Selective inhibition of hepatic collagen accumulation in experimental liver fibrosis in rats by a new prolyl 4-hydroxylase inhibitor.

Fibrosis and cirrhosis of the liver are often the result of chronic liver damage by a variety of different agents. Pathological accumulation of collagen, disruption of the lobular structure, and impaired hepatocellular function frequently lead to systemic involvement and fatal complications. Drugs inhibiting collagen hydroxylation and accumulation are expected to improve this situation, making prolyl 4-hydroxylase (P4H), the key enzyme of intracellular collagen processing, a rational target for pharmacological intervention. S 4682, a novel inhibitor of purified P4H (Ki = 155 nmol/L), reduced hydroxyproline (Hyp) synthesis in chicken embryo calvaria (IC50 = 8.2 micromol/L) and in cultured hepatic stellate cells (HSC) (IC50 = 39 micromol/L). S 4682 inhibited hepatic collagen hydroxylation in vivo after metabolic labeling with [14C]proline. In the CCl4 model of chronic hepatic injury, characterized by histologically and biochemically evident fibrosis and highly elevated levels of serum procollagen type III N-peptide, S 4682 reduced hepatic collagen accumulation, decreased prevalence of ascites, and lowered serum procollagen type III N-peptide (PIIINP) levels. The hepatic Hyp content of drug-treated animals was closely correlated with serum levels of PIIINP S 4682 had no influence on Hyp content of heart, lung, and kidney.

Prolyl hydroxylase activity in tissue homogenates of annelids from deep sea hydrothermal vents.

Tissue homogenates of the deep sea annelids Alvinella caudata and Alvinella pompejana were found to contain enzyme activity resembling vertebrate prolyl 4-hydroxylase. The release of 3H2O from [3,4-(3)H]proline labeled, under-hydroxylated chicken protocollagen type I depended on the presence of the cofactors 2-oxoglutarate, ascorbate, Fe2+ and O2. The release of 3H2O could be inhibited by the prolyl 4-hydroxylase inhibitors zinc, 2,2'-dipyridyl, 3,4-dihydroxybenzoic acid and pyridine-2,4-dicarboxylate, as well as by the synthetic peptide (Pro-Pro-Gly)10. This synthetic peptide could also serve as substrate, because it enhanced the decarboxylation of 2-oxo[5-(14)C]glutarate. Alvinella prolyl hydroxylase appeared to be related to type II vertebrate enzyme because of its lack of affinity for poly (L-proline) and resistance to inactivation by an irreversible peptide inhibitor of chicken prolyl 4-hydroxylase. Maximal enzyme activity was observed in solutions with less than 10% oxygen saturation. By contrast, chicken enzyme was most active at saturating oxygen concentrations. Further data suggest that the Alvinella enzymes are able to accept the 2-oxo acids pyruvate, oxaloacetate and 2-oxoadipinate as substitutes of the cosubstarate 2-oxoglutarate. The data explain the high hydroxylation of Alvinella collagens despite the low oxygen concentrations around hydrothermal vents.

The bradykinin B2 receptor antagonist Icatibant (HOE 140) corrects avid Na+ retention in rats with CCl4-induced liver cirrhosis: possible role of enhanced microvascular leakage.

Avid Na+ retention is a hallmark of liver cirrhosis. The aim of this study was to investigate whether and how bradykinin is involved in Na+ retention in rats with CCl4-induced liver cirrhosis. To this end the bradykinin B2 receptor antagonist Icatibant (HOE 140) was used. On one hand, bradykinin has a renal natriuretic action. On the other hand, bradykinin is a potent mediator of both vasodilation and microvascular leakage. Both vascular mechanisms, which are reported for cirrhosis, could cause vascular underfilling and Na+ retention by activating the renin-angiotensin-aldosterone system. Icatibant normalised Na+ retention and reduced the hyperactivity of the renin-angiotensin-aldosterone system, suggesting a bradykinin-induced vascular disturbance. Icatibant had no significant effect on the mild hypotension which developed with CCl4 treatment. However, there was indirect evidence for enhanced microvascular leakage that was strongly inhibited by Icatibant. Our experimental results demonstrate that bradykinin is a key mediator of Na+ retention in liver cirrhosis and suggest that a bradykinin-induced increase in microvascular leakage is mainly responsible.

