Urinary hydroxyproline peptides

Study on the Mechanism of the Blood-Glucose-Lowering Effect of Collagen Peptides from Sturgeon By-Products

In a previous study, we found that the collagen peptides prepared from the by-products of Bester sturgeon had an inhibitory effect on elevated blood glucose levels in a glucose tolerance test with ICR mice. In the present study, we examine the mechanism of the effect of sturgeon collagen peptides (SCPs) in detail. When glucose was orally administered to mice along with the SCPs, it was found that the glucose remained in the stomach for a longer time. In the above tests, the amount of glucose excreted in the feces of mice also increased. On the contrary, it was revealed that the SCPs have a dipeptidyl-peptidase-IV (DPP-IV) inhibitory ability in an in vitro test. In subsequent oral and intravenous glucose administration tests, glucagon-like peptide-1 (GLP-1) and insulin levels in the blood of mice were maintained at high levels. These results suggested the following three mechanisms: SCPs slow the rate of transportation of glucose from the stomach into the small intestine, resulting in delayed glucose absorption; SCPs suppress the absorption of glucose in the small intestine and excrete it from the body; SCPs inhibit DPP-IV in the blood and maintain a high GLP-1 level in blood, which in turn stimulates insulin secretion.

Oral Supplementation of Collagen Peptides Improves Skin Hydration by Increasing the Natural Moisturizing Factor Content in the Stratum Corneum: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial

INTRODUCTION

We aimed to investigate the effect of orally ingested collagen peptides (CPs) on skin condition and elucidate their mechanism of action.

METHODS

A randomized, placebo-controlled, double-blind trial was conducted in 99 healthy Japanese women, aged 35-50 years. The subjects were randomized into 3 groups (33 subjects/group) to receive 1 or 5 g of CP or placebo once daily for 12 weeks. Skin water content, transepidermal water loss (TEWL), skin elasticity, and skin thickness were evaluated before treatment and after 4, 8, and 12 weeks of treatment. The level of natural moisturizing factor (NMF) constituents in the stratum corneum (SC) was quantified before treatment and after 12 weeks of treatment.

RESULTS

Oral ingestion of CP increased the water content in the SC and epidermis and decreased TEWL. Furthermore, the NMF level in the SC was increased. However, skin elasticity and skin thickness remained unchanged.

CONCLUSIONS

The improvement in skin water content following the oral ingestion of CP can be attributed to an increase in the level of NMF in the SC.

TRIAL REGISTRATION

UMIN000030375 (retrospectively registered).

Effects of Collagen Hydrolysates on Human Brain Structure and Cognitive Function: A Pilot Clinical Study

This study investigated the effects of collagen hydrolysates (CH) on language cognitive function and brain structure. In this open-label study, 5 g CH was administered once a day for 4 weeks to 30 healthy participants aged 49-63 years. The primary outcome measures were the brain healthcare quotients based on gray matter volume (GM-BHQ) and fractional anisotropy (FA-BHQ). The secondary outcome measures were changes in scores between week 0 and week 4 for word list memory (WLM) and standard verbal paired associate learning (S-PA) tests as well as changes in the physical, mental, and role/social component summary scores of the Short Form-36(SF-36) quality of life instrument. CH ingestion resulted in significant improvements in FA-BHQ (p = 0.0095), a measure of brain structure, as well in scores for the WLM (p = 0.0046) and S-PA (p = 0.0007) tests, which measure cognitive function. There were moderate correlations between the change in WLM score and the change in GM-BHQ (r = 0.4448; Spearman's rank correlation) and between the change in S-PA score and the change in FA-BHQ (r = 0.4645). Daily ingestion of CH changed brain structure and improved language cognitive function.

