Adipocytes secrete a variety of bioactive molecules that affect the insulin sensitivity of other tissues. We now show that the abundance of monocyte chemoattractant protein-1 (MCP-1) mRNA in adipose tissue and the plasma concentration of MCP-1 were increased both in genetically obese diabetic (db/db) mice and in WT mice with obesity induced by a high-fat diet. Mice engineered to express an MCP-1 transgene in adipose tissue under the control of the aP2 gene promoter exhibited insulin resistance, macrophage infiltration into adipose tissue, and increased hepatic triglyceride content. Furthermore, insulin resistance, hepatic steatosis, and macrophage accumulation in adipose tissue induced by a high-fat diet were reduced extensively in MCP-1 homozygous KO mice compared with WT animals. Finally, acute expression of a dominant-negative mutant of MCP-1 ameliorated insulin resistance in db/db mice and in WT mice fed a high-fat diet. These findings suggest that an increase in MCP-1 expression in adipose tissue contributes to the macrophage infiltration into this tissue, insulin resistance, and hepatic steatosis associated with obesity in mice.

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Methylglyoxal (MG), an endogenous metabolite that increases in diabetes and is a common intermediate in the Maillard reaction (glycation), reacts with proteins and forms advanced glycation end products. In the present study, we identify a novel MG-arginine adduct and also characterize the structure of a major fluorescent adduct. In addition, we describe the immunochemical study on the MG-arginine adducts using monoclonal antibody directed to MG-modified protein. On the other hand, as an immunochemical approach to the detection of these MG adducts, we raised the monoclonal antibodies (mAb3C and mAb6B) directed to the MG-modified protein and found that they specifically recognized the major fluorescent product, argpyrimidine, as the dominant epitope. The immunohistochemical analysis of the kidneys from diabetic patients revealed the localization of argpyrimidine in intima and media of small artery walls. Furthermore, the accumulation of argpyrimidine was also observed in some arterial walls of the rat brain after middle cerebral artery occlusion followed by reperfusion. These results suggest that argpyrimidine may contribute to the progression of not only long term diabetic complications, such as nephropathy and atherosclerosis, but also the tissue injury caused by ischemia/reperfusion.Nonenzymatic glycation (Maillard reaction) is a complex series of reactions between reducing sugars and amino groups of proteins, which leads to browning, fluorescence, and crosslinking of the proteins. The reaction is initiated with the reversible formation of a Schiff's base, which undergoes a rearrangement to form a relatively stable Amadori product. The Amadori product further undergoes a series of reactions through dicarbonyl intermediates to form advanced glycation end products (AGEs) 1 (1). It has been shown that the formation of AGEs in vivo contributes to the pathophysiologies associated with aging and the long term complications of diabetes (2).A number of aldehydes and ketones, in addition to sugars, are known to form AGEs. Methylglyoxal (MG), among them, has recently received considerable attention as a mediator to form AGEs. MG is known to be formed nonenzymically by amine-catalyzed sugar fragmentation reactions (3-5) and by spontaneous decomposition of triose phosphate intermediates in glycolysis (5). It is also a product of the metabolism of acetol, an intermediate in the catabolism of both threonine (6) and the ketone body acetone (7). A recent study on the formation of AGEs in endothelial cells cultured under hyperglycemic conditions indicated that MG was the major precursor of AGEs (8). Chaplen et al. (9) have shown that high levels of MG are indeed present in cultured Chinese hamster ovary cells. In addition, increased levels of MG are also found in blood from diabetic patients and in the lens of streptozotosin-induced diabetic rats (10, 11). Che et al. (12) have reported that MG induces gene expression of heparin-binding epidermal growth factor-like growth factor by provoking oxidative stress. It is also known ...

Mutational activation of the ras proto-oncogenes is frequently found in skin cancers. However, the nature of downstream signaling pathways from Ras involved in skin carcinogenesis remains poorly understood. Recently, we and others identified phospholipase C (PLC) ⑀ as an effector of Ras. Here we have examined the role of PLC⑀ in de novo skin chemical carcinogenesis by using mice whose PLC⑀ is genetically inactivated. PLC⑀ ؊/؊ mice exhibit delayed onset and markedly reduced incidence of skin squamous tumors induced by initiation with 7,12-dimethylbenz(a)anthracene followed by promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA). Furthermore, the papillomas formed in PLC⑀ ؊/؊ mice fail to undergo malignant progression into carcinomas, in contrast to a malignant conversion rate of approximately 20% observed with papillomas in PLC⑀ ؉/؉ mice. In all of the tumors analyzed, the Ha-ras gene is mutationally activated irrespective of the PLC⑀ background. The skin of PLC⑀ ؊/؊ mice fails to exhibit basal layer cell proliferation and epidermal hyperplasia in response to TPA treatment. These results indicate a crucial role of PLC⑀ in ras oncogene-induced de novo carcinogenesis and downstream signaling from TPA, introducing PLC⑀ as a candidate molecular target for the development of anticancer drugs.

Ras gene mutations occur relatively early during colorectal tumor development and have been observed in 40-50% of malignant colorectal tumors. Advances in endoscopic techniques have made it possible to detect small, flat colorectal tumors that could not be detected by standard examinations. To determine whether ras gene mutations are also involved in the genesis of small, flat colorectal tumors, we examined ras point mutations in 34 cases of small polypoid or flat elevated colorectal tumors (32 adenomas, 2 carcinomas) and in 26 cases of small, flat colorectal tumors (13 adenomas, 13 carcinomas) by means of the polymerase chain reaction (PCR) and dot-blot hybridization. Ras gene point mutations were observed in 16 of the 34 tumors of the former type (47%), but in none of the 26 tumors of the latter type, even though the grade of dysplasia was severe in the flat tumors. Our results suggest that different genetic pathways for tumor progression may exist for polypoid and for flat colorectal carcinomas.