Somatostatin analogues improve health-related quality of life in polycystic liver disease: a pooled analysis of two randomised, placebo-controlled trials.

BACKGROUND: Polycystic liver disease is associated with impaired health-related quality of life (HRQL). Somatostatin analogues reduce hepatomegaly in polycystic liver disease. AIM: To determine whether somatostatin analogues improve HRQL and to identify factors associated with change in HRQL in polycystic liver disease. METHODS: We pooled data from two randomized, double-blind, placebo-controlled trials that evaluated HRQL using the Short-Form 36 (SF-36) in 96 polycystic liver disease patients treated 6-12 months with somatostatin analogues or placebo. The SF-36 contains a summarizing physical and mental component score and was administered at baseline and at the end of treatment. We used random effect models to delineate the effect of somatostatin analogues on HRQL. We determined the effect of demographics, height-adjusted liver volume, change in liver volume, somatostatin analogue-associated side effects with change in HRQL. In patients with autosomal dominant polycystic kidney disease, we estimated the effect of height-adjusted kidney volume and change in kidney volume in relation to HRQL. RESULTS: Physical component scores improved with somatostatin analogues, but remained unchanged with placebo (3.41 ± 1.29 vs. -0.71 ± 1.54, P = 0.044). Treatment had no impact on the mental component score. Large liver volume was independently associated with larger HRQL decline during follow up (-4.04 ± 2.02 points per logarithm liver volume, P = 0.049). In autosomal dominant polycystic kidney disease, patients with large liver and kidney volumes had larger decline in HRQL (5.36 ± 2.54 points per logarithm liver volume; P = 0.040 and -4.00 ± 1.88 per logarithm kidney volume; P = 0.039). CONCLUSION: Somatostatin analogues improve HRQL in symptomatic polycystic liver disease. Halting the progressive nature of polycystic liver disease is necessary to prevent further decline of HRQL in severe hepatomegaly.

Regulation of cellular gas exchange, oxygen sensing, and metabolic control.

Cells must continuously monitor and couple their metabolic requirements for ATP utilization with their ability to take up O2 for mitochondrial respiration. When O2 uptake and delivery move out of homeostasis, cells have elaborate and diverse sensing and response systems to compensate. In this review, we explore the biophysics of O2 and gas diffusion in the cell, how intracellular O2 is regulated, how intracellular O2 levels are sensed and how sensing systems impact mitochondrial respiration and shifts in metabolic pathways. Particular attention is paid to how O2 affects the redox state of the cell, as well as the NO, H2S, and CO concentrations. We also explore how these agents can affect various aspects of gas exchange and activate acute signaling pathways that promote survival. Two kinds of challenges to gas exchange are also discussed in detail: when insufficient O2 is available for respiration (hypoxia) and when metabolic requirements test the limits of gas exchange (exercising skeletal muscle). This review also focuses on responses to acute hypoxia in the context of the original "unifying theory of hypoxia tolerance" as expressed by Hochachka and colleagues. It includes discourse on the regulation of mitochondrial electron transport, metabolic suppression, shifts in metabolic pathways, and recruitment of cell survival pathways preventing collapse of membrane potential and nuclear apoptosis. Regarding exercise, the issues discussed relate to the O2 sensitivity of metabolic rate, O2 kinetics in exercise, and influences of available O2 on glycolysis and lactate production.

Increasing temperature speeds intracellular PO2 kinetics during contractions in single Xenopus skeletal muscle fibers.

