Free radical scavengers suppress the accumulation of platinum in the cerebral cortex

Review of the Role of the Brain in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common, debilitating, and dose-limiting side effect of many chemotherapy regimens yet has limited treatments due to incomplete knowledge of its pathophysiology. Research on the pathophysiology of CIPN has focused on peripheral nerves because CIPN symptoms are felt in the hands and feet. However, better understanding the role of the brain in CIPN may accelerate understanding, diagnosing, and treating CIPN. The goals of this review are to (1) investigate the role of the brain in CIPN, and (2) use this knowledge to inform future research and treatment of CIPN. We identified 16 papers using brain interventions in animal models of CIPN and five papers using brain imaging in humans or monkeys with CIPN. These studies suggest that CIPN is partly caused by (1) brain hyperactivity, (2) reduced GABAergic inhibition, (3) neuroinflammation, and (4) overactivation of GPCR/MAPK pathways. These four features were observed in several brain regions including the thalamus, periaqueductal gray, anterior cingulate cortex, somatosensory cortex, and insula. We discuss how to leverage this knowledge for future preclinical research, clinical research, and brain-based treatments for CIPN.

Ototoxic Model of Oxaliplatin and Protection from Nicotinamide Adenine Dinucleotide

Oxaliplatin, an anticancer drug commonly used to treat colorectal cancer and other tumors, has a number of serious side effects, most notably neuropathy and ototoxicity. To gain insights into its ototoxic profile, oxaliplatin was applied to rat cochlear organ cultures. Consistent with it neurotoxic propensity, oxaliplatin selectively damaged nerve fibers at a very low dose 1 μM. In contrast, the dose required to damage hair cells and spiral ganglion neurons was 50 fold higher (50 μM). Oxailiplatin-induced cochlear lesions initially increased with dose, but unexpectedly decreased at very high doses. This non-linear dose response could be related to depressed oxaliplatin uptake via active transport mechanisms. Previous studies have demonstrated that axonal degeneration involves biologically active processes which can be greatly attenuated by nicotinamide adenine dinucleotide (NAD+). To determine if NAD+ would protect spiral ganglion axons and the hair cells from oxaliplatin damage, cochlear cultures were treated with oxaliplatin alone at doses of 10 μM or 50 μM respectively as controls or combined with 20 mM NAD+. Treatment with 10 μM oxaliplatin for 48 hours resulted in minor damage to auditory nerve fibers, but spared cochlear hair cells. However, when cochlear cultures were treated with 10 μM oxaliplatin plus 20 mM NAD+, most auditory nerve fibers were intact. 50 μM oxaliplatin destroyed most of spiral ganglion neurons and cochlear hair cells with apoptotic characteristics of cell fragmentations. However, 50 μM oxaliplatin plus 20 mM NAD+ treatment greatly reduced neuronal degenerations and hair cell missing. The results suggested that NAD+ provides significant protection against oxaliplatin-induced neurotoxicity and ototoxicity, which may be due to its actions of antioxidant, antiapoptosis, and energy supply.

Antiemetic effect of dexamethasone on cisplatin-induced early and delayed emesis in the pigeon

We investigated the ability of dexamethasone to attenuate cisplatin (4 mg/kg, i.v.)-induced early and delayed emesis. These appear within the first 8-h period (early phase) and between 8 and 48 h (delayed phase), respectively, after cisplatin administration in the pigeon. Dexamethasone (0.1 and 1 mg/kg, i.m.) reduced significantly the number of emetic responses to cisplatin by 56% and 82% (P<0.05), respectively, in the early phase, and by 41% and 66% (P<0.05), respectively, in the delayed phase. Dexamethasone (1 and 10 microg/kg, i.c.v.) reduced the number of emetic responses by 66% and 91% (P<0.05), respectively, in the early phase, and by 56% and 87% (P<0.05), respectively, in the delayed phase. Indomethacin (10 mg/kg, i.m.) did not suppress cisplatin-induced early and delayed emesis. Dexamethasone (1 mg/kg, i.m.) did not affect the content of platinum in the medulla oblongata after cisplatin administration. The above results suggest that dexamethasone has antiemetic effects on both the early and delayed emetic responses to cisplatin in pigeons, partially via its central site of action, and that the antiemetic mechanism of dexamethasone is related to factors other than its inhibition of prostanoid synthesis or its membrane stabilizing effect which reduces influx of cisplatin into the medulla oblongata.

