mean age of 59.3 ± 6.3) and 33 healthy volunteers (mean age of 51.4 ± 12.6) were enrolled in this study. Univariate and multivariate analysis were used to evaluate the association of serum α-fetoprotein (AFP) values with HCC clinicopathological features, such as tumor size, number and presence of vascular and macrovascular invasion. The patients with HCC were divided into groups according to tumor size, number and presence of vascular invasion (diameters; ≤ 3 cm, 3-5 cm and ≥ 5 cm, number; 1, 2 and ≥ 3, macrovascular invasion; yes/no). Barcelona-clinic liver cancer (BCLC) criteria were used to stage HCC patients. Serum samples for measurement of prolidase and alpha-fetoprotein levels were kept at -80 °C until use. Prolidase levels were measured spectrophotometrically and AFP concentrations were determined by a chemiluminescence immunometric commercial diagnostic assay.

RESULTS: In patients with HCC, prolidase and AFP values were evaluated according to tumor size, number, presence of macrovascular invasion and BCLC staging classification. Prolidase values were significantly higher in patients with HCC compared with controls (P < 0.001). Prolidase levels were significantly associated with tumor size and number (P < 0.001, P = 0.002, respectively). Prolidase levels also differed in patients in terms of BCLC staging classification (P < 0.001). Furthermore the prolidase levels in HCC patients showed a significant difference compared with patients with cirrhosis (P < 0.001). In HCC patients grouped according to tumor size, number and BCLC staging classification, AFP values differed separately (P = 0.032, P = 0.038, P = 0.015, respectively). In patients with HCC, there was a significant correlation (r = 0.616; P < 0.001) between prolidase and AFP values in terms of tumor size, number and BCLC staging classification, whereas the presence of macrovascular invasion did not show a positive association with serum prolidase and AFP levels.

CONCLUSION: Considering the levels of both serum prolidase and AFP could contribute to the early diagnosing of hepatocellular carcinoma.

Prolidase activity in chronic plaque psoriasis patients

INTRODUCTION

Psoriasis is a chronic, inflammatory, T-cell-mediated and hyperproliferative skin disease characterized by erythematous, squamous, sharply circumscribed and infiltrated plaques. The metabolisms of the collagen proteins undergo considerable changes due to the acceleration of their turnovers as a result of increased prolidase activity in psoriasis patients.

AIM

To determine the level of prolidase activity in psoriasis patients and evaluate its relationship with the oxidative system.

MATERIAL AND METHODS

The serum prolidase enzyme activity, total antioxidant levels and total oxidant levels of 40 psoriasis patients and a control group including 47 healthy individuals were analyzed by using their serum samples, and their oxidative stress indices were calculated.

RESULTS

The prolidase levels (p < 0.01), total oxidant levels (p < 0.01) and oxidative stress index levels (p < 0.001) of the patient group were higher than the corresponding parameters in the control group. The total antioxidant level was low (p < 0.01). Although a positive correlation was found between the prolidase and total antioxidant levels and the total oxidant level, no correlation was found between prolidase and the oxidative stress index.

CONCLUSIONS

It has been determined that the activity of the prolidase enzyme increases due to the increased collage turnover in psoriasis patients. Increased serum oxidant levels and oxidative stress indices values may play a role in the pathogenesis of psoriasis.

Progress in the search for circulating biomarkers of nonalcoholic fatty liver disease

CONTEXT

The definitive standard for the diagnosis of nonalcoholic fatty liver disease (NAFLD) is clinico-pathological correlation, but frequently the only laboratory abnormality is an elevation of serum aminotransferases.

OBJECTIVE

This has resulted in the search for more specific laboratory biomarkers.

METHODS

The literature was searched for novel plasma/serum markers of NAFLD.

RESULTS

Studies reviewed here included histologically-confirmed patients presenting some stage of NAFLD and monitored one or more novel serum/plasma biomarkers.

