Mechanisms of gestational diabetes mellitus using rat model
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Date
2024
Authors
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Sokoine University of Agriculture
Abstract
Gestational diabetes mellitus (GDM) is a form of
hyperglycemia due to carbohydrate intolerance that begins
during pregnancy. This may be due to insulin resistance or
impairment of insulin secretion during pregnancy.
Knowledge on the pathophysiology of GDM is important for
its management. Thus, the main objective of the current
study was to explore the mechanisms of GDM development
due to high fat diet (HFD) or heat stress (HST) in a rat model.
Specifically, the study was done to evaluate the role of
differential adipose tissue (AT) expansion, influence of
oxidative stress (OS) and to determine the role of placental
cytokine (tumour necrosis factor-alpha (TNF-α) and
interleukin-6 (IL-6)) in the development of GDM.
The study used Wistar rats as experimental animals. Rats of
8 - 10 weeks old were used and experiments were
conducted at the Small Animal Research Unit (SARU),
College of Veterinary Medicine and Biomedical Science
(CVMBS), Sokoine University of Agriculture (SUA),
Morogoro, Tanzania. Samples were analysed in research
laboratories in the Departments of Physiology, Biochemistry
and Pharmacology and Veterinary Anatomy and Pathology.
This thesis is divided into three chapters. Chapter one is on
introduction and literature review. It includes a general
introduction, animal models for GDM, factors governing the
development of GDM, establishing GDM models,
histopathology of pancreas during GDM, placenta and GDM,
objectives of the study, and organization of the thesis.
Chapter two comprises three manuscripts describing the
research findings. The first manuscript describes the
contribution of HFD to the development of GDM. The second
manuscript is on evaluation of how OS due to HST
predisposes rats to GDM. Findings on assessment of theiv
role of placental cytokines (TNF-α and IL-6) in the
development of GDM are presented and discussed in the
third manuscript. Lastly, general discussion, conclusion and
recommendations of the study are provided in chapter three.
Work described in the first manuscript evaluated contribution
of HFD in differential AT expansion and subsequent
development of GDM in Wistar rats. Pregnant and non-
pregnant rats were given streptozotocin (STZ) by a single
intraperitoneal injection or HFD throughout the experiment.
The animals were sacrificed by a combination of ketamine
50 mg/kg and xylazine 5 mg/kg on days 1, 8, 15, and 21 of
the experiment. Blood, AT (both visceral (VAT) and
subcutaneous (SAT)) and pancreas were collected and
analysed. In this study, STZ-treated animals had a
significant increase (p<0.05) in serum glucose and a
decrease in insulin, without changes in the size of
adipocytes. The levels of both serum glucose and insulin
were significantly high in HFD-fed animals (p<0.05); being
higher in pregnant (p<0.05) than non-pregnant rats. The
increase in glucose and insulin levels was associated with
an increase in the size (hypertrophy) than the number
(hyperplasia) of adipocytes. The increase in adipocytes was
higher in VAT and corresponded to insulin resistance and
GDM development than in SAT. Histologically, β-cells were
decreased in number and deformed in STZ groups while
maintained in HFD groups in both pregnant and non-
pregnant animals. This study concluded that intake of HFD
during pregnancy leads to AT expansion, which is one of the
risk factors for the hyperglycemia and development of GDM.
This study demonstrates in the second manuscript the
association between HST and GDM. Pregnant and non-
pregnant Wistar rats were maintained at 41 - 42°C for 21
days. On days 1, 8, 15 and 21 the animals were humanely
sacrificed by a combination of ketamine 50 mg/kg andv
xylazine 5 mg/kg. Blood samples were collected from the
heart for glucose, insulin, malondialdehyde (MDA) and
glutathione peroxidase (GPx) analyses. Pancreatic tissues
were fixed in neutral buffered formalin, and processed for
histopathology. The findings demonstrated that, in pregnant
rats, HST induced a significant increase in glucose in
conjunction with a drop in insulin levels than non-pregnant
rats (p<0.05). In addition, heat treatment was accompanied
by an increase in MDA and a drop in GPx levels. Histological
examinations of the pancreas revealed damaged β-cells
from day 15 and a reduction in the number of β-cells by day
21 of the experiment in pregnant rats. These results suggest
that HST raises the levels of OS in pregnant rats more than
in non-pregnant rats and increases the chances of GDM as
it is associated with β-cell defects in the pancreas.
Findings on serum concentration and placental production of
TNF-α and IL-6 of HFD-given rats during pregnancy and
their correlation with the development of GDM are presented
and discussed in the third manuscript. Pregnant and non-
pregnant rats were given STZ single IP injection or HFD
throughout the experiment. On days 1, 8, 15 and 21, the
animals were humanely sacrificed by a combination of
ketamine 50 mg/kg and xylazine 5 mg/kg. Blood samples
were collected from the heart for glucose, insulin, TNF-α and
IL-6 analyses. Placenta samples were dissected, fixed in
neutral
buffered
formalin,
and
processed
for
histopathological and immunohistochemical analyses for
TNF-α and IL-6. The levels of serum glucose and insulin
were significantly high in HFD-fed animals (p<0.05); being
higher in pregnant (p<0.05) than non-pregnant rats. The
increase in glucose and insulin levels was associated with
an increase in serum levels of TNF-α and IL-6; which were
higher in HFD pregnant than non-pregnant animals on day
21 of the experiment. Histologically, placenta tissues of STZ-
treated animals were severely congested with blood vesselsvi
on days 15 and 21 compared with those from HFD-fed rats
which had low congestion on day 21. In both pregnant and
non-pregnant rats, immunostaining intensity for TNF-α and
IL-6 was high in HFD and STZ-treated animals on day 15
and 21. The findings of this study show that intake of HFD
during pregnancy leads to an increase in the levels of IL-6
and TNF-α in the placenta towards the end of gestation
resulting in insulin resistance and hyperglycemia that may
predispose to GDM.
Therefore, Intake of HFD during pregnancy causes AT
expansion as well as increase in the levels of placental
cytokines (TNF-α and IL-6) resulting in insulin resistance and
hyperglycemia, which are risk factors for GDM development.
In addition, exposing rats to HST during pregnancy raises
the levels of OS which is associated with β-cell defects
hence increasing the chances for GDM.
Description
PhD Thesis
Keywords
Diabetes, HUMANITIES and RELIGION::History and philosophy subjects::Archaeology subjects::African and comparative archaelogy, Rat, Mellitus, Hyperglycemia, Insulin, Pathophysiology