Kynurenine metabolites and migraine: experimental studies and therapeutic perspectives

C-3 alkoxymethylation of 4-oxo-1,4-dihydroquinoline 2-carboxylic acid esters via organic additives

Esters of kynurenic acid, a known neuroprotective agent were reacted with cyclic amino acids to yield novel alkoxymethylated products under optimized reaction conditions. The importance of amino acid based (primary, secondary, biogenic and synthetic) organic additives was proven by the conduction of numerous test reactions. Thoroughly extended investigations, directly focusing on amino acid catalysis, which is an emerging and up-to-date field of catalysis and green chemical processes, have been conducted. The mechanism of the alkoxymethylation reaction was proposed and later the findings supported the hypothesis of the first retro-Mannich step (formation of the ortho-quinone methide intermediate) and subsequent formation of the alkoxymethylated derivatives. As a preparative result, two novel kynurenic acid derivatives bearing an alkoxymethyl moiety and two additional derivatives having amino acid residues at the site C-3 were synthesized, thus setting the scope and limitations of the modified Mannich reaction of kynurenic acid derivatives using amino acid nucleophiles. The mechanistic investigations highlighted the significant physicochemical effects of used nucleophiles on the amino-acid driven one-pot retro-Mannich initiated alkoxylation of kynurenic acid.

Primary headache disorders among people living with HIV in Lusaka, Zambia

OBJECTIVE

We completed a cross-sectional survey study to determine headache prevalence and its association with HIV characteristics among people living with HIV (PLHIV) in Lusaka, Zambia.

BACKGROUND

Headaches are common but their association with HIV status is unknown.

METHODS

The HARDSHIP survey, a headache epidemiology questionnaire previously validated in Zambia, was distributed during a 3-month period to 3666 consecutive adult PLHIV attending routine clinic appointments at the Adult Infectious Diseases Centre at the University Teaching Hospital in Lusaka, Zambia. HIV disease characteristics were abstracted from their charts.

RESULTS

1015 (27.7%) participants responded to the survey. Adjusted for age, 64% reported having a headache within the last year unrelated to another illness. Among participants, 201 met criteria for migraine (20%), 259 for tension-type headache (26%), 18 for probable medication-overuse headache (2%), and 121 for undetermined headache (12%). Prevalence for tension-type headache was significantly higher than that of migraine (P < 0.001). After adjusting for age and sex, higher CD4 counts were associated with migraine. No other associations were observed between overall headache or headache type with HIV disease characteristics including CD4 count, viral load, antiretroviral regimen, and time since HIV diagnosis.

CONCLUSIONS

Headaches are highly prevalent among this cohort of PLHIV in Zambia. Optimizing headache treatment and integrating it into routine HIV care may improve quality of life for a substantial proportion of PLHIV in Zambia.

Ion Channel Disturbances in Migraine Headache: Exploring the Potential Role of the Kynurenine System in the Context of the Trigeminovascular System

Migraine is a primary headache disorder, which is an enormous burden to the healthcare system. While some aspects of the pathomechanism of migraines remain unknown, the most accepted theory is that activation and sensitization of the trigeminovascular system are essential during migraine attacks. In recent decades, it has been suggested that ion channels may be important participants in the pathogenesis of migraine. Numerous ion channels are expressed in the peripheral and central nervous systems, including the trigeminovascular system, affecting neuron excitability, synaptic energy homeostasis, inflammatory signaling, and pain sensation. Dysfunction of ion channels could result in neuronal excitability and peripheral or central sensitization. This narrative review covers the current understanding of the biological mechanisms leading to activation and sensitization of the trigeminovascular pain pathway, with a focus on recent findings on ion channel activation and modulation. Furthermore, we focus on the kynurenine pathway since this system contains kynurenic acid, which is an endogenous glutamate receptor antagonist substance, and it has a role in migraine pathophysiology.

