[Connective tissue and the origin of intracranial arterial aneurysms].
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Collagen↗
Biomedical subjects
K Majamaa
Publications and source records attributed to K Majamaa.
Metabolic interventions against complex I deficiency in MELAS syndrome.
The mitochondrial DNA (mtDNA) codes for essential hydrophobic components of the system of oxidative phosphorylation. Diseases caused by mtDNA defects are manifested as variable clinical phenotypes and the symptoms represent the involvement of tissues with high energy demand. Various approaches have been taken to treat mitochondrial diseases by administration of redox compounds, enzyme activators, vitamins and coenzymes or dietary measures. The MELAS mutation at the base pair 3243 of mitochondrial DNA demolishes a transcription termination sequence located within the tRNA(Leu)[UUR] gene, resulting in synthesis of an abnormally large derivative of 16 S rRNA and defective translation. The activity of NADH:Q oxidoreductase (complex I) is often decreased and lactic acidosis is a typical clinical finding. We hypothesized that defective translation of the seven mitochondrially coded subunits (of the total 41) of complex I may alter its affinity to the NADH substrate in which case the activity decrease may be compensated for by increasing the NADH concentration. A MELAS patient was treated with oral nicotinamide for 5 months. The blood NAD content representing the NAD + NADH pool of erythrocytes rose 24 fold and the blood lactate + pyrovate concentration fell by 50%. All these metabolic alterations suggested an improvement of the function of complex I or the whole mitochondrial respiratory chain. However, the kinetic properties of the patient's complex I were similar to the reference values. A tempting explanation is that the free NADH concentration in mitochondria is normally at the level of K(m), so that the decreased activity of the respiratory chain can be compensated for by increased mitochondrial [NADH]. Another possibility would be that the substrate shuttles for transport of reducing power of cytosolic NADH into mitochondria (the malate aspartate or glycerol-3-phosphate shuttles) may be enhanced by increased total NAD + NADH. Because the malate-aspartate shuttle is actually a pump for reducing equivalents driven by the mitochondrial membrane energization, it is proposed that the exacerbations of the MELAS syndrome be partly due to a vicious circle initiated by a defect of complex I and affecting the active transport of the hydrogen from cytosolic NADH into the mitochondrion.
Administration, Oral↗
Increase of blood NAD+ and attenuation of lactacidemia during nicotinamide treatment of a patient with the MELAS syndrome.
Decreased activity of complex I (NAD:ubiquinone oxidoreductase) is the most frequent biochemical finding associated with mutation at the base pair 3243 of the mitochondrial DNA. The mutation has been previously shown to lead to a defective translation. We hypothesized that due to an imperfect assembly of complex I subunits the substrate affinity of this enzyme may be lowered and this may be counteracted by increasing the mitochondrial NAD+NADH concentration. Therefore, we studied the effect and mechanism of action of nicotinamide treatment in a MELAS patient with the base pair 3243 mutation. Nicotinamide treatment was initiated after his first stroke-like episode. The blood NAD concentration (representing the intracellular concentration in erythrocytes) increased linearly being 24-fold at 6 weeks of treatment. Blood lactate and pyruvate concentration decreased by 50% within three days and 24 h urine lactate content within 2 weeks and we observed a clinical improvement together with a decrease in the lesion volume in magnetic resonance imaging within the first month. The cellular NAD increase upon nicotinamide administration was probably universal, because it occurred in a time and dose-dependent manner in cultured fibroblasts from both the patient and the controls. Alleviation of the lactate accumulation during the nicotinamide treatment suggests that an increase in the cellular NAD+NADH concentration leads to enhancement of the oxidation of reducing equivalents. However, the Km of complex I for NADH in skeletal muscle from the patient was similar to that of controls. This may indicate that physiologically mitochondrial complex I operates at non-saturating substrate concentration, and this may explain the effect of nicotinamide treatment.
Aged↗
Demyelinating polyneuropathy in a patient with the tRNA(Leu)(UUR) mutation at base pair 3243 of the mitochondrial DNA.
