Enhancement of TNF-alpha expression does not trigger apoptosis upon exposure of glial cells to lead and lipopolysaccharide

Phospholipid scramblase 3: a latent mediator connecting mitochondria and heavy metal apoptosis

Lead and mercury are the ubiquitous heavy metals triggering toxicity and initiating apoptosis in cells. Though the toxic effects of heavy metals on various organs are known, there is a paucity of information on the mechanisms that instigate the current study. A plausible role of phospholipid scramblase 3 (PLSCR3) in Pb2+ and Hg2+ induced apoptosis was investigated with human embryonic kidney (HEK 293) cells. After 12 h of exposure, ~30-40% of the cells were in the early stage of apoptosis with increased reactive oxygen species (ROS), decreased mitochondrial membrane potential, and increased intracellular calcium levels. Also, ~20% of the cardiolipin localized within the inner mitochondrial membrane was translocated to the outer mitochondrial membrane along with the mobilization of truncated Bid (t-Bid) to the mitochondria and cytochrome c from the mitochondria. The endogenous expression levels of PLSCR3, caspase 8, and caspase 3 were upregulated in Pb2+ and Hg2+ induced apoptosis. The activation and upregulation of PLSCR3 mediate CL translocation playing a potential role in initiating the heavy metal-induced apoptosis. Therefore, PLSCR3 could be the linker between mitochondria and heavy metal apoptosis.

N,N'bis-(2-mercaptoethyl) isophthalamide (NBMI) exerts neuroprotection against lead-induced toxicity in U-87 MG cells

N,N'-bis(2-mercaptoethyl)isophthalamide (NBMI) is a novel lipophilic heavy metal chelator and thiol redox antioxidant. This study was designed to investigate the neuroprotective activity of NBMI in U-87 MG cells exposed to lead acetate (PbAc). Cells were pretreated with NBMI for 24 h prior to a 48 h exposure to PbAc. Cell death (55%, p < 0.0001) and reduction of intracellular GSH levels (0.70-fold, p < 0.005) induced by 250 µM Pb were successfully attenuated by NBMI pretreatment at concentrations as low as 10 µM. A similar pretreatment with the FDA-approved Pb chelator dimercaptosuccinic acid (DMSA) proved ineffective, indicating a superior PKPD profile for NBMI. Pretreatment with NBMI successfully counteracted Pb-induced neuroinflammation by reducing IL-1β (0.59-fold, p < 0.05) and GFAP expression levels. NBMI alone was also found to significantly increase ferroportin expression (1.97-fold, p < 0.05) thereby enhancing cellular ability to efflux heavy metals. While no response was observed on the apoptotic pathway, this study demonstrated for the first time that necrotic cell death induced by Pb in U-87 MG cells is successfully attenuated by NBMI. Collectively these data demonstrate NBMI to be a promising neuroprotective compound in the realm of Pb poisoning.

Modulatory Effects of Pb2+ on Virally Challenged Chicken Macrophage (HD-11) and B-Lymphocyte (DT40) Cell Lines In Vitro

Elevated levels of lead have been found in waterfowl, due to human activities. Lead may cause immunomodulatory effects, but the mechanisms are largely unknown, especially after viral challenges. To characterize avian immunomodulatory hazards of lead (Pb)2+ , we used chicken macrophage (HD-11) and B-lymphocyte (DT40) cell lines, as in vitro models for the innate and adaptive immune systems, respectively. The cells were activated via toll-like receptor-3 by polyinosinic-polycytidylic acid sodium salt (poly I:C), mimicking viral infections. Our results indicate that Pb2+ is cytotoxic to both cell lines, macrophages being more sensitive. De novo synthesis of glutathione plays an important role in protecting macrophages from Pb2+ intoxication, which might also be closely involved in the induction of nitric oxide after Pb2+ exposure. Stimulatory effects on cell proliferation were noticed at noncytotoxic Pb2+ concentrations as well. Exposure to Pb2+ could also affect the inflammatory status by inhibiting the pro-inflammatory interferon (IFN)-γ while promoting the production of anti-inflammatory type I IFNs in both macrophages and B-cells, and increasing intracellular IgM levels in B-cells. These results suggest that the immunomodulatory effects of Pb2+ in birds are probably closely associated with disruption of immune cell proliferation and cytokine production, potentially causing disorders of the avian immune system. Environ Toxicol Chem 2020;39:1060-1070. © 2020 SETAC.

