Integrative Multi-Omics Analysis of Oncogenic EZH2 Mutants: From Epigenetic Reprogramming to Molecular Signatures

Somatic heterozygous mutations in the active site of the enhancer of zeste homolog 2 (EZH2) are prevalent in diffuse large B-cell lymphoma (DLBCL) and acute myeloid leukemia (AML). The methyltransferase activity of EZH2 towards lysine 27 on histone H3 (H3K27) and non-histone proteins is dysregulated by the presence of gain-of-function (GOF) and loss-of-function (LOF) mutations altering chromatin compaction, protein complex recruitment, and transcriptional regulation. In this study, a comprehensive multi-omics approach was carried out to characterize the effects of differential H3K27me3 deposition driven by EZH2 mutations. Three stable isogenic mutants (EZH2^Y641F, EZH2^A677G, and EZH2H^689A/F667I) were examined using EpiProfile, H3K27me3 CUT&Tag, ATAC-Seq, transcriptomics, label-free proteomics, and untargeted metabolomics. A discrete set of genes and downstream targets were identified for the EZH2 GOF and LOF mutants that impacted pathways involved in cellular proliferation, differentiation, and migration. Disruption of protein networks and metabolic signatures able to sustain aberrant cell behavior was observed in response to EZH2 mutations. This systems biology-based analysis sheds light on EZH2-mediated cell transformative processes, from the epigenetic to the phenotypic level. These studies provide novel insights into aberrant EZH2 function along with targets that can be explored for improved diagnostics/treatment in hematologic malignancies with mutated EZH2.

Adipose Tissue Myeloid-Lineage Neuroimmune Cells Express Genes Important for Neural Plasticity and Regulate Adipose Innervation

Peripheral nerves allow a bidirectional communication between brain and adipose tissues, and many studies have clearly demonstrated that a loss of the adipose nerve supply results in tissue dysfunction and metabolic dysregulation. Neuroimmune cells closely associate with nerves in many tissues, including subcutaneous white adipose tissue (scWAT). However, in scWAT, their functions beyond degrading norepinephrine in an obese state remain largely unexplored. We previously reported that a myeloid-lineage knockout (KO) of brain-derived neurotrophic factor (BDNF) resulted in decreased innervation of scWAT, accompanied by an inability to brown scWAT after cold stimulation, and increased adiposity after a high-fat diet. These data underscored that adipose tissue neuroimmune cells support the peripheral nerve supply to adipose and impact the tissue's metabolic functions. We also reported that a subset of myeloid-lineage monocyte/macrophages (Ly6c+CCR2+Cx3cr1+) is recruited to scWAT in response to cold, a process known to increase neurite density in adipose and promote metabolically healthy processes. These cold-induced neuroimmune cells (CINCs) also expressed BDNF. Here we performed RNAseq on CINCs from cold-exposed and room temperature-housed mice, which revealed a striking and coordinated differential expression of numerous genes involved in neuronal function, including neurotrophin signaling and axonal guidance, further supporting that CINCs fulfill a nerve-supporting role in adipose. The increased expression of leukocyte transendothelial migration genes in cold-stimulated CINCs also confirms prior evidence that they are recruited to scWAT and are not tissue resident. We now provide whole-depot imaging of scWAT from LysM-BDNF KO mice, revealing a striking reduction of innervation across the depot fitting with their reduced energy expenditure phenotype. By contrast, Cx3cr1-BDNF KO mice (a macrophage subset of LysM+ cells) exhibited increased thermogenesis and energy expenditure, with compensatory increased food intake and no change in adiposity or body weight. While these KO mice also exhibit a significantly reduced innervation of scWAT, especially around the subiliac lymph node, they displayed an increase in small fiber sympathetic neurite branching, which may underlie their increased thermogenesis. We propose a homeostatic role of scWAT myeloid-lineage neuroimmune cells together in nerve maintenance and neuro-adipose regulation of energy expenditure.

Multiple Imputation Approaches Applied to the Missing Value Problem in Bottom-Up Proteomics

Analysis of differential abundance in proteomics data sets requires careful application of missing value imputation. Missing abundance values widely vary when performing comparisons across different sample treatments. For example, one would expect a consistent rate of “missing at random” (MAR) across batches of samples and varying rates of “missing not at random” (MNAR) depending on the inherent difference in sample treatments within the study. The missing value imputation strategy must thus be selected that best accounts for both MAR and MNAR simultaneously. Several important issues must be considered when deciding the appropriate missing value imputation strategy: (1) when it is appropriate to impute data; (2) how to choose a method that reflects the combinatorial manner of MAR and MNAR that occurs in an experiment. This paper provides an evaluation of missing value imputation strategies used in proteomics and presents a case for the use of hybrid left-censored missing value imputation approaches that can handle the MNAR problem common to proteomics data.

Fibroblast-Specific Proteotranscriptomes Reveal Distinct Fibrotic Signatures of Human Sinoatrial Node in Nonfailing and Failing Hearts

BACKGROUND

Up to 50% of the adult human sinoatrial node (SAN) is composed of dense connective tissue. Cardiac diseases including heart failure (HF) may increase fibrosis within the SAN pacemaker complex, leading to impaired automaticity and conduction of electric activity to the atria. Unlike the role of cardiac fibroblasts in pathologic fibrotic remodeling and tissue repair, nothing is known about fibroblasts that maintain the inherently fibrotic SAN environment.