A novel feature of demyelinating polyneuropathy was observed in a patient with the tRNA(Leu(UUR)) mutation at base pair 3243 of the mitochondrial DNA. Based on electrodiagnostic examination, the polyneuropathy was defined as being of the demyelinating, mixed (motor more than sensory) type. In a 1-year follow-up we observed approximately 7% reduction in both the motor and sensory conduction velocities. The other clinical features of the proband included a mild to moderate cognitive impairment and a combined hearing loss with a moderate sensorineural component. The proportion of the mutant genome found in the muscle of the proband was 29%, but the mutation was not found in his blood. A wide variability of the clinical phenotype was observed in the family of the proband. Heteroplasmic mutation was detected in the blood of most family members. The proportion of abnormal mitochondrial DNA was highest in the proband's brother, who had clinically definite mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome, while the mutant genome was less frequent or absent in the subjects with less severe phenotypes and in healthy individuals. The findings on this pedigree emphasize the need for studies of complete families in the search for new clinical phenotypes of mutations in mitochondrial DNA.
Adult↗
Familial aggregation of cervical artery dissection and cerebral aneurysm.
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Adult↗
A disorder of collagen biosynthesis in patients with cerebral artery aneurysm.
12 patients with subarachnoid hemorrhage due to rupture of a cerebral aneurysm were examined clinically for symptoms and signs of a connective tissue disorder and biochemically for details of the biosynthesis of collagen. No uniform clinical pattern of any connective tissue disorder was seen in these patients, although selected signs were observed. Skin fibroblast cultures were then established. The rate of procollagen production in two cell lines was reduced by 40% and 50%, respectively, and the intracellular accumulation of hydroxy[14C]proline (as a percentage of total hydroxy[14C]proline) was increased by 70% in each relative to eight control cell lines. No difference was found in the degree of intracellular degradation of procollagen. After pulse-labelling, however, the radioactive procollagen was secreted into the medium in 1 h in the control cells, but required at least 3 h in the two aneurysm patient cell lines. The results, thus, suggest that delayed secretion of procollagen rather than increased intracellular degradation led to the reduction in the rate of procollagen synthesis in these two fibroblast lines from patients with cerebral artery aneurysm.
Adult↗
Specific non-enzymatic glycation of the rat histone H1 nucleotide binding site in vitro in the presence of AlF4-. A putative mechanism for impaired chromatin function.
We show here that an aluminium derivative, AlF4-, stimulates glycation of histone H1 selectively in the proximity of its nucleotide-binding site. This adduct formation interferes with nucleoside triphosphate hydrolysis by H1 and with nucleotide modulation of H1 DNA binding. The present mode of aluminium action may in part be responsible for its effects on the chromatin structure and expression of tissue-specific genes, and may constitute a mechanism in the pathogenesis of aluminium-induced encephalopathy and in that of Alzheimer's disease, for example.
Aluminum↗
Kearns-Sayre syndrome case presenting a mitochondrial DNA deletion with unusual direct repeats and a rudimentary RNAase mitochondrial ribonucleotide processing target sequence.
A mitochondrial DNA deletion in a case of Kearns-Sayre syndrome is described. The deletion is bracketed by direct repeats that were unusual in that one of them was located 11-13 nucleotides from the deletion seam and both were conserved, which should not occur in slip replication or illegitimate elongation. The deleted region was demarcated on the deletion side by sequences that could be predicted to form hairpin structures. The 5'-side of the deletion was flanked by a sequence homologous to a 9-nucleotide piece of the conserved sequence block II of the D-loop. This arrangement around the deletion in Kearns-Sayre syndrome bears some resemblance to the arrangement in the Pearson marrow-pancreas syndrome described by A. Rötig et al. (1991, Genomics 10: 502-504).
Adult↗
Exclusion of mutations in the gene for type III collagen (COL3A1) as a common cause of intracranial aneurysms or cervical artery dissections: results from sequence analysis of the coding sequences of type III collagen from 55 unrelated patients.
We performed detailed DNA sequencing analysis on type III collagen cDNA from 58 patients with either intracranial artery aneurysms or cervical artery dissections. The 58 patients were of seven different nationalities; among the patients were three pairs of relatives, so that 55 were unrelated, and of these, 29 had at least one blood relative with either an intracranial artery aneurysm or a cervical artery dissection. The age of the patients at the time of diagnosis ranged from 15 to 68 years (mean +/- SD = 40.3 +/- 11.0). The study group consisted of 25 males and 33 females. The analysis covered 3,232 nucleotides of significant (nonredundant) sequences per allele; therefore, we analyzed as many as 355,520 nucleotides. Mutations in the coding sequences for the triple-helical domain of type III collagen were excluded in 40 individuals with intracranial aneurysms and 18 individuals with cervical artery dissections. Direct sequencing of polymerase chain reaction products allowed mutations to be excluded with a high degree of confidence. Mutations that markedly decreased expression from one allele were also excluded in 42 of the 58 individuals, since the presence of both bases at one or more polymorphic sites in the 42 patients showed that two alleles were transcribed. The results indicated that mutations in the gene for type III procollagen (COL3A1) are not a common cause of either intracranial artery aneurysms or cervical artery dissections.
