Synergic effect of exogenous lactate and caffeine on fat oxidation and hepatic glycogen concentration in resting rats

PURPOSE

Although several physiological roles of lactate have been revealed in the last decades, its effects on energy metabolism and substrate oxidation remain unknown. Therefore, we investigated the effects of lactate on the energy metabolism of resting rats.

METHODS

Male rats were divided into control (Con; distilled water), caffeine (Caf; 10 mg/kg), L-lactate (Lac; 2 g/kg), and lactate-plus-caffeine (Lac+Caf; 2 g/ kg + 10 mg) groups. Following oral administration of supplements, resting energy expenditure (study 1), biochemical blood parameters, and mRNA expression involved in energy metabolism in the soleus muscle were measured at different time points within 120 minutes of administration (study 2). Moreover, glycogen level and Pyruvate dehydrogenase (PDH) activity were measured.

RESULTS

Groups did not differ in total energy expenditure throughout the 6 hour post-treatment evaluation. Within the first 4 hours, the Lac and Lac+Caf groups showed higher fat oxidation rates than the Con group (p<0.05). Lactate treatment decreased blood free fatty acid levels (p<0.05) and increased the mRNA expression of fatty acid translocase (FAT/CD36) (p<0.05) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) (p<0.05) in the skeletal muscle. Hepatic glycogen level in the Lac+Caf group was significantly increased (p<0.05). Moreover, after 30 and 120 minutes, PDH activity was significantly higher in lactate-supplemented groups compared to Con group (p<0.05).

CONCLUSION

Our findings showed that Lac+Caf enhanced fat metabolism in the whole body and skeletal muscle while increasing hepatic glycogen concentration and PDH activity. This indicates Lac+Caf can be used as a potential post-workout supplement.

Flow cytometric single cell analysis reveals heterogeneity between adipose depots

Understanding adipose tissue heterogeneity is hindered by the paucity of methods to analyze mature adipocytes at the single cell level. Here, we report a system for analyzing live adipocytes from different adipose depots in the adult mouse. Single cell suspensions of buoyant adipocytes were separated from the stromal vascular fraction and analyzed by flow cytometry. Compared to other lipophilic dyes, Nile Red uptake effectively distinguished adipocyte populations. Nile Red fluorescence increased with adipocyte size and granularity and could be combined with MitoTracker® Deep Red or fluorescent antibody labeling to further dissect adipose populations. Epicardial adipocytes exhibited the least mitochondrial membrane depolarization and highest fatty-acid translocase CD36 surface expression. In contrast, brown adipocytes showed low surface CD36 expression. Pregnancy resulted in reduced mitochondrial membrane depolarisation and increased CD36 surface expression in brown and epicardial adipocyte populations respectively. Our protocol revealed unreported heterogeneity between adipose depots and highlights the utility of flow cytometry for screening adipocytes at the single cell level.

Dietary α-linolenic acid supplementation alters skeletal muscle plasma membrane lipid composition, sarcolemmal FAT/CD36 abundance, and palmitate transport rates

The cellular processes influenced by consuming polyunsaturated fatty acids remains poorly defined. Within skeletal muscle, a rate-limiting step in fatty acid oxidation is the movement of lipids across the sarcolemmal membrane, and therefore, we aimed to determine the effects of consuming flaxseed oil high in α-linolenic acid (ALA), on plasma membrane lipid composition and the capacity to transport palmitate. Rats fed a diet supplemented with ALA (10%) displayed marked increases in omega-3 polyunsaturated fatty acids (PUFAs) within whole muscle and sarcolemmal membranes (approximately five-fold), at the apparent expense of arachidonic acid (-50%). These changes coincided with increased sarcolemmal palmitate transport rates (+20%), plasma membrane fatty acid translocase (FAT/CD36; +20%) abundance, skeletal muscle triacylglycerol content (approximately twofold), and rates of whole body fat oxidation (~50%). The redistribution of FAT/CD36 to the plasma membrane could not be explained by increased phosphorylation of signaling pathways implicated in regulating FAT/CD36 trafficking events (i.e., phosphorylation of ERK1/2, CaMKII, AMPK, and Akt), suggesting the increased n-3 PUFA composition of the plasma membrane influenced FAT/CD36 accumulation. Altogether, the present data provide evidence that a diet supplemented with ALA increases the transport of lipids into resting skeletal muscle in conjunction with increased sarcolemmal n-3 PUFA and FAT/CD36 contents.

