Selective cytotoxicity of the anti-diabetic drug, metformin, in glucose-deprived chicken DT40 cells

SPRTN and TDP1/TDP2 Independently Suppress 5-Aza-2'-deoxycytidine-Induced Genomic Instability in Human TK6 Cell Line

DNA-protein cross-links (DPCs) are generated by internal factors such as cellular aldehydes that are generated during normal metabolism and external factors such as environmental mutagens. A nucleoside analog, 5-aza-2'-deoxycytidine (5-azadC), is randomly incorporated into the genome during DNA replication and binds DNA methyltransferase 1 (DNMT1) covalently to form DNMT1-DPCs without inducing DNA strand breaks. Despite the recent progress in understanding the mechanisms of DPCs repair, how DNMT1-DPCs are repaired is unclear. The metalloprotease SPRTN has been considered as the primary enzyme to degrade protein components of DPCs to initiate the repair of DPCs. In this study, we showed that SPRTN-deficient (SPRTN^-/-) human TK6 cells displayed high sensitivity to 5-azadC, and the removal of 5-azadC-induced DNMT1-DPCs was significantly slower in SPRTN^-/- cells than that in wild-type cells. We also showed that the ubiquitination-dependent proteasomal degradation, which was independent of the SPRTN-mediated processing, was also involved in the repair of DNMT1-DPCs. Unexpectedly, we found that cells that are double deficient in tyrosyl DNA phosphodiesterase 1 and 2 (TDP1^-/-TDP2^-/-) were also sensitive to 5-azadC, although the removal of 5-azadC-induced DNMT1-DPCs was not compromised significantly. Furthermore, the 5-azadC treatment induced a marked accumulation of chromosomal breaks in SPRTN^-/- as well as TDP1^-/-TDP2^-/- cells compared to wild-type cells, strongly suggesting that the 5-azadC-induced cell death was attributed to chromosomal DNMT1-DPCs. We conclude that SPRTN protects cells from 5-azadC-induced DNMT1-DPCs, and SPRTN may play a direct proteolytic role against DNMT1-DPCs and TDP1/TDP2 also contributes to suppress genome instability caused by 5-azadC in TK6 cells.

DNA-binding activities of compounds acting as enzyme inhibitors, ion channel blockers and receptor binders

The DNA-binding activities of compounds used as remedies can display DNA-protection, but also damaging effects in biological systems. The current review compiles literature data on DNA-binding activities of drugs widely used as remedies with different therapeutic indications. The compounds are classified according their mechanism of action: enzyme inhibitors, ion channel inhibitors, inhibitors of viral RNA replication and HIV protease and receptor agonists. DNA binding was reported for such widely used drugs as paracetamol, aspirin, metformin, statins and many others. The capability of the drug to bind DNA is sometimes coupled to genotoxic effects, but in some cases - to genome protection. Data on atoms and chemical groups involved in the drug-DNA interactions are also presented. In many cases the same atoms are involved in both interactions of the compounds with proteins and DNA.

Antidiabetic profiling, cytotoxicity and acute toxicity evaluation of aerial parts of Phragmites karka (Retz.)

ETHNOPHARMACOLOGICAL RELEVANCE

Phragmites karka (Retz.) of family Poaceae is a pristine tropical plant that is well known to the local healers for ailments of diabetes, fever, diarrhea and CNS depression but lacks the scientific evidence behind its traditional usage. Hence, we explicated this plant to find the scientific basis of its traditional utilization.

AIM OF THE STUDY

The current study aims to find out the antidiabetic potential, toxicity after oral administration and in vitro cytotoxic activity of aerial parts of the plant on HeLa cells.

METHODS

The plant was extracted with methanol by maceration and the crude extract was then subjected to solvent partitioning with modified Kupchan method for preparing several fractions. Phytochemical screening and total phenolic content of the plant was first determined through established procedures. Acute toxicity of the plant was studied by orally administering a single high dose (5000 mg/kg) of drug. Cytotoxicity of the methanolic plant extract was determined by measuring the percentage of cell viability on human cervical cancer cell lines, HeLa. In vitro antidiabetic activity was determined through iodine starch and DNSA (3,5-dinitrosalicylic acid) method of α-amylase inhibition. Finally, in vivo oral glucose tolerance test and alloxan induced antidiabetic activity test was performed at 150 and 300 mg/kg body weight doses of plant extract to confirm the in vivo antidiabetic activity.

