Characterization of specific binding sites for alpha-trinositol (D-myo-inositol 1,2,6-trisphosphate) in rat tissues

Additional evidence that the rat renal interstitium contracts in vivo

We recently provided highly suggestive preliminary evidence that the renal interstitium contracts reactively in vivo. We demonstrated that renal medullary direct interstitial volume expansion (rmDIVE = 100 μl bolus infusion of 0.9% saline (SS)/30 s) brought about a biphasic renal interstitial hydrostatic pressure (RIHP) response which was abolished when dibutyryl-cAMP was concomitant and interstitially infused. To assess more deeply the feasibility of the concept that the renal interstitium contracts in vivo, two experimental series (S1, S2) were performed in hydropenic rats subjected to acute left renal-denervation, hormonal clamping, and control of renal arterial pressure. In S1, RIHP and renal outer medullary blood flow (RoMBF) were continuously measured before and after a sudden micro-bolus (5μl) injection, into the renal medullary interstitium, of SS containing α-trinositol (α-TNS, anti-inflammatory drug) to either two doses 2 or 4 mM (SS + 2 α-TNS and SS + 4 α-TNS groups). No overall differences between groups in either ΔRIHP or %ΔRoMBF time courses were found; however, in the SS + 2 α-TNS group the data were less scattered and the ΔRIHP time course tended to peak faster and then persisted there, so that, this α-TNS dose was selected for S2. In S2, RIHP and RoMBF were similarly measured in rats randomly assigned to three groups: the CTR group (sham time-control), SS group (SS alone), and SS + α-TNS group. The micro-bolus injection of SS alone (SS group) was unable to increase ΔRIHP. The group with no micro-bolus injection (CTR group) experienced a decrease in ΔRIHP. The micro-bolus injection of SS + 2 α-TNS was accompanied by a differential increase in ΔRIHP (vs. CTR and SS groups). These responses were not associated with differential changes among groups in %ΔRoMBF or hemodilution parameters. These results provide additional evidence that the renal interstitium contracts in vivo.

α-Trinositol inhibits FGF-stimulated growth of smooth muscle and breast cancer cells

alpha-Trinositol (d-myo-inositol-1,2,6-trisphosphate), an isomer of the intracellular messenger IP(3), has been studied for its anti-inflammatory and other effects in animal experiments and in human. The mechanisms of action remain unknown. Several human pathologies are associated with uncontrolled production of fibroblast growth factors (FGFs). FGF-2 induces vascular smooth muscle cell proliferation, which contributes to restenosis after coronary balloon angioplasty. The expression of several FGFs is also increased in tumors. We studied the effects of the water- and lipid-soluble derivatives of alpha-trinositol on the FGF-2- and/or FGF-8-induced proliferation of human pulmonary artery smooth muscle cells (HPASMC) and S115 mouse breast cancer cells. alpha-Trinositol decreased the FGF-mediated proliferation of HPASMC and S115 cells. Membrane permeability did not seem obligatory since the lipid-soluble form of alpha-trinositol was less effective than the water-soluble derivative. These results suggest a new biological function for certain phosphoinositides in the modulation of FGF-regulated processes.

D-myo inositol 1,2,6, triphosphate (alpha-trinositol, pp56): selective antagonist at neuropeptide Y (NPY) Y-receptors or selective inhibitor of phosphatidylinositol cell signaling?

1. D-myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, D-myo inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes anti-inflammatory and analgesic effects and antagonism of neuropeptide Y (NPY)-mediated cellular responses. 2. However, not all responses elicited by this neuropeptide are sensitive to antagonism by pp56. Evidence is emerging, at least in certain tissues, that other receptor populations, in addition to those for NPY, are also sensitive to inhibition by pp56. 3. A direct or allosteric interaction of pp56 at receptors for NPY is now considered unlikely and it is more probable that pp56 might interfere at some point in the phosphatidylinositol signaling pathway, possibly at the level of the plasmalemmal inositol 1,3,4,5, tetrakisphosphate receptor. 4. Full realization of the therapeutic potential of this novel compound, however, must await a thorough characterization of the cellular mechanism(s) associated with the various pharmacological effects of pp56.