METHODS

Intact SAN pacemaker complex was dissected from cardioplegically arrested explanted nonfailing hearts (non-HF; n=22; 48.7±3.1 years of age) and human failing hearts (n=16; 54.9±2.6 years of age). Connective tissue content was quantified from Masson trichrome-stained head-center and center-tail SAN sections. Expression of extracellular matrix proteins, including collagens 1 and 3A1, CILP1 (cartilage intermediate layer protein 1), and POSTN (periostin), and fibroblast and myofibroblast numbers were quantified by in situ and in vitro immunolabeling. Fibroblasts from the central intramural SAN pacemaker compartment (≈10×5×2 mm³) and right atria were isolated, cultured, passaged once, and treated ± transforming growth factor β1 and subjected to comprehensive high-throughput next-generation sequencing of whole transcriptome, microRNA, and proteomic analyses.

RESULTS

Intranodal fibrotic content was significantly higher in SAN pacemaker complex from HF versus non-HF hearts (57.7±2.6% versus 44.0±1.2%; P<0.0001). Proliferating phosphorylated histone 3⁺/vimentin⁺/CD31^- (cluster of differentiation 31) fibroblasts were higher in HF SAN. Vimentin⁺/α-smooth muscle actin⁺/CD31^- myofibroblasts along with increased interstitial POSTN expression were found only in HF SAN. RNA sequencing and proteomic analyses identified unique differences in mRNA, long noncoding RNA, microRNA, and proteomic profiles between non-HF and HF SAN and right atria fibroblasts and transforming growth factor β1-induced myofibroblasts. Specifically, proteins and signaling pathways associated with extracellular matrix flexibility, stiffness, focal adhesion, and metabolism were altered in HF SAN fibroblasts compared with non-HF SAN.

CONCLUSIONS

This study revealed increased SAN-specific fibrosis with presence of myofibroblasts, CILP1, and POSTN-positive interstitial fibrosis only in HF versus non-HF human hearts. Comprehensive proteotranscriptomic profiles of SAN fibroblasts identified upregulation of genes and proteins promoting stiffer SAN extracellular matrix in HF hearts. Fibroblast-specific profiles generated by our proteotranscriptomic analyses of the human SAN provide a comprehensive framework for future studies to investigate the role of SAN-specific fibrosis in cardiac rhythm regulation and arrhythmias.

Imaging temozolomide-induced changes in the myeloid glioma microenvironment

Rationale: The heterogeneous nature of gliomas makes the development and application of novel treatments challenging. In particular, infiltrating myeloid cells play a role in tumor progression and therapy resistance. Hence, a detailed understanding of the dynamic interplay of tumor cells and immune cells in vivo is necessary. To investigate the complex interaction between tumor progression and therapy-induced changes in the myeloid immune component of the tumor microenvironment, we used a combination of [¹⁸F]FET (amino acid metabolism) and [¹⁸F]DPA-714 (TSPO, GAMMs, tumor cells, astrocytes, endothelial cells) PET/MRI together with immune-phenotyping. The aim of the study was to monitor temozolomide (TMZ) treatment response and therapy-induced changes in the inflammatory tumor microenvironment (TME).

Methods: Eighteen NMRI^nu/nu mice orthotopically implanted with Gli36dEGFR cells underwent MRI and PET/CT scans before and after treatment with TMZ or DMSO (vehicle). Tumor-to-background (striatum) uptake ratios were calculated and areas of unique tracer uptake (FET vs. DPA) were determined using an atlas-based volumetric approach.

Results: TMZ therapy significantly modified the spatial distribution and uptake of both tracers. [¹⁸F]FET uptake was significantly reduced after therapy (-53 ± 84%) accompanied by a significant decrease of tumor volume (-17 ± 6%). In contrast, a significant increase (61 ± 33%) of [¹⁸F]DPA-714 uptake was detected by TSPO imaging in specific areas of the tumor. Immunohistochemistry (IHC) validated the reduction in tumor volumes and further revealed the presence of reactive TSPO-expressing glioma-associated microglia/macrophages (GAMMs) in the TME.

Conclusion: We confirm the efficiency of [¹⁸F]FET-PET for monitoring TMZ-treatment response and demonstrate that in vivo TSPO-PET performed with [¹⁸F]DPA-714 can be used to identify specific reactive areas of myeloid cell infiltration in the TME.

Tagging enhances histochemical and biochemical detection of Ran Binding Protein 9 in vivo and reveals its interaction with Nucleolin

The lack of tools to reliably detect RanBP9 in vivo has significantly hampered progress in understanding the biological functions of this scaffold protein. We report here the generation of a novel mouse strain, RanBP9-TT, in which the endogenous protein is fused with a double (V5-HA) epitope tag at the C-terminus. We show that the double tag does not interfere with the essential functions of RanBP9. In contrast to RanBP9 constitutive knock-out animals, RanBP9-TT mice are viable, fertile and do not show any obvious phenotype. The V5-HA tag allows unequivocal detection of RanBP9 both by IHC and WB. Importantly, immunoprecipitation and mass spectrometry analyses reveal that the tagged protein pulls down known interactors of wild type RanBP9. Thanks to the increased detection power, we are also unveiling a previously unknown interaction with Nucleolin, a protein proposed as an ideal target for cancer treatment. In summary, we report the generation of a new mouse line in which RanBP9 expression and interactions can be reliably studied by the use of commercially available αtag antibodies. The use of this line will help to overcome some of the existing limitations in the study of RanBP9 and potentially unveil unknown functions of this protein in vivo such as those linked to Nucleolin.