Serum laminin P1 levels do not reflect critically elevated portal pressure in patients with liver cirrhosis.

BACKGROUND/AIMS: Laminin P1 serum levels run parallel to the accumulation of hepatic extracellular matrix in patients with liver cirrhosis. Recent studies reported a correlation between laminin P1 and portal pressure, leading to the proposal that laminin P1 may be used to identify patients with critically elevated portal pressure in liver cirrhosis. So far, most of the data has been obtained from patients with alcoholic liver disease. METHODOLOGY: We studied the relationship between laminin P1 serum levels and portal hypertension in 34 patients with liver cirrhosis, mostly of non-alcoholic etiology. Using hepatic venous catheterisation the hepatic venous pressure gradient (HVPG), an estimate of portal hypertension, was measured. Laminin P1 was compared to the HVPG and the size of esophageal varices. RESULTS: Serum laminin P1 was elevated in all samples. However, laminin P1 did not significantly correlate with either portal hypertension or the size of esophageal varices. Furthermore, laminin P1 measurement did not identify patients with critically elevated portal pressure using a HVPG of either 12 mmHg or 16 mmHg as cut-off points. CONCLUSION: The use of laminin P1 serum levels to diagnose critically elevated portal pressure in liver cirrhosis cannot be supported for etiologies other than alcoholic liver disease.

Schistosoma mansoni-related morbidity on Ukerewe Island, Tanzania: clinical, ultrasonographical and biochemical parameters.

One thousand six hundred and ninety-five inhabitants of 3 rural villages on Ukerewe Island, Lake Victoria, Tanzania, were examined by clinical, parasitological, ultrasonographic and--in part--serological means to evaluate Schistosoma (S.) mansoni-related morbidity on a community level. Villagers frequently complained of typical colitis symptoms (abdominal pain 80.1%, bloody stools 43.1%, diarrhoea 35.1%); haematemesis, on the other hand, was rare (and reports doubtful in most cases). 16.9% of the population had been given praziquantel previously. Overall S. mansoni prevalence was 86.3%, with a median egg output of 176 eggs per gram (e.p.g.) and maximum output of 17,984 e.p.g. Children and adolescents were infected more severely than adults, men more severely than women. Pretreated individuals excreted significantly fewer ova (median 124 vs 192e.p.g., P < 0.001). Hepatomegaly (determined by ultrasonography) was present in 35%, splenomegaly in 80%. Organomegaly was significantly related to egg output. Pretreated persons had lower rates of splenomegaly and left lobe hepatomegaly. Low-degree periportal fibrosis was common, while severe grades of fibrosis (MANAGIL score II and III) were present in about 6%. About 10% had other abnormalities on liver sonography (irregular parenchymal texture and/or shape); these person passed significantly more S. mansoni ova than others. Clear sonographic signs of portal hypertension were seen in 2.1%. Serum procollagen-IV-peptide and gamma-glutamyl-transferase levels were increased in persons with severe periportal fibrosis, irregular liver texture of portofugal collateral vessels. Thus, S. mansoni infection in the western part of Ukerewe Island is frequent and often severe, leading to a high prevalence of gastrointestinal symptoms. Hepatosplenic involvement does occur, although symptomatic cases of portal hypertension were not identified beyond doubt. The overall level of schistosomal morbidity is thus considered intermediate. Serum procollagen-IV-peptide may be a promising marker of schistosomal liver disease. Our data suggest that S. mansoni infection may also be related to diffuse liver parenchyma alterations in this area.