Novel Eco-friendly, One-Pot Method for the Synthesis of Kynurenic Acid Ethyl Esters

The synthesis of kynurenic acid derivatives with potential biological effect was investigated and optimized for one-batch, two-step microwave-assisted reactions. Utilizing both chemically and biologically representative non-, methyl-, methoxy-, and chlorosubstituted aniline derivatives, in catalyst-free conditions, syntheses of seven kynurenic acid derivatives were achieved in a time frame of 2-3.5 h. In place of halogenated reaction media, tuneable green solvents were introduced for each analogue. The potential of green solvent mixtures to replace traditional solvents and to alter the regioisomeric ratio regarding the Conrad-Limpach method was highlighted. The advantages of the fast, eco-friendly, inexpensive analytic technique of TLC densitometry were emphasized for reaction monitoring and conversion determination in comparison to quantitative NMR. Moreover, the developed 2-3.5 h syntheses were scaled-up to achieve gram-scale products of KYNA derivatives, without altering the reaction time in the halogenated solvent DCB and more importantly in its green substitutes.

The NMDA receptor antagonists memantine and ketamine as anti-migraine agents

Migraine is a debilitating disorder affecting females more frequently than males. There is some evidence that drugs targeting glutamate receptors: memantine and ketamine might be beneficial in the therapy of this entity. Therefore, the purpose of this work is to present NMDA receptor antagonists, memantine and ketamine, as potential anti-migraine agents. We searched PubMed/MEDLINE, Embase, and clinical trials submitted to ClinicalTrials.gov to find publications describing eligible trials published between database inception and December 31, 2021. This comprehensive literature review summarizes data on the use of the NMDA receptor antagonists memantine and ketamine in the pharmacotherapy of migraine. Results from 20 previous and recent preclinical experiments are discussed and correlated with 19 clinical trials (including case series, open-label, and randomized placebo-controlled trials). For the purposes of this review, the authors hypothesized that the propagation of SD is a major mechanism in the pathophysiology of migraine. In several animal studies and in vitro studies, memantine and ketamine inhibited or reduced propagation of the SD. In addition, the results of clinical trials suggest that memantine or ketamine may be an effective treatment option for migraine. However, most studies on these agents lack control group. Although further clinical trials are needed, the results suggest that ketamine or memantine may be promising molecules for the treatment of severe migraine. Particular attention should be paid to people who have a treatment-resistant form of migraine with aura or have exhausted existing treatment options. For them, the drugs under discussion could represent an interesting alternative in the future.

Effect of pharmacological modulation of the kynurenine pathway on pain-related behavior and opioid analgesia in a mouse model of neuropathic pain

Dysfunction of the central nervous system are accompanied by changes in tryptophan metabolism, with the kynurenine pathway (KP) being the main route of its catabolism. Recently, KP metabolites, which are collectively called kynurenines, have become an area of intense research due to their ability to directly and indirectly affect a variety of classic neurotransmitter systems. However, the significance of KP in neuropathic pain is still poorly understood. Therefore, we designed several experiments to verify changes in the mRNA levels of KP enzymes in parallel with other factors related to this metabolic route after chronic constriction injury of the sciatic nerve (CCI model) in mice. The analysis revealed an increase in, Kmo, Kynu and Haoo mRNA levels in the spinal cord on the 7th day after CCI, while Kat1, Kat2, Tdo2, Ido2 and Qprt mRNA levels remain unchanged. Subsequent pharmacological studies provided evidence that modulation of KP by single intrathecal administration of 1-D-MT, UPF468 or L-kynurenine attenuates mechanical and thermal hypersensitivity and increases the effectiveness of selected opioids in mice as measured on day 7 after CCI. Moreover, our results provide the first evidence that the injection of L-kynurenine preceded by UPF468 (KMO inhibitor) is more effective at reducing hypersensitivity in animals with neuropathic pain. Importantly, L-kynurenine also exerts an analgesic effect after intravenous injections, which is enhanced by the administration of minocycline, an inhibitor of microglial activation. Additionally, L-kynurenine administered intrathecally and intravenously enhances analgesia evoked by all tested opioids (morphine, buprenorphine and oxycodone). Overall, our results indicate that the modulation of KP at different levels might be a new pharmacological tool in neuropathy management.

