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Biomedical subjects

W C Duckworth

Publications and source records attributed to W C Duckworth.

At least 19 recordsLinked to original sources
PubMed1992

Why intraperitoneal delivery of insulin with implantable pumps in NIDDM?

In the normal state, pancreatic secretion of insulin results in a portal/peripheral gradient with the highest concentrations of insulin in the liver. In diabetic patients with absent or insufficient pancreatic insulin secretion who require exogenous insulin, this normal gradient is lost, resulting in numerous abnormalities. This consideration led to interest in the intraperitoneal delivery of insulin, hoping to produce a therapeutic state more closely resembling normal physiology. The development of implantable insulin pumps, which can deliver insulin intraperitoneally, led to numerous studies on insulin-dependent diabetes mellitus (IDDM) patients, demonstrating that insulin delivered intraperitoneally is rapidly and predictably absorbed with most of it going into the portal system, resulting in hepatic delivery of insulin. Studies in IDDM patients have demonstrated that good glucose control can be achieved with intraperitoneal delivery of insulin from implantable pumps with lesser glycemic fluctuations and, therefore, fewer episodes of hypoglycemia. Furthermore, intraperitoneal insulin results in carbohydrate and particularly lipid metabolism that more closely mimics the normal physiological state than produced by injections of insulin. Thus, implantable insulin pumps are being studied for use in IDDM. Many non-insulin-dependent diabetes mellitus (NIDDM) patients have insufficient pancreatic secretion and require exogenous insulin. Because of alterations in hepatic sensitivity to insulin, increments in insulin delivery to the liver may be even more important in NIDDM than IDDM. Furthermore, insulin resistance, which is an integral part of NIDDM, results in higher physiological levels of insulin, which are required for glucose control, and thus significant peripheral hyperinsulinemia occurs in patients receiving exogenous insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Glucose↗
PubMed1992

Lipid status after pancreas-kidney transplantation.

OBJECTIVE: This study was performed to determine the net effects of euglycemia, resolution of renal failure, immunosuppressant drugs, and hyperinsulinemia on fasting lipid profiles of patients with renal failure and insulin-dependent diabetes mellitus (IDDM) after combined pancreas-kidney transplantation (PKT). RESEARCH DESIGN AND METHODS: Thirty subjects with IDDM received PKT between April 1989 and October 1990, and all were studied. Mean +/- SE age was 35.2 +/- 1.3 yr; 19 recipients were men, and 11 were women. All had a functioning pancreatic allograft post-PKT. Fasting lipid profiles including total cholesterol (C), triglyceride (TG), high-density lipoprotein cholesterol (HDL-chol), and C/HDL-chol were compared before and after PKT (38-555 days divided into groups: preoperation and 0-2, 3-8, and 9-19 mo). RESULTS: Significant hyperlipidemia was observed preoperatively (means +/- SE): C, 5.92 +/- 0.27 mM; HDL-chol, 1.07 +/- 0.09 mM; TG, 5.85 +/- 0.56 mM; and C/HDL-chol, 6.49 +/- 0.83. All lipids and C/HDL-chol dropped immediately after PKT (0-2 mo vs. preoperation, all P less than 0.01, except HDL-chol). After this immediate postoperative period, C, HDL-chol, and TG stabilized at new concentrations. C (5.44 +/- 0.22 mM) and TG (4.54 +/- 0.48 mM) levels were less than preoperation (not statistically significant and P less than 0.05, respectively). HDL-chol was greater than preoperative values (1.29 +/- 0.06 mM, P less than 0.05). C/HDL-chol dropped after PKT (0-2 mo, 4.85 +/- 0.18, P less than 0.01) and continued to decrease throughout the observation period (3-8 mo, 4.42 +/- 0.23; 9-19 mo, 4.23 +/- 0.23; both P less than 0.01 vs. preoperation). There was no statistical difference between lipid concentrations in male and female subjects. CONCLUSIONS: The lipid status of subjects with IDDM and renal failure was abnormal before PKT and once lipid concentrations stabilized after PKT (greater than 2 mo), HDL-chol was higher and TG and C/HDL-chol levels were significantly lower than preoperative values. If these changes are sustained, risk of future cardiovascular disease in this group of patients might be significantly reduced.

