Inhibition of glycosaminoglycan synthesis and protein glycosylation with WAS-406 and azaserine result in reduced islet amyloid formation in vitro.
Deposition of islet amyloid polypeptide (IAPP) as amyloid in the pancreatic islet occurs in approximately 90% of individuals with Type 2 diabetes and is associated with decreased islet beta-cell mass and function. Human IAPP (hIAPP), but not rodent IAPP, is amyloidogenic and toxic to islet beta-cells. In addition to IAPP, islet amyloid deposits contain other components, including heparan sulfate proteoglycans (HSPGs). The small molecule 2-acetamido-1,3,6-tri-O-acetyl-2,4-dideoxy-alpha-D-xylo-hexopyranose (WAS-406) inhibits HSPG synthesis in hepatocytes and blocks systemic amyloid A deposition in vivo. To determine whether WAS-406 inhibits localized amyloid formation in the islet, we incubated hIAPP transgenic mouse islets for up to 7 days in 16.7 mM glucose (conditions that result in amyloid deposition) plus increasing concentrations of the inhibitor. WAS-406 at doses of 0, 10, 100, and 1,000 microM resulted in a dose-dependent decrease in amyloid deposition (% islet area occupied by amyloid: 0.66 +/- 0.14%, 0.10 +/- 0.06%, 0.09 +/- 0.07%, and 0.004 +/- 0.003%, P < 0.001) and an increase in beta-cell area in hIAPP transgenic islets (55.0 +/- 2.6 vs. 60.6 +/- 2.2% islet area for 0 vs. 100 microM inhibitor, P = 0.05). Glycosaminoglycan, including heparan sulfate, synthesis was inhibited in both hIAPP transgenic and nontransgenic islets (the latter is a control that does not develop amyloid), while O-linked protein glycosylation was also decreased, and WAS-406 treatment tended to decrease islet viability in nontransgenic islets. Azaserine, an inhibitor of the rate-limiting step of the hexosamine biosynthesis pathway, replicated the effects of WAS-406, resulting in reduction of O-linked protein glycosylation and glycosaminoglycan synthesis and inhibition of islet amyloid formation. In summary, interventions that decrease both glycosaminoglycan synthesis and O-linked protein glycosylation are effective in reducing islet amyloid formation, but their utility as pharmacological agents may be limited due to adverse effects on the islet.
Hull
Rebecca L
RL
Division of Metabolism, Endocrinology, and Nutrition, Veterans Affairs Puget Sound Health Care System and University of Washington, Seattle, Washington 98108, USA. rhull@u.washington.edu
Zraika
Sakeneh
S
Udayasankar
Jayalakshmi
J
Kisilevsky
Robert
R
Szarek
Walter A
WA
Wight
Thomas N
TN
Kahn
Steven E
SE
D000606:Amino Sugars / Q000494:pharmacology*; D000682:Amyloid / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001377:Azaserine / Q000494:pharmacology*; D002460:Cell Line; D048429:Cell Size; D002470:Cell Survival; D002809:Chondroitin Sulfates / Q000378:metabolism; D003837:Deoxy Sugars / Q000494:pharmacology*; D003871:Dermatan Sulfate / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000037:antagonists & inhibitors / Q000378:metabolism; D006025:Glycosaminoglycans / Q000378:metabolism*; D006031:Glycosylation; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism; D006595:Hexosamines / Q000096:biosynthesis; D006801:Humans; D007328:Insulin / Q000378:metabolism; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism; D058228:Islet Amyloid Polypeptide; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008822:Mice, Transgenic; D009924:Organ Culture Techniques; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D013997:Time Factors