Suppression of immunopathology in schistosomiasis by interleukin-2-targeted fusion toxin, DAB389IL-2. I. Studies of in vitro and in vivo efficacy.

Schistosomiasis causes pathology in an estimated 200 million individuals. Clinical disease is caused by a complex immunopathologic response to the parasite ova, which are deposited in the host tissues. This immunopathologic response is caused by T lymphocytes which express the high-affinity IL-2 receptor (IL-2R). DAB389IL-2 is a diphtheria toxin-IL-2 fusion toxin protein which functionally inactivates or kills cells which bear the high-affinity IL-2R. DAB389IL-2 has been used in man to suppress IL-2R-dependent immune reactivity. Therefore, we reasoned that DAB389IL-2 might suppress immunopathology in schistosomiasis. In these studies we assessed the in vitro and in vivo effects of DAB389IL-2 on the development of immunopathology in murine schistosomiasis. DAB389IL-2 suppressed IL-2, lectin mitogen (Con A), and soluble Schistosoma mansoni egg antigen-induced lymphocyte proliferation and in vitro granuloma formation. In addition, DA-B389IL-2 suppressed in vitro IL-2R expression. DA-B389IL-2 also suppressed the development of granulomas and collagen deposition in vivo in the livers of infected animals. Therefore, DAB389IL-2 may have potential for the targeted reduction of immunopathology due to schistosomiasis in man.

Interference in clinical laboratory tests, with special regard to the bilirubin assay: effects of a metabolite of the new prolyl 4-hydroxylase inhibitor, Lufironil.

During the toxicological examination of the fibrosuppressive agent, Lufironil (INN), in rats a dose-dependent positive reaction for urinary bilirubin was observed. This positive reaction was found in quantitative assays, and when using test strips. The positive reaction for bilirubin in these assay systems was caused by a metabolite of Lufironil. It was not due to drug toxicity, and it was not caused by any endogenous substrate produced under the influence of Lufironil. The compound responsible for this reaction was isolated by HPLC and its structure determined by spectroscopic methods. The structure was confirmed by synthesis, starting from pyridine-2,4-dicarboxylate. The synthesized compound and the compound in urine gave an identical reaction with the test reagent for bilirubin.

Inhibition of prolyl 4-hydroxylase by oxalyl amino acid derivatives in vitro, in isolated microsomes and in embryonic chicken tissues.

The potency of oxalyl amino acid derivatives as inhibitors of prolyl 4-hydroxylase was studied in vitro, in isolated microsomes and in chicken embryonic-tissue culture. These compounds represent structural analogues of 2-oxoglutarate in which the -CH2- moiety at C-3 is replaced by -NH-, with or without further structural modifications. The most efficient inhibitor of purified prolyl 4-hydroxylase was oxalylglycine. Its mode of inhibition was competitive with respect to 2-oxoglutarate. The Ki value varied between 1.9 and 7.8 microM, depending on the variable substrate used. Oxalylalanine inhibited purified enzyme with a Ki of 40 microM. Other oxalyl amino acid derivatives showed little inhibitory activity. In microsomes isolated from embryonic chicken bone, oxalylglycine and oxalylalanine inhibited prolyl hydroxylation with IC50 values of 23 and 120 microM respectively. Dimethyloxalylglycine was not an inhibitor of purified prolyl 4-hydroxylase and only weakly active in the microsomal system, but efficiently suppressed hydroxyproline synthesis in embryonic chicken calvaria and lung. The data suggest that dimethyloxalyl amino acids are converted into active inhibitors in intact cells, most likely in the cytoplasmic compartment.

Structural requirements for the utilization of ascorbate analogues in the prolyl 4-hydroxylase reaction.

