The artificial pancreas: is it important to understand how the ß cell controls blood glucose?

It has been more than 7 years since the first fully automated closed-loop insulin delivery system that linked subcutaneous insulin delivery and glucose sensing was published. Since the initial report, the physiologic insulin delivery (PID) algorithm used to emulate the ß cell has been modified from the original proportional-integral-derivative terms needed to fit the ß cell's biphasic response to a hyperglycemic clamp to include terms emulating cephalic phase insulin release and the effect of insulin per se to inhibit insulin secretion. In this article, we compare the closed-loop glucose profiles obtained as each new term has been added, reassess the ability of the revised PID model to describe the ß cells' insulin response to a hyperglycemic clamp, and look for the first time at its ability to describe the response to a hypoglycemic clamp. We also consider changes that might be added to the model based on perfused pancreas data. We conclude that the changes introduced in the PID model have systematically improved the closed-loop meal response. We note that the changes made do not adversely affect the ability of the model to fit hyperglycemic clamp data but are necessary to fit the response to a hypoglycemic clamp. Finally, we note a number of ß cell characteristics observed in the perfused pancreas have not been included in the model. We suggest that continuing the effort to understand and incorporate aspects of how the ß cell achieves glucose control can provide valuable insights into how improvements in future artificial pancreas algorithms might be achieved.

Analysis of Bonding between Conjugated Organic Molecules and Noble Metal Surfaces Using Orbital Overlap Populations.

The electronic structure of metal-organic interfaces is of paramount importance for the properties of organic electronic and single-molecule devices. Here, we use so-called orbital overlap populations derived from slab-type band-structure calculations to analyze the covalent contribution to the bonding between an adsorbate layer and a metal. Using two prototypical molecules, the strong acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) on Ag(111) and the strong donor 1H,1'H-[4,4']bipyridinylidene (HV0) on Au(111), we present overlap populations as particularly versatile tools for describing the metal-organic interaction. Going beyond traditional approaches, in which overlap populations are represented in an atomic orbital basis, we also explore the use of a molecular orbital basis to gain significant additional insight. On the basis of the derived quantities, it is possible to identify the parts of the molecules responsible for the bonding and to analyze which of the molecular orbitals and metal bands most strongly contribute to the interaction and where on the energy scale they interact in bonding or antibonding fashion.

Is there a Au-S bond dipole in self-assembled monolayers on gold?

Self-assembled monolayers (SAMs) of functionalized thiols are widely used in organic (opto)electronic devices to tune the work function, Phi, of noble-metal electrodes and, thereby, to optimize the barriers for charge-carrier injection. The achievable Phi values not only depend on the intrinsic molecular dipole moment of the thiols but, importantly, also on the bond dipole at the Au-S interface. Here, on the basis of extensive density-functional theory calculations, we clarify the ongoing controversy regarding the existence, the magnitude, and the nature of that bond dipole.

Self-assembled monolayers of polar molecules on Au(111) surfaces: distributing the dipoles.

Quantum-mechanical calculations are performed to investigate the interface between Au(111) surfaces and self-assembled monolayers (SAMs) of organic thiols. Dipolar pyrimidine units act as building blocks to systematically tune the molecular dipole moments via the number of repeat units. The resulting work-function modifications and the energetic alignment of the frontier electronic states in the SAM with the Fermi level are analyzed. Compared to SAMs where strong dipole moments are realized only by end-group substitutions on otherwise non-polar molecules, an entirely different evolution with backbone length is found for the present systems, where dipoles are built directly into the backbone. In particular, the achievable work-function modifications depend on peculiarities in the relative alignment of the energy levels in the SAM and in the metal. We thus introduce an additional degree of freedom for tuning surface and interface electronic properties with functional self-assembled monolayers.

Understanding the electronic structure of metal/SAM/organic-semiconductor heterojunctions.

Computational modeling is used to describe the mechanisms governing energy level alignment between an organic semiconductor (OSC) and a metal covered by various self-assembled monolayers (SAMs). In particular, we address the question to what extent and under what circumstances SAM-induced work-function modifications lead to an actual change of the barriers for electron and hole injection from the metal into the OSC layer. Depending on the nature of the SAM, we observe clear transitions between Fermi level pinning and vacuum-level alignment regimes. Surprisingly, although in most cases the pinning occurs only when the metal is present, it is not related to charge transfer between the electrode and the organic layer. Instead, charge rearrangements at the interface between the SAM and the OSC are observed, accompanied by a polarization of the SAM.

