In Silico Approaches In Carcinogenicity Hazard Assessment: Current Status and Future Needs

Historically, identifying carcinogens has relied primarily on tumor studies in rodents, which require enormous resources in both money and time. In silico models have been developed for predicting rodent carcinogens but have not yet found general regulatory acceptance, in part due to the lack of a generally accepted protocol for performing such an assessment as well as limitations in predictive performance and scope. There remains a need for additional, improved in silico carcinogenicity models, especially ones that are more human-relevant, for use in research and regulatory decision-making. As part of an international effort to develop in silico toxicological protocols, a consortium of toxicologists, computational scientists, and regulatory scientists across several industries and governmental agencies evaluated the extent to which in silico models exist for each of the recently defined 10 key characteristics (KCs) of carcinogens. This position paper summarizes the current status of in silico tools for the assessment of each KC and identifies the data gaps that need to be addressed before a comprehensive in silico carcinogenicity protocol can be developed for regulatory use.

Intralymphatic Administration of Adipose Mesenchymal Stem Cells Reduces the Severity of Collagen-Induced Experimental Arthritis

Mesenchymal stem cells (MSCs) are multipotent stromal cells with immunomodulatory properties. They have emerged as a very promising treatment for autoimmunity and inflammatory diseases such as rheumatoid arthritis. Previous studies have demonstrated that MSCs, administered systemically, migrate to lymphoid tissues associated with the inflammatory site where functional MSC-induced immune cells with a regulatory phenotype were increased mediating the immunomodulatory effects of MSCs. These results suggest that homing of MSCs to the lymphatic system plays an important role in the mechanism of action of MSCs in vivo. Thus, we hypothesized that direct intralymphatic (IL) (also referred as intranodal) administration of MSCs could be an alternative and effective route of administration for MSC-based therapy. Here, we report the feasibility and efficacy of the IL administration of human expanded adipose mesenchymal stem cells (eASCs) in a mouse model of collagen-induced arthritis (CIA). IL administration of eASCs attenuated the severity and progression of arthritis, reduced bone destruction and increased the levels of regulatory T cells (CD25⁺Foxp3⁺CD4⁺ cells) and Tr1 cells (IL10⁺CD4⁺), in spleen and draining lymph nodes. Taken together, these results indicate that IL administration of eASCs is very effective in modulating established CIA and may represent an alternative treatment modality for cell therapy with eASCs.

Adipose-derived mesenchymal stromal cells modulate experimental autoimmune arthritis by inducing an early regulatory innate cell signature

Modulation of innate immune responses in rheumatoid arthritis and other immune-mediated disorders is of critical importance in the clinic since a growing body of information has shown the key contribution of dysregulated innate responses in the progression of the disease. Mesenchymal stromal cells (MSCs) are the focus of intensive efforts worldwide due to their key role in tissue regeneration and modulation of inflammation. In this study, we define innate immune responses occurring during the early course of treatment with a single dose of expanded adipose-derived MSCs (eASCs) in established collagen-induced arthritis. eASCs delay the progression of the disease during the early phase of the disease. This is accompanied by a transient induction of Ly6C⁺ monocytes that differentiate into IL10⁺F4/80⁺ cells in arthritic mice. Strikingly, the induced IL10⁺F4/80⁺ myeloid cells preferentially accumulated in the draining lymph nodes. This effect was accompanied with a concomitant declining of their frequencies in the spleens. Our results show that eASCs attenuate the arthritic process by inducing an early innate cell signature that involves a transient induction of Ly6C⁺ monocytes in periphery that differentiate into IL10⁺F4/80⁺ macrophages. Our findings demonstrate that early regulatory innate cell responses, involving the monocyte compartment, are targeted by the eASCs during the onset of collagen-induced inflammation.

