ABSTRACT
Regulation of neuroinflammation is critical for maintaining central nervous system (CNS) homeostasis and holds therapeutic promise in autoimmune diseases such as multiple sclerosis (MS). Previous studies have highlighted the significance of selective innate signaling in triggering anti-inflammatory mechanisms, which play a protective role in an MS-like disease, experimental autoimmune encephalomyelitis (EAE). However, the individual intra-CNS administration of specific innate receptor ligands or agonists, such as for toll-like receptor 7 (TLR7) and nucleotide-binding oligomerization-domain-containing protein 2 (NOD2), failed to elicit the desired anti-inflammatory response in EAE. In this study, we investigated the potential synergistic effect of targeting both TLR7 and NOD2 simultaneously to prevent EAE progression. Our findings demonstrate that simultaneous intrathecal administration of NOD2- and TLR7-agonists led to synergistic induction of Type I IFN (IFN I) and effectively suppressed EAE in an IFN I-dependent manner. Suppression of EAE was correlated with a significant decrease in the infiltration of monocytes, granulocytes, and natural killer cells, reduced demyelination, and downregulation of IL-1ß, CCL2, and IFNγ gene expression in the spinal cord. These results underscore the therapeutic promise of concurrently targeting the TLR7 and NOD2 pathways in alleviating neuroinflammation associated with MS, paving the way for novel and more efficacious treatment strategies.
Subject(s)
Encephalomyelitis, Autoimmune, Experimental , Multiple Sclerosis , Nod2 Signaling Adaptor Protein , Toll-Like Receptor 7 , Animals , Toll-Like Receptor 7/metabolism , Toll-Like Receptor 7/agonists , Nod2 Signaling Adaptor Protein/metabolism , Nod2 Signaling Adaptor Protein/genetics , Encephalomyelitis, Autoimmune, Experimental/drug therapy , Encephalomyelitis, Autoimmune, Experimental/metabolism , Encephalomyelitis, Autoimmune, Experimental/immunology , Encephalomyelitis, Autoimmune, Experimental/pathology , Multiple Sclerosis/drug therapy , Multiple Sclerosis/metabolism , Mice , Mice, Inbred C57BL , Immunity, Innate/drug effects , Female , Spinal Cord/metabolism , Spinal Cord/pathology , Spinal Cord/drug effects , Membrane Glycoproteins/metabolism , Interferon Type I/metabolism , Signal Transduction/drug effectsABSTRACT
Hepatic encephalopathy (HE) is a brain dysfunction caused by liver insufficiency with symptoms ranging from slight cognitive changes detectable only by neuropsychiatric testing to coma. Up to 60% of patients with cirrhosis have mild forms of HE and 35% will at some point experience overt HE. Even in its milder forms, HE impacts the patient's daily routines, self-sufficiency, quality of life, and, thereby, socio-economic status. HE is a condition affecting the whole household including formal and informal caregivers, who carry a heavy burden. Early identification, prophylaxis, and treatment of HE are essential for relieving patients and informal caregivers.
ABSTRACT
OBJECTIVES: In patients evaluated for hepatocellular carcinoma (HCC), magnetic resonance imaging (MRI) is often used secondarily when multiphase contrast-enhanced computed tomography (ceCT) is inconclusive. We investigated the clinical impact of adding MRI. MATERIALS AND METHODS: This single-institution retrospective study included 48 MRI scans (44 patients) conducted from May 2016 to July 2023 due to suspicion of HCC on a multiphase ceCT scan. Data included medical history, preceding and subsequent imaging, histology when available, and decisions made at multidisciplinary team meetings. RESULTS: In case of possible HCC recurrence, 63% of the MRI scans were diagnostic of HCC. For 80% of the negative MRI scans, the patients were diagnosed with HCC within a median of 165 days in the suspicious area of the liver. In case of possible de-novo HCC in patients with cirrhosis, 22% of the scans were diagnostic of HCC and 33% of the negative MRI scans were of patients diagnosed with HCC within a median of 109 days. None of the non-cirrhotic patients with possible de-novo HCC and negative MRI scans (64%) were later diagnosed with HCC, but 3/5 of the indeterminate scans were of patients diagnosed with HCC in a biopsy. CONCLUSIONS: Secondary MRI to a multiphase ceCT scan suspicious of HCC is highly valuable in ruling out HCC in non-cirrhotic patients and in diagnosing HCC non-invasively in cirrhotic patients and patients with prior HCC. Patients with cirrhosis or prior HCC are still at high risk of having HCC if MRI results are inconclusive or negative.