Are oxidative stress-activated signaling pathways mediators of insulin resistance and beta-cell dysfunction?

In both type 1 and type 2 diabetes, diabetic complications in target organs arise from chronic elevations of glucose. The pathogenic effect of high glucose, possibly in concert with fatty acids, is mediated to a significant extent via increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and subsequent oxidative stress. ROS and RNS directly oxidize and damage DNA, proteins, and lipids. In addition to their ability to directly inflict damage on macromolecules, ROS and RNS indirectly induce damage to tissues by activating a number of cellular stress-sensitive pathways. These pathways include nuclear factor-kappaB, p38 mitogen-activated protein kinase, NH(2)-terminal Jun kinases/stress-activated protein kinases, hexosamines, and others. In addition, there is evidence that in type 2 diabetes, the activation of these same pathways by elevations in glucose and free fatty acid (FFA) levels leads to both insulin resistance and impaired insulin secretion. Therefore, we propose here that the hyperglycemia-induced, and possibly FFA-induced, activation of stress pathways plays a key role in the development of not only the late complications in type 1 and type 2 diabetes, but also the insulin resistance and impaired insulin secretion seen in type 2 diabetes.

Oxidative stress and stress-activated signaling pathways: a unifying hypothesis of type 2 diabetes.

In both type 1 and type 2 diabetes, the late diabetic complications in nerve, vascular endothelium, and kidney arise from chronic elevations of glucose and possibly other metabolites including free fatty acids (FFA). Recent evidence suggests that common stress-activated signaling pathways such as nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases underlie the development of these late diabetic complications. In addition, in type 2 diabetes, there is evidence that the activation of these same stress pathways by glucose and possibly FFA leads to both insulin resistance and impaired insulin secretion. Thus, we propose a unifying hypothesis whereby hyperglycemia and FFA-induced activation of the nuclear factor-kappaB, p38 MAPK, and NH2-terminal Jun kinases/stress-activated protein kinases stress pathways, along with the activation of the advanced glycosylation end-products/receptor for advanced glycosylation end-products, protein kinase C, and sorbitol stress pathways, plays a key role in causing late complications in type 1 and type 2 diabetes, along with insulin resistance and impaired insulin secretion in type 2 diabetes. Studies with antioxidants such as vitamin E, alpha-lipoic acid, and N-acetylcysteine suggest that new strategies may become available to treat these conditions.

Hodgkin's disease as an indicator of AIDS.

Hodgkin's disease (HD) is not currently included within the Centers for Disease Control (CDC) classification system for AIDS. Upon HD diagnosis, HIV(human immunosuppressive virus)-positive patients are generally found within Stages III or IV of the Ann Arbor HD classification system, already exacerbating the problem of treatment. In contrast, HIV-negative patients diagnosed with HD are generally found within Stages I or II. Epidemiology and the presence of secondary lymphomas, opportunistic infections, or aggressive pathologies, accompanied by low survival rate and timing of HD diagnosis suggest that HD should be included among conditions indicating AIDS manifestation.

Dichotomy in the laminin-binding properties of soluble and membrane-bound human galactoside-binding protein.

Recent studies indicate that galactoside-binding proteins may bind the poly-N-acetyllactosamine sequences of laminin. We questioned whether human galactoside-binding protein (hL-31) binds to laminin and whether cells that express hL-31 on their surface use it as a laminin receptor to promote cellular attachment. The data show that both lectin and cells bind to immobilized laminin. The binding of soluble lectin to laminin is inhibited by lactose, while cell adhesion to it is not. The results indicate that laminin may be a ligand for soluble galactoside-binding proteins.

Manifestations of pediatric AIDS: proposed mechanisms of transmission.

Pediatric Acquired Immunodeficiency Syndrome (AIDS) is expected to increase by greater than 75% by 1993. Most of these infants will become infected with the Human Immunodeficiency Virus (HIV) through the mother. It is unclear exactly how the virus is passed from mother to child. The nature of HIV infection is described in this paper, and several mechanisms relevant to its transfer are proposed.

An angiotensin with prolonged action and blood pressure--lowering properties.

