Yoshifumi Hida

Counteraction of retinoic acid and 1,25-dihydroxyvitamin D3 on up-regulation of adipocyte differentiation with PPARγ ligand, an antidiabetic thiazolidinedione, in 3T3-L1 cells

Retinoic acid (RA) and 1,25-dihydroxyvitamin D3 (1,25 (OH)2 D3) inhibited adipocyte differentiation of 3T3-L1 preadipocytes in the presence of thiazolidinedione, a specific ligand for peroxisome proliferator-activated receptory (PPARgamma). These fat-soluble vitamins repressed the up-regulated protein expression of PPARgamma2 during the first 40 hours of initiation of 3T3-L1 preadipocyte differentiation. Compared with RA, 1,25 (OH)2 D3 inhibited PPARgamma2 expression more effectively and caused concomitantly a greater inhibition of adipocyte differentiation. These results suggest that the inhibitory action of adipocyte differentiation by RA or 1,25 (OH)2 D3 is exhibited through direct repression of the expression of PPARgamma2 protein, even in the presence of its ligand. They also raise the intriguing possibility that attenuation or amplification of the pharmacological effects of thiazolidinedione that are dependent on PPARgamma in adipose cells is caused by alteration of the levels of these fat-soluble vitamins.

Spatial distribution and seasonal changes of pesticides in Lake Biwa, Japan

The spatial distribution and seasonal variation in the concentrations in Lake Biwa of pesticides used in paddy fields were studied. Lake Biwa is the largest lake in Japan and is a recognized water resource for 14 million people in the Kinki district. Samples were collected nine times from April to December 2001 at ten sites within the lake and at the mouths of six influent rivers. Weekly sampling was also carried out at a single site on an effluent river. Among the 20 pesticides analyzed, the detection frequencies in surface water were almost 100% for simetryn, bromobutide, and isoprothiolane; around 75% for molinate and pyroquilon; around 30% for three herbicides and one fungicide; and almost zero for the remaining substances. The maximum concentrations of pesticides detected frequently in the lake were in the range 0.1–0.4 µg l−1. The occurrence of a few pesticides below the thermocline may be explained by thermal stratification and vertical circulation. Although the thermocline suppressed vertical diffusion in spring and summer during pesticide application periods, a few pesticides remaining at the surface of the lake in winter were transported to the hypolimnion by vertical circulation and remained there even after the reestablishment of the thermocline. The half-lives of pesticides in the lake were estimated to be more than a year for simetryn, half a year for bromobutide, 1.5 months for molinate, and 1 month for dimepiperate. The main cause of elimination for molinate and dimepiperate was estimated to be degradation, that for simetryn was outflow, and for bromobutide both degradation and outflow were significant.

Substrate Specificity of Rat Plasma Lecithin-cholesterol Acyltransferase towards a Molecular Species of Phosphatidylcholine

The substrate specificity and the affinity of rat purified lecithin-cholesterol acyltransferase towards the molecular species of phosphatidylcholine (PC) were studied in comparison with the human enzyme. The substrate vesicles were prepared with 40% of a test PC, 60% of egg yolk PC, and tritium cholesterol. Both human and rat enzymes showed similar high reactivity to the substrates containing three major PCs (16: 0-18: 1 PC, 16: 0-18: 2 PC, and 18: 0-18: 1 PC) of egg yolk compared with the vesicles of egg yolk PC alone. In the case of 18: 0-20: 4 PC, the rat enzyme had the highest activity among all the test PCs, but the human enzyme only had a moderate activity. Even when the substrate consisted of 18: 0-20: 4 PC alone, the rat enzyme had a high activity, but the activity of the human enzyme was not detected. Symmetrical diacyl-PCs (18: 2-18: 2 PC, 18: 1-18: 1 PC, 18: 0-18: 0 PC) were not a preferable substrate for either enzyme. The transfer of both the human and rat enzymes from the vesicles containing 18: 0-20: 4 PC to the egg yolk PC vesicles was on a higher level than that from the vesicles containing 18: 2-18: 2 PC. This suggests that the activity of the LCA T can be easily influenced by the kinds of PC molecular species and its relative content in the substrate and that the substrate may provide the extent of the enzyme transfer between the substrate particles.

Counteraction of the Active form of Vitamins A and D on Up-Regulation of Adipocyte Differentiation with PPARγ Ligand, a Thiazolidinedione, in 3T3-L1 Cells

The active form of vitamin A, retinoic acid (RA), and that of vitamin D, 1,25-dihydroxyvitamin D3 (1,25 (OH)2 D3) inhibited adipocyte differentiation of 3T3-L1 preadipocytes in the presence of thiazolidinedione, a specific ligand for peroxisome proliferator-activated (PPARγ) receptory These fat-soluble vitamins repressed the upregulated protein expression of PPARγ2 during the first 40 hours of initiation of 3T3-L1 preadipocyte differentiation. Compared with RA, 1,25 (OH)2 D3 inhibited PPARγ2 expression more effectively and caused concomitantly a greater inhibition of adipocyte differentiation. These results suggest that the inhibitory action of adipocyte differentiation by RA or 1,25 (OH)2 D3 is exhibited through direct repression of the expression of PPARγ2 protein, even in the presence of its ligand. They also raise the intriguing possibility that attenuation or amplification of the pharmacological effects of thiazolidinedione that are dependent on PPARγ in adipose cells is caused by alteration of the levels of these fat-soluble vitamins.