Quantitative determination of free intracellular amino acids in single human polymorphonuclear leucocytes. Recent developments in sample preparation and high-performance liquid chromatography

Pyruvate: immunonutritional effects on neutrophil intracellular amino or alpha-keto acid profiles and reactive oxygen species production

For the first time the immunonutritional role of pyruvate on neutrophils (PMN), free α-keto and amino acid profiles, important reactive oxygen species (ROS) produced [superoxide anion (O(2) (-)), hydrogen peroxide (H(2)O(2))] as well as released myeloperoxidase (MPO) acitivity has been investigated. Exogenous pyruvate significantly increased PMN pyruvate, α-ketoglutarate, asparagine, glutamine, aspartate, glutamate, arginine, citrulline, alanine, glycine and serine in a dose as well as duration of exposure dependent manner. Moreover, increases in O(2) (-) formation, H(2)O(2)-generation and MPO acitivity in parallel with intracellular pyruvate changes have also been detected. Regarding the interesting findings presented here we believe, that pyruvate fulfils considerably the criteria for a potent immunonutritional molecule in the regulation of the PMN dynamic α-keto and amino acid pools. Moreover it also plays an important role in parallel modulation of the granulocyte-dependent innate immune regulation. Although further research is necessary to clarify pyruvate's sole therapeutical role in critically ill patients' immunonutrition, the first scientific successes seem to be very promising.

Liquid chromatography-tandem mass spectrometric determination of a new antibacterial agent (AVE6971) in human white blood cells

An LC-MS/MS assay for the quantitative determination of a new antibacterial agent (AVE6971) has been developed and validated in human white blood cells (WBC). The assay involved a lysing procedure of white blood cells and ultra centrifugation of the extracts. Chromatography was performed on a Supelcosil ABZ+ C(18) (2.1 mm x 50 mm, 5 microm) column using a mobile phase consisting of methanol/acetonitrile/10mM ammonium formate mixture (10:30:60, v/v/v) at a flow rate of 0.2 ml/min. The linearity was within the range of 10-10000 ng/ml of extracts, corresponding to 0.5-500 ng of AVE6971 in WBC pellets tubes. The validated lower limit of quantification was 10 ng/ml. The inter- and intra-run coefficients of variation (CV) for the assay were <12.9% and the accuracy were from -9.0 to -1.2%. AVE6971 was stable in WBC for at least 1 month at -75 degrees C. This assay proved to be suitable for the determination of AVE6971 in WBC from clinical studies.

Which mechanisms are involved in taurine-dependent granulocytic immune response or amino- and α-keto acid homeostasis?

We examined the effects of beta-alanine (taurine analogue and taurine transport antagonist), taurine (regarding its role in neutrophil (PMN) immunonutrition) and taurine combined either with L-NAME (inhibitor of *NO-synthase), SNAP (*NO donor), DON (glutamine-analogue and inhibitor of glutamine-requiring enzymes), DFMO (inhibitor of ornithine-decarboxylase) and beta-alanine on neutrophil amino- and alpha-keto acid profiles or important PMN immune functions in order to establish whether taurine transport-, nitric oxide-, glutamine- or ornithine-dependent mechanisms are involved in any of the taurine-induced effects. According to the present findings, the taurine-mediated effect appears to be based primarily on a modulation of important transmembraneous transport mechanisms and only secondarily on directly or indirectly induced modifications in intragranulocytic amino- and alpha-keto acid homoeostasis or metabolism. Although a direct relation to the parallel observed immunological modifications can only be presumed, these results show very clearly that compositional modifications in the free intragranulocytic amino- and alpha keto-acid pools coinciding with changes in intragranulocytic taurine levels are relevant metabolic determinants that can significantly influence the magnitude and quality of the granulocytic immune response.