Citalopram Neuroendocrine Challenge Shows Altered Tryptophan and Kynurenine Metabolism in Migraine

Altered tryptophan (TRP) metabolism may have an important role in migraine susceptibility through its main metabolites, serotonin and kynurenine (KYN). Both affect pain processing and stress response by interfering with neural and brain hypersensitivity and by interacting with chemokines and cytokines that control vascular and inflammatory processes. The involvement of these pathways in migraine has been widely studied, but acute citalopram neuroendocrine challenge on TRP metabolism and cytokine profile has not been investigated yet. In our study, females with episodic migraine without aura and healthy controls were studied before and after acute citalopram or placebo in a double-blind setting. At baseline, increased TRP/large neutral amino acid (LNAA) ratio and decreased RANTES chemokine concentration were detected in migraine patients compared to controls. The challenge induced a significant increase in TRP, KYN, and TRP/LNAA in healthy controls, but not in migraine patients. Furthermore, migraine attack frequency negatively correlated with KYN/TRP ratio and positively correlated with the neuroendocrine-challenge-induced KYN concentration increase. Our results support a decreased breakdown of TRP via KYN pathway and a failure to modulate TRP–KYN pathway during citalopram-induced acute stress together with an increased vascular sensitivity in migraine. These mechanisms may provide useful drug targets for future drug development.

Organic anion transporter 1 is an HDAC4-regulated mediator of nociceptive hypersensitivity in mice

Persistent pain is sustained by maladaptive changes in gene transcription resulting in altered function of the relevant circuits; therapies are still unsatisfactory. The epigenetic mechanisms and affected genes linking nociceptive activity to transcriptional changes and pathological sensitivity are unclear. Here, we found that, among several histone deacetylases (HDACs), synaptic activity specifically affects HDAC4 in murine spinal cord dorsal horn neurons. Noxious stimuli that induce long-lasting inflammatory hypersensitivity cause nuclear export and inactivation of HDAC4. The development of inflammation-associated mechanical hypersensitivity, but neither acute nor basal sensitivity, is impaired by the expression of a constitutively nuclear localized HDAC4 mutant. Next generation RNA-sequencing revealed an HDAC4-regulated gene program comprising mediators of sensitization including the organic anion transporter OAT1, known for its renal transport function. Using pharmacological and molecular tools to modulate OAT1 activity or expression, we causally link OAT1 to persistent inflammatory hypersensitivity in mice. Thus, HDAC4 is a key epigenetic regulator that translates nociceptive activity into sensitization by regulating OAT1, which is a potential target for pain-relieving therapies.

Chronic pain is sustained by alterations in gene transcription. Here, the authors show that increased expression of Organic Anionic Transporter 1 in the spinal cord is epigenetically controlled and key to hypersensitivity in pathological pain.

Neurogenic Inflammation: The Participant in Migraine and Recent Advancements in Translational Research

Migraine is a primary headache disorder characterized by a unilateral, throbbing, pulsing headache, which lasts for hours to days, and the pain can interfere with daily activities. It exhibits various symptoms, such as nausea, vomiting, sensitivity to light, sound, and odors, and physical activity consistently contributes to worsening pain. Despite the intensive research, little is still known about the pathomechanism of migraine. It is widely accepted that migraine involves activation and sensitization of the trigeminovascular system. It leads to the release of several pro-inflammatory neuropeptides and neurotransmitters and causes a cascade of inflammatory tissue responses, including vasodilation, plasma extravasation secondary to capillary leakage, edema, and mast cell degranulation. Convincing evidence obtained in rodent models suggests that neurogenic inflammation is assumed to contribute to the development of a migraine attack. Chemical stimulation of the dura mater triggers activation and sensitization of the trigeminal system and causes numerous molecular and behavioral changes; therefore, this is a relevant animal model of acute migraine. This narrative review discusses the emerging evidence supporting the involvement of neurogenic inflammation and neuropeptides in the pathophysiology of migraine, presenting the most recent advances in preclinical research and the novel therapeutic approaches to the disease.

