Article Type : Research Article
Authors : Orien Lee Tulp
Keywords : Miglitol. Obesity,Diabetes,T2DM. Hemoglobin A1c. Glucokinase, G6PD, Malic enzyme
To determine the effect of delayed
carbohydrate (sucrose) digestion in type 2 diabetes mellites on the activity of
glycemic and lipogenic enzyme parameters, groups of young adult male obese T2DM
(diabetic) SHR/Ntul//-cp rats were fed a nutritionally complete USDA-formulated
diet containing 54% sucrose (CONTROL) or the same diet with 150 mg of the
luminal ?-glucosidase inhibitor miglitol (MIG) for up to 8 weeks. All animals
demonstrated profound (4+) glycosuria by 8 weeks of age to confirm T2DM. Body
Weight Gain (BWG), relative adiposity and glycosuria were elevated in control
animals, but decreased significantly following miglitol. Measures of oral
Glucose Tolerance (OGT, 250 mg glucose/kg BW, via gavage), AUC for glucose and
insulin response to OGT and glycated hemoglobin (HbA1c) were elevated in
controls and decreased by 20% after miglitol treatment. Hepatic Glucokinase
(GK), malic enzyme (ME) and glucose-6-phophate dehydrogenase (G6PD) were
elevated in the Controls and decreased toward normalization following miglitol
treatment. In conclusion, these observations indicate that an 8-week course of
miglitol is an effective agent in improving the magnitude of the elevated
glycemic and lipogenic enzymes and their impact on developing adiposity in the
SHR/Ntul//-cp genetic rat strain of obesity+T2DM and may be an effective
adjunct in clinical management of obesity, hyperlipidemia and T2DM.
Obesity and overweight conditions and their pathophysiologic
impacts continue to occur throughout much of the world, despite many advances
in understanding the multiple etiologies and management of the disorder. The
progression of adult onset, type 2 diabetes (T2DM) is among the most common
sequelae of the disorder and is also the most prevalent form of diabetes
worldwide [1-3]. The incidence of T2DM affects over 90% of the known diabetic
populations worldwide and currently affects approximately one sixth of the
populations of some Westernized nations. Unfortunately, many individuals that
may exhibit symptoms consistent with a predisposition for T2DM often remain
undiagnosed especially during the earlier, formative and somewhat asymptomatic
stages of the illness in addition to inadequate recognition in marginalized
populations [3]. The longstanding hallmark of treatment includes attention to
disordered factors of diet and lifestyle, deemed to be among the primary
contributors to the disorder [4,5]. Once an individual is diagnosed, however,
ameliorative dietary, pharmacologic and lifestyle treatment approaches are
typically continued throughout the remainder of the patient’s lifetime, but
often fall short of complete success in achieving a full stop return to a
prediabetes status [4,5]. The long-term nature of the disorder thereby enables
the progression of the pathophyiologic comorbidities of obesity and T2DM to
continue to develop. Both early diagnosis and later therapeutic regimens are
usually focused on an assessment of initial and ongoing glycemic status, via
measures of fasting blood glucose, glycated hemoglobin, glycosuria, assessment
of body fatness, vital signs and lifestyle contributors in an attempt to mark
the magnitude of progression of the disorder and to determine the intensity and
magnitude of treatment regimens to apply. While day-to-day efforts to control
the symptoms of T2DM focus primarily on monitoring measures of glycemic status,
longer term goals often include assessments of blood lipids, as
pathophysiological contributors to various cardiovascular disorders that are
also common comorbidities of T2DM. A common hallmark of T2DM is chronic
hyperinsulinemia, which also functions as a metabolic contributor to
hyperlipidemia via metabolic actions of insulin on lipid biosynthesis and storage
in liver and adipose tissues respectively [6,7]. The activities of certain insulin-linked glycemic and lipogenic enzymes
including glucokinase, malic enzyme, and glucose-6-phosphate dehydrogenase
typically become elevated in states of obesity+T2DM, as consistent contributors
to the elevations in plasma lipid profiles and relative adiposity that are also
typically observed in such individuals. In addition, obesity and overweight
conditions are also marked with systemic, chronic low-grade inflammation, thereby
adding an additional often unresolved burden to the clinical management and
progression of both neurologic and metabolic complications of T2DM [8,9].