A comparative study of the performance of acetonitrile and methanol in the multi-linear gradient separation of proteic primary amino acids

The performance of the separation of proteic primary amino acids using multi-linear gradients of acetonitrile and methanol was studied under an experimental-design basis, using an Inertsil ODS-3 column and pre-column derivatization with o-phthaldialdehyde (OPA) and N-acetyl-l-cysteine (NAC). Elution strength, peak properties, resolution, and analysis time, were examined. The optimal separation was established through modeling, using information obtained from isocratic data. By optimizing the separation with gradients of increasing complexity, acceptable resolution was possible, being glycine/threonine the critical pair. Multi-criteria decision-making (Derringer desirabilities) was applied to balance resolution and analysis time. The more favorable peak distribution for methanol gradients allowed a larger reduction of analysis times, keeping satisfactory resolution, but its smaller elution strength forces the use of concentrations significantly larger. Methanol is, however, less toxic, and the final cost is similar for both solvents.

Pathways involved in alanyl-glutamine-induced changes in neutrophil amino- and α-keto acid homeostasis or immunocompetence

We examined the effects of DON [glutamine-analogue and inhibitor of glutamine-requiring enzymes], alanyl-glutamine (regarding its role in neutrophil immunonutrition) and alanyl-glutamine combined with L-NAME, SNAP, DON, beta-alanine and DFMO on neutrophil amino and alpha-keto acid concentrations or important neutrophil immune functions in order to establish whether an inhibitor of *NO-synthase [L-NAME], an *NO donor [SNAP], an analogue of taurine and a taurine transport antagonist [beta-alanine], an inhibitor of ornithine-decarboxylase [DFMO] as well as DON could influence any of the alanyl-glutamine-induced effects. In summary, irrespective of which pharmacological, metabolism-inhibiting or receptor-mediated mechanisms were involved, our results showed that impairment of granulocytic glutamine uptake, modulation of intracellular glutamine metabolisation and/or de novo synthesis as well as a blockade of important glutamine-dependent metabolic processes may led to significant modifications of physiological and immunological functions of the affected cells.

Nitric oxide and polyamine pathway-dependent modulation of neutrophil free amino- and α-keto acid profiles or host defense capability

We have examined the effects of N(omega)-nitro-L-arginine-methylester-hydrochloride [L-NAME; inhibitor of nitric oxide synthase], S-nitroso-N-acetyl-penicillamine [SNAP; nitric oxide donor], alpha-difluoro-methyl-ornithine [DFMO; inhibitor of ornithine decarboxylase] arginine or ornithine as well as the combination of arginine or ornithine with L-NAME, SNAP or DFMO on intracellular free amino- and alpha-keto acid profiles and the immune function markers superoxide anion and hydrogen peroxide generation as well as released myeloperoxidase activity in neutrophils (PMN). Although the underlying mechanisms still remain unclear, we believe from our results that nitric oxide as well as polyamine-dependent pathways are involved in the signal transmission of free radical molecule, beneficial nutritional therapy or maleficient pharmacological stress-induced alterations in PMN nutrient composition. Relevant changes in intragranulocyte free amino- and alpha-keto acid homeostasis and metabolism, especially, may be one of the determinants in PMN nutrition that positively or negatively influences and modulate neutrophil host defence capability and immunocompetence.

Relationship of taurine and other amino acids in plasma and in neutrophils of septic trauma patients

Recently, an interdependency of plasma taurine and other amino acids as well as metabolic and clinical variables implicating therapeutic options was reported. This result may be an indication that plasma taurine levels are directly related to intracellular levels. Therefore, the aim of this study was to analyse the possible relationship between taurine levels in plasma and in neutrophils, the relationship to other amino acids, and variables quantifying metabolic impairment and severity of sepsis in multiple trauma patients developing sepsis. After multiple trauma taurine decreased significantly in plasma in thirty-two patients as well as within the neutrophil and does not recover in sepsis. Lower individual levels in the neutrophil did not follow lower individual levels in plasma and no correlation of taurine in plasma and in the neutrophils could be observed. In sepsis, only plasma showed an interdependency of taurine, aspartate, and glutamate. No association between taurine plasma or intracellular levels and SOFA score as indicator for severity of sepsis or metabolic variables was observed. After multiple trauma and in sepsis, taurine uptake in cells (which is regulated in different ways), and intracellular taurine (which serves e.g. as an osmolyte) can be influenced. Therefore a prediction of the neutrophil taurine pool seems not fully possible from taurine plasma levels. Intracellular taurine has some unique properties explaining the missing interdependency despite some similarities in osmoregulation and metabolic interactions to other amino acids. The association of taurine, aspartate, and glutamate in plasma cannot be simply transferred to the neutrophils intracellular level. The clinical meaning of the plasma correlation remains unclear. A dependency of plasma and neutrophil taurine to severity of sepsis and to metabolic variables seems not possible because of the multifactorial pathophysiology of sepsis.

