Turning up the heat on subzero fish: thermal dependence of sustained swimming in an Antarctic notothenioid

We determined the maximum sustained swimming speed (U_crit), and resting and maximum ventilation rates of the Antarctic fish Pagothenia borchgrevinki at five temperatures between −1°C and 8°C. We also determined resting metabolic rate (VO₂) at −1°C, 2°C, and 4°C. U_crit of P. borchgrevinki was highest at −1°C (2.7±0.1 BL s⁻¹) and rapidly decreased with temperature, representing a thermal performance breadth of only 5°C. This narrow thermal performance supports our prediction that specialisation to the subzero Antarctic marine environment is associated with a physiological trade-off in performance at high temperatures. Resting oxygen consumption and ventilation rate increased by more than 200% across the temperature range, which most likely contribute to the decrease in aerobic swimming capabilities at higher temperatures.     

Dietary nitrate reduces maximal oxygen consumption while maintaining work performance in maximal exercise

The anion nitrate—abundant in our diet—has recently emerged as a major pool of nitric oxide (NO) synthase-independent NO production. Nitrate is reduced stepwise in vivo to nitrite and then NO and possibly other bioactive nitrogen oxides. This reductive pathway is enhanced during low oxygen tension and acidosis. A recent study shows a reduction in oxygen consumption during submaximal exercise attributable to dietary nitrate. We went on to study the effects of dietary nitrate on various physiological and biochemical parameters during maximal exercise. Nine healthy, nonsmoking volunteers (age 30 ± 2.3 years, VO_2max 3.72 ± 0.33 L/min) participated in this study, which had a randomized, double-blind crossover design. Subjects received dietary supplementation with sodium nitrate (0.1 mmol/kg/day) or placebo (NaCl) for 2 days before the test. This dose corresponds to the amount found in 100–300 g of a nitrate-rich vegetable such as spinach or beetroot. The maximal exercise tests consisted of an incremental exercise to exhaustion with combined arm and leg cranking on two separate ergometers. Dietary nitrate reduced VO_2max from 3.72 ± 0.33 to 3.62 ± 0.31 L/min, P < 0.05. Despite the reduction in VO_2max the time to exhaustion trended to an increase after nitrate supplementation (524 ± 31 vs 563 ± 30 s, P = 0.13). There was a correlation between the change in time to exhaustion and the change in VO_2max (R² = 0.47, P = 0.04). A moderate dietary dose of nitrate significantly reduces VO_2max during maximal exercise using a large active muscle mass. This reduction occurred with a trend toward increased time to exhaustion implying that two separate mechanisms are involved: one that reduces VO_2max and another that improves the energetic function of the working muscles.     

Locomotion at –1.0°C: burst swimming performance of five species of Antarctic fish

We investigated the burst swimming performance of five species of Antarctic fish at −1.0°C. The species studied belonged to the suborder, Notothenioidei, and from the families, Nototheniidae and Bathydraconidae. Swimming performance of the fish was assessed over the initial 300 ms of a startle response using surgically attached miniature accelerometers. Escape responses in all fish consisted of a C-type fast start; consisting of an initial pronounced bending of the body into a C-shape, followed by one or more complete tail-beats and an un-powered glide. We found significant differences in the swimming performance of the five species of fish examined, with average maximum swimming velocities (U_max) ranging from 0.91 to 1.39 m s⁻¹ and maximum accelerations (A_max) ranging from 10.6 to 15.6 m s⁻². The cryopelagic species, Pagothenia borchgrevinki, produced the fastest escape response, reaching a U_max and A_max of 1.39 m s⁻¹ and 15.6 m s⁻², respectively. We also compared the body shapes of each fish species with their measures of maximum burst performance. The dragonfish, Gymnodraco acuticeps, from the family Bathdraconidae, did not conform to the pattern observed for the other four fish species belonging to the family Nototheniidae. However, we found a negative relationship between buoyancy of the fish species and burst swimming performance.     