Effects of administration of glucosamine and chicken cartilage hydrolysate on rheumatoid arthritis in SKG mice

Supplementation with cartilage constituents, such as glucosamine, chondroitin sulfate and collagen peptide, are believed to reduce pain associated with joint disorders, such as rheumatoid arthritis (RA). Here, we administered daily, 10 mg glucosamine or 100 mg chicken cartilage hydrolysate (CH) to SKG/Jcl mice, a model for spontaneous RA, for 5 weeks and evaluated their effects on RA development. In SKG mice, the administration of glucosamine had no reducing effect on RA score but suppressed the expression of Mmp13 and Col3a1 genes in articular cartilage. In contrast, administration of CH suppressed the RA score and levels of plasma interleukin-6 and interleukin-17 to half, although the differences were not significant. Mice administered with glucosamine also showed decreased bone strength of femur and these adverse effects could be eliminated when glucosamine was used in conjunction with CH. These results suggest that CH and glucosamine exert effects on different aspects in SKG mice.

Improved in Vivo Tracking of Orally Administered Collagen Hydrolysate Using Stable Isotope Labeling and LC-MS Techniques

Collagen-derived hydroxyproline (Hyp)-containing oligopeptides, known to have various physiological functions, are detected in blood at markedly higher concentrations after oral ingestion of collagen hydrolysate. Monitoring the absorption and metabolism of the bioactive peptides is essential to investigate the beneficial effects of collagen hydrolysate. We previously developed an internal standard mixture by sequential protease digestion of stable isotope-labeled collagen, which enabled highly accurate quantitation of collagen-derived oligopeptides by liquid chromatography-mass spectrometry (LC-MS). However, the use of proteases caused a profound imbalance in the generated peptides. Here, we employed partial acid hydrolysis to achieve more efficient and balanced peptide generation. Various stable isotope-labeled oligopeptides were detected after 0.5 h acid hydrolysis, and marked enhancement of peptide generation compared with the previous enzymatic method was observed, especially for Hyp-Gly (27.8 ± 0.6 ng/μg vs 0.231 ± 0.02 ng/μg). The acid hydrolysate was then heated to generate labeled cyclic dipeptides. Using the novel internal standard mixture in LC-MS, we were able to simultaneously quantitate 23 collagen-derived oligopeptides in human plasma and urine after oral administration of collagen hydrolysate.

Orally Available Collagen Tripeptide: Enzymatic Stability, Intestinal Permeability, and Absorption of Gly-Pro-Hyp and Pro-Hyp

Collagen-derived small peptides, such as Gly-Pro-Hyp (GPH) and Pro-Hyp (PH), play a role in various physiological functions. Although collagen degrades in the gastrointestinal tract randomly and easily, it is not readily cleaved into bioactive peptides. To increase the bioavailability of bioactive peptides, a collagen tripeptide (CTP) was prepared from fish scales by the digestion method using collagenase from nonpathogenic Bacillus bacteria. It was demonstrated that Hyp-containing peptides-GPH and PH-were better absorbed and reached higher plasma levels after the oral administration of CTPs in rats compared to high molecular weight collagen peptide (H-CP). GPH and PH were stable in gastrointestinal fluid and rat plasma for 2 h, and GPH was able to be transported across the intestinal cell monolayer. These results suggest that the ingestion of CTP is an efficient method for taking bioactive peptides orally due to the enzymatic stability and intestinal permeability of GPH and PH.

Ingestion of bioactive collagen hydrolysates enhance facial skin moisture and elasticity and reduce facial ageing signs in a randomised double-blind placebo-controlled clinical study

BACKGROUND

Several human studies have demonstrated occurrence of two major collagen peptides, prolyl-hydroxyproline (Pro-Hyp) and hydroxyprolyl-glycine (Hyp-Gly), in human peripheral blood. Some in vitro studies have demonstrated that Pro-Hyp and Hyp-Gly exert chemotaxis on dermal fibroblasts and enhance cell proliferation. Additionally, Pro-Hyp enhances the production of hyaluronic acid by dermal fibroblasts. These findings suggest that the amounts of Pro-Hyp and Hyp-Gly in blood are important factors to show the efficacy of collagen hydrolysates on skin health.

