The human amylin analog, pramlintide, corrects postprandial hyperglucagonemia in patients with type 1 diabetes.

Mealtime amylin replacement with the human amylin analog pramlintide as an adjunct to insulin therapy improves postprandial glycemia and long-term glycemic control in type 1 diabetes. Preclinical animal studies indicate that these complementary effects may result from at least 2 independent mechanisms: a slowing of nutrient delivery to the small intestine and a suppression of nutrient-stimulated glucagon secretion. The former effect of pramlintide has previously been demonstrated in patients with type 1 diabetes. The present studies characterize the effect of pramlintide on postprandial glucagon secretion in this patient population. Plasma glucagon and glucose concentrations were measured before and after a standardized liquid meal in 2 separate randomized, double-blind, placebo-controlled studies of pramlintide administration to patients with type 1 diabetes. In a 2-day crossover study, 18 patients received a 5-hour intravenous infusion of pramlintide (25 microg/h or 50 microg/h) or placebo in addition to subcutaneous (SC) insulin injections. In a 14-day parallel-group study, 84 patients received SC injections of 30, 100, or 300 microg of pramlintide or placebo 3 times daily in addition to SC injections of insulin. In both studies plasma glucagon concentrations increased in response to the meal in the placebo-plus-insulin group but not in any of the pramlintide-treated groups (all pramlintide treatment arms v placebo, P <.05). We conclude that mealtime amylin replacement with pramlintide prevents the abnormal meal-related rise in glucagonemia in insulin-treated patients with type 1 diabetes, an effect that likely contributes to its ability to improve postprandial glucose homeostasis and long-term glycemic control.

Plasma amylin immunoreactivity and insulin resistance in insulin resistant relatives of patients with non-insulin-dependent diabetes mellitus.

To explore the potential relationship between concentrations of circulating amylin and the insulin resistance observed in first-degree relatives of patients with non-insulin-dependent-diabetes mellitus (NIDDM), we studied 40 relatives compared to 35 matched controls. Two newly developed immunoassays that measure either non-glycosylated or total amylin were applied. All subjects were examined by an oral glucose tolerance test (OGTT) and by a hyperinsulinemic euglycemic clamp (insulin infusion: 0.6 mU/kg/min). Glucose tolerance was normal in all, but insulin-stimulated glucose uptake (Rd) was diminished in the relatives (p < 0.001). Area under the curves (AUCs) during OGTT for plasma glucose (p < 0.01) and serum insulin (p=0.08), but not for plasma total and non-glycosylated amylin, were higher in relatives versus controls. In both groups, inverse correlations were found between Rd and AUC for plasma total and non-glycosylated amylin (p [all]<0.05). However, in multiple linear regression analyses, plasma total and non-glycosylated amylin failed to influence Rd independent of serum insulin and family history-of NIDDM. In conclusion, this study demonstrated inverse correlations between Rd and circulating concentrations of plasma total and non-glycosylated amylin in relatives and matched controls. These data, however, do not support the hypothesis that physiological amylin concentration are a major importance for the insulin resistance in relatives of NIDDM patients.

Development and characterization of monoclonal antibodies specific for amylin.

Highly selective monoclonal antibodies to the peptide hormone human amylin have been produced and characterized. These antibodies are produced by hybridomas resulting from the fusions of BALB/c-derived myelomas and splenocytes from either inbred or outbred mouse strains. Certain of these antibodies recognize epitopes at the amino-terminus or the amidated carboxy-terminus, as well as conformational epitopes within the central region of the 37 amino acid peptide. Several of these antibodies show less than 0.1% cross-reactivity with related peptide hormones such as calcitonin and calcitonin gene-related peptide (CGRP) and have apparent affinities in the low nanomolar range. Antibody pairs were selected for use in two-site assays for the direct measurement of endogenous amylin and the synthetic human amylin analogue, pramlintide (25, 28, 29 tripro-human amylin), which is presently under clinical investigation for improving glucose control in patients with both Type I and Type II diabetes treated with insulin.

Development of sensitive immunoassays to detect amylin and amylin-like peptides in unextracted plasma.

