Time-course metabolic changes in high-fat diet-induced obesity rats: A pilot study using hyperpolarized 13C dynamic MRS

The purpose of this study was to investigate the time-course metabolic changes based on hyperpolarized 13C magnetic resonance spectroscopy (MRS) in high-fat diet (HFD)-induced obesity rats and the correlation between metabolic and serum enzyme levels. Sprague–Dawley rats were fed either HFD (60% fat) or normal diet (10% fat) for 6 weeks. A HyperSense DNP was used to hyperpolarize [1-13C] pyruvic acid and the hyperpolarized 13C MRS was examined every 2 weeks in the course of 6 weeks using a 3 T GE MR750 scanner. The body weight of HFD-induced obese rats was significantly increased compared to normal rats at the 6th week after the onset of feeding (p = 0.05). Simultaneously, the HFD-induced obese rats showed significantly increased levels of serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and low-density lipoprotein (LDL)-cholesterol compared to normal rats (p ≤ 0.05). In the dynamic 13C MR spectra acquired at the 6th week, the obese rats showed significantly increased ratios of [1-13C] lactate/[1-13C] pyruvate and [1-13C] alanine/[1-13C] pyruvate (p = 0.05). The 13C spectral outcomes are positively correlated with the enzyme levels of ALT and LDH in the HFD-induced obesity. The [1-13C] lactate and [1-13C] alanine are potentially considered as noninvasive biomarkers for the HFD-induced obesity.