Nitrate and phosphate uptake kinetics of the harmful diatom Eucampia zodiacus Ehrenberg,a causative organism in the bleaching of aquacultured Porphyra thalli

The diatom Eucampia zodiacus Ehrenberg is a harmful diatom which indirectly causes bleaching of aquacultured Nori (Porphyra thalli) through competitive utilization of nutrients during bloom events. In the present study, we experimentally investigated the nitrate (N) and phosphate (P) uptake kinetics of E. zodiacus, Harima-Nada strain. Maximum uptake rates (ρ_max), which were obtained by short-term experiments, were 0.777 and 0.916 pmol cell^?1 h^?1 for nitrate and 0.244 and 0.550 pmol cell^?1 h^?1 for phosphate at 9 and 20 °C, respectively. The half-saturation constants for uptake (K_s) were 2.59 and 2.92 μM N and 1.83 and 4.85 μM P at 9 and 20 °C, respectively. Although the maximum specific uptake rate (V_max; V_max = ρ_max/Q₀, Q₀; minimum cell quota) and V_max/K_s for nitrate at 9 °C are about 1/2 of those obtained at the optimum temperature (20 °C), they are still higher than those obtained for many other phytoplankton at their optimum temperature conditions for uptake. These results suggest that E. zodiacus utilizes nitrogen efficiently at low water temperature, and it is one of the important factors causing the serious damage to Porphyra thalli by bleaching due of this species. For phosphate, the K_s values of E. zodiacus were higher than those reported for other species; the V_max and V_max/K_s values were much lower than those of other diatoms such as Skeletonema costatum (Greville) Cleve. These results suggest that E. zodiacus is disadvantaged compared to other diatom species during competitive utilization of phosphate.     

The influence of starvation on fast-start performance of Spinibarbus sinensis

Juvenile Spinibarbus sinensis (n = 48, body length, 5.86 ± 0.10 cm, 25 °C) were fasted for 0, 0.5, 1, 2, 4 and 6 weeks. The fast-start performances of the experimental fish were assessed using high-speed video photography and the locomotive kinematics analysis. The morphological parameters including tail height (H₂), tail length (L₂), lateral body area (S₁), median fin area (S₂), dorsal cross section area (S₃) and tail cross section area (S₄) were also measured using TpsDig and the Photoshop. The results showed that 6 week starvation resulted in significant decreases in the escape distance (d), maximum linear velocity (V_max) and maximum linear acceleration (a_max) of center of mass in Stage 1 and Stage 2 of fast-start process (P < 0.05), however there were two relatively sTable phases in the V_max and d, during the week 1–2 (V_max = 0.67 ± 0.06 mm/ms; d = 8.86 ± 0.73 mm) and week 4–6 (V_max = 0.31 ± 0.04 mm/ms; d = 3.70 ± 0.56 mm). When compared with the control group (0 week starvation group), only the 6 week starvation group showed the significantly different response time (t) with average t = 9.20 ± 0.37 ms in week 1–4. There were no significant difference in mass center turning angles at first stage (T_a1) , second stage (T_a2) and the sum of two stages (T_a(1+2)) was also not different (P > 0.05). The fish did not show any directional preference for left or right during escape turning, and all of the related parameters also remained unchanged among treatment group (P > 0.05). The areas of dorsal body cross-section decreased more acutely (P < 0.05) than caudal body cross-section (45.4% vs 38.0%) during the entire starvation period while no significant differences were observed in both the tail height and tail length among all treatment groups (P > 0.05). The results indicated that fast-start performance of juvenile S. sinensis is affected by the starvation; metabolic energy related traits such as the maximum linear velocity and the maximum linear acceleration decreased significantly after starvation; whereas traits with no direct link to metabolic energy such as the response time and turning angle remained unchanged during starvation. The lack of starvation induced change in the maneuverability of the fish suggests that fast-start ability related to escape strategy is relatively well conservative in juvenile S. sinensis.     

