Progress Toward the Development of an Implantable Sensor for Glucose

The development of an electrochemically based implantable sensor for glucose is described. The sensor is needle-shaped, about the size of a 28-gauge needle. It is flexible and must be implanted subcutaneously by using a 21-gauge catheter, which is then removed. When combined with a monitoring unit, this device, based on the glucose oxidase-catalyzed oxidation of glucose, reliably monitors glucose concentrations for as long as 10 days in rats. Various design considerations, including the decision to monitor the hydrogen peroxide produced in the enzymatic reaction, are discussed. Glucose constitutes the most important future target analyte for continuous monitoring, but the basic methodology developed for glucose could be applied to several other analytes such as lactate or ascorbate. The success in implementation of such a device depends on a reaction of the tissue surrounding the implant so as not to interfere with the proper functioning of the sensor. Histochemical evidence indicates that the tissue response leads to enhanced sensor performance.

Cortical structural involvement and cognitive dysfunction in early Parkinson's disease

Magnetic resonance imaging (MRI) studies in early Parkinson's disease (PD) have shown promise in the detection of disease-related brain changes in the white and deep grey matter. We set out to establish whether intrinsic cortical involvement in early PD can be detected with quantitative MRI. We collected a rich, multi-modal dataset, including diffusion MRI, T₁ relaxometry and cortical morphometry, in 20 patients with early PD (disease duration, 1.9 ± 0.97 years, Hoehn & Yahr 1-2) and in 19 matched controls. The cortex was reconstructed using FreeSurfer. Data analysis employed linked independent component analysis (ICA), a novel data-driven technique that allows for data fusion and extraction of multi-modal components before further analysis. For comparison, we performed standard uni-modal analysis with a general linear model (GLM). Linked ICA detected multi-modal cortical changes in early PD (p = 0.015). These comprised fractional anisotropy reduction in dorsolateral prefrontal, cingulate and premotor cortex and the superior parietal lobule, mean diffusivity increase in the mesolimbic, somatosensory and superior parietal cortex, sparse diffusivity decrease in lateral parietal and right prefrontal cortex, and sparse changes to the cortex area. In PD, the amount of cortical dysintegrity correlated with diminished cognitive performance. Importantly, uni-modal analysis detected no significant group difference on any imaging modality. We detected microstructural cortical pathology in early PD using a data-driven, multi-modal approach. This pathology is correlated with diminished cognitive performance. Our results indicate that early degenerative processes leave an MRI signature in the cortex of patients with early PD. The cortical imaging findings are behaviourally meaningful and provide a link between cognitive status and microstructural cortical pathology in patients with early PD.

Differential immunomodulatory activity of tumor cell death induced by cancer therapeutic toll-like receptor ligands

Synthetic toll-like receptor (TLR) ligands stimulate defined immune cell subsets and are currently tested as novel immunotherapeutic agents against cancer with, however, varying clinical efficacy. Recent data showed the expression of TLR receptors also on tumor cells. In this study we investigated immunological events associated with the induction of tumor cell death by poly(I:C) and imiquimod. A human head and neck squamous cell carcinoma (HNSCC) cell line was exposed to poly(I:C) and imiquimod, which were delivered exogenously via culture medium or via electroporation. Cell death and cell biological consequences thereof were analyzed. For in vivo analyses, a human xenograft and a syngeneic immunocompetent mouse model were used. Poly(I:C) induced cell death only if delivered by electroporation into the cytosol. Cell death induced by poly(I:C) resulted in cytokine release and activation of monocytes in vitro. Monocytes activated by the supernatant of cancer cells previously exposed to poly(I:C) recruited significantly more Th1 cells than monocytes exposed to control supernatants. If delivered exogenously, imiquimod also induced tumor cell death and some release of interleukin-6, but cell death was not associated with release of Th1 cytokines, interferons, monocyte activation and Th1 recruitment. Interestingly, intratumoral injection of poly(I:C) triggered tumor cell death in tumor-bearing mice and reduced tumor growth independent of TLR signaling on host cells. Imiquimod did not affect tumor size. Our data suggest that common cancer therapeutic RNA compounds can induce functionally diverse types of cell death in tumor cells with implications for the use of TLR ligands in cancer immunotherapy.

Survival of residual neutrophils and accelerated myelopoiesis limit the efficacy of antibody-mediated depletion of Ly-6G+ cells in tumor-bearing mice

Expansion of Ly-6G(+) myeloid cells has been reported in most murine cancer models. However, divergent findings exist regarding the role and effect of these cells on host immunity and tumor progression. Antibody-mediated depletion of Ly-6G(+) cells is a common technique to assess the in vivo relevance of these cells. Interpretation of results crucially depends on the efficacy and course of depletion. We established murine head and neck cancer models and analyzed the efficacy of antibody-mediated depletion by flow cytometry, conventional histology, and intravital imaging with a novel Ly-6G-transgenic mouse model. The first phase of depletion was characterized by effective elimination of Ly-6G(+) cells from the peripheral blood. Nevertheless, viable, resistant cells were found to reside in the tumor tissue and spleen. This peripheral depletion phase was associated with high systemic levels of granulocyte colony-stimulating factor and KC and enhanced splenic production of Ly-6G(+) cells. Even under sustained treatment with either αGr-1 or αLy-6G antibodies, peripheral blood depletion ended after approximately 1 wk and was followed by reappearance of immature Ly-6G(+) cells with an immunoregulatory phenotype. Reappearance of these depletion-resistant immature cells was enhanced in tumor-bearing, compared with naïve, control mice. Collectively, our data suggest that depletion of Ly-6G(+) myeloid cells in tumor-bearing mice is counteracted by the persistence of intratumoral cells, enhanced extramedullary granulopoiesis, and accelerated reappearance of immature cells. Hence, extensive monitoring of in vivo kinetics and tissue distribution of Ly-6G(+) cells is required in depletion studies.