Adipose tissue represents an active endocrine tissue,
capable not only of energy deposition and storage primarily in the form of
triglycerides, but also a source of multiple hormonally active peptides
including leptin and others that impact factors of satiety, lipid deposition
and preadipocyte generation and expansion [10,11]. In contrast to brown
adipocytes, white adipocytes can continue to proliferate well into adulthood in
most visceral and subcutaneous fat depots [10]. In addition, white adipose
tissue hosts a broad variety of immune cells, including macrophages, capable of
responding to the state of energy balance, especially in visceral adipose
depots [12]. During periods of excess energy balance, insulin triggers both de
novo fatty acid biosynthesis in liver and adipose tissues and facilitates lipid
energy deposition and storage in adipocytes, in addition to enhancing
additional preadipocyte expansion. Once differentiated, white adipocytes can
remain active and preadipocytes appear to be able to continue to regenerate and
differentiate throughout much of the remaining lifespan of an animal or human in
most fat depots [8,10,11]. It is widely accepted that inflammatory responses
originating in visceral adipose tissue play a contributory role in the
development of the systemic insulin resistance commonly associated with the
obese state [8,9,12-15]. In addition, the metabolic state of positive energy
balance is associated with the activation of a population of M1 proinflammatory
macrophages which may develop into inflammatory M1 macrophages. The M1
macrophages can then bring about the generation of unhealthy, inflammatory
reactive oxygen species (iROS). The iROS can then further contribute to the
generation and activation of inflammatory responses in the form of inflammatory
cytokines including C-reactive protein and others that may also contribute to
atherogenic processes [14,15]. The formation of inflammatory cytokines occurs
in general proportion to the magnitude and duration of over nutrition and
central adiposity, and to the progression of inflammation of both the vascular
endothelium and neurologic tissues unless quenched by nutritional and/or
metabolic antioxidant actions. The end-result of the iROS may also impact on
the activity of the cell cycle, thereby contributing to genomic actions and
membrane viability and thereby impacting the potential for continued tissue
regeneration. In neural tissues including the CNS, the iROS can contribute to
apoptosis of neural cells, an acceleration of the shortening of telomeres,
impaired neuronal regeneration, and thus contribute to neuronal senescence. In
the worst-case scenario, a spontaneous voluminous release of inflammatory
cytokines can result in grave responses sometimes referred to as a ‘cytokine
storm’ that may result in severe respiratory collapse and the rapid demise of
the individual [14,15]. In contrast to the above dysregulations in energy
balance, a controlled state of energy balance brings about the maturation and
proliferation of alternative, healthy M2-macrophages in adipose tissue depots
[12]. The physiological effects of the M2 macrophages counter the negative
effects of the M1 macrophages via enhancing healthy immunogenic responses.
Thus, in healthy adipose tissue, the expression of M2 macrophages tends to
dominate and is associated with decreases in the rate of telomere shortening,
enhanced cellular lipid handling and essential mitochondrial functions,
production of healthful, anti-inflammatory cytokines, improved insulin
sensitivity, and further inhibition of iROS formation and thereby damping their
inflammatory and pathophysiological actions. Therefore, implementation of a
healthy diet and lifestyle and pharmacological agents as needed form important
key elements in the treatment and long-term management of obesity, overweight
conditions, and T2DM [8,10,14,15].
Hepatic tissues also form an important element in the
enzymatic contributions to energy balance and to an ordered, healthful
metabolism [13,16-19]. Glucokinase generally responds to rising plasma glucose
concentrations, where it provides a signal for pancreatic ?-cells to release
insulin, thereby facilitating the efficiency of glucose uptake and oxidation in
peripheral tissues. In T2DM, this can also bring about an increase in hepatic
glycogen synthesis and storage, in addition to providing 2 and 3-carbon
substrates to contribute to de novo fatty acid and triglyceride
biosynthesis and eventual storage in adipose tissues mostly in the form of
fatty acids, triglycerides or triacylglycerols. In addition, malic enzyme and
glucose 6 phosphate dehydrogenase actions generate NADPH, an essential co-substrate
for the de novo fatty acid biosynthesis in liver and adipose tissue.
