Association of sudden infant death syndrome with grossly deranged iron metabolism and nitric oxide overload

Ventilatory response to hypoxia during endotoxemia in young rats: role of nitric oxide

Administration of Escherichia coli endotoxin attenuates the ventilatory response to hypoxia (VRH) in newborn piglets, but the mechanisms responsible for this depression are not clearly understood. Nitric oxide (NO) production increases during sepsis and elevated NO levels can inhibit carotid body function. The role of endothelial NO on the VRH during endotoxemia was evaluated in 26 young rats. Minute ventilation (VE) and oxygen consumption (VO2) were measured in room air (RA) and during 30 min of hypoxia (10% O2) before and after E. coli endotoxin administration. During endotoxemia, animals received placebo (PL, n = 8); a nonselective nitric oxide synthase (NOS) inhibitor (NG-nitro-L-arginine methyl ester, L-NAME, n = 9), or a neuronal NOS (nNOS) inhibitor (7-nitroindazole, 7-NI, n = 9). During endotoxemia, a larger increase in VE was observed only during the first min of hypoxia in the L-NAME group when compared with PL or 7-NI (p < 0.001). VRH was similar in the PL and 7-NI groups. A larger decrease in VO2 at 30 min of hypoxia was observed in L-NAME and 7-NI groups when compared with PL (p < 0.03). These data demonstrate that the attenuation of the early VRH during endotoxemia is in part mediated by an inhibitory effect of endothelial NO on the respiratory control mechanisms.

Extramedullary haematopoiesis in liver of sudden infant death cases

AIMS

To determine the frequency of extramedullary haematopoiesis (EMH) in sudden infant death and control cases, and to provide descriptive data on extramedullary haematopoietic islands and diffuse cells.

METHODS

The study was carried out in 51 SIDS and 102 non-SIDS cases. Liver-tissue sections were stained with haematoxylin and eosin, and immunohistochemistry was done with streptavidin-biotin-peroxidase complexes by Polyclonal Haemoglobin "A" antibody. The prevalence of data was estimated statistically by Pearson chi-square test, descriptive statistics, and Kruskal-Wallis test.

RESULTS

The Pearson chi-square values (CI: 95%; OR: 0.071-0.49; p: 0.0474) show higher frequency of EMH islands in SIDS than in controls. The number of diffuse extramedullary haematopoetic cells was higher in SIDS cases compared to non-SIDS (p=0.017).

CONCLUSIONS

EMH is a frequent finding in SIDS cases, and this may be a consequence of anaemia associated with intrauterine hypoxia, or infections.

Unique Properties of Polyphenol Stilbenes in the Brain: More than Direct Antioxidant Actions; Gene/Protein Regulatory Activity

The 'French Paradox' has been typically associated with moderate consumption of wine, especially red wine. A polyphenol 3,4',5-trihydroxy-trans-stilbene (a member of the non-flavonoids family), better known as resveratrol, has been purported to have many health benefits. A number of these valuable properties have been attributed to its intrinsic antioxidant capabilities, although the potential level of resveratrol in the circulation is likely not enough to neutralize free radical scavenging. The brain and the heart are uniquely vulnerable to hypoxic conditions and oxidative stress injuries. Recently, evidence suggests that resveratrol could act as a signaling molecule within tissues and cells to modulate the expression of genes and proteins. Stimulation of such proteins and enzymes could explain some the intracellular antioxidative properties. The modulation of genes could suffice as an explanation of some of resveratrol's cytoprotective actions, as well as its influence on blood flow, cell death, and inflammatory cascades. Resveratrol stimulation of the expression of heme oxygenase is one example. Increased heme oxygenase activity has led to significant protection against models of in vitro and in vivo oxidative stress injury. Resveratrol could provide cellular resistance against insults; although more work is necessary before it is prescribed as a potential prophylactic in models of either acute or chronic conditions, such as stroke, amyotrophic lateral sclerosis, Parkinson, Alzheimer, and a variety of age-related vascular disorders.

Cerebral autoregulation improves in epilepsy patients after temporal lobe surgery

Patients with temporal lobe epilepsy (TLE) often show increased cardiovascular sympathetic modulation during the interictal period, that decreases after epilepsy surgery. In this study, we evaluated whether temporal lobectomy changes autonomic modulation of cerebral blood flow velocity (CBFV) and cerebral autoregulation. We studied 16 TLE patients 3-4 months before and after surgery. We monitored heart rate (HR), blood pressure (BP), respiration, transcutaneous oxygen saturation (sat-O(2)), end-expiratory carbon dioxide partial pressure (pCO(2)) and middle cerebral artery CBFV. Spectral analysis was used to determine sympathetic and parasympathetic modulation of HR, BP and CBFV as powers of signal oscillations in the low frequency (LF) ranges from 0.04-0.15Hz (LF-power) and in the high frequency ranges from (HF) 0.15-0.5Hz (HF-power). LF-transfer function gain and phase shift between BP and CBFV were calculated as parameters of cerebral autoregulation. After surgery, HR, BP(mean), CBFV(mean), respiration, sat-O(2), pCO(2) and HF powers remained unchanged. LF-powers of HR, BP, CBFV and LF-transfer function gain had decreased while the phase angle had increased (p<0.05). The reduction of LF powers and LF-gain and the higher phase angle showed reduced sympathetic modulation and improved cerebral autoregulation. The enhanced cerebrovascular stability after surgery may improve autonomic balance in epilepsy patients.

