T Lappalainen, M Kolehmainen, U Schwab, L Pulkkinen, D E Laaksonen, R Rauramaa, M Uusitupa and H Gylling
Serum amyloid A (SAA) is a novel link between increased adipose tissue mass and low-grade inflammation in obesity. Little is known about the factors regulating its serum concentration and mRNA levels. We investigated the association between SAA and leptin in obese and normal weight subjects and analyzed the effect of weight reduction on serum SAA concentration and gene expression in adipose tissue of the obese subjects.
Seventy-five obese subjects (60±7 years, body mass index (BMI) 32.9±2.8 kg/m2, mean±s.d.) with impaired fasting plasma glucose or impaired glucose tolerance and other features of metabolic syndrome, and 11 normal weight control subjects (48±9 years, BMI 23.7±1.9 kg/m2) were studied at the baseline. Twenty-eight obese subjects underwent a 12-week intensive weight reduction program followed by 5 months of weight maintenance. Blood samples and abdominal s.c. adipose tissue biopsies were taken at the baseline and after the follow-up. Gene expression was studied using real-time quantitative PCR.
The gene expressions in women and serum concentrations of leptin and SAA were interrelated independently of body fat mass in the obese subjects (r=0.54, P=0.001; r=0.24, P=0.039 respectively). In multiple linear regression analyses, leptin mRNA explained 38% of the variance in SAA mRNA (P=0.002) in the obese women. Weight loss of at least 5% increased SAA mRNA expression by 48 and 36% in men and women, but serum SAA concentrations did not change.
The association between SAA and leptin suggests an interaction between these two adipokines, which may have implications in inflammatory processes related to obesity and the metabolic syndrome.
Ursula Mager, Marjukka Kolehmainen, Vanessa D F de Mello, Ursula Schwab, David E Laaksonen, Rainer Rauramaa, Helena Gylling, Mustafa Atalay, Leena Pulkkinen and Matti Uusitupa
We examined the expression of ghrelin and ghrelin receptors in peripheral blood mononuclear cells (PBMCs) and evaluated the effect of weight loss or exercise on plasma ghrelin concentrations in subjects with the metabolic syndrome.
Design and methods
Data from 75 overweight/obese subjects randomized to a weight loss, aerobic exercise, resistance exercise or control group for a 33-week intervention period were analysed. The plasma ghrelin concentrations and indices of insulin and glucose metabolism were assessed, and mRNA expression of ghrelin, its receptors and various cytokines in PBMCs was studied using real-time PCR.
Ghrelin and GH secretagogue receptor 1b were expressed in PBMCs of subjects with metabolic syndrome. Ghrelin gene expression correlated positively with the expressions of tumour necrosis factor-α (P<0.001), interleukin-1β (P<0.001) and interleukin-6 (P=0.026) during the study, but was not associated with the plasma ghrelin concentration. Genotype-specific ghrelin gene expression in PBMCs was found for the −604G/A and the −501A/C polymorphisms in the ghrelin gene. At baseline, the plasma ghrelin levels were associated with fasting serum insulin concentrations, insulin sensitivity index and high-density lipoprotein cholesterol. However, longitudinally weight, BMI or waist circumference and acute insulin response in i.v. glucose tolerance test were stronger predictors of the ghrelin concentration. Plasma ghrelin did not change over the study period in the weight reduction group, but it tended to decrease in the control group (P=0.050).
Ghrelin mRNA expression in PBMCs suggests an autocrine role for ghrelin within an immune microenvironment. Moderate long-term weight loss may prevent a decline in ghrelin concentration over time in individuals with metabolic syndrome.