The Organ of Vision and the Stomatognathic System-Review of Association Studies and Evidence-Based Discussion

The stomatognathic system is a functional complex of tissues and organs located within the oral and craniofacial cavities. The craniofacial anatomical factors and the biomechanics of the temporomandibular joints affect many systems throughout the body, including the organ of vision. However, few scientific reports have shown a relationship between the organ of vision and the stomatognathic system. The purpose of this review is to provide an overview of connections along neural, muscle-fascial, and biochemical pathways between the organ of vision and the stomatognathic system. Based on the literature presented in this review, the connections between the organ of vision and the stomatognathic system seem undeniable. Understanding the anatomical, physiological, and biochemical interrelationships may allow to explain the interactions between the mentioned systems. According to the current knowledge, it is not possible to indicate the main linking pathway; presumably, it may be a combination of several presented pathways. The awareness of this relationship among dentists, ophthalmologists, physiotherapists, and optometrists should increase for the better diagnosis and treatment of patients.

Effect of 4-week physical exercises on tryptophan, kynurenine and kynurenic acid content in human sweat

The aim of the study was the detection of TRP, kynurenine (KYN), and kynurenic acid (KYNA) in human sweat, and determining whether physical activity affects their content in this secrete. Two different methods were used simultaneously—collection of sweat by means of an absorption pad from the inter scapular region, and collection of a drop of sweat from the region of the forehead. Quantitative determinations of TRP, KYN and KYNA were performed using high performance liquid chromatography with ultraviolet and fluorescence detection. Determinations of sodium was carried out by the method of inductively coupled plasma collision/reaction cell ionization mass spectrophotometry. It was found that physical exercises evoked a decrease in the amount of KYN, and an increase in the amount of KYNA in sweat recorded on day 14, but not on day 28 of training. It appears that physical exercises result in a long-term increase in the kynurenine transaminase activity responsible for the formation of KYNA from KYN. Based on this results, it can be suggested that measurement of TRP, KYN and KYNA in sweat may have diagnostic potential and may help to establish an exercise regime appropriate for the age, gender and health status of rehabilitation patients.

The Therapeutic Impact of New Migraine Discoveries

BACKGROUND

Migraine is one of the most disabling neurological conditions and associated with high socio-economic costs. Though certain aspects of the pathomechanism of migraine are still incompletely understood, the leading hypothesis implicates the role of the activation of the trigeminovascular system. Triptans are considered to be the current gold standard therapy for migraine attacks; however, their use in clinical practice is limited. Prophylactic treatment includes non-specific approaches for migraine prevention. All these support the need for future studies in order to develop innovative anti-migraine drugs.

OBJECTIVE

The present study is a review of the current literature regarding new therapeutic lines in migraine research.

METHODS

A systematic literature search in the database of PUBMED was conducted concerning therapeutic strategies in a migraine published until July 2017.

RESULTS

Ongoing clinical trials with 5-HT1F receptor agonists and glutamate receptor antagonists offer promising new aspects for acute migraine treatment. Monoclonal antibodies against CGRP and the CGRP receptor are revolutionary in preventive treatment; however, further long-term studies are needed to test their tolerability. Preclinical studies show positive results with PACAP- and kynurenic acid-related treatments. Other promising therapeutic strategies (such as those targeting TRPV1, substance P, NOS, or orexin) have failed to show efficacy in clinical trials.