Heavy-Metals-Mediated Phospholipids Scrambling by Human Phospholipid Scramblase 3: A Probable Role in Mitochondrial Apoptosis

Human phospholipid scramblases are a family of four homologous transmembrane proteins (hPLSCR1-4) mediating phospholipids (PLs) translocation in plasma membrane upon Ca²⁺ activation. hPLSCR3, the only homologue localized to mitochondria, plays a vital role in mitochondrial structure, function, maintenance, and apoptosis. Upon Ca²⁺ activation, hPLSCR3 mediates PL translocation at the mitochondrial membrane enhancing t-bid-induced cytochrome c release and apoptosis. Mitochondria are important target organelles for heavy-metals-induced apoptotic signaling cascade and are the central executioner of apoptosis to trigger. Pb²⁺ and Hg²⁺ toxicity mediates apoptosis by increased reactive oxygen species (ROS) and cytochrome c release from mitochondria. To discover the role of hPLSCR3 in heavy metal toxicity, hPLSCR3 was overexpressed as a recombinant protein in Escherichia coli Rosetta (DE3) and purified by affinity chromatography. The biochemical assay using synthetic proteoliposomes demonstrated that hPLSCR3 translocated aminophospholipids in the presence of micromolar concentrations of Pb²⁺ and Hg²⁺. A point mutation in the Ca²⁺-binding motif (F258V) led to a ∼60% loss in the functional activity and decreased binding affinities for Pb²⁺ and Hg²⁺ implying that the divalent heavy metal ions bind to the Ca²⁺-binding motif. This was further affirmed by the characteristic spectra observed with stains-all dye. The conformational changes upon heavy metal binding were monitored by circular dichroism, intrinsic tryptophan fluorescence, and light-scattering studies. Our results revealed that Pb²⁺ and Hg²⁺ bind to hPLSCR3 with higher affinity than Ca²⁺ thus mediating scramblase activity. To summarize, this is the first biochemical evidence for heavy metals binding to the mitochondrial membrane protein leading to bidirectional translocation of PLs specifically toward phosphatidylethanolamine.

In vitro cyto-toxic assessment of heavy metals and their binary mixtures on mast cell-like, rat basophilic leukemia (RBL-2H3) cells

We investigated the cytotoxicity and mechanisms of cell death induced by salts of Cadmium (Cd²⁺), Lead (Pb²⁺), Arsenic (AsO₄^3-) and Chromium (Cr⁺⁶) on RBL-2H3 cells (a model mast cell line). In addition, cyto-toxic effect on cell viability was assessed to reveal their nature of interaction in binary mixture. The individual cytotoxic characteristics of these metals on RBL-2H3 cell viability showed a concentration-dependent reduction of cell viability. We observed that concentration-dependent cytotoxic potency on RBL-2H3 cells of these metals range in the following order Cd²⁺>Cr⁺⁶>As O₄^3-> Pb²⁺ with LC₅₀ values of 0.11 μM, 93.58 μM, 397.9 μM and 485.3 μM respectively. Additive effects were observed with Pb²⁺ + Cd²⁺, Pb²⁺ + AsO₄^3-, Pb²⁺ + Cr⁺⁶ and AsO₄^3- + Cr⁺⁶. The study revealed that Pb²⁺, Cd²⁺, AsO₄^3- and Cr⁺⁶ could induce significant (P < 0.01) cell death by apoptosis in RBL-2H3. Highly significant necrotic cell death was observed with Pb²⁺ and Cr⁺⁶ (P < 0.01) than Cd²⁺ and AsO₄^3- (P < 0.05). Overall, it can be deduced that several cell death executing pathways may be concomitantly activated on exposure to heavy metals and the predominance of one over others might depend on the type of heavy metal, concentration and the metabolic state of the cell. Eventually, binary mixtures of some of these metals showed less cytotoxicity than would be expected from their individual actions and may depend on the co-exposure of the metal ions and their modes of action.