The effect of exhaustive chasing training and detraining on swimming performance in juvenile darkbarbel catfish (<Emphasis Type="Italic">Peltebagrus vachelli</Emphasis>)

To investigate the effects of exhaustive chasing training and detraining on the swimming performance of juvenile darkbarbel catfish (Peltebagrus vachelli Richardson), we performed exhaustive chasing training daily for 14 days and subsequently detrained fish for 7 days. Chasing training resulted in significant increases in critical swimming speed (U _crit), post-chasing peak oxygen consumption rate (VO_{2 peak}), and heart and gill indexes compared with non-trained controls. Both resting oxygen consumption (VO_{2 rest}) and excess post-chasing VO₂ (EPOC) were unaffected by exhaustive chasing training. Fish that underwent chasing training had lower levels of whole-body lipid content and reduced food intake and growth compared with non-trained control fish; however, condition factor was not affected by chasing training. Seven days of detraining reversed the effects of exhaustive chasing training. Overall, these data suggested that short-term exhaustive chasing training improves aerobic swimming capacity in darkbarbel catfish, but the training effects are reversible over a short period of time.     

The use of spontaneous behavior,swimming performances and metabolic rate to evaluate toxicity of PFOS on topmouth gudgeon Pseudorasbora parva

Perfluorooctane sulfonate (PFOS) is a ubiquitous environmental contaminant that has been found to pose various risks to fish health and the safety of aquatic ecosystem. Swimming performance is an integrated index of fitness in fish. However, little research has sought on the effects of PFOS on swimming performances of fish. Experiments were carried out to clarify the impacts of acute exposure to PFOS on behavior, swimming ability and metabolic rate in topmouth gudgeon (Pseudorasbora parva), to understand the underlying ecotoxicological effects of waterborne PFOS exposure on fish physiology and behavior. Fish were exposed to PFOS (0, 0.5, 2, 8 or 32 mg/L) for 96 h. Afterwards, the routine metabolic rate (RMR), spontaneous swimming behavior (SSB), fast-start swimming performance (FSP) and critical swimming speed (U_crit) of the topmouth gudgeon were examined. The results show reduced behavioral performance and increased physiological stress with increasing PFOS concentration. Both RMR, SSB and U_crit were significantly affected by PFOS exposure (p < 0.05). The lowest observed effect concentration (LOEC) is 2 mg/L for SSB. PFOS treatment resulted in increased RMR (p = 0.001) and decreased U_crit (p = 0.005), whereas FSP was not influenced by PFOS (p > 0.05). The results indicate that the anaerobic swimming capacity was conserved, but the metabolic level, SSB and aerobic swimming performance in topmouth gudgeon were susceptible to PFOS contamination, and hence might be useful as considerable potential biomarkers of pollution.     

Flow velocity affects internal oxygen conditions in the seagrass Cymodocea nodosa

The internal oxygen status of seagrass tissues, which is believed to play an important role in events of seagrass die-off, is partly determined by the rates of gas exchange between leaves and water column. In this study, we examined whether water column flow velocity has an effect on gas exchange, and hence on internal oxygen partial pressures (pO₂) in the Mediterranean seagrass, Cymodocea nodosa. We measured the internal pO₂ in the horizontal rhizomes of C. nodosa in darkness at different mainstream flow velocities, combined with different levels of water column oxygen pO₂ using an experimental flume in the laboratory. Flow velocity clearly had an effect on the internal oxygen status. In stagnant, but fully aerated water the mean internal pO₂ was 6.9 kPa, corresponding to about 30% of air saturation. The internal pO₂ increased with increasing flow velocity reaching saturation of around 12.2 kPa (60% of air saturation) at flow velocities ≥7 cm s⁻¹. Flow had a relatively larger influence on internal pO₂ at lower water column oxygen concentrations. By extrapolating linear relationships between internal and water column pO₂ in this experimental setup, rhizomes would become anoxic at a water column oxygen pO₂ of 4–4.5 kPa (∼20% of air saturation) in flowing water, but already at 6.4 kPa (∼30% of air saturation) in stagnant water. Water flow may play an important role for seagrass performance and survival in areas with poor water column oxygen conditions and may, in general, be of importance for the distribution of submerged rooted plants.     

