Loss of Peroxisomes Causes Oxygen Insensitivity of the Histochemical Assay of Glucose-6-Phosphate Dehydrogenase Activity to Detect Cancer Cells

Targeting Apollo-NADP+ to Image NADPH Generation in Pancreatic Beta-Cell Organelles

NADPH/NADP⁺ redox state supports numerous reactions related to cell growth and survival; yet the full impact is difficult to appreciate due to organelle compartmentalization of NADPH and NADP⁺. To study glucose-stimulated NADPH production in pancreatic beta-cell organelles, we targeted the Apollo-NADP⁺ sensor by first selecting the most pH-stable version of the single-color sensor. We subsequently targeted mTurquoise2-Apollo-NADP⁺ to various organelles and confirmed activity in the cytoplasm, mitochondrial matrix, nucleus, and peroxisome. Finally, we measured the glucose- and glutamine-stimulated NADPH responses by single- and dual-color imaging of the targeted sensors. Overall, we developed multiple organelle-targeted Apollo-NADP⁺ sensors to reveal the prominent role of beta-cell mitochondria in determining NADPH production in the cytoplasm, nucleus, and peroxisome.

Slc25a17 Gene Trapped Mice: PMP34 Plays a Role in the Peroxisomal Degradation of Phytanic and Pristanic Acid

Mice lacking PMP34, a peroxisomal membrane transporter encoded by Slc25a17, did not manifest any obvious phenotype on a Swiss Webster genetic background, even with various treatments designed to unmask impaired peroxisomal functioning. Peroxisomal α- and β-oxidation rates in PMP34 deficient fibroblasts or liver slices were not or only modestly affected and in bile, no abnormal bile acid intermediates were detected. Peroxisomal content of cofactors like CoA, ATP, NAD+, thiamine-pyrophosphate and pyridoxal-phosphate, based on direct or indirect data, appeared normal as were tissue plasmalogen and very long chain fatty acid levels. However, upon dietary phytol administration, the knockout mice displayed hepatomegaly, liver inflammation, and an induction of peroxisomal enzymes. This phenotype was partially mediated by PPARα. Hepatic triacylglycerols and cholesterylesters were elevated and both phytanic acid and pristanic acid accumulated in the liver lipids, in females to higher extent than in males. In addition, pristanic acid degradation products were detected, as wells as the CoA-esters of all these branched fatty acids. Hence, PMP34 is important for the degradation of phytanic/pristanic acid and/or export of their metabolites. Whether this is caused by a shortage of peroxisomal CoA affecting the intraperoxisomal formation of pristanoyl-CoA (and perhaps of phytanoyl-CoA), or the SCPx-catalyzed thiolytic cleavage during pristanic acid β-oxidation, could not be proven in this model, but the phytol-derived acyl-CoA profile is compatible with the latter possibility. On the other hand, the normal functioning of other peroxisomal pathways, and especially bile acid formation, seems to exclude severe transport problems or a shortage of CoA, and other cofactors like FAD, NAD(P)+, TPP. Based on our findings, PMP34 deficiency in humans is unlikely to be a life threatening condition but could cause elevated phytanic/pristanic acid levels in older adults.

Peroxisomes and Kidney Injury

SIGNIFICANCE

Peroxisomes are organelles present in most eukaryotic cells. The organs with the highest density of peroxisomes are the liver and kidneys. Peroxisomes possess more than fifty enzymes and fulfill a multitude of biological tasks. They actively participate in apoptosis, innate immunity, and inflammation. In recent years, a considerable amount of evidence has been collected to support the involvement of peroxisomes in the pathogenesis of kidney injury.

RECENT ADVANCES

The nature of the two most important peroxisomal tasks, beta-oxidation of fatty acids and hydrogen peroxide turnover, functionally relates peroxisomes to mitochondria. Further support for their communication and cooperation is furnished by the evidence that both organelles share the components of their division machinery. Until recently, the majority of studies on the molecular mechanisms of kidney injury focused primarily on mitochondria and neglected peroxisomes.

CRITICAL ISSUES

The aim of this concise review is to introduce the reader to the field of peroxisome biology and to provide an overview of the evidence about the contribution of peroxisomes to the development and progression of kidney injury. The topics of renal ischemia-reperfusion injury, endotoxin-induced kidney injury, diabetic nephropathy, and tubulointerstitial fibrosis, as well as the potential therapeutic implications of peroxisome activation, are addressed in this review.