RESULTS

We conducted a randomised double-blind placebo-controlled clinical trial of ingestion of two types of collagen hydrolysates, which are composed of different amounts of the bioactive dipeptides Pro-Hyp and Hyp-Gly, to investigate their effects on the improvement of skin conditions. Improvement in skin conditions, such as skin moisture, elasticity, wrinkles, and roughness, were compared with a placebo group at baseline, and 4 and 8 weeks after the start of the trial. In addition, the safety of dietary supplementation with these peptides was evaluated by blood test. Collagen hydrolysate with a higher content of bioactive collagen peptides (H-CP) showed significant and more improvement than the collagen hydrolysate with a lower content of bioactive collagen peptides (L-CP) and the placebo, in facial skin moisture, elasticity (R2), wrinkles and roughness, compared with the placebo group. In addition, there were no adverse events during the trial.

CONCLUSION

This study demonstrated that the use of the collagen hydrolysate with a higher content of Pro-Hyp and Hyp-Gly led to more improvement in facial skin conditions, including facial skin moisture, elasticity, wrinkles and roughness. © 2016 Society of Chemical Industry.

Distribution of prolylhydroxyproline and its metabolites after oral administration in rats

Prolylhydroxyproline (Pro-Hyp), which is derived from collagen hydrolysate, has been shown to be beneficial for skin and joint health. However, little is known about the distribution of Pro-Hyp in these tissues. In the present study, we investigated the biodistribution of orally administered [(14)C]Pro-Hyp in rats. Whole-body autoradiography at 30 min after administration of [(14)C]Pro-Hyp showed that radioactivity is widely distributed in tissues including skin and articular cartilage, with the highest level of radioactivity observed in the gastric and intestinal walls. Incorporation of radioactivity into cells known to respond to Pro-Hyp such as dermal fibroblasts, synovial cells, chondrocytes, osteoblasts, and osteoclasts was observed. The chemical form of [(14)C]Pro-Hyp-derived radioactivity detected in the tissues was investigated by thin layer chromatography. The radioactive constituents in cartilage extract were two proline-modified peptides (56%), intact Pro-Hyp (5%), and two nonpeptide metabolites (28%). Similar results were obtained for skin and bone marrow. Plasma analysis at 3 to 30 min post-dose suggested that the majority of Pro-Hyp is modified in its proline residue by a first-pass effect without peptide bond hydrolysis. In conclusion, we demonstrated that Pro-Hyp is partly distributed in observed tissues including skin and cartilage in its intact form, which might be responsible for its biological functions.

Association between urinary IgG and relative risk for factors affecting proteinuria in type 2 diabetic patients

Abnormal glomerular permeability is the primary step towards the glomerulosclerosis. The progression rate of glomerulosclerosis is proportionate to abundance and severity of lesions created at incipient stage, which is reflected as proteinuria even though eGFR remains in the normal range. Therefore, there is a current need to find out the association between relative risks for the factors leading to proteinuria. The relations could be more informative, if it is with respect to the macromolecules like "IgG" excretion in urine. Type 2 diabetic patients were selected for this study with eGFR > 75 ml/min/1.73 m(2) and grouped into four quartiles based on UIgGCR. The markers of key factors affecting progression of proteinuria were estimated through biochemical tests. The impact of these markers on proteinuria was accessed by applying multinomial logistic regression. The adjusted odds ratio for the UGAGCR was 1.186 (95 % CI: 1.061-1.327) P < 0.003 in highest quartiles of UIgGCR, followed by odds ratio for markers of collagen catabolism 1.051 (95 % CI: 1.025-1.079) P < 0.001, and USACR 1.044 (95 % CI: 1.013-1.077) P < 0.006 respectively. The marker of glycation, i.e., glycated hemoglobin showed the highest odds ratio 5.449 (95 % CI: 1.132-26.236) P < 0.035. In addition, odds for the systolic blood pressure was observed 1.387 (95 % CI: 1.124-1.712) P < 0.002. The higher odds inform and could help to discriminate the diabetic patients with fast progressive diabetic nephropathy. The study describes critical relationship between the urinary excretion of IgG and factors leading to proteinuria in type 2 diabetic patients.

