Association of a bitter taste receptor mutation with Balkan Endemic Nephropathy (BEN)

Background

Balkan Endemic Nephropathy (BEN) is late-onset kidney disease thought to arise from chronic exposure to aristolochic acid, a phytotoxin that contaminates wheat supplies in rural areas of Eastern Europe. It has recently been demonstrated that humans are capable of perceiving aristolochic acid at concentrations below 40 nM as the result of high-affinity interactions with the TAS2R43 bitter taste receptor. Further, TAS2R43 harbors high-frequency loss-of-function mutations resulting in 50-fold variability in perception. This suggests that genetic variation in TAS2R43 might affect susceptibility to BEN, with individuals carrying functional forms of the receptor being protected by an ability to detect tainted foods.

Methods

To determine whether genetic variation in TAS2R43 predicts BEN susceptibility, we examined genotype-phenotype associations in a case–control study. A cohort of 88 affected and 99 control subjects from western Bulgaria were genotyped with respect to two key missense variants and a polymorphic whole-gene deletion of TAS2R43 (W35S, H212R, and wt/Δ), which are known to affect taste sensitivity to aristolochic acid. Tests for association between haplotypes and BEN status were then performed.

Results

Three major TAS2R43 haplotypes observed in previous studies (TAS2R43-W35/H212, -S35/R212 and –Δ) were present at high frequencies (0.17, 0.36, and 0.47 respectively) in our sample, and a significant association between genotype and BEN status was present (P = 0.020; odds ratio 1.18). However, contrary to expectation, BEN was positively associated with TAS2R43-W35/H212, a highly responsive allele previously shown to confer elevated bitter sensitivity to aristolochic acid, which should drive aversion but might also affect absorption, altering toxin activation.

Conclusions

Our findings are at strong odds with the prediction that carriers of functional alleles of TAS2R43 are protected from BEN by an ability to detect and avoid aristolochic acid exposure. Evidence for a positive association between high-sensitivity alleles and BEN status suggests instead that possession of toxin-responsive receptor variants may paradoxically increase vulnerability, possibly by shifting attractive responses associated with low-intensity bitter sensations. The broad-spectrum tuning of the ~25-member TAS2R family as a whole toward xenobiotics points to a potentially far-reaching relevance of bitter responses to exposure-related disease in both individuals and populations.

Genomic, genetic and functional dissection of bitter taste responses to artificial sweeteners

Bitter taste perception is initiated by TAS2R receptors, which respond to agonists by triggering depolarization of taste bud cells. Mutations in TAS2Rs are known to affect taste phenotypes by altering receptor function. Evidence that TAS2Rs overlap in ligand specificity suggests that they may also contribute joint effects. To explore this aspect of gustation, we examined bitter perception of saccharin and acesulfame K, widely used artificial sweeteners with aversive aftertastes. Both substances are agonists of TAS2R31 and -43, which belong to a five-member subfamily (TAS2R30-46) responsive to a diverse constellation of compounds. We analyzed sequence variation and linkage structure in the ∼140 kb genomic region encoding TAS2R30-46, taste responses to the two sweeteners in subjects, and functional characteristics of receptor alleles. Whole-gene sequences from TAS2R30-46 in 60 Caucasian subjects revealed extensive diversity including 34 missense mutations, two nonsense mutations and high-frequency copy-number variants. Thirty markers, including non-synonymous variants in all five genes, were associated (P< 0.001) with responses to saccharin and acesulfame K. However, linkage disequilibrium (LD) in the region was high (D', r(2) > 0.95). Haplotype analyses revealed that most associations were spurious, arising from LD with variants in TAS2R31. In vitro assays confirmed the functional importance of four TAS2R31 mutations, which had independent effects on receptor response. The existence of high LD spanning functionally distinct TAS2R loci predicts that bitter taste responses to many compounds will be strongly correlated even when they are mediated by different genes. Integrative approaches combining phenotypic, genetic and functional analysis will be essential in dissecting these complex relationships.

Optimal propofol-alfentanil combinations for supplementing nitrous oxide for outpatient surgery

BACKGROUND

The combination of propofol and alfentanil with nitrous oxide provides balanced anesthesia with rapid recovery and minimal emetic side effects. The object of this study was to compare recovery parameters at varying proportions of propofol and alfentanil, and to determine the dosing rate and plasma concentration of propofol necessary to supplement nitrous oxide in the presence of varying concentrations of alfentanil

METHODS

Forty-eight patients were anesthetized with nitrous oxide, targeted manual infusions of alfentanil (target plasma concentrations of 0, 50, 100, and 150 ng/ml), and propofol at rates that were varied up or down by 25% depending on the response (movement/no movement) of the preceding patient (at the same alfentanil target concentrations) to ulnar-nerve stimulation. The minimum concentrations of propofol and alfentanil required to prevent movement in 50% of patients (EC50) was determined by logistic regression. Speed of emergence and recovery of cognitive function, time to discharge, and incidence of side effects were compared for four different combinations of propofol and alfentanil with nitrous oxide.

