As we know, a calorie restriction (CR) diet improves the health and lifespan in animal models. In the ongoing search for human biomarkers to assess the effects of CR in humans, Crujeiras et al. analyzed sirtuin gene expression changes and blood antioxidant markers in obese patients who followed a 30% calorie restricted diet for 8 weeks.

The researchers selected two of the seven human sirtuins to study, SIRT1 and SIRT2, because of their known inhibitory role in adipocyte differentiation and lipid accumulation. They performed their analysis in circulating peripheral blood mononuclear cells (PBMCs). Many human gene expression analyses under calorie restriction have been done in adipose tissue or skeletal muscle. If changes could be seen in PBMCs, however, these cells could offer a less invasive method to assess biomarkers of calorie restriction diets in humans.

Sirtuin gene expression in human mononuclear cells is modulated by caloric restriction.

BACKGROUND: Sirtuins may provide novel targets for treating some diseases associated with oxidative stress, such as obesity and its comorbidities. However, there are a few in vivo studies in humans about the potential role of sirtuins as therapeutic targets among obese patients undergoing caloric restriction. Therefore, the aim of this study was to assess if the gene expression of sirtuins is modulated in peripheral blood mononuclear cells (PBMC) by a hypocaloric diet devised to lose weight in humans. MATERIALS AND METHODS: Gene expression of two sirtuins (SIRT1 and SIRT2) in the PBMC of obese subjects (32.3 +/- 5.5 kg m(-2)) before and following an 8-week hypocaloric diet was investigated. NADH-coenzyme Q reductase (NDUFS2) and cytochrome c oxidase assembly protein (COX15) gene expression was selected together with plasma antioxidant power and nitric oxide as markers of antioxidant status. A quantitative real-time polymerase chain reaction approach was performed to assess the nutrigenomics outcome. Moreover, 2-keto[1-(13)C]isocaproate breath test (KICA-BT) parameters were evaluated to study mitochondrial oxidation in vivo. RESULTS: The intervention up-regulated the expression of both sirtuins, being inversely associated with total antioxidant capacity and directly related to nitric oxide, mitochondrial oxidation assessed by the KICA-BT and the expression of the mitochondrial proteins COX15 and NDUFS2. CONCLUSION: SIRT1 and SIRT2 may serve as key regulators for some obesity comorbidities related to antioxidant status, while PBMC could be a model to study the effect of the sirtuin response in obesity therapy.

Overall, patients had a significant reduction in body weight, BMI, fat mass and cholesterol but showed no significant changes in glucose, triglycerides, insulin or insulin resistance (It’s possible that if these patients had maintained a CR diet for a longer period of time, significant changes would have been noted.) Total antioxidant capacity (AOP) and nitric oxide levels were significantly increased, and glutathione peroxidase was significantly decreased, indicating an improvement in the oxidative stress response.

The CR diet significantly upregulated expression of SIRT1 and SIRT2 in PBMCs, consistent with results obtained in the adipose tissue of calorie restricted mice. I would have liked to see a parallel gene expression analysis in the adipose tissue or skeletal muscle of these patients, in addition to PBMCs, to determine whether the gene expression changes observed in PBMCs were mirrored in the other tissues. That data would support the author’s claim that PBMCs are a valid source of cells for gene expression analysis in humans.

Finally, the authors utilized a non-invasive 13C-KICA breath test and gene expression analysis of two mitochondrial respiratory chain proteins (NDUFS2 and COX15) to evaluate in vivo mitochondrial oxidation in these patients before and after calorie restriction. Expression of NDUFS2 increased significantly after the 8-week diet, whereas expression of COX15 remained unchanged. No changes were noted in the 13C-KICA mitochondrial oxidation rate evolution after the dieting period.

While the researchers did not see significant changes in some of these assays, it is important to remember that short-term CR for weight loss has different physiological consequences than long-term CR for longevity. Hopefully, with additional human studies we will obtain data that will help us better understand the molecular pathways involved in CR diets for longevity in humans.