Absorption of hydroxyproline-containing peptides in vascularly perfused rat small intestine in situ

To assess the digestion and assimilation of gelatin and gelatin hydrolysates, the in situ absorption of typical hydroxyproline-containing dipeptides, Pro-Hyp, Hyp-Gly, Ser-Hyp Ala-Hyp, and pentadecapeptide, (Pro-Hyp-Gly)(5), was investigated in the rat small intestine. During vascular perfusion after the injection of Hyp-Gly, Pro-Hyp and (Pro-Hyp-Gly)(5) into the jejunum, peptide-form Hyp but not free-Hyp gradually increased in the perfusate. In contrast, in the case of Ser-Hyp and Ala-Hyp, both free- and peptide-form Hyp rapidly increased. The presence of these dipeptides and the pentadecapeptide in the perfusates was confirmed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using multiple reaction monitoring (MRM). Some digestive and absorbed forms from (Pro-Hyp-Gly)(5) were identified as Gly-(Pro-Hyp-Gly)(4), (Pro-Hyp-Gly)(4), Gly-(Pro-Hyp-Gly)(3), (Pro-Hyp-Gly)(3), Gly-(Pro-Hyp-Gly)(2), and (Pro-Hyp-Gly)(2) by MALDI-TOF/MS. The dipeptide hydrolase activity in intestinal mucosa toward Pro-Hyp and Hyp-Gly was extremely low, while Ser-Hyp and Ala-Hyp were substantially hydrolyzed in the cytosol. These results suggest that Hyp-peptides were resistant to intracellular hydrolysis and that a significant amount of these peptides was transported across the intestinal wall and may enter the portal circulation in an intact form.

Peptiduria in the Fanconi syndrome

Peptide excretion has been studied in 20 cases of Wilson's disease and in maleate-induced Fanconi syndrome in the rat, ligand-exchange column chromatography being used to separate peptides from free amino acids. There is a statistically significant increase in urinary peptides in both types of the Fanconi syndrome. In both man and the rat, a large fraction of the excreted peptides has been shown to contain hydroxyproline, and therefore to be derived from collagen degradation. In both groups there is a close correlation between the output of hydroxyproline and that of total peptide-bound amino acids. Arguments are advanced that the peptiduria is due to increased urinary clearance of plasma peptides rather than to a metabolic cause. Peptides excreted in patients with the Fanconi syndrome are shown to have a different proportionate amino acid composition to those in urine specimens from normal controls. The mean size of urinary peptides derived from collagen must be at least five or six amino acids per peptide chain. Maleate-induced Fanconi syndrome in the rat is thought to be a close analogue of the syndrome in man, and further results obtained in the animal model may well be directly applicable to human disease.

Bone markers in multiple myeloma

Bone disease, a hallmark of multiple myeloma occurs in the majority of the patients, is associated with bone pain, fractures, hypercalcemia and has major impacts on quality of life. Myeloma is characterized by a unique form of bone disease with osteolytic bone destruction that is not followed by reactive bone formation, resulting in extensive lytic lesions. This review will focus on the pathophysiology of osteoclast activation and osteoblast inhibition in multiple myeloma and on biochemical markers of bone turnover. Since osteolytic lesions do not rapidly heal in myeloma, X-rays cannot reflect the activity of bone disease during antimyeloma treatment. Activity in bone turnover does not parallel changes in monoclonal protein levels. Thus, there is a need for biochemical markers reflecting disease activity in bone. The utility, prognostic implications and limitations of classical and novel markers of bone remodeling (e.g. ICTP, NTx, TRACP-5b, osteoprotegerin, sRANKL) will be discussed in this overview.

Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates

In the present study, we identified several food-derived collagen peptides in human blood after oral ingestion of some gelatin hydrolysates. Healthy human volunteers ingested the gelatin hydrolysates (9.4-23 g) from porcine skin, chicken feet, and cartilage after 12 h of fasting. Negligible amounts of the peptide form of hydroxyproline (Hyp) were observed in human blood before the ingestion. After the oral ingestion, the peptide form of Hyp significantly increased and reached a maximum level (20-60 nmol/mL of plasma) after 1-2 h and then decreased to half of the maximum level at 4 h after the ingestion. Major constituents of food-derived collagen peptides in human serum and plasma were identified as Pro-Hyp. In addition, small but significant amounts of Ala-Hyp, Ala-Hyp-Gly, Pro-Hyp-Gly, Leu-Hyp, Ile-Hyp, and Phe-Hyp were contained.

The role of markers of bone remodeling in multiple myeloma

Osteolytic bone disease is a frequent complication of multiple myeloma, resulting in skeletal complications that are a significant cause of morbidity and mortality. A characteristic feature of myeloma bone disease is that the lesions rarely heal and bone scans are often negative in myeloma patients who have extensive lytic lesions, offering very little in the follow-up of bone disease. X-rays are also of limited value in monitoring bone destruction during anti-myeloma or anti-resorptive treatment. Biochemical markers of bone turnover, such as N- and C-terminal cross-linking telopeptide of type I collagen (NTX, CTX/ICTP, respectively), and newer ones such as the tartrate resistant acid phosphatase isoform 5b, provide information on bone dynamics that in turn may reflect disease activity in bone. Several studies have shown bone markers to be elevated in myeloma patients and reflect the extent of bone disease, while in some of them bone resorption markers correlate with survival. These markers may also be helpful in identifying those patients likely to respond to bisphosphonate treatment, and monitoring the effectiveness of bisphosphonate therapy in the management of myeloma bone disease. This review attempts to summarize the existing data for the role of markers of bone remodeling in assessing the extent of bone destruction in myeloma and monitoring bone turnover during specific anti-myeloma treatment. We also discuss some novel markers that may be of particular interest in the near future.

Protein intake and urinary excretion of protein-derived metabolites in aging female vegetarians and nonvegetarians

Relationships among age, protein intake, and urinary excretion of protein-derived metabolites were studied in 125 vegetarian and nonvegetarian women ages 40-92. There were 63 women in the vegetarian (AV) group and 62 women in the nonvegetarian (NV) group. Average daily intakes of energy and total animal and vegetable protein were calculated from 7-day dietary records. Twenty-four-hour urine samples were analyzed for total nitrogen, urea, creatinine, hydroxyproline, and inorganic sulfate. Energy intakes for the two groups were similar. AVs consumed less total and animal protein and more vegetable protein than NVs, even though both groups consumed more than the RDA for protein. No significant differences existed between the groups in the urinary excretion of total nitrogen, urea nitrogen, hydroxyproline, or inorganic sulfate. Energy and protein intakes and total nitrogen excretion were lower in older AVs than in younger AVs, while those of NVs increased between 40 and 55 years of age, and decreased among the older NV women. The relationship between these variables and age in NVs was more accurately described by polynomial rather than linear regression models.

