Delrae M. Eckman

Targeted Disruption of Kir2.1 and Kir2.2 Genes Reveals the Essential Role of the Inwardly Rectifying K + Current in K + -Mediated Vasodilation

The molecular bases of inwardly rectifying K(+) (Kir) currents and K(+)-induced dilations were examined in cerebral arteries of mice that lack the Kir2.1 and Kir2.2 genes. The complete absence of the open reading frame in animals homozygous for the targeted allele was confirmed. Kir2.1(-/-) animals die 8 to 12 hours after birth, apparently due to a complete cleft of the secondary palate. In contrast, Kir2.2(-/-) animals are viable and fertile. Kir currents were observed in cerebral artery myocytes isolated from control neonatal animals but were absent in myocytes from Kir2.1(-/-) animals. Voltage-dependent K(+) currents were similar in cells from neonatal control and Kir2.1(-/-) animals. An increase in the extracellular K(+) concentration from 6 to 15 mmol/L caused Ba(2+)-sensitive dilations in pressurized cerebral arteries from control and Kir2.2 mice. In contrast, arteries from Kir2.1(-/-) animals did not dilate when the extracellular K(+) concentration was increased to 15 mmol/L. In summary, Kir2.1 gene expression in arterial smooth muscle is required for Kir currents and K(+)-induced dilations in cerebral arteries.

Novel PPARγ Agonists GI 262570, GW 7845, GW 1929, and Pioglitazone Decrease Calcium Channel Function and Myogenic Tone in Rat Mesenteric Arteries

Novel non-thiazolidinedione, tyrosine-derived peroxisome proliferator-activated receptor γ agonists, GI 262570, GW 7845, GW 1929, developed by GlaxoSmithKline (GSK) along with pioglitazone and nisoldipine, were studied on currents through L-type voltage-dependent calcium channels (VDCC) in freshly isolated smooth muscle cells from mesenteric arteries, and on the diameter of pressurized mesenteric arteries in vitro. Using Ba2+ (10 mmol/l) as the charge carrier through VDCC, the half-inhibition constants (IC50) for GI 262570, GW 7845, GW 1929, and pioglitazone were 2.0 ± 0.5, 3.0 ± 0.5, 5.0 ± 0.7, and 10.0 ± 0.8 µmol/l, respectively. For arterial diameter measurements the IC50 values for GI 262570, GW 7845, GW 1929, and pioglitazone were 2.4, 4.1, 6.3, and 13.9 µmol/l, respectively. Each GSK compound and pioglitazone was effective at inhibiting VDCC and relaxing pressurized arteries, suggesting that the vasodilation of resistance arteries could be explained by the inhibition of calcium entry through VDCC.

PKC-dependent regulation of the receptor locus dominates functional consequences of cysteinyl leukotriene type 1 receptor activation

Leukotrienes are important lipid mediators of asthma that contribute to airway inflammation and bronchoconstriction. Critical mechanisms for physiological regulation of the main G protein‐coupled receptor (GPCR) mediating the leukotriene responses in asthma, cysteinyl leukotriene type 1 receptor (CysLT1R), have not been delineated. Although desen‐sitization of GPCRs is a well‐established phenomenon, studies demonstrating its physiological relevance are lacking. Here, we demonstrate that relief of PKC‐mediated desensitization of endogenous CysLT1Rs augments multiple LTD4‐stimulated cellular functions, with associated increases in intracellular signaling events. In analyses of airway smooth muscle contraction ex vivo, PKC inhibition augmented LTD4‐stimulated contraction, and increased phosphoinositide hydrolysis and calcium flux in both murine and human airway smooth muscle cells. Similarly, for human monocytes, PKC inhibition augmented LTD4‐stimulated calcium flux and cell migration assessed in transwell chamber experiments and also augmented LTD4‐induced production of monocyte chemotactic protein assessed by ELISA. In contrast, PKC inhibition had no effect or slightly attenuated these cell functions and signaling events promoted by other receptor agonists, suggesting that despite antithetical effects on downstream events, desensitization of the CysLT1R is the principal mechanism by which PKC regulates the functional consequences of CysLTIR activation.—Deshpande, D. A., Pascual, R. M., Wang, S.‐W., Eckman, D. M., Riemer, E. C., Funk, C. D., Penn, R. B. PKC‐dependent regulation of the receptor locus dominates functional consequences of cysteinyl leukotriene type 1 receptor activation. FASEB J. 21, 2335–2342 (2007)

Regulation of the fetal mouse ductus arteriosus is dependent on interaction of nitric oxide and COX enzymes in the ductal wall

