Introduction
As previously reviewed (1), the induction of metabolic syndrome in
rats by a fructose-rich diet has been, over recent years, the
subject of several extensive investigations (2–10).
The present study is founded on an extensive investigation of the
post-mortem findings collected from rats exposed for 8 weeks to
diets containing 64% starch and 5% sunflower oil (Ssun rats) or
containing 64% D-fructose mixed with 5% sunflower oil (Fsun rats),
3.4% sunflower oil and 1.6% salmon oil (Fsal rats) or 3.4%
sunflower oil and 1.6% safflower oil (Fsaf rats) (8–10).
The major aim of the present study was to explore the possible
correlation, at the individual level, between the percentage of
glycated hemoglobin, considered as indicative of glucose
homeostasis, and 55 other variables measured in plasma, liver,
heart, kidney, soleus muscle or visceral adipose tissue. For each
of these variables, individual data were collected from 20–23
animals.
Materials and methods
Biological variable analysis
The methods used to measure glycated hemoglobin
(5), plasma albumin, urea,
creatinine, calcium, iron, phospholipid, triglyceride and
HDL-cholesterol (8), hepatic
glucokinase activity and liver cholesterol, triglyceride and
phospholipid content (8), systolic
arterial blood pressure (9),
plasma leptin concentration (9),
kidney proliferating cell nuclear antigen index (9), liver, heart, kidney, soleus muscle or
visceral adipose tissue glutathione reductase, superoxide dismutase
and catalase activity (9), plasma,
liver heart, kidney, soleus muscle or visceral adipose tissue
thiobarbituric acid reactive substances, carbonyl derivatives,
hydroperoxides and nitric acid content (10) were previously described in the
references cited. This study was approved by the ethics committee
of the Université Libre de Bruxelles.
Correlation analysis
In the correlation data, the xy values refer to the
product of the differences, at the individual level and for the two
variables under consideration, between the recorded individual
measurement and the corresponding mean value. The correlation
analysis was performed by W.J. Malaisse, one of the authors of the
present article, without the use of any software.
Results
Correlation between glycated hemoglobin
and selected plasma variables
The percentage of glycated hemoglobin was considered
to be indicative of glucose homeostasis. Table I presents the results of a
correlation analysis between glycated hemoglobin and nine plasma
variables. Significant positive correlations were found between
glycated hemoglobin and plasma albumin, urea, creatinine,
phospholipids, triglycerides and total cholesterol concentrations,
whilst negative correlations were found between glycated hemoglobin
and plasma calcium, iron and HDL-cholesterol concentrations. In
several cases with positive correlations, no negative xy product
(two cases), or only two negative xy products (two cases) were
recorded among the 23 xy products.
 | Table ICorrelation between glycated
hemoglobin percentage and selected plasma variables. |
Table I
Correlation between glycated
hemoglobin percentage and selected plasma variables.
| Variable | Correlation |
|---|
| Albumin | +0.9111
(P<0.001) |
| Urea | +0.7378
(P<0.001) |
| Creatinine | +0.8360
(P<0.001) |
| Calcium | −0.4709
(P<0.03) |
| Iron | −0.5008
(P<0.02) |
| Phospholipids | +0.8680
(P<0.001) |
| Triglycerides | +0.9125
(P<0.001) |
| Total
cholesterol | +0.7837
(P<0.001) |
| HDL-cholesterol | −0.5431
(P<0.009) |
Correlation between glycated hemoglobin
and selected liver variables
The results from the correlation analysis between
glycated hemoglobin percentage and selected liver variables are
presented in Table II. No
significant correlation was observed between the percentage of
glycated hemoglobin and hepatic glucokinase activity. However, a
significant positive correlation was observed between glycated
hemoglobin and liver cholesterol, triglyceride and phospholipid
content, with either no negative xy product (two cases) or only one
negative xy product (one case).
| Table IICorrelation between glycated
hemoglobin percentage and selected liver variables. |
Table II
Correlation between glycated
hemoglobin percentage and selected liver variables.
| Variable | Correlation |
|---|
| Glucokinase
activity | −0.0781
(P>0.1)a |
| Cholesterol
content | +0.9310
(P<0.001) |
| Triglyceride
content | +0.9962
(P<0.001) |
| Phospholipid
content | +0.9818
(P<0.001) |
Correlation between glycated hemoglobin
and blood pressure, leptin and kidney proliferating cell nuclear
antigen index
A significant positive correlation (r=+0.9127; n=23;
P<0.001) was observed between the percentage of glycated
hemoglobin and the incremental area under the curve associated with
changes in systolic arterial blood pressure as a function of time
over a period of 56 days. Similarly, a highly significant positive
correlation was found between glycated hemoglobin and plasma leptin
concentration (r=+0.9890; n=23; P<0.001), without a negative xy
product. The correlation coefficient between glycated hemoglobin
and the kidney proliferating cell nuclear antigen index was +0.5589
(n=23), yielding P<0.008.
Correlation between glycated hemoglobin
and selected enzymatic activities
As shown in Table
III, no significant correlation was identified between glycated
hemoglobin percentage and the activity of glutathione reductase in
the liver, heart, kidney, soleus muscle or visceral adipose tissue.
