Caffeine promotes autophagy in skeletal muscle cells by increasing the calcium-dependent activation of AMP-activated protein kinase

Caffeine has been shown to promote calcium-dependent activation of AMP-activated protein kinase (AMPK) and AMPK-dependent glucose and fatty acid uptake in mammalian skeletal muscle. Though caffeine has been shown to promote autophagy in various mammalian cell lines it is unclear if caffeine-induced autophagy is related to the calcium-dependent activation of AMPK. The purpose of this study was to examine the role of calcium-dependent AMPK activation in regulating caffeine-induced autophagy in mammalian skeletal muscle cells. We discovered that the addition of the AMPK inhibitor Compound C could significantly reduce the expression of the autophagy marker microtubule-associated protein 1 light chain 3b-II (LC3b-II) and autophagic vesicle accumulation in caffeine treated skeletal muscle cells. Additional experiments using pharmacological inhibitors and RNA interference (RNAi) demonstrated that the calcium/calmodulin-activated protein kinases CaMKKβ and CaMKII contributed to the AMPK-dependent expression of LC3b-II and autophagic vesicle accumulation in a caffeine dose-dependent manner. Our results indicate that in skeletal muscle cells caffeine increases autophagy by promoting the calcium-dependent activation of AMPK.

Random urine bile acids in prediction of liver abnormality in asymptomatic alcoholics

We evaluated bile acids for prediction of abnormal serum liver profile in a random sample of urine (URNBA). Seventy-four subjects with excessive alcohol intake, self-referred for outpatient detoxification, had no history or physical findings of liver disease. Surprisingly, in 49% (36/74) of alcoholics, two or more of these were elevated: serum bile acids, aspartate aminotransferase (AST), alanine aminotransferase, alkaline phosphatase (ALP), and/or total bilirubin. All subjects were subdivided into 39 URNBA normal and 35 URNBA abnormal, using 2.6 mumol/g of creatinine as a dividing value. Serum tests confirmed the subgrouping made with URNBA. Compared with alanine aminotransferase, URNBA had better sensitivity, specificity, and overall diagnostic accuracy predicting abnormal serum bile acids, AST, and alkaline phosphatase values. A predictive potential for a multivariate discriminant function of laboratory tests, known to best identify biopsy-documented mild liver disease, was only mildly inferior for URNBA when compared with AST. Multiple abnormalities of liver test results are unexpectedly frequent in asymptomatic alcoholics. The URNBA are helpful in the detection of liver abnormality in its clinically latent phase, because of the convenience of testing a spot sample of urine.

Inhibition of renal gluconeogenesis by guinolinate and hydrazine in diabetic rats

Renal as well as hepatic gluconeogenesis is inappropriately accelerated in the diabetic state when plasma glucose levels are elevated. Known regulatory mechanisms influence gluconeogenesis in both organs. However, under certain circumstances gluconeogenesis may be affected in one organ and not the other. Recent studies with the tryptophan metabolite, quinolinate, suggest that hepatic gluconeogenesis in the diabetic is unaffected by this agent, whereas gluconeogenesis is blocked in the normal liver. These experiments have been interpreted as providing evidence for the lack of a specific physiologic repressor for gluconeogenesis in diabetic liver. In the present study quinolinate and hydrazine are shown to be effective inhibitors of the accelerated gluconeogenesis in the renal cortex of diabetic rats. Thus, the renal gluconeogenic mechanism in diabetics retains the capacity to recognize quinolinate as an inhibitor, but may be influenced by the depressed conversion of tryptophan to quinolinate in the intact diabetic organism.