The long non-coding RNA HOXB-AS3 regulates ribosomal RNA transcription in NPM1-mutated acute myeloid leukemia

Long non-coding RNAs (lncRNAs) are important regulatory molecules that are implicated in cellular physiology and pathology. In this work, we dissect the functional role of the HOXB-AS3 lncRNA in patients with NPM1-mutated (NPM1mut) acute myeloid leukemia (AML). We show that HOXB-AS3 regulates the proliferative capacity of NPM1mut AML blasts in vitro and in vivo. HOXB-AS3 is shown to interact with the ErbB3-binding protein 1 (EBP1) and guide EBP1 to the ribosomal DNA locus. Via this mechanism, HOXB-AS3 regulates ribosomal RNA transcription and de novo protein synthesis. We propose that in the context of NPM1 mutations, HOXB-AS3 overexpression acts as a compensatory mechanism, which allows adequate protein production in leukemic blasts.

A Microfluidic Chip Enables Isolation of Exosomes and Establishment of Their Protein Profiles and Associated Signaling Pathways in Ovarian Cancer

Because of limits on specificity and purity to allow for in-depth protein profiling, a standardized method for exosome isolation has yet to be established. In this study, we describe a novel, in-house microfluidic-based device to isolate exosomes from culture media and patient samples. This technology overcomes contamination issues because sample separation is based on the expression of highly specific surface markers CD63 and EpCAM. Mass spectrometry revealed over 25 exosome proteins that are differentially expressed in high-grade serous ovarian cancer (HGSOC) cell lines compared with normal cells-ovarian surface epithelia cells and fallopian tube secretory epithelial cells (FTSEC). Top exosome proteins were identified on the basis of their fold change and statistical significance between groups. Ingenuity pathway analysis identified STAT3 and HGF as top regulator proteins. We further validated exosome proteins of interest (pSTAT3, HGF, and IL6) in HGSOC samples of origin-based cell lines (OVCAR-8, FTSEC) and in early-stage HGSOC patient serum exosome samples using LC/MS-MS and proximity extension assay. Our microfluidic device will allow us to make new discoveries for exosome-based biomarkers for the early detection of HGSOC and will contribute to the development of new targeted therapies based on signaling pathways that are unique to HGSOC, both of which could improve the outcome for women with HGSOC. SIGNIFICANCE: A unique platform utilizing a microfluidic device enables the discovery of new exosome-based biomarkers in ovarian cancer.

Abstract 3335: Characterizing the MAXH28R secretome in endometrial cancer

We have previously shown that the recurrent endometrial cancer MAX p.His28Arg mutation (MAXH28R) is associated with a proangiogenesis phenotype in both in vitro and xenograft models. The purpose of this study is to characterize the MAXH28R secretome to identify the proangiogenic and other paracrine factors contributing to MAXH28R associated tumorigenesis. Bottom-up high-resolution liquid chromatography tandem mass spectrometry (LC-MS/MS) of secreted proteins coupled with microarray analysis of global gene expression was performed in AN3CA endometrial cancer cell lines that stably express the long isoform of MAX-wild type (MAXWT) or MAXH28R. Orthogonal validation of differentially expressed proteins was performed by Western blot (WB) and enzyme-linked immunosorbent assay (ELISA) using MAXWT- or MAXH28R-expressing AN3CA cell lines. Bioinformatic analysis of the proteins secreted into conditioned media (secretome) identified 114 proteins differentially expressed by MAXH28R compared to MAXWT-expressing AN3CA cells (P &lt; 0.05). Differential expression of proteins was highly correlated with mRNA expression (Pearson r = 0.75, P &lt; 0.001), indicating that a subset of the differentially expressed proteins are potential direct transcriptional targets of MAX. Secretome analysis revealed that Laminin-β1 expression in MAXH28R was reduced more than 100-fold compared to MAXWT (P &lt; 0.001), while ALCAM (CD166) expression was increased 3.5-fold (P &lt; 0.001). Decreased expression of TGFβ1 (5.9-fold decrease, P = 0.023) and TGFβ2 (3-fold decrease, P = 0.009) was seen for MAXH28R cells compared to MAXWT. Differential expression of Laminin-β1 and ALCAM was confirmed by WB analysis and TGFβ1 and TGFβ2 by ELISA. Our analyses revealed extensive changes in the MAXH28R secretome, as exemplified above. Reduced Laminin-β1 highlights alteration in the extracellular matrix with implications for cell adhesion and integrin signaling. Increased ALCAM expression indicates changes to cell-cell adhesion. Elevated levels of ALCAM in conditioned media are consistent with increased ALCAM shedding, which is a marker of more aggressive tumors in a variety of malignancies. Reduced TGFβ ligand levels suggest potential alterations in paracrine and autocrine TGFβ signaling. However, the impact on canonical and noncanonical TGFβ signaling in MAX mutant endometrial cancers remains unknown. ChIP-qPCR experiments are ongoing to assess MAXH28R binding at the promoters of differentially expressed genes. Biologic validation of MAXH28R effects on differential expression of secreted proteins is being performed in the Ishikawa and RL95-2 endometrial cancer cell lines that stably express MAXH28R and MAXWT. The effects of reduced Laminin-β1 on integrin signaling and anchorage independent growth will be reported, as will effects of altered TGFβ expression on canonical and noncanonical TGFβ signaling.

Citation Format: Craig M. Rush, Miranda L. Gardner, Caroline E. Sapp, Michael A. Freitas, Paul J. Goodfellow. Characterizing the MAXH28R secretome in endometrial cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3335.