White matter damage is related to ataxia severity in SCA3

Spinocerebellar ataxia type 3 (SCA3) is the most frequent inherited cerebellar ataxia in Europe, the US and Japan, leading to disability and death through motor complications. Although the affected protein ataxin-3 is found ubiquitously in the brain, grey matter atrophy is predominant in the cerebellum and the brainstem. White matter pathology is generally less severe and thought to occur in the brainstem, spinal cord, and cerebellar white matter. Here, we investigated both grey and white matter pathology in a group of 12 SCA3 patients and matched controls. We used voxel-based morphometry for analysis of tissue loss, and tract-based spatial statistics (TBSS) on diffusion magnetic resonance imaging to investigate microstructural pathology. We analysed correlations between microstructural properties of the brain and ataxia severity, as measured by the Scale for the Assessment and Rating of Ataxia (SARA) score. SCA3 patients exhibited significant loss of both grey and white matter in the cerebellar hemispheres, brainstem including pons and in lateral thalamus. On between-group analysis, TBSS detected widespread microstructural white matter pathology in the cerebellum, brainstem, and bilaterally in thalamus and the cerebral hemispheres. Furthermore, fractional anisotropy in a white matter network comprising frontal, thalamic, brainstem and left cerebellar white matter strongly and negatively correlated with SARA ataxia scores. Tractography identified the thalamic white matter thus implicated as belonging to ventrolateral thalamus. Disruption of white matter integrity in patients suffering from SCA3 is more widespread than previously thought. Moreover, our data provide evidence that microstructural white matter changes in SCA3 are strongly related to the clinical severity of ataxia symptoms.

The tremor network targeted by successful VIM deep brain stimulation in humans

OBJECTIVE

Deep brain stimulation (DBS) of the ventral intermediate nucleus of thalamus (VIM) is a treatment option in medically intractable tremor, such as essential tremor or tremor-dominant Parkinson disease (PD). Although functional studies demonstrated modulation of remote regions, the structural network supporting this is as yet unknown. In this observational study, we analyzed the network mediating clinical tremor modulation.

METHODS

We studied 12 patients undergoing VIM stimulation for debilitating tremor. We initiated noninvasive diffusion tractography from tremor-suppressive VIM electrode contacts. Moreover, we tested for the contribution of primary motor projections in this structural correlate of a functional tremor network, comparing the connectivity of effective DBS contacts with those of adjacent, but clinically ineffective, stimulation sites.

RESULTS

VIM stimulation resulted in decrease of tremor and improvement in quality of life. Tractography initiated from the effective stimulation site reconstructed a highly reproducible network of structural connectivity comprising motor cortical, subcortical, and cerebellar sites and the brainstem, forming the anatomic basis for remote effects of VIM stimulation. This network is congruent with functional imaging studies in humans and with thalamic projections found in the animal literature. Connectivity to the primary motor cortex seemed to play a key role in successful stimulation.

CONCLUSIONS

Patients undergoing DBS provide a unique opportunity to assess an electrophysiologically defined seed region in human thalamus, a technique that is usually restricted to animal research. In the future, preoperative tractography could aid with stereotactic planning of individual subcortical target points for stimulation in tremor and in other disease entities.

Progression of subtle motor signs in PINK1 mutation carriers with mild dopaminergic deficit

BACKGROUND

While homozygous mutations in the PINK1 gene cause recessively inherited early-onset Parkinson disease (PD), heterozygous mutations have been suggested as a susceptibility factor.

METHODS

To evaluate this hypothesis, 4 homozygous PINK1 patients with PD and 10 asymptomatic carriers of a single heterozygous mutation from a large German family (family W) were included in this study. Clinical follow-up of the heterozygous mutation carriers 3 years after the initial visit included a detailed videotaped neurologic examination using the Unified Parkinson's Disease Rating Scale III protocol and smell and color discrimination testing. At follow-up, PET with 18-fluorodopa (FDOPA) of 13 family members was obtained in order to evaluate the clinical phenotype in light of nigostriatal dopaminergic functioning. The clinical and PET data were compared to those of healthy controls.

RESULTS

While there was mild worsening of clinical signs in previously affected heterozygous mutation carriers upon follow-up, 3 additional individuals had newly developed signs of possible PD. Hyposmia was found in 7 of the heterozygous mutation carriers, diminished color discrimination in 4. The homozygous mutation carriers who were all definitely affected with PD showed a severe, 60% decrease of caudate and putaminal FDOPA uptake; heterozygous offspring also had a significant 20% putaminal FDOPA uptake reduction compared to controls.

CONCLUSIONS

Our findings strengthen the hypothesis that heterozygous PINK1 mutations act as a susceptibility factor to develop at least subtle Parkinson disease motor and nonmotor signs, as supported by the finding of a reduced striatal dopaminergic FDOPA uptake not only in homozygous but also, albeit to a lesser extent, in heterozygous mutation carriers.

Neurotransmitter changes in dementia with Lewy bodies and Parkinson disease dementia in vivo

OBJECTIVE

Although Parkinson disease with dementia (PDD) and dementia with Lewy bodies (DLB) show a wide clinical and neuropathologic overlap, they are differentiated according to the order and latency of cognitive and motor symptom appearance. Whether both are distinct disease entities is an ongoing controversy. Therefore, we directly compared patients with DLB and PDD with multitracer PET.