FUTURE DIRECTIONS

Despite recent progress, further studies are needed to elucidate the molecular mechanisms induced by dysfunctional peroxisomes and the role of the dysregulated mitochondria-peroxisome axis in the pathogenesis of renal injury. Antioxid. Redox Signal. 25, 217-231.

Quantification of Colonic Stem Cell Mutations

The ability to measure stem cell mutations is a powerful tool to quantify in a critical cell population if, and to what extent, a chemical can induce mutations that potentially lead to cancer. The use of an enzymatic assay to quantify stem cell mutations in the X-linked glucose-6-phosphate dehydrogenase gene has been previously reported.(1) This method requires the preparation of frozen sections and incubation of the sectioned tissue with a reaction mixture that yields a blue color if the cells produce functional glucose-6-phosphate dehydrogenase (G6PD) enzyme. If not, the cells appear whitish. We have modified the reaction mixture using Optimal Cutting Temperature Compound (OCT) medium in place of polyvinyl alcohol. This facilitates pH measurement, increases solubilization of the G6PD staining components and restricts diffusion of the G6PD enzyme. To demonstrate that a mutation occurred in a stem cell, the entire crypt must lack G6PD enzymatic activity. Only if a stem cell harbors a phenotypic G6PD mutation will all of the progeny in the crypt lack G6PD enzymatic activity. To identify crypts with a stem cell mutation, four consecutive adjacent frozen sections (a level) were cut at 7 µm thicknesses. This approach of making adjacent cuts provides conformation that a crypt was fully mutated since the same mutated crypt will be observed in adjacent sections. Slides with tissue samples that were more than 50 µm apart were prepared to assess a total of >10(4) crypts per mouse. The mutation frequency is the number of observed mutated (white) crypts÷by the number of wild type (blue) crypts in a treatment group.

T-cells enhance stem cell mutagenesis in the mouse colon

A role of inflammation in the etiology of cancer is attributed to the production of reactive oxygen/nitrogen species that can damage DNA. To test this hypothesis, we determined the mutation frequency (MF) in colonic stem cells in C57Bl/6 mice exposed to azoxymethane (AOM), dextran sulfate sodium (DSS) and a combination of AOM and DSS (AOM+DSS). AOM+DSS efficiently and rapidly produces colon tumors in B6 mice. AOM produces promutagenic O(6)-methylguanine lesions in DNA but does not induce colon tumors in C57Bl/6 mice as a single agent. DSS produces inflammation in the colon but does not produce tumors except upon multiple cycles of treatment in some DNA repair deficient mouse models. In addition, using TCRβ null mice we tested whether α/β T cells have any effect on the colonic stem cell MF in mice treated with AOM, DSS and AOM+DSS. The TCRβ(-/-) mice are devoid of the critical receptor required for normal cytolytic and regulatory α/β T-cell functions. The MF in the untreated and DSS treated WT and TCRβ(-/-) mice was the same (<10(-5)) indicating that DSS and subsequent inflammation does not generate stem cell mutations in mice that are WT for DNA repair. AOM yielded mutant crypts in WT and TCRβ(-/-) mice with MF's of ∼4×10(-4) and 2×10(-4), respectively, which represents a statistically significant decrease in the MF in the immune compromised mice. The combined treatment of AOM+DSS afforded fully mutated crypts in both strains with a statistically significant lower MF in the TCRβ(-/-) mice. In addition, the MF in both strains of mice after the combination of AOM+DSS is lower than observed with AOM alone indicating that DSS inflammation destroyed pre-existing AOM mutated crypts. Using the MF in WT mice, the efficiency for the conversion of promutagenic O(6)-methylguanine lesions into a stem cell mutations was calculated to be ∼0.4%.

The antitumor effects of tetrodotoxin and/or doxorubicin on Ehrlich ascites carcinoma-bearing female mice

The study aimed to investigate the antitumor effect of tetrodotoxin (TTX) and/or doxorubicin (DOX) on Ehrlich ascites carcinoma (EAC)-bearing mice through the investigated biochemical parameters. TTX and/or DOX with or without N-acetylcystiene were administrated after 10 days into EAC-female mice for a period of 2 weeks in six equal doses. Treatment with TTX or DOX caused a significant decrease in the mean tumor weight and an increase in the cumulative mean survival time when compared with EAC group. All the treatments reduced the elevated liver tumor markers and increased liver antioxidant enzymes under investigation in comparison with EAC. Hepatic cells, suffered severely from degeneration and karriolysis in EAC group, revealed some improvement as appearance of healthy hepatocytes by TTX treatment. The present results suggested that TTX had a more powerful inhibitor effect on EAC growth than DOX and TTX plus DOX treatments reflected by antitumor biochemical and histological studies.