Adult↗
PubMed1991

Identification of the metal associated with the insulin degrading enzyme.

Insulin degrading enzyme (IDE) is a thiol-dependent metalloendoprotease that is responsible for initiation of cellular insulin degradation. However, its exact mode of action and the factors controlling it are poorly understood. Since IDE is a metal requiring enzyme, we have examined which metal(s) is(are) endogenously associated with it. Using neutron activation analysis, we studied the metal content of a partially purified enzyme from three different tissues: rat skeletal muscle, rat liver, and human placenta. Our results indicate that zinc and manganese are associated with the enzyme with approximately 10 times more zinc as manganese being present. These results suggest that one or both of these two metals are endogenously associated with this enzyme and are a means of controlling the enzyme's activity.

Amino Acid Sequence↗
PubMed1991

Effects of sequence and timing of hormonal additions on adipose tissue: activation of low-Km cyclic adenosine monophosphate phosphodiesterase.

Epinephrine (EPI) is lipolytic and insulin (INS) antilipolytic in the isolated fat cell (IFC). We have previously demonstrated that in a perifusion system the antilipolytic action of INS is more powerful when IFC are exposed to INS before EPI. In contrast to their opposite effects on lipolysis, both INS and EPI stimulate low-Km cyclic adenosine monophosphate (cAMP) phosphodiesterase (PDE) in adipose tissue. In view of these observations, we decided to determine the effects of sequential addition of EPI and INS on stimulation of PDE from rat adipose tissue. Using previously published methods, the effects of INS and EPI on PDE were assessed alone, together with INS followed by EPI, and then with EPI followed by INS. The resulting data demonstrate that EPI and INS individually both stimulate PDE (P less than .001); EPI plus INS together stimulate PDE minimally compared with EPI or INS alone (P less than .001); when adipose tissue is included with INS first, then followed by EPI, activation of PDE is much less than INS or EPI alone (P less than .001); and when adipose tissue is stimulated by EPI then INS, there is no activation of PDE, different from EPI or INS alone (P less than .001). In conclusion, in perifused IFC, INS and EPI always oppose each other. In studies using activation of PDE, EPI and INS each stimulate PDE, but INS opposes EPI when incubated simultaneously. When adipose tissue is incubated first with INS followed by EPI, PDE is activated. In contrast, when the reverse order is applied, no activation of PDE is observed.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

Degradation of intraendosomal insulin by insulin-degrading enzyme without acidification.

The nature of insulin degradation within endosomes was studied in vitro. Radiolabeled insulin was perfused into rat liver via the portal vein, and insulin-containing endosomes were prepared by differential centrifugation. The endosomes were incubated in various buffers, and hormone degradation was monitored by Sephadex G-50 chromatography and high-performance liquid chromatography (HPLC). Endosomes incubated in simple imidazole or HEPES (pH 7.4) buffers rapidly degraded insulin to intermediate- and then to low-molecular-weight products that were lost from the vesicles. HPLC analysis of insulin-sized material showed the products to be the same as those produced by intact cells. The endosomes did not acidify in these buffers (as assessed by the acridine orange method), and ATP had no effects. When the endosomes were incubated in a chloride-containing buffer, degradation was greatly inhibited, and acidification did not occur. Both insulin degradation and acidification were activated when Mg-ATP was added to this buffer system. HPLC analysis of the products generated in this system revealed not only typical cellular products but additional less hydrophobic products. Western-blot analysis of endosomal protein with anti-insulin-degrading enzyme antibody showed this enzyme to be present. In conclusion, isolated endosomes rapidly and completely degrade insulin through products that are typical of cellular degradation without requiring acidification. Chloride-containing buffers inhibit endosomal degradation, which is reversed by Mg-ATP, but this system does not mimic cellular degradation. At least one of the enzymes responsible for insulin degradation is insulin-degrading enzyme.

Animals↗
PubMed1991

Combined pancreas--kidney transplantation in Nebraska.

