Here, we demonstrate that BBR supplementation increases skeletal muscle mitochondrial biogenesis and improves mitochondrial function in a rodent model of diet induced obesity. Furthermore, we show that these effects are SIRT1-dependent. These effects are associated with significant reductions in adiposity and improvements in overall insulin sensitivity...
3.3. Mitochondrial function is rescued by BBR
Mitochondria play an important role in the development of insulin resistance and hyperglycemia [
8,
44]. Boosting mitochondrial activity provides, at least in part, a potential mechanism by which several therapeutic agents act [
19–
21].
In order to address whether the beneficial effects of Berberine (BBR) are related to its ability to alter mitochondrial function, we evaluated the function of isolated mitochondria. As reported before, high fat diet (HFD) feeding induced mitochondrial dysfunction in skeletal muscle (
Fig. 2A–E). This was demonstrated by decreased oxygen consumption (State 3), and decreased maximal oxygen consumption in the presence of FCCP (vFCCP), which is dependent only on the oxidative efficiency of the electron transport chain (
Fig. 2A).
These defects in mitochondrial respiration were rescued by treatment with BBR. In accordance with decreased mitochondrial function, mitochondrial ATP content was also decreased by HFD feeding and this was rescued by BBR (
Fig. 2E). The changes in mitochondrial function induced by HFD feeding, seem to be the result of impairments in the mitochondrial ATPase (
Fig. 2D) and electron transport chain (ETC) complexes like Succinate dehydrogenase (SDH) (
Fig. 2B) and Cytochrome c Oxidase (COX) (
Fig. 2C).
BBR supplementation was able to revert mitochondrial dysfunction induced by HFD by restoring ATPase and ETC activities (
Fig. 2B–D).
Although BBR has previously been shown to negatively impact hepatic mitochondrial function in in vitro assays or in cells exposed to concentrations higher than the one used in our study [
27,
30,
45,
46], we also observed an improvement in the function of hepatic mitochondria isolated from animals treated with BBR (data not shown).
This suggests a dose-dependent, indirect but positive action of BBR on mitochondria....
3.4. BBR rescues mitochondrial function in a SIRT1-dependent manner...
...Here, we show for the first time, that the beneficial effects of BBR are accompanied by an increase in mitochondrial function and biogenesis in skeletal muscle. Our results also confirm these findings in a cell-based model.
It is important to note that short term treatments with BBR were previously reported to inhibit ETC complex I [
27], decrease ATP content in hepatocytes [
29] and cause mitochondrial fragmentation, depolarization, and oxidative stress in K1735-M2 cells when used at concentrations 2–5 times higher than the concentrations used in this study [
54]. Moreover, when BBR is incubated with isolated liver mitochondria, mitochondrial respiration is inhibited and mitochondrial permeability transition is induced [
55].
...Therefore, while our findings demonstrate improved mitochondrial function by BBR, they do not rule out the possibility of toxic effects of BBR on mitochondria under different conditions or at higher concentrations.