Glucose readily enters glycolysis in peripheral tissues, usually in concert
with insulin-linked GLUT4 glucose transporters located along the plasma
membranes of those tissues [13,17,18-21]. Glycolysis from glucose
moieties results in providing substrates for glycogen deposition in addition to
providing reducing equivalents for mitochondrial high energy phosphate
generation. In contrast, fructose, derived from luminal digestion of sucrose
into glucose and fructose, or from dietary sources of fructose such as high
fructose corn syrup (HFCS) sweeteners [18,19,21]. Once fructose is absorbed by
liver or intestinal tissues via GLUT5 and independently of insulin-linked GLUT4
activity, it is readily converted to fructose-1-phosphate and ADP, followed by
splitting the ketohexose into two trioses, namely dihydroxyacetone phosphate
(DHAP) and glyceraldehyde (GA). Both trioses can provide preferential substrate
including NADPH for de novo insulin-stimulated lipogenesis [13,17]. In
addition, the ADP may undergoe further spontaneous degradation to AMP and IMP,
and may eventually become further degraded into uric acid, a contributor to
metabolic disorders including gout due to its decreased solubility in plasma
and its potential to form crystals and induce inflammatory responses in other
physiologic tissues.17 Thus, as improvements in plasma insulin
concentration occur following dietary or pharmacologic intervention, the
activity and tissue levels of insulinogenic and lipogenic enzymes are likely to
undergo a favorable, more healthful improvement with concurrent shifts in
intermediary metabolism.
The compound [1,5 dideoxy-1,5-[(2-hydroxyethyl)
imino]-D glucitol; generic = miglitol; marketed as Glyset®) is an established water soluble competitive
inhibitor of luminal starch digestion in the ?-glucosidase and sucrase
inhibitor family, and acts within the brush border sucrase and ?-glucosidase
receptor domains of the small intestine [22-24]. Unlike other members of the
glucosidase inhibitor family, miglitol actions are confined to the uppermost
regions of the small intestine, where the agent undergoes virtually complete
luminal absorption within 2 hours of ingestion and luminal exposure, thereby
limiting the duration and magnitude of its direct pharmacologic effects. In
addition, due to its relatively short duration of action, miglitol limits
potential gastrointestinal side effects secondary to undigested carbohydrate
moieties entering the domain of the colonic microbiota, since typically, both
carbohydrate digestion and miglitol absorption are usually complete within two
hours or less in a healthy, unobstructed small intestine. The agent reportedly
bypasses hepatic metabolism and conjugation and undergoes complete renal
excretion without further chemical modification. The luminal physiological
effects of exposure to miglitol is a modest, dose-related delay in luminal
sucrose digestion in the upper regions of the small intestine, and in an
attenuated and delayed response in the glycemic excursions that normally follow
a carbohydrate meal [22,23]. Accordingly, the immediate and longer term
insulinogenic responses would also be predicted to become proportionately
attenuated over time, including the genomic expression of hepatic
insulin-linked enzymatic responses with continued glucosidase inhibition, and
likely generally proportional to the AUCglucose concentrations [24-27]. Also,
since the hemoglobin glycation reaction occurs via a non-enzymatic, non-reversible,
mass action kinetics process that corresponds to the mean 24-hour plasma
glucose concentrations the erythrocyte is exposed to during its lifespan, one
would predict that this glycemic marker would also become decreased within up
to 12 weeks of treatment as the hemoglobin-glycated erythrocytes undergo
replacement during the miglitol treatment [13,28,29]. Accordingly, the percent
of circulating glycated hemoglobin would also be predicted to decrease in
proportion to the lower mean plasma glucose concentrations in the weeks and
months that follow introduction of the glucosidase inhibitor agent. In
mammalian species, the duration of the lifespan of an erythrocyte once released
into the general circulation is typically 3 to 4 months in healthy adult humans
and animals [13,28,29]. As the proportion of glycated hemoglobin improves,
issue oxygen delivery would also be predicted to improve, as the processes of
oxygen dissociation and the transitions between taut and relaxed forms of adult
hemoglobin become inhibited in the presence of glycation [29]. Thus, the
purpose of the present study was to determine the effects of delayed sucrase
and glucosidase activity on the expression of key enzymatic markers of glycemic
status and of insulin-linked enzymes of carbohydrate oxidation and lipid
biosynthesis in liver homogenates of obese, T2DM animals after an 8 week trial
of luminal ?-glucosidase inhibition via miglitol. Studies were conducted in the
SHR/Ntul//-cp rat, a congenic genetic rodent model of early onset obesity and
T2DM, and where the T2DM develops soon after weaning and independently of
extraordinary dietary interventions [30]. Historically, dietary and lifestyle
changes remain the hallmark of conventional therapeutic approaches to treat and
manage the diabetes element of the obesity syndrome in a strategy designed to
improve glycemic markers, while luminal modulation represents a new approach
with regard to improvement in atherogenic parameters and enzymatic indicators
as contributors to lipid metabolism.
