First Observation of Cyclotron Radiation from MeV-Scale e^{±} following Nuclear β Decay

We present an apparatus for detection of cyclotron radiation yielding a frequency-based β^{±} kinetic energy determination in the 5 keV to 2.1 MeV range, characteristic of nuclear β decays. The cyclotron frequency of the radiating β particles in a magnetic field is used to determine the β energy precisely. Our work establishes the foundation to apply the cyclotron radiation emission spectroscopy (CRES) technique, developed by the Project 8 Collaboration, far beyond the 18-keV tritium endpoint region. We report initial measurements of β^{-}'s from ^{6}He and β^{+}'s from ^{19}Ne decays to demonstrate the broadband response of our detection system and assess potential systematic uncertainties for β spectroscopy over the full (MeV) energy range. To our knowledge, this is the first direct observation of cyclotron radiation from individual highly relativistic β's in a waveguide. This work establishes the application of CRES to a variety of nuclei, opening its reach to searches for new physics beyond the TeV scale via precision β-decay measurements.

First GPR119 PET Imaging Ligand: Synthesis, Radiochemistry, and Preliminary Evaluations

G-protein-coupled receptor 119 (GPR119) has emerged as a promising target for treating type 2 diabetes mellitus. Activating GPR119 improves glucose homeostasis, while suppressing appetite and weight gain. Measuring GPR119 levels in vivo could significantly advance GPR119-based drug development strategies including target engagement, occupancy, and distribution studies. To date, no positron emission tomography (PET) ligands are available to image GPR119. In this paper, we report the synthesis, radiolabeling, and preliminary biological evaluations of a novel PET radiotracer [18F]KSS3 to image GPR119. PET imaging will provide information on GPR119 changes with diabetic glycemic loads and the efficacy of GPR119 agonists as antidiabetic drugs. Our results demonstrate [18F]KSS3's high radiochemical purity, specific activity, cellular uptake, and in vivo and ex vivo uptake in pancreas, liver, and gut regions, with high GPR119 expression. Cell pretreatment with nonradioactive KSS3, rodent PET imaging, biodistribution, and autoradiography studies showed significant blocking in the pancreas showing [18F]KSS3's high specificity.

Consensus Statement on the definition and classification of metabolic hyperferritinaemia

Hyperferritinaemia is a common laboratory finding that is often associated with metabolic dysfunction and fatty liver. Metabolic hyperferritinaemia reflects alterations in iron metabolism that facilitate iron accumulation in the body and is associated with an increased risk of cardiometabolic and liver diseases. Genetic variants that modulate iron homeostasis and tissue levels of iron are the main determinants of serum levels of ferritin in individuals with metabolic dysfunction, raising the hypothesis that iron accumulation might be implicated in the pathogenesis of insulin resistance and the related organ damage. However, validated criteria for the non-invasive diagnosis of metabolic hyperferritinaemia and the staging of iron overload are still lacking, and there is no clear evidence of a benefit for iron depletion therapy. Here, we provide an overview of the literature on the relationship between hyperferritinaemia and iron accumulation in individuals with metabolic dysfunction, and on the associated clinical outcomes. We propose an updated definition and a provisional staging system for metabolic hyperferritinaemia, which has been agreed on by a multidisciplinary global panel of expert researchers. The goal is to foster studies into the epidemiology, genetics, pathophysiology, clinical relevance and treatment of metabolic hyperferritinaemia, for which we provide suggestions on the main unmet needs, optimal design and clinically relevant outcomes.

Diabetes and liver cancer risk: A stronger effect in Whites than Blacks?

BACKGROUND

Both diabetes and liver cancer are overrepresented among African Americans, but limited information is available on the interrelationship of these two diseases among African Americans. We examined the association of diabetes with the incidence of liver cancer and whether this varied by participant self-reported race/ethnicity.

METHODS

Using the Southern Community Cohort Study, we conducted a cancer follow up (2002-2016) of a cohort of mostly low-income participants aged 40-79 with diabetes (n = 15,879) and without diabetes (n = 59,077) at study baseline. Cox regression was used to compute Hazard Ratios (HR) and 95% CIs for the risk of incident liver cancer.

RESULTS

With 790,132 person years of follow up, 320 incident cases of liver cancer were identified. In analyses controlling for age, sex, race, BMI, current and former smoking, total alcohol consumption, family history of liver cancer, any hepatitis infection, hyperlipidemia and socioeconomic factors, the association between diabetes and risk of liver cancer differed significantly (p_interaction = 0.0001) between participants identifying as Black/African American (AA) or White/European American (EA). Diabetes was associated with 5.3-fold increased cancer risk among EAs (HR 5.4, 95% CI 3.2-9.3) vs an 80% increase (HR 1.8, 95% CI 1.3-2.5) among AAs. Furthermore, controlling for diabetes greatly attenuated the higher risk of liver cancer among AAs; indeed, while the cancer risk among those without diabetes was twice as high among AAs than EAs (HR = 2.0, 95% CI = 1.4-2.9), no excess in AAs was observed among those with diabetes (HR = 0.7, 95% CI = 0.4-1.1).

CONCLUSION

While liver cancer risk in general is greater in AAs than EAs and diabetes increases this risk in both racial/ethnic groups, diabetes appears to impact liver cancer to a much greater extent among EAs. The findings raise the possibility of racially different mechanisms and impacts of diabetes on this often fatal cancer among AAs and EAs.

Metformin Improves Cognition by Reducing Leaky Gut and Benefiting Gut Microbiome–Goblet Cell–Mucin Axis

Older adults are suffering from several aging-related illnesses including cognitive decline and effective strategies to prevent and/or treat them are lacking, because of a poor understanding of therapeutic targets. Low-grade inflammation is a key risk factor of aging-related morbidities and mortalities, and it is often higher in older adults. Although, precise reasons for increased inflammation remain unknown, however, emerging evidence indicates that abnormal (dysbiotic) gut microbiome and dysfunctional gut permeability (leaky gut) are linked with increased inflammation in older adults. However, no drugs are available to treat aging-related microbiome dysbiosis and leaky gut, and little is known about the cellular and molecular processes that can be targeted to reduce leaky gut in older adults. Here, we demonstrated that metformin, a safe FDA approved antidiabetic drug, decreased leaky gut and inflammation in older obese mice, by beneficially modulating the gut microbiota. In addition, metformin increased goblet cell mass and mucin production in the older gut, thereby decreasing leaky gut and inflammation. Mechanistically, metformin increased the goblet cell differentiation markers by suppressing Wnt signaling. Our results suggest that metformin can prevent and treat aging-related leaky gut and inflammation, by beneficially modulating gut microbiome/goblet cell/mucin biology.