High-performance liquid chromatographic method for the determination of prolyl peptides in urine

A rapid and accurate method is described for the determination of prolyl peptides in urine, with specific reference to the dipeptide prolylhydroxyproline, and free hydroxyproline and proline. Free amino acids and peptides were isolated from urine on cation-exchange minicolumns, and free imino acids and prolyl-N-terminal peptides were selectively derivatized with 4-chloro-7-nitrobenzofurazan, after reaction of amino acids and N-terminal aminoacyl peptides with o-phthalaldehyde. The highly fluorescent adducts of imino acids and prolyl peptides were separated on a Spherisorb ODS 2 column by isocratic elution for 12 min using as mobile phase 17.5 mM aqueous trifluoracetic acid solution containing 12.5% acetonitrile (eluent A), followed by gradient elution from eluent A to 40% of 17.5 mM aqueous trifluoroacetic acid solution containing 80% acetonitrile in 20 min. Analytes of interest, in particular the dipeptide prolylhydroxyproline, can be easily quantified by fluorimetric detection (epsilon ex = 470 nm, epsilon em = 530 nm) without interference from primary amino-containing compounds.

Further studies on the nutritional factors affecting the urinary excretion of acid-soluble peptides in rats

1. Nutritional factors affecting the urinary excretion of acid-soluble peptides (ASP) were studied in rats. The ratio, total urinary nitrogen: ASP-form leucine + valine was lowest in the rats fed on a protein-free diet and increased as retained N: absorbed N decreased. The ratio was not affected by dietary protein level when the level was below the National Research Council (1978) recommended requirement, but increased greatly when it exceeded the recommended requirement. 2. The excretion of ASP-form leucine + valine per kg body-weight was significantly lower in the protein-deficient rats than in those fed on protein-adequate diets. This variable decreased during the stage of rapid growth, but did not change as markedly after the onset of adolescence. It increased again when the rats became older. The patterns of change in the rate of excretion of ASP-form amino acids during growth and that of Nr-methylhistidine were different. 3. When labelled amino acids were injected into rats, the largest amount of the ASP-form label was excreted on the 1st day of injection. From the 2nd day the excretion of ASP-form label decreased exponentially. 4. The findings suggest that the rate of urinary excretion of ASP-form amino acids can be employed as an index of protein metabolism, particularly as a simple index of the assessment of the status of protein nutrition.

Influence of molecular structure on half-life and hydrolysis of dipeptides in plasma: importance of glycine as N-terminal amino acid residue

To investigate the effect of molecular structure on plasma disappearance and metabolism of dipeptides, rats were injected intravenously with individual dipeptides, and at various intervals after injection, dipeptide and amino acid concentrations were measured in plasma, tissues, and urine. In addition, plasma hydrolase activity against individual dipeptides was investigated. The half-lives of Ala-Leu, Ala-Tyr, and Ala-Gln were shorter than those of dipeptides with glycine substituting for alanine. Furthermore, the increases in plasma concentrations of leucine, tyrosine, and glutamine and rates of dipeptide hydrolysis by plasma enzymes were far greater with alanyl than glycyl dipeptides. In fact, Ala-Leu behaved like a mixture of corresponding free amino acids in raising the plasma concentration of leucine while Gly-Leu did not. There was no significant difference in either plasma half-life or hydrolysis when Leu-Gly and Leu-Ala were used as substrates, but both had rapid rates of hydrolysis in plasma. In comparison to Gly-Leu, Phe-Leu and Arg-Leu had shorter half-lives and greater rates of hydrolysis in plasma. On the other hand, Asp-Leu had a slower rate of plasma hydrolysis than Gly-Leu, but its excretion in the urine was much greater than that of Gly-Leu. In contrast to Gly-Leu and Ala-Leu, Gly-Pro was detected intracellularly in liver, muscle, and particularly, kidney. In fact, the intracellular concentration of Gly-Pro in kidney was either equal to or greater than Gly-Pro concentration in plasma. Increases in intracellular amino acid concentration after injection of individual dipeptides were considerably greater in the kidney than in either liver or muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

[The intestinal phase of peptide absorption]