RESULTS

No mortality was demonstrated by Phragmites karka in the acute toxicity test. However, signs of cellular toxicity was observed and histopathological studies on major organs exhibited necrosis in liver and kidney. In vitro cytotoxicity assay revealed the death of HeLa cells by DCM (dichloromethane) and n-hexane fractions of plant extract at 100 and 10 μg/mL concentrations. The IC50 value of the fractions were later evaluated by MTT assay (316.1 and 96.7 μg/mL for n-hexane and DCM fractions, respectively). In the iodine starch and DNSA method of α-amylase enzyme inhibitory activity test, substantial inhibition of enzyme was observed with the IC50 values of 2.05 and 2.08 mg/mL, respectively. In the in vivo antidiabetic activity test, considerable reduction in blood glucose level of diabetic mice was detected in both oral glucose tolerance test and alloxan induced antidiabetic activity test. In addition, the microscopic examination of pancreas showed noticeable recovery of pancreatic β cells and the blood lipid profile analysis represented a significant (p < 0.05) reduction of total cholesterol, LDL (low density lipoprotein) and triglyceride level in plant extract treated mice.

CONCLUSION

Results of this study reveals that the Phragmites karka extract is toxic at cellular level after oral administration and cytotoxic when tested on HeLa cells. The plant also evidenced hypoglycemic property, possibly through the inhibition of α-amylase enzyme and recovered the pancreatic beta cells along with the improvement of lipid profile of diabetic mice. However, robust studies on this plant is required to isolate the bioactive compounds, elucidate structures and evaluate their mechanism of actions in support of our findings.

CLASSIFICATION

Toxicology and Safety, Quality Traditional Medicine.

PXR-mediated idiosyncratic drug-induced liver injury: mechanistic insights and targeting approaches

INTRODUCTION

The human liver is the center for drug metabolism and detoxification and is, therefore, constantly exposed to toxic chemicals. The loss of liver function as a result of this exposure is referred to as drug-induced liver injury (DILI). The pregnane X receptor (PXR) is the primary regulator of the hepatic drug-clearance system, which plays a critical role in mediating idiosyncratic DILI.

AREAS COVERED

This review is focused on common mechanisms of PXR-mediated DILI and on in vitro and in vivo models developed to predict and assess DILI. It also provides an update on the development of PXR antagonists that may manage PXR-mediated DILI.

EXPERT OPINION

DILI can be caused by many factors, and PXR is clearly linked to DILI. Although emerging data illustrate how PXR mediates DILI and how PXR activity can be modulated, many questions concerning the development of effective PXR modulators remain. Future research should be focused on determining the mechanisms regulating PXR functions in different cellular contexts.

Participation of TDP1 in the repair of formaldehyde-induced DNA-protein cross-links in chicken DT40 cells

Proteins are covalently trapped on DNA to form DNA-protein cross-links (DPCs) when cells are exposed to DNA-damaging agents. Aldehyde compounds produce common types of DPCs that contain proteins in an undisrupted DNA strand. Tyrosyl-DNA phosphodiesterase 1 (TDP1) repairs topoisomerase 1 (TOPO1) that is trapped at the 3’-end of DNA. In the present study, we examined the contribution of TDP1 to the repair of formaldehyde-induced DPCs using a reverse genetic strategy with chicken DT40 cells. The results obtained showed that cells deficient in TDP1 were sensitive to formaldehyde. The removal of formaldehyde-induced DPCs was slower in tdp1-deficient cells than in wild type cells. We also found that formaldehyde did not produce trapped TOPO1, indicating that trapped TOPO1 was not a primary cytotoxic DNA lesion that was generated by formaldehyde and repaired by TDP1. The formaldehyde treatment resulted in the accumulation of chromosomal breakages that were more prominent in tdp1-deficient cells than in wild type cells. Therefore, TDP1 plays a critical role in the repair of formaldehyde-induced DPCs that are distinct from trapped TOPO1.