Adolescent↗
Adult-onset diabetes mellitus and neurosensory hearing loss in maternal relatives of MELAS patients in a family with the tRNA(Leu(UUR)) mutation.
We describe a family with three cases of "clinically incomplete mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS) syndrome" in which heteroplasmic tRNA(Leu(UUR)) mutation at nucleotide 3243 of the mitochondrial DNA was present in three generations. The amount of mutant genome varied among tissues: it was 60% in the kidney, 72% in the cardiac muscle, and 91% in the liver of the female proband's affected brother and 63% in the kidney, 71% in the cardiac muscle, and 71% in the liver of the female proband's perinatally deceased son. The tRNA(Leu(UUR)) mutation was also carried by the siblings of the proband's affected mother. None of them had any clinical signs of MELAS syndrome. This syndrome has the new feature of being associated with adult-onset diabetes mellitus, neurosensory hearing loss, and short stature.
Adult↗
Synthesis of structurally unstable type III procollagen in patients with cerebral artery aneurysm.
The biosynthesis of collagen was studied in skin fibroblast cultures established from 11 patients with cerebral artery aneurysms. Six patients had familial subarachnoid hemorrhage (SAH), while five patients were considered as sporadic cases. The structural stability of the triple-helical medium procollagen was studied by measuring the thermal denaturation temperature (Tm) of type I and type III procollagen molecules. Structural instability of type III procollagen was demonstrated in two patients with familial SAH. The Tm of type III procollagen was 39.0 degrees C and 39.5 degrees C in two of the cell lines, while the control value was 40.3 degrees C. The stability of type I procollagen did not differ from that of the controls, and the main features of the biosynthesis of collagen were similar in the aneurysm patient cell lines and in the controls. The results suggest that a structural defect of type III procollagen may serve as an etiological factor in the formation of cerebral artery aneurysms.
Adult↗
Mitochondrial DNA deletion diagnosed by analysis of an endomyocardial biopsy specimen from a patient with Kearns-Sayre syndrome and complete heart block.
Defects of mitochondrial DNA have been found at necropsy in the myocardium of patients with Kearns-Sayre syndrome. A patient with characteristics typical of Kearns-Sayre syndrome and a complete heart block is described. Southern blot analysis showed a deletion of 3.3 kb in the mitochondrial DNA in an endomyocardial biopsy specimen and in skeletal muscle. The deletion led to the disappearance of the genes for four transfer RNAs and four subunits of complex I (NADH:ubiquinone oxidoreductase) in the mitochondrial respiratory chain. The defect could not be demonstrated in whole blood despite amplification of the mitochondrial DNA region of interest by the polymerase chain reaction technique. There can be heteroplasmy--that is, normal and abnormal mitochondrial DNA populations in one cell--in different tissues, and the degree of heteroplasmy may be crucial in the development of organ-specific symptoms. This patient raises the possibility that some tissues can be specifically enriched with mitochondria with DNA defects and emphasises the need for elective sampling of the target tissue and polymerase chain reaction technique to exclude these defects. The role of mitochondrial DNA defects in idiopathic cardiomyopathies could perhaps be studied by analysis of mitochondrial DNA from endomyocardial biopsy specimens.
Adult↗
Interference of AlF4- with nucleotide and DNA binding of rat histone H1 in vitro. Implications for the pathogenesis of Alzheimer's disease.
We demonstrate here that the H2PO4- analogue AlF4- binds to the nucleotide-binding site of rat liver histone H1 in vitro, and interferes with nucleotide recognition and H1 DNA binding. AlF4- may thus compromise the genetically determined pattern of protein synthesis through binding to H1, the general repressor. The present findings are of interest as a number of studies have implicated aluminium as a factor in the pathogenesis of Alzheimer's disease.
Aluminum↗
Reduction of collagen production in keloid fibroblast cultures by ethyl-3,4-dihydroxybenzoate. Inhibition of prolyl hydroxylase activity as a mechanism of action.
