Gene expression signature predicts rate of type 1 diabetes progression

BACKGROUND

Type 1 diabetes is a complex heterogenous autoimmune disease without therapeutic interventions available to prevent or reverse the disease. This study aimed to identify transcriptional changes associated with the disease progression in patients with recent-onset type 1 diabetes.

METHODS

Whole-blood samples were collected as part of the INNODIA study at baseline and 12 months after diagnosis of type 1 diabetes. We used linear mixed-effects modelling on RNA-seq data to identify genes associated with age, sex, or disease progression. Cell-type proportions were estimated from the RNA-seq data using computational deconvolution. Associations to clinical variables were estimated using Pearson's or point-biserial correlation for continuous and dichotomous variables, respectively, using only complete pairs of observations.

FINDINGS

We found that genes and pathways related to innate immunity were downregulated during the first year after diagnosis. Significant associations of the gene expression changes were found with ZnT8A autoantibody positivity. Rate of change in the expression of 16 genes between baseline and 12 months was found to predict the decline in C-peptide at 24 months. Interestingly and consistent with earlier reports, increased B cell levels and decreased neutrophil levels were associated with the rapid progression.

INTERPRETATION

There is considerable individual variation in the rate of progression from appearance of type 1 diabetes-specific autoantibodies to clinical disease. Patient stratification and prediction of disease progression can help in developing more personalised therapeutic strategies for different disease endotypes.

FUNDING

A full list of funding bodies can be found under Acknowledgments.

Gambling disorder and chronic diseases in Finland: a nationwide register study

Background

Previous register-based studies on comorbidity have mainly focused on gambling disorder (GD) and psychiatric disorders. However, knowledge on somatic health of persons with GD is also needed. This nationwide register-based study aims to examine the gender-specific prevalence rates of chronic diseases and conditions among the Finnish adults with GD.

Methods

This study utilizes aggregated data of persons aged 18 and over with GD diagnosis (corresponding to pathological gambling, ICD-10; F63.0) in 2011-2020. The data were retrieved from the Finnish nationwide health registers: Register of Primary Health Care visits and Care Register for Health Care, including specialised outpatient and inpatient health care, and inpatient social care. All diagnostic groups were included. Corresponding figures for the total population with same age range were presented as reference numbers.

Results

The preliminary results showed that 2,617 persons with the median age of 33.5-36.0 were diagnosed with GD (men n = 1,858; women n = 759). Despite the fact that the prevalence rates of the general population were not age-adjusted, many chronic diseases and conditions were more prevalent among persons with GD compared with the general population. The prevalence rates of psychiatric disorders (87.5% vs 29.2%) and nervous system diseases (23.9% vs 15.2%) were particularly high. Musculoskeletal diseases (61.6% vs 55.8%) and digestive diseases (30.2% vs 27.6%) were also slightly more prevalent. Memory disorders (1.1% vs 5.3%), cardiovascular diseases (25.3% vs 41.0%), and cancer (15.6% vs 24.4%) were less prevalent. Among persons with GD, all comorbid diseases were more prevalent among women than among men.

Conclusions

Psychiatric disorders and nervous system diseases are exceptionally prevalent in persons with GD. These findings highlight the need for health and social care professionals to recognize that persons with GD may additionally have other disorders that need attention.

Key messages

• Mental disorders are the most common comorbidity among persons with GD, however, many somatic chronic diseases are also common.

• Comorbidities are more common among women with GD than among men with GD.

Umbilical cord blood DNA methylation in children who later develop type 1 diabetes

AIMS/HYPOTHESIS

Distinct DNA methylation patterns have recently been observed to precede type 1 diabetes in whole blood collected from young children. Our aim was to determine whether perinatal DNA methylation is associated with later progression to type 1 diabetes.

METHODS

Reduced representation bisulphite sequencing (RRBS) analysis was performed on umbilical cord blood samples collected within the Finnish Type 1 Diabetes Prediction and Prevention (DIPP) Study. Children later diagnosed with type 1 diabetes and/or who tested positive for multiple islet autoantibodies (n = 43) were compared with control individuals (n = 79) who remained autoantibody-negative throughout the DIPP follow-up until 15 years of age. Potential confounding factors related to the pregnancy and the mother were included in the analysis.