CONCLUSION

Due to their side-effects, current therapeutic approaches are not suitable for all migraine patients. Especially frequent episodic and chronic migraine represents a therapeutic challenge for researchers. Clinical and preclinical studies are needed to untangle the pathophysiology of migraine in order to develop new and migraine-specific therapies.

Chronic dietary supplementation with kynurenic acid, a neuroactive metabolite of tryptophan, decreased body weight without negative influence on densitometry and mandibular bone biomechanical endurance in young rats

Kynurenic acid (KYNA) is a neuroactive metabolite of tryptophan. KYNA naturally occurs in breast milk and its content increases with lactation, indicating the role of neonatal nutrition in general growth with long-term health effects. KYNA is also an antagonist of ionotropic glutamate receptors expressed in bone cells. The aim of this study was to establish the effects of chronic KYNA supplementation on bone homeostasis in young rats, using mandible as a model bone. Female and male newborn Wistar rats were divided into control and KYNA-administered groups until 60 days of age (25x10¹ mg/L or 25x10² mg/L in drinking water). Hemimandibles were subjected to densitometry, computed tomography analysis and mechanical testing. Rats supplemented with KYNA at both doses showed a decrease in body weight. There were no effects of KYNA administration and mandible histomorphometry. In males, a significant quadratic effect (P < 0.001) was observed in the densitometry of the hemimandible, where BMD increased in the group supplemented with 2.5x10¹ mg/L of KYNA. Analysis of mechanical tests data showed that when fracture forces were corrected for bone geometry and rats body weight the improvement of bone material properties was observed in male and female rats supplemented with lower dose of KYNA. This study showed that chronic supplementation with KYNA may limit weight gain in the young, without adversely affecting the development of the skeleton.

Pharmacological Inhibition of Indoleamine 2,3-Dioxygenase-2 and Kynurenine 3-Monooxygenase, Enzymes of the Kynurenine Pathway, Significantly Diminishes Neuropathic Pain in a Rat Model

Neuropathic pain caused by a primary injury or dysfunction in the peripheral or central nervous system is a tremendous therapeutic challenge. Here, we have collected the first evidence from a single study on the potential contributions to neuropathic pain development by enzymes in the kynurenine pathway [tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenase (IDO1/2), kynurenine 3-monooxygenase (KMO); kynureninase, 3-hydroxyanthranilate-3,4-dioxygenase (HAOO)] at the spinal cord and dorsal root ganglia (DRG) levels. At the spinal cord, mRNA levels of IDO2, KMO, and HAOO were elevated as measured on day 7 after chronic constriction injury in a rat model, parallel to the C1q-positive cell activation. According to our data obtained from primary microglial cell cultures, all enzymes of the kynurenine pathway except TDO were derived from these cells; however, the activation of microglia induced stronger changes in IDO2 and KMO. Our pharmacological studies gave evidence that the repeated intraperitoneal administration of minocycline, a microglia/macrophage inhibitor, not only attenuated tactile and thermal hypersensitivity but also diminished the levels of IDO2 and KMO mRNA. Our further pharmacological studies confirmed that IDO2 and KMO enzymes take part in the development of neuropathic pain, since we observed that the repeated administration of IDO2 (1-methyl-D-tryptophan) and KMO [UPF 648 – (1S,2S)-2-(3,4-dichlorobenzoyl)cyclopropanecarboxylic acid] inhibitors diminished hypersensitivity development as measured on days 2 and 7. The results of our studies show that the kynurenine pathway is an important mediator of neuropathic pain pathology in rats and indicate that IDO2 and KMO represent novel pharmacological targets for treating neuropathy.

Migraine: A disorder of metabolism?

The treatment and prevention of migraine within the last decade has become largely pharmacological. While there is little doubt that the advent of drugs (e.g. triptans) has helped many migraine sufferers to lead a normal life, there is still little knowledge with respect to the factors responsible for precipitating a migraine attack. Evidence from biochemical and behavioural studies from a number of disciplines is integrated to put forward the proposal that migraine is part of a cascade of events, which together act to protect the organism when confronted by a metabolic challenge.

