Accelerated cellular uptake and metabolism of L-thyroxine during acute Salmonella typhimurium sepsis

Exclusive dependence of IL-10Rα signalling on intestinal microbiota homeostasis and control of whipworm infection

The whipworm Trichuris trichiura is a soil-transmitted helminth that dwells in the epithelium of the caecum and proximal colon of their hosts causing the human disease, trichuriasis. Trichuriasis is characterized by colitis attributed to the inflammatory response elicited by the parasite while tunnelling through intestinal epithelial cells (IECs). The IL-10 family of receptors, comprising combinations of subunits IL-10Rα, IL-10Rβ, IL-22Rα and IL-28Rα, modulates intestinal inflammatory responses. Here we carefully dissected the role of these subunits in the resistance of mice to infection with T. muris, a mouse model of the human whipworm T. trichiura. Our findings demonstrate that whilst IL-22Rα and IL-28Rα are dispensable in the host response to whipworms, IL-10 signalling through IL-10Rα and IL-10Rβ is essential to control caecal pathology, worm expulsion and survival during T. muris infections. We show that deficiency of IL-10, IL-10Rα and IL-10Rβ results in dysbiosis of the caecal microbiota characterised by expanded populations of opportunistic bacteria of the families Enterococcaceae and Enterobacteriaceae. Moreover, breakdown of the epithelial barrier after whipworm infection in IL-10, IL-10Rα and IL-10Rβ-deficient mice, allows the translocation of these opportunistic pathogens or their excretory products to the liver causing organ failure and lethal disease. Importantly, bone marrow chimera experiments indicate that signalling through IL-10Rα and IL-10Rβ in haematopoietic cells, but not IECs, is crucial to control worm expulsion and immunopathology. These findings are supported by worm expulsion upon infection of conditional mutant mice for the IL-10Rα on IECs. Our findings emphasize the pivotal and complex role of systemic IL-10Rα signalling on immune cells in promoting microbiota homeostasis and maintaining the intestinal epithelial barrier, thus preventing immunopathology during whipworm infections.

SalmoNet, an integrated network of ten Salmonella enterica strains reveals common and distinct pathways to host adaptation

Salmonella enterica is a prominent bacterial pathogen with implications on human and animal health. Salmonella serovars could be classified as gastro-intestinal or extra-intestinal. Genome-wide comparisons revealed that extra-intestinal strains are closer relatives of gastro-intestinal strains than to each other indicating a parallel evolution of this trait. Given the complexity of the differences, a systems-level comparison could reveal key mechanisms enabling extra-intestinal serovars to cause systemic infections. Accordingly, in this work, we introduce a unique resource, SalmoNet, which combines manual curation, high-throughput data and computational predictions to provide an integrated network for Salmonella at the metabolic, transcriptional regulatory and protein-protein interaction levels. SalmoNet provides the networks separately for five gastro-intestinal and five extra-intestinal strains. As a multi-layered, multi-strain database containing experimental data, SalmoNet is the first dedicated network resource for Salmonella. It comprehensively contains interactions between proteins encoded in Salmonella pathogenicity islands, as well as regulatory mechanisms of metabolic processes with the option to zoom-in and analyze the interactions at specific loci in more detail. Application of SalmoNet is not limited to strain comparisons as it also provides a Salmonella resource for biochemical network modeling, host-pathogen interaction studies, drug discovery, experimental validation of novel interactions, uncovering new pathological mechanisms from emergent properties and epidemiological studies. SalmoNet is available at http://salmonet.org.

Molecular and cellular characterization of a Salmonella enterica serovar Paratyphi a outbreak strain and the human immune response to infection

Enteric fever is an invasive life-threatening systemic disease caused by the Salmonella enterica human-adapted serovars Typhi and Paratyphi. Increasing incidence of infections with Salmonella enterica serovar Paratyphi A and the spreading of its antibiotic-resistant derivates pose a significant health concern in some areas of the world. Herein, we describe a molecular and phenotypic characterization of an S. Paratyphi A strain accounted for a recent paratyphoid outbreak in Nepal that affected at least 37 travelers. Pulsed-field gel electrophoresis analysis of the outbreak isolates revealed one genetic clone (pulsotype), confirming a single infecting source. Genetic profiling of the outbreak strain demonstrated the contribution of specific bacteriophages as a prime source of genetic diversity among clinical isolates of S. Paratyphi A. Phenotypic characterization in comparison with the S. Paratyphi A ATCC 9150 reference sequenced strain showed differences in flagellar morphology and increased abilities of the outbreak strain with respect to its motility, invasion into nonphagocytic cells, intracellular multiplication, survival within macrophages, and higher induction of interleukin-8 (IL-8) secreted by host cells. Collectively, these differences suggest an enhanced virulence potential of this strain and demonstrate an interesting phenotypic variation among S. Paratyphi A isolates. In vivo profiling of 16 inflammatory cytokines in patients infected with the outbreak strain revealed a common profile of a remarkable gamma interferon (IFN-γ) induction together with elevated concentrations of tumor necrosis factor alpha (TNF-α), IL-6, IL-8, IL-10, and IL-15, but not IL-12, which was previously demonstrated as elevated in nontyphoidal Salmonella infections. This apparent profile implies a distinct immune response to paratyphoid infections.