RESULTS

No differences in the umbilical cord blood methylation patterns were observed between the cases and controls at a false discovery rate <0.05.

CONCLUSIONS/INTERPRETATION

Based on our results, differences between children who progress to type 1 diabetes and those who remain healthy throughout childhood are not yet present in the perinatal DNA methylome. However, we cannot exclude the possibility that such differences would be found in a larger dataset.

Early DNA methylation changes in children developing beta cell autoimmunity at a young age

AIMS/HYPOTHESIS

Type 1 diabetes is a chronic autoimmune disease of complex aetiology, including a potential role for epigenetic regulation. Previous epigenomic studies focused mainly on clinically diagnosed individuals. The aim of the study was to assess early DNA methylation changes associated with type 1 diabetes already before the diagnosis or even before the appearance of autoantibodies.

METHODS

Reduced representation bisulphite sequencing (RRBS) was applied to study DNA methylation in purified CD4⁺ T cell, CD8⁺ T cell and CD4^-CD8^- cell fractions of 226 peripheral blood mononuclear cell samples longitudinally collected from seven type 1 diabetes-specific autoantibody-positive individuals and control individuals matched for age, sex, HLA risk and place of birth. We also explored correlations between DNA methylation and gene expression using RNA sequencing data from the same samples. Technical validation of RRBS results was performed using pyrosequencing.

RESULTS

We identified 79, 56 and 45 differentially methylated regions in CD4⁺ T cells, CD8⁺ T cells and CD4^-CD8^- cell fractions, respectively, between type 1 diabetes-specific autoantibody-positive individuals and control participants. The analysis of pre-seroconversion samples identified DNA methylation signatures at the very early stage of disease, including differential methylation at the promoter of IRF5 in CD4⁺ T cells. Further, we validated RRBS results using pyrosequencing at the following CpG sites: chr19:18118304 in the promoter of ARRDC2; chr21:47307815 in the intron of PCBP3; and chr14:81128398 in the intergenic region near TRAF3 in CD4⁺ T cells.

CONCLUSIONS/INTERPRETATION

These preliminary results provide novel insights into cell type-specific differential epigenetic regulation of genes, which may contribute to type 1 diabetes pathogenesis at the very early stage of disease development. Should these findings be validated, they may serve as a potential signature useful for disease prediction and management.

Permutation-based significance analysis reduces the type 1 error rate in bisulfite sequencing data analysis of human umbilical cord blood samples

DNA methylation patterns are largely established in-utero and might mediate the impacts of in-utero conditions on later health outcomes. Associations between perinatal DNA methylation marks and pregnancy-related variables, such as maternal age and gestational weight gain, have been earlier studied with methylation microarrays, which typically cover less than 2% of human CpG sites. To detect such associations outside these regions, we chose the bisulphite sequencing approach. We collected and curated clinical data on 200 newborn infants; whose umbilical cord blood samples were analysed with the reduced representation bisulphite sequencing (RRBS) method. A generalized linear mixed-effects model was fit for each high coverage CpG site, followed by spatial and multiple testing adjustment of P values to identify differentially methylated cytosines (DMCs) and regions (DMRs) associated with clinical variables, such as maternal age, mode of delivery, and birth weight. Type 1 error rate was then evaluated with a permutation analysis. We discovered a strong inflation of spatially adjusted P values through the permutation analysis, which we then applied for empirical type 1 error control. The inflation of P values was caused by a common method for spatial adjustment and DMR detection, implemented in tools comb-p and RADMeth. Based on empirically estimated significance thresholds, very little differential methylation was associated with any of the studied clinical variables, other than sex. With this analysis workflow, the sex-associated differentially methylated regions were highly reproducible across studies, technologies, and statistical models.

Clinicopathological features and prognostic value of SOX11 in childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia is marked by aberrant transcriptional features that alter cell differentiation, self-renewal, and proliferative features. We sought to identify the transcription factors exhibiting altered and subtype-specific expression patterns in B-ALL and report here that SOX11, a developmental and neuronal transcription factor, is aberrantly expressed in the ETV6-RUNX1 and TCF3-PBX1 subtypes of acute B-cell leukemias. We show that a high expression of SOX11 leads to alterations of gene expression that are typically associated with cell adhesion, migration, and differentiation. A high expression is associated with DNA hypomethylation at the SOX11 locus and a favorable outcome. The results indicate that SOX11 expression marks a group of patients with good outcomes and thereby prompts further study of its use as a biomarker.

