Precision Medicine in Veterinary Science

Precision medicine focuses on the clinical management of the individual patient, not on population-based findings. Successes from human precision medicine inform veterinary oncology. Early evidence of success for canines shows how precision medicine can be integrated into practice. Decreasing genomic profiling costs will allow increased utilization and subsequent improvement of knowledge base from which to make better informed decisions. Utility of precision medicine in canine oncology will only increase for improved cancer characterization, enhanced therapy selection, and overall more successful management of canine cancer. As such, practitioners are called to interpret and leverage precision medicine reports for their patients.

Genomic analysis across 53 canine cancer types reveals novel mutations and high clinical actionability potential

A genomic understanding of the oncogenic processes and individual variability of human cancer has steadily fueled improvement in patient outcomes over the past 20 years. Mutations within tumour tissues are routinely assessed through clinical genomic diagnostic assays by academic and commercial laboratories to facilitate diagnosis, prognosis and effective treatment stratification. The application of genomics has unveiled a wealth of mutation-based biomarkers in canine cancers, suggesting that the transformative principles that have revolutionized human cancer medicine can be brought to bear in veterinary oncology. To advance clinical genomics and genomics-guided medicine in canine oncology, we have developed and validated a canine cancer next-generation sequencing gene panel for the identification of multiple mutation types in clinical specimens. With this panel, we examined the genomic landscapes of 828 tumours from 813 dogs, spanning 53 cancer types. We identified 7856 alterations, encompassing copy number variants, single nucleotide variants, indels and internal tandem duplications. Additionally, we evaluated the clinical utility of these alterations by incorporating a biomarker framework from comprehensive curation of primary canine literature and inferences from human cancer genomic biomarker literature and clinical diagnostics. Remarkably, nearly 90% of the cases exhibited mutations with diagnostic, prognostic or therapeutic implications. Our work represents a thorough assessment of genomic landscapes in a large cohort of canine cancers, the first of its kind for its comprehensive inclusion of multiple mutation types and structured annotation of biomarkers, demonstrating the clinical potential of leveraging mutation-based biomarkers in veterinary oncology.

Novel genomic prognostic biomarkers for dogs with cancer

BACKGROUND

Growing evidence from dogs and humans supports the abundance of mutation-based biomarkers in tumors of dogs. Increasing the use of clinical genomic diagnostic testing now provides another powerful data source for biomarker discovery.

HYPOTHESIS

Analyzed clinical outcomes in dogs with cancer profiled using SearchLight DNA, a cancer gene panel for dogs, to identify mutations with prognostic value.

ANIMALS

A total of 127 cases of cancer in dogs were analyzed using SearchLight DNA and for which clinical outcome information was available.

METHODS

Clinical data points were collected by medical record review. Variables including mutated genes, mutations, signalment, and treatment were fitted using Cox proportional hazard models to identify factors associated with progression-free survival (PFS). The log-rank test was used to compare PFS between patients receiving and not receiving targeted treatment before first progression.

RESULTS

Combined genomic and outcomes analysis identified 336 unique mutations in 89 genes across 26 cancer types. Mutations in 6 genes (CCND1, CCND3, SMARCB1, FANCG, CDKN2A/B, and MSH6) were significantly associated with shorter PFS. Dogs that received targeted treatment before first progression (n = 45) experienced significantly longer PFS compared with those that did not (n = 82, P = .01). This significance held true for 29 dogs that received genomically informed targeted treatment compared with those that did not (P = .05).

CONCLUSION AND CLINICAL IMPORTANCE

We identified novel mutations with prognostic value and demonstrate the benefit of targeted treatment across multiple cancer types. These results provide clinical evidence of the potential for genomics and precision medicine in dogs with cancer.

Standing in the canine precision medicine knowledge gap: Improving annotation of canine cancer genomic biomarkers through systematic comparative analysis of human cancer mutations in COSMIC

