Dennis J. Pillion

Enhanced Bioavailability of Calcitonin Formulated with Alkylglycosides Following Nasal and Ocular Administration in Rats

AbstractPurpose. The purpose of this study was to characterize the effects of alkylglycosides on the bioavailability of calcitonin following nasal and ocular administration. Methods. A salmon calcitonin specific radioimmunoassay kit was used to measure calcitonin levels in anesthetized rats at various times after nasal or ocular administration of calcitonin formulated with saline or with octylmaltoside, a medium chain length alkylglycoside or tetradecylmaltoside, a long chain alkylglycoside. The extent of calcitonin absorption was determined directly from the plasma calcitonin level-time curve and the bioavailability of calcitonin was determined from the area under the plasma calcium level-time curve. The calcium level was determined using a colorimetric method. Results. When the nasal formulation contained calcitonin plus saline or 0.125% octylmaltoside, little or no calcitonin was absorbed. However, plasma calcitonin levels were increased and plasma calcium levels were decreased when the nasal formulation contained calcitonin plus 0.125% or 0.25% tetradecylmaltoside. Maximal calcitonin levels were observed 7.5-10 min after nasal administration of the formulation. Ocular administration of calcitonin formulated with tetradecylmaltoside also resulted in calcitonin absorption, but less calcitonin absorption was found after ocular administration than after nasal administration. Conclusion. The experimental data indicate that tetradecylmaltoside, but not octylmaltoside, can be effectively used to enhance the bioavailability of nasally and ocularly administered calcitonin.

Receptors for insulin and insulin-like growth factor-I in the human adrenal gland

Human adrenal glands contain high-affinity receptors for insulin and insulin-like growth factor I (IGF-I). Comparative studies with rat, hamster and human adrenal membranes confirmed that IGF-I receptors are most abundant in rat and hamster adrenals, whereas insulin and IGF-I receptors are present in equivalent numbers in human adrenal glands. Covalent crosslinking studies revealed that the human adrenal gland IGF-I receptor binding subunit migrated on dodecyl sulfate polyacrylamide gels with Mr = 135,000, which is identical to the migration of IGF-I receptor binding subunits isolated from other tissues. Autoradiography of frozen human adrenal slices incubated with [125I]insulin showed prominent, displaceable binding of this radioligand to the zona reticularis, zona glomerulosa, vasculature and medulla; in contrast, [125I]IGF-I binding to human adrenal tissue was most prominent in the zona reticularis and negligible in the medullary region.

Cerebral cortical microvessels: An insulin-sensitive tissue

Abstract Cerebral cortical microvessels were isolated from bovine brains and incubated in the presence or absence of porcine insulin. The conversion of D-glucose to CO2 and lipids was increased significantly in insulin-treated microvessels. Insulin also caused a significant increase in the activity of cyclic-AMP phosphodiesterase in these microvessels. Specific binding of 125I-insulin to isolated brain microvessels, displaceable by cold insulin was also observed. The effects of insulin reported in this communication mark the first direct evidence that insulin is capable of regulating the metabolic activity of cerebral cortical microvascular tissue. The possible physiological significance of this finding is discussed.

Effects of the permeability enhancers, tetradecylmaltoside and dimethyl-β-cyclodextrin, on insulin movement across human bronchial epithelial cells (16HBE14o−)

The permeability of human bronchial epithelial cells (16HBE14o(-)) to radiolabelled insulin ([125I]insulin) formulated in the absence or presence of two different saccharide-containing permeability enhancers was investigated. In the absence of either enhancer, mannitol permeability and transepithelial electrical resistance (R(TE)) remained essentially unaffected for the duration of a 2-h experiment. Addition of either 0.125% tetradecylmaltoside (TDM) or 1% dimethyl-beta-cyclodextrin (DMBCD) to the apical surface of cells resulted in increased mannitol permeability and decreased R(TE), suggesting a loosening of cellular tight junctions and a concomitant increase in paracellular movement. Addition of [125I]insulin to the apical side of 16HBE14o(-) cells in the absence or presence of 1% DMBCD resulted in little or no [125I]insulin movement to the basolateral chamber or degradation in the apical chamber. However, in the presence of 0.125% TDM, the amount of intact [125I]insulin remaining in the apical chamber was substantially decreased, while [125I]insulin and 125I-labeled fragments were recovered on the basolateral side of the cells after 2 h. These findings provide evidence that the loosening of the tight junctions between cells achieved with DMBCD is not sufficient to stimulate transepithelial insulin movement, whereas exposure to 0.125% TDM causes an increase in [125I]insulin permeation and degradation.

Sucrose cocoate, a component of cosmetic preparations, enhances nasal and ocular peptide absorption.

Sucrose cocoate (SL-40), an emulsifier employed in emollient, skin-moisturizing cosmetic formulations, contains a mixture of sucrose esters of coconut fatty acids in aqueous ethanol solution. In order to determine its potential utility in enhancing nasal and ocular drug delivery, absorption studies were performed in anesthetized Sprague-Dawley male rats with calcitonin and insulin, two distinct therapeutic peptides. Administration of a nasal insulin formulation containing 0.5% sucrose cocoate caused a rapid and significant increase in plasma insulin levels, with a concomitant decrease in blood glucose levels. When insulin was administered ocularly in the presence of 0.5% sucrose cocoate, a smaller increase in plasma insulin levels, and a decrease in blood glucose levels, were observed. Administration of a nasal calcitonin formulation containing 0.5% sucrose cocoate caused a rapid increase in plasma calcitonin levels and a concomitant decrease in plasma calcium levels. Mass spectrometric analyses were used to characterize the nature of the sucrose fatty acid esters in the mixture. The most abundant sucrose ester in sucrose cocoate was sucrose monododecanoate, with smaller amounts of sucrose monodecanoate and sucrose monotetradecanoate. In vivo experiments confirmed that this ester was an effective enhancer of nasal peptide drug absorption.

