HOMOCYSTINURIA: ABSENCE OF CYSTATHIONINE IN THE BRAIN

The chronological evolution of small organic molecular fluorescent probes for thiols

Abnormal concentrations of biothiols such as cysteine, homocysteine and glutathione are associated with various major diseases. In biological systems, the structural similarity and functional distinction of these three small molecular thiols has not only required rigorous molecular design of the fluorescent probes used to detect each thiol specifically, but it has also inspired scientists to uncover the ambiguous biological relationships between these bio-thiols. In this minireview, we will discuss the evolution of small organic molecular fluorescent probes for the detection of thiols over the past 60 years, highlighting the potent methodologies used in the design of thiol probes and their particular applications in the semi-quantification of cellular thiols and real-time labelling. At the same time, the present challenges that limit their further application will be discussed. We hope that this minireview will promote future research to enable deeper insight into the crucial role of thiols in biological systems.

The chronological evolution of small organic molecular fluorescent probes for thiols: from separation dependency analysis to cellular specific analysis, what's next?

The effectiveness of correcting abnormal metabolic profiles

Inborn errors of metabolism cause disease because of accumulation of a metabolite before the blocked step or deficiency of an essential metabolite downstream of the block. Treatments can be directed at reducing the levels of a toxic metabolite or correcting a metabolite deficiency. Many disorders have been treated successfully first in a single patient because we can measure the metabolites and adjust treatment to get them as close as possible to the normal range. Examples are drawn from Komrower's description of treatment of homocystinuria and the author's trials of treatment in bile acid synthesis disorders (3β-hydroxy-Δ⁵ -C₂₇ -steroid dehydrogenase deficiency and Δ⁴ -3-oxosteroid 5β-reductase deficiency), neurotransmitter amine disorders (aromatic L-amino acid decarboxylase [AADC] and tyrosine hydroxylase deficiencies), and vitamin B6 disorders (pyridox(am)ine phosphate oxidase deficiency and pyridoxine-dependent epilepsy [ALDH7A1 deficiency]). Sometimes follow-up shows there are milder and more severe forms of the disease and even variable clinical manifestations but by measuring the metabolites we can adjust the treatment to get the metabolites into the normal range. Biochemical measurements are not subject to placebo effects and will also show if the disorder is improving spontaneously. The hypothesis that can then be tested for clinical outcome is whether getting metabolite(s) into a target range leads to an improvement in an outcome parameter such as abnormal liver function tests, hypokinesia, epilepsy control etc. The metabolite-guided approach to treatment is an example of personalized medicine and is a better way of determining efficacy for disorders of variable severity than a randomized controlled clinical trial.

Higher incidence of C677T polymorphism of the MTHFR gene in North Indian patients with vascular disease

Homocysteine is a sulfur-containing amino acid, which is derived from dietary methionine. Hyperhomocysteinemia has been implicated in vascular disease for over a decade now, and can be treated with B vitamins. Among its causes is polymorphism of the MTHFR gene, the most common being the cytidine to thymidine at position 677 (MTHFR C677T), which gives rise to three genotypes - normal homozygous CC, heterozygous CT and homozygous variant TT. An attempt was made to ascertain the prevalence of this MTHFR C677T in our population so that preventive measures may accordingly be instituted. Blood samples from 70 patients with vascular disease and 70 healthy controls were analyzed for plasma homocysteine levels (chemiluminescent immunoassay) and for the presence of MTHFR C677T (polymerase chain reaction analysis). Homocysteine was higher in the homozygous subjects (TT genotype) than in the heterozygous (CT genotype). In patients, the frequency of the C allele was significantly lower, and that of the T allele was significantly higher than the corresponding frequencies in controls. In conclusion, the North Indian urban population has higher homocysteine levels associated with the TT genotype. Hence, instituting measures towards reduction of homocysteine levels in the population would probably reduce the incidence and morbidity of vascular disease in our population.

Hypermethioninemias of genetic and non-genetic origin: A review

This review covers briefly the major conditions, genetic and non-genetic, sometimes leading to abnormally elevated methionine, with emphasis on recent developments. A major aim is to assist in the differential diagnosis of hypermethioninemia. The genetic conditions are: (1) Homocystinuria due to cystathionine β-synthase (CBS) deficiency. At least 150 different mutations in the CBS gene have been identified since this deficiency was established in 1964. Hypermethioninemia is due chiefly to remethylation of the accumulated homocysteine. (2) Deficient activity of methionine adenosyltransferases I and III (MAT I/III), the isoenzymes the catalytic subunit of which are encoded by MAT1A. Methionine accumulates because its conversion to S-adenosylmethionine (AdoMet) is impaired. (3) Glycine N-methyltrasferase (GNMT) deficiency. Disruption of a quantitatively major pathway for AdoMet disposal leads to AdoMet accumulation with secondary down-regulation of methionine flux into AdoMet. (4) S-adenosylhomocysteine (AdoHcy) hydrolase (AHCY) deficiency. Not being catabolized normally, AdoHcy accumulates and inhibits many AdoMet-dependent methyltransferases, producing accumulation of AdoMet and, thereby, hypermethioninemia. (5) Citrin deficiency, found chiefly in Asian countries. Lack of this mitochondrial aspartate-glutamate transporter may produce (usually transient) hypermethioninemia, the immediate cause of which remains uncertain. (6) Fumarylacetoacetate hydrolase (FAH) deficiency (tyrosinemia type I) may lead to hypermethioninemia secondary either to liver damage and/or to accumulation of fumarylacetoacetate, an inhibitor of the high K(m) MAT. Additional possible genetic causes of hypermethioninemia accompanied by elevations of plasma AdoMet include mitochondrial disorders (the specificity and frequency of which remain to be elucidated). Non-genetic conditions include: (a) Liver disease, which may cause hypermethioninemia, mild, or severe. (b) Low-birth-weight and/or prematurity which may cause transient hypermethioninemia. (c) Ingestion of relatively large amounts of methionine which, even in full-term, normal-birth-weight babies may cause hypermethioninemia.