METHODS

PET with (18)fluorodopa (FDOPA), N-(11)C-methyl-4-piperidyl acetate (MP4A), and (18)fluorodeoxyglucose (FDG) was performed in 8 patients with PDD, 6 patients with DLB, and 9 patients with PD without dementia vs age-matched controls. Data were analyzed with voxel-based statistical parametric mapping and region of interest-based statistics.

RESULTS

We found a reduced FDOPA uptake in the striatum and in limbic and associative prefrontal areas in all patient groups. Patients with PDD and patients with DLB showed a severe MP4A and FDG binding reduction in the neocortex with increasing signal diminution from frontal to occipital regions. Significant differences between PDD and DLB were not found in any of the radioligands used. Patients with PD without dementia had a mild cholinergic deficit and no FDG reductions vs controls.

CONCLUSIONS

Patients with dementia with Lewy bodies and Parkinson disease dementia share the same dopaminergic and cholinergic deficit profile in the brain and seem to represent 2 sides of the same coin in a continuum of Lewy body diseases. Cholinergic deficits seem to be crucial for the development of dementia in addition to motor symptoms. The spatial congruence of cholinergic deficits and energy hypometabolism argues for cortical deafferentation due to the degeneration of projection fibers from the basal forebrain.

Fatale familiäre Insomnie

Fatal familial insomnia (FFI) is a hereditary prion disease caused by a mutation in codon 178 of the prion protein gene PRNP on chromosome 20. It is characterized by disturbed night sleep, resulting in daily vigilance perturbations and a variety of other neurological symptoms. We present the case of a 46-year-old woman deteriorating despite immunosuppressive treatment which was initiated suspecting cerebral vasculitis as the cause of her progressive neurological symptoms. The correct diagnosis was established only post mortem. Based on the case presented here, we discuss typical clinical symptoms and imaging findings. In particular, we outline how modern diagnostic methods such as positron emission tomography with [(15)O]H(2)O and [(18)F]FDG and single photon emission computed tomography can add valuable information to results from conventionally performed imaging techniques and genetic testing.

Dementia in Parkinson disease: Functional imaging of cholinergic and dopaminergic pathways

OBJECTIVE

To assess neurochemical deficits in patients with Parkinson disease (PD) associated dementia (PDD) in vivo.

METHODS

The authors performed combined PET with N-[11C]-methyl-4-piperidyl acetate (MP4A) and 18F-fluorodopa (FDOPA) for evaluation of cholinergic and dopaminergic transmitter changes in 17 non-demented patients with PD and 10 patients with PDD. Data were compared to 31 age-matched controls by a combined region-of-interest and voxel-based Statistical Parametric Mapping analysis.

RESULTS

The striatal FDOPA uptake was significantly decreased in PD and PDD without differences between the groups. The global cortical MP4A binding was severely reduced in PDD (29.7%, p < 0.001 vs controls) and moderately decreased in PD (10.7%, p < 0.01 vs controls). The PDD group had lower parietal MP4A uptake rates than did patients with PD. Frontal and temporo-parietal cortices showed a significant covariance of striatal FDOPA reduction and decreased MP4A binding in patients with PDD.

CONCLUSIONS

While non-demented patients with Parkinson disease had a moderate cholinergic dysfunction, subjects with Parkinson disease associated dementia (PDD) presented with a severe cholinergic deficit in various cortical regions. The finding of a closely associated striatal FDOPA and cortical MP4A binding reduction suggests a common disease process leading to a complex transmitter deficiency syndrome in PDD.

Calibration of a subcutaneous amperometric glucose sensor. Part 1. Effect of measurement uncertainties on the determination of sensor sensitivity and background current

The calibration of a continuous glucose monitoring system, i.e. the transformation of the signal I(t) generated by the glucose sensor at time (t) into an estimation of glucose concentration G(t), represents a key issue. The two-point calibration procedure consists of the determination of a sensor sensitivity S and of a background current I(o) by plotting two values of the sensor signal versus the concomitant blood glucose concentrations. The estimation of G(t) is subsequently given by G(t) = (I(t)-I(o))/S. A glucose sensor was implanted in the subcutaneous tissue of nine type 1 diabetic patients during 3 (n = 2) and 7 days (n = 7). For each individual trial, S and I(o) were determined by taking into account the values of two sets of sensor output and blood glucose concentration distant by at least 1 h, the procedure being repeated for each consecutive set of values. S and I(o) were found to be negatively correlated, the value of I(o) being sometimes negative. Theoretical analysis demonstrates that this phenomenon can be explained by the effect of measurement uncertainties on the determination of capillary glucose concentration and of sensor output.

Calibration of a subcutaneous amperometric glucose sensor implanted for 7 days in diabetic patients. Part 2. Superiority of the one-point calibration method

Calibration, i.e. the transformation in real time of the signal I(t) generated by the glucose sensor at time t into an estimation of glucose concentration G(t), represents a key issue for the development of a continuous glucose monitoring system.

OBJECTIVE

To compare two calibration procedures. In the one-point calibration, which assumes that I(o) is negligible, S is simply determined as the ratio I/G, and G(t) = I(t)/S. The two-point calibration consists in the determination of a sensor sensitivity S and of a background current I(o) by plotting two values of the sensor signal versus the concomitant blood glucose concentrations. The subsequent estimation of G(t) is given by G(t) = (I(t)-I(o))/S.

