Mechanism of 2'-fucosyllactose degradation by human-associated Akkermansia

Among the first microorganisms to colonize the human gut of breastfed infants are bacteria capable of fermenting human milk oligosaccharides (HMOs). One of the most abundant HMOs, 2'-fucosyllactose (2'-FL), may specifically drive bacterial colonization of the intestine. Recently, differential growth has been observed across multiple species of Akkermansia on various HMOs including 2'-FL. In culture, we found growth of two species, A. muciniphila MucT and A. biwaensis CSUN-19,on HMOs corresponded to a decrease in the levels of 2'-FL and an increase in lactose, indicating that the first step in 2'-FL catabolism is the cleavage of fucose. Using phylogenetic analysis and transcriptional profiling, we found that the number and expression of fucosidase genes from two glycoside hydrolase (GH) families, GH29 and GH95, vary between these two species. During the mid-log phase of growth, the expression of several GH29 genes was increased by 2'-FL in both species, whereas the GH95 genes were induced only in A. muciniphila. We further show that one putative fucosidase and a β-galactosidase from A. biwaensis are involved in the breakdown of 2'-FL. Our findings indicate that the plasticity of GHs of human-associated Akkermansia sp. enables access to additional growth substrates present in HMOs, including 2'-FL. Our work highlights the potential for Akkermansia to influence the development of the gut microbiota early in life and expands the known metabolic capabilities of this important human symbiont.IMPORTANCEAkkermansia are mucin-degrading specialists widely distributed in the human population. Akkermansia biwaensis has recently been observed to have enhanced growth relative to other human-associated Akkermansia on multiple human milk oligosaccharides (HMOs). However, the mechanisms for enhanced growth are not understood. Here, we characterized the phylogenetic diversity and function of select genes involved in the growth of A. biwaensis on 2'-fucosyllactose (2'-FL), a dominant HMO. Specifically, we demonstrate that two genes in a genomic locus, a putative β-galactosidase and α-fucosidase, are likely responsible for the enhanced growth on 2'-FL. The functional characterization of A. biwaensis growth on 2'-FL delineates the significance of a single genomic locus that may facilitate enhanced colonization and functional activity of select Akkermansia early in life.

Byproducts of inflammatory radical metabolism provide transient nutrient niches for microbes in the inflamed gut

Louis Pasteur's experiments on tartaric acid laid the foundation for our understanding of molecular chirality, but major questions remain. By comparing the optical activity of naturally-occurring tartaric acid with chemically-synthesized paratartaric acid, Pasteur realized that naturally-occurring tartaric acid contained only L-tartaric acid while paratartaric acid consisted of a racemic mixture of D- and L-tartaric acid. Curiously, D-tartaric acid has no known natural source, yet several gut bacteria specifically degrade D-tartaric acid. Here, we investigated the oxidation of monosaccharides by inflammatory reactive oxygen and nitrogen species. We found that this reaction yields an array of alpha hydroxy carboxylic acids, including tartaric acid isomers. Utilization of inflammation- derived D- and L-tartaric acid enhanced colonization by Salmonella Typhimurium and E. coli in murine models of gut inflammation. Our findings suggest that byproducts of inflammatory radical metabolism, such as tartrate and other alpha hydroxy carboxylic acids, create transient nutrient niches for enteric pathogens and other potentially harmful bacteria. Furthermore, this work illustrates that inflammatory radicals generate a zoo of molecules, some of which may erroneously presumed to be xenobiotics.

Mechanism of 2'-Fucosyllactose degradation by Human-Associated Akkermansia

Among the first microorganisms to colonize the human gut of breastfed infants are bacteria capable of fermenting human milk oligosaccharides (HMOs). One of the most abundant HMOs, 2'-fucosyllactose (2'-FL), may specifically drive bacterial colonization of the intestine. Recently, differential growth has been observed across multiple species of Akkermansia on various HMOs including 2'FL. In culture, we found growth of two species, A. muciniphila Muc T and A. biwaensis CSUN-19, in HMOS corresponded to a decrease in the levels of 2'-FL and an increase in lactose, indicating that the first step in 2'-FL catabolism is the cleavage of fucose. Using phylogenetic analysis and transcriptional profiling, we found that the number and expression of fucosidase genes from two glycoside hydrolase (GH) families, GH29 and GH95, varies between these two species. During mid-log phase growth, the expression of several GH29 genes was increased by 2'-FL in both species, whereas the GH95 genes were induced only in A. muciniphila . We further show that one putative fucosidase and a β-galactosidase from A. biwaensis are involved in the breakdown of 2'-FL. Our findings indicate that that plasticity of GHs of human associated Akkermansia sp. enable access to additional growth substrates present in HMOs, including 2'-FL. Our work highlights the potential for Akkermansia to influence the development of the gut microbiota early in life and expands the known metabolic capabilities of this important human symbiont.