Enzymatic Processes to Unlock the Lignin Value

Main hurdles of lignin valorization are its diverse chemical composition, recalcitrance, and poor solubility due to high-molecular weight and branched structure. Controlled fragmentation of lignin could lead to its use in higher value products such as binders, coatings, fillers, etc. Oxidative enzymes (i.e., laccases and peroxidases) have long been proposed as a potentially promising tool in lignin depolymerization. However, their application was limited to ambient pH, where lignin is poorly soluble in water. A Finnish biotechnology company, MetGen Oy, that designs and supplies industrial enzymes, has developed and brought to market several lignin oxidizing enzymes, including an extremely alkaline lignin oxidase MetZyme^® LIGNO™, a genetically engineered laccase of bacterial origin. This enzyme can function at pH values as high as 10–11 and at elevated temperatures, addressing lignin at its soluble state. In this article, main characteristics of this enzyme as well as its action on bulk lignin coming from an industrial process are demonstrated. Lignin modification by MetZyme^® LIGNO™ was characterized by size exclusion chromatography, UV spectroscopy, and dynamic light scattering for monitoring particle size of solubilized lignin. Under highly alkaline conditions, laccase treatment not only decreased molecular weight of lignin but also increased its solubility in water and altered its dispersion properties. Importantly, organic solvent-free soluble lignin fragmentation allowed for robust industrially relevant membrane separation technologies to be applicable for product fractionation. These enzyme-based solutions open new opportunities for biorefinery lignin valorization thus paving the way for economically viable biorefinery business.

Genome-wide repression of eRNA and target gene loci by the ETV6-RUNX1 fusion in acute leukemia

Approximately 20%–25% of childhood acute lymphoblastic leukemias carry the ETV6-RUNX1 (E/R) fusion gene, a fusion of two central hematopoietic transcription factors, ETV6 (TEL) and RUNX1 (AML1). Despite its prevalence, the exact genomic targets of E/R have remained elusive. We evaluated gene loci and enhancers targeted by E/R genome-wide in precursor B acute leukemia cells using global run-on sequencing (GRO-seq). We show that expression of the E/R fusion leads to widespread repression of RUNX1 motif–containing enhancers at its target gene loci. Moreover, multiple super-enhancers from the CD19⁺/CD20⁺-lineage were repressed, implicating a role in impediment of lineage commitment. In effect, the expression of several genes involved in B cell signaling and adhesion was down-regulated, and the repression depended on the wild-type DNA-binding Runt domain of RUNX1. We also identified a number of E/R-regulated annotated and de novo noncoding genes. The results provide a comprehensive genome-wide mapping between E/R-regulated key regulatory elements and genes in precursor B cell leukemia that disrupt normal B lymphopoiesis.

SAP30L (Sin3A-associated protein 30-like) is involved in regulation of cardiac development and hematopoiesis in zebrafish embryos

The Sin3A-associated proteins SAP30 and SAP30L share 70% sequence identity and are part of the multiprotein Sin3A corepressor complex. They participate in gene repression events by linking members of the complex and stabilizing interactions among the protein members as well as between proteins and DNA. While most organisms have both SAP30 and SAP30L, the zebrafish is exceptional because it only has SAP30L. Here we demonstrate that SAP30L is expressed ubiquitously in embryonic and adult zebrafish tissues. Knockdown of SAP30L using morpholino-mediated technology resulted in a morphant phenotype manifesting as cardiac insufficiency and defective hemoglobinization of red blood cells. A microarray analysis of gene expression in SAP30L morphant embryos revealed changes in the expression of genes involved in regulation of transcription, TGF-beta signaling, Wnt-family transcription factors, and nuclear genes encoding mitochondrial proteins. The expression of the heart-specific nkx2.5 gene was markedly down-regulated in SAP30L morphants, and the cardiac phenotype could be partially rescued by nkx2.5 mRNA. In addition, changes were detected in the expression of genes known to be important in hemoglobin synthesis and erythropoiesis. Our results demonstrate that SAP30L regulates several transcriptional pathways in zebrafish embryos and is involved in the development of cardiac and hematopoietic systems.