Amylin is a 37-amino-acid polypeptide synthesized in and secreted from pancreatic beta cells along with insulin. Its biological actions include the slowing and reduction of postmeal increases in plasma glucose concentrations. Studies of the basic amylin biology in humans have been hampered by the lack of a rapid, sensitive assay capable of measuring physiological concentrations of amylin in small volumes of plasma. We report here two sandwich-type immunoassays that use pairs of monoclonal antibodies, the fluorescent substrate 4-methylumbelliferyl phosphate, and the enzyme alkaline phosphatase. The minimum detectable concentration of amylin in 50 microL of plasma was 0.5 to 2 pmol/L, and the dynamic range was 2 to 100 pmol/L. The assays had average intraassay CVs of <10%, average interassay CVs of <15%, and good linearity on dilution and recovery of added amylin. The two assays use the same detection antibody, which binds to the carboxyl terminus of the molecule, but different capture antibodies. One of the assays measures only human amylin; the other also detects amylin-like peptides. Examples of measurements in human plasma are provided in subjects with impaired glucose tolerance and in nondiabetic controls.

Molecular physiology of amylin.

Amylin is a 37-amino acid peptide first isolated, purified, and characterized from the amyloid deposits in the pancrease of type 2 diabetics. It is synthesized and secreted primarily from pancreatic beta cells along with insulin. The ability of amylin to potently reduce insulin-stimulated incorporation of glucose into glycogen in skeletal muscle requires both an intact 2Cys-7Cys disulfide bond and a COOH-terminal amide. Amylin has structural and functional relationships to two other messenger proteins, calcitonin and CGRP. Amylin has relatively potent calcitonin-like activity on bone metabolism and weaker CGRP-like activity on the vasculature. CGRP is a slightly weaker agonist than amylin for metabolic responses. Although rat calcitonins are weak, teleost fish calcitonins are very potent agonists for amylin's metabolic effects. This group of peptides appears to act on a family of related G protein-coupled receptors; several variant calcitonin receptors have recently been cloned and expressed. These receptors appear to be coupled to adenylyl cyclase in many instances; recent evidence supports the view that amylin's effects on skeletal muscle occur, at least in large part, through activation of the cAMP pathway.

Hyperamylinemia, hyperinsulinemia, and insulin resistance in genetically obese LA/N-cp rats.

The experimental evidence supporting a direct role for hyperinsulinemia as a cause of insulin resistance remains equivocal. Amylin, an islet beta-cell peptide cosecreted with insulin in response to nutrient stimuli, causes insulin resistance when infused into intact animals or applied to isolated skeletal muscles. We compared measures of amylin and insulin gene expression between control and genetically obese, insulin-resistant Lister Albany/NIH-(LA/N-cp) rats. Pancreatic amylin messenger RNA levels were increased 7.8 +/- 0.7-fold (mean +/- SEM), and plasma amylin-like immunoreactive material was increased 10.9 +/- 1.1-fold (LA/N-lean, 14 +/- 4 pM; LA/N-cp, 153 +/- 16 pM; p less than 0.0001) in obese rats. Pancreatic insulin I mRNA levels were increased 7.4 +/- 0.5-fold, and plasma insulin levels 20.0 +/- 5.0-fold, in these rats (LA/N-lean, 308 +/- 84 pM; LA/N-cp 6,120 +/- 1,540 pM; p less than 0.0001). The EC50 for insulin-stimulated incorporation of glucose into glycogen was about fourfold higher in muscles isolated from obese rats. The present results, coupled with previous observations, support the hypothesis that hyperamylinemia, rather than hyperinsulinemia per se, could have directly caused the insulin resistance in the obese LA/N-cp rats. Hyperamylinemia needs to be considered in future experimental studies probing the relation between hyperinsulinemia and insulin resistance.

Serum levels and biochemical characteristics of cancer-associated antigen CA-549, a circulating breast cancer marker.

CA-549 is a circulating breast cancer-associated antigen that reacts with monoclonal antibody BC4E 549. Biochemical characterization of CA-549 revealed that it is an acidic (isoelectric point 5.2) glycoprotein that exhibits two bands by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions of apparent molecular weights of 400,000 and 512,000. Immunohistochemical staining of unfixed frozen tissue sections of human breast tumors and a variety of benign tissues with BC4E 549 revealed no preferential staining of tumor over benign breast tissue and cross-reactivity with a wide range of other benign tissues including kidney, liver, lung, colon, pancreas, ovary, and spleen. Serum levels of CA-549 were initially tested by an enzyme-linked immunosorbent assay inhibition using BC4E 549. This assay showed that CA-549 concentrations were elevated in 19 of 27 sera from patients with advanced breast cancer compared to 0 of 22 and 0 of 129 sera from benign breast disease patients and healthy females, respectively. These preliminary data suggested that CA-549 was a useful breast tumor marker; thus BC4E 549 was adapted to a sandwich immunoradiometric assay format suitable for routine use in the clinical laboratory and its performance was evaluated on a panel of 668 serum samples. The test detected significant concentrations of CA-549 in the sera of 40 of 80 patients with advanced breast cancer, 1 of 30 with early breast cancer, 4 of 19 with advanced lung cancer, 2 of 40 with advanced colon cancer, and 5 of 29 with advanced prostate cancer. The test showed a high degree of specificity, producing false-positives in only 3 of 79 benign breast patients, 2 of 25 benign liver patients, 2 of 70 benign colon patients, 2 of 19 benign lung patients, 0 of 20 benign prostate patients, and 3 of 257 healthy individuals. These data represent an overall 50% sensitivity and 98% specificity as a test for advanced breast cancer. These data indicate that this immunoradiometric assay is a useful test for the detection of circulating CA-549 in advanced breast cancer patients and suggest that it may prove useful as a monitor in the management of that disease.