Cell interactions with collagen matrices in vivo and in vitro depend on phosphatidylinositol 3-kinase and free cytoplasmic calcium

We have investigated the role of phosphatidylinositol 3-kinase (PI3-kinase) in cellular interactions with collagenous matrices. Platelet-derived growth factor-BB (PDGF-BB) elicited a mobilization of intracellular Ca2+ in pig aortic endothelial (PAE) cells transfected with wild type PDGF beta-receptor. This response was greatly reduced in PAE cells transfected with PDGF beta-receptors mutated at positions Y740 and Y751 to prevent PI3-kinase binding. The experimental drug 1D-myo-inositol 1,2,6-trisphosphate (alpha-trinositol) induced a rapid increase and subsequent oscillations of the cytoplasmic Ca2+ concentration in cultured fibroblasts. This response was not due to an effect of alpha-trinositol on inositol 1,4,5-trisphosphate (IP3) receptors. alpha-Trinositol did not influence PDGF-BB elicited chemotaxis through collagen-coated membranes of PAE cells transfected with the wild-type PDGF beta-receptor, but restored PDGF-BB elicited chemotaxis of PAE cells transfected with the PI3-kinase binding-site mutated PDGF beta-receptor. Collagen gel contraction has been suggested to serve as a model for cellular control of interstitial fluid pressure (PIF) in dermis. The PI3-kinase inhibitors wortmannin (50 nM) and LY294002 (5 microM) inhibited the stimulation of fibroblast-mediated collagen gel contraction by 0.4 nM PDGF-BB. Injection of wortmannin in rat paw skin induced a lowering of PIF, and this effect was abolished in animals pre-treated with alpha-trinositol. Pretreatment of rats with alpha-trinositol abolished the decrease in PIF induced by injecting monoclonal anti-rat alpha 2 beta 1 integrin IgG in rat paw skin. Taken together our data indicate that cell-collagen interactions in vivo and in vitro depend on PI3-kinase, and that this dependence can be bypassed by a drug eliciting intracellular Ca2+ mobilization.

Inhibition of plasma extravasation after burns by D-myo-inositol-1,2,6-trisphosphate using digital image colour analysis

D-myo-inositol-1,2,6-triphosphate (1,2,6-IP3) has beneficial effects in experimental, progressive burn-induced ischaemia and oedema. A 1 cm2 full-thickness burn was made in the skin of 20 rats with a hot aluminium rod followed by infusion of 1,2,6-IP3 (60 mg.kg.-1 h-1) or isotonic saline (n = 10 in each group). One hour later Evans blue was injected intravenously. Colour photographs of the area of the burn were taken in a standard manner before the burn and at intervals for three hours afterwards. The photographs were analysed by digital image colour analysis using normalised red-green-blue values. The increase in normalised blue values between 60 and 180 minutes after the burn was significantly reduced in animals treated with 1,2,6-IP3 compared with control animals (p < 0.001). Spectrophotometric analysis of extravasated Evans blue in the skin 180 minutes after the burn showed that it had been significantly inhibited by treatment with 1,2,6-IP3 (p < 0.001). In conclusion, digital image analysis allowed repeated evaluation over time and confirmed previous data about the ability of 1,2,6-IP3 to inhibit extravasation of plasma after burns.

Postoperative analgesia by D-myo-inositol-1,2,6-trisphosphate in patients undergoing cholecystectomy

D-myo-inositol-1,2,6-trisphosphate (1,2,6-IP3) possesses antiinflammatory properties, such as reduced eicosanoid synthesis and inhibition of inflammation-induced edema. These properties suggest possible analgesic effects. The analgesic effect of 1,2,6-IP3 was evaluated in a double-blind, randomized study in 24 patients undergoing cholecystectomy. Ten patients received 1,2,6-IP3 as an intravenous (i.v.) bolus dose of 240 mg, followed by a continuous i.v. infusion at 90 mg/h for 24 h. The placebo group (n = 14) received corresponding volumes of isotonic saline. Postoperative pain (visual analog pain scale; VAS) and opiate analgesic requirements (ketobemidon) were evaluated during five postoperative days. Results showed significantly reduced pain during the first five postoperative days in patients treated with 1,2,6-IP3, as measured by using a VAS (P < 0.05). The requirements of opioid analgesics were significantly reduced during the first three postoperative days (P < 0.05). No drug-related side effects were observed. Results of the present study demonstrate a potent and long-lasting analgesic effect of 1,2,6-IP3, possibly related to its antiinflammatory properties.

