Massively parallel screen uncovers many rare 3' UTR variants regulating mRNA abundance of cancer driver genes

Understanding the function of rare non-coding variants represents a significant challenge. Using MapUTR, a screening method, we studied the function of rare 3' UTR variants affecting mRNA abundance post-transcriptionally. Among 17,301 rare gnomAD variants, an average of 24.5% were functional, with 70% in cancer-related genes, many in critical cancer pathways. This observation motivated an interrogation of 11,929 somatic mutations, uncovering 3928 (33%) functional mutations in 155 cancer driver genes. Functional MapUTR variants were enriched in microRNA- or protein-binding sites and may underlie outlier gene expression in tumors. Further, we introduce untranslated tumor mutational burden (uTMB), a metric reflecting the amount of somatic functional MapUTR variants of a tumor and show its potential in predicting patient survival. Through prime editing, we characterized three variants in cancer-relevant genes (MFN2, FOSL2, and IRAK1), demonstrating their cancer-driving potential. Our study elucidates the function of tens of thousands of non-coding variants, nominates non-coding cancer driver mutations, and demonstrates their potential contributions to cancer.

Exploring the ageing methylome in the model insect, Nasonia vitripennis

BACKGROUND

The ageing process is a multifaceted phenomenon marked by the gradual deterioration of cellular and organismal functions, accompanied by an elevated susceptibility to diseases. The intricate interplay between genetic and environmental factors complicates research, particularly in complex mammalian models. In this context, simple invertebrate organisms have been pivotal, but the current models lack detectable DNA methylation limiting the exploration of this critical epigenetic ageing mechanism. This study introduces Nasonia vitripennis, the jewel wasp, as an innovative invertebrate model for investigating the epigenetics of ageing. Leveraging its advantages as a model organism and possessing a functional DNA methylation system, Nasonia emerges as a valuable addition to ageing research.

RESULTS

Whole-genome bisulfite sequencing unveiled dynamic alterations in DNA methylation, with differentially methylated CpGs between distinct time points in both male and female wasps. These changes were associated with numerous genes, enriching for functions related to telomere maintenance, histone methylation, and mRNA catabolic processes. Additionally, other CpGs were found to be variably methylated at each timepoint. Sex-specific effects on epigenetic entropy were observed, indicating differential patterns in the loss of epigenetic stability over time. Constructing an epigenetic clock containing 19 CpGs revealed a robust correlation between epigenetic age and chronological age.

CONCLUSIONS

Nasonia vitripennis emerges as a promising model for investigating the epigenetics of ageing, shedding light on the intricate dynamics of DNA methylation and their implications for age-related processes. This research not only expands the repertoire of ageing models but also opens avenues for deeper exploration of epigenetic mechanisms in the context of ageing.

Widespread RNA hypoediting in schizophrenia and its relevance to mitochondrial function

RNA editing, the endogenous modification of nucleic acids, is known to be altered in genes with important neurological function in schizophrenia (SCZ). However, the global profile and molecular functions of disease-associated RNA editing remain unclear. Here, we analyzed RNA editing in postmortem brains of four SCZ cohorts and uncovered a significant and reproducible trend of hypoediting in patients of European descent. We report a set of SCZ-associated editing sites via WGCNA analysis, shared across cohorts. Using massively parallel reporter assays and bioinformatic analyses, we observed that differential 3' untranslated region (3'UTR) editing sites affecting host gene expression were enriched for mitochondrial processes. Furthermore, we characterized the impact of two recoding sites in the mitofusin 1 (MFN1) gene and showed their functional relevance to mitochondrial fusion and cellular apoptosis. Our study reveals a global reduction of editing in SCZ and a compelling link between editing and mitochondrial function in the disease.

LINE-associated cryptic splicing induces dsRNA-mediated interferon response and tumor immunity

RNA splicing plays a critical role in post-transcriptional gene regulation. Exponential expansion of intron length poses a challenge for accurate splicing. Little is known about how cells prevent inadvertent and often deleterious expression of intronic elements due to cryptic splicing. In this study, we identify hnRNPM as an essential RNA binding protein that suppresses cryptic splicing through binding to deep introns, preserving transcriptome integrity. Long interspersed nuclear elements (LINEs) harbor large amounts of pseudo splice sites in introns. hnRNPM preferentially binds at intronic LINEs and represses LINE-containing pseudo splice site usage for cryptic splicing. Remarkably, a subgroup of the cryptic exons can form long dsRNAs through base-pairing of inverted Alu transposable elements scattered in between LINEs and trigger interferon immune response, a well-known antiviral defense mechanism. Notably, these interferon-associated pathways are found to be upregulated in hnRNPM-deficient tumors, which also exhibit elevated immune cell infiltration. These findings unveil hnRNPM as a guardian of transcriptome integrity. Targeting hnRNPM in tumors may be used to trigger an inflammatory immune response thereby boosting cancer surveillance.

Single-Cell Analysis in Lung Adenocarcinoma Implicates RNA Editing in Cancer Innate Immunity and Patient Prognosis

RNA editing modifies single nucleotides of RNAs, regulating primary protein structure and protein abundance. In recent years, the diversity of proteins and complexity of gene regulation associated with RNA editing dysregulation has been increasingly appreciated in oncology. Large-scale shifts in editing have been observed in bulk tumors across various cancer types. However, RNA editing in single cells and individual cell types within tumors has not been explored. By profiling editing in single cells from lung adenocarcinoma biopsies, we found that the increased editing trend of bulk lung tumors was unique to cancer cells. Elevated editing levels were observed in cancer cells resistant to targeted therapy, and editing sites associated with drug response were enriched. Consistent with the regulation of antiviral pathways by RNA editing, higher editing levels in cancer cells were associated with reduced antitumor innate immune response, especially levels of natural killer cell infiltration. In addition, the level of RNA editing in cancer cells was positively associated with somatic point mutation burden. This observation motivated the definition of a new metric, RNA editing load, reflecting the amount of RNA mutations created by RNA editing. Importantly, in lung cancer, RNA editing load was a stronger predictor of patient survival than DNA mutations. This study provides the first single cell dissection of editing in cancer and highlights the significance of RNA editing load in cancer prognosis.