Bifidobacterium and Lactobacillus DNA in the human placenta

AIMS

Bifidobacteria and lactobacilli are part of the human normal intestinal microbiota and may possibly be transferred to the placenta. It was hypothesized that intestinal bacteria or their components are present in the placenta and that the foetus may be exposed to them. We investigated the presence of bifidobacteria and lactobacilli and their DNA in the human placenta.

METHODS AND RESULTS

We studied 34 human placentae (25 vaginal and nine caesarean deliveries) for the presence Bifidobacterium spp. and Lactobacillus rhamnosus. Cultivation was used for the detection of viable cells and genus and species-specific PCR for the detection of DNA. No bifidobacteria or lactobacilli were found by cultivation. Bifidobacterial DNA was detected in 33 and L. rhamnosus DNA in 31 placenta samples.

CONCLUSIONS

DNA from intestinal bacteria was found in most placenta samples. The results suggest that horizontal transfer of bacterial DNA from mother to foetus may occur via placenta.

SIGNIFICANCE AND IMPACT OF THE STUDY

Bacterial DNA contains unmethylated CpG oligodeoxynucleotide motifs which induce immune effects. Specific CpG motifs activate Toll-like receptor 9 and subsequently trigger Th-1-type immune responses. Although the newborn infant is considered immunologically immature, exposure by bacterial DNA may programme the infant's immune development during foetal life earlier than previously considered.

Maternal breast-milk and intestinal bifidobacteria guide the compositional development of the Bifidobacterium microbiota in infants at risk of allergic disease

BACKGROUND

The sources and the impact of maternal bacteria on the initial inoculum of the intestinal microflora of newborn infants remain elusive.

OBJECTIVE

To assess the association between maternal breast-milk and fecal bifidobacteria and infants' fecal bifidobacteria.

METHODS

Sixty-one mother-infant pairs were included, special emphasis being placed on the maternal allergic status. Bifidobacteria were analysed by a direct PCR method in fecal samples from mothers at 30-35 weeks of gestation and from infants at 1 month of age and from breast-milk samples 1 month post-partum.

RESULTS

Fecal Bifidobacterium adolescentis and Bifidobacterium bifidum colonization frequencies and counts among mother-infant pairs correlated significantly (P=0.005 and 0.02 for frequencies, respectively, and P=0.002 and 0.01 for counts, respectively). Only infants of allergic, atopic mothers were colonized with B. adolescentis. Each of the breast-milk samples contained bifidobacteria [median 1.4 x 10(3) bacterial cells/mL; interquartile range (IQR) 48.7-3.8 x 10(3)]. Bifidobacterium longum was the most frequently detected species in breast-milk. Allergic mothers had significantly lower amounts of bifidobacteria in breast-milk compared with non-allergic mothers [median 1.3 x 10(3) bacterial cells/mL (IQR 22.4-3.0 x 10(3)) vs. 5.6 x 10(3) bacterial cells/mL (1.8 x 10(3)-1.8 x 10(4)), respectively, (P=0.004)], and their infants had concurrently lower counts of bifidobacteria in feces [3.9 x 10(8) bacterial cells/g (IQR 6.5 x 10(6)-1.5 x 10(9)) in infants of allergic mothers, vs. 2.5 x 10(9) bacterial cells/g (6.5 x 10(8)-3.2 x 10(10)) in infants of non-allergic mothers, P=0.013].

CONCLUSIONS

Breast-milk contains significant numbers of bifidobacteria and the maternal allergic status further deranges the counts of bifidobacteria in breast-milk. Maternal fecal and breast-milk bifidobacterial counts impacted on the infants' fecal Bifidobacterium levels. Breast-milk bacteria should thus be considered an important source of bacteria in the establishment of infantile intestinal microbiota.