Sudden death of an 18-year-old man with homocystinuria and intracranial inflammatory pseudotumor (IPT)

An 18-year-old mentally deficient man with well-known homocystinuria died suddenly within a few minutes. He had a history of severe oligophrenia, bilateral ectopia lentis requiring extraction of both lenses and operatively corrected genu valgum on both sides. In 1993 a hypergammaglobulinemia was noticed and a decortication on the left side after purulent pneumonia became necessary. Four months before death multiple abscesses in the spleen and pancreas lead to splenectomy and resection of the pancreatic tail. Furthermore, an isolated inflammatory pseudotumor (IPT) of the brain was found. Autopsy revealed as cause of death a pulmonary embolism. The pathogenesis of the cause of death and concomitant diseases will be discussed.

The effects of chronic isoniazid intoxication on motor end plate sprouting in rat sternocostalis muscle and on responses to partial denervation and local botulinum toxin

Chronic dosing of rats with isoniazid (INH) leads to an increase in the incidence of short "spontaneous" sprouts on motor end plates in the rat sternocostalis muscle. After partial denervation there is a slight increase in terminal sprouting after 1 week of dosing: this changes to a significant decrease from 2 to 6 weeks of dosing. The same is noted after local botulinum toxin injection, and in both conditions sprout length is significantly reduced. In vitro studies show that glutathione, cysteine and cystathionine all increase the incidence of short, "spontaneous" sprouts from end plates, while homocysteine and cystine have no effect. These findings are interpreted in the light of the hypothesis that in INH intoxication there may be a reduction of available axonal glutathione and cysteine due to inhibition of the pyridoxal phosphate-dependent enzymes cystathionine synthetase and cystathioninase .

Ectopia lentis

Ectopia lentis was first described more than 200 years ago, but its value as a significant diagnostic clue to the presence of other ocular and systemic disorders has only recently been appreciated. Ectopia lentis may cause a marked reduction in visual acuity, which varies with the type and degree of dislocation and the presence of other ocular abnormalities. An approach to the diagnostic evaluation of the patient with ectopia lentis is outlined. The differential diagnosis is reviewed in detail both clinically and histologically. The complications of ectopia lentis and the appropriate management of affected patients are discussed.

Free amino acids and related substances in human glial tumours and in fetal brain: comparison with normal adult brain

An ion exchange automatic chromatographic analysis of the free amino acid concentrations of 18 human glial tumours and of 4 human fetal brains was carried out and the concentrations were compared to those of 13 biopsy specimens of normal adult brain. In addition, the concentrations of the amino acids of the glial tumours were compared to those of 7 intracerebral metastases of various origin. The chromatograms of several tumour specimens showed an unidentified peak overlapping proline. As far as the amino acid concentrations are concerned they varied depending upon the origin of the sample. The concentrations of most amino acids were higher in fetal brain than in adult brain with the exception of aspartic acid, glutamic acid, glutamine, cystathionine and GABA. Two peptides: glutathione and homocarnosine were absent in fetal brain and were present in adult brain. In glial tumours, homocarnosine and some amino acids, namely aspartic acid, glutamic acid and GABA, showed lower concentrations than in normal brain. Some amino acids were in the same concentration as in normal brain: taurine, phosphoethanolamine, glutamine and cystathionine. Most of the others were in higher concentrations than in normal brain, mainly proline. The results suggest that the concentrations of 5 compounds: taurine, proline, cystathionine, GABA and homocarnosine, taken as a whole, provide information on the origin of the sample.

Homocystine-induced arteriosclerosis. The role of endothelial cell injury and platelet response in its genesis

The atherogenic mechanism of homocystinemia has been defined by measuring endothelial cell loss and regeneration, platelet consumption, and intimal lesion formation in a primate model. Three groups of baboons were studied: (a) 8 control animals; (b) 15 animals after 3 mo of continuous homocystinemia; and (c) 11 animals after 3 mo of combined homocystinemia and oral treatment with dipyridamole. Experimental homocystinemia caused patchy endothelial desquamation comprising about 10% of the aortic surface despite a 25-fold increase in endothelial cell regeneration. Neither endothelial cell loss nor regeneration was changed significantly by dipyridamole. Homocystine-induced vascular deendothelialization produced a threefold increase in platelet consumption that was interrupted by dipyridamole inhibition of platelet function. All homocystinemic animals developed typical arteriosclerotic or preatherosclerotic intimal lesions composed of proliferating smooth muscle cells averaging 10-15 cell layers surrounded by large amounts of collagen, elastic fibers, glycosaminoglycans, and sometimes lipid. Intimal lesion formation was prevented by dipyridamole therapy. We conclude that homocystine-induced endothelial cell injury resulted in arteriosclerosis through platelet-mediated intimal proliferation of smooth muscle cells that can be prevented by drug-induced platelet dysfunction.