SIGNIFICANCE

RNA editing analysis in single lung adenocarcinoma cells uncovers RNA mutations that correlate with tumor mutation burden and cancer innate immunity and reveals the amount of RNA mutations that strongly predicts patient survival. See related commentary by Luo and Liang, p. 351.

scAllele: A versatile tool for the detection and analysis of variants in scRNA-seq

Single-cell RNA sequencing (scRNA-seq) data contain rich information at the gene, transcript, and nucleotide levels. Most analyses of scRNA-seq have focused on gene expression profiles, and it remains challenging to extract nucleotide variants and isoform-specific information. Here, we present scAllele, an integrative approach that detects single-nucleotide variants, insertions, deletions, and their allelic linkage with splicing patterns in scRNA-seq. We demonstrate that scAllele achieves better performance in identifying nucleotide variants than other commonly used tools. In addition, the read-specific variant calls by scAllele enables allele-specific splicing analysis, a unique feature not afforded by other methods. Applied to a lung cancer scRNA-seq dataset, scAllele identified variants with strong allelic linkage to alternative splicing, some of which are cancer specific and enriched in cancer-relevant pathways. scAllele represents a versatile tool to uncover multilayer information and previously unidentified biological insights from scRNA-seq data.

Multifaceted role of RNA editing in promoting loss-of-function of PODXL in cancer

PODXL, a protein that is dysregulated in multiple cancers, plays an important role in promoting cancer metastasis. In this study, we report that RNA editing promotes the inclusion of a PODXL alternative exon. The resulting edited PODXL long isoform is more prone to protease digestion and has the strongest effects on reducing cell migration and cisplatin chemoresistance among the three PODXL isoforms (short, unedited long, and edited long isoforms). Importantly, the editing level of the PODXL recoding site and the inclusion level of the PODXL alternative exon are strongly associated with overall patient survival in Kidney Renal Clear Cell Carcinoma (KIRC). Supported by significant enrichment of exonic RNA editing sites in alternatively spliced exons, we hypothesize that exonic RNA editing sites may enhance proteomic diversity through alternative splicing, in addition to amino acid changes, a previously under-appreciated aspect of RNA editing function.

Lipin 1 modulates mRNA splicing during fasting adaptation in liver

Lipin 1 regulates cellular lipid homeostasis through roles in glycerolipid synthesis (through phosphatidic acid phosphatase activity) and transcriptional coactivation. Lipin 1-deficient individuals exhibit episodic disease symptoms that are triggered by metabolic stress, such as stress caused by prolonged fasting. We sought to identify critical lipin 1 activities during fasting. We determined that lipin 1 deficiency induces widespread alternative mRNA splicing in liver during fasting, much of which is normalized by refeeding. The role of lipin 1 in mRNA splicing was largely independent of its enzymatic function. We identified interactions between lipin 1 and spliceosome proteins, as well as a requirement for lipin 1 to maintain homeostatic levels of spliceosome small nuclear RNAs and specific RNA splicing factors. In fasted Lpin1-/- liver, we identified a correspondence between alternative splicing of phospholipid biosynthetic enzymes and dysregulated phospholipid levels; splicing patterns and phospholipid levels were partly normalized by feeding. Thus, lipin 1 influences hepatic lipid metabolism through mRNA splicing, as well as through enzymatic and transcriptional activities, and fasting exacerbates the deleterious effects of lipin 1 deficiency on metabolic homeostasis.

RNA editing in cancer impacts mRNA abundance in immune response pathways

BACKGROUND

RNA editing generates modifications to the RNA sequences, thereby increasing protein diversity and shaping various layers of gene regulation. Recent studies have revealed global shifts in editing levels across many cancer types, as well as a few specific mechanisms implicating individual sites in tumorigenesis or metastasis. However, most tumor-associated sites, predominantly in noncoding regions, have unknown functional relevance.

RESULTS

Here, we carry out integrative analysis of RNA editing profiles between epithelial and mesenchymal tumors, since epithelial-mesenchymal transition is a key paradigm for metastasis. We identify distinct editing patterns between epithelial and mesenchymal tumors in seven cancer types using TCGA data, an observation further supported by single-cell RNA sequencing data and ADAR perturbation experiments in cell culture. Through computational analyses and experimental validations, we show that differential editing sites between epithelial and mesenchymal phenotypes function by regulating mRNA abundance of their respective genes. Our analysis of RNA-binding proteins reveals ILF3 as a potential regulator of this process, supported by experimental validations. Consistent with the known roles of ILF3 in immune response, epithelial-mesenchymal differential editing sites are enriched in genes involved in immune and viral processes. The strongest target of editing-dependent ILF3 regulation is the transcript encoding PKR, a crucial player in immune and viral response.

CONCLUSIONS

Our study reports widespread differences in RNA editing between epithelial and mesenchymal tumors and a novel mechanism of editing-dependent regulation of mRNA abundance. It reveals the broad impact of RNA editing in cancer and its relevance to cancer-related immune pathways.

Abiraterone acetate in metastatic castration-resistant prostate cancer - the unanticipated real-world clinical experience

Background

There is much interest in confirming whether the efficacy of abiraterone acetate (AA) demonstrated within the trial setting is reproducible in routine clinical practice. We report the clinical outcome of metastatic castration-resistant prostate cancer (mCRPC) patients treated with AA in real-life clinical practice.

Methods

The clinical records of mCRPC patients treated with AA from all 6 public oncology centers in Hong Kong between August 2011 and December 2014 were reviewed. The treatment efficacy and its determinants, and toxicities were determined.

Results

A total of 110 patients with mCRPC were treated with AA in the review period, of whom 58 were chemo-naive and 52 had received prior chemotherapy (post-chemo). The median follow-up time was 7.5/11.4 months for chemo-naive/post-chemo patients. 6.9/15.4 % of chemo-naive/post-chemo patients had visceral metastases. The median overall survival (OS) and progression-free survival (PFS) were 18.1/15.5 months and 6.7/6.4 months for chemo-naive/post-chemo patients, respectively. Among chemo-naive patients, those with visceral diseases had significantly inferior OS (2.8 vs 18.0 p = 0.0007) and PFS (2.8 vs 6.8 months, p = 0.0088) than those without. Pain control was comparable in both groups of patients. The most common grade 3 or above toxicities were hypertension (6.9/5.8 %) and hypokalemia (3.4/3.8 %) in chemo-naive/post-chemo patients. In multivariate analysis, the presence of prostate-specific antigen (PSA) response (≥50 % drop of PSA from baseline) within the first 3 months of therapy was associated with favorable OS and PFS in both chemo-naive and post-chemo group.

Conclusions

In clinical practice outside the trial setting, OS after AA in our chemo-naive patient cohort (18.1 months) was considerably shorter than that reported in the COU-AA-302 trial (34.7 months), and the OS was particularly short in those with visceral metastases (2.8 months). Conversely, AA was efficacious in post-chemo patients. AA resulted in comparable pain control in both groups of patients. The presence of PSA response within the first 3 months of treatment was a significant determinant of survival.

