Macrophage responses to hypoxia: relevance to disease mechanisms

Macrophages are ubiquitous in the stromal compartment of tissues under normal physiological conditions and the number of these cells increases markedly with the onset and progression of many pathological states. The mechanisms underlying this response are well described in such conditions as wound healing and malignant tumors, where tissue-specific signals enhance the extravasation of blood monocytes and their subsequent differentiation into macrophages. Recent evidence suggests that macrophages may also be stimulated by microenvironmental factors present in diseased tissues to perform distinct, tissue-specific activities. One such factor, hypoxia (low oxygen tension), results from insufficient vascular perfusion of a given tissue. Various studies have shown that experimental hypoxia alters the morphology, expression of cell surface markers, viability, phagocytosis, metabolic activity, and release of cytokines by macrophages. Here we review the evidence for these macrophage responses to hypoxia, the involvement of co-stimuli, and their implications for the role of macrophages in various disease processes. Because the intracellular mechanisms mediating the effects of hypoxia on gene expression in other cell types have been characterized recently, we discuss their possible involvement in the effects of hypoxia on gene expression in macrophages.

Cellular mechanisms of fatigue in skeletal muscle

Prolonged activation of skeletal muscle leads to a decline of force production known as fatigue. In this review we outline the ionic and metabolic changes that occur in muscle during prolonged activity and focus on how these changes might lead to reduced force. We discuss two distinct types of fatigue: fatigue due to continuous high-frequency stimulation and fatigue due to repeated tetanic stimulation. The causes of force decline are considered under three categories: 1) reduced Ca2+ release from the sarcoplasmic reticulum, 2) reduced myofibrillar Ca2+ sensitivity, and 3) reduced maximum Ca(2+)-activated tension. Reduced Ca2+ release can be due to impaired action potential propagation in the T tubules, and this is a principal cause of the tension decline with continuous tetanic stimulation. Another type of failing Ca2+ release, which is homogeneous across the fibers, is prominent with repeated tetanic stimulation; the underlying mechanisms of this reduction are not fully understood, although several possibilities emerge. Changes in intracellular metabolites, particularly increased concentration of Pi and reduced pH, lead to reduced Ca2+ sensitivity and reduced maximum tension, which make an important contribution to the force decline, especially with repeated tetanic stimulation.

Characterization of plasma lipoproteins separated and purified by agarose-column chromatography

1. A simple method for isolation of individual human plasma lipoprotein classes is presented. In this technique, lipoproteins are removed from plasma at d1.225 by ultracentrifugation, after which they are separated and purified by agarose-column chromatography. 2. Three major classes are obtained after agarose-column chromatography. Separation between classes is excellent; more than 95% of the lipoproteins eluted from the column are recovered in the form of a purified lipoprotein class. 3. Each lipoprotein class was characterized immunologically, chemically, electrophoretically and by electron microscopy. A comparison of the properties of the column-isolated lipoproteins was made with very-low-density lipoproteins, low-density lipoproteins, and high-density lipoproteins separated by sequential ultracentrifugation at densities of 1.006, 1.063 and 1.21 respectively. 4. By each criterion, peak-I lipoproteins from the agarose column are the same as very-low-density lipoproteins, peak-II lipoproteins are the same as low-density lipoproteins, and peak-III lipoproteins are the same as high-density lipoproteins. Thus the lipoprotein classes isolated by both methods are similar if not identical. 5. The agarose-column separation technique offers the advantage of a two- to three-fold saving in time. In addition, the column-elution pattern serves as a recording of the size distribution of lipoproteins in plasma. 6. The most complete characterization is reported for human plasma lipoproteins. The results with rhesus-monkey and rabbit lipoproteins were identical.

Melanomas of the eye and other noncutaneous sites: epidemiologic aspects

The Third National Cancer Survey, 1969-71, reported 432 patients with noncutaneous melanoma, 79% originating in the eye. As with skin melanoma, ocular tumors were more common in whites than blacks and predominated in females at younger ages and males after middle life. On the other hand, ocular melanoma did not show the strong North-South gradient seen with skin melanoma; this suggested no relation to sunlight exposure.