The role of human phospholipid scramblases in apoptosis: An overview

Human phospholipid scramblases (hPLSCRs) are a family of four homologous single pass transmembrane proteins (hPLSCR1-4) initially identified as the proteins responsible for Ca²⁺ mediated bidirectional phospholipid translocation in plasma membrane. Though in-vitro assays had provided evidence, the role of hPLSCRs in phospholipid translocation is still debated. Recent reports revealed a new class of proteins, TMEM16 and Xkr8 to exhibit scramblase activity challenging the function of hPLSCRs. Apart from phospholipid scrambling, numerous reports have emphasized the multifunctional roles of hPLSCRs in key cellular processes including tumorigenesis, antiviral defense, protein and DNA interactions, transcriptional regulation and apoptosis. In this review, the role of hPLSCRs in mediating cell death through phosphatidylserine exposure, interaction with death receptors, cardiolipin exposure, heavy metal and radiation induced apoptosis and pathological apoptosis followed by their involvement in cancer cells are discussed. This review aims to connect the multifunctional characteristics of hPLSCRs to their decisive involvement in apoptotic pathways.

Presence of nano-sized chitosan-layered silicate composites protects against toxicity induced by lead ions

Protecting cells from toxicosis even apoptosis induced by a variety of toxic heavy metals stimulus has drawn more and more attentions. This study was designed to elucidate whether chitosan-organic rectorite (CS-OREC) composites exhibited any protective effects on altered oxidative stress parameter in PC12 cells exposed to lead ions (Pb²⁺). The cells were exposed to Pb²⁺ either alone or in combination with CS-OREC composites for designated time to evaluate the efficacy of the composites on Pb²⁺-induced toxicity. The MTT assay results showed that the cell viability of PC12 was remarkably decreased when exposed to Pb²⁺, but significantly retained after adding CS-OREC composites compared to that of the control. The beneficial effect of CS-OREC composites on cytotoxicity was related, at least in part, to its ability to protect against apoptosis in PC12 cells exposed to 50μM Pb²⁺. Their protective effect was also associated with the inhibitory effect on Pb²⁺-induced activation of Bax/Bcl-2, P-38, and caspase-3 pathways, while was independent on JNK pathway.

Evaluation of Tumor Necrosis Factor-Alpha and Granulocyte Colony-Stimulating Factor Serum Levels in Lead-Exposed Smoker Workers

Inorganic lead (Pb) is able to modulate the immune response even at low to moderate exposure levels. It inhibits in vitro and in vivo activities of neutrophil leucocytes and influences their blood count in humans. Neutrophil functions are governed by a number of cytokines. Pb has been shown to affect leukocyte production of some of these cytokines in vitro. The objective of this study is to assess serum tumor necrosis factor-alpha (TNF-α) and granulocyte colony-stimulating factor (G-CSF) levels of thirty-three male lead-exposed (E) workers at a lead recycling plant as compared with twenty-eight male non-exposed (NE) workers at a food processing plant, whose current smoking habit was known. Serum TNF-α and G-CSF levels were measured by a quantitative sandwich enzyme immunoassay. Blood lead levels (Pb-B) were significantly higher in E (geometric mean (GM) 30.7 μg/dl, GSD 1.7; min-max: 9.1–81.6 μg/dl) workers than controls (GM 3.6 μg/dl, GSD 1.7; min-max: 1.0–11.0 μg/dl). E workers had significantly higher serum TNF-α (median: 107.1; min-max: 11.1–623.0 pg/ml) and G-CSF levels (median: 53.0, min-max: 31.1–197.0 pg/ml) than NE workers (TNF-α: median: 12.0; min-max: 9.4–18.8 pg/ml; G-CSF: median: 34.3, min-max: 25.1–52.2 pg/ml). In particular, the TNF-α level was shown to be significantly influenced by lead exposure and smoking habit, as well as by interaction between these two factors. Both serum TNF-α and G-CSF levels were correlated with Pb-B and absolute neutrophil count. This study is the first to detect higher serum levels of G-CSF in E over NE workers. Our data confirm that exposure to low to medium doses of lead may interfere in the complex cytokine network involved in inflammation, especially in workers who are current smokers.