Co-administration of finasteride and the pure anti-oestrogen ICI 182,780 act synergistically in modulating the IGF system in rat prostate

Prostate cancer is the most diagnosed invasive malignancy in males. Androgens and oestrogens have been implicated in the pathogenesis of prostate cancer. We report herein that the pure anti-oestrogen ICI 182,780 (ICI) reduces Ki-67 labelling index and IGF-I receptor levels in rat prostate. Increase of IGF-I mRNA and IGF-binding protein 3 (IGFBP-3) accumulation occur without any effect on prostate weight. Finasteride significantly decreases prostate weight and inhibits IGF-I gene expression. IGFBP-3 mRNA, Akt and phospho-Akt are not affected by finasteride. Co-administration of ICI plus finasteride reduces prostate weight by approximately 50% and causes acinar dilation with decreased luminal epithelial cell thickness. The acinar epithelial cells became atrophic and inactive with minimal cytoplasm. We also demonstrate a synergistic effect of ICI and finasteride on induction of IGFBP-3 accumulation and inhibition of Akt phosphorylation. Because the IGF and IGFBP-3 system plays an important role in prostate epithelial cell proliferation, apoptosis and tumour progression, the inhibitory effects of finasteride and ICI on IGF system may contribute to their anti-proliferative activity. These observations support a potential use of ICI in conjunction with finasteride in the prevention and/or treatment of prostate cancer.

Inhibition of insulin-like growth factor signaling pathways in mammary gland by pure antiestrogen ICI 182,780

The antiestrogens ICI 182,780 (ICI) and tamoxifen are clinically useful in the treatment of estrogen receptor-positive breast tumors. We assessed the in vivo effects of ICI, tamoxifen, and estradiol on the insulin-like growth factor (IGF) signaling pathway in the rat mammary gland. ICI significantly decreased the size of the lobular structures, Ki-67 labeling index, and insulin-like growth factor binding protein (IGFBP)-2 and IGFBP-5 gene expression. Treatment of rats with 1, 1.5, and 2 mg of ICI/kg body weight/week resulted in a 2-, 7-, and 8-fold increase in IGFBP-3 transcripts. High doses of ICI increased mammary IGF-1 gene expression by 2-fold (P < 0.01) but decreased IGF-1R and its autophosphorylation to approximately 30% of the control mammary gland. IRS-1, IRS-2, and c-Raf-1 levels in the ICI-treated mammary glands were approximately 30, 15, and 40% of controls, respectively. Basal phosphorylation of IRS-1, Akt-1, and the p85 subunit of phosphatidylinositol 3-kinase (PI-3K) were low but detectable after ICI treatment. Despite a significant reduction in levels of IGF-1R, IRS-1, and IRS-2 phosphorylation, phospho p42/p44 MAPK levels were only slightly decreased. Tamoxifen-induced growth inhibition was associated with slight stimulation of IGFBP-3 gene expression and reduction in IRS-2 levels. Basal phosphorylation of IGF-1R, IRS-1, and p85 subunit of PI-3K was decreased by tamoxifen. Estradiol-induced epithelial cell proliferation was associated with inhibition of IGFBP-3 gene expression, stimulation of IGFBP-2 gene expression, and increases in IGF-1R, IRS-1, IRS-2, and c-Raf-1 levels. Although basal phosphorylation of IGF-1R, IRS-1, IRS-2, Akt-1, and the p85 subunit of PI-3K was significantly increased by estradiol, basal phospho p44/42 MAPK was significantly reduced. The data indicate that in addition to their classic actions, antiestrogens have major effects on IGF signaling pathways.

Induction of mammary epithelial cell differentiation and inhibition of dimethylbenz(A)anthracene-induced mammary tumour by co-administration of a pure antiestrogen ICI 182,780 and testosterone enanthate

Epidemiological studies have shown that early first pregnancy is associated with a life-long reduction in breast cancer risk. The terminal differentiation associated with pregnancy and lactation has been proposed as a mechanism underlying the protective effect of pregnancy. We report that treatment of rats with ICI 182,780 (ICI) caused a marked reduction in epithelial cells and Ki-67 labelling index as compared to controls and testosterone enanthate-treated (TE) mammary glands. TE increased the Ki-67 labelling index, stimulated lobuloalveolar and ductal growth, as well as the secretory activity of acinar cells. Co-administration of TE and ICI resulted in a reduction in Ki-67 labelling index. Mammary epithelial cells became differentiated, resembling that observed at the end of pregnancy and during lactation as indicated by marked increase in secretory activity, lipid accumulation and presence of basal nuclei. The expression of differentiation markers such as whey acidic protein, mammary derived growth inhibitor, alpha-casein and beta-casein was detected only in TE plus ICI treated mammary tissues. Unlike TE, ICI caused a significant reduction in DMBA-induced tumour incidence, number of tumour bearing and tumour size. Tumour incidence was reduced to 8% when both ICI and TE were co-administered. Our data provide the novel molecular interactions between the estrogen and androgen in regulation of mammary growth and differentiation. These observations may give insight into novel actions of ICI and TE on breast differentiation and protection against carcinogenesis which may be useful in designing novel strategies for cancer prevention and/or treatment based on maximizing mammary epithelial cell differentiation.

Cloning and characterization of a novel pregnancy-induced growth inhibitor in mammary gland

Growth factors and growth inhibitors play crucial roles in the growth regulation and differentiation of mammary epithelial cells. Studies have shown that during pregnancy, with the onset of terminal differentiation, there is a dramatic decrease in the proliferation of the mammary epithelial cells. Here we report the cloning and characterization of a novel pregnancy-induced cDNA, OKL38, from a human ovarian cDNA library. This cDNA encodes for a protein of approximately 34.5 kDa. Tissue distribution studies through Northern analyses revealed the ubiquitous nature of OKL38 transcripts in most tissues, with the highest levels observed in the ovary, kidney, and liver. The onset and advancement of pregnancy also gave rise to a concomitant increase in OKL38 gene expression. In situ hybridization revealed that OKL38 mRNA was further detected in mammary secretory epithelial cells. However, low levels of OKL38 transcripts were observed in the various human breast cancer cell lines studied and were barely detectable in all dimethylbenz(A)anthracene-induced mammary tumors examined. Transfection studies with OKL38 cDNA with MCF-7 cells resulted in growth inhibition in vitro and reduction in tumor formation in vivo. These observations led to speculation that OKL38 may play a vital role in the growth regulation and differentiation of breast epithelial cells during pregnancy and its implications in tumorigenesis.