RESULTS

The EC50 for propofol alone with nitrous oxide was 6.1 microg/ml. AlfentaniL at concentrations of 41+/-17 (SD), 113+/-54, and 130+/-61 ng/mL reduced the EC50 of propofol to 3.3, 2.3, and 2.2 microg/ml, respectively, and decreased emergence time (eye opening) to 8.1, 4.9, and 3.4 min, compared with 24.3 min for propofol alone. Side effects did not differ between groups.

CONCLUSIONS

The authors conclude that there is a synergistic effect between propofol and alfentanil, and that combining alfentanil with propofol is associated with faster early recovery.

Voiding in patients managed with or without ultrasound monitoring of bladder volume after outpatient surgery

The goal of this study was to determine whether recovery room monitoring of bladder volume would affect patient outcome after ambulatory surgery. Incidence of urinary retention and times to void and to discharge were compared in 161 patients managed with ultrasound bladder monitoring versus 173 controls without bladder monitoring. Urinary retention was diagnosed by clinical means or by ultrasound, confirmed by bladder catheterization. Patients were required to void or were catheterized before discharge. In the control patients without underlying risk factors for retention, median time to void was 95 min, and retention occurred in 0.8%, which was not significantly different from the ultrasound group (80 min and 0%, respectively). After hernia/anal surgery or spinal/epidural anesthesia, voiding was delayed (130 and 213 min), incidence of retention was increased (17% and 13%), and there was a trend toward earlier voiding (168+/-99 vs. 138+/-68 min) with bladder monitoring. We conclude that most patients at low risk of retention void within 3 h of outpatient surgery; their outcome is unaffected by bladder monitoring. After hernia/anal surgery and spinal/ epidural anesthesia, the likelihood of urinary retention is increased, and ultrasound monitoring facilitates deciding whether such patients should be catheterized.

IMPLICATIONS

Incidence of bladder catheterization and urinary retention were compared in patients managed with and without ultrasound monitoring of bladder volume after outpatient surgery. Monitoring did not alter outcome in patients at low risk of retention, but it facilitated determining when to catheterize patients at high risk of retention (hernia/anal surgery, spinal/epidural anesthesia).

Propofol versus isoflurane for endoscopic sinus surgery

PURPOSE

A previous retrospective study reported that propofol anesthesia decreased bleeding during endoscopic sinus surgery compared with isoflurane. We performed a prospective study to compare the effects of propofol versus isoflurane on measured blood loss and the surgeon's subjective assessment of operating conditions during endoscopic sinus surgery.

PATIENTS AND METHODS

After receiving institutional review board approval and written informed consent, 56 patients undergoing endoscopic sinus surgery were randomly assigned to receive propofol (n = 30) or isoflurane (n = 26) supplemented with nitrous oxide-oxygen and alfentanil. Blood loss was calculated from the hemoglobin concentration in suction canisters. One surgeon, who was blinded to the anesthetic agent, performed every procedure and assessed bleeding as follows: 1, no bleeding; 2, modest bleeding; 3, bleeding interfering with operating conditions and cause for an agent switch; and 4, intolerable bleeding requiring a change in surgical plan. Results were compared in the two anesthetic groups using chi-squared test, unpaired t-test, Mann-Whitney Utest, and a permutation test. A P of .05 was considered significant.

RESULTS

Mean bleeding scores were less over time (P = .02) with propofol anesthesia, particularly in surgery in the ethmoid and sphenoid sinuses (P = .03), and the proportion of patients with a mean score >2 was less in the propofol group (30% v 54%; P = .033). Time until discharge to home or to a limited stay in a hospital bed was also less in the propofol group (183 v 243 minutes; P = .019).

CONCLUSION

In our study, surgical blood loss was the same for both anesthetic agents overall, but propofol appeared to offer an advantage in terms of subjective improvement in operating conditions, particularly in the ethmoid and sphenoid sinuses.

Assignment of the human alpha-tropomyosin gene TPM4 to band 19p13.1 by fluorescence in situ hybridization

Sequence-tagged sites (STSs) were developed for the human alpha-tropomyosin gene TPM4. One STS was used to amplify DNA from somatic cell hybrids to localize TPM4 to chromosome 19. The other, a product from a long-range PCR, was used directly as a probe to refine the localization of TPM4 to 19p13.1 by fluorescence in situ hybridization to metaphase chromosome spreads.

