Kenro Nishida

Ferrocene-mediated needle-type glucose sensor covered with newly designed biocompatible membrane

Abstract A ferrocene-mediated needle-type glucose sensor covered with a newly designed biocompatible membrane of 2-methacryloyloxyethyl phosphorylcholine (MPC) has been developed and its characteristics examined in vitro and in vivo. Application of ferrocene derivatives to the glucose sensor could solve the oxygen-limitation problems, and also compensate the sensor decay due to an insufficient microconvection and diffusion of oxygen resulting from protein fixation on the sensor surface during continuous subcutaneous tissue glucose monitoring. The MPC membrane, a hydrophobic polymer surface covered with a grafted hydrophilic phosphorylcholine chain, has the potential for supressing adsorption of biochemical molecules due to the mobility of the grafted polymer chain. With this glucose sensor covered with an MPC membrane, subcutaneous tissue glucose concentrations can be monitored for up to seven days without any in situ calibrations, followed by 14 days with one-point in situ calibrations. Therefore, we conclude that a ferrocene-mediated needle-type glucose sensor covered with an MPC membrane is stable and reliable, as compared to any other glucose sensors already developed, and can thus be applied for continuous glucose monitoring and for glycaemic control with a wearable artificial endocrine pancreas.

Development of a Miniaturized Glucose Monitoring System by Combining a Needle-Type Glucose Sensor With Microdialysis Sampling Method: Long-term subcutaneous tissue glucose monitoring in ambulatory diabetic patients

OBJECTIVE To develop a reliable and practical glucose monitoring system by combining a needle-type glucose sensor with a microdialysis sampling technique for long-term subcutaneous tissue glucose measurements. RESEARCH DESIGN AND METHODS A microdialysis Cuprophan hollowfiber probe (inner diameter, 0.20 mm; length, 15 mm) was perfused with isotonic saline solution (120 μl/h) and glucose concentrations in the dialysate were measured by a needle-type glucose sensor extracorporeally. This system was tested both in vitro and in vivo. Subcutaneous tissue glucose concentrations were then monitored continuously in 5 healthy and 8 diabetic volunteers for 7 to 8 days. A hollow-fiber probe was inserted into the abdominal subcutaneous tissue. RESULTS This monitoring system achieved excellent results in vitro. Subcutaneous tissue glucose concentrations were measured in a wide range from 1.7 to >027.8 mM glucose, with a time delay of 6.9 ±1.2 min associated with a rise in glucose and 8.8 ±1.6 min with a fall in the glucose level (means ± SE). The overall correlation between subcutaneous tissue (Y) and blood (X) glucose concentration was Y = 1.08X ± 0.19 (r = 0.99). The subcutaneous tissue glucose concentration could be monitored precisely for 4 days without any in vivo calibrations and for 7 days by introducing in vivo calibrations. CONCLUSIONS Glycemic excursions could be monitored precisely in the subcutaneous tissue by this microdialysis sampling method with a needle-type glucose sensor in ambulatory diabetic patients.

Noninvasive measurement of blood glucose concentrations by analysing fourier transform infra-red absorbance spectra through oral mucosa

Whether Fourier transform infra-red spectroscopy with an attenuated total reflection prism could be applied for noninvasive glucose measurement through oral mucosa was evaluated. As a result, the same absorbance peak at 1033 cm−1 as in glucose aqueous solution was found in the absorbance spectra through mucous membrane. However, these glucose specific peaks were interfered with by the baseline drifts owing to prism attachment and the background spectra from body constituents other than glucose. Therefore, to eliminate these interferences, the calibration curve between the second derivatives of the absorbance peak at 1033 cm−1 and those at 2920 cm−1 was calculated (r=0·910). By using this calibration curve, the spectral changes due to prism attachment were first eliminated. Secondly, by obtaining the second derivative of the difference between the postprandial absorbance peak and the fasting sample as a characteristic of an individual, high correlations between the corrected second derivatives of absorbance spectra through the mucous membrane of the lip at 1033 cm−1 and the increases in blood glucose concentrations above fasting levels were observed (r=0·910). In conclusion, it was suggested that Fourier transform infra-red spectroscopy could be useful for noninvasive monitoring of glucose through oral mucosa.