Lead exposure induced microgliosis and astrogliosis in hippocampus of young mice potentially by triggering TLR4-MyD88-NFκB signaling cascades

Proper proliferation and differentiation of neural stem cells or progenitors in hippocampus is critical to learn and memory functions, which might be disturbed by lead toxicity particularly in young individuals. While astroglial and microglial cells are known to play an important role in regulating neurogenesis of hippocampus, their abnormal response and influence on hippocampal neurogenesis remains unclear. In this study, therefore, glial response including microgliosis, astrogliogenesis and mediating involvement of TLR4-MyD88-NFκB signaling cascades were observed in hippocampus of young mice by animal model with lead (plumbum, Pb) exposure. It revealed that (1) significant microglial activation occurred in hippocampus soon following Pb exposure; (2) increased levels of TLR4, MyD88, NFκB expression were concomitantly detected; (3) BrdU-incorporated progenitor cells were observed in dentate gyrus with significantly-increased numbers at d28 in Pb insult group; (4) obvious astrogliogenesis was observed while these doublecortin-labeled differentiated neurons were not significantly changed in hippocampus; (5) administration of MyD88 inhibitory peptide attenuated or relieved above effects; (6) enhanced expression levels of IL-1β, TNFα, p38MAPK and ERK1/2 were also detected in hippocampus, indicating potential implication of inflammatory response and MAPK signaling activation in lead-induced microgliosis and astrogliosis. Data of this study overall have indicated that lead exposure could trigger or induce abnormal microgliosis and astrogliogenesis in the hippocampus of young mice through triggering TLR4-MyD88-NFκB signaling cascades, which might possibly thereafter disturb hippocampal neurogenesis and functional plasticity.

Elucidation of mechanisms underlying the protective effects of olive leaf extract against lead-induced neurotoxicity in Wistar rats

Recently, we identified that olive leaf extract (OLE) prevents lead (Pb)-induced abnormalities in behavior and neurotransmitters production in chronic Pb exposure in rats. The aim of the present study was to provide additional evidence that OLE acts as an anti-apoptotic, anti-inflammatory, and antioxidant mediator in Pb exposed rats. 4-weeks old Wistar rats were exposed or not to 250 mg/l Pb for 13-weeks and then exposed to tap water containing or not 0.1% OLE for additional 2-weeks. Atomic absorption spectrophotometry showed significantly elevated Pb levels in the hippocampus and serum and reaches 5 and 42 µg/mg tissue, respectively. In the hippocampus, the examination of markers of apoptosis and inflammation revealed an increase in caspase-3 activity and DNA fragmentation as well as tumor necrosis factor alpha, interleukin-1 beta and prostaglandin E2 in Pb-exposed rats. In addition, our findings showed that Pb induced 4-hydroxynonenal production and inhibited antioxidant-related enzyme activity, such as glutathione-S-transferase as wells as energy metabolism-related enzyme activity, such as NADP-isocitrate dehydrogenase and glucose transporter. Upon examination of signaling pathways involved in apoptosis process, we found that Pb induced p38 mitogen activated protein kinase (MAPK) and Akt phosphorylation, but in contrast, inhibited that of ERK(1/2). Interestingly, OLE administration diminished tissue Pb deposition and prevented all Pb effects. In the frontal cortex, our data also showed that OLE-abolished Pb-induced caspase-3 activity and DNA fragmentation. Collectively, these data support the use of OLE by traditional medicine to counter Pb neurotoxicity.

