Development and application of a self-referencing glucose microsensor for the measurement of glucose consumption by pancreatic beta-cells

Glucose gradients generated by an artificial source and beta-cells were measured using an enzyme-based glucose microsensor, 8-microm tip diameter, as a self-referencing electrode. The technique is based on a difference measurement between two locations in a gradient and thus allows us to obtain real-time flux values with minimal impact of sensor drift or noise. Flux values were derived by incorporation of the measured differential current into Fick's first equation. In an artificial glucose gradient, a flux detection limit of 8.2 +/- 0.4 pmol.cm(-2).s(-1) (mean +/- SEM, n = 7) with a sensor sensitivity of 7.0 +/- 0.4 pA/ mM (mean +/- SEM, n = 16) was demonstrated. Under biological conditions, the glucose sensor showed no oxygen dependence with 5 mM glucose in the bulk medium. The addition of catalase to the bulk medium was shown to ameliorate surface-dependent flux distortion close to specimens, suggesting an underlying local accumulation of hydrogen peroxide. Glucose flux from beta-cell clusters, measured in the presence of 5 mM glucose, was 61.7 +/- 9.5 fmol.nL(-1).s(-1) (mean +/- SEM, n = 9) and could be pharmacologically modulated. Glucose consumption in response to FCCP (1 microM) transiently increased, subsequently decreasing to below basal by 93 +/- 16 and 56 +/- 6%, respectively (mean +/- SEM, n = 5). Consumption was decreased after the application of 10 microM rotenone by 74 +/- 5% (mean +/- SEM, n = 4). These results demonstrate that an enzyme-based amperometric microsensor can be applied in the self-referencing mode. Further, in obtaining glucose flux measurements from small clusters of cells, these are the first recordings of the real-time dynamic of glucose movements in a biological microenvironment.

Apoptosis-inducing protein, AIP, from parasite-infected fish induces apoptosis in mammalian cells by two different molecular mechanisms

AIP (apoptosis-inducing protein) is a protein purified and cloned from Chub mackerel infected with the larval nematode, Anisakis simplex, which induces apoptosis in various mammalian cells including human tumor cell lines. AIP has shown structural and functional homology to L-amino acid oxidase (LAO) which oxidizes several L-amino acids including L-lysine and AIP-induced apoptosis has been suggested to be mediated by H2O2 generated by LAO activity of AIP. In this study, we confirmed that recombinant AIP generated enough H2O2 in culture medium to induce rapid apoptosis in cells and this apoptosis was clearly inhibited by co-cultivation with antioxidants such as catalase and N-acetyl-cysteine. Surprisingly, however, we found that AIP still could induce H2O2-independent apoptosis more slowly than H2O2-dependent one in HL-60 cells even in the presence of antioxidants. In addition, the HL-60-derived cell line HP100-1, which is a H2O2-resistant variant, underwent apoptosis on treatment with AIP with a similar delayed time course. The latter apoptosis was completely blocked by addition of L-lysine to the culture medium, which is the best substrate of AIP as LAO, indicating that decreased concentration of L-lysine in the culture medium by AIP-treatment induced apoptosis. We also showed that the both apoptosis by AIP were associated with the release of cytochrome c from mitochondria and activation of caspase-9, and overexpressed Bcl-2 could inhibit both of the AIP-induced apoptosis. These results indicate that AIP induces apoptosis in cells by two distinct mechanisms; one rapid and mediated by H2O2, the other delayed and mediated by deprivation of L-lysine, both of which utilize caspase-9/cytochrome c system.

