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Biomedical subjects

Tim Meyer

Publications and source records attributed to Tim Meyer.

At least 19 recordsLinked to original sources

A consensus view of protein dynamics.

The dynamics of proteins in aqueous solution has been investigated through a massive approach based on "state of the art" molecular dynamics simulations performed for all protein metafolds using the four most popular force fields (OPLS, CHARMM, AMBER, and GROMOS). A detailed analysis of the massive database of trajectories (>1.5 terabytes of data obtained using approximately 50 years of CPU) allowed us to obtain a robust-consensus picture of protein dynamics in aqueous solution.

Computational Biology↗

Treatment outcomes for hepatocellular carcinoma using chemoembolization in combination with other therapies.

BACKGROUND: Although transarterial chemoembolization (TACE) improves survival in patients with hepatocellular carcinoma (HCC), it is not known if TACE combined with other treatments is beneficial. AIM: To evaluate the evidence for improved outcomes in HCC with a multimodal treatment approach involving TACE. METHOD: PubMed search for all cohort and randomized trials (n=84) evaluating TACE combined with other therapies; meta-analysis performed where appropriate. RESULTS: A meta-analysis involving 4 RCTs showed a significant decrease in mortality favouring combination treatment (TACE plus percutaneous ablation) compared to monotherapy in patients with either small (<3cm) or large HCC nodules (>3cm) (OR, 0.534; 95% CI, 0.288-0.990; p=0.046). TACE combined with local radiotherapy improved survival in patients with tumour thrombosis of the portal vein in 7 non-randomized studies. Two RCTs and 13 non-randomized studies showed that TACE prior to hepatic resection does not improve survival nor tumour recurrence. Conversely, 2 RCTs and 5 comparative studies showed that transarterial injection of chemotherapeutic drugs mixed with lipiodol (TOCE) following hepatectomy confers survival benefit and less tumour recurrence. TACE before liver transplantation is safe and reduces drop-out rate from the waiting list, but there is no current evidence of improvement in subsequent survival or recurrence rate. CONCLUSIONS: A combined approach involving TACE and percutaneous ablation improves survival. Adjuvant TOCE improves outcome after hepatectomy. TACE is useful to control tumours burden while on the waiting list for OLT. Multimodal treatment seems to be the best way to optimize TACE outcomes in HCC.

Antineoplastic Combined Chemotherapy Protocols↗

A fast method for the determination of fractional contributions to solvation in proteins.

A fast method for the calculation of residue contributions to protein solvation is presented. The approach uses the exposed polar and apolar surface of protein residues and has been parametrized from the fractional contributions to solvation determined from linear response theory coupled to molecular dynamics simulations. Application of the method to a large subset of proteins taken from the Protein Data Bank allowed us to compute the expected fractional solvation of residues. This information is used to discuss when a residue or a group of residues presents an uncommon solvation profile.

Amino Acid Sequence↗

Bicarbonate infusion and pH clamp moderately reduce hyperventilation during ramp exercise in humans.

To test the hypothesis that the decrease in plasma pH contributes to the hyperventilation observed in humans in response to exercise at high workloads, five healthy male subjects performed a ramp exercise [maximal workload: 352 W (SD 35)] in a control situation and when arterialized plasma pH was maintained at the resting level (pH clamp) by intravenous infusion of sodium bicarbonate [129 mmol (SD 23), beginning at 59% maximal workload (SD 5)]. Bicarbonate infusion did not modify O(2) consumption (Vo(2)) but significantly (P < 0.05) increased arterial Pco(2), plasma bicarbonate concentration, and respiratory exchange ratio (P < 0.05). At the three highest workloads, pulmonary ventilation (Ve) and Ve/Vo(2) were approximately 5-10% lower (P < 0.05) when bicarbonate was infused than in the control situation, and hyperventilation was reduced by 15-30%. These data suggest that the decrease in plasma pH is one of the factors that contribute to the hyperventilation observed at high workloads.

Acid-Base Equilibrium↗

A phase I/II study of doxorubicin, ifosfamide, etoposide and interval methotrexate in patients with poor prognosis osteosarcoma.

