Biallelic inactivation of hMLH1 by epigenetic gene silencing, a novel mechanism causing human MSI cancers

Mutations of DNA mismatch repair genes, including the hMLH1 gene, have been linked to human colon and other cancers in which defective DNA repair is evidenced by the associated instability of DNA microsatellite sequences (MSI). Germ-line hMLH1 mutations are causally associated with inherited MSI colon cancer, and somatic mutations are causally associated with sporadic MSI colon cancer. Previously however, we demonstrated that in many sporadic MSI colon cancers hMLH1 and all other DNA mismatch repair genes are wild type. To investigate this class of tumors further, we examined a group of MSI cancer cell lines, most of which were documented as established from antecedent MSI-positive malignant tumors. In five of six such cases we found that hMLH1 protein was absent, even though hMLH1-coding sequences were wild type. In each such case, absence of hMLH1 protein was associated with the methylation of the hMLH1 gene promoter. Furthermore, in each case, treatment with the demethylating agent 5-azacytidine induced expression of the absent hMLH1 protein. Moreover, in single cell clones, hMLH1 expression could be turned on, off, and on again by 5-azacytidine exposure, washout, and reexposure. This epigenetic inactivation of hMLH1 additionally accounted for the silencing of both maternal and paternal tumor hMLH1 alleles, both of which could be reactivated by 5-azacytidine. In summary, substantial numbers of human MSI cancers appear to arise by hMLH1 silencing via an epigenetic mechanism that can inactivate both of the hMLH1 alleles. Promoter methylation is intimately associated with this epigenetic silencing mechanism.

Correlation between oxytocin receptor concentration and responsiveness to oxytocin in pregnant rat myometrium: effects of ovarian steroids

Marked changes in the uterine binding of oxytocin (OT) occur in rats at the time of parturition or after treatment of ovariectomized rats with estrogen or progesterone. To ascertain that these binding sites represent the biological receptors for OT, we measured the uterine response to OT in various groups of rats in which specific OT binding was also determined. Intact pregnant rats and rats ovariectomized on day 20 of gestation and treated thereafter with oil, estradiol benzoate (5 micrograms/24 h), progesterone (5 mg/24 h), or estradiol and progesterone together had indwelling balloons inserted on day 20 for the recording of uterine response to either iv bolus injections or iv infusions of OT. The uterus was removed 24-48 h after balloon insertion, and OT binding to the particulate fraction as well as nuclear estrogen and cytosolic estrogen receptor concentrations were determined. An inverse correlation (r2 = 0.758) was found between the concentration of OT-binding sites and the threshold dose of OT, and a linear correlation was found between the concentration of binding sites and the uterine activity induced by OT infusion (r2 = 0.852). We conclude, therefore, that the high affinity (Kd, 1-2 nM) binding sites for OT represent the physiological receptors. The concentration of these sites increased progressively during estrogen treatment. Progesterone completely inhibited this estrogen-induced rise. After ovariectomy, there was a modest, but significant, increase in OT receptor concentration which also was prevented by progesterone. The increase in OT receptor concentration was correlated with the estrogen receptor concentration in intact pregnant and estrogen-treated ovariectomized animals, but not in the other groups of animals. The apparent affinity of the receptors for OT was not significantly affected by hormone treatment. We conclude that the concentration of receptors is a major factor controlling the uterine responsiveness to OT, and that the receptor concentrations are regulated by ovarian hormones in a manner related to estrogen receptor activation. In addition, estrogen appeared to enhance the coupling of OT receptor occupancy to the tissue response to OT.

FKBP51 and Cyp40 are positive regulators of androgen-dependent prostate cancer cell growth and the targets of FK506 and cyclosporin A

Prostate cancer (PCa) growth is dependent on androgens and the androgen receptor (AR), which acts by modulating gene transcription. Tetratricopeptide repeat (TPR) proteins (FKBP52, FKBP51 and Cyp40) interact with AR in PCa cells, suggesting roles in AR-mediated gene transcription and cell growth. We report here that FKBP51 and Cyp40, but not FKBP52, are significantly elevated in PCa tissues and in androgen-dependent (AD) and -independent (AI) cell lines. Overexpression of FKBP51 in AD LNCaP cells increased AR transcriptional activity in the presence and absence of androgen, whereas siRNA knockdown of FKBP51 dramatically decreased AD gene transcription and proliferation. Knockdown of Cyp40 also inhibited androgen-mediated transcription and growth in LNCaP cells. However, disruption of FKBP51 and Cyp40 in the AI C4-2 cells caused only a small reduction in proliferation, indicating that Cyp40 and FKBP51 predominantly regulate AD cell proliferation. Under knock-down conditions, the inhibitory effects of TPR ligands, CsA and FK506, on AR activity were not observed, indicating that Cyp40 and FKBP51 are the targets of CsA and FK506, respectively. Our findings demonstrate that FKBP51 and Cyp40 are positive regulators of AR that can be selectively targeted by CsA and FK506 to achieve inhibition of androgen-induced cell proliferation. These proteins and their cognate ligands thus provide new strategies in the treatment of PCa

