Candidiasis: detection by gas-liquid chromatography of D-arabinitol, a fungal metabolite, in human serum

A novel molecular imprinting polymer for the selective adsorption of D-arabinitol from spiked urine

In this research, molecular imprinting polymers (MIPs) for D-arabinitol were synthesized using a bulk polymerization method through a noncovalent approach. The MIPs were prepared by using D-arabinitol as a template, acrylamide as a functional monomer, ethylene glycol dimethacrylateas cross-linker, benzoyl peroxide as an initiator and dimethyl sulfoxideas a porogen. MIPS was synthesized in several formulas with a different molar ratio of template to functional monomers and cross-linker. Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were used to characterize the MIPs produced. A batch rebinding assay was used to test the binding efficiency of each formula. Batch rebinding test results revealed that MIPsF3 with a molar ratio of the template: monomer and crosslinker ratio respectively (1: 4: 25) had the highest binding capacity at 1.56 mgg ^-1 . The results of isotherm adsorption showed that the MIPs produced followed the Freundlich equation with an R-value of 0.97. The MIPs produced was also selective toward its isomeric compounds (i.e. L-arabinitol, adonitol, xylitol, and glucose). The extraction efficiency of the MIPs against D-arabinitol was 88.98%.

Surface enhancement of a molecularly imprinted polymer film using sacrificial silica beads for increasingl-arabitol chemosensor sensitivity and detectability

Sacrificial silica beads, used for increasing the specific surface area of a molecularly imprinted polymer film, improve the performance of the chemosensor.

Modulation of Candida albicans Biofilm by Different Carbon Sources

In the present investigation, the role of carbon sources (glucose, lactate, sucrose, and arabinose) on Candida albicans biofilm development and virulence factors was studied on polystyrene microtiter plates. Besides this, structural changes in cell wall component β-glucan in presence of different carbon sources have also been highlighted. Biofilm formation was analyzed by XTT (2,3-bis[2-Methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) reduction assay. Glucose-grown cells exhibited the highest metabolic activity during adhesion among all carbon sources tested (p < 0.05). However, cells exposed to sucrose exhibited highest biofilm formation and matrix polysaccharides secretion after 48 h. The results also correlated with the biofilm height and roughness measurements by atomic force microscopy. Exposure to lactate induced hyphal structures with the highest proteinase activity while arabinose-grown cells formed pseudohyphal structures possessing the highest phospholipase activity. Structural changes in β-glucan characterized by Fourier transform infrared (FTIR) spectroscopy displayed characteristic band of β-glucan at 892 cm(-1) in all carbon sources tested. The β(1→6) to β(1→3) glucan ratio calculated as per the band area of the peak was less in lactate (1.15) as compared to glucose (1.73), sucrose (1.62), and arabinose (2.85). These results signify that carbon sources influence C. albicans biofilm development and modulate virulence factors and structural organization of cell wall component β-glucan.

Biochemical characterization of the CDP-D-arabinitol biosynthetic pathway in Streptococcus pneumoniae 17F

Streptococcus pneumoniae is a major human pathogen associated with many diseases worldwide. Capsular polysaccharides (CPSs) are the major virulence factor. The biosynthetic pathway of D-arabinitol, which is present in the CPSs of several S. pneumoniae serotypes, has never been identified. In this study, the genes abpA (previously known as abp1) and abpB (previously known as abp2), which have previously been reported to be responsible for nucleoside diphosphate (NDP)-D-arabinitol (the nucleotide-activated form of D-arabinitol) synthesis, were cloned. The enzyme products were overexpressed, purified, and analyzed for their respective activities. Novel products produced by AbpA- and AbpB-catalyzing reactions were detected by capillary electrophoresis, and the structures of the products were elucidated using electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. As a result, abpA was identified to be a D-xylulose-5-phosphate cytidylyltransferase-encoding gene, responsible for the transfer of CTP to D-xylulose-5-phosphate (D-Xlu-5-P) to form CDP-D-xylulose, and abpB was characterized to be a CDP-D-xylulose reductase-encoding gene, responsible for the conversion of CDP-D-xylulose to CDP-D-arabinitol as the final product. The kinetic parameters of AbpA for the substrates D-Xlu-5-P and CTP and those of AbpB for the substrate CDP-D-xylulose and the cofactors NADH or NADPH were measured, and the effects of temperature, pH, and cations on the two enzymes were analyzed. This study confirmed the involvement of the genes abpA and abpB and their products in the biosynthetic pathway of CDP-D-arabinitol.

Invasive mycoses: diagnostic challenges

Despite the availability of newer antifungal drugs, outcomes for patients with invasive fungal infections (IFIs) continue to be poor, in large part due to delayed diagnosis and initiation of appropriate antifungal therapy. Standard histopathologic diagnostic techniques are often untenable in at-risk patients, and culture-based diagnostics typically are too insensitive or nonspecific, or provide results after too long a delay for optimal IFI management. Newer surrogate markers of IFIs with improved sensitivity and specificity are needed to enable earlier diagnosis and, ideally, to provide prognostic information and/or permit therapeutic monitoring. Surrogate assays should also be accessible and easy to implement in the hospital. Several nonculture-based assays of newer surrogates are making their way into the medical setting or are currently under investigation. These new or up-and-coming surrogates include antigens/antibodies (mannan and antimannan antibodies) or fungal metabolites (d-arabinitol) for detection of invasive candidiasis, the Aspergillus cell wall component galactomannan used to detect invasive aspergillosis, or the fungal cell wall component and panfungal marker β-glucan. In addition, progress continues with use of polymerase chain reaction- or other nucleic acid- or molecular-based assays for diagnosis of either specific or generic IFIs, although the various methods must be better standardized before any of these approaches can be more fully implemented into the medical setting. Investigators are also beginning to explore the possibility of combining newer surrogate markers with each other or with more standard diagnostic approaches to improve sensitivity, specificity, and capacity for earlier diagnosis, at a time when fungal burden is still relatively low and more responsive to antifungal therapy.