Induction of UO-44 gene expression by tamoxifen in the rat uterus and ovary

A complementary DNA, uterine-ovarian-specific gene 44 (UO-44), has been isolated from tamoxifen-induced rat uterine complementary DNA library using differential display techniques. UO-44 transcripts are found to be abundant in the uterus and ovary. UO-44 gene expression in the uterus is strictly regulated by estrogens, tamoxifen, and GH, whereas the pure antiestrogen ICI 182780 is inhibitory. Treatment of ovariectomized rats and hypophysectomized rats with tamoxifen and GH, respectively, resulted in up-regulation of UO-44 expression in a dose-dependent manner. In situ hybridization revealed that UO-44 gene expression was restricted to the luminal and glandular epithelial cells of the uterus and to granulosa cells of medium-size ovarian follicles. Transfection studies showed that UO-44 was a membrane-associated protein. Because estrogens, tamoxifen, and GH are stimulators of uterine luminal epithelial cell growth in vivo, UO-44 protein may serve as a mediator of the effect of these compounds in inducing epithelial proliferation and differentiation in these tissues.

Antioxidative glucosides from the fruits of Ligustrum lucidum

The ethanol extract of the fruits of Ligustrum lucidum was shown to have inhibitory effects on the hemolysis of red blood cells induced by 2,2'-azo-bis-(2-amidinopropane) dihydrochloride. Bioassay-guided analysis led to the isolation of ten secoiridoid glucosides. Two of them were new, lucidumosides C and D. Their structures were elucidated by spectroscopic methods. The other eight compounds were identified as oleoside dimethyl ester, ligustroside, oleuropein, nuezhenide, isonuezhenide, neonuezhenide, lucidumoside A and lucidumoside B. Five compounds, oleoside dimethyl ester, oleuropein, neonuezhenide, lucidumoside B and lucidumoside C, exhibited strong antioxidant effect against hemolysis of red blood cells induced by free radicals.

Tetrapyrrole derivatives substituted with ferrocenylethynyl moieties. synthesis and electrochemical studies

Up to eight redox-active ferrocenyl units have been incorporated, through the unsaturated ethynyl linkers, on the periphery of a series of cyclic tetrapyrrole derivatives including zinc(II) phthalocyanine and 2,3-naphthalocyanine, and nickel(II) meso-diphenylporphyrin. The synthesis of the former two macrocycles 4 and 7 involves the Sonogashira coupling reaction of ferrocenylethyne with 4,5-dichlorophthalonitrile (1) or 6,7-dibromonaphthalonitrile (5), respectively, followed by a base-promoted cyclization. The meso-bis(ferrocenylethynyl)porphyrin 11 has been prepared from the dibromo analogue 10 also by a palladium-catalyzed coupling reaction. These novel macrocyclic compounds have been spectroscopically and electrochemically characterized. As revealed by cyclic voltammetry, the ferrocenyl moieties appear to be electrochemically independent in these complexes and there is no significant electronic coupling among the iron(II) centers.

Differentiation and authentication of Panax ginseng, Panax quinquefolius, and ginseng products by using HPLC/MS

An LC/MS-based method is established for the differentiation and authentication of specimens and commercial samples of Panax ginseng (Oriental ginseng) and Panax quinquefolius (American ginseng). This method is based on the separation of ginsenosides present in the ginseng methanolic extracts using high-performance liquid chromatography (HPLC), followed by detection with electrospray mass spectrometry. Differentiation of ginsenosides is achieved through simultaneous detection of intact ginsenoside molecular ions and the ions of their characteristic thermal degradation products. An important parameter used for differentiating P. ginseng and P. quinquefolius is the presence of ginsenoside Rf and 24-(R)-pseudoginsenoside F11 in the RICs of Oriental and American ginsengs, respectively. It is important to stress that ginsenoside Rf and 24(R)-pseudoginsenoside F11, which possess the same molecular weight and were found to have similar retention times under most LC conditions, can be unambiguously distinguished in the present HPLC/MS method. The method developed is robust, reliable, reproducible, and highly sensitive down to the nanogram level.

Modulation of transforming growth factor beta1 gene expression in the mammary gland by insulin-like growth factor I and octreotide

Transforming growth factor beta1 (TGF-beta1) has been shown to exhibit anti-proliferative activity for mammary gland epithelial cells and for human breast cancer cells. Insulin-like growth factor I (IGF-I), in contrast, is a well-characterized mitogenic and anti-apoptotic factor involved in mammary gland physiology. In order to examine the hypothesis that IGF-I suppresses TGF-beta1 expression in the mammary gland, we studied the effect of various manipulations of the growth hormone - IGF-I axis on TGF-beta1 mRNA abundance. Administration of IGF-I to intact animal suppressed TGF-beta1 mRNA levels in a dose-dependent manner to approximately 20% of control levels. Administration of the somatostatin analogue octreotide in a manner previously shown to acutely suppress the growth hormone - IGF-I axis increased mammary gland TGF-beta1 expression approximately 3-fold. Transgenic mice overexpressing growth hormone expressed TGF-beta1 in the mammary gland at only approximately 12% of the level of control animals, while mice IGF-I deficient due to the mutation expressed TGF-beta1 at slightly higher levels than control animals. The large differences in TGF-beta1 expression between control and GH-transgenic animals were correlated with major differences in architecture of the mammary gland, while the appearance of mammary glands of normal and animals was similar. These data document a previously unrecognized relationship between TGF-beta1 and IGF-I physiology in the mammary gland, and suggest a novel mechanism by which somatostatin analogues influence the proliferative behaviour of breast epithelial cells.

Differentiation of enantiomers using matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has successfully been used to differentiate pseudo-enantiomeric (isotopically labelled) amino acids by using cyclodextrin as complexing host. By using different pseudo-enantiomeric mixtures (i.e. R(Dn) + S; and R + S(Dn)), it has been demonstrated that the preference of cyclodextrin for S-enantiomers is not due to the size differences caused by the hydrogen/deuterium substitution. It is postulated that this method can be extended to differentiate enantiomers (and determine enantiomeric excess) by using a pair of enantiomeric hosts, as demonstrated previously using other ionization techniques, but with much higher sensitivity.

Effect of sample preparation methods on the analysis of dispersed polysaccharides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Effect of sample preparation methods on the matrix-assisted laser desorption/ionization (MALDI) analysis of dispersed polysaccharides is reported. By using the conventional drop-drying method, the measured number-averaged molecular weights were found to differ significantly from the values obtained from gel-permeation chromatography (GPC). These discrepancies were found to increase as the average masses of the polysaccharides increased. To understand the impact of the sample preparation method on the MALDI measurement, a dispersed dextran sample was separated into ten narrow-distribution fractions. Mixtures of different mass fractions were prepared and analyzed by using different mixing and preparation methods. By using the ratio of the signal intensity for the low-mass fraction to that of the high-mass fraction as an indicator, the impact of sample preparation conditions on the enhancement of low-mass components (or suppression of high-mass components) was determined. From the results obtained, it is postulated that the difference in solubilities between the low-mass and high-mass components for dispersed polymers might be large enough to induce an enhancement of low-mass components (or suppression of high-mass components) at the surface of the crystals during sample crystallization in the drop-drying method.

