Preconditioning with associated blocking of Ca2+ inflow alleviates hypoxia-induced damage to pancreatic β-cells.
OBJECTIVE
Beta cells of pancreatic islets are susceptible to functional deficits and damage by hypoxia. Here we aimed to characterize such effects and to test for and pharmacological means to alleviate a negative impact of hypoxia.


METHODS
Rat and human pancreatic islets were subjected to 5.5 h of hypoxia after which functional and viability parameters were measured subsequent to the hypoxic period and/or following a 22 h re-oxygenation period. Preconditioning with diazoxide or other agents was usually done during a 22 h period prior to hypoxia.


RESULTS
Insulin contents decreased by 23% after 5.5 h of hypoxia and by 61% after a re-oxygenation period. Preconditioning with diazoxide time-dependently alleviated these hypoxia effects in rat and human islets. Hypoxia reduced proinsulin biosynthesis ((3)H-leucine incorporation into proinsulin) by 35%. Preconditioning counteracted this decrease by 91%. Preconditioning reduced hypoxia-induced necrosis by 40%, attenuated lowering of proteins of mitochondrial complexes I-IV and enhanced stimulation of HIF-1-alpha and phosphorylated AMPK proteins. Preconditioning by diazoxide was abolished by co-exposure to tolbutamide or elevated potassium (i.e. conditions which increase Ca(2+) inflow). Preconditioning with nifedipine, a calcium channel blocker, partly reproduced effects of diazoxide. Both diazoxide and nifedipine moderately reduced basal glucose oxidation whereas glucose-induced oxygen consumption (tested with diazoxide) was unaffected. Preconditioning with diaxoxide enhanced insulin contents in transplants of rat islets to non-diabetic rats and lowered hyperglycemia vs. non-preconditioned islets in streptozotocin-diabetic rats. Preconditioning of human islet transplants lowered hyperglycemia in streptozotocin-diabetic nude mice.


CONCLUSIONS
1) Prior blocking of Ca(2+) inflow associates with lesser hypoxia-induced damage, 2) preconditioning affects basal mitochondrial metabolism and accelerates activation of hypoxia-reactive and potentially protective factors, 3) results indicate that preconditioning by K(+)-ATP-channel openers has therapeutic potential for islet transplantations.
Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden.
Zuheng
Z
Ma
Noah
N
Moruzzi
Sergiu-Bogdan
SB
Catrina
Ingrid
I
Hals
José
J
Oberholzer
Valdemar
V
Grill
Anneli
A
Björklund
D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015687:Cell Hypoxia; D002478:Cells, Cultured; D003921:Diabetes Mellitus, Experimental / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D003981:Diazoxide / Q000494:pharmacology; D045222:Electron Transport Chain Complex Proteins / Q000819:agonists / Q000378:metabolism; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000819:agonists / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism / Q000637:transplantation; D008297:Male; D051379:Mice; D009543:Nifedipine / Q000494:pharmacology*; D010100:Oxygen / Q000494:pharmacology*; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D011384:Proinsulin / Q000378:metabolism; D051381:Rats; D013311:Streptozocin; D014044:Tolbutamide / Q000494:pharmacology
D002121:Calcium Channel Blockers; D045222:Electron Transport Chain Complex Proteins; C497442:HIF1A protein, human; D007004:Hypoglycemic Agents; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007328:Insulin; D013311:Streptozocin; D011384:Proinsulin; D014044:Tolbutamide; D055372:AMP-Activated Protein Kinases; D009543:Nifedipine; D003981:Diazoxide; D011188:Potassium; D010100:Oxygen; D002118:Calcium