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Hepatocellular carcinoma is the second leading cause of cancer death worldwide. DNA microarray analysis identified the ornithine aminotransferase (OAT) gene as a prominent gene overexpressed in hepatocellular carcinoma (HCC) from Psammomys obesus. In vitro studies demonstrated inactivation of OAT by gabaculine (1), a neurotoxic natural product, which suppressed in vitro proliferation of two HCC cell lines. Alpha-fetoprotein (AFP) secretion, a biomarker for HCC, was suppressed by gabaculine in both cell lines, but not significantly. Because of the active site similarity between GABA aminotransferase (GABA-AT) and OAT, a library of 24 GABA-AT inhibitors was screened to identify a more selective inhibitor of OAT. (1S,3S)-3-Amino-4-(hexafluoropropan-2-ylidene)cyclopentane-1-carboxylic acid (2) was found to be an inactivator of OAT that only weakly inhibits GABA-AT, Laspartate aminotransferase, and L-alanine aminotransferase. In vitro administration of 2 significantly suppressed AFP secretion in both Hep3B and HepG2 HCC cells; in vivo, 2 significantly suppressed AFP serum levels and tumor growth in HCC-harboring mice, even at 0.1 mg/kg. Overexpression of the OAT gene in HCC and the ability to block the growth of HCC by OAT inhibitors support the role of OAT as a potential therapeutic target to inhibit HCC growth. This is the first demonstration of suppression of HCC by an OAT inactivator.

Based on titration microcalorimetry and Caco-2 cell line transfection studies, it has been suggested that the A54T of the FABP2 gene plays a significant role in the assimilation of dietary fatty acids. However, reports were divergent with regard to the in vivo interaction between this polymorphism and postprandial lipemia. We therefore determined the influence of this intestinal fatty acid-binding protein polymorphism on intestinal fat transport using the human jejunal organ culture model, thus avoiding the interference of various circulating factors capable of metabolizing in vivo postprandial lipids. Analysis of DNA samples from 32 fetal intestines revealed 22 homozygotes for the wild-type Ala-54/ Ala-54 genotype (0.83) and 10 heterozygotes for the polymorphic Thr-54/Ala-54 genotype (0.17). The Thr-encoding allele was associated with increased secretion of newly esterified triglycerides, augmented de novo apolipoprotein B synthesis, and elevated chylomicron output. On the other hand, no alterations were found in very low density lipoprotein and high density lipoprotein production, apolipoprotein A-I biogenesis, or microsomal triglyceride transfer protein mass and activity. Similarly, the alanine to threonine substitution at residue 54 did not result in changes in brush border hydrolytic activities (sucrase, glucoamylase, lactase, and alkaline phosphatase) or in glucose uptake or oxidation. Our data clearly document that the A54T polymorphism of FABP2 specifically influences small intestinal lipid absorption without modifying glucose uptake or metabolism. It is proposed that, in the absence of confounding factors such as environmental and genetic variables, the FABP2 polymorphism has an important effect on postprandial lipids in vivo, potentially influencing plasma levels of lipids and atherogenesis.

Animals with genetically or nutritionally induced insulin resistance and Type 2 diabetes comprise two groups: those with resilient beta-cells, e.g., ob/ob mice or fa/fa rats, capable of longstanding compensatory insulin hypersecretion and those with labile beta-cells in which the secretion pressure leads to beta-cell degranulation and apoptosis, e.g., db/db mice and Psammomys gerbils (sand rats). Psammomys features low insulin receptor density; on a relatively high energy diet it becomes hyperinsulinemic and hyperglycemic. In hyperinsulinemic clamp the hepatic glucose production is only partially suppressed by insulin, even in the normoglycemic state. The capacity of insulin to activate muscle and liver receptor tyrosine kinase is nearly abolished. GLUT4 content and mRNA are markedly reduced. Hyperinsulinemia was also demonstrated to inhibit insulin signaling and glucose transport in several other species. Among the factors affecting the insulin signaling pathway, phosphorylation of serine/threonine appears to be the prominent cause of receptor malfunction as inferred from the finding of overexpression of PKC epsilon isoforms in the muscle and liver of Psammomys. The insulin resistance syndrome progressing in animals with labile beta-cells to overt diabetes and beta-cell failure is a "thrifty gene" characteristic. This is probably also true for human populations emerging from food scarcity into nutritional affluence, inappropriate for their metabolic capacity. Thus, the nutritionally induced hyperinsulinemia, associated with PKC epsilon activation may be looked upon from the molecular point of view as "PKC epsilon overexpression syndrome."

The sand rat (Psammomys obesus) is an animal model of nutritionally induced diabetes. We report here that several protein kinase C (PKC) isoforms (␣, , and , representing all three subclasses of PKC) are overexpressed in the skeletal muscle of diabetic animals of this species. This is most prominent for the isotype of PKC. Interestingly, increased expression of PKC could already be detected in normoinsulinemic, normoglycemic (prediabetic) animals of the diabetes-prone (DP) line when compared with a diabetes-resistant (DR) line. In addition, plasma membrane (PM)-associated fractions of PKC␣ and PKC were significantly increased in skeletal muscle of diabetic animals, suggesting chronic activation of these PKC isotypes in the diabetic state. The increased PM association of these PKC isotypes revealed a significant correlation with the diacylglycerol content in the muscle samples. P sammomys obesus, often nicknamed "sand rat," is a herbivorous desert gerbil living in the eastern Mediterranean and North Africa. The Jerusalem colony was established by domesticating the animals collected from the shores of the Dead Sea (1,2). In its native habitat, the Psammomys feeds on the halophilic plant Atriplex halimus and has never been found to be hyperglycemic or hyperinsulinemic. In captivity, it remains nondiabetic when fed a low energy (LE) diet containing 2.4 cal/g. However, when transferred to a relatively high energy (HE) diet of 3.0 cal/g, similar to the regular rodent diet, it gradually develops hyperinsulinemia and hyperglycemia. Four generally consecutive stages of progression to diabetes have been described (3). The basal stage A is followed by hyperinsulinemia without hyperglycemia (stage B), which precedes hyperinsulinemia with hyperglycemia (stage C), and lastly, stage D, marked by pancreatic insulin secretion collapse with apoptosis (4) and dependence on external insulin supply for survival.Two Psammomys lines have been separated by selective breeding: the diabetes-resistant (DR) line, which remains normoglycemic and normoinsulinemic even on an HE diet, and the diabetes-prone (DP) line, which is susceptible to diabetes when exposed to the HE diet (4). The main difference between the two lines seems to be the cost of weight gain: the DP line uses 6.0 kcal/g for growth during 2 weeks after weaning, whereas the DR line requires 9.3 kcal/g (4). The DP animals exhibit insulin resistance even in the state of normoglycemia, as evidenced by the failure to induce hypoglycemia after external insulin administration and a minimal reduction of hepatic gluconeogenesis during the euglycemic-hyperinsulinemic clamp (5). Therefore, the insulin resistance in the Psammomys may be considered an innate characteristic of a desert animal according to the thrifty gene hypothesis (6).Alterations in the expression level and/or activity of several protein kinase C (PKC) isoforms were found to be associated with insulin resistance in type 2 diabetic patients, animal models of diabetes, and different cell models (7-10). The serine/threonine ...