A novel nonmetallized tip for electrospray mass spectrometry at nanoliter flow rate

We report the fabrication of a durable nonmetallized nanospray tip. This nanospray tip does not require complex preparation procedures such as chemical treatment, deposition of gold or SiOx vapor. It was fabricated by pulling a heated glass capillary of 1.1 mm internal diameter to produce a fine tip with an orifice of 10-15 microns in diameter. A 10 microns gold-plated tungsten wire was inserted through the capillary tip. This tungsten wire played a central role in the operation of this durable nanospray tip by providing electrical contact. This type of nanospray tip could withstand electrical discharges and sustained spraying of solution at nanoliter flow rate for more than 3 h. Using insulin (35 microM) and myoglobin (1 microM) solutions, useful mass spectrum could be acquired with low fmol sensitivity.

Interpretive algorithms for the symptom-limited exercise test: assessing dyspnea in Persian Gulf war veterans

Interpretation of symptom-limited exercise testing requires analysis of a large body of simultaneously recorded cardiopulmonary data. Karlman Wasserman has recommended an algorithmic approach to interpretation (WA) that leads to a dichotomous choice between pulmonary and cardiovascular impairment. An alternative algorithm published by William Eschenbacher (EA) provides for concurrent assessment of cardiovascular and pulmonary exercise impairment. We analyzed a group of 29 individuals referred to the Pulmonary Physiology Laboratory at the Washington Veterans Affairs Medical Center for evaluation of dyspnea following service in the Persian Gulf War to assess the concordance of the two algorithms in determining the cause of dyspnea and exercise impairment in these individuals. They each performed a progressive, ramped, symptom-limited exercise test on a bike for a minimum of 6 min. Exercise measurements were analyzed by both interpretive algorithms. Concordance was found in 28% of tests. The greatest discordance occurred in identifying pulmonary limitation. Eleven had pulmonary limitation by EA; of these, WA found 1 to have pulmonary limitation, 5 to be normal, 4 indeterminate, and 1 musculoskeletal limitation. Of the 11 with pulmonary limitation by EA, but not by WA, 5 had abnormal resting pulmonary function measurements. Analysis of the differences between these two interpretive approaches is given. The EA algorithm may be more sensitive for detecting exercise impairment of pulmonary origin, but its specificity remains to be determined.

Formulation of matrix solutions for use in matrix-assisted laser desorption/ionization of biomolecules

We report a simple method for converting solid matrices into useful matrix solutions for matrix-assisted laser desorption/ionization (MALDI). This method is based on the dissolution of the solid matrix in a liquid support of low volatility such as glycerol. An appropriate solubilizing reagent was added to promote the dissolution of the matrix materials into the liquid support. Selection of the solubilizing reagent is empirically related to an acid-base relationship, i.e., an acidic solid matrix requires a basic organic compound to form a stable matrix solution in the liquid support and vice versa. A tenfold increase in the solubility can be obtained for many solid matrices when appropriate solubilizing reagents are added into the glycerol support. This solubility enhancement is tentatively attributed to the ion-pair formation in a polar nonvolatile liquid support. In addition, the hydrophobicity of the solid matrix seems to play an important role in the efficiency of the resulting matrix solution. By using glycerol as liquid support, a hydrophilic matrix, such as 2,5-dihydroxybenzoic acid (DHB), showed a substantial "peripheral effect," in which good analyte ion signals could only be recorded at the peripheral region of the sample droplet. More hydrophobic matrices, such as alpha-cyano-4-hydroxycinnamic acid (alpha-CCA), exhibit better and more homogeneous responses at different regions of the droplets. The performance of these matrix solutions was evaluated in terms of the durability, reproducibility, sensitivity, high mass capability, and generality. A typical sample droplet can afford more than an hour of repeated sampling with excellent shot-to-shot reproducibility. A low picomole sensitivity was demonstrated using a luteinizing hormone releasing hormone (LHRH) in a Fourier transform ion cyclotron resonance mass spectrometer with a homemade external MALDI ion source. By using a commercial MALDI time-of-flight mass spectrometer, proteins with masses as high as 66,000 Da were successfully analyzed by using these matrix solutions.

Induction of seminal vesicle morphogenesis from dog epididymal epithelium

A number of carnivores, including the dog, do not have seminal vesicles (SVs). They have been induced experimentally by heterotypic recombination of adult dog epididymal epithelium with mesenchyme of neonatal rat SV and allowed to grow for 4 weeks under the renal capsule of male athymic nude mice. The induced SVs bore a striking similarity to rat SV both histologically and ultrastructurally. However, they secreted proteins which were different from those in the rat SV and reacted negatively to antibodies specific to rat SV secretory proteins and dog prostate secretory proteins. The results strongly suggested that the glands induced from dog epididymal epithelium were likely to be "dog" SVs.

Positive-ion electrospray-fourier transform ion cyclotron resonance mass spectra of polypeptides and proteins

We have determined the mass spectra of three polypeptides which have been designed as an effective reagent to be used in the diagnosis of a Chinese strain of Hepatitis E Virus (HEV). The spectra were determined by electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometer. These are peptide 30, peptide 33 and peptide 42, where the guanidine amino group of arginine in each polypeptide was protected. The molecular weights were respectively measured as 3575, 4094 and 5390 Dalton, against the molecular weights of bovine serum albumin (66430 Da) and bovine insulin (5732.77 Da).

Use of ammonium halides as co-matrices for matrix-assisted laser desorption/ionization studies of oligonucleotides

Four ammonium salts, NH4F, NH4Cl, NH4Br and NH4I were tested as co-matrices for the matrix-assisted laser desorption/ionization (MALDI) analysis of a number of DNA homopolymers, including phosphorylated d(T)8, d(A)4, d(C)4 and non-phosphorylated d(G)4, using 2-amino-5-nitropyridine (ANP) matrix. In the present study, all the ammonium halides displayed significant enhancement effects on the signal intensities of the intact molecular ions of the DNA homopolymers. Among the halides used, NH4F was found to exhibit the greatest enhancement effects. By comparison with results obtained using the corresponding isomorphous potassium halides as co-matrices, it is postulated that both the cationic and anionic portions of the co-matrix molecule play important roles in the desorption/ionization of the oligonucleotides under typical MALDI conditions. It was also demonstrated that the ANP matrix exhibits a strong inhibitory effect on the formation of alkali-metal adducts in oligonucleotide analysis.