BACKGROUND: The prognosis for patients with metastatic or axial-skeletal osteosarcoma is poor. A phase I/II study was conducted of intensive chemotherapy with interval methotrexate, to assess the feasibility, response rate and toxicity in this group of patients. PATIENTS AND METHODS: Thirteen patients, median age 18 (range: 8-34), with metastatic or axial-skeletal osteosarcoma were treated with ifosfamide 2.5 g/m(2), etoposide 150 mg/m(2), and doxorubicin 20 mg/m(2) on days 1-3, every 21 days, with interval methotrexate 12 g/m(2) given on day 14, for a maximum of eight cycles. Surgery to the primary was considered after four cycles for those with operable disease, or together with metastatic disease at completion of chemotherapy in those with inoperable tumours. RESULTS: A total of 85 cycles were given, median 6 per patient (range: 4-8). Only 6 of the 13 patients completed all 8 cycles of chemotherapy. Forty-eight cycles (56%) required a dose reduction. The principal toxicity was myelosuppression, with a median nadir neutrophil count of 0.1 (range: 0-4.1). Grade 3 or 4 infection was seen in 41 cycles (48%). Histological response was assessable in seven patients, all of whom achieved a >or=90% necrosis. Radiological response rate, evaluable in seven patients with lung metastases, was 43%. All but one patient has had subsequent disease progression or relapse, with a median event free survival of 13 months (range: 5-53). CONCLUSION: This regimen was associated with responses, but these were not sustained. Substantial toxicity was seen, preventing optimal delivery. More effective, less toxic regimens are needed in this group of patients.

Adolescent↗

Data mining of molecular dynamics trajectories of nucleic acids.

Analysis, storage, and transfer of molecular dynamic trajectories are becoming the bottleneck of computer simulations. In this paper we discuss different approaches for data mining and data processing of huge trajectory files generated from molecular dynamic simulations of nucleic acids.

Computer Simulation↗

Does cumulating endurance training at the weekends impair training effectiveness?

BACKGROUND: Due to occupational restrictions many people's recreational endurance activities are confined to the weekends. We intended to clarify if cumulating the training load in such a way diminishes endurance gains. DESIGN: We conducted a longitudinal study comparing training-induced changes within three independent samples. METHODS: Thirty-eight healthy untrained participants (45+/-8 years, 80+/-18 kg; 172+/-9 cm) were stratified for endurance capacity and sex and randomly assigned to three groups: 'weekend warrior' (n=13, two sessions per week on consecutive days, 75 min each, intensity 90% of the anaerobic threshold; baseline lactate+1.5 mmol/l), regular training (n=12, five sessions per week, 30 min each, same intensity as weekend warrior), and control (n=13, no training). Training was conducted over 12 weeks and monitored by means of heart rate. Identical graded treadmill protocols before and after the training program served for exercise prescription and assessment of endurance effects. RESULTS: VO2max improved similarly in weekend warrior (+3.4 ml/min per kg) and register training (+1.5 ml/min per kg; P=0.20 between groups). Compared with controls (-1.0 ml/min per kg) this effect was significant for weekend warriors (P<0.01) whereas there was only a tendency for the regular training group (P=0.10). In comparison with controls (mean decrease, 3 beats/min), the average heart rate during exercise decreased significantly by 11 beats/min (weekend warriors, P<0.01) and 9 beats/min (regular training, P<0.05). There was no significant difference, however, between the weekend warrior and regular training groups (P=0.99). CONCLUSION: In a middle-aged population of healthy untrained subjects, cumulating the training load at the weekends does not lead to an impairment of endurance gains in comparison with a smoother training distribution.

Adult↗

Reproducibility and clinical significance of exercise-induced increases in cardiac troponins and N-terminal pro brain natriuretic peptide in endurance athletes.

