The protein tyrosine kinase inhibitor, genistein, decreases the excitability of capsaicin-sensitive neurons

AIM : One of the primary mechanisms by which neurons regulate their excitability is through of ion channel phosphorylafion. Compounds that increase noeiceptor excitability can cause hyporalgesia or allodynia whereas compounds that decrease noeiceptor excitability can be used as analgesics to relieve pain arising from inflammation or trauma. METHODS:     

What would 5-HT do? Regional diversity of 5-HT1 receptor modulation of primary afferent neurotransmission

5-HT (serotonin) is a significant modulator of sensory input to the CNS, but the only analgesics that selectively target G-protein-coupled 5-HT receptors are highly specific for treatment of headache. Two recent papers in BJP shed light on this puzzling situation by showing that primary afferent neurotransmission to the superficial layers of the spinal and trigeminal dorsal is inhibited by different subtypes of the 5-HT₁ receptor – 5-HT_{1B(and 1D)} in the trigeminal dorsal horn and 5-HT_1A in the spinal dorsal horn. The inputs being studied probably include nociceptive afferents, and the similarities of the methods employed in the two studies minimize the possibility that the different findings are an experimental artefact. Rather, the findings raise interesting questions about the possible anatomical or functional basis for the apparent regional selectivity of 5-HT₁ receptor actions, and whether these differences could be exploited for therapy. The results also emphasize the relative lack of information we have about the molecular details of the pro- or anti-nociceptive actions of 5-HT itself on primary afferent neurotransmission.

LINKED ARTICLE

This article is a commentary on Choi et al., pp. 356–367 of this issue. To view this paper visit http://dx.doi.org/10.1111/j.1476-5381.2012.01964.x     

Rapid regulation of the dopamine transporter: role in stimulant addiction?

Dopamine (DA) and the DA transporter (DAT) play important roles in psychomotor stimulant behavioral activation and reward. By understanding how DAT activity is regulated, we will better appreciate its contribution to normal neurotransmission and to brain diseases like drug addiction. DAT is regulated long-term by chronic drug administration. It is also regulated in a rapid, dynamic fashion by many factors--including brief exposure to DAT substrates, e.g. DA and amphetamine, and inhibitors, e.g. cocaine. We found that individual differences in the initial and sensitized locomotor responsiveness of rats to cocaine reflect differences in in vivo DAT function. Our ex vivo studies have further suggested that differences in basal and/or rapid cocaine-induced expression of functional DATs in striatum contribute to the differences in initial responsiveness. Studies in model systems have demonstrated that short-term DAT regulation occurs by altered transporter trafficking, and thereby cell surface expression. For example, a rapid, complex regulation of DAT by DA is suggested. Amphetamine causes DAT internalization into early endosomal compartments whereas cocaine appears to up-regulate surface expression of DAT. Future studies are needed to confirm these observations in neurons, as well as to elucidate the mechanisms of rapid DAT endocytic trafficking at neuronal synapses.     

Regulation of vascular nitric oxide in vitro and in vivo; a new role for endogenous hydrogen sulphide?

BACKGROUND AND PURPOSE: The aim of these experiments was to evaluate the significance of the chemical reaction between hydrogen sulphide (H2S) and nitric oxide (NO) for the control of vascular tone. EXPERIMENTAL APPROACH: The effect of sodium hydrosulphide (NaHS; H2S donor) and a range of NO donors, such as sodium nitroprusside (SNP), either alone or together, was determined using phenylephrine (PE)-precontracted rat aortic rings and on the blood pressure of anaesthetised rats. KEY RESULTS:Mixing NaHS with NO donors inhibited the vasorelaxant effect of NO both in vitro and in vivo. Low concentrations of NaHS or H2S gas in solution reversed the relaxant effect of acetylcholine (ACh, 400 nM) and histamine (100 microM) but not isoprenaline (400 nM). The effect of NaHS on the ACh response was antagonized by CuSO(4) (200 nM) but was unaffected by glibenclamide (10 microM). In contrast, high concentrations of NaHS (200-1600 microM) relaxed aortic rings directly, an effect reduced by glibenclamide but unaffected by CuSO4. Intravenous infusion of a low concentration of NaHS (10 micromol kg(-1) min(-1)) into the anaesthetized rat significantly increased mean arterial blood pressure. L-NAME (25 mg kg(-1), i.v.) pretreatment reduced this effect. CONCLUSIONS AND IMPLICATIONS: These results suggest that H2S and NO react together to form a molecule (possibly a nitrosothiol) which exhibits little or no vasorelaxant activity either in vitro or in vivo. We propose that a crucial, and hitherto unappreciated, role of H2S in the vascular system is the regulation of the availability of NO.     