Chemical and biological tools for the preparation of modified histone proteins

Eukaryotic chromatin is a complex and dynamic system in which the DNA double helix is organized and protected by interactions with histone proteins. This system is regulated through a large network of dynamic post-translational modifications (PTMs) which ensure proper gene transcription, DNA repair, and other processes involving DNA. Homogenous protein samples with precisely characterized modification sites are necessary to understand better the functions of modified histone proteins. Here, we discuss sets of chemical and biological tools developed for the preparation of modified histones, with a focus on the appropriate choice of tool for a given target. We start with genetic approaches for the creation of modified histones, including the incorporation of genetic mimics of histone modifications, chemical installation of modification analogs, and the use of the expanded genetic code to incorporate modified amino acids. We also cover the chemical ligation techniques which have been invaluable in the generation of complex modified histones indistinguishable from their natural counterparts. We end with a prospectus on future directions.

Responding maintained under fixed-interval and fixed-time schedules of electric shock presentation

Following initial histories under a schedule of electric shock postponement, lever pressing in squirrel monkeys was maintained under fixed-interval and fixed-time schedules of electric shock presentation. No difference in either rate or pattern of responding was obtained when these schedules were presented as components of a multiple schedule. When they were presented singly for long periods of time, the fixed-interval schedule consistently maintained a higher response rate than the fixed-time schedule. The pattern of responding under both schedules was similar, typically consisting of a pause at the beginning of each interval followed by either a steady or a positively accelerating rate of responding. The results suggest that the response-shock dependency is of critical importance in the maintenance of high rates of responding under schedules of electric shock presentation, and support the general view that such responding may be conceptualized as operant behavior under control of many of the same variables that control responding under comparable schedules of food or water reinforcement.

Responding under sequence schedules of electric shock presentation

Lever pressing by squirrel monkeys was examined under second-order schedules of electric shock presentation in which different discriminative stimuli were associated with consecutive components (sequence schedules). Components were always two-minute fixed-interval schedules, and three different overall schedules were studied. Under an overall eight-minute fixed-interval schedule, the first component completion after at least eight minutes had elapsed produced electric shock. The number of components actually completed ranged from one to four; thus, different discriminative stimuli were occasionally associated with electric shock presentation. Under an overall "yoked" variable-ratio schedule, electric shock was presented after completion of a variable number of components; the required number and the distribution of components were matched to those obtained under the overall eight-minute fixed-interval schedule. Under an overall fixed-ratio schedule, electric shock was presented after completion of four components (chained schedule). Under all three sequence schedules, responding in early components was characterized by a pause followed by a single response after the end of the two-minute interval; responding in later components was characterized by a shorter pause followed by positively accelerated responding. Manipulation of overall schedules of shock presentation in these complex behavioral situations produced changes in responding comparable to those ordinarily obtained after similar manipulation of dependencies under both single and second-order schedules of food presentation. These experiments extend the range of conditions and levels of complexity under which responding can be maintained by presentation of electric shock.

Responding maintained under intermittent schedules of electric-shock presentation: "Safety" or schedule effects?

Four experiments were conducted in which lever pressing by squirrel monkeys was maintained under multiple, mixed, or chained schedules of electric-shock presentation. In the first two experiments, a multiple schedule was employed in which a fixed-interval schedule of shock presentation alternated with a signaled two-minute component. Initially, no events were scheduled during the two-minute component (a safety period). In the first experiment, the safety period was "degraded" by introducing and systematically increasing the frequency of periodic shocks presented during that component. In the second experiment, the proportion of overall safe time to unsafe time was decreased by decreasing the value of the fixed-interval schedule while holding constant shock frequency during the two-minute component. In the third experiment, the overall arrangement was changed from a multiple to a mixed schedule in an attempt to determine whether fixed-interval responding would be maintained when a single exteroceptive stimulus was associated with both components. In the fourth experiment, the overall arrangement was changed from a multiple to a chained schedule in an effort to determine whether fixed-interval responding would be maintained when its consequence was presentation of a signaled "unsafe" period. Fixed-interval responding was well maintained under all experimental conditions; the varied relationships obtained lend more support to conceptualizations of shock-maintained behavior as exemplifying schedule-controlled behavior than to suggestions that such behavior may be readily accounted for by "safety theory."

Elemental diets in the repair of small intestinal damage

We have investigated the possible benefits of elemental diets, especially a diet supplemented with L-glutamine, on maintenance of intestinal absorptive function in rat small intestine damaged by 5-fluorouracil. Although a standard rat diet sustained better body growth in control rats, each of the elemental diets and the diet containing intact casein in place of hydrolyzed casein was beneficial in promoting less body weight loss during the 3 d after 5-fluorouracil injection. The same significant benefit was seen in absorptive activity measured in small intestine in vitro 3 d after the cytotoxic injury. Glutamine supplementation, however, did not confer any significant advantages, although it did cause significant elevation of muscle glutamine pools. This elevation was substantially less than the corresponding increase in muscle glycine content after dietary supplementation with glycine.

Some considerations regarding the use of amino acid racemization in human dentine as an indicator of age at death

An HPLC method is described for simultaneously obtaining the enantiomeric ratio of three amino acids (aspartic acid, serine, and glutamic acid) from dental collagen, with a view to using this information for estimating age at death. Results are reported from a sample of twenty three known age modern teeth, six known age 19th C. AD teeth, and two unknown age Romano-British teeth. It was found (as expected) that all three D/L ratios changed significantly with chronological age. Standard calibration techniques were used to estimate ages for the six 19th C. AD specimens from regression equations estimated from the modern specimens, and also to predict (for the first time) the error associated with such estimates. Errors using aspartic acid were found to be similar to those obtained by other methods of age estimation from dental evidence, serine, and glutamic acid providing much poorer age estimates. Additionally, a systematic difference in the age-enantiomeric ratio relationship was observed between modern and older dental samples. It is concluded that there is some fundamental difference in the observed enantiomeric ratios between modern teeth and older samples, possibly as a result of the chemical alteration of the dental proteins.