IMPORTANCE

Akkermansia are mucin degrading specialists widely distributed in the human population. Akkermansia biwaensis has recently been observed to have enhanced growth relative to other human associated Akkermansia on multiple human milk oligosaccharides (HMOs). However, the mechanisms for enhanced growth are not understood. Here, we characterized the phylogenetic diversity and function of select genes involved in growth of A. biwaensis on 2'-fucosyllactose (2'-FL), a dominant HMO. Specifically, we demonstrate that two genes in a genomic locus, a putative β-galactosidase and α-fucosidase, are likely responsible for the enhanced growth on 2'-FL. The functional characterization of A. biwaensis growth on 2'-FL delineates the significance of a single genomic locus that may facilitate enhanced colonization and functional activity of select Akkermansia early in life.

Formate oxidation in the intestinal mucus layer enhances fitness of Salmonella enterica serovar Typhimurium

Salmonella enterica serovar Typhimurium induces intestinal inflammation to create a niche that fosters the outgrowth of the pathogen over the gut microbiota. Under inflammatory conditions, Salmonella utilizes terminal electron acceptors generated as byproducts of intestinal inflammation to generate cellular energy through respiration. However, the electron donating reactions in these electron transport chains are poorly understood. Here, we investigated how formate utilization through the respiratory formate dehydrogenase-N (FdnGHI) and formate dehydrogenase-O (FdoGHI) contribute to gut colonization of Salmonella. Both enzymes fulfilled redundant roles in enhancing fitness in a mouse model of Salmonella-induced colitis, and coupled to tetrathionate, nitrate, and oxygen respiration. The formic acid utilized by Salmonella during infection was generated by its own pyruvate-formate lyase as well as the gut microbiota. Transcription of formate dehydrogenases and pyruvate-formate lyase was significantly higher in bacteria residing in the mucus layer compared to the lumen. Furthermore, formate utilization conferred a more pronounced fitness advantage in the mucus, indicating that formate production and degradation occurred predominantly in the mucus layer. Our results provide new insights into how Salmonella adapts its energy metabolism to the local microenvironment in the gut. IMPORTANCE Bacterial pathogens must not only evade immune responses but also adapt their metabolism to successfully colonize their host. The microenvironments encountered by enteric pathogens differ based on anatomical location, such as small versus large intestine, spatial stratification by host factors, such as mucus layer and antimicrobial peptides, and distinct commensal microbial communities that inhabit these microenvironments. Our understanding of how Salmonella populations adapt its metabolism to different environments in the gut is incomplete. In the current study, we discovered that Salmonella utilizes formate as an electron donor to support respiration, and that formate oxidation predominantly occurs in the mucus layer. Our experiments suggest that spatially distinct Salmonella populations in the mucus layer and the lumen differ in their energy metabolism. Our findings enhance our understanding of the spatial nature of microbial metabolism and may have implications for other enteric pathogens as well as commensal host-associated microbial communities.

Reshaping of bacterial molecular hydrogen metabolism contributes to the outgrowth of commensal E. coli during gut inflammation

The composition of gut-associated microbial communities changes during intestinal inflammation, including an expansion of Enterobacteriaceae populations. The mechanisms underlying microbiota changes during inflammation are incompletely understood. Here, we analyzed previously published metagenomic datasets with a focus on microbial hydrogen metabolism. The bacterial genomes in the inflamed murine gut and in patients with inflammatory bowel disease contained more genes encoding predicted hydrogen-utilizing hydrogenases compared to communities found under non-inflamed conditions. To validate these findings, we investigated hydrogen metabolism of Escherichia coli, a representative Enterobacteriaceae, in mouse models of colitis. E. coli mutants lacking hydrogenase-1 and hydrogenase-2 displayed decreased fitness during colonization of the inflamed cecum and colon. Utilization of molecular hydrogen was in part dependent on respiration of inflammation-derived electron acceptors. This work highlights the contribution of hydrogenases to alterations of the gut microbiota in the context of non-infectious colitis.

Epithelial-Derived Reactive Oxygen Species Enable AppBCX-Mediated Aerobic Respiration of Escherichia coli during Intestinal Inflammation

The intestinal epithelium separates host tissue and gut-associated microbial communities. During inflammation, the host releases reactive oxygen and nitrogen species as an antimicrobial response. The impact of these radicals on gut microbes is incompletely understood. We discovered that the cryptic appBCX genes, predicted to encode a cytochrome bd-II oxidase, conferred a fitness advantage for E. coli in chemical and genetic models of non-infectious colitis. This fitness advantage was absent in mice that lacked epithelial NADPH oxidase 1 (NOX1) activity. In laboratory growth experiments, supplementation with exogenous hydrogen peroxide enhanced E. coli growth through AppBCX-mediated respiration in a catalase-dependent manner. We conclude that epithelial-derived reactive oxygen species are degraded in the gut lumen, which gives rise to molecular oxygen that supports the aerobic respiration of E. coli. This work illustrates how epithelial host responses intersect with gut microbial metabolism in the context of gut inflammation.

