Depression and tetrahydrobiopterin: the folate connection

Total biopterin, neopterin and creatinine were measured in spot urine samples from affective disorder patients on lithium therapy and control subjects. Folic acid was also measured in plasma in a sample of the patients. The mean neopterin: biopterin ratio was significantly higher in the 76 patients (3.2 +/- 0.5) than in the 61 controls (1.8 +/- 0.1). In female patients biopterin levels were significantly lower than in controls. In the control groups there was a significant correlation between the molar concentration of neopterin and biopterin. No such correlation was found in the patients. These data indicate that tetrahydrobiopterin (BH4) biosynthesis is reduced in this group. A significant positive correlation was found between plasma folate and urinary biopterin. It is suggested that folate deficiency may impair the synthesis of BH4, a cofactor essential for the synthesis of 5-HT and other monoamines that are involved in the pathogenesis of affective disorders.

Folate metabolism in the female weanling rat

The metabolism of a mixture of [2-14C] and [3',5',7,9-3H] folic acid was studied in female weanling rats. Intact folates and folate catabolites were excreted in the urine. Folate polyglutamates were found in the tissues. Rats treated with the oestrogen diethylstilbestrol and 17 -ethynyloestradiol exhibited marked changes in the metabolic handling of folic acid and folate catabolism was greatly increased compared to controls. Allopurinol treatment gave greater label retention in the gut, with a substantial increase in catabolism compared to normals. A dose response relationship was illustrated between allopurinol dose and folate catabolism. After lead acetate dosing there was little radioactivity in the urine and tissues over 72h and more radioactivity was retained in the faeces compared to normals. Excretion of intact folates was depressed, especially 5MeTHF and 10CHOTHF. A tenfold increase in both lead and folic acid dosage resulted in an even further decrease of radioactivity in the tissues and urine over 72h. Excretion in the faeces was further elevated. Ferrous sulphate administration resulted in increased catabolism. The retention of radioactivity in the liver, kidney and gut was greatly reduced. A new method of folate analysis; Sephadex LH-20 was introduced. In vitro superoxide anion formation was illustrated using an allopurinol/xanthine oxidase system. Histological studies were employed to qualitatively and quantitatively illustrate the oxidative status in livers and brains of allopurinol and ferrous sulphate dosed rats. Increased dose related formazan deposition was observed when livers of pretreated animals were incubated with nitroblue tetrazolium. Formazan deposition was reduced in pretreated animals also treated with the anti-oxidants vitamin E, mannitol or 4-hydroxy-methyl-4,6-ditertiary-butylphenol. A possible route of folate catabolism is scission by a non-enzymic oxidation involving active oxygen species.

Specific pH‐responsive folate‐conjugate microgels designed for antitumor therapy

Colloidal nanosized folate-conjugated hydrogels for targeted chemotherapy were prepared via a versatile and efficient postsynthetic modification pathway starting from P(NPA-co-NIPAM). The modifications included the introduction of 4-methylpyridine as pH-sensitive pendant groups and the conjugation of folic acid to the microgel network. The microgels showed a specific swelling at pH?

Downstream effects on human low density lipoprotein of homocysteine exported from endothelial cells in an in vitro system

A model system is presented using human umbilical vein endothelial cells (HUVECs) to investigate the role of homocysteine (Hcy) in atherosclerosis. HUVECs are shown to export Hcy at a rate determined by the flux through the methionine/Hcy pathway. Additional methionine increases intracellular methionine, decreases intracellular folate, and increases Hcy export, whereas additional folate inhibits export. An inverse relationship exists between intracellular folate and Hcy export. Hcy export may be regulated by intracellular S-adenosyl methionine rather than by Hcy. Human LDLs exposed to HUVECs exporting Hcy undergo time-related lipid oxidation, a process inhibited by the thiol trap dithionitrobenzoate. This is likely to be related to the generation of hydroxyl radicals, which we show are associated with Hcy export. Although Hcy is the major oxidant, cysteine also contributes, as shown by the effect of glutamate. Finally, the LDL oxidized in this system showed a time-dependent increase in uptake by human macrophages, implying an upregulation of the scavenger receptor. These results suggest that continuous export of Hcy from endothelial cells contributes to the generation of extracellular hydroxyl radicals, with associated oxidative modification of LDL and incorporation into macrophages, a key step in atherosclerosis. Factors that regulate intracellular Hcy metabolism modulate these effects. Copyright © 2005 by the American Society for Biochemistry and Molecular Biology, Inc.

Oxidative LDL modification is increased in vascular dementia and is inversely associated with cognitive performance

It is not known whether the association between increased plasma homocysteine (Hcy) associated with LDL modification and propensity for LDL uptake by macrophages in cardiovascular disease patients holds true in vascular dementia (VaD). Plasma from 83 subjects diagnosed with Alzheimer's disease (AD), VaD, mild cognitive impairment (MCI) and from controls was analysed to examine (1) whether LDL isolated from the plasma of VaD is biochemically and functionally distinct from that isolated from AD, MCI or controls; and (2) whether such biomarkers of LDL phenotype are related to plasma folate levels, Hcy levels and/or to disease severity. Folate and vitamin B6 levels were significantly lower in VaD subjects than in controls. VaD-LDL showed increased protein carbonyl content (p <0.05) and was more susceptible to scavenging by macrophages (p <0.05) than AD- or control-LDL. Patients from the VaD cohort were more prevalent in the lowest tertile for HDL:LDL and the upper tertile for LDL oxidation; the combined parameters of HDL cholesterol, LDL oxidation and scavenging by macrophages show 87% sensitivity towards VaD detection. The association between folate deficiency, LDL modification and dysfunction in VaD but not in AD may provide a novel biomarker assessment to discriminate between the diseases.

Structural studies on antifolate drugs

Single crystal X-ray structure determinations are reported for eleven compounds all of which are either biologically active or potentially biologically important. The compounds fall into two distinct classes:- 1. Substituted diaminopyrimidines 2. Substituted aminopyrimidinones The first class of compounds were all selected on the basis of their common diaminopyrimidine nucleus which has been demonstrated to be a vital requirement for antifolate activity. They may all be described as non-classical or small molecule lipophilic dihydrofolate reductase (DHFR) inhibitors, as opposed to the classical folate analogues, having the ability to cross the blood-brain barrier, enter cells via a rapid passive diffusion process, and achieve high intracellular concentrations. Thus they are an excellent choice in the search for crystallography in the solid state, providing geometrical and distance data not available from any other analytical techniques to date; supporting and enhancing data obtained in the lower resolution studies of protein crystallography. The biological importance of these compounds is discussed and an attempt is made to relate/predict their pharmacological activity to observed structural features in the crystalline environment. Special attention is focussed on hydrogen bonding, confirmational flexibility and hydrophobicity of substituents; each of which appear to make contributions to tight binding in the enzyme active site. Chapter 9 describes the use of data from the literature and the solid state modelling of an observed enzyme-substrate interaction in an attempt to define it more accurately in terms of its geometric flexibility. Of the second class, one compound (ABPP) is reported; studies in two different crystal forms. In demonstrating both antiviral and high interferon inducing activity it is possible that this compound could be useful against cancer and also viral infections.