[Sar1,Phe(Br5)8] angiotensin II (Br5Ang II) is a specific, quasi-irreversible antagonist of angiotensin II (Ang II) in vitro. In vivo, this compound is a very potent, Ang II-specific antagonist with a very long duration of action against Ang II-induced blood pressure (BP) increases. In the "low-sodium" dog, this compound induces a prolonged BP reduction during and after intravenous infusion at doses comparable to cilazapril, a potent ACE inhibitor. The physicochemical and pharmacokinetic behavior of this peptide was therefore assessed to understand and interpret the prolonged antagonistic and antihypertensive activity of this peptide. Binding studies using beef adrenocortical membranes indicated specific binding of Br5Ang and related analogues to Ang II receptors with a Kd of 1.41 x 10(-9) M against iodinated [Sar1, D-Phe8]Ang II, a standard radioligand antagonist. Iodinated Br5AngII exhibited a very high degree of nonspecific binding to the membranes. It had an octanol-water partitioning coefficient of log P of + 0.903, a coefficient 84-fold higher than for [125I][Sar1, D-Phe8]Ang II. Association kinetics of [125I]Br5Ang II were similar to the standard ligand [125I] [Sar1, D-Phe8]Ang II, but the half-life of dissociation was four times higher (60 vs. 15 min at 20 degrees C). Molecular modeling indicates a practically identical conformational behavior of both peptides, Br5Ang II and [Sar1, D-Phe8]Ang II but with an expanded hydration shell over the Br5 residue. It is concluded that the prolonged duration of action is due to the increased hydrophobicity of the peptide, which leads to a slow dissociation from the Ang II receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of three calcium entry blockers in conscious dogs.

The cardiovascular effects of N-(3,4-dimethoxyphenethyl)-2-(3,4-dimethoxyphenyl-N-methyl-m-dithiane-2- propylamine-1,1,3,3-tetraoxide HCl (tiapamil, Ro 11-1781, Larocord), a new calcium entry blocker, were investigated in chronically-instrumented conscious dogs and compared with those of verapamil and nifedipine. Oral administration of tiapamil to normotensive dogs dilated preferentially the arterial vascular bed as evidenced by marked increases in the coronary and abdominal aortic blood flow in the absence of a depression of the myocardial contractile force. The vasodilator effects induced a reflex increase in heart rate and cardiac output, which prevented a decrease in blood pressure in normotensive, but not in renal hypertensive dogs. By contrast, verapamil and nifedipine decreased blood pressure in both normotensive and renal hypertensive dogs. At equieffective vasodilating doses, a negative inotropic effect was not seen with tiapamil. By contrast, nifedipine caused a marginal fall and verapamil a marked decrease in myocardial contractile force. This favourable pattern of hemodynamic properties makes tiapamil appear to be a useful agent for the treatment of hypertension and angina pectoris.

Cilazapril prevents hypertension in spontaneously hypertensive rats.

Chronic daily administration of cilazapril (1 X 10 mg/kg/day p.o., from age 4 to 14 weeks) to young spontaneously hypertensive rats (SHR) prevented the development of hypertension. The antihypertensive effect of a single dose of cilazapril persisted greater than 24 h. Discontinuation of long-term treatment resulted in an increase of systolic arterial blood pressure (SAP) to control hypertensive levels within 4 days. Following 10 weeks of drug administration, comparative hemodynamic studies were carried out on age-matched (14 weeks) control SHR and cilazapril-treated SHR. Cilazapril-treated SHR had a significantly lower mean arterial blood pressure (MAP) and total peripheral vascular resistance than did control SHR. The antihypertensive effect of cilazapril was not associated with changes in heart rate (HR). The myocardial performance parameters, cardiac output, and stroke volume, were similar in treated and control SHR, suggesting that the antihypertensive effect of cilazapril following chronic administration to SHR is mainly due to a reduction in peripheral vascular resistance. Vasopressor responses to angiotensin I were significantly lower in cilazapril-treated SHR than in control SHR. By contrast, pressor responses to angiotensin II and a high dose of norepinephrine (1.0 microgram/kg i.v.) were significantly enhanced. Isoproterenol elicited a fall in blood pressure in both groups, the extent of which was dependent upon the magnitude of basal blood pressure levels. Chronic cilazapril treatment resulted in a reduction of heart weight, suggesting that the drug may prevent development of cardiac hypertrophy in SHR. Kidney and adrenal weights were unaffected by the chronic treatment. Specific renin activities (SRA) in tissues of SHR were increased by factors of 20 (plasma) or 2 (kidney and adrenal) following cilazapril administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of the new angiotensin-converting-enzyme inhibitor, cilazapril, in anesthetized and conscious dogs.