Precise determination of the effect of muscle temperature (T(m)) on mitochondrial oxygen consumption kinetics has proven difficult in humans, in part due to the complexities in controlling for T(m)-related variations in blood flow, fiber recruitment, muscle metabolism, and contractile properties. To address this issue, intracellular Po(2) (P(i)(O(2))) was measured continuously by phosphorescence quenching following the onset of contractions in single Xenopus myofibers (n = 24) while controlling extracellular temperature. Fibers were subjected to two identical contraction bouts, in random order, at 15°C (cold, C) and 20°C (normal, N; n = 12), or at N and 25°C (hot, H; n = 12). Contractile properties were determined for every contraction. The time delay of the P(i)(O(2)) response was significantly greater in C (59 ± 35 s) compared with N (35 ± 26 s, P = 0.01) and H (27 ± 14 s, P = 0.01). The time constant for the decline in P(i)(O(2)) was significantly greater in C (89 ± 34 s) compared with N (52 ± 15 s; P < 0.01) and H (37 ± 10 s; P < 0.01). There was a linear relationship between the rate constant for P(i)(O(2)) kinetics and T(m) (r = 0.322, P = 0.03). Estimated ATP turnover was significantly greater in H than in C (P < 0.01), but this increased energy requirement alone with increased T(m) could not account for the differences observed in P(i)(O(2)) kinetics among conditions. These results demonstrate that P(i)(O(2)) kinetics in single contracting myofibers are dependent on T(m), likely caused by temperature-induced differences in metabolic demand and by temperature-dependent processes underlying mitochondrial activation at the start of muscle contractions.

Enhanced mitochondrial sensitivity to creatine in rats bred for high aerobic capacity.

Qualitative and quantitative measures of mitochondrial function were performed in rats selectively bred 15 generations for intrinsic aerobic high running capacity (HCR; n = 8) or low running capacity (LCR; n=8). As estimated from a speed-ramped treadmill exercise test to exhaustion (15 degrees slope; initial velocity of 10 m/min, increased 1 m/min every 2 min), HCR rats ran 10 times further (2,375+/-80 m) compared with LCR rats (238+/-12 m). Fiber bundles were obtained from the soleus and chemically permeabilized. Respiration was measured 1) in the absence of ADP, 2) in the presence of a submaximally stimulating concentration of ADP (0.1 mM ADP, with and without 20 mM creatine), and 3) in the presence of a maximally stimulating concentration of ADP (2 mM). Although non-ADP-stimulated and maximally ADP-stimulated rates of respiration were 13% higher in HCR compared with LCR, the difference was not statistically significant (P>0.05). Despite a similar rate of respiration in the presence of 0.1 mM ADP, HCR rats demonstrated a higher rate of respiration in the presence of 0.1 mM ADP+20 mM creatine (HCR 33% higher vs. LCR, P<0.05). Thus mitochondria from HCR rats exhibit enhanced mitochondrial sensitivity to creatine (i.e., the ability of creatine to decrease the Km for ADP). We propose that increased respiratory sensitivity to ADP in the presence of creatine can effectively increase muscle sensitivity to ADP during exercise (when creatine is increased) and may be, in part, a contributing factor for the increased running capacity in HCR rats.

Measurement of activation energy and oxidative phosphorylation onset kinetics in isolated muscle fibers in the absence of cross-bridge cycling.

This study utilized N-benzyl-p-toluene sulfonamide (BTS), a potent inhibitor of cross-bridge cycling, to measure 1) the relative metabolic costs of cross-bridge cycling and activation energy during contraction, and 2) oxygen uptake kinetics in the presence and absence of myosin ATPase activity, in isolated Xenopus laevis muscle fibers. Isometric tension development and either cytosolic Ca2+ concentration ([Ca2+]c) or intracellular Po2 (PiO2) were measured during contractions at 20 degrees C in control conditions (Con) and after exposure to 12.5 microM BTS. BTS attenuated tension development to 5+/-0.4% of Con but did not affect either resting or peak [Ca2+]c during repeated isometric contractions. To determine the relative metabolic cost of cross-bridge cycling, we measured the fall in PiO2) (DeltaPiO2; a proxy for Vo2) during contractions in Con and BTS groups. BTS attenuated DeltaP(iO2) by 55+/-6%, reflecting the relative ATP cost of cross-bridge cycling. Thus, extrapolating DeltaPiO2 to a value that would occur at 0% tension suggests that actomyosin ATP requirement is approximately 58% of overall ATP consumption during isometric contractions in mixed fiber types. BTS also slowed the fall in PiO2) (time to 63% of overall DeltaPiO2) from 75+/-9 s (Con) to 101+/-9 s (BTS) (P<0.05), suggesting an important role of the products of ATP hydrolysis in determining the Vo2 onset kinetics. These results demonstrate in isolated skeletal muscle fibers that 1) activation energy accounts for a substantial proportion (approximately 42%) of total ATP cost during isometric contractions, and 2) despite unchanged [Ca2+]c transients, a reduced rate of ATP consumption results in slower Vo2 onset kinetics.