Associations between CD36 gene polymorphisms and metabolic response to a short-term endurance-training program in a young-adult population

Recent studies have shown that CD36 gene variants are associated with an increased prevalence of chronic disease. Although a genetic component to trainability has been proven, no data are available specifically on the influence of CD36 on training response. Two single nucleotide polymorphisms (SNPs) (rs1527479 and rs1984112) were assessed for associations with whole-body substrate oxidation, response to a 75-g dextrose oral glucose tolerance test, fasting plasma lipids, and cardiovascular disease risk factors in a young healthy cohort, both using cross-sectional analysis and following a 4-week endurance-exercise training program. Genotyping was performed using real-time polymerase chain reaction. Cross-sectional data were collected in 34 individuals (age, 22.7 ± 3.5 years), with 17 completing the training program. At baseline, TT SNP carriers at rs1527479 and wild-type GG carriers at rs1984112 were associated with significantly greater whole-body rate of fat oxidation (Fatox) during submaximal exercise (P < 0.05), whilst AA carriers at the same position were associated with elevated triglyceride (TG) levels. A significant genotype × time interaction in Fatox at SNP rs1984112 was identified at rest. Significant genotype × time interactions were present at rs1527479, with TT carriers exhibiting a favourable response to training when compared with C-allele carriers for fasting TG, diastolic blood pressure (DBP), and mean arterial pressure (MAP). In conclusion, cross-sectional assessment identified associations with Fatox and TG. Training response at both SNPs identified "at-risk" genotypes responding favourably to the training stimulus in Fatox, TG, DBP, and MAP. Although these data show potential pleiotropic influence of CD36 SNPs, assessment in a larger cohort is warranted.

Regulation of energy metabolism by long-chain fatty acids

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise. This review mainly focuses on the role of long chain fatty acids (LCFAs) in regulating energy metabolism as ligands of peroxisome proliferator-activated receptors (PPARs). PPAR-alpha expressed primarily in liver is essential for metabolic adaptation to starvation by inducing genes for beta-oxidation and ketogenesis and by downregulating energy expenditure through fibroblast growth factor 21. PPAR-delta is highly expressed in skeletal muscle and induces genes for LCFA oxidation during fasting and endurance exercise. PPAR-delta also regulates glucose metabolism and mitochondrial biogenesis by inducing FOXO1 and PGC1-alpha. Genes targeted by PPAR-gamma in adipocytes suggest that PPAR-gamma senses incoming non-esterified LCFAs and induces the pathways to store LCFAs as triglycerides. Adiponectin, another important target of PPAR-gamma may act as a spacer between adipocytes to maintain their metabolic activity and insulin sensitivity. Another topic of this review is effects of skin LCFAs on energy metabolism. Specific LCFAs are required for the synthesis of skin lipids, which are essential for water barrier and thermal insulation functions of the skin. Disturbance of skin lipid metabolism often causes apparent resistance to developing obesity at the expense of normal skin function.

1,3-Dichloro-2-propanol induced hyperlipidemia in C57BL/6J mice via AMPK signaling pathway

1,3-Dichloro-2-propanol (1,3-DCP) is a well-known contaminant that has been detected in a wide range of foods. Dietary intake represents the greatest source of exposure to 1,3-DCP. In the study, we first found 1,3-DCP could induce hyperlipidemia in C57BL/6J mice below 1 mg/kg/day. We investigated serum lipid profile, liver total cholesterol (TC) and triglyceride (TG), histopathology of Liver and adipose tissue. The results showed 1,3-DCP dose dependently increased serum TG, TC and low-density lipoprotein cholesterol (LDL-C), decreased serum high-density lipoprotein cholesterol (HDL-C), increased relative liver weight, liver TG and TC, relative adipose tissue weight and enlarged the size of adipose cells. Because AMPK signal pathway is important in the process of lipid metabolism, we further investigated the effects of 1,3-DCP on AMPK signaling pathway in murine models. The results showed that 1,3-DCP (0.1-1 mg/kg/day) decreased p-AMPK/tAMPK ratio, p-ACC/tACC ratio, PPARα expression, but increased FAT, SREBP1, HMGCR and FAS expression. These observations indicated that 1,3-DCP induced hyperlipidemia in C57BL/6J mice at least partially through regulating AMPK signaling pathway.

Fatty acid transport proteins chronically relocate to the transverse-tubules in muscle from obese Zucker rats but are resistant to further insulin-induced translocation

OBJECTIVES

Recently, we have demonstrated that FA transport proteins are located within the t-tubule fraction of rodent muscle, and that insulin stimulation causes their translocation to this membrane fraction. Chronic relocation of the FA transport protein FAT/CD36 to the sarcolemma is observed in obese rodents and humans, and correlates with intramuscular lipid accumulation and insulin resistance. It is not known whether in an obese, insulin resistant state FA transporters also chronically relocate to the t-tubules. Furthermore, it is not known whether the insulin-stimulated translocation of the various FA transport proteins to the t-tubules is impaired in insulin resistance.

METHODS

Sarcolemmal and t-tubule membrane fractions were isolated via differential centrifugation from muscles of lean and obese female Zucker rats during basal or insulin stimulated conditions. FA transport proteins were measured via western blot on both membrane fractions.

RESULTS

Our results demonstrate that in muscle from insulin resistant Zucker rats, FAT/CD36, FABPpm and FATP1 are all increased on the t-tubules in the basal state (+72%, +120%, and +69%, respectively), potentially contributing to the accumulation of intramuscular lipids. Insulin failed to increase the content of the FA transport proteins on either the t-tubule or sarcolemma above the elevated basal levels, analogous to the well characterized impairment of insulin-stimulated GLUT4 translocation to both membrane domains in obesity.

CONCLUSION

FA transport proteins chronically relocate to the t-tubule domain in insulin resistant muscle, potentially contributing to lipid accumulation. Further translocation of the FA transport proteins to this domain during insulin stimulation, however, is impaired.