Repeated administration of low-dose cisplatin in mice induces fibrosis.

Cisplatin, a chemotherapeutic used for the treatment of solid cancers, has nephrotoxic side effects leading to acute kidney injury (AKI). Cisplatin cannot be given to patients that have comorbidities that predispose them to an increased risk for AKI. Even without these comorbidities, 30% of patients administered cisplatin will develop kidney injury, requiring the oncologist to withhold or reduce the next dose, leading to a less effective therapeutic regimen. Although recovery can occur after one episode of cisplatin-induced AKI, longitudinal studies have indicated that multiple episodes of AKI lead to the development of chronic kidney disease, an irreversible disease with no current treatment. The standard mouse model of cisplatin-induced AKI consists of one high dose of cisplatin (>20 mg/kg) that is lethal to the animal 3 days later. This model does not accurately reflect the dosing regimen patients receive nor does it allow for the long-term study of kidney function and biology. We have developed a repeated dosing model whereby cisplatin is given once a week for 4 wk. Comparison of the repeated dosing model with the standard dosing model demonstrated that inflammatory cytokines and chemokines were induced in the repeated dosing model, but levels of cell death were lower in the repeated dosing model. The repeated dosing model had increased levels of fibrotic markers (fibronectin, transforming growth factor-ß, and α-smooth muscle actin) and interstitial fibrosis. These data indicate that the repeated dosing model can be used to study the AKI to chronic kidney disease progression as well as the mechanisms of this progression.

Kidney glycosphingolipids are elevated early in diabetic nephropathy and mediate hypertrophy of mesangial cells.

Glycosphingolipids (GSLs) play a role in insulin resistance and diabetes, but their role in diabetic nephropathy (DN) has received limited attention. We used 9- and 17-wk-old nondiabetic db/m and diabetic db/db mice to examine the role of GSLs in DN. Cerebrosides or monoglycosylated GSLs [hexosylceramides (HexCers); glucosyl- and galactosylceramides] and lactosylceramide (LacCers) were elevated in db/db mouse kidney cortices, specifically in glomeruli, and also in urine. In our recent paper (25), we observed that the kidneys exhibited glomerular hypertrophy and proximal tubular vacuolization and increased fibrosis markers at these time points. Mesangial cells contribute to hyperglycemia-induced glomerular hypertrophy in DN. Hyperglycemic culture conditions, similar to that present in diabetes, were sufficient to elevate mesangial cell HexCers and increase markers of fibrosis, extracellular matrix proteins, and cellular hypertrophy. Inhibition of glucosylceramide synthase or lowering glucose levels decreased markers of fibrosis and extracellular matrix proteins and reversed mesangial cell hypertrophy. Hyperglycemia increased phosphorylated (p)SMAD3 and pAkt levels and reduced phosphatase and tensin homolog levels, which were reversed with glucosylceramide synthase inhibition. These data suggest that inhibition of glucosylceramide synthase reversed mesangial cell hypertrophy through decreased pAkt and pSmad3 and increased pathways responsible for protein degradation. Importantly, urinary GSL levels were higher in patients with DN compared with healthy control subjects, implicating a role for these lipids in human DN. Thus, hyperglycemia in type II diabetes leads to renal dysfunction at least in part by inducing accumulation of HexCers and LacCers in mesangial cells, resulting in fibrosis, extracellular matrix production, and hypertrophy.

Sphingomyelin synthase 1 activity is regulated by the BCR-ABL oncogene.

Sphingomyelin synthase (SMS) produces sphingomyelin while consuming ceramide (a negative regulator of cell proliferation) and forming diacylglycerol (DAG) (a mitogenic factor). Therefore, enhanced SMS activity could favor cell proliferation. To examine if dysregulated SMS contributes to leukemogenesis, we measured SMS activity in several leukemic cell lines and found that it is highly elevated in K562 chronic myelogenous leukemia (CML) cells. The increased SMS in K562 cells was caused by the presence of Bcr-abl, a hallmark of CML; stable expression of Bcr-abl elevated SMS activity in HL-60 cells while inhibition of the tyrosine kinase activity of Bcr-abl with Imatinib mesylate decreased SMS activity in K562 cells. The increased SMS activity was the result of up-regulation of the Sms1 isoform. Inhibition of SMS activity with D609 (a pharmacological SMS inhibitor) or down-regulation of SMS1 expression by siRNA selectively inhibited the proliferation of Bcr-abl-positive cells. The inhibition was associated with an increased production of ceramide and a decreased production of DAG, conditions that antagonize cell proliferation. A similar change in lipid profile was also observed upon pharmacological inhibition of Bcr-abl (K526 cells) and siRNA-mediated down-regulation of BCR-ABL (HL-60/Bcr-abl cells). These findings indicate that Sms1 is a downstream target of Bcr-abl, involved in sustaining cell proliferation of Bcr-abl-positive cells.

