Role of Nitric Oxide-Signalling in Hypoxia-Induced Immune Escape in Cancer

A key step in malignant progression is the acquired ability of tumour cells to escape immune-mediated lysis. A potential mechanism by which tumour cells avoid immune destruction involves the shedding of MHC Class I Chain-Related Protein A (MICA), a Natural Killer (NK) cell-activating ligand, from the tumour cell membrane. Hypoxia has been shown to cause increased MICA shedding; however, this hypoxia-induced effect can be attenuated by pharmacological activation of the cyclic guanosine monophosphate (cGMP)-dependent nitric oxide (NO)-signalling pathway in cancer cells. The primary objective of the present study was to determine whether treatment of tumour-bearing nude mice with the NO-mimetic glyceryl trinitrate (GTN) attenuates in vivo tumour growth and if so, whether this effect is dependent on the presence of an intact NK cell compartment. Results indicated that continuous transdermal administration of GTN (1.8 µg/h) can significantly attenuate the growth of transplanted human DU-145 prostate tumours but that this effect of GTN is lost in mice whose NK-cells have been depleted. Tumours and serum from the mice in this study were analysed to determine whether GTN treatment had any effect on the expression levels of proteins integral to the proposed MICA shedding mechanism; however, the results of these studies were inconclusive. As phosphodiesterase (PDE) inhibition represents a potential method to enhance NO-signalling, experiments were performed to determine whether treatment with the PDE5/6 inhibitor zaprinast could also attenuate hypoxia-induced MICA shedding and decrease in vivo growth of DU-145 tumours. Results demonstrated that treatment with zaprinast (10 mg/kg) significantly attenuates MICA shedding in DU-145 cancer cells and significantly decreases in vivo tumour growth. Taken together, the results of these experiments indicate that GTN attenuates tumour growth by sensitising tumour cells to innate immunity, likely by increasing membrane-associated tumour cell MICA levels through the reactivation of NO-signalling, and that zaprinast decreases tumour growth likely through a similar mechanism. These findings are important because they indicate that agents capable of reactivating NO-signalling, such as NO-mimetics and PDE inhibitors, can potentially be used as immunosensitisers in the treatment and/or prevention of cancer.

Normal levels of prepulse inhibition in the euthymic phase of bipolar disorder.

BACKGROUND:Deficits in prepulse inhibition (PPI) of the acoustic startle response have been suggested as a potentially useful endophenotype for schizophrenia spectrum disorders and may explain certain symptoms and cognitive deficits observed in the psychoses. PPI deficits have also been found in mania, but it remains to be confirmed whether this dysfunction is present in the euthymic phase of bipolar disorder.METHOD: Twenty-three adult patients with DSM-IV bipolar disorder were compared to 20 controls on tests of acoustic startle reactivity and PPI of the startle response. Sociodemographic and treatment variables were recorded and symptom scores assessed using the Hamilton Depression Inventory and the Young Mania Rating Scale.RESULTS:Overall, the patient and control groups demonstrated similar levels of startle reactivity and PPI, although there was a trend for the inter-stimulus interval to differentially affect levels of PPI in the two groups.CONCLUSIONS: In contrast to bipolar patients experiencing a manic episode, general levels of PPI were normal in this euthymic sample. Further studies are required to confirm this finding and to determine the mechanisms by which this potential disruption/normalization occurs. It is suggested that an examination of PPI in a high-risk group is required to fully discount dysfunctional PPI as a potentially useful endophenotype for bipolar disorder.

Do vesicle cells of the red alga Asparagopsis (Falkenbergia stage) play a role in bromocarbon production?

The Rhodophyceae (red algae) are an established source of volatile halocarbons in the marine environment. Some species in the Bonnemaisoniaceae have been reported to contain large amounts of halogens in structures referred to as vesicle cells, suggesting involvement of these specialised cells in the production of halocarbons. We have investigated the role of vesicle cells in the accumulation and metabolism of bromide in an isolate of the red macroalga Asparagopsis (Falkenbergia stage), a species known to release bromocarbons. Studies of laboratory-cultivated alga, using light microscopy, revealed a requirement of bromide for both the maintenance and formation of vesicle cells. Incubation of the alga in culture media with bromide concentrations below 64 mg l-1 (the concentration of Br- in seawater) resulted in a decrease in the proportion of vesicle cells to pericentral cells. The abundance of vesicle cells was correlated with bromide concentration below this level. Induction of vesicle cell formation in cultures of Falkenbergia occurred at concentrations as low as 8 mg l-1, with the abundance of vesicle cells increasing with bromide concentration up to around 100 mg l-1. Further studies revealed a positive correlation between the abundance of vesicle cells and dibromomethane and bromoform production. Interestingly, however, whilst dibromomethane production was stimulated by the presence of bromide in the culture media, bromoform release remained unaffected suggesting that the two compounds are formed by different mechanisms.

Interaction of glucose and long chain fatty acids (C18) on antioxidant defences and free radical damage in porcine vascular smooth muscle cells in vitro.

Aims/hypothesis: Abnormalities of glucose and fatty acid metabolism in diabetes are believed to contribute to the development of oxidative stress and the long term vascular complications of the disease therefore the interactions of glucose and long chain fatty acids on free radical damage and endogenous antioxidant defences were investigated in vascular smooth muscle cells. Methods: Porcine vascular smooth muscle cells were cultured in 5 mmol/l or 25 mmol/l glucose for ten days. Fatty acids, stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2) and gamma-linolenic acid (18:3) were added with defatted bovine serum albumin as a carrier for the final three days. Results. Glucose (25 mmol/l) alone caused oxidative stress in the cells as evidenced by free radical-mediated damage to DNA, lipids, and proteins. The addition of fatty acids (0.2 mmol/l) altered the profile of free radical damage; the response was J-shaped with respect to the degree of unsaturation of each acid, and oleic acid was associated with least damage. The more physiological concentration (0.01 mmol/l) of gamma-linolenic acids was markedly different in that, when added to 25 mmol/l glucose it resulted in a decrease in free radical damage to DNA, lipids and proteins. This was due to a marked increase in levels of the antioxidant, glutathione, and increased gene expression of the rate-limiting enzyme in glutathione synthesis, gamma-glutamylcysteine synthetase. Conclusion/Interpretation: The results clearly show that glucose and fatty acids interact in the production of oxidative stress in vascular smooth muscle cells.