Xenosiderophore Utilization Promotes Bacteroides thetaiotaomicron Resilience during Colitis

During short-lived perturbations, such as inflammation, the gut microbiota exhibits resilience and reverts to its original configuration. Although microbial access to the micronutrient iron is decreased during colitis, pathogens can scavenge iron by using siderophores. How commensal bacteria acquire iron during gut inflammation is incompletely understood. Curiously, the human commensal Bacteroides thetaiotaomicron does not produce siderophores but grows under iron-limiting conditions using enterobacterial siderophores. Using RNA-seq, we identify B. thetaiotaomicron genes that were upregulated during Salmonella-induced gut inflammation and were predicted to be involved in iron uptake. Mutants in the xusABC locus (BT2063-2065) were defective for xenosiderophore-mediated iron uptake in vitro. In the normal mouse gut, the XusABC system was dispensable, while a xusA mutant colonized poorly during colitis. This work identifies xenosiderophore utilization as a critical mechanism for B. thetaiotaomicron to sustain colonization during inflammation and suggests a mechanism of how interphylum iron metabolism contributes to gut microbiota resilience.

Editing of the gut microbiota reduces carcinogenesis in mouse models of colitis-associated colorectal cancer

Enterobacteriaceae family members such as E. coli exacerbate development of intestinal malignancy. Zhu et al. report that targeting the metabolism of protumoral Enterobacteriaceae by tungstate prevents tumor development in murine models of colitis-associated colorectal cancer.

Chronic inflammation and gut microbiota dysbiosis, in particular the bloom of genotoxin-producing E. coli strains, are risk factors for the development of colorectal cancer. Here, we sought to determine whether precision editing of gut microbiota metabolism and composition could decrease the risk for tumor development in mouse models of colitis-associated colorectal cancer (CAC). Expansion of experimentally introduced E. coli strains in the azoxymethane/dextran sulfate sodium colitis model was driven by molybdoenzyme-dependent metabolic pathways. Oral administration of sodium tungstate inhibited E. coli molybdoenzymes and selectively decreased gut colonization with genotoxin-producing E. coli and other Enterobacteriaceae. Restricting the bloom of Enterobacteriaceae decreased intestinal inflammation and reduced the incidence of colonic tumors in two models of CAC, the azoxymethane/dextran sulfate sodium colitis model and azoxymethane-treated, Il10-deficient mice. We conclude that metabolic targeting of protumoral Enterobacteriaceae during chronic inflammation is a suitable strategy to prevent the development of malignancies arising from gut microbiota dysbiosis.

Abstract P5-10-02: Development and validation of a polygenic score to predict breast cancer risk in unaffected Hispanic women negative for mutations on a multi-gene hereditary cancer panel

Background: Breast cancer (BC) is the most commonly diagnosed cancer and the leading cause of cancer-related death among Hispanic women in the United States. For women of European ancestry, genome-wide association studies (GWAS) have identified common variants, primarily single-nucleotide polymorphisms (SNPs), that individually confer modest risk but together explain a significant proportion of genetic BC predisposition. For Hispanic women, the genetic contribution of SNPs to BC risk is not well understood. In these studies, we aim to develop and validate a polygenic score to improve risk assessment for Hispanic women who test negative for mutations in known BC susceptibility genes.

Methods: Genotypes and clinical histories were collected from consecutive development and validation cohorts of patients referred for hereditary cancer testing. Study subjects include women who report strictly Hispanic or Latin American ancestry, and who test negative for mutations in 11 genes associated with breast cancer (BRCA1, BRCA2, TP53, PTEN, STK11, CDH1, PALB2, CHEK2, ATM, NBN, BARD1).

Based on a development cohort ascertained through June 2017, we evaluated an 86-SNP Residual Risk Score (RRS) that was previously developed and validated for women of European ancestry. In the same cohort we are developing a Hispanic Residual Risk Score (HRRS) optimized for women of Hispanic ancestry. BC associations of individual SNPs are being established through meta-analysis of the development cohort and published Hispanic studies.

Multivariate logistic regression models were used to evaluate the 86-SNP RRS, and were the primary statistical tool for evaluation of individual SNPs and candidate polygenic scores. All models included personal/family cancer history and age as independent variables. P-values are based on likelihood ratio test statistics, and reported as two-sided. The development and validation studies are being conducted according to a protocol approved by the Quorum Institutional Review Board.

Results: The development cohort included 5,454 Hispanic women, 24% of whom reported a personal history of BC. The 86-SNP RRS was significantly associated with a personal history of BC after accounting for personal and family cancer history (p<10-19) with odds ratio per unit standard deviation 1.39 (95% CI = 1.30-1.50). To date, more than 5,000 Hispanic women have been ascertained for inclusion in the validation cohort. Results comparing discriminatory accuracy of the RRS and the HRRS will be presented.

