A Combination of Nutriments Improves Mitochondrial Biogenesis and Function in Skeletal Muscle of Type 2 Diabetic Goto–Kakizaki Rats

BACKGROUND: Recent evidence indicates that insulin resistance in skeletal muscle may be related to reduce mitochondrial number and oxidation capacity. However, it is not known whether increasing mitochondrial number and function improves insulin resistance. In the present study, we investigated the effects of a combination of nutrients on insulin resistance and mitochondrial biogenesis/function in skeletal muscle of type 2 diabetic Goto-Kakizaki rats. METHODOLOGY/PRINCIPAL FINDINGS: We demonstrated that defect of glucose and lipid metabolism is associated with low mitochondrial content and reduced mitochondrial enzyme activity in skeletal muscle of the diabetic Goto-Kakizaki rats. The treatment of combination of R-alpha-lipoic acid, acetyl-L-carnitine, nicotinamide, and biotin effectively improved glucose tolerance, decreased the basal insulin secretion and the level of circulating free fatty acid (FFA), and prevented the reduction of mitochondrial biogenesis in skeletal muscle. The nutrients treatment also significantly increased mRNA levels of genes involved in lipid metabolism, including peroxisome proliferator-activated receptor-alpha (Ppar alpha), peroxisome proliferator-activated receptor-delta (Ppar delta), and carnitine palmitoyl transferase-1 (Mcpt-1) and activity of mitochondrial complex I and II in skeletal muscle. All of these effects of mitochondrial nutrients are comparable to that of the antidiabetic drug, pioglitazone. In addition, the treatment with nutrients, unlike pioglitazone, did not cause body weight gain. CONCLUSIONS/SIGNIFICANCE: These data suggest that a combination of mitochondrial targeting nutrients may improve skeletal mitochondrial dysfunction and exert hypoglycemic effects, without causing weight gain

A Combination of Nutriments Improves Mitochondrial Biogenesis and Function in Skeletal Muscle of Type 2 Diabetic Goto-Kakizaki Rats

BackgroundRecent evidence indicates that insulin resistance in skeletal muscle may be related to reduce mitochondrial number and oxidation capacity. However, it is not known whether increasing mitochondrial number and function improves insulin resistance. In the present study, we investigated the effects of a combination of nutrients on insulin resistance and mitochondrial biogenesis/function in skeletal muscle of type 2 diabetic Goto–Kakizaki rats.Methodology/Principal FindingsWe demonstrated that defect of glucose and lipid metabolism is associated with low mitochondrial content and reduced mitochondrial enzyme activity in skeletal muscle of the diabetic Goto-Kakizaki rats. The treatment of combination of R-α-lipoic acid, acetyl-L-carnitine, nicotinamide, and biotin effectively improved glucose tolerance, decreased the basal insulin secretion and the level of circulating free fatty acid (FFA), and prevented the reduction of mitochondrial biogenesis in skeletal muscle. The nutrients treatment also significantly increased mRNA levels of genes involved in lipid metabolism, including peroxisome proliferator–activated receptor-α (Pparα), peroxisome proliferator–activated receptor-δ (Pparδ), and carnitine palmitoyl transferase-1 (Mcpt-1) and activity of mitochondrial complex I and II in skeletal muscle. All of these effects of mitochondrial nutrients are comparable to that of the antidiabetic drug, pioglitazone. In addition, the treatment with nutrients, unlike pioglitazone, did not cause body weight gain.Conclusions/SignificanceThese data suggest that a combination of mitochondrial targeting nutrients may improve skeletal mitochondrial dysfunction and exert hypoglycemic effects, without causing weight gain

Effect of mitochondrial nutriments on expression of Pparα, Pparδ and Mcpt-1.

<p>Total RNA was isolated from soleus muscle. <i>Ppara, Pparδ</i> and <i>Mcpt-1</i> mRNA were analyzed by means of quantitative RT-PCR with gene-specific oligonucleotide probes in muscle. The cycle number at which the various transcripts were detectable was compared to that of nuclear 18S rRNA as an internal control, and expressed as arbitrary units versus values in Wistar control taken 100. All values are mean±SEM of 12 animals in each group. *p<0.05, ** p<0.01 vs. Wistar control; #p<0.05, ##p<0.01 vs. GK control.</p

Effect of mitochondrial nutriments on expression of PPARGC1A, Nrf1 and Tfam.

<p>A: Western blot analysis in adipocytes of PPARGC1A. Quantitative values were tabulated with the ratio of densities of PPARGC1A: tubulin. Values are mean±SE of 12 animals in each group.*p<0.05, p<0.01 vs. Wistar control; # p<0.05, ##p<0.01 vs. GK control. B: Total RNA was isolated from soleus muscle. mRNA of <i>Nrf1</i> and <i>Tfam</i> were analyzed by means of quantitative RT-PCR with gene-specific oligonucleotide probes in muscle. The cycle number at which the various transcripts were detectable was compared to that of nuclear18S rRNA as an internal control, and expressed as arbitrary units versus values in Wistar control taken 100. All values are mean±SEM of 12 animals in each group.*p<0.05, ** p<0.01 vs. Wistar control; #p<0.05, ##p<0.01 vs. GK control.</p

Morphometric and plasma variables in GK rats with different treatments.

<p>Values are mean±SEM of 12 animals in each group.</p>*<p>p<0.05 vs. GK control;</p>**<p>p<0.01 vs. GK control.</p

Effect of mitochondrial nutriments on mitochondrial DNA and protein in soleus muscle.

<p>A: Total DNA was isolated from soleus muscle. The mtDNA contents were determined by real-time PCR. The DNA contents of mtDNA and nuclear 18S rRNA gene (18S rDNA) were calculated from the standard curve and the relative ratios of mtDNA contents against nuclear 18S rRNA gene were determined in each group. Results are expressed as percentage of Wistar control. Data are mean+SEM (n = 5). **P<0.01 vs. Wistar control; # p<0.05 vs. GK control. B: Protein (10 µg) was solubilized in SDS sample buffer and analyzed by western blotting with antibodies against tubulin, mitochondrial electron transport complex I and complex II. The quantitative analyses of the bands by densitometry are shown. Results are presented as percentage of Wistar control. *p<0.05 vs. Wistar control; #P<0.05, ##p<0.01 vs. GK control.</p

Effects of mitochondrial nutriments on OGTT and plasma free fatty acid (FFA).

<p>A: OGTT was carried out at the end of 12 weeks of nutrient administration. All rats fasted overnight before OGTT. Blood was taken from the retrobulbar vein at 0, 30, 60, 120 and 180 min after the oral glucose administration (5 g/kg body weight). Plasma glucose concentration was determined by the glucose oxidase method. Data are means±S.E. of 12 observations in each group. * p<0.05, **p<0.01 vs. the respective values in the GK control group. B: Plasma free fatty acid was measured in groups at beginning or after nutrient administration for 12 weeks. Serum levels of free fatty acids in different groups after overnight fasting. Data are means±S.E. of 12 animals in each group. **p<0.01 vs. the respective values in the Wistar control group. ##p<0.01 vs. the respective values in the GK control group.</p