With the exception of the adipose tissue, there was a trend towards
a negative correlation. However, even when the enzymatic
measurements obtained from the liver, heart and kidney were
expressed relative to the mean corresponding value recorded in Ssun
rats, the correlation coefficient between the normalized values and
those concerning glycated hemoglobin were not statistically
significant (r=−0.2148; n=69; P<0.08).
| Table IIICorrelation between glycated
hemoglobin percentage and selected enzymatic activities. |
Table III
Correlation between glycated
hemoglobin percentage and selected enzymatic activities.
| Organ | Glutathione
reductase | Superoxide
dismutase | Catalase |
|---|
| Liver | −0.2094
(P>0.1) | −0.8067
(P<0.001) | −0.4869
(P<0.03) |
| Heart | −0.1799
(P>0.1) | −0.9169
(P<0.001) | −0.4809
(P<0.03) |
| Kidney | −0.3768
(P<0.08) | −0.7388
(P<0.001) | −0.4282
(P<0.05) |
| Soleus muscle | −0.1428
(P>0.1)a | −0.9115
(P<0.001) | −0.4546
(P<0.04) |
| Adipose tissue | +0.2449
(P>0.1) | −0.9405
(P<0.001) | −0.5616
(P<0.008) |
By contrast, highly significant negative
correlations (P<0.001) were identified in all five organs
between the percentage of glycated hemoglobin and the activity of
superoxide dismutase (Table
III). Significant negative correlations (P<0.05 or less)
were also observed in these five organs between the individual
values for glycated hemoglobin percentage and catalase activity
(Table III).
Correlation between glycated hemoglobin
and selected metabolites
Positive correlations were observed between the
content of thiobarbituric acid reactive substances (TBARS),
carbonyl derivatives and hydroperoxides in the plasma, liver,
heart, kidney, soleus muscle and visceral adipose tissue, on one
hand, and glycated hemoglobin, on the other, such positive
correlations only failing to achieve statistical significance in
two out of eighteen comparisons (Table IV). Likewise, with the exception
of the soleus muscle, highly significant negative correlations
(P<0.001) were observed between glycated hemoglobin percentage
and the nitric oxide (NO) content of plasma, liver, heart, kidney
or visceral adipose tissue (Table
IV).
| Table IVCorrelation between glycated
hemoglobin percentage and selected metabolites. |
Table IV
Correlation between glycated
hemoglobin percentage and selected metabolites.
| Organ | TBARS | Carbonyls | Hydroperoxides | NO |
|---|
| Plasma | +0.9451
(P<0.001) | +0.6655
(P<0.001) | +0.8774
(P<0.001) | −0.9047
(P<0.001) |
| Liver | +0.7318
(P<0.001) | +0.7765
(P<0.001) | +0.6555
(P<0.001) | −0.6648
(P<0.001) |
| Heart | +0.6550
(P<0.001) | +0.6259
(P<0.003) | +0.7042
(P<0.001)a | −0.7585
(P<0.001) |
| Kidney | +0.7136
(P<0.001) | +0.3828
(P<0.08) | +0.4899
(P<0.03) | −0.8589
(P<0.001) |
| Soleus muscle | +0.7619
(P<0.001) | +0.5864
(P<0.006) | +0.8287
(P<0.001) | +0.4761
(P<0.03) |
| Adipose tissue | +0.8343
(P<0.001) | +0.4820
(P<0.03) | +0.3220
(P>0.1) | −0.8369
(P<0.001) |
Discussion
Only two variables failed to display a significant
correlation with the percentage of glycated hemoglobin. One of
these was liver glucokinase activity. The only difference between
the four groups of rats with regard to liver glucokinase activity
was that higher activity was observed in the Fsal rats compared
with the Ssun, Fsun or Fsaf rats (8). Therefore, it is hypothesized that
this difference may be attributed to the greater supply of
long-chain ω3 fatty acids in the diet of the Fsal rats compared
with that in the diets of the other three groups of rats (8). In addition, no significant
correlations were observed between glycated hemoglobin percentage
and the enzyme activity of glutathione reductase in the liver,
heart, kidney, soleus muscle and visceral adipose tissue. In these
organs, the trend was towards a negative correlation.
A positive correlation with glycated hemoglobin
percentage was observed for the plasma albumin concentration. Since
an opposite situation could speculatively be expected from either
liver dysfunction or renal albuminuria in the rats with severe
metabolic syndrome, this positive correlation may reflect a modest
degree of hemoconcentration in these rats. The positive
correlations observed for glycated hemoglobin percentage with
plasma urea and creatinine may reflect incipient nephropathy
(8).
In terms of the cause-and-effect relationship, the
negative correlations observed for glycated hemoglobin percentage
with plasma calcium or iron concentrations remain unclear. They
may, as discussed previously (8),
be attributed to impaired gastrointestinal absorption of these
metals.
The correlation between the percentage of glycated
hemoglobin and the plasma concentration or liver content of
cholesterol, triglycerides and phospholipids invariably yielded
significant positive correlations, whereas a negative correlation
was observed in the case of plasma HDL-cholesterol. These results
demonstrate the tight correlation between perturbations of glucose
homeostasis and the plasma concentrations or liver content of
distinct types of lipids.
