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Several in vitro and in vivo studies have shown that the mammalian target of rapamycin (mTOR) inhibitor sirolimus (rapamycin) suppresses thymus cellular respiration. The objective of this study is to investigate the chronic dose-dependent effects of sirolimus in the thymus. This was monitored using body weight, histomorphology, caspase-3 expression, cytochrome C immunohistochemistry, and cellular bioenergetics as surrogate biomarkers. BALB/c mice received intraperitoneal injections of either sirolimus (2.5, 5, or 10 µg/g) or dimethyl sulfoxide (0.1 µL/g) as a control for 4 weeks. At the end of the treatment, fragments were collected from the thymus, small intestine, adrenal gland, and kidney. They were processed for assessing histologic changes, measuring cellular respiration and ATP levels. Immunohistochemical stain of caspase-3 and cytochrome C was performed on paraffin-embedded tissue. The treated animals exhibited a dose-dependent reduction in weight gain despite adequate food intake. Sirolimus produced significant thymic derangements, manifested by dose-dependent tissue involution, increased cortical apoptotic bodies, increased caspase-3-positive lymphocytes, and increased rate of cellular respiration without a concomitant increase in cellular ATP. There were no similar changes in cellular ATP in the other assessed organs. The effects on thymic cellular bioenergetics suggest mitochondrial derangements, uncoupling of oxidative phosphorylation, and induction of apoptosis.

The purpose of this in vitro study was to develop a useful biomarker (e.g., cellular respiration, or mitochondrial O2 consumption) for measuring activities of mTOR inhibitors. It measured the effects of commonly used immunosuppressants (sirolimus - rapamycin, tacrolimus, and cyclosporine) on cellular respiration in target tissues (kidney, liver, and heart) from C57BL/6 mice. The mammalian target of rapamycin (mTOR), a serine/threonine kinase that supports nutrient-dependent cell growth and survival, is known to control energy conversion processes within the mitochondria. Consistently, inhibitors of mTOR (e.g., rapamycin, also known as sirolimus or Rapamune®) have been shown to impair mitochondrial function. Inhibitors of the calcium-dependent serine/threonine phosphatase calcineurin (e.g., tacrolimus and cyclosporine), on the other hand, strictly prevent lymphokine production leading to a reduced T-cell function. Sirolimus (10 μM) inhibited renal (22%, p = 0.002), hepatic (39%, p < 0.001), and cardiac (42%, p = 0.005) cellular respiration. Tacrolimus and cyclosporine had no or minimum effects on cellular respiration in these tissues. Thus, these results clearly demonstrate that impaired cellular respiration (bioenergetics) is a sensitive biomarker of the immunosuppressants that target mTOR.

Background: Cisplatin, carboplatin and oxaliplatin are structurally-related compounds, which are commonly used in cancer therapy. Cisplatin (Platinol®) has Boxed Warning stating: “Cumulative renal toxicity associated with PLATINOL is severe”, while carboplatin and oxaliplatin are less nephrotoxic. These drugs form platinum adducts with cellular DNA. Their bindings to cellular thiols (e.g., glutathione and metallothionein) are known to contribute to drug resistance while thiol depletion augments platinum toxicity. Methods: Using phosphorescence oxygen analyzer, this study investigated the effects of platinum drugs on renal cellular respiration (mitochondrial O2 consumption) in the presence and absence of the thiol blocking agent N-ethylmaleimide (used here as a model for thiol depletion). Renal cellular ATP was also determined. Kidney fragments from C57BL/6 mice were incubated at 37°C in Krebs-Henseleit buffer (gassed with 95% O2:5% CO2) with and without 100 μM platinum drug in the presence and absence of 100 μM N-ethylmaleimide for ≤ 6 h. Results: Platinum drugs alone had no effects on cellular respiration (P ≥ 0.143) or ATP (P ≥ 0.161). N-ethylmaleimide lowered cellular respiration (P ≤ 0.114) and ATP (P = 0.008). The combination of platinum drug and N-ethylmaleimide significantly lowered both cellular respiration (P ≤ 0.006) and ATP (P ≤ 0.003). Incubations with N-ethylmaleimide alone were associated with moderate-to-severe tubular necrosis. Incubations with cisplatin+N-ethylmaleimide vs. cisplatin alone produced similar severities of tubular necrosis. Tubular derangements were more prominent in carboplatin+N-ethylmaleimide vs. carboplatin alone and in oxaliplatin+N-ethylmaleimide vs. oxaliplatin alone. Conclusions: These results demonstrate the adverse events of thiol depletion on platinum-induced nephrotoxicities. The results suggest cellular bioenergetics is a useful surrogate biomarker for assessing drug-induced nephrotoxicities.