Regulation of oxytocin receptor concentration in rat uterine explants by estrogen and progesterone

Incubation of uterine explants from immature rats with 0.01-100 ng of 17 beta-estradiol/mL resulted in approximately a fivefold increase in the number of oxytocin receptors per milligram of protein in 48 h. This increase was maintained for at least an additional 48 h in the presence of estrogen. When the explants were incubated with 1 microgram progesterone/mL from the outset, the concentration of oxytocin receptors was the same as initial (0 time) levels. The estrogen-induced increase in oxytocin receptor concentration was blocked by incubation with cycloheximide, an inhibitor of protein synthesis. Once increased, however, the concentration of oxytocin receptors exhibited no turnover for at least a 48-h period in the presence of estrogen. The addition of progesterone and estrogen to explants with elevated receptor levels resulted in almost a 60% reduction in oxytocin receptor concentration by 24 h, with no change in affinity of the receptor for oxytocin. The reduction in receptor concentration by progesterone was not prevented by cycloheximide. The progesterone effect may involve inactivation or degradation of oxytocin receptors or activation of substances that are inhibitory to oxytocin binding. The effects of estradiol and progesterone on oxytocin receptor concentration in uterine explants are similar to those seen when the steroids are administered in vivo. The explant system, therefore, should prove useful in clarifying factors and processes that are involved in regulation of oxytocin receptor concentration in the uterus and in the initiation of parturition in the rat.

Synthesis and biological characterization of 1,4,5,6-tetrahydropyrimidine and 2-amino-3,4,5,6-tetrahydropyridine derivatives as selective m1 agonists

Previous studies identified several novel tetrahydropyrimidine derivatives exhibiting muscarinic agonist activity in rat brain. Such compounds might be useful in treating cognitive and memory deficits associated with low acetylcholine levels, as found in Alzheimer's disease. To determine the molecular features of ligands important for binding and activity at muscarinic receptor subtypes, the series of tetrahydropyrimidines was extended. Several active compounds were examined further for functional selectivity through biochemical studies of muscarinic receptor activity using receptor subtypes expressed in cell lines. Several amidine derivatives displayed high efficacy at m1 receptors and lower activity at m3 receptors coupled to phosphoinositide (PI) metabolism in A9 L cells. Four ligands, including 1b, 1f, 2b, and 7b, exhibited marked functional selectivity for m1 vs m3 receptors. Compound 1f also exhibited low activity at m2 receptors coupled to the inhibition of adenylyl cyclase in A9 L cells. Molecular modeling studies also were initiated to help understand the nature of the interaction of muscarinic agonists with the m1 receptor using a nine amino model of the m1 receptor. Several important interactions were identified, including interactions between the ester moiety and Thr192. Additional interactions were found for oxadiazoles and alkynyl derivatives with Asn382, suggesting that enhanced potency and selectivity may be achieved by maximizing interactions with Asp105, Thr192, and Asn382. Taken together, the data indicate that several amidine derivatives display functional selectivity for m1 muscarinic receptors, warranting further evaluation as therapeutic agents for the treatment of Alzheimer's disease. In addition, several amino acid residues were identified as potential binding sites for m1 agonists. These data may be useful in directing efforts to develop even more selective m1 agonists.