The accrual of cancer mutation data and related functional and clinical associations have revolutionised human oncology, enabling the advancement of precision medicine and biomarker-guided clinical management. The catalogue of cancer mutations is also growing in canine cancers. However, without direct high-powered functional data in dogs, it remains challenging to interpret and utilise them in research and clinical settings. It is well-recognised that canine and human cancers share genetic, molecular and phenotypic similarities. Therefore, leveraging the massive wealth of human mutation data may help advance canine oncology. Here, we present a structured analysis of sequence conservation and conversion of human mutations to the canine genome through a 'caninisation' process. We applied this analysis to COSMIC, the Catalogue of Somatic Mutations in Cancer, the most prominent human cancer mutation database. For the project's initial phase, we focused on the subset of the COSMIC data corresponding to Cancer Gene Census (CGC) genes. A total of 670 canine orthologs were found for 721 CGC genes. In these genes, 365 K unique mutations across 160 tumour types were converted successfully to canine coordinates. We identified shared putative cancer-driving mutations, including pathogenic and hotspot mutations and mutations bearing similar biomarker associations with diagnostic, prognostic and therapeutic utility. Thus, this structured caninisation of human cancer mutations facilitates the interpretation and annotation of canine mutations and helps bridge the knowledge gap to enable canine precision medicine.

Genomic tumor analysis provides clinical guidance for the management of diagnostically challenging cancers in dogs

OBJECTIVE

To evaluate the diagnostic, prognostic, and therapeutic utility of a cancer genomic diagnostic assay (SearchLight DNA; Vidium Animal Health) for diagnostically ambiguous cancer cases.

ANIMALS

69 privately owned dogs with ambiguous cancer diagnoses and for which the genomic assay was performed.

PROCEDURES

Genomic assay reports generated between September 28, 2020, and July 31, 2022, for dogs with malignancy or suspected malignancy were reviewed to determine the assay's clinical utility defined as providing diagnostic clarity, prognostic information, and/or therapeutic options.

RESULTS

Genomic analysis provided diagnostic clarity in 37 of 69 cases (54%; group 1) and therapeutic and/or prognostic information in 22 of the remaining 32 cases (69%; group 2) for which the diagnosis remained elusive. Overall, the genomic assay was clinically useful in 86% (59/69) of cases.

CLINICAL RELEVANCE

To our knowledge, this was the first study to evaluate the multifaceted clinical utility of a single cancer genomic test in veterinary medicine. Study findings supported the use of tumor genomic testing for dogs with cancer, particularly those that are diagnostically ambiguous and therefore inherently challenging to manage. This evidence-driven genomic assay provided diagnostic guidance, prognostic support, and therapeutic options for most patients with an unclear cancer diagnosis that would otherwise have an unsubstantiated clinical plan. Furthermore, 38% (26/69) of samples were easily obtained aspirates. Sample factors (sample type, percentage of tumor cells, and number of mutations) did not influence diagnostic yield. Our study demonstrated the value of genomic testing for the management of canine cancer.

Population characteristics of golden retriever lifetime study enrollees

BACKGROUND

Studying cancer and other diseases poses a problem due to their protracted and multifactorial nature. Prospective studies are useful to investigate chronic disease processes since collection of lifestyle information, exposure data and co-incident health issues are collected before the condition manifests. The Golden Retriever Lifetime Study is one of the first prospective studies following privately-owned dogs throughout life to investigate the incidence and risk factors for disease outcomes, especially cancer.Owners of golden retrievers in the contiguous United States volunteered their dogs in early life. Owners and veterinarians complete online questionnaires about health status and lifestyle; dogs undergo a physical examination and collection of biological samples annually. The data presented summarize the initial study visits and the corresponding questionnaires for 3044 dogs in the cohort.

RESULTS

The median age of dogs at enrollment was 14.0 months (interquartile range (IQR): 8-20 months). Approximately half of the population had undergone gonadectomy by their initial study visit. Medical conditions reported at enrollment consisted primarily of integumentary, gastrointestinal and urinary dysfunction. A large majority of the dogs have a record of having received preventive care (vaccines, parasiticides, flea and heartworm prevention) by the time of the initial study visit. Clinical pathology data were unremarkable.

CONCLUSIONS

This study represents one of the first lifetime observational investigations in veterinary medicine. The population characteristics reported here indicate a healthy cohort of golden retrievers cared for by owners committed to their dogs' health. Data acquired over the study period will provide valuable information about genetic, dietary and environmental risk factors associated with disease in golden retrievers and a framework for future prospective studies in veterinary medicine.