The ability of structural analogues of ascorbate to serve as substitutes for this reducing agent in the prolyl 4-hydroxylase reaction was studied. In experiments using the purified enzyme, variations of the compounds' side chain were compatible with co-substrate activity. The presence of very large hydrophobic substituents or a positively charged group caused an increase in the observed Km values. A negative charge and smaller modifications did not change the affinity to the enzyme when compared with L-ascorbate. 6-Bromo-6-deoxy-L-ascorbate had a lower Km than the physiological reductant. Substitution at the -OH group in ring position 3 prevented binding to the enzyme. The same pattern of activity was observed when the full and uncoupled prolyl 4-hydroxylase reactions were studied. The Vmax. values with all compounds were similar. The reaction of microsomal prolyl 4-hydroxylase was supported by D-isoascorbate, O6-tosyl-L-ascorbate and 5-deoxy-L-ascorbate, giving the same dose-response behaviour as L-ascorbate itself. Again, 6-bromo-6-deoxy-L-ascorbate gave a lower Km and a similar Vmax. value. L-Ascorbic acid 6-carboxylate produced substrate inhibition at concentrations above 0.3 mM. The Km and Vmax. values calculated from concentrations up to 0.2 mM were similar to those of L-ascorbate. The enzyme activity observed with 6-amino-6-deoxy-L-ascorbate was very low in the microsomal hydroxylation system. The calculated Vmax. value was lower than that of L-ascorbate, suggesting a restriction of the access of this compound to the enzyme.

A radioimmunoassay for the N-terminal propeptide of rat procollagen type III. Application to the study of the uptake of the N-terminal propeptide of procollagen type III in isolated perfused rat liver.

Antibodies against a synthetic peptide representing the 14 C-terminal amino acids of the N-terminal propeptide of rat and bovine procollagen type III were raised in rabbits and used to develop a radioimmunoassay. N-Terminal propeptide of procollagen type III, purified from calf skin, served as standard and tracer material. The IC50 of the standard inhibition curve was 2.1 micrograms/l, the lower limit of detection about 0.4 microgram/l, interassay variation was 8.5% and the intraassay variation 6.6% in typical experiments. Three peaks of antigenicity were detected in rat serum after gel chromatography. One peak coeluted with purified N-terminal propeptide of procollagen type III, one peak contained material approximately twice this size, and one peak eluted close to the void volume of the column. The antigen concentration in rat serum decreased in an age dependent manner. Rat, bovine, sheep and minipig serum antigen was sufficiently crossreactive to allow the application of the assay to these species, whereas human, goat and guinea pig samples were not. The degradation product Col 1, causing non-parallel inhibition in commercially available assays for human samples was not recognized since it does not contain the epitope represented by the synthetic peptide. The assay was used to study the half-life of bovine and endogenous N-terminal propeptide of procollagen type III in isolated perfused rat liver. [125I]-labeled antigen was cleared rapidly from the perfusate (t1/2 less than 5 min). The bovine antigen was removed from the perfusate with a half-life of 15 +/- 4 min. Endogenous propeptide was perfused for 120 min with little change in concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Laminin concentrations in serum and cerebrospinal fluid in aging and Alzheimer's disease.

Laminin, a basement membrane protein, and a potent promoter of neurite outgrowth, surrounds all peripheral nerves. It appears in the central nervous system during development and reappears in response to injury. In Alzheimer's disease (AD), there is a progressive loss of neurons in specific areas of the brain along with the presence of an increased number of senile plaques and neurofibrillary tangles. Laminin levels have been shown to be increased in injury, so we undertook to examine levels of laminin by radioimmunoassay (RIA), in cerebrospinal fluid and serum of patients with AD and age-matched controls. No difference in the CSF and serum laminin concentrations was found between Alzheimer's disease and age-matched controls. We found a lack of correlation between severity of clinical dementia and laminin concentrations. Finally, we show that the CSF and serum laminin concentrations increase with age.

Modification of vertebrate and algal prolyl 4-hydroxylases and vertebrate lysyl hydroxylase by diethyl pyrocarbonate. Evidence for histidine residues in the catalytic site of 2-oxoglutarate-coupled dioxygenases.