Groups of obese SHR/Ntul//-cp rats were selected from
the breeding colony at ~5 weeks of age (n=8 rats/treatment group) and
maintained on stock Purina rodent chow and house water, ad libitum, until 7
weeks of age, reared under conventional environmental conditions (20-22°C, 50%
RH and housed in plexiglass cages lined with ~1 inch of fresh pine shavings).
Animals were then switched to a USDA-formulated control diet containing 54%
carbohydrate as sucrose, 20% protein as equal parts lactalbumin and casein, 16
% fats as equal parts corn oil, beef tallow, lard and coconut oil, 5.9 %
cellulose, 3.1 % AIN vitamin and mineral salt mix, and 1% Teklad vitamin mix,
for the remainder of the study [31]. In addition a second group of littermates
were fed the same diet with the addition of miglitol ([1, 5 dideoxy-1,
5-[(2-hydroxyethyl) imino]-D glucitol; generic = miglitol; currently marketed
as Glyset®) at a dosage of 150 mg/kg (0.015%) of diet as an admixture,
calculated to provide ~ 2.5 mg of miglitol per animal per day based on typical
daily consumption of the control diet. Body weights were obtained weekly as an
indicator of animal wellness. Urines were collected in a metabolic cage
beginning at 8 weeks of age for measures of glycosuria to confirm the onset and
progression of diabetic status. After 6 weeks of the miglitol diet, rats were
subjected to an oral glucose tolerance (250 mg/kg BW via gavage administered
slowly within a one minute duration) and blood obtained periodically via tail
bleeding over a 2 hour duration for measures of glucose (glucose oxidase
method) and plasma insulin concentration via immunochemistry [32]. The area
under the glucose and insulin curves was determined via the method of Sagakuchi
et al. [33]. Measures of Hemoglobin A1c were determined via spectrophotometry
after microcolumn separation [34]. At the end of the study, rats were humanely
sacrificed with a small animal guillotine and principal fat pads including the
dorsal, retroperitoneal, and epididymal fat pads were dissected in their
entirety, weighed to the nearest 0.1 mg., and the sum of the 3 depots expressed
as a percent of body weight as a measure of relative adiposity. The liver
tissue was also dissected free in its entirety, weighed, and aliquots
homogenized in a sucrose-EDTA phosphate buffer for measures of glucokinase,
malic enzyme, and glucose-6-phosphate dehydrogenase activity and expressed as
units/mg protein/liver [19,35,36]. Tissue protein was determined with the
classic method of Lowry et al [36]. Data were analyzed via standard statistical
procedures including student t test, ANOVA, and Pages L test for trend analysis
[37,38]. The study was approved by the Institutional Animal Care and Use
Committee.