RESEARCH DESIGN AND METHODS

A glucose sensor was implanted in the abdominal subcutaneous tissue of nine type 1 diabetic patients during 3 (n = 2) and 7 days (n = 7). The one-point calibration was performed a posteriori either once per day before breakfast, or twice per day before breakfast and dinner, or three times per day before each meal. The two-point calibration was performed each morning during breakfast.

RESULTS

The percentages of points present in zones A and B of the Clarke Error Grid were significantly higher when the system was calibrated using the one-point calibration. Use of two one-point calibrations per day before meals was virtually as accurate as three one-point calibrations.

CONCLUSION

This study demonstrates the feasibility of a simple method for calibrating a continuous glucose monitoring system.

Intestinal toxicity and carcinogenic potential of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in DNA repair deficient XPA-/- mice

The effects of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) were studied in DNA repair deficient XPA(-/-) mice. The nullizygous XPA-knockout mice, which lack a functional nucleotide excision repair (NER) pathway, were exposed to dietary concentrations ranging from 10 to 200 p.p.m. The results show that PhIP is extremely toxic to XPA(-/-) mice, even at doses 10-fold lower than tolerated by wild-type C57BL/6 mice. XPA(-/-) mice rapidly lost weight and died within 2 and 6 weeks upon administration of 200 and 100 p.p.m., respectively. Intestinal abnormalities like distended and overfilled ileum and caecum, together with clear signs of starvation, suggests that the small intestines were the primary target tissue for the severe toxic effects. Mutation analysis in XPA(-/-) mice carrying a lacZ reporter gene, indicated that the observed toxicity of PhIP might be caused by genotoxic effects in the small intestine. LacZ mutant frequencies appeared to be selectively and dose-dependently increased in the intestinal DNA of treated XPA(-/-) mice. Furthermore, DNA repair deficient XPC(-/-) mice, which are still able to repair DNA damage in actively transcribed genes, did not display any toxicity upon treatment with PhIP (100 p.p.m.). This suggests that transcription coupled repair of DNA damage (PhIP adducts) in active genes plays a crucial role in preventing the intestinal toxicity of PhIP. Finally, PhIP appeared to be carcinogenic for XPA(-/-) mice at subtoxic doses. Upon treatment of the mice for 6 months with 10 or 25 p.p.m. PhIP, significantly increased tumour incidences were observed after a total observation period of one year. At 10 p.p.m. only lymphomas were found, whereas at 25 p.p.m. some intestinal tumours (adenomas and adenocarcinomas) were also observed.

Segmentation of vessel-like patterns using mathematical morphology and curvature evaluation

This paper presents an algorithm based on mathematical morphology and curvature evaluation for the detection of vessel-like patterns in a noisy environment. Such patterns are very common in medical images. Vessel detection is interesting for the computation of parameters related to blood flow. Its tree-like geometry makes it a usable feature for registration between images that can be of a different nature. In order to define vessel-like patterns, segmentation is performed with respect to a precise model. We define a vessel as a bright pattern, piece-wise connected, and locally linear, mathematical morphology is very well adapted to this description, however other patterns fit such a morphological description. In order to differentiate vessels from analogous background patterns, a cross-curvature evaluation is performed. They are separated out as they have a specific Gaussian-like profile whose curvature varies smoothly along the vessel. The detection algorithm that derives directly from this modeling is based on four steps: (1) noise reduction; (2) linear pattern with Gaussian-like profile improvement; (3) cross-curvature evaluation; (4) linear filtering. We present its theoretical background and illustrate it on real images of various natures, then evaluate its robustness and its accuracy with respect to noise.

Interstitial glucose concentration and glycemia: implications for continuous subcutaneous glucose monitoring

The changes in plasma glucose concentration and in interstitial glucose concentration, determined with a miniaturized subcutaneous glucose sensor, were investigated in anesthetized nondiabetic rats. Interstitial glucose was estimated through two different calibration procedures. First, after a glucose load, the magnitude of the increase in interstitial glucose, estimated through a one-point calibration procedure, was 70% of that in plasma glucose. We propose that this is due to the effect of endogenous insulin on peripheral glucose uptake. Second, during the spontaneous secondary decrease in plasma glucose after the glucose load, interstitial glucose decreased faster than plasma glucose, which may also be due to the effect of insulin on peripheral glucose uptake. Third, during insulin-induced hypoglycemia, the decrease in interstitial glucose was less marked than that of plasma glucose, suggesting that hypoglycemia suppressed transfer of glucose into the interstitial tissue; subsequently, interstitial glucose remained lower than plasma glucose during its return to basal value, suggesting that the stimulatory effect of insulin on peripheral glucose uptake was protracted. If these observations obtained in rats are relevant to human physiology, such discrepancies between plasma and interstitial glucose concentration may have major implications for the use of a subcutaneous glucose sensor in continuous blood glucose monitoring in diabetic patients.

Probing the mechanisms of enantioselective hydrogenation of simple olefins with chiral rhodium catalysts in the presence of anions

The strong influence of various anions upon the hydrogenation of 2-phenyl-1-butene, catalyzed by chiral rhodium catalysts was investigated. Both sulfonates and halides exert large increases in the enantioselectivity when [Rh[(-)-bdpp](NBD)]ClO4 (bdpp = 2,4-bis(diphenylphosphino)pentane, NBD = 2,5-norbornadiene) is used as the catalyst precursor at high pressures (70 atm) of dihydrogen in nonpolar solvents. A dihydride mechanism similar to that for Wilkinson's catalyst [RhCl(PPh3)3] was shown to be operating at both high- and low-pressure conditions through a combination of catalytic studies, 31P, 1H and parahydrogen-induced polarization (PHIP) NMR experiments. With sulfonate and in neat methanol, however, a mechanistic switch takes place from a dihydride route (dihydrogen addition before olefin binding) at high pressure to an unsaturate route (olefin binding before dihydrogen addition) at low pressures (<30 atm). Olefin isomerization is inhibited by halide addition, but occurs with sulfonate and in neat methanol through what is most likely a pi-allyl mechanism. A detailed understanding of the effects of addition of these anions is crucial for development of new classes of catalysts capable of efficient enantioselective reduction of prochiral olefins lacking a secondary polar binding group.