Biphasic stimulant and sedative effects of ethanol: are children of alcoholics really different?

Children of alcoholics (COAs) have an increased risk of developing alcoholism themselves. The mechanisms responsible are not yet known. One compelling theory postulates that COAs may have an increased sensitivity to the stimulant effects of alcohol during the ascending limb of the blood alcohol curve combined with a decreased sensitivity to the putatively undesirable sedative effects of the drug during the descending limb, providing a particularly strong motivation to drink. Consistent with this theory, we hypothesized that compared to children of nonalcoholics (CONAs), COAs would display higher levels of ascending limb stimulation and lower levels of descending limb sedation. In the present study, 100 college students, who were either COAs (n=18) or CONAs (n=82), completed the Biphasic Alcohol Effects Scale (a self-report measure of stimulation and sedation): (1) before consuming 0.85n ml/kg ethanol; (2) during the ascending limb of their BAC, and; (3) during the descending limb of their BAC. Although findings indicated that COAs and CONAs had comparable levels of sedation at each time point, a significant GroupxTime interaction (P<.02) indicated that COAs had greater increases in stimulation from baseline than CONAs, providing partial support for our hypothesis. Interestingly, simple effects analyses revealed that COAs had lower baseline levels of stimulation but almost identical levels of ascending and descending limb stimulation as CONAs, suggesting that increased sensitivity to alcohol among COAs may be the result of baseline understimulation. Overall, findings suggest that theorized differences between COAs and CONAs may be due in part to broader trait differences or other nonpharmacological factors.     

RB101-mediated protection of endogenous opioids: potential therapeutic utility?

The endogenous opioids met- and leu-enkephalin are inactivated by peptidases preventing the activation of opioid receptors. Inhibition of enkephalin-degrading enzymes increases endogenous enkephalin levels and stimulates robust behavioral effects. RB101, an inhibitor of enkephalin-degrading enzymes, produces antinociceptive, antidepressant, and anxiolytic effects in rodents, without typical opioid-related negative side effects. Although enkephalins are not selective endogenous ligands, RB101 induces these behaviors through receptor-selective activity. The antinociceptive effects of RB101 are produced through either the mu-opioid receptor alone or through activation of both mu- and delta-opioid receptors; the antidepressant-like and anxiolytic effects of RB101 are mediated only through the delta-opioid receptor. Although little is known about the effects of RB101 on other physiologically and behaviorally relevant peptides, these findings suggest that RB101 and other inhibitors of enkephalin-degrading enzymes may have potential as novel therapeutic compounds for the treatment of pain, depression, and anxiety.     

Hydrogen sulphide--a novel mediator of inflammation?

Hydrogen sulphide (H2S) is a naturally occurring gas synthesized from cysteine. It exhibits vasodilator activity (most probably by opening vascular smooth muscle K(ATP) channels), influences leucocyte chemotaxis and promotes vascular smooth muscle cell apoptosis. Increased biosynthesis of H2S has been demonstrated in animal models of septic/endotoxic and haemorrhagic shock, pancreatitis and carrageenan-evoked hindpaw oedema in the rat. In each case, pharmacological inhibition of H2S biosynthesis is anti-inflammatory.     

Protective effects of ditiocarb sodium against anoxic damage of primary cortical neurons in culture

取体外原代培养１４ｄ左右的大鼠皮层神经元，换上无血清除氧培养基并置通９５％Ｎ２＋５％ＣＯ２的缺氧罐中造成神经元缺氧．以研究缺氧对皮层神经元的损伤及二硫卡钠（ＤＴＣ）的保护作用．用存活神经元数目及神经元线粒体活性来评价神经元活力．乳酸脱氢酶（ＬＤＨ）活性及脂质过氧化产物丙二醛（ＭＤＡ）含量分别用紫外分光光度法和硫代巴比酸法测定，作为评价损伤的指标．原代培养皮层神经元分别缺氧４，５和６ｈ后，活细胞数显著减少，线粒体活性明显降低；ＬＤＨ释放及ＭＤＡ产生显著增加；而缺氧２ｈ后，仅活细胞数无明显变化．超氧阴离子清除剂超氧化物歧化酶（ＳＯＤ）可逆转上述变化，抑制缺氧对神经元的损伤，表明培养神经元缺氧损伤可能与自由基产生有关．类似ＳＯＤ作用，ＤＴＣ可显著对抗缺氧对神经元的损伤，剂量依赖地抑制缺氧引起的ＬＤＨ释放和ＭＤＡ形成的增加．结果表明：ＤＴＣ对神经元缺氧损伤具保护作用，其作用可能与清除自由基有关．     

