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Abstract:
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In the present study, the initial phase was directed to confirm the effects of
curcumin and vitamin D3 in preventing or delaying diabetes onset by studying the
blood glucose and insulin levels in the pre-treated and diabetic groups.
Behavioural studies were conducted to evaluate the cognitive and motor function
in experimental rats. The major focus of the study was to understand the cellular
and neuronal mechanisms that ensure the prophylactic capability of curcumin and
vitamin D3. To elucidate the mechanisms involved in conferring the antidiabetogenesis
effect, we examined the DNA and protein profiles using
radioactive incorporation studies for DNA synthesis, DNA methylation and
protein synthesis. Furthermore the gene expression studies of Akt-1, Pax, Pdx-1,
Neuro D1, insulin like growth factor-1 and NF-κB were done to monitor pancreatic beta cell proliferation and differentiation. The antioxidant and antiapoptotic
actions of curcumin and vitamin D3 were examined by studying the
expression of antioxidant enzymes - SOD and GPx, and apoptotic mediators like
Bax, caspase 3, caspase 8 and TNF-α. In order to understand the signalling
pathways involved in curcumin and vitamin D3 action, the second messengers,
cAMP, cGMP and IP3 were studied along with the expression of vitamin D
receptor in the pancreas. The neuronal regulation of pancreatic beta cell
maintenance, proliferation and insulin release was studied by assessing the
adrenergic and muscarinic receptor functional regulation in the pancreas, brain
stem, hippocampus and hypothalamus. The receptor number and binding affinity
of total muscarinic, muscarinic M1, muscarinic M3, total adrenergic, α adrenergic
and β adrenergic receptor subtypes were studied in pancreas, brain stem and
hippocampus of experimental rats. The mRNA expression of muscarinic and
adrenergic receptor subtypes were determined using Real Time PCR.
Immunohistochemistry studies using confocal microscope were carried out to
confirm receptor density and gene expression results. Cell signalling alterations in
the pancreas and brain regions associated with diabetogenesis and antidiabetogenesis
were assessed by examining the gene expression profiles of
vitamin D receptor, CREB, phospholipase C, insulin receptor and GLUT. This
study will establish the anti-diabetogenesis activity of curcumin and vitamin D3
pre-treatment and will attempt to understand the cellular, molecular and neuronal
control mechanism in the onset of diabetes.Administration of MLD-STZ to curcumin and
vitamin D3 pre-treated rats
induced only an incidental prediabetic condition. Curcumin and vitamin D3 pretreated
groups injected with MLD-STZ exhibited improved circulating insulin
levels and behavioural responses when compared to MLD-STZ induced diabetic
group. Activation of beta cell compensatory response induces an increase in
pancreatic insulin output and beta cell mass expansion in the pre-treated group.
Cell signalling proteins that regulate pancreatic beta cell survival, insulin release,
proliferation and differentiation showed a significant increase in curcumin and
vitamin D3 pre-treated rats. Marked decline in α2 adrenergic receptor function in
pancreas helps to relent sympathetic inhibition of insulin release. Neuronal
stimulation of hyperglycemia induced beta cell compensatory response is
mediated by escalated signalling through β adrenergic, muscarinic M1 and M3
receptors. Pre-treatment mediated functional regulation of adrenergic and
cholinergic receptors, key cell signalling proteins and second messengers
improves pancreatic glucose sensing, insulin gene expression, insulin secretion,
cell survival and beta cell mass expansion in pancreas. Curcumin and vitamin D3
pre-treatment induced modulation of adrenergic and cholinergic signalling in brain
stem, hippocampus and hypothalamus promotes insulin secretion, beta cell
compensatory response, insulin sensitivity and energy balance to resist
diabetogenesis. Pre-treatment improved second messenger levels and the gene
expression of intracellular signalling molecules in brain stem, hippocampus and
hypothalamus, to retain a functional neuronal response to hyperglycemia.
Curcumin and vitamin D3 protect pancreas and brain regions from oxidative stress
by their indigenous antioxidant properties and by their ability to stimulate cellular
free radical defence system. The present study demonstrates the role of adrenergic
and muscarinic receptor subtypes functional regulation in curcumin and vitamin
D3 mediated anti-diabetogenesis. This will have immense clinical significance in
developing effective strategies to delay or prevent the onset of diabetes. |