BACKGROUND: Cardiac troponins I and T and brain natriuretic peptide are the accepted standards to serologically identify myocardial necrosis and elevated wall stress. In addition, they allow risk stratification in cardiovascular patients. The clinical significance of increases in cardiac markers after strenuous endurance exercise in obviously healthy athletes is unclear. DESIGN: We therefore examined the reproducibility and clinical significance of exercise-induced increases in cardiac troponins I and T and N-terminal pro brain natriuretic peptide after two standardized endurance exercise trials in healthy endurance athletes with prior competition-induced elevations of cardiac troponins (I, 0.08-1.93 mug/l; T, 0.01-0.56 mug/l). METHODS: Twenty male athletes (36+/-7 years; VO2max: 60+/-5 ml/min per kg) completed a 1-h and a 3-h exercise study (exercise intensities 100 and 75%, respectively, of the individual anaerobic threshold) on two different days in randomized order to determine cardiac markers before, 30 min and 3 h after exercise. In addition to pre- and post-exercise echocardiography including tissue Doppler imaging, delayed enhancement magnetic-resonance-imaging was performed after a 3-h exercise study to detect myocardial necrosis. RESULTS: A marginal increase in cardiac troponin I was documented after both exercise trials (from 0.02 to 0.03 mug/l; P < 0.001). Cardiac troponin T remained without significant changes. N-terminal pro brain natriuretic peptide increased by 9 and 30 ng/l after 1-h and 3-h exercise studies, respectively (P < 0.001). In contrast to cardiac troponins, increases in N-terminal pro brain natriuretic peptide after competition correlated with those after 1-h exercise study (rho = 0.88) and 3-h exercise-study (rho = 0.82). No pathologies were demonstrated by echocardiography or delayed-enhancement magnetic resonance imaging. CONCLUSIONS: Due to the missing reproducibilty and evidence of myocardial damage, exercise-induced increases in cardiac troponins may represent a physiologic reaction under special conditions and seem to be without pathological significance in healthy athletes.

Adult↗

Effects of graded carbohydrate supplementation on the immune response in cycling.

PURPOSE: This study examined the acute immune response after three standardized cycling sessions of 4-h duration in the field with varying carbohydrate (CHO) supplementation in a randomized, double-blind, placebo-controlled fashion. We hypothesized that the ingestion of carbohydrate (6 or 12% CHO beverages; placebo (P) without CHO) during exercise attenuates the exercise-induced immune response in a dose-dependent manner. METHODS: A total of 14 male competitive cyclists and triathletes (age: 25 +/- 5 yr; height: 180 +/- 7 cm; weight: 72 +/- 9 kg; VO2max: 67 +/- 6 mL.min(-1).kg(-1)) cycled for 4 h on a 400-m track at a given workload of 70% of the individual anaerobic threshold (198 +/- 21 W). Leukocyte and lymphocyte subpopulations were measured by flow cytometry before, immediately, and 1 and 19 h after exercise. In addition, C-reactive protein (CRP) interleukin 6 (IL-6), and cortisol were determined. RESULTS: The exercise-induced increase in leukocytes, neutrophils, and monocytes was significantly attenuated to the same extent by 6 and 12% CHO (P < 0.001). No differences could be demonstrated for lymphocytes and natural killer cells. The increase in CRP was attenuated significantly by 12% CHO only (P < 0.05), whereas the increase in cortisol and IL-6 was significantly reduced by 6 and 12% CHO (P < 0.001). The postexercise neutrophilia, which dominated the exercise-induced leukocytosis, was strongly related to the postexercise concentration of cortisol (r = 0.72; P < 0.001). CONCLUSIONS: Because of the lacking dose-dependent difference, the ingestion of at least 6% CHO beverages can sufficiently attenuate the exercise-induced immune response and stress, especially in phagocytizing cells (neutrophils and monocytes) by the reduced release of cortisol.

Adult↗

Partition of protein solvation into group contributions from molecular dynamics simulations.

Linear response theory coupled to molecular dynamics simulations with an explicit solvent representation is used to derive fractional contributions of amino acid residues to the solvation of proteins. The new fractional methods developed here are compared with standard approaches based on empirical 1D and 3D statistical potentials, as well as with estimates obtained from the analysis of classical molecular interaction potentials. The new fractional methods, which have a clear physical basis and explicitly account for the effects due to protein structure and flexibility, provide an accurate picture of the contribution to solvation of different regions of the protein.

Computer Simulation↗

An alternative approach for exercise prescription and efficacy testing in patients with chronic heart failure: a randomized controlled training study.

