Search PubMed⌕ Search

Biomedical subjects

Adam Heller

Publications and source records attributed to Adam Heller.

At least 19 recordsLinked to original sources
PubMed2025

Evolution of the Artificial Pancreas: Components and Integration-CGMs, Insulin, and AP Systems.

The landmark Diabetes Control and Complications Trial (DCCT) showed that glucose control is critical to reducing the risk of diabetes-related complications. This chapter outlines a series of innovations and investigations that followed the DCCT, aimed at minimizing the risk of hypoglycemia while further improving glucose control. The chapter presents an example of innovations in wired enzyme technology that facilitated the movement from capillary glucose monitoring to continuous glucose monitoring (CGM) and ultimately, the first-factory calibrated CGM system. The next glycemic management innovation was to connect CGM data to an insulin pump containing an algorithm able to adjust insulin delivery based on the changing glucose levels and trends. The key features of automated insulin delivery (AID) systems, currently approved in the United States, are presented. The AID summary table includes type of pump, type and function of the insulin delivery algorithm, the data management system, and the indications for use. The next section explores the innovation of alternative routes of insulin delivery to move toward the goal of a fully automated insulin delivery system. The main trials in developing and implementing an implantable intraperitoneal programmable system are summarized. The last section explores if sensor input in addition to glucose levels such as continuous sensing of ketone, lactate, or insulin levels may provide valuable feedback to move us closer to a fully autonomous AID system. Much of this diabetes innovation and investigation work has been supported by the National Institute of Diabetes and Digestive and Kidney Diseases over that last 75 years.

Humans↗
PubMed2006

Electron-conducting redox hydrogels: Design, characteristics and synthesis.

Redox hydrogels constitute the only electron-conducting phase in which water-soluble chemicals and biochemicals dissolve and diffuse. The combination of solubility and diffusion makes the electron-conducting gels permeable to water-soluble biochemicals and chemicals. The electron-conducting redox hydrogels serve to electrically connect the redox centers of enzymes to electrodes, enabling their use whenever leaching of electron-shuttling diffusional redox mediators must be avoided, which is the case in subcutaneously implanted biosensors for diabetes management and in miniature, potentially implantable, glucose-O2 biofuel cells. Because the hydrogels envelope the redox enzymes, they electrically wire the reaction centers to electrodes irrespective of spatial orientation and connect to electrode redox centers of multiple enzyme layers. Hence, the attained current densities of enzyme substrate electrooxidation or electroreduction are much higher than with enzyme monolayers packed onto electrode surfaces.

Electrons↗
PubMed2006

Redox potentials of the blue copper sites of bilirubin oxidases.

The redox potentials of the multicopper redox enzyme bilirubin oxidase (BOD) from two organisms were determined by mediated and direct spectroelectrochemistry. The potential of the T1 site of BOD from the fungus Myrothecium verrucaria was close to 670 mV, whereas that from Trachyderma tsunodae was >650 mV vs. NHE. For the first time, direct electron transfer was observed between gold electrodes and BODs. The redox potentials of the T2 sites of both BODs were near 390 mV vs. NHE, consistent with previous finding for laccase and suggesting that the redox potentials of the T2 copper sites of most blue multicopper oxidases are similar, about 400 mV.

Amino Acid Sequence↗
PubMed2006

A laccase-wiring redox hydrogel for efficient catalysis of O2 electroreduction.

Laccase was earlier wired to yield an O2 electroreduction catalyst greatly outperforming platinum and its alloys. Here we describe the design, synthesis optimization of the composition, and characterization of the +0.55 V (AgAgCl) laccase-wiring redox hydrogel, with an apparent electron diffusion coefficient (D(app)) of 7.6 x 10(-7) cm2 s(-1). The high D(app) results in the tethering of redox centers to the polymer backbone through eight-atom-long spacer arms, which facilitate collisional electron transfer between proximal redox centers. The O2 flux-limited, true-area-based current density was increased from the earlier reported 560 to 860 microA cm(-2). When the O2 diffusion to the 7-microm-diameter carbon fiber cathode was cylindrical, half of the O2 flux-limited current was reached already at 0.62 V and 90% at 0.56 V vs Ag/AgCl, merely -0.08 and -0.14 V versus the 0.7 V (Ag/AgCl) reversible O2/H2O half-cell potential at pH 5.

Catalysis↗
PubMed2006

A potentially insect-implantable trehalose electrooxidizing anode.