Potent cyclic peptide inhibitors of VLA-4 (alpha4beta1 integrin)-mediated cell adhesion. Discovery of compounds like cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) compatible with depot formulation

Additional structure-activity relationship studies on potent cyclic peptide inhibitors of very late antigen-4 (VLA-4) are reported. The new N- to C-terminal cyclic hexa-, hepta- and octapeptide inhibitors like cyclo(MeIle/MePhe-Leu-Asp-Val-X) (X = 2-4 amino acids containing hydrophobic and/or basic side chains) were synthesized using solid phase peptide synthesis methods. The peptides were evaluated in in vitro cell adhesion assays and in in vivo inflammation models. Many of the peptides like cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) (17), cyclo(MeIle-Leu-Asp-Val-D-Arg-D-Arg-D-Phe) (20), cyclo(MeIle-Leu-Asp-Val-D-Arg-D-Arg-MePhe) (21) and cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg-D-Ala-D-Ala) (23) were potent inhibitors of VLA-4-mediated cell adhesion and inhibited ovalbumin-induced delayed type hypersensitivity (DTH) response in mice. The more potent compounds were highly selective and did not affect U937 cell adhesion to fibronectin (VLA-5), phorbolmyristate acetate or PMA-differentiated U937 cell adhesion to intercellular cell adhesion molecule-1 (ICAM-1)-expressing Chinese hamster ovary cells (LFA-1) and adenosine diphosphate (ADP)-induced platelet aggregation (GPIIb/IIIa). In contrast to the inhibitors like Ac-cyclo(D-Lys-D-Ile-Leu-Asp-Val) and cyclo(CH2CO-Ile-Leu-Asp-Val-Pip-CH2CO-Ile-Leu-Asp-Val-Pip) described earlier, the new compounds were much more compatible with the depot formulations based on poly(DL-lactide-co-glycolide) polymers. The hexapeptide cyclo(MePhe-Leu-Asp-Val-D-Arg-D-Arg) (ZD7349) (17) inhibited MOLT-4 cell adhesion to fibronectin and vascular cell adhesion molecule-1 (VCAM-1) with IC50 values of 260 and 330 nM, respectively, and did not show any significant effect against other integrins (IC50 > 300 microM). ZD7349 inhibited ovalbumin-induced DTH response in mice when administered continuously using a mini-pump (ED50 0.01 mg/kg/day) or when given as an s.c. or i.v. bolus injection at a dose of 1-10 mg/kg. ZD7349 was also active in type II collagen-induced arthritis (CIA) and experimental autoimmune encephalomyelitis (EAE) tests at a dose of 3-10 mg/kg. The peptide was released from some formulations over a period of 10-20 days. ZD7349 is currently undergoing pre-clinical investigation.

Potent cyclic monomeric and dimeric peptide inhibitors of VLA-4 (alpha4beta1 integrin)-mediated cell adhesion based on the Ile-Leu-Asp-Val tetrapeptide

Potent monomeric and dimeric cyclic peptide very late antigen-4 (VLA-4) inhibitors have been designed based on a tetrapeptide (Ile-Leu-Asp-Val) sequence present in a 25-amino acid peptide (CS-1) reported in the literature. The peptides, synthesized by the SPPS techniques, were evaluated in the in vitro cell adhesion assays and in the in vivo inflammation models. The N- to C-terminal cyclic peptides such as cyclo(Ile-Leu-Asp-Val-NH-(CH2)2-S-(CH2)2-CO) (28) and cyclo(MeIle-Leu-Asp-Val-D-Ala-D-Ala) (31), monomeric and dimeric peptides containing piperazine (Pip) or homopiperazine (hPip) residues as linking groups, e.g. cyclo(MeIle-Leu-Asp-Val-Pip-CH2CO-NH-(CH2)2-S-CH2-CO) (49) and cyclo(MeIle-Leu-Asp-Val hPip-CH2CO-MeIle-Leu-Asp-Val-hPip-CH2CO) (58) and cyclic peptides containing an amide bond between the side chain amino group of an amino acid such as Lys and the C-terminal Val carboxyl group, e.g. Ac-cyclo(D-Lys-D-Ile-Leu-Asp-Val) (62) and beta-Ala-cyclo(D-Lys-D-Leu-Leu-Asp-Val) (68) were more potent than CS-1 in inhibiting the adhesion of the VLA-4-expressing MOLT-4 cells to fibronectin. The more potent compounds were highly selective and did not affect U937 cell adhesion to fibronectin (VLA-5), PMA-differentiated U937 cell adhesion to intercellular cell adhesion molecule- 1-expressing Chinese hamster ovary cells (LFA-1) and ADP-induced platelet aggregation (GPIIb/IIIa). A number of the more potent compounds inhibited ovalbumin-induced delayed type hypersensitivity in mice and some were 100-300 times more potent (ED50 = 0.003-0.009 mg/kg/day, s.c.) than CS-1. Two peptides, Ac-cyclo(D-Lys D-Ile-Leu-Asp-Val) (62) and cyclo(CH2CO-Ile-Leu-Asp-Val-Pip-CH2CO-Ile-Leu-Asp-Val-Pip) (55), were formulated in poly(DL-lactide-co-glycolide) depots and the release profile was investigated in vitro over a 30-day period.