The results of urine volume and quantitative glucose excretion
at 8, 10 and 12 weeks of age are presented in (Figures1A and 1B) respectively
and indicate that the onset of glycosuria occurred by 8 weeks of age in both
groups. Both urine daily volume and 24-hour glucose excretion was similar in
both groups at the onset of the miglitol diet. By 10 and 12 weeks of age
however, urine volume in miglitol fed animals decreased by nearly 50%, while
daily glucose excretion in control fed rats increased dramatically, but became
decreased significantly after 2 to 4 weeks of the miglitol regimen to excretion
levels that were similar to those observed at 8 weeks of age, on day one of the
miglitol diet. The effects of miglitol on weight gain are depicted in (Figure 2)
and indicate that the effects of miglitol on weight gain resulted in an average
20% decrease in net weight gain after 8 weeks of the miglitol diet. Mean daily
energy intake was also similarly decreased by approximately 15% in the
miglitol-treated animals, (Control 20.83 g/d vs Miglitol 17.55 g/d). The effects of miglitol on oral glucose
tolerance when animals were 12 weeks of age after 5 weeks on diet are depicted
in (Figure 3A), and indicate that miglitol decreased the magnitude of the
glycemic response to an oral glucose tolerance by an average of 20% or more and
resulted in a significant decrease in the glucose area under the curve and in
the percent of glycated hemoglobin (HbA1c). The insulin response to an oral
glucose tolerance is depicted in (Figure 3B,3C) and indicates that miglitol
also decreased the AUCinsulin by approximately 18%, consistent with a reduction
in the insulin concentrations following the glucose challenge.
Figure
1A:
The effects of miglitol on urine volume in control and miglitol treated animals
and indicates that daily urine volume decreased at 10 and 12 weeks of age in
animals receiving the miglitol diet. (p = < 0.05).
Figure
1B:
The effects of miglitol on urine glucose excretion at 8, 10 and 12 weeks of
age, and indicate that daily urine glucose excretion became markedly increased
at 10 and 12 weeks of age, and remained at prediabetic levels following dietary
miglitol treatment (p = < 0.05).
Figure 2: Effects of miglitol on body weight and weight gain in
obese, T2DM rats. Gain = grams BW gained/8 weeks; Adiposity based on sum of 3
Fat depots / final body weight x 100. Data are mean ± 1 SEM, nrats/group.
Significance by Students T Test; trend (far right column) determined by Pages L
Test for trend analysis.
Figure
3A. Oral glucose tolerance in Miglitol treated
rats. Effect of miglitol on OGT in T2DM
rats. Data are mean ± 1 SEM, n = 8 rats/group. P = < 0.05 via ANOVA. The
mean AUCglc Control = 1034 vs miglitol = 812 (21% decrease).
Figure
3B:
Effect of miglitol on Insulin response to an oral glucose tolerance in T2DM
rats. Effect of miglitol on insulin response in OGT in T2DM rats. Data are mean
± 1 SEM, expressed as a percentage of control; n = 8 rats/group. P = < 0.05;
^Trend = < 0.05 via Pages L test for trend analysis at 90 min only. Mean
AUCins Control = 1903 vs. miglitol = 1572. (17.4% decrease, proportionately
similar to that observed in the glycemic response.).
Figure 3C: Effect of miglitol on AUC glucose and Glycated
hemoglobin A1C. Data are mean ± 1 SEM, n= 6 rats/group. P = < 0.05 (Students
T Test) of a significant trend (Pages L test for trend analysis).
Figure 4A: Effect miglitol on fat pad mass in obese, T2DM rats. Data are
mean ± 1 SEM, expressed as a percentage of control; n = 6-8 rats/group.* = p =
< 0.05; V= significant trend via Pages L test for trend analysis.
Figure
4B:
Effect of miglitol on combined adipose tissue depot mass. Data are the sum ± 1 SEM of the epididymal,
retroperitoneal and dorsal depots, expressed, grams of white adipose tissue as
percent of control (WAT, left panel) and as a proportion of body weight (Right
panel). Kcal consumed as a percent of control in far right panel.N = 6-8
rats/group.
Figure
5:
Effect of miglitol on hepatic metabolic enzymes. Data are mean ± 1 SEM, n=6
rats/group. P = < 0.05; ^ = trend via Pages L test for trend analysis.
The effects of miglitol on indicators of adiposity
without and following miglitol are depicted in (Figures 4A, 4B), respectively.