ABSTRACT
Portal hypertension has cerebral consequences via its causes and complications, namely hepatic encephalopathy (HE), a common and devastating brain disturbance caused by liver insufficiency and portosystemic shunting. The pathogenesis involves hyperammonemia and systemic inflammation. Symptoms are disturbed personality and reduced attention. HE is minimal or grades I to IV (coma). Bouts of HE are episodic and often recurrent. Initial treatment is of events that precipitated the episode and exclusion of nonhepatic causes. Specific anti-HE treatment is lactulose. By recurrence, rifaximin is add-on. Anti-HE treatment is efficacious also for prophylaxis, but emergence of HE marks advanced liver disease and a dismal prognosis.
Subject(s)
Hepatic Encephalopathy , Hypertension, Portal , Lactulose , Hepatic Encephalopathy/etiology , Hepatic Encephalopathy/physiopathology , Humans , Hypertension, Portal/etiology , Hypertension, Portal/complications , Hypertension, Portal/physiopathology , Lactulose/therapeutic use , Rifaximin/therapeutic use , Gastrointestinal Agents/therapeutic use , Hyperammonemia/etiology , Hyperammonemia/complicationsABSTRACT
AIM: Sacral neuromodulation (SNM) is approved for the treatment of faecal incontinence (FI) in a two-stage technique. With standardized implantation, approximately 90% of patients undergo successful Stage I operation and proceed to a permanent implant (Stage II). The aim of this work was to explore the feasibility of SNM as a one-stage procedure and report the 24-week efficacy. METHOD: This study included patients diagnosed with idiopathic FI or FI due to an external anal sphincter defect ≤160° and one or more episodes of FI per week despite maximal conservative therapy. Patients were offered a one-stage procedure if a motor response of the external anal sphincter was achieved in three or more poles with at least one at ≤1.5 mA at lead placement. Patients were followed for 24 weeks. Their evaluation included the Wexner/St Mark's Incontinence Score, Faecal Incontinence Quality of Life score (FIQoL), a visual analogue scale (VAS) for assessing patient satisfaction and a bowel habit diary. RESULTS: Seventy-three patients with a median age of 60 years (interquartile range 50-69 years) completed this prospective study. Episodes of FI were significantly reduced at the 24-week follow-up, from 13 (8-23) at baseline to 2 (0-5) (p-value = 0002). A ≥50% reduction in the number of FI episodes was achieved in 92% of participants. The Wexner score improved significantly from 16 (14-17) at baseline to 9 (5-13) (p-value < 0.001), and the St Mark's score improved significantly from 18 (16-20) to 11 (7-16) (p-value < 0.001). All domains in the FIQoL score and VAS for patient satisfaction improved significantly following the one-stage procedure. CONCLUSION: A one-stage implantation procedure is feasible in selected patients with FI, significantly improving continence, quality of life and patient satisfaction after 24 weeks of follow-up.
