Stress and inflammatory disease: widening roles for serotonin and substance P

Liquid chromatography-tandem mass spectrometry based simultaneous quantification of tryptophan, serotonin and kynurenine pathway metabolites in tissues and cell culture systems

BACKGROUND

Kynurenine and respective metabolites exhibit bioactivity as well as tryptophan, an essential amino acid, and the neurotransmitter serotonin. Dysregulations in the kynurenine pathway are involved in neurodegenerative/neuropsychiatric disorders and diabetes mellitus type 2 but also in cancer. Therefore, measurements of kynurenine-related metabolites will improve the general understanding for kynurenine pathway relevance in disease pathogenesis.

METHODS

Tryptophan, serotonin, picolinic acid, quinolinic acid, 3-OH-kynurenine, kynurenine, 3-OH-anthranilic acid, kynurenic acid, anthranilic acid as well as nicotinic acid and the redox cofactor NAD+ were analyzed in heterogeneous matrices by ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). After validation, the described method was applied for measurements of native metabolite concentrations in murine tissues and cellular systems including pathway-shift monitoring after treatment with the tryptophan-2,3-dioxygenase-inhibitor 680C91. In addition, the method was evaluated for its ability for integration into multi-omics approaches using a single sample metabolite extraction procedure.

RESULTS

A simple and sensitive UPLC-MS/MS method for simultaneous quantification of up to 10 kynurenine-related metabolites in four biological matrices was developed. Within a run time of 6.5 min, chromatographic separation of kynurenine-related metabolites, including the isomers nicotinic acid and picolinic acid, was achieved without derivatization. Validation parameters, including interday precision (<14.8%), mean accuracy (102.4% ± 12.9%) and linear detection ranges of more than three orders of magnitude, indicate method reliability. Depending the investigated sample matrix, the majority of metabolites were successfully detected and quantified in native murine and cell culture derived sample materials. Furthermore, the method allowed to monitor the impact of a tryptophan-2,3-dioxygenase-inhibitor on kynurenine pathway in a cellular system and is suitable for multi-assay analyses using aliquots from the same cell extract.

CONCLUSION

The described UPLC-MS/MS method provides a simple tool for the simultaneous quantification of kynurenine pathway metabolites. Due to its suitability for many physiological matrices, the method provides wide application for disease-related experimental settings.

Chronic psychosocial stress in tree shrews: effect of the substance P (NK1 receptor) antagonist L-760735 and clomipramine on endocrine and behavioral parameters

RATIONALE

Substance P and its preferred receptor, the neurokinin 1 receptor (NK(1)R), have been proposed as possible targets for new antidepressant therapies, although results of a recently completed phase III trial failed to demonstrate that the NK(1)R antagonist MK-869 is more effective than placebo in the treatment of depression.

METHODS

In the present study, we compared the effects of the NK(1)R antagonist L-760735 with the tricyclic antidepressant clomipramine on endocrine and behavioral parameters in chronically stressed tree shrews. Animals were subjected to a 7-day period of psychosocial stress before receiving daily oral administration of L-760735 (10 mg/kg/day) or clomipramine (50 mg/kg/day). The psychosocial stress continued throughout the treatment period of 21 days. Daily morning urine was collected to measure cortisol and norepinephrine levels. All animals were videotaped daily and three types of behavior were analyzed.

RESULTS

Chronic psychosocial stress resulted in a significant increase of urinary cortisol and norepinephrine concentrations. Moreover, stressed animals displayed decreased marking behavior and locomotor activity, while grooming remained unaffected. Neither treatment with clomipramine nor L-760735 was able to normalize the stress-induced elevation of cortisol or norepinephrine. On the behavioral parameters, L-760735 had a time-dependent restorative influence on marking behavior close to normal levels, without affecting locomotor activity. Grooming behavior was significantly increased by the 3 weeks of drug treatment.

CONCLUSIONS

These results suggest that L-760735 was able to counteract certain stress-induced behavioral alterations in an animal model of depression.

Substance P receptor antagonist and clomipramine prevent stress-induced alterations in cerebral metabolites, cytogenesis in the dentate gyrus and hippocampal volume

The neuropeptide substance P and its receptor, the neurokinin 1 receptor (NK(1)R) have been proposed as possible targets for new antidepressant therapies. The present study investigated the effect of the NK(1)R antagonist L-760,735 and the tricyclic antidepressant clomipramine in the chronic psychosocial stress paradigm of adult male tree shrews. Animals were subjected to a 7-day period of psychosocial stress before the onset of daily oral administration of L-760,735 (10 mg kg(-1) day(-1)) or clomipramine (50 mg kg(-1) day(-1)). The psychosocial stress continued throughout the treatment period of 28 days. Brain metabolite concentrations were determined in vivo by proton magnetic resonance spectroscopy. Cell proliferation in the dentate gyrus and hippocampal volume were measured post mortem. Stress significantly decreased in vivo concentrations of N-acetyl-aspartate (-14%), creatine and phosphocreatine (-15%) and choline-containing compounds (-15%). The proliferation rate of the granule precursor cells in the dentate gyrus was reduced (-45%), and hippocampal volume was decreased (-14%). The stress-induced changes of brain metabolites, hippocampal volume and dentate cytogenesis rate were prevented by concomitant drug administration. Elevated myo-inositol concentrations after both treatments hint to an astrocytic enhancement. These results suggest that-despite a different pharmacological profile-the NK(1)R antagonist L-760,735, a member of a novel class of antidepressant drugs, has comparable neurobiological efficacy to tricyclic antidepressants such as clomipramine.

Neuroendocrinology of autoimmunity

The HPA axis is fundamental for long-term survival and protection from the ravages of autoimmune disease. Continuing investigations suggest that the hypothesis linking susceptibility to autoimmune disease and a hyporesponsive HPA axis is somewhat simplistic. Instead, data from a number of different human diseases and from preclinical studies in a variety of models have suggested a more complicated picture. Alterations in the diurnal rhythms of ACTH, cortisol, and immune parameters appear to be linked to severity of disease. The use of low doses of steroids timed to target disrupted diurnal immune system changes in patients with RA may reduce the unfortunate side effects of long-term steroid use. Studies in cancer patients have related alterations in diurnal cortisol to survival. Whether differences in individual cortisol profiles are predictive of a deterioration in symptoms of autoimmune disease remains to be established. Responsiveness of the HPA axis to subtle challenges such as the dexamethasone suppression test and the related dexamethasone-CRF test suggest that there are different sub-populations of patients with RA and MS and these may have confounded earlier, apparently contradictory, studies. These different responses may be related to the severity of the disease. That these HPA axis differences can be altered beneficially through the use of antidepressants, as has been shown in MS, may impact on future health care strategies. However, reports of negative developments in arthritis associated with SSRI use suggest that the SSRIs may be unsuitable under some circumstances. The link of behavioral differences to alterations in neurotransmitter changes associated with disease is intriguing and opens new avenues of research. These future studies will require input from neuroscientists, neuroendocrinologists, psychologists, and immunologists working with the clinical specialties already involved in treating patients with autoimmune disease. These multidisciplinary studies reflecting the increased importance of hormonal and neurotransmitter involvement with the immune system hold great promise for the future.