Comparison between closed-loop portal and peripheral venous insulin delivery systems for an artificial endocrine pancreas.

To establish the ideal insulin delivery route for an artificial endocrine pancreas, we examined the effectiveness of closed-loop portal insulin delivery. We investigated the effects of the route of insulin delivery on net hepatic glucose balance (NHGB) in dogs under pancreatic clamp conditions with somatostatin plus basal glucagon and insulin infusions. A constant rate of suprabasal insulin was infused via the portal vein or a peripheral vein, and glucose was infused into the portal vein for 180 min. The mean net hepatic glucose uptake (NHGU) values in the portal insulin infusion group (PI group) were significantly greater than those in the peripheral venous insulin infusion group (VI group); the changes from the baseline values at 180 min were 3.54 ± 0.66 and 2.45 ± 0.82 mg kg−1 min−1 in the PI and VI groups, respectively, P < 0.05. Furthermore, dogs under pancreatic clamp conditions were controlled after a 2-g/kg oral glucose load by applying the closed-loop intraportal (PO) or intravenous (IV) insulin infusion algorithm. There were no significant differences in glycemic control and insulin requirements between these algorithms. However, the maximum peripheral venous and arterial plasma insulin concentrations with the PO algorithm were significantly lower than those with the IV algorithm [305.1 ± 68.9 and 468.1 ± 66.9 pmol/l (peripheral vein) and 305.3 ± 62.9 and 469.6 ± 85.1 pmol/l (artery) with the PO and IV algorithms, respectively, P < 0.05]. On the other hand, the maximum portal plasma insulin concentration with the PO algorithm was significantly higher than that with the IV algorithm (619.9 ± 101.7 and 414.3 ± 79.9 pmol/l with the PO and IV algorithms, respectively, P < 0.05). The mean NHGU values with the PO algorithm were significantly greater than those with the IV algorithm. Our results confirmed that closed-loop portal insulin delivery is feasible with regard to both insulin profiles and hepatic glucose handling in vivo, and indicated that the portal vein is the most suitable insulin delivery route for the artificial endocrine pancreas.

Strict glycemic control in diabetic dogs with closed-loop intraperitoneal insulin infusion algorithm designed for an artificial endocrine pancreas

Abstract The ultimate goal of the development of an artificial endocrine pancreas is to achieve long-term strict glycemic regulation. To establish the physiological insulin delivery route of the artificial endocrine pancreas, intraperitoneal insulin infusion may be important. For this purpose, we tried to develop a closed-loop intraperitoneal insulin infusion algorithm by analyzing the pharmacokinetics of intraperitoneal regular insulin absorption using a mathematical model. The parameters for this algorithm were calculated to simulate the plasma insulin profile after intraperitoneal insulin injection as closely as possible. To evaluate the appropriateness of this algorithm, we tried glycemic control after an oral glucose load of 2 g/kg or a meal load of 80 kcal/kg in diabetic dogs by applying the algorithm. With the use of the subcutaneous insulin lispro infusion algorithm, which we have previously reported, alloxan-induced diabetic dogs exhibited postprandial hyperglycemia and delayed hyperinsulinemia, followed by hypoglycemia after an oral glucose load of 2 g/kg. However, by using the intraperitoneal insulin infusion algorithm, excellent glycemic control (postprandial blood glucose levels of 9.1 ± 0.8 mmol/l at 70 min and 3.8 ± 0.3 mmol/l at 240 min, respectively) could be achieved without any associated delayed hyperinsulinemia or hypoglycemia. Glycemic excursion after a meal load of 80 kcal/kg was also controlled from 3.9 to 10.1 mmol/l. Our results confirm that the intraperitoneal insulin infusion algorithm in vivo is feasible and that this algorithm can be superior to the subcutaneous insulin lispro infusion algorithm in the regulation of blood glucose.