Overexpression of Ref-1 Inhibits Lead-induced Endothelial Cell Death via the Upregulation of Catalase

The role of apurinic/apyrimidinic endonuclease1/redox factor-1 (Ref-1) on the lead (Pb)-induced cellular response was investigated in the cultured endothelial cells. Pb caused progressive cellular death in endothelial cells, which occurred in a concentration- and time-dependent manner. However, Ref-1 overexpression with AdRef-1 significantly inhibited Pb-induced cell death in the endothelial cells. Also the overexpression of Ref-1 significantly suppressed Pb-induced superoxide and hydrogen peroxide elevation in the endothelial cells. Pb exposure induced the downregulation of catalase, it was inhibited by the Ref-1 overexpression in the endothelial cells. Taken together, our data suggests that the overexpression of Ref-1 inhibited Pb-induced cell death via the upregulation of catalase in the cultured endothelial cells.

Oxidative stress and apoptotic changes in primary cultures of rat proximal tubular cells exposed to lead

Lead is a known nephrotoxic element. In this study, primary cultures of rat proximal tubular (rPT) cells were treated with different concentrations of lead acetate (0.25, 0.5 and 1 microM) to investigate its cytotoxic mechanism. A progressive loss in cell viability together with a significant increase in the number of apoptotic and necrotic cells and lactate dehydrogenase release were seen in the experiment. Simultaneously, elevation of reactive oxygen species levels and intracellular [Ca(2+)]i, depletion of mitochondrial membrane potential and intracellular glutathione were revealed during the lead exposure. In addition, apoptotic morphological changes induced by lead exposure in rPT cells were demonstrated by Hoechst 33258 staining. The apoptosis was markedly prevented by N-acetyl-L-cysteine, while the necrosis was not affected. Moreover, catalase and superoxide dismutase activities in the living cells rose significantly. In conclusion, exposure of rPT cells to low-concentration lead led to cell death, mediated by an apoptotic and a necrotic mechanism. The apoptotic death induced by oxidative stress was the chief mechanism. Meanwhile, a group of cells survived lead action, mediated by their ability to activate antioxidant defense systems.

Endotoxin has acute and chronic effects on the cerebral circulation of fetal sheep

We studied the impact of endotoxemia on cerebral blood flow (CBF), cerebral vascular resistance (CVR), and cerebral oxygen transport (O2 transport) in fetal sheep. We hypothesized that endotoxemia impairs CBF regulation and O2 transport, exposing the brain to hypoxic-ischemic injury. Responses to lipopolysaccharide (LPS; 1 μg/kg iv on 3 consecutive days, n = 9) or normal saline ( n = 5) were studied. Of LPS-treated fetuses, five survived and four died; in surviving fetuses, transient cerebral vasoconstriction at 0.5 h (ΔCVR approximately +50%) was followed by vasodilatation maximal at 5–6 h (ΔCVR approximately −50%) when CBF had increased (approximately +60%) despite reduced ABP (approximately −20%). Decreased CVR and increased CBF persisted 24 h post-LPS and the two subsequent LPS infusions. Cerebral O2 transport was sustained, although arterial O2 saturation was reduced ( P < 0.05). Histological evidence of neuronal injury was found in all surviving LPS-treated fetuses; one experienced grade IV intracranial hemorrhage. Bradykinin-induced cerebral vasodilatation (ΔCVR approximately −20%, P < 0.05) was abolished after LPS. Fetuses that died post-LPS ( n = 4) differed from survivors in three respects: CVR did not fall, CBF did not rise, and O2 transport fell progressively. In conclusion, endotoxin disrupts the cerebral circulation in two phases: 1) acute vasoconstriction (1 h) and 2) prolonged vasodilatation despite impaired endothelial dilatation (24 h). In surviving fetuses, LPS causes brain injury despite cerebral O2 transport being maintained by elevated cerebral perfusion; thus sustained O2 transport does not prevent brain injury in endotoxemia. In contrast, cerebral hypoperfusion and reduced O2 transport occur in fetuses destined to die, emphasizing the importance of sustaining O2 transport for survival.