Peptides and not amino acids are the prevailing degradation products of protein digestion which are formed in the intestinal lumen and are absorbed from the mucosa. These two families differ in absorption. The differences become manifest when the absorption of peptide mixtures is compared with that of equimolecular mixtures of free amino acids. The absorption of peptides occurs in two different ways: 1. Transport of intact peptides through the membrane into the mucosal cell and subsequent hydrolysis by intracellular peptide hydrolases. 2. Hydrolysis of the peptides by peptide hydrolases localized on the luminal side of the mucosal cell membrane and subsequent transport of the amino acids thus formed through the membrane. The two mechanisms of absorption do not exclude each other. The way by which energy is supplied for the transport is not yet elucidated. The transport of intact peptides is of nutritive importance only in case of dipeptides and tripeptides. It enables in particular the introduction of peptides that cannot be cleft by membrane-bound peptide hydrolases. The hydrolysis of peptides by membrane-bound peptide hydrolases and the subsequent transport of released amino acids is of importance for long-chain peptides. The difference in absorbing behaviour between the free amino acids released in the intestinal lumen and the amino acids released by peptide hydrolases at the mucosal membrane is discussed.

Comparison of urinary excretion of UV-absorbing constituents in healthy subjects and patients with rheumatoid arthritis using analytical isotachophoresis

Analytical isotachophoresis has been applied to the separation of urinary constituents in healthy controls and patients with rheumatoid and osteoarthritis. Various methods of comparing isotachograms have been investigated. Significant differences have been demonstrated between the pattern of UV-absorbing components in patients with rheumatoid arthritis and healthy subjects.

Fractionation and structure of several hydroxyproline-containing urinary peptides, with special reference to some 3-hydroxyproline-containing peptides

After a preliminary separation of the hydroxyproline-containing peptides on Biogel P 2, the largest peptides are fractionated on phosphocellulose and the smallest ones on QAE-Sephadex. The fractions obtained from QAE-Sephadex are subfractionated on a column of Dowex 50-M-82. The total number of hydroxyproline-containing peptides from human urine is not less than 78. Sixteen di, tri and pentapeptides have been purified, their N-terminal amino acids and amino acid compositions determined and a structure is proposed. 3 of these peptides contain 3-hydroxyproline and one of these 3 peptides probably originates from basement membrane collagen.

Difficulties and pitfalls in the interpretation of screening tests for the detection of inborn errors of metabolism

A review of factors which may be responsible for false positive and false negative results in a screening program for the detection of inborn errors of metabolism is presented. Administration of medication, dietary therapy, chemical treatment of specimens, delay in analysis, hypersensitivity of procedures utilized, interfering metabolites and inadequate metabolic development or enzymatic maturation in the patient may all produce results resembling an actual inborn error of metabolism. Inadequate nutritional intake prior to procurement of specimen and loss of material during analytical procedures may produce false negative results. As well, certain less severe variants of inborn errors may present in an unusual manner or may only present during periods of stress to the patient. These factors are discussed in relation to the performance of a metabolic screening program. It is suggested that these progrms should be performed by specialized, central laboratories experienced in the complexities of detection of inborn errors of metabolism.

Bound hydroxyproline excretion following gelatin loading in prolidase deficiency

The excretion of peptide-bound hydroxyproline before and after gelatin loading was evaluated in two children with prolidase deficiency, two adult heterozygotes, and normal controls. On a low hydroxyproline diet, the patients with prolidase deficiency excreted 6.9 and 2.4 times more bound hydroxyproline than normal children. The bound hydroxyproline excretion for the heterozygotes was comparable to the adult controls. Children ingested 20 g of gelatin and adults 29 g. In the 24 hr following gelatin loading, the homozygotes excreted 14.4 and 17.3 times more of the ingested load of hydroxyproline than did normal children. This constituted 39% and 47% of the hydroxyproline ingested. Of the hydroxyproline excreted in 24 hr, 58%, and 61.4% was excreted in the first 6 hr. Over the 24 hr period, the normal children excreted 2.7% of the hydroxyproline ingested (97.8% in the first 6 hr). The heterozygotes excreted only slightly more than the adult controls. The normal adults excreted 6.0% of the ingested hydroxyproline (82.8% in the first 6 hr). In prolidase deficiency, large amounts of peptide-bound hydroxyproline can cross the intestinal wall unhydrolyzed. Prolidase appears to have an important role in normal hydrolysis of peptide-bound hydroxyproline.