Nitric oxide (NO) and cyclooxygenase (COX)-derived prostaglandins are critical regulators of the fetal ductus arteriosus. To examine the interaction of these pathways within the ductus wall, the ductus arteriosus of term and preterm fetal mice was evaluated by pressurized myography. The isolated preterm ductus was more sensitive to NOS inhibition than at term. Sequential NOS and COX inhibition caused 36% constriction of the preterm ductus regardless of drug order. In contrast, constriction of the term ductus was dependent on the sequence of inhibition; NOS inhibition prior to COX inhibition produced greater constriction than when inhibitors were given in reverse order (36+/-6% versus 23+/-5%). Selective COX-1 or COX-2 inhibition prior to N(G)-nitro-l-arginine methyl ester (l-NAME) induced the expected degree of constriction. However, NOS inhibition followed by selective COX-2 inhibition caused unexpected ductal dilation. These findings are consistent with NO-induced activation of COX in the ductus arteriosus wall and the production of a COX-2-derived constrictor prostanoid that contributes to the balance of vasoactive forces that maintain fetal ductus arteriosus tone.

The Effect of Botulinum Neurotoxin-A on Blood Flow in Rats: A Potential Mechanism for Treatment of Raynaud Phenomenon

PURPOSE Botulinum neurotoxin-A (BoNTA) is used to treat several disorders, including Raynaud phenomenon. Recent investigations cite toxin-induced increases in blood flow, but no mechanism for BoNTAs actions is proposed. This study hypothesized that local application of BoNTA causes arteriolar vasodilation through sympathetic blockade and results in increased blood flow. METHODS Microvascular effects of BoNTA were assessed using a rat cremaster preparation. Cremaster microvascular diameters were measured in the muscle before and after treatment with the muscle paralytic agent gallamine triethiodide. Preparations were then treated with one of the following: BoNTA (4, 6, or 10 units), BoNTA dilution vehicle, or denatured BoNTA. Arteriolar diameters were measured repeatedly over the observation period. Additional preparations were treated with either tetrodotoxin or prazosin and rauwolscine before BoNTA to confirm that the observed vasodilatory responses were the result of sympathetic neural inhibition. RESULTS The BoNTA application resulted in a significant dose-dependent vasodilation (13% to 15%) of observed cremaster arterioles. Control treatments did not cause vasodilation. Both tetrodotoxin and prazosin/rauwolscine treatments elicited similar vasodilatory effects, with no additional vasodilation elicited by BoNTA. Addition of sodium nitroprusside following BoNTA elicited further vasodilation. In addition, systemic arterial pressure was unaffected by the local administration of BoNTA. CONCLUSIONS Local application of BoNTA results in arteriolar dilation that yields an approximate 69% increase in blood flow, without changing systemic arterial pressure. A BoNTA-mediated vasodilation through sympathetic blockade is a likely mechanism to explain the increase in blood flow reported after treatment with the toxin. CLINICAL RELEVANCE The ability of BoNTA to inhibit sympathetic nervous input reduces vasoconstriction, which is the most likely mechanism for improvement seen in Raynaud phenomenon patients following BoNTA injection.

Arterial vimentin is a transglutaminase substrate: a link between vasomotor activity and remodeling?

Background/Aims: The transglutaminases (TG2 and factor XIIIa) may contribute to the stability of arteries by cross-linking a variety of substrates, including extracellular matrix proteins and protease inhibitors. The preferred substrates have never been determined, however. Methods: We used an amine donor, 5-biotinamidopentylamine, that is covalently linked to acceptor glutamine residues, to determine transglutaminase substrates in carotid endarterectomy tissue. Results: The incorporation of 5-biotinamidopentylamine was calcium dependent, resulting in the labeling of several proteins that were detected by streptavidin-peroxidase and purified over a monomeric avidin affinity column. A major band of 42 kDa that was eluted from the column was sequenced along with 2 additional bands (80 and 65 kDa), revealing an internal fragment of vimentin, transferrin and albumin, respectively. Vimentin dimers were detected in 5 out of 5 carotid plaque homogenates. Conclusions: Vimentin is a major arterial substrate for transglutaminases. It has previously been shown that TG2 activity and vimentin contribute to vasomotor activity of arteries. Furthermore, transglutaminases (both TG2 and factor XIIIa), as well as vimentin, regulate structural alterations (inward remodeling) that occur in response to low flow states. Transglutaminase-mediated vimentin dimerization produces a novel unifying pathway by which vasodilatory and remodeling responses may be regulated.

Weekly doxorubicin increases coronary arteriolar wall and adventitial thickness.