Osteoblastic activity and neoangiogenesis in distracted bone of irradiated rabbit mandible with or without hyperbaric oxygen treatment

The effects of irradiation and hyperbaric oxygenation (HBO) on osteoblastic activity and angiogenesis in rabbit mandibular distraction (DO) were evaluated. Three groups were studied. The mandible of two groups received a 22.4Gy dose of irradiation. One of the irradiated groups was also given HBO, 18 times at 2.5ATA for 90min per day preoperatively. The third group was given neither radiotherapy nor HBO. Mandibular lengthening was performed unilaterally. Osteoblastic activity was assessed ex vivo by [18F]fluoride digital autoradiography. Neovascularization of distracted bone was evaluated histomorphometrically. Osteoblastic activity was higher in non-irradiated than irradiated animals. In non-irradiated rabbits, the activity was evenly distributed over the distraction area. In the irradiated groups, the activity was greater in the central third of the lengthened bone than the peripheral thirds. HBO changed the osteogenic pattern towards that of non-irradiated bone. In the non-irradiated group the number of blood vessels was 1.7-fold as compared to irradiated rabbits without HBO (P=0.0012), and the fewest number of vessels was found in irradiated rabbits without HBO. Blood vessels were more numerous in the central region than in peripheral regions in non-irradiated animals and irradiated animals with HBO, but not in irradiated rabbits without HBO therapy. It is concluded that radiotherapy disturbs distraction bone formation and neovascularization related to DO. HBO increases osteoblastic activity, but not to the level of non-irradiated bone. Angiogenic response is markedly increased by HBO.

Focal and global cortical hypometabolism in patients with newly diagnosed infantile spasms

OBJECTIVE

To evaluate the occurrence and prognostic importance of focal defects in cerebral cortical glucose metabolism in infants with newly diagnosed symptomatic and cryptogenic infantile spasms.

PATIENTS AND METHODS

Ten children with symptomatic and seven with cryptogenic infantile spasms underwent MRI, video-EEG, and PET using fluorodeoxyglucose as a tracer within 2 weeks of diagnosis. PET was repeated at 1 year of age in 12 patients.

RESULTS

Cortical hypometabolic foci were found in 13 children (77%) with newly diagnosed spasms (six cryptogenic and seven symptomatic). The hypometabolic foci disappeared in seven of nine reexamined at age 1. The occipital foci disappeared in all (n = 6). Focal findings on PET correlated well with focal findings on video-EEG. There was no difference in quantitative cortical or subcortical glucose metabolic rate at the onset of infantile spasms between children with cryptogenic and symptomatic etiology of spasms. The glucose metabolic rate at the onset of spasms or focal lesions in glucose metabolism did not have prognostic value for seizure outcome.

CONCLUSIONS

Infantile spasms are often associated with transient cortical, especially occipital, hypometabolic foci that are not necessarily associated with structural lesions and do not indicate a poor prognosis.

2-[(18)F]fluoro-2-deoxy-D-glucose combined with microdialysis can be used for the comparison of tissue glucose metabolism in obese and lean rats

AIMS

Direct assessment of tissue metabolism in vivo is important to understand the pathogenesis of obesity. Labelled glucose analogues are potential candidates to be used for this purpose. The aim of this study was to compare the kinetics and metabolism of 2-[(18)F]fluoro-2-deoxy-D-glucose (FDG) in obese (fa/fa) and lean (Fa/?) Zucker rat tissues with microdialysis, and the measurement of uptake and phosphorylation with or without insulin bolus injection.

METHODS

Obese (n = 10) and lean (n = 11) anaesthetized rats underwent a microdialysis study after FDG-injection either with or without insulin stimulation. Microdialysis probes were inserted in the jugular vein, quadriceps muscle and liver. After 110 min, tissue [(18)F]-uptake and intracellular phosphorylation of FDG were studied in blood, liver, skeletal muscle, subcutaneous adipose tissue, intra-abdominal adipose tissue and hypothalamus.

RESULTS

When measured with microdialysis, insulin-enhanced FDG disappeared from the blood pool and interstitial space of skeletal muscle and liver more effectively in lean rather than in obese animals. Insulin-stimulated skeletal muscle and adipose tissue[(18)F]-uptake was impaired in obese Zucker rats compared with lean animals. Hypothalamic FDG uptake was six to sevenfold higher than in other measured tissues, but was attenuated in obese rats. In liver and in mesenteric fat, insulin-enhanced FDG phosphorylation in lean rats compared with obese animals.

CONCLUSIONS

Positron-emitting glucose analogue FDG, combined with microdialysis and tissue analysis, is a feasible method in studying glucose metabolism at the cellular level in animal studies.