Subject(s)
Anal Canal , Electric Stimulation Therapy , Feasibility Studies , Fecal Incontinence , Patient Satisfaction , Quality of Life , Humans , Fecal Incontinence/therapy , Middle Aged , Female , Prospective Studies , Aged , Male , Electric Stimulation Therapy/methods , Electric Stimulation Therapy/instrumentation , Treatment Outcome , Sacrum/innervation , Electrodes, Implanted , Lumbosacral Plexus , Implantable NeurostimulatorsABSTRACT
Many bacteria encode multiple toxin-antitoxin (TA) systems targeting separate, but closely related, cellular functions. The toxin of the Escherichia coli hipBA system, HipA, is a kinase that inhibits translation via phosphorylation of glutamyl-tRNA synthetase. Enteropathogenic E. coli O127:H6 encodes the hipBA-like, tripartite TA system; hipBST, in which the HipT toxin specifically targets the tryptophanyl-tRNA synthetase, TrpS. Notably, in the tripartite system, the function as antitoxin has been taken over by the third protein, HipS, but the molecular details of how activity of HipT is inhibited remain poorly understood. Here, we show that HipBST is structurally different from E. coli HipBA and that the unique HipS protein, which is homologous to the N-terminal subdomain of HipA, inhibits the kinase through insertion of a conserved Trp residue into the active site. We also show how auto-phosphorylation at two conserved sites in the kinase toxin serve different roles and affect the ability of HipS to neutralize HipT. Finally, solution structural studies show how phosphorylation affects overall TA complex flexibility.
Subject(s)
Antitoxins , Escherichia coli Proteins , Toxin-Antitoxin Systems , Escherichia coli/genetics , Escherichia coli/metabolism , Escherichia coli Proteins/metabolism , Toxin-Antitoxin Systems/genetics , Phosphorylation , Antitoxins/metabolismABSTRACT
Anal incontinence affects more than 7% of the population, but it is likely to be underreported due to its sensitive nature. This review summarises the current knowledge of managing this condition. Initial diagnosis and evaluation of anal incontinence, as well as basic conservative treatment, can be managed in primary care. This may include patient education about the nature of the condition, as well as advice about appropriate diet, toilet routine, and lifestyle adjustments. Incontinence due to diarrhoea or constipation may be treated pharmacologically. If necessary, patients should be referred for specialised evaluation and treatment.
Subject(s)
Fecal Incontinence , Humans , Adult , Fecal Incontinence/diagnosis , Fecal Incontinence/therapy , Constipation/diagnosis , Constipation/etiology , Constipation/therapy , Diarrhea , Life Style , Therapeutic IrrigationABSTRACT
BACKGROUND: In recent years, an increasing number of linezolid-resistant enterococci (LRE) was recognized at the German National Reference Centre (NRC) for Enterococci. National guidelines on infection prevention recommend screening for LRE in epidemiologically linked hospital settings without referring to a reliable and rapid diagnostic method. Since 2020, CHROMAgar™ provide a chromogenic linezolid screening agar, LIN-R, suitable to simultaneously screen for linezolid-resistant staphylococci and enterococci. OBJECTIVES: To assess the applicability of CHROMAgar™ LIN-R in clinical settings for detecting LRE directly from patient material and to infer prevalence rates of LRE amongst German hospital patients. METHODS: During the 3-month trial period, clinical samples were plated on CHROMAgar™ LIN-R. Antimicrobial susceptibility testing was performed using VITEK2 or disc diffusion. At the NRC, linezolid resistance was determined by broth microdilution, multiplex-PCR for cfr/optrA/poxtA and by a restriction-based assay for 23S rDNA mutations. RESULTS: The 12 participating study sites used 13â963 CHROMAgar™ LIN-R plates during the study period. Of 442 presumptive LRE, 192 were confirmed by phenotypic methods. Of these, 161 were received by the NRC and 121 (75%) were verified as LRE. Most of LR-E. faecium 53/81 (65%) exhibited a 23S rRNA gene mutation as the sole resistance-mediating mechanism, whereas optrA constituted the dominant resistance trait in LR-E. faecalis [39/40 (98%)]. Prevalence of LRE across sites was estimated as 1% (ranging 0.18%-3.7% between sites). CONCLUSIONS: CHROMAgar™ LIN-R represents a simple and efficient LRE screening tool in hospital settings. A high proportion of false-positive results demands validation of linezolid resistance by a reference method.