A permease encoded by STL1 is required for active glycerol uptake by Candida albicans

Candida albicans accumulates large amounts of the polyols glycerol and d-arabitol when the cells are exposed to physiological conditions relevant to stress and virulence in animals. Intracellular concentrations of glycerol are determined by rates of glycerol production and catabolism and of glycerol uptake and efflux through the plasma membrane. We and others have studied glycerol production in C. albicans, but glycerol uptake by C. albicans has not been studied. In the present study, we found that [(14)C]glycerol uptake by C. albicans SC5314 was (i) accumulative; (ii) dependent on proton-motive force; (iii) unaffected by carbon source; and (iv) unaffected by large molar excesses of d-arabitol or other polyols. The respective K(m) and V(max) values were 2.1 mM and 460 micromol h(-1) (g dry wt)(-1) in glucose medium and 2.6 mM and 268 micromol h(-1) (g dry wt)(-1) in glycerol medium. To identify the C. albicans glycerol uptake protein(s), we cloned the C. albicans homologues of the Saccharomyces cerevisiae genes GUP1 and STL1, both of which are known to be involved in glycerol transport. When multicopy plasmids encoding C. albicans STL1, C. albicans STL2 and C. albicans GUP1 were introduced into the corresponding S. cerevisiae null mutants, the transformants all acquired the ability to grow on minimal glycerol medium; however, only S. cerevisiae stl1 null mutants transformed with C. albicans STL1 actively took up extracellular [(14)C]glycerol. When both chromosomal alleles of C. albicans STL1 were deleted from C. albicans BWP17, the resulting stl1 null mutants grew poorly on minimal glycerol medium, and their ability to transport [(14)C]glycerol into the cell was markedly reduced. In contrast, deletion of both chromosomal alleles of C. albicans STL2 or of C. albicans GUP1 had no significant effects on [(14)C]glycerol uptake or the ability to grow on minimal glycerol medium. Northern blot analysis indicated that C. albicans STL1 was expressed in both glucose and glycerol media, conditions under which we detected wild-type active glycerol uptake. Furthermore, STL1 was highly expressed in salt-stressed cells; however, the stl1 null mutant was no more sensitive to salt stress than wild-type controls. We also detected high levels of STL2 expression in glycerol-grown cells, even though deletion of this gene did not influence glycerol uptake activity in glycerol-grown cells. We conclude from the results above that a plasma-membrane H(+) symporter encoded by C. albicans STL1 actively transports glycerol into C. albicans cells.

Measurement of serum D-arabinitol/creatinine ratios for initial diagnosis and for predicting outcome in an unselected, population-based sample of patients with Candida fungemia

D-Arabinitol (DA) is a useful diagnostic marker for candidiasis in patients with neutropenia and other high-risk groups, but its use in unselected patients with a broad range of underlying diseases and conditions has not been studied. We used an automated enzymatic fluorometric assay to measure serum DA/creatinine ratios (DA/cr's) in 30 healthy adults, 100 hospitalized controls without Candida fungemia, and 83 patients from a study of all Candida fungemias in Connecticut between October 1998 and September 1999. Sixty-three of 83 (76%) fungemic patients and 11 of 100 (11%) nonfungemic controls had serum DA/cr's >or=3.9 microM/mg/dl (mean + 3 standard deviations for 30 healthy adults). High serum DA/cr's were less frequent in patients with cancer or fungemia caused by the DA nonproducer Candida glabrata than in patients with cancer or fungemia caused by a DA producer, C. albicans, C. tropicalis, or C. parapsilosis. The serum DA/cr was first >or=3.9 microM/mg/dl before, on the same day as, or after the first positive blood culture was drawn for 30 (36%), 22 (27%), and 11 (13%) fungemia patients, respectively. Mortality did not differ significantly among the patients with high or normal initial or peak serum DA/cr's, but mortality was higher if any serum DA/cr value was >or=3.9 microM/mg/dl 3 or more days after the onset of fungemia (18/27 versus 4/24 patients, respectively; P < 0.001). We conclude that serum DA/cr's are useful both for the initial diagnosis of Candida fungemia and for prognostic purposes for unselected patients with a broad range of underlying diseases and conditions.

Syscan3, a kit for detection of anti-Candida antibodies for diagnosis of invasive candidiasis

Sera from 76 immunocompetent and 293 immunocompromised subjects were assayed for anti-Candida antibodies. The sensitivity, specificity, positive predictive value, and negative predictive value for invasive candidiasis were 74%, 75%, 62%, and 84% in the immunocompetent group and 15%, 60%, 1.7%, and 93% in the immunocompromised group, respectively. Syscan3 has high negative predictive value.

The MAP kinase Hog1p differentially regulates stress-induced production and accumulation of glycerol and d-arabitol in Candida albicans

Candida albicansproduces and accumulates large amounts of the polyolsd-arabitol and glycerol in culture, and/or in infected mammalian tissues. However, the effects of environmental stresses on production and accumulation of these polyols, and the means by which polyol production and accumulation are regulated have not been studied.C. albicansgrown in glucose at 30 °C (i) produced maximal amounts of glycerol within 6 h, (ii) produced maximal amounts ofd-arabitol and ribitol within 12 h, and (iii) released most of these polyols into the extracellular environment.C. albicansresponded to osmotic and citric acid stress by producing and accumulating more glycerol, and to temperature and oxidative stresses by producing mored-arabitol. The increase in intracellular glycerol was proportional to extracellular osmolarity, suggesting that glycerol functions as an osmolyte. The MAP kinase Hog1p is required for wild-type glycerol production in several fungal species subjected to osmotic stress, but it is not known if Hog1p plays a role in regulatingd-arabitol production. Therefore, twoC. albicans hog1null mutants were constructed and tested for the ability to produce glycerol andd-arabitol in response to environmental stresses. The ability to grow and produce glycerol when exposed to osmotic or citric acid stresses, and to produced-arabitol when exposed to oxidative stress, was partially dependent on Hog1p, but the ability to produced-arabitol when exposed to temperature stress was Hog1p independent. These results imply that multiple pathways regulate glycerol andd-arabitol synthesis inC. albicans.