Targeting of the kynurenic acid across the blood-brain barrier by core-shell nanoparticles

Core-shell nanoparticles (CSNPs) were developed to get over therapeutic amount of kynurenic acid (KYNA) across the blood-brain barrier (BBB). Bovine serum albumin (BSA) was used as core for encapsulation of KYNA and the BSA/KYNA composite was finally encapsulated by poly(allylamine) hydrochloride (PAH) polymer as shell. In the interest of the optimization of the synthesis the BSA and KYNA interaction was studied by two-dimensional surface plasmon resonance (SPR) technique as well. The average size of d~100 nm was proven by dynamic light scattering (DLS) and transmission electron microscopy (TEM), while the structure of the composites was characterized by fluorescence (FL) and circular dichroism (CD) spectroscopy. The in vitro release properties of KYNA were investigated by a vertical diffusion cell at 25.0 °C and 37.5 °C and the kinetic of the release were discussed. The penetration capacity of the NPs into the central nervous system (CNS) was tested by an in vitro BBB model. The results demonstrated that the encapsulated KYNA had significantly higher permeability compared to free KYNA molecules. In the neurobiological serial of in vivo experiments the effects of peripherally administered KYNA with CSNPs were studied in comparison with untreated KYNA. These results clearly proved that KYNA in the CSNPs, administrated peripherally is suitable to cross the BBB and to induce electrophysiological effects within the CNS. As the neuroprotective properties of KYNA nowadays are proven, the importance of the results is obvious.

Fathoming the kynurenine pathway in migraine: why understanding the enzymatic cascades is still critically important

Kynurenine pathway, the quantitatively main branch of tryptophan metabolism, has been long been considered a source of nicotinamide adenine dinucleotide, although several of its products, the so-called kynurenines, are endowed with the capacity to activate glutamate receptors, thus potentially influencing a large group of functions in the central nervous system (CNS). Migraine, a largely unknown pathology, is strictly related to the glutamate system in the CNS pathologic terms. Despite the large number of studies conducted on migraine etio-pathology, the kynurenine pathway has been only recently linked to this disease. Nonetheless, some evidence suggests an intriguing role for some kynurenines, and an exploratory study on the serum kynurenine level might be helpful to better understand possible alterations of the kynurenine pathway in patients suffering from migraine.

Kynurenines and other novel therapeutic strategies in the treatment of dementia

Dementia is a common neuropsychological disorder with an increasing incidence. The most prevalent type of dementia is Alzheimer's disease. The underlying pathophysiological features of the cognitive decline are neurodegenerative processes, a cerebrovascular dysfunction and immunological alterations. The therapeutic approaches are still limited, although intensive research is being conducted with the aim of finding neuroprotective strategies. The widely accepted cholinesterase inhibitors and glutamate antagonists did not meet expectations of preventing disease progression, and research is therefore currently focusing on novel targets. Nonsteroidal anti-inflammatory drugs, secretase inhibitors and statins are promising drug candidates for the prevention and management of different forms of dementia. The kynurenine pathway has been associated with various neurodegenerative disorders and cerebrovascular diseases. This pathway is also closely related to neuroinflammatory processes and it has been implicated in the pathomechanisms of certain kinds of dementia. Targeting the kynurenine system may be of therapeutic value in the future.

