The relationship between proline and hydroxyproline urinary excretion in human as an index of collagen catabolism

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.

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.

Optimum conditions of autoclaving for hydrolysis of proteins and urinary peptides of prolyl and hydroxyprolyl residues and HPLC analysis

A method for urinary peptide(s) and protein hydrolysis, involving autoclaving at 15psi (121 degrees C) for 60min, is described. Using three candidate proteins (bovine serum albumin, casein and gelatin) and urine specimens, the effect of autoclaving with respect to the optimum time required for hydrolysis under both acidic (6N HCl) and alkaline (6N KOH) conditions was studied. Recoveries of total amino acids from proteins and urine hydrolysate(s) suggest that complete hydrolysis of proteins and urinary peptides could be achieved by autoclaving for 30-60min instead of 16h of incubation at 110 degrees C. Further, stability of some of the individual amino acids was also studied. The observed differential stability of amino acids under acidic and alkaline conditions, as demonstrated in this study by HPLC analysis, makes it imperative to choose the appropriate hydrolytic condition while studying the composition of any given amino acids in urinary peptide(s)/protein hydrolysates. Further, the finding that both Pro and Hyp were stable under alkaline conditions of hydrolysis by autoclaving renders this method suitable for assaying these two amino acids from urine hydrolysates, hence its utility in the study of urinary peptide derived Hyp and Pro in bone/cartilage disorders.

Micellar electrokinetic chromatography of hydroxyproline and other secondary amino acids in biological samples with laser-induced fluorescence detection

Micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) was used for the rapid and sensitive detection of hydroxyproline in serum and hydrolyzed urine that were pre-column derivatized with 9-fluorenylmethyl chloroformate (FMOC). The application of the combined o-phthalaldehyde (OPA)/FMOC derivatization in MEKC for the selective detection of secondary amino acids in biological samples is investigated.

Selective and sensitive determination of urinary total proline and hydroxyproline by gas chromatography with flame photometric detection

A selective and sensitive method for the determination of total urinary proline (Pro) and hydroxyproline (Hyp) by gas chromatography (GC) was developed. After acid hydrolysis of urine, primary amino compounds were eliminated by reaction with o-phthaldialdehyde. Subsequently, Pro and Hyp were converted into their N-dimethylthiophosphoryl methyl ester derivatives and then determined by GC with flame photometric detection using a DB-5 capillary column. The derivatives were volatile and stable, giving single and symmetrical peaks. The detection limits for Pro and Hyp were 0.1 and 0.2 pmol injected, respectively. 3,4-Dehydroproline was used as an internal standard. The calibration curves for Pro and Hyp in the range 0.4-10 nmol were linear and sufficiently reproducible for quantitative determination. Overall recoveries of Pro and Hyp added to urine samples ranged from 93% to 103%. By using this method, Pro and Hyp in a small urine sample could be accurately and precisely determined without any influence from other constituent substances.

Toxicological effects of an organophosphorus pesticide (dimethoate) on urinary collagen metabolites in normal and high protein diets fed female albino rats

The effect of an organophosphorus pesticide (dimethoate) on the urinary excretion of hydroxyproline (total, nondialysable, dialysable and free fractions) and hydroxylysylglycosides, glucosylgalactosyl hydroxylysine and galactosehydroxylysine was investigated in two groups of female albino rats fed with normal and high protein diets. In comparison to controls, dimethoate treated animals were found to excrete significantly decreased amounts of urinary hydroxyproline fractions from 7th day onwards. The excretion of total hydroxylysylglycoside in urine parallels the excretion of hydroxyproline. The urinary output of both glu-gal-hyl and gal-hyl was also appreciably lower from dimethoate treated animals. The normal ratio of glu-gal-hyl and gal-hyl found in the urine of dimethoate treated animals was discussed in light of decreased turn over of collagen in both bone and skin. The effect of dimethoate in rats fed with high protein diet was comparatively less than those fed with normal diet.