Conclusions: The implementation of a clinically validated polygenic score may improve risk assessment and medical management of Hispanic women who test negative for monogenic BC mutations. The HRRS will be validated in an independent study population according to a pre-specified statistical analysis plan.

Citation Format: Hughes ER, Wagner S, Pruss D, Gallagher SK, Swedlund B, Bulka K, Hoff R, Jammulapati S, Morris B, Perry T, Lanchbury JS, Gutin A. Development and validation of a polygenic score to predict breast cancer risk in unaffected Hispanic women negative for mutations on a multi-gene hereditary cancer panel [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-10-02.

Abstract P4-09-04: Associations between clinical factors in v7.02 of the Tyrer-Cuzick model and a SNP-based residual risk score

Background: Genome-wide association studies (GWAS) have identified common variants, primarily single-nucleotide polymorphisms (SNPs), that individually confer modest risk but together explain a significant proportion of genetic breast cancer (BC) predisposition. GWAS have also demonstrated that SNPs cannot replace family history evaluation: familial BC assessment captures a large magnitude of risk information that is not captured by SNPs. Thus, improved BC risk stratification may be achieved by combining family history assessment with SNP markers. However, to avoid double-counting shared risk information, familial and/or SNP-based risks must be adjusted for confounding.

Additional clinical and biological factors that contribute to BC risk are included in version 7.02 of the Tyrer-Cuzick model. These include height; weight; BMI; age of menarche; parity and age of first childbirth; menopausal status and age of onset; and use of hormonal replacement therapy (HRT). Confounding of SNPs with these factors is not well understood. Here we present an analysis of associations between an 86-SNP Residual Risk Score (RRS) and factors included in version 7.02 of the Tyrer-Cuzick model.

Methods: De-identified clinical records and genotypes were collected from a consecutive series of patients referred for hereditary cancer testing with a multigene panel. Study subjects included unaffected women age 18-84 who reported European ancestry and tested negative for mutations in 11 genes associated with BC (BRCA1, BRCA2, TP53, PTEN, STK11, CDH1, PALB2, CHEK2, ATM, NBN, BARD1).

For each risk factor, we constructed a univariate linear regression model with RRS as the dependent variable and the clinical factor as the independent variable. From these models, we examined regression coefficients, p-values based on F-statistics, and Pearson correlation coefficients. Scatterplots and boxplots were used to visually assess associations. All analyses were conducted using R version 3.4.4. P-values were reported as two-sided with no corrections for multiple testing.

Results: 5,489 patients met the study selection criteria. The median age at hereditary cancer testing was 42 years. Nearly one third (33.1%) of women reported a BC diagnosis in a first degree relative.

The RRS was significantly associated with familial BC (p<10-08). We observed marginal evidence of association between the RRS and HRT use (p=0.04). However, this association would not survive a multiple testing correction, and was not significant after multivariate adjustment for family cancer history. We found no evidence for association of the RRS with height, weight, BMI, menopausal stage, age of menarche, age of menopause, duration of menarche, parity, age of first live birth, HRT type, or HRT length of use.

Conclusions: The RRS is largely independent from the non-familial risk factors in version 7.02 of the Tyrer-Cuzick model, but is significantly associated with BC family history. Risk assessment based on Tyrer-Cuzick and SNPs must be adjusted for confounding to avoid double-counting familial risk.

Citation Format: Hughes ER, Rosenthal E, Morris B, Wagner S, Lanchbury JS, Gutin A. Associations between clinical factors in v7.02 of the Tyrer-Cuzick model and a SNP-based residual risk score [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-09-04.

Precision editing of the gut microbiota ameliorates colitis

Inflammatory diseases of the gastrointestinal tract are frequently associated with dysbiosis, characterized by changes in gut microbial communities that include an expansion of facultative anaerobic bacteria of the Enterobacteriaceae family (phylum Proteobacteria). Here we show that a dysbiotic expansion of Enterobacteriaceae during gut inflammation could be prevented by tungstate treatment, which selectively inhibited molybdenum-cofactor-dependent microbial respiratory pathways that are operational only during episodes of inflammation. By contrast, we found that tungstate treatment caused minimal changes in the microbiota composition under homeostatic conditions. Notably, tungstate-mediated microbiota editing reduced the severity of intestinal inflammation in mouse models of colitis. We conclude that precision editing of the microbiota composition by tungstate treatment ameliorates the adverse effects of dysbiosis in the inflamed gut.