Evaluation of pentitol metabolism in mammalian tissues provides new insight into disorders of human sugar metabolism

To more completely elucidate the pathways of sugar metabolism in human, we have evaluated the formation and degradation of pentitols in human fibroblasts and erythrocytes. Cultured human fibroblasts were incubated with d-arabinose, d-ribose, d-ribulose, and d-xylulose. Formation of arabitol and ribitol was analyzed by gas chromatography of the incubation medium and cell homogenate. We found that the pentoses d-arabinose and d-ribose could cross cell membranes, which indicate possible pentitol formation from extracellular pentoses. Fibroblasts formed 17+/-4 nmol arabitol/4 days/mg protein from d-arabinose and ribitol production rates of 70+/-15 nmol/4 days/mg protein were found after d-ribose incubation. Following d-ribulose incubation 13 nmol ribitol/4 days/mg protein was found. Human cultured fibroblasts were also incubated with d-arabitol, ribitol, and xylitol. Analyzing the incubation medium and cell homogenate revealed an absence of pentose formation. However, export of the pentitols arabitol and ribitol across the cell membrane was demonstrated, indicating that pentitols can be cleared from the body without metabolic conversion. Finally, human erythrocytes were incubated with d-/l-arabitol, ribitol, sorbitol, and xylitol. Activities of potential pentitol dehydrogenases were evaluated by a fluorometric assay. No evidence for ribitol and arabitol degradation was observed in human erythrocytes, as compared to polyol dehydrogenase activities ranging from 1.3 to 6.1 pmol NADH/min/microl erythrocytes observed using sorbitol and xylitol. Our results indicate that ribitol and arabitol are metabolic end products in humans.

Development and application of a rapid diagnostic method for invasive Candidiasis by the detection of d-/l-arabinitol using gas chromatography/mass spectrometry

A rapid non-culture-based diagnostic method utilizing d-/l-arabinitol (DA/LA) ratios as a chemical marker of invasive candidiasis was developed and explored. The enantiomers-ratios detection was made possible by the use of gas chromatography coupled with mass spectrometry (GC/MS). The mean DA/LA ratios +/- standard deviation (range) in urine (n = 40) and serum (n = 20) were 2.08 +/- 0.78 (0.57 to 3.55) and 1.79 +/- 0.75 (0.74 to 3.54), respectively, from patients without evidence of fungal infection or colonization; in patients (n = 7) with culture-proven invasive candida infections, the figures were 9.91 +/- 3.04 (7.24 to 16.27) and 13.58 +/- 7.31 (5.57 to 25.88) in urine and serum, respectively. The differences in DA/LA ratios between the candidemic patients and the non-candidemic patients were statistically significant (p < 0.01) in both serum and urine samples. The DA/LA ratios were not significantly affected in patients with oral or vaginal candidiasis and candiduria.

Pseudomonas fluorescens mannitol 2-dehydrogenase and the family of polyol-specific long-chain dehydrogenases/reductases: sequence-based classification and analysis of structure-function relationships

Multiple sequence alignment and analysis of evolutionary relationships have been used to characterize a family of polyol-specific long-chain dehydrogenases/reductases (PSLDRs). At the present time, 66 known and putative NAD(P)H-dependent oxidoreductases of mainly prokaryotic origin and between 357 and 544 amino acids in length constitute this family. The family is shown to include D-mannitol 2-dehydrogenase, D-mannonate 5-oxidoreductase, D-altronate 5-oxidoreductase, D-arabinitol 4-dehydrogenase, and D-mannitol-1-phosphate 5-dehydrogenase which form individual sub-families (defined by internal sequence identity of >/=30%) having distant origin and divergent substrate specificity but clearly displaying entire-chain relationship. When all forms are aligned, only three residues, Gly-33, Asp-230, and Lys-295 (in the numbering of Pseudomonas fluorescens D-mannitol 2-dehydrogenase (PsM2DH)) are strictly conserved. By combining sequence alignment with the known structure of PsM2DH and results from site-directed mutagenesis, we have developed a structure/function analysis for the family. Gly-33 is in the N-terminal coenzyme-binding domain and part of a nucleotide fingerprint region for the family, and Asp-230 and Lys-295 are at an interdomain segment contributing to the active site in which the lysine likely functions as the catalytic general acid/base. PSLDRs do not require a metal cofactor for activity and are specific for transferring the 4-pro-S hydrogen from NAD(P)H. Comparisons reveal that the core part of the two-domain fold has been conserved throughout all family members, perhaps reflecting the recruitment of a stable oxidoreductase structure and extensive trimming thereof to acquire functional properties specific to each sub-family. They also identify interactions that define the chemical mechanism of oxidoreduction and likely contribute to substrate and co-substrate specificities and are thus relevant for protein engineering.

L-Arabinosuria: a new defect in human pentose metabolism

A female patient, the first child of healthy non-consanguineous parents, presented at the age of 16 months with delayed motor development and facial dysmorphism. In addition she displayed a palatoschizis and multiple skeletal abnormalities as hypoplastic scapulae, hypoplastic os ilea, and an extreme cervical kyphosis. Biochemical investigation of urine revealed no abnormalities except for the presence of large amounts of reducing sugars. The sugar was identified as L-arabinose, which mainly originated from fruit formula in her diet. In addition highly elevated levels of L-arabitol were found in urine, plasma, and cerebrospinal fluid. Although little is known about human arabinose metabolism, we presume that L-arabitol dehydrogenase is deficient in our patient. As polyols are potentially toxic to the central nervous system there could be deleterious long-term effects of this disorder. Withdrawal of dietary fruit led to normalization of polyol levels. The above-mentioned clinical abnormalities are probably not related to this new inborn error of metabolism and should be considered as a separate entity.