Subject(s)
Enterococcus faecium , Gram-Positive Bacterial Infections , Humans , Linezolid/pharmacology , Anti-Bacterial Agents/pharmacology , Prevalence , Drug Resistance, Bacterial/genetics , Enterococcus/genetics , Hospitals , Gram-Positive Bacterial Infections/epidemiology , Enterococcus faecium/genetics , Microbial Sensitivity Tests , Enterococcus faecalisABSTRACT
Second homes are much valued as recreational resources and also as important commodities on the property market. This study examines the trading patterns and regional price development of Danish second homes from 1992 to 2020. Second home sales volumes and prices reflect the general economic booms and busts and also the possibilities to rent out the property on sharing platforms. However, across regional clusters and over time, property price developments suggest a significant social rigidity in preferences and prospects. The investment and financialization logics and the underlying guiding conspicuous consumption behavior has not changed as an effect of the increased demand during the early phases of the COVID-19 pandemic. When controlling for factors such as house and land plot size, building year, location attractiveness the strong social class and spatial rigidity is reproduced in the data. The shifting of wealth accumulated in the second homes between generations supports the same tendency, and taxation does not rebalance regional effects. Accordingly, only to a limited extent does owning a second home contribute to social equality, even if some second-home owners and policy makers tend to think otherwise. Economic measures in planning and governance portfolios are found to be negligible.
ABSTRACT
Control of magnetization and electric polarization is attractive in relation to tailoring materials for data storage and devices such as sensors or antennae. In magnetoelectric materials, these degrees of freedom are closely coupled, allowing polarization to be controlled by a magnetic field, and magnetization by an electric field, but the magnitude of the effect remains a challenge in the case of single-phase magnetoelectrics for applications. We demonstrate that the magnetoelectric properties of the mixed-anisotropy antiferromagnet LiNi1-xFexPO4 are profoundly affected by partial substitution of Ni2+ ions with Fe2+ on the transition metal site. This introduces random site-dependent single-ion anisotropy energies and causes a lowering of the magnetic symmetry of the system. In turn, magnetoelectric couplings that are symmetry-forbidden in the parent compounds, LiNiPO4 and LiFePO4, are unlocked and the dominant coupling is enhanced by almost two orders of magnitude. Our results demonstrate the potential of mixed-anisotropy magnets for tuning magnetoelectric properties.
Subject(s)
Electricity , Magnetic Fields , Anisotropy , MagnetsABSTRACT
tRNAs and ribosomal RNAs are often considered stable RNAs. In contrast to this view, we recently proposed that tRNAs are degraded during amino acid starvation and drug-induced transcription inhibition. However, reevaluation of our experimental approach revealed that common RNA extraction methods suffer from alarming extraction and size biases that can lead to gross underestimation of RNA levels in starved Escherichia coli populations. Quantification of tRNAs suffers additional biases due to differing fractions of tRNAs with base modifications in growing versus starved bacteria. Applying an improved methodology, we measured tRNA levels after starvation for amino acids, glucose, phosphate, or ammonium and transcription inhibition by rifampicin. We report that tRNA levels remain largely unaffected in all tested conditions, including several days of starvation. This confirms that tRNAs are remarkably stable RNAs and serves as a cautionary tale about quantification of RNA from cells cultured outside the steady-state growth regime. rRNA, conversely, is extensively degraded during starvation. Thus, E. coli downregulates the translation machinery in response to starvation by reducing the ribosome pool through rRNA degradation, while a high concentration of tRNAs available to supply amino acids to the remaining ribosomes is maintained. IMPORTANCE We show that E. coli tRNAs are remarkably stable during several days of nutrient starvation, although rRNA is degraded extensively under these conditions. The levels of these two major RNA classes are considered to be strongly coregulated at the level of transcription. We demonstrate that E. coli can control the ratio of tRNAs per ribosome under starvation by means of differential degradation rates. The question of tRNA stability in stressed E. coli cells has become subject to debate. Our in-depth analysis of RNA quantification methods reveals hidden technical pitfalls at every step of the analysis, from RNA extraction to target detection and normalization. Most importantly, starved E. coli populations were more resilient to RNA extraction than unstarved populations. The current results underscore that the seemingly trivial task of quantifying an abundant RNA species is not straightforward for cells cultured outside the exponential growth regime.