Alternate pathways of thyroid hormone metabolism

The major thyroid hormone (TH) secreted by the thyroid gland is thyroxine (T(4)). Triiodothyronine (T(3)), formed chiefly by deiodination of T(4), is the active hormone at the nuclear receptor, and it is generally accepted that deiodination is the major pathway regulating T(3) bioavailability in mammalian tissues. The alternate pathways, sulfation and glucuronidation of the phenolic hydroxyl group of iodothyronines, the oxidative deamination and decarboxylation of the alanine side chain to form iodothyroacetic acids, and ether link cleavage provide additional mechanisms for regulating the supply of active hormone. Sulfation may play a general role in regulation of iodothyronine metabolism, since sulfation of T(4) and T(3) markedly accelerates deiodination to the inactive metabolites, reverse triiodothyronine (rT(3)) and T(2). Sulfoconjugation is prominent during intrauterine development, particularly in the precocial species in the last trimester including humans and sheep, where it may serve both to regulate the supply of T(3), via sulfation followed by deiodination, and to facilitate maternal-fetal exchange of sulfated iodothyronines (e.g., 3,3'-diiodothyronine sulfate [T(2)S]). The resulting low serum T(3) may be important for normal fetal development in the late gestation. The possibility that T(2)S or its derivative, transferred from the fetus and appearing in maternal serum or urine, can serve as a marker of fetal thyroid function is being studied. Glucuronidation of TH often precedes biliary-fecal excretion of hormone. In rats, stimulation of glucuronidation by various drugs and toxins may lead to lower T(4) and T(3) levels, provocation of thyrotropin (TSH) secretion, and goiter. In man, drug induced stimulation of glucuronidation is limited to T(4), and does not usually compromise normal thyroid function. However, in hypothyroid subjects, higher doses of TH may be required to maintain euthyroidism when these drugs are given. In addition, glucuronidates and sulfated iodothyronines can be hydrolyzed to their precursors in gastrointestinal tract and various tissues. Thus, these conjugates can serve as a reservoir for biologically active iodothyronines (e.g., T(4), T(3), or T(2)). The acetic acid derivatives of T(4), tetrac and triac, are minor products in normal thyroid physiology. However, triac has a different pattern of receptor affinity than T(3), binding preferentially to the beta receptor. This makes it useful in the treatment of the syndrome of resistance to thyroid hormone action, where the typical mutation affects only the beta receptor. Thus, adequate binding to certain mutated beta receptors can be achieved without excessive stimulation of alpha receptors, which predominate in the heart. Ether link cleavage of TH is also a minor pathway in normal subjects. However, this pathway may become important during infections, when augmented TH breakdown by ether-link cleavage (ELC) may assist in bactericidal activity. There is a recent claim that decarboxylated derivates of thyronines, that is, monoiodothyronamine (T(1)am) and thyronamine (T(0)am), may be biologically important and have actions different from those of TH. Further information on these interesting derivatives is awaited.

The pituitary-thyroid axis in severe falciparum malaria: evidence for depressed thyrotroph and thyroid gland function

Abnormal thyroid function is strongly associated with mortality in severe non-thyroidal illness. We have assessed the pituitary-thyroid axis serially in 18 Thai adults with severe falciparum malaria and in 18 matched controls. The admission total serum thyroxine (T4) concentrations of the patients (median [range]: 64 nmol/litre [less than 30-91]) were significantly lower than those of controls (81 nmol/litre [61-133]; 2P less than 0.01), and remained depressed until after fever and parasite clearance. Two patients who died in hospital had admission serum T4 concentrations less than 35 nmol/litre. The admission basal serum thyrotropin (TSH) levels of the patients (0.9 mU/litre [less than 0.2-3.1]) were similar to those of controls (1.3 mU/litre [less than 0.2-3.7], 2P greater than 0.1) and remained normal throughout fever and parasitaemia. Thirty-minute TSH increments during a thyrotropin-releasing hormone test on admission were reduced in 13 patients with severe malaria (4.1 mU/litre [0.7-8.1]) relative to those in convalescence (7.1 mU/litre [1.7-14.4], n = 10, 2P less than 0.01) and controls (5.6 mU/litre [3.3-12.9], n = 9, 2P less than 0.05). These findings suggest that thyrotroph and thyroid gland function are depressed during acute, severe malaria. As these changes may be an adaptation to accelerated catabolism, the role of thyroid replacement in such patients is uncertain.