Selective determination of hydroxyproline in urine by high-performance liquid chromatography using precolumn derivatization

A method to measure total hydroxyproline in human urine was developed. Primary amino acids were derivatized with ortho-phthaldialdehyde, followed by derivatization of imino acids with 9-fluorenylmethyl chloroformate. The fluorescent 9-fluorenylmethyl chloroformate derivatives were separated by reversed phase high-performance liquid chromatography. 3,4-Dehydroproline was used as internal standard. Calibration curves for hydroxyproline and internal standard were linear from 1 to 200 pmol injected. Both within- and between-run precision were below 3.2%. Analytical recovery of hydroxyproline added to urine samples was 99.2 +/- 2.6%. Values for excreted hydroxyproline were determined by analysis of urine samples from adult volunteers. The hydroxyproline/creatinine ratio was found to be 15.8 +/- 4.6 mmol/mol (range 7.0-27.3) with no significant sex-related difference.

Identification and quantification of 5-hydroxypipecolic acid and hydroxyproline in mammalian brain and blood by selected ion monitoring

A method for the analysis of 5-hydroxypipecolic acid and 4-hydroxyproline in mammalian brain and blood is reported. The identification and quantification of the two hydroxyimino acids were accomplished with gas chromatography/mass spectrometry including a selected ion-monitoring technique following HPLC prepurification. The lower limit of detection for the method is 2 to 10 pmol. The amounts of 5-hydroxypipecolic acid and 4-hydroxyproline in blood were 20 to 30 pmol/ml and 3 to 6 nmol/ml, respectively. Their concentrations in the rabbit whole brain were determined to be 5 and 120 pmol/g, respectively.

Parathyroid hormone, calcitonin and vitamin D metabolites in beta-thalassaemia major

Serum calcium (Ca), phosphorus (P), alkaline phosphatase (Al-P), parathyroid hormone (PTH), calcitonin (CT), 25-hydroxyvitamin D3 (25OHD3), 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) levels and urinary excretion of Ca, P, hydroxyproline (OH-P) and cyclic AMP (cAMP) were determined in summer and in winter in 13 thalassaemic children (7 aged 3-5 years-group 1-; and 6 aged 10-13 years-group 2-), who had never taken vitamin D supplements or therapy, and in two groups of 14 controls of the same age. In thalassaemics of group 1 only serum Al-P levels and OH-P urinary excretion were higher than in controls (P less than 0.01). In thalassaemics of group 2 Ca (P less than 0.05), P (P less than 0.05), PTH (P less than 0.001), CT (P less than 0.001), 25OHD3 (P less than 0.05), 1,25(OH)2D3 (P less than 0.001) levels and cAMP urinary excretion (P less than 0.001) were lower, whereas Al-P (P less than 0.001) and CT (P less than 0.001) levels and urinary excretion of P (P less than 0.05) and of OH-P (P less than 0.001) were higher than in controls, both in summer and in winter. Advancing age induces in thalassaemic patients a decrease in PTH secretion and a consequent deficit in synthesis of 1,25(OH)2D3 that may explain some aspects of bone changes, which CT hypersecretion may tend to counteract.

Clinical and biochemical characteristics of prolidase deficiency in siblings

Two brothers with recurrent skin ulcers of the lower limbs, subnormal intelligence, developmental abnormalities, and poliosis were found to excrete large quantities of several imidodipeptides in their urine. Glycylproline was the most prominent imidodipeptide excreted and was also detected in their blood. Prolidase activity was markedly deficient in red blood cells from both patients (4.1% and 3.7% of control mean) and skin fibroblasts from the one brother so examined (3.7% of control mean). A total of 20 patients with prolidase deficiency, including the two in this report, have been described in the literature. Their manifestations and various attempts at treatment are reviewed.

