Role of individual serum pentitol concentrations in the diagnosis of disseminated visceral candidiasis

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.

Urine D-arabinitol/L-arabinitol ratio in diagnosing Candida infection in patients with haematological malignancy and HIV infection

Adult patients with hematologic malignancies along with HIV infected patients were prospectively studied to determine the performance of urine D-arabinitol/L-arabinitol (DA/LA) ratio in diagnosing invasive candidiasis. Ten evaluable febrile neutropenic patients had proven invasive candidiasis and elevated DA/LA ratios were found in 5. Invasive candidiasis with normal DA/LA ratios was most frequently due to Candida krusei infection. This Candida species is a non-producer of arabinitol. Only 4 of 81 febrile neutropenic patients given either antifungal prophylaxis or empiric antifungal treatment had elevated DA/LA ratios. Only 1 of 15 HIV positive patients with either oropharyngeal or esophageal candidiasis had elevated DA/LA ratios. Widespread use of fluconazole prophylaxis in bone marrow transplantation patients at the study hospital has led to an increased prevalence of C. krusei infection. This is the likely reason for the low sensitivity of the test in proven and suspected invasive Candida infections reported here.

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.

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.

Determination of microbial chemical markers by gas chromatography-mass spectrometry--potential for diagnosis and studies on metabolism in situ. Review article

Different strategies for the application of gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) in medical microbiology research are discussed. GC can be used to determine specific microbial monomeric constituents and metabolites, so-called chemical markers, in cultures of microorganisms; in particular, analysis of cellular fatty acids has proven useful for species characterization and identification. GC-MS can be applied to study chemical markers directly in complex environmental samples, as exemplified by the analysis of airborne organic material as regards muramic acid (marker of peptidoglycan), 3-hydroxy acids (endotoxins), and ergosterol (fungal biomass). This methodological approach represents an alternative to various biological assays for characterization of airborne microbial structures, and forms a firm basis for correlating inhalation of such structures and development of symptoms. Direct GC-MS analysis of clinical samples provides possibilities for diagnosis (here exemplified by chiral separation of urine D- and L-arabinitol in disseminated candidiasis) and insight into microbial metabolism in the infected host (exemplified by observed indications of mycobacterial build-up of mycolic acids in vivo), with implications for drug development. Continued developments in MS technology will allow rapid advances to be made in GC-MS research in microbiology.

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.

Circulating Candida antigens and antibodies: useful markers of candidemia

To investigate the utility of the 48-kDa antigen from Candida albicans in its commercial form (Directigen; Becton Dickinson) and three other serodiagnostic methods (detection of one antigen by Pastorex Candida [Sanofi Diagnostics Pasteur] and detection of immunoglobulin G [IgG] and IgM antibodies to C. albicans blastoconidia [bioMerieux]) for diagnosis of invasive Candida infection, we conducted a prospective clinical trial among 10 patients with candidemia (group 1), 30 patients colonized by C. albicans (group 2), 20 patients with bacteremia (group 3), and 20 subjects without clinical or microbiological evidence of infection. The Directigen system was positive for at least one serum sample each from eight patients in group 1. In groups 2, 3, and 4, it was positive for only three patients. There was no reaction to the Pastorex system in any of the patients infected with or colonized by C. albicans or in the non-Candida-carrying controls. The IgG antibody concentration oscillated between 100 and 800 (mean, 510 +/- 268) IU/ml for the patients in group 1. In this group, eight patients had IgG antibody levels of > 400 IU/ml. The percentages of persons with IgG antibody levels of > 400 IU/ml in groups 2, 3, and 4 were 43.3, 0, and 0, respectively. Specific IgM antibody was present in all group 1 patients but not in those in groups 2, 3, and 4. The sensitivity and specificity of the Directigen test were 65 and 97.1%, respectively. For the Pastorex test, the sensitivity was 0%. The sensitivity of IgG antibodies was 80%, with a specificity of 81.4%, while the IgM antibodies were 100% specific and sensitive. Both the positive and negative predictive values of specific IgM antibodies appeared to be superior to those of the other three tests.

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.

Diagnosis of disseminated candidiasis based on serum D/L-arabinitol ratios using negative chemical ionization mass spectrometry

The main objective was to appraise the diagnostic specificity of the serum D/L-arabinitol ratio technique in a patient population biased for renal dysfunction. The D/L ratio (mean +/- S.D.) in normal serum (n = 29) was 1.76 +/- 0.47 (range 0.77-2.75). D/L-Arabinitol greater than 3.18 (mean + 3 S.D.) are considered indicative of disseminated candidiasis. Of 49 patients without candidiasis, but 46% with serum creatinine greater than 1.5 mg/dl, diagnostic specificity was 88%. In confirmed candidiasis (n = 16) sensitivity was 94% (D/L range 3.2-50.1). Switching from positive to negative chemical ionization permits the use of as little as 5 microliters sample (20 microliters used routinely; D/L ratios constant in the 5-200 microliters range) permitting the extension of the technique to pediatric applications. Results can obtained in 2 h. Suggested areas of clinical application include aiding diagnosis, monitoring patients as risk so that treatment could be initiated while fungus load is still small, and following the course of antifungal chemotherapy.

Rapid elimination of a synthetic adjuvant peptide from the circulation after systemic administration and absence of detectable natural muramyl peptides in normal serum at current analytical limits

Although it is clear that muramyl peptides are involved in sleep associated with bacterial infection, their role in normal physiological sleep is less certain. It has been speculated that "natural" muramyl peptides, derived from degraded gut flora, may pass into the bloodstream, where they play a role in normal sleep (M. Karnovsky, Fed. Proc. 45:2556-2560, 1986). Muramic acid serves as a chemical marker for muramyl peptides, since it is not synthesized by mammals. After injection of synthetic muramyl dipeptide in rabbits, muramic acid was readily detected (after release by acid hydrolysis) in the circulation; however, levels rapidly decreased. This was an important positive control in assessing circulating levels of natural muramyl peptides. Muramic acid was not found in normal serum (detection limit, approximately 500 pmol/ml), demonstrating the absence of appreciable amounts of circulating natural muramyl peptides. At this time we are unable to provide supportive evidence for Karnovsky's hypothesis.

Separation and quantification by gas chromatography-mass spectrometry of arabinitol enantiomers to aid the differential diagnosis of disseminated candidiasis

To differentiate increased arabinitol due to fungal (only D-arabinitol) and non-fungal origin, O-trifluoroacetyl derivatives of the enantiomers were separated using alpha-perpentylated cyclodextrin columns and measured by selected ion monitoring. Mean +/- S.D. D/L in normal serum: 1.40 +/- 0.42. D/L ratios greater than 2.24, defined as normal mean + 2S.D., were considered outside normal range. D/L was greater than 2.2 in 10 of 12 confirmed candidiasis cases with one false negative and one borderline. Renal dysfunction without candidiasis yielded normal D/L despite high arabinitol concentrations. D/L in normal urine was nearly identical to that in serum despite 60 times larger concentration. D/L ratios, determined by peak heights or areas, could be used without the need to determine concentrations.