HIF2α Is an Essential Molecular Brake for Postprandial Hepatic Glucagon Response Independent of Insulin Signaling

Glucagon drives hepatic gluconeogenesis and maintains blood glucose levels during fasting. The mechanism that attenuates glucagon action following refeeding is not understood. The present study demonstrates an increase in perivenous liver hypoxia immediately after feeding, which stabilizes hypoxia-inducible factor 2α (HIF2α) in liver. The transient postprandial increase in hepatic HIF2α attenuates glucagon signaling. Hepatocyte-specific disruption of HIF2α increases postprandial blood glucose and potentiates the glucagon response. Independent of insulin/AKT signaling, activation of hepatic HIF2α resulted in lower blood glucose, improved glucose tolerance, and decreased gluconeogenesis due to blunted hepatic glucagon action. Mechanistically, HIF2α abrogated glucagon-PKA signaling by activating cAMP-phosphodiesterases in a MEK/ERK-dependent manner. Repression of glucagon signaling by HIF2α ameliorated hyperglycemia in streptozotocin-induced diabetes and acute insulin-resistant animal models. This study reveals that HIF2α is essential for the acute postprandial regulation of hepatic glucagon signaling and suggests HIF2α as a potential therapeutic target in the treatment of diabetes.

Design, synthesis, and neurochemical evaluation of 5-(3-alkyl-1,2,4- oxadiazol-5-yl)-1,4,5,6-tetrahydropyrimidines as M1 muscarinic receptor agonists

A series of 5-(3-alkyl-1,2,4-oxadiazol-5-yl)-1,4,5,6-tetrahydropyrimidines+ ++ (7a-h) was synthesized for biological evaluation as selective agonists for M1 receptors coupled to phosphoinositide (PI) metabolism in the central nervous system. Each ligand bound with high affinity to muscarinic receptors from rat brain as measured by inhibition of [3H]-(R)-quinuclidinyl benzilate ([3H]-(R)-QNB) binding. 5-(3-Methyl-1,2,4-oxadiazol-5-yl)-1,4,5,6-tetrahydropyrimidine+ ++ trifluoroacetate (CDD-0098-J;7a) displayed high affinity (IC50 = 2.7 +/- 0.69 microM) and efficacy at muscarinic receptors coupled to PI metabolism in the rat cortex and hippocampus. Increasing the length of the alkyl substituent increased affinity for muscarinic receptors yet decreased activity in PI turnover assays. The hippocampal PI response of 7a was blocked by lower concentrations of pirenzepine (8) or by higher concentrations of either AF-DX 116 (9) or p-fluorohexahydrosiladifenidol (10), suggesting that at low concentrations 7a selectively stimulates PI turnover through M1 receptors.

Kappa opioid receptors stimulate phosphoinositide turnover in rat brain

The effects of various subtype-selective opioid agonists and antagonists on the phosphoinositide (PI) turnover response were investigated in the rat brain. The kappa-agonists U-50,488H and ketocyclazocine produced a concentration-dependent increase in the accumulation of IP's in hippocampal slices. The other kappa-agonists Dynorphin-A (1-13) amide, and its protected analog D[Ala]2-dynorphin-A (1-13) amide also produced a significant increase in the formation of [3H]-IP's, whereas the mu-selective agonists [D-Ala2-N-Me-Phe4-Gly5-ol]-enkephalin and morphine and the delta-selective agonist [D-Pen2,5]-enkephalin were ineffective. The increase in IP's formation elicited by U-50,488H was partially antagonized by naloxone and more completely antagonized by the kappa-selective antagonists nor-binaltorphimine and MR 2266. The formation of IP's induced by U-50,488H varies with the regions of the brain used, being highest in hippocampus and amygdala, and lowest in striatum and pons-medulla. The results indicate that brain kappa- but neither mu- nor delta-receptors are coupled to the PI turnover response.

Design, synthesis, and neurochemical evaluation of 2-amino-5-(alkoxycarbonyl)-3,4,5,6-tetrahydropyridines and 2-amino-5-(alkoxycarbonyl)-1,4,5,6-tetrahydropyrimidines as M1 muscarinic receptor agonists

