Improved resistance to ischemia and reperfusion, but impaired protection by ischemic preconditioning in patients with type 1 diabetes mellitus: a pilot study.

BACKGROUND: In patients with type 1 diabetes mellitus (T1DM), cardiovascular events are more common, and the outcome following a myocardial infarction is worse than in nondiabetic subjects. Ischemic or pharmacological preconditioning are powerful interventions to reduce ischemia reperfusion (IR)-injury. However, animal studies have shown that the presence of T1DM can limit these protective effects. Therefore, we aimed to study the protective effect of ischemic preconditioning in patients with T1DM, and to explore the role of plasma insulin and glucose on this effect. METHODS: 99mTechnetium-annexin A5 scintigraphy was used to detect IR-injury. IR-injury was induced by unilateral forearm ischemic exercise. At reperfusion, Tc-annexin A5 was administered, and IR-injury was expressed as the percentage difference in radioactivity in the thenar muscle between the experimental and control arm 4 hours after reperfusion. 15 patients with T1DM were compared to 21 nondiabetic controls. The patients were studied twice, with or without ischemic preconditioning (10 minutes of forearm ischemia and reperfusion). Patients were studied in either normoglycemic hyperinsulinemic conditions (n=8) or during hyperglycemic normoinsulinemia (n=7). The controls were studied once either with (n=8) or without (n=13) ischemic preconditioning. RESULTS: Patients with diabetes were less vulnerable to IR-injury than nondiabetic healthy controls (12.8 ± 2.4 and 11.0 ± 5.1% versus 27.5 ± 4.5% in controls; p<0.05). The efficacy of ischemic preconditioning to reduce IR-injury, however, was lower in the patients and was even completely abolished during hyperglycemia. CONCLUSIONS: Patients with T1DM are more tolerant to forearm IR than healthy controls in our experimental model. The efficacy of ischemic preconditioning to limit IR-injury, however, is reduced by acute hyperglycemia. TRIAL REGISTRATION: The study is registered at www.clinicaltrials.gov (NCT00184821).

Differential effects of sulfonylurea derivatives on vascular ATP-sensitive potassium channels.

Sulfonylurea drugs exert their insulinotropic action by inhibiting ATP-sensitive potassium channels in the pancreas. However, these channels are also expressed in myocardial and vascular smooth muscle, implicating possible detrimental cardiovascular effects. Aim of the present study was to investigate the inhibitory potency of various widely used sulfonylurea drugs in resistance arteries. Isolated mesenteric and renal resistance arteries mounted in a myograph and isolated perfused kidneys were used to measure drug responses. Pinacidil induced a dose-dependent relaxation of phenylephrine preconstricted mesenteric and renal arteries (pEC(50)=6.10 ± 0.01 and 5.66 ± 0.03, respectively). Schild plot analysis of pinacidil relaxation curves in mesenteric arteries in the presence of sulfonylurea antagonists revealed the following order of potency: glimepiride (pA(2)=7.22) ≥ glibenclamide (pA(2)=7.05) > glipizide (pA(2)=5.25) > gliclazide (pA(2)=4.31). The effects of glibenclamide in renal arteries were comparable. Furthermore, glibenclamide produced similar constrictive properties in isolated renal arteries as in isolated perfused whole kidneys. We conclude that sulfonylurea drugs exert differential effects on vascular smooth muscle K(ATP) channels. Our results suggest that glibenclamide and glimepiride will interact with these channels at therapeutic concentrations.

Oral therapy with dipyridamole limits ischemia-reperfusion injury in humans.

BACKGROUND: Adenosine receptor stimulation induces several effects that could limit ischemia-reperfusion injury. We hypothesize that treatment with the nucleoside uptake inhibitor dipyridamole increases endogenous adenosine and limits ischemia-reperfusion injury in humans. METHODS: Ischemia-reperfusion injury was studied in forearm skeletal muscle by technetium Tc 99m-labeled annexin A5 scintigraphy. Ischemia-reperfusion injury was induced by unilateral forearm ischemic exercise. Immediately on reperfusion, annexin A5 labeled with technetium Tc 99m was administered intravenously, and ischemia-reperfusion injury was expressed as the percentage difference in radioactivity between the experimental arm and the control arm 1 and 4 hours after reperfusion. Targeting was quantified in the region of the thenar muscle and forearm flexor muscles. This approach was used in 9 healthy male volunteers after a 1-week treatment with dipyridamole (200 mg, slow release, twice daily) and in 23 control subjects. RESULTS: Dipyridamole treatment significantly reduced annexin A5 targeting in skeletal muscle compared with the control group (thenar region, 13% +/- 7% versus 22% +/- 15% at 1 hour after reperfusion and 9% +/- 6% versus 27% +/- 13% at 4 hours for dipyridamole and control groups, respectively [P = .01]; flexor region, 4% +/- 8% versus 7% +/- 6% at 1 hour after reperfusion and 1% +/- 4% versus 10% +/- 9% at 4 hours for dipyridamole and control groups, respectively [P = .01]). CONCLUSIONS: One week of oral treatment with the nucleoside uptake inhibitor dipyridamole (200 mg, slow release, twice daily) significantly limits ischemia-reperfusion injury in humans in vivo, as assessed by technetium Tc 99m-labeled annexin A5 scintigraphy of forearm skeletal muscle.

Glibenclamide depletes ATP in renal proximal tubular cells by interfering with mitochondrial metabolism.

Sulfonylurea drugs, like glibenclamide, stimulate insulin secretion by blocking ATP-sensitive potassium channels on pancreatic beta cells. Renal tubular epithelial cells possess a different class of K(ATP) channels with much lower affinities for sulfonylurea drugs, necessitating the use of micromolar glibenclamide concentrations to study these channels. Here, we describe the toxic effects of these concentrations on mitochondrial energy metabolism in freshly isolated renal proximal tubular cells. Glibenclamide, at concentrations of 50 and 100 microM, reduced intracellular ATP levels by 28+/-4 and 53+/-5%, respectively (P<0.01). This decline in ATP could be attributed to a dose-dependent inhibition of mitochondrial respiration. Glibenclamide (10-500 microM) inhibited ADP-stimulated mitochondrial oxygen consumption. In addition to this toxic effect, specific association of radiolabeled and fluorescent glibenclamide to renal mitochondria was found. Association of [(3)H]glibenclamide with renal mitochondria revealed a low-affinity site with a K(D) of 16+/-6 microM and a B(max) of 167+/-29 pmol mg(-1). We conclude that micromolar concentrations of glibenclamide interfere with mitochondrial bioenergetics and, therefore, should be used with care for inhibition of epithelial K(ATP) channels.