Hepatic MR imaging with ferumoxides: a multicenter clinical trial of the safety and efficacy in the detection of focal hepatic lesions

PURPOSE

To assess the safety and diagnostic efficacy of intravenous ferumoxides, a superparamagnetic iron oxide, for depiction of focal hepatic lesions on magnetic resonance (MR) images.

MATERIALS AND METHODS

This open-label study included 208 patients with known or suspected focal hepatic lesions. MR images were obtained before and 45 minutes to 4 hours after intravenous infusion of ferumoxides (10 mumol/kg). The effect of ferumoxides on signal intensity of the liver was assessed with quantitative analysis. Safety was evaluated with patient monitoring and laboratory measurements.

RESULTS

Mean lesion-to-liver contrast-to-noise ratio on T2-weighted images was 9.1 on unenhanced images and 12.7 on enhanced images. Signal intensity of normal liver on enhanced images decreased to 37% of that on unenhanced images. In blinded image evaluations, additional lesions were identified on 27% of enhanced images. No serious adverse events occurred.

CONCLUSION

Ferumoxides is a safe and efficacious contrast agent for the detection of focal liver lesions on T2-weighted images.

The knowledge and attitude of Hong Kong secondary school teachers and students towards HIV infection and dentistry

Although human immunodeficiency virus (HIV) infection and acquired immune deficiency syndrome (AIDS) are firmly entrenched in Hong Kong no data are available on the knowledge and attitudes of Hong Kong secondary school teachers and teenage children towards this infection, and their perception of infection control measures currently undertaken by the dental profession to prevent such infectious diseases. Hence a postal questionnaire survey of a total of 2,886 teenagers and 372 school teachers of 21 secondary schools in Hong Kong was conducted. The questionnaire comprised a total of 13 questions divided into two categories; the first, aimed at assessing the respondents' general knowledge and attitudes towards AIDS, and the second related to AIDS, dentistry and infection control. More than half of the students and one quarter of the teachers surmised that HIV infection is equivalent to developing AIDS. Although the great majority of the respondents (85-97 per cent) were aware that HIV can not be transmitted through sharing combs and meals, one in two teachers and one in three students thought that the virus could be transmitted through saliva. A large majority of respondents believed television to be the most, and dentists the least, informative source on AIDS out of a list of eight options. Approximately one half of both groups were concerned about contracting HIV infection during dental treatment and 65 per cent of students and 57 per cent of teachers thought that dentists did not have sufficient knowledge to identify AIDS patients. Finally, more than three quarters of the respondents thought that it would be ill-advised to visit a dentist treating HIV-infected patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Case report: neovascularity of inferior vena cava tumour thrombus from renal cell carcinoma--CT and MRI appearance

Renal cell carcinoma is a highly vascular tumour that frequently invades vascular structures. Neovascularization within an intravascular mass has occasionally been demonstrated on CT and angiography. We report a case with MR evidence of neovascularity in the inferior vena cava secondary to a renal cell carcinoma.

Liver metastases from ovarian cystadenocarcinoma masquerading on CT as lobar fatty infiltration

The CT appearance of fatty infiltration can be variable and can mimic various lesions, including neoplasms. We report a case of ovarian carcinoma metastatic to the liver masquerading as focal lobar fatty infiltration.

The relationship between parenting stress and social support in mothers of children with learning disabilities: a Chinese experience

This study examined the relationship between parenting stress and social support in a random sample of 100 mothers with children at a school for children with learning disabilities, and a control group of 75 mothers with similarly aged non-handicapped children. Mothers of children at Zhi Ling school were found to have significantly more stress and significantly less support than those in the control group. Parenting stress in the control group was also found to be relatively high when compared with what are considered to be normal levels in the West. No significant correlation was found between total parenting stress and social support. It is suggested that further studies need to differentiate between satisfaction with support that is actually received and the perceived quality of available support.

Selective MR imaging of silicone with the three-point Dixon technique

Selective magnetic resonance (MR) imaging of silicone with the three-point Dixon technique was evaluated. This technique, which conventionally allows separation of lipid and water signals, was modified to allow calculation of a silicone-only image and a lipid-water image. Imaging of fat and silicone implant phantoms was performed with a 1.5-T imager and was optimized in vivo in two volunteers who had breast reconstruction or augmentation. Six additional volunteers were then imaged to evaluate selective MR imaging of silicone. With an optimum frequency shift of 105 Hz, a repetition time of 1,000 msec, and an echo time of 28 msec, the modified three-point Dixon technique produced a silicone-only image containing 97.0% +/- 1.0 (standard deviation) of the total silicone signal, 2.6% +/- 0.5 of the fat signal, and 16.6% +/- 6.4 of the water signal. The silicone-fat contrast-to-noise ratio was 47.9 +/- 12.1. This method may be potentially useful in the evaluation of implant-related complications such as rupture.

Magnetic resonance imaging of abscesses using lipid-coated iron oxide particles

RATIONALE AND OBJECTIVES

The authors investigated whether iron oxide particles can be used as a magnetic resonance imaging (MRI) contrast agent to image abscesses in a two-stage experimental design.

METHODS

Human buffy coat was incubated with iron oxide particles of different sizes and coatings. Smears of the incubation mixture were made on a glass slide and stained for iron. The percentage of iron oxide uptake was determined by counting 100 neutrophils and monocytes and scoring the number of cells that contain iron. Subcutaneous abscesses were created in the flanks of 18 Sprague-Dawley rats by injecting them with 0.1 mL of turpentine. Iron oxide was given intravenously, and the animals were imaged by MRI (1.5 T) 12 to 24 hours later. Different iron oxide coatings and doses were compared.

RESULTS

The four different types of coating (constant fragment [Fc] of IgG, bovine serum albumin [BSA], lipid [Ferrosome], and dextran) had an uptake of 72% +/- 5.3%, 61% +/- 6.2%, 30.5% +/- 6.8%, and 5% +/- 2.5%, respectively. Comparison of two particle sizes (mean, 90 versus 35 nm) showed the large particles to have higher uptake (61% +/- 6.2%) compared with the small particles (6% +/- 1.8%) (P less than .001). Post-contrast imaging of the rats showed a hypointense ring around the abscess only in the animals injected with the lipid-coated agent. The effect was discernible within 12 hours after contrast injection and at a dose of 25 mumols iron/kg. Histologic sections showed phagocytic cells with iron granules in the periphery of the abscess. No hypointense ring on MRI or iron granules on histologic sections was seen around the abscess of the control animals or those injected with BSA-iron oxide or Fc-iron oxide.

