Initial body weights, as intended, as well as final body weights and feed intake of rats, were similar among treatments (P > 0.05; Table 1). Similar to the results of the present work, unchanged final body weights of rats fed a diet supplemented with 6 mg biotin/kg of diet [23] and mice fed a diet supplemented with 97.70 mg of free biotin/kg diet [30, 31] has been reported.
Table 1
Effects of biotin supplementation on live weight changes and serum metabolites
Items
|
Treatments*
|
-- P --
|
B 0
|
B 1
|
B 100
|
MgB 0
|
MgB 1
|
MgB 100
|
Initial Body Weight, g
|
248.43 ± 4.42
|
251.43 ± 4.83
|
246.71 ± 3.43
|
252.29 ± 2.29
|
249.86 ± 5.91
|
251.29 ± 4.51
|
0.946
|
Final Body Weight, g
|
295.43 ± 4.87
|
298.57 ± 4.70
|
294.00 ± 5.57
|
296.29 ± 5.73
|
297.43 ± 5.01
|
299.29 ± 4.27
|
0.977
|
Feed Intake, g
|
24.00 ± 0.65
|
24.86 ± 0.59
|
24.43 ± 1.07
|
24.71 ± 0.87
|
24.14 ± 0.55
|
24.43 ± 0.57
|
0.963
|
Glucose, mg/dL
|
89.00 ± 2.44
|
89.29 ± 2.74
|
91.71 ± 2.35
|
90.71 ± 3.11
|
83.57 ± 3.92
|
87.43 ± 3.18
|
0.480
|
Insulin, mIU/L
|
14.10 ± 0.92
|
16.13 ± 0.71
|
15.96 ± 1.10
|
14.77 ± 1.67
|
17.33 ± 1.04
|
15.67 ± 1.05
|
0.428
|
ALT, U/L
|
82.29 ± 1.60
|
81.14 ± 4.66
|
85.57 ± 2.44
|
83.43 ± 3.27
|
82.71 ± 2.95
|
81.43 ± 2.96
|
0.928
|
AST, U/L
|
126.29 ± 6.23
|
121.86 ± 5.80
|
123.57 ± 10.39
|
121.86 ± 11.92
|
122.00 ± 10.40
|
118.14 ± 6.05
|
0.993
|
Creatine, mg/dL
|
0.47 ± 0.06
|
0.41 ± 0.08
|
0.43 ± 0.06
|
0.44 ± 0.04
|
0.44 ± 0.11
|
0.40 ± 0.05
|
0.987
|
Urea, mg/dL
|
23.87 ± 2.04
|
22.44 ± 2.23
|
23.09 ± 0.99
|
22.80 ± 1.83
|
23.27 ± 2.22
|
24.16 ± 1.73
|
0.988
|
Total cholesterol, mg/dL
|
73.00 ± 1.81a
|
64.57 ± 1.86b
|
64.00 ± 1.98b
|
74.00 ± 2.56a
|
54.29 ± 1.66c
|
60.86 ± 1.87bc
|
0.0001
|
Triglyceride, mg/dL
|
68.00 ± 2.46a
|
59.29 ± 4.86ab
|
60.29 ± 1.54ab
|
66.00 ± 3.18a
|
45.14 ± 2.52c
|
48.14 ± 1.91bc
|
0.0001
|
* Dietary treatments contained biotin supplements as either commercial biotin (d-biotin) at 0.01 (B0), 1 (B1) and 100 (B100) mg/kg body weight or a new form of biotin (magnesium biotinate) at 0.01 (MgB0), 1 (MgB1), and 100 (MgB100) mg/kg body weight. The doses used at 0.01, 1, and 100 mg of biotin supplementations from each source represented standard dietary dose (control), high dietary dose, and pharmacologic dose, respectively. Statistical comparisons are indicated with different superscript (a-c) in the same row (P < 0.05; ANOVA and Tukey's post-hoc test). Mean values are demonstrated with ± standard deviations. ALT: Alanine aminotransferase; AST: Aspartate aminotransferase.
|
In the present study, neither form of biotin influenced (P > 0.05) serum glucose or insulin concentrations. Although decreases in serum glucose concentrations in rats fed a diet supplemented with biotin have been reported [23], Lazo de la Vega-Monroy et al. [30] found increases in elevated glucose-stimulated serum insulin concentrations, but no changes in fasting glucose concentrations or insulin tolerance in mice fed a diet supplemented with biotin. Enhanced fasting serum glucose levels have been observed with biotin supplementation in individuals with Type 2 diabetes who had low serum biotin concentrations before supplementation [21]. However, biotin administration (6.14 µmol/d) for 28 days to individuals with Type 2 diabetes did not change concentrations of glucose, insulin, triacylglycerol, or cholesterol [32]. Inconsistent results from the present work and the literature in experimental animals and individuals with Type 2 diabetes [21, 23, 30, 32] could have been due to differences in biotin doses, duration of supplementation, or the severity of diabetes, among others.
