Andreas Laich

Neopterin production, tryptophan degradation, and mental depression—What is the link?

The cytokine interferon-gamma stimulates human monocytes/macrophages to release large amounts of neopterin. Increased neopterin concentrations in body fluids of patients are observed during diseases with activated cellular (=TH1-type) immune response such as allograft rejection, virus infections, autoimmune disorders, or malignant tumors but also in neurodegenerative diseases or during pregnancy. In various cells interferon-gamma induces indoleamine 2,3-dioxygenase (IDO) which degrades tryptophan via the kynurenine pathway. Therefore like increased neopterin formation, enhanced tryptophan degradation is observed in diseases concomitant with cellular immune activation. Disturbed metabolism of tryptophan affects biosynthesis of neurotransmitter 5-hydroxytryptamine (serotonin), and it appears to be associated with an increased susceptibility for depression. In fact, enhanced neopterin concentrations together with increased degradation of tryptophan and low serum levels of tryptophan correlate with neuropsychiatric abnormalities like cognitive decline and depressive symptoms especially in long-lasting and chronic diseases. Activation of IDO could represent an important link between the immunological network and the pathogenesis of depression.

Cell swelling stimulates cytosol to membrane transposition of ICln.

ICln is a multifunctional protein that is essential for cell volume regulation. It can be found in the cytosol and is associated with the cell membrane. Besides its role in the splicing process, ICln is critically involved in the generation of ion currents activated during regulatory volume decrease after cell swelling (RVDC). If reconstituted in artificial bilayers, ICln can form ion channels with biophysical properties related to RVDC. We investigated (i) the cytosol versus cell membrane distribution of ICln in rat kidney tubules, NIH 3T3 fibroblasts, Madin-Darby canine kidney (MDCK) cells, and LLC-PK1 epithelial cells, (ii) fluorescence resonance energy transfer (FRET) in living fibroblasts between fluorescently tagged ICln and fluorochromes in the cell membrane, and (iii) possible functional consequences of an enhanced ICln presence at the cell membrane. We demonstrate that ICln distribution in rat kidneys depends on the parenchymal localization and functional state of the tubules and that cell swelling causes ICln redistribution from the cytosol to the cell membrane in NIH 3T3 fibroblasts and LLC-PK1 cells. The addition of purified ICln protein to the extracellular solution or overexpression of farnesylated ICln leads to an increased anion permeability in NIH 3T3 fibroblasts. The swelling-induced redistribution of ICln correlates to altered kinetics of RVDC in NIH 3T3 fibroblasts, LLC-PK1 cells, and MDCK cells. In these cells, RVDC develops more rapidly, and in MDCK cells the rate of swelling-induced depolarization is accelerated if cells are swollen for a second time. This coincides with an enhanced ICln association with the cell membrane.

Hyperhomocysteinemia, Pteridines and Oxidative Stress

Tetrahydrofolate is an essential cofactor for the conversion of homocysteine to methionine, and hyperhomocysteinemia is considered as a risk factor for cardiovascular and cerebrovascular diseases. In subjects with hyperhomocysteinemia usually an inverse relationship exists to folic acid levels, and supplementation with folic acid is able to lower homocysteine concentrations. The pathogenesis of most if not all diseases which are accompanied with moderate hyperhomocysteinemia involves cellular immune activation and therefore in patients very often exists also a positive correlation between homocysteine concentrations and the degree of immune activation which is indicated, e.g. by increased neopterin concentrations. Since neopterin concentrations also serves as an estimate of oxidative stress merging from immune system activation, this association suggests that cellular immune activation and oxidative stress could be involved in the development of hyperhomocysteinemia. Because tetrahydrofolate is very susceptible to oxidation, an increased oxidative degradation of tetrahydrofolates may become relevant under oxidative stress conditions. In this way folate deficiency may develop despite normal dietary intake of the vitamin. In our patients, hyperhomocysteinemia is considered as an indirect consequence of hyperconsumption of antioxidant vitamins during prolonged states of immune activation.

Moderate hyperhomocysteinaemia and immune activation in Parkinson's disease

Summary. Moderate hyperhomocysteinaemia has been linked to an increased risk for cardiovascular diseases. Increased homocysteine concentrations may follow folate depletion due to insufficient dietary intake of the vitamin, but there is also some indication that immune activation could play a role. In this preliminary study, homocysteine, folate, and vitamin B12 concentrations were measured in 19 patients with Parkinsons disease, 61–90 years of age, and compared to a healthy control group of similar age and to neopterin concentrations as an indicator of immune activation. A subgroup of patients presented with increased homocysteine and low folate concentrations. Homocysteine levels correlated inversely with vitamins folate and B12 and positively with neopterin concentrations. Disturbed homocysteine metabolism in Parkinsons disease may be associated with vitamin deficiency and with immune system activation which may underlie folate depletion.

ICln: a chloride channel paramount for cell volume regulation.

Cell volume regulation is a ubiquitous cell regulatory mechanism based on meticulously controlled ion transport mechanisms. Keeping the absolute volume constant seems to be of the highest priority for most cells and is achieved at the expense of altered intracellular ion concentrations. We have been able to demonstrate that ICln, a chloride channel cloned from epithelial cells, is paramount for the ability of swollen cells to regulate their volume back to that under resting conditions. A unique feature of ICln is the distinct sensitivity of these channels for nucleotides and nucleoside analogues added to the extracellular fluid. In addition, cromolyn sodium and nedocromil sodium, drugs used by patients with asthma, are able to impede the function of these channels.

