Sensitivity of HaCat keratinocytes to diabetogenic toxins

Free Fatty Acid Receptor 1 Signaling Contributes to Migration, MMP-9 Activity, and Expression of IL-8 Induced by Linoleic Acid in HaCaT Cells

Keratinocytes and neutrophils are the main cellular components in wound healing during re-epithelization and inflammation. Free fatty acids such as linoleic acid (LA) present beneficial properties for wound healing by modulating the inflammatory response. LA is a natural ligand of free fatty acids receptor 1 (FFA1), a G protein-coupled receptor (GPCR), able to modulate inflammatory process; however, the role of FFA1 in keratinocytes and wound healing remains poorly understood. In this study, we investigated the role of FFA1 signaling in migration, matrix metalloproteinase-9 (MMP-9) activity, and IL-8 expression induced by LA in keratinocytes. We confirmed that HaCaT cells, a human keratinocyte cell line, expresses the FFA1 receptor and GW1100, a selective antagonist of FFA1, decreased LA-induced migration of HaCaT cells. Also, GW9508, a synthetic agonist of FFA1, increased migration of these cells. Furthermore, ERK1/2 and p38 MAPK inhibitors abolished the LA-induced increase in cell migration. Besides, HaCaT cells stimulated with LA or GW9508 increased the activity of MMP-9 and the expression of IL-8. GW1100 partially inhibited both responses. We further evaluated the effects of HaCaT cells conditioned media stimulated with LA or GW9508 on neutrophil chemotaxis. Conditioned media induced neutrophil chemotaxis. Furthermore, IL-8 secreted by HaCaT cells stimulated with LA or GW9508, contributed to neutrophil chemotaxis. In conclusion, LA increased migration, MMP-9 activity, and expression of IL-8 from HaCaT cells via FFA1. Hence, these results showed that the effects induced by LA in keratinocytes can be mediated through FFA1, thus explaining a possible mechanism by which this fatty acid could accelerate wound healing.

Hyperglycemia Induces Skin Barrier Dysfunctions with Impairment of Epidermal Integrity in Non-Wounded Skin of Type 1 Diabetic Mice

Diabetes causes skin complications, including xerosis and foot ulcers. Ulcers complicated by infections exacerbate skin conditions, and in severe cases, limb/toe amputations are required to prevent the development of sepsis. Here, we hypothesize that hyperglycemia induces skin barrier dysfunction with alterations of epidermal integrity. The effects of hyperglycemia on the epidermis were examined in streptozotocin-induced diabetic mice with/without insulin therapy. The results showed that dye leakages were prominent, and transepidermal water loss after tape stripping was exacerbated in diabetic mice. These data indicate that hyperglycemia impaired skin barrier functions. Additionally, the distribution of the protein associated with the tight junction structure, tight junction protein-1 (ZO-1), was characterized by diffuse and significantly wider expression in the diabetic mice compared to that in the control mice. In turn, epidermal cell number was significantly reduced and basal cells were irregularly aligned with ultrastructural alterations in diabetic mice. In contrast, the number of corneocytes, namely, denucleated and terminally differentiated keratinocytes significantly increased, while their sensitivity to mechanical stress was enhanced in the diabetic mice. We found that cell proliferation was significantly decreased, while apoptotic cells were comparable in the skin of diabetic mice, compared to those in the control mice. In the epidermis, Keratin 5 and keratin 14 expressions were reduced, while keratin 10 and loricrin were ectopically induced in diabetic mice. These data suggest that hyperglycemia altered keratinocyte proliferation/differentiation. Finally, these phenotypes observed in diabetic mice were mitigated by insulin treatment. Reduction in basal cell number and perturbation of the proliferation/differentiation process could be the underlying mechanisms for impaired skin barrier functions in diabetic mice.

Review of the mechanism of cell death resulting from streptozotocin challenge in experimental animals, its practical use and potential risk to humans

Streptozotocin (STZ) (2-deoxy-2-({[methyl(nitroso)amino]carbonyl}amino)-β-D-glucopyranose) is a naturally occurring diabetogenic compound, produced by the soil bacterium streptomyces achromogenes, that exhibits broad spectrum of antibacterial properties. Streptozotocin functions as a DNA synthesis inhibitor in both bacterial and mammalian cells. In mammalian cells, the actual mechanism and metabolic targets of STZ toxicity that results in cell death is not known. This review identifies four key areas that explain the mechanism of the cytotoxicity of STZ in mammalian cell lines, investigates the practical aspects of using STZ in experimental animals and the potential risks of its exposure to human health.