Aminoguanidine-provoked leukocyte adherence to rat mesenteric venules: role of constitutive nitric oxide synthase inhibition

1. The effects of aminoguanidine on neutrophil adherence to venules and on the diameter of arterioles in the mesenteric vascular bed of the pentobarbitone-anaesthetized rat have been compared with those of the nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). 2. Administration of L-NAME (1-10 mg kg-1, i.v.) caused a dose-dependent increase in leukocyte adherence and a reduction in leukocyte rolling velocity in postcapillary venules of the rat mesentery over 1 h. 3. Likewise, aminoguanidine (10-100 mg kg-1, i.v.) dose-dependently increased leukocyte adherence and decreased leukocyte rolling velocity over 1 h. 4. Both L-NAME and aminoguanidine caused a dose-dependent reduction in mesenteric arteriolar diameter and an increase in systemic arterial blood pressure. 5. The effects of aminoguanidine (50 mg kg-1, i.v.) on leukocyte adherence, arteriolar diameter and on blood pressure were significantly reversed by pretreatment with L-arginine (300 mg kg-1, i.v.). 6. These findings indicate that, like L-NAME, aminoguanidine can acutely promote leukocyte adherence to the mesenteric venular wall and reduce arteriolar diameter. Moreover, these acute effects were reversed by L-arginine, suggesting they are mediated through inhibition of constitutive NO synthase.

Endothelin-1 induces neutrophil-independent vascular injury in the rat gastric microcirculation

Local intra-arterial infusion of picomole quantities of endothelin-1 induced gastric vascular leakage of radiolabelled albumin. This leakage was partially inhibited by the platelet activating factor (PAF) receptor antagonist WEB 2086 (0.5-2 mg kg-1), but was unaffected by the thromboxane synthase inhibitor OKY 1581 (5 mg kg-1) or by pretreatment with anti-neutrophil serum. These results indicate a partial role of PAF, but demonstrate that neutrophils are not involved in the gastric vascular dysfunction induced by locally administered endothelin-1.

Calcitonin-gene related peptide can augment or prevent endothelin-1 induced gastric microvascular leakage

The effects of locally infused calcitonin gene-related peptide (CGRP) on the changes in microvascular permeability and tissue injury following close-arterial infusion of endothelin-1 (5 pmol kg-1 min-1, 10 min) in the rat gastric mucosa have been investigated. Pretreatment with rat alpha-CGRP (10-50 pmol kg-1 min-1) inhibited the leakage of radiolabelled albumin and reduced the haemorrhagic necrosis, an action inhibited by the CGRP receptor antagonist, hCGRP-(8-37) (2 nmol kg-1 min-1). By contrast, local infusion of CGRP immediately following endothelin-1 challenge had no such protective actions, and significantly exacerbated the microvascular leakage and tissue injury at the higher dose. These studies suggest that CGRP can exert both pro- and anti-inflammatory actions in the gastric microcirculation.

The involvement of endothelial dysfunction, nitric oxide and prostanoids in the rat gastric microcirculatory responses to endothelin-1

1. The role of endothelial dysfunction in the gastric microcirculatory responses during local endothelin-1 (ET-1) infusion has been investigated in the pentobarbitone-anaesthetized rat. Furthermore, the involvement of prostanoids or nitric oxide (NO) in these actions has been investigated by the use of indomethacin to inhibit cyclo-oxygenase and NG-nitro-L-arginine methyl ester (L-NAME) to inhibit NO synthase. 2. Close-arterial infusion of ET-1 (1-10 pmol kg-1 min-1 for 10 min) induced a dose-dependent increase in the gastric leakage of radiolabelled albumin, used as an index of endothelial cell dysfunction. 3. Close-arterial infusion of a submaximal dose of ET-1 (5 pmol kg-1 min-1 for 10 min) significantly increased gastric albumin leakage after 2 min infusion, which reached maximal levels after 10 min, and only slowly declined during the 30 min observation period. 4. By contrast, gastric blood flow, as assessed by laser Doppler flowmetry, did not significantly increase until after 5 min of infusion of ET-1 (5 pmol kg-1 min-1 for 10 min), reaching a maximum after 17 min, and was sustained for the 30 min observation period. 5. Pretreatment with L-NAME (2 mg kg-1, i.v.) or indomethacin (5 mg kg-1, i.v.) significantly reduced both the hyperaemic response to ET-1 and the increase in gastric albumin leakage, and in combination abolished these responses. 6. These results suggest that locally released NO and prostanoids mediate the gastric vasodilator response to close arterial infusion of ET-1. This hyperaemia is preceded by changes in gastric albumin extravasation and hence may be initiated as a response to direct endothelial injury by ET-1.