Non-invasive assessment of muscle fiber conduction velocity during an incremental maximal cycling test

Muscle fiber conduction velocity (MFCV) gives critical information on neuromuscular control and can be considered a size principle parameter, being suggestive of motor unit recruitment strategies. MFCV has been recently measured during constant-load sub-maximal cycling exercise and was found to correlate positively with percentage of type I myosin heavy chain.The aim of this study was to test the hypothesis that MFCV measured during an incremental cycling test using surface electromyography (sEMG), can be sensitive to the different metabolic requests elicited by the exercise. In particular, the relationship between ventilatory threshold (T-vent), V^′O_2max and MFCV was explored.Eleven male physically active subjects (age 30 ± 9 years) undertook a 1-min incremental cycling test to exhaustion. T-vent and V^′O_2max were measured using an open circuit breath by breath gas analyzer. The sEMG was recorded from the vastus lateralis muscle with an adhesive 4-electrodes array, and the MFCV was computed on each sEMG burst over the last 30-s of each step.The mean V^′O_2max obtained during the maximal test was 53.32 ± 2.33 ml kg^?1 min^?1, and the T-vent was reached at 80.77 ± 3.49% of V^′O_2max. In all subjects reliable measures of MFCV were obtained at every exercise intensity (cross correlation values >0.8). MFCV increased linearly with the mechanical load, reaching a maximum value of 4.28 ± 0.67 m s^?1 at an intensity corresponding to the T-vent. Thereafter, MFCV declined until maximal work intensities. This study demonstrates that MFCV can be used as non-invasive tool to infer MUs recruitment/derecruitment strategies even during dynamic exercise from low to maximal intensities.     

Mitochondrial response in the apical and lateral flower buds of the Hanfu apple to cold stress during the dormancy stage

In order to study the different physiological bases of cold tolerance in the apical flower buds (AFB) and the lateral flower buds (LFB) of the Hanfu apple (Malus domestica Borkh), we used 4-year-old grafted Hanfu plants as material and evaluated the physiological characteristics of mitochondria in the flower buds, such as electron transport chains (cytochrome pathway and alternative pathway), H₂O₂ content, mitochondrial membrane permeability transition (mPT), and MDA content. AFBs and LFBs showed different changes in total respiratory rate (V_t) during low-temperature stress, except that both reached the lowest V_ts at ?30 °C. The AFB V_t increased to a peak at ?25 °C and decreased sharply to its minimal value at ?30 °C, and then remained relatively low. In contrast, the LFB V_t decreased to its minimal value at ?30 °C and increased sharply to a peak at ?35 °C and then decreased again. In both AFBs and LFBs, the cytochrome pathway was still the main electron transport chain throughout the whole process, and the contributions of the cytochrome pathway (ρV_cyt/V_t) and of the alternative pathway (ρV_alt/V_t) showed similar tendencies to those of V_t as temperature changed. Changes in the AFB mPT were different from those of AFB V_t. LFB mPT zigzagged from peaks at ?25 °C and 35 °C. The H₂O₂ content of the LFBs increased from ?10 °C to ?30 °C, then decreased slightly from ?30 °C to ?35 °C, and then increased again. H₂O₂ content in AFBs went up steadily throughout the whole process. During the early stage of low-temperature treatment, before temperatures reached ?35 °C, LFB MDA content remained relatively low and later increased. MDA content in AFBs began to increase from the beginning of treatment. It can be concluded that the higher cold tolerance of LFBs relative to AFBs could be closely related to their higher V_t and ρV_alt/V_t, which may aid adaptations to stress by supplying energy and metabolic substrates under low-temperature stress conditions.     

