The recovery of platelet cyclooxygenase activity explains interindividual variability in responsiveness to low-dose aspirin in patients with and without diabetes

BACKGROUND

Interindividual variability in response to aspirin has been popularized as 'resistance'. We hypothesized that faster recovery of platelet cyclooxygenase-1 activity may explain incomplete thromboxane (TX) inhibition during the 24-h dosing interval.

OBJECTIVE

To characterize the kinetics and determinants of platelet cyclooxygenase-1 recovery in aspirin-treated diabetic and non-diabetic patients.

PATIENTS/METHODS

One hundred type 2 diabetic and 73 non-diabetic patients on chronic aspirin 100 mg daily were studied. Serum TXB(2) was measured every 3 h, between 12 and 24 h after a witnessed aspirin intake, to characterize the kinetics of platelet cyclooxygenase-1 recovery. Patients with the fastest TXB(2) recovery were randomized to aspirin 100 mg once daily, 200 mg once daily or 100 mg twice daily, for 28 days and TXB(2) recovery was reassessed.

RESULTS AND CONCLUSIONS

Platelet TXB(2) production was profoundly suppressed at 12 h in both groups. Serum TXB(2) recovered linearly, with a large interindividual variability in slope. Diabetic patients in the third tertile of recovery slopes (≥ 0.10 ng mL(-1) h(-1) ) showed significantly higher mean platelet volume and body mass index, and younger age. Higher body weight was the only independent predictor of a faster recovery in non-diabetics. Aspirin 100 mg twice daily completely reversed the abnormal TXB(2) recovery in both groups. Interindividual variability in the recovery of platelet cyclooxygenase activity during the dosing interval may limit the duration of the antiplatelet effect of low-dose aspirin in patients with and without diabetes. Inadequate thromboxane inhibition can be easily measured and corrected by a twice daily regimen.

Effects of G/A polymorphism, rs266882, in the androgen response element 1 of the PSA gene on prostate cancer risk, survival and circulating PSA levels

Prostate-specific antigen (PSA) is a protease produced in the prostate that cleaves insulin-like growth factor binding protein-3 and other proteins. Production is mediated by the androgen receptor (AR) binding to the androgen response elements (ARE) in the promoter region of the PSA gene. Studies of a single nucleotide polymorphism (PSA -158 G/A, rs266882) in ARE1 of the PSA gene have been conflicting for risk of prostate cancer and effect on plasma PSA levels. In this nested case-control analysis of 500 white cases and 676 age- and smoking-matched white controls in the Physicians' Health Study we evaluated the association of rs266882 with risk and survival of prostate cancer and prediagnostic total and free PSA plasma levels, alone or in combination with AR CAG repeats. We used conditional logistic regression, linear regression and Cox regression, and found no significant associations between rs266882 (GG allele vs AA allele) and overall prostate cancer risk (RR=1.21, 95% confidence intervals (CI): 0.88-1.67) or prostate cancer-specific survival (RR=0.94, 95%CI: 0.56-1.58). Similarly, no associations were found among high grade or advanced stage tumours, or by calendar year of diagnosis. There was no significant association between rs266882 and baseline total or free PSA levels or the AR CAG repeats, nor any interaction associated with prostate cancer risk. Meta-analysis of 12 studies of rs266882 and overall prostate cancer risk was null.

Angiotensin II stimulates and atrial natriuretic peptide inhibits human visceral adipocyte growth

OBJECTIVE

Cardiovascular peptides such as angiotensin II (Ang II) and atrial natriuretic peptide (ANP) have metabolic effects on adipose cells. These peptides might also regulate adipocyte proliferation and visceral adipose tissue (VAT) expansion. Well-differentiated and stabilized primary cultures of human visceral mature adipocytes (MA) and in vitro-differentiated preadipocytes (DPA) were used as a model to study regulation of VAT expansion.

METHODS

Adipocyte differentiation was evaluated by Oil Red O staining and antiperilipin antibodies. MA and DPA from intra- and retro-peritoneal depots were treated with increasing Ang II (with or without valsartan, a highly selective, competitive, 'surmountable' AT1 antagonist devoid of peroxisome proliferator-activated receptor gamma agonistic activity) or ANP concentrations. Cell counts and bromodeoxyuridine incorporation were used to evaluate proliferation. Apoptosis was evaluated by Hoechst 33342 staining. 8-Bromo cyclic guanosine monophosphate (8Br-cGMP) was used to investigate ANP effects, and real-time PCR to evaluate Ang II and ANP receptors' expression.

RESULTS

Cell proliferation was progressively stimulated by increasing Ang II concentrations (starting at 10-11 M) and inhibited by ANP (already at 10-13 M) in both MA and DPA. Co-incubation with increasing Ang II concentrations and valsartan indicated that Ang II effects were AT1-mediated. Indeed, AT2 receptors were not expressed. Valsartan alone slightly inhibited basal proliferation indicating an autocrine/paracrine growth factor-like effect of endogenous, adipocyte-derived Ang II. 8Br-cGMP experiments indicated that the effects of ANP were mediated by the guanylyl cyclase type A receptor.