A strategy for liquid chromatography/tandem mass spectrometric assays of intracellular drugs: application to the validation of the triphosphorylated anabolite of antiretrovirals in peripheral blood mononuclear cells

The pharmacokinetics of intracellular drugs have recently aroused new interest because monitoring a drug's behaviour near the site of action can enhance knowledge of its efficacy and toxicity. Liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) is particularly attractive for intracellular analytes. Very few papers deal precisely with special features encountered in intracellular drug assay or with how closely the assay matches the actual recommendations. Particular problems are encountered mainly because the analytes are located intracellularly. This mainly concerns the handling of biological media, including provision of blank samples using Ficoll gradient separation, cell counts, optimisation of cell lysis, sample extraction, plotting standard curves using either fmol/10(6) cells or fmol/ml of extract or fmol/sample, the matrix effect as a function of the number of cells, stability before and during cell separation, as well as in storage conditions using clinical samples, biological matrix replacement and interference by endogenous compounds. This paper describes a strategy for the full validation and routine use of an LC/MS/MS assay applied to the simultaneous intracellular determination of the triphosphorylated anabolites of didanosine (2',3'-dideoxyadenosine triphosphate or ddA-TP) and stavudine (2',3'-didehydro-3'-deoxythymidine triphosphate or d4T-TP), two nucleoside reverse transcriptase inhibitors of HIV, in human peripheral blood mononuclear cells (PBMCs), as a guide for further LC/MS/MS assay of intracellular drugs.

Low plasma glutamine after multiple trauma: relationship with intracellular glutamine in polymorphonuclear neutrophils during prolonged ICU stay

BACKGROUND

Aim of the study was to evaluate whether low plasma glutamine (GLN) is related to low intracellular GLN in stress-affected cells such as polymorphonuclear neutrophil (PMN). We hypothesized, that because low plasma GLN is assumed to have an impact on clinical outcome, stress-affected cells may also show low GLN contents.

METHODS

Thirty-nine consecutive severely injured trauma patients staying at least 10 days at a surgical intensive care unit (ICU) of a university hospital were separated into two groups: group one (n = 16) with low plasma GLN (< 420 micromol/l in average during ICU stay), and group two (n = 23) with normal plasma GLN. Initial blood samples for GLN analyses were collected within 24 h of admission at ICU. Further blood samples were taken on days 5 and 10 at 08:00 hours.

RESULTS

Patients in both groups showed no differences regarding demographic data, surgical interventions or infections. Acute physiology and chronic health evaluation (APACHE) II and the sequential organ failure assessment (SOFA) score and mortality rate were also comparable. During the study period, intracellular PMN GLN contents and concentrations did not differ between both groups. On the first day, intracellular PMN GLN content in the low plasma GLN group peaked at 5.01 +/- 3.06 x 10(-16) mol and in normal plasma GLN group at 4.73 +/- 2.57 x 10(-16) mol above the level of healthy individuals. In both groups, content decreased significantly towards the end of the observation period (group one: 2.79 +/- 1.59 x 10(-16) mol and group two: 2.63 +/- 1.71 x 10(-16) mol). A correspondent course could be observed for cell volumes. In contrast, variation of intracellular GLN concentrations remained within the reference range throughout the observation period: group one 836 +/- 510 micromol/l on day 1 and 582 +/- 331 micromol/l on day 10, and group two 788 +/- 428 micromol/l on day 1 and 548 +/- 356 micromol/l on day 10. No correlation between plasma GLN and intracellular GLN was found in either group.

CONCLUSION

No association between low plasma GLN and low intracellular GLN in PMN was found in a cohort of severely injured trauma patients with a minimum stay of 10 days at ICU.