Furthermore, although glutathione reductase activity
had no correlation with glycated hemoglobin concentration, the
activity of superoxide dismutase or catalase in liver, heart,
kidney, soleus muscle and visceral adipose tissue, as well as the
plasma concentration or tissue content of TBARS, carbonyl
derivatives and hydroperoxides were all correlated with the
measurements of glycated hemoglobin, with only one clear exception
(P>0.1) out of 28 comparisons. The negative correlations found
for superoxide dismutase and catalase coincided with positive
correlations in the case of variables indicative of oxidative
stress, including the accumulation of TBARS, carbonyl derivatives
and hydroperoxides.
Furthermore, the NO content of plasma, liver, heart,
kidney or adipose tissue, but not that of soleus muscle, was
negatively correlated with the glycated hemoglobin percentage.
In conclusion, without prejudging the
cause-and-effect link between distinct variables, the present study
documents the tight coordination in the metabolic, enzymatic and
functional response to changes in the dietary supply of long-chain
polyunsaturated ω3 and ω6 fatty acids to rats displaying a
fructose-induced metabolic syndrome. All the correlations between
the 55 variables under consideration were calculated by reference
to the measurements of glycated hemoglobin. Hence, the latter
measurements appear as most appropriate to judge the severity of
biochemical and biophysical alterations in this animal model of the
metabolic syndrome.
References
|
1
|
Boukortt FO, Madani Z, Mellouk Z, Louchami
K, Sener A and Ait Yahia D: Nutritional factors and
fructose-induced metabolic syndrome. Metab Funct Res Diab. 4:18–34.
2011.
|
|
2
|
Cancelas J, Prieto PG,
Villanueva-Peñacarrillo ML, Zhang Y, Portois L, Sener A, Carpentier
YA, Valverde I and Malaisse WJ: Glucose intolerance associated to
insulin resistance and increased insulin secretion in rats depleted
in long-chain polyunsaturated ω3 fatty acids. Horm Metab Res.
39:823–825. 2007.PubMed/NCBI
|
|
3
|
Prieto PG, Cancelas J, Moreno P,
Villanueva-Peñacarrillo ML, Malaisse WJ and Valverde I: Effect of
diet supplementation with olive oil and guar upon fructose-induced
insulin resistance in normal rats. Endocrine. 31:294–299. 2007.
View Article : Google Scholar : PubMed/NCBI
|
|
4
|
Mellouk Z, Hachimi Idrissi T, Louchami K,
Hupkens E, Malaisse WJ, Ait Yahia D and Sener A: The metabolic
syndrome of fructose-fed rats: Effects of long-chain
polyunsaturated ω3 and ω6 fatty acids. I Intraperitoneal glucose
tolerance test. Int J Mol Med. 28:1087–1092. 2011.
|
|
5
|
Mellouk Z, Hachimi Idrissi T, Louchami K,
Hupkens E, Sener A, Ait Yahia D and Malaisse WJ: The metabolic
syndrome of fructose-fed rats: Effects of long-chain
polyunsaturated ω3 and ω6 fatty acids. II Time course of changes in
food intake, body weight, plasma glucose and insulin concentrations
and insulin resistance. Int J Mol Med. 29:113–118. 2012.
|
|
6
|
Mellouk Z, Zhang Y, Bulur N, Louchami K,
Malaisse WJ, Ait Yahia D and Sener A: The metabolic syndrome of
fructose-fed rats: Effects of long-chain polyunsaturated ω3 and ω6
fatty acids. III Secretory behaviour of isolated pancreatic islets.
Int J Mol Med. 29:285–290. 2012.
|
|
7
|
Mellouk Z, Zhang Y, Bulur N, Louchami K,
Malaisse WJ, Ait Yahia D and Sener A: The metabolic syndrome of
fructose-fed rats: Effects of long-chain polyunsaturated ω3 and ω6
fatty acids. III Secretory behaviour of isolated pancreatic islets.
Int J Mol Med. 29:285–290. 2012.
|
|
8
|
Mellouk Z, Louchami K, Hupkens E, Sener A,
Ait Yahia D and Malaisse WJ: The metabolic syndrome of fructose-fed
rats: effects of long-chain polyunsaturated ω3 and ω6 fatty acids.
V Post-mortem findings. Mol Med Reports. 6:1399–1403. 2012.
|
|
9
|
Mellouk Z, Hupkens E, Antoine M-H, Sener
A, Ait Yahia D and Malaisse WJ: The metabolic syndrome of
fructose-fed rats: Effects of long-chain polyunsaturated ω3 and ω6
fatty acids. VI Further post-mortem investigations. Mol Med
Reports. 6:1404–1408. 2012.
|
|
10
|
Mellouk Z, Sener A, Ait Yahia D and
Malaisse WJ: The metabolic syndrome of fructose-fed rats: Effects
of long-chain polyunsaturated ω3 and ω6 fatty acids. VII Oxidative
stress. Mol Med Reports. 6:1409–1412. 2012.
|