Imaging of blood flow and hypoxia in head and neck cancer: initial evaluation with [(15)O]H(2)O and [(18)F]fluoroerythronitroimidazole PET

Hypoxia is a characteristic feature of malignant tumors that should be evaluated before the start of therapy. (18)F-labeled fluoroerythronitroimidazole (FETNIM) is a possible candidate for imaging tumor hypoxia with PET. Quantitative analysis of [(18)F]FETNIM uptake in vivo is necessary before proceeding to assays predicting hypoxia.

METHODS

Eight patients with untreated head and neck squamous cell carcinoma were enrolled in the study. All patients underwent dynamic PET imaging with [(18)F]FETNIM, coupled with measurements of blood flow with [(15)O]H(2)O and blood volume with [(15)O]CO. The metabolically active tumor volume was determined from [(18)F]FDG PET performed on a separate day. [(18)F]FETNIM uptake in the tumor was correlated with that in neck muscles and arterial plasma and compared with the findings of other PET studies.

RESULTS

Blood flow in tumor was 5- to 30-fold greater than in muscle, in contrast to blood volume, which did not significantly differ in the 2 tissues. With [(18)F]FETNIM PET, muscle activity remained invariably less than plasma activity, whereas activity in whole tumors was always greater than that in muscle. In 4 instances, the maximum tumor uptake of [(18)F]FETNIM was 1.2-2.0 times higher than plasma activity in the late dynamic phase. A kinetic model developed for calculation of distribution volume of reversibly trapping tracers was successfully applied in the [(18)F]FETNIM studies. Tumor distribution volume correlated strongly with the standardized uptake value of [(18)F]FETNIM between 60 and 120 min and with blood flow but not with the standardized uptake value of [(18)F]FDG. The relationship between [(18)F]FETNIM uptake and the blood flow of the tumor was less obvious on a pixel-by-pixel level.

CONCLUSION

Uptake of [(18)F]FETNIM in head and neck cancer is highly variable and seems to be governed by blood flow at least in the early phase of tissue accumulation. Maximum tumor-to-muscle tracer uptake ratios > 180 min were in the range of 1-4, comparing favorably with those reported previously for [(18)F]fluoromisonidazole. Assessment of the distribution volume of [(18)F]FETNIM after the initial blood-flow phase is feasible for subsequent evaluation of hypoxia-specific retention.

Pharmacokinetics of [18F]FETNIM: a potential marker for PET

18F-labeled fluoroerythronitroimidazole (FETNIM) has been suggested as a marker of tumor hypoxia for use with PET. Our goal was to evaluate the pharmacokinetic properties of [18F]FETNIM in rats and analyze metabolites in human, dog, and rat plasma and urine. Metabolites in liver and tumor homogenates from tumor-bearing rats, as well as the biodistribution of the tracer, were also studied.

METHODS

Radio-thin-layer chromatography and digital autoradiography were used to distinguish metabolites from the parent drug in urine and plasma from 8 patients, 3 dogs, and 18 rats, as well as in liver and tumor homogenates from Sprague-Dawley rats bearing 7,12-dimethylbenzanthracene-induced rat mammary carcinoma. Biodistribution of [18F]FETNIM was also studied in rats at 15, 30, 60, 120, and 240 min after tracer injection.

RESULTS

Most of the radioactivity in plasma and urine was the unchanged tracer, whereas rat liver homogenates contained almost only metabolites of [18F]FETNIM. None of the species studied showed binding of tracer to plasma proteins. A large variation-3%-70%-in the radioactivity represented by unchanged [18F]FETNIM was found in rat tumor. A negative correlation was found between the percentage of radioactivity represented by unchanged [18F]FETNIM in tumor tissue and tumor uptake (percentage injected dose per gram of tissue) at later times. The highest radioactivity was seen in urine and kidney; the lowest uptake was in fat, cerebellum, and bone matrix. In contrast to matrix, bone marrow had high uptake of 18F. The tumor-to-blood ratio reached a maximum of 1.80 +/- 0.64 at 2 h.

CONCLUSION

We conclude that [18F]FETNIM shows low peripheral metabolism, little defluorination, and possible metabolic trapping in hypoxic tumor tissue. These suggest a potential use for this tracer in PET studies on hypoxia of cancer patients.