Quantitative determination of free intracellular alpha-keto acids in neutrophils

For the first time, a procedure is described for the quantitative analysis of free alpha-keto acid content in human neutrophils (PMNs) relative to single cell number by reversed-phase fluorescence high-performance liquid chromatography. The procedure is minimally invasive and is unsurpassed in the quality of PMN separation, ease of sample preparation as well as sample stability. This method can satisfy the rigorous demands for an ultra-sensitive, comprehensive and rapid intracellular alpha-keto acid analysis in particularly for the surveillance of severe diseases as well as cellular or organ dysfunction.

Effects of propofol and taurine on intracellular free amino acid profiles and immune function markers in neutrophils in vitro

We have examined the effects of propofol, taurine, and the combination of propofol and taurine on amino acid profiles and the immune function markers superoxide anion (O2-), hydrogen peroxide (H2O2), and released myeloperoxidase (MPO) activity in neutrophils (PMN). Propofol led to significant changes in the dynamic PMN-free amino acid pool. Exogenous taurine significantly reduced PMN neutral amino acid and alpha-aminobutyrate (alpha-aba) as intracellular taurine increased. Incubation with propofol plus taurine resulted in lower intracellular taurine levels and elevated alpha-aba and neutral amino acid concentrations compared to propofol alone. Concerning PMN immune function markers, propofol significantly decreased O2- and H2O2 formation and released MPO. Taurine led to an increased release of MPO and concomitant significantly reduced O2- and H2O2 levels. When propofol and taurine were applied together they appeared to act additively with regard to superoxide and hydrogen peroxide formation. In the case of MPO, taurine neutralized propofol's effects, supporting the idea that MPO activity may be regulated by taurine. We believe therefore that taurine is important for strengthening PMN host defense capability, although the mechanisms are not yet clear. Moreover, taurine appears to act primarily by altering the PMN osmotic balance, while propofol seems to affect PMN amino acid metabolism and/or uptake and release.

The role of taurine in diabetes and the development of diabetic complications

The ubiquitously found beta-amino acid taurine has several physiological functions, e.g. in bile acid formation, as an osmolyte by cell volume regulation, in the heart, in the retina, in the formation of N-chlorotaurine by reaction with hypochlorous acid in leucocytes, and possibly for intracellular scavenging of carbonyl groups. Some animals, such as the cat and the C57BL/6 mouse, have disturbances in taurine homeostasis. The C57BL/6 mouse strain is widely used in diabetic and atherosclerotic animal models. In diabetes, the high extracellular levels of glucose disturb the cellular osmoregulation and sorbitol is formed intracellularly due to the intracellular polyol pathway, which is suspected to be one of the key processes in the development of diabetic late complications and associated cellular dysfunctions. Intracellular accumulation of sorbitol is most likely to cause depletion of other intracellular compounds including osmolytes such as myo-inositol and taurine. When considering the clinical complications in diabetes, several links can be established between altered taurine metabolism and the development of cellular dysfunctions in diabetes which cause the clinical complications observed in diabetes, e.g. retinopathy, neuropathy, nephropathy, cardiomyopathy, platelet aggregation, endothelial dysfunction and atherosclerosis. Possible therapeutic perspectives could be a supplementation with taurine and other osmolytes and low-molecular compounds, perhaps in a combinational therapy with aldose reductase inhibitors.

Methohexital affects neutrophil (PMN) dynamic free amino acid pool and immune functions in vitro

BACKGROUND AND OBJECTIVE

The objective of this study was to determine the dose as well as the duration of exposure-dependent effects of methohexital on neutrophil [polymorphonuclear leucocyte (PMN)] free amino acid profiles and, in a parallel study, on PMN immune functions.

METHODS

Whole blood samples were taken from 20 volunteers and incubated with methohexital [0 (control), 3.6, 26, 130 and 260 microg mL-1] for 10, 30, 60 or 120 min. PMN amino acid profiles were documented using advanced PMN separation and high-performance liquid chromatography procedures. Superoxide anion (O2-) and hydrogen peroxide production (H2O2), and activity of released myeloperoxidase (MPO), were determined photometrically.