Unexpected effects of peripherally administered kynurenic acid on cortical spreading depression and related blood-brain barrier permeability

Cortical spreading depression (CSD) involves a slowly-propagating depolarization wave in the cortex, which can appear in numerous pathophysiological conditions, such as migraine with aura, stroke, and traumatic brain injury. Neurons and glial cells are also depolarized transiently during the phenomena. CSD is followed by a massive increase in glutamate release and by changes in the brain microcirculation. The aim of this study was to investigate the effects of two N-methyl-D-aspartate receptor antagonists, endogenous kynurenic acid (KYNA) and dizocilpine, on CSD and the related blood-brain barrier (BBB) permeability in rats. In intact animals, KYNA hardly crosses the BBB but has some positive features as compared with its precursor L-Kynurenine, which is frequently used in animal studies (KYNA cannot be metabolized to excitotoxic agents such as 3-hydroxy-L-kynurenine and quinolinic acid). We therefore investigated the possible effects of peripherally administered KYNA. Repetitive CSD waves were elicited by the application of 1 M KCl solution to the cortex. Direct current-electrocorticograms were measured for 1 hour. Four parameters of the waves were compared. Evans blue dye and fluorescent microscopy were used to study the possible changes in the permeability of the BBB. The results demonstrated that N-methyl-D-aspartate receptor antagonists can reduce the number of CSD waves and decrease the permeability of the BBB during CSD. These results suggest that KYNA itself or its derivatives may offer a new approach in the therapy of migraines.

Kynurenines in the CNS: recent advances and new questions

Various pathologies of the central nervous system (CNS) are accompanied by alterations in tryptophan metabolism. The main metabolic route of tryptophan degradation is the kynurenine pathway; its metabolites are responsible for a broad spectrum of effects, including the endogenous regulation of neuronal excitability and the initiation of immune tolerance. This Review highlights the involvement of the kynurenine system in the pathology of neurodegenerative disorders, pain syndromes and autoimmune diseases through a detailed discussion of its potential implications in Huntington's disease, migraine and multiple sclerosis. The most effective preclinical drug candidates are discussed and attention is paid to currently under-investigated roles of the kynurenine pathway in the CNS, where modulation of kynurenine metabolism might be of therapeutic value.

Effect of systemic kynurenine on cortical spreading depression and its modulation by sex hormones in rat

BACKGROUND

The aura symptoms in migraine are most likely due to cortical spreading depression (CSD). CSD is favored by NMDA receptor activation and increased cortical excitability. The latter probably explains why migraine with aura may appear when estrogen levels are high, like during pregnancy. Kynurenic acid, a derivative of tryptophan metabolism, is an endogenous NMDA receptor antagonist whose cerebral concentrations can be augmented by systemic administration of its precursor L-kynurenine.

OBJECTIVE

To determine if exogenous administration of L-kynurenine is able to influence KCl-induced CSD in rat, if the effect is sex-dependent and if it differs in females between the phases of the estrous cycle.

METHODS

Adult Sprague-Dawley rats (n=8/group) received intraperitoneal (i.p.) injections of L-kynurenine (L-KYN, 300 mg/kg), L-KYN combined with probenecid (L-KYN+PROB) that increases cortical concentration of KYNA by blocking its excretion from the central nervous system, probenecid alone (PROB, 200 mg/kg) or NaCl. Cortical kynurenic acid concentrations were determined by HPLC (n=7). Thirty minutes after the injections, CSDs were elicited by application of 1M KCl over the occipital cortex and recorded by DC electrocorticogram. In NaCl and L-KYN groups, supplementary females were added and CSD frequency was analyzed respective to the phases of the estrous cycle determined by vaginal smears.

RESULTS

In both sexes, PROB, L-KYN and L-KYN+PROB increased cortical kynurenic acid level. PROB, L-KYN and L-KYN+PROB with increasing potency decreased CSD frequency in female rats, while in males such an effect was significant only for L-KYN+PROB. The inhibitory effect of L-KYN on CSD frequency in females was most potent in diestrus.

CONCLUSION

L-Kynurenine administration suppresses CSD, most likely by increasing kynurenic acid levels in the cortex. Females are more sensitive to this suppressive effect of L-kynurenine than males. These results emphasize the role of sex hormones in migraine and open interesting novel perspectives for its preventive treatment.