The paradoxical vascular interactions between endothelin-1 and calcitonin gene-related peptide in the rat gastric mucosal microcirculation

1. The interactions between local intra-arterial infusion of endothelin-1 (ET-1) and rat alpha-calcitonin gene-related peptide (alpha-CGRP) on gastric mucosal damage and blood flow have been investigated in the pentobarbitone-anaesthetized rat. 2. Close-arterial infusion of ET-1 (2-200 pmol kg-1 min-1) induced a significant and dose-dependent increase in gastric mucosal haemorrhagic injury. 3. Close-arterial infusion of the higher doses of ET-1 (100 and 200 pmol kg-1 min-1) resulted in a biphasic effect on mucosal blood flow, as determined by laser Doppler flowmetry (LDF). This consisted of an initial transient increase followed by a pronounced and sustained fall in LDF. 4. Local microvascular constriction may thus contribute to the mechanisms underlying the gastric injury induced by these higher doses of ET-1. 5. However, close-arterial infusion of lower doses of ET-1 (2-50 pmol kg-1 min-1), that also provoked substantial mucosal damage, induced only a sustained and significant mucosal hyperaemia, which may be secondary to microvascular injury. 6. Concurrent dose-arterial administration of rat alpha-CGRP (50 pmol kg-1 min-1) significantly inhibited the extent of gastric mucosal injury induced by ET-1 (5 pmol kg-1 min-1). 7. Furthermore, concurrent close-arterial infusion of this dose of alpha-CGRP, which itself increased mucosal LDF, significantly inhibited the hyperaemic response induced by close-arterial infusion of ET-1 (5 pmol kg-1 min-1). 8. These results indicate a damaging action on the gastric mucosa by low doses of ET-1 which is independent of local vasoconstriction, that may involve a direct injury of the microvascular endothelium. The protective action of alpha-CGRP thus seems unlikely to be due to a local vasodilator effect but may reflect protective actions on the microvascular endothelium

Actions and interactions of endothelins, prostacyclin and nitric oxide in the gastric mucosa

The modulation of the gastric mucosal microcirculation plays a key role in the maintenance of gastric integrity. Disruption of the balance between the local release of vasodilator and vasoconstrictor mediators could therefore be involved in the pathogenesis of mucosal injury. Thus, the endothelium derived peptide endothelin-1 (ET-1), induces mucosal injury following local administration. In contrast, the vasodilator prostanoids, prostacyclin and PGE2 can protect against gastric damage, while inhibition of endogenous prostanoid formation by cyclo-oxygenase inhibitors augment mucosal damage, including that induced by ET-1. Sensory neuropeptides such as calcitonin gene-related peptide (CGRP) may also play a local protective role, since acute intragastric administration of capsaicin which stimulates neuropeptide release, protects against mucosal injury induced by ET-1, as does local infusion of CGRP. Furthermore, chronic administration of capsaicin which deplete primary sensory neurones augments gastric damage induced by a number of ulcerogens including ET-1. Nitric oxide (NO) synthesized from L-arginine can regulate gastric mucosal blood flow, both under resting conditions and following stimulation of acid secretion. Inhibition of NO biosynthesis alone does not induce acute mucosal injury, yet extensive haemorrhagic damage results from concurrent inhibition of NO formation, cyclo-oxygenase inhibition and depletion of sensory neuropeptides. NO donors can protect against ulceration, although the unregulated release of high levels of NO can lead to mucosal injury. Thus, NO has a critical interactive role with other local protective mediators such as the prostanoids and sensory neuropeptides in the physiological regulation of mucosal integrity.