The mass of the interscapular brown adipose tissue, and the epididymal
retroperitoneal and dorsal depots are depicted in Figure 4A and indicate that
miglitol was associates with decreased mass in the retroperitoneal depot, and a
trend toward a net decrease in total fat pad mass in the dorsal depot.In
contrast, the mass of the intescapular brown adipose tissue and the epidymal
fat pads were similar in both treatment groups, likely because those depots
attain their maximum mass prior to adolescence in the rat. The combined mass of
the fat pads as an indator of adiposity are depicted in Figure 4B, and indicate
that miglitol resulted in a modest decrease in adiposity both as a percent of
weight gain (Figure 2) and as a proportion of final body weight (center column
Fig 4B). The effects of miglitol on total energy intake as a percent of control
are depicted in the far right panel of Figure 4B, and indicate that net energy
intake over the 8 weeks of study was decreased by an average of 14%, qualitatively
similar to the reduction in WAT mass. The effects of miglitol on hepatic
glycemic and lipogenic enzymes after 8 weeks of study are depicted in (Figure 5).
The effects of miglitol on glucokinase are shown in the left panel and indicate
that miglitol resulted in a significant decrease in glucokinase enzyme
activity, consistent with the significant improvements in AUCglucose,
AUCinsulin and HbA1c.The effects of miglitol on the lipogenic enzymes Malic
Enzyme and Glucose-6-phosphate Dehydrogenase are depicted in the central and
right panels, respectively, and indicate that the capacity for generation of
NADPH, essential for de novo fatty acid biosynthesis, was also decreased
following 8 weeks of miglitol treatment.
The effects of this study indicate that a nominal
dosage of miglitol as a dietary admixture resulted in significant decreases in
both glycemic and lipogenic enzyme parameters in the SHR/Ntul//-cp rat, a
genetic rodent model of early onset obesity, insulin resistance, and T2DM.38
The animals were fed a nutritionally complete USDA-formulated moderate
carbohydrate, sucrose-enriched diet, while a subgroup received the same diet
regimen but containing an admixture of 0.015% generic miglitol, with both diets
ad libitum. The macronutrient distribution of the semisynthetic diet fed is
similar to that which a large segment of the population consumes in much of
industrialized society. Miglitol was associated with a modest decrease in daily
and cumulative energy intake, and which decreases may have contributed to the
improvements in glycemic and lipogenic enzyme activity noted. The effects of
the miglitol dietary admixture were of similar magnitude to those reportd in
other studies of ?-glucosidase inhibition on dietary intakes reported elsewhere
[22,39,40]. The onset of glycosuria, indicative of T2DM typically occurs by 6
to 8 weeks of age in the obese phenotype of this strain, regardless of the
dietary composition consumed, and progresses to severe levels of glycosuria by
10 weeks of age. Once glycosuria is observed, it typically remains present
thereafter throughout the remainder of their lifespan unless therapeutic
intervention is initiated. Typical lifespan among obese T2DM in this strain is
decreased by 30% or more compared to congenic lean littermates or to
non-diabetic LA/Ntul//-cp rats that carry the same trait for obesity but in a
genetically non-diabetic background [20,41]. The biologic basis for the
decreased adiposity following miglitol treatment in the present study is
proposed to be secondary to cumulative decreases in plasma insulin responses
and improved insulin sensitivity, in addition to decreases in net energy intake
when consuming the miglitol supplemented, sucrose-enriched diet. The luminal
uptake and post ingestion plasma glucose concentrations following an orally
administered glucose challenge in fasted animals would not be expected to occur
differently in animals previously fed the glucosidase inhibitor or not in the
absence of improved insulin sensitivity since the luminal glucose uptake would
not be expected to become compromised by a glucosidase inhibitor. However, the
cumulative effect of the glucosidase inhibitor over time would be expected to
decrease insulin demand due to the miglitol induced delay in enzymatic
digestion of sucrose to its monosaccharide moieties glucose and fructose and
their subsequent luminal absorption as glucose and fructose. The decreased rate
of sugar moieties for absorption would be predicted to decrease insulin
requirements and gradually improve peripheral glucose uptake and insulinogenic
responses secondary to decreasing the magnitude of insulin resistance while
improving insulin sensitivity in peripheral tissues including the liver and
adipose tissue depots. Whether the improved insulin sensitivity occurred via
improvement in insulin-mediated GLUT4- glucose transporter activity or some
other insulin-linked physiologic factors could not be determined, but
regardless of the biophysiologic mechanism, the genomic expression and activity
of key regulatory hepatic enzymes of glycemic and lipogenic mechanisms as
demonstrated.20 The significant, down-regulated improvement in those enzymes
likely contributed at least in part to the modest trend toward a decrease in
the progression of glycogenesis, adiposity and systemic clearance of a glucose
challenge via decreases in a primary enzyme of glycogen deposition in addition
to impacting two key enzymes linked to de novo lipogenesis. Malic enzyme and
G6PD provide NADPH+, an essential cofactor for de novo lipid biosynthesis in
especially in liver and adipose tissue, while hepatic glucokinase serves as a
signal for the release of insulin from ?-cells, and with secondary effects on
glycogen formation and deposition [19,36,42].