Prolidase and prolidase deficiency

Prolidase deficiency seems to be a rather rare metabolic disorder. However, many new cases can be detected because screening is easy to perform and enzymatic confirmation allows the differentiation from other iminodipeptidurias . Clinical symptoms are briefly reviewed, while biological considerations and prolidase properties are exhaustively described. Methods for investigating urinary iminodipeptides are given with results. Moreover, several collagen modifications observed in this disorder led us to formulate a hypothesis for their mechanism. Genetic considerations and treatment attempts are discussed.

Optimal conditions for prolidase assay by proline colorimetric determination: application to iminodipeptiduria

Prolidase assay was reinvestigated by determining proline, using Chinard's method. Although several authors had previously tested this colorimetric reaction, accurate details regarding enzyme activity were not available. The need for greater sensitivity led to the introduction of several modifications: dialysis was eliminated and the substrate concentration and incubation time were changed. In addition, the reaction mixture was preincubated with Mn2+ for 24 h in order to triple prolidase activity. Color development followed at 90 degrees C, because of partial glycylproline hydrolysis at higher temperatures. The effect of several divalent cations on prolidase activity were tested with and without Mn2+. This modified assay was applied to erythrocytes, plasma and skin fibroblasts from a female patient with iminodipeptiduria.

Normal hydroxylation of proline in collagen synthesized by skin fibroblasts from a patient with prolidase deficiency

The extent of hydroxylation of proline in collagen synthesized and secreted into the culture medium by skin fibroblasts derived from a patient with prolidase deficiency has been examined and found to be normal. It would seem likely that to a considerable extent the urinary proline-containing dipeptides apparent in this condition are derived from sources other than collagen.

tuberous sclerosis: hydroxyproline content in urine and tissues

To elucidate the nature of an overabundance of collagen seen on microscopic examination in tuberous sclerous (TS), the hydroxyproline content in tissues and urine was determined. TS tissues of 5 patients were obtained on necropsy or plastic surgery. Urine was collected from 10 patients with TS and 19 controls. Tumors in kidney, pancreas, lung and heart but not brain contained more hydroxyproline than the surrounding tissues. In brain with the lowest hydroxyproline content, the tumor showed reduced hydroxyproline compared to normal. Collagen sheet in TS skin and shagreen patch showed the same hydroxyproline content as control skin. Th urinary hydroxyproline: creatinine ratios of the patients with TS were all higher than those in age-matched controls with or without anticonvulsant treatment except for congenital muscular dystrophy. The higher content of hydroxyproline in several affected tissues and urine of patients with TS might indicate that an increase in collagen synthesis occurs in TS.

Automated analysis of hydroxyproline with elimination of non-specific reacting substances

A modified urinary hydroxyproline method is presented which utilizes an automated technique, Technicon instrumentation and Ehrlich's reagent. Acid hydrolysates are neutralized automatically. Non-specific reacting substances are determined simultaneously with each sample and subtracted as a blank. This method has been found to be superior to the use of charcoal-resin as an absorbent. After blank correction, the mean hydroxyproline excretion of normal and osteoporotic patients are similar. In all groups studied, including Paget's disease, the blanks reresent a significant fraction of total reacting substances and show wide variation between samples. Multiple samples from patients over a two year period show little variation in hydroxyproline excretion when corrected for non-specific reacting substances.

Parathyroid hormone and calcitonin levels in vitamin D deficient rickets

In six infants aged between 5 and 8 months with vitamin D deficient rickets, we have studied blood levels of calcium (Ca), phosphorus (P), alkaline phosphatase, immunoreactive parathyroid hormone (PTH) and calcitonin (CT), as well as urinary excretion of Ca, P, hydroxyproline and cyclic AMP, both under basal conditions and during a 4h infusion of 20 mg/kg 10% Ca gluconate in normal saline. Under basal conditions all the infants had high alkaline phosphatase (range: 470--770 U.I./1); PTH (range: 620--1200 pg Eq/ml) and CT (range: 440--750 pg/ml) but two infants had hypocalcaemia and four had normocalcaemia and hypophosphataemia. The urinary Ca excretion was low whereas the urinary P, hydroxyproline and cyclic AMP excretions were high. During Ca infusion the total serum Ca and CT levels increased, while alkaline phosphatase and PTH fell. After the end of the infusion, CT levels fell perceptibly; phosphaturia, hydroxyprolinuria and cyclic AMP decreased on the day of the infusion.