The induction of the alpha-1-adrenoceptor signal transduction system on human melanocytes

Human melanocytes established in MCDB-153 culture medium do not express alpha 1-, beta 1-, beta-2 adrenoceptors without extracellular stimulation. The addition of 50 x 10-9 M norepinephrine to the medium causes a time-dependent induction of alpha-1-adrenoceptors with 4.278 receptors/melanocyte after 24 h. Under the same experimental conditions, the dendricity of melanocytes as well as melanogenesis was unaffected over 60 h. Since keratinocytes hold the full capacity for catecholamine biosynthesis but melanocytes lack this system, the secretion of catecholamines from keratinocytes appears to be of critical importance to the alpha-1-adrenoceptor in melanocytes, underlining the symbiosis of both cells in the epidermal unit.

A specific tetrahydrobiopterin binding domain on tyrosinase controls melanogenesis

(6R)5,6,7,8-tetrahydrobiopterin (6-BH4) directly regulates tyrosinase activity by specifically binding to a putative 13 amino acid domain. This domain has sequence homology to 6-BH4 binding sites already identified on phenylalanine hydroxylase and 4a-carbinolamine dehydratase. Furthermore, this binding sequence appears to have been conserved during the evolution of tyrosinase as it has also been identified in the frog, mouse and human enzymes. 6-BH4 controls tyrosinase activity by an uncompetitive mechanism requiring the presence of L-tyrosine for effective down-regulation. When L-dopa is substrate, 6-BH4 does not inhibit the enzyme implicating separate binding sites for L-dopa and L-tyrosine on tyrosinase. Dihydropterin and 6-biopterin, the oxidation products of 6-BH4, do not inhibit tyrosinase significantly, indicating that melanin biosynthesis is controlled by a 6-BH4/6-biopterin redox-switch mechanism which can be initiated by photo-oxidation of 6-BH4.

Intestinal absorption of the intact peptide carnosine in man, and comparison with intestinal permeability to lactulose

1. Healthy humans ingested the dipeptide carnosine (L-beta-alanyl-L-histidine). Their plasma levels and urinary outputs of carnosine and beta-alanine were monitored over the following 5 h. 2. Large amounts of intact carnosine (up to 14% of the ingested dose) were recovered in the urine over the 5 h after ingestion. However, carnosine was undetectable in the plasma unless precautions were taken to inhibit blood carnosinase activity ex vivo during and after blood collection. 3. The amount of carnosine recovered in urine varied substantially between subjects. It correlated negatively with carnosinase enzymic activity in the plasma. Highest carnosinase activities were observed in those subjects who regularly underwent physical training. 4. Urinary recovery of the disaccharide lactulose also varied considerably between subjects, but was substantially lower than that of carnosine. There was no significant correlation between the recoveries of carnosine and lactulose. 5. When lactulose was ingested with a hypertonic solution, the urinary recovery of lactulose was generally increased. When carnosine was ingested with a hypertonic solution, the urinary recovery of carnosine was reduced: hence the paracellular route probably is not dominant for absorption of intact carnosine. 6. Intact carnosine must have crossed the intestine to an extent much greater than hitherto recognized. Rapid post-absorptive hydrolysis is a severe obstacle to quantification of intact peptide absorption.

Simple, optimized liquid-chromatographic method for measuring total hydroxyproline in urine evaluated

We have optimized a method for measuring total hydroxyproline (HYP) in urine by HPLC after release from urinary peptides by solid-phase hydrolysis on Dowex 50W x 8 ion-exchange resin. The HYP was derivatized with 4-chlor-7-nitrobenzo-2-oxa-1,3-diazole, and excess reagent was removed with the use of a 100-mg C18 Bond-Elut cartridge. The HYP derivative was separated isocratically at 30 degrees C on a 250 x 4.6 mm reversed-phase column containing 5-microns particles of Spherisorb S5 ODS-2, with S-carboxymethylcysteine as internal standard. Total assay time was 14 min. The standard curve for the method was linear from the detection limit for HYP, 3.6 mumol/L, to 10 mmol/L. The between-batch CV was less than 5.1% and the mean analytical recovery of HYP was 95% +/- 1.4%. Comparison with a commercially available colorimetric method showed good correlation: y = 1.158x + 19.76 mumol/L (Syx = 74, n = 120), but HPLC results were 15% higher, probably from incomplete hydrolysis with the colorimetric method. This method offers a considerable improvement in assay time, specificity, sensitivity, precision, and cost compared with the colorimetric method.

Sodium loading treatment for amphotericin B-induced nephrotoxicity

The increased frequency and duration of antifungal treatment with amphotericin B in immunocompromised patients has stimulated a great deal of research into the mechanisms of its nephrotoxic effects and treatment modalities designed to attenuate these effects. A review of amphotericin B-induced nephrotoxicity, the underlying pathophysiologic mechanisms, and the role of salt loading as a means of minimizing renal impairment are described. Both animal and human studies regarding the efficacy of sodium loading are presented as well as a case report describing the use of salt supplementation over a prolonged course of therapy.

Treatment of encainide proarrhythmia with hypertonic saline

We report a case of successful treatment of encainide-induced ventricular tachycardia with 3% hypertonic saline. To our knowledge, no other report exists in the literature of this treatment for proarrhythmic ventricular tachycardia from a type 1C agent. Metabolic consequences of the treatment included severe hypernatremia, hyperosmolarity, hypocalcemia, and hypophosphatemia, which were reversible over 24 hours. In spite of the risks, treatment of incessant ventricular tachycardia induced by type 1C agents with hypertonic saline may be life saving.