Intracellular calcium and tension during fatigue in isolated single muscle fibres from Xenopus laevis

1. Single muscle fibres were dissected from Xenopus lumbrical muscles and microinjected with the photoprotein aequorin in order to measure the myoplasmic free calcium concentration ([Ca2+]i). Fatigue was produced by repeated intermittent tetanic stimulation continued until tension had declined to approximately 50% of the initial level. Fibres were then allowed to recover by giving tetani at less frequent intervals. Aequorin light (a measure of [Ca2+]i) and tension were measured during fatiguing stimulation and recovery. 2. During fatiguing stimulation, tetanic tension declined steadily, but peak aequorin light first increased before declining substantially. The largest light signal was about 155% of initial control while at the end of fatiguing stimulation the tetanic light fell to about 14% of control. 3. Fibres showed a characteristic slowing of relaxation in the fatigued state. This was associated with a slowing of the rate of decline of the aequorin light signal. 4. Intracellular acidosis produced by equilibrating the Ringer solution with either 5 or 15% CO2 caused an increase in the light signal associated with a tetanus. Carbon dioxide also caused a reduction of tension and a slowing of relaxation. 5. In vivo pCa-tension curves were constructed by exposing the fibres to a series of K+ concentrations which produced contractures of different sizes. Light and tension were measured during periods when both were relatively stable and the light signal was subsequently converted to pCa. 6. Exposure of fibres to 5 or 15% CO2 caused the pCa-tension curve to be shifted to the right of the control curve. This indicates a reduced Ca2+ sensitivity of the contractile proteins, which is in agreement with results from skinned fibre studies. 7. The pCa-tension points obtained from tetani during the early part of fatiguing stimulation also deviated to the right of the control pCa-tension curve, suggesting a reduced Ca2+ sensitivity of the contractile proteins. At the end of fatiguing stimulation, however, pCa-tension points did not differ greatly from the control pCa-tension curve, suggesting that Ca2+ sensitivity was approximately normal. Thus the reduced [Ca2+]i during tetani at the end of fatiguing stimulation (when tension was reduced to approximately 50%) could explain all of the reduction in tension. 8. After fatiguing stimulation, tension and light recovered monotonically in some fibres; however, in the majority of fibres, tension and light showed a secondary decline followed by a slower recovery (post-contractile depression). 9. During post-contractile depression, caffeine contractures or tetani in the presence of caffeine gave increased aequorin light signals and the tension developed was close to that produced in an unfatigued tetanus.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of proline accumulation in halophytes

It is shown that in the majority of higher plant halophytes examined proline is the major component of the amino acid pool in plants collected from the field. In Triglochin maritima L. free proline can represent 10-20% of the shoot dry weight. Under non-saline conditions proline levels are low and increase as the salinity is raised. Comparisons of inland and coastal populations of Ameria maritima Willd. suggest that the capacity to accumulate proline is correlated with salt tolerance. It is suggested that proline functions as a source of solute for intracellular osmotic adjustments under saline conditions.

Association of proinflammatory cytokines and chemotherapy-associated cognitive impairment in breast cancer patients: a multi-centered, prospective, cohort study

BACKGROUND

Existing evidence suggests that proinflammatory cytokines play an intermediary role in postchemotherapy cognitive impairment. This is one of the largest multicentered, cohort studies conducted in Singapore to evaluate the prevalence and proinflammatory biomarkers associated with cognitive impairment in breast cancer patients.

PATIENTS AND METHODS

Chemotherapy-receiving breast cancer patients (stages I-III) were recruited. Proinflammatory plasma cytokines concentrations [interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor, interferon-γ and tumor necrosis factor-α] were evaluated at 3 time points (before chemotherapy, 6 and 12 weeks after chemotherapy initiation). The FACT-Cog (version 3) was utilized to evaluate patients' self-perceived cognitive disturbances and a computerized neuropsychological assessment (Headminder) was administered to evaluate patients' memory, attention, response speed and processing speed. Changes of cognition throughout chemotherapy treatment were compared against the baseline. Linear mixed-effects models were applied to test the relationships of clinical variables and cytokine concentrations on self-perceived cognitive disturbances and each objective cognitive domain.

RESULTS

Ninety-nine patients were included (age 50.5 ± 8.4 years; 81.8% Chinese; mean duration of education = 10.8 ± 3.3 years). Higher plasma IL-1β was associated with poorer response speed performance (estimate: -0.78; 95% confidence interval (CI) -1.34 to -0.03; P = 0.023), and a higher concentration of IL-4 was associated with better response speed performance (P = 0.022). Higher concentrations of IL-1β and IL-6 were associated with more severe self-perceived cognitive disturbances (P = 0.018 and 0.001, respectively). Patients with higher concentrations of IL-4 also reported less severe cognitive disturbances (P = 0.022).

CONCLUSIONS

While elevated concentrations of IL-6 and IL-1β were observed in patients with poorer response speed performance and perceived cognitive disturbances, IL-4 may be protective against chemotherapy-associated cognitive impairment. This study is important because cytokines would potentially be mechanistic mediators of chemotherapy-associated cognitive changes.