Biotin supplementation has been shown to increase glucose-stimulated insulin secretion in rats [33] and mice [30] via affecting morphology and the number of cells in the pancreas. Tixi-Verdugo et al. [34] found that mice fed a diet supplemented with 100 mg of biotin/kg diet had greater beta-cell proportions (%) and an elevated number of islets per pancreatic area. Biotin is known to improve glycemic control through stimulating pancreatic and hepatic glucokinases while inhibiting the hepatic gluconeogenic enzyme phosphoenolpyruvate carboxykinase [35]. Glucose is considered the major lipogenic substrate for most tumor cells, which have greater lipid synthesis and requirement for amino acids [36]. Therefore, supplementing biotin can be indirectly involved in the prevention and therapy of cancer, diabetes, obesity, and other diseases.
Serum ALT and AST enzyme activities, as well as concentrations of creatine and urea, remained similar among treatments (P > 0.05). Similarly, [31] found no changes in the ALT activity of urea concentrations but greater AST enzyme activities in biotin-supplemented mice (97.70 mg of free biotin/kg diet). Although greater AST enzyme activity was found in the biotin-supplemented group, the values were within the normal range (55.0-352 U/L). Results from the present work and the literature [31] indicate that neither pharmacological doses of commercial d-biotin or magnesium biotinate influence indicators of liver damage.
Serum total cholesterol and triglyceride concentrations in the rats decreased with biotin supplementation from both sources (P < 0.05). However, supplementing with magnesium biotinate provided greater decreases in blood lipid concentrations, particularly with the 1 mg/kg dose (P < 0.05), compared to commercial biotin. In accordance with the results of the present work, Turgut et al. [23] also reported decreases in serum concentrations of cholesterol and triglyceride in rats fed a diet supplemented with 6 mg/kg biotin. Larrieta et al. [5] also found reduced serum triglyceride concentrations in mice fed a diet supplemented with 97.7 mg of free biotin/kg diet. Similarly, plasma concentrations of triacylglycerol and VLDL-cholesterol were reported to decrease in biotin-supplemented (61.4 µmol/day) individuals with Type 2 diabetes [4].
As expected, biotin supplementation with both forms resulted in increases in serum, liver, and brain biotin concentrations (P < 0.05, Table 2). However, biotin concentrations of the blood and the organs were greater with magnesium biotinate compared with the same doses of commercial d-biotin, particularly in the 1 and 100 mg/kg BW groups (P < 0.05). Similarly, elevated serum biotin concentrations were also reported in a previous study where mice were fed a diet supplemented with biotin [30].
Table 2
Effects of biotin supplementation on biotin and liver cGMP contents
Items
|
Treatments*
|
-- P --
|
B 0
|
B 1
|
B 100
|
MgB 0
|
MgB 1
|
MgB 100
|
Serum biotin, nmol/L
|
23.65 ± 2.60c
|
136.67 ± 2.73c
|
3517.14 ± 87.93b
|
23.41 ± 2.31c
|
171.13 ± 3.02c
|
5161.43 ± 250.96a
|
0.0001
|
Liver biotin, nmol/g
|
0.02 ± 0.01e
|
0.56 ± 0.04d
|
1.38 ± 0.02b
|
0.03 ± 0.01e
|
0.71 ± 0.03c
|
1.62 ± 0.02a
|
0.0001
|
Brain biotin, nmol/g
|
0.14 ± 0.01e
|
0.42 ± 0.05d
|
1.37 ± 0.04b
|
0.14 ± 0.01e
|
0.66 ± 0.04c
|
1.65 ± 0.03a
|
0.0001
|
Liver cGMP, pmol/mg protein
|
8.46 ± 0.26d
|
12.01 ± 0.26c
|
14.68 ± 0.32b
|
8.60 ± 0.28d
|
13.04 ± 0.98bc
|
17.07 ± 0.28a
|
0.0001
|
*Dietary treatments contained biotin supplements as either commercial biotin (d-biotin) at 0.01 (B0), 1 (B1) and 100 (B100) mg/kg body weight or a new form of biotin (magnesium biotinate) at 0.01 (MgB0), 1 (MgB1), and 100 (MgB100) mg/kg body weight. The doses used at 0.01, 1, and 100 mg of biotin supplementations from each source represented standard dietary dose (control), high dietary dose, and pharmacologic dose, respectively. Statistical comparisons are indicated with different superscript (a-e) in the same row (P < 0.05; ANOVA and Tukey's post-hoc test). Mean values are demonstrated with ± standard deviations.