Comparison of a fixed combination of domperidone and paracetamol (Domperamol) with sumatriptan 50 mg in moderate to severe migraine: a randomised UK primary care study

Migraine is a common and debilitating condition routinely managed in primary care. A number of treatment options--both acute and prophylactic--are currently available but may differ in terms of efficacy, tolerability and cost. The aim of this study was to compare the effectiveness and tolerability of a fixed combination of domperidone and paracetamol (Domperamol; Servier), which has anti-nauseant and anti-emetic activity, with sumatriptan 50 mg in moderate to severe migraine. To do this, 120 patients were recruited from 23 primary care practices throughout the UK and were enrolled into the six-month trial. Patients were randomised at entry to one of the comparator regimens (used to treat their first migraine attack) and then crossed over to the alternative treatment for their second attack. Detailed diary cards were completed for each attack using a scale of pain severity. At two hours and four hours post-dose, the two treatments showed comparable efficacy (< or = 15% difference) in relieving headache and reducing nausea and vomiting. Both were well tolerated and there were no serious adverse effects. In the management of migraine patients typically seen in routine general practice, this trial showed that the effects of Domperamol and sumatriptan 50 mg were broadly comparable. Since Domperamol is considerably less expensive than sumatriptan (and other triptans), a first-line role for this agent appears appropriate.

Anti-inflammatory activity of c(ILDV-NH(CH2)5CO), a novel, selective, cyclic peptide inhibitor of VLA-4-mediated cell adhesion

1. Small, N- to C-terminal cyclized peptides containing the leucyl-aspartyl-valine (LDV) motif from fibronectin connecting segment-1 (CS-1) have been investigated for their effects on the adhesion of human T-lymphoblastic leukaemia cells (MOLT-4) to human plasma fibronectin in vitro mediated by the integrin Very Late Antigen (VLA)-4 (alpha4beta1, CD49d/CD29). 2. Cyclo(-isoleucyl-leucyl-aspartyl-valyl-aminohexanoyl-) (c(ILDV-NH(CH2)5CO)) was approximately 5 fold more potent (IC50 3.6+/-0.44 microM) than the 25-amino acid linear CS-1 peptide. Cyclic peptides containing two more or one less methylene groups had similar potency to c(ILDV-NH(CH2)5CO) while a compound containing three less methylene groups, c(ILDV-NH(CH2)2CO), was inactive at 100 microM. 3. c(ILDV-NH(CH2)5CO) had little effect on cell adhesion mediated by two other integrins, VLA-5 (alpha5,beta1, CD49e/CD29) (K562 cell adhesion to fibronectin) or Leukocyte Function Associated molecule-1 (LFA-1, alphabeta2, CD11a/CD18) (U937 cell adhesion to Chinese hamster ovary cells transfected with intercellular adhesion molecule-1) at concentrations up to 300 microM. 4. c(ILDV-NH(CH2)5CO) inhibited ovalbumin delayed-type hypersensitivity or oxazolone contact hypersensitivity in Balb/c mice when dosed continuously from subcutaneous osmotic mini-pumps (0.1-10 mg kg(-1) day(-1)). Maximum inhibition (approximately 40%) was similar to that caused by the monoclonal antibody PS/2 (7.5 mg kg(-1) i.v.) directed against the alpha4 integrin subunit. 5. c(ILDV-NH(CH2)5CO) also inhibited oxazolone contact hypersensitivity when dosed intravenously 20 h after oxazolone challenge (1-10 mg kg(-1)). Ear swelling was reduced at 3 h and 4 h but not at 1 h and 2 h post-dose (10 mg kg(-1)). 6. Small molecule VLA-4 inhibitors derived from c(ILDV-NH(CH2)5CO) may be useful as anti-inflammatory agents.