Heparin — an Introduction

Seventy-five years after its discovery (1,2), heparin remains an important tool in medicine. Among its established uses are the prevention of postoperative thrombosis, the treatment of acute venous thrombosis, and the prevention of clot formation in the heart-lung machine (3). Little was known about the structure of heparin when the first clinical trials began in the mid-1930s, and it is only during the 1980s that the detailed structural basis of heparin action has been elucidated through the characterization of a specific, antithrombin-binding pentasaccharide segment in the polysaccharide molecule. In the following, we shall retrace some of the steps that have led to this goal.

Polyamines stimulate d-glucose transport in isolated renal brush-border membrane vesicles

Polyamines are natural constituents of most living organisms. However, their function in normal or pathological conditions is not fully understood. We have investigated in vitro effects of polyamines on characteristic properties of isolated renal brush-border membrane vesicles in order to determine whether polyamines have a regulatory role in membrane transport processes. The polyamines putrescine, spermidine and spermine were found to stimulate D-glucose uptake. Diffusional L-glucose uptake was not altered, indicating that the polyamines affected the active transport of D-glucose, rather than inducing nonspecific changes in membrane lipid properties. The amiloride-sensitive Na+ /H + exchange was slightly inhibited by polyamines while Mg2+ -ATPase activity was stimulated. The polyamine effects could not be explained solely by the polycationic properties of these agents, since polycationic polypeptides had an opposite effect. For example, lysozyme was found to inhibit D-glucose transport. Spermine was incorporated into the trichloroacetic acid-insoluble fraction of brush-border membrane proteins. Results indicated that this incorporation process consisted of at least two components: a Ca2+ -independent component and a Ca2+ -dependent component, possibly as a result of transglutaminase activity which was present in the isolated renal brush-border membranes. By using SDS-polyacrylamide gel electrophoresis in conjunction with fluorography, [3H]spermine was shown to be incorporated into several brush-border membrane proteins, mainly the 57 kDa, 74 kDa, 100 kDa, a heavy molecular weight band (greater than 200 kDa) and a low molecular weight band (less than 10 kDa). Our results suggest that the polyamine effects on membrane function may be due to a covalent modification of membrane proteins, possibly via a transglutaminase-mediated incorporation of polyamines or to the crosslinking of membrane proteins.

Angiotensin II and bradykinin stimulate phosphoinositide breakdown in intact rat kidney glomeruli but not in proximal tubules: Glomerular response modulated by phorbol ester

We have investigated the effect of angiotensin II, bradykinin, insulin and insulin-like growth factor I on phosphoinositide turnover in intact rat glomeruli and tubules. Angiotensin II produced a dose-dependent increase in inositol monophosphate formation with an IC50 of 10(-7)M, when added to isolated rat glomeruli. Angiotensin II-stimulated inositol phosphates formation was inhibited by the angiotensin receptor antagonist [Sar-Leu8]angiotensin II, indicating that the above response was mediated through activation of an angiotensin receptor in intact glomeruli. Besides angiotensin, in intact glomeruli, only bradykinin stimulated a phosphoinositide response, while in intact proximal tubules, none of the agonists tested produced an activation of the inositol phosphate formation. Angiotensin II- and bradykinin-stimulated inositol phosphate accumulation in intact glomeruli was inhibited by phorbol myristate acetate, an activator of protein kinase C.

Nocturnal polyuria in type 2 diabetes: A symptom of obstructive sleep apnea

PURPOSE Polyuria and nocturia in individuals with type 2 diabetes may be due to obstructive sleep apnea (OSA), a recently recognized etiology of excess nighttime urine production. This exploratory study examined the relationships among glucose control, OSA, and nocturnal urine production. METHODS A sample of community-dwelling older adults (20 nondiabetic subjects and 10 poorly controlled type 2 diabetes subjects) was recruited based on self-report of nocturia more than twice per night. Participants were monitored on a metabolic research unit for 24 hours to track intake/output, collect blood and urine samples, and conduct an overnight polysomnography sleep study. RESULTS None of the subjects had fasting serum glucose levels above the renal threshold. OSA was found in 65% of subjects. Those with moderate/severe OSA had significantly greater overnight urine production than subjects without OSA. Subjects with type 2 diabetes and moderate/severe OSA had the highest nocturnal urine production. CONCLUSIONS The high incidence of undetected OSA in subjects with type 2 diabetes with nocturia suggests that nocturia, OSA, and type 2 diabetes frequently coexist and may be interrelated.

Distribution of receptors for insulin and insulin-like growth factor I (somatomedin C) in the adrenal gland

Rat adrenal glands contain cell surface high-affinity receptors for several peptide hormones. Receptors for IGF-I were abundant in this tissue, but receptors for insulin were relatively scarce. The behavior of adrenal membrane IGF-I receptors in radioligand binding assays was similar to the behavior of IGF-I receptors from other tissues, with a KD congruent to 6.2 x 10(-9) M. Covalent cross-linking studies with [125I]IGF-I revealed an IGF-I receptor alpha-subunit with Mr congruent to 135,000 on dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions, as well as a smaller radiolabeled peptide, Mr = 116,000. In contrast, little binding of [125I]insulin to adrenal membranes was observed and no labeling occurred in cross-linking studies using [125I]insulin. These results contrast with the findings of whole-body autoradiographic studies that indicated substantial binding of [125I]insulin to adrenal glands and suggest that IGF-I, rather than insulin, may play a critical role in the growth and development of the adrenal gland.