|
Cyclic guanosine monophosphate (cGMP) functions as anti-apoptotic and anti-inflammatory in cells and regulates multiple physiologic processes in the cardiovascular system [37]. Biotin supplementation to the diet of mice has been shown to decrease blood triglyceride concentrations through increased cGMP content [6, 9]. Comparable to the results reported by other researchers [6, 9], liver cGMP contents of animals in the present work also increased with biotin supplementation. However, liver cGMP contents were higher in rats supplemented with magnesium biotinate compared with the same doses of commercial d-biotin, particularly when comparing the 100 mg/kg BW groups (P < 0.05). Cyclic guanosine monophosphate has also been proposed to have a substantial effect on beta-cell functions [38]. In the present study, although cGMP contents of the liver increased with biotin supplementation, neither serum glucose nor insulin concentrations were significantly altered.
Biotin is thought to reduce levels of blood lipids (hypotriglyceridemia) and glucose (hypoglycemia) through regulation of the mRNA abundance of lipogenic enzymes and transcription factors such as SREBP-1c, FAS, ACC, and pyruvate kinase, among others [39]. One of the main objectives of the present work was to detail the effects of biotin on such factors to determine the mechanism by which biotin, particularly the new form of biotin, works. Liver SREBP‐1c and FAS levels decreased while the level of AMPK-alpha increased with both biotin forms (P < 0.05; Fig. 1). The magnitudes of responses were more emphasized with magnesium biotinate, particularly when comparing the 1 mg/kg dose groups for SREBP‐1c and the 100 mg/kg dose groups for FAS and AMPK-alpha (P < 0.05). Liver ACC-1, ACC-2, PCC, and MCC levels increased (P < 0.05; Fig. 2) with both biotin forms. This effect was more apparent with magnesium biotinate when compared to similar doses of commercial d-biotin (P < 0.05). The liver PC level increased with biotin supplementation, with no differences found from dose or biotin form (P > 0.05).
The functions of SREBP-1c involve activating several enzymes including FAS and ACC in catalyzing various steps in fatty acid and TG synthesis pathways [40]. Therefore, decreases in both SREBP‐1c and FAS were consistent with reduced serum lipid concentrations of total cholesterol and triglycerides seen in the present work. Over-nutrition or intake of energy-dense molecules (sugar and saturated fatty acids) results in an increase in SREBP-1c expression and consequently lipogenesis in the liver [41]. Through regulation of energy metabolism, biotin supplementation, particularly magnesium biotinate, can reduce SREBP-1c levels and consequently reduce serum lipid concentrations.
Low cellular energy causes activation of AMPK which inactivates both ACC isoforms, ACC-1, and ACC-2, resulting in reduced de novo lipogenesis and increased fatty acid oxidation [42]. Similarly, biotin supplementation in mice and rats has been reported to increase the active form of AMPK, which phosphorylates ACC-1 and ACC-2, resulting in decreases in the rate of lipid synthesis and increases in fatty acid oxidation rates [43, 44]. Biotin supplementation in mice has also been shown to increase the level of the active form of AMPK and decrease FAS and SREBP-1c levels [6, 44]. Moreno-Méndez et al. [44] found that ACC-1 and FAS reduced the acetate incorporations into total lipid fractions in response to biotin supplementation, resulting in lower fatty acid synthesis in mice adipose tissues.
While ACC is related to fatty acid metabolism via generating malonyl-CoA for fatty acid synthesis, MCC is involved in leucine catabolism, and PC and PCC are anaplerotic, meaning they form intermediates of a metabolic pathway such as the TCA cycle [45]. Therefore, changing activities of these enzymes influence not only lipid but also carbohydrate and protein metabolism. However, in the present study, only lipid parameters were influenced by altered levels of carboxylases, namely ACC, PC, PCC, and MCC.
In the present study, the magnitude of the responses was more emphasized (greater) with magnesium biotinate compared with commercial d-biotin. This effect could be attributed to the fact that magnesium biotinate is a bioavailable form of biotin and is 40 times more soluble than d-Biotin and is more significantly absorbed into the blood and tissues in rats [46]. This idea is supported by evidence from a clinical study that showed that healthy female subjects orally supplemented with 10, 40, or 100 mg of magnesium biotinate had dose-dependent increases of biotin levels in the blood with no adverse effects [46].