Lethal chronotoxicity induced by seven metal compounds in mice

Diurnal variation of cisplatin-induced renal toxicity in ICR mice

Cisplatin (CDDP) is a platinum-based anticancer drug widely prescribed for its effectiveness in treating various forms of cancer. However, its major side effect is nephrotoxicity. Although several methods have been developed to mitigate CDDP-induced nephrotoxicity, an optimal approach has yet to be established. This study aimed to investigate the "chronotoxicity" of CDDP as a potential strategy to reduce its side effects. Male ICR mice were treated with CDDP (20 mg/kg, intraperitoneal injection, one shot) at zeitgeber time (ZT) 2 or ZT14 (light or dark phase). After 72 h, we collected plasma and kidney and evaluated several markers. We found that body weight change between ZT2 and ZT14 by CDDP was comparable. In contrast, many toxicological factors, such as plasma blood urine nitrogen, plasma creatinine, renal oxidative stress (malondialdehyde), DNA damage (γH2AX), acute kidney injury biomarker (KIM-1), and inflammation (Tnfα), were significantly induced at ZT14 compared to than that of ZT2. Our present data suggested that chronotoxicology might provide beneficial information on the importance of administration timings for toxic evaluations and unacceptable side effects.

Copper-induced diurnal hepatic toxicity is associated with Cry2 and Per1 in mice

BACKGROUND

This study aimed to investigate diurnal variations in copper-induced hepatic toxicity and the molecular mechanisms underlying this chronotoxicity.

METHODS

Male C57BL/6J mice were intraperitoneally injected with copper chloride (CuCl2) at zeitgeber time 2 (ZT2) or 14 (ZT14), twice per week for 5 or 8 weeks. Seventy-two hours after the final CuCl2 injection, the mice were euthanized, and plasma samples were collected. The livers and kidneys were collected and weighed. In vitro experiments were performed to assess cell viability and fluctuations in clock gene expression levels in Hepa1-6 cells after CuCl2 treatment. We examined copper homeostasis- and apoptosis-related genes under clock genes overexpression.

RESULTS

Repeated CuCl2 administration for 8 weeks resulted in more severe toxicity at ZT14 compared to ZT2. CuCl2 administration at ZT14 elevated plasma aspartate aminotransferase, hepatic tumor necrosis factor-α, and interleukin-6 for 5 weeks, whereas the toxic effects of CuCl2 administration at ZT2 were weaker. Moreover, CuCl2 treatment inhibited Hepa1-6 cell viability in a dose-dependent manner. We observed increased expression of three clock genes (Ciart, Cry2, and Per1) after CuCl2 treatment. Among them, overexpression of Cry2 and Per1 accelerated CuCl2-induced inhibition of Hepa1-6 cell viability. Moreover, we found that the overexpression of Cry2 and Per1 regulates cleaved caspase-3 by modulating the copper transporter genes ATP7B and CTR1.

CONCLUSION

These results suggest that CuCl2-induced diurnal toxicity is associated with Cry2 and Per1 expression through the regulation of copper transporter genes in mice.

Chronotoxicity of Streptomycin-Induced Renal Injury in Mice

The aim of the present study was to investigate the "chronotoxicity" of streptomycin (SM) in relation to its circadian periodicity. Male ICR mice were injected intraperitoneally with SM (780 mg/kg, one shot) one of six time points throughout the day. Mortality was monitored until 14 d after the injection and clearly differed depending on the timing of the injection (i.e., mice were more sensitive to injection during the dark phase). Moreover, when mice were administered with non-lethal doses of SM (550 mg/kg, every 24 h for 3 d, in the light phase or dark phase), the levels of nephrotoxicity indicators (blood urea nitrogen and renal levels of malondialdehyde and cyclooxygenase-2) were significantly increased by the injection in the dark phase, but not in the light phase. These results suggested that SM showed clear chronotoxicity. Our current data indicated that chronotoxicology may provide valuable information on the importance of injection timings for evaluations of toxicity and undesirable side effects.

Effects of work schedule and period of exposure on changes in urinary chromium and nickel excretion among rotating shift workers in a stainless-steel plant

We investigated the association between the period of exposure and changes in urinary excretion of chromium and nickel among rotating shift workers in a stainless-steel plant. The study participants were composed of two groups: the workers who were occupationally exposed to metals ("exposed group") and those who were not occupationally exposed to metals ("unexposed group"). The exposed and unexposed groups consisted of 56 and 40 male rotating shift workers, respectively. Urine samples were collected immediately before and immediately after the day shift, evening shift, and night shift. Urinary chromium and nickel were measured using inductively coupled plasma mass spectrometry. To correct for variations in urine dilution, urinary metal concentrations were expressed as a ratio to urinary creatinine concentration. In the exposed group, post-shift urinary excretion of chromium was significantly higher than pre-shift excretion. However, although urinary chromium excretion clearly increased after the day and night shift [63% (p < .0001) and 87% (p < .0001), respectively], urinary chromium excretion after the evening shift was only slightly higher than that measured before the evening shift (8%, p = .028). Similar patterns were found for urinary nickel excretion (p = .0001, 0.20, and 0.18 for the day, evening, and night shifts, respectively). Non-uniform urinary excretion of metals between the day shift, evening shift, and night shift were observed in the exposed group; specifically, urinary metal excretion increased only slightly during the evening shift. In the unexposed group, no significant increase or decrease was found in median urinary chromium or nickel excretion (p= .63-0.87). Work shift-specific permissible exposure level would be necessary.

Working Time Society consensus statements: Circadian time structure impacts vulnerability to xenobiotics-relevance to industrial toxicology and nonstandard work schedules

The circadian time structure (CTS) has long been the subject of research in occupational medicine, but not to industrial toxicology, including methods of setting threshold limit values (TLVs) and employee biological monitoring. Numerous animal and human investigations document vulnerability to chemical, contagion, and other xenobiotics varies according to the circadian time of encounter. Permanent and rotating nightshift personnel are exposed to industrial contaminants in the same or higher concentration as dayshift personnel, and because of incomplete CTS adjustment to night work, contact with contaminants occurs during a different biological time than day workers. Thus, the amount of protection afforded by certain TLVs, especially for employees of high-risk settings who work night and other nonstandard shift schedules, might be inadequate. The CTS seems additionally germane to procedures of employee biological monitoring in that high-amplitude 24 h rhythms in biomarkers indicative of xenobiotic exposure may result in misjudgment of health risks when data are not gathered in sufficient frequency over time and properly interpreted. Biological reference values time-qualified for their rhythmic variation, currently of interest to laboratory medicine practice, are seemingly important to industrial medicine as circadian time and work-shift specific biological exposure indices to improve surveillance of personnel, particularly those working nonstandard shift schedules.