Four regioisomers of 2-amino-(methoxycarbonyl)-3,4,5,6-tetrahydropyridine (2a-5a) were synthesized as the racemates to evaluate the utility of exocyclic amidines in the development of novel agonists for M1 muscarinic receptors. Of the four regioisomers, only racemic 2-amino-5-(methoxycarbonyl)-3,4,5,6-tetrahydropyridine (4a; CDD-0075-A) displayed high affinity (IC50 = 10 +/- 3.0 microM) and activity at muscarinic receptors coupled to PI metabolism in the rat cortex (260 +/- 4.5% stimulation above basal levels at 100 microM). A series of 2-amino-5-(alkoxycarbonyl)-3,4,5,6-tetrahydropyridines then was synthesized for further evaluation as M1 agonists. Only the propargyl derivative (4d) retained substantial agonist activity (120 +/- 14% at 100 microM) in this series. On the basis of the activity of the 5-(alkoxycarbonyl)-1,4,5,6- tetrahydropyrimidines (1a and 1d) and the 2-amino-5-(alkoxycarbonyl)-3,4,5,6-tetrahydropyridines, the corresponding cyclic guanidine derivatives were synthesized and tested. 2-Amino-5-(methoxycarbonyl)-1,4,5,6-tetrahydropyrimidine (7a) displayed a modest affinity for muscarinic receptors in the CNS (22 +/- 5.3 microM) and an ability to stimulate PI turnover in rat cerebral cortex (81 +/- 16% at 100 microM). The propargyl derivative (7d) also had modest binding affinity (31 +/- 15 microM) and high activity (150 +/- 8.5% at 100 microM), as expected based on the activity of propargyl esters of 1,4,5,6-tetrahydropyrimidine and 2-amino-3,4,5,6-tetrahydropyridine. Computational chemical studies revealed five distinct minimum-energy conformations for 1a, (R)-4a, and 7a, and three for 1d, (R)-4d, and 7d, each with a unique orientation of the ester moiety. Each of the five conformations for 1a could be superimposed upon a unique conformer of (R)-4a and 7a, suggesting that the compounds interact with muscarinic receptors in a similar fashion. Taken together, the data indicate the general utility of amidine systems as suitable replacements for the ammonium group of acetylcholine in developing ligands with activity at M1 muscarinic receptors in the central nervous system. Such compounds might be useful in the treatment of patients with Alzheimer's disease.

Repression of transforming growth factor-beta receptor type I promoter expression by Sp1 deficiency

In this report, we describe the mechanism of TGF-beta receptor type I (RI) repression in the GEO human colon carcinoma cells. Treatment of GEO cells with the DNA methyltransferase inhibitor, 5 azacytidine induced RI expression and restored TGF-beta response. A stably transfected RI promoter-reporter construct (RI-Luc) expressed higher activity in the 5 aza C treated GEO cells, suggesting the activation of a transactivator for RI transcription. Gel shift analysis indicated enhanced binding of proteins from the 5 aza C treated nuclear extracts to radiolabeled Sp1 oligonucleotides specifically contained in the RI promoter. Protein stability studies after cyclohexamide treatment suggested an increase in the Sp1 protein stability from the 5 aza C treated GEO cells. Further, transfection of Sp1 cDNA into untreated GEO control cells increased RI promoter activity and thus induced RI expression. 5 aza C mediated Sp1 expression in Sp1 deficient GEO colon and MCF-7 breast cancer cells also enhanced the activity of several other Sp1 dependent promoters such as TGF-beta receptor type II (RII), Cyclin A and p21/waf1/cip1. These results indicate that restoration of Sp1 in several different types of Sp1 deficient cells leads to enhanced activation of a wide range of Sp1 dependent promoters.

Systemic and local regulation of oxytocin receptors in the rat uterus, and their functional significance

Rats were made unilaterally pregnant by tying the right oviduct on the day after mating, to compare the oxytocin receptor concentrations in a nondistended, nonpregnant uterine horn with those in a distended, pregnant horn. On day 20, they were subjected to bilateral ovariectomy and indwelling balloons were inserted into both uterine horns. Following ovariectomy, the rats were injected im with either oil, estradiol benzoate (5 micrograms/rat per 24 h), or estradiol and progesterone together. For comparison, intact rats were studied on days 21 and 22, 24 and 48 h after insertion of the indwelling balloons. Spontaneous uterine activity and the response to increasing amounts of oxytocin were recorded 20-24 h and 44-48 h after surgery, following which the uteri were excised and assayed for oxytocin and estrogen receptors. The oxytocin receptor concentrations in the two horns were different on day 20 before the treatments were begun, the distended pregnant horn having a higher concentration per milligram DNA than the nonpregnant horn. The various treatments always changed the oxytocin receptor concentrations in the same direction; estrogen increased and progesterone inhibited the estrogen-induced rise in oxytocin receptor concentrations. In intact rats, the distention-induced increase in oxytocin receptor concentrations present on day 20 disappeared near term, but in the absence of the ovaries distention of the uterus had a significant influence on the myometrial oxytocin receptor concentrations, potentiating the effect of estrogen. Progesterone selectively inhibited the distention-induced increase in oxytocin receptor concentrations without inhibiting the hypertrophic effect of distention in general. A good correlation between oxytocin receptor numbers and tissue responsiveness was observed in all instances. The changes in spontaneous activity induced by the various treatments were distinct from the changes in oxytocin responsiveness. Estrogen exerted a strong inhibitory action on the activity stimulated by hormone withdrawal, while progesterone had no inhibitory effect. The pregnant distended horn always showed more spontaneous activity than the nonpregnant horn. There was an overall significant correlation between nuclear estrogen receptor and oxytocin receptor concentrations per milligram DNA, although the partial correlations were not significant in all groups (oil and progesterone).(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of heat shock transcription factor by GR

