Effect of age and day time on the adenosine modulation of basal and insulin-stimulated glucose transport in rat adipocytes

Impact of Adenosine Analogue, Adenosine-5'-N-Ethyluronamide (NECA), on Insulin Signaling in Skeletal Muscle Cells

Materials and Methods

Rat L6 skeletal muscle cells were cultured in 25 cm² flasks. These differentiated cells were treated, and then, quantitative reverse transcription-polymerase chain reaction (qRT-PCR) (probe-based) was used to measure the relative mRNA expression level for metabolic, inflammatory, and nuclear receptor genes including peroxisome proliferator-activated receptor gamma (PGC-1α), carnitine palmitoyl transferase 1 beta (CPT1B), long-chain acyl-CoA de hydrogenase (LCAD), acetyl-CoA carboxylase beta (ACCβ), pyruvate dehydrogenase kinase 4 (PDK4), hexokinase II (HKII), phosphofructokinase (PFK), interleukin-6 (IL-6), and nuclear receptor subfamily 4, group A (NR4A) at different treatment conditions.

Results

Adenosine-5′-N-ethyluronamide (NECA), a stable adenosine analogue, significantly stimulate inflammatory mediator (IL-6) (p < 0.001) and nuclear receptors (NR4A) (p < 0.05) and significantly modulate metabolic (PFK, LCAD, PGC-1α, and CPT1B) gene expressions in skeletal muscle cells (p < 0.05, p < 0.05, p < 0.001, and p < 0.01, respectively). This present study shows that there is a noteworthy crosstalk between NECA and insulin at various metabolic levels including glycolysis (HKII), fatty acid oxidation (ACCβ), and insulin sensitivity (PDK4).

Conclusions

A novel crosstalk between adenosine analogue and insulin has been demonstrated for the first time; evidence has been gathered in vitro for the effects of NECA and insulin treatment on intracellular signaling pathways, in particular glycolysis and insulin sensitivity in skeletal muscle cells.

Possible therapeutic benefits of adenosine-potentiating drugs in reducing age-related degenerative disease in dogs and cats

Adenosine is a ubiquitous, biologically important molecule that is a precursor of other biologically active molecules. It also is a component of some co-factors and has distinct physiological actions in its own right. Levels are maintained by synthesis from dietary precursors and re-cycling. The daily turnover of adenosine is very high. Adenosine can act either as a hormone by binding to adenosine receptors, four adenosine receptor subtypes have been identified, and as an intracellular modulator, after transport into the cell by membrane transporter proteins. One of the principal intracellular actions of adenosine is inhibition of the enzyme phosphodiesterase. Extracellular adenosine also has specific neuromodulatory actions on dopamine and glutamate. Selective and nonselective agonists and antagonists of adenosine are available. The tasks of developing, evaluating and exploiting the therapeutic potential of these compounds is still in its infancy. Adenosine has actions in the central nervous system (CNS), heart and vascular system, skeletal muscle and the immune system and the presence of receptors suggests potential actions in the gonads and other organs. Adenosine agonists improve tissue perfusion through actions on vascular smooth muscle and erythrocyte fluidity and they can be used to improve the quality of life in aged dogs. This article reviews the therapeutic potential of adenosine-potentiating drugs in the treatment of age-related conditions in companion animals, some of which may be exacerbated by castration or spaying at an early age.

Decrease in cold tolerance of aged rats caused by the enhanced endogenous adenosine activity

During severe cold exposure, old rats (24-28 months) were less capable of maintaining their body temperature compared to young rats (3-6 months) due to lower rate of heat production. Single injection of adenosine deaminase (AD) (converts adenosine to inosine) significantly increased thermogenesis in both young and old rats. However, doubling the dose of AD was required for optimal thermogenic response in old rats. In contrast, the similar enhancements in both thermogenesis and cold tolerance were observed in both young and old rats receiving the same optimal doses of specific adenosine receptor antagonists. These results lead to the suggestion that the lower capability of aged rats to withstand cold exposure could be due to an increase in adenosine stimulation because of the decreased endogenous AD activity rather than an increase in adenosine receptor sensitivity. This notion is further supported by the finding that the AD activity in the neck muscle, a key site for shivering thermogenesis, was significantly lower in old rats as compared to their younger counterparts before and after cold exposure.