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Alkaline Phosphatase Inhibitors Attenuate Renovascular Responses to Norepinephrine.

ABSTRACT: Tissue nonspecific alkaline phosphatase (TNAP) contributes to the production of adenosine by the kidney, and A1-receptor activation enhances renovascular responses to norepinephrine. Therefore, we hypothesized that TNAP regulates renovascular responsiveness to norepinephrine. In isolated, perfused rat kidneys, the TNAP inhibitor l-p-bromotetramisole (0.1 mmol/L) decreased renal venous levels of 5'-AMP (adenosine precursor) and adenosine by 61% (P<0.0384) and 62% (P=0.0013), respectively, at 1 hour into treatment and caused a 10-fold rightward shift of the concentration-response relationship to exogenous norepinephrine (P<0.0001). Similarly, 2 other TNAP inhibitors, levamisole (1 mmol/L) and 2,5-dimethoxy-N-(quinolin-3-yl)benzenesulfonamide (0.02 mmol/L), also right shifted the concentration-response relationship to norepinephrine. The ability of TNAP inhibition to blunt renovascular responses to norepinephrine was mostly prevented or reversed by restoring A1-adenosinergic tone with the A1-receptor agonist 2-chloro-N6-cyclopentyladenosine (100 nmol/L). All 3 TNAP inhibitors also attenuated renovascular responses to renal sympathetic nerve stimulation, suggesting that TNAP inhibition attenuates renovascular responses to endogenous norepinephrine. In control propranolol-pretreated rats, acute infusions of norepinephrine (10 ?g/kg/min) increased mean arterial blood pressure from 95±5 mm?Hg to a peak of 169±4 mm?Hg and renovascular resistance from 12±2 mm?Hg/mL/min to a peak of 55±12 mm?Hg/mL/min; however, in rats also treated with intravenous l-p-bromotetramisole (30 mg/kg), the pressor and renovascular effects of norepinephrine were significantly attenuated (blood pressure: basal and peak, 93±7 and 146±6 mm?Hg, respectively; renovascular resistance: basal and peak, 13±2 and 29±5 mm?Hg/mL/min, respectively). TNAP inhibitors attenuate renovascular and blood pressure responses to norepinephrine, suggesting that TNAP participates in the regulation of renal function and blood pressure.

SUBMITTER: Jackson EK

PROVIDER: S-EPMC5310812 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature

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Alkaline Phosphatase Inhibitors Attenuate Renovascular Responses to Norepinephrine.

Jackson Edwin K EK Zhang Yumeng Y Cheng Dongmei D

Hypertension (Dallas, Tex. : 1979) 20170130 3

Tissue nonspecific alkaline phosphatase (TNAP) contributes to the production of adenosine by the kidney, and A1-receptor activation enhances renovascular responses to norepinephrine. Therefore, we hypothesized that TNAP regulates renovascular responsiveness to norepinephrine. In isolated, perfused rat kidneys, the TNAP inhibitor l-p-bromotetramisole (0.1 mmol/L) decreased renal venous levels of 5'-AMP (adenosine precursor) and adenosine by 61% (P<0.0384) and 62% (P=0.001 ...[more]