Alteration in regulation of inflammatory response to influenza a virus and endotoxin in suckling rat pups: a potential relationship to sudden infant death syndrome

Data increasingly implicate a possible role of immune and inflammatory responses to infection in sudden infant death syndrome (SIDS). We have previously described a dual challenge model that results in pathology, organ damage, vascular collapse and unexplained death similar to that seen in SIDS. In this study, we examined changes in inflammatory cytokine mRNA in the lung and liver and regulation of pathways associated with nitric oxide production. Our data suggest that priming of the immune system by mild viral infection disturbs normal inflammatory response to endotoxin. This results in an increased nitric oxide synthase production, most likely the cause of liver pathology and clotting abnormalities.

Hyperoxia, reactive oxygen species, and hyperventilation: oxygen sensitivity of brain stem neurons

Hyperoxia is a popular model of oxidative stress. However, hyperoxic gas mixtures are routinely used for chemical denervation of peripheral O2 receptors in in vivo studies of respiratory control. The underlying assumption whenever using hyperoxia is that there are no direct effects of molecular O2 and reactive O2 species (ROS) on brain stem function. In addition, control superfusates used routinely for in vitro studies of neurons in brain slices are, in fact, hyperoxic. Again, the assumption is that there are no direct effects of O2 and ROS on neuronal activity. Research contradicts this assumption by demonstrating that O2 has central effects on the brain stem respiratory centers and several effects on neurons in respiratory control areas; these need to be considered whenever hyperoxia is used. This mini-review summarizes the long-recognized, but seldom acknowledged, paradox of respiratory control known as hyperoxic hyperventilation. Several proposed mechanisms are discussed, including the recent hypothesis that hyperoxic hyperventilation is initiated by increased production of ROS during hyperoxia, which directly stimulates central CO2 chemoreceptors in the solitary complex. Hyperoxic hyperventilation may provide clues into the fundamental role of redox signaling and ROS in central control of breathing; moreover, oxidative stress may play a role in respiratory control dysfunction. The practical implications of brain stem O2 and ROS sensitivity are also considered relative to the present uses of hyperoxia in respiratory control research in humans, animals, and brain stem tissues. Recommendations for future research are also proposed.

Dietary vitamin E and selenium and toxicity of nitrite and nitrate

Nitrites and nitrates are important antimicrobial and flavoring/coloring agents in meat and fish products. However, nitrites and nitrates may cause methemoglobinemia and other illness, and may react with certain amines to form carcinogenic nitrosamines. The nutritional status of vitamin E and selenium has long been associated with nitrite and nitrate toxicity, although the mechanism involved is not yet clear. Information available recently shows that nitrites and nitrates are both oxidation products and ready sources of nitric oxide (NO*), that NO* reacts rapidly with superoxide to form highly reactive peroxynitrite (ONOO-), and that vitamin E may mediate the generation and availability of superoxide and NO*. Increased formation of ONOO- resulting from nitrite treatment and low intake of vitamin E and selenium may thus be the critical event leading to tissue damage and animal mortality observed previously. The protection against the adverse effects of nitrites/nitrates by vitamin E is attributed to its ability to reduce ONOO- formation, while selenium exerts its protective effects via seleno-enzymes/compounds, which reduce ONOO- formed.

Sudden infant death syndrome Part 2: the response of the reticuloendothelial system to hypoxemia and infection

The incidence of ascites in chicks raised in a high-altitude chamber doubled from 6500 feet to 8000 feet. A similar condition developed in calves transported to pasture at high altitude. Chicks raised in a high-altitude chamber (compared to controls) produced more plasma cells in the germinal centres of the spleen about four days after an antigen challenge. Children usually suffering from a mild respiratory infection at sea level often developed pulmonary edema (HAPE) on transfer to high altitude. Sudden infant death syndrome (SIDS) victims produced more plasma cells in the germinal centers of the spleen. In one survey of SIDS, about half of the infants suffered an upper respiratory tract infection in the two weeks prior to death and the lungs were filled with fluid at autopsy. Elevated levels of hypoxanthine indicated hypoxemia before death, and a presumed response to hypoxemia in SIDS was the presence of extramedullary hematopoiesis in the liver. The effect of prolonged hypoxemia and infection are additive in increasing vascular permeability and the accumulation of edema fluid. The preferential uptake of zinc by edema fluid proteins at the expense of inflammatory cells increases the motility and metabolism of zinc-deprived activated macrophages. Activated macrophages release cytokines which in turn stimulate the release of pro-inflammatory peptides which increase vascular permeability and mortality. These inflammatory peptides are under proteolytic control. The neutral endopeptidase (NEP) is a cell-surface zinc metalloproteinase which modulates toxic shock.Zinc also modulates the inflammatory response of the activated macrophage. Interleukin-12 (IL-12), predominantly a product of macrophages, is involved in regulating both hematopoiesis and the adaptive immune response. IL-12 promotes interferon gamma (IFNgamma) production by T cells. IFNgamma acts on macrophages to release large amounts of nitric oxide (NO). An elevated immune response leads to NO overload, dilation of the cardiovascular system and toxic shock. A mechanism resulting in cardiovascular failure and a shock-like sequence is described in some cases of SIDS.Bradycardia, recorded on cardiorespiratory monitors in six SIDS infants, was considered a late event. Cytokines regulate all aspects of the immune response. Extramedullary hematopoiesis in the liver was one anatomical marker of hypoxemia in SIDS. This survey traces the function of the activated macrophage with the cytokines regulating extramedullary hematopoiesis and the precocious immune response in SIDS.