Uremic toxins inhibit renal metabolic capacity through interference with glucuronidation and mitochondrial respiration

During chronic kidney disease (CKD), drug metabolism is affected leading to changes in drug disposition. Furthermore, there is a progressive accumulation of uremic retention solutes due to impaired renal clearance. Here, we investigated whether uremic toxins can influence the metabolic functionality of human conditionally immortalized renal proximal tubule epithelial cells (ciPTEC) with the focus on UDP-glucuronosyltransferases (UGTs) and mitochondrial activity. Our results showed that ciPTEC express a wide variety of metabolic enzymes, including UGTs. These enzymes were functionally active as demonstrated by the glucuronidation of 7-hydroxycoumarin (7-OHC; K_m of 12 ± 2 μM and a V_max of 76 ± 3 pmol/min/mg) and p-cresol (K_m of 33 ± 13 μM and a V_max of 266 ± 25 pmol/min/mg). Furthermore, a wide variety of uremic toxins, including indole-3-acetic acid, indoxyl sulfate, phenylacetic acid and kynurenic acid, reduced 7-OHC glucuronidation with more than 30% as compared with controls (p < 0.05), whereas UGT1A and UGT2B protein expressions remained unaltered. In addition, our results showed that several uremic toxins inhibited mitochondrial succinate dehydrogenase (i.e. complex II) activity with more than 20% as compared with controls (p < 0.05). Moreover, indole-3-acetic acid decreased the reserve capacity of the electron transport system with 18% (p < 0.03). In conclusion, this study shows that multiple uremic toxins inhibit UGT activity and mitochondrial activity in ciPTEC, thereby affecting the metabolic capacity of the kidney during CKD. This may have a significant impact on drug and uremic retention solute disposition in CKD patients.     

Alkoxyresorufin (methoxy-, ethoxy-, pentoxy- and benzyloxyresorufin) O-dealkylase activities by in vitro-expressed cytochrome P450 1A4 and 1A5 from common cormorant (Phalacrocorax carbo)

Here we report the inter-paralog comparison of cytochrome P4501A (CYP1A) catalytic function in common cormorant (Phalacrocorax carbo) using the recombinant proteins synthesized by yeast-based vector system. CYP1A4 and CYP1A5 proteins from common cormorant were heterologously expressed in yeast Saccaromyces cerevisiae. Kinetic analyses revealed that among alkoxyresorufin (methoxy-, ethoxy-, pentoxy- and benzyloxyresorufin) O-dealkylase (AROD) activities V_max value for ethoxyresorufin O-deethylase (EROD) activity was the highest for both enzymes, reaching 0.91 ± 0.034 and 1.8 ± 0.043 nmol/min/nmol CYP for CYP1A4 and CYP1A5, respectively. Similar results were obtained for the catalytic efficiencies represented as the ratios of V_max to K_m (V_max/K_m). Meanwhile, distinct substrate preferences were also observed; CYP1A4 had V_max and V_max/K_m values for benzyloxyresorufin O-debenzylase (BROD) activity 12- and 46-fold greater than CYP1A5, respectively, while CYP1A5 was about 13- and 4.5-fold more efficient in methoxyresorufin O-demethylase (MROD) activity than CYP1A4. The K_m values showed no significant change among MROD, EROD, pentoxyresorufin O-depenthylase (PROD) and BROD activities for both enzymes, except for significant differences between PROD and other three activities for CYP1A4. Comparing the results in the present study with previous studies addressing chicken and rat CYP1A enzymes, it is also clear that CYP1A orthologs have different catalytic preferences for AROD activities between cormorant and rat and even between cormorant and chicken. Variations in CYP1A catalytic function between cormorant CYP1A paralogs and between CYP1A orthologs from cormorant and other species indicate that enzymatic properties should be characterized on the basis not only of a limited model species such as chicken, but also of multiple species to further understand the mechanism underlying differences in substrate selectivity and the interaction with environmental contaminants in avian species.     

Calibrating acoustic acceleration transmitters for estimating energy use by wild adult Pacific salmon