RESULTS

After methohexital, significant dose (> or = 26 microg mL-1) as well as duration of exposure-dependent (> or = 30 min) increases in histidine, isoleucine, leucine, valine, methionine, serine, glycine, threonine, and decreases in glutamine, glutamate, aspartate, asparagine, arginine, ornithine, citrulline, alanine and taurine were observed (P < or = 0.05). Concerning PMN immune functions, methohexital significantly decreased O2-, H2O2 formation and MPO (> or = 26 microg mL-1, > or = 30 min, P < or = 0.05).

CONCLUSIONS

Altogether, there is significant relevance to the pharmacological regimens which enhance the supply of methohexital in whole blood. In regards to our results, we suggest that considerable changes in PMN 'dynamic free amino acid pool', for example induced by methohexital, may be one of the determinants in cell nutrition adversely affecting PMN metabolism. It is partially through its effect on the PMN free amino acid pool that maleficent pharmacological stress may have an unintentional influence on PMN immune functions.

Effects of diazepam on neutrophil (PMN) free amino acid profiles and immune functions in vitro. Metabolical and immunological consequences of L-alanyl-L-glutamine supplementation

The objective of this study was to determine the effects of diazepam, L-alanyl-L-glutamine (ala-gln) or diazepam combined with ala-gln on polymorphonuclear leukocyte (PMN) free amino acid profiles. In a parallel study the effects on PMN immune functions were also documented for the first time. The incubation of whole blood with diazepam led to significant changes in PMN free glutamine, aspartate, glutamate, ornithine, arginine, citrulline, taurine and methionine as well as branched chain and neutral amino acid concentrations. Ala-gln caused significant increases in PMN glutamine and alanine and asparagine, aspartate, glutamate, ornithine, arginine, serine and glycine profiles. Regarding PMN immune functions, diazepam significantly decreased superoxide anion (O(2)(-)) and hydrogen peroxide production (H(2)O(2)) and myeloperoxidase activity (MPO) while ala-gln significantly increased PMN immune functions. Ala-gln supplemented to diazepam largely reversed the changes in PMN amino acid profiles and PMN immune functions brought about by diazepam. Overall, diazepam or ala-gln lead to significant changes in PMN free amino acids. Important PMN immune functions also seem to be affected. In regards to the results, there is significant relevance to the pharmacological regimens which enhance the supply of diazepam or ala-gln in whole blood suggesting that considerable changes in PMN "labile free amino acid pool" occur. These regimens often follow beneficial nutritional therapy or maleficent pharmacological stress and may be one of the determinants in cell nutrition which influence PMN function. It is partially through its effect on PMN labile free amino acid pool that ala-gln supplemented to diazepam may maintain PMN immune functions in vitro.

Effects of etomidate on free intracellular amino acid concentrations in polymorphonuclear leucocytes in vitro

BACKGROUND

Previous studies have shown the inhibitory effects of etomidate on polymorphonuclear leucocyte (PMN) function. No reports exist, however, regarding free intracellular amino acid metabolism, although physiological cell metabolism and basic cell functions rely upon a balanced intracellular amino acid content and the cell membrane-mediated separation of cellular amino acids from the extracellular plasma amino acid pool. Thus, in the current study, we evaluated the effects of etomidate on free intracellular amino acid metabolism in PMN.

METHODS

With ethics committee approval, blood was withdrawn from 35 healthy volunteers and incubated (1 h) either with 0 microg/ml, 0.0156 microg/ml, 0.0625 microg/ml or 0.5 microg/ml of etomidate as well as with its additives (propylene glycol and Lipofundin MCT 10%). The PMN were separated using standardized Percoll-gradient and centrifugation procedure before deep-freezing and lyophilization techniques were employed. All PMN samples were dissolved in methanol/H2O, and the concentrations of free intracellular amino acids were monitored using both novel advanced PMN-separation and high-performance liquid chromatography techniques.

RESULTS

Etomidate influenced important free amino acid profiles in PMN in a dose-dependent manner, indicating complex changes of cellular amino acid turnover. Neither propylene glycol nor Lipofundin MCT 10% changed free amino acid concentrations in PMN.

CONCLUSIONS

For the first time, the effects of etomidate on free intracellular amino acid metabolism in PMN have been investigated. Our results draw attention to the biochemical pathways which may be involved in etomidate-induced alterations in PMN function and cellular immunocompetence.