Intracellular pH during sequential, fatiguing contractile periods in isolated single Xenopus skeletal muscle fibers.

The purpose of the present study was to test the hypothesis that a preceding contractile period in isolated single skeletal muscle fibers would attenuate the decrease in pH during an identical, subsequent contractile period, thereby reducing the rate of fatigue. Intact single skeletal muscle fibers (n = 9) were isolated from Xenopus lumbrical muscle and incubated with the fluorescent cytosolic H+ indicator 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) AM for 30 min. Two identical contractile periods were performed in each fiber, separated by a 1-h recovery period. Force and intracellular pH (pHi) fluorescence were measured simultaneously while fibers were stimulated (tetanic contractions of 350-ms trains with 70-Hz stimuli at 9 V) at progressively increasing frequencies (0.25, 0.33, 0.5, and 1 contraction/s) until the development of fatigue (to 60% initial force). No significant difference (P < 0.05) was observed between the first and second contractile periods in initial force development, resting pHi, or time to fatigue (5.3 +/- 0.5 vs. 5.1 +/- 0.6 min). However, the relative decrease in the BCECF fluorescence ratio (and therefore pHi) from rest to the fatigue time point was significantly greater (P < 0.05) during the first contractile period (to 65 +/- 4% of initial resting values) compared with the second (77 +/- 4%). The results of the present study demonstrated that, when preceded by an initial fatiguing contractile period, the rise in cytosolic H+ concentration in contracting single skeletal muscle fibers during a second contractile period was significantly reduced but did not attenuate the fatigue process in the second contractile period. These results suggest that intracellular factors other than H+ accumulation contribute to the fall in force development under these conditions.

Trimetazidine reduces basal cytosolic Ca2+ concentration during hypoxia in single Xenopus skeletal myocytes.

We tested the hypotheses that: (1) Ca(2+) handling and force production would be irreversibly altered in skeletal muscle during steady-state contractions when subjected to severe, prolonged hypoxia and subsequent reoxygenation; and (2) application of the cardio-protective drug trimetazidine would attenuate these alterations. Single, living skeletal muscle fibres from Xenopus laevis were injected with the Ca(2+) indicator fura 2, and incubated for 1 h prior to stimulation in 100 micro M TMZ-Ringer solution (TMZ; n = 6) or standard Ringer solution (CON; n = 6). Force and relative free cytosolic Ca(2+) concentration ([Ca(2+)](c)) were measured during continuous tetanic contractions produced every 5 s as fibres were sequentially perfused in the following manner: 3 min high extracellular P(O(2)) (159 mmHg), 15 min hypoxic perfusion (3-5 mmHg) then 3 min high P(O(2)). Hypoxia caused a decrease in force and peak [Ca(2+)](c) in both the TMZ and CON fibres, with no significant (P < 0.05) difference between groups. However, basal [Ca(2+)](c) was significantly lower during hypoxia in the TMZ group vs. the CON group. While reoxygenation generated only modest recovery of relative force and peak [Ca(2+)](c) in both groups, basal [Ca(2+)](c) remained significantly less in the TMZ group. These results demonstrated that in contracting, single skeletal muscle fibres, TMZ prevented increases in basal [Ca(2+)](c) generated during a severe hypoxic insult and subsequent reoxygenation, yet failed to protect the cell from the deleterious effects of prolonged hypoxia followed by reoxygenation.

Two cases of non-O157:H7 Escherichia coli hemolytic uremic syndrome caused by urinary tract infection.