Effect of Chronic Hyperglycemia on Glucose Metabolism in Subjects With Normal Glucose Tolerance

Chronic hyperglycemia causes insulin resistance, but the inheritability of glucotoxicity and the underlying mechanisms are unclear. We examined the effect of 3 days of hyperglycemia on glucose disposal, enzyme activities, insulin signaling, and protein O-GlcNAcylation in skeletal muscle of individuals without (FH^-) or with (FH⁺) family history of type 2 diabetes. Twenty-five subjects with normal glucose tolerance received a [3-³H]glucose euglycemic insulin clamp, indirect calorimetry, and vastus-lateralis biopsies before and after 3 days of saline (n = 5) or glucose (n = 10 FH^- and 10 FH⁺) infusion to raise plasma glucose by ∼45 mg/dL. At baseline, FH⁺ had lower insulin-stimulated glucose oxidation and total glucose disposal (TGD) but similar nonoxidative glucose disposal and basal endogenous glucose production (bEGP) compared with FH^- After 3 days of glucose infusion, bEGP and glucose oxidation were markedly increased, whereas nonoxidative glucose disposal and TGD were lower versus baseline, with no differences between FH^- and FH⁺ subjects. Hyperglycemia doubled skeletal muscle glycogen content and impaired activation of glycogen synthase (GS), pyruvate dehydrogenase, and Akt, but protein O-GlcNAcylation was unchanged. Insulin resistance develops to a similar extent in FH^- and FH⁺ subjects after chronic hyperglycemia, without increased protein O-GlcNAcylation. Decreased nonoxidative glucose disposal due to impaired GS activation appears to be the primary deficit in skeletal muscle glucotoxicity.

Hyperglycemia during first-line R-CHOP or dose adjusted R-EPOCH chemotherapy for non-Hodgkin lymphoma is prevalent and associated with chemotherapy alteration - a retrospective study

High-dose glucocorticoids such as prednisone are combined with cytotoxic chemotherapy in the R-CHOP or dose adjusted R-EPOCH regimens used for non-Hodgkin lymphoma (NHL). In this retrospective study, our primary objective was to evaluate the incidence of hyperglycemia during first-line R-CHOP or DA-EPOCH-R. The secondary objectives were to evaluate the incidence of chemotherapy alteration and overall survival in those with and without hyperglycemia. One hundred and sixty patients were eligible. We found that 47% of all patients had at least one hyperglycemic episode and hyperglycemia was associated with chemotherapy alteration (p = .028). Multivariate analysis revealed international prognostic index (IPI) ≥ 3 (p = .045) and chemotherapy alteration (p = .001) were associated with decreased overall survival. We conclude that hyperglycemia is common during first-line NHL treatment with R-CHOP or DA-EPOCH-R, even in the absence of known diabetes and is associated with alterations of chemotherapy. Baseline pre-PET scan fasting blood glucose of 100 mg/dL or higher may predict hyperglycemia during therapy.

Mechanisms Linking Glucose Homeostasis and Iron Metabolism Toward the Onset and Progression of Type 2 Diabetes

OBJECTIVE

The bidirectional relationship between iron metabolism and glucose homeostasis is increasingly recognized. Several pathways of iron metabolism are modified according to systemic glucose levels, whereas insulin action and secretion are influenced by changes in relative iron excess. We aimed to update the possible influence of iron on insulin action and secretion and vice versa.

RESEARCH DESIGN AND METHODS

The mechanisms that link iron metabolism and glucose homeostasis in the main insulin-sensitive tissues and insulin-producing β-cells were revised according to their possible influence on the development of type 2 diabetes (T2D).

RESULTS

The mechanisms leading to dysmetabolic hyperferritinemia and hepatic overload syndrome were diverse, including diet-induced alterations in iron absorption, modulation of gluconeogenesis, heme-mediated disruption of circadian glucose rhythm, impaired hepcidin secretion and action, and reduced copper availability. Glucose metabolism in adipose tissue seems to be affected by both iron deficiency and excess through interaction with adipocyte differentiation, tissue hyperplasia and hypertrophy, release of adipokines, lipid synthesis, and lipolysis. Reduced heme synthesis and dysregulated iron uptake or export could also be contributing factors affecting glucose metabolism in the senescent muscle, whereas exercise is known to affect iron and glucose status. Finally, iron also seems to modulate β-cells and insulin secretion, although this has been scarcely studied.

CONCLUSIONS

Iron is increasingly recognized to influence glucose metabolism at multiple levels. Body iron stores should be considered as a potential target for therapy in subjects with T2D or those at risk for developing T2D. Further research is warranted.

Local release of masitinib alters in vivo implantable continuous glucose sensor performance

Continuous glucose monitoring (CGM) sensors are often advocated as a clinical solution to improve long-term glycemic control in the context of diabetes. Subcutaneous sensor inflammatory response, fouling and fibrous encapsulation resulting from the host foreign body response (FBR) reduce sensor sensitivity to glucose, eventually resulting in sensor performance compromise and device failure. Several combination device strategies load CGM sensors with drug payloads that release locally to tissue sites to mitigate FBR-mediated sensor failure. In this study, the mast cell-targeting tyrosine kinase inhibitor, masitinib, was released from degradable polymer microspheres delivered from the surfaces of FDA-approved human commercial CGM needle-type implanted sensors in a rodent subcutaneous test bed. By targeting the mast cell c-Kit receptor and inhibiting mast cell activation and degranulation, local masitinib penetration around the CGM to several hundred microns sought to reduce sensor fibrosis to extend CGM functional lifetimes in subcutaneous sites. Drug-releasing and control CGM implants were compared in murine percutaneous implant sites for 21 days using direct-wire continuous glucose reporting. Drug-releasing implants exhibited no significant difference in CGM fibrosis at implant sites but showed relatively stable continuous sensor responses over the study period compared to blank microsphere control CGM implants.

