The role of citric acid in the physiology of the prostate. A chromatographic study of citric acid cycle intermediates in benign and malignant prostatic tissue

Developments in proton MR spectroscopic imaging of prostate cancer

In this paper, we review the developments of 1H-MR spectroscopic imaging (MRSI) methods designed to investigate prostate cancer, covering key aspects such as specific hardware, dedicated pulse sequences for data acquisition and data processing and quantification techniques. Emphasis is given to recent advancements in MRSI methodologies, as well as future developments, which can lead to overcome difficulties associated with commonly employed MRSI approaches applied in clinical routine. This includes the replacement of standard PRESS sequences for volume selection, which we identified as inadequate for clinical applications, by sLASER sequences and implementation of 1H MRSI without water signal suppression. These may enable a new evaluation of the complementary role and significance of MRSI in prostate cancer management.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Integration of tissue metabolomics, transcriptomics and immunohistochemistry reveals ERG- and gleason score-specific metabolomic alterations in prostate cancer

Integrated analysis of metabolomics, transcriptomics and immunohistochemistry can contribute to a deeper understanding of biological processes altered in cancer and possibly enable improved diagnostic or prognostic tests. In this study, a set of 254 metabolites was determined by gas-chromatography/liquid chromatography-mass spectrometry in matched malignant and non-malignant prostatectomy samples of 106 prostate cancer (PCa) patients. Transcription analysis of matched samples was performed on a set of 15 PCa patients using Affymetrix U133 Plus 2.0 arrays. Expression of several proteins was immunohistochemically determined in 41 matched patient samples and the association with clinico-pathological parameters was analyzed by an integrated data analysis. These results further outline the highly deregulated metabolism of fatty acids, sphingolipids and polyamines in PCa. For the first time, the impact of the ERG translocation on the metabolome was demonstrated, highlighting an altered fatty acid oxidation in TMPRSS2-ERG translocation positive PCa specimens. Furthermore, alterations in cholesterol metabolism were found preferentially in high grade tumors, enabling the cells to create energy storage. With this integrated analysis we could not only confirm several findings from previous metabolomic studies, but also contradict others and finally expand our concepts of deregulated biological pathways in PCa.

Citrate Concentrations in Human Seminal Fluid and Expressed Prostatic Fluid Determined via 1 H Nuclear Magnetic Resonance Spectroscopy Outperform Prostate Specific Antigen in Prostate Cancer Detection

PURPOSE

We compared the performance of citrate concentration measurements in unprocessed human semen and expressed prostatic secretions from controls and from patients with biopsy confirmed prostate cancer to that of prostate specific antigen testing with respect to specificity and sensitivity for prostate cancer detection.

MATERIALS AND METHODS

Semen and expressed prostatic secretions were collected in biopsy proven, prostate cancer bearing and noncancer bearing cases. Citrate concentrations were determined by quantitative in vitro, high field, water suppressed proton nuclear magnetic resonance spectroscopy. Assessments of the diagnostic performance of citrate and prostate specific antigen results in our study populations were made by ROC curve analysis.

RESULTS

Citrate was measured in samples from 61 participants, of whom 16 without and 21 with cancer donated semen, and 17 without and 7 with cancer donated expressed prostatic secretions. Mean citrate +/- SE compared to that in controls was 2.7-fold lower in patients with cancer samples in semen (132.2 +/- 30.1 vs 48.0 +/- 7.9 mM, p < 0.05) and expressed prostatic secretions (221.4 +/- 55.4 vs 81.5 +/- 36.0 mM, p < 0.05). ROC curve analysis showed that measurements of citrate in semen performed as well as measurements of citrate in expressed prostatic secretion for detecting prostate cancer (AUC 0.81, 95% CI 0.60 to 0.92 and AUC 0.73, 95% CI 0.38 to 0.90, respectively, p > 0.05). ROC curve analysis also showed that the measurement of citrate in either fluid outperformed prostate specific antigen measurement for detecting prostate cancer in these subjects (AUC 0.61, 95% CI 0.44 to 0.74).

CONCLUSIONS

In vitro nuclear magnetic resonance spectroscopic measurement of the citrate concentration in semen or expressed prostatic secretions outperforms prostate specific antigen testing for detecting prostate cancer.

Ionic and pharmacologic characteristics of epithelial cells in a semi-intact preparation of the rat ventral prostate gland

BACKGROUND

The essential ionic and pharmacologic characteristics of epithelial cells within the ducts of the prostate gland are not well known.