Biodistribution of [11C] methylaminoisobutyric acid, a tracer for PET studies on system A amino acid transport in vivo

[N-methyl-11C]alpha-Methylaminoisobutyric acid (11C-MeAIB) is a potentially useful tracer for positron emission tomography (PET) studies on hormonally regulated system A amino acid transport. 11C-MeAIB is a metabolically stable amino acid analogue specific for system A amino acid transport. We evaluated the biodistribution of 11C-MeAIB in rats and humans to estimate the usefulness of the tracer for in vivo human PET studies, for example, on regulation of system A amino acid transport and on tumour imaging. Healthy Sprague-Dawley rats (n=14) were killed 5, 20, 40 or 60 min after the injection of 11C-MeAIB, and the tissue samples were weighed and counted for 11C radioactivity. Ten lymphoma patients with relatively limited tumour burden underwent whole-body (WB) PET imaging with 11C-MeAIB. In addition, three other patients had dynamic PET scanning of the head and neck area, and the tracer uptake was quantitated by calculating the kinetic influx constants (Ki values) for the tracer. In animal studies, the highest activity was detected in the kidney, pancreas, adrenal gland and intestines. In humans, the highest activity was found in the salivary glands, and after that in the kidney and pancreas, similar to the results in animal studies. Rapid uptake was also detected in the skeletal muscle. In the graphical analysis, linear plots were obtained, and the mean fractional tracer uptake values (Ki) of the parotid glands (n=3) and cervical muscles (n=3) were 0.039+/-0.008 min(-1) and 0.013+/-0.006 min(-1), respectively. The Ki value of the tumour (n=1) was 0.064 min(-1). Higher uptake of 11C-MeAIB into the tumour tissue was encountered. These results encourage further 11C-MeAIB PET studies in humans on the physiology and pathology of system A amino acid transport and on tumour detection.

Nodal staging of lymphoma with whole-body PET: comparison of

Accurate staging is elementary for optimal management of malignant lymphoma. Advanced cases may be curable with multidrug chemotherapy combined with radiotherapy, whereas limited disease can sometimes be cured by local radiotherapy only. Recently, FDG imaging with whole-body PET (WB PET) has been introduced as an accurate method for staging lymphoma. We evaluated the usefulness of L-[methyl-11C]methionine (MET) in comparison with FDG as a tracer for nodal staging of lymphoma with WB PET.

METHODS

Nineteen patients with untreated, histologically proven malignant lymphoma underwent WB PET imaging with MET and FDG within 1 wk before treatment. Fourteen patients had non-Hodgkin's lymphoma (NHL), and 5 had Hodgkin's disease (HD). Two of these 19 patients were excluded from the final analysis because of hyperglycemia. WB PET images using FDG and MET were visually compared by 3 independent interpreters, and the PET findings were correlated with the data on the basis of conventional staging studies.

RESULTS

Fifty-five of 178 lymph node regions were classified as diseased both by FDG PET and by CT, and 54 of 178 were classified as diseased both by MET PET and by CT. In addition, 11 lymph node regions that CT showed to be normal avidly accumulated FDG. Ten of these lymph node regions also had clear uptake of MET. Another 4 and 5 lymph node regions were enlarged at CT but were judged to be normal by FDG and MET PET, respectively. In nodal staging, both FDG PET and MET PET would have upstaged the disease in 3 patients. MET PET would also have downstaged the disease in 1 patient.

CONCLUSION

FDG and MET seem to be comparable in the detection of lymphoma by WB PET. However, visual interpretation of the images tends to be hampered more by physiologic accumulations of MET than by normal accumulations of FDG, and MET may be preferable to FDG in hyperglycemic patients undergoing staging studies with PET.