CONCLUSION

The most promising application of some of these novel biomarkers for the detection and quantification of NAFLD and particularly NASH appears to be in the combination of several into diagnostic panels.

Cordyceps cicadae induces G2/M cell cycle arrest in MHCC97H human hepatocellular carcinoma cells: a proteomic study

Background

Cordyceps cicadae is a medicinal fungus that is often used for treating cancer. However, the anticancer mechanisms of C. cicadae are largely unknown. This study aims to investigate the anticancer mechanisms of C. cicadae against hepatocellular carcinoma cells in vitro using a proteomic approach.

Methods

Human hepatocellular carcinoma MHCC97H cells were treated with a water extract of C. cicadae (0, 100, 250, 500, and 1000 μg/mL) for 48 h and harvested for cell viability assays. The significant differences in protein expression between control and C. cicadae-treated cells were analyzed by two-dimensional gel-based proteomics coupled with matrix-assisted laser desorption ionization-time of flight mass spectrometry. Flow cytometry analysis was employed to investigate the cell cycle and cell death. The anticancer molecular mechanism was analyzed by whole proteome mapping.

Results

The water extract of C. cicadae (0, 100, 250, 500, and 1000 μg/mL) inhibited the growth of MHCC97H cells in a dose-dependent manner via G2/M phase cell cycle arrest with no evidence of apoptosis. Among the identified proteins with upregulated expression were dynactin subunit 2, N-myc downstream-regulated gene 1, heat shock protein beta-1, alpha-enolase isoform 1, phosphatidylinositol transfer protein, and WD repeat-containing protein 1. Meanwhile, the proteins with downregulated expression were 14-3-3 gamma, BUB3, microtubule-associated protein RP/EB family member 1, thioredoxin-like protein, chloride intracellular channel protein 1, ectonucleoside triphosphate diphosphohydrolase 5, xaa-Pro dipeptidase, enoyl-CoA delta isomerase 1, protein-disulfide isomerase-related chaperone Erp29, hnRNP 2H9B, peroxiredoxin 1, WD-40 repeat protein, and serine/threonine kinase receptor-associated protein.

Conclusion

The water extract of C. cicadae reduced the growth of human hepatocellular carcinoma MHCC97H cells via G2/M cell cycle arrest.

Evaluation of the utility of serum prolidase as a marker for liver fibrosis

BACKGROUND

Liver dysfunction is common and often unrecognized. Liver biopsy is the gold standard in the assessment of liver fibrosis, but has disadvantages. We assessed the diagnostic accuracy of serum prolidase enzyme activity (SPA) in predicting the presence and degree of liver fibrosis, as compared with liver biopsy. Further, we evaluated the effect of hemolysis on measured SPA levels.

METHODS

We undertook a prospective case control study. Thirty eight outpatients without apparent liver illness and 20 patients with liver pathology scheduled to undergo liver biopsy had their SPA levels measured.

RESULTS

Patients undergoing liver biopsy had higher SPA levels (361 (268) IU/l [median (interquartile range)]) compared with controls (169 (160) (P < 0.001)). A SPA cutoff value of 200 IU/l yielded a sensitivity of 89%, specificity of 59%, an odds ratio of 11.5, negative predictive value of 92%, and a positive predictive value of 50%. Hemolysis causes an apparent increase in SPA levels.

CONCLUSION

Higher SPA levels in patients undergoing liver biopsies compared with controls may reflect the presence of liver fibrosis. SPA levels could not be used to stage the degree of fibrosis. SPA measurement may be useful in the diagnostic workup of suspected liver disease.