Current status of nonculture methods for diagnosis of invasive fungal infections

The incidence of invasive fungal infections has increased dramatically in recent decades, especially among immunocompromised patients. However, the diagnosis of these infections in a timely fashion is often very difficult. Conventional microbiologic and histopathologic approaches generally are neither sensitive nor specific, and they often do not detect invasive fungal infection until late in the course of disease. Since early diagnosis may guide appropriate treatment and prevent mortality, there has been considerable interest in developing nonculture approaches to diagnosing fungal infections. These approaches include detection of specific host immune responses to fungal antigens, detection of specific macromolecular antigens using immunologic reagents, amplification and detection of specific fungal nucleic acid sequences, and detection and quantitation of specific fungal metabolite products. This work reviews the current status and recent developments as well as problems in the design of nonculture diagnostic methods for invasive fungal infections.

New enzymatic method for determining D-arabinitol in serum

A new reagent has been developed to determine D-arabinitol. This utilizes D-arabinitol 2-oxidoreductase derived from Bacillus sp. with high stability, and water-soluble tetrazolium salt, that can detect NADH with high sensitivity. Since this enzyme does not react to D-mannitol, elimination of D-mannitol is unnecessary. Thus, this is a much simpler process than currently available with commercial kits use D-arabinitol 4-oxidoreductase. The within-run and between-run precisions (CV) were 2.4-6.9% and 3.1-8.7%, respectively, whilst the correlation (r) between the results obtained with our proposed method (y) and those obtained with the commercial "Arabinitec-auto" kit (x) was 0.964 (y = 1.02x + 0.933 mumol/l; n = 69). However, some samples deviated remarkably from correlation in both methods. Our analyzing accuracy is satisfactory in clinical application, as it does not miss positive sample over cut-off value. We are refining this method by investigating why some specimens are apart from correlation significantly.

A rapid, automated enzymatic fluorometric assay for determination of D-arabinitol in serum

A rapid enzymatic fluorometric assay for measuring D-arabinitol in serum was developed using recombinant D-arabinitol dehydrogenase from Candida albicans (rArDH). rArDH was produced in Escherichia coli and purified by dye-ligand affinity chromatography. rArDH was highly specific for D-arabinitol, cross-reacting only with xylitol (4.9%) among all polyols tested. A Cobas Fara II centrifugal autoanalyzer (Roche) was used to measure NADH fluorometrically when rArDH and NAD were added to serum extracts, and D-arabinitol concentrations were calculated from standard curves derived from pooled human serum containing known amounts of D-arabinitol. The method was precise (mean intra-assay coefficients of variation [CVs], 0.8%, and mean interassay CVs, 1.6%) and rapid (3.5 min per assay) and showed excellent recovery of added D-arabinitol in serum (mean recovery rate, 101%). The mean and median D-arabinitol/creatinine ratios were 2.74 and 2.23 microM/mg/dl, respectively, for the 11 patients with candidemia compared to 1.14 and 1.23 microM/mg/dl, respectively, for 10 healthy controls (P < 0.01). These results confirm earlier studies showing that serum D-arabinitol measurement may help to promptly diagnose invasive candidiasis. The technique shows a significant improvement in terms of accuracy, cost, simplicity, specificity, and speed compared with gas chromatography, mass spectrometry, and earlier enzymatic assays.

D-arabinitol--a marker for invasive candidiasis

The five-carbon sugar alcohol D-arabinitol (DA) is a metabolite of most pathogenic Candida species, in vitro as well as in vivo, and can be determined by gas chromatography or enzymatic analysis. Endogenous DA and L-arabinitol (LA) are present in human body fluids, and serum DA and LA increase in renal dysfunction. In prospective clinical studies, elevated DA/LA or DA/creatine ratios in serum or urine have been found in immunocompromised, usually neutropenic, patients with invasive candidiasis. In addition, positive DA results have been obtained several days to weeks before positive blood cultures, and the normalization of DA levels has been correlated with therapeutic response in both humans and animals. However, to date, only a few prospective studies have been conducted in which adequate analytical methods were used. Thus, further investigation of various patient groups is needed to establish the applicability of the 'arabinitol method' in the diagnostic battery for invasive Candida infections.

Expression of bacterial mtlD in Saccharomyces cerevisiae results in mannitol synthesis and protects a glycerol-defective mutant from high-salt and oxidative stress

Polyols, or polyhydroxy alcohols, are produced by many fungi. Saccharomyces cerevisiae produces large amounts of glycerol, and several fungi that cause serious human infections produce D-arabinitol and mannitol. Glycerol functions as an intracellular osmolyte in S. cerevisiae, but the functions of D-arabinitol and mannitol in pathogenic fungi are not yet known. To investigate the functions of mannitol, we constructed a new mannitol biosynthetic pathway in S. cerevisiae. S. cerevisiae transformed with multicopy plasmids encoding the mannitol-1-phosphate dehydrogenase of Escherichia coli produced mannitol, whereas S. cerevisiae transformed with control plasmids did not. Although mannitol production had no obvious phenotypic effects in wild-type S. cerevisiae, it restored the ability of a glycerol-defective, osmosensitive osg1-1 mutant to grow in the presence of high NaCl concentrations. Moreover, osg1-1 mutants producing mannitol were more resistant to killing by oxidants produced by a cell-free H2O2-FeSO4-NaI system than were controls. These results indicate that mannitol can (i) function as an intracellular osmolyte in S. cerevisiae, (ii) substitute for glycerol as the principal intracellular osmolyte in S. cerevisiae, and (iii) protect S. cerevisiae from oxidative damage by scavenging toxic oxygen intermediates.