IMPLICATIONS

A new antiinflammatory drug under investigation, inositol-1,2,6-trisphosphate, was evaluated as a possible analgesic in a pilot study during the postoperative period in cholecystectomized patients. Results showed significantly lower pain assessment and opioid consumption, which should encourage further studies.

Use of D-myo inositol 1,2,6 trisphosphate to inhibit contractile activity in rat ventricular cardiomyocytes induced by neuropeptide Y and other cardioactive peptides through phospholipase C

1. D-Myo inositol 1,2,6 trisphosphate (alpha-trinositol, pp56), an isomer of the second messenger substance, inositol 1,4,5 trisphosphate, has an interesting pharmacological profile that includes antagonism of a number of neuropeptide Y (NPY)-mediated cellular processes. The ability of pp56 to inhibit selectively the myocardial contraction mediated by NPY in relation to the responses to other cardioactive peptides, including endothelin-1, calcitonin gene-related peptide (CGRP), secretin and vasoactive intestinal peptide (VIP), was assessed. In order to investigate the possible interaction of pp56 with mechanisms of inositol phosphate signalling generated in heart muscle cells by activation of the beta-isoenzyme of phospholipase C (PLC beta), noradrenaline was used as a positive control, and isoprenaline and forskolin were included as negative controls. 2. Ventricular cardiomyocytes, isolated from the hearts of adult rats, were stimulated to contract at 0.5 Hz in the presence of calcium ion (2 mM). The concentrations of agonists used were in the region of their maximally effective concentrations for myocyte contraction and the concentration of pp56 was in the range of 1-100 microM. Contractile activity was monitored by video microscopy and maximum shortening determined by image analysis. 3. In the absence of agonist, contractile amplitudes following 20 min preincubation with pp56 were not different from that observed in the absence of pp56. Pp56 (1-100 microM) inhibited significantly the positive contractile response to noradrenaline (5 microM) in the presence of propranolol (500 nM), such that the response was almost completely attenuated at the highest concentration of the inhibitor. Pp56 did not inhibit the positive contractile responses to forskolin (40 microM) or isoprenaline (100 nM). 4. NPY alone does not influence the basal level of contraction of cardiomyocytes, but can attenuate isoprenaline-stimulated contraction and can increase contractile amplitude from basal when the transient outward current is blocked with 4-aminopyridine. In the presence of isoprenaline (100 nM), the negative response to NPY (100 nM) was attenuated significantly by pp56 (1-100 microM). With 4-aminopyridine, the positive contractile response to NPY (200 nM) was decreased by pp56, although this was not statistically significant. 5. Pp56 inhibited the positive contractile responses to CGRP (1 nM) and endothelin-1 (20 nM) completely, but did not affect the responses to secretin (20 nM) or VIP (20 nM). 6. In conclusion, these data challenge the previously obtained selectivity of pp56 as an antagonist of NPY-mediated cellular processes, since responses to CGRP and endothelin-1 were at least equally sensitive. Furthermore, as pp56 discriminated clearly in its inhibition of responses to alpha-adrenoceptor by comparison with beta-adrenoceptor/adenylate cyclase stimulation, it appears that pp56 may be a useful pharmacological agent with which to distinguish between PLC beta-dependent and PLC beta-independent coupling mechanisms. On this basis, further evidence has been obtained that, in rat cardiomyocytes, the contractile responses to NPY, CGRP and endothelin-1 are attributable to the activation of PLC beta-dependent pathways, whereas the responses to secretin and VIP are mediated by PLC beta-independent pathways.