Studies on the possible role of thyroid hormone in altered muscle protein turnover during sepsis

Five days after thyroidectomy (Tx) or sham-Tx in young male Sprague-Dawley rats, sepsis was induced by cecal ligation and puncture (CLP). Control animals underwent laparotomy and manipulation of the cecum without ligation or puncture. Sixteen hours after CLP or laparotomy, protein synthesis and degradation were measured in incubated extensor digitorum longus (EDL) and soleus (SOL) muscles by determining rate of 14C-phenylalanine incorporation into protein and tyrosine release into incubation medium, respectively. Triiodothyronine (T3) was measured in serum and muscle tissue. Protein synthesis was reduced by 39% and 22% in EDL and SOL, respectively, 16 hours after CLP in sham-Tx rats. The response to sepsis of protein synthesis was abolished in Tx rats. Protein breakdown was increased by 113% and 68% in EDL and SOL, respectively, 16 hours after CLP in sham-Tx animals. The increase in muscle proteolysis during sepsis was blunted in hypothyroid animals and was 42% and 49% in EDL and SOL, respectively. T3 in serum was reduced by sepsis, both in Tx and sham-Tx rats. T3 in muscle, however, was maintained or increased during sepsis. Abolished or blunted response of muscle protein turnover after CLP in hypothyroid animals may reflect a role of thyroid hormones in altered muscle protein metabolism during sepsis. Reduced serum levels of T3, but maintained or increased muscle concentrations of the hormone, suggests that increased T3 uptake by muscle may be one mechanism of low T3 syndrome in sepsis, further supporting the concept of a role for thyroid hormone in metabolic alterations in muscle during sepsis.

Prevalence of thyroid disease and abnormal thyroid tests in older hospitalized and ambulatory persons

To determine the utility of laboratory tests for diagnosing thyroid disease in the hospitalized elderly, we measured serum thyroid-stimulating hormone (TSH), thyroxine (T4), free thyroxine index (FT4I), triiodothyronine (T3), and free triiodothyronine index (FT3I) in 125 geriatric inpatients, mostly men, and compared the results to those in elderly ambulatory patients. Hypothyroidism (TSH greater than 10 microU/mL with a low T4 and FT4I or clinical findings) was present in 7.8% (nine of 116) of male inpatients compared to only 0.7% of male ambulatory controls (P less than 0.01). Only a few women were studied but 17% (two of 12) were hypothyroid compared to 2.4% of ambulatory elderly women. Three of the hypothyroid inpatients had no clinical clue to their hypothyroidism. Further, decreased thyroid reserve or subclinical hypothyroidism (TSH greater than 10 microU/mL with a normal T4 and FT4I and no overt clinical findings), a condition which may lead to overt hypothyroidism, was more common in male inpatients (4.3%) than in male ambulatory controls (1.8% [P less than 0.01]). Thus, a clearly elevated serum TSH (greater than 10 microU/mL) was more common in inpatient (12.1%) than in ambulatory (2.4%) elderly men (P less than 0.01). Four inpatients and nine ambulatory controls had an elevated T4 and FT4I, but in only one (0.8%) inpatient and one (0.6%) control was a final diagnosis of hyperthyroidism made; the others had no clinical findings and a normal or low T3 and FT3I.(ABSTRACT TRUNCATED AT 250 WORDS)

Extracellular metabolism of thyroid hormones by stimulated granulocytes

Stimulated polymorphonuclear leukocytes have been shown by this laboratory to release a reactive-oxygen species (ROS) which is detectable in the supernatant and is capable of oxidizing reduced glutathione and reacting with methionine (Sagone et al., Blood 63:96-104, 1984). This ROS is dependent on H2O2 and heme for its production and is postulated to be a stable oxidant derived from hypochlorous acid, such as a chloramine. Further, this ROS was also shown to be able to oxidize and fix iodide to protein. This latter characteristic was the theoretical basis for our present study in which the same ROS was shown to be able to carry out the iodination of 3,3,5'-triiodothyronine to thyroxine in the presence of I-. Our results provide further support that granulocytes have a role in the peripheral utilization of thyroid hormones in patients with infectious diseases or other illnesses in which granulocytes may be activated, and our results indicate that the reactions may occur extracellularly.