Serum prolidase activity, oxidant and antioxidant status in nonulcer dyspepsia and healthy volunteers

Helicobacter pylori (H. pylori) infection is associated with increased oxidative stress and serum prolidase activity (SPA) in many diseases. We aimed to observe SPA and oxidative stress in nonulcer dyspepsia (NUD) infected with and without H. pylori among eastern Indians. 106 patients with H. pylori positive NUD, 82 patients with H. pylori negative NUD, and 50 healthy individuals were selected. SPA, total antioxidant capacity (TAOC), and total oxidant status (TOS) were measured with the use of spectrophotometer and an automated measurement method. SPA, TOS, and oxidative stress index (OSI) were significantly higher in patients with H. pylori positive than H. pylori negative NUD and healthy individuals (all P < 0.0001), whereas TAOC was significantly lower (P < 0.0001). Nonsignificant, increased SPA (P value = 0.6083) and decreased TAOC (P value = 0.1186) were observed in patients with H. pylori negative NUD than healthy individuals, while increased TOS and OSI were significant (P < 0.0001). Weak, nonsignificant correlations were observed between serum prolidase activity and TAOC, TOS, and OSI in H. pylori positive cases. Thus, increased SPA along with increased oxidative stress was observed, which seem to be closely associated with H. pylori infection. SPA and oxidative stress seem to be used as biomarkers for H. pylori infection in NUD.

Serum prolidase activity in diabetic foot ulcers

Impaired wound healing is an important problem in diabetes mellitus; however, its pathogenesis remains unclear. We aimed to evaluate serum prolidase activity (SPA), an important marker of collagen turnover, in subjects with and without diabetic foot ulcers as compared with healthy controls. Twenty-seven patients with diabetic foot ulcers (foot ulcer group), 27 patients without diabetic foot ulcers (diabetic control group) and 27 healthy controls were enrolled. The study groups had similar age, sex distribution and body mass index. Metabolic and inflammatory parameters as well as SPA were determined. The diabetic foot ulcer group had significantly higher SPA (both p < 0.001) when compared with the diabetic and the healthy control groups. SPA showed a positive correlation with high-sensitive C-reactive protein and a negative correlation with high-density lipoprotein cholesterol levels (r = 0.313, p = 0.021 and r = -0.233, p = 0.036, respectively). No correlation was detected between SPA and glycaemic parameters. SPA appears to be higher in patients with diabetic foot ulcers when compared with patients without diabetic foot ulcers and healthy controls. The underlying mechanisms of elevated SPA and its clinical significance in predicting the natural course of wound healing in diabetic foot ulcers needs to be further evaluation.

Prolidase could act as a diagnosis and treatment mediator in lung fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic lung disease with unknown etiology and pathogenesis. With high mortality risks, most of the IPF cases emerged after a damage of alveolar epithelium, where this situation stimulates the over expression of matrix components. Inflammatory process observed as a reaction to emerged damage. Prolidase as an iminodipeptidase significantly increased during the development of fibrosis. The aim of this study is to measure prolidase activity as a marker of treatment and diagnosis in an experimental lung fibrosis animal model. Thirty male Wistar rats randomly divided into three experimental groups, with ten rats in each group. Group 1, control group; group 2, bleomycin (BLM)-induced lung fibrosis group, and group 3, BLM-induced lung fibrosis treated with palosuran (urotensin-II receptor antagonist). For histopathology, the middle lobes of right lungs were embedded in paraffin, followed by fixation in 10 % buffered formalin, and evaluation of IPF was performed using the Ashcroft scoring method. Prolidase activity was determined by a photometric method based on the measurement of proline levels produced by prolidase. The fibrosis scores and the prolidase activity were significantly enhanced by BLM stimulation. The BLM + palosuran treatment decreased prolidase activity in group 3. There was a positive correlation between prolidase activity and fibrosis scores. Palosuran seems to be effective in the treatment of lung fibrosis, and prolidase activity can be used for the diagnosis and/or for management of the treatment. However, further clinical and experimental studies with animals and/or patients are needed to verify these conclusions.

