12 research outputs found
Effect of pyridoxamine on chemical modification of proteins by carbonyls in diabetic rats: characterization of a major product from the reaction of pyridoxamine and methylglyoxal
Abstract Advanced glycation end products (AGEs) from the Maillard reaction contribute to protein aging and the pathogenesis of ageand diabetes-associated complications. The a-dicarbonyl compound methylglyoxal (MG) is an important intermediate in AGE synthesis. Recent studies suggest that pyridoxamine inhibits formation of advanced glycation and lipoxidation products. We wanted to determine if pyridoxamine could inhibit MG-mediated Maillard reactions and thereby prevent AGE formation. When lens proteins were incubated with MG at 37°C, pH 7.4, we found that pyridoxamine inhibits formation of methylglyoxal-derived AGEs concentration dependently. Pyridoxamine reduces MG levels in red blood cells and plasma and blocks formation of methylglyoxallysine dimer in plasma proteins from diabetic rats and it prevents pentosidine (an AGE derived from sugars) from forming in plasma proteins. Pyridoxamine also decreases formation of protein carbonyls and thiobarbituric-acid-reactive substances in plasma proteins from diabetic rats. Pyridoxamine treatment did not restore erythrocyte glutathione (which was reduced by almost half) in diabetic animals, but it enhanced erythrocyte glyoxalase I activity. We isolated a major product of the reaction between MG and pyridoxamine and identified it as methylglyoxal-pyridoxamine dimer. Our studies show that pyridoxamine reduces oxidative stress and AGE formation. We suspect that a direct interaction of pyridoxamine with MG partly accounts for AGE inhibition. Ó 2002 Elsevier Science (USA). All rights reserved
ALPHA2 Adrenergic and High Affinity Serotonergic Receptor Changes in the Brain Stem of Streptozotocin induced Diabetic Rats
The brain stems (13S) of streptozotocin (STZ)-diabetic rats were studied lo see the changes in
neurotransmitter content and their receptor regulation. The norepinephrine (NE) content
determined in the diabetic brain stems did ^ control. an E showed la
while
PI turnover
hri
content increased significantly compared N^r eNveFa o the recep
significant increase. The alpha2 adrenergic receptor
IneP utisoulinntreat d ratsetheNE contentt dec^ sled
was significantly reduced during diabetes. in
versedcto reanorm
sed
ulcrea e tK
reatment
the
state.
while EPI content remained increased as in die diabetic
B,, for a]pha2 adrenergic receptors slw^nificantly while
Unlabelled clonidine inhibited [31-I]NE binding in BS of control, diabetic and insulin treated
ulations bindi
diabetic rats showed that alpha2 adrenergicre^ punks cojnidiabetic animal the ligand bound
sites with Hill slopes significantly away from unity.
weaker to the low affinity site than in controls. Insulin treatment reversed[ this allumbmn to
control levels. The displacement analysis using (-)-epinephrine age in
control and diabetic animals revealed two populations of receptor affinidtyo=tat ss. In control
animals, when GTP analogue added with epinephrine, the curve nagnlde caofnfitnroit yS
model; but in the diabetic BS this effect `not
aobserved. In
bintact
oth the diabetic
data thus showlthat
the effects of monovalent cations on affinity
alphaz adrenergic receptors have a reduced affinity v
due
in stem ialtered Itscppeomson(5-
regulation. The serotonin (5-HT) coat
hydroxy) tryptophan (5-HTP) showed an increase and its breakdown metabolite (5-hydroxy)
indoleacetic acid (5-I{IAA) showed a significant decrease. This showed that in serotonergic
which l
nerves there is a disturbance in both synthetic and breankduomwnbers pretma'med ana
increased 5-HT. The high affinity serotonin receptor um ese serotonerg
decrease in the receptor affinity. The insulin ^treatmentsturtiy showsha decreased serotonergic
receptor kinetic parameters to control level.
receptor function. These changes in adrenergic and serotonergic receptor function were
suggested to be important in insulin function during STZ diabetes
Brain Adrenergic and Serotonergic Receptor Function in Streptozotocin-Diabetic Rats
Department of Biotechnology, Cochin University of Science and
Technolog
Proton-Translocating Nicotinamide Nucleotide Transhydrogenase: A Structural Perspective
Nicotinamide nucleotide transhydrogenase (TH) is an enzyme complex in animal mitochondria and bacteria that utilizes the electrochemical proton gradient across membranes to drive the production of NADPH. The enzyme plays an important role in maintaining the redox balance of cells with implications in aging and a number of human diseases. TH exists as a homodimer with each protomer containing a proton-translocating transmembrane domain and two soluble nucleotide binding domains that mediate hydride transfer between NAD(H) and NADP(H). The three-domain architecture of TH is conserved across species but polypeptide composition differs substantially. The complex domain coupling mechanism of TH is not fully understood despite extensive biochemical and structural characterizations. Herein the progress is reviewed, focusing mainly on structural findings from 3D crystallization of isolated soluble domains and more recently of the transmembrane domain and the holo-enzyme from Thermus thermophilus. A structural perspective and impeding challenges in further elucidating the mechanism of TH are discussed
Kinetic Studies of Purified malate Dehydrogenase in Liver of Streptozotocindiabetic Rats and the Effect of Leaf Extract of Aegle Marmelose (L.) Correa ex Roxb
The functional basis of diabetes-mellitus to a certain extent,
can be elucidated by studying diabetes-induced changes
in metabolic enzymes. Malate dehydrogenase (MDH),
is an enzyme directly involved in glucose metabolism. The
kinetic parameters of MDH and its purified cytosolic isozyme,
S-MDH, have been studied in the liver of streptozotocin-
diabetic rats; also the potential of the leaf extract of A.
marmelose as an was investigated. The
Km of the liver enzyme increased significantly, in both
crude and purified preparations in the diabetic state when
compared to Lhe respective controls. Insulin as well as leaf-
•extract treatment of the diabetic rats brought about a reversal
of K. values to near normal. Vmax of purified S-MDH
was significantly higher in the diabetic state when compared
to the control. Insulin and leaf extract treatment did not
reverse this change. Since MDH is an important enzyme in
glucose metabolism, the variation in its quantitative and
qualitative nature may contribute to the pathological status
of diabetes. The fact that leaf extract of A. marmelose
was found to be as effective as insulin in restoration of blood
glucose and body weight to normal levels, the use of A.
marmelose as potential hypoglycemic agent is suggested