Swelling and damage of glial cells by lactacidosis and glutamate: effect of alpha-trinositol

The therapeutical efficacy of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate), an isomer of the intracellular messenger IP3, was analyzed on cytotoxic swelling and damage of glial cells in vitro from lactacidosis or glutamate. C6 glioma cells suspended in a physiological medium were either exposed to pH 5.0 by administration of lactic acid, or to 1 mM glutamate. Cell swelling and viability were quantified by flow cytometry. Lactacidosis of pH 5.0 led to an increase in cell volume to 139.7 +/- 1.3% within 20 min whereas alpha-trinositol was reducing the swelling response by approximately 25% (P < 0.01). In addition, at pH 5.0 the fraction of viable cells was lowered from 94.3 +/- 0.2% (control) to only 53.8 +/- 3.1% after 60 min. Alpha-trinositol was found to protect also cell viability; at 60 min of lactacidosis 70.2 +/- 1.6% of the cells still were viable (P < 0.01). The addition of glutamate (1 mM) to the cell suspension led to a steady increase in cell size, reaching 110% of control at 120 min, irrespectively of whether alpha-trinositol was added or not.

Noradrenergic and peptidergic sympathetic regulation of cutaneous microcirculation in the rat

Cutaneous microcirculatory changes were measured by laser-Doppler flowmetry in response to electrical stimulation of sympathetic efferent fibres of the rat's saphenous nerve. After perineural capsaicin (2%) pretreatment, electrical stimulation of the peripheral stump of the cut saphenous nerve evoked a reduction in blood flow (vasoconstriction) followed by a minimal enhancement. This late vasodilatation was further reduced by resiniferatoxin (1 microg/kg i.v.), and vasoconstriction was abolished by guanethidine (8 mg/kg i.v.), indicating the involvement of sensory and sympathetic fibres in the respective responses. The vasoconstrictor response was analysed after blockade of antidromic vasodilatation by combined capsaicin-resiniferatoxin pretreatment. alpha-Adrenoceptor antagonists (1 mg/kg phentolamine, 0.5 mg/kg prazosin and 1 mg/kg GYKI-12743 (RS-2-(3)N-(2-benzo;1,4i-dioxanyl)-methylamino(propyl)-3(2H) -piridazinone hydrochloride) inhibited, but did not eliminate the blood flow reduction evoked by 3 Hz stimulation. At 10 Hz stimulation significant inhibition was obtained only with GYKI-12743. No inhibition was observed with propranolol (10 microg/kg) on any occasion. A functional neuropeptide Y antagonist, alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate, PP56; 50 mg/kg i.v.), markedly diminished the vasocontrictor response remaining after treatments with the alpha-adrenoceptor blocking agents. Inhibition was more pronounced at 10 Hz. Since 3 Hz corresponds to an average, and 10 Hz approaches the maximal firing rate of the sympathetic efferents, these results emphasise the significant role of neuropeptide Y in regulation of the cutaneous microcirculation by sympathetic fibres under physiological circumstances, particularly during high activity.

The effect of alpha-trinositol (D-myo-inositol 1,2,6-trisphosphate) on formalin-evoked spinal amino acid and prostaglandin E2 levels

The effect of the inositol trisphosphate analog alpha-trinositol on noxious-evoked behavior, amino acid and prostaglandin E2 (PGE2) release was examined in unanesthetized rats using intrathecal microdialysis probes. Subcutaneous injection of 50 microliters 5% formalin solution produced two phases of pain-like behavior and significant elevation of glutamate, aspartate, glycine, taurine and serine during phase 1. PGE2 concentrations were increased during both phases 1 and 2. Intraperitoneal delivery of 300 mg/kg alpha-trinositol significantly suppressed both phases 1 and 2 of formalin-induced behavior and the associated elevation of amino acids and PGE2. These data demonstrate that the antinociceptive effect of alpha-trinositol corresponds to suppression of noxious-evoked release of amino acids and PGE2 from the spinal cord.

