Diabetes mellitus (DM) is a metabolic disorder of
multiple etiologies characterized by Chronic hyperglycemia with disturbances of
carbohydrate, fat and protein metabolism, resulting from defects in insulin
secretion, insulin action, or both (1).
The vast majority of cases of diabetes fall into two broad categories: type 1
and 2 diabetes. Type 2 diabetes, which accounts for ?90–95% of those with
diabetes, encompasses individuals who have insulin resistance and usually have
relative (rather than absolute) insulin deficiency (1, 2).Type1diabetes is characterized by an absolute deficiency of
insulin secretion caused by pancreatic ?- cell destruction, usually resulting
from an autoimmune attack. It accounts for approximately 10% of all cases (3).
of both type 1 and type 2 DM (T2DM) is increasing worldwide. T2DM is rising
much more rapidly, presumably because of increasing obesity, reduced activity
levels as countries become more industrialized, and the aging of the population
(4). According to International
Diabetics Federation( IDF) DM Atlas 2015 report, more than 75% of people with DM
live in low and middle income countries (5). In Africa region DM is expected to the highest increase
in the future time. It also reported
regional prevalence of 3.8% of DM and rise to 4.3% in 2030 (6).
Risk factors for
DM include older age, obesity, and
family history of DM, prior history of gestational DM, impaired glucose
tolerance, physical inactivity, and race/ethnicity (7). Recently
there are also intestinal micro biotas that can be one of the risk factors for
the development of DM. The human gut micro biota is a complex ecosystem, which
is now known as a key component in gastrointestinal tract (GIT) homeostasis.
Its involvement in immune diseases has recently been demonstrated and bacterial
imbalance (dysbiosis) has been associated with pathologies such as inflammatory
bowel disease and obesity (8-10).
Evidence reveals that the gut micro
biota plays a critical role in the development of obesity, T2DM, and insulin
resistance (11-13). The total number of bacteria in the
gut is estimated at; ?1014, it has been proposed that the genome
size of this exteriorized organ largely exceeds the human genome size (14, 15).
The gut micro biota plays an
important role in the development of pre diabetes conditions, such as insulin
resistance. Studies suggested that obese people with insulin resistance were
characterized by an altered composition of gut micro biota, particularly an
elevated Firmicutes/Bacteroidetes ratio compared with healthy
people (16, 17).
T2DM patients showed an
altered intestinal micro biota which is characterized by a decrease of Bacteroidetes/Firmicutes
ratio and some functional bacteria (e.g. Bifidobacteria) with an
increase of various opportunistic pathogens and some endotoxins-producing Gram negative
bacteria (18-20) that
modify the host energy metabolism through a specific polysaccharide utilization
loci mechanism (20).
Moreover, the accumulation of gut-derived bacterial
inflammatory molecules (e.g. LPS, peptidoglycans and flagellin) in intestine is
thought to accelerate the inflammation in T2DM (21, 22).
Each human intestine harbors
not only hundreds of trillions of bacteria, but also bacteriophage particles,
viruses, fungi and archaea, which constitute a complex and dynamic ecosystem
with which we live in symbiosis throughout our lifetime (23). Host genetics is thought to contribute to the profile of the
gut micro biome, all living conditions, including dietary habits, exposure to xenobiotic
(such as drugs, toxicants and additives) or stresses (such as surgery and
infections) will modulate the gut micro biota, occasionally for a limited
period of time due to the resilience of this ecosystem (24). Therefore, T2DM, a complex disease that is often associated
with obesity, develops via the interaction between genetic and environmental
factors. So, gut micro biota represents an environmental factor of T2DM that
was neglected in the past due to the complexity of its analysis (25) and to the lack of an understanding of the mechanisms
underlying the interactions between gut microbes and host metabolism.
The gut micro biota is now considered a
separate organ that is involved in the regulation of numerous physiological
path-ways by impacting different functions of the host (26).
Among these regulatory actions, the influence of gut microbes on energy
metabolism is of particular interest, as it has been proposed to be a driving
force in the pathogenesis of metabolic diseases, especially obesity. Intestinal
microbes have developed a mutually beneficial relationship with their host, and
can influence physiological systems by modulating gut motility, intestinal
barrier homoeostasis, nutrient absorption and fat distribution (27-29). Therefore micro biotas are
important microorganisms not only monitors the body homeostasis but also for
the driving force in the pathogenesis of metabolic disease. So, studding about
gut micro biota for the contribution of T2DM is vital and current issue for the
therapeutic development of T2DM to know about the full mechanism of actions of micro
biotas for the development of T2DM.