The dominant sugar in the body fluids of many insects is not glucose, the sugar of the vertebrates, but trehalose. In a step toward a cell that would operate in insects, we describe here a trehalose electrooxidizing anode. The novel component of the anode is its engineered, trehalose oxidation catalyzing, FAD-glucose-3-dehydrogenase (G3DH). Screening for gene-sources of G3DH pointed to the G3DH of Agrobacterium tumefaciens. Sequencing of the A. tumefaciens genome revealed a 1.7 kb fragment which contained the G3DH coding gene. The fragment was isolated, cloned and expressed in E. coli strain BL-21, to yield the approximately 65 kDa his-tagged flavoenzyme, with a specific activity of approximately 2.5U/mg protein. Electrical wiring of its reaction center to a carbon electrode through a high apparent electron diffusion coefficient (5.8 x 10(-6)cm(2)/s) redox hydrogel with a -0.2V versus Ag/AgCl redox potential resulted in the trehalose electrooxidizing anode. Trehalose was electrooxidized at pH 7.2 already at -0.36 V versus Ag/AgCl. At 0 V versus Ag/AgCl the trehalose electrooxidation current density was 0.1 mA/cm(2).

Animals↗
PubMed2006

Potentially implantable miniature batteries.

All presently used batteries contain reactive, corrosive or toxic components and require strong cases, usually made of steel. As a battery is miniaturized, the required case dominates its size. Hence, the smallest manufactured batteries are about 50 mm3 in size, much larger then the integrated circuits or sensors of functional analytical packages, as exemplified by implantable glucose sensors for diabetes management. The status of the miniaturization of the power sources of such implantable packages is reviewed. Three microcells, consisting only of potentially harmless subcutaneously implantable anodes and cathodes, are considered. Because their electrolyte would be the subcutaneous interstitial fluid, the cells do not have a case. One potentially implantable cell has a miniature Nafion-coated Zn anode and a biocompatible hydrogel-shielded Ag/AgCl cathode. The core innovation on which the cell is based is the growth of a hopeite-phase Zn2+ conducting solid electrolyte film on the discharging anode. The film blocks the transport of O2 to the Zn, preventing its corrosion, while allowing the necessary transport of Zn2+. The second cell, with the same anode, would have a bioinert hydrogel-shielded wired bilirubin oxidase-coated carbon cathode, on which O2 dissolved in the subcutaneous fluid would be electroreduced to water. In the third cell, the glucose of the subcutaneous interstitial would be electrooxidized to gluconolactone at an implanted wired glucose anode, similar to that tested now for continuous glucose monitoring in diabetic people, and O2 in the subcutaneous fluid would be electroreduced to water on its wired bilirubin oxidase cathode.

Electricity↗
PubMed2006

Mode of action of poly(vinylpyridine-N-oxide) in preventing silicosis: effective scavenging of carbonate anion radical.

Small particles of crystalline silicon dioxide (crystallites) are exceptionally toxic. Inhalation of quartz crystallites causes silicosis, a devastating lung disease afflicting miners, particularly coal and stone workers. Poly(vinylpyridine-N-oxide)s (PVPNOs) have been applied in the prevention and treatment of silicosis, but their mode of action has been obscure. Recently, the sites of inducible *NO synthase activation and of nitrotyrosine formation were associated anatomically with the pathological quartz particle-caused lesions in the lungs. It has been suggested that the *NO formed combines rapidly with O2*- to yield ONOO-, a potential mediator of lung injury following silica exposure. Here, we show that PVPNOs do not react with peroxynitrite but scavenge exceptionally rapidly CO3*- radicals, which are produced in the decomposition of ONOO- in bicarbonate solutions. The rate constant for the reaction of CO3*- with PVPNO was found to be independent of the type and size of PVPNO, i.e., k = (1.9 +/- 0.2) x 10(5) M(-1) s(-1) per monomer. In contrast, the rate constant for the reaction of CO3*- with the small molecule 4-methylpyridine N-oxide did not exceed 1 x 10(4) M(-1) s(-1). The underlying reason for the difference is that, in the dissolved polymeric PVPNOs, the electrostatic repulsion between the N-oxide zwitterions destabilizes them, increasing dramatically their pKa. The protonated N-oxides at physiological pH have abstractable hydrogen atoms and are expected to react rapidly with CO3*-, just as cyclic hydroxylamines do. It is also shown that PVPNO inhibits tyrosine nitration by peroxynitrite at pH 7.6 in the presence of excess of CO2 in a concentration-dependent manner. Hence, binding of PVPNO to the quartz particles and eliminating CO3*- could prevent the killing of macrophages, the associated release of macrophage-recruiting cytokines, and the amplification of the local concentration of *NO by the recruited macrophages. The latter causes necrosis of the macrophage-infiltrated lung tissue and, upon repair of the necrotic lesion, results in the growth of the dysfunctional fibrotic tissue, which is the hallmark of silicosis.

Bicarbonates↗
PubMed2005

Reduction of the nonspecific binding of a target antibody and of its enzyme-labeled detection probe enabling electrochemical immunoassay of an antibody through the 7 pg/ml-100 ng/mL (40 fM-400 pM) range.