Increased dermal perfusion after skin burn injury by D-myo-inositol-1,2,6-trisphosphate

Full-thickness burn injury results in a continuous deterioration of blood flow due to vascular sludging, thrombosis formation and oedema leading to irreversible ischaemia and tissue necrosis. D-myo-inositol-1,2,6-trisphosphate (IP3) has previously been shown to reduce burn-induced oedema formation and inflammation involved in the pathophysiology of progressive ischaemia. A full-thickness burn injury (1 cm2) was induced in the abdominal skin of anaesthetized rats using an electrically heated thermoprobe. Blood flow in the experimental area was measured by laser Doppler flowmetry during 6.5 h postburn. The experiments included five groups. Three burned groups were treated intravenously with IP3 and received respectively: a bolus dose of 4 mg/kg followed by a continuous intravenous infusion of 20 mg/kg/h, 8 mg/kg + 40 mg/kg/h or 16 mg/kg + 60 mg/kg/h. One burned and one unburned control group received a corresponding bolus dose and infusion of saline. Results showed a significant inhibition of dermal ischaemia in the burned groups receiving IP3 at all dose intervals as compared to saline-treated burned rats (all P < 0.001). We conclude that IP3 improved local dermal perfusion in burned skin. Probable mechanisms of action could be the vasodilatory and anti-inflammatory properties of the agent.

Binding sites for alpha-trinositol (inositol 1,2,6-trisphosphate) in porcine tissues; comparison with Ins(1,4,5)P3 and Ins(1,3,4,5)P4-binding sites

1. The molecular mechanism of action of the inositol trisphosphate isomer, alpha-trinositol (Ins(1,2,6)P3) which has potential therapeutic use in treatment of inflammation and burn oedema, is still unclear. Therefore we have studied binding sites for alpha-trinositol in different tissues. 2. In membranes from pig cerebellum, liver, kidney, heart, and spleen, the density of specific [3]-alpha-trinositol binding sites was maximal at pH 5.0. Cerebellum and spleen showed only one binding site (cerebellum KD = 9.1 microM, spleen KD = 7.3 microM). In the other tissues, there were a high-affinity site (heart KD = 70 nM, liver KD = 790 nM and kidney KD = 1800 nM), besides a low-affinity site with a KD ranging between 32 and 120 microM. In cerebellar membranes, the affinity and density (107 pmol mg-1 protein) of alpha-trinositol binding sites were not affected by phosphate (0 to 25 mM). 3. Binding of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 to membranes from different porcine tissues was also determined. Ins(1,3,4,5)P4, the isomer stereochemically related to alpha-trinositol, binds with an affinity of 1.2 nM in cerebellum, but in the other tissues the binding site density was too low to determine the affinity. With cerebellar membranes heterologous displacement of [3H]-Ins(1,3,4,5)P4 by alpha-trinositol yielded a K1 of 11 microM. The Ins(1,4,5)P3 receptor displayed an affinity of 15 nM in cerebellum and of 5 to 7 nM in the other tissues investigated. 4. The solubilized Ins(1,3,4,5)P4 receptor preparation from cerebellum did not show Ins(1,2,6)P3 binding. Ins(1,2,6)P3 binding was found in the pellet obtained after solubilization of the membranes with the detergent Brij 58. 5. Thus, in different tissues alpha-trinositol binds to proteins with different affinity. They are obviously not related to binding sites for Ins (1,4,5)P3 or for Ins(1,3,4,5)P4. Future experiments have to unravel the identity of the binding protein(s) for alpha-trinositol.

The effect of alpha-trinositol on cholera toxin-induced hypersecretion and morphological changes in pig jejunum

alpha-Trinositol (D-myo-inositol 1,2,6-trisphosphate, PP56) is a novel antiinflammatory drug. This study elucidates the effect of intravenous alpha-trinositol on basal and acute fluid transport and morphological changes following cholera toxin administration in pig jejunum in vivo. Using isolated jejunal tied-off loops, the fluid hypersecretory (accumulation) effect of different doses of cholera toxin was studied in pigs treated intravenously with saline added different doses (0, 4, 8, 16 and 32 mg x kg-1 x hr-1) of alpha-trinositol. Levels of alpha-trinositol, as well as stereomicroscopical, light microscopical and scanning electron microscopical morphological studies were performed. Cholera toxin evoked a dose-dependent fluid hypersecretion. Treatment with alpha-trinositol caused a dose-dependent inhibition of the cholera toxin-induced fluid hypersecretion and did not affect basal fluid absorption. The 16 mg x kg-1 x hr-1 alpha-trinositol dose gave a maximal inhibition of 36%. Morphological studies showed only minor changes following 6 hr of exposure to 20 micrograms x loop-1 cholera toxin. These changes consisted of dilation of the villus capillaries, an increase of apical membrane blebbing and a reduction of the intercellular space. Treatment with 16 mg x kg-1 x hr-1 alpha-trinositol alone did not induce any morphological changes, and did not alter the morphological changes induced by cholera toxin, which caused fluid hypersecretion and only minor acute morphological changes. In conclusion, alpha-trinositol treatment reduced cholera toxin-induced fluid hypersecretion without altering basal fluid absorption, basal morphology, or cholera toxin-induced morphological changes in pig jejunum in vivo.