The 3T3-L1 adipocyte glycogen proteome

Background

Glycogen is a branched polysaccharide of glucose residues, consisting of α-1-4 glycosidic linkages with α-1-6 branches that together form multi-layered particles ranging in size from 30 nm to 300 nm. Glycogen spatial conformation and intracellular organization are highly regulated processes. Glycogen particles interact with their metabolizing enzymes and are associated with a variety of proteins that intervene in its biology, controlling its structure, particle size and sub-cellular distribution. The function of glycogen in adipose tissue is not well understood but appears to have a pivotal role as a regulatory mechanism informing the cells on substrate availability for triacylglycerol synthesis. To provide new molecular insights into the role of adipocyte glycogen we analyzed the glycogen-associated proteome from differentiated 3T3-L1-adipocytes.

Results

Glycogen particles from 3T3-L1-adipocytes were purified using a series of centrifugation steps followed by specific elution of glycogen bound proteins using α-1,4 glucose oligosaccharides, or maltodextrins, and tandem mass spectrometry. We identified regulatory proteins, 14-3-3 proteins, RACK1 and protein phosphatase 1 glycogen targeting subunit 3D. Evidence was also obtained for a regulated subcellular distribution of the glycogen particle: metabolic and mitochondrial proteins were abundant. Unlike the recently analyzed hepatic glycogen proteome, no endoplasmic proteins were detected, along with the recently described starch-binding domain protein 1. Other regulatory proteins which have previously been described as glycogen-associated proteins were not detected, including laforin, the AMPK beta-subunit and protein targeting to glycogen (PTG).

Conclusions

These data provide new molecular insights into the regulation of glycogen-bound proteins that are associated with the maintenance, organization and localization of the adipocyte glycogen particle.

Nonmodulation as the mechanism for salt sensitivity of blood pressure in individuals with hypertension and type 2 diabetes mellitus

CONTEXT

It is assumed that in individuals with type 2 diabetes mellitus (T2DM), blood pressure sensitivity to salt intake and the frequency of a low renin state are both increased compared with the nondiabetic population. However, studies supporting these assumptions may have been confounded by participant inclusion criteria, and study results may reflect target organ damage.

OBJECTIVE

The objective of this study was to examine in a cohort of T2DM 1) the frequency of salt sensitivity of blood pressure and 2) whether alterations of the renin-angiotensin-aldosterone system (RAAS) contribute to salt sensitivity in this population.

DESIGN, PATIENTS, AND METHODS

Within participants of the HyperPATH cohort, four groups were analyzed: 1) T2DM with hypertension (HTN), n=51; 2) T2DM without HTN, n=30; 3) HTN only, n=451; and 4) normotensive, n=209. Phenotype studies were conducted after participants completed two dietary phases: liberal sodium (200 mmol/d) and low sodium (10 mmol/d) for 7 d each. Participants were admitted overnight to a clinical research center after each diet, and supine measurements of the RAAS before and after a 60-min angiotensin II infusion (3 ng/kg·min) were obtained.

RESULTS

Multivariate regression analysis demonstrated that T2DM status (all individuals with T2DM vs. individuals without T2DM) was not associated with the change in mean arterial pressure between the low and liberal sodium diets after accounting for age, gender, body mass index, race, and baseline blood pressure (T2DM status, P=0.5). Furthermore, two intermediate phenotypes of altered RAAS, low renin, and nonmodulation (NMOD), were associated with salt-sensitive blood pressure but occurred at different frequencies in the T2DM-HTN and HTN groups (low renin, 12% T2DM-HTN vs. 29% HTN; NMOD, 41% T2DM-HTN vs. 27% HTN; P=0.01).

CONCLUSION

The frequency of NMOD in participants with T2DM was significantly higher compared with HTN, suggesting that the salt sensitivity often seen in T2DM is driven by NMOD.

Systemic PPARγ deletion impairs circadian rhythms of behavior and metabolism

Compelling evidence from both human and animal studies suggests a physiological link between the circadian rhythm and metabolism but the underlying mechanism is still incompletely understood. We examined the role of PPARγ, a key regulator of energy metabolism, in the control of physiological and behavioral rhythms by analyzing two strains of whole-body PPARγ null mouse models. Systemic inactivation of PPARγ was generated constitutively by using Mox2-Cre mice (MoxCre/flox) or inducibly by using the tamoxifen system (EsrCre/flox/TM). Circadian variations in oxygen consumption, CO₂ production, food and water intake, locomotor activity, and cardiovascular parameters were all remarkably suppressed in MoxCre/flox mice. A similar phenotype was observed in EsrCre/flox/TM mice, accompanied by impaired rhythmicity of the canonical clock genes in adipose tissues and liver but not skeletal muscles or the kidney. PPARγ inactivation in isolated preadipocytes following exposure to tamoxifen led to a similar blockade of the rhythmicity of the clock gene expression. Together, these results support an essential role of PPARγ in the coordinated control of circadian clocks and metabolic pathways.

Analysis of hepatic glycogen-associated proteins

Glycogen particles are associated with a population of proteins that mediate its biological functions, including: management of glucose flux into and out of the glycogen particle, maintenance of glycogen structure and regulation of particle size, number, and cellular location. A survey of the glycogen-associated proteome would be predicted to identify the relative representation of known members of this population, and associations with unexpected proteins that have the potential to mediate other functions of the glycogen particle. We therefore purified glycogen particles from both mouse and rat liver, using different techniques, and analyzed the resulting tryptic peptides by MS. We also specifically eluted glycogen-binding proteins from the pellet using malto-oligosaccharides. Comparison of the rat and mouse populations, and analysis of specifically eluted proteins allow some conclusions to be made about the hepatic glycogen sub-proteome. With the exception of glycogen branching enzyme all glycogen metabolic proteins were detected. Novel associations were identified, including ferritin and starch-binding domain protein 1, a protein that contains both a transmembrane endoplasmic reticulum signal peptide and a carbohydrate-binding module. This study therefore provides insight into the organization of the glycogen proteome, identifies other associated proteins and provides a starting point to explore the dynamic nature and cellular distribution of this metabolically important protein population.