METHODS

Experiments were carried out on segments of ventral prostate glands from adult male rats. By using sharp microelectrodes, intracellular epithelial cell and transepithelial (lumen) potentials were recorded in response to ionic substitution and application of ion channel blockers, hormones, and other pharmacologic agents related to prostatic function.

RESULTS

Membrane permeabilities to K(+), Na(+), and Cl(-) were found to account for approximately 43% of the resting membrane potential, whereas some 39% was likely to be metabolic in origin. The membrane potential also responded to adrenaline, acetylcholine, insulin, prolactin, testosterone, nerve growth factor, and nitric oxide. The lumen potential was found to be particularly sensitive to citrate, prolactin, and testosterone.

CONCLUSION

It was concluded that the basal membrane potential of prostatic epithelial cells is associated with a relatively high Na(+):K(+) permeability ratio and metabolic dependence. The hormonal and pharmacologic sensitivity observed is consistent with the functional characteristics of the prostate gland.

Citrate in the diagnosis of prostate cancer

BACKGROUND

One of the major current problems involved in prostate cancer (PCa) is the unavailability of sensitive, accurate, and preferably noninvasive procedures for the diagnosis of PCa. Moreover, procedures are needed which will permit the early detection, staging, location, and estimation of the volume of malignancy, and preferably a mapping of the prostate for follow-up of progression and regression of the malignancy.

METHODS

The unique citrate relationships of the prostate, coupled with recent developments and technological advancements in magnetic resonance spectroscopy (MRS) for the in situ determination of citrate levels, now provides an excellent diagnostic procedure which can achieve all these goals. There exist strong, compelling basic and clinical studies in support of the employment of 1H MRS measurements of citrate and other associated metabolites in the diagnosis of PCa.

RESULTS

This review provides the background leading to the current status of MRS citrate analysis, summarizes the data from clinical trials, and describes the applications of the procedure for the diagnosis of PCa and follow-up of patients. The use of MRS studies in defining the functional, as well as pathological relationships of the prostate, is also discussed.

CONCLUSIONS

This review is intended to be informative to the prostate- and oncology-interested community, and, hopefully, to engender much-needed interest and support in future research regarding the prostate relationships described in this report.

Novel role of zinc in the regulation of prostate citrate metabolism and its implications in prostate cancer

The prostate gland of humans and many other animals has the major function of accumulating and secreting extraordinarily high levels of citrate. This specialized metabolic process of "net citrate production" is the result of unique metabolic capabilities of the secretory epithelial cells. Most importantly, in prostate cancer (Pca) the capability for net citrate production is lost. In addition to citrate, the normal and BPH (benign prostatic hyperplasia) prostate also accumulates the highest levels of zinc in the body. As with citrate, in Pca the ability for high zinc accumulation is diminished. These and other correlations between zinc and citrate in the prostate have been indicative of an important role of zinc in the regulation of citrate metabolism in normal and malignant prostate epithelial cells. The link between zinc and citrate metabolism has now been established. The intramitochondrial accumulation of high zinc levels inhibits mitochondrial (m-) aconitase activity, which inhibits citrate oxidation. This essentially truncates the Krebs cycle and markedly decreases the cellular energy (ATP) production normally coupled to citrate oxidation. It is also clear that zinc accumulation in citrate-producing prostate epithelial cells is regulated by testosterone and by prolactin. These relationships form the basis for a new concept of the role of zinc and citrate-related energy metabolism in prostate malignancy. The inability of malignant prostate cells to accumulate high zinc levels results in increased citrate oxidation and the coupled ATP production essential for the progression of malignancy. The concept offers new approaches to the treatment of Pca.

Bioenergetic theory of prostate malignancy

Normal and benign prostate hyperplasia (BPH) prostate is characterized by the presence of extraordinarily high levels of citrate. Presumably, this results from the inability of the prostate epithelial cells to oxidize citrate due to a limiting mitochondrial (m-) aconitase. In contrast, prostate carcinoma (CA) is not characterized by high citrate levels. Malignant prostate epithelial cells apparently undergo a metabolic transformation from citrate-producing to citrate-oxidizing cells. A consequence of citrate production in normal and BPH cells is an inefficient and low level of ATP production. It is proposed that the process of malignancy necessitates an energy production that cannot be provided by citrate-producing cells. Consequently, the transformation of prostate epithelial cells to citrate-oxidizing cells which increases the energy production capability is essential to the process of malignancy and metastasis. The metabolic transformation likely occurs as a premalignant or early malignant stage. This bioenergetic theory of prostate malignancy, if correct, will provide new approaches to the diagnosis and treatment of CA.