This study is the first to calibrate acceleration transmitters with energy expenditure using a vertebrate model species. We quantified the relationship between acoustic accelerometer output and oxygen consumption across a range of swim speeds and water temperatures for Harrison River adult sockeye salmon (Oncorhynchus nerka). First, we verified that acceleration transmitters with a sampling frequency of 10 Hz could be used as a proxy for movement in sockeye salmon. Using a mixed effects model, we determined that tailbeat frequency and acceleration were positively correlated (p < 0.0001), independent of tag ID. Acceleration (p < 0.0001) was positively related to swim speed while fork length (p = 0.051) was negatively related to swim speed. Oxygen consumption and accelerometer output (p < 0.0001) had a positive linear relationship and were temperature dependent (p < 0.0001). There were no differences in swim performance (F_2,12 = 1.023, p = 0.820) or oxygen consumption (F_1,12 = 0.054, p = 0.332) between tagged and untagged individuals. Five tagged fish were released into the Fraser River estuary and manually tracked. Of the five fish, three were successfully tracked for 1 h. The above relationships were used to determine that the average swim speed was 1.25 ± 0.03 body lengths s^? 1 and cost of transport was 3.39 ± 0.17 mg O₂ kg^? 1 min^? 1, averaged across the three detected fish. Acceleration transmitters can be effectively used to remotely evaluate fine-scale behavior and estimate energy consumption of adult Pacific salmon throughout their homeward spawning migration.     

Immobilization of apricot pectinesterase (Prunus armeniaca L.) on porous glass beads and its characterization

Pectinesterase isolated from Malatya apricot pulp was covalently immobilized onto glutaraldehyde-containing amino group functionalized porous glass beads surface by chemical immobilization at pH 8.0. The amount of covalently bound apricot PE was found 1.721 mg/g glass support. The properties of immobilized enzyme were investigated and compared to those of free enzyme. The effect of various parameters such as pH, temperature, activation energy, heat and storage stability on immobilized enzyme were investigated. Optimum pH and temperature were determined to be 8.0 and 50 °C, respectively. The immobilized PE exhibited better thermostability than the free one. Kinetic parameters of the immobilized enzyme (K_m and V_max values) were also evaluated. The K_m was 0.71 mM and the V_max was 0.64 μmol min^?1 mg^?1. No drastic change was observed in the K_m and V_max values. The patterns of heat stability indicated that the immobilization process tends to stabilize the enzyme. Thermal and storage stability experiments were also carried out. It was observed that the immobilized enzyme had longer storage stability and retained 50% of its initial activity during 30 days.     

The role of nest surface temperatures and the brain in influencing ant metabolic rates

Thermal limits of insects can be influenced by recent thermal history: here we used thermolimit respirometry to determine metabolic rate responses and thermal limits of the dominant meat ant, Iridomyrmex purpureus. Firstly, we tested the hypothesis that nest surface temperatures have a pervasive influence on thermal limits. Metabolic rates and activity of freshly field collected individuals were measured continuously while ramping temperatures from 44 °C to 62 °C at 0.25 °C/minute. At all the stages of thermolimit respirometry, metabolic rates were independent of nest surface temperatures, and CT_max did not differ between ants collected from nest with different surface temperatures. Secondly, we tested the effect of brain control on upper thermal limits of meat ants via ant decapitation experiments (‘headedness’). Decapitated ants exhibited similar upper critical temperature (CT_max) results to living ants (Decapitated 50.3±1.2 °C: Living 50.1±1.8 °C). Throughout the temperature ramping process, ‘headedness’ had a significant effect on metabolic rate in total (Decapitated V̇CO₂ 140±30 µl CO₂ mg⁻¹ min⁻¹: Living V̇CO₂ 250±50 CO₂ mg⁻¹ min⁻¹), as well as at temperatures below and above CT_max. At high temperatures (>44 °C) pre- CT_max the relationships between I. purpureus CT_max values and mass specific metabolic rates for living ants exhibited a negative slope whilst decapitated ants exhibited a positive slope. The decapitated ants also had a significantly higher Q₁₀:25–35 °C when compared to living ants (1.91±0.43 vs. 1.29±0.35). Our findings suggest that physiological responses of ants may be able to cope with increasing surface temperatures, as shown by metabolic rates across the thermolimit continuum, making them physiologically resilient to a rapidly changing climate. We also demonstrate that the brain plays a role in respiration, but critical thermal limits are independent of respiration levels.     