Cilazapril is a new angiotensin-converting-enzyme inhibitor. In conscious renal-hypertensive dogs, cilazapril (2 X 10 mg/kg/day p.o.) caused a long-lasting (greater than 24 h) decrease in systolic arterial blood pressure, the magnitude of which was potentiated by pretreatment with furosemide. A maximal fall in systolic blood pressure of 39 +/- 6 mm Hg (from 145 +/- 5 to 106 +/- 7 mm Hg) was recorded. The antihypertensive effect did not decline with repeated administration and was accompanied by only a slight increase in heart rate. Cilazapril also reduced systolic blood pressure in furosemide-pretreated normotensive dogs. Hemodynamic studies in anesthetized dogs revealed that cilazapril (0.03-1 mg/kg i.v.) caused a fall in mean arterial and left ventricular systolic pressures. At the highest dose of 1 mg/kg i.v., the blood-pressure-lowering effect (-27%) was due to a decrease in total peripheral resistance (-12%) and cardiac output (-16%). Intravenous administration of cilazapril to anesthetized dogs resulted in a rise in plasma renin activity and a significant fall in plasma angiotensin II levels. In conscious normotensive dogs, cilazapril (0.3-10 mg/kg p.o.) exerted diuretic and saluretic effects, which were accompanied by a significant increase in renal plasma flow (46%), but only a slight rise in the glomerular filtration rate. These results characterize cilazapril as an effective and long-lasting antihypertensive drug, with diuretic activity and, possibly, preload- as well as afterload-reducing properties.

Calcium entry blockers inhibit vasoconstrictor responses to sympathetic nerve stimulation mediated by alpha 1-adrenoceptors.

Stimulation of the sympathetic outflow (spinal cord segments T 7-9) in pithed rats resulted in an increase in mean arterial pressure, heart rate, total peripheral vascular resistance and cardiac output. The increase in blood pressure and peripheral resistance was markedly depressed by prazosin and to a lesser extent by yohimbine, suggesting that these responses were mediated primarily by postjunctional alpha 1-adrenoceptors. The calcium entry blockers nifedipine, tiapamil and verapamil also depressed pressor responses and the increase in total peripheral resistance to electrical stimulation of the sympathetic outflow in these rats. This depression resulted primarily from an effect on peripheral vascular resistance components, as cardiac output remained unaffected by the calcium entry blockers. This conclusion was supported by studies on isolated, perfused rat renal arteries. Vasoconstrictor responses of this in vitro preparation to perivascular nerve stimulation were depressed by 1,000-fold lower concentrations of prazosin than rauwolscine, demonstrating the predominantly alpha 1-adrenoceptor nature of these effects. Likewise, these vasoconstrictor responses were depressed by nifedipine, tiapamil and verapamil in a concentration-dependent manner. The results of this study suggest that vasoconstrictor responses of rat resistance vessels to sympathetic nerve stimulation are mediated primarily by postjunctional alpha 1-adrenoceptors and can be inhibited by calcium entry blockers. This implies that contractile responses of these resistance vessels to alpha 1-adrenoceptor stimulation are not independent of the availability of extracellular calcium.

Chronic administration of tiapamil prevents hemodynamic alterations accompanying development of high blood pressure in hypertensive rats.

Daily oral administration of tiapamil (2 X 50-2 X 150 mg/kg, for 13 weeks) to spontaneously hypertensive rats (SHR) resulted in a dose-dependent inhibition of hypertension development, with complete prevention occurring at the highest dose. Tiapamil (2 X 100 mg/kg/day, p.o.) also prevented development of high blood pressure in deoxycorticosterone acetate-NaCl hypertensive rats (DOCA). A comparative hemodynamic analysis was carried out on age-matched (17-week-old) control SHR, tiapamil-treated (2 X 150 mg/kg/day, p.o.) SHR, and normotensive Wistar-Kyoto rats (WKY). Tiapamil-treated SHR and WKY had a significantly lower mean arterial pressure and total peripheral resistance as well as a higher cardiac output than untreated SHR. Vasoconstrictor responses to norepinephrine as well as to angiotensin I and II were significantly lower in tiapamil-treated than in untreated SHR. By contrast, isoproterenol elicited a fall in blood pressure in all three groups, the extent of which correlated directly with the magnitude of basal blood pressure levels. Tiapamil also caused a concentration-dependent depression of depolarization-induced vasoconstrictor responses in isolated mesenteric and renal arteries from SHR. The results of this study indicate that chronic administration of tiapamil will prevent the development of hypertension in SHR and DOCA rats as well as protect against accompanying hemodynamic alterations. This inhibitory effect on blood vessels that maintain peripheral resistance at elevated levels is a consequence of the vascular-selective calcium entry blocking properties of tiapamil.