D-Aspartate stimulation of testosterone synthesis in rat Leydig cells

D-Aspartate increases human chorionic gonadotropin-induced testosterone production in purified rat Leydig cells. L-Aspartate, D-,L-glutamate or D-,L-asparagine could not substitute for D-aspartate and this effect was independent of glutamate receptor activation. Testosterone production was enhanced only in cells cultured with D-aspartate for more than 3 h. The increased production of testosterone was well correlated with the amounts of D-aspartate incorporated into the Leydig cells, and L-cysteine sulfinic acid, an inhibitor of D-aspartate uptake, suppressed both testosterone production and intracellular D-aspartate levels. D-Aspartate therefore is presumably taken up into cells to increase steroidogenesis. Intracellular D-aspartate probably acts on cholesterol translocation into the inner mitochondrial membrane, the rate-limiting process in steroidogenesis.

Effects of acidosis on ventricular muscle from adult and neonatal rats

We compared the response of ventricular muscle from adult and neonatal rats to hypercapnic acidosis. In adult muscle, acidosis caused an initial rapid fall of developed tension to 30 +/- 5% of control (mean +/- SEM, n = 6). However, tension recovered slowly to a steady state that was 56 +/- 6% of control. In neonatal muscle, acidosis caused a significantly smaller initial fall in tension to 43 +/- 3% (n = 8, p less than 0.05), but the tension then showed a subsequent slower fall to a steady state that was 29 +/- 4% of control, significantly less than in the adult (p less than 0.01). We have attempted to identify the mechanisms underlying these differences in response. In detergent-skinned myofibrils, reducing the pH from 7.0 to 6.5 caused a reduction in the pCa50 of 0.61 units in the adult muscle, but only 0.27 units in the neonatal ventricular muscle. Myofibrillar Ca2+ sensitivity in neonatal ventricular muscle is thus less susceptible to the effects of acidic pH than that of adult muscle. Since intracellular pH decreases rapidly on application of increased external CO2, these results are consistent with the finding that, initially, developed tension in neonatal muscles is less sensitive to the effects of acidosis. Sodium dodecylsulfate gel electrophoresis of myofibrillar preparations from adult and neonatal rats demonstrated differences in thin filament proteins, including troponin I, which may underlie the observed differences in Ca2+ sensitivity. In adult rat ventricular muscles, the slow recovery of tension during acidosis is associated with an increase in the amplitude of the Ca2+ transients to 263 +/- 34% of control (n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Case-control study of malignant melanoma in Washington State. II. Diet, alcohol, and obesity

Intakes of vitamin A, dietary antioxidants, and other dietary components were examined for their relation to the risk of malignant melanoma among 234 cases and 248 controls in three counties of western Washington State. Cases were drawn from persons diagnosed with melanoma between 1984 and 1987 and identified through a Seattle-Puget Sound cancer registry. Population controls were identified through random digit dialing and were randomly selected, stratified by age, sex, and county. Subjects completed a telephone interview and a mailed food frequency questionnaire asking for information on diet, demographic factors, and factors known to be associated with melanoma. Subjects were asked to estimate their food intake 7 years prior to diagnosis for cases and during a comparable time period for controls. Among data on 16 nutrients calculated from reported food intake, one significant finding emerged: Vitamin E obtained from food was inversely related to risk of melanoma (for highest quartile vs. lowest quartile, age-, education-, and energy intake-adjusted odds ratio (OR) = 0.34, 95% confidence interval (CI) 0.16-0.72; p for trend = 0.01). When intake of nutrients from food plus vitamin and mineral supplements was considered, zinc from food and supplements was associated with a decreased risk of melanoma (for highest quartile vs. lowest quartile, adjusted OR = 0.46, 95% CI 0.24-0.91; p for trend = 0.01). There was no evidence that vitamin A, preformed retinol, or carotenoids were associated with a decreased risk of melanoma or that alcohol or polyunsaturated fats were associated with an increased risk. Body mass index (weight (kg)/height (m)2) was significantly related to melanoma risk; cases were more obese than controls (for highest quartile vs. lowest quartile, age-, sex-, and education-adjusted OR = 1.90, 95% CI 1.10-3.27; p for trend = 0.02). These results provide limited support for the hypothesis that antioxidants such as vitamin E or cofactors in protection from oxidative damage such as zinc may be protective for melanoma, and they suggest that obesity should be measured in future studies of melanoma.

