الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Insulin resistance is the lowered sensitivity of target tissues (liver, skeletal muscle, and adipose tissue) to the physiological effects of insulin that may take several forms. These include type 2 diabetes mellitus/obesity induced insulin resistance and insulin resistance of late pregnancy. While the former seem to be a pathological state the latter is considered as a physiological adaptation to the intense metabolic alterations of pregnancy. Pregnant female further adapts to this insulin resistance by β-cell hyperplasia and hyperinsulinemia so as to maintain blood glucose levels within the normal range.
Various insulin resistance-inducing agents such as, adipokines, free fatty acids, and cellular oxidative stress lead to both activation of several serine/threonine kinases and phosphorylation of IRS1.These agents are known to negatively regulate the IRS1 functions by phosphorylation . In addition, they have all been proven to be elevated in pregnancy together with the rise of placental hormones that have been implicated to cause defective GLUT4 translocation.
Oxidative stress arises when excessive ROS are produced from the cells and/or are not met with sufficient antioxidants. Increased ROS causes defective cellular functions, differentiation and cell signaling. The placenta has a high metabolic activity with overproduction of ROS on top of the defective free-radical scavenging ability of the placenta and deficiency in enzymes such as SOD and GPx.
GDM is a shift from the physiological adaptive phase to a pathological phase which results from β-cell dysfunction and development of hyperglycemia. Hyperglycemia itself is a trigger for many inflammatory actions and ROS production and causing further release of cytokines (TNF-α), inhibiting proper insulin signaling, destruction of β-cells and insulin.
HO-1 is the enzyme that catalyzes the oxidative degradation of haem into iron, CO and bilirubin. Being a rich source of natural antioxidants, several researches have investigated the role of this enzyme system in various chronic diseases including diabetes and insulin resistance.
HO-1 is induced by heavy metals and all kinds of stimuli that cause oxidative stress and pathological conditions such a hypoxia, ultra violet radiation, and reactive nitrogen oxides. MAPK system mediates the regulation of HO-1 expression and regulates other multiple cellular functions like cell proliferation, differentiation and apoptosis. MAPK system is regulated by oxidants.
Besides its heam degrading ability , HO-1 has been shown in previous studies to improve insulin sensitivity and glucose metabolism by its induction in type II DM, obesity and different experimental animal models of insulin resistance. HO-1 induction also attenuates TNF-α levels, JNK (which normally inhibits insulin),and inhibits NF-κB which when activated leads to production of inflammatory cytokines (TNF-α) and leads to apoptotic changes. NF-κB is known to interact with estrogen receptors and cause decreased GLUT4 expression. Adding to this, HO-1 induction raises adiponectin levels (insulin-sensitizing protein).
The present study aimed at investigating the effects and consequences of induction and suppression of HO-1in serum, on insulin resistance and oxidative stress markers in late pregnancy. In addition, it also aimed at correlating these findings to the risk of progression of physiological insulin resistance to gestational diabetes.
This study was carried out on 40 albino female pregnant adult rats.
Rats were randomly divided into 3 groups:
Group (I): (control pregnant group): consisted of 10 pregnant rats. Rats were injected once daily intraperitoneally (ip) with 0.5ml of the vehicle phosphate buffered saline.
Group (II): (HO-1 induced group): consisted of 15 pregnant rats that received hemin (HO-1 inducer ). Hemin (15 mg/kg ip) injections (0.5 ml) were given on day 1 of pregnancy, twice weekly for 6 doses.
Group (III): (HO-1 suppressed group ): consisted of 15 pregnant rats. Tin protoporphyrin IX(SnPP IX), an HO-1 inhibitor was administered to this group in a the dose of 50μmol/kg of body weight. Rats were injected i.p with 0.5ml once daily for 19-20 days starting from Day1 of pregnancy.
On day 19 or 20 of gestation, rats were fasted overnight, then euthanized. Blood samples were collected by cardiac puncture, sera were separated and FBG levels were measured immediately. The remaining fraction was stored and assayed for the following parameters:
8. Haem-oxygenase-1 level (ng/L).
9. Bilirubin (mM/L.)
10. Total antioxidant capacity (mM/L.)
11. Fasting serum Insulin (mIU/L)
12. Estrogen (pg/ml)
13. Progesterone (ng/mL)
14. TNF-α (pg/ml)
HOMA-IR(homeostasis model assessment- insulin resistance) was calculated from fasting insulin and glucose levels.
Pancreatic tissues were extracted out and stored in10% formalin. They were further, processed, and paraffin embedded. Sections of 5-µm thickness were cut and stained with hematoxylin and eosin for histological analysis.
The results showed that HO-1 was clearly induced by hemin as shown by the high levels of HO-1 when compared to control group, and was significantly suppressed by tin protoporphyrin. Accordingly bilirubin and TAC were concomitantly increased in the hemin group and decreased in the tin group showing a positive correlation between the three parameters.
Induction of HO-1 was accompanied by a DROP in FBG, and an increase in insulin levels which was explained by the provision of antioxidants by the HO-1 that allowed for the proper β-cell function ,insulin secretion and attenuated insulin destruction. As a result there was a DROP in HOMA-IR, indicating improved insulin sensitivity. On the other hand HO-1 suppression exerted opposite effects. There was a negative correlation between HO-1 and FBG and HOMA-IR.
To further clarify how HO-1 imposed such change in insulin sensitivity , TNF-α levels were measured and were found to be lowered in HO-1 induced group but increased in HO-1 suppressed group. Furthermore, there was a significant negative correlation between the HO-1 and TNF-α, and a significant positive correlation between TNF-α and HOMA-IR, suggesting a role of TNF-α in insulin resistance in pregnancy that was suppressed by HO-1 induction.
Although estrogen and progesterone have long known to be responsible for insulin resistance of pregnancy, however the present study could not prove that HO system can modulate their levels. There were no significant relation between estrogen and progesterone levels with HOMA-IR. Although there was a consistent rise in these hormones with the fall in insulin sensitivity throughout pregnancy. Several literature state that there’s a complimentary action with other hormones like glucocorticoids, HPL, and PL.
Pancreatic sections revealed interesting findings. The control pregnant group showed islet cell hyperplasia (β-cell hyperplasia). Hemin treated group showed more evident islets suggesting that the upregulated HO-1 served as a shield that allowed adequate adaptation and even rendered any environmental factor that might cause OS, negligible. On the contrary, tin treated group showed necrotic changes, inflammatory cellular infiltration, fibrosis, vacuolization and interstitial oedema. All of which are pathological findings of overt diabetes and were consistent with the high FBG and lower insulin levels.