The role of mPer2 clock gene in glucocorticoid and feeding rhythms

The circadian clock synchronizes the activity level of an organism to the light-dark cycle of the environment. Energy intake, as well as energy metabolism, also has a diurnal rhythm. Although the role of the clock genes in the sleep-wake cycle is well characterized, their role in the generation of the metabolic rhythms is poorly understood. Here, we use mice deficient in the clock protein mPer2 to study how the circadian clock regulates two critical metabolic rhythms: glucocorticoid and food intake rhythms. Our findings indicate that mPer2-/- mice do not have a glucocorticoid rhythm even though the corticosterone response to hypoglycemia, ACTH, and restraint stress is intact. In addition, the diurnal feeding rhythm is absent in mPer2-/- mice. On high-fat diet, they eat as much during the light period as they do during the dark period and develop significant obesity. The diurnal rhythm of neuroendocrine peptide alphaMSH, a major effector of appetite control, is disrupted in the hypothalamus of mPer2-/- mice even though the diurnal rhythm of ACTH, the alphaMSH precursor, is intact. Peripheral injection of alphaMSH, which has been shown to enter the brain, restored the feeding rhythm and induced weight loss in mPer2-/- mice. These findings emphasize the requirement of mPer2 in appetite control during the inactive period and the potential role of peripherally administered alphaMSH in restoring night-day eating pattern in individuals with circadian eating disorders such as night-eating syndrome, which is also associated with obesity.

Thermocompression bonding of vertically aligned carbon nanotube turfs to metalized substrates

Vertically aligned carbon nanotube turfs (VACNTs), consisting of entwined, nominally vertical carbon nanotubes, are being proposed for use as electrical and thermal contact materials. Issues in their implementation include high contact resistance, the van der Waals interactions of carbon nanotubes, and a low temperature limit during processing. One route for circumventing the 750 degrees C temperatures required for VACNT growth using chemical vapor deposition is for the VACNTs to be grown separately, and then transferred to the device. A method of mechanical transfer, using thermocompression bonding, has been developed, allowing dry mechanical transfer of the VACNTs at 150 degrees C. This method can be used for the construction of both a thermal switch or a permanent conducting channel. The conductivity of the bonded structure is shown to be independent of the imposed strain, up to strains in excess of 100%.

Saturated fatty acids inhibit hepatic insulin action by modulating insulin receptor expression and post-receptor signalling

Free fatty acids (FFAs) are proposed to play a pathogenic role in both peripheral and hepatic insulin resistance. We have examined the effect of saturated FFA on insulin signalling (100 nM) in two hepatocyte cell lines. Fao hepatoma cells were treated with physiological concentrations of sodium palmitate (0.25 mM) (16:0) for 0.25-48 h. Palmitate decreased insulin receptor (IR) protein and mRNA expression in a dose- and time-dependent manner (35% decrease at 12 h). Palmitate also reduced insulin-stimulated IR and IRS-2 tyrosine phosphorylation, IRS-2-associated PI 3-kinase activity, and phosphorylation of Akt, p70 S6 kinase, GSK-3 and FOXO1A. Palmitate also inhibited insulin action in hepatocytes derived from wild-type IR (+/+) mice, but was ineffective in IR-deficient (-/-) cells. The effects of palmitate were reversed by triacsin C, an inhibitor of fatty acyl CoA synthases, indicating that palmitoyl CoA ester formation is critical. Neither the non-metabolized bromopalmitate alone nor the medium chain fatty acid octanoate (8:0) produced similar effects. However, the CPT-1 inhibitor (+/-)-etomoxir and bromopalmitate (in molar excess) reversed the effects of palmitate. Thus, the inhibition of insulin signalling by palmitate in hepatoma cells is dependent upon oxidation of fatty acyl-CoA species and requires intact insulin receptor expression.

The coordinated buckling of carbon nanotube turfs under uniform compression

Complex structures consisting of intertwined, nominally vertical carbon nanotubes (CNTs), referred to as turfs, have unique properties that arise from their complex nanogeometry and interactions between individual CNT segments. For applications such as contact switches for electrical or thermal transfer it is necessary to understand the properties that arise from the collective behavior of an assemblage of CNTs rather than the properties of a single tube. In this study, the mechanical response of turfs bonded to substrates under compressive loading is demonstrated experimentally; coordinated alignment and buckling takes place under uniform loads. The mechanical response of turf structures provides some surprising results regarding parameters that control permanent deformation and buckling in assemblages of nanostructures; buckling of the turf structure is controlled by the height and effective modulus of the turf, but not the aspect ratio of the structure. We present and verify a model which describes the coordinated buckling phenomena relevant for applications such as CNT turfs for thermal transfer media.

Hyperglycemia and Inhibition of Glycogen Synthase in Streptozotocin-treated Mice

Glycogen synthase is post-translationally modified by both phosphate and O-linked N-acetylglucosamine (O-GlcNAc). In 3T3-L1 adipocytes exposed to high concentrations of glucose, O-GlcNAc contributes to insulin resistance of glycogen synthase. We sought to determine whether O-GlcNAc also regulates glycogen synthase in vivo. Glycogen synthase activity in fat pad extracts was inhibited in streptozotocin (STZ)-treated diabetic mice. The half-maximal activation concentration for glucose 6-phosphate (A(0.5)) was increased to 830 +/- 120 microm compared with 240 +/- 20 microm in control mice (C, p < 0.01), while the basal glycogen synthase activity (%I-form) was decreased to 2.4 +/- 1.4% compared with 10.1 +/- 1.8% in controls (p < 0.01). Glycogen synthase activity remained inhibited after compensatory insulin treatment. After insulin treatment kinetic parameters of glycogen synthase were more closely correlated with blood glucose (A(0.5), r(2) = 0.70; %I-form, r(2) = 0.59) than insulin levels (A(0.5), r(2) = 0.04; %I-form, r(2) = 0.09). Hyperglycemia also resulted in an increase in the level of O-GlcNAc on glycogen synthase (16.1 +/- 1.8 compared with 7.0 +/- 0.9 arbitrary intensity units for controls, p < 0.01), even though the level of phosphorylation was identical in diabetic and control mice either with (STZ: 2.9 +/- 1.0 and C: 3.2 +/- 0.8) or without (STZ: 12.2 +/- 2.8 and C: 13.8 +/- 3.0 arbitrary intensity units) insulin treatment. In all mice the percent activation of glycogen synthase that could be achieved in vitro by recombinant protein phosphatase 1 (230 +/- 30%) was significantly greater in the presence of beta-d-N-acetylglucosaminidase (410 +/- 60%, p < 0.01). This synergistic stimulation of glycogen synthase due to codigestion by protein phosphatase 1 and beta-d-N-acetylglucosaminidase was more pronounced in STZ-diabetic mice (310 +/- 70%) compared with control mice (100 +/- 10%, p < 0.05). The findings demonstrate that O-GlcNAc has a role in the regulation of glycogen synthase both in normoglycemia and diabetes.