A search for conserved amino acid residues within the cDNA-derived amino acid sequences of 2-oxoglutarate-coupled dioxygenases revealed the presence of two distinct motifs, spaced 49-71 amino acids apart, toward the C-terminal regions of these proteins. Each of the two common motifs contains an invariant histidine residue at a conserved position. The 2-oxoglutarate-coupled dioxygenases function in diverse processes, including the post-translational hydroxylation of proline and lysine residues in vertebrate collagens and the biosynthesis of microbial cephalosporins, yet they have a common reaction mechanisms, which requires the binding of Fe2+, 2-oxoglutarate, O2 and ascorbate at the catalytic site. The two regions of homology, and specifically the identical histidines, potentially represent functionally important sites related to their catalytic activity. Modification of histidine residues by diethyl pyrocarbonate inactivated vertebrate and algal prolyl 4-hydroxylase and vertebrate lysyl hydroxylase, indicating that histidine residues function in the catalytic site of these 2-oxoglutarate-coupled dioxygenases. Inactivation was prevented by the presence of co-substrates, but not by the peptide substrate. It is proposed that the histidine residues in the conserved motifs may function as Fe(2+)-binding ligands.

Hepatic fibrosis in rats produced by carbon tetrachloride and dimethylnitrosamine: observations suggesting immunoassays of serum for the 7S fragment of type IV collagen are a more sensitive index of liver damage than immunoassays for the NH2-terminal propeptide of type III procollagen.

Liver fibrosis was induced in rats both with carbon tetrachloride and dimethylnitrosamine. Assays were performed on steady-state levels of messenger RNAs in the liver for several collagens and basement membrane components. The results indicated marked increases in the steady-state levels of messenger RNA for type I collagen, type III collagen, type IV collagen and the B2 component of laminin. In the same animals, immunoassays were performed for serum levels of the N-terminal propeptide of type III procollagen and the 7S fragment of type IV collagen. The results demonstrated an increase in the serum levels of 7S fragment that occurred early and closely paralleled the increase in the steady-state levels of messenger RNA for the alpha 1(IV) chain of type IV collagen. In contrast, no significant increase was seen in the serum levels of the N-propeptide of type III procollagen. The results suggest that immunoassays for 7S fragment of type IV collagen in serum are a more sensitive index for liver cell damage and fibrosis than assays for the N-propeptide of type III procollagen. The results suggest that greater attention should be paid to assays of 7S fragments in assessing hepatic fibrosis in man.

[Experimental studies of the inhibition of fibrogenesis]. / Experimentelle Untersuchungen zur Hemmung der Fibrogenese.

Colchicine as well HOE 077 were found to be effective in the inhibition of hepatic collagen accumulation after bile duct ligation in rats. The effect was additive and was truly reflected by changes in the serum PIIIP and 7s-collagen (IV) concentration. Extrahepatic effects on collagen synthesis were not detected when HOE 077 was used. Thus further studies on the potential clinical usefulness of these compounds are clearly indicated.

Thalidomide in human immunodeficiency virus (HIV) patients. A review of safety considerations.

The sedative thalidomide was withdrawn from the market 30 years ago because of its teratogenic and neurotoxic adverse effects. The compound was later discovered to be extremely effective in the treatment of erythema nodosum leprosum, a complication of lepromatous leprosy. This effect is probably due to a direct influence on the immune system, because thalidomide possesses no antibacterial activity. The compound is presently used as an experimental drug in the treatment of a variety of diseases with an autoimmune character, including recurrent aphthosis of nonviral and nonfungal origin in human immunodeficiency virus (HIV) patients. This article reviews the most important chemical and pharmacokinetic properties of thalidomide. The possible mechanisms of the nonsedative effects of thalidomide with respect to the safety of its use in HIV patients are discussed. Because the mechanism of the immunomodulatory effect of thalidomide is unknown, the possibility that the administration of this compound will accelerate the deterioration of the immunological status of HIV patients cannot be excluded. Clinical evidence suggests that thalidomide may aggravate the condition of patients with preexisting peripheral neuropathy. Hypersensitivity reactions to thalidomide may occur more frequently in HIV patients than in other patient groups. Because of the teratogenic activity of thalidomide, reliable contraception must be provided to female patients of childbearing age. Before the introduction of thalidomide therapy to an HIV patient presenting with oral ulcers, a fungal or viral origin of the lesions should be excluded. Thalidomide should not be used in patients with preexisting HIV-related peripheral polyneuropathy, polyradiculopathy or encephalopathy. In patients experiencing a complete remission, the discontinuation of thalidomide treatment and its reintroduction in the case of a relapse are preferable to maintenance therapy.