Is there circadian variation in villus height in rat small intestine?

Measurements of villus height, crypt depth and mucosal thickness were made for each of duodenum, jejunum and ileum of rat small intestine from animals on both unrestricted and restricted feeding regimens. Contrary to a previous report, there was no evidence for consistent or synchronized diurnal variation in villus height at any region of small intestine on any of the feeding regimes. Likewise, no diurnal variation was seen in crypt depth or mucosal thickness. Variation in villus cell numbers, therefore, cannot account for previously reported diurnal variation in absorptive and digestive activities in rat small intestine. The present results support the hypothesis that the stimulus for exfoliation is probably cell recruitment and migration up the villi.

Gastrointestinal absorption of intact proteins

There is now no reasonable doubt that small quantities of intact proteins do cross the gastrointestinal tract in animals and adult humans, and that this is a physiologically normal process required for antigen sampling by subepithelial immune tissue in the gut. It is too small to be nutritionally significant in terms of gross acquisition of amino-nitrogen, but since it has important implications relating to dietary composition it must receive consideration from nutritionists. The process of intact protein absorption occurs without eliciting harmful consequences for most individuals, but it appears likely that a small number of people absorbing these "normal" amounts may react idiosyncratically; also, some individuals may absorb excessive amounts, and they may suffer clinically significant consequences. Likewise, individuals with diminished absorption of intact protein may be at risk. Normal absorption probably occurs predominantly by transcellular endocytosis with some possible contribution by a route between cells; increased net entry of protein to the circulation may reflect (a) increased paracellular (intercellular) passage, (b) increased transcellular passage, and/or (c) decreased lysosomal proteolysis. Tests to distinguish among these possibilities are strongly desirable. Intact protein absorption may be involved in the pathogenesis of inflammatory bowel disease, "food allergies," and other diseases, including even major psychiatric disorders, but the current evidence is mainly indirect and suggestive. Great caution and careful objective studies are needed to establish whether such relationships with disease do exist and to unravel the underlying basic physiological mechanisms. Now that interest has developed in the assessment of intestinal permeability to small- and medium-sized molecules, it is hoped that equally simple methods for studying macromolecular permeability will be developed and applied. Therapeutic methods for enhancing intact polypeptide absorption would be valuable for vaccine and peptide drug administration by the oral route. Therapeutic reduction of the process may be relevant in food-sensitive patients.

Alternate models for shared carriers or a single maturing carrier in hexose uptake into rabbit jejunum in vitro

The uptake (tissue accumulation) of three hexoses into rabbit jejunum was measured in a flux chamber in conditions of effective stirring. Glucose uptake was inhibited by galactose or 3-O-methylglucose: 1-40 mM galactose caused a progressive decline in glucose uptake; 1-5 mM 3-O-methylglucose inhibited glucose uptake but higher concentrations of 3-O-methylglucose had no further effect. When 1-40 mM 3-O-methylglucose was added to glucose plus galactose there was a further decrease in the uptake of glucose; adding 1-40 mM galactose to glucose plus 3-O-methylglucose also produced a decrease in glucose uptake. Both glucose and 3-O-methylglucose inhibited uptake of galactose but the pattern of inhibition varied between the two sugars. The uptake of 3-O-methylglucose was also inhibited by glucose and by galactose, but the uptake of 3-O-methylglucose in the presence of either galactose or glucose was no further reduced by adding the third hexose. Graphical analysis and analysis by non-linear regression both showed that neither the single Michaelis-Menten function, nor the single Michaelis-Menten-plus-competitive-inhibition function was appropriate for any of these data. The results are consistent with the hypothesis that either there are multiple (at least three) intestinal carriers for hexoses; alternatively that there is a single carrier whose transport properties for the three hexoses change differentially during cell maturation and migration up the villus.

A comparison of the structural integrity of several commonly used preparations of rat small intestine in vitro

The structural integrities of various preparations of rat small intestine for the study of absorption in vitro have been compared after incubation or perfusion. Perfused intestines removed from anaesthetized rats, and thus never deprived of a supply of oxygen, maintain their structural integrity even after perfusion for 1 h provided that a Krebs-Henseleit bicarbonate perfusate is used. However, intestines removed from freshly killed rats show severe villus disruption and oedema after perfusion for only 20 min. Extensive damage to both crypts and villi is observed in everted sacs of small intestine incubated for 20 min, regardless of the buffer system used. Intestinal rings show damage at the tips of the villi after incubation for 2 min, but otherwise remain morphologically intact; this damage is progressive with time. It is concluded that the exact mode of preparation of intestinal tissue is critical for preservation of structural and functional integrity and that this is especially important in quantitative studies on transport processes. Further, it is recommended that routine monitoring of the integrity of intestinal preparations in vitro is desirable and that histological assessment is an appropriate technique.

A comparison of internal and external standardization in amino acid analysis

To assess quantitatively the merits of internal standardization, an amino acid mixture of known composition has been analyzed by conventional automated amino acid analysis before and after being subjected to total acid hydrolysis. Both the precision (reproducibility) and the accuracy (lack of bias) were generally, but not invariably, greatly enhanced by the use of internal standardization with norleucine as opposed to external standardization. Incorporation of internal standards into samples is strongly recommended.