CONCLUSION

A cell-culture model to study VAT growth showed stimulation by Ang II and inhibition by ANP at physiological concentrations. Because similar effects are likely to occur in vivo, Ang II and ANP might be important modulators of VAT expansion and associated metabolic and cardiovascular consequences.

Low carbohydrate-high protein diet and mortality in a cohort of Swedish women

OBJECTIVE

The long-term health consequences of diets used for weight control are not established. We have evaluated the association of the frequently recommended low carbohydrate diets - usually characterized by concomitant increase in protein intake - with long-term mortality.

DESIGN

The Women's Lifestyle and Health cohort study initiated in Sweden during 1991-1992, with a 12-year almost complete follow up.

SETTING

The Uppsala Health Care Region.

SUBJECTS

42,237 women, 30-49 years old at baseline, volunteers from a random sample, who completed an extensive questionnaire and were traced through linkages to national registries until 2003.

MAIN OUTCOME MEASURES

We evaluated the association of mortality with: decreasing carbohydrate intake (in deciles); increasing protein intake (in deciles) and an additive combination of these variables (low carbohydrate-high protein score from 2 to 20), in Cox models controlling for energy intake, saturated fat intake and several nondietary covariates.

RESULTS

Decreasing carbohydrate or increasing protein intake by one decile were associated with increase in total mortality by 6% (95% CI: 0-12%) and 2% (95% CI: -1 to 5%), respectively. For cardiovascular mortality, amongst women 40-49 years old at enrolment, the corresponding increases were, respectively, 13% (95% CI: -4 to 32%) and 16% (95% CI: 5-29%), with the additive score being even more predictive.

CONCLUSIONS

A diet characterized by low carbohydrate and high protein intake was associated with increased total and particularly cardiovascular mortality amongst women. Vigilance with respect to long-term adherence to such weight control regimes is advisable.

Are there age-dependent effects of diet on prostate cancer risk?

OBJECTIVES

To examine whether there are age-dependent effects of diet on prostate cancer risk.

METHODS

We have postulated that nutritional factors that may affect the risk of initiation would be more likely to be identified among younger patients, whereas those that may affect the risk of progression would be more clearly identifiable among older patients. Study subjects were 320 patients with prostate cancer and 246 controls with no systematic disease, hospitalised in six major hospitals in Athens, Greece. Logistic regression models were fitted separately for men under 70 years and 70 years or older.

RESULTS

Polyunsaturated lipids substantially increased the risk among younger subjects, but played little role among older ones (p for interaction 0.21). Cooked tomatoes had a strong protective effect among older persons, but not among younger subjects (p for interaction 0.009). Last, vitamin E was strongly inversely related to prostate cancer risk among younger subjects, but not among older subjects (p for interaction 0.15).

CONCLUSIONS

Even a simple straight forward interpretation of the data, i.e., that older cases of prostate cancer have a different dietary risk profile than younger ones, has potentially useful implications.

Estrogens, testosterone and sex hormone binding globulin in relation to liver cancer in men

OBJECTIVE

Liver disease in men has been associated with an imbalance of serum estradiol and testosterone. We have evaluated whether serum estradiol and testosterone levels are altered in male liver cancer patients as a result of a specific effect of the disease or because of the associated liver damage.

METHODS

We have performed a hospital-based case-control study in Greece. The study subjects were all men; 73 patients with hepatocellular carcinoma (HCC), 25 with metastatic liver cancer (MLC) patients and 111 control subjects. Serum estradiol, testosterone and sex hormone binding globulin (SHBG) levels were measured for each subject. Data were analyzed by multiple linear regression.

RESULTS

Mean serum estradiol levels were significantly higher among HCC patients as well as among patients with MLC compared to controls. Mean serum testosterone levels were significantly lower among HCC patients as well as among patients with MLC compared to controls. The mean SHBG levels did not differ significantly between the groups. After controlling for the degree of liver damage, the elevated serum estradiol and reduced serum testosterone levels among HCC and MLC patients were no longer significant.

CONCLUSIONS

Changes in sex steroid levels among patients with liver damage are due to the liver damage per se and not to specific disease processes.

Reliability of Information Collected by Proxy in Family Studies of Alzheimer’s Disease

The study evaluated the reliability of data obtained from proxy informants. The index subjects in this study were 81 nondemented participants in the Multi-Institutional Research in Alzheimer Genetic Epidemiology (MIRAGE) study. These index subjects and 159 proxy informants, identified by the index subjects, participated in the study. The kappa statistic with multiple raters per subject (for dichotomous variables) and the intraclass correlation coefficient (for continuous variables) were used to measure reliability. Among proxy respondents who provided answers, there was excellent agreement between proxy responses and the responses of the index subjects (0.7 < or = kappa < or =0.9), with the exception of questions about head injury (kappa = 0.4). A large proportion (>90%) of the proxy informants in this study were able to provide information on most items. Higher nonresponse rates (as high as 30%) were observed for medication history and women's health questions. This study supports the reliability of proxy responses for most categories of questions that are elicited in typical epidemiological studies, including the MIRAGE study.