PMID: 28137984

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Project description:Here, we tested the hypothesis that TNAP (tissue nonspecific alkaline phosphatase) modulates vascular responsiveness to norepinephrine. In the isolated, Tyrode's-perfused rat mesentery, 50 µmol/L of L-p-bromotetramisole (L-p-BT; selective TNAP inhibitor, Ki=56 µmol/L) significantly reduced TNAP activity and caused a significant 9.0-fold rightward-shift in the norepinephrine concentration versus vasoconstriction relationship. At 100 µmol/L, L-p-BT further reduced mesenteric TNAP activity and caused an additional significant right-shift of the norepinephrine concentration versus vasoconstriction relationship. A higher concentration (200 µmol/L) of L-p-BT had no further effect on either mesenteric TNAP activity or norepinephrine-induced vasoconstriction. L-p-BT did not alter vascular responses to vasopressin, thus ruling-out nonspecific suppression of vascular reactivity. Since in the rat mesenteric vasculature α1-adrenoceptors mediate norepinephrine-induced vasoconstriction, these finding indicate that TNAP inhibition selectively interferes with α1-adrenoceptor signaling. Additional experiments showed that the effects of TNAP inhibition on norepinephrine-induced vasoconstriction were not mediated by accumulation of pyrophosphate or ATP (TNAP substrates) nor by reduced adenosine levels (TNAP product). TNAP inhibition significantly reduced the Hillslope of the norepinephrine concentration versus vasoconstriction relationship from 1.8±0.2 (consistent with positive cooperativity of α1-adrenoceptor signaling) to 1.0±0.1 (no cooperativity). Selective activation of A1-adenosine receptors, which are known to participate in coincident signaling with α1-adrenoceptors, reversed the suppressive effects of L-p-BT on norepinephrine-induced vasoconstriction. In vivo, L-p-BT administration achieved plasma levels of ≈60 µmol/L and inhibited mesenteric vascular responses to exogenous norepinephrine and sympathetic nerve stimulation. TNAP modulates vascular responses to norepinephrine likely by affecting positive cooperativity of α1-adrenoceptor signaling via a mechanism involving A1 receptor signaling.

Project description:The presence of alkaline phosphatases has been observed in several species and has been known to play a crucial role in various biological functions. Higher expressions of alkaline phosphatase have been found in several multifactorial disorders and cancer patients, which has led it to be an interesting target for drug discovery. A strong structural similarity exists between intestinal alkaline phosphatases (IAPs) and tissue-nonspecific alkaline phosphatases (TNAPs), which has led to the discovery of only a few selective inhibitors. Therefore, a series of 22 derivatives of 6-(chloromethyl)-4-(4-hydroxyphenyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (1) and ethyl 6-(chloromethyl)-4-(2-hydroxyphenyl)-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate (2) were synthesized to evaluate the anticancer potential of these compounds against breast cancer. The compounds were characterized through spectral and elemental analyses. The inhibitory effect of dihydropyrimidinone derivatives on alkaline phosphatases was evaluated using the calf alkaline phosphatase assay. The antioxidant activity of these compounds was performed to study the radical scavenging effect. In silico molecular docking and molecular dynamic simulations were performed to elucidate the binding mode of active compounds. Moreover, the two-dimensional qualitative-structure-activity relationship (2D-QSAR) was performed to study the structural requirements for enzyme inhibition. The calf alkaline phosphatase inhibitory assay revealed significant inhibition of the enzyme by compound 4d with IC50 1.27 μM at 0.1 mM concentration as compared to standard KH2PO4 having IC50 2.80 μM. The compounds 4f, 4e, and 4i also showed very good inhibition with IC50 values of 2.502, 2.943, and 2.132 μM, respectively, at the same concentration. The antioxidant assay revealed efficient radical scavenging activity of compounds 4f, 4e, and 4g at 100 μg/mL with IC50 values of 0.48, 0.61, and 0.75 μg/mL, respectively. The molecular docking and simulation studies revealed efficient binding of active compounds in the active binding site of the target enzyme. The final QSAR equation revealed good predictivity and statistical validation having R 2 = 0.958 and Q 2 = 0.903, respectively, for the generated model. The compound 4d showed the highest inhibitory activity with stable binding modes acting as a future lead for identifying alkaline phosphatase inhibitors. The molecular simulations suggested the stable binding of this compound, and the QSAR studies revealed the importance of autocorrelated descriptors in the inhibition of alkaline phosphatase. The investigated compounds may serve as potential pharmacophores for potent and selective alkaline phosphatase inhibitors. We intend to further investigate the biological activities of these compounds as alkaline phosphatase inhibitors.

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Alkaline Phosphatase Inhibitors Attenuate Renovascular Responses to Norepinephrine.

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Alkaline Phosphatase Inhibitors Attenuate Renovascular Responses to Norepinephrine.

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