Different apoptotic responses of human and bovine pericytes to fluctuating glucose levels and protective role of thiamine.
BACKGROUND
Vascular cells in diabetes are subjected to daily fluctuations from high to low glucose. We aimed at investigating whether pulsed exposure to different glucose concentrations influences apoptosis in human retinal pericytes (HRP) versus bovine retinal pericytes (BRP), with consequences on the onset of diabetic retinopathy, and the possible protective role of thiamine.


METHODS
BRP and HRP (wild-type and immortalized) were grown in physiological/high glucose for 7 days, and then returned to physiological glucose for another 24, 48 or 72 h. Cells were also kept intermittently at 48-h intervals in high/normal glucose for 8 days, with/without thiamine/benfotiamine. Apoptosis was determined through ELISA, TUNEL, Bcl-2, Bax and p53 expression/concentration.


RESULTS
Continuous exposure to high glucose increased apoptosis in BRP, but not HRP. BRP apoptosis normalized within 24 h of physiological glucose re-entry, while HRP apoptosis increased within 24-48 h of re-entry. Intermittent exposure to high glucose increased apoptosis in HRP and BRP. Bcl-2/Bax results were consistent with DNA fragmentation, while p53 was unchanged. Thiamine and benfotiamine countered intermittent high glucose-induced apoptosis.


CONCLUSIONS
Human pericytes are less prone to apoptosis induced by persistently high glucose than bovine cells. However, while BRP recover after returning to physiological levels, HRP are more vulnerable to both downwardly fluctuating glucose levels and intermittent exposure. These findings reinforce the hypotheses that (1) glycaemic fluctuations play a role in the development of diabetic retinopathy and (2) species-specific models are needed. Thiamine and benfotiamine prevent human pericyte apoptosis, indicating this vitamin as an inexpensive approach to the prevention and/or treatment of diabetic complications.
Beltramo
Elena
E
Laboratory of Diabetic Retinopathy, Department of Internal Medicine, University of Turin, Torino, Italy. elena.beltramo@unito.it
Berrone
Elena
E
Tarallo
Sonia
S
Porta
Massimo
M
D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage / Q000494:pharmacology; D017209:Apoptosis; D002417:Cattle; D002460:Cell Line; D002478:Cells, Cultured; D053938:DNA Fragmentation / Q000187:drug effects; D003930:Diabetic Retinopathy / Q000517:prevention & control; D005786:Gene Expression Regulation; D005947:Glucose / Q000008:administration & dosage*; D006801:Humans; D006943:Hyperglycemia / Q000503:physiopathology; D020287:In Situ Nick-End Labeling; D008954:Models, Biological; D009997:Osmotic Pressure; D020286:Pericytes / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D012171:Retinal Vessels / Q000166:cytology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013045:Species Specificity; D018709:Statistics, Nonparametric; D013831:Thiamine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology*; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
D000975:Antioxidants; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; D005947:Glucose; D013831:Thiamine; C013835:benphothiamine