The mitogen-activated protein kinase homolog HOG1 gene controls glycerol accumulation in the pathogenic fungus Candida albicans

The Candida albicans HOG1 gene (HOG1CA) was cloned by functional complementation of the osmosensitive phenotype associated with Saccharomyces cerevisiae hog1 delta mutants. HOG1CA codes for a 377-amino-acid protein, 78% identical to S. cerevisiae Hog1p. A C. albicans hog1 null mutant was found to be sensitive to osmotic stress and failed to accumulate glycerol on high-osmolarity media.

Postinflammatory hydrocephalus and intracranial mass lesion from Candida in an immunocompetent child

Central nervous system Candida infection may occur in systemic Candida infection when host defenses are impaired. We report here a 20-month-old boy with normal immune status and no history of immunosuppressive therapy who developed left facial weakness, decreased left hand strength and coordination, and worsening gait. This paper describes the diagnostic procedures and management strategies employed in this unique case.

D-mannitol in cerebrospinal fluid of patients with AIDS and cryptococcal meningitis

Cryptococcal meningitis (CM) is associated with raised intracranial pressure which is linked with serious neurological sequelae. Cryptococcus neoformans produces D-mannitol in vitro and in experimental meningitis in rabbits. Mannitol present in the cerebrospinal fluid (CSF) of CM patients could exacerbate raised intracranial pressure and contribute to neurological damage. To link CSF mannitol to cryptococcal infection, levels of mannitol in the CSF of AIDS patients with CM were measured by gas-liquid chromatography. Mannitol was detected in 19 of 21 samples (range, 1.5 to 26.2 mg/liter), but there was no quantitative correlation between the mannitol concentration and the cryptococcal antigen titer.

Diagnosis and therapeutic monitoring of invasive candidiasis by rapid enzymatic detection of serum D-arabinitol

BACKGROUND

Using a rapid automated enzymatic assay, we prospectively investigated serum D-arabinitol (DA), a biochemical marker of invasive candidiasis, in a large population of high-risk patients to determine its potential diagnostic, therapeutic, and prognostic significance in invasive candidiasis.

PATIENTS AND METHODS

A total of 3,223 serum samples were collected from 274 patients with cancer. Serum DA concentrations were determined in coded serum samples analyzed by rapid enzymatic assay. Creatinine also was analyzed in the same system to determine a serum DA and creatinine ratio (DA/Cr). The sensitivity, specificity, correlation with therapeutic response, and prognostic significance were analyzed for all patient study groups.

RESULTS

A DA/Cr of > or = 4.0 mumol/L per mg/dL was detected in 31 (74%) of all 42 cases of fungemia and 25 (83%) of the 30 cases of the subset of persistent fungemia. Elevated DA/Cr was detected in 4 (40%) of 10 patients with tissue-proven, deeply invasive candidiasis and negative blood cultures (eg, hepatosplenic candidiasis or localized abscess) and 7 (44%) of 16 cases of deep mucosal candidiasis (eg, esophageal candidiasis). Elevated serial DA/Cr levels also were detected in persistently febrile and granulocytopenic patients requiring empirical amphotericin B. Among 26 assessable cases of fungemia, abnormally elevated DA/Cr values were detected in 14 (54%) before, 10 (38%) after, and 2 (8%) simultaneously with the first microbiologic report of fungemia. The trends of serial DA/Cr values correlated with therapeutic response in 29 (85%) of 34 patients with assessable cases of fungemia, decreasing in 8 (89%) of 9 patients with clearance of fungemia and increasing in 21 (84%) of 25 patients with persistence of fungemia. Among the 34 assessable patients with fungemia, mortality was directly related to the trend of serial DA/Cr determinations over time: 71% among fungemic patients who had persistently elevated or increasing DA/Cr, and 18% among the fungemic patients who had resolving DA/Cr or never had elevated DA/Cr (P < 0.01).

CONCLUSIONS

Rapid enzymatic detection of DA in serially collected serum samples from high-risk cancer patients permitted detection of invasive candidiasis, early recognition of fungemia, and therapeutic monitoring in DA-positive cases. Serially collected serum DA determinations complement blood cultures for improving detection and monitoring therapeutic response in patients at risk for invasive candidiasis.

D-arabitol metabolism in Candida albicans: construction and analysis of mutants lacking D-arabitol dehydrogenase

Candida albicans produces large amounts of the acyclic pentitol D-arabitol in culture and in infected animals and humans, and most strains also grow on minimal D-arabitol medium. An earlier study showed that the major metabolic precursor of D-arabitol in C. albicans was D-ribulose-5-PO4 from the pentose pathway, that C. albicans contained an NAD-dependent D-arabitol dehydrogenase (ArDH), and that the ArDH structural gene (ARD) encoded a 31-kDa short-chain dehydrogenase that catalyzed the reaction D-arabitol + NAD <=> D-ribulose + NADH. In the present study, we disrupted both ARD chromosomal alleles in C. albicans and analyzed the resulting mutants. The ard null mutation was verified by Southern hybridization, and the null mutant's inability to produce ArDH was verified by Western immunoblotting. The ard null mutant grew well on minimal glucose medium, but it was unable to grow on minimal D-arabitol or D-arabinose medium. Thus, ArDH catalyzes the first step in D-arabitol utilization and a necessary intermediate step in D-arabinose utilization. Unexpectedly, the ard null mutant synthesized D-arabitol from glucose. Moreover, 13C nuclear magnetic resonance studies showed that the ard null mutant and its wild-type parent synthesized D-arabitol via the same pathway. These results imply that C. albicans synthesizes and utilizes D-arabitol via separate metabolic pathways, which was not previously suspected for fungi.