The GR is a hormone-activated transcription factor that acts to regulate specific gene expression. In the absence of hormone, the GR and other steroid receptors have been shown to form complexes with several mammalian heat shock proteins. As heat shock proteins are produced by cells as an adaptive response to stress, speculation has existed that communication between the heat shock and glucocorticoid hormone signal pathways must exist. Only recently has evidence to support this hypothesis been reported. In almost all cases, the evidence has been of an ability of heat shock to cause a potentiation of the glucocorticoid hormone response. In this proposal, evidence is now presented that heat shock signaling can, in turn, be regulated by glucocorticoids. In mouse L929 cells stably expressing a chloramphenicol acetyltransferase reporter controlled by the human heat shock protein70 promoter and containing known binding sites for heat shock transcription factor 1 treatment with glucocorticoid agonist (dexamethasone) results in a dose-dependent decrease of stress-induced chloramphenicol acetyltransferase gene expression. In these cells, inhibition of heat shock protein70 promoter activity by dexamethasone was completely blocked by GR antagonist (RU486). Similar treatment of L929 cells stably expressing a chloramphenicol acetyltransferase reporter under the control of the constitutively active SV40 promoter showed no such inhibition by dexamethasone. More importantly, dexamethasone was also found to inhibit heat shock-induced expression of the major heat shock proteins-heat shock proteins70, 90, and 110. Thus, the inhibitory effect of dexamethasone appears to apply to most, if not all, heat shock transcription factor 1-regulated genes. Although dexamethasone did not prevent the DNA-binding function of heat shock-activated heat shock transcription factor 1, it did inhibit a constitutively active mutant of human heat shock transcription factor 1 under nonstress conditions, suggesting that dexamethasone repression of heat shock transcription factor 1 was primarily through an inhibition of heat shock transcription factor 1 transcription enhancement activity. To more accurately characterize the stage of GR signaling responsible for inhibition of heat shock transcription factor 1, a series of Chinese hamster ovary cells containing either no GR, wild-type mouse GR, or single-point mutations of GR were employed. Dexamethasone inhibition of heat shock-induced heat shock transcription factor 1 activity was observed in the presence of wild-type GR, but not in Chinese hamster ovary cells lacking GR, suggesting that signaling cascades other than GR were not involved in this effect of dexamethasone. Consistent with this conclusion was the observation that dexamethasone had no effect on activity of the MAPKs (ERK1, ERK2, or c-jun N-terminal kinase), which are known to negatively regulate heat shock transcription factor 1. Dexamethasone inhibition of heat shock transcription factor 1 was not seen in Chinese hamster ovary cells expressing GR defective for DNA-binding function. Moreover, dissociation of GR/Hsp90/Hsp70 complexes was observed in response to hormone for both the wild-type and DNA binding-defective forms of GR, demonstrating that release of Hsp90 or Hsp70 (both of which are known to keep heat shock transcription factor 1 in its inactive state) could be ruled out as a potential mechanism. Thus, it appears that GR-mediated transactivation or transrepression is required for the inhibitory effect of dexamethasone on heat shock transcription factor 1 activity. Taken as a whole, these results provide evidence for a novel mechanism of cross-talk in which signaling by the GR can attenuate the heat shock response in cells through an inhibition of the transcription enhancement activity of HSF1.