Heparan sulfate proteoglycans from mouse mammary epithelial cells. Cell surface proteoglycan as a receptor for interstitial collagens.

A heparan sulfate-rich proteoglycan is on the surface of NMuMG mouse mammary epithelial cells apparently intercalated into their plasma membranes. Mild treatment of the cells with trypsin releases the GAG-bearing region (ectodomain) of this molecule as a discrete proteoglycan which is readily purified. At physiological pH and ionic strength, the ectodomain binds collagen types I, III, and V but not types II, IV, or denatured type I. The proteoglycan binds to a single class of high affinity saturable sites on type I collagen fibrils, sites which are selective for heparin-like glycosaminoglycans. The binding of NMuMG cells to type I collagen duplicates that of their cell surface proteoglycan; cells bind to native but not denatured collagen, and binding is inhibited by heparin but not by other glycosaminoglycans. These binding properties suggest that cell surface heparan sulfate proteoglycans could act as receptors for interstitial collagens and mediate changes in cell behavior induced by collagenous matrices.

Heparan sulfate proteoglycans from mouse mammary epithelial cells. Basal extracellular proteoglycan binds specifically to native type I collagen fibrils.

Mouse mammary epithelial cells (NMuMG cells) deposit at their basal surfaces an extracellular heparan sulfate-rich proteoglycan that binds to type I collagen. The binding of the purified proteoglycan to collagen was studied by (i) a solid phase assay, (ii) a suspension assay using preformed collagen fibrils, and (iii) a collagen fibril affinity column. The binding interaction occurs at physiological pH and ionic strength and can be inhibited only by salt concentrations that greatly exceed those found physiologically. Binding requires the intact proteoglycan since the protein-free glycosaminoglycan chains will not bind under the conditions of these assays. However, binding is mediated through the heparan sulfate chains as it can be inhibited by block-sulfated polysaccharides, including heparin. Binding requires native collagen structure which may be optimal when the collagen is in a fibrillar configuration. Binding sites on collagen fibrils are saturable, high affinity (Kd approximately 10(-10) M), and selective for heparin-like glycosaminoglycans. Because a culture substratum of type I collagen fibrils causes NMuMG cells to accumulate heparan sulfate proteoglycan into a basal lamina-like layer, binding of heparan sulfate proteoglycans to type I collagen may lead to the formation of a basal lamina and may link the basal lamina to the connective tissue matrix, an association found in basement membranes.

Remodelling of the basement membrane: morphogenesis and maturation.

We have analysed the reciprocal interactions between mouse embryo submandibular epithelium and mesenchyme which result in branching morphogenesis of the epithelium. The interactions modify the composition and metabolism of the basal and reticular laminae which comprise the basement membrane lying between these tissues. The mesenchyme remodels the basement membrane by depositing a type I collagen-rich matrix on the basal lamina and by producing a neutral hyaluronidase, which degrades hyaluronate and chondroitin sulphate, components of this basal lamina. By analogy with mouse mammary epithelial cells, the submandibular epithelial cells have a heparan sulphate-rich proteoglycan on their cell surfaces which is anchored to the cells. The extracellular domain of this integral membrane proteoglycan binds to interstitial collagen. Interfering with the collagen-proteoglycan interaction appears to reduce the morphological stability of the cells. Together with other processes, including epithelial cell proliferation, this remodelling leads to branching epithelial morphogenesis. Basement membrane remodelling may be a general process for regulating cell behaviour during development and is one of the mechanisms of morphogenetic tissue interaction. Remodelling may also cause maturation of basement membranes from a dynamic state of high turnover in the embryo to their persistence and stability in the adult organism.