Forming nanoparticles of α-amylase and embedding them into solid surfaces

In the current work nanoparticles (NPs) of α-amylase were generated in an aqueous solution using high-intensity ultrasound, and were subsequently immobilized on polyethylene (PE) films, or polycarbonate (PC) plates, or on microscope glass slides. The α-amylase NPs coated on the solid surfaces have been characterized by ESEM, TEM, FTIR, XPS and AFM. The substrates immobilized with α-amylase were used for hydrolyzing soluble potato starch to maltose. The amount of enzyme introduced in the substrates, leaching properties, and the catalytic activity of the immobilized enzyme were compared. The catalytic activity of the amylase deposited on the three solid surfaces was compared to that of the same amount of free enzyme at different pHs and temperatures. α-Amylase coated on PE showed the best catalytic activity in all the examined parameters when compared to native amylase, especially at high temperatures. When immobilized on glass, α-amylase showed better activity than the native enzyme over all pH and temperature values studied. However, the immobilization on PC did not improve the enzyme activity at any pH and any temperature compared to the free amylase. The kinetic parameters, K_m and V_max were also calculated. The amylase coated PE showed the most favorable kinetic parameters (K_m = 5 g L⁻¹ and V_max = 5E−07 mol mL⁻¹ min⁻¹). In contrast, the anchored enzyme-PC exhibited unfavorable kinetic parameters (K_m = 16 g L⁻¹, V_max = 4.2E−07 mol mL⁻¹ min⁻¹). The corresponding values for amylase-glass were K_m = 7 g L⁻¹, V_max = 1.8E−07 mol mL⁻¹ min⁻¹, relative to those obtained for the free enzyme (K_m = 6.6 g L⁻¹, V_max = 3.3E−07 mol mL⁻¹ min⁻¹).     

Nitrate and phosphate uptake kinetics of the harmful diatom Coscinodiscus wailesii,a causative organism in the bleaching of aquacultured Porphyra thalli

The large diatom Coscinodiscus wailesii is one of the problematic species which indirectly cause bleaching damage to “Nori” (Porphyra thalli) cultivation through competitive utilization of nutrients during its bloom. In the present study, we experimentally investigated the nitrate (N) and phosphate (P) uptake kinetics of C. wailesii, Harima-Nada strain. Maximum uptake rates (ρ_max), obtained by short-term experiments, were 58.3 and 95.5 pmol cell⁻¹ h⁻¹ for nitrate and 41.9 and 59.1 pmol cell⁻¹ h⁻¹ for phosphate at 9 and 20 °C, respectively. The half saturation constants for uptake (K_s) were 2.91 and 5.08 μM N and 5.62 and 6.67 μM P at 9 and 20 °C, respectively. The ρ_max values of C. wailesii, much higher than those of other marine phytoplankton species, suggest that C. wailesii is able to take up large amounts of nutrients from the water column. On the other hand, V_max/K_s (V_max; V_max = ρ_max/Q₀, Q₀; minimum cell quota) values of C. wailesii, which is a better measure to evaluate the competitive ability for nutrient uptake, were low in dominant diatom species. This parameter indicates that C. wailesii is disadvantaged compared to other diatom species in competing for nutrients, and the decreasing nutrient concentrations from winter to spring is an important factor limiting C. wailesii blooming in early spring.     

Human mitochondrial haplogroup H: The highest VO2max consumer – Is it a paradox?

Mitochondrial background has been demonstrated to influence maximal oxygen uptake (VO_2max, in mL kg^?1 min^?1), but this genetic influence can be compensated for by regular exercise. A positive correlation among electron transport chain (ETC) coupling, ATP and reactive oxygen species (ROS) production has been established, and mitochondrial variants have been reported to show differences in their ETC performance. In this study, we examined in detail the VO_2max differences found among mitochondrial haplogroups. We recruited 81 healthy male Spanish Caucasian individuals and determined their mitochondrial haplogroup. Their VO_2max was determined using incremental cycling exercise (ICE). VO_2max was lower in J than in non-J haplogroup individuals (P = 0.04). The H haplogroup was responsible for this difference (VO_2max; J vs. H; P = 0.008) and this group also had significantly higher mitochondrial oxidative damage (mtOD) than the J haplogroup (P = 0.04). In agreement with these results, VO_2max and mtOD were positively correlated (P = 0.01). Given that ROS production is the major contributor to mtOD and consumes four times more oxygen per electron than the ETC, our results strongly suggest that ROS production is responsible for the higher VO_2max found in the H variant. These findings not only contribute to a better understanding of the mechanisms underneath VO_2max, but also help to explain some reported associations between mitochondrial haplogroups and mtOD with longevity, sperm motility, premature aging and susceptibility to different pathologies.     