Efficiency of diagnostic biomarkers among colonic schistosomiasis Egyptian patients

The schistosomal parasite plays a critical role in the development of malignant lesions in different organs. The pathogenesis of cancer is currently under intense investigation to identify reliable prognostic indices for disease detection. The objective of this paper is to evaluate certain biochemical parameters as diagnostic tools to efficiently differentiate between colonic carcinoma and colonic carcinoma associated with schistosomal infection among Egyptian patients. The parameters under investigation are interleukin 2 (IL-2), tumour necrosis factor alpha (TNF-α), carcinoembryonic antigen (CEA) levels, tissue telomerase, pyruvate kinase (PK), glucose-6-phosphate dehydrogenase (G-6-PD) and lactate dehydrogenase (LDH) enzyme activities. The results revealed a significant elevation in the level of the tumour markers IL-2, TNF-α and CEA as well as the activities of LDH, telomerase and G-6-PD among non-bilharzial and bilharzial colonic cancer groups, with a more potent effect in bilharzial infection-associated colonic cancer. A significant inhibition in PK activity was recorded in the same manner as compared to normal tissues. The efficacy of this biomarker was also evaluated through detecting sensitivity, specificity, negative and positive predictive values. In conclusion, schistosomal colonic carcinoma patients displayed more drastic changes in all parameters under investigation. The combination of the selected parameters succeeded in serving as biomarkers to differentiate between the two malignant types.

Renal cell carcinoma and oxidative stress: The lack of peroxisomes

Oxidative stress plays an important role in carcinogenesis because of induction of DNA damage and its effects on intracellular signal transduction pathways. Here, we investigated the relationship between the defence against oxidative stress and human renal cell carcinoma that originates from proximal tubular epithelium. Oxygen insensitivity of the histochemical assay of glucose-6-phosphate dehydrogenase (G6PD) activity is a diagnostic tool for the detection of carcinomas. Its mechanism is based on high G6PD activity, reduced superoxide dismutase activity and reduced numbers of peroxisomes in the cancer cells. Five out of the 8 renal carcinomas studied here demonstrated oxygen insensitivity. These carcinomas showed high G6PD activity, whereas the other 3 carcinomas contained lower G6PD activity and were oxygen sensitive like non-cancer cells. Oxygen insensitivity did not correlate with tumour grade, staging or presence of metastases. Electron microscopy and immunofluorescence of catalase showed large numbers of peroxisomes in epithelial cells of proximal tubules of normal human kidney, whereas these organelles were completely absent in cancer cells of all carcinomas. As a consequence of the absence of peroxisomes in cancer cells, fatty acid metabolism is disturbed in addition to the altered glucose metabolism that is generally observed in cancer cells. Therefore, therapeutic approaches should focus on metabolism in addition to other strategies targeting signal transduction and angiogenesis.

Rapid combined light and electron microscopy on large frozen biological samples

The use of large unfixed frozen tissue samples (10 x 10 x 5 mm(3)) for combined light microscopy (LM) and electron microscopy (EM) is described. First, cryostat sections are applied for various LM histochemical approaches including in situ hybridization, immunohistochemistry and metabolic mapping (enzyme histochemistry). When EM inspection is needed, the tissue blocks that were used for cryostat sectioning and are stored at -80 degrees C, are then fixed at 4 degrees C with glutaraldehyde/paraformaldehyde and prepared for EM according to standard procedures. Ultrastructurally, most morphological aspects of normal and pathological tissue are retained whereas cryostat sectioning at -25 degrees C does not have serious damaging effects on the ultrastructure. This approach allows simple and rapid combined LM and EM of relatively large tissue specimens with acceptable ultrastructure. Its use is demonstrated with the elucidation of transdifferentiated mouse stromal elements in human pancreatic adenocarcinoma explants grown subcutaneously in nude mice. Combined LM and EM analysis revealed that these elements resemble cartilage showing enchondral mineralization and aberrant muscle fibres with characteristics of skeletal muscle cells.