CONCLUSIONS

Lipid-coated iron oxide particles can be used to image abscesses by virtue of their phagocytosis into surrounding inflammatory cells. Positive uptake of these particles by human phagocytes in vitro suggests that similar results may be applicable in humans.

Rectal carcinoma: staging at MR imaging with endorectal surface coil. Work in progress

To increase the accuracy of local staging of rectal carcinomas at magnetic resonance (MR) imaging, the authors placed on endorectal coil mounted on a balloon in a position adjacent to the lesion. Use of such a local coil resulted in increased signal-to-noise ratio compared with use of a body coil; higher-resolution images were obtained because the field of view was decreased. The depth of wall invasion by rectal carcinoma was correctly staged with endorectal MR imaging in 11 of 12 patients. In the detection of perirectal adenopathy, use of MR enabled correct identification of positive perirectal nodes in four of seven patients (57%). There were no false-positive diagnoses of perirectal adenopathy at MR. Endorectal MR imaging is an evolving and promising technique for the local staging of rectal carcinomas, but further studies are needed to demonstrate its efficacy.

Combined chemical-shift and phase-selective imaging for fat suppression: theory and initial clinical experience

Incomplete fat suppression with a chemical-shift-selective (CHESS) or phase-selective (Dixon) technique is partially due to the olefinic fat component, which precesses at the same frequency as water. The authors developed a new method of fat suppression--the opposed-fat saturation (OP-ES) sequence--that combines both techniques to obtain superior fat saturation. Fat suppression was verified in phantom studies, which showed that the CHESS portion can eliminate most of the aliphatic fat signal except for a small residual component because of steady state effects and magnetic field imperfections. This residual component is cancelled by the olefinic fat with the phase-selective opposed portion of the sequence. Furthermore, this sequence was superior to another hybrid technique, chopper Dixon in combination with CHESS. When used in 10 healthy volunteers, the OP-FS sequence showed consistently better suppression of the subcutaneous and retroperitoneal fat compared with CHESS alone. Additional advantages for clinical abdominal imaging include its compatibility with respiratory compensation, use of a single excitation, and ease of implementation with gradient-echo imaging. Preliminary application in 10 patients illustrated other potential advantages, including clarification of fat-containing diseases and increasing conspicuity of some lesions.

Differential diagnosis of hepatic neoplasms: spin echo versus gadolinium-diethylenetriaminepentaacetate-enhanced gradient echo imaging

Early results are reported of hepatic neoplasms studied with dynamic gadolinium-diethylenetriaminepentaacetate (Gd-DTPA)-enhanced magnetic resonance imaging (MRI). The purpose of this study was to evaluate the potential of the Gd enhancement pattern for characterizing these neoplasms and to compare the performance of spin-echo (SE) to SE plus dynamic Gd-enhanced gradient-echo (GRE) pulse sequences. Forty-two patients with hepatic neoplasms were examined at 1.5 T field strength. In each patient, short and long repetition time/echo time (TR/TE) SE images were obtained, followed by pre- and post-Gd-DTPA (0.1 mmol/kg body wt), single-slice, breath-hold (13 s/scan) GRE images, which were serially acquired less than or equal to 12 min postinjection. The patterns of contrast enhancement of the various hepatic lesions were documented and analyzed. The time to peak Gd signal enhancement-to-noise ratio (SE/N), contrast-to-noise ratio (C/N), contrast (defined as the signal intensity ratio [SIR]), as well as the peak values of these quantities, were determined. The C/N and SIR values on the short and long TR/TE SE and pre-Gd GRE images for all hepatic neoplasms were also obtained. The discriminating abilities (hemangiomas vs. malignant neoplasms) of these quantities were analyzed statistically. In addition, the impact of lesion characterization on the SE versus the SE plus the Gd-enhanced GRE scans was assessed by means of a blinded reader study. Malignant hepatic neoplasms could be differentiated from hemangiomas by visual inspection of their enhancement patterns (p = 0.0009), by the time to peak C/N on Gd-enhanced images (p = 0.0002), and by the magnitude of such peak (p = 0.02). Combined SE + Gd-enhanced GRE scans afforded minor, though statistically significant (p less than 0.01), improvement of the accuracy in differentiating benign from malignant hepatic neoplasms. Late scans (12 min post-Gd) may be particularly useful in identifying hemangiomas that, unlike other neoplasms, have a significant high signal of their enhancing portions on such images.

Prostate and seminal vesicles after irradiation: MR appearance

Familiarity with the morphologic changes in the prostate and seminal vesicles (SV) after pelvic irradiation is important to the correct interpretation of follow-up magnetic resonance (MR) studies. A retrospective study of 38 patients with prostatic or other pelvic tumors treated with radiation showed that 31.6% had a normal prostatic zonal pattern (peripheral zone hyperintense to central gland) on T2-weighted images, and 7.9% showed reversal of the zonal pattern; among the rest, the entire gland was diffusely isointense to fat in 42.1%, hypointense to fat in 10.5%, and hyperintense to fat in 7.9%. Sixty-three percent of the SV had a normal appearance, 21% had fewer tubules but normal signal intensity (SI), 8% had diffuse loss of SI (hypointense to fat), and 8% were hypointense to muscle. Quantitative measurements of SI of the prostate and SV demonstrated a statistically significant lower mean value for the irradiated patients relative to 10 control patients. A decrease in the size of both the prostate and SV was observed in 33% of patients with baseline studies. Use of additional treatment modalities in patients with prostatic carcinoma appeared to correlate with increased likelihood of developing abnormal changes. The authors conclude that in the irradiated patient, the prostate and SV can develop several patterns of SI abnormalities; in particular, diffuse low SI in the prostate and SV should establish radiation fibrosis as an important differential diagnosis to consider.

Biceps tendon dislocation: evaluation with MR imaging

The magnetic resonance (MR) images from six patients with biceps tendon dislocation--two in whom it was surgically proved and four in whom it was suspected--were retrospectively evaluated. The dislocated tendon can be identified medial to the bicipital groove, best seen on the axial and oblique coronal and sagittal images. Associated abnormalities of the biceps tendon include thickening (n = 3), high signal intensity (n = 3), and surrounding fluid (n = 4). The factors thought to contribute to dislocation can also be well seen on MR images. These include abnormal shape of the bicipital groove (n = 2), disruption of the coracohumeral ligament (n = 6), disruption (n = 4) and thinning (n = 1) of the subscapularis tendon, and supraspinatus tendon tear (n = 4). Since MR imaging is becoming the modality of choice for the evaluation of shoulder derangements, familiarity with the appearance of biceps tendon dislocation on MR images is important.