Heat and chemical shock potentiation of glucocorticoid receptor transactivation requires heat shock factor (HSF) activity. Modulation of HSF by vanadate and wortmannin

Heat shock and other forms of stress increase glucocorticoid receptor (GR) activity in cells, suggesting cross-talk between the heat shock and GR signal pathways. An unresolved question concerning this cross-talk is whether heat shock factor (HSF1) activity is required for this response. We addressed this issue by modulating HSF1 activity with compounds acting by distinct mechanisms: sodium vanadate (SV), an inhibitor of protein phosphatases; and wortmannin, an inhibitor of DNA-dependent protein kinase. Using HSF1- and GR-responsive CAT reporters, we demonstrate that SV inhibits both HSF1 activity and the stress potentiation of GR, while having no effect on the hormone-free GR or HSF1. Paradoxically, SV increased hormone-induced GR activity in the absence of stress. In contrast, wortmannin increased HSF1 activity in stressed cells and had no effect on HSF1 in the absence of stress. Using the pMMTV-CAT reporter containing the negative regulatory element 1 site for DNA-dependent protein kinase, wortmannin was found to increase the GR response. However, in cells expressing a minimal promoter lacking negative regulatory element 1 sites, wortmannin had no effect on the GR in the absence of stress but increased the stress potentiation of GR. Our results show that the mechanism by which GR activity is increased in stressed cells requires intrinsic HSF1 activity.

Biochemical and behavioral responses of pilocarpine at muscarinic receptor subtypes in the CNS. Comparison with receptor binding and low-energy conformations

Pilocarpine was tested biochemically in vitro for its ability to stimulate phosphoinositide (PI) turnover in the hippocampus (M1/M3 responses) where it displayed 35% of the maximal carbachol response with an EC50 value of 18 microM, and low-Km GTPase in the cortex (M2 response), where it had 50% of the maximal carbachol response with an EC50 value of 4.5 microM. Behaviorally, pilocarpine was able to restore deficits in a representational memory task (sensitive to M1 antagonists) produced by intrahippocampal injections of AF64A. Twenty-three low-energy conformations of protonated pilocarpine were generated using the program MacroModel. The data indicate that pilocarpine is a partial agonist at both M1 and M2 muscarinic receptors in the CNS. Behaviorally, with respect to the memory task, M1 effects of pilocarpine apparently predominate. It also is conceivable that different conformations of pilocarpine are active as agonists at different muscarinic receptor subtypes.

Synthesis and biochemical activity of novel amidine derivatives as m1 muscarinic receptor agonists

As part of a continuing effort aimed at the development of selective, efficacious, and centrally active m1 muscarinic agonists for the treatment of Alzheimer's disease, a series of amide and hydrazide amidine derivatives (2a-e and 3b-d) was synthesized and examined for muscarinic agonist activity. Preliminary biochemical studies indicated that 2b, 2d, and 3d bound to muscarinic receptors in rat brain and stimulated phosphoinositide (PI) metabolism in rat cerebral cortex. Compounds 2b and 2d were also highly efficacious at m1 muscarinic receptors expressed in cultured A9 L cells. Molecular modeling studies suggest slightly different modes of interaction with m1 receptors for the ester and amide derivatives. Also, hydrogen-bond formation with a Thr residue may be important for m1 muscarinic agonist potency. The data suggest that the amide moiety can replace the ester group found in muscarinic agonists and provide further support for the utility of amidine derivatives in the development of efficacious m1 agonists.

Staging Liver Fibrosis by Fibroblast Activation Protein Inhibitor PET in a Human-Sized Swine Model

Current methods of staging liver fibrosis have notable limitations. We investigated the utility of PET in staging liver fibrosis by correlating liver uptake of ⁶⁸Ga-labeled fibroblast activation protein inhibitor (FAPI) with histology in a human-sized swine model. Methods: Five pigs underwent baseline ⁶⁸Ga-FAPI-46 (⁶⁸Ga-FAPI) PET/MRI and liver biopsy, followed by liver parenchymal embolization, 8 wk of oral alcohol intake, endpoint ⁶⁸Ga-FAPI PET/MRI, and necropsy. Regions of interest were drawn on baseline and endpoint PET images, and SUV_mean was recorded. At the endpoint, liver sections corresponding to regions of interest were identified and cut out. Fibrosis was histologically evaluated using a modified METAVIR score for swine liver and quantitatively using collagen proportionate area (CPA). Box-and-whisker plots and linear regression were used to correlate SUV_mean with METAVIR score and CPA, respectively. Results: Liver ⁶⁸Ga-FAPI uptake strongly correlated with CPA (r = 0.89, P < 0.001). ⁶⁸Ga-FAPI uptake was significantly and progressively higher across F2 and F3/F4 fibrosis stages, with a respective median SUV_mean of 2.9 (interquartile range [IQR], 2.7-3.8) and 7.6 (IQR, 6.7-10.2) (P < 0.001). There was no significant difference between ⁶⁸Ga-FAPI uptake of baseline liver and endpoint liver sections staged as F0/F1, with a respective median SUV_mean of 1.7 (IQR, 1.3-2.0) and 1.7 (IQR, 1.5-1.8) (P = 0.338). Conclusion: The strong correlation between liver ⁶⁸Ga-FAPI uptake and the histologic stage of liver fibrosis suggests that ⁶⁸Ga-FAPI PET can play an impactful role in noninvasive staging of liver fibrosis, pending validation in patients.