UNLABELLED: In the last 2 years, we have performed combined pancreas-kidney transplantation in 38 Type I diabetics with nephropathy. The mean age of the recipient group was 35 years (range 24-51) with a mean duration of diabetes of 22 years (range 13-41). All patients received quadruple immunosuppression with OKT3 induction. All patients are normoglycemic and insulin independent with a mean glycosylated hemoglobin level of 5.2 +/- 1.1% and a mean serum creatinine of 1.9 +/- 0.5 mg/dl. Metabolic effects of pancreas transplantation included fasting hyperinsulinemia and hyperglucagonemia with exaggerated insulin and glucagon responses to glucose and arginine, respectively, that improved slightly with time. Patient and kidney graft survival are 100% and pancreas graft survival is 94.7% after a mean follow-up interval of 15 months. CONCLUSION: Combined pancreas-kidney transplantation is the treatment of choice for selected Type I diabetics with nephropathy and results in euglycemia despite immunosuppression.

Adult↗
PubMed1991

Intensive management of type II diabetes.

The goals of intensive treatment of type II diabetes are to restore blood glucose levels to normal; correct hyperlipidemia, hypertension, and other cardiovascular risk factors; and prevent hyperinsulinemia. Treatment should begin with attempts to reduce weight through diet and exercise. In fact, diet and exercise should be stressed as vital components of a diabetic patient's life-style no matter what treatment method is used. Drug treatment may consist of a sulfonylurea to increase insulin secretion and improve insulin resistance or of exogenous insulin to achieve glucose control and avoid the dangers of chronic hyperglycemia. A combination of the two appears attractive but is still under investigation. Control of hypertension is mandatory and may require use of an angiotensin-converting enzyme inhibitor or calcium channel blocker. Normalization of serum lipid levels is also important in these patients, and agents that adversely affect glucose levels must be avoided.

Diabetes Mellitus, Type 2↗
PubMed1991

Combined pancreas-kidney transplantation: preliminary results and metabolic effects.

UNLABELLED: Vascularized pancreas transplantation (PT) results in a self-regulating endogenous source of insulin. In the last 18 months, we have performed combined pancreas-kidney transplantation in 25 type I diabetics with nephropathy. The mean age of the recipient group was 35 yr (range 24-51) with a mean duration of diabetes of 22 yr (range 13-41). All patients received quadruple immunosuppression with OKT3 induction. All patients remained normoglycemic and insulin independent with a mean glycosylated hemoglobin level of 6.0 +/- 1.1% and a mean serum creatinine of 1.7 +/- 0.5 mg/dl. Metabolic control and hormonal profiles were assessed by intravenous glucose challenge followed by arginine stimulation. Metabolic effects of PT included fasting hyperinsulinemia and hyperglucagonemia with exaggerated insulin and glucagon responses to glucose and arginine, respectively. Patient and graft survival is 100% after a mean follow-up interval of 8 months. CONCLUSION: combined pancreas-kidney transplantation is a valid treatment option for diabetic nephropathy, and results in near-complete normalization of glucose metabolism.

Actuarial Analysis↗
PubMed1990

Human red blood cell insulin-degrading enzyme and rat skeletal muscle insulin protease share antigenic sites and generate identical products from insulin.

The mechanisms of cellular insulin degradation remain uncertain. Considerable evidence now exists that the primary cellular insulin-degrading activity is a metallothiol proteinase. Two similar degrading activities have been purified and characterized. Insulin protease has been purified from rat skeletal muscle and insulin-degrading enzyme from human red blood cells. Whereas the two degrading activities share a number of similar properties, significant differences have also been reported; and it is not at all established that they are the same enzyme. To examine this, we have compared antigenic and catalytic properties of the two enzymatic activities. Monoclonal antibodies against the red blood cell enzyme adsorb the skeletal muscle enzyme; and on Western blots, the antibodies react with an identical 110-kDa protein. Immunoaffinity-purified enzymes from both red blood cells and skeletal muscle degrade [125I]iodo(B26)insulin to the same products as seen with purified insulin protease and with intact liver and kidney. Chelator-treated muscle and red blood cell enzymes can be reactivated with either Mn2+ or Ca2+. Thus, insulin-degrading enzyme and insulin protease have similar properties. These results support the hypothesis that these activities reside in the same enzyme.

Animals↗
PubMed1990

Bronchial epithelial cells respond to insulin and insulin-like growth factor-I as a chemoattractant.