BACKGROUND: Prescription of endurance training and documentation of its efficacy in patients with chronic heart failure (CHF) is usually done with reference to maximal ergometric measurements which are subject to form on the day changes and motivational influences. However, the use of submaximal parameters might represent an alternative approach. METHODS: This was tested in 54 patients with CHF (57 +/- 10 years, NYHA II: n = 40; NYHA III: n = 14) who were randomized into training (T; n = 26) or control group (CO; n = 28). Training consisted of 45 minutes cycling at an intensity corresponding to the anaerobic threshold (AT) and was conducted for 12 weeks, 4 to 5 times per week. Cardiorespiratory exercise testing was done before and after the experimental phase. Changes in well-being were investigated using a 5-point Likert scale. RESULTS: A significant rightward shift in the heart rate curve was demonstrated in T compared with CO (P = .01; T: decrease in resting heart rate by 8 per minute, during exercise by 7 to 11/min; CO: -1 and -1 to -3 per minute, respectively). Anaerobic threshold increased significantly by 11.6% in T (+0.11 +/- 0.11 L min(-1) oxygen uptake) compared with CO (-0.02 +/- 0.10 L min(-1)). Positive changes in well-being were significantly larger in T (P < .01). CONCLUSIONS: In patients with CHF, training can be prescribed and its efficacy can be evaluated by the exclusive use of submaximal parameters. Anaerobic threshold represents an appropriate training intensity in this population.

Aged↗

Running 8000 m fast or slow: Are there differences in energy cost and fat metabolism?

PURPOSE: To compare energy requirements and substrate use for running a given distance fast versus slow under field conditions. METHODS: Ten males and four females who were moderately endurance trained (32 +/- 6 yr; 71 +/- 11 kg; body mass index: 22.7 +/- 2.3 kg x m(-2); VO2max: 62.0 +/- 6.0 mL x min(-1) x kg(-1); individual anaerobic threshold [IAT]: 13.7 +/- 1.4 km x h(-1)) performed an incremental running protocol to determine IAT. Subsequently, two 8000-m runs at 70 and 95% IAT were performed on separate days in randomized order on an indoor track. Energy expenditure (EE) was measured by means of a portable metabolic device (indirect calorimetry). A meaningful difference in EE was defined as >10%. RESULTS: EE was significantly greater during the 95% IAT run than during the 70% IAT run (2650 +/- 276 and 2554 +/- 348 kJ, respectively). However, this difference was only 3.8 +/- 4.8%. Including measurements up to 10 min postexercise, the difference rose to 5.1 +/- 4.7% (95% IAT: 2830 +/- 301 kJ; 70% IAT: 2692 +/- 368 kJ). There was no significant difference between the absolute amounts of fat oxidized during the runs (70% IAT: 26 +/- 5 g; 95% IAT: 20 +/- 5 g). During the 95% IAT run, significantly more carbohydrates were metabolized than during the 70% IAT run (108 +/- 14 and 90 +/- 5 g, respectively). The difference in EE between the two runs increased from the first to the third part of the running distance (first: no significance; second: P < 0.01; third: P < 0.001). CONCLUSION: Energy requirements for a commonly run distance in recreational endurance training differ significantly but not relevantly between slow and fast speeds. However, increasing total running distance might lead to larger differences.

Adipose Tissue↗

Linear response theory: an alternative to PB and GB methods for the analysis of molecular dynamics trajectories?

We explore the use of classical Linear Response Theory (LRT) as an alternative strategy to the use of Molecular Mechanics/Poisson-Boltzmann strategies to compute the solvation free energy of macromolecules from molecular dynamics simulations using an explicit representation of solvent. The method reproduces well the free energy of solvation of standard amino acid side chains, small peptides, and proteins. The use of a fully discrete representation of solvent avoids the possible problems of continuum models to represent the solvation of systems containing tightly bound water molecules.

Alanine↗

Bimolecular interaction of insulin-like growth factor (IGF) binding protein-2 with alphavbeta3 negatively modulates IGF-I-mediated migration and tumor growth.

Both the integrin and insulin-like growth factor binding protein (IGFBP) families independently play important roles in modulating tumor cell growth and progression. We present evidence for a specific cell surface localization and a bimolecular interaction between the alpha v beta 3 integrin and IGFBP-2. The interaction, which could be specifically perturbed using vitronectin and alpha v beta 3 blocking antibodies, was shown to modulate IGF-mediated cellular migration responses. Moreover, this interaction was observed in vivo and correlated with reduced tumor size of the human breast cancer cells, MCF-7 beta 3, which overexpressed the alpha v beta 3 integrin. Collectively, these results indicate that alpha v beta 3 and IGFBP-2 act cooperatively in a negative regulatory manner to reduce tumor growth and the migratory potential of breast cancer cells.