A new G6PD knockdown tumor-cell line with reduced proliferation and increased susceptibility to oxidative stress

Glucose-6-phosphate dehydrogenase (G6PD) has been implicated in the regulation of cellular antioxidative mechanisms. Tumor cells often lose the balance of oxidation and antioxidation, but the role of G6PD in such an imbalance is still largely unknown. To investigate the related function of G6PD in tumor cells, we established a stable line of A375 human melanoma cells with G6PD gene knockdown by a shRNA lentiviral cloning and expression system. The A375-G6PDDelta cells displayed the stable GFP coexpression after repeated freeze-thaw cycles and multiple passages, accompanied by an 88.83% suppression of the endogenous G6PD expression and a 78.47% decrease in G6PD activity. In comparison with the A375-WT cells, they were characterized by a reduced proliferation with the MTT proliferation assay, a 25% decrease in colony-forming efficiency, and an up to 40% increase of apoptotic rate with flow cytometry analysis. When further challenged by diamide-induced oxidative stress, these cells showed that a median lethal dose (LD(50)) of 1.2 mM decreased from that of the A375-WT cells (1.8 mM), and levels of NADPH and GSH decreased by 2.4-, 8.8-fold, respectively, with a 7.3-fold increase of H(2)O(2), as those of A375-WT cells. These results demonstrated that A375-G6PDDelta is a new, stable G6PD-deficient human tumor cell line, and that silencing G6PD expression decreased tumor-cell proliferation and enhanced apoptosis. In addition, G6PD gene knockdown rendered tumor cells more susceptible to diamide-induced oxidative stress. Together, our data support the important functions of G6PD in the regulation of cell growth and antioxidative capacity of tumor cells.

Elevated activity of the oxidative and non-oxidative pentose phosphate pathway in (pre)neoplastic lesions in rat liver

(Pre)neoplastic lesions in livers of rats induced by diethylnitrosamine are characterized by elevated activity of the first irreversible enzyme of the oxidative branch of the pentose phosphate pathway (PPP), glucose-6-phosphate dehydrogenase (G6PD), for production of NADPH. In the present study, the activity of G6PD, and the other NADPH-producing enzymes, phosphogluconate dehydrogenase (PGD), isocitrate dehydrogenase (ICD) and malate dehydrogenase (MD) was investigated in (pre)neoplastic lesions by metabolic mapping. Transketolase (TKT), the reversible rate-limiting enzyme of the non-oxidative branch of the PPP, mainly responsible for ribose production, was studied as well. Activity of G6PD in (pre)neoplastic lesions was highest, whereas activity of PGD and ICD was only 10% and of MD 5% of G6PD activity, respectively. Glucose-6-phosphate dehydrogenase activity in (pre)neoplastic lesions was increased 25 times compared with extralesional parenchyma, which was also the highest activity increase of the four NADPH-producing dehydrogenases. Transketolase activity was 0.1% of G6PD activity in lesions and was increased 2.5-fold as compared with normal parenchyma. Transketolase activity was localized by electron microscopy exclusively at membranes of granular endoplasmic reticulum in rat hepatoma cells where G6PD activity is localized as well. It is concluded that NADPH in (pre)neoplastic lesions is mainly produced by G6PD, whereas elevated TKT activity in (pre)neoplastic lesions is responsible for ribose formation with concomitant energy supply by glycolysis. The similar localization of G6PD and TKT activity suggests the channelling of substrates at this site to optimize the efficiency of NADPH and ribose synthesis.

NADPH production by the pentose phosphate pathway in the zona fasciculata of rat adrenal gland

Biosynthesis of steroid hormones in the cortex of the adrenal gland takes place in smooth endoplasmic reticulum and mitochondria and requires NADPH. Four enzymes produce NADPH: glucose-6-phosphate dehydrogenase (G6PD), the key regulatory enzyme of the pentose phosphate pathway, phosphogluconate dehydrogenase (PGD), the third enzyme of that pathway, malate dehydrogenase (MDH), and isocitrate dehydrogenase (ICDH). However, the contribution of each enzyme to NADPH production in the cortex of adrenal gland has not been established. Therefore, activity of G6PD, PGD, MDH, and ICDH was localized and quantified in rat adrenocortical tissue using metabolic mapping, image analysis, and electron microscopy. The four enzymes have similar localization patterns in adrenal gland with highest activities in the zona fasciculata of the cortex. G6PD activity was strongest, PGD, MDH, and ICDH activity was approximately 60%, 15%, and 7% of G6PD activity, respectively. The K(m) value of G6PD for glucose-6-phosphate was two times higher than the K(m) value of PGD for phosphogluconate. As a consequence, virtual flux rates through G6PD and PGD are largely similar. It is concluded that G6PD and PGD provide the major part of NADPH in adrenocortical cells. Their activity is localized in the cytoplasm associated with free ribosomes and membranes of the smooth endoplasmic reticulum, indicating that NADPH-demanding processes related to biosynthesis of steroid hormones take place at these sites. Complete inhibition of G6PD by androsterones suggests that there is feedback regulation of steroid hormone biosynthesis via G6PD.