Escherichia coli serotype O157:H7 is a leading cause of diarrhea and hemolytic uremic syndrome (HUS). Because of the limitations of current diagnostic techniques, the prevalence of non-O157:H7 Shiga toxin-producing E coli strains is not known. We describe two patients with HUS in whom no E coli O157:H7 was demonstrable in stool cultures. On culture of the urine, the first patient was found to have E coli O113:H21 strain, and the second patient had E coli O6:H1 serotype. Shiga toxin production (stx2) by the O113:H21 isolate was confirmed. The first patient required 15 days of peritoneal dialysis and subsequently recovered renal function. At last follow-up, serum creatinine was 0.9 mg/dL. The second patient had preservation of renal function throughout the acute illness with serum creatinine of 0.5 mg/dL. The clinical presentation, bacteriology, course, and outcome as well as epidemiologic implications of the increasing number of patients with E coli urinary tract infections associated with HUS are discussed. These cases illustrate the need to investigate patients with nondiarrheal HUS for infection with Shiga toxin-producing E coli of the non-O157 strain variety.

Intracellular PO(2) decreases with increasing stimulation frequency in contracting single Xenopus muscle fibers.

There is currently some controversy regarding the manner in which skeletal muscle intracellular PO(2) changes with work intensity. Therefore, this study investigated the relationship between intracellular PO(2) and stimulation frequency in intact, isolated, single skeletal muscle fibers. Single, living muscle fibers (n = 7) were microdissected from the lumbrical muscles of Xenopus and injected with the oxygen-sensitive probe palladium-meso-tetra(4-carboxyphenyl)porphine (0.5 mM). Fibers were mounted with platinum clips to a force transducer in a chamber, which was continuously perfused with Ringer solution (pH = 7.0) at a PO(2) of approximately 30 Torr. Fibers were then stimulated sequentially for 3 min, followed by a 3-min rest, at each of five contraction frequencies (0.15, 0.2, 0.25, 0.33, and 0.5 Hz), in a random order, using tetanic contractions. Resting intracellular PO(2) averaged 31.2 +/- 0.9 Torr. During steady-state stimulation, intracellular PO(2) declined to 21.2 +/- 2.3, 17.1 +/- 2.4, 15.3 +/- 1.9, 9.8 +/- 2.0, and 5.8 +/- 1.4 Torr for 0.15, 0.2, 0.25, 0.33, and 0.5-Hz stimulation, respectively. Significant fatigue, as defined by a decrease in force to <50% of the initial force, occurred only at the highest (0.5 Hz) stimulation frequency in five of the cells and at 0.33 Hz in the other two. Regression analysis demonstrated that there was a significant (P < 0.0001, r = 0.82) negative correlation between intracellular PO(2) and contraction frequency in these isolated, single cells. The linear decrease in intracellular PO(2) with stimulation frequency, and thus energy demand, suggests that a fall in intracellular PO(2) correlates with increased oxygen uptake in these single contracting cells.

Preconditioning improves function and recovery of single muscle fibers during severe hypoxia and reoxygenation.

Reperfusion following prolonged ischemia induces cellular damage in whole skeletal muscle models. Ischemic preconditioning attenuates the deleterious effects. We tested whether individual skeletal muscle fibers would be similarly affected by severe hypoxia and reoxygenation (H/R) in the absence of extracellular factors and whether cellular damage could be alleviated by hypoxic preconditioning. Force and free cytosolic Ca2+ ([Ca2+]c) were monitored in Xenopus single muscle fibers (n = 24) contracting tetanically at 0.2 Hz during 5 min of severe hypoxia and 5 min of reoxygenation. Twelve cells were preconditioned by a shorter bout of H/R 1 h before the experimental trial. In preconditioned cells, force relative to initial maximal values (P/P(o)) and relative peak [Ca2+]c fell (P < 0.05) during 5 min of hypoxia and recovered during reoxygenation. In contrast, P/P(o) and relative peak [Ca2+]c fell more during hypoxia (P < 0.05) and recovered less during reoxygenation (P < 0.05) in control cells. The ratio of force to [Ca2+]c was significantly higher in the preconditioned cells during severe hypoxia, suggesting that changes in [Ca2+]c were not solely responsible for the loss in force. We conclude that 1) isolated skeletal muscle fibers contracting in the absence of extracellular factors are susceptible to H/R injury associated with changes in Ca2+ handling; and 2) hypoxic preconditioning improves contractility, Ca2+ handling, and cell recovery during subsequent hypoxic insult.