Subject(s)
Escherichia coli , RNA, Transfer , Escherichia coli/genetics , Escherichia coli/metabolism , RNA, Transfer/metabolism , Amino Acids/metabolism , Ribosomes/metabolism , RNA, Ribosomal/geneticsABSTRACT
BACKGROUND: Increasing incidence of non-alcoholic fatty liver disease (NAFLD) calls for improved understanding of how the disease affects metabolic liver function. AIMS: To investigate in vivo effects of different NAFLD stages on metabolic liver function, quantified as regional and total capacity for galactose metabolism in a NAFLD model. METHODS: Male Sprague Dawley rats were fed a high-fat, high-cholesterol diet for 1 or 12 weeks, modelling early or late NAFLD, respectively. Each NAFLD group (n = 8 each) had a control group on standard chow (n = 8 each). Metabolic liver function was assessed by 2-[18F]fluoro-2-deoxy-D-galactose positron emission tomography; regional galactose metabolism was assessed as standardised uptake value (SUV). Liver tissue was harvested for histology and fat quantification. RESULTS: Early NAFLD had median 18% fat by liver volume. Late NAFLD had median 32% fat and varying features of non-alcoholic steatohepatitis (NASH). Median SUV reflecting regional galactose metabolism was reduced in early NAFLD (9.8) and more so in late NAFLD (7.4; p = 0.02), both significantly lower than in controls (12.5). In early NAFLD, lower SUV was quantitatively explained by fat infiltration. In late NAFLD, the SUV decrease was beyond that attributable to fat; probably related to structural NASH features. Total capacity for galactose elimination was intact in both groups, which in late NAFLD was attained by increased fat-free liver mass to 21 g, versus 15 g in early NAFLD and controls (both p ≤ 0.002). CONCLUSION: Regional metabolic liver function was compromised in NAFLD by fat infiltration and structural changes. Still, whole liver metabolic function was preserved in late NAFLD by a marked increase in the fat-free liver mass.
Subject(s)
Non-alcoholic Fatty Liver Disease , Animals , Rats , Male , Non-alcoholic Fatty Liver Disease/pathology , Galactose/metabolism , Rats, Sprague-Dawley , Liver/pathology , Diet, High-Fat/adverse effectsABSTRACT
Hepatic encephalopathy (HE) is a frequent and devastating but generally reversible neuropsychiatric complication secondary to chronic and acute liver failure. During HE, brain energy metabolism is markedly reduced and it remains unclear whether this is due to external or internal energy supply limitations, or secondary to depressed neuronal cellular functions - and if so, which mechanisms that are in play. The extent of deteriorated cerebral function correlates to blood ammonia levels but the metabolic link to ammonia is not clear. Early studies suggested that high levels of ammonia inhibited key tricarboxylic acid (TCA) cycle enzymes thus limiting mitochondrial energy production and oxygen consumption; however, later studies by us and others showed that this is not the case in vivo. Here, based on a series of translational studies from our group, we advocate the view that the low cerebral energy metabolism of HE is likely to be caused by neuronal metabolic depression due to an elevated GABAergic tone rather than by restricted energy availability. The increased GABAergic tone seems to be secondary to synthesis of large amounts of glutamine in astrocytes for detoxification of ammonia with the glutamine acting as a precursor for elevated neuronal synthesis of vesicular GABA.