Dysbiosis-Associated Change in Host Metabolism Generates Lactate to Support Salmonella Growth

During Salmonella-induced gastroenteritis, mucosal inflammation creates a niche that favors the expansion of the pathogen population over the microbiota. Here, we show that Salmonella Typhimurium infection was accompanied by dysbiosis, decreased butyrate levels, and substantially elevated lactate levels in the gut lumen. Administration of a lactate dehydrogenase inhibitor blunted lactate production in germ-free mice, suggesting that lactate was predominantly of host origin. Depletion of butyrate-producing Clostridia, either through oral antibiotic treatment or as part of the pathogen-induced dysbiosis, triggered a switch in host cells from oxidative metabolism to lactate fermentation, increasing both lactate levels and Salmonella lactate utilization. Administration of tributyrin or a PPARγ agonist diminished host lactate production and abrogated the fitness advantage conferred on Salmonella by lactate utilization. We conclude that alterations of the gut microbiota, specifically a depletion of Clostridia, reprogram host metabolism to perform lactate fermentation, thus supporting Salmonella infection.

Enterococcus faecalis: E. coli's Siderophore-Inducing Sidekick

Many infectious diseases involve polymicrobial infections, which are characterized by synergistic interactions between different microorganisms colonizing a host. In this issue of Cell Host & Microbe, Keogh et al. (2016) show that Enterococcus faecalis promotes Escherichia coli biofilm formation in low-iron conditions, thus facilitating polymicrobial growth.

Microbial Respiration and Formate Oxidation as Metabolic Signatures of Inflammation-Associated Dysbiosis

Intestinal inflammation is frequently associated with an alteration of the gut microbiota, termed dysbiosis, which is characterized by a reduced abundance of obligate anaerobic bacteria and an expansion of facultative Proteobacteria such as commensal E. coli. The mechanisms enabling the outgrowth of Proteobacteria during inflammation are incompletely understood. Metagenomic sequencing revealed bacterial formate oxidation and aerobic respiration to be overrepresented metabolic pathways in a chemically induced murine model of colitis. Dysbiosis was accompanied by increased formate levels in the gut lumen. Formate was of microbial origin since no formate was detected in germ-free mice. Complementary studies using commensal E. coli strains as model organisms indicated that formate dehydrogenase and terminal oxidase genes provided a fitness advantage in murine models of colitis. In vivo, formate served as electron donor in conjunction with oxygen as the terminal electron acceptor. This work identifies bacterial formate oxidation and oxygen respiration as metabolic signatures for inflammation-associated dysbiosis.

An Oxidative Central Metabolism Enables Salmonella to Utilize Microbiota-Derived Succinate

The mucosal inflammatory response induced by Salmonella serovar Typhimurium creates a favorable niche for this gut pathogen. Conventional wisdom holds that S. Typhimurium undergoes an incomplete tricarboxylic acid (TCA) cycle in the anaerobic mammalian gut. One change during S. Typhimurium-induced inflammation is the production of oxidized compounds by infiltrating neutrophils. We show that inflammation-derived electron acceptors induce a complete, oxidative TCA cycle in S. Typhimurium, allowing the bacteria to compete with the microbiota for colonization. A complete TCA cycle facilitates utilization of the microbiota-derived fermentation product succinate as a carbon source. S. Typhimurium succinate utilization genes contribute to efficient colonization in conventionally raised mice, but provide no growth advantage in germ-free mice. Mono-association of gnotobiotic mice with Bacteroides, a major succinate producer, restores succinate utilization in S. Typhimurium. Thus, oxidative central metabolism enables S. Typhimurium to utilize a variety of carbon sources, including microbiota-derived succinate.

Empirical angle-dependent Biot and MBA models for acoustic anisotropy in cancellous bone

The Biot and the modified Biot-Attenborough (MBA) models have been found useful to understand ultrasonic wave propagation in cancellous bone. However, neither of the models, as previously applied to cancellous bone, allows for the angular dependence of acoustic properties with direction. The present study aims to account for the acoustic anisotropy in cancellous bone, by introducing empirical angle-dependent input parameters, as defined for a highly oriented structure, into the Biot and the MBA models. The anisotropy of the angle-dependent Biot model is attributed to the variation in the elastic moduli of the skeletal frame with respect to the trabecular alignment. The angle-dependent MBA model employs a simple empirical way of using the parametric fit for the fast and the slow wave speeds. The angle-dependent models were used to predict both the fast and slow wave velocities as a function of propagation angle with respect to the trabecular alignment of cancellous bone. The predictions were compared with those of the Schoenberg model for anisotropy in cancellous bone and in vitro experimental measurements from the literature. The angle-dependent models successfully predicted the angular dependence of phase velocity of the fast wave with direction. The root-mean-square errors of the measured versus predicted fast wave velocities were 79.2 m s(-1) (angle-dependent Biot model) and 36.1 m s(-1) (angle-dependent MBA model). They also predicted the fact that the slow wave is nearly independent of propagation angle for angles about 50 degrees , but consistently underestimated the slow wave velocity with the root-mean-square errors of 187.2 m s(-1) (angle-dependent Biot model) and 240.8 m s(-1) (angle-dependent MBA model). The study indicates that the angle-dependent models reasonably replicate the acoustic anisotropy in cancellous bone.