A multimodal registration algorithm of eye fundus images using vessels detection and Hough transform

Image registration is a real challenge because physicians handle many images. Temporal registration is necessary in order to follow the various steps of a disease, whereas multimodal registration allows us to improve the identification of some lesions or to compare pieces of information gathered from different sources. This paper presents an algorithm for temporal and/or multimodal registration of retinal images based on point correspondence. As an example, the algorithm has been applied to the registration of fluorescein images (obtained after a fluorescein dye injection) with green images (green filter of a color image). The vascular tree is first detected in each type of images and bifurcation points are labeled with surrounding vessel orientations. An angle-based invariant is then computed in order to give a probability for two points to match. Then a Bayesian Hough transform is used to sort the transformations with their respective likelihoods. A precise affine estimate is finally computed for most likely transformations. The best transformation is chosen for registration.

Lack of mammalian mutagenicity of the potent bacterial mutagen tris(2,3-dibromopropyl) phosphate and its metabolite 2-bromoacrolein

The flame retardant tris(2,3-dibromopropyl)phosphate (Tris-BP) and its metabolite 2-bromoacrolein (2BA) are very potent bacterial mutagens in Salmonella typhimurium (S. typhimurium) TA 100. In this study, we showed that 2BA and Tris-BP are also mutagenic in S. typhimurium TA 104, which detects mutations at AT base pairs, while TA 100 detects mutations at CG basepairs. We also studied the mutagenicity of 2BA in mammalian cells in vitro and in the rat in vivo. Firstly, 2BA was tested in the human lymphoblastoid cell line TK6. The results showed that there was no increase in mutation frequency at the hprt locus, whereas there was a large decrease in cell survival. Secondly, a shuttle vector system was used to study the induction of mutations by 2BA:DNA adducts. The vector was modified by insertion of a single-stranded oligonucleotide containing on average one 2BA:DNA adduct. No increase in mutation frequency above background was detected after replication of this vector in SV40 transformed normal human fibroblasts. Because the liver is a major site for bioactivation of Tris-BP to 2BA in vivo, we tested the initiating capacity of Tris-BP in the rat liver in a modified Solt & Farber initiation and promotion system. Administration of Tris-BP resulted in a small increase in the number of preneoplastic gamma-glutamyl-transpeptidase positive (GGT+) foci in the liver compared to control animals (only significant in the lowest size class). Modification of the experimental protocol by performing partial hepatectomy 24 h after the administration of Tris-BP, did not increase the number of GGT+ or glutathione S-transferase-P (GST-P+) positive foci above the control level. Taken together, these results indicate that, in spite of a high mutagenicity in S. typhimurium, 2BA and Tris-BP have low or negligible mutagenic effects in mammalian systems. The lack of mutagenic activity may explain why Tris-BP is not a carcinogen in the rat liver.

Continuous glucose monitoring in the free-moving rat

The aim of this work was to set up an experimental model of glycemic fluctuations for assessing in the conscious freely moving rat, the performance of a continuous glucose-monitoring system, using a pocket-calculator-size electronic control unit and a miniaturized subcutaneous glucose sensor. The well-known triphasic glycemic pattern following streptozotocin injection (initial peak and secondary hypoglycemia preceding the establishment of permanent hyperglycemia) was used as a way to obtain spontaneous changes in blood glucose level over a wide concentration range. This report demonstrates that streptozotocin injection produced highly reproducible changes in the current generated by the sensor: an initial peak and a secondary nadir, during which blood sampling provided the evidence of hyperglycemia associated with immunoreactive hypoinsulinemia, and of hypoglycemia associated with hyperinsulinemia, respectively. This reproducible experimental model should be valuable for the assessment of a continuous glucose-monitoring system.

A user-friendly method for calibrating a subcutaneous glucose sensor-based hypoglycaemic alarm

A crucial step in developing a glucose monitoring system using a subcutaneous implanted glucose sensor is the transformation of the sensor signal (a current) into an estimation of a blood glucose concentration. We have developed an Electronic Control Unit (ECU) able to recognize, before and after a glucose load, that the sensor current presents a plateau, thus triggering an alarm asking for blood glucose determination. The system, fed with these results, subsequently transforms the current into an estimation of glucose concentration by linear extrapolation based on the sensor sensitivity and the background current computed from the two sets of current and glycaemia values (two-point calibration). In addition, the system is able to trigger an alarm when this estimation decreases below a threshold that can be set by the user. This system was evaluated in experiments performed in 12 normal rats. The quality of the calibration was assessed by comparing, by error grid analysis, the data displayed on the liquid-crystal display of the ECU to concomitant plasma glucose concentration determined at frequent intervals, 65 +/- 6 and 26 +/- 5% of the values were in zones A (good) and B (acceptable estimation) of the grid, respectively. The system was set to trigger an alarm when the estimation of glucose concentration decreased below 70 mg/dl. Following an insulin administration, the alarm was triggered when the system displayed a 64 +/- 2 mg/dl glucose concentration. The concomitant plasma glucose concentration was 59 +/- 5 mg/dl (NS). In conclusion, this work validates experimentally the new, user-friendly method for calibrating the glucose sensor integrated into the ECU, based on an automatic detection of plateaus. The quality of the sensor calibration performed with this procedure is compatible with the appropriate functioning of this continuous glucose monitoring system, which was demonstrated by its ability to detect mild hypoglycaemia following insulin injection.