Isolation, characterization and expression of the gene that encodes D-arabinitol dehydrogenase in Candida tropicalis

The gene (ARD) that encodes NAD-dependent D-arabinitol dehydrogenase (ArDH) in the pathogenic fungus Candida tropicalis (Ct) was cloned by transforming Escherichia coli (Ec) BW31M (araCc) with a plasmid library of Ct genomic DNA and selecting for D-arabinitol-utilizing (D-arab+) clones. Plasmid DNA from a D-arab+ clone retransformed fresh Ec BW31M cells to D-arab+; these cells produced both ArDH catalytic activity and a 31-kDa protein recognized by antibodies to native Ct ArDH. The plasmid contained an 846-bp open reading frame (ORF) that encoded a deduced protein of 282 amino acids (aa) (30,748 Da). Four partial aa sequences from Ct ArDH were present in the deduced aa sequence, thus verifying that Ct ARD had been cloned. Ct ArDH was 95% identical to ArDH from Candida albicans (Ca), 85% identical to a xylitol dehydrogenase (XDH) from Pichia stipitis (Ps) and 20-25% identical to many other short-chain dehydrogenases. Ct ArDH, Ca ArDH and Ps XDH were typical short-chain dehydrogenases except that they lacked an N-terminal Gly that is conserved in other members of this family. Thus, these enzymes may represent a subclass of closely-related fungal pentitol dehydrogenases. Large amounts of recombinant ArDH (re-ArDH) were produced in Ec and purified by dye ligand affinity chromatography. The physical and catalytic properties of re-ArDH were similar to those of native Ct ArDH, and re-ArDH and native ArDH performed similarly in an automated enzymatic assay for D-arabinitol in human serum.

Gas chromatographic determination of D-arabinitol/L-arabinitol ratios in urine: a potential method for diagnosis of disseminated candidiasis

A gas chromatographic procedure was developed to determine the relative amounts of D- and L-arabinitol in urine. Samples were filtered, diluted, purified through extractions, evaporated, and treated with trifluoroacetic anhydride; the arabinitol derivatives thus obtained were separated on a chiral stationary phase and registered by using an electron-capture detector. Urine samples from a patient with disseminated candidiasis had higher D-arabinitol/L-arabinitol ratios (referred to as D/L-arabinitol ratios)--up to 19.0--than samples from 96 study individuals with no signs of deep Candida infections (range, 1.1 to 4.5). D/L-Arabinitol ratios in urine samples from hospitalized patients without Candida infections were slightly higher than those in samples from healthy individuals; ratios in urine from children were slightly higher than those in adult urine samples. The D/L-arabinitol ratios in several urine samples culture positive for Candida albicans, but from patients without symptoms of disseminated candidiasis, did not differ from those in the urine of healthy individuals. The described gas chromatographic method is straightforward and can be implemented clinically to determine urine D/L-arabinitol ratios as a means of diagnosing disseminated candidiasis.

Evaluation of enzyme immunoassay for Candida cytoplasmic antigens in neutropenic cancer patients

A Candida albicans cytoplasmic antigen enzyme immunoassay (CACP antigen EIA) was developed with antibodies raised against antigens prepared from yeast cells grown under standardized growth conditions. The C. albicans components reactive in the EIA were shown to be predominantly proteins with associated carbohydrates. Denaturing gel electrophoresis revealed the presence of five major CACP proteins with molecular weights between 36,000 and 44,000. The clinical usefulness of the CACP EIA was evaluated by retrospective blinded measurement of 89 serum samples from 31 granulocytopenic patient episodes. Twice-weekly surveillance cultures, sequential serum samples (approximately once per week or with change of the clinical course), and standard diagnostic criteria of fungal infection were used to categorize patients. The sensitivity and specificity of the CACP assay on the basis of serum samples were 82 and 100%, respectively (67 and 100% on the basis of patient episodes). The positive and negative predictive values were 100 and 97% for serum (100 and 93% for patient episodes). By comparison, the CANDTEC assay had low sensitivity (33%) and poor positive predictive values (50%). The CACP EIA may be a useful test suitable for further evaluations as a method for the diagnosis of invasive Candida infection in neutropenic cancer patients.

Serum D-arabinitol measured by automated quantitative enzymatic assay for detection and therapeutic monitoring of experimental disseminated candidiasis: correlation with tissue concentrations of Candida albicans

In order to further understand serum D-arabinitol (DA) as a marker for the diagnosis of disseminated candidiasis and for monitoring response to antifungal therapy, we studied the serum levels of this Candida carbohydrate metabolite by rapid automated enzymatic assay in rabbits with experimental disseminated candidiasis. The enzymatic reaction steps were performed on a standard automated clinical chemistry analyser. As a correction for renal impairment, data were expressed as serum D-arabinitol/creatinine ratio (DA/Cr). Serum creatinine concentrations were determined from the same sample with the same instrument, thereby allowing rapid determination of the DA/Cr within one laboratory. The DA/Cr was determined in 321 samples from 132 rabbits. The mean serum DA/Cr in 31 normal non-infected rabbits was 1.51 +/- 0.2 microM mg-1 dl-1. Among 84 rabbits with disseminated candidiasis and pre-terminal samples, there was a direct correlation between DA/Cr and tissue concentration of Candida albicans (r = 0.80; P < 0.001). A threshold of elevated DA/Cr (> or = 3.0 microM mg-1 dl-1) was evident in rabbits with a tissue concentration of C. albicans > or = 3 x 10(4) colony forming units (CFU) g-1. Elevated DA/Cr was detected in 48 (89%) of 54 rabbits at a C. albicans tissue concentration of > or = 3 x 10(4) CFU g-1 vs. one (3%) of 30 rabbits with < 3 x 10(4) CFU g-1 (P < 0.0001). Among all 101 rabbits with disseminated candidiasis, an elevated DA/Cr was detected at any point during infection in 60 (92%) of 65 rabbits having a C. albicans tissue concentration > or = 3 x 10(4) CFU g-1 vs. 13 (36%) of 36 rabbits with < 3 x 10(4) CFU g-1 (P < 0.0001). The relationship between the tissue response to antifungal therapy and change in DA/Cr was then further analysed. Ten (91%) of 11 rabbits with a tissue-proven response to antifungal therapy (defined as > or = 10(2)-fold reduction of CFU g-1 in comparison to untreated controls) had a > 50% reduction in elevated DA/Cr levels. By comparison, 10 (83%) of 12 treated rabbits with no response to therapy had persistently elevated DA/Cr levels (P < 0.001). These findings provide an experimental basis for understanding the patterns of expression of serum DA in disseminated candidiasis and further indicate that serial DA/Cr measurements may be useful for diagnosis and therapeutic monitoring of disseminated candidiasis.