Ultrasonic propagation in cancellous bone: a new stratified model

The theoretical modeling of ultrasonic propagation in cancellous bone is pertinent to improving the ultrasonic diagnosis of osteoporosis. First, this paper reviews applications of Biot's theory to this problem. Next, a new approach is presented, based on an idealization of cancellous bone as a periodic array of bone-marrow layers. Schoenberg's theory is applied to this model to predict wave properties. Bovine bone samples were tested in vitro using pulses centered at 1 MHz over various angles relative to the orientated cancellous structure. Two longitudinal modes (fast and slow waves) were observed for propagation parallel to the structure, but only one was observed for propagation normal to the structure. Angular-dependence of velocities was examined, and the fast wave was found to be strongly anisotropic. These results gave qualitative agreement with predictions of Schoenberg's theory. Although this new model is a simplification of the cancellous architecture, it has potential for future research.

Hepatobiliary disorders in inflammatory bowel disease

Every physician managing patients with inflammatory bowel disease should be alert to the possibility of the development of hepatobiliary disorders, especially in patients with extensive colonic involvement. There is the question concerning type of follow-up study to be instituted in patients with IBD. Elevation of the level of serum alkaline phosphatase appears to be the most useful and consistent biochemical indicator of hepatic dysfunction (101). This should be estimated at six monthly intervals. A persistent elevation of the level of serum alkaline phosphatase or more overt clinical manifestations, such as pain in the right upper quadrant, hepatomegaly, obstructive jaundice or weight loss, would all indicate the need for further investigations. This would normally take the form of roentgenologic investigation of the biliary tree and biopsy of the liver. Once a patient with IBD has been diagnosed as having one or more hepatobiliary disorders, what is the appropriate management? Each instance should be treated individually according to the nature of the disorder. In general, most of these conditions are histologic abnormalities and are of little clinical importance. There is the question of whether or not there is a role for prophylactic colectomy. There has been conflicting evidence to both support and refute the rationale that colectomy will prevent the development of, or arrest, existing disease of the liver. In the view of the authors, based upon a large experience with the management of these patients, the indication for colectomy should be based upon the severity and extent of colonic disease and almost never upon the existence of associated hepatobiliary disorders.

The lung lamellar body as a functioning membrane in protein-catalyzed phosphatidylcholine transfer

Lung lamellar bodies and liver mitochondria were used to demonstrate that soluble phospholipid transfer proteins from lung transfer phosphatidylcholine to both of these acceptors. The initial rate of transfer to lung lamellar bodies is about half that of the rate of transfer to the liver mitochondria when both acceptor membranes are present at saturating concentrations. Phosphatidylcholine unilamellar vesicles were used to demonstrate that the fatty acyl composition of the membrane phosphatidylcholine is a significant determinant of the rate of phosphatidylcholine transfer catalyzed by these proteins. The lamellar bodies have a unique phosphatidylcholine composition, and these studies suggest that this is an important factor in determining the lower initial rate of transfer to lamellar bodies. The studies have also characterized two phospholipid transfer proteins in rat lung in terms of isoelectric point. Isoelectric points for the two proteins which transfer phosphatidylcholine were found to be 5.6 +/- 0.08 and 6.2 +/- 0.03.

Glucocorticoid effects on the embryonic chick heart. I. Glucocorticoid enlargement of the heart

Cortisol increases the heart weight relative to body weight following injection of growth suppressing amounts of the hormone on incubation days 9, 10, 13, and 15. Hormone administration increases glycogen, glycosaminoglycan (GAG), and total lipid concentration in the embryonic myocardium. Deoxyribonucleic acid (DNA) and protein concentration are decreased proportionally. Glycogen synthetase and radiosulphate incorporation into GAG are increased by the glucocorticoid. Lack of growth inhibition of the embryonic myocardium by glucocorticoids is not due to absence of glucocorticoid receptors. [3H]-Dexamethasone was shown to bind to a cytoplasmic and nuclear fraction of the chick heart. Binding to a cytoplasmic protein could be demonstrated in the heart at nine days of embryonic development and increased with developmental age. The increase in cardiac mass appears to be specific for the glucocorticoid hormones when compared with epinephrine and deoxycorticosterone. The latter two hormones did not increase cardiac mass.

Glucocorticoid effects on the embryonic chick heart. II. Alteration of oxidative metabolism

The injection of cortisol phosphate (0.5 mg per egg) onto the chorioallantoic membrane of embryonic chicks at 12 days incubation depresses the rate of oxygen consumption in heart mitochondria isolated from the chicks 24 or 48 hours after the injection as compared to a saline injected control. The oxygen consumption is depressed using either reduced nicotinamide-adenine dinucleotide (NADH)-linked or flavin adenine dinucleotide (FADH)-linked substrates. The progressive inhibition of oxidation and adenosine triphosphate (ATP) production rate is related to the time after cortisol is injected. The treated mitochondria appear to function differently when NADH-linked and FADH-linked respiratory substrates are compared. Using NADH-linked substrates (site 1), adenosine diphosphate (ADP) was phosphorylated by mitochondria, even though the rate of phosphorylation was decreased; however, when FADH-linked substrates were used, incomplete phosphorylation was observed. The rate and the extent of calcium accumulation by embryonic chick heart mitochondria were also depressed by cortisol. These data suggest a defect in phosphorylation at site 2 following cortisol treatment but not at the site 1 linked energy transducing step. Whether these impairments of mitochondrial function result from catabolic turnover of the mitochondrial membrane components, excessive calcium accumulation by the mitochondria, or from the digestion of mitochondrial constituents, has not been delineated.