The actions of nitric oxide donors in the prevention or induction of injury to the rat gastric mucosa

1. The protective or damaging actions on the gastric mucosa, of locally infused nitrovasodilators that donate nitric oxide (NO), have been investigated in the pentobarbitone-anaesthetized rat. 2. Local intra-arterial infusion of endothelin-1 (ET-1; 5 pmol kg-1 min-1 for 10 min) induced extensive, macroscopically apparent, haemorrhagic injury to the rat gastric mucosa. This damage was dose-dependently reduced by concurrent local intra-arterial infusion of glyceryl trinitrate (GTN; 10-40 micrograms kg-1 min-1) which liberates NO on metabolic transformation, or the nitrosothiol, S-nitroso-N-acetyl-penicillamine (SNAP, 2.5-10 micrograms kg-1 min-1) which spontaneously liberates NO. 3. Local infusion of higher doses of SNAP (20 and 40 micrograms kg-1 min-1, i.a.) did not, however, significantly protect against mucosal injury induced by ET-1. 4. Furthermore, local infusion alone of these higher doses of SNAP, as well as sodium nitroprusside (10-40 micrograms kg-1 min-1, i.a.) which also spontaneously liberates NO, induced significant mucosal injury, as assessed macroscopically and confirmed by histology. 5. Local infusion of these higher doses of SNAP and nitroprusside reduced systemic arterial blood pressure (BP), but this was not correlated with the extent of mucosal injury. 6. Furthermore, local infusion of GTN (10-40 micrograms kg-1 min-1, i.a.) alone, which also reduced BP, failed to induce gastric mucosal damage. 7. These findings suggest that exogenous NO can protect the rat gastric mucosa from damage induced by the vasoconstrictor peptide ET-1, which may reflect local microcirculatory interactions. However, the unregulated release of high levels of NO within the microvasculature induces mucosal injury.

Nitric oxide mediates rat mucosal vasodilatation induced by intragastric capsaicin

The role of endogenous nitric oxide (NO) in the gastric mucosal vasodilatation induced by acute intragastric perfusion with capsaicin or close-arterial infusion of rat alpha-calcitonin gene-related peptide (CGRP) was evaluated in the pentobarbitone-anaesthetised rat using laser Doppler flowmetry (LDF). The mucosal vasodilatation induced by intraluminal capsaicin (160 microM) was dose dependently reduced by the inhibitor of NO synthesis, NG-nitro-L-arginine methyl ester (L-NAME; 1-5 mg kg-1 i.v.), effects reversed by concurrent administration of L-arginine (100 mg kg-1 i.v.). L-NAME (2 mg kg-1) induced a small reduction in the mucosal vasodilatation induced by close-arterial infusion of rat alpha-CGRP (50 pmol kg-1 min-1). These findings indicate a role of NO in the gastric vasodilatation induced by stimulation of sensory neurones with intragastric capsaicin.

Interactions between the vascular peptide endothelin-1 and sensory neuropeptides in gastric mucosal injury