Inhibitors of protein kinases/phosphatases are known to alter cellular metabolism. Effects of these rapidly identified small molecules on cellular respiration (mitochondrial O2 consumption) have not been adequately investigated, especially in healthy organs. This in vitro study measured cellular respiration in tissues from C57BL/6 mice with and without GSK2126458 (PI3K/mTOR inhibitor), BEZ235 (PI3K/mTOR inhibitor), GDC0980 (PI3K/mTOR inhibitor), GSK1120212 (trametinib, MEK inhibitor), sorafenib, regorafenib (multikinase inhibitors), and cyclosporine (calcineurin inhibitor). Cellular respiration was measured by the phosphorescence oxygen analyzer, aided by the O2 probe Pd(II)-meso-tetra-(4-sulfonatophenyl)-tetrabenzoporphyrin. Cyanide inhibited O2 consumption, confirming the oxidation occurred in the respiratory chain. Renal cellular respiration decreased 26-34% in the presence of 10 μM GSK2126458 (p

Biguanides (metformin, buformin and phenformin) have been developed for oral treatment of non-insulindependent diabetes mellitus. Metformin, the drug of choice in this class, controls blood glucose primarily by lowering hepatic gluconeogenesis (e.g., decreasing glucagon-mediated hepatic glucose output). Its mode-of-action, however, is more complex and may involve “refining” cellular bioenergetics (improving energy efficiency) in various cell types including myocytes. Buformin and phenformin presumably have similar mechanisms of action. The main purpose of this in vitro study was to assess the effects of these drugs on bioenergetics - cellular respiration (mitochondrial O2 consumption) and ATP content - in tissue fragments from the heart muscle (cardiomyocytes) and liver (hepatocytes) of C57BL/6 mice. Cardiomyocyte respiration decreased by 10-26% in the presence of 100 μM metformin (p=0.093), buformin (p=0.028) or phenformin (p=0.015). Similar effects on cardiomyocyte respiration were noted with 1.0 mM drugs. Cardiomyocyte ATP, on the other hand, increased by 17-31% in the presence of 100 μM metformin (p=0.093), buformin (p=0.445) or phenformin (p=0.093). Hepatocyte respiration and ATP decreased by 11-26% and 8-25%, respectively in the presence of 1.0 mM drugs. Decreased respiration and ATP were also noted in hepatocytes exposed to 100 μM metformin for 1 ≤ t ≤ 6 hours (13% and 5%, respectively). Thus, the effects of biguanides on cardiomyocyte bioenergetics differed from that on hepatocyte bioenergetics. These findings suggest that biguanides regulate cardiomyocyte energy conversion, favoring better fuel efficiency (↓respiration/↑ATP). The drug effects in hepatocyte are ↓respiration/↓ATP, favoring less fuel production (↓hepatic gluconeogenesis). Biguanide activities in various tissues may be coupled.

Sorafenib and regorafenib are structurally-related small-molecular-weight inhibitors of cellular kinases. Regorafenib has a Boxed Warning stating: “Severe and sometimes fatal hepatotoxicity has been observed in clinical trials”, while sorafenib is considered less hepatotoxic. This ex vivo study assessed the effects of sorafenib (2.5 and 50 μM) and regorafenib (5.0 and 50 μM) on liver structure, ultrastructure, cellular respiration (mitochondrial O2 consumption), ATP, caspase activity, urea synthesis, and glutathione. Liver fragments from Taylor Outbred mice were incubated in Krebs-Henseleit buffer (continuously gassed with 95% O2:5% CO2) with and without the drugs for 3 to 4 h. The presence of sorafenib or regorafenib had insignificant effects on liver structure, cellular respiration, ATP, caspase-3 activity, urea synthesis, and glutathione. At 3 h, liver histology with and without 2.5 μM sorafenib or 5.0 μM regorafenib was similar. Liver histology with 50 μM sorafenib was slightly worse than untreated tissue at 3 h, showing single hepatocyte necrosis and cellular disintegration. With 50 μM regorafenib, the histology was closely mirroring untreated tissue at 3 h. Similarly, caspase-3, caspase-9, cytochrome c, BAX and annexin A2 immunostains showed no significant drug effects at 4 h (2.5 μM sorafenib or 5.0 μM regorafenib). Electron microscopy revealed a more prominent loss of rough endoplasmic reticulum (rER) integrity with regorafenib treatment compared with sorafenib treatment. Thus, derangements in the rER were more prominent with regorafenib. Otherwise, the studied hepatic surrogate biomarkers did not distinguish between the two compounds.