Antibodies, Monoclonal↗

Systemic treatment and liver transplantation for hepatocellular carcinoma: two ends of the therapeutic spectrum.

Hepatocellular carcinoma is the fifth most common malignant disorder and causes nearly 1 million deaths a year worldwide. A background of cirrhosis is the major risk factor, and in Asia and subSaharan Africa, cirrhosis is attributable mainly to endemic hepatitis B infection. In Europe and the USA the incidence of hepatocellular carcinoma is increasing as a result of the high prevalence of hepatitis C. The only curative treatments are surgical resection or liver transplantation, but only a few patients are eligible for these procedures. Local ablative treatments such as ethanol injection can lengthen survival in selected patients, and radiofrequency ablation also shows promise. Unfortunately, most patients are suitable only for palliative treatment because of the extent of their tumour or background liver disease or both. For these patients, a wide range of therapeutic interventions have been assessed, including transarterial embolisation (with or without chemotherapy), hormone therapy with antioestrogens and androgens, octreotide, interferon, and both arterial and systemic chemotherapy, of which only chemoembolisation improves survival over symptomatic care. Tamoxifen is ineffective, and there are insufficient randomised data to show the benefit of any other intervention. In this review, we focus on two ends of the therapeutic spectrum--transplantation, which is highly effective but applicable to only a few patients, and systemic chemotherapy, which is of uncertain benefit but widely applicable.

Antineoplastic Agents↗

Different effects of two regeneration regimens on immunological parameters in cyclists.

PURPOSE: To investigate the effect of 4-d active regeneration of different duration on immunological parameters after 2 wk of intensive training. METHODS: In a cross-over design 11 male cyclists conducted 13 d of intensive training followed by 4 d of low-intensity cycling for either 1 or 3 h each day (sequence randomized). Before the intensive training (test 1), between training and regeneration (test 2), and after the regeneration period (test 3), subjects were tested in the lab: venous blood sampling (immunological parameters; flow cytometry) and incremental exercise stage test on acycle ergometer. RESULTS: Average values of lymphocytes and natural killer (NK) cells decreased significantly from test 1 to test 2 and were influenced differently by 1- and 3-h cycling (P = 0.018 and 0.039, respectively); 1-h cycling restored values from test 1, whereas 3 h led to a further decrease in lymphocyte and NK cell concentrations. This pattern was resembled by the courses of maximal heart rate and maximal blood lactate concentration during incremental cycling exercise. In leukocytes, tests 2 and 3 differed significantly from test 1 (P = 0.048 and 0.031, respectively), but there was no significant effect of the regeneration duration (P = 039). Neither the concentration of neutrophils nor the neutrophil oxidative burst was significantly influenced by the training period or by one of the regeneration phases. CONCLUSIONS: The present results indicate that low-intensity regenerative training sessions in cyclists should preferably be conducted for shorter durations than 3 h. It was demonstrated that 4-d cycling of 1 h each day reversed ergometric and immunological changes indicative of fatigue after 2 wk of intensive training.

Adult↗

Exercise programmes for patients with chronic heart failure.

The safety and efficacy of exercise training in patients with chronic heart failure (CHF) have been reported in a large number of scientific studies, with endurance training representing the most frequently applied training stimulus. Beneath the common continuous method of endurance training, the interval method (short bouts of intense exercise interspersed with pre-scheduled rest intervals), was also applied in some studies. Ergometric testing is a prerequisite for all individualised training prescription and is an appropriate method of efficacy documentation. However, there is a surprisingly large range of exercise intensities being prescribed to patients with CHF. Most of the prescription models refer to maximal ergometric measurements. Submaximal references from lactate and ventilatory curves represent an alternative method in measuring accuracy and efficacy of training. The course of heart rate during submaximal incremental exercise can be reliably used to indicate endurance gains in CHF. Some positive reports exist for carefully executed strength endurance training for patients with CHF and there are convincing arguments for the use of coordination and flexibility exercises; however, substantial scientific evidence is lacking.

Cardiovascular System↗