Vitamin C suppresses the cisplatin toxicity on blood platelets

The effects of vitamin C on the oxidative stress in blood platelets induced by cisplatin were studied. In the presence of vitamin C we measured in blood platelets the production of thiobarbituric acid reactive substances (TBARS), the generation of superoxide radicals (O2*-), other reactive oxygen species (H2O2, singlet oxygen and organic radicals) and catalase activity. Vitamin C at a low concentration (0.1 mM), like cisplatin (20 microM), induced blood platelet oxidative stress: an increase of TBARS, chemiluminescence and generation of superoxide radicals. After treatment of blood platelets with vitamin C at a high concentration (3 mM), chemiluminescence (p>0.05), the levels of O2*- (p<0.01) and TBARS (p<0.002) were reduced. We have shown that vitamin C at a high concentration (3 mM) had a protective effect against oxidative stress in platelets caused by cisplatin (20 microM). It diminished platelet lipid peroxidation and reactive oxygen species generation induced by cisplatin. In the presence of vitamin C, the catalase activity was suppressed.

Reduced sensitivity of HeLa cells to cis-platinum by simultaneous overexpression of copper, zinc-superoxide dismutase and catalase

The overexpression of catalase or Cu,Zn-superoxide dismutase (Cu,Zn-SOD) did not affect the sensitivity of HeLa cells to cis-platinum. However, the cytotoxicity of cis-platinum was depressed significantly by the simultaneous overexpression of catalase and Cu,Zn-SOD. We concluded that cis-platinum accelerated the generation of superoxide anion in the cells, and the superoxide anion produced was converted into H2O by the cooperative roles of catalase and Cu,Zn-SOD.

Penetration of cisplatin into mouse brain by lipopolysaccharide

We investigated the penetration of cisplatin into the mouse cerebral cortex-rich region (CCR) induced by lipopolysaccharide (LPS). With the injection of cisplatin into mice 3 h after the LPS treatment, platinum was detected in the CCR during the 7 days after the injection, while platinum was not detected in the CCR of cisplatin-injected mice without LPS pretreatment and of mice simultaneous treated with cisplatin and LPS. The N(G)-nitro-L-arginine methyl ester dose-dependently lowered the platinum level. A dose of 5 mg/kg of aminoguanidine reduced the increase in the platinum level of the LPS-treated mouse, and platinum was no longer detected at doses of 20 mg/kg in the aminoguanidine-injected group. At doses of 500 mg/kg aminoguanidine, however, no effect was seen on the platinum level of the CCR induced by LPS. Regarding indomethacin, the injection of 5 mg/kg resulted in a decrease in the platinum content of the CCR, but not undetectable level. These results suggest that LPS increases the penetration of cisplatin into the mouse brain, and platinum may be accumulated in the CCR. Nitric oxide and prostaglandins contribute to the penetration of platinum into the cerebral cortex.

Roles of nitric oxide and prostaglandins in the increased permeability of the blood-brain barrier caused by lipopolysaccharide

We investigated the involvement of nitric oxide (NO) and prostaglandins (PGs) in the damage to the blood-brain barrier (BBB) induced by lipopolysaccharide (LPS), using fluorescein as a tracer in mice. Aminoguanidine, a competitive inhibitor of inducible NO synthase (iNOS), when administered s.c. at 5 mg/kg, but not 500 mg/kg, reduced significantly the increase in brain fluorescein level after its i.v. injection in LPS-treated mice. When 1000 mg/kg of l-arginine, a substrate of NOS, were co-administered with 5 mg/kg of aminoguanidine to LPS-treated mice, the inhibitory effect of aminoguanidine on the increased fluorescein level disappeared. N(G)-Nitro-l-arginine methyl ester (l-NAME), a non-isoenzyme-selective NOS inhibitor, when administered s.c. at 5 mg/kg, only slightly reduced the LPS-induced increase in the brain fluorescein level. A pretreatment with dexamethasone, which suppressed the induction of both iNOS and cyclooxygenase 2 (COX-2), tended to decrease the brain fluorescein level in LPS-treated mice. Indomethacin, a COX inhibitor, at 5 mg/kg, but not 10 mg/kg, suppressed significantly the LPS-induced increase in the brain fluorescein level. These results involve that both the NO produced by iNOS and the PGs produced by COX contribute to enhance BBB permeability in LPS-administered mice.