Purification and cloning of an apoptosis-inducing protein derived from fish infected with Anisakis simplex, a causative nematode of human anisakiasis

While investigating the effect of marine products on cell growth, we found that visceral extracts of Chub mackerel, an ocean fish, had a powerful and dose-dependent apoptosis-inducing effect on a variety of mammalian tumor cells. This activity was strikingly dependent on infection of the C. mackerel with the larval nematode, Anisakis simplex. After purification of the protein responsible for the apoptosis-inducing activity, we cloned the corresponding gene and found it to be a flavoprotein. This protein, termed apoptosis-inducing protein (AIP), was also found to possess an endoplasmic reticulum retention signal (C-terminal KDEL sequence) and H2O2-producing activity, indicating that we had isolated a novel reticuloplasimin with potent apoptosis-inducing activity. AIP was induced in fish only after infection with larval nematode and was localized to capsules that formed around larvae to prevent their migration to host tissues. Our results suggest that AIP may function to impede nematode infection.

Correlated oscillations in glucose consumption, oxygen consumption, and intracellular free Ca(2+) in single islets of Langerhans

Micron-sized sensors were used to monitor glucose and oxygen levels in the extracellular space of single islets of Langerhans in real-time. At 10 mM glucose, oscillations in intraislet glucose concentration were readily detected. Changes in glucose level correspond to changes in glucose consumption by glycolysis balanced by mass transport into the islet. Oscillations had a period of 3.1 +/- 0.2 min and amplitude of 0.8 +/- 0.1 mM glucose (n = 21). Superimposed on these oscillations were faster fluctuations in glucose level during the periods of low glucose consumption. Oxygen level oscillations that were out of phase with the glucose oscillations were also detected. Oscillations in both oxygen and glucose consumption were strongly dependent upon extracellular Ca(2+) and sensitive to nifedipine. Simultaneous measurements of glucose with intracellular Ca(2+) ([Ca(2+)](i)) revealed that decreases in [Ca(2+)](i) preceded increases in glucose consumption by 7.4 +/- 2.1 s during an oscillation (n = 9). Conversely, increases in [Ca(2+)](i) preceded increases in oxygen consumption by 1.5 +/- 0.2 s (n = 4). These results suggest that during oscillations, bursts of glycolysis begin after Ca(2+) has stopped entering the cell. Glycolysis stimulates further Ca(2+) entry, which in turn stimulates increases in respiration. The data during oscillation are in contrast to the time course of events during initial exposure to glucose. Under these conditions, a burst of oxygen consumption precedes the initial rise in [Ca(2+)](i). A model to explain these results is described.

Oxygen microsensor and its application to single cells and mouse pancreatic islets

An oxygen microsensor with a < 3-micron tip diameter was developed for monitoring oxygen levels at single cells and mouse pancreatic islets. The sensor was fabricated by electrochemically recessing an etched Pt wire inside a pulled glass micropipet and then coating with cellulose acetate. This fabrication process was found to be simpler than previous oxygen electrode designs of comparable size. The microsensors had a average sensitivity of 0.59 +/- 0.29 pA/mmHg (mean +/- SD, n = 42), signals that were minimally perturbed by convection, and response times of < 1 s. The electrode was used to measure the oxygen gradient around and inside single mouse islets. The measurements demonstrate that oxygen levels within even the largest islets at maximal glucose stimulation are 67 +/- 1.6 mmHg (mean +/- SD, n = 5), indicating that islets have adequate oxygen supplies by diffusion under tissue culture conditions to support insulin secretion. The electrode was also used to record the dynamics of oxygen level at single islets as a function of glucose concentration. As glucose level was changed from 3 to 10 mM, oxygen level decreased by 15.8 +/- 2.3 mmHg (mean +/- SEM, n = 6) and oscillations with a period of 3.3 +/- 0.6 min (mean +/- SEM, n = 6) appeared in the oxygen level. In islets bathed in quiescent solutions containing 10 mM glucose, similar oscillations could be observed. In addition, in the quiet solutions it was possible to detect faster oscillations with a period of 12.1 +/- 1.7 s (mean +/- SEM, n = 6) superimposed on the slower oscillations. Oxygen consumption could also be observed at single insulinoma cells using the electrode. Individual cells also showed oscillations in oxygen consumption with a period of a few seconds. The results demonstrate that the electrode can be used for dynamic oxygen level recordings in biological microenvironments.

