Advanced Glycation End Products Stimulate Angiotensinogen Production in Renal Proximal Tubular Cells

Background

Elevated advanced glycation end products (AGE) in diabetes mellitus (DM) are implicated in the progression of DM-associated tissue injury, including diabetic nephropathy. The intrarenal renin-angiotensin system, in particular augmentation of angiotensinogen (AGT) in proximal tubular cells (PTC), plays a crucial role in the development of diabetic nephropathy. This study investigated hypothesis that AGE stimulates AGT production in PTC.

The effect of folate analogues and vitamin B12 on provision of thymine nucleotides for DNA synthesis in megaloblastic anemia

The role of vitamin B12 in the folate dependent biosynthesis of thymidine nucleotides is controversial. In an attempt to clarify this, three methods have been used to assess the relative efficacy of vitamin B12 (hydroxocobalamin) and various folate analogues in titrated concentrations at correcting 'de novo' thymidylate synthesis by megaloblastic human marrow cells: (1) The deoxyuridine (dU) suppression test which analyses the reduction in (3H)-thymidine labeling of DNA by unlabeled dU. Marrow cells were also labeled with (6-3H)-dU with assessment of (2) its incorporation into DNA and (3) the accumulation of (6-3H)-deoxyuridine monophosphate (3H-dUMP). The three methods gave similar results. In both, N6-formyl tetrahydrofolate (formyl-FH4) was the most effective agent at correcting thymidylate synthesis in megaloblastic anemia due to vitamin B12 or folate deficiency. Vitamin B12 corrected the lesion in vitamin B12 deficiency but not in folate deficiency. Tetrahydrofolate (FH4) and folic acid were effective in deficiency of vitamin B12 or folate, although in both deficiencies they were less effective than formyl-FH4. Methyl-FH4 was effective in folate deficiency but not in vitamin B12 deficiency. These results confirm the failure of methyl-FH4 utilisation in vitamin B12 deficiency. They suggest that if vitamin B12 is needed in the formylation of FH4, this is a minor role in provision of the correct coenzyme for thymidylate synthesis compared with its major role of provision of FH4 from methyl- FH4.     

Role of ADP-ribosyl transferase in differentiation of human granulocyte- macrophage progenitors to the macrophage lineage

Nuclear adenosine diphosphate-ribosyl (ADP-ribosyl) transferase is a chromatin-bound enzyme catalyzing the transfer of ADP-ribose from NAD+ to chromatin proteins. The physiologic function of this covalent modification of chromatin has not been fully established, but roles in both DNA repair and in differentiation have been proposed. We demonstrate that three specific inhibitors of ADP-ribosyl transferase (5-methylnicotinamide, 3-methoxybenzamide, 3-aminobenzamide) inhibit differentiation of human granulocyte-macrophage progenitor cells to the macrophage lineage. Differentiation to the neutrophil-granulocyte lineage is much less affected. The inhibition of macrophage differentiation seems to relate to the ability of these compounds to inhibit ADP-ribosyl transferase. A structural analogue (3- methoxybenzoic acid), which is not inhibitory for the enzyme, did not inhibit macrophage differentiation. Additional evidence for a role of ADP-ribosyl transferase in the differentiation of granulocyte- macrophage progenitors was obtained from experiments in which enzyme activity levels were measured in permeabilized marrow cells. Marrow cell ADP-ribosyl transferase activity increased after 3-hr stimulation by the differentiation/proliferation stimulus--granulocyte-macrophage colony-stimulating activity (GM-CSA). Unstimulated marrow cells showed low or undetectable levels of enzyme activity.     

Estrogen-induced microsatellite DNA alterations are associated with Syrian hamster kidney tumorigenesis

Exposure to estrogens is associated with an increase in cancers, including malignancies of the breast and uterus in humans, and of the kidney in hamsters. DNA damage induced by metabolic activation of estrogen has been postulated to result in gene mutations critical for the development of estrogen-induced kidney tumors in hamsters. As part of our examination of the genetic consequences of estrogen-induced DNA damage, we searched for estrogen-induced alterations in microsatellite DNA, a frequent site of mutation in tumors. Genomic DNA isolated from kidney of hamsters treated with estradiol, from estrogen-induced kidney tumors and from untreated age-matched controls, was examined by Southern blot analysis with three multi-locus oligonucleotide probes: (GACA)4, (CAC)6 and (CAG)6. Alterations in DNA fragments containing GACA and CAC tandem repeats were detected in kidney DNA of hamsters treated with hormone for 3 and 4 months, whereas no such effects were seen in control animals. In estrogen-induced tumors, microsatellite alterations were observed in fragments that contain these same two repeat sequences and also CAG repeat sequences. The induction of microsatellite alterations by estradiol in kidney DNA preceding estrogen-induced renal malignancy may play a role in hormone-induced tumorigenesis.      

Morphine decreases the voltage sensitivity of slow sodium channels

Cell membrane recordings were made in conditions of voltage clamping with tight attachment of the microelectrode—patch clamping— to study the effects of morphine on tetrodotoxin-resistant (TTX_r) sodium channels in rat spinal ganglion neurons in culture. The effects of a number of biologically active substances which regulate the receptor-mediated actions of morphine were studied. The effects of morphine were found to involve a chain of sequential reactions leading to decreases in the transfer of effective charge (Z_eff) by the activatory gate system of TTX_r sodium channels, depending on the concentration of agonist in the extracellular solution. A value of 8 nM was obtained forK _D , with a Hill coefficient of X=0.5. Non-specific antagonists of opioid receptors blocked the actions of morphine; these included ouabain at a concentration of 100 μM. An inhibitor, and activator, and a blocker of G-proteins had no effect on the effective charge. These data provide evidence that morphine decreases the voltage sensitivity of TTX_r sodium channels. Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 85, No. 2, pp. 225–236, February, 1999.