Subject(s)
Hepatic Encephalopathy , Hyperammonemia , Ammonia/metabolism , Brain/metabolism , Energy Metabolism , Glutamine/metabolism , Hepatic Encephalopathy/etiology , Hepatic Encephalopathy/metabolism , Humans , Hyperammonemia/metabolism , Neurons/metabolismABSTRACT
The stationary phase is the general term for the state a bacterial culture reaches when no further increase in cell mass occurs due to exhaustion of nutrients in the growth medium. Depending on the type of nutrient that is first depleted, the metabolic state of the stationary phase cells may vary greatly, and the subsistence strategies that best support cell survival may differ. As ribosomes play a central role in bacterial growth and energy expenditure, ribosome preservation is a key element of such strategies. To investigate the degree of ribosome preservation during long-term starvation, we compared the dynamics of rRNA levels of carbon-starved and phosphorus-starved Escherichia coli cultures for up to 28 days. The starved cultures' contents of full-length 16S and 23S rRNA decreased as the starvation proceeded in both cases, and phosphorus starvation resulted in much more rapid rRNA degradation than carbon starvation. Bacterial survival and regrowth kinetics were also quantified. Upon replenishment of the nutrient in question, carbon-starved cells resumed growth faster than cells starved for phosphate for the equivalent amount of time, and for both conditions, the lag time increased with the starvation time. While these results are in accordance with the hypothesis that cells with a larger ribosome pool recover more readily upon replenishment of nutrients, we also observed that the lag time kept increasing with increasing starvation time, also when the amount of rRNA per viable cell remained constant, highlighting that lag time is not a simple function of ribosome content under long-term starvation conditions. IMPORTANCE The exponential growth of bacterial populations is punctuated by long or short periods of starvation lasting from the point of nutrient exhaustion until nutrients are replenished. To understand the consequences of long-term starvation for Escherichia coli cells, we performed month-long carbon and phosphorus starvation experiments and measured three key phenotypes of the cultures, namely, the survival of the cells, the time needed for them to resume growth after nutrient replenishment, and the levels of intact rRNA preserved in the cultures. The starved cultures' concentration of rRNA dropped with starvation time, as did cell survival, while the lag time needed for regrowth increased. While all three phenotypes were more severely affected during starvation for phosphorus than for carbon, our results demonstrate that neither survival nor lag time is correlated with ribosome content in a straightforward manner.
Subject(s)
Carbon , Phosphates , Carbon/metabolism , Escherichia coli/metabolism , Phosphates/metabolism , Phosphorus/metabolism , RNA, Ribosomal , Ribosomes/metabolismABSTRACT
INTRODUCTION: Cardiovascular disease is the major cause of mortality in non-alcoholic fatty liver disease (NAFLD), a disease affecting one quarter of the world's population. Coagulation imbalance may be a contributing factor but is yet to be convincingly disclosed. AIM: To perform an extensive mapping of the hemostatic system; primary and secondary hemostasis and the fibrinolytic system in non-diabetic NAFLD patients. MATERIALS AND METHODS: Twenty-five non-diabetic, biopsy-proven NAFLD patients [12 simple steatosis; 13 non-alcoholic steatohepatitis (NASH)] investigated by a comprehensive panel of coagulation and fibrinolysis tests in a cross-sectional study. Fifty age- and sex-matched healthy persons served as controls for each of the dynamic analyses: platelet aggregation, thrombin generation, fibrin formation and lysis. Body composition, insulin resistance makers, and liver fat assessed by proton density magnetic resonance imaging were measured in the patients. RESULTS: Fibrinolytic function was impaired in simple steatosis [median 50% clot lysis time 1123 (min-max, 618-1967) s] and NASH [1448 (521-2618) s] compared to healthy controls [403 (184-1179) s] (p < 0.0001). Plasminogen activator inhibitor-1 (PAI-1) increased stepwise above reference interval from simple steatosis [54 (29-80) ng/ml] to NASH patients [109 (65-153) ng/ml; p = 0.03]. Impaired fibrinolysis correlated with hepatic fat fraction and insulin resistance; PAI-1 correlated with obesity and insulin resistance (ρ ≥ 0.42; p ≤ 0.04). Platelet aggregation, coagulation factors, natural anticoagulants, and thrombin generation were comparable to healthy controls and established reference intervals. CONCLUSIONS: NAFLD patients had impaired fibrinolysis without significant prothrombotic changes in coagulation. The impact of this abnormality on the increased cardiovascular risk remains to be investigated.