Elevation of an endogenous inhibitor of nitric oxide synthase in diabetic rat serum

目的：测定糖尿病大鼠血中内源性ＮＯ合酶抑制物二甲基精氨酸（ＤＭＡ）的含量．方法：在链佐星诱发的糖尿病大鼠测定血清ＤＭＡ的含量和乙酰胆碱（ＡＣｈ）诱导血管内皮依赖性舒张．结果：与对照组相比，糖尿病大鼠ＤＭＡ血清浓度显著增加（５４±１０ｖｓ０７±０３μｍｏｌ·Ｌ－１，Ｐ＜００１）；丙二醛含量也高于对照组（２５±０３ｖｓ１５±０１μｍｏｌ·Ｌ－１，Ｐ＜００１）；糖尿病大鼠ＡＣｈ舒血管效应减弱，其作用可被左旋精氨酸所改善．结论：链佐星诱发糖尿病大鼠高血糖症引起内源性ＤＭＡ含量升高，同时血管内皮依赖性舒张功能被削弱．     

Does phenylethylamine act as an endogenous amphetamine in some patients?

In brain capillary endothelium and catecholaminergic terminals a single decarboxylation step effected by aromatic amino-acid decarboxylase converts phenylalanine to phenylethylamine, at a rate comparable to that of the central synthesis of dopamine. Phenylethylamine, however, is not stored in intra-neuronal vesicles and is rapidly degraded by monoamine oxidase-B. Despite its short half-life, phenylethylamine attracts attention as an endogenous amphetamine since it can potentiate catecholaminergic neurotransmission and induce striatal hyperreactivity. Subnormal phenylethylamine levels have been linked to disorders such as attention deficit and depression; the use of selegiline (Deprenyl) in Parkinson's disease may conceivably favour recovery from deficient dopaminergic neurotransmission by a monoamine oxidase-B inhibitory action that increases central phenylethylamine. Excess phenylethylamine has been invoked particularly in paranoid schizophrenia, in which it is thought to act as an endogenous amphetamine and, therefore, would be antagonized by neuroleptics. The importance of phenylethylamine in mental disorders is far from fully elucidated but the evolution of phenylethylamine concentrations in relation to symptoms remains a worthwhile investigation for individual psychotic patients.     

Perspective: 4β-hydroxycholesterol as an emerging endogenous biomarker of hepatic CYP3A

A key goal in the clinical development of a new molecular entity is to quickly identify whether it has the potential for drug–drug interactions. In particular, confirmation of in vitro data in the early stage of clinical development would facilitate the decision making and inform future clinical pharmacology study designs. Plasma 4β-hydroxycholesterol (4β-HC) is considered as an emerging endogenous biomarker for cytochrome P450 3A (CYP3A), one of the major drug metabolizing enzymes. Although there are increasing reports of the use of 4β-HC in academic- and industry-sponsored clinical studies, a thorough review, summary and consideration of the advantages and challenges of using 4β-HC to evaluate changes in CYP3A activity has not been attempted. Herein, we review the biology of 4β-HC, its response to treatment with CYP3A inducers, inhibitors and mixed inducer/inhibitors in healthy volunteers and patients, the association of 4β-HC with other probes of CYP3A activity (e.g. midazolam, urinary cortisol ratios), and present predictive pharmacokinetic models. We provide recommendations for studying hepatic CYP3A activity in clinical pharmacology studies utilizing 4β-HC at different stages of drug development.     

Pharmacoepigenetics: an element of personalized therapy?

Introduction: Epigenetics is a rapidly growing field describing heritable alterations in gene expression that do not involve DNA sequence variations. Advances in epigenetics and epigenomics have influenced pharmacology, leading to the development of a new specialty, pharmacoepigenetics, the study of the epigenetic basis for the individual variation in drug response.

Areas covered: We present an overview of the major epigenetic mechanisms and their effects on the expression of drug metabolizing enzymes and drug transporters, as well as the epigenetic status of drug protein targets affecting therapy response. Recent advances in the development of pharmacoepigenetic biomarkers and epidrugs are also discussed.

Expert opinion: There is growing evidence that pharmacoepigenetics has the potential to become an important element of personalized medicine. Epigenetic modifications influence drug response, but they can also be modulated by drugs. Moreover, they can be monitored not only in the affected tissue, but also in body fluids. Nevertheless, there are very few examples of epigenetic biomarkers implemented in the clinical setting. Explanation of the interplay between genomic and epigenomic changes will contribute to the personalized medicine approach. Ultimately, both genetic biomarkers and epigenetic mechanisms should be taken into consideration in predicting drug response in the course of successful personalized therapy.     

Cancer immunotherapy: an embarrassment of riches?