Observation of radiation-specific damage in human cells exposed to depleted uranium: dicentric frequency and neoplastic transformation as endpoints

Depleted uranium (DU) is a dense heavy metal used primarily in military applications. Published data from our laboratory have demonstrated that DU exposure in vitro to immortalised human osteoblast cells (HOS) is both neoplastically transforming and genotoxic. DU possesses both a radiological (alpha-particle) and chemical (metal) component. Since DU has a low specific activity in comparison to natural uranium, it is not considered to be a significant radiological hazard. The potential contribution of radiation to DU-induced biological effects is unknown and the involvement of radiation in DU-induced biological effects could have significant implications for current risk estimates for internalised DU exposure. Two approaches were used to address this question. The frequency of dicentrics was measured in HOS cells following DU exposure in vitro. Data demonstrated that DU exposure (50 microM, 24 h) induced a significant elevation in dicentric frequency in vitro in contrast to incubation with the heavy metals, nickel and tungsten which did not increase dicentric frequency above background levels. Using the same concentration (50 microM) of three uranyl nitrate compounds that have different uranium isotopic concentrations and therefore, different specific activities, the effect on neoplastic transformation in vitro was examined. HOS cells were exposed to one of three-uranyl nitrate compounds (238U-uranyl nitrate, specific activity 0.33 microCi.g-1; DU-uranyl nitrate, specific activity 0.44 microCi.g-1; and 235U-uranyl nitrate, specific activity 2.2 microCi.g-1) delivered at a concentration of 50 microM for 24 h. Results showed, at equal uranium concentration, there was a specific activity dependent increase in neoplastic transformation frequency. Taken together these data suggest that radiation can play a role in DU-induced biological effects in vitro.

Suppression of depleted uranium-induced neoplastic transformation of human cells by the phenyl fatty acid, phenyl acetate: chemoprevention by targeting the p21RAS protein pathway

Depleted uranium is a dense heavy metal used primarily in military applications. Published data from our laboratory have demonstrated that exposure to depleted uranium in vitro can transform immortalized human osteoblast (HOS) cells to the tumorigenic phenotype (associated with aberrant RAS oncogene expression and tumor suppressor protein production). Since depleted uranium is used in military applications, it would therefore be beneficial to identify and test potential antitumor-promoting agents. Chemopreventive interventions that target deregulated signal transduction pathways may be effective strategies to prevent carcinogenesis. Since the RAS protein plays a key role in signal transduction, disruption of its signaling pathway may be particularly effective. The phenyl fatty acid, phenyl acetate, a differentiation inducer that affects post-translational processing of RAS, was tested for its ability to prevent depleted uranium-induced neoplastic transformation using HOS cells. After a 24-h exposure to insoluble depleted uranium-uranium dioxide (1 mg/ml), cells were incubated for 1 day to 6 weeks with 2.5 mM phenyl acetate. Treatment with depleted uranium resulted in transformation to the tumorigenic phenotype. In contrast, HOS cells exposed to depleted uranium and then treated with phenyl acetate did not exhibit transformation to the tumorigenic phenotype. These data suggest that depleted uranium-induced neoplastic transformation in vitro can be prevented by targeting the RAS protein.

Effects of glucosamine infusion on insulin secretion and insulin action in humans

Glucose toxicity (i.e., glucose-induced reduction in insulin secretion and action) may be mediated by an increased flux through the hexosamine-phosphate pathway. Glucosamine (GlcN) is widely used to accelerate the hexosamine pathway flux, independently of glucose. We tested the hypothesis that GlcN can affect insulin secretion and/or action in humans. In 10 healthy subjects, we sequentially performed an intravenous glucose (plus [2-3H]glucose) tolerance test (IVGTT) and a euglycemic insulin clamp during either a saline infusion or a low (1.6 micromol x min(-1) x kg(-1)) or high (5 micromol x min(-1) x kg(-1) [n = 5]) GlcN infusion. Beta-cell secretion, insulin (SI*-IVGTT), and glucose (SG*) action on glucose utilization during the IVGTT were measured according to minimal models of insulin secretion and action. Infusion of GlcN did not affect readily releasable insulin levels, glucose-stimulated insulin secretion (GSIS), or the time constant of secretion, but it increased both the glucose threshold of GSIS (delta approximately 0.5-0.8 mmol/l, P < 0.03-0.01) and plasma fasting glucose levels (delta approximately 0.3-0.5 mmol/l, P < 0.05-0.02). GlcN did not change glucose utilization or intracellular metabolism (glucose oxidation and glucose storage were measured by indirect calorimetry) during the clamp. However, high levels of GlcN caused a decrease in SI*-IVGTT (delta approximately 30%, P < 0.02) and in SG* (delta approximately 40%, P < 0.05). Thus, in humans, acute GlcN infusion recapitulates some metabolic features of human diabetes. It remains to be determined whether acceleration of the hexosamine pathway can cause insulin resistance at euglycemia in humans.

Effects of insulin on prenylation as a mechanism of potentially detrimental influence of hyperinsulinemia

To investigate the cause and effect relationship between hyperinsulinemia and the increased amounts of farnesylated p21Ras, we performed hyperinsulinemic euglycemic clamps in normal weight volunteers as well as in normal mice and dogs. Insulin infusions significantly raised the amounts of farnesylated p21Ras in the white blood cells of humans, in liver samples of mice and dogs, and in aorta samples of mice. Obese hyperinsulinemic individuals and dogs (made hyperinsulinemic by surgical diversion of the pancreatic outflow from the portal vein into the vena cava) displayed increased amounts of farnesylated p21Ras before the hyperinsulinemic clamps. Infusions of insulin did not alter the already increased levels of farnesylated p21Ras in these experimental models. To further investigate the role of acquired insulin resistance in modulating insulin's effect on p21Ras prenylation, we induced insulin resistance in rats by glucosamine infusion. Insulin-resistant glucosamine-treated animals displayed significantly increased farnesylated p21Ras in response to insulin infusion compared to that in control saline-treated animals. Transgenic models of insulin resistance (heterozygous insulin receptor substrate-1 knockout mice, A-ZIP/F-1 fatless mice, and animals overexpressing glutamine:fructose-6-phosphate amidotransferase) contained increased amounts of farnesylated p21Ras. We conclude that hyperinsulinemia, either endogenous (a prominent feature of insulin resistance) or produced by infusions of insulin, increases the amounts of farnesylated p21Ras in humans, mice, and dogs. This aspect of insulin action may represent one facet of the molecular mechanism of the potentially detrimental influence of hyperinsulinemia.

