Cyclic AMP dependent protein kinase (PKA) from Pichia pastoris yeast cells was found to be activated by either cAMP or cGMP. Analogs of cAMP such as 8-chloro-cAMP and 8-bromo-cAMP were as potent as cAMP in PKA activation while N6,2'-O-dibutyryl-cAMP did not stimulate the enzyme activity. It was shown that protamine sulfate was almost equally phosphorylated in the presence of 1-2 × 10-6 M cAMP or cGMP while other substrates such as Kemptide, ribosomal protein S6, were phosphorylated to a lower extent in the presence of cGMP. It was demonstrated that pyruvate kinase is a substrate of PKA which co-purified with the P. pastoris enzyme. Moreover, pyruvate kinase was phosphorylated by PKA in the presence of cAMP and cGMP to comparable levels.
Purpose: Tadalafil, the phosphodiesterase type 5 inhibitor (PDE5I), has been shown to reduce visceral adipose tissue in rabbit and to improve lean mass content in non-obese men. In order to clarify this effect in humans, in the present study we determined the impact of an acute oral tadalafil administration on lipolysis by evaluating plasma free fatty acids (FFAs) and glycerol. FFAs are potential modulator of inflammation response that we evaluated through tumor necrosis factor alpha (TNFα), interleukin 6 (IL6), interleukin 8 (IL8) and interleukin 10 (IL10) plasma levels. Moreover, we determined whether the effects of tadalafil would be reflected in variation of plasma levels of cGMP and NO, two important molecules involved in PDE5Is signaling. Methods: Twelve healthy subjects were supplemented with 20 mg of tadalafil or a placebo, in a double-blind, randomized, cross-over design. Blood samples were collected immediately before, and at 2, 6, and 24 hours post ingestion, and assayed for biochemical analysis. Results: A condition effect was noted for FFAs and glycerol, with values higher for tadalafil when compared to the placebo group, at 2 and 6 hours post ingestion. No statistically significant effects were noted for glucose, cGMP, nitrate and nitrite. No inflammatory response was induced by tadalafil. Conclusion: Tadalafil, in human subjects, increases lipolysis as evidenced by a significant increase in circulating FFAs and glycerol, without affecting the plasma cGMP and NO levels; noticeably, the increase in FFAs did not develop an inflammatory response. Further well-controlled studies are warranted to assess the impact of tadalafil administration on weight/fat loss.
Recent medical advances suggest that the cellular natriuretic peptide/cGMP and NO/cGMP effector systems represent important signal transduction pathways especially in the cardiovascular system. These pathways also appear to be very interesting targets for the possible prevention of cardiovascular diseases. Exciting candidates for prevention include cGMP-dependent signaling networks initiated by natriuretic peptides (NP) and nitric oxide (NO) which are currently explored for their diagnostic and therapeutic potential. cGMP signaling contributes to the function and interaction of several vascular cell types, and its dysfunction is involved in the progression of major cardiovascular diseases such as atherosclerosis, hypertension and diabetic complications. This review will take a focussed look at key elements of the cGMP signaling cascade in vascular tissue. Recent advances in our knowledge of cGMP-dependent protein kinases (cGK, also known as PKG), the potential for assessing the functional status of cGMP signaling and the possible cross talk with insulin signaling will be reviewed.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.