Diagnosis and monitoring of disseminated candidiasis based on serum/urine D/L-arabinitol ratios

Disseminated candidiasis, a devastating disease with high morbidity and mortality in immunosuppressed patients, is difficult to diagnose because of the protean nature of symptoms and the lack of rapid and reliable laboratory diagnostic procedures. The subject of this review is the status of gas chromatographic-mass spectrometric techniques for the determination of D-arabinitol, a unique metabolite of pathogenic Candida species, in serum and urine. The enantiomers are separated by chiral chromatography followed by specific and sensitive detection using chemical ionization and selected ion monitoring. Using D/L-arabinitol ratios, instead of individual concentrations, eliminates the need for knowing the volume of samples and for calibration curves. A new filter paper technique requires only an unmeasured drop of whole blood (venous or finger/heel puncture) or urine; paper spots are mailable. Parallel determinations of D/L-arabinitol ratios in serum and urine in normal subjects and cancer patients with both normal and increased D/L-arabinitol ratios revealed constant (1.2-1.3 range) ratios of serum D/L-arabinitol/urine D/L-arabinitol for all populations studied. Analyzing two body fluids taken at the same time increases reliability by reducing false positives.

An automated enzymatic method for measurement of D-arabinitol, a metabolite of pathogenic Candida species

An automated enzymatic method was developed for the measurement of D-arabinitol in human serum. The assay is based on a novel, highly specific D-arabinitol dehydrogenase from Candida tropicalis. This enzyme catalyzes the oxidation of D-arabinitol to D-ribulose and the concomitant reduction of NAD+ to NADH. The NADH produced is used in a second reaction to reduce p-iodonitrotetrazolium violet (INT) to INT-formazan, which is measured spectrophotometrically. The entire reaction sequence can be performed automatically on a COBAS MIRA-S clinical chemistry analyzer (Roche Diagnostic Systems, Inc., Montclair, N.J.). Replicate analyses of human sera supplemented with D-arabinitol over a concentration range of 0 to 40 microM demonstrated that the pentitol could be measured with an accuracy of +/- 7% and a precision (standard deviation) of +/- 0.4 microM. Serum D-arabinitol measurements correlated with those determined by gas chromatography (r = 0.94). The enzymatic method is unaffected by L-arabinitol, D-mannitol, or other polyols commonly found in human serum. Any of 17 therapeutic drugs potentially present in serum did not significantly influence assay performance. Data illustrating the application of the assay in patients for possible diagnosis of invasive candidiasis and the monitoring of therapeutic intervention are presented. The automated assay described here was developed to facilitate the investigation of D-arabinitol as a serum marker for invasive Candida infections.

Nonculture methods for diagnosis of disseminated candidiasis

Two of the nonculture approaches to the diagnosis of DC, enzymatic-fluorometric determination of serum D-arabinitol and detection of marker antigens in antigenemia (enolase and CWMP), have been commercialized and have shown promise in limited clinical trials. These approaches are not new but are the culmination of efforts made over 10 or more years. Clearly, further fine-tuning of both metabolite and antigen detection is needed to simplify the methods and to improve their sensitivity and specificity so that they will be valuable in guiding clinical treatment decisions. An alternative approach, detection of DC by DNA amplification methods such as PCR, is a special case of a compelling technology and one that is capable of standardization across microbial genera. The availability of simplified PCR diagnostic methods for DC remains a tantalizing prospect. Nevertheless, the development of methods to release DNA from very small numbers of Candida organisms in the blood in a form that is sufficiently free of inhibitors of PCR will require further intensive effort. The maturation of these converging laboratory approaches to nonculture diagnosis of DC leads to more optimism about the eventual use of these methods in clinical laboratories.

D-arabitol metabolism in Candida albicans: studies of the biosynthetic pathway and the gene that encodes NAD-dependent D-arabitol dehydrogenase

Candida albicans produces large amounts of the pentitol D-arabitol in culture and in infected mammalian hosts, but the functional and pathogenic significance of D-arabitol in C. albicans is not known. In this study, we sought to elucidate the pathway by which C. albicans synthesizes D-arabitol and to identify and characterize key enzymes in this pathway. C. albicans B311 produced D-[14C-1]arabitol from [14C-2]glucose; this finding implies on structural grounds that D-ribulose-5-PO4 from the pentose pathway is the major metabolic precursor of D-arabitol. NAD- or NADP-dependent pentitol dehydrogenases catalyze the final steps in D-arabitol biosynthesis in other fungi; therefore, lysates of C. albicans B311 were tested for enzymes of this class and were found to contain a previously unknown NAD-dependent D-arabitol dehydrogenase (ArDH). The ArDH structural gene was cloned by constructing a new D-arabitol utilization pathway in Escherichia coli. The C. albicans ArDH gene expressed in E. coli and Saccharomyces cerevisiae an enzyme that catalyzes the reaction D-arabitol + NAD <-->D-ribulose + NADH; this gene was present as a single copy per haploid genome, and its deduced peptide sequence was homologous with sequences of several members of the short-chain dehydrogenase family of enzymes. These results suggest that (i) C. albicans synthesizes D-arabitol by dephosphorylating and reducing the pentose pathway intermediate D-ribulose-5-PO4 and (ii) ArDH catalyzes the final step in this pathway.

