Playing with Pearson's concept: orthogonally functionalized 1,4-diaza-1,3-butadienes leading to heterobinuclear complexes.

By reacting 1,2-diketones and ortho- diphenylphosphinoyl aniline in the presence of zinc(ii) as a templating agent, cationic zinc(ii) complexes of novel phosphine oxide functionalized 1,4-diaza-1,3-butadiene ligands are acessible. Herein the zinc(ii) site is bound to all four donor atoms of the ligand. Depending on the flexibility of the 1,4-diaza-1,3-butadiene backbone, the bonds to zinc(ii) from the 1,4-diaza-1,3-butadiene donors can be broken. Reaction with oxalate cleaves the zinc(ii) coordination completely and makes accessible the free ligands possessing orthogonal (N,N: soft; O,O: hard) sets of donor sites. This allows for the specific coordination of soft and hard Lewis acids and thus for the generation of heterobimetallic complexes, here exemplarily shown for the combination of palladium(ii) (soft) and zinc(ii) (hard) centres.

Role of protein kinase C and cyclic AMP/protein kinase A in high glucose-stimulated transcriptional activation of collagen alpha 1 (IV) in glomerular mesangial cells.

The elevated mRNA levels encoding matrix components in glomeruli isolated from streptozotocin-induced diabetic rats provide evidence that stimulation of matrix synthesis is important in early phases of diabetic glomerulopathy. We and others have demonstrated that high glucose stimulates collagen mRNA levels in short-term mesangial cell culture. To test whether transcriptional activation is operative and to gain insights into the underlying mechanisms, we studied a murine mesangial cell line stably transfected with a minigene expressing luciferase driven by 5'-flanking and first-intron regions of the alpha 1(IV) gene. High glucose stimulated luciferase activity dose and time dependently, with optimal stimulation (two-fold) achieved after 48 h in 450 mg/dL glucose (G450) versus 100 mg/dL (G100). We next tested the involvement of protein kinase C (PKC) because high glucose has been shown to stimulate de novo synthesis of diacylglycerol (DAG). Increasing PKC activity by treatment with a DAG analogue or active phorbol ester stimulated luciferase activity preferentially in G100; addition of the PKC inhibitors staurosporine or calphostin C markedly inhibited luciferase activity preferentially in G450. Thus high glucose promotes transcriptional activity of alpha 1(IV) gene through PKC activation. We also tested the involvement of protein kinase A (PKA). Intracellular cyclic AMP levels were increased two fold after 48 h in G450 versus G100, and addition of 8-Br-cAMP (0.1 mM) preferentially stimulated luciferase activity by almost three fold in G100 versus only 1.2-fold in G450. Hence, the signal-transduction mechanisms underlying the transcriptional activation of alpha 1(IV) gene in mesangial cells by high glucose are mediated by pathways involving the PKC system and possibly the cAMP/PKA system.

PKC and high glucose stimulate collagen alpha 1 (IV) transcriptional activity in a reporter mesangial cell line.

Increased glomerular collagen IV mRNA in streptozotocin-diabetic rats and stimulation of matrix transcripts by high glucose levels in short-term mesangial cell culture provide evidence that stimulation of matrix synthesis is important in early diabetic glomerulopathy. To test whether transcriptional modulation of collagen IV genes is operative, we stably transfected a murine mesangial cell line with a "minigene" expressing luciferase driven by 5'-flanking and first-intron regions of the murine COL4A1 gene to assess the response to high glucose and the associated signaling pathway. Luciferase activity was stimulated in a dose- and time-dependent manner [near-maximal stimulation in 450 mg/dl glucose (G450) was more than twofold the level in 100 mg/dl (G100) at 48 h]; high concentrations of D-mannitol were without effect. Neither low (2 ng/ml) nor high doses (2 micrograms/ml) of insulin modified luciferase activity in either G100 or G450. We next studied whether activation of protein kinase C (PKC) mediates the effect of high glucose. Treatment with the active phorbol ester phorbol 12-myristate 13-acetate for 2-4 h or with a diacylglycerol analogue for 24 h significantly stimulated luciferase activity preferentially in G100; the PKC inhibitors staurosporine or calphostin C significantly reduced the activity preferentially in G450. Thus high glucose levels promote transcriptional activity of COL4A1 gene in this reporter mesangial cell line, perhaps through PKC activation.

Polyol pathway mediates high glucose-induced collagen synthesis in proximal tubule.

The polyol pathway in diabetes is activated in tissues that are not dependent on insulin for glucose uptake. To examine the role of the polyol pathway in renal extracellular matrix accumulation, we incubated murine proximal tubule cells in either normal or high glucose concentration in the presence or absence of the aldose reductase inhibitor sorbinil. Rising medium glucose from 100 to 450 mg/dl for 72 hours increased cell sorbitol levels sevenfold. Addition of 0.4 mM sorbinil reduced sorbitol content to virtually undetectable levels as measured by gas chromatography. Sorbinil (0.1 to 0.2 mM) also reduced the secretion of collagens types IV and I in the high glucose concentration after 48 to 72 hours but had no appreciable effect in the normal glucose concentration. Concordantly, 0.1 mM sorbinil inhibited the high glucose-induced stimulation of alpha 1(IV) and alpha 2(I) mRNA levels without affecting levels in normal glucose concentration. To study the role of transcriptional activation of collagen genes, we transfected proximal tubule cells with a chloramphenicol acetyltransferase (CAT) reporter gene linked to the promoter and regulatory elements of alpha 1(IV) gene. CAT activity increased several-fold in the cells grown in the high versus normal glucose concentration; this transcriptional activation in culture media containing high glucose concentration was reduced by treatment of the cells with 0.1 mM sorbinil. Thus, high ambient glucose activates the polyol pathway in proximal tubule cells, and may mediate the high glucose-induced stimulation of gene expression for collagens types IV and I.(ABSTRACT TRUNCATED AT 250 WORDS)