Migration of epithelial cells to cover areas of injury is thought to be important in the repair process following airway insult. Insulin is reported to be a growth factor for bronchial epithelial cells, and growth factors have been known to be chemotactic for many types of cells. Thus, we hypothesized that insulin may be a chemoattractant for bronchial epithelial cells. To evaluate this, we prepared bronchial epithelial cells and measured their chemotactic activity toward insulin. Bronchial epithelial cells were isolated by overnight digestion with bacterial protease, filtered through 100-microns nitex mesh, and then cultured at 1 x 10(6) cells/ml in tissue culture dishes in medium 199 supplemented with transferrin, insulin, epidermal growth factor, hydrocortisone, antibiotics, and 10% FCS for 3 d. The cultured cells were rinsed twice to remove supplements, trypsinized and resuspended at 1 x 10(6) cells/ml in medium 199 without supplements, and used as the cell source for chemotaxis. Chemotactic activity of bronchial epithelial cells was measured by the blindwell chamber technique using 8-microns Nuclepore filter membranes coated with 0.1% gelatin. The cells were added to the top wells in a 48-multiwell chamber with insulin in the bottom wells and incubated for 6 h at 37 degrees C, 5% CO2. Bronchial epithelial cells migrated in response to insulin in a dose-dependent manner up to an optimal dose of insulin, 100 micrograms/ml, and decreased at higher concentrations. The number of migrated cells per 10 high power fields was 33.7 +/- 1.9 at the optimum and 3.7 +/- 0.7 without insulin (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Effect of bacitracin on retroendocytosis and degradation of insulin in cultured kidney epithelial cell line.

In an earlier study, we described the presence of a retroendocytotic pathway for insulin in a cultured kidney epithelial cell line. Derived from the opossum kidney (OK), these cells possess many features of proximal tubule epithelium, which is the major site of kidney insulin metabolism. We studied the interaction between the retroendocytotic and the degradative pathways with bacitracin as a pharmacological probe. Monolayers of OK cells were loaded with 125I-labeled insulin over 30 min, acid washed to remove membrane-bound insulin, then incubated in fresh medium for 60 min while the release of intracellular radioactivity was monitored. In experiments carried out in the presence of bacitracin (2 mM), there was a two-thirds increase in intracellular radioactivity at the end of the loading phase. Measurements made during the subsequent release phase showed that bacitracin reduced the release of degradation products. Thus, although controls released 72.1 +/- 8.1% of the internalized radioactivity as trichloroacetic acid (TCA)-soluble products, bacitracin-treated cells released 59.2 +/- 9.4% (P less than 0.02). In contrast, release of TCA-precipitable insulin increased from 15.2 +/- 4.6% in controls to 25.8 +/- 3.7% in bacitracin-treated cells (P less than 0.01). In separate experiments analyzed by gel-exclusion chromatography, 6.4 +/- 0.6% of radioactivity released from preloaded control cells into medium over 60 min was insulin sized compared to 29.7 +/- 1.4% in bacitracin-treated cells. High-performance liquid chromatography revealed that 61.5 +/- 3.5% of this insulin-sized material released from control cells preloaded with A14-insulin eluted as intact insulin and the remainder as unidentified intermediate degradation products.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Drosophila insulin degrading enzyme and rat skeletal muscle insulin protease cleave insulin at similar sites.

Insulin degradation is an integral part of the cellular action of insulin. Recent evidence suggests that the enzyme insulin protease is involved in the degradation of insulin in mammalian tissues. Drosophila, which has insulin-like hormones and insulin receptor homologues, also expresses an insulin degrading enzyme with properties that are very similar to those of mammalian insulin protease. In the present study, the insulin cleavage products generated by the Drosophila insulin degrading enzyme were identified and compared with the products generated by the mammalian insulin protease. Both purified enzymes were incubated with porcine insulin specifically labeled with 125I on either the A19 or B26 position, and the degradation products were analyzed by HPLC before and after sulfitolysis. Isolation and sequencing of the cleavage products indicated that both enzymes cleave the A chain of intact insulin at identical sites between residues A13 and A14 and A14 and A15. Sequencing of the B chain fragments demonstrated that the Drosophila enzyme cleaves the B chain of insulin at four sites between residues B10 and B11, B14 and B15, B16 and B17, and B25 and B26. These cleavage sites correspond to four of the seven cleavage sites generated by the mammalian insulin protease. These results demonstrate that all the insulin cleavage sites generated by the Drosophila insulin degrading enzyme are shared in common with the mammalian insulin protease. These data support the hypothesis that there is evolutionary conservation of the insulin degrading enzyme and further suggest that this enzyme plays an important role in cellular function.