Excessive accumulation of collagen is the hallmark of several clinical conditions characterized by tissue fibrosis. Previously, 3,4-dihydroxybenzoic acid, a structural analog of alpha-ketoglutarate and ascorbate, has been shown to inhibit the activity of purified prolyl 4-hydroxylase, the enzyme catalyzing the synthesis of 4-hydroxyproline during intracellular biosynthesis of procollagen. In this study a hydrophobic modification, an ethyl ester, of 3,4-dihydroxybenzoic acid was tested for its effects on collagen synthesis and prolyl hydroxylase activity in human skin fibroblast cultures. The results indicated that 0.4 mM ethyl-3,4-dihydroxybenzoate markedly inhibited the synthesis of 4-hydroxyproline in normal cell cultures apparently as a result of reduced prolyl 4-hydroxylase activity, and the synthesis and secretion of both type I and type III procollagens were markedly reduced. Control experiments indicated that the test compound did not affect the viability, proliferation, or plating efficiency of the cells, and it had little, if any, effect on the synthesis of noncollagenous proteins. Furthermore, determinations of type I and type III procollagen mRNA steady-state levels by slot-blot hybridizations suggested that the inhibition of procollagen production did not occur on the pretranslational level. Thus, ethyl-3,4-dihydroxybenzoate selectively reduced procollagen production in fibroblast cultures by inhibiting the post-translational synthesis of 4-hydroxyproline. Similar inhibition was also observed in keloid fibroblast cultures, demonstrating the potential applicability of ethyl-3,4-dihydroxybenzoate, or other structural alpha-ketoglutarate or ascorbate analogs, for treatment of fibrotic diseases.
Collagen↗
Inhibition of prolyl hydroxylation during collagen biosynthesis in human skin fibroblast cultures by ethyl 3,4-dihydroxybenzoate.
The enzymatically catalyzed formation of 4-hydroxyproline plays a key role in the intracellular biosynthesis of collagen, since a critical number of 4-hydroxyprolyl residues is required for synthesis and secretion of triple-helical procollagen molecules under physiologic conditions. The enzyme catalyzing the conversion of prolyl residues to 4-hydroxyproline, prolyl 4-hydroxylase, requires ferrous ion, alpha-ketoglutarate, and ascorbate for its activity. 3,4-Dihydroxybenzoic acid has been known to act as potent competitive inhibitor of purified prolyl 4-hydroxylase with respect to one or several of the cofactors or cosubstrates of the enzyme. 3,4-Dihydroxybenzoic acid, however, is a poor inhibitor of prolyl hydroxylation in intact cells, probably due to its polarity not allowing it to enter the cells. In this study, several hydrophobic modifications of 3,4-dihydroxybenzoic acid were tested in human skin fibroblast cultures for their efficacy to inhibit the synthesis of 4-hydroxyproline. The results indicated that the ethyl ester of 3,4-dihydroxybenzoic acid was an efficient inhibitor of prolyl hydroxylation in fibroblast cultures, with Ki of approximately 0.4 mM. Ethyl 3,4-dihydroxybenzoate had little, if any, effect on the hydroxylation of lysyl residues, and it did not affect total protein synthesis or DNA replication in these cells. To test the hypothesis that ethyl 3,4-dihydroxybenzoate might serve as a potential antifibrotic agent, its efficacy in inhibiting prolyl hydroxylation in scleroderma fibroblasts was also tested. The results indicated that the synthesis of 4-hydroxyproline in scleroderma cell cultures was similarly reduced by ethyl 3,4-dihydroxybenzoate. Thus, structural analogs of the cofactors or cosubstrates of prolyl 4-hydroxylase, such as ethyl 3,4-dihydroxybenzoate tested here or its further modifications, may serve as inhibitors of posttranslational hydroxylation of prolyl residues also in vivo. These compounds could potentially provide a novel means of reducing collagen deposition in tissues in fibrotic diseases, such as scleroderma.
Cells, Cultured↗
Partial identity of the 2-oxoglutarate and ascorbate binding sites of prolyl 4-hydroxylase.