Parathyroid hormone and calcitonin secretion in uraemic infants

In six infants aged between 4 and 8 months with chronic renal failure, we have studied blood levels of calcium (Ca), phosphorus (P), alkaline phosphatase, immunoreactive parathyroid hormone (PTH), and calcitonin (CT), as well as urinary excretion of Ca, P, hydroxyproline and cyclic AMP under basal conditions and during an infusion of 20 mg/kg of 10% Ca gluconate in normal saline over 4 h. Under basal conditions four infants had normal serum Ca and P values, alkaline phosphatase levels at the upper limit of normal, and very high PTH (range: 1450--2550 pg Eq/ml) and CT (range: 700--1900 pg/ml) levels. The urinary Ca excretion was low, whereas the urinary excretion of P, hydroxyproline and cyclic AMP was high. During Ca infusion, the total serum Ca and CT levels increased, PTH fell without however reaching the normal upper limit, and urinary P and cyclic AMP excretion decreased. In two infants with osteodystrophy and the highest levels of PTH (2900 and 3500 pg Eq/ml respectively) there was no suppression of PTH during Ca infusion.

Gas chromatographic determination of hydroxyproline in urine hydrolysates

A simple and specific method for the determination of hydroxyproline in urine hydrolysates has been described. Hydroxyproline was converted into its N-isobutyloxycarbonyl methyl ester derivative without elaborate cleanup, which was analyzed by gas chromatography. Hydroxyproline was clearly separated from other urinary constituents on a 0.60% FFAP on dimethyldichlorosilane-treated Gas-Chrom P column. Kainic acid was used as the most convenient internal standard available. The relative standard deviations of peak height ratios were 1.15--2.51% at the 10--150 microgram levels. Percent recoveries of hydroxyproline added to urine hydrolysates ranged from 98.8 to 107.3%.

Prolidase deficiency: report of a second case with quantitation of the excessively excreted amino acids

The second documented case of prolidase deficiency is presented. Clinical manifestations include chronic otitis media and sinusitis, dermatitis, and splenomegaly. Prolidase is undetectable in the white blood cells of the patient and near or less than the lower range of normal in each parent. The peptide chromatographic pattern of the urine is similar to that of the previously reported patient with prolidase deficiency. The quantity of amino acids excreted in urine per 24 hours is at least three times that of the upper range of normal (of these same amino acids) for the patients age group. More than 80% of the total amino acids excreted are in peptide form. The proline-to-hydroxyproline ratio suggests that the dipeptides are the catabolic products of other proteins in addition to collagen.

Total hydroxyproline in urine of 4 to 6 year-old children--an investigation on its relationship to growth and nutrition

We analysed over a period of 30-32 days the daily total hydroxyproline and creatinine excretine in urine from 9 healthy, normally fed 4 to 6 year-old children (2 girls, 7 boys). The average urinary hydroxyproline excretion was 45.6 mg/24 hr, with a coefficient of variation of 25.6%. Urinary hydroxyproline for individual children showed distinct differences from day to day, which were independent of urine volume. There were significant differences between the mean values for urine hydroxyproline in individual children, which were independent of age. The average creatinine in urine was 346/24 hr with a coefficient of variation of 17.7%. The hydroxyproline-index did not define the nutritional state of these normally developed children on a normal diet. Dietary hydroxyproline contributed 7.4% to the total urinary hydroxyproline in our investigation. There was a close correlation between urine hydroxyproline excretion and growth velocity in each child.