Homonuclear broad-band-decoupled chemical shift imaging by singular value decomposition with optimization

The conventional viewpoint of localized NMR spectroscopy is to acquire spectral information through time-domain data, while leaving spatial information to phase encoding by incremental magnetic field gradients. A second viewpoint, much less frequently used, places the emphasis on the acquisition of spatially well-resolved images by conventional means, leaving the chemical shift segregation through phase encoding in the incremental t(1) period (in a 2-DNMR parlance). The feasibility and practicality of the second viewpoint are demonstrated by implementation of a modified version of the SLIM technique, which was originally designed for the first viewpoint, using simulated and real phantom data with optimization of the t(1)-encoding parameters.

Concepts of citrate production and secretion by prostate. 1. Metabolic relationships

Accumulation and secretion of extraordinarily high levels of citrate are principal functions of the prostate gland of humans and other animals. To achieve this, prostate secretory cells must possess unique metabolic relationships which distinguish them from virtually all other cells. Furthermore, citrate metabolism is markedly altered in benign prostatic hyperplasia (BPH) and in prostatic carcinoma (CA). This review assimilates existing information and presents current concepts related to 1) the pathway of metabolism associated with net citrate production, 2) the involvement of transporting mechanisms associated with citrate secretion, 3) energy implications of citrate production, 4) altered metabolic relationships in BPH and CA, and 5) the importance of citrate relationships as biochemical markers for characterizing prostate secretory epithelial cells. It is hoped that this review will bring attention to the importance and urgency of elucidating and understanding the metabolic relationships associated with citrate production by normal and neoplastic prostate epithelial cells. Research in these areas has been severely neglected despite the fact that the combined incidence of BPH and CA constitutes the most prevalent neoplastic disease among men.

Mitochondrial aspartate aminotransferase and the effect of testosterone on citrate production in rat ventral prostate

Mitochondrial aspartate transamination was investigated as a major source of oxalacetate for citrate synthesis in rat ventral prostate. Citrate accumulation was measured in isolated mitochondria incubated with acetyl coenzyme A and various combinations of amino acids. Aspartate plus alpha ketoglutarate in the presence of acetyl coenzyme A resulted in significant citrate accumulation. Neither aspartate nor alpha ketoglutarate alone resulted in any significant citrate accumulation. Aspartate and alpha ketoglutarate use was comparable to glutamate and citrate production. The results indicated the presence of a mitochondrial aspartate aminotransferase. Castration (3 days) caused a significant decrease in citrate production from aspartate plus alpha ketoglutarate as well as a decrease in mitochondrial AAT activity in prostate although no effect on kidney activity occurred. A single injection of 1 mg. testosterone propionate to castrate rats significantly increased prostate mitochondrial AAT activity within 24 hours while MDH activity was unaltered. A double reciprocal plot indicated that testosterone might regulate the level of mitochondrial AAT in prostate. Ventral prostate also contain a uniquely high level of endogenous aspartate. These studies indicate that aspartate might be the major 4-carbon source of oxalacetate for citrate synthesis. Also testosterone possibly regulated prostate citrate production by its effect on the level of mitochondrial AAT activity.

Indirect androgenic control of citrate accumulation in rat ventral prostate

Androgenic control of citrate metabolism was studied by measuring the conversion of (2-14C)acetate or (6-14C)glucose to (14C)citrate and 14CO2 in the ventral prostate of the rat. The decarboxylation of (2-14C)acetate showed that androgen preferentially increased (14C)citrate oxidation, probably to meet the increased energy demands of cellular synthetic reactions. This led to the decreased accumulation of (14C)citrate from (2-14C)acetate. On the other hand, both the production of (14C)citrate and the formation of 14CO2 from (6-14C)glucose were decreased by castration and increased by testosterone, this being mainly due to the androgenic control of pyruvate dehydrogenase. These changes were more marked and rapid than those in oxygen consumption, in (2-14C)acetate oxidation, or in the total content of prostatic citrate that was maintained by testosterone. Glucose as the main source of citrate in testosterone-treated rats can thus be replaced by alternative substrates in castrated rats. The rate of citrate accumulation could be more dependent on the number of secretory cells than their hormonal activation.