alpha-Trinositol: a functional (non-receptor) neuropeptide Y antagonist in vasculature

Neuropeptide Y is a sympathetic co-neurotransmitter released with noradrenaline upon sympathetic nerve stimulation. This study describes the ability of a synthetic inositol phosphate, alpha-trinositol(D-myo-inositol 1,2,6-triphosphate; PP 56) to antagonize vasoconstrictor responses to neuropeptide Y in-vitro as well as in-vivo. In human and guinea-pig isolated arteries alpha-trinositol potently (10 nM to 1 microM extracellular concentration) suppressed the constriction evoked by neuropeptide Y alone, the potentiation by neuropeptide Y of noradrenaline-evoked constriction, and the neuropeptide Y-induced inhibition of relaxation. Moreover, in the pithed (areflexive) rat, a non-adrenergic portion of the pressor response to preganglionic sympathetic nerve stimulation was sensitive to alpha-trinositol. As studied in the recently cloned human (vascular-type) Y1 receptor, the action of alpha-trinositol does not occur through antagonism at the neuropeptide Y recognition site nor does it induce allosteric changes of this receptor. However, we found alpha-trinositol to inhibit the rise in intracellular Ca2+ as well as inositol triphosphate concentrations induced by neuropeptide Y. It is, therefore, proposed that alpha-trinositol represents a non-receptor, but yet selective antagonist of neuropeptide Y in vasculature, opening up the possibility to investigate involvement of neuropeptide Y in sympathetic blood pressure control and in cardiovascular disorders.

Antinociceptive effect of alpha-trinositol, a novel D-myo-inositol phosphate derivative, in the formalin test in rats

The antinociceptive effect of alpha-trinositol was examined in rats using the formalin test following systemic, spinal and local subcutaneous administration. Injection of formalin into the paw evoked two phases (phase 1: 0-9 min; phase 2: 10-60 min) of flinching behavior of the injected paw. Intrathecal administration of alpha-trinositol resulted in a dose-dependent suppression of the first (ED50: 8 microg) and second (ED50: 9 microg) phase of formalin-evoked behavioral response. Similarly, intraperitoneal delivery showed a dose-dependent reduction of the first (ED50: 83 mg/kg) and second (ED50: 56 mg/kg) phase of the formalin test. Subcutaneous injection of 100 microg, but not 10 mu g, alpha-trinositol into the rat paw together with the formalin solution, had no effect on the first phase, but reduced by 20% the second phase of behavior. These data show that alpha-trinositol produces a suppression of acute and prolonged nociceptive behaviors with a central mechanism of action, although some peripheral component may contribute to the reduction of the late phase following systemic administration.

Effects of alpha-trinositol administered extra- and intracellularly (using liposomes) on rat aorta rings

The effects of alpha-trinositol, a D-myo-inositol [1,2,6]trisphosphate derivative, were studied on de-endothelised rat aorta rings. The substance was applied extracellularly as well as intracellularly (by using liposomes as drug carriers). Upon extracellular administration, the drug reduced the level of contraction induced by 40 mM K+ or by phenylephrine (10(-5) M). No effects were observed on relaxed preparations. Liposomes containing alpha-trinositol induced a dose-dependent contraction of the preparations under resting tension with a threshold of 10(-5) M in the aqueous phase. These contractions were heparin-insensitive but were significantly blocked by D-600 (10(-5) M) (an L-type Ca2+ channel blocker) or in Ca(2+)-free medium. Our data suggest that alpha-trinositol has a plasmalemmal mechanism of action which could involve Ca2+ influx from the extracellular space.