Use of a subcutaneous glucose sensor to detect decreases in glucose concentration prior to observation in blood

The development of a hypoglycemic alarm system using a subcutaneous glucose sensor implies that a decrease in blood glucose is rapidly followed by a decrease in the signal generated by the sensor. In a first set of experiments the linearity and the kinetics of the response of sensors implanted in the subcutaneous tissue of normal rats were investigated during a progressive increase in plasma glucose concentration: the sensitivities determined between 5 and 10 mM and between 10 and 15 mM were not significantly different, and a 5-10 min delay in the sensor's response was observed. In a second set of experiments, performed in diabetic rats, the kinetics of the decrease in subcutaneous glucose concentration following insulin administration was monitored during a decrease in plasma glucose level, from 15 to 3 mmol/L. During the 20 first min following insulin administration, the sensor monitored glucose concentration in subcutaneous tissue with no lag time. Subsequently, the decrease in the estimation of subcutaneous glucose concentration preceded that of plasma glucose. This phenomenon was not observed when the same sensors were investigated in vitro during a similar decrease in glucose concentration and may be due to a mechanism occurring in vivo, such as the effect of insulin on glucose transfer from the interstitial space to the cells surrounding the sensor. It reinforces the interest of the use of implantable glucose sensors as a part of a hypoglycemic alarm.

Irradiated (15N)DNA as an internal standard for analysis of base-oxidized DNA constituents by isotope dilution mass spectrometry

A simple and convenient procedure for the preparation of isotopically labeled DNA enriched in oxidized deoxynucleosides is described. 15N-Labeled DNA was isolated from Escherichia coli cells grown in an isotopically enriched medium, and the level of oxidative damage was increased by in vitro irradiation under oxygen. The resulting DNA was hydrolyzed and subsequently analyzed by GC/MS. Results indicated that the DNA was 99% 15N-enriched and that 1% of the total 2'-deoxyguanosine was converted into 8-hydroxy-2'-deoxyguanosine (8-OHdG). When applied to the analysis of 8-OHdG, [15N]DNA as internal standard gave a better reproducibility (CV, 7.9%; n = 5) as compared to the monomeric 8-[18O]hydroxy-2'-deoxyguanosine (CV, 16%; n = 4). Background levels of 8-OHdG in rat colon DNA determined with [15N]DNA and 8-18OHdG as internal standard were 26 +/- 11 and 15 +/- 7 8-OHdG per 10(6) deoxynucleosides, respectively.

Role of nucleotide excision repair in processing of O4-alkylthymines in human cells

O4-Alkylthymines have been implicated as potential carcinogenic DNA lesions. We have studied the effects of O4-methylthymine, O4-ethylthymine, and O4-n-propylthymine in a model system in which a single lesion was located at a defined position on a SV40-based shuttle vector and have found large differences in the effects of these lesions in repair-proficient and nucleotide excision repair-deficient cells. In repair-competent human HeLa cells, normal fibroblasts, and XP-A (2OS) revertant cells, all 3 residues were highly mutagenic; a mutation frequency of approximately 20% was found for both O4-methylthymine and O4-ethylthymine, whereas that of O4-n-propylthymine was approximately 12%. These frequencies were independent of the activity of the O6-alkylguanine DNA alkyltransferase. All three O4-alkylthymines induced T-->C transitions exclusively. In nucleotide excision repair-deficient XP-A cells, however, these lesions were not mutagenic but strongly inhibited plasmid replication (> 90%). These results indicate that O4-alkylthymines are efficiently recognized by the nucleotide excision repair system and cause a complete cessation of plasmid replication if this system is deficient. Nevertheless, proficiency in the nucleotide excision repair pathway correlates with a high frequency of mutation induction by these lesions.

Reduction of acetaminophen interference in glucose sensors by a composite Nafion membrane: demonstration in rats and man

Amperometric glucose sensors typically monitor the production of hydrogen peroxide generated in the course of the enzymatic oxidation of glucose. At the applied potential necessary to oxidize the peroxide produced, other species are also electroactive and contribute to the signal. Interference of ascorbate or urate has been effectively eliminated, but that resulting from the widely used analgesic acetaminophen is not. The aim of this work was to reduce this interference, which was found to be possible by introducing a membrane constructed of Nafion. We compared the in vitro sensitivity to acetaminophen of five Nafion sensors with that of five non-Nafion sensors with identical glucose sensitivity (2.0 +/- 0.4 vs 1.9 +/- 0.1 nA.mmol-1.l-1, NS): sensitivity to acetaminophen was 12.2 +/- 2.7 vs 30.8 +/- 6.3 nA.mmol-1.l-1, respectively (p < 0.05). These sensors were tested in rats by implanting in each animal one Nafion and one non-Nafion sensors. The in vivo sensitivity to glucose was similar (0.33 +/- 0.09 vs 0.30 +/- 0.05 nA.mmol-1.l-1, NS). The current generated by an acetaminophen infusion (plasma acetaminophen plateau = 140 +/- 10 mumol/l) was much decreased in the case of the Nafion sensor: 0.5 +/- 0.3 vs 2.0 +/- 0.7 nA, p < 0.05). Five Nafion sensors were implanted in the subcutaneous tissue of normal human volunteers who were given on oral dose of 500 mg acetaminophen.(ABSTRACT TRUNCATED AT 250 WORDS)

