Sustaining diabetes prevention and care interventions: A multiple case study of translational research projects.

BACKGROUND: This study identifies the barriers and enablers for sustainability of interventions in primary and secondary prevention of diabetes. In the context of translational research, sustainability is defined as the continued use of program components and activities for the continued achievement of desirable program and population outcomes. METHODS: In this study, eleven translational research projects, supported by the BRIDGES program of the International Diabetes Federation, were investigated. By theoretically-informed semi-structured interviews and analyses of project reports, qualitative data was collected on the sustainability outcomes and the barriers and enablers. RESULTS: The sustainability outcomes can be grouped in three main areas: (1) sustainability at the intervention site(s); (2) diffusion to the wider community; and (3) replication of the intervention at other site(s). Each of the outcomes has their own set of enablers and barriers, and thus requires consideration for a different sustainability strategy. CONCLUSIONS: This study is the first international study that relates the sustainability outcomes of translational research project to specific barriers and enablers, and develops an evidence-based framework which provides practical advice on how to ensure the sustainability of health interventions.

Development of diabetes mellitus post-renal transplantation is associated with poor short-term clinical outcomes.

BACKGROUND: Although posttransplant diabetes mellitus (PTDM) is associated with poor long-term outcomes short-term outcomes are not well studied in renal transplant recipients (RTRs). METHODS: RTRs between January 1999 and December 2000 (n = 181) stratified according to the occurrence of diabetes mellitus (DM), namely, non-DM (n = 72), previous DM (n = 88), and PTDM (n = 21) were compared for infections, hospital readmissions, and graft rejections during the first 6 months posttransplantation. RESULTS: PTDM showed patients affected by a significantly higher rate of infections (57.1% vs 29.2%) and recurrent infections (28.5% vs 11.1%) compared to non-DM and a trend toward an increase compared to previous DM. PTDM patients had a significantly higher incidence of multiple readmissions compared to both previous DM (52.4% vs 20.5%) and non-DM (52.4% vs 23.6%). Subjects with PTDM showed a significantly higher occurrence of rejection (28.6% vs 9.1%) and recurrent rejection (14.3% vs 2.3%) than previous DM and a greater trend compared to non-DM. CONCLUSION: PTDM is associated with poorer short-term outcomes than either non-DM or previous DM.

Insulin regulation of phosphoenolpyruvate carboxykinase gene expression does not require activation of the Ras/mitogen-activated protein kinase signaling pathway.

Expression of phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting step in hepatic gluconeogenesis, is primarily regulated at the level of gene transcription. Insulin and phorbol esters inhibit basal PEPCK transcription and antagonize the induction of PEPCK gene expression by glucocorticoids and glucagon (or its second messenger cAMP). Insulin activates a signaling cascade involving Ras --> Raf --> p42/p44 mitogen-activated protein (MAP) kinase kinase (MEK) --> p42/p44 MAP kinase (ERK 1 and 2). Recent reports suggest that activation of this Ras/MAP kinase pathway is critical for the effects of insulin on mitogenesis and c-fos transcription but is not required for insulin action on metabolic processes such as glycogen synthesis, lipogenesis, and Glut-4-mediated glucose transport. We have used three distinct approaches to examine the role of the Ras/MAP kinase pathway in the regulation of PEPCK transcription by insulin in H4IIE-derived liver cells: (i) chemical inhibition of Ras farnesylation, (ii) infection of cells with an adenovirus vector encoding a dominant-negative mutant of Ras, and (iii) use of a chemical inhibitor of MEK. Although each of these methods blocks insulin activation of MAP kinase, none alters insulin antagonism of cAMP- and glucocorticoid-stimulated PEPCK transcription. Although phorbol esters activate MAP kinase and mimic the effects of insulin on PEPCK gene transcription, inhibition of MEK has no effect on phorbol ester inhibition of PEPCK gene transcription. Using the structurally and mechanistically distinct phosphatidylinositol 3-kinase (PI 3-kinase) inhibitors, wortmannin and LY 294002, we provide further evidence supporting a role for PI 3-kinase activation in the regulation of PEPCK gene transcription by insulin. We conclude that neither insulin nor phorbol ester regulation of PEPCK gene transcription requires activation of the Ras/MAP kinase pathway and that insulin signaling to the PEPCK promoter is dependent on PI 3-kinase activation.