Sphingomyelin synthases regulate protein trafficking and secretion.

Sphingomyelin synthases (SMS1 and 2) represent a class of enzymes that transfer a phosphocholine moiety from phosphatidylcholine onto ceramide thus producing sphingomyelin and diacylglycerol (DAG). SMS1 localizes at the Golgi while SMS2 localizes both at the Golgi and the plasma membrane. Previous studies from our laboratory showed that modulation of SMS1 and, to a lesser extent, of SMS2 affected the formation of DAG at the Golgi apparatus. As a consequence, down-regulation of SMS1 and SMS2 reduced the localization of the DAG-binding protein, protein kinase D (PKD), to the Golgi. Since PKD recruitment to the Golgi has been implicated in cellular secretion through the trans golgi network (TGN), the effect of down-regulation of SMSs on TGN-to-plasma membrane trafficking was studied. Down regulation of either SMS1 or SMS2 significantly retarded trafficking of the reporter protein vesicular stomatitis virus G protein tagged with GFP (VSVG-GFP) from the TGN to the cell surface. Inhibition of SMSs also induced tubular protrusions from the trans Golgi network reminiscent of inhibited TGN membrane fission. Since a recent study demonstrated the requirement of PKD activity for insulin secretion in beta cells, we tested the function of SMS in this model. Inhibition of SMS significantly reduced insulin secretion in rat INS-1 cells. Taken together these results provide the first direct evidence that both enzymes (SMS1 and 2) are capable of regulating TGN-mediated protein trafficking and secretion, functions that are compatible with PKD being a down-stream target for SMSs in the Golgi.

Emerging role of Centella asiatica in improving age-related neurological antioxidant status.

Free radicals have been hypothesized to play an important role in ageing process. There exists an imbalance between free radical production and antioxidant defense mechanism, which may lead to cell death during ageing. Our study was designed to determine whether extract of Centella asiatica, an antioxidant, when administered orally (300 mg/kg body weight/day) for 60 days would prevent age-related changes in antioxidant defense system, lipid peroxidation (LPO) and protein carbonyl (PCO) content in rat brain regions such as cortex, hypothalamus, striatum, cerebellum and hippocampus. Aged rats elicited a significant decline in the antioxidant status and increased the LPO and PCO as compared to control rats in all five regions studied. The increase in LPO and PCO contents were (64%, 34%) in cortex, (86%, 30%) in cerebellum, (51%, 47%) in striatum, (77%, 27%) in hypothalamus and (58%, 45%) in hippocampus, respectively, in aged rats as compared to young rats. Supplementation of C. asiatica was effective in reducing brain regional LPO and PCO levels and in increasing the antioxidant status. Thus, C. asiatica by acting as a potent antioxidant exerted significant neuroprotective effect and proved efficacious in protecting rat brain against age related oxidative damage.

Arsenic intoxication-induced reduction of glutathione level and of the activity of related enzymes in rat brain regions: reversal by DL-alpha-lipoic acid.

The purpose of this study was to examine the effects of DL: -alpha-lipoic acid (LA) on arsenic (As) induced alteration of glutathione (GSH) level and of the activity of glutathione-related enzymes-glutathione peroxidase (GSH-Px), glutathione reductase (GR), and glucose-6-phosphate dehydrogenase (G6PDH)-in rat brain regions (cortex, hypothalamus, striatum, cerebellum and hippocampus). Male Wistar rats of 150+/-10 g weight were divided into four groups: control and three experimental groups supplemented with arsenic (sodium arsenite) alone (100 ppm mixed in drinking water), lipoic acid alone (70 mg kg(-1) body weight), arsenic plus lipoic acid (100 ppm arsenic in drinking water plus 70 mg lipoic acid kg(-1) body weight). The arsenic content of brain regions was found to increase with the administration of sodium arsenite. Arsenic exposure elicited a significant decline in glutathione content and in the activity of related enzymes, with the greatest decreases seen in the cortex, striatum, and hippocampus, whereas there were no significant differences between control rats and the group treated with lipoic acid alone. Highly elevated content of the thiobarbituric acid-reactive substance malondialdehyde (MDA) in the brain regions of arsenic-exposed rats reflected extensive lipid peroxidation (LPO) processes. Simultaneous lipoic acid treatment was effective in reducing brain regional arsenic levels and lipid peroxidation and in increasing the glutathione content and the activity of its related enzymes. Lipoic acid, by acting as an alternative sulfhydryl nucleophile to glutathione, prevents its oxidation to glutathione disulfide in detoxifying reactions against reactive oxygen species and consequently increases the activity of glutathione-related enzymes.