Infection and diabetes: the case for glucose control

This review summarizes data concerning the host resistance to infection in diabetes and the influence of an acute infection upon the endocrinologic-metabolite status of the diabetic patient. While it is well known that acute infections lead to difficulty in controlling blood sugar levels and the infection is the most frequently documented cause of ketoacidosis, controversy persists as to whether or not patients with diabetes mellitus are more susceptible to infection than age- and sex-matched nondiabetic control subjects. Our data obtained from the charts of 241 diabetic patients who were being followed as outpatients show a striking direct correlation between the overall prevalence of infection (p less than 0.001) and the mean plasma glucose levels (representing three or more fasting glucose determinations taken at times when no evidence of infection existed). There is a significant diminution in intracellular bactericidal activity of leukocytes with Staphylococcus aureus and Escherichia coli in subjects with poorly controlled diabetes in comparison with the control group. Serum opsonic activity for both Staph. Aureus and E. coli were significantly lower than in the control subjects. Taken together, the results from published reports as well as our data suggest to us that good control of blood sugar in diabetic patients is a desirable goal in the prevention of certain infections (Candida vaginitis, for example) and to ensure maintenance of normal host defense mechanisms that determine resistance and response to infection.

Thyroxine, triiodothyronine and thyrotrophin levels in meningococcal meningitis, typhoid fever and other febrile conditions

Thyroid status was estimated serially by measuring triiodothyronine (T3), thyroxine (T4) and thyrotrophin (hTSH) in 20 patients suffering from meningococcal meningitis, typhoid fever and other acute febrile illnesses. Significantly low T3 and only slightly increased T4 were observed in all the patients. hTSH was normal in all of these. A significant reciprocal relationship was found between the degree of fever and fall in T3 concentrations. T3 tended to rise in patients who recovered but in those who deteriorated or died, T3 remained persistently low.

Membrane (Na+ + K+)-ATPase of canine brain, heart and kidney. Tissue-dependent differences in kinetic properties and the influence of purification procedures

Effects of commonly used purification procedures on the yield and specific activity of (Na+ + K+)-ATPase (Mg2+-dependent, Na+ + K+-activated ATP phosphohydrolase, EC 3.6.1.3), the turnover number of the enzyme, and the kinetic parameters for the ATP-dependent ouabain-enzyme interaction were compared in canine brain, heart and kidney. Kinetic parameters were estimated using a graphical analysis of non-steady state kinetics. The protein recovery and the degree of increase in specific activity of (Na+ + K+)-ATPase and the ratio between (Na+ + K+)-ATPase and Mg2+-ATPase activities during the successive treatments with deoxycholate, sodium iodide and glycerol were dependent on the source of the enzyme. A method which yields highly active (Na+ + K+)-ATPase preparations from the cardiac tissue was not suitable for obtaining highly active enzyme preparations from other tissues. Apparent turnover numbers of the brain (Na+ + K+)-ATPase preparations were not significantly affected by the sodium iodide treatment, but markedly decreased by deoxycholate or glycerol treatments. Similar glycerol treatment, however, failed to affect the apparent turnover number of cardiac enzymes preparations. Cerebral and cardiac enzyme preparations obtained by deoxycholate, sodium iodide and glycerol treatments had lower affinity for ouabain than renal enzyme preparations, primarily due to higher dissociation rate constants for the ouabain.enzyme complex. This tissue-dependent difference in ouabain sensitivity seems to be an artifact of the purification procedure, since less purified cerebral or cardiac preparations had lower dissociation rate constants. Changes in apparent association rate constants were minimal during the purfication procedure. These results indicate that the presentyl used purification procedures may alter the properties of membrane (Na+ + K+)-ATPase and affect the interaction between cardiac glycosides and the enzyme. The effect of a given treatment depends on the source of the enzyme. For the in vitro studies involving purified (Na+ + K+)-ATPase preparations, the influence of the methods used to obtain the enzyme preparation should be carefully evaluated.

Reduced active thyroid hormone levels in acute illness

In acute and subacute disease the active thyroid hormones, triiodothyronine (T3) and tetraiodothyroacetic acid (tetrac), are decreased while serum-thyroxine (T4) levels tend to be slightly reduced. Conversely, the inactive metabolite, reverse triiodothyronine (reverse T3), is increased indicating a diversion of T4 metabolism from an activating to an inactivating pathway. With convalescence the serum levels of T3, tetrac, and T4 recover while reverse T3 decreases to normal. These changes occur without significant alterations in serum levels of thyroid-stimulating hormone, indicating maintenance of euthyroidism throughout disease.