There is clear evidence that certain forms of immunotherapy can be successful against certain cancers. However, it would appear that cancerous cells of various origin are exceptionally adept at subverting the immune response. Consequently, it is probable that the most efficacious therapy will be one in which multiple responses of the immune system are activated. There is currently an embarrassment of riches with regard to multiple vaccine strategies in the clinic, although no single method seems to hold the solution. Here, we draw together several of the humoral- and cellular-activating strategies currently under clinical investigation.     

G-CSF: boosting endogenous production--a new strategy?

Granulocyte colony-stimulating factor (G-CSF) has been in clinical use for over a decade. Its main applications are in adjunctive medication to chemotherapy and in mobilizing stem cells for bone marrow transplantation. However, it has additional effects in that it primes neutrophilic granulocytes for improved host defense, and reduces the release of pro-inflammatory cytokines. These effects have prompted trials for numerous other indications. New research into the production and regulation of G-CSF in health and disease may now enable tailored strategies to induce or boost G-CSF formation. Similarly, new forms of application may increase its effectiveness.     

Cutaneous lesions in capsaicin-pretreated rats. A trophic role of capsaicin-sensitive afferents?

Summary 1. The time course and regional distribution of spontaneous cutaneous lesions in rats desensitized to capsaicin as newborns was correlated to behavioural observations and regional distribution of substance P-like immunoreactivity (SP-LI) and tachykinin-like immunoreactivity (TK-LI) in various skin areas. 2. Spontaneous skin lesions in the form of wounds, scabs and areas of alopecia were observed in 80–90% of rats desensitized to capsaicin. No major sex-related differences were observed with regard to incidence and distribution of the lesions with the possible exception of a lesser tendency to bilateral lesions in female rats. 3. Spontaneous skin lesions were almost restricted to the head: the areas most frequently affected were snouts, periocular and retroauricular regions and ventral area of the neck. 4. No major differences were observed between capsaicin- or vehicle-treated animals in spontaneous or novelty-induced grooming as well as in open-field gross behaviour. Likewise, no differences were observed in the mouse-killing behaviour. 5. Both SP-LI and TK-LI in various skin areas were significantly reduced by systemic capsaicin pretreatment. The rank order of various skin areas for SP-LI or TK-LI levels was: snouts > thigh > neck > abdomen retroauricular region. 6. Intradermal injection of Arg-neurokinin B, a potent and water soluble derivative of neurokinin B, produced a similar plasma extravasation (Evans blue leakage technique) in the skin of vehicle- or capsaicin-pretreated rats. 7. In capsaicin-desensitized rats fur regrowth (measured at abdominal level, 28 days after shaving) was significantly less than in vehicle-treated animals. 8. The s. c. injection of 1 N HCl in the dorsal thoracic region (an area devoid of spontaneous lesions in capsaicin-desensitized animals) produced cutaneous ulcers whose area and depth were greater in capsaicin- than vehicle-treated rats. 9. These findings are consistent with the hypothesis that capsaicin-sensitive nerves play a trophic role in the rat skin and contribute to its ability to react and repair injuries. The most consistent explanation for the restricted localization of spontaneous skin lesions to the head seems to be that normal injurious factors (such as grooming) operate on a distrophic skin to induce lesions by repeated microtrauma. Send offprint requests to C. A. Maggi     

Assessing the bioequivalence of analogues of endogenous substances (��endogenous drugs��): considerations to optimize study design

BACKGROUND

Assessment of the bioequivalence of generic versions of certain reference drugs is complicated by the presence of endogenous levels of said compounds which cannot be distinguished from externally derived compound levels following drug administration. If unaccounted for, the presence of endogenous compound biases towards equivalence in bioequivalence studies of these drugs. Bioequivalence assessments may be complicated further as disposition of the exogenous analogue can be subject to various endogenous processes resulting in nonlinear pharmacokinetics. To overcome these inherent biases a number of different strategies have been employed.

AIMS

To critically review methods used to overcome confounding biases in bioequivalence studies of ‘endogenous’ drugs.

METHODS

A literature search of the EMBASE and PubMed databases was performed.

RESULTS

The following strategies were identified: ablation/modulation of baseline endogenous substance levels; recruitment of ‘substance-deficient’ populations; restriction of dietary intake of the relevant substance; standardization of conditions with the potential to affect relevant homeostatic mechanisms; correction for baseline substance levels; and administration of supra-therapeutic drug doses.

CONCLUSIONS

On the basis of this review key study design concepts, intended to optimize the design of future bioequivalence studies of these so-called ‘endogenous drugs’, are described. The dual stable isotope method, which could be used in a specific context, is also discussed.