In other studies, it was noted that miglitol and other
inhibitors of luminal starch digestion were associated with modest decreases in
dietary energy intake of a magnitude that was similar to the present study and
likely also contributed to the induced secondary satiety factors linked to
delayed intestinal digestive actions [39,40]. Since miglitol-linked brush
border actions would require additional time for the ingested meal to undergo
duodenal digestion followed by intestinal distention and further luminal
transit of the remaining digestive contents, the combined impact would be
predicted to reduce the overall quantity of caloric intake, in a manner
analogous to voluntary or programmed reductions in meal size, appetite and
energy density of the diet. Regardless of the physiological mechanism or mechanisms
impacted, the effects of the miglitol resulted in an attenuation in voluntary
daily energy intake resulted in modestly improved glycemic and lipogenic enzyme
activity. The effects of the glucosidase inhibitor on glycosuria, however, were
much more profound, thereby preserving the majority of the ingested
carbohydrate for metabolic processes. Despite the significant loss of
carbohydrate calories in the control animals, they still demonstrated a greater
propensity for regional fat accretion, despite of an equivalent of a daily loss
of over 1.7 kcals/day in excreted glucose assuming the caloric metabolic
equivalent of 4 kcals/gram for glucose, and which represents a total
conservation of approximately 100 kcals and over 10 grams of accumulated lipid
during the course of the miglitol treatment in the present study. In addition,
improvement in insulin actions responded differentially in an adipose tissue
depot-specific manner, consistent with the observations reported elsewhere
[40,41]. Although not specifically identified in the current study, the
miglitol-induced decreases in daily energy intake in association with reported
alterations in regional fat deposition would be consistent with a decreased
magnitude of systemic inflammation over time, including a potential decrease in
M1-macrophage iROS generation, a shift toward antiinflammatory M2-macrophages,
and in a progressive transition toward a more healthful plasma lipid profile in
obesity,T2DM and hyperinsulinemic states and their typical pathophysiologic
sequela. Effective therapeutic options for the management of the above
disorders impacts a lifelong attention. However, when doable pharmacologic
measures such as those that may occur following miglitol administration are
effectively incorporated into the potentially additive factors of diet and
lifestyle, the clinical outcomes can become the real winners in an otherwise
compromising metabolic state, should the progression of comorbidities remain
unchecked [2,14,15,43,44]. Thus, in future studies, it would be productive to
continue the luminal therapeutic options beyond the post-adolescent lifestage
of the present investigation to more fully determine the long term potential of
the physiological benefits of luminal ?-glucosidase inhibition health and longevity
in an animal model predisposed to early onset obesity, insulin resistance and
T2DM.
The effects of a modest dosage of miglitol resulted in favorable responses in the activity of key glycemic and lipogenic enzymes, in association with modest decreases in energy intake and body fat accretion in some but not all adipose tissue depots. In other studies, miglitol was found to decrease daily food and energy intake, which may also have been a contributing factor to the favorable responses in the insulin-linked enzymes in the instant study.
Acknowledgements
The author is grateful for the Institutional resources of USAT Montserrat to develop this manuscript, and to the Carbohydrate Nutrition Research Laboratory at the US Dept of Agriculture, Beltsville, Maryland USA for assistance in diet preparation.
Use of Artificial Intelligence (AI)
No applications of AI were utilized in the preparation
of this manuscript.