Inhibition of prolyl hydroxylation and procollagen processing in chick-embryo calvaria by a derivative of pyridine-2,4-dicarboxylate. Characterization of the diethyl ester as a proinhibitor.

The biochemical and morphological consequences of procollagen prolyl 4-hydroxylase inhibition by pyridine-2,4-dicarboxylic acid (2,4-PDCA) and its diethyl ester (diethyl-2,4-PDC) were studied in chick-embryo calvaria, which predominantly synthesize type I collagen. Half-maximal inhibition of tissue hydroxyproline formation required 650 microM-2,4-PDCA, whereas the Ki with respect to chicken prolyl 4-hydroxylase in vitro was 2 microM. In contrast, half-maximal inhibition was caused by 10 microM-diethyl-2,4-PDC in the intact calvaria, although chicken prolyl 4-hydroxylase in vitro was not inhibited even at 1 mM. The collagenous material produced in the presence of diethyl-2,4-PDC showed an altered 'melting' profile and a lowering of the transition temperature by 10 degrees C, indicating misalignment and thermal instability of its triple-helical structure. Amount and electrophoretic mobility of procollagen type I chains were increased in a dose-dependent manner. The amounts of partially processed species and alpha-chains were decreased, without change in mobility. This marked effect on procollagen-collagen conversion in the intact calvaria suggests that the underhydroxylated collagenous material generated in the presence of diethyl-2,4-PDC is resistant to or acts as endogenous secondary inhibitor of type I procollagen N-proteinase. Electron microscopy of treated calvaria cells showed dilated rough endoplasmic reticulum and numerous phagolysosomes, indicating intracellular retention and lysosomal degradation of the newly synthesized underhydroxylated collagenous material. In summary, these results identify 2,4-PDCA and diethyl-2,4-PDC as the first prolyl 4-hydroxylase-directed inhibitor/proinhibitor pair that affects intra- and extra-cellular events during collagen formation.

Beneficial effects of inhibitors of prolyl 4-hydroxylase in CCl4-induced fibrosis of the liver in rats.

S 0885 and HOE 077 inhibit CCl4-induced liver fibrosis in rats, as shown by significantly reduced hydroxyproline content of the liver and improved liver histology. Mortality of drug-treated animals is significantly diminished. Serum collagen parameters correlate well with the hydroxyproline content of the liver and can be used as noninvasive markers for the fibrotic process. HOE 077 is a proinhibitor, which by itself does not inhibit prolyl 4-hydroxylase. HOE 077 is well absorbed from the gastrointestinal tract. It is taken up by rat liver and is converted to the active metabolites. At a concentration of 1 mM, HOE 077 does not affect collagen synthesis in human fibroblasts, bovine chondrocytes and chicken calvaria. At therapeutic doses the compound does not reduce collagen content of kidney, lung, aorta, femur epiphysis, skin and tendon of the rat, validating the high specifity of the liver selective prodrug/inhibitor conversion. From animal experiments, a human daily dose of 0.5-1 g can be extrapolated.

Fibrosis of the liver in rats induced by bile duct ligation. Effects of inhibition by prolyl 4-hydroxylase.

