Mitochondrial dysfunction as the cause of the failure to precondition the diabetic human myocardium.
OBJECTIVE
We have shown previously that human diabetic myocardium cannot be preconditioned. Here, we have investigated the basis of this cardioprotective deficit.


METHODS
Right atrial sections from four patient groups-non-diabetic, insulin-dependent diabetes mellitus (IDDM), non-insulin-dependent diabetes mellitus (NIDDM) receiving glibenclamide, and NIDDM receiving metformin-were subjected to one of the following protocols: aerobic control, simulated ischemia/reoxygenation, ischemic preconditioning before ischemia, and pharmacological preconditioning with alpha 1 agonist phenylephrine, adenosine, the mito-K(ATP) channel opener diazoxide, the protein kinase C (PKC) activator phorbol-12-myristate-13-acetate (PMA), or the p38 mitogen-activated protein kinase (p38MAPK) activator anisomycin. Cellular damage was assessed using creatine kinase leakage and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction. In mitochondrial preparations from non-diabetic and diabetic myocardium, mitochondrial membrane potential (Psi(m)) was assessed using JC-1 dye, and production of reactive oxygen species was determined.


RESULTS
Preconditioning with ischemia, phenylephrine, adenosine, or diazoxide failed to protect diabetic myocardium. However, activation of PKC or p38MAPK was still protective. In isolated non-diabetic mitochondria, diazoxide partially depolarized Psi(m), an effect not seen in diabetic mitochondria. Furthermore, diazoxide increased superoxide production in non-diabetic but not in diabetic mitochondria.


CONCLUSIONS
Our results show that the cardioprotective deficit in diabetic myocardium arises upstream of PKC and p38MAPK. We suggest that mitochondrial dysfunction in diabetic myocardium, possibly dysfunctional mito-K(ATP) channels, leads to impaired depolarization and superoxide production, and that this causes the inability to respond to preconditioning.
Hassouna
Ashraf
A
Cardiac Surgery Unit, Department of Cardiovascular Sciences, University of Leicester, Glenfield Hospital, Leicester LE3 9QP, UK.
Loubani
Mahmoud
M
Matata
Bashir M
BM
Fowler
Alan
A
Standen
Nicholas B
NB
Galiñanes
Manuel
M
D000241:Adenosine / Q000494:pharmacology; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D003920:Diabetes Mellitus / Q000378:metabolism*; D003922:Diabetes Mellitus, Type 1 / Q000188:drug therapy / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000188:drug therapy / Q000378:metabolism; D003981:Diazoxide / Q000494:pharmacology; D004789:Enzyme Activation; D005905:Glyburide / Q000627:therapeutic use; D006325:Heart Atria; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use; D066298:In Vitro Techniques; D019157:Ischemic Preconditioning, Myocardial; D008564:Membrane Potentials; D008687:Metformin / Q000627:therapeutic use; D008929:Mitochondria, Heart / Q000378:metabolism / Q000502:physiology*; D017202:Myocardial Ischemia / Q000378:metabolism / Q000517:prevention & control*; D010656:Phenylephrine / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D017382:Reactive Oxygen Species; D010656:Phenylephrine; D008687:Metformin; D011493:Protein Kinase C; D048051:p38 Mitogen-Activated Protein Kinases; D000241:Adenosine; D013755:Tetradecanoylphorbol Acetate; D003981:Diazoxide; D005905:Glyburide