Animals↗
PubMed1989

Retroendocytosis of insulin in a cultured kidney epithelial cell line.

It has been generally accepted that in renal tubular epithelium endocytosed proteohormones are transported to lysosomes where they undergo complete hydrolysis. En route, as endosomal pH falls, the proteohormone uncouples from the endocytosed membrane binding site, which recycles to the cell surface. However, studies in other tissues have uncovered alternate intracellular pathways for proteins. One such pathway is retroendocytosis (endocytosis then exocytosis). To determine whether a retroendocytotic pathway exists for insulin in renal epithelium, a study was carried out with confluent monolayers of a proximal-like opossum kidney cell line that exhibits receptor-mediated endocytosis of insulin. Cells were preloaded with 125I-labeled insulin (4 X 10(-10) M) for 30 min, surface-bound insulin was then removed by acid washing, and over the next 60 min the release of intracellular radioactivity into the medium was monitored. At 37 degrees C, control cells released on average 7-15% of the intracellular radioactivity as intact insulin [trichloroacetic acid (TCA)-precipitable radioactivity] and approximately 62% as TCA-soluble degradation products. In the presence of 0.1 mM chloroquine (an acidotropic agent) the release of intact insulin increased approximately twofold while degradation fell by nearly one-half. With Sephadex G-50 chromatography we found that the released radioactivity included insulin-size material that increased in the presence of chloroquine. High-performance liquid chromatography revealed that 53 (controls) and 81% (chloroquine treatment) of this latter material consisted of intact insulin. We conclude that, in addition to a major degradative pathway, cultured kidney epithelial cells exhibit a retroendocytotic pathway for insulin. Chloroquine inhibits degradation and appears to divert insulin from the degradative into the retroendocytotic pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Insulin degradation products from perfused rat kidney.

The kidney is a major site for insulin metabolism, but the enzymes involved and the products generated have not been established. To examine the products, we have perfused rat kidneys with insulin specifically iodinated on either the A14 or the B26 tyrosine. Labeled material from both the perfusate and kidney extract was examined by Sephadex G50 and high-performance liquid chromatography (HPLC). In perfusate from a filtering kidney, 22% of the insulin-sized material was not intact insulin on HPLC. With the nonfiltering kidney, 10.6% was not intact insulin. Labeled material from HPLC was sulfitolyzed and reinjected on HPLC. By use of 125I-iodo(A14)-insulin, almost all the degradation products contained an intact A-chain. By use of 125I-iodo(B26)-insulin, several different B-chain-cleaved products were obtained. The material extracted from the perfused kidney was different from perfusate products but similar to intracellular products from hepatocytes, suggesting that cellular metabolism by kidney and liver are similar. The major intracellular product had characteristics consistent with a cleavage between the B16 and B17 amino acids. This product and several of the perfusate products are also produced by insulin protease suggesting that this enzyme is involved in the degradation of insulin by kidney.

Animals↗
PubMed1988

Hepatic metabolism of insulin.

The liver plays a major role in the metabolism of insulin, but the precise cellular mechanisms, the enzymes involved, and the products generated have only recently become clarified. The initial step in insulin degradation by the liver is binding to a cell membrane receptor, following which some insulin is degraded and the products released into the incubation medium, whereas some insulin is internalized and degraded intracellularly. Recently, it has been demonstrated that the degradation of insulin by hepatocytes produces products identical to those generated by the enzyme insulin protease. With both enzyme and intact hepatocytes, two A-chain cleavages and four major and three minor B-chain cleavages occur in intact insulin. It has also been demonstrated that internalized insulin is degraded in early endosomes, primarily by cleavages in the B chain and occurring prior to acidification of the endosome and thus prior to dissociation of insulin from its receptor. The initial cleavages in the B chain of insulin occur in the same sites as are cleaved by insulin protease, supporting a role for this enzyme, both in the extracellular and intracellular metabolism of insulin. These findings also indicate that lysosomes probably play a minor or secondary role for hepatic insulin metabolism.

Animals↗