We describe a simple, potentially low-cost, amperometric, enzyme-amplified, sandwich-type immunoassay, monitoring IgG at a concentration as low as approximately 7 pg/mL with a dynamic range of 10(4). The assay utilizes a screen-printed carbon electrode on which a redox hydrogel and avidin are co-electrodeposited. To neutralize nonspecifically binding positively charged microdomains of the avidin, two polyanions, poly(acrylic acid-co-maleic acid) and poly(acrylic acid), are applied. These polyanions bind to the film not only electrostatically but also by Michael addition reaction to cysteine, lysine, or arginine functions of the avidin. The electrode is then made specific for the analyte, for which rabbit IgG was chosen, by conjugating the film-bound avidin to biotin-labeled anti-rabbit IgG. After exposure to the tested solution and capture of rabbit IgG, the sandwich is completed by conjugation of horseradish-peroxidase (HRP)-labeled anti-rabbit IgG. Electrical contact between the HRP and the electrode-bound hydrogel results in the formation of an electrocatalyst for the electroreduction of H2O2 to water. The application of the poly(acrylic acid-co-maleic acid) and the poly(acrylic acid) reduces the nonspecific adsorption-associated noise, lowers the detection limit from 3 ng/mL (approximately 20 pM analyte antibody concentration) to approximately 7 pg/mL (approximately 40 fM analyte antibody concentration), and also expands the dynamic range to 10(4).

Adsorption↗
PubMed2005

Ionic conduction in Zn3(PO4)2.4H2O enables efficient discharge of the zinc anode in serum.

Batteries contain corrosive or reactive components necessitating containment in a case, setting a limit to their miniaturization. Miniature, small-capacity batteries could power medical sensors in the body, for example sensing glucose for diabetes management. A miniature, case-less Zn-Ag/AgCl battery would consist merely of a zinc anode and a bioinert gel-coated Ag/AgCl cathode, if both operated efficiently in the interstitial fluid. Such a battery has not previously been built, primarily because of rapid corrosion of Zn. We show that the corrosion of zinc is significantly reduced by growth of Zn2+-ion-conducting, O2-impermeable, hopeite [Zn3(PO4)2.4H2O] lamellae on the Nafion-coated Zn anode. The hopeite lamellae allow discharge of the Zn anodes over three weeks at 86% current efficiency in physiological buffer and at 60% efficiency over two weeks in serum. The Zn|physiological buffer|Ag/AgCl cell operates at 1.00 V at 13 muA cm-2 and at 0.94 V at 0.2 mA cm-2 anodic current density.

Electric Conductivity↗
PubMed2005

Bioelectrochemical propulsion.

A carbon fiber having a terminal glucose oxidizing microanode and an O2 reducing microcathode is propelled at the water-O2 interface. The electron current in the fiber is accompanied by a flux of hydrated protons that is so fast at the solution-air interface, where the viscous drag is small, that the fiber's velocity is 1 cm s-1.

Biosensing Techniques↗
PubMed2005

On the stability of the "wired" bilirubin oxidase oxygen cathode in serum.

Oxygen is electroreduced to water on the "wired" bilirubin oxidase (w-BOD) catalyst at a considerably lesser potential than on pure platinum. The w-BOD catalyst could be of value in an implantable glucose-O2 biofuel cell, operating living tissue, if it were stable in serum. We found, however, that w-BOD loses its activity in a few hours in the combined presence of the urate and O2, both of which are normal serum constituents (Bioelectrochemistry, 2004, 65, 83-88). Here we report a second major instability: When the disconnected w-BOD cathode is allowed, in the absence of urate, to poise itself at the potential of the O2/H2O half cell at pH 7.2, it loses its activity rapidly. Unlike the urate/O2 caused loss, this loss can be avoided either by applying a potential that is reducing relative to the O2/H2O half-cell potential, or by excluding O2 and adding a mildly reducing reagent, such as urate. The w-BOD cathode can be stored, therefore, in deoxygenated serum, which contains urate.

Animals↗
PubMed2005

Osmium tetroxide, used in the treatment of arthritic joints, is a fast mimic of superoxide dismutase.