Lead-induced alteration of apoptotic proteins in different regions of adult rat brain

In our earlier investigations, we have demonstrated the alteration of antioxidant enzymes in adult rat brain exposed to lead. This study was carried out to investigate the effect of lead on inducing apoptosis by choosing poly (ADP-ribose) polymerase (PARP), bcl-2 and caspase-3 expression as marker proteins in the cerebellum, the hippocampus, the brain stem and the frontal cortex. Adult male rats were treated with lead acetate (500ppm) through drinking water for a period of 8 weeks and parallel controls were maintained on sodium acetate. Both control and exposed rats were sacrificed at intervals of 4 and 8 weeks, brains were isolated and different regions namely the cerebellum, the hippocampus, the frontal cortex and the brain stem were separated and processed to investigate PARP, bcl-2 and caspase-3 expression using western blotting. The results suggest that lead induces region-specific response of expression in apoptotic proteins of rat brain showing more effect in hippocampus and cerebellum and less effect in frontal cortex and brain stem and it is tissue specific. However, results appear to conclude that PARP induced expression in hippocampus and cerebellum was more followed by mitochondrial and cytosolic damage.

Metals and apoptosis: recent developments

Apoptosis, also known as programmed cell death is a highly regulated and crucial process found in all multicellular organisms. It is not only implicated in regulatory mechanisms of cells, but has been attributed to a number of diseases, i.e. inflammation, malignancy, autoimmunity and neurodegeneration. A variety of toxins can induce apoptosis. Carcinogenic transition metals, viz. cadmium, chromium and nickel promote apoptosis along with DNA base modifications, strand breaks and rearrangements. Generation of reactive oxygen species, accumulation of Ca(2+), upregulation of caspase-3, down regulation of bcl-2, and deficiency of p-53 lead to arsenic-induced apoptosis. In the case of cadmium, metallothionein expression determines the choice between apoptosis and necrosis. Reactive oxygen species (ROS) and p53 contribute in apoptosis caused by chromium. Immuno suppressive mechanisms contribute in lead-induced apoptosis whereas in the case of mercury, p38 mediated caspase activation regulate apoptosis. Nickel kills the cells by apoptotic pathways. Copper induces apoptosis by p53 dependent and independent pathways. Beryllium stimulates the formation of ROS that play a role in Be-induced macrophage apoptosis. Selenium induces apoptosis by producing superoxide that activates p53. Thus, disorders of apoptosis may play a critical role in some of the most debilitating metal-induced afflictions including hepatotoxicity, renal toxicity, neurotoxicity, autoimmunity and carcinogenesis. An understanding of metal-induced apoptosis will be helpful in the development of preventive molecular strategies.

Amelioration of lead toxicity on rat liver with Vitamin C and silymarin supplements

The aim of the present study was to investigate the impact of the combined administration of Vitamin C and silymarin on lead toxicity. Male albino rats were subdivided into three groups: the first was a control group, the second received lead acetate in diet as 500 mg/kg diet daily, the third received the same lead acetate dose and supplemented with Vitamin C (1 mg/100g body weight) and silymarin (1 mg/100g body weight) by gastric tube three times per week. Blood samples were taken after 2, 4 and 6 weeks of treatment. Significant lead-induced elevations in serum ALT, AST, GGT and ALP activities were observed after different periods of treatment. However, serum LDLc was decreased. The intensities of RNA and apoptotic fragments of DNA were measured as optical density by Gel-pro program. Lead acetate decreased the intensity of DNA at 6 weeks and induced apoptotic DNA fragments reversibly with time. After 2 weeks of lead administration dilation and congestion of terminal hepatic veins and portal vein branches were observed. Lead also induced hepatocyte proliferation without any localized distribution among zones 1-3. Portal inflammatory infiltrate with disruption of the limiting plates (interface hepatitis), steatosis, apoptosis and mild fibrosis were detected especially by sixth week of lead administration. Combined treatment of lead-exposed animals with Vitamin C and silymarin showed marked improvement of the biochemical, molecular and histopathological findings. These experimental results strongly indicate the protective effect of Vitamin C and silymarin against toxic effects of lead on liver tissue.

