Mitochondrial reactive oxygen species generation in obese non-diabetic and type 2 diabetic participants

Abstract

Aims/hypothesis The aim of this study was to measure mitochondrial reactive oxygen species (ROS) production directly from skeletal muscle biopsies obtained from obese insulin-resistant non-diabetic and type 2 diabetic participants. Methods Ten lean healthy, ten obese non-diabetic and ten type 2 diabetic participants received a euglycaemichyperinsulinaemic clamp to measure whole body insulin sensitivity. Mitochondria were isolated from skeletal muscle biopsies, and mitochondrial ATP synthesis and hydrogen peroxide production were measured ex vivo under conditions that maximally stimulate ATP synthesis and ROS production using chemiluminescent and fluorescent techniques, respectively. Results Compared with lean controls, both obese nondiabetic and type 2 diabetic participants were resistant to insulin, and had a reduced rate of mitochondrial ATP production. Obese insulin-resistant participants had a decreased rate of mitochondrial ROS production, while ROS production rate in participants with type 2 diabetes was similar to that in lean healthy participants. In nondiabetic participants, the rate of ROS production was strongly correlated with the rate of ATP synthesis and the glucose disposal rate measured with the euglycaemichyperinsulinaemic clamp. The ROS/ATP ratio in obese insulin-resistant participants was similar to that in lean insulin-sensitive participants, while the ratio was significantly elevated in type 2 diabetes participants.Conclusions/interpretation Since, in absolute terms, the maximal capacity for mitochondrial ROS production was not increased in either obese insulin-resistant participants or in type 2 diabetic participants, these results do not favour a role for increased mitochondrial ROS production in the pathogenesis of insulin resistance in human skeletal muscle. However, care should be taken in extrapolating these ex vivo observations to the in vivo situation.

Effect of physical training on mitochondrial respiration and reactive oxygen species release in skeletal muscle in patients with obesity and type 2 diabetes

“…Human studies have shown that obesity and high-fat diet increase mitochondrial hydrogen peroxide release [18]. Furthermore, a recent study showed that mitochondrial ROS release was higher in muscle of patients with type 2 diabetes than in obese controls, but similar to that observed in lean control participants [19]. Interestingly, studies have also shown that a transient physiological increase in ROS may be essential for a training-induced increase in insulin sensitivity in type 2 diabetes patients [20] and for protection against high-fat diet-induced insulin resistance in rodents [21].…”

“…It has also been shown that type 2 diabetes patients had significantly higher ROS release than lean participants when related to ATP production, but similar ROS release when related to mitochondrial protein [19]. Similarly to the protocol used by Abdul-Ghani et al [19], ROS rot was determined in the presence of rotenone, which inhibits the unphysiological backflow of electrons from complex II to complex I. The fate of the electrons is therefore: (1) to be donated to oxygen, forming water in complex IV; or (2) to be donated to oxygen, forming superoxide in complex III.…”

“…We showed that type 2 diabetes patients tended to have higher ROS rot , which training tended to decrease. A recent study showed that type 2 diabetes patients had higher mitochondrial ROS release than matched obese control participants [19]. It has also been shown that type 2 diabetes patients had significantly higher ROS release than lean participants when related to ATP production, but similar ROS release when related to mitochondrial protein [19].…”

“…A recent study showed that type 2 diabetes patients had higher mitochondrial ROS release than matched obese control participants [19]. It has also been shown that type 2 diabetes patients had significantly higher ROS release than lean participants when related to ATP production, but similar ROS release when related to mitochondrial protein [19]. Similarly to the protocol used by Abdul-Ghani et al [19], ROS rot was determined in the presence of rotenone, which inhibits the unphysiological backflow of electrons from complex II to complex I.…”

“…The higher mitochondrial ROS release in type 2 diabetes patients [19] may explain the lower intrinsic mitochondrial activity seen in some studies [6,12,13]. It is, however, possible that mitochondrial ROS release is influenced by the level of physical fitness [23], which was not assessed in the previous studies [19]. Thus, it remains to be established whether mitochondrial ROS production differs between type 2 diabetes and control participants who are matched for physical fitness.…”