The gastric H,K-ATPase blocker lansoprazole is an inhibitor of chloride channels.

It was postulated that swelling dependent chloride channels are involved in the proton secretion of parietal cells. Since omeprazole, lansoprazole and its acid activated sulphenamide form AG2000 are structurally related to phenol derivatives known to block swelling dependent chloride channels, we set out to test, whether these substances – which are known to block the H,K‐ATPase – could also lead to an inhibition of swelling‐dependent chloride channels. Swelling‐dependent chloride channels – characterized in many different cell types – show highly conserved biophysical and pharmacological features, therefore we investigated the effect of omeprazole, lansoprazole and its acid activated sulphenamide form AG2000 on swelling‐dependent chloride channels elicited in fibroblasts, after the reduction of the extracellular osmolarity. Omeprazole, lansoprazole and its acid activated sulphenamide form AG2000 are able to block swelling‐dependent chloride channels (IClswell). Lansoprazole and its protonated metabolite AG2000 act on at least two different sites of the IClswell protein: on an extracellular site which seems to be in a functional proximity to the nucleotide binding site, and on an intracellular site which allows the formation of disulfide‐bridges. The inhibition of the proton pump and the simultaneous blocking of chloride channels by omeprazole, lansoprazole and its acid activated sulphenamide form AG2000, as described here could be an effective mode to restrict proton secretion in parietal cells.

Immunologic Alterations in Schizophrenia: Neopterin, L-Kynurenine, Tryptophan and T-Cell Subsets in the Acute Stage of Illness

Abstract It is well established now that in diseases with activated cell-mediated immunity increased formation of neopterin and degradation of tryptophan is an indication of endogenous production of interferon-γ in patients. Therefore increased neopterin levels are associated with increased kynuremne levels and decreased tryptophan in patients suffering from virus infections, malignant diseases or autoimmunity. To investigate cell-mediated immunity m schizophrenia, neopterin, L-kynurenine, L-tryptophan and T-cell-subsets were measured in 10 chronic schizophrenic patients, addmitted to hospital due to acute psychiatric relapse. Low neopterin concentrations were found at the beginning of hospitalisation and followed by a significant increase at the time of discharge (p = 0.02). Mean neopterin values were still within the 95th percentile of healthy controls. Kynuremne levels showed a similar development (p = 0.03) as neopterin whereas tryptophan values were low at admission without any significant changes thereafter. CD3 + and CD4+-cells presented with highest numbers at admission, followed by a continuous decrease and NK-cells were found lowest on day 0 with a gradual increase by day 7. These findings argue against acute virus infection in acutely ill schizophrenic patients because this would be associated with incerased neopterin fromation and tryptophan dagradation, rather the data would be in line with a shift from TH-1 to TH-2-type immune reaction which which is common in chronic infections.

Neopterin, an Immunodiagnostic and Oxidative Stress Indicator

Neopterin, D-erythro-trihydroxypropylpterin, is a stable, low-molecular mass molecule which is produced in humans and primates by monocytes/macrophages upon stimulation with interferon-(IFN)-γ. In other species only scarce amounts of neopterin are detected. Measurement of neopterin in body fluids provides a sensitive method to estimate the degree of cellular immune activation. IFN-γ is the only known cytokine to directly stimulate neopterin production although others like tumor necrosis factor-α or Interleukin-12 superinduce the quantity of neopterin secretion (1, 2).

Moderate Hyperhomocysteinemia in Patients with Huntington's Disease

Abstract Hyperhomocysteinemia is considered to be an independent risk factor for cardiovascular diseases and atherosclerosis. Also patients with dementia, either of Alzheimers or of vascular type, may present with elevated homocysteine levels. All these disorders are linked with older age and since hyperhomocysteinemia is also frequent in the healthy elderly, we were interested to determine homocysteine concentrations in a younger population of demented patients suffering from Huntingtons disease. In 15 patients with Huntingtons disease and in a control group of similar age, serum homocysteine concentrations were measured and changes were compared to concentrations of folate and neopterin, the latter being an indicator of immune activation. A subgroup of patients with Huntingtons disease presented with elevated homocysteine concentrations compared to healthy controls of similar age. Moderate hyperhomocysteinemia was related to lower folate concentrations and also to higher neopterin levels which indicate increased immune activation. The correlation of homocysteine with neopterin concentrations points to a possible relationship between the development of hyperhomocysteinemia and immune activation in the patient

IS MODERATE HYPERHOMOCYSTEINEMIA DUE TO FOLIC ACID DEPLETION RATHER THAN INSUFFICIENT DIETARY INTAKE

Hyperhomocysteinemia is considered as a risk factor for cardio- and cerebrovascular diseases. For the conversion of homocysteine to methionine, tetrahydrofolic acid is an essential cofactor. Usually hyper-homocysteinemia coincides with low folate levels, and supplementation with folic acid is able to lower homocysteine concentrations. Very often in patients there exists also a positive correlation between homocysteine and neopterin concentrations. Increased neopterin concentrations indicate cellular immune activation and allow an estimate of oxidative stress resulting from this immune activation. Therefore, the findings suggest that oxidative stress could be involved in the development of hyperhomo-cysteinemia. Because tetrahydrofolate is very susceptible to oxidation, an increased oxidative degradation of tetrahydrofolate may become relevant under oxidative stress conditions. In this way folate deficiency may develop despite normal dietary intake of the vitamin. Thus, hyperhomocysteinemia could be considered as an indirect consequence of hyperconsumption of antioxidant vitamins during prolonged states of immune activation.