Malignant melanoma: social status and outdoor work

The incidence of, and mortality from, malignant melanoma of skin in whites are strongly influenced by socio-economic conditions. Professional and administrative workers have the highest rates of all. Clerks and salesmen have higher rates than skilled manual workers, who have higher rates than unskilled workers. Women, when classified by the occupation of their husbands, show a similar relationship to social status. The biases of incidence data from systems of cancer registration, and mortality data from death certificates are different, and the consistency of the data from different periods and from different populations suggests that the relationship is real. The bulk of the data is from Britain, but there is sufficient from the U.S. to indicate that the effect is not restricted to one country. No consistent increase in risk was found in outdoor workers compared with indoor workers of similar socio-economic status.

Changes in intracellular calcium during mechanical alternans in isolated ferret ventricular muscle

Alternans in heart is important as pulsus alternans in cardiac failure and electrophysiological alternans in myocardial ischemia. The explanation of this phenomenon is still unclear. We attempted to investigate the cellular mechanisms of alternans by measuring intracellular free calcium concentration [( Ca2+]i) with the photoprotein aequorin in isolated ferret papillary muscles. Tension and length were also recorded simultaneously. Transient mechanical alternans lasting five to 20 contractions could be reliably induced in this preparation by following a 30-second rest period with stimulation at a fast rate (2-4 Hz). Production of sustained mechanical alternans, which lasted longer than 20 contractions and could persist for several hundred contractions, required additional interventions, consisting of a lower temperature (25 degrees C), a lower external calcium concentration (1 mM), and a lower pH (6.91) than control conditions (0.33-0.5 Hz, 30 degrees C, 2 mM Ca2+, pH 7.36). Transient mechanical alternans was associated with transient in-phase alternation of aequorin light and, hence, [Ca2+]i. Sustained mechanical alternans was associated with sustained in-phase alternation of aequorin light as well as incomplete relaxation of tension. However, when muscles were switched from isometric to unloaded isotonic contraction, relaxation between stimuli was complete but contraction and the aequorin light signal continued to alternate. The addition of 10 mM caffeine or 10 microns ryanodine abolished transient and sustained mechanical alternans and also abolished the associated alternation of aequorin light. Commensurate with the action of ryanodine, which allows the sarcoplasmic reticulum to reaccumulate calcium to a limited extent after a period of rapid stimulation, sustained mechanical alternans sometimes reappeared in an attenuated form 30 to 50 contractions after the addition of ryanodine. These results demonstrate that incomplete muscle relaxation between beats need not be present for alternans to occur, and support the hypothesis that alternans is caused by intracellular calcium cycling involving the sarcoplasmic reticulum.

Regulatory interaction between the cystic fibrosis transmembrane conductance regulator and HCO3- salvage mechanisms in model systems and the mouse pancreatic duct

The pancreatic duct expresses cystic fibrosis transmembrane conductance regulator (CFTR) and HCO3- secretory and salvage mechanisms in the luminal membrane. Although CFTR plays a prominent role in HCO3- secretion, the role of CFTR in HCO3- salvage is not known. In the present work, we used molecular, biochemical, and functional approaches to study the regulatory interaction between CFTR and the HCO3- salvage mechanism Na+/H+ exchanger isoform 3 (NHE3) in heterologous expression systems and in the native pancreatic duct. We found that CFTR regulates NHE3 activity by both acute and chronic mechanisms. In the pancreatic duct, CFTR increases expression of NHE3 in the luminal membrane. Thus, luminal expression of NHE3 was reduced by 53% in ducts of homozygote DeltaF508 mice. Accordingly, luminal Na+-dependent and HOE694- sensitive recovery from an acid load was reduced by 60% in ducts of DeltaF508 mice. CFTR and NHE3 were co-immunoprecipitated from PS120 cells expressing both proteins and the pancreatic duct of wild type mice but not from PS120 cells lacking CFTR or the pancreas of DeltaF508 mice. The interaction between CFTR and NHE3 required the COOH-terminal PDZ binding motif of CFTR, and mutant CFTR proteins lacking the C terminus were not co-immunoprecipitated with NHE3. Furthermore, when expressed in PS120 cells, wild type CFTR, but not CFTR mutants lacking the C-terminal PDZ binding motif, augmented cAMP-dependent inhibition of NHE3 activity by 31%. These findings reveal that CFTR controls overall HCO3- homeostasis by regulating both pancreatic ductal HCO3- secretory and salvage mechanisms.