Cardiac performance in inbred rat genetic models of low and high running capacity

1. Previous work demonstrating that DA inbred rats are superior to COP inbred rats in aerobic treadmill running capacity has indicated their utility as genetic models to explore this trait. We tested the general hypothesis that intermediate phenotypes of cardiac function and calcium metabolism are responsible for the difference in capacity between these strains. 2. Logical cardiac trait differences were estimated at a tissue (isolated papillary muscle), cellular (isolated left ventricular cells), and biochemical level of organization. 3. DA hearts were found to give significantly higher values than COP hearts for: (1) maximal developed tension (38.3 % greater), and rates of tension change in contraction (61 %) or relaxation (59 %) of isolated papillary muscle, (2) fractional shortening (50 %), amplitude of the Ca(2+) transient (78.6 %), and caffeine-induced release of Ca(2+) from the sarcoplasmic reticulum (SR; 260 %) in isolated ventricular myocytes, and (3) Na(+),K(+)-ATPase activity of isolated myocytes (17.3 %). 4. Our results suggest that these trait differences may prove useful for further studies into the genes responsible for natural variations in both ventricular function and aerobic endurance capacity. Understanding the genetic basis of aerobic capacity will help define the continuum between health and disease.

A second messenger role for monoacylglycerols is suggested by their activating effects on the sodium pump

Receptor-mediated activation of the sodium pump has been noted in several intact tissues. To test the hypothesis that this may be due to the direct effects of the second messenger diacylglycerols on the pump, we studied the effects of various long-chain acylglycerols on the purified Na+/K(+)-ATPase. With optimal ATP, acylglycerols had no effect on enzyme activity. When ATP was suboptimal, tri- and diacylglycerols had no effects, but monoacylglycerols caused up to 3-fold increase in ATPase activity. Using sealed vesicles of red cell membranes and cardiac sarcolemma, stimulation of the ion transport function of the enzyme by monoacylglycerols in the presence of suboptimal ATP was also shown. Since the sodium pump may not be saturated with ATP in the intact cell, the possibility arises that monoacylglycerols are the second messengers for the receptor-mediated regulation of the pump.

Histotripsy Ablations in a Porcine Liver Model: Feasibility of Respiratory Motion Compensation by Alteration of the Ablation Zone Prescription Shape

BACKGROUND

Previous human-scale porcine liver model studies of histotripsy have resulted in ablation zones elongated in the cranial-caudal (CC) dimension due to uninterrupted respiratory motion during the ablation procedure.

PURPOSE

The purpose of this study is to compensate for elongation of hepatic histotripsy ablation zones in the cranial-caudal (CC) dimension caused by respiratory motion by prescribing ellipsoid-shaped ablations.

METHODS

Six female swine underwent 12 hepatic histotripsy ablations using a prototype clinical histotripsy system under general anesthesia. Each animal received two ablation zones prescribed as either an ellipsoid (2.5 cm (AP) × 2.5 cm (ML) × 1.7 cm (CC), prescribed volume = 5.8 cc) or a sphere (2.5 cm all dimensions, prescribed volume 8.2 cc). Ventilatory tidal volume was held constant at 400 cc for all ablations. Post-procedure MRI was followed by sacrifice and gross and microscopic histology.

RESULTS

Ablations on MRI were slightly larger than prescribed in all dimensions. Ellipsoid plan ablations (2.8 × 3.0 × 3.1 cm, volume 13.2 cc, sphericity index 0.987) were closer to prescribed volume than spherical plan ablations (2.9 × 3.1 × 3.7 cm, volume 17.1 cc, sphericity index 0.953). Ellipsoid plan ablations were more spherical than sphere plan ablations, but the difference did not reach statistical significance (p = .0.06). Pathologic analysis confirmed complete necrosis within the center of each ablation zone with no widening of the zone of partial ablation on the superior and inferior as compared to the lateral borders (p = .0.22).

CONCLUSION

Altering ablation zone prescription shape when performing hepatic histotripsy ablations can partially mitigate respiratory motion effects to achieve the desired ablation shape and volume.

