We observed that a relationship between serum ferritin levels and insulin resistance exists in women but not in men. This sexual dimorphism merits further investigation.

Dietary induced obesity in rodents is associated with a resistance to leptin. We have investigated the hypothesis that dietary fat per se alters the feeding response to peripheral leptin in rats that were fed either their habitual high- or low-fat diet or were naively exposed to the alternative diet. Osborne-Mendel rats were adapted to either high- or low-fat diet. Food-deprived rats were given either leptin (0.5 mg/kg body wt ip) or saline, after which they were provided with either their familiar diet or the alternative diet. Food intake of rats adapted and tested with the low-fat diet was reduced 4 h after leptin injection, whereas rats adapted and tested with a high-fat diet did not respond to leptin. Leptin was injected again 1 and 5 days after the high-fat diet-adapted rats were switched to the low-fat diet. Leptin reduced the food intake on both days. In contrast, when low-fat diet-adapted rats were switched to a high-fat diet, the leptin inhibitory response was present on day 1 but not observed on day 5. Peripheral injection of leptin increased serum corticosterone level and decreased hypothalamic neuropeptide Y mRNA expression in rats fed the low-fat but not the high-fat diet for 20 days. The data suggest that dietary fat itself, rather than obesity, may induce leptin resistance within a short time of exposure to a high-fat diet.

Cell-penetrating peptides (CPPs) are short peptides which can carry various types of molecules into cells; however, although most CPPs rapidly penetrate cells in vitro, their in vivo tissue-targeting specificities are low. Herein, we describe cell-binding, internalization, and targeting characteristics of a newly identified 10-residue CPP, denoted ECP32–41, derived from the core heparin-binding motif of human eosinophil cationic protein (ECP). Besides traditional emphasis on positively charged residues, the presence of cysteine and tryptophan residues was demonstrated to be essential for internalization. ECP32–41 entered Beas-2B and wild-type CHO-K1 cells, but not CHO cells lacking of cell-surface glycosaminoglycans (GAGs), indicating that binding of ECP32–41 to cell-surface GAGs was required for internalization. When cells were cultured with GAGs or pre-treated with GAG-digesting enzymes, significant decreases in ECP32–41 internalization were observed, suggesting that cell-surface GAGs, especially heparan sulfate proteoglycans were necessary for ECP32–41 attachment and penetration. Furthermore, treatment with pharmacological agents identified two forms of energy-dependent endocytosis, lipid-raft endocytosis and macropinocytosis, as the major ECP32–41 internalization routes. ECP32–41 was demonstrated to transport various cargoes including fluorescent chemical, fluorescent protein, and peptidomimetic drug into cultured Beas-2B cells in vitro, and targeted broncho-epithelial and intestinal villi tissues in vivo. Hence this CPP has the potential to serve as a novel vehicle for intracellular delivery of biomolecules or medicines, especially for the treatment of pulmonary or gastrointestinal diseases.

This study investigates the mechanism of cell death induced by cadmium (Cd) in Chinese hamster ovary (CHO) cells. Cells exposed to 4 microM Cd for 24 h did not show signs of apoptosis, such as DNA fragmentation and caspase-3 activation. The pro-apoptotic (Bax) or anti-apoptotic (Bcl-2 and Bcl-xL) protein levels in the Bcl-2 family were not altered. However, an increase in propidium iodide uptake and depletion of ATP, characteristics of necrotic cell death, were observed. Cd treatment increased the intracellular calcium (Ca2+) level. Removal of the Ca2+ by a chelator, BAPTA-AM, efficiently inhibited Cd-induced necrosis. The increased Ca2+ subsequently mediated calpain activation and intracellular ROS production. Calpains then triggered mitochondrial depolarization resulting in cell necrosis. Cyclosporin A, an inhibitor of mitochondrial permeability transition, recovered the membrane potential and reduced the necrotic effect. The generated ROS reduced basal NF-kappaB activity and led cells to necrosis. An increase of NF-kappaB activity by its activator, PMA, attenuated Cd-induced necrosis. Calpains and ROS act cooperatively in this process. The calpain inhibitor and the ROS scavenger synergistically inhibited Cd-induced necrosis. Results in this study suggest that Cd stimulates Ca2+-dependent necrosis in CHO cells through two separate pathways. It reduces mitochondrial membrane potential by activating calpain and inhibits NF-kappaB activity by increasing the ROS level.

No abstract

The effects of protein kinase C (PKC) inhibitors on the metallothionein (MT) gene expression induced by metals were investigated. When PKC inhibitor (H7 or chelerythrine) was administered to Cd resistant, MT gene-amplified Chinese hamster ovary (Cd ) cells, the induction of MT mRNA by Cd or Zn was blocked. Treating the Cd cells with a PKA-specific inhibitor, HA1004, did not cause an inhibition of metal-induced MT gene transcription. The inhibitory effect was effectuated by adding inhibitors within 40 min of exposing the cells to Cd. Apparently, AP1 was not involved in this down-regulatory effect of PKC inhibitor on MT gene expression since the inducibility of MT promoter was blocked by H7 even in the absence of the AP1-binding sequence. For Cd-treated cells, Cd accumulation in the cell was similar with or without H7 treatment. However, H7 markedly reduced cellular Zn accumulation when the cells were treated with Zn. Cycloheximide treatment increased the level of MT mRNA. This elevation can also be blocked by treating the cell with PKC inhibitor. Results in this study suggest that PKC participates in the process of metal-induced MT gene expression.z 1997 Federation of European Biochemical Societies.

No abstract

No abstract