The Role of EGFR/ERK/ELK-1 MAP Kinase Pathway in the Underlying Damage to Diabetic Rat Skin

Background:

Diabetes mellitus (DM) is a highly prevalent disease. Atrophy and spontaneous ulcers are the most common cutaneous manifestation of diabetic dermopathy (DD). Before spontaneous ulcers, we believe there is an underlying damage stage although the mechanism is unknown.

Aims:

To explore the expression of extracellular signal-regulated kinase1/2 (ERK1/2), its correlated upstream protein epidermal growth factor receptor (EGFR) and its downstream transcription factor E twenty-six (ETS)-like 1(ELK-1)in the damage of the diabetic rat skin, and to explore the role of ERK1/2 on the recessive damage to diabetic rat skin.

Materials and Methods:

Eighty Sprague-Dawley (SD) rats weighing 260-300 g were randomly divided into control and streptozotocin (STZ)-induced diabetes groups. After 0.5, 2, 4, and 8 weeks, the shaved skin specimens from the back of rats in both groups were collected to observe the histological characteristics of the skin, to measure the thickness of the epidermis and the dermis, and to observe the ultrastructure. Immunohistochemistry (IHC) and Western blot techniques were used to detect the expression and activation of ERK1/2, EGFR, ELK-1 in the skin of the rats. Results: There are ultrastructural changes in the DM skin. With the continuance of the diabetes course, the thicknesses of the epidermis and dermis decreased, and the expression of phospho-ERK1/2 (P-ERK1/2), EGFR, and ELK-1 was decreased gradually in the back skin of the diabetes rats. It was significantly lower in 4 and 8 week DM than that of the normal control (P < 0.05). The expression of P-EGFR and P-ERK1/2 in the back skin of the diabetes rats was positively correlated (r = 0.572 P < 0.05), and the positive correlation was also obtained between P-ERK1/2 and P-ELK-1 (r = 0.715, P < 0.05).

Conclusion:

The phenomenon of recessive damage exists in the skin of diabetes rats, which probably may relate to the weakness of the signal transduction: P-EGFR → ERK1/2 → ELK-1.

Streptozotocin-induced cytotoxicity, oxidative stress and mitochondrial dysfunction in human hepatoma HepG2 cells

Streptozotocin (STZ) is an antibiotic often used in the treatment of different types of cancers. It is also highly cytotoxic to the pancreatic beta-cells and therefore is commonly used to induce experimental type 1 diabetes in rodents. Resistance towards STZ-induced cytotoxicity in cancer cells has also been reported. Our previous studies have reported organ-specific toxicity and metabolic alterations in STZ-induced diabetic rats. STZ induces oxidative stress and metabolic complications. The precise molecular mechanism of STZ-induced toxicity in different tissues and carcinomas is, however, unclear. We have, therefore, investigated the mechanism of cytotoxicity of STZ in HepG2 hepatoma cells in culture. Cells were treated with different doses of STZ for various time intervals and the cytotoxicity was studied by observing the alterations in oxidative stress, mitochondrial redox and metabolic functions. STZ induced ROS and RNS formation and oxidative stress as measured by an increase in the lipid peroxidation as well as alterations in the GSH-dependent antioxidant metabolism. The mitochondria appear to be a highly sensitive target for STZ toxicity. The mitochondrial membrane potential and enzyme activities were altered in STZ treated cells resulting in the inhibition of ATP synthesis. ROS-sensitive mitochondrial aconitase activity was markedly inhibited suggesting increased oxidative stress in STZ-induced mitochondrial toxicity. These results suggest that STZ-induced cytotoxicity in HepG2 cells is mediated, at least in part, by the increase in ROS/RNS production, oxidative stress and mitochondrial dysfunction. Our study may be significant for better understanding the mechanisms of STZ action in chemotherapy and drug induced toxicity.

Evolutionary interactions between diabetes and development

Because of the complications of diabetes affecting the mothers and their fetus/newborns are less known, this review examined the epidemiologic and mechanistic issues involved in the developmental programming of diabetic mothers. This overview showed that sperm, egg, zygote or blastocyst derived from diabetic parents may develop into offspring with high risk of any type of diabetes, even if placed in a normal uterus, producing developmental delay, embryopathy, geno- and cyto-toxicity, teratogenic changes, free radicals and apoptosis. These early insults may then lead to an increased rate of miscarriage and congenital anomalies depending on free radicals signaling and cell-death pathways involved by the diabetogenic agents. Furthermore, sperm, egg, zygote or blastocyst from normal parents will have an increased risk of diabetes if placed in a diabetic uterus. Interestingly, diabetes has deleterious effect on male/female reproductive functions and on the development of the blastocysts/embryos. Indeed, this review hypothesized that the long-term effects of diabetes during the pregnancy (gestational diabetes) may influence, generally, on the health of the embryos, newborns (perinatal life) and adulthood. However, there are obvious species differences between pregnant women and animal models. Thus, maintaining normoglycaemia during pregnancy may play an important role in a healthy life for the newborns.