Insulin and glucosamine infusions increase O-linked N-acetyl-glucosamine in skeletal muscle proteins in vivo

O-linked N-acetylglucosamine (O-GlcNAc) is an abundant posttranslational modification of serine/threonine residues of nuclear and cytoplasmic proteins. We determined whether insulin or coinfusion of glucosamine (GlcN) with insulin alters O-GlcNAc of skeletal muscle proteins. Three groups of conscious fasted rats received 6-hour infusions of either saline (BAS), insulin 18 mU/kg.min and saline (INS), or insulin and GlcN 30 micromol/kg.min (GLCN) during maintenance of normoglycemia. At 6 hours, the concentrations of muscle UDP-GlcNAc, UDP-N-acetylgalactosamine (UDP-GalNAc), UDP-glucose (UDP-Glc), UDP-galactose (UDP-Gal), glycogen, and N and O-linked GlcNAc (galactosyltransferase labeling followed by beta elimination) were measured in freeze-clamped abdominis muscle. Insulin increased whole-body glucose uptake from 49 +/- 5 to 239 +/- 8 micromol/kg.min (P < .001) and glycogen in abdominis muscle from 138 +/- 11 to 370 +/- 26 mmol/kg dry weight (P < .001). Insulin increased the amount of cytosolic N - and O-linked GlcNAc by 56% from 362 +/- 30 to 564 +/- 45 dpm/microg protein . 100 min (P < .02), and O-GlcNAc from 221 +/- 16 to 339 +/- 27 dpm/microg . 100 min (P < .02). Glycogen content was positively correlated with the amount of total (r = .90, P < .005) and O-linked GlcNAc in insulin-infused animals. Coinfusion of GlcN with insulin increased muscle UDP-GlcNAc about fourfold (100 +/- 6 nmol/g) compared with insulin (27 +/- 1, P < .001) or saline (25 +/- 1, P < .001) infusion. GlcN also decreased glucose uptake over 6 hours by 30% to 168 +/- 8 micromol/kg . min (P < .001 for GLCN v INS) and muscle glycogen to 292 +/- 24 mmol/kg dry weight (P < .05 for GLCN v INS). Both total (635 +/- 60 dpm/microg . 100 min, P < .002) and O-linked GlcNAc (375 +/- 36 dpm/microg . 100 min, P < .002) in the cytosol were significantly higher in GLCN rats (635 +/- 60 dpm/microg) versus BAS rats (P < .002). As in INS rats, muscle glycogen and O-GlcNAc were positively correlated in GLCN rats (r = .54, P < .05). Variation in total and O-linked GlcNAc in GLCN rats was due both to GlcN (P < .02) and to variation in the glycogen content (P < .005).

Activation of the hexosamine pathway by glucosamine in vivo induces insulin resistance in multiple insulin sensitive tissues

We determined the effect of infusion of glucosamine (GlcN), which bypasses the rate limiting reaction in the hexosamine pathway, on insulin-stimulated rates of glucose uptake and glycogen synthesis in vivo in rat tissues varying with respect to their glutamine:fructose-6-phosphate amidotransferase (GFA) activity. Three groups of conscious fasted rats received 6-h infusions of either saline (BAS), insulin (18 mU/kg x min) and saline (INS), or insulin and GlcN (30 micromol/ kg x min, GLCN). [3-(3)H]glucose was infused to trace whole body glucose kinetics and glycogen synthesis, and rates of tissue glucose uptake were determined using a bolus injection of [1-(14)C]2-deoxyglucose at 315 min. GlcN decreased insulin-stimulated glucose uptake (315-360 min) by 49% (P < 0.001) at the level of the whole body, and by 31-53% (P < 0.05 or less) in the heart, epididymal fat, submandibular gland and in soleus, abdominis and gastrocnemius muscles. GlcN completely abolished glycogen synthesis in the liver. GlcN decreased insulin-stimulated glucose uptake similarly in the submandibular gland (1.3 +/- 0.2 vs. 2.0 +/- 0.3 nmol/mg protein x min, GLCN vs. INS, P < 0.05) and gastrocnemius muscle (1.4 +/- 0.3 vs. 3.1 +/- 0.5 nmol/mg protein x min), although the activity of the hexosamine pathway, as judged from basal GFA activity, was 10-fold higher in the submandibular gland (286 +/- 35 pmol/mg protein x min) than in gastrocnemius muscle (27 +/- 3 pmol/mg protein x min, P < 0.001). These data raise the possibility that overactivity of the hexosamine pathway may contribute to glucose toxicity not only in skeletal muscle but also in other insulin sensitive tissues. They also imply that the magnitude of insulin resistance induced between tissues is determined by factors other than GFA.

UDP-N-acetylglucosamine transferase and glutamine: fructose 6-phosphate amidotransferase activities in insulin-sensitive tissues

Glutamine:fructose 6-phosphate amidotransferase (GFA) is rate-limiting for hexosamine biosynthesis, while a UDP-GlcNAc beta-N-acetylglucosaminyltransferase (O-GlcNAc transferase) catalyses final O-linked attachment of GlcNAc to serine and threonine residues on intracellular proteins. Increased activity of the hexosamine pathway is a putative mediator of glucose-induced insulin resistance but the mechanisms are unclear. We determined whether O-GlcNAc transferase is found in insulin-sensitive tissues and compared its activity to that of GFA in rat tissues. We also determined whether non-insulin-dependent diabetes mellitus (NIDDM) or acute hyperinsulinaemia alters O-GlcNAc transferase activity in human skeletal muscle. O-GlcNAc transferase was measured using 3H-UDP-GlcNAc and a synthetic cationic peptide substrate containing serine and threonine residues, and GFA was determined by measuring a fluorescent derivative of GlcN6P by HPLC. O-GlcNAc transferase activities were 2-4 fold higher in skeletal muscles and the heart than in the liver, which had the lowest activity, while GFA activity was 14-36-fold higher in submandibular gland and 5-18 fold higher in the liver than in skeletal muscles or the heart. In patients with NIDDM (n = 11), basal O-GlcNAc transferase in skeletal muscle averaged 3.8 +/- 0.3 nmol/mg.min, which was not different from that in normal subjects (3.3 +/- 0.4 nmol/mg.min). A 180-min intravenous insulin infusion (40 mU/m2.min) did not change muscle O-GlcNAc transferase activity in either group. We conclude that O-GlcNAc transferase is widely distributed in insulin-sensitive tissues in the rat and is also found in human skeletal muscle. These findings suggest the possibility that O-linked glycosylation of intracellular proteins is involved in mediating glucose toxicity. O-GlcNAc transferase does not, however, appear to be regulated by either NIDDM or acute hyperinsulinaemia, suggesting that mass action effects determine the extent of O-linked glycosylation under hyperglycaemic conditions.