Lumped constant for [(18)F]fluorodeoxyglucose in skeletal muscles of obese and nonobese humans

Quantitative 2-[(18)F]fluoro-2-deoxy-D-glucose ([(18)F]FDG) positron emission tomography (PET) has been widely used to calculate glucose utilization in skeletal muscle. FDG-PET results depend partly on the lumped constant (LC), which accounts for the differences in the transport and phosphorylation between [(18)F]FDG and glucose. In this study, we estimated the LC for [(18)F]FDG directly in normal and in insulin-resistant obese subjects by combining FDG PET with the microdialysis technique. Eight obese [age 29.4 +/- 1.0 yr, body mass index (BMI) 33.6 +/- 1.0 kg/m(2)] and eight nonobese (age 25.0 +/- 1.0 yr, BMI 23.1 +/- 1.0 kg/m(2)) males were studied during euglycemic hyperinsulinemia (1 mU. kg(-1).min(-1) for 150 min). Muscle blood flow was measured using (15)O-labeled water and PET. Muscle [(18)F]FDG uptake (rGU(FDG)) was calculated with Patlak graphic analysis. Interstitial glucose concentration of the quadriceps femoris muscle was measured simultaneously with [(18)F]FDG scanning using microdialysis. Muscle glucose uptake (by microdialysis, rGU(MD)) was calculated by multiplying glucose extraction by regional muscle blood flow. A significant correlation was found between rGU(MD) and rGU(FDG) (r = 0.78, P < 0.01). The LC was determined as the ratio of the rGU(FDG) to the rGU(MD). The LC averaged 1.16 +/- 0.16 and was similar in the obese and nonobese subjects (1.15 +/- 0.11 vs. 1.16 +/- 0.07, respectively, not significant). In conclusion, the microdialysis technique can be reliably combined with FDG PET to measure glucose uptake in skeletal muscle. Direct measurements with these two independent techniques suggest an LC value of 1.2 for [(18)F]FDG in human skeletal muscle during insulin stimulation, and the LC appears not to be sensitive to insulin resistance.

Blood metabolism of [methyl-11C]choline; implications for in vivo imaging with positron emission tomography

[methyl-11C]choline (11C-choline) is a radioligand potentially useful for oncological positron emission tomography (PET). As a first step towards the development of a kinetic model for quantification of 11C-choline uptake, blood metabolism of 11C-choline during PET imaging was studied in humans. High-performance liquid chromatography (HPLC) and thin-layer chromatography (TLC) were used for the analysis of 11C-choline and its radioactive metabolites. Prior to human PET imaging we studied ex vivo the biodistribution and metabolism of intravenously administered 11C-choline in rats. Our results revealed that the radioactivity accumulated particularly in kidney, lung, adrenal gland and liver. Chromatographic analysis showed that the level of unmetabolized 11C-choline in rat plasma decreased from 42% +/- 20% (mean +/- SD) at 5 min to 21% +/- 10% at 15 min after injection. In accordance with these findings, in humans the unmetabolized 11C-choline represents 62% +/- 19% of the total radioactivity in arterial plasma at 5 min after injection and 27% +/- 12% at 15 min. In human venous plasma the corresponding values were 85% +/- 12% and 48% +/- 12% at 5 and 10 min, respectively. The major metabolite observed in both human and rat plasma was identified as 11C-betaine. In human arterial plasma this maximally represented 82% +/- 9% of the total radioactivity at 25 min after radiotracer injection. By 20 min after injection, the 11C-choline and 11C-betaine in human arterial plasma reached a plateau, and their fractional activities remained nearly constant thereafter. Although most of the circulating 11C-choline in blood is transported to tissues, it does not disappear totally from blood within the first 40 min after tracer injection.

Myocardial blood flow, oxygen consumption, and fatty acid uptake in endurance athletes during insulin stimulation

We have previously demonstrated reduced myocardial glucose uptake rates in hearts of endurance athletes, which could be due to increased use of alternative fuels or reduced energy demands. In the present study myocardial blood flow, oxygen consumption, and free fatty acid uptake were measured with [(15)O]H(2)O, [(15)O]O(2), [(18)F]FTHA, and positron emission tomography (PET) in 9 endurance athletes and 11 sedentary men during euglycemic hyperinsulinemia. Compared with sedentary men, athletes had 33% lower myocardial blood flow, 27% lower oxygen consumption, and 20% lower estimated myocardial work per gram of tissue. Myocardial fatty acid uptake rates were not significantly different in endurance athletes (0.83 +/- 0.29) and sedentary men (1.0 +/- 0.31 micromol. 100 g(-1). min(-1), P = 0.232). In conclusion, myocardial blood flow and oxygen consumption per unit mass of myocardium are reduced at rest in endurance athletes. This can be explained by reduced energy requirements per gram of tissue due to anatomic and physiological changes of the athlete's heart.