Calcium-dependent protein kinase activity is decreased in diabetic rat sciatic nerve.

The effects of 4 weeks of streptozotocin-induced diabetes in the rat on sciatic nerve homogenate protein kinase activities were studied. There was a 47 +/- 7% inhibition of Ca+2-dependent protein kinase activity in nerves from the diabetic rats compared to that in their paired normal controls. This Ca+2-dependent activity did not require the addition of phospholipid and was only minimally affected by Sephadex G-50 gel filtration, suggesting that endogenous phospholipid activation was not responsible for this activity. The addition of phospholipid in the presence of Ca+2 revealed an additional activity in these homogenates which probably represents the Ca+2-phospholipid-dependent protein kinase (protein kinase-C). The diabetic state did not appear to alter that activity. The Ca+2-dependent protein kinase was sensitive to agents known to inhibit calmodulin-dependent protein kinase or protein kinase-C. The IC50 values of the inhibitors for the Ca+2-dependent protein kinase, however, differed from those reported for the other two kinases.

Insulin inhibition of hepatic cAMP-dependent protein kinase: decreased affinity of protein kinase for cAMP and possible differential regulation of intrachain sites 1 and 2.

In hepatocytes stimulated with 8-bromo-cAMP, insulin decreases the affinity of the cAMP-dependent protein kinase for cAMP, shifting the Ka without affecting the Vmax activity. This occurs under conditions where cyclic adenine nucleotide concentrations are unchanged. We report here that glycogenolysis stimulated by 8-(4-chlorophenylthio)-cAMP, an analog with 100 times tighter affinity than cAMP for the protein kinase regulatory subunit, was only slightly antagonized by insulin. The tight binding of this analog appears to overcome the protein kinase affinity change induced by insulin. The relative importance of the two intrachain cAMP binding sites of the cAMP-dependent protein kinase regulatory subunit was investigated by using analogs with relative selectivity for each site. Analogs exhibiting preferential binding to site 2 were far less sensitive to insulin antagonism than were analogs binding preferentially at site 1 and less well at site 2. No other property of these analogs, including the rate of hydrolysis by phosphodiesterase, the IC50 for phosphodiesterase, the Ka for protein kinase, or the type I versus type II kinase specificity, could account for the ability of insulin to antagonize glycogenolysis stimulated by these analogs. These data indicate that insulin may act to decrease the affinity of protein kinases for cAMP through a possible regulation of intrachain site 2 binding.

Methylisobutylxanthine blocks insulin antagonism of cAMP-stimulated glycogenolysis at a site distinct from phosphodiesterase. Evidence favoring an insulin-insensitive calcium release mechanism.

The widely used phosphodiesterase inhibitor MIX (1-methyl 3-isobutyl xanthine) blocked insulin antagonism of cAMP-stimulated glycogenolysis in rat hepatocytes but other phosphodiesterase inhibitors including Ro 20-1724 had no effect. Dose-response curves for MIX potentiation of cAMP-stimulated glycogenolysis and for MIX inhibition of the effects of insulin on cAMP-stimulated glycogenolysis suggested that at higher concentrations (250 microM) MIX may act at a site other than phosphodiesterase inhibition. MIX, at 250 microM, attenuated the insulin antagonism of glucose release stimulated by 8-bromo-cAMP, an extremely poor substrate for phosphodiesterase; other phosphodiesterase inhibitors did not. The possibility that MIX acts as an adenosine antagonist interfering with a postulated role for adenosine in insulin action was examined using N6-phenylisopropyladenosine (PIA), an Ra adenosine receptor agonist which increases hepatic cAMP levels. MIX inhibited insulin antagonism of PIA-stimulated glycogenolysis under conditions where it did not act as an adenosine antagonist (MIX and Ro 20-1724 both increased the response to PIA equally). The effect of concanavalin A on cAMP-stimulated glycogenolysis was antagonized by MIX, suggesting a post-receptor site of action for MIX. MIX paradoxically increased lactate production in the presence of 8-bromo-cAMP, reminiscent of the reported actions of calcium mobilizing hormones on lactate formation in fed hepatocytes. Cytosolic free Ca2+, as measured in Quin 2-loaded cells, was increased by MIX. In cells depleted of calcium, MIX no longer blocked insulin antagonism of 8-bromo-cAMP-stimulated glucose release, suggesting that MIX may function through an insulin-insensitive release of calcium. MIX greatly potentiated the stimulation of glycogenolysis by phenylephrine but did not alter the response to vasopressin. The relationship of this effect of MIX to the mechanism of insulin action and the ability of insulin to antagonize only alpha-adrenergic responses and not those of vasopressin is discussed.