The model of biliary cirrhosis by bile duct ligation was further characterized using PIIIP, 7S-collagen as well as standard enzymes in the serum, prolyl 4-hydroxylase and total hydroxyproline in the liver and light microscopical histology. Five weeks after bile duct ligation there was an increase in total collagen content of the liver to 510% of initial values accompanied by an increase of serum-PIIIP (225%) and 7S-collagen (389%). The time-course of this connective tissue proliferation was biphasic with an initial phase of cholestasis and cellular damage followed by rapidly increasing collagen accumulation. The novel prolyl 4-hydroxylase inhibitor HOE 077 reduced the accumulation of collagen in the liver over 6 weeks by 48%. There were no apparent side effects and treated animals showed a tendency towards less functional impairment. The drug's effects, however, were not dose-dependent between daily doses of two times 2 mg/kg and two times 10 mg/kg. These results emphasize the usefulness of the bile duct ligation model for studies of collagen metabolism. They show HOE 077 to be a promising agent for the inhibition of hepatic fibrosis.

Specific inactivation of prolyl 4-hydroxylase and inhibition of collagen synthesis by oxaproline-containing peptides in cultured human skin fibroblasts.

The crucial role of collagen in fibrotic disorders has prompted attempts to develop drugs that inhibit collagen accumulation. Peptides containing the unphysiological amino acid 5-oxaproline (Opr) have recently been found to act as specific syncatalytic inactivators of pure prolyl 4-hydroxylase, the enzyme that catalyzes the formation of 4-hydroxyproline in collagens. The present study indicates that oxaproline-containing peptides benzyloxycarbonyl-Phe-Opr-Gly-benzyl ester (I) and benzyloxycarbonyl-Phe-Opr-Gly-ethyl ester (II) inactivate prolyl 4-hydroxylase in cultured human skin fibroblasts, peptide I being about twice as potent as peptide II. Inactivation by 50% was observed after culturing with about 20-40 microM concentrations of peptide I for 48 h. The inactivation appears to be specific, as no changes were found in the activities of two other intracellular enzymes of collagen synthesis, lysyl hydroxylase and galactosylhydroxylysyl glucosyltransferase. Synthesis of 4-hydroxyproline by the cells was markedly decreased, and 4-hydroxyproline-deficient procollagen accumulated intracellularly, whereas no changes were found in the incorporation of [14C]leucine into protein after culturing of the cells with a 30 microM concentration of peptide I for 48 h. No changes were seen in the viability of the cells or the release of lactate dehydrogenase from them into the culture medium. No significant changes were found in the steady-state levels of the mRNAs for the pro-alpha 1 chains of type I and type III procollagens or for the alpha and beta subunits of prolyl 4-hyroxylase or fibronectin after culturing with 75 microM peptide I for 48 h. The data indicate that inactivation of cellular prolyl 4-hydroxylase has marked effects on cellular 4-hydroxyproline formation and collagen secretion but no effects on the steady-state levels of mRNAs for type I and III procollagens or the two types of subunit of prolyl 4-hydroxylase.

Assay for 2-oxoglutarate decarboxylating enzymes based on the determination of [1-14C]succinate: application to prolyl 4-hydroxylase.

A method for the assay of 2-oxoglutarate decarboxylating enzymes based on determination of the reaction product [1-14C]succinate after precipitation of remaining 2-oxo[5-14C]glutarate with 2,4-dinitrophenyl hydrazine is reported. It is particularly useful for the study of the 2-oxoglutarate-coupled dioxygenase prolyl 4-hydroxylase (EC 1.14.11.2); it is superior to previously described assay methods of this enzyme with respect to simplicity of the procedure, speed, cost, and radiochemical safety. The results are highly reproducible, the standard deviation of repeated measurements being about 2% of the mean. The commercially available 2-oxo[5-14C]glutarate used in this study contained approximately 3% of radioactivity coeluting with succinate in HPLC and 1.5% of an unidentified radioactive compound as impurities, which contributed to the background.