Aqueous solutions of osmium tetroxide (OsO4) have been injected into arthritic knees for the past 45 years to chemically destroy diseased tissue, in a procedure termed "chemical synovectomy." Arthritis is an inflammatory disease. The primary inflammatory chemical species are the superoxide anion radical (O2.-) and nitric oxide (.NO), which combine to form the peroxynitrite anion (ONOO-). Here we show that OsO4 does not react with ONOO- but very efficiently catalyzes the dismutation of O2.- to O2 and H2O2. Using the pulse-radiolysis technique, the catalytic rate constant has been determined to be (1.43+/-0.04) x 10(9) M-1 s-1, independent of the pH in the 5.1-8.7 range. This value is about half that for the natural Cu,Zn-superoxide dismutase (Cu,Zn-SOD). Per unit mass, OsO4 is about 60 times more active than Cu,Zn-SOD. The catalytically active couple is OsVIII/OsVII, OsVIII oxidizing O2.- to O2 with a bimolecular rate constant of k=(2.6+/-0.1)x10(9) M-1 s-1 and OsVII reducing it to H2O2 with a bimolecular rate constant of (1.0+/-0.1)x10(9) M-1 s-1. Although lower valent osmium species are intrinsically poor catalysts, they are activated through oxidation by O2.- to the catalytic OsVIII/OsVII redox couple. The OsVIII/OsVII catalyst is stable to biochemicals other than proteins and peptides comprising histidine, cysteine, and dithiols.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

Detection of glucose at 2 fM concentration.

We report the amperometric detection of glucose at 2 fM concentration in a physiological buffer solution at 1 atm O2 pressure. The sensitive assay is based on the close to absolute electroreductive stripping of O2 from the solution near the glucose electrooxidizing anode. The glucose was detected by its electrooxidation on a stationary glassy carbon disk surrounded by an also stationary platinum ring. The disk was coated with a film of glucose oxidase (GOx), electrically "wired" with PVP-[Os(N,N'-dimethyl-2,2'-biimidazole)3]2+/3+ (polymer I), having a redox potential of -0.19 V versus Ag/AgCl. The ring was coated with bilirubin oxidase (BOD) "wired" with PAA-PVI-[Os(4,4'-dichloro-2,2'-bipyridine)2Cl]+/2+ (polymer II), having a redox potential of + 0.36 V versus Ag/AgCl. The ring-disk electrode was held facing up, and a 30-microL drop was placed on it for the assay, with the ring poised at -0.3 V/ AgAgCl and the disk poised at -0.1 V/ Ag/AgCl. Even though the atmosphere over the drop was O2 at 1 atm pressure, the wired BOD disk scavenged the O2 so effectively that the glucose-reduced FADH2 of GOx was not oxidized by O2, the natural cosubstrate of the enzyme.

Electrochemistry↗
PubMed2004

Detection of approximately 10(3) copies of DNA by an electrochemical enzyme-amplified sandwich assay with ambient O(2) as the substrate.

The electrochemical sandwich-type, enzyme-amplified assay of Zhang, Kim, and Heller (Anal. Chem. 2003, 75, 3267-3269) was simplified by replacing the amplifying horseradish peroxidase with bilirubin oxidase (BOD). BOD catalyzes the reduction of ambient O(2) to water and obviates the need for adding H(2)O(2). Femtomolar (10(-)(15) M) concentrations of DNA were detected at a 10-microm-diameter tip of a carbon fiber electrode. Correspondingly, a few thousand copies of DNA were detected in approximately 5-microL samples. The sandwich is formed in an electron-conducting redox hydrogel, to the polymer of which a DNA capture sequence is bound. Capture of the analyte DNA and its hybridization with a BOD-labeled complementary DNA sequence, electrically connects the BOD label to the electron-conducting redox polymer, which is in electrical contact with the electrode. Placing the BOD in contact with the redox polymer thus converts the noncatalytic base layer into a catalyst for the electroreduction of O(2) to water at +0.12 V (vs Ag/AgCl) (Figure 1). In an exemplary assay, approximately 3000 copies of the iron transporting sequence of the sit gene of Shigella flexneri were detected without PCR amplification.

Animals↗
PubMed2004

A four-electron O(2)-electroreduction biocatalyst superior to platinum and a biofuel cell operating at 0.88 V.

O2 was electroreduced to water, at a true-surface-area-based current density of 0.5 mA cm-2, at 37 degrees C and at pH 5 on a "wired" laccase bioelectrocatalyst-coated carbon fiber cathode. The polarization (potential vs the reversible potential of the O2 /H2O half-cell in the same electrolyte) of the cathode was only -0.07 V, approximately one-fifth of the -0.37 V polarization of a smooth platinum fiber cathode, operating in its optimal electrolyte, 0.5 M H2SO4. The bioelectrocatalyst was formed by "wiring" laccase to carbon through an electron conducting redox hydrogel, its redox functions tethered through long and flexible spacers to its cross-linked and hydrated polymer. Incorporation of the tethers increased the apparent electron diffusion coefficient 100-fold to (7.6 +/- 0.3) x 10-7 cm 2 s-1. A miniature single-compartment glucose-O2 biofuel cell made with the novel cathode operated optimally at 0.88 V, the highest operating voltage for a compartmentless miniature fuel cell.

Journal Article↗