Accuracy of continuous jugular bulb venous oximetry during intracranial surgery

We compared readings obtained from the Baxter-Edwards continuous jugular bulb venous oximetry catheter with those obtained from blood gas analysis of simultaneously drawn samples from the catheter in 12 patients undergoing neurosurgical procedures. Within the range studied (SjvO2, 42-95%), the 111 (median, nine samples per patient; range five to 17) oximetric catheter readings correlated well with hemoglobin oxygen saturation values obtained from in vitro analysis of simultaneously drawn blood samples from the catheter (y = 0.93x + 3.4, r = 0.94, p < 0.001). Fiberoptic light signal was suboptimal (signal quality index = 3 or 4) on fewer than five occasions per patient during an average surgical procedure duration of seven h, and these occurrences were generally corrected by flushing the catheter. We conclude that the Baxter-Edwards jugular bulb oximetric catheter provides an accurate measure of SjvO2 during neurosurgical procedures.

Successful treatment of autoimmunity in (NZB X NZW)F1 mice with cyclosporin and (Nva2)-cyclosporin: I. Reduction of autoantibodies

Autoimmune (NZB X NZW)F1 mice were treated with the immunosuppressive agent, cyclosporin, and its new derivative (Nva2)-cyclosporin. Both compounds prevented the development of autoantibodies in young mice, and also reduced the levels of the autoantibodies in old mice. These findings established that autoantibodies, at least in the (NZB X NZW)F1 mice, can be controlled pharmacologically. This study supports the possibility that treatment with cyclosporin and (Nva2)-cyclosporin might be effective in the treatment of certain autoimmune diseases in man.

Successful treatment of autoimmunity in (NZB X NZW)F1 mice with cyclosporin and (Nva2)-cyclosporin: II. Reduction of glomerulonephritis

Autoimmune (NZB X NZW)F1 mice were treated with the immunosuppressive agent, cyclosporin, and its new derivative (Nva2)-cyclosporin. Both compounds prevented the deposition of immunocomplexes in the kidneys, and the subsequent development of glomerulonephritis and proteinuria in young mice. They also reduced established proteinuria in old mice. Therefore, we feel that both cyclosporin and (Nva2)-cyclosporin may be useful in the treatment of human glomerulonephritis where there is an autoimmune component.

Comparison of the pharmacological profiles of cyclosporine, (Nva2)-cyclosporine and (Val2)dihydro-cyclosporine

The pharmacological profiles of two new derivatives of the immunosuppressive drug, cyclosporine, is presented here. (Nva2)-CS has very similar properties to CS, but lacks the nephrotoxic side-effects. This derivative appears to be a potential successor to cyclosporine. (Val2)DH-CS seems to have a different spectrum of activities. It does not suppress humoral immunity and allograft rejection, but suppresses some types of cell-mediated immune responses. This derivative may prove useful in autoimmune situations where T cells are involved in the disease process.

Murine T cell suppression demonstrable in the absence of cytotoxicity and the effect of Cyclosporin A on this system

In vitro culture of murine spleen cells in FCS without prior immunization or allogeneic stimulation leads to the development of spontaneous cytotoxicity. This cytotoxicity is not H-2 restricted and can affect any subsequent in vitro assays using syngeneic cells, especially if those assays include prolonged culture in FCS. Studies on murine spleen cells cultured in NMS, however, led to the detection of a suppressor system that did not display cytotoxic effects. Furthermore, it was found that this suppression, in contrast to the cytotoxicity and suppression generated during culture in FCS, was not sensitive to CYA. The suppressor cell may be an effector or an inducer of suppression and is sensitive to treatment with anti-Thy-1.2 and complement. It is suggested that some in vitro suppression is really due to cytotoxicity that may be directed toward FCS determinants adsorbed onto syngeneic targets.

Murine T cell suppression demonstrable in the absence of cytotoxicity and the effect of Cyclosporin A on this system

In vitro culture of murine spleen cells in FCS without prior immunization or allogeneic stimulation leads to the development of spontaneous cytotoxicity. This cytotoxicity is not H-2 restricted and can affect any subsequent in vitro assays using syngeneic cells, especially if those assays include prolonged culture in FCS. Studies on murine spleen cells cultured in NMS, however, led to the detection of a suppressor system that did not display cytotoxic effects. Furthermore, it was found that this suppression, in contrast to the cytotoxicity and suppression generated during culture in FCS, was not sensitive to CYA. The suppressor cell may be an effector or an inducer of suppression and is sensitive to treatment with anti-Thy-1.2 and complement. It is suggested that some in vitro suppression is really due to cytotoxicity that may be directed toward FCS determinants adsorbed onto syngeneic targets.