Comparison of the angiotensin II receptor antagonist irbesartan with atenolol for treatment of hypertension

In this multicenter, double-blind study, the antihypertensive efficacy and safety of irbesartan were compared with those of atenolol in patients with mild-to-moderate hypertension. Following a 4- to 5-week placebo lead-in period, 231 patients with seated diastolic blood pressure (SeDBP) 95-110 mmHg were randomized to irbesartan 75 mg or atenolol 50 mg once daily for 24 weeks. Doses were doubled at Week 6 for SeDBP > or = 90 mmHg. At Week 12, or anytime thereafter, doses were doubled for SeDBP > or = 90 mmHg if not done at Week 6, and hydrochlorothiazide and then nifedipine were added. Efficacy was determined by change from baseline in blood pressure and by therapeutic response rates. Safety was assessed by monitoring adverse events (AEs). Both treatments significantly lowered blood pressure from baseline. There were no significant differences between treatment groups with respect to blood pressure changes or therapeutic response. Atenolol significantly reduced seated heart rate compared with irbesartan at Week 12. The incidences of serious AEs and discontinuations due to AEs were approximately twice as high in the atenolol group compared with the irbesartan group. Thus, in comparison to atenolol, irbesartan < or = 150 mg provided at least equivalent blood pressure control while demonstrating an excellent safety and tolerability profile.

Comparison of the effects of xamoterol and isoprenaline on rat cardiac beta-adrenoceptors: studies of function and regulation

1. The effects of the beta 1-selective partial agonist xamoterol and the full agonist isoprenaline on rat cardiac beta-adrenoceptors were compared in functional studies of heart rate response in vivo and in vitro. In addition, the ability of both agents to cause receptor down-regulation in the rat heart following chronic (6 days) subcutaneous infusions was assessed by radioligand binding with [125I]-pindolol. 2. In the functional studies, xamoterol produced a maximal effect equivalent to approximately 65% of that of isoprenaline and was overall less potent than the full agonist. 3. Compared to saline control, the density of beta-adrenoceptors was reduced approximately 39% in ventricular membranes prepared from animals after 6 days of isoprenaline infusion but was unaffected by xamoterol. The relative proportions of the beta-adrenoceptor subtypes were unchanged by either active treatment. 4. Plasma xamoterol level at the end of the infusion period was equivalent to that associated with maximum tachycardia in vivo and to the concentration producing maximal stimulation of the rat isolated atrium in vitro. Thus suggesting 100% beta-adrenoceptor occupancy during the period of xamoterol infusion. 5. These results indicate that in this animal model xamoterol does not induce cardiac beta-adrenoceptor down-regulation during chronic treatment, with doses that produce a maximal functional response both in vitro and in vivo.

Radioimmunoassay of LTB4 in plasma from different species: a cautionary note

In clinical and pre-clinical research the pharmacodynamics of selective 5-lipoxygenase and dual 5-lipoxygenase/cyclo-oxygenase inhibitors may be studied by direct RIA of plasma LTB4. Although immunoreactive LTB4 in plasma from A23187 stimulated human blood has the characteristics of authentic LTB4 our results show, particularly in mice and rats, that exposure to A23187 produces large quantities of 12-HETE. Since in different species the levels of 12-HETE increase with platelet concentration we suggest that the 12(S)-HETE is produced by platelet lipoxygenase. However, we do not rule out the possibility that a proportion of 12-HETE may exist as the (R)-stereoisomer. The latter has greater potential for interference in the direct RIA of LTB4. Biosynthesis of 12-HETE may be measured either by RPHPLC/U.V. abs. (8) or by RIA (9) and LTB4 by a more specific antibody described in this report. We conclude that the combined ex vivo RIA of plasma TXB2, LTB4 and 12-HETE has utility in determining the selectivity of inhibitors of arachidonate metabolism and in distinguishing between selective 5-lipoxygenase inhibitors which interact directly with the enzyme and anti-oxidant or free radical scavenging types which may be less specific.