Various hydroxybenzenes, hydroxybenzoic acids, and related compounds resemble structurally both 2-oxoglutarate and ascorbate, two reactants needed in the reaction of prolyl 4-hydroxylase. These substances were found to inhibit prolyl 4-hydroxylase competitively with respect to both cosubstrates. Ortho-dihydroxy derivatives, which are capable of chelating the enzyme-bound iron, were the most effective inhibitors, with Ki values of about 5 microM. In contrast, pyridine 2-carboxylates, which have previously been reported to inhibit the enzyme competitively with respect to 2-oxoglutarate, were found to inhibit it uncompetitively with respect to ascorbate. In a separate set of experiments the side chain of the ascorbate molecule was shown to make no significant contribution to the binding of the reductant to the enzyme, as D(-)-isoascorbate and 5,6-O-isopropylidene ascorbate gave essentially the same Vmax and Km values as ascorbate. On the other hand, structural modifications of the ring atoms that abolished the chelating capacity destroyed both the cosubstrate and inhibitory activity, as in L-galactono gamma-lactone. The ascorbate binding site therefore appears to consist of two cis-positioned coordination sites of the enzyme-bound iron and is thus partially identical to the binding site of 2-oxoglutarate. This mode of interaction suggests that ascorbate reduces the enzyme-bound iron through an "inner-sphere" mechanism. The inhibitors studied appear to react at different phases of the catalytic cycle, determined by the oxidation state of the enzyme-bound iron atom.
Animals↗
Differences between collagen hydroxylases and 2-oxoglutarate dehydrogenase in their inhibition by structural analogues of 2-oxoglutarate.
Inhibition of lysyl hydroxylase and prolyl 3-hydroxylase was studied with 23 selected aromatic and aliphatic structural analogues of 2-oxoglutarate and the results were compared with those previously reported for prolyl 4-hydroxylase. All the compounds inhibited the hydroxylases competitively with respect to 2-oxoglutarate and noncompetitively with respect to Fe2+ and the peptide substrate. The inhibition patterns for the three collagen hydroxylases were basically similar, but certain differences in detail emerged. One systematic difference was that lysyl hydroxylase had a higher Ki for almost all the compounds than had the two prolyl hydroxylases. Another interesting difference was that pyridine-2,4-dicarboxylate was the most potent inhibitor of lysyl hydroxylase and prolyl 3-hydroxylase, with Ki values of 50 microM and 3 microM respectively, whereas pyridine-2,5-dicarboxylate was the most potent inhibitor of prolyl 4-hydroxylase. These and other data suggest that the three collagen hydroxylases have similar but not identical 2-oxoglutarate-binding sites. Pyridine-2,4-dicarboxylate and pyridine-2,5-dicarboxylate and their corresponding benzene derivatives were also found to inhibit 2-oxoglutarate dehydrogenase, but with this enzyme, unlike the collagen hydroxylases, no distinct difference in the Ki values was found between the corresponding pyridine and benzene derivatives. This demonstrates the importance of the metal ion for the binding of various compounds at the 2-oxoglutarate-binding site of the collagen hydroxylases. 2-Oxoadipate was shown to replace 2-oxoglutarate in the lysyl hydroxylase and 2-oxoglutarate dehydrogenase reactions, as has previously been reported for prolyl 4-hydroxylase, whereas no other 2-oxo acid tested had any co-substrate activity. The 2-oxoglutarate-binding site of these enzymes is thus flexible to a certain degree, as it can accommodate molecules of different shapes and volumes. On the basis of the present data pyridine-2,5-dicarboxylate seems to be a quite specific inhibitor of prolyl 4-hydroxylase, the Ki for 2-oxoglutarate dehydrogenase being about 4000-fold higher.
Adipates↗
Synthesis of collagen: chemical regulation of post-translational events.
Collagen biosynthesis involves many unique post-translational events. Inhibition of some of these will lead either to decreased formation of the extracellular collagen fibres or to an accumulation of fibres with altered functional properties. The events that would seem most suitable targets for chemical regulation are triple helix formation, the cleavage of propeptides from the procollagen molecules and cross-link formation. Attempts have recently been made to develop inhibitors of prolyl 4-hydroxylase in particular, as inhibition of this enzyme will prevent triple helix formation and thus lead to a non-functional protein. Prolyl 4-hydroxylase is inhibited competitively with respect to ferrous ion by several bivalent cations, especially zinc, with respect to 2-oxoglutarate by pyridine 2,5-dicarboxylate, pyridine 2,4-dicarboxylate, 3,4-dihydroxybenzoate and many related compounds, with respect to oxygen by superoxide dismutase-active copper chelates and with respect to the peptide substrate by a number of peptides. Triple helix formation can also be inhibited by administering certain proline analogues such as cis-4-hydroxyproline and L-azetidine-2-carboxylic acid, which are incorporated into proteins in place of proline. Only preliminary data are available on the possibilities for using any of these substances to inhibit collagen accumulation in fibrotic processes.
Animals↗