Increased glutamine:fructose-6-phosphate amidotransferase activity in skeletal muscle of patients with NIDDM

Overactivity of the hexosamine pathway mediates glucose-induced insulin resistance in rat adipocytes. Glutamine:fructose-6-phosphate amidotransferase (GFA) is the rate-limiting enzyme of this pathway. We determined GFA activity in human skeletal muscle biopsies and rates of insulin-stimulated whole-body, oxidative, and nonoxidative glucose disposal using the euglycemic insulin clamp technique combined with indirect calorimetry (insulin infusion rate (1.5 mU x kg-1 x min-1)) in 12 male patients with NIDDM (age 54 +/- 2 years, BMI 27.5 +/- 0.9 kg/m2, fasting plasma glucose 8.5 +/- 0.6 mmol/l) and 9 matched normal men. GFA activity was detectable in human skeletal muscles and completely inhibited by uridine-5'-diphospho-N-acetylglucosamine (UDP-GlcNAc) in all subjects. GFA activity was 46% increased in the NIDDM patients compared with the normal subjects (9.5 +/- 1.3 vs. 6.5 +/- 1.2 pmol, P < 0.05). Whole-body glucose uptake was 58% decreased in patients with NIDDM (20 +/- 3 micromol x kg body wt-1 x min-1) compared with normal subjects (47 +/- 4 micromol x kg body wt-1 x min-1, P < 0.001). This decrease was attributable to decreases in both glucose oxidation (9 +/- 1 vs. 15 +/- 1 micromol x kg-1 x min-1, NIDDM patients vs. control subjects, P < 0.002) and nonoxidative glucose disposal (11 +/- 2 vs. 31 +/- 4 micromol x kg-1 x min-1, P < 0.001). In patients with NIDDM, both HbA1c (r= 0.51, P < 0.05) and BMI (r= -0.57, P < 0.05) correlated with whole-body glucose uptake. HbA1c but not BMI or insulin sensitivity was correlated with basal GFA activity (r = -0.57,P < 0.01) in NIDDM patients and control subjects. We conclude that GFA is found in human skeletal muscle and that all this activity is sensitive to feedback inhibition by UDP-GlcNAc. Chronic hyperglycemia is associated with an increase in skeletal muscle GFA activity, suggesting that increased activity of the hexosamine pathway may contribute to glucose toxicity and insulin resistance in humans.

Insulin receptor kinase activation releases a constraint maintaining the receptor on microvilli

To examine whether the surface redistribution of the insulin receptor from microvilli, where it sits in its unoccupied form, to the nonvillous domain, where it is internalized through clathrin-coated pits, is an active movement or a passive redistribution linked to the release of a restraint maintaining it on microvilli, we have generated a mutated insulin receptor with a truncation of exons 17-22 and tracked it biochemically and morphologically. Biochemical analysis indicates that this mutated receptor is constitutively internalized and recycled even in the absence of ligand. Quantitative electron microscope autoradiography analysis reveals that it does not preferentially associate with microvilli in its unoccupied form but is normally segregated in clathrin-coated pits through the preserved signal sequence(s) of exon 16. We conclude that (a) insulin receptor internalization initiated through receptor kinase activation and autophosphorylation, which free the receptor from constraints maintaining it on microvilli; (b) the signal sequences contained in exon 16 are entirely sufficient to promote clathrin-coated pit-mediated internalization of insulin receptors; (c) these sequences are not uncovered by kinase activation; and (d) the "code" maintaining the unoccupied receptors on microvilli is contained within exons 17-21 of the receptor.

Definition of the complete Schistosoma mansoni hemoglobinase mRNA sequence and gene expression in developing parasites

Schistosoma mansoni uses a variety of proteases termed hemoglobinases to obtain nutrition from host globin. Previous reports have characterized cDNAs encoding 1 of these enzymes. However, these sequences did not define the primary structures of the mRNA and protein. The complete sequence of the 1390 base mRNA has now been determined. It encodes a 50 kDa primary translation product. In vitro translations coupled with immunoprecipitations and Western blots of parasite lysates allowed visualization of the 50 kDa form. Production of the 31 kDa mature hemoglobinase from the 50 kDa species involves removal of both NH2 and COOH terminal residues from the primary translation product. Expression of hemoglobinase mRNA and protein was examined during larval parasite development. Low levels were observed in young schistosomula. After 6-9 days in culture, high hemoglobinase levels were seen which correlated with the onset of red blood cell feeding. Immunoelectron microscopy was employed to examine hemoglobinase location and function. In adult worms the enzyme was associated with the gut lumen and gut epithelium. In cercariae, the protease was observed in the head gland, suggesting new roles for the protease.

18 S rRNA degradation is not accompanied by altered rRNA transport at early times following irradiation of HeLa cells

The effect of ionizing radiation (137Cs) on processing and transport of ribosomal RNA (rRNA) was studied by pulse-labeling HeLa S3 cells with [3H]uridine immediately prior to irradiation. This approach permits kinetic analysis of processing of 45 S rRNA (radiolabeled predominantly prior to irradiation) into its 28 S and 18 S rRNA daughter species following irradiation. By this technique, we have recently demonstrated an increase in the normal 28 S:18 S rRNA stoichiometric ratio of 1:1 to as high as 1.6:1 during the interval 5 to 20 h following irradiation of HeLa cells at greater than or equal to 7.5 Gy. Alterations in 28 S:18 S ratio were evaluated in greater detail at early times following irradiation, up to 2 h. The 28 S:18 S ratio was found to be maximal at 1 h after radiation, at about 2:1, following 5 or 10 Gy. Using a method for rapid separation of nucleus from cytoplasm, transport of rRNA from nucleus to cytoplasm was also evaluated during this period. Despite an increase in the rate of 45 S rRNA processing, as well as an increased 28 S:18 S ratio, no alterations in transport from nucleus to cytoplasm were detected. This lack of transport alteration suggests that accumulation of excess 28 S rRNA is restricted to the nucleus, where it may represent an early step in the process of radiation-induced cell killing.