Possible role of an endogenous opiate in the cardiovascular effects of central alpha adrenoceptor stimulation in spontaneously hypertensive rats

In unanesthetized sponatneously hypertensive rats (SHR), naloxone (0.5--2 mg/kg ip.) or naltrexone (2 mg/kg) inhibited the hypotension and bradycardia produced by clonidine (5--20 micrograms/kg iv.). Chronic treatment of SHR with clonidine (3 x 20 micrograms/kg/day orally for 12 days) reduced blood pressure and heart rate and these effects were acutely reversed by a single injection of naloxone. Naloxone also reversed the hypotension produced by a single injection of alpha-methyldopa (50--300 mg/kg ip.). In pentobarbital-anesthetized SHR, the hypotension and bradycardia produced by 5 micrograms/kg of clonidine were inhibited either by naloxone (2 mg/kg) or by yohimbine (1 mg/kg ip.). Morphine (0.33 mg/kg iv.) also reduced blood pressure and heart rate in these animals but these effects were only antagonized by naloxone and not by yohimbine. In conscious and anesthetized normotensive Wistar Kyoto rats, the reduction in blood pressure and heart rate by clonidine or alpha-methyldopa were smaller than in SHR, and these effects were not influenced by naloxone. These results confirm and extend earlier observations and suggest the existence of an "opioidergic" component in the antihypertensive action of central alpha adrenoceptor stimulants in SHR. They also show that a similar mechanism is either absent or inactive in the normotensive Wistar Kyoto rats.

The influence of hormonal and neuronal factors on rat heart adrenoceptors

1 The influence of hormonal and neuronal factors on adrenoceptors mediating increased cardiac force and rate of contraction were studied in rat isolated atria. The pharmacological properties of these receptors were deduced from the relative potencies of agonists and from the effects of selective alpha- and beta-adrenoceptor antagonists. The numbers and affinities of alpha- and beta-adrenoceptors were also determined by radioligand binding to ventricular membrane fragments.2 Hypophysectomy reduced the inotropic potency of isoprenaline and increased the potency of phenylephrine and methoxamine in left atria. The effect of phenylephrine was inhibited by propranolol less effectively and by phentolamine or phenoxybenzamine more effectively in hypophysectomized than in control rats. The difference in block was smaller at low than at high antagonist concentrations. Similar but smaller changes were observed for chronotropic responses of right atria.3 The decreased beta- and increased alpha-receptor response after hypophysectomy was similar to that observed earlier in thyroidectomized rats (Kunos, 1977). These changes developed slowly after hypophysectomy (>2 weeks), they were both reversed within 2 days of thyroxine treatment (0.2 mg/kg daily), but were not affected by cortisone treatment (50 mg/kg every 12 h for 4 days).4 Treatment of hypophysectomized rats for 2 days with thyroxine increased the density of [(3)H]-dihydroalprenolol ([(3)H]-DHA) binding sites from 27.5 +/- 2.7 to 45.5 +/- 5.7 fmol/mg protein and decreased the density of [(3)H]-WB-4101 binding sites from 38.7 +/- 3.1 to 18.7 +/- 2.5 fmol/mg protein. The affinity of either type of binding site for agonists or antagonist was not significantly altered by thyroxine treatment and the sum total of alpha(1)- and beta-receptors remained the same.5 Sympathetic denervation of thyroidectomized rats by 6-hydroxydopamine increased the inotropic potency of isoprenaline and noradrenaline and the blocking effect of propranolol, and decreased the potency of phenylephrine and the blocking effect of phenoxybenzamine to or beyond values observed in euthyroid controls. The density of [(3)H]-DHA binding sites was higher and that of [(3)H]-WB-4101 binding sites was lower in the denervated than in the innervated hypothyroid myocardium. Depletion of endogenous noradrenaline stores by reserpine did not significantly alter the adrenoceptor response pattern of the hypothyroid preparations and did not influence the density or affinity of [(3)H]-DHA and [(3)H]-WB-4101 binding sites.6 These results indicate that thyrotropin or steroids do not contribute to the reciprocal changes in the sensitivity of cardiac alpha(1)- and beta-adrenoceptors in altered thyroid states. These thyroid hormone-dependent changes are probably due to a parallel, reciprocal change in the numbers but not the affinities of alpha(1)- and beta-adrenoceptors. Reciprocal regulation of cardiac alpha(1)- and beta-adrenoceptors by thyroid hormones requires intact sympathetic innervation but not the presence of normal stores of the neurotransmitter.