Inhibition of carbachol-stimulated phosphoinositide turnover by U-50,488H in rat hippocampus--involvement of GTP-binding protein

The effect of U-50,488H, a selective kappa-opioid agonist, on carbachol-stimulated phosphoinositide (PI) turnover response in rat hippocampal slices was examined. U-50,488H which stimulates PI turnover response in this preparation (Periyasamy and Hoss, 1990, Life Sci. 47, 219), inhibited carbachol-stimulated PI turnover in a concentration-dependent manner with an IC50 value of 33 +/- 9.0 microM. The inhibitory effect of U-50,488H was not blocked by the kappa-selective antagonists, e.g., nor-binaltorphimine (10 microM), and MR2266 (10 microM), or tetrodotoxin (1 microM) suggesting that the effect of U-50,488H was mediated neither through the kappa-receptors nor through the release of an endogenous neurotransmitter(s). A Lineweaver-Burke plot of the stimulation of PI turnover by carbachol in the presence and absence of U-50,488H showed that the Km was not changed (11.4 +/- 3.4 and 11.5 +/- 2.6 microM) whereas the Vmax was reduced from 3849 +/- 460 to 1534 +/- 31 cpm indicating that the inhibition was non-competitive. U-50,488H also inhibited guanosine 5'-[beta, gamma-imido]triphosphate (Gpp[NH]p)-stimulated PI turnover in rat hippocampal membranes in a concentration-dependent manner with an IC50 value of 33 +/- 12 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Displaceable binding of [3H]l-glutamic acid to non-receptor materials

[3H]L-glutamic acid binding to microfuge tubes and glass was investigated in four buffers. Background binding to these materials was negligible, but was increased by centrifugation or suction in Tris-HCl and Tris-citrate buffer. This binding was much less or eliminated when HEPES-KOH, or Tris-acetate buffer was used instead. [3H]L-glutamate binding to microfuge tubes was inhibited by L- but not D-isomers of glutamate and aspartate. DL-2-amino-7-phosphonoheptanoic acid also did not inhibit the binding. Other compounds which showed low to moderate inhibition were: N-methyl-D-aspartate, quisqualate, L-glutamic acid diethyl ester, N-methyl-L-aspartate, kainate, and 2-amino-4-phosphonobutyrate. Binding was inhibited by denatured rat brain membranes. A protein-dependent [3H]glutamate binding was obtained with a repeatedly frozen-thawed membrane preparation when binding was done in Tris-acetate buffer. It is recommended that Tris-acetate or HEPES-KOH buffer should be used in the glutamate binding assay. If Tris-HCl or Tris-citrate buffer is used, appropriate control experiment should be done to correct for binding to microfuge tubes or glass fiber filters.

An X-Ray C-Arm Guided Automatic Targeting System for Histotripsy

OBJECTIVE

Histotripsy is an emerging noninvasive, nonionizing and nonthermal focal cancer therapy that is highly precise and can create a treatment zone of virtually any size and shape. Current histotripsy systems rely on ultrasound imaging to target lesions. However, deep or isoechoic targets obstructed by bowel gas or bone can often not be treated safely using ultrasound imaging alone. This work presents an alternative x-ray C-arm based targeting approach and a fully automated robotic targeting system.

METHODS

The approach uses conventional cone beam CT (CBCT) images to localize the target lesion and 2D fluoroscopy to determine the 3D position and orientation of the histotripsy transducer relative to the C-arm. The proposed pose estimation uses a digital model and deep learning-based feature segmentation to estimate the transducer focal point relative to the CBCT coordinate system. Additionally, the integrated robotic arm was calibrated to the C-arm by estimating the transducer pose for four preprogrammed transducer orientations and positions. The calibrated system can then automatically position the transducer such that the focal point aligns with any target selected in a CBCT image.

RESULTS

The accuracy of the proposed targeting approach was evaluated in phantom studies, where the selected target location was compared to the center of the spherical ablation zones in post-treatment CBCTs. The mean and standard deviation of the Euclidean distance was 1.4 ±0.5 mm. The mean absolute error of the predicted treatment radius was 0.5 ±0.5 mm.

CONCLUSION

CBCT-based histotripsy targeting enables accurate and fully automated treatment without ultrasound guidance.

SIGNIFICANCE

The proposed approach could considerably decrease operator dependency and enable treatment of tumors not visible under ultrasound.