MRI appearance of femoral head osteonecrosis following core decompression and bone grafting

We used magnetic resonance imaging (MRI) to evaluate retrospectively 32 hips with avascular necrosis of the femoral head before and after core decompression and bone grafting. At a median follow-up time of 15 months, 4 of 9 large lesions had undergone femoral head collapse; 2 small lesions had decreased in size; and 14 small, 6 moderate, and 5 large lesions were unchanged. One hip with biopsy-proven avascular necrosis had diffuse marrow edema which resolved after surgery. The signal pattern within the lesions was analyzed in 17 hips. Fifteen lesions were unchanged, while one fat-like lesion became fibrous-like and one edema-like lesion resolved. Analysis of the femoral neck marrow signal in one patient revealed that premature fatty marrow conversion had reverted to hemopoietic marrow 2 years after surgery. Most lesions that appeared stable on MRI were clinically stable or improved. MRI can demonstrated changes in size and signal characteristics as well as femoral head collapse after core decompression and bone grafting. Changes in the surrounding marrow signal, including resolution of marrow edema and reconversion from fatty to hemopoietic marrow, can also be detected.

Formulation of vaccine adjuvant muramyldipeptides (MDP). 1. Characterization of amorphous and crystalline forms of a muramyldipeptide analogue

A relatively nonhygroscopic crystalline form of the glycopeptide, N-acetylmuramyl-L-alpha-aminobutyryl-D-isoglutamine (I), containing approximately one molecule of water was prepared from amorphous material. The crystalline material, consisting of a mixture of the alpha and beta anomers, exhibited better physical and chemical stability than the lyophilized amorphous material. The alpha/beta-anomer ratios of I in both the crystalline and the amorphous state were approximately equal but different from that in solution.

Glucose regulates its own transport in Ehrlich ascites tumour cells

The capacity of Ehrlich ascites tumour cells to take up 2-deoxy-D-glucose and to bind cytochalasin B varies adaptatively with the level of glucose in the plasma or culture medium. The effect of glucose is exerted directly on the cells and does not necessarily require the participation of hormones such as insulin, glucagon or corticosterone, although glucagon and the glucocorticoids, but not insulin, can also increase the number of glucose carrier molecules administered in vitro. Cycloheximide suppresses the acute inductive effect of glucose, suggesting that protein synthesis might be required for the increased transport activity.

Suppression of Ehrlich ascites tumor growth in mice by starvation and streptozotocin-induced diabetes

Starvation-induced hypoglycaemia and streptozotocin-induced diabetes suppressed the growth of Ehrlich ascites tumor in mice. The suppression of tumor growth by diabetes was alleviated by administration of insulin. The number of glucose carriers on tumour cells was found to be reduced in diabetes and partial resumption of glucose carriers was observed in tumour cells of diabetes after insulin administration. Insulin had no direct effect on tumour growth in vivo and did not affect the number of glucose carriers on tumour cells in vitro. The physiological significance of these observations is discussed.

Glucose transport in developing Ehrlich ascites tumor cells: parallel changes in the rate of glucose uptake and cytochalasin B binding activity during tumor development and methotrexate treatment

The ability of Ehrlich ascites tumor cells to take up glucose increased progressively during the course of tumor development. Simultaneously as the rate of uptake rose, the density of a class of glucose-reversible binding sites for cytochalasin B on the cell surface also increased. In its stereospecificity requirement toward competing sugars and in its sensitivity to phloretin and diethylstilbestrol, this class of binding sites resembled the putative glucose carriers identified in various other cell systems and may represent the glucose transporter in Ehrlich ascites cells. Work with methotrexate (MTX) substantiated this view. Methotrexate arrested tumor growth, inhibited glucose uptake, and reduced the number of cytochalasin B binding sites. In both MTX-treated and untreated cells, the magnitude of changes in number of cytochalasin B binding sites closely paralleled and sufficiently accounted for the magnitude of changes in glucose uptake. Qualitative changes in the turnover and affinity for substrate of the putative glucose carrier need not be invoked.

Effects of viral pneumonia on lung macrophage lysosomal enzymes

During viral pneumonitis in mice, lung fluid protein and free lysosomal enzyme activity are increased while macrophage lysosomal enzymes are decreased.

Importance of C4a- and N5-covalent adducts in the flavin oxidation of carbanions

The reaction of nitroalkanes, furoin, and phenacyl alcohol with 7- and 8-cyano-3,10-dimethylisoalloxazine (7-CNFlox, 8-CNFlox), 5-ethyl-3-methyllumiflavinium ion (Flox+Et), and 2.6-dichloroindophenol (DCI) have been studied. Nitromethane anion forms an adduct on reaction with Flox +Et. The condensation reaction has been shown (nuclear magnetic resonance) to occur through addition of the methylene carbon of the nitromethane anion to the 4a position of Flox+Et. This adduct undergoes spontaneous dissociation to its components in acid. It does not undergo conversion in base to reduced flavin (1,5-F1EtH), NO2-, and CH2O. For this reason one may conclude that nitroalkane anion oxidation by flavin does not involve the intermediacy of a 4a-covalent intermediate. Oxidation of nitroalkane anion through formation of an N5-flavin adduct is discussed in terms of the peculiar requirements of the substrate when compared with carbanions derived from normal flavoenzyme substrates. It is concluded that the mechanism of nitroalkane oxidation by flavin must bear no relationship to the flavin oxidation of normal substrates. Furoin and phenacyl alcohol (compounds containing the-CH(OH)--CO-functionality) are oxidized by 8-CNFlOX, 7-CNFlOX, DCI and by the N5-blocked flavin Flox+Et. These reactions are found to be zero order in oxidant at the concentrations of oxidants (approximately 1.0 X 10(-5) M) and reductant (approximately 10(-3) to 10(-4) M) employed. This finding, and that of an 1H/2H kinetic isotope effect of 3.5, as well as certain equalities of the determined rate constants establish the rate-determining step in all these oxidations to be carbanion formation. That the N5-blocked flavin (Flox+Et) serves just as well as an oxidant as do substituted and unsubstituted isoalloxazines provides evidence that the flavin oxidation of carbanions of general structure (-C-(OH)--CO-) does not require the formation of an intermediate N5-flavin adduct. This conclusion when taken with the fact that the N5-flavin adduct formed on reaction of dihydroflavin with -C(=O)--CO-is not an intermediate in the reduction of -C(=O)--CO-to -CH(OH)--CO- by dihydroflavin shows that N5 adducts do not arise as intermediates in these oxidations. Remaining mechanisms (4a addition and radical pair formation) are discussed. 4a addition of carbanions to Flox+Et is shown to be subject to considerable steric strain by the instability of the nitroethane adduct and the inability to observe the formation of the 2-nitropropane adduct.