A glucose monitoring system for on line estimation in man of blood glucose concentration using a miniaturized glucose sensor implanted in the subcutaneous tissue and a wearable control unit

We have developed a miniaturized glucose sensor which has been shown previously to function adequately when implanted in the subcutaneous tissue of rats and dogs. Following a glucose load, the sensor output increases, making it possible to calculate a sensitivity coefficient to glucose in vivo, and an extrapolated background current in the absence of glucose. These parameters are used for estimating at any time the apparent subcutaneous glucose concentration from the current. In the previous studies, this calibration was performed a posteriori, on the basis of the retrospective analysis of the changes in blood glucose and in the current generated by the sensor. However, for clinical application of the system, an on line estimation of glucose concentration would be necessary. Thus, this study was undertaken in order to assess the possibility of calibrating the sensor in real time, using a novel calibration procedure and a monitoring unit which was specifically designed for this purpose. This electronic device is able to measure, to filter and to store the current. During an oral glucose challenge, when a stable current is reached, it is possible to feed the unit with two different values of blood glucose and their corresponding times. The unit calculates the in vivo parameters, transforms every single value of current into an estimation of the glucose concentration, and then displays this estimation. In this study, 11 sensors were investigated of which two did not respond to glucose. In the other nine trials, the volunteers were asked to record every 30 s what appeared on the display during the secondary decrease in blood glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytokeratins expressed in experimental rat bronchial carcinomas

Cytokeratin expression in rat lung tumors was studied using polypeptide-specific monoclonal antibodies (MAbs) to human cytokeratins 4, 5, 7, 8, 10, 13, 14, 18 and 19. Experiments were performed on tumor fragments derived from 5 experimental rat squamous-cell lung tumors and one adenocarcinoma, as well as on cell lines obtained from the same tumors. The aims of this study were to investigate the differentiation profile of the rat tumor tissue and established tumor cell lines based on light and electron microscopical features and on cytokeratin phenotype, to characterize the tumor type and degree of differentiation of the lung tumors maintained during passaging in experimental animals, and to compare the cytokeratin expression pattern in transplanted tumors with that of the cultures derived from these tumors. Our results indicate that, in general, the antibodies used cross-react with rat cytokeratins and that these MAbs can be used to phenotype rat lung carcinomas. Both the tumor fragments and the cultured cells revealed a similar pattern of cytokeratin expression. In addition, the degree of differentiation was maintained upon prolonged culturing in vitro. MAbs to cytokeratin sub-types can therefore be used to distinguish the main sub-types of rat lung tumors and can give an indication about the degree of differentiation.

Repair and replication of plasmids with site-specific 8-oxodG and 8-AAFdG residues in normal and repair-deficient human cells

The in vivo mutagenicity of 7-hydro-8-oxo-2'-deoxyguanosine (8-oxodG) and N-(guanin-8-yl)-N-acetyl-2-aminofluorene (8-AAFdG) in human cells was determined by transfecting various cell lines with plasmids that carried a single adduct at a defined site. 8-OxodG is one of the many DNA modifications formed by oxygen radicals, and was found to be highly miscoding during replication with purified DNA polymerases in vitro. Here we show that the frequency of mutations induced by 8-oxodG during replication in vivo is at most only 2% above background. The most predominant mutation found was a single G----T transversion. The frequency of this transversion was found to be 3 to 5-fold increased in excision repair deficient XP-A cells. Interestingly, also the replication of 8-oxodG containing plasmids was significantly impaired (approximately 4-fold) in the XP-A cells, but not in HeLa cells, normal fibroblasts or XP-A revertant cells. When 8-AAFdG containing plasmids were used, the mutation frequencies did not exceed background levels (less than 2%) with any of the cell lines tested. The presence of 8-AAFdG almost completely inhibited plasmid replication (more than 50-fold) in XP-A cells. Apparently, both 8-AAFdG and 8-oxodG are not or poorly repaired in these cells, causing a block of DNA replication. This suggests that both lesions are substrates for excision repair, although to a varying extent.

Progress toward the development of an implantable sensor for glucose

The development of an electrochemically based implantable sensor for glucose is described. The sensor is needle-shaped, about the size of a 28-gauge needle. It is flexible and must be implanted subcutaneously by using a 21-gauge catheter, which is then removed. When combined with a monitoring unit, this device, based on the glucose oxidase-catalyzed oxidation of glucose, reliably monitors glucose concentrations for as long as 10 days in rats. Various design considerations, including the decision to monitor the hydrogen peroxide produced in the enzymatic reaction, are discussed. Glucose constitutes the most important future target analyte for continuous monitoring, but the basic methodology developed for glucose could be applied to several other analytes such as lactate or ascorbate. The success in implementation of such a device depends on a reaction of the tissue surrounding the implant so as not to interfere with the proper functioning of the sensor. Histochemical evidence indicates that the tissue response leads to enhanced sensor performance.

Use of shuttle vectors to study the molecular processing of defined carcinogen-induced DNA damage: mutagenicity of single O4-ethylthymine adducts in HeLa cells

We developed a simian virus 40 based shuttle vector system to study the molecular consequences of distinct carcinogen-induced DNA lesions in human cells. To establish the mutagenicity of O4-ethylthymine adducts, oligonucleotides carrying a single O4-ethylthymine adduct at a unique position were ligated into the vector molecules. Following replication in HeLa cells on average 23% of the progeny molecules carried a mutation in the region of modification. The vast majority of these mutations represented single T----C transitions at the position of the modified base, most probably as a consequence of mispairing of the O4-ethylthymine residues during replication. To a minor extent the O4-ethylthymine adduct may also induce T----A transversions or double point mutations. The in vivo mutation frequency of the adduct was found to be comparable to that of a C-A mismatch at the same position, but was lower than that expected from in vitro experiments with adducted DNA templates and purified DNA polymerases.