Dosimetric comparison of RapidPlan and manually optimized plans in volumetric modulated arc therapy for prostate cancer

PurposeThis study evaluated whether RapidPlan based plans (RP plans) created by a single optimization, are usable in volumetric modulated arc therapy (VMAT) for patients with prostate cancer.MethodsWe used 51 previously administered VMAT plans to train a RP model. Thirty RP plans were created by a single optimization without planner intervention during optimization. Differences between RP plans and clinical manual optimization (CMO) plans created by an experienced planner for the same patients were analyzed (Wilcoxon tests) in terms of homogeneity index (HI), conformation number (CN), D_95%, and D_2% to planning target volume (PTV), mean dose, V_50Gy, V_70Gy, V_75Gy, and V_78Gy to rectum and bladder, monitor unit (MU), and multi-leaf collimator (MLC) sequence complexity.ResultsRP and CMO values for PTV D_95%, PTV D_2%, HI, and CN were significantly similar (p < 0.05 for all). RP mean dose, V_50Gy, and V_70Gy to rectum were superior or comparable to CMO values; RP V_75Gy and V_78Gy were higher than in CMO plans (p < 0.05). RP bladder dose-volume parameter values (except V_78Gy) were lower than in CMO plans (p < 0.05). MU values were RP: 730 ± 55 MU and CMO: 580 ± 37 MU (p < 0.05); and MLC sequence complexity scores were RP: 0.25 ± 0.02 and CMO: 0.35 ± 0.03 (p < 0.05).ConclusionsRP plans created by a single optimization were clinically acceptable in VMAT for patient with prostate cancer. Our simple model could reduce optimization time, independently of planner’s skill and knowledge.     

Novel nicotine analogues with potential anti-mycobacterial activity

Tuberculosis (TB) is the second leading lethal infectious disease in the world after acquired immuno deficiency (AIDs). We have developed a series of twenty-five novel nicotine analogues with de-addiction property and tested them for their activity against Mycobacterium tuberculosis (MTB). In an effort to increase the specificity of action and directing nicotine analogues to target MTB, four promising compounds were further optimized via molecular docking studies against the Dihydrofolate reductase of MTB. After lead optimization, one nicotine analogue [3-(5-(3fluorophenyl)nicotinoyl)-1-methylpyrrolidin-2-one] exhibited minimum inhibitory concentration of 1 μg/mL (2.86 nM) against M. tuberculosis (H37Rv strain), a human pathogenic strain of clinically significant importance. Pharmacokinetic analysis of [3-(5-(3fluorophenyl)nicotinoyl)-1methylpyrrolidin-2-one] with lowest MIC value via oral route in Wistar rats revealed that at a dosage of 5 mg/kg body weight gave a maximum serum drug concentration (C_max) of 2.86 μg/mL, T_max of one hour and a half-life (T_1/2) of more than 24 h and Volume of distribution (V_d) of 27.36 L. Whereas the parenteral (intra venous) route showed a C_max of 3.37 μg/mL, T_max of 0.05 h, T_1/2 of 24 h and V_d equivalent to 23.18 L. The acute oral toxicity and repeated oral toxicity studies in female Wistar rats had an LD₅₀ > 2000 mg/kg body weight. Our data suggests that nicotine derivatives developed in the present study has good metabolic stability with tunable pharmacokinetics (PK) with therapeutic potential to combat MTB. However, further in vivo studies for anti-tuberculosis activity and elucidation of mode of action could result in more promising novel drug for treating MTB. To the best of our knowledge this is the first report revealing the anti-mycobacterial potential of nicotine analogue at potential therapeutic concentrations.