Quinolinate inhibition of gluconeogenesis is dependent on cytosolic oxalacetate concentration. An explanation for the differential inhibition of lactate and pyruvate gluconeogenesis.

In isolated rat hepatocytes, the phosphoenolpyruvate carboxykinase (PEPCK) inhibitor, quinolinate decreased gluconeogenesis from lactate more than from pyruvate (78 vs 44%). Quinolinate inhibition of PEPCK has been reported to be competitive with oxalacetate (OAA), and therefore higher cytosolic OAA concentrations could be expected to alleviate quinolinate inhibition of PEPCK and hence reduce its effect on gluconeogenesis. With pyruvate as a carbon source, the cytosolic concentration of OAA was higher than with lactate (40 vs 9.7 microM). The levels of OAA were manipulated metabolically by adding asparagine (which provides more cytosolic OAA through the urea cycle) or oleate (which increases malate efflux from the mitochondria). In each of the 8 conditions studied, quinolinate inhibition of gluconeogenesis was inversely related to the levels of OAA in the cytosol. Quinolinate inhibition of asparagine gluconeogenesis was not due to a non-specific effect on urea synthesis.

The antilipolytic effect of insulin does not require adenylate cyclase or phosphodiesterase action.

Insulin antagonized the lipolytic actions of epinephrine in rat epididymal adipocytes when the phosphodiesterase inhibitor, Ro 20-1724, was present. Adipocytes were depleted of functional cAMP by inhibiting adenylate cyclase with N6-phenylisopropyladenosine in the presence of adenosine deaminase such that Ro 20-1724 no longer stimulated lipolysis. The cAMP analogs 8-thioisopropyl-cAMP or 8-thiomethyl-cAMP, which are resistant to phosphodiesterase hydrolysis, were subsequently added to bypass adenylate cyclase and phosphodiesterase action. Under these conditions, insulin antagonized the lipolytic effects of these analogs, even in the presence of Ro 20-1724.

Site of insulin inhibition of cAMP-stimulated glycogenolysis.

Insulin antagonized the glycogenolytic actions of cAMP in isolated hepatocytes even in the presence of the phosphodiesterase inhibitors, 1-methyl-3-isobutylxanthine or d-4-(3-butoxy-4-methoxybenzyl)-2- imidizolidione . Stimulation of glucose release by 8-bromo-cAMP, which is not appreciably hydrolyzed by phosphodiesterase, was also inhibited by insulin in the presence of d-4-(3-butoxy-4-methoxybenzyl)-2- imidizolidione . This demonstrates that insulin can antagonize cAMP stimulation of glycogenolysis independent of possible effects of insulin on adenylate cyclase or phosphodiesterase. Under conditions where changes in cyclic adenine nucleotide concentrations (cAMP and 8-bromo-cAMP) were prevented, insulin depressed the 8-bromo-cAMP-stimulated protein kinase activity ratio. We conclude that phosphodiesterase activation is not required for insulin antagonism of cAMP-stimulated glycogenolysis. The effect of insulin under these conditions can be explained by an action of insulin on cAMP-dependent protein kinase independent of changes in cAMP levels.