Background Doxorubicin (DOX) is associated with premature cardiovascular events including myocardial infarction. This study was performed to determine if the weekly administration of DOX influenced coronary arteriolar medial and/or adventitial wall thickening. Methods Thirty-two male Sprague-Dawley rats aged 25.1± 2.4 weeks were randomly divided into three groups and received weekly intraperitoneal injections of normal saline (saline, n = 7), or low (1.5 mg/kg to 1.75 mg/kg, n = 14) or high (2.5 mg/kg, n = 11) doses of DOX. The animals were treated for 2–12 weeks, and euthanized at pre-specified intervals (2, 4, 7, or 10+ weeks) to obtain histopathologic assessments of coronary arteriolar lumen diameter, medial wall thickness, adventitial wall thickness, and total wall thickness (medial thickness + adventitial thickness). Results Lumen diameter was similar across all groups (saline: 315±34 µm, low DOX: 286±24 µm, high DOX: 242±27 µm; p = 0.22). In comparison to animals receiving weekly saline, animals receiving weekly injections of 2.5 mg/kg of DOX experienced an increase in medial (23±2µm vs. 13±3µm; p = 0.005), and total wall thickness (51±4µm vs. 36±5µm; p = 0.022), respectively. These increases, as well as adventitial thickening became more prominent after normalizing for lumen diameter (p<0.05 to p<0.001) and after adjusting for age, weight, and total cumulative DOX dose (p = 0.02 to p = 0.01). Animals receiving low dose DOX trended toward increases in adventitial and total wall thickness after normalization to lumen diameter and accounting for age, weight, and total cumulative DOX dose (p = 0.06 and 0.09, respectively). Conclusion In conclusion, these data demonstrate that weekly treatment of rats with higher doses of DOX increases coronary arteriolar medial, adventitial, and total wall thickness. Future studies are warranted to determine if DOX related coronary arteriolar effects are reversible or preventable, exacerbate the known cardiomyopathic effects of DOX, influence altered resting or stress-induced myocardial perfusion, or contribute to the occurrence of myocardial infarction.

Antenatal betamethasone alters vascular reactivity in adult female ovine cerebral arteries.

Although the use of antenatal glucocorticoids has resulted in decreased neonatal morbidity/mortality, recent animal studies have raised concerns regarding adverse effects of these medications on postnatal cardiovascular function. We hypothesized that antenatal betamethasone (Beta) exposure alters cerebral vascular reactivity in adult female sheep. We observed that K+-induced constriction was comparable in middle cerebral artery (MCA) from Beta-exposed animals and age-matched controls. Pressure-induced constriction was significantly attenuated in MCA from Beta-exposed compared with control sheep. Inhibition of NOS significantly augmented pressure-induced constriction in MCA from both Beta-exposed and control sheep, whereas cyclooxygenase (COX) inhibition augmented pressure-induced constriction only in MCA from Beta-exposed sheep. Furthermore, NOS and COX inhibition significantly attenuated bradykinin (BK)-induced dilation in MCA from both Beta-exposed and control sheep. However, there seemed to be a greater contribution of both NOS and COX to BK-induced dilation in Beta-exposed compared with control MCA. Our findings demonstrate that fetal exposure to a clinically relevant course of Beta alters cerebral vascular tone and reactivity in adult female sheep.

Persistent erythema with niacin is not attributable to aspirin resistance

BACKGROUND Niacin is suboptimally used in patients because it causes flushing and erythema. These side effects have been attributed to release of the vasodilating prostaglandin D2, generated in a reaction catalyzed by cyclooxygenase-1. Aspirin reduces but does not completely eliminate these side effects. Because some patients are resistant to its antiplatelet effects, we hypothesized that patients with persistent niacin-induced erythema might be aspirin resistant. METHODS Platelet function studies (via the use of a whole-blood platelet function aggregometer [VerifyNow; Accumetrics, San Diego, CA] with end points of aspirin reaction unit [ARUs] and P2Y12 reaction units [PRUs]) were performed on 32 healthy, drug-free subjects before and after 324 mg of aspirin. A niacin skin test with the use of topical methylnicotinate was also performed before and after the administration of aspirin. Responses to methyl nicotinate were assessed by a reaction score and by counting the time to first visible redness (TTR). RESULTS All subjects had an expected decrease in arachidonic acid induced platelet response (ARU 642.8 ± 47.20 before to 431.5 ± 41.1 after aspirin, P < .0001) without a significant change in the PRU. The reaction score and TTR were prolonged by aspirin at methylnicotinate concentrations ≥ 0.001 M. Although no subject had aspirin resistance (defined as ARU > 550), there was considerable variability in skin responses with erythema elicited in all subjects at the greatest concentrations. There was no difference in the ARU for subjects with TTR values above and below the mean, indicating that aspirin resistance does not explain the variation in skin responses to a topical niacin derivative. CONCLUSION Aspirin resistance is unlikely to be a significant contributor to the persistent erythema and flushing in niacin-treated patients.