Cysteine: a potential source of error in amino acid analysis of mercaptoethane sulfonic or hydrochloric acid hydrolysates of proteins and peptides

Hydrolysis of proteins and peptides with mercaptoethane sulfonic acid is liable to produce overestimation of the proline content owing to the production of ninhydrin-positive material (probably cysteine) which coelutes with proline on many ion-exchange analytical systems. A similar error occurs with HCl hydrolysis (especially in the presence of mercaptoethanol or thioglycollic acid) if care is not taken to oxidize cysteine during reconstitution of the hydrolysate before amino acid analysis.

Can elemental diets reduce the intestinal toxicity of 5-fluorouracil?

In order to test the hypothesis that elemental diets protect the intestinal mucosa against 5-fluorouracil toxicity, we have estimated water absorption, cytoplasmic peptide hydrolase activities, and mucosal DNA contents in isolated intestines from rats fed on one of three elemental diets or a standard diet and injected with 5-fluorouracil. Water absorption rates were significantly increased when rats, not injected with 5-fluorouracil, were fed on Flexical or Vivonex-HN. However, water absorption was severely impaired 3 days after administration of 5-fluorouracil and none of the elemental diets alleviated this impairment of absorption. Cytoplasmic peptide hydrolase activities and mucosal DNA contents were also severely decreased after 5-fluorouracil injection, the changes observed being independent of the diet. Also, none of the elemental diets reduced the body weight losses observed after 5-fluorouracil administration. Although the effects of the sodium salt of 5-fluorouracil on body weight and food intakes were much less severe than those of the Tris salt the two salts had identical effects on intestinal absorption even when an elemental diet was used. Although there was a smaller incidence of diarrhea after 5-fluorouracil administration when the rats had been fed on one of the elemental diets, diet B, the results do not support the suggestion that elemental diets might reduce the intestinal toxicity of 5-fluorouracil.

Trans-mucosal passage of intact peptides in the guinea-pig small intestine in vivo: a re-appraisal

1. Re-examination of data for the chemical analysis of peptide-bound amino acids in the mesenteric venous blood of anaesthetized guinea-pigs suggests that there are small, but significant, amounts of small peptides in the blood of fasted animals. 2. Furthermore, there is a significant increase in the peptide content of the mesenteric venous blood during intraduodenal infusion of a partial digest of casein. 3. The data are consistent with the view that some 10% of the amino nitrogen entering the mesenteric blood during absorption of a casein digest in vivo may be in the form of small peptides, although it is not possible to define confidence limits for this estimate.

Absorption of intact peptides: studies on transport of protein digests and dipeptides across rat small intestine in vitro

Passage of intact peptides across isolated rat small intestine has been studied during luminal perfusion with partial digests of proteins or with dipeptides. Significant passage of intact peptide does occur, the amount depending upon the luminal concentration. It probably reflects the 'digestibility' of the protein or protein digest. Previous studies are discussed and, although intact peptide transport is probably not of major nutritional importance, it is suggested that the pathophysiological significance of this process and of peptidaemia merits further attention.

Diurnal variation in the intestinal toxicity of 5-fluorouracil in the rat

1. Water absorption rates by small intestine in vitro and the incidence of diarrhoea in vivo were estimated after 5-fluorouracil was injected into rats at various times of day and night. 2. Impairment of water absorption and the incidence of diarrhoea were minimal in rats on a normal dietary regimen when the 5-fluorouracil was injected at around 02.00 hours. 3. The DNA content of the mucosa of the small intestine from uninjected animals also showed a diurnal variation, with a maximum at around 03.00 hours. 4. Manipulation of the time of injections (possibly in relation to feeding time) provides a potential means for increasing the therapeutic value of 5-fluorouracil.

Differential toxicity and pharmacokinetics of sodium and Tris salts of 5-fluorouracil in the rat

1. Rats injected intraperitoneally (i.p.) with the Tris salt of 5-fluorouracil (1.44 mmol/kg) showed severe toxic symptoms and a 15% mortality. No mortality and no obvious toxicity, apart from intestinal toxicity, resulted after injection of the sodium salt at equimolar dosage. 2. The plasma pharmacokinetics of the two salts of 5-fluorouracil (1.44 mmol/kg) were different after i.p. injection: higher plasma levels were achieved and were sustained for longer after the Tris salt than after the sodium salt. 3. No differences in plasma pharmacokinetics were observed after intra-arterial (i.a.) injection of the two salts of 5-fluorouracil (6.576 mmol/kg). 4. Thus there are fundamental (and potentially important) differences between the biological properties of the sodium and Tris salts of 5-fluorouracil. These cannot be explained at present.

Studies on the absorption of the pancreatic function test peptide, N-benzoyl-L-tyrosyl-p-aminobenzoic acid, and related compounds by isolated rat small intestine

The peptide, N-benzoyl-L-tyrosyl-p-aminobenzoic acid, which is used in an oral test of pancreatic function, has been perfused through isolated rat small intestine in order to determine whether it can be absorbed across the intestine in intact form, and whether it is hydrolysed appreciably by intestinal enzymes. For comparison, transport of N-benzoyl-DL-tyrosine, L-tyrosine, L-tyrosyl-L-leucine and p-aminobenzoic acid has also been studied. Very small amounts of bound tyrosine (probably mainly intact peptide plus some benzoyl-tyrosine) and of free p-aminobenzoic acid crossed the intestine during perfusion with N-benzoyl-L-tyrosyl-p-aminobenzoic acid. Adsorbed pancreatic enzymes were possibly responsible for the very small amount of hydrolysis of the peptide. However, no detectable free tyrosine crossed the intestine during perfusion with N-benzoyl-L-tyrosyl-p-aminobenzoic acid or with N-benzoyl-DL-tyrosine. In contrast, substantial quantities of free tyrosine crossed the intestine during perfusion with L-tyrosine or with L-tyrosyl-L-leucine. Net transport of tyrosine from L-tyrosyl-L-leucine was less than that from equimolar free L-tyrosine; no detectable intact L-tyrosyl-L-leucine crossed the intestine. During perfusion with free p-aminobenzoic acid the concentration in the serosal secretion apparently exceeded that in the lumen by a factor of 1.7; this suggests active transport of p-aminobenzoic acid.

