2011 ADA Posters 1261-2041.indd - Diabetes

independent risk factor for diabetic heart failure. However, the underlying
mechanisms remain poorly understood. Previous studies suggest an
association between diabetic cardiac injury and disturbed autophagylysosome
pathway, but the specifi c changes and their signifi cance are not
fully characterized. Here, we show that the expression and distribution of
Cathepsin D, an aspartyl protease normally restricted within lysosome,
were dramatically altered in cultured cardiomyocytes exposed to high
glucose. Specifi cally, Western blotting and RT-PCR showed that high glucose
(17 or 30 nmol/l) markedly increased the protein and mRNA expression levels
of Cathepsin D in cardiomyocytes. Moreover, immunostaining analysis
indicated that Cathepsin D lost its punctate distribution and was diffused in
cardiomyocytes after high glucose treatment. To investigate the functional
signifi cance of altered Cathepsin D in hyperglycemic toxicity, we treated
cardiomyocytes with a low dose of the lysosome inhibitor Bafi lomycin A1
(BFA, 0.2nmol/l). Remarkably, BFA inhibited Cathepsin D maturation and
attenuated high glucose-induced myocyte injury, as shown by reduced
cleavage of Poly (ADP-ribose) polymerase (PARP). Together, these fi ndings
suggest that increased expression and altered distribution of Cathepsin
D may contribute to hyperglycemic cardiotoxicity. Consistently, we found
that Cathepsin D was also increased in the hearts of type 1 diabetic mice
(Streptozotocin induced or OVE26 genetic model). Thus, future studies are
warranted to determine if Cathepsin D plays a similar role in diabetic cardiac
damage in vivo.
ADA-Funded Research
& Guided Audio Tour poster
INTEGRATED CATEGORY
PHYSIOLOGY—MUSCLE
ADA-Funded Research
1744-P
Increased Inducible Nitric Oxide Synthase Activity Is Responsible
for Reduced Endothelin-1 Vasoconstrictor Responsiveness in Insulin
Resistance
CAROL T. BUSSEY, MICHELLE A. KESKE, STEPHEN RATTIGAN, STEPHEN M.
RICHARDS, Hobart, Australia
Increased levels of the potent vasoconstrictor endothelin-1 (ET-1) have
been implicated in the development of insulin resistance, type 2 diabetes
and hypertension, and particularly the endothelial dysfunction seen in
these states. Endogenous ET-1 activity is consistently increased in these
pathologies, but opinion is divided as to whether ET-1 vasoconstrictor
responsiveness is enhanced or impaired. Our study examined the sensitivity
of skeletal muscle vasculature to ET-1 in rats made insulin resistant by high
fat feeding, using the isolated, pump-perfused hindlimb preparation. Male
Sprague-Dawley rats were fed a high-fat diet for 4 weeks, resulting in an
81% increase in epididymal fat pad weight, accompanied by increased
fasting plasma insulin, but not glucose. Vasoconstriction by ET-1 (1 or 3nM)
was reduced by the high-fat diet. Basal perfusion pressure was unaffected.
Treatment with the nitric oxide (NO) synthase (NOS) inhibitor N G -nitro-Larginine
methyl ester (L-NAME) signifi cantly increased ET-1 vasoconstriction
in both normal and high-fat fed animals, reaching the same level, indicating
increased NO bioavailability in insulin resistance. In the presence of 1400W,
a specifi c inhibitor of the inducible NOS (iNOS) isoform, ET-1 reactivity in highfat
fed rats was restored to that from rats on normal chow. These fi ndings
support the notion that high fat feeding increases muscle iNOS activity,
counteracting ET-1 vasoconstriction. Alterations in the balance between
constriction and NO-mediated dilation may account for differences observed
in ET-1 responsiveness in metabolic syndrome pathologies. Furthermore,
the raised NO production in high fat fed rats may reduce responsiveness to
further NO-mediated dilation, and may explain the impairment of endothelial
function seen in insulin resistant states.
A473
1745-P
Losartan Recruits Muscle Microvasculature and Prevents Lipid-
Induced Metabolic Insulin Resistance
NASUI WANG, WEIDONG CHAI, EUGENE J. BARRETT, ZHENQI LIU, Charlottesville,
VA
Patients with diabetes have increased plasma concentrations of free fatty
acids (FFAs) which cause insulin resistance in multiple insulin responsive
tissues, including the microvasculature. Microvascular insulin resistance
contributes signifi cantly to metabolic insulin resistance seen in diabetes.
Blockade of angiotensin II type 1 receptor with losartan recruits muscle
microvasculature and may improve insulin sensitivity. Whether losartan
recruits muscle microvasculature and rescues insulin’s metabolic action in
the presence of high FFA concentrations is not known.
After an overnight fast, male Sprague-Dawley rats received a systemic
infusion of either saline or intralipid + heparin (3.3% and 30 U/ml) for 3
hrs after an overnight fast, with a 3 mU/min/kg euglycemic insulin clamp
superimposed for the last 2 hrs. A third group received the same infusion
of intralipid + heparin and insulin, with a losartan injection (0.3 mg/kg, i.v.
bolus) 5 min before starting the insulin infusion. Muscle microvascular blood
volume (MBV) and microvascular fl ow velocity (MFV) were measured using
contrast-enhanced ultrasound before and at 30, 60 and 120 min of insulin
infusion. Muscle microvascular blood fl ow (MBF) was calculated as the
product of MBV and MFV. Steady state whole body glucose disposal rates
were calculated.
Insulin infusion doubled muscle MBV at 30 min and this effect lasted
for the entire 120 min (p