Detection of multiple patterns of oscillatory oxygen consumption in single mouse islets of Langerhans

A novel oxygen microsensor was used to measure oxygen levels in single mouse islets as a function of glucose concentration. Oxygen consumption of individual islets was 5.99 +/- 1.17, 9.21 +/- 2.15, and 12.22 +/- 2.16 pmol/min at 3, 10, and 20 mM glucose, respectively (mean +/- SEM, n = 10). Consumption of oxygen was islet-size dependent as larger islets consumed more oxygen than smaller islets but smaller islets consumed more oxygen per unit volume than larger islets. Elevating glucose levels from 3 to 10 mM induced pronounced fast oscillations in oxygen level (period of 12.1 +/- 1.7 s, n = 6) superimposed on top of large slow oscillations (period of 3.3 +/- 0.6 min, n = 6). The fast oscillations could be completely abolished by treatment with the L-type Ca2+-channel blocker nifedipine (40 microM) with a lesser effect on slow oscillations. Slow oscillations were almost completely dependent upon extracellular Ca2+. The oxygen patterns closely mimic those that have previously been reported for intracellular Ca2+ levels and are suggestive of an important role for Ca2+ in amplifying metabolic oscillations.

Cellulitis due to Escherichia coli in three immunocompromised subjects

In adults, cellulitis is usually caused by group A streptococci and Staphylococcus aureus. However, in patients with underlying disease, it may be caused by other organisms, such as Acinetobacter, Clostridium septicum, Enterobacter, Haemophilus influenzae, Proteus mirabilis or Escherichia coli. We report three cases of cellulitis of the lower legs where E. coli was the causative bacterial organism. It is important to suspect E. coli as a causative organism if blistering cellulitis occurs, especially in patients with underlying diseases.

Preferential cytotoxicity to tumor cells of 3,5-diprenyl-4-hydroxycinnamic acid (artepillin C) isolated from propolis

A tumoricidal substance was isolated from Brazilian propolis as guided by cytotoxicity assay on HuH 13 (human hepatocellular carcinoma) cell and was characterized to be 3-[4-hydroxy-3,5-bis (3-methyl-2-butenyl) phenyl]-2-propenoic acid (3,5-diprenyl-4-hydroxycinnamic acid (artepillin C)). It exhibited preferential cytotoxicity to tumor cells cultured in vitro. The cytotoxicity observed seemed to be partly attributable to apoptosis-like DNA fragmentation. The compound showed anti-tumor activity more effective than that of 5-fluorouracil to transplantable human tumor cell lines when tested on histoculture drug response assay system.

A novel beta-galactoside-binding lectin in cultured murine lymphocytic leukemia cells

Using affinity chromatography on lactosyl-Sepharose, a beta-galactoside-binding protein of 38 kDa was detected in mouse L1210 lymphocytic leukemia cells. Immunoblotting analysis revealed that it is distinct from any known larger molecular weight galectin. The partial amino acid sequences of the 38 kDa protein indicated that it is a novel member of the galectin family. This 38 kDa lectin is expressed in lymphocytic cell lines but not macrophage-like cell lines.

Polymeric mercaptosilane-modified platinum electrodes for elimination of interferants in glucose biosensors

An oxidase-based glucose sensor has been developed that uses a mercaptosilane-modified platinum electrode to achieve selectivity of electrochemical interferants. A platinum-iridium (9:1) wire (0.178 mm o.d., sensing area of 1.12 mm2) is modified with (3-mercaptopropyl)trimethoxysilane. The modified sensors show excellent operational stability for more than 5 days. Glucose oxidase is immobilized on the modified surface (i) by using 3-maleimidopropionic acid as a linker or (ii) by cross-liking with bovine serum albumin using glutaraldehyde. Sensitivities in the range of 9.97 nA/mM glucose are observed when the enzyme is immobilized by method ii. Lower sensitivities (1.13 x 10(-1) nA/mM glucose) are observed when immobilization method i is employed. In terms of linear response range, the sensor enzyme-immobilized by method i is superior to that immobilized by method ii. The linearity is improved upon coating the enzyme layer with polyurethane. The sensor immobilized by method ii and coated with polyurethane exhibits a linear range to 15 mM glucose and excellent selectivity to glucose (0.47 nA/mM) against interferants such as ascorbic acid, uric acid, and acetaminophen.

