Diet-induced obesity alters dural CGRP release and potentiates TRPA1-mediated trigeminovascular responses.

Background Clinical studies suggest a link between obesity and the primary headache disorder migraine. In our study we aimed to reveal the effect of obesity on meningeal nociceptor function in rats receiving a high-fat, high-sucrose diet. Methods Transient receptor potential ankyrin 1 (TRPA1) receptor activation-induced changes in meningeal blood flow, release of calcitonin gene-related peptide (CGRP) from trigeminal afferents and TRPA1 protein expression in the trigeminal ganglia were measured in control and obese rats. Metabolic parameters of the animals were assessed by measuring glucose and insulin homeostasis as well as plasma cytokine concentrations. Results The present experiments revealed an enhanced basal and TRPA1 receptor agonist-induced CGRP release from meningeal afferents of obese insulin-resistant rats and an attenuated CGRP release to potassium chloride. Obesity was also associated with an augmented vasodilatation in meningeal arteries after dural application of the TRPA1 agonist acrolein, a reduction in TRPA1 protein expression in the trigeminal ganglia and elevations in circulating proinflammatory cytokines IL-1ß and IL-6 in addition to increased fasting blood glucose and insulin concentrations. Conclusions Our results suggest trigeminal sensitisation as a mechanism for enhanced headache susceptibility in obese individuals after chemical exposure of trigeminal nociceptors.

Diet-Induced Obesity Enhances TRPV1-Mediated Neurovascular Reactions in the Dura Mater.

OBJECTIVE: Exploring the pathophysiological changes in transient receptor potential vanilloid 1 (TRPV1) receptor of the trigeminovascular system in high-fat, high-sucrose (HFHS) diet-induced obesity of experimental animals. BACKGROUND: Clinical and experimental observations suggest a link between obesity and migraine. Accumulating evidence indicates that metabolic and immunological alterations associated with obesity may potentially modulate trigeminovascular functions. A possible target for obesity-induced pathophysiological changes is the TRPV1/capsaicin receptor which is implicated in the pathomechanism of headaches in a complex way. METHODS: Male Sprague-Dawley rats were fed a regular (n = 25) or HFHS diet (n = 26) for 20 weeks. At the end of the dietary period, body weight of the animals was normally distributed in both groups and it was significantly higher in animals on HFHS diet. Therefore, experimental groups were regarded as control and HFHS diet-induced obese groups. Capsaicin-induced changes in meningeal blood flow and release of calcitonin gene-related peptide (CGRP) from dural trigeminal afferents were measured in control and obese rats. The distribution of TRPV1- and CGRP-immunoreactive meningeal sensory nerves was also compared in whole mount preparations of the dura mater. Metabolic parameters of the animals were assessed by examining glucose and insulin homeostasis as well as plasma cytokine concentrations. RESULTS: HFHS diet was accompanied by reduced food consumption and greater fluid and energy intakes in addition to increased body weight of the animals. HFHS diet increased fasting blood glucose and insulin concentrations as well as levels of circulating proinflammatory cytokines interleukin-1ß and interleukin-6. In obese animals, dural application of the archetypal TRPV1 agonist capsaicin resulted in significantly augmented vasodilatory and vasoconstrictor responses as compared to controls. Diet-induced obesity was also associated with enhanced basal and capsaicin-induced CGRP release from meningeal afferents ex vivo. Except for minor morphological changes, the distribution of dural TRPV1- and CGRP-immunoreactive afferents was similar in control and obese animals. CONCLUSIONS: Our results suggest that obesity induced by long-term HFHS diet results in sensitization of the trigeminovascular system. Changes in TRPV1-mediated vascular reactions and CGRP release are pathophysiological alterations that may be of relevance to the enhanced headache susceptibility of obese individuals.

Insulin sensitivity is modified by a glycogen phosphorylase inhibitor: glucopyranosylidene-spiro-thiohydantoin in streptozotocin-induced diabetic rats.

The major role of liver glycogen is to supply glucose to the circulation maintaining the normal blood glucose level. In muscle and liver the accumulation and breakdown of glycogen are regulated by the reciprocal activities of glycogen phosphorylase and glycogen synthase. Glycogen phosphorylase catalyses the key step of glycogen degradation and its activity can be inhibited by glucose and its analogues. Obviously, any readily accessible inhibitor of glycogen phosphorylase can be used as a potential therapy of non-insulin-dependent or type 2 diabetes. Hepatic glycogen phosphorylase has been identified as a new target for drugs that control blood glucose concentration. In our experiments glucopyranosylidene-spirothiohydantoin (TH) was tested on the insulin sensitivity and blood glucose level of control and streptozotocin-treated rats. The streptozotocin-treated rats failed to gain weight and exhibited stable hyperglycemia (4.7 ± 0.5 mmol/L glucose in control vs. 7.8 ± 0.5 mmol/L) and low plasma insulin levels (9.6 ± 1.9 µIU/mL in control vs. 3.2 ± 2.2 µIU/mL). When insulin supplementation with slow-release implants (2 IU/day) was started 8 weeks after streptozotocin injection, blood glucose concentration remained suppressed, plasma insulin level dramatically increased and the insulin sensitivity restored. TH administration significantly reduced the high blood glucose concentration and restored the insulin sensitivity of STZtreated rats.