Determination of serum arabinitol levels by mass spectrometry in patients with postoperative candidiasis

A combined gas chromatography-mass spectrometry (GC-MS) technique was used for serial determination of serum arabinitol levels in patients with postoperative candidiasis. Forty subjects were investigated, 18 patients with candidiasis, 7 patients with superficial Candida colonization and 15 postoperative control patients. The arabinitol levels were highly elevated, slightly elevated and normal in 13, 1 and 4 patients respectively with candidiasis; in 2, 2 and 3 colonized patients and in 1, 1 and 13 control patients (p < 0.001, chi 2, between all the groups). The sensitivity of a single arabinitol determination for detection of postoperative candidiasis was 27.6 % and the specificity 89.2 %. Use of multiple samples improved sensitivity up to 72.2% per patient (123 samples) with a specificity of 86.4 %. Highly elevated arabinitol concentrations were detected in only one patient before the onset of therapy. Determination of arabinitol levels by GC-MS is a specific test for diagnosing candidiasis, but multiple samples are required for adequate sensitivity, and the initiation of therapy must still be on an empirical basis.

An evaluation of serodiagnostic tests in patients with candidemia: beta-glucan, mannan, candida antigen by Cand-Tec and D-arabinitol

The serodiagnostic tests, beta-glucan, mannan, candida antigen by Cand-Tec, and D-arabinitol were evaluated in 10 patients with candidemia, 14 patients with suspected fungemia, and 10 healthy persons. By blood culture or lysis centrifugation, C. albicans was isolated from 5 patients, C. parapsilosis from 4, and C. tropicalis from 1 patient; no organisms were isolated from the 14 patients with suspected fungemia or the 10 healthy subjects. Beta-glucan was measured by the difference between two chromogenic limulus tests (Endotoxin test-D and Endospecy), which was more than 60 pg/ml in 7 of 9 (78%) candidemic patients and 1 of 12 (8%) patients with suspected fungemia. Mannan was positive in 6 of 10 (60%) candidemic patients and 1 of 13 (8%) patients with suspected fungemia. Both antigens were very sensitive and highly specific for candidemia. However, the Cand-Tec assay was less specific, because titers of more than 4 were observed in 5 of 14 (34%) patients with suspected fungemia. D-Arabinitol was the least sensitive, because a D-arabinitol/creatinine ratio greater than 2.0 mumol/mg was observed in only 2 of 7 (29%) candidemic patients. The titers of serodiagnostic tests decreased after successful treatment with an anti-fungal agent. Our results show that the combined use of the assays in necessary for accurate serological diagnosis of candidemia.

Increased D-arabinitol/creatinine ratio in sera of patients with Behçet's disease during an active phase

The ratios of D-arabinitol (a major metabolite of Candida species) to creatinine were examined in 46 sera of 40 patients with ocular inflammatory disease and in 50 age-matched normal controls (25 men and 25 women). The mean ratio in patients with endogenous Candida endophthalmitis was higher than in the normal controls. Seven samples taken from patients with Behçet's disease during an active phase showed higher values than in the controls. Fourteen patients with Behçet's disease in remission showed D-arabinitol/creatinine values within normal range. In four patients with sarcoidosis, in two patients with Vogt-Koyanagi-Harada disease, and in 16 patients with bilateral uveitis of an unknown cause, the ratios were within normal range. It is possible that D-arabinitol, or a metabolite of Candida species, may be related in part to the active phase of Behçet's disease.

Diagnosis of invasive candidiasis by detection of mannan antigen by using the avidin-biotin enzyme immunoassay

The diagnosis of invasive candidiasis was attempted by detection of circulating mannan antigen by using an avidin-biotin-amplified enzyme-linked immunosorbent assay (AB-ELISA), and this method was compared with the conventional culture method. Mannan antigen was detected by AB-ELISA in the sera of 16 (84.2%) of the 19 patients with invasive candidiasis. On the other hand, for 34 immunocompromised candidiasis-free patients, including 8 with aspergillosis or cryptococcosis, mannan antigen was positive during only 1 of the 67 febrile episodes and in the serum of none of the 50 outpatients without infections. The results were also negative for all patients with deep-seated mycoses other than candidiasis. However, the mannan level was low (less than 2.0 ng/ml) in the serum of 63.2% of the patients with invasive candidiasis. The positivity rate of blood cultures was 31.6%, and that of blood cultures and/or cultures of samples from sterile sites combined was 47.4%. The advantages of the diagnosis based on antigen detection by AB-ELISA are considered to be a higher sensitivity and elimination of nonspecific reactions by the introduction of the avidin-biotin system and pretreatment of sera by heating. In addition, it is considered essential for high sensitivity that transient mannan antigenemia be determined frequently so that it is not overlooked. In light of its sensitivity and specificity, this method is considered to be clinically useful in the diagnosis of invasive candidiasis.

Arabinitol enantiomers in cerebrospinal fluid

D-Arabinitol is a metabolite of Candida species, and its presence in serum above endogenous concentration may indicate disseminated candidiasis. The o-trifluoroacetylated derivatives of arabinitol enantiomers in cerebrospinal fluid (CSF) were separated using perpentylated cyclodextrin capillary columns and measured by selected ion monitoring using negative chemical ionization mass spectrometry. The presence of D-arabinitol was confirmed using highly specific D-arabinitol dehydrogenase. The mean D/L-arabinitol ratio, 16.7 +/- 4.8 (range: 8.6-22.8), in CSF of the "controls" is approximately 10-fold higher than the ratio previously found in normal serum and urine. At the same time, the mean L-arabinitol concentration, 0.13 +/- 0.05 (range: 0.09-0.2), is virtually identical to that in serum. Therefore, the high D/L-arabinitol ratio in CSF is attributed to D-arabinitol. Persistently high D/L ratios were found in a variety of diseases (without Candida infection). The finding of D-arabinitol in CSF suggests that serum D-arabinitol may originate from the brain or the spinal cord, rather than from resident Candida species in the gut, and that the accumulation of D-arabinitol in CSF may be caused by non-consumption or, conversely, the high concentration may be maintained in order to have it readily available for metabolism in the brain.