Differential behavior of human bronchial carcinoma cells in culture

A feeder layer culture system suited to grow carcinoma cells derived from solid human lung tumors was developed. This report deals with culturing of the four main histological types of lung carcinomas observed in 37 patients: 19 squamous cell, 6 adenocarcinomas, 7 small cell, and 5 large cell carcinomas. The cultures were initiated from 24 fresh human surgical specimens and from 14 human lung tumors grown as xenografts in nude mice. Three different patterns of behavior in culture were found to be characteristic for squamous cell, adenocarcinomas, and small cell carcinomas, respectively. The culture pattern presented by the primary cultures did not appreciably change after passaging in vitro for periods of up to 2 years, even after infinite cell lines were established. Cultures of large cell carcinoma showed one or more of these patterns. From these patterns cells could be cloned and subsequently cultured as separate stable lines. The system described facilitates the identification of specific types of human lung carcinomas almost immediately (within 1 h) after plating (Phase I) as well as during culture.

A rapid and simple hapten conjugation method for monoclonal antibodies to be used in immunoenzyme single and double staining procedures

A rapid and simple method was developed for the haptenization of monoclonal antibodies (MAbs), to be used in immunoenzyme single and double staining techniques. Using this method minute amounts of MAbs can be haptenized without purification of the antibody or removal of the excess hapten. The haptenized MAb can be ready for use with 2.5 h. The method consists of a direct incubation of the antibody with the haptenizing agent and subsequent addition of an amino acid solution to stop the reaction. Commonly available reagents were tested, of which dinitrofluorobenzene, trinitrobenzene sulfonic acid and an oxazolone derivative gave the best results. The procedure was evaluated by using MAbs directed against lymphoid cell surface membrane antigens in an indirect immunoenzyme staining on frozen sections using peroxidase or alkaline phosphatase-conjugated anti-hapten antibodies as second step antibody. It was found that those MAbs, which show good staining results in conventional indirect immunoenzyme procedures, can also be used successfully after haptenization in single as well as double staining procedures. Combination of haptenized and biotynilated MAbs gave good results when weakly reactive MAbs had to be included in immunoenzyme double staining.

Nasal respiratory function and craniofacial growth

Nasal respiratory function and its relationship to growth development of the craniofacial structure has been a subject of interest and controversy for over 100 years. The otolaryngologist as the primary physician with responsibility of managing the upper respiratory tract is obviously most intimately involved with diagnosis and treatment of upper respiratory tract problems. To further evaluate the evidence regarding causes of craniofacial growth, a study was done involving pretreatment orthodontic subjects and their manifestation of classic signs of adenoid facies ("long-face syndrome"). Randomly selected were 106 subjects, ranging in age from 6 to 13 years, for evaluation of the facial features and medical history associated with long-face syndrome. No conclusive proof was found that nasal respiratory obstruction alters facial growth development. Studies of the nasal respiratory function need to be done utilizing clear definitions of respiratory mode and objective; reproducible techniques of measuring respiratory modes must be employed. Highly selected orthodontic patients can benefit from adenoidectomy and/or tonsillectomy.

Metformin reduces post-prandial insulin needs in type I (insulin-dependent) diabetic patients: assessment by the artificial pancreas

It has been suggested that biguanides should be used in Type 1 (insulin-dependent) diabetic patients in order to diminish insulin requirements and reduce the chances of insulin reactions. The efficacy of these compounds in such patients has been controversial. We have studied the effect of metformin (850 mg) given at 08.00 h in diminishing insulin needs after a 60 g carbohydrate mixed meal taken at 12.00 h, using an artificial pancreas and a sequential analysis of the results. The morning test dose of metformin or placebo was preceded by 48 h treatment with metformin (850 mg twice daily) or placebo. After the eighth patient a 26% saving of insulin need was demonstrated in the metformin-treated group (p less than 0.01). Metformin is thus effective in reducing post-prandial insulin needs in Type 1 diabetic patients, although its use in such circumstances requires consideration of several other issues.

Correlation between the nature and amount of carbohydrate in meal intake and insulin delivery by the artificial pancreas in 24 insulin-dependent diabetics

We have studied the effects of mixed meals and dextrose intake on blood glucose and insulin delivery by the artificial pancreas in 24 insulin-dependent diabetics. A group of 12 patients had 3 mixed meals containing at random 20, 40, and 60 g of complex carbohydrate along with protein and fat; another group of 12 diabetics, comparable in weight, age, and duration of diabetes, received at random 20, 40, and 60 g of dextrose. Dextrose ingestion led to a higher initial blood glucose increase than did the mixed meal, but the duration of blood glucose increase lasted significantly longer after the mixed meal than after the dextrose load. The areas under the curves of hyperglycemia were not significantly different. There was a high (but not linear) correlation between the total amount of insulin delivered in order to restore initial blood glucose values and the amount of CHO consumed. There was no correlation with age, body weight, duration of diabetes, nor with the nature and order of administration of the CHO load; 5.1 +/- 1.6 to 13.7 +/- 2.1 units of insulin were needed for a period of 94 +/- 11 to 132 +/- 11 min. It is suggested that some of the data obtained in this study might be useful in the programming of an open-loop insulin infusion system.