Prolidase and oxidative stress in chronic hepatitis C

BACKGROUND

Hepatitis C infection represents a common healthcare issue worldwide. The present trial was designed to investigate the role of prolidase, an enzyme that is significantly involved in the biosynthesis of collagen, and of the oxidative stress that is considered to be involved in the pathogenesis of various diseases, in the chronic hepatitis C infection. The trial was performed to assess the serum prolidase enzyme level and the oxidative-antioxidative status and to determine the relation between the serum prolidase activity and the oxidative stress parameters.

METHODS

A total of 95 individuals, including 55 patients with chronic hepatitis C infection (CHC) and 40 healthy adults, were enrolled in the trial. The values for prolidase, the total antioxidant status (TAS), the total oxidative stress (TOS), the oxidative stress index (OSI), sulfhydryl (SH), lipid peroxidation LOOH, catalase (CAT), and ceruloplasmin were measured and compared between the patient groups.

RESULTS

The prolidase, TOS, LOOH, CAT, and the OSI values were higher in the chronic hepatitis C group compared to the control group (P < 0.001). The TAS, SH, and ceruloplasmin levels were lower in the CHC group relative to the control group (P < 0.001).

CONCLUSION

We suppose that the values of prolidase and the oxidative stress are increased while the antioxidant levels are decreased in CHC. As a result, prolidase and the oxidative stress seem to be related with the progression of the disease.

Metabolomic analysis of the toxic effect of chronic low-dose exposure to acephate on rats using ultra-performance liquid chromatography/mass spectrometry

To study the toxic effect of chronic exposure to acephate at low-dose levels, a metabolomics approach based on ultra-performance liquid chromatography/mass spectrometry (UPLC-MS) was applied. Three different doses of 0.5 mg/kg/day, 1.5 mg/kg/day, and 4.5 mg/kg/day acephate were administered to Wistar rats for 24 weeks. Endogenous metabolite profiles were obtained with UPLC-MS for all rats at six time points after treatment. Some metabolites like dimethylthiophosphate and uric acid in urine were detected at week 4. Dimethylthiophosphate, which had the most significant elevations compared with other biomarkers, was considered as an early, sensitive biomarker of exposure to acephate. Moreover, there were some endogenous metabolite changes, which demonstrated that the doses of 1.5 mg/kg/day and 4.5 mg/kg/day of acephate led to renal injury and perturbed the normal metabolic processes of rats, including glucose, nucleic acid, and protein metabolism. A connection between exposure to acephate and the metabolic disturbance has been found and interpreted. Our study indicates that the metabolomics approach based on UPLC-MS of urine provides more information on toxicity than the conventional toxicological evaluation methods in measuring changes and can be considered as a promising technique for the study of the toxic effect of acephate.

Improved prolidase activity assay allowed enzyme kinetic characterization and faster prolidase deficiency diagnosis

BACKGROUND

Prolidase is a metallo-exopeptidase hydrolyzing X-Pro and X-Hyp dipeptides. Its absence or reduced level is typical in prolidase deficiency (PD) patients, and altered prolidase activity was reported in various diseases. Therefore, standardized and accurate measurement of prolidase activity is essential for PD diagnosis, as well as to elucidate the pathophysiology of other disorders.

METHODS

Human recombinant prolidase was used to optimize a spectrophotometric enzyme activity assay. Kinetic parameters and Mn(2+) affinity were evaluated. The method was validated on blood and fibroblasts from PD patients.

RESULTS

An activation step consisting in prolidase incubation with 1 mmol/l MnCl(2) and 0.75 mmol/l reduced glutathione at 50°C for 20 min was necessary to obtain the maximum activity and to accurately determine, for the recombinant enzyme, V(max) (489 U/mg), K(m) (5.4 mM) and Mn(2+) affinity (54 mM(-1)). The method applied to PD diagnosis revealed an intra-assay CV=8% for blood and 9% for fibroblasts lysates. The inter-assay CV was 21% for blood and 20% for cell lysates.

CONCLUSION

We optimized a faster spectrophotometric method to measure the activity when the enzyme is fully activated, this is crucial to allow a reliable evaluation of prolidase activity from different sources.