18 S ribosomal RNA is degraded during ribosome maturation in irradiated HeLa cells

The effects of ionizing radiation (137Cs) on processing of ribosomal RNA (rRNA) were studied by pulse-labeling HeLa S3 cells with [3H]uridine immediately prior to irradiation. The 45 S rRNA precursor, and its two major daughter species, 28 and 18 S rRNA, were separated by gel electrophoresis and the extent of radiolabel incorporation into each was determined at various times after irradiation. This approach permitted kinetic analysis of processing of the 45 S rRNA which had been predominantly synthesized (radiolabeled) prior to irradiation. Since they both derive from the same 45 S pre-rRNA transcript, 28 and 18 S rRNA are produced with a stoichiometry of 1:1, as observed in control cells in the present studies. However, within 1 h following 10 Gy an altered stoichiometry of 28 S:18 S rRNA was apparent, reaching 1.6:1 by 5-7 h following irradiation. This alteration was also observed following the higher dose of 20 Gy, but not following exposures of 5 Gy or less. The 18 S portion of the 45 S pre-rRNA is transcribed prior to the 28 S portion. Consequently, an increase in the 28 S/18 S ratio can only be due to degradation of the 18 S species during or after processing. This alteration may represent a response to radiation-induced growth arrest, by reducing the number of newly synthesized ribosomes that would otherwise be required for cell propagation.

Effects of insulin and insulin-like growth factor I on growth of human leukemia cells in serum-free and protein-free medium

Human myeloid leukemia cells (HL60) and malignant lymphocytes (Namalwa) were grown in protein-free, Fe-supplemented media and used to study growth responses to insulin and insulin-like growth factor 1 (IGF-I). HL60 cells previously grown in serum-free medium containing microgram quantities of insulin showed an 18-fold reduction in cumulative cell production when grown without insulin. However, the same cells showed reduced or absent growth stimulation with 1 to 100 ng/mL insulin or IGF-I for at least four days following insulin deprivation, indicating that culture conditions modified insulin and IGF-I responses. When the same cells were grown in Fe-supplemented, protein-free medium (RPMI-Fe), insulin and IGF-I caused dose-dependent stimulation of HL60 cell growth with half-maximal stimulation at nanogram concentrations. Namalwa cells grown in protein-free medium showed no response to either hormone. Radioligand binding showed the presence of insulin and IGF-I receptors on both HL60 and Namalwa cells grown in RPMI-Fe. HL60 cells grown in fetal bovine serum had higher, and cells grown with microgram quantities of insulin dramatically reduced, insulin binding. Competitive binding studies and cultures with anti-IGF-I receptor antibody showed insulin and IGF-I stimulated growth through their respective specific receptors. Both insulin and IGF-I stimulate growth of some cultured human leukemia cells, but the presence of insulin or IGF-I receptors alone does not predict growth responses. Culture conditions affect both cellular responses and ligand binding by these hormones and must be closely controlled to study growth responses.

Development of USDA-FSIS method for isolation of Listeria monocytogenes from raw meat and poultry

A method was developed specifically to detect naturally occurring Listeria monocytogenes in meat because the traditional cold enrichment procedure was extremely slow and other procedures were ineffective. This method could identify beta-hemolytic Listeria colonies in 3-4 days. The use of a 2-stage enrichment, highly selective LPM agar, and a thin-layer horse blood agar plate for the detection of beta-hemolytic Listeria isolates are the important steps of this method. L. monocytogenes was recovered from 20 of 41 samples of frozen ground beef, 12 of 23 samples of pork sausage, and 7 of 22 samples of poultry. These results indicate that L. monocytogenes is common in raw meat and that this method is effective for its recovery.

Improved Listeria monocytogenes selective agar

By increasing the LiCl concentration to 5 g/liter and adding 20 mg of moxalactam per liter to modified McBride agar base, it was possible to inhibit the growth of many bacteria which interfered with the recovery of Listeria monocytogenes from beef.

A note on the use of 3-section plates for the estimation of the numbers of bacteria and to obtain isolated colonies in 1 day

By streaking with an open loop and then swabbing a 4-5 cm2 area on 3-section agar plates, it is possible to obtain isolated colonies and to estimate bacterial densities from 100 to 10(7)/ml on the swabbed area.

The microbiology of raw, eviscerated chickens: a ten year comparison

In 1979 a survey of selected chicken eviscerating plants was conducted to determine the levels of coliforms, Escherichia coli, and Salmonellae sp. on eviscerated chickens under current manufacturing practices. A comparison was made of the data from this survey and one conducted in 1969. The 1979 survey found that the chickens did not have a statistically significant reduced incidence of salmonella compared to chickens analyzed in 1969. Also, much of the bacterial contamination on a carcass at the end of the evisceration line was transient and was readily removed by the final spray washer. The addition of chlorine to chiller water did not appear to have an unusually beneficial effect on the microbiological quality of the chickens. In 1969, in the nine plants studied, the incidence of salmonella on chickens at the exit of the chillers was 20.5%. In 1979, in the nine plants studied, the incidence of salmonella on chickens at the exit of the chillers was 11.6%. In 1979 there was about a 45% reduction in the incidence of salmonella in eviscerated chickens in the nine plants studied compared to the incidence of salmonella in eviscerated chickens in 1969.

Two modified selenite media for the recovery of Yersinia enterocolitica from meats

Yersinia enterocolitica is one of the few human pathogens that grows at the proper food refrigeration temperatures of 0 to 5 degrees C. Although the isolation of environmental biotypes of Y. enterocolitica from many types of food and water has been reported in the literature, the recovery of the sensitive strains inoculated into foods has been slow and uncertain. Rapid recovery of several clinical strains inoculated into meats was accomplished by using two modified selenite broths without added nutrients. It was critical to restrict the sample size of the blended meat suspension at the 0.2-g/100 ml level, thereby restricting the growth of the total bacterial population in the selenite enrichment media. Otherwise, the slower growing Y. enterocolitica would be overwhelmed by the faster growing normal bacterial flora from the meat. Both the resistant serotype O:3 and the sensitive O:8 clinical isolates of Y. enterocolitica were recovered from the modified selenite enrichment media after 2 and 3 days of incubation at 22 degrees C.