Differential Induction of Apoptosis by Antidepressants in Glioma and Neuroblastoma Cell Lines: Evidence for p-c-Jun, Cytochrome c, and Caspase-3 Involvement

Several antidepressants, mainly selective serotonin-reuptake inhibitors (SSRIs) and some tricyclic antidepressants (TCAs), have been shown to possess potent apoptotic activity in different cell lines. Our aim was to screen and select those agents with significant activity and elucidate the molecular pathway underlying this process in rat glioma and human neuroblastoma cell lines. We studied the effect of different antidepressants on apoptotic markers, including: cell viability, DNA fragmentation, cytochrome c (Cyt c) release from mitochondria, and caspase-3- like activity. In addition, the involvement of MAPK genes, c-Jun, and ERK was determined. Paroxetine and fluoxetine, SSRIs, clomipramine, a TCA, but not imipramine or mianserin (an atypical antidepressant), caused apoptosis in both cell lines, as assessed by flow cytometry of propidium iodide-stained C6 cells and typical fluorescence microscopy in glioma cells. These apoptotic changes were preceded by rapid increase in p-c-Jun levels, Cyt c release from mitochondria, and increased caspase-3-like activity. Assessment of paroxetine cytotoxicity in primary mouse brain and neuronal cultures showed significantly lower sensitivity to the drug's proapoptotic activity. These results strongly suggest that selected antidepressants induce apoptosis in neuronal and glial cell lines. Activation of p-c-Jun and subsequent increased Cyt c mitochondrial release participate in the apoptotic mechanism of the antidepressant. The high sensitivity to these drugs of the cancer cell, compared with primary brain tissue, suggests the potential use of these agents in the treatment of brain-derived tumors.

Characterization of phenothiazine-induced apoptosis in neuroblastoma and glioma cell lines: clinical relevance and possible application for brain-derived tumors

In this study we aimed to (1). screen phenothiazines for cytotoxic activity in glioma, neuroblastoma, and primary mouse brain tissue; and (2). determine the mechanism of the cytotoxic effect (apoptosis, necrosis) and the roles of calmodulin inhibition and sigma receptor modulation. Rat glioma (C6) and human neuroblastoma (SHSY-5Y) cell lines were treated with different phenothiazines. All agents induced a dose-dependent decrease in viability and proliferation, with the highest activity elicited by thioridazine. Sensitivity to thioridazine of glioma and neuroblastoma cells was significantly higher (p < 0.05) than that of primary mouse brain culture (IC50 11.2 and 15.1 microM vs 41.3 microM, respectively). The N-mustard fluphenazine induced significantly lower cytotoxicity in glioma cells, compared to fluphenazine. The sigma receptor selective ligand (+)-SK&F10047 increased viability slightly while combined with fluphenazine; SK&F10047 did not alter fluphenazine activity. Flow cytometry of propidium iodide (PI)-stained glioma cells treated with thioridazine, fluphenazine, or perphenazine (6-50 microM) resulted in a concentration-dependent increase of fragmented DNA up to 94% vs 3% in controls by all agents. Thioridazine (12.5 microM)-treated glioma cells costained with PI and Hoechst 33342 revealed a red fluorescence of fragmented nuclei in treated cells and a blue fluorescence of intact control nuclei. After 4-h exposure to thioridazine (25 and 50 microM), a 25- to 30-fold increase in caspase-3 activity in neuroblastoma cells was noted. Overall, the marked apoptotic effect of phenothiazines in brain-derived cancer cells, and the low sensitivity of primary brain tissue suggest the potential use of selected agents as therapeutic modalities in brain cancer.

Genotoxicity of streptozotocin

Streptozotocin (Streptozocin, STZ, CAS No. 18883-66-4) is a monofunctional nitrosourea derivative isolated from Streptomyces achromogenes. It has broad spectrum antibiotic activity and antineoplastic properties and is often used to induce diabetes mellitus in experimental animals through its toxic effects on pancreatic beta cells. STZ is a potent alkylating agent known to directly methylate DNA and is highly genotoxic, producing DNA strand breaks, alkali-labile sites, unscheduled DNA synthesis, DNA adducts, chromosomal aberrations, micronuclei, sister chromatid exchanges, and cell death. This antibiotic was found to be mutagenic in bacterial assays and eukaryotic cells. STZ is also carcinogenic; a single administration induces tumors in rat kidney, liver, and pancreas. Several lines of evidence indicate that free radicals are involved in the production of DNA and chromosome damage by this compound. Because of the use of STZ as an antineoplastic agent, the study of its genotoxicity has considerable practical significance. The purpose of this review is to present our current knowledge regarding the genotoxicity of STZ.