Fetal lung disaturated phosphatidylcholine. Ostensible increase following exposure to dexamethasone

Fetal rat lung removed at 15 days gestation and placed in organ culture incorporates choline into phosphatidylcholine. Addition of 10(-9) M dexamethasone resulted in increased rates of choline incorporation per micrograms protein after both 6 and 12 days culture. This concentration of dexamethasone did not increase tissue phosphatidylcholine or disaturated phosphatidylcholine. Thus, at a culture time when dexamethasone had a significant effect on choline incorporation, there was no change in either the total phospholipid or disaturated phosphatidylcholine content of the lung tissue. The transplacental administration of dexamethasone decreased fetal lung DNA and phospholipid content. At the mid-range dosage tested (400 micrograms), dexamethasone depressed DNA (51%) appreciably more than total phosphatidylcholine (28%) and disaturated phosphatidylcholine (33%). These results show that the hormone does not increase the total amount of surfactant per lung. The increased disaturated phosphatidylcholine per mg DNA results in an ostensible beneficial effect of dexamethasone on surfactant and may reflect an increased proportion of Type II cells in fetal lung both in vitro and in vivo following hormone exposure. Disaturated phosphatidylcholine per Type II alveolar cell is no doubt increased but the trade-off is fewer total cells in the lung.

Alteration of cartilage glycosaminoglycan protein acceptor by somatomedin and cortisol

The effect of somatomedin and cortisol on embryonic chick cartilage in vitro indicates that somatomedin stimulates 35SO4 uptake while cortisol decreases it with no effect on glycosaminoglycan turnover. Xylosyltransferase activity is increased in crude fractions of somatomedin-treated cartilage but decreased in cortisol-treated cartilage. By using a Smith-degraded proteoglycan as an exogenous acceptor, xylosyltransferase activities from both treatments were equivalent, suggesting that the enzyme was not rate limiting. The results of xylosyltransferase assays conducted by mixing enzyme and endogenous acceptor from control, cortisol-treated and somatomedin-treated cartilage, suggest both effects to be at the level of the acceptor protein.

Differentiation of the pulmonary surfactant system. Disaturated phosphatidylcholine accumulation in fetal rat lung in vivo and in vitro

Fetal rat lung was placed in organ culture at 15 days gestation (22 days total gestation period), before biochemical and morphological development of the pulmonary surfactant system. At the fifth day of culture numerous Type II cells containing lamellar bodies were present as determined by electron micrography. Phospholipid accumulation in the cultures increased abruptly beginning at 6 days in culture. The phospholipid which accumulated between the sixth and twelfth culture days was composed of 21--27% disaturated phosphatidylcholines. Both the percent of disaturated phosphatidylcholines in the phospholipid fraction and the qualitative pattern of accumulation as a function of time were similar to observations for fetal rat lung developing in vivo. The data presented provide evidence for development of the pulmonary surfactant system in organ culture in vitro.

Uridine diphosphate xylosyltransferase activity in cartilage from manganese-deficient chicks

The glycosaminoglycan content of cartilage is decreased in manganese deficiency in the chick (perosis). The activity of xylosyltransferase, the first enzyme in the biosynthetic pathway of sulphated glycosaminoglycans, was studied in the epiphysial cartilage of 4-week-old chicks which had been maintained since hatching on a manganese-deficient diet. Enzymic activity was measured by the incorporation of [14C]xylose from UDP-[14C]xylose into trichloroacetic acid precipitates. Optimal conditions for the xylosyltransferase assay were established and shown to be the same for both control and manganese-deficient cartilage. Assay of the enzyme by using an exogenous xylose acceptor showed no difference in xylosyltransferase activity between control and manganese-deficient tissue. Further, the extent of xylose incorporation was greater in manganese-deficient than in control cartilage preparations, suggesting an increase in xylose-acceptor sites on the endogenous acceptor protein in the deficient cartilage. 35S turnover in the manganese-deficient cartilage was also increased. The data suggest that the decreased glycosaminoglycan content in manganese-deficient cartilage is due to decreased xylosylation of the acceptor protein plus increased degradation of glycosaminoglycan.