Release of dipeptide hydrolase activities from rat small intestine perfused in vitro and in vivo

1. Hydrolase activities against three dipeptides were measured in mucosal cytoplasm in unperfused intestines and in mucosal cytoplasm, luminal effluents and serosal secretions after perfusion in vitro and in vivo for 1 h. Intestines in vitro were preparted both from anaesthetized rats and from freshly killed rats. 2. Only 0.6--1.9% of the initial cytoplasmic activity was recovered in the luminal effluent when intestines in vitro were prepared from anaesthetized rats. Recoveries in luminal effluents were similar (1.3--3.3%) during perfusion in vivo. 3. Losses of dipeptidases into the luminal effluent were four to eight times greater when intestines in vitro were prepared from freshly killed animals. 4. Similar losses of dipeptidases into the secretion on to the serosal surface were observed: they too were much greater when intestines were prepared from freshly killed animals. 5. Small losses of mucosal DNA during perfusion were also observed; however, losses of cytoplasmic peptidases were consistently slightly greater. 6. Enzyme loss therefore probably occurs both by sloughing of whole cells and by a more specific process which is greatly influenced by experimental procedure. Caution is necessary in the interpretation of peptide transport experiments in vitro, although the possibility that intraluminal hydrolysis is of physiological significance must not be excluded.

Superficial or membrane digestion of peptides in dinitrophenol-inhibited rat small intestine

1. Hydrolysis of peptides has been measured in isolated rat small intestine perfused with a pancreatic digest of lactalbumin in the presence of 2,4-dinitrophenol. 2. Although transport of water and amino acids was severely inhibited by 2,4-dinitrophenol, peptide hydrolysis to free amino acids was apparently unimpaired. 3. Only a small fraction of the hydrolysis observed could be accounted for by leakage of enzymes into the lumen. 4. The results show that the brush-border enzymes proximal to the transport mechanism(s) can be an important site of hydrolysis of peptides to amino acids under conditions where the transport of unhydrolysed peptides is inhibited. The results are consistent with the concept of membrane (contact) digestion, although the significance of intracellular hydrolysis and of transmural transport of intact peptides is also discussed.

Effects of 'elemental' diets on absorptive and enzymic activities and on 5-fluorouracil toxicity in rat small intestine

1. Water absorption and cytoplasmic dipeptidase activities were determined in isolated rat small intestine after animals had fed on various 'elemental' diets or a standard rat diet and after a single injection of 5-fluorouracil. 2. Vivonex diets were associated with a decrease in dry weight of the small intestine and an increase in glucose and water absorption in vitro. 3. The nature of the dietary nitrogen profoundly affects the activities of intestinal peptidases. 4. Water absorption was severly depressed 3 days after 5-fluorouracil administration: the extent of depression was independent of the diet. Thus, any ameliorative effects of 'elemental' diets on 5-fluorouracil toxicity are unlikely to be mediated by direct protection of intestinal absorption.

Amino acid and peptide absorption from partial digests of proteins in isolated rat small intestine

1. Absorption of each of sixteen amino acids, free and peptide-bound, has been measured in isolated rat small intestine perfused with five partial digests of proteins. 2. At low concentrations net absorption of each amino acid was proportional to its luminal concentration and independent of the nature of the amino acid. 3. A series of first-order multiple regressions was found to describe well the characteristics of absorption. 4. Rate constants for disappearance of free and peptide-bound amino acids from the lumen were closely similar. However, substantial back-flux occurred of amino acids derived from peptide hydrolysis. Hence 60-70% of the amino-N entering the serosal tissue fluid probably had left the lumen as free amino acids. 5. Intact peptides crossed the mucosa during absorption from a soy bean hydrolysate and in substantial quantities during absorption from one casein digest but not from another. With other hydrolysates there was no evidence for passage of peptides to the serosa. 6. In several cases there was a serious discrepancy between the amount of amino-N absorbed from the lumen and the amount accounted for as peptide or free amino acid in the serosal secretion. 7. The characteristics of absorption were similar (apart from the exceptions in 5 above) for all the digests studied except for soy bean hydrolysate.

Changes in absorptive and peptide hydrolase activities in rat small intestine after administration of 5-fluorouracil

1. Glucose absorption, water absorption and dipeptide hydrolase activities have been determined in isolated rat small intestine at 1, 3, 5 and 21 days after a single intraperitoneal injection of 5-fluorouracil. 2. Absorption rates and enzyme activities were elevated 1 day after treatment, but were reduced to 40% of control values at 3 and 5 days. Changes were seen regardless of whether absorption was expressed per unit length or per unit dry weight of intestine. 3. There were highly significant positive correlations between glucose or water absorption rates and peptidase activities, especially in proximal jejunum. The most significant correlation was observed between water absorption rate and jejunal L-Leu-Gly hydrolase activity. 4. Malabsorption may account for some of the gastrointestinal side effects associated with treatment with 5-fluorouracil. Enzyme measurements may be useful as an index of intestinal function.