1. The interactions between endogenous and exogenous sensory neuropeptides on gastric mucosal injury induced by endothelin-1 (ET-1) have been investigated in the anaesthetized rat. 2. Close intra-arterial infusion of ET-1 (4-20 pmol kg-1 min-1) dose-dependently induced vasocongestion and haemorrhagic necrosis in the gastric mucosa. 3. Capsaicin-pretreatment, two weeks earlier to deplete sensory neuropeptides from primary afferent neurones, augmented the mucosal damage induced by ET-1, as assessed by both macroscopic and histological examination. 4. The damage induced by threshold doses of ET-1 alone or in capsaicin-pretreated rats was further enhanced by administration of indomethacin (5 mg kg-1, i.v.), indicating a modulatory influence of endogenous prostanoids. 5. Morphine administration (3 mg kg-1, i.v.), which can prevent neuropeptide release, augmented the damage induced by threshold doses of ET-1, this effect being reversed by naloxone (1 mg kg-1, i.v.). 6. Concurrent local intra-arterial infusion of rat alpha-calcitonin gene-related peptide (10-50 pmol kg-1 min-1) dose-dependently reduced the mucosal injury induced by ET-1. 7. These findings suggest interactions between ET-1 and sensory neuropeptides, which may reflect an important influence of these peptide mediators in the regulation of mucosal integrity.

Regulation of gastric mucosal integrity by endogenous nitric oxide: interactions with prostanoids and sensory neuropeptides in the rat

1. The interactions between nitric oxide (NO), prostacyclin and sensory neuropeptides in the maintenance of gastric mucosal integrity have been investigated in the anaesthetized rat. 2. Administration of either NG-monomethyl-L-arginine (L-NMMA) to inhibit endothelium-derived NO formation, indomethacin to inhibit prostanoid biosynthesis or chronic capsaicin pretreatment to deplete sensory neuropeptides, did not induce acute mucosal injury. 3. In capsaicin-pretreated rats, however, L-NMMA (12.5-100 mg kg-1 i.v.) dose-dependently induced acute mucosal damage, characterized as vasocongestion and haemorrhagic necrosis. The enatiomer D-NMMA (100 mg kg-1 i.v.) did not induce any detectable mucosal damage. 4. This mucosal injury induced by L-NMMA was inhibited by concurrent administration of L-arginine (300 mg kg-1 i.v.). 5. In indomethacin (5 mg kg-1 i.v.)-pretreated rats, L-NMMA also induced mucosal damage. Furthermore, following indomethacin administration in capsaicin-pretreated rats, L-NMMA induced widespread, severe haemorrhagic necrotic damage. 6. These findings suggest a role for endogenous NO formed from L-arginine, acting in concert with prostacyclin and sensory neuropeptides, in the modulation of gastric mucosal integrity.

Modulation of the vasodepressor actions of acetylcholine, bradykinin, substance P and endothelin in the rat by a specific inhibitor of nitric oxide formation

1. The effects of the specific inhibitor of nitric oxide (NO) formation, NG-monomethyl-L-arginine (L-NMMA), on resting systemic arterial blood pressure (BP) and on the actions of both endothelium-dependent and endothelium-independent vasodilators were investigated in the anaesthetized, normotensive rat. 2. Intravenous administration of L-NMMA (12.5-50 mg kg-1; 47-188 mumol kg-1) but not its enantiomer, D-NMMA, induced a dose-related increase in BP, which was reversed by the intravenous administration of L-arginine (150-600 mumol kg-1), but not D-arginine. 3. The vasodepressor responses to intravenous administration of the endothelium-dependent vasodilators, acetylcholine, bradykinin and substance P were significantly inhibited by L-NMMA (94 and 188 mumol kg-1 i.v.), but not by D-NMMA. 4. The inhibition by L-NMMA of these vasodepressor responses was reversed by administration of L-arginine, but not D-arginine. 5. Endothelin (ET-1) induced dose-related vasodepressor responses following bolus intravenous administration, which were significantly inhibited by L-NMMA but not by D-NMMA. This inhibition was reversed by administration of L-arginine. 6. The vasodepressor effects of the endothelium-independent vasodilators, glyceryl trinitrate or prostacyclin, were not significantly inhibited by L-NMMA. 7. These findings with L-NMMA suggest that resting blood pressure in the rat is modulated by endogenous NO biosynthesis and that endothelium-dependent vasodilators act through the formation of endogenous NO to exert their actions in vivo.