Simple procedure for measuring the pharmacodynamics and analgesic potential of lipoxygenase inhibitors

A model is described for determining the pharmacodynamics of inhibitors of arachidonate metabolism in mice. Bioavailability and selectivity were assessed by ex vivo RIA of TXB2, LTB4, and 12-HETE from ionophore-challenged blood. Inhibition of LTB4 and 12-HETE was measured using a single LTB4 RIA, following extraction and separation of these eicosanoids from plasma. Separation on cyanopropyl mini-columns yielded hexane/ether and methanol fractions, which contained 12-HETE and LTB4, respectively. Analgesic efficacy was measured by inhibition of phenylbenzoquinone-induced abdominal constriction. The NSAIDs, indomethacin ibuprofen, flurbiprofen, and benoxaprofen, were analgesic and selective cyclo-oxygenase inhibitors. BW775C was also analgesic, but inhibited cyclo-oxygenase, 5-lipoxygenase and 12-HETE formation. Other in vitro 5-lipoxygenase inhibitors, NDGA, quercetin, and nafazatrom, were inactive in vivo, although NDGA reduced abdominal constrictions. The results indicate that this model has utility in determining the mechanism/selectivity of action and analgesic potential of 5-lipoxygenase inhibitors.

Pro-inflammatory effects of bradykinin, sigma-cyclo[Lys1,Gly6]bradykinin and sigma-cyclo-kallidin in the rat

A comparison of the effects of bradykinin (BK), sigma-cyclo-BK and sigma-cyclo-kallidin (sigma-cyclo-KD) to induce oedema, hyperalgesia and blood flow in the rat paw was made. BK produced dose-dependent increases in oedema and blood flow and a reduction in the nociceptive pressure threshold. Sigma-Cyclo-BK and sigma-cyclo-KD were more potent than BK at inducing oedema and increasing blood flow but had no effect on nociceptive pressure threshold at the doses used. The relative lack of hyperalgesic activity of sigma-cyclo-BK and sigma-cyclo-KD compared with BK raises the possibility of differences between kinin receptors mediating permeability and blood flow changes and those involved in nociception in this model.

Thromboxane synthase inhibition: implications for prostaglandin endoperoxide metabolism. I. Characterisation of an acute intravenous challenge model to measure prostaglandin endoperoxide metabolism

It has been proposed that thromboxane synthase inhibition (TXSI) may be a useful form of anti-thrombotic therapy and that this is due, in part, to redirection of PGH2 metabolism in favour of PGI2, a potent vasodilator and anti-platelet agent. While redirection has been observed ex vivo there are conflicting reports of its occurrence in vivo. We now describe the characterisation of an acute intravenous challenge model using thrombin, collagen, arachidonic acid (AA) and PGH2 for the study of PGH2 metabolism. Following challenge, plasma concentrations of TXB2, 6-oxo-PGF1 alpha, alleged metabolites of PGI2 (PGI2m) and PGE2 were measured by radioimmunoassay (RIA). Thrombin and collagen challenge resulted in a dose-related increase in plasma TXB2 while AA and PGH2, in addition, elevated 6-oxo-PGF1 alpha and PGI2m. Injection of PGH2 elevated 6-oxo-PGF1 alpha, PGI2m, TXB2 and PGE2 levels. Experimental conditions were defined such that challenge with thrombin (40 NIH units kg-1), collagen (100 micrograms kg-1), AA (1 mg kg-1) and PGH2 (5 micrograms kg-1) and measurement of eicosanoids 0.5 min following challenge were optimal for detection of redirection of PGH2 metabolism in vivo. The identity of immunoreactive TXB2 and 6-oxo-PGF1 alpha was further supported by experiments in which the extracted immunoreactive eicosanoids co-eluted with authentic [3H]standards when subject to reverse phase high performance liquid chromatography (RPHPLC). Evidence is also presented that the levels of plasma eicosanoids measured in this model reflect in vivo biosynthesis.

Thromboxane synthase inhibition: implications for prostaglandin endoperoxide metabolism. II. Testing the 'redirection hypothesis' in an acute intravenous challenge model

In the preceding paper we described the characterisation of an acute intravenous challenge model for the evaluation of the effects of thromboxane synthase inhibition (TXSI) on eicosanoid metabolism. Herein we describe the biochemical pharmacology of two TXSI and aspirin in this model. Both TXSI caused significant inhibition of plasma TXB2 in vivo without elevation of 6-oxo-PGF1 alpha levels. Similar results were obtained when combined levels of 6-oxo-PGF1 alpha,13,14 dihydro 6-oxo-PGF1 alpha,13,14 dihydro 6,15-dioxo-PGF1 alpha and 6-oxo-PGE1 were measured as an index of PGI2 biosynthesis (PGI2m). Thus no evidence of in vivo redirection of PGH2 to PGI2 was found. Ex vivo experiments performed in serum gave an apparent stimulation of immunoreactive 6-oxo-PGF1 alpha following TXSI but RPHPLC analysis of extracted serum showed that this stimulation was accounted for by increase in a product co-eluting with [3H]PGF2 alpha. The implications of these findings in relation to TXSI and receptor antagonists are discussed.