Brain injury induced by intracerebral injection of interleukin-1beta and tumor necrosis factor-alpha in the neonatal rat

To examine the possible role of inflammatory cytokines in mediating neonatal brain injury, we investigated effects of intracerebral injection of IL-1beta (IL-1beta) or tumor necrosis factor-alpha (TNFalpha) on brain injury in the neonatal rat. A stereotaxic intracerebral injection of IL-1beta or TNFalpha (10 ng per pup) was performed in postnatal day 5 (P5) SD rats. Although no necrosis of neurons was found, increased astrogliosis, as indicated by GFAP positive staining was observed 24 and 72 h following the injection of IL-1beta or TNFalpha. IL-1beta induced apoptotic cell death in the rat brain 24 h after the injection, as indicated by increases in positive TUNEL staining and caspase-3 activity, and apoptotic cell death was partially blocked by systemic administration of NBQX, an antagonist of the AMPA glutamate receptor. IL-1beta also significantly reduced the number of developing oligodendrocytes (OLs) 24 h after the injection and this impairment was not prevented by NBQX. On the contrary, TNFalpha induced a much smaller increase in the number of TUNEL positive cells and did not reduce the number of developing OLs. By P8, myelin basic protein (MBP) was clearly detected in the control rat brain, while MBP positive staining was very weak, if any, in the IL-1beta treated rat brain. MBP expression in the TNFalpha treated rat brain was less affected. The overall results indicate that IL-1beta may directly cause injuries to developing OLs and impair myelination in the neonatal rat brain and TNFalpha may have different roles in mediating brain injury.

Differential roles of tumor necrosis factor-alpha and interleukin-1 beta in lipopolysaccharide-induced brain injury in the neonatal rat

Increasing data provide support for the hypothesis that inflammatory cytokines mediate inflammation-induced injury to developing white matter. In the present study, roles of tumor necrosis factor-alpha (TNFalpha) and interleukin-1 beta (IL-1beta) in mediating lipopolysaccharide (LPS)-induced brain injury were investigated by co-administration of LPS with IL-1 receptor antagonist (IL-1ra) or TNFalpha antibody in the 5-day-old rat brain. Intracerebral injection of LPS and other agents was performed in a stereotaxic apparatus at the location of 1.0 mm posterior and 1.0 mm lateral to the bregma, and 2.0 mm deep to the skull surface at the left hemisphere. Brain injury was examined in brain sections 3 and 11 days after LPS injection. LPS-induced inflammatory responses were evidenced by great increases in TNFalpha and IL-1beta concentrations in the neonatal rat brain 6 h after LPS injection. White matter rarefaction was observed in 71% (five out of seven) of the rat brains 3 days after LPS injection and bilateral ventricle dilation was found in 71% (five out of seven) of the P8 rat brains and in 100% of the P16 rat brains (four out of four). These alterations were not found in the control rat brains. No apparent histological changes in gray matter were observed in the LPS-injected rat brains. LPS injection also resulted in injuries to oligodendrocytes (OLs) and hypomyelination, as indicated by reduced immunostaining for O4 and myelin basic protein (MBP). Increased astrogliosis, as indicated by increased glial fibrillary acidic protein (GFAP) immunostaining, was also observed in the LPS-injected, but not the control rat brain. Co-administration of LPS with IL-1ra, but not with TNFalpha antibody, significantly attenuated LPS-induced white matter injury, as indicated by decreases in ventricle dilation, white matter rarefaction, GFAP positive staining and by improved O4 and MBP immunostaining. Co-administration of LPS with IL-1ra significantly reduced LPS-induced elevation of caspase-3 activity in the rat brain. While TNFalpha antibody had no effect on LPS-induced elevation of caspase-3 activity, co-administration of LPS with TNFalpha antibody partially, but significantly, decreased LPS-stimulated increase in IL-1beta in the neonatal rat brain. These data suggest that IL-1beta may play an important role in mediating LPS-induced brain injury and TNFalpha may have complicated, probably dual, effects in LPS-induced brain injury.