D-aspartate uptake into cultured rat pinealocytes and the concomitant effect on L-aspartate levels and melatonin secretion

Significant amounts of D-aspartate (Asp) are found in mammalian tissues and D-Asp is presumed to play some significant, but as yet undefined physiological role. However, it is not known whether D-Asp is synthesized in mammals. In this study, we addressed this issue in cultured rat pinealocytes, parenchymal cells of the pineal gland, which contain significant amounts of D-Asp. Biosynthesis of D-Asp was found to be minimal to non-existent in cultured rat pinealocytes. We then investigated the mechanism of uptake of D-Asp into these cells and its consequent effect on cell function. D-Asp was efficiently taken up into cells, in a time- and dose-dependent manner. Interestingly, the L-Asp levels in the cells and media decreased concomitantly with the uptake of D-Asp. This decrease was not due to D-Asp cytotoxicity, since the cellular levels of othernted. D-Serine and D-alanine were not taken up efficiently into the cells and the cellular levels of L-serine and L-alanine were unchanged. Also, immunocytochemical staining with anti-D-Asp antibody showed that D-Asp, which had been taken up into the cells, was dispersed throughout the cytoplasm. In response to norepinephrine stimulation, pinealocytes, which had been pretreated with D-Asp released D-Asp as well as L-Asp. In these cells, norepinephrine-induced secretion of melatonin, a pineal hormone, was suppressed. The mechanism of this suppression is discussed here.

Spatial gradients of intracellular calcium in skeletal muscle during fatigue

We have measured the distribution of intracellular calcium concentration in isolated single muscle fibres from Xenopus laevis using the fluorescent calcium indicator fura-2 with digital imaging fluorescence microscopy. Under control conditions, resting and tetanic calcium were uniform throughout a fibre. When fatigue was produced using a prolonged, high-frequency tetanus, the distribution of calcium within muscle fibres became non-uniform, with greater levels near the outer parts of a fibre than near the centre. This non-uniform distribution of calcium was rapidly abolished by lowering the stimulation frequency. When fatigue was produced using a series of repeated intermittent tetani, tetanic calcium showed an initial small increase, followed by a decrease as stimulation was continued. The distribution of calcium remained uniform under these conditions. Calcium distribution was also uniform during recovery from intermittent tetanic stimulation. Although fibres varied considerably in their fatigue resistance, the time for tension to fall to 50% was correlated with the reduction in tetanic calcium seen at this time. These results indicate that there are at least two patterns of reduced calcium release that can contribute to the development of fatigue. The appearance of a calcium gradient is consistent with impaired t-tubular conduction, while a uniform reduction of calcium is likely to be due to the action of metabolic factors on systems controlling calcium homeostasis within the cell.

Changes in tetanic and resting [Ca2+]i during fatigue and recovery of single muscle fibres from Xenopus laevis

1. Single muscle fibres were dissected from the toe muscles of Xenopus laevis and microinjected with Fura-2 to measure myoplasmic calcium concentration ([Ca2+]i). Injected fibres were illuminated at 340 and 380 nm and the ratio of the resulting fluorescence at 505 nm (the Fura-2 ratio) was taken as a measure of [Ca2+]i. Fibres were fatigued at 21 degrees C by repeated tetani until developed tension had fallen to 50% of control. 2. Tetanic tension declined monotonically during fatiguing stimulation, whereas the tetanic Fura-2 ratio first increased and then declined. At the 10th tetanus, tension was 87% of control whereas the Fura-2 ratio was 106% of control. At the end of fatiguing stimulation, where tension was around 50% of control, the tetanic Fura-2 ratio was reduced to 71%. The rate of decline of both tension and the Fura-2 ratio after a tetanus slowed during fatigue. During recovery, the tension and the tetanic Fura-2 ratio recovered in parallel. 3. The resting Fura-2 ratio increased throughout fatigue reaching 237% of control when tension had declined to 50%. There was a rapid phase of recovery, complete within 1 min, by which time the resting Fura-2 ratio was 198% of control. Subsequent recovery was slower and took 20-30 min to reach a stable level which was 121% of control. 4. The resting Fura-2 ratio towards the end of fatiguing stimulation was greater than the tetanic Fura-2 ratio in the early part of recovery although there was no detectable increase of resting tension during fatiguing stimulation. This observation suggests that the Ca2+ sensitivity of the contractile proteins was reduced at the end of fatiguing stimulation. 5. Plots of the tetanic tension against tetanic Fura-2 ratios throughout fatiguing stimulation and recovery also suggested that Ca2+ sensitivity was reduced during fatiguing stimulation when compared to recovery. 6. The increases in resting [Ca2+]i caused by raised [K+]o (from 2.5 to 10 mM) and/or by application of 15% CO2 were much less than those produced by fatiguing stimulation. Much of the elevated [Ca2+]i in fatigue could be reversed by application of dantrolene (25 microM). 7. The results suggest that both reduced tetanic [Ca2+]i and reduced Ca2+ sensitivity contribute to the decline of tension during fatigue.(ABSTRACT TRUNCATED AT 400 WORDS)