Prostacyclin and Thromboxane in Non-Insulin Dependent Diabetes: The Chlorpropamide Alcohol Flush Reaction Revisited

1. Levels of immunoreactive 6-oxo-prostaglandin F1α (6-oxo-PGF1α) and thromboxane B2 (TXB2) were measured in peripheral venous plasma in a group of volunteers and non-insulin dependent diabetic patients (NIDDS). Levels of these eicosanoids were close to the limit of sensitivity of the radioimmunoassays and consequently data are reported as maximal values. Basal plasma levels of 6-oxo-PGF1α did not exceed 5 pg/ml in either group and maximal levels of immunoreactive TXB2 were 125 ± 14 and 128 ± 8 pg/ml for volunteers and NIDDS respectively.

2. Attempts to elicit peripheral vascular prostacyclin biosynthesis in volunteers by using forearm ischaemia produced no increase in plasma 6-oxo-PGF1α levels. Measurement of the combined plasma levels of 6-oxo-PGF1α, 13,14-dihydro-6-oxo-PGF1α, 13,14-dihydro-6,15-dioxo-PGF1α and 6-oxo-PGE1 indicated that these were also low (less than 5 pg/ml) and that failure to demonstrate increased 6-oxo-PGF1α levels was unlikely to have arisen from metabolism of prostacyclin to one or more of these metabolites.

3. Measurement of 6-oxo-PGF1α and TXB2 in peripheral venous plasma before and during chloropropamide alcohol flushing (CPAF) did not provide evidence for a role for these eicosanoids in the etiology of this phenomenon.

4. These findings point to the need for a reappraisal of studies that have described altered plasma levels of 6-oxo-PGF1α and TXB2 in CPAF and other pathophysiological conditions in man.

Effects of vascular trauma and transient myocardial ischaemia on coronary venous prostaglandin levels in the dog

The plasma concentrations of immunoreactive thromboxane B2 and 6-keto-prostaglandin-F1 alpha were determined in coronary venous blood sampled from open-chested, anaesthetised beagle dogs by local vein catheterisation. Thromboxane levels were high immediately following catheterisation (2.08 +/- 0.75 ng X ml-1, mean +/- SEM, n = 6) and fell over 25 min to 0.48 +/- 0.07 ng X ml-1. Initial trauma of the coronary veins (agitation of the catheter) produced a large but variable increase to 5.13 +/- 2.27 ng X ml-1 (0.1 greater than P greater than 0.05) within 2 min, but arterial trauma (repeated momentary occlusions) produced 0.4 +/- 0.03 ng X ml-1, a value not significantly different from control. After 7 min ischaemia an increase to 0.98 +/- 0.26 ng X ml-1 was detected (P less than 0.05). Reperfusion after 15 min ischaemia caused a fall to 0.43 +/- 0.09 ng X ml-1 at 2 min. In contrast, 6-keto-prostaglandin-F1 alpha levels varied little with trauma but increased to 0.64 +/- 0.14 ng X ml-1 (P less than 0.01) within 2 min ischaemia, remaining elevated. On reperfusion, levels fell to 0.27 +/- 0.06 ng X ml-1 (P less than 0.05) at 2 min, progressively increasing to 0.35 +/- 0.05 ng X ml-1 at 30 min. We conclude that intimal trauma of coronary veins induced thromboxane release and that the physical effects of venous sampling may contribute to apparent thromboxane release from ischaemic muscle. Although transient arterial and venous trauma had no significant effect on 6-keto-prostaglandin-F1 alpha, it is still possible that its release during ischaemia may follow prolonged arterial clamping.

Hyperbaric system for oxygen toxicity studies in the toad urinary bladder

A hyperbaric research system to study the effects on membrane function of oxygen at pressures as high as 20 ATA has been designed. The system includes a pressure chamber capable of holding eight isolated toad bladder short-circuit current apparatuses and unique experimental gassing, diluent addition, and sampling systems which are monitored by a control panel mounted on the side of the pressure chamber. These externally controlled gassing, diluent, and sampling systems permit experimental manipulations at any ambient pressure and are a significant addition to the methodology of hyperbaric research.