Evidence for two different modes of tripeptide disappearance in human intestine. Uptake by peptide carrier systems and hydrolysis by peptide hydrolases

The intestinal fate of two tripeptides (triglycine and trileucine), which differ markedly in solubility and molecular weight, have been investigated by jejunal perfusion in healthy human volunteers. Rates of glycine or leucine uptake from test solutions containing triglycine or trileucine were greater than from test solutions containing corresponding amounts of free glycine or free leucine, respectively. The rate of glycine uptake from a 100 mM triglycine solution was greater than that from a 150 mM diglycine solution. At each infused load of triglycine (e.g., 1,000 mumol/min) the rates (micromoles/minutes per 30 cm) of either triglycine disappearance (810 +/- 40) or glycine absorption (2,208 +/- 122) were markedly greater than the luminal accumulation rates of either diglycine (56 +/- 10) or free glycine (110 +/- 18). The luminal accumulation rate of free leucine during infusion of a 5 mM trileucine solution was over threefold greater than that of free glycine during the infusion of a 5 mM triglycine solution. Luminal fluid exhibited no hydrolytic activity against triglycine, but contained some activity against trileucine. Saturation of free amino acid carrier system with a large load of leucine did not affect glycine absorption rate from a triglycine test solution, but isoleucine markedly inhibited the uptake from a trileucine solution. When the carrier system for dipeptides was saturated with a large amount of glycylleucine, the disappearance rate of triglycine was considerably reduced while that of trileucine remained unaffected. After addition of glycylleucine to tripeptide solutions, there was a minimal increase in the luminal accumulation of diglycine, while dileucine accumulation was incresed by 62-fold.

Urinary polypeptides related to collagen synthesis

Of the total urinary hydroxyproline in normal subjects and those with skeletal disorders, between 4 and 20% was nondialyzable. In some patients with Paget's disease of bone, hyperparathyroidism with osteitis fibrosa, hyperphosphatasia, and extensive fibrous dysplasia the total urinary hydroxyproline was sufficiently high to permit purification of this polypeptide hydroxyproline by gel filtration and ion exchange chromatography. The partially purified polypeptides had molecular weights between 4500 and 10,000 and amino acid compositions and physical properties resembling those of gelatin. The polypeptide fractions also contained neutral sugar and glucosamine. These fragments had been shown to be susceptible to cleavage by purified bacterial collagenase suggesting the presence of the sequence-Pro-X-Gly-Pro-Y-. After administration of proline-(14)C to patients with Paget's disease hydroxyproline-(14)C was excreted in the urine. The hydroxyproline-(14)C specific activity reached a peak in 2-4 hr and declined rapidly. The specific activity of the polypeptide (retentate) portion was severalfold greater than that of the raw urine and diffusate. When the labeled urines were subjected to gel filtration the hydroxyproline-(14)C fractions of highest molecular weight which were eluted first from the columns had the highest specific activities. Exposure of the hydroxyproline-(14)C-containing polypeptides to bacterial collagenase rendered them dialyzable. Four patients with hyperparathyroidism and osteitis fibrosa were studied before and after removal of a parathyroid adenoma, a period of transition from a predominance of bone collagen resorption to one of relatively increased bone collagen synthesis. The total urinary hydroxyproline fell rapidly after operation whereas the ratio of the polypeptide fraction to the total rose three- to fourfold. The results of these studies suggest that the urinary polypeptides represent fragments of collagen related to collagen synthesis. Changes in the ratio of these peptides to total hydroxyproline in the urine may serve as an index of new bone formation in patients with skeletal disorders.