Development of a highly responsive needle-type glucose sensor using polyimide for a wearable artificial endocrine pancreas

To produce a long-life, stable, miniature glucose sensor for a wearable artificial endocrine pancreas (WAEP), we developed a novel microneedle-type glucose sensor using polyimide, designated the PI sensor (outer diameter, 0.3 mm; length, 16 mm), and investigated its characteristics in vitro and in vivo. In the in vitro study, we tested the sensor in 0.9% NaCl solution with varying glucose concentrations and observed an excellent linear relationship between the sensor output and glucose concentration (range: 0–500 mg/100 ml). In in vivo experiments, the PI sensor was inserted into the abdominal subcutaneous tissue of beagle dogs (n = 5), and interstitial fluid glucose concentrations were monitored after sensor calibration. Simultaneously, blood glucose concentrations were also monitored continuously with another PI sensor placed intravenously. The correlation and time delay between subcutaneous tissue glucose (Y) and blood glucose concentrations (X: 30–350 mg/100 ml) were Y = 1.03X + 7.98 (r = 0.969) and 6.6 ± 1.2 min, respectively. We applied the new WAEP system/PI sensor and an intravenous insulin infusion algorithm developed previously for glycemic control in diabetic dogs. The use of the WAEP system resulted in excellent glycemic control after an oral glucose challenge of 1.5 g/kg (post-challenge blood glucose levels: 176 ± 18 mg/100 ml at 65 min and 93 ± 23 mg/100 ml at 240 min), without any hypoglycemia. Thus, we confirmed that our new PI sensor has excellent sensor characteristics in vitro and in vivo. The new WAEP using this sensor is potentially suitable for clinical application.

Biocompatibility of MPC: in vivo evaluation for clinical application

Biocompatibility is important to assure a mild body reaction to an implanted device and its long-term stability and functionality. In diabetes research, subcutaneously implanted glucose monitoring systems need biocompatible surfaces for long-term application. The biocompatibility of poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (MPC), a material similar to the phospholipid layer of a cell membrane, was compared in vivo with the biocompatibility of polyurethane (PU), polyvinyl alcohol (PVA), and cuprophane (CUP). Needle-type glucose sensors and hollow-fiber probes used for microdialysis were coated with these four different biomaterials and implanted subcutaneously in 18 rats and 7 healthy volunteers. At set intervals, the implants and, in the case of the rats, also the surrounding tissue were removed and characterized by light and electron microscopy. MPC-coated sensors and hollow-fiber probes showed smooth and thin deposits in flat layers, whereas the surface deposits on PU- and PVA-coated sensors and those on CUP hollow-fiber probes appeared as rough, irregular, and dense attachments of aggregated cells and protein. This study confirmed results from earlier in vitro tests by showing the biocompatibility and reliability of MPC. Even though the amount of protein and cells attached to the MPC surface was not as low as expected from in vitro experiments, the biocompatibility and long-term stability of the implanted devices were superior to those of PU, PVA, and CUP.

Ezetimibe improves glucose metabolism by ameliorating hepatic function in Japanese patients with type 2 diabetes

Aims/Introduction:  Several experimental studies have shown that ezetimibe improves steatosis and insulin resistance in the liver. This suggests that ezetimibe may improve glucose metabolism, as well as lipid metabolism, by inhibiting hepatic lipid accumulation. Therefore, we compared HbA1c levels after 3 months ezetimibe treatment with baseline levels in patients with type 2 diabetes and examined the factors associated with reductions in HbA1c following ezetimibe administration.

Artificial endocrine pancreas and optimal blood glucose regulation in diabetic patients — from bedside-type to wearable-type

The artificial endocrine pancreas is a feedback control system regulating insulin delivery on a minute-by-minute basis according to the measured blood glucose levels. The bedside-type artificial endocrine pancreas has been proven to be useful not only as a therapeutic tool for diabetes mellitus but also as an elegant research tool for investigating the pathophysiology of the disease. With significant advances in the development of a subcutaneous tissue glucose monitoring system, the wearable-type artificial endocrine pancreas has been applied to diabetic patients. With this system, perfect glycemic control can be obtained for longer periods in ambulatory diabetic patients. The trend in the development of the artificial endocrine pancreas is now directed to implantable devices. Much efforts have been conducted to realize these devices.

Comparison of the efficacy of sitagliptin and glimepiride dose‐up in Japanese patients with type 2 diabetes poorly controlled by sitagliptin and glimepiride in combination

The goal of the study was to examine the effects of sitagliptin dose‐up or glimepiride dose‐up in Japanese patients with type 2 diabetes who were controlled inadequately by sitagliptin and glimepiride in combination.