TLC characterization of liposomes containing D-myo-inositol derivatives

The thin-layer chromatographic (TLC) behaviour of liposomes containing inositol phosphates (IPs) was studied. The liposomes contained different concentrations of D-myo-inositol 1,4,5k-trisphosphate (IP3), D-myo-inositol 1,2,6-trisphosphate (alpha-trinositol, PP 56, a novel Perstorp Pharma derivative), D-myo-inositol 1,3,4,5-tetrakisphosphate (IP4), D-myo-inositol 1,3,4,5,6-pentakisphosphate (IP5) and D-myo-inositol 1,2,3,4,5,6-hexakisphosphate (IP6). Migration of all liposome batches was compared to that of control liposomes (containing only triple distilled water), and to that of free phosphatidylcholine (PC); the same amount of lipid was used in all situations. Thin-layer chromatography was performed on silica gel as adsorbent. As solvent we used an n-buthanol:ethanol:water mixture in a 4:3:3 volume ratio. Significant differences were found between PC and all liposome batches, as well as between control liposomes and the ones containing IP3, alpha-trinositol, IP4, or IP5, in various concentrations. Liposomes containing IP6 migrate completely differently compared not only to phosphatidylcholine and control liposomes, but also to the ones containing other IPs ( < 10(-3) M). Unlike the other IPs studied, liposome-entrapped IP6 elicits dose-dependent contractions of the isolated rat aorta. This suggests that liposomes loaded with IP6 undergo, during or after their preparation, physico-chemical alterations that eventually change their drug-delivery capacity.

Characteristics of [3H]inositol(1,3,4,5)tetrakisphosphate recognition sites in human cerebellar membranes

The characteristics of specific [3H]Ins(1,3,4,5)P4 binding sites in human cerebellar membranes were determined in this study. Binding rapidly reached steady state, possessed a pH optimum of 4.5-5.1 and was greater in the absence of BSA than in its presence. Heparin inhibited both specific and pseudospecific binding of the ligand, whereas only the specific binding was inhibited by non-radioactive Ins(1,3,4,5)P4. Calcium at a concentration of 1 mM, reduced binding by 27%. Competition studies with other inositol phosphates showed specificity for Ins(1,3,4,5)P4 with a pI50 value of 6.87 and a Hill coefficient of 0.27, indicating two sites. Ins(1,2,5,6)P4, Ins(1,3,4,6)P5, Ins(3,4,5,6)P4 displaced binding with IC50 values ranging from 0.1-1 microM, Ins(1,2,5,6)P4 and Ins(1,3,4,5,6)P5 being the most potent. Ins(1,4)P2 and Ins(1,5,6)P3 had lesser effects on binding. Rosenthal analysis of [3H]Ins(1,3,4,5)P4 saturation binding data at low ligand concentrations gave a KD of 27 nM and a Bmax of 33 pmol/mg protein. It is concluded that [3H]Ins(1,3,4,5)P4 binding sites in human cerebellar membranes have similar characteristics to these sites reported in the literature in animal cerebellar tissue, but are in greater abundance.

Intrathecal alpha-trinositol facilitates the flexor reflex but does not block the depressive effect of neuropeptide Y

We have studied the effects of alpha-trinositol (D-myo-inositol-1,2,6-trisphosphate, PP56), a putative antagonist of neuropeptide Y receptors, on the nociceptive flexor reflex in decerebrate, spinalized rats after intrathecal and intravenous administration. Intrathecal alpha-trinositol caused strong and prolonged facilitation of the flexor reflex, which was usually associated with an increase in spontaneous motoneuron activity. The reflex depressive effect of intrathecal neuropeptide Y was neither blocked nor reversed by alpha-trinositol. Intravenous alpha-trinositol at low doses had no effect on the flexor reflex and at high dose, reflex facilitation was sometimes observed. It is concluded that alpha-trinositol acts as a spinal excitant and is not an antagonist of the neuropeptide Y receptor in the rat spinal cord.