A novel beta-galactoside-binding lectin in adult rat kidney

Two carbohydrate-binding proteins with subunit molecular weight of about 17,500 and 16,500, respectively, were isolated from Triton X-100 extracts of rat kidney using a lactose affinity column. They did not require Ca2+ for the carbohydrate-binding nor reducing agents for maintaining their activity. The partial amino acid sequence of the 17.5-kDa protein (rkCBP-17.5), the main component, revealed that this protein is a novel member of a superfamily of beta-galactoside-binding animal lectins. The N-terminal amino acid sequence of the 16.5 kDa component (rkCBP-16.5) indicated that it is a fragment derived from the IgE-binding protein (IgEBP). Monoclonal antibodies to rkCBP-17.5 were prepared and used to examine the distribution of the lectin in various organs of adult rats. Immunoreactive protein with the same molecular weight was found in lung, spleen and liver, in lesser amounts in heart, and in trace amounts in brain and skeletal muscle. rkCBP-17.5 exhibits binding activity to various saccharides with the following order of affinity: N-acetyllactosamine > lactose > D-galactose > methyl alpha-D-galactopyranoside > N-acetyl-D-galactosamine > methyl beta-D-galactopyranoside. It binds to Engelbreth-Holm-Swarm(EHS) tumor laminin and rat plasma fibronectin, but does not bind to human plasma fibronectin.

Interaction of human plasma fibronectin with alpha-elastin

Because there are contradictory reports about the interaction of plasma fibronectin with elastin, we investigated the interaction in vitro. When human plasma was applied to an alpha-elastin-Sepharose column at 4 degrees C, the column-binding fraction contained fibronectin. When isolated plasma fibronectin was applied to the same column at 4 degrees C, most of the fibronectin bound to the column and was eluted with 1 M KBr. However, the binding affinity of plasma fibronectin to the alpha-elastin-Sepharose column was much weaker at 25 degrees C than at 4 degrees C. The elastin-plasma fibronectin interaction was further confirmed by demonstrating the binding of alpha-elastin to fibronectin on polyvinylidene difluoride membranes using an alpha-elastin specific antibody. The elevation of the surface hydrophobicity of plasma fibronectin at 4 degrees C was observed by hydrophobic chromatography, using alkyl-Sepharose columns. It seems that the binding of plasma fibronectin to alpha-elastin involves hydrophobic interaction, which is affected by temperature and possibly by other factors.

Active oxygen-induced modification alters properties of collagen as a substratum for fibroblasts

Acid-soluble collagen from rat skin was modified by active oxygen in vitro, and properties of the modified collagen as a substratum for fibroblasts were studied. When collagen was treated with ascorbate-copper ion systems, cross-linking and a little degradation occurred rapidly. The cells attached but spread poorly on the modified collagen gel as compared with on the untreated collagen gel. On the other hand, when collagen was treated with H2O2-copper ion systems, only degradation of collagen molecule occurred rapidly. This treatment did not affect the attachment and spreading of the cells on the collagen gel, but when the incubation was continued for a long time, the cells migrated actively and gathered. Thymidine incorporation by the cells was suppressed on both modified collagen gels as compared with that on untreated collagen gel, and the extent of the suppression on the H2O2-copper-treated collagen was larger than that on the ascorbate-copper-treated collagen. These results indicate that the active oxygen-induced cross-linking and degradation significantly alter properties of collagen as a substratum for fibroblasts.

Spinal cord injuries in children in British Columbia

Fifteen children who sustained traumatic spinal cord injury in British Columbia over a 13-year period have been reviewed. The aetiology, incidence of spinal fracture, length of hospitalisation and subsequent spinal surgery, and their self-care, transfer and ambulatory abilities, bowel and bladder management, schooling, employment and place of abode have been determined.