Michal Grabowski

Inhibition of renal gluconeogenesis contributes to hypoglycaemic action of NADPH oxidase inhibitor, apocynin.

NADPH oxidase, catalysing superoxide radical (O₂(.-)) formation, is considered as a main source of reactive oxygen species in kidneys and its increased activity is supposed to be involved in the development of diabetic nephropathy. The aim of this study was to investigate the effect of NADPH oxidase inhibitor, apocynin, on renal gluconeogenesis, which is an important source of endogenous glucose under diabetic conditions. The following observations were made during the experiments performed on isolated renal proximal tubules of control and alloxan diabetic rabbits: (1) apocynin (200 μM) inhibited the rate of glucose synthesis by 45-80%, depending on the substrate applied; (2) the rate of glucose production was also significantly diminished in the presence of TEMPOL (5mM), a superoxide radical scavenger, suggesting that the decrease in O₂(.-) formation might be involved in apocynin-evoked gluconeogenesis inhibition; (3) the activities of phosphoenolpyruvate carboxykinase (PEPCK) and/or aldolase were lowered in the presence of either apocynin or TEMPOL, as concluded from the intracellular levels of gluconeogenic intermediates. The data from in vivo experiments indicated that apocynin treatment (2g/l of drinking water): (1) significantly (by about 30%) attenuated serum glucose concentration in diabetic rabbits and did not affect glycaemia in control animals; (2) normalized diabetes-stimulated rate of glucose synthesis and slightly inhibited gluconeogenesis in control rabbits; (3) normalized diabetes-increased activity of mitochondrial PEPCK and lowered cytosolic PEPCK activity by about 20% below the value for untreated control animals; (4) slightly decreased the activity of mitochondrial PEPCK and did not change the activity of cytosolic one in control rabbits. Thus, it is concluded that: (1) the inhibition of NADPH oxidase might contribute to lowered rate of renal gluconeogenesis, probably due to decreasing PEPCK activity; (2) inhibition of renal gluconeogenesis is involved in apocynin hypoglycaemic action in vivo; (3) apocynin might be beneficial for diabetes treatment.

ERK1/2 pathway is involved in renal gluconeogenesis inhibition under conditions of lowered NADPH oxidase activity

The aim of this study was to elucidate the mechanisms involved in the inhibition of renal gluconeogenesis occurring under conditions of lowered activity of NADPH oxidase (Nox), the enzyme considered to be one of the main sources of reactive oxygen species in kidneys. The in vitro experiments were performed on primary cultures of rat renal proximal tubules, with the use of apocynin, a selective Nox inhibitor, and TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl), a potent superoxide radical scavenger. In the in vivo experiments, Zucker diabetic fatty (ZDF) rats, a well established model of diabetes type 2, were treated with apocynin solution in drinking water. The main in vitro findings are the following: (1) both apocynin and TEMPOL attenuate the rate of gluconeogenesis, inhibiting the step catalyzed by phosphoenolpyruvate carboxykinase (PEPCK), a key enzyme of the process; (2) in the presence of the above-noted compounds the expression of PEPCK and the phosphorylation of transcription factor CREB and ERK1/2 kinases are lowered; (3) both U0126 (MEK inhibitor) and 3-(2-aminoethyl)-5-((4-ethoxyphenyl)methylene)-2,4-thiazolidinedione (ERK inhibitor) diminish the rate of glucose synthesis via mechanisms similar to those of apocynin and TEMPOL. The observed apocynin in vivo effects include: (1) slight attenuation of hyperglycemia; (2) inhibition of renal gluconeogenesis; (3) a decrease in renal PEPCK activity and content. In view of the results summarized above, it can be concluded that: (1) the lowered activity of the ERK1/2 pathway is of importance for the inhibition of renal gluconeogenesis found under conditions of lowered superoxide radical production by Nox; (2) the mechanism of this phenomenon includes decreased PEPCK expression, resulting from diminished activity of transcription factor CREB; (3) apocynin-evoked inhibition of renal gluconeogenesis contributes to the hypoglycemic action of this compound observed in diabetic animals. Thus, the study has delivered some new insights into the recently discussed issue of the usefulness of Nox inhibition as a potential antidiabetic strategy.

On relative completeness of Hoare logics

In this paper a generalization of a certain theorem of Lipton (“Proc. 18th IEEE Sympos. Found. of Comput Sci.” (1977), pp. 1–6) is presented. Namely, we show that for a wide class of programming languages the following holds: the set of all partial correctness assertions true in an expressive interpretation I is uniformly dedicable (in I) in the theory of I iff the halting problem is decidable for finite interpretations. In the effect we show that such limitations as effectiveness or Herbrand-definability of interpretation (they are relevant in the previous proofs) can be removed in the case of partial correctness.

On the existence of effective Hoare logics

Every proof system for (partial) correctness yields an enumeration procedure for correctness assertions. Other researchers have proved results on the existence of (sound and complete) enumeration procedures for assertions about programs from an acceptable programming language where the assertion language is first-order logic. It is shown that some of the assumptions are stronger than necessary, whereas others must not be weakened. Two novel procedures are given that work for more interpretations with a smaller oracle than those known up to now.<<ETX>>

On the Relative Incompleteness of Logics for Total Correctness

It is proved that it does not exist an acceptable /cf.4/ programming language having a sound and relatively complete /in the sense of Cook/ proof system for total correctness. This implies that the result of Clarke, German and Halpern concerning total correctness /cf.[4]/ cannot be essentially strengthened.

Arithmetical completeness versus relative completeness

In this paper we study the status of the arithmetical completeness of dynamic logic. We prove that for finitistic proof systems for dynamic logic results beyond arithmetical completeness are very unlikely. The role of the set of natural numbers is carefully analyzed.

On relative completeness of programming logics

In this paper a generalization of a certain Liptons theorem (see Lipton [5]) is presented. Namely, we show that for a wide class of programming languages the following holds: the set of all partial correctness assertions true in an expressive interpretation I is uniformly decidable (in I) in the theory of I iff the halting problem is decidable for finite interpretations. In the effect we show that such limitations as effectiveness or Herbrand definability of interpretation (they are relevant in the previous proofs) can be removed in the case of partial correctness.

On the status of proving program properties in effective interpretations

We present a sufficient condition for a class C of effective interpretations in order that C has a uniform procedure enumerating (when first-order oracle and recursive presentation of the interpretation involved are given) dynamic theories of interpretations in C. Under some additional assumption on the enumerating procedure, this condition is necessary. The main result states that if arithmetical notions are first-order-definable by universal or existential formulas within interpretations in C then C has an appropriate uniform procedure.