Glucocorticoid therapy in children. Effect on somatomedin secretion

Glucocorticoids cause growth retardation in children. We have studied the effect of these hormones on serum somatomedin (Sm) levels in seven children with nephrosis. Intravenous administration of methylprednisolone sodium succinate, 2.2 mg/kg, causes a rapid fall in serum Sm activity. The activity remains suppressed during continuous therapy, but returns toward normal when medication is omitted during the course of alternate-day therapy. We conclude that one reason for growth retardation secondary to continuous glucocorticoid therapy is suppression of Sm generation. A direct effect of these hormones on the cartilage cell or induction of an Sm inhibitor cannot be excluded by the reported experiments.

Somatomedin and the regulation of skeletal growth

Somatomedin is a polypeptide(s) which "mediates" the actions of growth hormone. This pituitary dependent hormone was previously called "sulfation factor," a term derived from the bioassay technique which measures the incorporation of radioactive sulfate into cartilage glycosaminoglycans. Somatomedin has a more general effect upon cartilage; it is necessary for the cell multiplication and cartilage maturation which results in the growth of long bones. Somatomedin is not found in the plasma in growth hormone deficiency and appears following growth hormone administration. A genetic defect in somatomedin synthesis has been identified in the Laron's dwarf. Growth hormone is present in excess in the plasma and growth hormone administration does not stimulate somatomedin synthesis in this syndrome. Insufficient data are available to delineate the role for somatomedin in other growth disturbances. It has been demonstrated that glucocorticoid hormones interfere with both somatomedin synthesis and its biological activity. Purification of somatomedins in plasma has been achieved and radioreceptor or radioimmunoassays will be available in the future for study of growth problems in children.

Alterations in glycosaminoglycan metabolism in beta-aminopropionitrile-treated chick embryos

1. Na(2) (35)SO(4), [1-(14)C]glucosamine and [1-(14)C]acetate were used as precursors of the sulphated glycosaminoglycans to study the biochemical effect of beta-aminopropionitrile in chick embryos. The incorporation of all three precursors was decreased in the treated embryos between days 7 and 10 of embryonic development. No inhibition of incorporation of these precursors occurred between days 16 and 20 of embryonic development at the dosages of beta-aminopropionitrile used. 2. beta-Aminopropionitrile treatment also decreased the amount of N-acetylhexosamines in the chick embryo and decreased the percentage of the hexosamine esterified by nucleotides. Respiration was decreased by homogenates prepared from treated embryos. Likewise, UDP-xylosyl- and UDP-galactosyl-transferase activities were decreased in treated embryos and cartilage from embryos and growing chicks. 3. The data suggest that beta-aminopropionitrile, in addition to the known lathyrogenic activity, either is or gives rise to a potent metabolic poison that interferes with basic cellular metabolism. The results are consistent with a decreased rate of ATP generation as an explanation for the decrease in glycosaminoglycan synthesis.

Slow turnover of manganese in active rheumatoid arthritis accelerated by prednisone

Total body and area counts of intravenously injected (54)Mn were measured periodically in 29 in-patients. A heterogeneous group of 19 control patients showed fair reproducibility in the immediate distribution, and considerable individual variance in the subsequent loss of the isotope. Eight studies of the effects of feeding excesses of manganous sulfate to five patients showed acceleration of the rate of loss of the radioisotope from the whole body and the liver. These findings seem compatible with the presence of control mechanisms in man, operating to vary the metal's excretion, while tending to preserve constancy of its concentration in tissues. Slow turnover rates of the metal were demonstrated in seven out of eight patients with active rheumatoid arthritis, in one with hydralazine disease, but not in one arthritic undergoing an impressive, spontaneous remission. Statistically significant differences were encountered in the measurements of (54)Mn turnover of the total body, the thyroid, and the liver. Administration of prednisone induced clinical improvement and significant acceleration of these turnovers. Slow turnovers are characteristic of nutritional manganese deficiency. Therefore, serum and blood manganese determinations were performed by neutron activation analysis on 14 control patients, and on six patients with active rheumatoid arthritis. A statistically significant elevation of the red cell manganese concentration was encountered in patients with rheumatoid arthritis. This argued against the presence of classical tracemetal deficiency and called for an alternative explanation of these findings.

Prevention of wasting disease by pregnancy associated with hypertrophy of the fetal thymus

Neonatally thymectomized female mice were studied and compared to appropriate controls. Neonatal thymectomy appears to decrease fertility significantly in the female C3H/HeJ mouse. However, if a thymectomized female mouse becomes pregnant, pregnancy offers significant protection against wasting disease and death. The maternal thymus appears to play no significant role in the development of the fetus as measured by gross examination and organ weights. Offspring of thymectomized females had comparable body and organ weights when compared to offspring from sham-operated females, except for the thymus gland and gastrointestinal tract. The absence of the maternal thymus gland did stimulate a significant increase in the gland weight of her offspring compared to sham-operated control female offspring. Parity, per se, in intact females also causes a significant increase in the weights of the thymus of newborn offspring.