Cardiovascular profile of Ro 13-6438, a novel positive inotropic agent with vasodilating properties.

The cardiovascular properties of Ro 13-6438 (R-6-chloro-1,5-dihydro-3- methylimidazo -[2,1-b] quinazolin -2[ 3H]-one), a novel nonglycoside , noncatechol cardiotonic agent, were investigated in vitro and in vivo by both intravenous and oral administration. Ro 13-6438 increased tension development of isolated guinea pig left atria in a concentration-dependent manner with an EC50 of 30 microM, but had no stimulant effect on the spontaneous rate of right atria. The positive inotropic effect of Ro 13-6438 was additive to that of ouabain (0.1 microM); Ro 13-6438 suppressed the arrhythmogenic activity of high concentrations of ouabain (10 microM). IN anesthetized open-chest dogs 10-300 micrograms/kg Ro 13-6438 i.v. produced a significant and dose-dependent increase in myocardial force, with a duration of action exceeding 60 min following the highest dose. It also slightly increased heart rate, cardiac output, and blood flow. Ro 13-6438 decreased systolic and diastolic blood pressure, left ventricular end-diastolic pressure, and total peripheral resistance. Thus, the direct positive inotropic effects of Ro 13-6438 were supported by a decrease in preload and afterload. In chronically instrumented, conscious dogs Ro 13-6438 increased myocardial contractility after administration of 0.03-0.3 mg/kg i.v. or 3-10 mg/kg p.o. The effects persisted for greater than 8 h after oral administration of 10 mg/kg. The inotropic effects were accompanied by a modest increase in heart rate, which, however, had a clearly shorter duration of action than the former.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of bufuralol, a beta-adrenoceptor antagonist with predominant beta 2-adrenoceptor agonistic activity, in the cat and the dog.

The effects of bufuralol and its carbinol metabolite have been compared with those of propranolol in the anaesthetised and conscious cat and dog. Bufuralol and its carbinol metabolite are nonselective beta-adrenoceptor antagonists; the former has equivalent potency to propranolol, whereas the latter is six times more potent. In anaesthetised animals both bufuralol and its metabolite exhibited partial agonistic activity, resulting in tachycardia and vasodilation. In conscious cats there was no change in heart rate or slight bradycardia, whereas in dogs both compounds again produced tachycardia. In anaesthetised and conscious cats and conscious dogs, both bufuralol and the metabolite increased abdominal aortic blood flow. There was a reduction in blood pressure in the conscious dog. It is concluded that the partial agonistic activity of bufuralol and its carbinol metabolite is exerted mainly at the beta 2-adrenoceptor, producing vasodilation and reducing peripheral resistance, resulting in a reduction in blood pressure with a long duration of action.

alpha 2-Adrenoceptors in rat resistance vessels.

In pithed rats increases in blood pressure were induced by i.v. injections of the alpha 1-agonist methoxamine and the alpha 2-agonists clonidine, oxymetazoline and B-HT 920. The pressor responses were further analyzed by repeated measurements of cardiac output with the thermodilution technique and by calculation of total peripheral vascular resistance. During the pressor phase both vascular resistance and cardiac output were found to be elevated. This indicates that increases in both haemodynamic variables contributed to the pressure rise. Under the assumption that elevated vascular resistance reflected constriction of arterioles and elevated cardiac output constriction of capacitance vessels via increased venous return to the heart, and considering that the magnitude of the increase of both haemodynamic parameters was similar for all three agonists, the results suggest the existence of both alpha 1- and alpha 2-adrenoceptors in resistance as well as in capacitance vessels of rats. For alpha 2-adrenoceptors in resistance vessels this conclusion was supported by the finding that the calcium antagonists verapamil and/or tiapamil virtually abolished the increases of blood pressure and vascular resistance in response to clonidine, oxymetazoline or B-HT 920, but not to methoxamine. The calcium antagonists did not affect the increases in cardiac output, irrespective of which type of alpha-agonist was administered. While the present results support the existence of alpha 2-adrenoceptors in resistance vessels of the rat, they do not allow a firm conclusion as to their occurrence in rat capacitance vessels.