Subject(s)
Insulin Resistance , Non-alcoholic Fatty Liver Disease , Thrombophilia , Cross-Sectional Studies , Fibrin Clot Lysis Time , Fibrinolysis , Humans , Non-alcoholic Fatty Liver Disease/complications , Plasminogen Activator Inhibitor 1 , Thrombin , Thrombophilia/etiologyABSTRACT
BACKGROUND: Charcot osteoarthropathy of the foot (COA) can currently only be treated using prolonged periods of immobilization of the affected extremity. Therefore, the hypothesis is that COA leads to altered body composition and increased sarcopenia. OBJECTIVE: To investigate the changes over several years in sarcopenia, body composition, and fat distribution in diabetes patients with previous COA compared to diabetes patients without previous COA. METHODS: Prospective observational clinical study. Twenty-one subjects were included and had two DXA scans done with mean 8.6-year intervals to compare changes in lean mass and fat distribution. The lean mass of limbs was used as an estimate of appendicular lean mass (aLM). Fat mass and aLM were then used to detect sarcopenic individuals using different methods. Results and Conclusions. As compared to baseline, both groups had significant loss of lean mass, and diabetics without COA had significant gain of total fat percentage. No statistically different prevalence of sarcopenia between the groups could be established. Likewise, no difference was found in total lean and fat mass changes. None of the groups had statistically significant changes of android fat distribution. As compared with published data on sarcopenia, people with diabetes might be more prone to sarcopenia than healthy individuals.
Subject(s)
Body Composition/physiology , Diabetes Mellitus/physiopathology , Gait Disorders, Neurologic/physiopathology , Sarcopenia/complications , Absorptiometry, Photon/methods , Absorptiometry, Photon/statistics & numerical data , Aged , Diabetes Mellitus/epidemiology , Female , Gait Disorders, Neurologic/complications , Humans , Male , Middle Aged , Sarcopenia/epidemiology , Sarcopenia/physiopathologyABSTRACT
The vast majority of a bacterial population is killed when treated with a lethal concentration of antibiotics. The time scale of this killing is often comparable with the bacterial generation time before the addition of antibiotics. Yet, a small subpopulation typically survives for an extended period. However, the long-term killing dynamics of bacterial cells has not been fully quantified even in well-controlled laboratory conditions. We constructed a week-long killing assay and followed the survival fraction of Escherichia coli K12 exposed to a high concentration of ciprofloxacin. We found that long-term survivors were formed during exponential growth, with some cells surviving at least 7 d. The long-term dynamics contained at least three time scales, which greatly enhances predictions of the population survival time compared with the biphasic extrapolation from the short-term behavior. Furthermore, we observed a long memory effect of a brief starvation pulse, which was dependent on the (p)ppGpp synthase relA Specifically, 1 h of carbon starvation before antibiotics exposure increased the surviving fraction by nearly 100-fold even after 4 d of ciprofloxacin treatment.
Subject(s)
Anti-Bacterial Agents/pharmacology , Escherichia coli/drug effects , Escherichia coli/growth & development , Ciprofloxacin/pharmacology , Dose-Response Relationship, Drug , Escherichia coli Infections/microbiology , Microbial Viability/drug effectsABSTRACT
Protein synthesis is the most energetically costly process in the cell. Consequently, it is a tightly regulated process, and regulation of the resources allocated to the protein synthesis machinery is at the heart of bacterial growth optimization theory. However, the molecular mechanisms that result in dynamic downregulation of protein synthesis in response to nutrient starvation are not well described. Here, we first quantify the Escherichia coli response to phosphate starvation at the level of accumulation rates for protein, RNA and DNA. Escherichia coli maintains a low level of protein synthesis for hours after the removal of phosphate while the RNA contents decrease, primarily as a consequence of ribosomal RNA degradation combined with a reduced RNA synthesis rate. To understand the molecular basis for the low protein synthesis rate of phosphate-starved cells, template mRNA for translation was overproduced in the form of a highly induced long-lived mRNA. Remarkably, starved cells increased the rate of protein synthesis and reduced the rate of ribosomal RNA degradation upon mRNA induction. These observations suggest that protein synthesis in phosphate-starved cells is primarily limited by the availability of template, and does not operate at the maximum capacity of the ribosomes. We suggest that mRNA limitation is an adaptive response to phosphate starvation that prevents the deleterious consequences of overcommitting resources to protein synthesis. Moreover, our results support the model that degradation of ribosomal RNA occurs as a consequence of the availability of idle ribosomal subunits.